Hierarchical In(OH) < inf > 3 < /inf > as a precursor to mesoporous In < inf > 2 < /inf > O < inf > 3 < /inf > nanocubes: A facile synthesis route, mechanism of self-assembly, and enhanced sensing response toward hydrogen

Abstract

Mesoporous In2O3 nanocubes were achieved in this present work following a transformation from hierarchical structures of mesoporous In(OH)3 nanocubes synthesized hydrothermally. Appreciable control on the morphology of In(OH)3 nanostructures was attained by optimizing the reactant concentration, ratio of structure directing agent in the reaction medium (water/PEG ratio), the reaction temperature, and time. The synthesized samples were characterized extensively by XRD, TG-DTA, micro-Raman, and UV-DRS. Surface area and pore size distribution were determined from N 2 adsorption and desorption isotherms. Morphological evaluations carried out using electron microscopy in scanning (FE-SEM) and transmission (TEM) mode not only provided information on the size and shape of the materials but also revealed the hierarchical assembly consisting of primary and secondary structures. Controlled studies as a function of various reaction parameters and the morphological evolution observed are rationally correlated to propose a plausible formation mechanism. Further, hydrogen gas sensing properties (sensitivity, sensor response, and recovery time) of the as-prepared In 2O3 nanostructures (nanocubes, nanobricks, nanoflakes, and nanoparticles) were investigated to demonstrate the influence of morphology. Owing to the porous structures and large surface area, In2O 3 nanocubes exhibit superior sensitivity with short response/recovery times at concentrations as low as 100 ppb. Surface decoration with Pd nanoparticles activates these nanocubes, promoting excellent sensing response and selectivity toward hydrogen at room temperature. © 2014 American Chemical Society.