ZnO Nanorod-Immobilized Polyurethane Foams for Efficient Removal of Gaseous Volatile Organic Compounds

Abstract

Nanoscale semiconductor materials are highly effective catalysts due to their high surface-to-volume ratio, enhanced charge carrier separation, and increased active site density. Integrating them into three-dimensional porous supports optimizes mass transport, facilitating efficient adsorption of volatile organic compounds (VOCs) and catalytic interactions. A flexible hybrid photocatalyst was designed by immobilizing zinc oxide (ZnO) nanorods (NR) on the three-dimensional polyurethane (PU) foam support. The polymer surface was functionalized by chemical solution treatment to increase the adhesion between the catalyst and the surface. ZnO NRs were grown on all strut surfaces of the PU foam via a seed-mediated approach. Photocatalytic experiments were carried out in a laboratory-scale plug flow type photoreactor under UVA light irradiation. The effects of parameters such as initial concentration (ppm), relative humidity (RH) (from 0% to 65%), air flow rate (0.3, 0.6, and 1 L/min), and temperature (from 21 to 35 °C) on the gas phase toluene, ethylbenzene, and chlorobenzene removal were evaluated. In the presence of RH, photoreactions accelerated, leading to an increase in the CO₂ conversion rate. The optimum RH value was determined as 30% according to the maximum removal rate. Similarly, removal efficiencies were improved at temperatures higher than room temperature, and the optimum temperature was evaluated as 30 °C. However, as the initial concentration and air flow rate increased, the degradation rates decreased. Maximum VOC degradation rates of toluene, ethylbenzene, and chlorobenzene were obtained as 81%, 71%, and 92% by simultaneous adsorption and photocatalytic oxidation under UVA light at 30% RH and 30 °C, respectively. Chlorobenzene showed a higher removal efficiency than toluene and ethylbenzene for all conditions. The hydrophilic nature of the ZnO NR surface promoted the adsorption of chlorinated compounds. The interaction of VOCs with the catalyst surface revealed that surface chemistry plays a significant role in photocatalytic removal.