Photo-Fenton degradation of carbamazepine and ibuprofen by iron-based metal-organic framework under alkaline condition

Fe-MOFs nanosheets for photo-Fenton degradation of carbamazepine

Iron(II)-based metal organic framework (Fe(II)-MOF) nanosheets have emerged as promising candidates for photo-Fenton catalysis. However, efficiently synthesizing Fe(II)-MOF nanosheets remains a significant challenge. Here, a bottom-up synthesis strategy is proposed to prepare two-dimensional Fe-MOF nanosheets (TFMN) with micrometer lateral dimensions and nanometer thickness, featuring Fe(II) as the metal nodes. The application of TFMN in the photo-Fenton degradation of carbamazepine (CBZ) demonstrates remarkable CBZ degradation performance and excellent efficiency across a wide range of pH values. The electron density and density of states are further calculated by density functional theory. Mechanism analysis identifies h+, •OH and •O2- as the predominant active species contributing to the catalytic oxidation process in the Vis/TFMN/H2O2 system.

In situ synthesis of oxygen-doped carbon quantum dots embedded in MIL-53(Fe) for efficient degradation of oxytetracycline

Introducing carbon quantum dots (CQDs) into photocatalysts is believed to boost the charge transfer rate and reduce charge complexation. Doping heteroatoms such as N, S, or P enable CQDs to have an uplifting electron transfer capability. However, the application of oxygen-doped CQDs to improve the performance of photocatalysts has rarely been reported. Herein, a type of carbon-oxygen quantum dots (COQDs) was in situ embedded into MIL-53(Fe) to aid peroxydisulfate (PDS)-activated degradation of oxytetracycline (OTC) under visible light irradiation. The successful embedding of COQDs was confirmed by XRD, FT-IR, XPS, SEM, and TEM techniques. Photoelectrochemical testing confirmed its better performance. The prepared COQDs1/MIL-53(Fe) showed 88.2% decomposition efficiency of OTC in 60 min, which was 1.45 times higher than that of pure MIL-53(Fe). In addition, the performance of the material was tested at different pH, OTC concentrations, catalyst dosing, and PDS dosing. It was also subjected to cyclic testing to check stability. Moreover, free radical trapping experiments and electron paramagnetic resonance were conducted to explore the possible OTC deterioration mechanism. Our work provides a new idea for the development of MOFs for water treatment and remediation.

Removal of oxytetracycline from water by S-doped MIL-53(Fe): Synergistic effect of surface adsorption and persulfate activation

In this study, a novel catalyst based on MIL-53(Fe) was synthesized and modified through sublimed sulfur (S-MIL-53(Fe)) to induce a synergistic effect of surface adsorption and persulfate activation. The S-doped modification not only increased the surface area but also accelerated the electron transfer process of the iron cycle. The performance of the newly synthesized S-MIL-53(Fe) adsorptive catalyst was evaluated by chemical adsorption and peroxydisulfate (PDS) activated removal of an emerging pollutants, oxytetracycline (OTC). The S-MIL-53(Fe) adsorptive catalyst was able to adsorb 61.7% of OTC after 120 min, and the removal efficiency reached 84.8% within 5 min after PDS dosing. The boosting effect of sulfur on the system was confirmed by characterization analysis and experimental testing. Even after 7 cycles, the removal efficiency of S-MIL-53(Fe) (69.0%) for OTC remained superior to that of pure MIL-53(Fe) (25.1%). Additionally, the adsorption kinetics and adsorption isotherm model of the material were investigated. The possible OTC degrading process was proposed based on radical quenching and electron paramagnetic resonance (EPR). This study provides a feasible way to fabricate an S-doped MIL-53(Fe) adsorptive catalyst for the remediation of antibiotics-containing wastewater.

Optimizing the performance of Fe-based metal-organic frameworks in photo-Fenton processes: Mechanisms, strategies and prospects

Contaminants in water pose a significant challenge as they are harmful and difficult to treat using conventional methods. Therefore, various new methods have been proposed to degrade organic pollutants in water, among which the photo-Fenton process is considered promising. In recent years, Fe-based metal-organic frameworks (Fe-MOFs) have gained attention and found applications in different fields due to their cost-effectiveness, non-toxic nature, and unique porous structure. Many researchers have applied Fe-MOFs to the photo-Fenton process in recent years and achieved good results. This review focuses on describing different strategies for enhancing the performance of Fe-MOFs in the photo-Fenton process. Also, the mechanism of MOF in the photo-Fenton process is described in detail. Finally, prospects for the application of Fe-MOFs in photo-Fenton systems for the treatment of organic pollutants in water are presented. This study provides information and ideas for researchers to use Fe-MOFs to remove organic pollutants from water by photo-Fenton process.

Hierarchical hollow α-Fe2O3/ZnFe2O4/Mn2O3 Janus micromotors as dynamic and efficient microcleaners for enhanced photo-Fenton elimination of organic pollutants

Micro/nanomotors that can promote mass transport have attracted more and more research concern in the photocatalysis field. Here we first report a newly-designed hierarchical α-Fe2O3/ZnFe2O4/Mn2O3 magnetic micromotor as a heterogeneous photocatalyst for the degradation of cationic dye methylene blue (MB) from wastewater. The resulting three-dimensional (3D) flower-like hollow Janus micromotors are fabricated through a green and scalable strategy, in which each component has different functions. ZnFe2O4 microspheres serve as a magnetic scaffold for the nucleation and growth of α-Fe2O3 nanosheets and for the recycling of the micromachine. α-Fe2O3 nanosheets have shown great potential as an ideal semiconductor material for the photocatalytic decontamination of pollutants. Mn2O3 nanoparticles are mainly utilized as a catalyst to produce O2 bubbles to propel the autonomic movement of the micromotors in the presence of H2O2 fuel and also as a Fenton-like catalyst to decompose H2O2 to generate reactive oxygen species. Furthermore, the resultant micromotors exhibited linear-like motion form with an average speed of 189.1 μm s-1 in 5 wt% H2O2 solution. Moreover, the self-driven micromotors exhibited a superior catalytic degradation property toward MB, which was attributed to the synergistic effect of heterogeneous photocatalyst and the boosted micro-mixing and mass transfer caused by the vigorous motion of the micro-actuator. The possible degradation intermediates and passways of MB by α-Fe2O3/ZnFe2O4/Mn2O3 micromotor were identified with time of flight mass spectroscopy (TOF-MS). The 3D Janus micromotors have the potential to be used as a high-efficiency and active heterogeneous photocatalyst for the degradation of organic pollutants.

Synthesis of cerium oxide embedded perovskite type bismuth ferrite nanocomposites for sonophotocatalysis of aqueous micropollutant ibuprofen

Ibuprofen is potentially toxic and carcinogenic for freshwater ecosystems and poses a serious threat to human health by affecting kidney function. The present study focused on the sunlight-controlled degradation of ibuprofen from water using a novel magnetically separable cerium oxide-embedded bismuth ferrite heterostructure. Catalysts were synthesized by solvothermal and co-precipitation methods and characterized by X-ray diffractometry, transmission electron microscopy, X-ray photoelectron spectroscopy, UV-vis optical absorption spectroscopy, and nitrogen adsorption. This study investigated the effect of photocatalysis, sonolysis, sonophotolysis, and sonophotocatalysis on the degradation of ibuprofen in water. Pseudo-first-order and second-order kinetics were applied to evaluate the rate of reaction for ibuprofen degradation. The addition of 5% CeO2 to the BiFeO3 significantly increased the surface area and pore volume of bismuth ferrite, which enhanced their photocatalytic degradation efficiency by 2.28 times in terms of ibuprofen mineralization. Sonolysis treatment alone and in combination with photolysis led to the degradation of ibuprofen, but with the formation of intermediate products. Positive synergy was observed when sonolysis was combined with photocatalysis in terms of the mineralization of ibuprofen and the degradation of intermediates along with their parent compound. It was proposed that, compared to photocatalytic mineralization, the ultrasound-assisted advanced oxidation process resulted in the conversion of ibuprofen to its mineralization products.

Role of persistent free radicals and lewis acid sites in visible-light-driven wet peroxide activation by solid acid biochar catalysts - A mechanistic study

We report the synthesis of H₂SO₄-modified biochars (SBCs) as solid-acid catalysts to activate H₂O₂ at circumneutral pH under visible light radiation. Spent coffee grinds were pyrolyzed with TiO₂ at 300, 500 and 600 °C followed by steeping in 5 M H₂SO₄ and were used for the Fenton-like degradation of methyl orange (MO). The catalytic activity of SBC depended on the pyrolysis temperature and correlated well with the surface acidity and persistent free radical (PFR) concentration. Results showed that a complete MO removal and a TOC reduction of 70.2% can be achieved with SBC500 under photo-Fenton conditions. However, poisoning of the Lewis acid sites on SBC by PO₄^3- led to a dramatic decrease in the removal of MO with inhibition effects more pronounced than with radical scavengers, suggesting the key role played by acid-sites on the activation of H₂O₂. Finally, electron paramagnetic resonance (EPR) studies identified •OH as the key transient in the degradation followed by •O₂^- and ¹O₂. These findings suggest that H₂O₂ was likely adsorbed on the surface oxygenated functional groups before being decomposed by accepting electrons from the PFRs on the SBC surface.

Cl-based functional group modification MIL-53(Fe) as efficient photocatalysts for degradation of tetracycline hydrochloride

MIL-53(Fe) catalyst has been widely used to treat the pollutants in water. However, the limited number of electrons in MIL-53(Fe) catalyst has always affected the rate at which Fe³⁺ can be reduced to Fe²⁺. We modulated iron-based metal-organic frameworks (MOFs) using organic ligands modified with chlorine functional groups. The characterization results indicate that the 2Cl-MIL-53(Fe) catalyst exhibited the optimal photoelectric properties while maintaining the original structural characteristics. The experimental analyses and the first-principles study suggest that the introduction of a chlorine functional group not only reduced the band gap width and enhanced the visible-light absorption capacity, but also significantly enhanced the electron cloud density of Fe-O clusters. This could further accelerate the redox cycle of Fe(III)/Fe(II), beneficial for H₂O₂ activation. The constructed Cl-MIL-53(Fe) catalyst exhibited a 3.8 times higher reaction rate constant than pure MIL-53(Fe) catalyst. The specific TCH degradation pathway and mechanism of 2Cl-MIL-53(Fe) treatment are proposed. This study provides a new strategy for iron-based MOFs as a heterogeneous photo-Fenton catalyst to degrade pollutants in water.

Degradation of Ibuprofen by the Electro/Fe3+/Peroxydisulfate Process: Reactive Kinetics, Degradation Products and Mechanism

Ibuprofen (IBU), a nonsteroidal anti-inflammatory drug, is one of the most widely used and frequently detected pharmaceuticals and personal care products in water bodies. This study examined the IBU degradation in aquatic solutions via ferric ion activated peroxydisulfate (PDS) coupled with electro-oxidation (EC/Fe3+/PDS). The degradation mechanisms involved three synergistic reactions in the EC/Fe3+/PDS system, including: (1) the electro-oxidation; (2) SO4•− generated from the activation of PDS by ferrous ions formed via cathodic reduction; (3) SO4•− generated from the electron transfer reaction. The radical scavenging experiments indicated that SO4•− and •OH dominated the oxidation process. The effects of the applied current density, PDS concentration, Fe3+ dosage, initial IBU concentration and initial pH as well as inorganic anions and humic acid on the degradation efficiency, were studied, and the degradation process of IBU followed the pseudo-first-order kinetic model. About 99.37% of IBU was removed in 60 min ((Fe3+ concentration) = 2.0 mM, (PDS concentration) = 12 mM, (initial IBU concentration) = 30 mg/L, current density = 15 mA/cm2, initial pH = 3). Finally, seven intermediate compounds were identified and probable IBU degradation pathways in the EC/Fe3+/PDS system were speculated.