A reexamination of the chemisorption and desorption of ozone on the exterior of a (5,5) single-walled carbon nanotube

Utility of structural engineering on the monitoring of acrolein by aluminum nitride nano tube

CONTEXT

The study delves into the adsorption process of acrolein (AC) onto both an untainted and a titanium-doped aluminum nitride nanotube (AlNNT) using computations based on density functional theory. As AC approaches the pure AlNNT, it exhibits a calculated adsorption energy (Ead) of -5.3 kcal/mol, underscoring the feeble nature of the adsorption. Furthermore, there has been very little change to the AlNNT's natural electrical characteristics. On the contrary, the introduction of titanium (Ti) enhances the performance of AlNNT, rendering it more susceptible and reactive to AC signals. Analyzing the conventional Gibbs free energy of formation computationally, we ascertain that replacing a nitrogen (N) atom with a titanium (Ti) atom within the aluminum nitride nanotube (AlNNT) structure presents a more advantageous prospect. Notably, there is a substantial alteration in the energy of adsorption (Ead) for AC as a Ti atom is incorporated onto the AlNNT surface, resulting in a shift from -5.3 to -24.6 kcal/mol.

METHODS

Energy calculations and geometric optimizations were conducted utilizing the dispersion-augmented B3LYP method, known as B3LYP-D. In this approach, Grimme's dispersion term, referred to as the "D" term, was employed to account for dispersion forces. The basis set adopted was 6-31 +  + G** (d), and all computational procedures were executed using the GAMESS software program. Following the incorporation of titanium (Ti), this adjustment leads to a substantial enhancement in sensing capability, reaching a value of 93.7. This indicates an improved electrical conductivity of the aluminum nitride nanotube (AlNNT). Remarkably, the Ti-doped AlNNT demonstrates the ability to detect AC distinctly, even in the presence of HCN, formaldehyde, ethanol, toluene, and acetone. The swift recovery process becomes evident as AC desorbs from the surface of Ti-doped AlNNT, with a calculated recovery time of 14.0 s.

Synergistic photocatalytic activity of a combination of carbon nanotubes-graphene-nickel foam nanocomposites enhanced by dielectric barrier discharge plasma technology for water purification

Degradation activity of plasma catalysis between dielectric barrier discharge (DBD) and carbon nanotubes-graphene-nickel foam (CNTs-G-Ni_f) has been studied in treatment of dye wastewater. CNTs-G-Ni_f was prepared through a two-step chemical vapor deposition (CVD) approach. The composite has been characterized by different techniques such as X-ray diffraction (XRD), scanning electron microscope (SEM) and Raman spectroscopy. SEM results showed that the Ni_f as the growth substrate was evenly wrapped by G and then CNTs were successfully grown on G as the support. The growth mechanism of composite was proposed. The possible coupled catalytic mechanism between DBD and CNTs-G-Ni_f were addressed. In addition, the modification on G-Ni_f was found by SEM during the discharge process in liquid phase. And the modification mechanism of DBD plasma (DBDP) acting on composites was discussed. Finally, by means of analyses of ultraviolet-visible (UV-Vis) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS), the general degradation pathway and stepwise degradation pathways of alizarin green (AG) were proposed in detail.

Reaction Mechanism of the Reduction of Ozone on Graphite

The kinetics of the ozonation of graphite with different particle sizes (106 μm, G₁₀₆; 6.20 μm, G_6.2) was studied at several temperatures under a flow of O₃ diluted in O₂. The reaction was first-order with respect to graphite and to the consumption of ozone. X-ray photoelectron spectrum (XPS) showed that the reactions occurring in the solid under steady-state conditions maintain the original stoichiometry, as predicted by the postulated mechanism for SO₂. The deoxygenation reaction occurred along with the ozonation reaction at 100 °C. The rate of oxygen elimination in the flow system has the same rate-determining kinetic barrier as ozone insertion. Ozonation and deoxygenation reactions are sequentially related. Ozonation occurs with the insertion of O₃, forming a 1,2,3-trioxolane followed by an oxygen transfer that produces a peroxide valence tautomer in equilibrium with 1,3-dicarbonyl, [peroxide ↔ dicarbonyl], and an oxirene that eliminates atomic oxygen. The decarboxylation reaction was studied at 600 °C from the ozonated G₁₀₆ (ΔG^≠ = 83.60 ± 0.08 kcal·mol^-1). Total decarboxylation at 600 °C matched the number of moles of CO₂ removed and the oxygen content after ozonation, showing that the reduction of ozone on graphite was essentially a clean reduction with no secondary oxidations. When ozonized graphite was heated to 600 °C, only [peroxide ↔ dicarbonyl] species remained in the matrix. The peroxide tautomer isomerized to dioxirane and eliminated CO₂ as a dioxicarbene. Total deoxygenation of decarboxylated graphite G₁₀₆ was obtained by pyrolysis. There was residual oxygen that arose from the atomic oxygen eliminated from the oxirene, intercalated in graphite layers, and formed basal epoxy groups. Also, incoming O atoms reacted with the intercalated O atoms to produce O₂ molecules. Thermal annealing deintercalated molecular oxygen (600-900 °C).

Bio-Inspired Carbon Monoxide Sensors with Voltage-Activated Sensitivity

Carbon monoxide (CO) outcompetes oxygen when binding to the iron center of hemeproteins, leading to a reduction in blood oxygen level and acute poisoning. Harvesting the strong specific interaction between CO and the iron porphyrin provides a highly selective and customizable sensor. We report the development of chemiresistive sensors with voltage-activated sensitivity for the detection of CO comprising iron porphyrin and functionalized single-walled carbon nanotubes (F-SWCNTs). Modulation of the gate voltage offers a predicted extra dimension for sensing. Specifically, the sensors show a significant increase in sensitivity toward CO when negative gate voltage is applied. The dosimetric sensors are selective to ppm levels of CO and functional in air. UV/Vis spectroscopy, differential pulse voltammetry, and density functional theory reveal that the in situ reduction of FeIII to FeII enhances the interaction between the F-SWCNTs and CO. Our results illustrate a new mode of sensors wherein redox active recognition units are voltage-activated to give enhanced and highly specific responses.

Removal of Ozone by Carbon Nanotubes/Quartz Fiber Film

Ozone is recognized as a harmful gaseous pollutant, which can lead to severe human health problems. In this study, carbon nanotubes (CNTs) were tested as a new approach for ozone removal. The CNTs/quartz fiber film was fabricated through growth of CNTs upon pure quartz fiber using chemical vapor deposition method. Ozone conversion efficiency of the CNTs/quartz fiber film was tested for 10 h and compared with that of quartz film, activated carbon (AC), and a potassium iodide (KI) solution under the same conditions. The pressure resistance of these materials under different airflow rates was also measured. The results showed that the CNTs/quartz fiber film had better ozone conversion efficiency but also higher pressure resistance than AC and the KI solution of the same weight. The ozone removal performance of the CNTs/quartz fiber film was comparable with AC at 20 times more weight. The CNTs played a dominant role in ozone removal by the CNTs/quartz fiber film. Its high ozone conversion efficiency, lightweight and free-standing properties make the CNTs/quartz fiber film applicable to ozone removal. Further investigation should be focused on reducing pressure resistance and studying the CNT mechanism for removing ozone.

Nitrous oxide adsorption on pristine and Si-doped AlN nanotubes

Using density functional theory, we studied the adsorption of an N(2)O molecule onto pristine and Si-doped AlN nanotubes in terms of energetic, geometric, and electronic properties. The N(2)O is weakly adsorbed onto the pristine tube, releasing energies in the range of -1.1 to -5.7 kcal mol(-1). The electronic properties of the pristine tube are not influenced by the adsorption process. The N(2)O molecule is predicted to strongly interact with the Si-doped tube in such a way that its oxygen atom diffuses into the tube wall, releasing an N(2) molecule. The energy of this reaction is calculated to be about -103.6 kcal mol(-1), and the electronic properties of the Si-doped tube are slightly altered.

Theoretical Studies of Substitutionally Doped Single-Walled Nanotubes

The rich chemistry of single-walled carbon nanotubes (SWCNTs) is enhanced by substitutional doping, a process in which a single atom of the nanotube sidewall is replaced by a heteroatom. These so-called heteroatom-substituted SWCNTs (HSWCNTs) exhibit unique chemical and physical properties not observed in their corresponding undoped congeners. Herein, we present theoretical studies of both main group element and transition metal-doped HSWCNTs. Within density functional theory (DFT), we discuss mechanistic details of their proposed synthesis from vacancy-defected SWCNTs and describe their geometric and electronic properties. Additionally, we propose applications for these nanomaterials in nanosensing, nanoelectronics, and nanocatalysis.

Removal of nickel ions from water by multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) were produced by chemical vapor decomposition using acetylene gas in the presence of Ferrocene catalyst at 800 degrees C, and then oxidized with concentrated nitric acid at 150 degrees C. Both (as-produced and oxidized) CNTs were characterized by TEM, Boehm titration, N2-BET and cation exchange capacity techniques. The adsorption capacity for nickel ions from aqueous solutions increased significantly onto the surface of the oxidized CNTs compared to that on the as-produced CNTs. The effects of adsorption time, solution pH and initial nickel ions concentrations on the adsorption uptake of Ni2+ for both the as-produced and oxidized CNTs were investigated at room temperature. Both Langmuir and Freundlich isotherm models match the experimental data very well. According to the Langmuir model the maximum nickel ions adsorption uptake onto the as-produced and oxidized CNTs were determined as 18.083 and 49.261 mg/g, respectively. Our results showed that CNTs can be used as an effective Ni2+ adsorbent due to the high adsorption capacity as well as the short adsorption time needed to achieve equilibrium.

Decomposition of nitrous oxide on carbon nanotubes

In this work, we have suggested the possibility of using carbon nanotubes to remove toxic gas. By taking an advantage of the density functional theory, we have investigated the decomposition of nitrous oxide (N(2)O) on the sidewalls of the perfect and the Stone-Wales defect armchair (5,5)-SWNTs at the B3LYP/6-31G(d) level of theory. There are two reaction mechanisms proposed: stepwise and concerted pathways. Our calculations predict that the former route is kinetically favored on both the perfect and defect SWNTs with barrier heights of the rate-determining steps of 37.23 and 34.38 kcal/mol for the perfect and the defect systems, respectively. In the second pathway, the decomposition of nitrous oxide gas takes place in a single step with higher reaction barriers of 48.60 and 40.27 kcal/mol on the sidewalls of the perfect and the defect SWNTs, respectively. Moreover, we also demonstrated that an encapsulation of electron rich species, such as chloride anion, inside the channel of the SWNT can boost up the reaction rate of the N(2)O decomposition on the SWNT. The chloride ion supplies excess electrons to the SWNT for transferring to the N(2)O molecule causing lower reaction barriers in the reaction pathways.

Ozonization at the Vacancy Defect Site of the Single-Walled Carbon Nanotube

The ozonization at the vacancy defect site of the single-walled carbon nanotube has been studied by static quantum mechanics and atom-centered density matrix propagation based ab initio molecular dynamics within a two-layered ONIOM approach. Among five different reaction pathways at the vacancy defect, the reaction involving the unsaturated active carbon atom is the most probable pathway, where ozone undergoes fast dissociation at the active carbon atom at 300 K. Complementary to the experiments, our work provides a microscopic understanding of the ozonization at the vacancy defect site of the single-walled carbon nanotube.

Effect of Ozone Oxidation on Single-Walled Carbon Nanotubes

Exposing single-walled carbon nanotubes to room-temperature UV-generated ozone leads to an irreversible increase in their electrical resistance. We demonstrate that the increased resistance is due to ozone oxidation on the sidewalls of the nanotubes rather than at the end caps. Raman and X-ray photoelectron spectroscopies show an increase in the defect density due to the oxidation of the nanotubes. Using ultraviolet photoelectron spectroscopy, we show that these defects represent the removal of pi-conjugated electron states near the Fermi level, leading to the observed increase in electrical resistance. Oxidation of carbon nanotubes is an important first step in many chemical functionalization processes. Because the oxidation rate can be controlled with short exposures, UV-generated ozone offers the potential for use as a low-thermal-budget processing tool.