Here we have used Raman spectroscopy to investigate molecular level changes in the zeolitic imidazolate framework ZIF-8 (a prototypical zeolite-like porous metal organic framework) as a function of temperature. Temperature dependent Raman spectra suggest that at low temperature the softening of the C-H stretching frequencies is due to the decrease in steric hindrance between the methyl groups of methyl imidazole. The larger separation between the methyl groups opens the window for increased nitrogen and methane uptake at temperatures below 153 K. The appearance of Raman bands at 2323 cm(-1) and 2904 cm(-1) at or below 153 K in ZIF-8 are characteristic signatures of the adsorbed nitrogen and methane gases respectively. Nanoscale ZIF-8 uptakes more molecules than bulk ZIF-8, and as a result we could provide evidence for encaged CO2 at 203 K yielding its Raman mode at 1379 cm(-1).

Photocatalytic reduction of carbon dioxide (CO) by visible light has the potential to mimic plant photosynthesis and facilitate the renewable production of storable fuels. Accomplishing desirable efficiency and selectivity in artificial photosynthesis requires an understanding of light-driven pathways on photocatalyst surfaces. Here, we probe with single-nanoparticle spatial resolution the dynamics of a plasmonic silver (Ag) photocatalyst under conditions of visible light-driven CO reduction. In situ surface-enhanced Raman spectroscopy captures discrete adsorbates and products formed dynamically on single photocatalytic nanoparticles, most prominent among which is a surface-adsorbed hydrocarboxyl (HOCO*) intermediate critical to further reduction of CO to carbon monoxide (CO) and formic acid (HCOOH). Density functional theory simulations of the captured adsorbates reveal the mechanism by which plasmonic excitation activates physisorbed CO leading to the formation of HOCO*, indicating close interplay between photoexcited states and adsorbate/metal interactions.

The ability of plasmonic nanoparticles to harness visible light can be being combined with their catalytic activity to drive photocatalytic transformations. This Review introduces the promise of this new class of photocatalysts for fulfilling the quest for sunlight-driven recycling of CO 2 into transportable liquid fuels. We discuss the prospects and challenges of such an approach. Despite considerable advances, a selective, stable, and efficient CO 2 reduction reaction (CO 2 RR) catalyst has been elusive. These open challenges may be addressable by the strategic utilization of plasmonic light excitation. Plasmonic catalysts have exhibited the ability to drive a rich milieu of CO 2 RR processes under visible light excitation. At this stage, improved mechanistic understanding and reaction control are needed. To motivate rational design of photocatalytic materials and processes by a future generation of researchers, we suggest potential pathways by which plasmonic-assisted CO 2 RR can take place. We describe unique physical and chemical aspects of plasmonic catalysis, some of which may allow modulation of CO 2 RR product selectivity in favor of higher hydrocarbons. The intertwining of the photophysics of plasmon resonances and chemistry of CO 2 RR creates a wide-open space for fundamental inquiry and technological development. Whether the future of artificial photosynthesis is "plasmonic" will be dictated by scientific understanding and engineering advances accomplished in the coming decade.

We herein report an unusual CO(2) adsorption behavior in a fluoro-functionalized MOF {[Zn(SiF(6))(pyz)(2)]·2MeOH}(n) (1) with a 1D channel system, which is made up of pyrazine and SiF(6)(2-) moieties. Surprisingly, desolvated 1 (1') adsorbs higher amounts of CO(2) at 298 K than at 195 K, which is in contrast to the usual trend. Combined Raman spectroscopic and theoretical studies reveal that slanted pyrazine rings in 1' with an angle of 17.2° with respect to the (200) Zn(II)-Si plane at low temperature block the channel windows and thus reduce the uptake amount.

Surface-enhanced Raman spectroscopy (SERS) has gained paramount importance in the recent past due to its widespread applications in biodetection, monitoring chemical reactions, small molecule protein interactions, etc. It is believed that SERS is a distance-dependent phenomenon and is effective within 1 nm from the nanoparticle surface. In this work, we have investigated this distance dependence of SERS as a function of nanoparticle size. Earlier attempts have made use of flexible separators, like DNA and chemical molecules, between nanoparticle and analyte to vary the distance. We have used silica coating to vary the distance, without ambiguity, of the analyte from the silver nanoparticle surface. Our results suggest that SERS is observed up to a distance of 1 nm for 20 nm silver nanoparticles juxtaposed to 5 nm in the case of 90 nm silver nanoparticles. This is due to large scattering cross sections and increased radiative damping in the case of the larger nanoparticles. This study gives direct correlation between the size of nanoparticles and distance probed through SERS which would aid in designing nanoparticle system for various applications and analytes in the future.