Investigation of basicred 46 adsorption using functionalized multi-walled carbon nanotubes

Dyes are among important types of water pollutants because of their large scale production, usage and toxic/mutagenic nature. There are lots of methods that can be used for dye removal from dye-containing wastewater. Among them, adsorption process is the most preferable due to its convenience, ease of operation and design simplicity. In recent years, researchers claimed that carbon nanotubes are among new nano adsorbents, which their superior hydrophobicity, high specific surface area, and hollow and layered structures make them particularly promising adsorbents. The main aim of this study is to investigate the adsorption behavior of Basic Red 46 (BR46) in aqueous solutions using functionalized multi-walled carbon nanotubes, having covalent attachments of carboxylic groups (MWCNT-COOH). The adsorbent and dye were purchased from Neutrino Corporation and AlvanSabet Company, respectively. Adsorption experiments were performed by adding 100 ml of the dye solution to 250 ml Erlenmeyer flasks. Then, the flasks were put into an ultrasonic bath device for 3 min in order to disperse the MWCNT-COOH. After that, solution and adsorbent were agitated by a standard shaker at 150 rpm agitation speed. All samples were centrifuged at 6000 rpm for 10 min prior to analysis, using a centrifuge. The dye concentrations were measured using a HACH spectrophotometer at 530 nm corresponding to the maximum absorbance for BR46.
There are many of parameters that affect the dye adsorption process including: contact time, initial pH, adsorbent dose, initial dye concentration, temperature, solution volume, agitation speed, etc. In this paper, the effect of 4 main parameters including contact time, initial pH, adsorbent dose and initial dye concentration on BR46 adsorption by MWCNT-COOH were evaluated, using classical experiments. In order to investigate the effect of contact time on dye adsorption, the three other parameters were fixed and the contact time was changed between 10 to 180 minutes. The corresponding data showed that the optimum contact time for BR46 adsorption by MWCNT-COOH was 80 minutes. Then, the experiments accomplished by fixed contact time (80 minutes), adsorbent dose and dye concentration and altering the solution pH from 3 to 10. The data showed that the optimum solution pH was 9 for BR46 adsorption by MWCNT-COOH. After that, contact time and pH were adjusted to their optimum values, dye concentration also was fixed and the adsorbent dose was altered from 0.05 g/l to 0.35 g/l, in order to evaluate the effect of adsorbent dose on the adsorption process. The data indicated that the optimum MWCNT-COOH dose for BR46 adsorption was 0.05 g/l. Finally, the contact time, solution pH and adsorbent dose were fixed to their optimum values and the initial dye concentration was varied from 50 mg/l to 200 mg/l. The obtained data showed that the optimum initial dye concentration for the BR46 dye removal by MWCNT-COOH was 150 mg/l. In order to obtain an interaction between the adsorbent and adsorbate, adsorption isotherm studies were conducted with different adsorbent doses ranging from 0.05 to 0.35 g/L at pH = 9 and initial dye concentration = 150 mg/L. Three isotherms including Langmuir, Freundlich and Tempkin were tested. In order to investigate the mechanism of sorption, the kinetics parameters for the adsorption process were also determined for contact times ranging from 10 to 80 minutes by monitoring the weight of dye adsorbed per weight of adsorbent. Eighty minutes were used for the adsorption kinetic study in order to have more accurate data. Kinetics models used in this study included the pseudo-first order, the pseudo-second order and the Elovich model.
The results indicated that the maximum dye removal efficiency occurs at a contact time of 80 minutes, an initial pH of 9, 0.05 g/l of the adsorbent and an initial dye concentration of 150 mg/l. The maximum adsorption capacity of the BR46 by MWCNT-COOH was obtained about 265 mg/g along with acceptable removal efficiency of 95%. The adsorption equilibrium data were analyzed using various adsorption isotherms, and the results showed that the adsorption behavior of the BR46 could be almost accurately described by Freundlich isotherm (R2= 0.9533). The Freundlich isotherm describes that the uptake of dye molecules occurs on a heterogeneous surface by monolayer adsorption. In addition, kinetic studies showed that the adsorption of the BR46 by MWCNT-COOH follows the pseudo-second order model with R2= 0.926.