Rare earth doped metal oxide nanoparticles for photocatalysis: a perspective

Metal oxides are well-known materials that have been considered as the prominent photocatalysts. Photocatalysis is a promising way to address the environmental issues which are caused by fossil fuel the combustion and industrial pollutants. Lot of efforts such as doping of metal oxides with metals, non-metals have been made to enhance their photocatalytic activity. More specifically, in this review we have discussed detailed synthesis procedures of rare earth doped metal oxides performed in the past decades. The advantage of doping metal oxides with rare earth metals is that they readily combine with functional groups due to the 4f vacant orbitals. Moreover, doping rare earth metals causes absorbance shift to the visible region of the electromagnetic spectrum which results to show prominent photocatalysis in this region. The effect of rare earth doping on different parameters of metal oxides such as band gap and charge carrier recombination rate has been made in great details. In perspective section, we have given a brief description about how researchers can improve the photocatalytic efficiencies of different metal oxides in coming future. The strategies and outcomes outlined in this review are expected to stimulate the search for a whole new set of rare earth doped metal oxides for efficient photocatalytic applications.

Boosting Photocatalytic Performance of Inactive Rutile TiO2 Nanorods under Solar Light Irradiation: Synergistic Effect of Acid Treatment and Metal Oxide Co-catalysts

In the present work, we accomplish the boosting of photocatalytic performance by the synergistic effect of acid treatment and transition metal oxide co-catalysts on molten salt rutile TiO₂ nanorods. FT-IR and XPS (oxygen deconvolution) results confirmed that the amount of hydroxyl groups increased on the surface of rutile TiO₂ nanorods (TO-NRs) after acid treatment. HR-TEM analysis revealed fine dispersion of metal oxide on the surface of acid treated TiO₂ nanorods (ATO-NRs). The photocatalytic activities of as-prepared (TO-NRs), acid treated (ATO-NRs), metal oxide loaded (MTO-NRs), and both acid treated and metal oxide loaded (MATO-NRs) nanorods were compared based on the rate kinetics and dye degradation efficiencies. Cobalt oxide (1 wt %) loaded and 1.0 M acid treated TiO₂ nanorods (Co/ATO-NR) exhibited the higher photocatalytic degradation efficiency for Orange-II dye degradation and inactivation of S. typhimurium pathogen compared to other photocatalysts under solar irradiation. Photoelectrochemical analysis demonstrated that the charge transfer process in Co/ATO-NR is significantly higher than that in the untreated samples. The improved photocatalytic activity of inactive TO-NRs might be due to enhanced charge transfer of finely dispersed metal oxides on the OH-rich surface of acid treated TiO₂ nanorods.

Physicochemical characterization of metal hexacyanometallate–TiO2composite materials

The paper describes the synthesis and characterization of novel TiO₂–metal hexacyanometallates (MHCMs) composite materials.

Iron-Based Nanoparticles for Toxic Organic Degradation: Silica Platform and Green Synthesis

Iron and iron oxide nanoparticles (NPs) are finding wide applications for the remediation of various toxic chloro-organic compounds (such as trichloroethylene, TCE), via reductive and oxidative processes. In this study, Fe NPs (30-50 nm) are synthesized by reduction from ferric ions immobilized (by ion exchange) on a platform (two types of sulfonated silica particles), in order to prevent the NP agglomeration. Next, the Fe NPs are oxidized and their effectiveness for the oxidative dechlorination of TCE via the heterogeneous decomposition of hydrogen peroxide to OH• on the surface of the iron oxide NPs was demonstrated. For the reductive approach, the use of ascorbic acid as a "green" reducing agent in conjunction with a secondary metal (Pd) inhibits NP oxidation and agglomeration through surface adsorbed species. The Fe/Pd NPs have been successfully applied for the dechlorination of TCE (k(SA), surface-area normalized reaction rate, = 8.1 ×10(-4) L/m(2)h).

Low temperature crystallization of transparent, highly ordered nanoporous SnO₂ thin films: application to room-temperature hydrogen sensing

High surface area highly ordered nanoporous thin films are the current gold standard for gas sensor use, however the nanostructure of such films is prone to collapse at annealing temperatures as low as 250 °C resulting in formation of a dense layer of limited utility. We report on a templating method used to deposit highly ordered nanoporous platinum (Pt)-doped tin dioxide (SnO(2)) thin films that are crystallized by a 100 °C water vapor hydrothermal treatment, with the low temperature process being compatible with a large variety of substrates including plastic. The resulting highly ordered nanoporous, transparent Pt-SnO(2) thin films are mechanically stable and can be annealed, as desired, at temperatures up to 800 °C for removal of the templating materials and tailoring of gas sensitivities without damage to the nanoporous structure. The synthesis method is general, offering a promising strategy for preparing high performance nanoporous metal oxide crystalline films for applications including gas sensing, photocatalysis, and 3(rd) generation photovoltaics. In our example application of the synthesized materials, we find that these Pt-SnO(2) films exhibit exceptional hydrogen gas sensing behavior, rapidly detecting low-level hydrogen concentrations at room temperature; for example, an eight order of magnitude change in electrical resistance is seen in response to 10 000 ppm H(2), with only minimal sensitivity to humidity.

Room temperature one-step synthesis of microarrays of N-doped flower-like anatase TiO2 composed of well-defined multilayer nanoflakes by Ti anodization

Microarrays of N-doped flower-like TiO(2) composed of well-defined multilayer nanoflakes were synthesized at room temperature by electrochemical anodization of Ti in NH(4)F aqueous solution. The TiO(2) flowers were of good anatase crystallinity. The effects of anodizing time, applied voltage and NH(4)F concentration on the flower-like morphology were systematically examined. It was found that the morphologies of the anodized Ti were related to the anodizing time and NH(4)F concentration. The size and density of the TiO(2) flowers could be tuned by changing the applied voltage. The obtained N-doped flower-like TiO(2) microarrays exhibited intense absorption in wavelengths ranging from 320 to 800 nm. Under both UV and visible light irradiation, the photocatalytic activity of the N-doped flower-like TiO(2) microarrays in the oxidation of methyl orange showed a significant increase compared with that of commercial P25 TiO(2) film.

Room temperature one-step polyol synthesis of anatase TiO2 nanotube arrays: photoelectrochemical properties

We describe an optimized anodization process to fabricate anatase TiO2 nanotube arrays at room temperature using a polyol electrolyte. The critical roles of water and anodization voltage are investigated, and mechanistic actions are considered. The as-fabricated electrodes show low efficiency when used as photoanodes to photoelectrochemically split water; however, their efficiency is remarkably enhanced upon their annealing at temperatures as low as 300 degrees C. The efficiency of the annealed samples was found to increase with the anatase content in the as-anodized electrodes, suggesting that these pre-existing crystallites can act as seeding layers that enhance the nucleation and growth of further anatase crystallites.