Poly(ethylenimine)-assisted synthesis of hollow carbon spheres comprising multi-sized Ni species for CO_(2) electroreduction

Electrochemical CO_(2) reduction to produce value-added chemicals and fuels is one of the research hotspots in the field of energy conversion.The development of efficient catalysts with high conductivity and readily accessible active sites for CO_(2) electroreduction remains challenging yet indispensable.In this work,a reliable poly(ethyleneimine)(PEI)-assisted strategy is developed to prepare a hollow carbon nanocomposite comprising a single-site Ni-modified carbon shell and confined Ni nanoparticles(NPs)(denoted as Ni@NHCS),where PEI not only functions as a mediator to induce the highly dispersed growth of Ni NPs within hollow carbon spheres,but also as a nitrogen precursor to construct highly active atomically-dispersed Ni-Nx sites.Benefiting from the unique structural properties of Ni@NHCS,the aggregation and exposure of Ni NPs can be effectively prevented,while the accessibility of abundant catalytically active Ni-Nx sites can be ensured.As a result,Ni@NHCS exhibits a high CO partial current density of 26.9 mA cm^(-2) and a Faradaic efficiency of 93.0% at-1.0 V vs.RHE,outperforming those of its PEI-free analog.Apart from the excellent activity and selectivity,the shell confinement effect of the hollow carbon sphere endows this catalyst with long-term stability.The findings here are anticipated to help understand the structure-activity relationship in Ni-based carbon catalyst systems for electrocatalytic CO_(2) reduction.Furthermore,the PEI-assisted synthetic concept is potentially applicable to the preparation of high-performance metal-based nanoconfined materials tailored for diverse energy conversion applications and beyond.

Uncovering gold nanoparticle synthesis using a microchip laser system through pulsed laser ablation in aqueous solution

The synthesis of gold nanoparticles(Au NPs)was carried out by utilising the pulsed laser ablation in liquids(PLAL)method with a microchip laser(MCL)system.This portable system features low power consumption and a giant-pulse laser.Aqueous solutions with and without the surfactant poly(N-vinyl-2-pyrrolidone)(PVP)were used for laser ablation of a bulk gold rod to achieve the successful formation of a colloidal solution of Au NPs.The gas bubbles formed by heating the aqueous medium around the surface of the gold target significantly reduced the efficiency of Au NP ablation.This effect was more pronounced and prolonged in high-viscosity solutions,hindering energy transfer from subsequent laser pulses to the target.Additionally,it was suggested that the chain length of PVP does not affect either the size of the Au NPs or the ablation efficiency.Videography experiments were conducted to explore the ablation mechanism employed by the MCL system.The relatively short pulse duration of the MCL system may contribute to the formation of NPs with consistent size,which were suppressed to grow in significantly smaller cavitation bubbles with short lifetimes.

Supramolecular photoresponsive polyurethane with movable crosslinks based on photoisomerization of azobenzene

Light-driven actuators are widely used for smart devices such as soft robots.One of the main challenges for actuators is achieving rapid responsiveness,in addition to ensuring favorable mechanical properties.Herein,we focused on photoresponsive polyurethane(CD-Azo-PU)based on controlling the crystallization of the hard segments in polyurethane(PU)by complexation between azobenzene(Azo)and cyclodextrins(CDs).CD-Azo-PU incorporated polyurethane as the main chain and a 1:2 inclusion complex between Azo andγCD as a movable crosslink point.Upon ultraviolet light(UV,λ=365 nm)irradiation,the photoresponsiveness of CD-Azo-PU bent toward the light source(defined as positive),while that of the linear Azo polyurethane(Azo-LPU)without peracetylatedγ-cyclodextrin diol(TAcγCD-diOH)as a movable crosslinker bent in the direction opposite the light source.The bending rates were determined to be 0.25◦/s for CD-Azo-PU and 0.083◦/s for Azo-LPU,indicating that the bending rate for CD-Azo-PU was faster than that for Azo-LPU.By incorporating movable crosslinks into CD-Azo-PU,we successfully achieved specific photoresponsive actuation with an enhanced rate.

Synthesis and Properties of a Through-Space Interacting Diradicaloid

Knowledge about electronic structures is important to gain an understanding of the unique functional properties of diradicaloids.In this study,we synthesized and characterized a diradicaloid in which two phenalenyl radical sites are coupled antiferromagnetically via a through-space interaction.The results of quantum chemical,physicochemical(^(1)H NMR,electronic absorption,cyclic voltammetry,SQUID,ESR),and chemical reactivity studies show that this diradicaloid has singlet diradical character.An assessment of the nature of the bonding interaction between two radical sites in this species using DFT calculations demonstrates that a small spatial overlap between the two SOMOs in this diradicaloid provides an efficient electron exchange path for the singlet state to be substantially lower in energy than the triplet state.

Optical nature of non-substituted triphenylmethyl cation:Crystalline state emission,thermochromism,and phosphorescence

Since the discovery of the triphenylmethyl(trityl)cation 120 years ago,a variety of aromatic cations having various colors and luminescence properties have been rigorously studied.Many,differently substituted trityl cations have been synthesized,and their optical properties have been elucidated.However,the optical properties of the parent,non-substituted and highly reactive trityl cation,which was observed to be very weakly luminescent,have not been subjected to detailed investigation.In the effort described herein,we explored the optical nature of non-substituted trityl hexafluorophosphate(PF_(6))in the crystalline state.Trityl PF_(6) was found to exist as two crystal polymorphs including a yellow(Y)and an orange(O)form.Moreover,we observed that these crystalline forms display crystalline-state emission with different colors.The results of X-ray crystallographic analysis showed that the two polymorphs have totally different molecular packing arrangements.Furthermore,an investigation of their optical properties revealed that the O-crystal undergoes a distinct color change to yellow upon cooling as a consequence of a change in the nature of the charge transfer interaction between the cation and PF6 anion,and that both the Y-and O-crystal exhibit phosphorescence.