Abstract
Hierarchical porous TiO2 photocatalytic nanomaterials were fabricated by impregnation and calcination using a peanut shell biotemplate, and TiO2/BiFeO3 composite nanomaterials with different doping amounts were fabricated using hydrothermal synthesis. The micromorphology, structure, element composition and valence state of the photocatalyst were analyzed using a series of characterization methods, including X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), BET surface area (BET), X-ray photoelectron spectroscopy (XPS), UV-visible diffuse reflectance (UV-vis), fluorescence spectroscopy (PL) and other technological means. Finally, the degradation mechanism and efficiency of BiFeO3 composite photocatalyst on the target pollutant triclosan were analyzed using a xenon lamp to simulate sunlight. The results showed that TiO2/BiFeO3 catalyst fabricated using a peanut shell biotemplate has a specific surface area of 153.64 m2/g, a band gap of 1.92 eV, and forms heterostructures. The optimum doping amount of TiO2/BiFeO3 catalyst was 1 mol/mol, and the degradation rate was 81.2%. The main active substances degraded were ·O2−and ·OH. The degradation process measured is consistent with the pseudo-first-order kinetic model.
HIGHLIGHTS
TiO2 loading can increase the specific surface area and empty volume of BiFeO3 and provide more active sites.
Through total organic carbon analysis, the mineralization rate of total organic carbon of TiO2/BiFeO3 photocatalyst is 58.9%.
h+ and ·OH are the active substances for degradation of triclosan. Relatively speaking, · OH has more obvious inhibition on triclosan and is the main active oxidizing substance.
INTRODUCTION
The anti-fungal and antibiotic agent triclosan (TCS) can be commonly found in hygiene products such as soaps and toothpaste. However, the ubiquity of TCS has led to concerns about its increasing presence in the water environment and its potential to cause harm. TCS is continuously accumulated and enriched by domestic sewage systems, and ultimately discharged into the environment. The sewage and sludge containing TCS seriously affect the water environment, not only endangering aquatic animals and plants but also threatening human health through food chain disruption (Chen et al. 2019a; Zheng et al. 2020). As a result of human activities and the large consumption of chemicals, many pollutants are released into the environment. Pharmaceuticals and personal care products (PPCPs) are frequently detected worldwide, which has become an emerging risk contaminant and attracted increasing international attention. PPCPs mainly include pharmaceuticals and other chemical consumer goods, veterinary medicine, nursing products and additives and inert ingredients used in the production and processing process. Triclosan (TCS) is a typical PPCP chemical, which is often added to consumers' daily care products as a broad-spectrum fungicide. It can be found in soap, toothpaste, cosmetics, medical disinfectants and other sanitary products. According to statistics (Zhao et al. 2013a), as early as 2006, the annual consumption of TCS in Europe exceeded 450 tons, and the annual consumption in the United States exceeded 600 tons. Many nursing products after daily use enter the sewage treatment system along with sewage and eventually enter the environment. At present, as one of the ten most common organic pollutants in organic wastewater, TCS has been listed as one of the most concerning emerging pollutants. With the continuous detection of TCS in the environment, the demand for efficient removal of TCS technology is particularly urgent. Research on the toxic effects of TCS can be traced back to the 1970s when researchers discovered that people with sensitive skin would develop allergic reactions when using soap, and the higher the content of TCS, the more obvious the degree of allergy (Ouyang et al. 2020; Farhadi et al. 2021; Saravanakumar & Park 2021). Now, researchers have found that the long-term presence of TCS in the environment may contaminate soil and harm aquatic organisms, mammals and human beings (Castro et al. 2017; Sharipova et al. 2017; Chen et al. 2019b; Subramanian et al. 2019).
Photocatalytic technology is a newly emerging technology, involving multiple fields, such as nanometer materials, catalytic chemistry and materials science (Schneider et al. 2014; Zhao et al. 2014). Since photocatalytic technology uses renewable solar energy to degrade pollutants under natural light (Dona-Rodriguez & Pulido Melian 2021) and is environmental-friendly, it has currently become an important means to treat micropollutants in sewage. In recent years, the development of new photocatalysts has become a much discussed subject, having far-reaching significance for the degradation of environmental organic matter. Photocatalysis refers to the process where semiconductor photocatalytic materials convert the energy gained from ultraviolet or visible light exposure into chemical energy. Through a series of reactions, this chemical energy is then used to decompose harmful organic matter into non-polluting organic matter (Zhang et al. 2007; Mao et al. 2020). The energy band theory can also explain the principles of semiconductor photocatalysis. The electronic energy levels at the interior of semiconductors are relatively independent, mainly including conduction band and valence band (Soltani & Lee 2016a; Singh & Rajput 2019). When the light shines on the surface of the semiconductor catalyst with a photon energy greater than the band gap width (Eg), the electrons on the semiconductor valence band are excited to transition from the valence band (VB) to the conduction band (CB), forming photogenerated electrons (e−) and holes (h+). The strong oxidation potential of h+ can generate hydroxyl radicals (•OH) from H20 adsorbed on the catalyst surface and generate superoxide radicals (•O2) through the interaction of photogenerated electrons (e−) and O2. These free radicals also with strong oxidation potential can degrade organic pollutants such as dyes into non-toxic or less toxic organic small molecules, even CO2 and H2O, to achieve the purpose of advanced treatment of pollutants.
The forbidden bandwidth of semiconductor materials determines the intrinsic electrical and optical properties of the materials. Specifically, under illuminated conditions, if the energy absorbed by valence electrons is greater than or equal to the forbidden band width energy gap, then electrons in the valence band of the material can be excited, and the electrons can migrate to the conduction band of the material. When the conduction band receives electrons to form photogenerated electrons, the valence band will lose electrons and form photogenerated holes (Kim et al. 2013; Soltani & Lee 2016b; Jiao et al. 2017; Chang et al. 2019). Photogenerated holes and electrons (photogenerated carriers) have oxidation and reduction potential and can oxidize organic pollutants into small inorganic molecules, and also generate strong oxidizing •OH through H2O on the surface of semiconductor materials to oxidize organic pollutants (Abraham & Mathew 2021).
Bismuth ferrite (BiFeO3) is widely studied as a multiferroic material (Rong et al. 2016; Sazali et al. 2019). Since the forbidden band width of bismuth ferrite is around 2.2 eV to 2.8 eV (Maleki et al. 2017; Wu et al. 2018; Xu et al. 2018; Yan & Liu 2019), it can respond to visible light to some extent, and belongs to a new type of photocatalytic materials (Maleki 2018; Greculeasa et al. 2019; Lu & Qi 2019). However, like most semiconductor materials, its low quantum efficiency prohibits its application in wastewater treatment (Soltani & Lee 2017; Li et al. 2018, 2019a). Therefore, the key to enhancing the activity of BiFeO3 materials is to control the migration and separation of photogenerated charges. At present, the common methods to improve the photocatalytic activity of BiFeO3 materials mainly include controlling the morphology and particle size, doping (Zhang et al. 2014; Yu et al. 2015; Guan et al. 2018; Abdul Satar et al. 2019; Li et al. 2019b) and forming composites with other semiconductor materials. The modified BiFeO3 can significantly inhibit the recombination of photogenerated carriers and enhance its response to visible light (Wang et al. 2019). While the research is currently in the early stages, the performance of BiFeO3 in current experiments shows great potential for future developments, such as the design and preparation of multi-dimensional nanostructured photocatalytic materials with more practical properties such as nanotubes, nanorods and nanofibers (Zhu et al. 2012; Pi et al. 2017; Zatsepin et al. 2017). In addition, the photocatalytic mechanism of the BiFeO3 complex can be further explored to comprehensively analyze its energy band structure and interface characteristics, and more intuitively understand the photon conversion and photocatalytic process. It can also be used to develop economical and environmentally friendly modified materials with strong light stability, and further explore the applications of BiFeO3 in the photocatalytic reduction of CO2 and the decomposition of water for hydrogen production (Pang & Lei 2016; Chandel et al. 2017; Wei et al. 2017).
By combining wide band-gap semiconductor TiO2 with narrow band-gap semiconductor BiFeO3, the TiO2/BiFeO3, heterostructure exhibits higher photocatalytic activity than either pure TiO2 or BiFeO3. The formation of the TiO2/BiFeO3 heterostructure improves the photocatalytic performance, enhances the photoinduced charge transfer and promotes the separation of photogenerated electrons and holes. As far as we know, there were no reports on the preparation of TiO2/BiFeO3 photocatalytic materials using peanut shell biotemplate. The biotemplate is used to prepare photocatalysts based on predetermined structures and functions, that have unique advantages such as variable structure and superior functions. The original morphology and microstructure of the template can be completely replicated with peanut shell biomimetic materials. In the following research, the preparation of hierarchical porous TiO2 catalyst from bio-templated peanut shells is presented in detail (Zhao et al. 2013b; Chandel et al. 2017; Wang et al. 2018). On this basis, a new type of TiO2/BiFeO3/biochar composite is explored using a hydrothermal synthesis method doped with different amounts of BiFeO3. Discussions focus on the synthesis and characterization of TiO2/BiFeO3 hierarchical porous material and the influencing factors on the photocatalytic degradation of TCS. Thus, the possible degradation mechanism can be deduced, which may contribute to the provision of a new green and efficient method for photocatalytic TCS degradation.
MATERIALS AND METHODS
Chemicals and reagents
Titanium dioxide (analytically pure, MacLean Biochemical Technology Co., Ltd), hydrochloric acid, ammonia, anhydrous ethanol (analytically pure, Beijing Chemical Plant), bismuth nitrate, iron nitrate (Tianjin Guangfu Fine Chemical Research Institute), triclosan (Shanghai Aladdin Bio-Chem Technology Co., Ltd), sodium oxalate, isopropanol, sodium thiosulfate, p-Benzoquinone (analytically pure, Tianjin Guangfu Fine Chemical Research Institute), and peanut shells (harvested cropland).
Glass instruments used in the experiment (Tianjin Tianbo Glass Instrument Co., Ltd), PL-X300D simulated fluorescent xenon lamp source (Beijing Prinsess Technology Co., Ltd), muffle furnace (KSI-60-16 Longkou Xianke Co., Ltd), high-performance liquid chromatography (1200LC Agilent), total organic carbon analyzer (TOC-VCPH, Shimadzu, Japan), X-ray photoelectron spectrometer (SmartLab (3KW), Japan Science of Physics), X-ray diffractometer (XD-3 Shimadzu, Japan), scanning electron microscope (XL-30ESEM, USA FEI), transmission electron microscope (FEI G2 F20, USA FEI), specific surface area and pore size analyzer (ASAP2020, USA Micrometrics), ultraviolet-visible spectrophotometer (UV-2550 Shimadzu, Japan).
Preparation of biomorphic TiO2/BiFeO3
Pretreatment of peanut shells
A number of peanut shells were selected and washed in water 3-5 times to remove impurities from the surface. The washed peanut shells were then soaked in 5% hydrochloric acid for 3 h to remove excess ions, to provide more growth sites, and then washed with distilled water repeatedly until pH neutral. Extracted peanut shells were soaked in hydrochloric acid with 5% dilute ammonia water for 3 h to increase the absorbability. The peanut shells after ammonia extraction and acid soaking were then washed with distilled water repeatedly, and dried in a 60 °C oven for standby.
Preparation of hierarchical porous TiO2
- (1)
Preparation of tetrabutyl titanate solution: 200 mL tetrabutyl titanate was added to 600 mL ethanol, and then 2 mL glacial acetic acid was added to prevent hydrolysis of the tetrabutyl titanate.
- (2)
The pretreated peanut shells were immersed in the prepared tetrabutyl titanate solution. This was sealed and placed aside for 48 h, and then the solution was poured out, leaving behind the peanut shells. The peanut shells were then washed with anhydrous ethanol three times to remove the tetrabutyl titanate adhering to the surface. The peanut shells were then washed three times with distilled water and dried.
- (3)
The dried peanut shells were calcined at around 100 °C in a muffle furnace, the temperature was then increased to 550 °C at a rate of 2 °C/min, this was then left to anneal for 4 h to remove the peanut shell template completely. Finally, pure TiO2 with a template was obtained.
Preparation of BiFeO3 and TiO2/BiFeO3 with different doping ratios by hydrothermal synthesis
Photocatalytic performance evaluation
TCS detection method:
X-bridge@C18 (4.6 mm*250 mm, 5 μm) reverse chromatographic column and Waters e2695 high-performance liquid chromatograph with Waters 2998 diode array tube detector detect TCS.
RESULTS AND DISCUSSION
Characterization results of catalyst structure
Band gap widths of different catalysts
Name of catalyst . | TiO2 photocatalyst . | BiFeO3 photocatalyst . | 0.5TiO2/BiFeO3 photocatalyst . | 0.8TiO2/BiFeO3 photocatalyst . | TiO2/BiFeO3 photocatalyst . | 1.5TiO2/BiFeO3 photocatalyst . |
---|---|---|---|---|---|---|
Absorption edge (nm) | 378 | 664 | 665 | 681 | 684 | 700 |
Band gap (eV) | 3.26 | 2.23 | 2.57 | 2.37 | 1.92 | 2.49 |
Name of catalyst . | TiO2 photocatalyst . | BiFeO3 photocatalyst . | 0.5TiO2/BiFeO3 photocatalyst . | 0.8TiO2/BiFeO3 photocatalyst . | TiO2/BiFeO3 photocatalyst . | 1.5TiO2/BiFeO3 photocatalyst . |
---|---|---|---|---|---|---|
Absorption edge (nm) | 378 | 664 | 665 | 681 | 684 | 700 |
Band gap (eV) | 3.26 | 2.23 | 2.57 | 2.37 | 1.92 | 2.49 |
XRD patterns of TiO2, BiFeO3 (a) and TiO2/BiFeO3 (b) composite photocatalysts.
The SEM results of peanut shell (a) and (b) and peanut shell loaded with TiO2 (c) and (d).
The SEM results of peanut shell (a) and (b) and peanut shell loaded with TiO2 (c) and (d).
The change in crystalline form of silica has a significant impact on the collapse of the residual structure of photocatalytic materials, indicating that the silica carbon network structure can act as a specific template (Gong et al. 2013). This template can provide natural microchannels for the photocatalytic materials, increasing the specific surface area of the TiO2 catalytic materials. After the peanut shells were soaked in tetrabutyl titanate, the peanut shells were completely immersed in the titanium solution, and the porous structure on the inner surface of the peanut shells was opened by high-temperature calcination, which allowed tetrabutyl titanate solution to enter its internal structure and react with carbon to form TiO2-CX structures (Khan et al. 2020). It can be seen from Figure 3(c) and 3(d) that the TiO2 photocatalyst was prepared using a peanut shell biotemplate had a spherical structure and smooth surface. Its structure was closely connected and closely arranged, which can present the characteristics of the hierarchical porous structure of peanut shells, increase the number of active sites and hence effectively improve the photocatalytic activity. However, it can be seen from the figure that there were some incomplete fragments. The reason for this may be that the peanut shell itself was damaged or the internal structure of the peanut shell template had defects.
The SEM results of TiO2/BiFeO3 photocatalyst 5k (a),10k (b, c), 20k (d) prepared by biological template in peanut shell.
The SEM results of TiO2/BiFeO3 photocatalyst 5k (a),10k (b, c), 20k (d) prepared by biological template in peanut shell.
The TEM results of TiO2/BiFeO3 photocatalyst 100 nm (a), 50 nm (b), 5 nm (c), 2 nm (d) prepared by biological template in peanut shell.
The TEM results of TiO2/BiFeO3 photocatalyst 100 nm (a), 50 nm (b), 5 nm (c), 2 nm (d) prepared by biological template in peanut shell.
Nitrogen adsorption isotherm (a) and pore size distribution curve (b) of 1TiO2/BiFeO3 photocatalyst.
Nitrogen adsorption isotherm (a) and pore size distribution curve (b) of 1TiO2/BiFeO3 photocatalyst.
XPS pattern of 1TiO2/BiFeO3 (a) full pattern; (b) Ti 2p; (c) Fe 2P; (d) Bi 4f; (e) O 1s; and (f) C 1s.
XPS pattern of 1TiO2/BiFeO3 (a) full pattern; (b) Ti 2p; (c) Fe 2P; (d) Bi 4f; (e) O 1s; and (f) C 1s.
UV-Vis DRS spectra of TiO2, BiFeO3 and TiO2/BiFeO3 with different parameter ratios.
UV-Vis DRS spectra of TiO2, BiFeO3 and TiO2/BiFeO3 with different parameter ratios.

Photoluminescence spectra of BiFeO3 and 1TiO2/BiFeO3 photocatalysts.
Study on the activity of photocatalytic degradation of TCS
wherein: C0 - the initial reaction concentration of TCS after dark reaction;
Ct – the concentration of TCS at time t after the beginning of the photoreaction process;
t – reaction time.
Kinetic equations of different catalysts
Catalyst name . | Quasi first-order kinetic equation . | R2 . |
---|---|---|
TiO2 photocatalyst | y = 0.10511t + 0.25393 | 0.9852 |
BiFeO3 photocatalyst | y = 0.14214t + 0.23107 | 0.9887 |
1TiO2/BiFeO3 photocatalyst | y = 0.17143t + 0.31112 | 0.9952 |
Catalyst name . | Quasi first-order kinetic equation . | R2 . |
---|---|---|
TiO2 photocatalyst | y = 0.10511t + 0.25393 | 0.9852 |
BiFeO3 photocatalyst | y = 0.14214t + 0.23107 | 0.9887 |
1TiO2/BiFeO3 photocatalyst | y = 0.17143t + 0.31112 | 0.9952 |
Effects (a) and kinetics (b) of TCS degradation by TiO2, BiFeO3 and 1TiO2/BiFeO3 photocatalysts.
Effects (a) and kinetics (b) of TCS degradation by TiO2, BiFeO3 and 1TiO2/BiFeO3 photocatalysts.
Kinetic equation of TiO2/BiFeO3 with different doping ratios
Catalyst name . | Quasi first-order kinetic equation . | R2 . |
---|---|---|
0.5 TiO2/BiFeO3 photocatalyst | y = 0.20357t + 0.6275 | 0.9532 |
0.8 TiO2/BiFeO3 photocatalyst | y = 0.23929t + 0.6937 | 0.9687 |
1 TiO2/BiFeO3 photocatalyst | y = 0.29786t + 0.9961 | 0.9737 |
1.5 TiO2/BiFeO3 photocatalyst | y = 0.25511t + 0.8075 | 0.9701 |
Catalyst name . | Quasi first-order kinetic equation . | R2 . |
---|---|---|
0.5 TiO2/BiFeO3 photocatalyst | y = 0.20357t + 0.6275 | 0.9532 |
0.8 TiO2/BiFeO3 photocatalyst | y = 0.23929t + 0.6937 | 0.9687 |
1 TiO2/BiFeO3 photocatalyst | y = 0.29786t + 0.9961 | 0.9737 |
1.5 TiO2/BiFeO3 photocatalyst | y = 0.25511t + 0.8075 | 0.9701 |
Effects (a) and kinetics (b) of TCS degradation by TiO2, BiFeO3 and 1TiO2/BiFeO3 photocatalysts of different doping ratios.
Effects (a) and kinetics (b) of TCS degradation by TiO2, BiFeO3 and 1TiO2/BiFeO3 photocatalysts of different doping ratios.
In order to explore the degradation process and mechanism of TCS degradation by TiO2/BiFeO3 composite photocatalyst, the 1TiO2/BiFeO3 photocatalyst with the best degradation effect was selected to for degradation process and mechanism analysis through the analysis of total organic carbon and trapping experiments.
Variation of TOC concentration (a) and kinetics (b) of photocatalytic degradation of TCS by TiO2/BiFeO3.
Variation of TOC concentration (a) and kinetics (b) of photocatalytic degradation of TCS by TiO2/BiFeO3.
Results of active species trapping for degradation of TCS solution by TiO2/BiFeO3 photocatalyst.
Results of active species trapping for degradation of TCS solution by TiO2/BiFeO3 photocatalyst.
Schematic diagram of a mechanism for the TiO2/BiFeO3 under visible light irradiation.
Schematic diagram of a mechanism for the TiO2/BiFeO3 under visible light irradiation.
Through the analysis of the results of the trapping experiment, we can infer the possible mechanism of degradation of TCS by the 1TiO2/BiFeO3 photocatalyst. When the light energy is greater than the forbidden band width of BiFeO3, electrons will be excited from the valence band and transferred to the conduction band, h+ (Zhang et al. 2022) will be generated around the valence band, electrons will be transferred to TiO2 photocatalyst, and oxygen molecules will be captured to produce •O2–. These h + oxidized water molecules in the valence band will produce •OH, •OH and •O2− (Wei et al. 2020) to oxidize the TCS molecules adsorbed onto the surface of BiFeO3. The peanut shell biotemplate has mesoporous structure, so it increases the specific surface area of TiO2 photocatalyst, the number of active sites and the photocatalytic activity (Jaffari et al. 2021). In addition, TiO2 and BiFeO3 form heterostructures, which can be fully confirmed by TEM, XPS and other characterization techniques. The heterostructure can effectively reduce the recombination rate of electron-hole and increase the photocatalytic activity. The forbidden band width of BiFeO3 catalyst is 2.23 eV, easily excited to generate electron hole pairs. The forbidden band width of TiO2 catalyst is 3.26 eV, not easy to be excited. When these two catalysts are doped with each other, as shown in Figure 14, the forbidden band width is 1.92 eV, forming a uniform lattice fringe. When the electrons are irradiated by xenon lamp, the conduction band of TiO2 photocatalyst will be transferred from BiFeO3 photocatalyst, thus inhibiting the electron-hole recombination, and improving the performance of photocatalysis.
It can be seen from the comparison in Table 4 that in terms of TCS removal, 1TiO2/BiTiO3 can achieve the same removal rate and specific surface area, and has good development prospects.
Comparison of TCS removal by different materials
Sample . | Target pollutant . | BET(m2/g) . | Active species . | Removal rate(%) . | Reference . |
---|---|---|---|---|---|
1TiO2/BiTiO3 | TCS | 59.59 | h+ /•OH | 81.6 | This research |
Bi7O9I3/Bi | TCS | / | •OH/•O2 | 85 | Chang et al. (2021) |
SnO2@ZnS | TCS | 123.1 | h+ /•OH | 40 | Hojamberdiev et al. (2020) |
Bi2O3/BiOI | TCS | / | •OH/•O2 | 73.2 | Xu et al. (2022) |
rGO–TiO2 | TCS | 50 | •OH | 87 | Kaur et al. (2020) |
Sample . | Target pollutant . | BET(m2/g) . | Active species . | Removal rate(%) . | Reference . |
---|---|---|---|---|---|
1TiO2/BiTiO3 | TCS | 59.59 | h+ /•OH | 81.6 | This research |
Bi7O9I3/Bi | TCS | / | •OH/•O2 | 85 | Chang et al. (2021) |
SnO2@ZnS | TCS | 123.1 | h+ /•OH | 40 | Hojamberdiev et al. (2020) |
Bi2O3/BiOI | TCS | / | •OH/•O2 | 73.2 | Xu et al. (2022) |
rGO–TiO2 | TCS | 50 | •OH | 87 | Kaur et al. (2020) |
CONCLUSION
In this experiment, peanut shells were used as a biotemplate to prepare a hierarchical porous TiO2 catalyst, which was then used to synthesize TiO2/BiFeO3 photocatalysts with different doping amounts using the hydrothermal method. Through a series of studies on their morphology, structure and photocatalytic activity, combined with the total organic carbon and capture experimental results, the possible degradation mechanism was determined, and the main conclusions are as follows:
- (1)
Through XRD analysis and comparison, it can be seen that the characteristic diffraction peak of 1TiO2/BiFeO3 photocatalyst is consistent with the standard card, showing a better phase crystalline form. Through scanning electron microscopy (SEM), we can see that 1TiO2/BiFeO3 photocatalyst shows a cotton-like structure, and nanometer-grade particle size, which was closely arranged and formed a heterogeneous structure. The lattice fringes of 1TiO2/BiFeO3 photocatalyst can be seen from the TEM image, wherein, the spacing of one group of lattice fringe is 0.19 nm, corresponding to the lattice plane of TiO2 photocatalyst (101), and the spacing of the other group of lattice fringes is 0.22 nm, corresponding to the lattice surface of BiFeO3 photocatalyst (110). The results confirm the existence of heterostructures, which expand the light frequency and wavelength response range. The average diameter of 1TiO2/BiFeO3 photocatalyst was 14.98 nm according to BET analysis, and the specific surface area was 153.64 m2/g. The XPS spectra show that the valence of Ti is tetravalent, and that of Fe and Bi is trivalent. It shows that the crystal structures of TiO2 and BiFeO3 do not affect each other, and each element keeps its original valence. The position of the composite diffraction peak of the two XRD patterns is consistent with that of the single diffraction peak. UV-Vis diffuse reflection analysis shows that the absorption edge of 1TiO2/BiFeO3 photocatalyst is about 550 nm, and its forbidden bandwidth is 1.92 eV. PL analysis shows that the recombination rate of photogenerated carriers in 1TiO2/BiFeO3 photocatalyst is low, which may be because the close bond between BiFeO3 and TiO2 makes the photo-generated carriers migrate at the interface so that the electrons generated in the BiFeO3 conduction band quickly transfer through TiO2, thus reducing the recombination probability of photo-generated electrons and holes and enhancing photocatalytic degradation activity.
- (2)
The degradation process and kinetics of TCS by TiO2, BiFeO3 and 1TiO2/BiFeO3 photocatalysts were compared and analyzed. The results showed that the degradation process conformed to quasi-first-order kinetics. The degradation rates of TiO2 photocatalyst, BiFeO3 photocatalyst and 1TiO2/BiFeO3 photocatalyst were 38.7%, 49.6% and 81.2%, respectively. By comparing the photodegradation effect of different doping amounts of TiO2/BiFeO3 photocatalyst, it is concluded that the best doping amount of photocatalyst is 1 mol/mol, that is, 1TiO2/BiFeO3 photocatalyst, and the degradation process conforms to the quasi first-order kinetics, indicating that the doping amount of BiFeO3 affects the photocatalytic performance of TiO2/BiFeO3 photocatalyst.
- (3)
The mineralization rate of total organic carbon in 1TiO2/BiFeO3 photocatalyst is 58.9%, which accords with the quasi-first-order kinetics. Through the analysis of the trapping experiment, it is concluded that OH plays the main role of strong oxidation in the degradation process, and O2− plays the secondary role of strong oxidation. We can generally infer the possible mechanism of degradation, that is when the light energy is greater than the forbidden band width of BiFeO3, electrons will be excited from the valence band and transferred to the conduction band, h+ will be generated around the valence band, electrons will be transferred to TiO2 photocatalyst, and oxygen molecules will be trapped to produce •O2−. The h+ oxidized water molecules in the valence band will produce •OH, •OH and •O2 - to oxidize the TCS molecules adsorbed on the surface of BiFeO3.
ACKNOWLEDGEMENTS
Our work was supported by the National Natural Science Foundation of China (Grant No. 51778267), the National Water Pollution Control and Treatment Science and Technology Major Project (No. 2012ZX07408001), the Jilin Province Science and Technology Department Project (No. 20220203047SF).
AUTHORS CONTRIBUTION DECLARATION
Gen Liu: Conceptualization, methodology, analysis, data curation, writing – original draft preparation, visualization, and investigation. Yingzi Lin: Reviewing. Siwen Li: Supervision. Chunyan Shi: Validation. Daihua Zhang: Methodology.
DATA AVAILABILITY STATEMENT
All relevant data are included in the paper or its Supplementary Information.
CONFLICT OF INTEREST
The authors declare there is no conflict.