Adsorption of CO2 on heterostructure CdS(Bi2S3)/TiO2 nanotube photocatalysts and their photocatalytic activities in the reduction of CO2 to methanol under visible light irradiation

TiO2 nanotubes (TNTs) photocatalyst was synthesized by hydrothermal reaction, while the heterostructure CdS(or Bi2S3)/TiO2 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 CO2 to CH3OH under visible light irradiation and the performance for CO2 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 m2/g. The amounts adsorbed of CO2 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 CO2 on three photocatalysts can be well described by the Freundlich adsorption equation. The modification of Bi2S3 or CdS can enhance the visible light absorbance and photocatalytic performance of TNTs photocatalyst. The photocatalytic activity, the amounts adsorbed of CO2 and visible light absorption capability of Bi2S3-modified TNTs photocatalyst are all better than those of CdS-modified TNTs photocatalyst. Especially, the largest yield of methanol on TNTs photocatalyst modified by Bi2S3 under visible light irradiation over 5 h is 224.6 μmol/g, which was about 2.2 times as large as that of TNTs.

► CO2 can be reduced to methanol on modified TNTs heterostructure under visible light.
► The modification of Bi2S3 (CdS) can enhance the photocatalytic activity of TNTs.
► The photocatalytic activity of TNTs–Bi2S3 is better than that of TNTs–CdS.
► The adsorption isotherms of CO2 can be described by the Freundlich equation.
► The largest yield of methanol on TNTs–Bi2S3 was 2.2 times as large as that of TNTs.