Photocatalysis

About: Photocatalysis is a research topic. Over the lifetime, 67088 publications have been published within this topic receiving 2145233 citations. The topic is also known as: photocatalyst.

Photocatalysis fundamentals revisited to avoid several misconceptions

Abstract: Photocatalysis has presently become a major discipline owing to two factors: (i) the intuition of the pioneers of last 20th century and (ii) the mutual enrichment of scientists arising from different fields: photochemistry, electrochemistry, analytical chemistry, radiochemistry, material chemistry, surface science, electronics, and hopefully catalysis. Since heterogeneous photocatalysis belongs to catalysis, all the bases of this discipline must be respected: (i) proportionality of the reaction rate to the mass of catalyst (below the plateau due to a full absorption of photons); (ii) implication of the Langmuir–Hinshelwood mechanism of kinetics with the initial rate being proportional to the coverages θ in reactants;(iii) conversions obtained above the stoichiometric threshold defined as the maximum number of potential active sites initially present at the surface of a mass m of titania used in the reaction. In addition, one should respect photonics, with the photocatalytic activity, i.e. the reaction rate being (i) parallel to the absorbance of the photocatalyst and (ii) proportional to the radiant flux Φ. In every study, one should determine the quantum yield (QY) (or efficiency), which, although dimensionless, is a “doubly kinetic” magnitude defined as the ratio of the reaction rate r (in molecules converted/second) to the efficient photonic flux (in photons/second) received by the solid. This is an instantaneous magnitude directly linked to the parameters mentioned above, in particular to the concentration. It can vary from a maximum value of ca. 40% in pure liquid phase to very low values (10−2%) in diluted media (pollutants trace eliminations). To establish true photocatalytic normalized tests, the above recommendations must be observed with a real catalytic activity independent of non-catalytic side-reaction. In particular, dye decolorization, especially in the visible, provides an apparent “disappearance” of the dye, due to a limited stoichiometric electron transfer from the photo-excited dye molecule to titania, subsequently compensated by an additional ionosorption of molecular oxygen.The energetics of photocatalysis on TiO2, being based on the energy E of the photons, i.e. E ≥ 3.2 eV, enables one to produce OH radicals, the second best oxidizing agent. The decrease of energy E to the visible may be thermodynamically detrimental for the generation of such highly cracking and degrading species. Concerning solid state chemistry, it is now finally admitted that cationic doping is detrimental for photocatalysis. In conclusion, all these recommendations have to be addressed and experiments have to be operated in suitable conditions before claiming that one deals with a true photocatalytic reaction.

Construction of Z-scheme Type Heterogeneous Photocatalysis Systems for Water Splitting into H2 and O2 under Visible Light Irradiation

Abstract: The water splitting under visible light irradiation has been achieved by the Z-scheme system constituted of an Fe3+/Fe2+ redox couple as an electron relay and two powdered heterogeneous photocataly...

for 2-mercaptobenzothiazole degradation in aqueous suspension for odour control

Abstract: A series of cerium ion-doped titanium dioxide (Ce 3+ –TiO2) catalysts with special 4 f electron configuration was prepared by a sol–gel process and characterized by Brunauer-Emmett-Teller method, X-ray diffraction, X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy (DRS), and also photoluminescence (PL) emission spectroscopy. The photocatalytic activity of Ce 3+ –TiO2 catalysts was evaluated in the 2-mercaptobenzothiazole (MBT) degradation in aqueous suspension under UV or visible light illumination. The experimental results demonstrated that the overall photocatalytic activity of Ce 3+ –TiO2 catalysts in MBT degradation was signigicantly enhanced due to higher adsorption capacity and better separation of electron-hole pairs. The experimental results verified that both the adsorption equilibrium constant (Ka) and the saturated adsorption amount (Gmax) increased with the increase of cerium ion content. The results of XPS analysis showed that the Ti 3+ ,C e 3+ , and Ce 4+ ions reside in the Ce 3+ –TiO2 catalysts. The results of DRS analysis indicated that the Ce 3+ –TiO2 catalysts had significant optical absorption in the visible region between 400 and 500 nm because electrons could be excited from the valence band of TiO2 or ground state of cerium oxides to Ce 4 f level. In the meantime, the dependence of the electron-hole pair separation on cerium ion content was investigated by the PL analysis. It was found that the separation efficiency of electron-hole pairs increased with the increase of cerium ion content at first and then decreased when the cerium ion content exceeded its optimal value. It is proposed that the formation of two sub-energy levels (defect level and Ce 4 f level) in Ce 3+ –TiO2 might be a critical reason to eliminate the recombination of

Facile Synthesis of Au/g‐C3N4 Nanocomposites: An Inorganic/Organic Hybrid Plasmonic Photocatalyst with Enhanced Hydrogen Gas Evolution Under Visible‐Light Irradiation

Abstract: Noble-metal Au nanoparticles deposited on graphitic carbon nitride polymer (g-C3N4) photocatalyst by a facile deposition–precipitation method exhibited high photocatalytic activity for hydrogen gas production under visible-light irradiation. The Au/g-C3N4 nanocomposite plasmonic photocatalysts were characterized by X-ray diffraction spectroscopy, diffuse reflectance UV/Vis spectroscopy, FTIR spectroscopy, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, selected-area electron diffraction, X-ray photoelectron spectroscopy, photoluminescence spectroscopy, and photoelectrochemical measurements. We studied the effect of Au deposition on the photocatalytic activity of g-C3N4 by investigation of optical, electronic, and electrical properties. Enhanced photocatalytic activity of Au/g-C3N4 naocomposite for hydrogen production was attributed to the synergic mechanism operating between the conduction band minimum of g-C3N4 and the plasmonic band of Au nanoparticles including high optical absorption, uniform distribution, and nanoscale particle size of gold. The mechanism of te photocatalytic activity of the nanocomposite photocatalyst is discussed in detail. Deposition of Au nanoparticles on g-C3N4 was optimized and it was found that 1 wt % Au-loaded g-C3N4 composite plasmonic photocatalyst generated a photocurrent density of 49 mA cm−2 and produced a hydrogen gas amount of 532 μmol under visible light, which were more than 3000 times higher and 23 times higher, respectively, than the values of neat g-C3N4.