Preparation method of floating type photo-thermal catalyst and application of floating type photo-thermal catalyst in degradation of blue-green algae

Abstract

The application discloses a preparation method of a floating type photo-thermal catalyst and application of the floating type photo-thermal catalyst in degradation of blue algae. First, graphite phase carbon nitride is modified by polydopamine, then graphite phase carbon nitride / silver molybdate is synthesized by a chemical precipitation method at room temperature, and then the graphite phase carbon nitride / silver molybdate is loaded on melamine sponge by cross-linking of sodium alginate and calcium ions, and by controlling adding parameters of each preparation raw material, the floating type photo-thermal catalyst, melamine sponge loaded graphite phase carbon nitride / silver molybdate, which has good photo-thermal catalytic performance and is convenient to recycle, is constructed. The application has the advantages of mild synthesis conditions and simple method, and overcomes the defects of long time, high energy consumption and poor repeatability of a traditional hydrothermal method, and the prepared floating type photo-thermal catalyst is convenient to recycle, has good photo-thermal conversion effect and photo-generated charge separation efficiency under visible light (λ>=420 nm) irradiation, and the degradation rate is above 99% in 150 min.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photocatalytic algae removal, and particularly relates to a preparation method of a floating type photo-thermal catalyst and application of the floating type photo-thermal catalyst in degradation of blue-green algae. BACKGROUND

[0002] Water bloom is a natural ecological phenomenon of algae proliferation in freshwater bodies, and is a feature of water eutrophication. It is mainly caused by the entry of waste water containing a large amount of nitrogen and phosphorus from life and industrial and agricultural production into water bodies, and a large number of harmful algae blooms such as blue-green algae, green algae and diatoms, which make the water bodies appear blue or green. The increase of harmful algae blooms and the various algal toxins produced thereby will pose a threat to the natural environment. Microcystis aeruginosa (M. aeruginosa) is one of the most common algae that causes harmful blue-green algae blooms in freshwater. It causes water quality deterioration and interferes with the survival of other organisms in the water body by consuming oxygen and releasing metabolites and microcystin (MCs). In addition to threatening phytoplankton and animals in the aquatic ecosystem, MCs also have hepatotoxicity, which eventually enters the human body through the food chain, causing human health problems. Therefore, it is of great significance to develop efficient, green and environmentally friendly new technologies to inhibit blue-green algae blooms.

[0003] As an environmentally friendly new technology for pollution control, photocatalysis technology has attracted much attention. This technology uses a semiconductor as a catalyst to absorb light energy, and uses the generated electrons and holes to participate in redox reactions. The strong oxidizing groups generated in the reaction can inhibit or kill algae cells, and at the same time, degrade and detoxify the released algal toxins, thereby achieving the purpose of photocatalytic algae removal and detoxification. However, different types of photocatalytic materials have different effects on photocatalytic degradation of algae. Even the same photocatalytic material will produce different treatment effects when applied to the treatment of different algae pollution.

[0004] Non-metallic semiconductor graphite phase carbon nitride has good thermal stability and rich raw material availability, and can be obtained from a variety of cheap and readily available carbon / nitrogen-rich precursors (such as dicyanamide, cyanamide, melamine and urea), which has potential for photocatalytic applications. However, graphite phase carbon nitride also has some defects, such as limited specific surface area, easy recombination of photo-generated electrons and holes, small number of exposed active sites, and low visible light utilization rate. These defects reduce the light absorption efficiency of graphite phase carbon nitride-based photocatalysts, shorten the lifetime of photo-generated carriers, and limit their photocatalytic performance.

[0005] In actual algae removal applications, in order to overcome the shortcomings of the powdered photocatalyst, such as easy agglomeration, precipitation, difficult recovery and secondary pollution in water bodies, the photocatalyst needs to be loaded on a carrier to construct a floating photocatalyst, but this method has the following defects: (1) the existing floating carrier is not environmentally friendly and stable; (2) the existing carrier and the loading process of the photocatalyst are single, without considering the organic combination of the two; (3) after the powdered photocatalyst is loaded on the carrier, the contact area of the photocatalyst and the algae is reduced, thereby affecting the algae removal effect.

[0006] Patent application with publication number CN105728010A discloses a preparation method of an antibacterial silver molybdate graphite phase carbon nitride composite visible light catalyst, which uses a hydrothermal method to synthesize the photocatalyst, has high energy consumption, long reaction time and a complex process, and the photocatalyst is applied to degrade rhodamine B. Patent application with publication number CN110465321A discloses a preparation method of a silver molybdate / carbon nitride composite visible light catalyst, which has a simple synthesis method, but does not solve the above-mentioned problems of graphite phase carbon nitride, and the photocatalyst is applied to degrade methyl orange. In addition, the two patent applications do not solve the actual problems of the powdered photocatalyst, such as easy agglomeration, precipitation, difficult recovery and secondary pollution. SUMMARY

[0007] The purpose of the present application is to overcome the problems existing in the prior art, provide a preparation method of a floating photocatalyst and its application in degrading blue-green algae, control the addition parameters of each raw material, reasonably control the matching and loading effect of graphite phase carbon nitride / silver molybdate and the carrier melamine sponge, thereby improving the ability of the floating photocatalyst to degrade Microcystis aeruginosa. Under visible light (λ≥420 nm) irradiation, the floating photocatalyst has good photo-thermal conversion effect and photo-generated charge separation efficiency, and can photo-thermally catalyze and remove Microcystis aeruginosa in 150 min, with a degradation rate of more than 99%.

[0008] The technical scheme of the present application is as follows:

[0009] The present application provides a preparation method of a floating photocatalyst, comprising the following steps:

[0010] (1) forging melamine, cooling to room temperature, taking out, grinding into powder, then performing secondary forging under the same conditions, and grinding to obtain graphite phase carbon nitride;

[0011] (2) taking the graphite phase carbon nitride obtained in step (1) and adding it into a tris-hydroxymethyl aminomethane hydrochloride buffer solution, dispersing uniformly, then adding dopamine hydrochloride, adjusting the pH value of the solution to 8.5, stirring uniformly, and washing, drying and grinding the product to obtain modified graphite phase carbon nitride;

[0012] (3) dispersing the modified graphite phase carbon nitride obtained in step (2) in deionized water, adding silver nitrate, stirring uniformly in dark conditions, then adding sodium molybdate solution drop by drop, stirring uniformly, and obtaining graphite phase carbon nitride / silver molybdate after washing the product with ethanol and deionized water, drying, and grinding;

[0013] (4) ultrasonic cleaning, drying, and reserving melamine sponge after cleaning with acetone, 15% hydrochloric acid, anhydrous ethanol, and deionized water respectively;

[0014] (5) dispersing the graphite phase carbon nitride / silver molybdate obtained in step (3) in deionized water, adding sodium alginate, and stirring vigorously to form a gelatinous suspension, putting the melamine sponge treated in step (4) into the gelatinous suspension to make it absorb the suspension fully, then putting the melamine sponge fully absorbing the suspension into a calcium chloride solution to make the sodium alginate crosslink with calcium ions, taking out after solidification, and obtaining a floating type photo-thermal catalyst after washing with deionized water and drying.

[0015] Preferably, in step (1), the calcination temperature of melamine is 400-600℃, the temperature rising rate is 2.5-5℃ / min, and the calcination time is 3-5h. More preferably, the calcination temperature of melamine is 500-550℃, the temperature rising rate is 3-5℃ / min, and the calcination time is 4-5h.

[0016] Preferably, in step (2), the mass fraction of graphite phase carbon nitride is 0.4-0.6 parts, the concentration of tris-hydroxymethyl aminomethane hydrochloride buffer solution is 7.5-12.5mM, and the volume fraction is 45-55 parts. The dispersion adopts ultrasonic dispersion, the ultrasonic frequency is 60-80 Hz, and the ultrasonic dispersion time is 15-25min. More preferably, the mass fraction of graphite phase carbon nitride is 0.5-0.6 parts, the concentration of tris-hydroxymethyl aminomethane hydrochloride buffer solution is 10-12mM, and the volume fraction is 50-55 parts. The dispersion adopts ultrasonic dispersion, the ultrasonic frequency is 60-70 Hz, and the ultrasonic dispersion time is 20-25min.

[0017] Preferably, in step (2), the mass fraction of dopamine hydrochloride is 0.02-0.09 parts, the stirring time is 22-26h, the drying temperature is 50-70℃, and the drying time is 8-12h. More preferably, the mass fraction of dopamine hydrochloride is 0.056-0.08 parts, the stirring time is 22-24h, the drying temperature is 60-70℃, and the drying time is 10-12h.

[0018] Preferably, in step (3), the mass fraction of the modified graphite phase carbon nitride is 0.3-0.5 parts, the volume fraction of deionized water is 80-120 parts, and the ultrasonic uniform dispersion time is 25-35 min. The mass fraction of silver nitrate is 0.13-0.22 parts, and the stirring time is 0.5-1.5 h. More preferably, the mass fraction of the modified graphite phase carbon nitride is 0.4-0.5 parts, the volume fraction of deionized water is 100-120 parts, and the ultrasonic uniform dispersion time is 30-35 min. The mass fraction of silver nitrate is 0.1528-0.2000 parts, and the stirring time is 1-1.5 h.

[0019] Preferably, in step (3), the mass fraction of the modified graphite phase carbon nitride is 0.3-0.5 parts, the volume fraction of deionized water is 80-120 parts, and the ultrasonic uniform dispersion time is 25-35 min. The mass fraction of silver nitrate is 0.13-0.22 parts, and the stirring time is 0.5-1.5 h. More preferably, the mass fraction of the modified graphite phase carbon nitride is 0.4-0.5 parts, the volume fraction of deionized water is 100-120 parts, and the ultrasonic uniform dispersion time is 30-35 min. The mass fraction of silver nitrate is 0.1528-0.2000 parts, and the stirring time is 1-1.5 h.

[0020] Preferably, in step (4), the density of the melamine sponge is 8.5-10 kg / m 3 , the length is 2-4 cm, the width is 2-4 cm, the height is 1-2 cm, the ultrasonic cleaning time is 25-35 min, the drying temperature is 50-70℃, and the drying time is 4-8 h. More preferably, the density of the melamine sponge is 8.5 kg / m 3 , the length is 3 cm, the width is 3 cm, the height is 1.5 cm, the ultrasonic cleaning time is 30-35 min, the drying temperature is 60-70℃, and the drying time is 6-8 h.

[0021] Preferably, in step (5), the mass fraction of the graphite phase carbon nitride / silver molybdate is 0.18-0.25 parts, the volume fraction of deionized water is 20-30 parts, and the ultrasonic time is 3-7 min. More preferably, the mass fraction of the graphite phase carbon nitride / silver molybdate is 0.20-0.23 parts, the volume fraction of deionized water is 25-30 parts, and the ultrasonic time is 5-7 min.

[0022] Preferably, the loading amount of the graphite phase carbon nitride / silver molybdate on the melamine sponge is 0.013-0.019 g / cm 3 .

[0023] Preferably, in step (5), the mass fraction of sodium alginate is 0.04-0.06 parts, the mass concentration of the calcium chloride solution is 2-5%, the volume fraction is 50-70 parts, the solidification time is 6-10 h, the drying temperature is 50-70 DEG C, and the drying time is 8-12 h.

[0024] The application further provides a floating type photo-thermal catalyst prepared by the method.

[0025] The application further provides application of the floating type photo-thermal catalyst in degradation of blue-green algae.

[0026] Preferably, the blue-green algae is Microcystis aeruginosa, and the application method comprises: adding the floating type photo-thermal catalyst into water containing Microcystis aeruginosa, and irradiating the water containing Microcystis aeruginosa under visible light (lambda >= 420 nm) for 150 min or more, so that the degradation rate of Microcystis aeruginosa is >= 99%.

[0027] Preferably, the addition amount of the floating type photo-thermal catalyst is 0.4-1.0 g / L.

[0028] Preferably, the initial algal density of Microcystis aeruginosa in the water is 0.4-0.7 in terms of optical density OD at a wavelength of 680 nm. 680

[0029] The application has the following beneficial effects:

[0030] 1. The floating type photo-thermal catalyst provided by the application can be applied in the field of photo-thermal catalytic removal of Microcystis aeruginosa. Microcystis aeruginosa has phototaxis, so it gathers and grows on the surface of water. The floating type photo-thermal catalyst, melamine sponge loaded with graphite phase carbon nitride / silver molybdate, can not only increase the contact area with Microcystis aeruginosa without stirring, but also improve the utilization rate of sunlight and active free radicals, so as to obtain a better photo-thermal catalytic algae removal effect. After irradiation for 150 min under visible light (lambda >= 420 nm), the degradation efficiency of the floating type photo-thermal catalyst on Microcystis aeruginosa is >= 99%, which is equivalent to the case without using a carrier (melamine sponge), which shows that the application solves the problem that the contact area of a powder type photocatalyst loaded on a carrier is reduced to affect the algae removal effect.

[0031] ​2、The application adopts a chemical precipitation method at room temperature to synthesize the floating type photo-thermal catalyst melamine sponge loaded graphite phase carbon nitride / silver molybdate, and most of the prior art adopts a hydrothermal method, a solvothermal method or a solid phase reaction method, and the reaction time is long, the energy consumption is high, the repeatability is poor and a certain danger exists, and the synthesis method of the application has mild synthesis conditions, is simple and safe to operate.

[0032] The application also improves the matching and loading effect of the graphite phase carbon nitride / silver molybdate and the carrier melamine sponge by controlling the addition amount of dopamine hydrochloride, silver nitrate, sodium molybdate dihydrate and sodium alginate during preparation of the photo-thermal catalyst, thereby improving the effect of the floating type photo-thermal catalyst on degradation of Microcystis aeruginosa.

[0033] 3、The biomimetic carbon material polydopamine has a conjugated pi structure, good electron transmission capacity and light trapping capacity. The electron delocalization between the pi-pi conjugated structure of the graphite phase carbon nitride and the polydopamine can produce a synergistic effect to promote carrier transfer.

[0034] The application utilizes the polymerization reaction of dopamine hydrochloride in an alkaline tris-hydroxymethyl aminomethane hydrochloride solution to form polydopamine, and utilizes the synergistic effect of electron delocalization between the polydopamine and the graphite phase carbon nitride to promote light trapping and photo-generated carrier migration. In addition, after the graphite phase carbon nitride is modified by the polydopamine, the material gradually changes from the original light yellow to dark brown, and the dark color property is conducive to full absorption of sunlight (from the ultraviolet region to the near infrared region) by the material and further conversion into heat energy to promote the light-heat synergistic catalytic reaction, thereby improving the utilization rate of solar energy by the material.

[0035] 4、The floating carrier selected in the application is melamine sponge, and compared with other floating carriers, the melamine sponge is an environmentally friendly, clean lightweight material with the advantages of mildew resistance, antibacterial property, acid and alkali resistance, high stability and the like. Therefore, the application loads the chemically stable powder-shaped graphite phase carbon nitride / silver molybdate onto the melamine sponge through cross-linking between sodium alginate and calcium ions, not only solves the problems of easy agglomeration and precipitation of the powder, but also facilitates recycling of the photo-thermal catalyst and improves the recycling property.

[0036] Figure 1 X-ray diffraction pattern of the floating type photo-thermal catalyst prepared in the present application;

[0037] Figure 2 X-ray photoelectron spectrogram of the floating type photo-thermal catalyst prepared in the present application, wherein (a) is the full spectrogram of the elements contained in the sample, (b) is the fine spectrogram of C element 1s orbital, (c) is the fine spectrogram of N element 1s orbital, (d) is the fine spectrogram of O element 1s orbital, (e) is the fine spectrogram of Ag element 3d orbital, and (f) is the fine spectrogram of Mo element 3d orbital;

[0038] Figure 3 Scanning electron microscope image of the floating type photo-thermal catalyst prepared in the present application;

[0039] Figure 4 Ultraviolet-visible diffuse reflectance spectrogram of the floating type photo-thermal catalyst prepared in the present application;

[0040] Figure 5 Infrared thermal imaging image of the floating type photo-thermal catalyst prepared in the present application, wherein (a) is melamine sponge, and (b) is melamine sponge loaded with graphite phase carbon nitride / silver molybdate;

[0041] Figure 6 Effect of the proportion of silver molybdate and the amount of sodium alginate added on the algae removal effect of the floating type photo-thermal catalyst;

[0042] Figure 7 Effect of the amount of dopamine hydrochloride added on the algae removal effect of the floating type photo-thermal catalyst;

[0043] Figure 8 Effect of the concentration of calcium chloride solution on the algae removal effect of the floating type photo-thermal catalyst;

[0044] Figure 9 Effect of the loading amount of graphite phase carbon nitride / silver molybdate on melamine sponge on the algae removal effect of the floating type photo-thermal catalyst;

[0045] Figure 10 Effect of the density of melamine sponge on the algae removal effect of the floating type photo-thermal catalyst. DETAILED DESCRIPTION

[0046] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0047] Unless otherwise specified, the reagents involved in the embodiments of the present application are all commercially available products, which can be purchased through commercial channels.

[0048] I. Preparation of floating photothermal catalyst (g-C3N4 / Ag2MoO4@MS) Example 1

[0049] (1) 8 g of melamine was weighed into a covered crucible and placed in a muffle furnace for calcination. The temperature was raised to 550℃ at a rate of 5℃ / min, and the sample was kept at this temperature for 4 h. After cooling to room temperature, the sample was ground into powder. Then, the sample was subjected to secondary calcination under the same conditions, and after grinding, graphite phase carbon nitride was obtained.

[0050] (2) 0.5 g of graphite phase carbon nitride obtained in step (1) was added to 50 mL of 10 mM Tris-HCl buffer solution, and ultrasonically dispersed for 20 min. Then, 0.056 g of dopamine hydrochloride was added, and the pH value of the solution was adjusted to 8.5. After stirring for 24 h, the product was washed with ethanol and deionized water, and dried at 60℃ for 12 h. After grinding, modified graphite phase carbon nitride was obtained.

[0051] (3) 0.4 g of modified graphite phase carbon nitride obtained in step (2) was added to 100 mL of deionized water, and ultrasonically dispersed for 30 min. Then, 0.1528 g of silver nitrate was added, and the mixture was stirred in the dark for 1 h. Then, 0.2178 g of sodium molybdate dihydrate was dissolved in 5 mL of deionized water, and the solution was added dropwise to the above mixture under dark conditions. After stirring for 1 h, the product was washed with ethanol and deionized water, and dried at 60℃ for 12 h. After grinding, graphite phase carbon nitride / molybdate silver was obtained.

[0052] (4) Melamine sponge with a density of 8.5 kg / m 3 , size of 3 cm x 3 cm x 1.5 cm was ultrasonically cleaned with acetone, 15% hydrochloric acid, anhydrous ethanol and deionized water for 30 min, and dried at 60℃ for 6 h.

[0053] (5) 0.2 g of graphite phase carbon nitride / molybdate silver obtained in step (3) was ultrasonically dispersed in 25 mL of deionized water, and 0.05 g of sodium alginate was added. The mixture was stirred vigorously to form a gel-like suspension. The melamine sponge treated in step (4) was placed in the gel-like suspension, and the sponge was allowed to fully absorb the suspension. Then, the melamine sponge fully absorbing the suspension was placed in a 60 mL 2% calcium chloride solution, and the cross-linking reaction between sodium alginate and calcium ions was allowed to occur. After solidification for 8 h, the sponge was taken out, washed with deionized water, and dried at 60℃ for 12 h. Floating photothermal catalyst melamine sponge loaded graphite phase carbon nitride / molybdate silver (g-C3N4 / Ag2MoO4@MS) was obtained. Example 2

[0054] (1) 8 g of melamine was weighed into a covered crucible and placed in a muffle furnace for calcination. The temperature was raised to 550 °C at a rate of 3 °C / min and maintained for 5 h. After cooling to room temperature, the product was ground into powder. Then, secondary calcination was carried out under the same conditions, and the product was ground to obtain graphite-phase carbon nitride.

[0055] (2) 0.4 g of graphite-phase carbon nitride obtained in step (1) was added to 55 mL of 7.5 mM tris-hydroxymethyl aminomethane hydrochloride buffer solution, ultrasonically dispersed for 15 min, then 0.02 g of dopamine hydrochloride was added, and the pH value of the solution was adjusted to 8.5. After stirring for 22 h, the product was washed with ethanol and deionized water, and dried at 65 °C for 11 h. After grinding, modified graphite-phase carbon nitride was obtained.

[0056] (3) 0.3 g of modified graphite-phase carbon nitride obtained in step (2) was added to 80 mL of deionized water, ultrasonically dispersed for 25 min, and 0.1333 g of silver nitrate was added. After stirring in the dark for 0.5 h, a mixed solution was obtained. Then, 0.1898 g of sodium molybdate dihydrate was dissolved in 6 mL of deionized water, and the above mixed solution was added dropwise under dark conditions. After stirring for 0.5 h, the product was washed with ethanol and deionized water, and dried at 50 °C for 12 h. After grinding, graphite-phase carbon nitride / silver molybdate was obtained.

[0057] (4) Melamine sponge with a density of 8.5 kg / m 3 , size of 3 cm x 3 cm x 1.5 cm was ultrasonically cleaned with acetone, 15% hydrochloric acid, anhydrous ethanol and deionized water for 30 min, and dried at 65 °C for 7 h.

[0058] (5) 0.18 g of graphite-phase carbon nitride / silver molybdate obtained in step (3) was ultrasonically dispersed in 20 mL of deionized water, and 0.045 g of sodium alginate was added. After vigorous stirring, a gel-like suspension was formed. The melamine sponge treated in step (4) was placed in the gel-like suspension to fully absorb the suspension. Then, the melamine sponge fully absorbing the suspension was placed in 65 mL of 3% calcium chloride solution to allow the cross-linking reaction of sodium alginate and calcium ions. After solidification for 9 h, it was taken out, washed with deionized water, and dried at 65 °C for 11 h to obtain a floating type photo-thermal catalyst, melamine sponge loaded graphite-phase carbon nitride / silver molybdate. Example 3

[0059] (1) 8 g of melamine was weighed into a covered crucible and placed in a muffle furnace for calcination. The temperature was raised to 600 °C at a rate of 4 °C / min and maintained for 3 h. After cooling to room temperature, the product was ground into powder. Then, secondary calcination was carried out under the same conditions, and the product was ground to obtain graphite-phase carbon nitride.

[0060] (2) 0.6 g of the graphite phase carbon nitride obtained in step (1) is added into 45 mL of 12.5 mM tris-hydroxymethyl aminomethane hydrochloride buffer solution, ultrasonic dispersion is carried out for 25 min, then 0.09 g of dopamine hydrochloride is added, and the pH value of the solution is adjusted to 8.5, stirring is carried out for 26 h, the product is washed with ethanol and deionized water, and drying is carried out at 70 DEG C for 10 h, and after grinding, modified graphite phase carbon nitride is obtained.

[0061] (3) 0.5 g of the modified graphite phase carbon nitride obtained in step (2) is added into 120 mL of deionized water, ultrasonic dispersion is carried out for 35 min, 0.2154 g of silver nitrate is added, stirring is carried out in dark conditions for 1.5 h, and a mixed solution is obtained. Then, 0.3067 g of sodium molybdate dihydrate is dissolved in 4.4 mL of deionized water, and the above mixed solution is added dropwise in dark conditions, stirring is carried out for 1.5 h, the product is washed with ethanol and deionized water, and drying is carried out at 70 DEG C for 10 h, and after grinding, graphite phase carbon nitride / silver molybdate is obtained.

[0062] (4) melamine sponge with a density of 8.5 kg / m 3 , and a size of 3 cm x 3 cm x 1.5 cm is ultrasonic cleaned with acetone, 15% hydrochloric acid, anhydrous ethanol and deionized water respectively for 35 min, and drying is carried out at 70 DEG C for 6 h, and the melamine sponge is prepared.

[0063] (5) 0.25 g of the graphite phase carbon nitride / silver molybdate obtained in step (3) is ultrasonic dispersed in 30 mL of deionized water, 0.04 g of sodium alginate is added, and a gel-like suspension is formed by stirring. The melamine sponge prepared in step (4) is put into the gel-like suspension, and the melamine sponge is allowed to fully absorb the suspension. Then, the melamine sponge fully absorbing the suspension is put into 70 mL of 2% calcium chloride solution, and a cross-linking reaction between sodium alginate and calcium ions is allowed to occur, and after solidification for 10 h, the melamine sponge is taken out, washed with deionized water, and dried at 70 DEG C for 10 h, and a floating type photo-thermal catalyst melamine sponge loaded graphite phase carbon nitride / silver molybdate is obtained.

[0064] II. Structure characterization of the floating type photo-thermal catalyst

[0065] The characteristics of the floating type photo-thermal catalyst (melamine sponge loaded polydopamine modified graphite phase carbon nitride / silver molybdate) prepared in the application are further characterized by X-ray diffraction patterns, X-ray photoelectron spectrograms, scanning electron microscope patterns, ultraviolet visible diffuse reflectance spectrograms and infrared thermal imaging patterns.

[0066] From the above, it can be seen that the floating type photo-thermal catalyst melamine sponge loaded polydopamine modified graphite phase carbon nitride / silver molybdate prepared in the application has the following advantages: Figure 1The X-ray diffraction pattern shows that the XRD diffraction peaks of the floating photothermal catalyst at 2θ = 27.4°, 29.8°, 32.6°, 40.3°, 44.7°, 56.5°, and 58.2° correspond to the (212), (004), (310), (115), (402), (424), and (503) crystal planes of the tetragonal α-Ag₂MoO₄ standard card (PDF#21-1340), respectively. This demonstrates the successful synthesis of the floating photothermal catalyst (melamine sponge-supported polydopamine-modified graphitic carbon nitride / silver molybdate).

[0067] from Figure 2 The X-ray photoelectron spectroscopy (XPS) spectrum shows that the graphitic carbon nitride / silver molybdate mainly contains five elements: C, N, O, Ag, and Mo. C, N, and O originate from the graphitic carbon nitride and polydopamine, while Ag and Mo originate from silver molybdate. The high-resolution XPS spectrum of the C 1s orbital exhibits strong characteristic peaks at 284.8 V, 286.33 eV, and 288.52 eV, which are attributed to the C / C bonds and CO bonds in the triazine ring, and the sp bonds on the N aromatic ring, respectively. 2 The high-resolution XPS spectrum of the NC=N N 1s orbital in hybrid carbon exhibits strong characteristic peaks at 397.28 eV, 398.81 eV, and 400.30 eV, which are attributed to the sp orbitals in CN=C, respectively. 2 The hybrid nitrogen atom, tertiary amine nitrogen structure N-(C)3, and hydrocarbon single bond NH. The high-resolution XPS spectrum of the O 1s orbital shows strong characteristic peaks at 530.35 V, 531.87 eV, and 532.97 eV, which are attributed to the Mo-O bond in silver molybdate, surface hydroxyl oxygen / defective oxygen, and adsorbed water / surface adsorbed oxygen, respectively. The high-resolution XPS spectrum of the Ag 3d orbital shows characteristic peaks at 368.08 eV and 374.08 eV, which are attributed to the Ag 3d... 5 / 2 and Ag3d 3 / 2 All belong to Ag + The high-resolution XPS spectra of the Mo 3d orbitals show characteristic peaks at 232.18 eV and 235.32 eV, which are attributed to Mo 3d orbitals. 5 / 2 and Mo3d 3 / 2 , all belong to Mo 6+ .

[0068] from Figure 3 As can be seen from the scanning electron microscope images, in the graphitic carbon nitride / silver molybdate prepared in this invention, the graphitic carbon nitride coated with polydopamine exhibits a relatively rough layered stacked structure, and the silver molybdate crystals are tightly anchored on the surface of the graphitic carbon nitride with an irregular morphology, indicating the successful synthesis of graphitic carbon nitride / silver molybdate.

[0069] fromFigure 4 The UV-Vis diffuse reflectance spectrum shows that graphitic carbon nitride / silver molybdate has strong absorption capacity in the visible and even near-infrared regions. This is because after modifying graphitic carbon nitride with polydopamine, the material gradually changes from the original light yellow to brownish-black, and the light absorption capacity of graphitic carbon nitride / silver molybdate is greatly enhanced. Therefore, the material has good light response in the entire wavelength range.

[0070] from Figure 5 The infrared thermal imaging shows that, compared to melamine sponge, melamine sponge loaded with graphitic carbon nitride / silver molybdate has stronger photothermal conversion performance. After 120s of visible light (λ≥420 nm) irradiation, the temperature increased from 41.6℃ to 99.1℃. This is because the layered stacked structure of graphitic carbon nitride / silver molybdate is conducive to multiple scattering of incident light, enhancing the absorption of light by the composite material, thereby producing a stronger photothermal effect.

[0071] III. Algae Removal Effect of Floating Photothermal Catalysts

[0072] 1. Algae Removal Test Method

[0073] The photocatalytic algae removal process was carried out in a 250mL jacketed beaker, using a 300W xenon lamp to simulate sunlight. An ultraviolet filter was added to block ultraviolet light with a wavelength of λ < 420 nm, and the distance between the algae solution surface and the 300W xenon lamp light source was fixed at 15cm. The algae density (OD) was based on typical algae density in eutrophic water bodies. 680 ≈0.6) was used as the initial algal density. 100 mL of algal solution was placed in a jacketed beaker, and the prepared floating photothermal catalyst (melamine sponge-supported polydopamine-modified graphitic carbon nitride / silver molybdate, 50 mg) was added. The solution was allowed to adsorb in the dark for 30 min to reach adsorption-desorption equilibrium on the catalyst surface. After irradiation with visible light (λ≥420 nm) for 150 min, 3 mL of algal solution was collected every 30 min, and the concentration change of chlorophyll a in the solution was measured using a UV-Vis spectrophotometer. This was used to evaluate the removal efficiency of the floating photothermal catalyst melamine sponge-supported graphitic carbon nitride / silver molybdate on *Microcystis aeruginosa*.

[0074] Wherein, algae removal rate (%) = 100% × (1 - C) t / C0), where C0 is the initial concentration of chlorophyll a, C t This represents the current concentration of chlorophyll a.

[0075] 2. The effect of the proportion of silver molybdate in floating photothermal catalysts

[0076] The proportion of silver molybdate in the floating type photo-thermal catalyst was controlled by changing the adding amount of silver nitrate and sodium molybdate dihydrate, and the influence of the proportion of silver molybdate on the algae removal effect of the floating type photo-thermal catalyst was verified. On the basis of Example 1, Comparative Example 1 to Comparative Example 3 were set:

[0077] Comparative Example 1

[0078] The difference between the present comparative example and Example 1 is that the mass of silver nitrate in step (3) is 0.0402 g, and the mass of sodium molybdate dihydrate is 0.0572 g.

[0079] Comparative Example 2

[0080] The difference between the present comparative example and Example 1 is that the mass of silver nitrate in step (3) is 0.0904 g, and the mass of sodium molybdate dihydrate is 0.1288 g.

[0081] Comparative Example 3

[0082] The difference between the present comparative example and Example 1 is that the mass of silver nitrate in step (3) is 0.2412 g, and the mass of sodium molybdate dihydrate is 0.3436 g.

[0083] The results are shown in Table 1 and Figure 6 It can be seen that the proportion of silver molybdate in the floating type photo-thermal catalyst has a significant influence on the algae removal effect. According to the method of Example 1, the content of silver molybdate is controlled, and the floating type photo-thermal catalyst prepared has a removal efficiency of 99.25% for Microcystis aeruginosa after visible light (λ≥420 nm) irradiation for 150 min, which is much higher than that of Comparative Example 1 to Comparative Example 3.

[0084] Table 1

[0085]

[0086] 3, Influence of the adding amount of sodium alginate

[0087] By changing the adding amount of sodium alginate, the influence of the adding amount of sodium alginate on the algae removal effect of the floating type photo-thermal catalyst was verified. On the basis of Example 1, Comparative Example 4 to Comparative Example 6 were set:

[0088] Comparative Example 4

[0089] The difference between the present comparative example and Example 1 is that the mass of sodium alginate in step (5) is 0.03 g.

[0090] Comparative Example 5

[0091] The difference between the present comparative example and Example 1 is that the mass of sodium alginate in step (5) is 0.1 g.

[0092] Comparative Example 6

[0093] The difference between the present comparative example and example 1 is that the mass of sodium alginate in step (5) is 0.15 g.

[0094] The results are shown in Table 2 and Figure 6 It can be seen that the addition amount of sodium alginate has a significant effect on the algae removal effect, and the addition of an appropriate amount of sodium alginate can promote the loading of graphite phase carbon nitride / silver molybdate on the melamine sponge, however, when the sodium alginate continues to increase, the pores of the melamine sponge are gradually filled, resulting in pore blockage, reducing light absorption, and too much sodium alginate will cover the active sites, thereby inhibiting the photocatalytic process. Compared with comparative examples 4 to 6, by controlling the addition amount of sodium alginate according to the method of example 1 of the present application, the prepared floating type photo-thermal catalyst has a better algae removal effect.

[0095] Table 2

[0096]

[0097] 4, Influence of the addition amount of dopamine hydrochloride

[0098] By changing the addition amount of dopamine hydrochloride, the influence of the addition amount of dopamine hydrochloride on the algae removal effect of the floating type photo-thermal catalyst was verified, and comparative examples 7 and 8 were set based on example 1.

[0099] Comparative example 7

[0100] The difference between the present comparative example and example 1 is that the mass of dopamine hydrochloride in step (2) is 0.01 g.

[0101] Comparative example 8

[0102] The difference between the present comparative example and example 1 is that the mass of dopamine hydrochloride in step (2) is 0.125 g.

[0103] The results are shown in Table 3 and Figure 7 It can be seen that the addition amount of dopamine hydrochloride has a significant effect on the algae removal effect, and compared with comparative examples 7 and 8, by controlling the addition amount of dopamine hydrochloride according to the method of example 1 of the present application, the graphite phase carbon nitride is moderately modified, and the prepared floating type photo-thermal catalyst has a better algae removal effect.

[0104] Table 3

[0105]

[0106] 5, Influence of the concentration of calcium chloride solution

[0107] By changing the concentration of the calcium chloride solution, the influence of the concentration of the calcium chloride solution on the algae removal effect of the floating type photo-thermal catalyst was verified, and comparative examples 9 and 10 were set based on example 1.

[0108] Comparative example 9

[0109] The difference between the present comparative example and Example 1 is that the concentration of the calcium chloride solution in step (5) is 1%.

[0110] Comparative Example 10

[0111] The difference between the present comparative example and Example 1 is that the concentration of the calcium chloride solution in step (5) is 5%.

[0112] The results are shown in Table 4 and Figure 8 It can be seen that the concentration of the calcium chloride solution has a significant effect on the algae removal effect. When the concentration of the calcium chloride solution in Comparative Example 9 is too low, the cross-linking effect of calcium chloride and sodium alginate is not obvious enough, which affects the loading of graphite phase carbon nitride / silver molybdate on melamine sponge. When the concentration of the calcium chloride solution in Comparative Example 10 is too high, the calcium chloride and sodium alginate are excessively cross-linked, which affects the active sites of the photothermal catalyst. According to the method of Example 1 of the present application, the concentration of the calcium chloride solution is controlled, and the prepared floating photothermal catalyst has a good algae removal effect.

[0113] Table 4

[0114]

[0115] 6. Effect of loading amount of graphite phase carbon nitride / silver molybdate on melamine sponge

[0116] By changing the loading amount of graphite phase carbon nitride / silver molybdate on melamine sponge, i.e. changing the addition amount of graphite phase carbon nitride / silver molybdate in step (5), the effect of the loading amount of graphite phase carbon nitride / silver molybdate on melamine sponge on the algae removal effect of the floating photothermal catalyst is verified. On the basis of Example 1 (the loading amount of graphite phase carbon nitride / silver molybdate on melamine sponge is 0.015 g / cm 3 ), Comparative Examples 11-13 are set up:

[0117] Comparative Example 11

[0118] The difference between the present comparative example and Example 1 is that the addition amount of graphite phase carbon nitride / silver molybdate in step (5) is 0.1 g, and at this time the loading amount of graphite phase carbon nitride / silver molybdate on melamine sponge is 0.007 g / cm 3 .

[0119] Comparative Example 12

[0120] The difference between the present comparative example and Example 1 is that the addition amount of graphite phase carbon nitride / silver molybdate in step (5) is 0.15 g, and at this time the loading amount of graphite phase carbon nitride / silver molybdate on melamine sponge is 0.011 g / cm 3 .

[0121] Comparative Example 13

[0122] The difference between the present comparative example and example 1 is that the amount of graphite phase carbon nitride / silver molybdate added in step (5) is 0.3 g, and at this time the loading amount of graphite phase carbon nitride / silver molybdate on the melamine sponge is 0.022 g / cm 3 .

[0123] The results are shown in Table 5 and Figure 9 It can be seen that the loading amount of graphite phase carbon nitride / silver molybdate on the melamine sponge has a significant effect on the algae removal effect, and compared with comparative examples 11-13, the floating type photo-thermal catalyst prepared by controlling the loading amount of graphite phase carbon nitride / silver molybdate on the melamine sponge according to the method of example 1 has a better algae removal effect.

[0124] Table 5

[0125]

[0126] 7, Effect of Melamine Sponge Density

[0127] By changing the density of the melamine sponge, the effect of the melamine sponge on the algae removal effect of the floating type photo-thermal catalyst was verified, and comparative example 14 was set based on example 1:

[0128] Comparative example 14

[0129] The difference between the present comparative example and example 1 is that the density of the melamine sponge in step (4) is 16 kg / m 3 .

[0130] The results are shown in Table 6 and Figure 10 It can be seen that the density of the melamine sponge has a significant effect on the algae removal effect, and compared with comparative example 14, the floating type photo-thermal catalyst prepared by controlling the density of the melamine sponge according to the method of example 1 has a better algae removal effect.

[0131] Table 6

[0132]

[0133] 8, Effect of Raw Material Addition

[0134] By changing the carrier melamine sponge and the addition of dopamine hydrochloride, the effect of the floating carrier and polydopamine modification on the algae removal effect of the floating type photo-thermal catalyst was verified, and comparative examples 15 and 16 were set based on example 1:

[0135] Comparative example 15

[0136] The difference between the present comparative example and example 1 is that the carrier melamine sponge is not used, i.e. steps (4) and (5) are not included.

[0137] Comparative example 16

[0138] The difference between the present comparative example and example 1 is that the polydopamine modified graphite phase carbon nitride / silver molybdate is not used, i.e. step (2) is not included.

[0139] The results are shown in Table 7, and it can be seen that the floating type photo-thermal catalyst (g-C3N4 / Ag2MoO4@MS) prepared by using the carrier melamine sponge in example 1 of the present application has an algal removal effect equivalent to that of the powder type graphite phase carbon nitride / silver molybdate directly used in comparative example 15 within 150 min, which indicates that the present application solves the problem that the contact area is reduced after the powder type photo-catalyst is loaded on the carrier, thereby affecting the algal removal effect, and also facilitates recycling.

[0140] Compared with comparative example 16, the floating type photo-thermal catalyst prepared by using the polydopamine modified graphite phase carbon nitride / silver molybdate according to the method of example 1 of the present application has a better algal removal effect.

[0141] Table 7

[0142]

[0143] Finally, it should be noted that the above description is only for the preferred embodiments of the present application and is not intended to limit the present application, and although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments or make equivalent replacements for some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. The application of a floating photothermal catalyst in the degradation of cyanobacteria, characterized in that: The preparation method of the floating photothermal catalyst includes the following steps: (1) Calcining melamine, cooling it to room temperature, taking it out, grinding it into powder, then calcining it a second time, and grinding it to obtain graphite phase carbon nitride; (2) Take the graphitic carbon nitride obtained in step (1) and add it to the tris(hydroxymethyl)aminomethane hydrochloride buffer solution. Disperse it evenly, then add dopamine hydrochloride and adjust the pH of the solution to 8.

5. Stir evenly, wash, dry and grind the product to obtain modified graphitic carbon nitride. (3) Disperse the modified graphitic carbon nitride obtained in step (2) in deionized water, add silver nitrate, stir evenly in the dark, then add sodium molybdate dihydrate solution dropwise, stir evenly, wash, dry and grind the product to obtain graphitic carbon nitride / silver molybdate. (4) Clean and dry the melamine sponge for later use; (5) The graphite phase carbon nitride / silver molybdate obtained in step (3) is ultrasonically dispersed in deionized water, sodium alginate is added, and the mixture is vigorously stirred to form a gel suspension. The melamine sponge treated in step (4) is placed into the gel suspension to fully absorb the suspension. Then the melamine sponge that has fully absorbed the suspension is placed into calcium chloride solution, solidified, taken out, washed, and dried to obtain a floating photothermal catalyst. In step (2), the mass fraction of the graphite phase carbon nitride is 0.4 to 0.6 parts, and the mass fraction of the dopamine hydrochloride is 0.02 to 0.09 parts; In step (3), the modified graphitic carbon nitride has a mass fraction of 0.3 to 0.5 parts, the silver nitrate has a mass fraction of 0.13 to 0.22 parts, and the sodium molybdate dihydrate has a mass fraction of 0.18 to 0.31 parts. In step (4), the density of the melamine sponge is 8.5~10 kg / m³. 3 ; In step (5), the loading amount of the graphitic carbon nitride / silver molybdate on the melamine sponge is 0.013~0.019 g / cm³. 3 .

2. The application according to claim 1, characterized in that: In step (1), the calcination temperature of melamine is 400~600℃, the heating rate is 2.5~5℃ / min, and the calcination time is 3~5h.

3. The application according to claim 1, characterized in that: In step (2), the concentration of the trihydroxymethylaminomethane hydrochloride buffer solution is 7.5~12.5mM.

4. The application according to claim 1, characterized in that: In step (3), the mass concentration of the sodium molybdate dihydrate solution is 3-7%.

5. The application according to claim 1, characterized in that: In step (4), the melamine sponge has a length of 2-4 cm, a width of 2-4 cm, and a height of 1-2 cm.

6. The application according to claim 1, characterized in that: In step (5), the mass fraction of the graphite phase carbon nitride / silver molybdate is 0.18~0.25 parts, the mass fraction of the sodium alginate is 0.04~0.06 parts, and the mass concentration of the calcium chloride solution is 2~5%.

7. The application according to claim 1, characterized in that: The cyanobacterium is Microcystis aeruginosa, and the application method includes: adding the floating photothermal catalyst to the water containing Microcystis aeruginosa, irradiating the water containing Microcystis aeruginosa under visible light λ≥420 nm for more than 150 min, and the degradation rate of Microcystis aeruginosa is ≥99%.

8. The application according to claim 7, characterized in that: The amount of the floating photothermal catalyst added is 0.4~1.0 g / L, and the initial algal density of Microcystis aeruginosa is expressed as the optical density OD at a wavelength of 680 nm. 680 The value is estimated to be 0.4~0.7.

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