CN113908873B - A Method for Photocatalytic Selective Oxidation of Glucose Using Carbon Nitride-Based Photocatalyst - Google Patents

Abstract

The invention belongs to the field of photocatalysis and biomass-based chemicals, and discloses a method for obtaining chemicals with high added value by utilizing the photocatalysis and selective oxidation of glucose by using a composite photocatalyst Ce6@BNCN.

Description

A method for photocatalytic selective oxidation of glucose using carbon nitride-based photocatalysts

technical field

The invention relates to the field of chemical industry, in particular to a method for photocatalytic selective oxidation of glucose. The method uses Ce6@BNCN as a photocatalyst and hydrogen peroxide as an oxidant to prepare high value-added chemicals by photocatalytically oxidizing glucose.

Background technique

As a renewable resource widely distributed on the earth, biomass can be used as an effective alternative to fossil energy to produce high value-added chemicals. Glucose is a sugar monomer that can be obtained from biomass through a series of pretreatments. Gluconic acid and glucaric acid are two major oxidation products of glucose. Glucaric acid is one of the 12 "most valuable biorefinery products", which can be used as raw materials to synthesize a variety of high-value products, and has great potential economic value. At present, gluconic acid is produced by enzymatic oxidation of glucose, and the production of glucaric acid mainly uses nitric acid or bleach to oxidize glucose. However, there are obvious obstacles to the practical application of these methods: for example, the biochemical process has problems of slow reaction speed and difficult separation of free enzymes, while the chemical method will produce toxic products and cause secondary pollution.

Photocatalytic selective oxidation technology has the advantage of mild reaction conditions and has received more and more attention. Polymer semiconductor graphitic carbon nitride (gC ₃ N ₄ ), because of its unique semiconductor band structure and excellent chemical stability, has been introduced into the field of photocatalysis as a metal-free visible light catalyst for Photolysis of water to produce hydrogen and oxygen, photocatalytic organic selective synthesis, photocatalytic degradation of organic pollutants, etc. have attracted widespread attention. Since gC ₃ N ₄ is not only cheap and stable, which meets people’s basic requirements for photocatalysts, but also has the characteristics of polymer semiconductor chemical composition and energy band structure, it is considered to be a research field of photocatalytic materials, which is worthy of further exploration. One of the research directions. However, obtaining desired highly selective oxidation products with water as the solvent remains a great challenge. Although heterogeneous photocatalysis provides a mild route for glucose conversion, it is still very difficult to control the selectivity of glucose oxidation at C1 or C1/C6 due to the multifunctional structure of glucose molecules. Therefore, there is an urgent need to develop new photocatalytic systems for the efficient conversion of glucose into gluconic acid and glucaric acid in water.

Like many other semiconductor photocatalysts, the main disadvantages of _gC3N4 are the low utilization efficiency _of visible light and the high recombination rate of photogenerated charges. In response to the above problems, researchers have proposed a variety of modification strategies through practice, including morphology control, element doping, semiconductor recombination, noble metal deposition, and coordination with metal ions. Among them, the design and regulation of the energy band structure of gC ₃ N ₄ through element doping and introduction of defects can significantly improve the light absorption ability, and at the same time inhibit the recombination of photogenerated carriers, thereby enhancing the photocatalytic activity.

Photosensitization is one of the main ways to extend the excitation wavelength range of photocatalysts. It mainly utilizes the strong adsorption of particles in the excitation wavelength range of _TiO2 to photoactive substances. By adding appropriate photoactive sensitizers, it can be physically or Chemically adsorbed on the surface of the catalyst. These substances have a large excitation factor under visible light. Under the irradiation of visible light, the adsorbed photoactive molecules are excited to generate free electrons after absorbing photons, and then the excited photoactive molecules inject electrons into the conduction band of the semiconductor, thereby expanding The range of excitation wavelength is widened, so that it can make full use of visible light. At present, several common sensitizers reported in the literature include inorganic sensitizers, pure organic dyes, metal-organic complexes, and composite sensitizers. In particular, the photosensitization strategy promotes the generation of singlet oxygen while inhibiting the generation of hydroxyl radicals, improving the selectivity of the reaction and avoiding excessive oxidation.

In summary, the current selective oxidation of glucose using photocatalysts still has the problems of low conversion rate, low selectivity and over-oxidation. Starting from the catalyst and reaction medium, in-depth study of the catalytic reaction system and reaction mechanism is the key to improving the reaction efficiency and efficient way to select the reaction.

Invention content:

The purpose of the present invention is to solve the problems of slow reaction speed, difficult separation of free enzymes, and production of toxic products in the existing glucose oxidation process, and to provide a method for photocatalytic selective oxidation of glucose using carbon nitride and photosensitizer composite materials to obtain a high-efficiency A way to add value to chemicals. The composite photocatalyst Ce6@BNCN prepared by the invention can efficiently photocatalyze and selectively oxidize glucose into gluconic acid, glucaric acid and arabinose.

In the present invention, Ce6 is loaded on modified carbon nitride BNCN to prepare composite photocatalyst Ce6@BNCN. Ce6@BNCN is used as photocatalyst, hydrogen peroxide is used as oxidant, and water is used as solvent. Research shows that under the irradiation of simulated sunlight , under normal temperature and pressure conditions, the composite photocatalyst Ce6@BNCN has the ability to efficiently photocatalyze the oxidation of glucose, and gluconic acid, glucaric acid, and arabinose can be obtained.

In order to realize the above-mentioned purpose of the present invention, the technical scheme that the present invention takes is:

(1) Put the nitrogen-rich organic matter into a covered alumina crucible, raise the temperature to 520°C at a heating rate of 5°C/min, calcinate at this temperature for 4h, and collect the yellow powder after cooling to room temperature.

(2) Mix the prepared gC ₃ N ₄ and NaBH ₄ in a certain proportion and grind them evenly, raise the temperature to 400°C at a heating rate of 10°C/min, and calcinate at this temperature for 1h. After cooling the obtained powder to room temperature, wash with ethanol Wash with deionized water several times to remove unreacted NaBH ₄ , and dry under vacuum at 80°C for 10 hours. The product is denoted as BNCN.

(3) At room temperature, a certain amount of BNCN was dispersed in 200ml of acidic solution A (1M), stirred rapidly by magnetic force for 5h, then centrifugally filtered, and washed three times with deionized water. Finally, it was vacuum-dried at 80°C for 12 hours to obtain protonated pBNCN in the form of yellow powder.

(4) 0.5 g of prepared pBNCN was uniformly dispersed in 100 mL of deionized water, and then a certain amount of Ce6 was added to the suspension, and magnetically stirred rapidly at room temperature for 2 h. Repeated centrifugal washing with deionized water 5 times. Ce6@BNCN was obtained after vacuum drying at 80 overnight.

(5) The composite photocatalyst Ce6@BNCN of the present invention can be applied in the field of photocatalysis. Preferably, the composite photocatalyst of the present invention is applied to the photocatalytic oxidation of glucose. Using Ce6@BNCN as photocatalyst, hydrogen peroxide as oxidant, under the irradiation of 300W xenon lamp and water as solvent, glucose was photocatalytically oxidized under normal temperature and pressure conditions to obtain gluconic acid, glucaric acid and arabinose.

(6) Composite photocatalyst is applied to photocatalytic oxidation of glucose, and its specific steps are as follows: Add glucose aqueous solution in the jacket photoreaction bottle, then add composite photocatalyst, make catalyst in reaction system by stirring action under the condition of lucifuge Fully disperse, turn on the circulating condensed water, then add a certain volume of hydrogen peroxide as an oxidant, and realize the oxidation of glucose under the irradiation of a 300W xenon lamp.

The method of using the composite photocatalyst Ce6@BNCN to photocatalytically selectively oxidize glucose to obtain high value-added chemicals, wherein the nitrogen-rich organic matter includes one of cyanamide, dicyandiamide, melamine, urea, and thiourea. It can be mixed in any proportion.

The method of using the composite photocatalyst Ce6@BNCN to photocatalytically selectively oxidize glucose to obtain high value-added chemicals, wherein the mass ratio of gC ₃ N ₄ and NaBH ₄ in step (2) is preferably 1-5:10, More preferably, the mass ratio is 5:2.

The method for obtaining high value-added chemicals by using the composite photocatalyst Ce6@BNCN to photocatalytically selectively oxidize glucose, wherein the acidic solution A includes hydrochloric acid, nitric acid, and sulfuric acid, preferably, the acidic solution A is hydrochloric acid.

The method of using composite photocatalyst Ce6@BNCN to photocatalytically selectively oxidize glucose to obtain high value-added chemicals, wherein the mass ratio of pBNCN and Ce6 in step (4) is preferably 5-20:1, more preferably, The mass ratio is 10.

The method of using the composite photocatalyst Ce6@BNCN to photocatalytically selectively oxidize glucose to obtain high value-added chemicals, wherein the concentration of the aqueous glucose solution in step (6) is preferably 1-7mmol/L, more preferably 1-3mmol /L, optimally 1mmol/L.

The method of using the composite photocatalyst Ce6@BNCN to photocatalytically selectively oxidize glucose to obtain high value-added chemicals, wherein the dosage of the composite photocatalyst Ce6@BNCN in step (6) is preferably 5-30mg, preferably, the dosage 10mg.

The method of using the composite photocatalyst Ce6@BNCN to photocatalytically selectively oxidize glucose to obtain high value-added chemicals, wherein the amount of hydrogen peroxide added in step (6) is preferably 10-40 microliters, preferably, adding The volume is 10 microliters.

Further, 30 mL of 1 mmol/L glucose aqueous solution was added to the jacketed photoreaction bottle, and then 100 mg of composite photocatalyst Ce6@BNCN was added, and magnetically stirred for 30 min under the condition of avoiding light, so that the catalyst was fully dispersed in the reaction system. Add 30 microliters of hydrogen peroxide, turn on circulating condensed water, and keep the temperature of the reaction system constant. Under the irradiation of 300W xenon lamp, react for 2 hours, the conversion rate of glucose is 65%, and the total selectivity of products is 60%.

The advantages and beneficial effects of the present invention are: the present invention provides a method of using the composite photocatalyst Ce6@BNCN to photocatalyze and selectively oxidize glucose to obtain high value-added chemicals, and the raw material of the composite photocatalyst Ce6@BNCN provided by the present invention is cheap The method is easy to obtain, has a simple preparation process and a wide range of applications, helps to improve the efficiency and selectivity of the selective oxidation of glucose, and has mild reaction conditions, reduces production costs, and is conducive to realizing large-scale applications.

Description of drawings

Figure 1 SEM image

Figure 2 TEM image

Figure 3 Effect of different catalysts

Figure 4 Effect of glucose substrate concentration on photocatalytic oxidation of glucose

Figure 5 Effect of catalyst dosage on photocatalytic oxidation of glucose

Figure 6 The effect of the amount of hydrogen peroxide added on the photocatalytic oxidation of glucose

Figure 7 Cycle experiment

Detailed ways

The present invention is further described in detail through the following examples, but the technical content described in this example is illustrative rather than limiting, and should not limit the protection scope of the present invention accordingly.

Example 1

Preparation of Composite Photocatalyst Ce6@BNCN

Put 2g of melamine into a covered alumina crucible, calcined in air at 520°C for 4h, and collected yellow powder after cooling to room temperature. 0.4 g of prepared _gC3N4 and 0.16 g of _NaBH4 were ground and then calcined at 400 _° C. In a nitrogen atmosphere, the pressure increase rate was 10 °C/min. After the obtained powder was cooled to room temperature, it was washed with ethanol and deionized water several times to remove unreacted NaBH ₄ , and dried at 80° C. under vacuum for 10 h. The product is denoted as BNCN. Disperse BNCN (1 g) in 200 ml of hydrochloric acid solution (1 M), stir rapidly with magnetic force for 5 h, then centrifuge and wash with deionized water three times. Finally, it was vacuum-dried at 80°C for 12 h to obtain protonated H-BNCN as a yellow powder. 0.5 g of the prepared pBNCN was uniformly dispersed in 100 mL of deionized water, then 0.05 g of Ce6 was added to the suspension, and magnetically stirred rapidly at room temperature for 2 h. Repeated centrifugal washing with deionized water 5 times. The composite photocatalyst Ce6@BNCN was obtained after vacuum drying at 80 overnight.

Example 2

Photocatalytic Selective Oxidation of Glucose Activity Experiment of Composite Photocatalyst Ce6@BNCN

30 mL of 1 mmol/L glucose was placed in the reactor, and then 10 mg of photocatalyst was added. The catalyst was dispersed by sonication for 10 minutes, and the suspension was magnetically stirred for 30 minutes in the dark before light exposure to achieve adsorption-desorption equilibrium. Then 30 microliters of 30% hydrogen peroxide aqueous solution was added to the suspension, and the suspension was irradiated with a xenon lamp for 2 h. After the reaction was completed, the photocatalyst Ce6@BNCN was isolated to obtain a product rich in gluconic acid, glucaric acid and arabinose. The conversion rate of glucose was 65%, and the total selectivity of the product was 60%, which was recorded as Entry1.

Example 3

Effect of glucose substrate concentration on the activity of composite photocatalyst Ce6@BNCN for photocatalytic selective oxidation of glucose

According to the operation steps of Example 2Entry 1, the glucose substrate concentration was changed, and the experiment of photocatalytic oxidation of glucose was carried out under the conditions of 1mM, 3mM, 5mM, and 7mM respectively, to investigate the influence of the concentration of glucose substrate on the photocatalytic oxidation of glucose. The effects on glucose conversion and oxidation product selectivity are shown in Fig. 4. It was observed that as the initial glucose concentration increased from 1 to 7mmol·L ^-1 , the glucose conversion rate gradually decreased from 62.3% to 10.7%. In all cases, glucose concentration had a limited effect on the overall selectivity to oxidation products with gluconic acid as the main product.

Example 4

Effect of catalyst dosage on the photocatalytic selective oxidation of glucose activity of composite photocatalyst Ce6@BNCN

According to the operation steps of Example 2Entry 1, the amount of catalyst was changed, and the experiment of photocatalytic oxidation of glucose was carried out under the conditions of 5mg, 10mg, 20mg, and 30mg respectively, to investigate the influence of catalyst amount on photocatalytic oxidation of glucose, and the effect of catalyst amount on glucose conversion rate and oxidation product selectivity are shown in Fig. 5. Although the glucose conversion was higher when the catalyst amount was low (5 mg), the overall selectivity to oxidation products was relatively low, similar to the results obtained using _H2O2 without _catalyst . It is worth noting that increasing the catalyst dosage to 10 mg resulted in a significant increase in product selectivity and a slight decrease in glucose conversion. As expected, a further increase in catalyst amount from 10 mg to 30 mg resulted in a significantly higher glucose conversion. On the contrary, when the amount of catalyst exceeds 10 mg, the selectivity of oxidation products tends to decrease. Considering the substrate conversion rate and product selectivity, the optimum catalyst dosage for glucose oxidation under the experimental conditions is 10mg.

Example 5

Effect of the amount of hydrogen peroxide on the activity of composite photocatalyst Ce6@BNCN for photocatalytic selective oxidation of glucose

According to the operation steps of Example 2, Entry 1, the amount of catalyst was changed, and the experiment of photocatalytic oxidation of glucose was carried out under the conditions of hydrogen peroxide addition of 10 μL, 20 μL, 30 μL, and 40 μL, respectively, to investigate the effect of hydrogen peroxide addition on photocatalytic oxidation of glucose. The effect of hydrogen peroxide addition on glucose conversion and oxidation product selectivity is shown in Figure 6. _A significant increase in glucose conversion was observed with increasing _H2O2 dosage. As the _{H2O2 addition} increased from 10 μL to 40 μL, the glucose conversion increased from 51.0% to 68.6%. Notably, the overall selectivity _of oxidation products was highest when _H2O2 was used at 30 μL. Glucose conversion was slightly higher when 40 μL _H2O2 was added than when 30 μL was added, but the selectivity of oxidation products was significantly lower _than the latter.

Example 6

Stability of Composite Photocatalyst Ce6@BNCN

According to the operation steps of implementing 2Entry 1, the recycling efficiency of the composite photocatalyst was measured. After each photocatalytic oxidation reaction is finished, the reaction system is filtered to obtain a catalyst, and then the catalyst is washed with deionized water and vacuum-dried, and the dried catalyst is used for the next photocatalytic oxidation reaction. The stability of the composite photocatalyst was investigated by measuring the efficiency of the composite photocatalyst for 4 cycles. The 1st use of the catalyst in the cycle experiment is recorded as Entry 1 (the previous time is the first use of the newly prepared catalyst); the 2nd use of the catalyst in the cycle experiment is recorded as Entry 2; the 3rd use of the catalyst in the cycle experiment The first use is recorded as Entry 3; the fourth use of the catalyst in the cycle experiment is recorded as Entry 4. The experimental results are shown in Table 5. The comparative experiments showed that after 4 cycles of the composite photocatalyst Ce6@BNCN, the changes in the conversion rate of glucose and the selectivity of oxidation products were small, indicating that the composite photocatalyst Ce6@BNCN had better stability.

Claims (7)

1. A method of using composite photocatalyst Ce6@BNCN to photocatalytically selectively oxidize glucose to obtain high value-added chemicals, comprising the following steps: (1) Put the nitrogen-rich organic matter into a covered alumina crucible, raise the temperature to 520°C at a heating rate of 5°C/min, calcinate at this temperature for 4 h, and collect the yellow powder after cooling to room temperature; (2) Mix the prepared gC ₃ N ₄ and NaBH ₄ in a certain proportion and grind them evenly, raise the temperature to 400°C at a heating rate of 10°C/min, and calcinate at this temperature for 1 h. After the obtained powder is cooled to room temperature, use Wash with ethanol and deionized water several times to remove unreacted NaBH ₄ , dry at 80°C under vacuum for 10 h, and the product is marked as BNCN; (3) At room temperature, a certain amount of BNCN was dispersed in 200ml of acidic solution A, the concentration of acidic solution A was 1 mol/L, stirred rapidly by magnetic force for 5 hours, then centrifugally filtered, washed with deionized water three times; finally, vacuum Dry for 12 hours to obtain protonated pBNCN in the form of yellow powder; (4) Disperse 0.5 g of the prepared pBNCN evenly in 100 mL of deionized water, then add a certain amount of Ce6 to the suspension, stir rapidly at room temperature for 2 h; wash with deionized water repeatedly for 5 times; vacuum dry at 80 overnight Then get Ce6@BNCN; (5) Using Ce6@BNCN as photocatalyst, hydrogen peroxide as oxidant, under the irradiation of 300W xenon lamp and water as solvent, glucose was photocatalytically oxidized under normal temperature and pressure conditions to obtain gluconic acid, glucaric acid and Arabic candy; (6) The composite photocatalyst is applied to the photocatalytic oxidation of glucose. The specific steps are as follows: Add glucose aqueous solution into the jacketed photoreaction bottle, then add the composite photocatalyst, and stir the catalyst in the reaction system under the condition of avoiding light. Fully disperse, turn on the circulating condensed water, then add a certain volume of hydrogen peroxide as an oxidant, and realize the oxidation of glucose under the irradiation of a 300W xenon lamp. 2. The method of using composite photocatalyst Ce6@BNCN to photocatalytically selectively oxidize glucose to obtain high value-added chemicals according to claim 1, wherein the nitrogen-rich organic matter includes cyanamide, dicyandiamide, melamine, urea, One of the thioureas. 3. The method of using composite photocatalyst Ce6@BNCN to photocatalytically selectively oxidize glucose to obtain high value-added chemicals according to claim 1, wherein the mass ratio of gC ₃ N ₄ to NaBH ₄ in step (2) is 1 -5:10. 4. The method of using composite photocatalyst Ce6@BNCN to photocatalytically selectively oxidize glucose to obtain high value-added chemicals according to claim 1, wherein the acidic solution A includes hydrochloric acid, nitric acid or sulfuric acid. 5. The method of using composite photocatalyst Ce6@BNCN to photocatalytically selectively oxidize glucose to obtain high value-added chemicals according to claim 1, wherein the mass ratio of pBNCN to Ce6 in step (4) is 5-20:1 . 6. The method for photocatalytic selective oxidation of glucose by composite photocatalyst Ce6@BNCN to obtain high value-added chemicals according to claim 1, wherein the concentration of the glucose aqueous solution in step (6) is 1-7 mmol/L. 7. The method of using the composite photocatalyst Ce6@BNCN to photocatalytically selectively oxidize glucose to obtain high value-added chemicals according to claim 1, wherein the dosage of the composite photocatalyst Ce6@BNCN in step (6) is 5-30 mg.

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