Controllable Preparation of Branched Polyolefins with Various Microstructural Units via Chain-walking Ethylene and Pentene Polymerizations

Chinese Journal of Polymer Science - Branched polyolefins with controllable topology structures were generated from the chain-walking (co)polymerizations of ethylene, 1-pentene (1P) and 2-pentene...     

Plasmon-Enhanced Electrochemiluminescence at the Single-Nanoparticle Level

Plasmon-enhanced electrochemiluminescence (ECL) at the single-nanoparticle (NP) level was investigated by ECL microscopy. The Au NPs were assembled into an ordered array, providing a high-throughput platform that can easily locate each NP in sequential characterizations. A strong dependence of ECL intensity on Au NP configurations was observed. We demonstrate for the first time that at the single-particle level, the ECL of Ru(bpy)₃²⁺-TPrA was majorly quenched by small Au NPs (<40 nm), while enhanced by large Au ones (>80 nm) due to the localized surface plasmon resonance (LSPR). Notably, the ECL intensity was further increased by the coupling effect of neighboring Au NPs. Finite Difference Time Domain (FDTD) simulations conformed well with the experimental results. This plasmon enhanced ECL microscopy for arrayed single NPs provides a reliable tool for screening electrocatalytic activity at a single particle.     

Photoinduced Reaction of α-Bromoacetophenone with Thiosulfonate: Synthesis of β-Keto Thiosulfone

A photoinduced synthesis of β-keto thiosulfone/β-keto selenosulfone by the reaction of α-bromoacetophenone with thiosulfonate/selenosulfonate under metal-free and visible light irradiation conditions is developed. Two C−S bonds or one C−S bond and one C−Se bond were constructed simultaneously.     

Highly Selective Photoelectroreduction of Carbon Dioxide to Ethanol over Graphene/Silicon Carbide Composites

Using sunlight to produce valuable chemicals and fuels from carbon dioxide (CO₂), i.e., artificial photosynthesis (AP) is a promising strategy to achieve solar energy storage and a negative carbon cycle. However, selective synthesis of C₂ compounds with a high CO₂ conversion rate remains challenging for current AP technologies. We performed CO₂ photoelectroreduction over a graphene/silicon carbide (SiC) catalyst under simulated solar irradiation with ethanol (C₂H₅OH) selectivity of>99 % and a CO₂ conversion rate of up to 17.1 mmol g_cat⁻¹ h⁻¹ with sustained performance. Experimental and theoretical investigations indicated an optimal interfacial layer to facilitate the transfer of photogenerated electrons from the SiC substrate to the few-layer graphene overlayer, which also favored an efficient CO₂ to C₂H₅OH conversion pathway.     

A Strong-Acid-Resistant [Th6] Cluster-Based Framework for Effectively and Size-Selectively Catalyzing Reductive Amination of Aldehydes with N,N-Dimethylformamide

Utilization of N,N-dimethylformamide (DMF) as an amine source and reductant for synthesizing tertiary amines is a promising way to replace the substrates formaldehyde and dimethylamine, and it is desirable to seek porous acid-resistant catalysts for heterogeneous catalysis of this reaction. Herein, a robust metal–organic framework (MOF) {[Th₆O₄(OH)₄(H₂O)₆(BCP)₃]⋅10 DMF}_n ( 1 ) containing stacked nanocages with a diameter of 1.55 nm was constructed. Compound 1 can maintain its single-crystal structure even kept in air at 400 °C for 3 h, and in DMF or water at 200 °C for 7 days. Density functional theory (DFT) calculations suggested that the high interaction energy between the [Th₆O₄(OH)₄(H₂O)₆]¹²⁺ clusters and ligands was responsible for the excellent stability of 1 . Catalytic investigations revealed that 1 can effectively and size-selectively catalyze the reductive amination of aldehydes with DMF, and it can be reused at least five times without obvious loss in catalytic activity.     

Two-dimensional Supramolecular Polymers Based on Selectively Recognized Aromatic Cation-π and Donor-Acceptor Motifs for Photocatalytic Hydrogen Evolution

Two-dimensional (2D) organic polymers have recently received considerable interest, especially those whose architectures are held together via supramolecular engineering. However, current approaches toward supramolecular 2D structures usually suffer from mutual interference of noncovalent interactions and lack of intrinsic functions. Herein, we report well-regulated 2D supramolecular polymers (2DSPs) through an aromatics-selective recognition strategy of cation-π and donor-acceptor (D-A) motifs, which are derived from C₄-symmetric cationic monomers and electron-withdrawing molecules. By subtly designing the strength and direction of noncovalent driving forces, the mutual interference between cation-π and D-A interactions is effectively avoided, enabling the construction of 2DSPs in aqueous solution. On this basis, the resultant 2DSPs possess boosted photocatalytic hydrogen evolution activity at a rate of 600 μmol g⁻¹ h⁻¹, which is mainly ascribed to the specific stacking mode of cation-π/D-A motifs and the ordered 2D structures.     

Unraveling the Oxidation Behaviors of MXenes in Aqueous Systems by Active-Learning-Potential Molecular-Dynamics Simulation

MXenes are 2D materials with great potential in various applications. However, the degradation of MXenes in humid environments has become a main obstacle in their practical use. Here we combine deep neural networks and an active learning scheme to develop a neural network potential (NNP) for aqueous MXene systems with ab initio precision but low cost. The oxidation behaviors of super large aqueous MXene systems are investigated systematically at nanosecond timescales for the first time. The oxidation process of MXenes is clearly displayed at the atomic level. Free protons and oxides greatly inhibit subsequent oxidation reactions, leading to the degree of oxidation of MXenes to exponentially decay with time, which is consistent with the oxidation rate of MXenes measured experimentally. Importantly, this computational study represents the first exploration of the kinetic process of oxidation of super-sized aqueous MXene systems. It opens a promising avenue for the future development of effective protection strategies aimed at controlling the stability of MXenes.     

Sterically-Hindered Molecular p-Dopants Promote Integer Charge Transfer in Organic Semiconductors

Molecular p-dopants designed to undergo electron transfer with organic semiconductors are typically planar molecules with high electron affinity. However, their planarity can promote the formation of ground-state charge transfer complexes with the semiconductor host and results in fractional instead of integer charge transfer, which is highly detrimental to doping efficiency. Here, we show this process can be readily overcome by targeted dopant design exploiting steric hindrance. To this end, we synthesize and characterize the remarkably stable p-dopant 2,2′,2′′-(cyclopropane-1,2,3-triylidene)tris(2-(perfluorophenyl)acetonitrile) comprising pendant functional groups that sterically shield its central core while retaining high electron affinity. Finally, we demonstrate it outperforms a planar dopant of identical electron affinity and increases the thin film conductivity by up to an order of magnitude. We believe exploiting steric hindrance represents a promising design strategy towards molecular dopants of enhanced doping efficiency.     

One-pot synthesis of CuO/TiO2 nanocomposites for improved photocatalytic hydrogenation of 4-nitrophenol to 4-aminophenol under direct sunlight

The excellent photocatalytic hydrogenation of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) with NaBH₄ in the aqueous medium is still a big challenge. Herein, we report a facile one-pot evaporation-induced self-assembly (EISA) method to synthesize a series of CuO/TiO₂ nanocomposites. The as-synthesized CuO/TiO₂ photocatalysts exhibit remarkable catalytic activity under direct sunlight in selective hydrogenation of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) due to the synergistic interaction of guest copper nanoparticles with host titanium dioxide (TiO₂) species. Especially, 5 wt% CuO/TiO₂ nanocomposite revealed superior reaction rate constant (k) value (0.306 min⁻¹) when compared to 3 wt% CuO/TiO₂ (0.192 min⁻¹) and 7 wt% CuO/TiO₂ (0.240 min⁻¹). Moreover, several characterization techniques (XRD, TEM, N₂ adsorption–desorption isotherm, DRS, and XPS) were executed to deeply investigate the effect of copper content on the bulk and interfacial properties of the catalysts. The characterization results proved that the superior photocatalytic hydrogenation over 5 wt% CuO/TiO₂ catalyst can be ascribed to moderate CuO loading as well as even dispersion of CuO species on the surface of active TiO₂ host, which can largely improve the light absorption ability within visible light region. Besides, the 5 wt% CuO/TiO₂ catalyst exhibits remarkable recyclability and durability, retaining its superior activity (above 95%) up to several repeating cycles, proving its practical applicability for hydrogenation reactions at domestic and industrial levels.     

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.