Engineering topics
Publications and source records attributed to Bren, Kara L..
Combining a molecular thiomolybdate cluster, [Mo 3 S 13 ] 2− , with cadmium selenide quantum dots capped with amphiphilic ligands results in a highly active photocatalytic system for the production of hydrogen under visible light irradiation.
Living bio-nano systems for artificial photosynthesis are of growing interest. Typically, these systems use photoinduced charge transfer to provide electrons for microbial metabolic processes, yielding a biosynthetic solar fuel. Here, we demonstrate an entirely different approach to constructing a living bio-nano system, in which electrogenic bacteria respire semiconductor nanoparticles to support nanoparticle photocatalysis. Semiconductor nanocrystals are highly active and robust photocatalysts for hydrogen (H 2 ) evolution, but their use is hindered by the oxidative side of the reaction. In this system, Shewanella oneidensis MR-1 provides electrons to a CdSe nanocrystalline photocatalyst, enabling visible light-driven H 2 production. Unlike microbial electrolysis cells, this system requires no external potential. Illuminating this system at 530 nm yields continuous H 2 generation for 168 h, which can be lengthened further by replenishing bacterial nutrients.
Metalloenzymes are remarkable for facilitating challenging redox transformations with high efficiency and selectivity. In the area of alternative energy, scientists aim to capture these properties in bioinspired and engineered biomolecular catalysts for the efficient and fast production of fuels from low-energy feedstocks such as water and carbon dioxide. In this short review, efforts to mimic biological catalysts for proton reduction and carbon dioxide reduction are highlighted. Two important recurring themes are the importance of the microenvironment of the catalyst active site and the key role of proton delivery to the active site in achieving desired reactivity. As a result, perspectives on ongoing and future challenges are also provided.
Here, a system for visible light-driven hydrogen production from water is reported. This system makes use of a synthetic mini-enzyme known as a mimochrome (CoMC6*a) consisting of a cobalt deuteroporphyrin and two attached peptides as a catalyst, [Ru(bpy) 3 ] 2+ (bpy = 2,2'-bipyridine) as a photosensitizer, and ascorbic acid as a sacrificial electron donor. The system achieves turnover numbers (TONs) up to 10,000 with respect to catalyst and optimal activity at pH 7. Comparison with related systems shows that CoMC6*a maintains the advantages of biomolecular catalysts, while exceeding other cobalt porphyrins in terms of total TON and longevity of catalysis. Herein, we lay groundwork for future study, where the synthetic nature of CoMC6*a will provide a unique opportunity to tailor proton reduction chemistry and expand to new reactivity.
Not provided.
A photocatalytic hydrogen (H 2 ) production system is reported using glutathione (GSH)-capped CdSe QDs with a cobalt precatalyst, yielding 130 000 mol H 2 per mol cobalt over 48 hours. Analysis of the reaction mixtures after catalysis indicates that the active catalyst is a labile complex of cobalt and GSH formed in situ.
Colloidal semiconducting nanocrystals (NCs) are powerful elements of a photocatalytic system useful for enabling a variety of chemical transformations owing to their strong light-absorbing properties and high degree of size-, shape-, and composition-tunability. Key to their utility is our understanding of the photoinduced charge transfer processes required for these photochemical transformations. This Perspective will focus on the implementation of semiconductor NCs for photochemical fuel formation. Three general system designs for photocatalytic proton reduction using semiconductor NCs will be reviewed: metal–semiconductor heterostructures, NC photosensitizers with molecular catalysts, and hydrogenase-based systems. Additionally, other relevant reactions toward solar fuel targets, such as CO 2 and N 2 reductions with NCs, will also be highlighted. Illustrating the versatile roles that NCs can play in light-driven chemical reactions, advances made toward NC-catalyzed organic transformations will be discussed. Finally, we will share a few concluding thoughts and perspectives on the future of the field, with a focus on goals toward improving and implementing NC-based technologies for solar fuel development.
Abstract Efforts to drive catalytic reactions with light, inspired by natural processes like photosynthesis, have a long history and have seen significant recent growth. Successfully engineering systems using biomolecular and bioinspired catalysts to carry out light‐driven chemical reactions capitalizes on advantages offered from the fields of biocatalysis and photocatalysis. In particular, driving reactions under mild conditions and in water, in which enzymes are operative, using sunlight as a renewable energy source yield environmentally friendly systems. Furthermore, using enzymes and bioinspired systems can take advantage of the high efficiency and specificity of biocatalysts. There are many challenges to overcome to fully capitalize on the potential of light‐driven biocatalysis. In this mini‐review, we discuss examples of enzymes and engineered biomolecular catalysts that are activated via electron transfer from a photosensitizer in a photocatalytic system. We place an emphasis on selected forefront chemical reactions of high interest, including CH oxidation, proton reduction, water oxidation, CO 2 reduction, and N 2 reduction.
Here, we report the improvement of photocatalytic proton reduction using molecular polyoxovanadate-alkoxide clusters as hole scavengers for CdSe quantum dots. The increased hydrogen production is explained by favorable charge interactions between reduced forms of the cluster and the charge on the quantum dots arising from the capping ligands.
Not provided.