A review of TiO2 nanostructured catalysts for sustainable H2 generation

Ultraselective and sensitive detection of xylene and toluene with minimum interferences of other indoor air pollutants such as benzene, ethanol, and formaldehyde is achieved using NiO hierarchical nanostructures doped with Cr. Pure and 1.15–2.56 at% Cr-doped NiO flower-like hierarchical nanostructures assembled from nanosheets are prepared by a simple solvothermal reaction and their gas sensing characteristics toward o-xylene and toluene gases are investigated. The 1.15 at% Cr-doped NiO hierarchical nanostructures show high responses to 5 ppm of o-xylene and toluene (ratio of resistance to gas and air = 11.61 and 7.81, respectively) and negligible cross-responses to 5 ppm of benzene, formaldehyde, ethanol, hydrogen, and carbon monoxide. However, pure NiO nanostructures show low responses to 5 ppm of o-xylene and toluene (ratio of resistance to gas and air = 2.01 and 1.14, respectively) and no selectivity toward any specific gas is observed. Significant enhancement of the response and selectivity to o-xylene and toluene is attributed to the decrease in the hole concentration in NiO and the catalytic oxidation of methyl groups by Cr doping.

Ultraselective and sensitive detection of xylene and toluene for monitoring indoor air pollution using Cr-doped NiO hierarchical nanostructures

A dip-coating technique was employed to prepare anatase phase of titania thin films. Fluorine doped tin oxide substrates were used to prepare titania thin films. The samples were annealed at 550 °C for 18 h. X-ray diffraction results revealed the amorphous and anatase phases of TiO2 for as-synthesized and annealed samples, respectively. The crystallite size of anatase TiO2 thin films was almost 25 nm for annealed samples. UV–visible confirmed the energy band gap 3.86 and 3.64 eV for as-prepared and calcinated titania thin films. The reduction in the energy band gap could be due to the change in crystallization and agglomeration of small grains after calcination. The morphology of the prepared films was investigated by field emission scanning electron microscopy which demonstrated the agglomeration of spherical particles of TiO2 with average particle size of about 30 nm. The molecular properties (chemical bonding) of the samples were investigated by means of Fourier Transform Infrared (FTIR) spectroscopy. FTIR analysis exhibited the formation of titania, functional group OH, hydroxyl stretching vibrations of the C–OH groups, bending vibration mode of H–O–H, alkyl C–H stretch, stretching band of Ti–OH, CN asymmetric band stretching, and C=O saturated aldehyde.

Characterization of titania thin films grown by dip-coating technique

In the present study, a simple hydrothermal approach has been successfully applied for a large scale synthesis of anatase titanium dioxide nanoparticles (TiO 2 NPs) using titanium glycolate precursors and is utilized for the fabrication of low-cost high performance acetone (CH 3 COCH 3 ) gas sensors after corroborating the crystallinity, phase-purity, and surface morphology investigations. Several randomly distributed TiO 2 aggregates, composed of NPs, are noticed from morphology analysis. Chemiresistive properties of as-fabricated TiO 2 sensors attempted towards host of oxidizing and reducing gases, reveal a superior selectivity to CH 3 COCH 3 with a maximum response of 15.24 (1000 ppm) @270 °C compared to other target gases. One of the key features of as-fabricated TiO 2 sensor is the lowest detection limit of 500 ppb to CH 3 COCH 3 with rapid response and recovery times, signifying commercial potential of the developed sensor materials. The effect of operating temperature along with various concentrations of CH 3 COCH 3 on the gas sensing properties of TiO 2 sensor has thoroughly been investigated and reported. Finally, the interaction mechanism between the CH 3 COCH 3 molecules and the TiO 2 NPs sensor was elaborated in depth for a thorough understanding sensor performance experimentally and supposedly.

Enhanced acetone sensing properties of titanium dioxide nanoparticles with a sub-ppm detection limit

Anatase hierarchical TiO2 with innovative designs (hollow microspheres with exposed high-energy {001} crystal facets, hollow microspheres without {001} crystal facets, and solid microspheres without {001} crystal facets) were synthesized via a one-pot hydrothermal method and characterized. Based on these materials, gas sensors were fabricated and used for gas-sensing tests. It was found that the sensor based on hierarchical TiO2 hollow microspheres with exposed high-energy {001} crystal facets exhibited enhanced acetone sensing properties compared to the sensors based on the other two materials due to the exposing of high-energy {001} crystal facets and special hierarchical hollow structure. First-principle calculations were performed to illustrate the sensing mechanism, which suggested that the adsorption process of acetone molecule on TiO2 surface was spontaneous, and the adsorption on high-energy {001} crystal facets would be more stable than that on the normally exposed {101} crystal facets. Further c...

Enhanced Gas-Sensing Properties of the Hierarchical TiO2 Hollow Microspheres with Exposed High-Energy {001} Crystal Facets

Effect of Ni doping on the microstructure and high Curie temperature ferromagnetism in sol–gel derived titania powders

Bare and Ag loaded TiO2 (0.05, 0.5, and 5.0 mol% Ag) powders prepared by sol–gel process have been used for the detection of ethanol, LPG, acetone and toluene gases. These materials were well characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray photoelectron spectroscopy (XPS) and Brunauer–Emmett–Teller (BET) specific surface area analysis techniques. Specific surface area increased with increasing Ag loading in these mesoporous materials. A thorough TEM/HRTEM investigation with X-ray maps of the modified particles shows the extent of TiO2 surface coverage by Ag nanoparticles. From the comparative study of the sensor response of Ag–TiO2 powders for various gases, it is observed that each Ag loading resulted in the highest response towards a particular gas or in other words, every gas responded best towards a particular Ag loading of the sensor material, i.e. 0.05 mol% Ag–TiO2 sensor showed highest response towards ethanol, 0.5 mol% Ag–TiO2 sensor showed best response towards toluene, whereas, bare TiO2 proved to be the best sensor for both acetone and LPG gases. This establishes that Ag loading is not required for detection of acetone and LPG gases. On the basis of detailed materials characterization, a mechanism for the gas sensing response of each analyte has been discussed.

Suresh Chand

Papers

Effect of Ni doping on the microstructure and high Curie temperature ferromagnetism in sol–gel derived titania powders

Selective gas sensing response from different loading of Ag in sol–gel mesoporous titania powders

Green Synthesis of Nanocrystalline Cu 2 ZnSnS 4 Powder Using Hydrothermal Route