Ultrafine Pt Nanoparticles on Defective Tungsten Oxide for Photocatalytic Ethylene Synthesis.

The selective conversion of ethane (C2H6) to ethylene (C2H4) under mild conditions is highly wanted, yet very challenging. Herein, it is demonstrated that a Pt/WO3-x catalyst, constructed by supporting ultrafine Pt nanoparticles on the surface of oxygen-deficient tungsten oxide (WO3-x) nanoplates, is efficient and reusable for photocatalytic C2H6 dehydrogenation to produce C2H4 with high selectivity. Specifically, under pure light irradiation, the optimized Pt/WO3-x photocatalyst exhibits C2H4 and H2 yield rates of 291.8 and 373.4 µmol g-1 h-1, respectively, coupled with a small formation of CO (85.2 µmol g-1 h-1) and CH4 (19.0 µmol g-1 h-1), corresponding to a high C2H4 selectivity of 84.9%. Experimental and theoretical studies reveal that the vacancy-rich WO3-x catalyst enables broad optical harvesting to generate charge carriers by light for working the redox reactions. Meanwhile, the Pt cocatalyst reinforces adsorption of C2H6, desorption of key reaction species, and separation and migration of light-induced charges to promote the dehydrogenation reaction with high productivity and selectivity. In situ diffuse reflectance infrared Fourier transform spectroscopy and density functional theory calculation expose the key intermediates formed on the Pt/WO3-x catalyst during the reaction, which permits the construction of the possible C2H6 dehydrogenation mechanism.

S-scheme heterojunction of crystalline carbon nitride nanosheets and ultrafine WO3 nanoparticles for photocatalytic CO2 reduction.

Highly crystalline carbon nitride polymers have shown great opportunities in overall water photosplitting; however, their mission in light-driven CO2 conversion remains to be explored. In this work, crystalline carbon nitride (CCN) nanosheets of poly triazine imide (PTI) embedded with melon domains are fabricated by KCl/LiCl-mediated polycondensation of dicyandiamide, the surface of which is subsequently deposited with ultrafine WO3 nanoparticles to construct the CCN/WO3 heterostructure with a S-scheme interface. Systematic characterizations have been conducted to reveal the compositions and structures of the S-scheme CCN/WO3 hybrid, featuring strengthened optical capture, enhanced CO2 adsorption and activation, attractive textural properties, as well as spatial separation and directed movement of light-triggered charge carriers. Under mild conditions, the CCN/WO3 catalyst with optimized composition displays a high photocatalytic activity for reducing CO2 to CO in a rate of 23.0 µmol/hr (i.e., 2300 µmol/(hr·g)), which is about 7-fold that of pristine CCN, along with a high CO selectivity of 90.6% against H2 formation. Moreover, it also manifests high stability and fine reusability for the CO2 conversion reaction. The CO2 adsorption and conversion processes on the catalyst are monitored by in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), identifying the crucial intermediates of CO2*-, COOH* and CO*, which integrated with the results of performance evaluation proposes the possible CO2 reduction mechanism.

Vinyl-Group-Anchored Covalent Organic Framework for Promoting the Photocatalytic Generation of Hydrogen Peroxide.

The artificial photosynthesis of H2O2 from water and oxygen using semiconductor photocatalysts is attracting increasing levels of attention owing to its green, environmentally friendly, and energy-saving characteristics. Although covalent organic frameworks (COFs) are promising materials for promoting photocatalytic H2O2 production owing to their structural and functional diversity, they typically suffer from low charge-generation and -transfer efficiencies as well as rapid charge recombination, which restricts their use as catalysts for photocatalytic H2O2 production. Herein, we report a strategy for anchoring vinyl moieties to a COF skeleton to facilitate charge separation and migration, thereby promoting photocatalytic H2O2 generation. This vinyl-group-bearing COF photocatalyst exhibits a H2O2-production rate of 84.5 µmol h-1 (per 10 mg), which is ten-times higher than that of the analog devoid of vinyl functionality and superior to most reported COF photocatalysts. Both experimental and theoretical studies provide deep insight into the origin of the improved photocatalytic performance. These findings are expected to facilitate the rational design and modification of organic semiconductors for use in photocatalytic applications.

Hydroxyl-Bonded Ru on Metallic TiN Surface Catalyzing CO2 Reduction with H2O by Infrared Light.

Synchronized conversion of CO2 and H2O into hydrocarbons and oxygen via infrared-ignited photocatalysis remains a challenge. Herein, the hydroxyl-coordinated single-site Ru is anchored precisely on the metallic TiN surface by a NaBH4/NaOH reforming method to construct an infrared-responsive HO-Ru/TiN photocatalyst. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (ac-HAADF-STEM) and X-ray absorption spectroscopy (XAS) confirm the atomic distribution of the Ru species. XAS and density functional theory (DFT) calculations unveil the formation of surface HO-RuN5-Ti Lewis pair sites, which achieves efficient CO2 polarization/activation via dual coordination with the C and O atoms of CO2 on HO-Ru/TiN. Also, implanting the Ru species on the TiN surface powerfully boosts the separation and transfer of photoinduced charges. Under infrared irradiation, the HO-Ru/TiN catalyst shows a superior CO2-to-CO transformation activity coupled with H2O oxidation to release O2, and the CO2 reduction rate can further be promoted by about 3-fold under simulated sunlight. With the key reaction intermediates determined by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and predicted by DFT simulations, a possible photoredox mechanism of the CO2 reduction system is proposed.

Electronic Transmission Channels Promoting Charge Separation of Conjugated Polymers for Photocatalytic CO2 Reduction with Controllable Selectivity.

Conjugated polymers (CPs) represent a promising platform for photocatalytic CO2 fixation owing to their suitable band structures that meet the requirements of the reduction potential of CO2 to value-added fuels. However, the photocatalytic performance of CPs is rather restrained by the low charge transfer efficiency. Herein, we rationally designed three CPs with a more delocalized electronic transmission channel and planar molecular structure, which are regarded to evidently reduce the exciton binding energy (Eb ) and accelerate the internal charge transfer process. Besides, the assembly of suitable electron-output "tentacles" and cocatalysts on the surface of CPs could effectively facilitate interfacial electron delivery. Accordingly, the optimal P-2CN exhibits an apparent quantum yield of 4.6 % at 420 nm for photocatalytic CO2 to CO. Further adjusting the amounts of cyano groups and cocatalysts, the CO selectivity could be obtained in the range of 0-80.5 %.

Bottom-up Synthesis of Single-Crystalline Poly (Triazine Imide) Nanosheets for Photocatalytic Overall Water Splitting.

Poly (triazine imide) (PTI/Li+ Cl- ), one of the crystalline versions of polymeric carbon nitrides, holds great promise for photocatalytic overall water splitting. In principle, the photocatalytic activity of PTI/Li+ Cl- is closely related to the morphology, which could be reasonably tailored by the modulation of the polycondensation process. Herein, we demonstrate that the hexagonal prisms of PTI/Li+ Cl- could be converted to hexagonal nanosheets by adjusting the binary eutectic salts from LiCl/KCl or NaCl/LiCl to ternary LiCl/KCl/NaCl. Results reveal that the extension of in-plane conjugation is preferred, when the polymerisation was performed in the presence of ternary eutectic salts. The hexagonal nanosheets bears longer lifetimes of charge carriers than that of hexagonal prisms due to lower intensity of structure defects and shorter hopping distance of charge carriers along the stacking direction of triazine nanosheets. The optimized hexagonal nanosheets exhibits a record apparent quantum yield value of 25 % (λ=365 nm) for solar hydrogen production by one-step excitation overall water splitting.

The Directional Crystallization Process of Poly (triazine imide) Single Crystals in Molten Salts.

Poly (triazine imide) photocatalysts prepared via molten salt methods emerge as promising polymer semiconductors with one-step excitation capacity of overall water splitting. Unveiling the molecular conjugation, nucleation, and crystallization processes of PTI crystals is crucial for their controllable structure design. Herein, microscopy characterization was conducted at the PTI crystallization front from meso to nano scales. The heptazine-based precursor was found to depolymerize to triazine monomers within molten salts and KCl cubes precipitate as the leading cores that guide the directional stacking of PTI molecular units to form aggregated crystals. Upon this discovery, PTI crystals with improved dispersibility and enhanced photocatalytic performance were obtained by tailoring the crystallization fronts. This study advances insights into the directional assembling of PTI monomers on salt templates, placing a theoretical foundation for the ordered condensation of polymer crystals.

Rh/Cr2 O3 and CoOx Cocatalysts for Efficient Photocatalytic Water Splitting by Poly (Triazine Imide) Crystals.

In situ photo-deposition of both Pt and CoOx cocatalysts on the facets of poly (triazine imide) (PTI) crystals has been developed for photocatalytic overall water splitting. However, the undesired backward reaction (i.e., water formation) on the noble Pt surface is a spontaneously down-hill process, which restricts their efficiency to run the overall water splitting reaction. Herein, we demonstrate that the efficiency for photocatalytic overall water splitting could be largely promoted by the decoration of Rh/Cr2 O3 and CoOx as H2 and O2 evolution cocatalysts, respectively. Results reveal that the dual cocatalysts greatly extract charges from bulk to surface, while the Rh/Cr2 O3 cocatalyst dramatically restrains the backward reaction, achieving an apparent quantum efficiency (AQE) of 20.2 % for the photocatalytic overall water splitting reaction.

Molecular Design of Covalent Triazine Frameworks with Anisotropic Charge Migration for Photocatalytic Hydrogen Production.

Covalent triazine frameworks (CTFs) represent promising polymeric photocatalysts for photocatalytic hydrogen production with visible light. However, the separation and transfer of charges in CTFs are isotropic because of the uniform distribution of donor-acceptor motifs in the skeleton. Herein, to achieve the anisotropic charge carrier separation and migration, thiophene (Th) or benzothiadiazole (BT) unit is selected as the dopant to modify the molecular structure of CTF-based photocatalysts. Both theoretical and experimental studies reveal that the incorporation of Th or BT units induces the anisotropic charge carrier separation and migration at the interface of CTFs. The optimized polymer manifests a much enhanced photocatalytic activity for photocatalytic hydrogen production with visible light, and thus this study provides a useful tool to design conjugated polymer photocatalysts at the molecular level for solar energy conversion.

Surface Engineering of Conjugated Polybenzothiadiazoles and Integration with Cobalt Oxides for Photocatalytic Water Oxidation.

Conjugated polymers feature promising structure and properties for photocatalytic water splitting. Herein, a hydrolysis strategy was demonstrated to rationally modulate the surface hydrophilicity and band structures of conjugated poly-benzothiadiazoles. High hydrophilicity not only enhances the dispersions of polymeric solids in an aqueous solution but also reduces the absorption energy of water molecules. Besides, both theoretical and experimental results reveal that a more positive valence band potential is generated, which contributes to enhancing the photocatalytic water oxidation performance. Accordingly, the surface-modified conjugated polymers show largely promoted photocatalytic water oxidation activities by deposition of cobalt oxides as cocatalysts.

CrowdMed-II: a blockchain-based framework for efficient consent management in health data sharing.

The healthcare industry faces serious problems with health data. Firstly, health data is fragmented and its quality needs to be improved. Data fragmentation means that it is difficult to integrate the patient data stored by multiple health service providers. The quality of these heterogeneous data also needs to be improved for better utilization. Secondly, data sharing among patients, healthcare service providers and medical researchers is inadequate. Thirdly, while sharing health data, patients' right to privacy must be protected, and patients should have authority over who can access their data. In traditional health data sharing system, because of centralized management, data can easily be stolen, manipulated. These systems also ignore patient's authority and privacy. Researchers have proposed some blockchain-based health data sharing solutions where blockchain is used for consensus management. Blockchain enables multiple parties who do not fully trust each other to exchange their data. However, the practice of smart contracts supporting these solutions has not been studied in detail. We propose CrowdMed-II, a health data management framework based on blockchain, which could address the above-mentioned problems of health data. We study the design of major smart contracts in our framework and propose two smart contract structures. We also introduce a novel search contract for searching patients in the framework. We evaluate their efficiency based on the execution costs on Ethereum. Our design improves on those previously proposed, lowering the computational costs of the framework. This allows the framework to operate at scale and is more feasible for widespread adoption.

Improved Charge Separation in Poly(heptazine-triazine) Imides with Semi-coherent Interfaces for Photocatalytic Hydrogen Evolution.

The construction of heterojunctions is a promising manner to accelerate the separation and transfer of the charge carriers at the interface. Herein, a binary poly(heptazine-triazine) imides (PHI/PTI) with semi-coherent interfaces was fabricated via a facile two-step salt-melt synthetic process. The built-in electric fields at the semi-coherent interface endow prompt exciton splitting and charge carrier separation. Hence, the optimized PHI/PTI-based copolymer presents a high apparent quantum yield (AQY=64 %) for visible-light driven hydrogen production, by the aids of K2 HPO4 as charge transfer mediator. This study provides physical insights for the rational promotion of the photocatalytic performance from the viewpoint of interfacial engineering of photocatalytic junctions on crystalline carbon nitride based semiconductors.

Ionothermal Synthesis of Covalent Triazine Frameworks in a NaCl-KCl-ZnCl2 Eutectic Salt for the Hydrogen Evolution Reaction.

Covalent triazine-based frameworks (CTFs) are typically produced by the salt-melt polycondensation of aromatic nitriles in the presence of ZnCl2 . In this reaction, molten ZnCl2 salt acts as both a solvent and Lewis acid catalyst. However, when cyclotrimerization takes place at temperatures above 300 °C, undesired carbonization occurs. In this study, an ionothermal synthesis method for CTF-based photocatalysts was developed using a ternary NaCl-KCl-ZnCl2 eutectic salt (ES) mixture with a melting point of approximately 200 °C. This temperature is lower than the melting point of pure ZnCl2 (318 °C), thus providing milder salt-melt conditions. These conditions facilitated the polycondensation process, while avoiding carbonization of the polymeric backbone. The resulting CTF-ES200 exhibited enhanced optical and electronic properties, and displayed remarkable photocatalytic performance in the hydrogen evolution reaction.

Fully Condensed Poly (Triazine Imide) Crystals: Extended π-Conjugation and Structural Defects for Overall Water Splitting.

Conventional polymerization for the synthesis of carbon nitride usually generates amorphous heptazine-based melon with an abundance of undesired structural defects, which function as charge carrier recombination centers to decrease the photocatalytic efficiency. Herein, a fully condensed poly (triazine imide) crystal with extended π-conjugation and deficient structure defects was obtained by conducting the polycondensation in a mild molten salt of LiCl/NaCl. The melting point of the binary LiCl/NaCl system is around 550 °C, which substantially restrain the depolymerization of triazine units and extend the π-conjugation. The optimized polymeric carbon nitride crystal exhibits a high apparent quantum efficiency of 12 % (λ=365 nm) for hydrogen production by one-step excitation overall water splitting, owing to the efficient exciton dissociation and the subsequent fast transfer of charge carriers.

Polymeric Donor-Acceptor Heterostructures for Enhanced Photocatalytic H2 Evolution without Using Pt Cocatalysts.

Polymeric carbon nitride (CN) is a promising material for photocatalytic water splitting. However, CN in its pristine form tends to show moderate activity due to fast recombination of the charge carriers. The design of efficient photocatalytic system is therefore highly desired, but it still remains a great challenge in chemistry. In this work, a pyrene-based polymer able to serve as an electron donor to accelerate the interface charge carrier transfer of CN is presented. The construction of donor-acceptor (D-A) heterojunction was confirmed to significantly restrain the charge recombination and, thus, improve the proton reduction process. This study provides a promising strategy to achieve solar H2 production in an efficient and low-cost manner.

Oxysulfide Semiconductors for Photocatalytic Overall Water Splitting with Visible Light.

Photocatalytic overall water splitting by sulfide-based materials is a great challenge because of the poor resilience of such materials against hole oxidation. In a recent study, Domen and co-workers developed an innovative strategy to stabilize sulfide-based photocatalysts by hybridizing S 3p with O 2p orbitals to produce oxysulfides in which S2- is stable. Further surface engineering of the oxysulfides with dual co-catalysts promoted charge separation and interface transfer, thus reducing the charge build-up that inhibits photocorrosion. The pH value of the reaction mixture is a critical consideration for achieving efficient stoichiometric H2 and O2 evolution by these oxysulfide photocatalysts.

Polymeric Carbon Nitride/Reduced Graphene Oxide/Fe2 O3 : All-Solid-State Z-Scheme System for Photocatalytic Overall Water Splitting.

The charge transfer between hydrogen evolution photocatalysts (HEPs) and oxygen evolution photocatalysts (OEPs) is the rate-determining step that controls the overall performance of a Z-scheme water-splitting system. Here, we carefully design reduced graphene oxide (RGO) nanosheets for use as solid-state mediators to accelerate the charge carrier transfer between HEPs (e.g., polymeric carbon nitride (PCN)) and OEPs (e.g., Fe2 O3 ), thus achieving efficient overall water splitting. The important role of RGO could also be further proven in other PCN-based Z-systems (BiVO4 /RGO/PCN and WO3 /RGO/PCN), illustrating the universality of this strategy.

Electron Deficient Monomers that Optimize Nucleation and Enhance the Photocatalytic Redox Activity of Carbon Nitrides.

Polymeric carbon nitride (PCN) is usually synthesized from nitrogen-rich monomers such as cyanamide, melamine, and urea, but is rather disordered in many cases. Now, a new allotrope of carbon nitride with internal heterostructures was obtained by co-condensation of very electron poor monomers (for example, 5-amino-tetrazole and nucleobases) in the presence of mild molten salts (for example, NaCl/KCl) to mediate the polymerization kinetics and thus modulate the local structure, charge carrier properties, and most importantly the HOMO and LUMO levels. Results reveal that the as-prepared NaK-PHI-A material shows excellent photo-redox activities because of a nanometric hetero-structure which enhances visible light absorption and promotes charge separation in the different domains.

Reducing the Exciton Binding Energy of Donor-Acceptor-Based Conjugated Polymers to Promote Charge-Induced Reactions.

Exciton binding energy has been regarded as a crucial parameter for mediating charge separation in polymeric photocatalysts. Minimizing the exciton binding energy of the polymers can increase the yield of charge-carrier generation and thus improve the photocatalytic activities, but the realization of this approach remains a great challenge. Herein, a series of linear donor-acceptor conjugated polymers has been developed to minimize the exciton binding energy by modulating the charge-transfer pathway. The results reveal that the reduced energy loss of the charge-transfer state can facilitate the electron transfer from donor to acceptor, and thus, more electrons are ready for subsequent reduction reactions. The optimized polymer, FSO-FS, exhibits a remarkable photochemical performance under visible light irradiation.

Tailoring the Grain Boundary Chemistry of Polymeric Carbon Nitride for Enhanced Solar Hydrogen Production and CO2 Reduction.

Photocatalytic water splitting is a promising and clean way to mimic plant photosynthesis in a sustainable manner. Improvements of the quantum efficiency and optical absorption in the relevant range are necessary steps to approach practicality. Herein, we reported that these issues can be readily addressed when 5-aminotetrazole, a monomer with high nitrogen content, is used for the synthesis of carbon nitride. The molten salt mixture NaCl/KCl is used as a high-temperature solvent to tailor the grain boundary structure and chemistry. Visible light quantum efficiency for H2 production of 0.65 could be obtained in the presence of K2 HPO4 as a double layer modifier. This value is very high, considering that this number depends on light to charge couple conversion, charge localization, as well as a successful oxidation and reduction reaction.