Generation of hydrogen from water by using a photocatalyst and solar light is a clean and sustainable way to harvest energy. However the photocatalysts developed so far have limited efficiencies under visible radiation, due to lack of suitable photophysical properties. Band engineering of wide band gap photocatalysts is a promising approach to develop highly efficient, visible light driven materials. NaTaO 3 is one of the most efficient photocatalysts for the water splitting reaction under UltraViolet (UV) radiation. NaTaO 3 has large overpotentials and thus allows sufficient space for the modification of the band structure. I would like to express my deep gratitude to Professor Chen Zhong for his invaluable guidance, constant support and encouragement during past four years. I am grateful to Dr. Jianwei Zheng from Institute of High Performance Computing for his invaluable advice, numerous discussions and generous help in the computational aspects of the project. I am thankful to Dr Martin Schreyer for fruitful discussions and help on the Rietveld refinements of the X-ray Data. Prof Alex Orlov (Stony Brook, NY, USA), Dr. Simo Pehkonen (CEWIC, Finland) has provided valuable suggestions and advice on this work. This work would not have been possible without the help of Gou Jun, Irene, Sithu, Dr. Zyvd, Swee Kaun, Mastura, Patrik, and Poh Tin. I thank these fine technicians for their timely help on the experimental operations. I further thank Stevin, Yan Yee and Tom for their assistance on the analysis and operations of XRD and TEM. I thank Institute of High Performance Computing (IHPC), and Institute of Chemical and Industrial Research (ICES) for the facilities provided for this work. The countless discussions and brain storming sessions with my colleagues,