Benefits of Electronic Wiring and Spacers on Lithium Storage in Nanostructured Lithium-Ion Battery Anodes

The demand for high power density lithium-ion batteries (LIBs) for diverse applications ranging from mobile electronics to electric vehicles have resulted in an upsurge in the development of nanostructured electrode materials worldwide. Graphite has been the anode of choice in commercial LiBs. Due to several detrimental electrochemical and environmental issues, efforts are now on to develop alternative non-carbonaceous anodes which are safe, nontoxic and cost effective and at the same time exhibit high lithium storage capacity and rate capability. Titania (TiO2) and tin (Sn) based systems have gained much attention as alternative anode materials. Nanostructuring of TiO2 and SnO2 have resulted in enhancement of structural stability and electrochemical performances. Additionally, electronic wiring of mesoporous materials using carbon also effectively enhanced electronic conductivity of mesoporous electrode materials. We discuss in this article the beneficial influence of structural spacers and electronic wiring in anatase titania (TiO2) and tin dioxide (SnO2).

Diffusion of pentane isomers in faujasite-type zeolites : NMR and molecular dynamics study

Diffusion of pentane isomers in zeolites NaX has been investigated using pulsed field gradient nuclear magnetic resonance (PFG-NMR) and molecular dynamics (MD) techniques respectively. Temperature and concentration dependence of diffusivities have been studied. The diffusivities obtained from NMR are roughly an order of magnitude smaller than those obtained from MD. The dependence of diffusivity on loading at high temperatures exhibits a type I behavior according to the classification of Karger and Pfeifer 1]. NMR diffusivities of the isomers exhibit the order D(n-pentane) > D(isopentane) > D(neopentane). The results from MD suggest that the diffusivities of the isomers follow the order D(n-pentane) < D(isopentane) < D(neopentane). The activation energies from NMR show E-a(n-pentane) < E-a(isopentane) < E-a(neopentane) whereas those from MD suggest the order E-a(n-pentane) > (isopentane) > E-a(neopentane). The latter follows the predictions of levitation effect whereas those of NMR appears to be due to the presence of defects in the zeolite crystals. The differences between diffusivities estimated by NMR and MD are attributed to the longer time and length scales sampled by the NMR technique, as compared to MD. (C) 2012 Elsevier Inc. All rights reserved.

Controlled synthesis of tunable nanoporous carbons for gas storage and supercapacitor application

A simple methodology has been developed for the synthesis of functional nanoporous carbon (NPC) materials using a metal-organic framework (IRMOF-3) that can act as a template for external carbon precursor (viz, sucrose) and also a self-sacrificing carbon source. The resultant graphitic NPC samples (abbreviated as NPC-0, NPC-150, NPC-300, NPC-500 and NPC-1000 based on sucrose loading) obtained through loading different amounts of sucrose exhibit tunable textural parameters. Among these, NPC-300 shows very high surface area (BET approximate to 3119 m(2)/g, Langmuir approximate to 4031 m(2)/g) with a large pore volume of 1.93 cm(3)/g. High degree of porosity coupled with polar surface functional groups, make NPC-300 remarkable candidate for the uptake of H-2 (2.54 wt% at 1 bar, and 5.1 wt% at 50 bar, 77 K) and CO2 (64 wt% at 1 bar, 195 K and 16.9 wt% at 30 bar, 298 K). As a working electrode in a supercapacitor cell, NPC-300 shows excellent reversible charge storage thus, demonstrating multifunctional usage of the carbon materials. (C) 2015 Elsevier Inc. All rights reserved.

Ag-doped hydroxyapatite as efficient adsorbent for removal of Congo red dye from aqueous solution: Synthesis, kinetic and equilibrium adsorption isotherm analysis

In the present study a versatile and efficient adsorbent with high adsorption capacity for adsorption of Congo red dye in aqueous solution at ambient temperature without adjusting any pH is presented over the Ag modified calcium hydroxyapatite (CaHAp). CaHAp and Ag-doped CaHAp materials were synthesized using facile aqueous precipitation method. The physico-chemical properties of the materials were determined by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Transmission electron microscopy (TEM), UV-Visible spectroscopy, N-2 physisorption and acidity was determined by n-butylamine titration and pyridine adsorption methods. XRD analysis confirmed all adsorbents exhibit hexagonal CaHAp structure with P6(3)/m space group. TEM analysis confirms the rod like morphology of the adsorbents and the average length of the rods were in the range of 40-45 nm. Pyridine adsorption results indicate increase in number of Lewis acid sites with Ag doping in CaHAp. Adsorption capacity of CaHAp was found increased with Ag content in the adsorbents. Ag (10): CaHAp adsorbent showed superior adsorption performance among all the adsorbents for various concentrations of Congo red (CR) dye in aqueous solutions. The amount of CR dye adsorbed on Ag (10): CaHAp was found to be 49.89-267.81 mg g(-1) for 50-300 ppm in aqueous solution. A good correlation between adsorption capacity and acidity of the adsorbents was observed. The adsorption kinetic data of adsorbents fitted well with pseudo second-order kinetic model with correlation coefficients ranged from 0.998 to 0.999. The equilibrium adsorption data was found to best fit to the Langmuir adsorption isotherm model. (C) 2015 Elsevier Inc. All rights reserved.

Argilas pilarizadas: uma tecnologia limpa na reação de isomerização do óxido de estireno

Neste trabalho, fracionou-se e tratou-se a argila Brasgel. Esta argila foi pilarizada em vários estágios de facionamento e/ou tratamento com 5 meq de Al / g de argila: (i) Al-PILC, a argila passou por todos os estágios de fracionamento e tratamento (ARG), (ii) Al-PILCFe, a argila não passou pela etapa de retirada de Fe livre (ARGFe) e (iii) Al-PILCFe/silte, a argila não passou pelas etapas de retirada de silte e Fe livre (ARGFE/silte). Em análise por DRX observou-se que as Al-PILCs apresentaram uma distância basal maior que as argilas de partida. A análise textural indicou que as argilas Al-PILCs e ARGs são materiais mesoporosos, com poros do tipo fenda estreita e do tipo fenda, respectivamente. Além disso, as Al-PILCs apresentaram área superficial razoavelmente maior que as ARGs correspondentes. Outras análises feitas nas argilas foram: teor de Si, Fe e Al; CTC; FTIR; TGA e TGD. As argilas Brasgel pilarizadas foram usadas como catalisador na reação de isomerização do óxido de estireno em hexano sob refluxo. A reação foi seletiva na formação de fenilacetaldeído. As argilas Al-PILCFe e Al-PILCFe/silte apresentaram melhor desempenho catalítico (100 % de conversão em 20 min de reação). Assim, as argilas Brasgel pilarizadas se apresentaram como uma Tecnologia Limpa na reação de isomerização do óxido de estireno ao fenilacetaldeído. Palavras-chave: Desenvolvimento Sustentável. Tecnologia Limpa. Química Verde. Argilas Pilarizadas. Isomerização de Epóxidos.

介孔材料的合成、性能以及应用

自从1992年美孚公司成功地研究开发出介孔材料M41S后，由于其具有不同寻常的结构特点-比较均一的孔径（2-50nm）而且连续可调、较高的比表面积、较大的孔体积、孔的长程有序性以及较好的热稳定性等，具有巨大的潜在应用价值，立即引起了全世界的关注。目前，世界各国的研究主要集中在研究介孔材料的特性、形成机理、介孔材料形貌、结构和孔径的控制、新一代介孔材料的研究开发、介孔材料的改性以及介孔材料的应用等方面。本论文主要在介孔材料的合成、性能以及应用方面开展了研究。选用头尾都是憎水的三嵌段共聚物为模板制备出具有三维无序虫状孔道的介孔材料和以有孔氧化铝膜为模板制备了形态可控的介孔材料，即具有介孔结构高有序纳米管。采用一步法合成了介孔Ag／silica和Y2O3：Eu／silica材料，采用基底受限法制备了银和Y2O3：Eu纳米粒子，同时研究了Ag／silic。作为催化剂时催化性能。（1）在酸性条件下，利用头尾都是憎水的三嵌段共聚物SBS为模板、TEOS为硅源，分别选用丁酮和甲苯作选择性溶剂，通过微乳技术制备出具有三维无序虫状孔道的介孔硅材料。我们通过在SBS胶束溶液中加入TEOS／水的油水混合乳液使SBS胶束与TEOS／水混合乳液之间形成一个界面，从而使TEOS这个界面上完全水解而且生成的小分子硅齐聚物包附在SBS胶束的外表面。经过加热则使TEOS凝聚同时形成具有介孔结构的SBS／硅材料。最后，通过锻烧以移除SBS，从而得到介孔硅材料。在选用甲苯作溶剂，研究发现随着SBS用量的增加或形成胶束温度的升高比表面积、孔体积和孔径等都相应减小。因此，这两个参数可以方便地调节介孔材料的孔径、表面积和孔体积等，进而更好地控制介孔材料的性能。所制备介孔材料的壁厚与SBS用量和形成胶束温度无关，且均超过IOnm，因而材料具有较好的热稳定性，这有利于其进一步在催化剂、吸附和分离等领域应用。（2）以有孔的氧化铝膜为模板制备了具有介孔结构高有序纳米管，即在加热条件下将P123一TEOS薄膜通过毛细力引入有孔的氧化铝膜孔内，同时根据优先润湿机理使P123一TEOS组分润湿氧化铝孔的内壁并同时伴随嵌段共聚物胶束的重排、TEOS组分的凝聚收缩，随后通过烧结手段除去嵌段共聚物、通过溶解手段除去氧化铝模板，这样便在硅基底上得到了形态可控的介孔材料即有序排列的具有介孔结构的纳米管。在一定时间范围内，退火时间对纳米管的形成和生长高度有一定的影响。纳米管垂直于硅基底且纳米管套内的介孔以六方形式排列在整个纳米管套同时介孔孔道相互平行，所制备的纳米管能保持受限在氧化铝模板时的尺寸而且稳定地粘附在硅基底上。（3）在酸性条件下，采用一步法即在模板剂（P123）形成胶束之后，加入硝酸银或氧化铺和氧化忆混合物同P123胶束形成新的复合体，随后加入硅源（TEOS）以包附在复合体的外表面，从而形成具有介孔相的复合物，通过热处理我们分别制备了高有序的具有二维六方结构的介孔Ag／silica和Y203：Eu／silica材料，其中金属银或YZO3：Eu纳米粒子分散在有序的介孔孔道内。二者的比表面积、孔体积和孔径分别为786m2／g、1．22cm3／g、6．Znm和791m2／g、0．95cm3／g、3．snm。另外，我们采用基底受限法，利用旋涂法分别使介孔Ag／silica和YZO3：E记silica材料分散在硅基底上，通过溶解法除去硅墙后便得到了没有聚集的且具有狭窄粒径分布的金属银（2．5-5．snm）和姚03：Eu（1．5-3．onm）纳米粒子。原子力显微镜（AFM）证实所得到的纳米粒子呈现良好的分散状态，具有狭窄的粒径分布而且粒子尺寸都小于其介孔材料孔径。（4）分别用一步法制备的介孔Ag／SBA－－15材料和金属银作为甲醇氧化制备甲醛反应的催化剂，利用甲醇转化率表示催化剂活性、甲醛和二氧化碳产率表示催化剂选择性来研究二者催化性能。由于具有高的比表面积（786扩／g）、较大的孔体积（1．22cm3／g）、较大的孔径（6．2nm）、狭窄的孔径分布和有序的介孔孔洞等特性，在反应温度473K-723K范围内，同本体银作催化剂相比尽管银仅占体系总重量的0．94wt％，介孔Ag／silic。材料却显示出极高的催化活性和催化选择性。