Removal of Reactive Yellow 84 from aqueous solutions by adsorption onto hydroxyapatite

The adsorption of a reactive dye, Reactive Yellow 84, from aqueous solution onto synthesized hydroxyapatite was investigated. The experiments were carried out to investigate the factors that influence the dye uptake by the adsorbent, such as the contact time under agitation, absorbent dosage, initial dye concentration, temperature and pH of dye solution. The experimental results show that the amount of dye adsorbed increases with an increase in the amount of hydroxyapatite. The maximum adsorption occurred at the pH value of 5. The equilibrium uptake was increased with an increase in the initial dye concentration in solution. The experimental isotherm data were analyzed using Langmuir isotherm equation. The maximum monolayer adsorption capacity was 50.25 mg/g. The adsorption has a low temperature dependency and was endothermic in nature with an enthalpy of adsorption of 2.17 kJ mol⁻¹.     

Removal of cationic methylene blue and malachite green dyes from aqueous solution by waste materials of Daucus carota

In present study adsorption capacity of waste materials of Daucus carota plant (carrot stem powder: CSP and carrot leaves powder: CLP) was explored for the removal of methylene blue (MB) malachite green (MG) dye from water. The morphology and functional groups present were investigated by scanning electron microscope (SEM) and Fourier transform infrared (FTIR) spectroscopy. The operating variables studied were pH, adsorbent dose, ionic strength, initial dye concentration, contact time and temperature. Equilibrium data were analysed using Langmuir and Freundlich isotherm models and monolayer adsorption capacity of adsorbents were calculated. Kinetic data were studied using pseudo-first and pseudo-second order kinetic models and the mechanism of adsorption was described by intraparticle diffusion model.Various thermodynamic parameters such as enthalpy of adsorption ΔH°, free energy change ΔG° and entropy ΔS° were estimated. Negative value of ΔH° and negative values of ΔG° showed that the adsorption process was exothermic and spontaneous. Negative value of entropy ΔS° showed the decreased randomness at the solid–liquid interface during the adsorption of MB and MG onto CSP and CLP.     

Synthesis and characterization of silica gel from siliceous sands of southern Tunisia

The present work aimed to achieve valorization of Albian sands for the preparation of sodium silicates that are commonly used as a precursor to prepare silica gel. A siliceous sand sample was mixed with sodium carbonate and heated at a high temperature (1060 °C) to prepare sodium silicates. The sodium silicates were dissolved in distilled water to obtain high quality sodium silicate solution. Hydrochloric acid was then slowly added to the hydrated sodium silicates to obtain silica gel. The collected raw siliceous sands, as well as the prepared silica gels, were characterized by different techniques, such as X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal analysis (DSC). XRF confirmed that the detrital sand deposits of southern Tunisia contain high amounts of silica, with content ranging from 88.8% to 97.5%. The internal porosity varied between 17% and 22%, and the specific surface area was less than 5 m²/g. After the treatment described above, it was observed that the porosity of the obtained silica gel reached 57% and the specific surface area exceeded 340 m²/g. Nitrogen adsorption isotherms showed that the prepared silica gels are microporous and mesoporous materials with high adsorption capacities. These results suggest that the obtained silica gels are promising materials for numerous environmental applications.     

Adsorption and Equilibrium Isotherm Study of Removal of Copper (II) Ions from Aqueous Solution by Chemically Modified Abelmoschus esculentus Fibers

The present study explores surface modification of Abelmoschus esculentus by graft copolymerization reaction using acrylonitrile as a monomer and ascorbic acid/H₂O₂ as a redox initiator. Further, polyacrylonitrile grafted fibers were treated with hydroxylamine to convert the nitrile group of the grafted fiber into the amidoxime group to enhance adsorption of copper ions from wastewater. The graft copolymers and amidoximated fibers were characterized by FT-IR and FE-SEM. The effects of physicochemical parameters such as pH of the solution, initial metal ion concentration, and time on Cu(II) adsorption were studied to optimize condition for maximum adsorption. In addition, Langmuir, Freundlich, and Tempkin models were applied to describe the adsorption isotherm of Cu²⁺ ions.     

Evaluation of selective composite cryogel for bromate removal from drinking water

Bromate, which is a potential carcinogen, should be removed from drinking water to levels of less than 10 μg/L. A chitosan‐based molecularly imprinted polymer (MIP) and a sol–gel ion‐exchange double hydrous oxide (Fe₂O₃·Al₂O₃·xH₂O) adsorbent (inorganic adsorbent) were prepared for this purpose. The sorption behavior of each adsorbent including sorption kinetics, isotherms, effect of pH and selective sorption were investigated in detail. Sorption experimental results showed that the MIP adsorbents had better selectivity for bromate, even in the presence of high concentrations of nitrate, as compared to the inorganic adsorbent. It was found that pH does not affect the adsorption of bromate when using the inorganic adsorbent. Additionally, both adsorbents were immobilized in a polymeric cryogel inside plastic carriers to make them more practical for using in larger scale. Regeneration of the cryogels either containing MIP or inorganic adsorbents were carried out by 0.1 M NaOH and 0.1 M NaCl, respectively. It was found that the regenerated MIP and inorganic adsorbents could be used at least three and five times, respectively, without any loss in their sorption capacity.     

微乳液脱除油泥砂中的原油

以煤油为油相, 十二烷基苯磺酸钠(SDBS)为主表面活性剂, 正戊醇为助表面活性剂, 通过改变NaCl浓度分别制备出上相、 中相和下相3种类型的微乳液, 研究了其对油泥砂中原油的脱除效率, 考察了微乳液类型、 油泥砂处理量、 时间和温度等的影响. 结果表明, 油相在下相微乳液中的脱油效率最高, 在中相中次之, 在上相中最低, 且油相脱油率与油泥砂处理量间具有良好的线性关系; 在所考察的时间(10~60 min)和温度(20~70℃)范围内, 脱油效率变化幅度不显著, 表明该体系可对油泥砂进行常温快速脱油处理.     

Self-assembly of a silylated steroid-based organogelator and its use as template for the in situ sol-gel polymerization of tetraethyl orthosilicate

In this paper we report the synthesis of a new steroid-based low-molecular weight organogelator, the analysis of the self-assembled fibrilar network (SAFIN) and its use as template for the preparation of SiO₂ nanotubes. This novel steroidal organogelator has a unique structure among the well known family of steroid-based organogelators, the most important characteristic of this molecule is the presence of a silyl ether group at C-3 together with a 6β,19-oxo bridge. It was capable to gelate hydrocarbons and tetraethyl orthosilicate at very low concentrations (<1 wt %). An insight into the aggregation mechanism is provided revealing that complementary interaction between an α-oriented hydrogen bond donor and a β-oriented acceptor on the steroid skeleton is the driving force for the primary 1D self-assembly. The SAFIN was successfully used as template to grow silica nanotubes (external diameter: 40-60 nm, internal diameter: 7 nm and several micrometers length) through a catalyst-free in situ co-assembly polymerization process. Hydrogen bond or electrostatic interactions between the anionic silicate intermediate species and the SAFIN are proposed to be the driving force for templating.     

Dye Pollutants removal from Waste water using Metal Oxide Nanoparticle embedded Activated Carbon: An Immobilization study

This study evaluated the feasibility of Rhodamine-B dye (Rh B) removal from aqueous solution, using Lead-Iron Oxide nanoparticles Loaded Activated Carbon (FePbO@AC). The parameters like pH, contact time, adsorbent/adsorbate dosage and temperature on adsorption was studied. Optimized conditions are pH of 7.0, 25?min contact time, 50?ppm of dye concentration and 200?mg of adsorbent concentration. The kinetics of adsorption was calculated using pseudo-first-order, pseudo-second-order, and intra-particle diffusion models. The calculations revealed that the pseudo-second-order kinetic equation best-fit the adsorption data. The Langmuir isotherm model best fit the equilibrium data. The maximum sorption capacity (Q_max) for dye is 1000?mg Rh B/g FePbO@AC. Change in entropy (ΔS), Gibb’s free energy change (ΔG), and enthalpy (ΔH) were calculated for the adsorption of Rh B dye.     

Diffusion of water in gelatin studied by a new refractometric method

Summary A refractometric method designed to study the diffusive behaviour of low molecular compounds in solid macromolecular substances in the form of thin layers is described. The layer thickness is determined interferometrically in the apparatus. The system gelatin-water is studied at three different thicknesses, 31 , 40 and 82 , at 25°C. The diffusion process is found to be characterized by a diffusion coefficient which is dependent on concentration only, i. e. independent of time. Also, the concentration at the surface of the layer is found to change instantly from the initial concentration to the equilibrium concentration at the beginning of a diffusion experiment.

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Zusammenfassung Es wird eine refraktometrische Methode zur Untersuchung der Diffusion von niedermolekularen Verbindungen in festen makromolekularen Substanzen in Form dünner Schichten beschrieben. Die Schichtdicke wird im Gerät interferometrisch bestimmt. Das System Gelatine-Wasser ist bei drei verschiedenen Dicken (31 , 40 und 82 ) bei 25°C gemessen. Es zeigt sich, daß der Diffusionskoeffizient allein von der Konzentration, also z. B. u. a. unabhängig von der Zeit ist. Auch wechselt die Konzentration an der Oberflächenschicht augenblicklich von der anfänglichen zur Gleichgewichtskonzentration bei Beginn eines Diffusions-experimentes.

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With 13 figures and 2 tables     

Preparation and morphology of SiO2/PMMA nanohybrids by microemulsion polymerization

Polymethylmethacrylate/SiO2 nanocomposite particles were prepared through microemulsion polymerization by using the silica particles coated with 3-(trimethoxysilyl) propyl methacrylate (MSMA) in both acidic and alkaline conditions. Core-shell and other interesting morphology nanocomposite particles were obtained depending on the pH of the microemulsion, the amount of silanol, and the coupling agent concentration employed. Then, by combining a modified microemulsion polymerization process, i.e., an additional monomer-adding process, the solid contents of the polymer/inorganic nanocomposite microemulsion could greatly increase. Thus, by adjusting these parameters and polymerization process, it was possible to control the morphology and size of the nanocomposites.     

Study of adsorption and preconcentration by using a new silica organomodified with [3‐(2,2′‐dipyridylamine)propyl] groups

In this work, a silica surface chemically modified with [3‐(2,2′‐dipyridylamine)propyl] groups, named [3‐(2,2′‐dipyridylamine)propyl]silica (Si‐Pr‐DPA) was prepared, characterized, and evaluated for its heavy metal adsorption characteristics from aqueous solution. To our knowledge, we are the first authors who have reported the present modification. The material was characterized using infrared spectroscopy, SEM, and NMR ²⁹Si and ¹³C solid state. Batch and column experiments were conducted to investigate for heavy metal removal from dilute aqueous solution by sorption onto Si‐Pr‐DPA. From a number of studies the affinity of various metal ions for the Si‐Pr‐DPA sorbent was determined to follow the order Fe(III) > Cr(III) >> Cu(II) > Cd(II) > Pb(II) > Ni(II). Two standard reference materials were used for checking the accuracy and precision of the method. The proposed method was successfully applied to the analysis of environmental samples. This ligand material has great advantage for adsorption of transition‐metal ions from aqueous medium due to its high degree of organofunctionalization associated with the large adsorption capacity, reutilization possibility, and rapidity in reaching the equilibrium.     

Removal of Thiram from Aqueous Solutions

In this study activated carbon was used for the removal of thiram from aqueous solutions. Adsorption experiments were carried out as a function of time, initial thiram concentration and temperature. Equilibrium data fitted well to the Freundlich and Langmuir equilibrium models in the studied concentration range. Adsorption kinetics followed a pseudo second‐order kinetic model rather than pseudo first‐order model. The results from kinetic experiments were used to describe the adsorption mechanism. Both boundary layer and intraparticle diffusion played important role in the adsorption mechanism of thiram. Thermodynamic parameters (ΔG₀, ΔH₀, and ΔS₀) were determined and the adsorption process was found to be an endothermic one. The negative values of ΔG⁰ at different temperatures were indicative of the spontaneity of the adsorption process.     

Removal of copper from aqueous solutions by adsorption on activated carbons

The adsorption isotherms of Cu(II) ions from aqueous solutions in the concentration range 40–1000 mg l⁻¹ on two samples of granulated and two samples of activated carbon fibres containing varying amounts of associated oxygen have been reported. The adsorption isotherms are type I of BET classification showing initially a rapid adsorption tending to be asymptotic at higher concentrations. The amounts of oxygen associated with the carbon surface has been enhanced by oxidation with nitric acid and ammonium persulphate in the solution phase and with oxygen gas at 350°C and decreased by degassing of the oxidized carbon samples at 400, 650 and 950°C. The adsorption of Cu(II) ions increases on oxidation and decreases on degassing. The increase in adsorption on oxidation depends on the nature of the oxidative treatment while the decrease in adsorption on degassing depends on the temperature of degassing. This has been attributed to the increase in the carbon–oxygen acidic surface groups on oxidation and their decrease on degassing. Suitable mechanisms consistent with the results have been proposed.     

Removal of heavy metal ions from water by using poly(ethyleneglycol dimethacrylate-co-acrylamide) beads

Poly(ethyleneglycol dimethacrylate-co-acrylamide) (poly(EDGMA-co-AAm)) copolymer beads have been prepared for use in the separation Pb(II), Hg(II), and Cd(II), metal ions in aqueous solution by a batch equilibration technique. Adsorption capacity were increased with pH for Pb(II), Cd(II) and Hg(II) and then reached almost plateau value around 6.0. The high initial rate of metal ions uptake (<10 min) suggests that the adsorption occurs mainly at the bead surface. The metal uptake results show that poly(EGDMA-co-AAm) can be used for the adsorption of the following metals in the indicated order: Pb(II) > Cd(II) > Hg(II) expressed on a molar basis. However, when the uptake was expressed in terms of the amount of metal removed from solution was as follows: Pb(II) > Hg(II) > Cd(II). The beads still showed preference toward Pb(II) when this metal was in a mixture with Hg(II) and Cd(II). A linearized form of the Freundlich and the Langmuir isotherm model fits the experimental equilibrium concentration data of Hg(II) and Cd(II) better than isotherm type model of Pb(II). The recovery of the metal ions after adsorption and the regeneration of the adsorbent can be carried out by treatment of the loaded beads with either 0.5 M NaCl, or 1 M HNO₃.     

Silica Coating of Water-Soluble CdTe/CdS Core-Shell Nanocrystals by Microemulsion Method

"Using Te powder as a tellurium source and Na2S as a sulfur source, core-shell CdTe/CdS NPs were synthesized at 50 oC. UV-visible and photoluminescence (PL) spectra were used to probe the effect of CdS passivation on the CdTe quantum dots. As the thickness of CdS shell increases, there is a red-shift in the optical absorption spectra, as well as the PL spectra. The broadening absorption peaks and PL spectra indicate that the size distributions of CdTe/CdS NPs widen increasingly with the increase of CdS coverage. The PL spectra also show that the fluorescence intensity of CdTe QDs will increase when the particles are covered with CdS shell with ratio of S/Te less than 1.0, otherwise it will decrease if the ratio of S/Te is larger than 1.0. Furthermore, the (CdTe/CdS)@SiO2 particles were prepared using a water-in-oil microemulsion method at room temperature in which hydrolysis of tetraethyl orthosilicate leads to the formation of monodispersed silica nanospheres. The obtained (CdTe/CdS)@SiO2 particles show bright photoluminescence with their fluorescence intensity being enhanced 18.5% compared with that of CdTe NPs. TEM imaging shows that the diameter of these composite particles is 50 nm. These nanoparticles are suitable for biomarker applications since they are much smaller than cellular dimensions."     

Study of Phenolic Compounds Removal from Aqueous Solution by Polymeric Sorbent

This study describes preparation of polymeric sorbent and its use in removal of some phenolic compounds from aqueous solution. The polymer [poly(ethylene glycol dimethacrylate ‐ co‐methacrylic acid)] is stable both thermally and chemically. High temperature (200°C) and strong acidic or alkaline solutions (4 M HCl or NaOH) are not effective on the adsorption characteristics of polymer. Removal process of phenols is pH‐dependent and from the obtained results pH = 7.0 was selected as an optimum pH. Different parameters affecting sorption process were tested, and it was found that the kinetic of sorption is fast; therefore, column experiment at higher flow rates or batch experiment can be used. Methanol was selected as a washing solvent in column experiments. Capacity of sorbent for the studied compounds was tested and the following order was obtained: p‐chlorophenol > p‐aminophenol > phenol.     

Comparative of the removal of Pb2+, Cd2+ and Ni2+ by nano crystallite hydroxyapatite from aqueous solutions: Adsorption isotherm study

Release of heavy metal onto the water and soil as a result of agricultural and industrial activities may pose a serious threat to the environment. In this study, the adsorption behavior of nano hydroxyapatite with respect to Pb²⁺, Cd²⁺ and Ni²⁺ has been studied in order to consider its application to purity metal finishing wastewater. The batch method has been employed, using metal concentrations in solution ranging from 100 to 400 mg/L. The uptake capacity and distribution coefficients (K_d) were determined for the adsorption system as a function of sorbate concentration. The Langmuir, Freundlich, and Dubinin–Kaganer–Radushkevich (DKR) isotherms applied for sorption studies showed that the amount of metal sorbed on nano hydroxyapatite. It was found that the adsorption phenomena depend on charge density and hydrated ion diameter. According to the equilibrium studies, the selectivity sequence can be given as Pb²⁺ > Cd²⁺ > Ni²⁺. These results show that nano hydroxyapatite holds great potential to remove cationic heavy metal species from industrial wastewater.     

Isotherm, kinetic and thermodynamic studies of lead and copper uptake by H2SO4 modified chitosan

The kinetic and thermodynamic adsorption and adsorption isotherms of Pb(II) and Cu(II) ions onto H₂SO₄ modified chitosan were studied in a batch adsorption system. The experimental results were fitted using Freundlich, Langmuir and Dubinin–Radushkevich isotherms; the Langmuir isotherm showed the best conformity to the equilibrium data. The pseudo-first order, pseudo-second order and intraparticle diffusion kinetic models were employed to analyze the kinetic data. The adsorption behavior of Pb(II) and Cu(II) was best described by the pseudo-second order model. Thermodynamic parameters such as free energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°) were determined; the adsorption process was found to be both spontaneous and exothermic. No physical damage to the adsorbents was observed after three cycles of adsorption/desorption using EDTA and HCl as eluents. The mechanistic pathway of the Pb(II) and Cu(II) uptake was examined by means of Fourier transform infrared (FTIR) and Energy dispersive X-ray (EDX) spectroscopy. The equilibrium parameter (R_L) indicated that chitosan–H₂SO₄ was favorable for Pb(II) and Cu(II) adsorption.     

The triazine ring as a scaffold for the synthesis of new organogelators

The synthesis of new organogelators based on a triazine nucleus is described together with the analysis of the properties of the main compound 15. This compound revealed an efficient organogelator in both polar and apolar solvents and represents a promising precursor of other functionalized organogelators.