Tuning the morphology, stability and photocatalytic activity of TiO2 nanocrystal colloids by tungsten doping
Graphical abstract
Introduction
In the past several decades, the efforts of scientists and technicians all over the world have realized the application of photocatalytic technology in air and water purification. It has been confirmed that almost all of organic pollutants dissolved in water can be completely mineralized into carbon dioxide, water and mineral acids by photocatalysts [1], [2]. TiO2 nanomaterials with wide bandgap are considered to be the most potential photocatalysts due to the unique size effect, surface effect, quantum effect, chemical stability and excellent photocatalytic activity.
During practical applications, both the photocatalytic efficiency and reusability should be considered. According to these requirements, the immobilized photocatalysts, such as TiO2 films supported on other substrates, are conveniently for reuse [3], [4]. However, the efficiency is usually restricted significantly by the limited catalyst surface area and mass transfer rate. In contrast, TiO2 nanoparticles usually show high photocatalytic efficiency due to the large surface area. However, it is very difficult for the powder-type photocatalysts to be separated from the purified water and reused. Although magnetic photocatalysts can be recovered easily from the suspension after treatment [5], [6], the complicated producing process makes the cost high.
The photocatalysis-membrane processes based on the hybridization of photocatalysis with membrane process can eliminate the conflict between the dispersion and recovery for the powder-type photocatalysts [7], [8]. To make better performance, the photocatalyst for the photocatalysis-membrane processes should combine the features of high dispersity, good stability and high photocatalytic activity. The colloidal photocatalyst shows a high potential for the application in photocatalysis-membrane process due to the high dispersity and good stability.
In the past decades, a lot of efforts have been devoted to improve the photocatalytic activity in UV range or visible range by metal ion doping, such as Fe3+, Cu2+, W6+, Cr6+, etc. [9], [10], [11], [12], [13], [14], [15]. However, the effects of metal ion doping on the dispersity and stability in solvent is still very interesting and worth to investigate.
Based on our previous research on the colloidal TiO2 nanocrystal suspension [16], [17], [18], we investigated herein the preparation of colloidal TiO2 nanocrystals with high dispersity and stability by tungsten ion doping. The effects of tungsten doping concentration on the dispersity and stability were discussed. And the photocatalytic activities were evaluated by the photocatalytic degradation of phenol. The results are encouraging that the tungsten doped TiO2 nanocrystal can possess the advantages of high dispersity in water and high UV-sensitive photocatalytic activity.
Section snippets
Materials
Titanium (IV) sulfate (Ti(SO4)2, CR) was provided by Shanghai Chemical Reagent Co. China. Aqueous ammonia solution (NH4OH, 25%, AR), aqueous hydrogen peroxide solution (H2O2, 30%, AR) and tungsten powder (AR) were purchased from Sinopharm Chemical Reagent Co. Ltd. All chemicals were used as received without further purification. Deionized water was used for solution preparation.
Preparation of tungsten doped TiO2 nanocrystal
Similar to the previous method synthesizing TiO2 nanocrystal [16], in a typical synthesis, 0.75 g of titanium (IV)
Results and discussion
Fig. 1 shows the TEM images of products with different W:Ti calculation molar ratio. For the pure TiO2 nanocrystals obtained by hydrothermal at 180 °C for 15 h, the length is about 34.2 nm, and the diameter is about 13.2 nm. With the increase of tungsten doping concentration, the shape of nanocrystals changed from rod-like to rectangular, and the aspect ratio of TW-0, TW-1, TW-2, TW-3 are 2.59, 1.76, 1.56 and 1.24, respectively, revealing the tungsten doping really affects the surface energy of the
Conclusions
Colloidal tungsten-doped TiO2 nanocrystals with high dispersity, stability and photocatalytic activity were synthesis by hydrothermal method. The analysis results reveal that the tungsten doping concentration has great effects on the morphology, zeta potential and photocatalytic activity of TiO2. The tungsten doped TiO2 combines the characters of high dispersity and high photocatalytic activity, which will be a promising candidate for the water purification in photocatalysis-membrane processes.
Acknowledgements
The authors acknowledge the supports of Shanghai Leading Academic Discipline Project (S30107), National Natural Science Foundation of China (51202138), Natural Science Foundation of Shanghai (12ZR1410500).
References (42)
- et al.
Int. J. Hydrogen Energy
(2007) - et al.
J. Hazard. Mater.
(2009) - et al.
Appl. Catal. B
(2011) - et al.
Appl. Catal. B
(2012) - et al.
Catal. Commun.
(2011) - et al.
J. Colloid Interface Sci.
(2008) - et al.
Appl. Surf. Sci.
(2012) - et al.
Acta Mater.
(2013) - et al.
Thin Solid Films
(2011) - et al.
Appl. Catal. B
(2010)