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Searching for suitable materials for NO 2 sensing has important scientific significance and application value. First-principles calculations have been performed on the adsorption of NO 2 and its various interfering gases on the pristine C 3 N monolayer (p-C 3 N) and the B-doped C 3 N monolayer. The studies on the adsorption stability, geometric structure, charge transfer, and electronic structure indicate that the p-C 3 N is a promising room-temperature NO 2 sensor, with high selectivity and sensitivity, and good reversibility. For the B-doped C 3 N monolayer, the calculated formation energies suggest that B doping into the C 3 N lattice is thermodynamically highly favorable. Furthermore, B doping by replacing the N atom in the C 3 N monolayer should can further improve the sensing selectivity and sensitivity of the C 3 N monolayer toward NO 2 . However, it is noted that a large adsorption energy for NO 2 indicates that the B-doped C 3 N monolayer may be reversibly operated above the room temperature. The possible reason for the distinct adsorption behaviors of the various molecules is also provided. Our theoretical studies indicate the great potential of the C 3 N-based two-dimensional semiconductor as good NO 2 gas sensors. [ABSTRACT FROM AUTHOR]

High performance NH 3 sensor is of great importance in various application fields such as environmental protection and early diagnosis of stomach cancer. Herein, carboxyl group functionalized mesoporous silica nanoparticles (C-MSNs) with ultrahigh specific surface area are developed as high performance mass-type sensing material for trace-level NH 3 detection. By using inkjet printing technology, C-MSNs material is precisely loaded on our lab-made integrated resonant microcantilever to construct a mass-type gas sensor. Based on the specific acid-base interaction between Brønsted acidic C-MSNs material and basic NH 3 molecules, our sensor exhibits satisfactory NH 3 sensing performance. The experimentally observed detection limit of our sensor reaches parts per billion (ppb) level. Exposed to NH 3 with identical concentration, our sensor outputs a higher response in wet air than that of in dry atmosphere. In real air, hydrate NH 3 molecule ( i.e. NH 3 · x H 2 O) has a larger molecular weight than anhydrous NH 3 in absolute dry experimental atmosphere. Therefore, our gravimetric sensor exhibits a higher response in real air. In order to in-depth elucidate the humidity-enhanced sensing effect, the micro-gravimetric sensing data obtained in wet air and in dry experimental environment are compared together. Based on our quantitatively measurement data, the molecular formula of hydrate NH 3 · x H 2 O existing in wet air (with 50–80% relative humidity) can be obtained as NH 3 ·2∼2.4H 2 O. [ABSTRACT FROM AUTHOR]