Photocatalysis
[4][6] After a hiatus, in 1921, Baly et al. used ferric hydroxides and colloidal uranium salts as catalysts for the creation of formaldehyde under visible light.
As the ultraviolet light was absorbed by the TiO2 electrode, electrons flowed from the anode to the platinum cathode where hydrogen gas was produced.
In 1977, Nozik discovered that the incorporation of a noble metal in the electrochemical photolysis process, such as platinum and gold, among others, could increase photoactivity, and that an external potential was not required.
However, in 2023 multiple patents were granted to a U.S. company, (Pure-Light Technologies, Inc.) that has developed various formulas and processes that allow for widespread commercialization for VOC reduction and germicidal action.
[19] Chu et al. (2017) assessed the future of electrochemical photolysis of water, discussing its major challenge of developing a cost-effective, energy-efficient photoelectrochemical (PEC) tandem cell, which would, “mimic natural photosynthesis".
Heterogeneous photocatalysis is a discipline which includes a large variety of reactions: mild or total oxidations, dehydrogenation, hydrogen transfer, 18O2–16O2 and deuterium-alkane isotopic exchange, metal deposition, water detoxification, and gaseous pollutant removal.
[22] Efforts to develop functional photocatalysts often emphasize extending exciton lifetime, improving electron-hole separation using diverse approaches that may rely on structural features such as phase hetero-junctions (e.g. anatase-rutile interfaces), noble-metal nanoparticles, silicon nanowires and substitutional cation doping.
Due to the generation of positive holes (h+) and excited electrons (e−), oxidation-reduction reactions take place at the surface of semiconductors irradiated with light.
In one mechanism of the oxidative reaction, holes react with the moisture present on the surface and produce a hydroxyl radical.
[22] The absorption of photons with energy equal to or greater than the band gap of the semiconductor initiates photocatalytic reactions.
The process by which the atmosphere self-cleans and removes large organic compounds is a gas phase homogenous photocatalysis reaction.
ZnO is strongly oxidative, chemically stable, with enhanced photocatalytic activity, and has a large free-exciton binding energy.
It is non-toxic, abundant, biocompatible, biodegradable, environmentally friendly, low cost, and compatible with simple chemical synthesis.
Several approaches have been suggested to overcome this limitation, including doping for reducing the band gap and improving charge carrier separation.
[37] One efficient photocatalyst in the UV range is based on sodium tantalite (NaTaO3) doped with lanthanum and loaded with a nickel oxide cocatalyst.
Due to TiO2 's wide band gap, light absorption by the semiconductor material and resulting superhydrophilic conversion of undoped TiO2 requires ultraviolet radiation (wavelength <390 nm) and thereby restricts self-cleaning to outdoor applications.
Photocatalysis of organic reactions by polypyridyl complexes,[52] porphyrins,[53] or other dyes[54] can produce materials inaccessible by classical approaches.
[55] Photocatalyst radical generation species allow for the degradation of organic pollutants into non-toxic compounds at a high efficiency.
Under visible light the reduction of Cr(VI) by a Ce-ZrO2 sol-gel on a silicon carbide was 97% effective at reducing the heavy metal to trivalent chromium.
[62] Specific FTIR systems are used to characterize photocatalytic activity or passivity, especially with respect to volatile organic compounds, and representative binder matrices.
2 ) disc, exciting electrons within the material. These then react with the water molecules, splitting it into its constituents of hydrogen and oxygen. In this experiment, chemicals dissolved in the water prevent the formation of oxygen, which would otherwise recombine with the hydrogen.
