Crystal Facet Engineering on SrTiO3 Enhances Photocatalytic Overall Water Splitting.

Single-crystal semiconductor-based photocatalysts exposing unique crystallographic facets show promising applications in energy and environmental technologies; however, crystal facet engineering through solid-state synthesis for photocatalytic overall water splitting is still challenging. Herein, we develop a novel crystal facet engineering strategy through solid-state recrystallization to synthesize uniform SrTiO3 single crystals exposing tailored {111} facets. The presynthesized low-crystalline SrTiO3 precursors enable the formation of well-defined single crystals through kinetically improved crystal structure transformation during solid-state recrystallization process. By employing subtle Al3+ ions as surface morphology modulators, the crystal surface orientation can be precisely tuned to a controlled percentage of {111} facets. The photocatalytic overall water splitting activity increases with the exposure percentage of {111} facets. Owing to the outstanding crystallinity and favorable anisotropic surface structure, the SrTiO3 single crystals with 36.6% of {111} facets lead to a 3-fold enhancement of photocatalytic hydrogen evolution rates up to 1.55 mmol·h-1 in a stoichiometric ratio of 2:1 than thermodynamically stable SrTiO3 enclosed with isotropic {100} facets.

Bridging Together Theoretical and Experimental Perspectives in Single-Atom Alloys for Electrochemical Ammonia Production.

Ammonia is an essential commodity in the food and chemical industry. Despite the energy-intensive nature, the Haber-Bosch process is the only player in ammonia production at large scales. Developing other strategies is highly desirable, as sustainable and decentralized ammonia production is crucial. Electrochemical ammonia production by directly reducing nitrogen and nitrogen-based moieties powered by renewable energy sources holds great potential. However, low ammonia production and selectivity rates hamper its utilization as a large-scale ammonia production process. Creating effective and selective catalysts for the electrochemical generation of ammonia is critical for long-term nitrogen fixation. Single-atom alloys (SAAs) have become a new class of materials with distinctive features that may be able to solve some of the problems with conventional heterogeneous catalysts. The design and optimization of SAAs for electrochemical ammonia generation have recently been significantly advanced. This comprehensive review discusses these advancements from theoretical and experimental research perspectives, offering a fundamental understanding of the development of SAAs for ammonia production.

Electroreduction of CO2 on Cu, Fe, or Ni-doped Diamane Sheets: A DFT Study.

Poor mass transfer behavior and inherent activity limit the efficiency of traditional catalysts in electrocatalyzing carbon dioxide reduction reactions. However, the development of novel nanomaterials provides new strategies to solve the above problems. Herein, we propose novel single-metal atom catalysts, namely diamane-based electrocatalysts doped with Cu, Fe, and Ni, explored through density functional theory (DFT) calculations. We thoroughly investigated the doping pattern and energetics for different dopants. Furthermore, we systematically investigated the conversion process of CO2 to C1 or C2+ products, utilizing the free energy analysis of reaction pathways. Our results reveal that dopants could only be introduced into diamane following a specific pattern. Dopants significantly enhance the CO2 adsorption ability of diamane, with Fe and Ni proving notably more effective than Cu. After CO2 adsorption, Cu- and Fe-doped diamane prefer to catalyze CO2RR, while Ni-doped diamane favors hydrogen evolution reaction (HER). The C-C coupling reaction on Cu-hollow diamane, Cu-bridge diamane, and Fe-hollow diamane tends to be from C2+ products. Among all examined catalysts, Cu-hollow diamane shows better electro-catalytic performance. Our study demonstrates the feasibility of and contributes to the development of diamane-based electro-catalysts for CO2RR.

Coordination Engineering of Heteronuclear Fe-Mo Dual-Atom Catalyst for Promoted Electrocatalytic Nitrogen Fixation: A DFT Study.

Developing efficient nanostructured electrocatalysts for N2 reduction to NH3 under mild conditions remains a major challenge. The Fe-Mo cofactor serves as the archetypal active site in nitrogenase. Inspired by nitrogenase, we designed a series of heteronuclear dual-atom catalysts (DACs) labeled as FeMoN6-a Xa (a=1, 2, 3; X=B, C, O, S) anchored on the pore of g-C3 N4 to probe the impact of coordination on FeMo-catalyzed nitrogen fixation. The stability, reaction paths, activity, and selectivity of 12 different FeMoN6-a Xa DACs have been systematically studied using density functional theory. Of these, four DACs (FeMoN5 B1 , FeMoN5 O1 , FeMoN4 O2 , and FeMoN3 C3 ) displayed promising nitrogen reduction reaction (NRR) performance. Notably, FeMoN5 O1 stands out with an ultralow limiting potential of -0.11 V and high selectivity. Analysis of the density of states and charge/spin changes shows FeMoN5 O1 's high activity arises from optimal N2 binding on Fe initially and synergy of the FeMo dimer enabling protonation in NRR. This work contributes to the advancement of rational design for efficient NRR catalysts by regulating atomic coordination environments.

Label-Free Imaging of Humic Substance Bioaccumulation by Pump-Probe Microscopy.

Humic substances (HS) are the most abundant forms of natural organic matter on the earth surface. Comprised of decomposed plant and animal materials rich in carbon, oxygen, hydrogen, nitrogen, and sulfur complexes, HS facilitate global carbon and nitrogen cycling and the transport of anthropogenic contaminants. While it is known that HS also interact with organisms at different trophic levels to produce beneficial and harmful effects whether HS exert these biological effects through accumulation remains unknown. Current radiolabeling techniques, which only detect the amount of accumulated radiolabels, cannot visualize the transport and accumulation behavior of HS. Here, using a label-free method based on pump-probe microscopy, we show HS entered the protozoan Tetrahymena thermophila, zebrafish embryos, and human cells and exerted direct effects on these organisms. HS accumulated in the nucleus of T. thermophila, chorion pore canals of zebrafish embryos, and nucleus of intestinal and lung cells in a concentration- and time-dependent way. Epigenetic and transcriptomics assays show HS altered chromatin accessibility and gene transcription in T. thermophila. In zebrafish larvae, HS induced neurotoxicity, altering spontaneous muscle contraction and locomotor activity. Detailed images showing HS accumulation in our study reveal new insights on the ecological and environmental behavior of HS.

Porous Hydrogel Photothermal Conversion Membrane to Facilitate Water Purification.

Solar water purification technology is one of the most potent methods to obtain freshwater due to its low cost and non-polluting characteristics. However, the purification efficiency is limited by the high ion concentration, organic pollution, and biological pollution during the actual water purification process. Here, we report a porous hydrogel membrane (Fe/TA-TPAM) for the purification of high ion concentration and contaminated water. The hydrogel membrane exhibits good light absorption and photothermal conversion ability, which shows high evaporation rates (1.4 kg m-2 h-1) and high solar efficiency for seawater. Furthermore, with the introduction of tannic acid (TA) and Ti3C2 MXenes, the Fe/TA-TPAM hydrogel membrane exhibits satisfied purification properties for organic-contaminated and biologically contaminated water. The excellent purification effect of Fe/TA-TPAM under light not only confirms the rationality of the hydrogel porous design and in situ generation of photosensitizer in improving the photothermal performance but also provides a novel strategy for designing advanced photothermal conversion membranes for water purification.

High Quantum Efficiency Rare-Earth-Doped Gd2O2S:Tb, F Scintillators for Cold Neutron Imaging.

High-resolution neutron radiography provides novel and stirring opportunities to investigate the structures of light elements encased by heavy elements. For this study, a series of Gd2O2S:Tb, F particles were prepared using a high-temperature solid phase method and then used as a scintillation screen. Upon reaching 293 nm excitation, a bright green emission originated from the Tb3+ luminescence center. The level of F doping affected the fluorescence intensity. When the F doping level was 8 mol%, the fluorescence intensity was at its highest. The absolute quantum yield of the synthesized particles reached as high as 77.21%. Gd2O2S:Tb, F particles were applied to the scintillation screen, showing a resolution on the neutron radiograph as high as 12 µm. These results suggest that the highly efficient Gd2O2S:Tb, F particles are promising scintillators for the purposes of cold neutron radiography.

Nitrate-to-Ammonia Conversion on Ru/Ni Hydroxide Hybrid through Zinc-Nitrate Fuel Cell.

The fuel cell is a basic device to generate electricity from chemical fuels. It is often operated with oxygen as the oxidizing agent, but its sluggish reduction has become a key challenge. Herein, a conceptual oxygen-free design is demonstrated, namely a zinc-nitrate fuel cell, which converts nitrate waste into valuable ammonia and generates electricity simultaneously. The cell is constructed with zinc foil as the anode and ruthenium (Ru) nanoparticles loaded on nickel foam as the cathode. Catalyzed by Ru/Ni hydroxide hybrid, the reaction rate of 384 mmol h-1  mgRu-1 (1.4 × 10-6  ± 0.1 × 10-6  mol s-1  cm-2 ) and Faradic efficiency (FENH3  = 97% ± 2%) at -0.6 V versus reverse hydrogen electrode are achieved for nitrate-to-ammonia conversion. During ammonia production, such zinc-nitrate fuel cell can further deliver a maximum power density of 51.5 mW cm-2 (0.25 cm2  electrode) and 23.3 mW cm-2  (1 cm2 electrode), keeping ultrahigh Faradic efficiency (97% ± 4% at 40 mA cm-2 ) after long tests.

Effect of local coordination on catalytic activities and selectivities of Fe-based catalysts for N2 reduction.

Electrochemical reduction of nitrogen is considered a promising route for achieving green and sustainable ammonia synthesis under ambient conditions. A transition metal atom loaded on N-doped graphene is commonly used in the nitrogen reduction reaction (NRR), but the effect of the graphene's coordination environment on electron transfer has rarely been studied. Herein, the NRR performance of Fe1/2/3 clusters, anchored on single-vacancy and N-doped graphene, is investigated systematically via density functional theory (DFT). The calculation results show that the Fe2 cluster supported by two N atom-modified single-vacancy graphene displays the highest catalytic performance of NRR with the lowest energy barrier of 0.62 eV among the 12 candidates, and exhibits efficient selectivity. It has superior performance because of the highly asymmetrical distribution of electrons on graphene, the large positive charge of the Fe2, and the strong adsorption of *NNH. This study provides a new strategy to improve the NRR performance by regulating the Fe1/2/3 clusters coordination environment.

Amorphous Boron Carbide on Titanium Dioxide Nanobelt Arrays for High-Efficiency Electrocatalytic NO Reduction to NH3.

Electrocatalytic NO reduction is regarded as an attractive strategy to degrade the NO contaminant into useful NH3 , but the lack of efficient and stable electrocatalysts to facilitate such multiple proton-coupled electron-transfer processes impedes its applications. Here, we report on developing amorphous B2.6 C supported on a TiO2 nanoarray on a Ti plate (a-B2.6 C@TiO2 /Ti) as an NH3 -producing nanocatalyst with appreciable activity and durability toward the NO electroreduction. It shows a yield of 3678.6 µg h-1 cm-2 and a FE of 87.6 %, superior to TiO2 /Ti (563.5 µg h-1 cm-2 , 42.6 %) and a-B2.6 C/Ti (2499.2 µg h-1 cm-2 , 85.6 %). An a-B2.6 C@TiO2 /Ti-based Zn-NO battery achieves a power density of 1.7 mW cm-2 with an NH3 yield of 1125 µg h-1 cm-2 . An in-depth understanding of catalytic mechanisms is gained by theoretical calculations.

In Operando Identification of In Situ Formed Metalloid Zincδ+ Active Sites for Highly Efficient Electrocatalyzed Carbon Dioxide Reduction.

Electrochemical CO2 -to-CO conversion provides a possible way to address problems associated with the greenhouse effect; however, developing low-cost electrocatalysts to mediate high-efficiency CO2 reduction remains a challenge on account of the limited understanding of the nature of the real active sites. Herein, we reveal the Znδ+ metalloid sites as the real active sites of stable nonstoichiometric ZnOx structure derived from Zn2 P2 O7 through operando X-ray absorption fine structure analysis in conjunction with evolutionary-algorithm-based global optimization. Furthermore, theoretical and experimental results demonstrated that Znδ+ metalloid active sites could facilitate the activation of CO2 and the hydrogenation of *CO2 , thus accelerating the CO2 -to-CO conversion. Our work establishes a critical fundamental understanding of the origin of the real active center in the zinc-based electrocatalysts for CO2 reduction reaction.

Hydrogen-Rich 2D Halide Perovskite Scintillators for Fast Neutron Radiography.

A fast neutron has strong penetration ability through dense and bulky objects, which makes it an ideal nondestructive technology for detecting voids, cracks, or other defects inside large equipment. However, the lack of effective fast neutron detection materials limits its application. Perovskites have shown excellent optical properties in many areas, but they are absent from fast neutron detection imaging because they cannot directly absorb fast neutrons and emit luminescence. Here, we demonstrate a hydrogen-rich long-chain organic amine modified two-dimensional (2D) perovskite fast neutron scintillator, Mn-(C18H37NH3)2PbBr4(Mn-STA2PbBr4). Its hydrogen density can reach 9.51 × 1028 m-3, and the photoluminescence quantum yield can reach 58.58%, so it is possible to integrate fast neutron absorption and luminescence into a single compound. More importantly, Mn-STA2PbBr4 can be made into a large-area self-supporting fast neutron scintillator plate with satisfactory spatial resolution (0.5 lp/mm (lp: line pairs)). This strategy provides a simple and promising choice for fast neutron scintillator nondestructive testing.

Efficient metal ion sieving in rectifying subnanochannels enabled by metal-organic frameworks.

Biological ion channels have remarkable ion selectivity, permeability and rectification properties, but it is challenging to develop artificial analogues. Here, we report a metal-organic framework-based subnanochannel (MOFSNC) with heterogeneous structure and surface chemistry to achieve these properties. The asymmetrically structured MOFSNC can rapidly conduct K+, Na+ and Li+ in the subnanometre-to-nanometre channel direction, with conductivities up to three orders of magnitude higher than those of Ca2+ and Mg2+, equivalent to a mono/divalent ion selectivity of 103. Moreover, by varying the pH from 3 to 8 the ion selectivity can be tuned further by a factor of 102 to 104. Theoretical simulations indicate that ion-carboxyl interactions substantially reduce the energy barrier for monovalent cations to pass through the MOFSNC, and thus lead to ultrahigh ion selectivity. These findings suggest ways to develop ion selective devices for efficient ion separation, energy reservation and power generation.

Insight into the Reactivity of Carbon Structures for Nitrogen Reduction Reaction.

Graphene-based structures have been widely reported as promising metal-free catalysts for nitrogen reduction reaction. To explain the reactivity origin, various structures have been proposed and debated, including defects, functional groups, and doped heteroatoms. This computational work demonstrates that these structures may evolve from one to another under electrochemical conditions, generating weakly coordinated carbons, which have been identified as the active sites for N2 adsorption and activation.

Rational Design of Graphene-Supported Single-Atom Catalysts for Electroreduction of Nitrogen.

Critically, the central metal atoms along with their coordination environment play a significant role in the catalytic performance of single-atom catalysts (SACs). Herein, 12 single Fe, Mo, and Ru atoms supported on defective graphene are theoretically deigned for investigation of their structural and electronic properties and catalytic nitrogen reduction reaction (NRR) performance using first-principles calculations. Our results reveal that graphene with vacancies can be an ideal anchoring site for stabilizing isolated metal atoms owing to the strong metal-support interaction, forming stable TMCx or TMNx active centers (x = 3 or 4). Six SACs are screened as promising NRR catalyst candidates with excellent activity and selectivity during NRR, and RuN3 is identified as the optimal one with an overpotential of ≥0.10 V via the distal mechanism.

Size-Dependent Nonlinear Optical Properties of Gd2O2S:Tb3+ Scintillators and Their Doped Gel Glasses.

With the advancement of ultra-fast and high-energy pulsed laser output, lasers have caused serious harm to precision instruments and human eyes. Therefore, the development of optical limiting materials with a fast response, low optical limiting threshold, and high damage threshold are important. In this work, for the first time, it is reported that phosphors Gd2O2S:Tb3+(GOS) displays exceptional functionality in laser protection. GOS with sizes of 11 µm, 1 µm, and 0.45 µm are prepared. Based on the optical limiting and Z-scan technology systems under 532 nm and 1064 nm nanosecond laser excitation, the nonlinear optical properties of GOS are investigated. It is found that GOS exhibits outstanding optical limiting properties. In addition, the optical limiting response of GOS is size-dependent. Concerning the largest particle size, GOS has the best nonlinear optical response, while the precursor shows no nonlinear optical performance. Meanwhile, GOS doped gel glass also displays excellent optical limiting properties with high transmittance, which preliminarily validates the application of GOS and other scintillators in nonlinear optics and encourages more research to better realize the potential of GOS.

Trace-Level Fluorination of Mesoporous TiO2 Improves Photocatalytic and Pb(II) Adsorbent Performances.

Fluorination is an effective way of tuning the physicochemical property and activity of TiO2 nanocrystallites, which usually requires a considerable amount of hydrofluoric acid (or NH4F) for a typical F/Ti molar ratio, RF, of 0.5-69.0 during synthesis. This has consequential environmental issues due to the high toxicity and hazard of the reactants. In the present work, an environmentally benign fluorination approach is demonstrated that uses only a trace amount of sodium fluoride with an RF of 10-6 during synthesis. While it maintained the desirable high surface area (102.4 m2/g), the trace-level fluorination enabled significant enhancements on photocatalytic activities (e.g., a 56% increase on hydrogen evolution rate) and heavy metal Pb(II) removal (31%) of the mesoporous TiO2. This can be attributed to enriched Ti3+ and localized spatial charge separation due to fluorination as proved by X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance spectroscopy (EPR), and density functional theory (DFT) analyses.

Electrocatalytic dinitrogen reduction reaction on silicon carbide: a density functional theory study.

It is challenging to identify effective electrocatalysts for nitrogen reduction in order to advance electrochemical nitrogen fixation under ambient conditions using methods that are powered by renewable energy. Silicon carbide was investigated computationally as a metal-free, surface-derived catalyst for the electrocatalytic nitrogen reduction reaction. As demonstrated by first-principle calculations, Si-terminated and C-terminated surfaces, with the Si and C as active sites, are all reactive for dinitrogen capture and activation, resembling the catalytic behavior of popular B-based electrocatalysts, but the latter (C-terminated) offers an ultralow over-potential of 0.39 V, which is lower than most metals and alloys, while retarding hydrogen evolution. This research enriches the design of catalysts for dinitrogen fixation under ambient conditions, and also highlights a new direction for Si-based materials for nitrogen reduction.

Single-Boron Catalysts for Nitrogen Reduction Reaction.

Boron has been explored as p-block catalysts for nitrogen reduction reaction (NRR) by density functional theory. Unlike transition metals, on which the active centers need empty d orbitals to accept the lone-pair electrons of the nitrogen molecule, the sp3 hybrid orbital of the boron atom can form B-to-N π-back bonding. This results in the population of the N-N π* orbital and the concomitant decrease of the N-N bond order. We demonstrate that the catalytic activity of boron is highly correlated with the degree of charge transfer between the boron atom and the substrate. Among the 21 concept-catalysts, single boron atoms supported on graphene and substituted into h-MoS2 are identified as the most promising NRR catalysts, offering excellent energy efficiency and selectivity against hydrogen evolution reaction.

Hydrogen Evolution in [NiFe] Hydrogenases: A Case of Heterolytic Approach between Proton and Hydride.

The mechanism for Hydrogen Evolution Reaction (HER) in [NiFe] hydrogenase enzymes distinguishes them from inorganic catalysts. The first H+/e- pair injected to the active site of the hydrogenases transforms into hydride, while the second H+/e- pair injection leads to the formation of the H-/H+ pair both binding to the active site. The two opposite charged hydrogens heterolytically approach each other in order to form dihydrogen (H2), which is enhanced by the Coulomb force. Two previously proposed reaction routes for this process have been examined by Conceptual Density Functional Theory (DFT) in this work. One presents better agreement with experimental spectra, while the other is thermodynamically more favorable. Both paths suggest that the approach and the charge transfer between the proton and hydride are motivated by the stabilization of the electronic activity and the electrophilicity of Ni. After the heterolytic approach of the proton and hydride moieties, the two hydrogen atoms attach to the Ni ion and combine homolytically.