Core-shell morphology of silica (SiO2) shell coated CdS nanorod core (SNR) of aspect ratio = 21 and SiO2 shell thickness (1.4 nm) has been made for better photostability and photochemical activity (similar to 66%) of CdS nanoparticles. The size of the CdS core was reduced (from 6 to 2.4 nm) as a function of wavelength using 488 nm Ar ion laser irradiation that displayed high fluorescence and improved photocatalytic activity (similar to 72%) due to more surface active atoms. Different transition metal particles in the size range of 2-5 nm have been deposited to form a metal-semiconductor junction that shows improved photodegradation of methyl orange (similar to 91%) in 45 min under visible light (250W, tungsten-halogen lamp) in an order - Pt > Au > Rh > Pd >Ag similar to Cu as a function of their nature, particle size distribution, redox potential, Fermi level equilibration, effective number of interfacial contacts, etc. Different parameters such as surface area, pH, light intensity, catalyst and dye concentration also play a significant role. Complete mineralization was studied by identifying different intermediates via GC-MS study and measuring CO2 (40 mu mol). A plausible mechanistic degradation pathway was proposed for the complete mineralization. (C) 2014 Elsevier B.V. All rights reserved.