Facet-dependent photocatalytic and antibacterial properties of α-Ag₂WO₄crystals: combining experimental data and theoretical insights

Abstract

In this paper, we have combined the various experimental results and first-principles calculations with a new and interesting discussion to explain the photocatalytic and antibacterial activities of α-Ag 2 WO 4 crystals, which were obtained using the microwave-hydrothermal (MH) method with anionic surfactants. The advantages of the insights gained through the present work are two-fold. First, the mechanism and origin of the photocatalytic and antibacterial activities can be rationalized. Second, this facile and controllable synthetic method is expected to encourage the synthesis of complex metal oxides with specific active facets, and these insights can contribute to the rational design of new materials for multifunctional applications. X-ray diffraction and Rietveld refinement analysis confirmed that all the crystals have an orthorhombic structure without deleterious phases. Ultraviolet-visible diffuse reflectance spectroscopy indicated the presence of intermediary energy levels and a variation in the optical band gap values (3.09-3.14 eV) with the crystal growth process.The geometry, electronic properties of the bulk, and surface energies of these crystals were evaluated using first-principles quantum mechanical calculations based on the density functional theory. The crystal shapes was experimentally and theoretically modeled based on Rietveld refinement data, emission scanning electron microscopy images, and Wulff construction. To obtain a wide variety of crystal shapes, the morphologies were gradually varied by tuning the surface chemistry, i.e., the relative stability of the faceted crystals. The growth mechanisms of different α-Ag 2 WO 4 crystals and their facet-dependent photocatalytic and antibacterial performances were explored in details. The combination of experimental and theoretical data revealed the presence of (110) and (011) planes with high surface energies together with the disappearance of faces related to the IJ010)/IJ010) planes in α-Ag 2 WO 4 crystals are key factors that can rationalize both the photocatalytic and antibacterial activities. The different activities may be attributed to the different number of unsaturated superficial Ag and W atoms capable of forming the main active adsorption sites. Finally, we discuss how knowledge of surface-specific properties can be utilized to design a number of crystal morphologies that may offer improved performance in various applications.

Photoluminescence and Photocatalytic Properties of Ag3PO4 Microcrystals: An Experimental and Theoretical Investigation

“…[1] This finding is intriguing in the senset hat ac ertain particle structure might be thek ey for achieving ah igh photocatalytic activity.T herefore, the morphology, not only the size, but also the shape, and the exposed facets, can be also important and play an important role in photocatalytic efficiency. [2] In this sense, the controllable synthesis of crystal facets of aw ide range of semiconductors, such as TiO 2 , [3] ZnO, [4] Fe 2 O 3 , [5] WO 3 , [6] Ag 3 PO 4 , [7] PbMoO 4 , [8] and a-Ag 2 WO 4 , [9] is becoming an active research field that offers an ew opportunity to further optimize the facet-dependent photocatalytic performance of semiconductor-based photocatalysts. [10] In particular, phosphates have attracted considerable attention from the scientific community owing to their wide range of applications,e specially as photocatalytic materials.…”

Effects of surface stability on the morphological transformation of metals and metal oxides as investigated by first-principles calculations

“…These transformations are due to the geometric constraints imposed by the crystal structure and are associated with the relative values of the surface energy of each face. In this context, Roca et al published some results about our simple way to use the theoretical morphology modulation in TiO 2 and α-Ag 2 WO 4 [60,61] nanocrystals in order to explain the surface energy changes observed in experimental conditions.…”

In situgrowth of Ag nanoparticles onα-Ag2WO4under electron irradiation: probing the physical principles

“…In the present article, we studied theoretically in detail one of the most stables surfaces of α-Ag 2 WO 4 : the (001) surface, and, this surface has been studied by TEM and x-ray diffraction experiments previously [81].…”