Porous ZnO microtubes with excellent cholesterol sensing and catalytic properties

Abstract

The controlled formation of porous ZnO microtubes via the formation of tubular hydrozincite under ambient conditions from bulk ZnO followed by calcination at 500 °C for 2 h is presented. The tubular structure is a hierarchical assembly of ZnO flowers to form uniform tubes, with ∼30 μm length, ∼2 to 7 μm width and ∼400 to 500 nm wall thickness, where the flowers are made of 3D assembled porous ZnO flakes. The surface area of the tubular ZnO structure is quite good (58 m² g⁻¹). The developed synthetic procedure is quite flexible, and we have also synthesized nanostructured ZnO of varying morphologies from bulk ZnO just by changing the synthetic conditions. The developed ZnO microtubes showed excellent microstructure-based sensing and catalytic properties. A novel biosensor based on the synthesized porous tubular ZnO exhibited high sensitivity (54.5 mA M⁻¹ cm⁻²) and low LOD (limit of detection, 0.2 mM (S/N = 3)) of cholesterol at room temperature, superior to that of sensors made of other porous ZnO shapes synthesized by varying the conditions, as well as other sensors reported in the literature. It is superior even in comparison with a nano gold modified sensor. The tubular ZnO structure also showed superior catalytic activity (92%) for the synthesis of 5-benzyl-1H-tetrazole to that of other reported solid catalysts. Thus, it is expected that the developed porous tubular ZnO should find potential industrial application in the sensor as well as the catalysis field. Moreover, the synthesis from bulk ZnO makes the procedure cost effective.