Brundabana Naik

Synthesis of mesoporous TiO2-xNx spheres by template free homogeneous co-precipitation method and their photo-catalytic activity under visible light illumination

The article presents preparation, characterization and catalytic activity evaluation of an efficient nitrogen doped mesoporous titania sphere photo-catalyst for degradation of methylene blue (MB) and methyl orange (MO) under visible light illumination. Nitrogen doped titania was prepared by soft chemical route i.e. template free, slow and controlled homogeneous co-precipitation from titanium oxysulfate sulfuric acid complex hydrate, urea, ethanol and water. The molar composition of TiOSO(4) to urea was varied to prepare different atomic % nitrogen doped titania. Mesoporous anatase TiO(2-x)N(x) spheres with average crystallite size of 10 nm and formation of titanium oxynitride center were confirmed from HRTEM, XRD and XPS study. UV-vis DRS showed a strong absorption in the range of 400-500 nm which supports its use in visible spectrum of light. Nitrogen adsorption-desorption study supports the porous nature of the doped material. All the TiO(2-x)N(x) samples showed higher photo-catalytic activity than Degussa P(25) and undoped mesoporous titania. Sample containing around one atomic % nitrogen showed highest activity among the TiO(2-x)N(x) samples.

Plasmon Induced Nano Au Particle Decorated over S,N-Modified TiO2 for Exceptional Photocatalytic Hydrogen Evolution under Visible Light

Nano Au deposited mesoporous S,N-TiO2 (SNT) nanocomposites have been fabricated through deposition precipitation technique by employing urea as the hydrolyzing agent. To investigate the structural, optical, and electronic properties, the photocatalysts are characterized through X-ray diffraction (XRD), UV-vis diffuse reflectance spectra, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and photoelectrochemical measurements. Here in addition to the co-catalyst nature of nano Au particles, surface plasmon resonance (SPR) effect in visible region enhances the light harvestation ability as well as transfer electrons to the conduction band of SNT. Furthermore, easy channelization of photogenerated charge carriers through sulfate facilitated redox couple makes the system more potential towards H2 evolution. TEM study exhibits well interconnective morphology in the matrix which helps easy channelization of electrons in the SNT nanocomposites. The photocatalytic activities have been evaluated for hydrogen generation under the irradiation of visible light and an enhanced activity has been observed for the Au promoted SNT due to the presence of nano Au particles, that is, 3.5 nm. The hydrogen generation activity of 3Au-SNT is nearly 9 times higher than that of neat SNT, and the energy conversion efficiency was found to be 17.6 %.

Facile fabrication of mesoporosity driven N–TiO2@CS nanocomposites with enhanced visible light photocatalytic activity

For the efficient utilization of visible light from solar light illumination, wormhole mesoporous N-doped TiO2 modified with carbon and sulfur (abbreviated as N–TiO2@CS nanocomposites) have been fabricated using a sol–gel auto-combustion method. The prepared samples under different calcination temperatures were thoroughly characterized by XRD, TEM, FTIR, BET Surface area, UV-Vis DRS, XPS and PL. It has been demonstrated that in N–TiO2@CS nanocomposites, incorporated N in the crystal lattice of TiO2 exist as N–Ti–O, sulfur exist as sulfate ions (S6+) on the TiO2 surface and carbon species were modified on the surface of the photocatalyst. N-doping narrows the band gap and sulfate species on the surface of TiO2 act as co-catalyst. Moreover, the presence of surface carbon species enhances visible light harvesting and stimulates to separate photo generated charge carriers, which makes the system more potential towards photocatalytic application. The photocatalytic activities of the as prepared catalyst were evaluated for phenol degradation under visible light irradiation. The higher photocatalytic activity of the N–TiO2@CS nanocomposite calcined at 400 °C (STU400) is attributed to the synergistic combination of C, N and S atoms, the wormhole mesoporous frame with high surface area and high crystalline anatase phase of TiO2. The overall photocatalytic activity and the proposed mechanism are further confirmed through PL spectra and trapping of hydroxyl radicals.

Facile Synthesis of Bi2O3/TiO2−xNx and its Direct Solar‐Light‐Driven Photocatalytic Selective Hydroxylation of Phenol

Mesoporous Bi2O3/TiO2−xNx nanocomposites (BiNT) have been synthesized by using a template‐free homogeneous coprecipitation technique. X‐ray diffraction, X‐ray photoelectron spectroscopy, high‐resolution transmission electron microscopy, UV/Vis diffuse reflectance spectroscopy, and photoluminescence studies are adapted to characterize the structural, electronic, and optical properties of the composites. The photocatalytic activities of the catalysts are evaluated for the hydroxylation of phenol under direct solar irradiation. The BiNT materials show excellent catalytic activity for selective phenol hydroxylation without using any oxidant. Notably, one of the nanocomposites shows a very high activity and results in a phenol conversion of 99 % in aqueous medium with 100 % selectivity towards hydroquinone and, in general, excellent selectivity is found for dihydroxybenzene compounds. The heterogeneous catalysts exhibit a successive slight decrease in catalytic activity if reused for five or more times.

Cr(VI) remediation from aqueous environment through modified-TiO2-mediated photocatalytic reduction

Cr(VI) exhibits cytotoxic, mutagenic and carcinogenic properties; hence, effluents containing Cr(VI) from various industrial processes pose threat to aquatic life and downstream users. Various treatment techniques, such as chemical reduction, ion exchange, bacterial degradation, adsorption and photocatalysis, have been exploited for remediation of Cr(VI) from wastewater. Among these, photocatalysis has recently gained considerable attention. The applications of photocatalysis, such as water splitting, CO2 reduction, pollutant degradation, organic transformation reactions, N2 fixation, etc., towards solving the energy crisis and environmental issues are briefly discussed in the Introduction of this review. The advantages of TiO2 as a photocatalyst and the importance of its modification for photocatalytic reduction of Cr(VI) has also been addressed. In this review, the photocatalytic activity of TiO2 after modification with carbon-based advanced materials, metal oxides, metal sulfides and noble metals towards reduction of Cr(VI) was evaluated and compared with that of bare TiO2. The photoactivity of dye-sensitized TiO2 for reduction of Cr(VI) was also discussed. The mechanism for enhanced photocatalytic activity was highlighted and attributed to the resultant properties, namely, effective separation of photoinduced charge carriers, extension of the light absorption range and intensity, increase of the surface active sites, and higher photostability. Advantages and limitations for photoreduction of Cr(VI) over modified TiO2 are depicted in the Conclusion. The various challenges that restrict the technology from practical applications in remediation of Cr(VI) from wastewater were addressed in the Conclusion section as well. The future perspectives of the field presented in this review are focused on the development of whole-solar-spectrum responsive, TiO2-coupled photocatalysts which provide efficient photocatalytic reduction of Cr(VI) along with their good recoverability and recyclability.