Flow synthesis development and photocatalytic activity optimization of copper oxide nanoparticles using design of experiments

Many studies have focused on reducing the impact of carbon dioxide (CO2) on climate change. A promising approach for CO2 utilization is to use a photocatalyst to activate CO2 and generate valuable chemical compounds. One of the most commonly synthetized photocatalysts is cuprous oxide (Cu2O); however, low efficiency and fast deactivation still limit its industrial application. Here, a batch synthesis in nonaqueous media of Cu2O containing small amounts of metallic copper (Cu0) is investigated. By adjusting the ratio between Cu2O and Cu0 an enhanced photocatalytic efficiency is obtained. To overcome the deactivation limitations of Cu2O, a flow synthesis is developed that continuously supplies fresh photocatalysts to the reaction environment. The flow synthesis has the potential to allow the separate evaluation of the intrinsic reaction kinetic from the photocatalyst deactivation. This work optimizes the flow synthesis using a design of experiments (DOE) approach coupled with response surface methodology (RSM). The obtained surface responses for the measured factors were highly significant (p-value < 0.01 and R2 > 0.95). This novel methodology makes it possible to identify the optimum process conditions to simultaneously improve photocatalytic performance of the obtained material and reaction productivity. This approach enabled us to obtain in flow a combination of Cu2O/Cu0 photocatalyst and to propose a reaction mechanism and kinetic model for the Cu2O formation. The optimization procedure for flow synthesis proposed here provides an efficient path that can be extended to flow synthesis of a wide range of nanoparticles for photocatalytic applications.