Comparison of two innovative precipitation systems for ZnO and Al-doped ZnO nanoparticle synthesis

This study presents a comparative approach to investigate the potentials of two innovative methods for the synthesis of ZnO and Al-doped ZnO. The first method is a precipitation system working in mild hydrothermal conditions (90°C) using a tubular reactor (Segmented Flow Tubular Reactor, SFTR). The second method is a microwave-assisted hydrothermal process working at 250°C - 38 atmospheres. Nanocrystalline ZnO with a high specific surface area (49–68 m2/g) was obtained with both systems. Smaller equiaxed particles (50–70 nm) were obtained with the SFTR, with an excellent homogeneity in size and morphology, which was attributed to an excellent control of the process parameters (mixing, temperature, volume of reaction). A higher luminescence signal was measured on these samples. The microwave method leads to particles with a higher crystallinity due to the temperature of the reaction. A significant effect of the aluminum was observed, which reduces the crystal growth to produce equiaxed morphologies. This effect was enhanced by adding poly(acrylic) acid (PAA).