CN105834447A - Method for revealing nano bi-metal CoNi adsorption mechanism based on density functional theory - Google Patents

Abstract

The invention provides a method for revealing a nano bi-metal CoNi adsorption mechanism based on the density functional theory and belongs to the technical field of chemical engineering. A nano adsorbent is prepared through simple reduction reaction under the room-temperature air, and the efficient adsorption mechanism of the adsorbent is deeply analyzed by applying a computer simulation auxiliary adsorption experiment result based on the density functional theory. The method comprises the following steps that 1, CoNi bi-metal nano particles are prepared; 2, the adsorption performance of the CoNi bi-metal nano particles is tested; 3, a CoNi bi-metal surface model is constructed; and 4, the surface property of the CoNi bi-metal surface model is calculated. According to the method for revealing the nano bi-metal CoNi adsorption mechanism based on the density functional theory, the method that density functional theory calculation and the experiment result are combined is adopted to illustrate that the adsorption performance of the CoNi bi-metal nano particles is superior to that of single metal (Co or Ni) on the molecule and atom level, and the efficient adsorption mechanism of the CoNi bi-metal nano particles is revealed by analyzing the surface energy, the work function, the state density, the surface atomic charge difference density and the d belt center of the surface model.

Description

The method disclosing bimetallic nano CoNi adsorption mechanism based on density functional theory

Technical field

The invention belongs to chemical technology field, be specifically related to one and utilize Materials Studio computed in software to combine with experiment, The method of research CoNi bimetal nano particles efficient absorption mechanism.

Background technology

Nano material has the unique advantages such as specific surface area is high, granularity is little, reactivity is high due to it, and is widely used in dirt During water processes.Absorption is very important process in method for treating water, reacts to have with surface and contacts closely, although numerous Experimental result the research that surface is reacted is served greatly help, but the principles of science of essence is explained and is but differed greatly, for Reduce theoretical and actual gap, use and explain that adsorption process has an important meaning based on Density function theory from point of theory Justice.Density function theory is the effective means exploring material microscopic nature from quantum-mechanical angle, the most widely used Characterize and detection means (such as XRD, SEM, TEM etc.) is difficult to meet in molecular atoms level and understands biological effect superficiality And reaction mechanism can be disclosed, and Density function theory compensate for the deficiency of this respect.The primary based on density functional theory Principle research can provide the explanation of detailed molecular atoms level in the character of prediction and research advanced material.Relative to inhale The macroscopic result such as attached capacity, adsorption dynamics adsorption kinetics, structure change, analyze and speculate the experimentation of adsorption mechanism, use theory Calculate the method that combines with experimental result, announcement adsorption reaction mechanism from molecular atoms level, to the development of scientific research just Seem the most meaningful.

Summary of the invention

For the deficiencies in the prior art, it is an object of the invention to provide one and utilize density functional theory to calculate on the server The surface nature of CoNi bimetal nano particles, analyzes the CoNi of low-crystallinity prepared by room temperature from molecular atoms level qualitatively The method of bimetal nano particles efficient absorption mechanism, establishes for disclosing the sustainable development of actual adsorption mechanism and nanosecond science and technology Theoretical basis.

The method of the present invention comprises the following steps:

The preparation of 1.1CoNi bimetal nano particles comprises the following steps:

1.1.1 0.2g cobalt chloride hexahydrate and 0.2g Nickel dichloride hexahydrate are uniformly mixed；

1.1.2 in the mixture of step 1.1.1, add 0.2g sodium borohydride powder, uniform by ground and mixed；

1.1.3 the powder of step 1.1.2 gained is dissolved in 20mL deionized water, to reaction completely, no longer produces bubble；

1.1.4, after having reacted described in step 1.1.3, isolate the black product in solution with Magnet, and with deionized water and Black product is cleaned 3 times by ethanol respectively, and drying at room temperature 24h obtains stable CoNi bimetal nano particles；

The absorption property test of 1.2CoNi bimetal nano particles:

The CoNi bimetal nano particles 5mg of step 1.1.4 gained is joined in the Congo red solution of 50mL, in room temperature Under carry out mechanical agitation, become colorless to solution；Carrying out four groups of parallel laboratory tests during test, the quality of the Congo red solution chosen is dense Degree is respectively as follows: 30,50,80 and 100mg L^-1；

The structure of 1.3CoNi bimetallic surface model:

Using material simulation software--Materials Studio builds by the CoNi bimetallic of 28 former molecular face-centred cubic structures Periodic surface model, in model, Co and Ni presses atomic ratio 1:1 ordered arrangement, builds three low index surface (100), (110) (111), for preventing the interaction between adjacent periods, employing is more thanVacuum layer；Defect is introduced in (111) surface, The CoNi bimetal nano particles surface that degree of crystallinity prepared by analog room temperature is low, carry defective surface model include a Co or The defect of Ni atom and the defect of two atoms of Co and Ni.

The calculating of 1.4CoNi bimetallic surface model surface character, comprises the following steps:

1.4.1 select Materials Studio as simulation software；

1.4.2 to step 1.3 build the geometry optimization of CoNi bimetallic surface model, surface energy, work function, surface atom The density of states, surface charge differential-density and the calculating at d band center, all in CASTEP module based on density functional theory Complete, and choose generalized gradient approximation GGA-PW91 as exchange correlation function；

1.4.3 the CoNi bimetallic surface model built step 1.3 first carries out geometry optimization, then to the surface model after optimizing Carry out from being in harmony computing, according to the result in calculated castep file, calculate surface energy and the work function of surface model, and Make electric charge difference density map and density of states figure, calculate the d band center of respective surfaces atom.

CoNi bimetal nano particles described in step 1.1, is the stable CoNi prepared by simple reducing process at ambient temperature Bimetal nano particles.

It is double that the defective surface model of tool set up in described step 1.3 contributes to disclosing the CoNi that in experiment, the degree of crystallinity of preparation is low The surface nature of metal nanoparticle.

Calculated surface energy, work function, the density of states of surface atom, surface charge differential-density and d in described step 1.4 With results such as centers for analyzing the surface nature of CoNi bimetal nano particles.

Experimental result in step 1.1 to 1.4 is combined with result of calculation, determines CoNi bimetal nano particles adsorption mechanism Key component.

The present invention passes through the material simulation software (Materials Studio) surface nature (surface energy, work function, surface to institute's established model Atomic state density, surface charge differential-density and d band center) Theoretical Calculation, Binding experiment result discloses the double gold of CoNi Belong to the mechanism of nanoparticle high efficiency of additive capability, can be the sustainable development based theoretical of nanosecond science and technology.

Utilize method based on Density function theory of the present invention to CoNi bimetal nano particles efficient absorption mechanism Analyze compared with traditional single experimental technique, there is following significant superiority:

The surface property of the nanoparticle participating in adsorption reaction can be studied in molecular atoms level.By the meter to surface property Calculate, the visual in image geographical distribution solving surface charge and change in molecular atoms level, from energy (surface energy and work function) Angle, nanoparticle surface activity is analyzed.By the way of experimental result combines with the calculated results, explanation Bimetal nano particles absorption property is better than single metal nanoparticle, and discloses the efficient suction of CoNi bimetal nano particles Random is managed.

Accompanying drawing explanation

Fig. 1 is that Congo red initial concentration affects schematic diagram to absorbability

Wherein: a is Co；B is CoNi；C is Ni.

Fig. 2 is point density of states figure of the 3d track of 3 layers of surface and body phase layer in CoNi bimetallic model

Fig. 3 is the electric charge difference density map of CoNi bimetallic (111) surface model

Wherein: a is surface；B is longitudinal section.

Fig. 4 is the 3d track point density of states figure of surface ground floor atom

Wherein: a is monometallic cobalt (111) surface；B is monometallic nickel (111) surface；C is CoNi bimetallic (111) surface；d For having CoNi bimetallic (111) surface of CoNi defect；Arrow mark is the d band center of top layer atom.

Fig. 5 is the adsorption mechanism figure of CoNi bimetal nano particles

Detailed description of the invention

Embodiment 1

Strong reductant by 0.4g cobalt chloride hexahydrate (or Nickel dichloride hexahydrate) Yu 0.2g--sodium borohydride (NaBH₄) by grinding Mix homogeneously, dissolves in the deionized water of 20ml, to reaction completely, no longer produces bubble.After question response is complete, use Magnet Isolate the black product (Co or Ni monometallic nanoparticle) in solution, and respectively that black product is clear with deionized water and ethanol Wash 3 times, drying at room temperature 24h.Obtained sample 5mg is joined in the Congo red solution of 50mL, at room temperature enter Row mechanical agitation, becomes colorless to solution.Carrying out four groups of parallel laboratory tests during test, the mass concentration of the Congo red solution chosen is divided It is not: 30,50,80 and 100mg L^-1；At the appointed time point (1min, 2min, 5min, 10min and 20min) Take the concentration after 2mL solution measures its absorption.Using material simulation software--Materials Studio builds and is made up of 28 atoms Three low index surface (100) of face-centred cubic structure Co (or Ni), (110) and the surface model of (111), in order to prevent adjacent periods Between interaction, employing is more thanVacuum layer.The surface model built comprises 7 layers of atom, wherein three layers of surface former Son allows relaxation during geometry optimization, and the cartesian coordinate of the four layers of atom in bottom is fixed, during geometry optimization not Allow to carry out relaxation.The geometry optimization of the surface model of surface model, surface energy, work function, the density of states of surface atom, table Surface charge differential-density and the calculating at d band center, all complete in CASTEP module based on density functional theory, chooses wide Justice gradient approximation GGA-PW91 is as exchange correlation function, and plane wave kinetic energy cut-off is that 400eV, k point sampling uses 10 × 10 × 1, all consider spin polarization during all calculating.

Embodiment 2

0.2g cobalt chloride hexahydrate and 0.2g Nickel dichloride hexahydrate are uniformly mixed, adds 0.2g sodium borohydride (NaBH₄) powder End, uniform by ground and mixed, dissolve in the deionized water of 20ml, to reaction completely, no longer produce bubble.Question response is complete After, the black product (CoNi bimetal nano particles) in solution is isolated with Magnet, and with deionized water and ethanol respectively by black Color product cleaning 3 times, drying at room temperature 24h.Obtained sample 5mg is joined in the Congo red solution of 50mL, Carry out mechanical agitation under room temperature, become colorless to solution.Four groups of parallel laboratory tests are carried out, the matter of the Congo red solution chosen during test Amount concentration is respectively as follows: 30,50,80 and 100mg L^-1；At the appointed time point (1min, 2min, 5min, 10min and 20min) take the concentration after 2mL solution measures its absorption.Amount (the mg g of absorption Congo red^-1) by following mass balance side Journey calculates:

$q_e=\frac{(C_0-C_e)\×V}{W}$

In formula: q_eIt is every gram of adsorbent absorbability (the mg g when absorption reaches balance^-1)；C₀It it is the initial concentration of Congo red solution (mg dm^-3)；V is the volume (dm of solution^-3)；C_eIt is to adsorb concentration (the mg dm of Congo red solution when reaching balance^-3)。

Adsorption experimental results (Fig. 1) shows: even if Congo red concentration reaches 100mg L^-1, three kinds of samples the most all can be complete by Congo red Full absorption.When Congo red concentration is from 30mg L^-1Increase to 100mg L^-1Time, adsorption capacity is from 300mg g^-1Increase to 1000 mg g^-1.The adsorption efficiency of monometallic nickel is minimum, and absorption completely needs 20min, and monometallic cobalt can complete to inhale in 5min Attached.CoNi bimetal nano particles has the highest adsorption efficiency, and absorption Congo red completely only needs 2min, is monometallic cobalt 2.5 times of adsorption efficiency.

Using material simulation software--Materials Studio builds by the CoNi bimetallic of 28 former molecular face-centred cubic structures Periodic surface model, in model, Co and Ni presses atomic ratio 1:1 ordered arrangement, builds three low index surface (100), (110) (111), for preventing the interaction between adjacent periods, employing is more thanVacuum layer；Defect is introduced in (111) surface, The CoNi bimetal nano particles surface that degree of crystallinity prepared by analog room temperature is low, carry defective surface model include a Co or The defect of Ni atom and the defect of two atoms of Co and Ni.The surface model built comprises 7 layers of atom, wherein the three of surface Layer atom allows relaxation during geometry optimization, and the cartesian coordinate of the four layers of atom in bottom is fixed, in geometry optimization process In do not allow to carry out relaxation.The geometry optimization of the surface model of surface model, surface energy, work function, the density of states of surface atom, Surface charge differential-density and the calculating at d band center, be all to complete in CASTEP module based on density functional theory, choosing Taking generalized gradient approximation GGA-PW91 as exchange correlation function, plane wave kinetic energy cut-off is that the sampling of 400eV, k point uses Be 10 × 10 × 1, all consider spin polarization during all calculating.Surface energy and work function are respectively by following equation (1) and (2) Calculating, result is listed in Table 1.Result of calculation shows, CoNi bimetallic (111) surface of face-centred cubic structure has low Surface can, can reflect that room temperature prepares the apparent condition of sample.Meanwhile, the existence of result of calculation display surface defect makes surface energy Increase, and make work function reduce, illustrate that crystallizing incomplete CoNi bimetal nano particles under room temperature has higher reaction work Property and electronation.

$\mathrm{\γ}=\frac{E_{surf}-0.5{\mathrm{\Σn}}_M{E}_M^{bulk}-0.5E_{surf}^{unrel}}{A}---\left(1\right)$

In formula, E_surfRepresent the gross energy of relaxation rear surface,Represent corresponding atom energy in body phase material, n_MRepresent The atom number (M represents Co or Ni) comprised in surface model.Representing the gross energy of relaxation front surface, A is face, surface Long-pending. parameter 0.5 therein represents three layers of atom generation relaxation process on only surface, and remaining atom is fixed on body phase Position.

Φ=E_vac(+∞)-E_F(2)

In formula, E_vacRepresenting vacuum level, it is to be calculated by the Average Static gesture of vacuum area mid portion.E_FRepresent phase The fermi level answered.

The surface energy of table 1 Density function theory and work function

Fig. 2 show point density of states figure of the 3d track of surface (3 layers) and body phase (4 layers) in CoNi bimetallic model.With body phase The density of states compare, the distribution of the atom of outermost layer (Layer-1) there occurs significantly change, and the density of states is concentrated mainly on-3～0eV High-energy regions, makes surface be in the higher-energy state of instability.

Fig. 3 show the electric charge difference density map of surface atom, relative to monometallic cobalt, nickel and do not have defective CoNi double Metal surface, the existence of defect makes electronics collect around at surface atom core.By the analysis of the density of states Yu differential charge density, The incomplete CoNi bimetal nano particles of crystallization can be speculated, than monometallic cobalt and nickel, there is higher electronation.

Fig. 4 show the 3d track point density of states figure of surface ground floor atom, and the d band center of respective surfaces, can from figure To find out: the bimetallic formation of CoNi and the introducing of defect, the change at d band center all can be caused.The change at d band center is also Promote the electron transfer between CoNi bimetallic sorbent and adsorbed molecule, and the intermediate product of surface adsorption is quick Remove.

Binding experiment result and the calculated results, can speculate that the adsorption process of the adsorbent of preparation is that electronation is inhaled with electrostatic Attached coefficient process, wherein electronation is the major way that absorption is carried out.CoNi bimetal nano particles has and compares Dan Jin Belong to cobalt and the more excellent absorption property of nickel.

Fig. 5 show adsorption mechanism figure, and Congo red molecules first passes through electrostatic attraction and is adsorbed onto CoNi bimetal nano particles table Face, owing to nanoparticle has high surface activity, makes a part-N=N-bond fission, makes the conjugation chromophore of Congo red molecules Group is destroyed, forms relatively small molecule, and then nanoparticle makes the-NH on aromatic rings further₂Chromophore rupture, finally by Congo red macromole divides the less pollutant group and adsorbs in nanoparticle surface.

Claims (2)

1. the method disclosing bimetallic nano CoNi adsorption mechanism based on density functional theory, it is characterised in that include following Step:

The preparation of 1.1CoNi bimetal nano particles comprises the following steps:

1.1.1 0.2g cobalt chloride hexahydrate and 0.2g Nickel dichloride hexahydrate are uniformly mixed；

1.1.2 in the mixture of step 1.1.1, add 0.2g sodium borohydride powder, uniform by ground and mixed；

1.1.3 the powder of step 1.1.2 gained is dissolved in 20mL deionized water, to reaction completely, no longer produces bubble；

1.1.4, after having reacted described in step 1.1.3, isolate the black product in solution with Magnet, and with deionized water and Black product is cleaned 3 times by ethanol respectively, and drying at room temperature 24h obtains stable CoNi bimetal nano particles；

The absorption property test of 1.2CoNi bimetal nano particles:

The CoNi bimetal nano particles 5mg of step 1.1.4 gained is joined in the Congo red solution of 50mL, at room temperature Carry out mechanical agitation, become colorless to solution；Four groups of parallel laboratory tests are carried out, the mass concentration of the Congo red solution chosen during test It is respectively as follows: 30,50,80 and 100mg L^-1；

The structure of 1.3CoNi bimetallic surface model:

Using material simulation software--Materials Studio builds by the CoNi bimetallic of 28 former molecular face-centred cubic structures Periodic surface model, in model, Co and Ni presses atomic ratio 1:1 ordered arrangement, builds three low index surface (100), (110) (111), for preventing the interaction between adjacent periods, employing is more thanVacuum layer；Defect is introduced in (111) surface, The CoNi bimetal nano particles surface that degree of crystallinity prepared by analog room temperature is low, carry defective surface model include a Co or The defect of Ni atom and the defect of two atoms of Co and Ni；

The calculating of 1.4CoNi bimetallic surface model surface character, comprises the following steps:

1.4.1 select Materials Studio as simulation software；

1.4.2 to step 1.3 build the geometry optimization of CoNi bimetallic surface model, surface energy, work function, surface atom The density of states, surface charge differential-density and the calculating at d band center, all in CASTEP module based on density functional theory Complete, and choose generalized gradient approximation GGA-PW91 as exchange correlation function；

1.4.3 the CoNi bimetallic surface model built step 1.3 first carries out geometry optimization, then to the surface model after optimizing Carry out from being in harmony computing, according to the result in calculated castep file, calculate surface energy and the work function of surface model, and Make electric charge difference density map and density of states figure, calculate the d band center of respective surfaces atom.

2. the method disclosing bimetallic nano CoNi adsorption mechanism based on density functional theory as described in claim 1, its feature It is the CoNi bimetal nano particles described in step 1.1, is the stable CoNi prepared by simple reducing process at ambient temperature Bimetal nano particles.