Nitrogen-phosphorus codoped carbon nanotube sponges for detecting volatile organic compounds: experimental and DFT calculations.

The sensing of harmful gases and vapors is of fundamental interest to control the industrial emissions and environmental contamination. Nitrogen/phosphorus codoped carbon nanotube sponges (NP-CNTSs) were used to detect ethanol, acetone, cyclohexane, isopropanol, and methanol. The NP-CNTSs were produced through the aerosol-assisted chemical vapor deposition (AACVD) method using acetonitrile and triphenylphosphine as precursors at 1020 °C. The sensors based on NP-CNTSs were tested with varying operating temperatures (25-100 °C) and gas vapor concentrations (5-50 ppm). For instance, for a gas vapor concentration of 30 ppm and an operating temperature of 65 °C, the sensors showed changes in the electrical resistance of 1.12%, 1.21%, 1.09%, 2.4%, and 1.34% for ethanol, acetone, cyclohexane, isopropanol, and methanol, respectively. We found that the response and recovery times for isopropanol gas vapor are up to 43.7 s and 95 s, respectively. The current sensor outperformed the sensors reported in the literature by at least two times in the response measurement. Additionally, we performed van der Waals density functional theory calculations to elucidate the role of nitrogen and phosphorous codoped single-walled carbon nanotubes (SWCNTs) and their interaction with the considered gas molecule. We analyzed the molecular adsorption energy, optimized structures, and the density of states and calculated the electrostatic potential surface for N-doped, P-doped, NP-codoped, and OH-functionalized NP-codoped metallic SWCNTs-(6,6) and semiconducting SWCNTs-(10,0). Adsorption energy calculations revealed that in most cases the molecules are adsorbed to carbon nanotubes via physisorption. The codoping in SWCNTs-(6,6) promoted structural changes in the surface nanotube and marked chemisorption for acetone molecules.

Nitrogen-phosphorus doped graphitic nano onion-like structures: experimental and theoretical studies.

Onion-like graphitic structures are of great importance in different fields. Pentagons, heptagons, and octagons are essential features of onion-like graphitic structures that could generate important properties for diverse applications such as anodes in Li metal batteries or the oxygen reduction reaction. These carbon nanomaterials are fullerenes organized in a nested fashion. In this work, we produced graphitic nano onion-like structures containing phosphorus and nitrogen (NP-GNOs), using the aerosol assisted chemical vapor deposition method. The NP-GNOs were grown at high temperature (1020 °C) using ferrocene, trioctylphosphine oxide, benzylamine, and tetrahydrofuran precursors. The morphology, structure, composition, and surface chemistry of NP-GNOs were characterized using different techniques. The NP-GNOs showed diameters of 110-780 nm with Fe-based nanoparticles inside. Thermogravimetric analysis showed that NP-GNOs are thermally stable with an oxidation temperature of 724 °C. The surface chemistry analysis by FTIR and XPS revealed phosphorus-nitrogen codoping, and several functionalities containing C-H, N-H, P-H, P-O, P[double bond, length as m-dash]O, C[double bond, length as m-dash]O, and C-O bonds. We show density functional theory calculations of phosphorus-nitrogen doping and functionalized C240 fullerenes. We present the optimized structures, electronic density of states, HOMO, and LUMO wave functions for P-doped and OH-functionalized fullerenes. The P[double bond, length as m-dash]O and P-O bonds attributed to phosphates or hydroxyl groups attached to phosphorus atoms doping the NP-GNOs could be useful in improving supercapacitor function.