Amination of Boron-Doped Diamond Surfaces

Functionalized, especially aminated boron-doped diamond (BDD), is of great interest for catalytic, molecular, and biosensing applications due to its attractive properties. Among various established techniques for diamond amination, UV irradiation in ammonia gas (NH3) has been adopted widely for its simplicity and cost-effectiveness. However, the resultant amination efficiency is found to be relatively low, hindering its usefulness in relevant technologies. In this work, we report a novel strategy for BDD amination by UV irradiation in NH3 that enhances the amination efficiency and results in primary amine dominance. We showed that with hydrobromic acid (HBr) treatment, the nitrogen concentration increased to greater than 6% on the BDD surface. Importantly, it was found that the partial concentrations of both amine groups (primary -NH2 and secondary =NH) strongly depend on the preoxidation states of hydrogenated BDD (HBDD). HBDD treated with sulfuric and nitric acids (H2SO4/HNO3) presented a primary amine group (-NH2) coverage of approximately 94%, whereas the one modified by piranha solution was approximately 63% after amination. Additionally, with such treatments, the sp(2) carbon cleaning and surface smoothening effects were also observed on the BDD, which provides an alternative to cleaning the diamond surface. Theoretical simulations provided insights into the mechanisms of HBr treatment, stability of nitrogen-related groups, and relative group formation. Our work demonstrates the improved amination efficiency and the dominant amine group coverage on the BDD surface, which will be useful for various applications.