Fabrication of dual Z-scheme MIL-53(Fe)/α-Bi2O3/g-C3N4 ternary composite with enhanced visible light photocatalytic performance

Encapsulation of Cu-modified SnO2 yolk-shell in V2O5-amalgamated wrinkled g-C3N4 lamella for boosting antibiotic photodegradation

The remarkable application of tin oxide in various domains is indebted to its photoelectronic merits. However, significant efforts to discover its photocatalytic potential were restricted through arduous challenges, which were the amelioration of light-harvesting and -utilizing. In fact, the uncommon light absorption energy has drawn veil over the brilliance of astounding oxidation potential, which is much more than that of TiO2. Herein, our attention was focused on the taking advantages of self-template structure for simultaneously enjoying the two sides of photoelectronic justification as well as the S-step system for eminent charge dissociation. In this regard, the optimized Cu-modified SnO2 yolk-shell ((5)YS-CuSnO) spheres were engineered through the copper modulation into glycerate-assisted metal-organic structure. As a result, the exceptional light-harvesting was achieved through desirable defects and oxygen vacancy resulted from Cu-doping, and also efficient light-utilization was obtained by the multi-scattering/reflection effect resulted from multi-shell configuration. After the effectual incorporation (40 wt⁒) of (5)YS-CuSnO was encapsulated into the V2O5-decorated wrinkled g-C3N4 lamella (VO-WCN), the dual S-step VO-WCN@(5)YS-CuSnO introduced unprecedented levofloxacin (LFC) decontamination performance, which was kinetically 5.2 and 30.2-times greater than of the (5)YS-CuSnO and bare SnO2 yolk-shell. The conspicuous fulfillment of nanocomposite was manifested in the LFC mineralization, pharmaceutical effluent treatment within 360 min, and successive cycling reactions. The fusion of the extraordinary architecture of YS-CuSnO with S-Step system not only initiates the facile and practical photocatalytic exploitation, but shade light on some undeveloped side of tin oxide.

Preparation of O-g-C3N4 nanowires/Bi2O2CO3 porous plate composite photocatalysts for the efficient degradation of tetracycline hydrochloride in wastewater

Both g-C3N4 and Bi2O2CO3 are good photocatalysts for the removal of antibiotic pollutants, but their morphological modulation and catalytic performance need to be further improved. In this study, the calcination-hydrothermal method is used to prepare a O-g-C3N4@Bi2O2CO3 (CN@BCO) composite photocatalyst from dicyandiamide and bismuth nitrate. The prepared catalyst is characterized through various methods, including X-ray diffraction (XRD) and transmission electron microscopy (TEM). Further, the effects of different parameters, such as catalyst concentration and initial pH of the reaction solution, on its photocatalytic activity are investigated. The results show that the CN@BCO sample achieves an optimal degradation rate of 98.1% for tetracycline hydrochloride (TCH) with a concentration of 20 mg/L and a removal rate of 69.4% for total organic carbon (TOC) at 40 min. The quenching experiments show that ·O2-, h+, and ·OH participate in the photocatalytic process, with ·O2- being the most dominant active species. The toxicity of the predicted TCH degradation intermediates is analyzed using Toxicity Estimation Software Tool (TEST). Overall, the CN@BCO composite exhibits excellent photocatalytic performance, making it a promising candidate for environmental purification and wastewater treatment.

Recent progress and prospect of graphitic carbon nitride-based photocatalytic materials for inactivation of Microcystis aeruginosa

The proliferation of harmful algal blooms is a global concern due to the risk they pose to the environment and human health. Algal toxins which are hazardous compounds produced by dangerous algae, can potentially kill humans. Researchers have been drawn to photocatalysis because of its clean and energy-saving properties. Graphite carbon nitride (g-C3N4) photocatalysts have been extensively studied for their ability to eliminate algae. These photocatalysts have attracted notice because of their cost-effectiveness, appropriate electronic structure, and exceptional chemical stability. This paper reviews the progress of photocatalytic inactivation of harmful algae by g-C3N4-based materials in recent years. A brief overview is given of a number of the modification techniques on g-C3N4-based photocatalytic materials, as well as the process of inactivating algal cells and destroying their toxins. Additionally, it provides a theoretical framework for future research on the eradication of algae using g-C3N4-based photocatalytic materials.

MOF-Based Photocatalytic Membrane for Water Purification: A Review

Photocatalytic membranes can effectively integrate membrane separation and photocatalytic degradation processes to provide an eco-friendly solution for efficient water purification. It is of great significance to develop highly efficient photocatalytic membranes driven by visible light to ensure the long-term stability of membrane separation systems and the maximum utilization of solar energy. Metal-organic framework (MOF) is an emerging photocatalyst with a well-defined structure and tunable chemical properties, showing a broad application prospect in the construction of high-performance photocatalytic membranes. Herein, this work provides a comprehensive review of recent advancements in MOF-based photocatalytic membranes. Initially, this work outlines the main tailoring strategies that facilitate the enhancement of the photocatalytic activity of MOF-based photocatalysts. Next, this work introduces commonly used methods for fabricating MOF-based photocatalytic membranes. Subsequently, this work discusses the application and mechanisms of MOF-based photocatalytic membranes toward organic pollutant degradation, metal ion removal, and membrane fouling mitigation. Finally, challenges in developing MOF-based photocatalytic membranes and their practical applications are presented, while also pointing out future research directions toward overcoming these existing limitations.

Characterization of an Iron-Copper Bimetallic Metal-Organic Framework for Adsorption of Methyl Orange in Aqueous Solution

Iron-based organic frame material MIL-53 (Fe) was synthesized by the hydrothermal method with Cu2+ incorporated to obtain bimetallic composite MIL-53 (Fe, Cu). The structure and morphology of the material were characterized by SEM, XRD, BET, FTIR, XPS, and zeta potential. The adsorption performance of MIL-53 (Fe, Cu) on methyl orange was tested under a variety of conditions, including the effects of pH and material dosage, by the static adsorption test. The results show that under the condition of pH = 7, a temperature of 30°C, and an adsorbent dosage of 20 mg, the removal rate of MIL-53 (Fe, Cu) for methyl orange can reach more than 96% within 4 h, and the maximum adsorption capacity after fitting by the thermodynamic model can reach 294.43 mg/g, showing the excellent adsorption performance of MIL-53 (Fe, Cu) on methyl orange. In addition, by exploring the adsorption mechanism of MIL-53 (Fe, Cu) on methyl orange, it is found that the adsorption of MIL-53 (Fe, Cu) on methyl orange depends on chemical adsorption, as evidenced by combining Fe3+ and Cu2+ in the material with methyl orange molecules to form complexes to achieve adsorption. While the specific surface area of the material had no obvious effect on adsorption, the effects of pH, temperature, and concentration were explored. At a pH of 6.5, greater adsorption occurred at higher temperatures, as determined by thermodynamic model fitting, as well as with higher initial methyl orange molecule concentration.

Enhanced catalytic reduction of emerging contaminant by using magnetic CuFe2O4@MIL-100(Fe) in Fenton-based electrochemical processes

Fenton-based electrochemical processes (FEPs) using newly engineered 3D photocatalyst nanocomposites have garnered significant attention owing to their ability to remove emerging contaminants. Despite the development of numerous materials, there is still a need to enhance their efficiency, stability, and recyclability to address the limitations of FEPs. This study seeks to address this issue by investigating sustainable methods to engineer novel 3D core-shell photocatalyst composites for application in FEPs. These materials can update the photo-assisted PEFs activity, and magnetism can be helpful for the easy recyclability of the catalyst. Herein, we successfully synthesized a magnetic and photoactive CuFe₂O₄@MIL-100(Fe) (CM) composite through sustainable methods and assessed its morphological structure and physicochemical and photocatalytic properties. The catalytic performance of CM was investigated in an undivided RuO₂/air-diffusion cell to treat Cefadroxil. The results show that heterogeneous photoelectro-Fenton (HPEF) (100% in 120 min) has higher degradation efficiency than electro-Fenton (100% in 210 min) and electrooxidation (73.3% in 300 min) processes. The superior degradation efficiency of HPEF is attributed to the formation of a large amount of hydroxyl radicals indicating the excellent photocatalytic activity of the material due to the direct excitation of the Fe-O cluster, which boosts the redox reaction of Fe²⁺/Fe³⁺. Key operational parameters such as pH, catalyst concentration, current density, and CuFe₂O₄ proportion on MIL-100(Fe) in the composite were optimized in the HPEF process. The optimized composite exhibited good stability and easy recyclability, allowing high removal efficiency, which can be kept up after five cycles of 90 min. High degradation performance was observed using natural sunlight radiations. Additionally, possible catalytic degradation mechanisms in HPEFs were proposed based on radical quenching experiments. This study has significant potential to contribute to the development of more sustainable and effective water treatment strategies.

Metal-organic frameworks in photocatalytic Z-scheme heterojunctions: an emerging technology

There is an urgent need for cleaner production processes for chemicals. An efficient and promising alternative for such reactions is heterogeneous photocatalysis, which works on the principle of converting (visible) light, including solar energy, into chemical energy. To that end, properly designed semiconductor based photocatalysts are necessary to trigger the photocatalytic reactions. Many commonly used photocatalysts have too large bandgaps (3-3.4 eV) to use visible light and a too low surface area for efficient production. Metal-organic frameworks (MOFs) have emerged as an encouraging class of materials for photocatalytic applications due to their (i) large surface area and porosity that facilitate adsorption towards chemicals, (ii) tunable crystallinity and optical and electronic properties for efficient light absorption in the visible region, (iii) tunable composition and functionality that make them versatile photocatalysts for a wide range of reactions, and (iv) facile development of composites with other semiconductors to produce Z-scheme heterojunctions that can effectively suppress the recombination of photogenerated charges. Ongoing research has started focusing on the judicious construction of Z-scheme heterojunctions in MOFs, to mimic natural photosynthesis, such that the MOF photocatalysts have higher light harvesting capacity, spatially separated reductive and oxidative active sites, and well-preserved redox ability. This review provides a concise compilation of the recent progress in the development and applications of MOF-based Z-scheme photocatalysts, their advanced characterization, and future perspectives for further advancements.

Direction regulation of interface carrier transfer and enhanced photocatalytic oxygen activation over Z-scheme Bi4V2O11/Ag/AgCl for water purification

Molecular oxygen activation is essential to the photocatalytic oxidation reaction, which is highly dependent on the construction of active sites and efficient charge transfer of photocatalysts. In this study, we constructed Bi₄V₂O₁₁/Ag/AgCl Z-type heterojunction photocatalysts with significantly enhanced molecular oxygen activation capacity. The systematic characterization and analysis including X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations confirmed that the formation of efficient Z-type heterostructure could be attributed to the introduction of Ag nanoparticles (NPs), which regulated the electron transfer direction from Bi₄V₂O₁₁ to AgCl. Owing to the advantage of enhanced charge transfer efficiency, the O₂^- generation capacity of Bi₄V₂O11/Ag/AgCl Z-scheme heterojunction was as high as 4.6 times that of pure Bi₄V₂O₁₁. Consequently, Bi₄V₂O₁₁/Ag/AgCl showed good degradation performance against tetracycline (TC), ciprofloxacin (CIP), ranitidine hydrochloride (RAN) and 2,4-dichlorophenoxyacetic acid (2,4-D) under visible light, and their degradation rates were 8.2 times, 5.9 times, 3.8 times and 11.9 times higher than those of Bi₄V₂O₁₁, respectively. This study provides an effective and feasible strategy to design photocatalyst with improved molecular oxygen activation efficiency.

MIL-53(Fe)@perylene Diimide All-Organic Heterojunctions for the Enhanced Photocatalytic Removal of Pollutants and Selective Oxidation of Benzyl Alcohol

Organic semiconductors are promising materials for the photocatalytic treatment of pollutants and organic synthesis. Herein, MIL-53(Fe)@perylene diimide (PDI) organic heterojunctions were constructed by ultrasonic assembly using PDI as the co-catalyst, and PDI organic supramolecular material was uniformly distributed on the surfaces of MIL-53(Fe). The most effective M53@PDI-20 organic heterojunctions achieved 72.7% photodegradation of rhodamine B (10 mg/L) within 50 min and a 99.9% reduction in Cr(VI) (10 mg/L) for 150 min, and the corresponding apparent degradation rate constants were higher than a single component. Meanwhile, the conversion rate of benzyl alcohol over M53@PDI-20 achieved 91.5% for 5 h with a selectivity of above 90% under visible light exposure, which was more than double that of PDI. The well-matched band structures and the strong π–π bonding interactions between MIL-53(Fe) and PDI can increase the electron delocalization effect to facilitate the transfer and separation of photogenerated carriers. Lots of oxidative reactive species (h+, •O2− and •OH) also played a great contribution to the strong oxidation capacity over the heterojunctions system. This work suggests that MIL-53(Fe)@PDI organic heterojunctions may be a promising material for pollutant removal and organic synthesis.

Ceftriaxone sodium degradation by carbon quantum dots (CQDs)-decorated C-doped α-Bi2O3 nanorods

A novel carbon quantum dots decorated C-doped α-Bi₂O₃ photocatalyst (CBO/CQDs) was synthesized by solvothermal method. The synergistic effect of adsorption and photocatalysis highly improved contaminants removal efficiencies. The ceftriaxone sodium degradation rate constant (k) of CBO/CQDs was 11.4 and 3.2 times that of pure α-Bi₂O₃ and C-doped α-Bi₂O₃, respectively. The interstitial carbon doping generated localized states above the valence band, which enhanced the utilization of visible light and facilitated the separation of photogenerated electrons and holes; the loading of CQDs improved the charge carrier separation and extended the visible light response; the reduced particle size of CBO/CQDs accelerated the migration of photogenerated carriers. The •O₂ ^- and h⁺ were identified as the dominant reactive species in ceftriaxone sodium degradation, and the key role of •O₂ ^- was further investigated by NBT transformation experiments. The Fukui index was applied to ascertain the molecular bonds of ceftriaxone sodium susceptible to radical attack, and intermediates analysis was conducted to explore the possible degradation pathways. The toxicity evaluation revealed that some degradation intermediates possessed high toxicity, thus the contaminants require sufficient mineralization to ensure safe discharge. The present study makes new insights into synchronous carbon dopping and CQDs decoration on modification of α-Bi₂O₃, which provides references for future studies.

A novel g-C3N4 nanosheet/Ag3PO4/α-Bi2O3 ternary dual Z-scheme heterojunction with increased light absorption and expanded specific surface area for efficient photocatalytic removal of TC

A novel ternary dual Z-scheme 2D g-C₃N₄ nanosheet/Ag₃PO₄/α-Bi₂O₃ (CNN/AP/BO) photocatalyst was successfully synthesized by an in situ deposition and hydrothermal-calcination method. The coupling of AP and BO remarkably enhanced the photocatalytic tetracycline (TC) degradation under visible light illumination, with an optimal removal efficiency of 91.6% (60 min), which can be attributed to the extended visible-light absorption and increased specific surface area owing to the interfacial intimate coupling with well-matched energy band positions between semiconductors. The improved photocatalytic activity resulted from the abundant free radicals by the order of ˙O₂^- > h⁺ > ˙OH based on the electron spin resonance (ESR) and quenching experiment results. In addition, the possible mechanism of TC degradation over the ternary dual Z-scheme heterojunction CNN/AP/BO was proposed.

Vertically grown CeO2 and TiO2 nanoparticles over the MIL53Fe MOF as proper band alignments for efficient H2 generation and 2,4-DCP degradation

The design of highly efficient photoca talysts for clean energy production and environmental remediation are the grand challenges of scientific research. Herein, TiO₂@MIL53Fe and CeO₂@MIL53Fe composite photocatalysts are synthesized via solvothermal technique. The SEM and TEM micrographs reveal that TiO₂ and CeO₂ nanoparticles are vertically grown onto the surface of MIL53Fe MOF. Further, HRTEM micrograph confirmed the formation of heterojunction. It has been investigated that the resultant TiO₂@MIL53Fe and CeO₂@MIL53Fe photocatalysts exhibit remarkably improved visible light activities for H₂ production and 2,4-dichlorophenol (2,4-DCP) degradation in comparison to the bare MIL53Fe photocatalyst. The enhanced photoactivities of the fabricated TiO₂@MIL53Fe and CeO₂@MIL53Fe photocatalysts are attributed to significantly promoted charge separation as confirmed via the surface photo voltage (SPV) and photoluminescence (PL) results. Further, the photocatalysts exhibit high stability and reusability as confirmed via the recyclable tests. This work will promote the design of MOF-based efficient photocatalysts for clean energy production and environment purification.

Photocatalytic inactivation of algae in a fluidized bed photoreactor with an external magnetic field

Practical applications of photocatalysis in algae removal often involve the use of photoreactors, which can be of many different configurations. In this study, a fluidized bed photoreactor (FBPR) with an external magnetic field was designed and constructed to achieve algae inactivation continuously and stably. Magnetic photocatalyst ZnFe₂O₄/Ag₃PO₄/g-C₃N₄ attached to Fe₃O₄ aggregate, was dispersed and fixed at the bottom of the reactor to form a flower-like structure, which can not only increase the effective irradiation area of the photocatalyst, but also enhances mass transfer by inducing flow disturbance. Under the optimal operating conditions, i.e., 0.04 m/s flow rate, 200 mT magnetic field strength, and 0.025 g photocatalyst loading, the photoreactor can effectively remove algae cells within 6 h. During the continuous operation experiment, the quality of the magnetic photocatalyst and aggregate did not decrease significantly, and there was still a 90% removal efficiency after 18 h of continuous operation. Furthermore, in the experiment where humic acid was added to simulate actual water environment, certain advantages can still be observed with the FBPR. As a continuous reactor using a magnetic photocatalyst, the FBPR has the characteristics of high availability, low cost, and low energy consumption.

Synthesis, modifications and applications of MILs Metal-organic frameworks for environmental remediation: The cutting-edge review

Ever-increasing anthropogenic activities are radically deteriorating the environment by causing severe pollution. Thus, curtailing the environmental pollution and promotion of sustainable development, are the hot issues confronted by scientists in this modern era. Metal-organic frameworks (MOFs) have been highly recognized as emerging promising materials for environmental remediation due to their versatile structure and extraordinary properties. Among them, MILs (MIL = Matérial Institute of Lavoisier) are the series of MOFs mostly known for their incredible stability, unique tailorable pore structures, and astounding versatile environmental applications. Their exclusive physiochemical properties and multifunctionality make them proficient for a wide range of pollutants removal in the exposure of versatile harsh environments, compared to other MOFs. This piece of research summarizes the state-of-the-art of development of MILs on the broad spectrum, highlighting their specificities, such as synthesis techniques, modifications and applications for environmental remediation. However, MILs wonderful properties and extraordinary applications in multiple fields, their deployment on practical and commercial-scale pollutants remediation is hindered by insufficient scientific research on underlying mechanisms and relationships. Henceforth, this review not only signifies the emerging importance of MILs for environmental applications but also indicates the urgency to maximize the scientific research for exploitation of MOFs on a practical level and promotion of green technologies for environmental remediation.

Use of an ultraviolet light-activated persulfate process to degrade humic substances: effects of wavelength and persulfate dose

Natural organic matter (NOM), commonly found in surface and ground waters, form disinfection by-products in drinking water. Generally, advanced oxidation processes (AOPs) featuring hydrogen peroxide are used to treat water; however, sulfate radical recently has been used to treat recalcitrant organics, because it is associated with a higher oxidation potential and more effective removal than hydroxyl radicals. Hence, in this research, we evaluated persulfate oxidation efficiency in terms of reductions in humic substance levels and investigated the degradation mechanism. The results showed that ultraviolet-activated persulfate effectively treated humic substances compared with hydrogen peroxide and direct irradiation. Treatment was dose and wavelength dependent; higher persulfate concentrations or shorter UV wavelengths were more effective for treating humic substances as high concentration sulfate radicals were created. The degradation mechanism was similar to that of hydrogen peroxide. Aromatic and chromophore components were more susceptible to degradation than were lower molecular weight components, being initially decomposed into the latter, reducing UV₂₅₄ absorbance and the SUVA₂₅₄. Lower molecular weight materials were eventually degraded to end products: NPOC levels fell. And we also treated the inflow of a drinking water treatment plant with persulfate, and humic substances were effectively removed.

A Comprehensive Review of Graphitic Carbon Nitride (g-C3N4)-Metal Oxide-Based Nanocomposites: Potential for Photocatalysis and Sensing

g-C3N4 has drawn lots of attention due to its photocatalytic activity, low-cost and facile synthesis, and interesting layered structure. However, to improve some of the properties of g-C3N4, such as photochemical stability, electrical band structure, and to decrease charge recombination rate, and towards effective light-harvesting, g-C3N4-metal oxide-based heterojunctions have been introduced. In this review, we initially discussed the preparation, modification, and physical properties of the g-C3N4 and then, we discussed the combination of g-C3N4 with various metal oxides such as TiO2, ZnO, FeO, Fe2O3, Fe3O4, WO3, SnO, SnO2, etc. We summarized some of their characteristic properties of these heterojunctions, their optical features, photocatalytic performance, and electrical band edge positions. This review covers recent advances, including applications in water splitting, CO2 reduction, and photodegradation of organic pollutants, sensors, bacterial disinfection, and supercapacitors. We show that metal oxides can improve the efficiency of the bare g-C3N4 to make the composites suitable for a wide range of applications. Finally, this review provides some perspectives, limitations, and challenges in investigation of g-C3N4-metal-oxide-based heterojunctions.

Magnetically separable ZnFe2O4/Ag3PO4/g-C3N4 photocatalyst for inactivation of Microcystis aeruginosa: Characterization, performance and mechanism

Water eutrophication leads to increasingly serious harmful algal blooms (HABs), which poses tremendous threats on aquatic environment and human health. In this work, a novel magnetically separable ZnFe₂O₄/Ag₃PO₄/g-C₃N₄ (ZFO/AP/CN) photocatalyst with double Z-scheme was constructed for Microcystis aeruginosa (M. aeruginosa) inactivation and Microcystin-LR (MC-LR) degradation under visible light. The photocatalyst was characterized by XRD, SEM, EDS, TEM, XPS, FTIR, UV-vis, PL, and VSM. Approximately 96.33% of chlorophyll a was degraded by ZFO/AP/CN (100 mg/L) after 3 h of visible light irradiation. During the photocatalytic process, the malondialdehyde (MDA) of M. aeruginosa increased, the activities of superoxide dismutase (SOD) and catalase (CAT) increased initially and decreased afterwards. Furthermore, the photocatalytic removal efficiency of M. aeruginosa (OD₆₈₀ ≈0.732) and MC-LR (0.2 mg/L) reached 94.31% and 76.92%, respectively, in the simultaneous removal of algae and algal toxin experiment. Reactive species scavenging experiments demonstrated that·O₂^- and·OH played key roles in inactivating M. aeruginosa and degrading MC-LR. The excellent recoverability and stability of ZFO/AP/CN were proved by cycling photocatalytic experiment which using magnetic recovery method. In summary, the synthesized magnetically separable ZFO/AP/CN photocatalyst has remarkable photocatalytic activity under visible light and shows promising potential for practical application of alleviating HABs.

Fabrication of MIL-53(Fe)/Ag3PO4 cooperated Photoreduction of Ag0 Particles with outstanding Efficiency on photo-driven H2 Evolution and Pollutant Degradation

The novel heterostructure photocatalyst includes photoreduction of Ag0 loaded MIL-53(Fe)/Ag3PO4 (MFAAx) composites were designed and successfully synthesized via hydrothermal with deposition and photoreduction method. Then the physicochemical and optical properties...

Construction of MOF/COF Hybrids for Boosting Sunlight-Induced Fenton-like Photocatalytic Removal of Organic Pollutants

In this work, a metal-organic framework (MOF) material of NH₂-MIL88B was hybridized with TpPa-1-COF through covalent bonding, and the hybrid was subsequently employed for the degradation of Rhodamine B (RhB) and tetracycline (TC) by simulated sunlight-induced Fenton-like exciting H₂O₂. The obtained results show that its photocatalytic activity is much better than those of its parent MOF and covalent organic framework (COF). Moreover, it is much higher than that of bare photocatalysis without Fenton-like excitation of H₂O₂. The high degradation efficiency is ascribed to two factors. One is the formation of hybrid, which promotes charge separation and light absorbance. Another is the Fenton-like excitation of H₂O₂, which produces more hydroxyl radicals (^•OH). This report presents a facile approach to greatly improve the photocatalytic property of MOF materials by the formation of hybrid with COFs and Fenton-like excitation of H₂O₂.

Recent Improvement Strategies on Metal-Organic Frameworks as Adsorbent, Catalyst, and Membrane for Wastewater Treatment

The accumulation of pollutants in water is dangerous for the environment and human lives. Some of them are considered as persistent organic pollutants (POPs) that cannot be eliminated from wastewater effluent. Thus, many researchers have devoted their efforts to improving the existing technology or providing an alternative strategy to solve this environmental problem. One of the attractive materials for this purpose are metal-organic frameworks (MOFs) due to their superior high surface area, high porosity, and the tunable features of their structures and function. This review provides an up-to-date and comprehensive description of MOFs and their crucial role as adsorbent, catalyst, and membrane in wastewater treatment. This study also highlighted several strategies to improve their capability to remove pollutants from water effluent.

Efficient photocatalytic degradation of doxycycline by coupling α-Bi2O3/g-C3N4 composite and H2O2 under visible light

Antibiotic pollutants have posed a huge threat to the ecological environment and human health. In this work, α-Bi₂O₃/g-C₃N₄ composite was prepared and coupled with H₂O₂ for the rapid and efficient degradation of doxycycline (DOX) in water under visible light irradiation. The composite exhibited enhanced photocatalytic activity and 80.5% of DOX could be degraded in 120 min. The addition of H₂O₂ significantly improved the degradation efficiency of DOX under visible light, resulting in 79.0% of it degraded within 30 min, and the degradation rate constant of DOX was 3.6 times than that without H₂O₂. On the one hand, the Z-scheme heterojunction of α-Bi₂O₃/g-C₃N₄ promoted the separation rate of photogenerated electron-hole pairs, thereby enhancing the photocatalytic activity of the composite. On the other hand, the improvement of photocatalytic efficiency also benefited from the extra hydroxyl radicals generated by the reaction of photogenerated electrons with H₂O₂ in the photocatalytic system. Free radicals trapping experiments and electron spin resonance tests proved that played prominent role in the degradation process. After adding H₂O₂, OH also became important active species. Cyclic degradation experiments demonstrated the recyclability of the composite photocatalyst in DOX elimination applications. This work provides an efficient, clean, and recyclable purification strategy for removing antibiotic contaminants from water.

Construction of C@WS2/g-C3N4 Z-scheme photocatalyst with C film as an effective electron mediator and its enhanced degradation of 2,4-dichlorophenol under visible light

A novel Z-scheme heterojunction C@WS₂/g-C₃N₄ composite was prepared with carbon as a bridge for improving the photocatalytic property. The results of composition and structure studies demonstrate that the introduced carbon was deposited on the surface of WS₂ with a film form in the ternary composites. The analysis of optical and photo-electrochemical properties reveals that the carbon film played as an electron-mediator in the ternary composites and could improve the separation and transportation of photogenerated charge. Meanwhile, it could change the pathway of photogenerated electrons between WS₂ and g-C₃N₄, thereby constructing a Z-scheme heterojunction for maintaining the redox ability of photogenerated charge. The ternary 2%-C@WS₂/g-C₃N₄ composite exhibited an excellent photodegradation rate towards 2,4-dichlorophenol (2,4-DCP) under visible light irradiation, which was 3.15 and 3.06 times of the pure g-C₃N₄ and binary WS₂/g-C₃N₄ composite, respectively. Besides, the degradation pathway of 2,4-DCP and photocatalytic degradation mechanisms were investigated and discussed in detail. The generated ·O₂^--, ·OH and h⁺ by ternary composites could promote the dechlorination reaction of 2,4-DCP effectively and decompose it into smaller organic molecules. This work extends the design of g-C₃N₄-based 2D/2D heterojunction or Z-scheme photocatalysts to remediate the environment.

A rational design of g-C3N4-based ternary composite for highly efficient H2 generation and 2,4-DCP degradation

In this work, g-C₃N₄ based ternary composite (CeO₂/CN/NH₂-MIL-101(Fe)) has been fabricated via hydrothermal and wet-chemical methods. The composite showed superior photoactivities for H₂O reduction to produce H₂ and 2,4-dichlorophenol (2,4-DCP) degradation. The amount of H₂ evolved over the composite under visible and UV-visible irradiations is 147.4 µmol·g^-1·h^-1 and 556.2 µmol·g^-1·h^-1, respectively. Further, the photocatalyst degraded 87% of 2,4-DCP in 2 hrs under visible light irradiations. The improved photoactivities are accredited to the synergistic-effects caused by the proper band alignment with close interfacial contact of the three components that significantly promoted charge transfer and separation. The 2,4-DCP degradation over the composite is dominated by OH radical rather than h⁺ and O₂^- as investigated by scavenger trapping experiments. This is further supported by the electron para-magnetic resonance (EPR) study. This work provides new directions for the development of g-C₃N₄ based highly efficient ternary composite materials for clean energy generation and pollution control.

Photocatalytic purification of vehicle exhaust using CeO2-Bi2O3 loaded on white carbon and tourmaline

Photocatalysts are environmentally friendly materials that can be used to degrade vehicle exhaust. CeO₂-Bi₂O₃ loaded on white carbon and tourmaline, as the favorable absorption materials, was prepared respectively for vehicle exhaust photocatalytic purification. Brunauer-Emmett-Teller (BET) adsorption isotherm, scanning electron microscope (SEM), Fourier transform infrared (FTIR), X-ray diffraction (XRD), transmission electron microscope (TEM), and X-ray photoelectron spectroscopy (XPS) were applied to characterize the composite materials. The optimum contents of the loading materials were obtained from the comparison of purification efficiency of vehicle exhaust components after a 60-min photocatalytic reaction under visible and ultraviolet (UV) irradiation, including hydrocarbons (HC), carbon monoxide (CO), carbon dioxide (CO₂), and nitrogen oxides (NO_x). The results show that the proposed preparation method could improve particle dispersion and distribution uniformity, reduce particle agglomeration, and increase specific surface area. The optical response range of the CeO₂-Bi₂O₃ with loading materials can be extended from UV light to visible light. CeO₂-Bi₂O₃ loaded on tourmaline show excellent photocatalytic purification effect under visible light. The purification efficiency of CeO₂-Bi₂O₃ loaded on tourmaline for HC, CO, CO₂, and NO_x were 30.8%, 30.6%, 35.3%, and 47.6%, respectively. Moreover, the concentrations of vehicle exhaust components decrease with time, which is well fitted by the Langmuir-Hinshelwood pseudo-first-order kinetics model, and the purification rate constant of CeO₂-Bi₂O₃ composites under visible light is greater than that under UV light. The prepared photocatalytic materials also exhibit the excellent reusability.

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.

Direct electrospinning preparation of Z-scheme mixed-crystal Bi2O3/g-C3N4 composite photocatalysts with enhanced visible-light photocatalytic activity

A novel Z-scheme mixed-crystal Bi₂O₃/g-C₃N₄ composite photocatalyst was successfully prepared by a simple electrospinning–calcination approach.

Facile synthesis of layered Co(OH)2 deposited g-C3N4 for activating peroxymonosulfate to degrade organic pollutants

Layered Co(OH)2 deposited g-C3N4 is found to be highly active in the activation of peroxymonosulfate (PMS) for pollutant removal.

Metal oxide integrated metal organic frameworks (MO@MOF): rational design, fabrication strategy, characterization and emerging photocatalytic applications

This review focuses on the possible synthesis route, characterization techniques, and mechanistic pathways involved in the photocatalytic applications of MO@MOFs.