Sorption of phenolics by framework materials containing β-cyclodextrin
Danquah, Michael Kojo
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This MSc thesis research is divided into two projects; (1) synthesis and characterization of non-porous Templated (T-) and Non-Templated (NT-) β-Cyclodextrin-Epichlorohydrin polymers to yield globular and linear sorbents for the sorption of para-nitrophenol (PNP) and trinitrophenol (TNP) and phenolphthalein (Phth); and (2) synthesis and characterization of porous framework polymer and fluorescent-based porous framework polymers for sorption of PNP, TNP and Phth and the detection of TNP (a nitroaromatic explosive compound) in aqueous solution. T- and NT- cross-linked materials containing β-cyclodextrin (β-CD) and epichlorohydrin (EPH) were prepared at variable β-CD: EPH ratios (1:15, 1:20, and 1:25) in the presence and absence of a molecular template (toluene). The structural characterization of the materials was carried out using spectroscopy (FT-IR, solids 13C NMR, and SEM) and thermogravimetric analysis (TGA). The adsorption properties were studied using phenolic dyes (TNP; 2,4,6-trinitrophenol and PNP; p-nitrophenol) as probes at equilibrium and kinetic conditions. The Sips model provided estimates of the monolayer adsorption capacity (Qm) for the T- and NT-polymers. The Qm value for T-polymer/TNP complex ranged from 0.0953 to 0.952 mmol/g, while the NT- materials had Qm values that ranged from 0.231 to 0.827 mmol/g. The Qm values for the T-polymer/ PNP systems ranged from 0.263 to 0.616 mmol/g, while the Qm values for the NT-polymer/ PNP systems were 0.234 to 0.399 mmol/g. T-polymers with greater EPH content had higher dye uptake over NT-polymers. The pseudo-second order (PSO) and pseudo-first order (PFO) kinetic models were used to evaluate the uptake properties of the polymer/phenolphthalein (phth) systems. The PSO model provided a satisfactory fit to the experimental results with a sorption capacity ranging from 40 to 60 mmol/g, whereas; estimates of the β-CD inclusion site accessibility of the polymer materials was variable (15-20 %). Porous framework polymers (PFP) containing binary components (β-CD-diisocyanate) and fluorescent-based polymer (FL-PFP) with a ternary composition polymer system (βCD- diisocyanate-tetrakis(4-hydroxyphenyl) ethene were synthesized. FT-IR spectroscopy, thermal gravimetric analysis (TGA) and solid-state 13 C NMR spectral measurements were used to confirm polymer structure. The determination of β-CD inclusion site accessibility using phenolphthalein showed that the PFP and FL-PFP had β-CD inclusion site accessibility values of 24% and 19% respectively. By comparison, nitrogen gas adsorption revealed that the surface area of the materials was estimated at 100 to 250 m2/g while carbon dioxide gas adsorption ranged from 5.5 to 20 m2/g. The uptake of TNP in aqueous solution (pH 4.5) was investigated with PFP and FL-PFP. PFP showed a greater uptake of TNP than FL-PFP with equilibrium TNP sorption capacities of 0.831 mmol/g and 0.341 mmol/g respectively. The dual-function of FL-PFP, the TNP detection and removal was exploited using quantum yield and lifetime measurements. FL-PFP showed a lifetime decay response to variable concentrations of TNP. The quantum yield of FL-PFP was estimated to be 0.399 and a detection limit of TNP at 50 nM signifying the sensitivity of FL-PFP. With the advantage of synthesis, high surface area, and high sensitivity, the β-CD-EPH and β-CD-PU polymers provide a promising candidate for the detection and removal of PNP and TNP from aqueous media.
DegreeMaster of Science (M.Sc.)
CommitteeEllis, Tom; Jones, Paul; Ward, Dale
Copyright DateDecember 2017
phenolics, β-Cyclodextrin, inclusion, interstitial