Green photocatalytic process

For green photocatalytic processes, the use of pollutants as an electron donor was also investigated. Li et al. (2003) reported enhanced photocatalytic hydrogen production using a mixture of pollutants (oxalic acid, formic acid, and formaldehyde) acting as electron donors. The authors reported that photocatalytic decomposition of... 

Using the photocatalytic process to reduce C02 into hydrocarbons could contribute to the control of C02 emission from industrial processes and both produced gases could become the key components of clean green energy systems in the future. 

Much interest has recently been shown in artificial photosynthesis. Photosynthesis is a system for conversion or accumulation of energy. It is also interesting that some reactions occur simultaneously and continuously. Fujishima et al. [338] pointed out that a photocatalytic system resembles the process of photosynthesis in green plants. They described that there are three important parts of the overall process of photosynthesis (1) oxygen generation by the photolysis of water, (2) photophosphorylation, which accumulates energy, and (3) the Calvin cycle, which takes in and reduces carbon dioxide. The two reactions, reduction of C02 and generation of 02 from water, can occur simultaneously and continuously by a sonophotocatalytic reaction. 

Sonication is a tool for improvement of chemical processes such as photocatalytic reaction. The improvements of reaction rates, yields and selectivity, the generation of reactive intermediate species and so on were reviewed.36) Some examples have been also shown in this chapter. The development of a new reaction pass by the combined effect of photocatalysis and sonolysis is expected in the near future. The contribution to Green Chemistry is one of typical examples. 

Applications of photocatalytic oxidations as a green alternative synthetic route has been investigated by several authors although these reactions have always been considered as highly nonselective processes. 

By far the most important role of manganese in nature is its direct involvement in the photocatalytic, four-electron oxidation of water to dioxygen in green plant photosynthesis, an essential process for the maintenance of life. Pirson, in 1937, first discovered the requirement of manganese in photosynthesis by showing that plants grown in a Mn-deficient medium lost their water oxidation capacity (184). During the next four decades, several researchers showed that two photosystems, photosystem I (PSI) and photosystem II (PSII), were involved in photosynthesis and that 02 evolution and Mn were localized at PSII (for a review, see Ref. 185). 

Oxidation is one of the most important reactions in industrial organic synthesis [1-3] and can be carried out in both gas [4] and liquid [5,6] phases. Catalytic oxidation reactions in liquid phase were achieved in conditions of catalytic [5], photocatalytic [7], electrocatalytic [8], and photoelectrocatalytic [9] processes. At the same time, the new developments in the synthesis of materials led to the discovery of a large variety of catalysts and applications, including new catalysts for the liquid-phase oxidation reactions. A special interest in this sense was addressed to green and sustainable sources of oxidation [10]. 

Further, as clearly indicated by its name, the unique phenomenon in photosynthesis is not the assimilation of carbon dioxide, nor the synthesis of sugars but the utilisation for these processes of the radiant energy of the sun. This means that photosynthesis involves, in contradistinction to the other metabolic processes so far mentioned, certain photochemical reactions, insensitive to temperature and mediated through a photocatalytic system. The chlorophyll pigments organised in special cellular structures called chloroplasts represent this system and give to photosynthetic tissues their green colour. 

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