TiO 2 was prepared by sol-gel method through the hydrolysis of TiCl 4 and its surface derivatization was carried out with molecular catalyst like Hemin (chloro(protoporhyinato)iron(III)). Catalyst was characterized by various analytical techniques like UV-vis spectroscopy, FT-IR, FE-SEM and XRD.The anchoring of Hemin on titania surface is confirmed by FT-IR spectra through the linkage of O C O Ti bond and also by TGA-DSC and elemental analysis. The photocatalytic activity of the surface modified catalyst is tested for the degradation of methyl orange (MO) as a model compound under UV light. The Hemin impregnated TiO 2 (H-TiO 2 ) in presence of H 2 O 2 shows an excellent photocatalytic activity compared to pristine TiO 2 , Hemin, H 2 O 2 , TiO 2 /H 2 O 2 , and Hemin/H 2 O 2 systems. The enhancement in the photocatalytic activity is attributed to the presence of iron (III) porphyrin ring on the TiO 2 surface, which reduces the electron-hole recombination rate and also by acting as a mediator for continuous production of enriched concentration of hydroxyl radicals along with various other reactive free radicals.
In order to utilize visible light more effectively in photocatalytic reactions, the surfaces of TiO 2 nanoparticles are sensitized by Hemin molecules (H-TiO 2 ) and the catalyst is characterized by various analytical techniques like powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), UV-Visible absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) with an energy-dispersive X-ray (EDX) technique, BET surface area measurements and thermogravimetric analysis (TGA). The results strongly confirm the chemisorption of Hemin molecules on the TiO 2 surface through OC-O-Ti bonds.The photocatalytic activity of H-TiO 2 was investigated by the degradation of 4-nitrophenol as a model compound in an aqueous solution under solar light irradiation with the assistance of an appropriate amount of a sacrificial electron donor. The enhanced activity of H-TiO 2 confirms the sensitization process.Intermediate products were identified by HPLC analysis and a possible degradation reaction mechanism was proposed. The development of this porphyrin-based photocatalyst provides an alternative approach in harnessing visible solar light and shows promise for waste water treatment in future industrial applications.
The synergistic effects between ␣-Sulfur (␣-S) and TiO 2 photocatalysts is studied under UV/solar light. An enhancement in photocatalytic activity was observed under UV light, due to formation of sulfate anions in the reaction mixture and these ions get adsorbed on TiO 2 surface by electrostatic force of attraction or it may react with holes/hydroxyl radicals to generate sulfate radical anion. An increase in quantum efficiency is observed with sulfated TiO 2 due to reduction in electron-hole recombination rate. The extended response of ␣-S under visible region is due to non-vertical absorption process, which paved a new way for elemental photocatalysis.
Third-generation solar cells are understood to be the pathway to overcoming the issues and drawbacks of the existing solar cell technologies. Since the introduction of graphene in solar cells, it has been providing attractive properties for the next generation of solar cells. Currently, there are more theoretical predictions rather than practical recognitions in third-generation solar cells. Some of the potential of graphene has been explored in organic photovoltaics (OPVs) and dye-sensitized solar cells (DSSCs), but it has yet to be fully comprehended in the recent third-generation inorganic-organic hybrid perovskite solar cells. In this review, the diverse role of graphene in third-generation OPVs and DSSCs will be deliberated to provide an insight on the prospects and challenges of graphene in inorganic-organic hybrid perovskite solar cells.
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