Ultra-fast adsorption of organic pollutants using TEMPO-oxidized Metaplexis japonica tomentum cellulose microtubes

Within the discipline of treating organic wastewater, the development of a bio-based adsorbent with both an ultra-fast adsorption rate and a high removal efficiency remain a challenging goal. An efficient adsorbent, named oxidized Metaplexis japonica tomentum cellulose microtubes (OMTC), was fabricated. This adsorbent came from the tomentum of Metaplexis japonica seeds. The C6 hydroxyl moieties of cellulose were transformed into carboxyl functionalities by means of a selective oxidation method. The process used a TEMPO/NaClO/NaClO₂ combination while maintaining a weakly acidic pH. The oxidation led to the creation of numerous active sites. At the same time, it preserved the intact natural microtube structure. The structure had a diameter of approximately 20 μm and a wall thickness of about 1.16 μm. An alkali treatment removed impurities. This treatment provided a uniform reaction interface for the subsequent oxidation. After the oxidation, the carboxyl group content on the cellulose surface reached 0.48 mmol/g ± 0.02 mmol/g. The surface also changed from hydrophobic to hydrophilic. The as-prepared OMTC showed a high removal performance toward cationic organic pollutants. Under alkaline conditions, its adsorption capacity increased. It also showed an ultra-fast adsorption rate. Specifically, it reached 79% of the equilibrium adsorption capacity within 10 s and achieved near-equilibrium within 2 min. The oxidized cellulose microtube adsorbent combines the natural high specific surface area with the high-density carboxyl sites introduced by oxidation. The synergistic effect of the two enables rapid and efficient treatment of organic wastewater.