Adsorption and catalytic conversion of hydrocarbons on nanosized gold particles immobilized on alumina

Gold and nickel particles immobilized on alumina were prepared by the metal vapor synthesis and anionic adsorption methods. The dispersion of metals was determined by X-ray diffraction and transmission electron microscopy. The activity of nanoparticles, tested in model catalytic reactions of CCl₄ addition to multiple bonds and allyl isomerization of allylbenzene, changes in a wide range (from 1 to 3000 (mole of product) (mole of Au)⁻¹ h⁻¹) and is parallel to the chromatographically measured heats of adsorption of the corresponding unsaturated substrates. The heat of adsorption of unsaturated hydrocarbons can serve as a criterion for the efficiency of the gold-containing catalyst in olefin conversion. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2215–2218, October, 2005.     

Adsorption of copper(II) ions from aqueous solutions on alumina industrial wastes

Equilibrium adsorption of copper(II) ions on red mud (alumina industrial wastes) modified by various methods was studied. The effect exerted by the nature the modifier (NaHSO₄, NaCl + HCl, and H₂SO₄) on the sorption activity of red mud was determined.     

Adsorption of polycyclic aromatic hydrocarbons from aqueous solutions by modified periodic mesoporous organosilica

A novel procedure was developed for the synthesis of a periodic mesoporous organosilica (PMO), which was used to remove polycyclic aromatic hydrocarbons (PAHs) from aqueous solutions. Adsorption equilibrium isotherms and adsorption kinetics experiments were carried out in solutions of PAHs (2-60 mg L(-1)), using the PMO as adsorbent. Adsorption models were used to predict the mechanisms involved. The adsorption kinetics data best fitted the pseudo-first-order kinetic model for naphthalene, and to the pseudo-second-order model for fluorene, fluoranthene, pyrene, and acenaphtene. The intraparticle model was also tested and pointed to the occurrence of such processes in all cases. The isotherm models which best represented the data obtained were the Freundlich model for fluoranthene, pyrene, and fluorene, the Temkin model for naphthalene, and the Redlich-Peterson model for acenaphtene. PAHs showed similar behavior regarding kinetics after 24 h of contact between adsorbent and PAHs. FTIR, XRD, BET, and SEM techniques were used for the characterization of the adsorbent material.     

Adsorption of phenol and toluene from the gas phase and aqueous solutions on cellulose

Adsorption of toluene and phenol from the gas phase and aqueous solutions on various celluloses was studied.     

Extraction of gold,palladium and silver ions using organically modified silica-coated magnetic nanoparticles and silica gel as a sorbent

Microchimica Acta - Two new adsorbents were synthesized by covalently grafting 2,3-Bis(2-formylphenoxy)-propan-1-ol (BH) onto the surface of silica-coated magnetic nanoparticles and silica gel by a...     

Adsorption of mercury on gold and silver surfaces

In order to study the adsorption mechanism of Hg on Au and Ag substrates, thin film Au(111) and Ag(111) substrates were exposed to gaseous metallic mercury, while the mercury concentration, substrate temperature, and exposure length were varied. The resulting changes in the surface morphology of the substrates were studied with scanning tunneling microscopy (STM). The amount of adsorbed Hg required to cause saturation, i.e. a decrease in the adsorption rate was found to be dependent on the mercury concentration and substrate temperature. The observations lead to the conclusion that the adsorption includes place exchange processes and concerted adsorption of more than one Hg atom in one process. The results show that the collection efficiency of single-crystalline surfaces is a function of both mercury concentration and temperature. Therefore, results from measurements performed at different conditions using single-crystalline surfaces may not be comparable. Received: 3 February 1999 / Revised: 7 June 1999 / Accepted: 9 June 1999     

Solid phase extraction of uranium and thorium on octadecyl bonded silica modified with Cyanex 302 from aqueous solutions

A simple and reliable method for rapid extraction and determination of uranium and thorium using octadecyl-bonded silica modified with Cyanex 302 is presented. Extraction efficiency and the influence of various parameters such as aqueous phase pH, flow rate of sample solution and amount of extractant has been investigated. The study showed that the extraction of uranium and thorium increase with increasing pH value and was found to be quantitative at pH 6; and the retention of ions was not affected significantly by the flow rate of sample solution. The extraction percent were found to be 89.55 and 86.27 % for uranium and thorium, respectively. The maximal capacity of the cartridges modified by 30 mg of Cyanex 302 was found to be 20 mg of uranium and thorium. The method was successfully applied to the extraction and determination of uranium and thorium in aqueous solutions. The percentage recovery of uranium and thorium in a number of natural as well as seawater samples of Iran were also investigated and found to be in the range of 85–95 %.     

Adsorption properties of alumina modified with nickel nanoparticles

Adsorption properties of parent γ-alumina, and γ-alumina, modified with nickel nanoparticles (from 0.6 to 18 wt %), are investigated by dynamic sorption. N-hexane, benzene, chloroform, diethyl ether, chlorobenzene, and o-dichlorobenzene are used as test adsorbates. Adsorption isotherms are measured, and isosteric adsorption heats are calculated. Electron-donating and electron-accepting characteristics of surfaces of parent γ-alumina and γ-alumina, modified with Ni nanoparticles, are estimated. It is established that the surface of parent γ-alumina has mainly electron-accepting properties, while the surface of γ-alumina modified with Ni nanoparticles has electron-donating properties. It is shown that benzene and chlorobenzene are sorbed via physical adsorption on the parent and modified γ-alumina, and o-dichlorobenzene is sorbed via chemosorption.     

Adsorption of hydrophilic-hydrophobic block copolymers on silica from aqueous solutions

Adsorption of a water-soluble diblock copolymer, poly(t-butylstyrene)-sodium poly(styrene sulfonate) (PtBS-NaPSS), on silica surfaces in aqueous solutions was studied using ellipsometry and atomic-force microscopy (AFM). Molar masses of 87 000 and 160 000 g/mol were used. The block copolymers used were compositionally asymmetric, with large, hydrophilic, PSS blocks and small, hydrophobic, PtBS blocks. Adsorption could not be observed in pure water without added salt. When the NaCl concentration was increased to 1 mol/L, adsorption could be readily observed. The measured adsorbed amount at long times was significantly larger for the 87 000 diblock compared with that for a polyelectrolyte homopolymer of comparable molecular size, demonstrating the role played by the uncharged block in anchoring the diblock at the solid surface. The kinetics of adsorption showed a two-stage process, an initial diffusion-limited stage, followed by a slower buildup of surface coverage in a brush-limited stage. The number density of molecules at the surface was smaller for the higher molecular weight species, in agreement with simple scaling arguments.     

Accumulation and stripping behavior of silver ions at dl-dithiothreitol self-assembled monolayer modified gold electrodes

Silver ions can be entrapped at the dl-dithiothreitol (HSCH₂(CHOH)₂CH₂SH, DTT) self-assembled monolayer films modified gold electrodes. When the potential was made moving, an anodic peak was observed at about 0.23 V (vs. SCE). When the electrode Au/DTT was modified with dodecyl mercaptan further, more Ag (I) can be accumulated and the peak grows. Conditions, such as solution pH and supporting electrolyte, were optimized for Ag (I) determination. Under the selected conditions, i.e. 0.010 M pH 4.3 potassium hydrogen phthalate, preconcentration time of 5 min at open circuit, the anodic peak height is linear to the concentration of Ag (I) in the small range of 0.6-2.4 μM. The influence of some ions on the determination of Ag (I) was examined. The Br⁻ ion makes the peak decrease and NCS⁻ makes the peak increase. But the determination is not interfered by 1000-fold Pb²⁺, Cd²⁺, Hg²⁺, Fe³⁺, Ni²⁺, Co²⁺, Cu²⁺ and Sn²⁺ when EDTA was added into the solution. The mechanism involved was discussed.     

Adsorption of neodymium ions on activated charcoal from aqeous solutions

Summary A commercial activated charcoal has been tested as an adsorbent for the removal of neodymium ions from aqueous solutions. The adsorption behavior of neodymium ions on activated charcoal from aqueous solutions has been studied as a function of shaking time, neodymium ions concentration and concentration of different acids. Results reveal that the adsorption equilibrium is attained within 30 minutes, and diffusion of neodymium ions into the pores of activated charcoal controls the adsorption process. The adsorption process follows the first order kinetics. The Langmuir isotherm equation was obeyed well in the whole range of concentration studied. The influence of different cations and anions on the adsorption of neodymium ion from aqueous solutions have also been investigated. Approximately 98% of neodymium ions adsorbed onto activated charcoal could be recovered with 40 ml of 3M HNO₃ solutions.     

Adsorption of atrazine from aqueous electrolyte solutions on humic acid and silica

The adsorption of, the still widely used, herbicide atrazine on model soil components, such as humic acid and humic acid-silica gel mixtures, was investigated in a series of batch experiments, under different experimental conditions (ionic strength, temperature, and pH). The investigation aimed at obtaining an estimate of the contribution of each of the soil components on the adsorption of atrazine from aqueous solutions. The kinetics of atrazine adsorption on humic acid showed two steps: a fast step, of a few hours duration, and a second slow step, which continued for weeks. The kinetics of adsorption data gave a satisfactory fit to the Elovich equation. Τhe adsorption of atrazine on the test substrates was found to be reversible in all cases. The atrazine uptake data on the test substrates were fitted best with the Freundlich adsorption isotherm. The ionic strength of the atrazine aqueous solutions did affect the amount of the atrazine adsorbed on the test substrates, suggesting that electrostatic forces between atrazine molecules and soil play a significant role in the adsorption process. An increase of temperature resulted in a decrease of atrazine adsorption on humic acid at low atrazine equilibrium concentrations. However, for higher levels of equilibrium concentrations (≥3 mg/L) the amount of atrazine adsorbed onto the test substrate increased as temperature increased. The calculated isosteric enthalpies of adsorption ranged between slightly exothermic at low atrazine uptake and slightly endothermic at high atrazine uptake, all values being in the range of physisorption.     

Adsorption of ions on surfaces modified with brushes of polyampholytes

We apply density functional theory to study adsorption of ions, treated in the framework of the restricted primitive model (RPM), on surfaces modified by tethered polyampholytes. The residual electrostatic contribution to the free energy functional is approximated by using the approach proposed by Wang et al. [J. Phys.: Condens. Matter 23, 175002 (2011)] for simple nonuniform RPMs systems. Our research concentrates on the problems how the distribution of the charges within chains of polyampholytes changes the selectivity of adsorption of ions species, the structure of the surface layer, and its electric properties.     

Adsorption of non-ionic and cationic polymers on silica from their mixed aqueous solutions

The adsorption of polyvinylpyrrolidone (PVP) and poly(dimethyldiallylammonium chloride) (PDC) on silica from their mixed aqueous solutions has been investigated as a function of PVP concentration in the presence of PDC. The adsorption of PVP is almost unchanged with the feed concentration of PVP, while the adsorption of PDC decreases with increasing PVP concentration, especially at high concentrations of PDC. The conformation of PVP in the adsorbed layer on silica is relatively flat at low concentrations of PDC, but is extended in solution at high concentrations of PDC. The stability of the silica dispersion is low and the ζ potential is relatively small at low concentrations of PDC, whereas a stable dispersion is obtained at high concentrations of PDC and the ζ potential is large. Thus the stability of the dispersion is well correlated with the electrostatic repulsion and steric repulsion forces operating at the particles.     

Comparative study on Th(IV) sorption on alumina and silica from aqueous solutions

The effects of pH, ionic strength and concentration on the sorption of Th(IV) on alumina and silica were investigated and the sorption isotherms of Th(IV) on alumina and silica at different pH values were determined. It was found for both sorbents that the absorbability of silica is less than that of alumina. The relative sorption rate of silica is similar to that of alumina. The sorption edges are similar to each other, that the insensitivity of sorption to ionic strength is about the same. These similarities between the sorbents suggest that the speciation of Th(IV) in aqueous solutions plays a significant, but subtle role, in controlling the sorption process, because the charges of both sorbents are distinctly different. The mechanism of Th(IV) sorption on alumina is distinctly different from that of the sorptions of Cs⁺, Eu³⁺ and Yb³⁺ on alumina, and similar to that of the sorption of Co(II) on alumina.     

Adsorption of bismuth ions on graphite chemically modified with gallic acid

Graphite modified with gallic acid to form 'gallic acid-carbon' is demonstrated to be efficient for the removal of bismuth(III) ions from aqueous solutions. The uptake is demonstrated to be rapid but not to follow standard adsorption isotherm models. Instead, the uptake was found to be further promoted by the presence of the adsorbed metal. Additionally, the bismuth uptake showed linear dependence on the square of its concentration suggesting the possible formation of polymeric bismuth species. The gallic acid-carbon shows great promise as a relatively inexpensive material for solid-phase extraction and water purification with extraction efficiency close to 98%.     

Adsorption of mercury ions by mercapto-functionalized amorphous silica

Amorphous silicas have been functionalized by two different methods. In the heterogeneous route the silylating agent, 3-chloropropyltriethoxysilane, was initially immobilized onto the silica surface to give the chlorinated silica Cl-Sil. In a second reaction, multifunctionalized N,S donor compounds were incorporated to obtain the functionalized silicas, which are denoted as L-Sil-Het (where L=mercaptothiazoline, mercaptopyridine or mercaptobenzothiazole). In the homogeneous route, the functionalization was achieved through a one-step reaction between the silica and an organic ligand containing the chelating functions; this gave the modified silicas denoted as L-Sil-Hom. The functionalized silicas were characterized by elemental analysis, IR spectroscopy and thermogravimetry. These materials were employed as adsorbents for mercury cations from aqueous and acetone solutions at room temperature. The results indicate that, in all cases, mercury adsorption was higher in the modified silicas prepared by the homogeneous method. Figure     

Adsorption of organic liquids on alkaline earth-metal modified silica

Summary Adsorption properties of alkaline earth-metal modified silica beads were investigated by the gas-solid chromatography (GSC) method. Silica beads, obtained from colloidal material, were characterized by their surface areas, crystallinity and amount of sorbed alkaline earth cations. Retentions of several aliphatic, alicyclic, chlorinated, and aromatic compounds were measured in the temperature range from 373 to 453 K.The gas/solid partition coefficients, K₅, and the related thermodynamic functions at zero surface coverage were determined. The results show that the specific surface areas of modified silica samples remain practically constant, whereas the modification leads to a decrease of silica surface heterogeneity.