Impact of intermediate products on benzene photocatalytic oxidation in pulp mills: Experimental and adsorption simulation study

Abstract The refractory benzene is revealed in the gaseous pollutants of pulp mills. Although it can be decomposed by photooxidation, the intermediates impact during benzene photooxidation needs to be studied comprehensively. Herein, the benzene photocatalysis was investigated in a reactor with nano-TiO2 colloid under different reaction conditions. The adsorption behavior of mixed benzene and intermediates on TiO2 (101) surface was simulated based on density functional theory, and the influencing mechanism of intermediates was also investigated. Experimental results showed that benzene degradation rate firstly stabilized and then decreased at high initial concentration, accompanying the photocatalyst deactivation and conversion of intermediates into aliphatic carboxylates. Adsorption simulations showed that benzene adsorption was promoted firstly and weakened finally due to the formations of several intermediates. Combined experimental results, adsorption simulation and influencing mechanisms showed that, the enhanced benzene adsorption and weakened photocatalysis contributed to a high and stable rate in the initial stage of benzene degradation. Then, the formed intermediate products weakened the adsorption and photocatalytic reaction of benzene, causing the decrease of degradation rate. The formed aliphatic carboxylates occupied almost all adsorption and catalytic sites, leading to the deactivation of nano-TiO2 photocatalyst. This study provides a comprehensive understanding of intermediates impact on benzene photooxidation.