Innovative visualization of the effects of crystal morphology on semiconductor photocatalysts. Tuning the Hückel polarity of the shape-tailoring agents: the case of Bi2WO6

Abstract

The shape-tailoring synthesis of different materials is a hot topic nowadays. The essence of morphology-controlling processes is to tune the geometry of the crystal in such a way that a desired property of the crystal can be preponderantly enhanced. However, the main issue of such synthesis approaches is to achieve simple morphological correlations with the applied shape-tailoring agents. This specific situation is also valid for shape-controlled photocatalytic materials. That is why in the present work Bi₂WO₆ microcrystals were obtained using two shape-tailoring agents: Triton-X and amino acids/(tio)carbamide structures. The first of these agents was applied as a binary variable (presence or absence), while in the case of the second one, the Hückel polarity of the chalcogen–carbon double bond (CO or S) was considered as the changing parameter. The as-prepared materials were characterized by XRD, DRS, SEM and IR spectroscopy and their activity was verified under visible light illumination using rhodamine B as the model pollutant to enhance the general validity of the results. It was found that an empiric geometric function, defined as the “rose similarity decay constant” (R_SDC), showed that a perfect rose shape (low R_SDC) or geometries with similarly low R_SDC exhibited high photocatalytic activity. Moreover, the introduced empiric value was correlated with the Hückel polarity of the samples, thus showing for the first time a direct association between a structural parameter of the shape-tailoring agent, the obtained crystal geometry and the photoactivity.