Photoinduced reactivity of titanium dioxide

Nano-sized TiO 2 photocatalytic water-splitting technology has great potential for low-cost, environmentally friendly solar-hydrogen production to support the future hydrogen economy. Presently, the solar-to-hydrogen energy conversion efficiency is too low for the technology to be economically sound. The main barriers are the rapid recombination of photo-generated electron/hole pairs as well as backward reaction and the poor activation of TiO 2 by visible light. In response to these deficiencies, many investigators have been conducting research with an emphasis on effective remediation methods. Some investigators studied the effects of addition of sacrificial reagents and carbonate salts to prohibit rapid recombination of electron/hole pairs and backward reactions. Other research focused on the enhancement of photocatalysis by modification of TiO 2 by means of metal loading, metal ion doping, dye sensitization, composite semiconductor, anion doping and metal ion-implantation. This paper aims to review the up-to-date development of the above-mentioned technologies applied to TiO 2 photocatalytic hydrogen production. Based on the studies reported in the literature, metal ion-implantation and dye sensitization are very effective methods to extend the activating spectrum to the visible range. Therefore, they play an important role in the development of efficient photocatalytic hydrogen production.

A review and recent developments in photocatalytic water-splitting using TiO2 for hydrogen production

Rising atmospheric levels of carbon dioxide and the depletion of fossil fuel reserves raise serious concerns about the ensuing effects on the global climate and future energy supply. Utilizing the abundant solar energy to convert CO2 into fuels such as methane or methanol could address both problems simultaneously as well as provide a convenient means of energy storage. In this Review, current approaches for the heterogeneous photocatalytic reduction of CO2 on TiO2 and other metal oxide, oxynitride, sulfide, and phosphide semiconductors are presented. Research in this field is focused primarily on the development of novel nanostructured photocatalytic materials and on the investigation of the mechanism of the process, from light absorption through charge separation and transport to CO2 reduction pathways. The measures used to quantify the efficiency of the process are also discussed in detail.

Photocatalytic reduction of CO2 on TiO2 and other semiconductors.

Global warming and climate change concerns have triggered global efforts to reduce the concentration of atmospheric carbon dioxide (CO2). Carbon dioxide capture and storage (CCS) is considered a crucial strategy for meeting CO2 emission reduction targets. In this paper, various aspects of CCS are reviewed and discussed including the state of the art technologies for CO2 capture, separation, transport, storage, leakage, monitoring, and life cycle analysis. The selection of specific CO2 capture technology heavily depends on the type of CO2 generating plant and fuel used. Among those CO2 separation processes, absorption is the most mature and commonly adopted due to its higher efficiency and lower cost. Pipeline is considered to be the most viable solution for large volume of CO2 transport. Among those geological formations for CO2 storage, enhanced oil recovery is mature and has been practiced for many years but its economical viability for anthropogenic sources needs to be demonstrated. There are growing interests in CO2 storage in saline aquifers due to their enormous potential storage capacity and several projects are in the pipeline for demonstration of its viability. There are multiple hurdles to CCS deployment including the absence of a clear business case for CCS investment and the absence of robust economic incentives to support the additional high capital and operating costs of the whole CCS process.

https://www.elsevier.com/__data/assets/pdf_file/0005/96980/Current-status-carbon-capture.pdf

An overview of current status of carbon dioxide capture and storage technologies

UV-Visible ار راد ن .د TiO2 ( تیفرظ راون مان هب نورتکلا یاراد یژرنا زارت لماش VB و ) رگید زارت ی یژرنا اب ( ییاناسر راون مان هب نورتکلا زا یلاخ و رتلااب VB یم ) .دشاب ت ود نیا نیب یژرنا توافت یژرنا فاکش زار ، پگ دناب هدیمان یم .دوش هک ینامز زا نورتکلا لاقتنا VB هب VB یم ماجنا دریگ ، TiO2 اب ودح یژرنا بذج د ev 2 / 3 ، نورتکلا تفج کی دیلوت یم هرفح .دیامن و نورتکلا هرفح ی نا اب هدش دیلوت یم کرتشم حطس هب لاقت ثعاب دناوت شنکاو ماجنا اه یی ددرگ . TiO2 دربراک ،دراد یدایز یاه هلمج زا یم ناوت اوه یگدولآ هیفصت یارب (CO2) و بآ و ... نآ زا هدافتسا درک .

Advanced Nanoarchitectures for Solar Photocatalytic Applications

Carbon dioxide was photocatalytically reduced to produce methanol in an aqueous solution using 254 nm UV irradiation. Titania and Cu-loaded titania were synthesized by an improved sol–gel method using a homogeneous hydrolysis technique. The grain size of TiO 2 and Cu/TiO 2 were uniform and average diameters were approximately 20 nm. Photocatalytic reduction was conducted in a quartz reactor with a UV lamp irradiating at the center. XPS analysis reveals that Cu 2p 3/2 is 933.4 eV indicating primary Cu 2 O species on the TiO 2 supports. EDX and XPS revealed that most copper clusters were on the TiO 2 surface. The optimum amount of copper loading was 2.0 wt.% for the highest dispersion among catalysts. The methanol yield of 2.0 wt.% Cu/TiO 2 was 118 μmol/g following 6 h of UV illumination. The yield was much higher than those of sol–gel TiO 2 and Degussa P25, whose yields were 4.7 and 38.2 μmol/g, respectively. The methanol yield reached a steady-state 250 μmol/g after 20 h of irradiation. Experimental results indicated that the methanol yield was significantly increased by adding NaOH. The caustic solution dissolved more CO 2 than did pure water. In addition, the OH − in aqueous solution also served as a strong hole scavenger. The redistribution of the electric charge and the Schottky barrier of Cu and TiO 2 facilitates electron trapping via supported Cu. The photocatalytic efficiency of Cu/TiO 2 was markedly increased because of the lowering the re-combination probability for hole–electron pairs. The highest quantum and energy efficiencies achieved were 10 and 2.5%, respectively.

/pdf/photoreduction-of-co2-using-sol-gel-derived-titania-and-45kfqsgtmh.pdf

Photoreduction of CO2 using sol–gel derived titania and titania-supported copper catalysts

Nanoparticles of titania and copper-loaded titania were synthesized by a refined sol-gel method using titanium butoxide. Unlike the conventional sol-gel procedure of adding water directly, the esterification of anhydrous butanol and glacial acetic acid provided the hydrolyzing water. In addition, acetic acid also served as a chelating ligand to stabilize the hydrolysis-condensation process and minimize the agglomeration of titania. Following the hydrolysis, Cu/TiO2 was prepared by adding copper chloride to titania sol. The sol was dried, then calcined at 500°C to remove organics and transformed to anatase titania which was verified by XRD. Cu/TiO2 was further hydrogen-reduced at 300°C. The recovery of Ti was exceeded by an average of 95% from titanium butoxide. TEM micrographs show that the Cu/TiO2 particles are near uniform. The average crystallite sizes are 17–20 nm estimated from the peak broadening of XRD spectra. The bandgaps of TiO2 and reduced Cu/TiO2 range from 2.70 to 3.15 eV estimated from the diffusive reflective UV-Vis spectra. XPS analysis shows that Cu 2p3/2 is 933.4 eV indicating primary Cu2O form on the TiO2 supports. The binding energy of Ti does not exhibit chemical shift suggesting negligible interaction of Cu cluster and TiO2 support.

Wan-Chen Chang

Papers

Photoreduction of CO2 using sol–gel derived titania and titania-supported copper catalysts

Synthesis of Titania-supported Copper Nanoparticles via Refined Alkoxide Sol-gel Process