Shipra Mital Gupta

A review on the synthesis of TiO2 nanoparticles by solution route

TiO2 can be prepared in the form of powder, crystals, or thin films. Liquid-phase processing is one of the most convenient and utilized methods of synthesis. It has the advantage of allowing control over the stoichiometry, production of homogeneous materials, formation of complex shapes, and preparation of composite materials. However, there may be some disadvantages such as expensive precursors, long processing times, and the presence of carbon as an impurity. In comparison, the physical production techniques, although environment friendly, are limited by the size of the produced samples which is not sufficient for a large-scale production. The most commonly used solution routes in the synthesis of TiO2 are reviewed.

An overview of commonly used semiconductor nanoparticles in photocatalysis

The depletion of non-renewable resources and rise in global warming has caused great concern to humankind. With a view to use renewable source of energy and to eliminate hazardous chemical compounds from air, soil, and water, photocatalysis utilizing solar energy is becoming a rapidly expanding technology. Semiconductor nanoparticles have the ability to undergo photoinduced electron transfer to an adsorbed particle governed by the band energy positions of the semiconductor and the redox potential of the adsorbate. A brief overview of metal oxides and sulphides that can act as sensitizers for light-induced redox processes due to their electronic structure is presented here.

Nanocrystalline ZrO2 and Pt-doped ZrO2 catalysts for low-temperature CO oxidation

Zirconia (ZrO2) nanoparticles were synthesized by solution combustion using urea as an organic fuel. Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), transmission electron microscopy (TEM), UV–vis and Fourier transform infrared (FTIR) measurements were performed in order to characterize the catalyst. The calculated crystallite size of ZrO2, calculated with the help of the Scherrer equation, was around 30.3 nm. The synthesized ZrO2 was scrutinized regarding its role as catalyst in the oxidation of carbon monoxide (CO). It showed 100% CO conversion at 240 °C, which is the highest conversion rate reported for ZrO2 in literature to date. It is found that through solution combustion, Pt2+ ions replace Zr4+ ions in the ZrO2 lattice and because of this, oxygen vacancies are formed due to charge imbalance and lattice distortion in ZrO2. 1% Pt was doped into ZrO2 and yielded excellent CO oxidation. The working temperature was lowered by 150 °C in comparison to pure ZrO2. Further, it is highly stable for the CO reaction (time-on-stream ≈ 40 h). This is because of a synergic effect between Pt and Zr components, which results in an increase of the oxygen mobility and oxygen vacancies and improves the activity and stability of the catalyst. The effects of gas hourly space velocity (GHSV) and initial CO concentration on the CO oxidation over Pt(1%)-ZrO2 were studied.

Low-temperature CO oxidation over Cu/Pt co-doped ZrO2 nanoparticles synthesized by solution combustion

Zirconia (ZrO2) nanoparticles co-doped with Cu and Pt were applied as catalysts for carbon monoxide (CO) oxidation. These materials were prepared through solution combustion in order to obtain highly active and stable catalytic nanomaterials. This method allows Pt2+ and Cu2+ ions to dissolve into the ZrO2 lattice and thus creates oxygen vacancies due to lattice distortion and charge imbalance. High-resolution transmission electron microscopy (HRTEM) results showed Cu/Pt co-doped ZrO2 nanoparticles with a size of ca. 10 nm. X-ray diffraction (XRD) and Raman spectra confirmed cubic structure and larger oxygen vacancies. The nanoparticles showed excellent activity for CO oxidation. The temperature T 50 (the temperature at which 50% of CO are converted) was lowered by 175 °C in comparison to bare ZrO2. Further, they exhibited very high stability for CO reaction (time-on-stream ≈ 70 h). This is due to combined effect of smaller particle size, large oxygen vacancies, high specific surface area and better thermal stability of the Cu/Pt co-doped ZrO2 nanoparticles. The apparent activation energy for CO oxidation is found to be 45.6 kJ·mol−1. The CO conversion decreases with increase in gas hourly space velocity (GHSV) and initial CO concentration.

Nickel Nanocatalyst Ex-Solution from Ceria-Nickel Oxide Solid Solution for Low Temperature CO Oxidation

In this work, in situ growth of Ni nanocatalysts to attach onto the ceria (CeO2) surface through direct Ni ex-solution from the NiO-CeO2 solid solution in a reducing atmosphere at high temperatures with an aim to improve the catalytic activity, and stability for low temperature carbon monoxide (CO) oxidation reaction have been reported. The NiO-CeO2 solid solutions were prepared by solution combustion method, and the results of XRD and RAMAN showed that doping of Ni increases the oxygen vacancies due to charge compensation. Ni is clearly visible in XRD and TEM of Ni ex-solved sample (R-UCe5Ni10) after reduction of NiO-CeO2 (UCe5Ni10) sample by 5% H2/Ar reduction at 1000 °C. TEM analysis revealed a size of 9.2 nm of Ni nanoparticle that is ex-solved on the surface CeO2. This ex-solved sample showed very high catalytic activity (T50 ~ 110 °C), and stability (100 h) for CO oxidation reaction as compared to prepared solid solution samples. This is due to the highly active metallic nano-phase which is ex-solved on the surface of CeO2 and strongly adherent to the support. The apparent activation energy Ni ex-solved sample is found out to be 48.4 kJ mol-1. Thus, the above Ni ex-solved sample shows a practical applicability for the CO reaction.

Synthesis and photophysics of leadsulphide nanocrystallites

Nanoparticles of lead sulphide have been stabilized in the presence of excess Pb2+ in aqueous basic medium by a simple chemical route of synthesis. These PbS nanoparticles were synthesized very conveniently at room temperature using hexametaphosphate as stabilizer. These nanoparticles have an absorption extending into the NIR region. A significant quantum confinement effect made the bandgap of lead sulphide nanoparticles produce a blue shift from 0.41 eV to about 1.5 eV. The size and morphology of the particles were studied by TEM. Particles were relatively small sized (about 6 nm) having narrow size distribution. XRD data analysis indicate that the product is a mixture of PbS, PbO and Pb(OH)2. Both XRD pattern and HRTEM images confirm the crystalline structure of lead sulphide crystals. IR spectroscopy indicates the formation of PbS. PbS nanoparticles were fairly stable and could be stored for about three weeks at room temperature and for about two months at 5°C without agglomeration. These particles were photoactive and sensitized the reaction of aniline by light leading to the formation of azobenzene.