A novel synthesis of oleophylic Fe2O3/polystyrene fibers by γ-Ray irradiation for the enhanced photocatalysis of 4-chlorophenol and 4-nitrophenol degradation
Graphical abstract
Introduction
With the industry development, water pollution, caused by organic dyes, toxic solvents and pesticides, has become one of the global issues that menaces humankind [1]. Photocatalytic degradation has been considered as a promising technology for organic pollution removal, because of the high degree of mineralization, mild reaction conditions and low energy consumption [[2], [3], [4]]. The photocatalyst is crucial for photocatalytic environmental purification [5]. Especially, semiconductor materials with chemical-physical stabilization, environmental friendliness and low cost properities, have been widely used as promising photocatalysts in organics degradation [6,7]. The semiconductor catalyst with a narrow band gap has been focused, which could be induced by visible-light and then efficiently make use of the solar energy [8].
Among the alternative visible-light-driven catalysts, Fe2O3 features favorable visible light response, natural abundance, eco-friendly property and chemical stability, and thus has attracted tremendous interests [9]. However, the low electrical conductivity and short hole diffusion length of Fe2O3 lead to a poor photocatalytic activity, which is not conducive to practical application [10]. Various methods including element doping, nanostructural construction and surface modification have been widely developed in the past few years [[9], [10], [11]]. Although a variety of strategies have been used to enhance the performance, the photocatalytic efficiency of Fe2O3 still needs to be dramatically elevated to meet the industrial application [12,13]. The utilization of active substances (such as hydroxyl radical, superoxide radical, hydroperoxide) in photocatalytic system greatly influenced the photocatalytic performance of semiconductors [14,15]. Especial for the active radicals with short lifetimes in solution, avoiding the barrier between radicals and pollutants was vital for the catalytic property in a pollutant degradation system [16]. The physical adsorption of pollutant could enhance its concentration around the photocatalyst, making direct contact between the generated radicals and pollutant molecules [17]. Hence, it is beneficial to improve the physical adsorption capacity of the photocatalyst. Li et al. [13] fabricated anti-fouling Fe2O3/TiO2 nanowire membranes, took the advantages of the enhanced humic acid adsorption onto Fe2O3 and achieved higher degradation efficiency. Qiu et al. [12] proved that the enhanced physical adsorption capacity of C/Fe2O3 nanosheets could promote the photocatalytic efficiency for methyl blue (MB) degradation. Therefore, it is imperative to develop a multifunctional material with superior organic pollutant adsorption capacity and photocatalytic activity.
The recycling of photocatalyst is as important as photocatalytic activity for the application of photocatalytic degradation [[18], [19], [20]]. Various carrier materials such as magnetic carrier, porous membrane and fiber have been utilized, which could not only enhance the dispersion of nano-catalysts, but also benefit the recovery of photocatalysts [[21], [22], [23]]. Ajay et al. [22] prepared the BiOCl/g-C3N4/Cu2O/Fe3O4 catalyst for sulfamethoxazole degradation, which could be recycled by magnet. Qi et al. [23] synthesized the recyclable graphene-based nanofiltration membrane, which degraded bisphenol A, ammonia and antibiotic efficiently under light illumination. Notably, the organic fiber exhibited high surface area and good chemical stability, enabling it to be an ideal carrier material of photocatalysts [24,25]. Polystyrene (PS) fiber, as a low cost, inert, non-toxic and low density thermoplastic polymer, could act as a carrier material or organic sorbent [26,27]. The agglomeration of nanoparticle-catalysts could be weakened by loading on the fiber surface [21]. Nyokong et al. [28] synthesized phthalocyanine-silver nanoparticle conjugates supported on PS fibers for methyl orange degradation, and proved that the agglomeration of photocatalysts was restrained due to the existence of supportive PS fibers. Therefore, the semiconductor-PS fiber composite is a potential efficient and recyclable photocatalyst with additional pollutant-adsorption ability for environmental purification [29,30].
In this study, a series of Fe2O3/PS fiber composites were synthesized by the electrospinning and γ-Ray irradiation methods. The influence of the Fe2O3 loading on the adsorption capacity of the composite fiber for multiple organics was investigated. The effect of hydrophobic property of the photocatalysts on the photocatalytic perforemance for 4-CP and 4-NP degradation was studied under visible-light (λ ≥ 400 nm) illumination. A possible photocatalytic mechanism for phenols degradation was studied.
Section snippets
Preparation of PS fibers
PS fibers were prepared via an electrospinning method. To generate uniform-sized PS fibers, 8.0 g of PS ball (Sigma-Aldrich) was added in the dimethyl formanide and chlorobenzene mixed solution (95/5 vol/volume). The optimum electrospinning conditions were the 1.75 wt% PS solution with a voltage of 19.0 kV and an injection rate of 3.6 mL/h.
Preparation of Fe2O3 nanoparticles
The Fe2O3 nanoparticles were obtained by a solvothermal method [24]. Typically, 5.05 g of Fe(NO3)3•9H2O was dissolved in 50 mL of ethanol. The resulting
Morphology and composition of photocatalyst
The morphologies of the materials were investigated by SEM and TEM measurements. A spherical morphology was observed for Fe2O3 sample (Fig. 2a). The size distribution (Fig. S1) was measured by about 100 nanoparticles, and the average size of Fe2O3 reached 13.5 nm. The nanoparticles were agglomerated because of the abundant hydroxyl groups on the Fe2O3 surface. In the HRTEM image (the inset of Fig. 2a), the lattice spacings of 0.252 and 0.269 nm were determined, which were attributed to the (1 1
Conclusions
Fe2O3/polystyrene (Fe2O3/PS) composite fibers were synthesized by γ-Ray irradiation method. The Fe2O3 nanoparticles were uniformly dispersed on the porous PS fibers. The Fe2O3/PS sample exhibited super-hydrophobic property, good salt resistance and acid-alkali stability. The γ-Ray irradiation treatment for composites not only formed the steady micro-nano construction of nanoparticles and fiber, but also reduced the hydroxyl group on Fe2O3 surface. The photocatalytic efficiencies of 0.3-Fe2O3/PS
Acknowledgements
This study was supported by National Natural Science Foundation of China (Nos. 51802082 and 21671059), Science and Technology Research Program of Henan Province (Nos. 182102311084 and 192102310231), Key Scientific Research Project of Colleges and Universities in Henan Province (Nos. 18A150027 and 19B150006) and Henan Postdoctoral Science Foundation.
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