Carbon Nitride-Modified Defective TiO2âx@Carbon Spheres for

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C: Surfaces, Interfaces, Porous Materials, and Catalysis 2-x

Carbon Nitride Modified Defective TiO @Carbon Spheres for Photocatalytic H Evolution and Pollutants Removal: Synergistic Effect and Mechanism Insight 2

Chengzhang Zhu, Xiao Chen, Jian Ma, Cheng Gu, Qiming Xian, Tingting Gong, and Cheng Sun J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b06624 • Publication Date (Web): 17 Aug 2018 Downloaded from http://pubs.acs.org on August 19, 2018

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The Journal of Physical Chemistry

Carbon Nitride Modified Defective TiO2-x@Carbon Spheres for Photocatalytic H2 Evolution and Pollutants Removal: Synergistic Effect and Mechanism Insight Chengzhang Zhu, Xiao Chen, Jian Ma, Cheng Gu, Qiming Xian,* Tingting Gong,* and Cheng Sun State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing, 210023, P. R. China *Corresponding authors: Qiming Xian, Tingting Gong Tel/Fax: +86 25 89680259; E-mail address: [email protected]

ABSTRACT: Inducing TiO2 sensitive to visible light and effectively restraining the possibility of electron-hole recombination are crucial for actual applications over TiO2-based catalysts. In this study, a facile strategy to fabricate 3D defective TiO2-x@carbon spheres (CSs) composite modified with 2D g-C3N4 nanosheets (NSs) is presented. During the synthesis process, 0D tiny TiO2-x nanoparticles (NPs) were evenly loaded onto CSs with intimate chemically bonded (Ti–O–C) interfaces. Simultaneously, loose g-C3N4 NSs were tightly coated on the hierarchical sphere-like TiO2-x@CSs, with the purpose of supporting an effectively protective layer to prevent the oxidation of the directly exposed Ti3+ and constructing highly efficient 2D/3D ternary heterostructures with strong interfacial interaction. The obtained CSs/TiO2-x@g-C3N4 heterojunction showed remarkably enhanced photocatalytic activity in hydrogen production and toxic pollutants degradation as compared to the binary composites or pristine components, mainly due to the cooperative effects of the enhanced visible-light harvesting capacity introduced by Ti3+ and CSs, effective interfacial charge separation (Ti–O–C structure and heterostructure), and the vectorial charge-transfer channel design. This work paves a green, gentle and economical way to design more efficient TiO2-x-new ternary materials with multistep electron transfer towards solar energy conversion (like CO2 reduction and H2 evolution). ACS Paragon Plus Environment 1

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INTRODUCTION The worldwide burgeoning population and industrialization have resulted in rising concerns among the modern human society on global environmental and energy problems.1−3 Since solar energy is the most available and sustainable natural energy source, photocatalysis has been considered as an attractive strategy for organic pollutants removal and hydrogen evolution owing to its potential utilization of solar energy.4,5 Anatase titanium oxide (TiO2), as an abundant, nontoxic and photostable n-type semiconductor, shows extensive applications in many fields, especially for photocatalysis and conversion of solar energy.6,7 Nevertheless, two major obstacles of TiO2 should be overcome before achieving the practical application in photocatalysis. First, no more than 5% of the total solar energy can be well utilized because TiO2 is mainly sensitive to ultraviolet light.8 Even worse, the rapid recombination rate of photoinduced carriers lead to its low quantum efficiency.9 Band gap engineering has been proved to be highly desirable not only to extend the optical response of TiO2 to visible light region, but also to hinder the chance of electron-hole recombination.10 Most of researchers focused on doping TiO2 with metal or non-metal elements, which normally formed impurity states acting as electron donors or acceptors in the band gap of TiO2, leading to colorful appearance and narrowed band-gap, as well as the enhanced visible light absorption.11−15 However, the photocatalysis behavior of the doped TiO2 may still be limited because of the thermolability and growing carrier recombination centers accompanied by the doping species.16 Without introducing any impurity elements, self-doping by Ti3+/oxygen vacancies provides a more valid alternative to the conventional doping methods. Since the zero-dimensional (0D) disorder-engineered black TiO2 nanoparticles (NPs), which exhibited substantial solar-driven photocatalytic activities than bare TiO2, was developed through hydrogenation,17 several synthetic methods were also employed to synthesize Ti3+ self-doped TiO2, such as laser irradiation,18 gel combustion,19 and plasma treatment.20 Unfortunately, these approaches with high costs of facilities and complicated procedures are not suitable for widespread use. Moreover, the serious aggregation of the fabricated 0D TiO2-x NPs and the facile oxidization of the direct exposure of surface Ti3+ ACS Paragon Plus Environment 2

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should also be concerned. Hence, the rising demand for milder experimental conditions capable of synthesizing stable Ti3+ self-doping and homogeneous-dispersed TiO2-x are highly desired. Three-dimensional (3D) carbon spheres (CSs) are one of the support materials with benefits of cost effectiveness, excellent conductivity and high specific surface areas.21,22 It has been verified that CSs with a large number of organic groups can not only have positive effects on the growth of nanosized semiconductors but also significantly enhance visible-light absorption.23,24 For instance, previous studies have reported the combination of CSs with ZnO25 and LaFeO3.26 In these binary systems, the NPs were dispersed on the surface of CSs without apparent aggregation, causing high specific surface areas, which was conducive to affording more reactive sites and increasing light-harvesting efficiency. Moreover, high electron mobility and improved separation efficiency of photoexcited carriers endowed carbon materials with superior electron acceptor and transport channels, thereby effectively suppressing the recombination of electron-hole pairs in the TiO2-x@CSs system.27 Despite the attractive superiority, the investigation of TiO2-x/carbon based composites is still rare up to now. From a practical point of view, further work is needed to construct a multicomponent heterojunction-type system, enabling them to induce a multistep electrons transfer (high rate of electron-hole separation) and eventually to enhance the photocatalytic performance significantly, as well as to strengthen the photostability. Recently, graphite-like carbon nitride (g-C3N4), a novel polymeric photocatalyst, has attracted much attention due to its abundance, high thermal and chemical stability, and unique electronic structure, rendering g-C3N4 a promising host for visible-light photocatalytic H2 generation, organic pollutant decomposition, and CO2 reduction.28−33 Particularly, two-dimensional (2D) structure can offer an accessible surface platform for the fabrication of heterostructure photocatalysts with intimate interfacial contact, exhibiting excellent photocatalytic performance by fully taking advantage of the integrated merits of these components.34−36 In this regard, g-C3N4 will be an ideal candidate because of its unique properties providing well-matched band structure and favoring the construction of heterojunction architecture.37,38 Moreover, the wrinkled g-C3N4 nanosheets (NSs) can support an ACS Paragon Plus Environment 3


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effectively protective layer, which covers on the surface of TiO2-x to improve the Ti3+ stability. Therefore, we predicate that substantially enhanced photocatalytic activity of well-designed CSs/TiO2-x@g-C3N4 heterojunction with relatively stable Ti3+ species and abundant coupling heterointerfaces can be achieved. Herein, we synthesized 3D defective sphere-like TiO2-x@CSs modified with 2D g-C3N4 NSs through a solvothermal method. In this case, it was feasible for the relative band alignment of g-C3N4 NSs, TiO2-x NPs and CSs to promote the migration of the excited electrons through the vectorial electron transfer of g-C3N4 NSs → TiO2-x NPs → CSs. To the best of our knowledge, the construction and application of such ternary composite for hydrogen production and pollutants photodegradation has not been reported previously. The superior photocatalytic behavior of CSs/TiO2-x@g-C3N4 could be attributed to the synergistic effects of the multistep transfer system improving separation efficiency of photoinduced charge carriers, the reduced bandgap increasing the utilization efficiency of visible light, the increased specific surface areas shortening the distance of mass transfer, and the multicomponent heterojunction providing more surface reactive sites. Furthermore, the possible mechanism toward the photocatalysis process of the ternary photocatalyst was also discussed based on the free radicals trapping experiments and ESR analysis. EXPERIMENTAL SECTION Materials. D-Glucose monohydrate (C6H12O6·H2O), acetic acid (CH3COOH), urea (CO(NH)2), tetrabutyl titanate (TBOT), titanium trichloride (TiCl3) and absolute ethanol (C2H5OH) applied by Sino-pharm Chemical Reagent Co., Ltd are of analytical reagent grade. 2,4,6-Trichlorophenol (2,4,6-TCP) and ciprofloxacin (CIP) were purchased from Aladdin Reagent Co., Ltd. Ultrapure water (18.2 MΩ·cm) was supplied by a Simplicity UV ultrapure water system (Merck Millipore). Synthesis of g-C3N4 (CN) NSs. Graphitic CN NSs were synthesized by directly heating urea under ambient pressure in an air atmosphere. Typically, urea powder (10 g) placed in a covered alumina crucible was heated to 600 °C, and then kept at this temperature for 4 h in a tube furnace.

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After cooling naturally, the yellow polymers were washed with water and ethanol to remove residual alkaline species adsorbed on the precipitate surface, and finally dried at 60 °C overnight. Constructing Graphitic CN Modified Sphere-Like CSs/TiO2-x. Glucose monohydrate (4.5 g) was added to ultrapure water (40 mL) to obtain a clear solution, which was transferred into a 50 mL Teflon-lined autoclave and heated at 180 °C for 5 h. After repeatedly washing and oven-drying, the resultant puce CSs was collected for subsequent synthesis. CSs/TiO2-x@CN ternary composite photocatalysts were fabricated by a facile solvothermal route. In detail, a desired amount of TBOT was dissolved in a mixture of acetic acid and absolute ethanol (35 mL) under vigorous stirring for 0.5 h, and then TiCl3 was slowly dispersed in the above homogeneous solution to form a glitter purple solution, in which a stoichiometric amount of CN and 0.2 g of newly prepared CSs dispersed in the mixture containing ultrapure water (0.1 mL) and ethanol (40 mL) was dropwise added. Subsequently, the above suspension was ultrasonicated for 1 h and sealed into a 100 mL Teflon-lined autoclave, followed by hydrothermal treatment at 180 °C for 12 h. The final products (CSs/TiO2-x@/CN) were centrifuged, washed five times with ethanol, and fully dried in a vacuum oven at 60 °C. Hierarchical sphere-like CSs/TiO2-x was synthesized through a similar procedure in the absence of CN. By varying the dosage of TBOT at 1, 3, 6 and 9 mL, different CSs/TiO2-x composites were obtained for the optimal loading content of TiO2-x, abbreviated as CSs/TiO2-x (1), CSs/TiO2-x, CSs/TiO2-x (6), CSs/TiO2-x (9), respectively. Moreover, a series of ternary composites with 10%, 15%, 20%, and 40% mass ratios of CN to CSs/TiO2-x were prepared, and defined as CSs/TiO2-x@/CN-1, CSs/[email protected], CSs/TiO2-x@CN-2, and CSs/TiO2-x@CN-4, respectively. Characterization. X-ray diffraction (XRD) was characterized by a LabX XRD-6000 powder diffractometer. X-ray photoelectron spectroscopy (XPS) equipped with a PHI5000 Versa Probe spectrometer was used to examine chemical composition and valence band (VB). The morphologies of the catalysts were examined with scanning electron microscopy (SEM, QUANTA FEG 250) and transmission electron microscopy (TEM, JEM-200CX). UV-Vis diffuse reflectance spectra (DRS) was obtained in a range of 200-800 nm using a UV-3600 spectrophotometer by taking BaSO4 as the ACS Paragon Plus Environment 5


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internal reference standard. The Raman, fourier transform infrared spectroscopy (FTIR) and electron paramagnetic resonance (EPR) spectra of samples were achieved on a R-XploRA Plus, Nicolet iS10 FT-IR and JEOL JESFA200 EPR spectrometer, respectively. Photoluminescence (PL) and time-resolved PL decay (TRPL) spectroscopy were obtained by a Horiba Fluorolog 3-22 type fluorescence spectrophotometer. The Brunauer-Emmett-Teller (BET) surface areas were examined by a Micromeritics ASAP 2010 N2 adsorption apparatus. Electron spin resonance (ESR) signals of spin-trapped paramagnetic species (•OH, •O2− and 1O2) with 5,5-diamethyl-1-pyrroline N-oxide (DMPO) and 4-oxo-2,2,6,6-tetramethyl (4-oxo-TEMP) were detected by an X-band Bruker EMX ESR spectrometer. The photocurrent and the electrochemical impedance spectroscopy (EIS) measurements were carried out on a Shanghai Chenhua CHI660D Instrument using a standard three-electrode cell with Na2SO4 electrolyte solution (0.1 M). The reference electrodes and the counter were saturated Ag/AgCl electrode and Pt wire, respectively. Typically, the modified electrodes were prepared by the following method: 2 mg of catalyst were ultrasonically dispersed in 2 mL of ethanol, and then spin-coated onto the Indium Tin Oxide (ITO) glass electrode, which was employed as working electrodes. A 500 W xenon lamp was served as the light source throughout the electrochemical measurements. Photocatalytic Text. The photocatalytic water splitting reaction was performed in a 100 mL Pyrex flask connected to a closed gas circulation system. As the light source, four low-power UV-LEDs (3 W, Shenzhen LAMPLIC Science Co. Ltd. China) equipped with a 420 nm cutoff filter were positioned 1 cm away from the reactor in four vertical directions. For each UV-LED, the focused intensity on the flask was ca. 80.0 mW∙cm−2. In a typical procedure, 50 mg of sample was dissolved and vigorously stirred in an aqueous solution (80 mL) containing 0.5 M Na2SO3 and 0.5 M Na2S. Prior to irradiation, nitrogen was bubbled for 40 min to completely remove the dissolved O2 and CO2, ensuring an anaerobic condition during the reaction process. A 0.4 mL gas was


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sampled once an hour, and the amount of H2 evolved was analyzed with a gas chromatography (GC-14C, Shimadzu, Japan, TCD, with nitrogen as the carrier gas and 5 Å molecular sieve column). The photodegradation experiments were executed with a circulating water system to prevent thermal catalytic effects, and were examined under UV, visible and simulated sunlight irradiation. Typically, 50 mg of photocatalyst with 50 mL of model pollutants (CIP and 2,4,6-TCP, 10 mg L-1) were magnetically stirred in darkness for approximately 1 h to obtain an adsorption-desorption equilibrium between the organic molecules and the catalyst surface. A 1000 W Xenon lamp with filter glasses ( IPA > AO > TEMPOL, revealing that h+, •O2− and •OH were produced. Simultaneously, the surface adsorbed O2 of the catalyst could acted as an electron traps to form •O2− through the direct interaction of the dissolved O2 and photoinduced electrons.58 Therefore, we could preliminarily conclude that h+, •O2− and •OH were of great importance in the reaction system with a major species of •O2− over CSs/TiO2-x@CN-2.


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Figure 8. Photocatalytic degradation of CIP (a-c) and 2,4,6-TCP (d) with different photocatalysts under visible-light irradiation (λ > 420 nm), recycling stability of CSs/TiO2-x@CN-2 irradiated by visible light (e), trapping experiment of the active species towards the degradation of CIP over CSs/TiO2-x@CN-2 heterojunction (f). Photoelectrical Properties. Photoluminescence (PL) emission is mainly originated from radiative recombination of free carriers, which can be applied to detecting the change of carrier concentration in a semiconductor.59,60 Figure 9a showed the PL spectra of a series of CN-based ACS Paragon Plus Environment 19


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composites under the 325 nm laser excitation. CN NSs presented emission peaks centered at around 460 nm, revealing the high recombination rate. However, the reduced PL intensities for CN-based heterojunctions were observed, which suggested that the heterogeneous structure along with the enhanced BET surface area facilitated the charge transport at the interface of heterojunction, leading to the low charge recombination. Thereinto, CSs/TiO2-x@CN-2 had the lowest intensity, implying the recombination of electrons and holes were largely inhibited. To study the separation of photoinduced carriers, the time-resolved PL spectra of different samples were measured and the results are shown in Figure 9b. When both of CSs and CN were simultaneously hybridized with TiO2-x, the PL lifetime was dramatically prolonged, which was proposed to derive from long range multistep electron transfer among three pristine components. The ternary CSs/TiO2-x@CN-2 displayed the longer lifetime of free carriers than others due to an accelerated charge transfer, which was bound to improve the photocurrent and photocatalytic activity. These results were in accordance with the above photocatalytic experiments and followed photoelectrical experiments. To carefully understand the efficient charge transfer of different samples, the electrochemical impedance spectroscopy (EIS) and photocurrent measurements were employed. It is well-known that both of the smaller arc radium in the EIS Nyquist plot and higher photocurrent intensity implied the more effective separation of the photogenerated hole-electron pairs and faster interfacial charge transfer.61 Note that the arc radius of Nyquist circle (Figure 9c) for the binary or ternary composites was smaller than that of single material, indicating a positive synergetic effect between the components, which could accelerate the interfacial charge-transfer process. Among them, CSs/TiO2-x@CN-2 showed the smallest semicircle domain, which indicated that the minimum charge-transfer resistance was achieved, owing to the successful formation of the heterojunction. Moreover, the photocurrent responses of the catalysts were studied to gain deeper insight into the electron transfer mechanism, and the results were quite consistent with the conclusions from EIS performances. Figure 9d illustrated that all of the samples electrode possessed a sensitive photocurrent response, directly proving that the separation of photo-generated electrons and holes ACS Paragon Plus Environment 20

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occurred under visible light irradiation. After CSs/TiO2-x@CN-2 being dropped onto the bare ITO electrode, the corresponding photocurrent intensity remarkably increased, rising up to 0.78 µA, which was about 3.4, 1.9 and 2.3 times higher than those of TiO2, CN and TiO2-x, respectively, further demonstrating the longer lifetime of the excitons and efficient charge separation.

Figure 9. (a) PL emission spectra, (b) time-resolved fluorescence decay spectra, (c) EIS Nyquist plots and (d) time-based photocurrent response of the as-prepared photocatalysts. Possible Photocatalytic Mechanism. The electron spin resonance (ESR) spin-trap technique was conducted to further identify the existence of •O2− and •OH radicals of CSs/TiO2-x and CSs/TiO2-x@CN-2 under visible-light exposure, as illustrated in Figure 10a,b. Prior to irradiation, no signals of DMPO–•O2− and DMPO–•OH were detected. Upon visible light irradiation for 70 s in the presence of CSs/TiO2-x and CSs/TiO2-x@CN-2, the characteristic peaks of •O2− were obviously observed, indicating that the photoinduced electrons in the CB of samples could be transformed into •O2− radicals in the photocatalytic degradation reaction.62 When CN was coupled with CSs/TiO2-x, the peak intensity of CSs/TiO2-x@CN-2 was strengthened in comparison with ACS Paragon Plus Environment 21


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CSs/TiO2-x, which suggested that ternary composite with increasing charge separation could effectively utilize the electrons to generate more •O2−. However, the weak signals of •OH adducts only appeared in CSs/TiO2-x@CN-2, demonstrating that few •OH were involved in the pollutant photodegradation. In addition, 4-oxo-TEMP was selected as the spin trap for the detection of singlet oxygen (1O2). It is well known that 1O2 formed from the reaction between electrons and holes, which was significant for treating aerobic.63 According the results shown in Figure 10c, and no ESR signal was detectable in darkness, whereas a three-line spectrum clearly appeared with relative intensities of 1:1:1 for TEMPONE during irradiation with light. As expected, CSs/TiO2-x@CN-2 still revealed the strongest intensity, consistent with the DMPO–•O2− results, which might be ascribed to the enhanced charge separation caused by the constructed ternary heterojunction. More importantly, abundant •O2− could also combine with h+ to generate 1O2.64 Combined with the trapping experiments results and ESR analysis, it could be inferred that •O2−, •OH, h+ and 1O2 as active species played crucial roles in the CIP oxidation process.

Figure 10. DMPO and TEMP spin-trapping ESR spectra with 0.1 mg/mL CSs/TiO2-x and CSs/TiO2-x@CN-2 samples in the dark and under visible light irradiation for 70 s for DMPO–•O2− in methanol dispersion (a), DMPO–•OH in aqueous dispersion (b), and TEMPONE–1O2 in aqueous dispersion (c). On the basis of the above experimental results, a probable charge carriers transport mechanism for the enhanced photocatalytic activity over CSs/TiO2-x@CN heterojunctions was proposed and schematically shown in Figure 11. Under visible light exposure, both TiO2-x and CN were capable ACS Paragon Plus Environment 22

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of being photoexcited to generate electron-hole pairs. Given the calculation results above, EVB edge potentials of TiO2-x (1.90 V vs. NHE) was more positive than that of CN (1.59 V vs. NHE), and the ECB edge potentials of CN (–1.11 V vs. NHE) was more negative than that of TiO2-x (–0.69 V vs. NHE). Hence, by the built-in potential in the heterojunction, the electrons could be easily transferred to the CB of TiO2-x from the CB of CN, leaving holes in the VB. Then, these transferred electrons (together with the electrons excited from the VB and Ti3+ defect states of TiO2-x) in the CB of TiO2-x could further move to neighboring CSs because the difference in the quasi Fermi energies formed a nonequilibrium charging state between the two.9 In this multi-step electrons transfer process, it was feasible for the relative band alignment of CN, TiO2-x and CSs to promote the migration of the excited electrons through the vectorial electron transfer of CN NSs → TiO2-x NPs → CSs, hindering the electron-hole recombination significantly. As the electrons accumulated on CSs surface, dissolved O2 (H+) was reduced by electrons to produce •O2− (H2), and then the •OH might be generated by the reaction of •O2− with electrons, while the holes left in the VB of CN could attack organic pollutant directly.37 Consequently, the synergetic catalytic effects through the interfacial modulation and design of the charge-transfer channels among three components resulted in the improvement of H2 production and photodegradation efficiency. As a result, the excellent photocatalytic activity of the elaborately desired CSs/TiO2-x@CN heterojunctions could be attributed to the following factors: (i) The moderate doping of Ti3+/oxygen vacancies on modified TiO2 narrowed the band gap (2.59 eV) and accelerated the mobility of photoinduced electrons and holes. Particularly, electrons on the defect states (Ti3+) were able to be easily excited to CBM and induced the optical absorption in visible light region. Simultaneously, Ti3+ defects were capable of trapping shallowly the initially photoinduced carriers to inhibit them from fast recombination because the excited Ti3+ states were unoccupied. Therefore, it was more difficult for the electrons to return back from CB to VB, eventually suppressing the chance of electron-hole recombination.



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(ii) The introduction of CSs could dramatically increase the visible-light absorption and reduce the reflection of light, facilitating the generation of more photogenerated carriers in the photocatalytic reaction. Besides, CSs with high electron mobility and charge storage ability worked as an electron acceptor, which offered conductive pathways to accelerate the transport of electron-hole pairs at the TiO2-x@CN junctions and Ti–O–C bond, and simultaneously kept them highly reactive. Moreover, the shallow trapping sites (Ti–O–C) proved by XPS results, promoted CSs and TiO2-x highly electronically coupled with superior charge separation property. Additionally, the presence of CSs greatly enhanced the BET surface area of samples. As we known, the higher surface areas could shorten the distance of mass transfer and provide efficient reactive sites for adsorption and surface reactions, thus favoring the photocatalytic activity.51 (iii) Wrinkled CN layers were tightly covered on the surface of binary sphere-like CSs/TiO2-x, with the purpose of supporting an effectively protective layer to improve Ti3+ stability in such ternary system. On the other hand, the well-designed heterostructures with abundant and strong coupling interfaces were constructed, which greatly improved the charge transport/separation at the interfacial interfaces, and the cycle stability of the ternary composites for their practical application. More importantly, the electrons in the CB of CN tended to be transferred to the CB of TiO2-x first, and subsequently migrated to CSs. In this process, a novel multistep electrons transfer was induced, rather than a single-step transfer, thereby leading to an efficient charge separation and a longer lifetime of the photoinduced charge carriers.


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Figure 11. Schematic illustration of the proposed multilevel charge transfer for enhanced visible light photocatalytic activities of the CSs/TiO2-x@CN ternary heterojunction. CONCLUSIONS In summary, novel visible-light-driven CSs/TiO2-x@CN heterostructures with strong interfacial interaction were successfully synthesized. The obtained ternary CSs/TiO2-x@CN exhibited impressive cyclic stability and drastically enhanced photocatalytic activity in H2 evolution and organic pollutants degradation in contrast to those of the binary composites and individual components, mainly because of the cocontributions of several positive factors including effective electron transport of the multilevel transfer between TiO2-x/g-C3N4 heterojunction and CSs (Ti–O–C bridge), good visible-light harvesting capacity, increased specific surface areas, and the multicomponent heterojunction with vectorial charge-transfer channel. This work demonstrated that the construction of multistep electron transfer system is an effective approach to design more efficient ternary materials towards the rising demand for energy and environmental problems. ASSOCIATED CONTENT Supporting Information XRD patterns of CSs/TiO2 composites in varying proportions, FTIR spectra of heterostructure, SEM images of g-C3N4 and CSs, XPS survey spectra, photocatalytic experiments under simulated sunlight and UV irradiation, XRD, XPS and SEM images of CSs/TiO2-x@CN after photocatalysis, ACS Paragon Plus Environment 25


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photocatalytic H2 evolution rate and pseudo-first-order constants of different photocatalysts, comparison of the photodegradation activity. AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected] (Q.X.). *E-mail: [email protected] (T.G.). Notes The authors declare no competing financial interest. ACKNOWLEDGEMENTS The authors gratefully acknowledge the financial support from the National Key R&D Program (2016YFC0502801), National Natural Science Foundation of China (Grant 51508264) and Jiangsu Key R&D Plan (BE2017711). REFERENCES (1) Kudo, A.; Miseki, Y. Heterogeneous Photocatalyst Materials for Water Splitting. Chem. Soc. Rev. 2009, 38, 253−278. (2) Lee, S. S.; Bai, H.; Liu, Z.; Sun, D. D. Green Approach for Photocatalytic Cu(II)-EDTA Degradation over TiO2: Toward Environmental Sustainability. Environ. Sci. Technol. 2015, 49, 2541−2548. (3) Zhang, J., Wang, Y., Jin, J., Zhang, J., Lin, Z., Huang, F., Yu, J. Efficient Visible-Light Photocatalytic Hydrogen Evolution and Enhanced Photostability of Core/Shell CdS/g-C3N4 Nanowires. ACS Appl. Mater. Interfaces 2013, 5, 10317−10324. (4) Yoon, T. P.; Ischay, M. A.; Du, J. Visible Light Photocatalysis as a Greener Approach to Photochemical Synthesis. Nat. Chem. 2010, 2, 527−532. (5) Rosseler, O.; Shankar, M. V.; Du, M. K.-L.; Schmidlin, L.; Keller, N.; Keller, V. Solar Light Photocatalytic Hydrogen Production from Water over Pt and Au/TiO2 (Anatase/Rutile) Photocatalysts: Influence of Noble Metal and Porogen Promotion. J. Catal. 2010, 269, 179−190. ACS Paragon Plus Environment 26

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Table of Contents Graphic

Constructing graphite-like carbon nitride modified defective TiO2-x/carbon spheres with vectorial charge-transfer channel for photocatalytic applications


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