Preparation of Fe−Co−LDH/MXene modified electrode for sensitive determination of arsenic (III) in aquatic system

3-dimensional (3D) Fe−Co−LDH/MXene composite was synthesized by in-situ synthesis and assembly of Fe−Co−LDH rod around MXene under hydrothermal condition. Due to the unique 3D configuration and good conductivity, the obtained Fe−Co−LDH/MXene modified glassy carbon electrode (Fe−Co−LDH/MXene/GCE) showed excellent electrochemical activity for As(III) detection. Via square-wave anodic stripping voltammetry, the response current on Fe−Co−LDH/MXene/GCE had good linear relationship with As(III) concentrations (1∼1000 ppt) with superior sensitivity (0.22 μA ppt⁻¹ cm⁻²) and low detection limit (0.9 ppt). The mechanism of As(III) adsorption was demonstrated. The electrode showed excellent anti-interference ability. Real water sample analysis demonstrated the Fe−Co−LDH/MXene/GCE was deployable in aqua-system.     

Synthesis and characterization of new homologue multinary selenides,M2Sb5Bi5Se17 (M = Sn,Pb)

New quaternary selenides M₂Sb₅Bi₅Se₁₇ (M = Sn, Pb) were synthesized using solid-state sintering reactions that crystallize in the monoclinic system with C2/m (No. 12) space group with lattice parameters a = 27.914(7) Å, b = 4.0804(11) Å, c = 15.512(4) Å, and β = 114.881(9)° for M = Sn, and a = 27.987(3) Å, b = 4.1062(5) Å, c = 15.6372(19) Å, and β = 115.318(3)° for M = Pb, respectively. The crystal structure is related to a homologous series [A⁺²_2x−4B⁺³₄ Se⁻²_2x−2][B⁺³_2y−2Se⁻²_3y−3] with (x, y) = (3, 4) that contains building units of two-dimensional slabs of NaCl¹¹¹-type [Sb₂Bi₄Se₁₁] separated by 1D ribbons NaCl¹⁰⁰-type [Pb₂Sb₃BiSe₆]. The NaCl¹¹¹ unit contains edge-shared octahedra filled with Sb³⁺ and Bi³⁺ cations, which are parallel and overlapped to form a step-layer 2D network stacking alone [001]. The NaCl¹⁰⁰ type ribbons containing Pb²⁺ and Sb³⁺ in square or trigonal pyramidal environments with the general formula [M₆Se₆] filled in the space between 2D layers of NaCl¹¹¹ units. The conductivity measurement revealed semiconducting property with band gaps of ~0.1 eV. Pb₂Sb₅Bi₅Se₁₇ exhibits low thermal conductivity 3,000 μW cm⁻¹ K⁻¹ in a temperature range of 300–480 K.     

An integrated strategy for the geographical origin traceability of Goji berries by antioxidants characteristic fingerprint based online ultra-performance liquid chromatography-2,2-diphenyl-1-picrylhydrazyl- photodiode array detector-mass spectrometry combined with multivariate statistics analysis

Goji berries are now becoming increasingly popular in the human diet due to their potential health benefits. Unscrupulous traders deliberately mislabel with certain origins to gain illegal profits, which seriously affected the consumers’ benefits. In this study, an online ultra-performance liquid chromatography-2,2-diphenyl-1 -picrylhydrazyl-photodiode array detector-electrospray ionization-quadrupole time of flight mass was developed for rapid screening and identification of the antioxidants from Goji berry; then, the antioxidants characteristic fingerprint was established and explored in the origins discrimination of Goji berries from China combined with multivariate statistics analysis. As a result, twenty-eight compounds were screened from Goji berry extract, 19 of which were identified by accurate molecular and ultraviolet information according to references. Principal components analysis and partial least squares discrimination analysis achieved the accurate classification from the four regions, eight compounds were selected as origin-related antioxidant markers with variable importance in projection >1 and one-way analysis of variance (P<0.05), including rutin, rutin di-hexose, P-coumaric acid tri-hexose, dicaffeoylquinic acid isomer, Quercetin-rhamno-di-hexoside, peak14, peak16, and peak27. This study provides a feasible strategy for the geographical origins discrimination of Goji berries based on antioxidant ingredients difference and will be helpful for improving the quality control level of Goji berries.     

Precision Graphene Nanoribbon Heterojunctions by Chain-Growth Polymerization

Graphene nanoribbons (GNRs) are considered promising candidates for next-generation nanoelectronics. In particular, GNR heterojunctions have received considerable attention due to their exotic topological electronic phases at the heterointerface. However, strategies for their precision synthesis remain at a nascent stage. Here, we report a novel chain-growth polymerization strategy that allows for constructing GNR heterojunction with N=9 armchair and chevron GNRs segments ( 9-AGNR/cGNR ). The synthesis involves a controlled Suzuki–Miyaura catalyst-transfer polymerization (SCTP) between 2-(6′-bromo-4,4′′-ditetradecyl-[1,1′:2′,1′′-terphenyl]-3′-yl) boronic ester ( M1 ) and 2-(7-bromo-9,12-diphenyl-10,11-bis(4-tetradecylphenyl)-triphenylene-2-yl) boronic ester ( M2 ), followed by the Scholl reaction of the obtained block copolymer ( poly-M1/M2 ) with controlled M_n (18 kDa) and narrow Đ (1.45). NMR and SEC analysis of poly-M1/M2 confirm the successful block copolymerization. The solution-mediated cyclodehydrogenation of poly-M1/M2 toward 9-AGNR/cGNR is unambiguously validated by FT-IR, Raman, and UV/Vis spectroscopies. Moreover, we also demonstrate the on-surface formation of pristine 9-AGNR/cGNR from the unsubstituted copolymer precursor, which is unambiguously characterized by scanning tunneling microscopy (STM).     

Improved Electrocatalytic Activity and Stability by Single Iridium Atoms on Iron-based Layered Double Hydroxides for Oxygen Evolution

Full understanding to the origin of the catalytic performance of a supported nanocatalyst from the points of view of both the active component and support is significant for the achievement of high performance. Herein, based on a model electrocatalyst of single-iridium-atom-doped iron (Fe)-based layered double hydroxides (LDH) for oxygen evolution reaction (OER), we reveal the first completed origin of the catalytic performance of such supported nanocatalysts. Specially, besides the activity enhancement of Ir sites by LDH support, the stability of surface Fe sites is enhanced by doped Ir sites: DFT calculation shows that the Ir sites can reduce the activity and enhance the stability of the nearby Fe sites; while further finite element simulations indicate, the stability enhancement of distant Fe sites could be attributed to the much low concentration of OER reactant (hydroxyl ions, OH⁻) around them induced by the much fast consumption of OH⁻ on highly active Ir sites. These new findings about the interaction between the main active components and supports are applicable in principle to other heterogeneous nanocatalysts and provide a completed understanding to the catalytic performance of heterogeneous nanocatalysts.     

A Polarized Gel Electrolyte for Wide-Temperature Flexible Zinc-Air Batteries

The development of flexible zinc-air batteries (FZABs) has attracted broad attention in the field of wearable electronic devices. Gel electrolyte is one of the most important components in FZABs, which is urgent to be optimized to match with Zn anode and adapt to severe climates. In this work, a polarized gel electrolyte of polyacrylamide-sodium citric (PAM-SC) is designed for FZABs, in which the SC molecules contain large amount of polarized −COO⁻ functional groups. The polarized −COO⁻ groups can form an electrical field between gel electrolyte and Zn anode to suppress Zn dendrite growth. Besides, the −COO⁻ groups in PAM-SC can fix H₂O molecules, which prevents water from freezing and evaporating. The polarized PAM-SC hydrogel delivers a high ionic conductivity of 324.68 mS cm⁻¹ and water retention of 96.85 % after being exposed for 96 h. FZABs with the PAM-SC gel electrolyte exhibit long cycling life of 700 cycles at −40 °C, showing the application prospect under extreme conditions.     

Organoboron Reagent-Controlled Selective (Deutero)Hydrodefluorination

(Deuterium-labeled) CF₂H- and CFH₂-moieties are of high interest in drug discovery. The high demand for the incorporation of these fluoroalkyl moieties into molecular structures has witnessed significant synthetic progress, particularly in the (deutero)hydrodefluorination of CF₃-containing compounds. However, the controllable replacement of fluorine atoms while maintaining high chemoselectivity remains challenging. Herein, we describe the development of a selective (deutero)hydrodefluorination reaction via electrolysis. The reaction exhibits a remarkable chemoselectivity control, which is enabled by the addition of different organoboron sources. The procedure is operationally simple and scalable, and provides access in one step to high-value building blocks for application in medicinal chemistry. Furthermore, density functional theory (DFT) calculations have been carried out to investigate the reaction mechanism and to rationalize the chemoselectivity observed.     

石墨烯-碳量子点复合材料的电化学性能研究

采用Hummers法和水热法,制备石墨烯和碳量子点溶液作为前驱体,然后通过一步煅烧法制得石墨烯-碳量子点复合材料。借助SEM、UV-Vis、FTIR等手段,对样品的形貌和结构进行表征;利用循环伏安法(CV)、差分脉冲伏安法(DPV)及恒流充放电循环测试等,重点考察了样品的电化学性能。结果表明,在石墨烯表面负载碳量子点可增加材料的比表面积并改善其机械性能,由于活性位点的增加,所制石墨烯-碳量子点复合电极具有较好的可逆性及电化学活性;在检测不同浓度双氧水时,复合电极的灵敏度为纯石墨烯电极的1.4倍左右;石墨烯-碳量子点复合材料作为锂离子电池负极使用时,与纯石墨烯材料相比具有更好的循环稳定性,且容量保持率提高了1.67倍。     

Organic Memristor Based on High Planar Cyanostilbene/Polymer Composite Films

Organic memristors with low power consumption, fast write/erasure speed, and complementary metal-oxide-semiconductor(CMOS) compatibility have attracted tremendous attention to mimic biological synapses to realize neuromorphic computation in recent years. In this paper, organic resistive switching memory(ORSM) based on (Z)-3-(naphthalen-2-yl)-2-(4-nitrophenyl)acrylonitrile(NNA) and polymer poly(N-vinylcarbazole)(PVK) composite film was prepared by spin-coating method. Device performance based on NNA:PVK composite films with different mass fractions of NNA were systematically investigated. The ORSM based on PVK:40%(mass fraction) NNA composite film exhibited non-volatile and bipolar memory properties with a switching ratio(I_on/I_off) of 24.1, endurance of 68 times and retention time of 10⁴ s, a “SET” voltage(V_set) of -0.55 V and a “RESET” voltage(V_reset) of 2.35 V. The resistive switching was ascribed to the filling and vacant process of the charge traps induced by NNA and the inherent traps in PVK bulk. The holes trapping and de-trapping process occurred when the device was applied with a negative or positive bias, which caused the transforming of the conductive way of charges, that is the resistive behaviors in the macroscopic. This study provides a promising platform for the fabrication of ORSM with high performance.     

ZIF-67/CeO2催化CO2和甲醇直接合成碳酸二甲酯

采用沉淀法将ZIF-67负载到CeO₂上,制备了具有多重活性位点的非均相催化剂ZIF-67/CeO₂,并研究其催化CO₂和甲醇直接反应生成碳酸二甲酯(DMC)的性能。采用X射线衍射、N₂吸附-脱附、傅里叶变换红外光谱和X射线光电子能谱研究了ZIF-67/CeO₂的各种理化性质。结果表明,ZIF-67的引入使ZIF-67/CeO₂催化剂产生更多的氧空位。在考察的ZIF-67/CeO₂系列催化剂中,0.3-ZIF-67/CeO₂(0.3为Co、Ce物质的量之比)在具有高的比表面积的同时还能保持介孔结构,具有丰富的酸碱位点,并且具有较高的CO₂吸附容量,表现出最好的催化性能。在反应温度为140℃、压力为4.5 MPa的条件下反应4 h,DMC收率可达到3.79 mmol_DMC·g_cat^-1。