Engineering surface of camphor biomass by extracting lignin and introducing multiple oxytropic sites via grafting tanning acid and iron trichloride

Pyrolysis and activation are common methods for preparing biochar adsorbents, but these treatments often increase porosity while destroying oxygen-containing functional groups that are important for pollutant binding. In this work, a non-carbonized strategy was developed to regulate biomass surface chemistry using camphor wood. Instead of thermal treatment, lignin was removed and the material was modified with tannic acid (TA) and Fe 3 + to construct adsorption sites. The degreasing–oxidation process removed lignin and hemicellulose, exposing cellulose surfaces rich in -OH. TA and Fe 3+ further introduced polar and coordination-active sites. Structural characterization showed that lignin removal triggered hydrogen‑bond rearrangement accompanied by pore contraction, which critically governed the subsequent adsorption behavior. These interfacial changes strongly affected adsorption behavior. Raw camphor showed almost no adsorption toward methylene blue because of the inaccessible functional groups. Fe-modified samples displayed limited adsorption due to site occupation by coordination. Oxidized camphor exhibited improved adsorption because more −OH and −COOH groups were exposed. TA modification alone produced only slight enhancement because of pore restriction and hydrogen-bond competition. In contrast, TA/Fe-modified oxidized camphor achieved the highest adsorption capacity of 312.07 mg/g, higher than oxidized camphor (164.09 mg/g). The improvement mainly resulted from the synergistic effect of exposed -OH, -COOH, and partially coordinated Fe 3+ sites. The material also maintained more than 80% of its initial adsorption capacity after five cycles. Overall, this work shows that adsorption enhancement mainly comes from interfacial reconstruction rather than pore development, providing a simple route for preparing biomass-based functional adsorbents.