Synthesized Fe0-rGO nanocomposite with ratio of 1/1 (w/w) was prepared and has been used as adsorbent for the removal of Carbamazepine (CBZ) from aqueous solution. The adsorbent was characterized by various techniques such as Fourier-transform infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and Field Emission Scanning Electron Microscopy (FE-SEM) analyses. Linear experiments were performed to compare the best fitting isotherms and kinetics. The Freundlich isotherm (R2>0.90) and pseudo second order kinetic (R2>0.99) fitted well the experimental data. On the basis of the Langmuir isotherm, the maximum adsorption capacity of Fe0-rGO for CBZ was up to 50 mg g−1 at 30 °C. The pH, adsorbent dose, and initial concentration of CBZ were observed to be the leading parameters that affected the removal of CBZ considering the analysis of variance (ANOVA; p<0.05). The optimum process value of variables obtained by numerical optimization corresponds to pH 3.07, an adsorbent dose of 36.2 mg, an initial CBZ concentration of 5 mg L–1 and at 30.15 °C. The results of optimum conditions reveal that a maximum of 94% removal efficiency can be achieved; whereas, this phenomenon was independent of temperature (p-value>0.05). Moreover, Fe0-rGO can be used to remove diclofenac (DIC) and cetirizine (CTZ) simultaneously. To sum up, the Fe0-rGO is a promising adsorbent not only for the efficient removal of CBZ but also for the reduction of coexisting drugs in aqueous solution.

  • The nanocomposite was successfully synthesized.

  • The adsorption of three hard to remove drugs was investigated.

  • The effect of various parameters on CBZ removal were determined.

  • The optimum condition for CBZ removal was obtained.

  • The interference of coexisting drugs on CBZ adsorption was investigated.

Graphical Abstract

Graphical Abstract
Graphical Abstract

The expanding production and consumption of pharmaceutical products have unavoidably brought about the arrival of a wide assortment of manmade organic compounds into the environment. These unregulated substances, namely contaminants of emerging concern (CECs), enter the environment at low concentrations mainly through municipal wastewater treatment plants (MWWTP) as these facilities are not designed for the removal of contaminants at ppb values (Bendz et al. 2005; Joss et al. 2005; Krzeminski et al. 2019). Among different classes of materials, pharmaceuticals are attracting greatest attention as they are exceptionally persistent in the environment, simultaneously showing an incredible affinity with regards to transformation, and creating intermediate products (metabolites), which, in numerous instances, are more harmful than the parent compounds (Grassi et al. 2013; Petrie et al. 2015). Carbamazepine (CBZ), which is monetarily known as ‘Tegretol’, is utilized for treatment of mental disorders, epilepsy, depression and trigeminal neuralgia (Gurung et al. 2018). Roughly, 72% of orally administered carbamazepine is absorbed, while 28% remains unchanged and eventually discharged through the faeces (RxList 2008). Carbamazepine has been one of the most frequently detected drugs in water bodies; thus, it is proposed as an anthropogenic marker in aqueous media (Clara et al. 2004; Patel et al. 2019). Investigations have shown that carbamazepine is persistent as its removal efficiency in WWTPs is nearly less than 10% (Strenn et al. 2004; Joss et al. 2005; Luo et al. 2014).

Various techniques have been developed to remove carbamazepine, including advanced oxidation process (Davididou et al. 2017), ozonation (Naddeo et al. 2015), biodegradation (Naghdi et al. 2018), ultra-sonication (Davididou et al. 2017), combined activated sludge and ionization (Kimura et al. 2012), membrane processes (Prado et al. 2017; Ravi et al. 2020), and adsorption (Deng et al. 2019; Bhattacharya et al. 2020). Adsorption is considered as the promising technique to remove pharmaceuticals from aqueous solution due to its straightforward design, cost-effective, easy operation, high performance, and most importantly, there is no generation of hazardous by-products in the environment (Rivera-Utrilla et al. 2013).

Zero-valent iron nanoparticles (nZVI- Fe0) have gained attention in recent years for environmental remediation, attributable to their ecological harmlessness, high reactivity, large surface area, and cost efficacy (Zhang 2003; Zou et al. 2016). Some exceptional exhibition has been reported for nZVI in removal of pollutants from contaminated soil and groundwater (Li et al. 2016; Eljamal et al. 2018). Nonetheless, due to the high magnetic and van der Waals forces, nZVI tends to agglomerate in aquifer media, which ultimately lessens its efficiency in pollutant removal (Mehrabi et al. 2019). Agglomeration of nZVI particles can be reduced either by modifying their surface, utilizing surfactant and polymers, or by loading these nanoparticles on an appropriate support. Owing to the extended surface area (almost 2,650 m2 g−1) and great mechanical durability, graphene and its products have been considered for supporting metal nanoparticles (Liu et al. 2010). Graphene is a two-dimensional carbonaceous nanomaterial shaped from a layer of sp2 hybridized carbon molecules. The graphene nanomaterial exhibits notable properties such as high particular surface area, exceptional electrocatalytic activity, high thermal conductivity, substantial strength, and expeditious electron mobility (Lee et al. 2008; Stoller et al. 2008). Besides, graphene has generally huge and delocalized π-electron framework, which may show binding properties for target pollutants (Kuila et al. 2012). Graphene has been applied in various fields as the forms of extended graphene single layers, graphene oxide (GO), and reduced graphene oxide (rGO) (Zhao et al. 2015). rGO is generally produced by GO reduction following chemical reaction methods, thermal annealing and hydrothermal (Kim et al. 2018). The basal plane of rGO empowers its recurrent changes by non-covalent physical sorption of both polymers and minor molecules by π–π stacking or van der Waals interactions. A low number of oxygen functional groups are observed in rGO, which enrich aqueous media with an electrical charge. Application of additional nanostructure on graphene may also improve its surface chemistry and physical characteristics (Sanchez et al. 2012).

The most common graphene-based materials applied for organic removals from water are GO and GO composites in which ππ interaction and cation–π bonding are known as the route of adsorption. The adsorption capacity of GO, however, has changed following its modification by metal oxide or metal nanoparticles, though there are no conclusive reports on the adsorption properties following the addition of second phase on graphene-based materials (Hazell et al. 2016; Yu et al. 2017; Huang et al. 2019). The effectiveness of modified graphene oxide with decafluorobiphenyl for carbamazepine removal was examined by Shan et al. (2017), who found the adsorption capacity of 340.5 μmoL·g−1. Gao et al. (2012) examined tetracycline removal by GO and reported varied sorption capacities ranging from 212.31 to 398.41 mg g−1. Bhunia et al. (2012) investigated the adsorption properties of rGO–Fe0 and rGO– Fe3O4 composite for As (III) removal from water. They concluded that the adsorption capacity was higher in rGO–Fe0 (37 mg g−1) as compared with rGO–Fe3O4 (21 mg g−1) due to the improvement of relative surface area in rGO–Fe0.

Few studied have been conducted to evaluate the adsorption properties of modified rGO for pharmaceuticals. In the current study, Fe0-rGO nanocomposite was prepared and used as adsorbent for CBZ removal from aqueous solution.

This research set out with the aim of assessing (1) the characteristic of synthesized Fe0-rGO using Fe-SEM, SEM, FTIR and XRD; (2) the effect of operation conditions (pH, temperature, adsorption dose, and initial CBZ concentration) on carbamazepine removal by fabricated adsorbent; (3) the equilibrium and adsorption kinetics of CBZ within Fe0-rGO nanocomposites; (4) the interference of two commonly persistent drugs (DIC and CTZ) on CBZ adsorption by Fe0-rGO.

Reagents

Carbamazepine, cetirizine and diclofenac powders, CBZ and DIC were purchased from Merck Company (C4024-Germany). CBZ and DIC were dissolved in analytically pure methanol (99.8%), while cetirizine was dissolved in distilled water and stock solutions of 1,000 mg L−1 of each were prepared and kept in a refrigerator for further experiments. Natural graphite powder was obtained from Beijing chemical factory (China). The following materials were purchased from Merck company (Germany): calcium hydride (%95), sulfuric acid (98%), hydrogen peroxide (30%), potassium permanganate (KMnO4, 99.9%), and phosphoric acid (≥85%). Iron (II) sulfate heptahydrate (FeSO4·7H2O, ≥99%), sodium borohydride (NaBH4, ≥96%), methanol (99.8%), hydrocloridric acid (37%), and diethyl malonate (99%) were obtained from Sigma Aldrich (USA).

Apparatus

rGO-Fe0 composites were characterised by ultra-high resolution scanning electron microscope (FE-SEM) and energy-dispersive X-ray spectroscopy (EDX) using TESCAN–MIRA III, Czech Republic. X-ray diffraction (XRD) patterns of composites were determined by BRUKER AXSD8 FOCUS, Karlsruhe, Germany. Fourier-transform infrared spectroscopy (FTIR) was explored by FTIR BRUKER TENSOR 27, Germany.

Quantitative determination of CBZ was developed by high performance liquid chromatography (HPLC) with ultraviolet absorbance detection (UV) at 250 nm (Waters Alliance 2695). The separation was conducted by an analytical Agilent Eclipse Thermo Column C18 (3.5, 4.6 and 100 μm). 100 mg L−1 stock solution of CBZ was prepared by diluting 0.1 g in 100 ml HPLC grade methanol. Linear standard curve with R2=99.8% was obtained by injection of various concentration of CBZ ranging from 1 to 50 mg L−1. The combined mobile phase constituted of water/acetonitrile (30/70), at a flow rate of 1 mL min−1 and an injection volume of 20 μl. The lowest concentration of the detectable (LOD limit of detection) by the proposed method was 0.1 mg L−1, while the minimum quantifiable concentration (LOQ) was obtained 20 mg L−1.

Development of rGO-Fe0

Preparation of graphene oxide

Graphene oxide was synthesized via the chemical desquamate based on Hummers procedure (Irannejad et al. 2018) and also according to the method comprehensively explained by Jafaryan et al. (2019). Concisely, the following steps were performed. (1) 13 mL H3PO4, 120 mL H2SO4, and 1 g of graphite powder were mixed together. The reaction was carried out in a water bath at 50 °C and after complete mixture, 6 g of KMnO4 was gently added by continuous stirring. (2) The solution was left in an ice bath over one night to let the temperature reach 0 °C, then the obtained suspension was diluted by adding the ultra-pure water to reach 130 mL and this stage was completed by 30 min of stirring. (3) In order to decrease the remaining KMnO4, the suspension was undergone with 2 mL of H2O2 30% till the color of solution turned into brown. (4) Finally, the attained precipitate was rinsed thoroughly with HCl aqueous solution and de-ionized water and dried at 60 °C for 12 h.

Fe0-rGO fabrication

The synthesis of Fe0-rGO (nZVI/rGO) was set out according to the previously reported experiment (Fan et al. 2016). In brief, Fe0-rGO composites were produced by both reduction of graphene oxide and FeSO4·6H2O with NaBH4. In this regard, first, prepared GO (1 g) was dispersed in 200 mL de-ionized water under ultrasonic, then of FeSO4·7H2O (4.9 g) was added to the solution and the mixture was consistently stirred by magnetic stirrer for 2 h. Second, the NaBH4 solution (5.46 g/50 mL) was added gradually at room temperature into the above solution during 30 min. The prepared composition then was centrifuged to separate solid phase from liquid and the black residue was finally vacuum-dried at 50 °C for 24 h. The coating of iron oxide nanoparticles due to magnetic properties with wide size distribution supported on various sized graphene oxide were reported earlier in some research (Urbas et al. 2014; Kilanski et al. 2021). Some research reported rGO-nZVI synthesis by reduction of GO and ferrous ions with potassium borohydride (Zhang et al. 2010; Ren et al. 2018); however, in current research Sodium tetrahydridoborate (NaBH4) was added as a reducing agent since sodium borohydride reduction presents an important advantage in synthetic applications over other materials. NaBH4 allows the reductive removal of some elements selectively without affecting other functional groups (Blanchet et al. 2005).

Batch adsorption investigation

Batch adsorption kinetic experiment was conducted by prepared adsorbent in 50 mL centrifugal tubes. The Fe0-rGO (40 mg) was added to 40 mL of 20 mg L−1 CBZ (C0) at various pH ranging from 3–8. The experiment was proceeding by shaking of tubes at room temperature for 40 min in incubator-shaker (at 150 rpm). The mixture was centrifuged (3,000 rpm, 3 min) and 2 mL of supernatant was withdrawn and analyzed by HPLC for the remaining CBZ concentration. The removal efficiency of CBZ and the amount of CBZ adsorbed on Fe0-rGO were calculated following Equations (1) and (2), respectively:
formula
(1)
formula
(2)
where C0, Ce, m, and V indicate initial and secondary concentration of CBZ (mg L−1), the amount of adsorbent (g), and volume of solution (L), respectively. All measurements performed twice and the average values are reported.

Adsorption isotherm study was performed by adding 40 mg adsorbent to 40 mL of CBZ solution with different concentrations (5–30 mg L−1) at various pH values (3–8), and stirred at room temperature for 40 min. The amount of CBZ adsorbed on Fe0-rGO was measured by Equation (1). The adsorption Equilibrium was tested by comparing two commonly used isotherms namely, Langmuir and Freundlich models, meanwhile the kinetic experimental studies were tested by considering pseudo-first order (PFO) and pseudo-second order (PSO) reaction models. Origin Pro (version 16) software was applied to examine the goodness of fit and validity of kinetic models and adsorption isotherms. To accomplish, R2 adjusted, as well as the correlation coefficient (R2) were assessed.

Desorption/reuse procedure

Reusability experiments were performed with retrieval and washing of Fe0-rGO with methanol after CBZ adsorption of 5 mg L−1 for three consecutive cycles. To achieve this, first, the experiment was conducted by adsorption process of CBZ (5 mg L−1) on adsorbent (30 mg) for 45 min. Secondly, the sample was centrifuged and the supernatant was removed by a micropipette sampler. Then, The remaining residues were subsequently filtered and dried in a nitrogen dry box overnight for next use. For the desorption procedure, the used dried adsorbent was shaken with desorption solution (methanol, 10 mL) at 150 rpm for 24 h. The adsorbent was then applied to remove CBZ (mg L−1) at 30 °C after 45 min of reaction. The remaining concentration of CBZ in solution was measured and compared with the first use of Fe0-rGO. The adsorbent was again separated and tested for CBZ removal for the next two cycles. The efficiency of the adsorbent was calculated as its ability to remove CBZ after three cycles of washing in comparison with the CBZ removal before washing.

Optimization using Box–Behnken Design

To determine the optimum condition for CBZ removal it is crucial that the impacts of influential variables such as pH values, initial CBZ concentration, temperature, and adsorbent dose are investigated. To achieve this, in the present work, the 3-level 4-factor Box–Behnken experimental design was applied. The 29 experiments were calculated by Box–Behnken experimental design. The pH (X1), temperature (X2), initial concentration of CBZ (X3), and adsorbent dose (X4) were assumed as independent variables while the removal percentage of CBZ (Y) was taken as the dependent variable. The factor levels of −1, 0 and 1 were coded for the low, central point, and high values. In fact, the coded value explains the statistical difference between the actual values of variable Xi (coded as Zi) against the real values of independent variable in the center point (Xo) as given in Equation (3):
formula
(3)
where Zi is the coded value and represents the difference between the high and the median values of the variable. In view of the general function of the model contemplating the interaction of dependent and independent variables, the experimental data were finally assessed by a quadratic polynomial response surface model as given in Equation (4):
formula
(4)
where Y represents the removal of CBZ (%); X1, X2, X3, and X4 show independent variables; a0 is the intercept (constant); and a1, a2, a3, and a4 are linear coefficients. a12, a13, a14, a23, a24, and a34 represent interaction coefficients, a11, a22, a33, and a44 stand for the quadratic coefficients, and is the experimental error (Shakeel et al. 2014). All tested ranges and levels of independent variables selected for Box–Behnken Design are shown in Table 1.
Table 1

The coded levels of the independent variables

VariablesFactorsLevels
−1 (low)0 (middle)1 (high)
pH X1 5.5 
Temperature (°C) X2 25 35 45 
CBZ initial concentration (mgL−1X3 12.5 20 
Adsorbent dosage (mg) X4 20 30 40 
VariablesFactorsLevels
−1 (low)0 (middle)1 (high)
pH X1 5.5 
Temperature (°C) X2 25 35 45 
CBZ initial concentration (mgL−1X3 12.5 20 
Adsorbent dosage (mg) X4 20 30 40 

Design-Expert (version 7.01) was utilized for regression analysis of the experimental data. Moreover, analysis of variance (ANOVA) was used to assess the significance of interactions between the assigned variables and the response, taking into account the F and p-values. The goodness of fit of the obtained regression model was confirmed through R2 and adjusted R2 (R2adj).

Effects of counter pollutants on CBZ adsorption

The simultaneous effects of two persistent drugs, diclofenac (DIC) and cetirizine (CTZ), on CBZ removal by 30 mg of Fe0-rGO were investigated. In this regard, stock solutions (100 mg L−1) of DIC and CTZ were prepared by dissolving their powders in methanol and de-ionized water, respectively. Two different concentrations of mentioned drugs (5 and 10 mg L−1) were diluted and added to 5 mg L−1 of CBZ to reach a 40 mL volume. The shaking was conducted at 25 °C for 60 min. After centrifugation, the supernatant was withdrawn and the remained concentrations of CBZ, DIC, and CTZ were measured by LC-Mass (HPLC: Waters Alliance 2695, Mass Spectrometer: Micromass Quattro micro API). To better clarify, the removal efficiency and adsorption amount of CBZ and the other two drugs were scrutinized by setting our experiment in two stages. In first stage, the experiment was run at optimal condition obtained for CBZ removal and adding a determined amount of DIC and CTZ with an initial concentration of 5 mg L−1. Secondly, the initial concentrations of DIC and CTZ were doubled while CBZ concentration was kept the same (optimum) in order to determine the influence of higher amounts of drugs on adsorption efficiency.

Characterization of synthesized Fe0-rGO composite

The morphology of Fe0-rGO composite was investigated by the FE-SEM and SEM and the results are shown in Figure 1(a) and 1(b). It can be clearly seen that the rGO shows the presence of paper-like structure with thin folded sheets. There were a large number of iron nanoparticles that were well-dispersed with the particle sizes of 30–50 nm on the surface of the rGO sheets, which confirmed the formation of Fe0-rGO composite.

Figure 1

Field emission scanning electron microscope (FE-SEM) (a); scanning electron microscope (SEM) (b); EDS spectrum and elemental mapping (c); Fourier transform infrared spectroscopy (FT-IR) spectra (d) and X-ray diffraction (XRD) patterns (e) of Fe0-rGO.

Figure 1

Field emission scanning electron microscope (FE-SEM) (a); scanning electron microscope (SEM) (b); EDS spectrum and elemental mapping (c); Fourier transform infrared spectroscopy (FT-IR) spectra (d) and X-ray diffraction (XRD) patterns (e) of Fe0-rGO.

The incorporation of the iron nanoparticles was also confirmed by EDS analysis. As Figure 1(c) illustrates, the synthesized Fe0-rGO composite contained Fe element, indicating the attachment of iron nanoparticles on the rGO nanosheets.

Figure 1(d) shows the FT-IR spectrum of Fe0-rGO in the range of 400–4,000 cm−1. In the FTIR spectrum of the prepared composite, the broad adsorption band at 3,420 cm−1 is associated with O–H stretching from water molecules and carboxylic acid groups. The spectrum also shows peaks at 1,030, 1,340, 1,570, 1,650 and the two adsorptions at 2,860, 2,920 cm−1, which indicates the presence of alkoxy (C-O), epoxy (C-O) groups, aromatic double bond (C=C), carbonyl (C=O) of carboxylic acids, and C-H bond, respectively. In addition, the FTIR spectrum represents the absorption bands at 490, 555, and 671 cm−1 which arise due to Fe–O vibrations (Jafaryan et al. 2019; Mehrabi et al. 2019).

The X-ray diffraction pattern of Fe0-rGO composite is shown in Figure 1(e); the XRD spectrum of the composite was not well developed, probably because the crystallinity of iron nanoparticles is low. The XRD spectrum shows a weak diffraction peak at 2θ =10.06°, corresponding to the characteristic (002) crystalline plane of GO plane; it also possessed a diffraction peak centered at around 26.0°, indicating that a part of the GO was converted into rGO during the modification processes.

Meanwhile, the characteristic peaks of the body-centered cubic (bcc) Fe, as indicated by the peaks for 2θ=44.7° (110) and 62° (200) (JCPDS No. 010-87-0722) (Chen et al. 2017), confirm that the nZVI was successfully supported on the rGO. Moreover, the characteristic peaks of iron-oxides at 2θ =30.4°, 35.5°, 41.5°, 53.62, 57.14, 62.78, 65.03 and 74.24 indicate the presence of the oxide-shell; that is, magnetite (Fe3O4), around nZVI particles (Mehrabi et al. 2019).

Investigation of Fe0-rGO composite efficiency in CBZ removal

The efficiency of synthesized Fe0-rGO composite was investigated in removal of CBZ in aqueous solution. The simultaneous effects of contact time and initial concentration of CBZ on CBZ removal efficiency were studied at two pH, which are shown in Figure 2. Comparing the two graphs, it can be observed that the removal efficiency was escalated at lower pH (pH=3) regardless of the initial concentration of CBZ. Another main finding was the highest removal efficiency, which peaked at almost 90% during the first 10 min of reaction then reached a plateau at 40 min. Thus, at this stage of evaluation it appeared that a great amount of CBZ is adsorbed on the high specific surface area of Fe0-rGO and as many adsorption sites were filled with the adsorbate, the removal efficiency reached a plateau with increasing contact time. In addition, it can be observed that with increasing initial concentration, the removal efficiency decreased. Indeed, at the initial concentration of 5 mg L−1 CBZ, the highest removal efficiency of 93 and 70% was achieved at pH 3 and 8, respectively, while as the initial concentration increased to 30 mg L−1, the removal efficiency declined to 10%. In accordance with the present results, previous studies have demonstrated that adsorption behavior of reduced graphene oxide towards cationic and anionic dyes was better at lower dye concentrations (Minitha et al. 2017). This study produced results that also corroborate the findings of a great deal of the previous work in which considerable reduction in removal efficiency of organic pollutants by rGO was noticed due to the fact that extra concentration of the targets exceeded the maximum adsorption capacities of the adsorbents (Wu et al. 2020; Xu et al. 2021). These findings confirm the best performance of synthesized Fe0-rGO composite under acidic condition and lower concentration of CBZ, which can be further validated by adsorption kinetics, isotherms, and optimization approaches.

Figure 2

Removal efficiency of CBZ with different initial concentrations at pH 3 (a) and pH 8 (b) (volume: 40 mL; Fe0-rGO doses: 40 mg).

Figure 2

Removal efficiency of CBZ with different initial concentrations at pH 3 (a) and pH 8 (b) (volume: 40 mL; Fe0-rGO doses: 40 mg).

Study of adsorption isotherms of CBZ over Fe0-rGO composite

The reciprocal action between CBZ and Fe0-rGO has great importance to understanding of the chemical/physical reaction involved in the adsorption process. Thus, adsorption isotherms can provide information on the optimized dosage of adsorbents since they can both evaluate the adsorption capacity and interaction between adsorbate and adsorbents. Therefore, two widely used isotherms, namely Langmuir and Freundlich, were applied in our research. The Langmuir model assumes that the adsorption process occurs monomolecularly with a uniform surface and no interaction exists between the adsorbates. The Freundlich model explains the multilayer approach of adsorbate on adsorption sites with different energy and heterogeneity. These models are shown in Equations (5) and (6), respectively.
formula
(5)
formula
(6)
where in Equation (5), qe (mg g−1), Ce (mg L−1), Q (mg g−1), and KL (L mg−1) represent the amount of CBZ adsorbed on adsorbent at equilibrium, the equilibrium concentration of CBZ remaining in solution after reaction, the maximum adsorption capacity and the Langmuir adsorption constant, respectively.

In Equation (6), KF (mg1−1/n/Ln. g) and n−1 are indicative of adsorption capacity of adsorbent and adsorption intensity (surface heterogeneity index). The value of n−1 represent the heterogeneous character of the adsorbent as it approaches 0 while the adsorbent become homogeneous when this value is equal to 1. Generally, when the value of n=1, the Freundlich model reduces to its linear form, whereas when n < 1 or n >1 the adsorption process is considered as favorable and unfavorable, respectively (Alkurdi et al. 2021). Isotherms fitting Langmuir and Fruendlich at various pH for CBZ adsorption onto synthesized adsorbent are depicted in Figure 3(a) and 3(b). It is clear that the equilibrium of adsorption amplified as the initial concentration of CBZ increased. The calculated coefficients and constants obtained from the Langmuir and Freundlich isotherms are summarized in Table 2. It can be found from the table that the Freundlich isotherm better fitted to the data with R2 > 0.96, especially at higher CBZ concentrations, suggesting that the binding sites that have different energies are not uniformly distributed on the adsorbent and multilayer adsorption of CBZ. Furthermore, the low differences between R2 and R2adj indicate the data adherence to the Freundlich model. The values calculated for n in our study were all > 1, which confirms the unfavorable adsorption of CBZ on Fe0-rGO. Moreover, it is obvious that n values boosted with an enhancement of pH, indicating that at lower pH, the adsorbent sites becomes more heterogeneous, accompanied by the low energy sites with enhanced surface concentration (Cai & Larese-Casanova 2020). The values of KF decreased by increase in pH, which shows adsorption capacities arise at low pH. These results corroborate the ideas of Bernal et al. (2017), who reported that the pH of a solution plays a major role in the sorption process as it can affect both adsorbent and adsorbate properties. In fact, solution pH is known as a crucial factor that determines the adsorption rate of adsorbents. The main factor that contributes to the various adsorption rate is the pH of Zeta potential (pH value at the point of zero charge) (pHpzc) of the adsorbent. Reduced graphene oxide-iron nanocomposites are reported to have a pHpzc value in extremely acidic conditions (Ray et al. 2017). When the solution pH goes above or below the pHpzc negative or positive surface charges are dominant, respectively, leading to diminishing of the adsorption rate. Additionally, it is noteworthy to mention that Liu et al. (2014) reported that the adsorption of CBZ on rGO is pH-independent over the range of 2–12. The same result was obtained in our research; in fact, first the rGO was prepared, it was solely tested for CBZ removal (data not shown), and no remarkable removal efficiency of CBZ was noticed between pH=3 and pH=8. Likewise, in our experiment CBZ remained neutral in the range of pH 3–8, too. However, the effect of some other drugs' pH solution on rGO adsorption have been evidently reported in the body of literature, so it can be inferred that the only driving force of their adsorption must have been the production of the different forms or species of adsorbate. Surprisingly, by the modification of rGO with Fe0 in the current study, the adsorbent was more efficient at lower pH values. Similarly, Abdel-Aziz et al. (2019) asserted that acidic conditions favor CBZ removal by nZVFe. Similar results of a higher removal of organic pollutants at low pH by an iron-functionalized nanocarbon composite have been reported by other researchers (Li et al. 2012; Kakavandi et al. 2016; Ray et al. 2017). In addition, maximum adsorption capacity (Q) on Fe0-rGO from the Langmuir isotherm (Table 2) in our study obtained 50 mg.g−1, which is comparable with other materials that have been explored for CBZ removal from aqueous solution (Abdel-Aziz et al. 2019; Cai & Larese-Casanova 2020; Al-Mashaqbeh et al. 2021) and reveals its outperformance characterization over some of them.

Table 2

Isotherm parameters for CBZ adsorption onto Fe0-rGO

pHLangmuir model
Freundlich model
KLQR2R2adjn−1KFR2R2adj
2.8 50 0.694 0.592 0.43 11.51 0.899 0.866 
5.5 5.12 32.25 0.832 0.766 0.53 5.91 0.972 0.962 
8.10 33.30 0.973 0.965 0.66 3.97 0.995 0.994 
14 38.46 0.917 0.889 0.73 2.86 0.994 0.992 
pHLangmuir model
Freundlich model
KLQR2R2adjn−1KFR2R2adj
2.8 50 0.694 0.592 0.43 11.51 0.899 0.866 
5.5 5.12 32.25 0.832 0.766 0.53 5.91 0.972 0.962 
8.10 33.30 0.973 0.965 0.66 3.97 0.995 0.994 
14 38.46 0.917 0.889 0.73 2.86 0.994 0.992 
Figure 3

Isotherms fitting of Langmuir (a) and Freundlich (b) for CBZ onto magnetic Fe0-rGO at various pH (CBZ initial concentration: 5–30 mg L−1; volume: 40 mL; Fe0-rGO doses: 40 mg).

Figure 3

Isotherms fitting of Langmuir (a) and Freundlich (b) for CBZ onto magnetic Fe0-rGO at various pH (CBZ initial concentration: 5–30 mg L−1; volume: 40 mL; Fe0-rGO doses: 40 mg).

Study of adsorption kinetics of CBZ over Fe0-rGO composite

The adsorption efficiency of materials can be evaluated by adsorption rate. This issue is governed by two phenomena; (1) the arrival rate of molecules on the surface of an adsorbent and (2) the ratio of molecules in collision, which encounter the adsorption (Davis & Davis 2012). Thus, the time extension of CBZ adsorption at wide ranges of pH was evaluated applying the pseudo-first order and pseudo-second order kinetic models. The obtained information was then used as the basis for indicating the mechanism of the adsorption process. Linear mathematical expressions of the adsorption kinetics are given in Equations (7) and (8).
formula
(7)
formula
(8)
where and (mg g−1) represent the adsorption capacity of CBZ on the Fe0-rGO in equilibrium and at various time intervals (min), respectively. (min −1) and (g. mg−1. min−1) show each equation's rate constant, respectively. The slope of the linear plot of against t reveals the rate constant (K1), while K2 can be obtained by the intercept of the fitting curve of versus t.

The fitting linear curves of and versus t in constant initial concentration of CBZ (20 mg L−1) at various pH are depicted in Figure 4, and the calculated kinetic parameters from these models are summarized in Table 3. Inspection of Figure 4 confirms that the experimental data were fitted well with both adsorption kinetic models. Nevertheless, the comparison of the best fit is based on the coefficient of determination and minimal differences between R2 and R2adj. Thus, at this stage of evaluation it appeared that adsorption closely followed the pseudo-second order model. Hence, the adsorption of CBZ on Fe0-rGO can be explained by the chemical interaction between CBZ and Fe0-rGO (Tan & Hameed 2017). Moving on to consider the consequence of pH of the solution on , what stands out in Table 3 is the decline in when the pH rises from 3 to 8, indicating the pivotal role of pH on the adsorption capacity of Fe0-rGO in equilibrium.

Table 3

Adsorption rate constants for three kinetic models of CBZ adsorption on Fe0-rGO

pHPseudo-first order
Pseudo-second order
Intrapartcile diffusion
K1 (min−1)qe (mg.g−1)R2R2adjK2 (g.mg−1. min−1)qe (mg.g−1)R2R2adjKi (kg (mg min0.5)−1)C (mg.g−1)R2R2adj
3.0 0.079 10.73 0.984 0.972 0.0137 19.67 0.999 0.999 2.14 5.92 0.933 0.910 
5.5 0.076 10.32 0.974 0.966 0.0079 17.54 0.998 0.998 2.10 2.92 0.933 0.912 
7.0 0.056 9.91 0.985 0.978 0.0070 15.38 0.996 0.995 1.91 2.04 0.963 0.951 
8.0 0.064 8.98 0.954 0.949 0.0120 15.15 0.999 0.999 1.80 3.60 0.930 0.913 
pHPseudo-first order
Pseudo-second order
Intrapartcile diffusion
K1 (min−1)qe (mg.g−1)R2R2adjK2 (g.mg−1. min−1)qe (mg.g−1)R2R2adjKi (kg (mg min0.5)−1)C (mg.g−1)R2R2adj
3.0 0.079 10.73 0.984 0.972 0.0137 19.67 0.999 0.999 2.14 5.92 0.933 0.910 
5.5 0.076 10.32 0.974 0.966 0.0079 17.54 0.998 0.998 2.10 2.92 0.933 0.912 
7.0 0.056 9.91 0.985 0.978 0.0070 15.38 0.996 0.995 1.91 2.04 0.963 0.951 
8.0 0.064 8.98 0.954 0.949 0.0120 15.15 0.999 0.999 1.80 3.60 0.930 0.913 
Figure 4

Linear plots of pseudo-first (a)- and pseudo-second (b)- order kinetic equations (CBZ initial concentration: 20 mg L−1; volume: 40 mL; adsorbent doses: 20 mg).

Figure 4

Linear plots of pseudo-first (a)- and pseudo-second (b)- order kinetic equations (CBZ initial concentration: 20 mg L−1; volume: 40 mL; adsorbent doses: 20 mg).

As a general rule, the adsorption kinetics of adsorbates onto the surface of adsorbents chiefly consists of two phases of transport and attachment separation (Vasanth Kumar et al. 2004; Wang et al. 2010). To put it another way, the adsorption of targeted constituents into adsorbents can be achieved either by intraparticle diffusion, pore diffusion or both mechanisms (Malash & El-Khaiary 2010). The transport of molecules is governed by diffusion, which is caused by the attraction of the targeted adsorbate to the surface of the adsorbents (Crini et al. 2018). It has been argued that the pseudo-order kinetic models lacks the ability to identify the diffusion mechanism of pollutants in the adsorption process (Derco & Vrana 2018). Hence, to further analyze the adsorption kinetics, the Weber–Morris intraparticle diffusion model (IDF) (Valderrama et al. 2008) was applied as follows:
formula
(9)
where ki (kg (mg min0.5)−1) stands for the intraparticle diffusion rate constant; and c is a constant (mg.g−1). IDF has been widely used to delineate diffusion-controlled processes for liquid-solids adsorption kinetics (Haerifar & Azizian 2013). It was claimed that the larger the intercept, the more substantial the contribution of the surface adsorption in the rate-limiting step will be.

Figure 5 depicts the adsorption uptake of CBZ against the square root of time (t0.5) at various pH. Intercept values (c in Equation (9)) of fitted lines and the responding correlation coefficient (R2) are also shown in Table 3. As can be seen, the intercepts do not pass through the point of origin (C=0), suggesting that the intraparticle diffusion is not merely control the adsorption rate, with other mechanisms substantially playing a crucial role. The large C values obtained in our research represent a thicker boundary layer (Ofomaja et al. 2020). Indeed, larger intercepts indicate the substantial role of the surface adsorption in the rate-limiting step (Ofomaja et al. 2020). On the other hand, the values of the intercept, C, indicate that boundary diffusion or surface adsorption decreased with pH, which further suggests that surface adsorption became ineffective as pH rose. Similarly, it was also observed that the values of intraparticle diffusion rate constant, ki, decreased with increasing solution pH; indicating that the adsorbent became less effective for CBZ removal at high pH values .Overall, the results of this investigation show that the adsorption process comprises simultaneously a certain degree of boundary layer control and extra- nano diffusion processes (Zhang et al. 2014).

Figure 5

Non-linear plot of intraparticle diffusion (CBZ initial concentration: 20 mg L−1; volume: 40 mL; adsorbent doses: 20 mg).

Figure 5

Non-linear plot of intraparticle diffusion (CBZ initial concentration: 20 mg L−1; volume: 40 mL; adsorbent doses: 20 mg).

Thermodynamic study

The adsorption thermodynamics of CBZ on Fe0-rGO were analyzed by the distribution coefficient (Kd) from the adsorption experiment conducted at various temperatures ranging from 298 to 318 K and initial CBZ concentration of 5 mg L−1 (pH=5.5 and adsorbent dosage of 30 mg). The distribution coefficient was calculated by the following equation (Equation (10)):
formula
(10)
where all the parameters were described in Equation (1). Parameters, such as the standard enthalpy (ΔH°, kJ mol−1), and the standard entropy (ΔS°, J (mol K)−1), for CBZ adsorption were obtained directly from the slope and intercept of the linear plot of Ln(Kd) versus T−1 based on the following equation (Equation (11)):
formula
(11)
where Kd is the distribution coefficient, T is the absolute temperature (K), and R is the ideal gas constant (8.314 J(mol K)−1). The Gibbs free energy changes (ΔG°) were then calculated by Equation (12).
formula
(12)

All the thermodynamic parameters for CBZ adsorption are illustrated in Table 4.

Table 4

Thermodynamics parameters of CBZ adsorption

T (K)Ln KdΔ G°(KJ mol−1)ΔH° (kJ mol−1)ΔS° J (mol K)−1
298 2.27 −17.04 −2,799 9.50 
308 2.33 −17.61   
318 2.20 −18.18   
T (K)Ln KdΔ G°(KJ mol−1)ΔH° (kJ mol−1)ΔS° J (mol K)−1
298 2.27 −17.04 −2,799 9.50 
308 2.33 −17.61   
318 2.20 −18.18   

The negative values of ΔG° represent a spontaneous and exothermic sorption of CBZ on Fe0-rGO. As a matter of fact, ΔG0 values between 0 and −20 kJ/mol confirm physiosorption. Furthermore, the negative value of ΔH° is an indicator of the exothermic sorption process, suggesting lower temperatures are more favorable. Additionally, the positive value of ΔS° suggests a spontaneous sorption process (Mohseni-Bandpi et al. 2015). It is worth paying attention to the statically insignificant values of ΔG0 obtained in various temperatures; indicating the trivial role of temperature in CBZ adsorption on Fe0-rGO.

Box Behnken model analysis and optimization process

Model evolution and interactive effects of variables

As shown in Table 1, the three levels of each of the four assigned parameters were chosen by the model and the removal efficiencies obtained from the batch adsorption experiment were input. The response surface methodology and Box Behnken model were applied to specify the best fitted model. The interaction influence of four variables, including pH (3–8; X1), temperature (25–45; X2), initial concentration of CBZ (5–20; X3) and adsorbent dosage (20–40; X4) on CBZ removal efficiency was investigated through 29 runs. The removal efficiency varied between 60 to 92.8%, with the average value of 70.9% (Std. Dev ±7.037). Taking into account the coefficient of variation (R2), adjusted coefficient of variation (R2adj), Fisher's F-test value (F value) and p-values obtained using the ANOVA test, the best fitted model was selected. Large F-value, small p-value (<0.05) and high R2 and R2adj are representative of a statistically significant model. Quadratic expression better obeyed the mentioned criteria so it was selected as the most appropriate model (R2=0.951; R2adj=0.903; F-value=10.84; p-value=0.01) and the relevant Equation consisting of 15 coefficients was achieved (Equation (13)). As given in Table 5, the significance of each factor and their corresponding interactions on CBZ removal were all examined by the ANOVA test. Since p-values less than 0.05 indicate the model terms' influences are significant, in the current study X1, X3, X4, X1X3, X3X4, X12, and X22 were computed as the significant terms by the simulated model. It is noticeable that some coefficients (X4, X1X2, X1X3, X1X4, X2X3, X12, X32 and X42) imposed positive impacts on the CBZ removal; while (X1, X2, X3, X2X3, X3X4 and X22) negatively affected the process. Markedly, the highest coefficient value of pH demonstrates its crucial effect on the adsorption process.
formula
(13)
Table 5

ANOVA for analysis of variance and adequacy of the quadratic model

Sum of squaresF-ValueP-value Prob>F
Model 123.15 19.65 <0.0001 
A-pH 1,158.37 184.87 <0.0001 
B-Temperature 25.52 4.07 0.0632 
C-CBZ 70.08 11.18 0.0048 
D-Adsorbent 51.25 8.18 0.0126 
AB 21.16 3.38 0.0874 
AC 47.61 7.60 0.0154 
AD 8.12 1.30 0.2740 
BC 0.16 0.026 0.8753 
BD 0.063 9.975E-003 0.9219 
CD 73.96 11.80 0.0040 
A2 174.55 27.86 0.0001 
B2 47.73 7.62 0.0153 
C2 0.26 0.041 0.8417 
D2 3.90 0.62 0.4435 
Residual 87.72   
Lack of fit 86.92 43.46 0.0012 
Pure error 0.7   
Sum of squaresF-ValueP-value Prob>F
Model 123.15 19.65 <0.0001 
A-pH 1,158.37 184.87 <0.0001 
B-Temperature 25.52 4.07 0.0632 
C-CBZ 70.08 11.18 0.0048 
D-Adsorbent 51.25 8.18 0.0126 
AB 21.16 3.38 0.0874 
AC 47.61 7.60 0.0154 
AD 8.12 1.30 0.2740 
BC 0.16 0.026 0.8753 
BD 0.063 9.975E-003 0.9219 
CD 73.96 11.80 0.0040 
A2 174.55 27.86 0.0001 
B2 47.73 7.62 0.0153 
C2 0.26 0.041 0.8417 
D2 3.90 0.62 0.4435 
Residual 87.72   
Lack of fit 86.92 43.46 0.0012 
Pure error 0.7   

Following on from these results, we then decided to investigate the response surface plots of the second-order polynomial equation, obtained as the continuous function of two factors on CBZ removal that are given in Figure 6. Figure 6(a)–6(d) illustrate the counter plot of the combined effect of pH with adsorbent dose, temperature, and initial concentration of CBZ, respectively. It is clear in these three figures that the adsorption process was more favorable at lower pH and the highest removal efficiency was achieved at pH=3. What stands out in Figure 6(a) is the adsorbent dose-independent role on CBZ removal at lower pH. This phenomenon was also earlier supported by Equation (13), in which the coefficient of pH (9.88) was much higher than that of adsorbent dosage (2.07) and their combined coefficient obtained (1.43). It should also be noted that from Table 5 their combined interaction was not statically significant (0.27). The combined effects of pH and temperature was not statistically significant (0. 087). Inspection of Figure 6(b), at pH=3 the removal efficiency of Fe0–rGO enhanced at temperatures ranging from 25 to 36 °C, though it gently declined over 36 °C. The simultaneous influence of pH and initial concentration of CBZ (Figure 6(c)) indicates that the removal efficiency was quite high at both lower pH and initial concentration of CBZ, which was also verified by the low p-value (0.015). As stated from Equation (13), a moderately high negative coefficient of CBZ initial concentration (−2.42) represents its adverse significant role on the adsorption process following pH (−9.81). Figure 6(e) and 6(f) depict coinciding effects of temperature with initial concentration of CBZ and adsorbent dose, respectively. As can be seen from Figure 6(e), at lower initial concentration of CBZ and temperature ranges between 27 to almost 39 °C removal efficiency increased. Additionally, at elevated initial concentration of CBZ the surface of adsorbent (even at doses higher than 30 mg) become saturated and in efficient in CBZ removal. Nonetheless, based on Table 5, the observed trend was not significant (0.845). This result is also in line with the obtained coefficient of these two variables from Equation (10), which is so small (+ 0.2). The combined effect of temperature and adsorbent dose on the removal efficiency of CBZ (Figure 6(e)) reveals that maximum removal was reached at the highest dosage of adsorbent (40 mg) and temperature of almost 31 °C. Low combined coefficient of adsorbent-temperature variables (-0.12) and their corresponding p- value over 0.05 are indicative of their statically insignificant roles. Overall, this final result highlights the trivial contribution of temperature as compared with other tested variables that also led to the deviation of the quadratic model from its well-fitted form by almost 0.05 (R2=0.951). Non-uniform adsorption trend with temperature changes has been proven in many studies. (Fontecha-Cámara et al. 2008) investigated diuron adsorption on carbon fibers. Their findings suggested that diuron adsorption capacity escalated with the change of temperature in the range 15–45 °C, while at 35 and 45 °C its adsorption on the carbon fibers remained at the same level. This results was explained by the frailty of hydrogen bonds between solvent, adsorbed substance and adsorbent, which in turn ended in curtailment of the herbicide mass transfer resistance. Likewise, Daneshvar et al. (2007) hold the view that the effect of different temperatures on Imidacloprid adsorption by granular activated carbon was minor and insignificant. Adopting a similar position, Green-Ruiz (2009) argued that the initial concentration of Hg (II) and salinity were effective in the adsorption process, though no significant influence was observed between the measured variables and temperature.

Figure 6

Counterplots for CBZ removal (%) at various temperatures (25–35 °C), initial CBZ (5–20) and pH (3–8).

Figure 6

Counterplots for CBZ removal (%) at various temperatures (25–35 °C), initial CBZ (5–20) and pH (3–8).

Processes optimization

The optimization module explores a combination of factor levels that concurrently satisfy the criteria placed on each of the responses (CBZ removal in our research) and factors. In order to achieve this goal, the optimization process was run based on the software-calculated statistical criteria and the optimum condition (the most desirable) to maximize targeted removal (carbamazepine) considering influencing variables. The desirability function distinguishes and generates a function for each response and then specifies the global function for desired responses by adopting the optimum values for variables in addition to considering the interaction between them. Hence, desirability is scaled in the range of 0–1, with zero and one exhibiting undesirable and the most desirable conditions, respectively. This scale is applied to detect a global function that should be boosted by efficacious selection and optimization of variables. In our study, desirability was selected based on maximum removal of CBZ and in the range values of other parameters. The optimum values of the selected variables obtained as following; pH=3.07, initial concentration of CBZ=5 mgL−1, temperature 30.15 °C and adsorbent dose=36.2 mg. At these conditions, roughly 96.25% removal of CBZ was anticipated by the model. The desirability value of the procedure optimization was found to be 1.00.

Reusability study

Practically, reusability is an important characteristic of adsorbents. The regeneration (sorption) efficiency of the adsorbent was obtained as 80, 72 and 70% for three successive sorption–desorption cycles, respectively. Hence, it can be concluded that methanol can be used to promote recovery due to carbamazepine's higher solubility in ethanol (0.108 moL L−1) compared to water (0.001 moL L−1). These findings suggest that operational cost can significantly diminish owing to the dominant operational reusability of synthesized Fe0-rGO.

Coexisting effects of CTZ and DIC

Since the presence of other organic pollutants in the environment can vary the adsorption performance of adsorbents toward targeted martial, the effects of two common and persistent drugs (DIC and CIT) on CBZ adsorption by Fe0-rGO were investigated. Figure 7 shows the amount of each drug adsorbed on Fe0-rGO and the removal percentage after 40 minutes of experiment in two stages as: (1) all drugs concentration were Equal (5 mg L−1) (Figure 7(a) and 7(c)) and (2) the concentration of CBZ was 5 mg L−1 while the concentration of DIC and CTZ doubled (10 mg L−1) (Figure 7(b) and 7(d)). Figure 7(a) depicts that the Fe0-rGO had high adsorption capacity for CTZ and DIC. The adsorption capacity was in the following order: CTZ> CBZ> DIC, implying that the adsorption affinity between CTZ and CBZ with adsorbent was higher than that of DIC. Concerning removal efficiency, it is clear from Figure 7(c) that CTZ removal was quite high as almost 99% of its removal was achieved. It is noted that no significant changes in removal rate and adsorption value of CBZ were observed in this stage. On the other hand, in mixed solution with the doubled concentration of DIC and CTZ, a slight reduction in both removal efficiency and adsorption value of all species were noticed, indicating the adsorbent became saturated and was not highly efficient for CBZ removal at higher concentrations of DIC and CTZ. Overall, it is evident that Fe0-rGO quite sustain a comparable removal ability for two coexisting drugs and can be used to considerably remove CBZ, CTZ and to some extent DIC from water.

Figure 7

Coexisting effects of CTZ and DIC on CBZ removal by Fe0-rGO.

Figure 7

Coexisting effects of CTZ and DIC on CBZ removal by Fe0-rGO.

Comparison of current adsorbent with other adsorbents for CBZ removal

The performance of Fe0-rGO for removal of CBZ was compared with other adsorbents in literature based on adsorption capacities and contact time and the results are presented in Table 6. According to the maximum adsorption capacity (Q) it can be deduced that synthesized adsorbents are much more effective for CBZ removal than natural adsorbents like bentonite and modified diatomaceous. Moreover, the results of current study determined a maximum sorption of 50 mg g−1, which is higher than those of some other adsorbents. More importantly, the lower time of reaching the maximum adsorption capacity (equilibrium) is quite low in our work which is an advantage from economical points of view.

Table 6

Comparison the efficiency of various adsorbents for CBZ removal

AdsorbentQ (mg.g−1)Contact time (min)References
Carbon dot-modified magnetic carbon nanotubes 65 180 Deng et al. (2019)  
UiO-66 derived zirconia/porous carbon nanocomposites 190 60 Chen et al. (2020)  
Multi-walled carbon nanotubes 224.6 120 Ncibi & Sillanpää (2017)  
Synthesized magnetic activated carbon 182.9 – Baghdadi et al. (2016)  
Bentonite clay 2.35 15 Özçelik et al.(2020)  
UiO-66 and UiO-66/graphene nanoplatelet composite 51.17 – ElHussein et al. (2020)  
Iron oxide modified diatomaceous earth 0.44 180 Jemutai-Kimosop et al. (2020)  
Magnetic black carbon 31.8 <10 Cai & Larese-Casanova (2020)  
Magnetic CoFe2O4/rGO nanocomposites 50.5 10 Jiang et al. (2018)  
Reduced graphene oxide-nano zero valent iron (Fe0-rGO) composite 50 40 This study 
AdsorbentQ (mg.g−1)Contact time (min)References
Carbon dot-modified magnetic carbon nanotubes 65 180 Deng et al. (2019)  
UiO-66 derived zirconia/porous carbon nanocomposites 190 60 Chen et al. (2020)  
Multi-walled carbon nanotubes 224.6 120 Ncibi & Sillanpää (2017)  
Synthesized magnetic activated carbon 182.9 – Baghdadi et al. (2016)  
Bentonite clay 2.35 15 Özçelik et al.(2020)  
UiO-66 and UiO-66/graphene nanoplatelet composite 51.17 – ElHussein et al. (2020)  
Iron oxide modified diatomaceous earth 0.44 180 Jemutai-Kimosop et al. (2020)  
Magnetic black carbon 31.8 <10 Cai & Larese-Casanova (2020)  
Magnetic CoFe2O4/rGO nanocomposites 50.5 10 Jiang et al. (2018)  
Reduced graphene oxide-nano zero valent iron (Fe0-rGO) composite 50 40 This study 

The Fe0-rGO was successfully synthesized and used to remove CBZ from aqueous solution. The adsorption isotherms and kinetic studies in multi-batch experiments revealed that the data well obey the Freundlich model and pseudo-second order kinetic model, respectively. Batch adsorption experiments demonstrated that the adsorbent pH is a significant factor, which influences the adsorption properties of CBZ on Fe0-rGO, and vast removal of CBZ occurred in 10 min while it approaches equilibrium after 40 minutes. When the pH value of CBZ solution was adjusted to acidic conditions (pH=3–5) almost 90% of CBZ (5 mg·L−1) was removed within 10 minutes at 30.15 °C by little Fe0-rGO (100 mg·L−1). The combined influence of different variables including adsorbent dose, pH, initial CBZ concentration and temperature were assessed using the Box–Behnken design. In brief, the quadratic model fitted well to the data according to the ANOVA results, p-value = 0.0003, and high coefficient of regression, R2=0.951. Furthermore, interactive effects of pH-initial concentration of CBZ and adsorbent dose-initial concentration of CBZ were significant terms with p-values <0.05 in the model, which indicates the crucial control over the CBZ adsorption process. The results also revealed that the process temperature and its interaction with other variables were not significant. Moreover, the novel rGO-Fe0 exhibited wide-spectrum and can be used to remove coexisting CBZ, CTZ and DIC.

All relevant data are included in the paper or its Supplementary Information.

Abdel-Aziz
H. M.
,
Farag
R. S.
&
Abdel-Gawad
S. A.
2019
Carbamazepine removal from aqueous solution by green synthesis zero-valent iron/Cu nanoparticles with Ficus Benjamina leaves’ extract
.
International Journal of Environmental Research
13
(
5
),
843
852
.
Al-Mashaqbeh
O. A.
,
Alsafadi
D. A.
,
Alsalhi
L. Z.
,
Bartelt-Hunt
S. L.
&
Snow
D. D.
2021
Removal of carbamazepine onto modified zeolitic tuff in different water matrices: batch and continuous flow experiments
.
Water
13
(
8
),
1084
.
Bendz
D.
,
Paxéus
N. A.
,
Ginn
T. R.
&
Loge
F. J.
2005
Occurrence and fate of pharmaceutically active compounds in the environment, a case study: Höje River in Sweden
.
Journal of Hazardous Materials
122
(
3
),
195
204
.
Bernal
V.
,
Erto
A.
,
Giraldo
L.
&
Moreno-Piraján
J. C.
2017
Effect of solution pH on the adsorption of paracetamol on chemically modified activated carbons
.
Molecules
22
(
7
),
1032
.
Bhattacharya
S.
,
Banerjee
P.
,
Das
P.
,
Bhowal
A.
,
Majumder
S. K.
&
Ghosh
P.
2020
Removal of aqueous carbamazepine using graphene oxide nanoplatelets: process modelling and optimization
.
Sustainable Environment Research
30
(
1
),
1
12
.
Bhunia
P.
,
Kim
G.
,
Baik
C.
&
Lee
H.
2012
A strategically designed porous iron–iron oxide matrix on graphene for heavy metal adsorption
.
Chemical Communications
48
(
79
),
9888
9890
.
Chen
L.
,
Feng
S.
,
Zhao
D.
,
Chen
S.
,
Li
F.
&
Chen
C.
2017
Efficient sorption and reduction of U (VI) on zero-valent iron-polyaniline-graphene aerogel ternary composite
.
Journal of Colloid and Interface Science
490
,
197
206
.
Crini
G.
,
Lichtfouse
E.
,
Wilson
L. D.
&
Morin-Crini
N.
2018
Adsorption-oriented Processes Using Conventional and non-Conventional Adsorbents for Wastewater Treatment, Green Adsorbents for Pollutant Removal
.
Springer
,
Paris, France
, pp.
23
71
.
Davididou
K.
,
Monteagudo
J. M.
,
Chatzisymeon
E.
,
Durán
A.
&
Expósito
A. J.
2017
Degradation and mineralization of antipyrine by UV-A LED photo-Fenton reaction intensified by ferrioxalate with addition of persulfate
.
Separation and Purification Technology
172
,
227
235
.
Davis
M. E.
&
Davis
R. J.
2012
Fundamentals of Chemical Reaction Engineering. Courier Corporation. McGraw-Hill Chemical Engineering Series
.
McGraw-Hill Higher Education
,
New York, NY
.
ISBN 007245007X
Deng
Y.
,
Ok
Y. S.
,
Mohan
D.
,
Pittman
C. U.
Jr
&
Dou
X.
2019
Carbamazepine removal from water by carbon dot-modified magnetic carbon nanotubes
.
Environmental Research
169
,
434
444
.
Derco
J.
&
Vrana
B.
2018
Introductory chapter: biosorption
. In:
Biosorption
.
IntechOpen
, pp.
1
19
.
ElHussein
E. A. A.
,
Şahin
S.
&
Bayazit
Ş. S
, .
2020
Removal of carbamazepine using UiO-66 and UiO-66/graphene nanoplatelet composite
.
Journal of Environmental Chemical Engineering
8
(
4
),
103898
.
Eljamal
R.
,
Eljamal
O.
,
Khalil
A. M.
,
Saha
B. B.
&
Matsunaga
N.
2018
Improvement of the chemical synthesis efficiency of nano-scale zero-valent iron particles
.
Journal of Environmental Chemical Engineering
6
(
4
),
4727
4735
.
Fontecha-Cámara
M.
,
López-Ramón
M.
,
Pastrana-Martínez
L.
&
Moreno-Castilla
C.
2008
Kinetics of diuron and amitrole adsorption from aqueous solution on activated carbons
.
Journal of Hazardous Materials
156
(
1–3
),
472
477
.
Gao
Y.
,
Li
Y.
,
Zhang
L.
,
Huang
H.
,
Hu
J.
,
Shah
S. M.
&
Su
X.
2012
Adsorption and removal of tetracycline antibiotics from aqueous solution by graphene oxide
.
Journal of Colloid and Interface Science
368
(
1
),
540
546
.
Gurung
K.
,
Ncibi
M. C.
,
Shestakova
M.
&
Sillanpää
M.
2018
Removal of carbamazepine from MBR effluent by electrochemical oxidation (EO) using a Ti/Ta2O5-SnO2 electrode
.
Applied Catalysis B: Environmental
221
,
329
338
.
Hazell
G.
,
Hinojosa-Navarro
M.
,
McCoy
T. M.
,
Tabor
R. F.
&
Eastoe
J.
2016
Responsive materials based on magnetic polyelectrolytes and graphene oxide for water clean-up
.
Journal of Colloid and Interface Science
464
,
285
290
.
Huang
D.
,
Wu
J.
,
Wang
L.
,
Liu
X.
,
Meng
J.
,
Tang
X.
,
Tang
C.
&
Xu
J.
2019
Novel insight into adsorption and co-adsorption of heavy metal ions and an organic pollutant by magnetic graphene nanomaterials in water
.
Chemical Engineering Journal
358
,
1399
1409
.
Irannejad
L.
,
Ahmadi
S. J.
,
Sadjadi
S.
&
Shamsipur
M.
2018
Synthesis of N-hydroxy-imidamide-functionalized graphene: an efficient metal-free electrocatalyst for oxygen reduction
.
Journal of the Iranian Chemical Society
15
(
1
),
111
119
.
Jafaryan
A.
,
Sadjadi
S.
,
Gharib
A.
&
Ahmadi
S. J.
2019
Optimization of cadmium adsorption from aqueous solutions by functionalized graphene and the reversible magnetic recovery of the adsorbent using response surface methodology
.
Applied Organometallic Chemistry
33
(
9
),
e5085
.
Jemutai-Kimosop
S.
,
Orata
F.
,
Shikuku
V. O.
,
Okello
V. A.
&
Getenga
Z. M.
2020
Insights on adsorption of carbamazepine onto iron oxide modified diatomaceous earth: kinetics, isotherms, thermodynamics, and mechanisms
.
Environmental Research
180
,
108898
.
Jiang
Y.
,
Chen
D.
,
Yang
W.
,
Wu
S.
&
Luo
X.
2018
Reduced graphene oxide enhanced magnetic nanocomposites for removal of carbamazepine
.
Journal of Materials Science
53
(
22
),
15474
15486
.
Joss
A.
,
Keller
E.
,
Alder
A. C.
,
Göbel
A.
,
McArdell
C. S.
,
Ternes
T.
&
Siegrist
H.
2005
Removal of pharmaceuticals and fragrances in biological wastewater treatment
.
Water Research
39
(
14
),
3139
3152
.
Kakavandi
B.
,
Jahangiri-rad
M.
,
Rafiee
M.
,
Esfahani
A. R.
&
Babaei
A. A.
2016
Development of response surface methodology for optimization of phenol and p-chlorophenol adsorption on magnetic recoverable carbon
.
Microporous and Mesoporous Materials
231
,
192
206
.
Kilanski
L.
,
Jedrzejewski
R.
,
Sibera
D.
,
Kuryliszyn-Kudelska
I.
,
Gorantla
S.
,
Idczak
R.
,
Tran
V. H.
&
Jedrzejewska
A.
2021
Magnetic interactions in graphene decorated with iron oxide nanoparticles
.
Nanotechnology
32
(
30
),
305703
.
Kim
S.
,
Park
C. M.
,
Jang
M.
,
Son
A.
,
Her
N.
,
Yu
M.
,
Snyder
S.
,
Kim
D. H.
&
Yoon
T.
2018
Aqueous removal of inorganic and organic contaminants by graphene-based nanoadsorbents: a review
.
Chemosphere
212
,
1104
1124
.
Kimura
A.
,
Osawa
M.
&
Taguchi
M.
2012
Decomposition of persistent pharmaceuticals in wastewater by ionizing radiation
.
Radiation Physics and Chemistry
81
(
9
),
1508
1512
.
Krzeminski
P.
,
Tomei Popi Karaolia
M. C.
,
Langenhoff
A.
,
R. Almeida
C. M.
,
Felis
E.
,
Gritten
F.
,
Andersen
H. R.
,
Fernandes
T.
,
Manaia
C. M.
,
Rizzo
L.
&
Fatta-Kassinos
D.
2019
Performance of secondary wastewater treatment methods for the removal of contaminants of emerging concern implicated in crop uptake and antibiotic resistance spread: a review
.
Science of the Total Environment
648
,
1052
1081
.
Kuila
T.
,
Bose
S.
,
Mishra
A. K.
,
Khanra
P.
,
Kim
N. H.
&
Lee
J. H.
2012
Chemical functionalization of graphene and its applications
.
Progress in Materials Science
57
(
7
),
1061
1105
.
Li
J.
,
Zhang
S.
,
Chen
C.
,
Zhao
G.
,
Yang
X.
,
Li
J.
&
Wang
X.
2012
Removal of Cu (II) and fulvic acid by graphene oxide nanosheets decorated with Fe3O4 nanoparticles
.
ACS Applied Materials & Interfaces
4
(
9
),
4991
5000
.
Li
J.
,
Chen
C.
,
Zhu
K.
&
Wang
X.
2016
Nanoscale zero-valent iron particles modified on reduced graphene oxides using a plasma technique for Cd (II) removal
.
Journal of the Taiwan Institute of Chemical Engineers
59
,
389
394
.
Liu
C.
,
Yu
Z.
,
Neff
D.
,
Zhamu
A.
&
Jang
B. Z.
2010
Graphene-based supercapacitor with an ultrahigh energy density
.
Nano Letters
10
(
12
),
4863
4868
.
Luo
Y.
,
Guo
W.
,
Ngo
H. H.
,
Nghiem
L. D.
,
Hai
F. I.
,
Zhang
J.
,
Liang
S.
&
Wang
X. C.
2014
A review on the occurrence of micropollutants in the aquatic environment and their fate and removal during wastewater treatment
.
Science of the Total Environment
473
,
619
641
.
Mehrabi
N.
,
Masud
A.
,
Afolabi
M.
,
Hwang
J.
,
Calderon Ortizc
G. A.
&
Aich
N.
2019
Magnetic graphene oxide-nano zero valent iron (GO–nZVI) nanohybrids synthesized using biocompatible cross-linkers for methylene blue removal
.
RSC Advances
9
(
2
),
963
973
.
Minitha
C.
,
Lalitha
M.
,
Jeyachandran
Y.
,
Senthilkumar
L.
&
RT
R. K.
2017
Adsorption behaviour of reduced graphene oxide towards cationic and anionic dyes: co-action of electrostatic and π–π interactions
.
Materials Chemistry and Physics
194
,
243
252
.
Mohseni-Bandpi
A.
,
Kakavandi
B.
,
Kalantary
R. R.
,
Azari
A.
&
Keramati
A.
2015
Development of a novel magnetite–chitosan composite for the removal of fluoride from drinking water: adsorption modeling and optimization
.
RSC Advances
5
(
89
),
73279
73289
.
Naddeo
V.
,
Uyguner-Demirel
C. S.
,
Prado
M.
,
Cesaro
A.
,
Belgiorno
V.
&
Ballesteros
F.
2015
Enhanced ozonation of selected pharmaceutical compounds by sonolysis
.
Environmental Technology
36
(
15
),
1876
1883
.
Naghdi
M.
,
Taheran
M.
,
Brar
SK.
,
Kermanshahi-pour
A.
,
Verma
M.
&
Surampalli
R. Y.
2018
Biotransformation of carbamazepine by laccase-mediator system: kinetics, by-products and toxicity assessment
.
Process Biochemistry
67
,
147
154
.
Ofomaja
A. E.
,
Naidoo
E. B.
&
Pholosi
A.
2020
Intraparticle diffusion of Cr (VI) through biomass and magnetite coated biomass: a comparative kinetic and diffusion study
.
South African Journal of Chemical Engineering
32
(
1
),
39
55
.
Özçelik
G.
,
Bilgin
M.
&
Şahin
S.
2020
Carbamazepine sorption characteristics onto bentonite clay: Box-Behnken process design
.
Sustainable Chemistry and Pharmacy
18
,
100323
.
Patel
M.
,
Kumar
R.
,
Kishor
K.
,
Mlsna
T.
,
Pittman
C. U.
&
Mohan
D.
2019
Pharmaceuticals of emerging concern in aquatic systems: chemistry, occurrence, effects, and removal methods
.
Chemical Reviews
119
(
6
),
3510
3673
.
Prado
M.
,
Borea
L.
,
Cesaro
A.
,
Liu
H.
,
Naddeo
V.
,
Belgiorno
V.
&
Ballesteros
F.
2017
Removal of emerging contaminant and fouling control in membrane bioreactors by combined ozonation and sonolysis
.
International Biodeterioration & Biodegradation
119
,
577
586
.
Ray
S. K.
,
Majumder
C.
&
Saha
P.
2017
Functionalized reduced graphene oxide (fRGO) for removal of fulvic acid contaminant
.
RSC Advances
7
(
35
),
21768
21779
.
Rivera-Utrilla
J.
,
Sánchez-Polo
M.
,
Ferro-García
M. Á.
,
Prados-Joya
G.
&
Ocampo-Pérez
R.
2013
Pharmaceuticals as emerging contaminants and their removal from water. A review
.
Chemosphere
93
(
7
),
1268
1287
.
RxList
R
, .
2008
The internet drug index. Aldactone®, (spironolactone) Tablets, USP: 1-8. Available from: https://www.rxlist.com/aldactone-drug.htm
Sanchez
V. C.
,
Jachak
A.
,
Hurt
R. H.
&
Kane
A. B.
2012
Biological interactions of graphene-family nanomaterials: an interdisciplinary review
.
Chemical Research in Toxicology
25
(
1
),
15
34
.
Shan
D.
,
Deng
S.
,
Li
J.
,
Wang
H.
,
He
C.
,
Cagnetta
G.
,
Wang
B.
,
Wang
Y.
,
Huang
J.
&
Yu
G.
2017
Preparation of porous graphene oxide by chemically intercalating a rigid molecule for enhanced removal of typical pharmaceuticals
.
Carbon
119
,
101
109
.
Stoller
M. D.
,
Park
S.
,
Zhu
Y.
,
An
J.
&
Ruoff
R. S.
2008
Graphene-based ultracapacitors
.
Nano Letters
8
(
10
),
3498
3502
.
Tan
K.
&
Hameed
B.
2017
Insight into the adsorption kinetics models for the removal of contaminants from aqueous solutions
.
Journal of the Taiwan Institute of Chemical Engineers
74
,
25
48
.
Urbas
K.
,
Aleksandrzak
M.
,
Jedrzejczak
M.
,
Jedrzejczak
M.
,
Rakoczy
R.
,
Chen
X.
&
Mijowska
E.
2014
Chemical and magnetic functionalization of graphene oxide as a route to enhance its biocompatibility
.
Nanoscale Research Letters
9
(
1
),
1
12
.
Valderrama
C.
,
Gamisans
X.
,
De las Heras
X.
,
Farran
A.
&
Cortina
J.
2008
Sorption kinetics of polycyclic aromatic hydrocarbons removal using granular activated carbon: intraparticle diffusion coefficients
.
Journal of Hazardous Materials
157
(
2–3
),
386
396
.
Vasanth Kumar
K.
,
Subanandam
K.
&
Bhagavanulu
D.
2004
Making GAC sorption economy
.
Pollution Research
23
(
3
),
439
444
.
Wang
Z.
,
Yu
X.
,
Pan
B.
&
Xing
B.
2010
Norfloxacin sorption and its thermodynamics on surface-modified carbon nanotubes
.
Environmental Science & Technology
44
(
3
),
978
984
.
Yu
B.
,
Bai
Y.
,
Ming
Z.
,
Yang
H.
,
Chen
L.
,
Hu
X.
,
Feng
S.
&
Yang
S. T.
2017
Adsorption behaviors of tetracycline on magnetic graphene oxide sponge
.
Materials Chemistry and Physics
198
,
283
290
.
Zhang
W.-x.
2003
Nanoscale iron particles for environmental remediation: an overview
.
Journal of Nanoparticle Research
5
(
3
),
323
332
.
Zhang
Q.-l.
,
Yang
Z.-M.
,
Ding
B.-j.
,
Lan
X.-z.
&
Guo
Y.-j.
2010
Preparation of copper nanoparticles by chemical reduction method using potassium borohydride
.
Transactions of Nonferrous Metals Society of China
20
,
s240
s244
.
Zhao
J.
,
Liu
L.
&
Li
F.
2015
Graphene Oxide: Physics and Applications
.
Springer-Verlag, Berlin Heidelberg
,
Germany
.
Series ISSN 2191-5423.
Zou
Y.
,
Wang
X.
,
Khan
A.
,
Wang
P.
,
Liu
Y.
&
Alsaedi
A.
2016
Environmental remediation and application of nanoscale zero-valent iron and its composites for the removal of heavy metal ions: a review
.
Environmental Science & Technology
50
(
14
),
7290
7304
.
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