Synthesis and characterisation of materials for photoelectrochemical applications

Abstract

The preparation of visible light driven photocatalysts for photocatalytic water splitting has been achieved by a CO₂ free, low cost and simple novel method. Combination of peroxide based route with organic free solvent and titanium nitride, carbon free precursor and air and moisture stable, would be useful. Clear red-brown solution of titanium peroxo species was obtained by dissolution of TiN in H₂O₂ and HNO₃ acid at room temperature without stirring. The resultant red brown solution is then used as a titanium solution precursor for yellow amorphous and yellow crystalline TiO₂ synthesis. Visible light photoactivity of the samples was evaluated by photooxidation of methylene blue and photoreduction producing hydrogen from water splitting. The high surface area of yellow amorphous TiO₂ exhibits an interesting property of being both surface adsorbent and photoactive under visible light for photodecolourisation of aqueous solution of methylene blue. However, it might not appropriate for hydrogen production. Nanoparticulate yellow crystalline TiO₂ with defect disorder of Ti³⁺ and oxygen vacancies depending upon synthesis conditions has been characterised by ESR, XPS, CHN analysis and SQUID. Single phase rutile can be produced at low temperature. It is stable at high temperature and the red shift of absorption edge increases with the treatment temperature. Yellow crystalline TiO₂ exhibits an interesting property of being photoactive under visible light. The best photocatalytic performance was observed for 600°C calcination, probably reflecting a compromise between red shift and surface area with changing temperature. Moreover, overall water splitting into hydrogen and oxygen might be obtained by using this material even in air atmosphere. Photoactivity can be improved by testing under anaerobic atmosphere and/or adding sacrificial agent. Quantum efficiency under visible light is still low but comparable to other reports. The maximum efficiency varies from 0.03 % to 0.37 % for hydrogen production and from 0.03 % to 0.12 % for oxygen production, depending on photon energy and sacrificial agents.