KR20200086981A - Fabrication of photocatalytic concretes having photodecomposition of pollutants and method of increasing its recyclability - Google Patents

Abstract

The present invention relates to concrete having photocatalytic properties, a method for manufacturing the same, and a method for regenerating the same. The present invention can provide the concrete with photocatalytic properties, comprising: a concrete substrate; a SiO_2 coating layer positioned on the surface of the substrate; and a TiO_2 coating layer positioned on the SiO_2 coating layer.

Description

Manufacturing method and photocatalytic concretes having photodegradation function of pollutant and its recycling method {Fabrication of photocatalytic concretes having photodecomposition of pollutants and method of increasing its recyclability}

It relates to a method for manufacturing photocatalytic concrete having a photolysis function of contaminants and a method for regeneration thereof.

In general, concrete is mixed by mixing water into aggregates and cements, which are raw materials, and then adding and mixing admixtures and pigments as subsidiary materials, and adding the blended material into the mold of the product to apply vibration and hydraulic pressing to mold the product The finished product is loaded into the curing room and supplied with high-temperature and high-humidity steam to accelerate the hydration reaction of concrete to harden the product.

Looking at some points that are pointed out as a problem with materials used in the manufacture of concrete, a large amount of carbon dioxide is generated in the manufacture of cement, which is the main raw material for concrete, and some of the recycled industrial by-products and environmentally harmful substances (such as hexavalent chromium) are used as raw materials for cement. Due to the detection and the like, the solution to the social distrust phenomenon is urging due to a decrease in awareness of concrete.

It is to provide a photoactive concrete capable of decomposing various environmentally harmful substances by adding a photocatalytic function to concrete.

In one embodiment of the invention, the concrete substrate; SiO ₂ coating layer located on the surface of the substrate; And a TiO ₂ coating layer positioned on the SiO ₂ coating layer.

The TiO ₂ coating layer within the TiO ₂ may be anatase sangil. In this case, it means that most of the phases are anatase phases, and preferably, all TiO ₂ particles may be anatase phases.

The SiO ₂ layer and the TiO ₂ layer are divided into layers, and may be a composite (TiO ₂ -SiO ₂ ) having a strong bond.

The optical band gap (Eg) of the composite may be 2.90 eV or less. For the method for calculating the band gap, an experimental example described later may be referred to.

The concrete may have porosity characteristics. This is due to the role of the SiO ₂ layer, and the photocatalytic efficiency may be improved due to the porosity characteristics.

The weight ratio of Ti to Si in the concrete may be 5 to 6. However, this range may be changed to control the bonding strength of the catalyst layer and the photocatalytic efficiency.

The photocatalytic reaction rate of the concrete to toluene may be 0.05 min ^{-1 or} more. As can be seen from the examples described below, this effect can be achieved from a composite of SiO ₂ -TiO ₂ .

In another embodiment of the present invention, preparing a concrete substrate; Preparing a Si sol and a Ti sol; Coating the Si sol on the concrete substrate; And coating the Ti sol on the surface of the coated Si sol.

Coating the Si sol on the concrete substrate; Then, drying and calcining the coated Si sol; may further include.

Coating a Ti sol on the coated Si sol surface; Then, calcining the coated Ti sol; may further include.

In the step of preparing a Si sol and a Ti sol; In the Si sol, the Si raw material may be prepared by hydrolyzing alcohol and water in the presence of an acid.

In the step of preparing a Si sol and a Ti sol; In the Ti sol, the Ti raw material may be prepared by hydrolyzing alcohol and water in the presence of an acid.

Dispersibility may be improved due to the presence of alcohol, which may later affect the uniformity of the layer.

In another embodiment of the present invention, the concrete substrate; SiO ₂ coating layer located on the surface of the substrate; And a TiO ₂ coating layer positioned on the SiO ₂ coating layer; preparing concrete having photocatalytic properties, including; Photodegrading contaminants using the photocatalytic concrete; It provides a method for manufacturing a concrete having a photocatalytic property (or a regeneration method), including; and regenerating by heat treatment of the concrete having the photocatalytic properties.

It may further include the step of photodegrading contaminants using the concrete having the photocatalytic properties; previously, heat-treating the concrete having the photocatalytic properties to increase the photoactivity.

By coating a photocatalytic material on concrete, it is possible to provide a photocatalytic concrete capable of photodegrading various environmentally harmful substances.

1 is an optical photograph of a sample prepared according to an embodiment of the present invention.
2 is an XRD analysis result of a sample prepared according to an embodiment of the present invention.
3 is a result of UV-DRS analysis of a sample prepared according to an embodiment of the present invention.
4 is a result of FE-SEM analysis of a sample prepared according to an embodiment of the present invention.
5 is an EDS analysis result of a sample prepared according to an embodiment of the present invention.
6 is a result of FTIR analysis of a sample prepared according to an embodiment of the present invention.
7 is a photocatalyst performance analysis result of a sample prepared according to an embodiment of the present invention.
8 is a result of calculating a reaction rate of a sample prepared according to an embodiment of the present invention.
9 shows a schematic reaction mechanism of a photocatalyst according to an embodiment of the present invention.
10 and 11 are cycle characteristics of a sample prepared according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail. However, this is provided as an example, and the present invention is not limited thereby, and the present invention is only defined by the scope of claims to be described later.

Example

material

The cement mortar used in the experiment was manufactured by Hanju PVT, LTD, and Titanium(IV) butoxide (Ti(OBu) ₄ ) and Tetraethyl Orthosilicate were manufactured by Sigma Aldrich. Ethanol, hydrochloric acid, and Pluronic P123 were obtained from Dukasan Korea, and all were in A grade.

Produce

Concrete sample manufacturing

A concrete sample (CS) was prepared using cement mortar cement from Hanju PVT, LTD, Korea, and the ratio of sand to cement was 1:0.6.

This concrete sample was specifically designed to produce a thin concrete substrate with a thickness of 1 cm.

1 Kg of cement mortar was mixed with 150 ml of water for 20 minutes using a sand mixer, and then the slurry of cement mortar was poured into a circular plastic mold having a diameter of 10 cm and a thickness of 1 cm.

Thereafter, the concrete sample was dried at room temperature and cured at room temperature for 28 days.

The concrete sample thus prepared is shown in Fig. 1(a).

SiO ₂ Preparation and coating of sol

SiO ₂ sol was prepared by hydrolysis of Tetraethyl Orthosilicate with ethanol and deionized water in the presence of HCl as a catalyst. The reaction took place under magnetic stirring for 3 hours.

TEOS: ethanol: H ₂ O: HCl molar ratio of from 1: 3: 11.05: 0.5 and, Pluronic 123 was so added in small portions.

After stirring, a stable SiO ₂ sol was formed, the sol was spray coated on a concrete substrate, and the silicon wafer (SW) was dried at 100° C. for 12 hours.

Thereafter, the silicon wafer as well as the concrete substrate coated with SiO ₂ were calcined at 450° C. for 2 hours.

TiO ₂ Sol production and coating

Titanium(IV) butoxide hydrolyzed with ethanol and water under acidic conditions. At this time, the reaction was performed under magnetic stirring conditions for 1 hour.

The molar ratio of Ti(OBu) ₄ : Ethanol: H ₂ O: HCl was 1:3:11.05:0.5.

After stirring, a stable TiO ₂ sol was formed, and the sol was coated on a SiO ₂ coated and uncoated concrete substrate, as well as a silicon wafer dried at 100° C. for 12 hours. TiO ₂ coated concrete and silicon wafer samples were calcined at 450°C. 1(b) is a photograph of a TiO ₂ coated concrete sample.

Experimental Example

Assessment Methods

Of toluene gas Photocatalyst Decomposition experiment method

The photocatalytic decomposition experiment of toluene gas was performed as follows.

A concrete sample coated with TiO ₂ and TiO ₂ -SiO ₂ was inserted into a 2L Teflon film bag and toluene gas (10 ppm) was added.

It was then kept in the dark for 30 minutes to achieve adsorption equilibrium for photolysis experiments of toluene gas.

Thereafter, two 6W UV light tubes having an intensity rating of 2 mWcm ^-2 were used to irradiate ultraviolet rays to a bag containing a coated concrete sample.

After a certain time interval, the irradiated gas sample (1 ml) was recovered by syringe. The photolysis rate of toluene gas was evaluated using a gas chromatography (GC) system.

Method for evaluating physical properties

범위에서 CuKα 선 (

= 1.5418

)을 갖는 X선 회절계 (XRD, Bruker AXS 8 advanced)를 사용하여 평가 하였다. Phase and structural parameters are 10°-80° 2

CuKα line in range (

= 1.5418

It was evaluated using an X-ray diffractometer (XRD, Bruker AXS 8 advanced).

Optical measurements of coated samples were performed using a UV-vis diffuse reflection spectrophotometer (UV-vis DRS, UV3600, Shimadzu, Japan).

The morphology of the coated concrete samples was evaluated using a field emission scanning electron microscope (FE-SEM, Hitachi Field Emission S-4300).

Energy dispersive X-ray spectroscopy was used for elemental analysis of coated concrete samples.

The photolysis of toluene gas was monitored by gas chromatography (Alginate Technology 7890A GC system).

Evaluation results

X-ray diffraction evaluation result

XRD peak analysis is therefore difficult because a specific sample contains many elements. As a result, XRD analysis of the sol coated on the silicon wafer was performed, and the XRD pattern is shown in FIG. 2.

To compare the characteristic peaks of the silicon wafer with SiO ₂ and TiO ₂ , the XRD pattern of the uncoated silicon wafer was also recorded.

Silicon wafers exhibit broad peaks in the 10° to 25° range.

However, when coated with SiO ₂ or TiO ₂ sol, it can be seen that the wide peak disappeared as shown in FIG. 2.

The SiO ₂ coated silicon wafer XRD pattern shows characteristic peaks at 21.89° and 24.2°.

The XRD pattern coated with TiO ₂ shows the characteristic peak of the silicon wafer at 24.5° and the characteristic peak of TiO ₂ at 25.6°.

This means that coated TiO ₂ is present in the anatase phase and no peak on the rutile or brookite phase of TiO ₂ is observed.

In the TiO ₂ -SiO ₂ coated sample, very small peaks were observed for the silicon wafer and SiO ₂ , but the peaks of TiO ₂ were observed with good intensity levels, which peaks matched very closely to the standard JCPDS card 21-1272. Is the result.

The excellent strength of the peak means strong bonding of the TiO ₂ sol to the previously coated SiO ₂ surface. In addition, TiO ₂ -SiO ₂ improves the crystal properties of the TiO ₂ coating.

Similarly, for concrete samples, the first layer of the SiO ₂ coating is expected to play a very important role in improving the stability of the TiO ₂ coating as well as improving the photocatalytic efficiency.

UV- vis DRS result

The UV-vis DRS of the concrete samples coated with SiO ₂ and TiO ₂ was analyzed to determine the optical properties, and the uncoated concrete samples were used as a reference for DRS measurement.

The absorbance spectrum was measured in the range of 200 nm to 700 nm as shown in FIG. 3.

Samples coated with SiO ₂ show broad absorbance in the range of 200 nm to 500 nm, but samples coated with TiO ₂ are very broad in the wavelength range of 200 nm to 400 nm and show high absorbance.

As expected, TiO ₂ coating samples show absorbance only in the UV region of the electromagnetic spectrum.

Concrete samples coated with TiO ₂ -SiO _{2 show} broad absorbance peaks in the wavelength range from 200 nm to 500 nm.

The optical band gap (Eg) values of the TiO ₂ and TiO ₂ -SiO ₂ composites were estimated using the Tauc equation. A concrete sample coated with SiO ₂ -TiO ₂ has a value of 2.90 eV, while a concrete sample coated with TiO ₂ has a band gap of 3.18 eV.

The reduction in band gap energy of the TiO ₂ -SiO ₂ coating may be due to the chemical or physical bond formed between TiO ₂ and SiO ₂ . In addition, SiO ₂ helps to improve the stability of the TiO ₂ coating and improve the absorbance of the electromagnetic spectrum.

Morphology evaluation results

The FE-SEM analysis was used to analyze the shape of the TiO ₂ -SiO ₂ coated concrete sample and the silicon wafer, and the results are shown in FIG. 4.

Figure 4 (a) is for a concrete sample, Figure 4 (b) ~ (c) shows a photomicrograph of the concrete sample coated with SiO ₂ and TiO ₂ , respectively.

The concrete sample coated with SiO ₂ shows high porosity compared to the sample coated with TiO ₂ .

Figure 4 (d) shows a FE-SEM image of a concrete sample coated with TiO ₂ -SiO ₂ . It can be confirmed that there are small microcracks by calcining at 450°C. In addition, it showed high porosity with uniform coating of TiO ₂ .

The insertion of the SiO ₂ layer between the concrete sample and the TiO ₂ coating plays a very important role in the formation of a pure anatase phase of the TiO ₂ nanoparticles, as well as the adhesion of TiO ₂ to the concrete sample.

It is also well known that concrete samples contain many elements in the form of oxides such as magnesium, calcium, aluminum and carbon.

Direct coating of TiO ₂ can react with metal oxides and affect the photocatalytic efficiency of the TiO ₂ layer.

4(e) to (f) show micrographs of TiO ₂ -SiO ₂ coated on a silicon wafer. From this, the uniformity of the SiO ₂ layer to which the silicon wafer and TiO ₂ nanoparticles are attached can be clearly seen. The formation of a bond between SiO ₂ and TiO ₂ improves the stability of the TiO ₂ layer.

Energy dispersive X-ray spectroscopy evaluation results

Elemental analysis of samples coated with TiO ₂ -SiO ₂ was performed based on the EDS spectrum.

5 (a) shows the EDS spectrum of TiO ₂ -SiO ₂ coated on a concrete sample. From this, it can be seen that various elements such as Ti, O, Si, Ca, Mg, Al, S and C exist.

The weight percentage values of these elements are shown in Table 1.

[Table 1]

The EDS spectrum of the silicon wafer sample coated with TiO ₂ -SiO ₂ is shown in FIG. 5(b). This spectrum only showed the presence of Ti, Si, O and C.

Fourier transform infrared spectroscopy evaluation results

6 shows FTIR spectra of TiO ₂ , SiO ₂ and TiO ₂ -SiO ₂ coated on concrete samples in a wavenumber range of 400-2000 cm ^-1 .

The characteristic peaks of Si-O-Si observed between 900-1200 cm ^-1 were also generally observed in metallic oxygen bonds.

The peak observed at 870 cm ^-1 is due to the Si-O-Si symmetrical stretching. The peak observed at 1635 cm ^-1 is due to OH vending vibration and is due to the chemically adsorbed water molecules.

The broad absorption peak observed at 3450 cm ⁻¹ shows the OH stretching vibration. The band observed at 450 cm ^-1 is due to Ti-O stretching.

The broad peak observed at 900-1200 cm ^-1 increased because the characteristic peak of Ti-O-Si was observed at 970 cm ^-1 for the concrete samples coated with TiO ₂ -SiO ₂ .

Hydroxyl radicals in the range of 3200-3600 cm ^-1 show a decrease in the degree and strength of broadening, and free hydroxyl radicals present in the SiO ₂ coated sample form a strong bond with TiO ₂ which increases the stability of the coating. And indirectly it helps to improve the photocatalyst.

Photocatalyst Performance evaluation

The photocatalytic performance of the samples coated with TiO ₂ and TiO ₂ -SiO ₂ was evaluated by photolysis of toluene gas under UV light irradiation.

7 shows the photocatalytic performance of TiO ₂ and TiO ₂ -SiO ₂ coated samples as a function of irradiation time.

In order to determine the effect of UV light on toluene gas, a pure sample experiment without a coating layer was performed under the same conditions, and as a result, it was confirmed that there was no activity when there was no coated sample or light irradiation.

Therefore, it was found that the sample coated with TiO ₂ -SiO ₂ has photocatalytic activity for photocatalytic decomposition of toluene gas under UV light irradiation.

The photolysis efficiency of the sample was calculated using equation (1).

The concrete sample coated with TiO ₂ -SiO ₂ showed a photolysis efficiency of 69%, while the TiO ₂ concrete sample showed a photolysis efficiency of 57%.

This result means that the first layer of SiO _{2 on} the concrete sample improves the photocatalytic efficiency of TiO ₂ . In addition, the above-described UV-vis DRS results support that the photocatalytic efficiency of the TiO ₂ coating is improved.

The photolysis reaction of toluene followed pseudo-first order kinetics.

By plotting ln(C0/C) over time, the rate constant of the photocatalytic reaction was determined, where C0 is the initial concentration of toluene gas, C is the concentration of toluene gas after irradiation of the concrete sample, and the corresponding time interval. The reaction rate constants of TiO ₂ and TiO ₂ -SiO ₂ concrete samples under UV light irradiation were 0.048 min ^-1 and 0.052 min ^{- 1} , respectively.

It has been found that concrete samples coated with TiO ₂ -SiO ₂ have higher photocatalytic efficiency than concrete samples coated with TiO ₂ .

Because the concrete substrate is porous and absorbs toluene gas on the surface, TiO ₂ and concrete samples play a very important role.

Subsequently, when a sample coated with TiO ₂ and TiO ₂ -SiO ₂ is irradiated with ultraviolet rays, OH radicals that react with phenyl rings of toluene and various intermediate products such as phenol, benzaldehyde, and benzoic acid are generated and reacted. Finally these compounds were converted to CO ₂ and H ₂ O. Fig. 9 shows this schematic mechanism.

TiO ₂ -SiO ₂ Stability of concrete samples coated with

The stability and lifetime of concrete samples coated with TiO ₂ -SiO ₂ are very important variables for applying these photocatalytic concrete to industrial sites to reduce environmental pollutants.

In order to determine the stability and lifetime of concrete coated with TiO ₂ -SiO ₂ , photocatalytic concrete specimens were repeatedly used for photolysis of toluene gas under the same experimental apparatus, the experiment was repeated three times and the results are shown in FIG. 10. Did.

It can be seen that the photolysis efficiency of the sample repeatedly used 3 times decreased from 69 to 58%. The decrease in photocatalytic efficiency may be due to changes in the internal microstructure of the concrete specimen due to hydration.

Another rationale for the potential loss of photocatalytic activity may be due to the reduced number of active sites due to the continued hydration of the hydrated concrete sample.

The formed hydration product, calcium silicate hydrate, can inhibit the photocatalytic activity by interfering with the toluene gas and the TiO ₂ active site interaction and preventing photon diffusion.

Therefore, to overcome this limitation, a photocatalytic concrete sample regenerated by heat treatment can be used.

Each cycle, the photocatalytic concrete sample is heated at 120° C. for 2 hours and used for photolysis of toluene gas.

In the heat treatment process, the intermediate sample evaporated on the concrete sample and deposited on the active site of the active site were exposed to interact with the reactive molecules again, and this phenomenon restored the photocatalytic activity.

It is possible to remove toluene gas and decomposed products that are not deteriorated as well as heat treatment.

After heat treatment, a recyclability test for toluene gas decomposition was performed, and the results are shown in FIG. 11. The photocatalytic efficiency after concrete sample regeneration was negligibly low. That is, it was confirmed that the concrete sample was very stable and reusable.

The present invention is not limited to the above embodiments, but may be manufactured in various different forms, and a person having ordinary skill in the art to which the present invention pertains may have other specific forms without changing the technical spirit or essential features of the present invention. It will be understood that can be carried out as. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive.

Claims (13)

Concrete substrate;
SiO ₂ coating layer located on the surface of the substrate; And
A TiO ₂ coating layer located on the SiO ₂ coating layer;
Concrete having a photocatalytic property comprising a.
According to claim 1,
The TiO ₂ coating TiO ₂ in the concrete with the photocatalytic property will anatase merchant.
According to claim 1,
The SiO ₂ layer and the TiO ₂ layer are divided into layers, and concrete having a photocatalytic property that is a composite (TiO ₂ -SiO ₂ ) having a strong bond.
According to claim 1,
Concrete having a photocatalytic property that the optical band gap (Eg) of the composite is 2.90 eV or less.
According to claim 1,
The concrete is a concrete having a photocatalytic property that has a porous property.
According to claim 1,
The weight ratio of Ti to Si in the concrete is concrete having a photocatalytic property of 5 to 6.
According to claim 1,
The concrete has a photocatalytic property that the photocatalytic reaction rate to toluene is 0.05 min ^-1 or more.
Preparing a concrete substrate;
Preparing a Si sol and a Ti sol;
Coating the Si sol on the concrete substrate; And
Coating a Ti sol on the coated Si sol surface;
Method for producing concrete having a photocatalytic property comprising a.
The method of claim 8,
Coating the Si sol on the concrete substrate; after,
Drying and calcining the coated Si sol; further comprising a method for producing concrete having photocatalytic properties.
The method of claim 8,
Coating a Ti sol on the coated Si sol surface; after,
Calcining the coated Ti sol; The manufacturing method of the concrete having a photocatalytic property further comprising a.
The method of claim 8,
In the step of preparing the Si sol and Ti sol; In,
The Si sol is a method for producing concrete having photocatalytic properties, which is produced by hydrolyzing alcohol and water in the presence of an acid as an Si raw material.
The method of claim 8,
In the step of preparing the Si sol and Ti sol; In,
The Ti sol is a method for producing concrete having photocatalytic properties, wherein the Ti raw material is produced by hydrolyzing alcohol and water in the presence of an acid.
Concrete substrate; SiO ₂ coating layer located on the surface of the substrate; And a TiO ₂ coating layer positioned on the SiO ₂ coating layer; preparing concrete having photocatalytic properties, including;
Photodegrading contaminants using the photocatalytic concrete; And
Heat treating and regenerating the concrete having the photocatalytic properties;
Concrete regeneration method having a photocatalytic property comprising a.

Images