Modified Polyvinyl Alcohol Membranes For Membrane Capacitive Deionization

Membrane capacitive deionization(MCDI)technology is a combination of capacitive deionization(CDI)and ion exchange membrane(IEM).In this paper,PVA,the polymer matrix commonly used in IEM,was further modified to improve the total ion adsorption capacity and desalination efficiency of MCDI and reduce the cost of membrane.(I)The sulfosuccinic acid(SSA)crosslinked PVA composite membrane was prepared by chemical cross-linking method.When the mass fraction of SSA is 5% and the crosslinking temperature is 100 ?,the ion selectivity of the membrane is the best.Combining the modified membrane with an activated carbon electrode and applied it to the capacitance deionization test.With the membrane,the adsorption capacity and the charge efficiency can be enhanced by 15% and 25%.(II)Using SSA and citric acid(CA)as cross-linking agents to modify PVA.The addition of cheap and non-toxic CA successfully reduced the amount of SSA from 5% to 1%,and the cost was reduced from 9 RMB per square meter to 2 RMB.In the desalination test,the adsorption capacity and charge efficiency were improved by 18% and 28%,respectively,compared with the conventional CDI,and about 3% compared with the membrane electrode prepared in(I).(III)The catalyst acetic acid is used to catalyze the cross-linking reaction of malic acid(MA)and PVA.When the mass fraction of the crosslinking agent MA is 5% and the crosslinking temperature is 130 °C,the selectivity of the prepared composite membrane is optimal.Comparative experiments showed that the adsorption capacity and charge efficiency of the membrane electrode were increased by 6.5% and 10.8% respectively,compared with the pure activated carbon electrode,and the cost was reduced to 0.8 RMB per square meter.