Effect of Synthesis Time and Treatment on Porosity of Mesoporous Silica Materials

Nitrogen adsorption at 77 K on mesoporous silica materials (MPS) with varying synthesis time and treatment conditions was investigated. Scanning electron microscope (SEM) and X-ray diffraction (XRD) were also used to characterize the mesoporous materials. This study was performed at 6, 24 and 72-h synthesis times. It is shown that 6-h is not enough for complete formation of the MPS material and at least 24-h is necessary. The pore structure starts decaying for the 72-h synthesis time. The three-after-synthesis treatment conditions used were 1) washed, 2) washed and calcined and 3) directly calcined after synthesis. Ethanol/HCl mixtures were used for washing and calcinations were performed at 550°C. Among these samples, directly washed sample yields the lowest adsorption capacity while washed and calcined sample yields the highest adsorption capacity. Hence, it is concluded that washing stabilizes the structure before high temperature treatment

Effect of Synthesis Time and Treatment on Porosity of Mesoporous Silica Materials

Nitrogen adsorption at 77 K on mesoporous silica materials (MPS) with varying synthesis time and treatment conditions was investigated. Scanning electron microscope (SEM) and X-ray diffraction (XRD) were also used to characterize the mesoporous materials. This study was performed at 6, 24 and 72-h synthesis times. It is shown that 6-h is not enough for complete formation of the MPS material and at least 24-h is necessary. The pore structure starts decaying for the 72-h synthesis time. The three-after-synthesis treatment conditions used were 1) washed, 2) washed and calcined and 3) directly calcined after synthesis. Ethanol/HCl mixtures were used for washing and calcinations were performed at 550°C. Among these samples, directly washed sample yields the lowest adsorption capacity while washed and calcined sample yields the highest adsorption capacity. Hence, it is concluded that washing stabilizes the structure before high temperature treatment

IN-SITU GROWTH OF POROUS ALUMINO-SILICATES AND FABRICATION OF NANO-POROUS MEMBRANES

Feasibility of depositing continuous films of nano-porous alumino-silicates, primarily zeolites and MCM-41, on metallic and non-metallic substrates was examined with an aim to develop membranes for separation of gaseous mixtures and also for application as hydrogen storage material. Mesoporous silica was deposited in-side the pores of these nano-porous disks with an aim to develop membranes for selective separations. Our study involves supported zeolite film growth on substrates using in-situ hydrothermal synthesis. Faujasite, Silicalite and Mesoporous silica have been grown on various metallic and non-metallic supports. Metallic substrates used for film growth included anodized titanium, sodium hydroxide treated Titanium, Anodized aluminum, and sintered copper. A non-metallic substrate used was nano-porous aluminum oxide. Zeolite film growth was characterized using Scanning Electron Microscope (AMRAY 1820) and High Resolution Transmission electron microscope. Silicalite was found to grow uniformly on all the substrates to form a uniform and closely packed film. Faujasite tends to grow in the form of individual particles which do not inter-grow like silicalite to form a continuous film. Mesoporous silica was found to grow uniformly on anodized aluminum compared to growth on sintered copper and anodized titanium. Mesoporous silica growth on Anodisc® was found to cover more than half the surface of the substrate. Commercially obtained Anodisc® was found to have cylindrical channels of the pore branching into each other and since we needed pore channels of uniform dimension for Mesoporous silica growth, we have fabricated nano-porous alumina with uniform pore channels. Nano-porous alumina membranes containing uniform distribution of through thickness cylindrical pore channels were fabricated using anodization of aluminum disks. Free-standing nano-porous alumina membranes were used as templates for electro-deposition in order to fabricate nickel and palladium nano-wire mesh with large surface area to volu

In-Situ Growth of Zeolites and Mesoporous Silica on Metal Substrates

Hydrogen economy in the forthcoming years demands a need to find viable methods for on-board storage of hydrogen for transportation purposes. Our study is aimed at developing sub-nanostructured metal grids for hydrogen absorption in storage applications. Metal phase will be grown into a zeolite mold which is uniformly grown on the cathode by in- situ hydrothermal synthesis of zeolites. The various parameters involved in modeling in-situ hydrothermal synthesis of zeolite are Al/Si ratio, synthesis reaction chemistry, time-temperature combination for the synthesis and the substrate used for zeolite deposition. Various zeolites synthesized for developing a zeolite layer were faujasite, mesoporous silica and silicalite. Crystal morphology changed with change in concentration of the reaction chemistry. The aspect ratio of silicalite crystals increased by two-fold and the crystal size decreased five fold length and ten fold in width with a four-fold decrease in the reaction chemistry. Time of synthesis also affected change in the zeolite phase, for instance Zeolite-X going to Zeolite-P for longer synthesis times. Choice of the substrate and its surface morphology also affects the growth of the zeolite layer. Micro-scale roughening of the metal surface serves as nucleation sites during zeolite synthesis and thus provides better adhesion between the metal and zeolite film. For this reason, sintered copper surface with particle size in the range 50 microns - 75 microns were employed as the substrate. Hydrothermal faujasite synthesis is performed to control morphology for better adhesion to the cathode. Physical characterization techniques include SEM, AFM, HRTEM and XRD. The technical approach involves, coating a cathode with zeolites to act as template