Low Concentration Adsorption Research Articles

Reactive dye adsorption onto a novel mesoporous carbon

A new mesoporous carbon (MCSG60) was developed using an inexpensive commercial mesoporous silica gel as a template and sucrose as the carbon source. The surface area, porosity and density of the carbon were determined. The material possesses a high specific surface area and pore volume accessible for most typical aqueous pollutants. The adsorbent material was tested in a batch dye adsorption system. The behaviour of three reactive dyes adsorbed onto MCSG60 was evaluated (Naphthol Blue Black, NBB; Reactive Black 5, RB5; and Remazol Brilliant Blue R, RBBR). The maximum adsorption capacities obtained for the dyes were: 270mg/g for NBB; 270mg/g for RB5; and 280mg/g for RBBR. Kinetic studies indicated that the adsorption process onto the mesoporous carbon was rapid and that equilibrium was reached in less than 1h for all the dye systems investigated. Further batch experiments showed MCSG60 successfully adsorbed the dyes over a wide pH range and at low adsorbate concentration. The adsorption potential of MCSG60 for dye removal was further evaluated using a fixed-bed adsorption column.

Modeling studies on simultaneous adsorption of phenol and resorcinol onto granular activated carbon from simulated aqueous solution

The modelling study on simultaneous adsorption of phenol and resorcinol onto granular activated carbon (GAC) in multicomponent solution was carried out at 303 K by conducting batch experiments at initial concentration range of 100–1000 mg/l. Three equilibrium isotherm models for multicomponent adsorption studies were considered. In order to determine the parameters of multicomponent adsorption isotherms, individual adsorption studies of phenol and resorcinol on GAC were also carried out. The experimental data of single and multicomponent adsorption were fitted to these models. The parameters of multicomponent models were estimated using error minimization technique on MATLAB R2007a. It has been observed that for low initial concentration of adsorbate (100–200 mg/l), modified Langmuir model represents the data very well with the adsorption constant ( Q 0), 216.1, 0.032 and average relative error (ARE) of 8.34, 8.31 for phenol and resorcinol respectively. Whereas, for high initial concentration of adsorbate (400–1000 mg/l), extended Freundlich model represents the data very well with adsorption constant ( K F) of 25.41, 24.25 and ARE of 7.0, 6.46 for phenol and resorcinol respectively. The effect of pH of solution, adsorbent dose and initial concentrations of phenol and resorcinol on adsorption behaviour was also investigated.

Adsorption kinetics and isotherm characteristics of selected endocrine disrupting compounds on activated carbon in natural waters

Bisphenol A (BPA) and ethynylestradiol (EE2), two representative endocrine disrupting compounds (EDCs), were tested for their adsorbabilities onto two powdered activated carbons (PACs). The main aim of the study was to create a prediction tool for the determination of the EDCs adsorbabilities at low ng.L−1 level. Single solute solution adsorption isotherms at high concentrations, for prediction purposes, and low concentrations, for verification of the prediction, were performed for one EDC/PAC couple. Over the whole range of concentration, results showed that the Langmuir-Freundlich model better suits the adsorption phenomenon than the Freundlich or Langmuir model. Kinetics experiments were carried out on the same EDC/PAC couple. HSDM modelling of single solute adsorption kinetics at high concentration allowed determining the kinetic coefficients kf and Ds; both were shown to dominate the mass transfer mechanism. Competitive adsorption isotherms at high and low concentrations showed that downward extrapolation of low concentration adsorption capacities from solely high concentration information results in acceptable error compared to the total range isotherm. The IAST-EBC approach combined with the Langmuir-Freundlich single solute model, for the target compound, and the Langmuir model, for the EBC, appears as an acceptable global model.

Fabrication of Ag nanoparticles by γ-irradiation: Application to surface-enhanced Raman spectroscopy of fungicides

This paper is concerned with the surface enhanced Raman scattering (SERS) activity of silver colloids obtained by a radiolytic method. Ag nanoparticles were successfully prepared by γ-radiolysis of Ag + aqueous solution containing t-BuOH or i-PrOH at room temperature without the addition of aggregating or stabilizing substances. The metal colloids were characterised by UV/vis spectroscopy and scanning electron microscopy. Many experimental conditions were tested (i.e. Ag + concentration, dose and OH scavenger alcohol) in order to obtain the best controlled size of nanoparticles as well as the high stability of colloidal silver with time. The use of relatively low irradiation doses and Ag + concentrations allowed to obtain very stable suspensions of Ag nanoparticles without adding any colloid stabiliser, a source of further spurious bands in the Raman spectra. The suitability of the γ-irradiated colloids in SERS spectroscopy was tested by using thiram, a known fungicide. Micro-SERS and SERS spectra of good quality were achieved at very low concentration of adsorbate, without the overlapping of impurities normally present in conventional citrate colloidal suspensions of Ag nanoparticles.

First-principles studies of water adsorption on graphene: The role of the substrate

We investigate the electronic properties of graphene upon water adsorption and study the influence of the SiO2 substrate in this context using density functional calculations. Perfect suspended graphene is rather insensitive to H2O adsorbates, as doping requires highly oriented H2O clusters. For graphene on a defective SiO2 substrate, we find a strongly different behavior: H2O adsorbates can shift the substrate’s impurity bands and change their hybridization with the graphene bands. In this way, H2O can lead to doping of graphene for much lower adsorbate concentrations than for free hanged graphene. The effect depends strongly on the microscopic substrate properties.

Chromatographic determination of the differential isosteric adsorption enthalpies and differential entropies on ordered silica materials

The adsorption properties of the ordered mesoporous siliceous materials: MCM-41C16 (denoted as C16), MCM-41C16-SH and MCM-41C16-NH 2 (known as MCMs) having different surface functionalities were studied by inverse gas chromatography to assess their suitability for adsorption of analytes from gas and liquid phases. Polar and non-polar adsorbates were employed. The differential isosteric enthalpies, −Δ H ads, and differential entropies, −Δ S ads, of adsorption of different ‘molecular probes’ were determined chromatographically. A mathematical link between the −Δ H ads, and −Δ S ads magnitudes and experimental data was derived through an Antoine-type equation. The present studies have been entirely restricted to the region of low adsorbate concentration. The problem of the interrelationship between the −Δ H ads, and −Δ S ads values, known as the ‘thermodynamic compensation effect’, and interpretation of chromatographic data for the adsorption of different adsorbates on the MCMs have been considered in the light of both experimental data obtained in the present studies and the data available in the literature for siliceous adsorbents with randomly ordered structures. It was shown chromatographically that there is substantial parallelism between the magnitudes of the differential isosteric enthalpy and differential entropy for some ‘molecular probes’ chromatographed on C16 and its derivatives. Complementary information was obtained by atomic-force microscopy (AFM), X-ray photoelectron spectroscopy and X-ray diffraction (XRD) spectroscopy.

Adsorption of volatile organic compounds onto porous clay heterostructures based on spent organobentonites

AbstractModel spent cetyltrimethylammonium bromide (CTMAB)-bentonite, and cetyl pyridinium chloride (CPC)-bentonite used for sorbing p-nitrophenol (PNP) from wastewater, as well as virgin CTMAB-bentonite and CPC-bentonite, were employed as the starting materials to prepare porous clay heterostructures (PCHs). The BET surface areas and total pore volumes of the PCHs based on these spent and virgin organobentonites (PNP-CTMAB-PCH, CTMAB-PCH, PNP-CPC-PCH and CPC-PCH) are 661.5 m2/g and 0.25 cm3/g, 690.4 m2/g and 0.27 cm3/g, 506.3 m2/g and 0.30 cm3/g, and 525.4 m2/g and 0.30 cm3/g, respectively. These values approximate those of activated carbon (AC), at 731.4 m2/g and 0.23 cm3/g, and are much larger than those of bentonite and CTMAB-bentonite, at 60.9 m2/g and 0.12 cm3/g, and 3.7 m2/g and 0.0055 m2/g, respectively. The PCHs have slightly higher adsorption capacities for benzene and CC14 than AC at higher relative pressures despite their comparatively lower benzene and CC14 adsorption capacity at lower relative pressures. The existence of PNP in organobentonites also enhances the volatile organic compounds (VOCs) adsorption capacity of PCHs at lower adsorbate concentrations, although some adsorption capacity is lost at higher concentrations. The hydrophobicity order of the adsorbents is: CTMAB-bentonite > AC > PCHs > bentonite. The micro- to mesoporous pore sizes, superior VOC adsorption properties, thermal stability to 750°C and hydrophobicity and negligible influences of PNP on PCHs make spent PNP-containing organobentonites ideal starting materials for synthesis of PCHs and especially attractive adsorbents for VOC sorption control.

Ampicillin adsorption by some antacids

In certain situations of peptic ulcers ampicillin has been co-administered with bismuth carbonate with an implication for adsorption of the ampicillin. To quantify this effect the kinetics and extent of adsorption of ampicillin by some commonly used antacids were measured; these are bismuth carbonate, magnesium trisilicate and aluminium hydroxide. The adsorption of ampicillin by bismuth carbonate followed the Langmuir adsorption isotherm, which suggests chemisorptions. It was characterized by a strong adsorption at a low adsorbate (ampicillin) concentration but the % adsorption decreased with increase in adsorbate concentration, which is a feature of a saturated monolayer adsorption. On the other hand, the adsorption by magnesium trisilicate and aluminium hydroxide followed the Freundlich adsorption isotherm characterized by a low adsorption at a low adsobate concentration but this increased slightly with increase in adsorbate concentration, suggesting a weak physical adsorption. The adsorption capacities (mg/g) of the adsorbate were 1.64 (bismuth carbonate) 0.04 (magnesium carbonate) and 0.03 (aluminium hydroxide). Bismuth carbonate thus gave by far the highest degree of adsorption. The conclusion is that the co-administration of ampicillin and bismuth carbonate in the treatment of certain peptic ulcers is erroneous.

Adsorption of anionic dyes on aluminium treated corn cobs powder

Untreated textile effluents are highly toxic as they contain a large number of metal complex dyes. The effluents discharged from various textile and dyeing industries are hazardous coloured effluents. The uptake of anionic dyes by aluminium treated corn cobs powder have been studied by hatch technique. Maximum adsorption of dyes was observed at low adsorbate concentration, acidic pH and 30° temperature. The adsorption process follows Freundlich sorption isotherm and the process was found to he exothermic as adsorption decreases with increasing temperature.

Colour Removal from Dye Wastewater Using Sugar Cane Dust as an Adsorbent

Decolouration of dilute solutions of basic dye stuff was carried out using sugar cane dust as an adsorbent. It was found that low adsorbate concentration, small particle size of the adsorbent, a temperature of 25°C and a pH value of 7.5 for the medium all favour the removal of dye from aqueous solutions. The percentage of dye adsorbed by sugar cane dust decreased from 96.48% to 83.32% and from 90.78% to 78.02% for Malachite Green and Methylene Blue, respectively, when the concentration of the dye was increased from 6 mg/l to 12 mg/l. Similarly, the adsorption of Crystal Violet and of Rhodamine B also decreased with increasing dye concentration in the solutions. The amount of dye (Malachite Green and Rhodamine B) adsorbed decreased from 3.04 mg/g to 2.57 mg/g and from 2.53 mg/g to 2.17 mg/g when the temperature of the solution was increased from 25°C to 45°C, indicating that the process was exothermic. The values of the adsorption capacity (Q0) of Malachite Green and Rhodamine B on the adsorbent varied from 4.87 to 4.08 and from 4.26 to 3.82, respectively, as the temperature increased from 25°C to 45°C. The equilibrium data obey the requirements of the Langmuir adsorption model, demonstrating the formation of a monolayer of dye molecules on the outer surface of the adsorbent. The variation in the extent of removal with pH has been explained on the basis of surface ionisation and complexation. Various thermodynamic parameters (ΔG0, ΔH0 and ΔS0) have also been determined in order to explain the results.

Surface Enhanced Raman Scattering from Acridine on Copper Electrodes at Low Adsorbate Concentration

AbstractSurface enhanced Raman spectra of acridine in a concentration range 6.7·10−9 to 3.6·10−3 M were obtained on a copper electrode in a chloride‐containing solution at pH 2.5. A conclusion was made that acridine adsorbs as an ion pair formed from acridinium cation and chloride anion. An adsorption isotherm for acridine on an activated copper electrode was obtained.

Evaluation of Competitive Adsorption in Anaerobic GAC Reactors

This study primarily investigates the role of competition in completely mixed anaerobic granular activated carbon (GAC) reactors treating a synthetic wastewater consisting of acetic acid, phenol, and o-cresol, and also addresses dual substrate biodegradation. The fate of the biodegradable nonadsorbable substrate followed very closely that of the biodegradable adsorbable substrate. As adsorption complemented biodegradation in this system, with the two being oppositely influenced by the GAC replacement rate, the removal of both biodegradable substrates exhibited both a maximum and minimum at GAC residence times of 30 and 12 days, respectively. On comparing the experimental capacities for o-cresol, which resisted biodegradation in the GAC reactors, with the o-cresol isotherm capacities, the effect of phenol competition for adsorption was found to be negligible when the effluent o-cresol concentrations were orders of magnitude higher than the concentrations of the biodegradable phenol. Competition effects decreased the adsorptive capacities of the reactors` GAC for o-cresol when phenol and o-cresol concentrations were of the same order of magnitude, although phenol sorptive capacities were predicted much more closely than at very low phenol concentration. The ideal adsorbed solution theory (IAST) was found to fairly describe the competition for adsorption between phenol and o-cresol despite some discrepancies betweenmore » the experimental and the model-predicted capacities at low adsorbate concentrations.« less

IR Studies of adhesion promoters. Part 1.—Methoxytrimethylsilane on silica at the solid/liquid interface

The adsorption of methoxytrimethylsilane on silica immersed in heptane or carbon tetrachloride primarily involves hydrogen-bonding interactions between surface silanol groups and the O atoms of MeOSiMe3 molecules. A 1 : 1 interaction is dominant for isolated SiOH groups but adjacent interacting pairs of silanol groups adsorb a single silane molecule at low adsorbate concentrations, changing to pairs of silane molecules with increasing concentration. Hydrogen-bonded silane is removed from the surface by evacuation at 293 K but removal of solvent initially promotes a low level of chemisorption resulting in —SiOMe and —SiOSiMe3 on the silica.

Quantitative structure-activity relationship using molecular connectivity for the activated carbon adsorption of organic chemicals in water

Quantitative structure-activity relationships (QSARs) for estimating the adsorption of organic chemicals on activated carbon were developed using molecular connectivity. The QSARs were based on adsorption data for 363 chemicals [expressed as ( X/ C) min] obtained from six literature sources, representing a wide range of aromatic and aliphatic chemical classes. In order to test the predictive capabilities of the QSAR equations and to illustrate their use, the QSARs were applied to data from three additional data sources. The existence of divergent literature values for the same chemicals was addressed in one QSAR by a “dummy variable” to identify the data source. The resulting QSARs are well suited for use in the water treatment industry because they are based on a wide range of chemicals, use readily calculated parameters, and represent adsorption at low adsorbate concentrations. However, in applying QSARs based on literature data, it is imperative to consider the relevance of the data source to one's own investigative situation.

Toxic effects of omega chrome red ME and its treatment by adsorption

Toxic effects of Omega Chrome Red ME, a popular textile dye, on the nitrogen fixing cyanobacterium Nostoc calcicola were studied. The growth of N. calcicola was found to be suppressed at 10 and 20 mg liter −1 initial concentrations of dye, whereas a low initial concentration of 5 mg liter −1 slightly favors growth. Removal of the dye was carried out by adsorption using some cheap and unconventional adsorbents like coal, fly ash, wollastonite, and china clay. It has been observed that, in all cases, the low adsorbate concentration, the low temperature, and an acidic medium favor the dye removal process. The process of uptake follows first-order adsorption rate expression and obeys Langmuir's model of adsorption. The removal process is also partially diffusion controlled. Thermodynamic and pH studies were run to explain the results.

Thermodynamic limitations for pigment adsorption during the bleaching of triglyceride oils

Triglyceride oils are complex multi-component mixtures, so that the adsorption of chlorphylls is limited by co-adsorption of other components. Efforts to evaluate the effect of co-adsorbates on the capacity of adsorbents for a chlorophyll model compound were undertaken for two-component systems by means of the Ideal Dilute Solution Theory, (IDST). Single-component isotherms were measured for adsorption of the model compounds protoporphyrin IX dimethyl ester (PPIX), tripalmitin, trilinolein, stearic acid and linolenic acid onto both acid-activated clay (ABE) and an experimental adsorbent (EXP1) in a non-interacting solvent (CH2Cl2). Adsorbent affinities, as qualitatively measured by the initial slope of the isotherms, were in the order porphyrin (pKb = 4.8) » fatty acid (pKb ∼ 20.0) > triglyceride (pKb ∼ 20.5) for EXP1, while for ABE the affinities were in the order porphyrin » fatty acid, triglyceride. These affinities roughly correlate with the adsorbate basicity so that the mechanism of adsorption is acid-base reaction. Isotherms for binary mixtures of PPIX with the other adsorbates were calculated from single-component isotherm data by using IDST. Calculated isotherms for the adsorption of low concentrations of prophyrin in the presence of higher concentrations of triglyceride or fatty acid dramatically demonstrate the ability of these co-adsorbates to suppress the adsorption of porphyrin. Thus, competitive adsorption has a predominant effect on the behavior of adsorbents in the edible oil application. Improvements in adsorbent selectivity or the removal of co-adsorbing components are necessary to substantially improve bleaching performance.

Fly ash for the treatment of Zn(II) rich effluents

The ability of fly ash to remove Zn(II) from water by adsorption has been tested at different concentrations, temperatures and pH of the solution. It was found that low adsorbate concentration, small particle size of adsorbent and higher temperature favoured the removal of Zn(II) from aqueous solution. The Langmuir isotherm was used to represent the equilibrium data at different temperatures. The apparent heat of adsorption has been found to be 17.325 Kcal mol−1, which indicates the process to be endothermic. The uptake of Zn(II) is diffusion controlled and the mass transfer coefficient is 3.56 × 10−5 cm s −1.The maximum removal was noted at pH 7.5.

A molecular dynamics study of cage-to-cage migration in sodium Y zeolite: role of surface-mediated diffusion

The details of cage-to-cage migration have been obtained from an analysis of the molecular dynamics trajectory of a probe adsorbate. It is observed that particles utilize the region within a radius of 2 angstrom from the window center but with diffusion taking place predominantly at 1.6 angstrom from the window center and a potential energy of nearly -12 kJ/mol. A barrier of about 0.5 kJ/mol is observed for surface-mediated diffusion. Surprisingly, for diffusion without surface mediation for a particle going from one cage center to another, there is an attractive well near the window instead of a barrier. At low adsorbate concentrations and room temperature, the predominant mode for cage-to-cage migration is surface-mediated diffusion. The analysis suggests that particles slide along the surface of the inner walls of the alpha-cages during migration from one cage to another.

Removal of chrome dye from aqueous solutions by mixed adsorbents: Fly ash and coal

The removal of Omega Chrome Red ME (a popular chrome dye) from its aqueous solutions by adsorption on a homogeneous mixture of fly ash and coal in different proportions has been carried out. It has been noted that low adsorbate concentration, small particle size of adsorbent, low temperature and acidic medium favour the removal of the dye. A 100% removal of the said dye was achieved at 10 mg1 −1, 30°C, 2.0 pH and 53 μm particle size, using a 1:1 ratio of fly ash and coal. The kinetics and mass transfer studies were made using the models suggested by Lagergren and McKay et al. respectively. The equilibrium data fit well in the Langmuir model of adsorption, showing the formation of monolayer coverage of dye molecules at the outer surface of the adsorbent. Effect of temperature was explained on the basis of solubility and chemical potential of the adsorbate. An attempt has been made to explain the results thus obtained on the basis of various physiochemical properties of the solid-solution interface involved in the process of removal.

Use of a Polynomial Equation for Analyzing Low-Concentration Adsorption Measurements of Ethane on Activated Carbons

Abstract A polynomial equation is used for analyzing ethane adsorption measurements in the low-concentration region carried out by a dynamic chromatographic method for two microporous activated carbons. For low gas-phase concentrations, this equation reduces to Henry's law. It is shown that this polynomial equation gives a good description of hydrocarbon adsorption on microporous activated carbons.