Degradation of nitrogen-containing hazardous compounds using advanced oxidation processes: A review on aliphatic and aromatic amines, dyes, and pesticides

A nitrogen-specific detector for high performance liquid chromatography

We describe a nitrogen-specific detector (NSD) for aqueous mobile phase-based high performance liquid chromatography (HPLC). It is based by means of total hydrophilic organic nitrogen detection. Separated analytes are photooxidized online and converted to nitrate, followed by an ultravilet absorbance detector. It features response dependant on the product of nitrogen number in the molecule and its molar concentration, no matter what is ultravilet-absorbing or not. The HPLC equipped with NSD can quantify nitrogen-containing analytes via a sole standard of potassium nitrate for calibration. This results in identical calibration curve for all nitrogen-containing analytes, obviating individual calibration. The limit of detection of NSD is 4.3 μM N/L, and its linear range is up to 4 mM N/L.

A new perspective on contaminants as "activators": Aromatic amine groups promoted degradation of tetracycline by ferrate(VI)

Occasionally, our group found that the degradation of tetracycline by ferrate(VI) could be promoted by four co-exist contaminants, containing aromatic amines (ofloxacin, diatrizoic acid, sulfadiazine and alachlor). This study investigated the promotion of aromatic amine groups on tetracycline degradation by ferrate(VI) by using aniline as a model compound. The results implied that the presence of aniline increased the degradation rate of tetracycline by 2.76 times, and the enhancement was weakened gradually with the decrease of pH from 10 to 7.5. The generation of Fe(IV) and·OH by the reaction between ferrate(VI) and aniline was proposed to enhance the degradation of tetracycline, supported by quenching experiments, electron paramagnetic resonance (EPR) and theoretical calculations. A positive correlation was found between the rate constant of tetracycline degradation and the electron-donating ability of the substituted amines (quantified by the Hammett substituent constants). In addition, the degradation of tetracycline was remarkably inhibited by HA and some inorganic ions such as NO3-, SO42-, Cl-, Ca2+, and Mg2+, and the inhibition also happened in the Songhua River water and the secondary effluent. The present study provided an insight into the complex oxidation process for the degradation of micropollutants containing aromatic amine by ferrate in water treatment.

SbSeI for High-Efficient Photocatalytic Degradation of Multiple Pollutants

Photocatalytic degradation is an effective technology for degrading water pollution that plays a significant role in environmental remediation. Ternary 2D ternary V-VI-VIIA semiconductors are ideal candidates for photocatalytic degradation of pollutants due to effective light absorption and high charge carrier mobility. In this work, high-quality SbSeI crystals were prepared using the chemical vapor transport (CVT) method and their photocatalytic degradation performance for multiple pollutants was studied. SbSeI exhibits excellent photocatalytic performance in the degradation of potassium dichromate (Cr (VI)), rhodamine B (RhB), tetracycline hydrochloride (TC-HCl) and methyl orange (MO). More than 98% of Cr (VI) and RhB can be removed after irradiation with an Xe lamp for 10 mins and 40 mins, respectively. The capture experiments and electron spin resonance results indicated that ·O2- plays a major role in reducing Cr (VI), while h+ plays a primary role in the degradation of MO, RhB and TC-HCl. Interestingly, the degradation rate of Cr (VI) is 1.3 times higher than that of a single pollutant system, and the degradation rate of RhB is 1.6 times higher, due to the enhanced separation and utilization of holes and electrons. The results demonstrate that SbSeI is a potential photocatalytic degradation material.

Anaerobic treatment of nitrogenous industrial organic wastewater by carbon-neutral processes integrated with anaerobic digestion and partial nitritation/anammox: Critical review of current advances and future directions

Anaerobic digestion combined with partial nitritation/anammox technology holds promising potential for the carbon-neutral treatment of nitrogenous industrial organic wastewater, boasting remarkable advantages in effective removal of both organic matters and nitrogen, bio-energy recovery and carbon emission reduction. This study provides a concise overview of the development and advantages of anaerobic digestion combined with partial nitritation/anammox technology for treating nitrogenous industrial organic wastewater. The process excels in removing organic matter and nitrogen, recovering bio-energy, and reducing carbon emissions, compared to traditional physicochemical and biological methods. Case studies highlight its energy-saving and efficient attributes, especially for carbon-neutral nitrogen removal. Challenges for achieving stable operation in the future are discussed, and the study offers insights into the broader application of this integrated process in industrial wastewater treatment.

Metal oxide-based photocatalysts for the efficient degradation of organic pollutants for a sustainable environment: a review

Photocatalytic degradation is a highly efficient technique for eliminating organic pollutants such as antibiotics, organic dyes, toluene, nitrobenzene, cyclohexane, and refinery oil from the environment. The effects of operating conditions, concentrations of contaminants and catalysts, and their impact on the rate of deterioration are the key focuses of this review. This method utilizes light-activated semiconductor catalysts to generate reactive oxygen species that break down contaminants. Modified photocatalysts, such as metal oxides, doped metal oxides, and composite materials, enhance the effectiveness of photocatalytic degradation by improving light absorption and charge separation. Furthermore, operational conditions such as pH, temperature, and light intensity also play a crucial role in enhancing the degradation process. The results indicated that both high pollutant and catalyst concentrations improve the degradation rate up to a threshold, beyond which no significant benefits are observed. The optimal operational conditions were found to significantly enhance photocatalytic efficiency, with a marked increase in degradation rates under ideal settings. Antibiotics and organic dyes generally follow intricate degradation pathways, resulting in the breakdown of these substances into smaller, less detrimental compounds. On the other hand, hydrocarbons such as toluene and cyclohexane, along with nitrobenzene, may necessitate many stages to achieve complete mineralization. Several factors that affect the efficiency of degradation are the characteristics of the photocatalyst, pollutant concentration, light intensity, and the existence of co-catalysts. This approach offers a sustainable alternative for minimizing the amount of organic pollutants present in the environment, contributing to cleaner air and water. Photocatalytic degradation hence holds tremendous potential for remediation of the environment.

Preliminary analysis: Effect of a rotary generator of hydrodynamic cavitation on rheology and methane yield of wastewater sludge

Slightly acidic (pH 5.1) waste sludge with 4.7 % Total Solids (TS) was treated on a laboratory scale pined disc rotary generator of hydrodynamic cavitation (PD RGHC). Influence of four rotor discs with different number of cavitation generation units (CGUs) was investigated: 8-pins, 12-pins, 16-pins and 8-prism elements. The effect of hydrodynamic cavitation (HC) was investigated by analyzing rheological properties, surface tension, dewaterability, and particle size distribution. After subjecting the sludge to 30 cavitation passes, the dewatering ability of the sludge significantly decreased, resulting in a more than two-fold increase in Capillary Suction Time (CST). All regimes were successful in disintegrating particles to smaller sizes. A slight increase of sludge surface tension was measured post cavitation. Cavitated samples displayed a zero-shear viscosity, in contrast to the untreated sample, where viscosity noticeably increased as shear stress decreased. HC did not improve methane yield. Statistically significant correlations between physio-chemical properties and apparent viscosity at low shear stress were identified. Although there were no discernible statistical differences in sludge characteristics, some trends are visible among investigated CGU designs and warrant further research.

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.

Nitrogen-doped metal-free granular activated carbons as economical and easily separable catalysts for peroxymonosulfate and hydrogen peroxide activation to degrade bisphenol A

The fabrication of low-cost, highly efficient, environmentally friendly, and easily separable metal-free heterogeneous catalysts for environmental remediation remains a challenge. In this study, granular nitrogen-doped highly developed porous carbons with a particle size of 0.25-0.30 mm were prepared by preoxidation and subsequent NH3 modification of a commercially available coconut-based activated carbon, and used to activate peroxymonosulphate (KHSO5) or hydrogen peroxide (H2O2) to degrade bisphenol A (BPA). The nitrogen-doped carbon (ACON-950) prepared by NH3 modification at 950 °C, with the addition of only 0.15 g/L could remove 100% of 50 mg/L BPA in 150 min, and more than 90% of the removed BPA was due to degradation. The removal rates of total organic carbon of ACON-950/KHSO5 and ACON-950/H2O2 systems reached 60.4% and 66.2% respectively, indicating the excellent catalytic activity of ACON-950. The reaction rate constant was significantly positively correlated with the absolute content of pyridinic N (N-6) and graphitic N (N-Q) and negatively and weakly positively correlated with pyrrolic N (N-5) and defects. Quenching experiments combined with electron paramagnetic resonance demonstrated that singlet oxygen was the dominant reactive oxidative species for BPA degradation. ACON-950 was characterized before and after the degradation reaction using N2 adsorption-desorption analyzer, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The results confirmed the prominent contribution of both the N-6 and N-Q to the catalytic performance of nitrogen-doped carbons. The reusability of ACON-950 and its application in actual water bodies further demonstrated its remarkable potential for the remediation of organic pollutants in wastewater.

Rapid, Massive, and Green Synthesis of Polyoxometalate-Based Metal-Organic Frameworks to Fabricate POMOF/PAN Nanofiber Membranes for Selective Filtration of Cationic Dyes

Developing high-efficiency membrane materials for the rapid removal of organic dyes is crucial but remains a challenge. Polyoxometalates (POMs) clusters with anionic structures are promising candidates for the removal of cationic dyes via electrostatic interactions. However, their shortcomings, such as their solubility and inability to be mass-produced, hinder their application in water pollution treatment. Here, we propose a simple and green strategy utilizing the room temperature stirring method to mass produce nanoscale polyoxometalate-based metal-organic frameworks (POMOFs) with porous rhomboid-shaped dodecahedral and hexagonal prism structures. The products were labeled as POMOF1 (POMOF-PW12) and POMOF2 (POMOF-PMo12). Subsequently, a series of x wt% POMOF1/PAN (x = 0, 3, 5, and 10) nanofiber membranes (NFMs) were prepared using electrospinning technology, where polyacrylonitrile (PAN) acts as a "glue" molecule facilitating the bonding of POMOF1 nanoparticles. The as-prepared samples were comprehensively characterized and exhibited obvious water stability, as well as rapid selective adsorption filtration performance towards cationic dyes. The 5 wt% POMOF1/PAN NFM possessed the highest removal efficiency of 96.7% for RhB, 95.8% for MB, and 86.4% for CV dyes, which realized the selective separation over 95% of positively charged dyes from the mixed solution. The adsorption mechanism was explained using FT-IR, SEM, Zeta potential, and adsorption kinetics model, which proved that separation was determined via electrostatic interaction, hydrogen bonding, and π-π interactions. Moreover, the POMOF1/PAN membrane presented an outstanding recoverable and stable removal rate after four cycles. This study provides a new direction for the systematic design and manufacture of membrane separation materials with outstanding properties for contaminant removal.

Machine learning analysis to interpret the effect of the photocatalytic reaction rate constant (k) of semiconductor-based photocatalysts on dye removal

Photocatalytic reactions with semiconductor-based photocatalysts have been investigated extensively for application to wastewater treatment, especially dye degradation, yet the interactions between different process parameters have rarely been reported due to their complicated reaction mechanisms. Hence, this study aims to discern the impact of each factor, and each interaction between multiple factors on reaction rate constant (k) using a decision tree model. The dyes selected as target pollutants were indigo and malachite green, and 5 different semiconductor-based photocatalysts with 17 different compositions were tested, which generated 34 input features and 1527 data points. The Boruta Shapley Additive exPlanations (SHAP) feature selection for the 34 inputs found that 11 inputs were significantly important. The decision tree model exhibited for 11 input features with an R2 value of 0.94. The SHAP feature importance analysis suggested that photocatalytic experimental conditions, with an importance of 59%, was the most important input category, followed by atomic composition (39%) and physicochemical properties (2%). Additionally, the effects on k of the synergy between the metal cocatalysts and important experimental conditions were confirmed by two feature SHAP dependence plots, regardless of importance order. This work provides insight into the single and multiple factors that affect reaction rate and mechanism.

Occurrence, multiphase partition and risk assessment of organic amine pesticides in drinking water source of Xiang River, China

The extensive use of organic amine pesticides (OAPs) in agricultural practices has resulted in the contamination of water environments, posing threats to ecosystems and human health. This study focused on the Xiang River (XR), a representative drinking water source, as the research area to investigate the occurrence characteristics of 34 OAPs. Diphenylamine emerged as the most prevalent OAP in surface water due to industrial and agricultural activities, while cycloate dominated in sediments due to cumulative effects. Generally, the concentration of OAPs in a mixed tap water sample was lower than those in surface water samples, indicating OAPs can be removed by water plants to a certain extent. The water-sediment distribution coefficients (kd) of ΣOAPs were much less than 1 L/g, the majority of OAPs maintained relatively high concentrations in water samples instead of accumulating in sediments. Furthermore, risk assessment revealed that carbofuran showed a moderate risk to the aquatic environment, with a risk quotient of 0.23, while other OAPs presented minor risks. This study provided crucial insights for regional pesticide management and control in the XR basin, emphasizing the importance of implementing strategies to minimize the release of OAPs into the environment and protect human health.

Visible Light-Driven Photocatalytic Degradation of Methylene Blue Dye Using a Highly Efficient Mg-Al LDH@g-C3N4@Ag3PO4 Nanocomposite

The issue of water resource pollution resulting from the discharge of dyes is a matter of great concern for the environment. In this investigation, a new ternary heterogeneous Mg-Al LDH@g-C3N4X@Ag3PO4Y (X = wt % of g-C3N4 with respect to Mg-Al layered double hydroxide (LDH) and Y = wt % of Ag3PO4 loaded on Mg-Al LDH@g-C3N430) nanocomposite was prepared with the aim of increasing charge carrier separation and enhancement of photocatalytic performance to degrade methylene blue (MB) dye. The prepared samples were subjected to characterization via Fourier-transform infrared spectroscopy, field emission scanning electron microscopy, energy-dispersive X-ray, transmission electron microscopy, X-ray diffraction, UV-vis diffuse reflectance spectroscopy, photoluminescence, and photoelectrochemical analysis. It was observed that in the presence of the composite of Mg-Al LDH and g-C3N4, the photocatalytic decomposition of MB under 150 W mercury lamp illumination increases significantly as opposed to Mg-Al LDH alone, and the Mg-Al LDH@g-C3N4 level with Ag3PO4 coating causes the complete degradation of MB to occur in less time. The outcomes show that the Mg-Al LDH@g-C3N430@Ag3PO45 nanocomposite demonstrated the highest photodegradation activity (99%). Scavenger tests showed that the two most effective agents in the photodegradation of MB are holes and hydroxyl radicals, respectively. Finally, a type II heterojunction photocatalytic degradation mechanism for MB by Mg-Al LDH@g-C3N430@Ag3PO45 was proposed.

Unveiling the metallic size effect on O2 adsorption and activation for enhanced electro-Fenton degradation of aromatic compounds

Metal-atom-modified nitrogen-doped carbon materials (M-N-C) have emerged as promising candidates for electro-Fenton degradation of pollutants. Nonetheless, a comprehensive exploration of size-dependent M-N-C catalysts in the electro-Fenton process remains limited, posing challenges in designing surface-anchored metal species with precise sizes. Herein, a heterogeneous-homogeneous coupled electro-Fenton (HHC-EF) system was designed and various M-N-C catalysts anchored with Co single atoms (CoSA-N-C), Co clusters (CoAC-N-C), and Co nanoparticles (CoNP-N-C) were successfully synthesized and employed in an HHC-EF system. Intriguingly, CoAC-N-C achieved outstanding removal efficiencies of 99.9% for BPA and RhB within 10 and 15 min, respectively, with the fastest reaction kinetics (0.70 min-1 for BPA and 0.34 min-1 for RhB). Electron spin resonance and trapping experiments revealed that·OH played a crucial role in the HHC-EF process. Moreover, experiments and theoretical calculations revealed that the unique metallic size effect facilitate the in-situ electro-generation of H2O2. Specifically, the atomic interaction between neighboring Co atoms in clusters enhanced O2 adsorption and activation by strengthening the Co-N bond and transforming O2 adsorption configuration to the Yeager-type. This study provides valuable insights that could inspire the size-oriented metal-based catalyst design from the perspective of the potential atomic distance effect.

Deciphering Microbe-Mediated Dissolved Organic Matter Reactome in Wastewater Treatment Plants Using Directed Paired Mass Distance

Understanding the reaction mechanism of dissolved organic matter (DOM) during wastewater biotreatment is crucial for optimal DOM control. Here, we develop a directed paired mass distance (dPMD) method that constructs a molecular network displaying the reaction pathways of DOM. It couples direction inference and PMD analysis to extract the substrate-product relationships and delta masses of potentially paired reactants directly from sequential mass spectrometry data without formula assignment. Using this method, we analyze the influent and effluent samples from the bioprocesses of 12 wastewater treatment plants (WWTPs) and build a dPMD network to characterize the core reactome of DOM. The network shows that the first step of the transformation triggers reaction cascades that diversify the DOM, but the highly overlapped subsequent reaction pathways result in similar effluent DOM compositions across WWTPs despite varied influents. Mass changes exhibit consistent gain/loss preferences (e.g., +3.995 and -16.031) but different occurrences across WWTPs. Combined with genome-centric metatranscriptomics, we reveal the associations among dPMDs, enzymes, and microbes. Most enzymes are involved in oxygenation, (de)hydrogenation, demethylation, and hydration-related reactions but with different target substrates and expressed by various taxa, as exemplified by Proteobacteria, Actinobacteria, and Nitrospirae. Therefore, a functionally diverse community is pivotal for advanced DOM degradation.

Streptomyces spp. as biocatalyst sources in pulp and paper and textile industries: Biodegradation, bioconversion and valorization of waste

Complex polymers represent a challenge for remediating environmental pollution and an opportunity for microbial-catalysed conversion to generate valorized chemicals. Members of the genus Streptomyces are of interest because of their potential use in biotechnological applications. Their versatility makes them excellent sources of biocatalysts for environmentally responsible bioconversion, as they have a broad substrate range and are active over a wide range of pH and temperature. Most Streptomyces studies have focused on the isolation of strains, recombinant work and enzyme characterization for evaluating their potential for biotechnological application. This review discusses reports of Streptomyces-based technologies for use in the textile and pulp-milling industry and describes the challenges and recent advances aimed at achieving better biodegradation methods featuring these microbial catalysts. The principal points to be discussed are (1) Streptomyces' enzymes for use in dye decolorization and lignocellulosic biodegradation, (2) biotechnological processes for textile and pulp and paper waste treatment and (3) challenges and advances for textile and pulp and paper effluent treatment.

Reactive Oxygen Species and Chromophoric Dissolved Organic Matter Drive the Aquatic Photochemical Pathways and Photoproducts of 6PPD-quinone under Simulated High-Latitude Conditions

The photochemical degradation pathways of 6PPD-quinone (6PPDQ, 6PPD-Q), a toxic transformation product of the tire antiozonant 6PPD, were determined under simulated sunlight conditions typical of high-latitude surface waters. Direct photochemical degradation resulted in 6PPDQ half-lives ranging from 17.5 h at 20 °C to no observable degradation over 48 h at 4 °C. Sensitization of excited triplet-state pathways using Cs+ and Ar purging demonstrated that 6PPDQ does not decompose significantly from a triplet state relative to a singlet state. However, assessment of processes involving reactive oxygen species (ROS) quenchers and sensitizers indicated that singlet oxygen and hydroxyl radical do significantly contribute to the degradation of 6PPDQ. Investigation of these processes in natural lake waters indicated no difference in attenuation rates for direct photochemical processes at 20 °C. This suggests that direct photochemical degradation will dominate in warm waters, while indirect photochemical pathways will dominate in cold waters, involving ROS mediated by chromophoric dissolved organic matter (CDOM). Overall, the aquatic photodegradation rate of 6PPDQ will be strongly influenced by the compounding effects of environmental factors such as light screening and temperature on both direct and indirect photochemical processes. Transformation products were identified via UHPLC-Orbitrap mass spectrometry, revealing four major processes: (1) oxidation and cleavage of the quinone ring in the presence of ROS, (2) dealkylation, (3) rearrangement, and (4) deamination. These data indicate that 6PPDQ can photodegrade in cool, sunlit waters under the appropriate conditions: t1/2 = 17.4 h tono observable decrease (direct); t1/2 = 5.2-11.2 h (indirect, CDOM).

Nanoparticles of the Perovskite-Structure CaTiO3 System: The Synthesis, Characterization, and Evaluation of Its Photocatalytic Capacity to Degrade Emerging Pollutants

In this research work, the photocatalytic capacity shown by the nanoparticles of the CaTiO3 system was evaluated to degrade two pollutants of emerging concern, namely methyl orange (MO)-considered an organic contaminating substance of the textile industry that is non-biodegradable when dissolved in water-and levofloxacin (LVF), an antibiotic widely used in the treatment of infectious diseases that is released mostly to the environment in its original chemical form. The synthesis process used to obtain these powders was the polymeric precursor method (Pechini), at a temperature of 700 °C for 6 h. The characterization of the obtained oxide nanoparticles of interest revealed the presence of a majority perovskite-type phase with an orthorhombic Pbnm structure and a minority rutile-type TiO2 phase, with a P42/mnm structure and a primary particle size <100nm. The adsorption-desorption isotherms of the synthesized solids had H3-type hysteresis loops, characteristic of mesoporous solids, with a BET surface area of 10.01m2/g. The Raman and FTIR spectroscopy results made it possible to identify the characteristic vibrations of the synthesized system and the characteristic deformations of the perovskite structure, reiterating the results obtained from the XRD analysis. Furthermore, a bandgap energy of ~3.4eV and characteristic emissions in the violet (437 nm/2.8 eV) and orange (611 nm/2.03 eV) were determined for excitation lengths of 250 nm and 325 nm, respectively, showing that these systems have a strong emission in the visible light region and allowing their use in photocatalytic activity to be potentialized. The powders obtained were studied for their photocatalytic capacity to degrade methyl orange (MO) and levofloxacin (LVF), dissolved in water. To quantify the coloring concentration, UV-visible spectroscopy was used considering the variation in the intensity of the characteristic of the greatest absorption, which correlated with the change in the concentration of the contaminant in the solution. The results showed that after irradiation with ultraviolet light, the degradation of the contaminants MO and LVF was 79.4% and 98.1% with concentrations of 5 g/L and 10 g/L, respectively.

Effects of wavelength on the treatment of contaminants of emerging concern by UV-assisted homogeneous advanced oxidation/reduction processes

Pollutants of emerging concern in aqueous environments present a significant threat to both the aquatic ecosystem and human health due to their rapid transfer. Among the various treatment approaches to remove those pollutants, UV-assisted advanced oxidation/reduction processes are considered competent and cost-effective. The treatment effectiveness is highly dependent on the wavelength of the UV irradiation used. This article systematically discusses the wavelength dependency of direct photolysis, UV/peroxides, UV/chlor(am)ine, UV/ClO2, UV/natural organic matter, UV/nitrate, and UV/sulfite on the transformation of contaminants. Altering wavelengths affects the photolysis of target pollutants, photo-decay of the oxidant/reductant, and quantum yields of reactive species generated in the processes, which significantly impact the degradation rates and formation of disinfection byproducts. In general, the degradation of contaminants is most efficient when using wavelengths that closely match the highest molar absorption coefficients of the target pollutants or the oxidizing/reducing agents, and the contribution of pollutant absorption is generally more significant. By matching the wavelength with the peak absorbance of target compounds and oxidants/reductants, researchers and engineers have the potential to optimize the UV wavelengths used in UV-AO/RPs to effectively remove pollutants and control the formation of disinfection byproducts.

Designing advanced S-scheme CdS QDs/La-Bi2WO6 photocatalysts for efficient degradation of RhB

Finding effective strategies to design efficient photocatalysts and decompose refractory organic compounds in wastewater is a challenging problem. Herein, by coupling element doping and constructing heterostructures, S-scheme CdS QDs/La-Bi2WO6 (CS/LBWO) photocatalysts are designed and synthesized by a simple hydrothermal method. As a result, the RhB degradation efficiency of the optimized 5% CS/LBWO reached 99% within 70 min of illumination with excellent stability and recyclability. CS/LBWO shows improvement in the adsorption range of visible light and promotes electron-hole pair generation/migration/separation, attributing the superior degradation performance. The degradation RhB mechanism is proposed by a free radical capture experiment, electron paramagnetic resonance, and high-performance liquid chromatography-mass spectrometry results, indicating that h+ and •O2 - play a significant role during four degradation processes: de-ethylation, chromophore cleavage, ring opening, and mineralization. Based on in situ irradiated X-ray photoelectron spectroscopy, Mulliken electronegativity theory, and the work function results, the S-scheme heterojunction of CS/LBWO promotes the transfer of photogenerated electron-hole pairs and promotes the generation of reactive radicals. This work not only reports that 5% CS/LBWO is a promising photocatalyst for degradation experiments but also provides an approach to design advanced photocatalysts by coupling element doping and constructing heterostructures.

Catalytically enhanced direct degradation of nitro-based antibacterial agents using dielectric barrier discharge cold atmospheric pressure plasma and rhenium nanoparticles

The common utilization of antimicrobial agents in medicine and veterinary creates serious problems with multidrug resistance spreading among pathogens. Bearing this in mind, wastewaters have to be completely purified from antimicrobial agents. In this context, a dielectric barrier discharge cold atmospheric pressure plasma (DBD-CAPP) system was used in the present study as a multifunctional tool for the deactivation of nitro-based pharmacuticals such as furazolidone (FRz) and chloramphenicol (ChRP) in solutions. A direct approach was applied to this by treating solutions of the studied drugs by DBD-CAPP in the presence of the ReO4- ions. It was found that Reactive Oxygen Species (ROS) and Reactive Nitrogen Species (RNS), generated in the DBD-CAPP-treated liquid, played a dual role in the process. On the one hand, ROS and RNS led to the direct degradation of FRz and ChRP, and on the other hand, they enabled the production of Re nanoparticles (ReNPs). The produced in this manner ReNPs consisted of catalytically active Re+4, Re+6, and Re+7 species which allowed the reduction of -NO2 groups contained in the FRz and ChRP. Unlike the DBD-CAPP, the catalytically enhanced DBD-CAPP led to almost FRz and ChRP removals from studied solutions. The catalytic boost was particularly highlighted when catalyst/DBD-CAPP was operated in the synthetic waste matrix. Re-active sites in this scenario led to the facilitated deactivation of antibiotics, achieving significantly higher FRz and ChRP removals than DBD-CAPP on its own.

Iron oxide nanoparticles/nanocomposites derived from steel and iron wastes for water treatment: A review

Iron oxide nanoparticles (IONPs) are characterized by superior magnetic properties, high surface area to volume ratio, and active surface functional groups. These properties aid in removal of pollutants from water, through adsorption and/or photocatalysis, justifying the choice of IONPs in water treatment systems. IONPs are usually developed from commercial chemicals of ferric and ferrous salts alongside other reagents, a procedure that is costly, environmentally unfriendly and limits their mass production. On the other hand, steel and iron industries produce both solid and liquid wastes which in most cases are piled, discharged into water streams or landfilled as strategies to dispose them off. Such practices are detrimental to environmental ecosystems. Given the high content of iron present in these wastes, they can be used to generate IONPs. This work reviewed published literature through selected key words on the deployment of steel and/or iron-based wastes as IONPs precursors for water treatment. The findings reveal that steel waste-derived IONPs have properties such as specific surface area, particle sizes, saturation magnetization, and surface functional groups that are comparable or sometimes better than those synthesized from commercial salts. Furthermore, the steel waste-derived IONPs have high removal efficacy for heavy metals and dyes from water with possibilities of being regenerated. The performance of steel waste-derived IONPs can be enhanced by functionalization with different reagents such as chitosan, graphene, and biomass based activated carbons. Nonetheless, there is need to explore the potential of steel waste-based IONPs in removing contaminants of emerging concern, modifying pollutant detection sensors, their techno-economic feasibility in large treatment plants, toxicity of these nanoparticles when ingested into the human body, among other areas.

Recent advances in the removal of emerging contaminants from water by novel molecularly imprinted materials in advanced oxidation processes-A review

Recently, there has been a global focus on effectively treating emerging contaminants (ECs) in water bodies. Advanced oxidation processes (AOPs) are the primary technology used for ECs removal. However, the low concentrations of ECs make it difficult to overcome the interference of background substances in complex water quality, which limits the practical application of AOPs. To address this limitation, many researchers are developing new catalysts with preferential adsorption. Molecular imprinting technology (MIT) combined with conventional catalysts has been found to effectively enhance the selectivity of catalysts for the targeted catalytic degradation of pollutants. This review presents a comprehensive summary of the progress made in research on molecularly imprinted polymers (MIPs) in the selective oxidation of ECs in water. The preparation methods, principles, and control points of novel MIP catalysts are discussed. Furthermore, the performance and mechanism of the catalysts in photocatalytic oxidation, electrocatalytic oxidation, and persulfate activation are analyzed with examples. The possible ecotoxicological risks of MIP catalysts are also discussed. Finally, the challenges and prospects of applying MIP catalysts in AOP are presented along with proposed solutions. This review provides a better understanding of using MIP catalysts in AOPs to target the degradation of ECs.

Oxidation of simulated wastewater by Fe2+-catalyzed system: The selective reactivity of chlorine radicals and the oxidation pathway of aromatic amines

Aromatic amines (AAs), a characteristic pollutant with electron-donating groups in textile industry, having high reactivity with reactive chlorine free radicals, is probably the precursor of chlorinated aromatic products in advanced oxidation treatment. In this study, Fe2+/peroxydisulfate (PDS)/Cl- and Fe2+/H2O2/Cl-systems were used to treat four kinds of AAs (5-Nitro-o-toluidine (NT), 4-Aminoazobenzol (AAB), O-Aminoazotoluene (OAAT), 4,4'-Methylene-bis(2-chloroaniline) (MBCA)) in simulated wastewater, and the selectivity of various reactive species to AAs, the oxidation law and pathway of AAs were explored. The results showed that dichloride anion radical (Cl2·-) could effectively oxidize four AAs, and chlorine radical (·Cl) was strongly reactive to AAB and MBCA, especially MBCA. The largest f - (Fukui function) of MBCA is 0.0822, which is the lowest of the four AAs, so ·Cl might be more sensitive to electrophilic point than hydroxyl radical (·OH). The oxidation pathway of NT and MBCA showed that ·Cl mainly played the role of electron transfer to AAs instead of generating chlorinated products, but the addition of ·OH to -NH2 generated aromatic nitro compounds with higher toxicity than NT and MBCA. Therefore, the electron transfer of ·Cl and Cl2·- could not only improve the removal of AAs but also reduce the generation of toxic products. This study found that the reactivity of reactive chlorine free radicals was not necessarily related to chlorination, which provided a theoretical basis for the further studies into the formation mechanism of chlorination products.

New outlook on hazardous pollutants in the wastewater environment: Occurrence, risk assessment and elimination by electrodeionization technologies

Over the decades, water contamination has increased substantially and has become a severe global issue. Degradation of natural resources is taking place at an alarming rate as a result of the use of chemicals like dyes, heavy metals, fertilizers, pesticides, and many more, necessitating the development of long-term pollution remediation methods/technologies. As a new development in the field of environmental engineering, electrodeionization incorporates both traditional ion exchange and electrodialysis. This communication provides an overview of hazardous contaminants such as dyes, heavy metals, fertilizers, and pesticides, as well as their converted forms, which are present in water. It highlights the risks of water pollutants to public health and the environment. Various electrochemical methods with a focus on electrodeionization for the treatment of wastewater and removal of hazardous contaminants are outlined in this review. Additionally, this review discusses the challenges and the future outlook for the development in this field of research.

A Review on Rotary Generators of Hydrodynamic Cavitation for Wastewater Treatment and Enhancement of Anaerobic Digestion Process

The issue of ever-increasing amounts of waste activated sludge (WAS) produced from biological wastewater treatment plants (WWTPs) is pointed out. WAS can be effectively reduced in the anaerobic digestion (AD) process, where methanogens break down organic matter and simultaneously produce biogas in the absence of oxygen, mainly methane and CO2. Biomethane can then be effectively used in gas turbines to produce electricity and power a part of WWTPs. Hydrodynamic cavitation (HC) has been identified as a potential technique that can improve the AD process and enhance biogas yield. Rotary generators of hydrodynamic cavitation (RGHCs) that have gained considerable popularity due to their promising results and scalability are presented. Operation, their underlying mechanisms, parameters for performance evaluation, and their division based on geometry of cavitation generation units (CGUs) are presented. Their current use in the field of wastewater treatment is presented, with the focus on WAS pre/treatment. In addition, comparison of achieved results with RGHCs relevant to the enhancement of AD process is presented.

Changes to Soil Microbiome Resulting from Synergetic Effects of Fungistatic Compounds Pyrimethanil and Fluopyram in Lowbush Blueberry Agriculture, with Nine Fungicide Products Tested

Lowbush blueberries (Vaccinium spp.) are a crop of economic significance to Atlantic Canada, Quebec, and Maine. The fruit is produced by the management of naturally occurring plant populations. The plants have an intimate relationship with the soil microbiome and depend on it for their health and productivity. Fungicides are an important tool in combatting disease pressure but pose a potential risk to soil health. In this study, amplicon sequencing was used to determine the effects of six fungistatic compounds both alone and in combination via nine commercially available fungicide products on the bacterial and fungal microbiomes associated with lowbush blueberries and to study whether these effects are reflected in crop outcomes and plant phenotypes. One fungicide, Luna Tranquility, a combination of fluopyram and pyrimethanil, was found to impart significant effects to fungal and bacterial community structure, fungal taxonomic abundances, and bacterial functions relative to control. The two fungicides which contained fluopyram and pyrimethanil as single ingredients (Velum Prime and Scala, respectively) did not induce significant changes in any of these regards. These results suggest the possibility that these microbiome changes are the result of the synergistic effect of fluopyram and pyrimethanil on soil microbiomes. While these results suggest a significant disruption to the soil microbiome, no corresponding changes to crop development and outcomes were noted. Ultimately, the majority of the fungicides analysed in this trial did not produce significant changes to the soil microbiome relative to the untreated group (UTG). However, one of the fungicide treatments, Luna Tranquility, did produce significant changes to the soil ecosystem that could have longer-term effects on soil health and its future use may merit additional investigation onto its ecotoxicological properties.

The multiple roles of phenols in the degradation of aniline contaminants by sulfate radicals: A combined study of DFT calculations and experiments

Recent research revealed inhibition or enhancement of dissolved organic matter (DOM) to the degradation of trace organic contaminants (TrOC) in natural and engineered water systems. Phenols containing acetyl, carboxyl, formyl, hydroxy, and methoxy groups were selected as the model DOM to quantitatively study their roles in the degradation of simple anilines, sulfonamide antibiotics, phenylurea pesticides by sulfate radicals (SO₄^•-). Experimental results found that p-methoxyphenol inhibited aniline and sulfamethoxazole degradation by thermally activated peroxydisulfate (TAP), while p-acetylphenol slightly promoted aniline degradation. Quantum chemical calculations were applied to study the microscopic mechanism and kinetics of phenols affecting the degradation of aniline pollutants (AN) in three ways: competitively reacting with SO₄^•-, repairing aniline cationic radicals (AN^•+) and phenylaminyl radicals (AN(-H)^•), and generating phenoxy radicals to degrade anilines. Generally, the degradation of sulfonamides and phenylureas prefer to be inhibited by hydroxy- and methoxy-phenols with low oxidation potential (E_ox), due to their diffusion-limiting reaction with SO₄^•- and rapid back-reduction AN^•+ with the calculated rate constants of (0.02 - 6.38) × 10⁹ M^-1 s^-1. Phenols repairing AN(-H)^• through H abstraction reaction is speculated to possibly dominate the joint degradation of phenols and anilines by TAP, which has a poor correlation with E_ox. This study provides mechanistic insight into the chemical behavior of complex and heterogeneous DOM in complex aqueous environments.

Role of UV-based advanced oxidation processes on NOM alteration and DBP formation in drinking water treatment: A state-of-the-art review

Oxidative treatment of drinking water has been practiced for more than a century. UV-based advanced oxidation processes (UV-AOPs) have emerged as promising oxidative treatment technologies to eliminate recalcitrant chemicals and biological contaminants in drinking water. UV-AOPs inevitably alter the properties of natural organic matter (NOM) and affect the disinfection byproduct (DBP) formation in the post-disinfection. This paper provides a state-of-the-art review on the effects of UV-AOPs on the changes of NOM properties and the consequent impacts on DBP formation in the post-chlorination process. A tutorial review to the connotations of NOM properties (e.g., bulk properties, fractional constituents, and molecular structures) and the associated state-of-the-art analytical methods are firstly presented. The impacts of different radical-based AOPs on the changes of NOM properties together with the underlying NOM-radical reaction mechanisms are discussed. The impacts of alteration of NOM properties on DBP formation in the post-chlorination process are then reviewed. The current knowledge gaps and future research needs are finally presented, with emphases on the needs to strengthen the comparability of research data in literature, the accuracy in quantifying the reactive moieties of NOM, and the awareness of unknown DBPs in oxidative water treatment processes. The review and discussion improve the fundamental understanding of NOM-radical and NOM-chlorine chemistry. They also provide useful implications on the engineering design and operation of next-generation drinking water treatment plants.

Insights into the degradation of microplastics by Fenton oxidation: From surface modification to mineralization

This work aims at evaluating the fate of microplastics (MPs) along Fenton oxidation. For such goal, realistic MPs (150-250 μm) of five representative polymer types (PET, PE, PVC, PP and EPS) were obtained from commercial plastic products by cryogenic milling. Experiments (7.5 h) were performed under relatively severe operating conditions: T = 80 °C; pH₀ = 3; [H₂O₂]₀ = 1000 mgL^-1 (15 doses, 1 every 0.5 h); [Fe³⁺]₀ = 10 mgL^-1 (5 doses, 1 every 1.5 h). Slight MPs weight losses (∼10%) were achieved after Fenton oxidation regardless the MP nature. Nevertheless, oxidation yield clearly increased with decreasing the particle size given their higher exposed surface area (up to 20% weight loss with 20-50 μm EPS MPs). Clearly, MPs suffered important changes in their surface due to the introduction of oxygenated groups, which made them more acidic and hydrophilic. Furthermore, MPs progressively reduced their size. In fact, they can be completely oxidized to CO₂, as demonstrated in the oxidation of PS nanoplastics (140 nm), where 70% mineralization was achieved. The nature of the plastic particles had a relevant impact on its overall oxidation, being more prone to be oxidized those polymers which contain aromatic rings in their structures (EPS and PET) compared to those formed by alkane chains (PE, PP and PVC). In the latter, the presence of substituents also reduced their oxidation potential. Remarkably, possible leachates released along reaction were more quickly oxidized than the MPs/NPs, so it can be assumed that these dissolved compounds would be completely removed once the solid particles are eliminated. Notably, the leachates obtained upon MPs oxidation were more biodegradable than the released from the fresh solids. All this knowledge is crucial for the understanding of MPs oxidation by the Fenton process and opens the door for the design and optimization of this technology either for water treatment or for analytical purposes (MPs isolation).

Integrated ozone-sono-Fenton for the enhanced degradation of acid orange 7: process optimization and kinetic evaluation

The performance of novel hybrid advanced oxidation, ozone-sono-Fenton process in degradation of acid orange 7 (AO7), as a model of azo dyes was modelled and optimized using response surface methodology (RSM) based on central composite design (CCD). Utilizing a bubbling reactor equipped with an ultrasound probe and in the presence of Fenton reagents, a promising hybrid homogeneous AOP, ozone-sono-Fenton, was investigated. According to the experimental results, the variation trend of degradation efficiency (DE%) with pH, reaction time and Fe²⁺/H₂O₂ molar ratio was modelled with the reduced quadratic model. Additionally, the suitability of the model was indicated with close to unity regression coefficient [Formula: see text]. Furthermore, the comparative study of degradation efficiency and COD removal for the individual methods including ozonation, sonication and Fenton reagents as well as their hybrid processes reveals that the novel proposed technique, ozone-sono-Fenton process, is able to rapid and complete degradation of acid orange 7 with initial concentration of 300 mg L^-1, 100% in only 12 min. The complete degradation was obtained under optimum conditions such as pH = 6, reaction time = 12 min and Fe²⁺/H₂O₂ molar ratio = 0.0040. The kinetics evaluation of the acid orange 7 concentration during the processing implied the first-order reaction. Considering the synergetic effect and cost-effectiveness of the hybrid method, the promising ozone-sono-Fenton method could effectively degrade using a wide range of organic contaminants.

Progress in pre-treatment and extraction of organic and inorganic pollutants by layered double hydroxide for trace-level analysis

Continuous release of pollutants into the environment poses serious threats to environmental sustainability and human health. For trace-level analysis of pollutants, layered double hydroxide (LDH) is an attractive option to impart enhanced sorption capability and sensitivity toward pollutants because of its unique layered structure, tunable interior architecture, high anion-exchange capacities, and high porosity (e.g., Zn/Cr LDH/DABCO-IL, Ni/Al LDH, CS-Ni/Fe LDH, SDS-Fe₃O₄@SiO₂@Mg-Al LDH, Boeh/Mg/Al LDH/pC, and Fe@NiAl LDH). In concert with the well-defined analytical methodologies (e.g., HPLC and GC), the LDH materials can be employed to detect trace-level targets (e.g., as low as ∼ 20 fg/L for phenols) in aqueous environments. This review highlights LDH as a promising material for pre-treatment of a variety of organic and inorganic target pollutants in complex real matrices. Challenges and future requirements for research into LDH-based analytical methods are also discussed.

Influence of pH on the Kinetics and Products of Photocatalytic Degradation of Sulfonamides in Aqueous Solutions

The aims of the study were to determine the kinetics of the photocatalytic degradation of six sulfonamides in the presence of TiO2-P25 in acidic, neutral, and alkaline solutions and to identify the structures of the stable products. It was stated that the pH of the solution significantly affected the photocatalytic degradation rate of sulfonamides in acidic and alkaline environments, and the effect likely depended on the susceptibility of sulfonamides to attack by hydroxyl radicals. In the post-reaction mixture, we identified the compounds resulting from the substitution of the aromatic rings with a hydroxyl group; the amide hydrolysis products; the hydroxylamine-, azo, and nitro derivatives; and the compounds formed via the elimination of the sulfone group. Moreover, previously unknown azo compounds were detected. Some degradation products of sulfonamides may exhibit marked bacteriostatic activity and high phytotoxicity. The azo and nitro compounds formed in an acidic environment may be potentially more toxic to aquatic ecosystems than the initial compounds.

Bridged-ozonolysis of mixed aromatic hydrocarbons and organic amines: Inter-inhibited decay rate, altered product yield and synergistic-effect-enhanced secondary organic aerosol formation

Ozonolysis of aromatic hydrocarbons (AHs) or organic amines (OAs) occurs via different transformation processes, with varying rate constants and contributions to secondary organic aerosol (SOA) formation. However, to date no data is available on the ozonolysis of mixtures of AHs and OAs. This study investigated the kinetics, products and SOA yield from ozonolysis of mixture of trimethylamine with styrene, toluene or m-xylene. In the mixed system, the decay rates of styrene and trimethylamine were (1.32 ± 0.26) × 10^-4 s^-1 and (0.80 ± 0.02) × 10^-4 s^-1, decreasing up to 36.5 % and 54.4 % compared with their respective individual systems. This inter-inhibition of decay rates increased the yield of main products from styrene (i.e. benzaldehyde) by 23.5 % and trimethylamine (i.e. nitromethane) by 346.4 %. Ozonolysis of styrene or trimethylamine produced formaldehyde, which acted as a bridged product connecting the ozonolysis pathways of these two substrates, altering the yields of all products. Ozonolysis of styrene to benzaldehyde determined the increase of SOA particle number concentration (from 9.5 × 10⁵ to 1.9 × 10⁶ particles cm^-3), while trimethylamine ozonolysis to N, N-dimethylformamide contributed to synergistic-effect-enhanced SOA yield (from (64.3 ± 3.5)% to (68.1 ± 4.8)%). The findings provide a novel insight into the kinetics and mechanism of ozonolysis, as well as the resulting SOA formation from mixtures of AHs and OAs, helping to comprehensively understand the transformation and fate of organics in real atmospheric environments.

Engineering hierarchical FeS2/TiO2 nanotubes on Ti mesh as a tailorable flow-through catalyst belt for all-day-active degradation of organic pollutants and pathogens

The increasing organic and microbiological pollutions in fresh water caused by human activities and industrial development have become a global concern nowadays. In this study, three-dimensional (3D) hierarchical FeS₂/TiO₂ structures with nanotube geometries were grown on a Ti mesh (M-TNTAs-FeS₂). Benefitting from the abundant available reactive sites on the open 3D micro/nanoporous structures, excellent photocatalytic activity of FeS₂/TiO₂ heterostructure in solar light, and satisfactory Fenton activity of FeS₂, the obtained M-TNTAs-FeS₂ exhibits outstanding performance as an all-day-active catalyst. Importantly, flexible meshes can be easily tailored and enveloped into fluorinated ethylene propylene (FEP) pockets in a series as a flow-through belt for large-capacitance applications (998 L m^-2 at a flow rate of 417 L m^-2 h^-1 for a four-pockets belt), as indicated by the degradation of azo dyes, antibiotics, pesticides, and pathogens. This study may inspire a new tailorable catalyst design for a promising point-of-use purification device.

Printing ink wastewater treatment using combined hydrodynamic cavitation and pH fixation

Printing ink wastewater (PIW) carries a heavy load of pollutants, the composition of which makes treatment difficult, especially when trying to minimize the pollution load. According to the latter, the present study aims to investigate PIW treatment with different various methods and to determine the maximum color, COD (chemical oxygen demand) and TSS (total suspended solids) removal. First, hydrodynamic cavitation (HC) was tested and the effect of hydrogen peroxide dosage (0-10 g L^-1), and pH (3, 5, 8, 10) was examined concerning the removal of PIW initial COD concentrations 4000 and 8000 mg L^-1. Removal was high (more than 81%) only at pH 5 in HC reactor. The second method involved treatment with separate pH fixation of the undiluted PIW (COD 17000 mg L^-1, actual pH 8 ± 0.2). This treatment, maximized removals, reaching reduction of the initial values more than 91%, at pH 5. Finally, PIW was treated with a combination of the above methods, leading to 93-97% removals for 8000 mg L^-1 PIW treatment and 97-99% for 17000 mg L^-1 PIW respectively. Process cost calculations showed that the latter method is an effective and affordable treatment method for PIW streams, while toxicity tests of the treated PIW showed substantial toxicity reduction.

Degradation of dyes by UV/Persulfate and comparison with other UV-based advanced oxidation processes: Kinetics and role of radicals

This study investigated the degradation of methylene blue (MeB), methyl orange (MeO), and rhodamin B (RhB) by the UV/Persulfate (UV/PS) process. The dye degradation in the investigated UV-based Advanced Oxidation Processes (UV/AOPs) followed the first-order kinetic model. The second-order rate constant of the dyes with •OH, SO₄^•-, and CO₃^•- were calculated and found to be: k_•OH,MeB = 5.6 × 10⁹ M^-1 s^-1, [Formula: see text]  = 3.3 × 10⁹ M^-1 s^-1, [Formula: see text]  = 6.9 × 10⁷ M^-1 s^-1; k_•OH,MeO = 3.2 × 10⁹ M^-1 s^-1, [Formula: see text]  = 13 × 10⁹ M^-1 s^-1, [Formula: see text]  = 4.4 × 10⁶ M^-1 s^-1; k_•OH,RhB = 14.8 × 10⁹ M^-1 s^-1, [Formula: see text]  = 5 × 10⁹ M^-1 s^-1, [Formula: see text]  = 1 × 10⁷ M^-1 s^-1. The steady-state concentrations of •OH and SO₄^•- (including other reactive species) were determined using both chemical probes and modeling methods (Kintecus® V6.8). In the UV/PS, the dye degradation depends on the pH of the solution with the order: k_dye (at pH of 7) > k_dye (in acidic conditions) > k_dye (in alkaline conditions). The presence of water matrices had different impacts on dye degradation: 1) The HCO₃^- and Cl^- promoted the degradation efficiency of one dye, but also inhibited the degradation of other dyes; 2) Humic acid (HA) inhibited dye degradation as it scavenged both •OH and SO₄^•-. The degradation of the dyes by UV/PS was also compared with the UV/Chlorine (UV/HOCl) and UV/H₂O₂ and it was established that: 1) In UV/PS and UV/HOCl, SO₄^•- and RCS contributed to dye degradation more than •OH, while •OH played a major role in dye degradation by UV/H₂O₂; 2) The calculated toxicity in UV/PS was the lowest probably due to the low toxicity of by-products; 3) For MeO and RhB, the UV/PS process is more beneficial for the total organic carbon (TOC) removal compared to that of the UV/HOCl and UV/H₂O₂ processes; 4) The UV/PS showed lower cost than the UV/HOCl and UV/H₂O₂ systems for MeO, and RhB degradation but higher cost for MeB removal.

Reactive uptake of ozone to azo dyes in a coated-wall flow tube

Azo dyes are the most common colorants in consumer products, including clothing and cosmetics. Some azo dyes and their products from reductive degradation are known to be mutagenic, so dermal exposure to these species has been studied extensively. In contrast, oxidative degradation of azo dyes in consumer products has not been studied so thoroughly. In the indoor environment, ozone is ubiquitous, so reactive uptake of ozone to azo dyes could lead to dermal exposure to other classes of degradation products. Here, we report the first measurements of the reactive uptake of ozone to thin films of three widely used commercial azo dyes: sunset yellow, amaranth, and tartrazine. Steady-state uptake was observed for all three dyes, under all conditions investigated, even at the lowest relative humidity (RH) of 0%. The uptake coefficients increased with RH. For sunset yellow at 100 ppb of ozone, the value at 80% RH, (2.0 ± 0.5) × 10^-7, was 2.5 times greater than that at 0% RH, (8 ± 1) × 10^-8, consistent with plasticization of the thin film due to absorption of water. The uptake coefficient of sunset yellow at 80% RH exhibited an inverse dependence on the ozone mixing ratio, approaching an asymptote of 1 × 10^-7 above 250 ppb. At 80% RH and 100 ppb of ozone, the uptake coefficients for the three dyes were similar, (2.0 ± 0.5) × 10^-7 for sunset yellow, (2.7 ± 0.6) × 10^-7 for amaranth, and (3.2 ± 0.3) × 10^-7 for tartrazine, despite differences in structural parameters related to the number of reactive sites at the surface. Together, these results are consistent with ozone diffusing into the thin film and the dye molecules mixing between the layers, such that reaction is not restricted to the surface of the film. Finally, the results are suggestive of a role for azo dyes, including the occurrence of their oxidation products, in indoor chemistry.

The structure-activity relationship of aromatic compounds in advanced oxidation processes：a review

Advanced oxidation processes (AOPs) are widely used as efficient technologies to treat highly toxic and harmful substances in wastewater. Taking the most representative aromatic compounds (monosubstituted benzenes, substituted phenols and heterocyclic compounds) as examples, this paper firstly introduces their structures and the structural descriptors studied in AOPs before, and the influence of structural differences in AOPs with different reactive oxygen species (ROS) on the degradation rate was discussed in detail. The structure-activity relationship of pollutants has been previously analyzed through quantitative structure-activity relationship (QSAR) model, in which ROS is a very important influencing factor. When electrophilic oxidative species attacks pollutants, aromatic compounds with electron donating groups are more favorable for degradation than aromatic compounds with electron donating groups. While nucleophilic oxidative species comes to the opposite conclusion. The choice of advanced oxidation processes, the synergistic effect of various active oxygen species and the used catalysts will also change the degradation mechanism. This makes the structure-dependent activity relationship uncertain, and different conclusions are obtained under the influence of various experimental factors.

Active site regulated Z-scheme MIL-101(Fe)/Bi2WO6/Fe(III) with the synergy of hydrogen peroxide and visible-light-driven photo-Fenton degradation of organic contaminants

Water pollution control is one of the major challenges currently faced. With the development of photocatalytic technology, an increasing number of new and efficient catalysts have been developed, but most of the catalysts have limited light capture ability and catalytic degradation efficiency. Therefore, in this work, hydrogen peroxide was further introduced to establish a photo-Fenton system to improve the photocatalytic effect by constructing a Z-scheme, and the degradation ability of the catalyst was maximized. Moreover, we successfully adhered bismuth tungstate nanosheets onto the surface of a MIL-101(Fe) framework and changed the number of active sites with iron ions of different doping amounts. We found that the number of active sites in the photo-Fenton system does not increase linearly, but increases and decreases regularly, which is similar to the change in band structure after doping. In addition, the results of the radical scavenger experiment and electron paramagnetic resonance (EPR) revealed that both hydroxide radical (˙OH) and superoxide radical (˙O₂^-) participated in methylene blue (MB) degradation, of which ˙OH was the main active species for pollutant degradation. Based on high-performance liquid chromatography-mass spectrometry (HPLC-MS) analysis, the possible degradation pathways were proposed. We believed that this work will provide insights into the heterojunction photo-Fenton system.