Multi-walled carbon nanotubes (MWCNTs) have been successfully modified with TiO2 nanoparticles via a two-step hydrolysis technique. Firstly, the pristine MWCNTs are functionalized in nitric acid (HNO3) to creation of oxygen containing groups. Secondly, TiO2 nanoparticles are synthesized on the surface of functionalized MWCNTs through hydrolysis method. The synthesized samples have been used as photocatalyst for decomposition of methyl orange (MO) as dye organic pollutant. The characterization

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... samples using x-ray diffraction pattern (XRD) confirm the presence of TiO2 nanoparticles with mixture of anatase and rutile phases. Regarding the photocatalytic performance of TiO2 nanoparticles and modified MWCNTs with TiO2 nanoparticles, it observed that the degradation rate of MO increases by increasing the irradiation time from 5 min to 35 min. The variation of degradation rate upon pH of suspension reveals that the maximum and minimum degradation rate are in acidic (pH=3) and neutral condition (pH=7). Meanwhile, the results show that the presence of MWCNTs leads to the enhancement of degradation rate. The analysis of variance (ANOVA) results confirm that both of main factors (irradiation time and pH) and their interaction have a significant influence on the degradation rate of MO. However, the effect of irradiation time is more than that of pH and their interaction. The graphical methods verify the quality and adequacy of the statistical models for prediction of the degradation rate.