MXene Ti₃C₂T_x-Derived Nitrogen-Functionalized Heterophase TiO₂ Homojunctions for Room-Temperature Trace Ammonia Gas Sensing

Abstract

In this work, MXene Ti3C2T x -derived nitrogen-functionalized heterophase TiO2 homojunctions (N-MXene) were prepared via the urea-involved solvothermal treatment with varying reaction time as the sensing layer to detect trace NH3 gas at room temperature (20 °C). Compared with no signal for the pristine MXene counterpart, the 18 h-treated sensors (N-MXene-18) achieved a detection limit of 200 ppb with an inspiring response that was 7.3% better than the existing MXene-involved reports thus far. Also, decent repeatability, stability, and selectivity were demonstrated. It is noteworthy that the N-MXene-18 sensors delivered a stronger response, more sufficient recovery, and quicker response/recovery speeds under a humid environment than those under dry conditions, proving the significance of humidity. Furthermore, to suppress the effect of the fluctuation of humidity on NH3 sensing during the tests, a commercial waterproof polytetrafluoroethylene (PTFE) membrane was anchored onto the sensing layer, eventually bringing about humidity-independent features. Both nitrogen doping and TiO2 homojunctions constituted by mixed anatase and rutile phases were primarily responsible for the performance improvement with respect to pristine MXene. This work showcases the enormous potential of N-MXene materials in trace NH3 detection and offers an alternative strategy to realize both heteroatom doping and partial oxidation of MXene that is applicable in future optoelectronic devices.

Moisture-Resistant Gas Sensor Derived from ZIF-8/Layered Double Hydroxide/Ti3C2Tx Nanocomposites for Trace Isopropanol Detection

“…The C 1s spectrum could be separated into three subpeaks, with binding energies of 284.1, 285.0, and 284.7 eV, which are ascribed to sp 2 hybridized C atoms in aromatic imidazole rings, NC–N, and C–C, respectively. , The N 1s spectrum could be split into two main peaks of the Zn–N bonds (398.6 eV) and N–H (399.5 eV). The O 1s spectra were deconvoluted into O–Ti, C-Ti-O x , C-Ti­(OH) x , and H 2 O-Ti bonds, which were located at 529.3, 530.4, 531.4, and 532.4 eV . The above result indicates that the ZIF-8/LDHs/Ti 3 C 2 T x nanocomposite was successfully synthesized.…”

TiO2 Hollow Nanofiber/Polyaniline Nanocomposites for Ammonia Detection at Room Temperature

“…The sheath and core solutions were transferred into 3 mL syringes and pumped separately through the concentrically aligned outer (1.02 mm) and inner (0.65 mm) needles, respectively. The employed electrospinning parameters, optimized in subsidiary experiments (not shown), [a,3] ~35 [5] ~60 [5] -[55] 3D SWNT/TiO2 nanoparticles 190 0.0597 [a,3] ---[56] PANI/SnO2 nanoparticles RT ~0.37 [a,1] 12-15 [1] 80 [1] -[57] Sn-TiO2@rGO/CNT RT 0.86 [a,2] 99 [2] 66 [2] -[58] PANI/TiO2 nanoparticles RT ~0.35 [a,4] ~54 [4] ~460 [4] -[59] PANI/TiO2 hollow nanofibers RT 0.98 [a,4] [37] .…”

“…For instance, the US National Institute for Occupational Safety and Health has set its recommended exposure limit as 25 ppm (for eight hours) and odor threshold at 5 ppm [2,3] . In this regard, it becomes important to develop gas sensors for real-time detection of NH 3 [4,5] as well as other gas pollutants in varied environments [6,7] . Chemiresistive sensors based on semiconductor metal oxides (e. g., ZnO [8][9][10] , V 2 O 5 [11] , TiO 2 [12] , SnO 2 [13] ) have been widely explored for this purpose, owing to their good selectivity, sensitivity and fast response towards ammonia detection.…”

Whole-Process Mildly Prepared TiO2@Ag Composite Material for Printed, Flexible, and Room-Temperature NH3 Sensing

“…Chemoresistive sensors outperform their optical, electrochemical, photoelectrochemical, and mass-sensitive counterparts due to their easy fabrication and testing characteristics. Metal-oxide semiconductors represent an important and indispensable category of material for chemoresistive gas sensors that have been studied extensively. − As a typical n-type semiconductor, TiO 2 is an ideal gas-sensitive material for measuring NH 3 because it can effectively adsorb NH 3 and achieve complete desorption. − Still, the selectivity and sensing property of pure TiO 2 needs further optimization to improve the detection accuracy. Additive doping has proven to be an appealing method to lower the sensing temperature or to improve the sensitivity of semiconductive materials including TiO 2 . − Doping noble metals can effectively modify the wide gap energy of TiO 2 to improve the performance of the sensor .…”