Visible-light-photocatalyzed composite light-transmitting concrete as well as preparation method and application thereof

Abstract

A visible-light-photocatalyzed composite light-transmitting concrete contains several bundles of optical fibers, the optical fibers are coated with a protective layer on their outer surface, the protective layer contains a visible light photocatalyst, and the concrete has several gas-permeable pores. Such concrete is prepared by mixing a visible light photocatalyst and a light-transmitting glue, applying the mixture to the surface of optical fibers to form a protective layer, and using optical fibers in the concrete. The resulting concrete has dual properties of light transmittance and photocatalytic oxidation of gas-phase pollutants under visible light irradiation. The visible-light-photocatalyzed composite light-transmitting concrete significantly breaks through the limitation of photocatalytic concrete to light sources, so that gas-phase pollutants can be removed under visible light irradiation through photocatalysis of light-transmitting concrete. It also has good mechanical properties, decorativeness, and functional practicability due to coated optical fibers.

Claims

1. A visible-light-photocatalyzed composite light-transmitting concrete, comprising a plurality of bundles of optical fibers passing through the visible-light-photocatalyzed composite light-transmitting concrete, wherein an outer surface of the optical fibers are coated with a protective layer comprising a visible light photocatalyst, and the visible-light-photocatalyzed composite light-transmitting concrete has a plurality of gas-permeable pores; wherein the plurality of bundles of the optical fibers are arrayed in the visible-light-photocatalyzed composite light-transmitting concrete, and the protective layer is a mixture of a light-transmitting glue and the visible light photocatalyst; the concrete comprises cement, wherein the visible light photocatalyst is dispersed in the cement; the visible light photocatalyst is at least one diatomite-supported visible light photocatalyst selected from the group consisting of a diatomite-supported g-C.sub.3N.sub.4 photocatalyst and a diatomite-supported bismuth-based compound photocatalyst; the diatomite-supported bismuth-based compound photocatalyst is at least one selected from the group consisting of a diatomite-supported Bi.sub.2WO.sub.6-VO photocatalyst, a diatomite-supported Bi.sub.2WO.sub.6 photocatalyst, a diatomite-supported Bi.sub.2MoO.sub.6 photocatalyst, a diatomite-supported bismuth oxyhalide photocatalyst, and a diatomite-supported bismuth oxide photocatalyst; the diatomite-supported bismuth oxyhalide photocatalyst is at least one selected from the group consisting of a diatomite-supported BiOBr photocatalyst, a diatomite-supported BiOCl photocatalyst, and a diatomite-supported BiOCl.sub.xBr.sub.1−x photocatalyst, wherein x is more than or equal to 0 and less than or equal to 1; the diatomite-supported visible light photocatalyst is prepared as follows: the diatomite-supported g-C.sub.3N.sub.4 photocatalyst is separately prepared by a method comprising the following steps: 1) ultrasonically dispersing a first amount of diatomite powder in an alcohol solution to obtain a diatomite suspension; 2) adding melamine to the diatomite suspension of step 1) to obtain a first reaction solution, stirring the first reaction solution at 20-30° C. for 2-6 h, drying a resulting mixture at 60-80° C. for 4-8 h to obtain a dried mixture, and calcining the dried mixture in a muffle furnace at 500-600° C. for 2-6 h to obtain the diatomite-supported g-C.sub.3N.sub.4 photocatalyst; the diatomite-supported bismuth-based compound photocatalyst is separately prepared by a method comprising the following steps: 1) dispersing a second amount of the diatomite powder in a first mixed solution of a water-soluble bismuth salt, ethylene glycol, and water; 2) adding a water-soluble salt to the first mixed solution to obtain a second mixed solution, stirring the second mixed solution for 2 h, and conducting a first hydrothermal reaction at 120-180° C. for 2-24 h; 3) after the first hydrothermal reaction, washing and drying a product of the first hydrothermal reaction to obtain the diatomite-supported bismuth-based compound photocatalyst, wherein when the water-soluble salt is a water-soluble tungstate, a water-soluble molybdate, a water-soluble carbonate, a water-soluble chloride salt, or a water-soluble bromine salt, the diatomite-supported bismuth-based compound photocatalyst obtained is respectively the diatomite-supported Bi.sub.2WO.sub.6 photocatalyst, the diatomite-supported Bi.sub.2MoO.sub.6 photocatalyst, the diatomite-supported bismuth oxide photocatalyst, the diatomite-supported BiOCl photocatalyst, or the diatomite-supported BiOBr photocatalyst; the diatomite-supported Bi.sub.2WO.sub.6-VO photocatalyst is separately prepared by a method comprising the following steps: adding Bi(NO.sub.3).sub.3.Math.5H.sub.2O to ethylene glycol under stirring to form a third mixed solution; meanwhile, dissolving Na.sub.2WO.sub.4.Math.2H.sub.2O in ethylene glycol under stirring to form a fourth mixed solution; then, adding the fourth mixed solution dropwise to the third mixed solution under stirring to obtain a resulting solution, stirring the resulting solution at room temperature for 0.5 h, transferring the resulting solution to a first diatomite-filled reactor, and keeping the first diatomite-filled reactor at 160° C. for 6-24 h to perform a first reaction; after the first reaction is completed, naturally cooling the first diatomite-filled reactor to the room temperature, collecting and washing a solid precipitate, drying the solid precipitate at 60° C. overnight to obtain diatomite-supported Bi.sub.2WO.sub.6 with a high oxygen vacancy defect; then, annealing the diatomite-supported Bi.sub.2WO.sub.6 in an air atmosphere at 250-550° C. for 4 h to obtain the diatomite-supported Bi.sub.2WO.sub.6-VO photocatalyst with a predetermined oxygen vacancy concentration; the diatomite-supported BiOCl.sub.xBr.sub.1−x photocatalyst is separately prepared by a method comprising the following steps: dissolving Bi(NO.sub.3).sub.3.Math.5H.sub.2O in HNO.sub.3 under stirring to obtain a first transparent solution; dissolving KCl and KBr at an amount-of-substance ratio of x: (1−x) in water, adding citric acid to obtain a second transparent solution, wherein x is more than or equal to 0 and less than or equal to 1; adding the second transparent solution dropwise to the first transparent solution under stirring, adjusting a pH to 7.0, continuing stirring to obtain a fifth mixed solution, transferring the fifth mixed solution to a second diatomite-filled hydrothermal reactor to obtain a reaction mixture, conducting a second hydrothermal reaction with the reaction mixture at a constant temperature of 120° C. for 10 h, after the second hydrothermal reaction is completed, naturally cooling the reaction mixture, removing a supernatant from the reaction mixture, washing and filtering a product of the second hydrothermal reaction, and drying the product at 60° C. to obtain the diatomite-supported BiOCl.sub.xBr.sub.1−x photocatalyst, wherein x is more than or equal to 0 and less than or equal to 1; the diatomite-supported bismuth oxide photocatalyst is prepared by a method comprising the following steps: dissolving bismuth citrate in water and stirring to obtain a bismuth citrate solution; adding Na.sub.2CO.sub.3 to distilled water and dissolving Na.sub.2CO.sub.3 under stirring to obtain a Na.sub.2CO.sub.3 solution; adding the Na.sub.2CO.sub.3 solution dropwise to the bismuth citrate solution to obtain a sixth mixed solution under stirring; transferring the sixth mixed solution to a third diatomite-filled hydrothermal reactor, keeping the third diatomite-filled hydrothermal reactor at 160° C. for 18 h to perform a third hydrothermal reaction, after the third hydrothermal reaction is completed, centrifuging and washing a product of the third hydrothermal reaction, and drying the product at 60° C. to obtain a precursor; calcining the precursor at 300° C.-500° C. to obtain the diatomite-supported bismuth oxide photocatalyst.

2. A preparation method of the visible-light-photocatalyzed composite light-transmitting concrete of claim 1, comprising the following steps: 1) optical fiber coating, comprising: mixing and dispersing uniformly a light-transmitting glue and a powder of the visible light photocatalyst to obtain a mixture, applying the mixture to the outer surface of the optical fibers, and solidifying the mixture to form the protective layer, so as to obtain the optical fibers coated with the protective layer on the outer surface; 2) fabricating a concreting mold with the optical fibers fixed therein, comprising: arranging the optical fibers of step 1) at intervals and fixing the optical fibers in the concreting mold; and 3) preparing the visible-light-photocatalyzed composite light-transmitting concrete, comprising: pouring a cement matrix into the concreting mold of step 2) to obtain the visible-light-photocatalyzed composite light-transmitting concrete through forming, curing, and demolding.

3. The preparation method of claim 2, wherein the cement matrix comprises the visible light photocatalyst.

4. The preparation method of claim 3, wherein the cement matrix further comprises cement, a polycarboxylate superplasticizer, water, fly ash, and recycled coarse aggregate.

5. The preparation method of claim 2, wherein the visible light photocatalyst is at least one diatomite-supported visible light photocatalyst selected from the group consisting of a diatomite-supported g-C.sub.3N.sub.4 photocatalyst and a diatomite-supported bismuth-based compound photocatalyst; the diatomite-supported bismuth-based compound photocatalyst is at least one selected from the group consisting of a diatomite-supported Bi.sub.2WO.sub.6-VO photocatalyst, a diatomite-supported Bi.sub.2WO.sub.6 photocatalyst, a diatomite-supported Bi.sub.2MoO.sub.6 photocatalyst, a diatomite-supported bismuth oxyhalide photocatalyst, and a diatomite-supported bismuth oxide photocatalyst; the diatomite-supported bismuth oxyhalide photocatalyst is at least one selected from the group consisting of a diatomite-supported BiOBr photocatalyst, a diatomite-supported BiOCl photocatalyst, and a diatomite-supported BiOCl.sub.xBr.sub.1−x photocatalyst, wherein x is more than or equal to 0 and less than or equal to 1.

6. The preparation method of claim 3, wherein the visible light photocatalyst is at least one diatomite-supported visible light photocatalyst selected from the group consisting of a diatomite-supported g-C.sub.3N.sub.4 photocatalyst and a diatomite-supported bismuth-based compound photocatalyst; the diatomite-supported bismuth-based compound photocatalyst is at least one selected from the group consisting of a diatomite-supported Bi.sub.2WO.sub.6-VO photocatalyst, a diatomite-supported Bi.sub.2WO.sub.6 photocatalyst, a diatomite-supported Bi.sub.2MoO.sub.6 photocatalyst, a diatomite-supported bismuth oxyhalide photocatalyst, and a diatomite-supported bismuth oxide photocatalyst; the diatomite-supported bismuth oxyhalide photocatalyst is at least one selected from the group consisting of a diatomite-supported BiOBr photocatalyst, a diatomite-supported BiOCl photocatalyst, and a diatomite-supported BiOCl.sub.xBr.sub.1−x photocatalyst, wherein x is more than or equal to 0 and less than or equal to 1.

7. The preparation method of claim 4, wherein the visible light photocatalyst is at least one diatomite-supported visible light photocatalyst selected from the group consisting of a diatomite-supported g-C.sub.3N.sub.4 photocatalyst and a diatomite-supported bismuth-based compound photocatalyst; the diatomite-supported bismuth-based compound photocatalyst is at least one selected from the group consisting of a diatomite-supported Bi.sub.2WO.sub.6-VO photocatalyst, a diatomite-supported Bi.sub.2WO.sub.6 photocatalyst, a diatomite-supported Bi.sub.2MoO.sub.6 photocatalyst, a diatomite-supported bismuth oxyhalide photocatalyst, and a diatomite-supported bismuth oxide photocatalyst; the diatomite-supported bismuth oxyhalide photocatalyst is at least one selected from the group consisting of a diatomite-supported BiOBr photocatalyst, a diatomite-supported BiOCl photocatalyst, and a diatomite-supported BiOCl.sub.xBr.sub.1−x photocatalyst, wherein x is more than or equal to 0 and less than or equal to 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the effect of the dose by volume of optical fibers on the compressive strength in application example 1.

(2) FIG. 2 is a curve of the formaldehyde concentration varying with time in application example 2.

(3) FIG. 3 shows NO degradation ratios corresponding to concrete with three different doses of a diatomite@g-C.sub.3N.sub.4 photocatalyst in application example 3.

(4) FIG. 4 is an XRD spectrum of diatomite@Bi.sub.2WO.sub.6-VO, B.sub.2WO.sub.6-VO, diatomite@Bi.sub.2WO.sub.6and Bi.sub.2WO.sub.6 photocatalysts in example 4.

(5) FIG. 5 is an XRD spectrum of diatomite@BiOBr, diatomite@BiOCl.sub.xBr.sub.1−x-1:3, diatomite@BiOCl.sub.xBr.sub.1−x-1:1, diatomite@BiOCl.sub.xBr.sub.1−x-3:1 and diatomite@BiOCl photocatalysts in example 4.

(6) FIG. 6 is an SEM image of a diatomite@Bi.sub.2WO.sub.6 photocatalyst in example 4.

(7) FIG. 7 is a NO removal curve of diatomite@Bi.sub.2WO.sub.6, Bi.sub.2WO.sub.6, Bi.sub.2WO.sub.6-VO and diatomite@Bi.sub.2WO.sub.6-VO in application example 3, with the abscissa as time and the ordinate as the NO removal rate (C/C.sub.0%).

(8) FIG. 8 shows the cyclic stability of NO removal with diatomite@Bi.sub.2WO.sub.6under visible light (λ≥420 nm) irradiation in application example 3, with the abscissa as time and the ordinate as the NO removal rate.

(9) FIG. 9 is a test device for measuring the photocatalytic performance of a visible-light-photocatalyzed composite light-transmitting concrete in application example 3.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(10) The contents of the present invention will be further described below through specific embodiments.

Example 1

(11) Example 1 provides a method for preparing a diatomite-supported g-C.sub.3N.sub.4 photocatalyst as follows:

(12) 1. Diatomite pretreatment: 1.0 g of diatomite was put in a plastic beaker. 20 ml of a 2.0 mol/L NaOH aqueous solution was added and mixed with diatomite under magnetic stirring. After a reaction at room temperature for 12 h, a sample was collected, washed to pH 7.0, dried at 80° C. overnight, and ground into diatomite powder.

(13) 2. Synthesis of diatomite-supported g-C.sub.3N.sub.4 photocatalyst (diatomite@g-C.sub.3N.sub.4):

(14) First, 0.01 g, 0.02 g, 0.04 g, 0.10 g or 0.20 g of diatomite powder of step 1 was taken and dispersed in 30 mL of methanol with continuous ultrasonic waves at room temperature for 30 min to obtain a well-dispersed diatomite suspension. Next, 4.0 g of melamine was added to the diatomite suspension and stirred at 25 for 4 h. Then, through drying at 70° C. for 6 h, a dried mixture was calcined at 550° C. for 4 h in a muffle furnace to obtain a diatomite-supported g-C.sub.3N.sub.4 photocatalyst (diatomite@g-C.sub.3N.sub.4 photocatalyst). g-C.sub.3N.sub.4 was a product of reactive synthesis.

(15) According to thermogravimetric (TG) analysis, when the dose of diatomite powder was 0.01 g, 0.02 g, 0.04 g, 0.10 g or 0.20 g, respectively, the content by weight of diatomite in the obtained diatomite@g-C.sub.3N.sub.4 photocatalyst was 1.22 wt %, 2.32 wt %, 5.46 wt %, 13.88 wt % or 25.21 wt %, respectively.

Example 2

(16) A method for preparing optical fibers coated with a protective layer used in concrete is as follows:

(17) A mixture of UV glue and the diatomite-supported g-C.sub.3N.sub.4 photocatalyst prepared in example 1 was applied to the surface of optical fibers to form a protective layer. The optical fibers (OF) had polymethyl methacrylate (PMMA) plastic filaments with a diameter of 1-2 mm.

(18) Optical fiber coating was intended to protect the surface of optical fibers from damage, improve the mechanical strength and reduce attenuation; when combined with concrete, it could improve light transmittance and energy transfer performance, and enhance mechanical properties of light-transmitting concrete to some extent; in addition, a small amount of a diatomite@g-C.sub.3N.sub.4 photocatalyst was added to UV glue applied to optical fibers, which enabled a rapid reaction between optical fibers and a photocatalytic material, and the photocatalytic reaction was improved due to the porosity of concrete and diatomite.

(19) The specific operations of optical fiber coating are as follows:

(20) In this example, a coating fixture was used for coating operations, and the coating fixture was a commercially available optical fiber fixture, FH-40-LT900, for loose-tube optical fibers. This step can also be completed by any other method on the premise that the surface of optical fibers is uniformly coated with the mixture of UV glue and the diatomite-supported g-C.sub.3N.sub.4 photocatalyst, which is cured to form a protective layer on the surface of optical fibers.

(21) (1) The coating fixture was cleaned:

(22) Dust attached to the surface of a quartz plate needs to be removed, and dust-free paper dipped in alcohol can be used for this purpose. The quartz plate was gently wiped with dust-free paper dipped in alcohol. Residual alcohol evaporated or the quartz plate was wiped again with dry dust-free paper prior to the next step.

(23) (2) A power supply was connected.

(24) (3) A coating machine was powered on.

(25) (4) Optical fibers were placed: 1. The upper cover of the coating fixture as well as upper covers of left and right fixtures were opened. 2. The coating fixture and optical fiber fixtures were ensured to be clean. 3. A vacuum adsorption control switch was turned on. 4. The position was aligned so that the required coating section of optical fibers was placed in a semicircular groove of the coating fixture, optical fibers were placed in a vacuum V-shaped groove, and the position of the required coating section of optical fibers was checked again. 5. The fixture on one side was closed, optical fibers were gently straightened to ensure they were under tension, and the fixture on the other side was closed. The optical fibers should always be in a straight line and all in the corresponding groove. 6. The coating fixture was gently closed, optical fibers were ensured to be in the optical fiber groove without displacement, and the adsorption key was turned off.

(26) (5) UV glue and diatomite-supported g-C.sub.3N.sub.4 photocatalyst powder were mixed and dispersed uniformly, glue injection was started by pressing the glue injection control button, the direction of light-transmitting glue was observed from the upper transparent quartz plate the coating glue covered both sides of the required coating section of optical fibers, and glue injection was stopped by pressing the glue injection control button.

(27) (6) Curing was conducted: 1. A UV lamp control button was pressed, and the UV lamp continued to light up for the set time and then went out; a curing key was “one-time” triggered to automatically complete the curing time without a long press. 2. 10 s later, the upper cover of the fixture was opened. 3. Both ends of the upper cover of the coating fixture were held with hands and gently opened upwards. 4. The coated optical fibers may stick to the upper or lower quartz plate. In this case, optical fibers and the quartz plate can be separated by holding both ends of optical fibers with hands and apply a little force. 5. The coated optical fibers should be observed for its quality, smoothness, and bubbles. If no bubbles are observed, optical fibers coated with the protective layer of the present invention will be obtained and used for the next step.

Example 3

(28) Example 3 provides a visible-light-photocatalyzed composite light-transmitting concrete, wherein the concrete contains several bundles of optical fibers, the optical fibers are coated with a protective layer on their outer surface, the protective layer contains a visible light photocatalyst, the optical fibers are arrayed in the concrete, the protective layer is a mixture of light-transmitting glue and the visible light photocatalyst, and the concrete contains cement and the visible light photocatalyst dispersed in cement.

(29) Raw materials: diatomite@g-C.sub.3N.sub.4 photocatalyst obtained in example 1, several bundles of optical fibers coated with the protective layer obtained in example 2, cement, a polycarboxylate superplasticizer, water, fly ash and recycled coarse aggregate. The optimal mixing ratios in the cement matrix were as follows: The water-glue ratio (referring to the ratio of water consumption per cubic meter of concrete to the dose of all cementing materials) was 0.35, the glue-aggregate ratio (referring to the weight ratio of powder (cement and fly ash) to aggregate (sand, referring to the sum of recycled coarse aggregate and natural coarse aggregate in this document) was 3, the dose of fly ash was 5%, and the replacement rate of recycled coarse aggregate was 50%.

(30) The preparation process of recycled coarse aggregate was as follows: A suitable particle size was obtained through primary crushing, secondary crushing, impurity removal and screening. The basic properties of natural coarse aggregate and recycled coarse aggregate used for this test are shown in Table 1.

(31) TABLE-US-00001 TABLE 1 Basic properties of natural coarse aggregate and recycled coarse aggregate Apparent density Bulk density Water absorption (kg/m.sup.3) (kg/m.sup.3) (%) Natural coarse 2812 1450 0.41 aggregate Recycled coarse 1780.2 1123.3 6.32 aggregate

(32) In order to ensure that the matrix still has good integrity and high strength with a high dose of optical fibers, cement at a grade above 42.5 was used. The water-reducing rate of the polycarboxylate superplasticizer was more than 25%.

(33) A method for preparing the visible-light-photocatalyzed composite light-transmitting concrete is as follows:

(34) (1) Waste concrete was crushed and screened to obtain recycled coarse aggregate. The aggregate was soaked in a suspension with 0.6 wt % of the diatomite@g-C.sub.3N.sub.4 photocatalyst obtained in example 1 for 24 h, put in a 105° C. oven for 12 h to complete dryness, and cooled to room temperature to obtain recycled coarse aggregate supported with the diatomite@g-C.sub.3N.sub.4 photocatalyst, i.e., a photocatalytic recycled coarse aggregate component.

(35) Natural coarse aggregate, 50% of mixing water and recycled coarse aggregate supported with the diatomite@g-C.sub.3N.sub.4 photocatalyst were weighed according to mixing ratios, added to a mixer and stirred for 30 s to make the surface of aggregate uniformly wet. Then, cement and fly ash were added to the mixer and stirred for 60 s, so that the surface of aggregate was effectively coated with cementing materials. Finally, the remaining water and superplasticizer were added to the mixer and stirred for 120 s to obtain a cement matrix.

(36) (2) Fabrication of concreting mold with fixed light guide: The plastic plate was cut to make 1 bottom plate and 4 side plates with an internal clearance size of 120×120×120 mm. Layout lines were delineated on side plates with a specified spacing according to needs and shape requirements. A bit with a diameter of 1.0 mm was used to drill holes. The optical fibers obtained in example 2 were manually passed through holes layer by layer, knotted at a suitable length and fixed on the outside of side plates, so that they were arrayed in a concreting mold. In this step, the dose by volume of optical fibers was controlled to 2%, namely, the volume of optical fibers accounted for 2% of the total volume of concrete (i.e., the volume of the concreting mold).

(37) (3) Preparation of visible-light-photocatalyzed composite light-transmitting concrete:

(38) The cement matrix of step (1) was poured into the mold of step (2). In this process, the cement matrix was divided into three layers for tamping. Each layer was tamped 20-30 times. Tamping was conducted in a manner of spiral entry from all sides to the center. When a layer was tamped, about 20 mm of the next layer was tamped. After filled, the mold was placed on a vibrating table and vibrated for 5 s to make filled concrete compact. Then, the test piece was smoothed to obtain a concrete matrix.

(39) (4) Curing of visible-light-photocatalyzed composite light-transmitting concrete:

(40) The surface of the concrete matrix of step (3) was covered with a film for curing, and the film was removed after 1 d. Then, the test piece was cured in a standard curing room (with a temperature of (20±2)° C. and a humidity of >95%) for 28 days and demolded to obtain the visible-light-photocatalyzed composite light-transmitting concrete of the present invention. Optical fibers passed through the concrete, and both end faces of optical fibers were flush with end faces of the concrete.

Application Example 1

(41) A series of a visible-light-photocatalyzed composite light-transmitting concrete only with different doses by volume of optical fibers was prepared by the method of example 3 to test the effect of the dose by volume of optical fibers on the compressive strength of concrete. As shown in FIG. 1, the abscissa is the dose by volume of optical fibers, i.e., the ratio of the volume of optical fibers to the total volume of concrete, and the ordinate is the compressive strength of concrete in 28 days.

(42) According to FIG. 1, the compressive strength was about 65 MPa when the dose by volume of optical fibers was 0-2%, and gradually decreased to about 52 MPa when the dose by volume of optical fibers was 2-12%.

Application Example 2

(43) Performance test of diatomite@g-C.sub.3N.sub.4 photocatalyzed light-transmitting concrete for catalyzing formaldehyde oxidation and removal under visible light irradiation:

(44) Three types of a visible-light-photocatalyzed composite light-transmitting concrete only with different doses (0.2, 0.4% and 0.8%) of a diatomite@g-C.sub.3N.sub.4 photocatalyst were prepared by the method of example 3 to test the effect of the dose of g-C.sub.3N.sub.4 on the performance of concrete for formaldehyde removal. The dose of the diatomite@g-C.sub.3N.sub.4 photocatalyst was the mass content of the dose of the diatomite@g-C.sub.3N.sub.4 photocatalyst in the visible-light-photocatalyzed composite light-transmitting concrete. The photocatalyst was sourced from the protective layer of optical fibers and the cement matrix.

(45) The test method is as follows: The above-mentioned three types of the visible-light-photocatalyzed composite light-transmitting concrete (120×120×120 mm) only with different doses of a diatomite@g-C.sub.3N.sub.4 photocatalyst were placed in a 1 m.sup.3 sealed glass jar with an initial formaldehyde concentration of 1.05 mg/m.sup.3 for visible light irradiation, so that the diatomite@g-C.sub.3N.sub.4 photocatalyst in concrete catalyzed a formaldehyde oxidation reaction for 48 h under visible light irradiation. The formaldehyde concentration in the sealed glass jar was tested and recorded every 12 h. The results are shown in FIG. 2 as a curve of the formaldehyde concentration varying with time.

(46) According to FIG. 2:

(47) (1) During the test period, the formaldehyde concentration in the sealed glass jar corresponding to concrete without diatomite@g-C.sub.3N.sub.4 merely decreased a bit and was still about 1 mg/m.sup.3.

(48) (2) During the test period, the formaldehyde concentration in the sealed glass jar corresponding to concrete with 0.8% of diatomite@g-C.sub.3N.sub.4 decreased significantly. It decreased rapidly to about 0.65 mg/m.sup.3 at 12 h, and decreased to about 0.35 mg/m.sup.3 at 48 h.

(49) (3) During the test period, the formaldehyde concentration in the sealed glass jar corresponding to concrete with 1.6% of diatomite@g-C.sub.3N.sub.4 decreased the most. It decreased rapidly to about 0.15 mg/m.sup.3 at 12 h, and decreased to about 0.05 mg/m.sup.3 at 48 h. Therefore, in this application example, as long as 15 wt % of g-C.sub.3N.sub.4 was kept, most of formaldehyde can be oxidized and removed within 12 h.

Application Example 3

(50) Performance test of diatomite@g-C.sub.3N.sub.4 photocatalyzed light-transmitting concrete for catalyzing NO oxidation and removal under visible light irradiation:

(51) Three types of a visible-light-photocatalyzed composite light-transmitting concrete only with different doses (0.2, 0.4% and 0.8%) of a diatomite@g-C.sub.3N.sub.4 photocatalyst were prepared by the method of example 3 to test the effect of the dose of the diatomite@g-C.sub.3N.sub.4 photocatalyst (this dose was the mass content of the dose of the diatomite@g-C.sub.3N.sub.4 photocatalyst in the visible-light-photocatalyzed composite light-transmitting concrete, and the photocatalyst was sourced from the protective layer of optical fibers and the cement matrix) on the performance of concrete for NO removal.

(52) The test method is as follows:

(53) The photocatalytic activity of a sample was verified by measuring the NO removal rate in a rectangular reactor (30×15×10 cm) at room temperature. According to the principle of photocatalysis, a designed test device was used to measure the photocatalytic performance of the visible-light-photocatalyzed composite light-transmitting concrete as shown in FIG. 9. In FIG. 9, 1—simulated exhaust source; 2—pressure valve; 3—glass rotameter; 4—photocatalytic reaction tank; 5—cement concrete specimen; 6—exhaust analyzer (model: 42c-TL). The core of the test device is a sealed gas reaction chamber that can accommodate a specimen with a size of 1.00×100×100 mm. For the test, cool daylight within a range of 420-650 nm were emitted with 3 8W daylight lamps to simulate visible light, with 3 prominent peaks at 460 nm, 560 nm and 600 nm. According to main components of automobile exhaust, NOx was selected as a main pollutant model for a photocatalytic degradation test, and a gas containing NO as a main component was selected to evaluate the photocatalytic degradation effect. The NO removal rate (η) was calculated according to the formula η=(1 C/C.sub.0) 100%, where C.sub.0 is the NO concentration of a feed stream and C is the NO concentration of outlet steam.

(54) According to FIG. 3:

(55) (1) During the test period, the NO degradation ratio corresponding to concrete with 0.2% of the diatomite@g-C.sub.3N.sub.4 photocatalyst was about 38.6%, the NO degradation ratio corresponding to concrete with 0.4% of the diatomite@g-C.sub.3N.sub.4 photocatalyst was about 48.8%, and the NO degradation ratio corresponding to concrete with 0.8% of the diatomite@g-C.sub.3N.sub.4 photocatalyst was about 70.5%.

(56) Therefore, in this application example, as the dose of the diatomite@g-C.sub.3N.sub.4 photocatalyst was increased, the NO degradation ratio increased. This strategy is expected to be extended to other g-C.sub.3N.sub.4-supported materials for potential applications in pollutant removal.

Example 4

(57) Preparation of a diatomite@bismuth-based compound photocatalyst:

(58) Purified diatomite, as a carrier for supporting a bismuth-based photocatalyst, was dispersed in a mixed solution of Bi(NO.sub.3).sub.3, ethylene glycol and water, wherein proportions of ethylene glycol and water were adjustable. Na.sub.2WO.sub.4, Na.sub.2MoO.sub.4, Na.sub.2CO.sub.3, NaCl and NaBr solutions with different concentrations were added to the mixed solution to prepare different bismuth-based photocatalytic materials. The resulting solution was stirred with a magnetic stirrer for 2 h. Then, a hydrothermal reaction was conducted at 120-180° C. for 2-24 h. After the reaction, the product was washed with water and ethanol, and dried at 60° C. to obtain different diatomite@bismuth-based compound photocatalyst samples, including diatomite@Bi.sub.2WO.sub.6, diatomite@Bi.sub.2MoO.sub.6, diatomite@Bi.sub.2O.sub.2CO.sub.3, diatomite@bismuth oxyhalide, etc.

(59) The specific preparation conditions of the diatomite@bismuth-based compound photocatalyst are as follows:

(60) 1. Preparation of diatomite@Bi.sub.2WO.sub.6-VO photocatalyst:

(61) 2 mmol Bi(NO.sub.3).sub.3.Math.5H.sub.2O was added to 20 mL of ethylene glycol under stirring to form a solution A. Meanwhile, 1 mmol Na.sub.2WO.sub.4.Math.2H.sub.2O was dissolved in 10 mL of ethylene glycol under stirring to form a solution B. After solutions A and B became transparent and uniform (about 2 h later), the solution B was added dropwise under stirring. The resulting solution was intensely magnetically stirred at room temperature for 0.5 h, transferred to a 50 mL PTFE-lined reactor filled with 45 mg of diatomite, and kept at 160° C. for 6, 12, 18 and 24 h; After the reaction is completed, the reactor was naturally cooled to room temperature. The product was collected, and washed with ethanol and deionized water several times to remove residual substances. The precipitate was dried at 60° C. overnight to obtain samples with high oxygen vacancy defects, i.e., diatomite-supported Bi.sub.2WO.sub.6-6, diatomite-supported Bi.sub.2WO.sub.6-12, diatomite-supported Bi.sub.2WO.sub.6-18, and diatomite-supported Bi.sub.2WO.sub.6-24, respectively. Diatomite-supported Bi.sub.2WO.sub.6-18 was annealed in an air-rich atmosphere at different temperatures (250° C., 350° C., 450° C. and 550° C.) for 4 h to obtain diatomite@Bi.sub.2W0.sub.6-VO catalysts with different oxygen vacancy concentrations respectively: diatomite-supported Bi.sub.2WO.sub.6-250, diatomite-supported Bi.sub.2WO.sub.6-350, diatomite-supported Bi.sub.2WO.sub.6-450, and diatomite-supported WO.sub.6-550.

(62) 2. Simultaneous preparation of Bi.sub.2WO.sub.6-VO for comparison by the following method:

(63) The preparation method was the same as that of diatomite-supported Bi.sub.2WO.sub.6-250, diatomite-supported Bi.sub.2WO.sub.6-350, diatomite-supported Bi.sub.2WO.sub.6-450, and diatomite-supported Bi.sub.2WO.sub.6-550, except that diatomite was not added.

(64) 3. Preparation of diatomite@Bi.sub.2WO.sub.6 photocatalyst:

(65) 4.85 g of Bi (NO.sub.3).sub.3 and 1.65 g of Na.sub.2wo.sub.4 were weighed and dissolved in 35 ml of deionized water respectively. A Na.sub.2wo.sub.4 solution was slowly added dropwise to a Bi(NO.sub.3).sub.3 solution under rapid stirring. After stirring was continued for 30 min, a white suspension was transferred to a 100 ml reactor filled with 60 mg of diatomite, and put in a 180° C. oven for a reaction for 24 h. After natural cooling, the product was repeatedly washed with deionized water and ethanol 5 times, and dried at 80° C. for 10 h to obtain the diatomite@Bi.sub.2WO.sub.6catalyst.

(66) 4. Simultaneous preparation of Bi.sub.2WO.sub.6 for comparison by the following method:

(67) The preparation method was the same as that of diatomite@Bi.sub.2WO.sub.6, except that diatomite was not added.

(68) 5. Preparation of diatomite@BiOBr, diatomite@BiOCl.sub.xBr.sub.1−x-1:3, diatomite@BiOCl.sub.xBr.sub.1−x-1:1, diatomite@BiOCl.sub.xBr.sub.1−x-3:1, and diatomite@BiOCl photocatalysts:

(69) 0.01.5 mol Bi(NO.sub.3).sub.3.Math.5H.sub.2O was weighed and dissolved in 40 mL of 2 mol.Math.L.sup.−1 HNO.sub.3 under stirring to obtain a transparent solution A. A certain amount of KBr was dissolved in 30 mL of deionized water, and 1 g of citric acid was added to obtain a solution B. The solution B was added dropwise to the solution A under stirring. The pH was adjusted to 7.0 with NH.sub.3.Math.H.sub.2O. Magnetic stirring was continued for 1 h. Then, the mixed solution was transferred to a PTFE-lined stainless steel hydrothermal reactor filled with 60 mg of diatomite. A reaction was conducted at a constant temperature of 120° C. for 10 h. After the reactor was naturally cooled upon the completion of the reaction, the supernatant was removed, washed with deionized water and absolute ethanol several times, filtered, and dried at 60° C. for 8 h to obtain a final powder sample.

(70) The amount-of-substance ratios of KCl and KBr added to diatomite@BiOBr, diatomite@BiOCl.sub.xBr.sub.1−x-1:3, diatomite@BiOCl.sub.xBr.sub.1−x-1:1, diatomite@BiOCl.sub.xBr.sub.1−x-3:1 and diatomite@BiOCl photocatalysts were 0:1, 1:3, 1:1, 3:1, and 1:0, respectively.

(71) An XRD spectrum of diatomite@Bi.sub.2WO.sub.6-VO, Bi.sub.2WO.sub.6-VO, diatomite@Bi.sub.2WO.sub.6 and Bi.sub.2WO.sub.6 photocatalysts is given in FIG. 4. Specifically, diatomite@Bi.sub.2WO.sub.6-VO is diatomite-supported Bi.sub.2WO.sub.6-550, and Bi.sub.2WO.sub.6-VO is Bi.sub.2WO.sub.6-550.

(72) An XRD spectrum of diatomite@BiOBr, diatomite@BiOCl.sub.xBr.sub.1−x-1:3, diatomite@BiOCl.sub.xBr.sub.1−x-1:1, diatomite@BiOCl.sub.xBr.sub.1−x-3:1 and diatomite@BiOCl photocatalysts is given in FIG. 5.

(73) According to FIGS. 4-5, bismuth-based compounds were successfully supported on diatomite.

(74) An SEM image of the diatomite@Bi.sub.2WO.sub.6photocatalyst is given in FIG. 6.

(75) It can be seen from FIG. 6 as the SEM image of the diatomite@Bi.sub.2WO.sub.6photocatalyst that the prepared sample has a hierarchical bouquet-like structure with good dispersiveness. Compared with diatomite having a smooth surface, diatomite@Bi.sub.2WO.sub.6has a rougher outer surface with a crystalline structure that is more conducive to the attachment of pollutants and more beneficial to the separation of photogenerated electrons and holes on the surface of the catalyst.

Application Example 3

(76) Performance and stability test of a diatomite@bismuth-based compound catalyst for NO oxidation and removal under visible light irradiation

(77) Test methods and conditions:

(78) Diatomite@Bi.sub.2WO.sub.6, Bi.sub.2WO.sub.6, Bi.sub.2WO.sub.6-VO and diatomite@Bi.sub.2WO.sub.6-VO prepared in example 4 were used as four samples for the test. Bi.sub.2WO.sub.6 and Bi.sub.2WO.sub.6-VO were used for comparison. Specifically, diatomite@Bi.sub.2WO.sub.6-VO is diatomite-supported Bi.sub.2WO.sub.6-550, and Bi.sub.2WO.sub.6-VO is Bi.sub.2WO.sub.6-550.

(79) The photocatalytic activity of a sample was verified by measuring the NO removal rate in a rectangular reactor (30×15×10 cm) at ambient temperature. A 150 W commercial tungsten halogen lamp with an ultraviolet cut-off filter (420 nm) for removing ultraviolet rays was placed vertically outside the reactor to detect the visible-light photocatalytic activity. The adsorption-desorption equilibrium was achieved after the lamp was turned on. For each test, a prepared sample (0.20 g) was dispersed with ethanol and spread onto two glass petri dishes with a diameter of 12.0 cm. The glass petri dishes with the sample were dried at 60° C. to remove ethanol from a suspension, cooled to room temperature and placed in the center of the reactor. NO gas was supplied from a compressed. NO gas cylinder at a concentration of 100 ppm (equilibrium state). Initial NO was diluted to about 550 ppb with a gas stream. The gas stream was well premixed with a three-way valve. Flow rates of NO and gas streams were set to 15 mL min.sup.−1 and 2.4 L min.sup.−1 respectively with a mass flow controller. The nitrogen oxide content was measured every 1 min with a nitrogen oxide analyzer (model: 42c-TL) to monitor the NO concentration. The NO removal rate (η) was calculated as follows: The NO removal rate (η) was calculated according to the formula η=(1C/C.sub.0) 100%, where C.sub.0 is the NO concentration of a feed stream and C is the NO concentration of outlet steam.

(80) FIG. 7 is a NO removal curve of diatomite@Bi.sub.2WO.sub.6, Bi.sub.2WO.sub.6, Bi.sub.2WO.sub.6-VO and diatomite@Bi.sub.2WO.sub.6-VO, with the abscissa as time and the ordinate as the NO removal rate (C/C.sub.0%).

(81) According to FIG. 7, after the incorporation of photocatalytic materials, the NO content decreased rapidly with time, indicating that diatomite@Bi.sub.2WO.sub.6, Bi.sub.2WO.sub.6, Bi.sub.2WO.sub.6-VO and diatomite@Bi.sub.2WO.sub.6-VO have excellent photocatalytic activity. The degradation rate of pollutants increased rapidly in the early stage of light irradiation, and then increased at a lower speed with time. Through a comparison under the same dose and the same exposure time, the degradation efficiency of Bi.sub.2WO.sub.6with diatomite (diatomite@Bi.sub.2WO.sub.6) was significantly superior to that of Bi.sub.2WO.sub.6 without diatomite. This is because, on the one hand, diatomite improved the agglomeration of Bi.sub.2WO.sub.6, and on the other hand, the contact area with pollutants was increased, and thereby the degradation efficiency was improved. Due to oxygen vacancy defects, Bi.sub.2WO.sub.6-VO and diatomite@Bi.sub.2WO.sub.6-VO not only narrowed the band gap of Bi.sub.2WO.sub.6 and enhanced the absorption of visible light, but also acted as an electron trap to inhibit the recombination of electrons and holes. As a result, separation and transport efficiencies of carriers were significantly improved, and thereby the photocatalytic efficiency was improved. There was no significant difference in the photocatalytic efficiency between Bi.sub.2WO.sub.6-VO and diatomite@Bi.sub.2WO.sub.6-VO.

(82) FIG. 8 shows the cyclic stability of NO removal with diatomite@Bi.sub.2WO.sub.6 under visible light (λ≥420 nm) irradiation, with the abscissa as time and the ordinate as the NO removal rate.

(83) According to FIG. 8, the photocatalytic efficiency was reduced due to the accumulation of photocatalytic NO oxidation products (nitrates) on the surface of the catalyst. Nitrates were removed through washing. The catalyst was dried after washed with water every time. The washed catalyst still maintained relatively long-lasting NO removal activity. After five cycles, diatomite@Bi.sub.2WO.sub.6exhibited excellent stability and recyclability.

(84) The foregoing are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. All changes or substitutions that can easily occur to those skilled in the art within the technical scope disclosed by the present invention should fall within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to that of the claims.