Synthesis & Other Chemical Processes


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Recently, graphitic carbon nitride (g-CN), a metal-free polymeric semiconductor with visible light activated band gap (2.70 eV) has been proposed as photocatalyst in the applications involving water splitting and decomposition of organic pollutants for advantages of earth abundance, appropriate reduction potential, exceptional physical properties, unique electronic structure, and outstanding visible light absorption.12-18 However, the quick recombination of photo-generated electron/hole pairs and small surface area limit the photocatalyst performance of g-CN materials. Hitherto, a variety of techniques involving template inversion of mesoporous silica (KIT-6, SBA-15, colloidal silica) and exfoliation were employed in increasing the surface area of the g-CN for sensing, hydrogen production, and visible light photocatalysis applications.

The negative potential (-1.12 eV vs NHE) of g-CN implies that it can easily form heterojunctions with TiO2 to attain superior visible light degradation performance. In this context, Shi et al. have synthesized nitrogen doped TiO2/g-C3N4 photocatalysts through a cyanamide precursor by utilizing in-situ impregnation calcination method. The nanocomposite was able to efficiently produce hydrogen under visible light irradiation (λ ≥ 420 nm) in the absence of noble metal as co-catalyst.20 The group of Wei et al. have prepared noble metal (Ag, Pt, Au) doped TiO2/g-C3N4 heterostructured nanofibers by a combination of Electrospinning and thermal oxidation/reduction process and reported the excellent photocatalytic activity.21 Similarly, Shen et al. have synthesized TiO2 nanobelts laminated on g-C3N4 nanosheet and demonstrated excellent degradation performance of methyl orange (95%) and hydrogen evolution. Wei et al. have prepared mesoporous TiO2/g-C3N4 microspheres using facile nanocoating process using cyanamide as g-CN precursor. They have reported excellent phenol degradation using the photocatalyst.

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Albanna et al. have synthesized metal free nanocomposite (g-C3N4 nanosheets/TiO2 mesocrystals) and realized that the presence of TiO2 increases the photocatalytic efficiency for H2 evolution. The results endorses that the g-CN and TiO2 heterojunctions exhibited higher degradation performance for Azo dye than pristine TiO2 or g-CN. In addition, TiO2 has also remained as an important counterpart material in designing high performance gas sensing material.25,26 The key requisite for gas sensors remains the high intrinsic surface area of the material which improves the sensing performance by providing enormous surface active sites for gaseous molecules to desorb upon and also enhances the rate of adsorption, transportation and desorption of charge carriers across the sensor surface. TiO2 also has been utilized to form composites with 2D materials for achieving superior gas sensing performances.25-29 Till date, however, nanocomposites of TiO2 and g-CN have been prepared using conventional methods for water splitting20-23,30 and electrode material applications,31 but this novel cubic mesoporous nanocomposite using ordered KIT-6 template has never been reported for photocatalysis and gas sensing applications.

In this work, we report a novel two step method (hydrothermal and nanocasting) to prepare Au-TiO2 loaded cubic g-CN nanohybrids using hard template of ordered mesoporous silica, KIT-6 to obtain high photodegradation efficiency (90.4%) towards the organic pollutant methyl orange (MO) dye under 90 min irradiation of visible light and optimized conditions of dye concentration, pH and catalyst dosage. Comparative degradation studies on organic dyes including cresol red (CR), acid orange (AO7), direct blue (DB) and methylene red (MR) have also been performed. The prepared catalyst shows excellent reusability without noticeable losses, suggesting that excellent applicability of Au-TiO2@g-CN nanohybrids in degrading aqueous dye solutions. Meanwhile, the Au-TiO2@g-CN nanonybrids respond to a variety of volatile organic amines, such as triethylamine, butylamine, triethanolamine and benzylamine, for potential sensing applications. Au nanoparticles, because of their exceptional catalytic nature and sensing characteristics,32,33 were employed for enhancing the performance of the TiO2@g-CN nanocomposite. The novel outcomes of this study can be highly useful in designing 2D layered materials and also shows promising glimpse in designing mesoporous materials with extended multi-functionalities.

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