Adsorption and kinetic studies of cationic and anionic dyes on pyrophyllite from aqueous solutions

The adsorption of cationic Methylene Blue (MB) and anionic Procion Crimson H-EXL (PC) dyes from aqueous medium on pyrophyllite was studied. Changes in the electrokinetics of pyrophyllite as a function of pH were investigated in the absence and presence of multivalent cations. The results show that pyrophyllite in water exhibits a negative surface charge within the range pH 2-12. Pyrophyllite is found to be a novel adsorbent for versatile removal of cationic and anionic dyes. The negative hydrophilic surface sites of pyrophyllite are responsible for the adsorption of cationic MB molecules. The adsorption of anionic PC dye is possible after a charge reversal by the addition of trivalent cation of Al. Nearly 2 min of contact time are found to be sufficient for the adsorption of both dyes to reach equilibrium. The experimental data follow a Langmuir isotherm with adsorption capacities of 70.42 and 71.43 mg dye per gram of pyrophyllite for MB and PC, respectively. For the adsorption of both MB and PC dyes, the pseudo-second-order chemical reaction kinetics provides the best correlation of the experimental data.     

Removal of dyes from water by conducting polymeric adsorbent

Chemically synthesized conducting polyaniline (PANI) was investigated as adsorbent for its possible application in the removal of organic dyes, such as methylene blue (MB) and procion red (PR) from their aqueous solution. PANI adsorbent behaves as a charged surface upon post‐synthesis treatment of the polymer with acid and base. The adsorbent thus treated shows a high selectivity for the removal of dyes in the adsorption process. The Langmuir adsorption isotherm was used to represent the experimental adsorption data. The cationic dye, MB can be preferentially removed by the base‐treated PANI while the anionic dye, PR is predominately removed by the acid‐treated one. These observations were further evidenced from the measurements of molar conductance and pH of the dye solutions employed for adsorption. The finding can be explained considering the electrostatic nature of adsorption coupled with the morphology of the PANI surface thus treated. Copyright © 2004 John Wiley & Sons, Ltd.     

Modeling and Thermodynamics of Methylene Blue and Acid Blue 80 Adsorption onto Potato Residue Based Activated Carbon

A study was made on the adsorption kinetics and thermodynamics of methylene blue(MB) and acid blue 80(AB80) onto powder of activated carbon(PAC) prepared by chemical method from dry potato residue(DPR). The PAC was characterized by N₂ adsorption-desorption isotherms analysis and scanning electron microscopy. The ma- ximum adsorption capacities of PAC for MB and AB80 at 303 K are 532.19 and 156.22 mg/g, respectively. The results indicate that the adsorption kinetics of the selected dyes on PAC is well-described by the pseudo-second order model. And their thermodynamic data were analyzed via the isotherms of Langmuir, Freundlich, Redlich-Peterson, Toth and Sips, and the thermodynamic parameters were calculated. The results show that PAC is a fast and effective adsorbent for removing the cationic dyes from aqueous solutions.     

Characterization and Mechanism Elucidation of Dye Adsorption Using Cuprous Selenide Nanoparticles from Aqueous Solutions

The removal of cationic dyes, methylene blue(MB) and rhodamine B(RB), and anionic dyes, methyl or-ange(MO) and eosin Y(EY), from aqueous solutions by adsorption using Cu₂Se nanoparticles(Cu₂SeNPs) was studied. The effects of the initial pH values, adsorbent doses, contact time, initial dye concentrations, salt concentrations, and operation temperatures on the adsorption capacities were investigated. The adsorption process was better fitted the Langmuir equation and pseudo-second-order kinetic model, and was spontaneous and endothermic as well. The adsorption mechanism was probably based on the electrostatic interactions and π-π interactions between Cu₂SeNPs and dyes. For an adsorbent of 0.4 g/L of Cu₂SeNPs, the adsorption capacities of 23.1(MB), 22.9(RB) and 23.9(EY) mg/g were achieved, respectively, with an initial dye concentration of 10 mg/g(pH=8 for MB and pH=4 for RB and EY) and a contact time of 120 min. The removal rate of MB was still 70.4% for Cu₂SeNPs being reused in the 5th cycle. Furthermore, the recycled Cu₂SeNPs produced from selenium nanoparticles adsorbing copper were also an effective adsorbent for the removal of dyes. Cu₂SeNPs showed great potential as a new adsorbent for dyes removal due to its good stability, functionalization and reusability.     

Removal of Congo red from aqueous solutions by neem saw dust carbon

Neem sawdust was used to develop an effective carbon adsorbent. This adsorbent was used for the removal of Congo Red (CR) from aqueous solution. The data suggest that the pH of aqueous solutions influences CR removal due to the decrease of removal efficiency with increasing pH. An optimal pH < 3 for the adsorption of CR onto neem sawdust carbon (NSDC) was determined. The experimental data were analysed by the Langmuir, Freundlich, Redlich-Peterson, Toth, Temkin, Sips and Dubinin-Radushkevich models of adsorption. Three simplified kinetic models based on pseudo-first-order, pseudo-second-order and intraparticle diffusion equations were used to describe the adsorption process. It was shown that the adsorption of CR could be described by the pseudo-second-order equation, suggesting that the adsorption occurs as a chemisorption process. The results indicate that the NSDC can be used as a low cost adsorbent alternative to commercial activated carbon for the removal of dyes from wastewaters.     

Adsorption of uranium(VI) from aqueous solution by diethylenetriamine-functionalized magnetic chitosan

In this paper, the modified magnetic chitosan resin containing diethylenetriamine functional groups (DETA-MCS) was used for the adsorption of uranium ions from aqueous solutions. The influence of experimental conditions such as contact time, pH value and initial uranium(VI) concentration was studied. The Langmuir, Freundlich, Sips and Dubinin–Radushkevich equations were used to check the fitting of adsorption data to the equilibrium isotherm. The best fit for U(VI) was obtained with the Sips model. Adsorption kinetics data were tested using pseudo-first-order and pseudo-second-order models. Kinetic studies showed that the adsorption followed the pseudo-second-order kinetic model, indicating that the chemical adsorption was the rate-limiting step. The present results suggest that DETA-MCS is an adsorbent for the efficient removal of uranium(VI) from aqueous solution.     

Equilibrium and fractal-like kinetic studies of the sorption of acid and basic dyes onto watermelon shell (<Emphasis Type="Italic">Citrullus vulgaris</Emphasis>)

In the present study, batch experiments were used to determine adsorption characteristics of Watermelon Shell Biosorbent (WSB) for the uptake of anionic and cationic dyes from aqueous solution. Various factors such as initial dye concentration, adsorbent dosage, pH, contact time and temperature were systematically investigated and discussed. WSB was characterized by Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy and Fourier Transform Infrared Spectroscopy. The adsorption kinetics was best described by Elovich and Diffusion-Chemosorption models for Basic red 2 (BR2) (cationic dye) and Orange G (OG) (anionic dye) respectively. However, the fractional time index “α” and non-integer “n” order by Fractal-like pseudo-first order kinetic affirmed that the mechanism of interaction of both dyes with WSB was by chemical reaction. The applicability of four adsorption isotherm models for the present system was tested. The equilibrium data were found to be well represented by the Extended Langmuir isotherm equation. The monolayer adsorption capacity of WSB for BR2 and OG adsorption was found to be 125 and 27 mg/g, respectively. The effect of temperature on the adsorption process was also investigated and the values of thermodynamic parameters ΔG°, ΔH° and ΔS° revealed that the adsorption system was spontaneous.     

Fabrication of flexible graphene oxide paper-like adsorbent doped with magnetite nanoparticles for removal of dyes

Organic dyes are used in many industries, e.g., textile, cosmetics and food. Hence, contamination of organic dyes to water sources is a critical issue. To reduce water pollution by organic dyes, we propose a paper-like adsorbent with a practical and economical production procedure. Subsequently, a flexible adsorbent was produced using a one-step approach by vacuum filtration of graphene oxide (GO) and iron oxide nanoparticles (Fe₃O₄-NPs) containing dispersion through a membrane and quoted as GO/Fe₃O₄ paper. For comparison, GO paper was also prepared using the same procedure. Both papers were characterized using UV–VIS absorption spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, electron diffraction X-ray analysis, X-ray photoelectron spectroscopy, and powder X-ray diffraction techniques. At the steady-state conditions, GO/Fe₃O₄ and GO papers were performed as adsorbent for cationic dyes of methylene blue, neutral red, and anionic dyes of methyl orange and fluorescein. In general, the removal efficiency of GO/Fe₃O₄ paper was higher than that of GO paper for adsorption of all dyes and this adsorbent revealed satisfactory adsorption properties for cationic dyes when compared to anionic dyes.

     

Chemical and biological treatment of waste water with a novel silver/ordered mesoporous alumina nanocomposite

One of the serious problems in the present century is chemical and biological pollution of the environment. Nanocomposites are multiphase solid materials that have been used as adsorbent of pollutants such as dyes, pesticides, anions and etc. in the last decades. In this study, a novel nanocomposite including silver nanoparticles and ordered mesoporous alumina (OMA) has been synthesized and used for the removal of dyes pollutants (methyl orange, bromothymol blue and reactive yellow) from aqueous solution. The characterization of synthesized nanocomposite has been performed by TEM, N₂ adsorption/desorption, XRD and energy dispersive X-ray spectroscopy analysis. The adsorption kinetic and equilibrium data have been obtained by UV–vis spectroscopy. The results show that the silver/OMA nanocomposite (Ag/OMA nanocomposite) is good adsorbent for the removal of anionic dyes from aqueous solution, and also this nanocomposite has a biocidal action against both Gram-negative and Gram-positive bacteria.     

Fast and highly efficient removal of anionic organic dyes with a new Cu modified nanoclinoptilolite

Adsorption of anionic dyes onto most of zeolites with net negative charge may be restricted. In this article, a natural nanoclinoptilolite was modified with Cu and the obtained nanomaterial was used as an effective adsorbent for removal of methyl red as an anionic model azo dye up to 90% in 20 min.This new adsorbent was characterized utilizing X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy and energy-dispersive X-ray spectroscopy. Also, effects of methyl red concentration, mass of sorbent and pH on the removal percent were examined. Moreover, the adsorption mechanism was investigated by plotting the Langmuir and Freundlich adsorption isotherms. The results showed that the data can be fitted with both models. The most adsorption capacity obtained from Langmuir isotherm was about 200 mg/g. Moreover, the Cu modified nanoclinoptilolite was successfully employed for adsorption of another anionic dye, bromothymol blue. The results confirmed that this new adsorbent can be effectively applied for removing of anionic dyes from waste waters.     

Synthesis and characterization of hexagonal boron nitride used for comparison of removal of anionic and cationic hazardous azo-dye: kinetics and equilibrium studies

The purpose of this study was to compare the adsorption behavior of cationic and anionic dyes onto a hexagonal boron nitride (hBN) nanostructure that was rich in a negative charge. Herein, the hBN nanostructure was synthesized using boric acid as a precursor material. The characteristic peaks of the hBN nanostructure were performed using Fourier transform infrared (FT-IR) and Raman spectroscopies. The morphology and the particle size of hBN nanostructure were determined by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). During the studies, various essential adsorption parameters were investigated, such as the initial dye concentration, pH of the dye solution, adsorbent dose, and contact time. Under optimal conditions, the removal of 42.6% Metanil yellow (MY) and 90% Victoria blue B (VBB) from aqueous solution was performed using a 10-mg hBN nanostructure. Furthermore, the equilibrium studies showed that the Freundlich isotherm model fitted well for the removal of MY. However, the Langmuir isotherm model fitted well for the removal of VBB. Moreover, according to the results obtained from the kinetic studies, while the first-order kinetic model was suited for the adsorption of the MY, the second-order kinetic model was found to well fit for the adsorption of VBB.     

Graphene and graphene oxide as effective adsorbents toward anionic and cationic dyes

In the present study, exfoliated graphene oxide (EGO) and reduced graphene oxide (rGO) have been used for the adsorption of various charged dyes such as methylene blue, methyl violet, rhodamine B, and orange G from aqueous solutions. EGO consists of single layer of graphite decorated with oxygen containing functional groups such as carboxyl, epoxy, ketone, and hydroxyl groups in its basal and edge planes. Consequently, the large negative charge density available in aqueous solutions helps in the effective adsorption of cationic dyes on EGO while the adsorption is negligible for anionic dyes. On the other hand, rGO that has high surface area does not possess as high a negative charge and is found to be very good adsorbent for anionic dyes. The adsorption process is followed using UV-Visible spectroscopy, while the material before and after adsorption has been characterized using physicochemical and spectroscopic techniques. Various isotherms have been used to fit the data, and kinetic parameters were evaluated. Raman and FT-IR spectroscopic data yield information on the interactions of dyes with the adsorbent.     

Removal of malachite green from dye wastewater using mesoporous carbon adsorbent

Mesoporous carbon was synthesized for the removal of a cationic dye malachite green (MG) from aqueous solution. The studies were carried out under various experimental conditions such as contact time, dye concentration, adsorption dose and pH to assess the potentiality of mesoporous carbon for the removal of malachite green dye from wastewater. The sorption equilibrium was reached within 30 min. In order to determine the adsorption capacity, the sorption data were analyzed using linear form of Langmuir and Freundlich equation. Langmuir equation showed higher conformity than Freundlich equation. More than 99% removal of MG was reached at the optimum pH value of 8.5. From kinetic experiments, it was concluded that the sorption process followed the pseudo-first-order kinetic model. This study showed that mesoporous carbon can be recommended as an excellent adsorbent at high pH values.     

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.     

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.     

Superabsorbent amphoteric nanohydrogels: Synthesis,characterization and dyes adsorption studies

The goal of the present research is to remove high percentage of cationic and anionic dyes such as,Neutral Red, Safranin O and Indigo Carmine from aqueous solutions by poly(NIPAAm/N,Ndiallylpyrrolidinium bromide/AA) superabsorbent amphoteric nanohydrogels synthesized using the inverse microemulsion polymerization method. Effect of various parameters such as, treatment time,initial dye concentration, p H and adsorbent dose were investigated. Furthermore, kinetics and isotherms adsorption models were applied to determine the maximum adsorption and mechanism for adsorption,which shows that adsorption obeyed the pseudo-second order kinetics. From the results, removal of dyes within the nanohydrogel was found to be in the order: AB-74 BR-2 BR-5.     

Polypyrrole-coated cotton textile as adsorbent of methylene blue dye

Pollution caused by organic dyes is of serious environmental and health concern to the population. Dyes are widely used in textile coloring applications. In the present work, cotton textile was coated with a conducting polymer, polypyrrole (PPy), in situ during the oxidative polymerization of pyrrole. The resulting materials were utilized as easily separated and recyclable adsorbent for the removal of methylene blue (MB) as a model of cationic dyes in alkaline solutions. It showed also some affinity to remove Acid Green 25 as an anionic dye in acidic medium. The adsorption was assessed by monitoring the decrease in dye concentration by UV–Visible absorption spectroscopy. The influence of various parameters such as initial dye concentration, contact time, pH, temperature, and adsorbent dose on the adsorption process was studied. The pseudo-second-order kinetic model and Freundlich isotherm model were found to describe the adsorption process. The thermodynamic study revealed that the adsorption of MB by PPy was feasible, spontaneous, and exothermic process. Investigation of the substrate regeneration revealed that PPy deposited on cotton textile can be reused for dye adsorption several times with good efficiency and it allows for the recovery of MB for recycling purposes.     

Facile synthesis of mesoporous magnesium oxide–graphene oxide composite for efficient and highly selective adsorption of hazardous anionic dyes

Mesoporous magnesium oxide–graphene oxide composite (MGC) has been synthesized using a facile post-immobilization method by mixing pre-synthesized magnesium oxide (MgO) with graphene oxide (GO). MgO used for fabrication of the composite has been synthesized using an environment-friendly method involving gelatin as a template. XRD, Raman and EDX analyses have confirmed the presence of MgO and GO in the composite. FTIR and SEM analyses of synthesized MGC have further elucidated the surface functionalities and morphology, respectively. Using N₂ adsorption–desorption isotherm, BET surface area of MGC has been calculated to be 55.9 m² g^?1 and BJH analysis confirmed the mesoporous nature of MGC. The application of synthesized MGC as a selective adsorbent for various toxic anionic dyes has been explored. Batch adsorption studies have been carried out to investigate the influence of different adsorption parameters on the adsorption of two anionic dyes: indigo carmine (IC) and orange G (OG). The maximum adsorption capacities exhibited by MGC for IC and OG are 252.4 and 24.5 mg g^?1, respectively. Plausible mechanism of dye adsorption has been explained in detail using FTIR analysis. In a mixture of cationic and anionic dyes, MGC selectively adsorbs anionic dyes with high separation factors, while in binary mixtures of anionic dyes, both dyes are adsorbed efficiently. Thus, MGC has been shown to be a potential adsorbent for the selective removal of anionic dyes from wastewater.

     

Surface-bound humic acid increased rhodamine B adsorption on nanosized hydroxyapatite

In this study, humic acid-bound nanosized hydroxyapatite (HA-nHAP) was developed as a novel adsorbent, and the potential of using HA-nHAP for the adsorption of rhodamine B (RhB) from aqueous solution as functions of pH, adsorbent dosage, contact time, ionic strength, and temperature was investigated. The results indicated that the HA binding significantly increased the adsorption of RhB due to the introduction of abundant negatively charged functional groups. The adsorption capacity of HA-nHAP for RhB was found to be pH-dependent, and the optimal pH value was found to be 6.0. The adsorption equilibrium data obeyed Sips and Freundlich isotherms and the kinetic data were well described by the Elovich kinetic model. According to the Sips equation, the maximum adsorption capacity for RhB was 24.12 mg/g. The temperature and ionic strength experiment showed that they both had an effect on the adsorption capacity of HA-nHAP. Thermodynamic study confirmed that the adsorption was a spontaneous, endothermic, and more random arrangement process. The present investigation showed that HA-nHAP is a promising adsorbent for the removal of RhB from aqueous solution.