Novel synthesis of SiO_x/C composite as high-capacity lithium-ion battery anode from silica-carbon binary xerogel

Micro/nanostructured SiOx/C composite was firstly synthesized by carbothermal reduction of silica-carbon binary xerogel.The homogeneous dispersion feature of the two components in binary xerogel contributes to effectively carbothermally reduce the O/Si atomic ratio,enhancing the electrochemical activity of the SiOx component.The micron-sized SiOx/C spheres are composed of many near-spherical nanoparticles.The synthesized SiOx/C exhibits a stable and high reversible capacity of 830 m A·h·g^-1 for 100 cycles,and excellent rate-capability.The homogeneous dispersion structure of phases,the micro/nanostructure and the high electrochemical activity of SiOx component combinedly contribute the excellent electrochemical performance.

Characterization and Photocatalytic Activity of Mixed Nanocrystalline TiO_2 Powders Prepared by Xerogel-Hydrothermal Method in Different Acid Solutions

TiO_2 nanoparticles(NPs)were prepared via the hydrothermal route of TiO_2 xerogel in nitric acid, hydrochloric acid and acetic acid. The physico-chemical properties of the powders were characterized by X-ray diffraction(XRD)and N_2 adsorption desorption techniques. The effects of the different acids on the structure(crystal phase)and texture(primary particle size and porosity)of the TiO_2 powders were explored. Results indicated that acetic acid facilitated the formation and stability of pure anatase phase. On the other hand, nitric acid and hydrochloric acid led to the transformation from anatase to rutile. The catalyst synthesized via the hydrothermal route of TiO_2 xerogel in the low concentration hydrochloric acid solution(Ti-HCl-0.15)had the highest photocatalytic activity than the catalysts obtained in the other two acid solutions. The effects of the different acids were discussed in terms of acid strength, chelating effect and the thermal stability of the adsorbed acidic anions.

Synthesis and functionalization of carbon xerogels to be used as supports for fuel cell catalysts

The synthesis and properties of carbon xerogels are briefly described in this mini-review, emphasizing the methods used for tuning their surface chemistry and textural properties in order to design efficient electrocatalysts for fuel cells. In particular, the role played by the surface functional groups in determining the loading, dispersion, oxidation state and stability of the metal phases is addressed.

Lithium Insertion in Poly(ethylene oxide)/MoO_3 Xerogel Nanocomposite Films

The nanocomposite films were prepared by direct intercalation of poly(ethylene oxide) and PEO into MoO 3 xerogel via sol-gel route.The electrochromic behavior and the chemical conditions of Li + ions were investigated by cyclic voltammograms,UV-visible spectral transmittance and XPS.The results show that the cycling efficiency and the reversibility of insertion/extraction of Li + ions in (PEO) 1MoO 3·nH 2O nanocomposite film were improved.The intercalation of PEO into MoO 3 xerogel modulated the wavelength range of electrochromism and enhanced the electrochromic efficiency.Two different chemical conditions of Li + ions existing in the interlayer and interstitial positions of MoO 3 lattice were observed in MoO 3 xerogel and (PEO) 1MoO 3·nH 2O nanocomposite films.

Bright blue photoluminescence from a mixed tin and manganese oxide xerogel prepared via sol-hydrothermal-gel process

A new blue photoluminescent material, a mixed tin and manganese oxide xerogel, is prepared via sol-hydrothermalgel process assisted by citric acid. The composition xerogel exhibits strong blue emission at room temperature, with an emission maximum at 434 nm under short （234 nm） or long-wavelength （343 nm） ultraviolet excitation. The photoluminescent excitation spectrum of the mixed tin and manganese oxide xerogel, monitored at an intensity maximum wavelength of 434 nm of the emission, consists of two excitation peaks at 234 nm and 343 am. With heat treatment temperature increasing from 110 ℃ to 200 ℃, the blue emission intensity increases remarkably, whereas it is almost completely quenched after being treated at 300 ℃. The carbon impurities in the mixed tin and manganese oxide xerogel, confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, should be responsible for the bright blue photoluminescence.

THE NANOCOMPOSITE FILM OF POLYMER INTERCALATION IN V_2O_5 XEROGEL

The nanocomposite films were prepared by poly(ethylene oxide), PEO, intercalation in V2O5 xero-gel in sol-gel. The synthesis and state of the films are investigated by the XRD, IR, SEM, etc. The results show that V2O5, xerogel is a layered structure which arranges in c-direction. The mterlayer distance of V2O5 xerogel increases remarkably when PEO is intercalated in V2O5 xero-gel interlayer. PEO has strong interaction with V2O5 host. The surface of the films is homogeneous without holes and cracks.

Novel Preparation and XPS Analysis of V_2O_5 Xerogel

The V 2O 5 sol was fabricated by ultra fast quenching.The vanadium with low valence (V 4+ ) was found in V 2O 5 xerogel films by XPS analysis.The technology of oxygen top blown was applied to analyze the XPS spectrum difference of V 2O 5 xerogel when the powder of V 2O 5 was melting in air or in oxygen atmosphere.The results show that the different melting atmosphere has certain influences on the chemical valence of V 2O 5 xerogel.

Effect of Fe_(3)O_(4) nanoparticles on magnetic xerogel composites for enhanced removal of fluoride and arsenic from aqueous solution

Fe_(3)O_(4)magnetic xerogel composites were prepared by polycondensation of resorcinol(R)-formaldehyde reaction via a sol-gel process in an aqueous solution through varying the molar ratio of Fe_(3)O_(4)nanoparticles(MNPs),catalyst(C),and water(W)content.MNPs were obtained by co-precipitation(MC),oxidation of iron salts(MO),or solvothermal synthesis(MS).Both MNPs and magnetic xerogels were examined regarding the performance of arsenic and fluoride removal in a batch system.The MC-based MNPs had higher adsorption capacities for both fluoride(202.9 mg/g)and arsenic(3.2 mg/g)than other MNPs in optimum conditions.The X-ray diffraction,Fourier transform infrared spectroscopy,and energy-dispersive X-ray spectroscopy confirmed that Fe was composed into the polymeric matrix of magnetic xerogels that contained 0.59%-4.42%of Fe with a molar ratio of MNPs(M)to R between 0.01 and 0.10.With low R/C and optimum M/R ratios,an increase in the surface area of magnetic xerogels affected the fluoride and arsenic adsorption capacities.The magnetic xerogel composites with the MC-based MNPs prepared at a fixed R/C ratio(100)and at different R/W(0.05-0.06)and M/R(0.07-0.10)ratios had a high arsenic removal efficiency of 100%at an As(V)concentration of 0.1 mg/L and pH of 3.0.The maximum adsorption capacities of magnetic xerogels were approximately five times higher than those of the xerogels without MNP composites.Therefore,Fe_(3)O_(4)nanoparticles enhanced the adsorption of arsenate and fluoride.The variations of alkaline catalyst and water content significantly affected the resulting properties of textural and surface chemistry of magnetic xerogel composites.

P-Doped Titania Xerogels as Efficient UV-Visible Photocatalysts

In the present study, sol-gel process is used to synthesize P-doped TiO2 xerogels by the cogelation method of a functionalized P alkoxide, (NH2-(CH2)2-NH-(CH2)2-P(O)-(OC2H5)2) with Ti(OC3H7)4 in either 2-methoxyethanol or isopropanol. The phosphorus-doping improved the thermal stability of titania and decreased the phase transformation of anatase into rutile. This modification by phosphorus shifted the absorption edge of titania to the visible region as proved by Diffuse reflectance measurements, and thus offers the possibility to produce visible light effective TiO2 photocatalyst. The excellent photocatalytic activity of P-doped TiO2 xerogels compared to pure TiO2 could be explained by its high surface area and small TiO2-anatase crystallite size. From these results, it was proved by using three different models that phosphorus intrinsically influences the photocatalytic activity.

Electrochemical impedance spectra of V_2O_5 xerogel films with intercalation of lithium ion

Vanadium pentoxide xerogel films used for lithium rechargeable batteries were prepared from crystalline c-V2O5 by melt quenching method,then the electrochemical process of lithium intercalation into vanadium pentoxide xerogel films was simulated with an equivalent circuit model, which was derived from the mechanism of electrode reactions. Measured electrochemical impedance spectra at various electrode potentials were analyzed by using the complex non-linear least-squares fitting method. The results show that impedance spectra consist of 2 high-to- medium frequency depressed arcs and a low frequency straight line. The high frequency arc is attributed to the absorption reaction of lithium ions into the oxide film, the medium frequency arc is attributed to the charge transfer reaction at the vanadium oxide/electrolyte interface and the low frequency is characterized by a straight line with a phase angle of 45° corresponding to the diffusion of lithium ion through vanadium oxide phase. The experimental and calculated results are compared and discussed focusing on the electrochemical performance and the state of charge of the electrode. Moreover, the high consistence of the fitted values of the model to the experimental data indicates that this mathematical model does give a satisfying description of the intercalation process of vanadium pentoxide xerogel films.

Electrochemical properties of vanadium pentoxide xerogel films

Vanadium pentoxide xerogel(VXG) films were prepared by rapid quenching, then coin type 2016 size lithium rechargeable batteries were assembled and tested with the VXG film electrodes and lithium anodes. Electrochemical impedance spectroscopy(EIS) analysis result reveals the expected response for intercalation, except that there is almost no Warburg (diffusion) component. Analyses results of cyclic voltammetry(CV), constant discharge(CD) and discharge-charge(DC) indicate that the sample achieves a high initial discharge specific capacity of approximate 400mA·h/g and a corresponding efficiency of 97 % in the voltage diapason of 1.54.0 V with a draining current of 60 mA/g. Its preservation ratio of capacity still keeps as high as 85 % even after 100 cycles. The good electrochemical performance indicates that VXG film material is a promising cathode for lithium rechargeable batteries.

Influence of polyethylene glycol on pore structure and electric double-layer capacitance of carbon xerogel

Mesoporous polyethylene glycol-resorcinol and formaldehyde（PEG-RF） carbon xerogels were prepared by a new polymer blend method in which PEG-RF mixed organic xerogels were synthesized by blending thermally unstable polyethylene glycol with organic monomers, resorcinol and formaldehyde and then subjected to pyrolization at 1 000 ℃. The influences of mass ratio of PEG to the theoretical yield of RF xerogel, m（PEG）/m（RF） and the （relative） molecular mass of PEG on the pore structure and electric double layer capacitance（EDLC） performance of PEG-RF carbon xerogels were investigated. The results show that PEG under different conditions leads to the difference of phase separation structure of the polymer blend and thus the change of pore structure of PEG-RF carbon xerogels. Specific surface area and capacity of PEG-RF carbon xerogels in 30% H2SO4 solution can reach （755 m2/g） and 150 F/g, respectively. Their surface can be fully utilized to form electric double layer. However, the pore structure differences of PEG-RF carbon xerogels result in their different EDLC performances. The distributed capacitance effect increases with decreasing the pore size of PEG-RF carbon xerogels.

ZnO/CeO_(2)/carbon xerogel composites with direct Z-scheme heterojunctions:Enhancing photocatalytic remediation of 4-chlorophenol under visible light

This paper aims to create visible light driven ternary photocatalysts using zinc oxide(ZnO),cerium(IV)oxide(CeO_(2)),and carbon xerogel(CX) as constituent materials.The use of CeO_(2) is based on the creation of direct-Z-scheme heterojunctions with the ZnO and the consequent diminishing of charge recombination,whereas the carbon xerogel inclusion is predicted to minimize bandgap energy,decrease electro n-hole reco mbination,and boost specific surface area.Furthermo re,the choice of the black-wattle tannin as a carbonaceous precursor was targeted at the development of an environmentally friendly and affordable composite.The existence of the hexagonal phase of zinc oxide and cubic structure of the cerium(IV) oxide in the ternary material was confirmed by X-ray diffractometry and X-ray photoelectron spectroscopy,with the latter also suggesting chemical bonding between the ZnO and the CX due to the creation of zinc oxycarbide complexes.The inclusion of the carbon xerogel provokes a significant modification in the morphology of the ternary material,resulting in an increased surface area and smaller particle aggregates.The CX/ZnO-CeO_(2) ternary composite obtains the highest photocatalytic efficiency among all the materials studied,degrading 100% of 4-chlorophenol under simulated sunlight and 68% under visible radiation,after 5 h.The increased photocatalytic activity can be attributed to the formation of direct Z-scheme heterojunctions between the semiconductors,higher visible light response,and higher specific surface area,as evidenced by the results obtained by active radical scavenging,chronoamperometry,diffuse reflectance spectroscopy,and N_(2) adsorption-desorption isotherms.

Single atom Cu-N-C catalysts for the electro-reduction of CO_(2) to CO assessed by rotating ring-disc electrode

The electrochemical CO_(2) reduction reaction(CO_(2)RR) to controllable chemicals is considered as a promising pathway to store intermittent renewable energy. Herein, a set of catalysts based on copper-nitrogendoped carbon xerogel(Cu-N-C) are successfully developed varying the copper amount and the nature of the copper precursor, for the efficient CO_(2)RR. The electrocatalytic performance of Cu-N-C materials is assessed by a rotating ring-disc electrode(RRDE), technique still rarely explored for CO_(2)RR. For comparison, products are also characterized by online gas chromatography in a H-cell. The as-synthesized Cu-NC catalysts are found to be active and highly CO selective at low overpotentials(from -0.6 to -0.8 V vs.RHE) in 0.1 M KHCO_(3), while H_(2) from the competitive water reduction appears at larger overpotentials(-0.9 V vs. RHE). The optimum copper acetate-derived catalyst containing Cu-N_(4) moieties exhibits a CO_(2)-to-CO turnover frequency of 997 h^(-1) at -0.9 V vs. RHE with a H_(2)/CO ratio of 1.8. These results demonstrate that RRDE configuration can be used as a feasible approach for identifying electrolysis products from CO_(2)RR.

桥联配体对钛凝胶吸附砷锑性能的影响及机制

针对钛凝胶吸附剂中桥联配体与吸附性能之间的关系不明问题,本文对比考察了由11种配体(有机羧酸类、醇胺类以及双酮类)合成的钛凝胶材料吸附砷(As)、锑(Sb)的性能.乙酰丙酮(AcAc)作为桥联配体合成的钛凝胶材料表现出优异的As、Sb去除能力,其对As(Ⅲ)、As(Ⅴ)、Sb(Ⅲ)和Sb(Ⅴ)的吸附容量分别达到了329、461、584、805 mg·g^(−1)(以钛计),吸附速率分别比无配体组提高了10.1、8.1、11.5、1.9倍.各类配体对钛凝胶吸附容量的提升效果相当,但对吸附速率提升效果差异明显.有机羧酸类配体调控后对As、Sb吸附速率仅为AcAc的30%—60%,而丁二酮等弱配体调控后几乎没有提升吸附速率.与其他配体相比,AcAc的配位能力介于丁二酮和酒石酸、三乙醇胺等强配体之间,其适中的配位能力兼顾了制备过程中抑制钛快速水解和吸附过程中新活性位点的快速释放特性.当AcAc中心碳或端基碳被甲基取代后,烯醇式AcAc的含量以及配位能力降低,进而减弱材料的砷锑吸附性能.

Determination of specific surfaces of silica xerogels by SAXS

Small angle X-ray scattering (SAXS) with synchrotron radiation as X-ray source has been used to study the structure of silica xerogels prepared by sol-gel process. Both the agreement of SAXS profiles with and the deviation from Porod’s law and Debye’s theory have been found, showing that there are differences between the structures of these xerogels. The specific surfaces of the samples whose SAXS profiles agreed with Porod’s law and Debye’s theory have been determined by analyzing SAXS data according to the methods of Porod and Debye, respectively, and the results of both methods used were found to be similar. We have proposed the corresponding Porod and Debye analysis methods to determine the specific surfaces of samples whose SAXS profiles do not agree with Porod’s law and Debye’s theory, i.e. the negative or positive deviation. The results of both methods used here were also found to be close to each other. The specific surfaces fell between approximately 80-150 m2/cm3 for the samples prepared

Carbon Xerogel-supported Iron as a Catalyst in Combustion Synthesis of Carbon Fibrous Nanostructures

The catalytically assisted self-propagating high-temperature synthesis of carbon fibrous nanostructures, where the iron-doped colloidal carbon xerogel is proposed as a catalyst system, was examined. The carbon xerogel was prepared through carbonization of an iron doped organic xerogel at temperatures ranging from 600 to 1050℃. The reaction between calcium carbide and hexachloroethane in the presence of sodium azide is exothermic enough to proceed at a high temperature, self-sustaining regime. The combustion reactions of those mixtures enriched with iron-doped carbon xerogels were conducted in a stainless steel reactor---calorimetric bomb under an initial pressure of 1 MPa of argon. Scanning electron microscopy analysis of the combustion products revealed low yield of various type of carbon fibers （presumably nanotubes）, which grew via the tip-growth mechanism. The fibrous nanostructures were found in the vicinity of the spot of ignition, while in the outer and cooler area of the reactor, dusty products with soot-like morphology dominated. No significant correlation between the pyrolysis temperature of the carbon xerogel and the morphology of the obtained carbon fibrous nanostructures was observed.

A functional approach toward xerogel immobilization for encapsulation biocompatibility of Rhizobium toward biosensor

Sol-gel derived silica has tremendous applications as a biocompatible scaffold for the immobilization of cells. The use of xerogel as a matrix in the blueprint of biosensors is an appealing proposition due to several inimitable characteristics of xerogels, primarily because of their high porous nature, amendable pore size, and exceptionally large internal surface area. Morphological （X-Ray Diffraction and Thermogravimmetric Analysis） and optical （Fourier Transform Infrared and UV-Vis absorption） studies of the silica matrices with entrapped Rhizobial （Rz） structure of the biomaterial has been made. Temporal and concentration dependent studies were conducted for impregnated samples; it showed that the response time for the new biosensor for determining the concentration of Rz is less than 20 min. In this work, first time a novel avenue to create a generic approach for the fabrication of biosensor has been created.