Photodegradation of Organic Pollutants Coupled with Simultaneous

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Photodegradation of organic pollutants coupled with simultaneous photocatalytic evolution of hydrogen using quantum dot modified g-C3N4 catalysts under visible light irradiation Xun-Heng Jiang, Lai-Chun Wang, Fan Yu, Yu-Chun Nie, QiuJu Xing, Xia Liu, Yong Pei, Jian-Ping Zou, and Weili Dai ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b01695 • Publication Date (Web): 17 Aug 2018 Downloaded from http://pubs.acs.org on August 19, 2018

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ACS Sustainable Chemistry & Engineering

Photodegradation of organic pollutants coupled with simultaneous photocatalytic evolution of hydrogen using quantum dot modified g-C3N4 catalysts under visible light irradiation Xun-Heng Jiang,a,b Lai-Chun Wang,b,c Fan Yu,b Yu-Chun Nie,b Qiu-Ju Xing,b,* Xia Liu,d Yong Pei,d Jian-Ping Zou,a,b∗ Wei-Li Daib a

School of Resources Environmental & Chemical Engineering, Nanchang University,

Nanchang 330000, P. R. China b

Key Laboratory of Jiangxi Province for Persistent Pollutants Control and Resources

Recycle, Nanchang Hangkong University, Nanchang 330063, P. R. China. c

d

Yixing Envirnomental Research Institute, Nanjing University, Yixing 214200, P. R. China. Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of

Education, Xiangtan University, Xiangtan 411105, P.R. China

ABSTRACT: Carbon quantum dots/CdS quantum dots/g-C3N4 (CDs/CdS/GCN) photocatalysts have been designed and prepared. Systematic characterization such as XRD, SEM, TEM, UV, and XPS, were done to confirm the composite catalysts of CDs/CdS/GCN. The simultaneous photocatalytic production of hydrogen coupled with degradation of organic contaminants (p-chlorophenol, bisphenol A and tetracycline, called 4-NP, BPA and TTC, respectively) was efficiently realized over the resultant CDs/CdS/GCN composites. The as-prepared 3%CDs/10%CdS/GCN exhibits high efficiency of photocatalytic hydrogen evolution from water splitting and photodegradation rates of organic pollutants in aqueous solutions of 4-NP,

*E-mail: zjp [email protected] (J.-P. Zou) or [email protected] (Q.-J. Xing); Tel: +86 791 83953373; Fax: +86 791 83953373. 1

ACS Paragon Plus Environment

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BPA and TTC under visible light illumination since the formation of interfaces between CdS quantum dots and GCN nanosheets leads to an efficient charge separation efficiency. Furthermore, as compared to that in pure water system, the photocatalytic evolution rate of H2 over the 3%CDs/10%CdS/GCN catalyst in the presence of 4-NP solution is decreased, while the H2 evolution rates increase when BPA or TTC solution were used instead of 4-NP solution under visible light irradiation. Consequently, the 4-NP shows higher photodegradation efficiency than those of BPA and TTC in the simultaneous photocatalytic oxidation and reduction system. Aiming at making clear the relationship between the photocatalytic H2 production and the photocatalytic pollutants degradation, density functional theory (DFT) calculations and liquid chromatography mass spectrometry (LC-MS) were used for a systematic

investigation.

The

present

work

reports

a

plausible

mechanism

of

photodegradation of different organic contaminants with synchronous photocatalytic H2 evolution from water, and the photocatalytic enhancement of the CDs/10%CdS/GCN catalysts. Keywords: Degradation; Hydrogen evolution; Organic pollutants; Photocatalysis; Quantum dots INTRODUCTION Currently, environmental pollution and energy crisis have become two major challenges.1-3 Especially, water pollution caused by dyes, aromatics, hormones, and pesticides are seriously environmental issues and have attracted major worldwide attention because they are highly unbiodegradable, toxic species and potentially are able to be transformed into carcinogenic, teratogenic, and even mutagenic agents.4-7 Therefore, development of new technologies for organic pollutant decomposition are imperative. Until now, many methods or technologies have been developed for the treatment of organic pollutants in wastewater, including anaerobic biological treatments, advanced 2


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oxidation processes (AOPs) (like ultraviolet (UV) photocatalysis, UV/H2O2 and UV/Fenton), and photocatalytic processes.8-14 Among them, photocatalysis technology possesses clean and low-cost advantages, and can synchronously solve the problems of energy shortage and environmental contamination.15-19 Recently, a great number of literature studies have reported on the photocatalysis of the organic pollutant degradations, H2 production, and CO2 reduction.20-24 But most of the catalysts suffer high recombination rates, low quantum efficiency and low utilization ratio of carriers, leading to the overall low photocatalytic efficiency. In addition, its high cost makes industrial applications difficult. The photocatalysis consists of oxidation process and reduction process owing to the photo-redox properties of photocatalyst. Taking the organic pollutant degradation as an example, the photo-generated holes or a variety of free radical (hydroxyl radicals and superoxide anions) from solar energy transformations, are usually used for organics oxidation to form CO2 and H2O over photocatalysts.25-28 In addition, solar energy can also be converted to chemical energy in reduction reaction like CO2 reduction and water reduction to generate H2 in the assistance of photo-generated electrons in photocatalysts.29-32 Therefore, the separation of photo-generated electrons and holes and the light quantum efficiency of catalysts would be greatly improved if we could design a system that can make the photocatalytic organic pollutant degradation cooperated with the hydrogen evolution over the same catalyst. It is totally predictable that the economic efficiency of photocatalysis in practical wastewater treatment will be markedly raised when the degradation of organic pollutants can efficiently combine with the hydrogen production. However, only few reports on photocatalytic contaminant treatment with simultaneous H2 production, till now, have been reported in an one-pot photocatalytic system.33-35 The photocatalytic reduction and oxidation techniques were just simply combined in the literature and the catalytic efficiencies of the reported catalysts were still low.36-37 Furthermore, they did 3



not investigate the influence of degradation of organic pollutants on photocatalytic H2 production. Therefore, for the sake of markedly improving the photocatalytic efficiency and quantum efficiency and clearly understanding how the organic pollutant degradation takes effects on H2 evolution, it is urgent to build up a new system to photocatalytically degrade organic pollutants and simultaneously convert solar energy into clean H2 energy and do in-depth studies on the synergetic mechanism of photocatalytic H2 evolution and photodegradation of organic pollutants. Recently, graphitic carbon nitride (g-C3N4, hereafter abbreviated as GCN) has been considered as a promising visible-light-responsive photocatalyst for water reduction due to its unique electronic band structure and high stability.38-40 However, the utilization efficiency of photogenerated electrons is still low in the visible light. Till now, some modification methods have been reported such as doping of some ions, loading of noble metals or quantum dots and constructing heterojunction structures.41-46 Particularly, the loading of quantum dots can well improve the photocatalytic performance of g-C3N4 for hydrogen production and photodegradation of organic pollution.47-50 But the recombination rate of photogenerated electrons and holes are still high. In order to further improve the photocatalytic performance of g-C3N4, in this work, we loaded CdS quantum dots (hereafter abbreviated as CdS QDs) and carbon dots (hereafter abbreviated as CDs) on the surface of g-C3N4 to obtain a novel photocatalyst. Furthermore, CdS has good bandgap matching with g-C3N4,51 while CDs shows good upconversion properties, resulting in a marked enhancement of photocatalytic performance of g-C3N4. Herein, we systematically investigate the relationship between photocatalytic degradation of different organic pollutants and the photocatalytic H2 production over the novel photocatalyst for the first time. The effect of different proportions of co-catalysts of CDs and CdS QDs on the photocatalytic performance of GCN is also researched. In the present work, we not only 4


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make clear the synergistic mechanism of photocatalytic organic pollutant degradations with simultaneous H2 production, but also open a new avenue to enhance the economic efficiency of photocatalysis technology in practical wastewater treatment.

EXPERIMENTAL SECTION Preparation of bulk GCN The bulk GCN was synthesized according to previously reported methods.52 In a typical process, urea (6.5 g) was placed in a dry alumina crucible with a cover and heated to 550 ℃ in a muffle furnace for 2 h at a heating rate of 8 ℃·min-1. After the alumina crucible was cooled to room temperature, a faint yellow powder was obtained. Preparation of GCN nanosheets The GCN nanosheets were prepared according to the procedures reported in the literature.53-54 Typically,

bulk GCN powder (100 mg) was dispersed in deionized water (100

mL), and then ultrasonicated for about 16 h. The initially formed suspension was then centrifuged at about 5000 rmp to remove the residual unexfoliated GCN nanoparticles and a large-area nanosheet was obtained. Preparation of CDs The CDs were prepared following the methods reported in the literature.55 The graphite rod as the anode was inserted into ultrapure water (18.4 MΩ·cm-1, 600 mL), placed parallelly to the other graphite rod that acted ascounter-electrode with a space of 7.5 cm. Static potentials of 50 V were applied to the two electrodes using a direct current power supply. After 120 h continuous stirring, the resultant solution was centrifuged at 22000 rpm for 30 min to remove the precipitated graphite oxide and graphite particles. Finally, the obtained solution was water-soluble CDs. Preparation of CdS/GCN nanocomposites 5



In-situ growth of CdS quantum dots (CdS QDs) on GCN nanosheet was performed out by the addition of Cd(Ac)2·2H2O (133 mg) and different amounts of the as-prepared GCN nanosheet into DMSO (50 mL) under stirring conditions. The obtained suspension was then transferred into a Teflon-lined stainless-steel autoclave (100 mL) and heated to 180 ℃ for 12 h. The obtained product was collected and washed with water and ethanol for several times, and dried in a vacuum oven. Photocatalyst samples with weight percentages of CdS QDs of 1, 5, 10, 15, and 20 wt.% were prepared. Preparation of CDs/CdS/GCN nanocomposites In a typical preparation of CDs/CdS/GCN, stoichiometric CDs were added to the as-obtained 10%CdS/GCN suspension, and stirred for 30 min. The resulting solids were collected by filtration and dried at 75 ℃. The obtained gray powder is denoted as CDs/10%CdS/GCN nanocomposites. CDs/CdS/GCN containing 1%, 3%, 5%, and 7% (wt.%) CDs are denoted as 1%CDs/10%CdS/GCN, 3%CDs/10%CdS/GCN, 5%CDs/10%CdS/GCN, and 7%CDs/10%CdS/GCN, respectively. Characterizations The crystalline phases of samples were collected on a Bruker D8 Advance X-ray diffractometer (Cu-Kα radiation, λ = 1.541 Å in a 2θ range from 10° to 70° at room temperature with a scanning speed of 2°/min). The photoluminescence (PL) measurements were performed on a Hitachi F-7000 spectrophotometer equipped with a 150 W xenon lamp being the excitation source. Fourier transformed infrared (FT-IR) spectra were recorded using KBr pellets with a VERTEX-70 spectrometer. The morphologies of the as-prepared samples were examined by a field emission scanning electron microscope (FESEM). Compositional analyses on the samples of as-prepared catalysts were performed on an FESEM equipped with an energy dispersive X-ray spectrometer (EDX). Further morphological and structural characterizations were based on transmission electron microscopy (TEM, Tecnai F20) and 6


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high-resolution transmission microscopy (HRTEM). UV-vis diffuse reflectance spectra (DRS) were record with a PE Lambda 900 UV/vis spectrophotometer at room temperature. Electrochemical measurements were performed on a CHI 660D electrochemical workstation (Shanghai Chenhua, China) using a standard three-electrode cell. Experimental condition for Mott schottky plots test: calomel electrode is used as a reference electrode, a platinum electrode as a counter electrode, and the as-prepared catalysts coated on a 1 cm × 1 cm ﬂuorine-tin oxide (FTO) glass as a working electrode; 0.5 M Na2SO4 was used as the electrolyte; the step frequency is 15KHz. Experimental condition for photocurrent test is same to that of Mott schottky plots test except for the platinum electrode replaced by a carbon rod as a reference electrode. X-ray photoelectron spectroscopy (XPS) measurements were taken with a VG Escalab 250 spectrometer equipped with an Al anode (Al-Kα = 1486.7 eV). Test of photocatalytic activity All photocatalytic H2 evolution experiments were carried out in a Pyrex glass reaction cell connected to a closed gas-circulation and evacuation system (Prefect Light, Beijing, Labsolar-III (AG), Fig. S1 in SI). About 50 mg photocatalyst was dispersed in 80 mL of aqueous solution (pure water or 10 mg/L organic pollutants solution (p-nitrophenol, bisphenol A or tetracycline)).Then 1% Pt was loaded onto the sample surfaces by photodeposition of H2PtCl6. The suspension was evacuated several times to completely remove air and irradiated by a 300 W Xe-lamp (Perfect light PLS-SXE300C). A cutoff filter was employed to achieve visible-light (λ > 420 nm) irradiation. The amount of hydrogen evolution from photocatalytic splitting of water was analyzed by using an online gas chromatograph with a thermal conductivity detector (TCD) and a capillary column (5 Å molecular sieve). High purity argon gas was used as a carrier gas. During the test, the temperature of the reaction solution was maintained at 6 ℃ by a flow of cooling water. In order to ensure the reliability of the experimental results, the photocatalytic experiments were repeated three times and the final 7



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values are shown in the text and supporting information (Figures 4, 5 and S10) are the mean values of triplicate results. Analytic methods The solution of p-chlorophenol was detected by recording the absorbance at the characteristic band using a Hitachi U-3900H UV-visible spectrophotometer. Solutions of BPA and TTC were measured on a Waters Acquity UPLC system, coupled with a Micromass Quattro Premier Tandem quadrupole mass spectrometric system. The identification of intermediates was also conducted by Liquid chromatography mass spectrometry (LC-MS) (Thermo, Finnigan, LCQ-Deca xp) equipped with an electrospray ionization (ESI) source. The samples were injected at a flow rate of 0.4 mL/min under isocratic conditions. The ion mode was set on positive mode and the mobile phase was methanol-water (0.1% formic acid) (60:40, v/v). Density functional theory (DFT) DFT

calculations

were

carried

out

utilizing

DMol3

package

with

Perdew-Burke-Ernzerhof/Double-Numerical Dasis 4.4 set. All computations were established on the basis of a true energy minimum, which was confirmed by the absence of imaginary frequencies with cutoff radius of 4 Å. Based on the Frontier Orbital Theory, the electrophilic reaction most likely takes place at the atoms with high values of highest occupied molecular orbital (HOMO), whereas the nucleophilic reaction most likely occurs at the atoms with high values of the lowest unoccupied molecular orbital (LUMO).56 Accordingly, the FEDs of the HOMO and LUMO of compounds were calculated.57

RESULTS AND DISCUSSION Characterizations The XRD patterns of the as-prepared GCN, GCN nanosheets, CdS QDs, 10%CdS/GCN 8


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and 3%CDs/10%CdS/GCN nanocomposites are shown in Figs. 1a and S2. The strong peak at 27.4° corresponds to the typical (0 0 2) crystal planes and the weak diffraction peak at 12.9° corresponding to the (1 0 0) crystal planes, which are consistence with the XRD pattern of g-C3N4 reported in the literature.4 The XRD pattern of CdS QDs shows three distinct diffraction peaks at 26.8°, 43.9° and 52.1°, which can be attributed to the (1 1 1), (2 2 0), and (3 1 1) crystal planes of hawleyite CdS (JCPDS 75-0581),59 respectively. The CdS/GCN heterojunction shows the XRD patterns containing diffraction peaks of both CdS and GCN, demonstrating the presence of the two phases. At the same time, the combination of CDs quantum dots would not affect the crystal phase and structure of CdS/GCN heterojunctions. The optical properties of the as-obtained GCN, GCN nanosheets, the physical mixture of 10%CdS and GCN (denoted as PM CdS/GCN), 10%CdS/GCN, and 3%CDs/10%CdS/GCN were revealed by UV-vis diffuse reflectance spectroscopy (Figs. 1b, S3 and S4). As depicted in Fig. 1b, GCN shows an absorption edge extending to around 443 nm, and the other samples also have a strong absorption in the visible light region. Among the prepared catalysts, 3%CDs/CdS/GCN shows the best absorption intensity in the visible region and markedly red-shifts due to the good light absorption property of CDs and CdS QDs. The charge-carrier separation/recombination was monitored by photoluminescence (PL) measurements. Fig. 1c shows that GCN exhibits a strong emission peak centered at 450 nm with an excitation wavelength of 325 nm. As a comparison, the PL intensities of the GCN nanosheets, PM CdS/GCN, 10%CdS/GCN, and 3%CDs/10%CdS/GCN significantly decrease, indicating more efficient separation rate of photogenerated electrons and holes. The 3%CDs/10%CdS/GCN shows the lowest PL intensity among the as-prepared samples, indicating the highest separation efficiency of photogenerated electrons and holes, which is attributed to the special structure of the composite catalyst. The CDs show up-converted PL properties. The CDs generate emissions located in the range of 454 to 478 nm when CDs were 9



excited by wavelengths ranging from 550 to 750 nm, leading to full use of visible light at long wavelengths (Fig. 1d)

Fig. 1. (a) XRD patterns of pure GCN, GCN nanosheets, CdS QDs, 10%CdS/GCN, and 3%CDs/10%CdS/GCN; (b) UV-vis diffuse reflectance spectra and (c) PL spectra of the GCN, GCN nanosheets, PM CdS/GCN (the physical mixture of 10%CdS and GCN), 10%CdS/GCN and 3%CDs/10%CdS/GCN with the excitation wavelength of 325 nm; (d) Upconverted PL spectra of CDs under the excitation of light ranging from 550 to 750 nm and (e) Transient photocurrent response of the GCN, GCN nanosheets, PM CdS/GCN (the physical mixture of 10%CdS and GCN), 10%CdS/GCN and 3%CDs/10%CdS/GCN.

The transient photocurrent responses of as-prepared samples were tested at bias potential 10


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of 0.34 V vs. SCE. As shown in Figs. 1e and S5, the as-prepared 10%CdS/GCN shows better photocurrent intensity than that of GCN, GCN nanosheets, and PM CdS/GCN but lower than that of 3%CDs/10%CdS/GCN. The results indicate that 3%CDs/10%CdS/GCN owns the best efficiency among the as-synthesized samples in terms of both interfacial charge transfer and separation of photogenerated electrons and holes. FT-IR spectra of the GCN nanosheets and CDs/10%CdS/GCN composites with different content of CDs are shown in Fig. S6. The characteristic peaks at 810, 1245, 1324, 1458, and 1632 cm-1 are attributed to the skeletal vibrations of tri-s-triazine ring (C6N7) units of GCN nanosheets, whereas the peak at 1410 cm-1 corresponds to the stretching vibrations of the s-triazine ring (C3N3) units. The peaks at 1638 cm-1 and 1245 cm-1 are attributed to the C=N and C-N stretching vibrational modes, respectively. The peaks between 3200 cm-1 and 3500 cm-1 are assigned to N-H and O-H stretches, associated with amino groups and surface absorbed H2O molecules. The peaks at about 3000, 1600, and 1500 cm-1 correspond to the C=C stretches of polycyclic aromatic hydrocarbons. But the existence of CDs cannot be found in the infrared spectra, mainly resulting from the fact that the peaks of C-C in CDs overlap with that of triazine rings in GCN. Details can be seen in the text of the S1. TEM and HRTEM images were used to analyze the morphology and structures of the samples. As shown in Fig. 2a, the as-prepared GCN shows a nanosheet structure with smooth surfaces of the parent GCN. Fig. 2b shows that CdS QDs and CDs possess a diameter of 3-8 nm, suggesting that the as-synthesized CdS and carbon nanoparticles are quantum dots. For 3%CDs/10%CdS/GCN (Fig. 2c and Fig. S7), CdS QDs and CDs uniformly load on the surface of the GCN nanosheets with less than 10 nm diameter. The energy dispersive X-ray data (Fig. S7 in SI) for 3%CdS/10%CdS/GCN shows the existence of C, N, S, and Cd elements in the composite, confirming that GCN, CdS QDs, and CDs exist in 3%CDs/10%CdS/GCN. HRTEM images of the 3%CDs/10%CdS/GCN material confirm the 11



existence of GCN, CdS QDs and CDs in Fig. 2d. The lattice spacings of 0.336 and 0.321 nm are ascribed to the (0 0 2) planes of hexagonal GCN and the (0 0 2) spacing of carbon, respectively, while the lattice spacings of 0.337, 0.292, and 0.206 nm correspond to the (1 1 1), (2 0 0), and (2 2 0) crystal planes of CdS, respectively. The HRTEM data also indicate that there is close contact between GCN, CdS QDs, and CDs in 3%CDs/10%CdS/GCN, which is very helpful for rapid charge transfer between the components of the composite.

Fig. 2. TEM images of (a) GCN nanosheets, (b) CDs and (c) 3%CDs/10%CdS/GCN nanocomposites; (d) HRTEM images of the 3%CDs/10%CdS/GCN.

The 3%CDs/10%CdS/GCN and 10%CdS/GCN samples were further studied by XPS analyses. As shown in Fig. 3a, the XPS spectrum in the C 1s region can be deconvoluted into three peaks at 284.6 eV, 286.2 eV, and 288.2 eV. The peak located at 284.6 eV can be attributed to sp2 C-C bonds. Compared with 10%CdS/GCN, the peak intensity of the 3%CDs/10%CdS/GCN at 284.6 eV was enhanced, indicating the CDs successfully load on the surface of the GCN nanosheets. The peak at 288.2 eV is assigned to sp2-hybridized carbon 12


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in N-containing aromatic rings (N-C=N), which represent the major carbon species in GCN. The weak peak at 286.2 eV is assigned to sp3-coordinated carbon bonds from the defects on GCN surfaces. The corresponding binding energies of the N 1s spectrum (Fig. 3b) are determined to be 398.8 eV, 400.0 eV, and 401.2 eV. The main peak centered at 398.8 eV is originated from the sp2-bonded N involved in the triazine rings (C-N=C) dominant in GCN. The weak peak at 400.0 eV is assigned to the tertiary nitrogen N-(C)3 groups, while the weak peak at 401.2 eV indicates the presence of amino groups (C-N-H). The S 2p peaks at 161.2 and 162.4 eV are ascribed to the sulfide in CdS (Fig. 3c), whereas the Cd 3d peaks at 404.9 and 411.7 eV are assigned to the Cd2+ of the CdS (Fig. 3d).5-6 The above results demonstrate that GCN, CdS QDs, and CDs exist in 3%CDs/10%CdS/GCN.

Fig. 3. XPS spectra of (a) C 1s, (b) N 1s, (c) Cd 3d, and (d) S 2p (I: 3%CDs/10%CdS/GCN and II: 10%CdS/GCN).

Photocatalytic activity 13



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Photocatalytic activities of the as-obtained GCN nanosheets and GCN nanosheets loaded with different amounts of CdS QDs (CdS/GCN) were evaluated by H2 evolution reactions under visible light irradiation in p-nitrophenol solution (4-NP). As shown in Fig. 4a, the GCN nanosheets exhibit no detectable H2, while the removal rate of 4-NP reaches 57%. After loading with CdS QDs, both the H2 evolution rate and the simultaneous 4-NP degradation rate of the GCN nanosheets significantly improved. The optimum loading amount of CdS QDs is 10 wt.%, showing the best H2 evolution rate of 9.4 µmol·g-1·h-1 with a 4-NP removal rate of 98%. When the loading amount of CdS QDs is further increased, the photocatalytic active sites on the GCN could be overlapped by CdS QDs, lowering the photocatalytic performance. These demonstrate that the visible-light-driven photocatalytic activity of the GCN nanosheets can be efficiently improved by the deposition of CdS QDs. In order to investigate the effect of CDs on the photocatalytic H2 production and simultaneous 4-NP degradation of 10%CdS/GCN, six samples were studied (sample I: the physical mixture of 3%CDs, 10%CdS, and GCN nanosheets; sample II: 10%CdS/GCN; samples III-VI: 10%CdS/GCN loaded with different amounts of CDs (1%, 3%, 5%, and 7% (wt.%)). It was found that the production rate of H2 and the 4-NP degradation rate over CDs/10%CdS/GCN rapidly increase with an increase of loading amounts of CDs and decreases when the loading amount is larger than 3% (Fig. 4b). This case could be explained that too much CDs would decrease the absorption ability of GCN in the visible light, resulting in the decrease of photocatalytic activity. In addition, the H2 evolution rate is 5µmol·g-1·h-1, while the simultaneous 4-NP degradation efficiency is 39.5% under excitation source above 700 nm (Fig. S8), confirming the upconverted PL effect of CDs in the composite 3%CDs/10%CdS/GCN.

The

3%CDs/10%CdS/GCN

sample

exhibits

the

highest

photocatalytic activity among the as-obtained catalysts, which could be due to the upconverted PL properties, good visible light absorption, and good electrical conductivity of 14


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CDs, as well as suitable loading amount of CDs and CdS QDs in the composite 3%CDs/10%CdS/GCN. Besides, we investigated the effect of different loading amount of Pt on the H2 production and 4-NP degradation efficiency. As shown in Fig. S9, the rate of H2 production and 4-NP degradation efficiency increase with the increase of Pt loading amount from 0.5 % to 1 %, whereas the rate of H2 production and 4-NP degradation efficiency have a little decrease with the increase of Pt loading amount from 2% to 5%. Pt clusters would form on the surface of catalysts when the Pt loading amount exceeds 1%, resulting in the utilization efficiency of Pt decreases and the recombination rate of photogenerated electrons and holes increases, and finally the photocatalytic effectively of degradation 4-NP became weaken accordingly. The results are also observed in those previously reported literatures.61-64 In order to gain insight into the relationship between photocatalytic H2 production and the degradation of organic pollutants, the photocatalytic H2 production experiments are carried out in the presence of different aqueous solutions containing different organic pollutants over 3%CDs/10%CdS/GCN under visible light irradiation. And we selected three kinds of typical organic pollutants of p-nitrophenol (4-NP), bisphenol A (BPA) or tetracycline (TTC) because 4-NP belongs to common compound in printing and dyeing wastewater, whereas BPA and TTC are common compounds in pharmaceutical wastewater. As shown in Figs. 4c and S10, the photocatalytic H2 evolution rate is 3.4 µmol·g-1·h-1 over 3%CDs/10%CdS/GCN in pure water, whereas the evolution rate of H2 evidently decreases with the addition of 4-NP, and the removal rate of 4-NP is about 100%. As a comparison, the photocatalytic H2 evolution rate can be markedly enhanced when bisphenol A (BPA) or (TTC) was added in the photocatalytic system. The photocatalytic hydrogen production rate is 6.4 and 5.2 µmol·g-1·h-1 in the presence of BPA and TTC, respectively, and the corresponding degradation rate of BPA and TTC is 72% and 91%, respectively. The results suggest that the 15



different kind of organic pollutants have a significant influence on the photocatalytic H2 production, and the optimal photocatalytic performance in terms of H2 evolution and coinstantaneous photocatalytic organic pollutant degradations can be achieved over the 3%CDs/10%CdS/GCN composite.

Fig. 4. Production of H2 with simultaneous degradation in the presence of 4-NP over (a) the GCN loaded with different amount of CdS and (b) six samples (sample I: the physical mixture of 3%CDs, 10%CdS and GCN nanosheets; sample II: 10%CdS/GCN; samples III-VI: the 10%CdS/GCN loaded with different amount of CDs (1%, 3%, 5%, and 7% (wt.%)) under visible light irradiation for 2 h; (c) Production of H2 with simultaneous degradation of organic pollutants over the 3%CDs/10%CdS/GCN in the presence of different organic pollutants under visible light irradiation for 2 h; (d) Cycling runs of photocatalytic H2 evolution over the 3%CDs/10%CdS/GCN in 4-NP solution under visible light irradiation. (The experimental data are taken three times the average of the experimental results).

16


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In addition, the influence of different initial concentration of organic pollutants on H2 evolution was studied over the 3%CDs/10%CdS/GCN composite catalyst under visible light. It is found that the evolution rate of H2 decreases with an increase of initial concentration of 4-NP, in the meanwhile the removal rate of 4-NP increases with an increase of initial concentration of 4-NP (Fig. S11). The result could be well explained that in higher initial concentration, more 4-NP molecules will absorb on the surface of the catalyst and be favorable for degradation, and the photogenerated electrons will be more efficiently consumed by the generated intermediates, thus leading to a lower photocatalytic H2 evolution rate. Furthermore, the long-term stability of the 3%CDs/10%CdS/GCN was also investigated by a four-run test. As shown in Fig. 4d, production of the H2 rate steadily increases with prolonged reaction time and there is only a small decrease of the production of H2 rate after four consecutive runs (20 h), while the simultaneous photodegradation rate of 4-NP also is nearly unchanged (above 95%) during the long term photoreaction process (Fig. S12). The results suggest excellent photocatalytic activity and good stability of 3%CDs/10%CdS/GCN. Photocatalytic mechanism In order to clarify the mechanism of photodegradation of organic pollutants with simultaneous photocatalytic H2 evolution, trapping experiments were done to investigate the major radical

species

in

the

photodegradation

of

organic

pollutants

over

the

3%CDs/10%CdS/GCN. Experiments of the capture of electrons (e-), hydroxyl radicals (·OH), and holes (h+) were done by adding 1.0 mM AgNO3, tert-butyl alcohol (t-Bu(OH)2) and ethylenediaminetetraacetic acid (EDTA-Na2), respectively. As shown in Fig. 5, the addition of 1 mM t-Bu(OH)2 hardly affects the photocatalytic degradation efficiency of 4-NP, BPA, and TTC, whereas the removal efficiency of 4-NP, BPA, and TTC markedly decrease with the addition of EDTA-Na2, suggesting that the holes (h+) but not the hydroxyl radicals are the main active species involved in the photocatalytic degradation of 4-NP, BPA, and TTC. In 17



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addition, the addition of AgNO3 can lower the photocatalytic degradation efficiency of 4-NP, whereas the photocatalytic degradation efficiency of BPA, and TTC remain unchanged. The result shows that e- species take effect on the 4-NP degradation, while it does little work on the degradation of BPA and TTC. This is in consistent with the experimental results of effect of different initial concentration of 4-NP on H2 production. In other words,

in part of

photogenerated electrons are used for photodegradation of 4-NP, whereas almost all photocgenerated electrons are utilized to produce hydrogen from water splitting in the photodegradation of BPA and TTC.

Fig. 5. (a) Effects of different reactive species scavengers on the photodegradation of 4-NP, (b) BPA and (c) TTC over the 3%CDs/10%CdS/GCN under visible light irradiation for 2 h.

According to the Mott-Schottky plots of CdS and GCN nanosheets, the conduction band potentials of CdS and GCN nanosheets are calculated as -0.51 V and -0.74 V vs. NHE, respectively (Fig. S13). Accordingly, the valence band potentials of CdS and GCN are calculated as +2.2 V and +1.9 V vs. NHE (ECB = EVB - Eg), respectively. Therefore, the photo-induced holes of GCN nanosheets cannot directly oxidize absorbed H2O to form hydroxyl radicals (·OH) because the valence band potentials of CdS and GCN nanosheets are 18


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more negative than the redox potential of ·OH/H2O (E0 = +2.8 V vs. NHE).5 The oxidation potentials of 4-NP, BPA, and TTC are +0.936 V, +0.454 V and +1.15 V, respectively, which are all smaller than the VB of the CdS and GCN nanosheets. Thus, the organic pollutants of 4-NP, BPA and TTC can be directly oxidized by the photogenerated holes on the VB of GCN. This analysis is consistent with the above experimental results. Furthermore, density functional theory (DFT) calculations were used to elucidate the different photodegradation rates of 4-NP, BPA, and TTC over 3%CDs/10%CdS/GCN in the photocatalytic system. According to calculation results as displayed in Fig. 6, the highest degradation rate of 4-NP over the 3%CDs/10%CdS/GCN catalyst could mainly be ascribed to the smaller molecules of 4-NP, which is more easily degraded than those bigger molecules of BPA and TTC. In addition, the overlapping of electron clouds in the LUMO and HOMO of BPA would accelerate the recombination of e- and h+ in the organic molecules, whereas the electron clouds in the LUMO and HOMO of TTC are partially separated, resulting in better separation of electrons and holes. This explains why the photodegradation rate of TTC is better than BPA over the as-prepared catalyst.

Fig. 6. Frontier electron densities of LUMO and HOMO of p-nitrophenol, tetracycline and bisphenol A.

19



To explain why the photocatalytic rate of hydrogen production is different in the presence of different organic pollutants, Liquid chromatography mass spectrometry (LC-MS) studies were also investigated. As shown in Figs. 7a and S14a, the MS fragmentation pattern at m/z=138 is assigned to the 4-NP characteristic ion peak. With an increase of irradiation time, some mass peaks at 194, 110, 116, 122, 139, and 155 are observed in the spectra, indicating that 4-NP is oxidized into small molecule organic matter and further mineralized to form CO2 and H2O. As shown in Figs. 7b and S14b, BPA shows a base peak corresponding to the MS fragmentation pattern at m/z=228, and under the attack of holes, the aromatic ring would be destroyed to produce some intermediates (m/z=120, 122, 136, and 138) and are ultimately mineralized to CO2 and H2O. According to the LC-MS results, during the whole process of degradation of 4-NP, some intermediates utilize some photogenerated electrons for the reduction reaction so that the photogenerated electrons are not fully consumed for photocatalytic hydrogen production, finally leading to a decrease of the photocatalytic evolution rate of H2. For BPA, there are no intermediate products consuming electrons for reduction reactions, resulting in a much higher photocatalytic evolution rate of H2 than that in the 4-NP solution. In addition, according to the results of LC-MS, there is no hydrogen generation (H+/H2) during the degradation of organic pollutants, which also proves that the hydrogen evolution comes from water splitting but not decomposition of organic pollutants.

20


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Fig. 7. (a) Photodegradation process of 4-NP and (b) BPA.

The photocatalytic mechanism is described in Scheme 1. Upon visible light irradiation, CDs in 3%CDs/10%CdS/GCN catalyst can absorb long-wavelength light (550-750 nm) and emit short-wavelength light (< 480 nm), which will be further absorbed by the GCN nanosheets and CdS to generate electrons (e-) and holes (h+) because of the up-conversion effect of CDs. Meanwhile, both GCN nanosheets and CdS are excited to produce electrons and holes under visible light irradiation. On the one hand, part of the photo-induced electrons at the conduction band of GCN nanosheets can move to the conduction band of CdS through the heterojunction interface, which allows electrons and holes to be effectively separated. On the other hand, the photogenerated electrons in the conduction band of GCN nanosheets as well as CdS can be also quickly transferred to the attached CDs or Pt nanoparticles (Pt plays the role of electron enrichment) and then react with H2O (or H+) for generation of H2 in solutions of BPA or TTC. But in the solution of 4-NP, some photogenerated electrons in the 21



conduction bands of GCN and CdS react with the intermediates for the reduction reaction. At the same time, these generated holes as strong oxidants can efficiently decompose organic pollutants of 4-NP, BPA, and TTC to H2O/CO2. This mechanism explains the multiple roles of CDs in the 3%CDs/10%CdS/GCN composite and the efficient separation of photogenerated electrons and holes, as well as the process of photocatalytic

organic pollutant degradations

cooperated with photocatalytic H2 evolution.

Scheme 1. Illustration for the photocatalytic mechanism over the 3%CDs/10%CdS/GCN catalyst under visible-light irradiation.

CONCLUSIONS In summary, CDs/CdS/GCN composite catalysts have been successfully designed and prepared through the combination of solvothermal and physical co-precipitation methods. The CDs/CdS/GCN composite catalysts were systematically characterized. Among the as-prepared catalysts, the 3%CDs/10%CdS/GCN catalyst exhibits the best efficiency of photocatalytic hydrogen evolution from water splitting in aqueous solution containing organic pollutants under visible light irradiation due to suitable loading amount of CdS QDs and CDs. 22


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Compared with the pure water system, the photocatalytic H2 evolution rate decreases with the addition of 4-NP because some photogenerated electrons are used to degrade 4-NP, whereas the H2 evolution rate increases with the addition of BPA or TTC in the simultaneous photocatalytic oxidation and reduction system because all of photogenerated electrons are used to split water for H2 production. Consequently, the photodegradation rate of 4-NP is higher than those of BPA and TTC. The present work for the first time systematically elucidates the influence of different kinds of organic pollutants on the photocatalytic H2 evolution, as well as the different photodegradation rates of 4-NP, BPA, and TTC over the same composite catalyst through DFT calculations and LC-MS analyses. A possible mechanism was presented to well explain the enhancement of photocatalytic performance over the 3%CDs/10%CdS/GCN catalyst and the different effects of organic pollutants on photocatalytic H2 evolution.

ASSOCIATED CONTENT Supporting Information. The photocatalytic H2 evolution rate of the heterostructured 3%CDs/10%CdS/GCN catalyst after four recycles; UV-vis diffuse reflectance the plots of (ahν)2 vs. FT-IR spectra of GCN naosheets and CDs/10%CdS/GCN. Absorption spectra of p-nitrophenol, bisphenol A and tetracycline; Mott-Schottky plots spectra of GCN and CdS; and EIS spectra of 4-NP and BPA. These supplementary materials can be found in the online version at http://pubs.acs.org.

NOTES The authors declare no competing financial interest.

ACKNOWLEDGEMENTS We gratefully acknowledge the financial support of the NSF of China (51622806 and 23



51378246) and the NSF of Jiangxi Province (20162BCB22017, 20165BCB18008 and 20171ACB20017).

REFERENCES (1) Zheng, Q.; Durkin, D. P.; Elenewski, J. E.; Sun, Y.; Banek, N. A.; Hua, L.; Chen, H.; Wagner, M. J.; Zhang, W.; Shuai, D. Visible-light-responsive graphitic carbon nitride: rational design and photocatalytic applications for water treatment. Environ. Sci. Technol. 2016, 50 (23), 12938-12948, DOI:10.1021/acs.est.6b02579. (2) Fang, X.; Shang, Q.; Wang, Y.; Jiao, L.; Yao, T.; Li, Y.; Zhang, Q.; Luo, Y.; Jiang, H. L. Single Pt Atoms Confined into a Metal–Organic Framework for Efficient Photocatalysis. Adv. Mater. 2018, 30 (7), 1705112, DOI: 10.1002/adma.201705112. (3) Huang, Y.; Liang, Y.; Rao, Y.; Zhu, D.; Cao, J.-j.; Shen, Z.; Ho, W.; Lee, S. C. Environment-Friendly Carbon Quantum Dots/ZnFe2O4 Photocatalysts: Characterization, Biocompatibility, and Mechanisms for NO Removal. Environ. Sci. Technol. 2017, 51 (5), 2924-2933, DOI:10.1021/acs.est.6b04460. (4) Liu, J.; Zhang, X.; Li, Y. Photoconversion of chlorinated saline wastewater DBPs in receiving seawater is overall a detoxification process. Environ. Sci. Technol. 2016, 51 (1), 58-67, DOI:10.1021/acs.est.6b04232. (5) Lan, S.; Feng, J.; Xiong, Y.; Tian, S.; Liu, S.; Kong, L. Performance and Mechanism of Piezo-Catalytic Degradation of 4-Chlorophenol: Finding of Effective Piezo-Dechlorination. Environ. Sci. Technol. 2017, 51 (11), 6560-6569, DOI:10.1021/acs.est.6b06426. (6) Liu, G.; You, S.; Tan, Y.; Ren, N. In situ photochemical activation of sulfate for enhanced degradation of organic pollutants in water. Environ. Sci. Technol. 2017, 51 (4), 2339-2346, DOI:10.1021/acs.est.6b05090. (7) Qin, Y.; Li, G.; Gao, Y.; Zhang, L.; Ok, Y. S.; An, T. Persistent free radicals in 24


Page 24 of 34

Page 25 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


carbon-based materials on transformation of refractory organic contaminants (ROCs) in water: A critical review. Water Res. 2018, 137, 130-143, DOI: 10.1016/j.watres.2018.03.012. (8) Ng, T. W.; Zhang, L.; Liu, J.; Huang, G.; Wang, W.; Wong, P. K. Visible-light-driven photocatalytic inactivation of Escherichia coli by magnetic Fe2O3–AgBr. Water Res. 2016, 90, 111-118, DOI: 10.1016/j.watres.2015.12.022. (9) Matafonova, G.; Batoev, V. Recent advances in application of UV light-emitting diodes for degrading organic pollutants in water through advanced oxidation processes: A review. Water Res. 2018, 132, 177-189, DOI: 10.1016/j.watres.2017.12.079. (10) Yang, J.; Zhao, Y.; Ma, S.; Zhu, B.; Zhang, J.; Zheng, C. Mercury removal by magnetic biochar derived from simultaneous activation and magnetization of sawdust. Environ. Sci. Technol. 2016, 50 (21), 12040-12047, DOI: 10.1021/acs.est.6b03743. (11) Wang, Z.; Huang, Y.; Ho, W.; Cao, J.; Shen, Z.; Lee, S. C. Fabrication of Bi2O2CO 3/g-C3N4

heterojunctions for efficiently photocatalytic NO in air removal: In-situ

self-sacrificial synthesis, characterizations and mechanistic study. Appl. Catal. B-Environ. 2016, 199, 123-133, DOI: 10.1016/j.apcatb.2016.06.027. (12) Cheng, D.; Yuan, S.; Liao, P.; Zhang, P. Oxidizing impact induced by mackinawite (FeS) nanoparticles at oxic conditions due to production of hydroxyl radicals. Environ. Sci. Technol. 2016, 50 (21), 11646-11653, DOI: 10.1021/acs.est.6b02833. (13) Li, G.; Nie, X.; Chen, J.; Jiang, Q.; An, T.; Wong, P. K.; Zhang, H.; Zhao, H.; Yamashita, H. Enhanced visible-light-driven photocatalytic inactivation of Escherichia coli using g-C3N4/TiO2 hybrid photocatalyst synthesized using a hydrothermal-calcination approach. Water Res. 2015, 86, 17-24, DOI: 10.1016/j.watres.2015.05.053. (14) Wang, W.; Li, G.; Xia, D.; An, T.; Zhao, H.; Wong, P. K. Photocatalytic nanomaterials for solar-driven bacterial inactivation: recent progress and challenges. Environmental Science: Nano 2017, 4 (4), 782-799. DOI:10.1039/C7EN00063D. 25



(15) Chen, M.; Yao, J.; Huang, Y.; Gong, H.; Chu, W. Enhanced photocatalytic degradation of ciprofloxacin over Bi2O3/(BiO)2CO3 heterojunctions: Efficiency, kinetics, pathways, mechanisms and toxicity evaluation. Chem. Eng. J. 2018, 334, 453-461, DOI: 10.1016/j.cej.2017.10.064. (16) Li, H.; Li, J.; Ai, Z.; Jia, F.; Zhang, L. Oxygen Vacancy℃Mediated Photocatalysis of BiOCl: Reactivity, Selectivity and Perspective. Angew. Chem. Int. Edit. 2017, 130 (1), 128-145, DOI: 10.1002/ange.201705628. (17) Li, H.; Shang, J.; Zhu, H.; Yang, Z.; Ai, Z.; Zhang, L. Oxygen vacancy structure associated photocatalytic water oxidation of BiOCl. ACS Catal. 2016, 6 (12), 8276-8285, DOI: 10.1021/acscatal.6b02613. (18) Qi, N.; Wang, P.; Wang, C.; Ao, Y. Effect of a typical antibiotic (tetracycline) on the aggregation of TiO2 nanoparticles in an aquatic environment. J. Hazard. Mater. 2018, 341, 187-197. DOI: 10.1016/j.jhazmat.2017.07.046. (19) Jiang, X.-H.; Xing, Q.-J.; Luo, X.-B.; Li, F.; Zou, J.-P.; Liu, S.-S.; Li, X.; Wang, X.-K. Simultaneous photoreduction of Uranium (VI) and photooxidation of Arsenic (III) in aqueous solution over g-C3N4/TiO2 heterostructured catalysts under simulated sunlight irradiation. Appl. Catal. B-Environ. 2018,228, 29-38. DOI: 10.1016/j.apcatb.2018.01.062. (20) Zou, J. P.; Ma, J.; Luo, J. M.; Yu, J.; He, J. K.; Meng, Y. T.; Luo, Z.; Bao, S. K.; Liu, H. L.; Luo, S. L.; Luo, X. B.; Chen, T. C.; Suib, S. L. Fabrication of novel heterostructured few layered WS2-Bi2WO6/Bi3.84W0.16O6.24 composites with enhanced photocatalytic performance. Appl. Catal. B-Environ. 2015, 179, 220-228, DOI: 10.1016/j.apcatb.2015.05.031. (21) Zou, J. P.; Wang, L. C.; Luo, J. M.; Nie, Y. C.; Xing, Q. J.; Luo, X. B.; Du, H. M.; Luo, S. L.; Suib, S. L. Synthesis and efficient visible light photocatalytic H2 evolution of a metal-free g-C3N4/graphene quantum dots hybrid photocatalyst. Appl. Catal. B-Environ. 2016, 193, 103-109, DOI: 10.1016/j.apcatb.2016.04.017. 26


Page 26 of 34

Page 27 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(22) Zou, J. P.; Wu, D. D.; Luo, J. M.; Xing, Q. J.; Luo, X. B.; Dong, W. H.; Luo, S. L.; Du, H. M.; Suib, S. L. A Strategy for One-Pot Conversion of Organic Pollutants into Useful Hydrocarbons through Coupling Photodegradation of MB with Photoreduction of CO2. ACS Catal. 2016, 6 (10), 6861-6867, DOI: 10.1021/acscatal.6b01729. (23) Wang, W.; An, T.; Li, G.; Xia, D.; Zhao, H.; Jimmy, C. Y.; Wong, P. K. Earth-abundant Ni2P/g-C3N4 lamellar nanohydrids for enhanced photocatalytic hydrogen evolution and bacterial inactivation under visible light irradiation. Appl. Catal. B-Environ. 2017, 217, 570-580. DOI: 10.1016/j.apcatb.2017.06.027. (24) Zhang, W.; Li, G.; Wang, W.; Qin, Y.; An, T.; Xiao, X.; Choi, W. Enhanced photocatalytic mechanism of Ag3PO4 nano-sheets using MS2(M= Mo, W)/rGO hybrids as co-catalysts for 4-nitrophenol degradation in water. Appl. Catal. B-Environ. 2018, 232, 11-18. DOI: 10.1016/j.apcatb.2018.03.006. (25) Dong, W.-H.; Wu, D.-D.; Luo, J.-M.; Xing, Q.-J.; Liu, H.; Zou, J.-P.; Luo, X.-B.; Min, X.-B.; Liu, H.-L.; Luo, S.-L. Coupling of photodegradation of RhB with photoreduction of CO2 over rGO/SrTi0. 95Fe0. 05O3−δ catalyst: A strategy for one-pot conversion of organic pollutants

to

methanol

and

ethanol.

J.

Catal.

2017,

349,

218-225,

DOI:

10.1016/j.jcat.2017.02.004. (26) Nie, Y.-C.; Yu, F.; Wang, L.-C.; Xing, Q.-J.; Liu, X.; Pei, Y.; Zou, J.-P.; Dai, W.-L.; Li, Y.; Suib, S. L. Photocatalytic degradation of organic pollutants coupled with simultaneous photocatalytic H2 evolution over Graphene quantum dots/Mn-N-TiO2/g-C3N4 composite catalysts: performance and mechanism. Appl. Catal. B-Environ. 2018, 227, 312-321, DOI: 10.1016/j.apcatb.2018.01.033. (27) Tian, B.; Yang, B.; Li, J.; Li, Z.; Zhen, W.; Wu, Y.; Lu, G. Water splitting by CdS/Pt/WO3-CeOx photocatalysts with assisting of artificial blood perfluorodecalin. J. Catal. 2017, 350, 189-196, DOI: 10.1016/j.jcat.2017.03.012. 27



(28) Li, G.; Nie, X.; Gao, Y.; An, T. Can environmental pharmaceuticals be photocatalytically degraded and completely mineralized in water using g-C3N4/TiO2 under visible light irradiation?—Implications of persistent toxic intermediates. Appl. Catal. B-Environ. 2016, 180, 726-732. DOI: 10.1016/j.apcatb.2015.07.014. (29) Yan, H.; Xie, Y.; Jiao, Y.; Wu, A.; Tian, C.; Zhang, X.; Wang, L.; Fu, H. Holey Reduced Graphene Oxide Coupled with an Mo2N–Mo2C Heterojunction for Efficient Hydrogen Evolution. Adv. Mater. 2017, 30 (2), 1704156, DOI: 10.1002/adma.201704156. (30) Won, D.-I.; Lee, J.-S.; Ba, Q.; Cho, Y.-J.; Cheong, H.-Y.; Choi, S.; Kim, C. H.; Son, H.-J.; Pac, C.; Kang, S. O. Development of a Lower Energy Photosensitizer for Photocatalytic CO2 Reduction: Modification of Porphyrin Dye in Hybrid Catalyst System. ACS Catal. 2018, 8, 1018-1030, DOI: 10.1021/acscatal.7b02961. (31) Jiang, Z.; Wan, W.; Li, H.; Yuan, S.; Zhao, H.; Wong, P. K. A Hierarchical Z℃Scheme α℃Fe2O3/g℃C3N4 Hybrid for Enhanced Photocatalytic CO2 Reduction. Adv. Mater. 2018, 30 (10), 1706108, DOI: 10.1002/adma.201706108. (32) Wei, R.-B.; Huang, Z.-L.; Gu, G.-H.; Wang, Z.; Zeng, L.; Chen, Y.; Liu, Z.-Q. Dual-cocatalysts decorated rimous CdS spheres advancing highly-efficient visible-light photocatalytic hydrogen production. Appl. Catal. B-Environ. 2018, 231, 101-107. DOI: doi.org/10.1016/j.apcatb.2018.03.014. (33) Zhang, S. Q.; Wang, L. L.; Liu, C. B.; Luo, J. M.; Crittenden, J.; Liu, X.; Cai, T.; Yuan, J. L.; Pei, Y.; Liu, Y. T. Photocatalytic wastewater purification with simultaneous hydrogen production using MoS2 QD-decorated hierarchical assembly of ZnIn2S4 on reduced graphene oxide photocatalyst. Water Res. 2017, 121, 11-19, DOI: 10.1016/j.watres.2017.05.013. (34) Wang, G. M.; Ling, Y. C.; Lu, X. H.; Wang, H. Y.; Qian, F.; Tong, Y. X.; Li, Y. Solar driven hydrogen releasing from urea and human urine. Energ. Environ. Sci. 2012, 5 (8), 8215-8219, DOI: 10.1039/c2ee22087c. 28


Page 28 of 34

Page 29 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(35) Hou, H.-J.; Zhang, X.-H.; Huang, D.-K.; Ding, X.; Wang, S.-Y.; Yang, X.-L.; Li, S.-Q.; Xiang, Y.-G.; Chen, H. Conjugated microporous poly (benzothiadiazole)/TiO2 heterojunction for visible-light-driven H2 production and pollutant removal. Appl. Catal. B-Environ. 2017, 203, 563-571, DOI: 10.1016/j.apcatb.2016.10.059. (36) Lu, D.; Wang, H.; Zhao, X.; Kondamareddy, K. K.; Ding, J.; Li, C.; Fang, P. Highly efficient

visible-light-induced

photoactivity

of

Z-scheme

g-C3N4/Ag/MoS2

ternary

photocatalysts for organic pollutant degradation and production of hydrogen. ACS Sustain. Chem. Eng. 2017, 5 (2), 1436-1445, DOI: 10.1021/acssuschemeng.6b02010. (37) Iervolino, G.; Vaiano, V.; Murcia, J.; Rizzo, L.; Ventre, G.; Pepe, G.; Campiglia, P.; Hidalgo, M.; Navío, J.; Sannino, D. Photocatalytic hydrogen production from degradation of glucose over fluorinated and platinized TiO2 catalysts. J. Catal. 2016, 339, 47-56, DOI: 10.1016/j.jcat.2016.03.032. (38) Zhang, G.; Lan, Z.-A.; Wang, X. Surface engineering of graphitic carbon nitride polymers with cocatalysts for photocatalytic overall water splitting. Chem. Sci. 2017, 8 (8), 5261-5274, DOI: 10.1039/C7SC01747B. (39) Tian, N.; Zhang, Y.; Li, X.; Xiao, K.; Du, X.; Dong, F.; Waterhouse, G. I.; Zhang, T.; Huang, H. Precursor-reforming protocol to 3D mesoporous g-C3N4 established by ultrathin self-doped nanosheets for superior hydrogen evolution. Nano Energy. 2017, 38, 72-81, DOI: 10.1016/j.nanoen.2017.05.038. (40) Tan, S.; Xing, Z.; Zhang, J.; Li, Z.; Wu, X.; Cui, J.; Kuang, J.; Zhu, Q.; Zhou, W. Ti 3+

-TiO2/g-C3N4 mesostructured nanosheets heterojunctions as efficient visible-light-driven

photocatalysts. J. Catal. 2018, 357, 90-99, DOI: 10.1016/j.jcat.2017.08.006. (41) Zhu, M.; Kim, S.; Mao, L.; Fujitsuka, M.; Zhang, J.; Wang, X.; Majima, T. Metal-Free Photocatalyst

for

H2

Evolution

in

Visible

to

Near-Infrared

Region:

Black

Phosphorus/Graphitic Carbon Nitride. J. Am. Chem. Soc. 2017, 139 (37), 13234-13242, DOI: 29



Page 30 of 34

10.1021/jacs.7b08416. (42) Zhou, X.; Shao, C.; Li, X.; Wang, X.; Guo, X.; Liu, Y. Three dimensional hierarchical heterostructures of g-C3N4 nanosheets/TiO2 nanofibers: Controllable growth via gas-solid reaction and enhanced photocatalytic activity under visible light. J. Hazard. Mater. 2018, 344, 113-122, DOI: 10.1016/j.jhazmat.2017.10.006. (43) Wei, R.-B.; Kuang, P.-Y.; Cheng, H.; Chen, Y.-B.; Long, J.-Y.; Zhang, M.-Y.; Liu, Z.-Q. Plasmon-enhanced photoelectrochemical water splitting on gold nanoparticle decorated ZnO/CdS nanotube arrays. ACS Sustainable Chemistry & Engineering 2017, 5 (5), 4249-4257. DOI: 10.1021/acssuschemeng.7b00242. (44) Kuang, P. Y.; Zheng, P. X.; Liu, Z. Q.; Lei, J. L.; Wu, H.; Li, N.; Ma, T. Y. Embedding Au quantum dots in rimous cadmium sulfide nanospheres for enhanced photocatalytic hydrogen evolution. Small 2016, 12 (48), 6735-6744. DOI: 10.1002/smll.201602870. (45) Wang, P.; Wu, T.; Wang, C.; Hou, J.; Qian, J.; Ao, Y. Combining Heterojunction Engineering with Surface Cocatalyst Modification To Synergistically Enhance the Photocatalytic Hydrogen Evolution Performance of Cadmium Sulfide Nanorods. ACS Sustainable

Chemistry

&

Engineering

2017,

5

(9),

7670-7677.

DOI:

10.1021/acssuschemeng.7b01043. (46) Ao, Y.; Wang, K.; Wang, P.; Wang, C.; Hou, J. Synthesis of novel 2D-2D pn heterojunction BiOBr/La2Ti2O7 composite photocatalyst with enhanced photocatalytic performance under both UV and visible light irradiation. Appl. Catal. B-Environ. 2016, 194, 157-168. DOI: 10.1016/j.apcatb.2016.04.050. (47) Qu, D.; Liu, J.; Miao, X.; Han, M.; Zhang, H.; Cui, Z.; Sun, S.; Kang, Z.; Fan, H.; Sun, Z. Peering into water splitting mechanism of g-C3N4-carbon dots metal-free photocatalyst. Appl. Catal. B-Environ. 2018, 227, (5) 418-424, DOI: 10.1016/j.apcatb.2018.01.030. (48) Yu, X.; Li, Z.; Liu, J.; Hu, P. TaOC chemical bond enhancing charge separation between 30


Page 31 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Ta4+ doped Ta2O5 quantum dots and cotton-like g-C3N4. Appl. Catal. B-Environ. 2017, 205, 271-280, DOI: 10.1016/j.apcatb.2016.12.040. (49) Wang, F.; Wang, Y.; Feng, Y.; Zeng, Y.; Xie, Z.; Zhang, Q.; Su, Y.; Chen, P.; Liu, Y.; Yao, K. Novel ternary photocatalyst of single atom-dispersed silver and carbon quantum dots co-loaded with ultrathin g-C3N4 for broad spectrum photocatalytic degradation of naproxen. Appl. Catal. B-Environ. 2018, 221, 510-520, DOI: 10.1016/j.apcatb.2017.09.055. (50) Wang, W.; Feng, W.; Du, J.; Xue, W.; Zhang, L.; Zhao, L.; Li, Y.; Zhong, X. Cosensitized quantum dot solar cells with conversion efficiency over 12%. Adv Mater 2018, 30 (11), 1705746. DOI: 10.1002/adma.201705746. (51) Wu, T.; Wang, P.; Qian, J.; Ao, Y.; Wang, C.; Hou, J. Noble-metal-free nickel phosphide modified CdS/g-C3N4 nanorods for dramatically enhanced photocatalytic hydrogen evolution under visible light irradiation. Dalton. Trans. 2017, 46 (40), 13793-13801. DOI: 10.1039/C7DT02929B. (52) Fukui, K. Role of frontier orbitals in chemical reactions. Science. 1982, 218 (4574), 747-754, DOI: jstor.org/stable/1689733. (53) Wang, Y.; Maeda, K.; Thomas, A.; Takanabe, K.; Xin, G.; Carlsson, J.; Domen, K. and M. Antonietti. Nat. Mater. 2008, 10 (1038), 50, DOI: 10.1038/nmat2317. (54) Zhang, X.; Xie, X.; Wang, H.; Zhang, J.; Pan, B.; Xie, Y. Enhanced photoresponsive ultrathin graphitic-phase C3N4 nanosheets for bioimaging. J. Am. Chem. Soc. 2012, 135 (1), 18-21, DOI: 10.1021/ja308249k. (55) Ming, H.; Ma, Z.; Liu, Y.; Pan, K.; Yu, H.; Wang, F.; Kang, Z. Large scale electrochemical synthesis of high quality carbon nanodots and their photocatalytic property. Dalton. Trans. 2012, 41 (31), 9526-9531, DOI: 10.1039/C2DT30985H. (56) Yao, J.-J.; Hoffmann, M. R.; Gao, N.-Y.; Zhang, Z.; Li, L. Sonolytic degradation of dimethoate: Kinetics, mechanisms and toxic intermediates controlling. Water Res. 2011, 45 31



(18), 5886-5894, DOI: 10.1016/j.watres.2011.08.042. (57) Wang, C.; Wang, D.; Xu, F.; Pan, B.; Wan, B. Iron-Catalyzed Cycloaddition Reaction of Diynes and Cyanamides at Room Temperature. J. Organic. Chem. 2013, 78 (7), 3065-3072, DOI: 10.1021/jo400057t. (58) Wang, X. C.; Maeda, K.; Thomas, A.; Takanabe, K.; Xin, G.; Carlsson, J. M.; Domen, K.; Antonietti, M. A metal-free polymeric photocatalyst for hydrogen production from water under visible light. Nat. Mater. 2009, 8 (1), 76-80, DOI: 10.1038/nmat2317. (59) Cao, S. W.; Yuan, Y. P.; Fang, J.; Shahjamali, M. M.; Boey, F. Y. C.; Barber, J.; Loo, S. C. J.; Xue, C. In-situ growth of CdS quantum dots on g-C3N4 nanosheets for highly efficient photocatalytic hydrogen generation under visible light irradiation. Int. J. Hydrogen. Energ. 2013, 38 (3), 1258-1266, DOI: 10.1016/j.ijhydene.2012.10.116. (60) Ge, L.; Zuo, F.; Liu, J. K.; Ma, Q.; Wang, C.; Sun, D. Z.; Bartels, L.; Feng, P. Y. Synthesis and Efficient Visible Light Photocatalytic Hydrogen Evolution of Polymeric g-C3N4 Coupled with CdS Quantum Dots. J. Phys. Chem. C. 2012, 116 (25), 13708-13714, DOI: 10.1021/jp3041692. (61) Lu, Z.; Song, W.; Ouyang, C.; Wang, H.; Zeng, D.; Xie, C. Enhanced visible-light photocatalytic performance of highly-dispersed Pt/g-C3N4 nanocomposites by one-step solvothermal treatment. Rsc Adv 2017, 7 (53), 33552-33557. DOI:10.1039/C7RA04931E. (62) Fina, F.; Menard, H.; Irvine, J. T. S. The effect of Pt NPs crystallinity and distribution on the photocatalytic activity of Pt-g-C3N4. Phys. Chem. Chem. Phys. 2015, 17 (21), 13929-13936. DOI:10.1039/C5CP00560D. (63) Li, X.; Bi, W.; Zhang, L.; Tao, S.; Chu, W.; Zhang, Q.; Luo, Y.; Wu, C.; Xie, Y. Single℃Atom Pt as Co℃Catalyst for Enhanced Photocatalytic H2 Evolution. Advanced Materials 2016, 28 (12), 2427-2431. DOI: 10.1002/adma.201505281. (64) Liu, M.; Xia, P.; Zhang, L.; Cheng, B.; Yu, J. Enhanced photocatalytic H2-production 32


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activity of g-C3N4 nanosheets via optimal photodeposition of Pt as cocatalyst. ACS Sustainable Chem. & Eng. 2018. DOI:10.1021/acssuschemeng.8b01835.

For Table of Contents Use Only

Synopsis. Quantum dots modified g-C3N4 catalyst was rationally designed for simultaneous photodegradation of organic pollutants and hydrogen evolution under visible light irradiation.

33



196x137mm (150 x 150 DPI)


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Photodegradation of Organic Pollutants Coupled with Simultaneous

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