Electrochemical Preparation Of Sulfur-Free Expanded Graphite And Study On Adsorption Of Cu(Ⅱ) And Reuse Of Waste Adsorbent

As a common heavy metal industrial wastewater,copper-containing wastewater has attracted much attention due to its difficulty in treatment and high hazard.Expanded graphite materials have the characteristics of large specific surface area,many pores and strong adsorption capacity.Expanded graphite and composites based on it are widely used in various industries.Expanded graphite with high sulfur content is prepared by traditional method,and its application is limited.Based on this background,the expanded graphite composite material was fabricated for the treatment of copper-containing wastewater.Firstly,two electrochemical oxidation systems,HCl O₄-C₂H₂O₄ and Na Cl O₄-C₂H₂O₄,were established to prepare sulfur-free expandable graphite（EG1 and EG2）.Secondly,the expanded graphite was modified with hexadecyl trimethyl ammonium bromide（CTAB）by hydrothermal synthesis to enrich the surface functional groups of the expanded graphite and provide a new idea for the removal of copper ions in water.Finally,the waste adsorbent reuse system was constructed,which conforms to the concept of green cycle.The best preparation conditions of EG1 was as follows:perchloric acid（m L）:deionized water（m L）:oxalic acid（g）=50 m L:50 m L:2 g.The largest expanded volume of EG1 was 505 m L/g when the current density was 70 m A/cm² and electrolysis lasted for 100min.The best preparation conditions of EG2 was as follows:sodium perchlorate（g）:oxalic acid（g）:deionized water（m L）=10 g:2 g:100 m L,with the maximum expanded volume of290 m L/g at the current density of 48 m A/cm² for 60 min.For the hydrothermal synthesis reaction of CTAB/EG composite,the optimum reaction temperature was 210℃and the reaction time was 6 h.The above materials were characterized by XRD,SEM,EDS,FTIR and other test techniques,which proved that the required materials with good performance were obtained.The CTAB/EG composite material adsorption system for Cu（Ⅱ）was built.The removal rate was 86.7%,and the adsorption amount was 1.8 mg/g when the initial concentration of Cu（Ⅱ）was 50 mg/L,p H=6.0,the dosage of adsorbent was 24 g/L,and the reaction time was60 min at 298 K.Under all conditions,the adsorption equilibrium has been nearly reached in 20 min,with high adsorption efficiency and low energy consumption.This system conforms to the quasi-second order adsorption kinetic model,which proves that the chemical adsorption is the main one,and accords with the Langmuir isotherm model,which certifies that Cu（Ⅱ）is mainly adsorbed on the surface of the composite in the form of single molecular layer.Thermodynamic analysis indicates that the adsorption process is exothermic and spontaneous.Cu（Ⅱ）in waste adsorbent was oxidized to Cu O by high-temperature roasting.Cu O/EG catalyst catalytic ozonation system for phenol degradation was constructed.The phenol removal rate was 91.2%after 30 minutes of reaction,which was 24%higher than that of ozonation alone,when the initial concentration of the solution was 300 mg/L,the p H value was about 6,the catalyst dosage was 1.2 g/L,and the ozone concentration was 1.8 mg/L.At the same time,the degradation rate was faster than that of ozonation alone.It can be seen that catalytic ozone oxidation has a good effect on the degradation of phenol and the reuse of waste adsorbent is completed.After five cycles of use,the Cu O/EG catalyst still has relatively high stability.