One-step combustion synthesis of undoped c-ZrO2 for Cr(VI) removal from aqueous solutions

Abstract

Abstract The active practical application of materials based on cubic zirconium dioxide (c-ZrO2) for catalysis, luminescence, and sorption of heavy metals demands the development of methods for its preparation in a nanostructured form. In this work, nanoparticles of undoped cubic zirconia were obtained by solution combustion method, the features of their structure and morphology were investigated, and the efficiency of their use as a basis for sorbents for the removal of hexavalent chromium Cr(VI) from aqueous solutions was evaluated. Based on XPS, it was established that the stabilization of the high-temperature cubic phase of c-ZrO2 occurred due to multiple oxygen vacancies which were formed during the synthesis by glycine-nitrate combustion. The results of PXRD and Raman spectroscopy confirmed the cubic structure of the obtained zirconium dioxide nanoparticles, the average crystallite size was approximately 2 nm. Adsorption structural analysis and SEM indicated aggregation of c-ZrO2 nanocrystals into primary (45-95 nm) and secondary (submicron) agglomerates. The specific BET surface of the nanocrystals was 25.4 m2/g, the pore volume was 0.1670 cm3/g, the major part of which is associated with interparticle porosity. Using kinetic pH-metry, it was found that on the surface of synthesized c-ZrO2, rapidly hydrated aprotic Lewis acid centers predominated, and the point of zero charge (PZC) was 6.33. The results of Cr(VI) sorption from aqueous solutions with concentrations varying from 0.25 to 1.25 mmol/L were described by the Freundlich isotherm (R2 = 0.971), which corresponds to the multilayer adsorption. The maximum adsorption capacity according to Langmuir was 33 mg/g or 1.34 mg/m2 per unit area. These results allow us to consider the obtained undoped zirconium dioxide as a promising base for sorbents of heavy metals.