Organic Pollutants Research Articles

Three-dimensional porous SiC/BDD electrode with long-term robustness and enhanced electrochemical degradation performance for refractory organic pollutants

Boron-doped diamond (BDD) electrodes with a three-dimensional (3D) porous network structure can overcome the mass transfer limitations and increase substantially the utilization rate of active oxygen species. Nonetheless, the 3D porous network structure was invariably built using metallic substrates, which inherently have inferior stability because of their non-corrosion resistance and the severe thermal mismatch between BDD films and substrates. Herein, we reported, for the first time, the use of a commercially porous silicon carbide (SiC) as the substrate to construct a 3D SiC/BDD electrode to simultaneously alleviate the problematics of substrate corrosion and thermal mismatch. This novel electrode exhibited a long-term service lifetime of 800 h in 3 M H2SO4 under the current density of 50 mA cm−2, over 500 times longer than the conventional metallic substrate-based BDD electrodes. The optimum p-SiC/BDD electrode exhibited a high oxygen evolution potential of 2.04 V vs. SHE, a low charge transfer resistance of 18.4 Ω, a high mass transfer coefficient of 2.78 × 10−5 m s−1, and a thin diffusion layer thickness of 25.2 μm. The proposed electrode had a threefold larger pseudo-first-order reaction rate constant than a flat BDD electrode, although it consumed just a fourth of the latter’s electric energy. The superior performance was attributable to an increased mass transfer rate confirmed by computational fluid dynamics (CFD) simulations as well as a high yield of reactive oxygen species verified by electron spin resonance (ESR). Furthermore, the proposed SiC/BDD electrode could work effectively under different water matrices in the presence of diverse salt electrolytes, thus paving a new avenue for the structure design of robust non-active anode materials.

CO2(OH)2CO3 and Fe doped Co2(OH)2CO3 prepared as efficient and stable catalysts for activation of PMS: Two systems comparison and key role of high-valent metal-oxo species in mechanism revealing

High-valent metal-oxo species [M(IV) = O] exhibited high selectivity and chemical efficiency in advanced oxidation processes for removing organic pollutants, making their manipulation essential in catalytic systems. However, the low and unsustainable efficiency of generating M(IV) = O posed significant challenges. In this research, Co2(OH)2CO3 were successfully prepared via a one-pot hydrothermal method to efficiently activate peroxymonosulfate (PMS) with high-valent cobalt-oxo species [Co (IV) = O] as the primary active oxidation species. Building upon this foundation, COC was modified through variations in metal types and elemental ratios, in which magnetically enriched FexCo2-x(OH)2CO3 was synthesized by gradient Fe doping with higher catalytic efficiency and stability. The insertion of Fe resulted in the lengthening of the Co-O bond and improved the valence distribution of cobalt on the COC surface. Besides, it enabled part of the electrons to be transferred from the Fe active center to the Co active center, breaking the limitation of the traditional two-electron transfer and realizing the stable generation of more high-valent metals. Both reaction systems achieved efficient degradation of sulfadimethoxine (SDM) within 30 min and were able to completely degrade SDM within 30 min even after three cycles. FexCo2-x(OH)2CO3 maintained excellent catalytic performance even after 30 days of exposure to air. In both systems, high-valence metals played a dominant role, while the contributions of hydroxyl radicals and sulfate radicals were negligible. Overall, the two groups of developed catalysts both showed remarkable stability and pollutant removal performance in anions, humic acid, Different antibiotics and real water systems, which provided a new perspective on antibiotic removal.

Determination of three dechloranes in environmental water by magnetic solid-phase extraction-gas chromatography-negative chemical ionization mass spectrometry based on the covalent organic framework material

Dechloranes are additive-type chlorine flame retardants that are widely used in processing industrial products, such as electronic equipment and textiles. Dechloranes, which can enter the human body through various routes, pose significant health risks because of their toxicity, persistence, and bioaccumulation. In 2023, dechlorane plus was listed in the Stockholm Convention on Persistent Organic Pollutants. In the same year, China recognized this compound as a priority-controlled substance. Dechloranes are commonly found at trace levels in water, which is extremely harmful to the environment and human health. Therefore, the development of detection methods for dechloranes is crucial. Magnetic solid-phase extraction (MSPE) has attracted considerable attention because of its low organic solvent consumption, simplicity of adsorbent separation, and ease of operation. In general, the selectivity and efficiency of MSPE depend on the characteristics of the adsorbent. Covalent organic frameworks (COFs) have regular porosity, structural predictability and stability, high specific surface areas, and adjustable pore sizes, which are advantageous for a wide range of separation and analysis applications. In this study, Fe3O4 magnetic nanoparticles and a COF material (TpBD) were combined to prepare Fe3O4@TpBD as an adsorbent for dechloranes. Subsequently, an effective method for analyzing dechlorane in environmental water was established by coupling MSPE with gas chromatography-negative chemical ionization mass spectrometry (GC-NCI/MS). The successful synthesis of Fe3O4@TpBD was confirmed using transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and vibrating sample magnetometry. A single-factor method was used to optimize the extraction conditions, including the Fe3O4@TpBD dosage, pH of water sample, elution solvent type and volume, extraction time, elution time, and ionic strength. The target analytes were separated on a TG-5SILMS column (30 m×0.25 mm×0.25 μm) and quantified using the external standard method in the selected-ion monitoring (SIM) mode. Under the optimal extraction conditions, the method validation results showed a linear range of 2-1000 ng/L. The limits of detection (LODs) and quantification (LOQs) were 0.18-0.27 ng/L and 0.60-0.92 ng/L, respectively, for the three analytes. The intra-day and inter-day precisions at three spiked levels were 4.2%-16.2% and 6.9%-15.7%, respectively. This method was successfully applied to the determination of dechloranes in environmental water samples (laboratory tap water, reservoir water, wastewater treatment plant effluent, and landfill leachate treatment effluent). The recoveries of the three dechloranes at different spiked levels ranged from 77.8% to 113.3% with relative standard deviations (RSDs) of 2.5%-16.3% (n=3). With the advantages of operational simplicity, high sensitivity, and good reproducibility, the proposed method is suitable for the qualitative and quantitative determination of dechloranes in environmental water.

Emerging Organic Pollutant Detection, Classification, and Quantification Using a LED Spectrofluorimeter and Decision Trees

Emerging Organic Pollutant Detection, Classification, and Quantification Using a LED Spectrofluorimeter and Decision Trees

Micro-Nano Bubbles in Action: AC/TiO2 Hybrid Photocatalysts for Efficient Organic Pollutant Degradation and Antibacterial Activity

Developing highly active and sustainable photocatalysts is crucial for environmental remediation. This work focuses on the enhanced photocatalytic degradation efficiency of synthetic dyes using TiO2-coated AC hybrid photocatalysts under MNB aeration. The TiO2-coated AC hybrid photocatalyst (HP) was synthesized via a sol-gel method and characterized using XRD, FTIR, SEM, EDS, HR-TEM, and DRS. The study investigated the photocatalytic degradation of three dyes indigo carmine (IC), reactive black 5 (RB5), and methylene blue (MB) in wastewater, with initial dye concentrations ranging from 10 to 100 μM. Under UVA irradiation, the hybrid photocatalyst with MNB aeration (HP+UVA+MNB) achieved the highest degradation efficiencies of 69.09%, 60.06%, and 55.19% for IC, MB, and RB5, respectively. Further analysis showed that the chromophores and complex structures of these dyes were broken into intermediate products. The Langmuir-Hinshelwood kinetic model was used to describe the reaction mechanisms. The HP+UVA+MNB system demonstrated superior photocatalytic degradation activity, making it suitable for operational and environmental applications in dye wastewater treatment. Additionally, the antibacterial properties of AC and HP were tested at 100 μg/mL, showing effectiveness against both Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli.

Sequential adsorption- dehalogenation removal of PFOA and 2,4,6-TCP with F-CTF as the adsorbent and hydrated electron as the reduction species

Perfluorooctanoic acid (PFOA) and 2,4,6-trichlorophenol (2,4,6-TCP) were typical POPs (Persistent Organic Pollutants) in water. In this study, fluorine-doped covalent triazine framework (F-CTF) was synthesized using an ionothermal method, and the adsorption behavior for PFOA and 2,4,6-TCP on F-CTF was investigated using batch experiments and adsorption kinetic tests. Characterization results showed that the large surface area and abundant pore structure of F-CTF provide a large number of adsorption sites for PFOA and 2, 4, 6-TCP. Batch adsorption tests showed that F-CTF adsorbent exhibited high adsorption affinity to PFOA and 2,4,6-TCP, and the adsorption ability could be described well by the Langmuir adsorption model. The maximum adsorption capacity (qmax) of F-CTF for PFOA and 2,4,6-TCP reached 262.5mg/g and 709.2mg/g, respectively. The adsorption process obeyed the pseudo-second-order kinetics. The adsorption mechanism including electrostatic attraction, hydrophobic interaction, and ion-dipole interaction was further confirmed by pH and ionic strength experiments. Additionally, the UV/Na2SO3/KI system achieved 100% degradation rate of PFOA and 2, 4, 6-TCP within 40minutes and the influence factors were further studied. The eaq− was the main active species for the high reduction of PFOA and 2,4,6-TCP in the UV/Na2SO3/KI system.

Facile green synthesis of Sm2O3@g–C3N4 for enhanced photocatalytic and catalytic degradation of organic pollutant

Facile green synthesis of Sm2O3@g–C3N4 for enhanced photocatalytic and catalytic degradation of organic pollutant

Micro-plastics in soil environment: A review

Environmental scientists and other stakeholders have paid serious attention to soil pollution by microplastics in the last ten years. In soils, the microplastic particles act as a vector for the toxic persistent organic pollutants and potentially toxic metals that are easily sorbed by plants and enter the food chain. Microplastics are emerging as persistent terrestrial pollutants due to mismanagement and indiscriminate use. Microplastic contaminants affect the physicochemical characteristics of the soil as well as the feeding patterns of the soil biota. Sewage sludge, bio waste compost additions, plastic mulching, wastewater irrigation, landfill leachate, and air deposition are the causes of microplastics in soils. The amount of microplastics particles per kilogram of soil ranged from zero to thirteen thousand pieces. There are 523 times as many microplastic particles in the soil as there are in the ocean. Plant growth and seed germination are slowed down by the microplastic in the soil. Microplastics also affect the soil's enzymatic activities. The environmental sources of microplastic include plastic pellets, city dust, abrasion of road markings, tires, synthetic textiles, personal care products, and cosmetics. Human consumption through food can have a variety of harmful effects, including cytotoxicity, immunotoxicity, pulmonary toxicity, and reproductive toxicity. The current study describes the origins, distribution, and effects of microplastics on plants, soil biota, and human health in the soil environment. Bangladesh J. Nuclear Agric, 38(1): 1-19, 2024

Interpreting the removal behaviours of aniline and 3,4-diaminotoluene on aromatic carbon-rich magnetic polymer: Statistical modelling, DFT quantitative calculations and new perspectives

The widespread presence of harmful and stubborn amine organic contaminants in aquatic environments motivated the exploration of efficient technologies for alleviating their serious environmental crisis. Herein, the recyclable magnetic Schiff base polymer (Fe3O4-TENE) with satisfactory and promising capacity in treating aniline and 3,4-diaminotoluene as representative amine organic contaminants was fabricated via a simple in-situ polymerization method, which combined the magnetic separability advantage of magnetic oxides with the abundant aromatic carbon content properties of Schiff base polymer. Multiple characterization methods verified the effectiveness of the in-situ polycondensation coating reaction and analyzed the physicochemical properties of Fe3O4-TENE. The Fe3O4-TENE possessed abundant homogeneous reaction sites and excellent regeneration performance, multiple diffusion driving forces and micro-mechanisms co-participated in the removal reaction. The adsorption pathway, underlying reaction mechanism and the most probable bonding system were identified based on the statistical modelling and DFT quantitative calculations. Especially, the visible electrostatic potential molecular and molecular orbitals verified the π-π interaction and electrostatic forces greatly contributed to the removal reaction. The Driving forces – Challenges – Breakthrough – Application framework was proposed for comprehensively assessing the possible environmental application of Fe3O4-TENE. Overall, this work not only provides important insights into the utilization of magnetic polymer composite to alleviate ecological and environmental risks caused by amine organic pollutants, but also contributes to an in-depth excavation of the bonding types and removal mechanisms from both micro and macro perspectives.

Kinetics of the Decomposition of Reactive Black 5 on Carbon Nanostructured Adsorbents

Textile industry effluents, containing vast quantities of toxic organic pollutants and synthetic dyes like Reactive Black 5 (RB5), pose a significant environmental threat. RB5 contamination can harm ecosystems and human health, necessitating effective treatment for water recycling and compliance with quality standards. Traditional methods like filtration often fall short in removing dye chemicals. This study examines the efficiency of nanocarbon-based adsorbents in removing RB5 from textile industry effluents. RB5 solutions at concentrations of 10 µM, 30 µM, 60 µM and 100 µM were investigated and characterized using scanning electron microscopy (SEM) and UV-Vis spectrophotometry. Activated carbon (AC) demonstrated the highest degree of RB5 decomposition, outperforming graphene nanoplatelets (GNPs) and graphene oxide (GO) and offering a promising solution for mitigating textile wastewater pollution. Kinetic studies revealed that RB5 adsorption follows a pseudo-second-order model for all adsorbents. The rate constants were determined using PSO kinetics and they were comparable with the rate constants of prior studies, indicating the applicability of the model to the study of the kinetics of similar dye adsorption and decomposition processes.

An overview on analytical methods and the occurrence of organic pollutants in cigarette litter

Cigarette litter, such as cigarette ash, cigarette butts, and cigarette butt leachates, can contain organic pollutants similar to those in cigarette smoke, but studies on these waste types are still relatively limited. This review article compiles information from studies published over the past four decades on organic pollutants in cigarette ash, cigarette butts, and leachates from cigarette butts, to provide insights into quantitatively analytical methods and the presence of these toxicants in cigarette litter. The main organic pollutants found in cigarette litter include: volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs), polycyclic aromatic hydrocarbons (PAHs), nicotine, and aromatic amines. Gas chromatography or liquid chromatography coupled with mass spectrometry detection have been the most frequently used methods to characterize organic pollutants in cigarette litter. Toxic substances in improperly disposed cigarette waste can pollute the environment through evaporation into the air or leakage through leachates into the water environment, seepage into soil, accumulate in sediment, and cause negative effects on organisms. Further studies on analytical method development, pollution monitoring, and risk assessment related to organic pollutants in cigarette waste are needed.

Nanostructured materials as hazardous wastewater micropullutants: Sources, behavior, and impact on functional bacterial community of activated sludge

Unique properties of nanoscale materials make them attractive for industrial, medical, agricultural, and environmental applications. Nevertheless, the release of nanoparticles into the environment is a major concern due to the lack of knowledge about their behavior in the environment and potential widespread environmental impacts. On the one hand, nanomaterials are perceived as pollutants that may affect activated sludge microorganisms and, consequently, the efficiency of wastewater treatment processes. On the other hand, some nanomaterials can be intentionally added to activated sludge systems to improve their performance in terms of, e.g., sludge settling and removing heavy metals or organic pollutants. As a result, nanoparticles are frequently accumulated in wastewater, which is considered to be a major source of nanoparticle release to the surrounding environment. Processes that involve the action of activated sludge are used worldwide in wastewater treatment plants due to their excellent capacity of removing nutrients, degrading toxins, and retaining biomass. High concentrations of nanoparticles entering activated sludge systems can affect their growth and metabolism. The research studies, which are reviewed in the present article, show that nanoparticles significantly reduce the relative abundance of the activated sludge microbial community associated with nitrification, denitrification, and phosphorus removal. The knowledge about the structure of the activated sludge microbial community with an assessment of nanomaterial toxicity can contribute to optimizing the sludge population and improving the performance of wastewater treatment plants.

Assessing anthropogenic influences on the water quality of Gomati River using an innovative weighted fuzzy soft set based water pollution rating system

The increasing pollution of river systems poses a significant challenge to water quality management and public health. This study was conducted to evaluate the water quality of the Gomati River in India, focusing on the impact of anthropogenic activities on pollution levels across different seasons. The primary objective was to develop a comprehensive assessment model using an effective weighted fuzzy soft expert system (WFSES) to derive a weighted water pollution score (WWP-score) for rating water pollution levels based on various water quality parameters. To achieve this, we employed a fuzzy soft set (FSS) methodology integrated with a weighted fuzzy soft set (WFSS) model to analyze water quality indices at six sampling stations along the Gomati River, the largest river in Tripura, India. Originating from the Raima and Sarma streams, the river flows westward through key regions, providing 249.39 million cubic meters of water annually, essential for drinking, agriculture, fishing, and transportation. The study utilized crisp data summaries of key water quality parameters, including pH, total dissolved solids, total suspended solids, electrical conductivity, biochemical oxygen demand, dissolved oxygen, total hardness, chloride, total alkalinity, and total coliform, across the pre-monsoon, monsoon, and post-monsoon seasons from May 2022 to April 2023, guided by the distribution of waste discharge points. Fuzzy membership functions were defined for these parameters, and the root mean square (RMSQR) operation was used to combine multiple FSSs. The results revealed that the WWP-scores, a measure of water quality, ranged from 0.744 to 0.872 across the sampling stations, with Srimantapur exhibiting the highest level of pollution and Udaipur showing comparatively better quality. These scores indicate that water quality at all sites falls into the poor category, with Srimantapur experiencing the most severe contamination due to high levels of coliform bacteria and organic pollutants. The analysis highlights the impact of domestic wastewater and agricultural runoff on the river's health. This research offers a novel application of FSS and WFSS theory in environmental management, providing a robust framework for evaluating and ranking water quality across multiple parameters. The findings are valuable to the scientific community as they offer detailed insights into the pollution dynamics of the Gomati River and propose a methodological approach for assessing water quality in other river systems facing similar challenges. The study's results underscore the need for targeted pollution control measures and continuous monitoring to safeguard water resources and public health.

Modification of poly (vinylidene fluoride-co-hexafluoropropylene) membranes by sulfonated poly (ether ether keton) coating for membrane distillation of textile wastewater

The textile and related industries can produce a large amount of wastewater with organic dyes pollutants which can cause uncertain environmental impacts. In this study, the improved poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) hollow fiber membranes were used in a continuous air gap membrane distillation (AGMD) operation for wastewater treatment of the Hamadan textile factory, Iran. The porous membranes were fabricated by a phase-inversion process and the inner surface was coated by a thin layer of sulfonated poly (ether ether keton) (SPEEK). After SPEEK coating, the water contact angle of the membrane decreased from about 93° to 57°. The SPEEK coated membrane presented mean pore size and overall porosity of 10 nm and 82.2%, respectively. For the wastewater treatment, the improved membrane presented the water flux and color rejection of 24.7 kg/m2 h and 99.8% during 72 h of the AGMD operation, respectively. Additionally, the treated wastewater reduced to the turbidity of ∼2 NTU, total dissolved solid (TDS) of 16 mg/L and chemical oxygen demand (COD) of 10 mg/L. The coated membrane presented a reasonable anti-fouling property with a flux recovery ratio (FRR) of 91.7% after 72 h of the operation. Hence, the improved PVDF-HFP membrane can be a potential alternative for the removal of organic dyes from wastewater via a membrane distillation process.

Removal of Lead Cations by Novel Organoclays Derived from Bentonite and Amphoteric and Nonionic Surfactants

For many decades, natural and modified clay minerals have been used as adsorbents to clean up aquatic and soil ecosystems contaminated with organic and inorganic pollutants. In this study, organoclays based on bentonite and various amphoteric and nonionic surfactants were synthesized and tested as effective sorbents for lead ions. The maximum values of R were obtained when describing the sorption processes using the Langmuir model, which ranged from 0.97 to 0.99. The adsorption of lead ions by these organoclays was investigated using different sorption models including the Langmuir, Freundlich, and BET. It was found that, according to the values of limiting adsorption to the Langmuir equation, the synthesized organoclays formed an increasing series: organoclay with cocamide diethanolamine < bentonite < organoclay with lauramine oxide < organoclay with sodium cocoiminodipropionate < organoclay with disodium cocoamphodiacetate < organoclay with alkyl polyglucoside. The Gibbs energy for all of the analyzed samples was calculated and found to be negative, indicating the spontaneity of the cation adsorption process in the forward direction. The maximum value of the adsorption capacity of lead cations on organoclay-based bentonite with alkyl polyglucoside was 1.49 ± 0.05 mmol/g according to the Langmuir model, and 0.523 ± 0.003 mmol/g as determined by the BET model. In the process of modifying bentonite, there was an increase in negative values of the zeta potential for organoclays compared to the initial mineral, which clearly enhanced their electrostatic interactions with the positively charged lead ions. It was hypothesized, based on the physicochemical principles, that exchange adsorption is the main mechanism for lead absorption. Based on chemical approaches, organoclays based on amphoteric surfactants absorb lead mainly through the mechanisms of electrostatic attraction, ion exchange, and complexation as well as the formation of insoluble precipitates. Organoclays based on nonionic surfactants, on the other hand, absorb lead through mechanisms of complexation (including chelation) and the formation of insoluble chemical precipitates. The comparison of isotherms from different models allows us to find the most accurate match between the model and the experimental data, and to better understand the nature of the processes involved.

Degradation of organic dyes by Peroxymonosulfate activated with Zn/Co-ZIF

In this study, we successfully synthesized a bimetallic metal-organic framework material Zn/Co-ZIF to start Peroxymonosulfate (PMS) for organic dye degradation in the water body. Material characterization was evaluated by advanced methods, such as XRD, FT-IR, SEM, EDX, and BET. The influence of different factors on methylene blue (MB) decomposition rate was investigated. The results show that Zn/Co-ZIF has a porous structure, a high specific surface area and decomposes 98.22% MB (20 mg/L) in 4 minutes under reaction conditions of 40 mg/L catalyst, 0.814mM PMS, pH = 7. The decomposition efficiency of dyes increases in the order CR (79.85%) <RhB (90.81 %) < DB71 (96.07%) < MO (97.63%) < MB (98.22%). The main ROS for the degradation MB in this study were SO4—-, O2—- and 1O2. This shows that Zn/Co-ZIF materials are potential heterogeneous catalysts to activate PMS to decompose organic pollutants in water.

One-pot hydrothermal synthesis of g-C3N4/BiOBr/Bi2MoO6 as a Z-scheme heterojunction for efficient photocatalytic degradation of ciprofloxacin (CIP) antibiotic and Rhodamine B (RhB) dye

Photocatalytic degradation of toxic organic pollutants using natural sunlight is a rapidly advancing area of research, particularly involving binary or ternary component photocatalysts with Z-type heterojunctions. In this study, ternary g-C3N4/BiOBr/Bi2MoO6 photocatalysts were fabricated using a simple one-pot solvothermal method. The morphology and physicochemical properties of the samples were characterized using various techniques, including X-ray diffraction analysis (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), confirming the presence of BiOBr, Bi2MoO6, and g-C3N4 components. The inclusion of g-C3N4 increased the BET surface area of the composite up to 46 m2/g, compared with BiOBr. In addition, g-C3N4 also enhanced the light absorption capability of the composite into the visible light range, while BiOBr and Bi2MoO6 significantly improved separation of electron-hole pairs, as evidenced by photoluminescence (PL) intensity. Under visible light illumination (LED lamp), the prepared photocatalyst showed high efficiency, achieving 94 % degradation of ciprofloxacin (CIP) antibiotic in 180 min and 92 % degradation of Rhodamine B (RhB) dye in 240 min. Moreover, under natural sunlight irradiation, the photocatalyst achieved degradation efficiencies of approximately 91 % for CIP and 100 % for RhB within 180 minutes. The photodegradation of the pollutants followed first-order kinetics with a Z-scheme type heterojunction. The photogenerated electrons played a crucial role as the main active species involved in detoxification of the organic contaminants. The photocatalyst exhibited excellent structural stability and good cycling ability, maintaining its original photocatalytic performance even after five cycles of use. This work demonstrates a promising strategy for developing sunlight-active ternary heterojunctions for environmental remediation.

Advanced Processes in Water Treatment: Synergistic Effects of Hydrodynamic Cavitation and Cold Plasma on Rhodamine B Dye Degradation

The increasing pollution of water bodies, due to the constant release of highly toxic and non-biodegradable organic pollutants, requires innovative solutions for environmental remediation and wastewater treatment. In this study, the effectiveness of different Advanced Oxidation Processes (AOPs) for the purification of water contaminated with Rhodamine B (RhB) dye at a concentration of 5 mg/L were investigated and compared. Using the classical ozonation strategy as a benchmark treatment, the research showed over 99% degradation of RhB within 4 min in a laboratory-scale batch setup with a capacity of 0.2 L. In contrast, a “chemical-free” process exploiting ultrasound (US) technology achieved a 72% degradation rate within 60 min. Further experiments were conducted using a pilot-scale rotor-stator hydrodynamic cavitation (HC) reactor on a 15 L solution leading to 33% of RhB removal in the presence of hydrogen peroxide (H2O2) at 75 mg/L. However, the use of an innovative cavitational reactor, which hybridizes HC with cold plasma, showed remarkable efficiency and achieved 97% degradation of RhB in just 5 min when treating a 5 L solution at an inlet pressure of 20 bar in a loop configuration. In addition, a degradation rate of 58% was observed in a flow-through configuration, emphasising the robustness and scalability of the HC/electrical discharge (ED) plasma technology. These results underline the potential of hybrid HC/ED plasma technology as an intensified and scalable process for the purification of water, as it offers a catalyst- and oxidant-free protocol.

Biodegradation of <i>n</i>-Alkanes in Oil-Contaminated Bottom Sediments under Bioelectrochemical Stimulation

Degradation of oil hydrocarbons artificially introduced into bottom sediments in a bioelectrochemical system of a membrane-free (silt) type was studied. Passive bioelectrochemical stimulation by means of electrodes connected by an external circuit with a resistance of 1 kΩ, with an average electric current of ~85 µA was found to cause an increase in degradation during two months from 23.0 to 57.9%. Contamination of bottom sediments with oil (1.32 g/kg) slightly decreased the current in the external circuit of the bioelectrochemical system. The relationship was revealed between the degree of oil degradation and predominant utilization of the lighter n-alkanes in the C14H30–C30H62 series, compared with both the original oil and the residual hydrocarbons of the control. An increase in the representation of the alkB alkane monooxygenase genes relative to the 16S rRNA gene in the total DNA isolated from the sediments was induced by the introduction of hexadecane, both in the case of electrochemical stimulation and in the control. The results may be of interest for the development of new methods of bioelectrochemical removal of organic pollutants from anaerobic environments.

Zeolite-decorated black TiOx quantum dots for photocatalytic degradation of organic cationic dyes under LED light irradiation

Defect engineering is a promising strategy to reduce the band gap of semiconductors, enhancing their photocatalytic activity under visible light by introducing intra-bandgap energy states. Among the materials studied, oxygen-deficient black TiOx stands out due to its potential in photocatalytic reduction and hydrogen evolution. However, the valence band edge maximum (VBM) of TiOx is not thermodynamically favorable for the direct oxidation of water to hydroxyl radicals (H2O/•OH). Although the formation of extensive oxygen vacancies is necessary to extend the light absorption of black TiOx to longer wavelengths, a high density of oxygen vacancies (Ov) significantly shortens the diffusion length of charge carriers within the TiOx, leading to increased recombination of electrons and holes (e-/h+), thereby suppressing photocatalytic activity. To overcome these limitations, confining TiOx particles to the quantum dot (QD) size range and constructing heterojunctions with a secondary phase can substantially improve charge carrier separation and photocatalytic performance. In addition to engineering the electronic structure of composite photocatalysts, the preaccumulation of pollutants and their subsequent degradation is an effective strategy. This method decreases the distance between the adsorbed pollutant and the active sites for reactive oxygen species (ROSs) generation, enhancing the efficiency of the photocatalytic degradation process. In this study, we confined TiOx particles to the quantum dot size range by constructing a heterojunction with H-Beta zeolite, which contains defect-induced energy states within its wide band gap. This type of zeolite is particularly effective in adsorbing cationic azo dyes, facilitating pre-accumulation and degradation. The synthesized catalysts were extensively characterized using HRTEM to determine the average size of the TiOx particles and photoluminescence (PL) analysis to investigate charge carrier separation. Our results demonstrated that while TiOx alone showed negligible degradation efficiency, and no •OH were detected, the QD TiOx/Z4 composite achieved complete oxidation of CV by •OH, as confirmed by TOC analysis. The photocatalytic degradation mechanism was proposed based on these experimental findings. These insights could be of significant interest to researchers exploring defective semiconductors for photocatalytic oxidation of organic pollutants in the liquid phase under visible light (LED) irradiation.