In-situ construction of abundant active centers on hierarchically porous carbon electrode toward high-performance phosphate electrosorption: Synergistic effect of electric field and capture sites

Phosphate removal is crucial for eutrophication control and water quality improvement.Electro-assisted adsorption,an eco-friendly elec-trosorption process,exhibited a promising potential for wastewater treatment.However,there are few works focused on phosphate electro-sorption,and reported electrodes cannot attach satisfactory removal capacities and rates.Herein,electro-assisted adsorption of phosphate via in-situ construction of La active centers on hierarchically porous carbon(LaPC)has been originally demonstrated.The resulted LaPC composite not only possessed a hierarchically porous structure with uniformly dispersed La active sites,but also provided good conductivity for interfacial electron transfer.The LaPC electrode achieved an ultrahigh phosphate electrosorption capability of 462.01 mg g^(-1) at 1 V,outperforming most existing electrodes.The superior phosphate removal performance originates from abundant active centers formed by the coupling of electricfield and capture sites.Besides,the stability and selectivity toward phosphate capture were maintained well even under comprehensive conditions.Moreover,a series of kinetics and isotherms models were employed to validate the electrosorption process.This work demonstrates a deep understanding and promotes a new level of phosphate electrosorption.

Conductive and stable polyphenylene/CNT composite membrane for electrically enhanced membrane fouling mitigation

Nanocarbon-based conductive membranes, especially carbon nanotube (CNT)-based membranes, have tremendous potential for wastewater treatment and water purification because of their excellent water permeability and selectivity, as well as their electrochemically enhanced performance (e.g., improved antifouling ability). However, it remains challenging to prepare CNT membranes with high structural stability and high electrical conductivity. In this study, a highly electroconductive and structurally stable polyphenylene/CNT (PP/CNT) composite membrane was prepared by electropolymerizing biphenyl on a CNT hollow fiber membrane. The PP/CNT membrane showed 3.4 and 5.0 times higher electrical conductivity than pure CNT and poly(vinyl alcohol)/CNT (PVA/CNT) membranes, respectively. The structural stability of the membrane was superior to that of the pure CNT membrane and comparable to that of the PVA/CNT membrane. The membrane fouling was significantly alleviated under an electrical assistance of −2.0 V, with a flux loss of only 11.7% after 5 h filtration of humic acid, which is significantly lower than those of PP/CNT membranes without electro-assistance (56.8%) and commercial polyvinylidene fluoride (PVDF) membranes (64.1%). Additionally, the rejection of negatively charged pollutants (humic acid and sodium alginate) was improved by the enhanced electrostatic repulsion. After four consecutive filtration-cleaning cycle tests, the flux recovery rate after backwashing reached 97.2%, which was much higher than those of electricity-free PP/CNT membranes (67.0%) and commercial PVDF membranes (61.1%). This study offers insights into the preparation of stable conductive membranes for membrane fouling control in potential water treatment applications.

Electro-assisted CNTs/ceramic flat sheet ultrafiltration membrane for enhanced antifouling and separation performance

Ultrafiltration is employed as an important process for water treatment and reuse,which is of great significance to alleviate the shortage of water resources.However,it suffers from severe membrane fouling and the trade-off between selectivity and permeability.In this work,a CNTs/ceramic flat sheet ultrafiltration membrane coupled with electro-assistance was developed for improving the antifouling and separation performance.The CNTs/ceramic flat sheet membrane was fabricated by coating cross-linked CNTs on ceramic membrane,featuring a good electroconductivity of 764.75 S/m.In the filtration of natural water,the permeate flux of the membrane with the cell voltage of-2.0 V was 1.8 times higher than that of the membrane without electro-assistance and 5.7-fold greater than that of the PVDF commercial membrane.Benefiting from the electro-assistance,the removal efficiency of the typical antibiotics was improved by 50%.Furthermore,the electro-assisted membrane filtration process showed 70%reduction in energy consumption compared with the filtration process of the commercial membrane.This work offers a feasible approach for membrane fouling mitigation and effluent quality improvement and suggests that the electro-assisted CNTs/ceramic membrane filtration process has great potential in the application of water treatment.

Electro-assisted regeneration of ion exchange resins

Electro-assisted regeneration(EAR)for the mixed bed of strongly acidic cation and weakly basic anion exchange resins with the Al(OH)_(3) suspension in a three-compartment cell was investigated.The desalination experiments were carried out to evaluate the characteristic of the regenerated mixed resins.Experimental results showed that the efficiency of resin regeneration was strictly dependent on the voltage,regeneration time,and feed regenerant flow rate.The amount of the effluent reached 50 times the volume of the resins bed,and the conductivity was less than 1.0 ms/cm.Compared to the conventional ER,the total effluent volume of EAR was about 1000 mL more than that of ER under the same conditions,and the outlet conductivity was significantly lower.The desalination and regeneration reaction mechanisms of the mixed resins indicated the regeneration efficiency of resin with Al(OH)_(3) as the regenerant was much higher than that with H2O.

Electro-conductive crosslinked polyaniline/carbon nanotube nanofiltration membrane for electro-enhanced removal of bisphenol A

Nanofiltration(NF)has attracted increasing attention for wastewater treatment and potable water purification.However,the high-efficiency removal of micropollutants by NF membranes is a critical challenge.Owing to the adsorption and subsequent diffusion,some weakly charged or uncharged micropollutants,such as bisphenol A(BPA),can pass through NF membranes,resulting in low removal rates.Herein,an effective strategy is proposed to enhance the BPA removal efficiency of a crosslinked polyaniline/carbon nanotube NF membrane by coupling the membrane with electro-assistance.The membrane exhibited a 31.9%removal rate for 5 mg/L BPA with a permeance of 6.8 L/(m2·h·bar),while the removal rate was significantly improved to 98.1%after applying a voltage of 2.0 V to the membrane.Furthermore,when BPA coexisted with humic acid,the membrane maintained 94%removal of total organic carbon and nearly 100%removal of BPA at 2.0 V over the entire filtration period.Compared to continuous voltage applied to the membrane,an intermittent voltage(2.0 V for 0.5 h with an interval of 3.5 h)could achieve comparable BPA removal efficiency,because of the combined effect of membrane adsorption and subsequent electrochemical oxidation.Density functional theory calculations and BPA oxidation process analyses suggested that BPA was adsorbed by two main interactions:π–πand hydrogen-bond interactions.The adsorbed BPA was further electro-degraded into small organic acids or mineralized to CO_(2) and H2O.This work demonstrates that NF membranes coupled with electro-assistance are feasible for improving the removal of weakly charged or uncharged micropollutants.

Electroconductive RGO-MXene membranes with wettabilityregulated channels: improved water permeability and electro-enhanced rejection performance

Reduced graphene oxide(RGO)membranes are theoretically more conducive to the rapid transport of water molecules in their channels compared with graphene oxide(GO)membranes,as they have fewer oxygen-containing functional groups and more non-oxidized regions.However,the weak hydrophilicity of RGO membranes inhibits water entry into their channels,resulting in their low water permeability.In this work,we constructed wettable RGO-MXene channels by intercalating hydrophilic MXene nanosheets into the RGO membrane for improving the water permeance.The RGO-MXene composite membrane exhibits high pure water permeance of 62.1 L/(m^(2)·h·bar),approximately 16.8 times that of the RGO membrane(3.7 L/(m^(2)·h·bar)).Wettability test results and molecular dynamics simulations suggest that the improved water permeance results from the enhanced wettability of RGO-MXene membrane and increased rate of water molecules entering the RGOMXene channels.Benefiting from good conductivity,the RGO-MXene membrane with electroassistance exhibits significantly increased rejection rates for negatively charged dyes(from 56.0%at 0 V to 91.4%at 2.0 V for Orange G)without decreasing the permeate flux,which could be attributed to enhanced electrostatic repulsion under electro-assistance.