Multi-walled and single-walled carbon nanotubes were used as nanoadsorbents for the successful removal of Reactive Blue 4 textile dye from aqueous solutions. The adsorbents were characterised by infrared and Raman spectroscopy, N(2) adsorption/desorption isotherms and scanning and transmission electron microscopy. The effects of pH, shaking time and temperature on adsorption capacity were studied. In the acidic pH region (pH 2.0), the adsorption of the dye was favourable using both adsorbents. The contact time to obtain equilibrium isotherms at 298-323 K was fixed at 4 hours for both adsorbents. The general order kinetic model provided the best fit to the experimental data compared with pseudo-first order and pseudo-second order kinetic adsorption models. For Reactive Blue 4 dye, the equilibrium data (298 to 323 K) were best fitted to the Liu isotherm model. The maximum sorption capacity for adsorption of the dye occurred at 323 K, attaining values of 502.5 and 567.7 mg g(-1) for MWCNT and SWCNT, respectively. Simulated dyehouse effluents were used to check the applicability of the proposed nanoadsorbents for effluent treatment (removal of 99.89% and 99.98%, for MWCNT and SWCNT, respectively). The interaction of Reactive Blue 4 textile dye with single-walled carbon nanotubes (SWCNTs) was investigated using first principles calculations based on density functional theory. Results from ab initio calculations indicated that Reactive Blue 4 textile dye could be adsorbed on SWCNT through an electrostatic interaction; these results are in agreement with the experimental predictions.

The interactions of sodium diclofenac drug (s-DCF) with different graphene species were investigated using both first principles calculations based on Density Functional Theory (DFT) and adsorption experiments. Through batch adsorption experiments, it was found that rGO was a good adsorbent for removing the s-DCF drug from aqueous solutions. The general-order kinetic model shows the best fit to the experimental data compared with pseudo-first order and pseudo-second order kinetic adsorption models. The equilibrium data (at 25 °C) were fitted to the Liu isotherm model. The maximum sorption capacity for adsorption of the s-DCF drug was 59.67 mg g(-1) for rGO. The s-DCF adsorption onto pristine graphene, graphene with a vacancy, reduced oxide graphene (rGO) and functionalized graphene nanoribbons were simulated providing a good understanding of the adsorption process of this molecule on graphene-family surfaces. The results predict a physisorption regime in all cases. Based on these results, the ab initio calculations and the adsorption experiments point out that the graphene-family are promising materials for extracting s-DCF from wastewater effluents.

This study evaluated the feasibility of removing Alizarin Red S dye (ARS) from aqueous solutions, using nanoadsorbents such as single and multiwalled carbon nanotubes (SWCNT and MWCNT, respectively). The effect of pH, shaking time, and temperature on adsorption was studied. The pH 2.0 was observed to show optimum removal for both of the carbon nanotubes. The equilibrium time (298−318 K) was fixed at 65 and 100 min for SWCNT and MWCNT, respectively. The kinetics of adsorption was calculated using pseudo-first-order, pseudo-second-order, and general-order equations. The calculations revealed that the general-order kinetic equation best-fit the adsorption data. The Liu isotherm model best fit the equilibrium data (298−318 K). The maximum sorption capacity at 318 K for ARS dye was 312.5 and 135.2 mg g −1 for SWCNT and MWCNT, respectively. Change in entropy (ΔS°), Gibb's free energy change (ΔG°), and enthalpy (ΔH°) were calculated for the adsorption of ARS dye. The electrostatic interaction between nanoadsorbent−adsorbate was conveyed using the magnitude of change in enthalpy. Ab initio simulation was used to study the interaction of ARS with (5,5) and (8,0) SWCNTs, and (16,0) and (25,0) SWCNTs with and without vacancy. The theoretical calculations showed that the binding energies between ARS dye and SWCNTs are enhanced as the nanotube diameter gets bigger; however, the distance of binding remains unchanged. Therefore, the results from first principle calculations indicated that electrostatic interaction may be responsible for the adsorption of ARS dye onto SWCNT. The theoretical outcomes were found to be in coordination with the experimental estimates.

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