Effects of synthesis temperature on the microstructures and basic dyes adsorption of titanate nanotubes

The adsorption of two basic dyes (Basic Green 5 (BG5) and Basic Violet 10 (BV10)) onto titanate nanotubes (TNT) that were prepared via a hydrothermal method with different synthesis temperatures was studied to examine the potential of TNT for the removal of basic dyes from aqueous solution. Effects of synthesis temperature on the microstructures of TNT were characterized with transmission electron microscopy (TEM), X-ray diffraction (XRD), and nitrogen adsorption–desorption isotherms. For synthesis temperature greater than 160 °C, the microstructure of titanate might transform from nanotube into nanorod accompanying with the sharp decrease in the titanate interlayer spacing, BET surface area, and pore volume. Effects of the pore structure variation on the basic dyes adsorption of TNT were discussed. Moreover, the adsorption mechanisms of basic dyes from aqueous solution onto TNT were examined with the aid of model analyses of the adsorption equilibrium and kinetic data of BG5 and BV10. The regeneration of TNT was also briefly discussed.     

Kinetics and equilibrium studies for the adsorption of Acid Red 57 from aqueous solutions onto calcined-alunite

The adsorption of Acid Red 57 (AR57) onto calcined-alunite was examined in aqueous solution in a batch system with respect to contact time, pH and temperature. The first-order, pseudo-second-order kinetic and the intraparticle diffusion models were used to describe the kinetic data and the rate constants were evaluated. The experimental data fitted very well the pseudo-second-order kinetic model and also followed the intraparticle diffusion model up to 90 min. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms and the isotherm constants were also determined. The equilibrium data are successfully fitted to the Langmuir adsorption isotherm. The Langmuir isotherm constant, K(L), was used to evaluate the changes of free energy, enthalpy and entropy of adsorption for the adsorption of AR57 onto calcined-alunite. The results indicate that calcined-alunite could be employed as low-cost material for the removal of acid dyes from textile effluents.     

Sorption of reactive dye from aqueous solution on biomass fly ash

This study investigates the adsorption behavior of Reactive Black 5 (RB) and Reactive Yellow 176 (RY) from aqueous solution on coal fly ash (FA-CO), HCl-treated coal fly ash (TFA-HCl), and biomass fly ash (FA-BM). In preliminary study, the FA-BM showed the greatest dye adsorption capacity of both dyes, compared to FA-CO and TFA-HCl. Hence only for the FA-BM, the effects of various experiment parameters (e.g. solution pH, ionic strength, initial dye concentration, contact time) were spectrophotometrically determined. At the final pH of 8.1-8.5, the adsorption capacity of both dyes on the FA-BM was maximum and decreased above or below this pH. A positive effect of salt addition on the dye adsorption capacity was observed. The adsorption capacity of dye on the FA-BM increased with increasing C0. The equilibrium data of both dyes on the FA-BM were fitted to both Langmuir and Freundlich isotherms, but the experimental data of the RB was found to be little better fitted by the Langmuir model. The sorption data was good fit with the pseudo-second-order kinetic model. These results indicate that biomass fly ash is an interesting alternative for dye removal from the wastewater.     

Absorbents based on maleic anhydride-modified cellulose fibers/diatomite for dye removal

In this work, an absorbent consisting of the maleic anhydride-modified cellulose beads combined with alkali-treated diatomite (MCDBs) was prepared in an attempt to remove basic dyes. An appropriate amount of calcium carbonate was added during the formation of MCDBs to increase the pore structure under an acidic condition. The synthesized MCDBs were characterized with FT-IR, TGA, and BET. The degree of carboxylation of MCDBs was quantified using a polyelectrolyte titration method. The removal of basic dyes such as methylene blue (MB) and methyl violet (MV) from aqueous solution was systematically investigated. The influence of pH, shaking time, and temperature on the removal process was identified. The results indicated that the MCDBs had a strong adsorption capacity toward basic dyes. The adsorption capacity increased from 51.6 to 116.6 mg/g for MB, depending on the initial concentration of the dye. A similar trend was also found for MV, i.e., adsorption increased from 30.5 to 61.1 mg/g. The experimental data fitted two kinetic models; the results demonstrated that the adsorption of MB and MV onto the MCDBs fits the pseudo-second-order model very well. The removal efficiencies of the basic dyes under the optimal conditions were up to 97.5 %. The adsorption data were also fitted using Langmuir, Freundlich, and Temkin isotherms, separately. It was found that the adsorption process for the basic dyes was better described by the Langmuir isotherm model.     

Adsorption of Acid Red 57 from aqueous solutions onto surfactant-modified sepiolite

The adsorption of Acid Red 57 (AR57) onto surfactant-modified sepiolite was investigated in aqueous solution in a batch system with respect to contact time, pH and temperature. The surface modification of surfactant-modified sepiolite was controlled using the FTIR technique. The pseudo-first-order, pseudo-second-order kinetic models and the intraparticle diffusion model were used to describe the kinetic data and the rate constants were evaluated. The experimental data fitted very well the pseudo-second-order kinetic model and also followed the intraparticle diffusion model up to 90 min, whereas diffusion is not only the rate controlling step. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms and the isotherm constants were also determined. The Freundlich model agrees with experimental data well. The activation energy, change of free energy, enthalpy and entropy of adsorption were also evaluated for the adsorption of AR57 onto surfactant-modified sepiolite. The results indicate that surfactant-modified sepiolite could be employed as low-cost material for the removal of textile dyes from effluents.     

Adsorption of anionic dyes on ammonium-functionalized MCM-41

Investigations were conducted in a batch reactor system to study the adsorption behavior of four anionic dyes (Methyl orange (MO), Orange IV (OIV), Reactive brilliant red X-3B (X-3B), and Acid fuchsine (AF)) on ammonium-functionalized MCM-41 (NH(3)(+)-MCM-41) from aqueous medium by varying the parameters such as contact time, initial dye concentration, pH and competitive anions. Dye adsorption was broadly independent of initial dye concentration. The intraparticle diffusion model was the best in describing the adsorption kinetics for the four anionic dyes on NH(3)(+)-MCM-41. The adsorption data for the four dyes were well fitted with the Langmuir model. The electrostatic interaction was considered to be the main mechanism for the dye adsorption. Finally, it was observed that the anion of soft acid inhibited the adsorption capacity significantly.     

The removal of basic dyes from aqueous solutions using agricultural by-products

The adsorption of two basic dyes, namely, Malachite Green and Methylene Blue onto both agricultural by-products (i.e. rice bran and wheat bran) has been investigated in this study. The adsorption of both basic dyes was solution pH-dependent. The kinetic experimental data were analyzed using four kinetic equations including pseudo-first-order equation, pseudo-second-order equation, external diffusion model and intraparticle diffusion model to examine the mechanism of adsorption and potential rate-controlling step. The best-fit equation was identified using normalized standard deviation. The Langmuir and Freundich isotherms were used to fit the equilibrium data and the results showed that the Langmuir isotherm exhibited a little better fit to the Methylene Blue adsorption data by both adsorbents while the Freundlich isotherm seemed to agree better with the Malachite Green adsorption. The Gibbs free energy changes at 20 degrees C were calculated and the obtained values supported the conclusion that two dyes molecules adsorbed by physical processes. The effects of particle size, adsorbent concentration and solution ionic strength on the adsorption of the two basic dyes were also studied.     

酰腙类化合物修饰MCM-41吸附Cr(Ⅵ)性能

合成了2-羰基丙酸-4-甲基苯甲酰腙(简称酰腙1)和2-羰基丙酸-4-硝基苯甲酰腙(简称酰腙2)两种酰腙化合物,采用红外光谱法和X射线单晶衍射法对其进行了表征,并将其应用于修饰MCM-41分子筛中。用两种酰腙修饰后的MCM-41分子筛吸附废水中的铬(Ⅵ),考察了吸附时间、溶液pH值、吸附剂用量和温度对吸附效果的影响,同时对吸附过程进行了热力学和动力学拟合。测试结果表明,在吸附时间为40 min,分子筛加入量为0.3 g,溶液pH值为6,溶液温度为20℃时,吸附效果最好,MCM-41-酰腙1和MCM-41-酰腙2对铬(Ⅵ)的去除率分别可以达到97.6%和98.2%。吸附过程是熵减小的放热过程,反应过程分别遵循准一级反应和准二级反应动力学。     

Batch study of liquid-phase adsorption of methylene blue using cedar sawdust and crushed brick

This paper presents a study on the batch adsorption of basic dye, methylene blue, from aqueous solution (40 mg L(-1)) onto cedar sawdust and crushed brick in order to explore their potential use as low-cost adsorbents for wastewater dye removal. Adsorption isotherms were determined at 20 degrees C and the experimental data obtained were modelled with the Langmuir, Freundlich, Elovich and Temkin isotherm equations. Adsorption kinetic data determined at a temperature of 20 degrees C were modelled using the pseudo-first and pseudo-second-order kinetic equations, liquid-film mass transfer and intra-particle diffusion models. By considering the experimental results and adsorption models applied in this study, it can be concluded that equilibrium data were represented well by a Langmuir isotherm equation with maximum adsorption capacities of 142.36 and 96.61 mg g(-1) for cedar sawdust and crushed brick, respectively. The second-order model best describes adsorption kinetic data. Analysis of adsorption kinetic results indicated that both film- and particle-diffusion are effective adsorption mechanisms. The Influence of temperature and pH of the solution on adsorption process were also studied. The extent of the dye removal decreased with increasing the solution temperature and optimum pH value for dye adsorption was observed at pH 7 for both adsorbents. The results indicate that cedar sawdust and crushed brick can be attractive options for dye removal from dilute industrial effluents.     

Equilibrium and kinetic adsorption study of Basic Yellow 28 and Basic Red 46 by a boron industry waste

In this study, the adsorption characteristics of Basic Yellow 28 (BY 28) and Basic Red 46 (BR 46) onto boron waste (BW), a waste produced from boron processing plant were investigated. The equilibrium adsorption isotherms and kinetics were investigated. The adsorption equilibrium data were analyzed by using various adsorption isotherm models and the results have shown that adsorption behavior of two dyes could be described reasonably well by a generalized isotherm. Kinetic studies indicated that the kinetics of the adsorption of BY 28 and BR 46 onto BW follows a pseudo-second-order model. The result showed that the BW exhibited high-adsorption capacity for basic dyes and the capacity slightly decreased with increasing temperature. The maximum adsorption capacities of BY 28 and BR 46 are reported at 75.00 and 74.73mgg(-1), respectively. The dye adsorption depended on the initial pH of the solution with maximum uptake occurring at about pH 9 and electrokinetic behavior of BW. Activation energy of 15.23kJ/mol for BY 28 and 18.15kJ/mol for BR 46 were determined confirming the nature of the physisorption onto BW. These results indicate that BW could be employed as low-cost material for the removal of the textile dyes from effluents.     

Molecular simulation of fluid adsorption in buckytubes and MCM-41

We report grand canonical Monte Carlo (GCMC) molecular-simulation studies of argon and nitrogen in models of two novel adsorbents, buckytubes and MCM-41. Buckytubes are monodisperse carbon tubes with internal diameters of 1–5 nm and a regular pore structure. MCM-41 is one member of a new family of highly uniform mesoporous aluminosilicates produced by Mobil. The pore size of MCM-41 can be accurately controlled within the range 1.5-I.0 nm. The adsorption of argon in a buckytube and the adsorption of nitrogen in two different MCM-41 pores are studied at 77 K. Both fluids are modeled as Lennard-Jones spheres. and an averaged fluid-wall potential, dependent only on the distance of the adsorbed molecule from the center of the tube or pore is used. Isotherms and isosteric heats are calculated. Layering transitions and a hysteresis loop are observed for the buckytube and good agreement is found between simulated and experimental isotherms for the MCM-41 systems.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

金属Pt团簇在氧化钛修饰MCM-41中的组装

采用光沉积的合成方法将纳米金属Ｐｔ组装于氧化钛修饰ＭＣＭ－４１孔道中,并对合成的样品进行了ＸＲＤ、ＸＰＳ、ＵＶ－vis、Ｎ₂吸附－脱附等结构表征．光电子能谱表明组装的Ｐｔ呈金属状态;Ｎ_２吸附－脱附数据表明组装于孔道中的Ｐｔ虽然使ＭＣＭ－４１的ＢＥＴ比表面和孔容下降,但是由于Ｐｔ的组装量较小,使其对孔径分布的影响较小．由于Ｐｔ的引入,使其紫外－可见光漫反射吸收光谱与氧化钛修饰的ＭＣＭ－４１不同．     

Assessment of adsorption-desorption characteristics of adsorbents for adsorptive desiccant cooling system

The performance of various dehumidification materials was assessed in terms of effective adsorption amount of water vapor based on the adsorption isotherms to find a suitable dehumidification element for an economical adsorptive desiccant cooling system being developed. The effective adsorption amount is an important factor for regeneration at lower temperatures. Three types of silica gels, S(a), S(b), and S(c), with different pore volumes and pore size distributions, and zeolite with various molar ratios of Si/Al, 5.6, 29, 47, 91, and 220, prepared from a Y-type zeolite treated with hydrochloric acid, an activated carbon with silica gel added to improve the hydrophobic surface, and MCM-41 were examined. Silica gels having effective adsorption amounts of 0.25 g/g, and activated carbon with silica gel added were assessed to be candidate desiccant materials.     

Removal of basic dye by modified Unye bentonite, Turkey

The adsorption behavior of crystal violet (CV(+)) from aqueous solution onto raw (RB) and manganese oxide-modified (MMB) bentonite samples was investigated as a function of parameters such as initial CV(+) concentration, contact time and temperature. The Langmuir, Freundlich and Dubinin-Radushkevich (D-R) adsorption models were applied to describe the equilibrium isotherms. The Langmuir monolayer adsorption capacities of RB and MMB were estimated as 0.32 and 1.12 mmol/g, respectively. The mean adsorption energy derived from D-R isotherm for MMB showed that the type of adsorption of dye molecules on this material may be defined as chemical adsorption. The adsorption rate was fast and more than half of the adsorbed-CV(+) was removed in the first 55 min for RB and 5 min for MMB at the room temperature. The pseudo-first-order, pseudo-second-order kinetic and the intraparticle diffusion models were used to describe the kinetic data and rate constants were evaluated. The thermodynamic parameters such as DeltaH, DeltaS and DeltaG were found 117.41 kJ/mol, 41.50 J/(molK), -5.07 kJ/mol (RB) and 21.19 kJ/mol 98.34 J/(molK), -7.84 kJ/mol (MMB) at 295.15 K, respectively. The quite high adsorption capacity and high adsorption rate of MMB will provide an important advantage for using of this material in basic dye solution.     

Novel nanocomposites based on gelatin/HPET/chitosan with high performance acid red 150 dye adsorption

In this study, the properties of gelatin and chitosan are combined in the presence of hydrolyzed poly(ethylene terphthalate), HPET, and laponite to produce a novel hybrid natural-synthetic material for anionic dyes removal applications. Adsorption studies of acid red 150 from aqueous solution with respect to the initial dye concentration, temperature, time, pH, and sorbent dosage were investigated. The Langmuir adsorption model was applied to describe the equilibrium isotherms. The prepared nanocomposites were characterized using different techniques, such as FTIR, DSC, SEM, and TEM. The suitability of the adsorbent was tested by fitting the adsorption data with Langmuir isotherm. The results showed that the adsorption of AR150 was increased with an increasing in both of the dye and chitosan concentrations.     

纳米Au团簇在氧化钛修饰的介孔分子筛MCM-41中的组装

以钛酸丁酯为ＴｉＯ_２前驱体,使ＴｉＯ_２均匀分散于纯硅介孔分子筛ＭＣＭ－４１的介孔孔道内表面,利用ＴｉＯ_２光学性质将ＡｕＣｌ－４还原为Ａｕ（０）并组装于氧化钛修饰的ＭＣＭ－４１孔道中．对所合成的Ａｕ负载的氧化钛修饰的ＭＣＭ－４１进行了ＸＲＤ,ＸＰＳ,Ｎ_２吸附－脱附曲线,及固体ＵＶ－Ｖｉｓ漫反射等多种结构表征．由ＸＰＳ谱和固体ＵＶ－Ｖｉｓ漫反射吸收光谱的ｐｌａｓｍｏｎ吸收峰证明Ａｕ团簇呈现０价的金属状态．     

Removal of cationic dyes from aqueous solution using magnetic multi-wall carbon nanotube nanocomposite as adsorbent

A magnetic multi-wall carbon nanotube (MMWCNT) nanocomposite was synthesized and was used as an adsorbent for removal of cationic dyes from aqueous solutions. The MMWCNT nanocomposite was composed of commercial multi-wall carbon nanotubes and iron oxide nanoparticles. The properties of this magnetic adsorbent were characterized by scanning electron microscopy, X-ray diffraction and BET surface area measurements. Adsorption characteristics of the MMWCNT nanocomposite adsorbent were examined using methylene blue, neutral red and brilliant cresyl blue as adsorbates. Experiments were carried out to investigate adsorption kinetics, adsorption capacity of the adsorbent and the effect of adsorption dosage and solution pH values on the removal of cationic dyes. Kinetic data were well fitted by a pseudo second-order model. Freundlich model was used to study the adsorption isotherms. The prepared MMWCNT adsorbent displayed the main advantage of separation convenience compared to the present adsorption treatment.     

Characterization and use of high surface area activated carbons prepared from cane pith for liquid-phase adsorption

Carbonaceous adsorbents with controllable surface areas were chemically activated with KOH at 780 degrees C from char that had been carbonized from cane pith at 450 degrees C. The pore properties including the BET surface area, pore volume, pore size distribution, and mean pore diameter of these activated carbons were characterized and derived using the t-plot method based on N(2) adsorption isotherms. The activated cane pith carbons, with KOH/char ratios of 2-6, exhibited BET surface areas ranging from 912 to 2299 m(2) g(-1). The scanning electron microscopic (SEM) observations revealed that the surface morphology of honeycombed holes on all activated cane pith carbons was significantly influenced by the KOH/char ratio. The adsorption kinetics and equilibrium isotherms of acid blue 74, methylene blue, basic brown 1, p-nitrophenol, p-chlorophenol, p-cresol, and phenol from water at 30 degrees C on the activated carbons were studied. The adsorption kinetics were suitably described by a simplified kinetic model, the Elovich equation. All adsorption equilibrium isotherms were in agreement with the Langmuir equation, and were used to compare the covered area (S(c)/S(p)) of the activated carbons at different KOH/char ratios. The high-surface-area activated carbons were proven to be promising adsorbents for pollution control and for other applications.     

Removal of direct blue-106 dye from aqueous solution using new activated carbons developed from pomegranate peel: adsorption equilibrium and kinetics

The use of cheap, high efficiency and ecofriendly adsorbent has been studied as an alternative source of activated carbon for the removal of dyes from wastewater. This study investigates the use of activated carbons prepared from pomegranate peel for the removal of direct blue dye from aqueous solution. A series of experiments were conducted in a batch system to assess the effect of the system variables, i.e. initial pH, temperature, initial dye concentration adsorbent dosage and contact time. The results showed that the adsorption of direct blue dye was maximal at pH 2, as the amount of adsorbent increased, the percentage of dye removal increased accordingly but it decreased with the increase in initial dye concentration and solution temperature. The adsorption kinetics was found to follow pseudo-second-order rate kinetic model, with a good correlation (R(2)>0.99) and intra-particle diffusion as one of the rate determining steps. Langmuir, Freundlich, Temkin, Dubinin-RadushKevich (D-R) and Harkins-Jura isotherms were used to analyze the equilibrium data at different temperatures. In addition, various thermodynamic parameters, such as standard Gibbs free energy (DeltaG degrees ), standard enthalpy (DeltaH degrees ), standard entropy (DeltaS degrees ), and the activation energy (E(a)) have been calculated. The adsorption process of direct blue dye onto different activated carbons prepared from pomegranate peel was found to be spontaneous and exothermic process. The findings of this investigation suggest that the physical sorption plays a role in controlling the sorption rate.