Rapid degradation of tetracycline hydrochloride by heterogeneous photocatalysis coupling persulfate oxidation with MIL-53(Fe) under visible light irradiation

Novel Z-scheme binary zinc tungsten oxide/nickel ferrite nanohybrids for photocatalytic reduction of chromium (Cr (VI)), photoelectrochemical water splitting and degradation of toxic organic pollutants

A simple hydrothermal approach was demonstrated for synthesizing a coupled NiFe₂O₄-ZnWO₄ nanocomposite, wherein one-dimensional ZnWO₄ nanorods were inserted into two-dimensional NiFe₂O₄ nanoplates. Herein, we evaluated the photocatalytic removal of Cr(VI), and degradation of tetracycline (TC) and methylene blue (MB) by the nanocomposite, as well as its ability to split water. The ZnWO₄ nanorods enriched the synergistic interactions, upgraded the solar light fascination proficiency, and demonstrated outstanding detachment and migration of the photogenerated charges, as confirmed by a transient photocurrent study and electrochemical impedance spectroscopy measurements. Compared to pristine NiFe₂O₄ and ZnWO_4, the NiFe₂O₄-ZnWO₄ nanocomposite exhibited a higher Cr(VI) reduction (93.5%) and removal of TC (97.9%) and MB (99.6%). Radical trapping results suggested that hydroxyl and superoxide species are dominant reactive species, thereby facilitating the Z-scheme mechanism. Furthermore, a probable photocatalytic mechanism was projected based on the experimental results. The photoelectrochemical analysis confirmed that NiFe₂O₄-ZnWO₄ exhibited minor charge-transfer resistance and large photocurrents. We propose a novel and efficient approach for designing a coupled heterostructured nanocomposites with a significant solar light ability for ecological conservation and water splitting.

Pharmaceuticals removal by synergistic adsorption and S-scheme photocatalysis using nano-CeO2-coupled Fe3O4 on a CTAB matrix and investigation of the nanocomposite's antibacterial and antibiofilm activities: intrinsic degradation mechanism

S-Scheme photocatalytic mechanism of a fabricated nano-heterojunction.

Persulfate assisted photocatalytic degradation of tetracycline by bismuth titanate under visible light irradiation

Tetracycline is a commonly used broad-spectrum antibiotic to prevent and cure the bacterial infections. However, the incompletely metabolic tetracycline molecules by organisms discharged into aquatic environment increase the ecological toxicity....

Ibuprofen degradation by a synergism of facet-controlled MIL-88B(Fe) and persulfate under simulated visible light

The photocatalysis/persulfate (PS) hybrid system has proven to be a promising method for degrading organic pollutants from aqueous solutions. In this study, three MIL-88B(Fe) iron-based metal-organic framework (MOF) phases with different facet content were prepared and used both as photocatalysts and catalysts for PS activation to remove ibuprofen (IBP). The results showed that there was a close correlation between the exposed facets and the catalytic activity. MIL-88B(Fe)-1 (M88B1) with exposed {100} facets and proportionally more {101} facets showed the best catalytic activity. The optimum PS dosage used in this study was 60 mg/L. The presence of Cl^-, SO₄^2-, and NO₃^- all inhibited the degradation of IBP. X-ray photoelectron spectroscopy (XPS) showed that M88B1 possessed more Fe²⁺ than the other two MIL-88B(Fe) MOF phases, making it easier to generate active radicals through PS activation. The UV-vis diffuse reflectance spectra (DRS), photoluminescence (PL), and electrochemical analysis indicated that M88B1 possessed the highest light absorption, most active sites, and fastest charge transfer ability. Radical scavenging and electron spin resonance (ESR) experiments demonstrated that SO₄^-•, ^•OH, O₂^-•, and ¹O₂ species participated in the IBP degradation process. Furthermore, density functional theory (DFT) calculations were performed to identify the crystallographic facets, band structure, and total density of states of MIL-88B(Fe) to further confirm the mechanism of MIL-88B(Fe) as a photocatalyst and a PS activator. This work provides new insights into the synergism between photocatalysis and persulfate activation by facet-controlled MOFs for environmental remediation.

Assembling Ultrafine SnO2 Nanoparticles on MIL-101(Cr) Octahedrons for Efficient Fuel Photocatalytic Denitrification

Effectively reducing the concentration of nitrogen-containing compounds (NCCs) remains a significant but challenging task in environmental restoration. In this work, a novel step-scheme (S-scheme) SnO2@MCr heterojunction was successfully fabricated via a facile hydrothermal method. At this heterojunction, MIL-101(Cr) octahedrons are decorated with highly dispersed SnO2 quantum dots (QDs, approximate size 3 nm). The QDs are evenly wrapped around the MIL-101(Cr), forming an intriguing zero-dimensional/three-dimensional (0D/3D) S-scheme heterostructure. Under simulated sunlight irradiation (280 nm < λ < 980 nm), SnO2@MCr demonstrated superior photoactivity toward the denitrification of pyridine, a typical NCC. The adsorption capacity and adsorption site of SnO2@MCr were also investigated. Tests using 20%SnO2@MCr exhibited much higher activity than that of pure SnO2 and MIL-101(Cr); the reduction ratio of Cr(VI) is rapidly increased to 95% after sunlight irradiation for 4 h. The improvement in the photocatalytic activity is attributed to (i) the high dispersion of SnO2 QDs, (ii) the binding of the rich adsorption sites with pyridine molecules, and (iii) the formation of the S-scheme heterojunction between SnO2 and MIL-101(Cr). Finally, the photocatalytic mechanism of pyridine was elucidated, and the possible intermediate products and degradation pathways were discussed.

Photochemical Behavior of Microbial Extracellular Polymeric Substances in the Aquatic Environment

Microbially derived extracellular polymeric substances (EPSs) occupy a large portion of dissolved organic matter (DOM) in surface waters, but the understanding of the photochemical behaviors of EPS is still very limited. In this study, the photochemical characteristics of EPS from different microbial sources (Shewanella oneidensis, Escherichia coli, and sewage sludge flocs) were investigated in terms of the production of reactive species (RS), such as triplet intermediates (³EPS*), hydroxyl radicals (^•OH), and singlet oxygen (¹O₂). The steady-state concentrations of ^•OH, ³EPS*, and ¹O₂ varied in the ranges of 2.55-8.73 × 10^-17, 3.01-4.56 × 10^-15, and 2.08-2.66 × 10^-13 M, respectively, which were within the range reported for DOM from other sources. The steady-state concentrations of RS varied among different EPS isolates due to the diversity of their composition. A strong photochemical degradation of the protein-like components in EPS isolates was identified by excitation emission matrix fluorescence with parallel factor analysis, but relatively, humic-like components remained stable. Fourier-transform ion cyclotron resonance mass spectrometry further revealed that the aliphatic portion of EPS was resistant to irradiation, while other portions with lower H/C ratios and higher O/C ratios were more susceptible to photolysis, leading to the phototransformation of EPS to higher saturation and lower aromaticity. With the phototransformation of EPS, the RS derived from EPS could effectively promote the degradation of antibiotic tetracycline. The findings of this study provide new insights into the photoinduced self-evolution of EPS and the interrelated photochemical fate of contaminants in the aquatic environment.

Efficient degradation of tetracycline hydrochloride by photocatalytic ozonation over Bi2WO6

Photocatalytic ozonation technique for wastewater treatment has received much attention for their efficient capability in the mineralization of persistent organic pollutants. In this study, nanostructured Bi₂WO₆ was prepared by hydrothermal method and applied in the photocatalytic ozonation process for tetracycline hydrochloride (TCH) degradation under simulated solar light irradiation. Bi₂WO₆ triggered an effective synergy between photocatalysis and ozonation, and it showed a good activity and adaptability in the degradation of organic compounds. Besides, the influence of experimental factors on the total organic carbon removal (including catalyst dosage, ozone concentration, initial pH, reaction temperature and coexisting ions) was also investigated comprehensively. Spin-trapping electron paramagnetic resonance measurements and quenching experiments demonstrated that O₂^-, OH, ¹O₂ and h⁺ contributed to TCH degradation. The possible degradation pathways of TCH were proposed by identifying the intermediates with liquid chromatography-mass spectroscopy.

Photocatalytic cascade reactions and dye degradation over CdS-metal-organic framework hybrids

Two bifunctional CdS–MOF composites have been designed and fabricated. The hybrids exhibited synergistic photocatalytic performance toward two cascade reactions under visible light integrating photooxidation activity of CdS and Lewis acids/bases of the MOF. The composite further promoted the photodegradation of dyes benefiting from effective electron transfer between the MOF and CdS.

Two bifunctional CdS–MOF composites have been successfully fabricated and exhibited synergistic photocatalytic performance toward two-step cascade reactions and dye photodegradation.

Peroxymonosulfate activation through 2D/2D Z-scheme CoAl-LDH/BiOBr photocatalyst under visible light for ciprofloxacin degradation

The synergistic effect between photocatalytic and peroxymonosulfate (PMS) activation has been widely applied in the field of sewage treatment. In this work, we synthesized a two-dimensional/two-dimensional (2D/2D) CoAl-LDH/BiOBr Z-scheme photocatalyst via a simple method. Then, multiple detection results demonstrated that CoAl-LDH was successfully anchored onto BiOBr, as well as formed an intimate interaction. Moreover, the photocatalytic degradation performance of the catalysts/PMS/vis system had been explored under several conditions (e.g., different catalyst doses, PMS doses, anions and pollutants). The 8 wt% CoAl-LDH/BiOBr composite exhibited the highest degradation efficiency (96%) of ciprofloxacin (CIP). In addition, radicals quenching experiments and electron paramagnetic resonance (EPR) indicated that •O₂- and ¹O₂ were the primary radicals for CIP degradation. The photoelectrochemical measurement and photoluminescence (PL) confirmed that 8 wt% CoAl-LDH/BiOBr exhibited the highest separation and transfer rate of charge carriers. The liquid chromatography-mass spectrometer (LC-MS) analysis revealed that oxidation of the piperazine ring and defluorination were the main CIP degradation pathways. Density functional theory (DFT) calculation, including the laplacian bond order (LBO) and Fukui index, which was consistent with the results of LC-MS. This study explained the superiority of the synergistic effect between photocatalysis and PMS activation on the degradation of pollutants.

Preparation of Mn2O3/MIL-100(Fe) composite and its mechanism for enhancing the photocatalytic removal of rhodamine B in water

In this study, Mn₂O₃/MIL-100(Fe) composite was successfully synthesized by the hydrothermal method and applied for photocatalytic removal of rhodamine B (RhB) in water. The physical and chemical properties of the synthesized materials were characterized by XRD, FTIR, SEM, UV-visible, and BET analyses. Experimental results showed a great enhancement in the photocatalytic ability of the Mn₂O₃/MIL-100(Fe) composite as compared to individual Mn₂O₃ or MIL-100(Fe) under visible light and persulfate activation. The affecting factors such as pH, photocatalyst dose, RhB concentration, and Na₂S₂O₈ concentration were investigated to find out the best conditions for efficient photocatalysis. By conducting a radical quenching test, all radicals of HO˙, SO₄˙^-, ¹O₂, and O₂˙^- were found to be important in photocatalytic decomposition. The mechanism was proposed for the enhancement of photocatalytic RhB removal via band potential calculation, charge separation, surface redox reaction, and key reactive oxidation species. With its durability, reusability, and high efficiency, the Mn₂O₃/MIL-100(Fe) composite emerges as a potential photocatalyst working under visible light for application in wastewater treatment.

Boron nitride nanosheets decorated MIL-53(Fe) for efficient synergistic ibuprofen photocatalytic degradation by persulfate activation

In this study, based on one-step hydrothermal method, boron nitride nanosheets (BNNs) and MIL-53(Fe) composites (BNFe-X) were successfully prepared and the catalytic performance of BNFe-X on persulfate (PS) activation for ibuprofen (IBP) photodegradation was investigated. The introduction of BNNs changed the morphology of MIL-53(Fe) to be a unique prism-like structure and enhanced the degradation efficiency of IBP, which followed the pseudo-first-order rate kinetics. Among the prepared composites, BNFe-3 (3% BNNs) exhibited the highest IBP degradation activity and possessed strong stability after four cycles. Over 99% IBP removal was achieved at the irradiation time of 60 min. The promoted decomposition rate of IBP could be ascribed to be the activation of PS and the enhanced electrons transfer efficiency between BNNs and MIL-53(Fe). The scavenger studies and electron spin-resonance spectroscopy (ESR) demonstrated the generation of SO₂^-, OH and O₂^-, and all these radicals had the different contributions in IBP degradation. Based on the LC-MS-MS and TOC results, the possible decomposition pathways of IBP in BNFe-3/PS system were proposed. This work suggested that the BNNs/Fe-based MOFs composites and PS system had great potential in organic pollutants degradation in aqueous solution.

Remediation of antibiotic wastewater by coupled photocatalytic and persulfate oxidation system: A critical review

Recently, antibiotics with high ecotoxicity have been ubiquitously detected in aquatic environment. The photocatalysis/persulfate-oxidation hybrid (PPOH) system has been proved as a promising strategy for antibiotic degradation. The efficient antibiotic removal is due to the favorable synergistic effects between photocatalysis and persulfate activation. To our best knowledge, relevant reviews on the photo-assisted persulfate activation (PPA) system have been reported, while the research progress on persulfate-assisted photocatalysis (PAP) and concurrent photocatalysis-persulfate activation (CPPA) systems for antibiotic wastewater treatment have yet been summarized. Hence, the PPOH systems are categorized into PPA, PAP and CPPA systems in this review. Besides, the performance of antibiotic degradation and internal mechanism in the coupled oxidation system are summarized and analyzed comprehensively. Finally, conclusions and future prospects of PPOH systems in antibiotic wastewater treatment are proposed. This study provides an overview of PPOH system and outlines the future research direction of the system in practical treatment of antibiotic wastewater.

Insights into the Stability and Activity of MIL-53(Fe) in Solar Photocatalytic Oxidation Processes in Water

MIL-53(Fe) is a metal organic framework that has been recently considered a heterogeneous photocatalyst candidate for the degradation of water pollutants under visible or solar radiation, though stability studies are rather scarce in the literature. In this work, MIL-53(Fe) was successfully synthesized by a solvothermal method and fully characterized by X-ray diffraction (XRD), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), N2 adsorption–desorption isotherm, Thermogravimetric analysis coupled with mass spectrometry (TGA-MS), UV-visible diffuse reflectance spectroscopy (DRS), elemental analysis and wavelength dispersive X-ray fluorescence (WDXRF). The effects of pH, temperature, solar radiation and the presence of oxidants (i.e., electron acceptors) such as ozone, persulfate and hydrogen peroxide on the stability of MIL-53(Fe) in water were investigated. The as-synthetized MIL-53(Fe) exhibited relatively good stability in water at pH 4 but suffered fast hydrolysis at alkaline conditions. At pH 4–5, temperature, radiation (solar and visible radiation) and oxidants exerted negative effect on the stability of the metal–organic framework (MOF) in water, resulting in non-negligible amounts of metal (iron) and linker (terephthalic acid, H2BDC) leached out from MIL-53(Fe). The photocatalytic activity of MIL-53(Fe) under simulated solar radiation was studied using phenol and metoprolol as target pollutants. MIL-53(Fe) on its own removed less than 10% of the pollutants after 3 h of irradiation, while in the presence of ozone, persulfate or hydrogen peroxide, complete elimination of pollutants was achieved within 2 h of exposure to radiation. However, the presence of oxidants and the formation of some reaction intermediates (e.g., short-chain carboxylic acids) accelerated MIL-53(Fe) decarboxylation. The findings of this work suggest that MIL-53(Fe) should not be recommended as a heterogeneous photocatalyst for water treatment before carrying out a careful evaluation of its stability under actual reaction conditions.

Enhanced adsorption of tetracycline by an iron and manganese oxides loaded biochar: Kinetics, mechanism and column adsorption

A Fe/Mn oxides loaded biochar (FeMn-BC) was prepared to enhance the adsorption of tetracycline (TC). γ-Fe₂O₃ and MnO₂ were assigned to the Fe and Mn oxides, respectively. The enhanced adsorption of TC was dominated by the loaded γ-Fe₂O₃ and MnO₂. According to Akaike-Information-Criteria evaluation, Elovich kinetic and Langmuir isotherm models could best describe the adsorption with a maximum capacity of 14.24 mg/g. During adsorption process, the γ-Fe₂O₃ and MnO₂ hydrolyzed into hydroxides (FeOOH and MnOOH) which acted as bases to complex with TC^2- ion under alkaline condition (pH = 11). After the adsorption, the concentrations of leached Fe and Mn could meet the requirements PRC standards GB13456-2012 and GB8978-1996, respectively. The FeMn-BC had ~24% on TC removal (initial concentration of 20 mg/L) after four-cycles regeneration. The FeMn-BC was also available for TC adsorptions in column tests and actual wastewater.

In Situ Generation of Prussian Blue by MIL-53 (Fe) for Point-of-Care Testing of Butyrylcholinesterase Activity Using a Portable High-Throughput Photothermal Device

Butyrylcholinesterase (BuChE), the primary source of serum cholinesterase activity, is an indispensable biochemical marker for clinical diagnosis of liver function and organophosphorus poisoning. The requirement for bulky and expensive instruments represents a huge hindrance for point-of-care testing (POCT) of BuChE, especially in resource-limited settings. Herein, an easy-operated, economic, and portable photothermal (PT) biosensing platform for high-throughput BuChE detection was rationally designed. BuChE could "light up" the PT signal through in situ generation of Prussian blue (PB) by MIL-53 (Fe), which allowed us to translate biological signals into temperature signals. Such temperature change signals could be monitored at high throughput (six samples for a single measurement) by a miniature self-made integrated PT device via combining separable 96-well plates, a three-dimensional (3D) printed sample bracket, 808 nm lasers, and thermometers, satisfying the requirement for rapid on-site detection in a large batch with low cost. In addition, the large specific surface area, 3D network structure, and high porosity of MIL-53 (Fe) offered a beneficial platform for its reaction with enzymatic hydrolysate, resulting in high sensing sensitivity and low detection limit (0.3 U L^-1), which was at least 20 000 times lower than the normal human serum BuChE activity. This facile, affordable, and broad applicability PT sensing platform provides a beneficial reference for the rational design of other disease diagnostic approaches suitable for POCT.

Photocatalytic Advanced Oxidation Processes for Water Treatment: Recent Advances and Perspective

Nowadays, an ever-increasing variety of organic contaminants in water has caused hazards to the ecological environment and human health. Many of them are persistent and non-biodegradable. Various techniques have been studied for sewage treatment, including biological, physical and chemical methods. Photocatalytic advanced oxidation processes (AOPs) have received increasing attention due to their fast reaction rates and strong oxidation capability, low cost compared with the non-photolytic AOPs. This review is dedicated to summarizing up-to-date research progress in photocatalytic AOPs, such as Fenton or Fenton-like reaction, ozonation and sulfate radical-based advanced oxidation processes. Mechanisms and activation processes are discussed. Then, the paper summarizes photocatalytic materials and modification strategies, including defect chemistry, morphology control, heterostructure design, noble metal deposition. The future perspectives and challenges are also discussed.

Visible Light Driven Spherical CuBi2O4 with Surface Oxygen Vacancy Enhanced Photocatalytic Activity: Catalyst Fabrication, Performance, and Reaction Mechanism

Here, a spherical CuBi2O4 catalyst with surface oxygen vacancy was fabricated through a facile hydrothermal method, which exhibited remarkable enhanced photocatalytic activity of refractory chemicals in the heterogeneous sulfate radical-based Fenton-like reaction under visible light emitting diode (LED) light irradiation. The property of the catalysts was systematically characterized by scanning electron microscopy (SEM)/high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV/vis methods. The effects of parameters of solution pH, potassium peroxymonosulfate (PMS) concentration, catalyst dosage, and catalyst reusability on Rhodamine B (RhB) degradation were investigated. In the interface reaction, the improved photodegradation efficiency could be attributed to the decomposition of PMS, which produced sulfate radicals and hydroxyl radicals owing to the transmission of photo-generated electron/hole pairs. Herein, the introduction of surface oxygen vacancy as well as the cycling of copper valence states (Cu(II)/Cu(I) pairs) can facilitate the production of free reactive radicals, leading to the high degradation efficiency. The catalyst showed high removal efficiency and presented good cycle stability in the reaction. Additionally, the free radical quencher experiment and electron spin resonance (EPR) experiments were conducted, and a proposed photocatalytic mechanism was also illustrated.