Poly(α-olefins) (PAOs) are nonvolatile and nontoxic liquid hydrocarbon oligomeric solvents with solubility properties similar to heptane. PAOs can be used in traditional liquid–liquid extractions, but handling difficulties arise due to the formation of emulsions. In this study, PAO432, a low viscosity PAO with a molar mass of 432 g/mol, is encapsulated in a polymer-based shell using a Pickering emulsion stabilized by graphene oxide nanosheets and interfacial polymerization. The capsules are spherical with a diameter of approximately 50 μm and are 70 wt % PAO432. We demonstrate that these capsules can remove different low molecular weight organic contaminants from water, specifically benzene, toluene, ethylbenzene, and p-xylene (BTEX). In suspension, capsules of PAO432 were able to remove 97% of benzene from a saturated water solution, and >93% removal was observed for all BTEX components. We also showed that passing a contaminated aqueous solution through a column packed with the capsules resulted in removal of the contaminant and collection of water as the eluent. Encapsulation of PAO thus removes the need for emulsification as with traditional liquid–liquid extractions, allows for a lower PAO432:water ratio to be used, and gives the opportunity to develop a continuous extraction system. The favorable properties also indicate that PAO432 capsules might be suitable for other applications, including removal of BTEX gases from air.
Encapsulation of ionic liquids (ILs) has been shown to be an effective technique to overcome slow mass transfer rates and handling difficulties that stem from the high viscosity of bulk ILs. These systems commonly rely on diffusion of small molecules through the encapsulating material (shell), into the IL core, and thus the composition of the shell impacts uptake performance. Herein, we report the impact of polymer shell composition on the uptake of the small molecule dye methyl red from water by encapsulated IL. Capsules with core of 1-hexyl-3-methylimidazolium bis(trifluorosulfonyl)imide ([Hmim][TFSI]) were prepared by interfacial polymerization in emulsions stabilized by graphene oxide (GO) nanosheets; the use of different diamines and diisocyanates gave capsule shells with polyureas that were all aliphatic, aliphatic/aromatic, and aliphatic/polar aprotic. These capsules were then added to aqueous solutions of methyl red at different pH values, and migration of the dye into the capsules was monitored by UV–vis spectroscopy, compared to the capsule shell alone. Regardless of the polymer identity, similar extents of dye uptake were observed (>90% at pH = 2), yet capsules with shells containing polyureas with polar aprotic linkages took longer to reach completion. These studies indicate that small changes in capsule shell composition can lead to different performance in small molecule uptake, giving insight into how to tailor shell composition for specific applications, such as solvent remediation and gas uptake.
While hydrocarbon solvents such as alkanes are ineffective in extraction of polar substances such as phenols from water, polymeric alkanes such as poly(α-olefin)s (PAOs) when modified with phase-anchored hydrogen bond-accepting polyisobutylene (PIB) additives can be designed so that these hydrocarbon solvent systems efficiently extract many phenols from water. Phenols such as bisphenol-A (BPA), 4-chlorophenol, 2,4-dichlorophenol, 2-naphthol, and alkyl- or aryl-substituted phenols are sequestered from water with >95% efficiency. For example, using a PIB oligomer with imidazole as a terminal group as an additive at a concentration of 0.1 M in a PAO that is a hydrogenated trimer of 1-decene (PAO432), >99% of the BPA present in an aqueous solution of deionized water containing 200 mg of BPA/L of water is extracted into the PAO phase. With PIB-imidazole in PAO432 at 0.6 or 1.0 M, an array of other chlorinated, brominated, and alkylated phenols, which were typically initially present between 200 and 500 mg/L water, were additionally extracted with >95% efficiency. Using 0.3 M PIB-imidazole in PAO432, other bisphenols such as phenolphthalein and fluorescein at concentrations of ca. 3 mg/L in water could be reduced to concentrations of <20 or 2 μg/L, respectively. While very polar phenols with methoxy, hydroxy, and amino substituents are less efficiently extracted, most of these phenols could ultimately be extracted and sequestered with >80% efficiency. PAO432/PIB-imidazole phases that contain sequestered phenol can be recycled by mixing the PAO phase with solid NaOH. This regenerates the starting PAO432/PIB-imidazole mixture. Recycling of these nonvolatile PAO solvent systems for at least five cycles is described. Substituted imidazoles bound to PIB were also shown to be similarly effective sequestering agents for phenols.
Covalent and noncovalent chemical methods that use oligomeric lipophilic agents to solubilize silica nanoparticles in heptane and poly(α-olefin) (EPAO) solvents are described. While only modest solubilization efficiencies are seen with an octadecyl group, a variety of terminally functionalized polyisobutylene (PIB) derivatives are more efficient. Both covalent and noncovalent chemistry was found to be effective. Covalent modification solubilized up to 34 wt% of silica nanoparticles (SiNPs) as stable solutions in heptane or PAOs.Noncovalent modification was however more effective, solubilizing up to 70% of SiNPs in heptane or PAOs. The most successful covalent approach used PIB oligomers containing terminal triethoxysilane groups to covalently modify SiNPs. Alternatively, SiNPs that were first functionalized with amine groups could be solubilized in heptane or PAOs with polyisobutylene containing sulfonic acid groups using acid-base chemistry. Studies of these and other solubilization chemistry was also carried out using fluorescent labels, studies that confirmed the gravimetric analyses of the heptane-solubilized SiNPs. Transmission electron microscopy of a PAO solution of these solutions showed that these SiNPs were present as small aggregates dispersed in the PAOs.
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