Adsorption of CO 2 on heterostructure CdS(Bi 2S 3)/TiO 2 nanotube photocatalysts and their photocatalytic activities in the reduction of CO 2 to methanol under visible light irradiation

Abstract

TiO 2 nanotubes (TNTs) photocatalyst was synthesized by hydrothermal reaction, while the heterostructure CdS(or Bi 2S 3)/TiO 2 nanotube photocatalysts were prepared by direct precipitation reaction. The photocatalysts were studied by TEM, EDX, XRD and XPS to characterize its structure and chemical compostion. Their photocatalytic activities for reducing CO 2 to CH 3OH under visible light irradiation and the performance for CO 2 adsorption were also investigated. The results indicate that the synthetical TNTs photocatalyst is almost in good and uniform shapes, with the diameter of 17.77 nm and the surface area of 99.57 m 2/g. The amounts adsorbed of CO 2 on TNTs are 0.269 mmol/g at 1 atm pressure and 298 K,which are larger than those on other two heterostructure photocatalysts. The adsorption isotherms of CO 2 on three photocatalysts can be well described by the Freundlich adsorption equation. The modification of Bi 2S 3 or CdS can enhance the visible light absorbance and photocatalytic performance of TNTs photocatalyst. The photocatalytic activity, the amounts adsorbed of CO 2 and visible light absorption capability of Bi 2S 3-modified TNTs photocatalyst are all better than those of CdS-modified TNTs photocatalyst. Especially, the largest yield of methanol on TNTs photocatalyst modified by Bi 2S 3 under visible light irradiation over 5 h is 224.6 μmol/g, which was about 2.2 times as large as that of TNTs.