Insitu synthesis of highly efficient visible light driven stannic oxidegraphitic carbon nitride heterostructured photocatalysts

Accepted Manuscript In-situ synthesis of highly efficient visible light driven stannic oxide/graphitic carbon nitride heterostructured photocatalysts Binglin Tao, Zifeng Yan PII: DOI: Reference: S0021-9797(16)30460-X http://dx.doi.org/10.1016/j.jcis.2016.07.009 YJCIS 21395 To appear in: Journal of Colloid and Interface Science Received Date: Revised Date: Accepted Date: 26 April 2016 July 2016 July 2016 Please cite this article as: B Tao, Z Yan, In-situ synthesis of highly efficient visible light driven stannic oxide/ graphitic carbon nitride heterostructured photocatalysts, Journal of Colloid and Interface Science (2016), doi: http:// dx.doi.org/10.1016/j.jcis.2016.07.009 This is a PDF file of an unedited manuscript that has been accepted for publication As a service to our customers we are providing this early version of the manuscript The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain In-situ synthesis of highly efficient visible light driven stannic oxide/graphitic carbon nitride heterostructured photocatalysts Binglin Tao and Zifeng Yan* State Key Laboratory of Heavy Oil Processing, Key Laboratory of Catalysis, China University of Petroleum, Qingdao 266580, China *Corresponding Author Phone: +86 532 86981296; Fax: +86 532 86981295; Email: zfyancat@upc.edu.cn Abstract Novel and efficient visible-light-driven stannic oxide/graphitic carbon nitride heterostructured photocatalysts are prepared via a simple in-situ solvothermal method Characterization results demonstrate that there exist strong interactions between SnO2 nanoparticles and g-C3N4 matrix, which indicates the formation of SnO2/g-C3N4 heterojunction The as-synthesized SnO2/g-C3N4 composite exhibits improved efficiency for photodegradation of rhodamine B in aqueous solutions, with an apparent rate constant 6.5 times higher than that of commercial TiO2 (Degussa P25) The enhanced photocatalytic activity is attributed to synergistic effect between SnO2 and gC3N4, resulting in effective interfacial charge transfer and prolonged charge-hole separation time Moreover, SnO2/g-C3N4 composite photocatalysts possess excellent durability and stability after recycling runs, and a possible photocatalytic mechanism is also proposed This research highlights the promising applications of two dimensional g-C3N4 based composite photocatalysts in the field of waste water disposal and environmental remediation Keywords: composite, solvothermal, catalytic property, heterojunction Introduction Photocatalysis is of great interest because it provides a simple technique to solve selected environmental pollutions (e.g., gas and water purification [1]) and energy issues (e.g., water splitting [2] and carbon dioxide conversion [3]) facing the modern society During the last 40 years, titanium oxide (TiO2) has attracted much attention for its high efficiency, low cost and availability in the fields of water splitting for hydrogen production [4], water detoxification [5], air treatment [6], CO2 reduction [7] and organic synthesis [8] As the most widely used commercial photocatalyst, Degussa P25, composing of about 80% anatase and 20% rutile, is well-known to possess an insurmountable photocatalytic activity Despite these remarkable advantages and considerable achievements, TiO2 (P25) has also been much criticized for its two intrinsic shortcomings: the wide band gap and high recombination rate of photoinduced electronhole pairs Besides, the toxicity and safety for TiO2 need to be further studied in detail [9] Thus, numerous novel photocatalytic materials, for example, metal oxides [10, 11], metal sulfides [12], metallates [13, 14], metal halide [15], and even some metal-free semiconductors [16] have been proposed as substitutes for conventional TiO2 photocatalysts Since the first report about hydrogen production by graphitic carbon nitride (g-C3N4) in 2009 [17], this kind of metal-free polymer has attracted much attention in the field of photocatalysis due to its stability, low cost, and nontoxic properties However, g-C3N4 possesses a high recombination rate, indicating its short lifetime and low separation efficiency of photogenerated electron-hole pairs, which leads to low quantum efficiency Many approaches have been proposed to enhance the photocatalytic activity of g-C3N4, including exfoliation of bulk g-C3N4 into nanosheets [18], preparation of mesoporous g-C3N4 with large specific surface area [19], doping protogenous g-C3N4 with transition metals [20], and fabrication of g-C3N4 based semiconductor heterojunctions [21, 22] Among them, combining g-C3N4 with metal oxides to prepare heterostructured photocatalysts is supposed to be the most effective way to fully address the above mentioned issue Consequently, a variety of g-C3N4 based composites, including Ag2O/g-C3N4 [21], TiO2/g-C3N4 [23], Bi2WO6/g-C3N4 [24], AgVO4/g-C3N4 [25] and In2O3/g-C3N4 [26] were prepared, which exhibited improved separation efficiency of photogenerated charge carriers and enhanced photocatalytic activities Stannic oxide (SnO2), as an n-type semiconductor with a band gap of ~3.60 eV, was shown to be a less active photocatalyst for water detoxification [27] However, SnO2 has been more widely employed as an additive to improve catalytic behaviors of the main photocatalysts For example, ZnO-SnO2 nanofibers prepared via sol-gel method and electrospining technology possessed a much higher photocatalytic activity than the pure ZnO and SnO2 nanofibers for the degradation of rhodamine B under ultraviolet irradiation, possibly owing to the formation of ZnO-SnO2 heterojunctions which could facilitate the separation of electron-hole pairs [28] Theoretically, the combination of SnO2 and g-C3N4 could lead to the formation of a new kind of semiconductor heterojunction (SnO2/g-C3N4), which possesses a well matched band structure and reduces the electron-hole recombination rate There are few publications focused on the preparation of SnO2/g-C3N4 heterostructured photocatalysts Most recently, SnO2/g-C3N4 composite was synthesized by a traditional solvent evaporation method [29] The combination of SnO2 and g-C3N4 was beneficial for effective interfacial charge transfer thus prolonged electron-hole pairs’ lifetime However, the large crystal size (20 nm), small specific surface area (38.5 m2/g-1), and bulk g-C3N4 sheets render SnO2/g-C3N4 composite possesses a limited photocatalytic activity Besides, the synthesis procedure was still tedious A novel in-situ method for the fabrication of SnO2/g-C3N4 heterostructured photocatalysts is described here These new composites were prepared via a solvothermal method in which urea- derived g-C3N4 acted as matrix and stannic acetate served as SnO2 precursor They exhibited considerable activity for rhodamine B degradation in aqueous solutions, which was directly related to their unique structures Experiment section 2.1 Materials Urea and dimethylsulfoxide were obtained from Sinopharm Chemical Reagent Co., Ltd (China) Stannic acetate was purchased from Alfa Aesar TiO2 (Degussa P25, 20% rutile and 80% anatase) was provided by Degussa (China) Co., Ltd All the reagents were analytical pure and used as received without further purification Ultrapure water (resistivity•18 MΩ cm) was produced by a Millipore system 2.2 Synthesis of g-C3N4 The metal-free semiconductor g-C3N4 powders were synthesized by simply heating urea in a muffle furnace Typically, 20.0 g of urea was placed in a 100 mL semiclosed crucible with a cover Then temperature was raised to 550 oC at an accelerating rate of 15 o C min-1 and the condensation process was maintained at 550 oC for h [30] After the crucible was cooled down to room temperature naturally, the yellow product was collected and ground into fine powders For 20.0 g of urea, the g-C3N4 yield was 0.87-0.89 g 2.3 Fabrication of SnO2/g-C3N4 composite photocatalysts SnO2/g-C3N4 composite photocatalysts were synthesized via an ordinary solvothermal method In a typical synthesis, 0.4 g of g-C3N4 and 0.1571 g of stannic acetate were sequentially added into 70 mL of dimethylsulfoxide contained in a 250 mL beaker After sonication for 60 min, the above solution was transferred into a 100 mL Teflon-lined stainless steel autoclave, and then heated at 180 oC for 20 h Subsequently, the precipitate was collected by filtration, washed with water and ethanol for several times, and dried at ambient conditions Finally the composite photocatalysts were annealed at 400 oC for h According to this method, a series of SnO2/g-C3N4 composites with selected mass ratios of SnO2 and g-C3N4 (1:20, 1:10, 1:4, 1:1, and 2:1) were prepared by changing the dosages of stannic acetate Pure SnO2 particles were prepared by decomposing stannic acetate in dimethylsulfoxide directly 2.4 Characterization Crystal structure of the as-prepared products were characterized by a PANalytical PRO X-ray Diffractometer equipped with Cu K radiation ( =1.5406nm) Fourier transform infrared (FT-IR) spectra were recorded on a Nicolet 6700 spectrometer using KBr disc technique Nitrogen adsorption-desorption isotherms were obtained on a Micromerities Tristar 3000 equipment at -196 oC Prior to measurement, all the samples were degassed at 300 oC for hours Surface property analysis was performed on an Escalab 250 X-ray photoelectron spectrometer The C1s binding energy of 284.6 eV of adventitious carbon was used as the reference Morphologies of the as-prepared composites were obtained from a Hitachi S-4800 scanning electron microscope at an accelerating voltage of kV The lattice structure and selected area electron diffraction were observed on a JEM-2100UHR transmission electron microscope Diffuse reflectance spectra were recorded by a Jena SPECORD 210 PLUS UV-Vis spectrophotometer equipped with an integrating sphere attachment, while BaSO4 powder was used as reference The transient photocurrent measurement was performed on an electrochemical workstation (CHI 660E, Chenhua Instrument Corporation, Shanghai, PR China) with a standard three-electrode system The preparation of working electrodes and testing method were according to the literature[31] 2.5 Evaluation of photocatalytic activity The photocatalytic activities of the samples were evaluated by using the visible-light-driven degradation of rhodamine B in aqueous solution as a probe reaction A double layered Pyrex glassware was used as the reactor Typically, 10 mg of the catalyst was dispersed in 50 mL of rhodamine B aqueous solution (10-5 mol L-1) to form a suspension After magnetically stirred in the dark for 30 min, the Pyrex reactor was irradiated under a 350 W xenon lamp equipped with a 420 nm cut off filter, which was placed 20 cm above the solution At regular time intervals of min, mL of aliquots were sampled and centrifuged for further analysis The concentration of rhodamine B was analyzed by recording the maximum absorption peak of rhodamine B solution (initially value = 554 nm, very slightly blue shift could be observed during the reaction process) on a Jena SPECORD 210 PLUS UV-Vis spectrophotometer During the photoreactions, no oxygen was bubbled into the system and the temperature was maintained at 20 oC by using a circulating water bath 2.6 Determination of reactive species In order to detect the active species generated in the reaction system, various representative scavengers, including silver nitrate (AgNO3, mmol L-1, scavenger for e-), ethylenediaminetetraacetic acid disodium salt (EDTA-2Na, mmol L-1, scavenger for h+), tert-butanol (TBA, mmol L-1, scavenger for •OH), sodium bicarbonate (NaHCO3, mmol L-1, scavenger for h+ and •OH) and 1, 4-benzoquinone (PBQ, mmol L-1, scavenger for O2•-) were introduced into the solution before illumination The next experimental steps were the same as above mentioned photocatalytic activity test Result and discussion 3.1 Structure and composition X-ray diffraction patterns (XRD) of SnO2/g-C3N4 composites are shown in Fig Spectra of pure SnO2 and g-C3N4 are also provided for comparison purpose For pure SnO2 sample, all diffraction peaks could be clearly indexed as (110), (101), (211), and (301) planes of rutile stannic oxide (JCPDS 72-1147) In the pattern of pure g-C3N4 sample, there are two diffraction peaks at 13.2o and 27.3o, which are stemmed from the lattice planes parallel to the c-axis and the graphite-like layer stacking of the conjugated aromatic units, respectively These two characteristic peaks are in agreement with graphitic carbon nitride reported in previous literatures [17] In the spectrum of SnO2/g-C3N4 composite with the mass ratio of 1:4, all diffraction peaks of SnO2 and g-C3N4 could be detected, and the overlap of diffraction patterns leads to broadening of (110) peak These results indicate the coexistence of SnO2 and g-C3N4 in SnO2/g-C3N4 composites Also, there are no detectable impurities, such as, SnO, SnS or Sn2S3 in the resulting composites SnO2 crystalline sizes in different samples are estimated according to (101) peak by Scherrer equation, and the results are shown in Table S1 Fig shows the FT-IR spectra of pure SnO2, g-C3N4, and a series of SnO2/g-C3N4 composites with selected mass ratios The board peak appears at wave number of 656 nm-1 can be attributed to Sn-O bond vibration [32, 33] The characteristic peak at 808 cm-1 corresponds to the breathing mode of triazine units [34] A series of small peaks in the range of 1200-1700 cm-1 are directly related to skeletal stretching modes of s-triazine or tri-s-triazine units [35] It is obvious that the intensity of the peak at 808 cm-1 weakens with the decrease of g-C3N4 content, which is consistent with the (002) peak variations in XRD analysis The composition and valence status of the SnO2/g-C3N4 composites were also characterized by X-ray photoelectron spectroscopy (XPS) technique Fig S1 depicts the survey spectra of pure SnO2, g-C3N4 and SnO2/g-C3N4 composite with a mass ratio of 1:4 (the best performing one in photodegradation) These results reveal that elemental Sn, O, C, N coexist in the SnO2/g-C3N4 composites The high resolution XPS spectra of Sn 3d, O 1s, C 1s, and N 1s in SnO2/g-C3N4-1:4 composite are shown in Fig For the sample of pure SnO2 (Fig 3A), the coupled peaks at binding energies of 487.2 eV and 495.7 eV are ascribed to Sn 3d5/2 and Sn 3d3/2, which are close to the literature values [36] Besides, the ratio of their integral areas conforms to 3:2 While in the SnO2/g-C3N4-1:4 heterostructured photocatalyst, the binding energies for Sn 3d5/2 and Sn 3d3/2 have shifted to 486.8eV and 495.7 eV, respectively This phenomenon is probably due to the intimate interactions between Sn4+ and g-C3N4 matrix Similarly, the binding energy of O 1s has an obvious opposite direction shift, from 531.2 eV to 532.0 eV, as shown in Fig 3B In Fig 3C, the signal of C 1s peak in SnO2/g-C3N4-1:4 composite is deconvoluted to individual peaks, with binding energies at 284.5 eV, 286.0 eV, 287.8 eV and 289.0 eV It is believed that the strong peak centered at binding energy of 284.5 eV corresponds to the C-C coordination of sp2 hybrid carbon atoms [37], and the peak centered at binding energy of 286.0 eV is attributed to C-N bond in N-containing groups [29] Besides, the peak signals at 287.8 eV and 289.0 eV are ascribed to C=N and N-C=N coordination, respectively [38] The N 1s spectra in Fig 3D shows three deconvoluted peaks, which are centered at 398.3 eV, 399.7 eV, and 400.7 eV According to previous reports, these peaks are derived from N-sp2C (pyridinic nitrogen, sp2 hybridization), N(C)3 (graphitic nitrogen, sp3 hybridization), and marginal N-H structures [39] All the above analysis indicates strong interactions between SnO2 and g-C3N4, demonstrating the formation of SnO2/g-C3N4 heterojunction 3.2 Texture and optical properties Nitrogen adsorption-desorption isotherms and BarrettJoyner-Halenda (BJH) pore size distribution curves of pure SnO2, g-C3N4, and SnO2/g-C3N4 composites are shown in Fig S2 Obviously, adsorption-desorption isotherms of all samples are of type • (IUPAC classification) with hysteresis loops, confirming the presence of mesopores The hysteresis loop is type H1 of pure SnO2 sample, indicating mesopores are derived from aggregated particles Similarly, the hysteresis loops are type H3 of all g-C3N4 based samples, which are well consistent with the slit-shaped pores formed by layer stacking of g-C3N4 sheets The Brunauer-Emmett-Teller (BET) surface areas of pure SnO2 and g-C3N4 are 98.2 and 82.0 m2/g, respectively It is worth mentioning that when SnO2 particles loaded on g-C3N4, BET surface areas of SnO2/g-C3N4 composites are much higher than that of both pure SnO2 and g-C3N4 This kind of “synergistic effect” has scarcely been reported before, possibly relates to the high dispersity of SnO2 particles on g-C3N4 sheets [38] Apparently, an enlarged specific surface area is beneficial for the improvement of photocatalytic activity All the texture properties are summarized in Table S1 The optical properties pure SnO2, g-C3N4, and SnO2/g-C3N4 composites were characterized by UV-Vis diffuse reflectance technique (Fig 4) As depicted in Fig S3, pure SnO2 particles show an absorption edge at about 320 nm, which corresponds to a band gap of 3.88 eV While all the g-C3N4 based materials, including pure g-C3N4 and SnO2/g-C3N4 composites, exhibit similar optical absorption abilities These results indicate that the introduction of SnO2 particles on the surface of g-C3N4 matrix would not change the absorption edges, even with an extremely high SnO2 content at mass ratio of 2:1 Considering the uncertain optical transition types of SnO2/gC3N4 composites materials (direct band-gap semiconductor for pure SnO2 and indirect band-gap semiconductor for g-C3N4), the band gap energies of all samples are estimated by using the empirical equation: Eg=1240/ (1) where represents the wavelength of absorption edge Thus it can be concluded that the band gap energies are in the range of 2.69-2.84 eV for g-C3N4 based composite materials, showing their strong visible light absorption abilities For better comparison, the absorption edges and corresponding calculated band gap energies of all samples are summarized in Table S1 3.3 Morphology Fig 5A and 5B present the SEM images of pure g-C3N4 sheets with lamella structures It is apparent that the surface of g-C3N4 sheets is quite smooth, and the thickness of a slice is in the range of 30-40 nm This estimation can be verified by Fig 5C and 5D, and the dimensions of g-C3N4 sheets were several micrometers After loading with SnO2 particles, there 10 are no significant morphology changes of the layer structure, as shown in SEM image of Figure 5E While the presence of numerous SnO2 particles could be verified by TEM image (Fig 5F) All the SnO2 particles dispersed evenly on the surface of g-C3N4 sheets, and the particle size is about nm (as depicted in Fig 5G), which can also be identified by XRD analysis The HRTEM image and corresponding SAED patterns of SnO2/g-C3N4-1:4 composite photocatalyst were displayed in Fig 5G and Fig 5H, respectively These diffraction rings could be indexed as the (110), (101), (211), and (301) planes of rutile SnO2 from inner to outside, and two sets of lattice fringes could be recognized (Fig 5I and 5K) By measuring the lattice spacing in Fig 5J and 5L, the interplanar distances were determined to be about 0.33 and 0.26 nm, in accordance with the (110) and (101) planes of rutile stannic oxide, respectively Moreover, the elemental mapping images of Sn, O, C, and N (Fig S4) suggest the uniform spatial distribution, which is a direct evidence for the high dispersity of SnO2 nanoparticles on g-C3N4 sheets 3.4 Photocatalytic activity The photocatalytic activities of different samples were evaluated by degradation of rhodamine B solution under visible light (420-760 nm) irradiation For comparison, one of the best commercial photocatalysts, Degussa P25, was used as the reference As displayed in Fig 6A and 6B, pure SnO2 shows the weakest ability to decompose rhodamine B, only 4.4 % of the dye was degraded in 15 The SnO2/g-C3N4-1:4 composite photocatalyst possesses the best photocatalytic performance, and 97.5 % of the rhodamine B was decomposed under the same conditions While the reference, commercial Degussa P25 displayed a relatively weaker degradation efficiency of 38.0 % The present SnO2/g-C3N4 heterostructured photocatalysts exhibit fairly high efficiency for the photodegradation of rhodamine B, and a comparison between the previous literatures and this study are summarized in Table S2 In this experiment, the photocatalytic activity of pure g-C3N4 is higher than that of Degussa P25, 11 possibly due to its relatively larger specific surface area and narrower band gap energy With respect to SnO2/g-C3N4 composites, it is apparent that trace amount of SnO2 slightly decreases the photocatalytic activity, because the SnO2 loading amount is too small to achieve collaborate effect, while the percentage of g-C3N4 matrix is discounted after loading with adventitious species Further increasing the SnO2 content in SnO2/g-C3N4 composites could improve photocatalytic activity promptly At the mass ratio of SnO2 and g-C3N4 is 1:4, the composite shows the highest photocatalytic activity When the amount of SnO2 is too small, the cooperativity could not be realized, while considerable amount of SnO2 particles loaded on gC3N4 sheets would improve the synergistic effect significantly The enhanced photocatalytic activity may be derived from the formation of heterojunctions between SnO2 and g-C3N4, thus inhibiting the recombination of photoinduced electron-hole pairs The photocatalytic activity decreases when the mass ratio of SnO2 and g-C3N4 is higher than 1:4, because excessive SnO2 particles would cover the surface of g-C3N4 sheets thus reduce the utilization efficiency of visible light From the above analysis, it can be concluded that a suitable mass ratio between SnO2 and g-C3N4 is crucial for the enhancement of photocatalytic activity It is believed that when concentrations of the dye substrates are within the millimolar range, the photocatalytic degradation process could be fitted to Langmuir-Hinshelwood pseudo-firstorder kinetics model [40], as expressed by using the following equation: ln(C/C0)=-kt (2) where C0 and C are dye concentrations in solution at reaction times of and t, respectively, and k is the apparent reaction rate constant As confirmed by Fig 6B, all data points scattered evenly on both sides of the straight lines, suggesting the feasibility of pseudo-first-order linear fitting In order to quantitatively investigate the reaction kinetics of rhodamine B degradation, the 12 comparison analysis of rate constants is shown in Fig S5 It can be seen that SnO2/g-C3N4-1:4 composite was the best performing sample, with a rate constant 78.3, 2.5 and 6.5 times higher than that of pure SnO2, pure g-C3N4, and Degussa P25, respectively From the viewpoint of practical applications, durability and stability of photocatalysts are also very important Herein, the SnO2/g-C3N4-1:4 composite photocatalyst was selected to evaluate these properties After recycling for times, the specified photocatalyst maintained a similar degradation level, as depicted in Fig The extraordinary photocatalytic activity and superior stability suggest that SnO2/g-C3N4 composites can be regard as a kind of effective visible-lightdriven photocatalyst, which could be applied in the field of waste water treatment 3.5 Possible mechanism In order to elucidate the possible mechanism, active species trapping experiments were designed As is known to all, the degradation process could possibly be depressed by several common scavengers, including AgNO3, EDTA-2Na, TBA, NaHCO3, and PBQ All the above mentioned scavengers were introduced to reaction system, and the results are shown in Fig It is clear that in the degradation process, no conspicuous changes could be observed after the addition of mmol L-1 AgNO3, indicating the obliteration of e- would not suppress the reaction significantly Interestingly, the same concentration of EDTA-2Na promoted the reaction to some extent, because the obliteration of h+ can improve the lifespan of e- [14] In addition, the degradation of rhodamine B was remarkably depressed by adding mmol L-1 TBA (scavenger for •OH), NaHCO3 (scavenger for h+ and •OH) and 1, 4-benzoquinone (scavenger for O2•-) These results demonstrate that both O2•- and •OH radicals are reactive species, while O2•- is the most important one responsible for rhodamine B degradation On the basis of above experimental results, a schematic diagram for possible photodegradation mechanism was proposed and illustrated in Fig Determined by diffuse reflectance spectra 13 technique, g-C3N4 is a kind of visible-light-driven photocatalyst with a narrow band gap of 2.69 eV, while SnO2 is ultraviolet-driven photocatalyst with a wide band gap of 3.88 eV (Table S1) The conduction band and valance band edge position could be estimated by Mulliken electronegativity theory [41], as depicted by the equation EVB=X-EC+0.5Eg (3) where X is the electronegativity of the semiconductor, EC represents the energy of free electrons on the hydrogen scale (4.5 eV), and Eg symbolizes the band gap of semiconductor The conduction band bottom of g-C3N4 (-1.2 eV vs SHE) is more negative than that of SnO2 (-0.19 eV vs SHE), while the valance band top of SnO2 (3.69 eV vs SHE) is much more positive than that of g-C3N4 (1.49 eV vs SHE) When exposed to visible light, SnO2/g-C3N4 composites were stimulated to produce electron-hole pairs which play crucial roles in photocatalytic reactions Because of the electrical potential differences and closely interfacial interaction between g-C3N4 and SnO2, the photoinduced electrons have tendency to transfer from the conduction band of gC3N4 to that of SnO2 Because the O2/ O2•– was –0.16 eV, lower than conduction band bottom of SnO2, electrons retained at the conduction band of SnO2 can react with dissolved O2 to generate O2·- free radicals, then O2·- free radicals combine with free water molecules to form ·OH, which is the main ·OH source in rhodamine B degradation At the same time, the photogenerated holes would be consumed by the adsorbed rhodamine B molecules also More importantly, migration of electrons in the SnO2/g-C3N4 heterojunction prolonged the separation time and inhibited recombination of electron-hole pairs, leading to a significantly enhanced photocatalytic activity than pure SnO2 and g-C3N4 The efficient separation of photogenerated electron-hole pairs in SnO2/g-C3N4 composite was also confirmed by transient photocurrent measurements, which is depicted in Figure S6 Therefore, the main reaction process could be described as follows: 14 SnO2/g-C3N4+h → e- (SnO2) + h+ (g-C3N4); e- +O2 → O2·-, O2·- +H2O → HO2· +OH-, HO2· + H2O → H2O2 +·OH, H2O2 → 2·OH; h+/O2•–/·OH +rhodamine B→ CO2+H2O Conclusions This paper presented a simple solvothermal method for the preparation of SnO2/g-C3N4 heterojuction photocatalysts The synergistic effect of SnO2 and g-C3N4 was attributed to effective charge transfer between interfaces, and O2·- was supposed to be the pivotal radical in rhodamine B degradation Considering the cost-effective precursors and easy fabrication procedure, SnO2/g-C3N4 is potential to be powerful photocatalyst candidates for pollution treatment Moreover, this work paves a new way for the fabrication of two dimensional g-C3N4 based composite via a facile in-situ strategy, which could play an important role in the field of photocatalysis, electrocatalysis, bio-imaging or energy storage& conversion Acknowledgements This work has been financially supported by National Natural Science Foundation of China (No U0136222 and No 51271215) The authors also thank Prof Mark J Rood (University of Illinois, Urbana-Champaign, United States) and Zhiping (Gordon) Xu (University of Queensland, Australia) for revising this work References [1] G Busca, S Berardinelli, C Resini, L Arrighi, Technologies for the removal of phenol from fluid streams: A short review of recent developments, J Hazard Mater 160 (2008) 265-288 [2] J Yang, D Wang, H Han, C Li, Roles of cocatalysts in photocatalysis and photoelectrocatalysis, Acc Chem Res 46 (2013) 1900-1909 15 [3] E.V Kondratenko, G Mul, J Baltrusaitis, G.O Larrazábal, J Pérez-Ramírez, Status and perspectives of CO2 conversion into fuels and chemicals by catalytic, photocatalytic and electrocatalytic processes, Energy Environ Sci (2013) 3112-3135 [4] A Fujishima, K Honda, Photolysis-decomposition of water at the surface of an irradiated semiconductor, 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[41] H Xu, Y Xu, H Li, J Xia, J Xiong, S Yin, C Huang, H Wan, Synthesis, characterization and photocatalytic property of AgBr/BiPO4 heterojunction photocatalyst, Dalton Trans 41 (2012) 3387-3394 Appendix A Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org Figure captions Fig XRD patterns of the as-prepared pure SnO2, g-C3N4, and SnO2/g-C3N4 composites with different mass ratios Fig FT-IR spectra of the as-prepared pure SnO2, g-C3N4, and SnO2/g-C3N4 composites with different mass ratios Fig High-resolution XPS spectra for Sn 3d peaks (A) and O 1s peaks (B) of pure SnO2 and SnO2/g-C3N4-1:4 composite; C 1s peaks (C) and N 1s peaks (D) of SnO2/g-C3N4-1:4 composite Fig UV-Vis diffuse reflectance spectra of pure g-C3N4 and SnO2/g-C3N4 composite photocatalysts 18 SEM M im maagess off puure g-C C3N4 ssheets (A A), aandd a slicce of g-C C3N4 (B B); Loow maagnnificcatioon Figg 55 S TE EM imaagee off a slicce oof gg-C C3N4 (C C), aandd hiigh maagnnificcation TE EM im magee off puure g-C C3N4 ssheeets (D)); S SEM M (E E) andd TE EM M (F F) iimaagess off SnnO2/g-C3N4-11:4 compposiite; High ressoluutioon T TEM M imaage of SnnO2//g-C C3N4-11:4 coompposiite (G G) witth corrressponnding SA AED D pattterrn iinseet (H)); P Parrtiallly mpliffiedd reegioon (I),, (K K) iin ppannel G G; The laattice spaacinng ((J), (L L) oof S SnO O2 inn ppaneel ((I) aandd (K K), am respecctivvelyy A) Noormalizzed deegraadattionn cuurves oof rrhoodam minne ssoluutioon in thhe ppreesennce of purre S SnO O2, Figg 66 (A g-C C3N4, S SnO O2/gg-C C3N4 coom mpossitee phhotoocaatalyystss, aandd coomm merrciaal P P255; ((B) Thhe corrressponndinng firsst-oordeer kkineeticss fittinng pplotts Figg 77 P Phottodeegrradaatioon ccurvves of rhoodaamine B ssoluutioon iin suucceessiive reaactiionss caatallyzeed bby thee SnnO2//g-C C3N4-11:4 com mpoositte pphotocataalystt Figg 88 P Photoddegrradaatioon kkineticcs oof rrhodam minne B soluutionn inn thhe ppreesennce of SnnO2//g-C C3N4-11:4 witth ddiffe ferennt sscavvenngerrs Figg A scchem mattic diaagrram m foor possibble phhotodeegraadaationn m mecchaanissm off S SnO O2/g C3N4 com mpoositte pphottocatallystts uunder vvisiiblee-ligght irraadiaatioon 19 Fiig Fiig 20 Fiig Fiig Fiig 21 Fiig Fiig 22 Fig Fig 23 Graphical abstract SnO2 particles are highly dispersed on g-C3N4 sheets to form a new kind of heterojunctions The as-fabricated SnO2/g-C3N4 heterojunctions demonstrate extraordinary photocatalytic activity for degradation of rhodamine B The large specific surface area, narrow band gap, strong interactions between two components, and high stability make them excellent candidate for water detoxification 24 ...In-situ synthesis of highly efficient visible light driven stannic oxide/graphitic carbon nitride heterostructured photocatalysts Binglin Tao and Zifeng Yan* State Key Laboratory of Heavy Oil... 86981295; Email: zfyancat@upc.edu.cn Abstract Novel and efficient visible- light- driven stannic oxide/graphitic carbon nitride heterostructured photocatalysts are prepared via a simple in-situ solvothermal... technique, g-C3N4 is a kind of visible- light- driven photocatalyst with a narrow band gap of 2.69 eV, while SnO2 is ultraviolet -driven photocatalyst with a wide band gap of 3.88 eV (Table S1) The