Han Sen Soo

Photocatalytic CO2 reduction reaction from practical gas sources is often severely compromised by the competitive O2 reduction reaction. Herein, we report an approach to switch O2 from a competitor into a promoter by arresting the oxygen reduction reaction pathway at the *OOH intermediate stage on BiOBr photocatalysts. The introduction of oxygen vacancies (VO) facilitates O2 reduction to *OOH, which is robustly anchored by VO-induced Lewis acidic Bi sites to form stable Bi-OOH motifs. The Bi-OOH motifs arrest further oxygen reduction pathways and preferentially adsorb CO2 to stabilize *COOH intermediates. A clear linear correlation between the VO concentration and the activity further verifies the vital role of these sites. The BiOBr-VO-0.7 photocatalyst with an optimized VO concentration achieves a 3.4-fold enhancement under 20% O2 (69.2 μmol g–1 h–1) and a 2.9-fold enhancement under simulated flue gas compared to anaerobic conditions for CO2 reduction to CO. Isotope-labeling experiments with 13C confirmed that the CO originated from CO2 reduction. Its practical viability is further demonstrated under natural sunlight and ambient air with a CO generation rate of 5.6 μmol g–1 h–1. This work provides a paradigm shift in the design of catalysts that can use real CO2 sources.

Direct photocatalytic upcycling of nonbiodegradable plastics using single‑atom catalysts (SACs) remain limited by the symmetric coordination of isolated metal sites, which constrains intermediate binding and charge transfer. Here, we reconstruct the heptazine units of polymeric carbon nitride (PCN) via a salt‐induced strategy, transforming S─CoPCN with a predominantly symmetric Co─N ₄ coordination environment into A─CoPCN featuring predominantly asymmetric Co─N ₃ configurations. Under white‐light irradiation at room temperature and 1 bar O ₂ , A─CoPCN enables the conversion of polystyrene to benzoic acid with a yield of 39.6% and a carbon recovery of 71.6%. Compared with previously reported systems that often require elevated temperatures, high O ₂ pressures, or external oxidants, this system operates under markedly milder conditions. The catalyst further demonstrates broad applicability across diverse nonbiodegradable plastics, including polystyrene, polyisobutylene, polylactic acid, polypropylene, polyethylene, and polyvinyl acetate. Mechanistic studies combining advanced spectroscopy and density functional theory calculations reveal that symmetry breaking suppresses electron delocalization, upshifts the Co d‐band center, and lowers exciton binding energy, thereby facilitating charge separation and transfer, promoting O ₂ adsorption and activation to generate reactive •O ₂ ⁻ species for efficient plastic upcycling. This work identifies coordination asymmetry as a key design principle for SACs and provides a general strategy for enhancing photocatalytic plastic upcycling.

We describe the synthesis of a family of photoemissive linear Cu(I) complexes bearing mesoionic carbenes (MIC) and amido ligands of the general formula Cu(MIC)NR ₂ (NR ₂ = carbazolide, diphenylamide). Careful tuning of the electronic and structural properties of both ligands enables modulation of the emission wavelengths from 400 to 520 nm and determines whether emission occurs mainly from locally excited or charge‐transfer states. Complexes containing naphthyl substituents in the MIC fragment generally show structured locally excited emissions, which is consistent with the presence of a low‐lying triplet state localized on the naphthyl fragment. In contrast, complexes without the naphthyl group generally display broader emission with a larger charge transfer contribution. The Cu complex supported by ^Naph 2 ^Mes NPh ₂ represents a unique case, displaying both a high‐energy fluorescence and a lower‐energy vibronically structured phosphorescence band. These results show that tuning the ligand‐centered triplet state enabled us to exert exquisite control over the nature of the absorption and emission mechanisms of these emissive linear Cu(I) complexes.

Photoelectrocatalysis offers a powerful method for driving organic transformations by combining light and electrical energy to access more extreme potentials to generate reactive intermediates under milder conditions. Herein, we report the first application of a metal halide perovskite photoelectrocatalytic system for C­(sp³)-H activation, leading to C–C and C–N bond formation via alkylation. A lead-free, alloyed double perovskite, Cs₂Ag_0.95Na_0.05BiBr₆, was engineered as a relatively stable photoanode and used catalytically (0.5–1 mol %) under visible-light irradiation and ambient conditions with 9,10-diphenylanthracene as a cocatalyst to facilitate cross-coupling organic syntheses. Extensive characterization of the photoanode by electrochemical analyses, powder X-ray diffraction, ultraviolet photoelectron spectroscopy, and scanning electron microscopy confirmed the structural integrity and photoelectrocatalytic activity of the Cs₂Ag_0.95Na_0.05BiBr₆ anode. Under optimal conditions, aliphatic substrates underwent C–H activation and coupling with electron-deficient SOMOphiles to afford C–C coupled products in up to 94% yield and C–N coupled products in up to 99% yield. Mechanistic studies, including isotope labeling, kinetic isotope effect competition experiments, and density functional theory calculations, reveal that the reaction proceeds via photogenerated •Br radicals that induce hydrogen atom transfer from the solvent molecules to generate nucleophilic alkyl radicals. These nucleophilic alkyl radicals then underwent polarity-matched addition to electron-deficient alkenes or azo compounds to form the desired products, with C–H activation of the substrate identified as the rate-determining step. This work demonstrates C–H functionalization and cross-coupling reactions under remarkably mild ambient conditions and establishes a new frontier for the application of metal halide perovskites in the photoelectrocatalytic activation and tandem transformation of small organic molecules.

Metal halide perovskites are attractive for optoelectronic applications, but the existing solution-based synthetic methods rely on hazardous solvents and lack reproducibility. To overcome these challenges, solvent-free mechanochemical synthesis of perovskites can be conducted, although traditional opaque ball milling equipment hinder real-time monitoring of the reaction progress. Herein, mechanochemistry was performed with time-lapsed in situ (TLIS) measurements to elucidate the optical properties during the synthesis. The TLIS spectrometer enabled real-time observation of the impact of varying the compositions on the absorption properties of formamidinium/methylammonium lead iodide (FA_xMA_1-xPbI₃, x = 0 to 1) and facilitated optimization of the synthesis duration. Moreover, we can accelerate the evaluation and directly observe the effects of different synthetic strategies for enhancing the photoluminescence quantum yield and stability of the perovskites, providing near-infrared (NIR) emitting tin-based perovskites FASnI_zBr_3-z (where z = 0 to 3) with core-shell structures. Intriguingly, halide ion migration was deduced in lead-free double perovskites Cs₂Na_yAg_1-yBiCl₆ (y = 0 to 1.0) at room temperature during aging after mechanochemical activation. Our work provides insights into the mechanochemistry of compounds with low thermodynamic barriers.

Metal halide perovskites, both lead‐based and lead‐free variants, have emerged as highly versatile materials with widespread applications across various fields, including photovoltaics, optoelectronics, and photocatalysis. This review provides a succinct overview of the recent advancements in the utilization of lead and lead‐free halide perovskites specifically in photocatalysis. We explore the diverse range of photocatalytic reactions enabled by metal halide perovskites, including organic transformations, carbon dioxide reduction, pollutant degradation, and hydrogen production. We highlight key developments, mechanistic insights, and challenges in the field, offering our perspectives on the future research directions and potential applications. By summarizing recent findings from the literature, this review aims to provide a timely resource for researchers interested in harnessing the full potential of metal halide perovskites for sustainable and efficient photocatalytic processes.

Dew harvesting, minimally influenced by climate and geographical locations, is an ideal method for addressing water shortage problems. Superhydrophilic surfaces, characterized by their highest affinity for water, are particularly attractive for this purpose as they can attract more water molecules via condensation. However, a significant challenge arises from the high surface capillary force that impedes water from sliding down and being effectively collected. The resulting water film on the superhydrophilic surface tends to stay around the edge of the water collection surface, leading to evaporation loss and reduced collection efficacy. To overcome this problem, triangular patterns with low surface adhesion to water were introduced at the edge of superhydrophilic surfaces. This modification, achieved through a wet chemical method and masked oxygen plasma treatment, has significantly improved the efficiency of water collection. Results indicate that the hybrid surface reduced the time for the first water droplet to slide down by half and increased water collection efficiency by 78% compared to uniform superhydrophilic surfaces and by 536% compared to uniform superhydrophobic surfaces under a relative humidity of 55% with a temperature difference of 15 °C. The underlying principles were elucidated through computational simulations, and the mechanisms driving the enhancement in collection efficiency were explained.

We describe the synthesis of a family of photoemissive linear Cu(I) complexes bearing mesoionic carbenes (MIC) and amido ligands of the general formula Cu(MIC)NR2 (NR2 = carbazolide, diphenylamide). Careful tuning of the electronic and structural properties of both ligands enables modulation of the emission wavelengths from 400 to 520 nm. We observe that the emission mechanism is highly dependent on the nature of the ligands and exhibits a dichotomy in behavior. Complexes bearing diphenylamide ligands CuMesMICNaphNPh2 and CuMesMIC3,5-CF3PhNPh2 and complexes containing a combination of carbazolide and electron-rich MIC ligands such as CuMesMICNaphCz and Cu3,5-MePhMICNaph Cz emit from locally excited (LE) states, while complexes bearing electron-rich carbazolide and electron-poor MIC ligands emit from charge transfer (CT) states. A rational design of the ligands enabled us to exert exquisite control over the nature of the absorption and emission mechanisms of these emissive linear CuI complexes.