Cellulose nanocrystals as promising adsorbents for the removal of cationic dyes

Cellulose nanocrystals (CNCs) prepared from cellulose fibre via sulfuric acid hydrolysis was used as an adsorbent for the removal of methylene blue (MB) from aqueous solution. The effects of pH, adsorbent dosage, temperature, ionic strength, initial dye concentration were studied to optimize the conditions for the maximum adsorption of dye. Adsorption equilibrium data was fitted to both Langmuir and Freundlich isotherm models, where the Langmuir model better described the adsorption process. The maximum adsorption capacity was 118 mg dye/g CNC at 25 °C and pH 9. Calculated thermodynamic parameters, such as free energy change (ΔG = ?20.8 kJ/mol), enthalpy change (ΔH = ?3.45 kJ/mol), and entropy change (ΔS = 0.58 kJ/mol K) indicates that MB adsorption on CNCs is a spontaneous exothermic process. Tunability of the adsorption capacity by surface modification of CNCs was shown by oxidizing the primary hydroxyl groups on the CNC surface with TEMPO reagent and the adsorption capacity was increased from 118 to 769 mg dye/g CNC.     

Scalable sulfonate-coated cotton fibers as facile recyclable adsorbents for the highly efficient removal of cationic dyes

Adsorbents that exhibit a high adsorption capacity and facile recyclability are considered promising materials for dye wastewater remediation. In this work, a novel sulfonate-decorated cotton fiber was fabricated as a recyclable adsorbent for the highly efficient removal of cationic dyes. Herein, poly(sodium p-styrene sulfonate-co–N-methylol acrylamide) (P(SSNa-co-NMAM)) with SSNa units as adsorption sites and NMAM units as thermal-crosslinking points was synthesized for the modification of cotton fibers. As expected, the as-obtained P(SSNa-co-NMAM)-coated cotton fibers (PCFs) presented outstanding adsorption capacities toward cationic dyes, even in the simulated effluents. The processes of cationic dye absorbing onto the PCFs were well fitted by the Langmuir isotherm model and pseudo-second-order kinetics. The thermodynamic study revealed that the adsorption reaction of the cationic dyes onto PCF was spontaneous, and the efficiency of adsorption was more desirable at higher temperatures. The maximum adsorption capacities of PCF toward methylene blue (MEB), rhodamine B (RhB), and malachite green (MG) were 3976.10, 2879.80, and 3071.55 mg/g, respectively. The dye removal mechanism was ascribed predominantly to electrostatic interactions. Moreover, the adsorption capacity of the PCFs toward cationic dyes was slightly influenced by the pH of the solutions because of the sulfonate moieties, which exhibit stability under acidic and alkaline conditions. Furthermore, the recyclability and reusability of the as-prepared PCFs were satisfactory and good mechanical properties and thermal stability were observed compared to those of pristine cotton fibers. Given the aforementioned results, the as-obtained PCFs are highly promising as ideal adsorbents for the remediation of dye-contaminated wastewater.

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Synthesis of poly (acrylamide-co-aconitic acid) adsorbents by gamma-irradiation,characterization, adsorption studies and application for cationic dyes removal

In this study, acrylamide (AAm)/aconitic acid (ACA) copolymers were prepared with two different mol% of aconitic acid 4%, 17% and were irradiated with gamma irradiation at different irradiation doses (4 - 25kGy). The percent yield was assigned by gravimetrical method. The effect of irradiation dose, pH and involved amounts of monomers (AAm/ACA) in hydrogels on swelling properties were investigated. The conversion of monomers to hydrogels was 100% at 25kGy. Poly(acrylamide-co-aconitic acid) P(AAm/ACA) hydrogels have been used for the adsorption of some aqueous solutions of dyes such as Methylene Blue (MB) and Safranine-O (S). The hydrogels were swollen in distilled water at pH 3, 5, 7, 8 and in aqueous solutions of dyes. The initial swelling rates of hydrogels are increased by increasing of pH. The effects of concentration of the aqueous solutions of dye and hydrogel composition on the adsorption were investigated. The adsorption is increased and changed depending on the structure of dye and composition of hydrogel.     

Thermodynamic parameters for adsorption equilibrium of heavy metals and dyes from wastewater with low-cost adsorbents

This note revisits the literature evaluating the thermodynamic parameters of adsorption equilibrium uptakes of heavy metals and dyes from water and wastewater streams using low-cost adsorbents derived from agricultural waste, industrial wastes, inorganic particulates, or some natural products. We highlighted the possible flaws in some adsorption studies when their thermodynamic parameters were assessed, since compensation effects during enthalpy and entropy evaluation were possibly overlooked.     

Thermodynamic study of fatty acids adsorption on different adsorbents

This work has as objective the study about the adsorption behavior of fatty acids (acetic, propionic, and butyric) on activated carbon and on modified and unmodified montmorillonite clays as a function of temperature and initial concentration of the adsorbate, through adsorption isotherms and their thermodynamic parameters (ΔG, ΔH, and ΔS). The activated carbon presented a higher adsorption capacity due to its relatively large surface area, compared to others adsorbents. The polar characteristic of fatty acids decreased with the increase in the length of non-polar hydrocarbon chain, improving the affinity between the activated carbon (non-polar adsorbent) and the acids. The adsorption capacity of modified montmorillonite (polar adsorbent) was favored due to the presence of the organic cation among its layers, which make the surface more hydrophobic and organophilic when compared to the unmodified montmorillonite surface. The amount of fatty acids adsorbed in the adsorbents surface increased with the concentration, at constant temperature, and decreased with the increase of temperature, at constant concentration. The amount of fatty acids adsorbed in the three adsorbents was related to the surface area and polarity of the adsorbent, concentration and solubility of the adsorbate and temperature of the solution. The negative values of ΔG and ΔH showed that the adsorption on activated carbon and on modified and unmodified montmorillonite clays was a spontaneous and an exothermic process. The decrease in the values of ΔG, with the increase of temperature, demonstrated that the adsorption was benefited by the high temperature and the positive values of ΔS showed that the fatty acids molecules were in a more randomic condition in the adsorbed state than in solution. The experimental results obtained at the temperatures of (298, 303, 313, and 323) K showed that experimental data were well represented by the Langmuir and Freundlich isotherms models.     

Modification of microcrystalline cellulose with pyridone derivatives for removal of cationic dyes from aqueous solutions

Microcrystalline cellulose (MCC) was modified with pyridone derivatives such as pyridone diester (PDE) and pyridone diacid (PDA) by using succinic acid anhydride as a linker. The modified MCCs were characterized by the fourier transform infrared spectroscopy, scanning electron microscopy, thermal gravimetric analysis, elemental analysis and solid state ¹³C NMR. The adsorption capacities of the modified MCCs to cationic dyes were examined by using methylene blue (MB) as a model dye. It was found that the kinetic adsorption data followed the pseudo-second-order kinetic model, and the adsorption equilibriums were reached less than 10 min. The isothermal adsorption data were fitted with the Langmuir isotherm model very well, from which the maximum adsorption capacities of the MCCs modified with PDE and PDA were determined to be 101.01 and 142.86 mg/g, respectively. Further investigation showed that the modified MCCs were pH-dependent for adsorption of MB in aqueous solutions. The modified MCCs could be used for removal of MB from an aqueous solution at pH 8, and reused by regeneration in an acidic solution. It was tested that the modified MCCs had a high reusability for removal of MB from aqueous solutions, and still maintained high adsorption capacities even after multiple cycles of desorption–adsorption processes. Hence, the MCCs modified with PDE and PDA could be an effective and efficient approach to removal of cationic dyes from aqueous solutions.     

Starch-modified filters used for the removal of dyes from waste water

The present article proposes the use of starch-enriched flour as low-cost adsorbent of dyes. The adsorbents have been prepared by reticulation of starch-enriched flour using epichlorohydrin as crosslinking agent. These starch-modified filters exhibit interesting properties in terms of sorption rate. Studies concerning the sorption capacity are presented. The influence of the amine groups and the chemical structure of dyes are also studied. The regeneration procedure of the filters is showed and discussed. In order to explain the results, an adsorption mechanism mainly based on physical adsorption and interactions such as hydrogen bonds and ion-exchange due to the nature of the polymer network is proposed.     

Electrochemical techniques for the removal of Reactofix Golden Yellow 3 RFN from industrial wastes

Electrochemical methods for pollution abatement have been shown to be viable alternatives or complementary to biological treatment in some instances, especially when pollutants are recalcitrant to biological processing. Electrochemical oxidation and reduction have been found successful in decomposing the most resilient compounds, and electrolysis is assigned an important role in the elucidation of the electrode process. Small well-defined cathodic and anodic peak were observed that on controlled-potential electrolysis (CPE) reduced substantially with a considerable decrease in color and absorbance. The rate of decrease of the current and absorbance was found to exhibit a first-order dependence. The COD of the solutions showed a decrease from 1416 to 352 mg/L. No peak could be observed in the voltammograms after CPE, indicating the absence of any electroactive substance left in the solutions. Results show that electrochemical reduction is a superior technology for treatment of dyes, as there is no simultaneous addition of anions, such as sulfate or chloride.     

Binding interaction of cationic phenazinium dyes with calf thymus DNA: a comparative study

Absorption, steady-state fluorescence, steady-state fluorescence anisotropy, and intrinsic and induced circular dichroism (CD) have been exploited to explore the binding of calf thymus DNA (ctDNA) with three cationic phenazinium dyes, viz., phenosafranin (PSF), safranin-T (ST), and safranin-O (SO). The absorption and fluorescence spectra of all the three dyes reflect significant modifications upon interaction with the DNA. A comparative study of the dyes with respect to modification of fluorescence and fluorescence anisotropy upon binding, effect of urea, iodide-induced fluorescence quenching, and CD measurements reveal that the dyes bind to the ctDNA principally in an intercalative fashion. The effect of ionic strength indicates that electrostatic attraction between the cationic dyes and ctDNA is also an important component of the dye-DNA interaction. Intrinsic and induced CD studies help to assess the structural effects of dyes binding to DNA and confirm the intercalative mode of binding as suggested by fluorescence and other studies. Finally it is proposed that dyes with bulkier substitutions are intercalated into the DNA to a lesser extent.     

A study of interaction of cationic dyes with anionic polyelectrolytes

The interactions of Acridine Orange with Sodium Alginate and Pinacyanol Chloride with Heparin have been investigated by spectrophotometric method. The polymers induce metachromasy in the dye as evidenced from the considerable blue shift in the absorption maxima of the corresponding dyes. The interaction constant and thermodynamic parameters of polymer–dye interactions have been determined. The effect of additives such as alcohols, and urea on the reversal of metachromasy has been studied. The data has been used to determine the stability of the metachromatic complex and the nature of binding. The thermodynamic parameters of interaction revealed that binding between Acridine Orange and Sodium Alginate involved only electrostatic forces while that between Pinacyanol Chloride involved both electrostatic and hydrophobic forces. The reversal studies using surfactants indicated the involvement of both electrostatic and hydrophobic forces in binding. Based on the results it can be concluded that Pinacyanol Chloride is more effective inducing metachromasy than Acridine Orange.     

Quartzite an efficient adsorbent for the removal of anionic and cationic dyes from aqueous solutions

Quartzite obtained from local source was investigated for the removal of anionic dye congo red (CR) and cationic dye malachite green (MG) as an adsorbent from aqueous solution in batch experiment. The adsorption process was studied as a function of dye concentration, contact time, pH and temperature. Adsorption process was described well by Langmuir and Freundlich isotherms. The adsorption capacity remained 666.7 mg/g for CR dye and 348.125 mg/g for MG dye. Data was analyzed thermodynamically, ΔH⁰ and ΔG⁰ values proved that adsorption of CR and MG is an endothermic and spontaneous process. Adsorption data fitted best in the pseudo-first order kinetic model. The adsorption data proved that quartzite exhibits the best adsorption capacity and can be utilized for the removal of anionic and cationic dyes.     

Polyamine chitosan adsorbent for the enhanced adsorption of anionic dyes from water

A simple synthesis route for amine protected-introduced-released chitosan (APIR-CS) was investigated to improve the adsorption of anionic dyes. The C₂ amine groups of the chitosan (CS) were initially protected via a Schiff-base reaction by benzaldehyde. They were then synthesized by the introduction of ethylenediamine into C₆ hydroxyl groups on CS via epichlorohydrin. The final product was obtained after removal of the Schiff base with dilute hydrochloride solution. Amine-introduced chitosan (AI-CS) was directly synthesized at the C₂ amine groups. The adsorbents were characterized by FTIR, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). For Congo red (CR) and methyl orange (MO), most of the amine groups in CS were converted to–N?CH₂ groups after the benzaldehyde treatment. Hydrochloric acid treatment after the cross-linking reaction released protected nitrogen atoms into the form of the primary amine again. APIR-CS had significantly greater adsorption capacities than AI-CS. The increased adsorption performance was attributed to the large number of primary amine groups on the surfaces. The adsorption mechanism was based on electrostatic interaction, while the adsorption process was mainly physisorption.     

A comparative study of the ability of different solvents and adsorbents to extract aroma compounds from alcoholic beverages

Seven liquid solvent systems--dichloromethane, dichloromethane-pentane (1:1), freon 113, diethyl ether-pentane (1:1 and 1:9), ethyl acetate-pentane (with and without an additional salting-out effect) (1:3 and 1:20), and seven solid-phase extraction (SPE) systems (Amberlite XAD-2, 4, 7, and 16; Porapak Q; C8; and C18)--are comparatively studied. The distribution coefficients between the extraction system and a hydroalcoholic solution (12% v/v in ethanol, pH = 3.2) of 14 selected volatile compounds belonging to different chemical families and polarities are calculated. The results are processed by factor analysis and cluster analysis, and the following conclusions are reached. First, the efficiency of extraction decreases in this order: polymeric sorbents > silica-based sorbents > liquid-liquid systems with salting-out effect approximately dichloromethane > rest of liquid solvents. Second, the addition of salt mainly increases the recovery of compounds with Lewis acid properties. Third, the efficiency of the extraction of a liquid solvent depends not only on its polarity but also on its solubility in water. Fourth, in regards to the selectivity of the SPE systems, Porapak Q is the best to extract nonpolar compounds, Amberlite XAD 4 and 16 provide the least selective extraction profiles, and C8 and C18 have a special ability to extract compounds with a Br?nstedt-Lowry character. Results indicate that in all cases liquid solvents can be replaced satisfactorily by SPE systems.     

Facile synthesis of bioglass nanospheres for the adsorption of cationic and anionic dyes from aqueous solution

A novel adsorbent, bioglass nanospheres (BGN), has been prepared by a facile process. The BGN were spheres with an amorphous structure and a relatively high specific surface area, as indicated by SEM, transmission electron microscopy, BET, FTIR, and XRD. This paper was aimed at evaluating the adsorption behavior of this new material for the adsorptive removal of cationic (methylene blue, neutral red) and anionic (congo red) dyes from aqueous solution. The effects of the initial dye concentration, contact time, solution pH, and temperature were investigated. The adsorption kinetics showed that the adsorption behavior followed the pseudo-second-order kinetic model. The adsorption isotherm fit well to the Langmuir model. Thermodynamic analyses showed that the adsorption was physisorption, and it was also a spontaneous and endothermic process. The BGN exhibited a good reusability after five consecutive cycles for cationic dyes. In addition, the possible adsorption mechanism was also proposed based on the above experimental results.     

Industrial wastes as low-cost potential adsorbents for the treatment of wastewater laden with heavy metals

Industrial wastes, such as, fly ash, blast furnace slag and sludge, black liquor lignin, red mud, and waste slurry, etc. are currently being investigated as potential adsorbents for the removal of the heavy metals from wastewater. It was found that modified industrial wastes showed higher adsorption capacity. The application of low-cost adsorbents obtained from the industrial wastes as a replacement for costly conventional methods of removing heavy metal ions from wastewater has been reviewed. The adsorption mechanism, influencing factors, favorable conditions, and competitive ions etc. on the adsorption of heavy metals have also been discussed in this article. From the review, it is evident that certain industrial waste materials have demonstrated high removal capacities for the heavy metals laden with wastewater. However, it is to be mentioned that adsorption capacities of the adsorbents vary depending on the characteristics of the adsorbents, the extent of chemical modification and the concentration of adsorbates. There are also few issues and drawbacks on the utilization of industrial wastes as low-cost adsorbents that have been addressed. In order to find out the practical utilization of industrial waste as low-cost adsorbents on the commercial scale, more research should be conducted in this direction.     

Metal-modified silica adsorbents for removal of humic substances in water

As novel adsorbents for humic substances, Fe-, Mg-, and Ca-modified silica gels SiO(2)Fe, SiO(2)Mg, and SiO(2)Ca were prepared, and their adsorbabilities to humic and fulvic acids were evaluated in water at 25 degrees C for 20 h. Among these adsorbents, SiO(2)Fe indicated the highest adsorbability, in which removing humic substances in water was accomplished to 80-97%. By calcination at 600 degrees C and washing with water, adsorbabilities of the silica adsorbents deteriorated except for the case of calcination of SiO(2)Ca. This is due to changing metal modification structures and losing chlorine, judging from elemental analysis, TG-DTA, and XPS. Especially, the modifier Fe was tightly fixed on the silica surface of SiO(2)Fe, since the metal content was almost constant even after the calcination and water washing unlike the other adsorbents. Therefore, we found that SiO(2)Fe is the most useful adsorbent among the silica adsorbents and that its modification structure is composed of SiOFe, FeCl, and FeOH. In addition, the adsorption mechanism is explained by an interaction between Fe and humic substance molecule having carboxylate and phenolate groups, accompanied with anion exchange of chloride ion Cl(-) for the humic substance molecule via the silica pores. SiO(2)Fe may be applied to an adsorbent alternative for charcoal in water purification plants, and the used SiO(2)Fe may be further reused as a fertilizer since humic substances have plant-glowing ability and silica strengthens plant parts.     

Characterization of water adsorption onto carbonaceous materials produced from food wastes

The recycling of organic wastes has become very important and the development of technology for recycling organic wastes needs to sustain industrial development. In this study, techniques for producing carbonaceous materials from organic wastes are described and water adsorption is characterized. The organic wastes used are coffee grounds and oolong tea leaves carbonized at 673 to 1073 K. The iodine adsorption capacity of the carbonaceous materials increased with increased carbonization temperature. The amount of water adsorbed onto the carbonization materials produced from oolong tea leaves at 873 K for 2 h was the highest. The Freundlich constant 1/n and the differential heat of adsorption of the carbonaceous materials produced from oolong tea leaves were greater than that of the carbonaceous materials produced from coffee grounds. The ability to humidity control can be estimated by the difference between the amount of water adsorbed relative pressure 0.90 and that at relative pressure 0.55. The ability to humidity control was the greatest for the carbonaceous materials produced from the oolong tea leaves at 873 K for 2 h and did not depend upon the adsorption temperature. These results indicated that the carbonaceous materials produced from oolong tea leaves at 873 K for 2 h could have more humidity control.     

Removal of anionic and cationic dyes from wastewater by adsorption using multiwall carbon nanotubes

This paper evaluated the efficiency and reusability of multiwall carbon nanotubes (MWNTs) on removal of cationic and anionic dyes under effect of pH, dose of MWNTs and concentration of dyes. The characterization of MWNTs is characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), Raman spectra and BET (Brunauer, Emmett and Teller) surface area. SEM and TEM analyses showed that MWNTs had size within nano scale range of 10–50 nm. The experimental results indicated that the efficiency of removal of MWNTs increase under condition of normal pH, at contact time 60 min with agitation speed 240 rpm and initial concentration of dyes 10 mg/l. Under these optimal conditions, the removal reached 98.7% and 97.2% for anionic dyes and cationic dyes, respectively. For economic use, MWNTs can be used more than one time where the same experiments with the already used MWNTs was repeated and it was found that the percent removal is almost the same.