Advancing electrochemical nitrogen reduction: Efficacy of two-dimensional SiP layered structures with single-atom transition metal catalysts.

Researchers are interested in single-atom catalysts with atomically scattered metals relishing the enhanced electrocatalytic activity for nitrogen reduction and 100 % metal atom utilization. In this paper, we investigated 18 transition metals (TM) spanning 3d to 5d series as efficient nitrogen reduction reaction (NRR) catalysts on defective 2D SiPV layered structures through first-principles calculation. A systematic screening identified Mo@SiPV, Nb@SiPV, Ta@SiPV and W@SiPV as superior, demonstrating enhanced ammonia synthesis with significantly lower limiting potentials (-0.25, -0.45, -0.49 and -0.15 V, respectively), compared to the benchmark -0.87 eV for the defective SiP. In addition, the descriptor ΔG*N was introduced to establish the relationship between the different NRR intermediates, and the volcano plot of the limiting potentials were determined for their potential-determining steps (PDS). Remarkably, the limiting voltage of the NRR possesses a good linear relationship with the active center TM atom Ɛd, which is a reliable descriptor for predicting the limiting voltage. Furthermore, we verified the stability (using Ab Initio Molecular Dynamics - AIMD) and high selectivity (UL(NRR)-UL(HER) > -0.5 V) of these four catalysts in vacuum and solvent environments. This study systematically demonstrates the strong catalytic potential of 2D TM@SiPV(TM = Mo, Nb, Ta, W) single-atom catalysts for nitrogen reduction electrocatalysis.

Iron/cobalt/nickel regulation for efficient photocatalytic carbon dioxide reduction over phthalocyanine covalent organic frameworks.

Using solar photocatalytic CO2 reduction to produce high-value-added products is a promising solution to environmental problems caused by greenhouse gases. Metal phthalocyanine COFs possess a suitable band structure and strong light absorption ability, making them a promising candidate for photocatalytic CO2 reduction. However, the relationship between the electronic structure of these materials and photocatalytic properties, as well as the mechanism of photocatalytic CO2 reduction, is still unclear. Herein, the electronic structure of three MPc-TFPN-COFs (M = Ni, Co, Fe) and the reaction process of CO2 reduction to CO, HCOOH, HCHO and CH3OH were studied using DFT calculations. The calculated results demonstrate that these COFs have a good photo response to visible light and are new potential photocatalytic materials. Three COFs show different reaction mechanisms and selectivity in generating CO2 reduction products. NiPc-TFPN-COFs obtain CO through the reaction pathway of CO2 → COOH → CO, and the energy barrier of the rate-determining step is 2.82 eV. NiPc-TFPN-COFs and FePc-TFPN-COFs generate HCHO through CO2 → COOH → CO → CHO → HCHO, and the energy barrier of the rate step is 2.82 eV and 2.37 eV, respectively. Higher energies are required to produce HCOOH and CH3OH. This work is helping in understanding the mechanism of photocatalytic reduction of CO2 in metallophthalocyanine COFs.

Chitosan-Urushiol nanofiber membrane with enhanced acid resistance and broad-spectrum antibacterial activity.

Due to the large specific surface area and rich pore structure, chitosan nanofiber membrane has many advantages over conventional gel-like or film-like products. However, the poor stability in acidic solutions and relatively weak antibacterial activity against Gram-negative bacteria severely restrict its use in many industries. Here, we present a chitosan-urushiol composite nanofiber membrane prepared by electrospinning. Chemical and morphology characterization revealed that the formation of chitosan-urushiol composite involved the Schiff base reaction between catechol and amine groups and the self-polymerization of urushiol. The unique crosslinked structure and multiple antibacterial mechanisms endowed the chitosan-urushiol membrane with outstanding acid resistance and antibacterial performance. After immersion in HCl solution at pH 1, the membrane maintained its intact appearance and satisfactory mechanical strength. In addition to its good antibacterial performance against Gram-positive Staphylococcus aureus (S. aureus), the chitosan-urushiol membrane exhibited synergistic antibacterial activity against Gram-negative Escherichia coli (E. coli) that far exceeded that of neat chitosan membrane and urushiol. Moreover, cytotoxicity and hemolysis assays revealed that the composite membrane had good biocompatibility similar to that of neat chitosan. In short, this work provides a convenient, safe, and environmentally friendly method to simultaneously enhance the acid resistance and broad-spectrum antibacterial activity of chitosan nanofiber membranes.

Electrospun cationic nanofiber membranes for adsorption and determination of Cr(vi) in aqueous solution: adsorption characteristics and discoloration mechanisms.

In this study, a novel cationic nanofiber membrane with various functional groups, good structural stability, and high adsorption capacity of Cr(vi) is presented. This nanofiber membrane is prepared by electrospinning a mixed aqueous solution of a cationic polycondensate (CP) and polyvinyl alcohol (PVA). With the aid of PVA, CP can be smoothly electrospun without using any organic solvents, and the cross-linking between CP and PVA improves the stability of membrane in acidic solution. Chemical and morphology characterization reveals that the CP/PVA membrane is composed of interwoven nanofibers that contain numerous cationic groups. Due to its high cationicity and hydrophilicity, the CP/PVA membrane shows great affinity for HCr2O7 - and Cr2O7 2-. Adsorption experiments indicate that the CP/PVA membrane can remove Cr(vi) from simulated wastewater rapidly and efficiently in both batch and continuous mode. Besides, the presence of most coexisting ions will not interfere with the adsorption. Due to the redox reaction between the CP/PVA membrane and adsorbed Cr(vi), the CP/PVA membrane exhibits distinct color change after Cr(vi) adsorption and the discoloration is highly dependent on the adsorption amount. Therefore, in addition to serving as a highly efficient adsorbent, the CP/PVA membrane is also expected to be a convenient and low-cost method for semi-quantitative determination of Cr(vi) in wastewater.

MWW-Type Titanosilicate Synthesized by Simply Treating ERB-P Zeolite with Acidic H2TiF6 and Its Catalytic Performance in a Liquid Epoxidation of 1-Hexene with H2O2.

Synthesis of a Ti-incorporated zeolite using a simple and economical method has recently become a focus of attention. The direct hydrothermal synthesis of Ti-MWW is most commonly applied; however, it is challenging to perform and exhibits low titanium utilization. An innovative strategy of synthesizing Ti-MWW is proposed in the present study by simply treating the ERB-1 precursor of an MWW-type boron silicate with a H2TiF6/HNO3 solution. This significantly shortens the Ti grafting process from 5 days to only a few hours and reduces the use of the structure-directing agent hexamethyleneimine (HMI); furthermore, no extraframework Ti is observed in the precursor, indicating good atomic economy. Typically, a piperidine (PI)-treated sample Ti-MWW2-1-PI exhibits a higher conversion (76.6%) than the original Ti-MWW (44.8%) in the epoxidation of 1-hexene. X-ray diffraction (XRD), inductively coupled plasma (ICP), and transmission electron microscopy (TEM) techniques are used to explain in detail the probable mechanism underlying the incorporation of Ti species into the MWW framework. X-ray photoelectron spectroscopy (XPS) is employed to study the coordinate state of the Ti and F species in the samples after treatment with a piperidine solution. This method can be applied to synthesize other kinds of lamellar-structured zeolites with heteroatoms.

Fabrication of a Self-Cleaning Surface via the Thermosensitive Copolymer Brush of P(NIPAAm-PEGMA).

Surface hydrophilicity and the inherent washing force are two crucial factors for constructing an underwater self-cleaning surface. Following this self-cleaning mechanism, we fabricated thermosensitive copolymer brushes of N-isopropylacrylamide (NIPAAm) and poly(ethylene glycol) methacrylate (PEGMA) on the polypropylene (PP) surface. Benefiting from the hydrophilic poly(ethylene glycol) (PEG) side chains, the copolymer brushes with the PEGMA content exceeding 5 mol % exhibited good surface hydrophilicity, whenever at temperatures below or above the lower critical solution temperatures (LCST). Hence their underwater oleophobicity was greatly improved with oil contact angles higher than 141° and oil adhesive forces lower than 20 µN. In addition, the sharp volume-phase transition feature was reserved in their copolymer backbones, as proved by the AFM result. Self-cleaning evaluation of the modified surfaces was performed by a simple temperature-change water cleaning method, after which only 0.2 wt % of oil residues remained on the brush surface of P(NIPAAm-5PEGMA) (with 5 mol % of PEGMA contents). The excellent self-cleaning capability is believed to be ascribed to its balanced surface features in hydrophilicity and the sharper volume-phase transition, when a hydrophilic surface can facilitate oil desorption and an intense conformation change of chain stretching and shrinking can offer the strong washing force to assist oil detachment. This study contributes to development of the underwater self-cleaning surface based on a hydrophilic surface with the chain motion.