Insights into the degradation mechanisms and pathways of cephalexin during homogeneous and heterogeneous photo-Fenton processes

Insight into the catalytic performances of Fe0@chitosan/cellulose green hybrid structure for enhanced photo-Fenton's oxidation of levofloxacin toxic residuals: Pathway and toxicity

A green hybridized structure of Fe0 painted chitosan/cellulose base (Fe0@CS/CF) has been developed using cellulose extracted from sugarcane bagasse along with reduction agents sourced from Khaya senegalensis leaves. The composite was assessed as an affordable, powerful, and multifunctional catalyst for enhancing the degradation of Levofloxacin (LVX) remnants within water supplies via photo-Fenton's interactions. Using a dosage of 0.5 g/L, the Fe0@CS/CF blend demonstrated noteworthy catalytic qualities, resulting in the complete photo-Fenton's degradation of LVX at a level of 25 mg/L after 40 min. However, the complete diminution of organic carbon (TOC) occurred only after 100 min, suggesting the presence of significant intermediate residues. The identified intermediate chemicals and confirmed hydroxyl radicals as the main oxidizer suggest that the degradation pathway involves carboxylation/decarboxylation, hydroxylation, demethylation, and oxidation of quinolone rings. The toxicity properties of untreated LVX solutions and their subsequent oxidized byproducts were assessed by evaluating their inhibiting impact on Vibrio fischeri over various durations. The samples that experienced partial oxidation at initial testing demonstrated a higher level of toxicity in comparison to the parent LVX. However, the sample that was treated for 100 min demonstrated substantial biological safety and a non-toxic nature. The blend of ingredients has a synergistic impact that enhances the uptake, Fenton's, photocatalytic, and photo-Fenton's characteristics of the hosted Fe0 nanoparticles.

MoS2-based nanocomposites and aerogels for antibiotic pollutants removal from wastewater by photocatalytic degradation process: A review

Photocatalytic technologies based on molybdenum disulfide (MoS2) catalysts are effective, eco-friendly, and promising for antibiotic pollutants treatment. The technologies used by MoS2-based nanocomposites and aerogels for efficient degradation of antibiotics are reviewed in detail for the first time in this paper. The fundamental aspects of MoS2 were comprehensively scrutinized, encompassing crystal structure, optical properties, and photocatalytic principle. Then, the main synthesized methods and advantages/disadvantages for the preparation of MoS2-based nanocomposites and aerogels were systematically presented. Besides, a comprehensive overview of diverse MoS2-based nanocomposites and aerogels photo-degradation systems that enhanced the degradation of antibiotic pollutants were revealed. Meanwhile, the photo-degradation mechanism concentrated on the photoelectron transfer pathways and reactive oxygen species (ROS) were systematically evaluated. Finally, the challenges and perspectives for deeply development of MoS2-based nanocomposites and aerogels were discussed. This review may help researchers to deeply understand the research status of MoS2-based nanocomposites and aerogels for antibiotics removal, and makes clear the photo-degradation mechanism from photoelectron transfer pathways and ROS aspects of MoS2-based nanocomposites and aerogels.

Solar-driven persulfate degradation of caffeine and cephradine in synthetic human urine

Urine source separation, as an innovative concept for the reuse of microlevel nutrients in human urine, has drawn increasing attention recently. Consequently, removing coexisting pharmaceuticals in urine is necessary for further reuse. This study is the first to apply the solar-driven persulfate process (Solar/PS) to the investigation of cephradine (CFD) and caffeine (CAF) degradation in synthetic human urine. The results showed that significantly more degradation of CFD and CAF occurs with the Solar/PS process than with persulfate oxidation and direct sunlight photolysis, respectively. The generated reactive species ·OH, SO4·-, O2·- and 1O2 were identified in the Solar/PS process. While SO4·- played a dominant role at pH 6, it played a minor role at pH 9 due to the lower amount generated under alkaline conditions. The presence of chloride and ammonia negatively impacted the photodegradation of both compounds. In contrast, bicarbonate exhibited no effect on CAF but enhanced CFD degradation owing to its amino-acid-like structure, which has a higher reactivity toward CO3·-. Although total organic carbon (TOC) was partially mineralized after 6 h of operation, no Microtox® toxicity was observed.

Comparative study of Fe2+/H2O2 and Fe2+/persulfate systems on the pre-treatment process of real pharmaceutical wastewater

Advanced oxidation technologies based on hydroxyl radical (•OH) and sulfate radical (SO4-•) are two common types of advanced oxidation technologies, but there are not many reports on the application of advanced oxidation methods in actual wastewater pretreatment. This article compares the pre-treatment performance of Fe2+/H2O2 and Fe2+/Persulfate systems in actual pharmaceutical wastewater, and combines EEM, GC-MS, and toxicity testing results to explore the differences in TOC, COD, and NH3-N removal rates, optimal catalyst dosage, applicable pH range, toxicity of effluent after reaction, and pollutant structure between the two systems. The results indicate that the Fe2+/H2O2 system has a higher pollutant removal rate (TOC: 71.9%, COD: 66.9%, NH3-N: 34.1%), but also requires a higher catalyst (Fe2+) concentration (6.0 g/L), and its effluent exhibits characteristic peaks of aromatic proteins. The Fe2+/Persulfate system has a wider pH range (pH ≈ 3-7) and is more advantageous in treating wastewater containing more cyclic organic compounds, but the effluent contains some sulfur-containing compounds. In addition, toxicity tests have shown that the toxicity reduction effect of the Fe2+/Persulfate system is stronger than that of the Fe2+/H2O2 system.

Synergistic photogeneration of reactive oxygen species by Fe species self-deposited on resorcinol-formaldehyde towards the degradation of phenols under visible light

In this study, a heterogeneous photo-Fenton catalyst of Fe species/resorcinol-formaldehyde (Fe/RF) was synthesized in the degradation process of phenols under visible light in a homogeneous photo-Fenton system. The in situ generated H2O2 by bare RF in the medium and the follow-added Fe2+ can construct homogeneous photo-Fenton system, and Fe/RF heterogeneous photo-Fenton catalyst was formed after the reaction through Fe species self-deposition. Due to the addition of Fe2+, more hydroxyl radical (·OH) generated in the homogeneous Fenton system, which lead to the higher degradation efficiency of phenols that achieved 90.5 % with 150 min. Fe/RF was subsequently formed and more C=O functional group in the structure appeared, which was beneficial to the production of H2O2. The above-mentioned results can be proved by the involved calculation and experimental results. Fe species, including Fe2+ and Fe3+, were beneficial to the conversion of reactive oxygen species (ROSs), and further improved the degradation efficiency of Phenols. Since the existence of photo-generated electrons, Fe2+ concentration in the solution can maintain a stable level. Interestingly, the degradation efficiency of Phenols was higher when Fe3+ was used instead of Fe2+ as the additive, which may be caused by the promotive effect of Fe3+ on singlet oxygen (1O2) generation. In addition, the degradation efficiency of Phenols under alkaline conditions was higher than that under acid conditions, which broke the limit of traditional Fenton process that works mostly in acidic medium. This study shows promising results in terms of synergistic photocatalytic/photo-Fenton processes for the degradation of organic pollutants in water.

Insights into antibiotic cefaclor mineralization by electro-Fenton and photoelectro-Fenton processes using a Ti/Ti4O7 anode: Performance, mechanism, and toxic chlorate/perchlorate formation

A comparative degradation of antibiotic cefaclor (CEC) between Ti/Ti4O7 and Ti/RuO2 anodes, in terms of degradation kinetics, mineralization efficiency, and formation of toxic chlorate (ClO3-) and perchlorate (ClO4-), was performed with electrochemical-oxidation (EO), electro-Fenton (EF), and photoelectro-Fenton (PEF) processes. Besides, CEC degradation by EF with boron-doped diamond (BDD) anode was also tested. Results showed CEC decays always followed pseudo-first-order kinetics, with increasing apparent rate constants in the sequence of EO < EF < PEF. The mineralization efficiency of the processes with Ti/Ti4O7 anode was higher than that of Ti/RuO2 anode, but slightly lower than that of BDD anode. Under the optimal conditions, 94.8% mineralization was obtained in Ti/Ti4O7-PEF, which was much higher than 64.4% in Ti/RuO2-PEF. The use of Ti/RuO2 gave no generation of ClO3- or ClO4-, while the use of Ti/Ti4O7 yielded a small amount of ClO3- and trace amounts of ClO4-. Conversely, the use of BDD led to the highest generation of ClO3- and ClO4-. The reaction mechanism was studied systematically by detecting the generated H2O2 and •OH. The initial N of CEC was released as NH4+ and, in smaller proportion, as NO3-. Four short-chain carboxylic acids and nine aromatic intermediates were also detected, a possible reaction sequence for CEC mineralization was finally proposed.

One-pot synthesis of graphene hydrogel/M (M: Cu, Co, Ni) nanocomposites as cathodes for electrochemical removal of rifampicin from polluted water

Nowadays, the removal of pharmaceutical contaminants from water resources and wastewater is of great importance due to environmental and health issues. Over the decades, various methods have been reported to remove pollutants from wastewater. Among the developed methods, advanced oxidation processes (AOPs) have received significant attention from researchers. In this study, we report the one-pot synthesis of graphene hydrogel-metal (GH-M, M: Co, Ni, Cu) nanocomposites via the combination of polyol and hydrothermal methods. The structure of the resulting nanocomposites was examined by transmission electron microscopy (TEM), inductively coupled plasma-mass spectroscopy (ICP-MS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and Raman spectroscopy methods. Afterward, as-prepared GH-Cu, GH-Co, and GH-Ni nanocomposites were used to prepare cathodes for the electro-Fenton (EF) process to remove rifampicin (RIF) from polluted water. The effect of operational parameters, including current density (mA/cm²), initial pH, initial RIF concentration (mg/L), and process time (min) was investigated via response surface methodology (RSM). The optimal values for current density, pH, initial RIF concentration, and process time using GH-Ni as cathode were 30 mA/cm², 5, 30 mg/L, and 90 min, respectively. The results at optimal values showed that the maximum RIF removal efficiency for GH-Cu, GH-Co, and GH-Ni cathodes was 90.47, 92.60, and 93.69%, respectively. Brunauer Emmett Teller (BET), atomic force microscopy (AFM), energy-dispersive X-ray (EDX), and cyclic voltammetry (CV) analyses were performed to investigate the performance of the cathodes for the RIF removal. Finally, total organic carbon (TOC), gas chromatography-mass spectrometry (GC-MS), and atomic absorption spectroscopy (AAS) analyses were performed for further investigation of the RIF removal from polluted water. The results claimed that one-pot synthesized GH-M cathodes can effectively remove RIF from polluted water through EF process.

Visible-Light Photocatalytic Chlorite Activation Mediated by Oxygen Vacancy Abundant Nd-Doped BiVO4 for Efficient Chlorine Dioxide Generation and Pollutant Degradation

Visible-light photocatalytic chlorite activation has emerged as an efficient oxidation process for micropollutant elimination. However, the in-depth mechanism of chlorite activation is not understood. In this study, using neodymium-doped bismuth vanadate (Nd_xBi_1-xVO_4-δ) as a model catalyst, we describe the oxygen vacancy (OV)-mediated chlorite activation process for efficient ClO₂ generation and cephalexin (CPX) degradation. DFT calculations and in situ DRIFTS suggest that the OV-introduced surface -OH serves as the Brønsted acidic center for chlorite adsorption. The OV-mediated chlorite activation involves multistep reactions that surface hydroxylation and proton transfer from the surface -OH to chlorite, forming metastable chlorous acid (HClO₂) and further disproportionating to ClO₂. As compared with vis-photocatalysis, the vis-photocatalysis coupled with chlorite activation (vis/chlorite) technique exhibits superior performance in antibiotic degradation and achieves efficient microorganism inactivation. This work uncovers the role of OVs on chlorite activation and provides a rational strategy for designing visible-light-driven oxidation techniques in water and wastewater treatment.

Trends in Fenton and photo-Fenton processes for degradation of antineoplastic agents in water matrices: current knowledge and future challenges evaluation using a bibliometric and systematic analysis

Antineoplastic agents present potential hazards to human health and the environment. For this reason, these compounds have attracted a great deal of attention from researchers in the environmental sciences field. In order to help guide future research, it is important to understand the current state of investigation of the occurrence of these microcontaminants and methods for their removal, especially focusing on Fenton and photo-Fenton processes applied to various aqueous matrices in which this class of pharmaceuticals is present. For this purpose, a systematic review of these topics was performed by bibliometric analysis of articles published during the last decade and available in the Scopus and Web of Science databases. This study enables visualization of the current panorama and trends in this field, providing a guide for future collaborative research and exchange of knowledge. Various strategies have been suggested to improve the efficiency of Fenton and photo-Fenton processes, mainly by means of the application of multiples additions of iron, the use of heterogeneous catalysts, and/or the use of chelating agents. Some studies have evaluated different radiation sources employed for photo-Fenton processes, such as solar and/or artificial radiation. In turn, the identification of transformation products generated by Fenton and photo-Fenton treatments, together with their evaluation by in silico (Q)SAR predictions or experimental toxicological bioassays, are related subjects that have been less reported in published works and that should be studied in depth. These subjects can support treatment evaluations that are more realistic, considering their limitations or potentials.

Cephalexin removal by persulfate activation using simulated sunlight and ferrous ions

This study presents the main results related to the use of activated persulfate (PS) in the elimination of the beta-lactam antibiotic cephalexin (CPX). Experiments were done using K₂S₂O₈ and simulated sunlight. A face-centered central composite experimental design was used to analyze the effects of the solution pH and the PS concentration on the reaction, and to determine the optimized conditions that favor the CPX elimination. The results indicated that the removal of CPX is promoted by an acidic pH and under the higher evaluated PS dose (7.5 mg L^-1). CPX total removal was achieved in 30 min. The analysis of the effect of the pollutant initial concentration indicated that a pseudo-first-order kinetics model can be used to describe the reaction. Likewise, the use of Fe²⁺ ions for PS activation (in the dark) was evaluated and established that a higher concentration of ions favors the pollutant removal. Control tests and under the presence of scavenger agents indicated that both HO• and SO₄^-• radicals would be present in the solution and promote the CPX elimination. The assessment of the solution dissolved organic carbon, nitrates and sulfates was also carried out, and indicated that a portion of the organic matter was mineralized.