Photocatalytic dehydrogenative C-C coupling of acetonitrile to succinonitrile

Photocatalytic Coproduction of Diesel Fuel Precursors and H2 Promoted by [HSO4 -] and Water

Photocatalytic CC coupling of 2,5-dimethylfuran (DMF) derived from processing lignocellulosic biomasses coproduces drop-in fuels and green hydrogen with a low-carbon footprint. However, the high reaction barrier for CH bond breaking and uphill overall reaction lead to the slow kinetics of DMF coupling. Here, we reveal that [HSO4 -] and water can collaboratively promote the rate-limiting step of the CH bond breaking on the Ru-ZnIn2S4 catalyst. An in-depth study suggests that water mediates hole transfer to the CH bond while [HSO4 -] facilitates electron extraction, thus promoting electron and proton transfer on the Ru-ZnIn2S4 surface. Consequently, photocatalytic DMF coupling over Ru-ZnIn2S4 produces diesel fuel precursors (DFPs) and H2 with benchmarking formation rates of 1.5 g gcatal. -1 h-1 and 9.7 mmol gcatal. -1 h-1, respectively. Moreover, the selectivity of branched-chain DFPs reaches 55%. This work puts forward new insight and strategy for photocatalytic CC coupling for the synthesis of biofuels.

Artificial Photosynthesis of Formamide via an Oxidant-Free Photoinduced Radical Coupling Route over Pt-CdS

Large-scale manufacturing of formamide is always involved with the use of carbon monoxide, hence developing a series of eco-friendly synthesis routes is of great significance. Alternative feedstock of low-cost methanol is expected to fulfill this breakthrough due to its green and renewable nature; however, the overoxidation of methanol severely inhibits the efficacious formamide synthesis from methanol and ammonia through the conventional catalytic route. Herein, we report the successful development of a direct radical coupling route for converting methanol and ammonia into high-selectivity formamide and hydrogen without extra oxidants under ambient conditions. The optimized Pt-CdS photocatalysts offered an impressive formamide production rate of 1.45 mmol g-1 h-1, as well as an exceptional hole selectivity reaching up to 63.5%. The oxidant-free radical mechanism of high-efficiency formamide generation as revealed by in situ characterizations (e.g., in situ electron paramagnetic resonance and in situ transient absorption spectroscopy), stems from the photogenerated holes oxidizing the methanol to hydroxymethyl radical for subsequently direct C─N coupling with amino radical. This work demonstrates an efficient oxidant-free photoinduced radical coupling strategy with the promise of an acceptable alternative to current technologies for artificial photosynthesis formamide using clean and abundant solar energy.

Photocatalytic synthesis of ethylene glycol and hydrogen from methyl tert-butyl ether

In this work, we have developed a green and sustainable strategy for the synthesis of ethylene glycol, which is a highly valuable compound in chemical industry. In contrast to the currently applied energy-intensive process based on petroleum resources, this work demonstrates the photocatalytic pathway of methanol dehydrogenative coupling to produce ethylene glycol, utilizing methyl tert-butyl ether as the substrate to protect the hydroxyl group against oxidation. Photocatalytic tests reveal efficient C-C coupling of methyl tert-butyl ether with Pt/C-TiO(B)-650 catalyst under light irradiation, with the target product 1,2-di-tert-butoxyethane at a selectivity of 67% and a Pt-based turnover frequency of 2754 h-1. Scale up test demonstrates high stability of the system, reaching an accumulated turnover number of 120 000 as well as isolation of 13 g of the coupling product after 130 h irradiation. The target ethylene glycol is obtained by the hydrolysis of the dimer using the regenerable acidic resin catalyst.

Photocatalytic Methanol Dehydrogenation with Switchable Selectivity

Switchable selectivity achieved by altering reaction conditions within the same photocatalytic system offers great advantages for sustainable chemical transformations and renewable energy conversion. In this study, we investigate an efficient photocatalytic methanol dehydrogenation with controlled selectivity by varying the concentration of nickel cocatalyst, using zinc indium sulfide nanocrystals as a semiconductor photocatalyst, which enables the production of either formaldehyde or ethylene glycol with high selectivity. Control experiments revealed that formaldehyde is initially generated and can either serve as a terminal product or intermediate in producing ethylene glycol, depending on the nickel concentration in the solution. Mechanistic studies suggest a unique role of ionic nickel as an additional photoelectron competitor that can significantly influence selectivity, alongside its well-established function as a hydrogen evolution reaction cocatalyst under photocatalytic conditions. The demonstrated switchable selectivity provides a new tool for producing diverse products from methanol, while advancing the understanding of cocatalyst behavior for versatile catalytic performance.

A Protocol for Unveiling the Nature of Photocatalytic Hydrogen Evolution Reactions: True Water Splitting or Sacrificial Reagent Acceptorless Dehydrogenation?

Photocatalytic water splitting for hydrogen evolution is a highly topical subject in academic research and a promising approach for sustainable fuel production from solar energy. Due to the mismatched energy diagram of the photosensitizer (especially semiconductor-based materials where band-edge engineering is not trivial) and the redox potential of the half-reactions of water splitting, photocatalytic H2 generation from water splitting is usually accelerated by the addition of hole scavengers, i.e. sacrificial reagents such as alcohols, amines, and thiols. However, the source of the protons of the evolved H2 is often neglected, and it is questionable whether such systems are really water splitting. Here, we discuss recent reports on sacrificial reagent-assisted photocatalytic water splitting and present our recent findings, which showcase that the sacrificial reagent in the investigated photocatalytic water splitting systems inherently undergoes acceptorless dehydrogenation, with H2O serving as the proton shuttle, the amount of which doesn't change during the course of the reaction.

Enhancing the Photocatalytic Performance of CsPbBr3 Nanocrystals through Ferrocene-Assisted Exciton Dissociation and Halide Vacancies

Excited-state interactions at the interfaces of nanocrystals play a crucial role in determining photocatalytic efficiency. CsPbBr3 nanocrystals (CPB NCs), celebrated for their exceptional photophysical properties, have been explored for organic photocatalysis. However, their intrinsic limitations, such as charge carrier recombination and stability issues, hinder their full potential. Strategies to enhance exciton dissociation, such as complexing CPB NCs with charge-shuttling molecules, have shown promise but remain underexplored for fully realizing their potential in improving the photocatalytic performance. We coupled ferrocene carboxylic acid (FcA) with CPB to extract the photogenerated holes, leveraging them to oxidize (1,2-dibromoethyl)benzene to phenacyl bromide. Optimization using pristine CPB NCs achieved a production rate of 5 μmol gcat-1 h-1, which increased to 13.1 μmol gcat-1 h-1 upon FcA incorporation, marking a 2.5-fold enhancement. Mechanistic investigations revealed the simultaneous involvement of electrons and holes, with oxygen acting as a reactant contributing to the oxygenated product. Halide vacancies were identified as critical adsorption sites for the substrate, with post-synthetic treatments enhancing these vacancies, resulting in over a 2-fold increase in the reaction rate. This work not only establishes an effective approach for phenacyl bromide synthesis but also highlights the potential of leveraging dissociated charge carriers to enhance photocatalysis using CPB NCs.

Photocatalytic applications of covalent organic frameworks: synthesis, characterization, and utility

Photocatalysis has emerged as an energy efficient and safe method to perform organic transformations, and many semiconductors have been studied for use as photocatalysts. Covalent organic frameworks (COFs) are an established class of crystalline, porous materials constructed from organic units that are easily tunable. COFs importantly display semiconductor properties and respectable photoelectric behaviour, making them a strong prospect as photocatalysts. In this review, we summarize the design, synthetic methods, and characterization techniques for COFs. Strategies to boost photocatalytic performance are also discussed. Then the applications of COFs as photocatalysts in a variety of reactions are detailed. Finally, a summary, challenges, and future opportunities for the development of COFs as efficient photocatalysts are entailed.

Photocatalytic Transformation of Organics to Valuable Chemicals - Quo Vadis?

Recent development in photocatalysis is increasingly focused on transforming organic compounds toward producing fine chemicals. Simple, non-selective oxidation reactions (degradation of pollutants) and very demanding solar-to-chemical energy conversion processes (production of solar fuels) face severe economic limitations influenced by still low efficiency and insufficient stability of the systems. Synthesis of fine chemicals, including reductive and oxidative selective transformations, as well as C-C and C-N coupling reactions, can utilise the power of photocatalysis. Herein, we present the recent progress in photocatalytic systems designed to synthesise fine chemicals. In particular, we discuss the factors influencing the efficiency and selectivity of the organic transformations, dividing them into intrinsic (related to individual properties of photocatalysts) and extrinsic (originating from the reaction environment). A rational design of the photocatalytic systems, based on a deep understanding of these factors, opens new perspectives for applied photocatalysis.

Iron(II) Phthalocyanine-Catalyzed Homodimerization and Tandem Diamination of Diazo Compounds with Primary Amines: Access to Construct Substituted 2,3-Diaminosuccinonitriles in One-Pot

We herein first report the homodimerization and tandem diamination of diazo compounds with primary amines catalyzed by the iron(II) phthalocyanine (PcFe(II)), which can construct one C-C bond and two C-N bonds within 20 min in one-pot. Compared to the traditional metal-catalyzed N-H insertion reaction between amines with diazo reagents, the developed reaction almost does not generate the N-H insertion product, but the homodimerization/tandem diamination product. The proposed mechanism studies indicate that primary amines play a crucial role in the homocoupling of diazo compounds via dimerization of iron(III)-acetonitrile radical generated from the reaction between diazoacetonitrile with PcFe(II) coordinated by bis(amines); the β-hydride elimination is involved, and then, the attack of primary amines toward the carbon atoms on the formed C-C bond is followed. Moreover, this novel reaction can be used to effectively prepare substituted 2,3-diaminosuccinonitriles with high yields and even up to >99:1 d.r., encouragingly these products contain both 1,2-diamines and succinonitrile motifs, which are two classes of important organic compounds with significant applications in many yields. This reaction is also suitable for the gram-scale preparation of 2,3-bis(phenylamino)succinonitrile (2a) with a yield of 84%. Therefore, the developed reaction represents a new type of transformation.

Catalyzing Artificial Photosynthesis with TiO2 Heterostructures and Hybrids: Emerging Trends in a Classical yet Contemporary Photocatalyst

Titanium dioxide (TiO2) stands out as a versatile transition-metal oxide with applications ranging from energy conversion/storage and environmental remediation to sensors and optoelectronics. While extensively researched for these emerging applications, TiO2 has also achieved commercial success in various fields including paints, inks, pharmaceuticals, food additives, and advanced medicine. Thanks to the tunability of their structural, morphological, optical, and electronic characteristics, TiO2 nanomaterials are among the most researched engineering materials. Besides these inherent advantages, the low cost, low toxicity, and biocompatibility of TiO2 nanomaterials position them as a sustainable choice of functional materials for energy conversion. Although TiO2 is a classical photocatalyst well-known for its structural stability and high surface activity, TiO2-based photocatalysis is still an active area of research particularly in the context of catalyzing artificial photosynthesis. This review provides a comprehensive overview of the latest developments and emerging trends in TiO2 heterostructures and hybrids for artificial photosynthesis. It begins by discussing the common synthesis methods for TiO2 nanomaterials, including hydrothermal synthesis and sol-gel synthesis. It then delves into TiO2 nanomaterials and their photocatalytic mechanisms, highlighting the key advancements that have been made in recent years. The strategies to enhance the photocatalytic efficiency of TiO2, including surface modification, doping modulation, heterojunction construction, and synergy of composite materials, with a specific emphasis on their applications in artificial photosynthesis, are discussed. TiO2-based heterostructures and hybrids present exciting opportunities for catalyzing solar fuel production, organic degradation, and CO2 reduction via artificial photosynthesis. This review offers an overview of the latest trends and advancements, while also highlighting the ongoing challenges and prospects for future developments in this classical yet rapidly evolving field.

CsPbBr3 Nanocrystals as Efficient Photocatalysts for Dehydrohalogenation: Toward Environmentally Friendly Trichloroethylene Synthesis

The demand for a benign alternative to energy-intensive industrial chemical transformations is critical. Lead halide perovskites have emerged as promising candidates due to their unique optoelectronic properties, including high absorption coefficients in the visible region, tunable band gaps, and long charge carrier-diffusion lengths. In this study, we present a model reaction to showcase the photocatalytic utility of perovskite nanocrystals (NCs). Specifically, we demonstrate the synthesis of trichloroethylene (TCEt) from 1,1,2,2-tetrachloroethane (TCE) using CsPbBr3 NCs under white light illumination. The band-edge positions of the NCs and the redox potential of TCE enable efficient electron transfer for C-Cl bond activation. Furthermore, while ensuring operational stability, CsPbBr3 NCs undergo light-controlled modification, leading to the formation of mixed-halide perovskite (CsPbBrxCl3-x) NCs during the reaction. This procedure yields a mixed-halide perovskite that maintains stability while containing the desired halide content. Additionally, the reaction produces HBr as a byproduct, serving as a self-cleaning technique to eliminate excess Br- ions from the solution. Ultimately, we achieve nearly 100% conversion of CsPbBr3 to pure CsPbCl3 NCs, with a full width at half-maximum of approximately 11.2 nm. Our clean and efficient approach to synthesizing TCEt using perovskite NCs provides interesting insights into violet light-emitting diode (LED) fabrication and color patterning. This study highlights the promising potential of perovskite materials for sustainable chemical transformations and optoelectronic applications.