A carbon-coated raspberry-like SiO 2 Nanomaterials, their preparation methods and applications

Abstract

This invention discloses a carbon-coated raspberry-like SiO2 2 Nanomaterials, including carbon layers and modified raspberry-like SiO2 encapsulated within the carbon layers. 2 Nanomaterials with a carbon layer thickness of 10–300 nm and a surface roughness Ra of 10–100 nm, modified raspberry-like SiO 2 The nanomaterials exhibit positively charged groups on their surface under acidic conditions and have a particle size of 10–300 nm. This invention also discloses the aforementioned carbon-coated raspberry-like SiO₂. 2 The preparation method of nanomaterials first involves preparing raspberry-like SiO₂ with different roughness through weak alkaline etching. 2 Nanomaterials, and then prepare raspberry-like SiO 2 The nanomaterials are modified, hydrothermally carbonized, dried, and washed. This invention features a simple, low-energy-consumption, and environmentally friendly preparation process, resulting in a carbon layer that coats raspberry-like SiO₂. 2 Nanomaterials have rough surfaces, large specific surface areas, are rich in hydrophilic oxygen-containing groups, and have controllable carbon layer morphology, which can promote the efficient hydrolysis of cellulose into sugars in low-acid aqueous systems.

Description

A carbon-coated raspberry-like SiO2 nanomaterial, its preparation method and application Technical Field

[0001] This invention belongs to the field of nanomaterials, specifically relating to a carbon-coated raspberry-like silica nanomaterial, its preparation method, and its application. Background Technology

[0002] Carbon is one of the most abundant basic elements in nature and forms the fundamental framework of living organisms. With continuous technological advancements, research on carbon materials has deepened. Due to their superior performance, carbon materials have permeated all aspects of our lives and demonstrated enormous potential in fields such as catalysis, energy storage, construction, and analysis. In the past few decades, carbon materials derived from biomass resources have received widespread attention due to their broad availability and excellent sustainability.

[0003] Hydrothermal carbonization (HTC) is a simple, efficient, environmentally friendly, and sustainable method. HTC utilizes inexpensive and abundant carbohydrates under mild conditions (below 250°C) through water as a medium and the pressure it generates, converting them into attractive carbon nanostructures. The final products are rich in hydrophilic oxygen-containing groups (carboxyl and hydroxyl groups), which can be designed for applications in key fields such as catalysis, energy storage, separation, and environmental protection. HTC can produce multifunctional materials through a simple direct conversion process, thus showing great promise in the industrial production of biomass carbon materials.

[0004] Hydroxyl-rich carbon microspheres synthesized via the HTC method serve as catalysts. These microspheres interact with cellulose in an aqueous system, disrupting the recalcitrant structure of cellulose and enhancing its accessibility and degradability, particularly the glycosidic bonds within the cellulose matrix. Therefore, a process for hydrolyzing cellulose into sugars in a completely aqueous system using a purely chemical method has been established, meeting the requirements for environmentally friendly production of high-quality products.

[0005] However, since the catalytic hydrolysis of cellulose by hydroxyl-rich carbon microspheres is a solid-solid interface reaction, it is limited by the spherical shape and smooth surface of the synthesized carbon microspheres, allowing only point contacts to form within a small area. Considering the numerous hydroxyl groups and hydrogen bonds formed between cellulose molecular chains, the single catalytic activity of hydroxyl-rich carbon microspheres for cellulose hydrolysis remains insufficient. In other words, regulating the structure and composition of the surface of hydroxyl-rich carbon microspheres becomes a key factor in increasing interfacial interactions with cellulose, improving local adsorption capacity, and driving future application potential.

[0006] In Chinese patent document CN114870759A, raspberry-shaped silanol magnetic microspheres were prepared. By adjusting the protrusions on the surface of the microspheres, the surface roughness can be increased and the surface area can be improved, thereby greatly improving its performance. However, the process is very complicated and difficult to scale up production. Nevertheless, this raspberry-shaped structure is inspiring.

[0007] In Chinese patent document CN115043404A, tubular silica is prepared directly and then coated with carbon to maintain the tubular shape of the carbon layer. However, the process requires high-temperature sintering under an inert gas atmosphere and soaking in a large amount of inorganic acid.

[0008] A one-step hydrothermal carbonization method can also endow carbon spheres with special functions. For example, Chinese patent document CN116239104A describes a one-step hydrothermal reaction of water-soluble sugars and phosphate-containing compounds to obtain hydroxyl-rich carbon materials modified with phosphate groups. However, due to the introduction of phosphate groups, the size of the carbon spheres increases significantly, and the required temperature for cellulose hydrolysis is relatively high. Although phosphate groups are introduced, their local adsorption capacity is limited.

[0009] Therefore, given the aforementioned existing technologies, controlling the size and morphology of hydrothermal carbon spheres to improve the single-point catalytic activity of local areas on the surface of solid catalysts remains a challenge. Summary of the Invention

[0010] To address the shortcomings of the existing technology, this invention provides a carbon-coated raspberry-like SiO2 nanomaterial. This carbon-coated raspberry-like SiO2 nanomaterial has an adjustable particle size, controllable carbon layer morphology, and a large specific surface area. Furthermore, its surface contains a large number of hydroxyl groups, which can induce strong local adsorption and promote the efficient hydrolysis of cellulose into sugars in a low-acid aqueous system.

[0011] A carbon-coated raspberry-like SiO2 nanomaterial includes a carbon layer and a modified raspberry-like SiO2 nanomaterial coated inside the carbon layer. The thickness of the carbon layer is 10-300 nm, and the surface roughness Ra is 10-100 nm. The modified raspberry-like SiO2 nanomaterial has positively charged groups on its surface under acidic conditions and a particle size of 10-300 nm.

[0012] The present invention also provides a method for preparing the aforementioned carbon-coated raspberry-like SiO2 nanomaterial, comprising the following steps:

[0013] S1. By etching SiO2 nanomaterials with a weak alkaline solution, raspberry-like SiO2 nanomaterials with different surface roughness were obtained;

[0014] S2. Modify raspberry-like SiO2 nanomaterials with different surface roughness using a modifier to obtain modified raspberry-like SiO2 nanomaterials;

[0015] S3. A hydrothermal carbonization reaction is carried out using modified raspberry-like SiO2 nanomaterials and a carbon source as raw materials to coat the surface of the modified raspberry-like SiO2 nanomaterials with a carbon layer. After the reaction is completed, the product is washed and dried to obtain the carbon-coated raspberry-like SiO2 nano-silica material.

[0016] This invention uses raspberry-like SiO2 nanomaterials with varying roughness, obtained by etching with a weak alkali for different times, as a substrate. Surface modification of this substrate yields modified raspberry-like SiO2 nanomaterials, which are positively charged on the surface under acidic conditions. Further hydrothermal carbonization, relying on electrostatic interactions, uniformly coats the surface with a hydrothermal carbon layer, forming carbon-coated raspberry-like SiO2 nanomaterials. The size and surface carbon layer morphology of these nanomaterials are tunable, allowing them to be applied to the efficient hydrolysis of cellulose in dilute acid aqueous systems.

[0017] Preferably, in step S1, the weak alkaline solution is at least one of sodium carbonate solution, sodium bicarbonate solution, ammonia water or potassium carbonate solution, and the concentration of the weak alkaline solution is 0.2-0.5M.

[0018] Preferably, the mass-to-volume ratio of the SiO2 nanomaterial to the weak alkaline solution is 4-6 g: 1 L.

[0019] Preferably, in step S1, the etching temperature is 40-60℃ and the etching time is 30-90 min. Extending the etching time increases the surface roughness of the SiO2 nanomaterial.

[0020] The SiO2 nanomaterials of the present invention can be obtained commercially or prepared in the laboratory.

[0021] Preferably, in step S1, the SiO2 nanomaterial is synthesized by a template method, a sol-gel method, or a gas-phase method.

[0022] Preferably, the method for preparing SiO2 nanomaterials using the template method is as follows: using CTAB as a template, a silicon source is added under alkaline conditions, and the mixture is heated and stirred at 10–100°C for 1–3 hours, followed by centrifugation and washing. The CTAB is then removed after heating at 100–1000°C for 3–9 hours to obtain the SiO2 nanomaterials. The silicon source is selected from tetraethyl orthosilicate, silicon tetrachloride, or sodium silicate. The surface of the SiO2 nanomaterials prepared using the template method exhibits a raspberry-like appearance.

[0023] Preferably, in step S2, the modifier is a silane coupling agent, including at least one of APTES, KH550, KH560, or KH570. Through the action of the modifier, positively charged amino groups can be grafted onto the silanol groups on the surface of the raspberry-like SiO2 nanomaterials, either partially or completely.

[0024] Preferably, in step S2, the concentration of the modifier is 0.5-1 mol / L, and the mass ratio of the raspberry-like SiO2 nanomaterials with different surface roughness to the modifier is 1:10-20.

[0025] Preferably, in step S2, the modification temperature is 70-90℃ and the time is 1-12h.

[0026] Preferably, in step S3, the carbon source includes any one or more of fructose, glucose, xylose, cyclodextrin, sucrose, HMF, and cellobiose, but is not limited thereto.

[0027] Preferably, in step S3, the temperature of the hydrothermal carbonization reaction is 100–200°C, and the time is 1–8 hours.

[0028] Preferably, in step S3, the mass ratio of the modified raspberry-like SiO2 nanomaterial to the carbon source is 1:1-5; when the carbon source concentration is 0.01-0.04 mol / L, the surface roughness Ra of the carbon-coated raspberry-like SiO2 nanomaterial is 70-100 nm, and the surface completely replicates the uneven morphology of the raspberry-like SiO2 nanomaterial; when the carbon source concentration is 0.04-0.07 mol / L, the surface roughness Ra of the carbon-coated raspberry-like SiO2 nanomaterial is 10-70 nm, and the surface gradually becomes smoother as the carbon layer thickness increases. The carbon-coated raspberry-like SiO2 nanomaterial prepared by this invention can generate strong local interfacial adsorption capacity with cellulose, thereby breaking the aggregate structure of cellulose. The greater the surface roughness, the stronger the local adsorption capacity.

[0029] This invention primarily controls the surface morphology of carbon-coated raspberry-like SiO2 nanomaterials by controlling the etching time of the weak alkaline solution and the carbon source content. At high carbon source concentrations, the carbon-coated raspberry-like SiO2 nanomaterials exhibit a smooth surface structure; at low carbon source concentrations, the carbon layer can completely replicate the raspberry-like SiO2 nanostructure, maintaining its original roughness. Increased surface roughness leads to the formation of tiny "grooves," allowing the carbon-coated raspberry-like SiO2 nanomaterials to provide the largest specific surface area and generate the most hydroxyl groups. Minor local fluctuations do not reduce the ability of hydroxyl groups to form hydrogen bonds with cellulose in the local area. In this case, it generates the strongest effect of multiple hydrogen bonds, exceeding the interactions between cellulose molecular chains, and thus enhancing the hydrolytic activity of cellulose for sugars.

[0030] Preferably, in step S3, the modified raspberry-like SiO2 nanomaterials are added to the carbon source solution and fully dispersed, and then placed in a sealed high-pressure reactor for hydrothermal carbonization reaction. The dispersion process can be carried out by one or a combination of methods such as magnetic stirring, cell disruptor, and microwave ultrasound, but is not limited to these methods.

[0031] Preferably, in step S3, the washing and drying are performed by washing with at least two of methanol, water, ethanol or cyclohexane, followed by drying at 60-90°C to remove the solvent, thereby obtaining black carbon-coated raspberry-like SiO2 nanomaterials.

[0032] This invention also provides the application of the aforementioned carbon-coated raspberry-like SiO2 nanomaterials in the catalytic hydrolysis of cellulose into sugars. The hydroxyl-rich structure and certain roughness of the surface of the carbon-coated raspberry-like SiO2 nanomaterials of this invention enable them to exhibit strong local adsorption capacity for cellulose, thus efficiently catalyzing the hydrolysis of cellulose into sugars.

[0033] Preferably, the application method is as follows: under high temperature and sealed conditions, the carbon layer coated raspberry-like SiO2 nanomaterial catalyzes the hydrolysis of cellulose into sugar in a dilute acid aqueous phase system, wherein the high temperature and sealed conditions are: the hydrolysis reaction is carried out in a hydrothermal reactor at a reaction temperature of 100-200℃ for a time of 30-180 min.

[0034] Preferably, the hydrogen ion concentration in the dilute acid solution is 0.005-0.02 mol / L.

[0035] Preferably, the dilute acid is selected from at least one of HCl, H2SO4, maleic acid, or formic acid.

[0036] Preferably, the mass ratio of the carbon-coated raspberry-like SiO2 nanomaterial to cellulose is 1:2-60.

[0037] When the carbon-coated raspberry-like SiO2 nanomaterials of the present invention are used for cellulose hydrolysis, the yield of reducing sugars in the cellulose hydrolysis products can reach 80% and the yield of glucose can reach 70%. Moreover, the carbon-coated raspberry-like SiO2 nanomaterials of the present invention can be reused, and the cellulose conversion rate and glucose yield decrease by no more than 3-20% within 3 uses.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0039] (1) The present invention prepares raspberry-like SiO2 nanomaterials with different roughness by weak alkaline etching, changes the charge on its surface, and causes strong electrostatic interaction between the carrier and the polysaccharide intermediate during hydrothermal process, so that the reaction mainly occurs on the surface of the raspberry-like SiO2 nanomaterials rather than in the surrounding water medium, forming a carbon layer to coat the raspberry-like SiO2 nanomaterials.

[0040] (2) This invention mainly controls the surface morphology of carbon-coated raspberry-like SiO2 nanomaterials by controlling the weak alkali etching time and carbon source content, rather than using high-energy-consuming processing methods. At high carbon source concentrations, the carbon-coated raspberry-like SiO2 nanomaterials exhibit a smooth surface structure. At low carbon source concentrations, the carbon layer can completely replicate the raspberry-like SiO2 nanostructure, maintaining the original roughness. Increased surface roughness leads to the formation of tiny "grooves." The carbon-coated raspberry-like SiO2 nanomaterials can provide the largest specific surface area and generate the most hydroxyl groups, while minor local fluctuations do not reduce the ability of hydroxyl groups to form hydrogen bonds with cellulose in the local area. In this case, it will generate the strongest effect of multiple hydrogen bonds, exceeding the interaction between cellulose molecular chains, and thus enhancing the hydrolytic activity of cellulose for sugars.

[0041] (3) The method of the present invention can control the size and surface morphology of the hydrothermal carbon layer. The method is simple, the raw materials are widely available, the stability is good, and the material can be reused. It meets the requirements of environmentally friendly production of high-quality products. The carbon layer coated raspberry-like SiO2 nanomaterials prepared have high application value in the fields of environment, energy, and electronics.

[0042] (4) The carbon-coated raspberry-like SiO2 nanomaterials of the present invention exhibit a strong local adsorption capacity for cellulose during the catalytic hydrolysis of cellulose into sugar due to their hydroxyl-rich surface structure and certain roughness. This enables highly efficient catalysis of cellulose hydrolysis into sugar. Furthermore, the reduced acid concentration in the dilute acid solution avoids equipment corrosion problems, making the process more economical and safer. Attached Figure Description

[0043] Figure 1 is a scanning electron microscope image of the unmodified raspberry-like silica nanospheres in Example 1;

[0044] Figure 2(a) shows the FT-IR of raspberry-shaped silica nanospheres before and after modification in Example 1; Figure 2(b) shows the zeta potential of raspberry-shaped silica nanospheres before and after modification in Example 1.

[0045] Figure 3 is a scanning electron microscope image of the carbon-coated raspberry-like silica nanomaterial (MSN-30-NH2@C) in Example 1;

[0046] Figure 4 is a transmission electron microscope image of the carbon-coated raspberry-like silica nanomaterial (MSN-30-NH2@5C) in Example 8;

[0047] Figure 5(a) is a SEM image of commercial silica in Example 26; Figure 5(b) is a TEM image of carbon-coated commercial silica in Example 26.

[0048] Figure 6 shows a scanning electron microscope image of the carbon-coated unmodified raspberry-like silica nanomaterial in Comparative Example 1.

[0049] Figure 7 shows the SEM image of the carbon-coated raspberry-like silica nanomaterial (MSN-90-NH2@C) of Example 3;

[0050] Figure 8(a) is the EDS elemental distribution diagram of the carbon-coated raspberry-like silica nanomaterial (MSN-90-NH2@C) of Example 3. Figures 8(b), 8(c), 8(d) and 8(e) are the elemental distribution diagrams of C, N, O and Si, respectively.

[0051] Figure 9 shows a SEM image of the cellulose hydrolysis process catalyzed by carbon-coated raspberry-like silica nanomaterials (MSN-30-NH2@C) in Example 1.

[0052] Figure 10(a) is an FT-IR image of the carbon-coated raspberry-like silica nanomaterial (MSN-90-NH2@C-3cycles) after 3 cycles in Example 6, and Figure 10(b) is an XPS image of the carbon-coated raspberry-like silica nanomaterial (MSN-90-NH2@C-3cycles) after 3 cycles. Detailed Implementation

[0053] The present invention will be further illustrated below with reference to the accompanying drawings and embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0054] Example 1

[0055] In this embodiment, carbon-coated raspberry-like silica nanomaterials are prepared by hydrothermal reaction of raspberry-like silica nanomaterials and glucose; corn cob cellulose is pretreated to prepare regenerated cellulose; then, the prepared carbon-coated raspberry-like silica nanomaterials and regenerated cellulose are mixed in deionized water and placed in a high-pressure reactor for hydrothermal reaction. The specific steps are as follows:

[0056] (1) Dissolve 2g of CTAB in 600ml of water, add 5ml of 2M NaOH, stir slowly and heat to 60℃, then stir vigorously for 30 minutes to form micelles; add 10mL of TEOS and stir for 2h to form a white precipitate; collect the raw material by centrifugation, wash with ethanol and water 3 times respectively, and dry under vacuum at 70℃; in order to remove CTAB, calcine the product in a muffle furnace at 550℃ for 6h, and grind to obtain silica nanomaterials (MSN).

[0057] (2) The silica nanomaterials prepared in step (1) were etched with Na2CO3 at 50°C for 30 min (the silica nanomaterials in the system were 5 g / L and 50 mL of Na2CO3) to obtain raspberry-like silica nanomaterials (MSN-30) with rough surfaces; the SEM of the raspberry-like silica nanomaterials is shown in Figure 1, and the particle size is in the range of 180-250 nm.

[0058] (3) The silica nanomaterials obtained in step (2) were dispersed in toluene with 0.8 mol / L of modifier APTES (the silica nanomaterials in the system were 10 g / L) and reacted at 85 °C for 6 h. The unreacted product was centrifuged and washed with ethanol and then vacuum dried at 70 °C to obtain modified raspberry-like silica nanomaterials (MSN-30-NH2). The modified raspberry-like silica nanomaterials showed characteristic amino peaks in the infrared (Figure 2(a)), and the zeta potential turned positive under acidic conditions (Figure 2(b)). The particle size was in the range of 200-260 nm.

[0059] (4) The modified raspberry-like silica nanomaterials obtained in step (3) were placed in a 0.01M glucose solution. The mixture was dispersed in an ultrasonic cell grinder at 20% power for 5 min. The suspension was then placed in a Teflon-sealed autoclave and heated at 190°C for 5 h. The resulting brown product was filtered, washed with deionized water and ethanol, and vacuum dried at 70°C to obtain carbon-coated raspberry-like silica nanomaterials (MSN-30-NH2@C). The SEM image of the carbon-coated raspberry-like silica nanomaterials is shown in Figure 3. It completely replicates the morphology of the carrier silica, and the surface roughness Ra is 100 nm.

[0060] (5) Take 100g of corn cob cellulose and mix it with 85% concentrated phosphoric acid at a mass ratio of 1:2. Heat and stir at 50°C to form a uniform solution. Add ethanol to the solution to obtain regenerated cellulose precipitate. Wash, dry and grind it to obtain regenerated cellulose (crystallization 50%, polymerization degree 3000) for later use.

[0061] (6) The modified carbon-coated raspberry-like silica nanomaterials obtained in step (3) and the regenerated cellulose obtained after pretreatment in step (5) are added to 20 mL of 0.01 M dilute hydrochloric acid at a mass ratio of 1:10. The mixture is added to a high-pressure reactor and hydrothermally reacted at 170 °C for 1 h. After the reaction is completed, the hydrolysate is obtained, filtered, and the residue is dried for use in the next reaction.

[0062] Example 2

[0063] The difference between this embodiment and embodiment 1 is that the Na2CO3 etching time in step (2) is 60 min.

[0064] Example 3

[0065] The difference between this embodiment and embodiment 1 is that the Na2CO3 etching time in step (2) is 90 min.

[0066] Example 4

[0067] The difference between this embodiment and embodiment 1 is that the hydrolysate filter residue from step (6) of embodiment 1 is added in step (6) as a catalyst for catalytic regeneration of cellulose hydrolysis, and the recycling capacity of the carbon-coated raspberry-like silica nanomaterial is tested.

[0068] Example 5

[0069] The difference between this embodiment and embodiment 4 is that the hydrolysate filter residue from embodiment 3 is added in step (6) as a catalyst for catalytic regeneration of cellulose hydrolysis, and the recyclability of the carbon-coated raspberry-like silica nanomaterial is tested.

[0070] Example 6

[0071] The difference between this embodiment and embodiment 5 is that the hydrolysate filter residue from embodiment 4 is added in step (6) as a catalyst for catalytic regeneration of cellulose hydrolysis. The hydrolysate filter residue obtained by filtration in step (6) of this embodiment is named MSN-90-NH2@C-3cycles, and the recycling capacity of the carbon-coated raspberry-like silica nanomaterial is tested.

[0072] Example 7

[0073] The difference between this embodiment and Embodiment 1 is that a 0.03M glucose solution is added in step (4). The carbon-coated raspberry-like silica nanomaterial obtained in step (4) of this embodiment is named MSN-30-NH2@3C, and its surface roughness Ra is 75nm.

[0074] Example 8

[0075] The difference between this embodiment and Embodiment 1 is that a 0.05M glucose solution is added in step (4). The carbon-coated raspberry-like silica nanomaterial obtained in step (4) of this embodiment is named MSN-30-NH2@5C.

[0076] The TEM of the carbon-coated raspberry-like silica nanomaterials prepared in this embodiment is shown in Figure 4. The particle size is 200-300 nm, the hydrothermal carbon layer surface is relatively smooth, the thickness is about 30-100 nm, and the surface roughness Ra is 10 nm.

[0077] Example 9

[0078] The difference between this embodiment and Example 1 is that the catalyst added in step (6) is uncoated modified raspberry-like silica nanomaterial (MSN-30-NH2).

[0079] Example 10

[0080] The difference between this embodiment and Example 1 is that the concentration of the modifier APTES in step (3) is 0.5 mol / L and the modification time is 1 h.

[0081] Example 11

[0082] The difference between this embodiment and Example 1 is that the concentration of the modifier APTES in step (3) is 1 mol / L and the modification time is 12 h.

[0083] Example 12

[0084] The difference between this embodiment and embodiment 1 is that the hydrothermal carbonization temperature in step (4) in the high-pressure reactor is 100°C.

[0085] Example 13

[0086] The difference between this embodiment and embodiment 1 is that the hydrothermal carbonization temperature in step (4) in the high-pressure reactor is 200°C.

[0087] Example 14

[0088] The difference between this embodiment and embodiment 1 is that the hydrothermal carbonization time in the high-pressure reactor in step (4) is 1 hour.

[0089] Example 15

[0090] The difference between this embodiment and embodiment 1 is that the hydrothermal carbonization time in the high-pressure reactor in step (4) is 8 hours.

[0091] Example 16

[0092] The difference between this embodiment and embodiment 1 is that in step (4), the product is washed with deionized water and ethanol and then vacuum dried at 60°C.

[0093] Example 17

[0094] The difference between this embodiment and embodiment 1 is that in step (4), the product is washed with deionized water and ethanol and then vacuum dried at 90°C.

[0095] Example 18

[0096] The difference between this embodiment and embodiment 1 is that the hydrolysis temperature in step (6) in the high-pressure reactor is 100°C.

[0097] Example 19

[0098] The difference between this embodiment and embodiment 1 is that the hydrolysis temperature in step (6) in the high-pressure reactor is 200°C.

[0099] Example 20

[0100] The difference between this embodiment and embodiment 1 is that the hydrolysis reaction time in the high-pressure reactor in step (6) is 30 min.

[0101] Example 21

[0102] The difference between this embodiment and embodiment 1 is that the hydrolysis reaction time in the high-pressure reactor in step (6) is 180 min.

[0103] Example 22

[0104] The difference between this embodiment and embodiment 1 is that 20 mL of 0.005 M dilute hydrochloric acid was added to the high-pressure reactor in step (6).

[0105] Example 23

[0106] The difference between this embodiment and embodiment 1 is that 20 mL of 0.2 M dilute hydrochloric acid was added to the high-pressure reactor in step (6).

[0107] Example 24

[0108] The difference between this embodiment and embodiment 1 is that in step (6), the raspberry-like silica nanomaterial coated with modified carbon layer and the regenerated cellulose obtained after pretreatment are in a mass ratio of 1:2.

[0109] Example 25

[0110] The difference between this embodiment and embodiment 1 is that in step (6), the modified carbon layer-coated raspberry-like silica nanomaterial and the pretreated regenerated cellulose are in a mass ratio of 1:60.

[0111] Example 26

[0112] (1) Commercially available silica microspheres with a size of 200 nm and a completely smooth surface with silanol groups (SEM shown in Figure 5a) were used. The silica and silane coupling agent APTES were added to a toluene solution (the concentration of silica in the system was 5 g / L and the concentration of silane coupling agent APTES was 0.8 mol / L). The reaction was heated at 80 °C for 6 h. After centrifugation, the product was washed three times with water and ethanol and then vacuum dried to obtain modified silica with a smooth surface and a particle size of 180-210 nm.

[0113] (2) The modified silica was placed in a 0.01M glucose solution and placed in a Teflon-sealed high-pressure reactor. It was heated at 190°C for 5 hours. The resulting brown product was filtered, washed with deionized water and ethanol, and vacuum dried at 70°C to obtain silica with a smooth carbon layer.

[0114] (3) The smooth carbon layer coated with silica and the pretreated regenerated cellulose were added to 20 mL of 0.01 M dilute hydrochloric acid at a mass ratio of 1:10. The mixture was added to a high-pressure reactor and hydrothermally reacted at 170 °C for 1 h. After the reaction was completed, the hydrolysate was obtained, filtered, and the residue was dried for use in the next reaction.

[0115] The TEM image of the carbon-coated commercial silica prepared in this embodiment is shown in Figure 5b. The particle size is 180-210 nm, the hydrothermal carbon layer has a smooth surface, and the thickness is about 20-40 nm.

[0116] Comparative Example 1

[0117] In this comparative example, the preparation method of the raspberry-like silica nanomaterials is the same as in Example 1, except that the unmodified raspberry-like silica nanomaterials are directly dispersed in a 0.01M glucose solution without modification by a silane coupling agent, and placed in a high-pressure reactor for hydrothermal reaction at 190°C for 5 hours. The resulting brown product is filtered, washed with deionized water and ethanol, and then vacuum dried to obtain the silica nanomaterials.

[0118] Figure 6 shows the SEM image of the unmodified raspberry-like silica nanomaterials coated with carbon layers after hydrothermal treatment. It can be seen that the silica forms small hydrothermal carbon particles due to the repulsion between it and the polysaccharide intermediate, and no coating behavior occurs. This indicates that the change in the surface potential of silica is necessary for its coating process.

[0119] Test Result Analysis

[0120] The particle size of the carbon-coated raspberry-like silica nanomaterials prepared in the above embodiments is in the range of 150-300 nm. Figure 7 shows the SEM image of the carbon-coated raspberry-like silica nanomaterial (MSN-90-NH2@C) prepared in Example 3. This carbon material exhibits a raspberry-like structure, completely replicating the carrier structure. Figure 8 shows the EDS elemental mapping characterization of the surface elemental composition of the carbon-coated raspberry-like silica nanomaterial (MSN-90-NH2@C) prepared by the method in Example 3, which is a distribution map of the four main elements on the surface of the carbon material. Notably, the hydrothermal method successfully coated carbon onto the silica surface.

[0121] Figure 9 shows the SEM images of the carbon-coated raspberry-like silica nanomaterials prepared in Example 1 during the catalytic hydrolysis of cellulose. As can be seen from Figure 9, the catalyst with a larger surface roughness has a larger specific surface area and surface hydroxyl density. When in contact with pretreated regenerated cellulose, it forms a local adsorption region. Within this local region, a large number of hydroxyl groups and numerous hydrogen bonds between cellulose accumulate, resulting in a combined effect. This combined effect undoubtedly promotes the relaxation or even destruction of the local structure, thereby generating a strong local adsorption, allowing it to bind tightly to the regenerated cellulose and enhancing its hydrolytic activity.

[0122] Figure 10(a) shows the infrared display of the carbon-coated raspberry-like silica nanomaterial (MSN-90-NH2@C-3cycles) after three cycles in Example 6. A large number of C-OH, C=O and C=C bonds still exist on the surface. The XPS analysis results (Figure 10(b)) show that the amount of various elements (such as Si, O, C and N) does not change much. This fully demonstrates that the carbon-coated raspberry-like silica nanomaterial has good reusability as a catalyst for hydrolyzing cellulose to produce sugar.

[0123] The hydrolysate obtained in the above examples or comparative examples was tested for reducing sugar concentration using the DNS method. The specific operation method is as follows:

[0124] Take 0.3 mL of hydrolysate, 2.7 mL of deionized water, and 3 mL of DNS reagent, mix them, and develop the color at 90 °C for 30 min. Measure the absorbance of the developed solution at 540 nm. The specific calculation method is as follows:

[0125]

[0126] The method for calculating glucose yield is as follows:

[0127]

[0128] The method for calculating cellulose conversion rate is as follows:

[0129]

[0130] Where n is the dilution factor; m RC The initial mass of added cellulose is represented in grams (g); m rRC The mass of the cellulose remaining after hydrolysis is expressed in grams (g); m TRS This indicates the mass of TRS, in grams; 0.9 is C6H. 10 O5(162) and C6H 12 The ratio of the relative molecular masses of O6(180), C Glucose This refers to the concentration of glucose in the hydrolysis products detected by HPLC, in g / L; while 0.02 represents the volume of the hydrolysate, in L.

[0131] The conversion rate of cellulose hydrolysis, the yield of reducing sugar, and the yield of glucose in the examples or comparative examples, calculated using the formula, are shown in Table 1.

[0132] Table 1 shows that the addition of carbon-coated raspberry-like silica nanomaterials can promote the efficient hydrolysis of cellulose into sugars. The carbon material itself has good thermal stability, and the increased content of localized hydroxyl groups on its surface will affect the hydrolysis efficiency. As a highly efficient catalyst, it induces interfacial interactions with cellulose in aqueous systems. By controlling the surface roughness of the carbon-coated raspberry catalyst, the formation of strong localized absorption regions is induced, thereby enhancing the ability to disrupt the cellulose aggregation structure. In low-acid aqueous systems, using MSN-90-NH2@C, the cellulose conversion rate can reach 91.99%, and the sugar yield is 81.46%. This study provides a new perspective for designing and preparing nano-solid catalysts with controllable surface topology to more efficiently enhance their adsorption capacity with cellulose.

[0133] Table 1. Cellulose hydrolysis results in Examples 1-9 and Comparative Examples.

[0134] Group Example 1 Example 2 Example 3 Example 4 Conversion Rate (%) 80.23 86.54 91.99 90.08 Reducing Sugar (%) 70.12 76.92 81.46 81.02 Glucose (%) 52.34 60.32 79.12 78.22 Group Example 5 Example 6 Example 9 Example 26 Conversion Rate (%) 88.23 87.34 40.23 60.78 Reducing Sugar (%) 80.02 78.99 30.65 51.12 Glucose (%) 76.98 75.36 23.24 43.66 surface

[0135] The above-described preferred embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of the invention. Any obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing carbon-coated raspberry-like SiO2 nanomaterials, wherein the carbon-coated raspberry-like SiO2 nanomaterials comprise a carbon layer and modified raspberry-like SiO2 nanomaterials coated within the carbon layer, wherein the thickness of the carbon layer is 10-300 nm, the surface roughness Ra is 10-100 nm, and the modified raspberry-like SiO2 nanomaterials have positively charged groups on their surface under acidic conditions and a particle size of 10-300 nm; characterized in that, The method for preparing carbon-coated raspberry-like SiO2 nanomaterials includes the following steps: S1. Etching the SiO2 nanomaterials with a weak alkaline solution to obtain raspberry-like SiO2 nanomaterials with different surface roughness; the weak alkaline solution is at least one of sodium carbonate solution, sodium bicarbonate solution, ammonia water, or potassium carbonate solution, the concentration of the weak alkaline solution is 0.2-0.5M, and the mass-to-volume ratio of the SiO2 nanomaterials to the weak alkaline solution is 4-6 g:1 L; the etching temperature is 40-60 °C. o C. The time is 30~90 min; S2. Modify the raspberry-like SiO2 nanomaterials with different surface roughness using a modifier to obtain modified raspberry-like SiO2 nanomaterials; S3. Perform a hydrothermal carbonization reaction using the modified raspberry-like SiO2 nanomaterials and a carbon source as raw materials to coat the surface of the modified raspberry-like SiO2 nanomaterials with a carbon layer. After the reaction is completed, wash and dry the product to obtain the carbon-coated raspberry-like SiO2 nano-silica material.

2. The method for preparing carbon-coated raspberry-like SiO2 nanomaterials according to claim 1, characterized in that, The SiO2 nanomaterials were prepared by the following method: using CTAB as a template, a silicon source was added under alkaline conditions, and the temperature was increased to 10~100℃. o After heating and stirring at C for 1-3 hours, centrifuge and wash, then rinse at 100-1000 ml. o After heating at C for 3-9 h, CTAB is removed to obtain the SiO2 nanomaterial, wherein the silicon source is selected from tetraethyl orthosilicate, silicon tetrachloride or sodium silicate.

3. The method for preparing carbon-coated raspberry-like SiO2 nanomaterials according to claim 1, characterized in that, The modifier is a silane coupling agent, including at least one of APTES, KH550, KH560 or KH570, and the concentration of the modifier is 0.5~1 mol / L. The mass ratio of the raspberry-like SiO2 nanomaterials with different surface roughness to the modifier is 1:10-20.

4. The method for preparing carbon-coated raspberry-like SiO2 nanomaterials according to claim 3, characterized in that, The modification temperature is 70-90°C. o C, the time is 1~12 hours.

5. The method for preparing carbon-coated raspberry-like SiO2 nanomaterials according to claim 1, characterized in that, The temperature of the hydrothermal carbonization reaction is 100~200℃. o C, the time is 1~8 hours.

6. The method for preparing carbon-coated raspberry-like SiO2 nanomaterials according to claim 1, characterized in that, In step S3, the mass ratio of the modified raspberry-like SiO2 nanomaterial to the carbon source is 1:1-5; when the carbon source concentration is 0.01~0.04 mol / L, the surface roughness Ra of the carbon layer-coated raspberry-like SiO2 nanomaterial is 70~100 nm; when the carbon source concentration is 0.04~0.07 mol / L, the surface roughness Ra of the carbon layer-coated raspberry-like SiO2 nanomaterial is 10~70 nm.

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