EDTAD-modified cassava stalks loaded with Fe3O4: highly efficient removal of Pb2+ and Zn2+ from aqueous solution.

In this study, a novel magnetic cassava stalk composite (M-EMCS) was prepared through modification with ethylenediamine tetraacetic anhydride (EDTAD) and loading of Fe3O4. The surface morphology, molecular structure, and magnetic characteristics of the composite were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), vibrating-sample magnetometer (VSM), and X-ray diffraction (XRD). It was shown that EDTAD and Fe3O4 were successfully modified and loaded in cassava straw (CS), respectively. The capacity of M-EMCS to absorb heavy metals under different influencing factors was tested by atomic absorption spectroscopy. The adsorption processes of both Pb2+ and Zn2+ were suitably described by second-order kinetic models and Langmuir models, indicating monolayer chemisorption. M-EMCS had high adsorption rates and adsorption capacities for these two metal ions. The adsorption of Pb2+ and Zn2+ reached a plateau after 10 min, and the adsorption capacity of Pb2+ (163.93 mg/g) was higher than that of Zn2+ (84.74 mg/g). Thermodynamic analysis showed that the adsorption of two metals by M-EMCS was spontaneous, endothermic, and irreversible. XPS analysis showed that M-EMCS mainly removes Pb2+ and Zn2+ through ion exchange, chelation, and redox. Graphical abstract.

Removal of Zn(II), Mn(II) and Cu(II) by adsorption onto banana stalk biochar: adsorption process and mechanisms.

Low-cost banana stalk (Musa nana Lour.) biochar was prepared using oxygen-limited pyrolysis (at 500 °C and used), to remove heavy metal ions (including Zn(II), Mn(II) and Cu(II)) from aqueous solution. Adsorption experiments showed that the initial solution pH affected the ability of the biochar to adsorb heavy metal ions in single- and polymetal systems. Compared to Mn(II) and Zn(II), the biochar exhibited highly selective Cu(II) adsorption. The adsorption kinetics of all three metal ions followed the pseudo-second-order kinetic equation. The isotherm data demonstrated the Langmuir model fit for Zn(II), Mn(II) and Cu(II). The results showed that the chemical adsorption of single molecules was the main heavy metal removal mechanism. The maximum adsorption capacities (mg·g-1) were ranked as Cu(II) (134.88) > Mn(II) (109.10) > Zn(II) (108.10)) by the single-metal adsorption isotherms at 298 K. Moreover, characterization analysis was performed using Fourier transform infrared spectroscopy, the Brunauer-Emmett-Teller method, scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The results revealed that ion exchange was likely crucial in Mn(II) and Zn(II) removal, while C-O, O-H and C = O possibly were key to Cu(II) removal by complexing or other reactions.

A sensitive magnetic nanoparticle-based immunoassay of phosphorylated acetylcholinesterase using protein cage templated lead phosphate for signal amplification with graphite furnace atomic absorption spectrometry detection.

We developed a new magnetic nanoparticle sandwich-like immunoassay using protein cage nanoparticles (PCN) for signal amplification together with graphite furnace atomic absorption spectrometry (GFAAS) for the quantification of an organophosphorylated acetylcholinesterase adduct (OP-AChE), the biomarker of exposure to organophosphate pesticides (OPs) and nerve agents. OP-AChE adducts were firstly captured by titanium dioxide coated magnetic nanoparticles (TiO2-MNPs) from the sample matrixes through metal chelation with phospho-moieties, and then selectively recognized by anti-AChE antibody labeled on PCN which was packed with lead phosphate in its cavity (PCN-anti-AChE). The sandwich-like immunoreaction was performed among TiO2-MNPs, OP-AChE and PCN-anti-AChE to form a TiO2-MNP/OP-AChE/PCN-anti-AChE immunocomplex. The complex could be easily isolated from the sample solution with the help of magnet, and the released lead ions from PCN were detected by GFAAS for the quantification of OP-AChE. Greatly enhanced sensitivity was achieved because PCN increased the amount of metal ions in the cavity of each apoferritin. The proposed immunoassay yielded a linear response over a broad range of OP-AChE concentrations from 0.01 nM to 2 nM, with a detection limit of 2 pM, which has enough sensitivity for monitoring of low-dose exposure to OPs. This new method showed an acceptable stability and reproducibility and was validated with OP-AChE spiked human plasma.

One-step displacement dispersive liquid-liquid microextraction coupled with graphite furnace atomic absorption spectrometry for the selective determination of methylmercury in environmental samples.

A novel method for the selective determination of methylmercury (MeHg) was developed by one-step displacement dispersive liquid-liquid microextraction (D-DLLME) coupled with graphite furnace atomic absorption spectrometry. In the proposed method, Cu(II) reacted with diethyldithiocarbamate (DDTC) to form Cu-DDTC complex, which was used as the chelating agent instead of DDTC for the dispersive liquid-liquid microextraction (DLLME) of MeHg. Because the stability of MeHg-DDTC is higher than that of Cu-DDTC, MeHg can displace Cu from the Cu-DDTC complex and be preconcentrated in a single DLLME procedure. MeHg could be extracted into the extraction solvent phase at pH 6 while Hg(II) remained in the sample solution. Potential interference from co-existing metal ions with lower DDTC complex stability was largely eliminated without the need of any masking reagent. Under the optimal conditions, the limit of detection of this method was 13.6ngL(-1) (as Hg), and an enhancement factor of 81 was achieved with a sample volume of 5.0mL. The proposed method was successfully applied for the determination of trace MeHg in some environmental samples with satisfactory results.

A label-free DNAzyme-cleaving fluorescence method for the determination of trace Pb(2+) based on catalysis of AuPd nanoalloy on the reduction of rhodamine 6G.

The substrate chain of double-stranded DNA (dsDNA) could be specifically cleaved by Pb(2+) to release single-stranded DNA (ssDNA) that adsorbs onto the AuPd nanoalloy (AuPdNP) to form a stable AuPdNP-ssDNA complex, but the dsDNA can not protect AuPdNPs in large AuPdNP aggregates (AuPdNPA) under the action of NaCl. AuPdNP-ssDNA and large AuPdNPA could be separated by centrifugation. On increasing the concentration of Pb(2+) , the amount of released ssDNA increased; AuPdNP-ssDNA increased in the centrifugation solution exhibiting a catalytic effect on the slow reaction of rhodamine 6G (Rh6G) and NaH2 PO2 , which led to fluorescence quenching at 552 nm. The decrease in fluorescence intensity (ΔF) was linear to the concentration of Pb(2+) within the range 0.33-8.00 nmol/L, with a detection limit of 0.21 nmol/L. The proposed method was applied to detect Pb(2+) in water samples, with satisfactory results.

Catalysis of aptamer-modified AuPd nanoalloy probe and its application to resonance scattering detection of trace UO(2)2+.

AuPd nanoalloy and nanopalladium with a diameter of 5 nm were prepared, using sodium citrate as the stabilizing agent and NaBH(4) as the reductant. The nanocatalyst containing palladium on the surface exhibited a strong catalytic effect on the slow NiP particle reaction between NiCl(2) and NaH(2)PO(2), and the NiP particle system showed a resonance scattering (RS) peak at 508 nm. The RS results showed that the Pd atom on AuPd nanoalloy surface is the catalytic center. Combining the aptamer cracking reaction of double-stranded DNA (dsDNA)-UO(2)(2+), AuPd nanoalloy aggregation, and AuPd nanoalloy catalysis, both AuPd nanoalloy RS probe and AuPd nanoalloy catalytic RS assays were developed for the determination of 40-250 pmol L(-1) UO(2)(2+) and 5.0-50 pmol L(-1) UO(2)(2+), respectively.

[Resonance scattering detection of trace Hg2+ using herring sperm DNA modified nanogold].

In pH 7.0 tris-HCl buffer solutions and in the presence of 0.017 mol x L(-1) NaCl, herring sperm DNA was combined with gold nanoparticles in size of 10 nm to form stable complex, and the NaCl did not cause the aggregation of the gold nanoparticles. Upon addition of Hg2+, that reacted with DNA to form more stable complex of Hg(2+)-DNA, and the gold nanoparticles aggregated to from larger nanogold clusters that led to considerable enhancement of the resonance scattering intensity at 572 nm enhanced considerably. The effect of GN concentration, DNA concentration, NaCl concentration, incubation time, and temperature, and ultrasonic irradiation was considered respectively, the conditions of 3.87 microg x mL(-1) GN, 11.7 microg x mL(-1) DNA, pH 7.0 Tris-HCl buffer solutions, 17 mmol x L(-1) NaCl, and incubation 10 min at 37 degrees C under the ultrasonic irradiation were chosen for use. Under the conditions, the enhanced resonance scattering intensity at 572 nm was linear to the Hg2+ concentration in the range of 3.3-3 333.3 nmol x L(-1), with regress equation of delta572 nm = 0.019c+5.0, coefficient of 0.999 1, and a detection limit of 2.5 nmol x L(-1) Hg2+. Results of interference tests showed that 30 micromol x L(-1) Mn2+, 33 micromol x L(-1) Mg2+ and Zn2+, 100 micromol x L(-1) Cd2+, 200 micromol x L(-1) Fe3+, and 420 micromol x L(-1) Mo6+, Pb2+ and Cu2+ did not interfered with the determination of 0.33 micromol x L(-1) Hg2+. That is, this resonance scattering spectral assay is of good selectivity. This assay was applied to the detection of Hg(II) in water sample, with a relative standard deviation of 5.1%, and the results were in agreement with that of the cool vapor atomic absorption spectrophotometry.

[A fluorescence quenching method for the determination of trace chlorite in water with rhodamine B].

In acidic sodium acetate-HCl buffer solution containing KI, Rhodamine B (RhB) has a fluorescence peak at 580 nm. When ClO2(-) exists fluorescence quenching occur. The fluorescence quenching intensity is linear with the concentration of ClO2(-) in the range of 0.0218-0.51 microg x mL(-1). Based on this, a new, simple, sentisive fluorescence method has been proposed for the determination of ClO2(-) in water, with satisfactory results.

[A new fluorescence quenching method for the determination of trace ClO2 in water using silver nanoparticles].

In pH 9.1 NH4Cl-NH3 x H2O buffer solution, there is a fluorescence peak at 470 nm for silver nanoparticles. A fluorescence quenching takes place when it was oxidized by ClO2. The intensity of fluorescence quenching is linear with the concentration of ClO2 in the range of 0.0011-0.185 microg x mL(-1). The detection limit is 0.004 7 microg x mL(-1). A new fluorescence method has been proposed for the determination of ClO2 in water samples with satisfactory results.

Resonance scattering effect of rhodamine dye association nanoparticles and its application to respective determination of trace ClO2 and Cl2.

A new resonance scattering method, based on resonance scattering (RS) effect, for the respective determination of ClO2 and Cl2 in water samples was developed. In HCl-NaAc buffer solutions with the pH value of 1.42, chlorine dioxide, or chlorine, oxidizes I- to form 12, which then reacts with the excess I- to form I3-. The resulting 13- would combine, respectively, with four rhodamine(Rh) dyes, including rhodamine B (RhB), butyl rhodamine B (b-RhB), rhodamine 6G (RhG), and rhodamine S (RhS), to form association particles which exhibit a stronger resonance scattering (RS) effect at 420 nm. For four systems of RhB, bRhB, RhG, and RhS, chlorine dioxide was, respectively, determined in the concentration range of 0.0056 to approximately 0.787 mg/L, 0.0034 to approximately 0.396 mg/L, 0.0057 to approximately 0.795 mg/L, and 0.0052 to approximately 0.313 mg/L, with the detection limits of 0.0011 mg/L, 0.006 mg/L, 0.0054 mg/ L, and 0.0023 mg/L ClO2, respectively. At the same experimental conditions as those for the determination of ClO2, chlorine was, respectively, determined in the concentration range of 0.013 to approximately 0.784 mg/L, 0.0136 to approximately 0.522 mg/ L, 0.014 to approximately 0.81 mg/L, and 0.014 to approximately 0.42 mg/L, with the detection limits of 0.0016 mg/L, 0.0104 mg/L, 0.0079 mg/L, and 0.0037 mg/L Cl2, respectively. The total RS value originally from ClO2 and Cl2 was recorded in the buffer solution, while the RS value from ClO2 was obtained by using dimethyl sulfoxide to mask chlorine. Thus the RS value of chlorine was calculated by deducting the RS value of chlorine dioxide from the total RS value. The RhB RS method was chosen for the determination of ClO2 and Cl2 in drinking water, with advantages of high sensitivity, good selectivity, simplicity, rapidity, and convenience.

A novel, simple and sensitive resonance scattering spectral method for the determination of chlorite in water by means of rhodamine B.

A new resonance scattering method was proposed for the determination of chlorite, basing on the resonance scattering effect of rhodamine dye. In HCl-sodium acetate buffer solution, chlorite oxidizes I- into I2 and the reaction of I2 and excess I- results in I3- It is respectively combined with rhodamine dyes, including rhodamine B (RhB), butyl rhodamine B (b-RhB), rhodamine G (RhG) and rhodamine S (RhS), to form association complex particles, which exhibit stronger resonance scattering (RS) effect at 400 nm. The chlorite concentration of ClO2- in the range of 0.00726-0.218 microg/ml, 0.0102-0.292 microg/ml, 0.00726 0.145 microg/ml and 0.0290 0.174 microg/ml is respectively linear to the RS intensity of association complex particle systems at 400 nm for the RhB, b-RhB, RhG and RhS. The detection limits of the four systems were respectively 0.00436, 0.00652, 0.00580 and 0.01450 microg/ml ClO2-. In the four systems, the RhB system possesses good stability and high sensitivity. It has been applied to the analysis of chlorite in wastewater with satisfactory results.

A novel and selective spectral method for the determination of trace chlorine in water basing on the resonance scattering effect of rhodamine B-I(3) association nanoparticles.

In Na(2)HPO(4)-citric acid buffer solution, Cl(2) can oxidize I(-) to form I(2) and then it reacts with excess I(-) to form I(3)(-). The I(3)(-) combines respectively with rhodamine dyes, including rhodamine B (RhB), butyl rhodamine B (b-RhB), rhodamine 6G (RhG) and rhodamine S (RhS), to form association particles which give stronger resonance scattering (RS) effect at 400 nm. The RS intensity of the RhB, b-RhB, RhG and RhS systems is proportional to chlorine concentrations in the range of 0.008-1.74, 0.019-1.33, 0.021-2.11 and 0.019-2.04 microg/mL Cl(2), respectively. The detection limits of the systems were 0.0020, 0.0048, 0.0063 and 0.0017 microg/mL, respectively. In them, the RhB system has good stability and high sensitivity, and has been applied to the analysis of chlorine in drinking water, with satisfactory results which is in agreement with that of the methyl orange (MO) spectrophotometry.

Luminescence properties of metal(II)-diethyldithiocarbamate chelate complex particles and its analytical application.

In a suitable pH buffer solutions, sodium diethyldithiocarbamate (DDTC) reacts with some divalence metal ions M(II) to form (M-DDTC)( n ) chelate complex nanoparticles, which exhibit different luminescence properties. There is a strongest luminescence peak at 470 nm for the Co(II)-DDTC system, three peaks at 330, 470, and 630 nm for the Cu(II)-DDTC system, three peaks at 420, 470, and 630 nm for the Cd(II)-DDTC system, four peaks at 350, 400, 435, and 470 nm for the Ni(II)-DDTC system, two peaks at 408 and 470 nm for the Pb(II)-DDTC system, two peaks at 415 and 470 nm for the Fe(II)-DDTC system. The different luminescence properties of (M-DDTC)( n ) chelate complex nanoparticles was explained. Under the optimal conditions, the luminescence intensity of (Co-DDTC)( n ) chelate complex nanoparticles at 470 nm (F (470 nm)) is linear to Co(II) concentration in the range of 0.012-1.44 microg/mL. The detection limit is 0.0023 microg/mL. A novel luminescence method has been proposed for the determination of cobalt in Vitamin B(12) samples, with satisfactory results.

[Effect of cation surfactants on absorption spectra of silver nanoparticle in liquid phase].

Yellow Ag nanoparticles, with diameter of 20 nm, exhibit a resonance absorption peak at 400 nm. After adding some cation surfactants (CS), the absorbance at 400 nm becomes weak, (namely, there exists hypochromic effect), but the absorbance at wavelengths longer than 400 nm is enhanced and shows a red shift. When adding concentration of CS, the absorbance at wavelengths longer than 400 nm becomes weak again, the peak at 400 nm is enhanced (namely, there exists hyperchromic effect) and the absorption peaks show a blue shift. The results showed that this is caused by the strong hydrophobic force and electrostatic force between the CS and silver nanoparticls, which results in a change in the silver nanoparticle shape.

A new and sensitive resonance-scattering method for determination of trace nitrite in water with rhodamine 6G.

In the medium HCl-KI-rhodamine dye, NO(2) (-) reacts with excess I(-) to form I(3) (-) and the I(3) (-) and rhodamine dye combine to form an association particle which gives three resonance-scattering (RS) peaks at 320 nm, 400 nm, and 595 nm. In systems containing rhodamine 6G (Rh6G), rhodamine B (RhB), rhodamine S (RhS), and butyl rhodamine B (BRhB) the resonance scattering intensity at 400 nm is proportional to nitrite concentrations in the range 2.3-276 ng mL(-1), 9.2-184 ng mL(-1), 9.2-184 ng mL(-1), and 9.2-92 ng mL(-1), respectively. Because of the high sensitivity, wide linear range, and good stability of the Rh6G system, it has been used for determination of nitrite in water samples, with satisfactory results. The spectral results have been used to verify that the formation of (Rh6G.I(3))(n) association particles and their interface with the system are main factors that cause the RS enhancement.

[Spectral properties of the association particle system of quinine-[PtI6]2- and its analytical application].

In 0.01 mol x L(-1) HCl medium, red color [PtI6]2- and quinine combine to form association molecule. The molecules aggregate automatically owing to strong hydrophobic and molecular forces. And PtI6-quinine association particles with violet-red color formed. It exhibits three resonance scattering peaks at 310 nm, 400 nm and 610 nm, and a Rayleigh scattering peak at 470 nm. The absorption values all increase in the wavelength range of 350-740 nm, and the fluorescence peak at 450 nm was quenched. Under the conditions chosen, the quinine concentration in the range of 0-40 x 10(-6) mol x L(-1) is linear to the A(620 nm) value. The mole absorption coefficient epsilon(620 nm) is 1.31 x 10(4) L x mol(-1) x cm(-1). The results show that the association particles produce the resonance scattering effect, fluorescence quenching and the violet-red color.