RESUMO
Aromatic hydrocarbons are extensive environmental pollutants occurring in both water and air media, and their removal is a priority effort for a healthy environment. The use of adsorbents is among the several strategies used for the remediation of these compounds. In this paper, we aim the synthesis of an amphiphilic hydrogel with the potential for the simultaneous sorption of a set of monocyclic and polycyclic aromatic hydrocarbons associated with toxicity effects in humans. Thus, we start by the synthesis of a copolymer-based in chitosan and ß-cyclodextrin previously functionalized with the maleic anhydride. The presence of ß-cyclodextrin will confer the ability to interact with hydrophobic compounds. The resulting material is posteriorly incorporated in a cryogel of poly(vinyl alcohol) matrix. We aim to improve the amphiphilic ability of the hydrogel matrix. The obtained hydrogel was characterized by swelling water kinetics, thermogravimetric analysis, rheological measurements, and scanning electron microscopy. The sorption of aromatic hydrocarbons onto the gel is characterized by pseudo-first-order kinetics and Henry isotherm, suggesting a physisorption mechanism. The results show that the presence of maleic anhydride-ß-cyclodextrin and chitosan into hydrogels leads to an increase in the removal efficiency of the aromatic compounds. Additionally, the capacity of this hydrogel for removing these pollutants from a fossil fuel sample has also been tested.
RESUMO
Petroleum comprises the monoaromatic and polycyclic aromatic hydrocarbons, which exhibit acute toxicity towards living animals. Consequently, their removal from natural environment is a priority challenge. On the other hand, biomaterials are increasingly being used as adsorbents. Pectin and chitosan are well-known polysaccharides able to form coacervate hydrogels. Aiming an increase of sorption ability by hydrophobic compounds, pectin was also functionalized with two amphiphilic compounds: ß-cyclodextrin (ß-CD) and poly(vinyl alcohol) (PVA). Both the modified pectin and the hydrogels were evaluated using nuclear magnetic resonance (NMR), infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The hydrogels were further characterized in terms of thermogravimetric analysis (TGA) and swelling kinetics. The interaction between the hydrogel and mix solutions containing six different aromatic compounds (BTXs and the following PAHs: pyrene, benzo(b)fluoranthene and benzo(a)pyrene) has been evaluated through sorption isotherms and kinetics. The mechanism of sorption interaction and the selectivity of the adsorbents towards different aromatic compounds were discussed. The results clearly show that the presence of ß-CD and PVA into gel leads to an increase in the removal efficiency of both, BTXs and PAHs. The gels were subjected to two sorption/desorption cycles to have an assessment of the capability of adsorbents for re-use. Finally, the sorption quantification of those six aromatic compounds from a real gasoline sample onto gels has been tested.
RESUMO
The release of DNA from cryogel PVA-DNA gel matrices to different electrolyte aqueous solutions was investigated. The rate of release and the distribution coefficient of DNA have been quantified by using a first order kinetic law equation, developed in the frame of a partition-based model. The release of DNA from gels to 1:1 sodium and nitrate salts shows that the transport properties are dependent on the ability of anions/cations to solubilise the DNA in the aqueous phase which, with the exception of bromide, can be related to the Hofmeister series; in the presence of multivalent electrolytes, or increasing the ionic strength, the condensation of DNA inside the gel, followed by a phase separation as seen by scanning electron microscopy, induces the retention of DNA inside the polymer matrix. The DNA condensation and/or phase separation, which contribute to a decrease in the water volume fraction inside the gel, determined by swelling degree experiments, also lead to a decrease in the rate constant of DNA release; such decrease can be justified by the difficulty of the molecular aggregate to move through out the polymeric structure. The DNA release is also dependent on the pH of the bulk solution. The effect of uni- and di-valent cationic surfactants on the release properties of DNA was also evaluated. Our findings suggest that the kinetics of DNA release depends on a complex balance between different structural properties of the surfactants, namely charge, bulkiness of the headgroup and alkyl chain length.
