Heavy Metal Ions In Environment Research Articles

A sensitive electrochemical sensor based on 3D porous melamine-doped rGO/MXene composite aerogel for the detection of heavy metal ions in the environment

Herein, we developed a unique screen-printed carbon electrode (SPCE) with three-dimensional melamine-doped graphene oxide/MXene composite aerogel (3D MGMA) modification, which is used for the simultaneous and sensitive detection of three metal ions (Zn2+, Cd2+, and Pb2+) in the environment. A self-assembly method was used to fabricate 3D MXene aerogels based on MXene, graphene oxide (GO), and melamine. Notably, the network-like 3D structure combining 2D MXene and rGO sheets can provide a high ratio of surface area and enriched functional clusters, which are beneficial for improving the electrical conductivity and promoting the uptake of heavy metal ions. In the linear range of 3–900 μg L-1, the constructed innovative sensing platform can sensitively detect Zn2+, Cd2+, and Pb2+ simultaneously, with detection limits of 0.48 μg L-1,0.45 μg L-1 and 0.29 μg L-1 respectively. This work reflects precision and reliability in the detection of three water samples (tap water, Minzhu lake and Yangtze River) and four cereal samples (sorghum, rice, wheat and corn), proposing a novel strategy for monitoring heavy metal ions in the natural environment.

Effect of layer charge density and cation concentration on sorption behaviors of heavy metal ions in the interlayer and nanopore of montmorillonite: A molecular dynamics simulation

Soil and ground water pollution by heavy metal is an identified global environment concern. Montmorillonite is widely adopted as an adsorbent used in retardation of heavy metals due to its excellent adsorption capacity, conveniency, and stability. However, the adsorption mechanism of heavy metal ions in the interlayer and nanopore of montmorillonite needs to be further studied. The classical grand canonical monte carlo (GCMC) and molecular dynamics (MD) simulations were performed to quantify the structural and dynamic properties of heavy metal ions in the interlayer and nanopore of montmorillonite (MMT). Two layer charge densities of MMT, two cation concentrations, and three typical heavy metal ions (Pb2+, Ba2+, and Cs+) were considered. With the increase of layer charge density, outer-sphere adsorption (OSA) was transformed into inner-sphere adsorption (ISA) for three heavy metal ions. The adsorption quantity increased with the increase of layer charge density and cation concentration. The calculated diffusion coefficients of three heavy metal caions in montmorillonite was bulk solution > nanopore > interlayer. The results and adsorption mechanism are helpful for understanding the natural processes of heavy metal ions in environment and developing more efficient remediation materials.

The effect of surface heterogeneity between α-quartz and α-cristobalite on adsorption behaviors toward Cu2+ solution

Mineral surface microstructure and properties not only exert an important influence on the surface dissolution and growth of minerals, but also control the reaction rate and model between mineral and heavy metal ions in environment. The surface difference of silica polymorphs had been verified in some previous studies. To further study the effect of surface heterogeneity between α-quartz and α-cristobalite on adsorption behaviors toward heavy metal ions, the adsorption characteristics of Cu2+ ions were investigated by adsorption experiments. Cu2+ ions were predominantly adsorbed on α-quartz because of its larger surface site density. The reaction between α-quartz/α-cristobalite and Cu2+ ions was an endothermic process. The increase of pH could prompt the formation of Cu precipitation on the surface, corresponding to the declined intensity of EPR signal of g=2.08/2.05 at a higher pH. Cu2+ ions were bonded with surface oxygen atoms to form an inner-sphere structure at lower pH and initial concentration solutions. The intensity loss of g=2.08 in α-quartz in a higher initial concentration demonstrated the formation of Cu(II) dimeric/polynuclear species, resulting from the larger surface site density. While, from the increased EPR signal of g=2.08, mononuclear adsorption was still the predominant form on α-cristobalite under the same reaction conditions.

Study of the effect of weathered coal activated by ultrasonic on speciation of Cr in soil

The humic acid in weathered coal contains a large number of reactive functional groups which can stably combine with heavy metal ions in the environment. This changes its biochemical stability and water solubility, reducing the migration of heavy metal ions in the soil environment to achieve the purpose of remediation of heavy metal pollution. The goal of this paper is to investigate the effects of ultrasonic activated weathered coal on the speciation of chromium (Cr) in soil and bioavailability of Cr under pakchoi cultivation. The results showed that in comparison to the control group, both the content of exchangeable, reducible and oxidizable Cr and the absorption of Cr in the soil decreased after adding weathered coal. Under the conditions of 60g/kg of ultrasonic activated weathered coal, the content of Cr absorbed by pakchoi plants was the lowest, which was 62.0% lower than that of the control group. Additionally, the content of Cr in soil reached the maximum value, which was 12.7% higher than that of the control group. Cr mainly exists as a residual state in the environment and this was 755.8% higher than that of the control group. Under the same conditions of weathered coal addition, U-WC can significantly reduce the Cr content of the weak acid extracted, reducible and oxidizable fraction in the soil, and the effective Cr content is reduced, thereby reducing Cr migration and biotoxicity in soil. This provides a theoretical basis for the application of weathered coal humic acid fertiliser in the application of weathered coal fertiliser in Cr-polluted areas.

New strategy for fabricating Cd(II) sensing electrochemical interface based on enhanced adsorption followed by redox processes: Ferro-cerium oxide nanocomposite as an example

Cd(II) is a biologically active element that requires rapid and reliable monitoring for its pollution control. We designed the electrochemical sensing nanocomposite with enhanced adsorption followed by redox processes, which was synthesized by incorporating ferric ions into cerium oxide substrate（hereafter CeFe2O5）via the sol-gel combustion method. The CeFe2O5 nanocomposite modified glassy carbon electrode (CeFe2O5/GCE) was used for selective detection of Cd(II) by square wave anode stripping voltammetry (SWASV). At optimal experimental conditions, the observed sensitivity and detection limits of CeFe2O5/GCE are 31.68 μA/μM and 0.94 nM, respectively. Our CeFe2O5/GCE exhibits excellent stability (RSD 3.34%) and analytical precision for Cd(II). The CeFe2O5/GCE can also be used in trace detection of heavy metal ions spiked in environmental samples. The nanocomposites with high electrochemical performance would be of great interest for constructing novel sensing platforms for monitoring heavy metal ions in environment.

Lab-on-cloth integrated with gravity/capillary flow chemiluminescence (GCF-CL): towards simple, inexpensive, portable, flow system for measuring trivalent chromium in water

Flow chemiluminescence (CL) is widely applied for detection of heavy metal ions in environment, but it is seldom used in economical, practical, or affordable settings because non- and minimally instrumented flow driving is difficult to achieve. Here, we first report a gravity and capillary force-driven flow CL (GCF-CL) lab-on-cloth device, toward development of low-cost, easy-to-use, portable, minimally-instrumented platform for determination of trivalent chromium [Cr(III)] in water, where a difference in height between two zones on cloth creates a fast flow of CL trigger solution. Wax screen-printing was used to fabricate ultra-low-cost cloth-based devices, and the light emitted from the Cr(III)-catalysed oxidation of luminol by H2O2 was imaged using an inexpensive portable CCD camera. Under optical conditions, Cr(III) could be determined over the range of 0.01–100mg/L, with a detection limit of 6.2μg/L, an analysis time of less than 30s per sample, and RSDs of 6.2%, 3.1% and 1.7% for 0.05, 0.5 and 5mg/L Cr(III) (n=5). The proposed GCF-CL lab-on-cloth was successfully applied for measuring Cr(III) in water samples, with recoveries of 100.67-111.70% and RSDs of 4.73–6.88%. Thus, the presented method should have the potential for portable field applications in environmental and public health fields.

Thermo-responsive electrospun nanofibers doped with 1,10-phenanthroline-based fluorescent sensor for metal ion detection

Heavy metal ion pollution is one of the important environmental problems, and many efforts have been devoted to develop highly sensitive sensors for detection of heavy metal ions in environment. In this study, an 1,10-phenanthroline-based fluorescent sensor (F-phen) was synthesized and doped into poly(N-isopropylacrylamide-co-N-hydroxymethyl-acrylamide) (Poly(NIPAAm-co-NMA)) nanofiber films via simple electrospinning technique, where the moieties of NIPAAm and NMA were designed to exhibit thermo-responsive and chemical crosslinking functions, respectively. The electrospun nanofibers prepared from the appropriate composition of NMA in the copolymer (P3) could stabilize their fibrous morphology in aqueous environment. Among different weight ratios of F-Phen doped in nanofibers, P3-3 (3 wt% corresponding to copolymer) showed significant quenching of fluorescence as chelating with Cu2+ ion. The linear Stern–Volmer plot of nanofibers for Cu2+ was observed, and the calculated Stern–Volmer constant (K sv ) was 5.5 × 104 M−1. As compared to dip-coating films, the downward deviation to linear Stern–Volmer plots of thin films was observed, indicating a fraction of F-Phen was inaccessible to the quencher (Cu2+). The enhanced sensitivity of F-Phen-doped electrospun nanofibers is attributed to their higher surface area compared to dip-coating films. In addition, the F-Phen-doped nanofibers also exhibited an on/off switchable sensing behavior. This is due to the hydrophilic–hydrophobic change of PNIPAAm as varying temperature that controlled the metal ions to be accessible to the sensors. All of the results indicate the thermo-responsive electrospun sensing nanofibers not only enhance the sensitivity and have an on–off sensing characteristic, but also provide a simple strategy to design and fabricate effective sensing materials for detection of metal ions.