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

Efficient hydrogen production through water splitting has been the challenging task to be achieved in the present context of energy crisis. Among the various catalysts employed, nitrogen doped Titanium dioxide/Reduced graphene oxide (N-TiO2/RGO) nanocomposite has been established to be a promising photocatalytic material for this purpose. However, nuances of doping nitrogen on TiO2 and the type of nitrogen (pyridinic, pyrrolic and graphitic) stabilized on RGO responsible for facilitating the H-2 production has not yet been addressed mechanistically. In the present investigation, an attempt has been made to synthesise N-Titanium dioxide/N-Reduced graphene oxide (NTNG) nanocomposite under ultrasonication followed by hydrothermal treatment. A stainlesssteel ultrasonic bath, of 6.5 L tank size (LxBxH) 300 x 150 x 150 mm, was used for ultrasonic treatments. The transducers located at the bottom of the ultrasonic bath generate a frequency of 40 kHz with maximum power of 200 W. A mechanism has been proposed including the nuances of formation and the stabilisation of each type of nitrogen on N-RGO as a function of ultrasonication time. The present work supports the stabilization of a given type of nitrogen on RGO through keto enol tautomerism. XPS and FTIR studies have been undertaken to identify the different types of nitrogen doping and the presence of functional groups respectively. XRD, UV-Vis DRS and PL investigations have been made to establish morphological profile and band gap structure of the nanocomposite. It was observed that pyrrolic type nitrogen stabilized on N-RGO augments the efficiency of photocatalytic activity through hydrogen production by water splitting.