Synthesis of cellulosic microsystems with magnetic inclusions

AURELIA CRISTINA NECHIFOR1, 2, DANUT-LUCIAN GHINDEANU2,

LACRAMIOARA NAFTANAILA2, ALINA CRISTEA2, EUGENIA EFTIMIE TOTU2

1National Institute for Microtechnologies IMT Bucharest, Str. Erou Iancu Nicolae nr. 126A, 077190 Bucharest

2Department of Analytical Chemistry and Environment Engineering University “Politehnica” of Bucharest 1 -5 Polizu Str., Sector 1, Bucharest

ROMANIA nechiforus@yahoo.com

Abstract – This paper presents a liquid membrane system containing magnetic particles and thio-calix[4]arene embedded in the pores of a cellulose membrane which was realized in two ways: a) the carrier dissolved in the solvent of the magnetic fluid and b) with the carrier bound to the magnetic particles from the magnetic fluid. The supported liquid membranes, cellulose - magnetic fluid type, presenting a high stability, could achieve a turbulent transport through the membrane system and could also manage the transportation based on optimal process parameters. Keywords: liquid membranes, magnetic fluid, cellulose support, ferrofluid.

1 Introduction The microporous membrane separators are ideal for processes whose determinant is the pressure gradient. These membranes can be successfully used in processes driven by the concentration gradient, by filling their pores with suitable liquid, thus obtaining supported or immobilized liquid membranes. Such membranes have two main disadvantages: instability (loss of the liquid from the pores of the supported membrane) and a low mass transfer (diffusion of the chemical species into liquid, which might be increased by stirring). The mentioned disadvantages have been overcome so far, because most research has been directed toward improving the interaction between the liquid membrane and the membrane's support pore size (diameter, length, shape) [1-8]. This study has focused on altering the characteristics of the liquid membrane, using ferrofluids for making liquid membranes on microporous cellulose support. A liquid with magnetic properties could be obtained by dispersing of magnetic particles into a suitable solvent. The colloidal solution with pronounced magnetic properties and

behavior of homogeneous and uniform fluid is known as magnetic fluid or ferrofluid. The stable magnetic fluids commonly contain 1020 particles/l [9-14]. The dispersed colloidal system with magnetic properties contains dispersed colloidal particles from 100 to 500 Å which are kept suspended by the Brownian motion. A magnetic fluid is non-magnetic in the absence of a magnetic field, but such fluid presents strong magnetic properties in its presence, free from hysteresis. The interaction of a magnetic fluid with a magnetic field imparts it a series of properties that have resulted in many practical applications. The most important applications are: an amount of magnetic fluid may be suspended in space by the action of a magnetic field; a permanent magnet can be stable levitated (self-suspended) in a magnetic liquid; specific gravity that the bodies acquire apparently varying depending on intensity of the magnetic field and the magnetization of the magnetic fluid; the possibility of flowing and conducting the magnetic flux; spontaneous formation of liquid drops of high stability in the presence of a magnetic field perpendicular on the liquid

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surface; rotating a magnetic fluid in a rotating magnetic field. The highlighted properties of ferrofluids justify their use to eliminate the disadvantages of supported liquid membranes. Although calix [n]arenes are macrocyclic compounds with limited specificity and selectivity and lower than the macrocyclic ethers, though these are of increasingly higher interest because they allow more opportunities for derivatization, are easy to be synthesized, are using available raw materials and therefore they are becoming the cheapest macrocyclic compounds. A step forward to improve calixarenes selectivity was the replacement of the p-methylene bridges from tert-butil calix [4] arene with sulfur atoms. Synthesis of this compound, p-tert-butil tio calix [4] arene, since 1993, had not yet the expected impact on studies of transport and separation through liquid membranes, probably due to deficiencies in the membrane systems that have been used p-tert-butil thio calix [4] arene obtained by direct reaction of phenol and p-tert-butyl phenol and sulfur. The membrane system, in which the thio calixarene was included as carrier is the liquid membrane on cellulosic support.

2 Experimental 2.1. Obtain the liquid membranes on

cellulosic support

a) Preparation of p-tert butyl thio calix [4]

arene A mixture of 64.5 g (0.43 mol) p-tert butyl phenol, 27.5 g (0.86 mol) elemental sulfur (S8) and an amount of 8.86 g (0.215 mol) NaOH dispersed in 19 mL of tetraethylene dimethyl ether is heated for 3 hours at 2300C under nitrogen purging and mechanical stirring. Meanwhile the hydrogen sulfide is removed by bubbling-drive with nitrogen. The dark reaction mixture is cooled to room temperature by adding a mixture of toluene and ether, then it turns into a dispersion by adding 0.5 M sulfuric acid solution. The crude product is separated by filtration and then recrystallized from chloroform, dried by vacuum heating (104oC, for 4 h) when it is obtained 30.3 g p-tert butil

thio calix [4] arene (η = 39%, against to p-phenol tert-butyl), colorless crystals, with melting point 3200C-3220C. b) Grafting procedure of p-tert butyl thio calix

[4] arene on magnetic nanoparticles The magnetic nanoparticles obtained by a variant of Massart method (which consists in co-precipitation of ferric and ferrous ions with a concentrated solution of potassium hydroxide) were coated with ω-10-amino acid (Merck) and functionalized with amino crown ethers (Merck) using cyanuril chloride (Aldrich) as spacer. The succession stages of synthesis is shown in Scheme 1, and the main morpho-structural features were studied by help of (HRSEM, EDAX, FTIR).

Scheme 1. Schematic representation of synthesis stages.

To obtain magnetic nanoparticles through the modified Massart method, ferric and ferrous salts are precipitated with concentrated potassium hydroxide, but the source of iron is quite particular. Thus, the ferric ion comes from ferri ammoniacal alum (double sulphate of iron

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(III) and ammonium) and the ferrous ion from Mohr's salt (sulphate of iron (II) and ammonium). In these conditions the precipitation occurs at a pH maintained constant by the couple NH3/NH4

+. Practically, 250 cm3 of 0.1 M Mohr's salt solution and 250 cm3 of solution of ferri ammonia alum are mixed in a 4L container with 1.5L of 1M potassium hydroxide solution, added in five equal portions. After four hours, the black suspension obtained is separated in a magnetic field, washed five times with 500 mL of deionized water. The magnetic nanoparticles obtained are dialyzed in a regenerated cellulose bag dialysis until in dialyser is obtained a pH = 9. Nanoparticles were washed three times with methanol, ethanol and then acetone, in portions of 300 mL. After concentrating in magnetic field, to remove the residual solvent, it starts the covering with ω-10-amino acid and then with cyanuril chloride. The cyanuril chloride grafting and binding are done in a colloid mill Retch ceramic bowl. There are introduced 50g magnetic nanoparticles and 5g ω-10-amino acid in 150 cm3 chloroform, then all are mixed. After four hours, in the tank are introduced 3g of cyanuril chloride and the grinding is continued for another four hours. The black dispersion obtained was washed with three portions of deionized water, 100 mL each, to remove the hydrochloric acid formed, then it is reintroduce in the Retch mill ceramic bowl with a quantity of 0.1 g p-terŃbutil tiocalix [4] arene and 1 mL of triethylamine for taking over the hydrochloric acid formed in the reaction. After 24 hours of grinding, the black suspension is washed five times with 50 mL deionized water. For characterization, a part of the dispersion is dried by vacuum evaporation of the solvent. The obtained nanoparticles were characterized by scanning electron microscopy (SEM), infrared spectroscopy (FTIR) and thermal analysis. c) Obtain the liquid membranes on cellulosic

support

The commercial cellulose membranes were activated for 48 hours with a 10% solution of zinc chloride, after which they were thoroughly washed three times with distilled water (10 hours standing in contact with distilled water in

a 10L wash tank), followed by drying in a vacuum oven at 1050C for 6 hours. The transport of ions through liquid membranes on cellulosic support considered three types of liquid membranes on cellulose support: - based on 10-5M thio-calix [4] arene in n-octoanol, immobilized by soaking, on a commercial cellulosic support enabled (MCS); - based on magnetic fluid with 10-5 M thio-calix [4] arene dissolved in n-octoanol, immobilized by soaking, on a commercial cellulosic support enabled(MCF1); - based on magnetic fluid with 10-5 M thio-calix [4] arene grafted onto magnetic nanoparticles in n-octoanol, immobilized by soaking, on a commercial cellulosic support enabled (MCF2). Liquid membrane preparation procedure consists is immersing for 24 hours the membrane cellulosic support in n-octanol solution with 10-5M thio-calix [4] arene for MCS, and in a suitable magnetic fluid on n-octanol basis for MCF1 and MCF2, respectively. The cellulosic substrate is presented as discs with a diameter of 90 mm and the immersion is achieved in Petri dishes of 100 mm diameter containing 25 cm3 liquid membranes.

3 Results and Discussions The nanoparticles obtained were characterized by scanning electron microscopy (SEM) - Fig. 1, EDAX - Fig. 2 and infrared spectroscopy (FTIR) - Fig. 3.

a.

b.

Fig.1. a. HRSEM images of nanoparticles. b. HRSEM images of magnetite functionalized with thio calix [4] arene.

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a.

b.

Fig. 2. EDAX analysis for magnetite nanoparticles (a) and magnetite functionalized with thio calix [4] arene (b)

4000,0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 550,0

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1817,85;93,49

1716,72;84,72

1660,07;88,89

1583,28;86,35

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1119,52;77,82

1083,97;79,27

1022,74;75,66

929,85;83,68

884,93;77,50

833,93;82,05

790,89;75,32

758,94;78,82

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1569,53;73,25

1498,14;88,84

1414,53;76,40

1277,33;92,00

988,82;67,42

782,77;82,90

b.

Fig. 3. FTIR spectra for magnetite nanoparticles (a) and magnetite functionalized with thio calix [4] arene (b). Magnetic fluid used in this paper is based on n-octanol and ferro ferric oxide containing magnetic particles with sizes of 10 - 15 nm (Fig. 4).

Fig. 4. Magnetic nanoparticles based on magnetite - HFSEM. The best results were obtained for the cellulosic membrane with magnetic inclusions based on n-octanol and magnetic nanoparticles grafted with thio calix [4] arene, as is presented in Fig.5.

Fig.5. Scheme of the ferrofluid with grafted particles (b). The symmetric cellulose membrane allows the solvent access or the ferrofluid in the cellulose membrane's macropores (Fig. 6) then, in the second case, it is immobilized by placing a magnet on the microporous surface where the macropores are closing.

Fig. 6. Cellulosic symetric membrane with ferrofluid inclusions (SEM).

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Distribution of elements (Fe) onto the microporous and macroporous surface (Fig. 7) obtained by EDAX shows that most of ferrofluid is found in the macropores of support membrane, and on the surface is forming a ferrofluid film which appears as a "blanket" of Fe nanoparticles at scanning electron microscopy and EDAX analysis. Of course, this observation is justified by the evaporating of the whole organic mass (n-octanol and carrier) during preparation of samples for SEM which is performed in vacuum.

Fig. 7. EDAX on ferrofluid cellulose composite membrane - active surface.

4 Conclusions The supported liquid membranes, magnetic fluid - cellulose type, have a high stability. Also, they could achieve a turbulent transport through the membrane system. In mean time, such membranes could manage the transportation through the process parameters as pH and rH. The use of thio calix [4] arene as carrier in composite liquid membrane, cellulose and magnetic fluid in n-octanol, allows the transport, the separation and the concentration of metallic ions. Acknowledgements

Authors recognize the financial support from the European Social Fund through project POSDRU/89/1.5/S/63700, 2010-2013, ‘Human Resource Development by Postdoctoral Research on Micro and Nanotechnologies’ (project which financed Aurelia Cristina Nechifor) and also through project POSDRU/107/1.5/S/76813.

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