HOME

TheInfoList



OR:

In
chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds made of atoms, molecules and ions ...
, photocatalysis is the acceleration of a photoreaction in the presence of a
catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
. In catalyzed
photolysis Photodissociation, photolysis, photodecomposition, or photofragmentation is a chemical reaction in which molecules of a chemical compound are broken down by photons. It is defined as the interaction of one or more photons with one target molecule. ...
,
light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 tera ...
is absorbed by an
adsorbed Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the ''adsorbate'' on the surface of the ''adsorbent''. This process differs from absorption, in which a ...
substrate. In photogenerated catalysis, the photocatalytic activity depends on the ability of the catalyst to create electron–hole pairs, which generate
free radical A daughter category of ''Ageing'', this category deals only with the biological aspects of ageing. Ageing Ailments of unknown cause Biogerontology Biological processes Causes of death Cellular processes Gerontology Life extension Metabo ...
s (e.g.
hydroxyl radical The hydroxyl radical is the diatomic molecule . The hydroxyl radical is very stable as a dilute gas, but it decays very rapidly in the condensed phase. It is pervasive in some situations. Most notably the hydroxyl radicals are produced from the ...
s: •OH) able to undergo secondary reactions. Its practical application was made possible by the discovery of
water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
electrolysis In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from n ...
by means of
titanium dioxide Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound with the chemical formula . When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or CI 77891. It is a white solid that is insolubl ...
().


History


Early mentions (1911–1938)

The earliest mention came in 1911, when
German German(s) may refer to: * Germany (of or related to) ** Germania (historical use) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizens of Germany, see also German nationality law **Ge ...
chemist Dr. Alexander Eibner integrated the concept in his research of the illumination of
zinc oxide Zinc oxide is an inorganic compound with the formula . It is a white powder that is insoluble in water. ZnO is used as an additive in numerous materials and products including cosmetics, food supplements, rubbers, plastics, ceramics, glass, cemen ...
(ZnO) on the bleaching of the dark blue pigment, Prussian blue. Around this time, Bruner and Kozak published an article discussing the deterioration of oxalic acid in the presence of
uranyl The uranyl ion is an oxycation of uranium in the oxidation state +6, with the chemical formula . It has a linear structure with short U–O bonds, indicative of the presence of multiple bonds between uranium and oxygen. Four or more ligands may ...
salts under illumination, while in 1913, Landau published an article explaining the phenomenon of photocatalysis. Their contributions led to the development of actinometric measurements, measurements that provide the basis of determining photon flux in photochemical reactions. After a hiatus, in 1921, Baly et al. used ferric hydroxides and colloidal uranium salts as catalysts for the creation of
formaldehyde Formaldehyde ( , ) (systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section F ...
under visible light. In 1938 Doodeve and Kitchener discovered that , a highly-stable and non-toxic oxide, in the presence of oxygen could act as a photosensitizer for bleaching dyes, as
ultraviolet light Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30  PHz) to 400 nm (750  THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...
absorbed by led to the production of active oxygen species on its surface, resulting in the blotching of organic chemicals via
photooxidation In polymer chemistry photo-oxidation (sometimes: oxidative photodegradation) is the degradation of a polymer surface due to the combined action of light and oxygen. It is the most significant factor in the weathering of plastics. Photo-oxidatio ...
. This was the first observation of the fundamental characteristics of heterogeneous photocatalysis.


1964–1981

Research in photocatalysis again paused until1964, when V.N. Filimonov investigated
isopropanol Isopropyl alcohol (IUPAC name propan-2-ol and also called isopropanol or 2-propanol) is a colorless, flammable organic compound with a pungent alcoholic odor. As an isopropyl group linked to a hydroxyl group (chemical formula ) it is the simple ...
photooxidation from ZnO and ; while in 1965 Kato and Mashio, Doerffler and Hauffe, and Ikekawa et al. (1965) explored oxidation/photooxidation of and
organic solvents A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for p ...
from ZnO radiance. In 1970, Formenti et al. and Tanaka and Blyholde observed the oxidation of various
alkene In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond. Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...
s and the photocatalytic decay of N2O, respectively. A breakthrough occurred in 1972, when
Akira Fujishima is a Japanese chemist and president of Tokyo University of Science. He is known for significant contributions to the discovery and research of photocatalytic and superhydrophilic properties of titanium dioxide (TiO2), which is also known as t ...
and
Kenichi Honda Kenichi Honda (本多健一, August 23, 1925 – February 26, 2011) was a Japanese chemist. He made a significant contribution to the discovery and characterization of photocatalytic properties of titanium dioxide (TiO2), for which he shared the ...
discovered that electrochemical
photolysis Photodissociation, photolysis, photodecomposition, or photofragmentation is a chemical reaction in which molecules of a chemical compound are broken down by photons. It is defined as the interaction of one or more photons with one target molecule. ...
of water occurred when a electrode irradiated with ultraviolet light was electrically connected to a
platinum Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver". Platinu ...
electrode. As the ultraviolet light was absorbed by the electrode, electrons flowed from the anode to the platinum cathode where
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...
gas was produced. This was one of the first instances of hydrogen production from a clean and cost-effective source, as the majority of hydrogen production comes from natural gas reforming and
gasification Gasification is a process that converts biomass- or fossil fuel-based carbonaceous materials into gases, including as the largest fractions: nitrogen (N2), carbon monoxide (CO), hydrogen (H2), and carbon dioxide (). This is achieved by reacting ...
. Fujishima's and Honda's findings led to other advances. In 1977, Nozik discovered that the incorporation of a noble metal in the electrochemical photolysis process, such as platinum and
gold Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile met ...
, among others, could increase photoactivity, and that an external potential was not required. Wagner and Somorjai (1980) and Sakata and Kawai (1981) delineated hydrogen production on the surface of strontium titanate (SrTiO3) via photogeneration, and the generation of hydrogen and
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Eart ...
from the illumination of and PtO2 in
ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an Alcohol (chemistry), alcohol with the chemical formula . Its formula can be also written as or (an ethyl ...
, respectively. Photocatalysis has not been developed for commercial purposes. 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".


Types of photocatalysis


Homogeneous photocatalysis

In homogeneous photocatalysis, the reactants and the photocatalysts exist in the same phase. The most commonly used homogeneous photocatalysts include ozone and photo- Fenton systems (Fe+ and Fe+/H2O2). The reactive species is the •OH radical, which is used for various purposes. The mechanism of hydroxyl radical production by ozone can follow two paths: :O3 + hν → O2 + O(1D) :O(1D) + H2O → •OH + •OH :O(1D) + H2O → H2O2 :H2O2 + hν → •OH + •OH Similarly, the Fenton system produces hydroxyl radicals by the following mechanism: :Fe2+ + H2O2→ HO• + Fe3+ + OH :Fe3+ + H2O2→ Fe2+ + HO•2 + H+ :Fe2+ + HO• → Fe3+ + OH In photo-Fenton type processes, additional sources of OH radicals should be considered, such as photolysis of H2O2 and reduction of Fe3+ ions under UV light: :H2O2 + hν → HO• + HO• :Fe3+ + H2O + hν → Fe2+ + HO• + H+ The efficiency of Fenton type processes is influenced by several operating parameters like the concentration of hydrogen peroxide, pH and intensity of UV. The main advantage of this process is the ability of using sunlight with light sensitivity up to 450 nm, thus avoiding the high costs of UV lamps and electrical energy. These reactions have been proven more efficient than other examples of photocatalysis but the disadvantages of the process are the low pH values, which are required since iron precipitates at higher pH values and the fact that iron has to be removed after treatment. Homogeneous photocatalysis can also be conducted by Cu(II)/Cu(I) complexes.The photoredox behavior of Cu(II) complexes, similar to Fe(III) complexes, is derived mostly from the reactive decay of their LMCT states. Excitation to LMCT states can be achieved by direct sunlight when the ionization energy of the
ligand In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electr ...
s coordinated to Cu(II) is not very high. In consequence of the reactive decay of the LMCT excited state by
inner-sphere electron transfer Inner sphere electron transfer (IS ET) or bonded electron transfer is a redox chemical reaction that proceeds via a covalent linkage—a strong electronic interaction—between the oxidant and the reductant reactants. In inner sphere electron trans ...
, the Cu(II) central atom is reduced to Cu(I), whereas the ligand is oxidized to its radical and leaves the coordination sphere: u^Lx2 ->[][] [Cu^Lx-1]^+ +L^ The photoredox behaviour is demonstrated by the simple Cu(II) complexes with halogens. After excitation of [CuClx] 2−x the metal centre is reduced and Cl• and Cl2 radicals are formed: uClx->[][] Cl. + [CuCl]^ Cl. + Cl^- -> Cl2.^ The Cl2 radicals are strong oxidation and Chlorination reaction, chlorination agents. For instance they are able to oxidize
phenol Phenol (also called carbolic acid) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile. The molecule consists of a phenyl group () bonded to a hydroxy group (). Mildly acidic, it req ...
and its derivatives to para- benzochinone and CO2.


Heterogeneous photocatalysis

In heterogeneous catalysis the catalyst is in a different phase from the reactants. Heterogeneous photocatalysis is a discipline which includes a large variety of reactions: mild or total oxidations, dehydrogenation, hydrogen transfer, 18O216O2 and deuterium-alkane isotopic exchange, metal deposition, water detoxification, and gaseous pollutant removal. Most heterogeneous photocatalysts are transition metal oxides and semiconductors. Unlike metals, which have a continuum of electronic states, semiconductors possess a void energy region where no energy levels are available to promote recombination of an electron and hole produced by photoactivation in the solid. The void region of energy, which extends from the top of the filled valence band to the bottom of the vacant conduction band, is called the band gap. When a photon with energy equal to or greater than the material's band gap is absorbed by the semiconductor, an electron is excited from the valence band to the conduction band, generating a hole in the valence band. Such a photogenerated electron-hole pair is termed an
exciton An exciton is a bound state of an electron and an electron hole which are attracted to each other by the electrostatic Coulomb force. It is an electrically neutral quasiparticle that exists in insulators, semiconductors and some liquids. The ...
. The excited electron and hole can recombine and release the energy gained from the excitation of the electron as heat. Such exciton recombination is undesirable and higher levels cost efficieny. 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 Anatase is a metastable mineral form of titanium dioxide (TiO2) with a tetragonal crystal structure. Although colorless or white when pure, anatase in nature is usually a black solid due to impurities. Three other polymorphs (or mineral form ...
-
rutile Rutile is an oxide mineral composed of titanium dioxide (TiO2), the most common natural form of TiO2. Rarer Polymorphism (materials science), polymorphs of TiO2 are known, including anatase, akaogiite, and brookite. Rutile has one of the highest ...
interfaces), noble-metal
nanoparticle A nanoparticle or ultrafine particle is usually defined as a particle of matter that is between 1 and 100 nanometres (nm) in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 1 ...
s,
silicon nanowire Silicon nanowires, also referred to as SiNWs, are a type of semiconductor nanowire most often formed from a silicon precursor by etching of a solid or through catalyzed growth from a vapor or liquid phase. Such nanowires have promising applications ...
s and substitutional cation doping. The ultimate goal of photocatalyst design is to facilitate reactions of the excited electrons with oxidants to produce reduced products, and/or reactions of the generated holes with reductants to produce oxidized products. Due to the generation of positive holes and excited electrons, 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. The reaction starts by photo-induced exciton generation in the metal oxide (MO) surface: :MO + hν → MO (h+ + e) Oxidative reactions due to photocatalytic effect: :h+ + H2O → H+ + •OH :2 h+ + 2 H2O → 2 H+ + H2O2 :H2O2→ 2 •OH Reductive reactions due to photocatalytic effect: :e + O2 → •O2 :•O2 + H2O + H+ → H2O2 + O2 :H2O2 → 2 •OH Ultimately, hydroxyl radicals are generated in both reactions. These radicals are oxidative in nature and nonselective with a redox potential of ''E''0 = +3.06 V. is a common choice for heterogeneous catalysis. Inertness to chemical environment and long-term photostability has made an important material in many practical applications. is a wide band-gap semiconductor. It is commonly investigated in the
rutile Rutile is an oxide mineral composed of titanium dioxide (TiO2), the most common natural form of TiO2. Rarer Polymorphism (materials science), polymorphs of TiO2 are known, including anatase, akaogiite, and brookite. Rutile has one of the highest ...
(bandgap 3.0 eV) and
anatase Anatase is a metastable mineral form of titanium dioxide (TiO2) with a tetragonal crystal structure. Although colorless or white when pure, anatase in nature is usually a black solid due to impurities. Three other polymorphs (or mineral form ...
(bandgap 3.2 eV) phases. Photocatalytic reactions are initiated by the absorption of illumination with energy equal to or greater than the band gap of the semiconductor. This produces electron-hole (e /h+) pairs: Text was copied from this source, which is available under
Creative Commons Attribution 3.0 (CC BY 3.0)
license.
TiO2 ->[][] e-(TiO2) + h+(TiO2) where the electron is in the Valence and conduction bands, conduction band and the hole is in the Valence and conduction bands, valence band. The irradiated particle can behave as an electron donor or acceptor for molecules in contact with the semiconductor. It can participate in
redox Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate (chemistry), substrate change. Oxidation is the loss of Electron, electrons or an increase in the oxidation state, while reduction ...
reactions with adsorbed species, as the valence band hole is strongly oxidizing while the conduction band electron is strongly reducing.


Plasmonic antenna-reactor photocatalysis

A plasmonic antenna-reactor photocatalyst is a
photocatalyst In chemistry, photocatalysis is the acceleration of a photoreaction in the presence of a catalyst. In catalyzed photolysis, light is absorbed by an adsorbed substrate. In photogenerated catalysis, the photocatalytic activity depends on the abil ...
that combines a
catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
with attached antenna that increases the catalyst's ability to absorb light, thereby increasing its efficiency. A catalyst combined with an Au light absorber accelerated hydrogen sulfide-to-hydrogen reactions. The process is an alternative to the conventional
Claus process The Claus process is the most significant gas desulfurizing process, recovering elemental sulfur from gaseous hydrogen sulfide. First patented in 1883 by the chemist Carl Friedrich Claus, the Claus process has become the industry standard. Th ...
that operates at . A Fe catalyst combined with a Cu light absorber can produce hydrogen from
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...
() at ambient temperature using visible light. Conventional Cu-Ru production operates at .


Applications

Photoactive catalysts have been introduced over the last decade, such as and ZnO nano rodes. Most suffer from the fact that they can only perform under UV irradiation due to their band structure. Other photocatalysts, including a graphene-ZnO nanocompound counter this problem.


Bioethanol

Photocatalytic
bioethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an Alcohol (chemistry), alcohol with the chemical formula . Its formula can be also written as or (an ethyl ...
production, research by Professor
Linda Lawton Linda Lawton, Ph.D., FRSE is a Scottish researcher in microcystins and toxins produced by cyanobacteria and has researched into the impact of the so-called 'blue-green algae" from drinking water supply. Her detection method is now used worldwi ...
,
Robert Gordon University Robert Gordon University, commonly called RGU, is a public university in the city of Aberdeen, Scotland. It became a university in 1992, and originated from an educational institution founded in the 18th century by Robert Gordon (philanthropist), ...
and her collaborators under ''CyanoSol'' was funded by
BBSRC Biotechnology and Biological Sciences Research Council (BBSRC), part of UK Research and Innovation, is a non-departmental public body (NDPB), and is the largest UK public funder of non-medical bioscience. It predominantly funds scientific rese ...
.


Paper

Micro-sized ZnO tetrapodal particles added to pilot
paper production The pulp and paper industry comprises companies that use wood as raw material and produce pulp, paper, paperboard and other cellulose-based products. Manufacturing process The pulp is fed to a paper machine where it is formed as a paper web a ...
. The most common are one-dimensional nanostructures, such as
nanorod In nanotechnology, nanorods are one morphology of nanoscale objects. Each of their dimensions range from 1–100 nm. They may be synthesized from metals or semiconducting materials. Standard aspect ratios (length divided by width) are 3-5. Na ...
s,
nanotube A nanotube is a nanometer-scale hollow tube-like structure. Kinds of nanotubes * BCN nanotube, composed of comparable amounts of boron, carbon, and nitrogen atoms * Boron nitride nanotube, a polymorph of boron nitride * Carbon nanotube, includes g ...
s, nanofibers, nanowires, but also nanoplates, nanosheets, nanospheres, tetrapods. ZnO is strongly oxidative, chemically stabile, with enhanced photocatalytic activity, and has a large free-exciton
binding energy In physics and chemistry, binding energy is the smallest amount of energy required to remove a particle from a system of particles or to disassemble a system of particles into individual parts. In the former meaning the term is predominantly use ...
. It is non-toxic, abundant,
biocompatible Biocompatibility is related to the behavior of biomaterials in various contexts. The term refers to the ability of a material to perform with an appropriate host response in a specific situation. The ambiguity of the term reflects the ongoing de ...
, biodegradable, environmentally friendly, low cost, and compatible with simple chemical synthesis. ZnO faces limits to its widespread use in photocatalysis under solar radiation. Several approaches have been suggested to overcome this limitation, including doping for reducing the band gap and improving charge carrier separation.


Water splitting

Photocatalytic
water splitting Water splitting is the chemical reaction in which water is broken down into oxygen and hydrogen: :2 H2O → 2 H2 + O2 Efficient and economical water splitting would be a technological breakthrough that could underpin a hydrogen economy, base ...
separates water into hydrogen and oxygen. The most prevalently investigated material, , has limited production efficiency, was mixed with nickel oxide (NiO). NiO allows a significant explоitation of the visible spectrum. One efficient photocatalyst in the UV range is based on sodium
tantalite The mineral group tantalite Fe,_manganese.html"_;"title="iron.html"_;"title="iron">Fe,_manganese">Mn)Tantalum">Ta2oxygen.html" ;"title="manganese">Mn)Tantalum.html" ;"title="iron">Fe,_manganese.html" ;"title="iron.html" ;"title="iron">Fe, manga ...
(NaTaO3) doped with lanthanum and loaded with a
nickel oxide Nickel oxide may refer to: * Nickel(II) oxide, NiO, green, well-characterised oxide * Nickel(III) oxide Nickel (III) oxide is the inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydr ...
cocatalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
. The surface is grooved with ''nanosteps'' from doping with
lanthanum Lanthanum is a chemical element with the symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes slowly when exposed to air. It is the eponym of the lanthanide series, a group of 15 similar elements between lantha ...
(3–15 nm range, see
nanotechnology Nanotechnology, also shortened to nanotech, is the use of matter on an atomic, molecular, and supramolecular scale for industrial purposes. The earliest, widespread description of nanotechnology referred to the particular technological goal o ...
). The NiO particles are present on the edges, with the oxygen evolving from the grooves.


Self-cleaning glass

Titanium dioxide Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound with the chemical formula . When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or CI 77891. It is a white solid that is insolubl ...
takes part in
self-cleaning glass Self-cleaning glass is a specific type of glass with a surface that keeps itself free of dirt and grime. The field of self-cleaning coatings on glass is divided into two categories: hydrophobic and hydrophilic. These two types of coating both clea ...
.
Free radical A daughter category of ''Ageing'', this category deals only with the biological aspects of ageing. Ageing Ailments of unknown cause Biogerontology Biological processes Causes of death Cellular processes Gerontology Life extension Metabo ...
s generated from oxidize
organic matter Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have c ...
. The rough wedge-like surface can be modified with a hydrophobic monolayer of
octadecylphosphonic acid Octadecylphosphonic acid is a chemical compound most commonly used in thermal paper A thermal column (or thermal) is a rising mass of buoyant air, a convective current in the atmosphere, that transfers heat energy vertically. Thermals are cr ...
(ODP). surfaces that were
plasma Plasma or plasm may refer to: Science * Plasma (physics), one of the four fundamental states of matter * Plasma (mineral), a green translucent silica mineral * Quark–gluon plasma, a state of matter in quantum chromodynamics Biology * Blood pla ...
etched for 10 seconds and subsequent surface modifications with ODP showed a water contact angle greater than 150◦. The surface was converted into a superhydrophilic surface (water contact angle = 0◦) upon UV illumination, due to rapid decomposition of octadecylphosphonic acid coating resulting from photocatalysis. Due to 's wide band gap, light absorption by the semiconductor material and resulting superhydrophilic conversion of undoped requires ultraviolet radiation (wavelength <390 nm) and thereby restricts self-cleaning to outdoor applications.


Disinfection and cleaning

* Water disinfection/decontamination, a form of solar water disinfection (
SODIS Solar water disinfection, in short SODIS, is a type of portable water purification that uses solar energy to make biologically-contaminated (e.g. bacteria, viruses, protozoa and worms) water safe to drink. Water contaminated with non-biological age ...
). Adsorbents attract organics such as
tetrachloroethylene Tetrachloroethylene, also known under the systematic name tetrachloroethene, or perchloroethylene, and many other names (and abbreviations such as "perc" or "PERC", and "PCE"), is a chlorocarbon with the formula Cl2C=CCl2 . It is a colorless li ...
. Adsorbents are placed in packed beds for 18 hours. Spent adsorbents are placed in regeneration fluid, essentially removing organics still attached by passing hot water opposite to the flow of water during adsorption. The regeneration fluid passes through fixed beds of silica gel photocatalysts to remove and decompose remaining organics. * self- sterilizing coatings (for application to food contact surfaces and in other environments where microbial pathogens spread by indirect contact). *Magnetic nanoparticle oxidation of organic
contaminant Contamination is the presence of a constituent, impurity, or some other undesirable element that spoils, corrupts, infects, makes unfit, or makes inferior a material, physical body, natural environment, workplace, etc. Types of contamination Wi ...
s agitated using a
magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
. *Sterilization of surgical instruments and removal of fingerprints from electrical and optical components.


Hydrocarbon production from

conversion of into gaseous hydrocarbons. The proposed reaction mechanisms involve the creation of a highly reactive carbon radical from carbon monoxide and carbon dioxide which then reacts with photogenerated protons to ultimately form
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Eart ...
. Efficiencies of -based photocatalysts are low, although nanostructures such as
carbon nanotube A scanning tunneling microscopy image of a single-walled carbon nanotube Rotating single-walled zigzag carbon nanotube A carbon nanotube (CNT) is a tube made of carbon with diameters typically measured in nanometers. ''Single-wall carbon na ...
s and
metal A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...
lic nanoparticles help.


Paints

ePaint is a less-toxic alternative to conventional antifouling marine paints that generates hydrogen peroxide. Photocatalysis of organic reactions by polypyridyl complexes, porphyrins, or other dyes can produce materials inaccessible by classical approaches. Most photocatalytic dye degradation studies have employed . The
anatase Anatase is a metastable mineral form of titanium dioxide (TiO2) with a tetragonal crystal structure. Although colorless or white when pure, anatase in nature is usually a black solid due to impurities. Three other polymorphs (or mineral form ...
form of has higher photon absorption characteristics.


Filtration membranes

Antifouling coatings for filtration
membrane A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. B ...
s, can act as a separation layer for
contaminant Contamination is the presence of a constituent, impurity, or some other undesirable element that spoils, corrupts, infects, makes unfit, or makes inferior a material, physical body, natural environment, workplace, etc. Types of contamination Wi ...
degradation. or
Cr(VI) Hexavalent chromium (chromium(VI), Cr(VI), chromium 6) is chromium in any chemical compound that contains the element in the +6 oxidation state (thus hexavalent). Virtually all chromium ore is processed via hexavalent chromium, specifically the ...
removal.


Crude oil

nanoparticle decomposition of crude oil can turn hydrocarbons into H2O and CO2. The particles can be placed on floating substrates, which are easier to recover and catalyze the reaction. This is relevant since oil slicks float on the ocean suface and photons from the sun reach the surface. Covering floating substrates with epoxy adhesives prevents waterlogging and particles can stick to them. Decomposition of
polyaromatic hydrocarbons A polycyclic aromatic hydrocarbon (PAH) is a class of organic compounds that is composed of multiple aromatic rings. The simplest representative is naphthalene, having two aromatic rings and the three-ring compounds anthracene and phenanthrene. P ...
(PAHs).
Triethylamine Triethylamine is the chemical compound with the formula N(CH2CH3)3, commonly abbreviated Et3N. It is also abbreviated TEA, yet this abbreviation must be used carefully to avoid confusion with triethanolamine or tetraethylammonium, for which TEA ...
(TEA) solvates and extracts PAHs in crude oil. TEA attracts the PAHs to itself. slurries can degrade the PAHs. Recoveries of 93–99% of these contaminants have been demonstrated at ambient pressure and temperature, and at lower cost.


Construction

Light2CAT was a project funded by the
European Commission The European Commission (EC) is the executive of the European Union (EU). It operates as a cabinet government, with 27 members of the Commission (informally known as "Commissioners") headed by a President. It includes an administrative body o ...
from 2012 to 2015. It aimed to develop a modified that can absorb visible light and include this modified into construction concrete. The degrades harmful pollutants such as NOx into NO3. The modified was utilized in Copenhagen and Holbæk, Denmark, and Valencia, Spain. This “self-cleaning” concrete led to a 5-20% reduction in NOx over the course of a year.


Quantification

ISO 22197-1:2007 specifies a test method for the measurement of removal for materials that contain a photocatalyst or have superficial photocatalytic films. Specific FTIR systems are used to characterize photocatalytic activity or passivity, especially with respect to
volatile organic compounds Volatile organic compounds (VOCs) are organic compounds that have a high vapour pressure at room temperature Colloquially, "room temperature" is a range of air temperatures that most people prefer for indoor settings. It feels comfortable to a ...
, and representative binder matrices. Mass spectrometry allows measurement of photocatalytic activity by tracking the decomposition of gaseous pollutants such as nitrogen NOx or


See also

*
Light harvesting materials Light harvesting materials harvest solar energy that can then be converted into chemical energy through photochemical processes. Synthetic light harvesting materials are inspired by photosynthetic biological systems such as light harvesting comple ...
* Photoelectrochemical cell *
Photolysis Photodissociation, photolysis, photodecomposition, or photofragmentation is a chemical reaction in which molecules of a chemical compound are broken down by photons. It is defined as the interaction of one or more photons with one target molecule. ...
*
Photocatalytic water splitting Photocatalytic water splitting is an artificial photosynthesis process using photocatalysis for the dissociation of water (H2O) into hydrogen () and oxygen (). Only light energy (photons), water, and a catalyst(s) are needed, since this is what ...
* Photoredox catalysis *
Photoelectrochemical oxidation A "photoelectrochemical cell" is one of two distinct classes of device. The first produces electrical energy similarly to a dye-sensitized photovoltaic cell, which meets the standard definition of a photovoltaic cell. The second is a photoelect ...
*
Photosensitizer Photosensitizers produce a physicochemical change in a neighboring molecule by either donating an electron to the substrate or by abstracting a hydrogen atom from the substrate. At the end of this process, the photosensitizer eventually returns to ...


References

{{Authority control Photochemistry Catalysis