Dependence of photoactivity of niobium pentoxide (Nb2O5) on crystalline phase and electrokinetic potential of the hydrocolloid

Abstract

Multiphasic crystallite complex of the most popular photocatalyst – TiO2 has consistently shown better UV and/or visible photoactivity than its pristine monophasic counterparts. An identical behaviour is reported in the studies conducted on ZnO as well. This motivated the present study i) to explore the possibility to establish this as generic behavior for all such materials, and ii) to look for a better material with high photocatalytic activity. The choice of niobium pentoxide for the purpose lies in its uniqueness in terms of its existence in different oxidation states and crystalline phases. Additionally it offers a novel and promising alternative to the existing photoactive nanomaterials due to its apposite band gap, band edge location, stability, sorption characteristics and recyclability. Herein, an attempt has been made to prepare niobium pentoxide with different crystalline phases, including mixed, and analyze their photoactivity in UV and visible ranges. The results show that niobium pentoxide, calcined between 500-800°C, crystallizes predominantly in orthorhombic and 900°C and above in monoclinic phase. The results reveal that under both UV and visible radiation the monophasic (monoclinic phase) niobia has high photoactivity as compared to the other phases in degradation of aqueous probe pollutant. This result is contrary to the expected result. The samples have been characterized by X-ray diffraction(XRD), UV-VIS spectroscopy (UV-VIS DRS), X-ray photoelectron spectroscopy(XPS), photoluminescence(PL) spectroscopy, transmission electron microscopy(TEM), and scanning electron microscopy(SEM) to arrive at a conclusive explanation of the results. The sorption characteristics of the hydrocolloid system, among others, have been found to be responsible for this behavior.