Physisorption-chemisorption coupling mechanism in the 1D-2D network stacking of carbon-based materials with COOH-surface functionalization

Carbon allotropes are remarkable materials with diverse applications, including aquatic pollutant degradation via physisorption and/or chemisorption mechanisms. Different forms of carbon allotropes exhibit different adsorption mechanisms, which make them suitable as a role model to develop highly efficient adsorbents. Here, we manipulate the adsorption mechanism of multiwall carbon nanotube (MWCNT), which is known to possess dominant physisorption through COOH-functionalization to enable its chemisorption for effective use in water treatment applications. We expect that the -COOH functionalization could play a significant role in enhancing hydrogen bonding and - interaction while also improving nanocomposite dispersibility, which further increases dye adsorption capacity. Moreover, by connecting the -COOH roots on the MWCNT surface with graphene, which is also known to have a good physisorption, a one-dimensional-two-dimensional (1D-2D) stacking structure was formed and constructed a three-dimensional (3D) network nanocomposite accordingly. In this model, we found that the -COOH not only provokes a chemisorption, but also serves as a bridge to promote a well-ordered structured 1D-2D stacking, optimizing surface energy both MWCNT and graphene, and further improving methylene blue dye degradation via strong physisorption. Among the tested samples, graphene/MWCNT-COOH nanocomposite with 60% graphene demonstrated the highest dye adsorption ability, achieving 98.02% adsorption efficiency and 82.87 mg/g adsorption capacity uptakes surpassing the control sample without -COOH functionalization and their pristine states. The findings from this study provide insights into the surface modification strategies for advanced carbon-based adsorption materials and open up the potential of -COOH-functionalized carbon nanomaterials for efficient water pollutant degradation.