Calcium carbonate crystallisation at charged graphite surfaces

Calcium carbonate crystallisation on surfaces has been studied extensively due to its prominence in biomineralisation, but the role of surface charge in nucleation and growth is not well understood. We have employed potential-controlled Highly Oriented Pyrolytic Graphite (HOPG) surfaces to demonstrate the significant impact of surface charge on calcium carbonate crystallisation: at negatively charged HOPG surfaces, calcite, aragonite and vaterite all nucleate from high energy positively-charged crystal faces, contrasting with the stable (104) calcite planes nucleated at positively charged surfaces. These observations are explained and rationalised. For identical solution conditions, the crystallisation of calcium carbonate (polymorph and crystal orientation) at Highly Oriented Pyrolytic Graphite substrates is highly dependent on substrate surface charge.