CN115074120A

CN115074120A - Carbon dot/diatomite fluorescent composite powder and preparation method and application thereof

Info

Publication number: CN115074120A
Application number: CN202210660773.7A
Authority: CN
Inventors: 袁传军
Original assignee: China Criminal Police University
Current assignee: China Criminal Police University
Priority date: 2022-06-13
Filing date: 2022-06-13
Publication date: 2022-09-20
Anticipated expiration: 2042-06-13
Also published as: CN115074120B

Abstract

The invention discloses carbon dot/diatomite fluorescent composite powder and a preparation method and application thereof. Respectively preparing a carbon dot solution and purified diatomite, and dispersing the carbon dots into the mesoporous structure of the purified diatomite to obtain the catalyst. The purified diatomite has rich mesoporous structure and good optical permeability, and can effectively disperse and stabilize carbon dots, so that the composite powder shows good fluorescence emission performance; meanwhile, the carbon dot/diatomite fluorescent composite powder can be efficiently excited in the visible wavelength range, the property can obviously improve the background interference resistance, and the carbon dot/diatomite fluorescent composite powder is an ideal material for developing fluorescent powder as a fingerprint.

Description

Carbon dot/diatomite fluorescent composite powder and preparation method and application thereof

Technical Field

The invention relates to carbon dot/diatomite fluorescent composite powder and a preparation method and application thereof, belonging to the technical field of fingerprint visualization.

Background

The handprint is the impression left on the surface of the object when the fingers and the palm contact the object, and can be used for identity recognition of human bodies. Most fingerprints in the field of the case are latent fingerprints invisible to naked eyes, and fingerprint visualization technology is needed to increase the contrast between fingerprint lines and an object background so as to convert the latent fingerprints into visible fingerprints. The most commonly used fingerprint visualization technique for field surveyors to visualize potential fingerprints on the surface of impermeable or semi-permeable objects is powder visualization. The fingerprint display powder is easy to adsorb on fingerprint lines, and less or no adsorption is carried out on the object background, so that the fingerprint can be displayed by utilizing the color or the luminous property of the powder. However, for objects with complex patterns, text or strong background fluorescence, background interference can seriously affect the visualization effect of the powder visualization method.

The development of novel efficient fingerprint display fluorescent powder is an effective way for weakening the interference of an object background and improving the fingerprint display effect. Among them, the preparation and application of carbon dot-based fingerprint visualization fluorescent powder is a feasible technical route. The carbon dots are also called carbon quantum dots or carbon nano-dots, are nearly spherical carbon nano-particles with the particle size of less than 10nm, and have the advantages of good luminous performance, rich synthesis method, low chemical toxicity, strong photobleaching resistance and the like. However, the use of carbon dots as the fingerprint developing fluorescent powder faces the following two problems: firstly, after the liquid-phase dispersed carbon dots are dried into powder, fluorescence quenching can be caused by aggregation of the carbon dots; secondly, most carbon dots show blue/green fluorescence under the excitation of ultraviolet light, which is similar to the background fluorescence of many objects. Therefore, the carbon dot-based fingerprint appearing fluorescent powder with high fluorescence intensity and strong background interference resistance is designed.

Disclosure of Invention

The purpose of the invention is as follows: the first purpose of the invention is to provide a carbon dot/diatomite fluorescent composite powder; the second purpose of the invention is to provide a preparation method of the carbon dot/diatomite fluorescent composite powder; the third purpose of the invention is to provide the application of the carbon dot/diatomite fluorescent composite powder in developing latent fingerprints.

The technical scheme is as follows: the carbon dot/diatomite fluorescent composite powder comprises carbon dots and purified diatomite, wherein the carbon dots are dispersed in a mesoporous structure of the purified diatomite and are obtained by a hydrothermal reaction of rhodamine 6G dissolved in water.

The preparation method of the carbon dot/diatomite fluorescent composite powder comprises the following steps:

(1) adding rhodamine 6G into water, dissolving by ultrasonic to form a solution, carrying out hydrothermal reaction on the solution to obtain a mixed solution, centrifuging the mixed solution to obtain a supernatant, filtering the supernatant, and dialyzing to obtain a carbon dot solution;

(2) adding a hydrochloric acid solution into diatomite, heating and stirring, carrying out suction filtration, washing a filter cake with deionized water, calcining the filter cake, cooling to room temperature to obtain diatomite powder, adding the diatomite powder into a saturated sucrose solution, carrying out low-speed centrifugation, washing with water, and drying to obtain purified diatomite;

(3) dispersing purified diatomite in water to obtain diatomite suspension, adding a carbon dot solution into the diatomite suspension to form a mixed solution, ultrasonically mixing uniformly, and drying in vacuum to obtain the carbon dot/diatomite fluorescent composite powder.

Wherein in the step (1), the solid-to-liquid ratio of rhodamine 6G to water is 20-30 mg/mL.

In the step (1), the hydrothermal reaction is carried out for 1-3 hours at 180-200 ℃.

In the step (2), the concentration of the hydrochloric acid solution is 0.5-1.0 mol/L.

Wherein in the step (2), the solid-to-liquid ratio of the diatomite to the hydrochloric acid solution is 0.05-0.1 g/mL

In the step (2), the heating and stirring are carried out for 1-3 hours at 50-70 ℃.

In the step (2), the calcination is carried out for 1-3 h at 450-550 ℃.

Wherein, in the step (2), the calcination is in an air atmosphere.

In the step (2), the solid-to-liquid ratio of the diatomite powder to the saturated sucrose solution is 0.1-0.3 g/mL.

In the step (2), the rotation speed during low-speed centrifugation is 1500-2500 rpm.

Wherein in the step (3), the solid-to-liquid ratio of the purified diatomite to the water is 40-60 mg/mL.

In the step (3), the mass ratio of the diatomite to the carbon dots in the mixed solution is 100-800: 1.

in the step (3), ultrasonic mixing is performed for 10-30 min under the power of 180-250W.

Wherein, in the step (3), the vacuum drying is carried out for 12-24 hours at the temperature of 40-60 ℃.

The carbon dot/diatomite fluorescent composite powder is applied to displaying potential fingerprints.

Wherein the application comprises the visualization of latent fingerprints on the surface of an impermeable guest with or without background fluorescence interference.

The non-permeable object with background fluorescence interference comprises colored plastic, composite wood floor, packaging paper and the like.

Wherein the colored plastic is red plastic or blue plastic.

The non-permeable object without background fluorescence interference comprises stainless steel, aluminum alloy, glass, glazed ceramic tiles and the like.

The invention also comprises a method for displaying the potential fingerprints, which comprises the following steps:

dipping the carbon dot/diatomite fluorescent composite powder of claim 1 with a brush, flicking the carbon dot/diatomite fluorescent composite powder with a brush handle uniformly to a region to be displayed, brushing the brush tip lightly, then displaying the fingerprint lines along the lines after the fingerprint lines appear until the fingerprint lines are clear, and taking a fluorescent photo showing the fingerprint by taking a multiband light source as an excitation light source and a digital single-lens reflex camera with a long-wavelength-pass filter in a dark room environment.

Wherein the hairbrush is a geranium hairbrush.

Wherein the multi-band light source has a wavelength of 510 +/-10 nm.

Wherein, the wavelength of the long-wave pass filter is 550 +/-10 nm.

According to the invention, rhodamine 6G is hydrothermally treated to synthesize a carbon dot solution with strong fluorescence emission under excitation of a visible light wavelength range, then the carbon dot solution and purified diatomite are used for preparing carbon dot/diatomite fluorescent composite powder, the carbon dots are dispersed in a rich mesoporous structure of the purified diatomite, aggregation of liquid-phase dispersed carbon dots in a drying process is inhibited, a stable novel structure is constructed, and the carbon dot/diatomite fluorescent composite powder shows good fluorescence performance.

Has the advantages that: compared with the prior art, the invention has the following remarkable advantages: the carbon dot/diatomite fluorescent composite powder consists of carbon dots and purified diatomite, and the purified diatomite has a rich mesoporous structure and good optical permeability, and can effectively disperse and stabilize the carbon dots, so that the carbon dot/diatomite fluorescent composite powder shows good fluorescence emission performance; meanwhile, the carbon dot/diatomite fluorescent composite powder can be efficiently excited in the visible wavelength range, the property can obviously improve the background interference resistance, and the carbon dot/diatomite fluorescent composite powder is an ideal material for developing fluorescent powder as a fingerprint.

Drawings

FIG. 1 is a transmission electron micrograph of a carbon dot prepared in example 1;

FIG. 2 is a plot of the nitrogen adsorption desorption isotherm of the purified diatomaceous earth prepared in example 1;

FIG. 3 is a mesoporous pore size distribution diagram of purified diatomaceous earth prepared in example 1;

FIG. 4 is a graph showing UV-VIS absorption and fluorescence emission spectra of the carbon dot/diatomaceous earth fluorescent composite powder prepared in example 1;

FIG. 5 is a fluorescent photograph of the carbon dot/diatomaceous earth fluorescent composite powder prepared in example 1 showing fingerprints on the surface of the impermeable object;

FIG. 6 is a fluorescence emission spectrum of the carbon dot/diatomaceous earth fluorescent composite powder prepared in example 2;

FIG. 7 is a fluorescence emission spectrum of the carbon dot/diatomaceous earth fluorescent composite powder prepared in example 3;

FIG. 8 is a fluorescence emission spectrum of the carbon dot/diatomaceous earth fluorescent composite powder prepared in example 4;

FIG. 9 is a fluorescent photograph showing fingerprints on the surface of stainless steel of the carbon dot powder prepared in comparative example 1;

FIG. 10 is a transmission electron micrograph of a carbon dot prepared in comparative example 2;

FIG. 11 is a UV-VISIBLE absorptance and fluorescence emission spectrum of a carbon dot/diatomaceous earth fluorescent composite powder prepared in comparative example 2;

FIG. 12 is a fluorescent photograph showing fingerprints on the surface of stainless steel of the carbon dot/diatomite fluorescent composite powder prepared in comparative example 2;

FIG. 13 is a fluorescent photograph of the carbon dot powder prepared in comparative example 2 showing fingerprints on the surface of stainless steel;

FIG. 14 is a fluorescent photograph showing the surface fingerprints of impermeable objects with background fluorescence interference between the carbon dot/diatomite fluorescent composite powder prepared in comparative example 2 and the carbon dot/diatomite fluorescent composite powder prepared in example 1;

fig. 15 is a fluorescent photograph showing a fingerprint of the surface of the non-permeable guest from the carbon dot/silica fluorescent composite powder prepared in comparative example 3.

Detailed Description

The technical scheme of the invention is further explained by combining the attached drawings.

The raw materials adopted by the invention can be purchased from the market.

Example 1

Preparing carbon dot/diatomite fluorescent composite powder:

(1) preparation of carbon dot solution: 0.5G of rhodamine 6G is weighed and added into a beaker, then 20mL of deionized water is weighed and added, and the rhodamine 6G is completely dissolved by ultrasonic treatment for 5 min. The obtained solution is added into a 50mL stainless steel reaction kettle with a PPL liner and reacted for 2h under the hydrothermal condition of 190 ℃. After the reaction is finished, cooling to room temperature, centrifuging the obtained mixed solution at the rotation speed of 8000rpm for 10min, filtering supernate with a nylon 6 microporous filter membrane with the pore diameter of 0.22 mu m, filling the filtrate into a dialysis bag with the molecular weight cutoff of 1000Da, dialyzing with deionized water for 48h, and diluting the carbon dot solution obtained from the dialysis bag with the deionized water to 1mg/mL to obtain the carbon dot solution.

(2) Weighing 20g of diatomite, adding the diatomite into a beaker, weighing 200mL of prepared 0.5mol/L hydrochloric acid solution, adding the solution into the beaker, stirring the solution for 2 hours under the heating condition of 60 ℃, washing a filter cake with deionized water after suction filtration until the pH value of the filtrate is 7, transferring the filter cake into a ceramic crucible, calcining the filter cake for 1 hour in an air atmosphere at 500 ℃, and cooling the filter cake to room temperature. 5g of the acid-washed and calcined diatomaceous earth was added to 50mL of a saturated sucrose solution, centrifuged at 2000rpm for 5min, 30mL of the upper layer liquid was removed and an equal amount of the saturated sucrose solution was replenished, and the process was repeated three times. And after suction filtration, washing a filter cake with a large amount of deionized water, and drying the filter cake at 40 ℃ to obtain the purified diatomite.

(3) 1g of purified diatomaceous earth was weighed into a beaker, and then 20mL of deionized water was weighed and added thereto, and stirred uniformly to obtain a diatomaceous earth suspension. 10mL of carbon dot solution was added to the diatomaceous earth suspension and sonicated at 250W power for 30 min. And finally, drying the mixed solution at 40 ℃ for 24 hours in vacuum to obtain the carbon dot/diatomite fluorescent composite powder.

The transmission electron microscope analysis of the carbon dot solution prepared in this example was performed, and the result is shown in fig. 1, fig. 1 is a transmission electron microscope image of the carbon dot prepared in example 1, and it can be seen from fig. 1 that the carbon dot was prepared by a hydrothermal method using rhodamine 6G as a precursor.

The purified diatomaceous earth prepared in this example was subjected to a nitrogen desorption experiment, and the results are shown in FIGS. 2 to 3. Fig. 2 is a nitrogen adsorption/desorption isotherm diagram of the purified diatomaceous earth prepared in example 1, and the mesoporous distribution of the purified diatomaceous earth calculated from the nitrogen adsorption/desorption isotherm of the purified diatomaceous earth in fig. 2 is shown in fig. 3. Fig. 3 is a mesoporous distribution diagram of the purified diatomite prepared in example 1, and it can be seen from fig. 3 that the purified diatomite has a large number of mesopores with a pore size of 5 nm.

The carbon dot/diatomite fluorescent composite powder prepared in this example was subjected to uv-vis absorption and fluorescence spectrum analysis, and the results are shown in fig. 4. FIG. 4 is a UV-VIS absorption and fluorescence emission spectrum of the carbon dot/diatomaceous earth fluorescent composite powder prepared in example 1. As can be seen from fig. 4, the carbon dot/diatomite fluorescent composite powder has good fluorescent properties.

The carbon dot/diatomite fluorescent composite powder prepared in the embodiment is used for displaying the potential handprint on the surface of the non-permeable object, a proper amount of powder is dipped by a geranium brush, the powder is evenly shaken off in a region to be displayed by a flicking brush handle, the powder is lightly swept by a brush tip, and the powder is printed and displayed along the flow direction of the handprint lines after the handprint lines appear until the handprint lines are clear. In a darkroom environment, a fluorescence photograph showing a fingerprint is taken with a digital single lens reflex equipped with a 550nm long-wave pass filter with the wavelength band of 510nm of a multiband light source as excitation light, and the result is shown in fig. 5. FIG. 5 is a fluorescent photograph showing fingerprints on the surface of an impermeable object of the carbon dot/diatomite fluorescent composite powder prepared in example 1, wherein, a is a fluorescent photograph showing a fingerprint on the surface of stainless steel of the carbon dot/diatomite fluorescent composite powder prepared in example 1, b is a fluorescent photograph showing a fingerprint on the surface of glass of the carbon dot/diatomite fluorescent composite powder prepared in example 1, c is a fluorescent photograph showing a fingerprint on the surface of aluminum alloy of the carbon dot/diatomite fluorescent composite powder prepared in example 1, d is a fluorescent photograph showing a fingerprint on the surface of wrapping paper of the carbon dot/diatomite fluorescent composite powder prepared in example 1, e is a fluorescent photograph showing a fingerprint on the surface of wood floor of composite wood floor of the carbon dot/diatomite fluorescent composite powder prepared in example 1, and f is a fluorescent photograph showing a fingerprint on the surface of glazed tile of the carbon dot/diatomite fluorescent composite powder prepared in example 1. As can be seen from fig. 5, for the latent fingerprint on the surface of the impermeable object, the carbon dot/diatomite fluorescent composite powder shows high fingerprint definition and obvious contrast with the background.

Example 2

Preparing carbon dot/diatomite fluorescent composite powder:

(1) preparation of carbon dot solution: 0.4G of rhodamine 6G is weighed and added into a beaker, then 20mL of deionized water is weighed and added, and the rhodamine 6G is completely dissolved by ultrasonic treatment for 5 min. The obtained solution is added into a 50mL stainless steel reaction kettle with a PPL lining and reacts for 3h under the hydrothermal condition of 180 ℃. After the reaction is finished, cooling to room temperature, centrifuging the obtained mixed solution at 8000rpm for 10min, filtering the supernatant by using a nylon 6 microporous filter membrane with the pore diameter of 0.22 mu m, filling the filtrate into a dialysis bag with the molecular weight cutoff of 1000Da, dialyzing for 48h by using deionized water, and diluting the carbon dot solution obtained from the dialysis bag to 1mg/mL by using the deionized water to obtain the carbon dot solution.

(2) Weighing 20g of diatomite, adding the diatomite into a beaker, weighing 200mL of prepared 1.0mol/L hydrochloric acid solution, adding the solution into the beaker, stirring the solution for 3 hours under the heating condition of 50 ℃, washing a filter cake with deionized water after suction filtration until the pH value of the filtrate is 7, transferring the filter cake into a ceramic crucible, calcining the filter cake for 3 hours in an air atmosphere at 450 ℃, and cooling the filter cake to room temperature. 15g of the acid-washed and calcined diatomaceous earth was added to 50mL of a saturated sucrose solution, centrifuged at 1500rpm for 5min, 30mL of the upper layer liquid was removed and an equal amount of the saturated sucrose solution was supplemented, and the process was repeated three times. And after suction filtration, washing a filter cake with a large amount of deionized water, and drying the filter cake at 40 ℃ to obtain the purified diatomite.

(3) 0.8g of purified diatomaceous earth was weighed into a beaker, and then 20mL of deionized water was weighed into the beaker, and stirred well to obtain a diatomaceous earth suspension. 2mL of carbon dot solution was added to the diatomaceous earth suspension and sonicated at 200W power for 30 min. And finally, drying the mixed solution at 50 ℃ for 18h in vacuum to obtain the carbon dot/diatomite fluorescent composite powder.

The carbon dot/diatomite fluorescent composite powder prepared in this example was subjected to fluorescence spectrum analysis, and the results are shown in fig. 6. FIG. 6 is a fluorescence emission spectrum of the carbon dot/diatomite fluorescent composite powder prepared in example 2. As can be seen from fig. 6, the carbon dot/diatomite fluorescent composite powder has good fluorescent properties.

Example 3

Preparing carbon dot/diatomite fluorescent composite powder:

(1) preparation of carbon dot solution: 0.6G of rhodamine 6G is weighed and added into a beaker, then 20mL of deionized water is weighed and added, and the rhodamine 6G is completely dissolved by ultrasonic treatment for 5 min. The obtained solution is added into a 50mL stainless steel reaction kettle with a PPL liner and reacted for 1h under the hydrothermal condition of 200 ℃. After the reaction is finished, cooling to room temperature, centrifuging the obtained mixed solution at 8000rpm for 10min, filtering the supernatant by using a nylon 6 microporous filter membrane with the pore diameter of 0.22 mu m, filling the filtrate into a dialysis bag with the molecular weight cutoff of 1000Da, dialyzing for 48h by using deionized water, and diluting the carbon dot solution obtained from the dialysis bag to 1mg/mL by using the deionized water to obtain the carbon dot solution.

(2) Weighing 20g of diatomite, adding the diatomite into a beaker, weighing 400mL of prepared 0.75mol/L hydrochloric acid solution, adding the solution into the beaker, stirring the solution for 1h under the heating condition of 70 ℃, washing a filter cake with deionized water after suction filtration until the pH value of the filtrate is 7, transferring the filter cake into a ceramic crucible, calcining the filter cake for 2h in an air atmosphere at 550 ℃, and cooling the filter cake to room temperature. 10g of the acid-washed and calcined diatomaceous earth was added to 50mL of a saturated sucrose solution, centrifuged at 2500rpm for 5min, 30mL of the upper layer liquid was removed and an equal amount of the saturated sucrose solution was supplemented, and the process was repeated three times. And after suction filtration, washing a filter cake with a large amount of deionized water, and drying the filter cake at 40 ℃ to obtain the purified diatomite.

(3) 1.2g of purified diatomaceous earth was weighed into a beaker, and then 20mL of deionized water was weighed into the beaker, and stirred well to obtain a diatomaceous earth suspension. 6mL of carbon dot solution was added to the diatomaceous earth suspension and sonicated at 180W power for 20 min. And finally, drying the mixed solution at 60 ℃ for 12 hours in vacuum to obtain the carbon dot/diatomite fluorescent composite powder.

The carbon dot/diatomite fluorescent composite powder prepared in this example was subjected to fluorescence spectrum analysis, and the results are shown in fig. 7. FIG. 7 is a fluorescence emission spectrum of the carbon dot/diatomite fluorescent composite powder prepared in example 3. As can be seen from fig. 7, the carbon dot/diatomite fluorescent composite powder has good fluorescent properties.

Example 4

Preparing carbon dot/diatomite fluorescent composite powder:

(1) preparation of carbon dot solution: 0.4G of rhodamine 6G is weighed and added into a beaker, then 20mL of deionized water is weighed and added into the beaker, and the rhodamine 6G is completely dissolved by ultrasound for 5 min. The obtained solution is added into a 50mL PPL stainless steel reaction kettle with a lining and reacts for 3h under the hydrothermal condition of 190 ℃. After the reaction is finished, cooling to room temperature, centrifuging the obtained mixed solution at 8000rpm for 10min, filtering the supernatant by using a nylon 6 microporous filter membrane with the pore diameter of 0.22 mu m, filling the filtrate into a dialysis bag with the molecular weight cutoff of 1000Da, dialyzing for 48h by using deionized water, and diluting the carbon dot solution obtained from the dialysis bag to 1mg/mL by using the deionized water to obtain the carbon dot solution.

(2) Weighing 10g of diatomite, adding the diatomite into a beaker, weighing 200mL of prepared 0.5mol/L hydrochloric acid solution, adding the solution into the beaker, stirring the solution for 3 hours under the heating condition of 60 ℃, washing a filter cake with deionized water after suction filtration until the pH value of the filtrate is 7, transferring the filter cake into a ceramic crucible, calcining the filter cake for 3 hours in an air atmosphere at 550 ℃, and cooling the filter cake to room temperature. 5g of the acid-washed and calcined diatomaceous earth was added to 50mL of a saturated sucrose solution, centrifuged at 1500rpm for 5min, 30mL of the upper layer liquid was removed and an equal amount of the saturated sucrose solution was supplemented, and the process was repeated three times. And after suction filtration, washing a filter cake with a large amount of deionized water, and drying the filter cake at 40 ℃ to obtain the purified diatomite.

(3) 0.8g of purified diatomaceous earth was weighed into a beaker, and then 20mL of deionized water was weighed into the beaker, and stirred well to obtain a diatomaceous earth suspension. To the diatomaceous earth suspension was added 1mL of a carbon dot solution and sonicated at 180W power for 10 min. And finally, drying the mixed solution at 40 ℃ for 18h in vacuum to obtain the carbon dot/diatomite fluorescent composite powder.

The carbon dot/diatomite fluorescent composite powder prepared in this example was subjected to fluorescence spectrum analysis, and the results are shown in fig. 8. FIG. 8 is a fluorescence emission spectrum of the carbon dot/diatomaceous earth fluorescent composite powder prepared in example 4. As can be seen from fig. 8, the carbon dot/diatomite fluorescent composite powder has good fluorescent properties.

Comparative example 1

Preparation of carbon dot powder: 0.5G of rhodamine 6G is weighed and added into a beaker, then 20mL of deionized water is weighed and added, and the rhodamine 6G is completely dissolved by ultrasonic treatment for 5 min. The obtained solution is added into a 50mL stainless steel reaction kettle with a PPL liner and reacted for 2h under the hydrothermal condition of 190 ℃. After the reaction is finished, cooling to room temperature, centrifuging the obtained mixed solution at 8000rpm for 10min, filtering the supernatant by using a nylon 6 microporous filter membrane with the pore diameter of 0.22 mu m, filling the filtrate into a dialysis bag with the molecular weight cutoff of 1000Da, dialyzing for 48h by using deionized water, and diluting the carbon dot solution obtained from the dialysis bag to 1mg/mL by using the deionized water to obtain the carbon dot solution. And (3) drying the carbon dot solution at 40 ℃ for 24 hours in vacuum to obtain carbon dot powder.

The carbon dot powder prepared by the comparative example shows the latent fingerprint on the surface of the stainless steel object, and the appearance and shooting method are the same as those of example 1, and the result is shown in fig. 9. Fig. 9 is a fluorescent photograph showing fingerprints on the surface of stainless steel of the carbon dot powder prepared in comparative example 1. As can be seen from a comparison between fig. 9 and fig. 5, the carbon dot powder prepared in comparative example 1 aggregates during the drying process to cause fluorescence quenching, while the carbon dot/diatomite fluorescent composite powder prepared in example 1 exhibits good fluorescent performance due to the dispersion of rich mesopores of purified diatomite, and for the latent fingerprint on the surface of the stainless steel object, the carbon dot/diatomite fluorescent composite powder prepared in example 1 of the present invention exhibits higher fingerprint definition, more obvious contrast with the background, and significantly better effect than the carbon dot powder prepared in comparative example 1.

Comparative example 2

(1) Preparation of carbon dot solution: 0.5g of rhodamine B is weighed and added into a beaker, then 20mL of deionized water is weighed and added, and the rhodamine B is completely dissolved by ultrasonic treatment for 5 min. The obtained solution is added into a 50mL stainless steel reaction kettle with a PPL liner and reacted for 2h under the hydrothermal condition of 190 ℃. After the reaction is finished, cooling to room temperature, centrifuging the obtained mixed solution at 8000rpm for 10min, filtering the supernatant by using a nylon 6 microporous filter membrane with the pore diameter of 0.22 mu m, filling the filtrate into a dialysis bag with the molecular weight cutoff of 1000Da, dialyzing for 48h by using deionized water, and diluting the carbon dot solution obtained from the dialysis bag to 1mg/mL by using the deionized water to obtain the carbon dot solution.

(2) 1g of purified diatomaceous earth was weighed into a beaker, and then 20mL of deionized water was weighed and added thereto, and stirred uniformly to obtain a diatomaceous earth suspension. 10mL of carbon dot solution was added to the diatomaceous earth suspension and sonicated at 250W power for 30 min. And finally, drying the mixed solution at 40 ℃ for 24 hours in vacuum to obtain the carbon dot/diatomite fluorescent composite powder.

(3) The carbon dot solution prepared in the step (1) of the comparative example was dried in vacuum at 40 ℃ for 24 hours to obtain carbon dot powder.

The transmission electron microscope analysis was performed on the carbon dot solution prepared in the present comparative example, and the result is shown in fig. 10, fig. 10 is a transmission electron microscope image of the carbon dot prepared in the comparative example 2, and it can be seen from fig. 10 that the carbon dot was prepared by a hydrothermal method using rhodamine B as a precursor.

The carbon dot/diatomite fluorescent composite powder prepared in the present comparative example was subjected to uv-visible absorption and fluorescence spectrum analysis, and the results are shown in fig. 11. Fig. 11 is a uv-vis absorption and fluorescence emission spectrum of the carbon dot/diatomite fluorescent composite powder prepared in comparative example 2, and it can be seen from fig. 11 that the fluorescence emission peak of the carbon dot/diatomite fluorescent composite powder prepared in comparative example 2 is significantly red-shifted compared to the carbon dot/diatomite fluorescent composite powder prepared in example 1.

The carbon dot/diatomite fluorescent composite powder prepared in the comparative example is used for displaying potential fingerprints on the surface of a stainless steel object, a proper amount of powder is dipped by a geranium brush, the powder is evenly shaken off in a region to be displayed by a brush handle, the tip of the brush is lightly swept by the brush, and after fingerprint lines appear, the fingerprint lines are printed along the line flow direction until the fingerprint lines are clear. In a darkroom environment, a fluorescence photograph showing a fingerprint is taken by a digital single lens reflex equipped with a 580nm long-wave pass filter with a 530nm waveband of a multiband light source as excitation light, and the result is shown in fig. 12. Fig. 12 is a fluorescent photograph showing fingerprints on the surface of stainless steel of the carbon dot/diatomite fluorescent composite powder prepared in comparative example 2, and it can be seen from fig. 12 that, for the potential fingerprints on the surface of the stainless steel object without significant background interference, the carbon dot/diatomite fluorescent composite powder prepared in comparative example 2 has the effect similar to that of the carbon dot/diatomite fluorescent composite powder prepared in example 1.

The carbon dot powder prepared by the comparative example is used for showing potential fingerprints on the surface of the stainless steel object. The results are shown in FIG. 13. Fig. 13 is a fluorescent photograph showing fingerprints on the surface of stainless steel of the carbon dot powder prepared in comparative example 2. As can be seen from a comparison between fig. 13 and fig. 12, for the latent fingerprint on the surface of the stainless steel object, the carbon dot/diatomite fluorescent composite powder prepared in the present comparative example shows higher fingerprint definition, more obvious contrast with the background, and an effect obviously better than the effect of the carbon dot powder prepared in the present comparative example, which indicates that the carbon dot powder prepared in the comparative example 2 is aggregated during the drying process to cause fluorescence quenching, whereas the carbon dot/diatomite fluorescent composite powder prepared in the comparative example 2 shows good fluorescence performance due to the dispersion effect of rich mesopores of the purified diatomite, and proves that the purified diatomite is a key component for ensuring the fluorescence performance of the carbon dot/diatomite fluorescent composite powder.

Stainless steel and glass objects belong to non-permeable objects without background fluorescence interference, and many non-permeable objects with background fluorescence interference can be encountered in field investigation, so that the requirement on the background interference resistance of fluorescent powder for developing handprints is higher. The carbon dot/diatomite fluorescent composite powder prepared in comparative example 2 and the carbon dot/diatomite fluorescent composite powder prepared in example 1 were used for developing the latent fingerprint on the surface of the impermeable object with background fluorescence interference, and the developing and photographing methods were the same as those of comparative example 2 and example 1, respectively, and the results are shown in fig. 14. Fig. 14 is a fluorescent photograph showing a fingerprint of the surface of an impermeable object with background fluorescence interference between the carbon dot/diatomite fluorescent composite powder prepared in comparative example 2 and the carbon dot/diatomite fluorescent composite powder prepared in example 1, wherein a is a fluorescent photograph showing a fingerprint of the surface of a red plastic package of the carbon dot/diatomite fluorescent composite powder prepared in comparative example 2, b is a fluorescent photograph showing a fingerprint of the surface of a blue plastic package of the carbon dot/diatomite fluorescent composite powder prepared in comparative example 2, c is a fluorescent photograph showing a fingerprint of the surface of a red plastic package of the carbon dot/diatomite fluorescent composite powder prepared in example 1, and d is a fluorescent photograph showing a fingerprint of the surface of a blue plastic package of the carbon dot/diatomite fluorescent composite powder prepared in example 1. As can be seen from fig. 14, for the latent fingerprint on the surface of the impermeable object with background fluorescence interference, the carbon dot/diatomite fluorescent composite powder prepared in example 1 of the present invention has the advantages of higher fingerprint definition, more obvious contrast with the background, stronger background interference resistance, and significantly better effect than the carbon dot/diatomite fluorescent composite powder prepared in comparative example 2.

Comparative example 3

(1) Preparation of carbon dot solution: 0.5G of rhodamine 6G is weighed and added into a beaker, then 20mL of deionized water is weighed and added, and the rhodamine 6G is completely dissolved by ultrasonic treatment for 5 min. The obtained solution is added into a 50mL stainless steel reaction kettle with a PPL liner and reacted for 2h under the hydrothermal condition of 190 ℃. After the reaction is finished, cooling to room temperature, centrifuging the obtained mixed solution at 8000rpm for 10min, filtering the supernatant by using a nylon 6 microporous filter membrane with the pore diameter of 0.22 mu m, filling the filtrate into a dialysis bag with the molecular weight cutoff of 1000Da, dialyzing for 48h by using deionized water, and diluting the carbon dot solution obtained from the dialysis bag to 1mg/mL by using the deionized water to obtain the carbon dot solution.

(2) 1g of commercially available micron-sized silica is weighed into a beaker, and then 20mL of deionized water is weighed into the beaker, and the mixture is stirred uniformly to obtain a silica suspension.

(3) To the above silica suspension, 10mL of a carbon dot solution was added and sonicated at 250W power for 30 min. And finally, drying the mixed solution at 40 ℃ for 24 hours in vacuum to obtain the carbon dot/silicon dioxide fluorescent composite powder.

The carbon dot/silica fluorescent composite powder prepared by the comparative example was used to visualize the latent fingerprints on the surface of the impermeable object, and the visualization and photographing methods were the same as those of example 1, and the results are shown in fig. 15. Fig. 15 is a fluorescent photograph showing fingerprints on the surface of the impermeable object of the carbon dot/silica fluorescent composite powder prepared in comparative example 3, wherein a is a fluorescent photograph showing fingerprints on the surface of glass of the carbon dot/silica fluorescent composite powder, and b is a fluorescent photograph showing fingerprints on the surface of red plastic package of the carbon dot/silica fluorescent composite powder. As can be seen by comparing a in fig. 15 with b in fig. 5, for the potential fingerprint on the surface of the glass object without background fluorescence interference, the carbon dot/diatomite fluorescent composite powder prepared in example 1 of the present invention shows higher fingerprint definition, more obvious contrast with the background, and the effect is obviously better than the effect of the carbon dot/silica fluorescent composite powder prepared in comparative example 3; as can be seen from a comparison between b in fig. 15 and c in fig. 14, for the potential fingerprint on the surface of the red plastic package with background fluorescence interference, the carbon dot/diatomite fluorescent composite powder prepared in example 1 of the present invention shows higher fingerprint definition, more obvious contrast with the background, and a better effect than the carbon dot/silica fluorescent composite powder prepared in comparative example 3. It is illustrated that although the carbon dot/diatomite fluorescent composite powder prepared in example 1 and the carbon dot/silica fluorescent composite powder prepared in comparative example 3 contain the same carbon dots as a luminescent component, the dispersion effect of purified diatomite on the carbon dots is better than that of commercially available micron-sized silica on the carbon dots, so that the carbon dot/diatomite fluorescent composite powder prepared in example 1 has higher fluorescence intensity and better fingerprint appearance effect.

Claims

1. The carbon dot/diatomite fluorescent composite powder is characterized in that: the composite powder comprises carbon dots and purified diatomite, wherein the carbon dots are dispersed in a mesoporous structure of the purified diatomite and are obtained by a hydrothermal reaction of rhodamine 6G dissolved in water.

2. The method for preparing the carbon dot/diatomite fluorescent composite powder according to claim 1, which is characterized by comprising the following steps:

3. The method for preparing the carbon dot/diatomite fluorescent composite powder according to claim 2, wherein in the step (1), the solid-to-liquid ratio of rhodamine 6G to water is 20-30 mg/mL, and the hydrothermal reaction is performed at 180-200 ℃ for 1-3 h.

4. The method for preparing the carbon dot/diatomite fluorescent composite powder according to claim 2, wherein in the step (2), the concentration of the hydrochloric acid solution is 0.5-1.0 mol/L, the solid-to-liquid ratio of the diatomite to the hydrochloric acid solution is 0.05-0.1 g/mL, the heating and stirring are performed at 50-70 ℃ for 1-3 h, and the calcination is performed at 450-550 ℃ for 1-3 h.

5. The method for preparing the carbon dot/diatomite fluorescent composite powder according to claim 2, wherein in the step (2), the calcination is performed in an air atmosphere, the solid-to-liquid ratio of the diatomite powder to the saturated sucrose solution is 0.1-0.3 g/mL, and the rotation speed during the low-speed centrifugation is 1500-2500 rpm.

6. The method for preparing the carbon dot/diatomite fluorescent composite powder according to claim 2, wherein in the step (3), the solid-to-liquid ratio of the purified diatomite to the water is 40-60 mg/mL, and the mass ratio of the diatomite to the carbon dot in the mixed liquid is 100-800: 1.

7. the preparation method of the carbon dot/diatomite fluorescent composite powder according to claim 2, wherein in the step (3), ultrasonic mixing is performed for 10-30 min under the power of 180-250W, and vacuum drying is performed for 12-24 h under the condition of 40-60 ℃.

8. Use of the carbon dot/diatomaceous earth fluorescent composite powder of claim 1 for latent fingerprint development.

9. The use of claim 8, wherein the use comprises the visualization of latent fingerprints on non-permeable guest surfaces with or without background fluorescence interference.

10. A method for latent fingerprint appearance comprising the steps of:

dipping the carbon dot/diatomite fluorescent composite powder of claim 1 with a brush, flicking the carbon dot/diatomite fluorescent composite powder with a brush handle to uniformly shake the carbon dot/diatomite fluorescent composite powder onto a to-be-displayed area, brushing the brush tip lightly, then displaying the fingerprint lines along the lines after the fingerprint lines appear until the fingerprint lines are clear, and taking a fluorescent photo showing the fingerprint by using a digital single-lens reflex camera with a filter in a darkroom environment by using a multiband light source as an excitation light source.