Direct conversion of furfural to levulinic acid/ester in dimethoxymethane:Understanding the mechanism for polymerization

This study investigated the conversion of furfural to 5-hydroxymethylfurfural(HMF)and further to levulinic acid/ester in dimethoxymethane under acidic conditions,with the particular focus on understanding the mechanism for polymer formation.The results showed that furfural could react with dimethoxymethane via electrophilic substitution reaction to form HMF or the ether/acetal of HMF,which were further converted to levulinic acid and methyl levulinate.The polymerization of furfural and the cross-polymerization between dimethoxymethane and the levulinic acid/ester produced were the main side reactions leading to the decreased yields of levulinic acid/ester.Comparing to the other solvent,methanol as the co-solvent helped to alleviate but not totally inhibited the occurrences of the polymerization,as the polymerization reactions via aldol condensation did not eliminate the C=O functionalities.As a consequence,the polymerization reactions continued to proceed.Other co-solvent used such as guaiacol,dimethyl sulfoxide and acetone interfered with the transformation of furfural to HMF or aided the polymerization reactions.The polymer produced from the reactions between furfural and DMM was different from that produced from levulinic acid/ester.The former had a higher crystallinity,while the latter was more aliphatic.The DRIFTS and TG-MS studies showed that the polymer had the carboxylic group,methyl group and the aliphatic structure in the skeleton.The removal of these functionalities was accompanied by the aromatization of the polymer.The condensation of DMM with levulinic acid/ester was the key reason for the diminished production of levulinic acid/ester.

Ultrasensitive photochromism and impedance dual response to weak visible light by solvated Pb(Ⅱ) modified polyoxomolybdate

Polyoxometalates (POMs) are important inorganic photochromic materials to be potentially applied in photo-induced switch,energy storage,and even the detection of light.However,due to the limited sensitivity of POMs,it is difficult to realize the photochromic response to weak visible light.In this paper,by the coordination of solvated Pb(Ⅱ),a new structure-defined chain-like polyoxomolybdate complex of[(Pb(DMF)_(4))^(3)(P_(2)Mo_(18)O_(62))_(2)]n(Pb_(3)Mo_(18) ,DMF=dimethylformamide) has been demonstrated by a facile solvent-diffusion approach.By virtue of interactions between Pb(DMF)_(4) and polyoxoanions,Pb_(3)Mo_(18) shows an ultrasensitive photochromic response to weak visible lights and forms the reduced’heteropoly blue’species through ligand-to-metal charge transfer (LMCT) process.A new mechanism is firstly proposed here that the 6s orbital lone electron pair on Pb(II) can effectively stabilize the generated hole of oxygen atoms as a result of O→Mo charge transfer.Through the proposed mechanism,the LMCT barrier is drastically lowered and allows the coloration to be occurred even upon weak visible light.Also,because the conductivity of Pb_(3)Mo_(18) enhances with the increase of reduction extent,its electrochemical impedance signals are proportionally response to irradiation intensity.Especially,for the first time,the polyoxomolybdate composite can be used to detect weak visible light,in which the optical signal can be converted into electrical signal output.Moreover,Pb_(3)Mo_(18) can be drip-coated on the surface of the screen printed chip electrode,which is facile to the detection of light by portable devices compatible with computers,mobile phones and other electronic equipment.This work not only highlights a new approach to the molecular design of photochromic POMs by the coordination of metal ions with the effect of inert electron pair,but also lays a foundation to extend the application of POMs as light signal sensors.

Surface modification of hollow capsule by Dawson-type polyoxometalate as sulfur hosts for ultralong-life lithium-sulfur batteries

Reasonable construction of sulfur host with high conductivity,large sulfur storage gap,strong chemical adsorption,and fast oxidation–reduction kinetics of polysulfide is very significant for its practical use in lithium-sulfur batteries(LSBs).In this paper,the surface modification of MIL-88A(Fe)is carried out by Dawson-type polyoxometalate(POM),and a hollow capsule shell material with P_(2)W_(18),Fe_(3)O_(4),and C components is synthesized by the subsequent carbonization process.When applied as the sulfur host,the hollow capsule shell material can efficiently improve the conductivity of sulfur electrode and restrain the volumetric change of active sulfur while charging and discharging.On this foundation,electrochemical analysis and density functional theory(DFT)calculation show that the P_(2)W_(18)on the outer layer of the capsule shell have effective electrocatalytic activity and potent chemical bond on the lithium polysulfides(LiPSs),which is helpful to block the shuttle effect.Therefore,the as-assembled LSBs display the outstanding specific capacity and prominent cycle stability.Specifically,it delivers an excellent reversible capacity of 1063 mAh/g after 100 cycles of charge–discharge at a rate of 0.5 C,accounting for a preservation by 96%in comparison to that of the initial cycle.Moreover,even after 2000 cycles at 1 C,the reversible specific capacity of 585 mAh/g can still be maintained with an average decay rate of only 0.021%.