Navegando por Autor "Abreu, Christian Silva"

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Aqueous three-phase systems formed by poly(vinylpyrrolidone) + poly(ethyleneglycol) + lithium sulfate + water : phase behavior and partition data.
(2022) Abreu, Christian Silva; Neves, Dilaine Suellen Caires; Gomes, Vinícius Azevedo; Mageste, Aparecida Barbosa; Rodrigues, Guilherme Dias; Lemos, Leandro Rodrigues de
Aqueous three-phase systems (A3PSs) have been used to extract and separate several strategic analytes; however, there are several gaps in the characterization and theoretical principles of this technique. Therefore, an A3PS made up of 10,000 g‧mol−1 of polyvinylpyrrolidone (PVP), 10,000 g‧mol−1 of polyethylene glycol (PEG), lithium sulfate (Li2SO4), and water was characterized in this study. The results revealed that PEG, PVP, and Li2SO4 were concentrated in the top, middle, and bottom phases, respectively, whereas water was the main component in all phases. The three-dimensional coordinates of the phase composition points generated a plane with an area that increased as the difference in the phase compositions increased. The tie-plane area (TPA) decreased as the global composition and temperature decreased, indicating a strong temperature effect. Moreover, at relatively low overall concentrations, a phase inversion behavior between the electrolyte-rich phase and the PVP-rich phase was observed at 308.15 K. HE-4R dye molecules preferentially partitioned to the PVP-rich phase, and this trend increased as the TPA and temperature increased. A similar partition behavior was observed for Cu(II) ions, but they preferred to concentrate in the salt-rich phase. At relatively low overall concentrations, the Cu(II) ions promoted phase inversion at 298.15 K, a phenomenon similar to that observed in the temperature study. Thus, the phase diagram for a new A3PS was obtained, and as far as we know, this is the first work that quantitatively describes the TPA.
Aqueous two-phase systems formed by different phase-forming components : equilibrium diagrams and dye partitioning study.
(2020) Silva, Keycianne da Cruz; Abreu, Christian Silva; Vieira, Alício Wagner; Mageste, Aparecida Barbosa; Rodrigues, Guilherme Dias; Lemos, Leandro Rodrigues de
The present work aimed to characterize new aqueous two-phase system (ATPS) formed by Triton X-100 þ Li2SO4 þ H2O, polyvinylpyrrolidone Mw ¼ 10,000 g mol -1 (PVP10k) þ Li2SO4 þ H2O, and Triton X-100 þ PVP10k þ H2O, evaluating the effect of temperature and the nature of ATPS-forming components on the biphasic region. ATPSs formed by Li2SO4 showed greater efficiency in phase segregation compared to ATPSs formed by polymer/surfactant, with the biphasic area of ATPSs formed by Triton X-100 greater than that formed by PVP10k. For all ATPSs studied, temperature had a small effect on the biphasic region. The data were fitted with good correlation using the Merchuk equation for the binodal curves and OthmereTobias and Bancroft equations for the tie-lines. The partitioning studies show that there is an uneven distribution of Reactive Yellow HE-4R dye between the phases for all ATPSs and, with a tie-line length increase, there is an increase in the tendency of the dye to partition to the phase in which it interacts most strongly. For ATPSs formed by Li2SO4, the dye is preferentially transferred to the macromolecule-rich phase (top phase), whereas for the system formed by polymer/surfactant, the dye is partitioned to the PVP10k enriched phase (bottom phase). The present work aimed to characterize new aqueous two-phase system (ATPS) formed by Triton X -100 þ Li2SO4 þ H2O, polyvinylpyrrolidone Mw ¼ 10,000 g mol 1 (PVP10k) þ Li2SO4 þ H2O, and Triton X 100 þ PVP10k þ H2O, evaluating the effect of temperature and the nature of ATPS-forming components on the biphasic region. ATPSs formed by Li2SO4 showed greater efficiency in phase segregation compared to ATPSs formed by polymer/surfactant, with the biphasic area of ATPSs formed by Triton X-100 greater than that formed by PVP10k. For all ATPSs studied, temperature had a small effect on the biphasic region. The data were fitted with good correlation using the Merchuk equation for the binodal curves and OthmereTobias and Bancroft equations for the tie-lines. The partitioning studies show that there is an uneven distribution of Reactive Yellow HE-4R dye between the phases for all ATPSs and, with a tie-line length increase, there is an increase in the tendency of the dye to partition to the phase in which it interacts most strongly. For ATPSs formed by Li2SO4, the dye is preferentially transferred to the macromolecule-rich phase (top phase), whereas for the system formed by polymer/surfactant, the dye is partitioned to the PVP10k enriched phase (bottom phase).
Selective separation of Cu, Ni and Ag from printed circuit board waste using an environmentally safe technique.
(2018) Souza, Wagner Barbosa de; Abreu, Christian Silva; Rodrigues, Guilherme Dias; Mageste, Aparecida Barbosa; Lemos, Leandro Rodrigues de
Printed circuit boards (PCBs) make up a large part of e-waste and include high concentrations of high-value metals. Therefore, the recovery of these metals is interesting from both the environmental and economic points of view. Here, the extraction/separation of copper, nickel and silver from PCB leachate was studied using an aqueous two-phase system (ATPS) formed by triblock copolymers with an electrolyte and water, which is in compliance with the principles of green chemistry. The best conditions for the selective extraction consisted of 1-(2-pyridylazo)-2-naphthol (3.5 mmol kg−1) at pH = 6.0 in 6 sequential steps for the Cu(II), dimethylglyoxime (5.00 mmol kg−1) at pH = 9.0 for the Ni(II) and thiocyanate (5.20 mmol kg−1) at pH = 9.0 for the Ag(I). These conditions were applied sequentially for extraction of Cu, Ni and Ag from the PCB leachate, obtaining high separation factor (S) values between the analyte and the metallic concomitants (SCu,Ni = 1,460, SCu,Fe = 15,500, SCu,Ag = 15,900, SNi,Fe = 32,700, SNi,Ag = 34,700 and SAg,Fe = 4800). The maximum extraction percentages (%E) for Cu, Ni and Ag were 99.9%, 99.9% and 99.8%, respectively. After the extraction, a single step stripping process was performed, resulting in more than 82% of the ion available in a clean lower phase. For the first time, an ATPS has been used for sequential extraction of several metal analytes from a real sample.
Thermodynamics investigation of partition behavior of uric acid in aqueous two-phase systems.
(2020) Gonçalves, Laryssa Fernanda da Silva; Abreu, Christian Silva; Silva, Keycianne da Cruz; Mageste, Aparecida Barbosa; Rodrigues, Guilherme Dias; Santos, Wallans Torres Pio dos; Lemos, Leandro Rodrigues de
Uric acid (UA) is an important component in biological matrices, and the development of new methods for extracting/separating UA from several complex matrices is necessary. A viable alternative is the use of an aqueous two phase system (ATPS), which is an environmentally safe and efficient technique. In this work, an extensive study of the thermodynamic approach of UA partitioning was carried out in an ATPS formed with a polymer, sulfate salts, and water. Initially, the new ATPS formed with polyethylene glycol (400 g mol−1 ), lithium sulfate, and water was characterized by obtaining the position of the binodal curves and the phase compositions. The components’ segregation increases with the increase in the concentration of the polymer and salt where the top phase (TP) becomes richer in polymer and poorer in electrolyte, and the bottom phase has the inverse behavior. In the range of the pH studied, pH 2.40, 5.40, and 6.60 showed no effect on the binodal curve position and phase compositions, while the temperature (288.15, 298.15, and 308.15 K) evaluation indicated that the phase separation process was entropically driven. Afterward, a study of UA partitioning was carried out in several ATPSs, evaluating the effect of system composition, pH, temperature, and ATPS-forming components on the partition coefficient (K) of the UA. The K values ranged from 1.03 ± 0.04 to 6.05 ± 0.25, indicating a partition preference for the TP for all tie-line length (TLL) values. Furthermore, it is noted that the increase in TLL caused an increase in K, which decreases with increasing the temperature; that is, the partition of uric acid is temperature-dependent, and the phase transfer process of the UA is exothermic. The pH effect study showed that the ionized form of UA has a greater interaction with the components of the TP than that of the molecular form because the K value at pH 6.60 (K = 7.59 ± 0.23) is higher than at pH 2.40 (K = 1.98 ± 0.21), while at pH 5.40 (K = 3.84 ± 0.13), the value is intermediate. This behavior is due to the strong electrostatic interaction between the pseudopolycation, formed by Li+ ions plus polyethylene glycol in TP and the ionized form of UA. Finally, higher K values were obtained for the system formed with polyethylene glycol (400 g mol−1 ), lithium sulfate, and water. Thus, the balance of interactions between the system components and UA is the driving force that will drive the partition in the ATPS.