Kumarsrinivasan Sivaranjani

Porosity driven photocatalytic activity of wormhole mesoporous TiO2-xNx in direct sunlight

Results obtained by combining four important factors simultaneously, namely, wormhole mesoporosity with low diffusion length for charge carriers, high surface area, nanoparticles with high crystallinity, and visible light absorption due to N-doping, in titania (meso-TiO2-xNx) are reported. Meso-TiO2-xNx materials have been prepared by a combustion method within 10 min and by varying urea : Ti(NO3)4 between 1 (UT1) and 10 (UT10). All of the prepared materials have been thoroughly characterised. Nanocrystalline anatase phase with high surface area (234 m2 g−1), and type-IV H3-mesoporosity is observed with UT10. Photocatalytic rhodamine-B degradation was employed to screen for the activity of the materials, and p-anisyl alcohol oxidation to p-anisaldehyde was carried out successfully in aqueous solution under direct sunlight. High photocatalytic activity of UT10 in direct sunlight, in spite of high band gap (3.24 eV), is attributed to the better utilization of holes due to the low charge diffusion barrier associated with wormhole mesoporosity along with highly crystalline, however, nanoparticulate TiO2-xNx.

Molecular oxygen-assisted oxidative dehydrogenation of ethylbenzene to styrene with nanocrystalline Ti1−xVxO2

Oxidative dehydrogenation of ethylbenzene to styrene has been studied with vanadium-incorporated mesoporous nanocrystalline titania (Ti1−xVxO2) and molecular oxygen between 440 and 530 °C. Incorporation of V in TiO2 lattice framework has been achieved by simple solution combustion method. Incorporation of V in TiO2 lattice has been confirmed by X-ray diffraction, XPS and Raman spectra and other physicochemical analysis. High ethyl benzene conversion and stable styrene yield has been observed with 10% V-containing rutile phase titania at 500 °C. However, stable but relatively lower styrene yield has been observed with 2 and 5% V-containing catalysts between 440 and 500 °C. Highest selectivity is observed with lower vanadium content. Comparable activity has been observed under similar experimental conditions with four times higher air-flow than that of O2. In order to understand the structure activity relationship, spent catalysts were analyzed by all physico-chemical methods. Although there is a phase change from anatase to rutile Ti1−xVxO2 within 1 h of reaction, higher activity is primarily attributed to the ionic V5+ in Ti1−xVxO2 lattice, which prevents agglomeration to V2O5. It is to be underscored the reactivity is retained at the cost of textural properties and phase change from anatase to rutile, which is essential for the reaction.

Aminosilicate sol–gel stabilized N-doped TiO2–Au nanocomposite materials and their potential environmental remediation applications

A facile chemical reduction method to synthesize amine functionalized silicate sol–gel-supported gold-deposited nitrogen-doped Degussa-TiO2 nanocomposite materials (APS/(N-P25-Au)NCM) is reported and the materials are characterized by DRS, PL, XRD, TEM, Raman, XPS and BET surface area analysis. The application of the synthesized APS/(N-P25-Au)NCM towards environmental remediation processes are investigated by studying the catalytic oxidation of carbon monoxide (CO) and photocatalytic reduction of toxic mercuric (Hg(II)) ions. The catalytic and photocatalytic activity of the prepared catalysts are found to be in the order of APS/(N-P25-Au)NCM ≫ APS/(P25-Au)NCM > N-P25 > P25. The enhanced catalytic and photocatalytic activities of the APS/(N-P25-Au)NCM can be attributed to the synergistic effect of Aunps and N-doped P25. The catalytic activities of the APS/(N-P25-Au)NCM are very promising in the field of green technology for the environmental cleaning applications.

Recent developments in solar H2 generation from water splitting

AbstractHydrogen production from water and sunlight through photocatalysis could become one of the channels, in the not-so-distant future, to meet a part of ever growing energy demands. However, accomplishing solar water splitting through semiconductor particulate photocatalysis seems to be the ‘Holy Grail’ problem of science. In the present mini-review, some of the critical strategies of semiconductor photocatalysis are focused with the aim of enumerating underlying critical factors such as visible light harvesting, charge carrier separation, conduction and their utilization that determine the quantum efficiency. We attempted to bring out the essential requirements expected in a material for facile water splitting by explaining important and new designs contributed in the last decade. The newly emerged designs in semiconductor architecture employing nanoscience towards meeting the critical factors of facile photocatalysis are elucidated. The importance of band gap engineering is emphasized to utilize potential wide band gap semiconductors. Assistance of metal nanostructures and quantum dots to semiconductors attains vital importance as they are exuberant visible light harvesters and charge carrier amplifiers. Benevolent use of quantum dots in solar water splitting and photoelectrochemical water splitting provides scope to revolutionize the quantum efficiency by its multiple exciton generation features. A list of drawbacks and issues that hamper the much needed breakthrough in photocatalysis of water splitting is provided to invite attention to address them and move towards sustainable water splitting. Graphical AbstractPresent mini-review focuses on some of the major aspects of solar water splitting to produce hydrogen. Electronic structure changes due to doping of conventional oxides are correlated with visible light absorption. Quantum dot assisted water splitting and persistent problems associated, in general, with solar water splitting are highlighted with a possible path forward.

Highly Ordered Mesoporous WO3 with Excellent Catalytic Performance and Reusability for Deep Oxidative Desulfurization

Highly ordered mesoporous tungsten trioxide (WO3) with high surface area (75 m2/g) and well-defined mesopores were successfully prepared through a hard templating method using a mesoporous silica KIT-6 as a template and (NH4)6H2W12O40 ⋅ xH2O as a tungsten precursor. Oxidative desulfurization of a model oil with H2O2 as the oxidant was carried out at 50°C under atmospheric pressure in order to analyze the catalytic activity. The desulfurization reactions were optimized by various kinds of reaction parameters such as H2O2/S molar ratio, reaction temperatures and series of sulfur-containing compounds [dibenzothiophene (DBT), benzothiophene (BT) and 4,6-dimethyl dibenzothiophene (4,6-DMBT)]. Excellent catalytic activity for the removal of the sulfur-containing compounds from the model oil was observed with mesoporous WO3 catalyst, where the activity was maintained during 5 recycle tests without any regeneration process. The high catalytic activity and durability is mainly attributed to well-defined mesopores and high surface area of mesoporous WO3 catalyst.