Wastewater Purification Research Articles

Water remediation with a dielectric-free portable triple-electrode cold plasma discharge system

This paper presents the design and application of a portable multi-electrode cold plasma corona discharge system for pollutant degradation in wastewater. The system generated stable plasma without a dielectric barrier, producing active species such as hydroxyl radicals, hydrogen peroxide, nitrite, and nitrate. The experimental results presented a pollutant degradation efficiency of 100%, reducing methylene blue as a model pollutant from 6 ppm to 0 ppm within 125 s at an optimized electrode distance of 0.20 cm. This optimization minimizes the risks associated with the arcing and self-collision of plasma streams while sustaining continuous plasma discharge, ensuring the maximum breakdown voltage and high ion density for efficient plasma production. The system further demonstrated its application in treating hand washing as a target pollutant to reduce the risk of infection during the COVID-19 pandemic. A comparative analysis highlighted the advantages of the system in terms of rapid treatment, energy efficiency, and low-cost operation. The processed water met the World Health Organization (WHO) wastewater discharge standards and WHO guidelines for virus elimination, with residual nitrogen compounds maintained below 50 ppm and hydrogen peroxide levels kept under 5,000 ppm, confirming the effectiveness of the system in pathogen reduction and wastewater purification.

H‐Bonds in Carbon Quantum Dot‐anchored C3N5 to Boost Proton‐Coupled Electron Transfer for Piezoelectric‐Driven Hydrogen Peroxide Synthesis under Ambient Conditions

Tuning proton‐coupled electron transfer (PCET) is a promising strategy to boost the oxygen reduction reaction (ORR) for H2O2 synthesis, but the slow transmission rate of protons and electrons to active sites remains a significant bottleneck. To address this, we developed an H‐bond‐driven PCET process based on carbon quantum dotanchored C3N5 (CQDs‐C3N5) for piezo‐catalytic H2O2 synthesis. CQD‐C3N5 exhibited a remarkable piezo‐catalytic synthesis rate of 5025 μmol g⁻¹ h⁻¹ under ambient conditions. This efficiency is attributed to H‐bonds between CQDs and C3N5, which accelerate PCET in the ORR. The piezoelectric‐generated charges, from the dipole field of the C3N5 plane and protons in water, were rapidly transferred to the C rings of CQDs via H‐bonds. This process facilitated the adsorption of oxygen onto C2 sites adjacent to carboxyl groups of CQDs, which in turn led to the formation of H2O2 through a rapidly protonated, indirect 2e− pathway. Additionally, a piezo‐self‐Fenton reaction system was constructed for oxytetracycline‐rich wastewater purification, with effectively effects on chemical oxygen demand, antibiotic‐resistant bacteria and antibiotic‐resistant genes degradation. This study highlights the critical role of H‐bond networks for tuning PCET in the ORR and provides a comprehensive understanding for the precise control of catalytic reaction kinetics through molecular structural engineering.

Enhanced Removal of Acid Orange 7 onto Layered Interleaved Symmetrical 3D Flower-like CeO2 with Y(III) Doping

CeO2 has a potential application in the purification of organic dye wastewater because of the abundant oxygen vacancy (VO) defects in its crystals. In this study, a cubic CeO2 microsphere with layered interleaved symmetrical 3D flower-like morphology was synthesized, and its adsorption capacity for acid orange 7 (AO7) was further enhanced by Y doping. The impact of varying amounts of Y ions on the phase composition, lattice parameters, and morphology of the product was investigated, revealing that 4 mol.% was determined as the doping level limit of Y ions in CeO2 crystals. XPS, Raman, and H2−TPR techniques were employed to compare surface species changes before and after 4 mol.% Y doping in the CeO2 crystals, including O−Ce(III), O−Ce(IV), O−Y(III), and VO correlation, yielding a rough quantitative assessment of these species. The 4 mol.% Y-doped CeO2 (2.0 g/L) demonstrated the highest removal rate for 20 mg/L of AO7 dye within just 20 min to reach adsorption–desorption equilibrium, half the time required by undoped CeO2, achieving an impressive adsorption rate of 94.6%, compared to only 69.5% for undoped CeO2 at 20 min. The adsorption capacity of undoped CeO2 was enhanced by 19.05% through the doping of 4 mol.% Y, achieving a value of 16.56 mg/L. The feasibility of enhancing the adsorption capacity of CeO2 by Y doping provides a reference for the application of CeO2 and other metal oxides.

H-Bonds in Carbon Quantum Dot-anchored C3N5 to Boost Proton-Coupled Electron Transfer for Piezoelectric-Driven Hydrogen Peroxide Synthesis under Ambient Conditions.

Tuning proton-coupled electron transfer (PCET) is a promising strategy to boost the oxygen reduction reaction (ORR) for H2O2 synthesis, but the slow transmission rate of protons and electrons to active sites remains a significant bottleneck. To address this, we developed an H-bond-driven PCET process based on carbon quantum dotanchored C3N5 (CQDs-C3N5) for piezo-catalytic H2O2 synthesis. CQD-C3N5 exhibited a remarkable piezo-catalytic synthesis rate of 5025 μmol g⁻¹ h⁻¹ under ambient conditions. This efficiency is attributed to H-bonds between CQDs and C3N5, which accelerate PCET in the ORR. The piezoelectric-generated charges, from the dipole field of the C3N5 plane and protons in water, were rapidly transferred to the C rings of CQDs via H-bonds. This process facilitated the adsorption of oxygen onto C2 sites adjacent to carboxyl groups of CQDs, which in turn led to the formation of H2O2 through a rapidly protonated, indirect 2e- pathway. Additionally, a piezo-self-Fenton reaction system was constructed for oxytetracycline-rich wastewater purification, with effectively effects on chemical oxygen demand, antibiotic-resistant bacteria and antibiotic-resistant genes degradation. This study highlights the critical role of H-bond networks for tuning PCET in the ORR and provides a comprehensive understanding for the precise control of catalytic reaction kinetics through molecular structural engineering.

Integrated Purification Systems for the Removal of Disinfectants from Wastewater

The efficiency of integrated treatment systems for wastewater generated during the washing of disinfectant production lines was investigated. The high organic load (COD 2000 mg/L, TOC 850 mg/L) and 300 mg/L of toxic benzalkonium chloride (BAC) make wastewater an environmental hazard that requires advanced treatment. Initial tests on model BAC solutions (in concentrations corresponding to those found in wastewater), using nanofiltration and ultrafiltration membranes, resulted in up to 70% retention of BAC. To enhance purification, ion exchange and adsorption were introduced as post-membrane treatment steps. In the second part of the investigation, membrane modules characterized by the best separation properties were integrated together with macroporous cation-exchange resin and activated carbon into the purification system to treat wastewater. The research carried out showed that the purification of multicomponent wastewater is a complex task. Significantly lower BAC removal (30%) was achieved in membrane processes compared to the model solutions treatment. In integrated systems, the BAC concentration was reduced to 100 mg/L, TOC to 200 mg/L, and COD to 120 mg/L.

In situ construction of CuBi2O4/Bi4O5Br2 Z-scheme heterojunction with enhanced photocatalytic degradation performance for polyphenolic contaminant in wastewater

Photocatalytic technique is one of the clean and promising routes for wastewater purification. In this work, a different CuBi2O4/Bi4O5Br2 Z-scheme heterojunction were successfully prepared via an in-situ mechanical agitation method. The 10% CuBi2O4/Bi4O5Br2 (10% CBO/BOB) heterojunction showed the highest photocatalytic degradation activity for catechin, and ∼99.8% catechin was degrade within 40 min visible light stimulation, which is (0.0757/min) about 6.2-folds and 8.8-folds to that of Bi4O5Br2 (0.0122/min) and CuBi2O4 (0.0086/min), The pH=7 is the optimal reaction condition for catechin degradation. Besides, The photocatalytic degradation capacity of the 10% CBO/BOB heterojunction displayed the positive and negative relationship to the dosage of catalyst and initial concentration of catechin, respectively. The enhanced photocatalytic activity of CuBi2O4/Bi4O5Br2 Z-scheme heterojunction can be ascribed to the improvement of the charge separation and light utilization rate. The results of ESR and trapping experiments revealed that the ·O2-, h+ and ·OH are the primariy reactive substances for catechin degradation. Additionally, the transfer pathway of the photogenerated charges in the CuBi2O4/Bi4O5Br2 Z-scheme heterojunction as revealed by the ESR, Mott-Schottky curve and UV-Vis diffuse reflectance absorption spectroscopy. This work provide a new idea for designing and preparing the novel Bi4O5Br2-based photocatalyst for TCM wastewater purification.

Construction of a self-floating fabric based on CVD-assisted coating and its application in interfacial evaporation

The discharge of industrial wastewater and the shortage of fresh water resources are increasingly endangering human daily life. In this experiment, bismuth oxychloride with oxygen vacancies was attached to a fabric surface using the solution deposition method, and then perfluoro-trichlorosilane was grafted on the surface to prepare a multifunctional superhydrophobic fabric. After mechanical stability testing, the fabric retained a water contact angle that consistently exceeded 150°, which could realize the selective adsorption of insoluble oil such as cyclohexane. Through a capture experiment of active species, the conclusion drawn was that holes (h+) and superoxide free radicals (·O2−) were primary active species for the photocatalytic degradation process. After 4 cycles of photodegradation, the degradation efficiency could still reach 92.8 %, showing excellent cyclic degradation stability. An interfacial solar steam generator (ISSG) was assembled using the superhydrophobic fabric as the support layer and a polypyrrole sponge as the photothermal layer, whose evaporation efficiency under one sun reached 2.8376 kg·m−2·h−1, with a photothermal conversion efficiency of 92.255 %. This ISSG demonstrates excellent wastewater purification capabilities. Interfacial evaporation devices show promising prospects in solar-powered wastewater purification, which further expand the use of interfacial evaporation to solve the problem of water scarcity.

In situ purification of ammonium nitrogen wastewater in rare earth mine by native bacteria isolating from original mining area

Ammonium sulfate ((NH4)2SO4) leaching method to extract rare earth elements (REEs) of mine has produced a large amount of NH4+-N-enriched wastewater derived from ore body, leading to many serious environmental pollution problems. This study was the first time to establish an in-situ treatment for real REEs wastewater outside and inside the ore body by an isolated indigenous microorganism. The results stated that Citrobacter sp. X-9 achieved the highest NH4+-N removal efficiency among the isolated six microbial strains. Moreover, the microbe to treat the REEs wastewater outside ore body gave the greatest NH4+-N removal efficiency under the optimized conditions in the Erlenmeyer flask (250-mL) and bioreactor (10-L). Furthermore, compared to the others’ modes, the in-situ treatment by cyclic mode with Citrobacter sp. X-9 possessed superior performance in NH4+-N removal efficiency for wastewater inside of ore body, showing that the established in-situ treatment was the potential approach for REEs wastewater purification.

PEI-SiO2/GO Nanofiltration Membrane: Achieved high water permeability and dye rejection rate

Water pollution has long been a significant issue, and the purification of dye wastewater plays a crucial role in addressing this problem. Graphene oxide (GO) has found extensive applications in water treatment due to its unique two-dimensional (2D) structure and a surface rich in a large number of oxygen-containing functional groups. We introduced silica(SiO2) and polyethyleneimine(PEI) into GO to prepare a membrane. The experimental findings revealed that the 3-SiO2/GO binary composite membrane achieved a high water permeability of 45.6Lm-2 h-1 bar-1 while maintaining retention, which is nearly four times higher than that of the GO membrane (9.85Lm-2 h-1 bar-1).The water permeability of the PEI0.2-SiO2/GO ternary composite membrane achieved 42.37Lm-2 h-1 bar-1. The rejection rate for methyl orange dye reached 92.36%, with similar rejection rates all above 95% observed for other dyes.

Self-cleaning micro/nano graded porous groove structure fiber membranes by coaxial spinning for purification of dye wastewater.

Adjusting the structure of the membrane and improving its performance proved to be an effective technique for accomplishing efficient dye wastewater purification. Water erosion of polyvinylpyrrolidone (PVP) core in polyacrylonitrile (PAN) nanofiber membrane modified with UiO-66-NH2 was successfully achieved, in this study, using coaxial electrospinning, and ZIF-8 with excellent performance was further epitaxy-grown in situ. Two differently shaped and positively charged MOFs confer strong adsorption capacity (adsorption capacity >2042mg/g) on cationic dyes. In addition, the multi-dimensional separation pores brought by the micro/nano graded porous groove structure and MOFs not only make the membrane have excellent static adsorption performance, but also have excellent dynamic separation performance under the influence of toxic heavy ions (separation efficiency >99 %; Flux >1666Lm-2 h-1 bar-1). More importantly, this special structure of the membrane has an excellent photocatalytic activity for the dye, so the membrane can be used for a long time in a green and environmentally friendly way. Together, membranes show a significant deal of potential for the treatment of wastewater containing dyes due to the combination of these outstanding characteristics.

Swollen hydrogels with strong mechanical characteristics: A superior adsorbent for the sustainable removal of diclofenac sodium.

Hydrogel adsorbents that possess both good mechanical strength and adsorption capabilities are crucial for practical wastewater treatment. However, achieving this balance has been demanding due to the trade-off between swelling properties and adsorption capacities in hydrogels. Although swelling increases the availability of functional groups and facilitates the diffusion of pollutants, it compromises the mechanical integrity. In this study, we address this challenge by developing double-network hydrogels based on poly(vinyl) alcohol and poly[2-(acryloyloxy)ethyl]trimethyl ammonium chloride, prepared via free-radical polymerization, and subsequent freeze-thaw treatment. These hydrogels were investigated for their efficacy in removing diclofenac sodium, a prevalent drug pollutant in pharmaceutical wastewater. By leveraging the synergistic effect of the physical and chemical networks, the prepared hydrogels exhibit intrinsic toughness and compressibility even in a fully swollen state. Most importantly, the maximum adsorption capacity yielded by the Langmuir model fitting was 1012mg/g under natural conditions, they surpass all other hydrogel adsorbents proposed so far. Thermodynamic analysis implied the spontaneous and exothermic nature of diclofenac sodium adsorption process, while infrared and photoemission spectroscopy revealed that diclofenac sodium uptake is predominantly governed by ion exchange. Overall, double-network hydrogels offer considerable promise for eco-friendly and sustainable wastewater purification due to their high mechanical stability, outstanding adsorption performance, good reusability, and adaptability to diverse environmental conditions.

Design of S-Scheme CuInS2/CeO2 Heterojunction for Enhanced Photocatalytic Degradation of Pharmaceuticals in Wastewater.

The release of common medications and illegal drugs into the environment could be potentially harmful to the ecosystem and hamper the behavior and growth of plants and animals. These pollutants gain access to water through sewage and factory discharges and have been found to exceed safety limits in water bodies. Therefore, there is an urgent need for improved wastewater purification systems. In this study, semiconductor-based heterojunction photocatalyst CuInS2/CeO2, synthesized through a facile solvothermal process, was explored for the photocatalytic degradation of ciprofloxacin, commonly used antibiotics. Studies on the electronic properties of the heterojunction revealed interfacial characteristics that were suitable for enhanced charge carrier separation and transport and a potential S-scheme charge transfer mechanism. The heterojunction achieved ∼90% efficiency for the degradation of CIP compared to 60% and 12% reported for CeO2 and CuInS2, respectively. This shows an improvement in the activity, which results from the improved charge carrier properties of the heterojunction. Further investigation of the charge transfer mechanism through radical scavenging experiments identified •OH, O2•-, and h+ as active species contributing to the catalyst's efficacy. Based on X-ray photoelectron spectroscopy analysis, a proposed S-scheme charge transfer mechanism was suggested for the CuInS2/CeO2 heterojunction. The findings indicate the potential of the CuInS2/CeO2 heterojunction as a promising photocatalyst for treating waste effluents from the pharmaceutical industry.

A Fish-Gill-Inspired Biomimetic Multiscale-Ordered Hydrogel-Based Solar Water Evaporator for Highly Efficient Salt-Rejecting Seawater Desalination.

Solar energy-driven steam generation is a renewable, energy-efficient technology that can alleviate the global clean water shortage through seawater desalination. However, the contradiction between resistance to salinity accretion and maintaining high water evaporation properties remains a challenging bottleneck. Herein, we have developed a biomimetic multiscale-ordered hydrogel-based solar water evaporator for efficient seawater desalination. The as-prepared solar water evaporator consists of highly ordered ultralong hydroxyapatite (HAP) nanowires as a supporting backbone and heat insulator, MXene as a sunlight absorber, and hydrophilic hyaluronic acid methacryloyl (HAMA) as an interfacial bonding agent, and a modifier to reduce the water evaporation enthalpy. The MXene/ultralong HAP nanowires/HAMA (MHH) photothermal hydrogel evaporator with the multiscale-ordered hierarchical structure mimics the fish-gill structure. The highly ordered alignment of ultralong HAP nanowires is realized at multiple scales, from the nanoscale to the microscale to the macroscale and from 1D to 2D to 3D in the as-prepared photothermal hydrogel evaporator. The high-performance MHH photothermal hydrogel water evaporator exhibits high efficiency of photothermal conversion, low water evaporation enthalpy, excellent heat management capability, and high solar water evaporation performance. The water evaporation enthalpy decreases from 2431 J g-1 (pure water) to 1113 J g-1 using the MHH photothermal hydrogel evaporator. As a result, the high-performance MHH hydrogel water evaporator can realize a high water evaporation rate of 6.278 kg m-2 h-1 under one sun illumination (1 kW m-2). Moreover, the as-prepared MHH hydrogel evaporator is able to achieve a water evaporation rate of 4.931 kg m-2 h-1 using the real seawater sample, exhibiting excellent salt-rejecting performance. It is expected that the as-prepared MHH hydrogel evaporator has promising applications in high-performance seawater desalination and wastewater purification using the sustainable solar energy.

Rapid adsorption of industrial cationic dye pollutant using base-activated rice straw biochar: performance, isotherm, kinetic and thermodynamic evaluation

This work intends to effectively remove methylene blue (MB) dye from wastewater using an agricultural waste-derived sorbent made from pyrolyzing rice straw to generate biochar. This is done while keeping the sustainability idea in mind and tackling the crises arising from environmental contamination with dyes. The physicochemical scrutinization of the non-activated and the base-activated biochar materials showed that the materials have promising textural properties and surface functionalization, leading to high and fast capability to retrieve MB from aqueous solutions in alkaline conditions. The adsorption equilibrium for all the biochar was reached within a time span of 15 min, but 90 percent of the dye removed at equilibrium was already eliminated in less than 5 min. The behaviour of the equilibrium adsorption for the biochar materials was thoroughly assessed using Langmuir and Freundlich adsorption isotherms. Interestingly, the adsorption process for the base-activated biochar follows both Langmuir and Freundlich isotherms at higher pH. The base-activated biochar exhibited a maximum adsorption capacity of 129.87 mg/g at alkaline pH. The adsorption data analysis with various kinetic models revealed that the adsorption process follows a pseudo-second-order kinetics for all the biochar materials. The Gibbs free energy and activation energy studies clearly revealed the adsorption of MB on biochar to be spontaneous and physiosorption in nature. The adsorption mechanism of the fast and efficient removal of MB by the base-activated biochar involves electrostatic interactions, hydrogen bonding, n-π and π-π interactions. Overall, the base-activated biochar with higher and faster adsorption capacity in alkaline conditions is a promising low-cost bioadsorbent with a simple production process for the removal of cationic dyes from aqueous environments and practical dyeing wastewater purification.

Composites of YF3: Yb3+, Er3+, Tm3+@C3N4-Au with near-infrared light-driven ability for photocatalytic wastewater purification.

Photocatalytic technology for removing organic dye pollutants has gained considerable attention because of its ability to harness abundant solar energy without requiring additional chemical reagents. In this context, YF3 spheres doped with Yb3+, Er3+, Tm3+ (YF) are synthesized using a hydrothermal method and are subsequently coated with a layer of graphitic carbon nitride (g-C3N4) with Au nanoparticles (NPs) adsorbed onto the surface to create a core-shell structure, designated as YF3: Yb3+, Er3+, Tm3+@C3N4-Au (abbreviated as YF@CN-Au). The core-shell composites demonstrate remarkable stability, broadband absorption, and exceptional photocatalytic activity across the ultraviolet (UV) to near-infrared (NIR) spectral range. Notably, by optimizing the amount of Au loaded, excellent methyl orange (MO) degradation rates of 0.068 min-1 under UV light and 0.423 h-1 under light excitation with λ > 420 nm can be achieved. Even under low-energy NIR light (λ > 800 nm), a degradation rate of 0.087 h-1 was reached, indicating a significantly enhanced degradation effect compared to YF@CN without Au loading. The high performance of the core-shell composite is attributed to its unique structure, which enables efficient transfer of energy and charge carriers, thereby promoting charge separation and suppressing recombination. Furthermore, this article reveals and discusses three distinct photocatalytic mechanisms under UV, visible, and NIR light. This study underscores the considerable promise of core-shell composites in developing efficient g-C3N4-based broadband photocatalysts, focusing on comprehensive utilization of the solar spectrum through the synergistic effects of plasma and upconversion materials.

Optimized preparation of alginate/nanocellulose/polypyrrole composite hydrogel via in-situ polymerization for high-efficiency solar desalination and wastewater purification.

In the field of solar steam generation, hydrogels with interfacial evaporation configurations stand as a promising candidate for solar evaporators. Hydrogel-based photothermal materials provide excellent hydration channels for supplying water to an evaporative layer due to their porous structure and hydrophilic nature. This work proposed a facile and in-situ fabrication of sodium alginate hydrogel incorporated with cellulose nanocrystals and polypyrrole as an effective photothermal material. A robust and systematic statistical tool for the design of experiment (DOE) called Taguchi's method was employed to optimize processing conditions to achieve a maximum output. The optimized hydrogel composite demonstrated excellent evaporation rates of 1.47kgm-2h-1 under 1 sun and 2.81kgm-2h-1 under 2 sun along with the evaporation efficiency of 91.3% under 1 sun. Integrating polypyrrole and cellulose nanocrystals into the composite hydrogel has improved its light absorption, integrity, and hydrophilicity. Additionally, the optimized hydrogel revealed excellent removal of salts, hardness, dyes, and heavy metals contaminants.

DFT Computation-Assisted Design and synthesis of trisodium nickel triphosphate: Crystal Structure, Vibrational study, DFT Computation, Electronic Properties and Application in Wastewater Purification

DFT Computation-Assisted Design and synthesis of trisodium nickel triphosphate: Crystal Structure, Vibrational study, DFT Computation, Electronic Properties and Application in Wastewater Purification

Self-supported CoWO4 nanoarrays enhance the electrochemical reduction of nitrite to ammonia

The electrochemical reduction of nitrite (NO2−RR) is a novel and effective approach to achieving efficient NH3 electrosynthesis and wastewater purification, but the development of catalysts with high performance remains a...

Sulfur vacancy-rich molybdenum disulfide 3D evaporator enhanced photothermal conversion for seawater desalination and wastewater purification

Sulfur vacancy-rich molybdenum disulfide 3D evaporator enhanced photothermal conversion for seawater desalination and wastewater purification

Combining porous organic polymers with chelating agents: a facile strategy to develop effective and multi-purpose absorbents for wastewater treatment

A type of multifunctional absorbent for the concurrent and efficient removal of dyes and heavy metal ions from water was prepared by coupling carbamate-based porous organic polymer and chelating agent N-(2-hydroxyethyl) ethylenediaminetriacetic acid.