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.

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.

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.

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.

Direct OC-CHO coupling towards highly C2+ products selective electroreduction over stable Cu0/Cu2+ interface.

Electroreduction of CO2 to valuable multicarbon (C2+) products is a highly attractive way to utilize and divert emitted CO2. However, a major fraction of C2+ selectivity is confined to less than 90% by the difficulty of coupling C-C bonds efficiently. Herein, we identify the stable Cu0/Cu2+ interfaces derived from copper phosphate-based (CuPO) electrocatalysts, which can facilitate C2+ production with a low-energy pathway of OC-CHO coupling verified by in situ spectra studies and theoretical calculations. The CuPO precatalyst shows a high Faradaic efficiency (FE) of 69.7% towards C2H4 in an H-cell, and exhibits a significant FEC2+ of 90.9% under industrially relevant current density (j = -350 mA cm-2) in a flow cell configuration. The stable Cu0/Cu2+ interface breaks new ground for the structural design of electrocatalysts and the construction of synergistic active sites to improve the activity and selectivity of valuable C2+ products.

Coupled sorptive and oxidative antimony(III) removal by iron-modified biochar: Mechanisms of electron-donating capacity and reactive Fe species.

Sorption and oxidation are two potential pathways for the decontamination of trivalent antimony (Sb(III))-bearing water, using iron (Fe)-modified biochar (FeBC). Here we investigated the sorption and oxidation behavior of FeBC for Sb(III) in aqueous solutions. Results revealed that Sb(III) removal by FeBC was significantly improved showing the maximum Sb(III) sorption (64.0 mg g-1). Density functional theory (DFT) calculations indicated that magnetite (Fe3O4) in FeBC offered a sorption energy of -0.22 eV, which is 5 times that of non-modified biochar. With the addition of peroxymonosulfate (PMS), the sorption of Sb(III) on FeBC was 7 times higher than that on BC, indicating the sorption capacity of FeBC for Sb(III) could be substantially increased by adding oxidizing agents. Electrochemical analysis showed that Fe modification imparted FeBC higher electron-donating capacity than that of BC (0.045 v. s. 0.023 mmol e- (g biochar)-1), which might be the reason for the strong Sb(III) oxidation (63.6%) on the surface of FeBC. This study provides new information that is key for the development of effective biochar-based composite materials for the removal of Sb(III) from drinking water and wastewater. The findings from this study have important implications for protecting human health and agriculture.

Unique Cluster-Support Effect of a Co3O4/TiO2-3DHS Nanoreactor for Efficient Plasma-Catalytic Oxidation Performance.

For environmental catalysis, a central topic is the design of high-performance catalysts and advanced mechanism studies. In the case of the removal of flue gas pollutants from coal-fired power plants, highly selective nanoreactors have been widely utilized together with plasma discharge characteristics, such as the catalytic oxidation of NO. Herein, a novel reactor with a three-dimensional hollow structure of TiO2 confining Co3O4 nanoclusters (Co3O4/TiO2-3DHS) has been developed for plasma-catalytic oxidation of NO, whose performance was compared with that of the commercial TiO2 confining Co3O4 cluster (Co3O4/TiO2). Specifically, Co3O4/TiO2-3DHS presented a higher efficiency (almost 100%) within lower peak-peak voltage (VP-P). More importantly, the NO oxidation efficiency was between 91.5 and 94.5% after a long time of testing, indicating that Co3O4/TiO2-3DHS exhibits more robust sulfur and water tolerance. Density functional theory calculations revealed that such impressive performance originates from the unique cluster-support effect, which changes the distribution of the active sites on the catalyst surface, resulting in the selective adsorption of flue gas. This investigation provides a new strategy for constructing a three-dimensional hollow nanoreactor for the plasma-catalytic process.

A corrosion-resistant RuMoNi catalyst for efficient and long-lasting seawater oxidation and anion exchange membrane electrolyzer.

Direct seawater electrolysis is promising for sustainable hydrogen gas (H2) production. However, the chloride ions in seawater lead to side reactions and corrosion, which result in a low efficiency and poor stability of the electrocatalyst and hinder the use of seawater electrolysis technology. Here we report a corrosion-resistant RuMoNi electrocatalyst, in which the in situ-formed molybdate ions on its surface repel chloride ions. The electrocatalyst works stably for over 3000 h at a high current density of 500 mA cm-2 in alkaline seawater electrolytes. Using the RuMoNi catalyst in an anion exchange membrane electrolyzer, we report an energy conversion efficiency of 77.9% and a current density of 1000 mA cm-2 at 1.72 V. The calculated price per gallon of gasoline equivalent (GGE) of the H2 produced is $ 0.85, which is lower than the 2026 technical target of $ 2.0/GGE set by the United Stated Department of Energy, thus, suggesting practicability of the technology.

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 Strength Titanium with Fibrous Grain for Advanced Bone Regeneration.

Pure titanium is widely used in clinical implants, but its bioinert properties (poor strength and mediocre effect on bone healing) limit its use under load-bearing conditions. Modeling on the structure of collagen fibrils and specific nanocrystal plane arrangement of hydroxyapatite in the natural bone, a new type of titanium (Ti) with a highly aligned fibrous-grained (FG) microstructure is constructed. The improved attributes of FG Ti include high strength (≈950 MPa), outstanding affinity to new bone growth, and tight bone-implant contact. The bone-mimicking fibrous grains induce an aligned surface topological structure conducive to forming close contact with osteoblasts and promotes the expression of osteogenic genes. Concurrently, the predominant Ti(0002) crystal plane of FG Ti induces the formation of hydrophilic anatase titanium oxide layers, which accelerate biomineralization. In conclusion, this bioinspired FG Ti not only proves to show mechanical and bone-regenerative improvements but it also provides a new strategy for the future design of metallic biomaterials.

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.

Copper-based catalysts for the electrochemical reduction of carbon dioxide: progress and future prospects.

There is an urgent need for the development of high performance electrocatalysts for the CO2 reduction reaction (CO2RR) to address environmental issues such as global warming and achieve carbon neutral energy systems. In recent years, Cu-based electrocatalysts have attracted significant attention in this regard. The present review introduces fundamental aspects of the electrocatalytic CO2RR process together with a systematic examination of recent developments in Cu-based electrocatalysts for the electroreduction of CO2 to various high-value multicarbon products. Current challenges and future trends in the development of advanced Cu-based CO2RR electrocatalysts providing high activity and selectivity are also discussed.

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.

Spin regulation for efficient electrocatalytic N2 reduction over diatomic Fe-Mo catalyst.

Electrocatalytic nitrogen reduction reaction (eNRR) is a promising method for the sustainable production of ammonia as an alternative to the traditional energy-intensive Haber-Bosch process. In this work, an efficient strategy by atomic spin regulation to promote NRR through Fe-transition metal (TM) hybrid heteronuclear dual-atom catalysts has been studied. By means of DFT computations, the stability, activity, and selectivity of 30 kinds of Fe-based dual-atoms anchored on N-doped porous graphene are systematically investigated to evaluate their catalytic performance. Fe/MoNC is screened as an excellent NRR catalyst with the limiting potentials of 0.63 V, and also suppresses HER. In the Fe/MoNC, the neighboring Fe atom regulates the spin state of the Mo center in MoN4 from high-spin state (2.63 µB) to medium-spin state (0.74 µB), which can effectively relieve the strong overlapping between Mo 4d orbital with the NxHy intermediates, promote the desorption of reaction product, and eventually achieve a lower limiting potential. Interestingly, the archetype of the active center of nitrogenase is also a FeMo-cofactor, which is consistent with our screening results. The work may provide new insight into the mechanism of nitrogenase, and promote the rational design of efficient NRR catalysts by atomic spin regulation.

Graphite Nanoflake-Modified Mo2C with Ameliorated Interfacial Interaction as an Electrocatalyst for Hydrogen Evolution Reaction.

Molybdenum carbide (Mo2C) is anticipated to be a promising electrocatalyst for electrocatalytic hydrogen production due to its low cost, resourceful property, prominent stability, and Pt-like electrocatalytic activity. The rational design of Mo2C-based electrocatalysts is expected to improve hydrogen evolution reaction (HER) performance, especially by constructing ultrasmall Mo2C particles and appropriate interfaces. Herein, composites of molybdenum carbide (Mo2C) quantum dots anchored on graphite nanoflakes (Mo2C/G) were fabricated, which realized a stable overpotential of 136 mV at 10 mA cm-2 for the HER with a small Tafel slope of 76.81 mV dec-1 in alkaline media, and operated stably over 10 h and 2000 cycles. The superior HER performance can be attributed to the fact that graphite nanoflakes could act as a matrix to disperse Mo2C as quantum dots to expose more active sites and guarantee high electronic conductivity and, more importantly, provide ameliorated interfacial interaction between Mo2C and graphite nanoflakes with appropriate hydrogen binding energy and charge density distribution. To further explore which kind of interfacial interaction is more favorable to improve the HER performance, density functional theory calculations and corresponding contrast experiments were also performed, and it was interesting to prove that Mo2C quantum dots anchored to the basal planes of defective graphite nanoflakes exhibit better electrochemical performance than those anchored on the edges.

Oxygen mediated oxidative couplings of flavones in alkaline water.

Catalyzed oxidative C-C bond coupling reactions play an important role in the chemical synthesis of complex natural products of medicinal importance. However, the poor functional group tolerance renders them unfit for the synthesis of naturally occurring polyphenolic flavones. We find that molecular oxygen in alkaline water acts as a hydrogen atom acceptor and oxidant in catalyst-free (without added catalyst) oxidative coupling of luteolin and other flavones. By this facile method, we achieve the synthesis of a small collection of flavone dimers and trimers including naturally occurring dicranolomin, philonotisflavone, dehydrohegoflavone, distichumtriluteolin, and cyclodistichumtriluteolin. Mechanistic studies using both experimental and computational chemistry uncover the underlying reasons for optimal pH, oxygen availability, and counter-cations that define the success of the reaction. We expect our reaction opens up a green and sustainable way to synthesize flavonoid dimers and oligomers using the readily available monomeric flavonoids isolated from biomass and exploiting their use for health care products and treatment of diseases.

Molecularly Distorted Local Structure in Bi2 CuO4 Oxide to Stabilize Lattice Oxygen for Efficient Formate Electrosynthesis.

The electrochemical CO2 reduction reaction (CO2 RR) provides an economically feasible way for converting green energy into valuable chemical feedstocks and fuels. Great progress has been achieved in the understanding and synthesis of oxidized-based precatalysts; however, their dynamical changes of local structure under operando conditions still hinder their further applications. Here a molecularly distorted Bi2 CuO4 precatalyst for efficient CO2 -to-formate conversion is reported. X-ray absorption fine structure (XAFS) results and theoretical calculations suggest that the distorted structure with molecularly like [CuO4 ]6- unit rotation is more conducive to the structural stability of the sample. Operando XAFS and scanning transmission electron microscopy (STEM) results prove that quite a bit of lattice oxygen can remain in the distorted sample after CO2 RR. Electrochemical measurements of the distorted sample show an excellent activity and selectivity with a high formate partial current density of 194.6 mA cm-2 at an extremely low overpotential of -400 mV. Further in situ surface-enhanced infrared absorption spectroscopy (SEIRAS) and density functional theory (DFT) calculations illustrate that the retained oxygen can optimize the adsorption of *OCHO intermediate for the enhanced CO2 RR performance.

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.

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.

Spectroscopic investigations and density functional theory calculations reveal differences in retention mechanisms of lead and copper on chemically-modified phytolith-rich biochars.

A better understanding of different retention mechanisms of potentially toxic elements (PTEs) by biochars during the remediation of contaminated sites is critically needed. In this study, different spectroscopic techniques including synchrotron-based micro-X-ray fluorescence (µ-XRF), X-ray absorption fine structure (XAFS), and near-edge XAFS spectroscopy (NEXAFS), were used to investigate the spatial distributions and retention mechanisms of lead (Pb) and copper (Cu) on phytolith-rich coconut-fiber biochar (CFB), and ammonia, nitric acid and hydrogen peroxide modified CFB (MCFB) (i.e., ACFB, NCFB and HCFB). The µ-XRF analyses indicated that sorption sites on ACFB and NCFB were more efficient compared to those on CFB and HCFB to bind Pb/Cu. XAFS analyses revealed that the percentage of Pb species as Pb(C2H3O2)2 increased from 22.2% (Pb-loaded CFBs) to 47.4% and 41.9% on Pb-loaded NCFBs and HCFBs, while the percentage of Cu(OH)2 and Cu(C2H3O2)2 increased from 5.8% to 32.8% (Cu-loaded CFBs) to 41.5% and 43.4% (Cu-loaded NCFBs), and 27.1% and 35.1% (Cu-loaded HCFBs), respectively. Due to their similar atomic structures of Pb/Cu, Pb(C2H3O2)2/Pb-loaded montmorillonite and Cu(C2H3O2)2/Cu(OH)2 were identified as the predominant Pb/Cu species observed in Pb- and Cu-loaded MCFBs. The NEXAFS analyses of carbon confirmed that increasing amounts of carboxylic groups were formed on HCFB and NCFB by oxidizing carbon-containing functional groups, which could provide additional active binding sites for Pb/Cu retention. Results from the X-ray photoelectron spectroscopy analyses of nitrogen showed that azido-groups of ACFB played major roles in Pb/Cu retention, while amide-groups and pyridine-groups of NCFB primarily participated in Pb/Cu retention. Overall, density functional theory calculations suggested that silicate and the synergistic effect of hydroxyl and carboxylic-groups on MCFBs were highly efficient in Pb retention, while azido-groups and/or carboxylic-groups played major roles in Cu retention. These results provide novel insights into the PTE retention mechanisms of MCFBs.