ZrO2-modified TiO2 nanorod composites were synthesized by using the hydrothermal synthesis approach. The synthesized materials were characterized by XRD, SEM, TEM, Raman, IR, and XPS. It was found that both sizes and morphologies of ZrO2 particles significantly depended on the reaction temperatures and hydrothermal synthesis time. TEM results exhibited that large sized particles of ZrO2 of 50 nm were achieved at low hydrothermal synthesis temperature of 110 degrees C, while small sized particles of ZrO2 of 20 nm stably deposited on the surface of TiO2 nanorods are generated at high temperature of 200 degrees C. The ZrO2-TiO2 nanorod composite was further functionalized by sulfate groups and utilized as the solid superacid catalyst for upgrading of bio-oil model compound organic acid by esterification. Both IR and XPS approved the presence of sulfate groups on Zr and Ti adsorption sites. HPLC results for the conversion of model compound levulinic acid to ester showed that 81.2% of levulinic acid converted to ethyl levulinate at 110 degrees C in 2 h over a 20 wt% ZrO2 TiO2 nanorod composite. GC MS result displayed that ester was produced as the only product. (C) 2014 Elsevier B.V. All rights reserved.