Cobalt-based Polymerized Porphyrinic Network for Visible-light-driven CO2 Reduction.

Visible-light-driven conversion of carbon dioxide to valuable compounds and fuels is an important but challenging task due to the inherent stability of the CO2 molecules. Herein, we report a series of cobalt-based polymerized porphyrinic network (PPN) photocatalysts for CO2 reduction with high activity. The introduction of organic groups results in the addition of more conjugated electrons to the networks, thereby altering the molecular orbital levels within the networks. This integration of functional groups effectively adjusts the levels of the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO). The PPN(Co)-NO2 exhibits outstanding performance, with a CO evolution rate of 12 268 µmol/g/h and 85.8% selectivity, surpassing most similar photocatalyst systems. The performance of PPN(Co)-NO2 is also excellent in terms of apparent quantum yield (AQY) for CO production (5.7% at 420 nm). Density functional theory (DFT) calculations, time-resolved photoluminescence (TRPL), and electrochemical tests reveal that the introduction of methyl and nitro groups leads to a narrower energy gap, facilitating a faster charge transfer. The coupling reaction in this study enables the formation of stable C-C bonds, enhancing the structural regulation, active site diversity, and stability of the catalysts for photocatalytic CO2 reduction. This work offers a facile strategy to develop reliable catalysts for efficient CO2 conversion.

Theoretical Investigations of Hydrolysis Mechanisms of N(SiMe3)3.

Tris(trimethylsilyl)amine (N(SiMe3)3) is one of the most important intermediate products in the indirect synthesis of ammonia (NH3) from nitrogen (N2), which could be hydrolyzed to NH3 under mild conditions. Herein, the hydrolysis mechanism of N(SiMe3)3 has been systematically investigated using density functional theory (DFT) with explicit combined implicit water models. Under neutral conditions, the active barrier of the hydrolysis of N(SiMe3)3 is 17.6 kcal mol-1 in water solvent. The attacking of proton to N center and OH group to the Si atom from water is decoupled for the stabilization of OH group by solvent water molecules, which lower the hydrolysis energy barriers. Furthermore, under acid conditions, N(SiMe3)3 is easily coordinated with proton to form [NH(SiMe3)3]+, and the energy barrier of the hydrolysis reaction could be reduced to 11.5 kcal mol-1 of the first stage, making it being promoted according to the chemical equilibrium. Thus, the results provide an explanation for the possible mechanism of the quantitative conversion of N(SiMe3)3 to NH3 under mild conditions. The decoupled hydrolysis mechanism may play important role in other hydrolysis processes.

Molecular nitrogen induced structural evolution of single transition metal atoms supported by B/N co-doped graphene for enhanced nitrogen electroreduction performance.

The structural evolution of local coordination environments of single-atom catalysts (SACs) under reaction conditions plays an important role in the catalytic performance of SACs. Using density functional theory calculations, the possible structural evolution of transition metal single atoms supported by B/N codoped-graphene (TM-B2N2/G) under nitrogen reduction reaction (NRR) conditions is explored and the catalytic performance based on reconstructed SACs is theoretically evaluated. A novel nitrogen adsorption mode on TM-B2N2/G is discovered and the protonation of one of the N atoms results in the TM atoms binding with three N atoms, among which one associates with two B atoms (TM-N3B2/G). It is suggested that the N3B2/G supported tungsten single atom (W-N3B2/G) exhibits excellent N2 activity with a limiting potential of -0.27 V and high ammonia selectivity. Electronic structure analysis indicates that the coordination of N3B2/G redistributes the charge density of central W, shifts its d band center upward and strengthens the interaction of W and the adsorbed nitrogen molecule, thereby endowing it with better NRR performance, compared with that supported by pyridine-3N-doped graphene and pyrrolic-3N-doped graphene.

Growing Electrocatalytic Conjugated Microporous Polymers on Self-Standing Carbon Nanotube Films Promotes the Rate Capability of Li-S Batteries.

Lithium-sulfur (Li-S) batteries hold great promise for widespread application on account of their high theoretical energy density (2600 Wh kg-1 ) and the advantages of sulfur. Practical use, however, is impeded by the shuttle effect of polysulfides along with sluggish cathode kinetics. it is reported that such deleterious issues can be overcome by using a composite film (denoted as V-CMP@MWNT) that consists of a conjugated microporous polymer (CMP) embedded with vanadium single-atom catalysts (V SACs) and a network of multi-walled carbon nanotubes (MWNTs). V-CMP@MWNT films are fabricated by first electropolymerizing a bidentate ligand designed to coordinate to V metals on self-standing MWNT films followed by treating the CMP with a solution containing V ions. Li-S cells containing a V-CMP@MWNT film as interlayer exhibit outstanding performance metrics including a high cycling stability (616 mA h g-1 at 0.5 C after 1000 cycles) and rate capability (804 mA h g-1 at 10 C). An extraordinary area-specific capacity of 13.2 mA h cm-2 is also measured at a high sulfur loading of 12.2 mg cm-2 . The underlying mechanism that enables the V SACs to promote cathode kinetics and suppress the shuttle effect is elucidated through a series of electrochemical and spectroscopic techniques.

A Space-Confined Polymerization Templated by Ice Enables Large-Scale Synthesis of Two-Dimensional Polymer Sheets.

Despite significant progress in the preparation and characterization of two-dimensional (2D) materials, the synthesis of 2D organic materials remains challenging. Here, we report a novel space-confined polymerization method that enables the large-scale synthesis of 2D sheets of a functional conjugated polymer, namely, poly(3,4-ethylenedioxythiophene) (PEDOT). A key step in this method is the confinement of monomer to the boundaries of ice crystals using micelles. This spatial confinement directs the polymerization to form 2D PEDOT sheets with high crystallinity and controlled morphology. Supercapacitors prepared from the 2D PEDOT sheets exhibit outstanding performance metrics. In aqueous electrolyte, a high areal specific capacitance of 898 mF cm-2 at 0.2 mA cm-2 along with an excellent rate capability is achieved (e.g., capacitance retention of 67.6 % at a 50-fold higher current). Moreover, the 2D PEDOT-based supercapacitors exhibit outstanding cycling stability (capacitance retention of 98.5 % after 30,000 cycles). Device performance is further improved when an organic electrolyte is used.

P-Doping a Porous Carbon Host Promotes the Lithium Storage Performance of Red Phosphorus.

Red phosphorus (RP) is a promising anode material for use in lithium-ion batteries (LIBs) due to its high theoretical specific capacity (2596 mA h g-1). However, the practical use of RP-based anodes has been challenged by the material's low intrinsic electrical conductivity and poor structural stability during lithiation. Here, we describe a phosphorus-doped porous carbon (P-PC) and disclose how the dopant improves the Li storage performance of RP that was incorporated into the P-PC (designated as RP@P-PC). P-doping porous carbon was achieved using an in situ method wherein the heteroatom was added as the porous carbon was being formed. The phosphorus dopant effectively improves the interfacial properties of the carbon matrix as subsequent RP infusion results in high loadings, small particle sizes, and uniform distribution. In half-cells, an RP@P-PC composite was found to exhibit outstanding performance in terms of the ability to store and utilize Li. The device delivered a high specific capacitance and rate capability (1848 and 1111 mA h g-1 at 0.1 and 10.0 A g-1, respectively) as well as excellent cycling stability (1022 mA h g-1 after 800 cycles at 2.0 A g-1). Exceptional performance metrics were also measured when the RP@P-PC was used as an anode material in full cells that contained lithium iron phosphate as the cathode material. The methodology described can be extended to the preparation of other P-doped carbon materials that are employed in contemporary energy storage applications.

Rational design of trimetallic AgPt-Fe3O4 nanozyme for catalyst poisoning-mediated CO colorimetric detection.

Carbon monoxide (CO) is not only a highly poisonous gas that brings great health risk, but also a significant signaling molecule in body. However, it is still challengeable for development of alternative colorimetric probes to traditional organic chromophores for simple, sensitive and convenient CO sensing. Here, for the first time, we rationally design a novel hydrophilic AgPt-Fe3O4 nanozyme with a unique heterodimeric nanostructure for colorimetric sensing of CO based on the excellent peroxidase-like catalytic activity as well as highly poisonous effect of CO on the nanozyme's catalytic activity. Both experimental evidence and theoretical calculations reveal the trimetallic AgPt-Fe3O4 nanozyme is susceptible to poisoning with the strongest affinity towards CO compared to individual Fe3O4 or Ag-Fe3O4, which is attributed to the adequate exposure of the active metallic sites and efficient interfacial synergy of unique heterodimeric nanostructure. Accordingly, a novel nanozyme-based colorimetric strategy is developed for CO detection with a low detection limit of 5.6 ppb in solution. Furthermore, the probe can be prepared as very convenient test strips and integrated with the portable smartphone platforms for detecting CO gas samples with a low detection limit of 8.9 ppm. Overall, our work proposes guidelines for the rational design of metallic heterogeneous nanostructure to expand the analytical application of nanozyme.

Fast analysis of selected compounds in inhaled and exhaled vapor phase of cigarette smoke to evaluate components retained in the upper respiratory tract.

RATIONALE: The aim of this work is to use a new design of online sampling photoionization mass spectrometer to analyze chemical ingredients in inhaled and exhaled cigarette smoke directly without separation. METHODS: Based on vacuum ultraviolet photoionization time-of-flight mass spectrometry (VUV-PI-TOFMS) and a sampling system, a newly developed rapid online sampling design approach was used for the upper respiratory tract retention study of gaseous mainstream cigarette smoke components during smoking. The cigarette smoke inhaled or exhaled by seven subjects who displayed three different smoking patterns was directly sampled into a vacuum chamber, photoionized, and analyzed using TOFMS. RESULTS: Fourteen species, comprising aldehydes, ketones, phenol, methanethiol, nitrogen-containing heterocyclic compounds and unsaturated hydrocarbons, were identified in the cigarette smoke obtained from Virginia-type cigarettes. The upper respiratory tract results for these compounds were similar for smokers with the three different smoking patterns: aldehyde and ketone constituents had a high retention level of more than 60%; phenol, methanethiol, and nitrogen-containing heterocyclic compounds were retained at between 30% and 70%; and the retention of unsaturated hydrocarbons was about 20%-60%. The retention trend of the same smoke components in Virginia-type cigarettes by subjects from the three smoking patterns (A, B, and C) was consistent, and the retentions all increased with increased smoking age (A < B < C). CONCLUSIONS: This is the first report of a new online sampling design approach to the study of cigarette smoke components in inhaled and exhaled breath, to evaluate components retained in the upper respiratory tract by subjects with different smoking patterns. This method has good repeatability, and the results indicated that this is a very promising tool for the study of the retention of cigarette smoke constituents.

Biocatalytic performance of pH-sensitive magnetic nanoparticles derived from layer-by-layer ionic self-assembly of chitosan with glucoamylase.

Based on the characteristics of polycations of chitosan and glucoamylase, which are oppositely charged, they were successfully alternatingly deposited onto the surface of aldehyde-modified Fe3O4 nanoparticles by using a layer-by-layer ion exchange method to form magnetic carriers to construct multilayer films (designated as Fe3O4@(CS/GA)n). The (CS/GA)n film systems were endowed with the pH-dependent properties of chitosan as well as the catalytic activity of glucoamylase. The changes in weight loss and surface chemistry, morphology, and magnetic sensitivity were monitored and verified by UV/Vis spectroscopy, zeta potential, TEM, and a vibrating sample magnetometer. Subsequently, the influence of the number of bilayers, storage stability, pH, temperature, and reusability of Fe3O4@(CS/GA)5 biocatalysts on catalytic activity were investigated. The results from characterization and determination remarkably indicate that Fe3O4@(CS/GA)5 presents excellent catalytic activity, storage stability, pH stability, and reusability in comparison with free enzyme. Fe3O4@(CS/GA)5 retained >60% of its initial activity at 65 °C over 6 h; the optimum temperature and pH also increased to the ranges of 45-65 °C and 2.5-3.5, respectively, and only 27% activity was lost after 10 cycles. This new strategy simplifies the reaction protocol and improves encapsulation efficiency and catalytic activity for new potential applications in biotechnology.

Preparation of superparamagnetic Fe3O4@alginate/chitosan nanospheres for Candida rugosa lipase immobilization and utilization of layer-by-layer assembly to enhance the stability of immobilized lipase.

Superparamagnetic alginate nanospheres with diameter of 50 nm were prepared by self-assembly of alginate in the Ca(2+) solution; and then superparamagnetic alginate/chitosan nanospheres, which have positive charge and could adsorb lipase directly, were obtained with a following assembly of chitosan based on the electrostatic interaction between alginate and chitosan. Subsequently, oxidic poly (ethylene glycol) was used to functionalize the magnetic alginate/chitosan nanospheres. Thus, the magnetic nanospheres with aldehyde groups and a brushlike structure were formed. With various characterizations, it was verified that the magnetic alginate/chitosan nanospheres held small diameters (around 60 nm) and displayed superparamagnetism with high saturation magnetization. The Candida rugosa lipase (CRL), meanwhile, was immobilized onto the magnetic alginate/chitosan nanospheres by electrostatic adsorption and covalent bonding, respectively. Afterward, a layer-by-layer (LBL) assembly process was utilized to coat the immobilized CRL (ICRL) with covering layers made up of alginate and chitosan. After studying the properties of ICRL such as activity, kinetic behaviors, stability and reusability, it was proved that the ICRL prepared with two methods displayed more excellent properties than that prepared with electrostatic adsorption only. Additionally, coating ICRL with covering layers showed good effect on improving the stability of ICRL.