Toxic Cationic Dye Research Articles

Kinetic Study of the Adsorption of Synthetic Dyes on Graphene Surfaces

Graphene (G) and Graphene oxide (GO) were employed in the present study in theremoval of two toxic cationic dyes, Basic Red 12 (BR 12) and Basic Red 46 (BR 46), from aqueous solutions. Graphene oxide was synthesized according to the modified Hummers’ method, and characterized by XRD and FTIR. The effect of various parameters such as contact time, solution pH, dye concentration and temperature, were studied. The kinetics and thermodynamics of the process of dye removal were investigated. The results indicate that the kinetics of the removal of BR 12 and BR 46 using G and GO as adsorbents follows a pseudosecond order model. G and GO exhibited high adsorption capacity for BR 12 and BR 46. The dye removal depends thereby on the initial pH of the solution with maximum uptake occurring at about pH=9.

Optimization of Simultaneous Removal of Methylene Blue, Crystal Violet, and Fuchsine from Aqueous Solutions by Magnetic NaY Zeolite Composite

In this study, the adsorbent, magnetic NaY zeolite was synthesized for simultaneous removal of three toxic cationic dyes, methylene blue, crystal violet, and fuchsine, from aqueous solutions. The influences of five dominant parameters of pH, temperature, time, initial dyes concentration, and adsorbent mass on dyes adsorption were investigated. The percentage of dye removal was mathematically described as a function of experimental parameters and was modeled through central composite design (CCD). According to the predicted experiments, optimum conditions of 10.3, 50 °C, 45 min, 10 mg L−1, and 46.2 mg, for pH, temperature, time, initial dyes concentration, and adsorbent mass were resulted, respectively. The maximum experimentally achieved dye removal percent of 98.4 ± 0.6, 98.1 ± 0.5, and 98.1 ± 0.3 were obtained, which were close to the percent of model dye removal prediction of 99.0, 98.6, and 98.4 for methylene blue, crystal violet, and fuchsine, respectively. This agreement showed that the central composite design model could ideally make an acceptable estimation of the process.

Kinetics, thermodynamics, and equilibrium evaluation of adsorptive removal of methylene blue onto natural illitic clay mineral

The natural illitic clay mineral (NICM) has been used as a low cost and highly effective adsorbent in the removal of a toxic cationic dye, methylene blue (MB), from aqueous solution by a batch adsorption technique. The effects of experimental parameters such as initial pH of the aqueous solution, contact time, initial MB concentration, adsorbent concentration, ionic strength, and temperature were studied in detail upon the adsorption process. The process was found to be independent of initial solution pH and the adequate equilibrium time for the adsorption of MB onto NICM was only 60 m. The experimental data were analyzed by the Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherm models and showed a good fit with both the Langmuir and Freundlich isotherm models. The monolayer adsorption capacity of NICM was found to be 24.87 mg g−1 by using Langmuir isotherm model. The kinetics of the adsorption were tested using pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. The results showed that the adsorption of MB onto NICM proceeds according to the pseudo-second-order model. Thermodynamic parameters indicated that the present adsorption process was feasible, spontaneous, and endothermic in nature.

Adsorption Characteristics of Modified Wheat Husk for the Removal of a Toxic Dye, Methylene Blue, from Aqueous Solutions

Adsorption characteristics of modified wheat husk for the removal of a toxic cationic dye, methylene blue, from aqueous solutions have been investigated. The adsorbent, wheat husk, was characterized by Fourier transform infrared spectra (FTIR) and scanning electron microscopy (SEM) for its functional group and surface characteristics. The removal decreased by increasing temperature from 303 to 373 K. The removal was found to be pH dependent, and it decreased from 96.2 to 40.7% by varying the pH of the solution from 4.5 to 9.5. It was observed that 93.4% removal of methylene blue was achieved at an initial dye concentration of 13.37 × 10 −2 mol=L at 303 K. Equilibrium adsorption data for the removal of methylene blue were analyzed by Langmuir, Freundlich, and Tempkin isotherm models. Values of thermo- dynamic parameters viz ΔG°, ΔH°, and ΔS° were determined. The negative value of ΔH° confirmed the exothermic nature of removal of methylene blue by adsorption on modified wheat husk. DOI: 10.1061/(ASCE)HZ.2153-5515.0000191. © 2014 American Society of Civil Engineers.

Surfactant-modified alumina: An efficient adsorbent for malachite green removal from water environment

Surface of alumina was modified with sodium dodecyl sulfate (SDS), an anionic surfactant. The surfactant-modified alumina (SMA) was characterized by FTIR and thermal analysis. The SMA was then used for the removal of malachite green (MG; Basic Green 4), a well-known toxic cationic dye from aqueous environment. The removal of MG takes place in the micellar structure formed on alumina surface, and the process is called adsolubilization. All the studies were carried out in batch mode. The kinetic studies showed that 1 h contact time was sufficient to attain equilibrium. SMA was very efficient to remove MG up to 99% under optimum conditions. The concentration range of MG was 20–100 mg/L. The isotherm studies showed that it follows Langmuir model better than the Freundlich model. The maximum adsorption capacity was 185 mg/g. The effects of various parameters such as pH, presence of interfering ions (Cl−, NO3 −, H2PO4 −, SO4 2−, Fe2 +, Ca2 +) and organics (pesticides such as 2,4-dichlorophenoxyacetic acid, atrazine, endosulfan, and humic acid) are evaluated. It was observed that H2PO4 −, Fe2 +, endosulfan, and humic acid have maximum interference. Desorption of MG from exhausted SMA using acetone, and its reuse was studied. The regenerated adsorbent shows ∼ 80% efficiency on the removal of MG. The usability of SMA for the removal of MG from real wastewater was also examined. The kinetic equilibrium was attained within 1 h and the removal could be achieved up to ∼ 95% at a dose of 20 g/L. The adsorption followed Freundlich isotherm model better than the Langmuir model.

Removal of cationic dyes from aqueous solutions by kaolin: Kinetic and equilibrium studies

Experimental investigations were carried out using commercially available kaolin to adsorb two different toxic cationic dyes namely crystal violet and brilliant green from aqueous medium. Kaolin was characterized by performing particle size distribution, BET surface area measurement and XRD analysis. The effects of initial dye concentration, contact time, adsorbent dose, stirring speed, pH, salt concentration and temperature were studied in batch mode. The extent of adsorption was strongly dependent on pH of solution. Free energy of adsorption (ΔG0), enthalpy (ΔH0) and entropy (ΔS0) changes were calculated. Adsorption kinetic was verified by pseudo-first-order, pseudo-second-order and intra-particle-diffusion models. The rate of adsorption of both crystal violet and brilliant green followed the pseudo-second-order model for the dye concentrations studied in the present case. The dye adsorption process was found to be external mass transfer controlled at earlier stage and intra-particle diffusion controlled at later stage. Calculated external mass transfer coefficient showed that crystal violet dye adsorbed faster than brilliant green on kaolin. Adsorption of crystal violet and brilliant green on kaolin followed the Langmuir adsorption isotherm.

Separation of congo red by surfactant mediated cloud point extraction

An attempt has been made to remove color from wastewater containing congo red (a toxic cationic dye) by surfactant mediated cloud point extraction (CPE) in batch mode using Triton X-100 (TX-100) as non-ionic surfactant. Most of the dye molecules get solubilized in the coacervate phase leaving a dye free dilute phase. The effects of the concentration of feed mixture (both dye and surfactant), temperature and salt concentration on the concentration of both dye and surfactant in the coacervate phase and dilute phase have been studied. An optimum set of surfactant concentration, temperature and salt concentration are obtained for removal of dye. Experimental investigations have also been carried out for the recovery of surfactant from dilute phase applying solvent extraction (SE) in batch condition using heptane as extracting medium.

Separation of congo red by surfactant mediated cloud point extraction

An attempt has been made to remove color from wastewater containing congo red (a toxic cationic dye) by surfactant mediated cloud point extraction (CPE) in batch mode using Triton X-100 (TX-100) as non-ionic surfactant. Most of the dye molecules get solubilized in the coacervate phase leaving a dye free dilute phase. The effects of the concentration of feed mixture (both dye and surfactant), temperature and salt concentration on the concentration of both dye and surfactant in the coacervate phase and dilute phase have been studied. An optimum set of surfactant concentration, temperature and salt concentration are obtained for removal of dye. Experimental investigations have also been carried out for the recovery of surfactant from dilute phase applying solvent extraction (SE) in batch condition using heptane as extracting medium.