Titanium dioxide has been proved as a promising photocatalyst for the environmentalcleanup in the field of photocatalysis because of its high activity, low cost, easyavailability, non-toxicity and chemical robustness.However, there are certainshortcomings, which hinder its photoactivity such as its large band gap of 3.2 eV andfast recombination of electrons and holes.Therefore, there is a dire need to modify it inorder to make it feasible for the photocatalysis under visible light irradiation and toreduce the recombination of electrons and holes.The main focus of the thesis was laid upon the single element doping and codopingwith the nonmetals and transition metals in order to shift the absorption of TiO2towards the visible light region and reduce the recombination of photoexcited chargecarriers to make it active under the visible light irradiation.The details of my works areas follows:　　1-In my first work, Ce and N codoped TiO2 samples were successfully prepared bykeeping in mind the advantages of Ce as a very powerful electron scavenger (evenmore than oxygen) with the ability to generate labile oxygen vacancies and bulkoxygen species, also N proved as a good candidate for the narrowing of the bandgap and enhancement of the visible light response.The samples were preparedthrough the hydrothermal method by using less expensive precursors such as ceriumnitrate, tetrabutyl orthotitanate (TBOT) and urea.These prepared samples werecharacterized by various techniques such as, X-ray Diffraction (XRD),Transmission Electron Microscopy (TEM), Raman spectroscopy, X-rayPhotoelectron Spectroscopy (XPS), Fourier Transformation Infrared Spectroscopy(FTIR), Thermogravimetric Analysis and Differential Thermal Analysis (TG/DTA),UV-Visible Diffuse Reflectance Spectroscopy (UV-vis DRS) and　　Photoluminescence Spectroscopy (PLS).The XRD and Raman spectra showed onlyanatase phase of TiO2 for the single doped and codoped samples.The XPS of Ceshowed the presence both Ce3+ and Ce4+ oxidation states.The PLS of the samplesshowed first decrease in the recombination centers when Ce was introduced incodoped TiO2 with the maximum decrease for 0.05 Ce/N codoped TiO2 and thenstarted increasing with the increase of Ce in the samples.There have been foundeda direct relationship between the number of recombination centers and photoactivityof the samples, which was measured by the decolorization of 25 mg/L solution ofAcid Orange 7 (AO-7).The activities of codoped samples were highly increased bythe incorporation of Ce with the maximum degradation exhibited by 0.05 Ce/N-TiO2 sample.2-Inspired by the previous results of the idea of codoping Ce with the N, here in thispart we tried the replacement of N with S, to check its effect on the efficiency of thedegradation of the pollutant under the visible light.Hence, Ce and S codoped TiO2nanoparticles were prepared through simple sol-gel method and variouscharacterization techniques were applied.The prepared samples showed the anatasetype of structure with the increase of the specific surface area and decrease of thepore size with the increase in the Ce amount in the samples as indicated by theXRD and BET.The photoluminescence spectra revealed first decrease in theintensity of the spectra sync with the reduction of recombination of electrons andholes.Also, the Ce and S codoping induces the formation of Ti3+ together with theincrease in the surface hydroxyl radical with the increase in the amount of Ce in thesamples.Thus, the increased photoactivity of the samples was attributed to theincrease of the surface area, increase of the surface hydroxyl groups and decrease ofthe recombination of electrons and holes as well as the formation of Ti3+ by thesynergistic effect of the Ce and S.