CN115350715A

CN115350715A - Co-doped ultrathin bismuth oxyhalide photocatalytic CO 2 Method for producing reduced material

Info

Publication number: CN115350715A
Application number: CN202210416451.8A
Authority: CN
Inventors: 邵玉梅; 黄佳琪; 隋雨洁; 章毅琴; 李书勤; 符盛桃; 张昕颖; 王奕桥; 谢宇
Original assignee: Nanchang Hangkong University
Current assignee: Nanchang Hangkong University
Priority date: 2022-04-20
Filing date: 2022-04-20
Publication date: 2022-11-18

Abstract

The invention uses a simple cation exchange strategy to prepare the BiOBr ultrathin nanosheet with the (110) exposed surface, and the BiOBr is modified by replacing part of Bi3+ on the surface of the BiOBr with Co3+ (figure 1). The prepared ion-exchange product reduced CO2 under visible light to have a CO rate of 11.71. Mu. Molg-1. Mu.h-1 that is nearly 4 times that of pure BiOBr. The influence of Co3+ substituting Bi3+ to enter BiOBr surface crystal lattice on BiOBr is researched by various characterization methods, and possible reasons of the promotion effect of the strategy on the photocatalytic reduction rate of CO2 are discussed.

Description

Co-doped ultrathin bismuth oxyhalide photocatalytic CO 2 Method for producing reduced material

Technical Field

The invention belongs to the field of doped photocatalytic material preparation, and particularly relates to a preparation method of a Co-doped ultrathin bismuth oxyhalide photocatalytic CO2 reduction material by a simple cation exchange strategy.

Background

The traditional photocatalysts TiO2 and ZnO show very low photocatalytic activity under the irradiation of visible light due to the excessively wide band gap. In order to improve the efficiency of solar utilization, researchers have developed many novel visible light driven catalytic materials. BiOX (X = Cl, br, I) has a unique ternary layered structure characteristic, and the band gap of the BiOX meets the basic requirement of high-efficiency photocatalytic performance, thereby attracting the wide attention of researchers. Wherein BiOBr is favored because of the characteristics of easy preparation, low cost, stable structure, no toxicity, no harm and the like. However, the problems of low conversion activity and poor selectivity to hydrocarbon products of BiOBr in photocatalytic CO2 conversion still exist. To overcome these disadvantages, the predecessors have explored numerous modification methods. For example, the generation efficiency of BiOBr carbon monoxide and methane is improved by using an ultra-thin thickness and bismuth-rich strategy; the rate of generating carbon monoxide and methane by BiOBr is respectively increased by 8.8 times and 5.8 times by preparing the oxygen-enriched vacancy BiOBr hollow sphere; the use of Gd3+ doped BiOBr microspheres increased the methanol generation rate of BiOBr by nearly 5 times. These methods improve the conversion efficiency of BiOBr to CO2 to a large extent, but are far from sufficient for practical applications.

Ion exchange strategies have made tremendous progress in designing electrocatalysts on an atomic scale. This is instructive in studying how to optimize the photocatalyst in atomic structure, thereby adjusting its electronic structure, enhancing electronic conductivity, and promoting adsorption/desorption of reaction intermediates. The cation exchange strategies are mainly faceting, heteroatom doping, defect formation and strain modulation at the catalyst surface. Heteroatom doping is considered to be one of the methods that can significantly improve catalyst performance, however growing high quality doped-atom nanocrystals is a huge challenge. In conventional methods, heteroatoms are typically incorporated into the host crystal material during crystal growth. However, this tends to destroy the original structure of the crystal, thereby causing the host crystal to lose some of its original excellent properties. Again, this results in poor stoichiometry control of the dopant due to the "self-cleaning" effect. In contrast, the cation exchange strategy carries out the growth of the host material and the doping profile of the heteroatoms, can skillfully retain the original structure of the host crystal, and can accurately control the doping amount of the heteroatoms by adjusting the stoichiometry of the heteroatoms or designing cation substitution kinetics. The BiOBr {110} surface shows two exposed ends of Bi and O, a cation exchange strategy is used for replacing part of Bi atoms on the BiOBr surface with heteroatoms, the amount of the introduced heteroatoms is controlled while the unique ternary layered structure characteristics in the BiOBr crystal are kept, the obtained heteroatoms bring beneficial properties, and a catalyst with higher photocatalytic activity is hopefully obtained.

Disclosure of Invention

The invention aims to solve the technical problem of providing a preparation method of a Co-doped ultrathin bismuth oxyhalide photocatalytic CO2 reduction material by a simple cation exchange strategy, which is used for meeting the requirement of solving the environmental problem.

The invention is realized in such a way, and the specific preparation method is as follows:

(1) Preparation of BiOBr nanosheet

1) Adding Bi (NO 3) 3 to 5H2O and CTAB to ultrapure water, and stirring the mixture for 10 minutes;

2) The pH of the resulting solution was adjusted to about 9 by adding aqueous NaOH (6M), and the solution was stirred vigorously for 1 hour;

3) Transferring the solution obtained in the step 2) into a stainless steel autoclave for reaction for 15h at the temperature of 170 ℃, washing and drying to obtain a precursor.

(2) Preparation of Co-BiOBr

4) Weigh BiOBr and Co (NO 3) 3. Mush.6H 2O, add ultrapure water and sonicate for 20min;

5) Stirring the solution obtained in the step 4) in a constant-temperature heating magnetic stirrer at 80 ℃ for 24 hours. ( The mass of the added Co (NO 3) 3. Mu.m.6H 2O was changed to 48, 96, 192mg. The resulting samples were designated BiOBr, co-BiOBr-0.25, co-BiOBr-0.5, co-BiOBr-1, co-BiOBr-2, respectively, according to the molar ratio of the reactants Co and Bi. )

The beverage prepared from Bi (NO 3) 3 ] 5H2O, supplied by MACKLIN, inc.;

co (NO 3) 3. Sup.6H 2O according to the present invention, supplied by MACKLIN Inc.;

the samples obtained in the step 4) are named BiOBr, co-BiOBr-0.25, co-BiOBr-0.5, co-BiOBr-1 and Co-BiOBr-2 respectively.

The invention controls different molar ratios of Co and Bi reactants, adopts a cation exchange method to prepare a novel Co-doped BiOBr material with visible light response, comprehensively analyzes the configuration and the microscopic morphology of the crystal, the photoelectric property of element composition, the energy band structure and the like, and tests the capability of a catalyst for reducing CO2 by visible light and the product obtained after reduction. The Co-doped BiOBr material prepared by the incomplete cation exchange method shows good photocatalytic activity, and the yield of CO reduced into CO2 by Co-BiOBr-0.5 under the irradiation of visible light is about 4 times that of pure BiOBr. The doping of Co on the surface of the BiOBr catalyst increases the visible light absorption range of BiOBr and reduces the recombination rate of photo-generated electrons and holes. In addition, the Co-BiOBr-0.5 prepared by the method has good stability, and has certain guiding significance for developing a new CO2 catalyst and further converting CO2 into valuable new energy.

The invention has the advantages that: from the aspect of doping the photocatalytic material, the Co-doped BiOBr material prepared by an incomplete cation exchange method shows good photocatalytic activity, and the yield of CO obtained by reducing CO2 by Co-BiOBr-0.5 under the irradiation of visible light is about 4 times that of pure BiOBr. The doping of Co on the surface of the BiOBr catalyst increases the visible light absorption range of BiOBr and reduces the recombination rate of photo-generated electrons and holes. In addition, the Co-BiOBr-0.5 prepared by the method has good stability, and has certain guiding significance for developing a new CO2 catalyst and further converting CO2 into valuable new energy.

Drawings

FIG. 1 is an X-ray diffraction analysis chart of the products obtained in examples 1 to 4.

FIGS. 2-4 are graphs of the degradation of the products prepared in examples 1-4 under simulated sunlight for degradation of 50ml of 10PPm methyl orange solution.

Detailed Description

The invention is further described below with reference to fig. 1-4, without limiting the scope of the invention.

Example 1

(1) Preparation of BiOBr nanosheet

1) Weigh 0.5g of Bi (NO 3) 3. 5H2O and 0.5g of CTAB into ultrapure water, and stir the mixture for 10 minutes;

2) The ph of the resulting solution was adjusted to about 9 by adding aqueous NaOH (6M) and the solution was stirred vigorously for 1 hour;

(2) Preparation of Co-BiOBr

4) Weighing 100mg BiOBr and 24mg Co (NO 3) 3. Mu.6H 2O, adding 100mL ultrapure water, and sonicating for 20min;

5) Stirring the solution obtained in the step 4) in a constant-temperature heating magnetic stirrer at the temperature of 80 ℃ for 24 hours to obtain the product.

The resulting product was Co-BiOBr-0.25, 15mg of catalyst was uniformly dispersed in a reactor containing 10mL of deionized water, and then CO2 gas was continuously injected into the reactor for 30min while stirring, ensuring that the reactor was filled with CO2 gas. The 300W xenon lamp provided a light source that was turned on. After the reaction process continued for 3h, the efficiency of reduction of CO2 to CO was 5.97. Mu. Mol. G-1. Multidot. H-1.

Example 2

Step 4) was performed with addition of Co (NO 3) 3 to 48mg, and the product of the molar ratio of Co to Bi added reactants was 0.5%, as in example 1 in steps (1) and (5).

The resulting product was Co-BiOBr-0.5, 15mg of catalyst was uniformly dispersed in a reactor containing 10mL of deionized water, and then CO2 gas was continuously injected for 30min while stirring in the reactor to ensure that the reactor was filled with CO2 gas. The lamp source provided by the 300W xenon lamp was turned on. After the reaction process continued for 3h, the efficiency of CO2 reduction to CO was 11.71. Mu. Mol. G-1. H-1.

Example 3

Step 4) was performed with 96mg of Co (NO 3) 3 and 96mg of H2O, and the molar ratio of the added reactants Co and Bi was 1%, and the steps (1) and (5) were the same as in example 1.

The resulting product was Co-BiOBr-1, 15mg of catalyst was uniformly dispersed in a reactor containing 10mL of deionized water, and then CO2 gas was continuously injected into the reactor for 30min while stirring, ensuring that the reactor was filled with CO2 gas. The 300W xenon lamp provided a light source that was turned on. After the reaction process continued for 3h, the efficiency of CO2 reduction to CO was 5.36. Mu. Mol. G-1. H-1.

Example 4

Step 4) was performed with Co (NO 3) 3 of 192mg and the molar ratio of Co to Bi of the added reactants was 2%, and the steps (1) and (5) were the same as in example 1.

The resulting product was Co-BiOBr-2, 15mg of catalyst was uniformly dispersed in a reactor containing 10mL of deionized water, and then CO2 gas was continuously injected into the reactor for 30min while stirring, ensuring that the reactor was filled with CO2 gas. The 300W xenon lamp provided a light source that was turned on. After the reaction process continued for 3h, the efficiency of CO2 reduction to CO was 5.93. Mu. Mol. G-1. Multidot. H-1.

In examples 1-4, the X-ray diffraction patterns of the resulting products showed no significant shift in the characteristic peaks of the modified samples compared to pure BiOBr, and no impurity peaks, indicating that the ion exchange modified BiOBr retained the original crystals, as shown in figure 1. As can be seen from FIG. 1, the diffraction peaks are at 10.95 °, 21.99 °, 25.26 °, 32.31 °, 39.43 °, 46.35 ° and 57.31 °, and correspond to (001), (002), (011), (110), (112), (020) and (212) planes of pure BiOBr (JCPDS card No. 73-2061), respectively. No other impurity peaks were found, indicating that BiOBr has been successfully synthesized. Compared with pure BiOBr, the characteristic peak of the modified sample has no obvious deviation and no impurity peak, which indicates that the BiOBr after ion exchange modification maintains the original crystal structure and the cobalt element is highly dispersed.

The photocatalytic performance of BiOBr and Co-BiOBr was evaluated by reducing CO2 under irradiation of visible light (. Lamda. Gtoreq.420 nm) with the products obtained in examples 1 to 4. Fig. 2 shows the rate of reduction of CO2, which is the major reduction product and additionally produces its trace amount of CH4. The CO2 reduction rates of pure BiOBr, co-BiOBr-0.25, co-BiOBr-0.5, co-BiOBr-1 and Co-BiOBr-2 are respectively 3.24 mu mol g-1. H-1, 5.97 mu mol g-1. H-1, 11.71 mu mol g-1. H-1, 5.36 mu mol g-1. H-1 and 5.93 mu mol g-1. H-1. The reaction stability of the catalyst is also one of the excellent properties of an excellent catalyst. Co-BiOBr-0.5 was subjected to four 12-hour cycles (FIG. 3) with rates of photocatalytic reduction of carbon dioxide of 11.71. Mu. Mol. G-1. Mu. H-1, 9.61. Mu. Mol. G-1. Mu. H-1, 7.59. Mu. Mol. G-1. Mu. H-1 and 7.57. Mu. Mol. G-1. Mu. H-1, respectively. The catalytic reduction efficiency is slightly reduced but still maintained at a higher level. And the XRD test (FIG. 4) was performed on the catalyst after four cycles, with the diffraction peaks identical to those of the catalyst before reaction, and still matching well with the standard card (JCPDS card No. 73-2061), indicating that the catalyst properties did not change after many cycles.

The molar ratio of Co to Bi raw materials is important in the experimental process, the Co doping can induce the O2 p orbit of BiOBr to form a doping energy level in the band gap of BiOBr, the middle energy level becomes a step for electron transition from a valence band to a conduction band, and the energy of electron transition is greatly reduced, so that the separation of photoproduction electrons and holes is promoted, the visible light receiving capability of the photocatalyst is greatly enhanced, and the CO2 reduction efficiency is improved by using Co-BiOBr catalysts with different molar ratios of pure water for 3 hours under the irradiation of visible light (lambda is more than or equal to 420 nm). From the above examples, it is clear that a Co-BiOBr-0.5, which is a product of the molar ratio of Co to BiOBr feedstock of 0.5%, has the best photocatalytic Co2 reduction efficiency, suggesting a possible reaction mechanism. VB and CB of Co-BiOBr-0.5 are 1.60eV and-0.63eV respectively, and standard redox potential E0 (CO 2/CO) =0.53eV for reduction of CO2 to CO. Co-BiOBr-0.5 can generate strong enough photo-generated electrons to reduce CO2 to CO 54. Under visible light irradiation, electrons in Co-BiOBr VB are first excited to an intermediate level, promoting the formation of holes in VB. At this point, the water is oxidized by H + to OH and. H +. Then, the electrons at the intermediate level are further excited to CB of Co-BiOBr and combined with Co2 and H +, generating Co and H2O. (Eq.1-5)

Co-BiOBr-0.5+light irradiation→e ^- +h ⁺ (1)

H ₂ O+h ⁺ →·OH+H ⁺ (2)

e ^- +Co ³⁺ →Co ²⁺ (3)

Co ²⁺ →Co ³⁺ +e ^- (4)

CO ₂ +H ⁺ +e ^- →CO+H ₂ O(-0.53V vs.NHE) (5)

In the following description, for purposes of clarity, not all features of an actual implementation are described, well-known functions or constructions are not described in detail since they would obscure the invention with unnecessary detail, it being understood that in the development of any actual embodiment, numerous implementation details must be set forth in order to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, changing from one implementation to another, and it being recognized that such development effort might be complex and time consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art.

While the invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

Claims

A preparation method of a Co-doped ultrathin bismuth oxyhalide photocatalytic CO2 reduction material is characterized by comprising the following steps: comprises the following steps:

preparation of BiOBr nanosheet

1) Adding Bi (NO 3) 3 to 5H2O and CTAB to ultrapure water, and stirring the mixture for 10 minutes;

2) The pH of the resulting solution was adjusted to about 9 by adding aqueous NaOH (6M), and the solution was stirred vigorously for 1 hour;

3) Transferring the solution obtained in the step 2) into a stainless steel autoclave for reaction for 15h at 170 ℃, washing and drying to obtain a precursor;

preparation of Co-BiOBr

4) Weigh BiOBr and Co (NO 3) 3. Mush.6H 2O, add ultrapure water and sonicate for 20min;

5) Stirring the solution obtained in the step 4) in a constant-temperature heating magnetic stirrer at 80 ℃ for 24 hours.
2. The method for preparing the Co-doped ultrathin bismuth oxyhalide photocatalytic CO2 reduction material by the simple cation exchange strategy according to the claim 1, is characterized in that: bi (NO 3) 3. Mu.m.5H 2O, supplied by MACKLIN; the obtained Co (NO 3) 3 was prepared from 6H2O, supplied by MACKLIN.
3. The method for preparing the Co-doped ultrathin bismuth oxyhalide photocatalytic CO2 reduction material by the simple cation exchange strategy according to the claim 1, is characterized in that: the samples obtained in step 4) are named BiOBr, co-BiOBr-0.25, co-BiOBr-0.5, co-BiOBr-1 and Co-BiOBr-2 respectively according to different molar ratios of the reactants Co and Bi.