Fe3O4-chitosan nanocomposite as a magnetic biosorbent for removal of nickel and cobalt heavy metals from polluted water

Recently, natural polymers like chitosan have gained attention as promising adsorbents for water treatment. By combining chitosan with magnetic nanoparticles, their adsorption capabilities can be enhanced. In this study, chitosan-magnetite nanocomposite (CMNC) was synthesized via coprecipitation method to remove nickel and cobalt from aqueous solutions. The physicochemical properties of the synthesized CMNC were investigated by various techniques, including FESEM, TEM, XPS, FTIR, XRD, and VSM. The electron microscopy results confirmed the uniform dispersion of magnetite nanoparticles within CMNC nanocomposites, while VSM confirmed their significant magnetic properties. The adsorption experiments showed that at optimal conditions (pH = 6, contact time = 2 h, adsorbent dosage = 2 g/l), CMNC has high adsorption capacities of 30.03 mg/g for Ni2+ and 53.19 mg/g for Co2+. Furthermore, the adsorption data fitted best with the Langmuir isotherm, show that the active sites on CMNC are energetically homogenous. According to kinetic analysis, the experimental data were in good agreement with both pseudo-second-order and intra-particle diffusion models, which suggest that chemical sorption, along with mass transfer steps, influence the overall adsorption process. Finally, investigating the thermodynamic parameters (∆Gads, ∆Hads, ∆Sads) showed that the adsorption process on CMNC was endothermic and spontaneous, with stronger interactions observed between CMNC and Co2+ compared to Ni2+.

Synthesis of a magnetic SBA-15-NH2@Dual-Template Imprinted Polymer for solid phase extraction and determination of Pb and Cd in vegetables; Box Behnken design

In this study, a simple one-step method was applied for extraction and determination of lead and cadmium. The significant variables in extraction and pre-concentration were identified using analysis of variance and their behavior was modeled. Dual-template imprinted polymer was synthesized on modified Mesoporous silica structures coated with Fe₃O₄ magnetic nanoparticles. The optimum condition was 6.12 for pH, 40.62 mg for the polymer amount and 17.38 for the ultrasonic time. Concentration range, correlation coefficient, limit of detection and relative standard deviation for lead were reported to be 0.5-950, 0.9988, 0.35 μg L^-1 and 3.5%, respectively. For cadmium the above mentioned figure of merits were 0.3-980, 0.9969, 0.15 μg L^-1 and 2.4%, respectively. The adsorption capacities for lead and cadmium were reported to be 10.28 and 10.38, while their imprinting factors were 5.89 and 6.36, respectively.

Multi-functional porous organic polymers for highly-efficient solid-phase extraction of β-agonists and β-blockers in milk

A simple, accurate, and highly sensitive analytical method was developed in this study for the determination of ten β-agonists and five β-blockers in milk. In this method, new adsorbent phosphonic acid-functionalized porous organic polymers were synthesized through a direct knitting method. The synthesis procedure of the materials and the extraction conditions (such as the composition of loading buffer and eluent) were optimized. Benefitting from the high surface area (545–804 m² g⁻¹), multiple functional framework and good porosity, the phosphonic acid-functionalized porous organic polymers showed a high adsorption rate and high adsorption capacity for β-agonists (224 mg g⁻¹ and 171 mg g⁻¹ for clenbuterol and ractopamine, respectively). The analytes were quantified by ultra-high-performance liquid chromatography coupled to high-resolution tandem mass spectrometry. It showed a good linearity (with R² ranging from 0.9950 to 0.9991 in the linear range of 3–5 orders of magnitude), with low limits of quantification ranging from 0.05 to 0.25 ng g⁻¹. The limits of detection of the method for the analytes were measured to be in the range of 0.02 to 0.1 ng g⁻¹. The recoveries of target analytes from real samples on the material were in the range of 62.4–119.4% with relative standard deviations of 0.6–12.1% (n = 4). Moreover, good reproducibility of the method was obtained with the interday RSD being lower than 11.7% (n = 5) and intraday RSD lower than 12.2% (n = 4). The proposed method was accurate, reliable and convenient for the simultaneous analysis of multiple β-agonists and β-blockers. Finally, the method was successfully applied for the analysis of such compounds in milk samples.

Novel phosphonic acid-functionalized porous organic polymers were synthesized through direct knitting method. It shows high adsorption efficiency and high adsorption capacity for multiple β-agonists and β-blockers analysis.

The conjunction of a new ultrasonic-assisted dispersive solid-phase extraction method with HPLC-DAD for the trace determination of diazinon in biological and water media

Herein, a new ultrasonic-assisted dispersive solid-phase extraction method was successfully developed for the trace detection of diazinon.

Study on the performance of micro-flow injection preconcentration method on-line coupled to thermospray flame furnace AAS using MWCNTs wrapped with polyvinylpyridine nanocomposites as adsorbent

An adsorbent nanocomposite based on multi-walled carbon nanotubes and polyvinylpyridine is used in the development of a micro-flow injection preconcentration method coupled to TS-FF-AAS for the determination of very low levels of Cd.

A tunable nanopore sensor for the detection of metal ions using translocation velocity and biphasic pulses

A tunable resistive pulse sensor, utilising a polyurethane nanopore, has been used to characterise nanoparticles as they traverse the pore opening. Herein we demonstrate that the translocation speed, conductive and resistive pulse magnitude, can be used to infer the surface charge of a nanoparticle, and act as a specific transduction signal for the binding of metal ions to ligands on the particle surface. Surfaces of silica nanoparticles were modified with a ligand to demonstrate the concept, and used to extract copper(ii) ions (Cu²⁺) from solution. By tuning the pH and ionic strength of the solution, a biphasic pulse, a conductive followed by a resistive pulse is recorded. Biphasic pulses are becoming a powerful means to characterise materials, and provide insight into the translocation mechanism, and herein we present their first use to detect the presence of metal ions in solution. We demonstrate how combinations of translocation speed and/or biphasic pulse behaviour are used to detect Cu²⁺ with quantitative responses across a range of pH and ionic strengths. Using a generic ligand this assay allows a clear signal for Cu²⁺ as low as 1 ppm with a short 5-minute incubation time, and is capable of measuring 10 ppm Cu²⁺ in the presence of 5 other ions. The method has potential for monitoring heavy metals in biological and environmental samples.

Doping of three-dimensional porous carbon nanotube-graphene-ionic liquid composite into polyaniline for the headspace solid-phase microextraction and gas chromatography determination of alcohols

In this work, ionic liquid (IL, i.e. 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate), carboxyl multiwall carbon nanotubes (MWCNTs) and reduced graphene oxide (rGO) were used to prepare three-dimensional porous material (MWCNTs-rGO-IL) by one-step self-assembly, then it was co-electrodeposited with polyaniline (PANI) on stainless steel wires by cyclic voltammetry. The resulting coating (PANI-MWCNTs-rGO-IL) was characterized by using FT-IR and scanning electron microscopy etc, and it showed porous structure and had high thermal stability. Furthermore, it was found to be very suitable for the headspace solid-phase microextraction of alcohols (i.e. octanol, nonanol, geraniol, decanol, undecanol and dodecanol). By coupling with gas chromatography, wide linear ranges and low limits of detection (i.e. 2.2-28.3 ng L^-1) were obtained for the alcohols. The coating also presented good repeatability and reproducibility; the relative standard deviations for intra-fiber and fiber-to-fiber were less than 5.6% (n = 5) and 7.0% (n = 5) respectively. In addition, the proposed method was successfully applied to the determination of alcohols in tea drinks, and the recoveries for standards added were 85.6-114%.

Simultaneous Enrichment of Polycyclic Aromatic Hydrocarbons and Cu(2+) in Water Using Tetraazacalix[2]arene[2]triazine as a Solid-Phase Extraction Selector

On the basis of the definite retention mechanism proven by the stationary phase for high-performance liquid chromatography, tetraazacalix[2]arene[2]triazine featuring multiple recognition sites was assessed as a solid-phase extraction (SPE) selector. The applicability of its silica support was used for the extraction of trace amounts of polycyclic aromatic hydrocarbons (PAHs) and Cu(2+) in aqueous samples, followed by high-performance liquid chromatography fluorometric and graphite furnace atomic absorption spectrometric determination. On the basis of the π-π interaction with PAHs and the chelating interaction with Cu(2+), the simultaneous extraction of PAHs and Cu(2+) and stepwise elution through tuning the eluent were successfully achieved, respectively. The SPE conditions affecting the extraction efficiency were optimized, including type and concentration of organic modifier, sample solution pH, flow rate, and volume. As a result of the special adsorption and desorption mechanism, high extraction efficiency was achieved with relative recoveries of 94.3-102.4% and relative standard deviations of less than 10.5%. The limits of detection were obtained with 0.4-3.1 ng L(-1) for PAHs and 15 ng L(-1) for Cu(2+), respectively. The method was applied to the analyses of PAHs and Cu(2+) in Xiliu Lake water samples collected in Zhengzhou, China.

Kinetic, isotherm and thermodynamic studies on biosorption of chromium(VI) by using activated carbon from leaves of Ficus nitida

Background

Kinetics, thermodynamics and equilibrium of the removal of chromium(VI) ions from aqueous solutions by using chemically activated leaves of Ficus nitida were investigated. Adsorption runs were performed as a function of pH, mass of biosorbent, contact time, initial concentration of chromium(VI) ions and temperature.

Results

The optimum conditions for maximum removal of chromium(VI) ion from aqueous solutions (about 99 %) were found to be 0.80 g of chemically activated leaves of F. nitida, 25 min, 50.0 mg/L of initial concentration of chromium(VI). Values of thermodynamic activation parameters proved that the biosorption process is spontaneous and endothermic. Results were analyzed by using Langmuir, Freundlich and Temkin models.

Conclusions

Results of the study showed that the chemically activated leaves of F. nitida can be used as low cost, ecofriendly and effective sorbent for the removal of chromium(VI) from aqueous solutions.Graphical abstract