The study of thermodynamics and kinetics methyl orange and malachite green by SWCNTs,SWCNT-COOH and SWCNT-NH2 as adsorbents from aqueous solution

The effective removal of dyes from aqueous wastes is among the most important issues for many industrialized countries. Removal of methyl orange (MO) and malachite green (MG) from aqueous solutions were studied using single-walled carbon nanotubes (SWCNTs), carboxylate functionalized single-walled carbon nanotubes (SWCNT-COOH) and amide functionalized single-walled carbon nanotubes (SWCNT-NH₂). The adsorption process was found to be controlled by temperature, ionic strength, initial concentration, adsorbent dosage and contact time. The microstructure of carbon nanotubes was characterized using SEM and FTIR. The adsorbents studied exhibits high efficiency for MO and MG adsorption and the equilibrium states could be achieved in 20, 20, 15 (min) for SWCNTs, SWCNT-COOH, SWCNT-NH₂, respectively. Adsorption capacity of each adsorbent increased with increasing active groups on the surface of carbon nanotube, where SWCNT-NH₂ was the most effectively adsorbent.     

Evaluation of Adsorption Characteristics of Malachite Green onto Almond Shell (Prunus dulcis)

The potential usage of almond shell (P. dulcis), which is an agricultural waste product, in the removal of malachite green from aqueous solutions was evaluated with respect to various experimental parameters including contact time, initial malachite green concentration, temperature, adsorbent concentration, etc. The adsorption kinetics of malachite green fitted well the pseudo-second-order kinetic model. The monolayer adsorption capacity of almond shell was found to be 29.0 mg g^?1. The adsorption of malachite green onto almond shell increased with raising the temperature. From the experimental results, almond shell could be employed as a low cost and easily available adsorbent for removal of malachite green in wastewater treatment process.     

Removal of Basic Dye from Aqueous Solution using Cinnamomum camphora Sawdust: Kinetics,Isotherms, Thermodynamics,and Mass-Transfer Processes

Cinnamomum camphora sawdust (CCS) was employed as a cheap and effective biosorbent to remove basic dye from aqueous solutions. The biosorbent was characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). Adsorption experiments were carried out in a batch system as a function of initial pH, adsorbent dose and particle size, ionic strength, initial dye concentration, and reaction temperature. The selected basic dye (malachite green) adsorption onto CCS significantly depended on these factors. By comparative kinetic analysis, the rate of sorption was conformed with good correlation to pseudo-second-order kinetics. Equilibrium data were fitted well by Langmuir isotherm with the maximum adsorption capacity of 155.0 mg/g at the temperature of 318 K and pH 7.0 ± 0.1. Thermodynamic parameters proved that malachite green dye biosorption process was spontaneous and endothermic within the investigated temperature range. The mechanism of adsorption was also studied. It was found that the adsorption of malachite green onto CCS was mainly governed by film diffusion. The electrostatic attractions and ionic interactions between malachite green dye and CCS might be responsible for the adsorption process. The comparative investigation suggested that the sawdust could be considered as a potential adsorbent for malachite green dye removal from wastewater.     

The use of nutshell firstly as a natural dye for cotton and wool and then as a natural adsorbent for colour removal of basic dye effluent

The aim of this study is to utilise nutshell, which is normally a waste. To this end, in the first part of our study we investigated the usability of nutshell extract solution as a natural dye for the coloration of cotton and wool fabrics. In order to optimise the fastness properties of dyed samples, mordant type was chosen as a variable in experiments and dyeings were carried out at 100 g l⁻¹ extract concentration. After extracting its dye, nutshell was used as adsorbent for colour removal of basic dye effluent. The effect of adsorbent dose, initial dye concentration, and contact time on the adsorption of malachite green (MG) onto nutshell was investigated. Adsorption isotherms and kinetics of MG adsorption onto nutshell were also studied.     

Preparation of hemicellulose‐g‐poly(methacrylic acid)/carbon nanotube composite hydrogel and adsorption properties

An organic–inorganic composite hydrogel was prepared based on hemicellulose and multi‐wall carbon nanotubes. The effects of hydrogel amount, initial concentration, contact time, and salt concentration on the adsorption performance of the prepared hydrogels were observed using methylene blue as a model hazardous material. The results indicated that the adsorption kinetic of methylene blue on the prepared adsorbent was well fitted to the pseudo‐second‐order kinetic model and the adsorption isotherm conformed to the Freundlich model. Removal percentage of methylene blue increased with increased adsorbent amount and kept higher than 98% when adsorbent amount was above 6 g L⁻¹. Adsorption amount of methylene blue on the prepared adsorbent also increased when increasing initial concentration over the range from 50 to 500 mg L⁻¹. Both of adsorption amount and removal percentage increased with an increase in the contact time, and removal efficiency obviously deteriorated as salt concentration increased. All obtained results reported that the prepared composite hydrogel would have an application prospect in water treatment. POLYM. COMPOS., 35:45–52, 2014. © 2013 Society of Plastics Engineers     

Coconut (Cocos nucifera) Shell Based Activated Carbon for the Removal of Malachite Green Dye from Aqueous Solutions

The adsorption of malachite green (MG) dye using coconut shell based activated carbon (CSAC) was investigated. Operational factors such as the effect of pH, initial dye concentration, adsorbent dosage, contact time, and solution temperature on the adsorption process were studied. Solution pH strongly affected the chemistry of both the dye molecule and CSAC in solution. Optimum dye removal was obtained at pH ≥ 8.0. Equilibrium was reached in 120 minutes contact time. The Langmuir, Freundlich, and Dubinin–Radushkevich (D-R) isotherm models were used to evaluate the adsorption data. The adsorption data fitted the Langmuir model most with maximum adsorption monolayer coverage of 214.63 mg/g. Pseudo-first-order, pseudo second-order, and intraparticle diffusion models were also used to fit the experimental data. Kinetic parameters, rate constants, equilibrium sorption capacities, and related correlation coefficients, for each model were calculated and discussed. Thermodynamic parameters such as ΔG⁰, ΔH⁰, and ΔS⁰ were evaluated and it was found that the sorption process was feasible, spontaneous, and exothermic in nature. The mean free energy obtained from D-R isotherm suggests that the adsorption process follows physiosorption mechanism. The results showed that coconut shells could be employed as a low-cost precursor in activated carbon preparation for the removal of MG dye from wastewaters.     

Removal of malachite green from aqueous solution by sorption on hydrilla verticillata biomass using response surface methodology

In the present study, the effect of adsorbent dose, pH, temperature, initial dye concentration and contact time on malachite green removal from an aqueous medium using hydrilla verticillata biomass has been investigated. The central composite face-centered experimental design (CFCD) in respons surface methodology (RSM) was used for designing the experiments as well as for full response surface estimation. The optimum conditions for maximum removal of malachite green from an aqueous solution of 75.52 mg/L were as follows: adsorbent dose (11.14 g/L), pH (8.4), temperature (48.4°C) and contact time (194.5 min). This was evidenced by the higher value of coefficient of determination (R ²= 0.9158).     

Adsorption of malachite green onto bentonite: Equilibrium and kinetic studies and process design

The adsorption of malachite green onto bentonite in a batch adsorber has been studied. The effects of contact time, initial pH and initial dye concentration on the malachite green adsorption by the bentonite have been studied. Malachite green removal was seen to increase with increasing contact time until equilibrium and initial dye concentration, and the adsorption capacity of bentonite was independent of initial pH in the range 3–11. Four kinetic models, the pseudo first- and second-order equations, the Elovich equation and the intraparticle diffusion equation, were selected to follow the adsorption process. Kinetic parameters; rate constants, equilibrium adsorption capacities and correlation coefficients, for each kinetic equation were calculated and discussed. It was shown that the adsorption of malachite green onto bentonite could be described by the pseudo second-order equation. The experimental isotherm data were analyzed using the Langmuir, Freundlich, Temkin and Dubinin–Radushkevich equations. Adsorption of malachite green onto bentonite followed the Langmuir isotherm. The thermodynamic parameters, such as ΔH, ΔS and ΔG, were also determined and evaluated. A single stage batch adsorber was designed for different adsorbent mass/treated effluent volume ratios using the Langmuir isotherm.     

Polyaniline‐functionalized magnetic nanoparticles for the removal of toxic dye from wastewater

A novel and inexpensive approach was adopted to develop a magnetic nanocomposite for the adsorption of cationic dye from an aqueous solution. This nanocomposite, which was based on a superparamagnetic iron oxide nanocore, was functionalized with a hydrophilic coating of polyaniline (PANI). The nanoparticle size, colloidal stability, surface chemistry, and magnetic properties were studied extensively by transmission electron microscopy, X‐ray diffraction, Fourier transform infrared spectroscopy, and vibrating sample magnetometry. The polymeric functionalized magnetic nanocomposite had an average core size of 20–40 nm and a shell size of 6–10 nm. To evaluate the potential of such nanocomposites for dye adsorption, malachite green (MG) was exposed with different operational parameters, such as the pH, temperature, initial concentration of the dye, contact time, and reusability. The rate of the adsorption followed pseudo‐second‐order kinetics with the adsorption isotherm fit the Langmuir isotherm model well. The maximum adsorption capacity was 240 mg of MG/g of adsorbent. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40840.     

Removal of Selected Basic Dyes using Activated Carbon from Tannery Wastes

Activated carbon prepared from tannery leather waste (TLW-AC) has been studied for its efficiency of removal of basic dyes, namely rhodamine B (RB), methylene blue (MB), and malachite green (MG) from aqueous solutions. Factors influencing dye adsorption such as the concentration of dye, pH, contact time, and temperature were investigated. The adsorption was found to be strongly dependent on the pH and temperature. The maximum sorption capacity of RB was obtained at pH 3 and for MB and MG was obtained at pH 11. Various thermodynamic parameters such as ΔG°, ΔH°, and ΔS° were calculated. The kinetic studies reveal that the adsorption process follows the pseudo second-order kinetic model. The equilibrium data have been well-described by the Langmuir and Freundlich models, and the data fitted well in both model equations. The study revealed that wastes from leather industry is an economically viable option for dye removal.     

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.     

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.     

Investigation of Reactive Red Dye 198 removal using multiwall carbon nanotubes in aqueous solution

The present study evaluates the performance of multiwalled carbon nanotubes (MWCNTs) for removing Reactive Red Dye 198 (RR198) from the color wastewater. In this study, the influence of pH, adsorbent dose, initial dye concentration, and contact time on the RR198 adsorption by MWCNTs was investigated. The results showed increasing the dye concentration from 20 to 200 mg/L, removal efficiency decreased from 99.62% to 66.99%. Moreover, by increasing the pH from 3 to 10, the efficiency of dye removal decreased from 76.34% to 54.98%. Freundlich isotherm and pseudo-second-order kinetic model were the best models for describing the adsorption reactions.     

Removal of Reactive Red 198 from aqueous solution by combined method multi-walled carbon nanotubes and zero-valent iron:Equilibrium,kinetics, and thermodynamic

Dyes often include toxic,carcinogenic compounds and are harmful to humans' health.Therefore,removal of dyes from textile industry wastewater is essential.The present study aimed to evaluate the efficiency of the combination of zero valent iron(ZVI) powder and multi-walled carbon nanotubes(MWCNTs) in the removal of Reactive Red 198(RR198) dye from aqueous solution.This applied research was performed in a batch system in the laboratory scale.This study investigated the effect of various factors influencing dye removal,including contact time,p H,adsorbent dose,iron powder dose,initial dye concentration,and temperature.The equilibrium adsorption data were analyzed using three common adsorption models:Langmuir,Freundlich and Temkin.Besides,kinetic and thermodynamic parameters were used to establish the adsorption mechanism.The results showed,in pH =3,contact time = 100 min,ZVI dose = 5000 mg·L~(-1),and MWCNTs dose = 600 mg·L~(-1)in 100 mg·L~(-1)dye concentration,the adsorption efficiency increased to 99.16%.Also,adsorption kinetics was best described by the pseudo-second-order model.Equilibrium data fitted well with the Freundlich isotherm(R2= 0.99).The negative values of ΔG0and the positive value of ΔH0(91.76) indicate that the RR198 adsorption process is spontaneous and endothermic.According to the results,the combination of MWCNTs and ZVI was highly efficient in the removal of azo dyes.     

Studies on auramine dye adsorption on psidium guava leaves

Removal of auramine dye from aqueous waste solutions was investigated by using very cheap and biosorbent, withered guava tree leaves and activated carbon. Guava leaves are readily available in the western and northern parts of India throughout the year, and hence form a cost effective alternative for removal of dyes from waste waters. The optimum contact time was found to be 120 min. in a pH range of 8–9 for 92–94% removal of the dye from aqueous solutions containing 150 mg/L of auramine dye using 2 g of the adsorbent. The effect of pH, dye concentration, sorbent dosage, temperature and contact time on the dye removal efficiency has been studied. Experimental results were found to fit both Freundlich and Langmuir models. Since the dye contains a cationic species, the removal efficiency was highest in a pH range of 8–9. Continuous adsorption studies in a packed column showed 100% removal efficiency for a flow rate of 10 ml·min⁻¹. When compared with the activated carbon, it was also found that adsorbent derived from guava leaves is more efficient in removal of dye.     

Adsorption studies on the removal of Malachite Green from aqueous solutions onto halloysite nanotubes

Halloysite nanotubes (HNTs) were used as nano-adsorbents for removal of the cationic dye, Malachite Green (MG), from aqueous solutions. The adsorption of the dye was studied with batch experiments. The natural HNTs used as adsorbent in this work were initially characterized by FT-IR and TEM. The effects of adsorbent dose, initial pH, temperature, initial dye concentration and contact time were investigated. Adsorption increased with increasing adsorbent dose, initial pH, and temperature. Equilibrium was rapidly attained after 30 min of contact time. Pseudofirst-order, pseudo-second-order and intraparticle diffusion models were considered to evaluate the rate parameters. The adsorption followed pseudo-second-order kinetic model with correlation coefficients greater than 0.999. The factors controlling adsorption process were also calculated and discussed. The maximum adsorption capacity of 99.6 mg g⁻¹ of MG was achieved in pH = 9.5. Thermodynamic parameters of ΔG°, ΔH° and ΔS° indicated the adsorption process was spontaneous and endothermic.     

Preparation of CTAB-functionalized aqai stalk and its efficient application as adsorbent for the removal of Direct Blue 15 and Direct Red 23 dyes from aqueous media

In this work, a new adsorbent material based on the chemical modification of aqai stalk (AS) with hexadecyltrimethylammonium bromide (CTAB) was proposed, forming a new material called AS-CTAB. The characterization data from the AS-CTAB adsorbent indicated that the biomass was chemically modified by the surfactant. The prepared material was successfully used as an adsorbent for the removal of Direct Blue 15 (DB-15) and Direct Red 23 (DR-23) from aqueous solutions. For both dyes, adsorption followed the Avrami kinetic model. The kinetic data were better fitted using the nonlinear Avrami fractional model for both dyes. The contact time between the adsorbent and adsorbate was fixed at 180 and 30?min for DB-15 and DR-23, respectively. This remarkable difference of contact time between the dyes with AS-CTAB adsorbent was attributed to the difference in the physicochemical characteristics of the dyes such as size of the molecule, hydrophilic–lipophilic balance, and polar surface area (PA). The Liu isotherm model displayed Q_max of 394.2 and 454.9?mg?g^?1 for DB-15 and DR-23, respectively, at 45°C. Since the AS-CTAB is not a porous material, electrostatic interaction was the main mechanism involved in the adsorption process for both dyes. The thermodynamic adsorption reaction was shown to be a spontaneous and endothermic process. The AS-CTAB adsorbent was also tested in the treatment of synthetic dye effluents and presented a removal of up to 95.41% of a simulated effluent containing several dyes and high saline concentration.     

Removal of methylene blue dye from aqueous solution by activated carbon prepared from cashew nut shell as a new low-cost adsorbent

Methylene blue dye was adsorbed on an adsorbent prepared from cashew nut shell. A batch adsorption study was carried out with variable adsorbent amount, initial dye concentration, contact time and pH. Studies showed that the pH of aqueous solutions affected dye removal as a result of removal efficiency increased with increasing solution pH. The experimental data were analyzed by the Langmuir, Freundlich, Redlich-Peterson, Koble-Corrigan, Toth, Temkin, Sips and Dubinin-Radushkevich models of adsorption using MATLAB 7.1. The experimental data yielded excellent fits within the following isotherm order: Redlich-Peterson>Toth>Sips>Koble-Corrigan>Langmuir>Temkin>Dubinin-Radushkevich>Freundlich, based on its correlation coefficient values. Three simplified kinetic models including a pseudofirst-order, pseudo-second-order and intraparticle diffusion equations were selected to follow the adsorption process. It was shown that the adsorption of methylene blue could be described by the pseudo-second-order equation. The results indicate that cashew nut shell activated carbon could be employed as a low cost alternative to commercial activated carbon in the removal of dyes from wastewater.     

Removal of methylene blue and safranin orange pollutants from liquid effluents by soy residue

Methylene blue and safranin orange dyes, which are used in the textile and pharmaceutical industries, can severely damage the environment and human health. This study investigated the use of okara residue as an alternative biosorbent for the removal of methylene blue and safranin orange dyes. Substantial amounts of okara residue are generated daily during the processing of soy milk in the agro-industrial sector. Dye adsorption was not affected by pH. An adsorption study identified the optimal experimental conditions as: 298 K, 0.03 g of adsorbent in 30 mL of dye solution at a concentration of 50 mg L⁻¹, and a contact time of 300 min for methylene blue dye, and 298 K, 0.02 g of adsorbent in 30 mL of dye solution at a concentration of 50 mg L⁻¹, and a contact time of 200 min for safranin orange dye; the maximum adsorption capacities were 93.201 ± 0.01 and 184 592 ± 0.02 mg g⁻¹, respectively. Okara has considerable advantages over other natural materials as an alternative for the treatment of industrial effluents. Because it is easily obtained and does not require any physicochemical treatment, adsorption does not require any specific operation temperature. In addition, okara exhibited a high adsorption capacity compared to other natural materials that require chemical and physical processing for adsorbent preparation.     

Adsorptive removal of congo red dye (CR) from aqueous solution by Cornulaca monacantha stem and biomass-based activated carbon: isotherm,kinetics and thermodynamics

Cornulaca monacantha stem (CS) and biomass stem-based activated carbon (CS^AC) were explored for the removal of congo red (CR) dye from water system. The biomaterial was characterized using Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET) and field emission scanning electron microscope (FESEM). The BET surface area of biomass stem-based activated carbon (CS^AC) was recorded to be 304.27 m²/g. The influence of different parameters such as initial CR concentration, adsorbent dosage, contact time, adsorbate pH and temperature onto CR adsorption were studied.The maximum adsorption of CR dye 97.19% and 86.43% were achieved at 55°C using CS^AC and CS adsorbents, respectively. The isotherm, kinetics and thermodynamic study were also investigated to explore the adsorption mechanism. The adsorption isotherm closely follow the Langmuir model (R² = 0.99) suggesting the monolayer adsorption of CR dye. Kinetic results indicated that pseudo second-order and Elovich model provide the better regression coefficient. Thermodynamic study revealed the feasible, spontaneous and endothermic nature of adsorption process. The regeneration study implies that adsorbent was efficiently recovered from CR dye with 0.01 mol/L NaOH solution. The CS^AC adsorbent possesses 75.75% uptake for CR dyes after 6th cycles of desorption-adsorption, respectively. .