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.

In this study, the structure and photoelectrochemical properties of CuWO 4 porous films synthesized by a co-precipitation method followed by a hydrothermal treatment were investigated. The film was deposited on fluorine-doped tin oxide (FTO)-conducting glass, from a suspension containing polyethylene glycol, and heat-treated at 500 C for 30 min. X-ray diffraction patterns, the Rietveld refinement data, and the micro-Raman spectrum showed that the CuWO 4 film has a triclinic structure. The optical band gap energy of the film was estimated to be 2.45 eV by the Tauc plot. Field emission scanning electron microcopy images of the films indicated that they are about 4.0 AE 0.5 mm thick. The photoelectrochemical properties of the film were investigated in a Na 2 SO 4 aqueous solution, in the absence of light and under polychromatic irradiation. The CuWO 4 film exhibited photoelectrochemical behavior of a n-type semiconductor, with a negative photopotential and an anodic photocurrent density of 68 mA cm À2 at 0.73 V vs. Ag/AgCl (1.23 V vs. RHE). The n-type photoelectrochemical behavior was confirmed by a chronoamperometry measurement biased condition at + 0.7 V, at different pH values. From these studies, it was noted that when the pH values increased from 3 to 11, the photocurrent density increased about 9 times. Also, the flat band potential (E fb) of the semiconductor was estimated by the Butler-Gärtner model at + 0.34 V, which was utilized to calculate the conduction band edge. The studies presented here reveal that the CuWO 4 porous film is a promising candidate to be applied as a photoanode in photocatalytic processes under irradiation by visible light.

In this paper, a new synthesis method was proposed to obtain anatase titanium oxide (TiO 2) nanocrystals anchored into SBA-15 molecular sieve, as a matrix assigned by the in-situ anchoring (ISA) method. Pure SBA-15 and modified with TiO 2 nanocrystals at different Si/Ti molar ratios (R = 75, 50, and 25) were structurally characterized by X-ray diffraction (XRD), Micro-Raman and Fourier Transform infrared (FTIR) spectroscopies. Specific surface area, pore volume and average pore diameter were estimated using both Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods, respectively. Morphological aspects of these samples were observed by means of field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). Optical properties were investigated by ultravioletvisible (UV-vis) diffuse reflectance spectroscopy. XRD patterns, Micro-Raman and FT-IR spectra indicate the TiO 2 nanocrystals crystallized in a tetragonal structure anchored into the SBA-15 mesopores. BET and BJH methods prove a large amount of TiO 2 nanocrystals were anchored inside of SBA-15 mesopores due to increase in surface area and average pore size of SBA-15 matrix. FE-SEM and TEM images showed the pure SBA-15 has an elongated hexagon-shaped microstructure, and an average size of 7.34 nm for 2D hexagonal mesopores. Moreover, ISA method was able to avoid blocking of mesopores, in addition promotes a significant increasing the impregnation rate of anatase TiO 2 nanocrystals in SBA-15 matrix. A growth mechanism was proposed in order to explain the stages involved in the formation of TiO 2-SBA mesoporous. UV-vis spectra revealed a dependence of the optical band gap energy (E gap) with the decreasing of Si/Ti molar ratios.

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