A method for preparing sawdust-based carbon dots and luminescent films thereof

Abstract

The present invention discloses a method for preparing sawdust-based carbon dots, explores the luminescent properties of carbon dots and their applications in the optical field, and also discloses a method for preparing sawdust-based carbon dot luminescent films. The preparation method comprises: preparing carbon dots: soaking sawdust in a sodium hypochlorite solution, sealing and stirring the solution for reaction, centrifuging the solution, removing the colloid layer, repeatedly rinsing the solution, and freeze-drying the solution to obtain freeze-dried cellulose; soaking the freeze-dried cellulose in deionized water and fully crushing the solution to obtain a solid-liquid mixture, pouring the mixture into a polytetrafluoroethylene liner, and performing a hydrothermal reaction in a vacuum drying oven; centrifuging the solution after the reaction is completed, dialyzing the obtained supernatant, and freeze-drying the solution to obtain the carbon dots; preparing a carbon dot-based film: dissolving the obtained carbon dot solid into a carbon dot solution, using a PVA film-forming method to obtain a mixed solution, fully crushing the solution, and drying the solution to obtain the carbon dot-based film. Investigations revealed that when the carbon dot concentration reached 30%, the film's fluorescence emission peak appeared at 472nm, exhibiting cyan light. This peak continued to redshift with increasing CDs concentration, demonstrating that luminescent films with varying carbon dot concentrations exhibit the same properties as CDs aqueous solutions, absorbing short-wavelength light and converting it into longer-wavelength emission. This preparation method not only facilitates the reuse of industrial waste, achieving environmental benefits, but also aligns with my country's current carbon neutrality goals.

Description

Technical Field

[0001] The present invention belongs to the technical field of nanomaterials, in particular to a method for preparing sawdust-based carbon dots and luminescent films thereof. Background Art

[0002] As a new type of zero-dimensional nanomaterial, carbon dots (CDs) have become the representative of the new generation of photoluminescent materials due to their advantages such as simple preparation, abundant raw materials, low price, adjustable emission, good optical stability and good biocompatibility. Among the many raw materials that can be used to prepare CDs, biomass has attracted much attention due to its advantages such as green environmental protection and sustainability. Wood, as a biomass resource with large reserves and wide applications, has significant advantages in the preparation of CDs. The preparation process of carbon quantum dots is simple and has the advantages of high yield, low cost and environmental friendliness. In addition, due to their small size, good biocompatibility, high chemical stability, adjustable hydrophilicity, rich surface functional groups and strong anti-pollution ability, they have broad application prospects in the field of luminescent functional materials.

[0003] In recent years, green chemistry has gradually been incorporated into the synthesis of carbon quantum dots. Biomass resources, with their numerous advantages such as low cost, renewable availability, high carbon content, and ease of preparation, have been widely used as carbon source precursors in the preparation of biomass-based carbon quantum dots. However, current biomass-based carbon dots suffer from issues such as uneven particle size and limited luminescence range, limiting their widespread adoption in high-end applications.

[0004] Therefore, developing an efficient and environmentally friendly method for preparing carbon dots based on sawdust and preparing thin films with high transparency and excellent luminescence properties has important research significance and application value. Summary of the Invention

[0005] The present invention aims to provide a method for preparing sawdust-based carbon dots and luminescent films thereof, so as to solve the problems of uneven particle size and limited luminescent range of biomass carbon dots in the prior art, and to improve the transparency and luminescent performance of the film. The method uses sawdust as the initial carbon source, processes the sawdust to obtain cellulose, and attempts to prepare biomass carbon quantum dots by a hydrothermal method. The use of sawdust as raw material to prepare carbon dots can not only complete the recycling of industrial waste and be green and environmentally friendly, but also conform to my country's current carbon neutrality concept. It has broad application prospects in biosensing, bioimaging, drug delivery, photovoltaic devices, and optoelectronic device preparation.

[0006] The present invention provides a method for preparing sawdust-based carbon dots and a luminescent film thereof, comprising the following steps:

[0007] (1) Using sawdust as raw material, completely immerse it in sodium hypochlorite solution, seal it with plastic wrap, and stir it on a magnetic stirrer until the sawdust in the solid-liquid mixture turns completely white;

[0008] (2) centrifuging the solid-liquid mixture obtained in step (1), taking out the lower colloid, and rinsing it in deionized water; centrifuging the mixture again, taking out the lower colloid, and rinsing it in deionized water three times to remove residual chemicals, thereby obtaining a white colloid, namely cellulose;

[0009] (3) freeze-drying the colloidal cellulose obtained in step (2), and then vacuum drying to obtain freeze-dried cellulose, dividing the cellulose into small pieces, soaking them in deionized water, and using an ultrasonic cell crusher to break up the resulting solid-liquid mixture until the freeze-dried cellulose is completely broken into a milky white suspension;

[0010] (4) stirring the milky white suspension obtained in step (3), pouring it into a polytetrafluoroethylene liner, placing it into a high-pressure reactor, reacting it using a hydrothermal method in a vacuum drying oven, and taking it out after the reactor cools down;

[0011] (5) Centrifuging the solid-liquid mixture obtained in step (4), removing the supernatant and filtering it, and freeze-drying the filtrate to obtain a viscous solid. The viscous solid is then dissolved in water and centrifuged and filtered repeatedly to obtain a dark brown viscous solid, i.e., a carbon dot solid.

[0012] (6) adding polyvinyl alcohol solid particles into deionized water, stirring and heating until completely dissolved, and then cooling to room temperature to obtain a polyvinyl alcohol (PVA) solution;

[0013] (7) Dissolving the carbon dot solid obtained in step (5) in deionized water to obtain a carbon dot solution, mixing the carbon dot solution with the polyvinyl alcohol solution obtained in step (6), adding the polyvinyl alcohol solution to the mixed solution until the total volume of the mixed solution is 20 ml, treating the mixed solution with an ultrasonic cell crusher, and then drying the mixed solution in a vacuum drying oven to obtain a light brown luminescent film.

[0014] Preferably, in step (1), the mass of sawdust is weighed to be 9 g, the concentration of the sodium hypochlorite solution is 4.8 wt %, 200 ml of the sodium hypochlorite solution is weighed, and the stirring time of the magnetic stirrer is 60 min.

[0015] Preferably, in step (2), the centrifugal speed of the centrifuge is 10,000 r / min, and the centrifugal time is 5 min.

[0016] Preferably, in step (3), the freeze-drying time is 4 hours, the vacuum drying time is 20 hours, the freeze-dried cellulose mass is weighed to be 0.171 g, 60 ml of deionized water is weighed, the power of the ultrasonic cell disruptor is set to 45%, the operation is 1.5 seconds, and the interval is 2 seconds.

[0017] Preferably, the speed of the magnetic stirrer in step (4) can be controlled below 300 r / min, 100 ml of the polytetrafluoroethylene liner is taken, and the temperature in the vacuum drying oven is adjusted to 200° C. for 720 min.

[0018] Preferably, in step (5), the centrifugal speed of the centrifuge is 10000 r / min, the centrifugal time is 5 min, and a 0.22 μm microfiltration membrane is used for filtration.

[0019] Preferably, in step (6), 40 g of polyvinyl alcohol solid particles and 460 ml of deionized water are weighed, the stirring speed of the thermomagnetic stirrer is 200 r / min, and the heating temperature does not exceed 80°C.

[0020] Preferably, in step (7), the mass volume ratio of carbon dot solid and deionized water is 5:1, the concentration of the polyvinyl alcohol solution is 8wt%, the polyvinyl alcohol is selected as 1788 low-viscosity type, the degree of alcoholysis is 87.0-89.0%, the power of the ultrasonic cell crusher is set to 45%, the operation is 1.5s, the interval is 2s, and the duration is 3min. The vacuum drying oven temperature is adjusted to 60°C and the vacuum drying time is 7h.

[0021] The present invention also provides a luminescent film prepared by the aforementioned method for preparing the sawdust-based carbon dots and the luminescent film.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The present invention uses sawdust as a carbon source, achieving effective utilization of biomass resources and conforming to the concepts of green environmental protection and sustainable development.

[0024] 2. The present invention optimizes the hydrothermal process parameters to prepare carbon dots with uniform particle size and excellent luminescence performance, solving the problems of uneven particle size and limited luminescence range of biomass carbon dots in the existing technology.

[0025] 3. The luminescent film prepared by the present invention has good transparency and excellent luminescent properties, and can be widely used in optical devices, display technology, anti-counterfeiting materials and other fields, with broad market prospects and application value.

[0026] The above content is an overview of the technical solution. The present invention will be further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to clearly illustrate the technical solutions implemented in the present invention, the following briefly introduces the implementation process and the drawings required for use in the embodiments. The following drawings only show some embodiments of the present invention and should not be regarded as limiting the present invention in any form.

[0028] Figure 1This is an optical photograph of the dry luminescent film prepared by the present invention;

[0029] Figure 2 The fluorescence emission spectra (PL) of the CDs solution prepared in the present invention at different excitation wavelengths;

[0030] Figure 3 The fluorescence emission spectra (PL) of the luminescent films with different concentrations of CDs (4.5–30% CDs) prepared in the present invention under excitation at a wavelength of 365 nm are shown;

[0031] Figure 4 The CIE (1931) coordinate diagram of CDs luminescent film (4.5–30% CDs) under 365 nm wavelength excitation;

[0032] Figure 5 These are images of 4.5% concentration CDs film and 30% concentration CDs film observed under 365nm ultraviolet light. DETAILED DESCRIPTION

[0033] In order to better understand the technical content of the present invention, the technical solution of the present invention is further described below in conjunction with specific embodiments and drawings. It should be understood that the embodiments of the present invention are only used to illustrate the present invention and are not intended to limit the present invention in any form.

[0034] Example 1

[0035] A method for preparing sawdust-based carbon dots and a luminescent film thereof comprises the following steps:

[0036] (1) Weigh 9 g of sawdust and 200 ml of sodium hypochlorite solution, immerse the sawdust completely in the 4.8 wt% sodium hypochlorite solution, seal with plastic wrap (perforations may be made in the plastic wrap to prevent excessive reaction), and stir on a magnetic stirrer for 60 min until the sawdust in the solid-liquid mixture completely turns white.

[0037] (2) centrifuging the solid-liquid mixture obtained in step (1) at a centrifugal speed of 10,000 r / min for 5 minutes, removing the lower layer of colloid, and rinsing it in deionized water. Centrifuging the mixture again at a centrifugal speed of 10,000 r / min for 5 minutes, removing the lower layer of colloid, and rinsing it in deionized water three times to remove residual chemicals, thereby obtaining a white colloid, namely cellulose;

[0038] (3) freeze-drying the colloidal cellulose obtained in step (2) for 4 h, and then vacuum-drying for 20 h to obtain freeze-dried cellulose; weighing 0.171 g of freeze-dried cellulose and dividing it into small pieces, soaking it in 60 ml of deionized water, and using an ultrasonic cell crusher to break up the resulting solid-liquid mixture. The ultrasonic cell crusher power was set to 45%, and the operation was performed for 1.5 seconds with an interval of 2 seconds until the freeze-dried cellulose was completely broken to form a milky white suspension;

[0039] (4) The milky white suspension obtained in step (3) was stirred on a magnetic stirrer at a speed of less than 300 r / min, and then poured into a 100 ml polytetrafluoroethylene-lined container. The mixture was placed in a high-pressure reactor and reacted hydrothermally in a vacuum drying oven. The temperature in the vacuum drying oven was adjusted to 200°C for 720 min, and the reactor was removed after cooling.

[0040] (5) The solid-liquid mixture obtained in step (4) was centrifuged at 10,000 rpm for 5 minutes, the supernatant was removed and filtered through a 0.22 μm microfiltration membrane, and the filtrate was freeze-dried to obtain a viscous solid. The viscous solid was then dissolved in water and centrifuged and filtered repeatedly to obtain a dark brown viscous solid, i.e., a carbon dot solid.

[0041] (6) Weigh 40 g of polyvinyl alcohol solid particles, divide them into eight portions, 5 g each, and add them in batches to 460 ml of deionized water. Stir thoroughly and heat to 80°C in a hot stirrer at 200 r / min until completely dissolved, then cool to room temperature to obtain an 8 wt% polyvinyl alcohol (PVA) solution.

[0042] (7) Weigh 170 mg of the carbon dot solid obtained in step (5) and dissolve it in deionized water at a ratio of 5 mg / mL to obtain 34 ml of carbon dot solution. Use a pipette to draw 0.9 ml of the carbon dot solution and place it in a beaker. Then use a measuring cylinder to weigh the 8 wt% concentration polyvinyl alcohol solution obtained in step (6). Add polyvinyl alcohol to the beaker and mix it with the carbon quantum dot solution until the total solution volume reaches 20 mL. At this time, the carbon dot concentration in the mixed solution is 4.5% wt. The mixture is treated with an ultrasonic cell crusher with the power set to 45%, working for 1.5 seconds, 2 seconds interval, and lasting for 3 minutes. Then, dry it in a vacuum drying oven at 60°C for 7 hours to obtain a light brown luminescent film.

[0043] After testing, the fluorescence emission spectra of the luminescent film prepared in this embodiment at different excitation wavelengths are shown in the figure below: Figure 2 shown. Figure 3 The fluorescence emission spectrum of the luminescent film of Example 1 under excitation at a wavelength of 365 nm is shown. Figure 4 The CIE chromaticity diagram of Example 1 is shown, and its coordinates are (0.2030.244).

[0044] Example 2

[0045] A method for preparing sawdust-based carbon dots and a luminescent film thereof comprises the following steps:

[0046] (1) Weigh 9 g of sawdust and 200 ml of sodium hypochlorite solution, immerse the sawdust completely in the 4.8 wt% sodium hypochlorite solution, seal with plastic wrap (perforations may be made in the plastic wrap to prevent excessive reaction), and stir on a magnetic stirrer for 60 min until the sawdust in the solid-liquid mixture completely turns white.

[0047] (2) centrifuging the solid-liquid mixture obtained in step (1) at a centrifugal speed of 10,000 r / min for 5 minutes, removing the lower layer of colloid, and rinsing it in deionized water. Centrifuging the mixture again at a centrifugal speed of 10,000 r / min for 5 minutes, removing the lower layer of colloid, and rinsing it in deionized water three times to remove residual chemicals, thereby obtaining a white colloid, namely cellulose;

[0048] (3) freeze-drying the colloidal cellulose obtained in step (2) for 4 h, and then vacuum-drying for 20 h to obtain freeze-dried cellulose; weighing 0.171 g of freeze-dried cellulose and dividing it into small pieces, soaking it in 60 ml of deionized water, and using an ultrasonic cell crusher to break up the resulting solid-liquid mixture. The ultrasonic cell crusher power was set to 45%, and the operation was performed for 1.5 seconds with an interval of 2 seconds until the freeze-dried cellulose was completely broken to form a milky white suspension;

[0049] (4) The milky white suspension obtained in step (3) was stirred on a magnetic stirrer at a speed of less than 300 r / min, and then poured into a 100 ml polytetrafluoroethylene-lined container. The mixture was placed in a high-pressure reactor and reacted hydrothermally in a vacuum drying oven. The temperature in the vacuum drying oven was adjusted to 200°C for 720 min, and the reactor was removed after cooling.

[0050] (5) The solid-liquid mixture obtained in step (4) was centrifuged at 10,000 rpm for 5 minutes, the supernatant was removed and filtered through a 0.22 μm microfiltration membrane, and the filtrate was freeze-dried to obtain a viscous solid. The viscous solid was then dissolved in water and centrifuged and filtered repeatedly to obtain a dark brown viscous solid, i.e., a carbon dot solid.

[0051] (6) Weigh 40 g of polyvinyl alcohol solid particles, divide them into eight portions, 5 g each, and add them in batches to 460 ml of deionized water. Stir thoroughly and heat to 80°C in a hot stirrer at 200 r / min until completely dissolved, then cool to room temperature to obtain an 8 wt% polyvinyl alcohol (PVA) solution.

[0052] (7) Weigh 170 mg of the carbon dot solid obtained in step (5) and dissolve it in deionized water at a ratio of 5 mg / mL to obtain 34 ml of carbon dot solution. Use a pipette to draw 1.5 ml of the carbon dot solution and place it in a beaker. Then use a measuring cylinder to weigh the 8 wt% concentration polyvinyl alcohol solution obtained in step (6). Add polyvinyl alcohol to the beaker and mix it with the carbon quantum dot solution until the total solution volume reaches 20 mL. At this time, the carbon dot concentration in the mixed solution is 7.5% wt. The mixture is treated with an ultrasonic cell crusher with the power set to 45%, working for 1.5 seconds, 2 seconds interval, and lasting for 3 minutes. Then, dry it in a vacuum drying oven at 60°C for 7 hours to obtain a light brown luminescent film.

[0053] After testing, the fluorescence emission spectra of the luminescent film prepared in this embodiment at different excitation wavelengths are shown in the figure below: Figure 2 shown. Figure 3 The fluorescence emission spectrum of the luminescent film of Example 2 under excitation at a wavelength of 365 nm is shown. Figure 4 The CIE chromaticity diagram of Example 2 is shown, and its coordinates are (0.2040.238).

[0054] Example 3

[0055] A method for preparing sawdust-based carbon dots and a luminescent film thereof comprises the following steps:

[0056] (1) Weigh 9 g of sawdust and 200 ml of sodium hypochlorite solution, immerse the sawdust completely in the 4.8 wt% sodium hypochlorite solution, seal with plastic wrap (perforations may be made in the plastic wrap to prevent excessive reaction), and stir on a magnetic stirrer for 60 min until the sawdust in the solid-liquid mixture completely turns white.

[0057] (2) centrifuging the solid-liquid mixture obtained in step (1) at a centrifugal speed of 10,000 r / min for 5 minutes, removing the lower layer of colloid, and rinsing it in deionized water. Centrifuging the mixture again at a centrifugal speed of 10,000 r / min for 5 minutes, removing the lower layer of colloid, and rinsing it in deionized water three times to remove residual chemicals, thereby obtaining a white colloid, namely cellulose;

[0058] (3) freeze-drying the colloidal cellulose obtained in step (2) for 4 h, and then vacuum-drying for 20 h to obtain freeze-dried cellulose; weighing 0.171 g of freeze-dried cellulose and dividing it into small pieces, soaking it in 60 ml of deionized water, and using an ultrasonic cell crusher to break up the resulting solid-liquid mixture. The ultrasonic cell crusher power was set to 45%, and the operation was performed for 1.5 seconds with an interval of 2 seconds until the freeze-dried cellulose was completely broken to form a milky white suspension;

[0059] (4) The milky white suspension obtained in step (3) was stirred on a magnetic stirrer at a speed of less than 300 r / min, and then poured into a 100 ml polytetrafluoroethylene-lined container. The mixture was placed in a high-pressure reactor and reacted hydrothermally in a vacuum drying oven. The temperature in the vacuum drying oven was adjusted to 200°C for 720 min, and the reactor was removed after cooling.

[0060] (5) The solid-liquid mixture obtained in step (4) was centrifuged at 10,000 rpm for 5 minutes, the supernatant was removed and filtered through a 0.22 μm microfiltration membrane, and the filtrate was freeze-dried to obtain a viscous solid. The viscous solid was then dissolved in water and centrifuged and filtered repeatedly to obtain a dark brown viscous solid, i.e., a carbon dot solid.

[0061] (6) Weigh 40 g of polyvinyl alcohol solid particles, divide them into eight portions, 5 g each, and add them in batches to 460 ml of deionized water. Stir thoroughly and heat to 80°C in a hot stirrer at 200 r / min until completely dissolved, then cool to room temperature to obtain an 8 wt% polyvinyl alcohol (PVA) solution.

[0062] (7) Weigh 170 mg of the carbon dot solid obtained in step (5) and dissolve it in deionized water at a ratio of 5 mg / mL to obtain 34 ml of carbon dot solution. Use a pipette to draw 1.8 ml of the carbon dot solution and place it in a beaker. Then use a measuring cylinder to weigh the 8 wt% concentration polyvinyl alcohol solution obtained in step (6). Add polyvinyl alcohol to the beaker and mix it with the carbon quantum dot solution until the total solution volume reaches 20 mL. At this time, the carbon dot concentration in the mixed solution is 9% wt. Use an ultrasonic cell crusher to process it. The ultrasonic cell crusher power is set to 45%, work for 1.5 seconds, and take a 2-second interval for 3 minutes. Then dry it in a vacuum drying oven at 60°C for 7 hours to obtain a light brown luminescent film.

[0063] After testing, the fluorescence emission spectra of the luminescent film prepared in this embodiment at different excitation wavelengths are shown in FIG. Figure 2 shown. Figure 3 The fluorescence emission spectrum of the luminescent film of Example 3 under excitation at a wavelength of 365 nm is shown. Figure 4 The CIE chromaticity diagram of Example 3 is shown, and its coordinates are (0.2100.246).

[0064] Example 4

[0065] A method for preparing sawdust-based carbon dots and a luminescent film thereof comprises the following steps:

[0066] (1) Weigh 9 g of sawdust and 200 ml of sodium hypochlorite solution, immerse the sawdust completely in the 4.8 wt% sodium hypochlorite solution, seal with plastic wrap (perforations may be made in the plastic wrap to prevent excessive reaction), and stir on a magnetic stirrer for 60 min until the sawdust in the solid-liquid mixture completely turns white.

[0067] (2) centrifuging the solid-liquid mixture obtained in step (1) at a centrifugal speed of 10,000 r / min for 5 minutes, removing the lower layer of colloid, and rinsing it in deionized water. Centrifuging the mixture again at a centrifugal speed of 10,000 r / min for 5 minutes, removing the lower layer of colloid, and rinsing it in deionized water three times to remove residual chemicals, thereby obtaining a white colloid, namely cellulose;

[0068] (3) freeze-drying the colloidal cellulose obtained in step (2) for 4 h, and then vacuum-drying for 20 h to obtain freeze-dried cellulose; weighing 0.171 g of freeze-dried cellulose and dividing it into small pieces, soaking it in 60 ml of deionized water, and using an ultrasonic cell crusher to break up the resulting solid-liquid mixture. The ultrasonic cell crusher power was set to 45%, and the operation was performed for 1.5 seconds with an interval of 2 seconds until the freeze-dried cellulose was completely broken to form a milky white suspension;

[0069] (4) The milky white suspension obtained in step (3) was stirred on a magnetic stirrer at a speed of less than 300 r / min, and then poured into a 100 ml polytetrafluoroethylene-lined container. The mixture was placed in a high-pressure reactor and reacted hydrothermally in a vacuum drying oven. The temperature in the vacuum drying oven was adjusted to 200°C for 720 min, and the reactor was removed after cooling.

[0070] (5) The solid-liquid mixture obtained in step (4) was centrifuged at 10,000 rpm for 5 minutes, the supernatant was removed and filtered through a 0.22 μm microfiltration membrane, and the filtrate was freeze-dried to obtain a viscous solid. The viscous solid was then dissolved in water and centrifuged and filtered repeatedly to obtain a dark brown viscous solid, i.e., a carbon dot solid.

[0071] (6) Weigh 40 g of polyvinyl alcohol solid particles, divide them into eight portions, 5 g each, and add them in batches to 460 ml of deionized water. Stir thoroughly and heat to 80°C in a hot stirrer at 200 r / min until completely dissolved, then cool to room temperature to obtain an 8 wt% polyvinyl alcohol (PVA) solution.

[0072] (7) Weigh 170 mg of the carbon dot solid obtained in step (5) and dissolve it in deionized water at a ratio of 5 mg / mL to obtain 34 ml of carbon dot solution. Use a pipette to draw 4 ml of the carbon dot solution and place it in a beaker. Then use a measuring cylinder to weigh the 8 wt% concentration polyvinyl alcohol solution obtained in step (6). Add polyvinyl alcohol to the beaker and mix it with the carbon quantum dot solution until the total solution volume reaches 20 mL. At this time, the carbon dot concentration in the mixed solution is 20% wt. Use an ultrasonic cell crusher to process it. The ultrasonic cell crusher power is set to 45%, and the operation is 1.5 seconds, with an interval of 2 seconds, and continued for 3 minutes. Then dry it in a vacuum drying oven at 60°C for 7 hours to obtain a light brown luminescent film.

[0073] After testing, the fluorescence emission spectra of the luminescent film prepared in this embodiment at different excitation wavelengths are shown in FIG. Figure 2 shown. Figure 3 The fluorescence emission spectrum of the luminescent film of Example 4 under excitation at a wavelength of 365 nm is shown. Figure 4 The CIE chromaticity diagram of Example 4 is shown, and its coordinates are (0.2210.269).

[0074] Example 5

[0075] A method for preparing sawdust-based carbon dots and a luminescent film thereof comprises the following steps:

[0076] (1) Weigh 9 g of sawdust and 200 ml of sodium hypochlorite solution, immerse the sawdust completely in the 4.8 wt% sodium hypochlorite solution, seal with plastic wrap (perforations may be made in the plastic wrap to prevent excessive reaction), and stir on a magnetic stirrer for 60 min until the sawdust in the solid-liquid mixture completely turns white.

[0077] (2) centrifuging the solid-liquid mixture obtained in step (1) at a centrifugal speed of 10,000 r / min for 5 minutes, removing the lower layer of colloid, and rinsing it in deionized water. Centrifuging the mixture again at a centrifugal speed of 10,000 r / min for 5 minutes, removing the lower layer of colloid, and rinsing it in deionized water three times to remove residual chemicals, thereby obtaining a white colloid, namely cellulose;

[0078] (3) freeze-drying the colloidal cellulose obtained in step (2) for 4 h, and then vacuum-drying for 20 h to obtain freeze-dried cellulose; weighing 0.171 g of freeze-dried cellulose and dividing it into small pieces, soaking it in 60 ml of deionized water, and using an ultrasonic cell crusher to break up the resulting solid-liquid mixture. The ultrasonic cell crusher power was set to 45%, and the operation was performed for 1.5 seconds with an interval of 2 seconds until the freeze-dried cellulose was completely broken to form a milky white suspension;

[0079] (4) The milky white suspension obtained in step (3) was stirred on a magnetic stirrer at a speed of less than 300 r / min, and then poured into a 100 ml polytetrafluoroethylene-lined container. The mixture was placed in a high-pressure reactor and reacted hydrothermally in a vacuum drying oven. The temperature in the vacuum drying oven was adjusted to 200°C for 720 min, and the reactor was removed after cooling.

[0080] (5) The solid-liquid mixture obtained in step (4) was centrifuged at 10,000 rpm for 5 minutes, the supernatant was removed and filtered through a 0.22 μm microfiltration membrane, and the filtrate was freeze-dried to obtain a viscous solid. The viscous solid was then dissolved in water and centrifuged and filtered repeatedly to obtain a dark brown viscous solid, i.e., a carbon dot solid.

[0081] (6) Weigh 40 g of polyvinyl alcohol solid particles, divide them into eight portions, 5 g each, and add them in batches to 460 ml of deionized water. Stir thoroughly and heat to 80°C in a hot stirrer at 200 r / min until completely dissolved, then cool to room temperature to obtain an 8 wt% polyvinyl alcohol (PVA) solution.

[0082] (7) Weigh 170 mg of the carbon dot solid obtained in step (5) and dissolve it in deionized water at a ratio of 5 mg / mL to obtain 34 ml of carbon dot solution. Use a pipette to draw 6 ml of the carbon dot solution and place it in a beaker. Then use a measuring cylinder to weigh the 8 wt% concentration polyvinyl alcohol solution obtained in step (6). Add polyvinyl alcohol to the beaker and mix it with the carbon quantum dot solution until the total solution volume reaches 20 mL. At this time, the carbon dot concentration in the mixed solution is 30% wt. Use an ultrasonic cell crusher to process it. The ultrasonic cell crusher power is set to 45%, work for 1.5 seconds, and take a 2-second interval for 3 minutes. Then dry it in a vacuum drying oven at 60°C for 7 hours to obtain a light brown luminescent film.

[0083] After testing, the fluorescence emission spectra of the luminescent film prepared in this embodiment at different excitation wavelengths are shown in FIG. Figure 2 shown. Figure 3 The fluorescence emission spectrum of the luminescent film of Example 5 under excitation at a wavelength of 365 nm is shown. Figure 4 The CIE chromaticity diagram of Example 5 is shown, and its coordinates are (0.2290.281). Figure 5Images of 4.5% and 30% CDs films observed under 365nm UV light are shown. The 30% CDs carbon dot film on the left is more cyan-colored than the 4.5% CDs film on the right, exhibiting a cyan glow. However, in optical material preparation, W-LEDs fabricated using this route often exhibit a cyan gap in their emission spectrum between 470-510nm, resulting in a trend different from sunlight, hindering their widespread application in high-quality general lighting. In this experiment, when the CDs concentration was 30%, the film's fluorescence emission peak already appeared at 472nm, indicating cyan light. Further increasing the carbon dot concentration could cause the film's fluorescence emission peak to further redshift, providing a path for fabricating W-LEDs with a cyan gap in the 470-510nm emission spectrum.

[0084] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made thereto. Therefore, such modifications and improvements, without departing from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. A method for preparing sawdust-based carbon dots and light-emitting films thereof, characterized in that: The following steps are included: (1) Using sawdust as raw material, completely immerse it in sodium hypochlorite solution, seal it with plastic wrap, and stir it on a magnetic stirrer until the sawdust in the solid-liquid mixture turns completely white; (2) centrifuging the solid-liquid mixture obtained in step (1), taking out the lower colloid, and rinsing it in deionized water; centrifuging the mixture again, taking out the lower colloid, and rinsing it in deionized water three times to remove residual chemicals, thereby obtaining a white colloid, namely cellulose; (3) freeze-drying the colloidal cellulose obtained in step (2), and then vacuum drying to obtain freeze-dried cellulose, dividing the cellulose into small pieces, soaking them in deionized water, and using an ultrasonic cell crusher to break up the resulting solid-liquid mixture until the freeze-dried cellulose is completely broken into a milky white suspension; (4) stirring the milky white suspension obtained in step (3), pouring it into a polytetrafluoroethylene liner, placing it into a high-pressure reactor, reacting it using a hydrothermal method in a vacuum drying oven, and taking it out after the reactor cools down; (5) centrifuging the solid-liquid mixture obtained in step (4), taking out the supernatant and filtering it, freeze-drying the filtrate to obtain a viscous solid, then dissolving the viscous solid in water, and repeating the centrifugal filtration several times to obtain a dark brown viscous solid, i.e., a carbon dot solid; (6) adding polyvinyl alcohol solid particles into deionized water, stirring and heating until completely dissolved, and then cooling to room temperature to obtain a polyvinyl alcohol (PVA) solution; (7) Dissolving the carbon dot solid obtained in step (5) in deionized water to obtain a carbon dot solution, mixing the carbon dot solution with the polyvinyl alcohol solution obtained in step (6), adding the polyvinyl alcohol solution to the mixed solution until the total volume of the mixed solution is 20 ml, treating the mixed solution with an ultrasonic cell crusher, and then drying the mixed solution in a vacuum drying oven to obtain a light brown luminescent film.

2. The method for preparing sawdust-based carbon dots and light-emitting films thereof according to claim 1, wherein: In step (1), the mass of sawdust is weighed to be 9 g, the concentration of the sodium hypochlorite solution is 4.8 wt %, 200 ml of the sodium hypochlorite solution is weighed, and the stirring time of the magnetic stirrer is 60 min.

3. The method for preparing sawdust-based carbon dots and light-emitting films thereof according to claim 1, wherein: In step (2), the centrifugal speed of the centrifuge is 10000 r / min, and the centrifugal time is 5 min.

4. The method for preparing sawdust-based carbon dots and light-emitting films thereof according to claim 1, wherein: In step (3), the freeze drying time was 4 h, the vacuum drying time was 20 h, the freeze-dried cellulose mass was weighed to be 0.171 g, 60 ml of deionized water was weighed, the power of the ultrasonic cell disruptor was set to 45%, the operation time was 1.5 s, and the interval time was 2 s.

5. The method for preparing sawdust-based carbon dots and light-emitting films thereof according to claim 1, wherein: In step (4), the speed of the magnetic stirrer can be controlled below 300 r / min, 100 ml of the polytetrafluoroethylene liner is taken, and the temperature in the vacuum drying oven is adjusted to 200° C. for 720 min.

6. The method for preparing sawdust-based carbon dots and light-emitting films thereof according to claim 1, wherein: In step (5), the centrifugal speed of the centrifuge is 10000 r / min, the centrifugal time is 5 min, and a 0.22 μm microfiltration membrane is used for filtration.

7. The method for preparing sawdust-based carbon dots and light-emitting films thereof according to claim 1, wherein: In step (6), 40 g of polyvinyl alcohol solid particles and 460 ml of deionized water were weighed, the stirring speed of the thermomagnetic stirrer was 200 r / min, and the heating temperature did not exceed 80°C.

8. The method for preparing sawdust-based carbon dots and light-emitting films thereof according to claim 1, wherein: In step (7), the mass volume ratio of carbon dot solid and deionized water is 5:1, the concentration of the polyvinyl alcohol solution is 8 wt %, the polyvinyl alcohol is selected as 1788 low-viscosity type, the degree of alcoholysis is 87.0-89.0%, the power of the ultrasonic cell disruptor is set to 45%, the operation is 1.5 s, the interval is 2 s, and the duration is 3 min. The vacuum drying oven temperature is adjusted to 60 ° C, and the vacuum drying time is 7 h.

9. Carbon dots prepared according to the method according to any one of claims 1 to 8 and a luminescent film thereof.

Images