Tuning the type of nitrogen on N-RGO supported on N-TiO2 under ultrasonication/hydrothermal treatment for efficient hydrogen evolution - A mechanistic overview

•Types of nitrogen doping on N-RGO is investigated under Ultrasonication.•Two hours of ultrasonication/hydrothermal reduction stabilises pyrrolic nitrogen.•Mechanism has been proposed for nitrogen doping types through keto–enol tautomerism.•Pyrrolic nitrogen shows highest H2 production than pyridinic and graphitic nitrogen.