TOC Removal Efficiency Research Articles

Interlayer single-atomic Fe−N4 sites on carbon-rich graphitic carbon nitride for notably enhanced photo-Fenton-like catalytic oxidation processes towards recalcitrant organic micropollutants

Glucose-assisted supramolecule self-assembly of melamine and cyanuric acid in the presence of Fe(NO3)3 combined with thermal polymerization is designed to fabricate C-rich g-C3N4-embedded interlayer single-atomic Fe−N4 sites catalyst (Fe1/C-CN). Fe1/C-CN exhibits outstanding photo-Fenton-like catalytic oxidation activity towards typical recalcitrant organic micropollutants. For example, the pseudo-first-order kinetic constant of Fe1/C-CN photo-Fenton-like system is 7.5 and 21.1 times higher than Fe1/C-CN photocatalysis and Fenton-like systems in degradation of p-nitrophenol, and TOC removal efficiency reaches up to 100% after reaction proceeds for 4 h. Mechanism studies reveal that synergy of maximum Fe atom utilization efficiency and boosted photoexcited charge separation dynamics accelerates regeneration of ≡Fe(II) and efficient H2O2 activation of Fe1/C-CN, leading to plentiful active oxygen species for deep oxidation of organic micropollutants. Fe1/C-CN also shows a robust reusability in long-term remediation of organic micropollutants, attributing to interlayer Fe−N coordination interactions for preventing single Fe atoms from agglomeration and leaching to reaction media.

High-efficiency nickel recovery from spent electroless nickel plating solution: effective degradation of high-concentration nickel complexes to form a nickel ferrite nanomaterial via Fe3O4 catalytic oxidation

High-concentration organic nickel complexes were efficiently degraded and converted into NiFe2O4 nanomaterials via Fe3O4 catalytic oxidation under alkaline conditions, with high removal efficiency of nickel (99.99%) and TOC (81.94%), respectively.

Using algae to treat wastewater from vegetables cooking: screeningScreening algal strains and assessing bacterial communities

Algae have the advantages of a fast growth rate, strong adaptability to various wastewater environments, and low biomass production costs. A total of seven algal species used in the current study, including two cyanobacterial species and five green algal strains belonging to three species were used to treat the wastewater from vegetable cooking (WWVC), and the algal species that could adapt to the wastewater with a high concentration of organic matter and had good purification ability for the WWVC were screened out. Among them, Desmodesmus sp. HXY3, Desmodesmus sp. HXY7, and Chlorella vulgaris FACHB 8 have good adaptability in the environment of WWVC. After 30 days of culture, the Chl-a content was basically stable at about 3 mg m–3. Flow cytometry and 16 S high-throughput results showed that there were bacteria in the Desmodesmus sp. HXY3 and Desmodesmus sp. HXY7 systems, accounting for 14.5% and 8.46%, respectively. The main phyla was Proteobacteria, and the main genus was Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium, accounting for 20.56% and 45.26%, respectively. Desmodesmus sp. HXY3, Desmodesmus sp. HXY7, and Chlorella vulgaris FACHB 8 have strong abilities to purify WWVC, and the removal efficiency of TDN, TDP, and TOC is 97.16%, 95.71%, and 95.09%, respectively. This experiment proves that Desmodesmus sp. HXY3, Desmodesmus sp. HXY7, and Chlorella vulgaris FACHB 8 have strong tolerance and an obvious treatment effect on WWVC.

4-Chloro-2-methylphenoxyacetic acid photo-reduction with sulfite excitation under UV irradiation: Kinetics, energy consumption, operational variables and toxicology with Daphnia magna

4-chloro-2-methylphenoxyacetic acid (MCPA) is persistent and emerging organic substances that cannot be removed by bio-degradation and simply enter the environment. Therefore, for its photo-reduction, new methods are needed, including advanced photo- reduction process. This work deals with use of MCPA photo-reduction process based on sulfite excitation under UV irradiation. The optimal pH was 9 and molar ratio 1:1 MCPA: Sulfite, and complete photo-reduction of MCPA was reached after 15 min reaction time. The effect of various parameters were optimized using one factor at time (OFAT). In kinetic investigation, reaction constant (kobs) reduced from 0.2794 to 0.1645 min−1 when MCPA concentration increase from 5 to 25 mg L−1. In addition, the reaction rate (robs) increased 1.397 to 4.1125 mg L−1 min−1. Also, EEO was determined by kinetics and IUPAC methods, which showed that the quantity of energy consumption increases with increasing MCPA concentration. 2-(o-tolyloxy)acetic acid, 1-ethoxy-2,4-dimethylbenzene, toluene, (E)− 2-(prop-l-en-l-yloxy)acetic acid, (E)− 1-ethoxyprop-1-ene, and (E)− 1-ethoxyprop-1-ene identified as intermediates. Improvement of biodegradability was investigated with tow indicators include AOS and COS and shows that with the passage of time, the improvement of degradability is noticeable. For explored the mineralization rate, COD, TOC removal efficiency reach > 99%, 74.7%, and 62%, respectively after 120 min reaction time. The acute toxicity test by Daphnia magna was utilized to assess the toxicity of UV/Sulfite process effluent, results showed that EC50 (96-hour) and toxicity unit (TU) were equal to 10.53 mg L−1 and 9.94 TU in raw solution of MCPA and 93.50 mg L−1 and 1.07 TU in treated solution respectively, which the effluent from the process was reduced significantly than the raw solution of pollutant. It can be disclosed that the UV/Sulfite process has a good performance in pollutant conversion to simple intermediate and improving biodegradability as well as wastewater detoxification to reach environmental standards.

A novel strategy for efficient utilization of carbon residue from biomass gasification loaded NiCo2O4 to construct composite catalysts for activation of peroxymonosulfate to effectively remove antibiotics

Carbon residue (CR) derived from biomass gasification is a type of solid waste discharged from the biomass gasifier. CR is a carbon-rich material with a large specific surface area. Herein, NiCo2O4 nanoparticles were generated in situ on CR via a facile solvothermal method and the NiCo2O4-CR (NCCR) composite catalysts were prepared via solvothermal synthesis followed calcination method. The catalytic activity of NCCR was investigated by activating peroxymonosulfate (PMS) for the ciprofloxacin (CIP) degradation. The NCCR/PMS system exhibited the degradation efficiency, TOC removal efficiency, and removal reaction rate constant (k) of 93.86 %, 44.09 %, and 0.049 min−1 for CIP in 60 min, respectively, which were 1.17, 1.21 and 1.20 times of those in the NiCo2O4/PMS system, suggesting that CR had a positive impact on the improvement of the catalytic properties of NiCo2O4. Significantly, NCCR showed remarkable performance in terms of pH adaptation range, resistance to environmental disturbances, reusability, and other contamination applications. SO4•–, O2•– and 1O2，as the dominant reactive oxygen species, disrupt the molecular structure of CIP. PMS activation with NCCR mainly form free radicals and non-free radicals catalyzed by the redox couples of Co (III)/Co (II) and Ni (III)/Ni (II). Specially, Co (IV) = O also form and participate in the CIP degradation via a non-free radical pathway. Three possible degradation pathways of CIP were suggested by the degradation intermediates. The CIP degradation in the NCCR/PMS system was a process of reducing toxicity, protecting water ecosystem. The study provides a method to improve the catalytic properties of transition metal for activating PMS to purify antibiotic contamination wastewater, and opens a novel insight to deal with the solid waste from biomass gasification.

Electrocoagulation Technique for Treating Swine Slaughterhouse Wastewater from Batch to Semicontinuous Operation Mode

In this study, industrial swine slaughterhouse wastewater was treated by electrocoagulation process using batch and semicontinuous operation systems. Electrochemical technique was carried out in batch operation mode during 2.5 h applying different current densities in sulfate and chloride media. After finding the best operating parameters in batch mode (lab-scale), the process was transferred to a semicontinuous pre-pilot scale process using a filter-press FM01-LC type electrochemical reactor fitted with flat plate aluminum electrodes. In this stage, distinct current densities and mean linear flow rates were assessed.Total organic carbon, chemical oxygen demand, total phosphorus, total nitrogen, and potassium among other parameters were analyzed during both treatments. The industrial swine slaughterhouse wastewater contained TOC 333 mg L–1, COD 1765 mg L–1, TP 13.55 mg L–1, TN 327 mg L–1, K 45 mg L–1, turbidity 102 NTU, color –absorbance 0.90 A.U. at 415 nm–, conductivity 1.9 mS cm–1, and pH 6.9. The highest TOC removal efficiency (72.7%), in semicontinuous process, was found at j = 25 mA cm-2 and ur = 0.64 cm s-1 with an energy consumption of 19.80 kW h m-3. Residual COD and TP concentrations met the international standard limits. Moreover, complete discoloration and disinfection were achieved. EDXRF, SEM, EDAX, XRD, and FTIR analyzes indicate pollutants were removed by adsorption on aluminum/iron hydroxides/oxyhydroxides.

Activation and stabilization of the Cu species via strong CuO-CeO2 interactions for enhanced decomposition of refractory aromatic organic pollutants in water

The copper (Cu)-driven advanced oxidation process (AOP) represents one green and efficient technology for the removal of refractory aromatic organic pollutants from water. However, its application remained challenged by the sluggish regeneration of the active Cu+ species and the environmental risk induced by Cu leaching. Herein we reported a facile approach to the bimetallic composite CuCeOx-A catalyst with strong CuO-CeO2 interactions (“A” referred to the acid-activation process). It enabled a TOC removal efficiency (δ%) of 92.4 % and a turnover frequency (TOF) of 1.57 min−1 for TOC removal from 100 mg/L 2-naphthol aqueous solution, outperforming the CuO (δ% = 82.9 % and TOF = 0.23 min−1) and most of the reported Cu-based catalysts. It was more active under neutral/weakly acidic conditions, and could keep high performances in a wide 2-NAP concentration window and in the presence of some impurity ions (PO43-, NH4+ or SiO32-). Additionally, the Cu leaching of CuCeOx-A maintained at a much lower level of ∼ 1.0 ± 0.2 mg/L than that of CuO (∼12.8 ± 1.9 mg/L). Mechanistic studies demonstrated that the enhanced AOP performance and chemical stability of CuCeOx-A originated from the strong CuO-CeO2 interactions, which facilitated the Cu+ regeneration by up-lifting the redox potential of Cu2+/Cu+ and stabilized Cu species via the Cu–O-Ce bonds. Further biological safety testing using chlorella cells as probe organism revealed that the CuCeOx-A-driven AOP was environmentally benign for aromatic organic pollutants removal.

Development of Ti4O7 reactive electrochemical membrane and electrochemical oxidation of naphthols in aqueous solution

Naphthols (NAPs), commonly used phenolic compounds, have significant impact on environmental risk and human health, necessitating advanced treatment methods for their degradation. In this study, a Ti4O7 reactive electrochemical membrane (REM) was developed for the electrochemical oxidation of NAPs. The Ti4O7 REM presented a porosity of 42.18 ± 2.3% and a median pore diameter of 1.21 µm. High permeability (846 LMH bar−1) was achieved at relatively low transmembrane pressure and resulted in a convection-enhanced rate constant for Fe (CN)64- oxidation of 1.7 × 10−4 m/s. The increase in current density and decrease in plate spacing had a positive influence on NAPs degradation. The TOC removal efficiencies of 1-naphthol (1-NAP) and 2-naphthol (2-NAP) were 68.6% and 63.5%, respectively at the current density of 6 mA/cm2 and plate spacing of 10 mm. Additionally, quantum chemical calculation using density functional theory (DFT) was employed to identify the active sites of NAPs through atom charge and frontier electron density (FED) calculations. Results showed that C14 and C10 were identified as the active sites for 1-NAP, while C9 and C13 were the active sites for 2-NAP. Hydroxyl radical and sulfate radical produced on the electrode surface were the main oxidants for NAPs degradation during the electro-oxidation process. The degradation pathway included hydroxylation, oxygenation, decarbonylation, and ring-open processes, which was in agreement with the theoretical calculations. Furthermore, the quantitative structure-activity relationship (QSAR) predictive model was used to assess the toxicity changes during the electrochemical oxidation process of NAPs, suggesting that the toxicity of intermediates increased at the beginning and significantly reduced at the end. This comprehensive study provides practical and theoretical insights into the application of electrochemical oxidation technique for the reduction of refractory compounds in wastewater.

Aluminum-based ozone catalysts prepared by mixing method: Characteristics, performance and carbon emissions

Green and low carbon is an essential direction for the development of water treatment technology. Ozone catalysts prepared by the mixing method have advantages in terms of energy consumption and CO2 emissions, but are considered to be insufficient in catalytic efficiency and stability. In this paper, an Mn–Cu–Ce/Al2O3 (MCCA) catalyst was prepared by optimizing the preparation conditions of the mixing method and the types and ratios of active components. Taking petrochemical secondary effluent (PCSE) as the treatment object, the performance of the catalyst and the carbon emission in the preparation process were studied; and compared with the impregnation method. Results showed that compared with catalysts loaded with other components, the MCCA had a higher removal efficiency for TOC (43.04%) and COD (53.18%), which was basically equivalent to the impregnation method, and the treated effluent reached the expected concentration. MCCA promoted the decomposition rate of O3 by ten times, and the main active species generated were found to be •OH and 1O. Similar to the catalytic ozonation by the catalyst prepared by the impregnation method, the adsorption sites and surface hydroxyl groups on the MCCA surface play a significant role in the degradation of pollutants. However, the carbon emission in the catalyst preparation process of the mixing method was 418.68 kg/ton, which was only 44% of the impregnation method (949.67 kg/ton). Under the global low-carbon transition, this study shows that the mixing method aligns more with the concept of green, clean, and efficient ozone catalyst preparation.

Enhancing industrial swine slaughterhouse wastewater treatment: Optimization of electrocoagulation technique and operating mode

In this study, industrial swine slaughterhouse effluents were treated by an electrocoagulation process (EC) with aluminum and iron electrodes. Batch and semicontinuous operation were performed. EC tests were carried out in batch operating mode for 2.5 h using fixed current densities (j = 10, 20, and 30 mA cm−2) in sulfate and chloride media. At the laboratory scale, higher TOC removal efficiencies were observed using aluminum electrodes at 20 mA cm−2 without the addition of a supporting electrolyte (82.7%). However, the EC process with Fe electrodes consumed 43.6% less energy.After the best operating parameters were found at the laboratory scale, the process was tested as a semicontinuous prepilot process using a filter-press FM01-LC-type electrochemical reactor equipped with flat plate aluminum electrodes. In this stage, current densities and mean linear flow rates were assessed. The highest TOC removal efficiency of 72.7% (i.e., residual TOC concentration of 85.18 mg L−1) in the semicontinuous process was achieved by the application of j = 25 mA cm−2 and ur = 0.64 cm s−1 with an energy consumption of 19.80 kW h m−3. The residual COD and TP concentrations met the international standard limits. Moreover, complete decoloration and disinfection were accomplished. EDXRF, SEM, EDAX, XRD, and FTIR analyses indicated that pollutants were removed by adsorption on aluminum/iron hydroxides/oxyhydroxides.

Treatment of landfill leachate nanofiltration concentrate by a three-dimensional electrochemical technology with waste aluminum scraps as particle electrodes: Efficacy, mechanisms, and enhancement effect of subsequent electrocoagulation

Landfill leachate nanofiltration concentrate is a kind of wastewater containing high concentrations of color and refractory organics. Herein, we proposed a novel three-dimensional electrochemical technology (3DET) with waste aluminum scraps as particle electrodes for its treatment. The planar and particle electrodes were first optimized. Ti/RuO2 and graphite were used as anodes in the two-dimensional electrochemical technology (2DET). In the light of contaminant removal (color, UV254, COD, and TOC), chlorine reduction, and energy consumption, graphite was selected as planar anodes and cathodes. Moreover, 3DET with Al particle electrodes (Al 3DET) outperformed that with conventional granular activated carbon electrodes, 2DET, and Al particles. At 120 min, the removal efficiencies of color, UV254, COD, and TOC using Al 3DET were 98.94 %, 84.72 %, 51.93 %, and 67.46 %, respectively. UV–vis and EEM spectroscopy, and GC–MS analyses indicate that macromolecular organic matter such as humic-like substances could be effectively degraded and simultaneously removed. Reactive species identification tests including free radical quenching and EPR spectra were conducted. The results indicate that in addition to anodic direct oxidation, indirect oxidation by oxidative species (H2O2, •OH, and RCS) and flocculation by Al species also played a vital role in contaminant removal. Continuous-flow experiments show that Fe EC as a post-treatment step of Al 3DET could effectively provide a neutralization effect for the 3DET effluent and enhance the removal efficiency of contaminants. The total operating cost of combined process was 1.307 USD/m3. This study shows that the Al 3DET-Fe EC process is a promising technology for the treatment of nanofiltration concentrate.

Regulated synthesis of cobalt phosphide/biochar utilizing phytic acid: Biochar enhances anion co-catalysis of cobalt phosphides in persulfate activation

Effective activation of persulfate (PS) contributes to the efficient degradation of emerging organic pollutants in water matrices. Cobalt phosphides (CoxP) have been testified as promising catalysts in efficiently activating PS, but their applications in water purification are still restricted by hazardous and costly chemical phosphorus sources used in traditional syntheses. Here, the synthesis of CoxP on biochar is regulated by an eco-friendly biomass phytic acid (PA) through low-speed ball milling combined with catalytic pyrolysis. Under the condition of 1 mM PS, 0.2 g/L catalyst, and pH 7, SMX (10 mg/L) can be thoroughly removed within 120 min with a TOC removal efficiency of 52 %. When dealing with low concentrations of SMX (0.25–1 mg/L), the oxidation is completed within 60 min. The simulated complex aqueous matrices (sodium humate solution and surface water) only exert trivial inhibition of SMX removal. Moreover, the leached Co2+ ion concentration is lower than the discharge standard (0.39 mg/L within 180 min). The crucial reactive oxygen species are identified as SO4−•, •OH, 1O2, and O2−•. Density functional theory (DFT) calculations indicate that the most pivotal active site in CoP/biochar is the P ion, while in Co2P/biochar is the Co ion. Biochar may potentially influence the electronic structure, thereby altering the oxidation states of ions and significantly enhancing the synergistic catalytic effect of anions in both cobalt phosphides. The more pronounced anion co-catalysis endows CoP/biochar with a better catalytic capacity than Co2P/biochar.

A novel chemical reaction between P25 and γ-Bi2O3 in CaTiO3 preparation constructing two new transfer channels of charge carriers to boost photocatalytic degradation activity

For the current design of heterojunction, only one new transfer channel of charge carriers was generated. In this paper, a novel chemical reaction between P25 and γ-Bi2O3 generated Bi4Ti3O12 to construct two new transfer channels in the preparation process of CaTiO3. The optimal sample CaTiO3/Bi4Ti3O12/γ-Bi2O3-12 could degrade 94 % of bisphenol A and 99 % of bisphenol AF, which was much higher than those of the pure phases and the two-phase junction samples. The photocatalytic efficiency of these two pollutants remained 94 % and 99 % in the five cycle tests to indicate that the above new channels were not destroyed after continuous utilization. The main active substances were hole, electron and superoxide radical O2–• in process of degradation. Different wastewater environments held a slight impact on photocatalytic efficiency to reveal a good applicability in real-world environments. After 90 min, the TOC and COD removal efficiencies of bisphenol A also attained 43 % and 44 % while those of bisphenol AF reached to 77 % and 83 %. The excellent photodegradation activity came from the formation of two new channels to accelerate the spatial separation of charge carriers. The colony numbers of Escherichia coli were 0.87 × 10-6 CFU/mL and 0.88 × 10-6 CFU/mL in the solution degraded by bisphenol A and bisphenol AF to show the non-toxicity of the final product. Thus two new transfer channels were obtained via P25 reacting with γ-Bi2O3 to enhance the catalyst activity, opening up a unique idea for heterojunction preparation.

Improving electro-fenton degradation performance using waste biomass-derived-modified biochar electrodes: A real environment textile water treatment

In this study, catalytically efficient biochar electrodes were obtained by pyrolysis and thermal modification from waste biomass. The effect of the gas type, temperature and time on the thermal modification was investigated in the designed Electro-Fenton system. Firstly, the most effective biochar electrode (CO2-700–1 h) was determined by evaluating the TOC, dye removal efficiencies and peroxide production. Then, the process parameters (pH, time, potential, catalyst-electrolyte concentration, electrolyte type) were examined to determine optimum wastewater treatment conditions. In the next step, the economic results of the study were analyzed in the optimum conditions by comparing 3 electrodes. The treatment cost obtained with the CO2-700–1 h was 34.9% and 8.64% lower than the raw biochar (N2-350–4 h) electrode and its nitrogen gas-modified counterpart (N2-700–1 h). Dye and TOC removal efficiency increased up to 2.12 and 4.65 times, respectively. The TOC efficiency of the regenerated electrode decreased by only 9.94% at the end of 10 cycles.

Hydrogen peroxide assisted advanced electrocoagulation for reducing the organic content of leachate nanofiltration concentrate

Integrated biological treatment-membrane filtration is widely applied in leachate treatment to ensure discharge standards. The most important waste of this integrated application is high volumes of membrane concentrate. In this study, the treatment of leachate nanofiltration concentrate (NFC) with high resistive organic matter content was investigated by hydrogen peroxide (HP) assisted advanced electrocoagulation process (EC-HP) using Al electrodes. To achieve maximum pollutant removal efficiencies, process optimization was carried out using the Box-Behnken design (BBD). Statistically, the fit of the model was evaluated by analysis of variance. Correlation coefficients (R2) of all mathematical models developed for system responses (COD, UV254, TOC, and color removal efficiency) with EC-HP process were close to 1, adjusted R2 values were close to R2 values, and the difference between adjusted R2 and predicted R2 values was less than 0.2. These values indicate that the BBD method is effective, appropriate, and meaningful in explaining the pollutant removal from leachate NFC with the EC-HP process. Under the optimized conditions (27.3 mM HP, 0.6 A, pH 5, and 45 min) 62.2 %, 55.3 %, 73.9 %, and 85.9 % COD, TOC, UV254, and color removal efficiencies, respectively were predicted by the model and by validation study, 57.3 % COD, 52.0 % TOC, 68.3 % UV254, and 85.0 % color removal yields were achieved. SEC and SECCOD values were calculated as 7.65 kWh/m3 and 2.78 kWh/kgCOD, respectively at optimum conditions. Moreover, ENC, ELC, CC, and TC values were 0.55 $/m3, 0.82 $/m3, 8.0 $/m3, and 9.37 $/m3, respectively. The results of the study showed that the EC-HP process is an effective method for pollutant removal from leachate NFC.

Effective remediation of leachate concentrate by peroxymonosulfate in a catalytic ceramic membrane filtration process: Performance and mechanism

Membrane concentrated landfill leachate has been characterized by complex component and degradation resistant. In this work, a new catalytic ceramic membrane (CuCM) was developed by in-situ integrating copper oxide in the membrane and used in combination with peroxymonosulfate (PMS) for leachate concentrate treatment. The performance and key factors of the CuCM/PMS system were systematically studied. Results showed that the CuCM/PMS system experienced promising efficiency in the pH range of 3 ∼ 11. The highest COD, TOC, UV254 and Color removal efficiency achieved by the CuCM-3/PMS system under the conditions of pH = 7.0 and CPMS = 10 mM, which reached up to 63.4%, 50.5%, 75.1% and 90.2%, respectively. The possible mechanism of leachate remediation was proposed and non-free radicals (Cu(Ⅲ), 1O2) played an important role in the CuCM/PMS system for leachate remediation. The fluorescence spectrum and GC–MS analysis showed that the refractory organics with a high molecular weight in the leachate concentrate were mostly oxidized into small molecules, which also alleviated the membrane fouling. In addition, the slight decrease in COD (7.4%) and TOC (9.7%) after 6 cycles revealed the good catalytic stability and reusability of CuCM-3/PMS. This work provides a feasible strategy for leachate concentrate remediation via a nonradical oxidation process.

Improved piezocatalytic activity with Ag2O@KNbO3: Mechanisms and performance in organic pollutant degradation

Constructing heterojunctions in a rational and effective way plays a vital role in enhancing the catalytic performance of piezo-/ferroelectric nanomaterials. In this paper, a new material called Ag2O@KNbO3 was fabricated using solvothermal and alkaline deposition methods. This material was found to be an effective catalyst for breaking down various organic pollutants, for example, Orange Ⅱ, Methyl orange, etc. Under optimal conditions, Ag2O@KNbO3 (1:1) demonstrated superior piezocatalytic activity with a degradation efficiency of 97.8% for Orange II within 120 min and a high TOC removal efficiency of 58.4%. The cycle stability for Orange II removal was also excellent. After 5 cycles, the degradation efficiency of Orange II still surpassed 95%. The related enhancement mechanism of the piezocatalytic activity was elaborated in detail, with Ag2O/KNbO3 heterojunctions promoting directed charge movement, reducing impedance of charge transport, and hindering electron-hole recombination, thereby improving charge transfer efficiency. Additionally, OH was confirmed to be the primary active species by electron spin resonance analysis and free radical capture experiment. Notably, a possible degradation pathway of Orange Ⅱ was inferred according to the LC-MS measurement. Overall, this study provides a promising approach for designing and synthesizing new piezoelectric catalytic materials.

Chloride ion enhanced oxidant-free in situ degradation of Ni-EDTA by electrochemical process with boron-doped diamond electrodes

Conventional advanced oxidation processes were used to treat heavy metal complexes. However, a considerable amount of oxidants was required to enable effective oxidative degradation, which led to a significant increase of the treatment costs and subsequent difficulties in the sludge disposal. Based on the abundance of anions in heavy metal wastewater, the effects of anions on the in-situ degradation of Ni-EDTA in an oxidant-free electrochemical system with boron-doped diamond (BDD) as the anode were investigated. The presence of Cl- was found to exert a significant effect on improving the degradation process. Moreover, pH had little effect on the removal of nickel (Ni) and Ni-EDTA within a specific pH range (1 < pH < 9). The removal efficiencies of Ni and TOC reached 100 % and 77.45 %, respectively, at pH 2.16 with 0.4 M NaCl electrolyte, 2 mM Ni-EDTA concentration, and a current density of 50 mA/cm2. •OH and Cl• played crucial roles in the removal of Ni-EDTA by disrupting the chelation sites of Ni and EDTA molecules. The released Ni2+ ions could active the H2O2 in-situ generated at the cathode to produce •OH. The formation of the precipitation products such as NiOOH, Ni(OH)2, and NiCO3 in the Cl-/BDD system were conform based on the XRD and XPS analyses, which suggested the possible pathways for the removal of Ni2+ and Ni3+. Finally, the possible degradation pathways of Ni-EDTA were proposed based on the identification of intermediate products using UPLC-MS.

Y-mediated optimization of 3DG-PbO2 anode for electrochemical degradation of PFOS

In our previous study, the three-dimensional graphene-modified PbO2 (3DG-PbO2) anode was prepared for the effective degradation of perfluorooctanesulfonat (PFOS) by the electrochemical oxidation process. However, the mineralization efficiency of PFOS at the 3DG-PbO2 anode still needs to be further improved due to the recalcitrance of PFOS. Thus, in this study, the yttrium (Y) was doped into the 3DG-PbO2 film to further improve the electrochemical activity of the PbO2 anode. To optimize the doping amount of Y, three Y and 3DG codoped PbO2 anodes were fabricated with different Y3+ concentrations of 5, 15, and 30 mM in the electroplating solution, which were named Y/3DG-PbO2-5, Y/3DG-PbO2-15 and Y/3DG-PbO2-30, respectively. The results of morphological, structural, and electrochemical characterization revealed that doping Y into the 3DG-PbO2 anode further refined the β-PbO2 crystals, increased the oxygen evolution overpotential and active sites, and reduced the electron transfer resistance, resulting in a superior electrocatalytic activity. Among all the prepared anodes, the Y/3DG-PbO2-15 anode exhibited the best activity for electrochemical oxidation of PFOS. After 120 min of electrolysis, the TOC removal efficiency was 80.89% with Y/3DG-PbO2-15 anode, greatly higher than 69.13% with 3DG-PbO2 anode. In addition, the effect of operating parameters on PFOS removal was analyzed by response surface, and the obtained optimum values of current density, initial PFOS concentration, pH, and Na2SO4 concentration were 50 mA/cm2, 12.21 mg/L, 5.39, and 0.01 M, respectively. Under the optimal conditions, the PFOS removal efficiency reached up to 97.16% after 40 min of electrolysis. The results of the present study confirmed that the Y/3DG-PbO2 was a promising anode for electrocatalytic oxidation of persistent organic pollutants.

Anti-fouling and self-cleaning ability of BiVO4/rGO and BiVO4/g-C3N4 visible light-driven photocatalysts modified ceramic membrane in high performance ultrafiltration of oily wastewater

Oily wastewater is one of the most harmful and resistant types of wastewater that cannot be treated with the usual and traditional methods. In this study, the visible light-driven photocatalysts BiVO4/rGO and BiVO4/g-C3N4 were made using the hydrothermal method. After that, a simple sol-gel method was used to make a photocatalytic ultrafiltration membrane with good self-cleaning and anti-fouling properties that can effectively separate oily wastewater. Photocatalyst properties were identified by using XRD, FTIR, DRS, N2 absorption-desorption, and zeta potential analysis. The performance of photocatalytic membranes was then investigated in oily wastewater treatment. Antifouling parameters, underwater oil contact angle, surface roughness, and electrochemical properties were measured to look into the membrane's antifouling properties. The use of a BiVO4/rGO composition with 20 wt% of rGO produced an underwater oil contact angle of 158°. Also, after 3 h of 3000 ppm oily wastewater filtration, the permeate flux was double that of the UF membrane without a photocatalytic coating, and the TOC removal efficiency was more than 99%. Measurement of antifouling parameters revealed that flux recovery was 89% compared to 51% for the UF membrane, and the total fouling ratio was reduced from 57% to 21%.