J. Mater. Sci. Technol., 2011, 27(7), 594-600. Role of ZnO-CeO 2 Nanostructures as a Photo-catalyst and Chemi-sensor M. Faisal 1) , Sher Bahadar Khan 1)† , Mohammed M. Rahman 1) , Aslam Jamal 1) , Kalsoom Akhtar 2) and M.M. Abdullah 1) 1) Centre for Advanced Materials and Nano-Engineering (CAMNE) and Department of Chemistry, Faculty of Sciences and Arts, Najran University, Najran 11001, Kingdom of Saudi Arabia 2) Division of Nano Sciences and Department of Chemistry, Ewha Womans University, Seoul 120-750, Korea [Manuscript received December 1, 2010, in revised form March 3, 2011] ZnO-CeO 2 nanostructures were synthesized by simple and efficient low temperature method. The structure and morphology of the ZnO-CeO 2 nanostructures were characterized by X-ray powder diffraction (XRD) and field emission scanning electron microscopy (FESEM), which revealed elongated shaped CeO 2 nanoparticles with diameters of 40–90 nm distributed on the surface of elongated ZnO nanostructures with diameters of 50–200 nm (edge–centre). Further the structure of the synthesized ZnO-CeO 2 nanostructure was supported by Raman spectra and Fourier transform infrared spectroscopy (FTIR). UV-vis absorption spectrum was used to confirm the optical properties of the CeO 2 doped ZnO nanostructures. Photo-catalytic activity of CeO 2 doped ZnO nanostructure was evaluated by degradation of acridine orange and methylene blue which de- graded 84.55% and 48.65% in 170 min, respectively. ZnO-CeO 2 nanostructures also showed good sensitivity (0.8331 μA·cm −2 ·(mol/l) −1 ) in short response time (10 s) by applying to chemical sensing using ethanol as a target compound by I - V technique. These degradation and chemical sensing properties of ZnO-CeO 2 nanos- tructures are of great importance for the application of ZnO-CeO 2 system as a photo-catalyst and chemical sensor. KEY WORDS: ZnO-CeO2 nanostructures; Structural properties; Optical properties; Photocatalytic activity; Ethanol sensing 1. Introduction Organic compounds such as dyes, pesticides, her- bicides, phenols, and various solvents are widely used in industries and daily life, and are the main con- taminants and effluents discharged by the industries. These organic pollutants distress the environment and human health due to their toxicity, carcinogenicity and hazardous effect [1–6] . Thus the detoxification of these toxic organic compounds from the environ- ment has received intense research to preserve human health and environmental safety. Many traditional techniques such as flocculation, precipitation, adsorption on granular activated car- bon, air stripping or reverse osmosis, chemical oxida- tion, combustion, and biological methods have been used so far for the treatment of organic waste ef- † Corresponding author. Prof., Ph.D.; E-mail address: drkhan- marwat@gmail.com (S.B. Khan). fluents, but they lose their importance due to some limitations and disadvantages such as high cost, in- effectiveness and inefficiency and cannot destroy the organic dye molecules but just transfer the organic pollutions from one phase to another, i.e. from wa- ter to another phase [3–8] . Therefore, there is an ur- gent demand for efficient and profitable method to eliminate these organic contaminants from the envi- ronment. Photo-catalysis as a method of treatment of wastewater in the presence of metal oxides is an excit- ing option for the detoxification of organic pollutants, whose mechanism has been broadly studied [1–10] . Acceleration in nanoscience and nano technol- ogy and the extension of new nanostructure ma- terial, nano-sensors, and micro-devices have been played a major role in the development of very ac- curate, sensitive, and reliable sensors. The expedi- tion for even smaller devices capable of nano-level imaging and controlling of nanomaterial, biological,