Organo-apatites for lead removal from aqueous solutions: A comparison between carboxylic acid and aminophosphonate surface modification

Organo-apatites were prepared by in situ incorporation of adipic acid, citric acid and nitrilotris(methylene)triphosphonic acid. The resulting powders consist of poorly-crystalline nanosized apatites with organic content in the 2–8 wt% range. All materials exhibit faster sorption rate and higher sorption capacity for Pb2+ in acidic solutions compared to the pure apatite. This is especially true for carboxylate-modified powders that exhibit the highest-to-date maximum lead sorption capacity (≈ g g−1). These properties can be correlated with the ability of introduced organic moieties to modify the acido-basic properties of the material surface and to form stable complexes with Pb2+.