Development of novel ZnZr-COOH/CNT composite electrode for selectively removing phosphate by capacitive deionization

The discharge of phosphate from sewage water can lead to water eutrophication and endanger the aquatic ecosystem. Capacitive deionization (CDI) has displayed great potential for salt removal and nutrient recovery to its excellent performance such as environmental friendliness and energy efficient. In this study, the terephthalic acid intercalated carbon nanotube composite material (ZnZr-COOH/CNT) was developed as an anode its selective removal of phosphate in CDI was investigated. At a applied voltage of 1.2 V, ZnZr-COOH/CNT electrode exhibited great adsorption capacity of phosphate with low concentration (~10 mg/L) at a range of pH (3 - 10), with the equilibrium concentration as low as 0.3 mg/L which was less than the national first-class emission standard (0.5 mg/L). Moreover, the adsorption of phosphate by ZnZr-COOH/CNT composite electrode was mildly disturbed by the coexisting ions (Cl-, NO3-, SO42-and HCO3-). X-ray Photoelectron Spectroscopy (XPS) analysis indicated that the zirconium and zinc were coordinated with phosphate to inner sphere complex, and the hydrogen bond was formed between the hydroxyl group of phosphate and carboxyl group of electrode material, which enhanced the selective adsorption of phosphate. Furthermore, energy consumption of CDI dephosphorization was calculated as low as 0.0075 kWh/g P and 0.043 kWh/m(3) water at 1.2 V. This study was expected to provide the potential electrode materials and theoretical basis for application of CDI dephosphorization.

Automated summary

This study developed a new composite material as the anode for capacitive deionization (CDI) and investigated its selective removal of phosphate. The results showed that the composite material exhibited excellent adsorption capacity for low concentration phosphate in sewage water under low voltage, and was not significantly disturbed by coexisting ions. Furthermore, the energy consumption of the CDI process was relatively low.