AUTO-COMBUSTION SYNTHESIS OF Al-DOPED ZnO NANOPARTICLES: STRUCTURAL AND ENERGY BAND GAP ENHANCEMENT

Abstract

Auto-combustion reaction has been developed as a new route in synthesizing ZnO and Al-doped ZnO nanoparticles with improved structural, and optical properties. In this work, the effects of Al doping concentrations and different calcination temperatures were investigated. The Zn(NO₃)₂ aqueous solution was mixed with Al(NO₃)₃, citric acid, and ammonia aqueous solutions to obtain a series of mixtures with varied Al molarity concentration, x from 0 to 0.5. The highly exothermic single-step auto-combustion reaction at around 230 °C has transformed the mixture into fine black ashes which yielded white powder during calcinated at various calcination temperature, T_cal for 1 h in a normal furnace atmosphere. The XRD results revealed that the transformation of amorphous ZnO ashes into highly crystalline ZnO with a hexagonal structure was completed at T_cal ≥ 700 °C where the c lattice constant in the samples was increased by the increases of Al doping concentration. The SEM images of the Zn_1-xAl_xO samples calcined at T_cal = 700 °C showed a dense and highly packed of ZnO nanoparticles due to the increased of Al diffusion in ZnO and higher grain growth rate of ZnO. The energy band gap obtained from UV-vis results was significantly improved in Zn_1-xAl_xO samples calcined at T_cal = 700 °C attributed to the well-controlled of Al doping concentration in effectively adjusting the electronic properties of the ZnO nanoparticles.