Sensitive determination of trace Cd(ii) and Pb(ii) in soil by an improved stripping voltammetry method using two different in situ plated bismuth-film electrodes based on a novel electrochemical measurement system

In this study, a simple but effective electrochemical method was developed to minimize the interference from real soil samples and increase the sensitivity of Pb(ii) and Cd(ii) detection by square-wave anodic stripping voltammetry (SWASV) using a novel electrochemical measurement system, which can be used for the on-site determination of trace Cd(ii) and Pb(ii) in real soil samples. The method involved performing SWASV following double deposition and stripping steps at two in situ plated bismuth-film electrodes with drastically different surface properties. Pb(ii) and Cd(ii) were first deposited on an in situ plated bismuth-film graphite carbon paste electrode (Bi/GCPE). When the first deposition was finished, the GCPE was moved to a micro-electrolytic cell to perform the first stripping step. The following measurements were performed with the other deposition and stripping steps using a highly sensitive in situ plated bismuth-film multiwalled carbon nanotube–Nafion composite modified glassy carbon electrode (Bi/MWCNT–Nafion/GCE) as the working electrode. Pb(ii), Cd(ii) and Bi(iii) stripped from the GCPE in the micro-electrolytic cell were partially deposited on the MWCNT–Nafion/GCE, and the stripping current signals were obtained from their oxidation during the second stripping step. Considering the small volume of the micro-electrolytic cell, the concentrations of Cd(ii) and Pb(ii) were drastically higher than those in the bulk solution, and therefore, the detection limits were reduced. Under the optimized conditions, the concentrations in the linear range spanned from 1.0 to 45.0 μg L⁻¹ for both Pb(ii) and Cd(ii), with a detection limit of 0.03 μg L⁻¹ for Pb(ii) and 0.02 μg L⁻¹ for Cd(ii) (S/N = 3). Finally, analyses of real samples were performed to detect trace levels of Pb(ii) and Cd(ii) in soil with satisfactory results.

A double-stripping voltammetry method was designed and developed to improve the sensitivity and anti-interference ability for detection of heavy metals.     

Graphene oxide/polydimethylsiloxane composite sponge for removing Pb(ii) from water

An efficient adsorbent to remove Pb(ii) from water was prepared by treating polydimethylsiloxane (PDMS) sponge with polyvinyl alcohol and then coating the sponge with graphene oxide (GO). The GO–PDMS sponge was highly hydrophilic, easily handled during and after use, and easily recycled. The kinetics and isotherms of Pb(ii) sorption onto the GO–PDMS sponge were investigated by performing batch sorption tests. The kinetics of Pb(ii) sorption onto the GO–PDMS sponge indicated that sorption equilibrium occurred rapidly (within 60 min) and that the sorption data could be described using a pseudo-second-order model. Maximum Pb(ii) sorption onto the GO–PDMS sponge occurred at pH > 5. Increasing GO loading on the PDMS sponge increased the amount of Pb(ii) that could be sorbed. The isotherm for Pb(ii) sorption onto the GO–PDMS sponge was non-linear and was well described by the Langmuir isotherm model, indicating that Pb(ii) sorption onto the GO–PDMS sponge was homogeneous and occurred through sorption of a monolayer of Pb(ii). The GO–PDMS sponge, used as a filter, removed Pb(ii) efficiently from water. The Pb(ii) removal efficiencies were more than 50% and the maximum was 85%.

A novel sorbent material for Pb(ii) sorption was created by coating graphene oxide (GO) on a pretreated PDMS sponge.     

Hydrogels derived from galactoglucomannan hemicellulose with inorganic contaminant removal properties

The adsorption of Cu(ii), Cd(ii), and Pb(ii) ions onto hydrogels derived from modified galactoglucomannan (GGM) hemicellulose was studied. GGM hemicellulose was modified with methacrylate groups (GGM-MA) to incorporate vinyl groups into the polymeric structure, which reacted later with synthetic monomers such as 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS). The results show that all the synthesized hydrogels were capable of adsorbing contaminating ions with high adsorption efficiency during short periods of time. Furthermore, an increase in the content of GGM-MA generated a hydrogel (H3) with a similar ion adsorption property to the other hydrogels but with a lesser degree of swelling. The H3 hydrogel had an adsorption capacity of 60.0 mg g⁻¹ Cd(ii), 78.9 mg g⁻¹ Cu(ii), and 174.9 mg g⁻¹ Pb(ii) at 25 °C. This result shows that modified GGM hemicelluloses can be employed as renewable adsorbents to remove Cu(ii), Cd(ii), and Pb(ii) ions from aqueous solutions.

The adsorption of Cu(ii), Cd(ii), and Pb(ii) ions onto hydrogels derived from modified galactoglucomannan (GGM) hemicellulose was studied.     

Characterization and adsorption properties of cross-linked yeast/β-cyclodextrin polymers for Pb(ii) and Cd(ii) adsorption

In this study, a crosslinked yeast/β-cyclodextrin polymer (Y–β-CDP), for use as an effective adsorbent for removal Pb(ii) and Cd(ii) ions from aqueous solution, has been innovatively prepared by grafting β-cyclodextrin (β-CD) onto the surface of baker''s yeast (BY) and thiomalic acid as a crosslinker. Several characterization techniques, such as SEM equipped with an EDS analyzer, FTIR, XRD, and XPS were employed characterize the Y–β-CDP. The impact of various operating parameters, such as pH, adsorbent dosage, initial concentration of metal ions, contact time and solution temperature, as well as adsorption kinetics, isotherms and thermodynamics were systematically investigated. The adsorption of Pb(ii) and Cd(ii) on Y–β-CDP reached equilibrium in 25 min, and the kinetic process conforms to the pseudo-second order model. The Langmuir model was used to describe the adsorption isotherm data better than the Freundlich model. The predicted maximum adsorption capacity at 25 °C for Pb(ii) and Cd(ii) was 150.08 and 102.80 mg g⁻¹, respectively, when the initial concentration of metal ions was 120 mg L⁻¹. The thermodynamic analysis revealed that the adsorption procedure of Pb(ii) and Cd(ii) onto Y–β-CDP was spontaneous and endothermic. Furthermore, regeneration experiments demonstrated that Y–β-CDP had excellent recyclability. Together, all results suggested that Y–β-CDP could potentially be a promising adsorbent in the purification of water contaminated with heavy metal ions.

A cross-linked yeast/β-cyclodextrin polymer (Y–β-CDP) was synthesized to remove Pb(ii) and Cd(ii) from aqueous solution.     

A simple and cost-effective paper-based and colorimetric dual-mode detection of arsenic(iii) and lead(ii) based on glucose-functionalized gold nanoparticles

We report a simple and cost-effective paper-based and colorimetric dual-mode detection of As(iii) and Pb(ii) based on glucose-functionalized gold nanoparticles under optimized conditions. The paper-based detection of As(iii) and Pb(ii) is based on the change in the signal intensity of AuNPs/Glu fabricated on a paper substrate after the deposition of the analyte using a smartphone, followed by processing with the ImageJ software. The colorimetric method is based on the change in the color and the red shift of the localized surface plasmon resonance (LSPR) absorption band of AuNPs/Glu in the region of 200–800 nm. The red shift (Δλ) of the LSPR band observed was from 525 nm to 660 nm for As(iii) and from 525 nm to 670 nm for Pb(ii). The mechanism of dual-mode detection is due to the non-covalent interactions of As(iii) and Pb(ii) ions with glucose molecule present on the surface AuNPs, resulting in the aggregation of novel metal nanoparticles. The calibration curve gave a good linearity range of 20–500 μg L⁻¹ and 20–1000 μg L⁻¹ for the determination of As(iii) and Pb(ii) with the limit of detection of 5.6 μg L⁻¹ and 7.7 μg L⁻¹ for both metal ions, respectively. The possible effects of different metal ions and anions were also investigated but did not cause any significant interference. The employment of AuNPs/Glu is successfully demonstrated for the determination of As(iii) and Pb(ii) using paper-based and colorimetric sensors in environmental water samples.

We report a simple and cost-effective paper-based and colorimetric dual-mode detection of As(iii) and Pb(ii) based on glucose-functionalized gold nanoparticles under optimized conditions.     

Kinetics,thermodynamics, equilibrium,surface modelling,and atomic absorption analysis of selective Cu(ii) removal from aqueous solutions and rivers water using silica-2-(pyridin-2-ylmethoxy)ethan-1-ol hybrid material

The removal of heavy metals is attracting considerable attention due to their undesirable effects on the environment. In this investigation, a new adsorbent based on silica functionalized with pyridin-2-ylmethanol (SiPy) was successfully synthesized to yield to a hybrid material. FTIR, SEM, TGA, and specific surface area analysis were used to characterize the structure and morphology of the SiPy hybrid material. Various heavy metal ions such as Cu(ii), Zn(ii), Cd(ii), and Pb(ii) were selected to examine the adsorption efficiency of the newly prepared adsorbent, optimized at varying solution pH, contact time, concentration, and temperature. The adsorbent SiPy displayed good adsorption capacity of 90.25, 75.38, 55.23, and 35.12 mg g⁻¹ for Cu(ii), Zn(ii), Cd(ii), and Pb(ii), respectively, at 25 min and pH = 6. The adsorption behaviors of metal ions onto the SiPy adsorbent fitted well with the pseudo-second-order kinetic mode and the isotherm was better described by the Langmuir isotherm. The thermodynamic studies disclose spontaneous and endothermic adsorption process. Furthermore, the SiPy adsorbent retained good selectivity and regeneration properties after five adsorption–desorption cycles of Cu(ii). A computational investigation of the adsorption mechanism indicates that the N-pyridine, O-hydroxyl, and ether O-atoms play a predominant role during the capture of Cu(ii), Zn(ii), Cd(ii), and Pb(ii). This study proposes the SiPy adsorbent as an attractive material for the selective removal of Cu(ii) from real river water and real industrial wastewater.

The removal of heavy metals is attracting considerable attention due to their undesirable effects on the environment.     

Functionalized biochar-supported magnetic MnFe2O4 nanocomposite for the removal of Pb(ii) and Cd(ii)

In this study, a novel magnetic biochar-MnFe₂O₄ nanocomposite (BC/FM) was prepared using low-cost corn straw and MnFe₂O₄ by sol–gel/pyrolyzing route using egg white, which has abundant functional groups (–NH₂ and –COOH). Following that, its composition, morphology and structure was characterized by various techniques including SEM-EDX, BET, XRD, and VSM. Batch experiment of the adsorption for Pb(ii) and Cd(ii) including influence of pH, kinetics, isotherm and thermodynamics was also studied. The results demonstrated that biochar could effectively support MnFe₂O₄, which displayed high dispersion on the surface of the biochar and possessed abundant functional groups and high surface area contributing to superior performance on Pb(ii) and Cd(ii) removal. Therein, MnFe₂O₄ with high magnetism is convenient for separating the magnetic BC/FM from an aqueous medium. Adsorption experiment results indicate that Pb(ii) and Cd(ii) removal by BC/FM was closely related to pH with the best value of pH 5.0, and the process reached equilibrium in 2 h. The adsorption process is well-described by the pseudo-second-order kinetic model and Sips (Freundlich–Langmuir) model. Thermodynamic studies suggest that the adsorption process is spontaneous and exothermic. The maximum experimental adsorption capacity of BC/FM is 154.94 and 127.83 mg g⁻¹ for Pb(ii) and Cd(ii), respectively, in single-solute system, which is higher than that of some of the other adsorbents of biochar or biochar-based composites. In bi-solute system, the preferential adsorption order of BC/FM for the two metals is Pb(ii) prior to Cd(ii). Finally, FTIR and XPS analysis verified that the main mechanism of Pb(ii) and Cd(ii) removal by BC/FM is by forming Pb/Cd–O or complexation of carboxyl and hydroxyl and ion exchange. Therefore, the prepared magnetic BC/FM composite, as an excellent adsorbent, exhibited potential applications for the removal of Pb(ii) and Cd(ii) from wastewater.

In this study, a novel magnetic biochar-MnFe₂O₄ nanocomposite (BC/FM) was prepared using low-cost corn straw and MnFe₂O₄ by sol–gel/pyrolyzing route using egg white, which has abundant functional groups (–NH₂ and –COOH).     

The kinetics process of a Pb(ii)/Pb(0) couple and selective fabrication of Li–Pb alloys in LiCl–KCl melts

The electrode reaction of Pb(ii) and co-reduction of Li(i) and Pb(ii) were investigated on a tungsten electrode in LiCl–KCl eutectic melts by a range of electrochemical techniques. From cyclic voltammetry and square wave voltammetry measurements, the reduction of Pb(ii) was found to be a one-step diffusion-controlled reversible process with the exchange of 2 electrons. The diffusion coefficients of Pb(ii) were computed, and they obey the Arrhenius law. Using the linear polarization technique, the kinetic parameters, such as exchange current intensity (j₀), standard rate constant (k⁰) and charge transfer resistance (R_ct) for the Pb(ii)/Pb(0) couple on a tungsten electrode were studied at different temperatures, and the activation energy is 27.32 kJ mol⁻¹, smaller than the one for diffusion of Pb(ii), which further confirmed that the reduction of Pb(ii) was controlled by diffusion. A depolarisation effect for Li(i) reduction was observed from the results of cyclic voltammetry, square wave voltammetry and chronopotentiometry due to the formation of Li–Pb alloys by co-reduction of Li(i) and Pb(ii). Furthermore, five Li–Pb intermetallic compounds, LiPb, Li₈Pb₃, Li₃Pb, Li₁₀Pb₃ and Li₁₇Pb₄ characterized by scanning electronic microscopy and X-ray diffraction, were selectively prepared by potentiostatic electrolysis on a tungsten electrode and galvanostatic electrolysis on a liquid Pb electrode, respectively.

Five Li–Pb intermetallic compounds are selectively prepared according to their deposition potentials and characterized by XRD and SEM.     

Synthesis and characterization of a surface-grafted Pb(ii)-imprinted polymer based on activated carbon for selective separation and pre-concentration of Pb(ii) ions from environmental water samples

Even the lowest concentration level of lead (Pb) in the human body is dangerous to health due to its bioaccumulation and high toxicity. Therefore, it is very important to develop selective and fast adsorption methods for the removal of Pb(ii) from various samples. In this paper, a new Pb(ii) ion-imprinted polymer (Pb(ii)-IIP) was prepared with surface imprinting technology by using lead nitrate as a template, for the solid-phase extraction of trace Pb(ii) ions in environmental water samples. The imprinted polymer was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy and N₂ adsorption–desorption isotherms. The separation/pre-concentration conditions for Pb(ii) were investigated, including the effects of pH, shaking time, sample flow rate, elution conditions and interfering ions. Compared with non-imprinted particles, the ion-imprinted polymer had a higher selectivity and adsorption capacity for Pb(ii). The pseudo-second-order kinetics model and Langmuir isotherm model fitted well with the adsorption data. The relative selectivity factor values (α_r) of Pb(ii)/Zn(ii), Pb(ii)/Ni(ii), Pb(ii)/Co(ii) and Pb(ii)/Cu(ii) were 168.20, 192.71, 126.13 and 229.39, respectively, which were all much greater than 1. The prepared Pb(ii)-imprinted polymer was shown to be promising for the separation/pre-concentration of trace Pb(ii) from natural water samples. The adsorption and desorption mechanisms were also proposed.

Even the lowest concentration level of lead (Pb) in the human body is dangerous to health due to its bioaccumulation and high toxicity.     

Lead and uranium sorptive removal from aqueous solution using magnetic and nonmagnetic fast pyrolysis rice husk biochars

This paper discusses the sorption characteristics of Pb(ii) and U(vi) on magnetic and nonmagnetic rice husk biochars. The porosity, specific surface area, hydrophobility, and reusability of biochar were effectively improved (1–2 times) after magnetic modification. The optimum adsorption conditions were as follows: biochar loading was 0.4 g L⁻¹, pH value was 7.0, and anion strength of NO₃⁻ and PO₄³⁻ were 0.01 mol L⁻¹ for Pb(ii) and 0.04 mol L⁻¹ for U(vi) respectively. Compared with U(vi), Pb(ii) had the faster adsorption rate and higher adsorption capacity on magnetic biochar (MBC). The adsorption experimental data were well fitted by pseudo-second-order kinetic and Langmuir isotherm models. The maximum adsorption capacity of Pb(ii) and U(vi) on MBC was 129 and 118 mg g⁻¹ at 328 K respectively, which was significantly higher than that of other sources biochars. Pb(ii) was mainly bonded to biochar by physisorption but the adsorption of U(vi) on biochar was mostly chemisorption. Fe oxides in MBC noticeably improved the ion exchange and complexation action between biochar and metal ion especially for U(vi). The experimental results confirmed MBC material can be used as a cost-effective adsorbent for the removal of Pb(ii) and U(vi) and can be separated easily from aqueous solution when application.

This paper discusses the sorption characteristics of Pb(ii) and U(vi) on magnetic and nonmagnetic rice husk biochars.     

Removal of Pb(ii) and Cr(vi) from aqueous solutions using the prepared porous adsorbent-supported Fe/Ni nanoparticles

In this study, Fe/Ni nanoparticles supported by a novel fly ash-based porous adsorbent (FBA-Fe/Ni) for Cr(vi) and Pb(ii) removal were investigated. In order to enhance the reactivity of zero-valent iron (ZVI), ZVI particles were deposited on the surface or in the inner pores of FBA as a support material and Ni nanoparticles were introduced. FBA was prepared with the solid waste such as Enteromorpha prolifera, bentonite and fly ash. FBA-Fe/Ni was characterized via Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction and the Brunauer–Emmett–Teller model and energy-dispersive spectrometry. The effects of various parameters on Cr(vi) and Pb(ii) removal by FBA-Fe/Ni, such as FBA-Fe/Ni dosage, pH of the solution, reaction temperature, Cr(vi) and Pb(ii) concentrations, co-existing ions and ionic strength were discussed. The possible removal mechanisms were proposed and the results indicated that there was a three-step reaction including the adsorption of Cr(vi) and Pb(ii) on the surface of FBA-Fe/Ni, the subsequent reduction and precipitation. The removal capacity of Cr(vi) and Pb(ii) by FBA-Fe/Ni was 25.07 mg g⁻¹ and 164.19 mg g⁻¹ at 303 K with an initial concentration of 1000 mg L⁻¹ and FBA-Fe/Ni dosage of 0.20 g. In conclusion, this work demonstrated that FBA-Fe/Ni was a promising alternative material for Cr(vi) and Pb(ii) removal.

In this study, Fe/Ni nanoparticles supported by a novel fly ash-based porous adsorbent (FBA-Fe/Ni) for Cr(vi) and Pb(ii) removal were investigated.     

Melamine-based functionalized graphene oxide and zirconium phosphate for high performance removal of mercury and lead ions from water

Heavy metal ions are highly toxic and widely spread as environmental pollutants. This work reports the development of two novel chelating adsorbents, based on the chemical modifications of graphene oxide and zirconium phosphate by functionalization with melamine-based chelating ligands for the effective and selective extraction of Hg(ii) and Pb(ii) from contaminated water sources. The first adsorbent melamine, thiourea-partially reduced graphene oxide (MT-PRGO) combines the heavier donor atom sulfur with the amine and triazine nitrogen''s functional groups attached to the partially reduced GO nanosheets to effectively capture Hg(ii) ions from water. The MT-PRGO adsorbent shows high efficiency for the extraction of Hg(ii) with a capacity of 651 mg g⁻¹ and very fast kinetics resulting in a 100% removal of Hg(ii) from 500 ppb and 50 ppm concentrations in 15 second and 30 min, respectively. The second adsorbent, melamine zirconium phosphate (M-ZrP), is designed to combine the amine and triazine nitrogen''s functional groups of melamine with the hydroxyl active sites of zirconium phosphate to effectively capture Pb(ii) ions from water. The M-ZrP adsorbent shows exceptionally high adsorption affinity for Pb(ii) with a capacity of 681 mg g⁻¹ and 1000 mg g⁻¹ using an adsorbent dose of 1 g L⁻¹ and 2 g L⁻¹, respectively. The high adsorption capacity is also coupled with fast kinetics where the equilibrium time required for the 100% removal of Pb(ii) from 1 ppm, 100 ppm and 1000 ppm concentrations is 40 seconds, 5 min and 30 min, respectively using an adsorbent dose of 1 g L⁻¹. In a mixture of six heavy metal ions at a concentration of 10 ppm, the removal efficiency is 100% for Pb(ii), 99% for Hg(ii), Cd(ii) and Zn(ii), 94% for Cu(ii), and 90% for Ni(ii) while at a higher concentration of 250 ppm the removal efficiency for Pb(ii) is 95% compared to 23% for Hg(ii) and less than 10% for the other ions. Because of the fast adsorption kinetics, high removal capacity, excellent regeneration, stability and reusability, the MT-PRGO and M-ZrP are proposed as top performing remediation adsorbents for the solid phase extraction of Hg(ii) and Pb(ii), respectively from contaminated water.

Two novel chelating adsorbents are developed for the effective and selective extraction of Hg(ii) and Pb(ii) ions from contaminated water sources.     

Selective removal of lead ions from aqueous solutions using 1,8-dihydroxyanthraquinone (DHAQ) functionalized graphene oxide; isotherm,kinetic and thermodynamic studies

An anthraquinone – graphene structure was fabricated and applied for the removal of lead(ii) from aqueous solution. The equilibrium occurred in about 10 min revealing the high adsorption rate at the beginning of the process. The maximum Pb(ii) adsorption capacity of the Fe₃O₄@DHAQ_GO nanocomposite was about 283.5 mg g⁻¹ that was observed at 323 K and pH 5.5. The Pb(ii) adsorption ability increased with the increasing pH. The isotherm and kinetic studies indicated that the Sips isotherm model and the linear form of the pseudo-second kinetic model had a better fit with the experimental results. The positive value of ΔH⁰ indicated endothermic interactions between Pb(ii) and Fe₃O₄@DHAQ_GO. The negative ΔG⁰ indicated that the reactions are spontaneous with a high affinity for Pb(ii). The positive ΔS⁰ values indicated increasing randomness at the solid–solute interface during the adsorption process. The selective removal of Pb(ii) by the nanocomposite confirms the presence of higher-affinity binding sites for Pb(ii) than Cd(ii), Co(ii), Zn(ii), and Ni(ii) ions. Furthermore, the Fe₃O₄@DHAQ_GO nanocomposite revealed an excellent preferential adsorbent for Pb(ii) spiked in drinking water samples containing natural ion matrices. EDTA-2NA 0.01 N was found to be a better elution agent than HCl 0.1 M for the nanocomposite regeneration. After five adsorption/desorption cycles using EDTA-2NA 0.01 N, more than 84% of the adsorbed Pb(ii) was still desorbed in 30 min. Capturing sub-ppm initial concentrations of Pb(ii) and the capability to selectively remove lead from drinking water samples make the Fe₃O₄@DHAQ_GO nanocomposite practically convenient for water treatment purposes. High adsorption capacity and facile chemical synthesis route are the other advancements.

The Fe₃O₄@DHAQ_GO nanocomposite can serve as an efficient adsorbent for the selective removal of lead from polluted water.     

Facile synthesis of graphene oxide from graphite rods of recycled batteries by solution plasma exfoliation for removing Pb from water

We herein present a simple, fast, efficient and environmentally friendly technique to prepare graphene oxide (GO) from graphite rods of recycled batteries by using solution plasma exfoliated techniques at atmospheric pressure. The prepared GO with an average 3 nm-thickness and 1.5 μm-length, having large surface area and high porosity, has been used to remove Pb(ii) ions from the water. The obtained results indicated that the adsorption of Pb(ii) onto GO depends on pH, contact time, temperature and initial concentration of Pb(ii). The maximum adsorption capacity of Pb(ii) onto GO determined from the Langmuir model (with a high R² value of 0.9913) was 180.1 mg g⁻¹ at room temperature. A removal efficiency of ∼96.6% was obtained after 40 min. Calculations of thermodynamic parameters (ΔG°, ΔH° và ΔS°) show the adsorption of Pb(ii) ions on the GO surface is spontaneous and intrinsically heat-absorbing. The potential mechanism can be suggested here to be the interaction of the π–π* bonding electrons and Pb(ii) as well as the electrostatic attraction between Pb(ii) and the oxygen-containing functional groups on GO.

Facile synthesis of graphene oxide from graphite rods of recycled batteries by solution plasma exfoliation for removing Pb from water.     

Efficient removal of heavy metals from polluted water with high selectivity for Hg(ii) and Pb(ii) by a 2-imino-4-thiobiuret chemically modified MIL-125 metal–organic framework

A highly porous adsorbent based on a metal–organic framework was successfully designed and applied as an innovative adsorbent in the solid phase for the heavy metal removal. MIL-125 was densely decorated by 2-imino-4-thiobiuret functional groups, which generated a green, rapid, and efficacious adsorbent for the uptake of Hg(ii) and Pb(ii) from aqueous solutions. ITB-MIL-125 showed a high adsorption affinity toward mercury(ii) ions of 946.0 mg g⁻¹ due to covalent bond formation with accessible sulfur-based functionality. Different factors were studied, such as the initial concentration, pH, contact time, and competitive ions, under same circumstances at the room temperature. Moreover, the experimental adsorption data were in excellent agreement with the Langmuir adsorption isotherm and pseudo-second order kinetics. At a high concentration of 100 ppm mixture of six metals, ITB-MIL-125 exhibited a high adsorption capacity, reaching more than 82% of Hg(ii) compared to 62%, 30%, 2%, 1.9%, and 1.6% for Pb(ii), Cu(ii), Cd(ii), Ni(ii), and Zn(ii), respectively.

A highly porous adsorbent based on a metal–organic framework was successfully designed and applied as an innovative adsorbent in the solid phase for the heavy metal removal.     

One-pot synthesis of spherical nanoscale zero-valent iron/biochar composites for efficient removal of Pb(ii)

In this study, a spherical Fe/C composite (AIBC) was successfully prepared via carbonization of Fe³⁺-crosslinked sodium alginate. The removal capacity and mechanism of AIBC were evaluated for the adsorption of Pb(ii) from aqueous solution and compared with that of commercial nanoscale zero-valent iron (nZVI). The effects of the initial concentration, pH of Pb(ii) solution, the contact time, coexisting anions, and aging under air were investigated. The results showed that the pH had a strong impact on the adsorption of Pb(ii) by AIBC. The adsorption data for AIBC followed the Langmuir model, while the maximum adsorption capacity at pH 5 was 1881.73 mg g⁻¹. The AIBC had a higher adsorption capability than nZVI, especially under the condition of relatively high Pb(ii) concentrations. The oxidation–reduction reaction between Fe and Pb(ii) was the main mechanism for the adsorption of Pb(ii) onto nZVI. AIBC converted the largest amount of Pb(ii) into PbO·XH₂O/Pb(OH)₂ mainly by generating Fe²⁺.

In this study, a spherical Fe/C composite (AIBC) was successfully prepared via carbonization of Fe³⁺-crosslinked sodium alginate.     

The (CF3C(O)NH)(C6H5CH2NH)2P(O) phosphoric triamide as a novel carrier with excellent efficiency for Cu(ii) in a liquid membrane transport system

Transport of Ag(i), Cd(ii), Co(ii), Cu(ii), Ni(ii), Pb(ii) and Zn(ii) cations across a bulk liquid membrane (BLM) containing N,N′-dibenzyl-N′′-(2,2,2-trifluoroacetyl)-phosphoric triamide (PTC) as a new carrier is studied by atomic absorption spectrometry. The results show selective and efficient transport of the copper(ii) cation from aqueous solution in the presence of the other cations. Various factors are optimized in order to obtain maximum transport efficiency. The PTC ligand is characterized by single crystal X-ray diffraction analysis, IR, NMR (¹⁹F, ³¹P, ¹H, ¹³C) and mass spectroscopy. The complex formation reaction between copper(ii) and PTC is studied by a conductometric method, which shows the 1 : 1 stoichiometry for ligand and copper(ii).

Selective transport of Cu(ii) cation in the presence of six other cations across a bulk liquid membrane containing a novel phosphoric triamide carrier is studied.     

Porous Fe0/C ceramsites for removal of aqueous Pb(ii) ions: equilibrium,long-term performance and mechanism studies

This study reports the equilibrium, long-term performance and mechanisms in removing Pb(ii) ions by metallic iron/carbon (Fe⁰/C) ceramsites (FCC). The Pb(ii) removal equilibrium data was analyzed using the Langmuir, Freundlich and Dubinin–Radushkevich isotherms. At the FCC dosage of 1.14 g L⁻¹, 95.97% of Pb(ii) ions were removed from 50 mg L⁻¹ Pb(ii) solution at initial pH 6.0. The Langmuir isotherm could fit well with the data at initial pH 3.0 with a maximum monolayer adsorption capacity of 112.36 mg g⁻¹ at 25 °C, while the data obtained at initial pH 6.0 could be described by the Freundlich model, indicating multilayer adsorption of Pb species on the FCC. Column tests demonstrated that FCC achieved the highest Pb(ii) removal of 65.86% after 12 days'' run compared to 32.35% for Fe⁰/activated carbon couples and only 1.24% for activated carbon. The X-ray diffraction and X-ray photoelectron spectroscopy analysis revealed that the PbO (dominant Pb species), Pb⁰, asisite and plumbojarosite appeared after Pb(ii) removal. Scanning electron microscopy with energy dispersive X-ray spectroscopy showed that PbO particles with numerous structures were deposited on the FCC surface in a high amount. The decrease of the Fe/C mass ratio from 7.5 : 1 to 0.298 : 1 revealed that microscale Fe⁰ could been readily corroded by forming galvanic couples between Fe⁰ and carbon. The mechanisms of Pb(ii) removal by the FCC were proposed.

Cost-effective Fe⁰/C microelectrolysis ceramsites were fabricated from magnetite, coal and paper mill sludge with high long-term performance in the removal of Pb(ii) ions.     

Three-dimensional mesoporous calcium carbonate–silica frameworks thermally activated from porous fossil bryophyte: adsorption studies for heavy metal uptake

In this paper, three-dimensional mesoporous calcium carbonate–silica frameworks have been created from the straw tufa (ST) originating from porous fossil bryophyte by a thermal activation technique. A batch of adsorption kinetic and thermodynamic experiments were used to investigate the adsorption capacity of Cd(ii) onto the samples. The ST after thermal activation has shown a significant ability for the uptake of heavy metals. It exhibited maximum adsorption capacities of 12.76 mg g⁻¹, 14.09 mg g⁻¹, 17.00 mg g⁻¹, and 33.81 mg g⁻¹ for Cd(ii) at the activation temperature of 300, 450, 600 and 750 °C, respectively. Through competitive adsorption for Cd(ii)and Pb(ii), the ST thermally activated at 750 °C exhibited maximum equilibrium adsorption capacities of 24.65 mg g⁻¹, 25.91 mg g⁻¹, and 30.94 mg g⁻¹ for Cd(ii) uptake at 298.1 K, 308.1 K and 318.1 K, respectively, whereas it exhibited values of 91.59 mg g⁻¹, 101.32 mg g⁻¹, and 112.19 mg g⁻¹ for Pb(ii) removal. The adsorption capacities of Cd(ii) and Pb(ii) both decrease with the addition of the other heavy metal cations, indicating that the adsorption is hindered by the competitive adsorption and the adsorption active sites on the mineral surface are readily exchangeable. The adsorption of Cd(ii) and Pb(ii) followed the pseudo-second order kinetics model well. In addition, the Langmuir model could accurately describe the adsorption isotherms. Based on the results of characterization with TEM, XRD and XPS, the adsorption mechanisms could be primarily explained as formation of Cd(OH)₂ and CdCO₃ as well as Cd(HCO₃)₂ precipitation on the surface of ST. These characteristics of ion-exchange and the adsorptive property for ST modified allow it to be widely used in artificial wetland landfill and environmental protection.

Three-dimensional mesoporous calcium carbonate–silica frameworks have been created and have shown excellent adsorption capacities for Cd(ii) and Pb(ii).     

Cd(ii) removal by Fe(ii) surface chemically modified layered double hydroxide–graphene oxide: performance and mechanism

Cd(ii) adsorption onto Fe(ii) modified Layered double hydroxide–graphene oxide (LDH–GO@Fe(ii)) was investigated using batch experiments. With the modification of Fe(ii), LDH–GO maintained its structure, while Fe(ii) species formed non-crystalline iron oxide clusters on the surface of the LDH/GO. A kinetics study indicated that adsorption obeyed a pseudo-second-order rate law. The equilibrium data were fitted well with the Langmuir isotherm model. The maximum adsorption capacity of LDH–GO@Fe(ii)₁₀ was 28.98 mg g⁻¹, higher those that of pure LDH–GO and LDH–GO@Fe(ii)₅₀. The increased sorption capacities could be explained by the increased specific surface area. Modification with Fe(ii) would lead to the generation of amorphous Fe oxides and Fe could occupy the binding sites for Cd(ii), thus excess Fe in the structure will restrain the adsorption of Cd(ii). The XRD and XPS patterns revealed the formation of Cd(OH)₂ after adsorption. Batch experiments indicated that precipitation and surface complexation were the main pathways for Cd(ii) removal.

Fe(ii)-decorated LDH–GO composites had a high capacity for Cd(ii) removal. The mechanisms were controlled by surface-induced precipitation and complex formation.