Chemical modification of alumina surface by immobilization of 1-((5-nitrofuran-2-yl)methylene)thiosemicarbazide for extractive concentration of silver ions

A column, solid phase extraction (SPE), preconcentration method was developed for determination of silver by using alumina coated with 1-((5-nitrofuran-2-yl)methylene)thiosemicarbazide and determination by flame atomic absorption spectrometry. The separation/preconcentration conditions for the quantitative recovery were investigated. At pH 2, the maximum sorption capacity of Ag⁺ was 7.5?mg?g^?1. The linearity was maintained in the concentration range of 0.02–11.0?µg?mL^?1 in the final solution or 0.14–1.10?×?10^4?ng?mL^?1 in the original solution for silver. The preconcentration factor of 140 and relative standard deviation of ±1.4% was obtained, under optimum conditions. The limit of detection (LOD) was calculated as 0.112?ng?mL^?1, based on 3σ_bl/m (n?=?8) in the original solutions. The proposed method was successfully applied to the determination trace amounts of silver in the environmental samples such as tea, rice and wheat flour, mint, and real water samples.     

Aspects of surface modification, structure characterization, thermal stability and metal selectivity properties of silica gel phases-immobilized-amine derivatives

Four silica gel phases-bound-amine derivatives (I-IV) were prepared based on chemical immobilization technique. The surface modification was identified by determination of the coverage values in mmol g⁻¹ via thermal desorption method (1.463-1.807) and elemental analysis of nitrogen and carbon contents (1.089-2.456). Structure characterization related to immobilization of the amine derivatives was accomplished and evaluated by means of infrared (IR) and secondary ion mass spectrometric (SIMS) technique. The modified silica gel phases (I-IV) along with their interaction products with copper(II) were also examined by electron impact mass spectrometric analysis (EI-MS) as a method for evaluation of their thermal stability and structure elucidation. Potentiometric titration as a method of characterization was applied for the modified silica gel phases (II-IV) and their copper(II)-adduct. A series of bi- and trivalent metal ions were selected to focus more aspects of the selectivity properties incorporated into the modified silica gel phases for binding and interaction with these metals based on determination of the distribution coefficient and separation factor. The results of these evaluation processes were found to prove higher selectivity and preference of these four phases for binding with lead(II) and cadmium(II) compared to other metal ions.     

Synthesis and characterisation of morin-functionalised silica gel for the enrichment of some precious metal ions

Silica gel was firstly functionalised with aminopropyltrimethoxysilane obtaining the aminopropylsilica gel (APSG). The APSG was reacted subsequently with morin yielding morin-bonded silica gel (morin-APSG). The structure was investigated and confirmed by elemental and thermogravimetric analyses, IR and (13)C NMR spectral studies. Morin-APSG was found to be highly stable in common organic solvents, acidic medium (<2molL(-1) HCl, HNO(3)) or alkaline medium up to pH 8. The separation and preconcentration of Ag(I), Au(III), Pd(II), Pt(II) and Rh(III) from aqueous medium using morin-APSG was studied. The optimum pH values for the separation of Ag(I), Au(III), Pd(II), Pt(II) and Rh(III) on the sorbent are 5.7, 2.2, 3.7, 3.7 and 6.8, giving rise to separation efficiencies of 43.9, 85.9, 97.7, 60.9 and 91.0%, respectively, where the activity was found to be >90% in the presence of acetate ion. The ion sorption capacity of morin-APSG towards Cu(II) at pH 5.5 was found to be 0.249mmolg(-1) where the sorption capacities of Ag(I) and Pd(II) were 0.087 and 0.121mmolg(-1) and 0.222 and 0.241mmolg(-1) at pH 2.2 and 5.7, respectively. This indicates a 1:1 and 1:2 morin/metal ratios at pH 2.2 and 5.7, respectively. Complete elution of the sorbed metal ions was carried out using 10mL (0.5molL(-1) HCl+0.01molL(-1) thiourea) in case of Au(III), Pd(II), Pt(II) and Rh(III) and 10mL 0.5molL(-1) HNO(3) in case of Ag(I). Morin-APSG was successfully employed in the separation and preconcentration of the investigated precious metal ions from some spiking water samples yielding 100-folds concentration factor. The relative standard deviation (R.S.D.) and the T-test (|t|(1)) were calculated.     

An infrared study of adsorbed metal ions on modified silica: Comparative chelation between mercury, cadmium, and lead divalent ions to silica functionalized with ortho- and para-aminothiophenoles

Chelating selectivity and capacity of silica functionalized 2- and 4-aminothiophenoles (2-ASP-[silica] and 4-ASP-[silica]) toward mercury, lead, and cadmium ions in aqueous medium are studied. In this comparative study, the three metal ions were allowed to interact individually and simultaneously with two aminothiophenol (ASP) derivatives namely, 2- and 4-ASP once as free chelates in solution and secondly as immobilized chelates on silica. Upon individually or simultaneously interacting the three metal ions with 4-ASP-[silica], Hg(II) ions are preferentially adsorbed where 100% of Hg(II) is removed compared to 83.0% of Pb(II) and 76% of Cd(II) ions. In solution, Hg(II) ions are found to be preferentially adsorbed by 2-ASP when compared to 4-ASP. Whereas, anchoring 4-ASP to a silica surface via amide linkage provides a significant enhancement in selectivity and extent of chelation toward Hg(II) over Cd(II) and Pb(II) ions. In the case of 4-ASP-[silica], the existence of a free SH group allows an easy-accessible and strain-free binding site for the incoming Hg(II) ions. Whereas, in 2-ASP-[silica], the SH group is sterically hindered due to proximity to the point of attachment with the surface. As a result, 2-ASP-[silica] showed less potential for Hg(II) binding compared to the modified analogue, 4-ASP-[silica] with less chelation extent observed in solution compared to that observed at the surface.     

New approach to the immobilization of glucose oxidase on non-porous silica microspheres functionalized by (3-aminopropyl)trimethoxysilane (APTMS)

The immobilization and encapsulation of glucose oxidase (GOD) onto the mesoporous and the non-porous silica spheres prepared by co-condensation of tetraethylorthosilicate (TEOS) and (3-aminopropyl)trimethoxysilane (APTMS) in the water-in-oil (W/O) emulsion system were studied. The terminal amine group was used as the important functionality for GOD immobilization on the silica substrate. When only TEOS is used as a silica source, the disordered mesoporous silica microspheres are obtained. As the molar ratio of APTMS to TEOS (R_AT) increases, the surface area and pore volume of the silica particles measured by nitrogen adsorption and desorption method and SEM decrease rapidly. Particularly, the largest change of the surface morphology is observed between R_AT = 0.20 and R_AT = 0.25. The amount and the adsorption time of immobilized enzyme were measured by UV spectroscopy. About 20 wt% of GOD was immobilized into the silica substrates above R_AT = 0.60 and was completely adsorbed into the substrate of R_AT = 0.80 with lapse of 4 h after addition. In the measurement of the thermal stability, GOD dissolved in buffer solution loses nearly all of its activity after 30 min at 65 °C. In contrast, GOD immobilized on the surface-modified silica particles still retains about 90% of its activity after the same treatment. At this temperature, the immobilized glucose oxidase retained half of its initial activity after 4 h. It is shown that the suitable usage of functionalizing agent like APTMS as well as the control of surface morphology is very important on the immobilization of enzyme.     

Preparation and characterization of monoliths covalently bonded chelating groups for capillary electrochromatographic separation of metal ions

In this work, a novel polymer-based monolithic column was prepared using an o-phthalaldehyde-l-phenylalanine Schiff base complex as the reactive center and a mixture of methanol and n-propanol as the porogen. The monolithic column was employed for the separation of a metal ion mixture including Pb(II), Mn(II), Cu(II), Ni(II), Cr(III), Fe(III) and Cr(VI). Tetrabutylammonium bromide (TBAB) was used as a mobile phase additive to enhance the separation efficiency of metal ions by EDTA precomplexation. Using a phosphate buffer (20 mM, pH 3.0), TBAB (10 mM), MeOH (15%, v/v), an applied voltage of −15 kV, and detection at 220 nm, the metal ion mixture was satisfactorily resolved. The average theoretical plate number was 17,900 plates/m. The separation was also carried out in the absence of TBAB, leading to dissimilar elution order and shorter retention time. The separation behavior of the monolithic column was also compared with that of the blank polymer. The unique properties of the monolithic column might be mediated by a combination of electrophoretic behavior and chromatographic retention involving hydrophobic and hydrophilic interactions, as well as ligand exchange.     

低能氮离子对苯甲酸钠溶液的化学改性

利用气体尖端放电产生低能氮离子,这些离子在放电间隙的电场加速下攻击苯甲酸钠(PhCOONa)水溶液,造成溶液中分子的损伤。氮离子的作用使溶液的紫外吸收发生显著的变化,与茚三酮呈正反应,表明进入溶液的氮元素形成了某种形式的氨基。红外吸收光谱的分析进一步表明低能氮离子与PhCOONa溶液作用形成了酰胺及亚硝基化合物。所有的实验结果都反映了低能离子通过损伤分子及进一步与损伤碎片化学合成的化学改性作用。     

Nanometer titanium dioxide immobilized on silica gel as sorbent for preconcentration of metal ions prior to their determination by inductively coupled plasma atomic emission spectrometry

Nanometer titanium dioxide immobilized on silica gel (immobilized nanometer TiO₂) was prepared by sol-gel method and characterized by using X-ray diffraction (XRD) and scanning electron microscope (SEM). The adsorptive potential of immobilized nanometer TiO₂ for the preconcentration of trace Cd, Cr, Cu and Mn was assessed in this work. The metal ions studied can be quantitative retained at a pH range of 8-9, and 0.5 mol L⁻¹ HNO₃ was sufficient for complete elution. The adsorption capacity of immobilized nanometer TiO₂ for Cd, Cr, Cu and Mn was found to be 2.93, 2.11, 6.69 and 2.47 mg g⁻¹, respectively. A new method using a microcolumn packed with immobilized nanometer TiO₂ as sorbent has been developed for the preconcentration of trace amounts of Cd, Cr, Cu and Mn prior to their determination by inductively coupled plasma atomic emission spectrometry (ICP-AES). The method has been successfully applied for the determination of trace elements in some environmental samples with satisfactory results.     

NIR studies of the surface modification in silica fillers

Methods of estimating the degree of condensation of the surface silanol groups of silica due to its modification by silane coupling agents are reported.Also, a procedure for estimating the surface silanol groups for the pre- and post-modified silicas for the NIR 7326 cm^–1 band is given.Using electron microscope studies and heats of immersion of silica surfaces, the silane effect on agglomeration of silica particles and, thus, on the physicochemical properties of its surface has been demonstrated.     

New synthesized ligands for detection of heavy metal ions

Some new chemo-sensors (4,4'-((1E,1′E)-(2,2′-dichloro-[1,1′-biphenyl]-4,4′-diyl)bis(diazene-2,1-diyl))bis(3,5-dihydroxybenzoic acid), 4-((E)-(4-(N-(4-((E)-(4-carboxy-2,6-dihydroxyphenyl)diazenyl)phenyl)sulfamoyl)phenyl)diazenyl)-3,5-dihydroxybenzoic acid, 4-((E)-(4-((4-((E)-(4-carboxy-2,6-dihydroxyphenyl)diazenyl)-2-sulfophenyl)amino)phenyl)diazenyl)-3,5-dihydroxybenzoic acid) were synthesized. These synthesized sensors were then characterized by FTIR, TLC, UV–Visible spectrophotometry, and NMR techniques. The sensors showed the best results for detection of all type of heavy metal ions simply by changing the colour of metal ion solution and by shifting in the λ_max values of sensors due to interactions.     

Retention of heavy metal ions on SBA-15 mesoporous silica functionalised with carboxylic groups

Three samples of SBA-15 functionalised with -(CH(2))(3)COOH groups have been prepared by co-condensation, starting from solutions of TEOS and 4-(triethoxysilyl)butyronitrile, acting as -(CH(2))(3)COOH precursor, of different molar compositions. Materials were characterised by X-ray diffraction, nitrogen adsorption, and FT-IR spectroscopy. The pK(a) and the acidic capacity were measured for all samples by potentiometric titration. The acidic capacity increases with increasing amount of -COOH precursor in the synthesis mixture only up to 10% molar of total alkoxysilane. The value for the pK(a)(4.75) is independent of the acidic capacity of the material. The sample prepared starting from an amount of -COOH precursor equal to 10% molar of total alkoxysilane was chosen to test selective interactions with heavy metals of environmental importance (Ag(+), Cd(2+), Fe(3+), Cu(2+), Zn(2+)) at different pH values and ionic strengths. The significant and selective adsorption exhibited by the material has been exploited in a preliminary cation-exchange chromatographic application showing the possibility of eluting the metal ions at different retention times.     

Chemical modification of Chitosan for metal ion removal

In the current work some modification reactions have been conducted to modify Chitosan with some organic compounds, such as aldehydes and organic acids. On the other hand, different blends of Chitosan with some carbohydrates were prepared to obtain Chitosan derivatives of certain physical and chemical properties. The obtained products have been characterized with the necessary chemical and spectroscopic techniques. The efficiency of the obtained modified materials has been investigated for separation of metal ions and for water uptake.     

Effect of metal ions on the bromination of 3,5-dimethylpyridine-N-oxide in acetic acid

Summary The influence of metal ions on -bromination and N-O bond reduction of 3,5-dimethylpyridine-N-oxide (2) in acetic acid is described.

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Effekt von Metallionen auf die Bromierung von 3,5-Dimethylpyridin-N-oxid in Essigsäure (Kurze Mitt.)

Zusammenfassung Es wird der Einfluß von Metallionen auf die -Bromierung und die Reduktion der N-O-Bindung von 3,5-Dimethylpyridin-N-oxid in Essigsäure beschrieben.

     

Cloud point extraction preconcentration for capillary electrophoresis of metal ions

The application of the cloud point extraction (CPE) technique for capillary electrophoresis (CE) determination of metal ions was demonstrated using Cu(II) and Co(II) as model metal ions. The preconcentration of Cu(II) and Co(II) in aqueous solution was achieved by CPE with 1-(2-pyridylazo)-2-naphthol (PAN) as the chelating agent and Triton X-114 as the extractant. Baseline separation of the PAN chelates of Cu(II) and Co(II) was realized by CE with a photodiaode array detector in a  μm i.d. fused-silica capillary at 17 kV. A 50 mM NH₄Ac buffer solution (pH 8.0) containing 0.2 mM of PAN in 80% (v/v) of acetonitrile and 20% (v/v) doubly deionized water (DDW) was used as the separation medium to avoid the adsorption of hydrophobic substances and nonionic surfactant Triton X-114 onto the inner surface of the separation capillary, ensuring the separation efficiency and reproducibility. The precision (relative standard deviation (R.S.D.), n=5) for five replicate injections of a mixture of 20 μg/l of Co(II) and Cu(II) were 0.74 and 1.8% for the migration time, 3.1 and 0.64% for the peak area measurement, respectively. The apparent concentration factor, which is defined as the concentration ratio of the analyte in the final diluted surfactant-rich extract ready for CE separation and in the initial solution, was 15.9 for Co(II) and 16.3 for Cu(II). The linear concentration range was from 3 to 100 μg/l for both Co(II) and Cu(II). The detection limits of Co(II) and Cu(II) were 0.12 and 0.26 μg/l, respectively. The developed method was successfully applied to the determination of Co(II) and Cu(II) in tap water, snow water, and flavor wines.     

Preparation and adsorption properties of crosslinked polystyrene-supported low-generation diethanolamine-typed dendrimer for metal ions

Two novel chelating resins, polystyrene supported G1.0 diethanolamine-typed dendrimer (PS-DEA) and G2.0 diethanolamine-typed dendrimer (PS-(DEA)₂), were prepared by anchoring low-generations diethanolamine-typed dendrimer into crosslinked polystyrene in this paper. Fourier transform-infrared spectra (FTIR), scanning electron microscopy (SEM) and elemental analysis were employed to character their structures. The results of adsorption for metal ions showed that the resins had good adsorption capacities for Cu²⁺, Ag⁺ and Hg²⁺, especially PS-DEA for Cu²⁺. The adsorption kinetics and adsorption isotherms of PS-DEA for Cu²⁺ and PS-(DEA)₂ for Hg²⁺ were studied. The results showed that the adsorption kinetics of the two resins can be modeled by pseudo second-order rate equation wonderfully and Langmuir and Freundlich equations could well interpret the adsorption of PS-(DEA)₂ for Hg²⁺ and PS-DEA for Cu²⁺, respectively. The adsorption mechanism of the resins for Cu²⁺ was confirmed by X-ray photoelectron spectroscopy (XPS).     

pH-dependent aggregation of citrate-capped Au nanoparticles induced by Cu ions: The competition effect of hydroxyl groups with the carboxyl groups

The citrate-capped Au nanoparticles were found to undergo pH-dependent aggregation induced by Cu²⁺ ions. At low pH value (8.9), the Au nanoparticles aggregated into fractal-like structure induced by the coordination interactions between the carboxyl groups of citrate ligands and Cu²⁺ ions. At high pH value (10.1), the Au nanoparticles aggregated into close-packed structure attributed to the increased concentration of hydroxyl groups. The coordination interactions between the metal ions and the ligands were suppressed as a result of the competition effect of the hydroxyl groups with the carboxyl groups. The aggregation process was identified to be dominated by the cluster–cluster mechanism at the low pH value and the particle–cluster mechanism at the high pH value.     

Room temperature ionic liquid as a novel medium for liquid/liquid extraction of metal ions

Room temperature ionic liquids (RTILs) have been used as novel solvents to replace traditional volatile organic solvents in organic synthesis, solvent extraction, and electrochemistry. The hydrophobic character and water immiscibility of certain ionic liquids allow their use in solvent extraction of hydrophobic compounds. In this work, a typical room temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate [C₄mim][PF₆], was used as an alternative solvent to study liquid/liquid extraction of heavy metal ions. Dithizone was employed as a metal chelator to form neutral metal-dithizone complexes with heavy metal ions to extract metal ions from aqueous solution into [C₄mim][PF₆]. This extraction is possible due to the high distribution ratios of the metal complexes between [C₄mim][PF₆] and aqueous phase. Since the distribution ratios of metal dithiozonates between [C₄mim][PF₆] and aqueous phase are strongly pH dependent, the extraction efficiencies of metal complexes can be manipulated by tailoring the pH value of the extraction system. Hence, the extraction, separation, and preconcentraction of heavy metal ions with the biphasic system of [C₄mim][PF₆] and aqueous phase can be achieved by controlling the pH value of the extraction system. Preliminary results indicate that the use of [C₄mim][PF₆] as an alternate solvent to replace traditional organic solvents in liquid/liquid extraction of heavy metal ions is very promising.     

Adsorption of graphene oxide/chitosan porous materials for metal ions

Porous graphene oxide/chitosan（PGOC） materials were prepared by a unidirectional freeze-drying method.Their porous structure,mechanical property and adsorption for metal ions were investigated.The results show that the incorporation of graphene oxide（GO） significantly increased the compressive strength of the PGOC materials.The saturated adsorption capacity of Pb²⁺ increased about 31%,up to 99 mg/g when 5 wt%GO was incorporated These biodegradable,nontoxic,efficient PGOC materials will be a potential adsorbent for metal ions in aqueous solution.     

Detection of metal ions by atomic emission spectroscopy from liquid-electrode discharge plasma

In this paper, the discharge ignited in a capillary connecting two beakers filled with electrolyte solution is investigated. During the experiment, an external electrical voltage is applied through two platinum electrodes dipped in the beakers. A gas bubble forms inside the capillary when the applied voltage is higher than 1000 V. Since the beakers are tilted slightly, after generation, the bubble moves slowly to the uphill outlet of the capillary due to buoyancy. When the bubble reaches the end of the capillary, it cracks and a bright discharge is ignited. The emission spectra of the discharge plasma are related to the metal ions dissolved in the solution and thus can be used for metal ion detection. An application of the system to measurement of water hardness is shown.