Trace Cr Research Articles

Reduced phosphomolybdate as photoassisted electrochemical crystalline sensor for trace Cr(VI) detection

Reduced phosphomolybdate as photoassisted electrochemical crystalline sensor for trace Cr(VI) detection

Effect of Trace Elements on the Thermal Stability and Electrical Conductivity of Pure Copper

Abstract: The impact of introducing trace transition elements on the thermal stability and conductivity of pure copper was examined through metallographic microscopy (OM), transmission electron microscopy (TEM), and electrical conductivity measurements; the interaction between trace transition element and trace impurity element S in the matrix was analyzed. The results show that the addition of trace Ti and trace Cr, Ni, and Ag elements significantly enhances the thermal stability of the pure copper grain size. After high-temperature treatment at 900 °C/30 min, the grain sizes of Cu, Cu-Ti-S, and Cu-Cr-Ni-Ag-S were measured and found to be 200.24 μm, 83.83 μm, and 31.08 μm, respectively, thus establishing a thermal stability ranking of Cu-Cr-Ni-Ag-S > Cu-Ti-S > Cu. Furthermore, the conductivities of pure copper remain high even after the addition of trace transition elements, with recorded values for Cu, Cu-Ti-S, and Cu-Cr-Ni-Ag-S of 100.7% IACS, 100.2% IACS, and 98.5% IACS, respectively. The enhancement of thermal stability is primarily attributed to the pinning effect of the TiS and CrS phases, as well as the solid solution dragging of Ni and Ag elements. Trace Ti and Cr elements can react with S impurities to form a hexagonal-structure TiS phase and monoclinic-structure CrS phase, which are non-coherent with the matrix. Notably, the CrS phase is smaller than the TiS phase. In addition, the precipitation of these compounds also reduces the scattering of free electrons by solute atoms, thereby minimizing their impact on the alloy’s conductivity.

Keggin type polyoxometalate-based metal-organic frameworks with electrocatalytive activity as effective multifunctional amperometric sensors for metal ions and ascorbic acid

Polyoxometalates (POMs) based metal-organic frameworks (POMOFs) integrate the merits of POMs with excellent redox properties and MOFs with highly ordered porous crystalline structures, which show potential electrochemical applications relying on the synergistic catalytic effect. Here, two new Keggin-type POMOFs [Cd(btbu)2(H2O)2(PMo12O40)] (CUST-636), [Cd(btbu)2(H2O)(SiW12O40)0.5](CUST-638) are synthesized using flexible ligand of 1,4-bis(1,2,4-triazol-1-yl)butane (abbreviated as btbu) as a ligand by hydrothermal method. PXRD, IR, and TG analysis were carried out on CUST-636 and CUST-638. Then, they were prepared into electrode materials (referred to as 636-GCE and 638-GCE), to explore the electrocatalytic properties. 636-GCE and 638-GCE show good electrocatalytic redox performance against KBrO3, KNO2, K2Cr2O7 and AA. Furthermore, detection of trace Cr(VI) was conducted using electrochemical sensors 636-GCE and 638-GCE. The low detection limits (LODs) of CUST-636 and CUST-638 were 0.32 and 0.45 μM, respectively, which were lower concentrations of Cr(VI) in drinking water than the maximum allowable concentration specified by the World Health Organization (WHO).

Metal-organic framework membrane-based probe for on-site and sensitive detection of Cr(VI) in groundwater using a portable system

Groundwater sources are often contaminated by heavy metal ions such as hexavalent chromium (Cr(VI)) produced by various industrial processes, which can accumulate in the human tissues through drinking of water, resulting in serious health hazards. For this reason, on-site and sensitive detection of heavy metals in contaminated groundwater is essential for effective heavy metal pollution evaluation. Here, we develop a carboxymethyl cellulose (CMC)-metal–organic framework (MOF) fluorescence sensing membrane and couple with portable laser-induced fluorescence spectrometers (LIFs) for on-site detection of trace Cr(VI) in groundwater. The membrane was prepared using coordination assembly approach between flexible CMC and MOF and subsequent vacuum-assisted filtration. The CMC-MOF membrane exhibits very sensitive behaviour to Cr(VI) with a detection limit as low as 3.72 ppb, lower than the World Health Organization defined action level (50 ppb). Density functional theory calculations show that the formation of coordination bonds between CMC and MOF results in the excellent stability of the CMC-MOF membrane, and Cr(VI) simultaneously binds to two nitrogen atoms in MOFs, enabling CMC-MOF membrane to enrich and be on-site detection of trace Cr(VI) in contaminated groundwater by portable LIFs. This work provides an approach for on-site and highly sensitive assessment of heavy metal in contaminated groundwater.

A new surface molecularly imprinted polyacrylamide nanoprobe for trace Cr(VI) with RRS technique

This article was used potassium dichromate as the template molecule, silver nanoclusters as the nano matrix, acrylamide as the monomer, ethylene glycol dimethacrylate (EGDMA) as the crosslinking agent, and azodiisobutyronitrile (AIBN) as the initiator to prepare a new silver nanocluster surface MIP (AgNCs@MIP) nanoprobe for chromate. Upon addition of Cr(VI), it selectively adsorbs on the surface of AgNCs@MIP nanoprobes. The dichromate ion absorption peak at 350 nm overlaps with the AgNCs@MIP RRS peak at 370 nm, resulting in strong RRS energy transfer (RRS-ET) and a decrease in the RRS intensity. The decreased RRS intensity is directly proportional to the concentration of dichromate ions in the range of 0.0025–0.015 µmol/L, with a detection limit of 0.8 nmol/L. Therefore, a simple, fast, sensitive and selective RRS method for the determination of trace Cr(VI) in mineral water has been established, with a relative standard deviation of 9.2–9.8 % and recovery of 95.20 %—103.60 %.

Bridging Component Strategy in Phosphomolybdate-Based Sensors for Electrochemical Determination of Trace Cr(VI).

Rapid and sensitive electrochemical determination of trace carcinogenic Cr(VI) pollutants remains an urgent and important task, which requires the development of active sensing materials. Herein, four cases of reduced phosphomolybdates with formulas of the (H2bib)3[Zn(H2PO4)]2{Mn[P4Mo6O31H7]2}·6H2O (1), (H2bib)2[Na(H2O)]2[Mn(H2O)]2{Mn[P4Mo6O31H6]2}·5H2O (2), (H2bib)3[Mo2(μ2-O)2(H2O)4]2{Ni[P4Mo6O31H2]2}·4H2O (3), and (H2bib)2{Ni[P4Mo6O31H9]2}·9H2O (4) (bib = 4,4'-bis(1-imidazolyl)-biphenyl) were hydrothermally synthesized under the guidance of a bridging component strategy, which function as effective electrochemical sensors to detect trace Cr(VI). The difference of hybrids 1-4 is in the inorganic moiety, in which the reduced phosphomolybdates {M[P4MoV6O31]2} (M{P4Mo6}2) exhibited different arrangements bridged by different cationic components ({Zn(H2PO4)} subunit for 1, [Mn2(H2O)2]4+ dimer for 2, and [MoV2(μ2-O)2(H2O)4]6+ for 3). As a result, hybrids 1 and 3 display noticeable Cr(VI) detection activity with low detection limits of 14.3 nM (1.48 ppb) for 1 and 6.61 nM (0.69 ppb) for 3 and high sensitivities of 97.3 and 95.3 μA·mM-1, respectively, which are much beyond the World Health Organization's detection threshold (0.05 ppm) and superior to those of the contrast samples (inorganic Mn{P4Mo6}2 salt and hybrid 4), even the most reported noble-metal catalysts. This work supplies a prospective pathway to build effective electrochemical sensors based on phosphomolybdates for environmental pollutant treatment.

Enhanced mechanical properties and strengthening mechanism of Cu-Ni-Si alloy with trace chromium addition

Cu-3Ni-0.7Si-xCr-0.05Mg (x = 0.1 and 0.4) (wt% nominal composition) alloys were fabricated to investigate the effect of Cr contents on properties evolution and precipitation behavior of Cu-Ni-Si alloy. The results of the property analysis show that trace addition of 0.1 wt% Cr element contributes a better strength (ultimate tensile strength of 823 MPa) after single cold rolling and aging treatment. The precipitation behavior is characterized by transmission electron microscopy. It is found that nanoscale FCC structural Cr precipitates shift into submicron Cr3Si particles with Cr content increasing from 0.1 wt% to 0.4 wt%. Meanwhile, such superior formation of Cr3Si particle decreases the fraction of δ-Ni2Si owing to quick consumption of Si element from Cu matrix. Further quantitative analysis of various strengthening mechanisms reveals that the changed precipitation behavior notably affects their strengthening contribution to Cr contained alloys, resulting in an increase of more than 5.6% in the Orowan-Ashby mechanism. Surprisingly, in the case of the aging state at a temperature of 460 °C for a duration of 2 h, it is confirmed that although a much larger strengthening effect origins from nanosized δ-Ni2Si precipitate, the strength variation relies more on the Cr precipitation. That is, the lower strength at higher Cr content is mainly caused by the lower strengthening effect from Cr element related phases. In addition, the effect of the addition of trace Cr element on the operating mechanism on conductivity is also clarified. The results are expected to provide an appropriate content of Cr element and a dependable processing theory guidance for improving the comprehensive properties of the Cu-Ni-Si alloys.

Improving the practicality of recombinant Escherichia coli biosensor in detecting trace Cr(VI) by modifying the cryogenic storage conditions of biosensors and applying simple pretreatment

Hexavalent chromium (Cr(VI)) is a global environmental pollutant. To reduce the risk caused by Cr(VI), a simple, accurate, reproducible, and inexpensive method for quantifying Cr(VI) in water and soil should be developed. In this study, three types of recombinant Escherichia coli biosensors (namely T7-lux-E. coli, T3-lux-E. coli, and SP6-lux-E. coli biosensor) containing promoters (T7, T3, and SP6), chromate-sensing regulator chrB, and the reporter gene luxAB were constructed. This study investigated the effects of cryogenic freezing temperature and time on trace Cr(VI) measurement by using recombinant E. coli biosensors. The results indicated that the activity of thawed frozen SP6-lux-E. coli cells stored at −20 °C for 270 days did not differ from that of freshly prepared cells. Turbidity and conductivity in water samples and organic matter in soil interfered with Cr(VI) measurement using the biosensor. The SP6-lux-E. coli biosensor exhibited a wide measurement range and a low deviation of <5% for measuring Cr(VI) in various Cr(VI)-contaminated water and soil samples and required only a simple pretreatment or extraction process even after 270-day storage at −20 °C. To the best of our knowledge, this is the first study to report the use of recombinant biosensors for accurately measuring Cr(VI) in both water and soil.

Sensitivity improvement in the measurement of minor components by spatial confinement in fiber-optic laser-induced breakdown spectroscopy

Nuclear power overhaul can benefit from a fiber-optic laser-induced breakdown spectroscopy (FO-LIBS) setup for in situ composition measurements. Regarding FO-LIBS, the pulsed energy of the fiber-delivery laser is limited, and the spot profile received by the sample surface is distorted from a Gaussian to a flat-top distribution. Therefore, the induced plasma in FO-LIBS is characterized by weakened emission, shortened lifetime, and insufficient sampling of minor components compared with that of conventional LIBS. This could not meet the quantitative demands of the minor component with a concentration of 0.01 wt% or lower in structural steel. In this study, by modifying the mechanical structure of the front-end sensor, a space constraint condition can be created for plasma emission enhancement. By combining the optical diagnostics of fast photograph and shadowgraph, shockwave propagation and plasma expansion can be visualized synchronously. The reflected shockwave decelerates in the process of propagating towards the plasma, accompanied by morphological changes from the oblate cylinder to the hemisphere. It can be demonstrated that the plasma is constricted by the reflected shockwave associated with a significant increase in the plasma temperature and electron number density. The plate spacing determines the time delay of spectral enhancement and also determines the enhancement factor corresponding to the velocity attenuation of shockwave propagation over a long distance. The enhancement factor is found to be inversely proportional to the quadratic square of the propagation velocity of shockwave just after reflection, and shows an upward trend with increasing upper-level energy of atomic transitions. A maximum enhancement factor of ∼3.52 is realized with a time delay of 4 μs at a plate spacing of 3 mm, and trace components Mo, V, and Cu are newly recognized, which cannot be observed in conventional FO-LIBS. Meanwhile, the calibration of trace Cr and Mn suggests that the quantitative results using the sensor coupled with spatial confinement are comparable, and the limits of detection are reduced to 31 ppm and 475 ppm, respectively.

Immobilization of diphenylcarbazide on paper-based analytical devices for the pre-concentration and detection of chromium VI in water samples

A novel approach using a smartphone for the detection of Cr (VI) has been developed. In this context, two different platforms were designed for the detection of Cr (VI). The first one was synthesized via a crosslinking reaction of chitosan with 1,5-Diphenylcarbazide (DPC-CS). The obtained material was integrated into a paper to develop a new paper-based analytical device (DPC–CS–PAD). The DPC–CS–PAD exhibited high specificity toward Cr (VI). The second platform (DPC-Nylon PAD) was prepared by covalent immobilization of DPC onto a Nylon paper and then its analytical performances regarding Cr (VI) extraction and detection were evaluated. DPC–CS–PAD presented a linear range of 0.1–5 ppm with detection and quantification limits of about 0.04 and 0.12 ppm, respectively. The DPC-Nylon-PAD exhibited a linear response of 0.1–2.5 ppm with detection and quantification limits of 0.06 and 0.2 ppm, respectively. Furthermore, the developed platforms were effectively applied for testing the effect of the loading solution volume for trace Cr (IV) detection. For the DPC-CS material, a volume of 20 mL allowed the detection of 4 ppb of Cr (VI). In the case of DPC-Nylon-PAD, the loading volume of 1 mL permitted the detection of the critical concentration of Cr (VI) in water.

The efficient removal of low concentration hexavalent chromium via combining charged microporous membrane and micellar adsorption filtration

Abstract It is challenging to effectively purge wastewater containing heavy metal ions at low concentration. In order to remove trace Cr (VI) from wastewater efficiently, a positively charged microporous membrane was prepared by firstly non-solvent induced phase separation (NIPS) of amphiphilic polymer and secondly surface quaternization modification. The morphologies, surface roughness, surface charge, hydrophilicity, and pore size of membranes were characterized. Based on the dual action of micellar adsorption and charge repulsion, when surfactant is 4 mM and Cr (VI) is 60 ppm, the surface quaternization membrane (Q-MPVD) achieves 99.8 % Cr (VI) rejection simultaneously accompanied by a permeability of 100 LMH/bar. Meanwhile, the effects of STAC concentration, Cr (VI) concentration, pH as well as inorganic salt concentration on the composite micellar size, and Cr (VI) rejection performance were investigated, respectively. Moreover, the Q-MPVD membrane shows an excellent separation stability over a wide pH range, indicating its application perspective in engineering process. In summary, this work provided a positively charged membrane with high-efficiency performance for treating practical trace Cr (VI)-containing industrial wastewater.

Highly sensitive determination of total chromium in seawater by inductively coupled plasma-mass spectrometry with sample introduction of ultrasound nebulization-dielectric barrier discharge vapor generation

A highly sensitive method for total chromium (Cr) determination in seawater by inductively coupled plasma-mass spectrometry (ICP-MS) with sample introduction of ultrasound nebulization-dielectric barrier discharge (UNDBD) vapor generation is proposed in this work. Using this sample introduction system, the sensitivity of Cr is increased 56 folds compared with the common pneumatic nebulization sample introduction system, and the interferences from the seawater matrix at 500 mg L−1 level are all found negligible for trace Cr determination. With these advantages, this method is proved to be applicable for rapid and accurate determination of total Cr in seawater, requiring only the oxidation of Cr(III) to Cr(VI) and dilution steps, without the matrix separation steps. The experimental parameters for Cr determination including the Cr species, the sample volume, the spray distance, the carrier gas flow rate, and the solution pH are evaluated in detail. Under optimal conditions, the relative standard deviation for Cr is 1.9% at the concentration of 5 μg L−1 and the detection limit for Cr is 0.004 μg L−1. The proposed method is thus successfully applied to determine total Cr in certified reference seawater samples and real seawater samples, all with satisfactory results. Comparing with other sample introduction systems, the proposed UNDBD sample introduction system not only has a much lower detection limit for Cr, but also can be operated with low sample consumption (40 μL) and low power (70 W).

Free-standing high-entropy alloy plate for efficient water oxidation catalysis: structure/composition evolution and implication of high-valence metals

We herein report free-standing FeCoNiCrMo high-entropy alloy (HEA) plate as an excellent oxygen evolution reaction (OER) catalyst with activity and durability superior to benchmarking NiFe layered double hydroxide (LDH). It requires overpotentials of 303 and 372 mV to reach current densities of 100 and 700 mA cm−2, respectively, and maintains its activity for at least 120 h in alkaline media. Its dynamic structural/compositional evolution is uncovered, in which Mo metals are rapidly oxidized and dissolved into electrolyte, provoking the concomitant Cr leakage and leaving behind reconstructed active NiFeCo oxyhydroxide nanostructures on the surface. Its enhanced OER (intrinsic) activity is found to be associated with the absorption of resultant Mo oxo-anion (MoO42-) and the persistence of trace Cr atoms in surficial NiFeCo oxyhydroxide phase. This work offers useful insights into the origin of high OER activity of HEA catalysts and also provides a feasible way for mass-production of active OER catalysts.

Trace Cr(OH)3 modified α-MnO2 electrocatalyst intercalated by Ag+ with superior activity and stability for oxygen reduction reaction

To achieve the practical application of MnO2-based oxygen reduction electrocatalysts, two important issues in terms of slow electrochemical kinetics and low stabilities must be resolved. In this work, α-MnO2 nanorods intercalated by Ag+ and decorated by trace amounts of Cr(OH)3 were designed by a simple two-step solution method to improve the electrocatalytic activity. The resulting catalysts exhibited efficient oxygen reduction reaction (ORR) activity with a high half-wave potential (E1/2 = 0.85 V vs RHE) and diffusion-limiting current density (Jlim = -5.99 mA cm−2) comparable to commercial 20 wt% Pt/C catalysts. More importantly, the catalysts displayed a more durable performance after 10 h in terms of the decrease in electrochemical current (3.5 %), much lower than that of Pt/C catalysts (9.1 %). The excellent electrocatalytic activity was attributed to the synergistic effects between MnO2, Ag+ and Cr(OH)3, reduced the charge transfer resistance of α-MnO2, adjusted the ratio of Mn3+/Mn4+, generated abundant oxygen vacancies, and promoted the adsorption and activation of surface O2. Furthermore, density functional theory calculations were also carried out to study the coupling interactions to reveal the mechanism of the excellent electrocatalytic performance. This study provides a co-modification strategy for the design of MnO2-based efficient and stable oxygen reduction electrocatalysts.

Simple solid-phase colorimetry for trace Cr(VI) by combination of complexation with diphenylcarbazide and ion-pair solid-phase extraction with sedimentable dispersed particulates.

A highly sensitive and simple solid-phase colorimetry for Cr(VI) was proposed. It was based on the ion-pair solid-phase extraction of Cr-diphenylcarbazide (DPC) complex with sedimentable dispersed particulates. The concentration of Cr(VI) was measured from the color tones obtained by image analysis of the photo of sediment. Various conditions, e.g., material and amounts of adsorbent particulates, chemical properties and concentration of counter ions, and pH, were optimized for the formation and quantitative extraction of the complex. In the recommended procedure, 1mL of sample was put into a 1.5mL microtube where powder form adsorbent and reagents, i.e., XAD-7HP particles, DPC, sodium dodecyl sulfate, amido sulfuric acid, and sodium chloride had been packed. The analytical operation was completed within 5min by gently shaking the microtube and allowing it to stand until enough amounts of particulates were deposited to take a picture. Chromium (VI) up to 2.0ppm was determined, and the detection limit was 0.0034ppm. The sensitivity was enough to determine Cr(VI) at lower concentrations than the water quality of standard (0.02ppm). This method was successfully applied to the analysis of simulated industrial wastewater samples. The stoichiometry of the extracted chemical species was also investigated by applying the same equilibrium model as the ion-pair solvent extraction.

Hourglass shaped polyoxometalate-based materials as electrochemical sensors for the detection of trace Cr(VI) in a wide pH range

Due to Chromium hexavalent Cr(VI) is one of the most carcinogenic toxic ions, it is essential for finding a low-cost, efficient and highly selective detection method. Considering the wide range of pH detection in water, a major issue is exploring high sensitive electrocatalyst. Thus, two crystalline materials with hourglass {P4Mo6} clusters in different metal centers were synthesized and had fabulous Cr(VI) detection performance in a wide pH range. At pH = 0, the sensitivities of CUST-572 and CUST-573 were 133.89 μA μM−1 and 30.05 μA μM−1, and the detection limits (LODs) of Cr(VI) were 26.81 nM and 50.63 nM which met World Health Organization (WHO) standard for drinking water. CUST-572 and CUST-573 also had good detection performance at pH = 1–4. In actual water samples, CUST-572 and CUST-573 also possessed sensitivities of 94.79 μA μM−1 and 20.09 μA μM−1 and LODs were 28.25 nM and 52.24 nM, showing high selectivity and chemical stability. The difference of the detection performance of CUST-572 and CUST-573 were mainly attributed to the interaction between {P4Mo6} and different metal centers of crystalline materials. In this work, electrochemical sensors for Cr(VI) detection in a wide pH range were explored, providing important guidance for the design of efficient electrochemical sensors for ultra-trace detection of heavy metal ions in practical environments.

Nitrogen-Doped Carbon Dots with Free Radical Scavenging Abilities as Fluorescence Probes for Cr(VI) Sensing in Bio-Systems

Carbon dots (CDs) are a new class of fluorescent nanomaterials that can be used in optical devices, fluorescence sensing and bio-imaging. Recently, the preparation of CDs from biomass gained great interest because the source is plentiful and they are friendly to environment. However, there still exist some problems including low quantum yield (QY) and limited application. Although CDs have been successfully applied in detection of various ions, the sensing of Cr(VI) and the corresponding mechanism is rarely proposed. Here, a facile and effective preparation of N-doped carbon dots (N-CDs) from sweet potatoes was developed through hydrothermal synthesis, using urea as passivator. The characterization was performed to demonstrate the morphology and chemical composition of the N-CDs. In particular, it is confirmed that N element exists in NH2 group on the surface of the N-CDs. Because of doing with N element, the QY of these CDs significantly increases to 31%. In addition, the N-CDs exhibit favorable free radical scavenging activities toward DPPH, hydroxyl and superoxide anion free radicals. This antioxidant property, combined with inner filter effect, endows the N-CDs with florescence response to Cr(VI). The further study showed that linear range of Cr(VI) concentration is from 1[Formula: see text][Formula: see text]M to 80[Formula: see text][Formula: see text]M with a detection limit of 0.61[Formula: see text][Formula: see text]M. Subsequently, the N-CDs were competent to detect trace Cr(VI) both in human serum and pig liver. Based on the fact that the N-CDs are biocompatible by MTT experiment, the N-CDs were excellent in fluorescent sensing of Cr(VI) in living cells. In a word, the N-CDs are suitable to be applied for Cr(VI) detection in bio-systems, as well as in antioxidant fields.

Construction of Effective Nanosensor by Combining Semiconducting Polymer Dots with Diphenylcarbazide for Specific Recognition of Trace Cr (VI) Ion in Water and Vitro.

Hexavalent chromium (Cr (VI)) ion, as highly toxic environmental pollution, severely endangers the ecological environment and public health. Herein, a fluorescent nanosensor (PFO-DPC) was constructed by combining semiconducting polymer dots with diphenylcarbazide (DPC) for sensing Cr (VI) ion in aqueous solution and living cells. DPC and poly (styrene-co-maleic anhydride) (PSMA) polymer mixed with polyfluorene (PFO) were utilized for selectively indicating Cr (VI) ion and improving the efficiency of detection, respectively. The presence of Cr (VI) ion effectively turned off the blue and green fluorescence of PFO-DPC in the aqueous environment, and the fluorescence quenching efficiency exhibited a good linear relationship between the range of 0.0 to 2.31 nM (R2 = 0.983) with a limit of detection (LOD) of 0.16 nM. The mechanism of fluorescence quenching could possibly be attributed to the internal filtration effect (IFE). Additionally, PFO-DPC showed a satisfactory performance in monitoring intracellular Cr (VI) ion. Our results indicate that the sensor is promising in various applications.

Magnetic porous coordination networks for preconcentration of various metal ions from environmental water followed by inductively coupled plasma mass spectrometry detection

Magnetic composites of Fe3O4@SiO2@PCN-224 (MPCN-224) was obtained by one-pot method with the interaction between PCN-224 monomer and silicon layer on magnetic core. MPCN-224 exhibited a core-shell structure with the specific surface area of 1114 m2 g−1 and good adsorption performance for various metal ions. With MPCN-224 used as the sorbent, a method combing magnetic solid phase extraction (MSPE) with inductively coupled plasma mass spectrometry (ICPMS) detection was established for the enrichment and determination of trace Cr(III), Zn(II), Pb(II) and Bi(III) in environmental water samples. Under the optimized conditions, the developed method exhibited low detection limits of 0.94–11.4 ng L−1 and wide linear range for target four metal ions. The analysis speed was fast (2/5 min for adsorption and desorption respectively). The MPCN-224 sorbent could be reused for at least 12 times, and the regeneration can be achieved easily by adjusting solution pH. The sorbent and the MSPE-ICPMS method have a great potential for adsorption and determination of trace metal ions in environmental water samples.

Adsorptive colorimetric determination of chromium(VI) ions at ultratrace levels using amine functionalized mesoporous silica

There is an urgent need for a rapid, affordable and sensitive analytical method for periodic monitoring of heavy metals in water bodies. Herein, we report for the first time a versatile method for ultratrace level metal detection based on colorimetric sensing. The method integrates preconcentration using a nanomaterial with a colorimetric assay performed directly on the metal-enriched nanomaterial surface. This method circumvents the need for tedious sample pre-processing steps and the complex development of colorimetric probes, thereby reducing the complexity of the analytical procedure. The efficacy of the proposed method was demonstrated for chromium(VI) ions detection in water samples. Amine functionalized mesoporous silica (AMS) obtained from a one-pot synthesis was utilized as a pre-concentration material. The structural and chemical analysis of AMS was conducted to confirm its physico-chemical properties. The pre-concentration conditions were optimized to maximise the colorimetric signal. AMS exhibited a discernible colour change from white to purple (visible to the naked eye) for trace Cr(VI) ions concentration as low as 0.5 μg L−1. This method shows high selectivity for Cr(VI) ions with no colorimetric signal from other metal ions. We believe our method of analysis has a high scope for de-centralized monitoring of organic/inorganic pollutants in resource-constrained settings.