Metal Ions In Aqueous Solution Research Articles

Utility of newly modified chitosan in the removal of heavy metal ions from aqueous medium: ion selectivity, XPS and TGA

The purpose of this study is to evaluate the newly prepared modified chitosan, a new environmentally friendly adsorbent, in the field of wastewater treatment. Chitosan (CS) reacted with 3-chloro-2,4-pentanedione to give CS derivatives, CS-CPD. Modified CS with O–O and N–O chelating centres was treated with aqueous solution containing different metal ions to investigate its metal uptake and selectivity. The concentration of metal ions in aqueous solution was measured by inductively coupled plasma-optical emission spectrometry. The structure of the complex was identified by elemental analysis, infrared and solid-nuclear magnetic resonance. In addition, the chelating centres were determined by X-ray photoelectron spectroscopy. The morphology of the modified polymer and its metal complexes was studied to show a dramatic change in cases of the CS-CPD–Pb, CS-CPD–Hg, CS-CPD–Cr and CS-CPD–Co complexes.

Versatile core/shell-like alginate@polyethylenimine composites for efficient removal of multiple heavy metal ions (Pb2+, Cu2+, CrO42-): Batch and fixed-bed studies

Versatile adsorptive materials that can efficiently capture anionic and cationic heavy metals are extremely significant in purification of complex wastewater systems. Herein, a new type of amine modified, biopolymer-derived core/shell-like adsorbents were employed in heavy metal anion and cation adsorption. The maximum adsorption capacities for Cr(VI), Pb(II), and Cu(II) were measured to be 497.1, 535.6, and 163.7 mg/g, respectively. The adsorbent also showed great performance in heavy metal cation adsorption in fixed bed column experiments. Additionally, removal efficiency and rapid adsorption kinetics on low concentration heavy metal pollutions for both anion and cations were well discussed to demonstrate the potential in real accidental heavy metal pollution. The prepared core/shell-like biopolymer adsorbents were demonstrated to be a kind of versatile adsorbent for both anionic and cationic heavy metal ions in aqueous solutions.

Novel graphene oxide/carboxymethyl chitosan aerogels via vacuum-assisted self-assembly for heavy metal adsorption capacity

In this work, we synthesized a new type of graphene oxide/carboxymethyl chitosan (GO/CMC) composite aerogels via vacuum-assisted self-assembly and freeze-drying method. Then we evaluated their adsorption performance for metal ions in aqueous solution. The three-dimensional porous network structures of as-prepared aerogels were established by the hydrogen bonding interaction between CMC chains and the surface of GO and crosslinks using triphosphoric acid (TPP) or glutaraldehyde (GA). The chemical structure, microstructure, mechanical and thermal properties, and absorption capability of these aerogels were investigated using many experimental techniques. The crosslinking methods of TPP and GA were the ionic and chemical crosslinking ones, respectively. GO/CMC aerogels contained abundant oxygen- and nitrogen- containing groups to provide adsorption sites and displayed the crosslinked porous structures to facilitate adsorbate diffusion. The CMC chains prevented brittle fracture, whereas GO resisted pressure resulting that in compressive strength and elastic modulus of GO/CMC aerogels to reach up to 16.77 and 368.35 MPa, respectively. The adsorption system of GO/CMC aerogels was accurately simulated using the pseudo-second-order kinetic and Langmuir isotherm models, in which the maximum adsorption capacities were 151.30 mg/g for Ag+, 95.37 mg/g for Cu2+ and 249.38 mg/g for Pb2+.

Enhancement of QCM Detection for Heavy Metal Ions Based on TGA Modified CdTe Nanospheres

Quartz crystal microbalance sensor was designed based on thioglycolic acid (TGA) modified CdTe nanospheres to detect heavy metal ions in aqueous solution. TGA plays an important role in the adsorption of heavy metal ions, and CdTe nanospheres are used to amplify mass signals. Experimental results show that the sensitivity of the sensor is six times that of the QCM sensor based on TGA only. Frequency shifts show a good linear relationship with the concentration of heavy metal ions. The detection limit for Pb2+, Cd2+ and Cu2+ is 0.096, 0.089 and 0.189 μg/L respectively. This sensing system is also found partially reversible by adding the strong chelating agent to remove the heavy metal ions on the electrode surface.

Experiments on the magnetic enrichment of rare-earth metal ions in aqueous solutions in a microflow device

An attempt is made to achieve a continuous enrichment of rare-earth metal ions from aqueous solutions in a microflow device by applying magnetic forcing. An aqueous solution containing holmium(III) ions is pumped through a small channel which was exposed to a strong inhomogeneous magnetic field. At the outflow, the near- and far-field parts of the flow are separated and analyzed using UV-Vis spectroscopy. The relative change of ion concentration is determined from the measured absorbance. Results are reported for three different types of flow cells at different flow rates and magnetic field strengths and for a cascaded application of cells. The change of concentration is found to be small, and no clear trend can currently be stated due to the error margin of the concentration measurement.

Time correlation functions and kinetic coefficients in systems with molecular or chemical exchange

We develop a kinetic theory for systems with molecular or chemical exchange. In such systems, particles can successively reside in two different dynamical states with the inter-state transition. A prominent example of the molecular exchange (ME) is aqueous solutions of macromolecules (proteins, DNA) or metal ions, where a water molecule can move freely in a bulk of the solution or perform a constrained motion in a bound state. This may be the surface of the macromolecule or the ion's hydration shell. Another example, which refers to the chemical exchange (CE), is a molecule in a solution, that reversibly alternates its conformation — different conformations imply different rotational and translational motion. We consider the case of Poissonian exchange between states and general, non-Poissonian exchange and derive general relations for time correlation functions and kinetic coefficients. The application of the theory is illustrated by computation of time correlation functions and kinetic coefficients for translational and rotational motion of particles in systems with exchange.

Non-Enzymatic Electrochemical Detection of Mercury Ions on Graphene Quantum Dot-Based Electrodes

This study adopts an efficient method to electrochemically detect Hg2+ ions in aqueous solutions using graphene quantum dot (GQD) based electrodes. Previous studies reported that GQDs are capable of detecting metal ions (e.g., Hg2+ and Fe2+) at ultralow concentrations, showing an obvious fluorescence quenching in the presence of metal ions in aqueous solutions. However, there are few studies focusing on electrochemical detection of metal ions using GQD-based electrodes. The electrochemical detection technique is a convenient and simple method to accurately estimate real concentration of the contaminants based on the change of peak current density or ohmic resistance. In this study, GQDs were prepared by a hydrothermal technique using organic compound as precursor. The as-prepared GQDs with an average particle size of 5 nm were functionalized by surface oxygen groups, including carbonyl, carboxyl, and hydroxyl groups attached to basal planes and edges of sp 2-domain graphene. The non-enzymatic electrochemical detection of Hg2+ ions on GQD-based electrodes was carried out using cyclic voltammetry within a potential range between 0 and 1.7 V vs. Ag/AgCl. Experimental results showed that the reduction of peak current at 0.35 V is proportional to the concentration of Hg2+ ions. The detection limit of mercury ions by GQD-based electrode can reach as low as 0.1 mg/L. Accordingly, the unique design of GQD-based electrode displays the feasibility in application to electrochemical detection of environmentally pollution micro-inspection. Future work on how N-doping and dopant concentration on the sensitivity and selectivity of GQD-based electrodes is on-going.

Selective removal of heavy metal ions in aqueous solutions by sulfide-selector intercalated layered double hydroxide adsorbent

Remaining largely under-appreciated, a majority of metal ion sorbents are limited in their target selectivity. In this work, a 3D sulfide intercalated NiFe-layered double hydroxide (NFL-S) hierarchical sorbent has been synthesized for selective heavy metal removal. The intercalation of sulfurated groups in the interlayer of the layered double hydroxide (LDH) nanosheets endows NFL-S as a selective heavy metal ion filter; the selectivity of NFL-S for heavy metals is in the order of Pb2+ > Cu2+ ≥ Zn2+ > Cd2+> Mn2+, and NFL-S has high kd values for Pb2+ (∼106 mL/g) and Cu2+ (∼105 mL/g). Scanning electron microscopy, X-ray photoelectron spectroscopy and powder X-ray diffraction were used to analyze the composition of the as-prepared nanoadsorbent. The selective adsorption behavior was systematically studied using batch experiments, and the performance was evaluated through kinetic and isotherm studies. Moreover, the adsorption mechanism of heavy metals by NFL-S through surface complexation was also investigated, which shows great potential for water decontamination.

Comprehensive spectroscopy studies of photoelimination process of toxic metals ions from aqueous solution by using CdS and CdS@magnetized powder activated carbon assisted magnetic stir bar.

In this study, a simple and novel photocatalytic tool was proposed and developed for photoelimination of toxic metal ions in aqueous solution. CdS quantum dots capped with thioglycolic acid and CdS @ magnetized powder activated carbon (CdS@MPAC) fixed on magnetic stir bar was constructed and applied for photoelimination of toxic metal ions in aqueous solutions. The production and contribution of hydroxyl (OH) and superoxide (O2-) species generated during photoelimination process were investigated. The photoelimination of Cd(II), Co(II), Cu(II), Mn(II), Ni(II) and Pb(II) metal ions was performed at neutral pH (7.0 ± 0.1) with the same experimental circumstances. Maximum removal efficiency was achieved with 0.360 M of CdS@MPAC under 3.0 h daylight irradiation. Photoelimination mechanisms of Cu2+ with CdS QDs were also investigated. Finally, this method was successfully applied for elimination of toxic metal ions from real sample.

Metallobacitracins: Affinity and structural study in aqueous solution

Metallobacitracins are complexes with an extensive antimicrobial and biological activity. In this work, we investigated the metal complexation of bacitracin with several divalent metal ions in aqueous solution. The binding constants of Zn(2+), Cd(2+), Hg(2+), Cu(2+), Ni(2+), Pd(2+), Fe(2+), Mn(2+) and Mg(2+) to bacitracin were measured by UV/Vis spectroscopy, isotermic titration calorimetry (ITC) and potentiometry while the complexes were studied by Circular Dichroism and Nuclear Magnetic Resonance (15N HSQC) for Zn(2+), Cd(2+) and Hg(2+) at different pH. By UV/Vis spectroscopy the affinity is in the range 104 to 105 M−1 at pH 6 and follows the order Ni(2+) > Cd(2+) > Hg(2+) > Zn(2+) > Fe(2+). By potentiometry, the binding constants were determined in the pH range 2–12. Microcalorimetry shows that the stoichiometry of metallobacitracins investigated is 1:1 with binding constants in the range 105–102 M−1 at pH 6 and with an order of stability of Ni(2+) > Cd(2+) > Zn(2+) > Hg(2+); ΔS, ΔH and ΔG parameters were also determined. NMR spectroscopy lets us establish the binding site of the metal ion when comparing 15N HSQC of free bacitracin and complex in natural abundance; these findings agree with calorimetric results. Chemical shift changes in complexes containing Zn(2+) and Cd(2+) exhibit a similar behavior despite pH differences. Conversely, there is not a significant change for Hg(2+) complex. The obtained data contribute to understand the mechanism of the biological activity of the metallobacitracins and give the guideline for the design of more powerful metalloantibiotics.

Importance of van der Waals effects on the hydration of metal ions from the Hofmeister series.

The van der Waals (vdW) interaction plays a crucial role in the description of liquid water. Based on ab initio molecular dynamics simulations, including the non-local and fully self-consistent density-dependent implementation of the Tkatchenko-Scheffler dispersion correction, we systematically studied the aqueous solutions of metal ions (K+, Na+, and Ca2+) from the Hofmeister series. Similar to liquid water, the vdW interactions strengthen the attractions among water molecules in the long-range, leading to the hydrogen bond networks softened in all the ion solutions. However, the degree that the hydration structure is revised by the vdW interactions is distinct for different ions, depending on the strength of short-range interactions between the hydrated ion and surrounding water molecules. Such revisions by the vdW interactions are important for the understanding of biological functionalities of ion channels.

Kinetics and mechanisms of the interaction between the calcite (10.4) surface and Cu2+-bearing solutions

Calcite dissolution, occurring in rocks, soils and sediments, is essential to indicate element cycles and local environments in the lithosphere, biosphere, hydrosphere and atmosphere. Calcite dissolution strongly depends on metal ions in aqueous solutions. Previous studies showed that aquatic Cu2+, a typical bio-toxic metal ion, can alter the calcite dissolution behavior. However, wide concentration ranges of Cu2+ coexisting with ubiquitous anions in local environments, such as waterways in the oxidation zones of copper deposits and soils near metal processing industry, was overlooked. When a considerable amount of aquatic Cu2+ ions are released into the environment, they migrate, diffuse, and hence become an environmental pollutant. Therefore, we focused on the interaction between calcite dissolution and wide concentration ranges of Cu2+-bearing solutions with different types of anions (SO42−, Cl− and NO3−). Comprehensive approaches including in situ atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM), and density functional theory (DFT) calculations were employed to investigate kinetics and mechanisms of the interaction between the calcite (10.4) surface and Cu2+-bearing solutions. Results demonstrated that both anion types and Cu2+ concentrations dramatically affect calcite dissolution. The morphology of etch pits generated in CuSO4 solutions can be fan-shaped but changed to tear-shaped in Cu(NO3)2 or CuCl2 solutions. Calcite dissolution kinetics is inhibited at cCu2+ ≤ 0.1 mM, caused by the coverage of active sites on calcite surfaces. As the Cu2+ concentration increases (1 mM ≤ cCu2+ ≤ 10 mM), calcite dissolution kinetics is enhanced due to the coupling effect of Cu2+-incorporated surface structure and solution chemistry. These results revealed the interactive mechanism between calcite dissolution and the migration of toxic Cu2+ in waterways, provided a practical consideration in dealing with the local environment.

Investigation on synthesis of ion-imprinted mesoporous adsorbents by using ultrasound- and microwave-assisted preparation and their dynamic adsorption properties on heavy metals.

Removal of the heavy metal ions in aqueous solution is an important technology for waste water treatment. The effects of using ultrasonic and microwave on synthesizing Pb2+, Zn2+, and Cu2+ imprinted mesoporous adsorbents (Pb-IMA-UM, Zn-IMA-UM, and Cu-IMA-UM) and their dynamic adsorption properties were studied. The microstructure and composition of the ion-imprinted mesoporous adsorbents were discussed in detail by TEM, FTIR, N2 adsorption-desorption, XRD, and EDS. The pore sizes of mesoporous absorbents were improved more uniformly by using ultrasonic agitation than magnetic stirring. The elution efficiency of imprinting ions can be enhanced by microwave elution. Prepared Pb-IMA-UM, Zn-IMA-UM, and Cu-IMA-UM were used for dynamic adsorption study of heavy metals. The detected optimal feed rate was 20.0mL/min and the influent concentration was 60mg/L; the equilibrium adsorption capacities of Pb-IMA-UM, Cu-IMA-UM, and Zn-IMA-UM could reach 198mg/g, 51.5mg/g, and 57.3mg/g, respectively. The dynamic regeneration performance of the adsorbent was also investigated with the Cu-IMA-UM sample. The adsorption rate remained above 89% after five dynamic regeneration experiments. At last, the actual wastewater from an electroplating industry was used as the research object. Three groups of dynamic adsorption coefficient contours of Pb-IMA-UM, Zn-IMA-UM, and Cu-IMA-UM were obtained when influents flowed into three adsorption columns separately. The experimental results showed that an ion-imprinted adsorbent had a much better adsorption capacity of imprinted ions under the various metals mixed conditions.

Plasmonic Sensing of Aqueous-Divalent Metal Ions by Biogenic Gold Nanoparticles

The chemical interaction between biogenic gold nanoparticles (AuNPs) and several metal (II) ions can be regarded as a practical, twofold, colorimetric, and plasmon resonance sensing method for the recognition of some divalent metal ions in aqueous solutions. The green synthesized AuNPs, using Camellia sinensis as a reducing agent, were characterized by a surface plasmon resonance (SPR) using UV-Vis spectroscopy, infrared spectroscopy, and transmission electron microscopy. The AuNP colloidal solutions obtained have a pink-reddish color with SPRs centered between 529 and 536 nm. AuNPs with spherical, triangular, and hexagonal shapes were found by TEM analyses. Despite their divergent morphologies, these AuNPs can be employed as colorimetric and plasmon resonance sensors for detection of Ca2+, Sr2+, Cu2+, and Zn2+, primarily, in aqueous solutions. Sensibility studies based on molar concentrations were also performed for these metal ions. Furthermore, solid biogenic AuNPs/cellulosic biocomposites were prepared with the aim of developing portable, fast, and dependable colorimetric sensors; nevertheless, these biocomposites resulted to be good adsorbent materials of metal ions.

Naked-eye chromogenic and fluorogenic chemosensor for mercury (II) ion based on substituted distyryl BODIPY complex

One kind of novel distyryl substituted BODIPY-based fluorescent chemosensor 2 for Hg2+ ion sensing has been reported. Large hypsochromic shift of the absorption band is observed upon titration with Hg2+ ion resulting in a solution color change from green to light yellow, enabling “naked-eye” detection possible. Meanwhile, the fluorescence intensity of 2 around 680 nm was quenched upon adding Hg2+ ion due to the blocking of the ICT process. Most importantly, chemosensor 2 exhibits high selectivity and sensitivity towards Hg2+ ion over other metal ions in aqueous solutions.

Understanding the high adsorption-reduction performance of triethanolamine modified graphene oxide for silver ions

Graphene oxide (GO) and its derivatives have attracted much attention for metal ions removal in aqueous solution. Here, the adsorption-reduction performance and mechanism of triethanolamine (TEOA) modified GO towards silver ions (Ag+) were investigated. Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) characterizations indicated that TEOA molecules were tightly anchored on GO surface through two types of interactions including chemical interaction and electrostatic interaction. The adsorption performance results showed that the electrostatic interaction TEOA on GO contributed to a high initial adsorption capacity towards Ag+, while chemical interaction TEOA on GO led to a constant rising of the adsorption capacity with increase of Ag+ concentration. Theoretical calculation, XPS and transmission electron microscopy (TEM) characterization further revealed the chemical interaction TEOA produced pyridine N species which exhibited strong reducibility, so that Ag+ was adsorbed and reduced to Ag metal thereon, and further aggregated into larger particles. Integrating the results of instrument characterizations, adsorption performance, and theoretical calculation, we proposed that the adsorption-reduction-aggregation-regeneration circulation led to the constant rising of adsorption capacity of Ag+ on GO with chemical-bonded TEOA. The conclusions in this paper provide us a new insight into the adsorption mechanism of Ag+ on TEOA modified GO and rendered an efficient alternative for the recovery and removal of metal ions in aqueous solution.

Highly selective and sensitive detection of Fe3+, Al3+ and picric acid by a water-stable luminescent MOF

A novel luminescent metal-organic framework (MOF) {[Co3(phen)2(HL)2]·(H2O)2}n (1) (H4L = 3,3′,5,5′-azoxybenzenetetracarboxylic acid, phen = Phenanthroline) was successfully prepared under solvothermal conditions. Its structure has been identified by single-crystal X-ray diffraction, infrared spectroscopy, elemental analysis, powder X-ray diffraction and thermogravimetric analysis. Additionally, the importance of the weak interactions to stabilize the structure of 1 has been discussed by Hirshfeld surfaces and the corresponding 2D fingerprint plots (FPs). Remarkably, 1 has high thermal stability up to 360 °C and excellent chemical stability in water with wide pH range of 2–11. Luminescence studies show 1 can recognize Fe3+ and Al3+ with high selectivity from mixed metal ions in aqueous solutions through the luminescence quenching and enhancement phenomenon, respectively. Furthermore, 1 can also detect PA with good selectivity and sensitivity among large common nitro-aromatic compounds (NACs).

Heavy Metal Ion Pollution in Aqueous Solution: An Environmental Hazard

Aquatic systems are indispensable part of a balanced ecosystem which is abode to natural flora and fauna, biodiversity etc. If the natural ingredients, mainly the compositional elements are in less proportional amount; there is no harm done as there remains a total balance in the overall process of stakeholders [1-3]. However, since last two decades, there happens to be a serious factor which is posing as a large threat to the existing aquatic systems. There is a rise in concentration of heavy metal ion in aqueous solution which is gradually surging alarmingly [4-6].

Covalent Construction of Sustainable Hybrid UiO-66-NH2@Tb-CP Material for Selective Removal of Dyes and Detection of Metal Ions

The development of quick and effective strategies for the removal of organic dyes and the detection of metal ions in aqueous solutions remains a challenge for protecting the public health and envir...

Fluorescent electronic tongue based on soluble conjugated polymeric nanoparticles for the discrimination of heavy metal ions in aqueous solution

A fluorescence sensing array (or fluorescent electronic tongue) based on six sorts of soluble conjugated polymeric nanoparticles (SCPNs) decorated with PEG chains is designed for the rapid identification of heavy metal ions in water.