SURFACE CHARACTERISTICS OF ZNS NANOCRYSTALLITES RELATING TO THEIR PHOTOCATALYSIS FOR CO2 REDUCTION

Hexagonal ZnS nanocrystallites (ZnS-DMF(OAc); ca. 2 nm in diameter) pr epared in N,N-dimethylformamide (DMF) using Zn(CH3COO)(2). 2H(2)O (Zn( OAc)(2). 2H(2)O) as the Zn2+ source and H2S as the sulfur source catal yzed selective photoreduction of CO2 to HCOO- in the presence of triet hylamine as an electron donor. When excess zinc acetate was added to t he system, the efficiency increased while still keeping the product se lectivity. The photocatalytic behavior of ZnS-DMF(OAc) is in contrast to that of ZnS-DMF(ClO4) prepared using Zn(ClO4)2 . 6H(2)O as the Zn2 source, where both HCOO- and CO were produced, especially when excess zinc perchlorate was added into the system. FT-IR analysis of the ZnS -DMF(OAc) system revealed the presence of SH groups on the surface, ex plaining the gradual growth of the size with the addition of excess zi nc acetate into the system. Extended X-ray absorption fine structure a nalysis revealed the correlation between the photocatalysis and the mi croscopic surface structure change of the ZnS nanocrystallites induced by the addition of Zn2+ to the nanocrystallite systems. The intimatel y interacting acetate ions to Zn atoms should prevent the formation of sulfur vacancies as catalytic sites of CO production, contributing to the enhanced photocatalytic activity for production of HCOO- due to t he formation of the DMF-coordinated nanocrystallites.