Latest ArticlesAs the greenhouse effect concerns increases, the development of new materials for the efficient capture and separation of CO2 gas from gas mixtures has become a matter of urgency. In this study, we performed density functional theory (DFT) calculations to investigate the adsorption and separation behavior of CO2/CH4/H2 on the surface of two-dimensional (2D) Al2C materials under positive/negative applied electric fields. In the absence of an electric field CO2 is weakly physisorbed on the Al2C surface, but with the application of an applied electric field, the adsorption state of CO2 gradually changes from physical to chemisorption (adsorption energy changes from −0.29 eV to −3.61 eV), while the negative electric field has little effect on the adsorption of CO2. We conclude that the C=O bond in adsorbed CO2 can be activated under an external electric field (maximum activation of 15% under an external electric field of 0–0.005 a.u.). Only in the presence of an applied electric field of 0.0033 a.u. and temperatures above 525 K/675 K can the adsorption/separation reaction of CO2 single adsorption and CO2/CH4/H2 mixture be spontaneous. The adsorption/desorption of CO2 on Al2C nanosheet in an electric field of 0.003–0.0033 a.u. is all exothermic, which can be easily controlled by switching on/off the electric field without any energy barriers. The capacity of Al2C to capture CO2 per unit electric field decreases with increasing CO2 concentration, but still has efficient gas separation properties for CO2/CH4/H2. Our theoretical results could provide guidance for designing high-capacity and high-selectivity CO2 capture materials.
Owing to its outstanding photoactivity, ferrioxalate is originally used as an actinometer and subsequent work has discovered that photochemistry of ferrioxalate is also fundamentally or technically important in atmospheric chemistry and water treatment. While the overall products generated from photolysis of ferrioxalate are known to include Fe(Ⅱ), a series of oxidizing (e.g., •OH, O2•−/HO2•−) or reducing (C2O4•−/CO2•−) radicals and H2O2, however, at the molecular level, the primary step of the photoreaction of ferrioxalate remains as an unsolved mystery due to the difficulty in examining such ultrafast processes. Benefiting from the development of time-resolved spectroscopy, this old question has been studied with increasing vigor recently, by means of such ever-more-sophisticated techniques (e.g., flash photolysis, time-resolved X-ray absorption spectroscopy (XAS), femtosecond infrared (IR) absorption spectroscopy, ultrafast photoelectron spectroscopy (PES)). There are two contrary views on the primary reaction mechanism: (1) Intramolecular electron transfer (ET) precedes the cleavage of the metal-ligand bond; (2) The dissociation of C–C or Fe–O bond occurs before intramolecular ET. Thus, this review presents a comprehensive summary about the overall reaction mechanism and molecular level mechanism of ferrioxalates. In chronological order, we have elaborated two predominant but controversial views from the perspectives of different experimental approaches. Some challenges and research opportunities in this active field are also briefly discussed.
Benzimidazoles are very important chemical materials in the pharmaceutical industry, and the most common synthetic route is cyclization of o-phenylenediamine with carbon sources, in which utilization of inexpensive and abundant CO2 as C1 source is very impressive. Porous aromatic frameworks (PAFs) with highly desired skeletons have attracted great attentions in gas capture and catalysis. Herein, B-based PAF-165 and PAF-166 are designed and synthesized via Friedel-Crafts alkylation reaction, which present high surface areas as well as high stability. Benefiting from the abundant electron-deficient B centers, both PAFs exhibit excellent selective CO2 adsorption abilities. The presence of sterically hindered B units in PAFs can act as Lewis acid active sites for the frustrated Lewis pairs (FLPs) in situ formation with o-phenylenediamine, thus promoting the synthesis of benzimidazole. The optimal reaction conditions for o-phenylenediamine cyclization with PAF catalysts are explored, and the reaction mechanism is also proposed. This work provides feasible ideas for incorporating FLPs within porous materials as reusable heterogeneous catalysts for CO2 capture and conversion.
Exploring remarkable oxygen reduction reaction (ORR) electrocatalysts for regenerative fuel cells and metal-air batteries is highly essential. Herein, a novel non-noble metal-based heterogeneous electrocatalyst with rich defects were successfully synthesized by liquid-liquid interfacial precipitation (LLIP) of fullerene (C60) and ferrotetraphenylporphyrin (FeTPP) followed by one step pyrolysis. The obtained product annealed at 700 ℃ (C60/FeTPP-700), when employed as ORR electrocatalyst, revealed a positive half-wave potential (E1/2) of 0.877 V vs. reversible hydrogen electrode (RHE), which was superior to that of the commercial 25% Pt/C. Delightfully, the assembled Zn-air battery (ZAB) using C60/FeTPP-700 as an air-electrode catalyst exhibited a high power density of 153 mW/cm2, specific capacity of 668 mAh/g and long-term cycling stability for more than 250 h. Experimental results proved that the excellent electrocatalytic ORR activity of C60/FeTPP-700 would attribute to the synergistic effect between FeNx sites, Fe3C/Fe nanoparticles and the structure defects. This work provides a feasible and simple method to prepare non-noble metal-based ORR electrocatalysts for the application of energy storage and conversion.
The dioxygen activation catalyzed by 4-hydorxylphenyl pyruvate dioxygenase (HPPD) were reinvestigated by using hybrid quantum mechanics/molecular mechanics (QM/MM) approaches at the B3LYP/6-311++G(d, p): AMBER level. These studies showed that this reaction consisted of two steps including the dioxygen addition/decarboxylation and hetero OO bond cleavage, where the first step was found to be rate-determining. The former step initially runs on a septet potential energy surface (PES), then switches to a quintet PES after crossing a septet/quintet minimum energy crossing point (MECP) 5-7M2, whereas the rest step runs on the quintet PES. The reliability of our theoretical predictions is supported by the excellent agreement of the calculated free-energy barrier value of 16.9 kcal/mol with available experimental value of 16–17 kcal/mol. The present study challenges the widely accepted view which holds that the O2 activation catalyzed by α-keto glutamate (α-KG) dioxygenase mainly runs on the quintet PES and provides new insight into the catalytic mechanism of α-KG dioxygenase and/or other related Fe(Ⅱ)-dependent oxygenase.
Design of electrochemical active boron (B) site at solid materials to understand the relationships between the localized structure, charge state at the B site and electrocatalytic activity plays a crucial role in boosting the green electrochemical synthesis of hydrogen peroxide (H2O2) via two-electron oxygen reduction (2eORR) pathway. Herein, we demonstrate a carbon (C) and nitrogen (N) localized bonding microenvironment to modulate the charge state of B site at the boron-carbon nitride solid (BCNs) to realize the efficient selective electrocatalytic H2O2 production. The localized chemical structure of N-B-N, N-B-C and C-B-C bonds at B site can be regulated through solid-state reaction between boron nitride (BN) and porous carbon (C) at variable temperatures. The optimized BCN-1100 achieves an outstanding H2O2 selectivity of 89% and electron transfer number of 2.2 (at 0.55 V vs. RHE), with the production of 10.55 mmol/L during 2.5 h and the catalytic stability duration for 15000 cycles. Further first-principles calculations identified the dependency of localized bonding microenvironment on the OOH* adsorption energies and relevant charge states at the boron site. The localized structure of B site with BNC2-Gr configuration is predicted to be the highest 2eORR activity.
Ultra-low dielectric loss (Df) and low dielectric constant (Dk) materials are urgently required in high-speed and large-capacity transmission, in which the wholly aromatic liquid crystal polymer (LCP) has gained attention due to its excellent dielectric properties. However, the relationship between molecular structure and dielectric properties is still not clear. In this study, two copolyesters containing phenyl or naphthyl structures are synthesized, as well as the effects of benzene and naphthalene mesogens on dielectric properties are investigated. The synthesized copolyesters containing naphthalene structure have good comprehensive properties with high thermal stability (T5% = 479 ℃ and Tg = 195–216 ℃), inherent flame retardance (LOI = 33.0–35.0 and UL-94 V-0 level at 0.8 mm), low Dk (2.9–3.0@10 GHz) and low Df (0.0027–0.0047@10 GHz). Naphthalene mesogen can reduce the dielectric loss more significantly than benzene at high frequency by reducing the density and mobility of polarizable groups, which leads to the effectively limited dipole polarization in copolyesters. Consequently, we proposed a new strategy for designing low Dk and low Df materials.
Mechanical force between cells relates to many biological processes of cell development. The cellular collective migration comes from cell-cell cooperation, and studying the intercellular mechanical properties helps elucidate collective cell migration. Herein, we studied cell-cell junctions, intercellular tensile force and the related cellular energetic costs in confined microchannels. Using the intercellular force sensor, we found that cells adapt to different confinement environments by regulating intercellular force, and thereby the relationship between collective cell migration and cell-cell junction were verified. Through the observation of cell orientation, actomyosin contractility, energetic costs, and glucose uptake, we can make a reasonable explanation of cell-force driven migration in different confined environments. Under highly confined conditions, the intercellular force and energetic costs are greater, and the cell orientation is more orderly. The collective migration behavior in confined spaces is closely related to the intercellular force and energetic costs, which is helpful to understand the collective migration behaviors in various confined spaces.
Carbon-mediated persulfate advanced oxidation processes (PS-AOPs) are appealing in contaminant remediation. For the first time, S,B-co-doped carbon-based persulfate activators were synthesized through direct carbonization of sodium lignosulfonate and boric acid. By degrading sulfamethoxazole (SMX), CSB-750 obtained 98.7% removal and 81.4% mineralization within 30 min. In comparison with solo S or B doping, S and B co-doped carbon showed the coupling effect for enhanced catalysis. The rate constant (kobs) of 0.1679 min–1 was 22.38- and 279.83-fold higher than those of CS-750 (0.0075 min–1) and CB-750 (0.0006 min–1), respectively. The degradation was efficient at strong acidic and weak basic conditions (pH 3–9). Substantial inhibition effect was presented at strong basic condition (pH 10.95) and in presence of CO32–. The CO32–-caused inhibition was the combined result of the cooperation of pH and quenching O2·–. Thiophene sulfur, BC3, BC2O, and structural defects were identified as the active sites for PS activation. Radical and nonradical pathways were both involved in the CSB-750/PS/SMX system, where 1O2 dominated the degradation, SO4·–, ·OH and direct electron transfer played the subordinate role, and O2·– served as a precursor for the formation of partial 1O2. The toxicity of degradation system, the effect of real water matrix, and the reusability of carbocatalysts were comprehensively analyzed. Nine possible degradation pathways were proposed. This work focuses on the catalytic performance improvement through the coupling effect of S, B co-doping, and develops an advanced heteroatom doping system to fabricate carbonaceous persulfate activators.
Coating inorganic ceramic particles on commercial polyolefin separators has been considered as an effective strategy to improve thermostability of separator. However, the introduction of the coating layer could induce pore blockage on the surface of the polyolefin separator. Herein, a ceramic composite layer that consists of alumina nanoparticles (n-Al2O3) and halloysite nanotubes (HNTs) is designed to modify the polyethylene (PE) separator (the modified separator is denoted as AH-PE). The HNTs with hollow nanotubular structure construct a light skeleton and provide fast ion transport channels while Al2O3 particles function as heat-resistant fillers to inhibit the shrinkage of the separator at elevated temperatures. The total thickness of AH-PE separator is only 14 µm. Consequently, the mass increment of AH-PE separator decreases from 5 g/m2 to 3.5 g/m2, and the Gurley value reduces by 23%, compared with Al2O3 coated PE separator (A-PE). Due to the synergistic effects of Al2O3 and HNTs, AH-PE separator exhibits highly improved thermal stability (almost no shrinkage at 170 ℃ for 30 min), high Li+ transference number (up to 0.47), and long cycle life of 450 h for Li|Li cells. Moreover, the LiFePO4/Li cells assembled with AH-PE separators demonstrate improved rate capability and safety performance.
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