Highly Selective Acetylene-to-Ethylene Electroreduction Over Cd-Decorated Cu Catalyst with Efficiently Inhibited Carbon-Carbon Coupling.

Electrochemical acetylene reduction (EAR) employing Cu catalysts represents an environmentally friendly and cost-effective method for ethylene production and purification. However, Cu-based catalysts encounter product selectivity issues stemming from carbon-carbon coupling and other side reactions. We explored the use of secondary metals to modify Cu-based catalysts and identified Cd decoration as particular effective. Cd decoration demonstrated a high ethylene Faradaic efficiency (FE) of 98.38 % with well-inhibited carbon-carbon coupling reactions (0.06 % for butadiene FE at -0.5 V versus reversible hydrogen electrode) in a 5 vol % acetylene gas feed. Notably, ethylene selectivity of 99.99 % was achieved in the crude ethylene feed during prolonged stability tests. Theoretical calculations revealed that Cd metal accelerates the water dissociation on neighboring Cu surfaces allowing more H* to participate in the acetylene semi-hydrogenation, while increasing the energy barrier for carbon-carbon coupling, thereby contributing to a high ethylene semi-hydrogenation efficiency and significant inhibition of carbon-carbon coupling. This study provides a paradigm for a deeper understanding of secondary metals in regulating the product selectivity of EAR electrocatalysts.

Photocatalytic ethylene production by oxidative dehydrogenation of ethane with dioxygen on ZnO-supported PdZn intermetallic nanoparticles.

The selective oxidative dehydrogenation of ethane (ODHE) is attracting increasing attention as a method for ethylene production. Typically, thermocatalysts operating at high temperatures are needed for C-H activation in ethane. In this study, we describe a low temperature ( < 140 °C) photocatalytic route for ODHE, using O2 as the oxidant. A photocatalyst containing PdZn intermetallic nanoparticles supported on ZnO is prepared, affording an ethylene production rate of 46.4 mmol g-1 h-1 with 92.6% ethylene selectivity under 365 nm irradiation. When we employ a simulated shale gas feed, the photocatalytic ODHE system achieves nearly 20% ethane conversion while maintaining an ethylene selectivity of about 87%. The robust interface between the PdZn intermetallic nanoparticles and ZnO support plays a crucial role in ethane activation through a photo-assisted Mars-van Krevelen mechanism, followed by a rapid lattice oxygen replenishment to complete the reaction cycle. Our findings demonstrate that photocatalytic ODHE is a promising method for alkane-to-alkene conversions under mild conditions.

Titania-Supported Cu-Single-Atom Catalyst for Electrochemical Reduction of Acetylene to Ethylene at Low-Concentrations with Suppressed Hydrogen Evolution.

Electrochemical acetylene reduction (EAR) is a promising strategy for removing acetylene from ethylene-rich gas streams. However, suppressing the undesirable hydrogen evolution is vital for practical applications in acetylene-insufficient conditions. Herein, Cu single atoms are immobilized on anatase TiO2 nanoplates (Cu-SA/TiO2 ) for electrochemical acetylene reduction, achieving an ethylene selectivity of ≈97% with a 5 vol% acetylene gas feed (Ar balance). At the optimal Cu-single-atom loading, Cu-SA/TiO2 is able to effectively suppress HER and ethylene over-hydrogenation even when using dilute acetylene (0.5 vol%) or ethylene-rich gas feeds, delivering a 99.8% acetylene conversion, providing a turnover frequency of 8.9 × 10-2  s-1 , which is superior to other EAR catalysts reported to date. Theoretical calculations show that the Cu single atoms and the TiO2 support acted cooperatively to promote charge transfer to adsorbed acetylene molecules, whilst also inhibiting hydrogen generation in alkali environments, thus allowing selective ethylene production with negligible hydrogen evolution at low acetylene concentrations.

Minimizing Temperature Bias through Reliable Temperature Determination in Gas-Solid Photothermal Catalytic Reactions.

Enormous advances in photothermal catalysis have been made over the years, whereas the temperature assessment still remains controversial in the majority of photothermal catalytic systems. Herein, we methodically uncovered the phenomenon of temperature determination bias arising from prominent temperature differences in gas-solid photothermal catalytic systems, which extensively existed yet has been overlooked in most relevant cases. To avoid the interference of temperature bias, we developed a universal protocol for reliable temperature evaluation of gas-solid photothermal catalytic reactions, with emphasis on eliminating the temperature gradient and temperature fluctuation of catalyst layer via optimizing the reaction system. This work presents a functional and credible practice for temperature detection, calling attention to addressing the effects of temperature differences, and reassessing the actual temperature-based performances in gas-solid photothermal catalysis.

Plasmonic Cu Nanoparticles for the Low-temperature Photo-driven Water-gas Shift Reaction.

The activation of water molecules in thermal catalysis typically requires high temperatures, representing an obstacle to catalyst development for the low-temperature water-gas shift reaction (WGSR). Plasmonic photocatalysis allows activation of water at low temperatures through the generation of light-induced hot electrons. Herein, we report a layered double hydroxide-derived copper catalyst (LD-Cu) with outstanding performance for the low-temperature photo-driven WGSR. LD-Cu offered a lower activation energy for WGSR to H2 under UV/Vis irradiation (1.4 W cm-2 ) compared to under dark conditions. Detailed experimental studies revealed that highly dispersed Cu nanoparticles created an abundance of hot electrons during light absorption, which promoted *H2 O dissociation and *H combination via a carboxyl pathway, leading to the efficient production of H2 . Results demonstrate the benefits of exploiting plasmonic phenomena in the development of photo-driven low-temperature WGSR catalysts.

Triphase Photocatalytic CO2 Reduction over Silver-Decorated Titanium Oxide at a Gas-Water Boundary.

Photocatalytic CO2 reduction reaction (CO2 RR) is an attractive process to convert CO2 into valuable chemicals. But this reaction is often restricted by the poor mass transfer of CO2 in the liquid phase. Here, we have developed a triphase photocatalytic CO2 RR system by supporting Ag-decorated TiO2 nanoparticles at a gas-water boundary with hydrophobic-hydrophilic abrupt interfacial wettability. Such a triphase system allows the rapid delivery of gas-phase CO2 to the surface of photocatalysts while maintaining an efficient water supply and uncovered active sites. Ag-TiO2 supported at the gas-water boundary showed a CO2 reduction rate of 305.7 µmol g-1 h-1 , without hole scavengers, approximately 8 times higher than the nanoparticles dispersed in the liquid phase. Even using diluted CO2 (10 %) as the reactant, the CO2 RR activity was superior to most reported Ag-TiO2 based photocatalysts using pure CO2 . The findings provide a general strategy to promote the interfacial CO2 mass transfer to improve photoactivity and selectivity.

Interfacial wettability and mass transfer characterizations for gas-liquid-solid triple-phase catalysis.

Heterogeneous catalysis is inseparable from interfacial mass transfer and chemical reaction processes determined by the structure and microenvironment. Different from high-temperature thermochemical processes, photo- and electrocatalysis operated at mild conditions often involve both gas and liquid phases, making it important but challenging to characterize the reaction process typically occurring at the gas-liquid-solid interface. Herein, we review the scope, feasibility, and limitation of ten types of currently available technologies used to characterize interfacial wettability and mass transfer properties of various triple-phase catalytic reactions. The review summarizes techniques from macroscopic contact angle measurement to microscopic environment electron microscopy for investigating the wettability-controlled structure of triple-phase interfaces. Experimental and computational methods in revealing the interfacial mass transfer process have also been systematically discussed, followed by a perspective on the opportunities and challenges of advanced characterization methods to help understand the fundamental reaction mechanism of triple-phase catalysis.

High-Efficiency Oxygen Reduction to Hydrogen Peroxide Catalyzed by Nickel Single-Atom Catalysts with Tetradentate N2 O2 Coordination in a Three-Phase Flow Cell.

Carbon-supported NiII single-atom catalysts with a tetradentate Ni-N2 O2 coordination formed by a Schiff base ligand-mediated pyrolysis strategy are presented. A NiII complex of the Schiff base ligand (R,R)-(-)-N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine was adsorbed onto a carbon black support, followed by pyrolysis of the modified carbon material at 300 °C in Ar. The Ni-N2 O2 /C catalyst showed excellent performance for the electrocatalytic reduction of O2 to H2 O2 through a two-electron transfer process in alkaline conditions, with a H2 O2 selectivity of 96 %. At a current density of 70 mA cm-2 , a H2 O2 production rate of 5.9 mol gcat. -1 h-1 was achieved using a three-phase flow cell, with good catalyst stability maintained over 8 h of testing. The Ni-N2 O2 /C catalyst could electrocatalytically reduce O2 in air to H2 O2 at a high current density, still affording a high H2 O2 selectivity (>90 %). A precise Ni-N2 O2 coordination was key to the performance.

A Nanozyme with Photo-Enhanced Dual Enzyme-Like Activities for Deep Pancreatic Cancer Therapy.

Nanozymes have attracted extensive interest owing to their high stability, low cost and easy preparation, especially in the field of cancer therapy. However, the relatively low catalytic activity of nanozymes in the tumor microenvironment (TME) has limited their applications. Herein, we report a novel nanozyme (PtFe@Fe3 O4 ) with dual enzyme-like activities for highly efficient tumor catalytic therapy. PtFe@Fe3 O4 shows the intrinsic photothermal effect as well as photo-enhanced peroxidase-like and catalase-like activities in the acidic TME, thereby effectively killing tumor cells and overcoming the tumor hypoxia. Importantly, a possible photo-enhanced synergistic catalytic mechanism of PtFe@Fe3 O4 was first disclosed. We believe that this work will advance the development of nanozymes in tumor catalytic therapy.

Pd Single-Atom Catalysts on Nitrogen-Doped Graphene for the Highly Selective Photothermal Hydrogenation of Acetylene to Ethylene.

The selective hydrogenation of acetylene to ethylene in an ethylene-rich gas stream is an important process in the chemical industry. Pd-based catalysts are widely used in this reaction due to their excellent hydrogenation activity, though their selectivity for acetylene hydrogenation and durability need improvement. Herein, the successful synthesis of atomically dispersed Pd single-atom catalysts on nitrogen-doped graphene (Pd1 /N-graphene) by a freeze-drying-assisted method is reported. The Pd1 /N-graphene catalyst exhibits outstanding activity and selectivity for the hydrogenation of C2 H2 with H2 in the presence of excess C2 H4 under photothermal heating (UV and visible-light irradiation from a Xe lamp), achieving 99% conversion of acetylene and 93.5% selectivity to ethylene at 125 °C. This remarkable catalytic performance is attributed to the high concentration of Pd active sites on the catalyst surface and the weak adsorption energy of ethylene on isolated Pd atoms, which prevents C2 H4 hydrogenation. Importantly, the Pd1 /N-graphene catalyst exhibits excellent durability at the optimal reaction temperature of 125 °C, which is explained by the strong local coordination of Pd atoms by nitrogen atoms, which suppresses the Pd aggregation. The results presented here encourage the wider pursuit of solar-driven photothermal catalyst systems based on single-atom active sites for selective hydrogenation reactions.

Nickel-Cobalt Diselenide 3D Mesoporous Nanosheet Networks Supported on Ni Foam: An All-pH Highly Efficient Integrated Electrocatalyst for Hydrogen Evolution.

Novel 3D Ni1-x Cox Se2 mesoporous nanosheet networks with tunable stoichiometry are successfully synthesized on Ni foam (Ni1-x Cox Se2 MNSN/NF with x ranging from 0 to 0.35). The collective effects of special morphological design and electronic structure engineering enable the integrated electrocatalyst to have very high activity for hydrogen evolution reaction (HER) and excellent stability in a wide pH range. Ni0.89 Co0.11 Se2 MNSN/NF is revealed to exhibit an overpotential (η10 ) of 85 mV at -10 mA cm-2 in alkaline medium (pH 14) and η10 of 52 mV in acidic solution (pH 0), which are the best among all selenide-based electrocatalysts reported thus far. In particular, it is shown for the first time that the catalyst can work efficiently in neutral solution (pH 7) with a record η10 of 82 mV for all noble metal-free electrocatalysts ever reported. Based on theoretical calculations, it is further verified that the advanced all-pH HER activity of Ni0.89 Co0.11 Se2 is originated from the enhanced adsorption of both H+ and H2 O induced by the substitutional doping of cobalt at an optimal level. It is believed that the present work provides a valuable route for the design and synthesis of inexpensive and efficient all-pH HER electrocatalysts.

Oxide-Modified Nickel Photocatalysts for the Production of Hydrocarbons in Visible Light.

Metallic nickel nanostructures that were partially decorated by discrete nickel oxide layers were fabricated by in situ reduction of calcinated Ni-containing layered double hydroxide nanosheets, the structure of which was confirmed by extended X-ray absorption fine structure spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. The existence of the abundant interfaces between the surface Ni oxide overlayer and metallic Ni altered the geometric/electronic structure of the Ni nanoparticles, making them apt for CO activation under light irradiation. Most importantly, the unique structure favors the C-C coupling reaction on its surface, which confers the catalyst unexpected reaction power towards higher hydrocarbons at moderate reaction conditions. This study leads to a green and sustainable approach for the photocatalytic production of highly valuable chemical fuels.

Copper(I) cysteine complexes: efficient earth-abundant oxidation co-catalysts for visible light-driven photocatalytic H2 production.

A copper(i) cysteine complex generated by mixing Cu(ii) ions with cysteine in aqueous solution greatly enhanced the activity of CdSe photocatalysts for H2 production in aqueous solution under visible light excitation. The complex can enhance the H2 evolution rate by as much as 150 times, by acting as an oxidation co-catalyst and increasing charge carrier lifetimes. The copper(i) cysteine complex can also be applied to enhance the H2 production performance of other semiconductor photocatalyst systems, thereby affording a new research direction in the development of co-catalysts for solar hydrogen production.

Fabrication of versatile cyclodextrin-functionalized upconversion luminescence nanoplatform for biomedical imaging.

Lanthanide-based upconversion nanoparticles (UCNPs) are a new type of luminescent tags that show great application potential in biomedical fields. However, a major challenge when applying UCNPs in biomedical research is the lack of a versatile strategy to make water-dispersible and biocompatible UCNPs with high simplicity in functionalization. To address this problem, in the present work, we employed 6-phosphate-6-deoxy-ß-cyclodextrin (ßPCD) as the novel ligand to fabricate a versatile upconversion luminescent nanoplatform. Using ßPCD as the surface ligand not only enhances the stability and biocompatibility of the UCNPs under physiological conditions but also enables simple conjugation with various functional molecules, such as organic dyes and biomolecules, via the host-guest interaction between those molecules and the cyclodextrin cavity. The conjugated upconversion nanoprobe then displays excellent capability in labeling the cancer cells and tumor tissue slices for luminescent imaging. These results demonstrate that the versatile cyclodextrin-functionalized upconversion nanoplatform appears particularly flexible for further modifications, indicating great potential for applications in biosensing and bioimaging.

Low-temperature crystallization of anodized TiO2 nanotubes at the solid-gas interface and their photoelectrochemical properties.

TiO2 nanotubular arrays formed by electrochemical anodization have attracted significant attention for photoelectrochemical applications that utilize solar energy. However, the as-anodized TiO2 nanotubes are amorphous, and need to be crystallized by high-temperature thermal annealing. Herein, we describe a low-temperature hydrothermal solid-gas route to crystallize TiO2 nanotubes. In this process, the as-anodized TiO2 hydroxo nanotubes are dehydrated to yield anatase phase via solid-gas interface reaction in an autoclave at a temperature of less than 180 °C. The solid-gas interface reaction alleviates the collapse of as-anodized TiO2 nanotubes during hydrothermal process efficiently. Compared with the common thermal annealing at the same temperature but at atmospheric pressure, the hydrothermal route improves the photocurrent density of TiO2 nanotubes by ~10 times in KOH electrolyte. The duration of the hydrothermal reaction has a substantial effect on the photoelectrochemical properties of TiO2 nanotubes, which is ascribed to the synergetic effect between the crystallization and structural evolution. Electron donors can further suppress the charge recombination in the low-temperature crystallized TiO2 nanotubes and boost the photocurrent density by ~120%.

Biocompatible nanofiber scaffolds on metal for controlled release and cell colonization.

This paper reports for the first time a preparation of biocompatible titanate nanofiber scaffolds on the surface of titanium foil/mesh via a one-step hydrothermal reaction. The length and diameter of the nanofibers can be controlled by varying the fabrication parameters, such as reaction temperature, precursor concentration, and reaction time. The nanofibers can self-organize into macroporous (mostly 0.5-10 microm in diameter) scaffolds potentially useful for developing new bioscaffolds, photocatalysts, sensors, and drug delivery vehicles.