Effect of ethanol on the fabrication of porous anodic alumina in sulfuric acid

Porous anodic alumina (PAA) films with small pore diameters and interpore distances are significantly important in many practical applications such as isolation of pathogens, catalysis and molecular sieving. This kind of PAA films is generally prepared in diluted sulfuric acid, and the film growth is very slow due to the low anodizing potential and current density. Many efforts were done to enhance the PAA formation, and the majorities focused on increasing growth rate by increasing the anodizing potential, which also increases the pore diameter and interpore distance of the obtained PAA. In our paper, the influence of ethanol addition in electrolyte of sulfuric acid was studied in details. Results show that the addition of ethanol can maintain the low self-ordering potentials in sulfuric acid and at the same time significantly increase the growth rate of PAA. With a series of ethanol addition, it was found that with the 10% ethanol addition, the growth rate increases by 5 times from 1.6 μm/h to 8 μm/h at 2 °C and 25 V, and there is a nonlinear relationship between ethanol addition amount and PAA growth rate. These findings are of great significance for further investigation on PAAs with ultrasmall nanopores, as well as for PAA commercialization.