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- The ultrafiltration performance of cellulose acetate asymmetric membranes: a new perspective on the correlation with the infrared spectraPublication . Figueiredo, Ana Sofia; Garcia, Ana Rosa; Minhalma, Miguel; ILHARCO, LAURA; Pinho, Maria deIntegral asymmetric cellulose acetate (CA) membranes were casted by phase-inversion with formamide varying content - 22, 30 and 34% - as pore promoter. These membranes, CA-22, CA-30 and CA-34, were analyzed by infrared spectroscopy in attenuated total reflection mode (ATR-FTIR) to investigate the porous membrane matrix influence on the polymer/water/solute interactions and the selective ultrafiltration of salts. The membranes covered a wide range of hydraulic permeabilities, from 3.5 to 81.0 kg.m-2.h-1.bar-1, and of molecular weight cut-offs, from 4.17 to 31.43 kDa. The experimental apparent rejection coefficients of neutral solutes of increasing molecular weight are related to their intrinsic rejection coefficients through the film model. The surface average pore radius, estimated by an iterative algorithm, ranges from 2.1 to 4.5 nm. The tighter membrane, CA-22, displays experimental apparent rejection coefficients to the Na2SO4, CaSO4, MgSO4 of 50% or higher values and this is in contrast with the lower values, between 14 and 18%, to the NaCl, CaCl2 and MgCl2 salts. The ATR-FTIR evidences that in the membranes with larger pores, CA-30 and CA-34, the water molecules are organized with a liquid-water-like structure, in which most molecules are hydrogen bonded to four or to two others; nevertheless, a fraction of water molecules is strongly bonded to the CA carbonyl groups. For the CA-22 membrane, there are more free carbonyl groups and a larger fraction of free water, both able to interact with solutes, such as the hydrated sulphate ions. Therefore, this ultrafiltration membrane has the capability of differentiating anionic species.
- Recovery of phenolic compounds from red grape pomace extract through nanofiltration membranesPublication . Arboleda Mejia, Jaime A.; Ricci, Arianna; Figueiredo, Ana Sofia; Versari, Andrea; Cassano, Alfredo; Parpinello, Giuseppina P.; De Pinho, Maria NorbertaThe winemaking process generates a large amount of residues such as vine shots, stalks, grape pomace, and wine lees, which were only recently considered for exploitation of their valuable compounds. The purpose of this work was to investigate the performance of nanofiltration for the recovery of phenolic compounds, with bioactive capacity like antioxidant, from red grape pomace extract. Four membranes were compared in this study-three cellulose acetate (CA series: lab-prepared by phase inversion) and one commercial (NF90). All membranes were characterized for their hydraulic permeability and rejection coefficients to reference solutes like saccharose, glucose, raffinose, polyethylene glycol, sodium chloride, and sodium sulfate. Permeation flowrates and rejection coefficients towards total phenolics content, antioxidant activity, proanthocyanidins, glucose and fructose were measured in the nanofiltration of grape pomace extract using selected operating conditions. Among the investigated membranes, the CA400-22 exhibited the highest permeate flux (50.58 L/m(2) h at 20 bar and 25 degrees C), low fouling index (of about 23%), the lowest rejection coefficients towards the reference solutes and the best performance in terms of separation between sugars and phenolic compounds. Indeed, the observed rejections for glucose and fructose were 19% and 12%, respectively. On the other hand, total phenolics content and proanthocyanidins were rejected for 73% and 92%, respectively.
- The role of silver nanoparticles on mixed matrix Ag/Cellulose acetate asymmetric membranesPublication . Sonawane, Shirish H.; Terrien, Antonine; Figueiredo, Ana Sofia; Gonçalves, Maria Clara; De Pinho, Maria NorbertaMixed matrix asymmetric membranes were prepared by the addition of silver nanoparticles to cellulose acetate/acetone/formamide casting solutions with ratios acetone/formamide varying from 1.44 to 2.77 to prepare ultrafiltration/nanofiltration membranes covering a wide range of hydraulic permeabilities. Binding of the silver nanoparticles to the polymer matrix is revealed through comparison of the FTIR spectra of the cellulose acetate and the Ag/cellulose acetate membranes. In the later, there is a decrease of the ratio between the bands intensities at 2,000–2,500 cm 21. Membrane surface charge of the mixed matrix membranes varies with the pore size and pH,and when compared with cellulose acetate membranes there is a decrease of the negative surface charge densities. The silver nanoparticles in all mixed matrix membranes results in an enhancement of the hydraulic permeabilities, ranging from 10.8 kg m 22 h 21 bar 21 to 67.1 kg m 22 h 21 bar21. POLYM. COMPOS., 38:32–39, 2017. VC 2015 Society of Plastics Engineers.
- Synthesis and bactericide activity of nanofiltration composite membranes - Cellulose acetate/silver nanoparticles and cellulose acetate/silver ion exchanged zeolitesPublication . Beisl, Stefan; Monteiro, Silvia; Santos, Ricardo; Figueiredo, Ana Sofia; SANCHEZ-LOREDO, MARIA GUADALUPE; Lemos, Maria Amélia; Lemos, Francisco; Minhalma, Miguel; De Pinho, Maria NorbertaThe present work addresses the synthesis of nanofiltration composite membranes with bactericide properties. The cellulose acetate based membranes with polyvinylpyrrolidone coated silver nano particles, silver ion-exchanged beta-zeolite and beta-zeolite are casted by the phase inversion technique and subjected to an annealing post-treatment. They are characterized in terms of the nanofiltration permeation performance and antibacterial properties. The incorporation of silver nanoparticles produces a threefold increase in the membrane hydraulic permeability when compared to the silver-free membranes and the incorporation of silver ion loaded zeolite resulted in a 56.3% increase in hydraulic permeability. In contrast to the influence of silver presence, either in nanometric or in the ionic form, the presence of zeolite does not significantly influence the hydraulic permeability. The rejection coefficients to salts range from 83% to 93% for the silver ion-exchanged zeolite membrane and from 84% to 97% for the polyvinylpyrrolidone coated silver nanoparticles membrane. They are higher for sulfate salts than for chloride salts. The antibacterial properties of the membranes were evaluated against Escherichia coli. The results have shown that the silver ion-exchanged beta-zeolite membrane was effective in inactivating Escherichia coli after just 210 min of contact time. No bacterial activity was detected following 24 h of contact time with the membrane containing polyvinylpyrrolidone coated silver nanoparticles. A reduction of more than 6-log, in the number of Escherichia coli, was achieved for both membranes. The different patterns of bactericide activity are associated to the silver speciation in metallic or ionic form. The high flux nanofiltration composite membranes with bactericidal properties represent a strong asset in water treatment biofouling control.