Carbonaceous nanomaterials as effective and efficient platforms for removal of dyes from aqueous systems

In this study, the feasibility of using carbonaceous nanomaterials was explored for adsorptive removal of methylene blue (MB) and methyl orange (MO) dyes from contaminated water under dark conditions. The morphology and crystalline nature of synthesized carbonaceous nanomaterials (e.g., multi-walled carbon nanotubes [MWCNTs], activated carbon [AC], and their nanocomposite) were characterized by different microscopic and spectroscopic techniques. Furthermore, adsorption experiments were carried out by controlling several key parameters including solution pH, adsorbent dosage, dye concentration, contact time, and temperature. First, the adsorptive behavior of MWCNTs was explained with the aid of adsorption isotherms and kinetics. Thereafter, the adsorptive performance of MWCNTs was compared with those of AC and MWCNTs/AC, and the maximum adsorption capacity (mg/g) of MB/MO was in the order of MWCNTs/AC nanocomposite (232.5/196.1) > MWCNTs (185.1/106.3) > AC (161.3/78.7). The improved adsorption performance (e.g., in terms of adsorption capacity and partition coefficient) of the MWCNTs/AC nanocomposite could be attributed to the presence of more active sites on its surface. Furthermore, their reusable efficiency was in the order of MWCNTs/AC nanocomposite (90.2%), MWCNTs (81%), and AC (67%) after the first step of recovery. The performance of these adsorbents was also evaluated for real field samples. In comparison to MWCNTs and AC, the MWCNTs/AC sorbents offered excellent performance in both single and binary systems, i.e., ~99.8% and 98.7% average removal of MB and MO, respectively.