Advancing Gas Sensing Through Innovative Composite Chemiresistors

Precise detection of gaseous species like acetone or NOx is essential for non-invasive diagnostics via breath analysis. While metal oxide-based chemiresistors are promising candidates, they often face limitations in selectivity and low-temperature responsiveness. This study addresses these challenges by engineering advanced nanocomposites through several distinct strategies. In the first approach, SnO2 was combined with a Zn(II) porphyrin at varying weight ratios (ZnTPPF20). The optimized 1:32 ZnTPPF20/SnO2 composite exhibited a detection limit of 200 ppb for acetone at 120 °C. DFT calculations confirmed that ZnTPPF20 enhances SnO2 conductivity via electron donation, boosting sensor performance. The second strategy involved incorporating p-type multi-walled carbon nanotubes (MWCNTs) and polyaniline (PANI) into a porous 3D ZnO network synthesized via flame spray pyrolysis. Among various ratios, the 32:1 ZnO@MWCNTs/PANI composite demonstrated the best response to acetone at 150 °C and maintained promising selectivity even at room temperature. This behavior was attributed to the nanoheterojunctions formation between p-type MWCNTs/PANI and n-type ZnO, which modulate resistance through depletion/accumulation layer dynamics, enhanced by improved carrier mobility from MWCNTs. Lastly, the third approach focused on innovative MXene-based 2D materials, specifically Ti3C2Tx and Nb2CTx, which showed promising preliminary results for both humidity sensing and NOx detection. Therefore, these findings underscore how incorporating Zn(II)-porphyrins or conductive p-type polymers into metal oxides, along with employing surface-tunable 2D MXenes, can substantially improve light-independent, low-temperature chemiresistive sensing, offering valuable design strategies for next-generation gas sensors.