We report an interesting interaction between oxidized multiwalled carbon nanotubes (oxi-MWCNTs), tetra n-heptylammonium bromide (ionic liquid) and total chromium ((Cr(VI)/Cr(III)) in this study. The interaction between the IL and oxidized MWCNTs primarily involves electrostatic affinity between the quaternary ammonium cation, and surface carboxyl and hydroxyl groups in oxi-MWCNTs. The IL-oxi-MWCNT adsorbent acts as a host in welcoming the incoming guest hydrochromate anions and several interesting interactions such as cation–π interactions, electrostatic interactions as well as anion–π interactions could be conceptualized in this process. The abundant oxygen-containing functional groups on the surfaces of oxi-MWCNTs play an important role in Cr(VI)/Cr(III) sorption. Characterization of the adsorbent was performed using various characterization techniques such as cross polarization magic angle spinning nuclear magnetic resonance (¹³CPMAS-NMR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), powder-X-ray diffraction (Powder-XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy analysis (TEM), Brunauer–Emmett–Teller (BET) isotherm studies, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). The capability of inductively coupled plasma mass spectrometry (ICP-MS) for Cr(VI) adsorption was extensively studied under different optimal parameters and the maximum adsorption capacity was found to be 85.83 mg g⁻¹ from a nonlinear Langmuir isotherm model. A kinetic study confirms a pseudo second order model and the process could be upgraded by column studies to a sample volume of 2000 mL. Effective regeneration of the adsorbent could be accomplished with sodium hydroxide and the potential of this novel adsorbent has been examined in the removal of Cr(VI)/Cr(III) from aqueous solutions.

Recently, two-dimensional transition metal dichalcogenides (TMDs) have received tremendous attention in many fields including environmental remediation. Magnetic nanoparticles (Fe₃O₄NPs) decorated with MoS₂ (MoS₂@Fe₃O₄NPs) have been synthesized via a new one-step synthesis route and utilized as an efficient adsorbent for removal of Cr(VI)/Cr(III) from aqueous solutions. The obtained MoS₂@Fe₃O₄NPs with numerous surface hydroxyl groups show uniform size and shape, excellent water-dispersibility, and superior magnetic property to enhance the adsorption. The physicochemical properties of the adsorbent prior to and after adsorption of Cr(VI)/Cr(III) were extensively characterized using several advanced instrumental techniques.The adsorption of Cr(VI)/Cr(III) on MoS₂@Fe₃O₄NPs was performed under batch conditions aiming at identification of optimal contact time, pH value of chromium solution, and influence of the presence of competitive ions. This study was supported by modeling of adsorption equilibrium and kinetics by using empirical equations.

A novel aluminium oxy hydroxide [Al–O(OH)] modified graphene oxide was prepared by a chemical precipitation method wherein Al³⁺ ions could interact effectively with the different functional groups of graphene oxide (GO). The prepared (GO–Al–O(OH) adsorbent was tested for the effective defluoridation of water. The Al³⁺ modified graphene oxide adsorbent was characterized using FT-IR, FT-Raman, SEM-EDS, XRD and XPS studies. The thermodynamically feasible adsorption is supported by the pseudo second order kinetics and a high Langmuir maximum adsorption capacity (51.42 mg g⁻¹) for the GO–Al–O(OH) adsorbent. Furthermore, we could treat 2.0 L of 5.0 mg L⁻¹ fluoride ion solution to bring the level within the permissible limits and the regeneration of the adsorbent was done using ammonium hydroxide.