ABSTRACT
Over the past decades, CO2 greenhouse emission has been considerably increased, causing global warming and climate change. Indeed, converting CO2 into valuable chemicals and fuels is a desired option to resolve issues caused by its continuous emission into the atmosphere. Nevertheless, CO2 conversion has been hampered by the ultrahigh dissociation energy of C=O bonds, which makes it thermodynamically and kinetically challenging. From this prospect, photocatalytic approaches appear promising for CO2 reduction in terms of their efficiency compared to other traditional technologies. Thus, many efforts have been made in the designing of photocatalysts with asymmetric sites and oxygen vacancies, which can break the charge distribution balance of CO2 molecule, reduce hydrogenation energy barrier and accelerate CO2 conversion into chemicals and fuels. Here, we review the recent advances in CO2 hydrogenation to C1 and C2 products utilizing photocatalysis processes. We also pin down the key factors or parameters influencing the generation of C2 products during CO2 hydrogenation. In addition, the current status of CO2 reduction is summarized, projecting the future direction for CO2 conversion by photocatalysis processes.
ABSTRACT
A hollow core-shell potassium phosphomolybdate (KMoP)@cadmium sulfide (CdS)@bismuth sulfide (Bi2S3) Z-scheme tandem heterojunction is fabricated by a simple hydrothermal strategy and kept in a water bath to continue the reaction. At the same time, the ternary structure combined Keggin-type polyoxometalate with two photosensitive sulfide semiconductors to form a stable hollow core-shell heterojunction. KMoP@CdS@Bi2S3 with a narrow band gap of â¼ 1.2 eV also has excellent photothermal performance, which may further promote photocatalytic efficiency. The hollow core-shell KMoP@CdS@Bi2S3 tandem heterojunction shows excellent H2 production performance, CrVI reduction ability and photocatalytic degradation performance of highly toxic tetracycline (TC). Under visible light irradiation, the photocatalytic H2 generation rate of the KMoP@CdS@Bi2S3 tandem heterojunction reaches 831 µmol h-1, which is 103 times higher than that of pristine KMoP. The photocatalytic reduction efficiency of CrVI and degradation efficiency of TC are as high as 95.5 and 97.51%, â¼4 times higher than that of KMoP. The boosted photocatalytic performance can be ascribed to the formation of core-shell Z-scheme tandem heterojunctions favoring spatial charge separation and the narrow band gap, which extends the photoresponse to visible light/NIR regions. When TC and CrVI exist at the same time, the reduction efficiency of CrVI can be as high as 99.64% because the intermediate of TC degradation can promote the reduction of CrVI. In addition, the photocatalytic performance of the KMoP@CdS@Bi2S3 heterojunction remains nearly constant after 4 recycles, which indicates high stability. The design strategy may provide new insights for preparing other high-performance core-shell tandem heterojunction photocatalysts for solar energy conversion.
