With current economic growth and consumption trends projected to bring about a precipitous and rapid rise of the global temperature, the world stands at a crossroads with regards to climate change. The rate at which greenhouse gas emissions from fossil fuels, industry, and land-use is curtailed over the next decade will determine the trajectory of global warming for the rest of the century. It is increasingly apparent that far-reaching decarbonization of the transportation infrastructure will need to be supplemented by extensive carbon capture, storage, and utilization. Taking a leaf from Nature's playbook, photocatalytic architectures that can utilize water or CO 2 in conjunction with energy harvested from sunlight and store it in the form of energy-dense chemical bonds represent an attractive proposition. Harnessing solar irradiance, through solar energy conversion involving photovoltaics, as well as the photocatalytic generation of solar fuels, and the photocatalytic reduction of CO 2 have emerged as urgent imperatives for the energy transition. Functional photocatalysts must be capable of efficiently absorbing sunlight, effectively separating electronhole pairs, and ensuring they are delivered at appropriate potentials to catalytic sites to mediate redox reactions. Such photocatalytic architectures must further direct redox events down specific pathways to yield desired products, and ensure the transport of reactants between catalytic sites; all with high efficiency and minimal degradation. In this Perspective, we describe a palette of heterostructures designed to promote robust and efficient direct solar-driven water splitting and CO 2 reduction. The heterostructures comprise M x V 2 O 5 or M x M y ′V 2 O 5 , where M is a p-block cation, M′ is an s-, p-, or d-block cation, and V 2 O 5 represents one of multiple polymorphs of this composition interfaced with semiconductor quantum dots (QDs, binary or ternary II−VI or III−V QDs). The stereochemically active 5/6s 2 electron lone pairs of p-block cations in M x V 2 O 5 give rise to filled midgap electronic states that reside above the O 2p-derived valence band. Within heterostructures, the photoexcitation of QDs results in the transfer of holes to the midgap states of M x V 2 O 5 or M x M y ′V 2 O 5 on subpicosecond time scales. Ultrafast charge separation minimizes the photoanodic corrosion of QDs, which has historically been a major impediment to their use in photocatalysis, and enables charge transport and the subsequent redox reactions underpinning photocatalysis to compete with electron−hole recombination. The energy positioning and dispersion of lone pair states is tunable through multiple chemical and compositional levers accessible across the palette of M x V 2 O 5 or M x M y ′V 2 O 5 compounds: choice of lone-pair cation M and its stoichiometry x, atomic connectivity of V 2 O 5 polymorphs, cointercalation of M′ cations in "quaternary" vanadium oxide bronzes, anionic substitution, and alternative lone pair vanadate frameworks with altogether different c...

We used linker-assisted assembly (LAA) to tether CdS quantum dots (QDs) to MoS 2 nanosheets via L-cysteine (cys) or mercaptoalkanoic acids (MAAs) of varying lengths, yielding ligand-bridged CdS/MoS 2 heterostructures for redox photocatalysis. LAA afforded precise control over the light-harvesting properties of QDs within heterostructures. Photoexcited CdS QDs transferred electrons to molecularly linked MoS 2 nanosheets from both band-edge and trap states; the electron-transfer dynamics was tunable with the properties of bridging ligands. Rate constants of electron transfer, estimated from time-correlated single photon counting (TCSPC) measurements, ranged from (9.8 ± 3.8) × 10 6 s −1 for the extraction of electrons from trap states within heterostructures incorporating the longest MAAs to >5 × 10 9 s −1 for the extraction of electrons from band-edge or trap states in heterostructures with cys or 3-mercaptopropionic acid (3MPA) linkers. Ultrafast transient absorption measurements revealed that electrons were transferred within 0.5− 2 ps or less for CdS-cys-MoS 2 and CdS-3MPA-MoS 2 heterostructures, corresponding to rate constants ≥5 × 10 9 s −1 . Photoinduced CdS-to-MoS 2 electron transfer could be exploited in photocatalytic hydrogen evolution reaction (HER) via the reduction of H + to H 2 in concert with the oxidation of lactic acid. CdS-L-MoS 2 -functionalized FTO electrodes promoted HER under oxidative conditions wherein H 2 was evolved at a Pt counter electrode with Faradaic efficiencies of 90% or higher and under reductive conditions wherein H 2 was evolved at the CdS-L-MoS 2 -heterostructure-functionalized working electrode with Faradaic efficiencies of 25−40%. Dispersed CdS-L-MoS 2 heterostructures promoted photocatalytic HER (15.1 μmol h −1 ) under white-light illumination, whereas free cys-capped CdS QDs produced threefold less H 2 and unfunctionalized MoS 2 nanosheets produced no measurable H 2 . Charge separation across the CdS/MoS 2 interface is thus pivotal for redox photocatalysis. Our results reveal that LAA affords tunability of the properties of constituent CdS QDs and MoS 2 nanosheets and precise, programmable, ligand-dependent control over the assembly, interfacial structure, charge-transfer dynamics, and photocatalytic reactivity of CdS-L-MoS 2 heterostructures.