Visible Light Sensitive Photocatalyst Research Articles

EPR study on paramagnetic species in nitrogen-doped ZnO powders prepared by a mechanochemical method

Paramagnetic species in nitrogen-doped ZnO (N-ZnO) powders, visible light sensitive photocatalysts exhibiting antibacterial activity, have been investigated using EPR spectroscopy. The N-ZnO photocatalysts showed two kinds of EPR signals due to a singly ionized nitrogen ( N 2 - ) and a shallow donor. Visible light irradiation to the N-ZnO particles shows reversible response of reduction of EPR signal of the N 2 - radical site and increase of that due to shallow donor. The results indicate that the N 2 - is converted to a diamagnetic neutral molecular nitrogen acceptor ( N 2 0 ) by visible light and photoinduced electrons are trapped to the shallow donor sites.

Visible Light Sensitive Photocatalyst, Delafossite Structured α-AgGaO2

Delafossite structured alpha-AgGaO(2) powder was successfully synthesized through a cation exchange reaction. alpha-AgGaO(2) has a band gap of 2.4 eV, absorbs visible light up to 520 nm, and effectively decomposes 2-propanol to CO2 via acetone by irradiating with either UV light (300-400 nm) or visible light (420-530 nm). The values of the quantum efficiency are similar (ca. 0.6%) under light irradiations with wavelengths of 365, 390, 430, 470, and 510 +/- 10 nm, but steeply decrease with wavelengths longer than 530 +/- 10 nm, which support a 2.4 eV band gap. In contrast, the other polymorph, alpha-AgGaO(2) powder, which has a band gap of 2.1 eV, shows a negligible activity when irradiating with either UV light or visible light. The higher oxidation activity of alpha-AgGaO(2) is probably due to its larger band gap, which is formed at the top of its valence band in a lower energy region as compared to alpha-AgGaO(2). Moreover, the first-principle calculations of alpha-AgGaO(2) and alpha-AgGaO(2) clearly indicate that alpha-AgGaO(2) has a remarkably larger dispersed valence band as compared to alpha-AgGaO(2), which is advantageous to the photocatalytic activity due to the efficient hole conduction.

Chromium-incorporated TUD-1 as a new visible light-sensitive photo-catalyst for selective oxidation of propane

Chromium was incorporated in the framework of TUD-1 mesoporous silica by a one-pot synthesis procedure, using triethanolamine as a bi-functional template. The Cr-TUD-1 catalyst was characterized by means of X-ray diffraction, high-resolution transmission electron microscopy, UV–vis and Raman spectroscopy, as well as elemental analysis and N 2 sorption measurements. The results indicate that chromium is incorporated as tetrahedrally co-ordinated Cr 6+ in the framework of TUD-1. When tested as a catalyst for the photo-oxidation of propane, Cr-TUD-1 showed high activity and high selectivity towards acetone under visible light irradiation ( λ = 435 nm).

Application of a metal ion-implantation for the preparation of visible-light sensitive zeolite photocatalyst: V ion-implanted Ti-containing HMS mesoporous molecular sieves

Visible light sensitive zeolite photocatalysts have been prepared by metal ion-implantation of Ti-containing mesoporous molecular sieves with V ions (V/Ti-HMS) which can operate under visible light irradiation (λ > 450 nm). The metal ion-implantation with V ions was effective to shift the absorption band of Ti-containing molecular sieves to longer wavelengths. This V/Ti-HMS performed the photocatalytic reactions for the NO decomposition under visible light irradiation, while no reaction proceeded on the original Ti-HMS. XAFS analysis indicated that implanted V-oxide moieties existed having tetrahedral coordination and interacted with the tetrahedrally coordinated titanium oxide moieties. These XAFS results as well as the analysis with UV-VIS absorption measurements indicate that the charge transfer excited state of the tetrahedrally coordinated titanium oxide moieties interacting with the tetrahedrally coordinated vanadium oxide moieties plays a significant role in the photocatalytic reaction under visible light irradiation.

Visible light sensitive photocatalysts In 1− xM xTaO 4 (M=3d transition-metal) and their activity controlling factors

A series of novel oxide semiconductors, 3d transition-metal doped In1−xMxTaO4 (M=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn), were synthesized by the ceramic method, and their photocatalytic properties for H2O decomposition under visible light irradiation were examined. It was found that the photocatalytic activity of InTaO4 was significantly enhanced while In was substituted by Ni, but suppressed in most of other substitutions. Theoretical calculations indicated that under the octahedral crystal field, the M 3d electron orbitals split into the lower energy t2g and the higher energy eg parts. With increase in the atomic number of transition-metal M, the 3d energy states shift to the lower energy side. Most of these 3d orbitals hybridize with O-2p or Ta 5d orbitals, localizing the charge carriers. However, Ni 3d–eg states, which lie slightly above the O-2p orbitals, play a role in narrowing the band gap of the un-doped InTaO4 and hence significantly enhance the photocatalytic activity. The controlling factors of photocatalytic activity, such as co-catalysts, surface area, crystallinity of these oxide semiconductors were also studied. The results indicate that not only a suitable energy band structure, but also nano-structured bulk and surface properties are crucial for photocatalysis reaction.

Lanthanum and nitrogen co-doped SrTiO 3 powders as visible light sensitive photocatalyst

Lanthanum and nitrogen co-doped SrTiO 3 was prepared by a mechanochemical reaction method using SrTiO 3, urea and La 2O 3 as the raw materials. Nitrogen-doped SrTiO 3 could be prepared by heating the mixture of SrTiO 3 and La 2O 3 under flowing NH 3 gas at 600 °C. The sample prepared with 0.2 mol% La 2O 3, 22 mol% urea and 77.8 mol% SrTiO 3 which has nearly the same nitrogen and lanthanum doping atomic fractions could be obtained by a mechanochemical method and exhibited high photocatalytic activities. Under the irradiation of light with wavelengths larger than 400 and 290 nm, the photocatalytic activity of nitrogen and lanthanum co-doped SrTiO 3 was 2.6 and two times greater than that of pure SrTiO 3. A new absorption edge, which was formed in the visible light region and higher visible light absorption after co-doping were the reason for the high visible light photocatalytic activity of this substance.

Research and Development of Visible Light Sensitive Photocatalysts

Research and Development of Visible Light Sensitive Photocatalysts

Carbon-doped Anatase TiO2 Powders as a Visible-light Sensitive Photocatalyst

Abstract Carbon-doped TiO2 powders in an anatase phase colored yellow were fabricated by oxidative annealing of TiC. Carbons were located at oxygen sites. The carbon substitution caused the absorbance edge of TiO2 to be shifted to the higher wavelength region. Carbon-doped TiO2 showed photocatalytic activities for the decomposition of IPA to CO2 via acetone under visible light (400–530 nm) irradiation.

LaMnO 3/CdS nanocomposite: a new photocatalyst for hydrogen production from water under visible light irradiation

A LaMnO 3/CdS nanocomposite was developed as a new type of visible light sensitive photocatalyst that can produce hydrogen from water containing electron donors. The nanocomposite catalyst, prepared by a reverse micelle method, was found to show high photocatalytic activity, as compared to that of CdS; on the other hand, LaMnO 3 showed no photocatalytic activity. The proposed energy diagrams for the LaMnO 3/CdS composite, based on the results obtained from photoemission yield measurements, suggest that photogenerated holes in the valence band of CdS could move to that of LaMnO 3, thus separating photogenerated charge-carriers and improving the activity.

Overall water splitting by sonophotocatalytic reaction: the role of powdered photocatalyst and an attempt to decompose water using a visible-light sensitive photocatalyst

The role of a photocatalyst in the sonophotocatalytic reaction of water was investigated using TiO 2 photocatalysts. Based on this investigation, sonophotocatalytic water splitting using visible light was attempted. BiVO 4 is a visible light-sensitive material and this material is one of the candidates for O 2 evolution photocatalyst. For example, O 2 is evolved from H 2O 2 solution by photocatalytic reaction under visible light irradiation. On the other hand, H 2 is produced together with H 2O 2 from water by irradiation of ultrasound. Thus, it is expected to obtain H 2 and O 2 from water when these two reaction systems are combined. Simultaneous irradiation of visible light and ultrasound was tried to perform. As the result, liquid water was decomposed to H 2 and O 2 continuously and stoichiometrically.