One of the few photoreactions applied in chemical industry is sulfoxidation of alkanes. In the reaction SO2 is the light absorbing species and therefore low pressure Hg lamps have to be employed. During the previous work on the photocatalytic properties of chloroplatinate titania (4%H2[PtCl6]/TH, TH = Titanhydrat-O), it was found that this compound surprisingly catalyses the visible light sulfoxidation of n-heptane. It was now the aim of this work to investigate the mechanism of this first catalytic photosulfoxidation of an alkane and to search for further semiconductor catalysts. In the first part of this work, in addition to 4%H2[PtCl6]/TH, also 1%H2[PtBr6]/TH, 2%H2[PtBr6]/TH, 3%H2[PtBr6]/TH, 6%H2[PtBr6]/TH, 4%RhCl3/TH, and 3%RhCl3/TH were prepared. For comparison also 4%H2[PtCl6]/SiO2, 8%H2[PtCl6]/SiO2, 32%H2[PtCl6]/SiO2, 4%H2[PtCl6]/SiO2 (grinding in ball mill), 4%H2[PtCl6]/Al2O3, and 4%H2[PtCl6]/Al2O3 (grinding in ball mill) were synthesised. Both 6%H2[PtBr6]/TH and 4%H2[PtCl6]/TH exhibited absorption already at about 550 nm. The diffuse reflectance spectra of 6%H2[PtBr6]/TH in accordance with its much deeper yellow colour compared to that of the chloro-modified, exhibits a stronger absorption than the latter. Unmodified TH showed a bandgap of 3.21 eV in excellent agreement with the literature value of 3.20 eV reported for anatase. 4%H2[PtCl6]/TH also showed almost the same bandgap of 3.21 eV, proving that modification does not contribute to change in bandgap. However, a bandgap of 3.03 eV was measured for 6%H2[PtBr6]/TH and the narrowing of the bandgap is proportional to the increasing amount of H2[PtBr6] added for the catalyst modification. Similarly, also for 4%RhCl3/TH and 3%RhCl3/TH the values of 2.97 and 3.1 eV respectively, indicate the bandgap narrowing. Determination of the quasi-Fermi level of electrons for 6%H2[PtBr6]/TH by pH dependent photovoltage measurements afforded a value of -0.24 „b 0.02 V (vs. NHE). This is in agreement with the previously reported quasi-Fermi level of 4%H2[PtCl6]/TH. There was an anodic shift of ~ 300 mV as compared to ¡V0.54 V of TH for both 4%H2[PtCl6]/TH and 6%H2[PtBr6]/TH. As a first test on photocatalytic properties of these new materials, the degradation of 4-CP was investigated. The photocatalyst 4%H2[PtCl6]/TH displayed a superior activity while bromo complex modified titania showed around 50% less activity. The lesser activity of bromo modifications may be due to the lower oxidation potential of the bromine atom compared to that of chlorine. Compared to these catalysts, the unmodified TH or P25 were almost inactive. When the TiO2 semiconductor support was changed to insulators like SiO2 or Al2O3, there was no activity. This confirms the role of the semiconductor in this reaction. Rhodium modified complexes exhibited a similar trend of high activity like 4%H2[PtCl6]/TH. The second and major part of the thesis deals with the visible light sulfoxidation of alkanes in the solvents methanol and acetic acid in the presence of metal complex modified titania and other semiconductor photocatalysts. Furthermore, the influence of some complexing agents like acetylacetone was investigated. Adamantane was employed as the model alkane and the analysis of 1-adamantanesulfonic acid was made by HPLC using the technique of Indirect Photometric Detection. The Turnover Number (TON, the ratio of amount of product (1-adamantanesulfonic acid) to amount of active material (Pt)) of the reaction in methanol after 10 h (which was the optimized irradiation time for maximum yield of 1-adamantanesulfonic acid) was 21. Photosulfoxidation of methanol did not occur as indicated by HPLC analysis. There was no formation of 1-adamantanesulfonic acid in the absence of the catalyst and the reaction ceases when the irradiation is stopped. The corresponding bromo complex was also active but induced a smaller TON of 8 after 10 h. Only traces of 1-adamantanesulfonic acid were observed when unmodified TH was employed, whereas 1-adamantanesulfonic acid was completely absent when hexachloroplatinic acid was supported onto silica, alumina or amorphous titania. Hexachloroplatinic acid itself and amorphous titania were also inactive. The mechanism of sulfoxidation is a photo-redox type similar to that proposed for 4-CP degradation by the same catalyst 4%H2[PtCl6]/TH. Since it was observed that the Cl ligand in the metal complex chemisorbed to TiO2 plays a vital role in the photocatalytic activity of 4%[H2PtCl6]/TH, we wanted to explore the role of better complexing agents other than Cl in our catalyst. As it is well known that acetylacetone is a good transition metal chelating agent, it was added in the system so that it could chelate with Pt to form a more stable and efficient complex replacing the Cl ligands and thereby possibly increasing visible light absorption. As an experimental support for this hypothesis, it was found that complexing agents like acetylacetone when added to the sulfoxidation of adamantane in methanol had significantly increased the yield. However, other complexing agents like hexafluoroacetylacetone, pyrophosphate, ethylene glycol, sodium-dihydrogen phosphate did not display any enhancing effect in the yield of sulfoxidation in methanol. All catalysts exhibited an enhanced activity in sulfoxidation in methanol in the presence of acetylacetone, especially in the case of 4%[H2PtCl6]/TH, the yield of 1-adamantanesulfonic acid increased from 12 to 39% which is more than three-fold increase. 6%H2[PtBr6]/TH also exhibited similar trends. Carbon modified titania (TiO2-C) also revealed an increase in yield of 1-adamantanesulfonic acid with acetylacetone i.e. from 10 to 30%. Special attention has to be given to anatase modifications of titania, TH and TiO2 (anatase) which are not active in the absence of acetylacetone, but displayed a prominent activity in its presence. It was observed that only anatase modifications of titania showed an significant activity in the presence of acetylacetone, while amorphous modifications were inactive both in the presence and absence of acetylacetone. However, when TH was premodified with acetylacetone and employed for sulfoxidation, it turned out to be inactive. Addition of acetylacetone to TiO2 makes this white powder pale yellow. The DRS shows a shift in absorption towards visible region for all commercially available TiO2 on contact with acetylacetone. The bandgap of titania (TH) also narrowed from 3.21 to 3.11 eV on addition of acetylacetone. Based on these observations and on the enhanced yield in the presence of acetylacetone, the mechanism of visible light sulfoxidation in the presence of acetylacetone is proposed by analogy with the sulfoxidation in the presence of metal complex modified titania. The main difference is that instead of a Pt-X (X = Cl or Br) cleavage, now a Pt-O of acetylacetonate occurs. In the case of naked TiO2 catalysing the reaction, it is postulated that surface titania centers are complexed with acetylacetone directly and now a Ti-O bond is cleaved in the primary step. Sulfoxidation in acetic acid as the solvent instead of methanol was also performed. It was observed that platinum modified catalysts were active only in the case of acetylacetone addition. 4%[H2PtCl6]/TH and 6%[H2PtBr6]/TH produced an yield of 18 and 11% of 1-adamantanesulfonic acid after 10 h irradiation respectively. There was no influence of acetylacetone in the 4.0%RhCl3/TH catalysed sulfoxidation as both in its presence and absence, produced an yield of 18% of 1-adamantanesulfonic acid after 10 h irradiation. Surprisingly, TH was found to be active in the visible light sulfoxidation of adamantane and there was a detrimental effect by the addition of acetylacetone. This may be justified due to the good bridging and chelating nature of the acetic acid itself. Generally addition of acetylacetone increased the yield of 1-adamantanesulfonic acid in the case of metalcomplexes, while it had a detrimental effect on yields in the case of on unmodified titania. TiO2-C followed a similar trend to that of TH. TiO2-N ((NH4)2CO3 modified) and TiO2-N (urea modified) were moderately active, however, failed to produce 1-adamantanesulfonic acid on acetylacetone addition.