Biotemplating Synthesis of Graphitic Carbon-Coated TiO2 and Its

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Bio-templating Synthesis of Graphitic Carbon Coated TiO2 and its Application as Efficient Visible-light-driven Photocatalyst for Cr6+ Remove Qing Cai, Chenglu Liu, Chaochuang Yin, Wei Huang, Lifeng Cui, Huancong Shi, Xueyou Fang, Lu Zhang, Shifei Kang, and Yangang Wang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b03126 • Publication Date (Web): 20 Mar 2017 Downloaded from http://pubs.acs.org on March 26, 2017

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ACS Sustainable Chemistry & Engineering

Bio-templating Synthesis of Graphitic Carbon Coated TiO2 and its Application as Efficient Visible-light-driven Photocatalyst for Cr6+ Remove Qing Cai1, Chenglu Liu1, Chaochuang Yin1, Wei Huang2, Lifeng Cui1, Huancong Shi1, Xueyou Fang1, Lu Zhang1, Shifei Kang1*,Yangang Wang1*

1. Department of Environmental Science and Engineering, University of Shanghai for Science and Technology, Shanghai, 200093, P.R. China. 2. State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing, 100012, P.R. China

*Corresponding authors: E-mail: [email protected], [email protected]

1

ACS Paragon Plus Environment


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ABSTRACT TiO2 and graphitic carbon (GC) composites with hierarchical pore structures were synthesized using Staphylococcus aureus (ATCC6538) as the bio-template to modify Degussa P25 TiO2 power. Then the composites were applied as photocatalysts for Cr6+ reduction under visible light irradiation. X-ray diffraction, Raman spectroscopy, transmission electron microscopy, nitrogen adsorption-desorption analysis, and X-ray photoelectron spectroscopy demonstrated the presence of a GC coating layer and a unique anatase/rutile mixed crystal phase of TiO2 even after heating at 800 oC. The novel TiO2@GC composites, especially the S-P25-800 sample, which possessed abundant hierarchical mesoporous structures, exhibited strong catalytic activities in Cr6+ photoreduction under visible light. This work provides light to overcome the challenge on synthesis of GC modified TiO2 photocatalysts with the highly reactive but heat-labile anatase main crystal phase at high temperature. Furthermore, the present results demonstrated that TiO2@GC heterojunctions has a great potential to be used as efficient and economical photocatalysts for environmental contaminants remove. KEYWORDS TiO2, graphitic carbon, visible-light-driven photocatalyst, Cr6+ reduction INTRODUCTION TiO2 as an n-type semiconductor photocatalyst has received much attention because it is able to address the worldwide energy and environmental problems due to its optical stability, low cost and non-toxicity.1 Nowadays, owing to their high photocatalytic activity under ultraviolet light, many commercial TiO2 products are widely used as photocatalysts in photochemical reactions. It is well-known that TiO2 has a wide band-gap energy of 3.2 eV, so when illuminated by photons at proper energy (< 400 nm), it can excite electrons jumping from the valence band to the conductive band, thereby generating electrons (e−) and holes (h+). Then these electron–hole pairs produce a series of oxidation or reduction reactions,2, 3 such as the reduction of highly toxic Cr6+ into hypotoxic Cr3+.4-7 Despite many benefits, some disadvantages still hinder the commercialization of TiO2 photocatalysts in the 2


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environmental energy field. Due to the wide band-gap energy, TiO2 can be activated simply by ultraviolet light which accounts for only 4%–5% of the sunlight. To efficiently utilize the visible region or the largest proportion of the solar spectrum, researchers find that it is a trend to develop visible-light-driven (VLD) TiO2 photocatalysts.8 However, the photocatalytic activity of these VLD photocatalysts is also restricted by the rapid recombination of photo-generated electron-hole pairs.8,9 Therefore, overcoming these weaknesses and forming high-performance TiO2-based VLD photocatalysts is a critical demand. To overcome the fast charge recombination and the limited visible-light absorption of TiO2, researchers have developed many strategies in recent years, such as textural design,9,10 metal or nonmetal ions doping,11-14 noble metals loading,15,16 dye sensitization and semiconductor heterojunction.17-19 Among these strategies, the construction of semiconductor heterojunction has attracted much attention due to its perfect effectiveness in improving photocatalytic activity. In particular, TiO2-carbon heterojunction systems have attracted much attention in photocatalytic applications because of the slow recombination of photogenerated electron-hole pairs, the extended excitation wavelength, and the increased surface-adsorption of reactant species.20-22 Recently, heterojunction systems of graphitic carbon (GC) and TiO2 have been proved to be effective to improve the photocatalytic activity of TiO2 under visible light. GC is considered as cheap and highly electron-conductive, and thus is appearing in design and construction of TiO2@GC heterojunction systems.23 Among all the TiO2 photocatalysts, Degussa P25 is the commercial benchmark TiO2 powder which consists of 80% of the anatase phase and 20% of the rutile phase of titanium dioxide. This unique mixcrystal structure allows the fast transport of photo-generated charges and thus has excellent photocatalytic activity under ultraviolet light. In attempt to design and construct TiO2@GC heterojunction as a high-performance VLD photocatalyst, researchers recommend P25 as the first choice of already-made titanium source. However, without a special protection mechanism, the mixcrystal structure of P25 TiO2 can only be maintained bellow 600 ºC, while the GC formation temperature is usually over 800 ºC.14 Thus, to synthesize TiO2@GC 3



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heterojunctions, we have to suppress the phase transition of P25 TiO2 by encountering a valid protecting agent. Additionally, the high temperature in GC formation also would severely decrease the pore structure and active sites of carbon. Recently, Zhu’s team prepared a GC-layer-coated hybridized TiO2 photocatalyst by a hydrothermalcalcination method, with glucose used as both the carbon source and the P25 mixcrystal protecting agent.22 Overall, the photocatalytic activity of TiO2@GC heterojunction under visible light was still unsatisfactory and the synthetic methods reported were usually low-yield, time-consuming and even bring further pollution. Recently, environmental-friendly methods, especially biosynthesis methods, have gained more attention in the chemical and engineering fields because of their simplicity and sustainability.24-27 In particular, bacteria and algae, due to their special multi-component and hollow porous structures, are recognized as advanced carbon sources and biotemplate to prepare functional nanomaterials. In this work, Staphylococcus aureus (ATCC6538) was used as the template to form P25-based TiO2@GC heterojunctions through a simple biosynthesis technique. Specifically, commercial P25 was added into the culture medium of S. aureus where the bacterium served as a carbon precursor as well as a pore-forming agent and a P25 phase transition suppressing agent for the first time. The TiO2@GC photocatalysts were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Brunauer Emmett and Teller (BET) area, X-ray photoelectron spectroscopy (XPS), Raman spectra and their photocatalytic activities were tested by photocatalytic reduction of Cr6+ under visible light. The formation of these heterojunctions and the hierarchical pore generation mechanism of S. aureus were also proposed and discussed. EXPEIMENTAL SECTION Synthesis of TiO2@GC Composites The GC coating layer was produced by using a strain of S. aureus 6538 obtained from American type culture collection (ATCC). S.aureus is a Gram-positive bacterium belonging to Firmicutes,28 whose cells are spherically-shaped with an average diameter of 0.8 µm and composed walls of 20-80 nm thick. Due to the simple internal 4


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structure of the microorganism, the thick cell walls contributed mostly to the dry weight of S. aureus. The cell walls were rich in teichoic acid, teichuroic acid and surface protein, and thus were considered as an N- and P- enriched carbon source. The medium main raw materials yeast extract and peptone were purchased from OXIDE Corp., England. NaCl of analytical grade (Shanghai Chemical Corp.) was used without further purification. Liquid Luria-Bertani medium was prepared by sterilization at 121 oC and natural cooling the mixed water solution containing 5 g of yeast extract, 10 g of peptone, and 10g of NaCl per liter. The TiO2@GC composites using the S. aureus template were synthesized in two steps. First, S. aureus (ATCC6538) was cultured on the liquid Luria-Bertani medium to form a saturated bacterial solution, which was added with 0.2g/200ml of P25. Second, after two days of culture at 37 oC, the binded S. aureus/P25 mixture was concentrated by 10,000 r/min centrifugation and washed with deionized water and ethanol to remove the spent medium. Then the yellow mixture was dried at 60oC overnight. Finally, the solid precursors were transferred into a quartz crucible and heated at a ramp of 5 oC/min up to 550, 800 or 1100 oC for 4h under a N2 flow in the tube furnace. The black products were labeled as S-P25-X, where X (=550, 800, 1100) was the calcination temperature. For the control experiment, a P25-800 sample was synthesized after calcination at 800oC under the same heat-treatment conditions. Characterization The crystal structural of the S-P25-X photocatalysts were investigated on a Bruker D8 Advance X-ray diffractometer (XRD) with Cu-Kα radiation, operated at 40 kV and 40 mA (scanning step: 0.02o/s) in the 2θ range of 10-80o. The X-ray photoelectron spectroscopy (XPS) data were obtained with an ESCALAB 250 XPS meter with Al Kα monochromatization. The Raman spectra were recorded on a Horiba XploRA Raman microscope using a 532 nm argon ion laser. Nitrogen adsorption-desorption isotherms at 77 K were measured on a automated volumetric apparatus NOVA2000e (Quantachrome Instruments, USA) to determine the Brunauer–Emmett–Teller (BET) surface area, pore volume, porosity, Barret–Joyner–Halenda (BJH) pore size and distribution. The micro-morphologies were observed on a transmission electron 5



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microscope (TEM, JEOL JEM-2010) at an acceleration voltage of 200 kV. Electron spin resonance (ESR) measurements were operated by a Bruker EMX-8/2.7 spectrometer at 77 K. The electrochemical Impedance Spectroscopy (EIS) data were performed on an electrochemical works tation (CHI 660E Chenhua Instrument Company, Shanghai, China) based on a conventional three-electrode system with a frequency range from 0.01 Hz to 100 kHz at the circuit potential. Photocatalytic Experiments Cr6+ was selected as the target pollutant to evaluate the photocatalytic performances. The experiments were conducted under a 500W xenon lamp with a 420 nm filter. In each experiment, 30 mg of a sample was dispersed into 50 mL of 40 mg/L Cr6+ solution under magnetic stirring. The reaction should be carried out in a 2.0~3.0 pH, which was adjust with HNO3, and add 1g EDTA to per 1L 40 mg/L Cr6+ solution as sacrificial agent. Prior to light irradiation, the suspensions were stirred in the dark for 40 min to allow the catalyst and Cr6+ solution to reach the adsorption/desorption equilibrium. Then the light was turned on, 0.3 mL of a solution was collected every 20 min and centrifuged to separate the solid catalyst. Then the Cr6+ concentration was tested on the UV-Vis spectrophotometer at 540 nm. RESULTS AND DISCUSSION Structure Characteristics XRD patterns of bare P25, P25-800 and S-P25-550, S-P25-800, S-P25-1100 in Figure1a show the peaks at 2θ = 25.3, 37.8, 48.0, 53.9, 55.1, 62.7, 68.9, 70.3 and 75.1o, which can be indexed to (101), (004), (200), (105), (211), (204), (116), (220) and (215) crystal planes of anatase TiO2. Moreover, the patterns clearly show the peaks of rutile TiO2, namely, the planes (110), (101) and (111) at 2θ of ca. 27.4, 36.1, 41.2º, respectively.1 No diffraction patterns from carbon species were detected, which was probably because the main characteristic peak of GC at 24.5o was concealed by the peak of anatase TiO2 at 25.4 º.7 As showed in Figure1, S-P25-550 and S-P25-800 were both composed of a mixture of anatase and rutile TiO2 (which was nearly the same crystal composition as P25 TiO2), while the anatase phase in S-P25-1100 and P25-800 was almost transformed into rutile. It is well-known that the anatase-to-rutile 6


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phase transformation occurs at around 600oC.29 However, we found that the anatase phase in GC-modified P25 TiO2 was sustained even above this temperature, suggesting that the presence of S. aureus (ATCC6538) carbide atop the P25 restrained its phase transformation, thus increasing the thermal stability. The crystalline phase of TiO2 and the existing state of carbon species in the representative S-P25-800 were further investigated by Raman spectra. The Raman spectra of S-P25-800 show five high-intensity Raman modes at 145, 196, 395, 515 and 635 cm-1(Figure 1b), which agree well with the typical Raman features of anatase TiO2 phase and confirm that TiO2 is in the main anatase phase. Meanwhile, the Raman spectrum of S-P25-800 also shows two characteristic peaks at about 1372 and 1592 cm-1,24 which correspond to the D-band and G-band of carbon, respectively. The low peak integrated relative intensity of the D-band to G-band clearly indicates the high carbon graphitization degree in S-P25-800.30,31 To study the surface element composition and chemical states of elements in S-P25-X, we carried out XPS on the representative S-P25-800. The XPS results of S-P25-800 in Figure 1c-f clearly exhibit the typical photoelectron peaks of C, O and Ti elements, which confirm the presence of these three elements. The survey spectra of S-P25-800 also show the Ti 2p (Figure1d), C 1s (Figure 1e) and O 1s (Figure1f) peaks. The Ti 2p spectrum of S-P25-800 shows two symmetrical peaks with binding energies at 459.4 and 465.1eV,32 which are attributed to Ti 2p3/2 and Ti 2p1/2, respectively. The separation gap between these two peaks is 5.7eV, slightly larger than the reported energy split of neat TiO2, which may be due to the encapsulation of TiO2 in GC. As shown in Figure 3c, the O1s binding energy (BE) at 530.5 eV may be attributed to TiO2, while the peak at 531.6 eV may originate from surface hydroxyl groups or adsorbed H2O, which accord well with the fitted C 1s peaks. Figure 1e displays the high-resolution spectrum at C 1s of S-P25-800 fitted to three peaks. The strong peak at 284.4 eV is attributed to graphitic carbon, while the peak at 285.1 eV can be assigned to disordered carbon or oxidant carbon. The peak around 286.1 eV is ascribed to the existence of C-OH and C-O-C bonds. There is no peak at 289 eV, which suggests the absence of carbonate species. This reveals that the oxygen sites in 7



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the TiO2 lattices maybe are partly substituted by carbon atoms to form a C-Ti-O structure.14,33-35 Compared to former reports, the GC peak is considerable, demonstrating the wide presence of GC because of the carbonization of bacteria source. Textural Properties and Morphology The textural properties of bare P25, P25-800 and S-P25-X obtained from N2 adsorption-desorption analysis are shown in Figure 2. Clearly, the isotherm curves of all samples exhibit a strong uptake of N2 as a result of capillary condensation in a wide range of relative pressure (P/P0) = 0.55-0.95, which suggests the existence of mesoporosity. The pore size distributions were determined by analyzing the absorption branch of the isotherms. All S-P25-X catalysts possess a bimodal pore size distribution centered at about 2.1 and 4.0 nm, while the bare P25 only shows a single pore distribution peak centered at around 2.0 nm (Figure 2b-c). The ~2 nm pores can be ascribed to the close packed gap of P25 nanoparticles, and the ~4 nm mesopores may originate from the gap between uncoated carbon species and P25 nanoparticles, which increased in S-P25-1100 at a higher temperature by deep graphitization. The N2 adsorption-desorption curves clearly prove the existence of hierarchical pore structure of S-P25-X, and this unique characteristic can be preserved after high-temperature treatment. Moreover, the calculated textural data in Table 1 and pore distribution properties show that the P25-800 formed in the absence of S. aureus has a much lower limited SBET compared with bare P25. Also the SBET change of S-P25-X is complex, so we

deduce the mesopore formation in the P25/bacterial mixture as below. First, with the temperature rise within 550 oC, the bacterial body broke into small pieces, which attached onto the P25 nanoparticles, but after the preliminary carbonization, the SBET of S-P25-550 decreased to 7.8 m2/g, which is significantly lower than bare P25 (52.3 m2/g).This decrease of SBET was due to the sintering effect of carbon and also the particle aggregation with the presence of amorphous carbon. When the temperature was up to 800 oC, the organic elements such as C, H, N and O produced abundant evaporated gas and GC layers were formed atop the TiO2, thus generating small pores 8


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between the bacterium and P25 and enlarging the SBET of S-P25-800 to 25.7 m2/g. Afterwards, at the temperature up to 1100 oC, the graphite degree of the bacterial carbon increased, so the SBET of S-P25-1100 reduced to 19.4m2/g. The SBET of S-P25-800 was higher than P25-800, indicating the addition of the bacterium benefited the mesoporous structure formation, in which the bacterium served as both a carbon source and a pore-forming agent. Mesoporous semiconductors are considered as excellent catalysts for environmental pollutant photo decomposition and water splitting due to the enhanced active sites and increased surface adsorption of reactant species. S-P25-800, which exhibits good crystallinity and abundant hierarchical pores, can be considered as an active photocatalyst. Figure 3 depicts the TEM images of bare P25, P25-800 and representative S-P25-800 sample. Clearly, the particles of S-P25-800 are roughly spherically-shaped and the particle sizes are distributed within 20 nm (Figure3c), which are similar as P25 without annealing, indicating the uniform particle size distribution can be maintained even after calcination under 800 oC. The high-resolution TEM image (Figure3d) shows that the particles of P25 are coated with a thin GC layer, which confirms the presence of the GC layer in the S-P25-800 sample,36 The clear lattice fringes for the identification of crystallographic spacing indicate a high crystallinity of P25.The lattices paces of 0.35 and 0.32 nm respectively correspond to the (101) and (110) plane of anatase TiO2 and rutile TiO2.37, 38 These results indicate that the unique mixture phase of anatase and rutile in P25 can be maintained during the heat treatment, which is also confirmed by the XRD patterns. The TEM, XRD, Raman and XPS together indicate that S-P25-800 consists of a TiO2 crystal core inside the GC shell. Photocatalytic Performance The probe reaction to investigate the photocatalytic performance of each catalyst was performed through Cr6+ photoreduction under visible light irradiation (Figure 4a). It can be found that bare P25 and graphitic carbon have almost no photoactivity on Cr6+ reduction, while S-P25-X composites exhibit significant progress, indicating a synergetic effect between TiO2 and graphitic carbon in the composites. Among S-P25-X, the S-P25-800 shows the highest performance and nearly 100% 9



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decomposition after 240 min. Whereas the photoreduction rates on S-P25-550 and S-P25-1100 are both lower than 50%. The excellent photocatalytic performance of S-P25-800 may be attributed to the co-presence of TiO2 with mixed crystal structure and the GC coating layer, which can achieve an ideal visible light harvest and a good charge pair separation rate. The carbon source S. aureus plays a crucial role in protecting the mixed crystal structure of P25 TiO2 even up to 800 oC. Without the protection, sample such as P25-800 cannot maintain the unique mixed crystal structure and have a very limited photocatalytic activity. To determine the stability of S-P25-X, we tested the repeated usage effect of S-P25-800 for reduction. All cycles of experiments were conducted under the same conditions. As shown in Figure 4b, the 5 cycles of recycled usage produced about 90% reduction of Cr6+, indicating that the efficiency of Cr6+ removal by S-P25-800 was sustainable and consistent. In other words, GC strongly interacted with P25 due to its strong chemisorption with TiO2 where it was not easily removed even after 5 cycles of repeated usage. To understand the role of potential oxygen vacancies on the improved Cr6+ reduction in S-P25-X composites, electron spin resonance (ESR) spectra of the bare P25, P25-800 and representative S-P25-800 sample were examined and the results were shown in Figure 4c. It can be seen that, for the bare P25 and P25-800, no apparent signal is detected. In contrast, for the S-P25-800, a symmetrical, sharp signal appearing at g = 2.004 gives confident evidence that the synthesized S-P25-800 sample contains a large number of oxygen vacancies.39,40 These oxygen defects may originate from the reduction of TiO2 concurrently with generation of GC, and the presence of oxygen vacancies is beneficial to photo-induced electrons transfer during photocatalytic process. In addition, electrochemical impedance spectroscopy (EIS) analysis is also utilized to investigate the photogenerated charge separation of as-prepared photocatalysts. Figure 4d shows the EIS Nynquist plots of bare P25, P25-800 and S-P25-800. The arc radius on the EIS Nynquist plot of S-P25-800 is smaller than that of P25 TiO2. The smaller arc radius of an EIS Nynquist plot indicates the higher efficiency of charge separation. Thus, in the case of S-P25-800, 10


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the photo induced electron-hole pairs are more easily separated and transferred to the catalyst surface due to the presence of oxygen defects and the surface coating of GC,23 thus the photo induced electrons and holes are separated more efficiently through the GC and TiO2 interfacial interaction. Overall, hierarchical mesoporous TiO2@GC composites were synthesized by a simple biosynthesis method and subsequent a calcination process. This approach involves S. aureus as a carbon source and a pore-forming agent. Due to the excellent suppressing effect of S. aureus on phase transition, the TiO2@GC composites contain GC as well as the ideal mixed crystal structure of TiO2. Therefore, the synthesis mechanism of S-P25-X was proposed (Figure 5). Thanks to its unique crystal structure and hierarchical mesopores, the TiO2@GC composites outperformed bare P25 TiO2 under visible light irradiation. The enhanced photocatalytic performance for the TiO2@GC composites can be ascribed to their unique structure with the following favorable properties: i) the hierarchical mesoporous structure with a relative high surface area can provide more active sites and increase surface adsorption of reactant species on the surface of composite photocatalysts; ii) the introduction of black graphitic carbon in TiO2@GC composite can effectively improve the light absorption in visible region; iii) the presence of graphitic carbon with high electrical conductivity as well as oxygen vacancies can greatly enhance photoinduced electron-hole separation efficiency for mixcystal structure of TiO2, and resulting in the improvement of photocatalytic activity under visible light irradiation. CONCLUSIONS We present a facile biotemplating method to fabricate TiO2@GC composites. The S. aureus (ATCC6538) used in this work acted as a low-cost biotemplate to induce unique hierarchical structures, and also as a sustainable carbon source to construct porous matrices by the decomposition of carbonaceous organics. Owing to the unique mixed crystal structure of TiO2 and hierarchical mesopores, the TiO2@GC composite catalysts displayed superior performance in Cr6+ photoreduction under visible light. We believe this green and economical photocatalyst is a promising candidate for treatment of energy and environmental problems. Also this work is expected to extend 11



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the scope of biotemplated synthesis to other nanomaterials for various applications.

ACKNOWLEDGEMENTS This work was supported by National Natural Science Foundation of China (Grant No. 51528202 21103024 51671136 and 51502172), "Shu Guang" project (Grant No. 13SG46) supported by Shanghai Municipal Education Commission and Shanghai Education Development Foundation, Technology Development Project of University of Shanghai for Science and Technology and Capacity-Building of Local University Project by Science and Technology Commission of Shanghai Municipality (Grant No. 12160502400).

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Figure legends Table.1 Textural properties of P25, P25-800 and S-P25-X catalysts. Figure 1 (a) XRD patterns of bare P25 and S-P25-X (r-Rutile phase; a-Anatase phase). (b) Raman spectra of bare P25 and S-P25-800. (c) XPS survey spectra and corresponding high-resolution spectra of Ti 2p (d) C 1s (e), O 1s (f) in S-P25-800. Figure 2 (a) N2 adsorption-desorption isotherms and (b-c) pore size distribution curves of P25, P25-800 and S-P25-X samples. Figure 3 TEM images of (a) bare P25, (b) P25-800, and (c-d) S-P25-800 sample. Figure 4 (a) Photocatalytic efficiency of S-P25-800 upon recycled applications in the photoreduction of Cr6+. (b) Photocatalytic performances of different catalysts in Cr6+ reduction under visible light irradiation. (c) Electron spin resonance (ESR) spectra of bare P25，P25-800 and S-P25-800. (d) Electrochemical impedance spectroscopy (EIS) Nynquist plots of bare P25， P25-800 and S-P25-800. Figure 5 Schematic diagram of the synthesis process of S-P25-X sample based on

Staphylococcus aureus bacteria.

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Figure 1 (a) XRD patterns of bare P25 and S-P25-X (r-Rutile phase; a-Anatase phase). (b) Raman spectra of bare P25 and S-P25-800. (c) XPS survey spectra and corresponding high-resolution spectra of Ti 2p (d) C 1s (e), O 1s (f) in S-P25-800.

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Figure 2 (a) N2 adsorption-desorption isotherms and (b-c) pore size distribution curves of P25, P25-800 and S-P25-X samples.

Table.1 Textural properties of P25, P25-800 and S-P25-X catalysts. Sample P25 P25-800 S-P25-550 S-P25-800 S-P25-1100

SBET(m2/g ) 52.3 19.8 7.8 25.7 19.4

Pore size(nm) ) 2.0 / 1.9 3.8 2.4 3.9 2.1 4.0

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Pore volume(cm3/g) 1.018 0.205 0.069 0.298 0.042


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Figure 3 TEM images of (a) bare P25, (b) P25-800, and (c-d) S-P25-800 sample.

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Figure 4 (a) Photocatalytic efficiency of S-P25-800 upon recycled applications in the photoreduction of Cr6+. (b) Photocatalytic performances of different catalysts in Cr6+ reduction under visible light irradiation. (c) Electron spin resonance (ESR) spectra of bare P25，P25-800 and S-P25-800. (d) Electrochemical impedance spectroscopy (EIS) Nynquist plots of bare P25， P25-800 and S-P25-800.

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.

Figure 5 Schematic diagram of the synthesis process of S-P25-X sample based on

Staphylococcus aureus bacteria.

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Table of Contents Graphic

Bio-templating Synthesis of Graphitic Carbon Coated TiO2 and its Application as Efficient Visible-light-driven Photocatalyst for Cr6+ Remove Qing Cai, Chenglu Liu, Chaochuang Yin, Wei Huang, Lifeng Cui, Huancong Shi, Xueyou Fang, Lu Zhang, Shifei Kang*,Yangang Wang* A facile biotemplating method was used to fabricate TiO2@GC composite catalysts which displayed superior performance in Cr6+ photoreduction under visible light.

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Biotemplating Synthesis of Graphitic Carbon-Coated TiO2 and Its

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