Recent Advances in Nanomaterials for Analysis of Trace Heavy Metals

A novel deep eutectic solvent modified magnetic covalent organic framework for the selective separation and determination of trace copper ion in medicinal plants and environmental samples

BACKGROUND

Pretreatment techniques should be introduced before metal ion determination because there is very low content of heavy metals in Chinese medicinal plants and environmental samples. Magnetic dispersive micro solid phase extraction (MDMSPE) has been widely used for the separation and adsorption of heavy metal pollutants in medicinal plants and environmental samples. However, the majority of MDMSPE adsorbents have certain drawbacks, including low selectivity, poor anti-interference ability, and small adsorption capacity. Therefore, modifying currently available adsorption materials has gained attention in research.

RESULTS

In this study, a novel adsorbent MCOF-DES based on a magnetic covalent organic framework (MCOF) modified by a new deep eutectic solvent (DES) was synthesized for the first time and used as an adsorbent of MDMSPE. The MDMSPE was combined with inductively coupled plasma optical emission spectrometry (ICP-OES) for selective separation, enrichment, and accurate determination of trace copper ion (Cu2+) in medicinal plants and environmental samples. Various characterization results show the successful preparation of new MCOF-DES. Under the optimal conditions, the enrichment factor (EF) of Cu2+ was 30, the limit of detection (LOD) was 0.16 μg L-1, and the limit of quantitation (LOQ) was 0.54 μg L-1. The results for the determination of Cu2+ were highly consistent with those of inductively coupled plasma mass spectrometry (ICP-MS), which verified the accuracy and reliability of the method.

SIGNIFICANCE

The established method based on a new adsorption material MCOF-DES has achieved the selective separation and determination of trace Cu2+ in medicinal and edible homologous medicinal materials (Phyllanthus emblica Linn.) and environmental samples (soil and water), which provides a promising, selective, and sensitive approach for the determination of trace Cu2+ in other real samples.

Polymeric Materials in Speciation Analysis Based on Solid-Phase Extraction

Speciation analysis is a relevant topic since the (eco)toxicity, bioavailability, bio (geo)chemical cycles, and mobility of a given element depend on its chemical forms (oxidation state, organic ligands, etc.). The reliability of analytical results for chemical species of elements depends mostly on the maintaining of their stability during the sample pretreatment step and on the selectivity of further separation step. Solid-phase extraction (SPE) is a matter of choice as the most suitable and widely used procedure for both enrichment of chemical species of elements and their separation. The features of sorbent material are of great importance to ensure extraction efficiency from one side and selectivity from the other side of the SPE procedure. This review presents an update on the application of polymeric materials in solid-phase extraction used in nonchromatographic methods for speciation analysis.

Nitrogen-doped porous carbon nanomaterials synthesized using a magadiite template as efficient peroxidase mimics for colorimetric detection of ascorbic acid as an antioxidant

Nanomaterials with intrinsic enzyme-like activity have gained substantial scientific attention as viable substitutes to natural biological enzymes owing to their cheap price and great stability. Numerous artificial enzyme mimics have been employed effectively in sectors such as sensing, environmental processing, and cancer treatment. In this study, novel nitrogen-doped porous carbon nanomaterials (CPs) were produced by modifying polypyrrole with magadiite using chemical oxidative polymerization and calcination methods. The obtained nitrogen-doped porous carbon nanomaterials exhibited improved peroxidase-like activity, which catalyzed the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2) to produce colorful compounds. Kinetic investigation revealed that the affinity for TMB of nitrogen-doped porous carbon peroxidase mimics was higher than that of genuine horseradish peroxidase (HRP). In addition, a sensitive assay with encouraging performance for the colorimetric detection of ascorbic acid (AA) was successfully fabricated employing nitrogen-doped porous carbon nanomaterials as peroxidase mimics. The results were satisfactory and demonstrated its potential application in antioxidant detection.

Dynamic crosstalk between silicon nanomaterials and potentially toxic trace elements in plant-soil systems

Agricultural soil pollution with potentially toxic trace elements (PTEs) has emerged as a significant environmental concern, jeopardizing food safety and human health. Although, conventional remediation approaches have been used for PTEs-contaminated soils treatment; however, these techniques are toxic, expensive, harmful to human health, and can lead to environmental contamination. Nano-enabled agriculture has gained significant attention as a sustainable approach to improve crop production and food security. Silicon nanomaterials (SiNMs) have emerged as a promising alternative for PTEs-contaminated soils remediation. SiNMs have unique characteristics, such as higher chemical reactivity, higher stability, greater surface area to volume ratio and smaller size that make them effective in removing PTEs from the environment. The review discusses the recent advancements and developments in SiNMs for the sustainable remediation of PTEs in agricultural soils. The article covers various synthesis methods, characterization techniques, and the potential mechanisms of SiNMs to alleviate PTEs toxicity in plant-soil systems. Additionally, we highlight the potential benefits and limitations of SiNMs and discusses future directions for research and development. Overall, the use of SiNMs for PTEs remediation offers a sustainable platform for the protection of agricultural soils and the environment.

Treatment of textile wastewater using carbon-based nanomaterials as adsorbents: a review

Waste derived from the textile industry can contain a wide variety of pollutants of organic and inorganic natures, such as dyes (e.g., acid, basic, reactive, mordant dyes) and toxic metals (e.g., lead, chromium, cadmium). The presence of pollutants at high concentrations in textile waste makes them relevant sources of pollution in the environment. To solve this problem, various technologies have been developed for the removal of pollutants from these matrices. Thus, adsorption emerges as an efficient alternative for textile waste remediation, providing advantages as simplicity of operation, economy, possibility of using different adsorbent materials, and developing on-line systems that allow the reuse of the adsorbent during several adsorption/desorption cycles. This review will initially propose an introduction to the adsorption world, its fundamentals, and aspects related to kinetics, equilibrium, and thermodynamics. The possible mechanisms through which a pollutant can be retained on an adsorbent will be explained. The analytical techniques that offer valuable information to characterize the solid phases as well as each adsorbate/adsorbent system will be also commented. The most common synthesis techniques to obtain carbon nano-adsorbents have been also presented. In addition, the latest advances about the use of these adsorbents for the removal of pollutants from textile waste will be presented and discussed. The contributions reported in this manuscript demonstrated the use of highly efficient carbon-based nano-adsorbents for the removal of both organic and inorganic pollutants, reaching removal percentages from 65 to 100%.

Preconcentration and Removal of Pb(II) Ions from Aqueous Solutions Using Graphene-Based Nanomaterials

Direct determination of lead trace concentration in the presence of relatively complex matrices is often a problem. Thus, its preconcentration and separation are necessary in the analytical procedures. Graphene-based nanomaterials have attracted significant interest as potential adsorbents for Pb(II) preconcentration and removal due to their high specific surface area, exceptional porosities, numerous adsorption sites and functionalization ease. Particularly, incorporation of magnetic particles with graphene adsorbents offers an effective approach to overcome the separation problems after a lead enrichment step. This paper summarizes the developments in the applications of graphene-based adsorbents in conventional solid-phase extraction column packing and its alternative approaches in the past 5 years.

Nanomaterials-Based Ion-Imprinted Electrochemical Sensors for Heavy Metal Ions Detection: A Review

Heavy metal ions (HMIs) pose a serious threat to the environment and human body because they are toxic and non-biodegradable and widely exist in environmental ecosystems. It is necessary to develop a rapid, sensitive and convenient method for HMIs detection to provide a strong guarantee for ecology and human health. Ion-imprinted electrochemical sensors (IIECSs) based on nanomaterials have been regarded as an excellent technology because of the good selectivity, the advantages of fast detection speed, low cost, and portability. Electrode surfaces modified with nanomaterials can obtain excellent nano-effects, such as size effect, macroscopic quantum tunneling effect and surface effect, which greatly improve its surface area and conductivity, so as to improve the detection sensitivity and reduce the detection limit of the sensor. Hence, the present review focused on the fundamentals and the synthetic strategies of ion-imprinted polymers (IIPs) and IIECSs for HMIs detection, as well as the applications of various nanomaterials as modifiers and sensitizers in the construction of HMIIECSs and the influence on the sensing performance of the fabricated sensors. Finally, the potential challenges and outlook on the future development of the HMIIECSs technology were also highlighted. By means of the points presented in this review, we hope to provide some help in further developing the preparation methods of high-performance HMIIECSs and expanding their potential applications.

Electrospun tannin-rich nanofibrous solid-state membrane for wastewater environmental monitoring and remediation

Heavy metal, organic dyes, and bacterial contamination in water endanger human/animals' health, and therefore, the detection, adsorption, and capturing of contaminants are essential for environmental safety. Ligand-rich membranes are promising for sensors, adsorption, and bacterial decontamination. Herein, tannin (TA)-reinforced 3-aminopropyltriethoxysilane (APTES) crosslinked polycaprolactone (PCL) based nanofibrous membrane (PCL-TA-APTES) was fabricated via electrospinning. PCL-TA-APTES nanofibers possess superior thermal, mechanical, structural, chemical, and aqueous stability properties than the un-crosslinked membrane. It changed its color from yellowish to black in response to Fe^2+/3+ ions due to supramolecular iron-tannin network (FeTA) interaction. Such selective sensing has been noticed after adsorption-desorption cycles. Fe³⁺ concentration, solution pH, contact time, and ligand concentration influence FeTA coordination. Under optimized conditions followed by image processing, the introduced membrane showed a colorimetric linear relationship against Fe³⁺ ions (16.58 μM-650 μM) with a limit of detection of 5.47 μM. The PCL-FeTA-APTES membrane could restrain phenolic group oxidation and result in a partial water-insoluble network. The adsorption filtration results showed that the PCL-FeTA-APTES membrane can be reused and had a higher methylene blue adsorption (32.04 mg/g) than the PCL-TA-APTES membrane (14.96 mg/g). The high capture efficiency of nanocomposite against Fe³⁺-based S. aureus suspension than Fe³⁺-free suspension demonstrated that Fe³⁺-bounded bacterium adhered to the nanocomposite through Fe³⁺/TA-dependent biointerface interactions. Overall, high surface area, rich phenolic ligand, porous microstructure, and super-wetting properties expedite FeTA coordination in the nanocomposite, crucial for Fe^2+/3+ ions sensing, methylene blue adsorption-filtration, and capturing of Fe³⁺-bounded bacterium. These multifunctional properties could promise nanocomposite membrane practicability in wastewater and environmental protection.

Natural and Engineered Nanomaterials for the Identification of Heavy Metal Ions—A Review

In recent years, there has been much interest in developing advanced and innovative approaches for sensing applications in various fields, including agriculture and environmental remediation. The development of novel sensors for detecting heavy metals using nanomaterials has emerged as a rapidly developing research area due to its high availability and sustainability. This review emphasized the naturally derived and engineered nanomaterials that have the potential to be applied as sensing reagents to interact with metal ions or as reducing and stabilizing agents to synthesize metallic nanoparticles for the detection of heavy metal ions. This review also focused on the recent advancement of nanotechnology-based detection methods using naturally derived and engineered materials, with a summary of their sensitivity and selectivity towards heavy metals. This review paper covers the pros and cons of sensing applications with recent research published from 2015 to 2022.

Ionic liquid-immobilized silica gel as a new sorbent for solid-phase extraction of heavy metal ions in water samples

In the current study, we have developed a solid-phase extraction (SPE) method with novel C18-alkylimidazolium ionic liquid immobilized silica (SiO₂–(CH₂)₃–Im–C₁₈) for the preconcentration of trace heavy metals from aqueous samples as a prior step to their determination by inductively coupled plasma mass spectrometry (ICPMS). The material was characterized by Fourier-transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA), Energy-Dispersive X-ray Spectroscopy (EDS), and Brunauer–Emmett–Teller (BET) analysis. A mini-column packed with SiO₂–(CH₂)₃–Im–C₁₈ sorbent was used for the extraction of the metal ions complexed with 1-(2-pyridylazo)-2-naphthol (PAN) from the water sample. The effects of pH, PAN concentration, length of the alkyl chain of the ionic liquid, eluent concentration, eluent volume, and breakthrough volume have been investigated. The SiO₂–(CH₂)₃–Im–C₁₈ allows the isolation and preconcentration of the heavy metal ions with enrichment factors of 150, 60, 80, 80, and 150 for Cr³⁺, Ni²⁺, Cu²⁺, Cd²⁺, and Pb²⁺, respectively. The limits of detection (LODs) for Cr³⁺, Ni²⁺, Cu²⁺, Cd²⁺, and Pb²⁺ were 0.724, 11.329, 4.571, 0.112, and 0.819 μg L⁻¹, respectively with the relative standard deviation (RSD) in the range of 0.941–1.351%.

Novel C18-alkylimidazolium ionic liquid immobilized silica (SiO₂–(CH₂)₃–Im–C₁₈) was synthesized through a four-step procedure. It showed high efficiency for the separation/preconcentration of trace heavy metal ions from aqueous samples.

Field-effect-transistor-based ion sensors: ultrasensitive mercury(II) detection via healing MoS2 defects

The contamination of water with heavy metal ions represents a harsh environmental problem resulting from societal development. Among various hazardous compounds, mercury ions (Hg²⁺) surely belong to the most poisonous ones. Their accumulation in the human body results in health deterioration, affecting vital organs and eventually leading to chronic diseases, and, in the worst-case scenario, early death. High selectivity and sensitivity for the analyte of choice can be achieved in chemical sensing using suitable active materials capable of interacting at the supramolecular level with the chosen species. Among them, 2D transition metal dichalcogenides (TMDCs) have attracted great attention as sensory materials because of their unique physical and chemical properties, which are highly susceptible to environmental changes. In this work, we have fabricated MoS₂-based field-effect transistors (FETs) and exploited them as platforms for Hg²⁺ sensing, relying on the affinity of heavy metal ions for both point defects in TMDCs and sulphur atoms in the MoS₂ lattice. X-ray photoelectron spectroscopy characterization showed both a significant reduction of the defectiveness of MoS₂ when exposed to Hg²⁺ with increasing concentration and a shift in the binding energy of 0.2 eV suggesting p-type doping of the 2D semiconductor. The efficient defect healing has been confirmed also by low-temperature photoluminescence measurements by monitoring the attenuation of defect-related bands after Hg²⁺ exposure. Transfer characteristics in MoS₂ FETs provided further evidence that Hg²⁺ acts as a p-dopant of MoS₂. Interestingly, we observed a strict correlation of doping with the concentration of Hg²⁺, following a semi-log trend. Hg²⁺ concentrations as low as 1 pM can be detected, being way below the limits imposed by health regulations. Electrical characterization also revealed that our sensor can be efficiently washed and used multiple times. Moreover, the developed devices displayed a markedly high selectivity for Hg²⁺ against other metal ions as ruled by soft/soft interaction among chemical systems with appropriate redox potentials, being a generally applicable approach to develop chemical sensing devices combining high sensitivity, selectivity and reversibility, to meet technological needs.

Application of Metallic Nanoparticles and Their Hybrids as Innovative Sorbents for Separation and Pre-concentration of Trace Elements by Dispersive Micro-Solid Phase Extraction: A Minireview

It is indisputable that separation techniques have found their rightful place in current analytical chemistry, considering the growing complexity of analyzed samples and (ultra)trace concentration levels of many studied analytes. Among separation techniques, extraction is one of the most popular ones due to its efficiency, simplicity, low cost and short processing times. Nonetheless, research interests are directed toward the enhancement of performance of these procedures in terms of selectivity. Dispersive solid phase extraction (DSPE) represents a novel alternative to conventional solid phase extraction (SPE) which not only delivers environment-friendly extraction with less solvent consumption, but also significantly improves analytical figures of merit. A miniaturized modification of DSPE, known as dispersive micro-solid phase extraction (DMSPE), is one of the most recent trends and can be applied for the extraction of wide variety of analytes from various liquid matrices. While DSPE procedures generally use sorbents of different origin and sizes, in DMSPE predominantly nanostructured materials are required. The aim of this paper is to provide an overview of recently published original papers on DMSPE procedures in which metallic nanoparticles and hybrid materials containing metallic particles along with other (often carbon-based) constituent(s) at the nanometer level have been utilized for separation and pre-concentration of (ultra)trace elements in liquid samples. The studies included in this review emphasize the great analytical potential of procedures producing reliable results in the analysis of complex liquid matrices, where the detection of target analyte is often complicated by the presence of interfering substances.

A Cd-MOF fluorescence sensor with dual functional sites for efficient detection of metal ions in multifarious water environments

A 2D MOF displays high performance luminescence quenching for detecting Fe3+ and Cu2+ in pure water, actual river water and simulated HEPES with superior low LODs. Multiple experiments and DFT calculations co-verify a weak interaction quenching mechanism.