Sustainable fabrication of Co-MOF@CNT nano-composite for efficient adsorption and removal of organic dyes and selective sensing of Cr(VI) in aqueous phase

In view of the fascinating applications of hybrid materials, a new nanocomposite is fabricated in order to achieve the excellent adsorption capacity for cationic dye as well as selective sensing ability toward Cr⁶⁺ ions in the aqueous phase. The present work deals with the synthesis of metal-organic framework (MOF) based nanocomposite, i.e., Co-MOF@CNT using Co-MOF and functionalized carbon nanotubes (CNTs) by adopting a facile, in-situ solvothermal approach for application in the field of wastewater treatment. The as-synthesized nanocomposite was characterized in detail through Fourier transform infrared spectroscopy (FTIR), Raman, powder X-ray diffraction (PXRD), thermal gravimetric analysis/differential thermal analysis (TGA/DTA), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques, revealing the successful fabrication of both parent materials in the hybrid nanocomposite. The developed nanocomposite (Co-MOF@CNT) was assessed for its application in metal sensing as well as for the selective adsorption and elimination of hazardous cationic dyes [from the mixture containing cationic dye, methylene blue (MB) and anionic dye, methyl orange (MO)] from wastewater. The nanocomposite exhibits high selectivity and metal-sensing response towards Cr⁶⁺ ion under ambient conditions with an ultra-low detection limit of ∼0.00649 ppm or 0.125 μM, as reported so far. Moreover, the detection ability of Co-MOF@CNT can be restored for up to five cycles significantly. In addition, the developed nanocomposite displayed a high removal rate of about 98% at equilibrium under optimum temperature (25 °C) and neutral pH for cationic (MB) dye with ultimate selectivity. The kinetic studies revealed that the adsorption proceeds via pseudo-second order reaction. The dye adsorption mechanism suggests the presence of electrostatic, ᴫ-ᴫ and hydrogen bonding interactions between nanocomposite and the dye. This hybrid nanocomposite also exhibited high reusability of up to four cycles for MB dye. All in all, Co-MOF@CNT nanocomposite with superior Cr⁶⁺ metal sensing performance and MB dye adsorption could pave a promising path for environmental applications in this high-tech industrial era.