KR101858094B1 - PHOTOCATALYST WITH CORE/SHELL STRUCTURE INCLUDING BASALT FIBER AND Zn-BASED PHOTOCATALYST - Google Patents

Abstract

The present invention relates to a photocatalyst having a core/shell structure, comprising: a core including a basalt fiber; and a shell including a zinc-based photocatalyst. In particular, the photocatalyst according to the present invention, which has a core/shell structure comprising a basalt fiber and a zinc-based photocatalyst, can selectively convert carbon dioxide (CO_2) into carbon monoxide (CO) while improving CO_2 photoreduction efficiency and scarcely forming other reduction by-products, by effectively adsorbing CO_2 gas and suppressing recombination of photogenerated electron-hole pairs. In particular, the CO_2 adsorption ability of a photocatalyst having BF-Zn_(1-x)Mg_xO core/shell structure was significantly higher than that of a photocatalyst having BF-ZnO core/shell structure; and the subsequent synergistic effect realized by the BF core and Zn_1-xMg_xO shell inside BF-Zn_(1-x)Mg_xO can convert carbon dioxide (CO_2) into carbon monoxide (CO) with higher efficiency.

Description

[0001] PHOTOCATALYST WITH CORE / SHELL STRUCTURE INCLUDING BASAL FIBER AND Zn-BASED PHOTOCATALYST [0002]

The present invention relates to a photocatalyst which can be used for photoreduction of carbon dioxide (CO ₂ ), and more particularly to a photocatalyst having a core / shell structure including a zinc-based photocatalyst material and a basalt fiber support.

The emission of carbon dioxide (CO ₂ ), the mainstay of greenhouse gases that cause global warming, has steadily increased over the past few centuries as a result of human activity. In recent years, the demand to meet global energy demand has led to the development of a series of strategies to reduce carbon dioxide emissions. As an example, the CO ₂ photoreduction process is clean and environmentally friendly because it converts carbon dioxide to carbon monoxide and hydrocarbon fuels using solar energy at room and atmospheric pressure without generating harmful by-products.

Of the semiconductor photocatalysts developed for use in the CO ₂ photoreduction process, titanium dioxide (TiO ₂ ) is readily available, has photo-stability and non-toxicity, Widely used.

Various methods have been attempted to further improve the photocatalytic activity of the titanium dioxide. For example, there have been proposed various methods such as crystal anisotropic growth, doping with ions, and heterojunction of semiconductor photocatalyst (hetero-structuring of semiconductor photocatalysts) is a technique for improving photocatalytic properties by changing the crystal structure, electronic structure, lifetime of charge carriers, and probability of electron-hole recombination.

However, existing studies including these are limited to TiO ₂ semiconductor, and it is necessary to develop various photocatalytic semiconductor materials.

In addition, there is no technology related to a photocatalyst for generating carbon monoxide (CO) through photoreduction of carbon dioxide by using basalt fiber as a support, and development of new technology therefor is required.

Korean Unexamined Patent Application Publication No. 10-2006-0012020 (Publication date: 2006.02.06) Korean Patent Laid-Open No. 10-2013-0102422 (Publication date: 2013.09.17) Korean Published Patent Application No. 10-2012-0026656 (published on March 20, 2012) Korean Patent Laid-Open Publication No. 10-2015-0104249 (published on 2015.09.15)

The object of the present invention is to provide a photocatalyst having a core / shell structure capable of reducing basalt fiber as a support and reducing carbon dioxide to carbon monoxide with high efficiency.

In order to achieve the above object, the present invention provides a core comprising basalt fibers; And a shell comprising a zinc-based photocatalyst.

Further, the present invention proposes a photocatalyst of a core / shell structure characterized in that the zinc-based photocatalyst is ZnO.

The present invention also provides a photocatalyst having a core / shell structure, wherein the zinc-based photocatalyst is Zn _1-x Mg _x O (where 0 <x <1).

The present invention also provides a photocatalyst having a core / shell structure, wherein the zinc-based photocatalyst is Zn _0.75 Mg _0.25 O.

The present invention also provides a photocatalyst of a core / shell structure, which is used for photoreduction of carbon dioxide (CO ₂ ).

The present invention also provides a photocatalyst of a core / shell structure characterized by being used for selective photoreduction of carbon dioxide (CO ₂ ) to carbon monoxide (CO).

And, in another aspect of the present invention, the present invention provides a method of manufacturing a semiconductor device, comprising: (a) preparing a sol solution containing a zinc precursor or a sol solution containing a zinc and magnesium precursor; (b) adding the basalt fiber to the sol solution containing the zinc precursor or the sol solution containing the zinc and magnesium precursor; And (c) heat treating the basalt fiber-containing sol solution obtained in the step (b). The present invention also provides a method for producing the core / shell structure photocatalyst.

Also, the present invention proposes a method for producing a photocatalyst of a core / shell structure, wherein the zinc precursor is zinc nitrate.

Also, the present invention provides a core / shell structure photocatalyst production method, wherein the magnesium precursor is magnesium nitrate.

The photocatalyst of the core / shell structure including the basalt fiber (BF) and the zinc-based photocatalyst according to the present invention effectively adsorbs CO ₂ gas and inhibits recombination of photogenerated electron-hole pairs, It is possible to selectively reduce carbon dioxide (CO ₂ ) to carbon monoxide (CO) while improving CO ₂ light reduction efficiency and hardly producing other reducing by-products.

In particular, was BF-ZnO core / shell structure in comparison to the photocatalyst _{BF-Zn 1-x Mg x} O core / shell structure of the photocatalyst of the CO ₂ adsorption capacity (adsorption ability) of a significantly higher, _{BF-Zn 1-x} accordingly The synergism exerted by the BF core in Mg _x O and the Zn _1-x Mg _x O shell can reduce carbon dioxide (CO ₂ ) to carbon monoxide (CO) at higher efficiencies.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a conceptual diagram showing the CO ₂ photoreduction mechanism in the presence of BF-Zn _1-x Mg _x O core-shell particles H ₂ O. FIG.
FIG. 2 is a schematic view showing a process and mechanism of a photocatalyst particle (BF-Zn _1-x Mg _x O) having a core-shell structure according to the present invention.
3 is a conceptual diagram of a reactor for CO ₂ photoreduction.
FIG. 4 is an X-ray diffraction (XRD) pattern and scanning electron microscope (SEM) image of BF-ZnO and BF-Zn _1-x Mg _x O particles.
5 is an energy dispersive X-ray spectroscopy (EDAX) spectrum of BF-ZnO and BF-Zn _1-x Mg _x O particles.
6 is an SEM element mapping image of BF-ZnO and BF-Zn _1-x Mg _x O particles.
FIG. 7 is a diffuse reflectance-UV-visible absorption spectra and photoluminescence (PL) curve of BF-ZnO and BF-Zn _1-x Mg _x O particles.
FIG. 8 is a photocurrent density curve of BF, BF-ZnO and BF-Zn _0.75 MgO _.25 O particles.
FIG. 9 is a CO2-TPD (Temperature programmed desorption) curve corresponding to CO ₂ desorption for BF-ZnO and BF-Zn _1-x Mg _x O particles.
Fig. 10 shows the results of measurement of the catalytic performance (carbon monoxide and methane production yield) for CO ₂ photolysis in the presence of H ₂ O, measured on BF-ZnO and BF-Zn _1-x Mg _x O particles.

In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

Embodiments in accordance with the concepts of the present invention can make various changes and have various forms, so that specific embodiments are illustrated in the drawings and described in detail in this specification or application. It should be understood, however, that the embodiments according to the concepts of the present invention are not intended to be limited to any particular mode of disclosure, but rather all variations, equivalents, and alternatives falling within the spirit and scope of the present invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, the terms "comprises ", or" having ", or the like, specify that there is a stated feature, number, step, operation, , Steps, operations, components, parts, or combinations thereof, as a matter of principle.

Hereinafter, the present invention will be described in detail.

The photocatalyst of the core / shell structure according to the present invention comprises a core comprising a basalt fiber (BF); And a shell comprising a zinc-based photocatalyst.

That is, the present invention relates to a semiconductor material which acts as a photosensitizer and uses basalt fibers as a support to expand adsorption of reactive species and utilization of incident light characteristics in order to improve photocatalytic efficiency, Is used.

The above-mentioned basalt fiber constitutes a core as a support and has a high content of MgO and CaO and a low content of SiO ₂ and an alkali oxide, which is a very preferable material for absorbing carbon dioxide. It can be used as a substrate mineral.

The zinc-based photocatalyst may be ZnO or Zn _1-x Mg _x O (where 0 < x < 1), and more preferably Zn _0.75 Mg _0.25 O. As described above, when Zn _1-x Mg _x O doped with magnesium (Mg) in the crystal structure of ZnO is used as a photocatalyst contained in the shell, the electron-hole charge separation and the carbon dioxide (CO ₂ ) Can be improved.

Thus, the photocatalyst according to the core / shell structure according to the present invention may be useful in selective light reduction to carbon monoxide (CO) of the optical reduction and, more particularly carbon dioxide (CO ₂₎ of carbon dioxide (CO _2).

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram schematically illustrating a CO ₂ photoreduction mechanism by BF-Zn _1-x Mg _x O core / shell photocatalyst particles, which is an example of the core / shell photocatalyst according to the present invention described above.

Referring to FIG. 1, Zn _1-x Mg _x O is pure ZnO Since it has a shorter band gap than the basalt fiber core / Zn _1-x Mg _x O Excitation by photons starts rapidly in Zn _1-x Mg _x O on the photocatalyst particles of the shell. The excited electrons can be efficiently transferred to carbon dioxide molecules. When the carbon dioxide molecules are preferentially adsorbed on the surface of the basalt fiber support, the holes of the valance band of Zn _1-x Mg _x O are trapped by H ₂ O species and OH radicals and proton, Lt; / RTI &gt; The protons are converted to H radicals by an electron, also, electrons in the conduction band of the Zn _1-x Mg _x O is CO ₂ reacts with CO ₂ ^molecules to form, the CO ₂ ^- has been reduced to form the CO .

Hole pairs photo-generated (photo-generated) e by a Zn _1-x Mg _x O obtained by adding Mg to ZnO as the ^- bar to facilitate the separation of the ^{(e / h +), BF} -Zn 1 _{- x} Mg _x O The synergistic effect exerted by the Mg bound in the shell of the basalt fiber core and ZnO in the photocatalytic particles of the core / shell structure can improve the CO ₂ reduction efficiency and increase the CO production.

Meanwhile, an example of a method for producing a photocatalyst of a core / shell structure according to the present invention includes: (a) preparing a sol solution containing a zinc precursor or a sol solution containing a zinc and magnesium precursor; (b) adding the basalt fiber to the sol solution containing the zinc precursor or the sol solution containing the zinc and magnesium precursor; And (c) heat treating the basalt fiber-containing sol solution obtained in the step (b).

Hereinafter, the present invention will be described in detail by way of examples with reference to the drawings.

However, the embodiments according to the present disclosure can be modified in various other forms, and the scope of the present specification is not construed as being limited to the embodiments described below. Embodiments of the present disclosure are provided to more fully describe the present disclosure to those of ordinary skill in the art.

EXAMPLES Photocatalyst particles of a basalt fiber core-zinc-based photocatalytic shell structure (BF-ZnO and BF-Zn _1-x Mg _x O)

As shown in FIG. 2, a core made of a basalt fiber (BF), which is a mineral support, and a shell made of ZnO or Zn _1-x Mg _x O nanoparticles grown on the core, (BF-ZnO and BF-Zn _1-x Mg _x O) were prepared using a modified sol-gel method.

First, zinc nitrate (Zn (NO ₃ ) ₂ .4H ₂ O, 99.99%, Junsei Chemical, Japan) and magnesium nitrate (Mg (NO ₃ ) ₂ .6H ₂ O, 99.99%, Junsei Chemical , Japan) were used as precursors of zinc and magnesium, respectively, and a sol mixture of ZnO or Zn _1-x Mg _x O was prepared using absolute ethanol as a solvent.

As shown in Fig. 2 (a), the zinc and magnesium precursors were added stepwise to 500 mL of ethanol and stirred for 1 hour until a homogeneous solution was obtained. During the synthesis, the pH of the solution was maintained at 2 to 3 to induce rapid hydrolysis of Zn and Mg precursors. Basalt fiber (BF) (YJC com., Hampyong, Jeonnam, Korea) was added to the sol solution, stirred for 2 hours, transferred to autoclave, and heat-treated at 200 ^° C for 4 hours to crystallize the solution.

As shown in FIG. 2 (b), zinc nitrate and magnesium nitrate are partially hydrolyzed with Zn (OR) ₄ and Mg (OR) ₆ in an ethanol solution, respectively, - [metal-O-metal] -OR, respectively. The nanocrystals grow after the Zn _1-x Mg _x O nanostructures are bonded on the surface of BF during the heat treatment process. The powder obtained after the synthesis was washed and dried to finally obtain a core / shell structure photocatalyst sample (BF-ZnO, BF-Zn _0.80 Mg _0.2 O, BF-Zn _0.75 Mg _0.25 O, BF-Zn _0.67 Mg _0.33 O and BF- _0.50 Mg _0.50 O core-shell particles).

<Experimental Example>

4 (a) is BF, BF-ZnO and _{BF-Zn 1-x Mg x} O The results of XRD pattern analysis of particles are shown.

According to Fig. 4 (a), BF does not show a peak corresponding to the metal oxide but appears to be amorphous.

The XRD peak of BF-ZnO was confirmed to be a hexagonal ZnO crystal phase having a P63mc space group. The 2θ values were 31.75 °, 34.44 °, 36.25 °, 47.54 °, 56.55 °, 62.87 °, 67.92 ° , And 69.06 degrees correspond to the (100), (002), (101), (102), (110), (103), (112) and (201) planes, respectively.

In the case of BF-Zn _1-x Mg _x O particles, the MgO peak was not observed, and the 2θ value of the XRD peak was almost the same as the BF-ZnO particle except for the case of Zn _0.75 Mg _0.25 O. A well-defined XRD peak of ZnO and Zn _1-x Mg _x O indicates that the core / shell structure between BF and the nanoparticles is highly aligned. In addition, the particles containing Zn _1-x Mg _x O have wider and narrower peaks than ZnO-containing particles, indicating that Zn _1-x Mg _x O has a smaller crystal size than ZnO do. The average crystal size was calculated using the (101) peak based on the Scherrer equation, ZnO, Zn grown on the BF surface _0.80 Mg of _{0.2 O, Zn 0.75 Mg 0.25 O} , Zn 0.67 Mg 0.33 O, and Zn _0.50 Mg _0.50 O The crystal sizes were 29.33, 26.55, 27.09, 38.01, and 42.21 nm, respectively, and it was confirmed that the crystal size decreased until the Mg addition amount reached 25%.

4B is an SEM image of ZnO particles, Zn _1-x Mg _x O particles and MgO particles, and Fig. 4C is an SEM image of BF, BF-ZnO and BF-Zn _1-x Mg _x O SEM image of particles.

In the SEM image shown in FIG. 4 (b), pure ZnO particles exhibit a hexagonal shape while Zn _1-x Mg _x O particles having a size of about 100 nm are mixed with cubic and hexagonal shapes Show. However, it has been confirmed that pure MgO has a shape similar to a thin cloth.

Referring to Fig. 4 (c), BF had a diameter of 15 [mu] m and its surface was smooth. The core / shell structure particles of BF-nanoparticles were prepared by growing ZnO and Zn _1-x Mg _x O nanoparticles. The regular arrangement of ZnO and Zn _1-x Mg _x O nanoparticles was clearly observed in all specimen shells, indicating that the alignment of the core-shell structure is well established. The nanoparticles ZnO and Zn _1-x Mg _x O completely covered the BF surface. The grown part consisted of uniform and fine spherical particles of about 100 nm in size with good dispersion, and all the shells had a flower shape. On the other hand, as the amount of magnesium added increases, the size of the plate-shaped part connecting the particles in a net shape increases. This part is probably regarded as a complex of ZnMgO, and the content of Zn _0.75 Mg _0.25 O particles greatly increased. When more magnesium was added, many thin particles were joined together to form the shape of a cotton wad.

5 and 6 are each energy dispersive X- ray spectroscopy (EDAX) analysis and SEM elemental mapping (elemental mapping) as an image, and ZnO-BF _{BF-Zn 1 - x Mg x} O metallic atoms on the surface of the particles It confirms existence. Table 1 below shows the results of the atomic composition analysis of the respective particles (BF-ZnO and BF-Zn _1-x Mg _x O particles) determined by EDAX.

The EDAX peak in Figure 5 shows that the basalt fiber contains oxides of various metals such as Na, K, Ca, Mg, Al, Si, Fe, and Ti.

Under pure BF in Table 1 was 15.8 at% of Si, 6.2% at% of the total, and include alkali metal, 0.59 at% of Ti, 2.59 at% of Fe and Al of 4.44 at%, Ca which acts as a CO ₂ absorbent And Mg contents were 2.34 at% and 1.89 at%, respectively.

The BF-ZnO particles contained 15.55 at% Zn and the contents of other elements were slightly decreased.

The Zn concentration in Zn _1-x Mg _x O particles increased with increasing Mg content in the synthesis step.

On the other hand, according to FIG. 6, it was confirmed that all the elements were uniformly dispersed on the surface of the basalt fiber.

7 (a) and 7 (b) show diffuse reflectance-UV-visible absorption spectra and photoluminescence spectra of BF-ZnO and BF-Zn _{1 - x} Mg _x O particles, , PL) spectrum.

According to Fig. 7 (a), pure BF absorbs a wide range of wavelengths due to the presence of transition metals such as Ti and Fe, and after the growth of ZnO and Zn _1-x Mg _x O nanoparticles, It became clear. The specimen of the BF-ZnO core-shell structure shows maximum band in the wavelength range of 300-400 nm, indicating that the Zn-O-Zn species is polymerized. These bands slightly shifted to larger wavelengths in BF-Zn _1-x Mg _x O than in BF-ZnO except for BF-Zn _0.5 Mg _0.5 O particles. On the other hand, the absorption spectrum had a steeper absorption edge, similar to the results obtained from Tauc's equation. The band gaps of pure BF, BF-ZnO, BF-Zn _0.80 Mg _0.2 O, BF-Zn _0.75 Mg _0.25 O, BF-Zn _0.67 Mg _0.33 O and BF-Zn _0.50 Mg _0.50 O particles were 1.58 , 3.11, 3.07, 3.09, 3.10, and 3.15 eV.

Also, referring to FIG. 7 (b), all the particles showed a PL signal having a similar curved shape, but BF-ZnO showed a strong PL signal (maximum excitation wavelength: 469 nm) in the wavelength range of 400-550 nm . The curve strength of BF-Zn _0.75 Mg _0.25 O rapidly decreased. However, since Mg acts as a recombination center, when the amount of added Mg atoms exceeds 0.25 mol%, the PL intensity becomes stronger. The decrease in PL emission was in the following order: BF-Zn _0.50 Mg _0.50 O> BF-Zn _0.67 Mg _0.33 O>BF-ZnO> BF-Zn _0.80 Mg _0.2 O BF-Zn _0.75 Mg _0.25 O.

The reduced PL intensity exhibited by the BF-Zn _0.75 Mg _0.25 O particles as described above may be due to defects that are generated by Mg ions intercalated into the ZnO structure to promote electron transfer and interfere with electron-hole pair recombination at the surface.

FIG. 8 is a graph showing the results of a comparison of BF, BF-ZnO, BF-Zn _0.75 Mg _0.25 O As a photocurrent density curve of BF, BF-ZnO and BF-Zn _0.75 MgO _.25 O particles measured to confirm the efficiency of photo-generated electron-hole generation in the particles, the light source is on- Time typical photocurrent response.

Referring to FIG. 8, a rapid increase in the photoreduction current was observed when the light was turned on, and stabilized in steady state a few seconds later. Further, when the light was turned off, the photocurrent immediately decreased to almost zero. When the light was turned on, the maximum photocurrents obtained from BF-ZnO and BF-Zn _0.75 Mg _0.25 O were 70.23 and 96.01 mA cm ^-2 , respectively, which was higher than the maximum photocurrent value of BF (30.50 mA cm ^-2 ). Therefore, it has been confirmed that the Mg component serves as an intermediate for promoting the effective separation of the photo-generated electron-hole pairs, and thus is advantageous for improving the photocurrent.

FIG. 9 is a graph showing the relationship between the core / shell structure of BF-ZnO and BF-Zn _1-x Mg _x O The CO ₂ desorption profile (CO ₂ -TPD) obtained at high temperature (> 800 ° C) of the particles. In the case of pure BF, the curve strength of CO ₂ desorption was very small. However, in the case of BF-ZnO, it was about three times higher. The amount of adsorbed CO ₂ is BF-Zn _1-x Mg _x O Significant improvement on the particles, which means that much more CO ₂ molecules are adsorbed on the BF-Zn _1-x Mg _x O surface. In particular, BF-Zn _0.75 Mg _0.25 O particles were the highest. Generally, a fast catalytic reaction occurs when many reactants are well adsorbed on the catalyst. The presence of Mg and Zn causes a relative increase in the number of adsorbed CO ₂ molecules and contributes significantly to the catalytic performance of the BF-Zn _1-x Mg _x O particles.

Fig. 10 shows the photoreduction ability of BF-ZnO and BF-Zn _1-x Mg _x O to CO ₂ with H ₂ O vapor.

In general, the reduction of the presence of H ₂ O CO ₂ is a positron (proton) by photolysis (photo decomposition) of H ₂ O produced, CO ₂ light division CO radical production by (photo cleavage), and a CO radical and It is accomplished through three sub-processes of hydrocarbon production derived from photosynthesis between positron.

The photo-generated electrons on the photocatalyst induced by ultraviolet irradiation induce CO ₂ reduction to generate CO ₂ radicals, which react with the adsorbed H ₂ O molecules to effect oxidation. Intermediate photogenerated species produce CO or CH ₄ through other reactions, but in previous studies, TiO ₂ Unlike the catalyst, the main product for the BF-ZnO-based catalyst is CO molecules and the amount of CH ₄ produced in the case of BF-ZnO is negligible as 0.065 μmolg _cat ^-1 L ^-1 . These results suggest that TiO ₂ Unlike catalysts ZnO facilitates the reaction to proceed to CO rather than CH ₄ , and as a result, CO can be selectively generated from carbon dioxide using Zn-based catalysts according to the present invention.

In particular, in the case of the CO ₂ photoreduction BF-Zn _0.80 Mg _0.2 O and BF-Zn _0.75 Mg _0.25 O catalyst has an optically active (photoactivity) higher than the BF-ZnO, BF-Zn0.75Mg0.25O 5.2 μmolg cat - ¹ L ^-1 of CO was produced. The difference in yield is due to the band gap and gas adsorption capacity of BF-ZnO and BF-Zn _1-x Mg _x O particles. However, the amount of CO ₂ reduction on catalysts containing more than 25% Mg was significantly reduced.

Claims (9)

A core comprising a basalt fiber; And a shell comprising zinc-based photocatalyst Zn _0.75 Mg _0.25 O,
A photocatalyst of core / shell structure characterized by being used for photoreduction of carbon dioxide (CO ₂ ). delete delete delete delete The method according to claim 1,
A photocatalyst in a core / shell structure characterized by being used for selective photoreduction of carbon dioxide (CO ₂ ) to carbon monoxide (CO). (a) preparing a sol solution containing zinc and a magnesium precursor;
(b) adding the basalt fiber to the sol solution containing the zinc and magnesium precursor; And
(c) heat treating the basalt fiber-containing sol solution obtained in the step (b)
The method of claim 1, wherein the zinc precursor is zinc nitrate, and the magnesium precursor is magnesium nitrate. delete delete

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