A polymer–metal–polymer–metal heterostructure for enhanced photocatalytic hydrogen production

Abstract

The tightly coupled heterostructure g-C₃N₄/Au/poly(3-hexylthiophene) (P3HT)/Pt was successfully prepared by a self-assembling method. The heterojunction photocatalyst displayed high activity for hydrogen production from water which contains triethanolamine as an electron donor under visible light irradiation. The samples were characterized by X-ray diffraction (XRD), UV-visible spectroscopy, photoluminescence (PL) spectra analysis and transmission electron microscopy (TEM). The experimental results demonstrated that the g-C₃N₄/Au/P3HT/Pt structure was conducive to the efficient separation of photo-generated electron–hole pairs, which can be explained by the strong junction of chemical bond between Au and P3HT. The effect of P3HT content on the activity of the photocatalysts was investigated with a series of g-C₃N₄/Au/P3HT heterostructure samples loaded with Pt as a cocatalyst in triethanolamine aqueous solutions. The optimal P3HT content was determined to be 0.5 wt%, and the corresponding hydrogen evolution rate was 320 μmol h⁻¹.

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Introduction

Hydrogen is widely regarded as a potential solution to solve the energy and environment issues at a global level. The photocatalytic splitting of water plays a vital role in hydrogen production methods for the transition from a carbon-based energy system to a hydrogen-based energy system. The photocatalytic splitting of water, without electricity, directly converting sunlight into hydrogen and oxygen, will be the trump card that does not involve carbon oxide emission like the manufacture of hydrogen from fossil fuels or biological reformation of biomass. Obtaining sustainable hydrogen production to supply the amounts required needs advanced materials, synthetic technologies and new design concepts.^1,2

Since Fujishima and Honda found that TiO₂ can cause cleavage of water under ultraviolet light,³ metal-based inorganic materials (including metal oxides, metal (oxy)nitrides, and metal oxysulfides) have occupied the field of photocatalysis with absolute dominance.⁴ Although these inorganic materials have led to remarkable achievements in this field, noble or rare elements are the main constituents of the metal-based complexes.⁵ Seeking green, sustainable and inexpensive photocatalysts made of abundant elements that we can obtain conveniently on the earth is significant for the utilization of solar energy in practical application. Therefore, organic photocatalysts for artificial photosynthesis have been developed to explore more economical and environmentally friendly methods. Recently, the polymeric organic semiconductor g-C₃N₄ has shown the ability of water splitting for hydrogen production under visible light.⁶ The utilization of polymeric organic semiconductors, which are cheap and easily available materials, opens up a new prospect to construct highly efficient and economical photocatalysis systems. However, the g-C₃N₄ photocatalysts suffer from many problems, such as high excitation dissociation energy, low charge mobility, low specific surface area, insufficient visible photon absorption and high level of the top of the valance band.⁷ In order to boost the photocatalytic efficiency of g-C₃N₄, several strategies, such as new synthesis methods,^8–15 doping with metal or non-metal elements,^16,17 dye sensitization,^18,19 surface modification^20–22 and construction of complexes based on g-C₃N₄,^23–30 have been developed. These methods have proved to be effective for the promotion of the photocatalytic activity of g-C₃N₄.

In our previous work, the physical adsorption of poly(3-hexylthiophene) (P3HT) on the surface of g-C₃N₄ was achieved by evaporation of the solvent using a water bath.²⁹ However, g-C₃N₄ with P3HT cannot be intimately combined because of the weak van der Waals force. This could reduce the photo-generated electron transfer efficiency between P3HT and g-C₃N₄. Herein, we adopted chemical bonding to ensure the tight conjunction between g-C₃N₄ and P3HT. Using chemical adsorption instead of physical adsorption can solve the separation problem of g-C₃N₄ and P3HT, and therefore we can realize the cyclic utilization of catalysts. The formation of a tight g-C₃N₄/Au heterojunction was obtained by the photodeposition method. In addition, 0.5 wt% Pt was loaded on the P3HT as a co-catalyst to provide chemical reactivity or active sites for H₂ evolution, and improve the photocatalytic activity of catalysts.²⁰ To the best of our knowledge, this is the first time of fabricating a polymer–metal–polymer–metal heterostructure for photocatalytic water splitting.

Experimental section

Sample preparation

Melamine, sulfuric acid (H₂SO₄), tetrahydrofuran (THF) and triethanolamine (TEA) were purchased from Chengdu Kelong Chemical Reagent Factory. Pluronic P123 was purchased from Aldrich. P3HT was bought from Luminescence Technology Corp. All reagents were used as received without further treatment.

Preparation of g-C₃N₄: the g-C₃N₄ was synthesized via a soft-templating method by using Pluronic P123 surfactant as soft template.¹² Pluronic P123 (5.0 g) and melamine (25.0 g) were dispersed in distilled water (500 mL) successively and heated at 100 °C for 1 h under magnetic stirring. Then sulfuric acid solution (10 mL, H₂SO₄ : H₂O = 1 : 1 v/v) was slowly added into the solution, and a white precipitate was produced. After cooling down to room temperature, the precipitate was collected by filtration. After drying in an oven at 80 °C overnight, the precipitate was heated from room temperature to 380 °C in 5 minutes and then to 600 °C at a heating rate of 1 °C min⁻¹ and then maintained at 600 °C for 4 hours in a muffle furnace in a flow of Ar gas. After the reaction, the product was cooled down to room temperature in a flow of Ar gas. Finally, the product was then calcined at 500 °C for 2 h in air.

The loading of 1 wt% Au on g-C₃N₄: g-C₃N₄ (1 g) was dispersed in 200 mL of 10% (v/v) TEA solution containing a certain amount of HAuCl₄ solution. After evacuating the air completely, the mixture was irradiated with a Xe lamp (300 W) for 30 minutes at room temperature. After irradiation, the sample was collected by filtration and then dried at 60 °C in an oven overnight.

Preparation of g-C₃N₄/Au/P3HT/Pt: P3HT/Pt was prepared by a photoreduction method. Typically, chloroplatinic acid (0.5 mg), P3HT (0.5 mg) and isopropyl alcohol (0.2 mL) were dissolved in THF (16 mL). The solution was irradiated by a Xe lamp (300 W) for 30 minutes at room temperature. Then, 0.1 g g-C₃N₄/Au was added to the solution. The solution was stirred at room temperature for 2 hours in the dark. The slurry was filtered and washed with THF, acetone and 10% TEA sequentially. Then the photocatalyst was transferred to the reaction cell for photocatalytic reaction tests.

Photocatalytic reaction

In a typical photocatalytic experiment, the reaction was performed in a top irradiation-type Pyrex vessel connected to a glass closed gas circulation system. Photoreduction of H⁺ to H₂ was conducted in the reaction system with an aqueous TEA solution (TEA, 10 vol%, 200 mL) as the sacrificial reagent. The light source was a 300 W xenon lamp fitted with a cutoff filter (λ > 420 nm). Prior to irradiation, the reactant solution was evacuated to remove dissolved air completely. During the reaction, a flow of cooling water was used to maintain the reactant solution at room temperature. The generated gases were detected by gas chromatography (SPSIC, GC-102AT, argon carrier).

Characterization

X-ray diffraction (XRD) patterns were obtained with an X-Pert Pro diffractometer with Cu Kα radiation (λ = 1.5406 Å) at a scan step size of 0.03°. UV-visible diffuse reflection spectra were recorded with a UV-visible spectrophotometer (UV3600, Shimadzu) and converted from reflection to absorbance by the Kubelka–Munk method. BaSO₄ was used as a reflectance standard in the UV-visible diffuse reflectance experiments. Photoluminescence (PL) measurements were obtained with a fluorescence spectrophotometer (Hitachi F-7000) and operated at room temperature. The excitation wavelength was 279 nm. Transmission electron microscopy (TEM) images were obtained with high-resolution transmission electron microscopy (HRTEM; JEM-2010F, JEOL). X-ray photoelectron spectroscopy (XPS) spectra were collected using a V4105 instrument (Thermo Electron, USA) with a Mn Kα radiation source.

Results and discussion

Phase structures, morphology and fine structure

The XRD patterns of g-C₃N₄, g-C₃N₄/Au, and g-C₃N₄/Au/P3HT/Pt nanosheets are shown in Fig. 1. All the diffraction curves have the same diffraction peaks at 27.7° and 12.9°, corresponding to the interplanar distances of 0.322 nm and 0.682 nm, respectively. The peak at 27.7° is due to the interlayer stacking of aromatic systems, while the peak at 12.9° is related to the in-plane repeat period (e.g. the hole-to-hole distance in the nitride pores).^6,15,31 The results were in good agreement with the previous reports about g-C₃N₄ and indicated that the main phase of g-C₃N₄ in the samples would not be changed by the metal loading or composite process. The diffraction peaks at 38.2° and 44.4° in the XRD patterns (see Fig. 1(b) and (c)) can be indexed to the (111) and (200) planes of Au metal particles. The diffraction peaks of both g-C₃N₄ and Au appeared in curves b and c, indicating that the Au was loaded on the g-C₃N₄ successfully. However, the diffraction peaks of P3HT and Pt were not detected in the sample of g-C₃N₄/Au/P3HT/Pt, because neither of their amounts was obviously high enough to form a separate phase alone.

Fig. 1 XRD patterns of (a) g-C₃N₄, (b) g-C₃N₄/Au, and (c) g-C₃N₄/Au/P3HT/Pt.

TEM was used to study the morphology and microstructures of g-C₃N₄, g-C₃N₄/Au, P3HT/Pt, and the heterostructure g-C₃N₄/Au/P3HT/Pt. As shown in Fig. 2(a), g-C₃N₄ has a layer structure and is a thin sheet with irregular morphology. Fig. 2(b) shows that the regularly shaped spherical Au nanoparticles with size of 3–5 nm were uniformly loaded on the surface of g-C₃N₄. The Au lattice fringes were distinctly observed as shown in the insert in Fig. 2(b). The distance of ten layers of the Au crystallites is determined as 2.35 nm (or 0.235 nm per lattice space), corresponding to the (1 1 1) crystallographic planes of cubic Au (JCPDS 04-0784). The morphology of P3HT/Pt was also investigated by TEM, as shown in Fig. 2(c). P3HT has a chain structure curled like irregular rings. The size of Pt nanoparticles is 3–5 nm as shown in the inset in Fig. 2(c). The distance of 10 layers of lattice spaces of Pt crystallite is determined as 2.26 nm (or 0.226 nm per interplanar spacing, inset in Fig. 2(c)), which matches the (1 1 1) crystallographic plane of Pt (JCPDS 04-0802). These results indicated that the two metal–polymer semiconductor heterojunction structures (g-C₃N₄/Au and P3HT/Pt) were indeed formed. Fig. 2(d) shows a TEM image of g-C₃N₄/Au/P3HT/Pt. The unobvious image contrast between g-C₃N₄ and P3HT may lead to us not being able to distinguish the two polymer semiconductors with TEM or even with HRTEM. Therefore, it is difficult to confirm the Au–P3HT heterostructure in g-C₃N₄/Au/P3HT/Pt by using TEM.

Fig. 2 TEM images of (a) g-C₃N₄, (b) g-C₃N₄/Au, (c) P3HT/Pt, and (d) g-C₃N₄/Au/P3HT/Pt obtained by the self-assembly method. The inset in (b) shows the HRTEM image of Au nanoparticles. The left inset in (c) shows the TEM image of Pt nanoparticles loaded on P3HT. The right inset in (c) shows the HRTEM image of Pt nanoparticles.

To confirm the formation of Au–P3HT heterostructure in g-C₃N₄/Au/P3HT/Pt, XPS was applied for elemental analysis and valence state analysis of the samples. As expected, in the sample of g-C₃N₄/Au/P3HT/Pt, the peak at binding energy of 163.85 eV for S 2p was observed (Fig. 3(a)). The observed sulfur signal suggested that P3HT exists in the sample of g-C₃N₄/Au/P3HT/Pt because of the component parts of the heterostructure only P3HT contains S element. The high-resolution Au 4f XPS spectra of g-C₃N₄/Au and g-C₃N₄/Au/P3HT/Pt are shown in Fig. 3(b). The Au 4f spectra consist of two peaks due to the electron spin. The binding energy of Au 4f_5/2 and Au 4f_7/2 for g-C₃N₄/Au was found at around 83.26 and 86.94 eV, respectively. However, the binding energy of Au 4f_5/2 and Au 4f_7/2 for g-C₃N₄/Au/P3HT/Pt was found at around 83.35 and 87.03 eV, respectively. There is about 0.09 eV shift towards high binding energy. This shift indicated the chemical state of Au loaded on the g-C₃N₄ changed after mixing g-C₃N₄/Au with P3HT/Pt. In consideration of the results of XPS, the experimental method and the Au–S bond formed between S element in the organics and Au,^32,33 we speculated that P3HT/Pt was successfully integrated with g-C₃N₄/Au and this combination was due to the formation of Au–S bond between Au on the g-C₃N₄ and S in the P3HT. It is the formation of these Au–S bonds that led the Au 4f spectral peaks of g-C₃N₄/Au/P3HT/Pt to shift towards high binding energy.

Fig. 3 The high-resolution XPS spectra of (a) S 2p for g-C₃N₄/Au/P3HT/Pt and (b) Au 4f for g-C₃N₄/Au and g-C₃N₄/Au/P3HT/Pt.

Optical properties of g-C₃N₄/Au/P3HT/Pt

The UV-visible diffuse reflectance spectra of g-C₃N₄, g-C₃N₄/Au, and g-C₃N₄/Au/P3HT/Pt are shown in Fig. 4. The strong absorption bands of all these photocatalysts are at wavelengths shorter than 400 nm, implying less of a condensation degree of g-C₃N₄. The weak tailed absorption band at 400–700 nm observed in the g-C₃N₄ spectrum is due to the incorporation of carbon into the melon-based carbon nitride structures.¹² The absorption intensity of the g-C₃N₄/Au and g-C₃N₄/Au/P3HT/Pt photocatalysts increases noticeably in the whole measured wavelength range. The absorption band around 530 nm is due to the surface plasmon resonance (SPR) of metallic Au nanoparticles.^20,22 For the sample of g-C₃N₄/Au/P3HT/Pt, the intensity of the absorption band around 530 nm increased further, indicating that combining g-C₃N₄/Au with P3HT/Pt enhanced the SPR effect of Au particles. These results further confirm the formation of conjunction between P3HT and Au.

Fig. 4 UV-visible diffuse reflectance spectra (DRS) of (a) g-C₃N₄, (b) g-C₃N₄/Au, and (c) g-C₃N₄/Au/P3HT/Pt.

PL spectral analysis was used to study the transfer and recombination processes of photogenerated electron–hole pairs in the photocatalysts. Fig. 5 shows the PL spectra of pure g-C₃N₄, g-C₃N₄/Au and g-C₃N₄/Au/P3HT/Pt under incident light with a wavelength of 279 nm. All PL spectra of the samples have the same major peak at 457 nm, which could be attributed to the recombination of photoexcited electron–hole in g-C₃N₄ with a band gap at 2.7 eV. Significant PL quenching was observed in g-C₃N₄/Au and g-C₃N₄/Au/P3HT/Pt. The quenching of g-C₃N₄/Au could be attributed to electron migration from g-C₃N₄ to the Au particles, which was more conducive to the photoreduction of H⁺ to H₂. Compared to g-C₃N₄, nearly 75% PL quenching was observed in the sample of g-C₃N₄/Au/P3HT/Pt, indicating that the g-C₃N₄/Au/P3HT/Pt photocatalyst has a lower recombination of the photogenerated electron–hole pairs and more efficient charge transfer between g-C₃N₄ and P3HT due to the tight conjunction between them.

Fig. 5 Photoluminescence (PL) emission spectra of (a) g-C₃N₄, (b) Au-loaded g-C₃N₄, and (c) g-C₃N₄/Au/P3HT/Pt heterostructure. The excitation wavelength was 279 nm.

Photocatalytic activity and photocatalytic mechanism

Photocatalytic H₂ production was evaluated under visible light irradiation (λ > 420 nm) using TEA as sacrificial reagent. Fig. 6 shows the H₂ evolution rate for different g-C₃N₄-based photocatalysts. As shown in Fig. 6, the g-C₃N₄/P3HT photocatalyst shows a negligible H₂ evolution rate. However, after loading of Pt on P3HT, the H₂ evolution rate of g-C₃N₄/P3HT/Pt reaches 74 μmol h⁻¹. This enhanced photocatalytic H₂ evolution rate could be ascribed to the efficient separation of the photogenerated electron–hole pairs in g-C₃N₄/P3HT/Pt photocatalyst and the platinum on the P3HT acts as an electron outlet or active site for the reduction of H⁺. The photocatalytic H₂ evolution rate on g-C₃N₄/Au and g-C₃N₄/Pt is 73 μmol h⁻¹ and 82 μmol h⁻¹, respectively. Loading both Au and Pt on g-C₃N₄ can enhance the photocatalytic performance further. The photocatalytic H₂ evolution rate on g-C₃N₄/Au–Pt is 171 μmol h⁻¹, approximately the sum of H₂ evolution rate on g-C₃N₄/Au and g-C₃N₄/Pt. These results also indicated that Au on g-C₃N₄ played a similar role to Pt as the electron outlet or active site. It is well known that the more electrons on the active site of Au surface (e.g. g-C₃N₄/Au) or the active site of Pt surface (e.g. g-C₃N₄/Pt or g-C₃N₄/Au/P3HT/Pt), the more conducive to H₂ generation. Compared to the H₂ evolution rate of g-C₃N₄/Au, the H₂ evolution rate of g-C₃N₄/Au/P3HT decreased from 73 μmol h⁻¹ to 56 μmol h⁻¹. This indicated that, after the combination of P3HT with g-C₃N₄/Au, the Au surface did not gain more effective electrons for H₂ evolution and the excited P3HT would not supply the electrons to the Au surface directly for H₂ evolution or transfer excited electrons to g-C₃N₄ then to the Au surface for H₂ evolution. The result reflected the fact that the combination of P3HT led the electrons on the Au surface to be efficiently consumed, which indicated that P3HT “grabbed” the electrons on the Au surface through the way that provides holes to the Au surface. The H₂ evolution rate of g-C₃N₄/Au/P3HT/Pt is 320 μmol h⁻¹, more than four times higher than that of g-C₃N₄/P3HT/Pt, g-C₃N₄/Au or g-C₃N₄/Pt. It is worth noting that the photocatalytic H₂ evolution rate of g-C₃N₄/Au/P3HT/Pt is more than two times higher than that of g-C₃N₄/Au–Pt. In this case, the P3HT can be compared to an “electric wire” which transferred the elections to the far end (the realization of separating electron–hole pairs) where Pt used them for H₂ generation. These results indicate that, in the heterostructure of g-C3N4/Au/P3HT/Pt, the combination of electrons on the Au surface with the holes from the HOMO of P3HT was favourable for preventing the recombination of electron–hole pairs in the body of g-C₃N₄ and P3HT. Therefore, Pt could obtain more electrons for H₂ evolution and g-C₃N₄ could retain more holes for the oxidation of TEA.

Fig. 6 The H₂ evolution rates of various photocatalysts. All the experimental data were obtained under identical reaction conditions. The light source was a 300 W Xe lamp (λ > 420 nm) and TEA (10% v/v) was chosen as the sacrificial reagent.

Fig. 7 shows the H₂ evolution rate on g-C₃N₄/Au/P3HT/Pt with different amounts of P3HT. As shown in Fig. 7, with an increase of the amount of P3HT, the photocatalytic H₂ evolution rate increases first and reaches a maximum of 320 μmol h⁻¹ when the amount of P3HT is about 0.5 wt%. However, further increasing the amount of P3HT leads to a decrease of the photocatalytic H₂ evolution.

Fig. 7 The rate of H₂ evolution on g-C₃N₄/Au/P3HT/Pt polymer composites with different amounts of P3HT under visible light (λ > 420 nm).

The mechanism of photocatalysis is shown in Scheme 1. Here we apply the metal–semiconductor contact theory and the Fermi level equilibration principle involving the Schottky–Mott limit demonstrated by Tang and Slyke³⁴ and the metal–organic interface proposed by Kahn et al.³⁵ to explain the photocatalysis mechanism of g-C₃N₄/Au/P3HT/Pt. The charge distribution leads to Fermi level equilibration in the metal–semiconductor system, so we can assume a quasi-Fermi level (E^*_F) in g-C₃N₄/Au/P3HT/Pt. The property of storing electrons in a quantized fashion in Au nanoparticles^36,37 leads to the shift of the Fermi level of Au towards more negative potential. This may result in the Fermi level of the composite shifting closer to the conduction band of the semiconductor in the ZnO/Au system or TiO₂/Au system.^38,39 In the g-C₃N₄/Au system, the upward shift of the Fermi level (E_F) of the composite to the quasi-Fermi level (E^*_F) in Scheme 1 has been used for reference and the photocatalytic performance of g-C₃N₄ improves due to the efficiency of interfacial charge-transfer process.²⁰

Scheme 1 Schematic of the photocatalytic mechanism of g-C₃N₄/Au/P3HT/Pt heterostructure.

On the other hand, the high work function of Au leads to small hole injection barriers (HIBs) at the metal–organic interface and it often was chosen as an electrode for hole injection.⁴⁰ The HIB is defined as the energy difference between the metal Fermi level (E_F) and the hole transport level in the organic semiconductor. In this scheme, the highest occupied molecular orbital (HOMO) can be regarded as the hole transport level in P3HT. However, contaminated Au surface work function values spanned the range between 4.7 and 5.1 eV and may even be larger when considering different environments.⁴¹ The HOMO of P3HT (π-conjugated polymer) was determined as 5.1 eV or 4.9 eV (bulk^42,43), 4.3 eV (film⁴⁴), 4.0 eV (a single strand⁴⁵). If we neglect the effect of interface dipoles (IDs), admitting that the Au–S bond was indeed formed between Au and P3HT, the values of Au surface work function and the HOMO of P3HT were so close that the HIB of the interface between the P3HT and Au was very low and even forms an ohmic contact.⁴⁶ The low potential barrier or ohmic contact of P3HT/Au favors charge carrier injection into each other. The holes, which transport through the P3HT network (good hole-transport material),⁴⁷ will be collected at the Au surface.

In our research, however, the formation of the Au–S bond was confirmed by XPS. Therefore, the energy level alignment in reactive interfaces is controlled by chemistry-induced electronic states.³⁷ The chemical reaction to form Au–S bonds leads to the formation of gap states and pinning of E_F at the interface. Just consider the interface of P3HT/Au: if the Au work function falls in the P3HT gap, the gap states pinning E_F2 lie in the upper part of the gap and increase the HIB,⁴⁸ while the contaminated Au has a larger work function, and the large surface dipole of Au work function also leads to a large interface dipole barrier.³⁵ The large HIB results in low hole transfer and reduces the photocatalytic efficiency. The HIB of P3HT/Au was determined as 0.59 eV (ref. 49) or even smaller at 0.35 eV,⁴⁰ because of the different preparative approaches or the presence of ambient contamination at the Au interfaces.⁴¹

Naturally, the interface charge-transfer of g-C₃N₄/Au and the chemical bond of P3HT/Au or other unforeseen mechanisms, like molecule-induced modification of the metal work function, contribute to the IDs and affect each other. This becomes more complex and difficult to differentiate between the various contributions.³⁵

In our experiment, by comparing the rate of photocatalytic H₂ evolution on g-C₃N₄/Au and g-C₃N₄/Au/P3HT, it is concluded that the effective electrons on the Au surface were consumed and that the P3HT “grabbed” the electrons on the Au surface through the way that provides holes to Au surface. This means the interface of P3HT/Au realized hole transport from P3HT to the Au surface. This led us to suspect a low potential barrier had been formed at the P3HT/Au interface for the injection of charge carriers into each other. The recombination of electrons generated in g-C₃N₄ with the holes from the HOMO level of P3HT on the Au nanoparticle surface promoted the efficient dissociation of electron–hole pairs generated in the two kinds of polymer semiconductors. The excited electrons in P3HT transferred to the Pt and achieved the reduction of H⁺ to H₂. The g-C₃N₄ got the compensation of electrons through the oxidation of TEA to TEA⁺. The recombination process of electrons and holes on the Au surface and the dissociation process of photo-generated electron–hole pairs in g-C₃N₄ and P3HT greatly enhanced the overall photocatalytic efficiency. The platinum metal introduced an ohmic contact that provided a quick transfer of electrons to the electrolyte.³⁸ This resulted in the Fermi energy of Pt remaining close to the solution redox level and had a negligible effect on the Fermi level of the semiconductor.

Conclusions

In summary, the tightly coupled heterostructure g-C₃N₄/Au/P3HT/Pt was successfully prepared. Au and Pt nanoparticles with size of 3–5 nm were uniformly loaded on g-C₃N₄ and P3HT, respectively. The XPS result indicates the formation of Au–S bonds in g-C₃N₄/Au/P3HT/Pt photocatalyst. The marked PL quenching of g-C₃N₄/Au/P3HT/Pt photocatalyst indicates less recombination of the photogenerated electron–hole pairs. The as-prepared g-C₃N₄/Au/P3HT/Pt heterojunction promoted the transfer of light-excited electrons from g-C₃N₄ to P3HT effectively and enhanced photocatalytic hydrogen production under visible light. The g-C₃N₄/Au/P3HT/Pt with an amount of P3HT of 0.5 wt% achieves the highest H₂ evolution rate, the photocatalytic H₂ evolution rate reaching 320 μmol h⁻¹.

Acknowledgements

We thank the National Natural Science Foundation of China (no. 21273157) for financial support. We thank Sichuan University Analytical & Testing Centre for the analysis of PL and XRD, and especially Dr S. L. Wang and Dr G. P. Yuan for TEM measurements.

Notes and references

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