Photocatalysis Langmuir-Hinshelwood

In most photocatalysis, Langmuir-Hinshelwood kinetics is observed, suggesting the importance of substrate adsorption in key steps of the reaction [83]. That is, the rate of photocatalysis is proportional to the concentration (or pressure) of the reactant, which in turn can be related to the surface coverage by the Langmuir expression, Eq. 8,... 

In classical kinetic theory the activity of a catalyst is explained by the reduction in the energy barrier of the intermediate, formed on the surface of the catalyst. The rate constant of the formation of that complex is written as k = k0 cxp(-AG/RT). Photocatalysts can also be used in order to selectively promote one of many possible parallel reactions. One example of photocatalysis is the photochemical synthesis in which a semiconductor surface mediates the photoinduced electron transfer. The surface of the semiconductor is restored to the initial state, provided it resists decomposition. Nanoparticles have been successfully used as photocatalysts, and the selectivity of these reactions can be further influenced by the applied electrical potential. Absorption chemistry and the current flow play an important role as well. The kinetics of photocatalysis are dominated by the Langmuir-Hinshelwood adsorption curve [4], where the surface coverage PHY = KC/( 1 + PC) (K is the adsorption coefficient and C the initial reactant concentration). Diffusion and mass transfer to and from the photocatalyst are important and are influenced by the substrate surface preparation. 

Keywords Photocatalysis and catalysis Photocatalytic activity Band structure and excitation Energy conversion Langmuir-Hinshelwood mechanism Electron-hole recombination Quantum efficiency Physical property-activity correlation Synergetic effect. 

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