Electro-assisted Adsorption Of Zn(Ⅱ)on Activated Carbon Cloth:experimental And Theoretical Investigations

High levels of zinc ion(Zn²⁺)in environmental scenarios have long been considered to be harmful.The research showed that while moderate amounts of Zn²⁺are important for metabolism of the organism,high concentrations of Zn²⁺would have detrimental effects on human health,resulting in irritability,muscular stiffness,growth retardation,gastrointestinal distress,lung disorders,and even cancer.The negative impact of Zn²⁺has prompted a demand for the purification of industrial zinc wastewater.At present,there are many different treatment technologies for the removal of Zn²⁺from wastewater.Among them,adsorption is considered as one of the most commonly measures due to its simple operation,rapid reaction,and low cost.However,the adsorption method often suffers from limited ion removal efficiency,and a complex and energy-intensive regeneration process.Electrosorption,also called capacitive deionization（CDI）,has attracted a great interest and appears to be a promising method for the removal of Zn²⁺from water due to its key advantages of environmental friendliness,cost-effectiveness,low energy consumption,and facile electrode regeneration.This study was experimentally and theoretically performed to explore the feasibility of electro-assisted adsorption of Zn²⁺on activated carbon cloth from aqueous solutions in batch-flow mode.The characteristics of carbon cloth were systematically evaluated using cyclic voltammetry and various surface characterization techniques.Effects of operating parameters,including charging voltage,feed Zn²⁺concentration,solution volume,and pump flow rate,p H on the dynamic removal process of Zn²⁺were examined.The optimal operation parameters of the activated carbon cloth electrode were determined as follows:a charging voltage of 1.2 V,a solution volume 100 m L,a pump flow rate of 44 m L min^-1.At this time,13%of the total adsorbed Zn²⁺were retained via physior chemisorption while 87%of the total adsorbed Zn²⁺were held via electrostatic interactions.Moreover,the carbon electrodes exhibited good regeneration performance achieved via a simple short-circuiting method and provided good reproducibility over consecutive runs for the removal of Zn²⁺.Meanwhile,a theoretical model was developed to quantitatively describe the electro-assisted adsorption of Zn²⁺,and an excellent agreement between the modeling results and the experimental data was observed.The Zn²⁺removal mechanisms involve both nonelectrostatic interactions and electrostatic interactions.Experimental and theoretical results demonstrated a significant enhancement of Zn²⁺adsorption capacity on the carbon electrodes under the electro-assistance.The validated model could be applied to predict the effects of important parameters such as micropore volume(V_mi),nonelectrostatic attraction term(μ_att),and electrode projected area（A）that are difficult to be experimentally manipulated.The prediction results show that the increase in V_mi and A favorably contributes to the enhancement of Zn²⁺adsorption amount via both physi-or chemisorption and electrosorption;the increase inμ_att has a huge positive impact on the Zn²⁺physi-or chemisorption but has a negative effect on the Zn²⁺electrosorption.Therefore,this theoretical model is expected to play an important role in establishing the electro-assisted adsorption as a viable treatment technology for zinc wastewater.