Adsorption of phosphate and nitrate anions on ammonium-functionalized MCM-48: effects of experimental conditions

In this study, ammonium-functionalized MCM-48 (Mobil Composite Material No. 48) was used as an adsorbent to remove nitrate (NO(-)(3)) and monobasic phosphate (H(2)PO(-)(4)) anions from aqueous solutions. The effects of operating conditions such as temperature, adsorbent loading, initial anion concentration, pH, and the presence of competitive ions on the adsorption performances were examined. Results showed that adsorption capacity decreased with increasing temperature. The adsorption capacity increased with adsorbent loading and initial anion concentration. The removal of nitrate was maximum at pH<8, while phosphate removal was maximized at pH 5. The adsorption was almost unaffected by the presence of competitive ions in the case of phosphate anions. However, their presence adversely affected nitrate adsorption. Desorption of both anions was rapidly achieved within 10 min using NaOH at 0.01 M. Regeneration tests showed that the adsorbent retained its capacity after 5 adsorption-desorption cycles.     

Phosphate adsorption on synthetic goethite and akaganeite

Low crystalline iron hydroxides such as goethite (alpha-FeOOH) and akaganeite (beta-FeOOH) were synthesized, and the selective adsorption of phosphate ions from phosphate-enriched seawater was examined. The results of the distribution coefficients (K(d)) of oxoanions in mixed anion solutions at pH 8 follow the selectivity order Cl-, NO3-, SO4(2-) < CO3(2-), HPO4(2-) for goethite, and Cl-, CO3(2-) < NO3- < SO4(2) < HPO4(2-) for akaganeite. In seawater, both adsorbents show high selectivity for phosphate ions despite the presence of large amounts of major cations and anions in seawater. The adsorption isotherms fitted better with the Freundlich equation and the maximum uptake of phosphate from phosphate-enriched seawater was 10 mg P/g at an equilibrium phosphate concentration of 0.3 mg P/L on both adsorbents. The phosphate adsorption/desorption cycles show that akaganeite is an excellent adsorbent even after 10 cycles and its chemical stability is good.     

Synthesis and Characterization of a Chitosan-bearing Binucleating Ligand and Its pH Dependency on Copper(II) Adsorption

A novel chitosan derivative has been synthesized by the condensation of a binucleating ligand, 2,6-bis[(N-methylpiperazine-1-yl)methyl]-4-formylphenol (BNL), with chitosan (CTS). The resulting material (CTS-BNL) was characterized and its adsorption properties towards copper(II) ions in aqueous solutions of various pH have been studied, the adsorption capacity (Q(e)) is about 0.94 mmol g(-1) at pH 6 and 1.45 mmol g(-1) at pH 8.5. This higher adsorption capacity may be due to the binucleating ligand anchored to chitosan.     

Modeling the adsorption of free and heavy metal complex-bound EDTA onto red mud by a nonelectrostatic surface complexation model

The adsorption of free and divalent heavy metal (copper, cadmium, and lead) complex-bound EDTA from metal-EDTA mixture solutions on a composite adsorbent having a heterogeneous surface, i.e., bauxite waste red mud, has been investigated and modeled with the aid of a nonelectrostatic surface complexation approach in respect to adsorbate concentration and pH dependency of EDTA adsorption. EDTA was selected as the modeling ligand in view of its wide usage as an anthropogenic chelating agent and its abundance in natural waters. The adsorption experiments were conducted for pure EDTA or metal-EDTA complexes alone, or in mixtures containing (EDTA+metal-EDTA). For all studied cases, the solid adsorbent phase concentrations of the adsorbed species were found by using the derived model equations with acceptable compatibility of experimental and theoretically generated adsorption isotherms. The model basically assumed two modes of metal bonding to the surface hydroxyls: ionic (outer-sphere) binding of the EDTA anion (H(2)Y(2-)) or anionic metal-EDTA complex (MY(2-)) to the cationic surface site ( approximately SOH(+)(2)), and outer-sphere binding of H(2)Y(2-) or MY(2-) to the neutral approximately SOH site, possibly via hydrogen-bonding. The model was useful for EDTA and metal-EDTA mixture solutions either at their natural pH of equilibration with the sorbent, or after pH elevation with NaOH titration up to pH相似文献   

Removal and recovery of Zn2+ and Pb2+ by imine-functionalized magnetic nanoparticles with tunable selectivity

This research investigated the adsorption of zinc and lead from binary metal solution with tunable selectivity. A nano adsorbent was prepared by introducing imine groups onto the surface of stability enhanced magnetic nanoparticles and then characterized by TEM and FTIR. Binary metal components adsorption was carried out in different concentration of metal and EDTA solution. Due to the interaction between metals and adsorbent in the presence of EDTA, the selective adsorption of zinc and lead could be achieved with 100% selectivity. To only remove zinc from binary metals, the solution condition was [EDTA]/[M(2+)] = 0.7 with pH of 6, and its saturated adsorption capacity was 1.25 mmol/g. For selective adsorption of lead, an equilibrium adsorption capacity of 0.81 mmol/g was obtained under the condition of [EDTA]/[M(2+)] = 0.7 and pH of 2. The exhausted adsorbent could be regenerated by simple acid or alkali wash, and high purity lead and zinc salt solutions were recovered and concentrated.     

The ELECTRICAL INTERFACIAL LAYER at theTiO2 (ANATASE)/ELECTROLYTE INTERFACE - ADSORPTION of Zn(II) and Cd(II) IONS

Mechanism of adsorption of Zn(II) and Cd(II) ions at the TiO₂ (anatase)/electrolyte interface has been studied by different experimental techniques (potentiometric titration, microelectrophoresis and adsorption measurements of zinc and cadmium species). It was found that the point of zero charge (pzc) of anatase (pH =5.8) was shifted to the lower pH values with increasing concentrations of Zn(II) or Cd(Il) ions. The surface charge of anatase in the presence of Zn(II) and Cd(II) for pH > pH_pzc was higher than that observed for original sample in NaClO₄ solutions only. Due to low coverage of anatase surface with Zn(II) or Cd(II) species almost no shift of the isoelectric point (iep) or charge reversal were observed. Adsorption density vs. pH plots for both Zn(Il) or Cd(II) showed, typical for multivalent ions, presence of “adsorption edge.”     

Surface electrochemical properties of mixed oxide ceramic membranes: Zeta-potential and surface charge density

The surface electrochemical properties of alumina based ceramic microfiltration membranes were studied by measuring electroosmotic rates and surface charge densities obtained from potentiometric titrations. The rate of electroosmosis, which determines the zeta-potential, was measured on the membrane itself, whereas the surface charge was titrated on a suspension obtained by crushing of the membrane. The zeta-potential was measured in the presence of salts including NaCl, CaCl₂ and Na₂SO₄, for a wide range of pH values (4–9) at ionic strengths of 0.01 and 0.001 M. The pH value of the isoelectric point (iep) show a specific adsorption of SO₄²⁻ and Ca²⁺ ions onto the membrane surface. The iep in NaCl solutions occurs at pH 4.7 ± 0.1. The low iep is due to the large amount of silicium oxide in the membrane. The surface charge density is relatively high with respect to the low values of zeta-potentials. The point of zero charge pH(pzc) determined from surface charge and pH profiles occurs at pH 8.2 ± 0.1 in NaCl solution. The pH(pzc) value was also determined by two ‘addition’ methods. Similar pH(pzc) values were obtained. The difference between the pH(pzc) and pH(iep) may be correlated to a loss of acidity that is due to using crushed-membrane powder to perform potentiometric measurements.     

Diethylenetriamine-grafted poly(glycidyl methacrylate) adsorbent for effective copper ion adsorption

Amine-functionalized adsorbents have attracted increasing interest in recent years for heavy metal removal. In this study, diethylenetriamine (DETA) was successfully grafted (through a relatively simple solution reaction) onto poly(glycidyl methacrylate) (PGMA) microgranules to obtain an adsorbent (PGMA-DETA) with a very high content of amine groups and the PGMA-DETA adsorbent was examined for copper ion removal in a series of batch adsorption experiments. It was found that the PGMA-DETA adsorbent achieved excellent adsorption performance in copper ion removal and the adsorption was most effective at pH>3 in the pH range of 1-5 examined. X-ray photoelectron spectroscopy (XPS) revealed that there were different types of amine sites on the surfaces of the PGMA-DETA adsorbent but copper ion adsorption was mainly through forming surface complexes with the neutral amine groups on the adsorbent, resulting in better adsorption performance at a higher solution pH value. The adsorption isotherm data best obeyed the Langmuir-Freundlich model and the adsorption capacity reached 1.5 mmol/g in the case of pH 5 studied. The adsorption process was fast (with adsorption equilibrium time less than 1-4 h) and closely followed the pseudo-second-order kinetic model. Desorption of copper ions from the PGMA-DETA adsorbent was most effectively achieved in a 0.1 M dilute nitric acid solution, with 80% of the desorption being completed within the first 1 min. Consecutive adsorption-desorption experiments showed that the PGMA-DETA adsorbent can be reused almost without any loss in the adsorption capacity.     

Modifying the surface of TEOS xerogel by metal ion Zn(II)

The removal of 2,4-dichlorophenol from aqueous solution by modified TEOS xerogel has been studied in batch experiments at varying pH (2.0–8.0). Tetraethyl orthosilicate (TEOS) xerogel recently has been considered as an adsorbent which is more active. Surface of the adsorbent due to the outward oxygen atoms in the molecular structure, is negatively charged, so this solid, shows good ability to adsorb metal ions. But because of the negative charge on the surface of the adsorbent, the anions, particularly organic anion compounds are not absorbed. To fix this problem, it can set the metal ions on the surface of the solid. By placing Zn ions on the xerogel, a positive charge on the surface of the adsorbent is made, which increases the ability of the adsorbent to attract 2, 4-dichlorophenol from aqueous solutions. Results show an increase in the adsorption by about 17% on empty xerogel, by about 60% in xerogel modified with metal Zn (II) ion.

     

Influence of temperature on the adsorption of mellitic acid onto kaolinite

The adsorption of mellitic acid (benzene-1,2,3,4,5,6-hexacarboxylic acid) onto kaolinite was investigated at five temperatures between 10 and 70 degrees C. Mellitic acid adsorption increased with increasing temperature at low pH (below pH 5.5), but at higher pH, the effect of increasing temperature was to reduce the amount adsorbed. Potentiometric titrations were conducted, adsorption isotherms were measured over the same temperature range, and the data obtained were used in conjunction with adsorption edge and ATR-FTIR spectroscopic data to develop an extended constant capacitance surface complexation model of mellitic acid adsorption. A single set of reactions was used to model all data at the five temperatures studied. The model indicates that mellitic acid sorbs via outer-sphere complexation to surface hydroxyl (SOH) groups on the kaolinite surface rather than to permanent charge sites. The reactions proposed are SOH + L6- + 2H+ <-->[(SOH2)+(LH)5-]4- and SOH + L(6-) <--> [(SOH)(L)6-]6-. Thermodynamic parameters calculated from the temperature dependence of the equilibrium constants for these reactions indicate that the adsorption of mellitic acid onto kaolinite is accompanied by a large entropy increase.     

Adsorption of arsenite and arsenate onto muscovite and biotite mica

Arsenite and arsenate sorption was studied on two silt-sized phyllosilicates, namely muscovite and biotite, as a function of solution pH (pH 3-8 for muscovite, and 3-11 for biotite) at an initial As concentration of 13 microM. The amount of arsenic adsorbed increases with increasing pH, exhibiting a maximum value, before decreasing at higher pH values. Maxima correspond to 3.22+/-0.06 mmol kg-1 As(V) at pH 4.6-5.6 and 2.86+/-0.05 mmol kg-1 As(III) at pH 4.1-6.2 for biotite, and 3.08+/-0.06 mmolkg-1 As(III) and 3.13+/-0.05 mmol kg-1 As(V) at pH 4.2-5.5 for muscovite. The constant capacitance surface complexation model was used to explain the adsorption behavior. Biotite provides greater reactivity than muscovite toward arsenic adsorption. Isotherm data obeyed the Freundlich or Langmuir equation for the arsenic concentration range 10(-7)-10(-4) M. Released total Fe, Si, K, Al, and Mg in solution were analyzed. Calculation of saturation indices by PHREEQC indicated that the solution was undersaturated with respect to aluminum arsenate (AlAsO42H2O), scorodite (FeAsO42H2O), and claudetite/arsenolite (As4O6).     

Mechanistic modeling of arsenic retention on natural red earth in simulated environmental systems

Arsenic retention on natural red earth (hereafter NRE) was examined as a function of pH, ionic strength, and initial arsenic loading using both macroscopic and spectroscopic methods. Proton binding sites on NRE were characterized by potentiometric titrations yielding an average pH(zpc) around 8.5. Both As(III)- and As(V)-NRE surface configurations were postulated by vibration spectroscopy. Spectroscopically, it is shown that arsenite forms monodentate complexes whereas arsenate forms bidendate complexes with NRE. When 4相似文献   

Adsorptive removal of arsenic from water by an iron-zirconium binary oxide adsorbent

Arsenate and arsenite may exist simultaneously in groundwater and have led to a greater risk to human health. In this study, an iron-zirconium (Fe-Zr) binary oxide adsorbent for both arsenate and arsenite removal was prepared by a coprecipitation method. The adsorbent was amorphous with a specific surface area of 339 m(2)/g. It was effective for both As(V) and As(III) removal; the maximum adsorption capacities were 46.1 and 120.0 mg/g at pH 7.0, respectively, much higher than for many reported adsorbents. Both As(V) and As(III) adsorption occurred rapidly and achieved equilibrium within 25 h, which were well fitted by the pseudo-second-order equation. Competitive anions hindered the sorption according to the sequence PO(4)(3-)>SiO(3)(2-)>CO(3)(2-)>SO(4)(2-). The ionic strength effect experiment, measurement of zeta potential, and FTIR study indicate that As(V) forms inner-sphere surface complexes, while As(III) forms both inner- and outer-sphere surface complexes at the water/Fe-Zr binary oxide interface. The high uptake capability and good stability of the Fe-Zr binary oxide make it a potentially attractive adsorbent for the removal of both As(V) and As(III) from water.     

Biosorption of chromium(VI) and arsenic(V) onto methylated yeast biomass

Yeast biomass was methylated in a 0.1 M HCl methyl alcohol solution at room temperature and the methylated yeast (MeYE) was applied to the adsorptive separation of Cr(VI) and As(V) anions from aqueous solutions. At near-neutral pH, while Cr(VI) and As(V) anions were scarcely adsorbed onto unmethylated yeast biomass, the amounts adsorbed increased with increasing methylation degree. The amount of Cr(VI) adsorbed onto MeYE was almost constant at pH 4-6 and decreased with increasing pH above pH 6. The amount of As(V) adsorbed onto MeYE was rather lower than that of Cr(VI) and it had a peak at about pH 7. A metal-binding model was used to describe the adsorption characteristics of Cr(VI) and As(V) on MeYE. The results showed that MeYE has two different types of adsorption sites. The saturated amount of Cr(VI) and As(V) adsorbed onto MeYE having methylation degree 0.94 was 0.55 mmol g(-1).     

Design and evaluation of functionalized multi-walled carbon nanotubes by 3-aminopyrazole for the removal of Hg(II) and As(III) ions from aqueous solution

Carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) were chemically modified with 3-aminopyrazole (MWCNTs-f) and applied as an efficient adsorbent to mercury and arsenic adsorption from aqueous solutions. The adsorbents were characterized by FT-IR, EDX, FE-SEM, TGA, and BET. The effects of pH, adsorbent dose, and initial ions concentration on the adsorption efficiency and the optimum conditions were investigated by central composite design. The optimum conditions were obtained at pH 7.6–7.9, adsorbent dose 20 mg, and initial ions concentration 20 ppm. So the maximum adsorption efficiencies in these conditions were 80.5 and 72.4% for the removal of Hg(II) and As(III) by MWCNTs-f, respectively. The quadratic model was used for the analysis of variance and indicated that adsorption of metal ions strongly depends on pH. Also, the pseudo-second-order model has been achieved from the adsorption kinetic studies. Furthermore, the experimental data were well fitted to the Langmuir isotherm and the maximum adsorption capacities obtained were 112 and 133 mg g^?1 for the adsorption of Hg(II) and As(III) by MWCNTs-f, respectively. Moreover, a thermodynamic study revealed that the adsorption reactions were spontaneous and endothermic with the increase in randomness. In addition, a desorption study showed the favorable regeneration ability of MWCNTs-f even after three adsorption–desorption cycles. Therefore, the MWCNTs-f adsorbent has good potential for the removal of Hg(II) and As(III) pollutants from aqueous solutions.     

CO adsorption on copper in alkaline electrolytes: an electrochemical and ellipsometric study

The influence of CO on the passive behavior of copper was analyzed in the potential region near the rest potential in borax solutions (pH 9.2) by cyclic voltammetry, ellipsometry, and surface charge determination techniques. The oxide formation is explained as a sequence of Cu(2)O growth, cation adsorption, Cu(II), and dissolution steps, similarly to previously reported investigations for the metal in free CO solutions. The CO adsorption hinders the cationic defect in the outer oxide layer and accelerates the Cu(2)O growth both at open circuit and in controlled potential experiments. The isoelectric point, iep, obtained at pH 10.8 for both the metal Cu and CuO particles in KCl solutions shifts to pH 10.1 for copper particles in the presence of CO. The iep indicates a CuO coating on Cu metallic particles in the absence of CO.     

Consolidation behavior in sedimentation of TiO(2) suspensions in the presence of electrolytes

The consolidation of TiO(2) suspensions (anatase and rutile) due to gravity sedimentation in the presence of electrolytes has been investigated as a function of pH. Sodium and barium nitrate were used as flocculating electrolytes. The particle interaction was related to the zeta potential and the thickness of the electrical double layer, kappa(-1), by utilizing the repulsive barrier in the classical DLVO theory. The stability of the suspensions was represented as the average final solids content of the sediment cake, phi(fin). The batch sedimentation process was followed by scanning the sample cell with X-rays, from which the solids content and the particle size were calculated. Generally, dense sediments, with phi(fin) up to volume fractions of 0.5, were found for stable suspensions. Flocculated suspensions produced sediments with low phi(fin). The phi(fin) was observed to increase linearly with increasing repulsive barrier. However, at pH values only slightly higher than the isoelectric point (pH(iep)) the phi(fin) remained low until it returned to linearity at a pH much higher than pH(iep). This was attributed to the stronger affinity of sodium than of nitrate for the particle surface, which may be explained by the higher negative hydration energy of sodium. The stronger affinity of sodium was also shown as unsymmetrical distribution of phi(fin) around pH(iep), with stronger flocculation at pH>pH(iep). The interpretation of phi(fin) as a function of the repulsive barrier (or kappa(-1)) also made it possible to distinguish between the adsorption mechanisms of ions from solution. Addition of electrolyte at a fixed low and high pH (surface positively and negatively charged, respectively) clearly showed the specificity in adsorption and consequent flocculation of the barium ion from the indifferent nitrate. Sodium was, however, again observed to flocculate the TiO(2) suspensions slightly more strongly than nitrate.     

Removal of As(V) by Cu(II)-, Ni(II)-, or Co(II)-doped goethite samples

The present study reports removal of As(V) by adsorption onto laboratory-prepared pure and Cu(II)-, Ni(II)-, and Co(II)-doped goethite samples. The X-ray diffraction patterns showed only goethite as the crystalline phase. Doping of ions in the goethite matrix resulted in shift of d-values. Various parameters chosen for adsorption were nature of adsorbent, percentage of doped cations in goethite matrix, contact time, solution pH, and percentage of adsorbate. It was observed that the pH(pzc) of the goethite surface depended on the nature and concentration of metal ions. The surface area as well as the loading capacity increased with the increase of dopant percentage in goethite matrix. A maximum loading capacity of 19.55 mg/g was observed for 2.7% Cu(II)-doped goethite. The adsorption kinetics for Ni(II), Co(II) and for undoped goethite attained a quasi-equilibrium state after 30 min with almost negligible adsorption beyond this time. In case of Cu(II)-doped goethite samples, the quasi-equilibrium state for As(V) adsorption was observed after 60 min. At each studied pH condition, it was observed that the percentage of adsorption of As(V) decreased in the order Cu(II)-doped goethite > or = Ni(II)-doped goethite > Co(II)-doped goethite > pure goethite. The adsorption followed: Langmuir isotherm, indicating monolayer formation.     

Protein adsorption characteristics of calcium hydroxyapatites modified with pyrophosphoric acids

Protein adsorption characteristics of calcium hydroxyapatite (Hap) modified with pyrophosphoric acids (PP(a)) were examined. The PP(a) modified Hap particles (abbreviated as PP-Hap) possessed anchored polyphosphate (PP: P-{O-PO(OH)}(n)-OH) branches on their surfaces. The proteins of bovine serum albumin (BSA: isoelectric point (iep)=4.7, molecular mass (M(s))=67,200 Da, acidic protein), myoglobin (MGB: iep=7.0, M(s)=17,800 Da, neutral protein), and lysozyme (LSZ: iep=11.1, M(s)=14,600 Da, basic protein) were examined. The zeta potential (zp) of PP-Hap particles as a function of pH overlapped; zp-pH curves were independent of the concentration of pyrophosphoric acids (abbreviated as [PP(a)]) used for modifying Hap surface. The saturated amounts of adsorbed BSA (Delta n(ads)(BSA)) were increased three-fold by the surface modification with PP(a) though they were independent of the [PP(a)]. Furthermore, the fraction of BSA desorption was independent of the [PP(a)]. This enhancement of BSA adsorption onto the PP-Hap is due to the hydrogen bonding between oxygen and OH groups of the PP-branches and functional groups of BSA molecules. In the case of LSZ, a more higher adsorption enhancement was observed; the saturated amount of adsorbed LSZ (Delta n(ads)(LSZ)) for Hap modified at [PP(a)]=6 mmol/dm(3) was nine-fold than that for Hap unmodified. This remarkable adsorption enhancement was explained by a three-dimensional binding mechanism; LSZ molecules were trapped inside of the PP-branches. Hence, a fraction of LSZ desorption was decreased with an increase in the [PP(a)]; as more PP-branches are presented on the surface the higher retardation of LSZ desorption was induced. It was expected from their small size that MGB adsorb between the PP-branches as well as LSZ. However, the amounts of adsorbed MGB (Delta n(ads)(MGB)) did not vary and were independent of the [PP(a)] due to the small numbers of functional groups of MGB. In addition, no dependence of the fraction of MGB desorption on the [PP(a)] was observed. The results of zp for all the protein systems supported the mode of protein adsorption discussed. The anchored structure of the PP-branches developed on the Hap surface to provide three-dimensional protein adsorption spaces was proved by a comparative experiment that was elucidating the effect of pyrophosphate ions for BSA adsorption onto Hap.     

pH-dependence of pesticide adsorption by wheat-residue-derived black carbon

The potential of black carbon as an adsorbent for pesticides in soils may be strongly influenced by the properties of the adsorbent and pesticides and by the environmental conditions. This study evaluated the effect of pH on the adsorption of diuron, bromoxynil, and ametryne by a wheat (Triticum aestivum L.) residue derived black carbon (WC) as compared to a commercial activated carbon (AC). The pH drift method indicated that WC had a point of zero charge of 4.2, much lower than that of 7.8 for AC. The density of oxygen-containing surface functional groups, measured by the Boehm titration, on WC was 5.4 times higher than that on AC, resulting in a pesticide adsorption by WC being 30-50% of that by AC, due to the blockage of WC surface by the waters associated with the functional groups. A small decrease (5.5%/unit pH) in diuron adsorption by WC with increase in pH resulted from increased deprotonation of surface functional groups at higher pH values. A much larger decrease (14-21%/unit pH) in bromoxynil adsorption by WC with increase in pH resulted from the deprotonation of both the adsorbate and surface functional groups of the adsorbent. The deprotonation reduced the adsorptive interaction between bromoxynil and the neutral carbon surface and increased the electrical repulsion between the negatively charged WC surface and bromoxynil anions. Deprotonation of ametryne with increase in pH over the low pH range increased its fraction of molecular form and thus adsorption on WC by 15%/unit pH. Further increase in pH resulted in a 20%/unit pH decrease in ametryne adsorption by WC due primarily to the development of a negative charge on the surface of WC. The pH-dependent adsorption of pesticides by black carbon may significantly influence their environmental fate in soils.