Polymer–Inorganic Core–Shell Nanofibers by Electrospinning and Atomic Layer Deposition: Flexible Nylon–ZnO Core–Shell Nanofiber Mats and Their Photocatalytic Activity

Abstract

Polymer−inorganic core−shell nanofibers were produced by two-step approach; electrospinning and atomic layer deposition (ALD). First, nylon 6,6 (polymeric core) nanofibers were obtained by electrospinning, and then zinc oxide (ZnO) (inorganic shell) with precise thickness control was deposited onto electrospun nylon 6,6 nanofibers using ALD technique. The bead-free and uniform nylon 6,6 nanofibers having different average fiber diameters (∼80, ∼240 and ∼650 nm) were achieved by using two different solvent systems and polymer concentrations. ZnO layer about 90 nm, having uniform thickness around the fiber structure, was successfully deposited onto the nylon 6,6 nanofibers. Because of the low deposition temperature utilized (200°C ), ALD process did not deform the polymeric fiber structure, and highly conformal ZnO layer with precise thickness and composition over a large scale were accomplished regardless of the differences in fiber diameters. ZnO shell layer was found to have a polycrystalline nature with hexagonal wurtzite structure. The core−shell nylon 6,6-ZnO nanofiber mats were flexible because of the polymeric core component. Photocatalytic activity of the core−shell nylon 6,6-ZnO nanofiber mats were tested by following the photocatalytic decomposition of rhodamine-B dye. The nylon 6,6-ZnO nanofiber mat, having thinner fiber diameter, has shown better photocatalytic efficiency due to higher surface area of this sample. These nylon 6,6-ZnO nanofiber mats have also shown structural stability and kept their photocatalytic activity for the second cycle test. Our findings suggest that core−shell nylon 6,6-ZnO nanofiber mat can be a very good candidate as a filter material for water purification and organic waste treatment because of their photocatalytic properties along with structural flexibility and stability. KEYWORDS: electrospinning, ALD (atomic layer deposition), nanofibers, ZnO, core−shell, photocatalytic activity, nylon ■ INTRODUCTIONOne-dimensional (1D) nanostructures such as nanofibers have distinctive properties that can offer good opportunities for developing advanced materials and devices.1−3 Among the other nanofiber fabrication methods, electrospinning has gained growing interest in the past decade because this technique is quite versatile and cost-effective for producing functional nanofibers from variety of materials including polymers, polymer blends, emulsions, suspensions, sol−gels, metal oxides, composite structures as well as nonpolymeric systems, etc. 2−8Electrospun nanofibers and their nanofiber mats have remarkable characteristics including a very high specific surface area, pore sizes within the nanoscale and very lightweight since the fiber diameter ranges from one micrometer down to a few tens of nanometers. Moreover, the control of the fiber surface morphology, fiber orientation, and cross-sectional configuration, and design flexibility for physical/chemical modification is quite feasible for obtaining multifunctional electrospun nanofibers. Because of their exceptional pr...

Role of zinc interstitials and oxygen vacancies of ZnO in photocatalysis: a bottom-up approach to control defect density

“…Therefore, the ALD process with sufficient cycle numbers yielded a conformal and layer-by-layer deposition of ZnO on PSU bers. 4,19,20,49 For cycle numbers $200, a continuous lm is formed because of the coalescence of grains/ islands. Fig.…”

Transformation of polymer-ZnO core–shell nanofibers into ZnO hollow nanofibers: Intrinsic defect reorganization in ZnO and its influence on the photocatalysis

“…Uniform and bead-free nylon 6,6 nanofibers with two different average fiber diameters were produced by varying the solvent system (FA or HFIP) based on our previous study [29]. Two solutions were prepared, viz.…”

“…surface area and density of defects in conjunction with thermal treatment [27]. To unveil the dependency of surface area and density of defects on PCA, we have chosen ZnO as a model semiconductor as it is vastly studied in the context of PCA [10,16,18,[28][29][30][31][32][33][34]. While reducing the dimensions of the catalysts (increasing the specific surface area), an increase in the density of surface states is inevitable due to the dangling orbitals [35], in addition to intrinsic lattice defects [36].…”

“…In this article, we compare the relative densities of some of the above listed intrinsic defects with reference to the calcination effect and PCA. The catalysts examined here were fabricated via a renounced and industrially applicable combination [10,11,18,28,29,[39][40][41], viz. electrospinning [42][43][44] and atomic layer deposition (ALD) [45][46][47][48][49].…”

“…We have extracted some results (X-ray diffraction and PCA) from core-shell structures [29] and compared it with the hollow counterpart, where the latter were produced by calcining the former. The calcination not only increases the surface area but also manipulates the relative densities of defects.…”