Abstract

As populations grow, global energy consumption in the next 30 years is predicted to rise by nearly 50%. Nowadays and many years before, the most energy worldwide is provided by fossil fuel which leads to severe pollution and contributes to the greenhouse effect. Hydrogen is the most ideal alternative clean energy, but currently, there is no significant hydrogen production from renewable sources. Hence, there is an urgent need for the development of new photocatalysts which will allow a water splitting for hydrogen production. The photocatalytic water splitting using TiO₂ offers a promising approach for clean, low-cost, and environmentally friendly production of hydrogen as a sustainable fuel. This paper reviews some recently used methods of synthesis such as hydrothermal, rapid breakdown anodization method, impregnation method, and sol-gel synthesis for the preparation of modified TiO₂ materials. These methods of synthesis provide the production of ultra-thin mesoporous TiO₂ nanosheets, nanorods, and nanotubes as well as heterojunction structures. Some investigations show that introduction of Ti³⁺ atomic defects is beneficial for the photocatalytic water splitting for hydrogen generation. Some progress has been achieved by hetero coupling the two or more semiconductors. There is experimental evidence that in the presence of alcohol as a sacrificial agent, H₂ production rates decreased from a higher number of hydroxyl groups i.e. in order 3>2>1. The H₂ generation is also larger when TiO₂ is modified with the addition of small quantity of metal nanoparticles such as Pt, Pd, and Ni. One study has shown that the samples sensitised with Pt nanoparticles were superior to Pd and Ni modified TiO₂, the other has shown that the co-catalyst activity followed the order Pd>Pt≈Au.

Keywords: Photocatalysis; Water splitting; Hydrogen production; Modified TiO₂; Nanoparticles

Abbreviations: °C: Degrees Celsius; NPs : Nanoparticles; NTs: Nanotubes; EC: European Commission; IRENA: International Renewable Energy Agency; IPCC: Intergovernmental Panel on Climate Change; EIA: Energy Information Administration; CB: Conduction Band; VB: Valance Band; CBE: Conduction Band Energy; E_g: Band Gap Energy; ΔG: Gibbs Free Energy