2D-Like Catalyst with a Micro-nanolinked Functional Surface for Water Purification.

In water purification, the performance of heterogeneous advanced oxidation processes significantly relies upon the utilization of the catalyst's specific surface area (SSA). However, the presence of the structural "dead volume" and pore-size-induced diffusion-reaction trade-off limitation restricts the functioning of the SSA. Here, we reported an effective approach to make the best SSA by changing the traditional 3D spherule catalyst into a 2D-like form and creating an in situ micro-nanolinked structure. Thus, a 2D-like catalyst was obtained which was characterized by a mini "paddy field" surface, and it exhibited a sharply decreased dead volume, a highly available SSA and oriented flexibility. Given its paddy-field-like mass-transfer routine, the organic capture capability was 7.5-fold higher than that of the catalyst with mesopores only. Moreover, such a catalyst exhibited a record-high O3-to-·OH transition rate of 2.86 × 10-8 compared with reported millimetric catalysts (metal base), which contributed to a 6.12-fold higher total organic removal per catalyst mass than traditional 3D catalysts. The facile scale preparation, performance stability, and significant material savings with the 2D-like catalyst were also beneficial for practical applications. Our findings provide a unique and general approach for designing potential catalysts with excellent performance in water purification.

Electric field-enhanced heterogeneous catalytic ozonation (EHCO) process for sulfadiazine removal: The role of cathodic reduction.

In this work, an electric field-enhanced heterogeneous catalytic ozonation (EHCO) was systematically investigated using a prepared FeOx/PAC catalyst. The EHCO process exhibited high sulfadiazine (SDZ) and TOC removal efficiency compared with electrocatalysis (EC) and heterogeneous catalytic ozonation (HCO) process. Almost 100% of SDZ was removed within 2 min, and the TOC removal reached approximately 85% within 60 min. Quenching experiments and EPR analysis suggested that the prominent SDZ and TOC removal performance is supported by the enhanced ·OH generation ability. Further study proved that H2O2 formed by O2 electrochemical reduction, peroxone reaction and electrochemical reduction of ozone contributed to improving ·OH generation. Furthermore, the EHCO system showed satisfactory stability and recyclability compared to conventional HCO systems, and the SDZ and TOC removal rates were maintained at ≥95% and ≥70% in 16 consecutive recycles, respectively. Meanwhile, XPS analysis and Boehm's titration for the FeOx/PAC catalyst used in HCO and EHCO process confirmed that the external electron supply could restrain the oxidation of surface functional groups of PAC and maintain a balance of the Fe(II)/Fe(III) ratio, which proved the critical role of cathode reduction in catalyst in situ regeneration during long consecutive recycles. In addition, the EHCO system could achieve more than 80% SDZ removal within 2 min in different water matrices. These results confirmed that the EHCO process has a wide application perspective for refractory organics removal in actual wastewater.

Comprehensive analysis of research trends and prospects in electrochemical advanced oxidation processes (EAOPs) for wastewater treatment.

Electrochemical advanced oxidation processes (EAOPs) have emerged as a promising approach for efficient wastewater treatment. However, despite their promising potential, there is a lack of comprehensive analysis regarding the research trends, bibliometric data, and research frontiers of EAOPs. To address this gap, this study conducted a thorough and comprehensive analysis of 2347 related articles in the Web of Science Core Collection Database from 2012 to 2022. The analysis included information on countries, authors, institutions, and more, with a focus on summarizing trends and cutting-edge research hotspots in the field. The University of Barcelona in Spain is the most effective institution. Brillas E. is the most productive author in the world. Research hotspots in EAOPs have evolved from traditional anodic oxidation (AO) to novel electro-Fenton (EF) technology, which focuses on efficient generation of H2O2 and the use of metal-organic frameworks to enhance performance and efficiency. Through systematic research hotspot analysis, the importance of performance comparison of different types of EAOPs, development of new materials, optimization of device parameters, and toxicity assessment of byproducts is highlighted. Concurrently, the rise and mechanisms of emerging EAOPs are predicted and analyzed. Finally, future research on EAOPs technologies should focus on technological coupling, development of new materials, reduction of energy consumption and cost, evaluation and minimization of toxicity, and exploration of green renewable energy sources for larger-scale applications in wastewater treatment pilot plants. In this way, these technologies can contribute to the sustainability of larger industrial wastewater treatment applications and make an important contribution to environmental protection and scientific and technological progress.

An extra-chelator-free fenton process assisted by electrocatalytic-induced in-situ pollutant carboxylation for target refractory organic efficient treatment in chemical-industrial wastewater.

For traditional Fenton processes, the quenching behavior of radical contenders (e.g., most aliphatic hydrocarbons) on hydroxyl radicals (·OH) usually hinders the removal of target refractory pollutants (aromatic/heterocyclic hydrocarbons) in chemical industrial wastewater, leading to excess energy consumption. Herein, we proposed an electrocatalytic-assisted chelation-Fenton (EACF) process, with no extra-chelator addition, to significantly enhance target refractory pollutant (pyrazole as a representative) removal under high ·OH contender (glyoxal) levels. Experiments and theoretical calculations proved that superoxide radical (·O2-) and anodic direct electron transfer (DET) effectively converted the strong ·OH-quenching substance (glyoxal) to a weak radical competitor (oxalate) during the electrocatalytic oxidation process, promoting Fe2+ chelation and therefore increasing radical utilization for pyrazole degradation (reached maximum of ∼43-fold value upon traditional Fenton), which appeared more obviously in neutral/alkaline Fenton conditions. For actual pharmaceutical tailwater treatment, the EACF achieved 2-folds higher oriented-oxidation capability and ∼78% lower operation cost per pyrazole removal than the traditional Fenton process, demonstrating promising potential for future practical applications.

Energy-efficient reuse of bio-treated textile wastewater by a porous-structure electrochemical PbO2 filter: Performance and mechanism.

In this work, a novel porous-structure electrochemical PbO2 filter (PEF-PbO2) was developed to achieve the reuse of bio-treated textile wastewater. The characterization of PEF-PbO2 confirmed that its coating has a variable pore size that increases with depth from the substrate, and the pores with a size of 5 µm account for the largest proportion. The study on the role of this unique structure illustrated that PEF-PbO2 possesses a larger electroactive area (4.09 times) than the conventional electrochemical PbO2 filter (EF-PbO2) and enhanced mass transfer (1.39 times) in flow mode. The investigation of operating parameters with a special discussion of electric energy consumption suggested that the optimal conditions were a current density of 3 mA cm-2, Na2SO4 concentration of 10 g L-1 and pH value of 3, which resulted in 99.07% and 53.3% removal of Rhodamine B and TOC, respectively, together with an MCETOC of 24.6%. A stable removal of 65.9% COD and 99.5% Rhodamine B with a low electric energy consumption of 5.19 kWh kg-1 COD under long-term reuse of bio-treated textile wastewater indicated that PEF-PbO2 was durable and energy-efficient in practical applications. Mechanism study by simulation calculation illustrated that the part of the pore of the PEF-PbO2's coating with small size (5 µm) plays an important role in this excellent performance which provides the advantage of rich ·OH concentration, short pollutant diffusion distance and high contact possibility.

Integrated electro-Fenton system based on embedded U-tube GDE for efficient degradation of ibuprofen.

Ibuprofen (IBP) is a carcinogenic non-steroidal anti-inflammatory drug (NSAID). It is of certain hazard to aquatic animals and may cause potential harm to human health. As traditional methods cannot effectively remove such a pollutant, many advanced oxidation processes (AOPs) have been developed for its degradation. The electro-Fenton process has the advantages of strong oxidative ability, a synergistic effect of various degradation processes, and a wide application range. This study developed a high-performance gas diffusion electrode (GDE) for electrochemical hydrogen peroxide (H2O2) production. The optimum system performance was found at the current density of 10 mA cm-2, pH of 7.0, and air flow rate at 0.6 L min-1, where the accumulation of H2O2 could reach as high as 769.82 mg L-1. The computational fluid dynamics (CFD) simulation results revealed a fast mass-transfer property in this electro-Fenton system with U-tube GDEs, which resulted in a deep-level degradation (∼100%) of the pollutant (IBP) and a low-concentration degradation of 10 mg L-1 within a 120-min reaction period. The high-performance liquid chromatography-mass spectrometry (LC-MS) studies demonstrated that the hydroxyl radicals were the primary active species in the electro-Fenton system and that the degradation intermediates of IBP were mainly 1-(4-isobutylphenyl) ethanol and 2-hydroxy-2-(4-isobutyl phenyl) propanoic acid through four probable electro-Fenton degradation pathways. This report provides a facile and efficient way to construct a high-performance electro-Fenton reactor, which could be effectively used in advanced oxidation processes (AOPs) to remove emerging contaminants in wastewater and natural water.

Membrane Fouling and Electrochemical Regeneration at a PbO2-Reactive Electrochemical Membrane: Study on Experiment and Mechanism.

Membrane fouling and regeneration are the key issues for the application of membrane separation (MS) technology. Reactive electrochemical membranes (REMs) exhibited high, stable permeate flux and the function of chemical-free electrochemical regeneration. This study fabricated a micro-filtration REM characterized by a PbO2 layer (PbO2-REM) to investigate the electro-triggered anti-fouling and regeneration progress within REMs. The PbO2-REM exhibited a three-dimensional porous structure with a few branch-like micro-pores. The PbO2-REM could alleviate Humic acid (HA) and Bisphenol A (BPA) fouling through electrochemical degradation combined with bubble migration, which achieved the best anti-fouling performance at current density of 4 mA cm-2 with 99.2% BPA removal. Regeneration in the electro-backwash (e-BW) mode was found as eight times that in the forward wash and full flux recovery was achieved at a current density of 3 mA cm-2. EIS and simulation study also confirmed complete regeneration by e-BW, which was ascribed to the air-water wash formed by bubble migration and flow. Repeated regeneration tests showed that PbO2-REM was stable for more than five cycles, indicating its high durability for practical uses. Mechanism analysis assisted by finite element simulation illustrated that the high catalytic PbO2 layer plays an important role in antifouling and regeneration.

Bifunctional Fe for Induced Graphitization and Catalytic Ozonation Based on a Fe/N-Doped Carbon-Al2O3 Framework: Theoretical Calculations Guided Catalyst Design and Optimization.

Heterogeneous catalytic ozonation is regarded as a feasible technology in advanced wastewater treatment. Catalytic performance, mass transfer, and mechanical strength are the key elements for large-scale applications of catalysts. To optimize those elements, Fe was selected for its dual role in graphitization and catalytic ozonation. A Fe/N-doped micron-scale carbon-Al2O3 framework (CAF) was designed and applied to a fluidized catalytic process for the treatment of secondary effluent from coal gasification. The chemical oxygen demand removal rate constant and the hydroxyl radical generation efficiency (Rct) of the Fe/N-doped CAF were 190% and 429% higher than those of pure ozone, respectively. Theoretical calculations revealed that higher Fe valence promoted ozone decomposition, which implied increasing FeIII content for further catalyst optimization. The rate constant and Rct with a higher FeIII-proportion catalyst were increased by 13% and 16%, respectively, compared to those with the lower one. Molecular dynamics and density functional theory calculations were performed to analyze the reaction kinetics qualitatively and quantitatively. The energy barrier corresponding to FeIII configuration was 1.32 kcal mol-1, 27% lower than that for FeII configuration. These theoretical calculations guided the catalyst optimization and provided a novel solution for designing ozonation catalysts. The Fe/N-doped CAF demonstrated a great potential for practical applications.

Membrane Separation Coupled with Electrochemical Advanced Oxidation Processes for Organic Wastewater Treatment: A Short Review.

Research on the coupling of membrane separation (MS) and electrochemical advanced oxidation processes (EAOPs) has been a hot area in water pollution control for decades. This coupling aims to greatly improve water quality and focuses on the challenges in practical application to provide a promising solution to water shortage problems. This article provides a summary of the coupling configurations of MS and EAOPs, including two-stage and one-pot processes. The two-stage process is a combination of MS and EAOPs where one process acts as a pretreatment for the other. Membrane fouling is reduced when setting EAOPs before MS, while mass transfer is promoted when placing EAOPs after MS. A one-pot process is a kind of integration of two technologies. The anode or cathode of the EAOPs is fabricated from porous materials to function as a membrane electrode; thus, pollutants are concurrently separated and degraded. The advantages of enhanced mass transfer and the enlarged electroactive area suggest that this process has excellent performance at a low current input, leading to much lower energy consumption. The reported conclusions illustrate that the coupling of MS and EAOPs is highly applicable and may be widely employed in wastewater treatment in the future.

A hybrid fluidized-bed reactor (HFBR) based on arrayed ceramic membranes (ACMs) coupled with powdered activated carbon (PAC) for efficient catalytic ozonation: A comprehensive study on a pilot scale.

Taking advantage of the high mass transfer in the bulk solution of fluidized-bed reactor (FBR), and the benefits of simultaneous particle separation and ozone catalysis on ceramic membranes, we proposed a hybrid fluidized-bed reactor (HFBR) based on arrayed ceramic membranes (ACMs) coupled with powdered activated carbon (PAC) for efficient catalytic ozonation. The optimum HFBR performance on a pilot scale was found at PAC addition of 3 g/L, ozone dosage of 25 mg/L, hydraulic retention time of 60 min and auxiliary aeration strength of 5 m3/h. During the 30-day treatment of coal-gasification secondary effluent (200 L/h), the HFBR system revealed not only a 117% increase in ozone utilization efficiency (ΔCOD/ΔO3) upon pure ozonation but also a highly purified effluent with better sterilization and low residual bromate (∼11 µg/L). Low-molecular-weight organic fragments and acids, as well as phthalate esters were identified as the main products in this process. By density functional theory (DFT) calculations, it was found the main functional groups (carbonyls, -C=O) on the PAC could be protected from direct ozonation in the presence of ozone-degradable organics (e.g. phenolic and aliphatic compounds) in the wastewater through an ozone-competing reaction, which prevented the rapid inactivation of the PAC in catalytic ozonation. A longer service life and cheaper materials for ceramic membranes would benefit low operation costs for the HFBR. Moreover, the addition of PAC could greatly reduce ozone demand by ∼60% in the HFBR, and therefore decrease energy consumption by ∼30%. Hence, the HFBR was proved to be a highly competitive technology for wide application in the near future.

Ni-Induced C-Al2O3-Framework (NiCAF) Supported Core-Multishell Catalysts for Efficient Catalytic Ozonation: A Structure-to-Performance Study.

During catalytic ozonation, Al2O3-supported catalysts usually have stable structures but relatively low surface activity, while carbon-supported catalysts are opposite. To encourage their synergisms, we designed a Ni-induced C-Al2O3-framework (NiCAF) and reinforced it with a Cu-Co bimetal to create an efficient catalyst (CuCo/NiCAF) with a core-multishell structure. The partial graphitization of carbon adjacent to Ni crystals formed a strong out-shell on the catalyst surface. The rate constant for total organic carbon removal of CuCo/NiCAF (0.172 ± 0.018 min-1) was 67% and 310% higher than that of Al2O3-supported catalysts and Al2O3 alone, respectively. The metals on CuCo/NiCAF contributed to surface-mediated reactions during catalytic ozonation, while the embedded carbon enhanced reactions within the solid-liquid boundary layer and in the bulk solution. Moreover, carbon embedment provided a 76% increase in ·OH-production efficiency and an 86% increase in organic-adsorption capacity compared to Al2O3-supported catalysts. During the long-term treatment of coal-gasification wastewater (∼5 m3 day-1), the pilot-scale demonstration of CuCo/NiCAF-catalyzed ozonation revealed a 120% increase in ozone-utilization efficiency (ΔCOD/ΔO3 = 2.12) compared to that of pure ozonation (0.96). These findings highlight catalysts supported on NiCAF as a facile and efficient approach to achieve both high catalytic activity and excellent structural stability, demonstrating that they are highly viable for practical applications.

The Role of Ion Exchange Membranes in Membrane Capacitive Deionisation.

Ion-exchange membranes (IEMs) are unique in combining the electrochemical properties of ion exchange resins and the permeability of a membrane. They are being used widely to treat industrial effluents, and in seawater and brackish water desalination. Membrane Capacitive Deionisation (MCDI) is an emerging, energy efficient technology for brackish water desalination in which these ion-exchange membranes act as selective gates allowing the transport of counter-ions toward carbon electrodes. This article provides a summary of recent developments in the preparation, characterization, and performance of ion exchange membranes in the MCDI field. In some parts of this review, the most relevant literature in the area of electrodialysis (ED) is also discussed to better elucidate the role of the ion exchange membranes. We conclude that more work is required to better define the desalination performance of the proposed novel materials and cell designs for MCDI in treating a wide range of feed waters. The extent of fouling, the development of cleaning strategies, and further techno-economic studies, will add value to this emerging technique.

Pesticide tailwater deeply treated by tubular porous electrode reactor (TPER): Purpose for discharging and cost saving.

Pesticide tailwater often contains residual and toxic contaminants of triazole fungicides (TFs) due to their poor biodegradability which will do great harm to local aquatic systems. For this case, a novel electrochemical reactor (TPER) equipped a tubular porous RuO2-Sb2O5-SnO2 electrode was assembled and then employed to deeply treat pesticide tailwater. Characterizations of the electrode studied by SEM, EDS and XRD analysis indicated that it owns a porous structure and a compact and crack-free surface. Influence of the porous structure on electrochemical property was examined by cyclic voltammetry and normal pulse voltammetry. The results indicated that porous structure can not only enlarge electrochemical active area but also increase mass transfer efficiency by 5.7-fold in flow-through mode compared with batch mode. Furthermore, the optimal operating conditions of TPER were flow rate of 250 mL min-1 and current density of 4 mA cm-2. After 1.5 h treatment under these conditions, Tz, TC and PPC were removed by 98.9%, 99.0% and 98.4% respectively, while 81.9% of COD was also removed. Additionally, the microbial content was dropped to 0 CFU mL-1 and fecal coliform was lower than 2 MPN (100 mL)-1. All results demonstrated that the treated tailwater has met the Class 1 of National Discharge Standard of China. Especially, operating cost of TPER was only $ 0.33 per ton. The excellent performance together with the low cost indicated that TPER is a promising option for depth treatment of industrial tailwater.

In situ preparation of Al-containing PVDF ultrafiltration membrane via sol-gel process.

Recently, inorganic nanoparticles blended within polymeric membranes have shown improved antifouling performance in wastewater treatment. However, agglomeration of nanoparticles remains as one of the major obstacles for generating a uniform surface. In this study, a new method for in situ preparation of Al-containing PVDF ultrafiltration membranes to improve the dispersion of nanoparticles is reported. The strategy of this method is to combine sol-gel process with traditional immersion precipitation process. Al sol was synthesized by the addition of anionic exchange resin in N,N-dimethylformamide (DMF) solvent containing aluminum chloride. Homogeneous Al-containing PVDF casting solution was then obtained by dissolving PVDF polymer in the Al sol. The membrane formation mechanism was investigated by precipitation kinetics and morphology. Results indicate that the addition of Al species can accelerate phase inversion of casting solution. Scanning electron microscopic images show that a typical transition from sponge-like structure to finger-like structure occurred with increasing Al species content. The existence and dispersion states of Al species in the resultant membrane matrix were further examined by transmission electron microscope and X-ray photoelectron spectrometer. The results indicate the Al species nanoparticles were well dispersed throughout PVDF matrix. Dynamic BSA fouling resistance experiments demonstrate the Al-containing PVDF membranes possess improved separation performances over the pure PVDF membranes.