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Abstract
Silicon constitutes 28% of the earth's mass. Its high abundance, lack of toxicity and low cost coupled with its electrical and optical properties, make silicon unique among the semiconductors for converting sunlight into electricity. In the quest for semiconductors that can make chemicals and fuels from sunlight and carbon dioxide, unfortunately the best performers are invariably made from rare and expensive elements. Here we report the observation that hydride-terminated silicon nanocrystals with average diameter 3.5 nm, denoted ncSi:H, can function as a single component heterogeneous reducing agent for converting gaseous carbon dioxide selectively to carbon monoxide, at a rate of hundreds of μmol h−1 g−1. The large surface area, broadband visible to near infrared light harvesting and reducing power of SiH surface sites of ncSi:H, together play key roles in this conversion. Making use of the reducing power of nanostructured hydrides towards gaseous carbon dioxide is a conceptually distinct and commercially interesting strategy for making fuels directly from sunlight.
Highlights
Silicon constitutes 28% of the earth’s mass
Subsequent extraction of the ncSi from the SiO2 surrounding matrix is accomplished using aqueous HF, and the product is a brown powder comprised of ncSi:H (Fig. 1a)
Scanning electron microscopy (SEM) investigations of the ncSi:H samples show they consist of aggregates of nanocrystals with textural nanoporosity (Fig. 1b), which is consistent with the large surface area measured
Summary
Silicon constitutes 28% of the earth’s mass. Its high abundance, lack of toxicity and low cost coupled with its electrical and optical properties, make silicon unique among the semiconductors for converting sunlight into electricity. Hydride functionalized silicon nanocrystals have not previously been imagined as a reagent for the heterogeneous gas-phase reduction of CO2 To amplify on the former, the first step in the solution phase hydrosilation of SiH bonds in molecular silyl hydrides with CO2 has been reported to involve the formation of a formoxysilane SiOCHO group containing a SiO bond[17]. We document the ability of surface hydride functionalized silicon nanocrystals, denoted ncSi:H, to selectively reduce gaseous CO2 to CO using the heat and light from the sun Compared with this gas-phase heterogeneous reduction of CO2 the aforementioned liquid-phase homogenous hydrogenation of CO2 has several disadvantages that include: (i) solubility, diffusion and temperature limitations of CO2 in the liquid-phase, (ii) requirement of a catalyst, (iii) recovery and regeneration of catalysts from the liquid-phase and (iv) the scalability of the process. If the reducing SiH surface of ncSi:H could be maintained under reaction conditions the reduction of CO2 could potentially be made catalytic
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