A Supported Bismuth Halide Perovskite Photocatalyst for Selective Aliphatic and Aromatic C–H Bond Activation

Unveiling Synergetic Photocatalytic Activity from Heterometallic Ti/Ce Clusters

Titanium-oxo clusters, with their robust structure and suitable optical and electronic properties, have been widely investigated as photocatalysts. Heterometallic Ti/M-oxo clusters provide additional tunability and functionality, which enable systematic structure-activity investigations to elucidate the reaction mechanisms and improve the catalyst design. Incorporating cerium into Ti-oxo clusters can provide additional redox (CeIV/CeIII) and oxygen harvesting ability, but to date, only a limited number of structurally defined titanium-cerium (Ti/Ce) clusters have been reported due to their synthetic challenges. Herein, we report the synthesis and photocatalytic properties of two structurally defined Ti/Ce-oxo clusters, Ti8Ce2(BA)16 and Ti9Ce4(BA)20, as well as a TiCe-BA cluster with a calculated formula of Ti20Ce9O36(BA)42. Photocatalytic study of these clusters demonstrates that the amount of Ce3+ species greatly impacts its photocatalytic oxidation performance, and their superior photocatalytic reactivity toward aerobic alcohol oxidation can be contributed to the synergistic effects of the multiple radical species generated upon light absorption. This work represents a significant milestone in the construction of stable Ti/Ce-oxo clusters, enriching the current library of known heterometallic Ti/M-oxo clusters, and providing a series of crystalline materials with great promise of photoluminescence and photovoltaic chemistry.

Recent progress of metal halide perovskite materials in heterogeneous photocatalytic organic reactions

Photocatalytic technology is widely regarded as an important way to utilize solar energy and achieve carbon neutrality, which has attracted considerable attentions in various fields over the past decades. Metal halide perovskites (MHPs) are recognized as "superstar" materials due to their exceptional photoelectric properties, readily accessible and tunable structure, which made them intensively studied in solar cells, light-emitting diodes, and solar energy conversion fields. Since 2018, increased attention has been focused on applying the MHPs as a heterogeneous visible light photocatalyst in catalyzing organic synthesis reactions. In this review, we present an overview of photocatalytic technology and principles of heterogeneous photocatalysis before delving into the structural characteristics, stability, and classifications of MHPs. We then focus on recent developments of MHPs in photocatalyzing various organic synthesis reactions, such as oxidation, cyclization, C-C coupling etc., based on their classifications and reported reaction types. Finally, we discuss the main limitations and prospects regarding the application of metal halide perovskites in organic synthesis.

Solar-Light-Driven Photocatalytic Oxidative Coupling of Phenol Derivatives over Bismuth-Based Porous Metal Halide Perovskites

The selective oxidative coupling of phenol derivatives, involving carbon-carbon (C-C) and carbon-oxygen (C-O) bond formation, has emerged as a critical approach in the synthesis of natural products. However, achieving precise control over the selectivity in coupling reactions of unsubstituted phenols utilizing solar light as the driving force remains a big challenge. In this study, we report a series of porous Cs3Bi2X9 (X=Cl, Br, I) photocatalysts with tailored band gaps and compositions engineered for efficient solar-light-driven oxidative phenol coupling. Notably, p-Cs3Bi2Br9 exhibited about 73 % selectivity for C-C coupling, displaying a high formation rate of 47.3 μmol gcat -1 h-1 under solar radiation. Furthermore, this approach enables control of the site-selectivity for phenol derivatives on Cs3Bi2X9, enhancing C-C coupling. The distinctive porous structure and appropriate band-edge positions of Cs3Bi2Br9 facilitated efficient charge separation, and surface interaction/activation of phenolic hydroxyl groups, resulting in the kinetically preferred formation of C-C over C-O bond. Mechanistic insights into the reaction pathway, supported by comprehensive control experiments, unveiled the crucial role of interfacial charge transfers and Lewis acid Bi sites in stabilizing phenolic intermediates, thereby directing the regioselectivity of diradical couplings and resulting in the formation of unsymmetrical biphenols.

Heterogeneous Photocatalytic Strategies for C(sp3 )-H Activation

Activation of ubiquitous C(sp3 )-H bonds is extremely attractive but remains a great challenge. Heterogeneous photocatalysis offers a promising and sustainable approach for C(sp3 )-H activation and has been fast developing in the past decade. This Minireview focuses on mechanism and strategies for heterogeneous photocatalytic C(sp3 )-H activation. After introducing mechanistic insights, heterogeneous photocatalytic strategies for C(sp3 )-H activation including precise design of active sites, regulation of reactive radical species, improving charge separation and reactor innovations are discussed. In addition, recent advances in C(sp3 )-H activation of hydrocarbons, alcohols, ethers, amines and amides by heterogeneous photocatalysis are summarized. Lastly, challenges and opportunities are outlined to encourage more efforts for the development of this exciting and promising field.

Perovskite Membranes: Advancements and Challenges in Gas Separation, Production, and Capture

Perovskite membranes have gained considerable attention in gas separation and production due to their unique properties such as high selectivity and permeability towards various gases. These membranes are composed of perovskite oxides, which have a crystalline structure that can be tailored to enhance gas separation performance. In oxygen enrichment, perovskite membranes are employed to separate oxygen from air, which is then utilized in a variety of applications such as combustion and medical devices. Moreover, perovskite membranes are investigated for carbon capture applications to reduce greenhouse gas emissions. Further, perovskite membranes are employed in hydrogen production, where they aid in the separation of hydrogen from other gases such as methane and carbon dioxide. This process is essential in the production of clean hydrogen fuel for various applications such as fuel cells and transportation. This paper provides a review on the utilization and role of perovskite membranes in various gas applications, including oxygen enrichment, carbon capture, and hydrogen production.

Precisely Tailoring Heterometallic Polyoxotitanium Clusters for the Efficient and Selective Photocatalytic Oxidation of Hydrocarbons

Photocatalysis is a promising yet challenging approach for the selective oxidation of hydrocarbons to valuable oxygenated chemicals with O₂ under mild conditions. In this work, we report an atomically precise material model to address this challenge. The key to our solution is the rational incorporation of Fe species into polyoxotitanium cluster to form a heterometallic Ti₄ Fe₁ cocrystal. This newly designed cocrystal cluster, which well governs the energy and charge transfer as evidenced by spectroscopic characterizations and theoretical calculations, enables the synergistic process involving C(sp³ )-H bond activation by photogenerated holes and further reactions by singlet oxygen (¹ O₂ ). Remarkably, the cocrystal Ti₄ Fe₁ cluster achieves efficient and selective oxidation of hydrocarbons (C₅ to C₁₆ ) into aldehydes and ketones with a conversion rate up to 12 860 μmol g^-1  h^-1 , 5 times higher than that of Fe-doped Ti₃ Fe₁ cluster. This work provides insights into photocatalyst design at atomic level enabling synergistic catalysis.

In-Situ Anchoring Pb-Free Cs3 Bi2 Br9 @BiOBr Quantum Dots on NHx -Rich Silica with Enhanced Blue Emission and Satisfactory Stability for Photocatalytic Toluene Oxidation

All-inorganic metal halide perovskite quantum dots (QDs) have attracted attention from researchers with their fascinating optoelectronic properties. However, blue-emitting perovskite QDs typically have low photoluminescence quantum yield (PLQY). For potential commercial applications, it is preferable to replace Pb with an element having low toxicity. Here, Pb-free Cs₃ Bi₂ Br₉ @BiOBr perovskite QDs were anchored on the surface of NH_x -rich monodisperse silica (A-SiO₂ ) via N-Bi chemical bonding to isolate QDs from each other, thus enhancing efficient surface passivation and suppressing optical decay. Compared to unanchored QDs, Cs₃ Bi₂ Br₉ @BiOBr QDs/A-SiO₂ composites exhibited significantly enhanced blue emission performance, the PLQY of which increased from 16.62 % to 77.26 %, in addition to good water and environmental stability. Finally, the novel composites as photocatalysts were used to drive the oxidation of toluene, a template reaction of C(sp³ )-H bond activation and demonstrated astonishing conversion rates (4317 μmol g^-1  h^-1 ) with high selectivity (around 87 %).

Cellulose-Derived Carbon Dot-Guided Growth of ZnIn2 S4 Nanosheets for Photocatalytic Oxidation of 5-Hydroxymethylfurfural into 2,5-Diformylfuran

Cellulose-derived carbon (CC) dot-directed growth of ZnIn₂ S₄ was achieved through hydrothermal treatment of carboxylated cellulose followed by in situ growth of ZnIn₂ S₄ nanosheets. The carbon dots inherited from carboxylated cellulose equip plenty of surface carboxyl groups, which induce the ionic interaction with Zn²⁺ and In³⁺ and the guided growth of ZnIn₂ S₄ . As a result, the nanosheets of ZnIn₂ S₄ are evenly and intimately grown on the small carbon dots, providing high-speed channels for charges transfer. In conjunction with the reinforced visible-light capture and good conductivity of carbon dots, the resultant CC/ZnIn₂ S₄ shows an outstanding photocatalytic activity. As a proof-of-concept, visible-light-driven 5-hydroxymethylfurfural oxidation into 2,5-diformylfuran was conducted. The evolution of 2,5-diformylfuran over the optimal CC/ZnIn₂ S₄ sample can reach ∼2980 μmol g^-1 , about 3.4 times that of pristine ZnIn₂ S₄ . Additionally, the apparent quantum yield could attain 3.4 % at a wavelength of 400 nm.

Boosted Inner Surface Charge Transfer in Perovskite Nanodots@Mesoporous Titania Frameworks for Efficient and Selective Photocatalytic CO2 Reduction to Methane

Exploring high-efficiency and stable halide perovskite-based photocatalysts for the selective reduction of CO₂ to methane is a challenge because of the intrinsic photo- and chemical instability of halide perovskites. In this study, halide perovskites (Cs₃ Bi₂ Br₉ and Cs₂ AgBiBr₆ ) were grown in situ in mesoporous TiO₂ frameworks for an efficient CO₂ reduction. Benchmarked CH₄ production rates of 32.9 and 24.2 μmol g^-1  h^-1 with selectivities of 88.7 % and 84.2 %, were achieved, respectively, which are better than most reported halide perovskite photocatalysts. Focused ion-beam sliced-imaging techniques were used to directly image the hyperdispersed perovskite nanodots confined in mesopores with tunable sizes ranging from 3.8 to 9.9 nm. In situ X-ray photoelectronic spectroscopy and Kelvin probe force microscopy showed that the built-in electric field between the perovskite nanodots and mesoporous titania channels efficiently promoted photo-induced charge transfer. Density functional theory calculations indicate that the high methane selectivity was attributed to the Bi-adsorption-mediated hydrogenation of *CO to *HCO that dominates CO desorption.

In-Depth Comparative Study of the Cathode Interfacial Layer for a Stable Inverted Perovskite Solar Cell

Achieving long-term device stability is one of the most challenging issues that impede the commercialization of perovskite solar cells (PSCs). Recent studies have emphasized the significant role of the cathode interfacial layer (CIL) in determining the stability of inverted p-i-n PSCs. However, experimental investigations focusing on the influence of the CIL on PSC degradation have not been systematically carried out to date. In this study, a comparative analysis was performed on the PSC device stability by using four different CILs including practical oxides like ZnO and TiOx . A new implemented co-doping approach was found to results in high device performance and enhanced device stability. The PSC with a thick film configuration of chemically modified TiOx CIL preserves over 77 % of its initial efficiencies of 17.24 % for 300 h under operational conditions without any encapsulation. The PSCs developed are among the most stable reported for methylammonium lead iodide (MAPbI3 ) perovskite compositions.

Visible-light photocatalytic selective oxidation of C(sp3)–H bonds by anion–cation dual-metal-site nanoscale localized carbon nitride

Anion–cation dual-metal-site nanoscale localized carbon nitride exhibits a significantly enhanced photocatalytic activity for the oxidation of alkanes and alcohols with a high activity and a wide functional group tolerance.

Photoredox Organic Synthesis Employing Heterogeneous Photocatalysts with Emphasis on Halide Perovskite

Lately, heterogeneous semiconductor materials have been explored as an emerging type of efficient photocatalyst for photoredox organic synthesis. Among these semiconductors, lead halide perovskite materials demonstrate unique properties towards excellent charge separation and charge transfer, extremely long charge carrier migration, high efficiency in visible light absorption, and long excited states lifetimes, etc., as proved in ground-breaking solar cell applications, garnering necessary merits for an efficient catalytic system for photoredox organic reactions. Here, the latest progress in heterogeneous semiconductor materials towards this endeavor is examined, with particular emphasis on lead halide perovskite nanocrystals (NCs) in photocatalytic organic synthesis.

Revealing the A-Site Effect of Lead-Free A3 Sb2 Br9 Perovskite in Photocatalytic C(sp3 )-H Bond Activation

The lead-free halide perovskite A₃ Sb₂ Br₉ is utilized as a photocatalyst for the first time for C(sp³ )-H bond activation. A₃ Sb₂ Br₉ nanoparticles (A₃ Sb₂ Br₉ NPs) with different ratios of Cs and CH₃ NH₃ (MA) show different photocatalytic activities for toluene oxidation and the photocatalytic performance is enhanced when increasing the amount of Cs. The octahedron distortion caused by A-site cations can change the electronic properties of X-site ions and further affect the electron transfer from toluene molecules to Br sites. After the regulation of A-site cations, the photocatalytic activity is higher with A₃ Sb₂ Br₉ NPs than that with classic photocatalysts (TiO₂ , WO₃ , and CdS). The main active species involved in photocatalytic oxidation of toluene are photogenerated holes (h⁺ ) and superoxide anions (^. O₂ ^- ). The octahedron distortion by A-site cations affecting photocatalytic activity remains unique and is also a step forward for understanding more about halide-perovskite-based photocatalysis. The relationship between octahedron distortion and photocatalysis can also guide the design of new photocatalytic systems involving other halide perovskites.

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.