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ChemSusChem ; 2020 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-32871053


Facilitating the charge separation of semiconductor photocatalysts to increase the photocatalytic CO2 reduction activity has become a great challenge for sustainable energy conversion. Herein, the surface halogen-modified defect-rich Bi2 WO6 nanosheets have been successfully prepared to address the aforementioned challenge. Importantly, the modification of surface with halogen atoms is beneficial for the adsorption and activation for CO2 molecules and charge separation. These properties have been analyzed by experimental and theoretical methods. DFT calculations revealed that the modification of the Bi2 WO6 surface with Br atoms can decrease the formation energy of the *COOH intermediate, which accelerates CO2 conversion. All halogen-modified defect-rich Bi2 WO6 nanosheets showed an enhanced photocatalytic CO2 reduction activity. Specifically, Br-Bi2 WO6 exhibited the best CO generation rate of 13.8 µmol g-1 h-1 , which is roughly 7.3 times as high as the unmodified defect-rich Bi2 WO6 (1.9 µmol g-1 h-1 ). Moreover, in the presence of a cocatalyst (cobalt phthalocyanine) and a sacrificial agent (triethanolamine), Br-Bi2 WO6 exhibited an even further improved CO generation rate of 187 µmol g-1 h-1 . This finding provides a new approach to optimize the CO2 reduction pathway of semiconductor photocatalysts, which is beneficial to develop highly efficient CO2 reduction photocatalysts.

J Phys Chem Lett ; : 4990-4997, 2020 Jun 12.
Artigo em Inglês | MEDLINE | ID: mdl-32498513


Polar surfaces of ionic crystals are of growing technological importance, with implications for the efficiency of photocatalysts, gas sensors, and electronic devices. The creation of ionic nanocrystals with high percentages of polar surfaces is an option for improving their efficiency in the aforementioned applications but is hard to accomplish because they are less thermodynamically stable and prone to vanish during the growth process. Herein, we develop a strategy that is capable of producing polar surface-dominated II-VI semiconductor nanocrystals, including ZnS and CdS, from copper sulfide hexagonal nanoplates through cation exchange reactions. The obtained wurtzite ZnS hexagonal nanoplates have dominant {002} polar surfaces, occupying up to 97.8% of all surfaces. Density functional theory calculations reveal the polar surfaces can be stabilized by a charge transfer of 0.25 eV/formula from the anion-terminated surface to the cation-terminated surface, which also explains the presence of polar surfaces in the initial Cu1.75S hexagonal nanoplates with cation deficiency prior to cation exchange reactions. Experimental results showed that the HER activity could be boosted by the surface polarization of polar surface-dominated ZnS hexagonal nanoplates. We anticipate this strategy is general and could be used with other systems to prepare nanocrystals with dominant polar surfaces. Furthermore, the availability of colloidal semiconductor nanocrystals with dominant polar surfaces produced through this strategy opens a new avenue for improving their efficiency in catalysis, photocatalysis, gas sensing, and other applications.