Using rice husk ash as a SiO2 source in the preparation of SiO2/Nb2O5 and SiO2/ZnS heterostructures for photocatalytic application.

This work presents the synthesis of SiO2/Nb2O5 and SiO2/ZnS heterostructures using the microwave-assisted hydrothermal (MAH) method, which is fast and has low temperature. The silica used in the synthesis was obtained by burning the rice husk without any pre- or post-treatments. The obtained samples were characterized using various techniques such as X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDX), scanning electron microscopy (SEM), Fourier transform infrared (FTIR), and UV-visible. The obtained silica was found to be amorphous, and the materials used for modification showed characteristic of the type of synthesis used. SEM images showed that Nb2O5 and ZnS interacted with the SiO2 surface, filling the voids. In the photocatalytic process, the heterostructures showed enhanced decolorization efficiency for dyes such as rhodamine B (RhB) and methylene blue (MB) compared to SiO2. For RhB, the silica decolorized approximately 24%, and for MB, it discolored approximately 27%; SiO2/Nb2O5 showed 91.24% decolorization efficiency for RhB and 72.77% MB, while SiO2/ZnS showed approximately 96% for RhB and 100% for MB. All samples were tested under the same conditions. This demonstrates that the use of rice husk residue not only improves the photocatalytic activity of heterostructures but also promotes the utilization of improperly discarded residues.

KNbO3 photoelectrode for DSSC: a structural, optical and electrical approach.

In this work, we present the potassium niobate (KNbO3) nanoparticles as a suitable mesoporous photoelectrode for dye-sensitized solar cells (DSSCs). The KNbO3 particles were synthesized by the microwave-assisted hydrothermal method using mild conditions and characterized by SEM, XRD, Raman, and UV-Vis diffuse reflectance. The particles presented a pyramidal tower-like shape with an orthorhombic structure and an indirect bandgap of (3.0 ± 0.1) eV. Dye-sensitized solar cells were assembled using the synthesized KNbO3 nanoparticles, which were deposited as a photoelectrode on a TiO2 recombination charge blocking layer. It is noticeable that the synergistic operation of the TiO2 blocking layer and KNbO3 photoelectrode is essential to achieve photovoltaic behaviour in our solar cells. The short-circuit current density of Jsc = 2.82 mA, open-circuit voltage Voc = 669 mV, fill factor FF = 0.62, and a power conversion efficiency PCE = 1.17%, reports elevated parameters if compared to other DSSCs alternative materials, becoming potassium niobate suitable as photoelectrode.

Properties of zinc titanates synthesized by microwave assisted hydrothermal method.

Zinc titanates are compounds that have shown great application versatility, including in the field of semiconductors. Solid state reactions, the polymeric precursor method and the hydrothermal method are the most mentioned synthesis of these compounds in the literature. In the present work, we use microwave assisted hydrothermal method (MAH) to synthesize zinc titanate and evaluate its potential for solar cell applications through structural and optical characterization techniques. The synthesized samples were also subjected to a variable temperature heat treatment in the range of 500 °C-800 °C. The analysis showed that the crystallization of the material starts at 500 °C and that samples submitted to temperatures of 600 °C-800 °C showed the formation of two phases of zinc titanates, being a cubic phase of ZnTiO3, considered rare in the literature, predominant up to a temperature of 800 °C. The optical characterization, based on the techniques of photoluminescence spectroscopy and UV-Visible spectroscopy, showed that the photoluminescent activity and the energy of the band gap increased with the increase of the temperature of the heat treatment, having the highest response in 700 °C, facts that can be linked to the predominant formation of the cubic phase of ZnTiO3 and simultaneous of the cubic and rhombohedral phases of ZnTiO3 at 700 and 800 °C. Finally, we highlight as the most important results, the fact that it was possible to obtain these titanates at a temperature lower than that reported in the literature, and that the heat-treated sample at 500 °C is the one with the lowest energy expenditure to be synthesized and the one with the greatest potential for application in dye-sensitized solar cells (DSSC's).