Synthesis of ZnO-TiO₂/activated carbon (ACZnO/TiO₂) nanoparticles and its application in adsorption of arsenic from aqueous media: study of isotherm and adsorption kinetics and optimization using response surface methodology- central composite design

Arsenic contaminated water is a serious threat to human health. Therefore, the aim of this study was to use a new method of stabilization of ZnO/TiO2 on activated carbon (I ZnO/TiO2) for the effective removal of arsenic from aqueous solutions. In this experimental study, a container with a useful volume of 3.14 L (height of 40 cm and diameter of 10 cm) was used. For this purpose, four main factors including pH (3-11), nanosorbent dose (1-3 g/L), initial arsenic concentration (1-10 mg/L), and reaction time (30-300 min) as effective factors in the arsenic removal efficiency. The results showed that arsenic adsorption increased with increasing contact time, adsorbent dose, and decreasing pH and arsenic concentration. A quadratic model was selected to estimate the removal of arsenic by the adsorption process with the modified adsorbent under study. The linear regression coefficient (R-2) between experiments and different response values in the model for arsenic was >0.99. The optimal value for the studied variables was obtained for pH of 6.75, arsenic concentration of 9.76 mg/L, reaction time of 287.62 min, and nanosorbent dosage of 2.45 g/L. The maximum arsenic adsorption capacity under optimal conditions was predicted to be 4.53 mg/g. The results showed that the studied adsorbent for arsenic removal follows the Langmuir isotherm and quadratic kinetics (R-2 > 0.99). The results of this study showed that the adsorption process using nano-photocatalytic adsorbents of TiO2 and ZnO has relatively high efficiency in arsenic adsorption and can be used as a suitable complementary treatment method for water and wastewater containing carcinogenic heavy metals such as arsenic.