Voc4Cat - A SKOS vocabulary for Catalysis.

A process which catalyzes a chemical reaction through the absorption of sufficient light energy by a photocatalyst.

A material that absorbs photons (light) of appropriate energy and initiates or accelerates a photochemical reaction, while it regenerates itself after each reaction cycle.

A material with electrical conductivity between that of a conductor and an insulator.

Broad families of semiconduction materials (e.g., metal oxides) that can be used as photocatalysts in various applications.

A chemical compound formed by the reaction of a metal with oxygen.

Characteristic properties of a semiconductor used in the field of photocatalysis. These properties determine its performance in the studied photocatalytic application.

The energy level in a semiconductor where the probability of finding an electron is 0.5.

The degree of a three-dimensional structural order of atoms which constitute the crystal lattice of a material.

Pore size distribution refers to the range of pore sizes in a material.

The energy difference between a semiconductor’s valence band top and conduction band bottom, which is required to excite an electron from the former to the latter.

The band of energy levels in a solid fully occupied by electrons at 0 K (273.15 °C).

The energy band of electronic levels of partially or fully filled mobile electrons in a metal or a semiconductor.

Α measure of the total surface area of a material per unit mass or volume.

Techniques used to modify the properties of a photocatalyst, with the aim to increase its efficiency in a photocatalytic application.

The introduction of foreign atoms into a semiconductor leading to the formation of new energy levels and charge concentrations.

The form in which the photocatalyst is introduced to the reaction chamber. This can include e.g., powders, pellets or thin films deposited on a substrate.

A photocatalyst introduced to the reaction chamber in the form of a powder. Usually the powdered photocatalyst is spread inside a quartz / glass plate.

Mass of a powdered photocatalyst used for an experiment.

A photocatalyst introduced to the reaction chamber in the form of a thin film. To form a thin film, a (powdered) photocatalyst is deposited on a substrate (e.g., glass or metal) using an appropriate deposition technique.

A technique used to deposit (immobilize) a (powdered) photocatalyst on a substate. These techniques indlude (but are not limited to): doctor blading, spin coating, spray coating, etc..

A technique used to deposit uniform thin films onto a substrate by spraying a solution of the material onto the surface.

A tape-casting method used to deposit thin films of a photocatalyst onto the surface of a substrate.

A technique used to deposit uniform thin films onto a substrate (e.g., metal or glass) by spinning at high speeds a solution (paste) of the material onto the surface.

The substate onto which a (powdered) photocatalyst is deposited. Such substrates include glass surfaces (e.g., borosilicate glass or conductive glass like ITO and FTO), ceramic substrates (e.g., alumina) or metal substrates (e.g., Ti foils, stainless steel etc.).

The material that the substrate is made of. Common materials include: glass (conductive or not), ceramics and metal.

A flat surface made of a metal (e.g., titanium, stainless steel) serving as a substrate for the deposition of a photocatalyst.

A flat surface made of glass serving as a substrate for the deposition of a photocatalyst.

Transparent conductive metal oxide (fluorine doped tin oxide) that can be used in the fabrication of transparent electrodes for thin films.

Transparent conductive metal oxide (indium tin oxide) that can be used in the fabrication of transparent electrodes for thin films.

A resistant to thermal shock type of glass, composed mainly of silica and boron trioxide.

A type of pure silicon dioxide, highly crystalline glass that allows the transmission of light in the UV wavelength range.

A surface made of a ceramic material (e.g., alumina) serving as a substrate for the deposition of a photocatalyst.

The diamensions of the substrate.

The width of the substrate.

The depth of the substrate.

The thickness of the substrate.

The surface area of the substrate.

A thin film of the photocatalyst deposited on an appropriate for the application substrate.

Mass of catalyst deposited onto the surface of a substrate.

The diamensions of the - deposited on the substrate - thin film.

The width of the film of the deposited photocatalyst.

The thickness of the film of the deposited photocatalyst.

The depth of the film of the deposited photocatalyst.

The area of the substrate covered by the deposited photocatalyst.

The process by which one or more chemical reactions are performed with the aim of converting a reactant or starting material into a product or multiple products.

Thorough search of available literature on the research topic of interest using online research platforms (e.g, Scopus, Google Scholar, Web of Science, Research Gate etc.) and / or libraries. Relevant literature can be found in the form of publications, books, abstracts and conference presentations.

Assembly of literature research to include only the most relevant sources of information for the application / experiment / catalysts of interest.

Addition and organization of relevant literature of interest using a citation management software (e.g., Mendeley, Zotero, EndNote etc.) allowing for easy access and categorization.

Necessary steps needed to follow in order to reach the desired photocatalyst.

Duration of each synthesis step needed to synthesize the desired photocatalyst.

Temperature externally applied (if necessary) in any of the synthesis step. Higher temperature values can be observed if an exothermic reaction takes place during the synthesis.

The pH value in each of the synthesis steps.

Pressure applied (if necessary) in any of the synthesis step. Changes in the pressure may be observed if variations in the temperature of the reaction occur (e.g., exothermic reaction).

Heat treatment to reach the desired final photocatalyst. The parameters of the heat treatment can vary between each calcination step.

A gas flow under which the calcination step takes place (e,g,, Ar or synthetic air).

The flow of gas (usually in ml min-1) used in the calcination steps during synthesis.

Initial temperature of the calcination step.

Final temperature of the calcination step.

Rate of increasing or decreasing the temperature during the calcination step. Usually mentioned in K min-1.

Time (usually in h) for which a desired temperature is held.

Equipment used in each step of the synthesis of the photocatalysts. The equipment can include (but not limited to): crucibles, pH meters, condensers, volumetric cylinders, centrifuges, test tubes, flasks, beakers, mechanical shakers, pipettes, syringes, magenetic stirrers, heating plates, filters, funnels and digital balances.

Chemical substances used in the synthesis process of a desired photocatalyst.

Mass of chemicals used for synthesis.

Volume of chemicals used for synthesis.

Concentration of chemicals used for synthesis.

Techniques used to identify the (physico)chemical, morphological, structural, mechanical, optical and electrical properties of the syntesized catalysts. Characterization is performed after the synthesis of the catalysts to evaluate the success of the synthetic approach, but also after the completion of the evaluation of the materials in a reaction to ensure their stability under the selected experimental parameters.

A non-destructive analytical technique which uses a high-energy X-ray source to expose a material and monitors the emitted characteristic fluorescent X-Rays.

An analytical technique used to measure the energy loss of electrons passing through a sample.

A spectroscopy technique studying the vibrational modes of molecules, by measuring the intensity and frequency of scattered by the sample of monochromatic light.

A high-resolution imaging technique that measures the interaction between a sharp probe and the sample’s surface to create a three-dimensional image of the surface’s morphology.

A thermal analysis technique which compares the heat flow in a sample and a reference material under controlled applied temperature profiles.

A thermal analysis technique used to measure the change of a sample’s mass under the influence of controlled applied temperature profiles.

A spectroscopic technique that uses a static magnetic field and radiofrequency radiation to measure the magnetic resonance of atomic nuclei protons or electrons.

Light emission of lower energy photons from a sample upon its photoexcitation.

An electron microscopy technique that produces high-resolution images under high magnification of a sample's surface by assessing the secondary and back-scattered electrons produced by a focused electron beam.

A technique that analyzes the chemical composition of an X-ray irradiated sample by measuring the energies of the emitted electrons.

A technique which analyses the diffraction pattern produced when X-rays are scattered by a sample bombarded by a focused electron beam.

Transmission electron microscopy is a technique that produces high-resolution images if the internal structure of a sample by using a beam of electrons to bombard the thin sample and measuring the intensity of the scattered transmitted electrons.

A technique used to measure the absorption, transmission or reflectance of light by a sample in the ultraviolet and visible regions of the electromagnetic spectrum.

A spectroscopic technique used to study the vibrational modes of chemical bonds of a sample using infrared radiation.

The study of physical adsorption of gas molecules on a solid surface for the calculation of the specific surface area of materials.

An electrochemical technique used to study the redox properties of a sample by measuring the current produced by an applied voltage sweep.

A method used in cyclic voltammetry to determine the charge carrier concentration and the flat-band potential of an electrochemical system by measuring the capacitance as a function of applied voltage.

The energy state occupied by an electron in a photocatalyst. This state cab affect the electron's ability to participate in a photocatalytic reaction.

Τhe lowest energy state of a system.

Τhe temporary state of a system with higher energy than its ground state caused by an external factor.

A multi-step process iniatiated by the absorption of photons by a photocatalyst. This process involves various sub-processes that include the photogeneration and transfer of electron and hole pairs.

The transfer of an electron initiated by the absorption of a photon of sufficient energy.

The transfer of a hole initiated by the absorption of a photon of sufficient energy.

The generation of electron - hole pairs in a semiconductor as a result of light absorption of sufficient energy to overcome the bandgap energy. Electrons (negative charge) get excited to the conduction band, while holes (positive charge) remain in the valence band.

The process by which photogenerated charges (electrons and holes) in a semiconductor recombine, resulting in the dissipation of energy in the form of e.g., heat or light.

Absorption is the process in which energy (e.g., photons) or an absorbent (e.g., a gas) is taken up by an absorbate.

The adhesion of a gas, liquid or dissolved solid chemical of interest onto a solid surface.

The process under which reactants, intermediates and products are released from the surface of the photocatalyst. Desoprtion can be facilitated by an increase in temperature or a change in the pH.

The process of separating positive and negative charges in a semiconductor, typically as a result of an external force, (e.g., photoexcitation).

The state caused by the transition of electrons from the valence band top to the conduction band bottom by absorption of photons of sufficient energy.

The loss of electrons or an increase in the oxidation state of a species.

The gain of electrons or a decrease in the oxidation state of a species.

The light-driven reduction (conversion) of carbon dioxide (CO2) to hydrocarbons and / or platform chemicals in presence of water. The absorption of light and the adsorption of the reactants is performed by a photocatalyst (usually a metal oxide).

A lab-scale experiment performed to test the efficiency of a studied photocatalyst in a photocatalytic application (e.g., dye degradation, CO2 photoreduction e.t.c.).

A starting substance that undergoes a chemical reaction to produce a desired product.

Concentration of the reactants (e.g., CO2 and H2O) used in the photocatalytic CO2 reduction experiments.

Purity of reactants (e.g., CO2, H2O, He) used in the photocatalytic CO2 reduction experiments. Purity is measure of the impurities contained in the reactants' supply. The highest purity reactants should be used to ensure the collection of reliable results.

The rate of flow of reactants (often in ml per min) in the photoreactor. Flow rates are usually controlled by mass flow controllers (MFCs).

Electron donors or hole scavengers used to reduce the recombination tendency of electrons and holes. Sacrificial reagents are used in photocatalysis to study an oxidation or reduction reaction separately.

A molecule that accepts electrons from photoexcited species in a redox reaction and is subsequently consumed or degraded.

A molecule that donates electrons from photoexcited species in a redox reaction and is subsequently consumed or degraded.

Operation mode under the which the experiment takes place: batch of continuous flow mode.

Under flow conditions, a continuous flow of reactants is supplied to the reaction chamber and the formed products are removed and identified by an appropriate technique.

Operation mode in which the reaction chamber is filled with the (reactant) gas(es) up to a certain pressure, and the photoreaction products acummulate over time.

The total duration of an experiment.

Time for which a gas is purged through the reaction chamber.

The time in between the collection of two data points.

The total duration in which the photocatalyst was under irradiation by the selected light source.

The temperature (range) under which the photocatalytic reaction takes place.

The temperature at the initiaton of the experiment.

The temperature at the end of the experiment.

The pressure (range) under which the photocatalytic reaction takes place.

The pressure at the initiaton of the experiment or before a sampling event.

The pressure at the end of the experiment or after a sampling event.

The pressure drop occurring when collecting a gaseous sample for the reaction chamber. This pressure drop should be taken into consideration when calculating the concentration of formed products.

Pretreatment of the photocatalyst before its intoduction to the reaction chamber.

Measurements performed to ensure that the studied photocatalytic reaction occurs because of the interaction of the photocatalyst with the reactants, and not from the environment or the photoreactor. Such blank experiment include experiments under dark conditions, experiments with light but without a photocatalyst and experiments under light in the presence of the photocatalyst but without the targeted reactants.

Quantitative and qualitative evaluation of the outcome of a photocatalytic reaction (e.g., product formation from the photoreduction of CO2). The evaluation can lead to changes in the synthesis of the photocatalyst and / or selecting different experimental parameters.

In photocatalytic processes where product formation is expected, selectivity describes the ability of a photocatalyst to produce only the desired product with minimal (or none) of byproducts.

A measure of the efficiency of a photocatalytic reaction. It is expressed as the number of consumed charge carriers divided by the number of incident photons.

The concentration (usually in ppm or mol) of the products formed during a reaction.

Details describing the construction, physical dimensions, and operation of the photoreactor used to perform a photocatalytic reaction.

Spectroscopic or chromatographic methods used to qualitatively and quantitatively identify the products of the photoreaction. Such devices are usually attached to the photoreactor, or a sample is being trasfered to an identification method via another medium (e.g., gastight syringes).

An analytical technique that separates and analyzes the components of a gas mixture by passing it though a stationary phase.

Detectors of the gas chromatogragh used to identify the reaction products and intemediates.

A type of gas chromatography detector that detects and quantifies the concentration of organic compounds in a gas sample emerging from a column, by measuring the electrical current generated by ionized gas constituents in a hydrogen flame.

A type of gas chromatography detector that measures the thermal conductivity of a gas sample and identifies its constituent molecules through changes in a filament’s temperature.

Detector incorporating Ionization via a new dielectric barrier discharge He plasma.

The minimum concentration of a product or intermediate that the gas chromatograph can identify.

A process in which gaseous substances of known purity and concentration are introduced to the gas chromatograph and the respective area and retention time of the resulting peaks are identified. This process when concluded, allows for the calculation of concentrations of products and intermediates of the photoreaction.

An analytical technique which determines the mass-to-charge ratio of ions in a sample to give information about the composition of the sample.

Detectors of the mass spectrometer used to identify the reaction products and intemediates.

The minimum concentration of a product or intermediate that the mass spectrometer can identify.

A process in which gaseous substances of known purity and concentration are introduced to the mass spectrometer and the respective mass-to-charge ratios are identified. This process when concluded, allows for the calculation of concentrations of products and intermediates of the photoreaction.

A sepation technique that uses a liquid mobile phase to separate the components of a mixture based on their interactions with a stationary phase and a mobile phase.

The range of critical for the safe operation of the photoreactor parameters.

Maximum and minimum of operation pressure range within the reactor can operate safely. Higher operation temperatures can lead to higher pressure values.

Maximum of operation pressure range within the reactor can operate safely.

Minimum of operation pressure range within the reactor can operate safely.

Equipment used for controlling and / or monitoring the pressure in various parts of a photoreactor. A vacuum pump is a typical example of such equipment.

Α mechanical device that removes gas molecules from a sealed chamber reaching pressures lower than the atmospheric pressure.

Maximum and minimum of operation temperature range within the reactor can operate safely.

Maximum of operation temperature range within the reactor can operate safely.

Minimum of operation temperature range within the reactor can operate safely.

Equipment used for controlling and/or monitoring the temperature in various parts of a photoreactor. This can include hot plates, heating elements and cryostats. Light sources in operation can also affect the temperature in the reaction chamber.

A construction inside of which the photocatalyst and the reactants coexist and the photoreaction takes place.

Volume of the reaction chamber, calculated by its dimensions. Volume of pipes and valves connected to the reaction chamber should also be calculated and added to the total volume.

Height, width and depth (in cubic- or rectangular- shaped reaction chambers) or diameter and height (in cylindrer - shaped reaction chambers).

The shape of the reaction chamber. In gas-phase reactions, reaction chambers have usually a cylindrical, cubical or rectangular shape.

Material used for the construction of the main body of the reaction chamber.

A transparent material optimized to allow the transmission of electromagnetic radiation with low reflectance and scattering.

Material that the window is made of. The window, usually attached to the lid sealing the reaction chamber, allows for the incoming light to enter the reaction chamber and interact with the photocatalyst. The material of the window influences the wavelenth range the the photocatalyst experieneces.

The dimension of the optical window (diameter / thickness) allowing the incoming light to enter the reaction chamber and interact with the photocatalyst.

Diameter of the optical window allowing the incoming light to enter the reaction chamber and interact with the photocatalyst.

Thickness of the optical window allowing the incoming light to enter the reaction chamber and interact with the photocatalyst.

Flow rates of gases used in an experiment. Gases can have either the role of a reactant (e.g., CO2) or be inert (e.g., Ar, He).

Equipment used for controlling and / or monitoring the flow of gases (reactant or inert) needed for a photocatalytic experiment. Mass flow controllers (MFCs) are commonly used to control gas flows.

A mass flow controller (MFC) is a device used to measure and control the flow of liquids and gases. A mass flow controller is designed and calibrated to control a specific type of liquid or gas at a particular range of flow rates.

The irradiation system includes all the necessary equipment needed to perform a photocatalytic experiment. The system apart from the light source can include, filters, power units, lamp cooling devices etc..

Light source used to irradiate a photocatalyst in a reaction chamber. These include sources with various intensities, powers and wavelength ranges, including Hg/Xe lamps, Xe lamps and LEDs.

A lamp containing a mixture of mercury (Hg) and xenon (Xe) gases. Under electric current, the gas mixture gets ionized through a discharge electric charge creating a plasma generating UV and visible light.

A lamp containing pure xenon (Xe) gas. Under electric current, the gas mixture gets ionized through a discharge electric charge creating a plasma generating UV and visible light.

A solid-state semiconductor emitting light at highly controllable (narrow) wavelength ranges.

Specific of roperties of the light source dictaning its operation and its adequacy in the studied photocatalytic reaction.

The distance of the light source from the reaction chamber and the photocatalyst.

The value of current (usually in A or mA) used to operate the selected light source.

The value of voltage (usually in V or mV) used to operate the selected light source.

The power of the light source (usually in W or mW). The power can be calculated by the multiplication of the current and voltage used to operate the light source.

The light intensity (usually in mW cm-2) of the selected light source. The light intensity should be measured at the same distance as the one between the light source and the reaction chamber / sample.

The distance between two successive peaks or troughs in a wave.

Electromagnetic radiation with wavelengths typically in the range of 800 nm - 20000 nm.

Electromagnetic radiation with wavelengths visible to the human eye, typically in the range of 400-800 nm.

Electromagnetic radiation with a wavelength typically in the range of 100-400 nanometers.