Effect of electron-hole separation in MoO3@Ni2P hybrid nanocomposite as highly efficient metal-free photocatalyst for H2 production

Pore-Engineered Hydrogen-Bonded Supramolecular Fluorosensor for Ultrasensitive Determination of Copper Ions

The selective quantification of copper ions (Cu2+) in biosamples holds great importance for disease diagnosis, treatment, and prognosis since the Cu2+ level is closely associated with the physiological state of the human body. While it remains a long-term challenge due to the extremely low level of free Cu2+ and the potential interference by the complex matrices. Here, a pore-engineered hydrogen-bonded organic framework (HOF) fluorosensor is constructed enabling the ultrasensitive and highly selective detection of free Cu2+. Attributing to atomically precise functionalization of active amino "arm" within the HOF pores and the periodic π-conjugated skeleton, this porous HOF fluorosensor affords high affinity toward Cu2+ through double copper-nitrogen (Cu─N) coordination interactions, resulting in specific fluorescence quenching of the HOF as compared with a series of substances ranging from other metal ions, metabolites, amino acids to proteins. Such superior fluorescence quenching effect endows the Cu2+ quantification by this new HOF sensor with a wide linearity of 50-20 000 nm, a low detection limit of 10 nm, and good recoveries (89.5%-115%) in human serum matrices, outperforming most of the reported approaches. This work highlights the practicability of hydrogen-bonded supramolecular engineering for designing facile and ultrasensitive biosensors for clinical free Cu2+ determination.

Elucidating the mechanism of photocatalytic reduction of bicarbonate (aqueous CO2) into formate and other organics

The photocatalytic reduction of CO2 under solar irradiation is an ideal approach to mitigating global warming, and reducing aqueous forms of CO2 that interact strongly with a catalyst (e.g., HCO3-) is a promising strategy to expedite such reductions. This study uses Pt-deposited graphene oxide dots as a model photocatalyst to elucidate the mechanism of HCO3- reduction. The photocatalyst steadily catalyzes the reduction of an HCO3- solution (at pH = 9) containing an electron donor under 1-sun illumination over a period of 60 h to produce H2 and organic compounds (formate, methanol, and acetate). H2 is derived from solution-contained H2O, which undergoes photocatalytic cleavage to produce •H atoms. Isotopic analysis reveals that all of the organics formed via interactions between HCO3- and •H. This study proposes mechanistic steps, which are governed by the reacting behavior of the •H, to correlate the electron transfer steps and product formation of this photocatalysis. This photocatalysis achieves overall apparent quantum efficiency of 27% in the formation of reaction products under monochromatic irradiation at 420 nm. This study demonstrates the effectiveness of aqueous-phase photocatalysis in converting aqueous CO2 into valuable chemicals and the importance of H2O-derived •H in governing the product selectivity and formation kinetics.

An electron-hole rich dual-site nickel catalyst for efficient photocatalytic overall water splitting

Photocatalysis offers an attractive strategy to upgrade H₂O to renewable fuel H₂. However, current photocatalytic hydrogen production technology often relies on additional sacrificial agents and noble metal cocatalysts, and there are limited photocatalysts possessing overall water splitting performance on their own. Here, we successfully construct an efficient catalytic system to realize overall water splitting, where hole-rich nickel phosphides (Ni₂P) with polymeric carbon-oxygen semiconductor (PCOS) is the site for oxygen generation and electron-rich Ni₂P with nickel sulfide (NiS) serves as the other site for producing H₂. The electron-hole rich Ni₂P based photocatalyst exhibits fast kinetics and a low thermodynamic energy barrier for overall water splitting with stoichiometric 2:1 hydrogen to oxygen ratio (150.7 μmol h^-1 H₂ and 70.2 μmol h^-1 O₂ produced per 100 mg photocatalyst) in a neutral solution. Density functional theory calculations show that the co-loading in Ni₂P and its hybridization with PCOS or NiS can effectively regulate the electronic structures of the surface active sites, alter the reaction pathway, reduce the reaction energy barrier, boost the overall water splitting activity. In comparison with reported literatures, such photocatalyst represents the excellent performance among all reported transition-metal oxides and/or transition-metal sulfides and is even superior to noble metal catalyst.

Interface engineering: Synergism between S-scheme heterojunctions and Mo-O bonds for promote photocatalytic hydrogen evolution

Simple high-temperature calcination and hydrothermal methods were followed to synthesize CeO₂ and Mo-S, respectively. The efficient photocatalytic hydrogen evolution activity exhibited by the composite catalysts can be attributed to the edge active sites in Mo-S. The Mo-O bonds formed between CeO₂ and Mo-S could further accelerate the processes of separation and migration of electrons between the catalyst interfaces. The hybrid catalyst 10%-CeO₂/Mo-S exhibiting the best hydrogen generation ability (4.3 mmol h^-1g^-1) was obtained by optimizing the content of CeO₂ in CeO₂/Mo-S. Analysis of the PL spectral profile and photocurrent response recorded for the system revealed that 10%-COMS exhibited excellent photogenerated carrier separation ability. Analysis of the LSV and EIS curves revealed that 10%-COMS exhibited the optimal hydrogen production potential. The charge migration resistance provided by the systems was lower than the charge migration resistance provided by CeO₂ and Mo-S. The synergism between the S-scheme heterojunctions and the Mo-O bonds helped accelerate the separation and migration of photo-induced carriers at the catalyst interfaces. The introduction of covalent bonds in the S-scheme heterojunctions and the results presented herein can potentially help develop a new method to realize photocatalytic hydrogen evolution.

Engineering a NiAl-LDH/CoSx S-Scheme heterojunction for enhanced photocatalytic hydrogen evolution

The use of semiconductors to construct heterojunctions to suppress the rapid recombination of photogenerated charges and holes is considered to be an effective way to improve the efficiency of photocatalytic hydrogen evolution. Herein, cobalt sulfide (CoS_x) nanoparticles are cultivated in situ in the folds of three-dimensional flower-like nickel-aluminium layered double hydroxides (NiAl-LDHs) using a facile solvothermal method. The hydrogen production rate of the binary CoS_x/NiAl-LDH heterojunction reaches 3678.59 μmol/g/h, which is 83.74 and 22 times the rates of CoS_x and NiAl-LDH, respectively. The unique three-dimensional structure of NiAl-LDH facilitates the growth of CoS_x and shortens the transfer pathway of photogenerated electrons. More importantly, the built-in electric field formed at the interface and the S-type charge transport mechanism caused by the bending of the energy band enhance not only charge separation but also maintain the strong oxidation ability of the holes. In this study, the newly designed S-scheme heterojunction offers a new strategy for enhancing photocatalytic water splitting.

MoP@MoO3 S-scheme heterojunction in situ construction with phosphating MoO3 for high-efficient photocatalytic hydrogen production

As important artificial photosynthesis, the construction of core-shell heterojunction materials is considered to be one of the effective strategies for designing highly active photocatalysts. Here, the Step-scheme (S-scheme) heterojunction photocatalyst is firmly grown by in situ phosphating. The calcination method uses MoO₃ nanoparticles as the substrate, and the surface of MoO₃ is phosphatized and etched gradually from the outside to the inside using the phosphine gas. The introduced phosphorus atoms can replace MoO₃ oxygen atoms to form Mo-P bonds to generate molybdenum phosphide. The interface interaction dominated by chemical bonds has a stronger interface interaction force, which can promote the interface charge transfer leading to optimizing the MoP@MoO₃ core-shell composite material, adjusting the quality of sodium hypophosphite, and phosphating MoO₃ to varying degrees, producing the best hydrogen production H₂ evolution rate is 10 000.02 μmol h^-1 g^-1. Density functional theory (DFT) calculations and a series of experiments were used to determine the S-scheme charge transfer mechanism in MoP@MoO₃. This design provides a new idea for the introduction of surface-active sites and the construction of mixed anion photocatalysts. At the same time, a new design scheme is provided for the in situ construction of S-scheme interface heterojunction materials.

Noble-metal-free hexagonal wurtzite CdS nanoplates with exposed (110) and (112) crystal facets for efficient visible-light H2 production

Hexagonal wurtzite CdS has been regarded as one of the most promising semiconductors for photocatalysis.

0D/2D spatial structure of CdxZn1−xS/Ni-MOF-74 for efficient photocatalytic hydrogen evolution

A novel zero-dimensional/two-dimensional Cd_xZn_1−xS/Ni-MOF-74 (CZS/NMF) heterojunction was rationally constructed via a simple hydrothermal and physical mixing method.

Phosphating 2D CoAl LDH anchored on 3D self-assembled NiTiO3 hollow rods for efficient hydrogen evolution

Two photo-active materials with opposite potential, NiTiO₃ and CoAl LDH are rationally integrated into a combinant. It efficiently accelerates the separation and migration of photo-excited electrons and enhance thermodynamic hydrogen evolution.

Controllable photodeposition of nickel phosphide cocatalysts on cadmium sulfide nanosheets for enhanced photocatalytic hydrogen evolution performance

As efficient cocatalysts in photocatalytic processes, transition metal phosphides are usually synthesized in harsh and tedious conditions. So to achieve their simple and controllable loading on photocatalyst surface is especially valuable.