Modeling and mechanism of the adsorption of proton onto natural bamboo sawdust

Natural bamboo sawdust with cellulose–lignin polymeric structure was used as a raw adsorbent to remove heavy metal and dyes in water. The analysis of surface properties showed that high proton affinity sites were mainly composed of phenolic and alcohol hydroxyl, while low proton affinity sites mainly consisted of carboxylic acid, silicon hydroxyl, aluminum hydroxyl and some low densities of sulfhydryl and phosphoryl groups. The results fitted by NEM surface complexation model showed: three-sites model fitted acid–base titration data better than two-sites and one-site model. Acid–base titration experiments showed the amount of acid and base consumed was not uniform between acid and alkali side. This was probably due to the swelling of cellulose in acid side, but the possibility that different reactions occurred in acid and alkali side cannot be completely excluded. Pznpc of sawdust was between pH 5.2 and 5.5.