Novel biosorbent with high adsorption capacity prepared by chemical modification of white pine (Pinus durangensis) sawdust. Adsorption of Pb(II) from aqueous solutions

•Modification of wood sawdust largely enhanced its capacity for adsorbing Pb(II).•Modified sawdust presented an exceptionally high adsorption capacity towards Pb(II).•Maximum capacity of modified sawdust for adsorbing Pb(II) was 304 mg/g.•Adsorption mechanisms of Pb(II) were ion exchange and electrostatic attraction.•Carboxylic sites played a key role in the adsorption of Pb(II) on modified sawdust.

The natural sawdust (NS) from white pine (Pinus durangensis) was chemically modified by a hydrothermal procedure using citric, malonic and tartaric acids. The adsorption capacity of modified sawdust (MS) towards Pb(II) was considerably enhanced due to the introduction of carboxylic groups on the surface of MS during the modification, and the adsorption capacity was almost linearly dependent on the concentration of carboxylic sites. The NS surface was acidic, and the MS surface became more acidic after the modification. At T = 25 °C and pH = 5, the maximum adsorption capacity of the optimal MS towards Pb(II) was 304 mg/g, which is exceptionally high compared to NS and other MS reported previously. The adsorption capacity of MS was considerably reduced from 304 to 154 mg/g by decreasing the solution pH from 5 to 3 due to electrostatic interactions. The adsorption of Pb(II) on MS was reversible at pH = 2, but not at pH = 5. The contribution percentage of ion exchange to the overall adsorption capacity ranged from 70 to 99% and 10–66% at the initial pH of 3 and 5, respectively. Hence, the adsorption of Pb(II) on MS was mainly due to ion exchange at pH = 3 and to both ion exchange and electrostatic attraction at pH = 5.

Graphical abstract(a) Modification of Natural Sawdust. (b) Adsorption of Pb(II) onto Modified Sawdust.Figure optionsDownload full-size imageDownload as PowerPoint slide