Synthesis of zeolite-iron oxide Nanocomposite using covalent method coated with carboxymethyl cellulose film and evaluation of its mechanical and electrical properties

Introduction: In recent years, Nanoscale composites have been considered for excellent physical, mechanical and electrical properties, such as extensive flow, catalytic activity, and more. Super paramagnetic nanoparticles based on magnetite (Fe₃O₄) have exhibiting striking characteristics, such as large surface area, mobility, and high mass transference. More than that, they can be easily recovered by applying an external magnetic field. In this study, zeolite micro particles with large internal contact surfaces and iron oxide nanoparticles were linked to each other by covalent technique then both were coated via CMC (Carboxy Methyl Cellulose) with the mixed-matrix method. The most important features of zeolites are: regular and uniform pore system and high ion exchange capacity, a large surface area, non-toxic and safe for environment (Nabiyouni et al. 2015). CMC is natural polyanion that have the features such as the ability to provide good films and mechanical resistance and it is augmenter of electron transfer (Cheng et al. 2013; Cui et al. 2011). The produced nanocomposite was designed as a support for the chemical alpha-amylase immobilization, and the loading efficiency calculated by Bradford reagent and UV-visible spectrophotometer and immobilization efficiency by the Miller method (Starch hydrolysis and optical absorption measurement of maltose produced) were calculated. The mechanical and electrical properties of nanocomposite film were also studied by Four probes device.
Material and methods: A commercial enzyme α-amylase (from Aspergillus oryzae, 30 U/mg protein), sodium salt of CMC (high molecular weight), phenol and sodium potassium tartrate were obtained from Sigma-Aldrich. Fe₃O₄ nanoparticles were obtained from Nanosany Corporation (Mashhad, Iran). Na A- zeolite was obtained from Kimia Khatam knowledge-based Co. (Tabriz, Iran). 3-Aminopropyl-trimethoxysilane (95% purity) (APTMS), Glutaraldehyde (25% aqueous solution), soluble starch and 3,5-Dinitrosalicylic acid (DNS) were obtained from Merck Chemicals (Darmstadt, Germany), All other materials were commercially accessible and they was used without any purification. The bonding of zeolite and iron oxide was done by a trimethoxysilylpropylamine solution, which was used to modify and bond simultaneously iron-zeolite magnetic nanoparticles. The modification and actuation of zeolite surface were performed by Fe₃O₄ and APTMS as the silane-coupling agent, respectively. In brief, a zeolite with a particle size of 1 to 2 micrometers and magnetite nanoparticle (10: 1) was immersed in 20 ml of toluene solvent. Then the mixture was dispersed in toluene for 5 min using probe-type sonicator (70w, 0.5 Hz), followed by addition of 1ml APTMS solution to the mixture for bringing the amino groups on the surface of zeolite and Fe₃O₄ (Hosseinipour, Khiabani, Hamishehkar & Salehi, 2015). The mixture was refluxed at 110  for 3 h to induce the surface hydroxyl groups of zeolite. The synthesized iron-zeolite was mixed with a good percentage of CMC plus 2% glycerol to prepare the film. To investigate the surface properties and scanning electron microscope particles, for the interaction of components the infrared spectroscopy and to study an X-ray diffraction the structure of crystalline materials was used. Mechanical properties were also obtained by a tensile and stress device, electrical properties such as I-V curve; electrical conductivity and electrical response stability for Nano composite film were obtained using a four-point probe. The surface of the support was active by glutaraldehyde (25%) and within 24 hours on an orbital agitator, immobilization the enzyme was performed. The loading efficiency was calculated by measuring the amount of unsaturated protein by Bradford Reagent and the Uv-visible spectrophotometry. The immobilization efficiency was calculated by measuring alpha-amylase activity by miller method (starch hydrolysis and optical absorption measurements from maltose production).
Results: The results of scanning electron microscopy showed that magnetic iron nanoparticles were bonded to each other by trimethoxysilyl propyl amine and made iron nanowires. Then, the same binder binds the nanowires to the zeolite microparticles. Iron nano-wires are also embedded in the zeolite microparticles and the bonding is well established. Interpretation of particle size revealed an average size of iron nano-diameter of 48.8 nm. The results of FTIR showed that the peak in the wave number of about 554 cm^-1 indicates the Fe-O groups present in the iron nanoparticles, which confirms the binding of the iron nanoparticles to the zeolite. But in this study, nanoparticle bonding cannot be ensured because of the overlap with the Si-O-Al peak in the zeolite structure. Therefore, X-ray diffraction (XRD) test and absorption test by external magnetic field were used to confirm the binding of iron magnetic nanoparticles to zeolite. Zeolite is known as a crystalline material while magnetic iron nanoparticles have more amorphous portions. As a result, the interference of the waves in the zeolite-iron oxide nanocomposite was of a destructive type. In result of XRD test a reduction in the crystalline peak in magnetized zeolites observed that confirm the binding of iron magnetic nanoparticles to zeolite. In the mechanical test of final tensile strength, the maximum elongation, elastic modulus and strain to breaking point were 1.31 MPa, 13.72 mm, 3.95 MPa and 34.31%, respectively. Electrical properties of nanocomposites were measured using a four-probe device. The potential-intensity difference curve was non-linear, indicating the semiconductor nature of the nanocomposite film. The electrical conductivity was calculated at 1 v potential difference and 0.1 mA current equal to 0.053 s / cm and the amperometric response was observed at 450 s for about 2.5 μA. Loading efficiency by Bradford method and immobilization efficiency by Miller method were 93.2% and 82%, respectively.
Conclusion: Comparison of the electrical and mechanical properties of the nanocomposite film with other studies showed that the mechanical properties of the prepared film and the electrical properties of this film are very suitable for use in biosensors. Also, due to the high loading efficiency and high enzyme immobilization efficiency, the potential of the synthesized nanocomposite support was found to be very desirable. Isolation of the substrate by an external magnetic field in the immobilization of biological molecules and use as a drug carrier (for example, the zeolite carrier for the anti-cancer drug 5-fluorouracil) is of great intereste.