In Situ Monitoring of the Generation of Monodisperse Silica Particles during the Hydrolysis of Tetraethyl Orthosilicate with Piezoelectric Quartz Crystal Impedance Analyzer

The piezoelectric quartz crystal (PQC) impedance analyzer was used to monitor in situ the generation of monodisperse silica particles during the hydrolysis of tetraethyl orthosilicate (TEOS) and their adsorption onto an Au electrode in alcohol solutions containing water (6-15 mol/L) and ammonia (0 2-2 0 mol/L). The equivalent circuit parameters, the resonance frequencies and the half peak width values of the conductance spectra of the PQC resonance were obtained. The resonant frequency decreased notably while the motional resistance changed very slightly (within 1 Ω) during the hydrolysis reaction, suggesting that the mass effect do^minated the adsorption of generated monodisperse silica particles on the gold electrode in this system. Changes in f 0 indicated that the ammonia concentration affected the hydrolytic reaction obviously, and the influence of water concentration on the reaction was small while the water was significantly excessive. Kinetics of monodisperse silica particle adsorption occurring at the electrode|solution interface was analyzed using a first order reaction scheme. In addition, the electrolyte induced precipitation of the monodisperse silica particles was monitored and discussed. The mean size, the number of adsorbed particles per area and the converge of monodisperse silica particles were obtained from scanning electron microscope (SEM) observations.

Effect of Aluminum Source on Adsorption Performance of Lithium Orthosilicate Based Adsorbents from Kaolin Clay

A novel lithium orthosilicate based adsorbent doping with halloysite nanotubes(HNTs) was synthesized with Kaolin clay and SiO_2 by an impregnation-precipitation method.The samples were characterized by X-ray diffraction and scanning electron microscopy,nitrogen adsorption-desorption isotherm analysis and thermo-gravimetry,respectively.The results indicate that the reactivity of Li_4SiO_4 for CO_2 absorption can be enhanced by doping alumina.Different aluminum sources result in different degrees of the CO_2 adsorption performance.It is also found that the CO_2 capture amount of the adsorbent doping with Halloysite nanotubes is 15.25 wt.%at 560 ℃,which is better than that of the adsorbent doping with γ-Al_2O_3(i.e.,10.88 wt.%).

Sol-Gel Preparation of Zn2 SiO4 :Mn Phosphor Layers on Silica Spheres and Their Luminescent Properties

The synthesis and luminescence properties of Zn2 SiO4: Mn phosphor layers on spherical silica spheres, i.e.,a kind of core-shell complex phosphor, Zn2SiO4: Mn@ SiO2 were described.Firstly, monodisperse silica spheres were obtained via the Stober method by the hydrolysis of tetraethoxysilane(TEOS) Si ( OC2H5 ) 4 under base condition ( using NH4 OH as the catalyst).Secondly, the silica spheres were coated with a Zn2 SiO4: Mn phosphor layer by a Pechini solgel process.X-ray diffraction ( XRD), scanning electron microscope ( SEM), energy-dispersive X-ray spectrum ( EDS )and photoluminescence (PL) were employed to characterize the resulting complex phosphor.The results confirm that1000 ℃ annealed sample consists of crystalline Zn2SiO4: Mn shells and amorphous SiO2 cores.The phosphor show the green emission of Mn2+ at 521 nm corresponding 4T1 (4G) - 6 A1 (6S) transition, and the possible luminescence mechanism is proposed.

Synthesis and Luminescence Properties of Red Phosphors:Mn^(2+) Doped MgSiO_3 and Mg_2SiO_4 Prepared by Sol-Gel Method

Sol-gel method was utilized to synthesize two different series of red silicate phosphors:MgSiO3 and Mg2SiO4 powder samples doped with Mn2+, conducted the investigation of red long-lasting phosphor: MgSiO3:Eu2+, Dy3+, Mn2+. TGA curves of the gel precursor for two series depicted that the loss of residual organic groups and NO3 groups occurs below 450 ℃. According to the XRD patterns, the major diffraction peaks of the MgSiO3 and Mg2SiO4 series are consistent with a proto-enstatite structure (JCPDS No.11-0273) and a forsterite structure (JCPDS No.85-1364) respectively. With the excitation at 415 nm, the red emission band of Mn2+ ions is peaked at 661 nm for MgSiO3:1%(atom fraction) Mn2+ or 644 nm for Mg2SiO4:1%(atom fraction) Mn2+. Compared with Mg2SiO4:Mn2+ samples, MgSiO3:Mn2+ samples exhibit higher luminescence intensity and higher quenching concentration. In addition, the two series co-doped with Eu2+, Dy3+, Mn2+ were also prepared. Photo-luminescence and afterglow properties of the two co-doped series were analyzed, which show that MgSiO3:Eu2+, Dy3+, Mn2+ is more suitable for a red long-lasting phosphor.

Protein Mediated Silica Particles with pH Controlled Porosity and Morphology

Background: The silica leaching activity of some of the mystifying non-pathogenic BKH1 bacteria present in the cluster of hot springs (temperatures range 35°C - 80°C) at Bakreshwar (West Bengal, India, 23°52'48"N;87°22'40"N) has provided some significant advancements in the field of nanotechnology. The present investigation was designed to synthesis the silica particles using bioremediase protein at different pH conditions. Methods: A secretary bacterial protein bioremediase (UniProt Knowledgebase Accession Number P86277) isolated from a thermophilic non-pathogenic bacterium BKH1 (GenBank Accession No. FJ177512) has been used to synthesis the silica particles at different pH conditions (pH at 3.0, 5.0, 8.0, 10.0, and 12.0 respectively). The silica particles were synthesized by the action of bioremediase protein on Tetra-ethyl-orthosilicate (TEOS) under ambient condition. Morphological and compositional studies of the biosynthesized silica particles were characterized by Field emission scanning electron microscope (FE-SEM) equipped with Energy dispersive X-ray analyser (EDX). Results: The Fourier transformed infra-red (FTIR) spectroscopic analysis confirmed the nature as well as occurrence of several functional groups surrounded on the silica particles. The amorphous nature of the prepared silica particles was confirmed by X-ray diffractometer (XRD) study. The Zeta potential (ζ) study revealed the stability of silica particles in neutral pH environment. The Brunauer-Emmett-Teller (BET) surface area measurement confirmed the porosity variation in all biosynthesized silica particles prepared at different pH conditions. Raman spectra analytically depend on their respective specific surface (BET) area. Thermogravimetry tool was used to monitor the effects of the thermal treatment on the surface properties of all the samples. Conclusions: The method for the synthesis of silica particles at different pH condition using the protein bioremediase has a special implication as it is an environmentally benign, cost-effective and facile technique which may have conceivable application in chromatographic packing. In addition, controlling of size as well as porosity of the silica particles can be achievable by pH as an only variable.

High Performance of Fly Ash Derived Li ₄SiO₄-Based Sorbents for High Temperature CO₂Capture

It is urgent to develop excellent solid CO2 sorbents with higher sorption capacity, simpler synthetic process, better thermal stability and lower costs of synthesis in CO2 capture and storage technologies. In this work, a number of Li4SiO4-based sorbents synthesized by lithium carbonate with three different kinds of fly ashes in various molar ratios were developed. The results indicate that the Li2CO3:SiO2 mole ratio used in the sorbents synthesis significantly affects the CO2 absorption properties. The sorption capacity increased with the excess of Li2CO3 first and then decreased when the excessive quantity was beyond a certain amount. The experiments found that FA-Li4SiO4_0.6, CFA-Li4SiO4_0.4, HCl/CFA-Li4SiO4_0.3 presented the best sorption ability among these fly ash derived Li4SiO4 samples, and the corresponding weight gain was 28.2 wt%, 25.1 wt% and 32.5 wt%, respectively. The three sorbents with the optimal molar ratio were characterized using various morphological characterization techniques and evaluated by thermogravimetric analysis for their capacity to chemisorb CO2 at 450°C - 650°C, diluted CO2 (10%, 20%) and in presence of water vapor (12%). The adsorption curve of FA- Li4SiO4_0.6 at different temperatures was simulated with the Jander-Zhang model to explore the influence of carbon dioxide diffusion on adsorption reaction. Further experiments showed that the adsorbent had a good sorption capacity in a lower partial pressure of CO2 and the presence of steam enhanced the mobility of Li+. What’s more, FA-Li4SiO4_0.6, CFA-Li4SiO4_0.4 and HCl/CFA-Li4SiO4_0.3 particles showed satisfactory sorption capacity in fixed-bed reactor and excellent cyclic sorption stability during 10 sorption/ desorption cycles.

Large Redshifts in Emission and Excitation from Eu²⁺-Activated Sr₂SiO₄and Ba₂SiO₄Phosphors Induced by Controlling Eu²⁺Occupancy on the Basis on Crystal-Site Engineering

The photoluminescence properties of Eu2+-activated α’-Sr2SiO4 and α’-Ba2SiO4 with a high Eu2+ concentration were investigated. In the case of Sr2-xEuxSiO4, emission was shifted from 585 to 611 nm with increasing the total Eu2+ concentration (x) from 0.1 to 0.8. This trend was similar to that in Ba2-xEuxSiO4, where the emission was shifted from 513 to 545 nm. The large redshifts in both the excitation and emission spectra were discussed in terms of the Eu2+ occupancies on two kinds of M sites and their local structural changes (M: Sr and Ba).

Improvement of hydrogen isotope exchange reactions on Li_4SiO_4 ceramic pebble by catalytic metals

Li4SiO4 ceramic pebble is considered as a candidate tritium breeding material of Chinese Helium Cooled Solid Breeder Test Blanket Module （CH HCSB TBM） for the International Thermonuclear Experimental Reactor （ITER）. In this paper, LiaSiO4 ceramic pebbles deposited with catalytic metals, including Pt, Pd, Ru and Ir, were prepared by wet impregnation method. The metal particles on Li4SiO4 pebble exhibit a good promotion of hydrogen isotope exchange reactions in H2-D20 gas system, with conversion equilibrium temperature reduction of 200-300 ~C. The out-of-pile tritium release experiments were performed using 1.0 wt% Pt/Li4SiO4 and Li4SiO4 pebbles irradiated in a thermal neutron reactor. The thermal desorption spectroscopy shows that Pt was effective to increase the tritium release rate at lower temperatures, and the ratio of tritium molecule （HT） to tritiated water （HTO） of 1.0 wt% Pt/LiaSiO4 was much more than that of Li4SiO4, which released mainly as HTO. Thus, catalytic metals deposited on LiaSiO4 pebble may help to accelerate the recovery of bred tritium particularly in low temperature region, and increase the tritium molecule form released from the tritium breedin~ materials.

Preparation of hydrophobic transparent paper via using polydimethylsiloxane as transparent agent

Transparent paper with good hydrophobicity and flexibility was expected to act as an alternative substrate in fabrication of flexible electronics.However,conventional paper made of cellulose fibers was opaque and hydrophilic without undergoing special processing.Herein,cellulose fiber paper was treated by impregnating with hydrolyzed tetraethyl orthosilicate(TEOS)followed by coating with hydrophobic polydimethylsiloxane(PDMS)to prepare hydrophobic transparent pa-per.The results showed that silica nanoparticles produced by the TEOS hydrolysis improved the paper transparency to some extent,increased the paper thermal stability,but still remained the hydrophilicity of paper.After the paper was further coated with the PDMS and the PDMS was consolidated,the paper became clearly transparent and hydrophobic.The processed paper had a transmittance of more than 90%at 550 nm.The water contact angle of the paper reached about 110°.This work provided a new approach for the fabrication of hydrophobic transparent paper with conventional cellulose fiber paper.

Effect of the addition of TEOS on the SiC fibers fabricated by electrospinning

Polycarbosilane(PCS)has been widely used to fabricate silicon carbide(SiC)fibers via pyrolysis.In this paper,for improving the morphology of SiC fibers,tetraethyl orthosilicate(TEOS,m=1 g,3 g and 5 g,respectively)was added into the PCS precursor solution(containing 1.5 g PCS).The continuous fibers have been prepared by electrospinning,and then the SiC fibers were synthesized by calcination at 1300℃,1400℃and 1600℃for 4 h respectively with a heating rate of 10℃/min in flowing nitrogen(N_(2)).The morphologies of the fibers were investigated by the scanning electron microscope(SEM)and it could be seen that the crystallinity of the SiC fibers was lower,the length of the SiC fibers was increased,and the diameter was uniform with the increase of the addition amount of TEOS.