Giant Electron–Hole Interactions in Confined Layered Structures for Molecular Oxygen Activation

The synergistic effect of Cl doping and Bi coupling to promote the carrier separation of BiOBr for efficient photocatalytic nitrogen reduction

Photocatalytic nitrogen reduction reaction (NRR) is a sustainable process for ammonia synthesis under mild conditions. However, photocatalytic NRR activity and are generally limited by inefficient carrier separation and transfer. Therefore, parallel engineering of bulk phase doping and surface coupling is critical to achieving the goal of efficient NRR. In this study, Cl doped BiOBr nanosheet assemblies (BiOBr/Cl) were constructed in delicately designed deep eutectic solvents (DESs), combined with ionothermal methods at low temperatures and Bi3+ exsolution reduction strategy at high temperatures. The unique liquid state and reducibility of DESs induce the reduction of Bi3+ and the in situ coupling of Bi quantum dots at the surface of BiOBr/Cl nanosheets along with the construction of Bi-BiOBr/Cl nanosheet assemblies. The experimental results show that Cl doping could reduce the exciton dissociation energy and promote its dissociation to free carriers. Bi quantum dots could form tightly coupled Schottky junction with BiOBr/Cl enabling the efficient and unidirectional transmission of photogenerated electrons from BiOBr/Cl to metal Bi. The formed electron deficient region at Schottky interface promotes the adsorption and activation of N2. The hierarchical structure of Bi-BiOBr/Cl nanosheet assembly benefits to providing more N2 adsorption active sites. The DFT calculation shows that the accumulation of high concentration of active hydrogen in Bi-BiOBr/Cl leads to a significant decrease of energy barrier of the first step hydrogenation of N2. Bi-BiOBr/Clis more inclined to adsorb nitrogen for NRR in comparison with H* for hydrogen production. The synergistic effect of Cl doping and Bi coupling result in a high NRR activity of Bi-BiOBr/Cl photocatalyst of 6.67 mmol·g-1·h-1, which was 11.3 times higher than that of initial BiOBr. This study provides a promising strategy for designing highly active NRR photocatalysts with high efficiency carrier dissociation and transport.

Moderate elimination of mycotoxins in vegetable oil triggered by superoxide anion and singlet oxygen

Establishing a moderate elimination strategy for mycotoxins with the maintained food nutrition is significant to food safety. Herein, the Au-NPs decorated defective Bi2WO6 (Au-BWO-OV) with modulated ROS generation was successfully synthesized, integrating the merits of defect-engineering and Au-NPs induced LSPR-effect. The Au-BWO-OV exhibited modified photoelectrochemical property and O2-adsorption capacity, supporting the selective generation of •O2- and 1O2 with moderate oxidizing ability. As a result, >90% of AFB1 and ZEN were eliminated within 100 and 50 min, along with the maintained nutrition in vegetable oil. Moreover, the reasonable degradation mechanism triggered by •O2- and 1O2 was proposed based on the trapping experiments, DFT calculations and LC-MS analysis for intermediate products, including the steps of hydrolysis, oxidative dissociation, cis-trans isomerization, and dehydroxylation. This work not only paved the way for balancing the contradiction between detoxification and nutrient retention, but also casted new insights into the ROS-mediated degradation mechanism.

Differentiating Reactive Oxygen Species with DNA Framework Monitors

The lifespan, oxidizing properties, bonding behaviors, and reactivity of reactive oxygen species (ROS) produced during photocatalytic activation can vary significantly due to the differences in electron configurations of ROS, which are dependent on their generation mechanisms: energy transfer or charge transfer. Hence, identifying and differentiating ROS of different mechanisms can improve our understanding of redox reactions and related diseases, providing a basis for the prevention and treatment of related diseases. Here, we have developed a DNA framework monitor (DFM) based on dynamic DNA structural changes to effectively distinguish the two types of ROS produced in photocatalytic activation of O2. This DFM provides a visualization tool for observing the reaction kinetics of ROS with DNA, not only distinguishing two types of ROS with different mechanisms but also serving as a universal system for evaluating the efficacy and performance of nanomaterials for ROS regulation.

Selective Generation of Reactive Oxygen Species in Photocatalytic Oxidation by Tuning Porphyrin-Based COFs' Dimensionality

Regulating the selective generation of reactive oxygen species (ROS) is a significant challenge in the field of photocatalytic oxidation, with successful approaches still being limited. Herein, we present a strategy to selectively generate singlet oxygen (1O2) and superoxide radicals (O2•-) by tuning the dimensionality of porphyrin-based covalent organic frameworks (COFs). The transformation of COFs from three-dimensional (3D) solids to two-dimensional (2D) sheets was achieved through the reversible protonation of the imine bond. Upon irradiation, both bulk and thin-layer COF-367 can transfer energy to O2 to generate 1O2. However, thin-layer COF-367 exhibited a superior performance compared to its bulk counterpart in activating O2 to form the O2•- radicals via electron transfer. After excluding the influences of the band structure, O2 adsorption energy, and frontier orbital composition attributed to the dimensionality of the COFs, it is reasonably speculated that the variance in ROS generation arises from the differential exposure ratios of the active surfaces, leading to distinct reaction pathways between the carrier and O2. This study is the first to explore the modulation mechanism of COF dimensionality on the activation of the O2 pathway, underscoring the importance of considering COF dimensionality in photocatalytic reactions.

Phosphate modified nanoarchitectonics for promoted photocatalytic singlet oxygen generation and carbamazepine degradation of (010) facet-exposed BiOCl

1O2 generation over (001) or (010) facet exposed BiOCl (B001 or B010) with/without phosphate modification were studied from the aspects of excitons involved energy transfer route, the O2- oxidation based charge transfer route and the H2O2 oxidation by HClO. Phosphate modification not only enhance charge separation thus result in H2O2 oxidation by HClO to release 1O2 but also weaken excitonic effect in the confined layer of BiOCl accordingly affect 1O2 generation via energy transfer. Considering [001] orientation favors the formation of excitons than that of [010] direction over BiOCl, excitons loss was hardly compensated by the H2O2 oxidation by HClO for 1O2 generation over phosphate modified B001. Nevertheless, limited excitonic effect makes the O2- oxidation by h+ via charge transfer as dominant route for 1O2 yielding over B010, the extra H2O2 oxidation with HClO after phosphate modification significantly enhance 1O2 generation over B010 followed with 2.2 times higher carbamazepine photodegradation activity. The initial attack of CC bond via 1O2 to form epoxide played important roles on carbamazepine degradation. This study demonstrated that the facet-specific phosphate modification of photocatalysts can finely tune reactive 1O2 species for superior pharmaceuticals degradations.

Hole Polaron-Mediated Suppression of Electron-Hole Recombination Triggers Efficient Photocatalytic Nitrogen Fixation

In the pursuit of successful photocatalytic transformations, challenges persist due to limitations in charge carrier utilization and transfer efficiency, which stemming from rapid recombination. Overcoming these limitations necessitates the exploration of novel mechanisms that enhance the effective separation of photogenerated electron-hole pairs. Herein, deviating from the conventional approach of enhancing carrier migration to separate photogenerated charges and extend their lifetime, the proposal is to directly prevent the recombination of photogenerated electrons and holes by forming hole polarons. Specifically, disordered pores are introduced on the surface of KTaO3 ultrathin sheets, and the clear-cut evidences in electron paramagnetic resonance, photoluminescence, and ultrafast spectroscopy unambiguously confirm the enhanced carrier-phonon coupling, which results in the formation of hole polarons to impede the recombination of photogenerated electron-hole pairs. Taking the challenging nitrogen oxidation reaction as an example, it is found that the hole polarons in atomic-disordered pore KTaO3 ultrathin nanosheets trigger outstanding photo-oxidation performance of  nitrogen (N2)to nitrate, with a nitrate-producing rate of 2.1 mg g-1 h-1. This scenario is undoubtedly applicable to a wide variety of photocatalytic reactions due to the common challenge of charge carrier recombination in all photocatalytic processes, manifesting broad implications for promoting photocatalysis performance.

Electron Delocalization Disentangles Activity-Selectivity Trade-Off of Transition Metal Phosphide Catalysts in Oxidative Desulfurization

Breaking the activity-selectivity trade-off has been a long-standing challenge in catalysis. Here, we proposed a nanoheterostructure engineering strategy to overcome the trade-off in metal phosphide catalysts for the oxidative desulfurization (ODS) of fuels. Experimental and theoretical results demonstrated that electron delocalization was the key driver to simultaneously achieve high activity and high selectivity for the molybdenum phosphide (MoP)/tungsten phosphide (WP) nanoheterostructure catalyst. The electron delocalization not only promoted the catalytic pathway transition from predominant radicals to singlet oxygens in H2O2 activation but also simultaneously optimized the adsorption of reactants and intermediates on Mo and W sites. The presence of such dual-enhanced active sites ideally compensated for the loss of activity due to the nonradical catalytic pathway, consequently disentangling the activity-selectivity trade-off. The resulting catalyst (MoWP2/C) unprecedentedly achieved 100% removal of thiophenic compounds from real diesel at an initial concentration of 2676 ppm of sulfur with a high turnover frequency (TOF) of 105.4 h-1 and a minimal O/S ratio of 4. This work provides fundamental insight into the structure-activity-selectivity relationships of heterogeneous catalysts and may inspire the development of high-performance catalysts for ODS and other catalytic fields.

Pyrene-Alkyne-Based Conjugated Porous Polymers with Skeleton Distortion-Mediated ⋅O2 - and 1O2 Generation for High-Selectivity Organic Photosynthesis

Reactive oxygen species (ROS) play a crucial role in determining photocatalytic reaction pathways, intermediate species, and product selectivity. However, research on ROS regulation in polymer photocatalysts is still in its early stages. Herein, we successfully achieved series of modulations to the skeleton of Pyrene-alkyne-based (Tetraethynylpyrene (TEPY)) conjugated porous polymers (CPPs) by altering the linkers (1,4-dibromobenzene (BE), 4,4'-dibromobiphenyl (IP), and 3,3'-dibromobiphenyl (BP)). Experiments combined with theoretical calculations indicate that BE-TEPY exhibits a planar structure with minimal exciton binding energy, which favors exciton dissociation followed by charge transfer with adsorbed O2 to produce ⋅O2 -. Thus BE-TEPY shows optimal photocatalytic activity for phenylboronic acid oxidation and [3+2] cycloaddition. Conversely, the skeleton of BP-TEPY is significantly distorted. Its planar conjugation decreases, intersystem crossing (ISC) efficiency increases, which makes it more prone for resonance energy transfer to generate 1O2. Therefore, BP-TEPY displays best photocatalytic activity in [4+2] cycloaddition and thioanisole oxidation. Both above reactant conversion and its product selectivity exceed 99 %. This work systematically reveals the intrinsic structure-activity relationship among the skeleton structure of CPPs, excitonic behavior, and selective generation of ROS, providing new insights for the rational design of highly efficient and selective CPPs photocatalysts.

Topological Transformation of Hydrogen-Terminated Germanium to Germanium Nanosheets for Fast Lithium Storage

Germanium has been recognized as a promising anode material for lithium-ion batteries (LIBs) due to its high theoretical capacity and excellent lithium-ion diffusivity. Nonetheless, it is challenging to enhance both the high-rate performance and long-term cycling stability simultaneously. This study introduces a novel heterostructure composed of germanium nanosheets integrated with graphene (Ge NSs@Gr). These nanosheets undergo an in situ phase transformation from a hydrogen-terminated multilayer germanium compound termed germanane (GeH) derived via topochemical deintercalation from CaGe2. This approach mitigates oxidation and prevents restacking by functionalizing the exfoliated germanane with octadecenoic organic molecules. The resultant germanium nanosheets retain their structural integrity from CaGe2 and present an exposed, active (111) surface that features an open crystal lattice, facilitating swift lithium-ion migration conducive to lithium storage. The composite material delivers a substantial reversible capacity of 1220 mA h g-1 at a current density of 0.2 C and maintains a capacity of 456 mA h g-1 even at an ultrahigh current density of 10 C over extended cycling. Impressively, a capacity of 316 mA h g-1 remains after 5000 cycles. The exceptional high-rate performance and durable cycling stability underscore the Ge NSs@Gr anode's potential as a highly viable option for LIBs.

Interior Exciton Extraction by Spatial-Controlled Iodine Doping in BiOBr Photocatalysts

Extracting interior photoinduced species to the surface before their recombination is of great importance in pursuing high-efficiency semiconductor-based photocatalysis. Traditional strategies toward charge-carrier extraction, mostly relying on the construction of an electric field gradient, would be invalid toward the neutral-exciton counterpart in low-dimensional systems. In this work, by taking bismuth oxybromide (BiOBr) as an example, we manipulate interior exciton extraction to the surface by implementing iodine doping at the edges of BiOBr plates. Spatial- and time-resolved spectroscopic analyses verified the accumulation of excitons and charge carriers at the edges of iodine-doped BiOBr (BiOBr-I) plates. This phenomenon could be associated with interior exciton extraction, driven by an energy-level gradient between interior and edge exciton states, and the following exciton dissociation processes. As such, BiOBr-I shows remarkable performance in photocatalytic C-H fluorination, mediated by both energy- and charge-transfer processes. This work uncovers the importance of spatial regulation of excitonic properties in low-dimensional semiconductor-based photocatalysis.

Developing Polymeric Carbon Nitrides for Photocatalytic H2O2 Production

Hydrogen peroxide (H2O2) plays a crucial role in various applications, such as green oxidation processes and the production of high-quality fuels. Currently, H2O2 is primarily manufactured using the indirect anthraquinone method, known for its significant energy consumption and the generation of intensive by-products. Extensive research has been conducted on the photocatalytic production of H2O2 via oxygen reduction reaction (ORR), with polymeric carbon nitride (PCN) emerging as a promising catalyst for this conversion. This review article is organized around two approaches. The first part main consists of the chemical optimization of the PCN structure, while the second focuses on the physical integration of PCN with other functional materials. The objective is to clarify the correlation between the physicochemical properties of PCN photocatalysts and their effectiveness in H2O2 production. Through a thorough review and analysis of the findings, this article seeks to stimulate new insights and achievements, not only in the domain of H2O2 production via ORR but also in other redox reactions.

Tuning interfacial oxygen vacancy level of bismuth oxybromide to enhance photocatalytic degradation of bisphenol A

Oxygen vacancies (OVs) have garnered significant interest for their role as active sites, enhancing the catalytic efficiency of various catalysts. Despite their widespread application in environmental purification processes, the generation of OVs conventionally depends on high-temperature conditions and strong reducing agents for the extraction of surface partial oxygen atoms from catalysts. In this work, bismuth oxybromide (BiOBr) nanosheets with varying levels of OVs were synthesized via a simple and effective solvothermal method. This novel method affords precise control over the conduction band (CB) and valence band (VB) positions of BiOBr. The presence of different OVs exhibited varying photocatalytic efficiencies in the degradation of bisphenol A (BPA) under visible light irradiation, with higher levels of OVs resulting in superior photocatalytic performance. Furthermore, radical scavenger experiments demonstrated that superoxide oxides (O2•-) and holes (h+) were the primary reactive oxygen species for BPA degradation. Additionally, BiOBr-OVs exhibited excellent anti-interference and stability in water matrices containing diverse inorganic anions and organic compounds. This work provides a simple and effective approach for the fine-regulating of catalysts through interfacial defect engineering, paving the way for their practical application in environmental decontamination.

Tailored Exfoliation of Polymeric Carbon Nitride for Photocatalytic H2O2 Production and CH4 Valorization Mediated by O2 Activation

The exfoliation of bulk C3N4 (BCN) into ultrathin layered structure is an effective strategy to boost photocatalytic efficiency by exposing interior active sites and accelerating charge separation and transportation. Herein, we report a novel nitrate anion intercalation-decomposition (NID) strategy that is effective in peeling off BCN into few-layer C3N4 (fl-CN) with tailored thickness down to bi-layer. This strategy only involves hydrothermal treatment of BCN in diluted HNO3 aqueous solution, followed by pyrolysis at various temperatures. The decomposition of the nitrate anions not only exfoliates BCN and changes the band structure, but also incorporates oxygen species onto fl-CN, which is conducive to O2 adsorption and hence relevant chemical processes. In photocatalytic O2 reduction under visible light irradiation, the H2O2 production rate over the optimal fl-CN-530 catalyst is 952 μmol g-1 h-1, which is 8.8 times that over BCN. More importantly, under full arc irradiation and in the absence of hole scavenger, CH4 can be photocatalytically oxidized by on-site formed H2O2 and active oxygen species to generate value-added C1 oxygenates with high selectivity of 99.2 % and record-high production rate of 1893 μmol g-1 h-1 among the metal-free C3N4-based photocatalysts.

Oxygen Vacancy Defect Enhanced NIR-II Photothermal Performance of BiOxCl Nanosheets for Combined Phototherapy of Cancer Guided by Multimodal Imaging

Narrow photo-absorption range and low carrier utilization are significant barriers that restrict the antitumor efficiency of 2D bismuth oxyhalide (BiOX, X = Cl, Br, I) nanosheets (NSs). Introducing oxygen vacancy (OV) defects can expand the absorption range and improve carrier utilization, which are crucial but also challenging. In this study, a series of BiOxCl NSs with different OV defect concentrations (x = 1, 0.7, 0.5) is developed, which shows full spectrum absorption and strong absorption in the second near-infrared region (NIR-II). Density functional theory calculations are utilized to calculate the crystal structure and density states of BiOxCl, which confirm that part of the carriers is separated by OV enhanced internal electric field to improve carrier utilization. The carriers without redox reaction can be trapped in the OV, leading to great majority of photo-generated carriers promoting the photothermal performance. Triggered by single NIR-II (1064 nm), BiOxCl NSs' bidirectional efficient utilization of carriers achieves synchronously combined phototherapy, leading to enhanced tumor ablation and multimodal diagnostic in vitro and vivo. It is thus believed that this work provides an innovative strategy to design and construct nanoplatforms of indirect band gap semiconductors for clinical phototheranostics.

2D/2D Heterojunction of BiOBr/BiOI Nanosheets for In Situ H2 O2 Production and Activation toward Efficient Photocatalytic Wastewater Treatment

The presence of toxic organic pollutants in aquatic environments poses significant threats to human health and global ecosystems. Photocatalysis that enables in situ production and activation of H2 O2 presents a promising approach for pollutant removal; however, the processes of H2 O2 production and activation potentially compete for active sites and charge carriers on the photocatalyst surface, leading to limited catalytic performance. Herein, a hierarchical 2D/2D heterojunction nanosphere composed of ultrathin BiOBr and BiOI nanosheets (BiOBr/BiOI) is developed by a one-pot microwave-assisted synthesis to achieve in situ H2 O2 production and activation for efficient photocatalytic wastewater treatment. Various experimental and characterization results reveal that the BiOBr/BiOI heterojunction facilitates efficient electron transfer from BiOBr to BiOI, enabling the one-step two-electron O2 reduction for H2 O2 production. Moreover, the ultrathin BiOI provides abundant active sites for H2 O2 adsorption, promoting in situ H2 O2 activation for •O2 - generation. As a result, the BiOBr/BiOI hybrid exhibits excellent activity for pollutant degradation with an apparent rate constant of 0.141 min-1 , which is 3.8 and 47.3 times that of pristine BiOBr and BiOI, respectively. This work expands the range of the materials suitable for in situ H2 O2 production and activation, paving the way toward sustainable environmental remediation using solar energy.

Mist Chemical Vapor Deposition of Bi13S18I2 for Photoelectrochemical-type Photodetection

Bismuth-based ternary compounds have attracted much attention owing to their various merits, such as low toxicity and tunable electrical and optical properties. However, these compounds are yet to be understood due to the lack of suitable targets limited by immature synthesis techniques. In this work, we aimed at the synthesis, properties investigation, and photodetection application of Bi13S18I2. Mist chemical vapor deposition was adopted for the deposition of the Bi13S18I2 thin film for the first time. The deposition mechanism was discussed from the perspective of crystal phase and surface morphology. Based on the Bi13S18I2 thin film synthesized at optimal temperature, we constructed a photoelectrochemical-type photodetector. The photodetection performance was evaluated from the points of electrolyte composition, working temperature, and bias voltage. This study would pave the way for the controllable synthesis and applications of bismuth-based ternary compounds.

Strain-Induced Surface Interface Dual Polarization Constructs PML-Cu/Bi12O17Br2 High-Density Active Sites for CO2 Photoreduction

The insufficient active sites and slow interfacial charge transfer of photocatalysts restrict the efficiency of CO2 photoreduction. The synchronized modulation of the above key issues is demanding and challenging. Herein, strain-induced strategy is developed to construct the Bi-O-bonded interface in Cu porphyrin-based monoatomic layer (PML-Cu) and Bi12O17Br2 (BOB), which triggers the surface interface dual polarization of PML-Cu/BOB (PBOB). In this multi-step polarization, the built-in electric field formed between the interfaces induces the electron transfer from conduction band (CB) of BOB to CB of PML-Cu and suppresses its reverse migration. Moreover, the surface polarization of PML-Cu further promotes the electron converge in Cu atoms. The introduction of PML-Cu endows a high density of dispersed Cu active sites on the surface of PBOB, significantly promoting the adsorption and activation of CO2 and CO desorption. The conversion rate of CO2 photoreduction to CO for PBOB can reach 584.3 μmol g-1, which is 7.83 times higher than BOB and 20.01 times than PML-Cu. This work offers valuable insights into multi-step polarization regulation and active site design for catalysts.

Turning on Singlet Oxygen Generation by Outer-Sphere Microenvironment Modulation in Porphyrinic Covalent Organic Frameworks for Photocatalytic Oxidation

Singlet oxygen (1 O2 ) is ubiquitously involved in various photocatalytic oxidation reactions; however, efficient and selective production of 1 O2 is still challenging. Herein, we reported the synthesis of nickel porphyrin-based covalent organic frameworks (COFs) incorporating functional groups with different electron-donating/-withdrawing features on their pore walls. These functional groups established a dedicated outer-sphere microenvironment surrounding the Ni catalytic center that tunes the activity of the COFs for 1 O2 -mediated thioether oxidation. With the increase of the electron-donating ability of functional groups, the modulated outer-sphere microenvironment turns on the catalytic activity from a yield of nearly zero by the cyano group functionalized COF to an excellent yield of 98 % by the methoxy group functionalized one. Electronic property investigation and density-functional theory (DFT) calculations suggested that the distinct excitonic behaviors attributed to the diverse band energy levels and orbital compositions are responsible for the different activities. This study represents the first regulation of generating reactive oxygen species (ROS) based on the strategy of outer-sphere microenvironment modulation in COFs.

Singlet oxygen: Properties, generation, detection, and environmental applications

Singlet oxygen (1O2) is molecular oxygen in the excited state with high energy and electrophilic properties. It is widely found in nature, and its important role is gradually extending from chemical syntheses and medical techniques to environmental remediation. However, there exist ambiguities and controversies regarding detection methods, generation pathways, and reaction mechanisms which have hindered the understanding and applications of 1O2. For example, the inaccurate detection of 1O2 has led to an overestimation of its role in pollutant degradation. The difficulty in detecting multiple intermediate species obscures the mechanism of 1O2 production. The applications of 1O2 in environmental remediation have also not been comprehensively commented on. To fill these knowledge gaps, this paper systematically discussed the properties and generation of 1O2, reviewed the state-of-the-art detection methods for 1O2 and long-standing controversies in the catalytic systems. Future opportunities and challenges were also discussed regarding the applications of 1O2 in the degradation of pollutants dissolved in water and volatilized in the atmosphere, the disinfection of drinking water, the gas/solid sterilization, and the self-cleaning of filter membranes. This review is expected to provide a better understanding of 1O2-based advanced oxidation processes and practical applications in the environmental protection of 1O2.

Photosynthesis of Benzonitriles on BiOBr Nanosheets Promoted by Vacancy Associates

Photocatalytic organic functionalization reactions represent a green, cost-effective, and sustainable synthesis route for value-added chemicals. However, heterogeneous photocatalysis is inefficient in directly activating ammonia molecules for the production of high-value-added nitrogenous organic products when compared with oxygen activation in the formation of related oxygenated compounds. In this study, we report the heterogeneous photosynthesis of benzonitriles by the ammoxidation of benzyl alcohols (99 % conversion, 93 % selectivity) promoted using BiOBr nanosheets with surface vacancy associates. In contrast, the main reaction of catalysts with other types of vacancy sites is the oxidation of benzyl alcohol to benzaldehyde or benzoic acid. Experimental measurements and theoretical calculations have demonstrated a specificity of vacancy type with respect to product selectivity, which arises from the adsorption and activation of NH3 and O2 that is required to promote subsequent C-N coupling and oxidation to nitrile. This study provides a better understanding of the role of vacancies as catalytic sites in heterogeneous photocatalysis.

Efficient Strategies to Use β-Cationic Porphyrin-Imidazolium Derivatives in the Photoinactivation of Methicillin-Resistant Staphylococcus aureus

Bacterial resistance to antibiotics is a critical global health issue and the development of alternatives to conventional antibiotics is of the upmost relevance. Antimicrobial photodynamic therapy (aPDT) is considered a promising and innovative approach for the photoinactivation of microorganisms, particularly in cases where traditional antibiotics may be less effective due to resistance or other limitations. In this study, two β-modified monocharged porphyrin-imidazolium derivatives were efficiently incorporated into polyvinylpyrrolidone (PVP) formulations and supported into graphitic carbon nitride materials. Both porphyrin-imidazolium derivatives displayed remarkable photostability and the ability to generate cytotoxic singlet oxygen. These properties, which have an important impact on achieving an efficient photodynamic effect, were not compromised after incorporation/immobilization. The prepared PVP-porphyrin formulations and the graphitic carbon nitride-based materials displayed excellent performance as photosensitizers to photoinactivate methicillin-resistant Staphylococcus aureus (MRSA) (99.9999% of bacteria) throughout the antimicrobial photodynamic therapy. In each matrix, the most rapid action against S. aureus was observed when using PS 2. The PVP-2 formulation needed 10 min of exposure to white light at 5.0 µm, while the graphitic carbon nitride hybrid GCNM-2 required 20 min at 25.0 µm to achieve a similar level of response. These findings suggest the potential of graphitic carbon nitride-porphyrinic hybrids to be used in the environmental or clinical fields, avoiding the use of organic solvents, and might allow for their recovery after treatment, improving their applicability for bacteria photoinactivation.

Elemental-Doping-Induced Orbital Redistribution in Conjugated Polymer Boosts Charge-Transfer-Mediated Singlet Oxygen Production

Beyond the traditional exciton-based energy transfer, carrier-involved charge transfer provides an alternative pathway to overcoming spin restriction in photocatalytic singlet oxygen (1O2) generation. However, the charge-transfer-mediated method usually suffers from insufficient charge-carrier concentration and distribution, which are related to the electronic band structure. Herein, exemplified by polymeric carbon nitride (PCN), we propose an orbital-redistribution strategy for facilitating charge-transfer-mediated 1O2 generation. On the basis of theoretical simulation and spectroscopic characterizations, we demonstrated that the incorporation of bromine could dramatically facilitate the redistribution of the HOMO and LUMO in PCN, resulting in promoted exciton dissociation and adjacent electron/hole distribution. Benefiting from those, bromine-doped polymeric carbon nitride (Br-PCN) exhibited an obvious enhancement in the production of 1O2 via a two-step charge-transfer process. This work not only uncovers a promising method for regulating photoexcitation in polymeric photocatalysts but also sheds new light on photocatalytic 1O2 generation.

Recent advances of semiconductor photocatalysis for water pollutant treatment: mechanisms, materials and applications

Semiconductor photocatalysis has become an increasing area of interest for use in water treatment methods. This review systematically presents the recent developments of emerging semiconductor photocatalysis system and their application in the removal of water pollutants. A brief overview of the semiconductor photocatalysis mechanism involved with the generation of reactive oxygen species (ROS) is provided first. Then a detailed explanation of the development of TiO2-based, g-C3N4-based, and bismuth-based semiconductor materials and their applications in the degradation of water pollutants are highlighted with recent illustrative examples. Furthermore, the future prospects of semiconductor photocatalysis for water treatment are critically analyzed.

Near-Ultraviolet Light-Driven Photocathodic Activity for (001)-Oriented BiOCl Thin Films Synthesized by Mist Chemical Vapor Deposition

Semitransparent and homogeneous bismuth oxychloride (BiOCl) thin films with (001) preferred orientation were synthesized on polycrystalline Sn:In₂O₃-glass substrates by mist chemical vapor deposition. The films showed photocathodic activity even under near-ultraviolet light within the band gap due to the in-gap states induced by oxygen vacancies. Higher synthesis temperatures resulted in a significant increase of photocurrent density under ultraviolet light. While the longer lifetime of photocarriers led to an increase of internal quantum efficiency, the larger band-edge absorption significantly contributed to the higher external quantum efficiency.

2D defect-engineered Ag-doped γ-Fe2O3/BiVO4: The effect of noble metal doping and oxygen vacancies on exciton-triggering photocatalysis production of singlet oxygen

The selectivity of singlet oxygen (1O2) holds promising applications in complex environmental systems due to its ability to preferentially oxidize target pollutants. Usually, 1O2 in photocatalytic systems is generated via the electron transfer pathway and •O2- plays an important role as an intermediate, while the exciton-based energy transfer pathway for 1O2 generation has been less studied. Here, a 2D Ag-γ-Fe2O3/BiVO4 with oxygen vacancies was designed which was capable of generating 1O2 by an exciton-based energy transfer-dominated approach, as strongly demonstrated by the results of steady-state fluorescence spectroscopy and phosphorescence spectroscopy. In the Z-type heterojunction photocatalyst system, Ag acted as an electron mediator to promote not only the generation of free carriers but also the generation of singlet excitons, while the appropriate concentration of oxygen vacancies further promotes the exciton-triggering photocatalysis production of 1O2. The Ag-γ-Fe2O3/BiVO4 could degrade 99.4% of sulfadiazine within 90 min, and 1O2 played an important role in the degradation of sulfadiazine, as shown by EPR and active species capture experiments. Ecotoxicity predictions indicated that the main byproducts of sulfadiazine degradation by Ag-γ-Fe2O3/BiVO4 were low in toxicity. The prepared photocatalysts provide a new idea for obtaining 1O2 and designing photocatalysts with selectivity.

Spatial confinement: A green pathway to promote the oxidation processes for organic pollutants removal from water

Organic pollutants removal from water is pressing owing to the great demand for clean water. Oxidation processes (OPs) are the commonly used method. However, the efficiency of most OPs is limited owing to the poor mass transfer process. Spatial confinement is a burgeoning way to solve this limitation by use of nanoreactor. Spatial confinement in OPs would (i) alter the transport characteristics of protons and charges; (ii) bring about molecular orientation and rearrangement; (iii) cause the dynamic redistribution of active sites in catalyst and reduce the entropic barrier that is high in unconfined space. So far, spatial confinement has been utilized for various OPs, such as Fenton, persulfate, and photocatalytic oxidation. A comprehensive summary and discussion on the fundamental mechanisms of spatial confinement mediated OPs is needed. Herein, the application, performance and mechanisms of spatial confinement mediated OPs are overviewed firstly. Subsequently, the features of spatial confinement and their effects on OPs are discussed in detail. Furthermore, environmental influences (including environmental pH, organic matter and inorganic ions) are studied with analyzing their intrinsic connection with the features of spatial confinement in OPs. Lastly, challenges and future development direction of spatial confinement mediated OPs are proposed.

Multiple Interface Coupling in Ultrathin Mn-based Composites for Superior Catalytic Oxidation: Implications of Interface Coupling on Structural Defects

Manganese oxide has been recognized as one of the most promising gaseous heterogeneous catalysts due to its low cost, environmental friendliness, and high catalytic oxidation performance. The modulation of the interfacial coupling effect of manganese oxides by chemical means is considered a critical and effective way to improve the catalytic performance. Herein, a novel one-step synthetic strategy of highly-efficient ultrathin manganese-based catalysts is proposed through optimal regulation of metal/manganese oxide multi-interfacial coupling. Carbon monoxide (CO) and propane (C₃H₈) oxidation are employed as probe reactions to investigate the structure-catalytic mechanism - catalytic performance relationship. The ultrathin manganese (Mn)-based catalyst exhibits superior low-temperature catalytic activity with a 90% conversion of CO/C₃H₈ realized at 106℃ and 350℃. Subsequently, the effect of "interfacial effect" on the intrinsic properties of manganese oxides is revealed. The ultrathin appearance of two-dimensional (2D) manganese dioxide (MnO₂) nanosheets changes the binding force in the vertical direction, thus resulting in an increase in the average manganese-oxygen (Mn-O) bond length and exposing more surface defects. Besides, the introduction of Copper (Cu) species into the catalyst further weakens the Mn-O bond and promotes the generation of oxygen vacancies, which subsequently enhances the oxygen migration rate. This study provides new insights into the optimal design of transition metal oxide interfacial assemblies for efficient catalytic reactions.

Vacancy-cluster-mediated surface activation for boosting CO2 chemical fixation

The cycloaddition of CO2 with epoxides towards cyclic carbonates provides a promising pathway for CO2 utilization. Given the crucial role of epoxide ring opening in determining the reaction rate, designing catalysts with rich active sites for boosting epoxide adsorption and C-O bond cleavage is necessary for gaining efficient cyclic carbonate generation. Herein, by taking two-dimensional FeOCl as a model, we propose the construction of electron-donor and -acceptor units within a confined region via vacancy-cluster engineering to boost epoxide ring opening. By combing theoretical simulations and in situ diffuse reflectance infrared Fourier-transform spectroscopy, we show that the introduction of Fe-Cl vacancy clusters can activate the inert halogen-terminated surface and provide reactive sites containing electron-donor and -acceptor units, leading to strengthened epoxide adsorption and promoted C-O bond cleavage. Benefiting from these, FeOCl nanosheets with Fe-Cl vacancy clusters exhibit enhanced cyclic carbonate generation from CO2 cycloaddition with epoxides.

Atomic design of dual-metal hetero-single-atoms for high-efficiency synthesis of natural flavones

Single-atom (SA) catalysts provide extensive possibilities in pursuing fantastic catalytic performances, while their preparation still suffers from metal aggregation and pore collapsing during pyrolysis. Here we report a versatile medium-induced infiltration deposition strategy for the fabrication of SAs and hetero-SAs (MaN4/MbN4@NC; Ma = Cu, Co, Ni, Mn, Mb = Co, Cu, Fe, NC = N-doped carbon). In-situ and control experiments reveal that the catalyst fabrication relies on the "step-by-step" evolution of Ma-containing metal-organic framework (MOF) template and Mb-based metal precursor, during which molten salt acts as both pore generator in the MOF transformation, and carrier for the oriented infiltration and deposition of the latter to eventually yield metal SAs embedded on hierarchically porous support. The as-prepared hetero-SAs show excellent catalytic performances in the general synthesis of 33 kinds of natural flavones. The highly efficient synthesis is further strengthened by the reliable durability of the catalyst loaded in a flow reactor. Systematic characterizations and mechanism studies suggest that the superior catalytic performances of CuN4/CoN4@NC are attributed to the facilitated O2 activating-splitting process and significantly reduced reaction energy barriers over CoN4 due to the synergetic interactions of the adjacent CuN4.

Enhanced Exciton Effect and Singlet Oxygen Generation Triggered by Tunable Oxygen Vacancies on Bi2MoO6 for Efficient Photocatalytic Degradation of Sodium Pentachlorophenol

Construction of the tunable oxygen vacancies (OVs) is widely utilized to accelerate molecular oxygen activation for boosting photocatalytic performance. Herein, the in-situ introduction of OVs on Bi2MoO6 was accomplished using a calcination treatment in an H2/Ar atmosphere. The introduced OVs can not only facilitate carrier separation, but also strengthen the exciton effect, which accelerates singlet oxygen generation through the energy transfer process. Superior carrier separation and abundant singlet oxygen played a crucial role in favoring photocatalytic NaPCP degradation. The optimal BMO-001-300 sample exhibited the fastest NaPCP degradation rate of 0.033 min-1, about 3.8 times higher than that of the pristine Bi2MoO6. NaPCP was effectively degraded and mineralized mainly through dechlorination, dehydroxylation and benzene ring opening. The present work will shed light on the construction and roles of OVs in semiconductor-based photocatalysis and provide a novel insight into ROS-mediated photocatalytic degradation.

Spatial Band Separation in a Surface Doped Heterolayered Structure for Realizing Efficient Singlet Oxygen Generation

Singlet oxygen (¹ O₂ ) with electrical neutrality and long lifetime holds great promise in producing high-added-value chemicals via a selective oxidation reaction. However, photocatalytic ¹ O₂ generation via the charge-transfer mechanism still suffers from low efficiency due to the mismatched redox capacities and low concentration of photogenerated carriers in confined systems. Herein, by taking bismuth oxysilicate (Bi₂ O₂ SiO₃ ) with alternating heterogeneous layered structure as a model, it is shown that iodine doping can facilitate the spatial redistributions of bands on alternated [Bi₂ O₂ ] and [SiO₃ ] layers, which can promote the separation and transfer of photogenerated charge carriers. Meanwhile, the band positions of Bi₂ O₂ SiO₃ are optimized to match the redox potential of ¹ O₂ generation. Benefiting from these features, iodine-doped Bi₂ O₂ SiO₃ exhibits efficient ¹ O₂ generation with respect to its pristine counterpart, leading to promoted performance in the selective sulfide oxidation reaction. A new strategy is offered here for optimizing charge-transfer-mediated ¹ O₂ generation.

Surface Boronizing Can Weaken the Excitonic Effects of BiOBr Nanosheets for Efficient O2 Activation and Selective NO Oxidation under Visible Light Irradiation

The photocatalytic O₂ activation for pollutant removal highly depends on the controlled generation of desired reactive oxygen species (ROS). Herein, we demonstrate that the robust excitonic effect of BiOBr nanosheets, which is prototypical for singlet oxygen (¹O₂) production to partially oxidize NO into a more toxic intermediate NO₂, can be weakened by surface boronizing via inducing a staggered band alignment from the surface to the bulk and simultaneously generating more surface oxygen vacancy (V_O). The staggered band alignment destabilizes excitons and facilitates their dissociation into charge carriers, while surface V_O traps electrons and efficiently activates O₂ into a superoxide radical (^•O₂^-) via a one-electron-transfer pathway. Different from ¹O₂, ^•O₂^- enables the complete oxidation of NO into nitrate with high selectivity that is more desirable for safe indoor NO remediation under visible light irradiation. This study provides a facile excitonic effect manipulating method for layered two-dimensional photocatalysts and sheds light on the importance of managing ROS production for efficient pollutant removal.

Facet Engineering in Constructing Lewis Acid-Base Pairs for CO2 Cycloaddition to High Value-Added Carbonates

Cycloaddition of epoxides with CO₂ to synthesis cyclic carbonates is an atom-economic pathway for CO₂ utilization with promising industry application value, while its efficiency was greatly inhibited for the lack of highly active catalytic sites. Herein, by taking BiOX (X = Cl, Br) with layered structure for example, we proposed a facet engineering strategy to construct Lewis acid-base pairs for CO₂ cycloaddition, where the typical BiOBr with (010) facets expose surface Lewis acid Bi sites and Lewis base Br sites simultaneously. By the combination of in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and theoretical calculations, the oxygen atom of the epoxide is interacted with the Lewis acid Bi site to activate the ternary ring, then facilitates the attack of the carbon atom by the Lewis base Br site for the ring-opening of the epoxide, which is the rate-determining step in the cycloaddition reaction. As a result, the BiOBr-(010) with rich surface Lewis acid-base pairs showed a high conversion of 85% with 100% atomic economy in the synthesis of cyclic-carbonates without any cocatalyst. This study provides a model structure for CO₂ cycloaddition to high value-added long chain chemicals.

Surface modification of ZnIn2S4 layers to realize energy-transfer-mediated photocatalysis

Photocatalytic selective aerobic oxidation reactions are crucial in designing advanced organic intermediates, but suffer from low conversion efficiency. Hence, activating O2 to create suitable reactive oxygen species, such as singlet oxygen (1O2), can significantly increase the yield of desired products. Herein, using ZnIn2S4 nanosheets as a model system, we build a surface-modified theoretical structure, where a surface-covered non-conductive macromolecular chain, polyvinyl pyrrolidone (PVP), is bound to ZnIn2S4 and influences the O2 adsorption process. PVP on the surface significantly changes the electronic structure and suppresses electron conduction of ZnIn2S4 nanosheets. Therefore, abundantly photogenerated and long-lived species transfer their energy to physically absorbed O2 to efficiently generate 1O2, which can oxidize sulphides into their corresponding sulphoxides. For sulphoxidation of different sulphides, surface modification brings a 3-9-fold increase in conversion efficiency and high selectivities ≥98%. This study provides a feasible way of boosting 1O2-generation-related photocatalytic reactions.

Construction of dual transfer channels in graphitic carbon nitride photocatalyst for high-efficiency environmental pollution remediation: Enhanced exciton dissociation and carrier migration

Graphitic carbon nitride (g-C₃N₄) is a promising candidate for photocatalysis, but exhibits moderate activity due to strongly bound excitons and sluggish charge migration. The dissociation of excitons to free electrons and holes is considered an effective strategy to enhance photocatalytic activity. Herein, a novel boron nitride quantum dots (BNQDs) modified P-doped g-C₃N₄ photocatalyst (BQPN) was successfully prepared by thermal polymerization method. Photoluminescence techniques and photoelectrochemical tests demonstrated that the introduction of P atoms and BNQDs promoted the dissociation of excitons and the migration of photogenerated carriers. Specifically, theoretical calculations revealed that P substitutions were the sites of pooled electrons, while BNQDs were the excellent photogenerated hole extractors. Accordingly, compared with g-C₃N₄, the BQPN showed improved performance in degrading four non-steroidal anti-inflammatory drugs (NSAIDs) under visible light irradiation. This work not only establishes an in-depth understanding of excitonic regulation in g-C₃N₄, but also offers a promising photocatalytic technology for environmental remediation.

Superoxide anion and singlet oxygen dominated faster photocatalytic elimination of nitric oxide over defective bismuth molybdates heterojunctions

Establishing an ideal photocatalytic system with efficient reactive oxygen species (ROS) generation has been regarded as the linchpin for realizing efficient nitric oxide (NO) removal and unveiling the ROS-mediated mechanism. In this work, a novel oxygen-deficient 0D/1D Bi_3.64Mo_0.36O_6.55/Bi₂MoO₆ heterojunctions (BMO-12-H) were successfully synthesized under the enlightenment of clarified crystal growth mechanism of bismuth molybdates. Because of the synergies between defect-engineering and heterojunction-construction, BMO-12-H demonstrated improved photoelectrochemical properties and O₂ adsorption capacity, which in turn facilitated the ROS generation and conversion. The enhancement of •O₂^- and ¹O₂ endowed BMO-12-H with strengthened NO removal efficiency (59%) with a rate constant of 12.6*10^-2 min^-1. A conceivable NO removal mechanism dominated by •O₂^- and ¹O₂ was proposed and verified based on the theoretical calculations and in-situ infrared spectroscopy tests, where hazardous NO was oxidized following two different exothermic pathways: the •O₂^--induced NO → NO₃^- process and the ¹O₂-induced NO → NO₂ → NO₃^- process. This work offers a basic guideline for accelerating ROS generation by integrating defect-engineering and heterojunction-construction, and provides new insights into the mechanism of efficient NO removal dominated by •O₂^- and ¹O₂.

Multi-channel charge transfer of hierarchical TiO2 nanosheets encapsulated MIL-125(Ti) hollow nanodisks sensitized by ZnSe for efficient CO2 photoreduction

Metal-organic frameworks-based hybrids with desirable components, structures, and properties have been proven to be promising functional materials for photocatalysis and energy conversion applications. Herein, we proposed and prepared ZnSe sensitized hierarchical TiO₂ nanosheets encapsulated MIL-125(Ti) hollow nanodisks with sandwich-like structure (MIL-125(Ti)@TiO₂\ZnSe HNDs) through a successive solvothermal and selenylation reaction route using the as-prepared MIL-125(Ti) nanodisks as precursor. In the ternary MIL-125(Ti)@TiO₂\ZnSe HNDs hybrid, TiO₂ nanosheets were transformed from MIL-125(Ti) and in situ grown on both sides of the MIL-125(Ti) shell, forming sandwich-like hollow nanodisks, and the ratio of MIL-125(Ti)/TiO₂ can be tuned by changing the solvothermal time. The ternary hybrids possess the advantages of enhanced incident light utilization and abundant accessible active sites originating from bimodal pore-size distribution and hollow sandwich-like heterostructure, which can effectively promote CO₂ photoreduction reaction. Especially, the formed multi-channel charge transfer routes in the ternary heterojunctions contribute to the charge transfer/separation and extend the lifespan of charge-separated state, thus boosting CO₂ photoreduction performance. The CO (513.1 μmol g^-1h^-1) and CH₄ (45.1 μmol g^-1h^-1) evolution rates over the optimized ternary hybrid were greatly enhanced compared with the single-component and binary hybrid photocatalysts.

Solvent-Induced Isomeric Cu13 Nanoclusters: Chlorine to Copper Charge Transfer Boosting Molecular Oxygen Activation in Sulfide Selective Oxidation

Isomers with minimal structural dissimilarities are promising research objects to obtain a comprehensive understanding of structure-property relationships; however, comparability of isomeric structures is a prerequisite. Herein, two quasi-structurally isomeric 13-nuclei copper nanoclusters (Cu NCs) (Cu13a and Cu13b) containing highly similar Cu₁₃ kernels and different arrangements of peripheral ligands were obtained using a solvent-induced strategy. The exotic chloride ion is shown to play a prominent role in inducing the selective formation of two quasi-isomers, where the comparative study to establish a structure-property relationship was realized. Due to the charge transition from chlorine to the copper core (X_(Cl)M_(Cu)CT), the molecular oxygen activation of Cu13a showed higher singlet oxygen (¹O₂) and lower superoxide radical (O₂^•-) yields compared to those of Cu13b, which gives it better catalytic selectivity for the ¹O₂ involved selective oxidation of sulfides. The present work not only offers a controllable strategy for the rational design and synthesis of quasi-structurally isomeric Cu NCs but also provides a pathway to boost catalytic selectivity by a halogen to metal core charge transition.

A Universally EDTA-Assisted Synthesis of Polytypic Bismuth Telluride Nanoplates with a Size-Dependent Enhancement of Tumor Radiosensitivity and Metabolism In Vivo

Bismuth telluride (Bi₂Te₃) is an available thermoelectric material with the lowest band gap among bismuth chalcogenides, revealing a broad application in photocatalysis. Unfortunately, its size and morphology related to a radio-catalysis property have rarely been explored. Herein, an ethylenediaminetetraacetic acid (EDTA)-assisted hydrothermal strategy was introduced to synthesize polytypic Bi₂Te₃ nanoplates (BT NPs) that exhibit size-dependent radio-sensitization and metabolism characteristics in vivo. By simply varying the molar ratio of EDTA/Bi³⁺ during the reaction, BT NPs with different sizes and morphologies were obtained. EDTA acting as chelating agent and "capping" agent contributed to the homogeneous growth of BT NPs by eliminating dangling bonds and reducing the surface energy of different facets. Further analyzing the size-dependent radio-sensitization mechanism, larger-sized BT NPs generated holes that preferentially catalyzed the conversion of OH^- to ·OH when irradiated with X-rays, while the smaller-sized BT NPs exhibited faster decay kinetics producing higher ¹O₂ levels to enhance radiotherapy effects. A metabolomic analysis revealed that larger-sized BT NPs were oxidized into Bi(O_x) in the liver via a citrate cycle pathway, whereas smaller-sized BT NPs accumulated in the kidney and were excreted in urine in the form of ions by regulating the metabolism of glutamate. In a cervical cancer model, BT NPs combined with X-ray irradiation significantly antagonized tumor suppression through the promotion of apoptosis in tumor cells. Consequently, in addition to providing a prospect of BT NPs as an efficient radio-sensitizer to boost the tumor radiosensitivity, we put forth a strategy that can be universally applied in synthesizing metal chalcogenides for catalysis-promoted radiotherapy.

Asymmetric surfaces endow Janus bismuth oxyhalides with enhanced electronic and catalytic properties for the hydrogen evolution reaction

The electronic and catalytic properties of Janus bismuth oxyhalide (Bi₂O₂XY, where X/Y = Cl, Br, or I, and X ≠ Y) for the hydrogen evolution reaction (HER) are evaluated through first-principles calculations. Janus Bi₂O₂XY shows an enhanced separation efficiency of electron-hole pairs and an augmented utilization of solar energy due to Janus asymmetry. The asymmetric halogen surfaces on both sides of Janus Bi₂O₂XY induce an electrostatic potential difference, which leads to a staggered band alignment. The solar-to-hydrogen (STH) efficiencies of Janus Bi₂O₂BrI and Bi₂O₂ClI have greatly improved compared to those of pristine BiOBr and BiOCl. Additionally, Janus Bi₂O₂XY achieves stronger internal electric fields (IEFs) and a more suitable Gibbs free energy of hydrogen adsorption (ΔG_H) than pristine BiOX. Moreover, the halogen layer with a smaller electronegativity in Janus Bi₂O₂XY forms a stronger IEF with the oxygen layer; consequently, the ΔG_H of terminations value is closer to the ideal value for the HER. The localized edge states in the p-orbital density of states (DOS) projected onto O atoms are responsible for the HER activity of terminations. This work provides a comprehensive understanding of Janus Bi₂O₂XY for the HER and provides a strategy for improving photocatalysis.

Engineering Lattice Disorder on a Photocatalyst: Photochromic BiOBr Nanosheets Enhance Activation of Aromatic C-H Bonds via Water Oxidation

Solar-driven photocatalytic reactions can mildly activate hydrocarbon C-H bonds to produce value-added chemicals. However, the inefficient utilization of photogenerated carriers hinders the application. Here, we report reversible photochromic BiOBr (denoted as p-BiOBr) nanosheets that were colored by trapping photogenerated holes upon visible light irradiation and bleached by water oxidation to generate hydroxyl radicals, demonstrating enhanced carrier separation and water oxidation. The photocatalytic coupling and oxidation reactions of ethylbenzene were efficiently realized by p-BiOBr in a water-based medium under ambient temperature and pressure (apparent quantum yield is 14 times that of pristine BiOBr). The p-BiOBr nanosheets feature lattice disordered defects on the surface, providing rich uncoordinated catalytic sites and inducing structural distortions and lattice strain, which further leads to an altered band structure and significantly enhanced photocatalytic performances. These hole-trapping materials open up the possibility of substantially elevating the utilization efficiency of photogenerated holes for high-efficiency photocatalytic activation of various saturated C-H bonds.

Exploring the photocatalytic conversion mechanism of gaseous formaldehyde degradation on TiO2-x-OV surface

To understand the conversion mechanism of photocatalytic gaseous formaldehyde (HCHO) degradation, strontium (Sr)-doped TiO_2-x-OV catalysts was designed and synthesized in this study, with comparable HCHO removal performance. Our results proved that foreign-element doping reduced Ti⁴⁺ to the lower oxidation state Ti^{(4- x)+}, and that the internal charge kinetics was largely facilitated by the unbalanced electron distribution. Oxygen vacancies (OVs) were developed spontaneously to realize an electron-localized phenomenon in TiO_2-x-OV, thereby boosting O₂ adsorption and activation for the enhanced generation of reactive oxygen species (ROS). At the chemisorption stage, in-situ DRIFTS spectra and density functional theory calculation results revealed that surface adsorbed O₂ (O_ads) and lattice O (O_lat) engaged in the isomerisation of HCHO to dioxymethylene (DOM) on TiO_2-x-OV and TiO₂, respectively. Time-resolved DRIFTS spectra under light irradiation revealed that the DOM was then converted to formate and thoroughly oxidized to CO₂ and H₂O in TiO_2-x-OV. While bicarbonate byproducts were detected from DOM hydroxylation or possible side conversion of CO₂ in TiO₂, owing to insufficient consumption of surface hydroxyl. Our study enhances the understanding on the photocatalytic oxidation of HCHO, thereby promoting the practical application in indoor air purification.