Remarkable adsorption capacity of Cu2+-doped ZnAl layered double hydroxides and the calcined materials toward phosphate

Abstract

In this study, Cu2+ was doped into ZnAl hydrotalcite by one-step urea homogeneous hydrolysis to produce ZnAlCu ternary hydrotalcite (ZnAlCu-1%-LDH). After that, it was roasted to obtain ZnAlCu layered trimetallic oxide (ZnAlCu-1%-LDO). The Jahn-Teller effect of Cu2+ is able to distort the ZnAlCu, thus increasing the hydrotalcite layer spacing and specific surface area. The influence of Cu2+ doping on phosphate adsorption was investigated, and adsorption mechanism was also analyzed. XRD proved that Cu2+ doping increased the interlayer spacing of adsorbent. The optimum copper doping amount of ZnAlCu-1%-LDO was 1% of the total metal molarity. The ZnAlCu-1%-LDO obtained the phosphate adsorption capacity of 199.28 mg P/g, which was 4.6 and 2.9 times higher than that of ZnAl-LDH and ZnAlCu-1%-LDH (phosphate concentration of 200 mg P/L, adsorbent dosage of 0.4 g/L), respectively. Experimental characterizations revealed that the phosphate adsorption mechanisms of ZnAlCu-1%-LDO were memory effect, electrostatic attraction, ligand exchange and surface precipitation. In addition, the phosphate removal efficiency of ZnAlCu-1%-LDO in the actual wastewater (3.43 mg P/L initial concentration) was also investigated, and the residual concentration after adsorption was 0.0664 mg P/L, which reached the A-level standard of phosphate effluent in China (0.5 mg P/L). The experiment provided a universal solution for other layered double hydroxides (LDHs) to improve their phosphate adsorption performance.