KR101804014B1 - Hydrogen generating metal photocatalyst immobilized to graphene carrier and preparation method thereof - Google Patents

Abstract

The present invention relates to a supported photocatalyst for a hydrogen generation reaction in which a metal catalyst is supported on a graphene support, and a process for producing the same. More particularly, the present invention relates to a photocatalyst for hydrogen generation reaction comprising a first conjugate compound as a center metal and at least one bidentate ligand; And a graphene carrier on which the photocatalyst is supported by non-covalent bond, and a method for producing the same.
The supported photocatalyst for the hydrogen production reaction of the present invention can improve the stability of the catalyst by supporting the metal photocatalytic composite on the graphene carrier through the non-covalent bond, and it is possible to transfer electrons more quickly and efficiently through the reduced graphene oxide The rate of hydrogen production reaction can be improved, and the amount of hydrogen production can be increased.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a supported photocatalyst for hydrogen generation reaction in which a metal catalyst is supported on a graphene support,

The present invention relates to a supported photocatalyst for a hydrogen generation reaction in which a metal catalyst is supported on a graphene support, and a process for producing the same.

Hydrogen is widely used as a raw material for chemical products and as a process gas in a chemical plant, and is attracting attention as an alternative energy source or an energy carrier for depletion of fossil fuels. When hydrogen is used as fuel, it can be used as clean energy because no air pollution is generated during combustion, and it is easy to store in various forms such as high pressure gas, liquid hydrogen, and metal hydride. Accordingly, the technology for the production, storage and utilization of hydrogen is continuously being developed.

Methods for preparing hydrogen through conversion of formic acid / formate in the presence of a homogeneous metal catalyst have been studied. Particularly, there have been reported methods of producing hydrogen by formic acid decomposition using metal complexes. However, most of them are not photochemical processes but include additives such as formic acid / formate and organic amine compound in combination with a metal catalyst Is further used.

Many catalytic systems used in the hydrogen production reaction use thermal energy to obtain a high conversion and yield, and studies using a photochemical system including a metal catalyst in a formic acid oxidation process are not widely known. In particular, in order to develop an effective catalytic system for hydrogen production using solar light, there is a need for a photochemical system that includes a photocatalytic mechanism and a metal catalyst capable of a wide range of light absorption and good electron transfer.

Recently, the use of reduced graphene oxide (rGO) with an organic chromophore in the process of collecting a wide range of visible light energy using a photoregeneration system containing a rhodium catalyst in a molecular form (Li Z et al., J. Photochem . Photobiol . C: Photochem . Rev , 2014, 18, 1-17). Also, in catalyst systems, conjugated carbon nanomaterials such as carbon nanotubes (CNT) and graphene; And Zao YL (Stoddart JF, Acc. Chem. Res ., 2009, 42, 1161-1170), which utilizes effective electronic communication through π-conjugation of various molecules.

The present inventors have made intensive researches to develop a photocatalyst having excellent catalytic stability and improved hydrogen production ability in a hydrogen photogeneration reaction using a metal catalyst and a formate, and as a result, it has been found that a metal catalyst containing an organic ligand capable of covalent bonding is reduced Supported catalysts supported on pin oxide (rGO) exhibited superior advantages and excellent stability in the hydrogen photogeneration reaction, and completed the present invention.

In order to achieve the above-mentioned object, a first aspect of the present invention is a photocatalyst for a hydrogen generation reaction comprising a center metal and at least one bidentate ligand as a first conjugate compound; And a graphene support carrying the photocatalyst on the non-covalent bond, wherein the bidentate coordination ligand comprises a linker containing a second conjugate compound as a covalent bond, and a second photocatalyst bonded to the bidentate coordination ligand, Wherein the photocatalyst is supported on the graphene carrier by non-covalent bonding through a π, π-interaction between the conjugate compound and the graphene surface.

The second aspect of the present invention is the method for producing the supported photocatalyst of the first aspect, wherein the first conjugate compound, in which the second conjugate compound is linked by a linker, is reacted with the coordinatively coordinating central metal- A step And a second step of supporting the photocatalytic composite for hydrogen production reaction on a graphene carrier through a π, π-interaction between the second conjugate compound and the surface of the graphene. do.

A third aspect of the present invention provides a method for producing hydrogen, which is characterized in that the hydrogen generation reaction is performed under light irradiation on the supported photocatalyst of the first aspect.

The present inventors prepared a rhodium photocatalyst composite for a hydrogen production reaction by reacting a phenanthroline ligand to which pyrene was connected with a rhodium catalyst and supported the rhodium photocatalyst complex on a graphene surface having excellent electrical conductivity through non- Thereby preparing an improved supported photocatalyst. In addition, it has been found that by carrying the rhodium photocatalytic composite on the graphene, rapid electron transfer during the photocatalytic reaction becomes possible, and the stability of the supported photocatalyst on which the rhodium complex is carried is increased, thereby improving the hydrogen production reaction. The present invention is based on this.

Hereinafter, the present invention will be described in detail.

The supported photocatalyst of the present invention comprises a photocatalyst for hydrogen generation reaction comprising a center metal and at least one bidentate ligand as a first conjugate compound; And a graphene support having the photocatalyst supported on a non-covalent bond, wherein the bidentate coordination ligand comprises a linker containing a second conjugate compound as a covalent bond, and a second photocatalyst bonded to the bidentate coordination ligand, Characterized in that the photocatalyst is supported on the graphene carrier by non-covalent bonding through a π, π-interaction between the conjugate compound and the graphene surface.

The center metal may be at least one selected from the group consisting of Rh, Ru, Co, Pt, Pd, Ti, Zr, V, Mo, But are not limited to, copper (Cu), silver (Ag), gold (Au), iridium (Ir), osmium (Os) For example, the reactivity can be improved by rhodium (Rh) in the hydrogen production reaction.

In one embodiment of the present invention, rhodium (Rh) may be a rhodium metal complex with at least one bidentate ligand and a pentamethylcyclopentadienyl ligand combined.

The first conjugate compound of the present invention may be a nitrogen-containing compound, and the second conjugate compound may be a compound having three or more aryls fused to each other to have a planar structure.

Non-limiting examples of the first conjugate compound include phenanthroline, 2,2'-bipyridine, 4,4'-bipyridine, , p-phenylenediamine, or mixtures thereof.

Non-limiting examples of the second conjugate compound include anthracene, pyrene, phenanthrene, pentacene, chrysene, fluorene, or mixtures thereof .

Specifically, the first conjugate compound may be phenanthroline, and the second conjugate compound may be pyrene, but is not limited thereto.

The first conjugate compound of 1,10-phenanthroline (phen) in one embodiment of the present invention has a linker containing a second conjugate compound, pyrene, as a covalent bond .

Specifically, the graphene may be reduced graphene oxide.

Reduced graphene oxide (rGO) has very good electrical conductivity properties and can be applied to conductors and semiconductors. It is mainly used for manufacturing systems applied to optical sensors, catalysts, optical antennas, etc., and graphene oxide (GO ), Which is known to exhibit excellent electrical properties.

The reduced graphene oxide in one embodiment of the present invention is reduced in oxygen function on the surface in a planar conjugated form so that the π, π-interaction between the planar second conjugate compound and the graphene surface is smoothly Whereby a supported photocatalyst having improved catalyst stability and improved hydrogen generation ability can be produced (Experimental Example 1).

In the hydrogen generating photoreaction carried out in the aqueous solution of the present invention, reduced graphene oxide can be used, but in the case of hydrogen generating photoreaction in an organic solvent, unreduced graphene can be applied as a support.

In another aspect, the present invention provides a method for producing a supported cocatalyst,

A first step of reacting a first conjugate compound having a second conjugate compound linked by a linker with a coordinatively-coordinating central metal-containing compound to prepare a photocatalytic composite for hydrogen generation reaction; And a second step of supporting the photocatalytic composite for hydrogen generation reaction on a graphene carrier through a π-π-interaction between the second conjugate compound and the graphene surface.

The first step is a step of preparing a photocatalytic composite for a hydrogen generation reaction by connecting a first conjugate compound in which a center metal-containing compound and a second conjugate compound are linked by a linker by coordinate bond. The molar ratio of the first conjugated compound to the central metal-containing compound: second conjugate compound linked by the linker may be 1: 2, and may be performed in an ethanol solution.

The central metal containing compound may be a compound containing pentamethyl cyclopentadienyl rhodium (III) ion.

Specifically, the central metal-containing compound of the present invention may be but is not limited to pentamethylcyclopentadienyl rhodium (III) chloride dimer ([Cp * RhCl] ₂ ²⁺ ).

Non-limiting examples of the first conjugate compound include phenanthroline, 2,2'-bipyridine, 4,4'-bipyridine, , p-phenylenediamine, or mixtures thereof.

Non-limiting examples of the second conjugate compound include anthracene, pyrene, phenanthrene, pentacene, chrysene, fluorene, or mixtures thereof .

The first conjugate compound may be phenanthroline, and the second conjugate compound may be pyrene, but is not limited thereto.

The first conjugate compound in which the second conjugate compound of the present invention is linked by a linker is prepared by linking 1,10-phenanthroline with a linker containing pyrene through a covalent bond (Example 1).

The second step is a step of supporting the photocatalytic composite for hydrogen production reaction prepared in the first step on a graphen support. Specifically, the second conjugate compound of the photocatalytic composite can be supported on the graphene carrier through a?,? -Interaction between the graphene surface and the second conjugate compound.

In another embodiment, the hydrogen production method of the present invention is characterized in that the hydrogen generation reaction is performed under light irradiation on the supported photocatalyst of the first aspect.

The light irradiation may be performed by visible light, but is not limited thereto.

A typical photochemical hydrogen production reaction is known to be carried out by reacting rhodium (III) -hydride generated by a chemical reaction between a rhodium compound and a formate with platinum nanoparticles and using visible light energy. It has been reported that the formate salt is photocatalytically oxidized through the rhodium compound and the platinum nanoparticles in the hydrogen production reaction to generate hydrogen.

The rhodium (III) -hydride generated from the rhodium compound and the formate is known to be applied to the reaction of reducing nicotinamide adenine dinucleotide (NAD ⁺ ) to nicotinamide adenine dinucleotide (NADH) In the reduction reaction formate is used as a proton / electron donor.

The hydrogen production reaction according to one experimental example of the present invention can be carried out using rhodium (III) photocatalytic complex, formic acid / formate and platinum nanoparticles, and can be carried out under visible light irradiation.

Specifically, the formic acid / formate is chemically decomposed through reaction with the rhodium (III) photocatalytic complex to produce rhodium (III) -hydride, which is activated by visible light irradiation from the rhodium (III) Hydrogen can be generated through electron transfer to platinum nanoparticles (Experimental Example 1).

The hydrogen production reaction of the present invention is schematically shown in the following Reaction Scheme 1.

[Reaction Scheme 1]

Cp * (phen) Rh ^III -OH ₂ + HCOO ^- ? Cp * (phen) Rh ^III -H + CO ₂

Cp * (phen) Rh ^III -H + H ⁺ ? Cp * (phen) Rh ^III -OH ₂ + H ₂

The supported cocatalyst for the hydrogen production reaction of the present invention can be produced by preparing a rhodium photocatalyst complex in the form of being supported on reduced graphene oxide to form rhodium (III) -hydride (III) complex formed by formic acid / formate salt and rhodium Can be transferred to platinum nanoparticles more quickly and efficiently through the reduced graphene oxide, and the hydrogen production amount and the hydrogen production rate can be improved (Experimental Example 1).

The supported photocatalyst for the hydrogen production reaction of the present invention can improve the stability of the catalyst by supporting the metal photocatalytic composite on the graphene carrier through the non-covalent bond, and it is possible to transfer electrons more quickly and efficiently through the reduced graphene oxide The rate of hydrogen production reaction can be improved, and the amount of hydrogen production can be increased.

1 is a transmission electron microscope (TEM) photograph of platinum nanoparticles of the present invention.
Figure 2 shows the reaction of a (pentamethylcyclopentadienyl) rhodium (L) (H ₂ O) catalyst (L = pyran-phen (1), 1,10-phenanthroline ) And ruthenium complex (3) [(pyr-phen) Ru (bpy) ₂ ] ²⁺ ; And π-π-stacking interaction of the rhodium catalyst (1) and the reduced graphene oxide (rGO).
FIG. 3 is a view showing a ¹ H-NMR spectrum of phenanthroline (pyr-phen) derivatized with pyrene.
Figure 4 shows the mass spectrum spectrum (ESI-MS) of the (a) rhodium complex (1); And (b) an isotope distribution pattern and a calculated pattern (bar graph).
FIG. 5 shows UV-vis absorption spectra of (a) reduced graphene oxide (rGO), (b) 30 μM rhodium complex (1) and (c) 0.2 mg / mL rGO on an aqueous phase.
FIG. 6 shows the results of a pyrene-derivatized phenanthroline (60 μM, phase), a rhodium complex (1) (60 μM, medium) and a rhodium complex (1) / reduction in 0.2 M phosphate buffer (RGO) (0.4 mg / mL, lower), and the excitation wavelength is 350 nm.
7 is a graph showing the ¹ H-NMR spectrum of the ruthenium complex (3).
8 is a graph showing the results of the hydrogen production reaction. (a) was prepared by dissolving reduced graphene oxide (rGO, 0.60 (1 mM)) using a rhodium complex (1) (128 μM), formic acid / formate (HCOOH / HCOO-, 400 mM) and platinum nanoparticles (PtNPs, 20 nM) mg / mL) (red square) / radish (black circle). The reaction was carried out by irradiation of visible light (420 nm cut-off filter) in a solution of phthalic acid buffer (50 mM, pH = 4.5): acetonitrile (1: 1, v / v). Also, under the same conditions as above, the reaction was carried out using the rhodium complex (2) instead of the rhodium complex (1) in the absence of reduced graphene oxide (rGO) (green triangle). (b) shows the emission quenching of the rhodium complex (1) (128 μM) according to the concentration change (0 to 0.6 mg / mL) of reduced graphene oxide (rGO).
9 is a graph showing the activity of the rhodium complex 1 (1) in the presence of reduced graphene oxide (0.60 mg / mL, black squares) and graphene oxide (0.60 mg / mL, pH = 8.3 (red circle) and pH = (128 μM), formic acid / formate (HCOOH / HCOO-, 400 mM), and platinum nanoparticles (PtNPs, 20 nM).
Fig. 10 is a graph showing the density effect of the rhodium complex (1) supported on reduced graphene oxide (rGO) in the hydrogen light generating reaction. (a) is a graph showing plots of rGO vs. hydrogen initial velocity (vs), and the plots in the graph show the interaction of three different concentrations of rGO and rhodium complexes (1). Each of the reaction solutions contained rhodium complex 1 (128 μM), formic acid / formate (HCOOH / HCOO-, 400 mM), platinum nanoparticles (PtNPs, 20 nM) and rGO , 0.6, 0.9, and 1.2 mg / mL) and was performed in a phthalic acid buffer (50 mM, pH = 4.5): acetonitrile (1: 1, v / v) solution. The dark gray rectangle represents rGO and the red hexagon represents pyrene. (b) is a TEM image of a rhodium complex (1) and rGO (0.6 and 1.2 mg / mL) prepared with platinum nanoparticles (PtNPs). (c) shows the luminescence decay (606 nm) curves of 3 / rGO (▲ 128/0, ◆ 128/6, ■ 128/1.2 μM / mg / mL) by 423 nm excitation . The solid line was drawn according to the triaxponential decay curve.
11 is a graph showing the amount of hydrogen light produced by the rhodium complex 1 (128 占 퐉, black square) and the rhodium complex 1 / pyr-phen (128 占 퐉, red circle, respectively). The hydrogen photo-generating reaction further comprises 50 mM phthalic acid / acetonitrile (100 mM), and further containing formic acid / formate (HCOOH / HCOO-, 400 mM), platinum nanoparticles (PtNPs, 20 nM) and rGO (420 nm cut-off filter) at room temperature using a solution (1: 1, v / v).
Figure 12 shows the effect of reduced graphene oxide (rGO) (0-1.2 mg / mL) in maximum hydrogen production. Hydrogen production was carried out in the presence of 50 mM phthalic acid / acetonitrile (1: 1) (1) (128 μM), formic acid / formate (HCOOH / HCOO-, 400 mM) and platinum nanoparticles (PtNPs, 20 nM) 1, v / v) solution for 9-12 hours.
13 is a graph showing hydrogen light generation amount with time. (a) shows the results of using the rhodium complex (1) (128 μM) / rGO (0.6 mg / mL) and (b) (50 mM, pH 4.5) solution in the presence of platinum nanoparticles (PtNPs, 20 nM) using formaldehyde / formic acid salt (DCOOH / DCOONa, (420 nm cut-off filter).
Fig. 14 is a schematic diagram showing the hydrogen light-generating reaction by the rhodium complex (1), formic acid / formate salt, reduced graphene oxide (rGO) and platinum nanoparticles (PtNPs).

Hereinafter, the present invention will be described in more detail with reference to Examples. These examples are for further illustrating the present invention, and the scope of the present invention is not limited by these examples.

material And devices

All reagents purchased from Aldrich were used without further purification. The water was purified with a MilliQ purification system. Chem . Ber . ([Cp * Rh (phen) Cl] ²⁺ ) was prepared according to the method known in the art and Organometallics (Kolle, U. et al. , Chem. Ber . , 1989, 122: 1869-1880 ; Steckhan, E. et al. , Organometallics , 1991, 10: 1568-1577).

Transmission electron microscopy (TEM) images were recorded on a JEOL 2010FX electron microscope driven at 200 kV. The UV-vis absorption spectrum was measured with an HP spectrophotometer. NMR spectra were recorded on a FT-NMR (300 MHz) spectrometer (Bruker Co. AVANCE III 3000). Emission spectra were collected on a Perkin-Elmer LS 55 emission spectrophotometer. Electrospray ionization mass spectra (ESI-MS) were obtained by directly injecting the sample to the source at 25 μL / min using a syringe pump and collecting in a Thermo Finnigan (San Jose, CA, USA) LCQTM Advantage MAX quadrupole ion trap device Respectively. The spray voltage was set at 4.7 kV and the capillary temperature was set at 70 ° C. Elemental analysis of carbon, nitrogen and hydrogen was carried out at Sogang University Organic Chemistry Research Center using Flash EA 1112 elemental analyzer (thermo).

Manufacturing example  1: Reduced Grapina Oxide (reduced graphene  oxide; rGO )

The modified Hummers method was used to prepare reduced graphene oxide (rGO) from graphene oxide (GO) obtained from graphite powder (Hummers, WS and Offeman, RE, J. Am. Chem . Soc . , 1958, 80: 1339; Si, Y. and Samulski, ET, Nano Lett . , 2008, 8: 1679-1682). Specifically, graphene oxide (GO) was dispersed in deionized water to a concentration of 0.05 wt% / L (100 mL). The pH of the solution was then adjusted to 9-10 using 1 M NaOH solution. To the graphene oxide (GO) solution was added sodium borohydride (10 g), and the mixture was stirred at 80 占 폚 for 1 hour. The reduced product was filtered and washed several times with water. The obtained product was ultrasonicated and dispersed in acetone, and the acetone was dried with an evaporator. The solid product was dispersed in 100 mL concentrated sulfuric acid and the solution was stirred at 120 < 0 > C for 12 hours. The solution was cooled in an ice water bath and diluted with 500 mM water. A small amount of 1 M NaOH was treated until the pH of the solution remained uniformly below 2.0. Reduced graphene oxide (rGO) was centrifuged at 4000 rpm for 15 minutes and the upper water layer was removed. Concentrated reduced graphene oxide (rGO) containing a small amount of water was dispersed in acetone and then centrifuged to remove acetone. The reduced graphene oxide (rGO) was dried with a rotary condenser, and the completely dried reduced graphene oxide (rGO) was redispersed in water to prepare a stock solution.

Manufacturing example  2: Platinum nanoparticles ( PtNPs ; Platinum nanoparticles )

Chem . Soc . Faraday Trans. Platinum nanoparticles (PtNPs) were prepared by reduction of polyvinylpyrrolidone (MW = 10k) using potassium tetrachloroplatinate (K ₂ PtCl ₄ ) according to the methods known in the literature and Encyclopedia of Nanoscience and Nanotechnology (Furlong DN et al., Chem . Soc . Faraday Trans. 1, 1984, 80: 571-588; Okura I, Encyclopedia of Nanoscience and Nanotechnology , 2004, 8: 41-42). To 120 mL of a hot K ₂ PtCl ₄ aqueous solution (12 mM) was added 3 g of polyvinylpyrrolidone and the mixture was stirred for 4 hours until it turned black.

The size and distribution of platinum nanoparticles (PtNPs) were observed using TEM and dynamic light scattering (Malvern, Zetasizer Nano ZS) (Fig. 1). The concentration of platinum nanoparticles (PtNPs) was measured using total reflection X-ray fluorescence (TXRF) analysis (S2 PICOFOX, Bruker, Germany). As a result of the measurement, the platinum nanoparticles of 5 ± 1 nm contained about 5100 platinum atoms.

Example  One: Pyrene - Induced  Rhodium complex ( pyrene - derivatized  Preparation of Rh complex (1)

Step 1: Pyrene - Induced  Phenanthroline ( pyrene - derivatized phenanthroline ; pyr-phen)

Which is a phenanthroline ligand coupled with pyrene through the coupling reaction of 1-bromo (methyl) pyrene and phenanthroline-5-amine, (Pyrene-2-ylmethyl) -1,10-phenanthroline-5-amine (pyr-phen).

2 mmol of 1, 10-phenanthroline-5-amine and 2 mmol of 1-bromo (methyl) pyrene were dissolved in tetrahydrofuran Was added to tetrahydrofuran and refluxed for 8 hours. After refluxing was complete, the mixture was cooled to room temperature and the precipitate was filtered to give 0.5732 g of pyrene-derivatized phenanthroline (70% yield) (FIGS. 2 and 3).

Anal. found for C ₂₉ H ₁₉ N ₃ : C, 50.37; H, 5.24; N, 5.31.

calcd: C, 85.06; H, 4.68; N, 10.26.

^{1 H-NMR (300 MHz,} DMSO-d 6) δ = 9.26 (t, 3H), 9.02 (d, 2H), 8.99 (m, 4H), 8.0-8.1 (m, 7H), 3.77 (s, 2H ).

Step 2: Pyrene - Induced  Rhodium complex ( pyrene - derivatized  Rh complex) ( 1) of  Produce

A pyrene-induced rhodium complex (1) was prepared using pyrene in a similar manner to the preparation of the rhodium complex (2) described above ([Cp * Rh (phen) Cl] ²⁺ . Methylcyclopentadienyl rhodium (III) chloride dimer, [Cp * RhCl] ₂ ²⁺ , Aldrich) and 20 mM pyrene-derivatized phenanthroline (pyr-phen) And the mixture was stirred at room temperature for 4 hours. The initial red solution turned orange after 2 hours passed. After stirring, the solution was concentrated by rotary evaporation to obtain a powder. (Yield: 75%) (Fig. 2).

Anal. found for C ₃₉ H ₃₄ Cl ₂ N ₃ Rh: C, 65.25; H, 4.83; N, 5.61.

calcd: C, 65.19; H, 4.77; N, 5.85.

LC-MS (ESI, m / z) = 682.15 (M + H) < ^{+ &}

The strong peak corresponding to the [pyr-phen + Rh ^{3 +} + Cp * + Cl] ⁺ ion of the rhodium complex (1) was analyzed by electrospray ionization mass spectrometry, 682.15 (Fig. 4).

The absorption spectrum of the rhodium complex (1) showed specific bands of pyrene at 230, 270 and 345 nm. Even in the rhodium complex (1) carried on reduced graphene oxide (rGO) Respectively. Also, bands induced by the rhodium complex moiety in the visible region were also identified (Figure 5).

As a result of observing the emission spectrum of the pyr-phen and rhodium complex (1) prepared in Example 1, specific bands of pyrene were observed at 355 and 390 nm of the pyr-phen emission spectrum, (1), indicating that intramolecular quenching occurred in the excited pyrene molecules by the rhodium complex (1) (FIG. 6). Further, the weak release shown in the rhodium complex (1) was extinguished by the addition of the reduced graphene oxide (rGO), and it was confirmed from the result that the rhodium complex (1) was carried on the reduced graphene oxide (rGO) 6).

Comparative Example  1: ruthenium complex ([ (pyrene-phen) Ru (bpy) ₂ ] ²⁺ ) ( 3) of  Produce

0.40 mmol of Ru (bpy) ₂ Cl ₂ And 0.40 mmol pyr-phen mixture were added to ethylene glycol and refluxed for 2 h under a nitrogen atmosphere. After the refluxed solution was cooled, 60 mL of distilled water was added. The solution was filtered and the filtrate NaClO ₄ The saturated solution was treated and the resulting precipitate was filtered and recrystallized. Recrystallization was performed by slowly evaporating the acetone from the acetone / distilled water solution in which the precipitate dissolved. The strong peak corresponding to the [pyr-phen + Ru ^{2 +} + 2bpy + Cl ^- ] ⁺ ion of the ruthenium complex (3) was analyzed by electrospray ionization mass spectrometry, = 682.15 (Fig. 7).

^{1 H-NMR (300 MHz,} DMSO-d 6) δ = 9.70 (t, 1H), 9.61 (t, 2H), 8.52 (m, 3H), 8.05 (t, 3H), 7.84 (t, 2H), 2H), 6.86 (d, 2H), 6.68 (d, 2H), 7.54 (m, 2H) t, 1 H), 5.11 (s, 2 H).

LC-MS (ESI, m / z) = 682.15 (M + H) < ^{+ &}

Experimental Example 1: Light generation (hydrogen photoproduction ) analysis

Each sample was dissolved in 28 mL of glass using deacetylated phthalic acid buffer (50 mM, pH 4.5): 2 mL of acetonitrile (1: 1, v / v) sample solution as a typical method of photocatalytic reaction. Cell (glass cell). The cell was sealed with a septum and degassed by adding bubbling argon to the solution for 7 minutes at room temperature. The Xenon lamp was irradiated using a 450 W xenon arc light source instrument (Ind. Newport corporation, Oriel product line M-69920) equipped with a 420 nm cut-off filter. The amount of hydrogen produced was measured by gas chromatography (DS6200 gas chromatograph, Donam Instrument Inc., Korea) equipped with OD SS Column (Carbosphere 80/100 Mesh, 6 ft x 1/8 "OD SS Column, Alltech, Part No.5682PC) .

< Reduced graphene Effect of hydrogen in the light generation of the oxide (rGO)>

As a result of conducting a hydrogen photogeneration reaction using formic acid / formate in the presence of platinum nanoparticles (PtNPs, 5 ± 1 nm) prepared in Preparation Example 2, rhodium loaded on reduced graphene oxide (rGO) The photoreaction rate in the case of using the complex 1 (1 / rGO) was increased 50 times as compared with the hydrogen production rate of the rhodium complex 1 not loaded in the reduced graphene oxide (rGO) (FIG. 8A). The hydrogen produced by the rhodium complex 1 (1 / rGO) loaded on the reduced graphene oxide (rGO) was about 700 TN (turnover number) and was produced when the reduced graphene oxide was not used Hydrogen was 14 TN. Under the same conditions as above, the reduced graphene oxide / platinum nanoparticles (rGO / PtNPs) did not produce appreciable hydrogen by formic acid / formate when the rhodium complex 1 was not used, Indicates that rhodium-hydride species (Rh-H species) produced by the rhodium complex (1) and formic acid / formate salt are important in the overall course of hydrogen production. The formation of hydrogen by the rhodium complex (1) / formate and platinum nanoparticles is possible even when there is no reduced graphene oxide (rGO), but the reduction of electrons of rhodium-hydride (graphene) Oxides (rGO) to platinum nanoparticles (PtNPs) more quickly and effectively.

As a result of performing the hydrogen generation reaction using the rhodium composite 2, the initial reaction speed was 2.8 μM / hr (the conversion number after 3 hours was 23 TN), and the rate was [Cp * Rh (bpy) (H ₂ O)] ²⁺ . Hydrogen was also produced (1.7 μM / hr and 14 TN) in the case of using the rhodium composite 1 instead of the rhodium composite 2 under the same conditions as above, but the reactivity was further reduced by the pyrene moiety included 8a).

On the other hand, as a result of titration of the rhodium complex 1 using reduced graphene oxide (rGO), the emission of the rhodium complex 1 (128 μM) was reduced to 0.6 mg / mL of reduced graphene oxide ( rGO), indicating that under these conditions the rhodium complex (1) was loaded onto fully reduced graphene oxide (rGO) (Fig. 8b).

As a result of a comparative experiment, hydrogen photogeneration reaction was carried out using graphene oxide (GO) in place of reduced graphene oxide (rGO). As a result, remarkable increase in hydrogen production (Fig. 9). This result is considered to be the result of interference of the oxygen function of the graphene oxide (GO) surface with the π, π-accumulation interaction between the rhodium complex 1 and the graphene oxide GO.

< Reduced graphene Oxide (rGO) Hydrogen production rate analysis by the density difference between the impregnated rhodium complex (1) (density difference)>

The influence of the density difference of the rhodium complex (1) carried on the reduced graphene oxide (rGO) by variously changing the ratio of the rhodium complex 1 (128 μM) and the reduced graphene oxide (rGO) Respectively.

As a result, the hydrogen production rate was 38 μmol / hr, the maximum value when using 0.6 mg / mL of reduced graphene oxide (rGO) (FIG. 10a), and the result indicated that the rhodium composite 1 was completely loaded (Fluorescence quenching) results.

On the other hand, when the amount of reduced graphene oxide (rGO) was used in excess of 0.9 and 1.2 mg / mL compared to 0.6 mg / mL, the hydrogen production rate was decreased. When the reduced graphene oxide (rGO) of 0.6 mg / mL or more was used, the rhodium complex (1) on the reduced graphene oxide (rGO) was thinner and when the rhodium complex (1) And the hydrogen production rate was relatively decreased.

The results show that the coverage density of the rhodium complex (1) on reduced graphene oxide (rGO) is closely related to the rate change, and particularly the rhodium complex (1) tightly packed on the reduced graphene oxide (1) It can be seen that the layer is important for rapid electron transfer.

A transmission electron microscope (TEM) image of the rhodium complex 1 / reduced graphene oxide 1 / rGO, 128 / 0.6 was compared with a TEM image of 1 / rGO (128 / 1.2) (Fig. 10B). &Lt; tb &gt; &lt; TABLE &gt; A larger amount of reduced graphene oxide (rGO) is present in the 1 / rGO (128 / 1.2) sample, but in the distribution of platinum nanoparticles (PtNPs) on reduced graphene oxide (rGO) 1 / rGO (128 / 0.6) and 1 / rGO (128 / 1.2). However, when 1 / rGO (128 / 1.2) was used, it was observed that the platinum nanoparticles (PtNPs) were dispersed along the folded side of the reduced graphene oxide (rGO).

At 1 / rGO (128 / 0.6), the rhodium complex (1) was loaded more densely, thereby reducing the crumpled of the reduced graphene oxide (rGO). This result is believed to be due to the pi, pi-interaction between pyrene contained in the reduced graphene oxide (rGO) and rhodium complex (1).

On the other hand, a rhodium complex (1) (128 μM) loaded with reduced graphene oxide (rGO) (1.2 mg / mL); And 128 μM phenanthroline ligand (pyr-phen) functionalized with pyrene was added to the 1 / rGO (128 / 1.2) sample solution. As a result, pyr- The addition of further did not increase the hydrogen production rate (FIG. 11).

When the rhodium complex 1 is rarely formed on reduced graphene oxide (rGO) at 1 / rGO (128 / 1.2), the phenanthroline ligand (pyr-phen) functionalized with pyrene is reduced to graphene oxide (rGO), the morphology of the reduced graphene oxide (rGO) was similar to 1 / rGO (128 / 0.6). From the above results, it can be seen that the morphology and the number of pyrene of the reduced graphene oxide (rGO) do not influence the hydrogen production reaction.

< Reduced graphene Oxide (rGO) The density difference between the impregnated rhodium complex (1) hydrogen production yield and catalyst stability analysis by (density difference)>

The maximum amount of hydrogen production by the rhodium complex (1) in the presence of each reduced graphene oxide (rGO) was analyzed by varying the amount of reduced graphene oxide (rGO) to 0 to 1.2 mg / mL, The stability of the catalyst loaded on the reduced graphene oxide (rGO) from the analysis was investigated (Figure 12).

As a result, when the largest amount of reduced graphene oxide (rGO) (1.2 mg / mL) was used, that is, when the rhodium complex 1 formed the thinnest layer on the reduced graphene oxide (rGO) (Maximum yield) of hydrogen production. 1 / rGO (128 / 0.6) and 1 / rGO (128 / 1.2) solutions show that when the rhodium complex 1 is formed close to the reduced graphene oxide (rGO) It can be seen that the catalytic cycle becomes unstable as compared with the case where it is thinly formed. That is, when the rhodium complex 1 is formed as a thin layer on the reduced graphene oxide (rGO), the stability of the catalyst becomes higher.

The deactivation process of the rhodium catalyst in proximity formation such as dimerization may affect the stability of the rhodium complex catalyst 1 but may result in a much higher yield in the presence of reduced graphene oxide (rGO) . From the results, it can be seen that the rhodium complex catalyst supported on the reduced graphene oxide (rGO) is more stable than the rhodium complex catalyst (1) present in the solution in a state of not supporting it.

< Hydrogen light generation Rate-limiting step analysis in reaction >

To the reactive species (reactive species) and analyzed for similarity rate limiting step (rate-limiting step), formate / formic acid (HCOOH / HCOO ^-) a formic acid / formate (DCOOH / DCOO substituted with deuterium in place ^- (1 / rGO) and the rhodium complex (2) were subjected to a hydrogen photogeneration reaction using a rhodium complex (1) / reduced graphene oxide (rGO) (1 / rGO) and a rhodium complex (2).

As a result, the rate of hydrogen production by formic acid / formate substituted with deuterium in 1 / rGO (128 / 0.6) and rhodium complex (2) decreased sharply (FIG. 13). On the other hand, the kinetic isotope effect of 1 / rGO (128 / 0.6) was 2.5 ± 0.4, which was similar to 2.1 ± 0.3 of the rhodium complex (2).

It can be seen from the above results that the photochemical reaction by the rhodium complex 1 / reduced graphene oxide rGO and the rhodium complex 2 is catalytic cycle, which shows a similar rate limiting step.

The results also show that the reaction of rhodium complex (1) and rhodium complex (2) with formic acid / formate produced similar rhodium (III) -hydride species (Rh (III) -H species) 1) / the reaction with reduced graphene oxide (rGO) and rhodium complex (2) all indicate that the rhodium (III) -hydride formation step is the same as the rate limiting step.

Experimental Example  2: Analysis of emission lifetime

The time-resolved photoluminescence spectrum was measured with a Hamamatsu R5509 PMT through a monochromator at a time of 0 to 30 ms. The polymer film loaded in the cryostat was cooled to 7K by a helium gas flow through a closed cycle cryogenic system. A fourth harmonics Q-switched Nd: YAG laser with a pulse duration of 6 ns, a repetition rate of 10 Hz and a light output of 50 mJ was loosely inserted into the sample with a diameter of less than 10 mm Focused.

To investigate the density effect of the rhodium complex (1) on reduced graphene oxide (rGO), the emission of ruthenium complex (3) (prepared in Comparative Example 1) loaded on reduced graphene oxide (rGO) The lifetime was observed. The ruthenium complex (3) was used instead of the rhodium complex (1) exhibiting low luminescence. The lifetime of the ruthenium moiety of the ruthenium complex 3 provided a good probe for electron transfer kinetics studies between reduced graphene oxide (rGO) and the excited ruthenium complex (3).

The emission decay curves obtained from the ruthenium complex (3) loaded with reduced graphene oxide (rGO) at 0, 0.6 and 1.2 mg / mL, respectively, are shown in Fig. The emission lifetime of 3 / rGO (128 / 0.6) (τ = 314 ns) was significantly lower than that of 3 / rGO (128/0) (512 ns) The lifetime was relatively reduced due to the ruthenium complex (3) loaded less densely on the reduced graphene oxide (rGO).

Claims (11)

A photocatalyst for a hydrogen production reaction comprising a central metal and a first conjugate compound as at least one bidentate ligand; And a photocatalyst carrier having a graphene carrier on which the photocatalyst is supported by non-covalent bond,
Wherein the bidentate coordination ligand comprises a linker containing a second conjugate compound as a covalent bond,
Characterized in that the photocatalyst is supported on the graphene carrier by non-covalent bonding through a π, π-interaction between the second conjugate compound bound to the bidentate coordination ligand and the graphene surface, and hydrogen from formic acid or formate Supported photocatalyst for reaction.
The method of claim 1, wherein the center metal is at least one selected from the group consisting of rhodium, ruthenium, cobalt, platinum, palladium, titanium, zirconium, vanadium, Wherein the photocatalyst is selected from the group consisting of molybdenum (Mo), copper (Cu), silver (Ag), gold (Au), iridium (Ir) and osmium (Os).
The supported photocatalyst according to claim 1, wherein the first conjugate compound is a nitrogen-containing compound, and the second conjugate compound is a compound having three or more aryls fused to each other to have a planar structure.
A photocatalyst for a hydrogen production reaction comprising a central metal and a first conjugate compound as at least one bidentate ligand; And a photocatalyst carrier having a graphene carrier on which the photocatalyst is supported by non-covalent bond,
Wherein the bidentate coordination ligand comprises a linker containing a second conjugate compound as a covalent bond,
Wherein the photocatalyst is supported on the graphene carrier by non-covalent bonding through a π, π-interaction between the second conjugate compound bonded to the bidentate coordination ligand and the graphene surface,
Wherein the first conjugate compound is phenanthroline.
4. The method of claim 3, wherein the first conjugate compound is selected from the group consisting of phenanthroline, 2,2'-bipyridine, 4,4'-bipyridine ) And p-phenylenediamine, or the second conjugate compound is selected from the group consisting of anthracene, pyrene, phenanthrene, pentacene, Wherein the photocatalyst is selected from the group consisting of chrysene and fluorene.
A method for producing a supported photocatalyst according to any one of claims 1 to 5,
A first step of reacting a first conjugate compound having a second conjugate compound linked by a linker with a coordinatively-coordinating central metal-containing compound to prepare a photocatalytic composite for hydrogen generation reaction; And
And a second step of supporting the photocatalytic composite for hydrogen generation reaction on a graphene carrier through a π-π-interaction between the second conjugate compound and the graphene surface. .
7. The method of claim 6, wherein the central metal-containing compound contains pentamethylcyclopentadienyl rhodium (III) ion.
7. The method of claim 6, wherein the first conjugate compound is selected from the group consisting of phenanthroline, 2,2'-bipyridine, 4,4'-bipyridine ) And p-phenylenediamine. &Lt; RTI ID = 0.0 &gt; 8. &lt; / RTI &gt;
The method of claim 6, wherein the second conjugate compound is selected from the group consisting of anthracene, pyrene, phenanthrene, pentacene, chrysene, and fluorene. &Lt; / RTI &gt; wherein the photocatalyst is selected from the group consisting of:
A method for producing hydrogen according to any one of claims 1 to 5, wherein the hydrogen generation reaction is carried out under light irradiation on the supported photocatalyst.
11. The method according to claim 10, wherein the light irradiation is performed with visible light.

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