Abstract

In the present work, the performance of Ag/ZnO/CoFe2O4 magnetic photocatalysts in the photocatalytic degradation of ibuprofen (IBP) was evaluated. This study considered the use of pure Ag/ZnO (5% Ag) and also the use of the Ag/ZnO/CoFe2O4 magnetic catalysts containing different amounts (5, 10 and 15% wt) of cobalt ferrite (CoFe2O4). The catalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoacoustic spectroscopy. To carry out the photocatalytic degradation reaction, different concentrations of the ibuprofen contaminant solution (10, 20 and 30 ppm) and different concentrations of photocatalyst were tested (0.3 g L−1, 0.5 g L−1 and 1.0 g L−1). The reaction parameters studied were: IBP concentration, catalyst concentration, adsorption and photolysis, influence of the matrix, radiation source (solar and artificial) and the effect of organic additive. At the end of the photocatalytic tests, the best operating conditions were defined. Considering the obtained results of degradation efficiency and magnetic separation, the optimal parameters selected to proceed with the other tests of the study were: ibuprofen solution concentration 10 ppm, Ag/ZnO/CoFe2O4 (5%) catalyst at a concentration of 0.3 g L−1 and pH 4.5 of the reaction medium. The results indicated the feasibility of magnetic separation of the synthesized catalysts. A long duration test indicated that the catalyst exhibits stability throughout the degradation reaction, as more than 80% of IBP was degraded after 300 minutes. The photocatalytic activity was directly affected by the ferrite load. The higher the nominal load of ferrite, the lower the performance in IBP degradation. It was also observed that the smallest amount of ferrite studied was enough for the catalyst to be recovered and reused. The adsorption and photolysis tests did not show significant results in the IBP degradation. In addition, it was possible to verify that the aqueous matrix, the use of solar radiation and the addition of additive (acid formic) were interfered directly in the process. The catalyst reuse tests indicated that it can be recovered and reused at least three times without considerable catalytic activity loss.

HIGHLIGHTS

  • Ag/ZnO/CoFe2O4 magnetic photocatalysts.

  • Magnetic separation.

  • Influence of the matrix, radiation source and presence of additive in ibuprofen degradation.

Graphical Abstract

Graphical Abstract
Graphical Abstract

INTRODUCTION

The drugs comprise a variety of products used for the most diverse diseases. Among the prescribed anti-inflammatory drugs, which are more than 70 million prescriptions per year (Macedo et al. 2021), there is the drug ibuprofen (IBP). ibuprofen is a drug formed by a chiral compound derived from arylpropionic acid, and is considered a non-steroidal and non-narcotic anti-inflammatory, this substance has been available since 1984 without a prescription, and can be freely administered to thousands of people all the days (Dasgupta & Krasowski 2020).

In a period of 24 hours after being consumed, ibuprofen is excreted in human and animal urine and will subsequently be present in wastewater, which, if disposed of incorrectly or without proper treatment, may end up reaching surface water and (Dasgupta & Krasowski 2020; Jia et al. 2021; Ren et al. 2021).

According to Ren et al. (2021), ibuprofen has been detected in surface waters and effluents since 2011, in varying concentrations ranging from 1,317 nm L−1 to 17,600 ng L−1. The authors also report that, although at low concentrations, the life of the ecosystem present in the receiving surface waters must be taken into account, carrying out studies that completely remove components called emerging contaminants such as ibuprofen.

Some studies conducted in several countries have already reported the removal of ibuprofen by several techniques such as: photocatalytic decomposition (Choina et al. 2013), adsorption (Malvar et al. 2020; Streit et al. 2021), ozonation (Huang et al. 2021), osmosis membrane bioreactor (Yao et al. 2021), enzymatic immobilization processes (Nunes et al. 2021), microbial degradation (Zhang et al. 2018), among others. Among all treatment processes, heterogeneous photocatalysis has shown to be a promising process in the removal of organic contaminants (Candido et al. 2016).

Heterogeneous photocatalysis uses inorganic semiconductors as catalysts which, when irradiated, can absorb photons with sufficient energy, allowing its electrons to migrate from the valence band to the conduction band of the semiconductor, creating holes that form highly oxidizing radicals, such as hydroxyl radicals (OH), when they come into contact with oxygen or water. These hydroxyl radicals are highly oxidizing agents, responsible for photodegrading the contaminant molecules (Josué et al. 2020). Heterogeneous photocatalysis is influenced by some factors such as: pH (Giacomni et al. 2017; Santos et al. 2019), light intensity (Ahmed et al. 2011), oxygen (Ahmed et al. 2011), catalyst calcination temperature (Shao et al. 2016), photocatalyst concentration (Wetchakun et al. 2019) and pollutant concentration (Teixeira & Jardim 2004).

Catalysts are compounds responsible for increasing the reaction speed, as they decrease the activation energy necessary for the reaction to occur, and are not consumed during the process (Gusmão et al. 2017). They can be used in powder form, especially titanium dioxide (TiO2) (Antezana & Hurtado 2016), niobium pentoxide (Nb2O5) (Lopes et al. 2015) and zinc oxide (ZnO) (Fontana et al. 2018), can be immobilized on alginate spheres (Dalponte et al. 2016), magnetic catalysts (Gonçalves et al. 2019; Fuziki et al. 2021), among others.

Since incorrect disposal of ibuprofen contaminated wastewater can be a threat to the aquatic ecosystem, it is very important and necessary to carry out studies like this one to develop efficient methods for removing ibuprofen and other emerging contaminants from wastewater. It is important that the catalyst used in the process is active and easily separated so that recovery and reuse can occur.

Some of the disadvantages of using powdered catalysts is the separation process after the reaction, as they can make the system more expensive and not be effective. Magnetic catalysts are promising alternatives in the heterogeneous photocatalysis process, as they develop an environmentally friendly process due to their ease of separation from the medium and their ability to be reused, in addition to presenting low costs and high efficiency and yield (Silva et al. 2019).

Besides providing greater ease of separation and recovery of the particles, the combination of magnetic nanoparticles with catalysts brings other beneficial results, such as increased durability. When combined with other photoactive material, ferrite (MFe2O4, where M is an additional metal) presents high photocatalytic activity. The development of paramagnetic materials, such as spinel ferrites, presents potential photocatalytic application. Cobalt ferrite is a well known magnetic material that belongs to the spinels family and presents good properties such as high coercivity and high physical and chemical stability (Hamad et al. 2015; Jacinto et al. 2020).

Some studies have been conducted using cobalt ferrite combined with catalysts for degradation of methylene blue (MB) dye and the results of the studies show the influence of CoFe2O4 on the catalytic activity. Haw et al. (2016) synthesized 3D urchin-like TiO2 microparticles decorated with CoFe2O4 magnetic nanoparticles (NPs) through a co-precipitation method. By applying this catalyst to MB degradation an improved photodegradation rate was obtained compared to pure urchin-like TiO2. The authors state that this increase can be attributed to the integration of urchin-like TiO2 with CoFe2O4 nanoparticles, which contributes to prolonging the life span of electron-hole separation (Haw et al. 2016). A combination of sol-gel and electrospinning technique methods was used to obtain TiO2/CoFe2O4 nanofibers. The photocatalytic activity of the photocatalyst was evaluated and compared with the commercial Degusa P25 photocatalyst. The results of the study showed that the presence of CoFe2O4 increases the photocatalytic activity, in addition, there was an increase in the absorption intensity of the nanofibers, which indicates that the absorption range was extended to the visible light region.

Some authors have already used magnetic catalysts for the degradation of pollutants, such as Hu et al. (2021) who used magnetic catalysts of Ag3PO4/rGO/CoFe2O4 to remove the antibiotic levofloxacin through the adsorption and photocatalysis processes and Liu et al. (2020), who evaluated the use of Fe3O4@MIL-53(Fe) magnetic catalyst for ibuprofen degradation through photocatalysis (Liu et al. 2020). Xia & Lo (2016), in turn, prepared a superparamagnetic nanocomposite (Bi2O4/Fe3O4) for photocatalytic degradation of ibuprofen (Xia & Lo 2016), while Li et al. (2019) used the magnetic catalyst Fe3O4@MIL-100(Fe) to remove sodium diclofenac from water by photocatalysis and adsorption (Li et al. 2019). Besides them, Khedkar et al. (2020) used Ag-Fe3O4 MSC magnetic catalyst to reduce organic dyes where, according to the authors, the catalyst showed excellent catalytic activity (Khedkar et al. 2020).

In this sense, the contribution of the present study was to combine the magnetic properties of CoFe2O4 and the photocatalytic performance of Ag/ZnO catalyst, to produce a magnetically recoverable and reusable Ag/ZnO/CoFe2O4 photocatalyst, synthesized by using the Pechini method, to be applied in the photocatalytic degradation of ibuprofen. In addition, a comparison was performed between the commercial P-25 and the Ag/ZnO/CoFe2O4 (5%) catalyst.

METHODS

Chemicals

The materials used in the synthesis of the photocatalysts, in the photocatalytic tests and in the HPLC analysis were: Co(NO3)2.6H2O (98%, Synth), Fe(NO3)3.9H2O (98% Synth), anhydrous citric acid (99.5%, Perquim), monoethylene glycol (99.5%, Dinâmica), acetonitrile (HPLC–supplied by J.T.Barker, Ciudad de México, México) PA-ACS–CH3CN (Panreac-AppliChem.), ZnO (supplied by DINAMICA with approximately 99% purity); AgNO3 (supplied by NEON with approximately 99.9% purity), ibuprofen (≥98% GC-supplied by Sigma-Aldrich, St Louis, USA). The molar concentration of aqueous solutions of metal nitrates used was 0.5 mol L−1.

Photocatalysts synthesis

Ag/ZnO (5% Ag)

Initially, ZnO doped with Ag (5%, wt. %) was prepared through the Pechini method, using ZnO and AgNO3 as precursors. The Ag/ZnO mass ratio and the calcination temperature of the catalyst were determined based on the best result obtained by Almeida et al. (2019). Initially, zinc oxide (ZnO) was dissolved in nitric acid (HNO3) and distilled water (H2O) solution, under mechanical stirring. Then AgNO3 aqueous solution was added to the solution in order to obtain Ag/ZnO (Ag:ZnO = 5:95, m/m). Next, citric acid (CA) 1.0 mol L−1 in water was added, in the Zn:AC molar ratio equal to 1:1.1. The mixture temperature was elevated to 60 °C and kept constant for 30 minutes. Then, monoethylene glycol (EG) was added, in the molar ratio of CA: EG = 1.5:1, and the solution was heated at 90 °C until the formation of the polymeric resin. This entire process was carried out inside a hood. The formed resin was dried at 110 °C for 16 hours and calcined in a muffle furnace at 400 °C for 5 h (heating rate equal to 1 °C min−1, with temperature kept constant at 100 °C). The final product was finally crushed to obtain fine particles.

Cobalt ferrite (CoFe2O4)

Similarly, cobalt ferrite was synthesized through the Pechini method, using Co(NO3)2.6H2O and Fe(NO3)3.9H2O as the metallic ions source (M = Co and Fe ions). Both salts were dissolved in water in stoichiometric proportions Co:Fe = 1:2. Citric acid (CA) solution was added to the mixture, in an M:CA molar equal to 1:1.1. Under mechanical stirring, the mixture was kept at 60 °C for 30 min. After this period, EG was added (CA:EG = 1.5:1), and the temperature was raised to 90 °C, end kept constant until a dark red resin was obtained. All the process was carried out inside a fume hood. The resin was dried and heat treated as described in the previous section. The resulting solid was crushed and stored.

Ag/ZnO/CoFe2O4

The CoFe2O4 particles were coated with a mixture of Ag/ZnO (Ag:ZnO = 5:95, m/m), using the Pechini method. The synthesis started with the dissolution of ZnO and AgNO3 in HNO3 aqueous solution and the addition of citric acid solution (Zn:CA = 1:1.1), as previously described (section 2.2.1). The solution temperature was maintained at 60 °C for 30 min, after which a CoFe2O4 suspension (which was sonicated for 30 min) was added. The CoFe2O4 mass used in the synthesis was varied to obtain photocatalysts with different CoFe2O4 content (5, 10 and 15%), in mass. As a result, four different photocatalysts were produced, which received the following nomenclature, respectively: Ag/ZnO/CoFe2O4(25%), Ag/ZnO/CoFe2O4(15%), Ag/ZnO/CoFe2O4(10%) and Ag/ZnO/CoFe2O4(5%). After the addition of the magnetic particles, EG was added (CA:EG = 1.5:1), and the temperature was raised to 90° C until the formation of a polymeric resin. All this process was carried out in a hood, and the formed resin was dried and calcined as described in section 2.2.1.

Characterization

As mentioned before, these techniques play a key role in predicting the catalyst properties. In this study, Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) and photoacoustic spectroscopy (PAS) in the UV-VIS region were used to characterize the developed catalysts.

X-ray diffraction

The samples were measured in a Rigaku-Denki diffractometer with Cu-Kα radiation (λ = 1.5406 Å) at a voltage of 140 V and current of 40 mA. Thus, the obtained patterns were compared with the diffraction dataset cards from the International Center for Diffraction Data (ICDD).

Photoacoustic spectroscopy (PAS)

The photoacoustic spectroscopy measurements in the UV-VIS spectral region were performed using a homemade experimental setup. The monochromatic light was obtained from a 1000 watt xenon arc lamp (66926, Oriel Corporation). The used monochromator was also from the Oriel Instruments (74100, CornerstoneTM 260 1/4 m). The light beam was modulated with a mechanical chopper (SR540, Stanford Research Systems) connected to the lock-in amplifier (SR830, Stanford Research Systems). The PA signal was detected by a sensitive microphone (4953, Brüel & Kjaer Instruments) coupled to a sealed photoacoustic cell.

Scanning electron microscopy (SEM)

SEM characterization was performed using a VEJA 3 LMU – TESCAN microscope with a 30 kV filament, 3.0 nm resolution SE and retractable BSE detectors, low-vacuum mode (500 Pa), chamber with 230 mm of inner diameter and CCD camera for preview of samples. Before performing the analyzes, all catalysts were metallized with gold for 10 minutes using the IC-50 ION COATER-SHIMADZU equipment.

Point of zero charge (PZC) determination

The point zero charge (PZC) was determined by applying a batch equilibration experiment (Guilarduci et al. 2006). In Erlenmyer flasks, 50 mg of catalyst and 50 ml of ultrapure water were mixed, under different initial pH values. Then constant stirring for 24 hours in a shaker at 298 K and 120 rpm, and the final pH measurements of the suspensions were performed. The pHPZC corresponded to the average of the final pH values which tended to a constant value, regardless of the initial pH value.

Photocatalytic tests

Solutions with different concentrations of ibuprofen (10, 20 and 30 ppm) were prepared in ultrapure water, with no pH adjustment, and used in photocatalytic tests, for comparison. The reaction mixture (250 mL) was transferred to a glass reactor consisting of a cylindrical Pyrex cell (2.5 × 10−4 m3) surrounded by a water jacket. The constant temperature (298 K) and the reaction homogeneity were assured by the use of an ultrathermostatic bath and a magnetic stirrer, respectively. The tests were performed under atmospheric conditions and air was pumped into the suspension at 8.3 × 10−9 m3 s−1. UV light was applied using a 125-W medium pressure mercury lamp (measured radiation incidence was 2.48 mW/cm2). The photocatalyst was added to the reaction mixture (concentration varied between 0.3, 0.5 and 1.0 g L−1) and the lamp was immediately turned on. Aliquots of the suspension were collected at regular intervals of time to monitor the IBP concentration.

The effects of different parameters in the photocatalytic efficiency were studied: IBP concentration, photocatalyst concentration, aqueous matrix (ultrapure water and tap water), the type of radiation source (artificial and solar) and the use of additive (formic acid). Also, in order to access the contribution of the adsorption and photolysis phenomena to the IBP removal, tests were performed using the same conditions previously described but with the lamp turned off (adsorption) or with the lamp turned on, but with no addition of the catalyst (photolysis). The tests were performed twice. Finally, a catalyst reuse test was performed, with three sequential reactions being conducted.

Determination of IBP concentration

Chromatographic analysis of ibuprofen were performed with a high performance liquid chromatograph YL Clarity model 9100 equipped with a pre-column, reverse phase C-18 column, and UV-VIS spectrophotometer (FEMTO, 800XI–λ = 215 nm).

It used the standard acetonitrile HPLC for chemical analysis and the pH control of sodium hydroxide and nitric acid. Different conditions were studied such as: pollutant initial concentration, catalyst concentration, matrix influence, solar radiation and additive addition (formic acid). The adsorption tests were performed by applying the same procedures as the previous photocatalytic test, but without the presence of light. The photolysis experiments were conducted using no catalysts and followed the same procedures as the photocatalytic tests.

RESULTS AND DISCUSSIONS

Magnetic separation of the photocatalysts

The synthesized catalysts and their respective magnetic separations processes were photographed and their images are shown in Figure 1. It was observed that the cobalt ferrite is strongly magnetic and could be easily separated from the aqueous medium with the aid of a magnet (Figure 1).

Figure 1

Magnetic separation of CoFe2O4 particles dispersed in water.

Figure 1

Magnetic separation of CoFe2O4 particles dispersed in water.

The magnetic particles coated with Ag/ZnO were still magnetic, since they were affected by the presence of the magnet (Figure 2). However, it was possible to notice a considerable decrease in the separation efficiency and a certain turbidity in the medium, even after 5 minutes of exposure to the magnetic field. This reduction in separation efficiency was more noticeable in photocatalysts with lower CoFe2O4 content (Figure 2). This effect of zinc oxide coating on the magnetic response of the particles was already expected, similarly to that previously reported by Fu et al. for TiO2/CoFe2O4 particles, whose coercivity and specific magnetization considerably decreased as the TiO2 percentage in the samples increased (Fu et al. 2005). To improve the magnetic separation of the particles, greater amounts of CoFe2O4 in the samples should be used Ag/ZnO/CoFe2O4.

Figure 2

Magnetic separation of CoFe2O4 particles coated with TiO2 dispersed in water.

Figure 2

Magnetic separation of CoFe2O4 particles coated with TiO2 dispersed in water.

Catalysts characterization

X-ray diffraction (XRD)

The diffractograms of the synthetized catalysts are shown in Figure 3.

Figure 3

XRD for catalysts (a) CoFe2O4; (b) Ag/ZnO/CoFe2O4(5%); (c) Ag/ZnO/CoFe2O4(10%); (d) Ag/ZnO/CoFe2O4(15%).

Figure 3

XRD for catalysts (a) CoFe2O4; (b) Ag/ZnO/CoFe2O4(5%); (c) Ag/ZnO/CoFe2O4(10%); (d) Ag/ZnO/CoFe2O4(15%).

The characteristic peaks of cobalt ferrite (JCPDS n° 79–1744, rhombohedral, space group R-3 m), notably the peaks located at 30.3° (1 0 4) and 35.6° (1 1 3), were identified in all samples (Figure 3). These peaks could be observed in the diffractograms even after the coating step, which led to a considerable decrease in the cobalt ferrite's peaks intensity. The rhombohedral structure of cobalt ferrite was previously reported in the literature for CoFe2O4 particles synthesized using an hydrothermal method with addition of ethylene glycol (Sun et al. 2011) and for cobalt ferrite particles produced through a sol-gel method (Ansari et al. 2018). The Ag/ZnO/CoFe2O4 samples presented the ZnO hexagonal phase (JCPDS no. 36-1451, space group P63mc), also known as wurtzite ZnO, which is considered to be the most stable phase of ZnO under ambient conditions (Kosera et al. 2017). Similar peaks were observed by Souza et al. (2017) in the diffractogram of ZnO commercial samples and by Andrade Neto (Andrade Neto et al. 2019) in the diffractograms of ZnO nanoparticles were synthesized using a microwave-assisted hydrothermal method. The present diffractograms also point out the considerable crystallinity of the samples calcined at 400 °C. Sahu et al. (2018), for example, obtained much less defined peaks for ZnO samples produced using a wet chemical method and dried at 80 °C without further calcination. It was also possible to identify in the Ag/ZnO/CoFe2O4 samples the presence of Ag with cubic structure (JCPDS no. 04-0783, space group Fm3m). This phase is associated with the peaks at 38.2° (1 1 1) and at 44.4° (2 0 0), which are similar to those observed by Li et al. in g-C3N4@Ag@Ag3PO4 nanocomposites (Li et al. 2017).

The Rietveld refinement performed in the diffractograms allowed the estimation of the phase percentage of the samples. The ZnO phase was the most abundant in the Ag/ZnO/CoFe2O4 samples (78.67%–90.23%) and the obtained result presented a good agreement with the CoFe2O4 nominal content considered in the synthesis (Table 1).

Table 1

Phase percentage of the samples estimated from the Rietveld refinement

CoFe2O4(R-3 m:H)ZnO (P63mc)Ag (Fm-3 m)
Ag/ZnO/CoFe2O4(5%) 5.25% 90.23% 4.52% 
Ag/ZnO/CoFe2O4(10%) 9.79% 86.20% 4.01% 
Ag/ZnO/CoFe2O4(15%) 17.79% 78.67% 3.54% 
CoFe2O4(R-3 m:H)ZnO (P63mc)Ag (Fm-3 m)
Ag/ZnO/CoFe2O4(5%) 5.25% 90.23% 4.52% 
Ag/ZnO/CoFe2O4(10%) 9.79% 86.20% 4.01% 
Ag/ZnO/CoFe2O4(15%) 17.79% 78.67% 3.54% 

Photoacoustic spectroscopy (PAS)

The UV-vis absorption spectra of pure ZnO, Ag and CoFe2O4, as well as the spectra of the photocatalysts Ag/ZnO, Ag/ZnO/CoFe2O4(5%), Ag/ZnO/CoFe2O4(10%) and Ag/ZnO/CoFe2O4(15%) are presented in Figure 4.

Figure 4

UV-Vis absorption spectra.

Figure 4

UV-Vis absorption spectra.

The ZnO spectrum exhibited a UV absorption band at 360 nm, which is a characteristic absorption peak of ZnO (Ramya et al. 2018). Ag exhibited a surface plasmon resonance (SPR) peak at approximately 404 nm (Das et al. 2016; Vijayakumar et al. 2020). However, the Ag/ZnO (5% Ag) absorption spectrum (in Figure 4(a)) was not a simple superposition of single materials spectrum. The SPR band of Ag/ZnO sample was subtly enlarged and shifted to red compared to that of pure Ag, probably due to the strong electronic coupling between the Ag and the ZnO layer and increased particle size. The red shift subtly increased with the increase of CoFe2O4 (see Figure 4(b)).

Figure 5 shows the phase of the PA signal for the samples. By applying the phase-resolved photoacoustic method (PRPA) (Fuziki et al. 2021), it was possible to observe that the Ag/ZnO (5% Ag) sample presented a phase difference of around 5° between the absorption peaks referring to ZnO (360 nm) and Ag (470 nm red shift). However, with the addition of CoFe2O4 this phase difference becomes less than 3°. Considering that 470 nm is related to SPR, it can be suggested that this resonance influences the non-radiative relaxation time of this absorbing center in cobalt ferrite presence.

Figure 5

Spectral separation.

Figure 5

Spectral separation.

Applying the linear method for calculating the band gap energy of the materials (Table 2), the values found for pure ZnO, Ag and CoFe2O4 were close to that already described in the literature (Das et al. 2016; Almeida et al. 2019). The Ag/ZnO (5% Ag) composite material showed two band gap, 2.95 eV associated with the Ag absorption band and 3.29 associated with ZnO. The addition of 5, 10 and 15% ferrite to the Ag/ZnO catalyst increased these values, however, did not imply a large variation in the band gap energy, resulting in an average value of (3.19 ± 0.03) eV for Ag and (3.37 ± 0.05) eV.

Table 2

Photocatalysts band gap energy (Eg) and wavelength (λ)

SampleEg (eV)
λ (nm)
CoFe2O4 2.78 (literature 2.7) (Holinsworth et al. 2013446
 
AgZnO (5% Ag) 2.95 3.29 420 377 
Ag/ZnO/CoFe2O4(5%) 3.21 3.43 386 362 
Ag/ZnO/CoFe2O4(10%) 3.20 3.36 387 369 
Ag/ZnO/CoFe2O4(15%) 3.16 3.33 392 372 
ZnO 3.20 (Literature: 3.1; 3.2; 3.3) (Srikant & Clarke 1998; Almeida et al. 2019387 
Ag 3.37 (Literature: 3.4) (Das et al. 2016368 
SampleEg (eV)
λ (nm)
CoFe2O4 2.78 (literature 2.7) (Holinsworth et al. 2013446
 
AgZnO (5% Ag) 2.95 3.29 420 377 
Ag/ZnO/CoFe2O4(5%) 3.21 3.43 386 362 
Ag/ZnO/CoFe2O4(10%) 3.20 3.36 387 369 
Ag/ZnO/CoFe2O4(15%) 3.16 3.33 392 372 
ZnO 3.20 (Literature: 3.1; 3.2; 3.3) (Srikant & Clarke 1998; Almeida et al. 2019387 
Ag 3.37 (Literature: 3.4) (Das et al. 2016368 

Scanning electron microscopy (SEM/EDS)

Figure 6 shows the SEM/EDS results. The incorporation of CoFe2O4 into the catalysts led to a change in the morphology of the material. It was noted that as the percentage of CoFe2O4 increased a more porous structure was formed. Conversely, this was not observed in the structure of pure CoFe2O4.

Figure 6

Scanning electron micrographs and energy dispersive spectra (a) 5%; (b) 10%; (c) 15%; (d) CoFe2O4.

Figure 6

Scanning electron micrographs and energy dispersive spectra (a) 5%; (b) 10%; (c) 15%; (d) CoFe2O4.

EDS analyzes indicated that for catalysts content 10 and 15% CoFe2O4 showed Zn, Ag, Co and Fe on the surface. Conversely, when the percentage is (5%), only Zn and Ag were observed, which suggests that all the cobalt ferrite is covered with Ag/ZnO.

Point of zero charge (PZC)

The results obtained for surface area and the PCZ values of the catalysts are shown in Figure 7.

Figure 7

PCZ of catalysts (a) ZnOAg; (b) ZnOAg@5%CoFe2O4; (c) ZnOAg@10%CoFe2O4; (d) ZnOAg@15%CoFe2O4.

Figure 7

PCZ of catalysts (a) ZnOAg; (b) ZnOAg@5%CoFe2O4; (c) ZnOAg@10%CoFe2O4; (d) ZnOAg@15%CoFe2O4.

The zero charge point of the catalysts were in the range between 7.2 and 7.5. Kosmulski (2009) described that the zero charge point depends mainly on the chemical nature of the particles, and also on the different crystalline planes of the compound. The PCZ value of TiO2 is 6.0 as indicated in the literature. In this context, Parks (1964) reports PCZ values for titanium dioxide in the rutile crystalline phase 5.8, and for anatase crystalline phase 5.6. For zinc oxide, the same author reports a PCZ value of about 8.6. Akyol et al. (2015) reports a ZnO PCZ value equal to 9.0.

Photocatalytic tests

Influence of the initial ibuprofen concentration

The results of tests performed with three different initial concentrations of ibuprofen are shown in Figure 8.

Figure 8

Influence of ibuprofen concentration (0.5 g L−1).

Figure 8

Influence of ibuprofen concentration (0.5 g L−1).

As shown in Figure 8, in the test using the lowest concentration of pollutant (10 ppm) a rapid IBP degradation was observed right at the beginning of the reaction, however an increase in the pollutant concentration was verified after 30 min of irradiation. This possibly refers to the kinetics being higher for the degradation and the generation of by-products, that is, with a lower concentration of ibuprofen it was degraded quickly generating by-products equally fast. Nevertheless, such behavior was not observed for the concentrations of 20 and 30 ppm.

Chen et al. (2020) studied the photocatalytic removal of ibuprofen using Eu/N-doped titanium dioxide coupled with cobalt ferrite as the catalyst, under visible light. The authors analyzed the influence of the initial concentration of the IBP solution, varying between 10, 15, 20, 25 and 30 mg L−1, and the results indicated removal percentages of 96.9%, 96, 6%, 96%, 95.6% and 95.1%, respectively, at the end of the reaction. The oxidation efficiency of IBP decreased with increasing initial pollutant concentration. The authors explained that the IBP can be adsorbed on the surface of the catalyst, blocking the active sites on the surface, causing the absorption of photons by the catalyst and preventing the formation of electron/hole pairs. Another explanation given by the authors is the possible competition of intermediate oxidation by-products with the IBP (Chen et al. 2020).

A study performed by Sarafraz et al. (2020) also evaluated the effect of the initial IBP concentration. The authors realized that by increasing the concentration from 2 to 10 mg L−1 the degradation reduced from 96% to 75%, respectively. The authors suggested that the increasing in the initial pollutant concentration increases the adsorption of IBP on the catalyst surface, leading to a decrease in the number of available active sites, which prevents O2 and OH from being adsorbed on the catalyst surface, reducing the generation of oxidizing species, thus decreasing the rate of degradation. In addition, the authors also explained that by increasing the initial concentration of pollutant, the amount of intermediates formed also increases, competing with the IBP molecules for active sites, in addition to consuming the oxidizing species, also impairing the degradation of the IBP (Sarafraz et al. 2020). Considering that faster reactions save time and energy, for the following tests the initial concentration of 10 ppm of ibuprofen was used.

Effect of catalyst concentration

Figure 9 shows the results obtained from experimental tests using different catalyst concentrations.

Figure 9

Catalyst concentration influence on photocatalytic removal of IBP for different catalysts: (a) (5%) Ag/ZnO; (b) Ag/ZnO/CoFe2O4(5%); (c) Ag/ZnO/CoFe2O4(10%); (d) Ag/ZnO/CoFe2O4(15%).

Figure 9

Catalyst concentration influence on photocatalytic removal of IBP for different catalysts: (a) (5%) Ag/ZnO; (b) Ag/ZnO/CoFe2O4(5%); (c) Ag/ZnO/CoFe2O4(10%); (d) Ag/ZnO/CoFe2O4(15%).

The general analysis of the tests (Figure 9) leads to the conclusion that the catalyst without ferrite (5% Ag/ZnO) presented a faster degradation kinetics in comparison with the other catalysts containing any percentage of ferrite. However, the ferrite-containing catalysts showed considerably good removal results and their use is still advantageous due to the possibility of magnetic separation. Interestingly, in the tests using 0.5 and 1.0 g L−1 of (5%) Ag/ZnO, the residual concentrations of the pollutant increased after 30 minutes of reaction, which may be related the formation of by-products as already mentioned in section 3.2.1.

Among the magnetic catalysts, the material containing 10% of ferrite (Figure 5(c)) showed the greater degradation efficiency. At the end of the reaction, the degradation rate obtained was 80, 70 and 66% in the reactions using 0.3 g L−1, 0.5 g L−1 and 1.0 g L−1 of the catalyst, respectively. However, the result obtained using 0.3 g L of this catalyst was not far from that obtained with 0.5 g L of Ag/ZnO/CoFe2O4(5%). Still, the use of the Ag/ZnO/CoFe2O4(10%) catalyst is preferable as it requires the use of a lower concentration to obtain a similar result.

Jing et al. (2016) studied the photocatalytic activity of CoFe2O4/Ag/Ag3VO4 magnetic catalysts in different weight proportions of CoFe2O4. The contents of CoFe2O4 studied were 1%, 5, 10 and 20%. When studying the catalytic activity of the material, the results showed that this activity increases with the increase in the CoFe2O4 content. However, the highest rate of degradation (90.3% in 16 min) was obtained using (5%) wt. of CoFe2O4. When the concentration of CoFe2O4 is greater than (5%), the degradation is close, but begins to decrease. The authors explained that the reason for this phenomenon is that the excess of CoFe2O4 can cover the surface of Ag/Ag3VO4, reducing the absorption of light by this compound and leading to a decrease in photocatalytic activity (Jing et al. 2016).

The same phenomenon happened in the present work when using the concentrations 5 and 10% cobalt ferrite. The percentage of degradation of the IBP was very close for both concentrations, being the excess of CoFe2O4 in the concentration of 10% responsible for preventing the absorption of light and making the photocatalytic activity very close to that exerted by the concentration (5%) CoFe2O4, making it unnecessary to use double ferrite in the 10% catalyst.

Regarding the best catalyst concentration to be used, by observing the behavior of the catalyst Ag/ZnO/CoFe2O4(5%) (Figure 9(b)), it can be concluded that values close to 0.5 g L−1 are possibly the optimum conditions for catalyst concentration, since there is no significant differences in the behavior of the kinetic curves when the amount of catalyst is doubled from 0.5 to 1.0 g L−1. In the case of catalysts containing 10 and 15% of CoFe2O4, the increase in the catalyst concentration came to harm the process, reducing the percentage of IBP removal.

Sarafraz et al. (2020) also studied the effect of the concentration of catalyst in the reaction medium. The researchers stated that by increasing the amount of catalyst in the medium, it increases the surface area that absorbs light and, consequently, increases the active sites available in the catalyst. This generates more active radicals that degrade more pollutant molecules. The study consisted of increasing the catalyst concentration from 0.1 to 0.4 g L−1 reflecting an increase in pollutant degradation from 57% to 96% respectively. However, by increasing the concentration of catalyst to 0.5 g L−1, the percentage of reduction decreased to approximately 90%, this fact was explained by the authors as an increase in the turbidity of the solution caused by the high amount of catalyst, causing a decrease in the absorption of light and, consequently, decrease in the efficiency of degradation (Sarafraz et al. 2020). Wetchakun et al. (2019) explains this phenomenon as a light screening effect, explaining that there is an optimum point regarding the concentration of catalysts in the reaction. If the amount of catalyst exceeds this optimum, there will be a difficulty in penetrating the light into the reaction, causing a decrease in the efficiency of the reaction (Wetchakun et al. 2019).

The work carried out by Mohamed et al. (2018), explained in section 3.2.1, also studied the effect of the amount of catalyst, ranging from 5 to 30 mg L−1, and the results showed an increase in the efficiency of pollutant degradation as the amount of catalyst increased, until it reached 15 mg L−1 where the degradation reached 100%, remaining the same at concentrations of 20, 25 and 30 mg L−1. The researchers attributed this to the increase in active sites in the solution, increasing the generation of electron pairs in the catalyst, forming more hydroxyl radicals and improving degradation (Mohamed et al. 2018).

Considering the obtained results and the fact that magnetic separation occurs for the two catalysts and the band gap obtain, with 5 and 10% of cobalt ferrite, it was decided to proceed using the catalyst Ag/ZnO/CoFe2O4(5%) in a concentration of 0.3 g L−1 in the following tests.

A comparison between the catalysts used in the study, in terms of ibuprofen kinetic and source of light, with other results found in the literature is presented in Table 3. The photocatalytic removal for different catalysts is also presented in Figure 10. The kinetic constant values selected for comparison refer to tests with 0.3 g L− 1 of catalyst. The analysis of the comparison results allows us to conclude that the photocatalytic degradation kinetics of ibuprofen depends on the catalyst used. However, we can observe that the studied catalyst indicated a result in the same order of magnitude as those found in the literature.

Table 3

Comparison of the catalyst in terms of kinetic parameters and source of light

CatalystKinetics rate constant (k) min−1Light sourceRefs.
Ag/ZnO 0.05819 min−1 UV 
Ag/ZnO/CoFe2O4(5%) 0.06961 min−1 UV 
Ag/ZnO/CoFe2O4(10%) 0.03905 min−1 UV 
Ag/ZnO/CoFe2O4(15%) 0.03874 min−1 UV 
Co-doped carbon matrix 0.0690 ** Ren et al. (2021)  
45#ferrosilicon 0.0262 ** Huang et al. (2021)  
Bi2O4/Fe3O4 0.0357 Visible light Xia & Lo (2016)  
BiOCl 0.2800 UV Arthur et al. (2018)  
CatalystKinetics rate constant (k) min−1Light sourceRefs.
Ag/ZnO 0.05819 min−1 UV 
Ag/ZnO/CoFe2O4(5%) 0.06961 min−1 UV 
Ag/ZnO/CoFe2O4(10%) 0.03905 min−1 UV 
Ag/ZnO/CoFe2O4(15%) 0.03874 min−1 UV 
Co-doped carbon matrix 0.0690 ** Ren et al. (2021)  
45#ferrosilicon 0.0262 ** Huang et al. (2021)  
Bi2O4/Fe3O4 0.0357 Visible light Xia & Lo (2016)  
BiOCl 0.2800 UV Arthur et al. (2018)  

*This work.

**No light source was used.

Figure 10

Photocatalytic removal of IBP for different catalysts.

Figure 10

Photocatalytic removal of IBP for different catalysts.

pH influence

To verify the pH influence, tests were performed for different pH ranges (acid–base). The results obtained were for pH 3, 4, 6, 7 and 11 of degradation of ibuprofen 33%, 36%, 32%, 37% and 38%, respectively (Figure 11). It was observed that pH was not a factor that significantly influenced the IBP degradation process.

Figure 11

IBP degradation in different pH [0.3 g L−1; 10 ppm, Ag/ZnO/CoFe2O4(5%)].

Figure 11

IBP degradation in different pH [0.3 g L−1; 10 ppm, Ag/ZnO/CoFe2O4(5%)].

Musmarra et al. (2016) studied the IBP degradation in water by hydrodynamic cavitation in a convergent–divergent nozzle. The pH influence was verified in values of 2, 9 and 6. The results indicated that pH does not affect the IBP degradation rate. A slight decrease in the degradation rate of IBP under acidic media was observed following the order pH 9 > pH 6 > pH 2 (Hama Aziz et al. 2017). Other authors have studied the degradation of ibuprofen at pH close to 6 (Hama Aziz et al. 2017; Sahmi et al. 2019).

Adsorption and photolysis

The adsorption and photolysis tests results are presented in Figure 11.

As can be seen in Figure 12(a), the pollutant concentration remained virtually constant throughout the 120 minutes of adsorption. Conversely, photolysis made a certain contribution to the IBP degradation, although in a smaller proportion than the photocatalytic tests, achieving a maximum removal of 20% in 30 minutes of reaction and remaining constant until the end of 120 minutes. Therefore, although photolysis shares in the contribution, it is necessary to combine radiation with the use of catalysts for a complete degradation of ibuprofen.

Figure 12

(a) Adsorption and (b) photolysis tests results.

Figure 12

(a) Adsorption and (b) photolysis tests results.

Influence of the matrix, radiation source and presence of additive

To check for possible influences on the degradation reaction of ibuprofen, other tests were carried out: with tap water matrix, solar radiation and with addition of an additive formic acid. All tests were carried out with the catalyst containing (5%) ferrite at a concentration of 0.5 g L−1 of catalyst and 10 ppm of ibuprofen. The results are shown in Figure 13.

Figure 13

Influence of (a) water matrix, (b) radiation source and (c) additive presence [0. 3 g L−1; 10 ppm, Ag/ZnO/CoFe2O4(5%)].

Figure 13

Influence of (a) water matrix, (b) radiation source and (c) additive presence [0. 3 g L−1; 10 ppm, Ag/ZnO/CoFe2O4(5%)].

The changes made in the variables aqueous matrix, radiation source and presence of additive had a negative influence on the degradation of ibuprofen. Starting with the change in the aqueous matrix to tap water, which contains other components that are not found in ultrapure water, such as chlorine ions (Cl), it was observed experimentally that the presence of these inorganic compounds may have interfered with the reaction. Cabrera-Reina and colleagues evaluated the use of TiO2 in the photodegradation of two antibiotics and verified a behavior similar to the one mentioned here, that is, in ultrapure water matrix the degradation was superior to the other matrices that were drinking river water and simulated effluent. The researchers reported that this reduction in photocatalytic activity is related to the presence of organic and inorganic compounds from the other matrices tested, and that, most likely, these compounds consumed the reactive molecules formed through photoreaction with TiO2, decreasing the photocatalytic activity of the material. degrading the pollutant (Cabrera-Reina et al. 2019). A similar phenomenon may have happened in the present study. Conversely, Fidelis et al. (2019) indicated the kinetics of higher formation in matrices containing Cl, applied in the triclosan degradation.

Another parameter that influenced the reaction was the radiation source. Using natural (solar) radiation is extremely advantageous, due to energy savings, however, in the present study, the use of solar radiation decreased the rate of reaction degradation when compared with artificial radiation from a 250 W lamp. The UVA/UVB radiation averages were in the range ∼10–13 mW cm−2. The tests under solar radiation were carried out in the months of February and March 2020, in the city of Ponta Grossa-PR, Brazil (Latitude: −25.0945, Longitude: −50.1633) between 9 am and 14 pm with an angle of 25° facing north for maximum efficiency in radiation incidence. The decrease in the catalytic activity was approximately 35%, which is the most influential among the tested parameters. Artificial radiation was constant at 10 mW cm−2.

Each semiconductor material used as a photocatalyst has a specific band gap energy. Thus, electronic excitation, and consequently the degradation of the pollutant, requires that the radiation source provides energy greater than the band gap energy of the photocatalyst. In terms of wavelength, Borges et al. exemplifies that for TiO2, whose band gap energy is 3.2 eV and absorption wavelength is close to 387 nm, it is necessary that the radiation provided has a wavelength less than 387 nm, that is, in the UV range. This type of wavelength can be provided by artificial radiation such as lamps. Conversely, when considering natural solar radiation, although UV radiation is emitted, it is known that its spectrum is composed only of approximately 5 to 8% of UV radiation, which may not make the process advantageous when using this radiation with TiO2 as a catalyst (Borges et al. 2016).

Following this same principle, it is noted that the catalysts tested here have a band gap energy close (Table 2) to that of TiO2 as exemplified by Borges et al. (2016) which, probably, when using solar radiation there was a decrease in activity catalytic effect of the material due to this relationship between the absorption wavelength of the catalyst and the wavelength of the emitted radiation.

As for the additive test, formic acid was used as the sacrifice agent. When looking at Figure 7(c), it can be seen that the addition of formic acid did not favor the degradation reaction of IBP, since the efficiency of the process was lower, as it may have generated organic intermediates in the reaction.

According to Marques et al. (2017), sacrificial agents are electron donor compounds that react irreversibly with the holes (h+) of the catalysts, resulting in greater quantum efficiency, that is, it prevents the deactivation of the catalyst that happens due to high electron/hole recombination speed (Marques et al. 2017). Momeni et al. (2020) explains that sacrificing agents can be used to minimize the recombination of electron-gap pairs in aqueous medium and, among the most used additives, methanol, ethanol, sugars, organic acids and glycerols, which have been used to increase the reaction rate (Momeni et al. 2020).

Bassaid et al. (2009) describe that one of the factors that limit the heterogeneous photocatalysis reaction is the rapid electron/hole recombination in the photocatalysts. The authors explain that one of the ways to solve this problem is the use of organic sacrificing agents, which work as electron donors. However, the authors report that in heterogeneous photocatalysis reactions, the use of an organic and soluble sacrifice agent can cause two main problems: the first is the formation of organic intermediates and the second is the elimination of the excess sacrifice agent (Bassaid et al. 2009). Such phenomena may have contributed to the lower degradation of the pollutant in the present work.

Reuse test

The result of sequential reuse of the catalyst containing (5%) ferrite is shown in Figure 14.

Figure 14

Reuse test using the Ag/ZnO/CoFe2O4(5%) catalyst (0.3 g L−1; 10 ppm).

Figure 14

Reuse test using the Ag/ZnO/CoFe2O4(5%) catalyst (0.3 g L−1; 10 ppm).

Through the analysis of Figure 13 it is possible to notice that the degradation of the IBP decreased after three cycles. In the first cycle, the degradation of IBP reached 100% in 120 minutes of reaction. In the second cycle, the percentage of degradation decreased to 91.6% and, at the end of the third cycle, the percentage of degradation reached 84.3%.

This loss of catalytic activity probably occurred due to the accumulation of IBP on the catalyst surface, decreasing the amount of active sites and the absorption of photons. As a consequence, there is a decrease in the degradation efficiency. Another possible cause is the loss of mass of catalyst during the recovery process, after the first and the second cycle, causing the amount of catalyst used in the subsequent tests to be less than 0.5 g L−1 and, consequently, the amount of active sites in the reaction medium was lower, also decreasing the degradation of the pollutant.

Raja et al. (2020) studied the degradation of IBP through the graphene oxide photocatalyst-HoVO4-TiO2 under visible light. The researchers carried out a photocatalyst reuse test for five consecutive cycles. The results showed a decrease in the efficiency of the process, from approximately 100% in the first cycle to 86% at the end of the 5th cycle. The authors justified this drop in efficiency with the absorption of IBP on the catalyst surface. However, the authors claim that the catalyst used is stable and reusable for decomposition of the IBP (Raja et al. 2020).

Lin et al. (2019) investigated the photocatalytic activity of titanium dioxide–boron nitride (TiO2–BN) nanocomposites for emergent contaminant removal in water, where IBP was used as a model compound. The authors stated that the reuse of catalysts in different treatment cycles is important to identify the practical application of a catalyst, as it can be harmed by some species (reaction intermediates) during the process. Therefore, the authors evaluated the recyclability of TiO2 and TB4 during 16 photocatalytic cycles. The results showed that the photocatalytic activity of TiO2 and TB4 remained, reaching 80 and 79% respectively, after eight consecutive cycles. However, there was a gradual decrease in the efficiency of degradation of IBP in the following eight cycles and the efficiency of TB4 was greater than that of TiO2. The authors justified that, through previous tests, it was noted that more IBP and intermediates were formed for TiO2 in relation to TB4 and attributed a decrease in photocatalytic activity to the generation and accumulation of intermediates, which remained in the catalyst and restricted the efficiency of pollutant degradation (Lin et al. 2019).

Comparison of commercial P25 and Ag/ZnO/CoFe2O4

A comparison between the commercial P-25 and the Ag/ZnO/CoFe2O4(5%) catalyst (Figure 15) was performed.

Figure 15

IBP photodegradation using TiO2–P25 and Ag/ZnO/CoFe2O4(5%) (a) TiO2–P25; (b) Ag/ZnO/CoFe2O4(5%) – chromatograms (HPLC).

Figure 15

IBP photodegradation using TiO2–P25 and Ag/ZnO/CoFe2O4(5%) (a) TiO2–P25; (b) Ag/ZnO/CoFe2O4(5%) – chromatograms (HPLC).

Results indicated that both photocatalysts (TiO2–P25 and Ag/ZnO/CoFe2O4(5%)) promoted a similar IBP degradation after 300 min of irradiation. However, the synthesized catalyst presented a more consistent photocatalytic activity, with the IBP concentration constantly decreasing during the photocatalytic test. Conversely, for TiO2–P25, an oscillation in the measured ibuprofen concentration was observed. The chromatograms (Figure 15(a) and 15(b)) indicated the presence of other peaks after the IBP retention time, suggesting the formation of intermediates. Conversely, after 300 min of photocatalysis, these peaks disappeared, indicating the degradation of these compounds. In addition, a shoulder formation in the IBP band was observed, when using the catalyst Ag/ZnO/CoFe2O4(5%), which also suggests the formation of different compounds (4-isobutylphenyl) ethanol and 4-isopropylacetophenone). Other authors have already described the formation of reaction intermediates during the IBP degradation (Da Silva et al. 2014; Quero-Pastor et al. 2014; Arthur et al. 2018).

CONCLUSIONS

The results obtained indicated that the Ag/ZnO/CoFe2O4 catalyst, used as a photocatalyst, proved to be an efficient alternative in the degradation of ibuprofen. Process optimization indicated that pH has no significant influence, with the zero charge point of the catalysts close to 7. Furthermore, the amount of cobalt ferrite did not affect the separation, conversely, the catalytic activity was higher for smaller amounts of CoFe2O4, that is, (5%). A smaller band gap was observed for the catalyst without ferrite (5% Ag/ZnO) and saturation of gap energy with an increase in the nominal load of cobalt ferrite.

It was observed that the higher the nominal load of cobalt ferrite, the greater the band gap. Solar radiation was not as effective in removing IBP as artificial radiation, which is constant. The results indicated a IBP removal used Ag/ZnO/CoFe2O4 [0.3 g L−1, pH 7] of 80 and 47%, artificial and solar radiation, respectively. The reuse of the catalyst made it possible for the percentage of degradation to reach 84.3% in the third cycle. The results of tests performed with TiO2–P25 indicated that the synthesized catalyst was more stable during the IBP degradation process.

ACKNOWLEDGEMENTS

This work was conducted using of the UTFPR. The authors are thankful to the Brazilian agencies CNPq and CAPES for financial support of this work and C2MMa the equipment. CBMM

DATA AVAILABILITY STATEMENT

All relevant data are available are included in the paper.

REFERENCES

Ahmed
S.
,
Rasul
M. G.
,
Brown
R.
&
Hashib
M. A.
2011
Influence of parameters on the heterogeneous photocatalytic degradation of pesticides and phenolic contaminants in wastewater: a short review
.
J. Environ. Manage.
92
,
311
330
.
https://doi.org/10.1016/j.jenvman.2010.08.028
.
Almeida
L. N. B.
,
Lenzi
G. G.
,
Pietrobelli
J. M. T. A.
&
Santos
O. A. A.
2019
Caffeine degradation using ZnO and Ag/ZnO under UV and solar radiation
.
Desalin. Water Treat.
153
,
85
94
.
https://doi.org/10.5004/dwt.2019.24045
.
Andrade Neto
N. F.
,
Matsui
K. N.
,
Paskocimas
C. A.
,
Bomio
M. R. D.
&
Motta
F. V.
2019
Study of the photocatalysis and increase of antimicrobial properties of Fe3+ and Pb2+ co-doped ZnO nanoparticles obtained by microwave-assisted hydrothermal method
.
Mater. Sci. Semicond. Process.
93
,
123
133
.
https://doi.org/10.1016/j.mssp.2018.12.034
.
Ansari
F.
,
Sobhani
A.
&
Salavati-Niasari
M.
2018
Simple sol-gel synthesis and characterization of new CoTiO3/CoFe2O4 nanocomposite by using liquid glucose, maltose and starch as fuel, capping and reducing agents
.
J. Colloid Interface Sci.
514
,
723
732
.
https://doi.org/10.1016/j.jcis.2017.12.083
.
Antezana
A. F. G.
&
Hurtado
T. L. L.
2016
Efectos sobre la salud en los trabajadores expuestos al dióxido de titanio
.
Med. Segur. Trab. (Madr)
62
, 79–95.
Arthur
R. B.
,
Bonin
J. L.
,
Ardill
L. P.
,
Rourk
E. J.
,
Patterson
H. H.
&
Stemmler
E. A.
2018
Photocatalytic degradation of ibuprofen over BiOCl nanosheets with identification of intermediates
.
J. Hazard. Mater.
358
,
1
9
.
https://doi.org/10.1016/j.jhazmat.2018.06.018
.
Bassaid
S.
,
Robert
D.
&
Chaib
M.
2009
Use of oxalate sacrificial compounds to improve the photocatalytic performance of titanium dioxide
.
Appl. Catal. B Environ.
86
,
93
97
.
https://doi.org/10.1016/j.apcatb.2008.07.027
.
Borges
M. E.
,
Sierra
M.
,
Méndez-Ramos
J.
,
Acosta-Mora
P.
,
Ruiz-Morales
J. C.
&
Esparza
P.
2016
Solar degradation of contaminants in water: TiO2 solar photocatalysis assisted by up-conversion luminescent materials
.
Sol. Energy Mater. Sol. Cells.
155
,
194
201
.
https://doi.org/10.1016/j.solmat.2016.06.010
.
Cabrera-Reina
A.
,
Martínez-Piernas
A. B.
,
Bertakis
Y.
,
Xekoukoulotakis
N. P.
,
Agüera
A.
&
Sánchez Pérez
J. A.
2019
TiO2 photocatalysis under natural solar radiation for the degradation of the carbapenem antibiotics imipenem and meropenem in aqueous solutions at pilot plant scale
.
Water Res.
166
,
115037
.
https://doi.org/10.1016/j.watres.2019.115037
.
Candido
J. P.
,
Andrade
S. J.
,
Fonseca
A. L.
,
Silva
F. S.
,
Silva
M. R. A.
&
Kondo
M. M.
2016
ibuprofen removal by heterogeneous photocatalysis and ecotoxicological evaluation of the treated solutions
.
Environ. Sci. Pollut. Res.
23
,
19911
19920
.
https://doi.org/10.1007/s11356-016-6947-z
.
Chen
Y.
,
Wang
X.
,
Wang
J.
&
Song
Y.
2020
Photocatalytic removal of ibuprofen using euxti1-xO2-yNy/CoFe2O4 decorated on diatomaceous earth under visible light irradiation
.
J. Environ. Chem. Eng.
8
,
1
12
.
https://doi.org/10.1016/j.jece.2020.104448
.
Choina
J.
,
Kosslick
H.
,
Fischer
C.
,
Flechsig
G. U.
,
Frunza
L.
&
Schulz
A.
2013
Photocatalytic decomposition of pharmaceutical ibuprofen pollutions in water over titania catalyst
.
Appl. Catal. B Environ.
129
,
589
598
.
https://doi.org/10.1016/j.apcatb.2012.09.053
.
Dalponte
I.
,
Mathias
A. L.
,
Jorge
R. M. M.
&
Weinschutz
R.
2016
Degradação fotocatalítica de tartrazina com TiO2 imobilizado em esferas de alginato
.
Quim. Nova.
39
,
1165
1169
.
https://doi.org/10.21577/0100-4042.20160141
.
Das
A. J.
,
Kumar
R.
,
Goutam
S. P.
&
Sagar
S. S.
2016
Sunlight irradiation induced synthesis of silver nanoparticles using glycolipid bio-surfactant and exploring the antibacterial activity
.
J. Bioeng. Biomed. Sci.
06
,
1000208
.
https://doi.org/10.4172/2155-9538.1000208
.
Dasgupta
A.
&
Krasowski
M. D.
2020
Chapter 14- Analgesics
. In:
Ther. Drug Monit. Data
, 4th edn, pp.
309
330
.
https://doi.org/10.1016/B978-0-12-815849-4.00014-1
.
Fidelis M. Z., Abreu E., Santos O. A. A., Chaves E. S., Brackmann R., Dias D. T. &, Lenzi G. G. 2019
Experimental design and optimization of triclosan and 2.8-diclorodibenzeno-p-dioxina degradation by the Fe/Nb2O5/UV System
. Catalysts 9, 343. https://doi:10.3390/catal9040343.
Fontana
K. B.
,
Chaves
E. S.
,
Kosera
V. S.
&
Lenzi
G. G.
2018
Barium removal by photocatalytic process: an alternative for water treatment
.
J. Water Process Eng.
22
,
163
171
.
https://doi.org/10.1016/j.jwpe.2018.01.017
.
Fu
W.
,
Yang
H.
,
Li
M.
,
Li
M.
,
Yang
N.
&
Zou
G.
2005
Anatase TiO2 nanolayer coating on cobalt ferrite nanoparticles for magnetic photocatalyst
.
Mater. Lett.
59
,
3530
3534
.
https://doi.org/10.1016/j.matlet.2005.06.071
.
Fuziki
M. E. K.
,
Brackmann
R.
,
Dias
D. T.
,
Tusset
A. M.
,
Specchia
S.
&
Lenzi
G. G.
2021
Effects of synthesis parameters on the properties and photocatalytic activity of the magnetic catalyst TiO2/CoFe2O4 applied to selenium photoreduction
.
J. Water Process Eng.
42
,
102163
.
https://doi.org/10.1016/j.jwpe.2021.102163
.
Giacomni
F.
,
Menegazzo
M. A. B.
,
da Silva
M. G.
,
da Silva
A. B.
&
de Barros
M. A. S. D.
2017
Importância da determinação do ponto de carga zero como característica de tingimento de fibras proteicas
.
Rev. Mater.
22
.
https://doi.org/10.1590/S1517-707620170002.0159
.
Gonçalves
R. L. d. N.
,
Costa
A. C. F. d. M.
&
Pereira
K. R. d. O.
2019
Uso de catalisador magnético do tipo ferrita níquel-zinco para a obtenção de biodiesel
.
J. Eng. Exact Sci.
5
,
0195
0198
.
https://doi.org/10.18540/jcecvl5iss2pp0195-0198
.
Guilarduci
V. V. D. S.
,
De Mesquita
J. P.
,
Martelli
P. B.
&
Gorgulho
H. D. F.
2006
Adsorção de fenol sobre carvão ativado em meio alcalino
.
Quim. Nova.
29
,
1226
1232
.
https://doi.org/10.1590/S0100-40422006000600015
.
Gusmão
K. B.
,
Pergher
S. B. C.
&
dos Santos
E. N.
2017
um panorama da catálise no brasil nos últimos 40 ansos
.
Quim. Nova.
40
,
650
655
.
Hama Aziz
K. H.
,
Miessner
H.
,
Mueller
S.
,
Kalass
D.
,
Moeller
D.
,
Khorshid
I.
&
Rashid
M. A. M.
2017
Degradation of pharmaceutical diclofenac and ibuprofen in aqueous solution, a direct comparison of ozonation, photocatalysis, and non-thermal plasma
.
Chem. Eng. J.
313
,
1033
1041
.
https://doi.org/10.1016/j.cej.2016.10.137
.
Haw
C.
,
Chiu
W.
,
Abdul Rahman
S.
,
Khiew
P.
,
Radiman
S.
,
Abdul Shukor
R.
,
Hamid
M. A. A.
&
Ghazali
N.
2016
The design of new magnetic-photocatalyst nanocomposites (CoFe2O4-TiO2) as smart nanomaterials for recyclable-photocatalysis applications
.
New J. Chem.
40
,
1124
1136
.
https://doi.org/10.1039/c5nj02496j
.
Holinsworth
B. S.
,
Mazumdar
D.
,
Sims
H.
,
Sun
Q. C.
,
Yurtisigi
M. K.
,
Sarker
S. K.
,
Gupta
A.
,
Butler
W. H.
&
Musfeldt
J. L.
2013
Chemical tuning of the optical band gap in spinel ferrites: CoFe2O4 vs NiFe2O4
.
Appl. Phys. Lett.
103
,
2
5
.
https://doi.org/10.1063/1.4818315
.
Huang
Y.
,
Liang
M.
,
Ma
L.
,
Wang
Y.
,
Zhang
D.
&
Li
L.
2021
Ozonation catalysed by ferrosilicon for the degradation of ibuprofen in water
.
Environ. Pollut.
268
,
115722
.
https://doi.org/10.1016/j.envpol.2020.115722
.
Jacinto
M. J.
,
Ferreira
L. F.
&
Silva
V. C.
2020
Magnetic materials for photocatalytic applications – a review
.
J. Sol-Gel Sci. Technol.
96
.
https://doi.org/10.1007/s10971-020-05333-9
.
Jia
Y.
,
Khanal
S. K.
,
Yin
L.
,
Sun
L.
&
Lu
H.
2021
Influence of ibuprofen and its biotransformation products on different biological sludge systems and ecosystem
.
Environ. Int.
146
,
106265
.
https://doi.org/10.1016/j.envint.2020.106265
.
Jing
L.
,
Xu
Y.
,
Huang
S.
,
Xie
M.
,
He
M.
,
Xu
H.
,
Li
H.
&
Zhang
Q.
2016
Novel magnetic CoFe2O4/Ag/Ag3VO4 composites: highly efficient visible light photocatalytic and antibacterial activity
.
Appl. Catal. B Environ.
199
,
11
22
.
https://doi.org/10.1016/j.apcatb.2016.05.049
.
Josué
T. G.
,
Almeida
L. N. B.
,
Lopes
M. F.
,
Santos
O. A. A.
&
Lenzi
G. G.
2020
Cr (VI) reduction by photocatalyic process: Nb2O5 an alternative catalyst
.
J. Environ. Manage.
268
,
1
9
.
https://doi.org/10.1016/j.jenvman.2020.110711
.
Khedkar
C. V.
,
Khupse
N. D.
,
Thombare
B. R.
,
Dusane
P. R.
,
Lole
G.
,
Devan
R. S.
,
Deshpande
A. S.
&
Patil
S. I.
2020
Magnetically separable Ag-Fe3O4 catalyst for the reduction of organic dyes
.
Chem. Phys. Lett.
742
,
1
33
.
https://doi.org/10.1016/j.cplett.2020.137131
.
Kosera
V. S.
,
Cruz
T. M.
,
Chaves
E. S.
&
Tiburtius
E. R. L. L.
2017
Triclosan degradation by heterogeneous photocatalysis using ZnO immobilized in biopolymer as catalyst
.
J. Photochem. Photobiol. A Chem.
344
,
184
191
.
https://doi.org/10.1016/j.jphotochem.2017.05.014
.
Kosmulski
M.
2009
Surface Charging and Points of Zero Charge
.
CRC Press
,
Boca Raton
.
Li
X.
,
Wan
T.
,
Qiu
J.
,
Wei
H.
,
Qin
F.
,
Wang
Y.
,
Liao
Y.
,
Huang
Z.
&
Tan
X.
2017
In-situ photocalorimetry-fluorescence spectroscopy studies of RhB photocatalysis over Z-scheme g-C3N4@Ag@Ag3PO4nanocomposites: a pseudo-zero-order rather than a first-order process
.
Appl. Catal. B Environ.
217
,
591
602
.
https://doi.org/10.1016/j.apcatb.2017.05.086
.
Li
S.
,
Cui
J.
,
Wu
X.
,
Zhang
X.
,
Hu
Q.
&
Hou
X.
2019
Rapid in situ microwave synthesis of Fe3O4@MIL-100(Fe) for aqueous diclofenac sodium removal through integrated adsorption and photodegradation
.
J. Hazard. Mater.
373
,
408
416
.
https://doi.org/10.1016/j.jhazmat.2019.03.102
.
Lin
L.
,
Jiang
W.
,
Bechelany
M.
,
Nasr
M.
,
Jarvis
J.
,
Schaub
T.
,
Sapkota
R. R.
,
Miele
P.
,
Wang
H.
&
Xu
P.
2019
Adsorption and photocatalytic oxidation of ibuprofen using nanocomposites of TiO2 nanofibers combined with BN nanosheets: degradation products and mechanisms
.
Chemosphere.
220
,
921
929
.
https://doi.org/10.1016/j.chemosphere.2018.12.184
.
Liu
N.
,
Wang
J.
,
Wu
J.
,
Li
Z.
,
Huang
W.
,
Zheng
Y.
,
Lei
J.
,
Zhang
X.
&
Tang
L.
2020
Magnetic Fe3O4@MIL-53(Fe) nanocomposites derived from MIL-53(Fe) for the photocatalytic degradation of ibuprofen under visible light irradiation
.
Mater. Res. Bull.
132
,
1
31
.
https://doi.org/10.1016/j.materresbull.2020.111000
.
Lopes
O. F.
,
De Mendonça
V. R.
,
Silva
F. B. F.
,
Paris
E. C.
&
Ribeiro
C.
2015
Niobium oxides: an overview of the synthesis of Nb2O5 and its application in heterogeneous photocatalysis
.
Quim. Nova.
38
,
106
117
.
Macedo
L. d. O.
,
Barbosa
E. J.
,
Löbenberg
R.
&
Bou-Chacra
N. A.
2021
Anti-inflammatory drug nanocrystals: state of art and regulatory perspective
.
Eur. J. Pharm. Sci.
158
,
105654
.
https://doi.org/10.1016/j.ejps.2020.105654
.
Malvar
J. L.
,
Martín
J.
,
Orta
M. d. M.
,
Medina-Carrasco
S.
,
Santos
J. L.
,
Aparicio
I.
&
Alonso
E.
2020
Simultaneous and individual adsorption of ibuprofen metabolites by a modified montmorillonite
.
Appl. Clay Sci.
189
,
105529
.
https://doi.org/10.1016/j.clay.2020.105529
.
Marques
F. C.
,
Stumbo
A. M.
&
Canela
M. C.
2017
Estratégias e materiais utilizados em fotocatálise heterogênea para geração de hidrogênio através da fotólise da água
.
Quim. Nova.
40
,
561
571
.
https://doi.org/10.21577/0100-4042.20170015
.
Mohamed
A.
,
Salama
A.
,
Nasser
W. S.
&
Uheida
A.
2018
Photodegradation of ibuprofen, Cetirizine, and Naproxen by PAN-MWCNT/TiO2–NH2 nanofiber membrane under UV light irradiation
.
Environ. Sci. Eur.
30
,
1
9
.
https://doi.org/10.1186/s12302-018-0177-6
.
Momeni
M. M.
,
Akbarnia
M.
&
Ghayeb
Y.
2020
Preparation of S–W-codoped TiO2 nanotubes and effect of various hole scavengers on their photoelectrochemical activity: alcohol series
.
Int. J. Hydrogen Energy.
45
,
33552
33562
.
https://doi.org/10.1016/j.ijhydene.2020.09.112
.
Musmarra D., Prisciandaro M., Capocelli M., Karatza D., Iovino P., Canzano S. & Lancia A. 2016
Degradation of ibuprofen by hydrodynamic cavitation: Reaction pathways and effect of operational parameters
. Ultrason. Sonochem. 29, 76–83. https://doi.org/10.1016/j.ultsonch.2015.09.002.
Nunes
Y. L.
,
de Menezes
F. L.
,
de Sousa
I. G.
,
Cavalcante
A. L. G.
,
Cavalcante
F. T. T.
,
da Silva Moreira
K.
,
de Oliveira
A. L. B.
,
Mota
G. F.
,
da Silva Souza
J. E.
,
de Aguiar Falcão
I. R.
,
Rocha
T. G.
,
Valério
R. B. R.
,
Fechine
P. B. A.
,
de Souza
M. C. M.
&
dos Santos
J. C. S.
2021
Chemical and physical Chitosan modification for designing enzymatic industrial biocatalysts: how to choose the best strategy?
Int. J. Biol. Macromol.
181
,
1124
1170
.
https://doi.org/10.1016/j.ijbiomac.2021.04.004
.
Parks
G. A.
1964
The isoelectric points of solid oxides, solid hydroxides, and aqueous hydroxo complex systems
.
Chem. Rev.
65
,
177
198
.
https://doi.org/10.1021/cr60234a002
.
Quero-Pastor
M. J.
,
Garrido-Perez
M. C.
,
Acevedo
A.
&
Quiroga
J. M.
2014
Ozonation of ibuprofen: a degradation and toxicity study
.
Sci. Total Environ.
466–467
,
957
964
.
https://doi.org/10.1016/j.scitotenv.2013.07.067
.
Raja
A.
,
Rajasekaran
P.
,
Selvakumar
K.
,
Arivanandhan
M.
,
Asath Bahadur
S.
&
Swaminathan
M.
2020
Rational fabrication of needle with spherical shape ternary reduced Graphene Oxide-HoVO4-TiO2 photocatalyst for degradation of ibuprofen under visible light
.
Appl. Surf. Sci.
513
,
1
11
.
https://doi.org/10.1016/j.apsusc.2020.145803
.
Ramya
E.
,
Rao
M. V.
,
Jyothi
L.
&
Rao
D. N.
2018
Photoluminescence and nonlinear optical properties of transition metal (Ag, Ni, Mn) doped ZnO nanoparticles
.
J. Nanosci. Nanotechnol.
18
,
7072
7077
.
https://doi.org/10.1166/jnn.2018.15521
.
Ren
Z.
,
Romar
H.
,
Varila
T.
,
Xu
X.
,
Wang
Z.
,
Sillanpää
M.
&
Leiviskä
T.
2021
ibuprofen degradation using a Co-doped carbon matrix derived from peat as a peroxymonosulphate activator
.
Environ. Res.
193
,
0
11
.
https://doi.org/10.1016/j.envres.2020.110564
.
Sahmi
A.
,
Omeiri
S.
,
Bensadok
K.
&
Trari
M.
2019
Electrochemical properties of the scheelite BaWO4 prepared by co-precipitation: application to electro-photocatalysis of ibuprofen degradation
.
Mater. Sci. Semicond. Process.
91
,
108
114
.
https://doi.org/10.1016/j.mssp.2018.11.017
.
Sahu
K.
,
Kuriakose
S.
,
Singh
J.
,
Satpati
B.
&
Mohapatra
S.
2018
Facile synthesis of ZnO nanoplates and nanoparticle aggregates for highly efficient photocatalytic degradation of organic dyes
.
J. Phys. Chem. Solids.
121
,
186
195
.
https://doi.org/10.1016/j.jpcs.2018.04.023
.
Santos
S. G. S.
,
Paulista
L. O.
,
Silva
T. F. C. V.
,
Dias
M. M.
,
Lopes
J. C. B.
,
Boaventura
R. A. R.
&
Vilar
V. J. P.
2019
Intensifying heterogeneous TiO2 photocatalysis for bromate reduction using the NETmix photoreactor
.
Sci. Total Environ.
664
,
805
816
.
https://doi.org/10.1016/j.scitotenv.2019.02.045
.
Sarafraz
M.
,
Amini
M. M.
,
Adiban
M.
&
Eslami
A.
2020
Facile synthesis of mesoporous black N–TiO2 photocatalyst for efficient charge separation and the visible-driven photocatalytic mechanism of ibuprofen degradation
.
Mater. Sci. Semicond. Process.
120
,
1
9
.
https://doi.org/10.1016/j.mssp.2020.105258
.
Shao
G. N.
,
Jeon
S. J.
,
Haider
M. S.
,
Abbass
N.
&
Kim
H. T.
2016
Investigation of the influence of vanadium, iron and nickel dopants on the morphology, and crystal structure and photocatalytic properties of titanium dioxide based nanopowders
.
J. Colloid Interface Sci.
474
,
179
189
.
https://doi.org/10.1016/j.jcis.2016.04.024
.
Silva
A. L.
,
Farias
A. F. F.
,
Costa
A. C. F. M.
,
Federal
U.
,
Grande
D. C.
&
Grande
C.
2019
Avaliação do tratamento térmico no catalisador magnético por transesterificação e esterificação simultânea do óleo de fritura
.
Cerâmica.
65
,
13
27
.
Souza
R. P.
,
Ambrosio
E.
,
Souza
M. T. F.
,
Freitas
T. K. F. S.
,
Ferrari-Lima
A. M.
&
Garcia
J. C.
2017
Solar photocatalytic degradation of textile effluent with TiO2, ZnO, and Nb2O5 catalysts: assessment of photocatalytic activity and mineralization
.
Environ. Sci. Pollut. Res.
24
,
12691
12699
.
https://doi.org/10.1007/s11356-017-8408-8
.
Srikant
V.
&
Clarke
D. R.
1998
On the optical band gap of zinc oxide
.
J. Appl. Phys.
83
,
5447
5451
.
https://doi.org/10.1063/1.367375
.
Streit
A. F. M.
,
Collazzo
G. C.
,
Druzian
S. P.
,
Verdi
R. S.
,
Foletto
E. L.
,
Oliveira
L. F. S.
&
Dotto
G. L.
2021
Adsorption of ibuprofen, ketoprofen, and paracetamol onto activated carbon prepared from effluent treatment plant sludge of the beverage industry
.
Chemosphere.
262
,
128322
.
https://doi.org/10.1016/j.chemosphere.2020.128322
.
Sun
D. H.
,
Zhang
J. L.
&
Sun
D. X.
2011
Synthesis and characterization of MFe2O4(M = Co,Ni) nanoparticles
.
Adv. Mater. Res.
236–238
,
1893
1896
.
https://doi.org/10.4028/www.scientific.net/AMR.236-238.1893
.
Teixeira
C. P. d. A. B.
&
Jardim
W. d. F.
2004
Caderno Temático - Processos Oxidativos Avançados, In: Cad. Temático, Campinas – SP
, pp.
1
83
.
Vijayakumar
S.
,
Malaikozhundan
B.
,
Parthasarathy
A.
,
Saravanakumar
K.
,
Wang
M. H.
&
Vaseeharan
B.
2020
Nano biomedical potential of biopolymer chitosan-capped silver nanoparticles with special reference to antibacterial, antibiofilm, anticoagulant and wound dressing material
.
J. Clust. Sci.
31
,
355
366
.
https://doi.org/10.1007/s10876-019-01649-x
.
Yao
M.
,
Duan
L.
,
Song
Y.
&
Hermanowicz
S. W.
2021
Degradation mechanism of ibuprofen via a forward osmosis membrane bioreactor
.
Bioresour. Technol.
321
,
124448
.
https://doi.org/10.1016/j.biortech.2020.124448
.
Zhang
L.
,
Lyu
T.
,
Zhang
Y.
,
Button
M.
,
Arias
C. A.
,
Weber
K. P.
,
Brix
H.
&
Carvalho
P. N.
2018
Impacts of design configuration and plants on the functionality of the microbial community of mesocosm-scale constructed wetlands treating ibuprofen
.
Water Res.
131
,
228
238
.
https://doi.org/10.1016/j.watres.2017.12.050
.
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