Polyethyleneimine-Starch Functionalization of Single-Walled Carbon Nanotubes for Carbon Dioxide Sensing at Room Temperature

[Image: see text] There is an ever-growing interest in the detection of carbon dioxide (CO(2)) due to health risks associated with CO(2) emissions. Hence, there is a need for low-power and low-cost CO(2) sensors for efficient monitoring and sensing of CO(2) analyte molecules in the environment. This study reports on the synthesis of single-walled carbon nanotubes (SWCNTs) that are functionalized using polyethyleneimine and starch (PEI-starch) in order to fabricate a PEI-starch functionalized SWCNT sensor for reversible CO(2) detection under ambient room conditions (T = 25 °C; RH = 53%). Field-emission scanning electron microscopy, high-resolution transmission electron microscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy are used to analyze the physiochemical properties of the as-synthesized gas sensor. Due to the large specific surface area of SWCNTs and the efficient CO(2) capturing capabilities of the amine-rich PEI layer, the sensor possesses a high CO(2) adsorption capacity. When exposed to varying CO(2) concentrations between 50 and 500 ppm, the sensor response exhibits a linear relationship with an increase in analyte concentration, allowing it to operate reliably throughout a broad range of CO(2) concentrations. The sensing mechanism of the PEI-starch-functionalized SWCNT sensor is based on the reversible acid–base equilibrium chemical reactions between amino groups of PEI and adsorbed CO(2) molecules, which produce carbamates and bicarbonates. Due to the presence of hygroscopic starch that attracts more water molecules to the surface of SWCNTs, the adsorption capacity of CO(2) gas molecules is enhanced. After multiple cycles of analyte exposure, the sensor recovers to its initial resistance level via a UV-assisted recovery approach. In addition, the sensor exhibits great stability and reliability in multiple analyte gas exposures as well as excellent selectivity to carbon dioxide over other interfering gases such as carbon monoxide, oxygen, and ammonia, thereby showing the potential to monitor CO(2) levels in various infrastructure.