FAPbBr3 / rGO photocatalytic material and preparation method and application thereof

Abstract

The application belongs to the field of new energy and photocatalysis technology, and particularly relates to a FAPbBr3 / rGO photocatalytic material and a preparation method and application thereof. The preparation method comprises the following steps: S1, stirring and mixing formamidinium acetate and an HBr solution in an ice water bath, then removing the solvent by rotary evaporation, and washing and drying the crude product to obtain FABr; S2, adding excessive FABr and PbBr2 in a stoichiometric ratio of 1:1 into a mixed solution of HBr and H3PO2 to obtain FAPbBr3 and a saturated solution thereof, heating the FAPbBr3 and the saturated solution thereof to reach a dynamic equilibrium, cooling, centrifuging, drying the obtained precipitate to obtain FAPbBr3; adding the FAPbBr3 into a saturated HBr solution to stir and disperse, adding GO to stir, then performing photoreduction, centrifuging, drying the collected precipitate to obtain the FAPbBr3 / rGO photocatalytic material. FAPbBr3 is precipitated by a saturated solution coprecipitation method, the carrier rGO can improve the carrier transmission and separation efficiency by loading a cocatalyst, high-efficiency photocatalytic decomposition of HBr to produce hydrogen can be realized, and the method has the advantages of simple preparation method, low cost, large-scale preparation and high catalytic activity.

Description

Technical Field

[0001] This invention belongs to the fields of new energy and photocatalysis technology, specifically relating to a FAPbBr3 / rGO photocatalytic material, its preparation method, and its application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] In recent years, halide perovskite photocatalysts have been used to catalyze hydrogen halides (HX, X=Br) - I - Hydrogen production via pyrolysis offers a promising new approach as an alternative to water splitting. This emerging research direction avoids the problems of insufficient light absorption capacity of semiconductor photocatalysts, unfavorable thermodynamics of water oxidation, and slow kinetic processes inherent in photocatalysis. On the one hand, halide perovskites possess excellent photoelectric properties such as narrow and suitable band gaps, high absorption coefficients, and long carrier diffusion lengths, making them ideal candidates for photocatalysis. On the other hand, halide ions (Br₂O₃)... - I - Low oxidation potential (E) θ (Br2 / Br - ) = 1.09V,E θ (I2 / I - =0.53V) than water (E) θ Oxidation is easier when the ratio of O2 / H2O is 1.23V, and the high ion concentration in hydrohalic acids leads to faster reaction kinetics. Therefore, photocatalytic hydrohalic acid cracking is a more readily achievable method for solar-powered hydrogen production.

[0004] In 2016, Nam et al. from Seoul National University in South Korea achieved hydrogen production from the decomposition of hydroiodic acid (HI) using MAPbI3 (MA = CH3NH3), bringing the photocatalytic hydrohalic acid cracking technology based on halide perovskite photocatalysts to the forefront for the first time, providing new insights into solar-powered hydrogen production. Subsequently, materials were modified to improve photocatalytic activity, including the construction of heterojunctions, compositional regulation, and surface loading, resulting in a significant improvement in photocatalytic efficiency. However, current research in this field mainly focuses on the photocatalytic decomposition of HI based on iodide perovskites, while research on the use of bromide perovskites for the decomposition of hydrobromic acid (HBr) is relatively limited. Photocatalytic HBr decomposition can not only realize the conversion of solar energy into hydrogen energy, but can also serve as a charging reaction for H2 / Br2 flow batteries, thus coupling with such batteries. Therefore, it is of great significance for solar energy collection, storage, and conversion into chemical and electrical energy. For the photocatalytic HBr splitting of halide perovskites, Academician Li Can's team at the Dalian Institute of Chemical Physics modified MAPbBr3 with Pt / Ta2O5 and PSS (poly(3,4-ethylenedioxythiophene)polystyrene sulfonate) as dynamic electron and hole transport channels, respectively, to promote charge transport and accelerate the reaction. However, the photocatalytic hydrogen evolution activity of HBr splitting is still low, far lower than that of HI splitting. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a FAPbBr3 / rGO photocatalytic material, its preparation method, and its applications. This invention precipitates FAPbBr3 via a saturated solution co-precipitation method. It can improve carrier transport and separation efficiency by supporting a co-catalyst to reduce graphene oxide (rGO), enabling highly efficient photocatalytic decomposition of HBr to produce hydrogen. This method offers advantages such as simple preparation, low cost, large-scale production capability, and high catalytic activity.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a FAPbBr3 / rGO photocatalytic material, comprising the following steps:

[0008] S1. Mix formamidine acetate and HBr solution in an ice-water bath, then remove the solvent by rotary evaporation. The crude product is washed and dried to obtain FABr.

[0009] S2. Add excess FABr and PbBr2 in a stoichiometric ratio of 1:1 to a mixed solution of HBr and H3PO2 or an HBr solution to obtain FAPbBr3 and its saturated solution. Heat FAPbBr3 and its saturated solution to reach dynamic equilibrium, then cool and centrifuge to obtain the precipitate, which is then dried to obtain FAPbBr3.

[0010] S3. Add FAPbBr3 to a saturated HBr solution and stir to disperse. Add GO and stir. Then perform photoreduction. Centrifuge and collect the precipitate and dry it to obtain the FAPbBr3 / rGO photocatalytic material.

[0011] Preferably, the HBr solution is a 48wt% HBr aqueous solution, and the ratio of formamidine acetate to HBr solution is 1mg:(1.3-1.5)mL.

[0012] Preferably, the volume ratio of HBr to H3PO2 in the mixed solution of HBr and H3PO2 is 3:(1 to 0), excluding 0.

[0013] Preferably, in step S2, FAPbBr3 and its saturated solution are heated to 60–100°C and kept at that temperature for 1–2 hours to reach dynamic equilibrium.

[0014] Preferably, in step S3, the mass ratio of FAPbBr3 to GO is (10-100):1.

[0015] Preferably, in step S3, the light source used for light reduction is a 300W full-spectrum xenon lamp, and the light reduction time is 2-4 hours.

[0016] In a second aspect, the present invention provides a FAPbBr3 / rGO photocatalytic material, which is obtained by the preparation method described in the first aspect.

[0017] Thirdly, the present invention provides the application of the FAPbBr3 / rGO photocatalytic material as described in the second aspect in the photocatalytic decomposition of HBr to produce hydrogen.

[0018] Fourthly, the present invention provides a method for photocatalytic decomposition of HBr to produce hydrogen, comprising the following steps:

[0019] The FAPbBr3 / rGO photocatalytic material as described in the second aspect is dispersed in a saturated HBr solution or a saturated HBr solution containing H3PO2, the air is removed by vacuuming, and the HBr is photocatalytically decomposed to produce hydrogen by irradiation with a light source.

[0020] Preferably, the volume fraction of H3PO2 in the saturated HBr solution containing H3PO2 is 0% to 30%, excluding 0%, and the proportion of FAPbBr3 / rGO photocatalyst material dispersed in the saturated HBr solution or saturated HBr solution containing H3PO2 is 1 to 3 mg / mL.

[0021] The beneficial effects achieved by one or more technical solutions of the present invention are as follows:

[0022] The FAPbBr3 / rGO photocatalyst of this invention has the advantages of simple preparation method, mild reaction conditions, low cost, large-scale preparation capability, and high catalytic activity.

[0023] The FAPbBr3 / rGO photocatalyst prepared in this invention possesses advantages such as efficient charge separation, abundant hydrogen-producing active sites, and a relatively small HBr splitting energy barrier, enabling efficient and stable photocatalytic hydrogen production. The optimal hydrogen production performance reaches 3867 μmol g / g. -1 h -1 It also exhibits excellent stability. Attached Figure Description

[0024] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0025] Figure 1 (a) XRD patterns of FAPbBr3 and FAPbBr3 / rGO in Example 1, (b) Raman patterns of GO and FAPbBr3 / rGO, (c) Infrared patterns of FAPbBr3, GO and FAPbBr3 / rGO, (d) SEM image of FAPbBr3, (e) SEM image of FAPbBr3 / rGO, (f) HRTEM image of FAPbBr3 / rGO, (g) EDS mapping image of FAPbBr3 / rGO, and (h) TEM image of FAPbBr3 / rGO.

[0026] Figure 2 XPS spectra of FAPbBr3, GO, and FAPbBr3 / rGO in Example 1, where (a) is the C1s spectrum of GO, (b) is the C1s spectrum of FAPbBr3 / rGO, (c) is the Pb 4f spectrum of FAPbBr3 and FAPbBr3 / rGO, and (d) is the O1s spectrum of GO and FAPbBr3 / rGO.

[0027] Figure 3 (a) Hydrogen production activity diagram and (b) stability diagram of FAPbBr3 and FAPbBr3 / rGO in Example 1, FAPbBr3 / Pt in Comparative Example 1, and MAPbBr3 in Comparative Example 2.

[0028] Figure 4 The images show (a) single-particle fluorescence and (c) lifetime of FAPbBr3, (b) single-particle fluorescence and (d) lifetime of FAPbBr3 / rGO, and (e) transient photoresponse and (f) impedance diagrams of FAPbBr3 and FAPbBr3 / rGO in Example 1. Detailed Implementation

[0029] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples.

[0030] Example 1

[0031] 10 g of (CH4N2·C2H4O2) and 14 mL of HBr (48 wt% aqueous solution) were mixed in an ice-water bath and stirred for 2 h. The solvent was removed by rotary evaporation at 60 °C. The crude product was recrystallized from ethanol and diethyl ether solution, washed three times with diethyl ether, and the resulting white FABr powder was finally dried in a vacuum oven at 65 °C for 6 h.

[0032] FAPbBr3 and its saturated solution were prepared by adding excess FABr and PbBr2 in a stoichiometric ratio of 1:1 to a mixed solution of HBr and H3PO2 (v / v = 4:1). The solution containing excess FAPbBr3 precursor was heated to 95°C and held for 1 h to reach dynamic equilibrium, then cooled to room temperature. After natural cooling, the FAPbBr3 precipitate and saturated solution were separated by centrifugation, and the precipitate was dried in a vacuum oven at 60°C for 6 h.

[0033] 100 mg FAPbBr3 was added to 50 mL of saturated HBr solution and dispersed by sonication and stirring. 5 mg GO was added to the above solution and stirred for 30 min, followed by photoreduction under a 300 W xenon lamp (full spectrum) for 3 h. The FAPbBr3 / rGO precipitate was collected by centrifugation and dried in a vacuum oven at 60 °C for 6 h.

[0034] like Figure 1 As shown in Figure a, the XRD pattern indicates that the obtained FAPbBr3 is cubic in phase and has good crystallinity. No peak shift occurred after loading rGO; the peak at 23.7° corresponds to the characteristic diffraction peak of the (002) plane of GO / rGO, and the peak at 26.8° indicates that rGO has an ordered crystal structure. Figure 1 As shown in b, the D band (~1350 cm⁻¹) in the Raman spectrum -1 sp 3 Carbon) and G-band (~1600cm) -1 sp 2 The signal strength of carbon is greater than that of I D / I G The increase in indicates that graphene oxide in FAPbBr3 / rGO is reduced. In, for example... Figure 1 In the infrared spectrum shown in c, the Pb-OC and Pb-O vibrations show two peaks at around 975 nm and 800 nm, respectively, indicating that rGO is bound to FAPbBr3 through oxygen bridging bonds. Figure 1The SEM image of d in the image shows that the prepared FAPbBr3 particles are quasi-dodecahedral in shape and have a particle size of 50-200 μm. Figure 1 The SEM image of e in the image shows that rGO is anchored on the FAPbBr3 surface in the prepared FAPbBr3 / rGO particles. For example... Figure 1 As shown in f, two distinct lattice fringes of 0.31 nm and 0.22 nm are clearly observed in FAPbBr3 / rGO, belonging to FAPbBr3 and rGO respectively, confirming the formation of the FAPbBr3 / rGO composite material after the photoreduction loading process. (EDS mapping image) Figure 1 The g) shows that the surface of FAPbI3 particles in the composite material is partially covered with rGO. Figure 1 The TEM image in h also shows that rGO is linked to FAPbBr3.

[0035] like Figure 2 As shown in a, the high-resolution C1s peak of GO shows that, except for the CC / C=C bond at 284.7 eV, GO exhibits strong peaks related to carbon-oxygen bonds, such as CO at 286.9 eV, C=O at 288.2 eV, and -OC=O at 289.3 eV. Figure 2 The 'b' indicates that the intensity of all three peaks decreased after photoreduction, indicating that GO was reduced to rGO. At the same time, the new peak at 285.9 eV indicates that a Pb-OC bond was formed between rGO and FAPbBr3. Figure 2 In the Pb 4f spectrum, the value is located at 144.6 eV (Pb 4f). 3 / 2 ) and 139.5 eV (Pb 4f 5 / 2 The peak corresponds to the formation of Pb-O. Furthermore, a high binding energy shift of approximately 0.2 eV is observed in the Pb 4f peak, while a contrasting low binding energy shift is observed in the O1s peak. Figure 2 The d) indicates that electrons in the composite material tend to shift from FAPbBr3 to rGO, which is beneficial for charge separation in subsequent photocatalytic reactions.

[0036] Comparative Example 1

[0037] 10 g of (CH4N2·C2H4O2) and 14 mL of HBr (48 wt% aqueous solution) were mixed in an ice-water bath and stirred for 2 h. The solvent was removed by rotary evaporation at 60 °C. The crude product was washed three times with diethyl ether, and the resulting white FABr powder was finally dried in a vacuum oven at 60 °C for 6 h.

[0038] FAPbBr3 and its saturated solution were prepared by adding excess FABr and PbBr2 in a stoichiometric ratio of 1:1 to a mixed solution of HBr and H3PO2 (v / v = 4:1). The solution with excess powder was heated to 95°C and held for 1 hour to reach dynamic equilibrium, then cooled to room temperature. After natural cooling, the FAPbBr3 precipitate and saturated solution were separated by centrifugation, and the precipitate was dried in a vacuum oven at 60°C for 6 hours.

[0039] 100 mg of FAPbBr3 was added to 50 mL of saturated HBr solution and dispersed by sonication and stirring. 10 mg of H2PtCl6·6H2O was added to the above solution and stirred for 30 min, followed by photoreduction under a 300 W xenon lamp (full spectrum) for 3 h. The FAPbBr3 / Pt precipitate was collected by centrifugation and dried in a vacuum oven at 60 °C for 6 h.

[0040] Comparative Example 2

[0041] MAPbBr3 and its saturated solution were prepared by adding excess MABr and PbBr2 in a stoichiometric ratio of 1:1 to a mixed solution of HBr and H3PO2 (v / v = 4:1). The solution containing the excess MAPbBr3 solute precursor was heated to 95°C and held for 1 h to reach dynamic equilibrium, then cooled to room temperature. After natural cooling, the MAPbBr3 precipitate and saturated solution were separated by centrifugation, and the precipitate was dried in a vacuum oven at 60°C for 6 h.

[0042] Example 2

[0043] Photocatalytic decomposition of HBr to produce hydrogen:

[0044] The photocatalytic reaction was carried out in a Pyrex reaction chamber connected to a closed gas circulation and vacuum system. Typically, 100 mg of photocatalyst (FAPbBr3 in Example 1, FAPbBr3 / rGO in Example 1, FAPbBr3 / Pt in Comparative Example 1, and FAPbBr3 in Comparative Example 2) was immersed in 50 mL of reaction solution. The system was evacuated for 30 minutes to ensure complete removal of air, and then irradiated from above using a 300 W xenon lamp (PLS-SXE300D, Beijing Pofila Technology Co., Ltd.) equipped with an AM1.5G filter. The reaction suspension was maintained at 298 K using a cooling water stream. The separated gases were analyzed by gas chromatography (GC-7290, TCD, with Ar as the carrier gas).

[0045] like Figure 3 As shown in a, pure FAPbBr3 (100 mg) under simulated sunlight irradiation (AM 1.5 G, 100 mW cm⁻¹) -2 The hydrogen evolution activity at ) is 745 μmol g -1 h-1 The FAPbBr3 / rGO composite material achieved a hydrogen evolution activity of 3867 μmol g under the same measurement conditions. -1 h -1 This represents an improvement of more than 5 times. Pt, as a common and highly efficient photocatalyst for hydrogen evolution, was also applied to photo-supported FAPbBr3, resulting in a hydrogen evolution activity of 1707 μmol g / L for the supported sample. -1 h -1 The performance of rGO is weaker than that of FAPbBr3 / rGO, indicating that rGO is superior to Pt in enhancing the photocatalytic hydrogen evolution performance of FAPbBr3 perovskite. Figure 3 As shown in b, FAPbBr3 / rGO exhibits good long-term stability in hydrogen evolution, with no significant decrease after 5 repeated cycles (10 h each).

[0046] We used single-particle photoluminescence (PL) microscopy to study charge dynamics and explore the role of rGO in improving charge separation. Figure 4 The inset in section a shows a bright PL image of FAPbBr3, compared to the FAPbBr3 / rGO sample ( Figure 4 The inset in b) shows a significant decrease in brightness, indicating PL quenching. Therefore, the PL intensity (integral intensity) of FAPbBr3 in the single-particle PL spectrum is... Figure 4 The a in the figure (corresponding to points 1, 2, and 3 in the inset) is stronger, with an intensity range of ~10000-30000 (au) at 545 nm, while the FAPbBr3 / rGO sample ( Figure 4 In example b), the PL spectra obtained from points 1, 2, and 3 are much weaker, with intensities of ~3000-6000 (au). Figure 4 As shown in Figures c and d, the fluorescence lifetime spectra indicate that the FAPbBr3 particles have a longer average fluorescence lifetime of 86.7 ns. However, after the introduction of rGO, the fluorescence lifetime of FAPbBr3 / rGO decreased to 2.8 ns. This suggests that the introduction of rGO accelerates the separation of photogenerated carriers in the FAPbBr3 perovskite, thereby improving the performance of photocatalytic HBr splitting for hydrogen evolution. Photoelectrochemical tests were performed on FAPbBr3 and FAPbBr3 / rGO. Figure 4 As shown in e, FAPbBr3 / rGO exhibits a higher photocurrent density compared to FAPbBr3 alone. Simultaneously, the semicircle radius in the Nyquist plot of the FAPbBr3 / rGO composite is significantly smaller than that of FAPbBr3 alone. Figure 4 (f) These results indicate that rGO in FAPbBr3 / rGO contributes to carrier separation during photocatalysis, thereby improving hydrogen evolution activity.

[0047] Example 3

[0048] 10 g of (CH4N2·C2H4O2) and 14 mL of HBr (48 wt% aqueous solution) were mixed in an ice-water bath and stirred for 2 h. The solvent was removed by rotary evaporation at 60 °C. The crude product was washed three times with diethyl ether, and the resulting white FABr powder was finally dried in a vacuum oven at 65 °C for 6 h.

[0049] FAPbBr3 and its saturated solution were prepared by adding excess FABr and PbBr2 in a stoichiometric ratio of 1:1 to a mixed solution of HBr and H3PO2 (v / v = 4:1). The solution containing the excess FAPbBr3 solute precursor was heated to 95°C and held for 1 h to reach dynamic equilibrium, then cooled to room temperature. After natural cooling, the FAPbBr3 precipitate and saturated solution were separated by centrifugation, and the precipitate was dried in a vacuum oven at 60°C for 6 h.

[0050] 100 mg FAPbBr3 was added to 50 mL of saturated HBr solution and dispersed by sonication and stirring. 1 mg GO was added to the above solution and stirred for 30 min, followed by photoreduction under a 300 W xenon lamp (full spectrum) for 3 h. The FAPbBr3 / rGO precipitate was collected by centrifugation and dried in a vacuum oven at 60 °C for 6 h.

[0051] Example 4

[0052] 10 g of (CH4N2·C2H4O2) and 14 mL of HBr (48 wt% aqueous solution) were mixed in an ice-water bath and stirred for 2 h. The solvent was removed by rotary evaporation at 60 °C. The crude product was washed three times with diethyl ether, and the resulting white FABr powder was finally dried in a vacuum oven at 60 °C for 6 h.

[0053] FAPbBr3 and its saturated solution were prepared by adding excess FABr and PbBr2 in a stoichiometric ratio of 1:1 to a mixed solution of HBr and H3PO2 (v / v = 4:1). The solution containing the excess FAPbBr3 solute precursor was heated to 95°C and held for 1 h to reach dynamic equilibrium, then cooled to room temperature. After natural cooling, the FAPbBr3 precipitate and saturated solution were separated by centrifugation, and the precipitate was dried in a vacuum oven at 60°C for 6 h.

[0054] 100 mg FAPbBr3 was added to 50 mL of saturated HBr solution and dispersed by sonication and stirring. 10 mg GO was added to the above solution and stirred for 30 min, followed by photoreduction under a 300 W xenon lamp (full spectrum) for 3 h. The FAPbBr3 / rGO precipitate was collected by centrifugation and dried in a vacuum oven at 60 °C for 6 h.

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. The application of a FAPbBr3 / rGO photocatalytic material in the photocatalytic decomposition of HBr to produce hydrogen, characterized in that, Includes the following steps: S1. Mix formamidine acetate and HBr solution in an ice-water bath, then remove the solvent by rotary evaporation. The crude product is washed and dried to obtain FABr. S2. Add excess FABr and PbBr2 in a stoichiometric ratio of 1:1 to a mixed solution of HBr and H3PO2 or an HBr solution to obtain FAPbBr3 and its saturated solution. Heat FAPbBr3 and its saturated solution to reach dynamic equilibrium, then cool and centrifuge to obtain the precipitate, which is then dried to obtain FAPbBr3. S3. Add FAPbBr3 to a saturated HBr solution and stir to disperse. Add GO and stir. Then perform photoreduction. Centrifuge and collect the precipitate and dry it to obtain the FAPbBr3 / rGO photocatalytic material. In step S2, FAPbBr3 and its saturated solution are heated to 60~100 ℃ and kept at this temperature for 1~2 h to reach dynamic equilibrium.

2. The application of the FAPbBr3 / rGO photocatalytic material as described in claim 1 in the photocatalytic decomposition of HBr to produce hydrogen, characterized in that, The HBr solution is a 48 wt% HBr aqueous solution, and the ratio of formamidine acetate to HBr solution is 1 mg:(1.3~1.5) mL.

3. The application of the FAPbBr3 / rGO photocatalytic material as described in claim 1 in the photocatalytic decomposition of HBr to produce hydrogen, characterized in that, The volume ratio of HBr to H3PO2 in the mixed solution of HBr and H3PO2 is 3:(1~0), excluding 0.

4. The application of the FAPbBr3 / rGO photocatalytic material as described in claim 1 in the photocatalytic decomposition of HBr to produce hydrogen, characterized in that, In step S3, the mass ratio of FAPbBr3 to GO is (10~100):

1.

5. The application of the FAPbBr3 / rGO photocatalytic material as described in claim 1 in the photocatalytic decomposition of HBr to produce hydrogen, characterized in that, In step S3, the light source used for light reduction is a 300W full-spectrum xenon lamp, and the light reduction time is 2~4 hours.

6. The application of the FAPbBr3 / rGO photocatalytic material as described in claim 1 in the photocatalytic decomposition of HBr to produce hydrogen, characterized in that, The photocatalytic decomposition of HBr to produce hydrogen includes the following steps: The FAPbBr3 / rGO photocatalytic material as described in claim 1 is dispersed in a saturated HBr solution or a saturated HBr solution containing H3PO2, the air is removed by vacuuming, and the HBr is photocatalytically decomposed to produce hydrogen by irradiation with a light source.

7. The application of the FAPbBr3 / rGO photocatalytic material as described in claim 6 in the photocatalytic decomposition of HBr to produce hydrogen, characterized in that, The volume fraction of H3PO2 in a saturated HBr solution containing H3PO2 is 0%~30%, excluding 0%, and the proportion of FAPbBr3 / rGO photocatalyst dispersed in a saturated HBr solution or saturated HBr solution containing H3PO2 is 1~3 mg / mL.

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