Toxic Heavy Metal Cations Research Articles

Zeolite performance in removal of multicomponent heavy metal contamination from wastewater

Efficient removal of heavy metal pollutants from wastewater by ion-exchange sorbents requires knowledge and understanding of the interplay between the adsorption patterns of the different components. The present study elucidates the simultaneous adsorption characteristics of six toxic heavy metal cations (Cd2+, Cr3+, Cu2+, Ni2+, Pb2+, and Zn2+) by two synthetic (13X and 4 A) and one natural (clinoptilolite) zeolite from solutions containing equimolar mixtures of the six metals. Equilibrium adsorption isotherms and equilibration dynamics were obtained by ICP-OES and complemented by EDXRF. An order of magnitude lower adsorption efficiency was exhibited by clinoptilolite (maximum of 0.12 mmol ions/g zeolite), relative to that obtained by the synthetic zeolites 13X and 4 A (a maximum of 2.9 and 1.65 mmol ions/g zeolite respectively). The strongest affinities to both zeolites were demonstrated by Pb2+ and Cr3+ (1.5 and 0.85 mmol/g zeolite respectively for 13X, and 0.8 and 0.4 mmol/g zeolite respectively for 4 A adsorbed from the highest solution concentration). The weakest affinities were observed by Cd2+ (0.1 mmol/g for both zeolites), Ni2+ (0.2 and 0.1 mmol/g for 13X and 4 A respectively), and Zn2+ (0.1 mmol/g for both zeolites). Large differences were observed between the two synthetic zeolites in terms of their equilibration dynamics and adsorption isotherms. Pronounced maxima were displayed in the adsorption isotherms for zeolites 13X and 4 A. The decline in adsorption of the weaker adsorbing ions with the increase in total solution concentration was attributed to the thermodynamic equilibrium between the ions adsorbed on the zeolite surface and those in the solution. Regeneration by 3 M KCL eluting solution resulted in considerable reduction in adsorption capacities following each desorption cycle.

Selective and Chemical-Free Removal of Toxic Heavy Metal Cations from Water Using Shock Ion Extraction.

Electrochemical methods are known to have attractive features and capabilities when used for ion separations and water purification. In this study, we developed a new process called shock ion extraction (shock IX) for selective and chemical-free removal of toxic heavy metals from water. Shock IX is a hybrid process that combines shock electrodialysis (shock ED) and ion exchange using an ion exchange resin wafer (IERW), and this method can be thought of functionally as an electrochemically assisted variation of traditional ion exchange. In particular, shock IX exhibits greater ion removal and selectivity for longer periods of time, compared to the use of ion exchange alone. The use of an IERW in shock ED also increases multivalent ion selectivity, reduces energy consumption, and improves the hydrodynamics and scalability of the system.

Sorption and continuous filtration of heavy metals and radionuclides using novel nano-Farringtonite: Mechanisms delineation using EXAFS

Simultaneous removal of a wide range of toxic heavy metal cations and potential radionuclides from water bodies and their continuous filtration with a single low-cost and eco-friendly material represents several scientific merits. Herein, for the first time, we report the simple and straightforward wet-chemical synthesis of novel nano-Farringtonite (FAR) composed of magnesium and phosphate ions. Further, the potential of known alternate nano-hydroxyapatite (HAP) and novel engineered nano-FAR including their non-stoichiometric variations was evaluated for the removal of mimicking radionuclide (Sr2+) and heavy metals (Cd2+, and Zn2+) from water bodies. Non-stoichiometric FAR (ns-FAR) have shown multifold higher contaminant removal capacities than HAP, i.e., Sr2+≈ 85 mg/g vs 49.5 mg/g, Cd2+≈ 560 mg/g vs 98.5 mg/g, and Zn2+ = 489 mg/g vs 62 mg/g in batch mode. NsFAR showed complete removal of Cd2+ and Zn2+ with <20% and 0% recovery, respectively in three consecutive sorption-recovery cycles, probing towards permanent incorporation of these ions. Spectroscopic analysis and extended x-ray absorption fine structure (EXAFS) spectroscopy fitting confirmed ion exchange and crystal incorporation as probable removal mechanisms. The high ionic potential of Mg2+ allows easy ion exchange with +2 charged metal toxins of varying ionic radius at both Mg1 and Mg2 sites of FAR. nsFAR showed instantaneous separation of these cations in continuous column mode with >2,00,000 L/kg of water filtration capacity (at 1 mg/L), justifying the adsorbent's candidature in water purification applications.

Effective removal of toxic heavy metal ions from wastewater using boroxine covalent organic framework

Elimination of toxic heavy metals from wastewater is a worldwide concern due to the severe detrimental effects that they can cause to the human life and to the surrounding environment. In this work, using density functional theory calculations and motivated by the first synthesis of a covalent organic framework based on the boronic acid (boroxine), we investigate an effective technique to remove toxic heavy metal cations (Cd2+, Hg2+, and Pb2+) from wastewater by the boroxine covalent organic framework. We proposed that the boroxine layer was an efficient material to capture the considered toxic heavy metal cations in the aqueous solution. We also found that the large HOMO-LUMO gap of the pristine boroxine can be reduced by adsorbing Cd2+, Hg2+, and Pb2+ pollutants. Furthermore, the results reveal that the cation/boroxine systems with higher electron transport rates, exhibit the higher binding energy as well as charge transfers between the cation and boroxine layer. Time-dependent density functional analysis showed “ligand to metal charge transfer” excitations for the studied complexes. In this respect, our theoretical resulta might be fruitful for experimental studies toward proposing high-efficient materials based on covalent organic framework for removing wastewater pollutants.

Removal of toxic heavy metal ions from waste water using superchalcogens: A theoretical study

One of the most exciting events in chemistry is the stable assemblies of atoms, denoted by superatoms, that could mimic the behaviors of elements in the periodic table. For the first time by Jena et al., a novel type of di-anions superchalcogens (BeAl122− and TiAu122-) has been introduced based on the various electron-counting rules. Inspired by the fascinating finding of these superatoms and guided by density functional theory calculations, we propose a novel and efficient strategy to capture pollutants from waste water via adsorbing the toxic heavy metal cations (Cd2+, Hg2+, and Pb2+) by the BeAl122− and TiAu122− superchalcogens. Our results reveal that the BeAl122− and TiAu122− superchalcogens were powerful to adsorb the Pb2+, Hg2+, and Cd2+ cations in the aqueous solution. Furthermore, by investigating the hydrated cations, the adsorption of hydrated [Pb(H2O)4]2+ on the BeAl122− and TiAu122− superatoms was found thermodynamically more favorable than the [Cd(H2O)4]2+ and [Hg(H2O)4]2+. Our calculations also showed that the adsorbing heavy metal cations can considerably narrow the wide HOMO-LUMO gap and remarkably enhance the first hyperpolarizability of the pristine BeAl122− and TiAu122− superchalcogens, due to electron transfer in this type of superatoms. Moreover, the results highlight the systems with higher electron transport rates, show the larger first hyperpolarizability as well as the higher nonlinear optical response. Time-dependent density functional calculations also revealed “ligand to metal charge transfer” vertical excitations for the cation/superchalcogen systems. However, these theoretical findings might be helpful for experimental scientists toward designing high-efficient adsorbents based on superatoms for eliminating water pollutants.

Promising Biocompatible, Biodegradable, and Inert Polymers for Purification of Wastewater by Simultaneous Removal of Carcinogenic Cr(VI) and Present Toxic Heavy Metal Cations: Reduction of Chromium(VI) by Poly(ethylene glycol) in Aqueous Perchlorate Solutions.

A spectrophotometric technique has been applied for studying the reduction of chromium(VI) by poly(ethylene glycol) (PEG) as water-soluble and nontoxic synthetic polymer at a constant ionic strength of 4.0 mol dm–3 in the absence and presence of the ruthenium(III) catalyst. In the absence of the catalyst, the reaction orders in [Cr(VI)] and [PEG] were found to be unity and fractional first orders, respectively. The oxidation process was found to be acid-catalyzed with fractional second order in [H+]. The addition of Ru(III) was found to catalyze the oxidation rates with observation of zero-order reaction in [CrO42–] and fractional orders in both [PEG] and [Ru(III)], respectively. The PEG reduces the soluble toxic hexavalent Cr(VI) as a model pollutant to the insoluble nontoxic Cr(III) complex, which is known to be eco-friendly and more safer from the environmental points of view. The acid derivative of PEG was found to possess high affinity for the removal of poisonous heavy metal ions from contaminant matters by chelation. Formation of the 1:1 intermediate complex has been kinetically revealed. A consistent reaction mechanism of oxidation was postulated and discussed.

Acrylic acid-chitosan blend hydrogel: a novel polymer adsorbent for adsorption of lead(II) and copper(II) ions from wastewater

Abstract Environmental pollution due to heavy metal contamination is a major environmental concern. A fully biodegradable and reusable adsorbent hydrogel for removal of heavy metal ions has been developed. The hydrogel was prepared from acrylic acid and chitosan using an irradiation method. The adsorbent was characterized using Fourier transform infrared analysis. Uptake of copper(II) and lead(II) at different contact times, pH, and metal ion concentrations was investigated by a batch method using atomic absorption spectroscopy. Kinetic adsorption data were studied using pseudo-first-order and pseudo-second-order equations. Experimental metal adsorption data were fitted with the Langmuir isotherm model. The maximum adsorption capacity of the hydrogel was found to be 192 and 171 mg/g for lead(II) and copper(II), respectively, from the Langmuir isotherm model. Reuse and desorption of the hydrogel were also successful. The adsorbent can be used to adsorb Cu(II) and Pb(II) by the column method with high removal efficiency. The data indicated that the designed hydrogel was environment friendly, regenerative, and can be used effectively for the removal of toxic heavy metal cations from wastewater for a sustainable environment.

A Lysosome-Targetable Fluorescence Sensor for Ultrasensitive Detection of Hg2+ in Living Cells and Real Samples.

A new lysosome-targetable fluorescence sensor, Lyso-HGP, was designed and synthesized based on 4-methyl-2,6-diformylphenol as a fluorophore. Lyso-HGP displays highly sensitive fluorescent detection of Hg2+ in HEPES buffer solution (10 mM, DMSO 1%) of pH 7.0 at 37 °C due to the formation of highly fluorescent formyl-functionalized derivative Lyso-HGP-CHO. The sensor triggered a "turn-on" fluorescence response to Hg2+ with a simultaneous increase of fluorescence intensity by 180-fold just after 10 min. The response is very selective over a variety of biologically relevant cations, anions, molecules, and competitive toxic heavy metal cations. The limit of detection (LOD) was calculated as low as 6.82 nM. So, it can be utilized to detect this toxic heavy metal in biology and environmental samples in an aqueous buffer medium. Also, the sensor is able to monitor the subcellular distribution of Hg2+ specifically localized in the lysosome's compartment in the MCF7 human breast cancer cell line by fluorescence microscopy.

Chemical clogging of granular media under acidic groundwater conditions

Generation of acidic groundwater attributed to pyrite oxidation in low-lying acid sulfate soil has caused substantial damage to the soil-water environment and civil infrastructure in coastal Australia. The installation of permeable reactive barriers (PRBs) is a frontier technology in the field of acid neutralisation and removal of toxic heavy metal cations – for example, soluble iron (Fe) and aluminium (Al). This study aims to assess the potential of limestone (calcite) aggregates as the PRB’s main reactive material in low-lying pyritic land. During long-term laboratory column experiments, a significant capacity of limestone for removing contaminant chemical species was observed. Nevertheless, the formation of secondary mineral precipitates upon geochemical reactivity within the granular media in the PRB caused armouring and chemical clogging, which diminished the rate of reactivity – that is, the treatment capacity of calcite aggregates – mainly at the entrance zone of the porous media. Flow properties were altered due to blockage of pores; for instance, hydraulic conductivity was reduced by 25% at the inlet zone. Non-homogeneous clogging towards the outlet was analysed, and the time-dependent effect on the longevity of a limestone column was studied and quantified.

A water-stable zinc(ii)-organic framework as a multiresponsive luminescent sensor for toxic heavy metal cations, oxyanions and organochlorine pesticides in aqueous solution.

A novel metal-organic framework with the formula [Zn3(DDB)(DPE)]·H2O (1) (H5DDB = 3,5-di(2',4'-dicarboxylphenyl)benzoic acid and DPE = 1,2-di(4-pyridyl)ethylene) has been solvothermally synthesized by employing a rigid carboxylate ligand H5DDB to assemble with Zn(ii) ions in the presence of a flexible bis(pyridyl) linker DPE. The Zn-MOF is a 3D framework with six-nuclear clusters and possesses remarkable water stability and pH stability. Interestingly, complex 1 can sensitively and selectively sense Fe(iii), Cr(iii), Cr(vi), Mn(vii) and the pesticide 2,6-Dich-4-NA with low detection limits in aqueous solution. Moreover, complex 1 also exhibits selectivity for 2,6-Dich-4-NA detection in real samples including carrot, grape and nectarine extracts, and its detection ability is almost unchanged in the presence of the surfactant sodium dodecyl sulfate (SDS). The possible mechanisms of luminescence quenching have been explained by the weak affinity of nitrogen atoms, resonance energy transfer, and photoinduced electron transfer. To our knowledge, this is the first example of a MOF-based multiresponsive fluorescent probe for the simultaneous detection of Fe(iii), Cr(iii/vi), Mn(vii) and the pesticide 2,6-Dich-4-NA in aqueous solution.

Enhancement of acidic-basic properties of silica by modification with CeO2-Fe2O3 nanoparticles via successive ionic layer deposition

α-CeO2 and α-Fe2O3 nanocrystals were successfully synthesized by successive ionic layer deposition (SILD). The size of the prepared nanocrystals of α-CeO2 and α-Fe2O3 is 6–8 nm and 13–14 nm, correspondingly. The developed method was used to modify silica gel. The obtained samples were characterized by EDX, SEM, TEM-ED, PXRD; and N2 adsorption-desorption analysis and analysis of acid-base properties were made. There was established that the silica gel modification with 4.1 mass % of α-CeO2 and α-Fe2O3 nanocrystals lead to increase of acidic/basic sites in 6.6 and 13.6 times, correspondingly, while maintaining the surface area of modified silica about 311 m2/g and almost unchanged pore structure. It was shown that α-CeO2 and α-Fe2O3 nanocrystals forming by SILD modification of silica gel are mainly found in the micropores and mesopores and define the phenomenon of the increase of active sites concentration in the prepared composite. The resulting materials can be used as the basis for promising acid-base catalysts and sorbents of toxic heavy metal cations and oxyanions.

Mercury Chemical Sensors Based on Chalcogenide Glasses

Mercury is one of the highly toxic heavy metal cations and its concentration is continuously increasing in the environment due to extensive industrial applications. Mercury species and Hg(II) ions have a serious impact on human health and may cause kidney intoxication, neurological damage, paralysis, chromosome breakage, and birth defects. Consequently, it is important to control mercury levels in natural and potable water. The highest concentration of mercury allowed in drinking water is 1 ppb. Chalcogenide glasses are promising membrane materials for chemical sensors. We will report R&D work on mercury sensors capable of continuous in situ monitoring of Hg(II) ions in natural and waste waters with a low detection limit of 2 ppb. Figure 1 shows typical sensor response in natural water at neutral pH 7.3 with mercury additions to determine low detection limit of the developed sensors. Sensor sensitivity, selectivity and stability will be discussed and applications to the analysis of natural and waste waters will be described. In addition, a special attention will be paid to sensor sensitivity mechanism since the sensor response is neither Nernstian nor linear. Figure 1

Nitrogen-doped chitosan-Fe(III) composite as a dual-functional material for synergistically enhanced co-removal of Cu(II) and Cr(VI) based on adsorption and redox

Efficient synergistic co-removal of Cu(II) and Cr(VI) was accomplished with a novel nitrogen-doped chitosan-Fe(III) composite (NFEC). Coexistent Cu(II) and Cr(VI) elevated mutual adsorptive capacities by 83.05% and 100.27%, and accelerated initial uptake rates by 23.58% and 123.10%, respectively. Moreover, common anions including NO3−, Cl−, SO42−, CO32− and PO43− all promoted Cu(II) adsorption, and toxic heavy-metal cations such as Ni(II) and Cr(III) also enhanced Cr(VI) removal. Synergistic adsorption and redox interactions occurred during the co-removal process based on Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The large enhancement of Cu(II) adsorption onto NFEC in the presence of Cr(VI) was driven by the electrostatic shielding of Cr(VI) against the repulsion force between Cu(II) cations. Meanwhile, the redox between Cr(VI) and chitosan matrix could significantly consume protons and thus weaken the site competition from protons with Cu(II). The preloaded Cu(II) conversely served as cation bridge for Cr(VI) enrichment via electrostatic attraction. Cu(II) also replaced protons of hydroxyl and carboxyl groups in NFEC via ion exchange, facilitating the redox of Cr(VI) and avoiding the unfavorable species conversion of HCrO4− to CrO42−. In addition, NFEC could be well regenerated for repeated use without significant capacity loss in continuous 5-cycle adsorption-regeneration runs. Overall, the facile fabrication, synergistic performance and excellent reusability suggest NFEC is qualified for practical application in integrated treatment of combined inorganic cation-anion pollutants.

Recent Progress on the Design and Applications of Polysaccharide‐Based Graft Copolymer Hydrogels as Adsorbents for Wastewater Purification

Gum polysaccharides are one of the most abundant bio‐based polymers. They are generally derived from plants as exudates or from microorganisms and have diverse applications in many industries, especially in the food industries where they are used as emulsifiers and thickeners. In their natural form, gum polysaccharides have poor mechanical and physical properties; therefore, they are frequently modified with various synthetic monomers such as acrylamide and acrylic acid using graft copolymerization. Graft copolymerization is one of the most trusted and widely used synthetic methods for the modification of gum polysaccharides. Gum polysaccharides modified in this way have improved mechanical and physicochemical properties. Furthermore, gum polysaccharides contain a variety of functional groups, for example, carboxylic acid and hydroxyl groups; therefore, they have been used extensively as adsorbents for the removal of different impurities from wastewater such as toxic heavy metal cations and synthetic dyes. Here, the chemical and physical properties of gum polysaccharides, different methods of graft copolymerization, and the use of graft copolymer gum‐polysaccharide‐based hydrogels are reviewed in detail for the removal of toxic heavy metal cations and synthetic dyes from aqueous solutions. image

A Bioluminescence Assay System for Imaging Metal Cationic Activities in Urban Aerosols.

A bioluminescence-based assay system was fabricated for an efficient determination of the activities of air pollutants. The following four components were integrated into this assay system: (1) an 8-channel assay platform uniquely designed for simultaneously sensing multiple optical samples, (2) single-chain probes illuminating toxic chemicals or heavy metal cations from air pollutants, (3) a microfluidic system for circulating medium mimicking the human body, and (4) the software manimulating the above system. In the protocol, we briefly introduce how to integrate the components into the system and the application to the illumination of the metal cationic activities in air pollutants.

Applicability and toxicity evaluation of an adsorbent based on jujube for the removal of toxic heavy metals

The removal of heavy metals from industrial wastewater is important, owing to its eco-toxicity in aqueous environment. In this study, the mechanism and efficiency of the removal of toxic heavy metals by an eco-friendly adsorbent was investigated. Various types of adsorbents made from jujube were synthesized by varying the drying temperature of gel-type beads and elution method for jujube constituents. The maximum adsorption capacity for lead and copper ions was determined using the Langmuir isotherm model, with DJB-A-S-F (freeze-dried jujube bead made from a solution of squeezed autoclaved jujube) having the highest values at 60.44mg/g (lead) and 20.33mg/g (copper). In addition, the characteristics of the various adsorbents were determined by the Brunauer–Emmett–Teller (BET) method, scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDX). Gas chromatography–mass spectrometry (GC–MS) was used to identify the constituents of DJB-A-S-F before and after adsorption of heavy metals (Pb- and Cu-DJB-A-S-F). Furthermore, in vitro cytotoxicity assay was performed to investigate whether the binding of heavy metals to DJB-A-S-F increases cellular toxicity. As a result, no differences in cell viability between DJB-A-S-F and the ones coupled to heavy metals were observed, indicating that the developed adsorbents are non-cytotoxic with good compatibility. Thus, DJB-A-S-F is a promising adsorbent for the removal of toxic heavy metal cations from wastewater.

ChemInform Abstract: Properties and Applications of Zeolites

AbstractReview: 207 refs.

Selective extraction of toxic heavy metal oxyanions and cations by a novel silica gel phase functionalized by vitamin B4

A novel silica gel phase [Si–NH 2 –VB4] is synthesized by a direct immobilization of Vitamin B4 (VB4), as an eco-friendly modification of a silica-amine phase [Si–NH 2 ]. The resulting modified silica amine phase [Si–NH 2 –VB4] with VB4 showed a bi-character for selective extraction of both cation and anion species from aqueous media. Surface coverage value, thermal stability, structure identification and confirmation, as well as interaction properties, were determined using thermal desorption method, thermal degradation analysis by TGA and FT-IR. The adsorption study showed that [Si–NH 2 –VB4] has a good affinity for binding and extracting toxic oxyanions including chromate, arsenate and arsenite via the incorporated anion exchange character. [Si–NH 2 –VB4] also showed a tendency to have high selectivity towards extraction of Hg(II) ions from aqueous solutions in a wide range of pH-values due to different possible binding sites. Other metal ions, such as Cu(II) and Cd(II), were highly extracted at high pH-values due to a single site of interaction. Based on environmental water samples, the potential application of [Si–NH 2 –VB4] is for selective extraction of Hg(II) from aqueous media under a wide range of pH conditions.

Properties and applications of zeolites.

Zeolites are aluminosilicate solids bearing a negatively charged honeycomb framework of micropores into which molecules may be adsorbed for environmental decontamination, and to catalyse chemical reactions. They are central to green-chemistry since the necessity for organic solvents is minimised. Proton-exchanged (H) zeolites are extensively employed in the petrochemical industry for cracking crude oil fractions into fuels and chemical feedstocks for other industrial processes. Due to their ability to perform cation-exchange, in which the cations that are originally present to counterbalance the framework negative charge may be exchanged out of the zeolite by cations present in aqueous solution, zeolites are useful as industrial water-softeners, in the removal of radioactive Cs+ and Sr2+ cations from liquid nuclear waste and in the removal of toxic heavy metal cations from groundwaters and run-off waters. Surfactant-modified zeolites (SMZ) find particular application in the co-removal of both toxic anions and organic pollutants. Toxic anions such as arsenite, arsenate, chromate, cyanide and radioactive iodide can also be removed by adsorption into zeolites that have been previously loaded with co-precipitating metal cations such as Ag+ and Pb2+ which form practically insoluble complexes that are contained within the zeolite matrix.

Synthesis and complexation study of calix[4]arene diamine derivative incorporated in a polymeric backbone with chiral monomers

The novel chiral polymeric compounds containing more than one calix[4]arene have been synthesized by reacting a new calix[4]arene diamine derivative with two chiral monomers. These newly prepared compounds were studied by extraction of toxic heavy metal (Cu2+, Co2+, Cd2+, Hg2+), silver and alkali metal (Na+, K+) cations from aqueous phase. It was observed that the resulting calixarene-based polymers have a good complexing ability towards silver, alkali metal and toxic heavy metal cations.