Photocatalysis Experiments

In heterogeneous photocatalysis experiments, especially in reactions dealing with water detoxification and gaseous pollutant removal, the disappearance of target chemicals, the degree of mineralization of total organic carbon (TOC), and the reaction intermediates can be detected by spectroscopic optical methods (UV-vis and IR), TOC measurements, and chromatographic analysis. 

Photocatalysis experiments were conducted using an established semiconductor system and for decoration with noble metals, combining it with size-selected clusters. The general synthesis and measurement approach is depicted in Fig. 3.17. Colloidal semiconductor CdS nano rods are spin coated onto conducting ITO glass substrates... 

Intriguing, is the unexpected high reactivity of Pt46 clusters in both reactor and photocatalysis experiments, further supported by the deviation of the trend for BE shifts for different sizes in XPS and the low activation energy, determined for CO oxidation in the reactors. A systematic study is necessary to shed light on this particular behavior, yet this observation is only possible due to the chosen approach with different techniques. 

Procedure 10% aqueous solution of potassium iodide, KI, when exposed to sunlight, liberated I2 due to the photolytic decomposition and gave blue colour with freshly prepared starch solution. The intensity of blue coloured complex with the starch increased many fold when the same solution was kept in the ultrasonic cleaning bath. As an extension of the experiment, the photochemical decomposition of KI could be seen to be increasing in the presence of a photocatalyst, Ti02, showing an additive effect of sonication and photocatalysis (sono-photocatalysis) However, the addition of different rare earth ions affect the process differently due to the different number of electrons in their valence shells. 

A similar combination of ultrasound and photocatalysis has also been reported to destroy 2,4,6-trichlorophenol in aqueous solution [39]. An ultrasonic probe (22 kHz) with a uv light source (15 W) was used to examine the effect of changing such operating conditions as ultrasonic intensity, reaction temperature and uv transmission. The experiments involved using 2,4,6-trichlorophenol (100 ppm) and TiOj (0.1 g L ) and showed that the degradation rates increased with the temperature of the solution. The cumulative effect was more pronounced at lower ultrasonic intensities with little additional benefit derived at increased ultrasonic powers. 

In the majority of cases, the oxidizing species involved in the photooxidation reactions is not well known because the nature of the species is inferred from indirect experiments. The 02 ion has been invoked as the precursor of the oxidizing species in a number of reactions because it is often the only species observed at room temperature using EPR. However, a variety of other species such as O and OJ have been identified on surfaces when the low-temperature photoreactions are observed by EPR. In addition, O" formed on the surface may have a very short lifetime (as discussed in Ref. 1, p. 93) and can only be detected by its reactivity. With these points in mind, we conclude that O-, and particularly OJ in the presence of excess oxygen, may play a much more important role in photocatalysis than has yet been generally realized. In this connection, the paper of Kubokawa et al. (410) is of particular importance but the use of 170-labeled oxygen is necessary to confirm the nature of the species involved. In order to explore... 

In addition to development of full laboratory courses, several individual experiments that can be included in such integrated laboratories have been developed recently. They include experiments on photocatalysis (148), synthesis, kinetics and thermodynamics of an inorganic compound (149), studies on conformational analysis (150), synthesis and variable temperature proton NMR of an inorganic compound (151), and the study of microemulsions (152). As such laboratories become more common, we can expect more of these experiments to appear in the literature. These integrated laboratory courses and experiments can be found in Table XL... 

Photocatalysis, A Laboratory Experiment for an Integrated Physical Chemistry-Instrumental Analysis Course 148... 

A comparison of these new processes with Ti02 photocatalysis for the degradation of aniline [148] showed that the former are faster. Although all these methods are considered to proceed via OH radicals, some different intermediates were detected in the electrochemical and photocatalytic experiments. p-Benzoquinone and NH4+ appeared in all solutions tested. A recent study [149] reports 87% and 99% TOC removals after 4 hr of... 

Figure 11 The absorption spectrum of a 0.2-mM NBB dye solution recorded at different time intervals following electrochemically assisted photocatalysis. An immobilized Ti02 particulate film cast on a conducting glass electrode was maintained at an electrochemical bias of 0.8 V SCE during the photocatalytic degradation experiment. (From Ref. 265.)...

With the findings of Sects. 5.1 and 5.2 in mind, we began a series of experiments to investigate the control of actinide oxidation states by photocatalysis. In order to avoid complications associated with the photolysis of... 

The effect of temperature is not so significant within the studied interval, probably due to the counter effect of a decrease in the adsorption constant of solute on the catalyst with increasing thermal levels. It is also to be noted that reactions carried out in heterogeneous photocatalysis display low activation energies. Moreover, most of the photocatalytic experiments are conducted at isothermal conditions (usually at room temperature), and therefore, temperature changes do not play a major role (Chen and Ray, 1999). 

Ibanez, J. G. Mena-Brito, R. Fregoso-Infante, A., Laboratory Experiments on the Electrochemical Remediation of the Environment. Part 8. Microscale Photocatalysis, J. Chem. Educ. 2005, 82, 1549-1551. 

This review has been written in order to clarify fundamental aspects of photocatalysis, an important subject in inorganic and material chemistry, not to present a list of studies on photocatalysis reported so far, since it seems rather difficult to make a complete review by introducing all or a large part of the reported studies on photocatalysis of relatively long history. This review is based on the author s experience in studies on photocatalysis and topics are limited to so-called semiconductor photocatalysis definition and examples of photocatalysis, its principle and kinetics, visible light-induced photocatalysis, and design of active photocatalysts are discussed in detail. 

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