Functionalized nanomaterials in dispersive solid phase extraction: Advances & prospects

Highlights

• Present era of functionalized nanomaterials for the dispersive solid phase extraction.

• Improvements in dSPE techniques and processes due to functionalized nanomaterials.

• Explore binding mechanisms of nanomaterials with analytes in dSPE.

• Describes challenges for proper implementation nanotechnology in dSPE applications.

Abstract

Because of the limited performance of conventional bulk-scale materials, the development of novel materials in nanoscale with enhanced properties has attracted increasing great attention of research from different fields of science. Significance progresses were made in nanotechnology and nanoscience in the past years. Compared with conventional materials, nanomaterials possess large surface area to volume ratio and unique intrinsic features including electrical, mechanical, optical and morphological features. These features of materials in nanoscale make them great candidates for the development of novel functionalized nanomaterials for the different applications of dispersive solid phase extraction (dSPE) technique.

The aim of this review paper is to demonstrate and highlight the recent advancements in the development of new functionalized nanomaterials for dSPE applications.

Introduction

Solid-phase extraction (SPE) is a powerful sample clean-up and pre-concentration technique for the effective extraction of the desired compound from complex matrices [[1], [2], [3]]. One of the variations of the SPE technique which significantly decreases the time and simplifies the extraction process is dispersive SPE (dSPE) [[4], [5], [6], [7]] in which the extraction process is conducted in the liquid sample by using dispersed material instead of using SPE column, disk or cartridge.

In the dSPE processes, the mass of the loaded sample is very important, as well as the solvent. The mass of the sample will affect the efficiency of the extraction process although the solvent containing the sample is key to ensuring retention of compounds on the adsorbent.

On the other hand, desorption solvent or solvent mixtures are used for washing and desorption steps which depends on the dSPE procedure. For the desorption procedure towards the target compounds, the polarity of the desorption solvent must approximately equal the polarity of the compounds considering the ‘like dissolves like’ principle [8].

The functionalized nanomaterials having different morphologies and compositions were successfully applied as excellent nanoadsorbents for dSPE applications [[9], [10], [11], [12], [13]]. The physical, chemical, electrical and optical properties of the functionalized nanomaterials differ depending on their size and shape, as compared to their larger structures. Because of their small size, the nanomaterials have a fairly large surface area and large surface/volume ratio. This ratio is one of the reasons why nanomaterials have superior chemical and physical properties such as large surface energy, reactivity, solubility and low melting point when it is compared to their larger particles. Decreasing the size of the material causes an increase in surface area. As the particle size decreases, the number of surface atoms increases and it becomes effective in the properties of materials. Increasing the number of atoms on the surface means increasing the surface energy. The surface energies of the atoms on the nanomaterial surface are high. These atoms tend to bind with adsorbate molecules, atoms, ions or to agglomerate by reducing their surface energies to stabilize and balance the force exerted upon them. The amount of adsorption is therefore directly proportional to the increase in the number of atoms on the surface. The tendency of the nanomaterial to agglomerate causes the sorbent specific surface area to be reduced. The increase in surface area and high surface/volume ratio are very important for adsorption processes. There are more binding sites on the surface of the nanomaterials used in adsorption processes. Therefore, nanomaterials are chemically more reactive than their micro or macro-dimensional states. The use of nanomaterials for sample preparation, sensor, separation and enrichment materials provides high adsorption capacity and pre-concentration factors, as well as easy functionalization and reusability of nanomaterials are also important factor for effectively using in these applications. In the literature, many studies have shown that nanomaterials provide higher efficiency in the adsorption of various compounds in gaseous or liquid phases [[12], [13], [14], [15]]. So far, carbon nanotubes, magnetic nanoparticles, metal oxide nanoparticles, metalic nanoparticles, nanoclays, polymer based nanoadsorbents can be used as efficient adsorbents for the adsorption of different substances in complex environment [16].

This review paper mainly focuses on the recent developments of functional nanomaterials for dSPE applications. First, it starts with introduction of SPE technique and nanomaterials utilized in selective recogniton and extraction processes for the desired compounds in complex matrices. Second, adsorption mechanism on functionalized nanomaterials is discussed. In the third section, types of SPE using nanomaterials are demonstrated. Then, reported studies on the dSPE applications of functionalized nanomaterials such as metal and metal oxide nanoparticles (i.e., Au nanoparticles, Ag nanoparticles, TiO₂ nanoparticles, magnetic Fe₃O₄ nanoparticles, ZnO nanoparticles) and carbon nanomaterials (i.e., carbon nanotubes (CNTs), graphene oxide (GO) and fullerenes) over the past years are provided. Finaly, safety concerns of functionalized nanomaterials are briefly discussed.