Efficient photoredox conversion of alcohol to aldehyde and H2 by heterointerface engineering of bimetal-semiconductor hybrids

Obtaining Ligand-Free Aqueous Au-Nanoparticles Using Reversible CsPbBr3 ↔ Au@CsPbBr3 Nanocrystal Transformation

Water-hexane interfacial preparation of photostable Au@CsPbBr3 (Au@CPB) hybrid nanocrystals (NCs) from pure CsPbBr3 (CPB) NCs is reported, with the coexistence of exciton and localized surface plasmon resonance with equal dominance. This enables strong exciton-plasmon coupling in these plasmonic perovskite NCs where not only the photoluminescence is quenched intrinsically due to ultrafast charge separation, but also the light absorption property increases significantly, covering the entire visible region. Using a controlled interfacial strategy, a reversible chemical transformation between CPB and Au@CPB NCs is shown, with the simultaneous eruption of larger-size ligand-free aqueous Au nanoparticles (NPs). An adsorption-desorption mechanism is proposed for the reversible transformation, while the overgrowth reaction of the Au NPs passes through the Au aggregation intermediate. This study further shows that the plasmonic Au@CPB hybrid NCs as well as ligand-free Au NPs exhibit clear surface enhanced Raman scattering (SERS) effect of a commercially available probe molecule. Overall, the beautiful interfacial chemistry delivers two independent plasmonic materials, i.e., Au@CPB NCs and ligand-free aqueous Au NPs, which may find important implications in photocatalytic and biomedical applications.

Near-Infrared Light-Driven Photocatalysis with an Emphasis on Two-Photon Excitation: Concepts, Materials, and Applications

Efficient utilization of sunlight in photocatalysis is widely recognized as a promising solution for addressing the growing energy demand and environmental issues resulting from fossil fuel consumption. Recently, there have been significant developments in various near-infrared (NIR) light-harvesting systems for artificial photosynthesis and photocatalytic environmental remediation. This review provides an overview of the most recent advancements in the utilization of NIR light through the creation of novel nanostructured materials and molecular photosensitizers, as well as modulating strategies to enhance the photocatalytic processes. A special focus is given to the emerging two-photon excitation NIR photocatalysis. The unique features and limitations of different systems are critically evaluated. In particular, it highlights the advantages of utilizing NIR light and two-photon excitation compared to UV-visible irradiation and one-photon excitation. Ongoing challenges and potential solutions for the future exploration of NIR light-responsive materials are also discussed.

Ni(OH)2 surface-modified hierarchical ZnIn2S4 nanosheets: dual photocatalytic application and mechanistic insights

The simultaneous utilization of electrons and holes to couple photocatalytic H2 production with selective biomass transformation has attracted immense interest toward achieving sustainability in the fields of energy and chemical industry. In this study, by assembling highly dispersed Ni(OH)2 onto ZnIn2S4 (ZIS), efficient H2 evolution along with highly selective photocatalytic oxidation of furfuryl alcohol (FA) to furfural (FF) in pure water was achieved under anaerobic conditions. The H2 production and FA conversion rates over the optimal Ni-ZIS sample reached about 686 and 583 μmol g-1 h-1, respectively, about 4.9 and 1.7 folds as those of pure ZIS. Moreover, the formation of by-products with C-C coupling was dramatically suppressed over Ni-ZIS, resulting in higher selectivity for FF (97%), which is about 2.7-fold that of pure ZIS (36%). Deep mechanistic studies were conducted to reveal the structural evolution and cocatalyst effects of Ni(OH)2. This study not only offers a feasible paradigm for modifying the surface of catalysts to tune the photoactivity and selectivity for product-oriented alcohol oxidation coupled with efficient H2 production in water but also reveals the working mechanism of the deposited Ni(OH)2 over ZIS toward coupling reactions.

Reticular framework materials for photocatalytic organic reactions

Photocatalytic organic reactions, harvesting solar energy to produce high value-added organic chemicals, have attracted increasing attention as a sustainable approach to address the global energy crisis and environmental issues. Reticular framework materials, including metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), are widely considered as promising candidates for photocatalysis owing to their high crystallinity, tailorable pore environment and extensive structural diversity. Although the design and synthesis of MOFs and COFs have been intensively developed in the last 20 years, their applications in photocatalytic organic transformations are still in the preliminary stage, making their systematic summary necessary. Thus, this review aims to provide a comprehensive understanding and useful guidelines for the exploration of suitable MOF and COF photocatalysts towards appropriate photocatalytic organic reactions. The commonly used reactions are categorized to facilitate the identification of suitable reaction types. From a practical viewpoint, the fundamentals of experimental design, including active species, performance evaluation and external reaction conditions, are discussed in detail for easy experimentation. Furthermore, the latest advances in photocatalytic organic reactions of MOFs and COFs, including their composites, are comprehensively summarized according to the actual active sites, together with the discussion of their structure-property relationship. We believe that this study will be helpful for researchers to design novel reticular framework photocatalysts for various organic synthetic applications.

Photoredox Coupling of CO2 Reduction with Benzyl Alcohol Oxidation over Ternary Metal Chalcogenides (ZnmIn2S3+m, m = 1-5) with Regulable Products Selectivity

Integrating photocatalytic CO2 reduction with selective benzyl alcohol (BA) oxidation in one photoredox reaction system is a promising way for the simultaneous utilization of photogenerated electrons and holes. Herein, ZnmIn2S3+m (m = 1-5) semiconductors (ZnIn2S4, Zn2In2S5, Zn3In2S6, Zn4In2S7, and Zn5In2S8) with various composition faults were synthesized via a simple hydrothermal method and used for effective selective dehydrocoupling of benzyl alcohol into high-value C-C coupling products and reduction of CO2 into syngas under visible light. The absorption edge of ZnmIn2S3+m samples shifted to shorter wavelengths as the atomic ratio of Zn/In was increased. The conduction band and valence band position can be adjusted by changing the Zn/In ratio, resulting in controllable photoredox ability for selective BA oxidation and CO2 reduction. For example, the selectivity of benzaldehyde (BAD) product was reduced from 76% (ZnIn2S4, ZIS1) to 27% (Zn4In2S7, ZIS4), while the selectivity of hydrobenzoin (HB) was increased from 22% to 56%. Additionally, the H2 formation rate on ZIS1 (1.6 mmol/g/h) was 1.6 times higher than that of ZIS4 (1.0 mmol/g/h), and the CO formation rate on ZIS4 (0.32 mmol/g/h) was three times higher than that of ZIS1 (0.13 mmol/g/h), demonstrating that syngas with different H2/CO ratios can be obtained by controlling the Zn/In ratio in ZnmIn2S3+m. This study provides new insights into unveiling the relationship of structure-property of ZnmIn2S3+m layered crystals, which are valuable for implementation in a wide range of environment and energy applications.

Omnidirectional Hydrogen Generation Based on a Flexible Black Gold Nanotube Array

Solar-driven hydrogen generation is emerging as an economical and sustainable means of producing renewable energy. However, current photocatalysts for hydrogen generation are mostly powder-based or rigid-substrate-supported, which suffer from limitations, such as difficulties in catalyst regeneration or poor omnidirectional light-harvesting. Here, we report a two-dimensional (2D) flexible photocatalyst based on elastomer-supported black gold nanotube (GNT) arrays with conformal CdS coating and Pt decoration. The highly porous GNT arrays display a strong light-trapping effect, leading to near-complete absorption over almost the entire range of the solar spectrum. In addition, they offer high surface-to-volume ratios promoting efficient photocatalytic reactions. These structural features result in high H₂ generation efficiencies. Importantly, our elastomer-supported photocatalyst displays comparable photocatalytic activity even when being mechanically deformed, including bending, stretching, and twisting. We further designed a three-dimensional (3D) tree-like flexible photocatalytic system to mimic Nature's photosynthesis, which demonstrated omnidirectional H₂ generation. We believe our strategy represents a promising route in designing next-generation solar-to-fuel systems that rival natural plants.

Surface‐Plasmon‐Enhanced Transmetalation between Copper and Palladium Nanoparticle Catalyst

Surface‐plasmon‐mediated phenylacetylide intermediate transfer from the Cu to the Pd surface affords a novel mechanism for transmetalation, enabling wavelength‐tunable cross‐coupling and homo‐coupling reaction pathway control. C−C bond forming Sonogashira coupling and Glaser coupling reactions in O₂ atmosphere are efficiently driven by visible light over heterogeneous Cu and Pd nanoparticles as a mixed catalyst without base or other additives. The reaction pathway can be controlled by switching the excitation wavelength. Shorter wavelengths (400–500 nm) give the Glaser homo‐coupling diyne, whereas longer wavelength irradiation (500–940 nm) significantly increases the degree of cross‐coupling Sonogashira coupling products. The ratio of the activated intermediates of alkyne to the iodobenzene is wavelength dependent and this regulates transmetalation. This wavelength‐tunable reaction pathway is a novel way to optimize the product selectivity in important organic syntheses.

π-d Electron-Coupled PBDIT/CdS Heterostructure Enables Hole Extraction for Efficient Photocatalytic Hydrogen Production

Construction of heterostructures is one of the most promising strategies for designing photocatalysts for highly efficient solar hydrogen (H₂) production because the introduction of an electron-donating counterpart contributes to more effective photon absorption, while the heterostructures benefit spatial carrier separation. However, the hole-transfer rate is usually 2-3 orders of magnitude slower than that of the electron-transfer rate within the heterostructures, ensuing serious charge recombination. Here, we find the energy band offset-driven charge-transfer behavior in a donor-acceptor (D-A)-conjugated polymer/CdS organic/inorganic heterostructure and realize hole-transfer improvement in cooperation with a further hole removal motif of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate. The photocatalytic H₂ production activity is increased by nearly 2 orders of magnitude with the apparent quantum yield hitting ca. 80% at 450 nm without co-catalysts. Ultrafast transient absorption together with surface photovoltage characterizations consolidates the hole extraction mechanism. The intimate bond formed at the interface between the polymer and the inorganic semiconductor acts as an interpenetrating network at the nanoscale level, thus providing a charge-transfer freeway for boosting charge separation.

Radical-Mediated C-C Coupling of Alcohols Induced by Plasmonic Hot Carriers

The C-C coupling reactions of aliphatic alcohols to aromatics and larger-mass compounds have large endothermicities and activation energies, calling for catalysts operating at high temperatures. Here, we demonstrate that plasmon-excited nanoparticles catalyze the C-C coupling of aliphatic alcohols at room temperature to produce polyaromatic hydrocarbons and graphene oxide. The conversion is quenched by radical and electron scavengers and by the surface passivation of metals, suggesting that the reaction proceeds through alkoxy, peroxyl, hydroxyalkyl, and alkyl radical intermediates created by the metal to molecule transfer of plasmonic hot carriers. Besides being the first realization of C-C coupling of aliphatic alcohols at room temperature, the result constitutes a rare example of an endothermic plasmon-induced reaction producing new bonds and a new method for photogenerating graphene derivatives. More importantly, the result demonstrates the facile generation of organic radicals directly from alcohols, which may be used as precursors for radical-based organic reactions.

Nanoscale Assembly of CdS/BiVO4 Hybrids for Coupling Selective Fine Chemical Synthesis and Hydrogen Production under Visible Light

Simultaneously utilizing photogenerated electrons and holes in one photocatalytic system to synthesize value-added chemicals and clean hydrogen (H₂) energy meets the development requirements of green chemistry. Herein, we report a binary material of CdS/BiVO₄ combining one-dimensional (1D) CdS nanorods (NRs) with two-dimensional (2D) BiVO₄ nanosheets (NSs) constructed through a facile electrostatic self-assembly procedure for the selectively photocatalytic oxidation of aromatic alcohols integrated with H₂ production, which exhibits significantly enhanced photocatalytic performance. Within 2 h, the conversion of aromatic alcohols over CdS/BiVO₄-25 was approximately 9-fold and 40-fold higher than that over pure CdS and BiVO₄, respectively. The remarkably improved photoactivity of CdS/BiVO₄ hybrids is mainly ascribed to the Z-scheme charge separation mechanism in the 1D/2D heterostructure derived from the interface contact between CdS and BiVO₄, which not only facilitates the separation and transfer of charge carriers, but also maintains the strong reducibility of photogenerated electrons and strong oxidizability of photogenerated holes. It is anticipated that this work will further stimulate interest in the rational design of 1D/2D Z-scheme heterostructure photocatalysts for the selective fine chemical synthesis integrated with H₂ evolution.

Revealing the role of surface elementary doping in photocatalysis

Doping CdS with manganese can catalyze hole extraction and facilitate interfacial electron transfer to metallic cocatalyst. This reduces the activation energy for spatial separation of photogenerated charge carriers and enhances photon utilization.

Cooperative Coupling of Oxidative Organic Synthesis and Hydrogen Production over Semiconductor-Based Photocatalysts

Merging hydrogen (H₂) evolution with oxidative organic synthesis in a semiconductor-mediated photoredox reaction is extremely attractive because the clean H₂ fuel and high-value chemicals can be coproduced under mild conditions using light as the sole energy input. Following this dual-functional photocatalytic strategy, a dreamlike reaction pathway for constructing C-C/C-X (X = C, N, O, S) bonds from abundant and readily available X-H bond-containing compounds with concomitant release of H₂ can be readily fulfilled without the need of external chemical reagents, thus offering a green and fascinating organic synthetic strategy. In this review, we begin by presenting a concise overview on the general background of traditional photocatalytic H₂ production and then focus on the fundamental principles of cooperative photoredox coupling of selective organic synthesis and H₂ production by simultaneous utilization of photoexcited electrons and holes over semiconductor-based catalysts to meet the economic and sustainability goal. Thereafter, we put dedicated emphasis on recent key progress of cooperative photoredox coupling of H₂ production and various selective organic transformations, including selective alcohol oxidation, selective methane conversion, amines oxidative coupling, oxidative cross-coupling, cyclic alkanes dehydrogenation, reforming of lignocellulosic biomass, and so on. Finally, the remaining challenges and future perspectives in this flourishing area have been critically discussed. It is anticipated that this review will provide enlightening guidance on the rational design of such dual-functional photoredox reaction system, thereby stimulating the development of economical and environmentally benign solar fuel generation and organic synthesis of value-added fine chemicals.

Synthesis of Ni modified Au@CdS core-shell nanostructures for enhancing photocatalytic coproduction of hydrogen and benzaldehyde under visible light

The development of visible light responsive photocatalysts for simultaneous production of hydrogen (H₂) fuel and value-added chemicals is greatly promising to solve the energy and environmental issues by improving the utilization efficiency of solar energy. Herein, the three-component Ni/(Au@CdS) core-shell nanostructures were constructed by the hydrothermal synthesis followed with photodeposition. The intimate integration of plasmonic Au nanospheres and visible-light responsive CdS shells modified with Ni cocatalyst facilitated the generation and separation of electron-hole pairs as well as reduced the overpotential of hydrogen evolution. The Ni/(Au@CdS) photocatalyst exhibited excellent performance toward the selective transformation of benzyl alcohol under anaerobic conditions, and the yields of H₂ and benzaldehyde reached up to 3882 and 4242 μmol·g^-1·h^-1, respectively. The apparent quantum efficiency (AQE) was determined to be 4.09% under the irradiation of 420 nm. The systematic studies have verified the synergy of plasmonic effect and metal cocatalyst on enhancing the photocatalysis. This work highlights the desirable design and potential application of plasmonic photocatalysts for solar-driven coproduction of H₂ fuel and high-value chemicals.

State of the Art and Prospects for Halide Perovskite Nanocrystals

Metal-halide perovskites have rapidly emerged as one of the most promising materials of the 21st century, with many exciting properties and great potential for a broad range of applications, from photovoltaics to optoelectronics and photocatalysis. The ease with which metal-halide perovskites can be synthesized in the form of brightly luminescent colloidal nanocrystals, as well as their tunable and intriguing optical and electronic properties, has attracted researchers from different disciplines of science and technology. In the last few years, there has been a significant progress in the shape-controlled synthesis of perovskite nanocrystals and understanding of their properties and applications. In this comprehensive review, researchers having expertise in different fields (chemistry, physics, and device engineering) of metal-halide perovskite nanocrystals have joined together to provide a state of the art overview and future prospects of metal-halide perovskite nanocrystal research.

State-of-the-art progress in tracking plasmon-mediated photoredox catalysis

Metal nanocrystals (NCs), particularly for plasmonic metal NCs with specific morphology and size, can strongly interact with ultraviolet-visible or even near-infrared photons to generate energetic charge carriers, localized heating, and electric field enhancement. These unique properties offer a promising opportunity for maneuvering solar-to-chemical energy conversion through different mechanisms. As distinct from previous works, in this review, recent advances of various characterization techniques in probing and monitoring the photophysical/photochemical processes, as well as the reaction mechanisms of plasmon-mediated photoredox catalysis are thoroughly summarized. Understanding how to distinguish and track these reaction mechanisms would furnish basic guidelines to design next-generation photocatalysts for plasmon-enhanced catalysis.

A semi-crystalline carbonaceous structure as a wide-spectrum-responsive photocatalyst for efficient redox catalysis

Herein, we synthesized an oxygen- and nitrogen-containing carbonaceous structure (ONCS). This ONCS possessed exceptional light-harvesting ranging from the visible to NIR light region. Characterization results confirmed that the ONCS was an n-type semiconductor. The ONCS can efficiently catalyze hydrogen photosynthesis and benzyl alcohol oxidation under visible light, even under NIR light irradiation.

Coupling Strategy for CO2 Valorization Integrated with Organic Synthesis by Heterogeneous Photocatalysis

Photocatalytic reduction of CO₂ to solar fuels and/or fine chemicals is a promising way to increase the energy supply and reduce greenhouse gas emissions. However, the conventional reaction system for CO₂ photoreduction with pure H₂ O or sacrificial agents usually suffers from low catalytic efficiency, poor stability, or cost-ineffective atom economy. A recent surge of developments, in which photocatalytic CO₂ valorization is integrated with selective organic synthesis into one reaction system, indicates an efficient modus operandi that enables sufficient utilization of photogenerated electrons and holes to achieve the goals for sustainable economic and social development. In this Review we discuss current advances in cooperative photoredox reaction systems that integrate CO₂ valorization with organics upgrading based on heterogeneous photocatalysis. The applications and virtues of this strategy and the underlying reaction mechanisms are discussed. The ongoing challenges and prospects in this area are critically discussed.

Visible-Light-Mediated Oxidative Amidation of Aldehydes by Using Magnetic CdS Quantum Dots as a Photocatalyst

A magnetic CdS quantum dot (Fe₃ O₄ /polydopamine (PDA)/CdS) was synthesized through a facile and convenient method from inexpensive starting materials. Characterization of the prepared catalyst was performed by means of FTIR spectroscopy, XRD, SEM, TEM, energy-dispersive X-ray spectroscopy, and vibrating-sample magnetometer techniques. Fe₃ O₄ /PDA/CdS was found to be a highly active photocatalyst for the amidation of aromatic aldehydes by using air as a clean oxidant under mild conditions. The photocatalyst can be recovered by magnetic separation and successfully reused for five cycles without considerable loss of its catalytic activity.

A photoredox catalysed Heck reaction via hole transfer from a Ru(ii)-bis(terpyridine) complex to graphene oxide

The attachment of homoleptic Ru bis-terpy complexes on graphene oxide significantly improved the photocatalytic activity of the complexes. These straightforward complexes were applied as photocatalysts in a Heck reaction. Due to covalent functionalization on graphene oxide, which functions as an electron reservoir, excellent yields were obtained. DFT investigations of the charge redistribution revealed efficient hole transfer from the excited Ru unit towards the graphene oxide.

Modulating the Plasmon-Mediated Oxidation of p-Aminothiophenol with Asymmetrically Grafted Thiol Molecules

A surface plasmon can drive many photochemical reactions, in which effective charge separation and migration is a key. In analogy to the plasmon-semiconductor interface, the plasmon-molecule interface may also be used to improve the separation and migration of hot carriers. In this work, by using in situ Raman spectroscopy, molecular grafting on silver nanostructures is found essential for modulating the charge separation and p-aminothiophenol (PATP) oxidation reaction. When the LUMO of the grafted molecules match well the energy distribution of the plasmon-generated hot electrons, the PATP oxidation process accelerates significantly. Moreover, compared with symmetrical grafting, asymmetrical grafting is more effective in regulating the charge separation and plasmon-mediated chemical reaction. This work provides an effective strategy for deep understanding and fine modulation of plasmon-mediated photochemistry.

Recent Progress in Engineering Metal Halide Perovskites for Efficient Visible-Light-Driven Photocatalysis

Artificial photosynthesis has attracted increasing attention due to recent environmental and energy concerns. Metal halide perovskites (MHPs) demonstrating excellent optoelectronic properties have currently emerged as novel and efficient photocatalytic materials. Herein, the structural features of MHPs that are responsible for the photoinduced charge separation and charge migration properties are briefly introduced, and then important and necessary photophysical and photochemical aspects of MHPs related to photoredox catalysis are summarized. Subsequently, the applications of MHPs for solar energy harvesting and photocatalytic conversion, including H₂ evolution, CO₂ reduction, degradation of organic pollutants, and photoredox organic synthesis, are extensively demonstrated, with a focus on strategies for improving the performance (e.g., selectivity, activity, stability, recyclability, and environmental compatibility) of these MHP-based photocatalytic systems. To conclude, existing challenges and prospects on the future development of MHP-based materials towards photoredox catalysis applications are detailed.

TiO2/Cu2O nanoparticle-catalyzed direct C(sp)-P bond formation via aerobic oxidative coupling in air and visible light

The synthesis of organophosphorus compounds is one of the important goals in organic chemistry. Among these compounds, alkynylphosphonates are significantly utilized as the main precursors for the synthesis of biologically active molecules in medicinal chemistry and have attracted extensive interest in the past few decades. Although few efforts have been made towards the direct and atom-economical synthesis of alkynylphosphonates, efforts towards the utilization of visible light as a green and renewable energy source have not been made to date. Here, we have promoted a strategy to construct a type of nano metal oxide composite photocatalyst (Cu2O decorated on TiO2) for the synthesis of alkynylphosphonates via direct C-P bond formation between terminal alkyne and H-phosphonate under visible light irradiation. In this p-n heterojunction photocatalyst, Cu2O acted as a visible-light absorber; moreover, the CB (conduction band) of TiO2 was favorable for accepting a photogenerated electron, and the generated electron hole (e-/h+) pair could initiate the reaction. The present study can provide a new way for the synthesis of this important class of phosphorus organic compounds.

Mechanochemical Forces as a Synthetic Tool for Zero- and One-Dimensional Titanium Oxide-Based Nano-photocatalysts

A new field where the utilization of mechanochemistry can create new opportunities is materials chemistry, and, more interestingly, the synthesis of novel nanomaterials. Ball-milling procedures and ultrasonic techniques can be regarded as the most important mechanochemical synthetic tools, since they can act as attractive alternatives to the conventional methods. It is also feasible for the utilization of mechanochemical forces to act synergistically with the conventional synthesis (as a pre-treatment step, or simultaneously during the synthesis) in order to improve the synthetic process and/or the material's desired features. The usage of ultrasound irradiation or ball-milling treatment is found to play a crucial role in controlling and enhancing the structural, morphological, optical, and surface chemistry features that are important for heterogeneous photocatalytic practices. The focus of this article is to collect all the available examples in which the utilization of sonochemistry or ball milling had unique effects as a synthesis tool towards zero- or one-dimensional nanostructures of a semiconductor which is assumed as a benchmark in photocatalysis, titanium dioxide.