Temperature dependent glycine-oxalate assisted synthesis of CuO nanocrystallites for catalytic reduction of 4-nitrophenol in water

The reduction of toxic 4-nitrophenol (4-NP) to commercially significant 4-aminophenol (4-AP) is constantly appreciated in a circular economy relevance. The temperature dependent synthesis of set of CuO materials (CuO-1 A to CuO-5B) was achieved via. glycine and oxalate precursor calcination route. The calcination temperatures for the precursors having varied proportion of glycine and sodium oxalate were determined by TG-DSC analysis as 400℃ and 600℃ to afford CuO-A and CuO-B series materials. The optical property and surface functionalities of the CuO materials were studied using UV and FT-IR spectroscopy respectively. The dominance of monoclinic ‘CuO’ phase along with minor ‘Cu2O and metallic Cu’ phases at low temperature and high oxalate concentration synthesis was perceived by XRD analysis of the materials. The surface morphology and elemental composition of the materials was explored using SEM-EDS analysis exhibiting coral-like to flowery morphology. In a mild and aqueous medium environmentally benign catalysis approach, the as synthesized CuO materials were applied towards the reduction of toxic 4-NP to commercially important 4-AP using NaBH4. In catalyst screening, the CuO-2B was found to be effective catalyst for rapid reduction of the 4-NP with higher reaction rate revealed from the kinetic studies. Among the studied catalysts, the CuO-2B obtained at 600℃ calcination temperature was found to be most effective in screening experiments with higher Kapp value, 0.166 min− 1 with R2 value 0.951 with 98.71% of 4-Nitrophenol (4-NP) reduction in 25 min. The comparatively faster reduction reaction in case of CuO-2B is may be due to a synergistic effect of fine flowery morphology, initial absence of metallic Cu phase and lower crystallite size. The 10 mg of CuO-2B, 20 mgL− 1 initial concentration of 4-NP and 5 mg amount of NaBH4 respectively was found to be optimum reaction conditions for efficient reduction of 4-NP to 4-Aminophenol (4-AP) in water.