Investigation into photocatalytic degradation of gaseous ammonia in CPCR

Addition of urea-based antifreeze admixtures during cement mixing in construction of buildings has led to increasing indoor air pollution because of continuous transformation and emission of urea to gaseous ammonia on indoor concrete walls. To control ammonia pollution from indoor concrete walls, a circulated photocatalytic reactor (CPCR) was designed to intensify the performance for the decomposition of gaseous ammonia in the present study and TiO2 film photocatalysts were prepared by the sol-gel method and coating onto the inner wall of this reactor using a bonder of polyacrylic ester emulsion, which was characterized by FTIR, TEM, and SEM. In particular, the influences of initial concentration of ammonia on the degradation conversion (D-p), apparent reaction rate constants (k(r)), initial degradation rate (r), deactivation, and regeneration of catalyst in CPCR were investigated. Furthermore, a designed equation of surface catalytic kinetics was developed for describing the decomposition of ammonia in CPCR. The total number of adsorption sites available for the gas molecules N-T and the adsorption equilibrium constant K-ads values were determined through a linear-fitting method. Finally, undesirable NO2- and NO3- were detected as the intermediates in the process of photodegradation at different initial concentration of ammonia, which was detected by catalytic kinetic spectrophotometry. The results indicated that the degradation conversion (D-p), initial degradation rate (r), degraded products, and half-life (t(1/2)) were closely correlated to the initial concentration of ammonia. It was found that the reaction kinetics fixed the pseudofirst-order kinetic equation of photocatalytic degradation of gaseous ammonia in CPCR, and the kinetic results are discussed in terms of adsorption of ammonia and products degraded.