Efficient Visible-Light-Driven Photocatalytic Hydrogen Evolution on

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Efficient Visible-Light-Driven Photocatalytic Hydrogen Evolution on Phosphorus-Doped Covalent Triazine-Based Frameworks Zhi Cheng, Wei Fang, Tiansu Zhao, Shengqiong Fang, Jinhong Bi, Shijing Liang, Liuyi Li, Yan Yu, and Ling Wu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b16013 • Publication Date (Web): 01 Nov 2018 Downloaded from http://pubs.acs.org on November 1, 2018

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ACS Applied Materials & Interfaces

Efficient Visible-Light-Driven Photocatalytic Hydrogen Evolution on Phosphorus-Doped Covalent Triazine-Based Frameworks Zhi Cheng,† Wei Fang,† Tiansu Zhao,† Shengqiong Fang,*,† Jinhong Bi,*,†,‡ Shijing Liang,†,‡ Liuyi Li,§ Yan Yu,§ and Ling Wu‡ †Department

of Environmental Science and Engineering, Fuzhou University,

Minhou, Fujian 350108, P. R. China ‡State

Key Laboratory of Photocatalysis on Energy and Environment, Fuzhou

University, Minhou, Fujian 350108, P. R. China §Key

Laboratory of Eco-materials Advanced Technology, Fuzhou University,

Minhou, Fujian 350108, P. R. China KEYWORDS: visible light, photocatalysis, hydrogen evolution, covalent triazine-based frameworks, phosphorus doping

ABSTRACT: Seeking efficient visible-light-driven photocatalysts for water splitting to produce H2 has attracted much attention. Chemical doping is an effective strategy to enhance photocatalytic performance. Herein, we reported phosphorus-doped

covalent

triazine-based

frameworks

(CTFs)

for

photocatalytic H2 evolution. Phosphorus-doped CTFs was fabricated by a facile 1 ACS Paragon Plus Environment

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thermal treatment using easily available red phosphorus as the external phosphorus species. The introduction of phosphorus atoms into the frameworks modified the optical and electronic property of CTFs, thus promoting the generation, separation and migration of photoinduced electron-hole pairs. Consequently, the photocatalytic H2-production efficiency of phosphorus-doped CTFs was greatly improved, which was 4.5, 3.9 and 1.8 times higher than that of undoped CTFs and phosphorus-doped g-C3N4 calcined from melamine and urea, respectively.

1. INTRODUCTION Seeking high active visible-light-driven photocatalysts that directly split water has been an urgent desire worldwide with respect to convert solar energy into clean and renewable hydrogen fuel.1-3 To achieve a high efficiency in photocatalytic H2 evolution, a suitable photocatalyst should satisfy several requirements: (i) a wide response range in the solar light spectrum; (ii) the conduction band (CB) potential should be more negative than the energy level of H2 evolution; (iii) effective charge separation and migration.4,5 As a new class of conjugated polymer materials, covalent triazine-based frameworks (CTFs) have been recently regarded as a type of promising visible-light-driven photocatalysts.6-8 The π-conjugated cyclic aromatic rings of CTFs are in favor of visible light absorption, and the π-stacked structure is beneficial for charge transfer.9 In our previous research, a kind of CTFs (CTF-1) was synthesized

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from

1,4-dicyanobenzene

in

trifluoromethanesulfonic

acid

at

room

temperature, which displayed photocatalytic activity for H2 evolution under visible light irradiation (λ≥420 nm).10 It has been revealed that CTF-1 has a band gap of 2.94 eV with the conduction band position at around −1.03 V vs. a normal hydrogen electrode (NHE), which is more negative than the reduction potential of H+/H2 (0 V, vs. NHE). However, the photocatalytic efficiency of pristine CTF-1 is usually restricted by its insufficient visible light absorption and low charge migration rate. Various attempts have been made to remedy these drawbacks, such as structure

modulation,11

co-catalyst

deposition,12

fabrication

of

hybrid

photocatalysts9,13 and chemical doping.14 Among the above-mentioned strategies, chemical doping is a simple and effective way to improve the catalytic performance through extending light absorption range and increasing charge mobility.15-17 Phosphorus atom is expected to be an ideal dopant to tune the optical and electronic property of CTFs for the enhancement of photocatalytic performance. Following the early reports of P-doping in conjugated polymer materials, most of the doping process required complicated P precursors under harsh synthetic condition.18,19 For example, Zhang et al. prepared P-doped g-C3N4 through a thermal treatment of the compound with dicyandiamide (DCDA) and 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF6) at 550 oC for 8 h.20 The results show that the P atoms most probably replace the corner or bay C atoms in the structure and 3 ACS Paragon Plus Environment


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form P−N bond in the doped g-C3N4 frameworks. Hu et al. reported a case of interstitial phosphorus doping for g-C3N4 by heating the mixture of DCDA and (NH4)2HPO4 at 520 oC for 2 h.21 Thus, exploring easily available P source and facile doping method are desirable. In this work, red phosphorus was selected as heteroatom dopant to improve the

photocatalytic

H2-production

activity

of

covalent

triazine-based

frameworks (CTFs). Phosphorus-doped CTFs was synthesized for the first time by a facile thermal treatment of the mixture of as-prepared CTFs and purchased red phosphorus at 250 oC for 1 h. The obtained phosphorus-doped CTFs showed enhanced photocatalytic activity than that of pristine CTFs, which was mainly ascribed to the enhanced visible light absorption, increased reducing-ability of photoelectrons and effective separation/transfer of photogenerated electron-hole pairs.

2. EXPERIMENTAL SECTION 2.1. Synthesis of CTF-1. CTF-1 was synthesized following our previous report.10 10 mL of trifluoromethanesulfonic acid was slowly injected into 1.28 g of 1,4-dicyanobenzene in a pre-dried round-bottom flask at 0 oC. The sticky solution was stirred in oil-bath at 30 oC until solidification. The resultant solid was kept under static condition for 3 days, and then rinsed with dichloromethane and ammonium hydroxide. The collected solid was stirred overnight in ammonium hydroxide. After washing with distilled water and


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methanol,

the

product

was

soxhlet

extracted

with

methanol

and

dichloromethane, dried in vacuum at 80 oC for 12 h and ground into powder. 2.2. Synthesis of P-doped CTF-1. CTF-1 (0.4 g) and red phosphorus (0.04 g) with a mass ratio of 10:1 were mixed and well ground in agate mortar. The mixture was heated at 250 oC for 1 h with a heating rate of 5 oC min-1. After cooling down to room temperature, the obtained solid was refluxed in ethanol for 32 h and dried at 60 oC. The final sample was denoted as PCTF-1. P-doped CTF-1 with different mass ratios of CTF-1 and red phosphorus were synthesized by the same procedure and denoted as PxCTF-1, which x represents to the mass ratio of red phosphorus and CTF-1 multiplied 100 (x=5, 20 and 30). The physical mixture sample of CTF-1 and red phosphorus with the mass ratio of 10:1 was prepared and denoted as PCTF-m. 2.3. Synthesis of P-doped g-C3N4. g-C3N4 was synthesized following the previous report.22 In a typical synthesis, a certain amount of melamine was heated at 550 oC for 4 h with a ramping rate of 2.3 oC min-1. After cooling naturally, the resultant solid was ground into powder and denoted as CN.

g-C3N4 using urea as precursor was also prepared by heating urea to 550 oC for 4 h in Ar atmosphere and denoted as CNU.23 The P-doped g-C3N4 was synthesized by the same procedure to P-doped CTF-1, except that CTF-1 was replaced by CN and CNU, respectively. The as-obtained P-doped g-C3N4 samples were denoted as PCN and PCNU, respectively.



2.4. Characterization. The scanning electron microscopy (SEM) images were obtained with a Nova Nano SEM 230 microscopy (FEI Corp.). The transmission electron microscopy (TEM) data were recorded using a TECNAI G2 F20 microscope at an accelerating voltage of 200 kV (FEI Corp.). The Brunauer-Emmett-Teller (BET) surface areas and pore volumes were measured with an ASAP 2020 apparatus (Micromeritics Instrument Corp.). Powder X-ray diffraction (PXRD) patterns were collected on a Rigaku MiniFlex 600 X-ray diffractometer with Ni-filtered Cu-Kα irradiation (α=1.5406 Å). Fourier transform infrared (FT-IR) spectra were recorded on a Thermo Scientific Nicolet iS10 spectrometer by using KBr pellets at a resolution of 4 cm-1. X-ray photoelectron spectroscopy (XPS) data were obtained on a PHI Quantum 2000 XPS system equipped with a monochromatic Al Kα X-ray source. All binding energies were referenced to the C 1s peak (284.6 eV) of the surface adventitious carbon. Elemental analysis was performed on an elemental analyzer (Vario EL Cube, Elementar, Germany) with speedy quantitative analysis of CHN. Solid-state UV-vis diffuse reflectance spectra (UV-vis DRS) were recorded on an Agilent Cary 5000 UV-Vis-NIR spectrophotometer and barium sulfate was used as a referent. The photoluminescence (PL) spectra were measured in an Edinburgh FL/FS900 spectrophotometer with an excitation wavelength at 360 nm. Electron paramagnetic resonance (EPR) signals were recorded on a Bruker ESP 300


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E electron paramagnetic resonance spectrometer. A 300 W Xe lamp (PLS-SXE300C) with a 420 nm cut-off filter was used as light source. To fabricate the working electrode, 5 mg of well ground catalyst and 0.5 mL of N, N-dimethylformamide were mixed under sonication for 4 h. 10 μL of the obtained suspension was dropped onto a piece of fluoride-tin oxide (FTO) glass substrates with a cover area of 0.25 cm2, and the uncovered parts of FTO glass were coated with epoxy. Then the working electrode was dried under ambient temperature. The Mott-Schottky and photocurrent analyses were recorded by an electrochemical workstation (CHI650E) equipped with a conventional three-electrode cell and 0.2 M Na2SO4 aqueous solution was used as an electrolyte. The electrochemical impedance spectroscopy (EIS) plots were performed by ZAHNER IM6 electrochemical workstation and 5 mM K3[Fe(CN)6]/5 mM K4[Fe(CN)6]/0.1 M KCl mixed aqueous solution was used as an electrolyte. A platinum plate electrode and an Ag/AgCl electrode were used as the counter electrode and the reference electrode, respectively. The working electrode was illuminated by a 300 W Xe lamp with a 420 nm cut-off filter from the backside to minimize the impact of thickness of the semiconductor layer. Each measurement was repeated three times under the same condition. 2.5. Photocatalytic Hydrogen Production. To access the photocatalytic performance of obtained samples, photocatalytic H2 evolution experiment was carried out in a glass-closed gas-circulation system and a 100 mL Pyrex glass 7 ACS Paragon Plus Environment


reaction vessel. Photocatalytic H2 production was performed by dispersing 20 mg of catalyst into ultrapure water (50 mL) containing triethanolamine (5 mL) as sacrificial electron donor in reaction vessel. A certain amount of H2PtCl6·6H2O was dissolved in the reactant solution to deposit 1 wt% of Pt onto the catalyst. Before irradiating under visible light (λ≥420 nm), the whole reaction system was evacuated several times to remove air completely. A flow of cooling water was used to maintain the temperature of reaction device. The generated gases were analyzed by an on-line gas chromatograph (SHIMADZU, GC-8A) with a thermal conductivity detector (TCD) and argon was used as the carrier gas. To evaluate the stability of the catalyst, the photocatalytic reaction was carried out as the similar procedure above by 40 mg catalyst for a total of 20 h with evacuation every 4 h. The apparent quantum efficiency (AQE) was measured with irradiation light by using 300 W Xe lamp equipped with a 420 nm band-pass filter. The AQE was calculated according to the following equation in the previous report24 AQE(%) = (2×H/I)×100 where H and I represent the number of the evolved H2 molecules and the number of incident photons, respectively. The number of incident photons was estimated by a calibrated Si photodiode and it was supposed that all incident photons were absorbed by the photocatalyst.

3. RESULTS AND DISCUSSION


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Scheme 1. Schematic Illustration of the Synthesis and Photocatalytic H2 Production under Visible Light Irradiation of P-doped CTF-1 Photocatalyst. P-doped CTF-1 (PCTF-1) was prepared by a facile thermal treatment of CTF-1 and red phosphorus (Scheme 1). After P doping, the compacted layered structure of PCTF-1 was remained (Figure 1a,b), which can be further discerned in TEM images (Figure 1c,d). The EDX elemental mapping images verified the uniform distribution of C, N and P within the frameworks (Figure 1e). The specific surface areas and pore structure of as-prepared CTF-1 and PCTF-1 samples were determined by N2 adsorption measurement. Both CTF-1 and PCTF-1 exhibited a type IV adsorption-desorption isotherms with a hysteresis loop in relative pressure range of 0.8-1.0 (Figure S1), illustrating the presence of mesoporous structure, which may derived from the layered stacking of samples.25 It is found that the specific surface area and pore volume of PCTF-1 were similar to that of undoped CTF-1 (Table S1). In the inset of Figure S1, the pore size distributions of CTF-1 and PCTF-1 samples



were about 6-45 nm, further confirming the hierarchical pore structure of the synthesized materials.26

Figure 1. SEM images of (a) CTF-1 and (b) PCTF-1. TEM images of (c) CTF-1 and (d) PCTF-1. (e) EDX elemental mapping images of PCTF-1. The crystal structure of CTF-1 and PCTF-1 were determined by PXRD patterns as depicted in Figure 2a. Three similar diffraction peaks were detected for CTF-1 and PCTF-1. The additional weak peak situated at ca. 15.4

o

was observed for PCTF-1, which can be ascribed to the residual red

phosphorus. The FT-IR spectra of CTF-1 and PCTF-1 exhibited similar prominent peaks, where the peaks at 1508 cm-1 and 1357 cm-1 were assigned to the typical stretching modes of the triazine ring (Figure 2b).27 PXRD and FT-IR results demonstrated that the conjugated backbone structure of CTF-1


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was well maintained after P doping, which was essential for π-delocalized electronic systems to generate and transport photoexcited electron-hole pairs for the subsequent redox reactions.28 To further study the surface chemical composition of PCTF-1 sample, X-ray photoelectron spectra (XPS) were recorded. The survey spectrum of PCTF-1 declared the presence of C, N, O and P species (Figure S2a). The P 2p spectrum (Figure 2c) in

Figure 2. (a) PXRD patterns of CTF-1, PCTF-1, and red phosphorus. (b) FT-IR spectra of CTF-1 and PCTF-1. (c) high-resolution XPS spectra of P 2p in PCTF-1



upon Ar+ sputtering from 0 to 420 s. (d) high-resolution XPS spectra of N 1s in CTF-1 and PCTF-1. PCTF-1 can be divided into two peaks located at about 133.4 eV and 129.5 eV, respectively. The peak at 133.4 eV can be assigned to P−N bond (P−C bonding is 1-2 eV lower),29 implying that P atoms may replace C atoms in the C−N frameworks of CTF-1. The nearly unchanged peak at 133.4 eV upon long time Ar+ sputtering manifested the homogeneous distribution of P in PCTF-1. The weak peak at 129.5 eV corresponding to red phosphorus disappeared after 40 s Ar+ sputtering,30 suggesting that red phosphorus was on the surface of PCTF-1. As shown in C 1s spectra (Figure S2b), two additional peaks of PCTF-1 at 288.0 eV and 286.5 eV were assigned to C atoms in N−C=N and C−P groups, respectively.31,32 The presence of C−P bond revealed that P atoms were indeed covalently bound to the backbone structure of CTF-1. The N 1s spectrum of PCTF-1 can be resolved into two peaks at binding energies of 399.2 eV and 398.6 eV (Figure 2d). The main peak centered at 399.2 eV was corresponded to sp2-hybridized aromatic N bonded to carbon atoms in triazine ring (C−N=C).33 While the peak at binding energy of 398.6 eV was assigned to P=N bond in PCTF-1, further confirming the substituting C atoms with P atoms.34,35 The P has five valence-electrons, whereas C has four. When the P atom was introduced into the frameworks, four of the valence-electrons formed covalent bonds with the C and N neighbors to adopt a planar structure. The remaining one lone electron of P 12 ACS Paragon Plus Environment

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atom will delocalize into the π-conjugated triazine ring, thus creating an electron-rich state of P-doped CTF-1.29 Moreover, the atomic concentration of C in CTF-1 and PCTF-1 can be calculated from XPS analysis as 74.7 at% and 72.5 at%, respectively, indicating the P introduction to CTFs resulted in the decreased concentration of C. This result was further confirmed by the elemental analysis as shown in Table S2. These results demonstrated that C atoms was really replaced by P atoms during the doping process. The optical property and electronic band structure of CTF-1 and PCTF-1 were investigated by UV-vis diffuse reflectance spectra. The introduction of P atoms enhanced the light absorption of CTF-1 over the entire visible light range (Figure 3a), which can be further verified by the color change from pale yellow (CTF-1) to brown (PCTF-1) in Figure S3. For PCTF-1, the additional absorption band ranging from 450 to 500 nm emerged due to the optical transition of the phosphorus impurity within the gap,23 while the absorption band from 500 to 700 nm might be ascribed to the light absorption of residual red phosphorus on the surface of PCTF-1.36 Moreover, the light absorption edge of PCTF-1 exhibited a weak red shift relative to CTF-1, illustrating a band gap narrowing and the electronic integration of the P-heteratoms in the frameworks of PCTF-1. Further analyses based on the Kubelka-Munk function showed that the corresponding band gap energy was decreased from 2.94 eV (CTF-1) to 2.68 eV (PCTF-1).37 The Mott-Schottky plots of CTF-1 and PCTF-1 exhibited positive slopes at different frequencies, which was a typical n-type 13 ACS Paragon Plus Environment


semiconductor feature (Figure 3b). The flat band potentials of CTF-1 and PCTF-1 were at approximately −1.23 and −1.30 V vs. the saturated Ag/AgCl reference electrode, respectively. For n-type semiconductor, the conduction band (CB) potential is very close to the flat band potential.37 Combining with the band gap energies, the valence band (VB) edges of CTF-1 and PCTF-1 were calculated to be 1.71 and 1.38 V, respectively. To further confirm the relative positions of the valence band maximum for CTF-1 and PCTF-1, the valence bands were further investigated by XPS. The extrapolated dominant edges of the valence band revealed that CTF-1 displayed a higher valence band maximum than PCTF-1 by ca. 0.33 eV (Figure S4). This is reasonable and consistent with the results calculated from the UV-vis band gap and flat band potential positioning determined by the Mott-Schottky plots. Based on the above results, the corresponding band gap structure of CTF-1 and PCTF-1 were presented in Figure 3c. Both CTF-1 and PCTF-1 satisfied the thermodynamical condition for photocatalytic H2 evolution. The more negative CB potential of PCTF-1 indicated that P doping could significantly enhance the photoreducibility of CTF-1, which will be beneficial for photocatalytic H2 evolution. The generation of photoinduced electron-hole pairs, as well as the separation and migration is regarded as the basic process in photocatalytic reaction. Photoluminescence (PL) measurement provided a useful tool to investigate the electronic property of CTF-1 and PCTF-1. A broad emission 14 ACS Paragon Plus Environment

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peak at ca. 460 nm was detected for CTF-1 and PCTF-1, reflecting the generation and recombination of photoinduced electron-hole pairs within semiconductors (Figure S5). PCTF-1 sample displayed higher PL intensity with respect to CTF-1, which indicated that a large number of electrons can be generated under visible light irradiation, owing to the enhanced visible light absorption after P doping.38 The generation rate of the electrons might overcome the migration rate of the electrons, leading to a strong PL signal for PCTF-1. More electronic property of CTF-1 and PCTF-1 were examined by room temperature electron paramagnetic resonance (EPR). As shown in Figure 3d, both CTF-1 and PCTF-1 displayed one single Lorentzian line centered at g-value of 2.0034 in dark, which was originated from unpaired electrons on π-conjugated aromatic rings of materials.39 Obviously, the EPR intensity was greatly strengthened after the introduction of P atoms in dark condition, certifying that the modification of P atoms can effectively accelerate the electrons transfer in the π-conjugated system of CTF-1.40 This is potentially due to the delocalization of the valance electron of P to the CTF-1 conjugation system which can widen the band distribution, thus improving charge migration. To further elucidate the accelerated charge transfer, photoelectrochemical measurements were conducted. In Figure 4a, a decreased EIS semicircular for PCTF-1 was observed as compared to pristine CTF-1, illustrating that P doping could facilitate the interfacial charge transfer.21 The separation 15 ACS Paragon Plus Environment


efficiency of photoinduced electron-hole pairs was studied by the transient photocurrent measurement. The rapid and stable photocurrent responses of CTF-1 and PCTF-1 under intermittent irradiation (λ≥420 nm) were observed in Figure 4b. Notably, PCTF-1 showed higher photocurrent density than that of pristine CTF-1, confirming the constructive effect of P doping in enhancing electrical conductivity.41

Figure 3. (a) UV-vis diffuse reflectance spectra of CTF-1, PCTF-m, and PCTF-1. (b) Mott-Schottky plots, (c) band structures, and (d) room-temperature EPR spectra of CTF-1 and PCTF-1. The photocatalytic activities of as-prepared samples were evaluated via H2 evolution from water under visible light irradiation (λ≥420 nm). As shown in Figure S6, P-doped CTF-1 with a mass ratio of 10:1 (PCTF-1) exhibited a higher H2 16 ACS Paragon Plus Environment

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evolution rate compared to PxCTF-1 (x=5, 20 and 30) series samples, which was 4.5, 3.9 and 1.8 times as high as that of pristine CTF-1 and P-doped g-C3N4 (Figure 4c). The apparent quantum efficiency (AQE) of the H2-evolving half-reaction for PCTF-1 was calculated to be 4.65 %. Such an impressive AQE for PCTF-1 endows the superiority of metal-free CTF-based photocatalysts. Notably, the physical mixture of CTF-1 and red phosphorus (PCTF-m) only exhibited low photocatalytic activity,

Figure 4. (a) Electrochemical impedance spectroscopy plots of CTF-1 and PCTF-1. (b) photocurrent responses under visible light irradiation of CTF-1 and PCTF-1. (c) H2 evolution rates of CTF-1, PCTF-m, PCN, PCNU and PCTF-1. (d) photocatalytic H2 production of PCTF-1 in cyclic reaction (5 cycles, 4 h/cycle). 17 ACS Paragon Plus Environment


demonstrating that the enhanced photocatalytic activity of PCTF-1 was stemmed from the incorporation of P atoms into the frameworks of CTF-1 during the thermal treatment. It is widely accepted that the photocatalytic reaction involves four consecutive steps as follows: (i) light absorption; (ii) photoexcitation to produce electron-hole pairs; (iii) electron-hole pairs separation and transfer to the surface of photocatalyst; (iv) surface redox reaction.42 PCTF-1 sample exhibited similar specific surface area to the pristine CTF-1, implying that the effect of surface area on the photocatalytic performance can be excluded. On the basis of UV-vis DRS analysis, PCTF-1 sample with enhanced visible light absorption can harvest more photons to photo-excite the electrons in the VB to the CB, while leaving the photogenerated holes in the VB. This is very in favor of the enhancement of the photocatalytic performance. On the other hand, the electronic and textural structures of CTF-1 were simultaneously tailored via the doping of P, resulting in more negative CB potential and improved charge mobility, which was proved by Mott-Schottky plots, EPR spectra and photoelectrochemical results. The more negative CB potential of PCTF-1 was beneficial to the formation of photoelectrons with more powerful reducing-ability, thus produced a higher photocatalytic H2-production activity. Therefore, the pronounced enhancement in photoreductive water splitting of P-doped CTF-1 can be mainly attributed to the enhanced visible light


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absorption, increased reducing-ability of photoelectrons and accelerated charge transfer. Stability is also a decisive factor when considering the practical application of a photocatalyst. To measure the active stability of PCTF-1, a cyclic H2 evolution test of PCTF-1 was carried out under a consecutive visible light irradiation (λ≥420 nm). The photocatalytic H2-evolution activity of PCTF-1 had negligible decline after a 20 h cyclic reaction in Figure 4d. To further confirm the stability of PCTF-1 after photocatalytic reaction, the used PCTF-1 sample was investigated by PXRD and FT-IR. As shown in Figure S7, there is no obvious change in the crystal and chemical structure of PCTF-1 before and after catalytic reaction, illustrating the high stability of PCTF-1. The excellent photocatalytic activity and stability of PCTF-1 underlined the overwhelming advantage of P-doped CTF-1 in photocatalytic H2 evolution.

4. CONCLUSION We introduced a new facile approach for the preparation of P doped conjugated polymer semiconductor. P atoms were introduced into the frameworks of CTF-1 through simple and facile thermal treatment of the as-prepared CTF-1 and purchased red phosphorus. The conjugated structure and texture were maintained after the incorporation of P into the frameworks of CTF-1. P-doped CTF-1 displayed superior photocatalytic activity and stability for H2 evolution over pristine CTF-1 and P-doped g-C3N4 under visible light irradiation. The improved photocatalytic activity can be attributed to the 19 ACS Paragon Plus Environment


enhanced visible light absorption, increased reducing-ability of photoelectrons and more efficient charge transfer after P doping. This work not only developed a simple and facile strategy to synthesize highly efficient conjugated polymer photocatalysts, but also advanced the understanding on the modification of CTF-based photocatalysts for future practical applications. ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge on the ACS Publications website at DOI: N2 adsorption-desorption isotherms of CTF-1 and PCTF-1 and the corresponding pore size distribution; table of the pore volumes, average pore sizes, and specific surface areas of CTF-1 and PCTF-1 samples; XPS survey spectra and high-resolution XPS spectra of C 1s in CTF-1 and PCTF-1; table of elemental composition of CTF-1 and PCTF-1; optical photograph images of CTF-1 and PCTF-1; valence band XPS spectra of CTF-1 and PCTF-1; photoluminescence spectra of CTF-1 and PCTF-1 with an excitation wavelength of 360 nm; H2 evolution rates of CTF-1, PCTF-1 and PxCTF-1 (x=5, 20 and 30); and PXRD patterns and FT-IR spectra of PCTF-1 before and after catalytic reaction (PDF) AUTHOR INFORMATION Corresponding Authors 20 ACS Paragon Plus Environment

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* E-mail: [email protected] (S.F.). * E-mail: [email protected] (J.B.). Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. ORCID Jinhong Bi: 0000-0002-8141-7742 Shijing Liang: 0000-0001-9963-5935 Liuyi Li: 0000-0002-3066-2991 Yan Yu: 0000-0001-6748-2620 Ling Wu: 0000-0003-2652-8105 Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS This work was financially supported by the National Natural Science Foundation of China (51672047, 21403238, 51672048), the Program for New Century Excellent Talents in University of Fujian Province, Independent Research Project of State Key Laboratory of Photocatalysis on Energy and Environment (2014C03) and Fuzhou University Testing Fund of Precious Apparatus (2018T001). REFERENCES



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Abstract Graphic


Efficient Visible-Light-Driven Photocatalytic Hydrogen Evolution on

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