Green synthesis of Microalgal biomass-silver nanoparticles composite showing antimicrobial activity and heterogenous catalysis of nitrophenol reduction

Abstract In this study we have demonstrated an integrated approach for utilization of microalga Scenedesmus sp, generated during CO2 sequestration, in fabrication of catalytic and antimicrobial silver nanoparticles composite. The algal biomass was grown in open raceway pond of 30,000 L scale for CO2 sequestration, after which it was harvested and dried. The dried biomass served as a reducing and immobilizing agent for silver nanoparticles. The biomass-silver nanoparticles composite was used for the first time, as a heterogenous catalyst for reduction of a prominent industrial pollutant, p-Nitrophenol, in aqueous medium under ambient condition. Series of experiments were conducted to evaluate the effect of calcination temperature, load and reuse of the material on its catalytic efficiency. The calcined composite material was found to be an excellent catalyst for reduction of p-Nitrophenol. As low as 5 mg mL− 1 calcined material could catalyse the reduction of more than 95% p-Nitrophenol at the rate of 0.60 mg L− 1 min − 1 in aqueous solution at 10 ppm concentration. The efficiency of catalysis was evaluated for ten cycles of reuse. The material was found to be a potential candidate as a reusable heterogenous catalyst for designing continuous flow system for remediation of industrial effluents rich in p-Nitrophenol. Furthermore the material served as a good antimicrobial agent against pathogenic bacteria and fungi. Two strains each of gram + ve and gram –ve bacteria and three strains of fungi were used in the antimicrobial studies using well diffusion method.