A sustainable approach for the adsorption of methylene blue from an aqueous background: an adsorbent based on DES/CGS modified GO@ZrO2

Gemini surfactants (GSs) and deep eutectic solvents (DESs) belong to two important classes of industrially important materials which can be used to modify the performances of other entities where they are used for functionalization. A graphene oxide-zirconium oxide (GO@ZrO2) nanocomposite has been synthesised and modified by using a cationic gemini surfactant (CGS, butanediyl-1,4, bis(N,N-hexadecyl ammonium) dibromide (16-4-16)) or by using a well-known DES (reline, choline chloride : urea, molar ratio 1 : 2). The adsorbent materials were characterized by various physicochemical techniques (FTIR, XRD, TEM, SEM-EDX, and TGA). Methylene blue (MB), a well-known industrially important colouring material, has been used as a model adsorbate to investigate its adsorption/removal from aqueous solution by using the above-modified nanocomposites (NCs, CGS-GO@ZrO2 and DES-GO@ZrO2). The adsorption process follows the Langmuir model (R2 ≈ 0.995) together with pseudo-second order rate kinetics. Adsorption variables were optimised in the light of [NC], [MB], pH, and contact time. DES-GO@ZrO2 has been found to be a better candidate for the fast removal of MB (∼100% at 20 mg L−1, 5 m with 2 mg ml−1 DES-GO@ZrO2) when compared with other similarly modified materials. To economize the method, desorption of adsorbed MB (performed by using ethanol) is necessary. It has been found that the DES-GO@ZrO2 performs efficiently even after 5 adsorption–desorption series. The findings of the present study can have potential applications in developing an economic strategy for the purification of industrial dye effluents with a concomitant redressal of aquatic pollution.