Robust materials are needed for efficient energy-conversion technologies. Metal nanoparticle deposition on semiconductor nanocrystals produces charge-separating hybrid heterostructures that convert solar-to-potential energy. Semiconductors provide unmatched light absorption capability and metals collect charges (electrons) after light absorption. These semiconductor-metal heterostructures become red-ox-active upon illumination and remain red-ox-active after dark-storage for several hours (Banin et al. Angew. Chem., Int. Ed. 2010 , 49, 4878; Kamat J. Phys. Chem. C 2007 , 111, 2834). We are encapsulating semiconductor-metal hybrids within surface-functionalized mesoporous silica nanoparticles (MSNs) using a templated approach. The porous silica shell will provides protection against leaching, carrier self-quenching, and control over electron transfer rates.  For the templated approach, functional groups such as thiols are used as seeding points for CdSe growth.  To quantify the amount of thiols, a colorimetric method based on Ellman's reagent was used to compare internally- with externally-thiol functionalized MSNs and non-functionalized MSNs.  Success of this research will allow the determination of the number of functional thiol groups and acquire better synthetic control of final photocatalyst nanocomposites. We used Ellman's reagent, a colorimetric method, to create a calibration curve using cysteine and with that performed quantification of thiols on internally- and externally-thiol functionalized and non-functionalized MSNs. Ellman's reagent is a versatile water-soluble compound for quantifying free sulfhydryl groups in solution. It reacts with a free sulfhydryl group to yield a mixed disulfide and 2-nitro-5-thiobenzoic acid (NTB), a measurable yellow colored product at 412nm. Ellman's reagent is very useful as a free thiol assay reagent due to its high distinction for -SH groups at neutral pH, high molar extinction coefficient and short reaction time. We compared the outcome of applying an acid treatment versus a calcination process to newly synthesized MSNs.

Quantification of surface thiol functional groups for templating semiconductor photocatalysts in mesoporous silica

245th National Meeting (2013)

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