High sensitivity portable humidity sensor based on the hydrophilic surface of carbon ring-carbon nitride nanosheets and its wireless application in respiration detection

Abstract

In this paper, carbon nitride(C3N4) coupled with carbon ring(Cring) with a similar aromatic structure was synthesized by a multi-step-heating method for real-time discrimination of relative humidity(RH) over a broad range of RH(10 %–90 %) at room temperature. Scanning electron microscopy revealed a sheet-like morphology of the as-synthesized sample, consistent with the layered structure observed by XRD analysis. Moreover, the specific surface area of the in-plane heterostructure of Cring-C3N4(68.7 m2g−1) is greater than that of pure g-C3N4(9.1 m2g−1). According to the electrochemical impedance spectroscopy, the introduction of Cring into the C3N4 contributed to the more efficient charge carrier transfer and greatly improved the electrical conductivity. Significant sensing attributes of the sensor, including the response, response/recovery time, hysteresis, repeatability, durability, and selectivity, were evaluated. The test results indicate the significantly enhanced humidity-sensing performance of the Cring-C3N4 sensor in terms of response value(∼416), an utterly reversible sensing process with short response/recovery times(2 s and 3 s, respectively), high stability, and negligible hysteresis compared to pure g-C3N4, a good property for utilization in respiration monitoring. The possible reason for the admirable humidity sensing property can be attributed to the high specific surface area as well as a high proportion of available active sites for water molecules' adsorption and reaction.