Enhanced visible light-driven photocatalysis of iron-oxide/titania composite: Norfloxacin degradation mechanism and toxicity study

Mechanisms in the photocatalytic breakdown of persistent pharmaceutical and pesticide molecules over TiO2-based photocatalysts: A review

Titanium dioxide (TiO2) based photocatalysts have been widely used as a photocatalyst for the degradation of various persistent organic compounds in water and air. The degradation mechanism involves the generation of highly reactive oxygen species, such as hydroxyl radicals, which react with organic compounds to break down their chemical bonds and ultimately mineralize them into harmless products. In the case of pharmaceutical and pesticide molecules, TiO2and modified TiO2photocatalysis effectively degrade a wide range of compounds, including antibiotics, pesticides, and herbicides. The main downside is the production of dangerous intermediate products, which are not frequently addressed in the literature that is currently available. The degradation rate of these compounds by TiO2photocatalysis depends on factors such as the chemical structure of the compounds, the concentration of the TiO2catalyst, the intensity, the light source, and the presence of other organic or inorganic species in the solution. The comprehension of the degradation mechanism is explored to gain insights into the intermediates. Additionally, the utilization of response surface methodology is addressed, offering a potential avenue for enhancing the scalability of the reactors. Overall, TiO2photocatalysis is a promising technology for the treatment of pharmaceutical and agrochemical wastewater, but further research is needed to optimize the process conditions and to understand the fate and toxicity of the degradation products.

Occurrence and dissemination of antibiotics and antibiotic resistance in aquatic environment and its ecological implications: a review

The occurrence of antibiotics and antibiotic-resistant bacteria (ARBs), genes (ARGs), and mobile genetic elements (MGEs) in aquatic systems is growing global public health concern. These emerging micropollutants, stemming from improper wastewater treatment and disposal, highlight the complex and evolving nature of environmental pollution. Current literature reveals potential biases, such as a geographical focus on specific regions, leading to an insufficient understanding of the global distribution and dynamics of antibiotic resistance in aquatic systems. There is methodological inconsistency across studies, making it challenging to compare findings. Potential biases include sample collection inconsistencies, detection sensitivity variances, and data interpretation variability. Gaps in understanding include the need for comprehensive, standardized long-term monitoring programs, elucidating the environmental fate and transformation of antibiotics and resistance genes. This review summarizes current knowledge on the occurrence and dissemination of emerging micropollutants, their ecological impacts, and the global health implications of antimicrobial resistance. It highlights the need for interdisciplinary collaborations among researchers, policymakers, and stakeholders to address the challenges posed by antibiotic resistance in aquatic resistance in aquatic systems effectively. This review highlights widespread antibiotic and antibiotic resistance in aquatic environment, driven by human and agricultural activities. It underscores the ecological consequences, including disrupted microbial communities and altered ecosystem functions. The findings call for urgent measures to mitigate antibiotics pollution and manage antibiotic resistance spread in water bodies.

Enhanced solar light-driven photocatalysis of norfloxacin using Fe-doped TiO2: RSM optimization, DFT simulations, and toxicity study

This study investigates the photocatalytic degradation of norfloxacin (NFX) utilizing Fe-doped TiO2 nanocomposite under natural sunlight. TiO2-based photocatalysts were synthesized using chemical precipitation varying Fe-dopant concentration and characterized in detail. Theoretical modelling, centred on density functional theory (DFT), elucidated that Fe ions within the TiO2 lattice are effectively confined, thereby narrowing the wide band gap of TiO2. The findings strongly support that Fe3+ ions augmented the photocatalytic activity of TiO2 by facilitating an intermediate interfacial route for electron and hole transfer, particularly up to an optimal dopant concentration of 1.5 M%. Subsequently, a three-level Box-Behnken design (BBD) was developed to determine the initial pH, optimal catalyst concentration, and drug dosage. High-performance liquid chromatography-mass spectrometry (HPLC-MS) was employed to identify reaction intermediates, thereby establishing a potential degradation pathway. Notably, sustained recyclability was achieved, with 82% degradation efficiency maintained over five cycles. Additionally, the toxicity of degradation intermediates was evaluated through bacterial and phytotoxicity tests, affirming the environmental safety of treated water. In vitro toxicity of the nanomaterial was also examined, emphasizing its environmental implications. Scavenger experiments revealed that hole and hydroxyl radicals were the primary active species in Fe-TiO2-based photocatalysis. Furthermore, the antibacterial potential of the synthesized catalyst was assessed using Escherichia coli and Staphylococcus aureus to observe their respective antibacterial responses.

Development of efficient and economic Bi2O3/BN/Co3O4 composite photocatalyst: Degradation mechanism, pathway and toxicity study of norfloxacin

The production of cheap, efficient, and stable photocatalysts for degrading antibiotic contaminants remains challenging. Herein, Bi2O3/boron nitride (BN)/Co3O4 ternary composites were synthesized using the impregnation method. The morphological characteristics, structural features, and photochemical properties of the prepared photocatalysts were investigated via X-ray diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy, and ultraviolet-visible (Vis) diffuse reflectance spectrum techniques. BN was used as a charge transfer bridge in the ternary composites, which afforded a heterojunction between the two semiconductors. The formation of the heterojunction substantially enhanced the charge separation and improved the photocatalyst performance. The degradation activity of the Bi2O3/BN/Co3O4 ternary composites against norfloxacin (NOR) under Vis light irradiation was investigated. The degradation rate of NOR using 5-wt% Bi2O3/BN/Co3O4 reached 98% in 180 min, indicating excellent photocatalytic performance. The ternary composites also exhibited high photostability with a degradation efficiency of 88.4% after five cycles. Hydroxyl radicals (•OH), superoxide radicals (•O2-), and holes (h+) played a synergistic role in the photocatalytic reaction, where h+ and •O2- were more important than •OH. Consequently, seven intermediates and major photocatalytic degradation pathways were identified. Toxicity experiments showed that the toxicity of the degradation solution to Chlorella pyrenoidosa decreased. Finally, the ecotoxicity of NOR and its intermediates were analyzed using the Toxicity Estimation Software Tool, with most intermediates exhibiting low toxicity.

Advancements in TiO2-based photocatalysis for environmental remediation: Strategies for enhancing visible-light-driven activity

Researchers have focused on efficient techniques for degrading hazardous organic pollutants due to their negative impacts on ecological systems, necessitating immediate remediation. Specifically, TiO2-based photocatalysts, a wide-bandgap semiconductor material, have been extensively studied for their application in environmental remediation. However, the extensive band gap energy and speedy reattachment of electron (e-) and hole (h+) pairs in bare TiO2 are considered major disadvantages for photocatalysis. This review extensively focuses on the combination of semiconducting photocatalysts for commercial outcomes to develop efficient heterojunctions with high photocatalytic activity by minimizing the e-/h+ recombination rate. The improved activity of these heterojunctions is due to their greater surface area, rich active sites, narrow band gap, and high light-harvesting tendency. In this context, strategies for increasing visible light activity, including doping with metals and non-metals, surface modifications, morphology control, composite formation, heterojunction formation, bandgap engineering, surface plasmon resonance, and optimizing reaction conditions are discussed. Furthermore, this review critically assesses the latest developments in TiO2 photocatalysts for the efficient decomposition of various organic contaminants from wastewater, such as pharmaceutical waste, dyes, pesticides, aromatic hydrocarbons, and halo compounds. This review implies that doping is an effective, economical, and simple process for TiO2 nanostructures and that a heterogeneous photocatalytic mechanism is an eco-friendly substitute for the removal of various pollutants. This review provides valuable insights for researchers involved in the development of efficient photocatalysts for environmental remediation.

Titanium Dioxide Nanoparticles Doped with Iron for Water Treatment via Photocatalysis: A Review

Iron-doped titanium dioxide nanoparticles are widely employed for photocatalytic applications under visible light due to their promising performance. Nevertheless, the manufacturing process, the role of Fe3+ ions within the crystal lattice of titanium dioxide, and their impact on operational parameters are still a subject of controversy. Based on these assumptions, the primary objective of this review is to delineate the role of iron, ascertain the optimal quantity, and elucidate its influence on the main photocatalysis parameters, including nanoparticle size, band gap, surface area, anatase-rutile transition, and point of zero charge. Moreover, an optimized synthesis method based on comprehensive data and insights from the existing literature is proposed, focusing exclusively on iron-doped titanium oxide while excluding other dopant variants.

Ni/Co/Carbon nitride derived from ZIF-67 (MOF) nanocomposite: Enhanced light-driven photocatalytic degradation of methylparaben, mechanism & toxicity

A nickel oxide/cobalt/carbon nitride (Ni/Co/CN) nanocomposite synthesized via co-precipitation was used for the degradation of methylparaben (MEP). Various analytical techniques were used to ascertain the structural, optical, and electrochemical characteristics of the synthesized nanocomposite. The unique nature of the compound without any free particles over the CN was established. Photocatalytic degradation studies demonstrated the superiority of 3-Ni/Co/CN over bare NiO, Co/CN, 1-Ni/Co/CN, and 5-Ni/Co/CN. Near complete MEP degradation (100%) was achieved after 120 min of incubation with MEP 75 mg L-1 in acidic medium pH (3) for an initial concentration of 3-Ni/Co/CN (10 mg/100 mL). HPLC-MS/MS analysis was used to elucidate the degradation pathway, and the catalyst was found stable for four subsequent cycles. Hence, our nanocatalyst effectively degraded MEP. Furthermore, microbial, aquatic, and animal studies demonstrated the environmental efficiency of the synthesized nanomaterials.

Magnetic Carbon Quantum Dots/Iron Oxide Composite Based on Waste Rice Noodle and Iron Oxide Scale: Preparation and Photocatalytic Capability

To provide an economical magnetic photocatalyst and introduce an innovative approach for efficiently utilizing discarded waste rice noodle (WRN) and iron oxide scale (IOS), we initially converted WRN into carbon quantum dots (CQDs) using a hydrothermal method, simultaneously calcining IOS to obtain iron oxide (FeOx). Subsequently, we successfully synthesized a cost-effective, magnetic CQDs/FeOx photocatalytic composite for the first time by combining the resulting CQDs and FeOx. Our findings demonstrated that calcining IOS in an air atmosphere enhanced the content of photocatalytically active α-Fe2O3, while incorporating WRN-based CQDs into FeOx improved the electron-hole pair separation, resulting in increased O2 reduction and H2O oxidation. Under optimized conditions (IOS calcination temperature: 300 °C; carbon loading: 11 wt%), the CQDs/FeOx composite, utilizing WRN and IOS as its foundation, exhibited exceptional and reusable capabilities in photodegrading methylene blue and tetracycline. Remarkably, for methylene blue, it achieved an impressive degradation rate of 99.30% within 480 min, accompanied by a high degradation rate constant of 5.26 × 10-3 min-1. This composite demonstrated reusability potential for up to ten photocatalytic cycles without a significant reduction in the degradation efficiency, surpassing the performance of IOS and FeOx without CQDs. Notably, the composite exhibited strong magnetism with a saturation magnetization strength of 34.7 emu/g, which enables efficient and convenient recovery in photocatalytic applications. This characteristic is highly advantageous for the large-scale industrial utilization of photocatalytic water purification.

Sustainable fabrication of hybrid silver-copper nanocomposites (Ag-CuO NCs) using Ocimum americanum L. as an effective regime against antibacterial, anticancer, photocatalytic dye degradation and microalgae toxicity

In this study, a sustainable fabrication of hybrid silver-copper oxide nanocomposites (Ag-CuO NCs) was accomplished utilizing Ocimum americanum L. by one pot green chemistry method. The multifarious biological and environmental applications of the green fabricated Ag-CuO NCs were evaluated through their antibacterial, anticancer, dye degradation, and microalgae growth inhibition activities. The morphological features of the surface functionalized hybrid Ag-CuO NCs were confirmed by FE-SEM and HR-TEM techniques. The surface plasmon resonance λ_max peak appeared at 441.56 nm. The average hydrodynamic size distribution of synthesized nanocomposite was 69.80 nm. Zeta potential analysis of Ag-CuO NCs confirmed its remarkable stability at -21.5 mV. XRD and XPS techniques validated the crystalline structure and electron binding affinity of NCs, respectively. The Ag-CuO NCs demonstrated excellent inhibitory activity against Vibrio cholerae (19.93 ± 0.29 mm) at 100 μg/mL. Anticancer efficacy of Ag-CuO NCs was investigated against the A549 lung cancer cell line, and Ag-CuO NCs exhibited outstanding antiproliferative activity with a low IC₅₀ of 2.8 ± 0.05 μg/mL. Furthermore, staining and comet assays substantiated that the Ag-CuO NCs hindered the progression of the A549 cells and induced apoptosis as a result of cell cycle arrest at the G₀/G₁ phase. Concerning the environmental applications, the Ag-CuO NCs displayed efficient photocatalytic activity against eosin yellow degradation up to 80.94% under sunlight irradiation. Microalgae can be used as an early bio-indicator/prediction of environmental contaminants and toxic substances. The treatment of the Ag-CuO NCs on the growth of marine microalgae Tetraselmis suecica demonstrated the dose and time-dependent growth reduction and variations in the chlorophyll content. Therefore, the efficient multifunctional properties of hybrid Ag-CuO NCs could be exploited as a regime against infective diseases and cancer. Further, the findings of our investigation witness the remarkable scope and potency of Ag-CuO NCs for environmental applications.

Cobalt-molybdenum-selenide nanoflowers for bifunctional visible light photocatalysis

The renewability and zero carbon emissions of hydrogen make it a promising clean energy resource to meet future energy demands. Owing to its benefits, photocatalytic water-splitting has been extensively investigated for hydrogen production. However, the low efficiency poses a serious challenge to its implementation. Herein, we attempted to synthesize bimetallic transition metal selenides, namely Co/Mo/Se (CMS) photocatalysts, with varying atomic compositions (CMSa, CMSb, and CMSc) and investigated their photocatalytic water splitting efficiencies. The observed hydrogen evolution rates were as follows: 134.88 μmol g^-1 min^-1 for CoSe₂, 145.11 μmol g^-1 min^-1 for MoSe₂, 167.31 μmol g^-1 min^-1 for CMSa, 195.11 μmol g^-1 min^-1 for CMSb, and 203.68 μmol g^-1 min^-1 for CMSc. Hence, we deemed CMSc to be the most potent photocatalytic alternative among the compounds. CMSc was also tested for its efficiency towards degradation of triclosan (TCN), and results substantiated that CMSc succeeded degrading 98% TCN while CMSa and b were able to degrade 80 and 90% TCN respectively-the attained efficiency being exponentially higher than CoSe₂ and MoSe₂ taken for comparative analysis in addition to complete degradation of the pollutants leaving no harmful intermediaries during the process. Thus, CMSc shall be identified as a highly potential photocatalyst with respect to both environmental and energy applications.

Antibiotics oxytetracycline removal by photocatalyst titanium dioxide and graphitic carbon nitride in aquaculture wastewater

The surge in the use of antibiotics, especially in aquaculture, has led to development of antibiotic resistance genes, which will harm environmental and public health. One of the most commonly used antibiotics in aquaculture is oxytetracycline (OTC). Employing photocatalysis, this study compared OTC degradation efficiency of two different types of common photocatalysts, TiO₂ and graphitic carbon nitride (GCN) in terms of their photochemical properties and underlying photocatalytic mechanism. For reference purpose, self-synthesized GCN from urea precursor (GCN-Urea) and commercial GCN (GCN-Commercial) were both examined. OTC adsorption-photocatalysis removal rates in pure OTC solution by TiO₂, GCN-Urea and GCN-Commercial were attained at 95%, 60% and 40% respectively. Photochemical properties evaluated included light absorption, band gap, valence and conduction band positions, photoluminescence, cyclic voltammetry, BET surface area and adsorption capability of the photocatalysts. Through the evaluations, this study provides novel insights towards current state-of-the-art heterogeneous photocatalytic processes. The electron-hole recombination examined by photoluminescence is not the key factor influencing the photocatalytic efficacies as commonly discussed. On the contrary, the dominating factors governing the higher OTC degradation efficiency of TiO₂ compared to GCN are the high mobility of electrons that leads to high redox capability and the high pollutant-photocatalyst affinity. These claims are proven by 86% and 40% more intense anodic and cathodic cyclic voltammetry curve peaks of TiO₂ as compared to both GCNs. OTC also demonstrated 1.7 and 2.3 times higher affinity towards TiO₂ than GCN-Urea and GCN-Commercial. OTC removal by TiO₂ in real aquaculture wastewater only achieved 50%, due to significant inhibition effect by dissolved solids, dissolved organic matters and high ionic contents in the wastewater.

Photodegradation of fleroxacin by g-C3N4/PPy/Ag and HPLC-MS/MS analysis of degradation pathways

To improve the photocatalytic activity of g-C₃N₄, graphitic phase carbon nitride was prepared using melamine as the substrate and modified with PPy and Ag nanoparticles. The structure, morphology, and optical properties of the photocatalysts were investigated using various characterization methods such as XRD, FT-IR, TEM, XPS, and UV-vis DRS. The degradation of fleroxacin, a common quinolone antibiotic, was isolated and measured using the HPLC-MS/MS technique to trace its intermediates and deduce the main degradation pathways. The results showed that g-C₃N₄/PPy/Ag had high photocatalytic activity and a degradation rate of more than 90%. The fleroxacin degradation reactions were primarily oxidative ring opening of the N-methyl piperazine ring structure, defluorination reactions on fluoroethyl, HCHO, and N-methyl ethylamine removal reactions.

A hybrid technique for sulfamethoxazole (SFM) removal using Enterobacter hormaechei HaG-7: Bio-electrokinetic degradation, pathway and toxicity

Prolonged exposure to antibiotics would likely favor the development of antibiotic resistance and their gene transfer among bacterial communities that are responsible for enriched antibiotic resistant microbes. Sulfamethoxazole (SFM) is a commonly used antibiotic that is released into the environment through human and animal wastes. Improper degradation of SFM poses severe threats to mankind and all life forms. The present study aims in analyzing the process and the probability of utilizing bio-electrokinetic degradation for elimination of SFM from artificially contaminated soil employing Enterobacter hormaechei HaG-7. The desired optimal conditions for SFM degradation (∼98%) were observed at SFM initial concentration (100 mg/L) with an inoculum dose (1% v/v) and applied potential voltage (1.5 V) at pH (7). The results indicated efficient and complete degradation of SFM when compared with the conventional biodegradation.

Two dimensional S-scheme Bi2WO6-TiO2-Ti3C2 nanocomposites for efficient degradation of organic pollutants under natural sunlight

Two-dimensional (2D) materials have fascinated the researchers to exploit their properties including large surface area, ability to act as a support and to form face-to-face interfacial contact with other 2D materials for fabricating efficient photocatalytic materials. In this work, Bi₂WO₆, TiO₂ and Ti₃C₂ nanosheets have been used synthesizing different series of binary Bi₂WO₆-TiO₂ and ternary Bi₂WO₆-TiO₂-Ti₃C₂ 2D nanocomposites by an electrostatic self-assembly synthesis route. The as-prepared pristine materials and binary and ternary nanocomposites were characterized by different structural, morphological and compositional characterization techniques to confirm their successful synthesis and 2D morphology. It was found that the optimized Bi₂WO₆-TiO₂ (20 wt%) and Bi₂WO₆-TiO₂ (20 wt%)-Ti₃C₂ (5 wt%) nanocomposites showed 97.0% and 98.5% degradation of methyl green in 80 min and 40 min, respectively, which was higher than their pristine counterparts. The enhanced activity was credited to the large surface area offered by 2D nanocomposites, pollutant adsorption and enhanced photogenerated charge separation and transfer facilitated by S-scheme mechanism and face-to-face interfacial contact of different components of these nanocomposites. This work delivers an example of highly efficient 2D nanocomposites and discusses the role of Ti₃C₂ as an electron acceptor in S-scheme photocatalytic system.

Improved visible-light-driven photocatalytic removal of Bisphenol A using V2O5/WO3 decorated over Zeolite: Degradation mechanism and toxicity

WO₃/Zeolite/V₂O₅ (TZV) composite synthesized through co-precipitation was used for the degradation of Bisphenol-A (BpA). XRD and Raman spectra were employed to ascertain the crystallinity of the composite. The pristine nature of the compound without any free particles over the zeolite surface was established through FESEM, thus, substantiating the composite character of the material. The enhancement in activity after doping with WO₃ was ascertained by DRS-UV. Photocatalytic degradation studies clearly established the superiority of TZV 10 over bare V₂O₅. Complete BpA degradation (100%) was attained at 50 min of incubation with 0.75 g/L TZV-10 in acidic medium (pH 3) for an initial BpA concentration of 100 mg/L. HPLC-MS/MS analysis was used to decipher the degradation pathway. The catalyst was stable even after 9 cycles. Phytotoxicity studies and lake water treatment results proved the environmental efficiency of the synthesized material.

Highly efficient visible light photocatalysis of Nix Zn1-x Fe2O4 (x= 0, 0.3, 0.7) nanoparticles: Diclofenac degradation mechanism and eco-toxicity

Pharmaceuticals and personal care products occupy a predominant position with respect to both utility and release into the ecosystem, thereby contributing to environmental pollution at alarming rates. Of the several methods identified to minimize the concentration of PPCPs, nanomaterial based photocatalysis seems to be a potential alternative for it being highly economical and eco-friendly. In this study, we synthesized Nickel zinc ferrite (Ni-ZF) [Ni_x Zn_1-x Fe₂O₄ (x = 0, 0.3, 0.7)] nanoparticles with an average diameter of ∼400 nm by a co-precipitation method towards diclofenac degradation. The composite showed greater degrees of crystallinity devoid of any impurities. Nearly complete DCF degradation (∼99%) was achieved after 50 min reaction time with the nanoparticles at pH 7 for an initial DCF concentration of 50 mg/L. The degradation process followed a pseudo first-order rate law with the rate constant of 0.1657 min^{- 1}. Microbial toxicity and phytotoxicity studies demonstrated negligible toxicity imposed by the contaminated water treated with the prepared composite, suggesting it as a promising photocatalyst benefitting in all aspects.

Fe@Fe2O3-loaded biochar as an efficient heterogeneous Fenton catalyst for organic pollutants removal

With increased demand for various chemical raw materials, sudden pollution incidents are more prone to occur during their transportation and usage, threatening the environment and human health. In this study, discarded tea stalks were recycled into composite materials (FSC-X00: X represents the calcination temperature) by impregnating tea stalks in Fe²⁺ solution combined with subsequent calcination. X-ray diffractometer (XRD) and X-ray photoelectron spectroscopy (XPS) patterns verified the existence of Fe⁰ and Fe₂O₃, and Fe₂O₃ was gradually reduced to Fe⁰ when the calcination temperature was raised from 700 °C to 900 °C. FSC-X00 was adopted as a heterogeneous catalyst for activating H₂O₂ to quickly degrade phenol in the water system. The degradation experiments indicated that FSC-600 exhibited superior degradation performance for phenol (20 mg/L) within 5 min and 80% total organic carbon (TOC) removal rate at pH = 3 within 30 min. The effects of the calcination temperature, the pH value and the amount of H₂O₂ on the degradation efficiency were investigated. Competing experiments showed that fulvic acid (FA) and inorganic salts Na⁺ had little effect on the degradation performance. The FSC-600 catalyst can be reused by thermal reduction. In addition, it was found that FSC-600 has a good degradation effect on ciprofloxacin (CIP), norfloxacin (NOR) and enrofloxacin (ENR), indicating that FSC-600 catalysts are a promising candidate for quick degradation of organic pollutants by Fenton reaction. Electron paramagnetic resonance (EPR) spectra analysis indicated that •OH is the dominant reactive oxygen species (ROS) and part ¹O₂ from O₂ also participated in the degradation. This study provides an example of creating catalysts from organic solid waste for use in emergency treatment for phenol.

ZrO2-Ag2O nanocomposites encrusted porous polymer monoliths as high-performance visible light photocatalysts for the fast degradation of pharmaceutical pollutants

This work reports a unique ZrO₂-Ag₂O heterojunction nanocomposite uniformly dispersed on a macro-/meso-porous polymer monolithic template to serve as simple and effective visible light-driven heterogeneous plasmonic photocatalysts for water decontamination. The monolithic photocatalysts' structural properties and surface morphology are characterized using various surface and structural characterization techniques. The photocatalytic performance of the proposed photocatalysts is evaluated by optimizing multiple operational parameters. The photocatalytic properties of the fabricated monolithic nanocomposite are monitored through time-dependent photocatalytic disintegration of norfloxacin drug, a widely employed antimicrobial, with considerable aquatic persistence. The analytical results conclude that a (60:40) ZrO₂-Ag₂O nanocomposite embedded polymer monolith exhibits superior photocatalytic activity for the complete mineralization of norfloxacin molecules under optimized conditions of solution pH (3.0), photocatalyst quantity (100 mg), pollutant concentration (15 mg/L), photosensitizers (2.0 mM KBrO₃), visible light intensity (300 W/cm² tungsten lamp) and irradiation time (≤ 1 h). The proposed new-age inorganic-organic hybrid visible light photo-catalysts with superior structural and surface properties exhibit brilliant performance and fast responsiveness for water decontamination applications, in addition to their excellent chemical stability, high durability, multi-reusability, and cost-effectiveness.

Light Promotes the Immobilization of U(VI) by Ferrihydrite

The environmental behaviors of uranium closely depend on its interaction with natural minerals. Ferrihydrite widely distributed in nature is considered as one main natural media that is able to change the geochemical behaviors of various elements. However, the semiconductor properties of ferrihydrite and its impacts on the environmental fate of elements are sometimes ignored. The present study systematically clarified the photocatalysis of U(VI) on ferrihydrite under anaerobic and aerobic conditions, respectively. Ferrihydrite showed excellent photoelectric response. Under anaerobic conditions, U(VI) was converted to U(IV) by light-irradiated ferrihydrite, in the form of UO2+x (x < 0.25), where •O2− was the dominant reactive reductive species. At pH 5.0, ~50% of U(VI) was removed after light irradiation for 2 h, while 100% U(VI) was eliminated at pH 6.0. The presence of methanol accelerated the reduction of U(VI). Under aerobic conditions, the light illumination on ferrihydrite also led to an obvious but slower removal of U(VI). The removal of U(VI) increased from ~25% to 70% as the pH increased from 5.0 to 6.0. The generation of H2O2 under aerobic conditions led to the formation of UO4•xH2O precipitates on ferrihydrite. Therefore, it is proved that light irradiation on ferrihydrite significantly changed the species of U(VI) and promoted the removal of uranium both under anaerobic and aerobic conditions.

Green synthesis of MIL-100(Fe) derivatives and revealing their structure-activity relationship for 2,4-dichlorophenol photodegradation

MIL-100(Fe), a kind of iron-based metal-organic framework materials (MOFs), can be synthesized at room temperature or hydrothermal conditions, which are promising precursor materials for preparing photocatalysts to degrade some recalcitrant chlorophenols in industrial wastewater. However, the relationship between the structural characterization of MIL-100(Fe) derivatives and their photodegradation behavior of chlorophenol pollutants is still unclear. Thus, in this work, a porous Z-scheme α-Fe₂O₃/MIL-100(Fe) composite was successfully fabricated via partial-pyrolysis of MIL-100(Fe) precursor synthesized through green synthesis route, which was further used for degrading high-concentration of 2,4-dichlorophenol under visible-light illumination (λ > 420 nm). The effects of synthesis route and pyrolysis temperature of MIL-100(Fe) on the degradation efficiencies of as-derived materials for 2,4-dichlorophenol were investigated. The structure-activity relationship was illuminated in detail. Otherwise, the influence of several process factors, i.e., initial concentration and pH of the 2,4-dichlorophenol solution, catalyst dosage on the degradation efficiency of 2,4-dichlorophenol has also been performed. The removal efficiency of 2,4-dichlorophenol with the initial concentration of 100 mg L^-1 reached up to 87.65% under optimized conditions. Lastly, the possible mechanism was explored based on trapping experiments and some other characterization results. The study in this paper not only exhibited new insight into the modified α-Fe₂O₃ material with high photocatalytic activity but also provided a promising method for treating wastewater containing 2,4-dichlorophenol or other similar organic pollutants.

Insight into the rapid elimination of low-concentration antibiotics from natural waters using tandem multilevel reactive electrochemical membranes: Role of direct electron transfer and hydroxyl radical oxidation

Herein, we reported a tandem multilevel reactive electrochemical membrane (REM) system was promising for the rapid and complete removal of trace antibiotics from natural waters. Results indicate that a four-stage REM module-in-series system achieved steady over 98% removal of model antibiotic norfloxacin (NOR, 100 μg·L^-1) from wastewater treatment plant final effluent and surface water with a residence time of 5.4 s, and the electric energy consumption was only around 0.007-0.011 kWh·m^-3. As for the oxidation mechanism, direct electron transfer (DET) oxidation process played an important role in NOR rapid oxidation, enabling the REM system to tolerate various ^•OH scavenges in natural waters, including natural organic matters, Cl^- and HCO₃^-, even at very high concentration levels. Meanwhile, ^•OH-mediated indirect oxidation process promotes the oxidation and mineralization of NOR. Although the DET-dominated oxidation mechanism makes the REM system cannot achieve the complete mineralization of NOR with residence times of few seconds, the antibacterial activity from NOR was completely eliminated. This REM system featured effective removal performance of trace contaminants with low energy cost and was tolerant to complex waster matrix, suggesting that it could be a powerful supplementary step for wastewater/water treatment.

Nickel decorated manganese oxynitride over graphene nanosheets as highly efficient visible light driven photocatalysts for acetylsalicylic acid degradation

In this work, we prepared nanocomposites of nickel-decorated manganese oxynitride on graphene nanosheets and demonstrated them as photocatalysts for degradation of acetylsalicylic acid (ASA). The catalyst exhibited a high degradation efficiency over ASA under visible light irradiation and an excellent structural stability after multiple uses. Compared to manganese oxide (MnO) and manganese oxynitride (MnON) nanoparticles, larger specific surface area and smaller band gap were observed for the nanocomposite accounting for the enhanced photocatalytic efficiency. Besides the compositional effect of the catalyst, we also examined the influence of various experimental parameters on the degradation of ASA such as initial concentration, catalyst dose, initial pH and additives. The best performance was obtained for the nanocomposite when the catalyst dose was 10 mg/mL and the initial pH 3. Detection of intermediates during photocatalysis showed that ASA undergoes hydroxylation, demethylation, aromatization, ring opening, and finally complete mineralization into CO₂ and H₂O by reactive species. For practical applications as a photocatalyst, cytotoxicity of the nanocomposite was also evaluated, which revealed its insignificant impact on the cell viability. These results suggest the nanocomposite of nickel-decorated manganese oxynitride on graphene nanosheets as a promising photocatalyst for the remediation of ASA-contaminated water.

A Novel N-Doped Nanoporous Bio-Graphene Synthesized from Pistacia lentiscus Gum and Its Nanocomposite with WO3 Nanoparticles: Visible-Light-Driven Photocatalytic Activity

This paper reports the synthesis of a new nitrogen-doped porous bio-graphene (NPBG) with a specific biomorphic structure, using Pistacia lentiscus as a natural carbon source containing nitrogen that also acts as a bio-template. The obtained NPBG demonstrated the unique feature of doped nitrogen with a 3D nanoporous structure. Next, a WO₃/N-doped porous bio-graphene nanocomposite (WO₃/NPBG-NC) was synthesized, and the products were characterized using XPS, SEM, TEM, FT-IR, EDX, XRD, and Raman analyses. The presence of nitrogen doped in the structure of the bio-graphene (BG) was confirmed to be pyridinic-N and pyrrolic-N with N1 peaks at 398.3 eV and 400.5 eV, respectively. The photocatalytic degradation of the anionic azo dyes and drugs was investigated, and the results indicated that the obtained NPBG with a high surface area (151.98 m²/g), unique electronic properties, and modified surface improved the adsorption and photocatalytic properties in combination with WO₃ nanoparticles (WO₃-NPs) as an effective visible-light-driven photocatalyst. The synthesized WO₃/NPBG-NC with a surface area of 226.92 m²/g displayed lower bandgap and higher electron transfer compared with blank WO₃-NPs, leading to an increase in the photocatalytic performance through the enhancement of the separation of charge and a reduction in the recombination rate. At the optimum conditions of 0.015 g of the nanocomposite, a contact time of 15 min, and 100 mg/L of dyes, the removal percentages were 100%, 99.8%, and 98% for methyl red (MR), Congo red (CR), and methyl orange (MO), respectively. In the case of the drugs, 99% and 87% of tetracycline and acetaminophen, respectively, at a concentration of 10 mg/L, were removed after 20 min.

Oxygen defective titanate nanotubes induced by iron deposition for enhanced peroxymonosulfate activation and acetaminophen degradation: Mechanisms, water chemistry effects, and theoretical calculation

The large consumption of acetaminophen (APAP) worldwide and unsatisfactory treatment efficiencies by conventional wastewater treatment processes give rise to the seeking of new technology for its effective removal. Herein, we proposed a facile one-step hydrothermal method to synthesize defective iron deposited titanate nanotubes (Fe/TNTs) for peroxymonosulfate (PMS) activation and APAP degradation. The retarded first-order reaction rate of APAP degradation by Fe/TNTs was 5.1 times higher than that of neat TNTs. Characterizations indicated iron deposition effectively induced oxygen vacancies and Ti³⁺, facilitating the electrical conductivity and PMS binding affinity of Fe/TNTs. Besides, oxygen vacancies could act as an electron mediator through PMS activation by iron. Moreover, the formation of Fe-O-Ti bond facilitated the synergistic redox coupling between Fe and Ti, further enhancing the PMS activation. SO₄^•- was the major radical, causing C-N bond cleavage and decreasing the overall toxicity. In contrast, APAP degradation by neat TNTs-PMS system mainly works through nonradical reaction. The Fe/TNTs activated PMS showed desired APAP removal under mild water chemistry conditions and good reusability. This work is expected to expand the potential application of titanate nanomaterials for PMS activation, and shed light on facile synthesis of oxygen defective materials for sulfate-radical-based advanced oxidation processes.

Highly efficient visible light driven photocatalytic activity of zinc/ferrite: Carbamazepine degradation, mechanism and toxicity assessment

In this present study, spherical shaped zinc ferrite (Zn/Fe₂O₄) was prepared as uniformly sized (65 ± 0.5 nm) nanoparticles with band gap (2.00 eV) in a visible light regime and employed for the photocatalytic degradation of carbamazepine (CBZ). The doping of Zn decreased the band gap (from 2.00 to 1.98 eV) and enhanced the absorption of visible light. Zinc doping also induced effective separation of photogenerated carriers and subsequent charge migration to the surface of the Zn/Fe₂O₄ nanoparticle. On account of the advantages of the material, a high removal efficiency (~ 100%) of CBZ through photocatalytic degradation was achieved. Kinetics of CBZ degradation follows a pseudo first-order with the rate constant 0.0367 min^-1. In-vitro and in-vivo toxicity of the nanoparticles were examined promoting the environmental implications.