Titanium Dioxide Nanomaterials: Synthesis, Properties, Modifications, and Applications

Energy harvested directly from sunlight offers a desirable approach toward fulfilling, with minimal environmental impact, the need for clean energy. Solar energy is a decentralized and inexhaustible natural resource, with the magnitude of the available solar power striking the earth’s surface at any one instant equal to 130 million 500 MW power plants.1 However, several important goals need to be met to fully utilize solar energy for the global energy demand. First, the means for solar energy conversion, storage, and distribution should be environmentally benign, i.e. protecting ecosystems instead of steadily weakening them. The next important goal is to provide a stable, constant energy flux. Due to the daily and seasonal variability in renewable energy sources such as sunlight, energy harvested from the sun needs to be efficiently converted into chemical fuel that can be stored, transported, and used upon demand. The biggest challenge is whether or not these goals can be met in a costeffective way on the terawatt scale.2

http://pubs.acs.org/doi/pdf/10.1021/cr1002326

Solar Water Splitting Cells

2.3. Evaluation of Photocatalytic Water Splitting 6507 2.3.1. Photocatalytic Activity 6507 2.3.2. Photocatalytic Stability 6507 3. UV-Active Photocatalysts for Water Splitting 6507 3.1. d0 Metal Oxide Photocatalyts 6507 3.1.1. Ti-, Zr-Based Oxides 6507 3.1.2. Nb-, Ta-Based Oxides 6514 3.1.3. W-, Mo-Based Oxides 6517 3.1.4. Other d0 Metal Oxides 6518 3.2. d10 Metal Oxide Photocatalyts 6518 3.3. f0 Metal Oxide Photocatalysts 6518 3.4. Nonoxide Photocatalysts 6518 4. Approaches to Modifying the Electronic Band Structure for Visible-Light Harvesting 6519

Semiconductor-based Photocatalytic Hydrogen Generation

TiO2 photocatalysis and related surface phenomena

When used as a photocatalyst, titanium dioxide (TiO(2)) absorbs only ultraviolet light, and several approaches, including the use of dopants such as nitrogen, have been taken to narrow the band gap of TiO(2). We demonstrated a conceptually different approach to enhancing solar absorption by introducing disorder in the surface layers of nanophase TiO(2) through hydrogenation. We showed that disorder-engineered TiO(2) nanocrystals exhibit substantial solar-driven photocatalytic activities, including the photo-oxidation of organic molecules in water and the production of hydrogen with the use of a sacrificial reagent.

https://science.sciencemag.org/content/sci/early/2011/01/19/science.1200448.full.pdf

Increasing Solar Absorption for Photocatalysis with Black Hydrogenated Titanium Dioxide Nanocrystals

Although n-type titanium dioxide (TiO2) is a promising substrate for photogeneration of hydrogen from water, most attempts at doping this material so that it absorbs light in the visible region of the solar spectrum have met with limited success. We synthesized a chemically modified n-type TiO2 by controlled combustion of Ti metal in a natural gas flame. This material, in which carbon substitutes for some of the lattice oxygen atoms, absorbs light at wavelengths below 535 nanometers and has a lower band-gap energy than rutile (2.32 versus 3.00 electron volts). At an applied potential of 0.3 volt, chemically modified n-type TiO2 performs water splitting with a total conversion efficiency of 11% and a maximum photoconversion efficiency of 8.35% when illuminated at 40 milliwatts per square centimeter. The latter value compares favorably with a maximum photoconversion efficiency of 1% for n-type TiO2 biased at 0.6 volt.

http://science.sciencemag.org/content/sci/297/5590/2243.full.pdf

Efficient photochemical water splitting by a chemically modified n-TiO2.

Some Experimental Techniques. The Interphasial Structure. Phenomenological Electrode Kinetics. Quantum-Oriented Electrochemistry. Photoelectrochemistry. Organoelectrochemistry. Bioelectrochemistry. Some Electrical Aspects of the Stability of Materials. Electrochemical Conversion and Storage of Energy. The Electrochemistry of Cleaner Environments. Index.

Surface Electrochemistry: A Molecular Level Approach

Semiconducting nanocrystalline thin films of n-Fe2O3 were synthesized by a spray−pyrolytic method. These films were used for the photoelectrochemical splitting of water to hydrogen and oxygen gases. The rates of photoelectrochemical splitting of water at these thin-film electrodes were found to depend on the spray time, substrate temperature, solvent composition in the spray solution, and the concentration of the spray solution. The maximum photocurrent density of 3.7 mA cm-2 at 0.7 V/saturated calomel electrode (SCE) was obtained at the n-Fe2O3 film synthesized using the optimum condition of substrate temperature of 350 °C, the spray time of 60 s, and the spray solution of 0.11 M FeCl3 in 100% ethanol. The band gap energy of this film was found 2.05 eV. The flatband potential of −0.74 V/SCE and the apparent donor density of 2.2 × 1020 cm-3 were found from the Mott−Schottky plots at the AC frequency of 1000 Hz. The n-Fe2O3 films synthesized using the optimum conditions gave rise to a total conversion effi...

Photoelectrochemical splitting of water at nanocrystalline n-fe2o3 thin-film electrodes

A non-enzymatic implantable blood glucose detector. The detector makes use of a non-reactive tin oxide semiconductor measurement electrode which is suitably energized by an electrical power source. Variations in current density at the measurement electrode are related to variations in glucose content of blood. The device also uses variable voltage to allow the electrode to be self-cleaning.

Implantable non-enzymatic electrochemical glucose sensor

The present research focused on wet process synthesis of visible light active carbon-modified (CM)- n -TiO 2 nanoparticles and their photocatalytic activity. The CM- n -TiO 2 was synthesized by hydrolysis of TiCl 4 in the presence of tetrabutylammonium hydroxide and also in the presence of glucose and sodium hydroxide. UV–vis spectra, X-ray diffraction (XRD), and FT-IR were used to characterize these photocatalysts. It was found that the CM- n -TiO 2 nanoparticles synthesized by hydrolysis with tetrabutylammonium hydroxide or with sodium hydroxide and glucose when subjected to extended aging and subsequent calcinations absorb well into the visible to near infrared region up to 800 nm and exhibit enhanced visible light photocatalytic activity on degradation of 4-chlorophenol. CM- n -TiO 2 synthesized using glucose as the carbon source generated 13-fold increase in the initial rate of photodegradation of 4-chlorophenol compared to those by regular n -TiO 2 , whereas, it increased only eight-fold when tetrabutylammonium hydroxide was used as the carbon source.

Shahed U. M. Khan

Papers

Efficient photochemical water splitting by a chemically modified n-TiO2.

Surface Electrochemistry: A Molecular Level Approach

Photoelectrochemical splitting of water at nanocrystalline n-fe2o3 thin-film electrodes

Implantable non-enzymatic electrochemical glucose sensor

Photocatalytic effect of carbon-modified n-TiO2 nanoparticles under visible light illumination