Research PaperAn efficient photo Fenton system for in-situ evolution of H2O2 via defective iron-based metal organic framework@ZnIn2S4 core-shell Z-scheme heterojunction nanoreactor
Graphical Abstract
Introduction
Environmental pollution and energy shortages are serious threats to human health and the natural environment and have aroused widespread concern (Di et al., 2018, Xie et al., 2021, Wu et al., 2020, Tritton et al., 2022, Chen et al., 2022a, Zhu et al., 2021). Due to its advantages of environmental protection, high efficiency and sustainability, photocatalytic technology has been deeply studied in the removal of refractory pollutants (Deng et al., 2020, Li et al., 2019), Cr (VI) reduction (Kumar et al., 2021, Ai et al., 2021), hydrogen production (Wang et al., 2021, Fang et al., 2018) and CO2 reduction (Pan et al., 2017, Lin et al., 2020). However, traditional semiconductor photocatalysts are hindered by problems such as a wide band gap, fast electron-hole pair recombination, and low solar energy utilization efficiency (Xiong and Tang, 2021, Jian et al., 2022). Over the past few decades, researchers have developed diverse strategies to improve photocatalytic activity. On the one hand, defect engineering can tune the semiconductor band structure to expand the light absorption range and provide highly active sites, which play a positive role in enhancing the photocatalytic performance (Wang et al., 2022, Li et al., 2021). It was reported that Zhang et al. (2022). developed N-defective g-C3N4 with dual defect sites, and the introduction of –CN groups and N vacancies enhanced photoabsorption and facilitated charge carrier separation, resulting in efficient photocatalytic H2O2 production performance. On the other hand, combining photocatalysis and other advanced oxidation processes (AOP), the synergy between them could significantly enhance the utilization rate of solar light. For example, Zhang et al. (2020a) developed a persulfate-based advanced oxidation (SR-AOPs) and MIL-53 (Fe)-based photocatalytic coupling, which demonstrated the highly efficient removal of tetracycline hydrochloride (99.7%). Therefore, the development of efficient photocatalysts and the advancement of photocatalytic technology are still the focus of photocatalysis.
Photocatalytic technology and heterogeneous Fenton oxidation have been combined to exert a synergistic effect to boost the efficiency of pollutant degradation, which is usually called photoFenton-like oxidation (Jiang et al., 2019). The Fenton system is the reaction of Fe ions with H2O2 to generate strong oxidizing hydroxyl radicals, which can destroy the structure of difficult-to-degrade organic pollutants (Zhu et al., 2019). Introducing ultraviolet or visible light into the Fenton system through a photoabsorbing semiconductor can increase the generation rate of ·OH and the cycle of Fe2+/Fe3+, making the repair of refractory wastewater more efficient. The photoFenton system actually combines H2O2 +Fe2+ with H2O2 +ultraviolet (UV), thereby reducing the amount of Fe2+ and increasing the utilization rate of hydrogen peroxide (Sun et al., 2020, López-Vinent et al., 2020). Supplementary H2O2 needs to be added to most of the Fenton-like systems, resulting in high cost and complicated processes (Wang et al., 2020a). Recent studies have shown that H2O2 can be spontaneously generated by the photocatalytic reaction at the water-photocatalyst interface, and enough oxygen in the water can be quickly captured by photogenerated electrons to generate H2O2 in-situ. In-situ H2O2 generation can greatly facilitate •OH generation and photoFenton performance. For example, Chen et al. (2022b). used BiVO4 as a photo-absorbing semiconductor and added Fe3+ to degrade antibiotics under light conditions. Without additional H2O2, they achieved an excellent photoFenton performance with a 96% norfloxacin degradation rate. Therefore, it is important to construct a photoFenton system with in-situ generated H2O2.
MOFs are widely applied in the field of photocatalysis due to their highly adjustable characteristics and large specific surface area (Hu et al., 2021, Wagner et al., 2020). The organic linking groups and metal oxygen clusters constituting the MOF can produce the ligand-metal charge transfer (LMCT) effect to promote the redox reaction in the photocatalytic process (Zhu et al., 2020). Among these MOF constituents, Fe-MOF is considered a remarkably valuable photocatalyst because it can provide abundant dispersed Fe sites to participate in the photocatalytic-Fenton coupling system (Zhang et al., 2021a, Xu et al., 2021). The Fe3-μ3-oxo clusters contained in Fe-MOF can realize the mutual conversion between Fe3+ and Fe2+ and generate ·OH with the help of spontaneous H2O2. Su et al. (2021). constructed a g-C3N4/NH2-MIL-101(Fe) photoFenton-like system, which greatly enhanced the photocatalytic performance. However, Fe-MOFs generally suffer from limited photoabsorption and poor charge separation, so we proposed to modify MOFs by defect engineering to improve the performance of MOFs. Gao et al. (2020). successfully integrated the tetrakis(4-carboxyphenyl)porphyrin (TCPP) linker into the MOF to synthesize defective TCPP@UiO-66 in-situ, which has the catalytic activity of efficiently degrading diclofenac (DF) with a removal efficiency of 99%. Wang et al. (2020b) prepared NH2-MIL-88B(Fe) with ligand defects by doping with monodentate ligands, which significantly enhanced the photoFenton catalytic degradation performance.
When MOF and metal sulfide construct a well-matched band structure, an effective heterojunction can be formed to promote the separation of photoexcited charge carriers (Liu et al., 2020, Zhao et al., 2021a). As a typical n-type semiconductor, the bimetallic sulfide ZnIn2S4 (ZIS) is considered compatible with Fe-MOF due to its suitable band gap (~2.5 eV), unique 2D hierarchical structure and high stability. Since ZIS nanosheets are effortless to self-assemble into flower-like microspheres, this approach is considered to grow 2D ZIS nanosheets on the MOF matrix to construct a MOF@shell structure, which can improve the water stability of MOFs and expose more surface active sites (Zhang et al., 2020b). The core-shell MOF-based composite provides a short electron transport distance and effective photogenerated charge separation, which significantly improves the photocatalytic activity (Liu et al., 2021). By improving the separation efficiency of photoexcited charge carriers on the surface of the core-shell composites, the photocorrosion of ZIS can be reduced. Porous Fe-MOF@ZIS possesses excellent carrier transport and molecular diffusion characteristics due to the outstanding interaction between Fe-MOF and ZIS and the formation of nanoreactors under visible and ultraviolet light irradiation, which provides a closed comprehensive catalytic environment to improve catalytic activity and stability. Therefore, in this work, the defective NH2-MIL-88B(Fe) and ZIS are proposed as the basic structure to construct a novel composite photocatalyst to improve the photoFenton catalytic performance.
Based on the above consideration and verification hypotheses, a photoFenton system with in-situ generated H2O2 was constructed by the synergistic integration of spindle-shaped NH2-MIL-88B(Fe) and 2D nanosheet-shaped ZIS. In this paper, the ligand defect in Fe-MOF was designed by using pyrrole 2-carboxylic acid (PDC) as a dopant, and the in-situ growth of ZIS nanosheets on the DNM88B was achieved by a simple oil bath heating method. Introducing ligand defects into MOFs expands the light absorption range, thereby reducing the band gap. In addition, the Z-scheme heterojunction formed between DNM88B and ZIS facilitates the separation of photogenerated electron-hole pairs, further enhancing the photocatalytic activity. In TOC measurements, the mineralization rates of the DNM88B@ZIS for bisphenol A (BPA) and ofloxacin (OFL) reached 89.5% and 86.5%, respectively, much higher than the mineralization rate of the pristine sample, showing excellent photoFenton performance. Finally, the photoFenton reaction mechanism of the DNM88B@ZIS Z-scheme heterojunction nanoreactor was proposed. This strategy provides a new idea for constructing an efficient photoFenton system.
Section snippets
Materials
Iron (III) chloride hexahydrate (FeCl3∙6H2O), Zinc chloride (ZnCl2) were purchased from Tianjin Kermel Chemical Reagent Co, LTD. 2-aminoterephthalic acid (NH2-BDC), Thioacetamide (TAA), Indium (III) chloride tetrahydrate (InCl3∙4H2O), Pyrrole-2-carboxllic acid (PDC) were purchased from Aladdin Industrial Corporation. Glycerol (GE) was purchased from Tianjin Kermel Chemical Reagent Co. Ltd, China.
Preparation of NM88B
NH2-MIL-88B(Fe) was synthesized by one-pot hydrothermal method, which was modified according to the
Chemical morphology and structure
Fig. 2a shows the XRD patterns of several synthesized catalysts. The characteristic diffraction peaks observed at 2θ = 9.2°, 10.1°, 12.8°, 16.7° and 20.2° correspond to the (002), (101), (102), (103) and (202) crystal planes of DNM88B, respectively, which are consistent with the simulated standard X-ray diffraction (XRD) patterns (Cambridge Crystallographic Data Centre (CCDC) 647646), indicating the successful formation of amine-functionalized MIL-88B. The ligand defect NM88B exhibits
Conclusion
In summary, a novel defective NH2-MIL-88B@ZnIn2S4 core-shell Z-scheme heterojunction nanoreactor was prepared via facile hydrothermal and oil bath methods, successfully constructing a photoFenton system for in-situ generation of H2O2 induced under visible light. By adapting the mass ratio of DNM88B and ZIS, DNM88B@ZIS-3 showed the outclass photoFenton performance compared to the two pure samples, removing ~ 99.4% BPA and ~ 98.5% of OFL within 180 min, and the hydrogen production reached 502
CRediT authorship contribution statement
Meijie Liu: Conceptualization, Methodology, Data curation, Writing – original draft, Visualization, Investigation, Software, Validation. Zipeng Xing: Conceptualization, Methodology, Supervision, Writing – review & editing. Huanan Zhao: Visualization, Investigation. Sijia Song: Visualization, Investigation. Yichao Wang: Visualization, Investigation. Zhenzi Li: Supervision, Writing – review & editing. Wei Zhou: Supervision, Writing – review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
We gratefully acknowledge the support of this research by the National Natural Science Foundation of China (52172206, 21871078), the Natural Science Foundation of Heilongjiang Province of China (JQ2019B001), the Natural Science Foundation of Shandong Province (ZR2021MB016), the Heilongjiang Provincial Institutions of Higher Learning Basic Research Funds Basic Research Projects (2021-KYYWF-0007), the Heilongjiang Postdoctoral Startup Fund (LBH-Q14135), the Heilongjiang University Science Fund
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