RESUMO
In this work, Raman spectroscopy and molecular dynamics simulations were used to elucidate key interactions between polyethylene glycol (PEG) and phosphoric acid (H3PO4) in aqueous two-phase systems for the extraction of phosphoric acid. Extensive molecular dynamics simulations were performed, and radial distribution functions as well as hydrogen bonds between PEG and other molecules were measured. Experimental data were used in combination with the slope method to infer PEG-H3PO4 interactions, and the interpretation is consistent with molecular simulation results. Based on our experimental and simulation results, we propose a solvation mechanism governed by hydrogen bonding interactions: at low concentrations of H3PO4 within the polymer-rich aqueous solution, entropy dominates and phosphoric acid molecules have weak interactions with PEG; as the concentration of phosphoric acid increases above a certain critical value, enthalpy dominates with PEG molecules interacting strongly with H3PO4 molecules via hydrogen bonds.
RESUMO
Supporting titanium oxide (TiO2) on polymeric membrane surfaces is a strategy to increase the photocatalytic activity of this material as well as to modify membrane surface with antifouling properties or to develop hybrid processes of water treatment. The chemical characteristics of the polymeric membrane surfaces are a determining factor in the correct impregnation of TiO2 particles. In this work, the titanium oxide was immobilized on polyvinylidene fluoride (PVDF) membrane surface by direct impregnation during the synthesis of the inorganic particles by sol-gel route. The PVDF membranes were previously modified by treatments based on an alkaline attack followed by acid treatment. The final TiO2-modified membranes were characterized by infrared and Raman spectroscopy, as well as by scanning electron microscopy. In addition, the changes on the surface characteristics were determined by contact angle measurements. Finally, the membranes were tested on the photocatalytic degradation of methyl orange (MO). The results obtained indicate that the basic/acid pretreatment allows the generation of active sites in the membrane and that when carrying out the synthesis of TiO2 on the membrane, it can be anchored stably on its surface and through the pores. The microscopies indicate that the structure of the membrane is not compromised by the pretreatment. The amount of TiO2 deposited on the membrane was of 0.1580 ± 0.01773 mg TiO2/cm2 membrane. With this amount of TiO2, a degradation percentage of 98.2% is achieved after 450 min; when the membrane is used for a second cycle, a degradation percentage of 82.0% is obtained, which remains constant for 3 subsequent cycles. This method, which uses the PVDF membrane as a support for TiO2 particles, represents a low-cost and easy-to-prepare insertion procedure, with good degradation percentages, which means that the membrane can be used for subsequent studies in filtration systems in the treatment of effluents from the textile industry.
