In this study, photocatalytic decolorization of an Azo reactive dye (Reactive yellow 84, RY84) from aqueous solutions by ZnO nanoparticles supported on light expanded clay aggregate (LECA) was investigated. The response surface methodology for evaluating the effects of experimental variables such as ZnO loading, initial concentration of solution, pH, and UV intensity on the dye removal efficiency was applied for optimization of the photocatalytic degradation of RY84. The results showed a good agreement with the experimental values and the sensitivity analysis revealed the UV intensity, initial solution concentration, and catalyst dosage as the most effective variables on the decolorization efficiency. Analysis of variance (ANOVA) showed a high determination coefficient value (R-2 = 0.909 and adjusted-R-2 = 0.863) and satisfactory prediction second-order regression model. The result of optimization showed the maximum efficiency of color removal (99.5%) at the optimal conditions of initial pH = 4, catalyst dosage 0.2 (g ZnO/g LECA), initial dye concentration 50 ppm, and UV intensity 250 W. (C) 2015 Elsevier B.V. All rights reserved.