Plasma-catalytic degradation of ciprofloxacin in aqueous solution over different MnO2 nanocrystals in a dielectric barrier discharge system

Interpretation of adsorption isotherm and kinetics behind fluorene degradation

The gradual release of slow-degrading polycyclic aromatic hydrocarbons into the environment creates a high level of threat to aquatic and terrestrial life worldwide. Remediation of these PAHs should be designed in such a way that it poses as few or no environmental hazards as possible. In our study, we examined the degradation ability of the synthesized MnO2 nanoparticles against fluorene. The MnO2 nanoparticle prepared was found to be spherical from the SEM analysis. XRD analysis confirms the average crystallite size as 31.8652 nm. Further, the characterization of nanoparticles was confirmed by UV-DRS, FT-IR, DLS, and HPLC techniques. The extent of adsorption potential of the synthesized nanoparticles was established from the batch adsorption studies and the kinetic and isotherm model was interpreted. The antimicrobial properties of the synthesized MnO2 nanoparticles were analyzed.

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.

Eliminating ciprofloxacin antibiotic contamination from water with a novel submerged thermal plasma technology

Thermal plasma is successfully used to degrade the model pharmaceutical wastewater ciprofloxacin (CIP) under submerged operating conditions at atmospheric pressure. The model aqueous solution is prepared for two different concentrations (10 and 25 mg/L) and treated separately at 7 kW discharge power with two different plasma-forming gas compositions, Ar/Air and Ar/CO₂. A direct current (DC) hollow cathode plasma torch produces a thermal plasma jet inside the solution. The effect of plasma gas compositions on the CIP degradation process is investigated, and the corresponding degradation and mineralisation efficiencies for different treatment times are systematically compared using high-performance liquid chromatography (HPLC) and total organic carbon (TOC) analysis, respectively. Submerged Ar/CO₂ plasma shows higher degradation and mineralisation efficiency than the Ar/Air plasma. Energy yields of 74.32 mg/kWh and 176.98 mg/kWh are achieved for a 5-min treatment by Ar/CO₂ submerged thermal plasma at concentrations of 10 mg/L and 25 mg/L, respectively. The degradation of CIP by submerged plasma shows a resemblance with first-order reaction kinetics having reaction rates 0.149 min^-1 and 0.073 min^-1 for Ar/CO₂ and Ar/Air, respectively. Density Functional Theory (DFT) calculations are used to identify the various reactive sites on CIP, and the results are consistent with the formation of various intermediates detected through liquid chromatography-mass spectrometry (LC-MS) analysis. These findings suggest that reactive species formed through thermal and photochemical processes in submerged thermal plasma play a significant role in the degradation of CIP. This study also offers a possible way of using CO₂ gas in wastewater treatment using submerged thermal plasma.

Enhanced degradation of oxytetracycline in aqueous solution by DBD plasma-coupled vacuum ultraviolet/ultraviolet (VUV/UVC) system

A systematic investigation of coupling dielectric barrier discharge (DBD) plasma and different ultraviolet bands (UVA, UVB, UVC, and VUV) was constructed for antibiotic-contaminant wastewater treatment. Compared with DBD, UV, or other combined DBD/UV systems, the DBD/VUV/UVC system exhibited excellent degradation and mineralization efficiencies for oxytetracycline (OTC), achieving 93.2% removal rate (reaction rate constant 1.05 min^-1) and higher decarbonization efficiency (mineralization rate 0.47 mg C min^-1) within 2.5 min treatment. The radical quenching tests revealed that HO⋅, [Formula: see text] , and ¹O₂ were all involved in the decomposition of OTC in the DBD/VUV/UVC system, among which [Formula: see text] played a dominant role. Possible degradation pathways of OTC in the DBD/VUV/UVC process were proposed using density functional theory and detected intermediates. Four indexes were used to assess the toxicity of OTC and its degraded intermediates. The inorganic anions and HA slightly reduced the degradation efficiency of the DBD/VUV/UVC system. This research provides new ideas to broaden the application of plasma and alleviate the water environment crisis.

Degradation of ciprofloxacin in aqueous solution using ozone microbubbles: spectroscopic, kinetics, and antibacterial analysis

Ciprofloxacin (CIP) has been listed in the last version of the surface water due to its ability to kill human cells by inhibiting the activity of DNA topoisomerase IV. Thus, CIP, along with other antibiotic pollution has become a serious threat to the environment and public health. Ozonation has been used as an advanced technique that is applied in wastewater treatment to remove CIP, but the primary limitation of this method is the low solubility of ozone in water. This study is the first report of CIP removal in a scale-up of its aqueous solution using a self-developed aerator pump-enhanced ozonation (APO) system, which only employs a propeller and a zigzag arrangement of meshes. This aerator pump decreased the size of ozone bubbles by 90% and increased the effective ozone solubility to 0.47 ppm. The mechanism of degradation of CIP is attributed to an oxidation reaction of the antibiotic with reactive oxygen species, such as hydroxyl, oxygen, and hydroperoxyl radicals, generated on the surface of the ozone microbubbles. It was found that the rate and efficiency of degradation of CIP using the APO system were 3.64 × 10⁻³/min and 83.5%, respectively, which is higher compared with those of conventional flow ozonation (FO) systems (1.47 × 10⁻³/min and 60.9%). The higher degradation efficiency of CIP by the APO system was also revealed by its higher electrical energy efficiency (0.146 g/kWh), compared to that of the FO system (0.106 g/kWh). The degradation of CIP was also monitored by the resulting antibacterial activity against Escherichia coli and Staphylococcus aureus.

Recent Advances of Emerging Organic Pollutants Degradation in Environment by Non-Thermal Plasma Technology: A Review

Emerging organic pollutants (EOPs), including endocrine disrupting compounds (EDCs), pharmaceuticals and personal care products (PPCPs), and persistent organic pollutants (POPs), constitute a problem in the environmental field as they are difficult to completely degrade by conventional treatment methods. Non-thermal plasma technology is a novel advanced oxidation process, which combines the effects of free radical oxidation, ozone oxidation, ultraviolet radiation, shockwave, etc. This paper summarized and discussed the research progress of non-thermal plasma remediation of EOPs-contaminated water and soil. In addition, the reactive species in the process of non-thermal plasma degradation of EOPs were summarized, and the degradation pathways and degradation mechanisms of EOPs were evaluated of selected EOPs for different study cases. At the same time, the effect of non-thermal plasma in synergy with other techniques on the degradation of EOPs in the environment was evaluated. Finally, the bottleneck problems of non-thermal plasma technology are summarized, and some suggestions for the future development of non-thermal plasma technology in the environmental remediation were presented. This review contributes to our better understanding of non-thermal plasma technology for remediation of EOPs-contaminated water and soil, hoping to provide reference for relevant practitioners.

Size effect of γ-MnO2 precoated anode on lead-containing pollutant reduction and its controllable fabrication in industrial-scale for zinc electrowinning

Lead (Pb) is the most widely used anode in zinc (Zn) electrowinning and other metallurgical industries. The resource loss and environmental pollution caused by Pb anode corrosion are urgent problems to be solved. A γ-MnO₂ precoated anode was prepared successfully to reduce the Pb-containing pollutant. The size effects with its controllable preparation on an industrial scale were studied. Severe nonuniform distribution of γ-MnO₂ film was observed with curbing the reduction of anode slime only 68%, when anode size increased from lab to industry. Nonuniform rate (R) and average thickness (d) were found to be the key indicators to determine the film structure distribution and their performance differences, which were random and difficult to be controlled in scale-up size. However, a controllable industrial γ-MnO₂ precoated anodes (IMPA) fabricated through optimized current density (J₀) and electrodeposition time (t) in our developed film-forming system. Then, the long-term performances of two IMPA with different indicators (IMPA-1: R = 34%, d = 108 μm, IMPA-2: R = 23%, d = 55 μm) were compared with the industrial typical Pb-based anode (ITPA). Of the three different anodes, the optimized IMPA-2 displayed the best performance. Within 24 d of electrowinning cycle, the corrosion inhibition effect and the anode slime reduction rate for IMPA-2 improved by 56% and 30% than IMPA-1, and improved by 100% and 91% than ITPA. Furthermore, the mechanism analysis of size effect change showed that R of IMPA was contributed to the local gas holdup distribution along the anode. Controlled size effect of uniform oxide film will have a future application prospect for the sustainability of industry, which provides an important cleaner production of Zn electrowinning and related hydrometallurgy industries.

Degradation of tetracycline hydrochloride in aqueous via combined dielectric barrier discharge plasma and Fe-Mn doped AC

Dielectric barrier discharge (DBD) plasma coupled with Fe-Mn doped AC (Fe-Mn/AC) was used to enhance the degradation of tetracycline hydrochloride (TCH) wastewater. Fe-Mn/AC catalysts with different Fe/Mn molar ratios were prepared by hydrothermal method, and the physical and chemical properties of the samples were explored by different characterization techniques, including XRD, SEM, TEM and XPS. The results showed that the combination of DBD with Fe₂-Mn₁/AC system had the highest effect, and the degradation efficiency of TCH could reach 98.8 % after 15 min treatment, which was 25.5 % higher than that of DBD-only. With the increase of discharge voltage and catalyst dosage, the degradation efficiency of TCH promoted. And initial pH had little effect on the degradation of TCH. In the combined system, the Fe₂-Mn₁/AC catalyst could retain an excellent stability and reusability. The addition of dimethyl sulfoxide (DMSO) showed that ·OH participated in the TCH degradation. The generated O₃ might be catalyzed by Fe-Mn/AC catalyst to produce more ·OH. And more H₂O₂ was produced in DBD-only system than that in DBD-catalytic system. Nine main degradation intermediate products in the combined system were detected by HPLC-MS, and three possible degradation pathways were proposed.

Degradation pathways of penthiopyrad by δ-MnO2 mediated processes: a combined density functional theory and experimental study

Penthiopyrad is a widely used succinate dehydrogenase inhibitor (SDHI) fungicide and frequently detected in natural environments. In order to better understand its fate in natural systems, the degradation of penthiopyrad by manganese dioxide (MnO₂) was investigated in this study. The results show that penthiopyrad is rapidly degraded in the δ-MnO₂ system. Moreover, density functional theory (DFT) calculations reveal that the atoms of C18, C12, and S1 in penthiopyrad have relatively high reactive active sites. The degradation products mainly include sulfoxides, sulfones, and diketone. A sulfoxide and sulfone are formed by the oxidation of the thioether group, and diketone is formed by the oxidation of the olefin group, respectively. Based on the DFT calculations and degradation products, the degradation pathway of penthiopyrad by MnO₂ is proposed. This study also reveals that the degradation of penthiopyrad by δ-MnO₂ is affected by various environmental factors. A warm environment, low pH, and co-existing humic acid are beneficial to the degradation of penthiopyrad in the δ-MnO₂ system, whereas, co-existing metal cations inhibit penthiopyrad degradation. This result provides theoretical guidance for predicting the potential fate of penthiopyrad in natural environments.

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.

Catalytic degradation of caffeic acid by DBD plasma and Mn doped cobalt oxyhydroxide catalyst

In this study, caffeic acid (CA) was degraded by electrical discharge plasma combined with Mn doped CoOOH catalyst. Doping of Mn significantly improve the catalytic activity of CoOOH. CA degradation efficiency was 75.6% with dielectric barrier discharge treatment for 10 min, and it reached 97% using CoOOH as the catalyst at the same treatment time. CA was 100% degraded with only 8 min using Mn/CoOOH as the catalyst. The introduction of Mn into the lattice of CoOOH induced the formation of oxygen vacancy, causing part of coordinate number of Co decreased from 6 to 5, and thus produces unsaturated Co to be the Lewis acid sites. Lewis acid sites (unsaturated Co) could coordinate with O₃ and H₂O₂ and break their chemical bonds to form O and -OH. Assisting in the conversion of O₃ to ·OH was the main role of H₂O₂ in the catalytic process. The degradation products and pathway of CA were studied by three-dimensional fluorescence, liquid chromatograph-mass spectrometer and density functional theory calculations.

MnO2 -Based Materials for Environmental Applications

Manganese dioxide (MnO₂ ) is a promising photo-thermo-electric-responsive semiconductor material for environmental applications, owing to its various favorable properties. However, the unsatisfactory environmental purification efficiency of this material has limited its further applications. Fortunately, in the last few years, significant efforts have been undertaken for improving the environmental purification efficiency of this material and understanding its underlying mechanism. Here, the aim is to summarize the recent experimental and computational research progress in the modification of MnO₂ single species by morphology control, structure construction, facet engineering, and element doping. Moreover, the design and fabrication of MnO₂ -based composites via the construction of homojunctions and MnO₂ /semiconductor/conductor binary/ternary heterojunctions is discussed. Their applications in environmental purification systems, either as an adsorbent material for removing heavy metals, dyes, and microwave (MW) pollution, or as a thermal catalyst, photocatalyst, and electrocatalyst for the degradation of pollutants (water and gas, organic and inorganic) are also highlighted. Finally, the research gaps are summarized and a perspective on the challenges and the direction of future research in nanostructured MnO₂ -based materials in the field of environmental applications is presented. Therefore, basic guidance for rational design and fabrication of high-efficiency MnO₂ -based materials for comprehensive environmental applications is provided.

Broad-spectrum response NCQDs/Bi2O2CO3 heterojunction nanosheets for ciprofloxacin photodegradation: Unraveling the unique roles of NCQDs upon different light irradiation

N-doped carbon quantum dots (NCQDs) decorated Bi₂O₂CO₃ heterojunction nanosheets have been successfully constructed by a facile hydrothermal method. The obtained NCQDs/Bi₂O₂CO₃ heterojunction exhibits a wide-spectrum absorption ability and remarkably enhanced photocatalytic activities for ciprofloxacin photodegradation from ultraviolet to near-infrared region. The critical roles of NCQDs and two different charge separation and transfer processes of NCQDs/Bi₂O₂CO₃ heterojunction under different light irradiations have been elucidated. Upon UV light irradiation, NCQDs act as electron reservoirs and a Z-scheme charge transfer process between Bi₂O₂CO₃ and NCQDs promotes electrons transfer and •O₂^- reactive species generation. Under visible and NIR light irradiation, NCQDs act as photosensitizer (hole reservoirs) to harvest solar light and a type-II heterojunction leads to an efficient charge carrier separation and thus high catalytic ability. The mechanisms and pathways of ciprofloxacin degradation driven by different lights are discussed accordingly. This work provides a versatile pathway to well design an efficient wide-spectrum response photocatalyst.

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.