Mechanochemical Synthesis of Visible Light Sensitive Titanium Dioxide Photocatalyst

Jan Šubrt,Nataliya Murafa,Vlasta Brezová,Lórant Szatmáry,Maria J Diánez-Millán,Jose M Criado,Luis A Pérez-Maqueda

doi:10.1155/2011/156941

Abstract

Phase transition of anatase nanoparticles into the phases TiO2-II and rutile under grinding was studied. The addition of ammonium carbamate to the reaction mixture inhibits the phase conversion and the cold welding of particles. The UV-visible absorption spectrum showed narrowing the band gap width after grinding with an ammonium carbamate additive resulting in shift of the light absorption of the ground sample towards the visible region. By EPR, intensive formation of OH•radical at irradiation of the sample with both UV (λ> 300 nm) and visible (λ> 435 nm) light was observed. High photocatalytic activity of the ground sample in visible light region was demonstrated also by measurement of kinetics of the photocatalytic decomposition of 4-chlorophenol.

Highlights

Titanium dioxide attracted a great attention since Fujishima and Honda discovered in 1972 the photocatalytic splitting of water on TiO2 electrode [1]
The comparison of the phase composition and specific surface data of samples “1.6 h” and “1.6 h AC” in Table 1 suggest that ammonium carbamate inhibits the phase conversion and the cold welding of particles during the grinding
The results show that after grinding is carried out with an additive like ammonium carbamate that behaves as an ammonia supplier, the light absorption edge moves to the visible light region

Summary

Introduction

Titanium dioxide attracted a great attention since Fujishima and Honda discovered in 1972 the photocatalytic splitting of water on TiO2 electrode [1]. TiO2 is an efficient photocatalyst, but UV light is necessary for its activation owing to a rather wide band gap energy (∼3.2 eV). In order to utilize the visible (solar) light efficiently for the photocatalytic reactions, titanium dioxide has to be modified in order to lower the energy necessary for excitation of the electron into the conduction band. The enhanced photoactivity in the visible light region is often compensated by sinking the activity at the UV light irradiation; the overall photoactivity of such material at sun light is often significantly lower in comparison to highly effective photocatalysts like, for example, DEGUSSA AEROXIDE TiO2 P 25. We observed that the anatase → rutile phase transformation of nanocrystalline anatase at the same grinding conditions proceeds significantly more slowly and the products are yellow coloured

Experimental

Results and Discussion

Conclusions