Colloidal photochemistry

It is possible that colloidal photochemistry will provide a new approach to prebiotic syntheses. The work described previously on redox reactions at colloidal ZnS semiconductor particles has been carried on successfully by S. T. Martin and co-workers, who studied reduction of CO2 to formate under UV irradiation in the aqueous phase. ZnS acts as a photocatalyst in the presence of a sulphur hole scavenger oxidation of formate to CO2 occurs in the absence of a hole scavenger. The quantum efficiency for the formate synthesis is 10% at pH 6.3 acetate and propionate were also formed. The authors assume that the primeval ocean contained semiconducting particles, at the surface of which photochemical syntheses could take place (Zhang et al 2007). 

An important aspect of semiconductor photochemistry is the retardation of the electron-hole recombination process through charge carrier trapping. Such phenomena are common in colloidal semiconductor particles and can greatly influence surface corrosion processes occurring particularly in small band gap materials, such... 

Spanhel L, Haase M, Weller H, Henglein A (1987) Photochemistry of colloidal semiconductors. 20. Surface modification and stability of strong luminescing CdS particles. J Am Chem Soc109 5649-5655... 

Hotchandani S, Kamat P (1992) Charge-transfer processes in coupled semiconductor systems. Photochemistry and photoelectrochemistry of the colloidal cadmium sulfide-zinc oxide system. J Phys Chem 96 6834—6839... 

In studies of this kind, methods developed in radiation chemistry and photochemistry are often applied The methods of pulse radiolysis and flash photolysis allow one to investigate the mechanism of reactions in which free radicals, electrons and positive holes are the intermediates. In order to understand the mechanisms of processes that occur on colloidal particles it is important to know how free radicals... 

Part II Macromolecules Catalysis Colloid Science Electrochemistry Electron Spin Resonance Environmental Chemistry Genetal and Synthetic Methods Mass Spectrometry Nuclear Magnetic Reson n e Organometallic Chemistry Organophosphorus Chemistry Photochemistry... 

There are new ideas and experiments on the rTCA cycle. A group from Harvard University studied some reaction steps in the rTCA cycle which were kept going by mineral photochemistry. The authors assumed that solar UV radiation can excite electrons in minerals, and that this energy is sufficient to initiate the corresponding reaction steps. In this photocatalytic process, semiconductor particles were suspended in water in the presence of a zinc sulphide colloid (sphalerite) the experiments were carried out in a 500 mL reaction vessel at 288 K. Irradiation involved a UV immersion lamp (200-410 nm) in the photoreactor. Five reactions out of a total of 11 in the rTCA cycle were chosen to check the hypothesis ... 

Weller, H., Koch, U., Gutierrez, M. and Henglein, A. (1984). Photochemistry of colloidal metal sulfides. 7. Absorption and fluorescence of extremely small ZnS particles (the world of the neglected dimensions). Ber. Bunsenges. Phys. Chem. 88, 649. 

The practice of physical chemistry came to include many subfields of research thermochemistry and thermodynamics, solution theory, phase equilibria, surface and transport phenomena, colloids, statistical mechanics, kinetics, spectroscopy, crystallography, photochemistry, and radiation. Here I concentrate only on three approaches within physical chemistry that had some promise for meeting the needs of organic chemists who wanted to explain affinity and reaction dynamics. 

Leigh, D.S. (1996) Soil chronosequence of Brasstown Creek, Blued Ridge Mountains, USA. Catena 26 99-114 Leland, J.K. Bard, A.J. (1987) Photochemistry of colloidal semiconducting iron oxide polymorphs. J. Phys. Chem. 91 5076-5083 Lengweiler, H. Buser.W. Feitknecht, W. 

Koch U, Fojtik A, Weller H, Henglein A (1985) Photochemistry of semiconductor colloids preparation of extremely small ZnO particles, fluorescence phenomena and size quantization effects. Chem Phys Lett 122 507-510... 

Kamat PV, Patrick B (1992) Photophysics and photochemistry of quantized ZnO colloids. J Phys Chem 96 6829-6834... 

Weller H, Koch U, Gutierrez M, Henglein A (1984) Photochemistry of Colloidal Metal Sulfides, 7. Absorption and Fluorescence of Extremely Small Zns Particles -the World of the Neglected Dimensions. Ber Bimsenges 88 649-656... 

Fischer CH, Weller H, Fojtik A, Lumepereira C, Janata E, Henglein A (1986) Photochemistry of Colloidal Semiconductors, 10. Exclusion Chromatography and Stop Flow Experiments on the Formation of Extremely Small Cds Particles. Ber Bimsen-ges 90 46-49... 

Kamat, P. V. Patrick, B. Photochemistry and photophysics of ZnO colloids, in Symp. Electron. Ionic Prop. Silver Halides, vol. 44, B. Levy, J. Deaton, P. V. Kamat, I. Leubner, A. Muenter, L. Slifkin, T. Tani, eds., The Society for Imaging Science and Technology Springfield, VA, 1991, p. 293. 

Vinodgopal, K. Kamat, P. V. Environmental photochemistry on surfaces. Charge injection from excited fulvic acid into semiconductor colloids, Environ. Sci. Technol. 1992, 26, 1963. 

Vinodgopal, K. Environmental photochemistry Electron transfer from excited humic acid to Ti02 colloids and semiconductor mediated reduction of oxazine dyes by humic acid, Res. Chem. Intermed. 1994, 20, 825. 

Kumar, A. and A.K. Jain (2001). Photophysics and photochemistry of colloidal CdS-Ti02 coupled semiconductors - photocatalytic oxidation of indole. Journal of Molecular Catalysis A-Chemical, 165(1-2), 265-273. 

Leland, J.K. and A.J. Bard (1987). Photochemistry of colloidal semiconducting iron oxide polymorphs. Journal of Physical Chemistry, 91, 5076-5083. 

Spanhel, L., H. Weller and A. Henglein (1987). Photochemistry of semiconductor colloids. 22. Electron ejection from illuminated cadmium sulfide into attached titanium and zinc oxide particles. Journal of the American Chemical Society, 109, 6632-6635. 

WHEELER AND THOMAS Photochemistry on Colloidal Silica Solutions 99... 

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