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Title: Synthesis, Characterization and Application of Silica based Hybrid Materials
Authors: Nasreen, Saima
Keywords: Natural Sciences
Environmental sciences
Issue Date: 2014
Publisher: Fatima Jinnah Women University, Rawalpindi December, 2014
Abstract: The development of new functionalized materials with increased performance is growing to meet the regulatory standards in response to public concerns for environment. This dissertation is an effort in this direction and describes the synthesis, characterization, and application of various functionalized silica hybrids keeping the perspective of recent technological advancements. The objective of present research is mostly driven by inadequate control of increasing concentration of toxic pollutants in environmental compartments. The synthesized functionalized hybrids are expected to find progressively their place as economical adsorbents. The direct method adopted for the synthesis of Mesoporous Silica and its functionalized hybrids offers advantage of providing uniform surface coverage and better control of the amount of incorporated organic moiety. The synthesized products are grouped as Mesoporous Silica (SBA- 15, MSU-H), Monodispersed ORMOSILS (VO, PO, MO), Functionalized Silica Hybrids (AS, GS, MS, VS, PS, AM, GM, MM, VM, PM), and Polysulfone Mixed Matrix Membranes (PM-15, PM-H, PM-VO, PM-PO, PM-MO). The resulting hybrid materials are thoroughly characterized to determine the surface and bulk properties and to develop understanding of intricate relationship of structural artifacts with its functionalities as adsorbents. The characteristics Si–O–Si stretching vibration bands at 1047cm-1 for Mesoporous Silica is identified on ATR-FTIR. The peculiar hexagons image is scanned under SEM. Further, the distribution of Si, O, and C element to locate the binding sites on fabricated membranes is clearly demonstrated through Mapping. The surface area of 521-580 m2/g is calculated by BET for Mesoporous Silica. The thermal stability is assessed by TG/DTA analysis. The synthesized Mesoporous Silica based hybrids were subjected to 13 C and 1H NMR studies and possible structure is deduced. The selection of novel adsorbents with multiple and diverse application range is a challenge. In the same spirit, the functionalized silica based hybrids are applied in batch mode for the removal of toxic species prevalent in air (N2, Polycyclic Aromatic Hydrocarbons-PAHs), soil and water (metal cations of Hg, As, Cr, Pb, and nitro-, amino-phenols). Each adsorbent demonstrates the removal efficiency for these pollutants. The qualitative performance scale of each adsorbent is characterized as Excellent for Chromium, Very good for Lead, Good for Arsenic and fairly good for Mercury. A general comparison of silica based hybrids as adsorbents for the removal of PAHs and Phenols highlight the different efficacy extent. Phenols are observed to take the lead by showing more adsorption than PAHs. Larger molecular weight and fused aromaticity likely appear as hindrances to better retention of selected PAHs. It is concluded that Mesoporous silica better retains the liquid pollutants (metals, phenols) attributed to its larger surface area. Desorption for SBA-15 and MSU-H follows Type IV and Type I hysteresis, respectively. It is reported here that –phenyl and –methacrylate substituted ORMOSILS (PO and MO) did not construct the breakthrough curve and deformed because of non-sustainability under the applied temperature-pressure conditions. It is generally concluded from the results that basic silica framework offers good adsorptive properties. Further, adsorption in functionalized hybrids is facilitated through binding sites provided by organic moiety. The present study, thus, proposes a decontamination model for pollutants ranging from metal cations to gases. The efficient removal with regeneration capacity offer direct compliance to 3R principles. That is to Reduce (pollutants), Reuse and Recycle (functionalized hybrids/membranes). It is expected that these materials will help to reduce the pollution load on the environment. The possibility for commercialization of mixed matrix membrane is also important output of this research. The application of these materials in existing industrial processes is another avenue to find niches for applications in advanced waste water treatment technologies with no comprise on improved industrial production and sustainable environment.
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