1. Introduction High efficiency photocatalysts driven by the sunlight irradiation have been extensively investigated due to their potential practical application in the wastewater 1

decontamination and the solar energy utilization [1]. TiO2 is regarded as one of the most promising photocatalysts because of its chemical stability, high photocatalytic activity, non-toxicity and low cost [2]. TiO2 is responsed to UV light and has weak response to the visible light due to the wide bandgap of 3.0-3.2 eV, however, UV light merely accounts for about 4% in sunlight, and the visible light takes up a large proportion of about 50% [3]. Therefore, much effort has been devoted to designing the heterojunction photocatalysts of TiO2 and other semiconductors with a narrow bandgap, by which the light response range of heterojunction photocatalysts can be extended to visible light region, therefore, TiO2-based heterojunction photocatalysts are beneficial for enhancing the utilization efficiency of solar energy [4-7] Graphtic carbon nitride (g-C3N4) as a metal-free photocatalyst has inspired extensive interests of many researchers due to the visible light response, solar energy conversion, removal of poisonous gas and environmental remediation [8-13]. The unique layered structure with π-conjugated system is helpful for the migration of charge carriers, and the narrow band gap of about 2.7 eV endows the photocatalyst splendid visible light absorption ability at about 460 nm [14,15]. The formation of g-C3N4/TiO2 heterojunction not only widens the light response range, but also suppresses the recombination of light-generated electron-hole pairs, and the photocatalytic efficiency is remarkably enhanced [16,17]. Therefore, there are many investigations exploring the g-C3N4/TiO2 heterojunction structure with different morphologies by the various methods, such as in situ calcined method [1,3,18-23], hydrothermal method [5,24-26], hydrothermal method combined with subsequent calcination process [27-30], hydrothermal method coupled with chemical vapor deposition process [31], in situ microwave-assisted method [16], ball-milling together with calcination [32], impregnation method [33,34], solvothermal strategy [4,35,36], mechanical mixing [37,38], biomimetic method [1], dipping process [39,40], combined electrospinning and calcination process [41,42] and so on. Particularly, Yu et al. have fabricated the Z-scheme g-C3N4/TiO2 by means of calcining the mixture of urea and P25, and the as-prepared Z-scheme photocatalysts possess improved photocatalytic performance [18]. Zhang et al. have achieved heterojunction of g-C3N4/TiO2 nanofibers via a direct calcination process of g-C3N4 and TiO2 nanofibers mixture, and the H2Ti3O7 nanofibers are prepared by the hydrothermal method using TiO2 powder and NaOH as the primary raw materials at 180 oC for 48 h, which is confronted with the calcination process to obtain the TiO2 nanofibers [27]. Wang et al. have successfully fabricated N-TiO2/g-C3N4 heterojunction, which involves the microwave-assisted process dealing with g-C3N4 and titanate solution and subsequent calcination process to achieve N-TiO2/g-C3N4 heterojunction, and the phase interface between TiO2 and g-C3N4 is helpful for the move of photo-induced electrons [16]. Tong et al. have prepared g-C3N4/TiO2 nanocomposites by coupling the arginine-enabled biomimetic mineralization of TiO2 with the thermal etched bulk g-C3N4, which exhibits the best photocatalytic degradation activity of RhB under the simulated sunlight irradiation [1]. Yan et al. have obtained the TiO2/g-C3N4 composite materials with the enhancement of photocatalytic activity, which involves the

2

ball-milling technique to mix the TiO2 and g-C3N4 and subsequent calcination process to achieve TiO2/g-C3N4 [32]. Electrospinning technique is often employed to easily fabricate 1D structure semiconductor nanofibers and nanotubes, 1D structure is helpful for the fast migration of electrons, which can weaken the recombination of holes and electrons, thus the photocatalytic performance can be improved [41-44]. Adhikari et al. have employed the two-nozzle electrospinning technique to prepare the g-C3N4 sheet modified porous TiO2 nanofiber, one nozzle contains PVAc and g-C3N4 particles, the other nozzle contains PVAc and TiO2 precursor, however, only a few g-C3N4 sheet is attached on the TiO2 nanofiber for the achieved TiO2/g-C3N4 composites [41], the two-nozzle electrospinning technique is complicated and the double solvent is consumed. Wang et al. have prepared TiO2/g-C3N4 nanofibers via the single-nozzle electrospinning technique, which involves the preparation of g-C3N4 particles by the calcination process, the preparation of PVP/Ti(OC4H9)4/g-C3N4 composite and subsequent calcination process [42], but the g-C3N4 particles are nonuniformly existed in the TiO2 nanofibers, moreover, the increasing g-C3N4 dosage is very difficult for the single-nozzle electrospinning technique, thus TiO2/g-C3N4 composite possesses the low content of 1% and the uneven distribution of g-C3N4, so the TiO2/g-C3N4 composite is examined only in the UV light not the solar light. Nevertheless, to the best of our knowledge, TiO2/g-C3N4 heterojunction photocatalysts fabricated by a facile electrospinning process combined with in situ evaporation and calcination process have not been reported, and the g-C3N4 content of TiO2/g-C3N4 composite can be easily adjusted and largely increased only by varying the melamine amount in the proposed method. In the present work, the electrospun nanofibrous TiO2/g-C3N4 heterojunction photocatalysts are fabricated for the first time, which involves the facile electrospinning process and subsequent in situ evaporation and calcination process. A series of electrospun nanofibrous TiO2/g-C3N4 heterojunction photocatalysts with different TiO2 nanofiber content are successfully prepared. It is worth mentioning that electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalysts with TiO2 content of 29.30 wt% possesses the best photocatalytic degradation efficiency for the RhB aqueous solution under simulated solar light. The crystalline structure, composition, morphology, component content, photocurrent response, EIS measurement, optical properties, PL spectra, photocatalytic activity and recycled photocatalytic degradation performance of as-prepared electrospun nanofibrous TiO2/g-C3N4 heterojunction photocatalysts are systematically investigated. Moreover, the effect of active species on the photocatalytic degradation of RhB over the electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalyst is also examined to make clear the improved photocatalytic mechanism.

2.Experimental section

2.1. Materials

3

Tetrabutyltitanate (TBT, 98%), CH3OH (98%) and Melamine (MEL) were purchased from Sinopharm Chemical Reagent Company. Poly(vinyl pyrrolidone) (PVP, Mw=1300000) was supplied by Aldrich Reagent Company, Acetic acid (HAc, 99.5%) was obtained from the Beijing Chemical Works. Rhodamine B (RhB) was provided by Tianjin Guangfu Chemical Reagents Company.

2.2. Fabrication of electrospun nanofibrous TiO2 Electrospun nanofibrous TiO2 were fabricated by a facile electrospinning and subsequent annealing method [43,45]. Firstly, 9 mL CH3OH, 0.3 mL HAc, 0.52 g PVP and 2.0 mL TBT were charged into the 25 mL triangle bottle with magnetic stirring for 4h to achieve homogeneous TiO2 precursor sol. Afterward, TiO2 precursor sol was injected into a syringe, which was connected with a steel needle, the steel needle is linked with a DC high voltage of 14 kV, the distance between the steel needle tip and the collector was 15 cm. Subsequently, the as-spun fiber membrane was calcined at 500 °C for 3 h with a heating rate of 2 °C/min to achieve the electrospun nanofibrous TiO2.

2.3. Fabrication of electrospun nanofibrous TiO2/g-C3N4 heterojunction photocatalysts Electrospun nanofibrous TiO2/g-C3N4 heterojunction photocatalysts were fabricated by a facile in situ evaporation and calcination process in the presence of nanofibrous TiO2 and MEL, and the overall schematic procedure was illustrated in the Fig. 1, the detailed strategy was depicted as followed. Typically, a certain amount of electrospun nanofibrous TiO2 and 50mL H2O were added into three-necked flask attached with a mechanical stirrer, which was sonicated at 200 W for 5min to break the TiO2 nanofibers, then 3.0g MEL was charged into the above suspension solution with vigorous stirring under 95 oC for 10min, and the water was evaporated at 100 oC to crystallize out the MEL on the surface of nanofibrous TiO2. The achieved white mixtures of TiO2/MEL were placed in the crucible with a cover and calcined in a muffle furnace at 520 oC for 2 h with 5 oC/min, and a series of the electrospun nanofibrous TiO2/g-C3N4 heterojunction photocatalysts with different TiO2 nanofiber content were obtained according to the recipes in the Table 1. MEL was directly confronted with the above calcination process to obtain pure bulk g-C3N4. In order to make a comparison with TiO2/g-C3N4-4, TiO2 nanofiber and g-C3N4 powder are directly grinded to obtain the TiO2/g-C3N4-4-mix (TiO2 content is fixed at 29.30 wt% based on the TG results).

2.4. Photocatalytic activity measurement RhB aqueous solution was degraded by the as-prepared photocatalysts to evaluate their photocatalytic activities. 50 mg photocatalyst was used to degrade 50 mL of RhB aqueous solution (10 mg/L) under the simulated solar light, which was emitted from a 500 W Xenon lamp. Before the light source was turned on, the above suspension solution was allowed to reach the absorption-desorption equilibrium with magnetic stirring for 30 min in dark. Then turned on the light source and sampled 4 mL suspension solution at a fixed time, finally, the RhB solution that filtered out the 4

photocatalyst was analyzed by the UV-Vis spectra to record the changes at the absorption band of 554 nm.

2.5. Photocurrent and EIS measurement An electrochemical system (CHI 760D, Shanghai Chenhua Instrument Co., Ltd., China) was employed to perform the photocurrent responses and EIS tests. The as-prepared photocatalysts, the platinum plate and Ag/AgCl electrode (saturated KCl) were used as the working electrode, counter electrode and the reference electrode, respectively, which constituted the standard three-electrode cell to study the photo-electrochemical property. The mixtures of 30 mg photocatalyst, 0.15 mL ethanol and 0.15 mL nafion aqueous solution (5 wt%) were homogeneously mixed by the ultrasonic cleaner for 30 min, then the slurry was dropped on the ITO glass (1x1cm), and the working electrode was achieved after the evaporation of ethanol. Moreover, Na2SO4 solution (0.1 mol/L) was utilized as the electrolyte, a 300 W Xenon lamp was used as the light source to perform the photocurrent and EIS test

2.6. Characterization Scanning electron microscope (SEM, TESCAN MAIA 3 LMH) and energydispersive X-ray analysis (EDX, attached to SEM) were used to examine the morphology and elementary composition of photocatalysts. JEOL JEM2100F transmission electron microscope was employed to provide the TEM, HRTEM and EDS element mapping images. A Nicolet Instruments Research Series 5PC FTIR spectrometer, a shimazu XRD 7000 diffractometer with Cu Kα radiation and a VG Multilab 2000 with Al-Kα operation at 300W were utilized to record the FTIR spectra, X-ray diffraction patterns and XPS analysis, respectively. UV-vis diffuse reflectance absorption spectra (DRS) was collected by a Shimadzu UV-3600 spectrophotometer equipped with an integrating sphere using BaSO4 as the reference sample. The RhB solution was analyzed by the UV-Vis spectra (Shimdzuuv-3600, Japan) to record the changes of absorption spectra. PerkinElmer LS55 fluorescence spectrophotometer was utilized to give PL spectra. TG analysis curves were collected by the SDT Q600 from TA Instruments under the air atmosphere with a heating rate of 10 oC/min from 25 to 800 o C. N2 adsorption–desorption isotherms were collected by a Micromeritics ASAP2020 at 77 K.

3. Results and discussion

3.1. Morphology of electrospun nanofibrous TiO2/g-C3N4 heterojunction Fig. 2 vividly shows the morphology evolution from the g-C3N4 to electrospun nanofibrous TiO2/g-C3N4 heterojunction with the increasing TiO2 content. The bulk g-C3N4 in Fig. 2(a) is seriously aggregated with the particle size of about 3 μm. It's obviously noted that the nanofibrous morphology counterparts in the Fig. 2(b-f) correspondingly increases with the increasing dosage of TiO2 nanofibers, and the nanofibrous morphology counterparts in the Fig. 2(b-f) represent the electrospun nanofibrous TiO2/g-C3N4 heterojunction. Moreover, the aggregation of g-C3N4 obviously weakens with the increased TiO2 dosage, especially, the aggregation of 5

g-C3N4 in Fig.2(b), (c) and (d) are very serious, however, the aggregation of g-C3N4 in Fig.2(e) is slight, and almost disappears in the Fig.2(f) when the its TiO2 content is 40.36%, the same phenomenon is reported in the references [1,21]. This phenomenon can be attributed to the in situ evaporation and calcination process in the presence of nanofibrous TiO2 and MEL, the MEL in the water is crystallized out by evaporating the water and directly deposited on the surface of nanofibrous TiO2, and the g-C3N4 directly forms on the surface of nanofibrous TiO2 during the calcination process, therefore, in situ loading of g-C3N4 on the surface of nanofibrous TiO2 is an efficient method not only to reduce the aggregation of g-C3N4, but also to construct the heterojunction structure between the g-C3N4 and TiO2 nanofiber, which is beneficial to move the photoinduced carriers, together with the improved photocatalytic performance [1,21]. Seen from the Fig. 2(g), the electrospun TiO2 nanofibers with the mean diameter of 185 nm possess the rough surface and perfect 1D profile, and there are many small pores on the surface of TiO2 nanofibers, which can remarkably improve light harvesting efficiency by multiple reflecting and scattering. Moreover, the 1D morphology is helpful for the migration and separation of photoinduced charge carriers [44,46,47], the photocatalyst with 1D morphology can be easily collected for the recycle [48]. As expected, only Ti and O elements are discovered in EDX spectrum in Fig. 2(h) except for Au element that comes from the spraying Au pretreatment, which suggests that pure TiO2 nanofibers are obtained. As for the EDX spectrums of TiO2/g-C3N4-4 in Fig. 2(i), besides Ti, O and Au elements, the C and N elements are also detected, which suggests that the g-C3N4 is formed in the TiO2/g-C3N4-4 heterojunction photocatalysts. Compared with the morphology of TiO2 nanofibers in Fig. 2(g), not only the electrospun nanofibrous TiO2 in the Fig. 2(b-f) become short, but also the surface morphology changes. This phenomenon can be explained as follows, the sonication process breaks the TiO2 nanofibers into short fibers during the fabrication of electrospun nanofibrous TiO2/g-C3N4 heterojunction photocatalysts, which is in favor of dispersing TiO2 short fibers in the solution of MEL and encapsulating the TiO2 short fibers with the MEL, moreover, the g-C3N4 is formed in situ on the surface of TiO2 nanofibers, thus the morphology is changed. HRTEM measurement is carried out to examine the morphology and structure of electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalyst. As depicted in Fig. 3(a), the electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalyst maintains splendid 1D structure after calcination. Moreover, seen from the Fig. 3(b), it is noted that the lattice fringes on left-upper and right-upper area are measured to be about 0.3518 and 0.1890 nm, respectively, which can be indexed to the (101) and (200) lattice plane of anatase TiO2, respectively [16], and the lower right region is recognized as the g-C3N4 phase [21], it's demonstrated that the interaction between the TiO2 nanofiber and g-C3N4 is strong, and the TiO2/g-C3N4 heterojunction structre is thus formed, which can effectively inhibit the recombination of electron-hole pairs [6,29] and improve the photocatalytic performance of electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalyst. EDS element mapping is employed to prove the distribution of representative elements in the electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalyst. As shown in Fig. 3, the representative 6

elements of N, O and Ti are detected and homogeneously distributed in the electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalyst. The element N originates from the g-C3N4, which suggests that the g-C3N4 phase is formed on the surface of TiO2 nanofiber, consequently, the electrospun nanofibrous TiO2/g-C3N4-4 heterojunction structure is effectively constructed.

3.2. FTIR spectra and XRD patterns FTIR spectra of g-C3N4, TiO2 nanofiber and electrospun nanofibrous TiO2/g-C3N4 heterojunction photocatalysts are represented in Fig. 4. Seen from Fig. 4(a), The feature adsorption regions of pristine g-C3N4 at 3000-3300, 1200-1600 and 810 cm-1 are detected in Fig. 4(a), the broad adsorption regions at 3000-3300 cm-1 are corresponded to the stretching vibrations of N-H, the strong band of 1200-1600 cm-1 with feature peaks at 1241, 1319, 1403, 1465 and 1573 cm-1 is assigned to the stretching vibration of C-N heterocycles [3,35], and the unique absorption peak at 810 cm-1 is indexed to the breathing mode of triazine units [35]. For the pureTiO2 nanofiber in Fig. 4(c), the broad band in the range of 400-800 cm-1 is corresponding to the Ti-O-Ti stretching vibration [3]. Based on the curve of Fig. 4(b), all the feature peaks of both g-C3N4 and TiO2 components are coexisted in the electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalysts, which further demonstrates that the g-C3N4 is formed in the presence of TiO2 nanofiber after the calcination process. Fig. 5. shows the XRD patterns of electrospun nanofibrous TiO2/g-C3N4 heterojunction photocatalysts with different TiO2 content. From the curve (a) to (e), TiO2 content in the TiO2/g-C3N4 heterojunction photocatalysts increases, it's noted that the characteristic peaks at 2θ=25.22, 37.75, 48.08, 55.18 and 62.65° are well indexed to the (101), (004), (200), (221) and (204) lattice planes of anatase TiO2 [6,29], which proves that the TiO2 in the TiO2/g-C3N4 heterojunction photocatalysts possesses pure crystal structure, moreover, the peak intensity of anatase TiO2 phase becomes stronger with the increasing TiO2 dosage. Meanwhile, the peak located at the 2θ=27.4° is assigned to the (002) diffraction planes of g-C3N4 [35,48], which is detected in all the TiO2/g-C3N4 heterojunction photocatalysts, and the peak intensity of g-C3N4 phase becomes weaker with the increasing TiO2 dosage. On the basis of above analysis, it's concluded that the presence of TiO2 has no obvious influence on the form of g-C3N4, moreover, both the TiO2 and g-C3N4 are existed in the electrospun nanofibrous TiO2/g-C3N4 heterojunction photocatalysts.

3.3. XPS analysis XPS is also employed to identify the surface composition and chemical valance state of Ti, O, C and N elements in the electrospun nanofibrous TiO2/g-C3N4 heterojunction photocatalyst. As shown the whole XPS survey spectrum in Fig. 6, the C, N, O and Ti elements are detected, which is coherent with EDX results. The magnified spectrum C 1s in Fig. 6(b) shows three peaks centered at 284.7, 288.2 and 293.8 eV, which are ascribe to adventitious hydrocarbon from the XPS instrument, sp3-bonded C of N-C=N [1,16]. The N 1s spectrum in Fig 6(c) is deconvolved into three peaks at 398.5, 399.3 and 401.2 eV after the Gaussian curve fitting, which are assigned to 7

sp2-hybridized nitrogen (C=N-C), tertiary nitrogen N-(C)3 and amino groups with a hydrogen atom (C-N-H), respectively. Moreover, the existence of N-(C)3 group demonstrates the polymerization of melamine [31]. The O 1s spectrum in Fig 6(d) are composed of two peaks at the 529.8 and 531.7eV, and the two peaks are corresponded to the O atoms in Ti-O and surface -OH group. In additon, the peaks located at 458.6 and 464.2 eV in Fig 6(e) are attributed to the Ti 2p3/2 and Ti 2p1/2, respectively [31,39]. The above analysis results are is agreement with the previous reports [5,31].

3.4 TG analysis and N2 sorption isotherm TG analysis is employed to determine the each compotent proportion in the electrospun nanofibrous TiO2/g-C3N4 heterojunction photocatalysts [1,21,29], the detailed curves are displayed in the Fig. 7 (A), the pure g-C3N4 shows no residual and loses the whole weight in the range of 500-750 oC, which results from the combustion of g-C3N4. Moreover, TiO2 nanofibers have no weight loss during the TG analysis, which has been demonstrated in the references [1,21]. Based on the weight remnant in Fig. 7(A), TiO2 content for the TiO2/g-C3N4-x (x=1-5) can be estimated to be 5.10, 11.57, 20.54, 29.30 and 40.36 wt%, respectively, the above results are in accordance with the dosage of TiO2 nanofiber in the synthesis process. Moreover, it's noted that all the electrospun nanofibrous TiO2/g-C3N4 heterojunction photocatalysts with different TiO2 content exhibit the weaker thermal stability than pure g-C3N4, it's because that the exist of TiO2 nanofiber weakens the cross-linked rings of g-C3N4 [1,9], and the weaken action becomes stronger with the increasing dosage of TiO2 nanofiber, therefore, it's noted that the temperature range of weight lose for TiO2/g-C3N4-x (x=1-5) is 500-731.5, 500-725.6, 500-719.8, 500-702.6 and 500-692.5 o C, respectively. The enlarged specific surface area can bring about the improvement of photocatalytic activity, thus N2 adsorption-desorption measurement of electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalyst and g-C3N4 are also performed, which are displayed in Fig. 7(B), BET specific surface area of TiO2/g-C3N4-4 is about 32.15 m2/g, which is 2.73 times larger than that of g-C3N4 (11.19 m2/g), it's ascribed to the introduction of porous electrospun nanofibrous TiO2.

3.5. UV-vis diffuse reflection spectra and PL spectra The UV-vis diffuse reflection spectroscopy is carried out to investigate the optical properties of g-C3N4, TiO2 nanofiber and electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalysts. Fig. 8A(a) represents the UV-vis spectrum of g-C3N4, which shows the intensitive absorption ability from the UV to the visible light region, and the absorption edge locates at the 459.2 nm, however, TiO2 in Fig. 8A(c) exhibits the strong UV absorption ability, the corresponding absorption edge is detected at the 390.7 nm. As for the electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalysts, an obvious absorption in both the UV and visible light region is found in Fig. 8A(b), which will be beneficial for photocatalytic activity under solar light irradiation, and the absorption edge is around 499.7 nm. Compared with the pure TiO2 nanofibers, electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalysts possesses an remarkable red shift, which results from the introduction of g-C3N4 and 8

the formation of heterojunction [1]. On the basis of the above analysis, it's demonstrated that the electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalysts can harvest the UV and visible light of solar light, by which the solar light can be fully utilized in a certain extent. The band gap energy of the as-prepared photocatalysts can be calculated from the equation of Eg=1240/λg, herein, Eg and λg refer to the the band gap energy and optical absorption edge of semiconductor, respectively [9], the as-mentioned above absorption edge of g-C3N4, TiO2 and electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalysts are 459.2, 390.7 and 499.7 nm, respectively, therefore, the corresponding band gap energy are estimated to be 2.70, 3.17 and 2.48 eV. The separation efficiency of photoinduced electrons and holes is evaluated by the PL emission spectra [49]. Seen from Fig. 8(B), the electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalyst exhibits the much weaker peak intensity than g-C3N4, which indicates that TiO2/g-C3N4-4 has a low recombination efficiency of electrons and holes [5], therefore, the photocatalytic activity is remarkably improved [49].

3.6. Photocatalytic activity and recycled photocatalytic degradation performance To assess the photocatalytic performance of electrospun nanofibrous TiO2/g-C3N4 heterojunction photocatalysts with different TiO2 content under the simulated sunlight irradiation, RhB is utilized as a model of organic pollutant [6]. For comparison, the photocatalytic activity of pure g-C3N4 and TiO2 nanofiber photocatalysts are also examined under the same conditions. Fig. 9(A) shows photocatalytic activities of TiO2/g-C3N4 heterojunction photocatalysts with different TiO2 content for the decolorization of RhB aqueous solution under simulated solar light irradiation, it's obviously noted that all the electrospun nanofibrous TiO2/g-C3N4-x (x=1-5) heterojunction photocatalysts possess a better photocatalytic efficiency than the pure g-C3N4. However, the electrospun nanofibrous TiO2/g-C3N4-1 (TiO2 content 5.10 wt%) and TiO2/g-C3N4-2 (TiO2 content 11.57 wt%) exhibit a lower photocatalytic degradation efficiency than the TiO2 nanofiber. When the TiO2 content increases to 20.54 wt% for the TiO2/g-C3N4-3，its photocatalytic activity is almost equal to the TiO2 nanofiber. Especially, when the TiO2 content increases to 29.30 wt% for the TiO2/g-C3N4-4, which exhibits the best photocatalytic degradation efficiency in comparison with all as-prepared photocatalysts, it may be ascribed to the formation of direct Z-scheme heterojunction for electrospun nanofibrous TiO2/g-C3N4 [18,29,50], and the two phase interface between TiO2 and g-C3N4 facilitates the move of photo-induced electrons, therefore, the synergistic effect between TiO2 and g-C3N4 plays a major role for the improved photodegradation activity [1,29]. However, when the TiO2 content increases continuously to 40.36 wt% for the TiO2/g-C3N4-5, its photocatalytic activity begins to decrease in Fig. 9A(f), this may be ascribed to the insufficient g-C3N4, which can not coat all the TiO2 nanofiber to construct the heterojunction structure, thus resulting in the reduction of photodegradation activity. Furthermore, the blank control experiment without photocatalyst is also tested, it's noted that the degradation of RhB can be almost ignored without photocatalyst. 9

The kinetic plots for the photodegradation of RhB over the electrospun nanofibrous TiO2/g-C3N4 heterojunction photocatalysts are displayed in Fig. 9B on the basis of the equation of -ln(C/C0)=kt, herein, the k, C and C0 represent the degradation rate constant, the concentration of pollution at a given time and the absorption equilibrium concentration of RhB, respectively [9]. The electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalysts possesses the highest kinetic constant, which is about 6.79 times as large as that of g-C3N4 and 4.93 times as large as that of TiO2. It can be explained as follows, the electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalyst not only possesses excellent separation efficiency of photoinduced electrons and holes, but also has the low charge migrate resistance at the interface, which can be demonstrated by the photoelectrochemical test in the following section, thus the photocatalytic efficiency is largely improved. In order to prove the contribution of heterojunction structure of electrospun nanofibrous TiO2/g-C3N4-4, a control sample of TiO2/g-C3N4-4-mix is directly prepared by grinding the TiO2 nanofiber and bulk g-C3N4 at the same component proportion as the TiO2/g-C3N4-4, the photodegradation efficiency of TiO2/g-C3N4-4-mix in Fig. 9C(b) is higher in comparison with pure TiO2 and bulk g-C3N4, but still much lower than that of electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalyst in Fig. 9C(a). As a consequence, the electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalyst possesses the better heterojunction structure and phase interface than TiO2/g-C3N4-4-mix. As is well known that the stability and separability of photocatalysts are very important factors in the practical use [44], therefore, the reuse cycle experiments of the photodegradation for RhB aqueous solution are conducted over the electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalysts, which maintain a relatively high photodegradation efficiency of 96% after four cycles based on the results in Fig. 9D, it's concluded that the electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalysts possess excellent photostability. Moreover, the electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalysts have unique 1D morphology, which can be easily separated from the aqueous solution by gravity sedimentation for the recycle application.

3.7. Photocurrent response and EIS analysis The high separation efficiency of photoinduced electrons and holes in the photocatalysts is benefical for enhancing the photocatalytic activity [29], therefore, the transient photocurrent and EIS measurement are employed to study the interfacial charge separation efficiency and mobility for the g-C3N4, electrospun nanofibrous TiO2 and electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalyst. Seen from the Fig. 10(A), the electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalyst has the highest photocurrent density in comparison with the g-C3N4 and electrospun nanofibrous TiO2, which suggests that the separation efficiency and lifetime of photogenerated electrons is enhanced for the electrospun nanofibrous TiO2/g-C3N4 heterojunction photocatalyst, because the photocurrent is formed when the photogenerated electrons is migrated to the counter electrode. Moreover, EIS 10

Nyquist analysis can provide the valid evidence for the mobility of electrons at the interfacial of solid electrode, and the results are displayed in the Fig. 10(B), the diameter of EIS Nyquist plots for the electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalyst is smallest in contrast with the g-C3N4 and electrospun nanofibrous TiO2, which demonstrates that electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalyst possesses the lowest charge migrate resistance at the interfacial electrolyte solution of and electrode [9,31], thus the electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalyst displays the excellent photocatalytic activity.

3.8. Scavenger experiment of reactive species and photocatalytic mechanism In order to identify which reactive species plays the major role in the photocatalytic degradation process of RhB over the electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalyst, different quenchers of p-benzoquinone (BQ), triethanolamine (TEOA) and isopropanol (IPA) are utilized to trap the superoxide radical anion (O2·-), hole (h+) and hydroxyl radical (OH·), respectively [44]. Seen from the Fig. 11(a), when the quencher of IPA is charged into the photocatalytic degradation system, the photodegradation efficiency is slightly weakened, while the BQ and TEOA are introduced into the photocatalytic degradation system, respectively, the degradation of RhB are obviously inhibited. It’s confirmed that both the O2·- and h+ are the primary reactive species, and the OH· is the secondary reactive species for the degradation of RhB over the electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalyst. Based on the upper analysis and discussion, a potential Z-scheme photocatalytic mechanism of electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalyst is proposed by consulting the related references [7,18,29,30,50], which is vividly depicted in Fig. 11(b). When the electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalyst is irradiated by the simulated solar light,TiO2 and g-C3N4 can be motivated to yield h+ and e-, simultaneously, due to the internal electrostatic effect between the VB h+ of g-C3N4 and CB e- of TiO2, CB e- of TiO2 will migrate to the VB h+ of g-C3N4, and the combination h+ and e- is largely inhibited, extending the spacial distance between the CB e- of g-C3N4 and VB h+ of TiO2, therefore, the photocatalytic activity of TiO2/g-C3N4-4 heterojunction photocatalyst is remarkably improved [18,29,30,50]. In addition, the O2 is captured by CB e- of g-C3N4 to form O2·-, and the H2O or OH- is trapped by VB h+ of TiO2 to yield the OH·. Under the action of O2·-, h+ and OH·, the organic pollutant of RhB can be effectively degraded [7,35].

4. Conclusion In summary, a series of electrospun nanofibrous TiO2/g-C3N4 heterojunction photocatalysts with different TiO2 content are successfully synthesized via a facile electrospinning process and subsequent in situ evaporation and calcination process for the first time. The obtained TiO2/g-C3N4-4 heterojunction possesses the larger BET specific surface area of about 32.15 m2/g in comparision with g-C3N4 (11.19 m2/g), 11

Especially, on the basis of TG analysis and photodegradation experiments, the electrospun nanofibrous TiO2/g-C3N4-4 heterojunction with TiO2 content of 29.30 wt% possesses the best photocatalytic degradation efficiency among the g-C3N4, TiO2 and their mixture for the RhB under simulated sunlight irradiation, which is mainly attributed to the Z-scheme heterojunction between TiO2 and g-C3N4. HRTEM and element mapping images demonstrate the formation of TiO2/g-C3N4 heterojunction structure. PL spectra, photocurrent responses and EIS tests prove that TiO2/g-C3N4-4 heterojunction possesses a low recombination efficiency of electrons and holes. Therefore, the TiO2/g-C3N4-4 heterojunction maintains a relatively high photocatalytic activity after four cycles, which can bring about broad applications in the photocatalytic field.

Acknowledgments This work was supported by the Scientific and Technological Support Project of Hubei Province (Nos. 2015BAA100 and 2014BAA110), Hubei Province excellent Science and Technology Innovation Team Project (NO. T201407).

References [1] Z. Tong, D. Yang, T. Xiao, Y. Tian, Z. Jiang,;1; Biomimetic fabrication of g-C3N4/TiO2 nanosheets with enhanced photocatalytic activity toward organic pollutant degradation, Chem. Eng. J. 260 (2015) 117-125. [2] C.P. Sajan, S. Wageh, A.A. Al-Ghamdi, J. Yu, S. Cao,;1; TiO2 nanosheets with exposed {001} facets for photocatalytic applications, Nano. Res. 9 (2015) 3-27. [3] F. Chang, J. Zhang, Y. Xie, J. Chen, C. Li, J. Wang, J. Luo, B. Deng, X. Hu,;1; Fabrication, characterization and photocatalytic performance of exfoliated g-C3N4-TiO2 hybrids, Appl. Surf. Sci. 311 (2014) 574-581. [4] L. Gu, J. Wang, Z. Zou, X. Han,;1; Graphitic-C3N4-hybridized TiO2 nanosheets with reactive {001} facets to enhance the UV and visible-light photocatalytic activity, J. Hazard. Mater. 268 (2014) 216-223. [5] R. Hao, G. Wang, C. Jiang, H. Tang, Q. Xu,;1; In situ hydrothermal synthesis of g-C3N4/TiO2 heterojunction photocatalysts with high specific surface area for Rhodamine B degradation, Appl. Surf. Sci. 411 (2017) 400-410. [6] F. Wu, X. Li, W. Liu, S. Zhang,;1; Highly enhanced photocatalytic degradation of methylene blue over the indirect all-solid-state Z-scheme g-C3N4-RGO-TiO2 nanoheterojunctions, Appl. Surf. Sci. 405 (2017) 60-70. [7] B. Zhu, P. Xia, Y. Li, W. Ho, J. Yu, Fabrication and;1; photocatalytic activity enhanced mechanism of direct Z-scheme g-C3N4/Ag2WO4 photocatalyst, Appl. Surf. Sci. 391 (2017) 175-183. [8] S. Cao, J. Low, J. Yu, M. Jaroniec,;1; Polymeric photocatalysts based on graphitic carbon nitride, Adv. Mater. 27 (2015) 2150-2176. [9] B. Chai, J. Yan, C. Wang, Z. Ren, Y. Zhu,;1; Enhanced visible light photocatalytic degradation of Rhodamine B over phosphorus doped graphitic carbon nitride, Appl. Surf. Sci. 391 (2017) 376-383. 12

[10] B. Chai, X. Liao, F. Song, H. Zhou,;1; Fullerene modified C3N4 composites with enhanced photocatalytic activity under visible light irradiation, Dalton Trans. 43 (2014) 982-989. [11] J. Wen, J. Xie, X. Chen, X. Li,;1; A review on g-C3N4-based photocatalysts, Appl. Surf. Sci. 391 (2017) 72-123. [12] S. Ye, R. Wang, M. Wu, Y. Yuan,;1; A review on g-C3N4 for photocatalytic water splitting and CO2 reduction, Appl. Surf. Sci. 358 (2015) 15-27. [13] F. Dong, Z. Wang, Y. Li, W. Ho, S.C. Lee,;1; Immobilization of polymeric g-C3N4 on structured ceramic foam for efficient visible light photocatalytic air purification with real indoor illumination, Environ. Sci. Technol. 48 (2014) 10345-10353. [14] Y. Ma, E. Liu, X. Hu, C. Tang, J. Wan, J. Li, J. Fan,;1; A simple process to prepare few-layer g-C3N4 nanosheets with enhanced photocatalytic activities, Appl. Surf. Sci. 358 (2015) 246-251. [15] F. Li, Y. Zhao, Q. Wang, X. Wang, Y. Hao, R. Liu, D. Zhao,;1; Enhanced visible-light photocatalytic activity of active Al2O3/g-C3N4 heterojunctions synthesized via surface hydroxyl modification, J. Hazard. Mater. 283 (2015) 371-381. [16] X. Wang, W. Yang, F. Li, Y. Xue, R. Liu, Y. Hao,;1; In situ microwave-assisted synthesis of porous N-TiO2/g-C3N4 heterojunctions with enhanced visible-light photocatalytic properties, Ind. Eng. Chem. Res. 52 (2013) 17140-17150. [17] J. Xu, G. Wang, J. Fan, B. Liu, S. Cao, J.;1; Yu, g-C3N4 modified TiO2 nanosheets with enhanced photoelectric conversion efficiency in dye-sensitized solar cells, J. Power Sources 274 (2015) 77-84. [18] J. Yu, S. Wang, J. Low, W. Xiao,;1; Enhanced photocatalytic performance of direct Z-scheme g-C3N4-TiO2 photocatalysts for the decomposition of formaldehyde in air, Phys. Chem. Chem. Phys. 15 (2013) 16883-16890. [19] J. Wang, J. Huang, H. Xie, A. Qu,;1; Synthesis of g-C3N4/TiO2 with enhanced photocatalytic activity for H2 evolution by a simple method, Int. J. Hydrogen Energy 39 (2014) 6354-6363. [20] J. Lei, Y. Chen, F. Shen, L. Wang, Y. Liu, J. Zhang,;1; Surface modification of TiO2 with g-C3N4 for enhanced UV and visible photocatalytic activity, J. Alloy. Compd. 631 (2015) 328-334. [21] H. Zhu, D. Chen, D. Yue, Z. Wang, H. Ding,;1; In-situ synthesis of g-C3N4-P25 TiO2 composite with enhanced visible light photoactivity, J. Nanopart. Res. 16 (2014) 2632-2641. [22] R. Hao, G. Wang, H. Tang, L. Sun, C. Xu, D. Han,;1; Template-free preparation of macro/mesoporous g-C3N4/TiO2 heterojunction photocatalysts with enhanced visible light photocatalytic activity, Appl. Catal. B: Environ. 187 (2016) 47-58. [23] H. Xiao, W. Wang, G. Liu, Z. Chen, K. Lv, J. Zhu,;1; Photocatalytic performances of g-C3N4 based catalysts for RhB degradation Effect of preparation conditions, Appl. Surf. Sci. 358 (2015) 313-318. [24] K. Sridharan, E. Jang, T.J. Park,;1; Novel visible light active graphitic C3N4-TiO2 composite photocatalyst: synergistic synthesis, growth and photocatalytic treatment of hazardous pollutants, Appl. Catal. B: Environ. 142-143 (2013) 718-728.

13

[25] G. Song, Z. Chu, W. Jin, H. Sun,;1; Enhanced performance of g-C3N4/TiO2 photocatalysts for degradation of organic pollutants under visible light, Chinese J. Chem. Eng. 23 (2015) 1326-1334. [26] K. Dai, L. Lu, C. Liang, Q. Liu, G. Zhu,;1; Heterojunction of facet coupled g-C3N4/surface-fluorinated TiO2 nanosheets for organic pollutants degradation under visible LED light irradiation, Appl. Catal. B: Environ. 156-157 (2014) 331-340. [27] L. Zhang, D. Jing, X. She, H. Liu, D. Yang, Y. Lu, J. Li, Z. Zheng, L. Guo,;1; Heterojunctions in g-C3N4/TiO2(B) nanofibres with exposed (001) plane and enhanced visible-light photoactivity, J. Mater. Chem. A 2 (2014) 2071-2078. [28] X. Zhong, M. Jin, H. Dong, L. Liu, L. Wang, H. Yu, S. Leng, G. Zhuang, X. Li, J. Wang,;1; TiO2 nanobelts with a uniform coating of g-C3N4 as a highly effective heterostructure for enhanced photocatalytic activities, J. Solid State Chem. 220 (2014) 54-59. [29] J. Li, M. Zhang, Q. Li, J. Yang,;1; Enhanced visible light activity on direct contact Z-scheme g-C3N4-TiO2 photocatalyst, Appl. Surf. Sci. 391 (2017) 184-193. [30] J. Li, M. Zhang, X. Li, Q. Li, J. Yang,;1; Effect of the calcination temperature on the visible light photocatalytic activity of direct contact Z-scheme g-C3N4-TiO2 heterojunction, Appl. Catal. B: Environ. 212 (2017) 106-114. [31] J. Wang, W. Zhang,;1; Modification of TiO2 nanorod arrays by graphite-like C3N4 with high visible light photoelectrochemical activity, Electrochim. Acta 71 (2012) 10-16. [32] H. Yan, H. Yang,;1; TiO2-g-C3N4 composite materials for photocatalytic H2 evolution under visible light irradiation, J. Alloy. Compd. 509 (2011) 26-29. [33] C. Miranda, H. Mansilla, J. Yanez, S. Obregon, G. Colon,;1; Improved photocatalytic activity of g-C3N4/TiO2 composites prepared by a simple impregnation method, J. Photoch. Photobio. A 253 (2013) 16-21. [34] J. Li, E. Liu, Y. Ma, X. Hu, J. Wan, L. Sun, J. Fan,;1; Synthesis of MoS2/g-C3N4 nanosheets as 2D heterojunction photocatalysts with enhanced visible light activity, Appl. Surf. Sci. 364 (2016) 694-702. [35] Z. Huang, Q. Sun, K. Lv, Z. Zhang, M. Li, B. Li,;1; Effect of contact interface between TiO2 and g-C3N4 on the photoreactivity of g-C3N4/TiO2 photocatalyst: (001) vs (101) facets of TiO2, Appl. Catal. B: Environ. 164 (2015) 420-427. [36] M. Huang, J. Yu, Q. Hu, W. Su, M. Fan, B. Li, L. Dong,;1; Preparation and enhanced photocatalytic activity of carbon nitride/titania (001 vs 101 facets)/reduced graphene oxide (g-C3N4/TiO2/rGO) hybrids under visible light, Appl. Surf. Sci. 389 (2016) 1084-1093. [37] M. Reli, P. Huo, M. Sihor, N. Ambrozova, I. Troppova, L. Matejova, J. Lang, L. Svoboda, P. Kustrowski, M. Ritz, P. Praus, K. Kocí,;1; Novel TiO2/C3N4 photocatalysts for photocatalytic reduction of CO2 and for photocatalytic decomposition of N2O, J. Phys. Chem. A 120 (2016) 8564-8573. [38] M. Zang, L. Shi, L. Liang, D. Li, J. Sun,;1; Heterostructured g-C3N4-Ag-TiO2 composites with efficient photocatalytic performance under visible-light irradiation, RSC Adv. 5 (2015) 56136-56144.

14

[39] B. Sun, N. Lu, Y. Su, H. Yu, X. Meng, Z. Gao,;1; Decoration of TiO2 nanotube arrays by graphitic-C3N4 quantum dots with improved photoelectrocatalytic performance, Appl. Surf. Sci. 394 (2017) 479-487. [40] T. Yu, L. Liu, F. Yang,;1; Heterojunction between anodic TiO2/g-C3N4 and cathodic WO3/W nano-catalysts for coupled pollutant removal in a self-biased system, Chinese J. Catal. 38 (2017) 270-277. [41] S. Adhikari, G. Awasthi, H. Kim, C. Park, C. Kim,;1; Electrospinning directly synthesized porous TiO2 nanofibers modified by graphitic carbon ntride sheets for enhanced photocatalytic degradation activity under solar light irradiation, Langmuir 32 (2016) 6163-6175. [42] M. Wang, Z. Liu, M. Fang, C. Tang, Z. Huang, Y.g. Liu, X. Wu, Y. Mao,;1; Enhancement in the photocatalytic activity of TiO2 nanofibers hybridized with g-C3N4 via electrospinning, Solid State Sci. 55 (2016) 1-7. [43] J. Yan, S. Gao, C. Wang, B. Chai, J. Li, G. Song, S. Chen,;1; A facile electrospinning and direct annealing method for the fabrication of multi-porous ZnFe2O4 nanotubes with enhanced photocatalytic activity, Mater. Lett. 184 (2016) 43-46. [44] C. Wang, X. Tan, J. Yan, B. Chai, J. Li, S. Chen,;1; Electrospinning direct synthesis of magnetic ZnFe2O4/ZnO multi-porous nanotubes with enhanced photocatalytic activity, Appl. Surf. Sci. 396 (2017) 780-790. [45] F. Zhang, Z. Cheng, L. Kang, L. Cui, G. Hou, H. Yang,;1; A novel preparation of Ag-doped TiO2 nanofibers with enhanced stability of photocatalytic activity, RSC Adv. 5 (2015) 32088-32091. [46] R. Pawar, S. Kang, J. Park, J. Kim, S. Ahn, C. Lee,;1; Room-temperature synthesis of nanoporous 1D microrods of graphitic carbon nitride (g-C3N4) with highly enhanced photocatalytic activity and stability, Sci. Rep. 6 (2016) 31147. [47] O. Jayakumar, C. Sudakar, C. Persson, V. Sudarsan, T. Sakuntala, R. Naik, A. Tyagi,;1; 1D Morphology stabilization and enhanced magnetic properties of Co: ZnO nanostructures on codoping with Li: a template-free synthesis, Cryst. Growth Des. 9 (2009) 4450-4455. [48] P. Kuang, Y. Su, G. Chen, Z. Luo, S. Xing, N. Li, Z.;1; Liu, g-C3N4 decorated ZnO nanorod arrays for enhanced photoelectrocatalytic performance, Appl. Surf. Sci. 358 (2015) 296-303. [49] J. Lei, Y. Chen, L. Wang, Y. Liu, J. Zhang,;1; Highly condensed g-C3N4-modified TiO2 catalysts with enhanced photodegradation performance toward acid orange 7, J. Mater. Sci. 50 (2015) 3467-3476. [50] J. Low, C. Jiang, B. Cheng, S. Wageh, A.A. Al-Ghamdi, J. Yu,;1; A review of direct Z-Scheme photocatalysts, Small Methods 1 (2017) 1700080.



15

Fig. 1. Schematic representation of the fabrication of electrospun nanofibrous TiO2/g-C3N4 heterojunction photocatalysts via a facile electrospinning process combined with in situ evaporation and calcination process.

Fig. 2. SEM images of g-C3N4, electrospun nanofibrous TiO2/g-C3N4 heterojunction photocatalysts with different TiO2 content and TiO2 nanofiber: (a) g-C3N4, (b) TiO2/g-C3N4-1, (c) TiO2/g-C3N4-2, (d) TiO2/g-C3N4-3, (e) TiO2/g-C3N4-4, (f) TiO2/g-C3N4-5, (g) TiO2, EDX spectrums of TiO2 (h) and TiO2/g-C3N4-4 (i).

Fig. 3. TEM (a) and HRTEM images (b) of electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalysts, EDS element mapping of electrospun nanofibrous TiO2/g-C3N4-4 heterojunction catalyst: (c) EDS layer image, (d) N element, (e) O element, and (f) Ti element.

Fig. 4. FTIR spectra: (a) g-C3N4, (b) electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalysts, (c) TiO2 nanofiber.

Fig. 5. XRD patterns of electrospun nanofibrous TiO2/g-C3N4 heterojunction photocatalysts with different TiO2 content: (a) TiO2/g-C3N4-1, (b) TiO2/g-C3N4-2, (c) TiO2/g-C3N4-3, (d) TiO2/g-C3N4-4, (e) TiO2/g-C3N4-5.

Fig. 6. XPS spectra of electrospun nanofibrous TiO2/g-C3N4 heterojunction photocatalyst: (a) XPS survey spectrum, (b) C 1s spectrum, (c) N 1s spectrum, (d) O 1s spectrum and (e) Ti 2p spectrum.

Fig. 7. (A) TG curves of electrospun nanofibrous TiO2/g-C3N4 heterojunction photocatalysts with different TiO2 content: (a) g-C3N4, (b) TiO2/g-C3N4-1, (c) TiO2/g-C3N4-2, (d) TiO2/g-C3N4-3, (e) TiO2/g-C3N4-4, (f) TiO2/g-C3N4-5. (B) N2 sorption isotherm: (a) g-C3N4, (b) TiO2/g-C3N4-4.

16

Fig. 8. (A) UV-vis diffuse reflection absorption spectra and (B) PL emission spectra: (a) g-C3N4, (b) electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalyst, (c) TiO2 nanofiber.

Fig. 9. (A) Photocatalytic degradation RhB aqueous solution over different TiO2/g-C3N4 photocatalysts under simulated solar light irradiation and (B) Kinetics curves for the RhB photodegradation: (a) g-C3N4, (b) TiO2/g-C3N4-1, (c) TiO2/g-C3N4-2, (d) TiO2/g-C3N4-3, (e) TiO2/g-C3N4-4, (f) TiO2/g-C3N4-5, (g) TiO2, (h) no catalyst; (C) Comparison of photocatalytic activities for the degradation of RhB aqueous solution: (a) TiO2/g-C3N4-4, (b) TiO2/g-C3N4-4-mix; (D) Recycled photocatalytic degradation performance of TiO2/g-C3N4-4.

Fig. 10. (A) Transient photocurrent response, (B) EIS Nyquist profile: (a) g-C3N4, (b) TiO2 nanofiber, (c) electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalyst.

Fig. 11. (a) Effect of different quenchers on the degradation of RhB, (b) Schematic showing the Z-scheme photocatalytic mechanism of the electrospun nanofibrous TiO2/g-C3N4-4 heterojunction photocatalyst under the simulated sunlight irradiation.

Table 1. Recipes of the fabrication of electrospun nanofibrous TiO2/g-C3N4 heterojunction photocatalysts and the TG analysis results.

Table 1. Recipes of the fabrication of electrospun nanofibrous TiO2/g-C3N4 heterojunction photocatalysts and the TG analysis results Samples

MEL (g)

TiO2 (mg)

TiO2 content (wt%)*

g-C3N4

3.0

0

0 17

TiO2/g-C3N4-1

3.0

90

5.10

TiO2/g-C3N4-2

3.0

180

11.57

TiO2/g-C3N4-3

3.0

270

20.54

TiO2/g-C3N4-4

3.0

360

29.30

TiO2/g-C3N4-5

3.0

540

40.36

TiO2

0

---

100

* TiO2 content is obtained from the TG analysis result, which is based on the weight of electrospun nanofibrous TiO2/g-C3N4 heterojunction photocatalysts.

STRIKE TEXT FOUND PLEASE VERIFY IT FROM INPUT DOC FILE THEN DELETE IT IF NOT REQUIRE::::::******************** TDENDOFDOCTD

18

×

Report "g-C3N4 heterojunction photocatalyst under simulated solar light"

Your name

Email

Reason -Select Reason- Pornographic Defamatory Illegal/Unlawful Spam Other Terms Of Service Violation File a copyright complaint

Description

Close Send

Our partners will collect data and use cookies for ad personalization and measurement. Learn how we and our ad partner Google, collect and use data. Agree & close