No abstract

The adsorption behavior of toxic gas molecules (NO, CO, NO 2 , and NH 3 ) on graphene-like BC 3 are investigated using first-principle density functional theory (DFT). The most stable adsorption configurations, adsorption energies, binding distances, charge transfers, electronic band structures, and the conductance modulations are calculated to deeply understand the impacts of the molecules above on the electronic and transport properties of the BC 3 monolayer. The graphene-like BC 3 monolayer is a semiconductor with a band gap of 0.733 eV. The semi-metal graphene has a low sensitivity to the abovementioned molecules. However, it is discovered that all the above gas molecules are chemically adsorbed on the BC 3 sheet with the adsorption energies less than −1 eV. The NO 2 gas molecule is totally dissociated into NO and O species through the adsorption process, while the other gas molecules retain their molecular forms. The amounts of charge transfer upon adsorption of CO and NH 3 gas molecules on BC 3 are found to be small. Hence, the band gap changes in BC 3 as a result of interactions with CO and NH 3 are only 4.63% and 16.7%, indicating that the BC 3 -based sensor has a low and moderate sensitivity to CO and NH 3 , respectively. Contrariwise, upon adsorption of NO or NO 2 on BC 3 , a significant charge is transferred from the molecules to the BC 3 sheet, causing a semiconductor-metal transition. It is found that the BC 3 -based sensor has high potential for NO detection due to the significant conductance changes, moderate adsorption energy, and short recovery time. More excitingly, the BC 3 is a likely catalyst for dissociation of the NO 2 gas molecule. Our findings divulge promising potential of the graphene-like BC 3 as a highly sensitive molecular sensor for NO and NH 3 detection and a catalyst for NO 2 dissociation.

MXenes, two-dimensional (2D) transition metal carbides and nitrides, have been arousing interest lately in the field of gas sensing thanks to their remarkable features such as graphene-like morphology, metal-comparable conductivity, large surface-to-volume ratio, mechanical flexibility, and great hydrophilic surface functionalities. With tunable etching and synthesis methods, the morphology of the MXenes, the interlayer structures, and functional group ratios on their surfaces were effectively harnessed, enhancing the efficiency of MXene-based gas-sensing devices. MXenes also efficiently form nanohybrids with other nanomaterials, as a practical approach to revamp the sensing performance of the MXene sensors. This Mini-Review summarizes the recent experimental and theoretical reports on the gas-sensing applications of MXenes and their hybrids. It also discusses the challenges and provides probable solutions that can accentuate the future perspective of MXenes in gas sensors.

We report the development of the nanotube-CTC-chip for isolation of circulating tumor cells of multiple phenotypes from peripheral blood.