Photocatalytic Carbon Disulfide Production via Charge Transfer Quenching of Quantum Dots

Charge Transfer from Quantum-Confined 0D, 1D, and 2D Nanocrystals

The properties of colloidal quantum-confined semiconductor nanocrystals (NCs), including zero-dimensional (0D) quantum dots, 1D nanorods, 2D nanoplatelets, and their heterostructures, can be tuned through their size, dimensionality, and material composition. In their photovoltaic and photocatalytic applications, a key step is to generate spatially separated and long-lived electrons and holes by interfacial charge transfer. These charge transfer properties have been extensively studied recently, which is the subject of this Review. The Review starts with a summary of the electronic structure and optical properties of 0D-2D nanocrystals, followed by the advances in wave function engineering, a novel way to control the spatial distribution of electrons and holes, through their size, dimension, and composition. It discusses the dependence of NC charge transfer on various parameters and the development of the Auger-assisted charge transfer model. Recent advances in understanding multiple exciton generation, decay, and dissociation are also discussed, with an emphasis on multiple carrier transfer. Finally, the applications of nanocrystal-based systems for photocatalysis are reviewed, focusing on the photodriven charge separation and recombination processes that dictate the function and performance of these materials. The Review ends with a summary and outlook of key remaining challenges and promising future directions in the field.

Shewanella oneidensis MR-1 respires CdSe quantum dots for photocatalytic hydrogen evolution

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 (H2) 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 H2 production. Unlike microbial electrolysis cells, this system requires no external potential. Illuminating this system at 530 nm yields continuous H2 generation for 168 h, which can be lengthened further by replenishing bacterial nutrients.

Strong Penetration-Induced Effective Photothermal Therapy by Exosome-Mediated Black Phosphorus Quantum Dots

Nanocancer medicine, such as photothermal therapy (PTT), as a promising way to solve cancer without side effects, faces a huge biological barrier during the circulation of nanoparticles in the body, including nanobiological interactions in the blood, isolation of nanoparticles in the macrophage system, tumor spillover effect, and especially uneven intratumoral distribution of nanoparticles, which cast a shadow over the hope. To address the problem of intratumoral distribution, an effective photothermal agent is introduced by packaging the black phosphorus quantum dots (BPQDs) into exosome vector (EXO) through electroporation method. With the improving and proper stability for better therapy, the resulting BPQDs@EXO nanospheres (BEs) exhibit good biocompatibility, long circulation time, and excellent tumor targeting ability, hence impressive PTT efficiency evidenced by highly efficient tumor ablation in vivo. Importantly, great permeability on organoids contributed by EXO appears with BEs, which strongly promotes the efficient killing ability. These BP-based nanospheres must promise high clinical potential due to the high PTT efficiency and minimal side effects.

Nanomaterial catalysts for organic photoredox catalysis-mechanistic perspective

Solar energy conversions play a vital role in the renewable energy industry. In recent years, photoredox organic transformations have been explored as an alternative way to use solar energy. Catalysts for such photocatalytic systems have evolved from homogeneous metal complexes to heterogeneous nanomaterials over the past few decades. Herein, three important carrier transfer mechanisms are presented, including charge transfer, energy transfer and hot carrier transfer. Several models established by researchers to understand the catalytic reaction mechanisms are also illustrated, which promote the reaction system design based on theoretical studies. New strategies are introduced in order to enhance catalytic efficiency for future prospects.

Highly Efficient and Controllable Methodology of the Cd0.25Zn0.75Se/ZnS Core/Shell Quantum Dots Synthesis

The surface of any binary or multi-component nanocrystal has imperfections and defects. The number of surface defects depends both on the nature of the nanomaterial and on the method of its preparation. One of the possibilities to confine the number of surface defects is the epitaxial growth of the shell, which leads to a change in the physical properties while maintaining the morphology of the core. To form a shell of the desired thickness, an accurate calculation of the amount of its precursors is substantial to avoid the appearance of individual crystals consisting of the shell material. This study aimed to develop an effective calculation method for the theoretical amount of precursors required for the formation of a ZnS shell on the surface of a Cd_0.25Zn_0.75Se core, followed by the practical implementation of theoretical calculations and characterization of the prepared nanomaterials. This method allows the complete control of the masses and volumes of the initial reagents, which will in turn prevent undesirable nucleation of nuclei consisting of the shell material. In the synthesis of Cd_0.25Zn_0.75Se/ZnS core/shell quantum dots (QDs), the sources of chalcogens were substituted seleno- and thioureas, which are capable of not only supplanting modern toxic sources of sulfur and selenium but also allowing one to perform the controlled synthesis of highly photoluminescent QDs with a low number of surface defects. The result of this shell overcoating method was an impetuous augmentation in the photoluminescence quantum yield (PL QY up to 83%), uniformity in size and shape, and a high yield of nanomaterials. The developed synthetic technique of core/shell QDs provides a controlled growth of the shell on the core surface, which makes it possible to transfer this method to an industrial scale.

Quantum Dot Photocatalysts for Organic Transformations

Quantum dots (QDs) with tunable photo-optical properties and colloidal nature are ideal for a wide range of photocatalytic reactions. In particular, QD photocatalysts for organic transformations can provide new and effective synthetic routes to high value-added molecules under mild conditions. In this Perspective, we discuss the advances of employing QDs for visible-light-driven organic transformations categorized into net reductive reactions, net oxidative reactions, and redox neutral reactions. We then provide our outlook for potential future directions in the field: nanostructure engineering to improve charge separation efficiencies, ligand shell engineering to optimize overall catalyst performance, in situ comprehensive studies to delineate underlying reaction mechanisms, and laboratory automation with the assistance of modern computing techniques to revolutionize the reaction optimization process.

Visible-to-NIR-Light Activated Release: From Small Molecules to Nanomaterials

Photoactivatable (alternatively, photoremovable, photoreleasable, or photocleavable) protecting groups (PPGs), also known as caged or photocaged compounds, are used to enable non-invasive spatiotemporal photochemical control over the release of species of interest. Recent years have seen the development of PPGs activatable by biologically and chemically benign visible and near-infrared (NIR) light. These long-wavelength-absorbing moieties expand the applicability of this powerful method and its accessibility to non-specialist users. This review comprehensively covers organic and transition metal-containing photoactivatable compounds (complexes) that absorb in the visible- and NIR-range to release various leaving groups and gasotransmitters (carbon monoxide, nitric oxide, and hydrogen sulfide). The text also covers visible- and NIR-light-induced photosensitized release using molecular sensitizers, quantum dots, and upconversion and second-harmonic nanoparticles, as well as release via photodynamic (photooxygenation by singlet oxygen) and photothermal effects. Release from photoactivatable polymers, micelles, vesicles, and photoswitches, along with the related emerging field of photopharmacology, is discussed at the end of the review.

Direct Optical Patterning of Quantum Dot Light-Emitting Diodes via In Situ Ligand Exchange

Precise patterning of quantum dot (QD) layers is an important prerequisite for fabricating QD light-emitting diode (QLED) displays and other optoelectronic devices. However, conventional patterning methods cannot simultaneously meet the stringent requirements of resolution, throughput, and uniformity of the pattern profile while maintaining a high photoluminescence quantum yield (PLQY) of the patterned QD layers. Here, a specially designed nanocrystal ink is introduced, "photopatternable emissive nanocrystals" (PENs), which satisfies these requirements. Photoacid generators in the PEN inks allow photoresist-free, high-resolution optical patterning of QDs through photochemical reactions and in situ ligand exchange in QD films. Various fluorescence and electroluminescence patterns with a feature size down to ≈1.5 µm are demonstrated using red, green, and blue PEN inks. The patterned QD films maintain ≈75% of original PLQY and the electroluminescence characteristics of the patterned QLEDs are comparable to thopse of non-patterned control devices. The patterning mechanism is elucidated by in-depth investigation of the photochemical transformations of the photoacid generators and changes in the optical properties of the QDs at each patterning step. This advanced patterning method provides a new way for additive manufacturing of integrated optoelectronic devices using colloidal QDs.

Highly selective visual sensing of copper based on fluorescence enhanced glutathione-Au nanoclusters

A blue emission glutathione stabilized Au nanoclusters prepared by an Au/Histidine complex with ligand-exchanges method was used for sensing of copper ions. We found that the glutathione stabilized Au NCs which has fluorescence emission hundred times higher than the Au/Histidine complex and has a highly selective fluorescence quenching response to copper ion. Other common metal ions, such as mercury, lead, iron and zinc, which could obviously quench or enhance the fluorescence of Au/Histidine complex, do not interfere the sensing of copper using glutathione stabilized Au nanocluster. The possible quenching mechanism and the dynamic quenching process for copper detection were also discussed. The results indicated that copper in the range from 0.5 to 300.0μM could be linearly detected and the detection could be finished quickly in 5min. A visual detection method for copper ion that may be used to fast warn copper pollution in waters by naked eyes observation was also be developed using the glutathione stabilized Au NCs probe.

Semiconductor nanocrystals for small molecule activation via artificial photosynthesis

The protocol of artificial photosynthesis using semiconductor nanocrystals shines light on green, facile and low-cost small molecule activation to produce solar fuels and value-added chemicals.

The systematic study of the precursor ratio effect in the Cd–Zn–S quantum dot synthesis

The controllable synthesis of highly photoluminescent Cd–Zn–S QDs with application of novel N-phenylmorpholine-4-carbothioamide as an eco-friendly sulphur source.

Direct Wavelength-Selective Optical and Electron-Beam Lithography of Functional Inorganic Nanomaterials

Direct optical lithography of functional inorganic nanomaterials (DOLFIN) is a photoresist-free method for high-resolution patterning of inorganic nanocrystals (NCs) that has been demonstrated using deep UV (DUV, 254 nm) photons. Here, we expand the versatility of DOLFIN by designing a series of photochemically active NC surface ligands for direct patterning using various photon energies including DUV, near-UV (i-line, 365 nm), blue (h-line, 405 nm), and visible (450 nm) light. We show that the exposure dose for DOLFIN can be ∼30 mJ/cm², which is small compared to most commercial photopolymer resists. Patterned nanomaterials can serve as highly robust optical diffraction gratings. We also introduce a general approach for resist-free direct electron-beam lithography of functional inorganic nanomaterials (DELFIN) which enables all-inorganic NC patterns with feature size down to 30 nm, while preserving the optical and electronic properties of patterned NCs. The designed ligand chemistries and patterning techniques offer a versatile platform for nano- and micron-scale additive manufacturing, complementing the existing toolbox for device fabrication.

Semiconductor Quantum Dots: An Emerging Candidate for CO2 Photoreduction

As one of the most critical approaches to resolve the energy crisis and environmental concerns, carbon dioxide (CO₂ ) photoreduction into value-added chemicals and solar fuels (for example, CO, HCOOH, CH₃ OH, CH₄ ) has attracted more and more attention. In nature, photosynthetic organisms effectively convert CO₂ and H₂ O to carbohydrates and oxygen (O₂ ) using sunlight, which has inspired the development of low-cost, stable, and effective artificial photocatalysts for CO₂ photoreduction. Due to their low cost, facile synthesis, excellent light harvesting, multiple exciton generation, feasible charge-carrier regulation, and abundant surface sites, semiconductor quantum dots (QDs) have recently been identified as one of the most promising materials for establishing highly efficient artificial photosystems. Recent advances in CO₂ photoreduction using semiconductor QDs are highlighted. First, the unique photophysical and structural properties of semiconductor QDs, which enable their versatile applications in solar energy conversion, are analyzed. Recent applications of QDs in photocatalytic CO₂ reduction are then introduced in three categories: binary II-VI semiconductor QDs (e.g., CdSe, CdS, and ZnSe), ternary I-III-VI semiconductor QDs (e.g., CuInS₂ and CuAlS₂ ), and perovskite-type QDs (e.g., CsPbBr₃ , CH₃ NH₃ PbBr₃ , and Cs₂ AgBiBr₆ ). Finally, the challenges and prospects in solar CO₂ reduction with QDs in the future are discussed.

Photo-induced thiol coupling and C–H activation using nanocrystalline lead-halide perovskite catalysts

Cesium lead halide perovskite nanocrystals have been the first time utilized as photocatalysts for organic bond formations.

Bandgap-tunable black phosphorus quantum dots: visible-light-active photocatalysts

Bandgap-tunable black phosphorus quantum dots were prepared by a liquid exfoliation method for the photocatalytic degradation of rhodamine B.

Biological Thiols and Carbon Disulfide: The Formation and Decay of Trithiocarbonates under Physiologically Relevant Conditions

Carbon disulfide is an environmental toxin, but there are suggestions in the literature that it may also have regulatory and/or therapeutic roles in mammalian physiology. Thiols or thiolates would be likely biological targets for an electrophile, such as CS₂, and in this context, the present study examines the dynamics of CS₂ reactions with various thiols (RSH) in physiologically relevant near-neutral aqueous media to form the respective trithiocarbonate anions (TTC^-, also known as "thioxanthate anions"). The rates of TTC^- formation are markedly pH-dependent, indicating that the reactive form of RSH is the conjugate base RS^-. The rates of the reverse reaction, that is, decay of TTC^- anions to release CS₂, is pH-independent, with rates roughly antiparallel to the basicities of the RS^- conjugate base. These observations indicate that the rate-limiting step of decay is simple CS₂ dissociation from RS^-, and according to microscopic reversibility, the transition state of TTC^- formation would be simple addition of the RS^- nucleophile to the CS₂ electrophile. At pH 7.4 and 37 °C, cysteine and glutathione react with CS₂ at a similar rate but the trithiocarbonate product undergoes a slow cyclization to give 2-thiothiazolidine-4-carboxylic acid. The potential biological relevance of these observations is briefly discussed.

Uncaging carbon disulfide. Delivery platforms for potential pharmacological applications: a mechanistic approach

We describe the kinetics of the formation and decay of a series of dithiocarbamates under physiological conditions. The goal is to provide a toolbox of compounds that release CS2 by well-defined kinetics in such media. Carbon disulfide is a known environmental toxin, but there is fragmentary evidence suggesting that CS2 may have bioregulatory and/or therapeutic roles in mammalian biology. Further investigation of such roles will require methodologies for controlled delivery of this bioactive small molecule to specific targets. Reported here are mechanistic and computational studies of CS2 release from a series of dithiocarbamate anions (DTCs), where R2N represents several different secondary amido groups. The various DTCs under physiologically relevant conditions show a tremendous range of reactivities toward CS2 dissociation with decay lifetimes ranging from ∼2 s for imidazolidyldithiocarbamate (ImDTC-) to ∼300 s for diisopropyldithiocarbamate (DIDTC-) to >24 h for pyrrolidinyldithiocarbamate (PDTC-) in pH 7.4 phosphate buffer solution at 37 °C. Thus, by making the correct choice of these tools, one can adjust the flux of CS2 in a biological experiment, while the least reactive DTCs could serve as controls for evaluating the potential effects of the dithiocarbamate functionality itself. Kinetics studies and density functional calculations are used to probe the mechanism of DTC- decay. In each case, the rate of CS2 dissociation is acid dependent; however, the DFT studies point to a mechanistic pathway for ImDTC- that is different than those for DIDTC-. The role of general acid catalysis is also briefly probed.

Carbon disulfide. Just toxic or also bioregulatory and/or therapeutic?

The overview presented here has the goal of examining whether carbon disulfide (CS₂) may play a role as an endogenously generated bioregulator and/or has therapeutic value.

Electronic Processes within Quantum Dot-Molecule Complexes

The subject of this review is the colloidal quantum dot (QD) and specifically the interaction of the QD with proximate molecules. It covers various functions of these molecules, including (i) ligands for the QDs, coupled electronically or vibrationally to localized surface states or to the delocalized states of the QD core, (ii) energy or electron donors or acceptors for the QDs, and (iii) structural components of QD assemblies that dictate QD-QD or QD-molecule interactions. Research on interactions of ligands with colloidal QDs has revealed that ligands determine not only the excited state dynamics of the QD but also, in some cases, its ground state electronic structure. Specifically, the article discusses (i) measurement of the electronic structure of colloidal QDs and the influence of their surface chemistry, in particular, dipolar ligands and exciton-delocalizing ligands, on their electronic energies; (ii) the role of molecules in interfacial electron and energy transfer processes involving QDs, including electron-to-vibrational energy transfer and the use of the ligand shell of a QD as a semipermeable membrane that gates its redox activity; and (iii) a particular application of colloidal QDs, photoredox catalysis, which exploits the combination of the electronic structure of the QD core and the chemistry at its surface to use the energy of the QD excited state to drive chemical reactions.

Photocatalytic Conversion of Nitrobenzene to Aniline through Sequential Proton-Coupled One-Electron Transfers from a Cadmium Sulfide Quantum Dot

This paper describes the use of cadmium sulfide quantum dots (CdS QDs) as visible-light photocatalysts for the reduction of nitrobenzene to aniline through six sequential photoinduced, proton-coupled electron transfers. At pH 3.6-4.3, the internal quantum yield of photons-to-reducing electrons is 37.1% over 54 h of illumination, with no apparent decrease in catalyst activity. Monitoring of the QD exciton by transient absorption reveals that, for each step in the catalytic cycle, the sacrificial reductant, 3-mercaptopropionic acid, scavenges the excitonic hole in ∼5 ps to form QD(•-); electron transfer to nitrobenzene or the intermediates nitrosobenzene and phenylhydroxylamine then occurs on the nanosecond time scale. The rate constants for the single-electron transfer reactions are correlated with the driving forces for the corresponding proton-coupled electron transfers. This result suggests, but does not prove, that electron transfer, not proton transfer, is rate-limiting for these reactions. Nuclear magnetic resonance analysis of the QD-molecule systems shows that the photoproduct aniline, left unprotonated, serves as a poison for the QD catalyst by adsorbing to its surface. Performing the reaction at an acidic pH not only encourages aniline to desorb but also increases the probability of protonated intermediates; the latter effect probably ensures that recruitment of protons is not rate-limiting.

Characterization of amine stabilized CdSe/ZnS core–shell quantum dots by using triarylpyrylium dyes

A new method to study the stabilizing primary amine ligands coordinated to the surface of CdSe/ZnS core–shell quantum dots has been developed.

Quantum confined colloidal nanorod heterostructures for solar-to-fuel conversion

Colloidal one-dimensional (1D) semiconductor nanorods (NRs) offer the opportunity to simultaneously maintain quantum confinement in radial dimensions for tunable light absorptions and bulk like carrier transport in the axial direction for long-distance charge separations.

Quantum-CORMs: quantum dot sensitized CO releasing molecules

Quantum dot sensitized photoactive CORMs show a 2 to 6-fold increase of the photodecomposition rate upon irradiation with visible light.