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Triple axial co-electrospun multifunctional double-shell TiO2@ZnO carbon hollow nanofibrous mat transformed to C-attached TiO2 brush-like nanotube arrays: An Mo+ adsorbent non-woven mat Zahed Shami, Naser Sharifi-Sanjani, Sepideh Khoee, and Reza Faridi-Majidi Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/ie502360r • Publication Date (Web): 01 Sep 2014 Downloaded from http://pubs.acs.org on September 8, 2014
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Triple axial co-electrospun multifunctional doubleshell TiO2@ZnO carbon hollow nanofibrous mat transformed to C-attached TiO2 brush-like nanotube arrays: An Mo+ adsorbent non-woven mat Zahed Shamia*, Naser Sharifi-Sanjania*, Sepideh Khoeea, Reza Faridi-Majidib a
Polymer Laboratory, Chemistry Department, School of Science, University of Tehran, Tehran,
Iran b
Department of Medical Nanotechnology, School of Advanced Technologies in Medicine,
Tehran University of Medical Sciences, Tehran, Iran Corresponding authors *E-mail:
[email protected];
[email protected] *E-mail:
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ABSTRACT
A triple axial co-electrospinning procedure followed with a two-step heat treatment was successfully employed to fabricate continuous heterostructured multifunctional double-shell TiO2@ZnO graphite carbon non-woven hollow nanofibrous mats. The as-synthesized TiO2@ZnO/C hollow heterojunctions were transformed to 3D high surface area rutile TiO2 brush-like nanotube arrays attached onto carbon tubular mats under the alkaline hydrothermal and ion exchange processes combined with the annealing. The obtained TiO2 nanotubes have a typical inner diameter of about 3.5 nm, wall thickness of about 4.0 nm, and length up to several hundred nanometers. Mathematical models, as well as the experimental results exhibited a higher self-adsorption capacity of Mo6+ pollutant over C-attached TiO2 nanotubes can be attributed to the larger surface area, providing more active sites for a contact with the reactants and pollutants. Furthermore, the kinetic studies suggested that the pseudo-second-order model is suitable to describe the adsorption mechanism of Mo6+ over the as-synthesized hollow nanostructures.
KEYWORDS: Triple axial co-electrospinning, double-shell TiO2@ZnO/C, C-attached rutile TiO2, molybdenum, self-adsorption
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Introduction Porous semiconducting multifunctional heterojunctions are well-known duo to their improved performance in the electrochemical devices ascribed to the superior combined electronic and structural characteristics, such as large specific surface area and abundant active sites for a contact with the reactants and products, the fast interfacial transport of the photo-generated charge carriers, and high light-harvesting
1-7
. Such unique characteristics are found to be more
achievable by the hierarchical core/shell tubular nanostructures8-12. Among the various synthesis techniques such as sol-gel13, hydrothermal and solvothermal14-15, vapor deposition16, and selfassembly16, the multi-axial co-electrospinning is believed to be a more straightforward strategy for synthesizing 3D well-arranged porous continued core/shell tubular hybrid materials with highly controllable chemical composition and morphology, as well as the fabrication capability of both polymeric and inorganic multi-components simultaneously17-28. The multi-axial coelectrospinning technique has been the subject of a great research interest because of its diverse properties and functionalities: (a) Low-spinnability polymers can be electrospun along with highspinnability polymers, thus the various characteristics of polymers can be combined into one fiber, (b) Non-spinnable materials, such as metal salts, oligomers, liquids, enzymes and drugs can be also immobilized into fibers to fabricate the functional multi-layered nanofibers, and (c) The as-spun multi-layered core/shell tubular nanofibers provide 3D open-channeled mats with a high porosity and large surface areas, supporting more active sites for a contact with the reactants and pollutants in the photocatalytic adsorbents. Particularly, scientific and technological interests have been assigned to fabricate TiO2 and TiO2-based multi-component nanostructures, indicating the specific physical and chemical properties in electronics, optics, and photocatalysis29-30. The separation and recycling of a
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photocatalytic adsorbent in powdered form from an aqueous solution after the pollutant degradation has been a critical issue for large-scale industrial photocatalytic adsorbent applications. Amongst types of nanostructured TiO2 forms, TiO2-based nanotubes with a high specific surface area and surface-to-volume ratio, and ion-changeable ability have attracted much interest in scientific research for extensive applications in gas sensors, ion-storage devices, and environmental purification (including photocatalysis)31-33. However, some above-mentioned limitations assigned to the powdered TiO2 photocatlytic adsorbents still are sustained. The continuous heterostructred electrospun TiO2-multi-layer semiconductors coupled with the polymeric support are found to be a promising candidate in the photocatalytic adsorbent industry due to 3D continuity and integrity in the structure, which remove or minimize the abovementioned drawbacks of the powdered nanostructures. Particularly, heterostructured TiO2 brushlike nanotube arrays attached onto conductive carbon tubular fibers are believed to be very beneficial in the photocatalytic adsorbent industry. The reason can be ascribed to enhanced texture properties of both the TiO2 nanotubes and the graphite carbon tubular nano-mats as a new trapping pollutant site, a good electron acceptor, an effective transfer pathway of electrons, and a strong support without the brittle problems of ceramic nanostructures, providing improved trapping and migration of the reactants and products34. The self-degradation in the dark, as well as the photo-induced decomposition of the organic pollutants in wastewater over the semiconducting metal oxide nanostructures have been widely investigated in the past decades35-36. However, the photocatalytic removal of inorganic compounds in wastewater has been studied to a lesser extent. The removal approach in the dark, based on the adsorption of an inorganic pollutant over mesoporous adsorbents known as “selfadsorption” is found to be more beneficial than that of the conventional precipitation and
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filtration methods, transforming the pollutants to another phase, which creates disposal problems again37-39. The removal or decrease of the molybdenum compounds (mostly as Mo6+ ion) present in water and wastewater can be environmentally important, because the molybdenum is widely used in petroleum, plastic, metallurgy and electronic industries. The common method for the removal of the molybdenum contained in wastewater discharge systems is the precipitation of molybdenum ion by the ferric sulfate solution at a pH
