Light-induced degradation of organic pollutants under high salinity conditions using titanium dioxide/ferrocene polymer nanocomposites as photocatalyst and H₂O₂ activator simultaneously

Abstract

In this study, TiO₂ nanocomposites immobilized with a ferrocene-containing polymer were facilely prepared according to mussel-inspired biomimetic strategy. The nanocomposites were used as heterogeneous catalysts for photocatalytic oxidation and photo-Fenton-like reactions simultaneously. Notably, mimetic wastewaters containing different organic pollutants could be treated via these synergistic photoreactions in high salinity conditions. A series of organic pollutants such as tetracyclines, bisphenol A, bisphenol S, and rhodamine B could be degraded within 30 minutes in the presence of high-concentration inorganic salts (500 mmol L⁻¹ NaCl or NaNO₃). It was possible to recycle the nanocomposites after the reactions for reuse, and the degradation efficiency was maintained stable in repeated consecutive experiments.

---

Environmental significance

As one of the most commonly used advanced oxidation processes (AOPs), the traditional Fenton reaction is often limited in treating high salinity wastewater. Novel AOPs dominated by singlet oxygen and superoxide radicals could avoid the side effects of inorganic salts and have recently drawn great attention. In this study, we demonstrate that TiO₂ nanocomposites immobilized with a ferrocene-containing polymer could act as heterogeneous catalysts for photocatalytic oxidation and photo-Fenton-like reactions simultaneously. Our study contributes to the treatment of wastewater containing different organic pollutants by the synergistic photoreactions based on nano photocatalysts in high salinity conditions.

1. Introduction

Owing to the efficient generation of oxidizing free radicals under conditions close to normal temperature and pressure, advanced oxidation processes (AOPs) are widely used to treat non-biodegradable pollutants in water.^1,2 Hydrogen peroxide (H₂O₂), peroxydisulfate (PDS), and peroxymonosulfate (PMS) are inexpensive and efficient oxidants used in the remediation of polluted water. Studies on the degradation of pollutants in water by activating oxidants in different ways to produce living oxygen species, such as hydroxyl radical (·OH), sulfate radical (·SO₄⁻), singlet oxygen (¹O₂), and superoxide radical (·O₂⁻), have been widely reported.^3–9 Among these AOPs, Fenton and Fenton-like reactions are the most common processes for treating wastewater containing complex pollutants.^10,11 Industrial wastewater usually contains a large amount of inorganic salts, which quench the ·OH and ·SO₄⁻ radicals produced in AOPs, thus affecting the performance of Fenton and Fenton-like reactions.^3,12–141O₂ is a non-radical reactive oxygen species (ROSs) that can selectively degrade pollutants and is not affected by inorganic salts in water.^3,15,16 Metal co-catalysts, such as copper, and organic acid catalysts, such as ascorbic acid, are widely used in AOPs dominated by non-radical ROSs.^17–20 However, some co-catalysts are difficult to recycle and can cause potential environmental pollution during application. The application of carbon materials avoided the metal leaching-induced secondary contamination of metal-based heterogeneous catalysts, but the preparation of carbon materials requires high temperatures of hundreds of degrees Celsius.^3,7,15 Ferrocene (Fc) and its derivatives can be grafted onto the carrier via a covalent bond under relatively mild conditions. In addition, Fc not only has good reversible redox properties but also exhibits an excellent electron transfer rate, and is widely used as a heterogeneous catalyst.^21–23 For example, the heterogeneous catalysts prepared by covalently bonding Fc can avoid the loss of Fe and exhibit excellent catalytic performance.^21,24–26 Fc-based heterogeneous catalysts can be prepared under mild conditions while avoiding metal leaching, so they have great prospects in water pollution remediation.

Photo-Fenton has economic advantages and is efficient and environmentally friendly. Therefore, photocatalysis has received widespread attention in recent years.^27–32 However, the low utilization of light is a challenge in traditional photo-Fenton reactions.³³ The combination of photo-Fenton and photocatalysis has excellent synergistic effects, which can greatly improve the utilization of light and the reaction efficiency.^34,35 TiO₂, as one of the most common photocatalysts, has the advantages of environmental safety, stability, and affordability.³⁶ It is our hypothesis that grafting ferrocene onto TiO₂ can yield a hybrid nanocomposite and hence combine the photo-Fenton reaction and photocatalytic oxidation reaction. However, to the best of our knowledge, there have been very few reports on the fabrication of TiO₂/ferrocene polymer hybrid nanocomposites as well as its application as the photocatalysts for AOP.

In this work, TiO₂@Fc polymer nanocomposites (TiO₂@Fc) were prepared by grafting Fc-containing polymer to TiO₂via dopamine-based bonding, which is inspired by the mussel adhesion protein.^37,38 The nanocomposites were characterized by XPS, FTIR, TGA, and SEM. Subsequently, TiO₂@Fc was used as the photocatalyst for simultaneous Fenton-like and photocatalytic oxidation reactions to degrade pollutants in high-salinity wastewater. The quenching experiment and electron paramagnetic resonance (EPR) were utilized to investigate the mechanism of the photo-Fenton-like reaction. Finally, the repeated experiments and degradation experiments on various organic pollutants demonstrated the potential of the catalyst in the treatment of high-concentration salt-containing organic wastewater.

2. Results and discussion

2.1. Preparation and characterization of TiO₂@Fc hybrid nanocomposites

As shown in Scheme 1, a ferrocene-containing polymer (poly(ferrocene)) was first prepared by radical polymerization with AIBN as the initiator and PEGA₄₈₀, FMMA, and DMA as the monomers. Among them, FMMA serves as an iron source, DMA serves as a chelating agent to graft poly(ferrocene) to TiO₂, and PEGA₄₈₀ is a hydrophilic monomer aiming to enhance the dispersibility of TiO₂@Fc in water. After polymerization, TiO₂ nanoparticles were directly added into the reaction tube to in situ immobilize poly(ferrocene) onto the surface via biomimetic interaction of catechol groups with TiO₂. The final product (named TiO₂@Fc) could be separated from the suspension via centrifugation following drying under vacuum.

Scheme 1 Synthetic route to TiO₂@Fc nanocomposites.

TEM, SEM-EDS, FTIR, TGA, and XRD techniques were then used to characterize TiO₂@Fc. The TEM image of TiO₂@Fc (Fig. 1A) showed that the particle size of the non-agglomerated catalyst was within 20 nm, and the enlarged crystal structure is shown in Fig. 1B. Based on the lattice fringes, the distance between two adjacent planes was estimated to be 0.352 nm, which corresponds to the (101) plane spacing of the anatase phase.³⁶ The surface morphology of the stacked catalyst was displayed in the SEM image (Fig. 1C) and the morphology of the dispersed catalysts showed irregular nanoparticles. The mapping image (Fig. 1D) confirmed the existence of the Fe element and revealed a uniform distribution of Fe on the catalyst. As shown in Fig. 1E, the peaks at 0.7 keV and 6.4 keV came from the Fe element, and the peaks at 2.3 keV and 2.5 keV came from the Ti element in the SEM-EDS data. Compared with TiO₂, the FTIR spectrum of TiO₂@Fc showed new peaks at 1100, 1731, and 2869 cm⁻¹, which were ascribed to poly(ferrocene) (Fig. 1F). The peaks at 1100 cm⁻¹ belonged to C–O, and the peak of 1731 cm⁻¹ and 2869 cm⁻¹ were because of the stretching vibration of the C=O and C–H, respectively. The TGA analysis (Fig. 1G) showed that 92.5% of poly(ferrocene) was degradable, and the 7.5% weight residual may be due to the presence of iron oxide after the TGA test. When the temperature reached 600 °C, there was 92.00% remaining TiO₂ and 87.14% remaining TiO₂@Fc, which further proved the presence of degradable poly(ferrocene) in the hybrid nanocomposites. The main peaks appearing in the XRD pattern (Fig. 1H) at 2θ = 25.4(101), 37.9(004), 48.1(200), 54.0(105), 55.1(211), 62.8(204), 69.0(116), 70.4(220), and 75.1(215) were all from anatase TiO₂ because Fc was grafted onto the surface of TiO₂ in the form of a polymer, which did not affect the crystal structure. Based on these characterizations, TiO₂ hybrid nanocomposites with the ferrocene-containing polymer on the surface were successfully prepared.

Fig. 1 TEM (A and B), SEM (C), mapping of Fe (D), EDS (E), FTIR spectra (F), TGA curves (G), and XRD (H) of TiO₂@Fc, and TiO₂.

Then, in order to test the optical and optoelectronic properties of TiO₂@Fc, the UV-visible diffuse reflection spectrum and photocurrent response were measured. The photocurrent response of TiO₂@Fc (Fig. 2A) showed the rapid and stable photocurrent effect of the catalyst under irradiation, indicating that TiO₂@Fc had good electron and hole separation efficiency. Generally, TiO₂ had good absorption capacity for light in the range of 200–400 nm, while TiO₂@Fc had good light absorption capacity in the range of 200–800 nm, indicating that the addition of Fc greatly increases the absorption range of the catalyst for light (Fig. 2B). The Tauc plots (Fig. 2C) showed that its band gap was approximately 2.02 eV. A smaller band gap indicated that the catalyst had good catalytic activity. Therefore, the UV-visible diffuse reflection spectrum and photocurrent response proved that TiO₂@Fc had good photocatalytic performance.

Fig. 2 Photocurrent response (A), UV-visible diffuse reflection spectrum (B), and Tauc plots (C) of TiO₂@Fc.

2.2. Photocatalytic oxidation reaction catalyzed by hybrid nanocomposites

Subsequently, to confirm its photocatalytic properties, the hybrid nanocomposites were used as catalysts for photocatalytic oxidation of organic compounds. The test used RhB as the model compound and simulated sunlight as the light source under different pH. As shown in Fig. 3, when the reaction was stopped at 60 minutes, the removal ratio of RhB with TiO₂@Fc as the photocatalysts could reach 40%, 50%, and 25% at pH 3.0 (Fig. 3A), 7.0 (Fig. 3B), and 11.0 (Fig. 3C), respectively. Generally, compared to TiO₂, TiO₂@Fc showed close or slightly lower catalytic performance, especially when the solution was neutral or alkaline. This is possibly due to the covering of the TiO₂ surface by poly(ferrocene) brushes, which will inevitably block the irradiation of TiO₂ by sunlight. Nevertheless, the surface coating of the hybrid nanocomposites maintained the photocatalytic activity of TiO₂ and could still degrade organic pollutants under the irradiation of simulated sunlight. Which might be caused by eqn (1)–(3).^39–41

TiO₂ + hν → h⁺ + e⁻ (1)

e⁻ + O₂ → ·O₂⁻ (2)

h⁺ + H₂O → ·OH + H⁺ (3)

Fig. 3 Removal ratio of RhB solution in the presence of TiO₂@Fc or TiO₂ with simulated sunlight at pH 3.0 (A), 7.0, (B), and 11.0 (C) (RhB: 20 mg L⁻¹, TiO₂@Fc: 1.0 g L⁻¹).

2.3. Fenton-like reaction catalyzed by TiO₂@Fc under visible light or simulated sunlight

Subsequently, we investigated the possibility of the hybrid nanocomposite acting as the catalyst for the photo-Fenton-like reaction. As shown in Fig. S2,† the adsorption of pollutants by catalysts in the dark can be negligible. In a typical photo-Fenton reaction system, TiO₂@Fc was used to activate H₂O₂ under the irradiation of visible light or simulated sunlight. RhB was used as a model compound during the reaction. As shown in Fig. 4A, the removal ratio of RhB by only TiO₂@Fc within 30 min was less than 10%, and the removal ratio increased slightly but was less than 20% after the addition of visible light, proving that adsorption and photocatalysis were very slow to remove RhB. However, under the irradiation of visible light, the removal ratio could reach 90% at 15 min after the addition of H₂O₂, and almost 100% at 30 min. This showed that the Fenton or Fenton-like reaction was the main process during the degradation of RhB. Without visible light, the removal ratio of RhB by the TiO₂@Fc/H₂O₂ system was less than 20% in 30 min, which further indicated that photo-Fenton was the leading cause of the degradation of RhB. When simulated sunlight was used as the light source (Fig. 4B), the photocatalysis of TiO₂@Fc in the absence of H₂O₂ was still slow, which may be due to the polymer blocking the photocatalytic sites on the surface of TiO₂. However, TiO₂@Fc/H₂O₂/simulated sunlight system degraded more than 90% of RhB within 10 min, which was even higher than that using visible light as the light source. This also proved that ultraviolet radiation has a positive effect on the Fenton-like reaction.

Fig. 4 Removal ratio of RhB solution in the presence of TiO₂@Fc, H₂O₂ with visible light (A) or simulated sunlight (B) (RhB: 20 mg L⁻¹, H₂O₂: 8 mmol L⁻¹, TiO₂@Fc: 1.0 g L⁻¹, pH = 3.0).

2.4. Study of the optimal dose of the photo-Fenton-like reaction

Subsequently, the optimal amounts of H₂O₂ and TiO₂@Fc in the photo-Fenton-like were explored. As shown in Fig. 5A, when TiO₂@Fc concentration increases from 0 to 1.0 g L⁻¹, the RhB degradation ratio increases accordingly. In addition, Fig. 5B shows that when the concentration of H₂O₂ increases from 0 mmol L⁻¹ to 8 mmol L⁻¹, the degradation ratio of RhB increases accordingly. When the concentration of H₂O₂ was 12 mmol L⁻¹, the removal rate of RhB showed no significant changes. The area of contact between TiO₂@Fc and H₂O₂ increased because of the increase of TiO₂@Fc or H₂O₂, promoting ROS generation. Thus, the optimized concentration of TiO₂@Fc was 1.0 g L⁻¹ and the optimal dosage of H₂O₂ was 8 mmol L⁻¹.

Fig. 5 Effects of concentrations of TiO₂@Fc (A, H₂O₂ was 8 mmol L⁻¹, pH = 3.0), H₂O₂ (B, TiO₂@Fc was 1.0 g L⁻¹, pH = 3.0) changes. RhB solution was 20 mg L⁻¹, and the light source was visible light.

Under the irradiation of visible light, when the solution was neutral or alkaline, the removal ratio of RhB decreased significantly (Fig. 6A). This was because Fc was more prone to oxidation–reduction reaction under acidic conditions and was more stable under neutral or alkaline conditions; therefore, the photo-Fenton-like reaction should be carried out under acidic conditions. When simulated sunlight was used as the light source (Fig. 6B), the removal ratio of RhB reached 60% under neutral conditions, which is far higher than the removal ratio when visible light was used, indicating that ultraviolet light can still promote the degradation of RhB by TiO₂@Fc under neutral conditions.

Fig. 6 Effects of different pH with visible light (A) or simulated sunlight (B) (RhB: 20 mg L⁻¹, H₂O₂: 8 mmol L⁻¹, TiO₂@Fc: 1.0 g L⁻¹).

2.5. Study of the mechanism of the photo-Fenton-like reaction

We explored the mechanism of the photo-Fenton-like reactions via a series of control experiments. As shown in Fig. 7A, under the irradiation of visible light, the removal ratio of RhB decreased from 100% to ∼80% because of TBA, and to ∼30% because of NaN₃, which indicated that ¹O₂ was the main active ROS in the reaction. After removing the dissolved oxygen in water with N₂, the removal ratio of RhB decreased from 100% to 60%, indicating that O₂ played an important role in the generation of ROSs. When visible light was replaced by simulated sunlight (Fig. 7B), the removal ratio of RhB decreased from 100% to ∼50% at 30 min because NaN₃ is the obligate scavenger. However, TBA as the obligate scavenger and removal of the dissolved oxygen only caused a decrease in the degradation rate; the removal ratio could still reach 100%. This proved that ¹O₂ is still the main active ROS in photo-Fenton-like reactions in the presence of simulated sunlight.

Fig. 7 Effect of TBA, NaN₃, and N₂ on the removal ratio of RhB with visible light (A) or sunlight (B) (RhB: 20 mg L⁻¹, H₂O₂: 8 mmol L⁻¹, TiO₂@Fc: 1.0 g L⁻¹, pH = 3.0).

To further explore the mechanism of the photo-Fenton-like reactions, EPR characterizations were also performed. As shown in Fig. 8, the EPR proved the existence of ·OH (Fig. 8A), ·O₂⁻ (Fig. 8B), and ¹O₂ (Fig. 8C) in this photo-Fenton-like reaction. In order to explore what role dissolved O₂ plays in the production of ROSs, a comparative experiment was conducted by removing dissolved O₂ from the solution by N₂. The signals of ·OH and ·O₂⁻ weakened, and the signal of ¹O₂ had no significant changes after N₂ bubbling, which may be caused by eqn (5) and (6).^9,17,20

TiO₂ + hν → h⁺ + e⁻ (4)

≡Fe²⁺ + O₂ → ≡Fe³⁺ + ·O₂⁻ (5)

·O₂⁻ + H₂O₂ → ≡O₂ + ·OH + OH⁻ (6)

≡Fe³⁺ + e⁻ → ≡Fe²⁺ (7)

≡Fe³⁺ + H₂O₂ → ≡Fe²⁺ + ·O₂⁻ + 2H⁺ (8)

≡Fe²⁺ + H₂O₂ → ≡Fe³⁺ + ·OH + OH⁻ (9)

Fig. 8 DMPO (50 mmol L⁻¹) spin-trapping EPR spectra for ·OH (A), ·O₂⁻ (B), and TEMP (50 mmol L⁻¹) spin-trapping EPR spectra for ¹O₂ (C and D).

After removing the simulated sunlight (Fig. 8D), the signal of ¹O₂ disappeared, indicating that light was a necessary condition for the production of ¹O₂ in this Fenton-like reaction. Thus, we infer that ¹O₂ may be caused by eqn (10) and (11).^42,43

H₂O₂ → H⁺ + HO₂⁻ (10)

2≡Fe³⁺ + HO₂⁻ + hν → 2≡Fe²⁺ + ¹O₂ + H⁺ (11)

Thus, the mechanism of the TiO₂@Fc-catalyzed photo-Fenton-like reaction is described in Scheme 2. Under light irradiation, ferrocene cation (Fc⁺) generates Fc after receiving electrons, then Fc activates H₂O₂ to generate ·OH, ·O₂⁻, and ¹O₂. In addition, ·O₂⁻ could also be generated by Fc activating O₂. ¹O₂ was believed to play the most significant role in this photo-Fenton-like reaction.

Scheme 2 Illustration of the TiO₂@Fc-catalyzed photo-Fenton-like reaction mechanism.

The TOC was then applied to test the mineralization degree of RhB during the photo-Fenton-like reaction, and LC-MS was used to determine the intermediates during the photo-Fenton-like reaction. Taking RhB as an example, the removal ratio of TOC reached 70% during the photo-Fenton-like reaction. As Fig. S1† shows, after 30 min of photo-Fenton-like reaction, the RhB signal (m/z = 443) was almost unobservable and the species of m/z = 166, 240, 317, 331, and 415 were found, indicating that RhB molecules would be attacked by the active species (¹O₂) and turned into intermediates. The intermediates were then further degraded into small organic molecules by the photo-Fenton-like reaction (Fig. S2†). Finally, some small organic molecules are converted into s CO₂ and H₂O.

2.6. Studies on high salinity wastewater treatment by photo-Fenton-like reaction

Furthermore, we investigated the effect of ions on this photo-Fenton-like reaction system. As Fig. 9 shows, the RhB solution containing 500 mmol L NaCl or NaNO₃ was used to simulate high-salinity wastewater treatment by TiO₂@Fc. In traditional Fenton reactions (Fig. 9A), ·OH could react with Cl⁻ and NO₃⁻, and produce weaker radicals, but ¹O₂ in this photo-Fenton-like system avoided attacks by the anions; therefore, it could degrade RhB effectively (Fig. 9B). Under acidic conditions, NO₃⁻ has oxidizing properties, so the degradation rate by adding NO₃⁻ is higher than that of adding Cl⁻. These results further confirmed that ¹O₂ plays the most important role in this photo-Fenton-like reaction.

Fig. 9 Effect of anions on the removal ratio of RhB without light (A) and under visible light (B) (NaCl and NaNO₃: 500 mmol L⁻¹, RhB: 20 mg L⁻¹, H₂O₂: 8 mmol L⁻¹, TiO₂@Fc: 1.0 g L⁻¹, pH: 3.0).

Afterward, different organic pollutants (BPA, BPS, and TC) were degraded by a photo-Fenton-like reaction to test the degradation effect of TiO₂@Fc on other organic pollutants. As shown in Fig. 10A, the Fenton-like reaction had good degradation effects on several organic pollutants. The degradation ratio of BPA and BPS could reach over 90% at 30 min, while the degradation ratio of TC could reach nearly 100% at 15 min. This proved that even just the photo-Fenton-like reaction is efficient in degrading different pollutants.

Fig. 10 Degradation of RhB, BPA, BPS, and TC with visible light (A) or sunlight (B) (RhB: 20 mg L⁻¹, H₂O₂: 8 mmol L⁻¹, TiO₂@Fc: 1.0 g L⁻¹, pH = 3.0).

After that, the light source was changed into simulated sunlight in order to combine a photo-Fenton-like reaction and photocatalytic oxidation reaction for the treatment of wastewater. As shown in Fig. 10B, as compared with Fig. 10A, the degradation rate of different pollutants was faster, indicating that photocatalytic oxidation under irradiation of UV light could accelerate the photodegradation rate.

Finally, under optimized experimental conditions, four repeated experiments were conducted to test the reusability of TiO₂@Fc. The degradation ratio of RhB after four consecutive Fenton-like reactions could still reach over 95% within 30 min, proving that TiO₂@Fc was recovered facilely and reused repeatedly (Fig. 11). Meanwhile, compared with the FTIR spectra of TiO₂@Fc before and after the reaction (Fig. S3†), the main peaks did not change, which also proved that TiO₂@Fc could maintain its properties during the reaction.

Fig. 11 Reusability experiment of TiO₂@Fc (RhB: 20 mg L⁻¹, H₂O₂: 8 mmol L⁻¹, TiO₂@Fc: 1.0 g L⁻¹, pH = 3.0, the light source was visible light).

3. Conclusions

In conclusion, we used radical polymerization to synthesize ferrocene-containing polymers, and TiO₂@Fc nanocomposites were prepared via biomimetic anchoring. This type of nanocomposite combines the catalytic properties of TiO₂ and ferrocene, which are used as heterogeneous catalysts for photo-Fenton-like reactions and photocatalytic oxidation simultaneously. In the photo-Fenton-like reaction, ¹O₂ was identified as the primary reactive oxygen species. Under the irradiation of visible light, the Fenton-like reaction TiO₂@Fc as a catalyst can degrade RhB, TC, BPA, and BPS within 30 min under high salinity conditions. When the light source was simulated sunlight, the combination of photocatalytic oxidation could accelerate the degradation rate. It is facile to recover TiO₂@Fc from water for repeated use, and the degradation efficiency was maintained stable in multiple consecutive experiments. We hypothesize that hybrid nanocatalysts may have potential applications in treating wastewater containing high concentrations of inorganic salts.

Conflicts of interest

The authors declare no competing financial interests.

Acknowledgements

Financial support from the Fundamental Research Funds for the Central Universities (No. 30922010811) is greatly appreciated.

Notes and references

1. X. Cheng, H. Guo, Y. Zhang, X. Wu and Y. Liu, Water Res., 2017, 113, 80–88.
2. Y. Rao, Y. Zhang, J. Fan, G. Wei, D. Wang, F. Han, Y. Huang and J.-P. Croué, Chem. Eng. J., 2022, 435, 134882.
3. S. Wu, C. Yang, Y. Lin and J. J. Cheng, J. Environ. Sci., 2022, 115, 330–340.
4. Y. Wen, C. H. Huang, D. C. Ashley, D. Meyerstein, D. D. Dionysiou, V. K. Sharma and X. Ma, Environ. Sci. Technol., 2022, 56, 2626–2636.
5. Y. Li, J. Li, Y. Pan, Z. Xiong, G. Yao, R. Xie and B. Lai, Chem. Eng. J., 2020, 384, 904–914.
6. C. Li, J. Wu, W. Peng, Z. Fang and J. Liu, Chem. Eng. J., 2019, 356, 904–914.
7. X. Cheng, H. Guo, Y. Zhang, G. V. Korshin and B. Yang, Water Res., 2019, 157, 406–414.
8. Y. Bu, H. Li, W. Yu, Y. Pan, L. Li, Y. Wang, L. Pu, J. Ding, G. Gao and B. Pan, Environ. Sci. Technol., 2021, 55, 2110–2120.
9. Y. Ahmed, J. Zhong, Z. Yuan and J. Guo, J. Hazard. Mater., 2022, 430, 128408.
10. M. Huang, T. Zhou, X. Wu and J. Mao, Water Res., 2017, 119, 47–56.
11. Y. Liu, W. Jin, Y. Zhao, G. Zhang and W. Zhang, Appl. Catal., B, 2017, 206, 642–652.
12. J. Wang and S. Wang, Chem. Eng. J., 2021, 411, 128392.
13. M. Li, Y. Yao, W. Zhang, J. Zheng, X. Zhang and L. Wang, Environ. Sci. Technol., 2017, 51, 9252–9260.
14. Y. Lei, X. Lei, P. Westerhoff, X. Zhang and X. Yang, Environ. Sci. Technol., 2021, 55, 689–699.
15. R. Luo, M. Li, C. Wang, M. Zhang, M. A. Nasir Khan, X. Sun, J. Shen, W. Han, L. Wang and J. Li, Water Res., 2019, 148, 416–424.
16. T. Zhang, Y. Chen, Y. Wang, J. Le Roux, Y. Yang and J. P. Croue, Environ. Sci. Technol., 2014, 48, 5868–5875.
17. Y. Pan, H. Su, Y. Zhu, H. Vafaei Molamahmood and M. Long, Water Res., 2018, 145, 731–740.
18. D. Yuan, C. Zhang, S. Tang, X. Li, J. Tang, Y. Rao, Z. Wang and Q. Zhang, Water Res., 2019, 163, 114861.
19. Y. Mao, P. Wang, D. Zhang, Y. Xia, Y. Li, W. Zeng, S. Zhan and J. C. Crittenden, Environ. Sci. Technol., 2021, 55, 13326–13334.
20. Q. Yi, J. Ji, B. Shen, C. Dong, J. Liu, J. Zhang and M. Xing, Environ. Sci. Technol., 2019, 53, 9725–9733.
21. Y. Zhang, S. Zhao, M. Mu, L. Wang, Y. Fan and X. Liu, Chem. Eng. J., 2022, 439, 135605.
22. Y. Li, B. Zhang, X. Liu, Q. Zhao, H. Zhang, Y. Zhang, P. Ning and S. Tian, J. Hazard. Mater., 2018, 353, 26–34.
23. Q. Wang, S. Tian, J. Cun and P. Ning, Desalin. Water Treat., 2013, 51, 5821–5830.
24. L. Zhang, H. Chen, X. Zhao, Q. Zhai, D. Yin, Y. Sun and J. Li, Appl. Catal., B, 2016, 193, 47–57.
25. M. Arshadi, M. K. Abdolmaleki, F. Mousavinia, A. Khalafi-Nezhad, H. Firouzabadi and A. Gil, Chem. Eng. Res. Des., 2016, 112, 113–121.
26. L. Li, J.-l. Shi, J.-n. Yan, X.-g. Zhao and H.-g. Chen, Appl. Catal., A, 2004, 263, 213–217.
27. C. Du, Y. Zhang, Z. Zhang, L. Zhou, G. Yu, X. Wen, T. Chi, G. Wang, Y. Su, F. Deng, Y. Lv and H. Zhu, Chem. Eng. J., 2022, 431, 133932.
28. Z. Cao, Y. Jia, Q. Wang and H. Cheng, Appl. Clay Sci., 2021, 212, 106213.
29. W. Shi, W. Sun, Y. Liu, K. Zhang, H. Sun, X. Lin, Y. Hong and F. Guo, J. Hazard. Mater., 2022, 436, 129141.
30. R. Li, M. Zheng, X. Zhou, D. Zhang, Y. Shi, C. Li and M. Yang, Chem. Eng. J., 2023, 464, 142584.
31. S. Li, H. Shang, Y. Tao, P. Li, H. Pan, Q. Wang, S. Zhang, H. Jia, H. Zhang, J. Cao, B. Zhang, R. Zhang, G. Li, Y. Zhang, D. Zhang and H. Li, Angew. Chem., Int. Ed., 2023, 62, e202305538.
32. Q. Li, J. Zhao, H. Shang, Z. Ma, H. Cao, Y. Zhou, G. Li, D. Zhang and H. Li, Environ. Sci. Technol., 2022, 56, 5830–5839.
33. C. Lu, J. Wang, D. Cao, F. Guo, X. Hao, D. Li and W. Shi, Mater. Res. Bull., 2023, 158, 112064.
34. Y. Liu, X. Wang, Q. Sun, M. Yuan, Z. Sun, S. Xia and J. Zhao, J. Hazard. Mater., 2022, 424, 127387.
35. H. Sun, L. Wang, F. Guo, Y. Shi, L. Li, Z. Xu, X. Yan and W. Shi, J. Alloys Compd., 2022, 900, 163410.
36. C. H. Nguyen, C.-C. Fu and R.-S. Juang, J. Cleaner Prod., 2018, 202, 413–427.
37. D. Wang, W. Ding, K. Zhou, S. Guo, Q. Zhang and D. M. Haddleton, Biomacromolecules, 2018, 19, 2979–2990.
38. D. Wang, S. Guo, Q. Zhang, P. Wilson and D. M. Haddleton, Polym. Chem., 2017, 8, 3679–3688.
39. A. S. M. Nur, M. Sultana, A. Mondal, S. Islam, F. N. Robel, A. Islam and M. S. A. Sumi, J. Water Process. Eng., 2022, 47, 102728.
40. T. Zhang, Y. Liu, Y. Rao, X. Li, D. Yuan, S. Tang and Q. Zhao, Chem. Eng. J., 2020, 384, 123350.
41. X. Li, Y. Pi, L. Wu, Q. Xia, J. Wu, Z. Li and J. Xiao, Appl. Catal., B, 2017, 202, 653–663.
42. J. Zhang, Y. Wang, M. Hong, B. Peng, C. Bao, X. Xu, D. Li, J. Chen, B. Wang and Q. Zhang, Chem. Eng. J., 2023, 464, 142450.
43. S. Yang, P. Wu, J. Liu, M. Chen, Z. Ahmed and N. Zhu, Chem. Eng. J., 2018, 350, 484–495.

---

Footnote

† Electronic supplementary information (ESI) available: Materials, characterization and analysis, experimental procedures, supporting data items, and supporting figures. See DOI: https://doi.org/10.1039/d3en00729d

---