Cerium doped catalyst was synthesized using Titanium isopropoxide as the Titanium source. The metal doped nanoparticles semiconductor catalyst was prepared by sol-sol method with the sol of Cerium. The synthesized catalyst samples were characterized by powder X-ray diffraction, BET surface area, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and UV-vis diffuse reflectance measurements (DRS) and compared with undoped TiO2 catalyst. The photocatalytic activity of the sample was investigated for the decomposition of nitrobenzene (NB) using visible light as the artificial light source. Cerium doped catalyst was found to have better degradation of nitrobenzene owing to its shift in the band gap from UV to visible region as compared to undoped TiO2 catalyst. The operational parameters were optimized with catalyst dosage of 0.1？g？L？1, pH of 9, and light intensity of 500？W. The degradation mechanism followed the Langmuir Hinshelwood kinetic model with the rate constant depending nonlinearly on the operational parameters as given by the relationship (theoretical) = 2.29 * 10？4 * Intensity0.584 * Concentration？0.230 * Dosage0.425 * pH0.336. 1. Introduction The mechanism of photocatalysis using a semiconductor is by charge carrier generation resulting in the formation of holes, charge carrier trapping to form hydroxyl radicals, and recombination of electrons and holes where heat is generated. Heterogeneous photocatalytic systems based on TiO2 catalysts show some limitations that reduce their impact in the domain of environmental protection. Important limitations are low photonic yield and little efficiency under visible light. These limitations have recently been the source of great development in the area of the production and characterization of TiO2-based photocatalysts, capable of being efficiently used under visible irradiation or showing a higher photochemical yield in the near UV region. Any semiconductor material could be activated using a light whose wavelength greatly depends on the band gap of the semiconductor catalyst. Apart from the band gap, there have been other properties like surface area, crystal composition, particle size distribution, and porosity which have an influential effect on the degradation of the compound. Band gap reduction could be done by dye sensitization, doping, bimetallic semiconductor, and surface modification. By reducing the band gap, use of visible light could be employed as an alternative to UV light which may result in better economics. Various nonmetal elements, such as B [1], C [2], N [3], V [4],
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