HETEROGENEOUS DECOMPOSITION OF INDOOR AMMONIA IN A PHOTOREACTOR WITH TiO_2-FINISHED COTTON FABRICS

摘要

Addition of urea-based antifreeze admixtures during cement mixing can make it possible to concrete cement in construction of buildings in cold weather. This, however has led to increasing indoor air pollution due to continuous transformation and emission from urea to gaseous ammonia in indoor concrete walls. In order to control ammonia from indoor concrete walls, aqueous dispersion of nano-titanium dioxide (TiO_2) was prepared and mixed with silicone additive to establish a treating bath. Cotton fabrics were finished with this treating bath by using pad-dry-cure process and then characterized by X-Ray Diffractometer, Infrared Fourier Transform Spectrometer and Scanning Electron Microscope. The gaseous ammonia was derived from an environmental condition simulated chamber. The heterogeneous decomposition of gaseous ammonia by UV/TiO_2 process in an annular photoreactor fixed with the TiO_2-coated cotton fabric was studied under various dosages of aqueous nano-TiO_2 dispersion, initial ammonia concentration, relative humidity and gas flow rate. A design equation of surface catalytic kinetics was developed for describing the decomposition of ammonia in air streams by UV/TiO_2 process at given operating conditions. Experimental results indicated that increasing dosage of aqueous nano-TiO_2 dispersion improved the ammonia decomposition of cotton fabric, which was prepared. At a constant temperature of 25℃, ammonia in the air stream was effective removed by decreasing initial ammonia concentration and gas flow rate. For moisture in the range of 15-65%, when the relatively humidity level was increased to 45%, the decomposition of ammonia was remarkably enhanced, and the decomposition of ammonia could be inhibited by excessive moisture.