Effect of TiO₂ on photocatalytic activity of polyvinylpyrrolidone fabricated via electrospinning

Abstract

Polyvinylpyrrolidone (PVP) is a promising material for electrospinning, and it has many desirable properties, including solubility in various solvents, physiological compatibility, chemical inertness, and excellent film-forming ability. Polymer–matrix composites of PVP–carbon fibers containing TiO₂ were prepared via electrospinning. Degradation of environmental pollutants by the electrospun webs was evaluated based on methylene blue degradation. The optimum photocatalytic activity was achieved with webs containing 7 wt% TiO₂. The results show that the proposed method is effective for improving the photocatalytic properties of TiO₂-doped nanofibers; the doping process also increased the nanofiber surface area.

Introduction

With rapid economic development, environmental pollution has emerged as an increasingly serious problem. Water pollution is an area of particular concern because pollution rates currently exceed the self-purification abilities of natural water reservoirs. Approximately 0.7 million tons of dyes are generated annually across the globe, 10–15% of which are discharged into water bodies. Environmentally friendly techniques therefore need to be developed to address pollution issues. In recent years, many studies on pollution mitigation have been performed [1], [2], [3], [4], [5]. These studies have shown that TiO₂ is potentially useful in a wide range of applications such as water remediation and air purification [6], [7], [8], [9], [10].

TiO₂ is a promising photocatalyst because of its high photocatalytic efficiency and thermostability. Furthermore, it is non-toxic, insoluble in water, and readily available. Many strategies have been used to enhance the photocatalytic ability of TiO₂, including the synthesis of novel hybrid TiO₂ photocatalysts [11], [12], [13].

Polyvinylpyrrolidone (PVP) is used in numerous areas such as medicine, pharmaceuticals, and cosmetics. PVP is physiologically compatible, non-toxic, chemically inert, temperature resistant, pH stable, non-ionic, and colorless [14], [15], [16]. In addition, the advantages of PVP such as high solubility in solvents of different polarities, excellent solubilizing and film-forming abilities, suspension- and emulsion-stabilizing effects, and binding properties make it one of the most important excipients in the pharmaceutical industry [17], [18], [19], [20]. PVP is a hydrophilic polymer and has been used as a surfactant to control the crystal facets of nanoparticles. Cheng et al. reported that PVP assisted the dispersion of TiO₂ particles and improved the adherence of TiO₂ to flexible substrates. Zhang et al. reported the synthesis of BiOBr nanosheets using PVP, and concluded that PVP can reduce the nanosheet thickness and accelerate the exposure of (001) facets, leading to enhanced photocatalytic activities [21], [22], [23].

In electrospinning, an electric field is used to control the deposition of polymer fibers on a target substrate. The method does not require the use of coagulants or high temperatures to produce solid fibers from solution. This process is therefore particularly suitable for the production of fibers from large and complex molecules. Electrospinning from molten precursors is also used, to ensure that no solvent is carried into the final product [24].

Previous studies have shown that the photocatalytic properties of various supporting materials can be improved by the addition of TiO₂ and electrospinning. PVP can be selectively attached on the plane, thereby reducing the surface tension and stabilizing the metal nanoparticles. This technique has been widely used to develop catalysts for the degradation of pollutants [25], [26], [27].

In this study, PVP was used as a support material for TiO₂ nanoparticles. The photocatalytic activities and structural features of the fibers generated by electrospinning PVP/ethanol solutions with different TiO₂ contents were investigated.