High photocatalytic decomposition of the air pollutant formaldehyde using nano-ZnO on bone char

Abstract

Air pollution is a major issue leading to many serious illnesses. Exposure to formaldehyde may occur by breathing contaminated indoor air, tobacco smoke, or ambient urban air. Exposure to formaldehyde has been associated with lung and nasopharyngeal cancer. Therefore, there is a need for methods to degrade formaldehyde. Here, we studied the photocatalytic decomposition of gaseous formaldehyde over nanosized ZnO particles on bone char. The conditions were UV/bone char, UV/ZnO nanoparticles, and UV/ZnO-bone char in continuous flow mode. We investigated the effects of humidity, initial formaldehyde concentration, and residence time on decomposition of formaldehyde. Agglomeration of ZnO particles in the bone char pores was characterized by Brunauer, Emmett, and Teller surface area, and scanning electron micrograph. Results show that maximum decomposition efficiency of formaldehyde was 73 %. The optimal relative humidity was by 35 %. Findings also indicated that immobilization of ZnO nanoparticles on bone char has a synergetic action on photocatalytic degradation. This is explained by the strong adsorption of formaldehyde molecules on bone char, resulting in higher diffusion to the catalytic ZnO and thus a higher rate of photocatalysis.