Degradation of antibiotic chloramphenicol in water by pulsed discharge plasma combined with TiO2/WO3 composites: mechanism and degradation pathway

Electro-, photo-, and photoelectrochemical degradation of chloramphenicol on self-doping Ti nanotubes

In this work, the photo-, electro-, and photo-electro-oxidation of chloramphenicol was investigated. The photo-experiments were carried out with different irradiation sources (an ultraviolet and a simulated solar source) using self-doped titanium nanotubes (SDTNT), a very promising and innovative material that deserves further investigations in the degradation of different pollutants. The photo-electrooxidation (j = 15 mA cm-2) under simulated solar irradiation presented the best efficiency, with ca. 100% degradation and kinetic constant of k = 0.04427 min-1. The FTIR analysis demonstrated a structural modification of the standard molecule occurred for all conditions used, suggesting a modification in functional groups responsible for the biological activity. Furthermore, the TOC analysis showed a significant mineralization of the pollutant (66% from the initial concentration). In addition, both photo-electrooxidation approaches have demonstrated a positive value of S, where the simulated solar irradiation reached the highest value S = 0.6960. The experimental results pointed out evidence that the methodology employed herein for chloramphenicol degradation is greatly interesting and the photo-electrooxidation under simulated solar irradiation is a promising approach for this purpose.

Direct Z-scheme Cu2O/WO3/TiO2 nanocomposite as a potential supercapacitor electrode and an effective visible-light-driven photocatalyst

This paper presents the synthesis of visible light-responsive ternary nanocomposites composed of cuprous oxide (Cu2O), tungsten trioxide (WO3), and titanium dioxide (TiO2) with varying weight percentages (wt.%) of the Cu2O. The resulting Cu2O/WO3/TiO2 (CWT) nanocomposites exhibited band gap energy ranging from 2.35 to 2.90 eV. Electrochemical and photoelectrochemical (PEC) studies confirmed a reduced recombination rate of photoexcited charge carriers in the CWT nanocomposites, facilitated by a direct Z-scheme heterojunction. The 0.50CWT nanocomposite demonstrated superior photodegradation activity (2.29 × 10-2 min-1) against Reactive Black 5 (RB5) dye under visible light activation. Furthermore, the 0.50CWT nanocomposite exhibited excellent stability with 80.51% RB5 photodegradation retention after five cycles. The 0.50CWT electrode achieved a maximum specific capacitance of 66.32 F/g at 10 mA/g current density, with a capacitance retention of 95.17% after 1000 charge-discharge cycles, affirming its stable and efficient supercapacitor performance. This was supported by well-defined peaks in cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) curves, indicating pseudocapacitive properties.

A comprehensive insight on plasma-catalytic degradation of organic pollutants in water: Comparison between ZnO and TiO2

A novel system combining underwater plasma bubbles and high voltage nanopulses was combined for the first time with ZnO and TiO2 for the degradation of organic pollutants in water. The effect of catalyst loading, discharge power and plasma gas on pollutant degradation was investigated whereas the plasma-catalytic mechanism was explored through the quantification of plasma species, COD/TOC measurements and scavenging experiments in the presence and absence of catalysts. The increased efficiency in the presence of either ZnO or TiO2, especially under plasma gases (air and oxygen) able to produce UV radiation in the range of wavelengths absorbed by both catalysts, lies on the increased concentration of the critical reactive species (e.g. ·O2-, ·ΟΗ, H2O2). Compared to plasma alone process, H2O2 was significantly enhanced in the presence of TiO2 and decreased in the presence of ZnO, whereas ·OH concentration was higher in the plasma-ZnO but lower in the plasma-TiO2 system which supports the overall superior performance of ZnO compared to TiO2. The synergy of plasma-ZnO process compared to that of plasma-TiO2 was ∼2.4 and ∼1.5 times higher for Orange II (OII) and Methylene Blue (MB), respectively, exhibiting a very low electrical energy per order (1.4 kWh m-3 for OII and 0.31 kWh m-3 or MB). The present effort contributes on providing fundamental insights and further expand of plasma-catalysis for water treatment.

Efficient photodegradation of paraquat herbicide over TiO2-WO3 heterojunction embedded in diatomite matrix and process optimization

Photodegradation of paraquat herbicide was assessed over several TiO2-WO3 heterojunctions embedded in the diatomite matrix. The characterization results indicated that WO3 embedding in the TiO2 decorated-diatomite matrix could not only enhance the adsorption capacity, visible-light response, and distribution of semiconductor species but also lessen the recombination rate and band gap energy. These characteristics were more noticeable as 5 wt.% of WO3 was embedded. Despite better optical properties of immobilized TiO2-WO3 nanocomposites, overloading WO3 generally alleviates the synergetic effect of tungsten due to surface coverage of diatomite matrix and, subsequently, the significant attenuation of textural properties, more formation of agglomerations and defects as trapping centers in the oxidation sites of heterostructures, and also, less likely of forming TiO2-WO3 heterojunction. In accordance with characterization results, the highest UV-photodegradation of paraquat was attained over heterostructured nanocomposite containing 5 wt.% WO3 (T25-W5/Di). The effects of significant operating parameters were also investigated, modeled, and optimized using response surface methodology (RSM)-central composite design (CCD). Under optimized operation conditions, the experimental removal efficiency of paraquat reached 97.1 and 80% using UV and simulated solar light, respectively. Moreover, the reusability results confirm the sustained activity of the T25-W5/Di nanocomposite.

Rapid self-heating synthesis of Fe-based nanomaterial catalyst for advanced oxidation

Iron-based catalysts are promising candidates for advanced oxidation process-based wastewater remediation. However, the preparation of these materials often involves complex and energy intensive syntheses. Further, due to the inherent limitations of the preparation conditions, it is challenging to realise the full potential of the catalyst. Herein, we develop an iron-based nanomaterial catalyst via soft carbon assisted flash joule heating (FJH). FJH involves rapid temperature increase, electric shock, and cooling, the process simultaneously transforms a low-grade iron mineral (FeS) and soft carbon into an electron rich nano Fe0/FeS heterostructure embedded in thin-bedded graphene. The process is energy efficient and consumes 34 times less energy than conventional pyrolysis. Density functional theory calculations indicate that the electron delocalization of the FJH-derived heterostructure improves its binding ability with peroxydisulfate via bidentate binuclear model, thereby enhancing ·OH yield for organics mineralization. The Fe-based nanomaterial catalyst exhibits strong catalytic performance over a wide pH range. Similar catalysts can be prepared using other commonly available iron precursors. Finally, we also present a strategy for continuous and automated production of the iron-based nanomaterial catalysts.

Degradation of methylene blue using a novel gas-liquid hybrid DDBD reactor: Performance and pathways

A novel gas-liquid hybrid double dielectric barrier discharge (DDBD) reactor with coaxial cylinder configuration was developed for the degradation of methylene blue (MB) in this study. In this DDBD reactor, the reactive species generation occurred in the gas-phase discharge, directly in the liquid, and in the mixture of the working gas bubbles and the liquid, which could effectively increase the contact area between the active substance and MB molecules/intermediates, resulting in an excellent MB degradation efficiency and mineralization (COD and TOC). The electrostatic field simulation analysis by Comsol was carried out to determine the appropriate structural parameters of the DDBD reactor. The effect of discharge voltage, air flow rate, pH, and initial concentration on MB degradation was evaluated. Besides, major oxide species, ·OH, the dissolved O₃ and H₂O₂ generated in this DDBD reactor were determined. Moreover, major MB degradation intermediates were identified by LC-MS, based on which, possible degradation pathways of MB were proposed.

Chemical decontamination of foods using non-thermal plasma-activated water

The presence of chemical contaminants in foods and agricultural products is one of the major safety issues worldwide, posing a serious concern to human health. Nonthermal plasma (NTP) containing richly reactive oxygen and nitrogen species (RONS) has been trialed as a potential decontamination method. Yet, this technology comes with multiple downsides, including adverse effects on the quality of treated foods and limited exposure to entire surfaces on samples with hard-to-reach spots, further hindering real-life applications. Therefore, plasma-activated water (PAW) has been recently developed to facilitate the interactions between RONS and contaminant molecules in the liquid phase, allowing a whole surface treatment with efficient chemical degradation. Here, we review the recent advances in PAW utilized as a chemical decontamination agent in foods. The reaction mechanisms and the main RONS contributors involved in the PAW-assisted removal of chemical contaminants are briefly outlined. Also, the comprehensive effects of these treatments on food qualities (chemical and physical characteristics) and toxicological evaluation of PAW (in vitro and in vivo) are thoroughly discussed. Ultimately, we identified some current challenges and provided relevant suggestions, which can further promote PAW research for real-life applications in the future.

Advances of non-thermal plasma discharge technology in degrading recalcitrant wastewater pollutants. A comprehensive review

With development and urbanization, the amount of wastewater generated due to human activities drastically increases yearly, causing water pollution and intensifying the already worsened water crisis. Although convenient, conventional wastewater treatment methods such as activated sludge, stabilization ponds, and adsorption techniques cannot fully eradicate the complex and recalcitrant contaminants leading to toxic byproducts generation. Recent advancements in wastewater treatment techniques, specifically non-thermal plasma technology, have been extensively investigated for the degradation of complex pollutants in wastewater. Non-thermal plasma is an effective alternative for degrading and augmenting the biodegradability of recalcitrant pollutants due to its ability to generate reactive species in situ. This article critically reviews the non-thermal plasma technology, considering the plasma discharge configuration and reactor types. Furthermore, the influence of operational parameters on the efficiency of the plasma systems and the reactive species generated by the system during discharge has gained significant interest and hence been discussed. Also, the application of non-thermal plasma technology for the degradation of pharmaceuticals, pesticides, and dyes and the inactivation of microbial activities are outlined in this review article. Additionally, optimistic applications involving the combination of non-thermal plasma and catalysts and pilot and industrial-scale projects utilizing non-thermal plasma technology have been addressed. Concluding perceptions on the challenges and future perspectives of the non-thermal technology on wastewater treatment are accentuated. Overall, this review outlines a comprehensive understanding of the non-thermal plasma technology for recalcitrant pollutant degradation from a scientific perspective providing detailed instances for reference.

Molecular Mechanism of Chloramphenicol and Thiamphenicol Resistance Mediated by a Novel Oxidase, CmO, in Sphingomonadaceae

Antibiotic resistance mediated by bacterial enzyme inactivation plays a crucial role in the degradation of antibiotics in the environment. Chloramphenicol (CAP) resistance by enzymatic inactivation comprises nitro reduction, amide bond hydrolysis, and acetylation modification. However, the molecular mechanism of enzymatic oxidation of CAP remains unknown. Here, a novel oxidase gene, cmO, was identified and confirmed biochemically. The encoded CmO oxidase could catalyze the oxidation at the C-1' and C-3' positions of CAP and thiamphenicol (TAP) in Sphingobium sp. strain CAP-1. CmO is highly conserved in members of the family Sphingomonadaceae and shares the highest amino acid similarity of 41.05% with the biochemically identified glucose methanol choline (GMC) oxidoreductases. Molecular docking and site-directed mutagenesis analyses demonstrated that CAP was anchored inside the protein pocket of CmO with the hydrogen bonding of key residues glycine (G) 99, asparagine (N) 518, methionine (M) 474, and tyrosine (Y) 380. CAP sensitivity tests demonstrated that the acetyltransferase and CmO could enable a higher level of resistance to CAP than the amide bond-hydrolyzing esterase and nitroreductase. This study provides a better theoretical basis and a novel diagnostic gene for understanding and assessing the fate and resistance risk of CAP and TAP in the environment. IMPORTANCE Rising levels of antibiotic resistance are undermining ecological and human health as a result of the indiscriminate usage of antibiotics. Various resistance mechanisms have been characterized-for example, genes encoding proteins that degrade antibiotics-and yet, this requires further exploration. In this study, we report a novel gene encoding an oxidase involved in the inactivation of typical amphenicol antibiotics (chloramphenicol and thiamphenicol), and the molecular mechanism is elucidated. The findings provide novel data with which to understand the capabilities of bacteria to tackle antibiotic stress, as well as the complex function of enzymes in the contexts of antibiotic resistance development and antibiotic removal. The reported gene can be further employed as an indicator to monitor amphenicol's fate in the environment, thus benefiting risk assessment in this era of antibiotic resistance.

Multi-catalysis of glow discharge plasma coupled with FeS2 for synergistic removal of antibiotic

Fe-based composites improved the energy utilization efficiency of plasma for removing contaminants through multi-catalysis have received much attention. However, the energy efficiency and catalytic activity are compromised by the slow transformation from Fe (Ⅲ) to Fe (Ⅱ). Here, given the electron-donating ability of reducing sulfur species, as well as the acidic environment generated by FeS₂, single FeS₂ was introduced into the glow discharge plasma (GDP) reactor for the removal of tylosin (TYL). The results showed that a significant synergistic effect between FeS₂ and GDP improved the energy efficiency of plasma and the removal efficiency of TYL (99.7%). FeS₂ boosted the generation of radicals (·OH, ·O₂^-) and nonradicals (h⁺, e^-) rather than H₂O₂ and O₃, which played an important role in TYL abatement. Moreover, the electrons donating sulfur and iron species from FeS₂ can accelerate the conversion of Fe(III) to Fe(II), which was conducive to the generation of radicals. Besides, acid solution self-adjustment resulted from the oxidation of FeS₂ improved heterogeneous Fenton reaction, the oxidation potential of ·OH and adsorption of positive charged TYL. The plausible degradation pathways of TYL were proposed in GDP/FeS₂ system. In summary, enhanced removal of TYL was mainly attributed to the catalytic pathway altered by FeS₂ through high-energy electrons, photocatalysis, heterogeneous Fenton and O₃ catalysis in the GDP system simultaneously. The strategy of integrating GDP with FeS₂ proposed in this work is expected to offer a feasible and potential technique for organic wastewater treatment.

Removal of chloramphenicol antibiotics in natural and engineered water systems: Review of reaction mechanisms and product toxicity

Chloramphenicol antibiotics are widely applied in human and veterinary medicine. They experience natural attenuation and/or chemical degradation during oxidative water treatment. However, the environmental risks posed by the transformation products of such organic contaminants remain largely unknown from the literature. As such, this review aims to summarize and analyze the elimination efficiency, reaction mechanisms, and resulting product risks of three typical chloramphenicol antibiotics (chloramphenicol, thiamphenicol, and florfenicol) from these transformation processes. The obtained results suggest that limited attenuation of these micropollutants is observed during hydrolysis, biodegradation, and photolysis. Comparatively, prominent abatement of these compounds is accomplished using advanced oxidation processes; however, efficient mineralization is still difficult given the formation of recalcitrant products. The in silico prediction on the multi-endpoint toxicity and biodegradability of different products is systematically performed. Most of the transformation products are estimated with acute and chronic aquatic toxicity, genotoxicity, and developmental toxicity. Furthermore, the overall reaction mechanisms of these contaminants induced by multiple oxidizing species are revealed. Overall, this review unveils the non-overlooked and serious secondary risks and biodegradability recalcitrance of the degradation products of chloramphenicol antibiotics using a combined experimental and theoretical method. Strategic improvements of current treatment technologies are strongly recommended for complete water decontamination.

Enhanced adsorption and catalytic degradation of antibiotics by porous 0D/3D Co3O4/g-C3N4 activated peroxymonosulfate: An experimental and mechanistic study

In this work, Co₃O₄/g-C₃N₄ catalyst with highly efficient adsorption and degradation of antibiotics was developed based on the combination of three-dimensional (3D) porous morphological controls of g-C₃N₄ and the loading of Co₃O₄ quantum dots (Co₃O₄ QDs). It was discovered that the catalyst can effectively activate peroxymonosulfate (PMS) through a non-photochemical path, and a high tetracycline elimination rate of 99.7% can be achieved within 18 min. The characterization and density functional theory calculation results demonstrated that the porous 3D structure can not only promote the substrate adsorption reaction but also provide large surface area and countless exposed active sites for catalytic reaction. The introduction of Co₃O₄ QDs lowered activation energy barrier and lead to high energy of PMS adsorption. More efficient charge migration between the catalyst and PMS further accelerated PMS activation. Thus, leading to the excellent catalytic performance. In addition, non-free radical mediated degradation mechanism of catalytic activity was also proposed. This work provides a scheme for designing novel and efficient PMS activators for the removal of abusive antibiotics from aqueous environments.

Activation and characterization of environmental catalysts in plasma-catalysis: Status and challenges

Plasma-catalysis has attracted great attentions in environmental/energy-related fields, but the synergetic mechanism still suffers intractable defects. Key issues are that what kind of catalysts are applicable for plasma system, how are they activated in plasma, and how to characterize them in plasma. This review systematically gives a comprehensive summarization of the selection of catalysts and its activation mechanism in plasma, based on the character of plasma, including physical effects containing the enhancement of discharge intensity and adsorption of reactants, and the utilization of plasma-generated active species such as·O, heat, O₃, ultraviolet light and e* . Focus is given to the illumination of the activation mechanisms of catalysts when placed in plasma zone. Subsequently, the novel characterization techniques for catalysts, which may associate properties to performance, are critically overviewed. The challenges and opportunities for the activation and characterizations of catalysts are proposed, and future perspectives are suggested about where the efforts should be made. It is expected that a bridge between catalysts design and character of plasma can be built to shed light on the synergetic mechanism for plasma-catalysis and design of new plasma-catalysis systems.

Photodegradation assessment of RB5 dye by utilizing WO3/TiO2 nanocomposite: a cytotoxicity study

Textile dyeing wastewater becomes one of the root causes of environmental pollution. Titanium dioxide (TiO₂) is one of the photocatalysts that shows prominent organic dye photodegradation ability. In this study, a porous tungsten oxide (WO₃)/TiO₂ composite was prepared through ultrasonic-assisted solvothermal technique with varying amounts of WO₃ ranging from 0.25 to 5 weight % (wt.%). The prepared 0.50 wt.% WO₃/TiO₂ (0.50WTi) composite exhibited the highest photodegradation activity (4.39 × 10^-2 min^-1) and complete mineralization in chemical oxygen demand (COD) reading towards 30 mg.L^-1 of Reactive Black 5 (RB5) dye under 60 min of light irradiation. Effects of large surface area, small crystallite size, high pore volume and size, and low electron-hole pair recombination rate attributed to the superiority of 0.50WTi. Besides, 0.50WTi could be reused, showing 86.50% of RB5 photodegradation at the fifth cycle. Scavenger study demonstrated that photogenerated hole (h⁺) was the main active species of 0.50WTi to initiate the RB5 photodegradation. Cytotoxicity assessment determined the readings of half-maximal inhibitory concentration (IC₅₀) were 1 mg.mL^-1 and 0.61 mg.mL^-1 (24 and 72 h of incubations) for the 0.50WTi composite.

Heterogeneous activation of H2O2/Na2S2O8 with iron ore from water distribution networks for pollutant removal

In this study, we investigated using the main composition of pipe deposits from water distribution networks as catalyst to activate dual-oxidant H₂O₂/Na₂S₂O₈ system to produce radicals for perchloroethylene and chloramphenicol removal. According to the results, the degradation efficiency of perchloroethylene by H₂O₂/Na₂S₂O₈ system was 92.05% within 8 h. Due to the slow conversion between ≡Fe³⁺ and ≡Fe²⁺, the hydroxylamine was introduced to reduce reaction time. As for the results, the degradation efficiency of chloramphenicol in the H₂O₂/Na₂S₂O₈ system with hydroxylamine assistance was 73.31% within 100 min. Meanwhile, several key affecting factors and the kinetic models were investigated. The primary radicals were identified by electron paramagnetic resonance and radical scavenging tests. Eleven degradation products were confirmed by high-resolution liquid chromatography-mass spectrometry. The result of this study provided the theoretical basis for resource utilization of pipe deposits in water treatment in case of emerging contamination events.

Photodegradation of chloramphenicol in micro-polluted water using a circulatory thin-layer inclined plate reactor

This study describes the photodegradation of chloramphenicol (CAP) in micro-polluted water with a thin-layer inclined plate reactor. Under simulated sunlight irradiation, the effect of reaction parameters including solution pH, initial CAP concentration, and co-existed humic acid (HA) or chloride was evaluated. The photodegradation of CAP was independent of initial pH in the range of 6.0-9.0, but sharply decreased by 25.5% with the increase of initial CAP concentration from 0.4 to 1.0 mg/L. The presence of HA exhibited a significant inhibitory effect, while Cl^- promoted the photoreaction. In this study, CAP was degraded through both direct and indirect photolysis, in which ¹O₂ was the main reactive species responsible for the indirect route. Its steady-state concentration in the micro-polluted water was determined to be 1.40 × 10^-13 mol/L. Transformation intermediates were identified to propose the degradation pathway of CAP, which substantially met the density functional theory (DFT) calculation results. Moreover, four other pharmaceuticals including tetracycline, doxycycline, oxytetracycline, and minocycline were also successfully photodegraded during 5 h irradiation. Therefore, the designed circulatory thin-layer inclined plate reactor is suggested to be effectively applied to the decontamination of organic micro-polluted water.

Treatment of hazardous organic amine wastewater and simultaneous electricity generation using photocatalytic fuel cell based on TiO2/WO3 photoanode and Cu nanowires cathode

Organic amines are regarded as high toxic, refractory chemicals due to the great damage on human body, and ecosystem. The treatment of organic amine wastewater involves the removal of total nitrogen and toxic organics simultaneously, which is one of the biggest difficulties in wastewater treatment. In this study, hazardous organic amine wastewater was purified by a photocatalytic fuel cell (PFC) with efficient nitrogen removal and organic degradation, and its chemical energy was recovered simultaneously based on hydroxyl radical (HO·) and chlorine radical (Cl·) reaction in a novel TiO₂/WO₃ and 3D Cu nanowires modified Cu foam (CuNWs/CF) system. TiO₂/WO₃ heterojunction as photoanode provided rapid charge separation and good stability, and the composite of poly-Si enhanced the light harvest and charge transfer. HO· played critical role in degrading organic amines, while Cl· was responsible for selectively oxidizing amine group or NH₄⁺ to N₂. Besides, trace amount of NO₂^- and NO₃^- formed by over-oxidation was eliminated on CuNWs/CF cathode due to large specific surface area and fast charge transfer. Moderate Cl^- concentration and initial pH had vital influence on strengthening Cl· and HO· generation in the system, and the optimal conditions were 50 mM NaCl and pH = 7. For methylamine, ethylamine and dimethylamine wastewater, the system showed total nitrogen removal efficiency of 94.93%, 91.81%, 93.10% and total organic carbon removal of 58.47%, 53.57%, and 56.71% within 2 h, respectively. Moreover, the corresponding maximum power densities of 2.49, 2.40, 2.27 mW cm^-2 were also generated, respectively. The study proposes an efficient, sustainable method for the treatment of hazardous organic amine wastewater and simultaneous energy recovery.

Catalytic ozonation of chloramphenicol with manganese-copper oxides/maghemite in solution: Empirical kinetics model, degradation pathway, catalytic mechanism, and antibacterial activity

The composite material of manganese-copper oxide/maghemite (Mn_xCu_yO_z/γ-Fe₂O₃) was synthesized by the co-precipitation-calcination method. With the initial concentration of 0.2 g/L Mn_xCu_yO_z/γ-Fe₂O₃ and 10 mg/L O₃, the chloramphenicol (CAP, 10 mg/L) could be completely degraded, which was about 2.22 times of that treated with ozonation alone. The contribution of O₃ and hydroxyl radical (•OH) for CAP degradation in the catalytic process was 6.9% and 93.1%, respectively. According to the effects of catalyst dosage, ozone dosage, and pH on the catalytic performance of Mn_xCu_yO_z/γ-Fe₂O₃, a predictive empirical model was developed for the ozonation with the Mn_xCu_yO_z/γ-Fe₂O₃ system. The HCO₃^-/CO₃^2- and phosphates in solution could inhibit the degradation of CAP with the inhibition ratios 8.45% and 13.8%, respectively. The HCO₃^-/CO₃^2- could compete with CAP and react with •OH, and the phosphates were considered as poisons for catalysts by blocking the surface active sites to inhibit ozone decomposition. The intermediates and possible degradation pathways were detected and proposed. The catalytic ozonation could effectively control the toxicity of the treated solution, but the toxicity was still not negligible. Furthermore, Mn_xCu_yO_z/γ-Fe₂O₃ could be easily and efficiently separated from the reaction system with an external magnet, and it possessed excellent reusability and stability.

2D/2D FeNi-layered double hydroxide/bimetal-MOFs nanosheets for enhanced photo-Fenton degradation of antibiotics: Performance and synergetic degradation mechanism

The photo-Fenton system exhibits great potential in environmental remediation. However, photo-Fenton process suffers from slow reaction kinetics, which is caused by the low yield of available charge carriers and active radicals. In this work, the 2D/2D FeNi-layered double hydroxide/bimetal-organic frameworks nanosheets (FeNi-LDH/BMNSs) photocatalyst was fabricated via an in-situ semi-sacrificial template strategy. The optimized FeNi-LDH/BMNSs + H₂O₂+Vis system showed excellent tetracycline hydrochloride (TC-HCl) removal rate of 95.76% in 60 min. Besides, the high TC-HCl degradation rates (above 80%) are obtained in a wide pH range and the total organic carbon (TOC) removal rate of 48.98% was remained after four cycles. Experiments and characterizations identified the fast catalysis process were ascribed to the synergetic effect between 2D/2D heterojunctions and Lewis acid sites with mixed-valence (Fe (III)/Ni (II)) in FeNi-LDH/BMNSs. As a result, the catalysis of H₂O₂ and the reduction of O₂ was accelerated by the continuous generation of Fe (II) and available photogenerated electrons, respectively, producing abundant active radicals including OH and O₂^-. Finally, this photo-Fenton system exhibited high removal rate to oxycycline, levofloxacin, norfloxacin and doxycycline and showed excellent performance for TC-HCl removal in different composed wastewater. The findings provide a new strategy towards creating 2D/2D active heterogeneous catalysts for photo-Fenton catalytic application.

Recent Progress and Prospects in Catalytic Water Treatment

Presently, conventional technologies in water treatment are not efficient enough to completely mineralize refractory water contaminants. In this context, the implementation of catalytic processes could be an alternative. Despite the advantages provided in terms of kinetics of transformation, selectivity, and energy saving, numerous attempts have not yet led to implementation at an industrial scale. This review examines investigations at different scales for which controversies and limitations must be solved to bridge the gap between fundamentals and practical developments. Particular attention has been paid to the development of solar-driven catalytic technologies and some other emerging processes, such as microwave assisted catalysis, plasma-catalytic processes, or biocatalytic remediation, taking into account their specific advantages and the drawbacks. Challenges for which a better understanding related to the complexity of the systems and the coexistence of various solid-liquid-gas interfaces have been identified.

Co/La modified Ti/PbO2 anodes for chloramphenicol degradation: Catalytic performance and reaction mechanism

Chloramphenicol (CAP) is widely used in daily life, and its abuse hurts human health, so a suitable method is needed to solve the problem. In this study, the Ti/PbO₂ electrodes prepared by the electroplating method were characterized. The CAP degradation effect and mechanism were investigated. It was shown that the electrode surface had a dense plating with a characteristic peak of β-PbO₂ as the active component. The electrode had an oxygen precipitation potential of 1.695 V and a corrosion potential of 0.553 V, and a long service life (505.4 d). The degradation of CAP at Ti/PbO₂ electrode followed a first-order kinetic reaction. The optimal degradation conditions (current density of 12.97 mA cm^-2, electrolyte concentration of 50 mM, and solution pH of 6.38) were obtained by the response surface curve method. The degradation rate of CAP was 99.0% at 60 min. The results showed that the reactive groups leading to CAP degradation were mainly ·OH and SO₄^2-, and only a tiny portion of CAP was directly oxidized on the electrode surface. The addition of Cl^- favored the degradation of CAP, but reduced the mineralization rate. LC-MS analysis showed that ·OH mainly attacked the asymmetric centers (C1, C2) of weakly bound hydrogen atoms, resulting in underwent addition and substitution reactions. CAP was converted into two substances with m/z = 306 and m/z = 165. Finally, inorganic substances such as CO₂ and H₂O were generated. This study provided a new idea for preparing Ti/PbO₂ electrode with high performance and the safe and efficient degradation of CAP.

Graphene oxide mediated Fe(III) reduction for enhancing Fe(III)/H2O2 Fenton and photo-Fenton oxidation toward chloramphenicol degradation

Slow reduction of Fe(III) in iron-mediated Fenton-like systems strongly limits the decomposition of H₂O₂ to produce hydroxyl radicals (^•OH). Here, we report that graphene oxide (GO) possesses excellent reactivity to enhance the Fe(III)/H₂O₂ Fenton and photo-Fenton oxidation for degrading chloramphenicol (CAP). EPR analysis and quenching tests reveal that ^•OH is the primary oxidant for CAP degradation. The characterization analysis and iron species transformation experiments demonstrate that Fe(III) can combine with the functional groups on the GO surface to form GO-Fe(III) complexes. The chronopotentiometry and cyclic voltammogram suggest that GO can donate electrons to Fe(III) via intramolecular electron transfer and promote H₂O₂ induced Fe(III) reduction by increasing the oxidation capability of Fe(III) due to the formation of GO-Fe(III) complexes, resulting in the strong promotion of the Fe(III)/Fe(II) cycle for producing OH. Moreover, the dark- and vis-GO/Fe(III)/H₂O₂ systems can effectively degrade CAP at initial pH ranging from 2.0 to 4.7. The reusability and stability of GO were evaluated by performing the cyclic degradation experiments of CAP. The OH induced degradation pathway of CAP was proposed involving three stages, based on intermediates analysis of UPLC-QTOF-MS/MS system. Therefore, the GO/Fe(III)/H₂O₂ system with or without visible light shows high potential for application in environmental remediation.

A review on non-thermal plasma treatment of water contaminated with antibiotics

Large amounts of antibiotics are produced and consumed worldwide, while wastewater treatment is still rather inefficient, leading to considerable water contamination. Concentrations of antibiotics in the environment are often sufficiently high to exert a selective pressure on bacteria of clinical importance that increases the prevalence of resistance. Since the drastic reduction in the use of antibiotics is not envisaged, efforts to reduce their input into the environment by improving treatment of contaminated wastewater is essential to limit uncontrollable spread of antibiotic resistance. This paper reviews recent progress on the use of non-thermal plasma for the degradation of antibiotics in water. The target compounds removal, the energy efficiency and the mineralization are analyzed as a function of discharge configuration and the most important experimental parameters. Various ways to improve the plasma process efficiency are addressed. Based on the identified reaction intermediates, degradation pathways are proposed for various classes of antibiotics and the degradation mechanisms of these chemicals under plasma conditions are discussed.

Dielectric barrier discharge plasma coupled with WO3 for bisphenol A degradation

Based on the difficulty of the refractory organic compounds degradation in water by the traditional wastewater treatment methods, the research relies on the technology of the dielectric barrier discharge plasma (DBDP) and the catalysis of the nano WO₃, investigating the bisphenol A (BPA) degradation in the synergistic system of DBDP/WO₃. The coupled degradation percentage of the BPA under different amounts of WO₃ addition, different initial solution pH and carrier gas were investigated to confirm the catalysis of the WO₃ in the DBDP system. It was obtained from the experimental results that the optimal additive amount of the WO₃ was 175 mg L^-1 and change of the solution pH value and the carrier gas variety could not change the catalysis of the WO₃. The BPA degradation percentage could reach 100% after treating 30 min in the DBDP/WO₃ system with 0.5 L min^-1 O₂ as the carrier gas. The WO₃ still had a better catalysis after four times usage and the discharge had little effect on the microstructure of the WO₃. The existence of the WO₃ in the DBDP system could result in the reduction of the O₃ concentration and the enhancement of the H₂O₂ concentration, which improve the catalysis of the WO₃ in the DBDP system, while the experiments on the scavengers' addition verified the major role of the OH on the BPA degradation. The catalytic mechanism of the WO₃ as well as the BPA degradation pathway was also speculated in the research.

In situ formation of 2-thiobarbituric acid incorporated g-C3N4 for enhanced visible-light-driven photocatalytic performance

Embedding heterocycles into the skeleton of g-C₃N₄ has been proved to be a simple and efficient strategy for improving light response and the separation of photo-excited charges. Herein, 2-thiobarbituric acid incorporated g-C₃N₄ (TBA/CN) with good photocatalytic efficiency for Rh B degradation and H₂ production was successfully achieved via a facile thermal copolymerization approach. The incorporation of aromatics and S atoms into the skeleton of g-C₃N₄ was identified via systematic characterizations. This unique structure contributed to the narrowed band-gap, extended delocalization of lone pair electrons and changed electron transition pathway, which led to the enhanced visible light utilization, accelerated charge migration and prolonged electron lifetime, subsequently resulting in the significant boost of photocatalytic activity. The optimal TBA/CN-3 sample yielded the largest Rh B degradation rate constant k value of 0.0273 min⁻¹ and simultaneously highest rate of H₂ evolution of 0.438 mmol g⁻¹ h⁻¹, which were almost 3.5 and 3.8 folds as fast as that of the pristine CN, respectively. Finally, the photocatalytic mechanism was proposed for the detailed elucidation of the process of Rh B degradation coupled with H₂ production.

Embedding heterocycles into the skeleton of g-C₃N₄ has been proved to be a simple and efficient strategy for improving light response and the separation of photo-excited charges.

Pulsed Discharge Plasma in High-Pressure Environment for Water Pollutant Degradation and Nanoparticle Synthesis

The application of high-voltage discharge plasma for water pollutant decomposition and the synthesis of nanoparticles under a high-pressure argon gas environment (~4 MPa) was demonstrated. The experiments were carried out in a batch-type system at room temperature with a pulsed DC power supply (15.4 to 18.6 kV) as a discharge plasma source. The results showed that the electrode materials, the pulsed repetition rates, the applied number of pulses, and the applied voltages had a significant effect on the degradation reactions of organic compounds. Furthermore, carbon solid materials from glycine decomposition were generated during the high-voltage discharge plasma treatment under high-pressure conditions, while Raman spectra and the HRTEM images indicated that titanium dioxide with a brookite structure and titanium carbide nanoparticles were also formed under these conditions. It was concluded that this process is applicable in practice and may lead to advanced organic compound decomposition and metal-based nanoparticle synthesis technologies.

Augmentation of chloramphenicol degradation by Geobacter-based biocatalysis and electric field

Electroactive microorganisms and electrochemical technologies have been separately used for environmental remediation such as antibiotics removal, yet the efficiency of coupling these two methods for chlorinated antibiotics removal is poorly known. Here we tested the synergy of Geobacter sulfurreducens PCA, an electroactive bacteria, and an electrical field, on chloramphenicol removal. Removal is increased two-fold by increasing the temperature from 30°C to 37°C. The cyclic voltammograms and chronoamperometry tests demonstrated that G. sulfurreducens PCA catalyzed chloramphenicol chemical reduction with electrode as excusive electron donor. A critical voltage, -0.6 to -0.5 V vs. Ag/AgCl, was discovered for chloramphenicol degradation with an increase of removal rate about 2.62-folds, from 31.06% to 81.41%. Combined removal with both G. sulfurreducens PCA and an electrical field increased the apparent rate constant and reached 82.77% removal at -0.5 V. Specially, the combined removal at -0.5 V even presented more robust removal efficiency compared to -0.6 V (78.64%) without G. sulfurreducens PCA. Mass spectrometry of degradation products indicates the reduction of nitro into amine groups, and dechlorination into less toxic compounds. Overall, combined biocatalysis and an electrical field is a promising method to remove antibiotics from polluted environments.

Enhanced visible light photoelectrocatalytic degradation of tetracycline hydrochloride by I and P co-doped TiO2 photoelectrode

Elimination of antibiotics such as tetracycline hydrochloride (TC) from wastewater is of great significance, but still faces challenges. Herein, for the first time, I and P co-doped TiO₂ catalysts were prepared via a hydrolysis method. We also reported a simple method to prepare I and P co-doped TiO₂ photoelectrodes, which exhibited preeminent photoelectrocatalytic (PEC) performance for the decomposition of TC. The synergistic effect of I and P co-doping could significantly improve the charge separation rate and enhance the light absorption capacity of TiO₂, leading to an enhancement of PEC activity. The main factors affecting the PEC performance were investigated, and the highest degradation rate constant (4.20 × 10^-2 min^-1) was achieved when the doping content of P was 4 at% (ITP-4 photoelectrode) at pH 11.02 under visible light. The Langmuir-Hinshelwood kinetic model and active species trapping experiments were selected to investigate the degradation mechanism of TC. The results suggest that the hydroxyl radicals and photogenerated holes were the main active species that were responsible for the decomposition of TC. Moreover, the degradation pathways of TC based on the intermediates also demonstrated that the hydroxyl radicals and holes showed a principal role in degrading TC.

Ultra-high synergetic intensity for humic acid removal by coupling bubble discharge with activated carbon

Humic acid (HA) removal research focuses on the global water treatment industry. In this work, efficient HA degradation with an ultra-high synergetic intensity is achieved by combined bubble discharge with activated carbon (AC). Adding AC to the discharge greatly improves HA removal efficiency and degradation speed; the synergetic intensity reaches 651.52% in the combined system, and the adsorption residual on AC is 4.52%. After 90 min of treatment, the HA removal efficiency reaches 98.90%, 31.29%, and 7.61% in the plasma-AC combined, solo bubble discharge, and solo AC adsorption systems, respectively. During the plasma process, the number of pore structures and active sites and the amount of oxygen-containing functional groups on the AC surface increase, resulting in a higher adsorption capacity to reactive species (H₂O₂ and O₃) and HA and promoting interactions on the AC surface. For HA mineralization, the presence of AC greatly promotes the destruction of aromatic structures and chromophoric HA functional groups.

Underwater microplasma bubbles for efficient and simultaneous degradation of mixed dye pollutants

Complete degradation of mixtures of organic pollutants is a major challenge due to their diverse degradation pathways. In this work, a novel microplasma bubble (MPB) reactor was developed to generate plasma discharges inside small forming bubbles as an effective mean of delivering reactive species for the degradation of the target organic contaminants. The results show that the integration of plasma and bubbles resulted in efficient degradation for all azo, heterocyclic, and cationic dyes, evidenced by the outstanding energy efficiency of 13.0, 18.1 and 22.1 g/kWh with 3 min of processing, in degrading alizarin yellow (AY), orange II (Orng-II) and methylene blue (MB), individually. The MPB treatment also effectively and simultaneously degraded the dyes in their mixtures such as AY + Orng-II, AY + MB and AY + Orng-II + MB. Scavenger assays revealed that the short-lived reactive species, including the hydroxyl (OH) and superoxide anion (O₂^-) radicals, played the dominant role in the degradation of the pollutants. Possible degradation pathways were proposed based on the intermediate products detected during the degradation process. The feasibility of this proposed strategy was further evaluated using other common water pollutants. Reduced toxicity was confirmed by the observed increases in human cell viability for the treated water. This work could support the future development of high performance- and energy-efficient wastewater abatement technologies.

Review on the treatment of organic wastewater by discharge plasma combined with oxidants and catalysts

Discharge plasma technology is a new advanced oxidation technology for water treatment, which includes the effects of free radical oxidation, high energy electron radiation, ultraviolet light hydrolysis, and pyrolysis. In order to improve the energy efficiency in the plasma discharge processes, many efforts have been made to combine catalysts with discharge plasma technology. Some heterogeneous catalysts (e.g., activated carbon, zeolite, TiO₂) and homogeneous catalysts (e.g., Fe²⁺/Fe³⁺, etc.) have been used to enhance the removal of pollutants by discharge plasma. In addition, some reagents of in situ chemical oxidation (ISCO) such as persulfate and percarbonate are also discussed. This article introduces the research progress of the combined systems of discharge plasma and catalysts/oxidants, and explains the different reaction mechanisms. In addition, physical and chemical changes in the plasma catalytic oxidation system, such as the effect of the discharge process on the catalyst, and the changes in the discharge state and solution conditions caused by the catalysts/oxidants, were also investigated. At the same time, the potential advantages of this system in the treatment of different organic wastewater were briefly reviewed, covering the degradation of phenolic pollutants, dyes, and pharmaceuticals and personal care products. Finally, some suggestions for future water treatment technology of discharge plasma are put forward. This review aims to provide researchers with a deeper understanding of plasma catalytic oxidation system and looks forward to further development of its application in water treatment.

Catalysis of rGO-WO3 nanocomposite for aqueous bisphenol A degradation in dielectric barrier discharge plasma oxidation process

Due to the multi-catalysis of the WO₃ and excellent properties of the graphene (GO), a series of rGO-WO₃ nanocomposites were prepared through the hydrothermal synthesis procedure by changing the material ratio, the reaction temperature and the reaction time in this paper, and then added it into a dielectric barrier discharge plasma (DBDP) system for investigating the bisphenol A (BPA)'s degradation and corresponding catalytic mechanism of the rGO-WO₃ in the DBDP system. The obtained results show that there was an optimum dosage of the rGO-WO₃ (40 mg/L) as well as the preparation conditions (5:1000 mass ratio of the GO and the WO₃, 18 h reaction time and 120 °C reaction temperature) for achieving the highest catalytic effect, and the highest degradation rate constant of the BPA was 0.03129 min^-1. The determined higher TOC removal, higher COD removal as well as UV-Vis analysis also demonstrated the catalysis of the rGO-WO₃. The measurement of the change of the O₃ and the H₂O₂ concentrations in the reaction system with or without the rGO-WO₃ and with or without the BPA proved the catalysis of the rGO-WO₃ on the ·OH formation, while the combination of the GO had the positive effect for enhancing the catalytic effect. A figure on the catalysis and degradation procedure of the BPA in the DBDP/rGO-WO₃ system was provided in the paper.

Non-Thermal Plasma Coupled with Catalyst for the Degradation of Water Pollutants: A Review

Non-thermal plasma is one of the most promising technologies used for the degradation of hazardous pollutants in wastewater. Recent studies evidenced that various operating parameters influence the yield of the Non-Thermal Plasma (NTP)-based processes. In particular, the presence of a catalyst, suitably placed in the NTP reactor, induces a significant increase in process performance with respect to NTP alone. For this purpose, several researchers have studied the ability of NTP coupled to catalysts for the removal of different kind of pollutants in aqueous solution. It is clear that it is still complicated to define an optimal condition that can be suitable for all types of contaminants as well as for the various types of catalysts used in this context. However, it was highlighted that the operational parameters play a fundamental role. However, it is often difficult to understand the effect that plasma can induce on the catalyst and on the production of the oxidizing species most responsible for the degradation of contaminants. For this reason, the aim of this review is to summarize catalytic formulations coupled with non-thermal plasma technology for water pollutants removal. In particular, the reactor configuration to be adopted when NTP was coupled with a catalyst was presented, as well as the position of the catalyst in the reactor and the role of the main oxidizing species. Furthermore, in this review, a comparison in terms of degradation and mineralization efficiency was made for the different cases studied.

Bioelectrochemical degradation of monoaromatic compounds: Current advances and challenges

Monoaromatic compounds (MACs) are typical refractory organic pollutants which are existing widely in various environments. Biodegradation strategies are benign while the key issue is the sustainable supply of electron acceptors/donors. Bioelectrochemical system (BES) shows great potential in this field for providing continuous electrons for MACs degradation. Phenol and BTEX (Benzene, Toluene, Ethylbenzene and Xylenes) can utilize anode to enhance oxidative degradation, while chlorophenols, nitrobenzene and antibiotic chloramphenicol (CAP) can be efficiently reduced to less-toxic products by the cathode. However, there still have several aspects need to be improved including the scale, electricity output and MACs degradation efficiency of BES. This review provides a comprehensive summary on the BES degradation of MACs, and discusses the advantages, future challenges and perspectives for BES development. Instead of traditional expensive dual-chamber configurations for MACs degradation, new single-chamber membrane-less reactors are cost-effective and the hydrogen generated from cathodes may promote the anode degradation. Electrode materials are the key to improve BES performance, approaches to increase the biofilm enrichment and conductivity of materials have been discussed, including surface modification as well as composition of carbon and metal-based materials. Besides, the development and introduction of functional microbes and redox mediators, participation of sulfur/hydrogen cycling may further enhance the BES versatility. Some critical parameters, such as the applied voltage and conductivity, can also affect the BES performance, which shouldn't be overlooked. Moreover, sequential cathode-anode cascaded mode is a promising strategy for MACs complete mineralization.