TiO2/graphitic carbon nitride nanosheet composite with enhanced sensitivity to atmospheric water

Understanding the fundamentals of transport properties in two-dimensional (2D) materials is essential for their applications in devices, sensors, and so on. Herein, we report the impedance spectroscopic study of carbon nitride nanosheets (CNNS) and the composite with anatase (TiO2/CNNS, 20 atom% Ti), including their interaction with atmospheric water. The samples were characterized by X-ray diffraction, N-2 adsorption/desorption, solid state H-1 nuclear magnetic resonance spectroscopy, thermogravimetric analysis, and transmission electron microscopy. It is found that CNNS is highly insulating (resistivity rho similar to 10(10) omega cm) and its impedance barely changes during a 20 min-measurement at room temperature and 70% relative humidity. Meanwhile, incorporating the semiconducting TiO2 nanoparticles (similar to 10 nm) reduces rho by one order of magnitude, and the decreased rho is proportional to the exposure time to atmospheric water. Sorbed water shows up at low frequency (<10(2) Hz) with relaxation time in milliseconds, but the response intrinsic to CNNS and TiO2/CNNS is evident at higher frequency (>10(4) Hz) with relaxation time in microseconds. These two signals apparently correlate to the endothermic peak at <= 110 degrees C and >250 degrees C, respectively, in differential scanning calorimetry experiments. Universal power law analysis suggests charge hopping across the 3D conduction pathways, consistent with the capacitance in picofarad typical of grain response. Our work demonstrates that the use of various formalisms (i.e., impedance, permittivity, conductivity, and modulus) combined with a simple universal power law analysis provides insights into water-induced transport of the TiO2/CNNS composite without complicated curve fitting procedure or dedicated humidity control.

Automated summary

In this study, the impedance spectroscopy of carbon nitride nanosheets (CNNS) and the composite with anatase (TiO2/CNNS) were investigated, along with their interaction with atmospheric water. The results showed that CNNS is highly insulating, while the incorporation of TiO2 nanoparticles significantly reduced the resistivity of the composite and the decrease in resistivity was proportional to the exposure time to atmospheric water. This study provides important insights into the water-induced transport of TiO2/CNNS composite without the need for complicated curve fitting procedures or dedicated humidity control.