N-doped Nanocomposite Research Articles

Effect of nitrogen doping on medium-amplitude oscillatory shear (MAOS) response of nanotube/polyvinylidene fluoride nanocomposites: Molecular simulations, rheology, and broadband electrical conductivity

This study sheds light on the effect of nitrogen (N) doping of carbon nanotubes (CNTs) on medium-amplitude oscillatory shear (MAOS) response of CNT/polyvinylidene fluoride (PVDF) nanocomposites within a rheologically percolated concentration regime. Custom-synthesized CNTs without and with nitrogen heteroatom (at a nitrogen atomic percent of 3.85 at. %) were incorporated into a PVDF matrix using a miniature melt-mixer at different concentrations. In both cases, as confirmed by TEM investigations, a nanoscopic state of dispersion in the PVDF matrix was achievable using the applied melt mixing procedure. Our results indicated that N-doped nanocomposites, well below their electrical percolation, form a hybrid, load-bearing network structure where network interconnectivity is driven by N-doped CNT domains and near-surface regions of the PVDF phase. This hybrid network formation behavior combined with N-doped CNTs inferior aspect ratio and their higher susceptibility to breakage and length loss during the melt mixing process have led to delayed electrical percolation. In contrast, localized clustering and contact aggregation in a submicrometer scale was the dominant mode of network formation in the undoped CNT/PVDF nanocomposites. These microstructural inferences were further validated in the frame of molecular simulations and optical microscopy investigations.

TiO2/GRAPHENE OXIDE HETEROSTRUCTURES FOR GAS-SENSING: INTERACTION OF NITROGEN DIOXIDE WITH THE PRISTINE AND NITROGEN MODIFIED NANOSTRUCTURES INVESTIGATED BY DFT

The gas response of metal oxide-based sensors depends strongly on its adsorption properties. To explore the potential sensing capability of pristine and nitrogen modified TiO2/graphene oxide (GO) heterostructures, the adsorption of NO2 molecule on the N-doped nanocomposites was investigated using density functional theory (DFT) calculations. Six possible configurations were simulated based on the estimated adsorption energies. The binding sites were located over the oxygen, doped nitrogen and five-fold coordinated titanium atoms of TiO2. The electronic properties including atomic Mulliken population, projected density of states and molecular orbitals were investigated in detail. The N–O bonds of the NO2 molecule were significantly increased after the adsorption process. The adsorption of NO2 molecule on the N-doped nanocomposite is more energetically favorable than the adsorption on the undoped one. The results suggest that NO2 chemisorbs on the considered nanocomposites. Mulliken population analysis reveals a noticeable charge transfer from the nanocomposite to the molecule, which indicate that NO2 acts as a charge acceptor. Molecular orbital calculations show that the highest occupied molecular orbitals (HOMOs) of the studied systems were mainly localized on the adsorbed NO2 molecule. The significant overlaps in the projected density of states (PDOS) spectra of the interacting atoms confirm the formation of chemical bonds between them. There is a direct relationship between the results of charge transfer and sensing responses. N-doped nanocomposites have better sensing response than the undoped ones. The results highlight the possibility to develop innovative highly efficient NO2 sensors based on novel TiO2/GO nanocomposites.

Preparation and photocatalytic performance of N-AZO/TiO2 nanocomposites

A convenient and efficient method is developed to massively synthesize N-aluminum-doped zinc oxide (AZO)/TiO2 nanocomposites (NCs) with good visible light photo-response and photocatalytic activity. The shortened band gap of the interstitial N-doped NCs led to a much easier electron excitation and effectively inhibited the recombination of the photo-excited electrons and holes, thus dramatically improving the photocatalytic activity during the photocatalytic process. The impact of N-doping content on N-AZO/TiO2 NCs’s photocatalytic activity toward gatifloxacin (GAT) degradation was studied. The results showed that the most optimal molar ratio of nitrogen atom to zinc atom was 1.2:1. The degradation rate of GAT reached 85% when given an illumination time of 30 min, which was 2.3 times higher than pure AZO materials and increased by 22% compared to the non-doping pure AZO/TiO2.

Investigation of the adsorption of ozone molecules on TiO2/WSe2 nanocomposites by DFT computations: Applications to gas sensor devices

The adsorption of O3 molecule on the undoped and N-doped TiO2/WSe2 nanocomposites was studied using first principles density functional theory calculations. O3 interaction with TiO2/WSe2 nanocomposites is considered so as to investigate WSe2 effects on the adsorption process. WSe2 favors the adsorption of O3 on TiO2 particles. In other words, WSe2 is conducive to the interaction of O3 molecule with fivefold coordinated titanium sites of TiO2. The effects of vdW interactions were taken into account in order to obtain equilibrium geometries of O3 molecules at TiO2/WSe2 interfaces. For all adsorption configurations, the binding site was positioned on the fivefold coordinated titanium atoms. The results show that the interactions between O3 and TiO2 in TiO2/WSe2 nanocomposites are stronger than those between O3 and bare TiO2, suggesting that WSe2 helps to strengthen the interaction of ozone molecule with TiO2 particles. The results also indicate that the adsorption of the O3 molecule on the N-doped TiO2/WSe2 nanocomposite is more energetically favorable than the adsorption of O3 on the pristine one, representing that the N-doped nanocomposites are more sensitive than the undoped ones. Our DFT results clearly show that the N-doped TiO2/WSe2 nanocomposite would be a promising O3 gas sensor. The electronic structure of the adsorption system was also investigated, including analysis of the total and projected density of states, and charge density differences of the TiO2/WSe2 with adsorbed O3 molecules. The charge density difference calculations indicate that the charges were accumulated over the adsorbed O3 molecule. Besides, the N-doped nanocomposites have better sensing response than the pristine ones. This work was devoted to provide the theory basis for the design and development of novel and advanced O3 sensors based on modified TiO2/WSe2 nanocomposites.

Adsorption of toxic SOx molecules on heterostructured TiO2/ZnO nanocomposites for gas sensing applications: a DFT study

Using density functional theory (DFT) calculations, we predict the SOx sensing performance of heterostructured TiO2/ZnO nanocomposites with and without nitrogen doping. The interaction of SO2 and SO3 molecules with the considered nanocomposites were examined based on different orientations of the gas molecules towards the nanocomposite. The fivefold coordinated titanium atoms were found to be the binding sites on the TiO2 side of nanocomposite, whereas, on the ZnO side, the oxygen atom acts as a binding site. Our theoretical results demonstrate that the interaction of SOx molecules with N-doped nanocomposites is more energetically favorable than that with undoped ones, indicating that N-doped TiO2/ZnO nanocomposites show stronger chemisorption and greater electron transfer effects than undoped TiO2/ZnO. The electronic properties of the adsorption systems were investigated in terms of the projected density of states and molecular orbitals. After the adsorption process, all S–O bonds of the SOx molecules were elongated, which is probably attributed the electron density transfer from the S–O bonds to the newly formed bonds between the nanocomposite and SOx molecules. The charge transfer analysis revealed that N-doped nanocomposite acts as a donor. The N-doped nanocomposite induce dramatic changes of electronic properties of TiO2/ZnO, which can be useful feature for improving the gas sensing performance. Our calculation results aim to provide some information for future experiment.

Molecular design of O3 and NO2 sensor devices based on a novel heterostructured N-doped TiO2/ZnO nanocomposite: a van der Waals corrected DFT study

We have presented a density functional theory study of the adsorption properties of NO2 and O3 molecules on heterostructured TiO2/ZnO nanocomposites. The most stable adsorption configurations, adsorption energies and charge transfers were calculated. The electronic properties of the complex TiO2/ZnO heterostructures were described using the density of states and molecular orbital analyses. For NO2 adsorption, it was found that the oxygen atoms preferentially move towards the fivefold coordinated titanium atoms, whereas the nitrogen atom binds to the zinc atom. In the case of O3 adsorption, the side oxygen atoms bind to the fivefold coordinated titanium sites, and the central oxygen atom does not contribute to the adsorption any longer. Thus, the interaction of NO2 and O3 molecules with TiO2 side of nanocomposite is strongly favored. On the N-doped TiO2/ZnO nanocomposites, the adsorption process is more energetically favorable than that on the pristine ones. The N-doped nanocomposites are far more sensitive to gas detection than the undoped ones. In TiO2/ZnO nanocomposites, the interactions of gas molecule and TiO2 are stronger than those between gas molecule and bare TiO2 nanoparticles, which reveals that ZnO is conducive to the interaction of NO2 and O3 molecules with TiO2 nanoparticles. Our theoretical results suggest multicomponent TiO2/ZnO nanocomposite as a potential material for gas sensing application.Graphical

Density functional theory (DFT) study of O3 molecules adsorbed on nitrogen-doped TiO2/MoS2 nanocomposites: applications to gas sensor devices

Density functional theory calculations were carried out to investigate the adsorption behaviors of O3 molecules on the undoped and N-doped TiO2/MoS2 nanocomposites. With the inclusion of vdW interactions, which correctly account the long-range dispersion energy, the adsorption energies and final geometries of O3 molecules on the nanocomposite surfaces were improved. For O3 molecules on the considered nanocomposites, the binding sites were located on the fivefold coordinated titanium atoms of the TiO2 anatase. The structural properties of the adsorption systems were examined in view of the bond lengths and bond angles. The variation of electronic structures was also discussed in view of the density of states, molecular orbitals and distribution of spin densities. The results suggest that the adsorption of the O3 molecule on the N-doped TiO2/MoS2 nanocomposite is more favorable in energy than that on the pristine one, indicating that the N-doped nanocomposite has higher sensing capability than the pristine one. This implies that the N-doped TiO2/MoS2 nanocomposite would be an ideal O3 gas sensor. However, our calculations thus provide a theoretical basis for the potential applications of TiO2/MoS2 nanocomposites as efficient O3 sensors, leading to very interesting results in the context of air quality measurement.

A novel strategy for SOx removal by N-doped TiO2/WSe2 nanocomposite as a highly efficient molecule sensor investigated by van der Waals corrected DFT

On the basis of density functional theory (DFT) calculations, we demonstrate the potential applicability of TiO2/WSe2 nanocomposite as a highly sensitive molecule sensor for SO2 and SO3 molecules. SOx molecules chemically adsorb on TiO2/WSe2 nanocomposite via strong chemical bonds. With vdW interactions included, the adsorption energies were corrected for long range dispersion energy, indicating adsorption energetic and possible configurations of SOx molecules towards TiO2/WSe2 nanocomposites. The fivefold coordinated titanium atoms in the TiO2 act as the binding sites. On the N-doped TiO2/WSe2 nanocomposite, the adsorption process is found to be more favorable in energy than the adsorption on the intrinsic one, indicating that the N-doped nanocomposites have higher sensing capability than the undoped ones. The charge transfer based on NBO analysis reveals that the SOx molecule behaves as an electron acceptor. The electronic properties of the system were also investigated in view of the projected density of states and molecular orbitals of the TiO2/WSe2 with adsorbed SOx molecules. Over the TiO2/WSe2 nanocomposites, SO3 molecule dissociates into SO2 and detached oxygen atom. The results present a great potential of TiO2/WSe2 nanocomposites for application as a highly efficient molecule sensor for SOx detection.

Physicochemical and photo-electrochemical characterization of novel N-doped nanocomposite ZrO2/TiO2 photoanode towards technology of dye-sensitized solar cells

This work introduces the synthesis of N-doped nanocomposite of ZrO2/TiO2 nanofibers (NFs) by use of both electrospinning and hydrothermal methods. The physicochemical properties of the introduced TiO2 NFs are investigated to describe the morphology, crystallinity and chemistry through FESEM, SEM-EDX, XRD, TEM and XPS. As the results, the investigated material can be described as N@ZrO2/TiO2 NFs. The crystal structure of the prepared TiO2 is only anatase structure. Then, the novel NFs are utilized to design novel photoanode and photo-electrochemical characterization such as current-potential response under light, incident photon-to-current efficiency (IPCE) and electrochemical impedance spectroscopy (EIS) of the dye-sensitized solar cell (DSC) are also investigated. The photovoltaic response showed that the efficiency of the DSCs employed N@ZrO2/TiO2 photoanode gave 4.95%, which was higher than those of DSCs designed with ZrO2/TiO2 NFs (4.51%) and N@TiO2 NFs (4.41%) photoanodes. The high photo-response of DSC by use of N@ZrO2/TiO2 NFs can be attributed to enhanced electrical conductivity, which is studied via EIS, and presence of active sites of N. These active sites can easily absorb dye-molecules in the step of dye-loading in the fabrication of DSC.

Theoretical study of the adsorption of NOx on TiO2/MoS2 nanocomposites: a comparison between undoped and N-doped nanocomposites

First-principle calculations within density functional theory were performed to investigate the interactions of NO and NO2 molecules with TiO2/MoS2 nanocomposites. Given the need to further comprehend the behavior of the NOx molecules positioned between the TiO2 nanoparticle and MoS2 monolayer, we have geometrically optimized the complex systems consisting of the NOx molecule oriented at appropriate positions between the nanoparticle and MoS2 monolayer. The structural properties, such as bond lengths, bond angles, adsorption energies and Mulliken population analysis, and the electronic properties, including the density of states and molecular orbitals, were also analyzed in detail. The results indicate that the interactions between NOx molecules and N-doped TiO2 in TiO2-N/MoS2 nanocomposites are stronger than those between gas molecules and undoped TiO2 in TiO2/MoS2 nanocomposites, which reveal that the N-doping helps to strengthen the interaction of toxic gas molecules with hybrid TiO2/MoS2 nanocomposites. The N-doped TiO2/MoS2 nanocomposites have higher sensing capabilities than the undoped ones, and the interaction of NOx molecules with N-doped nanocomposites is more favorable in energy than the interaction with undoped nanocomposites. Therefore, the obtained results also present a theoretical basis for the potential application of TiO2/MoS2 nanocomposite as an extremely sensitive gas sensor for NO and NO2 molecules.

Importance of the tuning of band position in optimizing the electronic coupling and photocatalytic activity of nanocomposite

The electronic coupling and photocatalytic activity of Ag2CO3–TiO2 nanocomposite can be optimized by the fine-tuning of the band position of titanium oxide with nitrogen doping. The increase of the valence band energy of TiO2 by N-doping leads not only to the enhanced absorption of visible light but also to the promoted hole transfer from Ag2CO3 to TiO2, resulting in the efficient spatial separation of photogenerated electrons and holes. While the undoped Ag2CO3–TiO2 nanocomposite shows an inferior photocatalytic activity to the pure Ag2CO3, the photocatalyst performance of N-doped nanocomposite is better than those of Ag2CO3 and undoped Ag2CO3–TiO2 nanocomposite. This observation underscores a significant enhancement of the photocatalytic activity of nanocomposite upon N-doping, a result of enhanced electronic coupling between the hybridized species. The present results clearly demonstrate the importance of the fine-tuning of band position in optimizing the photocatalytic activity of hybrid-type photocatalysts.

A Facile Approach to Fabricate an N‐Doped Mesoporous Graphene/Nanodiamond Hybrid Nanocomposite with Synergistically Enhanced Catalysis

AbstractOwing to their unique structural features and surface properties, graphene and nanodiamond have attracted tremendous attention in diverse fields. However, restacking of graphene and reagglomeration of dispersed nanodiamond inevitably depress their catalytic properties. Herein, inspired by the historic discovery of “pillared clay”, we successfully realized the simultaneous inhibition of their restacking by fabricating a N‐doped mesoporous graphene/nanodiamond (N‐RGO/ND) nanocomposite by a facile wet‐chemical approach. The electrocatalytic oxygen reduction reaction (ORR) and the thermocatalytic oxidant‐free and steam‐free direct dehydrogenation (DDH) of ethylbenzene were used to examine its catalytic properties. The nanocomposite showed synergistically improved catalytic DDH and electrocatalytic ORR activity relative to that of the individual components, which can be ascribed to synergy between graphene and nanodiamond and to the large surface area, well‐ordered mesoporous structure, small crystalline size, and rich defect and CO surface features. Moreover, the developed synthetic strategy in this work can be extended to diverse N‐doped nanocomposites from dispersion‐required carbon precursors.