Sustainable α Fe2O3/g-C3N4 catalyst for high-pressure CO2 photoreduction

Nowadays the world economy is still based on the use of oil as an energy vector and the massive CO2 emissions have become an enormous problem. When captured, CO2 can be converted into more valuable product and photoreduction of CO2 represent one of the most promising ways. One main problem is the very low conversion of the reaction, and Z-scheme heterojunction seems to be a possible solution to increase the catalyst efficiency. To make a Z-scheme possible, the two semiconductors should be stable against oxidation and reduction, such as hematite. This, together with the non-toxicity of iron oxides and the relatively small bandgap make it an excellent candidate for the exploitation of visible sunlight [1]. The fast recombination rate and the low energy of the conduction band, which represents the two main drawbacks of hematite, can be minimized exploiting a Z-scheme strategy [2] (Figure 1). Graphitic carbon nitride (g-C3N4) was directly synthetized by carrying out a sulphuric acid treatment [3] and α Fe2O3/g-C3N4 have been later synthetized by in situ precipitation of FeCl3 followed by a calcination at 350°C. Synthetized catalysts have been characterized though XRD, BET, DRS, SEM/TEM analysis and have been tested in a high-pressure setup under 18 bar of CO2. It has been found that a very high loading of hematite causes a decreasing of the productivity of the catalysts. Furthermore, tests demostrated that the contact between the two semiconductors of a Z-scheme is a key parameter for the overall activity of a such type of catalyst. [1] H. Guo, M. Chen, Q. Zhong, Y. Wang, W. Ma, J. Ding, J. CO2 Util. 33 (2019) 233–241 [2] Z. Jiang, W. Wan, H. Li, S. Yuan, H. Zhao, P.K. Wong, Adv. Mater. 30 (2018) 1706108 [3] J. Xi, H. Xia, X. Ning, Z. Zhang, J. Liu, Z. Mu, S. Zhang, P. Du, X. Lu, Small 15 (2019) 1902744