CN108256280A - Verify method of the nickel doping minor radius carbon nanotube to the adsorption capacity of sulfur dioxide - Google Patents

Abstract

A method for verifying the adsorption capacity of nickel-doped small-radius carbon nanotubes to SO ₂ comprises the following steps: taking (n, 0) SWCNT (n=4,5,6) small-radius carbon nanotubes as a surface model, establishing The simulation model receives the molecular spacing of the input gas molecules, and the simulation model adopts a tetragonal lattice supercell whose lattice constants are a, b, and c; different gas molecule adsorption positions are established in the simulation model, and the simulated doped The adsorption situation of different adsorption positions before and after doping; compare the energy difference before and after adsorption of different adsorption positions, obtain the preset data corresponding to the position with the lowest adsorption energy, and calculate the position of the lowest adsorption energy before doping and doping The subsequent adsorption energy. The method for verifying the adsorption capacity of nickel-doped small-radius carbon nanotubes to _SO2 provided by the present invention verifies the influence of nickel-doped small-radius carbon nanotubes on the adsorption capacity and gas sensitivity of _SO2 by establishing a rationally optimized simulation.

Description

Method for verifying the adsorption capacity of nickel-doped small-radius carbon nanotubes to sulfur dioxide

technical field

The invention relates to a method for verifying the adsorption capacity of sulfur dioxide and the influence of gas sensitivity, in particular to a method for verifying the adsorption capacity of nickel-doped small-radius carbon nanotubes to sulfur dioxide.

Background technique

Carbon nanotubes are quasi-one-dimensional materials with large surface area and light mass density, and are prone to strong interactions with pollutant molecules. Carbon nanotubes have excellent adsorption properties, especially single-walled carbon nanotubes with low carbon atom density, large tube diameter and gaps between tubes, which provide a large amount of embedded space for the adsorption of small molecules, so they can be widely used in sensors manufacturing.

People have done a lot of research on the gas-sensing properties of carbon nanotubes, and found that carbon nanotubes have good adsorption properties for many gas molecules. A large number of studies have shown that carbon nanotubes are excellent materials for manufacturing gas-phase sensitive devices. Shalabi.et al. et al. found that Co-doped carbon nanotubes have higher sensitivity to CO molecules (J.Nanopart.Res., 2012(14):1-15); Pd-doped carbon nanotubes have higher sensitivity to NO molecules Very sensitive (Sensor.Actuat.B-Chem., 2011(159):171-177). Its gas sensing mechanism comes from the sensitive change in conductivity caused by the charge transfer between carbon nanotubes and gas molecules. Compared with traditional electronic sensors, carbon nanotube sensors have strong gas selectivity, fast detection speed, and can be used at room temperature. work advantages.

Contents of the invention

The purpose of the present invention is to provide a method for verifying the adsorption capacity of nickel-doped small-radius carbon nanotubes to SO ₂ .

For this reason, the invention provides a kind of verification nickel-doped small-radius carbon nanotubes to _SO The method for the adsorption capacity, comprises the following steps:

Simulation model building steps: take (n, 0) SWCNT (n=4, 5, 6) small-radius carbon nanotubes as the surface model, build a simulation model and receive the molecular spacing of the input gas molecules, and the simulation model uses lattice Tetragonal lattice supercell with constants a, b, and c;

Adsorption simulation step: establishing different adsorption positions of gas molecules in the simulation model, and simulating the adsorption conditions of different adsorption positions before and after doping;

Analysis steps: compare the energy difference before and after adsorption at different adsorption positions, obtain the preset data corresponding to the position with the lowest adsorption energy, and calculate the adsorption energy before and after doping at the position with the lowest adsorption energy.

Preferably, the surface models include three types of surface models with 32, 40, and 48 carbon atoms, and the pipe diameters corresponding to the three types of surface models are respectively

Preferably, nickel atoms with doping concentrations of 2.13%, 2.56%, and 3.23% are respectively doped in the three types of surface models to establish a simulation model.

Preferably, the simulation model building step also includes:

use The lattice to remove the interaction of the periodic image of the simulation model.

Preferably, after establishing the simulation model, it also includes:

Using the Dmol3 module of the Materials Studio software to adjust the structure of the lattice supercell, a simulation model corresponding to nickel-doped small-radius carbon nanotubes is obtained.

Preferably, the adsorption simulation step also includes:

For the simulation model of different adsorption positions, the PBE+GGA algorithm is used under the Dmol3 module, and the simulation of the physical adsorption of SO ₂ is realized through structural adjustment under CUSTOM precision.

Preferably, the preset parameters in the analysis step include: structural symmetry, energy band structure, DOS density of states and charge density.

Preferably, the gas molecules are SO ₂ gas molecules.

Preferably, the small-radius carbon nanotubes are nickel-doped small-radius carbon nanotubes.

Preferably, the analysis step also includes:

Calculate the symmetry breaking factor δ used to measure the symmetry breaking brought by doping to the nickel-doped small-radius carbon nanotubes according to the following formula,

Among them, Dc-c represents the average bond length between the intrinsic carbon nanotube carbon atom and the surrounding three adjacent carbon atoms, and Dc _-Ni represents the bond length between the doped nickel atom and the surrounding three carbon atoms average value.

Preferably, the molecular distance of the gas molecules is the distance between S atoms and O atoms.

Compared with the prior art, the method for verifying the adsorption capacity of nickel-doped small-radius carbon nanotubes to _SO2 provided by the present invention is to verify the adsorption capacity of nickel-doped small-radius carbon nanotubes to _SO2 by establishing a rationally optimized simulation and gas sensitivity.

Description of drawings

Fig. 1 is a flow chart of an embodiment of the method for verifying the adsorption capacity of nickel-doped small-radius carbon nanotubes to SO ₂ according to the present invention.

2a-2f are the front view and the side view of the optimal adsorption position of nickel-doped small-radius carbon nanotubes for _SO2 molecules in an adsorption model of the present invention.

Fig. 3a～3f is the energy band structure diagram of intrinsic and nickel-doped small-radius carbon nanotube in a kind of adsorption model of the present invention, wherein, Fig. 3 a is (a) (4,0) SWCNT energy band structure diagram, Fig. 3b It is the band structure diagram of Ni-(4,0)SWCNT; Figure 3c is the band structure diagram of (5,0)SWCNT; Figure 3d is the band structure diagram of Ni-(5,0)SWCNT; Figure 3e is the band structure diagram of (6, 0) Band structure diagram of SWCNT; Figure 3f is the band structure diagram of Ni-(6,0)SWCNT.

Figures 4a to 4b are partial wave density of _states diagrams of SO2-intrinsic small-radius carbon nanotube _adsorption system in an adsorption model of the present invention. The density of states diagram corresponding to oxygen, sulfur and carbon atoms in the structure of SO ₂ is shown.

Fig. 5 is a partial wave density of state diagram of an adsorption model of SO ₂ -nickel-doped carbon nanotubes with small radius in the present invention;

Figures 6a to 6b are the electron density profiles of the SO ₂ -carbon nanotube adsorption system and the SO ₂ -Ni-carbon nanotube adsorption system in an adsorption model of the present invention, wherein Figure 6a is the SO ₂ -carbon nanotube adsorption system , Fig. 6b is the electron density profile of the SO ₂ -Ni-carbon nanotube (b) adsorption system.

Detailed ways

Below in conjunction with accompanying drawing, the present invention will be further described.

Fig. 1 is a flow chart of an embodiment of the method for verifying the adsorption capacity of nickel-doped small-radius carbon nanotubes to SO ₂ according to the present invention. As shown in FIG. 1 , the method for verifying the adsorption capacity of nickel-doped carbon nanotubes with small radius on SO ₂ includes the following steps S01-S03. In this embodiment, the small-radius carbon nanotubes are nickel-doped small-radius carbon nanotubes, and the gas molecules are SO ₂ gas molecules.

Step S01 (simulation model building step): take (n,0)SWCNT (n=4,5,6) small-radius carbon nanotubes as the surface model. Among them, the (n,0)SWCNT (n=4,5,6) system contains 32, 40, and 48 carbon atoms, respectively, and the tube diameters are Then, nickel atoms were doped with concentrations of 2.13%, 2.56%, and 3.23% in the three types of surface models. After doping, the Ni-(n,0)SWCNT (n=4,5,6) system contained 31 , 39, 47 carbon atoms and a nickel atom to establish a simulation model. The optimal calculation of the simulation model uses a tetragonal lattice supercell with lattice constants a, b, and c. The selection of a and b should ensure that the distance between the nearest atoms in the nanotubes of the periodic image is not less than Therefore, this embodiment chooses grid to remove periodic image interactions.

In this step, various parameters of the doped simulation model also need to be determined. Use the Dmol3 module of the Materials Studio software to optimize the structure of the lattice supercell, determine the corresponding structural optimization parameters, and control the error of the simulation simulation within 2%, which meets the verification requirements, thereby obtaining the optimized nickel-doped small-radius carbon nanometer Tube model.

The structural optimization mentioned in this application refers to the calculation of the minimum energy of the system based on the software after the standard database modeling of the Materials Studio software is used, and the structural optimization is also the process of calculating the minimum energy of the system. In this process, the interatomic distance of the simulation model will change, and the electrons between atoms will also be transferred. Therefore, the model parameters after structure optimization will be changed compared with the standard model parameters, and the parameter error is less than 2%. The simulation results are reliable. The model after structure optimization is the real model for simulation. If it is a model with gas in structure optimization, then structure optimization is the process of simulating adsorption. The obtained model is the model after adsorption, and the relevant adsorption energy can be calculated. The model is just a modeling, not an adsorbed model.

Among them, the standard model parameters of gas molecules are manually input, and then the structure is optimized. The optimized parameters are the parameters used in the actual modeling. The parameters specifically refer to the distance between molecules, that is, the distance between S atoms and O atoms. The distance between gas molecules and atoms is the distance measured before. After optimizing the model, the corresponding parameters of gas molecules are determined to complete the establishment of the simulation model.

Step S02 (adsorption simulation step): establishing different adsorption positions of gas molecules in the simulation model, and simulating the adsorption conditions of different adsorption positions before and after doping. For the simulation model of different adsorption positions, the PBE+GGA algorithm is used under the Dmol3 module, and the simulation of the physical adsorption of SO ₂ is realized through structural adjustment under CUSTOM precision.

Step S03 (analysis step): Comparing the energy difference before and after adsorption at different adsorption positions, the maximum adsorption energy indicates that this position is the most likely position for the object to adsorb gas, obtain the preset data corresponding to the position with the lowest adsorption energy, and calculate the adsorption energy The lowest position of the data before and after doping to compare the adsorption energy. The preset parameters in the analysis step include: structural symmetry, energy band structure, DOS density of states and charge density.

By optimizing the structure of the simulation model without adding gas molecules, the total energy of the system is obtained, and the structure of the model with added gas molecules is optimized to obtain the total energy of the system.

Among them, adsorption energy = total energy of added gas molecules - energy of gas molecules - energy of model without added gas molecules.

According to the above calculation formula of adsorption energy, the following analysis can be carried out:

1) Through the adsorption energy formula, the change of adsorption energy before and after doping can be compared. The results show that the _SO2 molecule exhibits the best performance when adsorbed on the surface of carbon nanotubes parallel to the axis of the carbon nanotubes in such a way that two O atoms are close to the Ni atoms of the dopant element at the same angle and distance, and the S atoms are far away from the Ni atoms. Good adsorption, the specific situation is shown in Fig. 2a-2f.

2) The smaller the adsorption energy, the lower the energy of the adsorption system and the more stable the structure. The adsorption energies of the (n,0)SWCNT (n=4,5,6) system for adsorbing SO ₂ molecules are -0.016eV, -0.019eV, -0.061eV, respectively, while Ni-(n,0)SWCNT(n =4,5,6) The adsorption energies of the system for SO ₂ molecules are significantly reduced to -0.911eV, -1.090eV, -1.182eV respectively, which means that the carbon nanotubes doped with nickel are more likely to adsorb SO ₂ molecules.

In this step, when the symmetry of the system structure changes, the physical properties of the crystal will change accordingly, and this change will also cause changes in the chemical properties. A new parameter "symmetry breaking factor δ" is defined to measure the effect of doping on the architecture. Calculate the symmetry breaking factor δ used to measure the symmetry breaking brought by doping to the nickel-doped small-radius carbon nanotubes according to the following formula,

Among them, Dc-c represents the average bond length between the intrinsic carbon nanotube carbon atom and the surrounding three adjacent carbon atoms, and Dc _-Ni represents the bond length between the doped nickel atom and the surrounding three carbon atoms average value.

It can be known from the above formula that the larger the symmetry breaking factor δ, the greater the structural change of the carbon nanotube after doping, and the greater the impact on the electronic performance and adsorption performance of the carbon nanotube. With the increase of tube diameter, the symmetry breaking factor decreases gradually, and the adsorption capacity of carbon tubes increases gradually.

Fig. 3a～3f is the energy band structure diagram of intrinsic and nickel-doped small-radius carbon nanotube in a kind of adsorption model of the present invention, wherein, Fig. 3 a is (a) (4,0) SWCNT energy band structure diagram, Fig. 3b It is the band structure diagram of Ni-(4,0)SWCNT; Figure 3c is the band structure diagram of (5,0)SWCNT; Figure 3d is the band structure diagram of Ni-(5,0)SWCNT; Figure 3e is the band structure diagram of (6, 0) Band structure diagram of SWCNT; Figure 3f is the band structure diagram of Ni-(6,0)SWCNT. As shown in Figures 3a-3f, the intrinsic carbon nanotubes (4,0), (5,0), and (6,0) are all metallic carbon nanotubes with a band gap of 0; the carbon nanotubes doped with nickel atoms It exhibits certain semiconductor properties, and its band gaps are 0.327eV, 0.260eV, and 0.390eV, respectively. This shows that nickel doping can transform small-radius carbon nanotubes from metallic to semiconducting properties, and has a strong influence on the conductivity of carbon nanotubes.

Figures 4a to 4b are partial wave density of states diagrams of _SO2 -intrinsic small-radius carbon nanotube adsorption system in an adsorption model of the present invention, wherein Figure 4a does not have a density of state diagram of carbon atoms when SO2 is adsorbed, and Figure 4b has adsorbed The density of state diagram corresponding to oxygen, sulfur and carbon atoms in the structure of SO ₂ , Fig. 5 is a partial wave density of state diagram of the SO ₂ -nickel-doped small-radius carbon nanotube adsorption system in an adsorption model of the present invention. From Figures 4a to 4b, and Figure 5, it can be seen that the structure of nickel-doped carbon nanotubes is transformed into metallic carbon tubes after adsorbing _SO2 molecules, and the peaks of the density of states of S and O atoms are added to the conduction band. The p-orbitals of O atoms and the d-orbitals of Ni atoms effectively overlap near the Fermi level, which indicates a strong interaction between _SO2 molecules and Ni atoms in the carbon nanotubes.

Figures 6a to 6b are the electron density profiles of the SO ₂ -carbon nanotube adsorption system and the SO ₂ -Ni-carbon nanotube adsorption system in an adsorption model of the present invention, wherein Figure 6a is the SO ₂ -carbon nanotube adsorption system , Fig. 6b is the electron density profile of the SO ₂ -Ni-carbon nanotube (b) adsorption system. As shown in Figures 6a-6b, during the process of intrinsic carbon nanotubes adsorbing SO ₂ molecules, the electron density values between the O atoms in the SO ₂ molecules and the C atoms in the carbon nanotubes are distributed between 0.0 and 0.1, almost There is no overlapping area, indicating that there is almost no charge transfer between _SO2 molecules and intrinsic carbon nanotubes, that is, the adsorbed _SO2 molecules have little effect on the charge distribution of intrinsic carbon nanotubes. In contrast, after Ni-doped carbon nanotubes adsorb _SO2 molecules, the electron density value between O atoms and Ni atoms is about 0.2, which is shown in the electron density profile diagram, that is, there is a large range of bright _The overlapping region, which is the result of the coupling of 3d electrons of Ni atoms and 2p electrons of O atoms, has a large number of electrons from SO ₂ molecules transferred to Ni-doped carbon nanotubes, which further indicates that O atoms and A chemical bond is formed between nickel atoms in nickel-doped carbon nanotubes, that is, there is a strong chemisorption between Ni-doped carbon nanotubes and _SO2 molecules.

3) The doping of nickel atoms makes the adsorption of _SO2 molecules by small-radius carbon nanotubes easier, and the larger the radius, the stronger the adsorption capacity. Moreover, compared with the undoped system, the Ni-doped system exhibits semiconducting properties, but after adsorbing SO ₂ , the energy gap drops to 0, and the resistance decreases significantly, making the Ni-carbon nanotube system resistant to SO ₂ The gas sensitivity is increased several times, which proves that Pd-doped small-radius carbon nanotubes can significantly improve the adsorption capacity and gas sensitivity of small-radius carbon nanotubes to SO ₂ .

The method for verifying the adsorption capacity of nickel-doped small-radius carbon nanotubes on SO ₂ provided in this embodiment verifies the influence of nickel-doped small-radius carbon nanotubes on the adsorption capacity and gas sensitivity of SO ₂ by establishing a rationally optimized simulation.

It should be understood that the present invention is not limited to the above-mentioned embodiments, and any changes or modifications to the present invention do not depart from the spirit and scope of the present invention, provided that these changes and modifications belong to the claims and equivalent technical scope of the present invention, then The present invention is also meant to include such changes and modifications.

Claims (10)

1. A method for verifying the adsorption capacity of nickel-doped small-radius carbon nanotubes to sulfur dioxide, is characterized in that, comprising the following steps: Simulation model building steps: take (n, 0) SWCNT (n=4, 5, 6) small-radius carbon nanotubes as the surface model, build a simulation model and receive the molecular spacing of the input gas molecules, and the simulation model uses lattice Tetragonal lattice supercell with constants a, b and c; Adsorption simulation step: establishing different adsorption positions of gas molecules in the simulation model, and simulating the adsorption conditions of different adsorption positions before and after doping; Analysis steps: compare the energy difference before and after adsorption at different adsorption positions, obtain the preset data corresponding to the position with the lowest adsorption energy, and calculate the adsorption energy before and after doping at the position with the lowest adsorption energy. 2. verification nickel-doped small-radius carbon nanotubes as claimed in claim 1 is to the method for the adsorption capacity of SO , it is characterized in that: described surface model comprises three types of _surface models of 32,40,48 carbon atoms, The pipe diameters corresponding to the three types of surface models are 3. The method for verifying the adsorption capacity of nickel-doped small-radius carbon nanotubes to sulfur dioxide as claimed in claim 2, characterized in that: the doping concentrations are respectively 2.13%, 2.56%, and 3.23% in the three types of surface models. % nickel atoms to establish a simulation model. 4. the method for verifying the adsorption capacity of nickel-doped small-radius carbon nanotubes to sulfur dioxide as claimed in claim 3, is characterized in that, simulation model establishment step also comprises: use The lattice to remove the interaction of the periodic image of the simulation model. 5. the method for verifying the adsorption capacity of nickel-doped small-radius carbon nanotubes to sulfur dioxide as claimed in claim 4, is characterized in that, after setting up described simulation model, also comprises: Using the Dmol3 module of the Materials Studio software to adjust the structure of the lattice supercell, a simulation model corresponding to nickel-doped small-radius carbon nanotubes is obtained. 6. the method for verifying the adsorption capacity of nickel-doped small-radius carbon nanotubes to sulfur dioxide as claimed in claim 5, is characterized in that, described adsorption simulation step also comprises: For the simulation model of different adsorption positions, the PBE+GGA algorithm is used under the Dmol3 module, and the simulation of the physical adsorption of SO ₂ is realized through structural adjustment under CUSTOM precision. 7. the method for verifying the adsorption capacity of nickel-doped small-radius carbon nanotubes to sulfur dioxide as claimed in claim 6, is characterized in that, the preset parameter in the described analysis step comprises: structural symmetry, energy band structure, DOS Density of states and charge density. 8. The method for verifying the adsorption capacity of nickel-doped small-radius carbon nanotubes to sulfur dioxide as claimed in claim 9, wherein said gas molecules are SO _gas molecules. 9. The method for verifying the adsorption capacity of nickel-doped small-radius carbon nanotubes to sulfur dioxide as claimed in claim 8, wherein the small-radius carbon nanotubes are nickel-doped small-radius carbon nanotubes. 10. verify the method for the adsorption capacity of nickel-doped small-radius carbon nanotubes to sulfur dioxide as claimed in claim 9, it is characterized in that, described analysis step also comprises: Calculate the symmetry breaking factor δ used to measure the symmetry breaking brought by doping to the nickel-doped small-radius carbon nanotubes according to the following formula, Among them, Dc-c represents the average bond length between the intrinsic carbon nanotube carbon atom and the surrounding three adjacent carbon atoms, and Dc _-Ni represents the bond length between the doped nickel atom and the surrounding three carbon atoms average value.