High-performance removal of toxic phenol by single-walled and multi-walled carbon nanotubes: Kinetics, adsorption, mechanism and optimization studies

•MWCNTs and SWCNTs are promising adsorbents for toxic phenol removal from wastewater.•Effect of process parameters on removal of toxic phenol was observed.•The maximum adsorption capacity of phenol adsorbed by MWCNTs and SWCNTs was found as 64.60 and 50.51mg/g.•Uptake of phenol was not hindered by the presence of the competing anions, such as SO42− and Cl−. The adsorption capabilities of two nano-sized adsorbents: multi-walled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs) were investigated for the removal of toxic phenol. The maximum adsorption capacities of MWCNTs and SWCNTs were determined as 64.60 and 50.51mg/g, respectively. Adsorption kinetics followed the pseudo-second order model for both adsorbents. The optimum conditions using SWCNTs and MWCNTs were pH 6.57 and 4.65, phenol concentration 50 and 50mg/L, dose 1.97 and 2g/L and contact time 36 and 56min, respectively. The results indicated that MWCNTs and SWCNTs were proven as high-performance adsorbents for toxic phenol removal from wastewater.