Nanocrystalline TiO2/Ti3C2Tx MXene composites with a tunable work function prepared using atmospheric pressure oxygen plasma

Composites of TiO₂ and Ti₃C₂T_x MXene are of great interest because they combine superior TiO₂ photocatalytic activity with excellent MXene conductivity. As these composites have conventionally been prepared using methods requiring high temperatures, a process for producing similar materials at reduced temperature could be beneficial for applications in flexible and printed electronics. Therefore, we used low-temperature dielectric barrier discharge to develop a method for forming crystalline TiO₂ by treating Ti₃C₂T_x MXene surfaces with high-power-density oxygen plasma comprising various energetic and reactive oxygen species, which oxidize MXene surfaces and form TiO₂ nanoparticles on disordered graphitic carbon sheets within a few seconds. Scanning electron microscopy was used to observe the plasma-induced morphological changes to elucidate the TiO₂ formation mechanism. The MXene surface chemistry was studied in detail using X-ray photoelectron spectroscopy and ab initio modelling. The crystalline phase of TiO₂ was further studied using transmission electron microscopy and Raman spectroscopy. The results presented here suggest the formation of small anatase nanoparticles on the surface of MXenes within just seconds of plasma exposure. Nanoparticles grew with prolonged plasma treatment and a transition from anatase to rutile was observed. Considering that the temperature of plasma was always below 70 °C, the oxygen plasma process for the preparation of TiO₂/Ti₃C₂T_x composites is an excellent candidate for application on temperature-sensitive substrates in flexible and printed electronics.