Solar-driven production of fuels such as hydrogen, hydrocarbons, and ammonia using semiconducting photocatalysts has the potential to be a sustainable alternative to current chemical processes. In ...recent years, silicon (Si) nanostructures have been recognized as a promising photocatalyst for hydrogen generation and organic oxidation reactions owing to its abundance, biocompatibility, and cost. While bulk Si has been studied extensively, on the nanoscale, plenty of opportunities exist to understand and engineer optimally performing Si photocatalysts. This perspective will highlight key results on the use of Si nanostructures for photocatalytic H2 production, CO2 reduction via light and heat-driven chemical looping, and current challenges in utilizing it for fuel-forming reactions. A brief guide on how these challenges can be addressed in the future and other unexplored questions that remain in the field are also discussed.
Display omitted
Catalysis; Energy systems
We explore the dynamics of blue emission from dodecylamine and ammonia functionalized silicon nanocrystals (Si NCs) with average diameters of ∼3 and ∼6 nm using time-resolved photoluminescence (TRPL) ...spectroscopy. The Si NCs exhibit nanosecond PL decay dynamics that is independent of NC size and uniform across the emission spectrum. The TRPL measurements reveal complete quenching of core state emission by a charge transfer state that is responsible for the blue PL with a radiative recombination rate of ∼5 × 10(7) s(-1). A detailed picture of the charge transfer state emission dynamics in these functionalized Si NCs is proposed.
In the presence of large excesses of borohydride salts, gold monolayer protected-clusters can be grown to larger sizes simply by controlling the amount of reducing agent added to smaller clusters. In ...addition, gold monolayer clusters can be used as catalysts for reduction reactions by sodium borohydride; results suggest such catalysts have sterically constrained active sites.
Silicon nanocrystals (SiNCs) have received much attention because of their exquisitely tunable photoluminescent response, biocompatibility, and the promise that they may supplant their CdSe quantum ...dot counterparts in many practical applications. One attractive strategy that promises to extend and even enhance the utility of SiNCs is their incorporation into NC/polymer hybrids. Unfortunately, methods employed to prepare hybrid materials of this type from traditional compound semiconductor (e.g., CdSe) quantum dots are not directly transferable to SiNCs because of stark differences in surface chemistry. Herein, the preparation of chemically resistant SiNC/polystyrene hybrids exhibiting exquisitely tunable photoluminescence is reported and material processability is demonstrated by preparing micro and nanoscale architectures.
Highly luminescent, solution processable silicon nanocrystals/polystyrene hybrid materials are synthesized using size‐independent radical‐initiated hydrosilylation. Combining the properties of nanocrystals with polymer significantly increases solubility and processability, provides the opportunity to fabricate uniform nano‐ and microscale architectures, and renders silicon particles chemically resistant to prolonged exposure to strongly basic conditions.
We report on the oxidative stability of thiol-passivated Au monolayer-protected clusters (MPCs) made via a modified Brust−Schiffrin method. A sequential oxidation of the anchored thiol groups to ...disulfide and sulfonate groups and the oxidation of Au atoms to Au3+ species is observed upon exposure of Au MPCs to air in the presence of halide anions. In addition, the average nanoparticle size grows via aggregation of the MPCs, leading eventually to partial oxidation of the Au MPCs and precipitation of the remaining nanoparticles from solution or to complete oxidation of the gold atoms at high halide concentrations. These results show that Au MPCs are prone to oxidation in air in the presence of halide anions, and therefore, particles made using phase transfer reagents such as tetraoctylammonium bromide must be thoroughly removed to avoid particle size growth, oxidation, and precipitation of the Au MPCs. In addition, for biological applications involving Au MPCs, care must be taken to ensure that oxidation of MPCs in air is not problematic when working in media containing halide anions.
Dithiolate ligands based on (±)-α-lipoic acid derivatives have been investigated as ligands for both Au monolayer-protected clusters (MPCs) and mixed alkanethiol/dithiolate Au MPCs. The oxidative and ...thermal stability of the MPCs were investigated by a combination of UV−vis spectroscopy, TEM, and 1H NMR experiments. Results show that the dithiolate-protected MPCs are much more prone to oxidation by oxygen under ambient conditions than their alkanethiolate-protected MPC analogues; in addition, the Au core of the dithiolate-protected Au MPCs could be etched by KCN at much faster rates than both alkanethiolate-protected and mixed monolayer MPCs. These results suggest that strategies to increase ligand−metal interactions by incorporating more thiolate linkers into the ligand must also take into account the packing efficiency and/or stability of such ligands on the metal surface, which can make them much more prone to oxidation under ambient conditions.
Hybrid materials consisting of covalently linked non‐toxic silicon nanocrystals and polystyrene are synthesized by J. G. C. Veinot and co‐workers. These materials exhibit a strong luminescent ...response throughout the visible and NIR spectral regions and are chemically resistant. Marrying the properties of silicon nanocrystals with polymers like polystyrene significantly increases their solubility and processability, thus providing the opportunity to fabricate robust nano‐ and microscale architectures that could find application in a variety of optical applications.
The search for new plasmonic materials that are low‐cost, chemically and thermally stable, and exhibit low optical losses has garnered significant attention among researchers. Recently, metal ...nitrides have emerged as promising alternatives to conventional, noble‐metal‐based plasmonic materials, such as silver and gold. Many of the initial studies on metal nitrides have focused on computational prediction of the plasmonic properties of these materials. In recent years, several synthetic methods have been developed to enable empirical analysis. This review highlights synthetic techniques for the preparation of plasmonic metal nitride nanoparticles, which are predominantly free‐standing, by using solid‐state and solid–gas phase reactions, nonthermal and arc plasma methods, and laser ablation. The physical properties of the nanoparticles, such as shape, size, crystallinity, and optical response, obtained with such synthetic methods are also summarized.
Standout stability: The search for plasmonic materials that are low‐cost, chemically and thermally stable, and exhibit low optical losses has attracted significant attention. Among new materials, plasmonic transition‐metal nitride nanostructures are promising non‐noble‐metal alternatives. Herein, new synthetic techniques for the preparation of these materials are summarized.
PDF
