TiO2 nanocomposite and their enhanced photocatalytic activity

Accepted Manuscript Title: Glutaraldehyde assisted synthesis of collagen derivative modified Fe3+ /TiO2 nanocomposite and their enhanced photocatalytic activity Author: Chongyi Li Feng Xue Enyong Ding Xiaoling He PII: DOI: Reference:

S0169-4332(15)01959-5 http://dx.doi.org/doi:10.1016/j.apsusc.2015.08.146 APSUSC 31093

To appear in:

APSUSC

Received date: Revised date: Accepted date:

20-4-2015 25-7-2015 17-8-2015

Please cite this article as: C. Li, F. Xue, E. Ding, X. He, Glutaraldehyde assisted synthesis of collagen derivative modified Fe3+ /TiO2 nanocomposite and their enhanced photocatalytic activity, Applied Surface Science (2015), http://dx.doi.org/10.1016/j.apsusc.2015.08.146 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.

Glutaraldehyde assisted synthesis of collagen derivative modified Fe3+/TiO2 nanocomposite and their enhanced photocatalytic activity Chongyi Li, Feng Xue, Enyong Ding*, Xiaoling He College of Material Science and Engineering, South China University of Technology,

ip t

Guangzhou 510641, PR China *

Corresponding author. Tel./fax: +86 20 87111290

an

us

cr

E-mail address: [email protected] (E. Ding).

M

Highlights

The cationic collagen derivative was successfully synthesized by introducing the

d

(2-methacryloyloxyethyl) trimethyl ammonium chloride (DMC) monomers onto

Ac ce pt e

the collagen backbone, which was extracted from the leather shavings. The Fe-doped TiO2 nanosphere with the average diameter about 125 nm was

fabricated, which showed the strong absorption in the visible region and narrower band gap, in addition, significant change in the crystal phase composition was also observed, due to Fe3+ ions diffusing into TiO2 lattice. The collagen-g-PDMC was chemically immobilized onto the Fe3+/TiiO2 surface

depending on the bridging effect of glutaraldehyde, because double –CHO groups could react with the –NH2 groups from hydroxylysine or lysine and the surface –OH groups of Fe3+/TiiO2, which also revealed the relatively lower PL intensity. The photocatalyst CFT-3 performed the best in the photocatalytic degradation of methyl orange under the solar irradiation because of the synergistic effect brought

Page 1 of 40

by Fe3+ ions doping and immobilized collagen-g-PDMC on the surface.

ip t

ABSTRACT A unique organic-inorganic hybrid nanocomposite was designed and synthesized

cr

by chemically anchoring the cationic collagen-based derivatives onto the surface of

us

Fe3+/TiO2 nanospheres for the significant enhancement in photocatalytic activity under the visible light irradiation. The NMR analysis suggested the successful fabrication of

an

cationic collagen-g-PDMC as grafted materials. In addition, the chemical structures, morphologies and properties of these samples were systematically characterized by

M

Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Raman spectrum, Ultra violet visible spectroscopy (UV–Vis), scanning electron microscopy

d

(SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy

Ac ce pt e

(XPS) and photoluminescence (PL). And obtained results clearly demonstrated that Fe3+ ions diffusing into TiO2 lattice could be responsible for slightly reducing the average diameter of nanospheres to about 125 nm, promoting phase transition from anatase to rutile to some extent and extending the light harvesting range into visible region markedly. Meanwhile, the achievement that collagen-g-PDMC molecules had been covalently immobilized onto the surface of Fe3+/TiO2 nanoparticles was also well supported by the information acquired. Furthermore, the photocatalytic activities of all the as-prepared products were carefully evaluated by adopting photocatalytic decoloration of methyl orange (MO) solution under the solar direct irradiation, and the sample CFT-3 performed the best in the photocatalytic degradation process, which was mainly attributed to the energetic synergistic effect brought about by Fe3+ ions

Page 2 of 40

doping and collagen-g-PDMC molecules immobilized on the surface. Keywords: collagen derivative; modified Fe3+/TiO2; synthesis; photocatalytic activity 1. Introduction It is well-known that among the various techniques for purifying environment,

ip t

semiconductor photocatalysis, an eco-friendly and clean method, has drawn much greater attention in the hot fields of photochemistry and environmental protection. In

cr

particular, Titanium dioxide (TiO2), as one of the most promising photocatalyst with

us

outstanding performances on wastewater and air purification[1-4], has won extensive popularity due to its easy availability, low cost and very high catalytic activity for

an

decomposing the toxic organic pollutants without special selectivity in the wastewater. However, significant importance should also be attached to the several fatal

M

limitations, such as the lower photo-quantum yield, higher recombination rate of charge carriers and the indispensable requirement of ultraviolet radiation (λ<400 nm)

d

for initiating the excitation because of the broad band gap about 3.2 ev, which have

Ac ce pt e

greatly restricted its scope in practical applications. Since UV light accounts for only a small fraction (4%) of the solar energy compared to visible light (43%), therefore, the increasingly strong demand for developing a cost-effective and efficient TiO2 based photocatalyst highly responsive to visible light is growing urgently[5-7]. In the last decade, the strategies for the improvement of photocatalytic efficiency

by effectively modifying the structure of TiO2 have become the research focus for a long time. And various advanced techniques have also been emerging in multitude in order to farthest narrow the bad gap and facilitate the separation of photo-generated electron-hole pairs[8-15]. As we know that the substantial reduction of band gap is an important guarantee to optimize the TiO2 solar light harvesting capability, by contrast, ions doping can be regarded as a quite significant attempt, which primarily involved

Page 3 of 40

the introduction of transition metal ions[16, 17] as well as nonmetal ions[18, 19] into the band structure of TiO2. But extremes meet, too high doping level will do harm to the photocatalytic reaction oppositely in that excess foreign impurity could serve as the recombination centers of charge carriers possibly, which is also the first issue

ip t

required to be solved for achieving the efficient photocatalytic activity naturally. In addition, a massive amount of documented evidences indicate that ions codoping has

cr

exactly proved to be a reasonably effective measure for the better improvement in

us

band gap as well, which is capable of offering much more new ways to extend the light absorption range of TiO2 particles into the visible region by taking advantage of

an

multiple dynamic combination of various ions with different energy band structures. Meanwhile, many such types of observations are easily found in the open literatures at

M

present[20-24]. Typically, an encouraging discovery was widely reported by Segomotso Bagwasi et al[25], where they prepared bismuth and boron co-doped TiO2

d

nano-powders capable of strongly responding to visible light. Similarly, E. Padmini et

Ac ce pt e

al[26] in their work had successfully fabricated the vanadium-cerium doped TiO2 NPs with exceptionally superior photocatalytic activity. Moreover, the other ions like cobalt[27], iron[28], carbon[29, 30], sulfur[31] and zinc[32] also seem to fairly benefit for transforming the preference of pristine TiO2 particles into the visible light significantly. Furthermore, another effective approach to improve the photocatalytic efficiency is to form the functional heterostructure by purposely depositing a small number of noble metal nanoparticles onto the TiO2 surface and hence help to increasing the light absorption efficiency and sensitivity at the higher wavelength to some extent. When compared with the other kinds of noble metals, the current interests have been mainly driven to massively use silver as the greatest promising candidate for realizing the above-mentioned desired objectives because of its strong

Page 4 of 40

electron trapping ability and distinct price advantage; in this case, majority of the study reports have presented lots of quite satisfactory findings[33-37]. For instance, a relevant result found by L. Gomathi Devi et al[38] clearly indicated that the only 0.05 percent loading sliver on the surface of TiO2 grains could dramatically enlarge the

photocatalytic performance for the oxidative degradation of phenol.

ip t

applied range of light into the visible region and further considerably maximize the

cr

From the perspective of solar energy utilization and much faster photocatalytic

us

efficiency, specifically designing a new organic-inorganic nanohybrid photocatalyst, synthesized by chemically immobilizing cationic modified collagen onto the surface

an

of ions doped TiO2 nanoparticles, should be the nice alternative, which could provide a bran-new means to greatly boost the enhancement in photocatalytic activity via the

M

structure-induced synergistic effects, namely, visible light driven TiO2 nanoparticles and surface covalent combination of cationic collagen-based derivatives both have

d

their advantages to work together, which will be in favor of giving full play to the

Ac ce pt e

following positive interaction that electrostatic attraction and photodegradation of poisonous dyes can simultaneously proceed with common promotion. Nevertheless, to the best of our knowledge, as yet there are few records on the fabrication of cationic collagen-based derivatives bound to the Fe3+ ions doped TiO2 particles surface for the significantly enhanced photocatalytic oxidation of azo dyes wastewater. In the present work, the idea related to covalently immobilization of cationic

collagen-based derivatives onto the surface of Fe3+/TiO2 nanoparticles was concerned, aiming to develop a novel efficient photocatalyst for decomposing the toxic pollutants under solar direct irradiation, and this kind of new nanocomposite was synthesized by adopting a simple and facile two-step method. Apart from different characterization tests used for determining the structures, composition and properties of these resultant

Page 5 of 40

products, the corresponding mechanism used to explain the significant enhancement in the photocatalytic activity was also proposed. 2. Experimental 2.1 Materials

ip t

Homemade collagen powders, which were directly extracted from the chromed leather shavings by using alkali hydrolysis; ceric ammonium nitrate (CAN, AR grade),

cr

(2-methacryloyloxyethyl) trimethyl ammonium chloride (DMC, 75 wt% water

us

solution; AR grade), Fe(NO3)3·9H2O (Ferric nitrate nonahydrate, AR grade) and titanium tetrachloride (TiCl4, AR grade) were supplied by Aladdin Industrial was

an

Corporation, China; glutaraldehyde (GA, 25 wt% water solution; AR grade)

obtained from Sinopharm Chemical Reagent Co., China. Deionized water was used

M

throughout the whole study, and all the chemicals were used as received without further purification.

d

2.2 Synthesis of collagen-g-PDMC

Ac ce pt e

A given amount of collagen powders were dissolved in the deionized water with

constant stirring under N2 atmosphere until this solution became clear and yellowish; followed that a certain amount of ceric ammonium nitrate as initiator was added into the above solution; and then the DMC aqueous solution was dropwise added within 30 min after 10 min of pretreatment by the initiators to trigger abundant active grafting points on the collagen backbone, and the weight ratio between collagen and DMC was fixed at 1:3. The reaction system was protected by N2 atmosphere in the whole process. After reacting at 50 ℃ for 5 h, the primary product was precipitated in the excess absolute alcohol and then collected through filtration. Furthermore, the obtained crude product was extracted for 48 h in Soxhlet apparatus by using acetone as the solvent to remove impurities contained in the product. Finally, the purified

Page 6 of 40

product, named collagen-g-PDMC, was vacuum-dried at 60 ℃ for 48 h. 2.3 Preparation of the pristine TiO2 The pristine TiO2 NPs were prepared by controlled hydrolysis of TiCl4 in ethyl alcohol/water mixture. Typically, 2 mL of TiCl4 was firstly dissolved in the 20 mL of

ip t

absolute ethanol rapidly at room temperature; followed that the obtained chartreuse solution was dropwise added into 100 mL of ethanol/water mixture (volume ratio

cr

about 1:5) under constant stirring within 60 min. After reacting at 80 ℃ for 5 h, the

us

resultant products were collected by centrifugation and then washed with ethanol and water repeatedly. Finally, the white powers were vacuum-dried at 60 ℃ for 48 h.

an

2.4 Preparation of Fe3+/ TiO2 NPs

The procedures for preparing Fe3+ ions doped TiO2 NPs were very similar to

M

those for fabricating TiO2 NPs, and the only difference mainly lied in that 0.18 mmol

d

of Fe(NO3)3·9H2O salt was dissolved in the ethanol/water mixture in advance. In

Ac ce pt e

addition, the other steps were the same as the fabrication of TiO2 NPs. By the way, the resultant yellowish powers were named Fe3+/TiO2. 2.5 Preparation of collagen-g-PDMC molecules bound to the Fe3+/TiO2 surface Based on the positive bridging effect brought by glutaraldehyde, the cationic

collagen-g-PDMC molecules could be chemically anchored onto the surface of Fe3+/TiO2 nanoparticles, because double -CHO groups were highly reactive with both –NH2 groups of hydroxylysine or lysine and –OH groups on the Fe3+/TiO2 surface. Briefly, about 2 mL of GA was firstly added into 100 mL of dispersion of Fe3+/TiO2 nanoparticles (1 wt%) with constant stirring, adjusted to pH 3.0 using dilute H2SO4 solution, and heated at 60 ℃, which was very favorable for the formation of surface modified Fe3+/TiO2 nanoparticles by the aldol condensation reaction between –CHO and surface –OH groups. Then, a given amount of collagen-g-PDMC powders were

Page 7 of 40

added into the above mixture in the form of solution with continuous stirring for the another 24 h at the same temperature, followed that the cross-linking period was finished, and the obtained primary products were rinsed with deionized water and alcohol for several times. Finally, the resultant products were vacuum-dried at 60 ℃

ip t

until became completely dry. By the way, the weight feeding percentage between collagen-g-PDMC powders and Fe3+/TiO2 powders were fixed at 3 wt% and 6 wt%,

cr

and the corresponding samples were named CFT-3 and CFT-6, respectively.

1

us

2.6 Characterization

H NMR spectra of the virgin collagen and collagen-g-PDMC powders were

an

obtained on a Bruker AVANCE Model DRX-500 spectrometer, operating at 500 MHz and using D2O as the solvent. The photocatalyst were evaluated by using Fourier

M

transformed infrared spectrometer (Nicolet Co.,MAGNA-IR760) with KBr pellet method in the range of wave numbers from 650 cm-1 to 3800 cm-1. Raman spectra of

d

the pristine TiO2, Fe3+/TiO2, CFT-3 as well as CFT-6 were also measured by using

Ac ce pt e

LabRAM Aramis laser Raman Spectrometer excited at 457.9 nm. The crystal structure of all the samples were recorded by the X-ray diffraction (XRD) performed on a MSALXD2 with Cu Kα radiation (40 kV, 20 mA, λ=1.54051 Å) at a scanning rate of 5°/min for 2θ ranging from 5° to 90°. Ultra violet visible spectroscopy (UV-Vis) measurement of all the products were performed on a UNICAM UV-500 UV-Vis spectrophotometer operated at a resolution of 1 nm. The photo-luminescence emission spectrum of all the samples were obtained by using Fluoromax~4 spectrofluorometer. The surface composition and elemental chemical states of the sample CFT-3 was identified by X-ray photoelectron spectroscopy with Al Kα radiation (XPS, Kratos Axis Ultra DLD, hv=1486.6 eV). SEM analysis was taken out by using the field emission scanning electron microscopy (NovaNanoSEM 430) operated at an

Page 8 of 40

accelerating voltage of 10 kV. Transmission electron microscopy analysis (TEM) was performed by using FEI Tecnai 12 instrument operated at an accelerating voltage of 200 kV. EDS analysis was carried out by energy dispersive X-ray spectrometry (JEOL-2010) using an accelerating voltage of 200 kV.

ip t

2.7 Evaluation of the photocatalytic activity The photocatalytic activities of all the as-prepared samples were assessed by the

cr

photocatalytic degradation of methyl orange (MO) solution under solar radiation from

us

11:00 to 14:00 in sunny days, when the solar intensity could reach the maximum. In a typical experiment performed at room temperature, a certain amount of photocatalyst

an

(about 80 mg) was firstly added into the 100 mL of MO solution with an initial concentration of 20 mg/L. After stirring for 3 min, the stabilized suspension was

M

placed in an open field for furthest absorbing the direct solar radiation and always kept still. Meanwhile, about 4 mL of samples were withdraw from the mixture at

d

regular time intervals of 15 min and then centrifuged to separate the photocatalyst.

Ac ce pt e

The residual concentration of MO solution was detected by UV-Vis spectrophotometer, and the intensity change of absorbance peak around 510 nm could be used to evaluate the photodegradation extent of MO solution. Similarly, the controlled experiment without adding any photocatalyst was also carried out, but as the irradiation time went on, the variation in concentration of MO solution could be negligible completely. 3. Results and discussion 3.1 NMR analysis

The chemical structures of collagen and the corresponding grafted product were characterized by 1H NMR spectroscopy presented in Fig.1. As previously expected, the signals from both of the two samples investigated were too intricate and indistinguishable to provide the definite peak identification, which was determined

Page 9 of 40

essentially by the complex ingredients of collagen, because collagen consisted of a series of different amino acids. However, in the case of collagen-g-PDMC, the striking differences were still clearly observed compared with collagen. Typically, the significant enhancements in the following four strongly sharp peaks located at 1.08

ip t

ppm, 2.14 ppm, 3.15 ppm and 3.56 ppm were assigned to the Hb protons from CH3-Cgroups, He protons from –N(CH3)3Cl groups, Hd protons from –CH2-N- groups and Hc

cr

from O=C-O-CH2- groups, respectively, which all came from the modified monomer

us

DMC. Apparently, the presence of these additional peaks could well support the fact that successful grafting PDMC chains onto the collagen backbone had taken place,

an

which was very attractive to MO molecules with negative charges because of the strong electrostatic interaction. In addition, there was also an inconspicuous peak

M

available at δ=1.56 ppm belonging to Ha protons, whose relatively intensity almost showed little change in comparison with that of collagen, indicating that the abundant

d

saturated –CH2- groups were supposed to exist in the collagen chains. Moreover, the

Ac ce pt e

grafting ratio of collagen-g-PDMC was estimated as 69.6% by precisely calculating the relatively area of the corresponding characteristic peaks. 3.2 FTIR analysis

The FTIR spectra of the pristine TiO2, Fe3+/TiO2 as well as the counter samples

chemically surface-modified by collagen-g-PDMC were illustrated in Fig.2. As was seen clearly that the spectrum of pristine TiO2 was the almost same as that of Fe3+/TiO2, indirectly indicating that the most of Fe3+ ions had penetrated into TiO2 lattices and no other iron-containing compounds were found. Specifically, a very strong peak located at 620 cm-1 was caused by the bending vibration of O-Ti-O bonds, while the other very broad peak approximately centered around 3400 cm-1 could be distinctly assigned to the stretching vibration of surface -OH groups and the absorbed

Page 10 of 40

water attached to lattice defect points, implying that the existence of abundant surface highly active –OH groups not only could provide innumerable reactive sites for the subsequent surface modification, but also benefited for the photocatalytic reaction. In addition, the small peak attributed to the bending vibration of –OH groups appeared at

ip t

1628 cm-1. However, by contrast, in the case of CFT-3 and CFT-6, there were some obvious additional bands present in comparison with the pristine TiO2. Typically, the

cr

new band not available before around 1242 cm-1 was very explicitly ascribed to C-O

us

stretching vibration from acetal structure, which was the most powerful evidence to demonstrate that aldolization reactions between surface –OH groups of Fe3+/TiO2 and

an

active –CHO groups from glutaraldehyde had taken place. Moreover, the presence of other peaks respectively located at 1660 cm-1 (amide I, C=O stretching), 1542 cm-1

M

(amide II, N-H bending vibration), 1443 cm-1 (C-N stretching in C-NH2), 1156 cm-1 (-CH2- wagging vibration), 1058 cm-1 (C-N stretching), 2971 cm-1 (-CH3 asymmetric

d

stretching) and 2932 cm-1 (-CH2- symmetric stretching) could also definitely confirm

Ac ce pt e

the successful immobilization of collagen-g-PDMC molecules onto the surface of Fe3+/TiO2 particles, because of bridging effect caused by glutaraldehyde. Furthermore, based on the comparison of relative intensities of the above-mentioned characteristic peaks, a clear conclusion could be easily drawn that grafting amount of CFT-6 was significantly superior to that of CFT-3. 3.3 UV-Vis analysis

The optical absorption properties of as-prepared products were also investigated,

and their corresponding UV-Vis absorption spectra were displayed in Fig.3(A). As references reported previously[39], the pristine TiO2 showed the greatly intense light absorption only in the UV region (λ<400 nm) and had no interest in visible light, which primarily arose from its much broader band gap. By contrast, the absorption

Page 11 of 40

edge of Fe3+/TiO2 showed significant red shift in that the sample showed much more evident light harvesting capability at the wavelength range from 420 nm to 600 nm in the visible region, suggesting that the new energy levels formed by Fe species were responsible for the reduction of band gap and could donate excited d-electrons for

ip t

readily producing free charge carriers when stimulated by visible light, which subsequently transferred to conduction band very quickly. The collagen-g-PDMC

cr

molecules were anchored onto the surface of Fe3+/TiO2 nanoparticles, which would

us

certainly exert important influence over their capacities of light absorption. For the CFT-3, the optical absorptivity was almost less affected because of the lower grafting

an

amount of modified collagen. However, in the case of CFT-6, larger grafting amount of cationic collagen derivatives obviously deteriorated the light harvesting to some

M

extent, which was mainly caused by the prominent physical shielding effect due to excess encapsulation of collagen-g-PDMC molecules on the surface. And on this basis,

d

the band gap energy (Eg) was approximately estimated from the diagram by plotting

Ac ce pt e

(Ahυ)1/2 against hυ as shown in Fig.3(B), while the optical absorption threshold (λg) could also be simply calculated by using the following equation: λg = 1240/Eg. By assuming that TiO2 was an indirect bandgap semiconductor, Eg value of Fe3+/TiO2 had been significantly narrowed from 3.18 eV to 2.26 eV, correspondingly, λg value of Fe3+/TiO2 also dramatically shifted from 389.9 nm to 548.7 nm, which clearly indicated that Fe3+ ions doped samples designed were capable of making more efficient use of the sunlight. 3.4 XRD analysis The crystal structure of the pristine TiO2, Fe3+/TiO2 and corresponding samples chemically surface-modified by collagen-g-PDMC molecules were also investigated by employing XRD for evaluating the variation of crystal phase composition. As

Page 12 of 40

distinctly shown in Fig.4, the data for the pristine TiO2 exhibited a series of diffraction peaks located at 25.3°, 37.6°, 48.0°, 54.3°, 55.1°, 62.8°, 69.0°and 75.1°, corresponding to the crystal plane (101), (004), (200), (105), (211), (204), (220) and (215), respectively, which matched very well with the face-center cubic (fac)

ip t

structured anatase phase (JCPDS No. 21-1272), indicating that pristine TiO2 was primarily characterized by anatase phase despite the presence of a trace amount of

cr

brookite, which was confirmed by the characteristic peak around 30.8°. However,

us

significant changes in the crystalline structure were visibly observed due to Fe3+ ions doping. Several new additional characteristic peaks at 27.3°, 36.1°and 41.3° could be

an

definitely assigned to crystalline plane (110), (101) and (111) of rutile phase , respectively, indicating that Fe3+ ions diffusing into TiO2 lattice helped to promoting

M

the phase transition from anatase to rutile to some extent in the proposed synthesis route. In addition, none of diffraction patterns assigned to the other iron-containing

d

compounds was found, suggesting most of Fe3+ ions had been firmly fixed inside the

Ac ce pt e

TiO2 lattice. Furthermore, the rutile content of CFT-6 was significantly higher than that of CFT-3, which might be attributed to the much longer drying time that the sample CFT-6 underwent in the vacuum-drying period. 3.5 Raman analysis

The structural characterization of all the as-prepared samples were also further

accomplished by employing the Raman technique, and the corresponding Raman spectra were presented in Fig.5. As shown in Fig.5(A), in addition to the strongest peak around 150.6 cm-1, the pristine TiO2 also showed several relatively broad and weak bands located at 198 cm-1, 399 cm-1, 515 cm-1 and 638 cm-1, corresponding to the following five Raman active modes belonging to anatase including Eg(1)，Eg(2), B1g(3), A1g+B1g(2), and Eg(5), respectively,. And not only that, trace amounts of

Page 13 of 40

brookite and rutile were detected in the pristine TiO2 as well, which were definitely confirmed by the presence of the fairly feeble peaks at 320 cm-1, 367 cm-1 and 448cm-1. Similarly, the other group of peaks at 212 cm-1, 254 cm-1, 320 cm-1 and 367 cm-1 could be severally attributed to the B1g, Ag, B1g and B2g modes of brookite,

ip t

while a series of bands present around 442 cm-1,448 cm-1 and 611 cm-1 were assigned to Eg, Eg and A1g modes classified as rutile, respectively. But compared with the

cr

pristine TiO2, the most significant changes for the Fe3+ ions doped products were

us

mainly concentrated on the emergence of the two new strong peaks assigned to rutile and the prominent enhancement in the peaks ascribed to brookite, which was the

an

convincing proof for supporting that Fe3+ ions dopant contributed to transforming the phase states of TiO2 from anatase into rutile and brookite partially. Likewise, no

M

characteristic peaks assigned to iron-containing compounds could be detected, and the obtained results were well consistent with XRD test. In addition, it was clearly seen in

d

Fig.5(B) that the Raman spectra for the samples CFT-3 and CFT-6 in the range from

Ac ce pt e

1000 cm-1 to 3000 cm-1 showed some evident characteristic bands located at 1081 cm-1, 1194 cm-1, 1325 cm-1, 1418 cm-1, 1512 cm-1, 1605 cm-1, 1696 cm-1, 1831 cm-1, 2871 cm-1 and 2939 cm-1, corresponding to C-N stretching, C-C bonds, -CH2wagging, benzene ring, C-N bending, C=O stretching, -N(CH3)3+ deformation, O=C-O stretching, -CH3 stretching and –CH2- stretching, respectively, which also provided the adequate proof once again for demonstrating the fact that the expectation of synthesizing collagen-g-PDMC molecules bound to the Fe3+/TiO2 surface by virtue of bridging effect caused by glutaraldehyde was achieved. 3.6 Morphology analysis The microstructures of the as-prepared pristine TiO2 and CFT-3 were observed directly by employing TEM and SEM, and the corresponding images were taken and

Page 14 of 40

given in Fig.6. As clearly shown in Fig.6(a), in spite of their powerful trends to roughly aggregate, the unmodified TiO2 nanoparticles were almost perfectly spherical in shape and possessed a relatively narrower particle size distribution with the average diameter about 140 nm. By contrast, the morphology of CFT-3 was significantly

ip t

affected by both of the surface immobilized collagen-g-PDMC molecules and Fe3+ ions doping. Obviously, a much denser and closer agglomerated tendency was clearly

cr

observed in Fig.6(b), because of the presence of many positively charged –N(CH3)3+

us

groups on the surface of Fe3+/TiO2 nanoparticles, which was most likely to arouse such intense stacking interactions among the particles that the creation of much huger

an

aggregations was induced. In addition, Fe3+ ions diffusing into TiO2 lattice still kept the particles in spherical structure and contributed to the moderate reduction of mean

M

particle size to about 125 nm, indicating the growth of TiO2 nanocrystals were slightly restricted by Fe3+ ions doping. Moreover, based on the Fig 6(c) and (d), a similar

d

conclusion could be readily drawn that compared with the CFT-3, which mainly

Ac ce pt e

showed the much larger blocky structures, the relatively uniform nanoparticles were remain faintly visible in the pristine TiO2 powders. This discrepancy was completely rooted in their different surface composition. In fact, the accurate images for intuitively reflecting the firm immobilization of collagen-g-PDMC molecules onto the surface of Fe3+/TiO2 nanoparticles could hardly be available, which was primarily ascribed to the much less grafting amounts. However, the EDS spectra analysis of the sample CFT-3 could provide valid data for confirming their existence and were illustrated in Fig.6(e) and (f), which showed the apparent peaks related to C and N elements but no signal assigned to Cl element, which was attributed to its very low levels under the limits of detection. 3.7 PL measurement

Page 15 of 40

In order to investigate the various motion modes of the excited charge carriers including trapping, migration, transfer and separation in semiconductor, PL spectra was carried out for providing reliable information in this regard since the rapid recombination of photoinduced electron-hole pairs was absolutely indispensable for

ip t

the generation of PL emission. Fig.7 presented the recorded PL spectra of all the as-prepared samples by employing an excitation wavelength of 320 nm. As was

cr

clearly seen in Fig.7 that the strongest peak around 397.6 nm for pristine TiO2

us

corresponded to the emission of band gap transition of anatase phase, and this process simultaneously released the just energy equivalent to the radiation emitted by the

an

activated electrons falling back from conduction band bottom to valance band top. Significantly, the peak corresponding to the band gap transition for the doped products

M

had distinctly shifted to 421 nm, which was completely attributed to the remarkable changes in crystal phase composition caused by the penetration of Fe3+ ions dopant,

d

and the overwhelmingly strong fluorescence quenching were also observed in this

Ac ce pt e

case. The lower PL intensities suggested the slower recombination rate of free charge carriers and hence predicted the higher photocatalytic efficiency accordingly, which indicated that excited electrons could be effectively trapped by the Fe3+ ions dopant. In addition, the peak around 437.5 nm was ascribed to the surface recombination transition, while the other two peaks located at 450 nm and 467 nm respectively, were assigned to bound excitonic PL, which happened by reason of the presence of the abundant surface oxygen vacancies and defects[38]. Furthermore, the PL intensity of CFT-3 reached the minimum level in all those samples, because the novel groups (-O-C-O-Ti) formed by aldol condensation reaction could further serve as the suitable acceptors to capture the photoinduced electrons, which was responsible for the effective separation of excited electron-hole pairs and hence striking enhancement in

Page 16 of 40

photocatalytic activity. On the contrary, excess surface bonding sites (-O-C-O-Ti) would become the potential recombination centers possibly, which could facilitate the rapid recombination of charge carriers oppositely. Obviously, this deduction was fully confirmed by the PL result of CFT-6 as well.

ip t

3.8 XPS analysis The surface information was quite important for further analyzing the structural

cr

features of photocatalysts, thus XPS technique was performed to determine the

us

chemical states and composition of the elements present on the surface of CFT-3. Fig.8 illustrated the survey XPS spectrum of the CFT-3 as well as the corresponding

an

high-resolution spectra of several surface elements. As was shown in Fig.8(a) that in addition to Ti and O, some other elements including C, N and Cl were also found,

M

indicating that successful anchoring collagen-g-PDMC molecules onto the surface of Fe3+/TiO2 nanoparticles had taken place. Typically, from the high-resolution spectrum

d

of Ti2p shown in Fig.8(b), the two individual peaks located at 458 eV and 463.7 eV

Ac ce pt e

could be assigned to Ti2p3/2 and Ti2p1/2, respectively; and their corresponding peak separation was about 5.7 eV, which was not only in good agreement with the accepted binding energy value for TiO2, but also suggested Ti existed in the form of Ti4+ state. Moreover, diverse C1s peaks were distinctly observed in Fig.8(c) and could be given definite identification. As previously reported[40], the peak at 284.5 eV could be assigned to collagen backbone and carbon tape possibly caused by the environment, while the presence of C-N bonds (285.0 eV), C-O bonds (286.5 eV), C=O bonds (287.8 eV) and benzene ring (291.7 eV) also well provided the strong evidences for supporting the effective surface immobilization of collagen-g-PDMC molecules. Furthermore, in the deconvolution of O1s shown in Fig.8(d), the binding energy at 529.1 eV, 528.9 eV, 530.5 eV, 531.4 eV and 533.5 eV were attributed to Ti-O bonds,

Page 17 of 40

Fe-O bonds, surface hydroxyl groups (O-H), C-O bonds and C=O bonds, respectively. However, an important focus should be paid close attention to was that the relative intensity of peak assigned to C-O bonds was significantly enhanced in comparison with that of C=O bonds, which primarily benefited from the occurrence of aldol

ip t

condensation for producing more -C-O-Ti- bonds on the Fe3+/TiO2 surface. Similarly, the high-resolution spectrum of Fe2p depicted in Fig.8(e) provided the two extremely

cr

weak signals around 712 eV and 721.5 eV, corresponding to Fe2p3/2 and Fe2p1/2

us

respectively, which indicated that Fe3+ ions could be substituted for Ti4+ ions and incorporated into the TiO2 lattice, because of their similar radius values. In addition, a

an

much weaker signal at 706.9 eV suggested the presence of Fe2+ ions, which might be explained by the fact that at the surface defect sites of Fe3+/TiO2 particles, a small

M

number of surface Fe3+ irons were able to accept electrons from -NH2 groups of the surface immobilized collagen-g-PDMC molecules and then reduced to Fe2+ ions.

d

3.9 Photocatalytic activity evaluation and the enhanced mechanism for CFT-3

Ac ce pt e

The photocatalytic activities of the as-prepared samples were carefully evaluated

by measuring the photocatalytic degradation of methyl orange (MO) solution used as a model pollutant under solar direct irradiation at room temperature. In order to learn more about the reaction kinetics features of MO degradation catalyzed by the various samples, the relationship between ln(Co/C) and irradiation time was also established with the help of data obtained from photodegradation test and illustrated in Fig.9(a). (where C and Co represented the residual concentration at a moment and the initial concentration of MO solution, respectively.) As was clearly seen in Fig.9(a), it could be predictable that compared with the other samples, the pristine TiO2 performed the worst under the same condition, because of the complete insensitivity to the visible light caused by the wider band gap. Moreover, one credible reason why the negligible

Page 18 of 40

degradation efficiency (about 14%) was still achieved within such a short time (120 min) was that in addition to the visible light, the sun also radiated ultraviolet in small amounts, which could activate pristine TiO2 to produce reactive oxygen species for degrading MO molecules, and infrared light, which was primarily responsible for

ip t

initiating the self-photosensitized decomposition of MO molecules[41]. By contrast, the significant enhancement in the photocatalytic activity was obviously observed for

cr

the CFT-3, whose maximal degradation efficiency could reach 96% approximately.

us

Apparently, both Fe3+ ions doping and the appropriate surface immobilization of collagen-g-PDMC molecules contributed a lot to the greatly improved photocatalytic

an

reaction, which were in favor of the higher light harvesting capability in the visible region and rapidly promoting MO molecules to migrate towards the Fe3+/TiO2 surface,

M

respectively. Nevertheless, as might be expected previously, excess concentration of collagen-g-PDMC molecules would cover the surface of Fe3+/TiO2 particles, which

d

not only partly deteriorated the capability of light absorption due to physical shielding

Ac ce pt e

effect, meanwhile, too many bonding sites might also act as recombination centers oppositely to seriously reduce the lifetimes of photogenerated charge carriers, and all these potentially discouraged the photocatalytic oxidation process of MO molecules. Therefore, the degradation rate of CFT-6 was substantially inferior to that of CFT-3. As for Fe3+/TiO2, depending on the relatively weak self-diffusion derived from concentration gradient, MO molecules moved onto the particle surface quite slowly. On account of the absence of surface immobilized collagen-g-PDMC molecules to provide power for attracting MO molecules in comparison with CFT-3, the much slower degradation rate and the lower degradation efficiency about 73% were undoubtedly logical. In addition, the degradation process of all the samples coincided well with the

Page 19 of 40

pseudo first order reaction dynamic model, and the corresponding kinetic constants (k) were roughly estimated for pristine TiO2, Fe3+/TiO2, CFT-3 and CFT-6, which were 1.08×10-3 min-1, 10.48×10-3 min-1, 26.21×10-3 min-1 and 19.92×10-3 min-1, respectively. Apparently, the larger constant usually suggested much faster reaction

ip t

rate, indicating that CFT-3 performed the best in the photocatalytic degradation of MO solution, by which the photocatalytic oxidation initiated took place far more than

cr

20 times faster than that started by pristine TiO2 under direct solar irradiation. This

us

significant improvement in photocatalytic activity should be mainly ascribed to the synergistic effect brought about by both of Fe3+ ions doping and surface immobilized

an

cationic collagen-g-PDMC molecules.

Based on the experimental results and analysis, a reasonable mechanism used to

M

account for the significant enhancement in photocatalytic activity of CFT-3 under direct solar radiation was also proposed, and the corresponding schematic diagram

d

was illustrated in Fig.9(b). As shown in Fig.9(b), the positively charged –N(CH3)3+

Ac ce pt e

groups were present on the surface of Fe3+/TiO2 nanoparticles, which came from the surface immobilized collagen-g-PDMC molecules, thus there were strong electrostatic attractions between –N(CH3)3+ groups and negatively charged MO molecules, which could provide a key and targeted driving force for speeding up the process that MO molecules quickly migrated onto the Fe3+/TiO2 surface to establish the adsorption equilibrium. And CFT-3 obviously possessed the capability required for accelerating this directional migration of MO molecules. In addition, the rigorous band structure of TiO2, originally only active in the UV region, was also significantly improved by creating two new impurity energy levels within the band gap of TiO2 due to Fe3+ ions doping, which could effectively facilitate photoelectrons rapid transfer from the lower energy state to conduction band. Consequently, both of narrow band gap and striking

Page 20 of 40

enhancement in visible light harvesting capability were acquired simultaneously for the CFT-3. Under the solar irradiation, for the dopant energy level (Fe3+/Fe4+) above the valance band of TiO2, a Fe3+ ion was readily oxidized into Fe4+ ion by gaining one photon and simultaneously emitting a conduction band electron, which would rapidly

ip t

migrate onto the surface of TiO2 particles and then reduced the absorbed oxygen to produce superoxide radical (·O2-) immediately. Additionally, the accumulated Fe4+

cr

ions or h+ along with the formed ·O2- radicals could further react with the absorbed

us

water molecules to generate hydroxyl radicals (·OH) of higher activity, which were responsible for quickly accomplishing the photocatalytic degradation of MO solution.

an

Obviously, Fe3+ ions were also able to serve as hole trapping centers for promoting the efficient charge separation. Similarly, for the other impurity energy level (Fe2+/Fe3+)

M

below the conduction band, because of the relative instability of 3d-orbit electrons in Fe2+ ions, the liberated electrons could induce the formation of a series of highly

d

active species above-mentioned as well, which could be in favor of powerfully

Ac ce pt e

accelerating the progress of photocatalytic degradation even further. Meanwhile, equivalent compensation charges were received from the valance band of TiO2. Furthermore, grafting sites could also provide enough space as electron trapping centers for accepting excited electrons. Taking into consideration the presence of abundant -O-C-O-Ti- bonds formed by aldol condensation reaction on the surface, the oxygen atoms would attract free electrons to settle down in the empty orbit to some extent, because of their strong electron-withdrawing properties. Attributing to the comprehensive influences of these factors, the rapid recombination of photoinduced electron-hole pairs was strongly inhibited. This enhanced photocatalytic degradation pattern, involving the rapid directional migration of MO molecules and efficient supply of excited charge carriers, would not stop until the complete depletion of MO

Page 21 of 40

molecules, which hence greatly improved the photocatalytic reaction rate and the degradation efficiency of CFT-3. 4. Conclusions In summary, a novel nanocomposite, namely collagen-g-PDMC bound to the

ip t

Fe3+/TiO2 surface, was synthesized by adopting a facile and simple two-step approach including the controlled hydrolysis of TiCl4 and the surface immobilization of cationic

cr

collagen-g-PDMC molecules by virtue of bridging effect induced by glutaraldehyde.

us

NMR analysis suggested the successful grafting PDMC chains onto the collagen backbone. And the morphologies observation from TEM and SEM measurements

an

indicated that in spite of their strong tendencies to form much larger agglomeration in comparison with the pristine TiO2, the CFT-3 showed the nearly regular spherical

M

structure with the mean diameter about 125 nm. In addition, phase transition from anatase to rutile was significantly promoted by Fe3+ ions diffusing into the TiO2

d

lattices, which was also well confirmed by XRD patterns and Raman spectra. UV-Vis

Ac ce pt e

analysis revealed that Fe3+ ions doping contributed a lot to both of the remarkable enhancement in visible light harvesting capability and considerable reduction of band gap. Moreover, cationic collagen-g-PDMC molecules had been successfully anchored onto the surface of Fe3+/TiO2 particles, which was evidently supported by the results from FTIR, EDS, and XPS analysis, while photoluminescence (PL) analysis implied that the rapid recombination of photoinduced electron-hole pairs were effectively inhibited, because of Fe3+ ions doping and the suitable surface immobilization of collagen-g-PDMC molecules. Furthermore, the CFT-3 showed the best performance in photocatalytic degradation of methyl orange (MO) solution under direct solar irradiation. Correspondingly, a reasonable mechanism was also put forward to explain this significantly accelerated photocatalytic process. As we could imagine, the unique

Page 22 of 40

CFT-3 nanocomposite was able to be regarded as a promising potential alternatives for the extensive application in the wastewater treatment field in the future. Acknowledgements The authors are sincerely grateful for the financial support from the National

ip t

Natural Science Foundations of China (Nos.21075043) and the Fundamental Research Funds for the Central Universities (No.2011ZM0008).

cr

References

us

[1] X. Li, X. Zou, Z. Qu, Q. Zhao, L. Wang, Photocatalytic degradation of gaseous toluene over Ag-doping TiO2 nanotube powder prepared by anodization coupled with

an

impregnation method, Chemosphere, 83 (2011) 674-679.

[2] Y. Gao, H. Wang, J. Wu, R. Zhao, Y. Lu, B. Xin, Controlled facile synthesis and

M

photocatalytic activity of ultrafine high crystallinity TiO2 nanocrystals with tunable anatase/rutile ratios, Applied Surface Science, 294 (2014) 36-41.

d

[3] M.A. Nawi, I. Nawawi, Preparation and characterization of TiO2 coated with a

Ac ce pt e

thin carbon layer for enhanced photocatalytic activity under fluorescent lamp and solar light irradiations, Applied Catalysis A: General, 453 (2013) 80-91. [4] Q. Wu, C.-C. Yang, R. van de Krol, A dopant-mediated recombination mechanism in Fe-doped TiO2 nanoparticles for the photocatalytic decomposition of nitric oxide, Catalysis Today, 225 (2014) 96-101.

[5] J. Lu, F. Su, Z. Huang, C. Zhang, Y. Liu, X. Ma, J. Gong, N-doped Ag/TiO2 hollow spheres for highly efficient photocatalysis under visible-light irradiation, RSC Advances, 3 (2013) 720-724. [6] S. Ko, C.K. Banerjee, J. Sankar, Photochemical synthesis and photocatalytic activity in simulated solar light of nanosized Ag doped TiO2 nanoparticle composite, Compos Part B: Engineering, 42 (2011) 579-583.

Page 23 of 40

[7] A. Khanna, V.K. Shetty, Solar light induced photocatalytic degradation of Reactive Blue 220 (RB-220) dye with highly efficient Ag@TiO2 core–shell nanoparticles: A comparison with UV photocatalysis, Solar Energy, 99 (2014) 67-76. [8] M.R. Bayati, M. Aminzare, R. Molaei, S.K. Sadrnezhaad, Micro arc oxidation of

ip t

nano-crystalline Ag-doped TiO2 semiconductors, Materials Letters, 65 (2011) 840-842.

cr

[9] A.K. Abdul Gafoor, M.M. Musthafa, K. Pradeep Kumar, P.P. Pradyumnan, Effect

us

of Ag doping on structural, electrical and dielectric properties of TiO2 nanoparticles synthesized by a low temperature hydrothermal method, Journal of Materials Science:

an

Materials in Electronics, 23 (2012) 2011-2016.

[10] R.M. Mohamed, I.A. Mkhalid, Characterization and catalytic properties of

M

nano-sized Ag metal catalyst on TiO2–SiO2 synthesized by photo-assisted deposition and impregnation methods, Journal of Alloys Compounds, 501 (2010) 301-306.

d

[11] R. Chauhan, A. Kumar, R.P. Chaudhary, Structural and optical characterization of

Ac ce pt e

Ag-doped TiO2 nanoparticles prepared by a sol–gel method, Research on Chemical Intermediates, 38 (2012) 1443-1453.

[12] Y. Li, M. Ma, W. Chen, L. Li, M. Zen, Preparation of Ag-doped TiO2 nanoparticles by a miniemulsion method and their photoactivity in visible light illuminations, Materials Chemitry and Physics, 129 (2011) 501-505. [13] X.-M. Yan, J. Kang, L. Gao, L. Xiong, P. Mei, Solvothermal synthesis of carbon coated N-doped TiO2 nanostructures with enhanced visible light catalytic activity, Applied Surface Science, 265 (2013) 778-783. [14] S. Zhang, F. Peng, H. Wang, H. Yu, S. Zhang, J. Yang, H. Zhao, Electrodeposition preparation of Ag loaded N-doped TiO2 nanotube arrays with enhanced visible light photocatalytic performance, Catalysis Communications, 12

Page 24 of 40

(2011) 689-693. [15] B. Aysin, A. Ozturk, J. Park, Silver-loaded TiO2 powders prepared through mechanical ball milling, Ceramics International, 39 (2013) 7119-7126. [16] S. Wang, J.S. Lian, W.T. Zheng, Q. Jiang, Photocatalytic property of Fe doped

ip t

anatase and rutile TiO2 nanocrystal particles prepared by sol–gel technique, Applied Surface Science, 263 (2012) 260-265.

and

characterization

of

nano

silver-doped

mesoporous

titania

us

Preparation

cr

[17] N.N. Binitha, Z. Yaakob, M.R. Reshmi, S. Sugunan, V.K. Ambili, A.A. Zetty,

photocatalysts for dye degradation, Catalysis Today, 147 (2009) S76-S80.

an

[18] Y. Gao, P. Fang, F. Chen, Y. Liu, Z. Liu, D. Wang, Y. Dai, Enhancement of

265 (2013) 796-801.

M

stability of N-doped TiO2 photocatalysts with Ag loading, Applied Surface Science,

[19] N.T. Nolan, D.W. Synnott, M.K. Seery, S.J. Hinder, A. Van Wassenhoven, S.C.

d

Pillai, Effect of N-doping on the photocatalytic activity of sol-gel TiO2, Journal of

Ac ce pt e

Hazardous Materials, 211-212 (2012) 88-94. [20] M.A. Behnajady, H. Eskandarloo, Silver and copper co-impregnated onto TiO2-P25 nanoparticles and its photocatalytic activity, Chemical Engineering Journal, 228 (2013) 1207-1213.

[21] H. Yan, S.T. Kochuveedu, L.N. Quan, S.S. Lee, D.H. Kim, Enhanced photocatalytic activity of C, F-codoped TiO2 loaded with AgCl, Journal of Alloys Compounds, 560 (2013) 20-26.

[22] Y. Zhang, J. Zhang, Z. Zhu, N. Yan, Q. Liu, Preparation and properties of sliver and nitrogen co-doped TiO2 photocatalyst, Materials Research Bulletin, 48 (2013) 4872-4876. [23] Y.-C. Wu, L.-S. Ju, Annealing-free synthesis of CN co-doped TiO2 hierarchical

Page 25 of 40

spheres by using amine agents via microwave-assisted solvothermal method and their photocatalytic activities, Journal of Alloys Compounds, 604 (2014) 164-170. [24] G. Zhang, Y.C. Zhang, M. Nadagouda, C. Han, K. O'Shea, S.M. El-Sheikh, A.A. Ismail, D.D. Dionysiou, Visible light-sensitized S, N and C co-doped polymorphic

ip t

TiO2 for photocatalytic destruction of microcystin-LR, Applied Catalysis B: Environmental, 144 (2014) 614-621.

cr

[25] S. Bagwasi, B. Tian, J. Zhang, M. Nasir, Synthesis, Characterization and

Chemical Engineering Journal, 217 (2013) 108-118.

us

application of bismuth and boron Co-doped TiO2: A visible light active photocatalyst,

an

[26] E. Padmini, L.R. Miranda, Nanocatalyst from sol–sol doping of TiO2 with Vanadium and Cerium and its application for 3,4 Dichloroaniline degradation using

M

visible light, Chemical Engineering Journal, 232 (2013) 249-258. [27] R.L. Narayana, M. Matheswaran, A.A. Aziz, P. Saravanan, Photocatalytic

d

decolourization of basic green dye by pure and Fe, Co doped TiO2 under daylight

Ac ce pt e

illumination, Desalination, 269 (2011) 249-253. [28] K. Elghniji, A. Atyaoui, S. Livraghi, L. Bousselmi, E. Giamello, M. Ksibi, Synthesis and characterization of Fe3+ doped TiO2 nanoparticles and films and their performance for photocurrent response under UV illumination, Journal of Alloys Compounds, 541 (2012) 421-427.

[29] M. Scarisoreanu, I. Morjan, R. Alexandrescu, C.T. Fleaca, A. Badoi, E. Dutu, A.M. Niculescu, C. Luculescu, E. Vasile, J. Wang, S. Bouhadoun, N. Herlin-Boime, Enhancing the visible light absorption of titania nanoparticles by S and C doping in a single-step process, Applied Surfae Science, 302 (2014) 11-18. [30] M.J. Mattle, K.R. Thampi, Photocatalytic degradation of Remazol Brilliant Blue® by sol–gel derived carbon-doped TiO2, Applied Catalysis B: Environmental,

Page 26 of 40

140-141 (2013) 348-355. [31] M. Hamadanian, A. Reisi-Vanani, P. Razi, S. Hoseinifard, V. Jabbari, Photodeposition-assisted synthesis of novel nanoparticulate In, S-codoped TiO2 powders with high visible light-driven photocatalytic activity, Applied Surface

ip t

Science, 285 (2013) 121-129. [32] L. Song, J. Xiong, Q. Jiang, P. Du, H. Cao, X. Shao, Synthesis and photocatalytic

cr

properties of Zn2+ doped anatase TiO2 nanofibers, Materials Chemisty and Physics,

us

142 (2013) 77-81.

[33] M. Wu, B. Yang, Y. Lv, Z. Fu, J. Xu, T. Guo, Y. Zhao, Efficient one-pot synthesis

an

of Ag nanoparticles loaded on N-doped multiphase TiO2 hollow nanorod arrays with enhanced photocatalytic activity, Applied Surface Science, 256 (2010) 7125-7130.

M

[34] X. Lin, F. Rong, D. Fu, C. Yuan, Enhanced photocatalytic activity of fluorine doped TiO2 by loaded with Ag for degradation of organic pollutants, Powder

d

Technology, 219 (2012) 173-178.

Ac ce pt e

[35] A. Hernandez-Gordillo, M. Arroyo, R. Zanella, V. Rodriguez-Gonzalez, Photoconversion of 4-nitrophenol in the presence of hydrazine with Ag NPs-TiO2 nanoparticles prepared by the sol-gel method, Journal of Hazardous Materials, 268 (2014) 84-91.

[36] L. Liang, Y. Meng, L. Shi, J. Ma, J. Sun, Enhanced photocatalytic performance of novel visible light-driven Ag–TiO2/SBA-15 photocatalyst, Superlattice Microst, 73 (2014) 60-70.

[37] A.A. Ashkarran, H. Hamidinezhad, H. Haddadi, M. Mahmoudi, Double-doped TiO2 nanoparticles as an efficient visible-light-active photocatalyst and antibacterial agent under solar simulated light, Applied Surface Science, 301 (2014) 338-345. [38] L.G. Devi, B. Nagaraj, K.E. Rajashekhar, Synergistic effect of Ag deposition and

Page 27 of 40

nitrogen doping in TiO2 for the degradation of phenol under solar irradiation in presence of electron acceptor, Chemical Engineering Journal, 181-182 (2012) 259-266. [39] H. Liu, X. Dong, G. Li, X. Su, Z. Zhu, Synthesis of C, Ag co-modified TiO2

ip t

photocatalyst and its application in waste water purification, Applied Surface Science, 271 (2013) 276-283.

cr

[40] Y. Song, J. Zhang, H. Yang, S. Xu, L. Jiang, Y. Dan, Preparation and visible

us

light-induced photo-catalytic activity of H-PVA/TiO2 composite loaded on glass via sol–gel method, Applied Surface Science, 292 (2014) 978-985.

an

[41] T. Harifi, M. Montazer, Fe3+:Ag/TiO2 nanocomposite: Synthesis, characterization

Ac ce pt e

d

General, 473 (2014) 104-115.

M

and photocatalytic activity under UV and visible light irradiation, Applied Catalysis A:

Page 28 of 40

ip t cr us an

M

Fig.1 1H NMR spectra of virgin collagen and PDMC grafted collagen

d

Fig.2 FTIR spectra of the various samples: (a) pristine TiO2; (b) Fe3+/TiO2; (c) CFT-3;

Ac ce pt e

(d) CFT-6

Fig.3 (a) UV-Visible absorption spectra of pristine TiO2, Fe3+/TiO2, CFT-3 and CFT-6; (b) Band gap calculated from the variation of (Ahv)1/2 vs photon energy of pristine TiO2 and Fe3+/TiO2

Fig.4 XRD patterns of (a) pristine TiO2; (b) Fe3+/TiO2; (c) CFT-3; (d) CFT-6

Fig.5 Raman spectra of (a) pristine TiO2; (b) Fe3+/TiO2; (c) CFT-3; (d) CFT-6

Page 29 of 40

Fig.6 TEM images of (a) pristine TiO2 and (b) CFT-3; SEM images of (c) pristine TiO2 and CFT-3; (e) EDS spectrum for elemental analysis of CFT-3 and (f) inset: EDS

ip t

spectrum for elemental analysis of CFT-3 (as enlarged scale)

us

cr

Fig.7 Photoluminescence spectra of the various samples

Fig.8 (a) Full survey XPS data for CFT-3 nanocomposite and high resolution XPS

an

data in the range of (b) titanium; (c) carbon; (d) oxygen; (e) iron; (f) nitrogen;

M

(g) chlorine binding energies

d

Fig.9 (a) the degradation curves of MO, presented as the logarithms of the

Ac ce pt e

time-dependent normalized concentration of MO under the solar irradiation for different samples; (b) Schematic illustration of the band structure and the proposed mechanism concerning the significantly enhanced photocatalytic activity of CFT-3 on the degradation of MO solution

Page 30 of 40

Ac

Page 31 of 40

Ac ce

Edited by Foxit Reader Copyright(C) by Foxit Software Company,2005-2007 For Evaluation Only.

Page 32 of 40

a M ed pt ce Ac Page 33 of 40

ed pt ce Ac

Page 34 of 40

pt ce Ac Page 35 of 40

an M d pt e ce Ac Page 36 of 40

Ac ce

Page 37 of 40

pt ce Ac Page 38 of 40

a

Ac

ce

pt

ed

M

d by Foxit Reader right(C) by Foxit Software Company,2005-2007 Evaluation Only.

Page 39 of 40

pt

Ac

ce

d by Foxit Reader right(C) by Foxit Software Company,2005-2007 Evaluation Only.

Page 40 of 40