Thiosemicarbazone modified zeolitic imidazolate framework (TSC-ZIF) for mercury(ii) removal from water

Zeolitic imidazolate frameworks (ZIF-8), and their derivatives, have been drawing increasing attention due to their thermal and chemical stability. The remarkable stability of ZIF-8 in aqueous and high pH environments renders it an ideal candidate for the removal of heavy metals from wastewater. In this study, we present the preparation of novel aldehyde-based zeolitic imidazolate frameworks (Ald-ZIF) through the integration of mixed-linkers: 2-methylimidazole (MIM) and imidazole-4-carbaldehyde (AldIM). The prepared Ald-ZIFs were post-synthetically modified with bisthiosemicarbazide (Bisthio) and thiosemicarbazide (Thio) groups, incorporating thiosemicarbazone (TSC) functionalities to the core of the framework. This modification results in the formation of TSC-functionalized ZIF derivatives (TSC-ZIFs). Thiosemicarbazones are versatile metal chelators, hence, adsorption properties of TSC-ZIFs for the removal of mercury(ii) from water were explored. Removal of mercury(ii) from homoionic aqueous solutions, binary and tertiary systems in competition with lead(ii) and cadmium(ii) under ambient conditions and neutral pH are reported in this study. MIM_3.5:Thio₁:Zn improved the removal efficiency of mercury(ii) from water, up to 97% in two hours, with an adsorption capacity of 1667 mg g⁻¹. Desorption of mercury(ii) from MIM_3.5:Thio₁:Zn was achieved under acidic conditions, regenerating MIM_3.5:Thio₁:Zn for five cycles of mercury(ii) removal. TSC-ZIF derivatives, designed and developed here, represent a new class of dynamically functionalized adsorption material displaying the advantages of simplicity, efficiency, and reusability.

Zeolitic imidazolate frameworks Ald-ZIF were obtained by mixing two imidazole-based linkers with zinc(ii). Post-synthetically modified Ald-ZIFs with thiosemicarbazide group improved mercury(ii) removal efficiency from water at a capacity of 1667 mg g⁻¹.     

A kinetic method for the determination of thyroxine iodine (author's transl)

A Kinetic Method for the Determination of Thyroxine IodineA simple and rapid kinetic method is described for the determination of thyroxine iodine in Chromatographic eluates. The advantages of the new method are discussed. Precision and correlation with isotopic thyroxine are very good.     

Development of a new electrochemical method for the determination of copper(ii) at trace levels in environmental and food samples

This paper presents the fabrication of a new modified carbon paste electrode (CPE) with N¹-hydroxy-N¹,N²-diphenylbenzamidine (HDPBA) and functionalized multi-walled carbon nanotubes (MWCNTs) (HDPBA–MWCNTs/CPE) for highly sensitive and selective determination of Cu(ii) using the square wave anodic stripping voltammetry (SWASV) technique. The fabricated electrode was characterized using various spectroscopic techniques to study its morphological, structural, and electrochemical properties. The accumulation of Cu(ii) on the surface of HDPBA–MWCNTs/CPE was done in 0.1 M ammonium chloride (NH₄Cl, pH 5) solution at an applied potential of −0.70 V versus Ag/AgCl for 180 s, followed by electrochemical stripping in the positive scan of the voltammetry after a resting time of 10 s. The developed HDPBA–MWCNTs/CPE was found to be highly selective, sensitive and reproducible. At optimal conditions of the experiment, the proposed method exhibited a very low limit of detection (0.0048 nM Cu(ii)), a wide linear dynamic range (0.00007–1.5000 μM Cu(ii)), and good reproducibility with relative standard deviation (RSD) value of 3.7%. The effect of various foreign ions on the voltammetric response of Cu(ii) was investigated and the electrode was found to be highly selective to Cu(ii). The practical applicability of the proposed HDPBA–MWCNTs/CPE was studied by applying the electrode for the quantification of Cu(ii) contents in environmental water (wastewater and tap water), soft drink (Fanta and Sprite), and food supplement (commercially available multi-mineral/vitamin tablets) samples. The present method was validated with atomic absorption spectrometry (AAS). The results found from the two methods are in good agreement with a 95% confidence level.

This paper presents a new modified carbon paste electrode with N¹-hydroxy-N¹,N²-diphenylbenzamidine and multi-walled carbon nanotubes for highly sensitive and selective determination of Cu(ii) usingsquare wave anodic stripping voltammetry technique.     

Adsorption of mercury(ii) from water by a novel sPAN fiber containing sulfhydryl,carboxyl and amino groups

A novel fiber containing sulfhydryl, carboxyl and amino groups (sPAN) with high adsorption capacity for mercury was facilely prepared by chemically grafting cysteine onto a commercial polyacrylonitrile (PAN) fiber in a one-step reaction. The as-prepared sPAN was characterized for its chemical structure, thermal stability, tensile strength, surface morphology and surface binding species. The adsorption and desorption performances for mercury were investigated by both batch and dynamic experiments. The results showed that sPAN was effective for mercury removal over pH 4–7, and ionic strength produced no obvious interference with the adsorption. The equilibrium adsorption capacity of mercury could be as high as 459.3 (±16.0) mg g⁻¹, much higher than for most previously reported materials due to the strong interaction between mercury ions and sulfhydryl, carboxyl, amino groups. More than 99% adsorbed mercury could be eluted by the mixture of hydrochloric acid and thiourea, and the regenerated sPAN could be reused for mercury removal with no significant loss of adsorption capacity even after 10 cycles. The dynamic adsorption results indicated that at initial mercury concentrations of 0.1 and 1.0 mg L⁻¹, the residual mercury concentration was less than 1 μg L⁻¹, which could meet the criterion for drinking water. Moreover, at an initial mercury concentration of 10 mg L⁻¹, the residual mercury concentration was less than 50 μg L⁻¹, which could satisfy the Chinese national industry water discharge standard.

A novel fiber containing sulfhydryl, carboxyl and amino groups (sPAN) with high adsorption capacity for mercury was facilely prepared by chemically grafting cysteine onto a commercial polyacrylonitrile (PAN) fiber in a one-step reaction.     

Highly-efficient removal of Pb(ii), Cu(ii) and Cd(ii) from water by novel lithium,sodium and potassium titanate reusable microrods

In this work, we report on the efficient removal of heavy metal ions with nanostructured lithium, sodium and potassium titanates from simulated wastewater. The titanates were obtained via a fast, easy and cost effective process based on extraction of sulfate ions from the crystals of titanyl sulfate and their replacement with hydroxyl groups of NaOH, LiOH and KOH solutions leaving the Ti–O framework intact. The as-prepared titanates were carefully examined by scanning and transmission electron microscopy. Furthermore, the effect of contact time, pH, annealing temperature, together with adsorption in real conditions including competitive adsorption and reusability were studied. It was found that the maximum adsorption capacity, as calculated from the Langmuir adsorption model, is up to 3.8 mmol Pb(ii) per g, 3.6 mmol Cu(ii) per g and 2.3 mmol Cd(ii) per g. Based on the characterization results, a possible mechanism for heavy metal removal was proposed. This work provides a very efficient, fast and convenient approach for exploring promising materials for water treatment.

This work provides a very efficient, fast and convenient approach for exploring promising materials for water treatment.     

Silicon-based fluorescent platforms for copper(ii) detection in water

The potential of silicon-based fluorescent platforms for the detection of trace toxic metal ions was investigated in an aqueous environment. To this aim, silicon chips were first functionalized with amino groups, and fluorescein organic dyes, used as sensing molecules, were then covalently linked to the surface via formation of thiourea groups. The obtained hybrid heterostructures exhibited high sensitivity and selectivity towards copper(ii), a limit of detection compatible with the recommended upper limits for copper in drinking water, and good reversibility using a standard metal–chelating agent. The fluorophore–analyte interaction mechanism at the basis of the reported fluorescence quenching, as well as the potential of performance improvement, were also studied. The herein presented sensing architecture allows, in principle, tailoring of the selectivity towards other metal ions by proper fluorophore selection, and provides a favorable outlook for integration of fluorescent chemosensors with silicon photonics technology.

Covalent linkage of fluorescein to silanized silicon chips yields solid-state platforms for detection of copper(ii) in water. This architecture represents a step forward towards the fabrication of sensors for remote water analysis applications.     

Novel sulfonamidospirobifluorenes as fluorescent sensors for mercury(ii) ion and glutathione

Novel spirobifluorene derivatives containing two and four sulfonamide groups are successfully synthesized from the commercially available bromo-9,9′-spirobifluorene by Sonogashira couplings. These compounds exhibit an excellent selective fluorescence quenching by Hg(ii) in DMSO/HEPES buffer mixture with three-times-noise detection limits of 10.4 to 103.8 nM. A static aggregation induced quenching mechanism is proposed based on the data from ¹H-NMR and UV-Vis spectroscopy, as well as the observation of the Tyndall effect. Quantifications of Hg(ii) using these sensors are in good agreement with those obtained from ICP-OES. The reversibility of these sensors is demonstrated by a complete fluorescence restoration upon addition of EDTA or l-glutathione. The application as a turn-on sensor for l-glutathione is demonstrated in a quantitative analysis of three samples of l-glutathione supplement drinks.

Two sulfonamide derivatives of spirobifluorene are synthesized and used as turn-off sensors for Hg(ii) ion. The signal restoration of the sensors by l-glutathione leads to a quantitative analysis of three supplement drinks.     

Selective preconcentration separation of Hg(ii) and Cd(ii) from water,fish muscles,and cucumber samples using recycled aluminum adsorbents

Modified aluminum scrap waste was used in the selective extraction of Hg(ii), and Cd(ii) ions. The aluminum scraps were modified with dibenzoylmethane, or isatoic anhydride, or 5-(2-chloroacetamide)-2-hydroxybenzoic acid. The modified aluminum sorbents were characterized by FT-IR, SEM, XRD, XPS, TGA, and elemental analysis. Modes of chelation between adsorbents and target metal ions were deduced via DFT. The highest adsorption capacity was observed for benzo-amino aluminum (BAA) toward Hg(ii), which reached 234.56 mg g⁻¹, while other modified sorbents ranged from 135.28 mg g⁻¹ to 229.3 mg g⁻¹. Under the optimized conditions, the BAA adsorbent showed a lower limit of detection (1.1 mg L⁻¹) and limit of quantification (3.66 mg L⁻¹) for mercury ions than other sorbents. The prepared aluminum adsorbents also exhibited significant selectivities for Hg(ii) and Cd(ii) ions in the presence of competing metal ions.

Modified aluminum scrap waste was used in the selective extraction of Hg(ii), and Cd(ii) ions.     

Direct kinetic method for the determination of phosphate

Serum phosphate can be measured accurately, precisely and economically using an initial rate spectrophotometric procedure. This procedure measures the formation of the unreduced phosphomolybdate heteropolyacid complex at 334 nm. The concentration of polyvinylpyrrolidone Mr = 40,000 has been optimised to allow the determination of serum inorganic phosphate on a discrete analyser, the Eppendorf Epos. Possible interference due to hyperlipaemia, high bilirubin or high protein content of the serum samples is discussed.     

A selective and easily recyclable dimer based on a calix[4]pyrrole derivative for the removal of mercury(ii) from water

A recyclable mercury(ii) selective dimer based on a calix[4]pyrrole derivative has been synthesised and characterised by mass and FT-IR spectrometry, Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX). Information regarding the ability of the dimer to interact with metal cations was obtained from FTIR and SEM-EDX analyses. A striking feature of micrographs of the loaded dimer is the change of morphology with the cation. Based on these results, optimal conditions for removing cations from water were assessed under different experimental conditions. Results obtained demonstrate that the removal process is fast. Capacity values and selectivity factors show that the dimer is selective for Hg(ii) in single and multiple component metal solutions relative to other cations. Single-ion transfer Gibbs energies from water to a solvent containing common functionalities to those of the dimer were used to assess the counter-ion effect on the removal process. Agreement is found between these data and energy calculations derived from molecular simulation studies. Studies on polluted water in the presence of normal water components in addition to toxic metal cations are reported. Further experimental work on wastewater from the mining industry is in progress.

A recyclable mercury(ii) selective dimer based on a calix[4]pyrrole derivative has been synthesised and characterised by mass and FT-IR spectrometry, Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX).     

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.     

Functionalised electrospun membranes (TETA-PVC) for the removal of lead(ii) from water

Driven by the need for delivering sustainable water purification solutions for the removal of heavy metals from water, electrospun PVC membranes were functionalised with triethylenetetramine (TETA) and were used to remove lead(ii) ions selectively from water. The membranes were characterised and their adsorption behavior towards the removal of lead from water was investigated. The incorporation of TETA on the membrane''s surface significantly improved the removal efficiency of lead(ii) up to 99.8% in 30 minutes and under ambient conditions, with the lowest concentration of 50 ppm. The adsorption mechanism was investigated and kinetic data showed a better correlation with the pseudo-second-order model. Similarly, the equilibrium data best fitted with the Langmuir adsorption isotherm model with a relatively high maximum adsorption capacity of 1250 mg g⁻¹ for lead(ii) ions, larger than recently reported adsorption capacities for similar membranes. The functionalised membrane also showed high selectivity to lead(ii) in a mixed solution containing lead(ii), mercury(ii), cadmium(ii), arsenic(iii), copper(ii), and zinc(ii). The functionalised membrane was regenerated, where desorption of lead(ii) was achieved, under mildly acidic conditions. The removal efficiency of the regenerated membrane after six cycles of adsorption/desorption was maintained at a high level of 98%. The proposed design offers a simple yet effective, sustainable, and environmentally friendly solution for water treatment.

Driven by the need for delivering sustainable water purification solutions for the removal of heavy metals from water, TETA functionalised electrospun PVC membranes were fabricated and used to remove lead(ii) ions selectively from water.     

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.     

A novel method for determination of beta-lactamase using the agar dilution method

A novel test procedure is described for the rapid assay of beta-lactamase using the agar dilution method. The susceptibility to beta-lactamase was measured by adding an appropriate amount of enzyme to the diluting culture broth of a test organism in the agar dilution method. By this method, beta-lactamase susceptibility can be expressed in the same way as the MIC assay for antibiotics (microgram/ml). The results obtained with Escherichia coli beta-lactamase were closely related to the MIC patterns of the strains producing beta-lactamases.