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.

State of the art and perspectives on materials and applications of photocatalysis over TiO2

Abstract: We present a short review of some recent trends, accomplishments, and problems pertaining to photocatalysis over TiO2 and related semiconductors. We have focused in particular on developments in TiO2-based materials, and on applications including continuing progress in longstanding uses such as photocatalytic water or air treatment as well as more recent ones such as self-cleaning surfaces and, finally, new applications. This article will not consider the topics of degradation mechanisms or reactor design, each of which would merit a lengthy review itself. Furthermore, the references cited are not intended to be comprehensive (for that we refer the reader to an extensive bibliography [1]), but to provide some highlights and examples regarding recent research and basic knowledge. Photon absorption by TiO2 results in the promotion of an electron from the valence band to the conduction band of the titania, leaving behind a ‘‘hole’’ (i.e, electron vacancy) in the valence band, provided the photon has an energy at least equal to that of the bandgap of the photocatalyst. The bandgaps for anatase and rutile being 3.2 and 3.0 eV, corresponding to wavelengths = 385 and 410 nm, respectively, ultraviolet light is needed for photoexcitation. The electron–hole pairs can either recombine or participate in chemical reactions with surface/adsorbed species (Scheme 1). Oxidation of water/hydroxide ion by the valence-band hole (hVB) can produce the hydroxyl radical, OH. The conduction-band electron (e CB) can react with molecular oxygen to form the superoxide radical-anion, O2 , which can be involved in further reactions (Scheme 1). In addition, hVB and e CB can react directly with adsorbed pollutants (Scheme 1). The radicals thus formed, dioxygen and water can participate in further reactions, resulting ultimately in mineralization of the organic pollutants.

Photocatalytic and Photoelectrochemical Water Oxidation over Metal‐Doped Monoclinic BiVO4 Photoanodes

Abstract: The visible-light-induced water oxidation ability of metal-ion-doped BiVO4 was investigated and of 12 metal ion dopants tested, only W and Mo dramatically enhanced the water photo-oxidation activity of bare BiVO4; Mo had the highest improvement by a factor of about six. Thus, BiVO4 and W- or Mo-doped (2 atom %) BiVO4 photoanodes about 1 μm thick were fabricated onto transparent conducting substrate by a metal–organic decomposition/spin-coating method. Under simulated one sun (air mass 1.5G, 100 mW cm−2) and at 1.23 V versus a reversible hydrogen electrode, the highest photocurrent density (JPH) of about 2.38 mA cm−2 was achieved for Mo doping followed by W doping (JPH≈1.98 mA cm−2), whereas undoped BiVO4 gave a JPH value of about 0.42 mA cm−2. The photoelectrochemical water oxidation activity of W- and Mo-doped BiVO4 photoanodes corresponded to the incident photon to current conversion efficiency of about 35 and 40 % respectively. Electrochemical impedance spectroscopy and Mott–Schottky analysis indicated a positive flat band shift of about 30 mV, a carrier concentration 1.6–2 times higher, and a charge-transfer resistance reduced by 3–4-fold for W- or Mo-doped BiVO4 relative to undoped BiVO4. Electronic structure calculations revealed that both W and Mo were shallow donors and Mo doping generated superior conductivity to W doping. The photo-oxidation activity of water on BiVO4 photoanodes (undoped

Harvesting Solar Light with Crystalline Carbon Nitrides for Efficient Photocatalytic Hydrogen Evolution

Abstract: Described herein is the photocatalytic hydrogen evolution using crystalline carbon nitrides (CNs) obtained by supramolecular aggregation followed by ionic melt polycon- densation (IMP) using melamine and 2,4,6-triaminopyrimi- dine as a dopant. The solid state NMR spectrum of 15 N- enriched CN confirms the triazine as a building unit. Control- ling the amount and arrangements of dopants in the CN structure can dramatically enhance the photocatalytic perfor- mance for H2 evolution. The polytriazine imide (PTI) exhibits the apparent quantum efficiency (AQE) of 15 % at 400 nm. This method successfully enables a substantial amount of visible light to be harvested for H2 evolution, and provides a promising route for the rational design of a variety of highly active crystalline CN photocatalysts. Producing hydrogen, an environmentally benign energy carrier with a high energy density, from water splitting is a primary goal of modern chemistry. (1) The rational design and synthesis of abundant, sustainable, and efficient metal-free photocatalytic materials that operate with visible light con- tinue to be challenges in this field. Recently, the polymeric carbon nitride (CN) semiconductor g-C3N4 has attracted significant attention because this catalyst exhibited stable performance in the photocatalytic water-splitting reaction (half reaction) under visible light. (2) The semiconductor properties of g-C3N4 result from the formation of an extended p-conjugated system from s-triazine units and largely rely on the extent of their polymerization. A structural character- ization revealed the presence of unreacted amino and/or cyano functionalities owing to incomplete polymerization. (3)