Simultaneous removal of Sb(iii) and Cd(ii) in water by adsorption onto a MnFe2O4–biochar nanocomposite

In this study, a jacobsite–biochar nanocomposite (MnFe₂O₄–BC) was fabricated and used to simultaneously remove Sb(iii) and Cd(ii) from water via adsorption. The MnFe₂O₄–BC nanocomposite was prepared via a co-precipitation method and analyzed using various techniques. The results confirm the successful decoration of the biochar surface with MnFe₂O₄ nanoparticles. The maximum Sb(iii) removal efficiency was found to be higher from bi-solute solutions containing Cd(ii) than from single-solute systems, suggesting that the presence of Cd(ii) enhances the removal of Sb(iii). The Langmuir isotherm model describes well Sb(iii) and Cd(ii) removal via adsorption onto the MnFe₂O₄–BC nanocomposite. The maximum adsorption capacities are 237.53 and 181.49 mg g⁻¹ for Sb(iii) and Cd(ii), respectively, in a bi-solute system. Thus, the prepared MnFe₂O₄–BC nanocomposite is demonstrated to be a potential adsorbent for simultaneously removing Sb(iii) and Cd(ii) ions from aqueous solutions.

In this study, a jacobsite–biochar nanocomposite (MnFe₂O₄–BC) was fabricated and used to simultaneously remove Sb(iii) and Cd(ii) from water via adsorption.     

Efficient removal of chromate ions from aqueous solution using a highly cost-effective ferric coordinated [3-(2-aminoethylamino)propyl]trimethoxysilane–MCM-41 adsorbent

The present investigation involves synthesis and characterization of MCM-41–AEAPTMS–Fe(iii)Cl using coordinated Fe(iii) on MCM-41–AEAPTMS for efficient removal of hazardous Cr(vi) ions from aqueous solution. The adsorbent MCM-41–AEAPTMS–Fe(iii)Cl was characterized using small-angle X-ray diffraction (SAX), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), Fourier-transform infrared (FT-IR) and Brunauer–Emmett–Teller (BET) surface analyzer techniques. The BET surface area was found to be 87.598 m² g⁻¹. The MCM-41–AEAPTMS–Fe(iii)Cl effectively adsorbs Cr(vi) with an adsorption capacity acquiring the maximum value of 84.9 mg g⁻¹ at pH 3 at 298 K. The data followed pseudo-second-order kinetics and obeyed the Langmuir isotherm model. The thermodynamic data proved the exothermic and spontaneous nature of Cr(vi) ion adsorption on MCM-41–AEAPTMS–Fe(iii). Further, the higher value of ΔH° (−64.339 kJ mol⁻¹) indicated that the adsorption was chemisorption in nature.

The present investigation involves synthesis and characterization of MCM-41–AEAPTMS–Fe(iii)Cl using coordinated Fe(iii) on MCM-41–AEAPTMS for efficient removal of hazardous Cr(vi) ions from aqueous solution.     

Pu(iii) and Cm(iii) in the presence of EDTA: aqueous speciation,redox behavior,and the impact of Ca(ii)

The impact of calcium on the solubility, redox behavior, and speciation of the An(iii)–EDTA (An = Pu or Cm) system under reducing, anoxic conditions was investigated through batch solubility experiments, X-ray absorption spectroscopy (XAS), density functional theory (DFT), and time-resolved laser fluorescence spectroscopy (TRLFS). Batch solubility experiments were conducted from undersaturation using Pu(OH)₃(am) as the solid phase in contact with 0.1 M NaCl–NaOH–HCl–EDTA–CaCl₂ solutions at [EDTA] = 1 mM, pH_m = 7.5–9.5, and [CaCl₂] ≤20 mM. Additional samples targeted brine systems represented by 3.5 M CaCl₂ and WIPP simulated brine. Solubility data in the absence of calcium were well-described by Pu(iii)–EDTA thermodynamic models, thus supporting the stabilization of Pu(iii)–EDTA complexes in solution. Cm(iii)–EDTA TRLFS data suggested the stepwise hydrolysis of An(iii)-EDTA complexes with increasing pH, and current Pu(iii)-EDTA solubility models were reassessed to evaluate the possibility of including Pu(iii)–OH–EDTA complexes and to calculate preliminary formation constants. Solubility data in the presence of calcium exhibited nearly constant log m(Pu)_tot, as limited by total ligand concentration, with increasing [CaCl₂]_tot, which supports the formation of calcium-stabilized Pu(iii)–EDTA complexes in solution. XAS spectra without calcium showed partial oxidation of Pu(iii) to Pu(iv) in the aqueous phase, while calcium-containing experiments exhibited only Pu(iii), suggesting that Ca–Pu(iii)–EDTA complexes may stabilize Pu(iii) over short timeframes (t ≤45 days). DFT calculations on the Ca–Pu(iii)–EDTA system and TRLFS studies on the analogous Ca–Cm(iii)–EDTA system show that calcium likely stabilizes An(iii)–EDTA complexes but can also potentially stabilize An(iii)–OH–EDTA species in solution. This hints towards the possible existence of four major complex types within Ca–An(iii)–EDTA systems: An(iii)–EDTA, An(iii)–OH–EDTA, Ca–An(iii)–EDTA, and Ca–An(iii)–OH–EDTA. While the exact stoichiometry and degree of ligand protonation within these complexes remain undefined, their formation must be accounted for to properly assess the fate and transport of plutonium under conditions relevant to nuclear waste disposal.

Combined advanced spectroscopy and solubility studies provide evidence for the formation of novel calcium-containing and hydrolyzed (Cm,Pu)(iii)–EDTA complex(es).     

Hydrothermal synthesis of a novel nanolayered tin phosphate for removing Cr(iii)

In this work, an outstanding nanolayered tin phosphate with 15.0 Å interlayer spacing, Sn (HPO₄)₂·3H₂O (SnP–H⁺), has been synthesized by conventional hydrothermal method and first used in the adsorptive removal of Cr(iii) from aqueous solution. A number of factors such as contact time, initial concentration of Cr(iii), temperature, pH, and ionic strength on adsorption were investigated by batch tests. Moreover, the isothermal adsorption characteristics and kinetic model of Cr(iii) onto SnP–H⁺ were studied. The results showed that the adsorption of Cr(iii) by SnP–H⁺ was in accordance with the Langmuir adsorption isotherm model and the pseudo-second-order kinetic model. The adsorption capacity of Cr(iii) onto SnP–H⁺ at temperature 40.0 °C and pH 3.0 could reach 81.1 mg g⁻¹. And the distribution coefficient K_d was 23.0 g L⁻¹. Overall, experiments certified that SnP–H⁺ was an excellent adsorbent that can effectively remove Cr(iii) from aqueous solution.

In this work, an outstanding nanolayered tin phosphate with 15.0 Å interlayer spacing, Sn (HPO₄)₂·3H₂O (SnP–H⁺), has been synthesized by conventional hydrothermal method and first used in the adsorptive removal of Cr(iii) from aqueous solution.     

Arsenic(iii) removal from aqueous solution using TiO2-loaded biochar prepared by waste Chinese traditional medicine dregs

Oxidation of As(iii) to As(v) is an effective way to improve the performance of most arsenic removal technologies. In this study, a new alternative biosorbent, TiO₂-loaded biochar prepared by waste Chinese traditional medicine dregs (TBC) was applied in remediation for As(iii) from aqueous solution. Compared with unmodified biochar, the specific surface areas and total pore volumes of TBC increased while the average aperture decreased due to the loading of nano-TiO₂. The X-ray diffraction (XRD) of TBC confirmed that the precipitated titanium oxide was primarily anatase. pH did not have a significant effect on the adsorption capacity at 10 mg L⁻¹ As(iii) in suspension with a pH ranging from 2 to 10. Adsorption kinetics data were best fitted by the pseudo-second-order model (R² > 0.999). The Sips maximum adsorption capacity was 58.456 mg g⁻¹ at 25 °C, which is comparable with other adsorbents reported in previous literature. The Gibbs free energy (ΔG) of As(iii) adsorption was negative, indicating the spontaneous nature of adsorption. The results of free radical scavenging and N₂ purging experiments indicated that O₂ acted as an electron accepter and O₂˙⁻ dominated the oxidation of As(iii). The oxidation of As(iii) obviously affected the adsorption capacity for As(iii) by TBC. X-ray photoelectron spectroscopy (XPS) studies showed that As(iii) and As(v) existed on the surface of TBC, suggesting that the oxidation of As(iii) occurred. TBC played multiple roles for As(iii), including direct adsorption and photocatalytic oxidation adsorption. Regeneration and stability experiments showed that TBC was an environment-friendly and efficient adsorbent for As(iii) removal.

TiO₂-loaded biochar prepared by waste Chinese traditional medicine dregs (TBC) was applied in remediation for As(iii) from aqueous solution.     

Fluorescence determination of Fe(iii) in drinking water using a new fluorescence chemosensor

A new fluorescence chemosensor based on (Z)-2-(1-(3-oxo-3H-benzo[f]chromen-2-yl)ethylidene)hydrazine-1-carbothioamide (CEHC) has been developed for the determination of Fe(iii) in drinking water. The optimum conditions were acetate buffer solution with a pH 5.0. In this approach, the determination of Fe(iii) is based on static quenching of the luminescence of the probe upon increasing concentrations of Fe(iii). The CEHC sensor binds Fe(iii) in a 1 : 1 stoichiometry with a binding constant K_a = 1.30 × 10⁴ M⁻¹. CEHC responds to Fe(iii) in a way that is more sensitive, selective, and quick to turn off the fluorescence than to other heavy metal ions. Selectivity was proved against seven other metal ions (Mn(ii), Al(iii), Cu(ii), Ni(ii), Zn(ii), Pb(ii), and Cd(ii)). The calibration curve was constructed based on the Stern–Volmer equation. The linear range was 2.50–150 μM with the correlation coefficient of 0.9994, and the LOD was 0.76 μM. The method was successfully applied to determine Fe(iii) in drinking water samples, and the accuracy of the chemosensor was validated by atomic absorption spectrometry.

A new fluorescence chemosensor based on (Z)-2-(1-(3-oxo-3H-benzo[f]chromen-2-yl)ethylidene)hydrazine-1-carbothioamide (CEHC) has been developed for the determination of the fluorescence probe of Fe(iii) in drinking water.     

Synthesis of FeO@SiO2–DNA core–shell engineered nanostructures for rapid adsorption of heavy metals in aqueous solutions

Creating novel and innovative nanostructures is a challenge, aiming to discover nanomaterials with promising properties for environmental remediation. In this study, the physicochemical and adsorption properties of a heterogeneous nanostructure are evaluated for the rapid removal of heavy metal ions from aqueous solutions. Core–shell nanostructures are prepared using iron oxide cores and silica dioxide shells. The core is synthesized via the co-precipitation method and modified in situ with citric acid to grow a carboxyl layer. The shell was hydrolyzed/condensed and then functionalized with amine groups for ds-DNA condensation via electrostatic interaction. The characterization techniques revealed functional FeO@SiO₂–DNA nanostructures with good crystallinity and superparamagnetic response (31.5 emu g⁻¹). The predominant superparamagnetic nature is attributed to the citric acid coating. This improves the dispersion and stability of the magnetic cores through the reduction of the dipolar–dipolar interaction and the enhancement of the spin coordination. The rapid adsorption mechanism of FeO@SiO₂–DNA was evaluated through the removal of Pb(ii), As(iii), and Hg(ii). A rapid adsorption rate is observed in the first 15 min, attributed to a heterogeneous chemisorption mechanism based on electrostatic interactions. FeO@SiO₂–DNA shows higher adsorption efficiency of 69% for Pb(ii) removal compared to As(iii) (51%) and Hg(ii) (41%). The selectivity towards Pb(ii) is attributed to the similar acid nature to ds-DNA, where the ionic strength interaction provides good affinity and stability. The facile synthesis and rapid adsorption suggest a promising nanostructure for the remediation of water sources contaminated with heavy metal ions and can be extended to other complex molecules.

Facile synthesis of well-dispersed and magnetic FeO@SiO₂–DNA nanostructures with electrostatic active sites for interaction and rapid adsorption of heavy metals.     

Mechanistic insights into dioxygen activation by a manganese corrole complex: a broken-symmetry DFT study

The Mn–oxygen species have been implicated as key intermediates in various Mn-mediated oxidation reactions. However, artificial oxidants were often used for the synthesis of the Mn–oxygen intermediates. Remarkably, the Mn(v)–oxo and Mn(iv)–peroxo species have been observed in the activation of O₂ by Mn(iii) corroles in the presence of base (OH⁻) and hydrogen donors. In this work, density functional theory methods were used to get insight into the mechanism of dioxygen activation and formation of Mn(v)–oxo. The results demonstrated that the dioxygen cannot bind to Mn without the axial OH⁻ ligand. Upon the addition of the axial OH⁻ ligand, the dioxygen can bind to Mn in an end-on fashion to give the Mn(iv)–superoxo species. The hydrogen atom transfer from the hydrogen donor (substrate) to the Mn(iv)–superoxo species is the rate-limiting step, having a high reaction barrier and a large endothermicity. Subsequently, the O–C bond formation is concerted with an electron transfer from the substrate radical to the Mn and a proton transfer from the hydroperoxo moiety to the nearby N atom of the corrole ring, generating an alkylperoxo Mn(iii) complex. The alkylperoxo O–O bond cleavage affords a Mn(v)–oxo complex and a hydroxylated substrate. This novel mechanism for the Mn(v)–oxo formation via an alkylperoxo Mn(iii) intermediate gives insight into the O–O bond activation by manganese complexes.

DFT calculations revealed a novel mechanism for the formation of Mn(v)–oxo in the dioxygen activation by a Mn(iii) corrole complex involving a Mn(iii)–alkylperoxo intermediate.     

Optical chemical sensor of Gd(iii) based on 5-(2′-bromophenyl- azo)-6-hydroxypyrimidine-2,4-dione immobilized on poly(methyl methacrylate) and 2-nitrophenyloctylether matrix

A novel optical chemical sensor (optode) was fabricated for the determination of Gadolinium ions. The optical sensor was prepared by incorporating a recently synthesized ionophore, 5-(2′-bromophenylazo)-6-hydroxy pyrimidine-2,4-dione (BPAHPD), and 2-nitrophenyloctylether (NPOE) as a plasticizer in poly(methyl methacrylate) (PMMA) membrane. The color of the sensing membrane in contact with Gd(iii) ions changed from yellow to red-orange due to the adsorption of Gd(iii) with the maximum absorbance (λ_max) at 563 nm. The chemical sensor responds optimally towards Gd(iii) ions at the optimum conditions of pH 7.5, contact time 10 min, 150 ng mL⁻¹ Gd(iii), and 5.0 mL solution. The linear regression equation achieved was A = 4.36C (μg mL⁻¹) – 0.15 (r = 0.9976). A linear Gd(iii) calibration curve can be established in the concentration range of 5.0–250 ng mL⁻¹ with R² = 0.9976. Detection and quantification limits are 1.47 and 4.75 ng mL⁻¹, respectively. The molar absorptivity and Sandell sensitivity are found to be 6.86 × 10⁷ L mol⁻¹ cm⁻¹ and 0.023 ng cm⁻², respectively. In addition to its stability and reproducibility, the optode revealed a great selectivity toward Gd(iii) ions as compared to other coexisting ions in real samples. The recovery of Gd(iii) ions from the sensor material was achieved using 0.4 M HNO₃^. The offered optode sensor membrane has been employed to monitor Gd(iii) in soil, sediments, river water, and urine with an internal standard addition method and compared statistically with the ICP-OES method. The results revealed calculated t-values between 1.11–1.85, whereas F values were in the range of 2.46–3.77 which did not exceed the theoretical values, indicating no significant difference at 95% confidence level. The observed percent recovery is in the range of 97.24–102.52%.

A novel optical chemical sensor (optode) was fabricated for the determination of Gadolinium ions.     

Positive effects of concomitant heavy metals and their reduzates on hexavalent chromium removal in microbial fuel cells

Cr(vi) laden wastewaters generally comprise a range of multiple heavy metals such as Au(iii) and Cu(ii) with great toxicity. In the present study, cooperative cathode modification by biogenic Au nanoparticles (BioAu) reduced from aqueous Au(iii) and in situ Cu(ii) co-reduction were investigated for the first time to enhance Cr(vi) removal in microbial fuel cells (MFCs). With the co-existence of Cu(ii) in the catholyte, the MFC with carbon cloth modified with nanocomposites of multi-walled carbon nanotubes blended with BioAu (BioAu/MWCNT) obtained the highest Cr(vi) removal rate (4.07 ± 0.01 mg L⁻¹ h⁻¹) and power density (309.34 ± 17.65 mW m⁻²), which were 2.73 and 3.30 times as high as those for the control, respectively. The enhancements were caused by BioAu/MWCNT composites and deposited reduzates of Cu(ii) on the cathode surface, which increased the adsorption capacity, electronic conductivity and electrocatalytic activity of the cathode. This study provides an alternative approach for efficiently remediating co-contamination of multiple heavy metals and simultaneous bioenergy recovery.

The cooperative cathode modification by BioAu from Au(iii) and in situ Cu(ii) co-reduction enhanced Cr(vi) removal and bioelectricity generation in MFCs.     

Insight into the adsorption mechanisms of methylene blue and chromium(iii) from aqueous solution onto pomelo fruit peel

In this study, the biosorption mechanisms of methylene blue (MB) and Cr(iii) onto pomelo peel collected from our local fruits are investigated by combining experimental analysis with ab initio simulations. Factors that affect the adsorption such as pH, adsorption time, adsorbent dosage and initial adsorbate concentration, are fully considered. Five isotherm models—Langmuir, Freundlich, Sips, Temkin, and Dubinin–Radushkevich—are employed to estimate the capacity of pomelo peel adsorption, whereas four kinetic models—pseudo-first-order, pseudo-second-order, Elovich and intra-diffusion models—are also used to investigate the mechanisms of the uptake of MB and Cr(iii) onto the pomelo fruit peel. The maximum biosorption capacities calculated from the Langmuir models for MB and Cr(iii) at 303 K are, 218.5 mg g⁻¹ and 11.3 mg g⁻¹, respectively. In particular, by combining, for the first time, the experimental FT-IR spectra with those obtained from ab initio calculations, we are able to demonstrate that the primary adsorption mechanisms of the uptake of MB onto pomelo fruit peel are electrostatic attraction and hydrogen-bond formations, whereas the adsorption mechanisms for Cr(iii) are electrostatic attraction and n–d interactions.

In this study, the biosorption mechanisms of methylene blue (MB) and Cr(iii) onto pomelo peel collected from our local fruits are investigated by combining experimental analysis with ab initio simulations.     

Synchronous oxidation and sequestration for As(iii) from aqueous solution by modified CuFe2O4 coupled with peroxymonosulfate: a fast and stable heterogeneous process

Bifunctional heterogeneous catalytic processes for highly efficient removal of arsenic (As(iii)) are receiving increased attention. However, the agglomerated nature and stability of nanoparticles are major concerns. Herein, we report a new process regarding the anchoring of CuFe₂O₄ nanoparticles on a substrate material, a kind of Fe–Ni foam, to form porous CuFe₂O₄ foam (CuFe₂O₄-foam) by in situ synthesis. The prepared material was then applied to activate peroxymonosulfate (PMS) for fast and efficient removal of As(iii) from water. The results of removal experiments show that the complete removal of arsenic (<10 μg L⁻¹) from 1 mg L⁻¹ As(iii) aqueous solution can be achieved within shorter time (<10 min) using this adsorbent coupled with PMS. The maximum adsorption capability of As(iii) and As(v) on the prepared adsorbent is observed to be about 105.78 mg g⁻¹ and 120.32 mg g⁻¹, respectively. CuFe₂O₄-foam/PMS couple could work effectively in a wide pH range (3.0–9.0) and temperature range (10–60 °C), which is more beneficial to its application in actual water treatment engineering. The exhausted adsorbents can be refreshed for cyclic runs (at least 7 cycles) with insignificant capacity loss using alkaline solution as a regeneration strategy, suggesting this process has good stability. Investigation of the mechanism reveals that the route to the removal of As(iii) is synchronous oxidation and sequestration in the arsenic removal process. The large As(iii) removal capability and stability of CuFe₂O₄-foam/PMS show its potential as a promising candidate in real As(iii)-contaminated groundwater treatment.

Bifunctional heterogeneous catalytic processes for highly efficient removal of arsenic (As(iii)) are receiving increased attention.     

An efficient mercapto-functionalized organic–inorganic hybrid sorbent for selective separation and preconcentration of antimony(iii) in water samples

This work reported on the application of mercapto-functionalized silica-supported organic–inorganic hybrid sorbent as a solid phase extraction (SPE) extractant for effective separation and preconcentration of Sb(iii) species in real water samples. The influences of pH, sorbent amounts, flow rates and the concentration of eluent on the adsorption and desorption of Sb(iii) species had been evaluated. The recovery of Sb(iii) species at pH 5 with 100 mg mercapto-functionalized hybrid sorbent at the flow rate of 5.0 mL min⁻¹ was greater than 95% without interference from all of metal ions tested. The trapped Sb(iii) species by extractant was then eluted with 5% HCl solution at the flow rate of 5.0 mL min⁻¹. The proposed procedure permitted large enrichment factors of about 200 and higher for 10 μg L⁻¹ of Sb(iii) species. The merits of analytical figures for the determination of Sb(iii) species were as follows: detection limit (3σ, n = 11), 2 ng L⁻¹; precision, 1.6% (n = 11) for 10 μg L⁻¹ of Sb(iii) species; the linear calibration curve presented in the concentration range of 1.0–200.0 μg L⁻¹. The validity of the proposed procedure was checked by the analysis of standard reference materials. Excellent agreement between the analytical results and the certified values (t-test at 95% confidence level) was found. The mercapto-functionalized hybrid sorbent as a SPE extractant was applied to the determination of Sb(iii) species in various water samples with satisfactory results.

This work reported on the application of mercapto-functionalized silica-supported organic–inorganic hybrid sorbent as a solid phase extraction (SPE) extractant for effective separation and preconcentration of Sb(iii) species in real water samples.     

Synthesis of Bi2WO6/Na-bentonite composites for photocatalytic oxidation of arsenic(iii) under simulated sunlight

Novel Bi₂WO₆/bentonite (denoted as BWO/BENT) composites were prepared via a typical hydrothermal process and employed for the photocatalytic oxidation of arsenic(iii) (As(iii)). The properties of the prepared samples were characterized through X-ray diffraction, transmission and scanning electron microscopy, UV-visible diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, and photoluminescence spectroscopy. Effects of the BENT ratio on the As(iii) removal were explored under simulated sunlight, and the best photocatalytic effect was observed for the composite with BWO : BENT = 7 : 3 w/w. Compared with the pure BWO, the BWO/BENT composites exhibited an improved photocatalytic ability in the removal of As(iii), which was mainly ascribed to the enlarged specific surface area and the suppressed electron–hole recombination by the incorporated BENT. Furthermore, photo-generated holes (h⁺) and superoxide radicals ·O₂⁻ were confirmed to be the major contributors to the oxidation of As(iii), and an associated mechanism of photocatalytic oxidation of As(iii) over BWO/BENT composites was proposed.

Novel Bi₂WO₆/bentonite (denoted as BWO/BENT) composites were prepared via a typical hydrothermal process and employed for the photocatalytic oxidation of arsenic(iii) (As(iii)).     

Non-aqueous solvent extraction of indium from an ethylene glycol feed solution by the ionic liquid Cyphos IL 101: speciation study and continuous counter-current process in mixer–settlers

A solvometallurgical process for the separation of indium(iii) and zinc(ii) from ethylene glycol solutions using the ionic liquid extractants Cyphos IL 101 and Aliquat 336 in an aromatic diluent has been investigated. The speciation of indium(iii) in the two immiscible organic phases was investigated by Raman spectroscopy, infrared spectroscopy, EXAFS and ¹¹⁵In NMR spectroscopy. At low LiCl concentrations in ethylene glycol, the bridging (InCl₃)₂(EG)₃ or mononuclear (InCl₃)(EG)₂ complex is proposed. At higher lithium chloride concentrations, the first coordination sphere changes to two oxygen atoms from one bidentate ethylene glycol ligand and four chloride anions ([In(EG)Cl₄]⁻). In the less polar phase, indium(iii) is present as a tetrahedral [InCl₄]⁻ complex independent of the LiCl concentration. After the number of theoretical stages had been determined using a McCabe–Thiele diagram for extraction by Cyphos IL 101, the extraction and scrubbing processes were performed in lab-scale mixer–settlers to test the feasibility of working in continuous mode. Indium(iii) was extracted quantitatively in four stages, with 19% co-extraction of zinc(ii). The co-extracted zinc(ii) was scrubbed selectively in six stages using an indium(iii) scrub solution. Indium(iii) was recovered from the loaded less polar organic phase as indium(iii) hydroxide (98.5%) by precipitation stripping with an aqueous NaOH solution.

Speciation studies give insight into the mechanism of non-aqueous solvent extraction of indium from ethylene glycol solution by the ionic liquid Cyphos IL 101.     

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.     

Adsorption performance of antimony by modified iron powder

Antimony pollution resulting from industrial production is a great threat to the environment, ecology and the human body. Zero-valent iron powder is low-cost and easy to obtain. Nevertheless, the lower adsorption capacity limits its application when it is used as an adsorbent. In the present study, ball-milling and acid modification were developed to change its surface characteristics and γ-Fe₂O₃, γ-FeOOH and Fe₃O₄ were obtained after treatment, which promoted its adsorption capacity. Compared with the raw iron powder, the adsorption capacities for Sb(iii) and Sb(v) using the modified material were increased from 12.93 mg g⁻¹ and 5.47 mg g⁻¹ to 17.96 mg g⁻¹ and 10.58 mg g⁻¹, respectively. The study showed that the experimental data fitted the Langmuir model and the pseudo-first-order kinetic model better; the adsorption process was monolayer and chemically controlled at pH 5.0 ± 0.2. XPS and FT-IR analysis showed that Fe–O–Sb bonds arose during the adsorption process. The effect of pH on the adsorption capacity was also studied and the pH affected the adsorption of Sb(v) more than the adsorption of Sb(iii). In addition, the modified iron powder presented better efficiency when applied to the removal of low levels of antimony in drinking water. Based on the increase of adsorption capacity and low cost, iron powder should be a promising adsorbent for aqueous antimony removal.

Modified iron powders were obtained by ball-milling and acid modification and the adsorption behavior and mechanism for Sb(iii) and Sb(v) analyzed. The improved adsorption capacity and low cost show the application potential of the modified material.     

Selective extraction of trivalent actinides using CyMe4BTPhen in the ionic liquid Aliquat-336 nitrate

The extraction of Am(iii), Cm(iii) and Eu(iii) by 2,9-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-1,10-phenanthroline (CyMe₄BTPhen) from nitric acid solution was studied using the ionic liquid Aliquat-336 nitrate ([A336][NO₃]) as diluent. Results show a high selectivity of the solvent for Am(iii) and Cm(iii) over Eu(iii), but rather slow extraction kinetics. The kinetics of CyMe₄BTPhen were largely improved by the addition of 0.005 mol L⁻¹N,N,N′,N′-tetra-n-octyl-diglycolamide (TODGA) as a phase transfer reagent and by the use of 1-octanol as co-diluent. The addition of the phase transfer catalyst and co-diluent did not compromise the selectivity towards the actinide/lanthanide separation and thus this four-component system can be successfully applied to separate Am(iii) and Cm(iii) from the lanthanides.

Improving the kinetics of selective An(iii) extraction from nitric acid feed solutions into an ionic liquid based solvent: combining CyMe₄BTPhen with TODGA in Aliquat-336 nitrate.     

Optimization of the adsorption and removal of Sb(iii) by MIL-53(Fe)/GO using response surface methodology

In this study, a graphene oxide metal–organic framework (MIL-53(Fe)/GO) composite adsorbent was successfully synthesized using a simple method at room temperature. The specific surface area of the synthesized MIL-53(Fe)/GO nanoparticles was 268.43 m² g⁻¹, with an average pore size of 2.52 nm. The Box–Behnken response surface method was applied to optimize the adsorption time, dosage, pH, temperature, and initial concentration of Sb(iii) in the MIL-53(Fe)/GO adsorption treatment employed for synthetic wastewater containing Sb(iii). We determined the optimal adsorption conditions and explored the isotherm model, adsorption kinetic model, and adsorption mechanism during the adsorption process. For an optimal adsorption of Sb(iii) by MIL-53(Fe)/GO, the adsorption time, dosage, pH, temperature, and initial Sb(iii) concentration should be set to 4.86 h, 85.79 mg L⁻¹, 10.00, 39.29 °C, and 10.09 mg L⁻¹, respectively. Under these optimal conditions, the removal rate of Sb(iii) will be as high as 97.97%. The adsorption of Sb(iii) by MIL-53(Fe)/GO conformed to the Freundlich isotherm adsorption model, and its maximum adsorption capacity was 69.014 mg g⁻¹. The adsorption kinetics process, which is a nonhomogeneous reaction, could be fitted using a quasi-first-order kinetic model. A Fourier transform infrared spectroscopy analysis showed that MIL-53(Fe)/GO hydroxyl and amine groups play a vital role in the adsorption process. MIL-53(Fe)/GO did not exhibit any changes in its adsorption efficiency in the presence of its anion and showed high specificity to Sb(iii). XPS characterization showed that Sb successfully adsorbed onto the adsorbent and that no oxidation–reduction reaction occurred during the adsorption process. The adsorption efficiency remained high even after four cycles of use. MIL-53(Fe)/GO is highly recyclable with significant application potential for treating wastewater containing Sb(iii).

In this study, a graphene oxide metal–organic framework (MIL-53(Fe)/GO) composite adsorbent was successfully synthesized using a simple method at room temperature.     

Experimental and theoretical studies on the extraction behavior of Cf(iii) by NTAamide(C8) ligand and the separation of Cf(iii)/Cm(iii)

In this work we studied the extraction behaviors of Cf(iii) by NTAamide (N,N,N′,N′,N′′,N′′-hexaocactyl-nitrilotriacetamide, C8) in nitric acid medium. Influencing factors such as contact time, concentration of NTAamide(C8), HNO₃ and NO₃⁻ as well as temperature were considered. The slope analysis showed that Cf(iii) should be coordinated in the form of neutral molecules, and the extraction complex should be Cf(NO₃)₃·2L (L = NTAamide(C8)), which can achieve better extraction effect under the low acidity condition. When the concentration of HNO₃ was 0.1 mol L⁻¹, the separation factor (SF_Cf/Cm) was 3.34. The extractant has application prospect to differentiate the trivalent Cf(iii) and Cm(iii) when the concentration of nitric acid is low. On the other hand, density functional theory (DFT) calculations were conducted to explore the coordination mechanism of NTAamide(C8) ligands with Cf/Cm cations. The NTAamide(C8) complexes of Cf(iii)/Cm(iii) have similar geometric structures, and An(iii) is more likely to form a complex with 1 : 2 stoichiometry (metal ion/ligands). In addition, bonding property and thermodynamics analyses showed that NTAamide(C8) ligands had stronger coordination ability with Cf(iii) over Cm(iii). Our work provides meaningful information with regard to the in-group separation of An(iii) in practical systems.

We performed basic chemical studies on Cf using NTAamide extractant. The results of experiments and DFT calculations show that NTAamide has a good coordination ability to Cf/Cm and is expected to be applied to Cf/Cm separation.