Optimization of Cr(VI) reduction by zero-valent bimetallic nanoparticles using the response surface modeling approach

Bimetallic iron–silver zero-valent nanoparticles were synthesized, characterised and studied for reduction of Cr(VI) in water solution. A four-factor, central composite design (CCD) combined with response surface modeling (RSM) and optimization was employed for maximizing the Cr(VI) reduction by the bimetallic system. Four independent variables, viz., temperature (10–50 °C), pH of solution (2–8), Cr(VI) concentration (30–70 mg/l), and particles dose (0.4–1.6 g/l) were transformed to coded values and a quadratic model was built to predict the responses. The significance of the independent variables and their interactions were tested by the analysis of variance (ANOVA) and t-test statistics. Adequacy of the model was tested by the correlation between experimental and predicted values of the response and enumeration of prediction errors. Model validation was performed using a second set of data. Optimization of the variables for maximum Cr-reduction by bimetallic nanoparticles was performed using the quadratic model. The model predicted maximum reduction capacity (55.96 mg/g) under the optimum conditions of Cr(VI) concentration 65.7 mg/l; temperature 43 °C; pH 2; and dose 0.4 g/l, which was very close to the experimental value (55.18 mg/g) determined in batch experiment and about 32% higher than the experimentally determined un-optimized reduction capacity (42.39 mg/g).

Research Highlights
► We synthesize and characterise zero-valent Fe/Ag nanoparticles for Cr(VI) reduction.
► Optimized pH, temperature, particles dose, Cr(VI) concentration for maximum reduction.
► Optimization performed by central composite design and response surface modeling.
► Optimization rendered 32% higher reduction than the experimentally determined value.
► pH of solution produced the largest effect on Cr(VI) reduction process.