Synthesis Of Hierarchical ZnO-Al₂O₃ Composite And Their Adsorption Properties

ZnO is a kind of semiconductor materials, which has a very wide range of applications in photocatalysis, gas sensitivity and photoelectric property research.However, the application of ZnO is restricted for adsorption due to the limitations of ZnO itself. In order to overcome the shortage, introducing another composite material which be consisted of ZnO and Al2O3 in this study. Sequentially, getting an excellent product which is better than a single ZnO or Al2O3 for the structure and properties. As-synthesized samples were characterized by XRD, TEM, SEM, FTIR, and TG-DTA to analyze the structure and morphology, and the adsorption behavior of ZnO-Al2O3 composite was studied.In this paper, the different morphologies of ZnO-Al2O3 composite were synthesized by one-step hydrothermal method using aluminium isopropoxide, oxalic acid and zinc nitrate hexahydrate. By adjusting the quantity of zinc nitrate, reaction time and temperature, ZnO-Al2O3 composite with different morphologies were synthesized.Hexagonal-like structure of ZnO-Al2O3 composite was obtained and the optimum reaction conditions were determined. Experimental results indicated that the adsorption capacity was enhanced with an increase in initial concentration. The high percentage removal of Pb2+ could be retained over a relatively wide pH range(4-7). The results showed that the adsorption process followed the Freunglich model and the kinetic adsorption could be described by a pseudo-second order model very well.The technology of in-situ was a new method of preparation for composite materials,and it was an effective, simple synthesis method. Firstly, the hierarchical Al2O3 was synthesized via a facile hydrothermal process. Secondly, the ZnO–Al2O3 composite was prepared by in-situ hydrothermal method on Al2O3 substrate. Finally, the adsorption performance of as-prepared products was studied by removal of methyl blue from aqueous solutions at ambient temperature. The results showed that the morphology of as-fabricated sample was dandelion flower-like structure and the adsorption capacity reached up 228.3mg/g. It was demonstrated that the adsorption efficiency was favorable for removal of methyl blue. The results indicated that pseudo-second-order kinetic equation model canbetter describe the adsorption kinetics of methyl blue onto ZnO-Al2O3 composite, and the adsorption equilibrium data were perfectly represented by the Langmuir isotherm.Thermodynamic analyses indicated that the methyl blue adsorption process was endothermic and spontaneous in nature.