Enhanced adsorption capacity of phosphoric acid-modified montmorillonite clay and ground coffee waste-derived carbon-based functional composite beads for the effective removal of methylene blue

Abstract

Clays, valued for their versatility, serve as economical adsorbents. Recent studies show that physical, thermal, and chemical modifications can enhance their adsorption capacity. In this study, the synthesis of a functional bead comprising phosphoric acid-modified montmorillonite (PMMT) and coffee waste carbon (CWC) and its application for the efficient adsorption of methylene blue (MeB) dye is investigated. A highly flexible and low-cost phyllosilicate, montmorillonite clay, MMT was treated with phosphoric acid to enhance the ionic density, composited with CWC, resulting in improved surface properties thereafter was transformed into easily recoverable bead form through subsequent cross-linking steps. These functional composite beads were characterized using various characterization techniques. As a result, the existing tetrahedral sheets possessed by the MMT having weak bonds between the layers are improved in a way that they can allow molecule exchange for the efficient enhancement of the adsorption capacity of the composite material. Moreover, after the necessary modifications, the adsorbent was found to be mechanically stable, inhibiting secondary pollutions from the use in powder forms while allowing the interlayers favorable for not just cationic but also anionic exchange whilst increasing the specific surface area and pore volume. The surface area was enhanced to 9.93 m2 /g. Following this, maximum adsorption capacity of 489.9mg/g was attained showing a superior removal efficiency for methylene blue dye (>80%). The adsorption equilibrium was analyzed using Freundlich and Langmuir models. The adsorption mechanism aligns with the Langmuir model which encompasses a monolayer adsorption. All in all, this study is anticipated to play a crucial role in the search for adsorbents with multiple functionalities and good structural stability during and after use.