Investigations On Synthesis Of Different Bridged Polysil Sesquioxane Ordered Mesoporous Materials And Adsorption Of Organic Pollutants With Benzene Ring

With the rapid development of modern industry, most of the industrialwastewater containing persistent organic pollutants (POPs) cause environmentalpollution, which harm human health. Therefore, POPs removal is a major challengein the world’s industrialized cities. The bridged silsesquioxane (BPS) mesoporousmaterials can adsorb POPs. Organic-inorganic hybrid materials were accomplishedby using an organic bridged triethyl [(R’O)3Si-R-Si(OR)3] as the organosilicaprecursor, sol-gel and alkyl chain surfactants as the template. surfactant wasremoved to yield highly order hexagonal and cubic mesoporous materials;Meanwhile, the hexagonal and cubic mesoporous materials were selected foradsorption and competitive adsorption experiments, which are expected in the fieldsof water treatment research and environment that have important theoretical valueand considerable potential applications.In this paper, a silsesquioxane was synthesized by the hydrolysis andpolycondensation of (EtO)3Si(CH2)3NHCONH(CH2)11CH3in tetrahydrofuran (THF)employing formic acid as catalyst. The silsesquioxane self-assembled into nanorodsdue to the strong H-bonds among urea groups and the tail-to-tail associations oforganic chains. The biuret BPS material was characterized by a variety ofexperimental techniques (FTIR,(29)Si NMR, XRD, TEM. HRTEM, and SAED). Acolloidal solution of the silsesquioxane in methanol was deposited on a carbon filmgenerating coffee ring structures with nanoparticles located at the boundary of rings.The result showed that the sample was ordered hexagonal mesopore that wasconfirmed by small angle X-ray scattering and transmission electron microscopy.Nitrogen adsorption analysis of the biuret BPS revealed their high surface area andmesopore.Three-dimensional cubic (Pm3n) periodic mesoporous bridged silsequioxane(BPS) with methylene, ethylene, hexylene, octylene, phenyl, and biphenyl-bridginggroup were synthesized using the five different types of silsequioxane precursors inthe presence of a Brij56(Polyethylene glycol Monocetyl ether, n=23) under acidiccondition. Three-dimensional cubic (Pm3n) periodic mesoporous BPS wassynthesized by condensation of1,6-bis(triethoxysilyl) hexane (BESH) in thepresence of hexadecyltrimethyl ammonium bromide (CTAB) andN-(3-trimethyl-ammoniumpropyl) hexadecyl ammonium dibromide (C16-3-1) underbasic conditions. The BPS mesoporous materials were characterized by a variety ofexperimental techniques (FTIR, small angle XRD, TGA,TEM.). Highly ordered3Dcubic (Pm3n) mesostructure was confirmed by small angle X-ray scattering and transmission electron microscopy. Nitrogen adsorption analysis of the methylene,ethylene, hexylene, octylene, phenyl, and biphenyl bridging samples revealed theirhigh surface area and accessible mesopores. The ageing duration, ageingtemperature, concentration of BESH, amount of water and amount of NaOH werevaried systematically in order to study their effects on the mesophase formed and onthe surface properties of the materials synthesized.Biuret, hexylene, octylene, phenyl and biphenyl BPS mesoporous materialswere selected for adsorption of pyrene, phenanthrene, nitrobenzene, and2,4-dichlorophenol (DCP). The adsorption properties were analyzed by a variety ofexperimental techniques (HPLC and UV-1750). Rigid aromatic BPS (phenyl andbiphenyl) showed higher sorption capacity than soft aliphatic BPS (biuret,hexylene and octylene). Hydrophobic interaction dominantly controlled organicpollutants’ sorption on BPS. Other interactions, e.g. π–π interactions, H-bondinteractions, also have effects on sorption as indicated by Kownormalized sorptionisotherms. Meanwhile, adsorption of pyrene, phenanthrene, nitrobenzene and DCPon BPS was greatly affected by adsorbate properties, i.e. Kow, solvation propertiesand molecular size.In this study, the pore blockage and site competition effect of hexylene BPS onphenanthrene,2,4-Dichlorophenol (DCP) and nitrobenzene adsorption isothermwere investigated. Hexylene BPS was tested to determine the roles of hexylene BPSpore size distribution and molecular weight distribution in the pore blockagemechanism. The adsorption properties were analysed by a variety of experimentaltechniques (HPLC and UV-1750). A decrease in phenanthrene, DCP andnitrobenzene removal was observed in a continuous sway hexylene BPS system afterallowing7days of contact. A hexylene BPS with a relatively large fraction ofmesopores was shown to suffer much less from the pore blockage effect comparedwith a hexylene BPS that had a much smaller fraction of mesopores. The hexyleneBPS with different organic pollutants molecular weight distribution caused differentextents of pore blockage. A conceptual model and formulae were proposed tofurther explain the observed phenomena.