Organic Pollutants In Wastewater Treatment Research Articles

Comparative study of photocatalysis with bulk and nanosheet graphitic carbon nitrides enhanced with silver

The main goal of this research is to investigate the effectiveness of graphitic carbon nitride (g-C3N4, g-CN) in both bulk and nanosheet forms, which have been surface-modified with silver nanoparticles (Ag NPs), as photocatalysts for the degradation of acid orange 7 (AO7), a model dye. The photodegradation of AO7 dye molecules in water was used to test the potential photocatalytic properties of these powder materials under two different lamps with wavelengths of 368 nm (UV light) and 420 nm (VIS light). To produce Ag NPs (Ag content 0.5, 1.5, and 3 wt%) on the g-CN materials, a new synthesis route based on a wet and low-temperature method was proposed, eliminating the need for reducing agents. The photodegradation activity of the samples increased with increasing silver content, with the best photocatalytic performances achieved for bulk g-CN samples and nanosheet silver-modified samples (with the highest content of 3 wt% Ag) under UV light, i.e., more than 75% and 78%, respectively. The VIS-induced photocatalytic activity of both examined series was higher than that of UV. The highest activities of 92% and 98% were achieved for the 1.5% Ag-modified g-CN bulk and nanosheet materials. This research presents an innovative, affordable, and environmentally friendly chemical approach to synthesizing photocatalysts that can be used for degrading organic pollutants in wastewater treatment.

Enhanced catalytic degradation of organic dye by Sn1-xLaxO2 nanoparticles under UV light for wastewater treatment

Effectively eliminating dyes and heavy metals from wastewater, without secondary contamination and with easy recovery, is a significant challenge. To address this, SnO2-based photocatalysts were fabricated using a straightforward sol–gel method, aiming to achieve high-value reutilization and environmental protection. Utilizing XRD, FTIR, and HRTEM, the investigation has conclusively confirmed the emergence of nanoparticles (NPs) through rigorous analysis and observation techniques. Raman, XPS, and PL spectroscopy probed electronic, optical properties, and lattice defects, offering comprehensive insights into material characteristics. Specific BET surface areas were observed to be 17.72 and 39.64 m2/g for 0 % and 5 % La samples. The introduction of dopant La to the SnO2 lattice resulted in enhanced optical properties, demonstrated by a significant red shift. La-SnO2 nanoparticles demonstrated remarkable catalytic efficacy, degrading 94 % of RB dye solution under 60 min of UV light exposure. Even after four cycles, the catalytic degradation activity remained high at 87 %, showcasing excellent structural stability. Enhanced adsorption capacity and effective separation of electron-hole pairs under light contribute to this improvement. Moreover, the study delved into defect-based room temperature ferromagnetism (RTFM) by examining the formation of a novel network, such as La3+-O-Sn4+. The results highlight the potential of these composites doped photocatalysts as effective materials for degrading harmful organic pollutants in wastewater treatment and for their application in spintronic devices. The present study aims to characterize the structural, magnetic, and optical attributes of La-doped SnO2 nanoparticles.

Exploring the peroxydisulfate activation by carbon nanotubes for pollutants degradation: Identification of the primary reaction mechanism and key molecular descriptor

Carbon nanotubes (CNT) have been proposed to activate persulfate over the past decade, resulting in successful degradation performance for organic pollutants in wastewater treatment. However, there is debate over the reaction mechanism involving radical versus non-radical pathways, setting up a roadblock to further developing persulfate activation by carbonaceous materials. This work focused on the carbon nanotubes/peroxydisulfate (CNT/PDS) system, investigated its reaction mechanism, and unveiled the relationship from the aspect of molecular descriptors. The involvement of radicals (e.g., SO4•− and HO•) and 1O2 was ruled out by the observation of quenching effect, oxidation products, chemical probes, solvent exchange, and electron paramagnetic resonance spectra. Then, mediated electron transfer was deemed as the primary reaction mechanism based on linear sweep voltammetry analysis, which was supported by the PDS consumption result. The substrate-dependent treatment capacity was found in the CNT/PDS for multiple contaminants degradation, and it turned out that EB3LYP was the most significant parameter in the relationship between degradation rates and molecular descriptors. Outstanding environmental application was exhibited based on the coexistence of various organic/inorganic substances and repeated degradation experiment. Therefore, the findings from this study would be helpful for both scientific research and technical development of persulfate activation by CNT.

Unveiling the photocatalytic property of La2O3–CuO nanocomposites for organic pollutants in wastewater treatment

Photocatalytic degradation was considered the best strategy for removing hazardous dye contaminants in water bodies from wastewater. The photocatalyst of pure La2O3 nanoparticles and La2O3–CuO nanocomposites synthesized by sonochemical method. The nanocomposites were used to investigate the degradation activity of Safranin (SR) and crystal violet (CV) under sunlight irradiation. The physicochemical characterization methods (e.g., Field emission scanning electron microscopy (FESEM), high resolution-transmission electron microscopy (HR-TEM), ultraviolet, visible spectroscopy (UV–Vis), and BET analysis indicate that the composite has been constructed successfully that enhances the widened visible light absorption, induces charge transfer and separation efficiency of electron–hole pairs. X-ray diffraction (XRD) experiment demonstrated that introducing copper into lanthanum resulted in alterations in the size of the crystallites and the average size of the nanoparticles, shifting from 21.93 to 43.19 nm. The photocatalytic activity of all samples was examined through the photodegradation of Safranin and crystal violet in an aqueous medium. The photocatalytic degradation rate of nanocomposite catalysts could eliminate 95.80 % and 97.05 % of Safranin and crystal violet dyes in 135 min, about 1.4 times that of pure La2O3 nanoparticles. The current study will give an efficient nanocomposite photocatalyst for removing biological and textile dye aqueous pollutants.

Monolithic CoMgAl mixed metal oxide nanosheets on Al2O3 granules for the efficient advanced oxidation process

Cobalt-based catalysts are good candidates for the degradation of organic pollutants in wastewater treatment due to their high activity, while powdered catalysts for practical applications face challenges like difficulty in regeneration. To solve the problem, this work designs a monolithic catalyst by in-situ growth of CoMgAl mixed metal oxide (CoMgAl-MMO) nanosheets on the Al2O3 granules. The obtained catalyst possesses a developed mesoporous structure with highly-dispersed Co on the surface. The catalytic activity of CoMgAl-MMO/AG in the dye degradation is dependent on the Co/Mg molar ratio. All monolithic catalysts show high degradation performance, of which the CoMgAl-MMO/AG catalyst with Co/Mg ratio of 0.8/1.2 exhibited the highest degradation rate, achieving 95 % acid orange (AO7) removal in 10 min testing.

Ammonium changes the pathway of tetrabromobisphenol S degradation by sulfate radical oxidation

Sulfate radical (SO4•-)-based advanced oxidation processes (SR-AOPs) show great potential in the elimination of organic pollutants in wastewater treatment and groundwater remediation. Tetrabromobisphenol S (TBBPS) as an emerging contaminant can be effectively degraded in SR-AOPs. However, the present study found that SO4•- also reacted with ammonium (NH4+), a ubiquitous inorganic nitrogen species in aquatic environments, thus markedly affected the rates and pathways of TBBPS degradation in SR-AOPs. TBBPS underwent β-scission and debromination upon SO4•- attack, leading to various transformation products. The released bromide (Br-) underwent further oxidation by SO4•- to form free bromine which reacted with certain TBBPS intermediates, generating disinfection byproducts (DBPs). When NH4+ was present in such system, the abatement of TBBPS was apparently suppressed. Meanwhile, NH4+ was oxidized by SO4•- to nitrogen dioxide radical (NO2•) which coupled with certain radical intermediates of TBBPS oxidation, yielding nitrophenolic products including 2,6-dibromo-4-nitrophenol (DBNP) and mono-nitro substituted TBBPS. When 10 μM TBBPS was treated by heat activated peroxydisulfate with 1 mM NH4+, the molar yield of DBNP reached 22% in 2 h. More importantly, NH4+ scavenged the in situ formed free bromine to form monobromamine (NH2Br), decreasing regulated DBPs formation but leading to highly toxic dibromoacetonitrile (DBAN). This study broadens the understanding of interactions between the transformation of halogens and NH4+ during SO4•- oxidation. It also reveals the potential environmental risks when SR-AOPs are employed for the organohalogen pollutants degradation in realistic environments where NH4+ is present.

Magnetically separable NiZn-ferrite/CeO2 nanorods/CNT ternary composites for photocatalytic removal of organic pollutants

Water scarcity and contamination are the foremost global one health challenges, which require immediate nano/biotechnology–based innovative interventions. Hybrid nanocomposites have emerged as novel nanoplatforms for wastewater remediation through photocatalytic degradation of persistent organic pollutants. This unprecedented study reports the economical fabrication of novel nanoplatforms based on Ni0.5Zn0.5Fe2O4 and CeO2 (using the modified hydrothermal method) and their binary and ternary hybrid nanocomposites of Ni0.5Zn0.5Fe2O4/CeO2 and Ni0.5Zn0.5Fe2O4/CeO2/multi-walled carbon nanotubes (MWCNT) (using facile ultra-sonication method) respectively, for water health management. The engineered nanocomposites were evaluated for the Z-scheme mechanism using morphological (SEM, TEM), structural (XRD), optical (UV–Visible spectroscopy), magnetic (VSM), electronic and compositional (XPS) analyses and employed for wastewater remediation. The ternary hybrid composites exhibit excellent photocatalytic degradation efficacy (93.5%) for removing rose bengal (RB) dye from wastewater on UV illumination. The high dye-removal efficacy of ternary hybrid is attributed to the suitable band gap positions of Ni0.5Zn0.5Fe2O4 and CeO2 metal oxides enhancing its photodegradation efficiency on UV illumination, and to the MWCNT enhancing the recombination time of photogenerated electron-hole pairs during dye-removal phenomena. Owing to their excellent performance and robust stability, the engineered ternary composites possess enormous potential for degrading diversified organic pollutants for wastewater treatment and contribute to One Health management, where photocatalytic degradation attributes are a prerequisite.

Enhanced Photocatalytic Degradation of Malachite Green Dye Using Silver-Manganese Oxide Nanoparticles.

Efficient and excellent nanoparticles are required for the degradation of organic dyes in photocatalysis. In this study, silver-manganese oxide nanoparticles (Ag-Mn-NPs) were synthesized through a wet chemical precipitation method and characterized as an advanced catalyst that has enhanced photocatalytic activity under sunlight irradiation. The nanoparticles were characterized using scanning electron microscopy (SEM), XRD, UV-vis light spectra, and energy-dispersive X-ray (EDX) spectroscopy, revealing their spherical and agglomerated form. The EDX spectra confirmed the composition of the nanoparticles, indicating their presence in oxide form. These bimetallic oxide nanoparticles were employed as photocatalysts for the degradation of malachite green (MG) dye under sunlight irradiation in an aqueous medium. The study investigated the effects of various parameters, such as irradiation time, catalyst dosage, recovered catalyst dosage, dye concentration, and pH, on the dye's photodegradation. The results showed that Ag-Mn oxide nanoparticles exhibited high photocatalytic activity, degrading 92% of the dye in 100 min. A longer irradiation time led to increased dye degradation. Moreover, a higher catalyst dosage resulted in a higher dye degradation percentage, with 91% degradation achieved using 0.0017 g of the photocatalyst in 60 min. Increasing the pH of the medium also enhanced the dye degradation, with 99% degradation achieved at pH 10 in 60 min. However, the photodegradation rate decreased with increasing dye concentration. The Ag-Mn oxide nanoparticles demonstrate excellent potential as a reliable visible-light-responsive photocatalyst for the efficient degradation of organic pollutants in wastewater treatment.

Self-cleaning photoelectrocatalytic filtration based on Ca(OH)2/Ti3C2Tx composite nanofiltration membranes for synergistically enhanced separation and degradation of phenolic compounds

Combining photoelectrocatalytic (PEC) and nanofiltration (NF) membranes has emerged as an attractive technology for removing organic pollutants in wastewater treatment, however, the separation and degradation performance are still challenging. Herein, novel composite NF membranes were constructed by cross-linking a Ca(OH)2/Ti3C2Tx (CT) catalyst to a polyamide membrane using tannic acid (TA). In these CT@TA (CTTP) membranes, Ti3C2Tx reduces the charge-transfer resistance and recombination rate of CT, leading to enhanced PEC activity. The optimal CTTP membrane had a high water flux (27.9 L·m−2·h−1·bar−1) and excellent rejection rates for phenolic compounds (phenol: 85.1 %, 4-nitrophenol: 91.1 %, and bisphenol A (BPA): 94.6 %). Under visible-light irradiation with electrical assistance (3 V), the BPA degradation rate (92.2 %) was 13.7 % higher than that under light irradiation alone, and a higher flux recovery rate was achieved (94.1 %). Superoxide (O2−) and hydroxyl (OH) radicals were critical active species in catalytic BPA degradation, and the observed intermediates suggested that the degradation pathway involves oxidation, hydroxylation, and aromatic ring cracking. The developed NF membranes, which exhibit synergistic separation and degradation effects and self-cleaning properties, provide an innovative solution for the treatment of organic pollutants in wastewater.

Design of hybrid g-C3N4/GO/MCE photocatalytic membranes with enhanced separation performance under visible-light irradiation

Photocatalytic membranes with concurrent catalytic oxidation and separating functions possess promising potentials for the degradation of organic pollutants in wastewater treatment. Herein, we designed a hybrid photocatalytic membrane (viz., g-C3N4/GO/MCE) by vacuum-filtration-assisted assembling method, consisting of graphitic carbon nitride (g-C3N4) nanosheets as a top layer, graphene oxide (GO) nanosheets as an interlayer, and commercial mixed cellulose ester (MCE) as a substrate layer. The microstructures, chemical compositions, and physicochemical properties of the designed g-C3N4/GO/MCE membranes were systematically characterized by a series of characterization techniques. Particularly, photocatalysis-filtration reactor cells were designed for the evaluation of the simultaneous separation and photocatalytic degradation performance in a single unit using both organic dyes and antibiotics as modeling pollutants in wastewater. Four parameters were adopted to represent the integrated photocatalysis-filtration performance of our designed photocatalytic membranes, including permeance (P), rejection (R’, filtration alone), removal (R, combined photocatalysis-filtration under light-irradiation), and degradation rate (D). The hybrid membranes showed superior permeance and solute removal under visible-light irradiation (300 W, λ > 420 nm), in which the permeance was 20% higher than that of no-irradiation conditions. In addition, 10 consecutive cycling tests and light-on/off cycles of the as-prepared g-C3N4/GO/MCE membrane toward RhB showed quite stable permeance in the range of 268.9 to 352.9 L h−1 m−2 bar−1, and the removal was maintained in the range of 88.4% to 95.4%, indicating excellent long-term stability. Remarkably, it also exhibited good removal performance of antibiotics (e.g., ofloxacin, norfloxacin, sulfamethoxazole, erythromycin, and roxithromycin). Accordingly, the designed hybrid g-C3N4/GO/MCE photocatalytic membranes with excellent photocatalytic activity and photocatalysis-filtration performance are promising for wastewater treatment and water purification applications.

Enhanced photocatalytic degradation of organic dye by CeO2/CNT/GO hybrid nanocomposites under UV light for wastewater treatment.

Development of nanocomposites as efficient photocatalysts for the removal of hazardous organic pollutants is always in dire demand due to increase in water pollution. In this article, a facile sol-gel method has been used to synthesize cerium oxide (CeO2) nanoparticles followed by their decoration over multi-walled carbon nanotubes (CNTs) and graphene oxide (GO) to construct binary as well ternary hybrid nanocomposites using ultrasonic treatment. The oxygen vacancy defects have been depicted using X-ray photoelectron spectroscopy (XPS) that may result into improved photocatalytic efficiency. The ternary hybrid nanocomposites (CeO2/CNT/GO) showed excellent photocatalytic efficiency towards degradation of rose bengal (RB) dye up to 96.9% in 50 min. CNTs and GO provide the interfacial charge transfer which inhibits the electron-hole pair recombination. The results obtained here indicate that these composites can be effectively utilized as promising materials for the degradation of harmful organic pollutants for wastewater treatment.

Novel Sb-SnO2 Electrode with Ti3+ Self-Doped Urchin-Like Rutile TiO2 Nanoclusters as the Interlayer for the Effective Degradation of Dye Pollutants.

Stable and efficient SnO2 electrodes are very promising for effectively degrading refractory organic pollutants in wastewater treatment. In this regard, we firstly prepared Ti3+ self-doped urchin-like rutile TiO2 nanoclusters (TiO2-x NCs) on a Ti mesh substrate by hydrothermal and electroreduction to serve as an interlayer for the deposition of Sb-SnO2 . The TiO2-x NCs/Sb-SnO2 anode exhibited a high oxygen evolution potential (2.63 V vs. SCE) and strong ⋅OH generation ability for the enhanced amount of absorbed oxygen species. Thus, the degradation results demonstrated its good rhodamine B (RhB), methylene blue (MB), alizarin yellow R (AYR), and methyl orange (MO) removal performance, with the rate constant increased 5.0, 1.9, 1.9, and 4.7 times, respectively, compared to the control Sb-SnO2 electrode. RhB and AYR degradation mechanisms are also proposed based on the results of high-performance liquid chromatography coupled with mass spectrometry and quenching experiments. More importantly, this unique rutile interlayer prolonged the anode lifetime sixfold, given its good lattice match with SnO2 and the three-dimensional concave-convex structure. Consequently, this work paves a new way for designing the crystal form and structure of the interlayers to obtain efficient and stable SnO2 electrodes for addressing dye wastewater problems.

Development of visible light-driven SrTiO3 photocatalysts for the degradation of organic pollutants for waste-water treatment: Contrasting behavior of MB & MO dyes

Semiconductor photocatalysts were utilized widely for degrading organic pollutants in water using the advanced, environment-friendly, low-cost, and highly efficient photocatalysis technique. There are various complex energy-consuming techniques used for the refinement of wastewater. However, the photocatalysis process is the cleanest technique used for degrading organic pollutants in wastewater into the water; carbon dioxide, other small molecules, and inorganic pollutants were reduced or oxidized into harmless substances.SrTiO3 nanoparticles (NPs) synthesized by the chemical method are the topic of attention among researchers because of their physical, chemical & photocatalytic properties under sunlight for water purification applications. This paper dealt with the study of The photocatalytic properties of SrTiO3 and its composites under sunlight irradiation. Here, we evaluated the photodegradation of methyl orange (MO) and methylene blue (MB) pollutants using SrTiO3 as a photocatalyst for de-ionized (DI) water and hard water, respectively. Later on, the ex-situ decoration of Ag and Au nanoparticles (NPs) on SrTiO3 NPs results in enhancing the photocatalytic activity of SrTiO3. This article shows the abnormal behaviour of MO degradation compared to MB dye because there was no degradation of methyl orange for both bare SrTiO3 and Ag, Au@SrTiO3 nanocomposites. However, for bare-SrTiO3, the photocatalytic degradation of MB dye for de-ionized and hard water was accomplished in 210 min and 300 min, respectively. Here, SrTiO3 with MB dye shows enhanced photocatalytic activity for de-ionized water than hard water, and thus we determined the degradation of SrTiO3 nanocomposites with DI water only. While in the case of SrTiO3 nanocomposites, degradation occurred in 210min for Ag and 180 min for Au in DI water which signifies that Au a better co-catalyst for photodegradation. Although, degradation of MO in both DI water and hard water does not show any photocatalytic activity even in 6 and 7 h, respectively, for bare SrTiO3 and its nanocomposites. Therefore, it gives an idea about the different behaviour of dyes in photocatalytic degradation of DI and hard water using bare SrTiO3 and noble metal doped SrTiO3 as photocatalysts for water remediation applications.At a glimpse, this work focus on the photocatalytic removal of various water pollutants using the efficient noble metal (Au & Ag) doped SrTiO3 as a photocatalyst and discusses the properties of those materials and also discuss the prospects for the utilization of those photocatalysts in complex form for the wastewater treatment.

Efficient activation of peracetic acid via a defect-rich carbon nanotube@Co3O4 three-dimensional network for antibiotic removal: mechanism insights and practical water remediation

Peracetic acid (PAA)-based advanced oxidation processes have garnered increasing attention for eliminating organic pollutants in wastewater treatment.

Photocatalytic Degradation of Methylene Blue using Fe2O3-TiO2/Kaolinite under Visible Light Illumination

<p>Combining TiO<sub>2</sub> and a semiconductor with a smaller band gap, such as Fe<sub>2</sub>O<sub>3</sub>, to form a heterojunction composite can increase its photocatalytic activity. In this work, the Fe<sub>2</sub>O<sub>3</sub>-TiO<sub>2</sub>/kaolinite composites were successfully synthesized by ultrasonic-assisted coprecipitation using titanium-tetraisopropoxide (TTIP) dan Fe (NO<sub>3</sub>)<sub>3</sub>.9H<sub>2</sub>O as precursors. Using kaolinite as a matrix also increases the photocatalyst’s surface area. The obtained Fe<sub>2</sub>O<sub>3</sub>-TiO<sub>2</sub>/kaolinite composites were characterized. The crystal phase was characterized using X-Ray Diffraction and resulted in anatase with a crystallite size average of 9,7 nm. Fourier Transform Infrared Spectrophotometer (FTIR) shows the peak at a wavenumber 574-1210 cm<sup>−1</sup> ascribed TiO<sub>2</sub> and Fe<sub>2</sub>O<sub>3</sub> incorporated into kaolinite. The Optical properties show the absorption edge of Fe<sub>2</sub>O<sub>3</sub>-TiO<sub>2</sub>/kaolinite is redshift toward the visible light region. The result showed that the photocatalytic activity of Fe<sub>2</sub>O<sub>3</sub>-TiO<sub>2</sub>/kaolinite composites with heterostructure was more active than the corresponding Fe<sub>2</sub>O<sub>3</sub> or pure TiO<sub>2</sub> in the degradation of methylene blue under visible light illumination, which can degrade 83% for 180 minutes. Fe<sub>2</sub>O<sub>3</sub> and kaolinite cause its synergistic effect as supporting materials. Furthermore, it indicates that the recombination of photo hole and photoelectron charge pair can be minimized. The Fe<sub>2</sub>O<sub>3</sub>-TiO<sub>2</sub>/kaolinite composite is a promising photocatalyst to degrade organic pollutants for wastewater treatment.</p>

Generation of reactive oxygen species through dissolved oxygen activation on defected porous carbon for efficient degradation of antibiotics

Reactive oxygen species (ROS) are the most important practical oxidant for the degradation of various refractory organic pollutants in wastewater treatment. However, it is still challenging to develop self-producing ROS systems without external auxiliary reagents and energies. Herein, a kind of defected porous carbon is constructed to sustainably release ROS for the effective degradation of antibiotics. The as-prepared porous carbon materials possess an outstanding performance yielding 98.0 % removal of common antibiotics at the concentrations of 20 mg/L in 60 min. The results show that superoxide free radical (·O2−) plays the key role in the antibiotic degradation and singlet oxygen (1O2) generation. Density functional theory calculations further reveal that the nonagonal ring structures of carbon-vacancies are likely dominating active centers to chemically adsorb and directly convert dissolved oxygen to ·O2−. This work not only provides a novel carbon material for efficient degradation of antibiotics but also improves the understanding of the oxygen molecule activation on carbon defects.

Fabrication of a novel Ti3C2-modified Sb-SnO2 porous electrode for electrochemical oxidation of organic pollutants

Sb-SnO2 is an appealing electrode for degrading organic pollutants in wastewater treatment, albeit further modifications are needed for its inefficient electrochemical oxidation capacity. In this work, we prepared Ti3C2-modified Sb-SnO2 electrode by electrodeposition technology. High-conductive MXene matrix regulated the Sb-Sn alloy nucleation process to decrease its domain size during deposition and generated pores during the annealing process. When introducing 20 mg MXene into the electrolyte, the obtained Sb-SnO2 electrode (Ti3C2-20) presented a larger oxygen evolution over-potential (2.32 V vsSCE), increased amount of active sites, and enlarged electrochemical specific surface area (∼4.4-fold) than the unmodified electrode, resulting in a promoted OH generation ability (∼7.4 times). Methylene blue (MB), methyl orange (MO), norfloxacin (NOR), and P-phenylenediamine (PPD) were effectively degraded by the Ti3C2-20 anode with economic energy consumption. Moreover, the Ti3C2-20 electrode also featured a longer lifetime, almost fivefold, than the unmodified Sb-SnO2 electrode due to its larger loading amount and decreased charge transfer resistance. Consequently, this work offers a new perspective for designing efficient and stable porous electrodes to address water pollution issues.

Enhanced production of hydroxyl radicals in plasma-treated water via a negative DC bias coupling

Hydroxyl radical (OH•) plays an important role in advanced oxidation processes (AOPs), which are employed to decompose organic pollutants in wastewater treatment. OH• is predominantly produced in AOPs for wastewater treatment via ultraviolet photolysis of hydrogen peroxide (H2O2) or ozone, which is a costly and difficult process. This paper introduces an enhanced OH• production method based on microwave-driven atmospheric pressure plasma with negatively biased water. Fluorescence analysis using terephthalic acid and 2-hydroxyterephthalic acid showed that the OH• concentration in a DC coupled plasma-treated water (PTW) can be increased by 1–2 orders of magnitude compared to the case with microwave plasma only. In addition, we found that there exists an optimal concentration of H2O2 in PTW for the ideal production of OH•. As a test case of AOPs, an Fe(III)-ethylenediaminetetraacetic acid solution containing H2O2 was treated with a DC coupled plasma for 10 min, and more than 80% decomposition was recorded.

Coupling photocatalytic water oxidation on decahedron BiVO4 crystals with catalytic wet peroxide oxidation for removing organic pollutions in wastewater

Catalytic wet peroxide oxidation (CWPO) is widely used to remove organic pollutants in industrial wastewater, however, the remained challenges in circulating Fe3+/Fe2+ ions, inevitably forming iron sludge and massively consuming H2O2 limit its applications. Herein, the coupling of CWPO and photocatalytic water oxidation on decahedron BiVO4 crystals was reported to solve the above challenges. Using spatial photogenerated charge separation between different facets of BiVO4, efficiently circulating Fe3+ to Fe2+ was realized with a selectivity of ~100%, which greatly inhibits the formation of iron sludge. Moreover, in-situ formation of H2O2 through two-hole-involved photocatalytic water oxidation on BiVO4 replenishes the H2O2 consuming in the CWPO process. The coupling system exhibits a much higher total organic carbon (TOC) removal than the CWPO process in various pollutants, giving an improvement of rate constant to more than 10 times. This work provides a potential coupling route for advanced degradation of organic pollutants in wastewater treatment.

When MXene (Ti3C2Tx) meet Ti/PbO2: An improved electrocatalytic activity and stability

Stable electrode materials with high catalytic activity are urgently required for electrochemical degradation of refractory organic pollutants in wastewater treatment. Herein, high conductive MXene (Ti3C2Tx) was firstly fabricated by electrophoretic deposition (EPD) as an interlayer for preparing a novel PbO2 electrode. The well-conducted Ti3C2Tx interlayer significantly improved the electrochemical performance of the EPD-2.0/PbO2 (EPD time was 2.0 min) electrode with the charge transfer resistance decreased by 9.51 times, the inner active sites increased by 5.21 times and the ∙OH radicals generation ability enhanced by 4.07 times than the control EPD-0/PbO2 anode. Consequently, the EPD-2.0/PbO2 electrode achieved nearly 100% basic fuchsin (BF) and 86.78% COD removal efficiency after 3.0 h electrolysis. Therefore, this new PbO2 electrode presented a promising potential for electrochemical degradation of BF and the new Ti3C2Tx middle layer could also be used to fabricate other efficient and stable anodes, such as SnO2, MnO2, TiO2, etc.