Degradation of levofloxacin in aqueous solution by non-thermal plasma combined with Ag3PO4/activated carbon fibers: Mechanism and degradation pathways

Insight on photocatalytic synchronous oxidation and reduction for pollutant removal: Chemical energy conversion between macromolecular organic pollutants and heavy metal

Collaborative treatment of pollutants is a promising approach for wastewater treatment. In this work, a covalent organic framework material (COFs) with an imine structure was synthesised by the Schiff base reaction, and photochemical tests showed good photochemical effects. It was used to explore the photocatalytic treatment of co-existing pollutants (heavy metal ions and antibiotics) and the performance of treating co-existing wastewater was investigated. The degradation performance of levofloxacin (LVX) and Cr(VI) was improved in the coexisting pollutants system, with the LVX degradation being 4.2 times more effective than that of the LVX solitary system. Moreover, this phenomenon was also observed in LVX/Ag(I), LVX/Fe(III), sulfadiazine/Cr(VI), norfloxacin/Cr(VI) and tetracycline/Cr(VI) systems. The analysis of active species suggesting that the synergistic promotion of photocatalytic oxidation-reduction systems was not only promoting from the improvement of simple charge separation, but it was also found that high-valent metal species can act directly in the oxidative decomposition of antibiotics. The interaction of pollutants and intermediates were rationally exploited and confirmed by control experiments and theoretical calculation. This conclusion helps us to re-examine the underlying mechanisms of photocatalytic synchronous oxidation and reduction reactions, simultaneously beneficial for the development of mixed pollutant control processes.

The Potential of Cold Atmospheric Pressure Plasmas for the Direct Degradation of Organic Pollutants Derived from the Food Production Industry

Specialized chemicals are used for intensifying food production, including boosting meat and crop yields. Among the applied formulations, antibiotics and pesticides pose a severe threat to the natural balance of the ecosystem, as they either contribute to the development of multidrug resistance among pathogens or exhibit ecotoxic and mutagenic actions of a persistent character. Recently, cold atmospheric pressure plasmas (CAPPs) have emerged as promising technologies for degradation of these organic pollutants. CAPP-based technologies show eco-friendliness and potency for the removal of organic pollutants of diverse chemical formulas and different modes of action. For this reason, various types of CAPP-based systems are presented in this review and assessed in terms of their constructions, types of discharges, operating parameters, and efficiencies in the degradation of antibiotics and persistent organic pollutants. Additionally, the key role of reactive oxygen and nitrogen species (RONS) is highlighted. Moreover, optimization of the CAPP operating parameters seems crucial to effectively remove contaminants. Finally, the CAPP-related paths and technologies are further considered in terms of biological and environmental effects associated with the treatments, including changes in antibacterial properties and toxicity of the exposed solutions, as well as the potential of the CAPP-based strategies for limiting the spread of multidrug resistance.

Exploring the Synergistic Mechanisms of Nanopulsed Plasma Bubbles and Photocatalysts for Trimethoprim Degradation and Mineralization in Water

In this study, the synergetic action of nanopulsed plasma bubbles (PBs) and photocatalysts for the degradation/mineralization of trimethoprim (TMP) in water was investigated. The effects of ZnO or TiO2 loading, plasma gas, and initial TMP concentration were evaluated. The physicochemical characterization of plasma-treated water, the quantification of plasma species, and the use of appropriate plasma species scavengers shed light on the plasma-catalytic mechanism. ZnO proved to be a superior catalyst compared to TiO2 when combined with plasma bubbles, mainly due to the increased production of ⋅OH and oxygen species resulting from the decomposition of O3. The air-PBs + ZnO system resulted in higher TMP degradation (i.e., 95% after 5 min of treatment) compared to the air-PBs + TiO2 system (i.e., 87%) and the PBs-alone process (83%). The plasma gas strongly influenced the process, with O2 resulting in the best performance and Ar being insufficient to drive the process. The synergy between air-PBs and ZnO was more profound (SF = 1.7), while ZnO also promoted the already high O2-plasma bubbles' performance, resulting in a high TOC removal rate (i.e., 71%). The electrical energy per order in the PBs + ZnO system was very low, ranging from 0.23 to 0.46 kWh/m3, depending on the plasma gas and initial TMP concentration. The study provides valuable insights into the rapid and cost-effective degradation of emerging contaminants like TMP and the plasma-catalytic mechanism of antibiotics.

Enhanced degradation and removal of ciprofloxacin and ofloxacin through advanced oxidation and adsorption processes using environmentally friendly modified carbon nanotubes

This study explores the utilization of adsorption and advanced oxidation processes for the degradation of ofloxacin (OFL) and ciprofloxacin (CIP) using a green functionalized carbon nanotube (MWCNT-OH/COOH-E) as adsorbent and catalyst material. The stability and catalytic activity of the solid material were proved by FT-IR and TG/DTG, which also helped to elucidate the reaction mechanisms. In adsorption kinetic studies, both antibiotics showed similar behavior, with an equilibrium at 30 min and 60% removal. The adsorption kinetic data of both antibiotics were well described by the pseudo-first-order (PFO) model. Different advanced oxidation processes (AOPs) were used, and the photolytic degradation was not satisfactory, whereas heterogeneous photocatalysis showed high degradation (⁓ 70%), both processes with 30 min of reaction. Nevertheless, ozonation and catalytic ozonation have resulted in the highest efficiencies, 90%, and 70%, respectively, after 30-min reaction. For AOP data modeling, the first-order model better described CIP and OFL in photocatalytic and ozonation process. Intermediates were detected by MS-MS analysis, such as P313, P330, and P277 for ciprofloxacin and P391 and P332 for ofloxacin. The toxicity test demonstrated that a lower acute toxicity was observed for the photocatalysis method samples, with only 3.1 and 1.5 TU for CIP and OFL, respectively, thus being a promising method for its degradation, due to its lower risk of inducing the proliferation of bacterial resistance in an aquatic environment. Ultimately, the analysis of MWCNT reusability showed good performance for 2 cycles and regeneration of MWCNT with ozone confirmed its effectiveness up to 3 cycles.

Effectively Controlled Structures of Si-C Composites from Rice Husk for Oxygen Evolution Catalyst

This work explores a simple way to regulate the morphology and structure of biomass-based carbon and effectively utilize its internal functional groups as the substrate for the next energy materials. The unique randomly oriented and highly interconnected cordyceps-like 3D structure of rice husk is formed by direct high-temperature carbonization, and the main component is SiC. The well-arranged cordyceps-like structure of SiC demonstrates a remarkable structural/chemical stability and a high rate of electron migration, and further could be used as a stable substrate for metal deposition and find application in the field of electrocatalysis. The oxygen evolution reaction catalyst (SiC-C@Fe3O4) prepared by chemical deposition exhibits a low overpotential (260 mV), low Tafel slope (56.93 mV dec-1), high electrochemical active surface area (54.92 mF cm-2), and low Rct value (0.15 Ω) at a current density of 10 mA cm-2 in 1 M KOH electrolyte. The produced natural Si-C composite materials overcome the limitations imposed by the intricate internal structure of silicon-rich biomass. The existence of this stable substrate offers a novel avenue for maximizing the utilization of rice-husk-based carbon, and broadens its application field. At the same time, it also provides a theoretical basis for the use of rice husks in the field of hydrogen production by electrolysis of water, thus promoting their high-value utilization.

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.

Study on low temperature plasma combined with AC/Mn + TiO2-Al2O3 catalytic treatment of sewage-containing polyacrylamide

With the introduction of tertiary oil recovery technology, polymer oil drive technology has effectively improved the recovery rate of crude oil, but the resulting oilfield wastewater-containing polyacrylamide (PAM) is viscous and complex in composition, which brings difficulties to wastewater treatment. The treatment of this kind of wastewater has become an urgent problem to be solved, and the removal of PAM is the key. In this paper, a dielectric barrier discharge (DBD) co-catalyst was used to treat PAM-containing solutions to investigate the effect of different catalytic reaction systems on the degradation of PAM. The morphological changes of the PAM solution before and after the reaction were also studied by the environmental electron microscope scanner (ESEM), and the information of the functional groups in the solution before and after the reaction was studied by infrared spectroscopy analysis of the PAM solution. The degradation rate rose by 26.3% in comparison to that without discharge when AC/Mn + TiO₂ and Al₂O₃ were combined and catalyzed at a mass ratio of 2:1 and a discharge period of 300 min. The degradation rate rose by 19.3 and 6.8%, respectively, in comparison to AC/Mn + TiO₂ and Al₂O₃-catalyzed alone. It demonstrates that this catalytic system has the optimum catalytic effect.

Degradation of ofloxacin by potassium ferrate: kinetics and degradation pathways

Drug residues, including various antibiotics, are being increasingly detected in aqueous environments. Ofloxacin (OFX) is one such antibiotic that is widely used in the treatment of several bacterial infections; however, chronic exposure to this antibiotic can have adverse impacts on human health. Hence, the identification of an effective OFX degradation method is essential. Thus, in this study, the degradation performance of OFX using potassium ferrate (Fe(VI)) under the influence of different initial concentrations, pH, temperature, and common ions in water was investigated. OFX degradation by Fe(VI) was directly proportional to the concentration of Fe(VI) and temperature and inversely proportional to the pH. Among the common ions in water, Fe³⁺ and NH₄⁺ could significantly promote the degradation of OFX by Fe(IV), while humic acid (HA) significantly inhibited it. Under the conditions of [Fe(VI)]:[OFX] = 15:1, T = 25℃, and pH = 7.0, the removal efficiency of 8 μM OFX reached more than 90% in 4 min. Seven intermediates were identified by quadrupole time-of-flight tandem ultra-performance liquid chromatography mass spectrometry (Q-TOF LC/MS), and two possible pathways for the degradation of OFX by Fe(VI) were proposed. Overall, the results suggest that advanced oxidation technology using Fe(VI) is effective for treating wastewater containing OFX.

A comprehensive review on recent advances toward sequestration of levofloxacin antibiotic from wastewater

Among various classes of antibiotics, fluoroquinolones, especially Levofloxacin, are being administered on a large scale for numerous purposes. Being highly stable to be completely metabolized, residual quantities of Levofloxacin get accumulated into the food chain proving a great global threat for aquatic as well as terrestrial ecosystems. Various removal techniques including both conventional and advanced methods have been reported for this purpose. This review is a novel attempt to make a critical analysis of the recent advances made exclusively toward the sequestration of Levofloxacin from wastewater through an extensive literature survey (2015-2021). Adsorption and advanced oxidation processes especially photocatalytic degradation are the most tested techniques in which assorted nanomaterials play a significant role. Several photocatalysts exhibited up to 100% degradation of LEV which makes photocatalytic degradation the best method among other tested methods. However, the degraded products need to be further monitored in terms of their toxicity. Biological degradation may prove to be the most environment-friendly with the least toxicity, unfortunately, not much research is reported in the field. With these key findings and knowledge gaps, authors suggest the scope of hybrid techniques, which have been experimented on other antibiotics. These can potentially minimize the disadvantages of the individual techniques concurrently improving the efficiency of LEV removal. Besides, techniques like column adsorption, membrane treatment, and ozonation, being least reported, reserve good perspectives for future research. With these implications, the review will certainly serve as a breakthrough for researchers working in this field to aid their future findings.

Sono-photo hybrid process for the synergistic degradation of levofloxacin by FeVO4/BiVO4: Mechanisms and kinetics

A novel FeVO₄/BiVO₄ heterojunction photocatalyst was synthesized by hydrothermal method. The FeVO₄/BiVO₄ nanostructures were characterized by XRD, SEM, XPS, UV-vis, and photoluminescence spectroscopy. The effects of catalyst dosage, contaminant concentration, initial hydrogen peroxide (H₂O₂) concentration, and pH value on the degradation of levofloxacin were investigated and several repeated experiments were conducted to evaluate the stability and reproducibility. The optimized process parameters were used for mineralization experiments. Reactive oxygen species, degradation intermediates, and possible catalytic mechanisms were also investigated. The results showed that the sonophotocatalytic performance of the FeVO₄/BiVO₄ heterojunction catalyst was better than that of sonocatalysis and photocatalysis. In addition, the Type II heterojunction formed by the material still had good stability in the degradation of levofloxacin after 5 cycles. The possible degradation pathway and mechanism of levofloxacin by sonophotocatalysis were put forward. This work develops new sono-photo hybrid process for potential application in the field of wastewater treatment.

Simultaneous degradation of glucocorticoids and sterilization using bubbling corona discharge plasma based systems: A promising terminal water treatment facility for hospital wastewater

Glucocorticoids (GCs) have drawn great concern due to their widespread contamination in the environment and application in treating patients with COVID-19. Due to the lack of data about GC removal using advanced treatment processes, a novel Paralleling and bubbling corona discharge reactor (PBCD) combined with iron-loaded activated-carbon fibre (Fe-ACF) was addressed in this study to degrade GCs represented by Hydrocortisone (HC) and Betamethasone (BT). The results showed that the PBCD-based system can degrade GCs effectively and can achieve effective sterilization. The removal rates of GCs were ranked as PBCD/Fe-ACF > PBCD/ACF > PBCD. The concentration of E. coli was reduced from 10⁹ to 10² CFU/mL after 60 min of PBCD-based system treatment. The abundance of bacteria in actual Hospital wastewater (HWW) was significantly reduced. Plasma changed the physical and chemical properties of ACF and Fe-ACF by etching axial grooves and enhancing stretching vibrations of surface functional groups, thus promoting adsorption and catalytic degradation. For GC degradation, the functional reactive species were identified as •OH, ¹O₂, and •O₂ radicals. Possible degradation pathways for HC and BT were proposed, which mainly included defluorination, keto acid decarboxylation, demethylation, intramolecular cyclization, cleavage and ester hydrolysis, indicating a reduction in GC toxicity. Since GCs are widely used in patients with COVID-19 and their wastewater needs to be sterilized simultaneously, the intensive and electrically driven PBCD-based system is promising in GC pollution control and sterilization in terminal water treatment facilities.

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.

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.

Removal of ammonia nitrogen and phenol by pulsed discharge plasma combined with modified zeolite catalyst

In this work, the removal of ammonia nitrogen and phenol by pulsed discharge plasma (PDP) and modified zeolite was investigated. The Fe-zeolite and Mn-zeolite catalysts were prepared by the impregnation method. Catalysts' morphology, specific surface area, and chemical bond structure were characterized. Based on the pollutants removal experiments, Fe-zeolite (0.01) in the PDP system had better catalytic oxidation of phenol and adsorption effect of ammonia nitrogen. The removal efficiency of the pollutants increased with the increase of discharge voltage and solution conductivity, but decreased with the increase of discharge distance. During the plasma discharge process, the pH value in the solution decreased, and the solution conductivity gradually increased. After PDP/Fe-zeolite system treatment, the toxicity of the wastewater was significantly reduced. This study provided a new treatment method for inorganic and organic pollutants treated by PDP.

Photocatalytic performance and interaction mechanism of reverse micelle synthesized Cu-TiO2 nanomaterials towards levofloxacin under visible LED light

The degradation performance of Cu-TiO₂ nanomaterials towards levofloxacin (LFX) antibiotic was investigated under an environmentally benign visible LED light source. Cu-TiO₂ nanomaterials were prepared using the reverse micelle sol-gel method with different copper content ranging from 0.25 to 1.0 wt% concerning titania. Characterization of Cu-TiO₂ samples was performed by XRD, TEM, UV-Vis, BET, ICP-MS, FTIR and XPS techniques. 0.5 wt% Cu-TiO₂ showed crystallite size below 6 nm, surface area (69.85 m²/g) and significant visible light absorption capacity. Both Cu¹⁺ and Cu²⁺ are formed in lower Cu-doped TiO₂ samples, whereas only Cu²⁺ is present in higher Cu-doped TiO₂ samples as evident in XPS analysis. 0.5 wt% Cu-TiO₂ has shown the optimum photocatalytic degradation of 75.5% under 6 h. of a visible light source. FTIR analysis of LFX adsorbed Cu-TiO₂ materials indicated the pollutant-catalyst interaction, where the declining trend was observed in photocatalytic degradation efficiency for higher Cu-doped TiO₂ samples due to copper-LFX complex formation. Copper-LFX complexes are formed due to the presence of Cu²⁺ in higher Cu-doped TiO₂ nanomaterials, which might have hindered the photocatalytic activity under visible light. Effects of initial pollutant concentration, catalyst loading and visible light intensity on the degradation of LFX are studied. Photocatalytic degradation pathways of LFX using best performing Cu-TiO₂ material were also proposed based on the LC-MS analysis.

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.

Degradation of aqueous methylparaben by non-thermal plasma combined with ZnFe2O4-rGO nanocomposites: Performance, multi-catalytic mechanism, influencing factors and degradation pathways

Non-thermal plasma (NTP) combined with zinc ferrite-reduced graphene oxide (ZnFe₂O₄-rGO) nanocomposites were used for the degradation of aqueous methylparaben (MeP). ZnFe₂O₄-rGO nanocomposites were prepared using the hydrothermal method, with the structure and photoelectric properties of nanocomposites then characterized. The effects of discharge power, initial MeP concentration, initial pH, and air flow rate on MeP degradation efficiency were investigated, and the multi-catalytic mechanism and MeP degradation pathways were established. Results showed that ZnFe₂O₄-rGO nanocomposites with a 10%:90% mass ratio of GO:ZnFe₂O₄ had an optimal catalytic effect. The MeP degradation efficiency of NTP combined with ZnFe₂O₄-rGO (10 wt%), was approximately 25% higher than that of NTP alone. Conditions favorable for MeP degradation included higher discharge power, lower MeP concentration, neutral pH value, and higher air flow rate. The degradation of MeP by NTP combined with ZnFe₂O₄-rGO nanocomposites followed pseudo-first-order kinetics. O₂^•-, •OH, H₂O_2, and O₃ were found to play important roles in the MeP degradation, as part of the multi-catalytic mechanism of NTP combined with ZnFe₂O₄-rGO nanocomposites. MeP degradation pathways were proposed based on the degradation intermediates detected by gas chromatography mass spectrometry, including demethylation, hydroxylation, carboxylation, ring-opening, and mineralization reactions. The prepared ZnFe₂O₄-rGO nanocomposites provide an approach for improved contaminant degradation efficiency, with reduced energy consumption in the NTP process.

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.