Synthesis, isolation and characterization of methyl levulinate from cellulose catalyzed by extremely low concentration acid

A direct synthesis of methyl levulinate from cellulose alcoholysis in methanol medium under mild condition(180 210 C)catalyzed by extremely low concentration sulfuric acid(0.01 mol/L)and the product isolation were developed in this study.Effects of different process variables towards the catalytic performance were performed as a function of reaction time.The results indicated that sulfuric acid concentration,temperature and initial cellulose concentration had significant effects on the synthesis of methyl levulinate.An optimized yield of around 50%was achieved at 210 C for 120 min with sulfuric acid concentration of 0.01 mol/L and initial cellulose concentration below 100 g/L.The resulting product mixture was isolated by a distillation technique that combines an atmospheric distillation with a vacuum distillation where n-dodecane was added to help distill the heavy fraction.The light fraction including mainly methanol could be reused as the reaction medium without any substantial change in the yield of methyl levulinate.The chemical composition and structural of lower heavy fraction were characterized by GC/MS,FTIR,1H-NMR and13C-NMR techniques.Methyl levulinate was found to be a major ingredient of lower heavy fraction with the content over 96%.This pathway is efficient,environmentally benign and economical for the production of pure levulinate esters from cellulose.

Effects of Zr/Ti molar ratio in SO_4^(2-)/ZrO_(2-)TiO_2 calcined at different temperatures on its surface properties and glucose reactivity in near-critical methanol

Effects of Zr/Ti molar ratio in SO42-/ZrO2-TiO2 solid acid catalyst calcined at different temperatures on its surface properties and catalytic activity were thoroughly investigated in this paper. The physicochemical characteristics of prepared samples were determined by N2 adsorptiondesorption, XRD, NH3-TPD and XPS techniques, respectively. It was found that the crystallization temperature of the samples increased after the combination of ZrO2 and TiO2; and phase transformations from the anatase to the rutile of TiO2 species and the tetragonal to the monoclinic of ZrO2 species were effectively suppressed at higher temperature. The sample with a Zr/Ti molar ratio of 3/1 calcined at 450℃ showed the highest surface area and the most acid sites among all the tested samples. The acid site densities of samples were relatively closed to each other if they were calcined at the same temperature, however, decreased with the calcination temperature. The result indicates that the sulfur content in samples is a crucial factor to control the acid site density. Calcining the sample at 650℃ and higher temperatures resulted in a significant desorption of sulfate ion on the samples. The synthesized samples were evaluated as a potential catalyst for glucose conversion under the near-critical methanol conditions （200℃/4 MPa）. The results suggested that the relatively weaker acid sites of the catalyst were more favorable for the accumulation of methyl glucosides, while the moderate acid sites were responsible for the formation of methyl levulinate. The catalytic activity for methyl levulinate production almost increases linearly with the catalyst acid site density. The catalyst deactivation is due to the loss of sulfate ion and the two catalysts with Zr/Ti molar ratios of 3/1 and 1/3 could effectively alleviate the deactivation caused by sulfate solution in the reaction medium and can be reused after calcination with the reuse rate of over 90% in terms of the methyl levulinate selectivity.

Enhanced high temperature cycling performance of LiMn_2O_4/graphite cells with methylene methanedisulfonate(MMDS) as electrolyte additive and its acting mechanism

The effects of methylene methanedisulfonate（MMDS） on the high-temperature（0℃） cycle performance of LiMnO/graphite cells are investigated.By addition of 2 wt%MMDS into a routine electrolyte,the high-temperature cycling performance of LiMn204/graphite cells can be significantly improved.The analysis of differential capacity curves and energy-dispersive X-ray spectrometry（EDX） indicates that MMDS decomposed on both cathode and anode.The three-electrode system of pouch cell is used to reveal the capacity loss mechanism in the cells.It is shown that the capacity fading of cells without MMDS in the electrolytes is due to irreversible lithium consumption during cycling and irreversible damage of LiMnOmaterial,while the capacity fading of cell with 2 wt%MMDS in electrolytes mainly originated from irreversible lithium consumption during cycling.

Porous core–shell CoMn_2O_4 microspheres as anode of lithium ion battery with excellent performances and their conversion reaction mechanism investigated by XAFS

Porous core-shell CoMn204 microspheres of ca. 3-5μm in diameter were synthesized and served as an-ode of lithium ion battery. Results demonstrate that the as-synthesized CoMn204 materials exhibit excel-lent electrochemical properties. The CoMn204 anode can deliver a large capacity of 1070 mAh g-1 in thefirst discharge, a reversible capacity of 500 mAh g^-1 after 100 cycles with a coulombic efficiency of 98.5% at a charge-discharge current density of 200 mA g^-l, and a specific capacity of 385 mAh g^-1 at a muchhigher charge-discharge current density of 1600mA g^-1. Synchrotron X-ray absorption fine structure（XAFS） techniques were applied to investigate the conversion reaction mechanism of the CoMn204 anode.The X-ray absorption near edge structure （XANES） spectra revealed that, in the first discharge-charge cy-cle, Co and Mn in CoMn204 were reduced to metallic Co and Mn when the electrode was discharged to0.01 V, while they were oxidized respectively to CoO and MnO when the electrode was charged to 3.0V.Experiments of both XANE5 and extended X-ray absorption fine structure （EXAFS） revealed that neithervalence evolution nor phase transition of the porous core-shell CoMn204 microspheres could happen inthe discharge plateau from 0.8 to 0.6V, which demonstrates the formation of solid electrolyte interface（SEI） on the anode.

High He-ion irradiation resistance of CrMnFeCoNi high-entropy alloy revealed by comparison study with Ni and 304SS

High entropy alloys(HEAs) have presented potential applications in nuclear power plants owing to their novel atomic structure based high irradiation resistance. However, understanding of He-ion irradiation of HEAs is still lacking. In this work, we reveal He-ion irradiation resistance of HEA CrMnFeCoNi by comparison study with a pure Ni and a 304 stainless steel(304SS). It is found that the damage structure in the three materials can be characterized with He bubbles and stacking faults/stacking fault tetrahedrons((SFs/SFTs), which show a similar depth distribution after He-ion irradiation at both RT and 450℃.Although the He bubbles have a similar size about 2nm after irradiation at RT, the He bubble sizes of the HEA, 304SS, and Ni increase to 4.0±0.9,5.3±1.0 and 6.7 ±1.0 nm after irradiation at 450℃, respectively. Moreover, the density of SFs/SFTs displays in an order of Ni < 304 SS < HEA at both RT and 450℃.The He-ion irradiation at RT causes significant hardness enhancement for the three materials, however,compared to RT, after irradiation at 450℃, the Ni presents softening, while the 304SS, especially the HEA,shows further hardening. Thus, the HEA CrMnFeCoNi possesses the smallest He bubble size, the densest SFs/SFTs, and the highest hardening, indicating the best structural stability, as well as the best He-ion irradiation resistance, which can be attributed to its low mobility of He atoms and point defects.

Luminescence properties of Sr2MgB2O6：Tb3＋,Li＋ green-emitting phosphor

A novel green phosphor,Sr2MgB2O6：Tb3＋,Li＋ for white light-emitting diodes was prepared by solid-state reactions,and its structure and luminescence properties were investigated.The excitation and emission spectra indicated that this as-prepared phosphor could be effectively excited by ultraviolet 368 nm,and exhibited bright green emission centered at 545 nm corresponding to the^5D_4→~7F_5 transition.9 mol.%of Tb^（3＋） was shown to be optimal.Good green emissions with the CIE chromaticity coordinates（0.262,0.583） could be achieved.Furthermore,the integrated emission intensity of Sr_2MgB_2O_6：0.09Tb^（3＋）,0.09Li~＋ phosphor decreased continuously to 72.1%at 300 ℃ with increasing temperature,and the activation energy of thermal quenching（E_a） was calculated to be0.175 eV,moreover,the quantum yield excited by 368 nm was measured as 11.1%.A green emission LED was made by coating Sr_2MgB_2O_6：0.09Tb^（3＋）,0.09Li~＋ phosphor on a NUV（365-370 nm） chip.Our results showed that Sr_2MgB_2O_6：Tb^（3＋）,Li~＋ is a kind of potential green-emitting phosphor and features good thermal stability.

Investigation of interfacial processes in graphite thin film anodes of lithium-ion batteries by both in situ and ex situ infrared spectroscopy

Graphite thin film anodes with a high IR reflectivity have been prepared by a spin coating method. Both ex situ and in situ microscope FTIR spectroscopy (MFTIRS) in a reflection configuration were employed to investigate interfacial processes of the graphite thin film anodes in lithium-ion batteries. A solid electrolyte interphase layer (SEI layer) was formed on the cycled graphite thin film anode. Ex situ MFTIRS revealed that the main components of the SEI layer on cycled graphite film anodes in 1 mol L -1 LiPF6 /ethylene carbonate + dimethyl carbonate (1:1) are alkyl lithium carbonates (ROCO2 Li). The desolvation process on graphite anodes during the initial intercalation of lithium ion with graphite was also observed and analyzed by in situ MFTIRS.

Interaction of citrate with Pt(100) surface investigated by cyclic voltammetry towards understanding the structure-tuning effect in nanomaterials synthesis

This study aims to understand the effects of functional agents such as capping agents, stabilizers, surfactants and additives in shape-controlled synthesis of nanomaterials. The well-defined Pt(100) single crystal surface was used as a model to investigate its interaction with citrate, a capping agent that is often used in shape-controlled synthesis of nanomaterials. It demonstrated that, through a systematic study of electrochemical cyclic voltammetry, the presence of citrate in solution could increase the current peak density of hydrogen adsorption at high potential (j p,L ), while decrease proportionally the current peak density of hydrogen adsorption at low potential (j p,S ). Furthermore, the increase of citrate concentration shifted negatively the peak potentials (E p,L and E p,S ) of both j p,L and j p,S . The results indicated that the interaction of citrate with Pt(100) surface could induce increasing the (100) surface domains of two-dimensional long range order (2D-(100)), and decreasing the (100) surface domains of one-dimensional short range order (1D-(100)). It also revealed that the interaction of citrate with Pt(100) surface could stabilize the 2D-(100) structure. The findings gained in this study implied that the citrate may lead to form stable 2D-(100) domains on Pt nanoparticles upon the shape-controlled synthesis of Pt nanomaterials.

Localized Corrosion of Binary Mg-Ca Alloy in 0.9 wt%Sodium Chloride Solution

To further understand the localized corrosion of magnesium alloy, various in situ electrochemical techmques and ex situ electron microprobe analysis and SEM were used to monitor the corrosion process of Mg-l.0Ca alloy in 0.9 wt% sodium chloride solution. The results indicated that the localized corrosion was accompanied by the formation and thickening of a corrosion product film on the Mg-l.0Ca alloy. A localized corrosion of the alloy initiated selectively on the eutectic micro-constituent zones, then enhanced with the exposure, developed in depth with ring-shaped corrosion products accumulated around and finally formed a volcanic-like pitting. Based on the measurements, an electrochemical corrosion model was proposed accordingly to describe the formation mechanism of the volcanic-like pitting on the alloy in 0.9 wt% sodium chloride solution.

Experimental investigations of granular shape effects on the generation of electrostatic charge

In solid processing systems, electrostatic problems are commonly observed for granules of various shapes. However, a complete understanding of the basic dependence of electrostatic charge generation on particle shape has yet to be established. This observation motivated the present study on examining the effect of granular shape on electrostatics. In this study, polyvinyl chloride （PVC） granules （diameter 1.1-4.1 ram, in the shape of a triangle or trapezium） were first discharged to remove any residual charges and sub- sequently their electrostatic charging characteristics were studied by allowing a granule to slide along a pipe wall. Several factors such as granular front-facing angle, length-ratio, sliding area, sliding orienta- tion, sliding times, and relative humidity were considered when studying their effects on the electrostatic charging of granules. It was found that triangular granules with smaller front-facing angles tended to generate more electrostatic charge. The amount of electrostatic charge increased with granular length- ratio and sliding area but decreased with humidity. In addition, granular sliding in the orientation of the front-facing angle （for triangular granules） or the short side （for trapezoidal granules） generated more electrostatic charge than that in the orientation of the long side. For both granule shapes, the elec- trostatic charge increased with granular sliding times and reached a saturated state after around 8-9 sliding movements. The saturated electrostatic charge increased with either granular length ratio or sliding area.

Electronic structure and luminescence properties of Tb^(3+)-activated NaBaBO_3 green-emitting phosphor

A novel green-emitting phosphor Tb3＋ doped NaBaBO3 was prepared using a conventional high temperature solid-state reaction method. The crystal structure and luminescence properties of NaBaBO3：Tb3＋ were studied. The NaBaBO3 host was also investigated using density functional theory calculations. Our calculated lattice parameters of NaBaBO3 host were found to be in excellent agreement with experiment. Theoretically, the host matrix NaBaBO3 was a wide-gap semiconductor with a direct band gap of 3.66 eV, where the bottom of conduction band and the top of valence band were dominated by Ba 5d state and O 2p state, respectively. The excitation spectra indicated that the phosphor could be effectively excited by near ultraviolet light. The phosphor featured a satisfactory green performance with the highest photoluminescence intensity located at 543 nm excited by 377 nm light and the measured Commission Intemationale de L＇Eclairage （CIE） chromaticity was determined to be （0.2860, 0.4640）. The op- timum Tb3＋ concentration in NaBaBO3 was 5.0 mol.%. The concentration quenching occurred when Tb3＋ concentration was be- yond 5.0 mol.% and the concentration quenching mechanism could be explained by the dipole-dipole interaction. The effects of charge compensators （including Li, Na＋ and K＋） and temperature on the photoluminescence of NaBaBO3：Tb3＋ were also studied. The present work suggested that the NaBaBO3：Tb3＋ phosphor was a promising green-emitting material for near ultraviolet white light-emitting diodes.

Promoted Li+ conduction in PEO-based all-solid-state electrolyte by hydroxyl-modified glass fiber fillers

In the polyoxyethylene(PEO)-based solid-state electrolytes,the low ionic conductivity of lithium ions limits its application in solid-state lithium batteries,so optimizing the conduction path of lithium ions is beneficial to improve the ionic conductivity.In this work,we report the use of hydrothermal carbon nano-sphere(HCS)modified glass fibers(GF)as a functional filler(GF@HCS)to improve the ionic conductivity of PEO composite solidstate electrolytes.The oxygen atoms in the hydroxyl groups on the surface of HCS can be complexed with Li ions as its transport sites,which means that it can promote the longdistance transport of Li ions along the glass fiber surface.With addition of 2 wt%GF@HCS fillers,the degree of crystallinity of PEO composite solid-state electrolyte is the smallest,and the ionic conductivity is significantly increased from 8.9×10^(-5) to 4.4×10^(-4) S·cm^(-1) at 60℃.Moreover,the PEO composite solid-state electrolyte exhibits better lithium-metal interface stability in symmetric lithium batteries and superior rate performance in LiFePO4 solid-state batteries.