Solid phase extraction of Pb(II) in water samples using a new hybrid inorganic-organic mesoporous silica prior to its determination by FAAS

A mesoporous silica has been chemically modified with 5-mercapto-1-methyltetrazole. The newly synthesized material was characterized by powder X-ray diffraction, N₂ adsorption, FT-IR, ¹³C-NMR spectroscopy and elemental analysis, and used to preconcentrate Pb(II) from aqueous solutions. The effect of several variables on the adsorption capacity (i.e. stirring time, pH, interfering ions, presence of other heavy metals in the medium, etc.) has been studied using batch and column techniques. The adsorption capacity of the material followed the order: Pb(II) >> Cu(II) > Cd(II) >>Mn(II) > Ni(II) > Co(II). In column experiments a pre-concentration factor of 200 was obtained for Pb(II). Spiked tap water, mineral water and river water were used for the preconcentration and determination of Pb(II) by flame atomic absorption spectrometry, and a 101–103% recovery was obtained. The limit of detection and quantification values of the method were found to be 2.22·10^?6 mM and 8.20·10^?6 mM, respectively. The relative standard deviation for four preconcentration experiments was found to be ≤9% in all cases.     

Functionalized HMS mesoporous silica as solid phase extractant for Pb(II) prior to its determination by flame atomic absorption spectrometry

In this work, a mesoporous silica has been chemically modified with 5-mercapto-1-methyl-1-H-tetrazol using the homogeneous route (MTTZ-HMS). This synthetic route involved the reaction of 5-mercapto-1-methyl-1-H-tetrazol with 3-chloropropyltriethoxysilane, prior to immobilization on the support. The resulting material has been characterized and employed as solid phase extractant for Pb(II). The effect of several variables (stirring time, pH, temperature, metal concentration, presence of other metals) has been studied using batch and column techniques. In batch experiments, 15 min stirring time, 55 degrees C and pH 8 were the optimal conditions for Pb(II) adsorption. In column experiments, sorption was quantitative for 1000 mL of 2.41 x 10(-4 )mM of Pb(II) solution and adsorbed ions were eluted out by 5 mL of 1 M HCl (preconcentration factor of 200). Spiked tap water was used for the preconcentration and determination of Pb(II) by flame atomic absorption spectrometry, and a 100% recovery was obtained. The LOD and LOQ values of the proposed method were found to be 3.52 x 10(-3) and 4.20 x 10(-3 )mM, respectively. The RSD for three preconcentration experiments was found to be 相似文献   

Determination of Cu,Ni, and Zn in fuel ethanol by FAAS after enrichment in column packed with 2-aminothiazole-modified silica gel

This work describes the synthesis and characterization of 2-aminothiazole-modified silica gel (SiAT), as well as its application for preconcentration (in batch and column technique) of Cu(II), Ni(II) and Zn(II) in ethanol medium. The adsorption capacities of SiAT determined for each metal ion were (mmol g(-1)): Cu(II)=1.20, Ni(II)=1.10 and Zn(II)=0.90. In addition, results obtained in flow experiments, showed a recovery of ca. 100% of the metal ions adsorbed in a column packed with 500 mg of SiAT. The eluent was 2.0 mol L(-1) HCl. The sorption-desorption of the studied metal ions made possible the development of a preconcentration method for metal ions at trace level in fuel ethanol using flame AAS for their quantification.     

Sorption of Cobalt on Modified Silica Gel Materials

Various silica gel materials were chemically modified with imidazole, diaza-18-crown-6 (DA18C6) and dibenzod-18-crown-6 (DB18C6). The degree of functionalization of the covalently attached molecule was calculated from C, H, N analysis and ranged between 0.270 and 0.552 mmol/g (for sorbents with imidazole) and between 0.043 and 0.062 mmol/g (for sorbents with DA18C6 and DB18C6). The degree of functionalization depends on the reflux time and silica gel matrix used. Experimental sorption capacity ranged between 0.038 and 0.228 mmol/g (for sorbents with imidazole) and between 0.019 and 0.050 mmol/g (for sorbents with DA18C6 and DB18C6). Synthesized hexagonal mesoporous silica matrix MCM-41 with uniform pore diameter <40 Å was used too. Change of pore diameters of silica gel support to larger pores should have a positive influence on access of cobalt ion to sorption centers to increase of sorption capacity of sorbents. The sorption kinetics of cobalt and the influence of cobalt concentration, pH of various kinds of silica gel matrix with immobilized imidazole group in static conditions on sorption were measured. The sorption of cobalt in various conditions (pH, contact time of phases) with constant liquid-solid ratio (V/m = 50 ml/g) was studied. The distribution coefficients ranged between 200 and 50 000 ml/g (for imidazole), 85 and 120 ml/g (for DB18C6) and between 230 and 500 ml/g (for DA18C6) according to silica gel matrix used and according to the method of sorbent preparation. pH plays important role in the sorption of cobalt on prepared sorbents with immobilized crown ethers due to protonization of crown ethers. Protons significantly competes to sorption of cobalt in acidic solutions. The influence of presence of other heavy or toxic metals (Hg(II), Cd(II), Mn(II), Zn(II), Cu(II), Fe(III), Cr(III), Al(III) and the influence of sodium and potassium on sorption Co(II) from aqueous solutions was investigated. Sorption of cobalt decreases in order Hg > Cu > Cd > Zn, Fe > Mn > Al, Cr. The presence of sodium and potassium ions at concentration 0.05 mol/l significantly influences on the sorption of cobalt with sorbent with immobilized DB18C6 functional group.     

Voltammetric analysis of Pb(II) in natural waters using a carbon paste electrode modified with 5-mercapto-1-methyltetrazol grafted on hexagonal mesoporous silica

A hexagonal mesoporous silica (HMS) functionalized with a 5-mercapto-1-methyltetrazole derivative was employed to prepare a chemically modified carbon paste electrode for Pb(II) detection in aqueous solution by square wave adsorptive stripping voltammetry. The optimal operating conditions were 5 min preconcentration time at pH 6.5, and 120 s electrolysis time in 0.2 mol L^?1 HCl. Under these conditions, the voltammetric signal increased linearly with the preconcentration time in the range 1 to 10 min and with the Pb(II) concentration in the range 1 to 100?µg L^?1. The electrode was reproducible and sensitive. Simultaneous determination of Pb, Cd and Cu was also carried out with the electrode. The accuracy of the method was validated by analysing Pb(II) in tap water and groundwater samples.     

Static and dynamic sorption study of heavy metal ions on amino-functionalized SBA-15

Amino-functionalized SBA-15 mesoporous silica (SBA-15-NN) was synthesized using the normal grafting procedure of SBA-15 with [3-(2-Aminoethyl) aminopropyl] trimethoxysilane. Under optimal conditions, SBA-15-NN exhibited a higher adsorption capacity toward metal ions than SBA-15 in static adsorption. The results showed that the flow rate of 2?mL?min^?1 might be the optimum flow rate in dynamic adsorption, and the higher initial metal ion concentration is favorable for the adsorption of Zn(II), Co(II), and Ni(II) onto SBA-15-NN. The results indicated that SBA-15-NN could effectively remove multiple metal ions from aqueous solution as a good adsorption material.     

EXAFS studies on adsorption irreversibility of Zn(II) on TiO2: temperature dependence

Adsorption irreversibility of Zn(II) on TiO2 at various temperatures was studied using a combination of classical macroscopic methods and extended X-ray absorption fine structure (EXAFS) spectroscopy. When the temperature was increased from 5 to 40 degrees C, the Zn(II) adsorption capacity increased by 130%, and adsorbed Zn(II) became more reversible. The standard Gibbs free energy change (DeltaG 0) of the adsorption reaction at 5, 20, and 40 degrees C was determined to be -19.58+/-0.30, -22.28+/-0.10, and -25.14+/-0.21 kJ mol(-1), respectively. And the standard enthalpy (DeltaH 0) and entropy (DeltaS 0) were 24.55+/-2.91 kJ mol(-1) and 159.13+/-0.53 J mol(-1)K(-1), respectively. EXAFS spectra results showed that the hydrated Zn(II) was adsorbed through fourfold coordination with an average ZnO bond distance of 1.98+/-0.01 A. Two ZnTi atomic distances of 3.25+/-0.02 and 3.69+/-0.03 A were observed, which corresponded to an edge-sharing linkage mode (strong adsorption) and a corner-sharing linkage mode (weak adsorption), respectively. As the temperature increased from 5 to 40 degrees C, the number of strong adsorption sites (N1) remained relatively constant while the number for the weak adsorption sites (N2) increased by 31%. These results indicate that the net gain in adsorption capacity and the decreased adsorption irreversibility at elevated temperatures were due to the increase in available weak adsorption sites (N2) or the decrease in the ratio of N1/N2. Both the macroscopic sorption/desorption equilibrium data and the molecular level evidence of this study suggest that in a given environmental system (e.g., soils or natural waters) zinc and other similar heavy metals are likely more mobile at higher temperatures.     

Synthesis and characterization of silica gel microspheres encapsulated by salicyclic acid functionalized polystyrene and its adsorption of transition metal ions from aqueous solutions

The present study was undertaken to develop a novel adsorbent for heavy metal ions, and this paper presents the synthesis and characterization of a composite material-silica gel microspheres encapsulated by salicyclic acid functionalized polystyrene (SG-PS-azo-SA) with a core-shell structure. SG-PS-azo-SA was used to investigate the adsorption of Mn(II), Co(II), Ni(II), Fe(III), Hg(II), Zn(II), Cd(II), Cr(VI), Pd(II), Cu(II), Ag(I), and Au(III) from aqueous solutions. The results revealed that SG-PS-azo-SA has better adsorption capacity for Cu(II), Ag(I) and Au(III). Langmuir and Freundlich isotherm models were applied to analyze the experimental data, the best interpretation for the experimental data was given by the Langmuir isotherm equation with the maximum adsorption capacity for Cu(II), Ag(I), and Au(III) at 1.288 mmol g⁻¹, 1.850 mmol g⁻¹ and 1.613 mmol g^t-1, respectively. Thus, silica gel encapsulated by salicyclic acid functionalized polystyrene (SG-PS-azo-SA) is favorable and useful for the removal of Cu(II), Ag(I) and Au(III) metal ions.     

中空介孔二氧化硅锚固聚偕胺肟吸附Cr(Ⅵ)

以硝酸铈铵为引发剂, 在自制的中空介孔二氧化硅(HMS)的空腔和通道内引发丙烯腈自由基聚合, 并将其氰基偕胺肟化, 用于制备具有吸附Cr(Ⅵ)的廉价有机无机复合吸附材料—中空介孔二氧化硅锚固聚偕胺肟. 通过傅里叶变换红外光谱(FTIR)、 扫描电子显微镜(SEM)及N₂吸附-脱附比表面分析对中空介孔二氧化硅锚固聚偕胺肟进行表征. 结果表明, 制备的中空微球直径约为400 nm, 其壁上孔径约为11.0 nm, 比表面积约为431 m²/g, 锚固聚偕胺肟后中空微球壁上孔道直径约为4.6 nm, 比表面积降低为347 m²/g. HMS锚固的聚偕胺肟对重铬酸钾溶液中铬的吸附量高达0.46 mmol/g, 吸附过程中伴随化学反应, 符合伪二级动力学模型, 可用作废水处理中重金属离子的高效廉价吸附材料.     

An investigation of gold adsorption from a binary mixture with selective mesoporous silica adsorbents

Gold-selective adsorbents were prepared from mesoporous MCM-41 silica by grafting organic amine groups (i.e., RNH2, R2NH, and R3N; R=propyl). NH2-MCM-41, NRH-MCM-41, and NR2-MCM-41 displayed strong affinity for gold and at 1 mmol/g loading adsorbed 0.40, 0.33, and 0.20 mmol/g of gold. Copper and nickel were not adsorbed on these adsorbents. Grafting surface chemical moieties introduces heterogeneity on an otherwise uniform MCM-41 pore surface and metal adsorption is best described by the Freundlich adsorption model. A series of binary adsorption equilibrium studies with NH2-MCM-41 containing 2.2 mmol RNH2/g shows that NH2-MCM-41 adsorbs only gold from solutions containing copper and nickel with an adsorption capacity of 0.6 mol of Au/mol of RNH2 (1.1 mmol of Au/g of NH2-MCM-41). Copper and nickel were not adsorbed by NH2-MCM-41 regardless of the solution concentration, composition, and pH (i.e., 2 to 4) in the presence of gold. The LeVan and Vermeulen adsorption model based on a single component Freundlich isotherm and corrected for the anion effect accurately predicted the binary adsorptions. The adsorbed gold was completely recovered by a simple acid wash and the recovered gold solution is 99% pure. The regenerated NH2-MCM-41 remained 100% selective for gold removal and exhibited the same adsorption capacity even after several uses.     

Fe(3+) coordinated to amino-functionalized MCM-41: an adsorbent for the toxic oxyanions with high capacity, resistibility to inhibiting anions, and reusability after a simple treatment

Fe(3+) coordinated to amino ligands fixed on MCM-41 mesoporous silica works as a strong adsorbent for toxic oxyanions. The maximum adsorption amounts were 1.56, 0.99, 0.81, and 1.29 mmol g(-1) for arsenate, chromate, selenate, and molybdate, respectively. When the initial concentrations of oxyanions were less than 1 mmol l(-1), they were removed completely by adsorption and the distribution coefficients K(d) were found to be more than 200000. Inhibition of oxyanion adsorption by abundant competing anions found in nature, NO(3)(-), SO(4)(-), PO(4)(3)(-) and Cl(-), was evaluated at adsorption saturation. Among these anions, the adsorption of the oxyanions was inhibited most in the presence of PO(4)(3)(-) , with which the selectivities for the target oxyanions were still more than 80%. The other coexisting anions, NO(3)(-), SO(4)(-), PO(4)(3)(-) and Cl(-), had little influence on adsorption of the oxyanions except in the case of selenate removal from sulfate solution. The high ability and selectivity to the target oxyanions are attributed to specific interactions between Fe(3+) and the oxyanions. The acid treatment and re-coordination of Fe(3+) lead to a reactivation of the used adsorbent, in which 87-90% of the original adsorption capacity was obtained and the oxyanion/Fe stoichiometries were not changed.     

Effect of Phosphorylation of Si-MCM-41 and Ti-Si-MCM-41 Mesoporous Molecular Sieves on Their Structure-Adsorption and Acid Properties

Transmission electron microscopy, X-ray diffraction, nitrogen and argon adsorption, thermal analysis, thermoprogrammed ammonia desorption, and ¹H MAS NMR spectroscopy were used to show that phosphorylation by POCl₃ yields MCM-41 silica gel and Ti-MCM-41 titanium-silica gel mesoporous molecular sieves with about 1.1 mmol/g acid sites consisting largely of hydroxyl group protons of supported phosphoric acid. These materials display catalytic activity in the esterification of acetic acid by ethanol.     

Isotherm Model Analysis for the Adsorption of Cd (II), Cu (II), Ni (II), and Zn (II) on Anaerobically Digested Sludge

Adsorption of Cd (II), Cu (II), Ni (II), and Zn (II) from aqueous solutions on anaerobically digested sludge has been investigated. Experimental data has been fit to Langmuir, Freundlich, and Redlich-Peterson isotherms to obtain the characteristic parameters of each model. Based on the maximum adsorption capacity obtained from the Langmuir and the Redlich-Peterson isotherm the affinity of the studied metals for the sludge has been established as Cu (II)>Cd (II)>Zn (II)>Ni (II). Adsorption tests from multimetal systems confirm the affinity order obtained in the individual metal tests. The adsorption capacity for Cu (II) measured in individual tests is not reduced by the presence of the other above referred metals. Desorption of Zn (II) and Cd (II) previously bound to the sludge in front of Cu (II) and HCl solutions is also reported. Copyright 2000 Academic Press.     

Determination of Cu, Zn, Fe, Ni and Cd by flame atomic absorption spectrophotometry after preconcentration by Escherichia coli immobilized on sepiolite

A method for the determination of Cu, Zn, Fe, Ni and Cd by flame atomic absorption spectrophotometry (FAAS) after preconcentrating on a column containing Escherichia coli immobilized on sepiolite has been developed. Optimum pH values, amount of adsorbent, elution solution and flow rate have been obtained for the elements studied. The effect of interfering ions on the recovery of the analytes has also been investigated. Recoveries of Cu, Zn, Fe, Ni and Cd by E. coli immobilized on sepiolite were 99.1+/-0.6, 98.2+/-0.6, 98.1+/-0.5, 97.2+/-0.8 and 98.2+/-0.4% at 95% confidence level, respectively. The adsorption capacity of E. coli immobilized on sepiolite was found as 0.148, 0.064, 0.098, 0.134 and 0.088 mmol/g for Cu, Zn, Fe, Ni and Cd, respectively. The proposed method was applied to the determination of trace metals in alloys (NBS SRM 85b). Trace metals have been determined with relative error lower than 10%.     

Determination of Metal Ions in Natural Waters by Flame-AAS after Preconcentration on a 5-Amino-1,3,4-Thiadiazole-2-Thiol Modified Silica Gel.

ABSTRACT

5-amino-1,3,4-thiadiazole-2-thiol groups attached on a silica gel surface have been used for adsorption of Cd(II), Co(II), Cu(II), Fe(III), Ni(II), Pb(II) and Zn(II) from aqueous solutions. The adsorption capacities for each metal ion were (in mmol.g^?1): Cd(II)= 0.35, Co(II)= 0.10, Cu(II)= 0.15, Fe(III)= 0.20, Hg(II)= 0.46, Ni(II)= 0.16, Pb(II)= 0.13 and Zn(II)= 0.15. The modified silica gel was applied in the preconcentration and quantification of trace level metal ions present in water samples (river, and bog water).     

Synthesis, amino-functionalization of mesoporous silica and its adsorption of Cr(VI)

Mesoporous silica materials with a centered rectangular symmetry (cmm) have been synthesized through a facile direct-templating method using tetraethylorthosilicate (TEOS) and amphiphilic block co-polymers Pluronic P123 under acidic conditions. The amino groups have been grafted to as-synthesized mesoporous silica by [1-(2-amino-ethyl)-3-aminopropyl]trimethoxysilane (AAPTS). Thus obtained amino-functionalized mesoporous silica (denoted as NN-silica) was used for sequestration of Cr(VI) from aqueous solution. After sequestration of Cr(VI), the sample was denoted as Cr(VI)-silica. The parent mesoporous silica, NN-silica and Cr(VI)-silica were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR) and N(2) adsorption-desorption isotherms. XRD and TEM results confirm that the structure of these samples is centered rectangular symmetry (cmm). N(2) adsorption-desorption isotherms show that there is a remarkable decrease in surface area and pore volume for NN-silica (S(BET)=54.5 m(2)g(-1), V(P)=0.09 cm(3)g(-1)) and Cr(VI)-silica (S(BET)=53.2 m(2)g(-1), V(P)=0.07 cm(3)g(-1)) compared to the parent mesoporous silica (S(BET)=444.0 m(2)g(-1), V(P)=0.71 cm(3)g(-1)). The BJH desorption average diameter of NN-silica, Cr(VI)-silica and the parent mesoporous silica is 4.40 nm, 4.07 nm and 5.11 nm, respectively. The results reveal the channels of as-synthesized mesoporous silica are essentially grafted with abundant amino groups and loaded with Cr(VI). The adsorption experiment results show that the functionalized mesoporous silica materials possess an increased Cr(VI) adsorption capacity and the maximum Cr(VI) loadings at 25, 35 and 45 degrees C can reach 2.28, 2.86 and 3.32 mmol/g, respectively.     

Controlled-pore silica glass modified with N-propylsalicylaldimine for the separation and preconcentration of trace Al(III), Ag(I) and Hg(II) in water samples.

Controlled-pore silica glass modified with N-propylsalicylaldimine (SCPSG) has been investigated as a surface-active matrix for the separation of some metal ions. The porous silica glass base was confirmed to have better stability towards hydrolysis in aqueous solution buffered at pH=9 in comparison to silica gel, which showed twice the surface area of controlled-pore silica glass. The different analytical parameters affecting the batch mode separation and preconcentration of trace Al(II), Ag(I) and Hg(II) in environmental samples using SCPSG, prior to their determination using inductively coupled plasma mass spectrometry (ICP-MS), were studied. The optimum conditions are pH 9.0 +/- 0.1, time of stirring 30 min and the eluent concentration 0.5 mol dm(-3) HNO3. The ion-exchange capacity of SCPSG with respect to Al(III), Ag(I) and Hg(II) was 0.27, 0.18 and 0.23 mmol g(-1), respectively. The recovery values for the metal ions were 96.8 +/- 0.86, 98.1 +/- 0.60 and 96.2 +/- 1.06%, and the analytical detection limits were 26.1, 1.49 and 0.44 pg cm(-3), respectively, for a preconcentration factor of 100. The method has been applied to the determination of the investigated metal ions in natural water samples as well as certified and reported samples and the results were found to be accurate.     

微孔/介孔复合分子筛的合成及其对CO2的吸附性能

采用两步晶化法将合成的沸石前驱液(S)或沸石固体粉末(P)经不同浓度(c)的NaOH处理后, 分别以表面活性剂十六烷基三甲基溴化铵(CTAB)软模板或介孔炭(Meso-C)硬模板为导向剂, 自组装合成S-β-MCM41(c)、P-β-MCM41(c)、P-ZSM-MCM41(c)、P-ZSM-C系列微孔/介孔复合分子筛. 考察了沸石分子筛种类、碱处理液浓度以及介孔模板剂对合成复合分子筛结构与性能的影响. X射线衍射(XRD)、透射电子显微镜(TEM)和氮气吸附-脱附表征结果表明产物具有微孔/介孔多级孔结构. 该材料对CO₂的吸附能力比纯微孔或介孔材料均有明显提高, 其中P-ZSM-MCM41(2)的CO₂吸附容量最大可达1.51 mmol·g^-1, 为ZSM-5沸石吸附量的两倍多.     

Prearation of Highly Ordered Mesoporous Silica Materials and Application as Enzeme Supports

An enzyme, horseradish peroxidase (HRP), was adsorbed in the manner of single immersion method on the silica mesoporous materials, FSM-16, MCM-41 and SBA-15 with various pore diameters from 27 to 92 and their enzymatic activity in an organic solvent and the thermal stability were studied. FSM-16 and MCM-41 showed larger amount of adsorption of HRP than SBA-15 or silica gel,when the pore sizes were larger than the spherical molecular diameter of HRP (ca 64×37). The increased enzyme adsorption capacity may be due to the surface characteristics of FSM-16 and MCM-41, which would be consistent with the observed larger adsorption capacity of cationic pigment compared with anionic pigment for these materials. The immobilized HRP on FSM-16 and MCM-41 with pore diameter above 50 showed the highest enzymatic activity in an organic toluene and thermal stability in aqueous solution at the temperature of 70℃. The immobilized enzymes on the other mesoporous materials including large or small pore sized FSM-16 showed lower enzymatic activity in an organic solvent and the thermal stability. Both surface character and size matching between pore sizes and the molecular diameters of HRP were important in achieving high enzymatic activity in organic solvent and high thermal stability.     

Sequestration of CO2 using Cu nanoparticles supported on spherical and rod-shape mesoporous silica

The CO₂ sequestration is one of the most promising solutions to tackle global warming. In this study, spherical mesoporous silica particles (MPS-S) and rod-shaped mesoporous silica particles (MPS-R) loaded with Cu nanoparticles were selectively prepared and employed for CO₂ adsorption. For the first time uniform Cu nanoparticles were incorporated into the rod-shaped mesoporous silica particles by post-synthesis modification using both N-[3-(trimethoxysilyl)propyl]ethylenediamine (PEDA) and ethylenediamine (EDA) as coupling agents. The physiochemical properties of the mesoporous and copper grifted silica composites were investigated by CHN elemental analysis, FTIR spectroscopy, thermogravimetric analysis, X-ray diffraction, energy dispersive X-ray spectroscopy (EDX), surface area analysis, scanning, transmission electron microscopy and gas analysis system (GSD 320, TERMO). The mesoporous silica shows highly ordered mesoporous structures, with the rod-shaped particles having a higher surface area than the spherical ones. Copper nanoparticles with an average diameter of 6.0 nm were uniformly incorporated into the MPS-S and MPS-R. Moreover, Cu-loaded mesoporous silica exhibits up to 40% higher CO₂ adsorption capacity than the bare MPS. The MPS-R modified with Cu nanoparticles showed a maximum CO₂ adsorption capacity of 0.62 mmol/g and the humidity showed a slight negative effect on CO₂ uptake process. The enhancement of CO₂ adsorption onto transition metal/mesoporous substrates provides basis for imminent CO₂ sequestration.