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. 2019 Jul 12;9(38):21660-21666.
doi: 10.1039/c9ra03435h. eCollection 2019 Jul 11.

Systematic study of TiO2/ZnO mixed metal oxides for CO2 photoreduction

Warren A Thompson  1 , Alberto Olivo  2 , Danny Zanardo  3 , Giuseppe Cruciani  4 , Federica Menegazzo  3 , Michela Signoretto  3 , M Mercedes Maroto-Valer  1
Affiliations

Systematic study of TiO2/ZnO mixed metal oxides for CO2 photoreduction

Warren A Thompson et al. RSC Adv. .

Abstract

A two component three degree simplex lattice experimental design was employed to evaluate the impact of different mixing fractions of TiO2 and ZnO on an ordered mesoporous SBA-15 support for CO2 photoreduction. It was anticipated that the combined advantages of TiO2 and ZnO: low cost, non-toxicity and combined electronic properties would facilitate CO2 photoreduction. The fraction of ZnO had a statistically dominant impact on maximum CO2 adsorption (β 2 = 22.65, p-value = 1.39 × 10-4). The fraction of TiO2 used had a statistically significant positive impact on CO (β 1 = 9.71, p-value = 2.93 × 10-4) and CH4 (β 1 = 1.43, p-value = 1.35 × 10-3) cumulative production. A negative impact, from the interaction term between the fractions of TiO2 and ZnO, was found for CH4 cumulative production (β 3 = -2.64, p-value = 2.30 × 10-2). The systematic study provided evidence for the possible loss in CO2 photoreduction activity from sulphate groups introduced during the synthesis of ZnO. The decrease in activity is attributed to the presence of sulphate species in the ZnO prepared, which may possibly act as charge carrier and/or radical intermediate scavengers.

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Conflict of interest statement

There are no conflicts to declare.

Figures

Fig. 1
Fig. 1. Overview of the experimental setup used for the MO photocatalyst mixture CO2 photoreduction tests (not to scale). Pipe lines in red were heated with a temperature controlled heating rope.
Fig. 2
Fig. 2. (a) Tauc plots for mixed MO photocatalysts (b) impact of increasing fraction of TiO2 on band gap.
Fig. 3
Fig. 3. XRD comparison of mixed MO photocatalysts on SBA-15 support.
Fig. 4
Fig. 4. (a) N2 adsorption isotherms of the mixed MO photocatalysts (b) impact of increasing fraction of TiO2 on BET specific surface area.
Fig. 5
Fig. 5. Impact of increasing fraction of TiO2 on of maximum CO2 adsorption.
Fig. 6
Fig. 6. Impact of increasing fraction of TiO2 on (a) CO cumulative production and (b) CH4 cumulative production.
Fig. 7
Fig. 7. XRD comparison of TiO2 and ZnO. A = anatase (TiO2 phase), Z = zincite (ZnO phase) and S = Zn3O(SO4)2.
Fig. 8
Fig. 8. SEM/EDX of MO1–MO7 and the SBA-15 support used. Zinc mapped on the left and sulphur on the right.
Fig. 9
Fig. 9. Impact of increasing fraction of TiO2 on approximated sulphur weight% from SEM/EDX.
Fig. 10
Fig. 10. Energy levels scheme for the proposed mechanism of sulphates as hole scavengers.
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