Towards surface acid–base property of the carboxylic multi-walled carbon nanotubes by zero current potentiometry

The surface acid–base property of carboxylic multi-walled carbon nanotubes (MWNTs) is investigated by zero current potentiometry with a new electrochemical measurement system. The pH dependent interface potential variation at the interface of carboxylic MWNTs/solution is investigated by measuring zero current potential Ezcp. In the pH range of 1–11, the pH response of carboxylic MWNTs exhibits two linear relationships according to the following equations: Ezcp = 0.791–0.0535 pH (pH 1–5.1) and Ezcp = 0.643–0.0241 pH (pH 5.1–11), respectively. The intersection at pH 5.1 of two regions indicates the surface pKa value of carboxylic group terminated MWNTs.