Controllable Crystallization of Two-Dimensional Bi Nanocrystals with Morphology-Boosted CO2 Electroreduction in Wide pH Environments.

Two-dimensional low-melting-point (LMP) metal nanocrystals are attracting increasing attention with broad and irreplaceable applications due to their unique surface and topological structures. However, the chemical synthesis, especially the fine control over the nucleation (reduction) and growth (crystallization), of such LMP metal nanocrystals remains elusive as limited by the challenges of low standard redox potential, low melting point, poor crystalline symmetry, etc. Here, a controllable reduction-melting-crystallization (RMC) protocol to synthesize free-standing and surfactant-free bismuth nanocrystals with tunable dimensions, morphologies, and surface structures is presented. Especially, ultrathin bismuth nanosheets with flat or jagged surfaces/edges can be prepared with high selectivity. The jagged bismuth nanosheets, with abundant surface steps and defects, exhibit boosted electrocatalytic CO2 reduction performances in acidic, neutral, and alkaline aqueous solutions, achieving the maximum selectivity of near unity at the current density of 210 mA cm-2 for formate evolution under ambient conditions. This work creates the RMC pathway for the synthesis of free-standing two-dimensional LMP metal nanomaterials and may find broader applicability in more interdisciplinary applications.

Controlled Synthesis of Intermetallic Au2 Bi Nanocrystals and Au2 Bi/Bi Hetero-Nanocrystals with Promoted Electrocatalytic CO2 Reduction Properties.

The electrocatalytic properties of metal nanoparticles (NPs) strongly depend on their compositions and structures. Rational design of alloys and/or heterostructures provides additional approaches to modifying their surface geometric and electronic structures for optimized electrocatalytic performance. Here, a solution synthesis of freestanding intermetallic Au2 Bi NPs, the heterostructures of Au2 Bi/Bi hetero-NPs, and their promoted electrocatalytic CO2 reduction reaction (CO2 RR) performances were reported. It was revealed that the formation and in-situ conversion of heterogeneous seeds (e. g., Au) were of vital importance for the formation of intermetallic Au2 Bi and Au2 Bi/Bi hetero-NPs. It was also found that the Au components would act as the structure promoter moderating the binding strength for key intermediates on Bi surfaces. The alloying of Bi with Au and the formation of heterogeneous Au2 Bi/Bi interfaces would create more surface active sites with modulated electronic structures and stronger adsorption strengths for key intermediates, promoting the CO2 -to-HCOOH conversion with high activity and selectivity. This work presents a novel route for preparing intermetallic nanomaterials with modulated surface geometric/electric structures and promoting their electrocatalytic activities with alloying effects and interfacial effects. Such strategy may find wide application in catalyst design and synthesis for more electrocatalytic reactions.

Promoting the Electrocatalytic Reduction of CO2 on Ultrathin Porous Bismuth Nanosheets with Tunable Surface-Active Sites and Local pH Environments.

Electrochemical CO2 reduction reaction (CO2RR) yielding value-added chemicals provides a sustainable approach for renewable energy storage and conversion. Bismuth-based catalysts prove to be promising candidates for converting CO2 and water into formate but still suffer from poor selectivity and activity and/or sluggish kinetics. Here, we report that ultrathin porous Bi nanosheets (Bi-PNS) can be prepared through a controlled solvothermal protocol. Compared with smooth Bi nanoparticles (Bi-NPs), the ultrathin, rough, and porous Bi-PNS provide more active sites with higher intrinsic reactivities for CO2RR. Moreover, such high activity further increases the local pH in the vicinity of the catalyst surfaces during electrolysis and thus suppresses the competing hydrogen evolution reaction. As a result, the Bi-PNS exhibit significantly boosted CO2RR properties, showing a Faradaic efficiency of 95% with an effective current density of 45 mA cm-2 for formate evolution at the potential of -1.0 V versus reversible hydrogen electrode.

Modulating the electrocatalytic CO2 reduction performances of bismuth nanoparticles with carbon substrates with controlled degrees of oxidation.

The catalytic performances of metal nanoparticles can be widely tuned and promoted by the metal-support interactions. Here, we report that the morphologies and electrocatalytic CO2 reduction reaction (CO2RR) properties of bismuth nanoparticles (BiNPs) can be rationally modulated by their interactions with carbon black (CB) supports by controlling the degree of surface oxidation. Appropriately oxidized CB supports can provide sufficient oxygen-containing groups for anchoring BiNPs with tunable sizes and surface areas, desirable key intermediate adsorption abilities, appropriate surface wettability, and adequate electron transfer abilities. As a result, the optimized Bi/CB catalysts exhibited a promoted CO2RR performance with a Faradaic efficiency of 94% and a current density of 16.7 mA cm-2 for HCOO- at -0.9 V versus a reversible hydrogen electrode. Our results demonstrate the significance of regulating the interactions between supports and metal nanoparticles for both synthesis of the catalyst and electrolysis applications, which may find broader applicability in more electrocatalyst designs.

Nanoporous Graphene via a Pressing Organization Calcination Strategy for Highly Efficient Electrocatalytic Hydrogen Peroxide Generation.

Nanoporous graphenes (NPGs) have recently attracted huge attention owing to their designable structures and diverse properties. Many important properties of NPGs are determined by their structural regularity and homogeneity. The mass production of NPGs with periodic well-defined pore structures under a solvent-free green synthesis poses a great challenge and is largely unexplored. A facile synthetic strategy of NPGs via pressing organization calcination (POC) of readily available halogenated polycyclic aromatic hydrocarbons is developed. The gram-scale synthesized NPGs have ordered structures and possess well-defined nanopores, which can be easily exfoliated to few layers and oxidized in controllable approaches. After being decorated with oxygen species, the oxidized NPGs with tunable catalytic centers exhibit high activity, selectivity, and stability toward electrochemical hydrogen peroxide generation.

Metal-organic framework membranes with single-atomic centers for photocatalytic CO2 and O2 reduction.

The demand for sustainable energy has motivated the development of artificial photosynthesis. Yet the catalyst and reaction interface designs for directly fixing permanent gases (e.g. CO2, O2, N2) into liquid fuels are still challenged by slow mass transfer and sluggish catalytic kinetics at the gas-liquid-solid boundary. Here, we report that gas-permeable metal-organic framework (MOF) membranes can modify the electronic structures and catalytic properties of metal single-atoms (SAs) to promote the diffusion, activation, and reduction of gas molecules (e.g. CO2, O2) and produce liquid fuels under visible light and mild conditions. With Ir SAs as active centers, the defect-engineered MOF (e.g. activated NH2-UiO-66) particles can reduce CO2 to HCOOH with an apparent quantum efficiency (AQE) of 2.51% at 420 nm on the gas-liquid-solid reaction interface. With promoted gas diffusion at the porous gas-solid interfaces, the gas-permeable SA/MOF membranes can directly convert humid CO2 gas into HCOOH with a near-unity selectivity and a significantly increased AQE of 15.76% at 420 nm. A similar strategy can be applied to the photocatalytic O2-to-H2O2 conversions, suggesting the wide applicability of our catalyst and reaction interface designs.

Metal-Organic Framework Membranes Encapsulating Gold Nanoparticles for Direct Plasmonic Photocatalytic Nitrogen Fixation.

Photocatalytic nitrogen fixation reaction can harvest the solar energy to convert the abundant but inert N2 into NH3. Here, utilizing metal-organic framework (MOF) membranes as the ideal assembly of nanoreactors to disperse and confine gold nanoparticles (AuNPs), we realize the direct plasmonic photocatalytic nitrogen fixation under ambient conditions. Upon visible irradiation, the hot electrons generated on the AuNPs can be directly injected into the N2 molecules adsorbed on Au surfaces. Such N2 molecules can be additionally activated by the strong but evanescently localized surface plasmon resonance field, resulting in a supralinear intensity dependence of the ammonia evolution rate with much higher apparent quantum efficiency and lower apparent activation energy under stronger irradiation. Moreover, the gas-permeable Au@MOF membranes, consisting of numerous interconnected nanoreactors, can ensure the dispersity and stability of AuNPs, further facilitate the mass transfer of N2 molecules and (hydrated) protons, and boost the plasmonic photocatalytic reactions at the designed gas-membrane-solution interface. As a result, an ammonia evolution rate of 18.9 mmol gAu-1 h-1 was achieved under visible light (>400 nm, 100 mW cm-2) with an apparent quantum efficiency of 1.54% at 520 nm.

Acidic preconditioning reduces lipopolysaccharide-induced acute lung injury by upregulating the expression of angiotensin-converting enzyme 2.

Acid preconditioning (APC) through carbon dioxide inhalation can exert protective effects during acute lung injury (ALI) triggered by ischemia-reperfusion. Angiotensin-converting enzyme 2 (ACE2) has been identified as a receptor for severe acute respiratory syndrome coronavirus and the novel coronavirus disease-19. Downregulation of ACE2 plays an important role in the pathogenesis of severe lung failure after viral or bacterial infections. The aim of the present study was to examine the anti-inflammatory mechanism through which APC alleviates lipopolysaccharide (LPS)-induced ALI in vivo and in vitro. The present results demonstrated that LPS significantly downregulated the expression of ACE2, while APC significantly reduced LPS-induced ALI and provided beneficial effects. In addition, bioinformatics analysis indicated that microRNA (miR)-200c-3p directly targeted the 3'untranslated region of ACE2 and regulated the expression of ACE2 protein. LPS exposure inhibited the expression of ACE2 protein in A549 cells by upregulating the levels of miR-200c-3p. However, APC inhibited the upregulation of miR-200c-3p induced by LPS, as well as the downregulation of ACE2 protein, through the NF-κB pathway. In conclusion, although LPS can inhibit the expression of ACE2 by upregulating the levels of miR-200c-3p through the NF-κB pathway, APC inhibited this effect, thus reducing inflammation during LPS-induced ALI.

Morphology-dependent electrocatalytic nitrogen reduction on Ag triangular nanoplates.

Electrocatalytic nitrogen reduction reactions (ENRR) can produce ammonia from nitrogen and water under ambient conditions. Here, we report the morphology-dependent electro-catalytic nitrogen reduction on Ag triangular nanoplates. Boosted by potassium cations, Ag triangular nanoplates with sharp edges exhibit a high faradaic efficiency of 25% with an ammonia yield of 58.5 mg gAg-1 h-1 at a low overpotential of -0.25 V vs. RHE. In comparison, rounded Ag nanoparticles mainly enclosed by {111} and {100} surfaces show a much smaller faradaic efficiency of 16% and ammonia yield of 38 mg gAg-1 h-1 at a larger overpotential (-0.35 V vs. RHE).

Promoting photocatalytic nitrogen fixation with alkali metal cations and plasmonic nanocrystals.

Photocatalytic nitrogen fixation can produce ammonia from nitrogen and water under ambient conditions in the presence of sunlight. Here, we report that alkali metal cations (Li+, Na+, and K+) can significantly promote nitrogen activation and plasmonic nanocrystals (Au and Ag) can sensitize photocatalysts under visible light. The ammonia yield and selectivity on Au/P25 under UV-vis irradiation could be increased from 0.085 mmol g-1 h-1 and 75% to 0.43 mmol g-1 h-1 and 94.5% when promoted by K+, showing a visible-light-driven activity of 0.14 mmol g-1 h-1 and an AQE of 0.62% at 550 nm. The activity could be further increased to 1.02 (UV-vis) and 0.32 (visible) mmol g-1 h-1 with AQE of 0.93% at 550 nm with methanol added as the sacrificial agent. This strategy could be applied to a series of photocatalysts (e.g. TiO2, ZnO, and BiOBr) and may represent a general approach for designing efficient nitrogen fixation processes.

Ultrathin cobalt oxide nanostructures with morphology-dependent electrocatalytic oxygen evolution activity.

Engineering compositions, structures, and defects can endow nanomaterials with optimized catalytic properties. Here, we report that cobalt oxide (CoOx) ultrathin nanosheets (UTNS, ∼1.6 nm thick) with a large number of oxygen defects and mixed cobalt valences can be obtained through a facile one-step hydrothermal protocol. The large number of oxygen defects make the ultrathin CoOx nanosheet a superior OER catalyst with low overpotentials of 315 and 365 mV at current densities of 50 and 200 mA cm-2, respectively. The stable framework-like architectures of the UTNS further ensure their high OER activity and durability. Our method represents a facile one-step preparation of CoOx nanostructures with tunable compositions, morphologies, and defects, and thus promotes OER properties. This strategy may find its wider applicability in designing active, robust, and easy-to-obtain catalysts for OER and other electrocatalytic systems.

Identification and in vitro pharmacological characterization of a novel and selective α7 nicotinic acetylcholine receptor agonist, Br-IQ17B.

AIM: Alpha7-nicotinic acetylcholine receptor (α7 nAChR) is a ligand-gated Ca(2+)-permeable ion channel implicated in cognition and neuropsychiatric disorders. Activation of α7 nAChR improves learning, memory, and sensory gating in animal models. To identify novel α7 nAChR agonists, we synthesized a series of small molecules and characterized a representative compound, Br-IQ17B, N-[(3R)-1-azabicyclo[2,2,2]oct-3-yl]-5-bromoindolizine-2-carboxamide, which specifically activates α7 nAChR. METHODS: Two-electrode voltage clamp (TEVC) recordings were primarily used for screening in Xenopus oocytes expressing human α7 nAChR. Assays, including radioisotope ligand binding, Western blots, whole-cell recordings of hippocampal culture neurons, and spontaneous IPSC recordings of brain slices, were also utilized to evaluate and confirm the specific activation of α7 nAChR by Br-IQ17B. RESULTS: Br-IQ17B potently activates α7 nAChR with an EC50 of 1.8±0.2 µmol/L. Br-IQ17B is selective over other subtypes such as α4ß2 and α3ß4, but it blocks 5-HT3A receptors. Br-IQ17B displaced binding of the α7 blocker [(3)H]-MLA to hippocampal crude membranes with a Ki of 14.9±3.2 nmol/L. In hippocampal neurons, Br-IQ17B evoked α7-like currents that were inhibited by MLA and enhanced in the presence of the α7 PAM PNU-120596. In brain slice recordings, Br-IQ17B enhanced GABAergic synaptic transmission in CA1 neurons. Mechanistically, Br-IQ17B increased ERK1/2 phosphorylation that was MLA-sensitive. CONCLUSION: We identified the novel, potent, and selective α7 agonist Br-IQ17B, which enhances synaptic transmission. Br-IQ17B may be a helpful tool to understand new aspects of α7 nAChR function, and it also has potential for being developed as therapy for schizophrenia and cognitive deficits.