CRYSTALLITE SIZES ON THE PHOTOCATALYTIC PERFORMANCE OF SUBMICRON WO3 PARTICLES

Strategies on designing optimum photocatalyst materials have attracted tremendous attention. One of the most important designing parameters is crystallite size. However, the effect of this parameter on photocatalytic performance is still not fully understood. Some reports confirmed positive impacts, while the others showed the opposite results. The main reason for the uncompromised reports is due to the inconsideration of interfering other parameters during the photocatalytic process, such as excessive surface area, quantum effect, and change structure in the catalyst such as porosity. This report evaluates correlations between crystallite sizes and photocatalytic performance of submicron photocatalyst particles. Experiments used submicron tungsten trioxide (WO3) as a model of catalyst for degrading curcumin in the batch photoreactor system. To ensure the evaluation precisely, this study makes the photocatalytic process to be restricting the reaction occurring on the surface of catalyst only. To achieve this condition, submicron dense WO3 particles were used and produced from pure ammonium tungstate pentahydrate with no additional chemicals, solvents, surfactants, and additives using a sequential ball-milling and crystallization route. Experimental results showed that the photocatalytic performance was strongly dependent on the crystallite sizes, in which it improved with the use of larger crystallite sizes. The impact of crystallite sizes was verified by testing the process using various catalyst particle outer diameter s (from 200 to 1200 mu m) and compositions of catalyst/curcumin. The catalytic rate is directly proportional to the crystallite size; in general, the improvement of the rate would be double when doubling the crystallite size. The proposal of the fundamental consideration was also added for explaining the phenomena in the photocatalytic process. Because the optimization of this crystallite size parameter offers essential information for practical applications, the results of this study are important and relevant to other functional catalytic properties.