Merck Chemical Experiment

Experimental procedure

Chemicals

Acid-functionalized multiwall carbon nanotubes (MWCNT–COOH, 30-50 nm in Outside diameter and length of approximately 20-30 nm, purity>95%) were purchased from US Research Nanomaterials, Inc. NaOH (97%), Fe(NO3)3.9H2O (99%) and Mn(NO3)2.4H2O (≥ 98.5 %) were supplied by Merck Chemicals Ltd (Gauteng, South Africa). Cationic yellow 40 (C20H20ClN3O2, molar mass 369 and ) and Direct Red 16 (C26H17N5Na2O8S2, molar mass 637.55 and ), as adsorbate were purchased from Alvan Sabet Companies (Iran). All the chemicals were used without further treatment. Deionized water was also used for all solution preparation.

Preparation of MnFe2O4/MWCNT–COOH nanocomposite

The composite used in this study were also synthesized by hydrothermal

A predetermined dose of nanoadsorbent was added to each tube containing a particular concentration of DR16 and Y40 and their final pH was adjusted to a certain value by HCl (0.1 M) and NaOH (0.1 M). The tubes were placed in an isothermal shaker at shaker speed of 250 rpm for a specific time. After that, the adsorbent were separated from dye solutions by an Nd-Fe-B magnet, and the concentration of residual dyes in solution was determined using UV–visible Spectrophotometer (UV2100- UNICO) with the λmax at 526.6 and 433 nm for DR16 and Y40, respectively. The adsorption capacity was calculated using mass balance equation written

The influence of pH on the DR16 and Y40 dyes sorption capability using MnFe2O4/MWCNT adsorbent is studied in the pH range of 2-5 and 2-14 with an adsorbent dose of 5 mg for the initial concentration of 50 mg L-1 and 298 k, respectively. It can be seen from the Fig. 6a that the adsorption amount of DR16 onto MnFe2O4/MWCNT decreased with the increasing of pH value, and there is on obvious decrement when the pH is higher than 4. At low pH values, the concentration of H+ ions increased in the system. This may attributed to the electrostatic repulsion between DR16, which is an anionic dye, and positive charged nanoadsorbent surface due to protonation reactions was increased, which leaded to the increase of adsorption capacity. Additionally, in pH ranges greater than pHPZC, the number of negatively charged sites on the surface of nanoadsorbent increased and therefore adsorption onto adsorbents was minimal. In fact, cationic adsorption is favored, when the pH of solution is higher than pHPZC. Fig. 6b, shows that the adsorption of Y40 onto nanoadsorbents. Observed Y40 is cationic at pH 2, and adsorption was minimal; when pH is changed from 2 to4 adsorption capacity of Y40 encountered a sudden rise, slightly increased at pH values between ‘4 to 12’. At pH from 4 to 12, interactions between Y40 and the negatively charged