Adsorption of Cd(II) from aqueous solution onto pyrite

The physicochemical factors such as equilibrium time, solution pH, initial concentration of Cd(II), particle size and temperature that control the adsorption of Cd(II) from aqueous solutions onto pyrite has been investigated through batch experiments. Prior to this study, pyrite was characterized through chemical and XRD-analysis. The point of zero charge, pH_pzc was determined using the batch equilibrium technique and was found to be 6.4. The equilibrium time was 30 min at the solution pH of 6.0. The pH influence of Cd(II) adsorption was remarkable and maximum metal uptake was observed at 6.0 which is closer to pH_pzc. Under this weakly acidic condition Cd(II) ions are responsible for adsorption. Concentration dependence of metal uptake indicates that saturation of pyrite surface by adsorbate occurs at an initial Cd(II) concentration of 350 mg/L and the corresponding metal uptake was 576.5 mg/L of −150 mesh size pyrite at pH 6.0 and 30 °C. Particle size affects the adsorption capacity to a great extent and a decrease in particle diameter enhances metal uptake. The effect of temperature on adsorption performance reveals that the effective temperature for Cd(II) adsorption is 30 °C. The empirical Freundlich isotherm was applied to represent the adsorption process, which fits the experimental data quite well. The work reveals that natural pyrite is a very good choice as an adsorbent for the removal of toxic metals from industrial wastewater and bears significant industrial implications.     

Adsorption of Reactive Blue 114 dye by using a new adsorbent: Pomelo peel

This paper describes the removal of Reactive Blue 114 dye from aqueous solutions by using pomelo (Citrus grandis) peel. Pomelo peel can be described as a new, low cost, abundantly available adsorbent. The optimum adsorbent mass, dye concentration, contact time and pH were determined in this study. The parameters of Langmuir, Freundlich and Temkin adsorption isotherms were also obtained using concentrations of the dyes ranging from 1.0 to 200 mg/L. Maximum adsorption capacity was obtained as 16 mg/g at pH 2 and 303 K solution temperature. The adsorption process was observed to be reaching equilibrium after about 90 min.     

Removal of basic yellow cationic dye by an aqueous dispersion of Moroccan stevensite

The aim of this study was to investigate the adsorption of basic yellow, a cationic dye, from aqueous solution by natural stevensite, with 104 m²/g of specific surface area. The kinetics and the effects of several experimental parameters such as the pH of the solution, adsorbent dose and initial dye concentration were researched using a batch adsorption technique. The results showed that an alkaline pH favoured basic yellow adsorption and the adsorption reached equilibrium in about 20 min. It was concluded that the adsorption process was governed by the electrostatic interaction. The isothermal data were fitted by means of Langmuir and Freundlich equations, and a monolayer adsorption capacity of 454.54 mg/g was calculated. Finally, a good agreement was found between the pseudo-second order model and the experimental data. A high maximum adsorption capacity was obtained (526 mg/g) and a maximum surface density of ~ 9 dye molecules/nm² was estimated, involving a columnar arrangement of the adsorbed molecules.     

Silica‐Based NTPC‐Fly Ash for Dye‐Removal Application and Effect of Its Modification

Silica‐based fly ash (FA) received from the National Thermal Power Corporation (NTPC), India has been utilized for determining its dye‐adsorption capacity. The dye adsorption using the NTPC‐FA has been examined by varying the initial methylene blue dye concentration (7.5–150 μM) and initial solution‐pH (2.5–11.5). The dye‐adsorption capacity of NTPC‐FA has been found to be 0.43 mg/g. To increase the dye‐adsorption capacity, the NTPC‐FA is subjected to the hydrothermal treatment and typical washing cycles without and with the coating of sol–gel derived anatase‐titania. The hydrothermally treated NTPC‐FA and hydrogen titanate–silica composite thus obtained exhibit dye‐adsorption capacity higher than that of NTPC‐FA.     

Radiation synthesis of graphene oxide/composite hydrogels and their ability for potential dye adsorption from wastewater

A high yield of graphene oxide (GO) was chemically synthesized from graphite powder utilizing adjusted Hummer's method. The contents of acidic functional groups in GO were determined using potentiometric titration. Composite hydrogels dependent on graphene oxide/poly(2-acrylamido-2-methylpropanesulfonic acid)/polyvinyl alcohol (GO/PAMPS/PVA) were synthesized utilizing a ⁶⁰Co gamma irradiation source at different doses. The synthesized graphene oxide and composite hydrogels were portrayed via X-ray diffraction, thermogravimetric analysis, and Fourier transform infrared analysis. The morphology of composite hydrogels was characterized by scanning electron microscope. The gel % and swelling % for the prepared hydrogel demonstrated that the swelling % of hydrogel increased with raising AMPS content. Whereas the increment of GO and increasing the irradiation dose lead to a reduction in the swelling %. The influences of pH, GO percentage, initial dye concentration, the adsorbent dosage, contact time, and temperature on the adsorption of basic blue 3 dye were evaluated and the adsorption capacity was 194.6 mg/g at optimum conditions; pH = 6, GO/PAMPS/PVA composite hydrogels with 5 wt% of GO, initial dye concentration = 200 mg/L, adsorbent dose = 0.1 g, solution volume = 50 mL after 360 min at room temperature (25°C). The adsorption of dye onto the GO/PAMPS/PVA composite hydrogels follows Pseudo-second-order adsorption kinetics, fits the Freundlich adsorption isotherm model.     

Adsorption kinetics and mechanism of acid dye onto montmorillonite from aqueous solutions: Stopped-flow measurements

The adsorption of acid dye, namely, acid fuchsin (AF), onto sodium montmorillonite (Na⁺-Mt) from aqueous solutions was investigated. The adsorption process was very fast and attained equilibrium within 1 h, which was an economically favorable requisite. The Freundlich and Langmuir adsorption models were applied to describe the equilibrium isotherms and the isotherm constants were calculated. The experimental data fit well with Freundlich model rather than the Langmuir model. The equilibrium adsorption constant, K_c, was determined and used to calculate the enthalpy and entropy of the adsorption process. The adsorption kinetics was followed up using a stopped-flow spectrophotometer under pseudo-first-order conditions. The influence of initial dye concentrations, amount of sodium montmorillonite, and temperature on the rate of adsorption were studied. The activation energy of adsorption was calculated and indicated a chemical adsorption process. The enthalpy of adsorption confirmed an exothermic process. A proper mechanism for adsorption supported by X-ray and atomic absorption data was proposed.     

Process optimization of solvent based polybenzimidazole adhesive for aerospace applications

The use of adhesive bonding for high temperature applications is becoming more challenging because of low thermal and mechanical properties of commercially available adhesives. However, the development of high performance polymers can overcome the problem of using adhesive bonding at high temperature. Polybenzimidazole (PBI) is one such recently emerged high performance polymer with excellent thermal and mechanical properties. It has a tensile strength of 160 MPa and a glass transition of 425 °C. Currently, PBI is available in solution form with only 26% concentration in Dimethyl-acetamide solvent. Due to high solvent contents, the process optimization required lot of efforts to form PBI adhesive bonded joints with considerable lap shear strength. Therefore, in present work, efforts are devoted to optimize the adhesive bonding process of PBI in order to make its application possible as an adhesive for high temperature applications. Bonding process was optimized using different curing time and temperatures. Epoxy based carbon fiber composite bonded joints were successfully formed with single lap shear strength of 21 Mpa. PBI adhesive bonded joints were also formed after performing the atmospheric pressure plasma treatment of composite substrate. Plasma treatment has further improved the lap shear strength of bonded joints from 21 MPa to 30 MPa. Atmospheric pressure plasma treatment has also changed the mode of failure of composite bonded joints.     

A new application of Hydroxyapatite extracted from dromedary bone: Adsorptive removal of Congo red from aqueous solution

The aim of this paper is to evaluate the efficiency of the natural hydroxyapatite powder for anionic dye (Congo red) elimination from water and optimization of adsorption process parameters that are contact time (0-360 min), solution pH (4-9), initial dye concentration (400-2400 mg/l), and adsorbent dosage (0.4-20 g/l). Natural hydroxyapatite with high surface area was prepared from animal agriculture waste dromedary bone. X-ray diffraction, transmission electron microscopy, transform infrared spectroscopy, and elemental analysis characterizations of the powder prepared show a hexagonal structure, the irregular form of hydroxyapatite and presence of other elements as trace element. The results of adsorption tests demonstrated the high efficiency of natural hydroxyapatite for removal of Congo red from water solution whose maximum experimental capacity adsorption of Congo red by natural hydroxyapatite is 900 mg/g at pH 4.5, equilibrium time 240 min and adsorbent dosage 2 g/l. According to the correlation coefficient value, the pseudo-second order kinetic model identified the sorption mechanism of pollutant used on natural hydroxyapatite. The Freundlich isotherm is the best representative theoretical model of the dye molecules’ adsorption on the natural hydroxyapatite support.     

Removal of methylene blue from aqueous solution by sorption on lignocellulose-g-poly(acrylic acid)/montmorillonite three-dimensional cross-linked polymeric network hydrogels

Batch lignocellulose-g-poly(acrylic acid)/montmorillonite (LNC-g-PAA/MMT) hydrogel nanocomposites were applied as adsorbents. The nanocomposites were characterized by FTIR, XRD, SEM, and TEM. The results showed that montmorillonite (MMT) could react with the monomers and change the structure of polymeric network of the traditional superabsorbent materials, an exfoliated structure was formed in the nanocomposites. The effect of process parameters such as MMT content (wt%), contact time (t), initial concentration of dye solution (C ₀), adsorption temperature (T), and pH value (pH) of the dye solution for the removal of methylene blue (MB) from aqueous solution were also studied. The results showed that the adsorption capacity for MB increased with increasing contact time, initial dye concentration, and pH value, but decreased with increasing MMT content and temperature. The adsorption kinetics were better described by the pseudo-second-order equation, and their adsorption isotherms were better fitted for the langmuir equation. By introducing 20 wt% MMT into LNC-g-PAA polymeric network, the obtaining hydrogel composite showed the high adsorption capacity 1994.38 mg/g and economic advantage for MB. The desorption studies revealed that the composite provided the potential for regeneration and reuse after MB dye adsorption, which implied that the composite could be regarded as a potential adsorbent for cationic dye MB removal in a wastewater treatment process.     

Efficient adsorption of dyes from aqueous solution by poly(vinyl alcohol‐co‐ethylene) nanofibre membranes modified with β‐cyclodextrin

In this paper, highly absorbent poly(vinyl alcohol‐co‐ethylene) nanofibre membranes modified by β‐cyclodextrin were prepared to adsorb dyestuff from water, and 1,2,3,4‐butanetetra carboxylic acid was used as a crosslinking agent, which greatly enhanced the adsorption capacity of the modified membranes. Field emission scanning electron microscopy and Fourier Transform–infrared spectroscopy were used to characterise the surface morphology and chemical structures of the membranes. Methylene Blue (MB) was used as the main adsorbed dye. The effect of pH value and concentration of the MB solution were also investigated, and equilibrium adsorption reached 139.2 mg/g when the pH value was 10.0. The adsorption process fitted well with the Langmuir adsorption isotherm model and was in accord with the pseudo‐second‐order kinetic model. Moreover, the modified membranes proved to have selective adsorption, especially for some cationic dyes other than MB, and had the potential to be recycled multiple times.     

Modeling of precipitation of ultra-fine particles by pressure reduction over CO2-expanded liquids

A mathematical model has been developed to describe the process of precipitation of ultrafine particles by pressure reduction over gas (CO₂)-expanded liquids. A rapid pressure reduction over a CO₂-expanded organic solution, from 30–70 to 1 bar at 303 K decreases the solution temperature by 30–80 K in a very short span of time (0.5–1.5 min), which generates a rapid, high, and uniform supersaturation of the dissolved solute in the solution and facilitates precipitation of ultrafine particles. The model developed in this work estimates the supersaturation attained, nucleation and growth rates obtained during the pressure reduction over CO₂-expanded organic solutions, and the particle size distribution of the precipitated particles. Cholesterol has been chosen as a model solute to be precipitated, and acetone has been chosen as a solvent. A new method has been developed for prediction of equilibrium solubility of solute which is affected by a decrease in CO₂ mole fraction as well as a simultaneous decrease in solution temperature during pressure reduction. This method combines the semi-empirical approach of using the partial molar volume fraction of solvent in a CO₂-solvent binary mixture and solid–liquid equilibrium data for a solute–solvent system. Size distributions of the precipitated particles have been calculated assuming primary nucleation (homogeneous as well as heterogeneous nucleation) and diffusion-limited growth kinetics. The predicted mean average particle sizes are then compared with the size of cholesterol particles precipitated by pressure reduction of a CO₂-expanded acetone solution of cholesterol. The particle sizes predicted assuming heterogeneous nucleation are found to be closer to the experimentally observed particle sizes, indicating that the heterogeneous nucleation could be the main mechanism of nucleation, which could occur at the gas–liquid interface of the CO₂ bubbling out of CO₂-expanded solution during pressure reduction.     

Photocatalytic activity of nanocrystalline mesoporous-assembled TiO2 photocatalyst for degradation of methyl orange monoazo dye in aqueous wastewater

In this work, nanocrystalline mesoporous-assembled TiO₂ photocatalyst was synthesized by a sol–gel process with the aid of a structure-directing surfactant and employed for the photocatalytic degradation of methyl orange azo dye (monoazo dye), as compared to various commercially available non-mesoporous-assembled TiO₂ powders. The experimental results showed that the synthesized mesoporous-assembled TiO₂ nanocrystal calcined at 500 °C provided superior decolorization and degradation performance to the non-mesoporous-assembled commercial TiO₂ powders. In addition, several operational parameters affecting the decolorization and degradation of methyl orange, namely photocatalyst dosage, initial dye concentration, H₂O₂ concentration, and initial solution pH, were systematically investigated, using the mesoporous-assembled TiO₂ nanocrystal. The optimum conditions were a photocatalyst dosage of 7 g/l, an initial dye concentration of 5 mg/l, a H₂O₂ concentration of 0.5 M, and an initial solution pH of 4.7, exhibiting the highest decolorization rate of methyl orange.     

Various carbon-based MgAl2O4 adsorbents and their removal efficiency of CR dye and antibiotics in aqueous media: High selective adsorption capacity,performance prediction and mechanism insight

Various carbon -based MgAl₂O₄ (MAO) adsorbents were synthesized by a simple ultrasound irradiation technology with the activated carbon (AC), carbon quantum dots (CQDs), C₃N₄ (CN) and graphene oxide (GO) as carbon sources. The optimum synthesis conditions for the carbon -based MAO adsorbents were determined by the study of the addition of different types of carbon and different mass ratios of m_{Various carbon}: m_MAO = 2.5%, 5.0%, 7.5% and 10%. The carbon -based MAO adsorbents were used for the adsorption of Congo red (CR) dye, tetracycline hydrochloride (TCH), oxytetracycline hydrochloride (OCH), ciprofloxacin (CIP), naproxen sodium (NPS) and tetrabromobisphenol A (TBBPA) and the seven factors affecting the adsorption behavior were discussed, including the type of carbon, AC content, initial dye concentration (C_CR), adsorbent dosage (C_{carbon -based MAO adsorbents}), adsorption time (A_t), pH value and reaction temperature (T). The corresponding adsorption isotherm models such as Langmuir, Tempkin, Koble-Corrigan, Toth and Freundlich models and thermodynamics of carbon -based MAO adsorbents for the adsorption of CR dye were also studied. When pH = 7.8, C_CR = 200 mg/L, A_t = 90 min, T = 287 K and C_{AC 5.0 wt%-MAO} = 1 g/L, the removal rate of CR dye reaches 89.7%. The back propagation (BP) neural network model was used to predict the adsorption percentage of carbon-based MAO adsorbents, which was consistent with the experimental results. The high adsorption capacity of AC 5.0 wt%-MAO adsorbents for the adsorption of CR dye can be assigned to the synergistic effects of electrostatic interaction, intermolecular force, n-π interaction and hydrogen bonding, while for the adsorption of TCH, OCH and CIP can be ascribed to the electrostatic interaction. This study demonstrated a huge potential of carbon -based MAO adsorbents as an eco-friendly adsorbent for the adsorption of dyes and drugs.     

Study of competitive adsorption of malachite green and sunset yellow dyes on cadmium hydroxide nanowires loaded on activated carbon

Cadmium hydroxide nanowires loaded on activated carbon (Cd(OH)₂-NW-AC) was applied for removal of malachite green (MG) and sunset yellow (SY) in single and binary component systems. This novel material was characterized and identified by different techniques such as Brunauer, Emmett and Teller (BET), scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis. Unique properties such as high surface area (>1271 m² g⁻¹) and low pore size (<35 Å) and average particle size lower than 50 Å in addition to high reactive atom and presence of various functional groups make it possible for efficient removal of these two dyes. In the single component system in this study, maximum adsorption capacity of 80.6 for SY and 19.0 mg g⁻¹ for MG at 25 °C was reported. The Langmuir model had very well fit with the experimental data (R² > 0.996). A better agreement between the adsorption equilibrium data and mono-component Langmuir isotherm model was found. The kinetics of adsorption for single and binary mixture solutions at different initial dye concentrations were evaluated by the nonlinear first-order and second-order models. The second-order kinetic model had very well fit with the dynamical adsorption behavior of a single dye for lower and higher initial dye concentrations. SY and MG without spectra overlapping were chosen and analyzed with high accuracy in binary solutions. The effect of multi-solute systems on the adsorption capacity was investigated. The isotherm constants for SY and MG were also calculated in binary component systems at concentrations within moderate ranges, the Langmuir isotherm model satisfactorily predicted multi-component adsorption equilibrium data. The competitive adsorption favored the SY in the A mixture solution (both SY and MG concentration at 10 mg L⁻¹) and B mixture solution (25 mg L⁻¹ of SY and 10 mg L⁻¹ of MG). Also, in both cases, kinetic data was fairly described by two-step diffusion model. An endothermic and spontaneous nature for the adsorption of the dyes studied were shown from thermodynamic parameters in single and binary component systems.     

高通量聚醚砜纳滤膜的制备及对染料浓缩脱盐

以聚醚砜（PES）为膜材料,以嵌段式聚醚 Pluronic F127为添加剂,利用特制刮膜设备通过相转化法制备出高通量PES/Pluronic F127复合纳滤膜,并将其用于染料的浓缩脱盐。研究了添加剂含量、溶剂蒸发温度和蒸发时间对膜结构和膜性能的影响,考察了不同操作压力和操作温度下膜对染料的分离性能。扫描电镜 （SEM）、接触角、孔隙率数据和蛋白吸附测试结果表明,Pluronic F127改善了膜孔结构,提高了孔隙率,并且显著提高了膜的抗污染性能。纯水通量、截留率以及膜表面孔径表征结果表明,当Pluronic F127含量为3%、溶剂蒸发温度为90℃、 蒸发时间为18 s时,膜的分离性能最佳。在0.6 MPa下该膜对低分子量染料的截留率可达99.9%,且通量达到110.2 L·m^-2·h^-1,对NaCl的截留率仅为5.5%。在12 h的染料浓缩脱盐中,膜对染料的通量维持在较高水平且截留率始终保持在99%左右,具有良好的稳定性和抗污染性。     

Adsorption of methylene blue from aqueous solutions by modified expanded graphite powder

The modified expanded graphite (MEG) powder was used as a porous adsorbent for the removal of the cationic dye, methylene blue (MB), from aqueous solutions. The dye adsorption experiments were carried out with the bath procedure. Experimental results showed that the basic pH, increasing initial dye concentration and high temperature favored the adsorption. The dye adsorption equilibrium was attained rapidly after 5 min of contact time. Experimental data related to the adsorption of MB on the MEG under different conditions were applied to the pseudo-first-order equation, the pseudo-second-order equation and the intraparticle diffusion equation, and the rate constants of first-order adsorption (k₁), the rate constants of second-order adsorption (k₂) and intraparticle diffusion rate constants (k_int) were calculated, respectively. The experimental data fitted very well in the pseudo-second-order kinetic model. The thermodynamic parameters of activation such as Gibbs free energy, enthalpy, and entropy were also evaluated. The results indicated that the MEG powder could be employed as an efficient adsorbent for the removal of textile dyes from effluents.     

Weak Base Anion Exchanger Amberlite FPA51 as Effective Adsorbent for Acid Blue 74 Removal from Aqueous Medium – Kinetic and Equilibrium Studies

In this work, the macroporous anion exchange resin – Amberlite FPA51, is proposed as the effective adsorbent for the removal of Acid Blue 74 from aqueous solutions. The sorption mechanism was investigated under static conditions taking into account the phase contact time, solution pH, initial dye concentration, and temperature. The equilibrium data were fitted to the Langmuir, Freundlich, and Dubinin-Radushkevich isotherm models. The maximum monolayer capacity Q ₀ was 123.8 mg/g. The adsorption kinetics was found to follow the pseudo-second order model. The sorption energy was equal to 14.5 kJ/mol and indicated that the adsorption process of the dye may be described via a chemical anion-exchange mechanism.     

Removal of Reactive Blue 21 onto magnetic chitosan microparticles functionalized with polyamidoamine dendrimers

Chitosan/poly(amidoamine) (MCS/PAMAM) microparticles were prepared as magnetic adsorbents for removal of Reactive Blue 21 (RB 21) dye from aqueous solution. Characterization of these particles was carried out using scanning electron microscopy, Fourier transform-infrared spectroscopy, X-ray diffractometry and vibrating sample magnetometry. The results indicate that the magnetic chitosan microparticles (MCS) were functionalized with PAMAM dendrimers and maintained its intrinsic magnetic properties. The effects of initial pH, adsorbent dose, initial concentration, contact time and temperature on adsorption were investigated. Kinetic studies showed that the dye adsorption process followed a pseudo-second-order kinetic model but that the adsorption rate was also influenced by intraparticle diffusion. Equilibrium adsorption isotherm data indicated a good fit to the Langmuir isotherm. The maximum adsorption capacities obtained from the Langmuir model were 555.56, 588.24, 625.00 and 666.67 mg g⁻¹ at 303, 313, 323 and 333 K, respectively. The thermodynamic parameters revealed the feasibility, spontaneity and endothermic nature of the adsorption. Recycling experiments confirmed the relative reusability of the adsorbent.