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

Abstract

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.

Evaluation of Adsorption Capacity of Methylene Blue in Aqueous Medium by Two Adsorbents: The Raw Hull of <i>Lophira Lanceolata</i> and Its Activated Carbon

“…Generally three steps are involved during the adsorption process by the porous adsorbent: i) transfer of the molecule adsorbed from the breast of the solution to the external surface of the adsorbent (external diffusion), ii) penetration of the adsorbed molecule to Adsorption of the molecule on the inner surface of pores [12]. To understand the mechanism of adsorption of the two dyes we use the equation of Weber et al (1963) [13]:…”

Adsorption of pyridine from aqueous solutions by polymeric adsorbents MN 200 and MN 500. Part 2: Kinetics and diffusion analysis

“…Chemical reaction or van der Waals interactions between the adsorbate and the adsorbent, in general, are not rate limiting unless chemical modifications prevalently occur during adsorption [24,25]. In most cases, intraparticle diffusion rate-controls the overall adsorption kinetics [24,[26][27][28][29].…”

Activated Carbon and Clay Minerals for the Sorptive Removal of Denatonium Ions from Denatonium Benzoate Solutions

“…Given the interlayer accessibility of denatonium ions, sorption to internal sites is expected, however the relative number of external sites versus internal sites could favor pH-dependent sorption resulting in hydrogen-ion concentration dependent isotherms. Since 1/n values generally fell between 0.803 and 1.194, the sorption of denatonium ions to each clay mineral could be classified as moderate to highly favorable under the conditions of our study [22].…”

“…Generally, 1/n values less than unity are interpreted as reflecting a favorable sorption process while values in excess of 2 imply an unfavorable sorption process [22]. The linearized Langmuir model's four types are:…”