Montmorillonite/carboxymethylated cellulose composite beads via the blending method: column adsorption behavior and mechanism for trimethoprim removal at low concentrations

The effective removal of trace trimethoprim (TMP) from aquatic environments remains a significant challenge due to the limited efficiency of conventional adsorbents at low concentrations. In this study, a novel composite adsorbent, MMT/CMCBs, was successfully fabricated by incorporating montmorillonite (MMT) into a carboxymethylated cellulose (CMC) matrix through an optimized extrusion-dropping method. The structural and chemical properties of the beads were systematically characterized using FESEM–EDS, FT-IR, XRD and XPS, revealing a stable macroporous structure (∼1.5 mm diameter) with well-dispersed MMT. Fixed-bed column experiments demonstrated that MMT/CMCBs exhibits exceptional performance for TMP removal, achieving a removal efficiency of 99.874% and maintaining over 90% performance after four regeneration cycles. The breakthrough curves were well-described by the Adams–Bohart model (R2 > 0.94), indicating favorable dynamic adsorption behavior. Mechanism analysis further revealed that the synergistic removal of TMP was driven by hydrogen bonding and chemisorption between the TMP molecules and the functional groups of the composite. This study provides a highly efficient, stable, and environmentally friendly strategy for the elimination of TMP from water, offering significant potential for continuous-flow water treatment.