Research On The Correlation For Photocatalytic Degradation Of Indoor Volatile Organic Compounds

Although many photocatalytic cleaners have been put into the market, the mechanism and actual performance of them still need further systematical study. The very first issue that should be taken into account is the catalytic activity, because it is directly related to the performance of degradation of volatile organic compounds (VOCs) and service life of cleaners. What is also worth studying here is multiple compounds effect. More than 300 kinds of VOCs have been found in indoor air. It is essential to investigate the issue of the degradation of multi-component VOCs. However, a lot of research only considered the interaction of them. In fact, some internal relations also exist.In this thesis, we have studied with benzene, toluene, ethylbenzene, p-xylene, o-xylene, 2-butanone, octane, and 1,1,2,2-tetrachloroethane as the target pollutants. The key results are as follows:(1)The shortcomings of L-H model have been pointed out when VOC concentration is high. Considering the possibility of the photoactivity decay, a new model nominated as"deactivation model"fits for various concentration levels. Besides, the concepts of deactivation region, maximum rate, maximum intensity, maximum optical efficiency and inhibiting concentration are proposed to explain the phenomena. The results would be used to design an appropriate photocatalytic cleaner.(2)According to the deactivation model, this thesis proposes to make use of interaction rateη=0.2 as the indicator whether multi-component interactions can be neglected, which have been obtained in all experiments. However, the linear terms of deactivation model of the target VOC remains equal, whenever the VOC is in single or multiple compounds. Thus the experimental results of multiple components can be used to predict the performance of degradation of the target VOC at low concentrations (such as below 0.5ppm). Therefore, a lot of experimental work can be decreased. (3)The correlation studies show that the apparent reaction rate constant k_a is proportional to the related items composed by some known physical or chemical parameters of the same type of VOCs. As long as one of the values of k_a has been derived from tests, k_a of other VOCs of the same type can be predicted. There are also some correlations in different types of VOCs only when the adsorption bond between VOCs and the catalyst is the same or similar. Otherwise, the uncertainty of mass transfer coefficient remark_ably influences on the value of k_a, especially when their values are in the same order of magnitude. This thesis proposes a method to accurately measure the value of mass transfer coefficient by altering the ultraviolet intensity.