Cationic Dyes In Aqueous Solution Research Articles

Kinetics of the Adsorption of Anionic and Cationic Dyes in aqueous solution by Low-Cost Activated Carbons Prepared from Sea Cake and Cotton Cake

Activated carbons prepared from shea cake (CA-K) and cotton cake (CA-C) were investigated for removal of four dyes in aqueous solutions (0 – 200 mg/L): Reactive Black 5 (RB5), Methylene blue (BM), Reactive Orange 16 (RO16) and Methyl Orange (MO) from water by adsorption. The activated carbons were prepared by chemical activation using phosphoric acid as activation agent. Chemical characteristics of these activated carbons was monitored by Bohem titration and the method of Lopez-Ramon et al. while surface areas of the samples were determined by nitrogen adsorption/desorption isotherm measurement. Activated carbons CA-K and CA-C have the following characteristics: BET surface and the pore volumes are respectively 1148 m/g and 0.607 cm/g for CA-K, 584 m/g and 0.298 cm/g for CA-C. The two activated carbons synthesized are microporous Research Article American Chemical Science Journal, 4(1): 38-57, 2014 39 activated carbon with micropores volume representing more than 70% of the total pore volume. The removal of dyes was studied using batch reactor. The nature of the activated carbon and the dyes are the key factors influencing the contact time. At the equilibrium times (35 to 270 min for CA-K and 60 to 300 min for CA-C), the removal of BM, MO and RO16 was quasi-total while for RB5 the amount adsorbed was about 83%. Based on the adsorption capacity, it was shown that CA-K was more effective than CA-C. Various kinetic models such as pseudo first-order, pseudo second-order and intraparticle diffusion were used to evaluate the mechanism of dyes adsorption on activated carbons. BM, RO16, and MO removal process was found to be governed by second-order kinetic while pseudo-first order kinetic is suitable for RB5 adsorption study. The pHs of the solutions and the amount of activated carbon have strong effect on the adsorption capacity of these dyes. An acid pH (for anionic dyes) and basic pH (for cationic dyes) were favorable for the maximum adsorption of dyes. The isotherm data could be well described by the Freundlich and Langmuir equations in the concentration range of 0–80 mg/L. For the present adsorption process intraparticle diffusion of dyes within the particle was identified to be rate limiting. Both activated carbons were shown to be promising materials for adsorption removal of dyes from aqueous solutions.

Synthesis of a poly-pendant 1-D chain based on 'trans-vanadium' bicapped, Keggin-type vanadtungstate and its photocatalytic properties.

A vanadtungstate cluster-based organic-inorganic hybrid material [NiL4V(IV)W(VI)10W(V)2O40(V(IV)O)2] (1, L = 1,4-bis(imidazol-1-ylmethyl)benzene) was synthesized and characterized by elemental analysis, IR spectra, thermal gravimetric analysis, and single crystal X-ray diffraction analysis. Structural analysis reveals that compound 1 contains a transition metal-centered, bicapped Keggin-type {VW12O40(VO)2} core, connected by nickel linkers into a 1-D chain. These 1D chains interdigitated with each other, achieving an interdigitated 3D supermolecular architecture. Photocatalytic studies indicate that compound 1 exhibits not only active photocatalytic degradation of dye molecules, but also selective photocatalytic activity for degradation of cationic dyes in aqueous solution. Further, this photocatalyst is stable and easily separated from the photocatalytic system for reuse as well.

Adsorption capacity of methylene blue, an organic pollutant, by montmorillonite clay

The isotherms and kinetics of the adsorption of a cationic dye in aqueous solution, methylene blue, on a local Algerian montmorillonite clay mineral (raw, sodium and thermally activated at 300 and 500°C) were determined experimentally. Various parameters influencing the adsorption were optimized, mainly solid–liquid contact time, mass of adsorbent, initial concentration of dye, pH of the solution and temperature. Results showed that the adsorption kinetics were fast: 30 min for the raw clay mineral, and 20 min for sodium clay mineral (SC) and thermally activated at 300°C, whereas with the clay mineral calcined at 500°C, the equilibrium was reached after 150 min only. The maximum adsorption capacity was reached at pH 6.6. Results deducted from the adsorption isotherms also showed that the retention follows the Langmuir model. In addition, it was found that the kinetics were in the order of 2 (K = 2.457 × 106 g/mg.h) for sodium clay and were limited by an intra-particle diffusion. SC was found to be a better adsorbent to remove methylene blue from industrial wastewater.

Flocculation of both anionic and cationic dyes in aqueous solutions by the amphoteric grafting flocculant carboxymethyl chitosan-graft-polyacrylamide

In the current work, a series of amphoteric grafting chitosan-based flocculants (carboxymethyl chitosan-graft-polyacrylamide, denoted as CMC-g-PAM) was designed and prepared successfully. The flocculants were applied to eliminate various dyes from aqueous solutions. Among different graft copolymers, CMC-g-PAM11 with a PAM grafting ratio of 74% demonstrated the most efficient performance for removal of both the anionic dye (Methyl Orange, MO) and the cationic dye (Basic Bright Yellow, 7GL) under the corresponding favored conditions (80mg/L of the flocculant at pH 4.0, and 160mg/L at pH 11.0). In comparison with its precursors, chitosan and carboxymethyl chitosan, CMC-g-PAM11 showed higher removal efficiencies and wider flocculation windows. More importantly, the graft copolymer produced notably more compacted flocs based on image analysis in combination with fractal theory, which was of great significance in practical water treatment. Furthermore, the flocculation mechanism was discussed in detail. The grafted polyacrylamide chains were found to contribute much to the improved bridging and sweeping flocculation effects, but reduced charge neutralization flocculation for the effect of charge screening.

Enhanced Adsorptive Removal of Methyl Orange and Methylene Blue from Aqueous Solution by Alkali-Activated Multiwalled Carbon Nanotubes

An alkali-acitvated method was explored to synthesize activated carbon nanotubes (CNTs-A) with a high specific surface area (SSA), and a large number of mesopores. The resulting CNTs-A were used as an adsorbent material for removal of anionic and cationic dyes in aqueous solutions. Experimental results indicated that CNTs-A have excellent adsorption capacity for methyl orange (149 mg/g) and methylene blue (399 mg/g). Alkali-activation treatment of CNTs increased the SSA and pore volume (PV), and introduced oxygen-containing functional groups on the surface of CNTs-A, which would be beneficial to improving the adsorption affinity of CNTs-A for removal of dyes. Kinetic regression results shown that the adsorption kinetic was more accurately represented by a pseudo second-order model. The overall adsorption process was jointly controlled by external mass transfer and intra-particle diffusion, and intra-particle diffusion played a dominant role. Freundlich isotherm model showed a better fit with adsorption data than Langmuir isotherm model. Adsorption interactions of dyes onto CNTs-A from aqueous solutions were investigated using Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), and Brunauer-Emmett-Teller (BET) method. The remarkable adsorption capacity of dye onto CNTs-A can be attributed to the multiple adsorption interaction mechanisms (hydrogen bonding, π-π electron-donor-acceptor interactions, electrostatic interactions, mesopore filling) on the CNTs-A. Results of this work are of great significance for environmental applications of activated CNTs as a promising adsorbent nanomaterial for organic pollutants from aqueous solutions.

Association of ionic liquids with cationic dyes in aqueous solution: A thermodynamic study

In this paper, the interactions between cationic dyes and the ionic liquids (ILs) have been studied by 31P nuclear magnetic resonance (NMR), UV–Vis spectroscopy and conductometric measurements at different temperatures. It was shown that a decrease in the measured specific conductance of the (dye + IL) mixtures was caused by the formation of non-conducting or less conducting (dye + IL) associates. The associates were formed by 1:1 ratio of cation of the cationic dyes and anion of the ILs by using the 31P NMR and UV–Vis spectroscopy methods. The association constants were calculated by theoretical model based on the deviation from linear behavior, and the association constants were as high as 10 6 (L · mol −1) 2. Thermodynamic results imply that the formation process of association was exothermic nature. It is expected that the associates reported here would have promising application as active materials for the preparation of ion-selective electrode used in the determination of ILs concentrations.

Interaction of sulfophthaleine anions with cationic dyes in aqueous solution

An interaction between the singly and doubly charged anions (HAn− and An2−) of sulfophthaleines (phenol red and its derivatives: bromophenol blue, bromocresol green, bromocresol purple, and bromothymol blue), and singly charged cations (Ct+) of a polymethine (pinacyanol, quinaldine red), results in formation in an aqueous solution of heteroassociate with stoichiometric composition (Ct+)·HAn− and (Ct+)2·An2−. On the basis of spectrophotometric data the association constants were estimated. By quantum-chemical methods AM1 and PM3 the values of formation and reaction enthalpies of the species formed were calculated and the most probable structure of the heteroassociates was determined.