Abstract

Does the hybridization of the surface of carbon nanoparticles (CNPs) affect the properties of the surface carboxyl and hydroxyl groups and the features of their deprotonation in water? To answer these questions in this work the structures of graphite-and diamond-like carbon cells with OH and COOH groups optimized by the DFT method were studied. It was found that in the same suspensions the OH and COOH groups deprotonate easier being on carbon with sp² hybridization rather than sp³. Theoretical estimates have shown that in aqueous suspensions of CNPs, “isolated” carboxyl COOH groups on sp²/sp3 hybridized carbon sites have pK_a in the ranges of 3.5–4.5/4.5–5, and the hydroxyl OH groups – in the ranges of 8.5–10/15–18, respectively. The conclusions made on the basis of theoretical calculations about the features of deprotonation of surface groups of CNPs are experimentally confirmed by the changes of the zeta-potentials of oxidized detonation nanodiamonds with the change of the pH of the environment.

摘要

碳纳米粒子（CNPs）表面的杂化是否会影响表面羧基和羟基的性质以及它们在水中去质子化的特征？为了在这项工作中回答这些问题，研究了通过 DFT 方法优化的具有 OH 和 COOH 基团的石墨和类金刚石碳电池的结构。发现在相同的悬浮液中，OH 和 COOH 基团在具有 sp ²杂化而不是 sp ³的碳上更容易去质子化。理论估计表明，在 CNP 的水悬浮液中，sp ² /sp3 杂化碳位点上的“孤立”羧基 COOH 基团具有 pK _a在 3.5–4.5/4.5–5 的范围内，羟基 OH 基团分别在 8.5–10/15–18 的范围内。基于理论计算得出的关于 CNPs 表面基团去质子化特征的结论通过氧化爆轰纳米金刚石的 zeta 电位随环境 pH 变化的变化而得到实验证实。