Mechanistic insight into the degradation of ciprofloxacin in water by hydroxyl radicals

BDD electrode pulsed alternating electrochemical oxidation of sulfamethazine in antibiotic wastewater: Process optimization and degradation mechanism

To address the issues of electrode passivation and high electric energy consumption (EEC) associated with the removal of antibiotic wastewater using traditional direct current electrocatalytic oxidation (DCEO) with Boron-Doped Diamond (BDD) electrodes, this study aims to develop an efficient, low-cost, and self-cleaning BDD electrode pulsed alternating electrocatalytic oxidation (BDD-PAEO) technology. The experimental findings demonstrated that, under optimal conditions, the BDD-PAEO mode achieved a 99.9% removal efficiency for sulfamethazine (SMZ). Furthermore, the removal efficiency of COD in the BDD-PAEO mode consistently remained above 93% in 10 experimental cycles. Compared with the BDD-DCEO mode, the EEC of the BDD-PAEO mode is reduced by 17.39%, and the current efficiency (CE) is increased by 47.15%. The ·OH was confirmed to be the main active oxidant species for degradation of SMZ by free radical quenching experiments, electron paramagnetic resonance (EPR) and three-dimensional excitation-emission matrix (3D-EEM) spectroscopy. The degradation pathway of SMZ was revealed by density functional theory (DFT) calculation and gas chromatography-mass spectrometry (GC-MS) analysis. Toxicity estimation illustrated that BDD-PAEO technology can effectively reduce the toxicity of wastewater after SMZ degradation. This study shows BDD-PAEO technology's high potential for efficient SMZ degradation and toxicity reduction in antibiotic wastewater, offering a novel treatment solution.

Hierarchically periodic macroporous bismuth vanadate with engineered oxygen vacancies for enhanced photo-oxidation performance

Controlling morphology and engineering surface defects are two widely employed strategies for enhancing catalyst activity, impacting the photodegradation of antibiotics and the photo-oxidation of water to generate oxygen. The hierarchical periodic macroporous structure reduces the migration distance of photo-excited carriers, lowers the electron-hole recombination rate, and increases the number of active sites by providing a larger surface area, all of which contribute to improved catalytic efficiency. A key aspect of surface defect engineering is the study of oxygen vacancies, which can act as electron donors, promoting carrier separation and thereby enhancing catalytic performance. The combined effects of these two features significantly enhance the catalyst's photo-oxidation capabilities. By contrast to traditional methods that create oxygen vacancies during the synthesis process, this study introduces additional oxygen vacancies through a secondary treatment applied after the catalyst has been produced.

Cashew gum-assisted synthesis of Zn0.98Nd0.02O photocatalyst: pH-dependent green approach and photocatalytic degradation of ciprofloxacin and ibuprofen pharmaceutical pollutants

The presence of pharmaceutical residues in aquatic environments represents a serious environmental problem, with negative impacts on ecosystems and public health. The removal of these contaminants from wastewater is a challenge that requires innovative and sustainable strategies. In this study, a green synthesis approach, assisted by cashew gum, was employed to synthesize the Zn0.98Nd0.02O photocatalysts at varying pH levels (5, 7, 9, 11, and 13) via the sol-gel method. The effects of synthesis pH on structural, optical, and photocatalytic properties were systematically investigated. The structural analysis revealed a hexagonal wurtzite structure, with crystallite sizes ranging from 69 nm (pH 5) to 235 nm (pH 9). Micrography images showed that pH significantly influenced morphology, with particles ranging from agglomerates to more dispersed spherical shapes. Porosity analysis indicated mesoporous structures with surface areas varying between 2.2 and 5.2 m2/g, depending on pH. Photoluminescence (PL) spectra highlighted the presence of oxygen-related defects, with emission peaks shifting due to structural disorder induced by doping and pH variation. Optical studies also indicated a tunable bandgap (3.284-3.218 eV) and Urbach energy (50.96-75.30 meV), signifying increased structural disorder at higher pH. Photocatalytic performance was evaluated against Ciprofloxacin (CIP) and Ibuprofen (IBU), achieving degradation efficiencies of 97.5 % (CIP at pH 7) and 74.1 % (IBU at pH 13) under UV light. Kinetic studies confirmed pseudo-first-order behavior with rate constants of 2.14 × 10-2 min-1 for CIP and 8.99 × 10-3 min-1 for IBU. Reactive species analysis identified hydroxyl radicals (•OH) as dominant contributors to pollutant degradation. Reusability tests demonstrated >96 % CIP removal over four cycles and consistent structural stability, validated via XRD. This study highlights the potential of the Zn0.98Nd0.02O photocatalysts synthesized under eco-friendly conditions for addressing pharmaceutical pollutants in wastewater treatment.

Enhanced pharmaceutical removal from building wastewater by the novel integrated system of anaerobic baffled biofilm-membrane bioreactor and UV/O3: Microbial community, occurrence of bio-intermediates and post-treatment

This research aimed to develop the novel integrated system of anaerobic baffled biofilm-membrane bioreactor (AnBB-MBR) (with and without microaeration) and UV/O3 for removal of target pharmaceuticals (ciprofloxacin (CIP), caffeine (CAF), sulfamethoxazole (SMX) and diclofenac (DCF)) from building wastewater. The investigation was performed to elucidate how microaeration affected the removal performances, degradation kinetics and pathways of bio-intermediates of the AnBB-MBR. Two AnBB-MBR reactors - R1: AnBB-MBR (without microaeration) and R2: AnBB-MBR with microaeration at 0.93 LO2/LFeed - were operated at the same hydraulic retention time (HRT) of 30 h. The UV/O3 was selected as the post-treatment system. While UV alone slightly removed CIP without the removal of other compounds. After 150 min of the UV/O3, the R1 with UV/O3 achieved 97.31-100% removal efficiency of targeted pharmaceuticals and increased to 99.47-100% with the R2 integrated with UV/O3. The obtained pseudo-first order kinetic rate constants of the UV/O3 in treating the permeate of R1 were 0.0235, 0.004, 0.0423 and 0.097 min-1 for CIP, CAF, SMX and DCF, respectively. Whereas the obtained pseudo-first order kinetic rate constants of the UV/O3 in treating the permeate of R2 were 0.021, 0.0338, 0.0511 and 0.0527 min-1 for CIP, CAF, SMX and DCF, respectively. For the major microorganisms involved in targeted pharmaceutical removal in the R2 under microaerobic conditions included ammonia oxidizing bacteria (AOB) and methanotrophs, while Bacillus, Longilinea, Clostridium and Lactivibrio were possibly responsible for pharmaceutical removal in the R1 under anaerobic conditions. The differences of bio-intermediates between anaerobic and microaerobic conditions were exclusively identified. In addition, the integration of AnBB-MBR with microaeration and UV/O3 was more effective in removing a wide variety of bio-intermediates than the case of the integrated system without microaeration. Therefore, the integrated system of AnBB-MBR with microaeration and UV/O3 can be a promising technology for pharmaceutical removal from building wastewater.

Uncovering Metal-Decorated TiO2 Photocatalysts for Ciprofloxacin Degradation-A Combined Experimental and DFT Study

Optimization of the efficiency of the photocatalytic degradation of organic and pharmaceutical pollutants represents a matter of fundamental and practical interest. The present experimental and DFT study deals with evaluation of OH radical binding energy as a simple computational descriptor of the catalytic activity of d-metal-decorated TiO2 photocatalysts for the photodegradation of the widely used antibiotic ciprofloxacin. Five d-metals commonly used in catalytic materials (Zr, Pt, Pd, Fe, and Cu) were deposited on the TiO2 surface, and the obtained photocatalysts were characterized experimentally (XRPD, ICP-OES, and SEM) and theoretically (DFT). Attention was also paid to the mechanistic insights and degradation byproducts (based on UV-Vis spectrometry and LC/MS analysis) in order to obtain systematic insight into their structure/performance relationships and confirm the proposed model of the degradation process based on OH radical reactivity.

High-efficiency electro-Fenton synergistic electrocoagulation for enhanced removal of refractory organic pollutants

The persistence and stability of refractory organic compounds such as dyes in water bodies cause serious toxicity to humans. The present study provides an in-depth investigation into the evolution law of electro-Fenton (EF) oxidation to in situ electrocoagulation (EC) process and its mechanism for highly efficient removal of refractory organic pollutants. A comprehensive evaluation of the energy efficiency by EC, EF (constant pH = 3) and electrocatalytic oxidation (EO) processes under the same research levels was conducted. The results showed that in the EF-EC mode, the removal efficiency of Rhodamine B (RhB) was enhanced by 33.41% compared to the EC system. Additionally, electrode consumption is 52.9% of the EF system, and current efficiency was improved by 272.98% compared to the EO system. Hydroxyl radical (·OH) and polynuclear species (Fe(b)) are the main species to remove refractory organics and intermediates. Unlike the synergistic effect of ·OH homogeneous oxidation and electrocoagulation in the EF-EC process, the ·OH produced in the EO process mainly undergoes heterogeneous oxidation at the electrode interface. The formed iron oxides were mainly Fe2O3 and ɑ-FeOOH. Density functional theory calculations and liquid chromatograph-mass spectrometer analysis indicated that the degradation of RhB mainly included deethylation, deamination, degradation, ring-opening and mineralization reactions. This study provides a valuable reference for related research in the field of environmental electrochemical remediation.

MXene-based composite aerogels with bifunctional ferrous ions for the efficient degradation of phenol from wastewater

Herein, MXene-based composite aerogel (MXene-Fe2+ aerogel) are constructed by a one-step freeze-drying method, using Ti3C2Tx MXene layers as substrate material and ferrous ion (Fe2+) as crosslinking agent. With the aid of the Fe2+ induced Fenton reaction, the synthesized aerogels are used as the particle electrodes to remove phenol from wastewater with three-dimensional electrode technology. Combined with the dual roles of Fe2+ and the highly conductive MXene, the obtained particle electrode possesses extremely effective phenol degradation. The effects of experiment parameters such as Fe2+ to MXene ratio, particle electrode dosage, applied voltage, and initial pH of solution on the removal of phenol are discussed. At pH = 2.5, phenol with 50 mg/L of initial concentration can be completely removed within 50 min at 10 V with the particle electrode dosage of 0.56 g/L. Finally, the mechanism of degradation is explored. This work provides an effective way for phenol degradation by MXene-based aerogel, which has great potential for the degradation of other organic pollutants in wastewater.

Mechanistic insight into the degradation of sulfadiazine by electro-Fenton system: Role of different reactive species

Sulfadiazine (SDZ), a widely used effective antibiotic, is resistant to conventional biological treatment, which is concerning since untreated SDZ discharge can pose a significant environmental risk. Electro-Fenton (EF) technology is a promising advanced oxidation technology for efficiently removing SDZ. However, due to the limitations of traditional experimental methods, there is a lack of in-depth study on the mechanism of ·OH-dominated SDZ degradation in EF process. In this study, an EF system was established for SDZ degradation and the transformation products (TPs) were detected by mass spectrometry. Dynamic thermodynamic, kinetic and wave function analysis of reactants, transition states and intermediates were proposed by density functional theory calculations, which was applied to elucidate the underlying mechanism of SDZ degradation. Experimental results showed that amino, benzene, and pyrimidine sites in SDZ were oxidized by ·OH, producing TPs through hydrogen abstraction and addition reactions. ·OH was kinetically more likely to attack SDZ- than SDZ. Fe(IV) dominated the single-electron transfer oxidation reaction of SDZ, and the formed organic radicals can spontaneously generate the de-SO2 product via Smiles rearrangement. Toxicity experiments showed the toxicity of SDZ and TPs can be greatly reduced. The results of this study promote the understanding of SDZ degradation mechanism in-depth. ENVIRONMENTAL IMPLICATION: Sulfadiazine (SDZ) is one of the antibiotics widely used around the world. However, it has posed a significant environmental risk due to its overuse and cannot be efficiently removed by traditional treatment methods. The lack of in-depth study on SDZ degradation mechanism under reactive species limits the improvement of SDZ degradation efficiency. Therefore, this work focused on SDZ degradation mechanism in-depth under electro-Fenton system through reactive species investigation, mass spectrometry analysis, and theoretical calculation. The results in this study can provide a theoretical basis for improving the SDZ degradation efficiency which will contribute to solving SDZ pollution problems.

Ag-based coordination polymer-enhanced photocatalytic degradation of ciprofloxacin and nitrophenol

Transition-metal coordination complexes have attracted wide attention in molecular chemistry, but their applications still confront a tremendous challenge. Herein, a novel silver coordination polymer with a formula of {[Ag9(TIPA)6](NO3)9·12H2O}n (Ag-TIPA) was prepared by a solvothermal reaction of silver nitrate with triangular tris(4-imidazolylphenyl)amine (TIPA). The crystalline molecular structure was determined by single-crystal X-ray diffraction, which showed that each Ag(I) was coordinated with two nitrogen atoms of TIPA ligands. Such Ag-TIPA was used as a catalyst for the photodegradation of ciprofloxacin and 4-nitrophenol under UV-visible light irradiation. The results exhibited excellent photocatalytic performance and reusability due to high structure stability in an acidic, neutral and alkaline environment. The experimental findings and density functional theory calculations revealed that metal-ligand charge transfer in Ag-TIPA extended the absorption range of light and improved the charge transfer properties of TIPA. To further understand the photodegradation process, the intermediates were predicted and analysed through electrostatic potential, orbital weighted dual descriptor, and liquid chromatography-mass spectrometry techniques. Based on these findings, a possible degradation mechanism was proposed. This study provides new insights into the design and synthesis of Ag-based coordination polymers with novel structures, excellent catalytic activity, and good durability.

Comparative study of electro-Fenton and photoelectro-Fenton processes using a novel photocatalytic fuel cell electro-Fenton system with g-C3 N4 @N-TiO2 and Ag/CNT@CF as electrodes

In this study, a novel photocatalytic fuel cell electro-Fenton (PFC-EF) system was constructed using g-C3 N4 @N-TNA and Ag/CNT@CF as electrodes. The composition, structure, and morphology of the electrodes were obtained. The g-C3 N4 @N-TNA, with its 2.37 eV band gap and 100 mV photovoltage, has excellent excitation properties for sunlight. Ag/CNT@CF with abundant pores, CNT 3D nanostructures, and Ag crystals on the surface can improve the electro-Fenton efficiency. A comparative study of rhodamine B (RhB) degradation was performed in this system. It has been shown that electric fields can greatly enhance the oxidation efficiency of both anode photocatalysis and the cathode electro-Fenton process. Under optimal conditions, RhB can be completely removed by the photoelectro-Fenton (PEF) process. The energy consumption of the PEF system was obtained. The electrical energy per order (EE/O) is only 9.2 kWh/m3 ·order, which is only 16.5% of EF and 2.2% of PFC-EF system. The mineralization current efficiency (MCE) of the PEF system reached 93.3% for a 2-h reaction. Therefore, the PEF system has the advantage of saving energy. The kinetic analysis shows that the RhB removal follows a first-order kinetic law, and the reaction rate constant reaches 0.1304 min-1 , which is approximately 5.2 times larger and 4.0 times larger than the electro-Fenton and PFC-EF processes, respectively. RhB removal is a coupling multimechanism in which an electric field enhances photoelectron migration, Ag loading improves H2 O2 generation, UV light coupled with H2 O2 promotes hydroxyl radical (٠OH) generation, and the nanoconfinement effect of CNTs promotes ٠OH accumulation in favor of RhB degradation. PRACTITIONER POINTS: Novel efficiency photocatalytic fuel cell electro-Fenton system was constructed. The electric field greatly enhances the photocatalytic fuel cell electro-Fenton system. Multiple coupling mechanisms of UV/H2O2, UV/Fenton and photo-electro-Fenton have been revealed.

Removal of typical pollutant ciprofloxacin using iron-nitrogen co-doped modified corncob in the presence of hydrogen peroxide

Iron-nitrogen co-doped modified corncob (Fe-N-BC) was synthesized using a hydrothermal and calcination method. The material shows excellent oxidation performance and environmental friendliness. When the dosage of Fe-N-BC was 0.6 g L-1, the concentration of H2O2 was 12 mM and pH was 4, ciprofloxacin (CIP) was virtually totally eliminated in 240 min under Fe-N-BC/H2O2 conditions. The TOC removal efficiency was 54.6%, and the effects of various reaction parameters on the catalytic activity of Fe-N-BC were thoroughly assessed. Through electron paramagnetic resonance (EPR) analyses and free radical quenching experiments, it was established that the reactive oxygen species (˙OH, ˙O2-, 1O2) were crucial in the elimination of CIP. Furthermore, the degradation of CIP was accelerated by the synergistic interaction between the transition metal and PFRs. A thorough evaluation was conducted to assess the respective contributions of adsorption and catalytic oxidation in the system. The degradation mechanism of CIP was proposed under Fe-N-BC/H2O2 conditions. Meanwhile, the possible degradation intermediates and pathways were proposed, and the toxicity of the degradation products of CIP was also meticulously investigated in the study. These findings offered the elimination of CIP in water a theoretical foundation and technical support.

Synthesis of Phosphovanadate-Based Porous Inorganic Frameworks with High Proton Conductivity

Materials with high proton conductivity have attracted significant attention for their wide-ranging applications in proton exchange membrane fuel cells. However, the design of new and efficient porous proton-conducting materials remains a challenging task. The structure-controllable and highly stable metal phosphates can be synthesized into layer or frame networks to provide proton transport capabilities. Herein, we have successfully synthesized three isomorphic metal phosphovanadates, namely, H2(C2H10N2)2[MII(H2O)2(VIVO)8(OH)4(PO4)4(HPO4)4] (C2H8N2 = 1,2-ethylenediamine; M = Co, Ni, and Cu), by the hydrothermal method employing ethylenediamine as a template. These pure inorganic open frameworks exhibit a cavity width ranging from 6.4 to 7.5 Å. Remarkably, the proton conductivity of compounds 1-3 can reach 1 × 10-2 S·cm-1 at 85 °C and 97% relative humidity (RH), and they can remain stable at high temperatures as well as long-term stability. This work provides a novel strategy for the development and design of porous proton-conducting materials.