Gelatin/sodium triphosphate hydrogel electrospun nanofiber mat as a novel nanosorbent for microextraction in packed syringe of La3+ and Tb3+ ions prior to their determination by ICP-OES

https://doi.org/10.1016/j.reactfunctpolym.2020.104627Get rights and content

Highlights

  • The GT/STP nanofiber was synthesized by electrospinning strategy from a single fluid.

  • GT/STP hydrogel nanofiber was suggested as an efficient, non-toxic and recyclable adsorbent.

  • The GT/STP nanofiber was introduced as a novel nanosorbent for microextraction in packed syringe.

  • The novel nanosorbent with three-dimensional structure showed a high tendency towards La3+ and Tb3+.

  • The MEPS-ICP-OES was introduced as an effective method for determination of Lanthanide ions at ppt levels.

Abstract

In the present study, the novel gelatin/sodium triphosphate hydrogel nanofiber mat (GT/STP HNFM) was fabricated using the electrospinning strategy. Owing to the formation of ionic complex between STP and GT, the water stability of synthesized nanofiber increased, thereafter, the synthesized water-insoluble nanofiber was applied as a novel nanosorbent in microextraction in packed syringe (MEPS) method, using for the preconcentration of La3+ and Tb3+ in environmental and industrial water samples to the detection of them by an inductively coupled plasma optical emission spectroscopy (ICP-OES). The characterization of nanosorbent was performed and the effect of main parameters on adsorption performance were investigated. Under the optimum condition, the method showed a good linearity ranging from 1 to 500 ng mL−1 with a correlation coefficient superior to 0.998. Additionally, the low detection limits (0.1–0.2 ng mL−1) revealed good sensitivity of the proposed method. Finally, the MESP-ICP-OES method was applied for the determination of La3+ and Tb3+ in environmental and industrial water samples with relative recoveries (RRs) ranging from 85 to 102% and relative standard deviations (RSDs) lower than 2.7%. The outcome of this study revealed an effective method for the extraction and recovery of La3+ and Tb3+ from aqueous solutions using a non-toxic, inexpensive, and efficient nanosorbent.

Introduction

Gelatin (GT) is a natural biopolymer derived from collagens. Considering the merits of GT including biodegradability, biocompatibility, low cost and high availability, GT has been widely used in the medical applications and pharmaceutical industry [[1], [2], [3], [4]]. The GT electrospun nanofiber, used in tissue engineering, bioactive encapsulation, and active packing, has been fabricated in different solvents, such as formic acid, ethylacaetate, and acetic acid [[5], [6], [7]]. Furthermore, GT is a hydrophilic polymer which can be used for the fabrication of hydrogel nanofiber with a 3D network. Hydrogel nanofibers have the spongy and loose network and can absorb a considerable amount of water. In this kind of nanofiber, analytes can penetrate from interior and exterior sites, resulting in a significant increase in the adsorption [8,9]. The main drawback of GT electrospun nanofiber is its poor water stability, which could be alleviated by adding crosslinking agents, such as glutaraldehyde and genipin. The toxicity of crosslinking agent is the main factor that should be considered in some applications, such as food industry [10,11]. Sodium triphosphate (STP) is a nontoxic inorganic ligand, utilized in ceramic industry, food, animal feeds, and cleaning products. The wide application of STP is in cleaning and washing process [12,13]. STP also can be applied as an effective complexing agent for Lanthanide ions (Ln3+) due to the presence of the oxygen groups, which can be served as the complexing sites. Here, STP was introduced as a non-toxic crosslinking agent for GT and the gelatin/sodium triphosphate hydrogel nanofiber mat (GT/STP HNFM) was applied as a novel sorbent for Ln3+.

Ln3+ are a group of rare earth elements (REEs), gaining much attention due to increasing applicability in different science fields, including industry, medicine and agriculture. One of the attractive features of these elements is photoluminescence properties, playing an important role in their widespread usage in medical, functional nanomaterials, cell imaging, and diagnostics. In recent decades, the widespread usage of Ln3+ in different fields, the wastes of which discharge into water sources, leads to the increasing environmental pollution issues threatening human health [[14], [15], [16], [17]]. So, the determination of these elements in water sources is necessary [18,19]. The extraction and recycling of these valuable elements are an effective method to provide these elements in a lower price [[20], [21], [22]].

Owing to the low concentration of elements in environmental samples and complex matrices, a preconcentration and purification step is necessary before instrumental detection [23,24]. Different methodologies have been used for the extraction and preconcentration of REEs. microextraction in packed syringe (MESP) is a new format of solid phase extraction (SPE) [25,26] introduced by Abdel-Rehim in 2004 [27]. This method has been utilized for environmental, biological and food analysis [28,29]. The advantages of this method include, but not limited to, less consumption of sorbent, sample, and solvent. The aforementioned method also is time and cost-effective. Generally, sorbent plays an important role in method selectivity, sensitivity and effeteness [30,31]. Therefore, the researchers focus on the introduction of the novel sorbents for MESP. By increasing the environmental awareness and understanding the danger of industrial materials, using the natural materials as the adsorbents can be considered as a good choice for sorbent-based microextraction techniques because these materials are inexpensive, non-toxic and biodegradable [32]. Chitosan [33], B-cyclodextrin [14], cellulose [34], electrospun Poly(acrylic acid)/Silica hydrogel nanofibers [8], modified Fe3O4 nanoparticles [35,36], silica gel [37], modified c18-cartridge [38] and modified carbon nanotube [39,40] have been applied as the sorbents for the determination and removal of REEs.

In the present study, we reported the synthesis of crosslinked GT/STP HNFM using a facile and green method thorough electrospinning strategy of GT and STP, and it was applied as a novel sorbent in MEPS method to extract and recover of La3+ and Tb3+ from environmental and industrial water samples. The GT/STP HNFM, an environmental friendly sorbent, with a three-dimensional structure, high surface area, porous fibrous morphology, and high stability showed high adsorption capacity for La3+ and Tb3+. This high adsorption capacity of GT/STP HNFM can be attributed to the presence of STP with a high density of oxygen groups that could be served as the coordination sites to form the complex with La3+ and Tb3+. Moreover, nanofiber has the hydrogel structure with plenty of water channels and spongy and loose network, improving the transfer of the metal ions into the interior. The extraction and recovery of La3+ and Tb3+ at ppt levels using the MEPS-ICP-OES method can be considered as an effective extraction method when the applied sorbent has the unique features, i.e. GT/STP HNFM.

Section snippets

Materials, solvents and standards

The polymer GT type A and STP were purchased from Sigma Aldrich (St. Louis, MO, USA, www.sigmaaldrich.com). LaCl3.6H2O (99/9%) and TbCl3.6H2O (99/9%) were obtained from Sigma Aldrich (St. Louis, MO, USA, www.sigmaaldrich.com). Stock standard solutions (1000 μg mL−1) of Cu2+, Cr3+, Al3+, Pb2+, Cd2+, Co2+, Fe3+ and Ni2+ were purchased from Merck Company (Darmstadt, Germany, www.merck.com). NaOH, HCl, HNO3 and H2SO4 were received from Merck (Darmstadt, Germany, www.merck.com). In all experiments,

Preparation and characterization of the GT/STP HNFM

To achieve a nanofiber with the smooth and beadles structure, the concentration of the spinning solution should be optimized. In this study, GT/STP solutions with different ratios were applied to prepare nanofibers. The nanofibers with different ratios of GT/STP were prepared, and their structures were compared with each other. The GT/STP solution in weight ratio of 3:1 (GT:STP) was chosen as the best solution to prepare nanofiber with uniform and beadles structure with good stability. The full

Conclusion

In summary, the novel nanosorbent for MEPS method was fabricated from non-toxic and natural materials, including GT and STP from a single fluid through electrospinning technique. Herein, STP has a dual function, including as a ligand in favor of absorbing and as a crosslinking agent over linking bonds with GT. The chemical structure and morphology of nanofiber were studied by FT-IR spectrum, FE-SEM images, and element mapping. The crosslinked GT/STP HNFM with three-dimensional structure, high

Declaration of Competing Interest

None.

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