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Chemical Engineering Journal, Volume 210, 1 November 2012, Pages 410-416
Nahid Sarlak, Mohammad Amin Farahmand Nejad, Saeed Shakhesi, Keyvan Shabani.
Department of Chemistry, Faculty of Science, Lorestan University, Khorramabad, Iran
Department of Nanotechnology, Engineering Research Institute, Tehran, Iran
Abstract
TiO2 nanofibers were electrospinned by using Polyvinylpyrrolidone (PVP) and Titanium tetraisopropoxide (TTIP) precursors. The effective parameters in this method such as the PVP content, TTIP content, distance between needle and collector, applied voltage, feed rate and pH were optimized by using Central Composite Design method and statistical software package Minitab ver.14. The results show that the PVP and TTIP concentrations have a direct and pH has an indirect relationship with the fiber diameter. Results showed that the PVP concentration was the most significant parameter in the fiber diameter of electrospun TiO2nanofibers, while TTIP content and pH value were the next important parameters respectively. The influence of these parameters on diameter and morphology of TiO2 nanofibers was studied via SEM analysis, i.e. raising the pH value from 2.3 to 4.6 lead to decrease of the fiber diameter from 718 ± 76 to 256 ± 39 nm and increasing the bead percent from 4% to 18%. Based on response surface plots, optimum conditions (PVP content: 6.5 wt.%, TTIP content: 5 wt.%, pH: 3.2, distance: 25 cm, voltage: 18.4 kV, flow rate: 0.7 ml/h) for producing TiO2 nanofibers with minimum diameter and fewer beads was obtained. According to DTA result, the optimum nanofibers were calcined at ∼560 and ∼685 °C for 2 h under air atmosphere. XRD analysis revealed the formation of anatase and rutile TiO2 phases after heat treatment at these temperatures respectively. Moreover, SEM images revealed an average shrinkage of the fiber diameter up to 50% (50.1 ± 18 nm) in the calcined nanofibers.
Additional Information
One-dimensional (1D) ceramic materials, TiO2 nanofibers has many attractive properties and is, thus, considered to be a promising material for diverse applications including chemical sensors, catalytic filters, solar cells and biocompatible materials. Many chemicals and/or physical methods have been demonstrated for producing 1D ceramic structure with various compositions.
To the best of our knowledge, this paper is the first report about investigating the effect of six parameters on the TiO2 diameter and morphology simultaneously. In this report we showed that using a mathematical model allows the statistical evaluation of selected parameters on the fiber diameter. As a general result, using mathematical model help us that have products with best quality.
The studied parameters divided in two categories; precursors solution parameters (PVP content, TTIP content and pH) and electrospinning parameters (high voltage, distance and flow rate). The mentioned parameters were incorporated in the design in five levels. Afterwards 53 runs were experimentally conducted and the responses were analyzed with statistical Minitab ver. 14. The prominent characteristics of the CCD method which used in this study are studying the influence of each parameter alone and the interaction of them also specify the best model for explaining the relation of parameters and responses and finally introducing the optimum condition for fabrication of best TiO2 nanofibers. The results show that the PVP and TTIP concentrations have a direct and pH has an indirect relationship with the fiber diameter. Results showed that the PVP concentration was the most significant parameter in the fiber diameter of electrospun TiO2 nanofibers, while TTIP content and pH value were the next important parameters respectively. Furthermore we understood which the diameter of the needle is effective on fiber diameter that with decreasing the inner needle diameter the fine fiber will be acquired.
The high voltage used in this study was in the 6.55–18.44 kV range. After optimizing conditions, TiO2 nanofibers were obtained with minimum diameter and best morphology simultaneously (diameter: 50.1 ± 18 nm, bead percent: beadless).
Therefore Tio2 electrospun can be produced by our procedure with high quality and also low energy in comparison with other recent reported methods that are clear in our paper.
This work was patented in my country. It’s copyright is for Lorestan University and Engineering Institute in IRAN. Also, we are looking for licensing opportunities.
