Synthesis and photocatalytic activity of mesoporous TiO2 nanoparticle using biological renewable resource of un-modified lignin as a template

Accepted Manuscript Synthesis and photocatalytic activity of mesoporous TiO2 nanoparticle using biological renewable resource of un-modified lignin as a template Xiaoyun Chen, Dong-Hau Kuo, Dongfang Lu, Yongxuan Hou, Yanrong Kuo PII:

S1387-1811(15)00604-6

DOI:

10.1016/j.micromeso.2015.11.005

Reference:

MICMAT 7391

To appear in:

Microporous and Mesoporous Materials

Received Date: 7 October 2015 Revised Date:

30 October 2015

Accepted Date: 5 November 2015

Please cite this article as: X. Chen, D.-H. Kuo, D. Lu, Y. Hou, Y. Kuo, Synthesis and photocatalytic activity of mesoporous TiO2 nanoparticle using biological renewable resource of un-modified lignin as a template, Microporous and Mesoporous Materials (2015), doi: 10.1016/j.micromeso.2015.11.005. 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.

ACCEPTED MANUSCRIPT

Graphic Abstract Synthesis activity

and of

photocatalytic

mesoporous

nanoparticle renewable

using

O

TiO2

TiCl4

Lignin

Ti

O Lignin

O

H2O, H+

biological

resource

O-H H-O

NH3 H2O

Ti

of

Lignin

Ti(OH)n(4-n)+

O

Lignin

O-H

H-O

Ti

Ti

O

Ti O

Lignin

Ti

un-modified lignin as a template TiO2 synthesized with lignin template exhibited high activity under ultraviolet light

Dongfang

irradiation. The mechanism for the improved photodegradation of the lignin-assisted

Lu,

Yongxuan

Hou,

TiO2 was proposed.

AC C

EP

TE D

M AN U

SC

Yanrong Guo.

RI PT

Xiaoyun Chen, Dong-Hau Kuo*,

ACCEPTED MANUSCRIPT Synthesis and photocatalytic activity of mesoporous TiO2 nanoparticle using

biological renewable resource of un-modified lignin as a template

a

RI PT

Xiaoyun Chen a,b, Dong-Hau Kuo a,*, Dongfang Lu c, Yongxuan Hou a, Yanrong Kuo a

Department of Materials Science and Engineering, National Taiwan University of Science and Technology,

Taipei 10607, Taiwan

College of Material Engineering, Fujian Agriculture & Forestry University, Fuzhou 350002, China

c

College of Landscape Architecture, Fujian Agriculture & Forestry University, Fuzhou 350002, China

*

Corresponding author.

Fax: +886-2-27303291.

AC C

EP

TE D

E-mail: [email protected]. (D. H. Kuo)

M AN U

SC

b

1

ACCEPTED MANUSCRIPT ABSTRACT Mesoporous TiO2 was synthesized by a hydrolysis precipitation method with the utilization of the biological renewable resource of lignin as template and TiCl4 as reactant. The photocatalytic activity of TiO2 was investigated by the degradation of phenol under UV light irradiation. The

RI PT

microstructure, crystallinity, powder characteristic, and chemical bonding of the catalyst were analyzed. The 500 oC-calcined TiO2 had average crystallite size of about 11.1 nm and a mesoporous structure with specific area of 165.8 m2/g and pore volume of 0.312 cm3/g. The results showed that

SC

TiO2 synthesized with lignin template exhibited high photocatalytic activity, which can be attributed to the electronegativity and the network skeleton of lignin to uniformly distribute the

M AN U

TiO2 precursor for forming TiO2 mesoporous particles. The mechanism for the improved photodegradation of the lignin-assisted TiO2 was proposed.

AC C

EP

TE D

Keywords: Mesoporous TiO2; Lignin; Template; Photocatalysis; Mechanism

2

ACCEPTED MANUSCRIPT

1. Introduction Mesoporous TiO2 nanoparticle has particularly become attractive due to its large specific surface area, good permeability, strong adsorption capability, and high photocatalytic performance

RI PT

in degrading organic compounds under UV light irradiation [1-5]. The traditional approach to prepare mesoporous TiO2 nanoparticle is to use the different kinds of templates such as surfactant, block copolymer, small non-surfactant organic molecule, microemulsion droplet, polymer

SC

microsphere-formed colloidal crystals etc. [6-13]. However, most of those templates are not from the biological renewable resource and need the harsh synthesis condition. Therefore, it is desirable

M AN U

to find an environment-friendly method for preparing porous TiO2 nanoparticle [14-18]. In forestry, the reserve of lignin is only lower than that of cellulose and has a regeneration rate of 50 billion tons per year. There is approximately 140 million tons of cellulose extracted from

TE D

plants each year in paper-making industries, meanwhile 50 million tons of lignin are generated as a by-product. However, more than 95% of lignin has been thrown into the rivers or burn after concentration, hence lignin has not been well utilized. Lignin is an electronegative and

EP

three-dimensional network macromolecule. It has a strong affinity for the positively charged metal

AC C

ions and its molecule with phenolic hydroxyl group, alcoholic hydroxyl group, and carboxyl group can chemically react with other polymers to form the hybrid composites [19,20]. On the other hand, cellulose, an organic polysaccharide consisting of a linear chain of several hundreds to many thousands of β(1→4) linked D-glucose units, is mainly used to produce paperboard and paper. It has multiple hydroxyl groups on one long chain to form hydrogen bonds with other oxygen atoms on a neighbor chain. With the side-by-side bonding, cellulose forms microfibrils with high tensile strength. Much attention has focused on using the biological renewable cellulose and lignin as templates 3

ACCEPTED MANUSCRIPT to provide a platform for synthesizing mesoporous materials [21,22]. Several studies for the successful application of cellulose and modified lignin templates in the preparation of mesoporous materials have been reported. Cai et al. [23] used cellulose nanofibril aerogel microsphere as template to prepare highly porous titanium dioxide microspheres by sol-gel method and the

RI PT

microspheres showed a typical super-hydrophobic property. Li et al. [24] prepared mesoporous TiO2 with a regular spherical structure by the acid-catalyzed hydrolysis with the nanocrystal

SC

cellulose (NCC) as a template. The authors claimed that a nano-scale reactor formed by bonding between the hydroxyl groups of the long-chain NCC inhibited the growth and aggregation of the

M AN U

TiO2 precursor, promoted the spherical structure by self-assembly, and avoided the phase transformation from anatase to rutile. Zhou et al. [25] adapted NCC as a morphology inducer to prepare square nano-TiO2. Miao et al. prepared mesoporous TiO2 films by calcining the ionic liquid solution containing titanium tetrabutyloxide and cellulose. Their TiO2 films were composed of

TE D

anatase nanocrystals of 10 – 20 nm in size and had the adjustable pore size with the cellulose concentration [26]. Our group proposed the utilization of different nano-celluloses as templates to

EP

prepare mesoporous TiO2 with the desirable pore structure, large specific surface area, and good photocatalytic activity [15,27]. As cellulose is a straight chain polymer, the inorganic precursor

AC C

attached on cellulose form the fibrous shape and becomes nano particles after calcination. The utilization of lignin as a template to prepare mesoporous TiO2 is few. Bai et al. [28] used the amine-modified lignin as a template to synthesize the macroporous SiO2 with the interconnected and adjustable pore size by the sol-gel method. Wang et al. [29] used the trimethyl quaternary ammonium salt-modified lignin as a template to prepare the porous and thermally stable SiO2 by sol-gel method followed by a calcination procedure at 600 – 800 oC. Sulfonated-modified lignin was used as template for the synthesis of porous carbon–CeO2 composites, which were used for the 4

ACCEPTED MANUSCRIPT photocatalytic removal of SO2 at room temperature [30]. Amine-modified lignin was also used to prepare metallic platinum (Pt) [31]. Depending upon the amount of lignin, Pt with different morphologies of smooth layer, porous coating, and 3D network was obtained. As lignin is a three-dimensional network macromolecule, the lignin-aided inorganic compounds form the

RI PT

mesoporous particles. The modification to form amine- or sulfonated-modified lignin requires adding the chemical reactants and has the difficulty in purification. The lignin obtained from the

SC

paper-making black liquid has only the phenolic hydroxyl, alcoholic hydroxyl, and carboxyl groups and has not been used for synthesizing the mesoporous TiO2 nanoparticle yet.

M AN U

This research intends to separate the lignin from black liquor as a raw material without modification to be used as a template for the synthesis of mesoporous TiO2 by hydrolysis precipitation of TiCl4 as a reactant, followed by a calcination step. The microstructure, crystallinity, and powder characterization of mesoporous TiO2 catalyst were examined. Photocatalytic activity of

TE D

TiO2 nanoparticle was examined by the photodegradation of phenol in aqueous solution under ultraviolet light irradiation. The formation mechanism of mesoporous TiO2 nanoparticle with the

AC C

2. Methods

EP

lignin as a template was also proposed.

2.1. Lignin preparation

The crude alkali lignin (Fujian Qingzhou mills, China) was dissolved in 10% NaOH solution to make the mass fraction of the lignin solution at and below 10%, followed by removing the insoluble sediments to obtain the purified alkali lignin solution. Under stirring, HCl was added dropwise to the purified lignin solution until pH=4, then the precipitation reaction continued for 1 h. After filtration, the sediment cake was washed 3 – 4 times with distilled water and dried in vacuum oven at 85 oC to obtain the lignin. 5

ACCEPTED MANUSCRIPT 2.2. Catalyst preparation With the water bath kept at 25 oC, 10 ml of TiCl4 (AR, Aladdin) was slowly added as droplets into the 100 ml lignin aqueous solution of 5 g/L, which was adjusted to pH= 5.0 with HCl under vigorous stirring. The mixture was kept stirring at 25 oC for 30 min, following with heating at 80 oC

RI PT

for 30 min. Then NH3·H2O was used to adjust the solution to pH = 7. After another 30 min stirring, the amorphous precipitates were filtered and aged at room temperature for 10 h. The obtained gel

SC

was washed with distilled water to remove Cl−, after that it was washed with ethanol for twice. The obtained product was vacuum dried at 85 oC, ground, and subsequently calcined at 300 – 900 oC in

M AN U

air for 2 h. TiO2 nanoparticle with lignin as template was obtained and labeled as TiO2-T. For comparison, TiO2 catalyst without using lignin template was prepared under the same condition and labeled as TiO2-UT. The commercially available P25-TiO2 catalyst produced by Degussa was used as the control sample.

TE D

2.3. Catalyst characterization

N2 adsorption-desorption experiments were performed on SSA4300 porosity and specific

EP

surface area analyzer with the sample degassed at 200 oC for 2 h before the test. Specific surface area was calculated according to the BET equation. Pore size distribution was calculated according

AC C

to the BJH formula. The sample particle size and morphology were examined by transmission electron microscopy (Tecanai10, Philips, Netherlands). The crystal structure of TiO2 was characterized by using X-ray diffraction analysis (Rigaku, Japan) using Cu Kα radiation. The average crystallite size was computed according to the Scherrer formula. TG/DSC analysis was performed on STA-449 thermal analyzer with a lid-covered platinum crucible at a heating rate of 10 o

C/min in air. Surface composition and chemical state of the catalyst were investigated by Physical

Electronics PHI5700 Type photoelectron spectrometer, which used Al Kα (hv=1486.6 eV) radiation 6

ACCEPTED MANUSCRIPT and was calibrated with carbon C1s (Ea=284.62 eV). Interphase development was studied on Nicolet-380 Fourier transform infrared spectrometer with TiO2 embedded in a KBr pellet. 2.4. Photocatalytic measurements Photocatalytic reaction was performed in a home-made and jacketed quartz reactor (250 ml)

RI PT

[32]. A 8 W mercury lamp (λML = 365 nm) built in the quartz tube was used as UV light source. The reaction temperature was maintained at 25 oC by flushing with the cooling water over the outer

SC

jacket of the reactor. The reactor was wrapped by aluminum foil in order to avoid additional interference. The photocatalytic degradation was tested in a 0.05 g/L phenol solution with the

M AN U

catalyst concentration kept at 1.0 g/L. The reactant mixture was under magnetic stirring in the dark for 30 min to obtain the adsorption-desorption equilibrium between phenol and catalyst before illumination. Air supply to the reactor was maintained at a flow rate of 80 ml/min in order to mix phenol with dissolve oxygen. 5 ml sample was taken every 20 min from the reactor, followed by Absorbance of the supernatant

TE D

centrifugation.

was

measured

with

TU-1901

UV-Vis

spectrophotometer at 270 nm. The concentration of phenol was calculated based on the

EP

Lambert-Beer law.

AC C

3. Results and discussion

3.1. Surface area and pore size analyses Fig. 1 shows N2 adsorption-desorption isotherms and the pore size distribution diagram for TiO2-UT and TiO2-T nanoparticles prepared at 500 oC. Fig. 1(a) shows that two samples exhibit the type IV adsorption-desorption isotherm and the hysteresis loops. At a relatively low pressure, the adsorption capacity gradually increased with the increase of relative pressure, as the N2 molecules adsorbed at the mesoporous surface as monolayer or multilayer. When the relative pressure of N2 reached 0.8, the adsorption capacity drastically increased due to the capillary condensation of N2 on 7

ACCEPTED MANUSCRIPT TiO2 mesopores. The hysteresis loop proves the presence of a mesoporous structure in the catalyst [33]. The curve of pore size distribution is shown in Fig. 1(b). The pore diameter of 1 – 20 nm and the total pore volume of 0.312 cm3/g were obtained for mesoporous TiO2-T nanoparticles, while they were 1 – 35 nm and 0.168 cm3/g, respectively, for TiO2-UT. The calculated data from the BET

RI PT

measurements are summarized in Table 1. The specific surface area of TiO2-T is 165.8 m2/g, which is higher than that of TiO2-UT (43.8 m2/g) and P25-TiO2 (50.0 m2/g). The results showed that the

SC

utilization of lignin template is advantageous for a narrow pore size distribution and the increased pore volume and specific surface area, which can be attributed to the lignin decomposition at high

M AN U

temperature and the formation of a porous network structure in TiO2 particles. 3.2. TEM analysis

Fig. 2 shows the TEM images of (a) TiO2-UT and (b) TiO2-T prepared at 500 oC. TiO2-UT nanoparticles aggregated and had a larger particle size of 50-200 nm. In contrast, TiO2-T

TE D

nanoparticles had a smaller particle size of 30-80 nm and were porous with a uniform pore size of 2-6 nm well distributed in particles. After the comparison between TiO2-UT and TiO2-T, the role of

EP

lignin becomes clear, i.e. it creates the loose structure with nano pores in each grain. The advantages of the TiO2 with many uniform nano pores can not only enhance the surface

AC C

permeability and improve its adsorption performance but also enable the rapid transfer of light-excited carrier to the particle surface for effectively reducing the carrier recombination rate and accelerating the photocatalytic reactions [1,5,34]. 3.3. XRD analysis Fig. 3 shows the XRD diffraction patterns of TiO2-UT and TiO2-T prepared at different temperatures. Comparing Figs. 3(a) and 3(b), it is obvious that lignin template does not affect the characteristic peak positions at 25.27o and 27.48o of anatase and rutile, respectively. The structure of 8

ACCEPTED MANUSCRIPT un-calcined TiO2-T precursor was amorphous. After calcination at 300 oC, TiO2 started to transform into anatase. After calcination at 400 oC, crystallinity of anatase had improved. However, 6%, 38%, and 100% rutile were formed if TiO2-T was calcined at 500, 600, and 700 oC, respectively. In contrast, TiO2-UT started to show the minor rutile phase at 450 oC, had the major rutile phase at 500 C, and completely transformed into the rutile at 600 oC. Thus, the addition of lignin template had

RI PT

o

made the anatase-to-rutile transition comparatively difficult, because the crystallization of TiO2 was

SC

blocked by the trapped lignin and its pyrolyzed carbon. The average crystallite sizes of the TiO2-UT and TiO2-T catalysts calculated by Scherrer formula are listed in Table 1. For the template-free TiO2,

M AN U

it had a crystallite size of 11.3 – 52.7 nm and grew at a faster rate as the calcination temperature reached 600 oC. For TiO2-T, it had the crystallite size of 8.5 – 18.2 nm after calcination at 300 – 600 o

C but rapidly increased to 30.5 nm at 700 oC. The template-made TiO2-T kept its nano size until it

was fired at much high temperature of 700 oC.

TE D

The crystallite size and specific surface area of TiO2-UT and TiO2-T are shown in Table 1. It is obvious that the lignin-templated TiO2-T has the much higher surface area and smaller crystallite

EP

size than TiO2-UT, after calcination at 300-900 oC. TiO2-UT and TiO2-T have few differences in crystallite size and specific surface, if they are calcined at temperatures at and below 500 oC. When

AC C

the calcination temperature is higher than 500 °C, the crystallite size and surface area of both samples are significantly changed. Lignin is a polycyclic and three-dimensional mesh macromolecule with higher electronegativity due to many hydroxyl groups. Therefore, it has a strong affinity for the highly positive-charged metal ions or groups. The positively charged Ti(OH)n(4-n)+, the partially hydrolyzed product of TiCl4, can be strongly absorbed on the surface of lignin through the columbic interaction. With the further hydrolysis, TiO2 precursor is formed and well distributed on the template without aggregation, therefore it can be transform into the 9

ACCEPTED MANUSCRIPT mesoporous TiO2 with high porosity and fine particle size after pyrolysis [24,25]. 3.4. TG/DSC analysis Fig. 4 shows the DSC analysis results for (a) TiO2-UT and (b) TiO2-T precursors. For TiO2-UT precursor shown in Fig 4(a), the endothermic peak between 50 and 140 oC was generated by the

RI PT

evaporation of water and the exothermic peak at 400 – 440 oC corresponded to the transition from the anatase to the rutile. For TiO2-T precursor shown in Fig. 4(b), the endothermic peak at 50 – 190 o

SC

C was generated from the evaporations of water and organic residues from lignin black liquor, the

exothermic peak at 220 – 316 oC was produced by the lignin combustion, and the exothermic peak

M AN U

at 385 – 515 oC came from the anatase-to-rutile transition and the combustion of the pyrolyzed carbon. The data from the TG/DSC analysis further confirm that lignin template increases the anatase-to-rutile transition temperature, which is consistent with the results from XRD. Fig. 4 also shows the thermalgravimetric analyses for (a) TiO2-UT and (b) TiO2-T precursors.

TE D

The weight loss of TiO2-UT precursor mainly took place at two temperature intervals: 30 – 190 oC and 190 – 450 oC, which corresponded to the volatile weight losses of physically adsorbed water on

EP

the surface and the bonded water in TiO2 catalyst, respectively [15,35]. The weight loss percentages were 21.4% and 5.8% in these two intervals. In comparison, the weight loss of TiO2-T precursor

AC C

took place at three temperature intervals: 30 – 190 oC, 170 – 316 oC, and 316 – 568 oC, which corresponded to the volatile weight losses of physically adsorbed water and organic species on the surface, organic combustion, and the oxidation of residual carbon in TiO2 catalyst [15,35]. The weight loss percentages were 22.7%, 7.2%, and 9.5% for these three temperature intervals. 3.5. XPS analysis Fig. 5 shows the XPS spectra of (a) Ti2p and (b) O1s for the TiO2-UT and TiO2-T prepared at 500 oC. In Fig. 5(a), the peaks at 458.4 eV and 464.1 eV corresponded to Ti2p3/2 and Ti2p1/2, 10

ACCEPTED MANUSCRIPT respectively, of the Ti

4+

cation. There were no detectable Ti3+ peaks. In Fig. 5(b), the asymmetric

shape of O1s peaks indicates the presence of different chemical states of oxygen in the sample. Peaks of the lattice oxygen (529.6 eV) and hydroxyl oxygen (531.3 eV) can be inferred in accordance with the order of binding energy. According to the size of the peak area, the ratio of

RI PT

lattice oxygen and hydroxyl oxygen was calculated. The results are presented in Table 2. TiO2 made with lignin template had the surface hydroxyl group of 22.79% and the lattice oxygen of 77.21% in

SC

TiO2-T, while it was 28.58% and 71.42%, respectively, for TiO2-UT. The FTIR analysis results further validated the XPS results that TiO2-T nanoparticles made with lignin template had a lower

M AN U

content of surface hydroxyl group. The explanation for TiO2-T with a lower content of surface hydroxyl group is related to the hydrolysis process of TiCl4 on the lignin surface. During the hydrolysis process, the TiO2 precursor with the surface hydroxyl groups can have stronger interactions with the hydroxyl groups of lignin. After calcination, TiO2-T has a much complete

TE D

reaction and a less amount of hydroxyl groups left. It has been reported that an optimal amount of surface hydroxyl oxygen on TiO2 is beneficial for photocatalytic reaction [36,37].

EP

3.6. Photocatalytic activity

To evaluate the photocatalytic activity of the different TiO2-UT and TiO2-T calcined at 500 oC,

AC C

phenol was used as a model organic substitute in the photo reaction system with suspended TiO2 nanoparticles. The results for phenol degradation are shown in Fig. 6. It was observed that the photocatalytic degradation rate of phenol on TiO2-T was faster than on TiO2-UT and P25-TiO2. 97.9% phenol could be removed within 120 min with TiO2-T. However, TiO2-UT and P25-TiO2 showed relatively lower activity and only removed 76.3% and 86.3% phenol, respectively. According to the kinetic analysis, photocatalytic phenol degradation fitted the pseudo-first-order kinetics well. The first-order reaction rate constant (k) sequence is TiO2-T (k=0.01110 min-1) > 11

ACCEPTED MANUSCRIPT -1

P25-TiO2 (k=0.00894 min ) > TiO2-UT (k=0.00618 min-1). Table 3 shows the phenol photocatalytic degradation of TiO2-UT and TiO2-T calcined at different temperatures after UV illumination for 120 min. There was an optimal calcination temperature of 500 oC for each TiO2-UT and TiO2-T to maximize their own photocatalytic activity.

RI PT

The reasons for the better performance of the 500 oC-calcined TiO2-T can be attributed to the well crystallinity, the content of the anatase phase, and the utilization of lignin template, which has led to

SC

higher specific surface area and a smaller grain size. In addition, the lignin-templated TiO2-T had showed a wide calcination temperature range of 450~600°C to remain the high catalytic activity. .

M AN U

The lignin template is to fabricate the mesoporous TiO2, to have high surface area and finer crystallite size, and to further improve the photocatalytic reactions.

3.7. Mechanism for the lignin template synthesis of mesoporous TiO2 Titanium atom has a relatively low electronegativity and can react rapidly with a nucleophilic

TE D

reaction medium, in order to obtain their preferred ligand. Therefore, TiCl4 can be hydrolyzed very fast in the water-only condition through reaction (1) [24,38-41] to form the amorphous TiO2.

TiCl4 + 2H 2O

H+

EP

TiO2 + 4H+ + 4Cl-

TiCl4 + 2H2O

AC C

Ti(OH)n(4-n)+ + Lignin OH ( Lignin O )4 Ti

+

Ti(OH)n(4-n) + (4-n)H + + 4Cl-

NH 3 H 2 O

Lignin O Ti(OH)3 + H2O

Lignin-TiO 2

(1) (n=1, 2 ,3) ........ ( Lignin O) Ti + H2O 4

(2) (3) (4)

Lignin is a polycyclic and three-dimensional mesh organic macromolecule with many electronegative OH groups. It has a strong affinity for the metal ions or complex. When TiCl4 is added as droplets into the acidic lignin suspension, the TiCl4-hydrolyzed products of Ti(OH)n(4-n)+, as shown in reaction (2), are affected by the role of the electronegativity of lignin to form strong adhesion on the lignin surface (Fig. 7). Then the attached Ti(OH)n(4-n)+ is further hydrolyzed to 12

ACCEPTED MANUSCRIPT produce Ti-(O-lignin)4 coated on the lignin surface and to form the TiO2 nuclei, as shown in reaction (3). Further reactions with the added NH3·H2O can lead to the TiO2 precursor (reaction (4)). The TiO2 precursor, affected by the affinity and the three-dimensional network structure of lignin, has covered the inside and outside of the template. After calcination, the lignin template is burned

RI PT

out and leaves the uniform voids in TiO2 particle.

4. Conclusions

SC

Mesoporous TiO2 was synthesized by hydrolysis precipitation followed by a calcination step

M AN U

with the utilization of the biological renewable resource of lignin as a template and TiCl4 as a reactant. It had average crystallite size of about 11.1 nm and exhibited a mesoporous structure with specific area of 165.8 m2/g and pore volume of 0.312 cm3/g. With the function of lignin affinity and the interactions between its hydroxyl group and the surface hydroxyl group of TiO2 precursor, the

TE D

calcined TiO2 particles can have finer crystallite size, be mesoporous, and be well separated to avoid the grain growth. The 500 oC-calcined mesoporous TiO2 exhibited high activity under UV irradiation. It degraded 97.9% phenol in 120 min. A schematic formation mechanism of

EP

mesoporous TiO2 with the aid of lignin has been proposed. Lignin from the black liquor waste of

AC C

the paper-making industry has shown the great potential for fabricating the TiO2 particles filled with uniformly distributed nano pores.

Acknowledgements This work was supported by Ministry of Science and Technology of the Republic of China under the Grant No. MOST 104-2218-E-035-004 and by National Natural Science Foundation of China under the Grant No. 31000269.

13

ACCEPTED MANUSCRIPT

References [1] X. Chen, S.S. Mao, Chem. Rev. 107 (2007) 2891–2959. [2] G.G. Tang, D. Zhang, L. Zhao, M.S Zhang, H. Tang, H. Huang, C.H. Li, Mater. Lett. 118 (2014)

RI PT

192–195. [3] N. Kumar, S.N. Hazarika, S. Limbu, R. Boruah, P. Deb, N.D. Namsa, S.K. Das, Micropor. Mesopor. Mater. 213 (2015) 181–187.

SC

[4] Z.L. Feng, W.R. Wei, L.T. Wang, R.Y. Hong, Appl. Surf. Sci. 357 (2015) 759–765.

ACS Nano. 4 (2010) 1893–1900.

M AN U

[5] B. Balasubramanian, K.L. Kraemer, N.A. Reding, R. Skomski, S. Ducharme, D.J. Sellmyer,

[6] S. Biswas, V. Sundstrom, S. De, Mater. Chem. Phys. 147 (2014) 761–771. [7] F.P. Deng, Y. Li, X.H. Qi, S.Y. Wu, W.H. Zhang, J. Inorg. Mater. 24 (2009) 39–42.

TE D

[8] T. Preethi, B. Abarna, G,R. Rajarajeswari, Appl. Surf. Sci. 317 (2014) 90–97. [9] J.C. Ramos, I. Mejia, J. Murphy, M. Quevedo, P. Garcia, C.A. Martinez, J. Alloy. Compd. 643 (2015) S84–S89.

EP

[10] K.O. Hamaloglu, B. Celebi, E. Sag, A. Tuncel, Micropor. Mesopor. Mater. 207 (2015) 17–26

AC C

[11] E.O. Oseghe, S. Maddila, P.G. Ndungu, S.B. Jonnalagadda, Appl. Catal. B: Environ. 176–177 (2015) 288–297.

[12] D.A. Erdogan, M. Polat, R. Garifullin, M.O. Guler, E. Ozensoy, Appl. Surf. Sci. 308 (2014) 50–57.

[13] B.A. Sifontes, M. Rosales, J.F. Mendez, O. Oviedo, T. Zoltan, J. Nano. Mater. 2013 (2013) 1–9. [14] T.T. Vu, G. Marbán, Appl. Catal. B: Environ. 152–153 (2014) 51–58. [15] X.Y. Chen, X. Chen, S.W. Hong, X. Chen, B. Huang, Chin. J. Catal. 32 (2011) 1762–1767. 14

ACCEPTED MANUSCRIPT [16] K.J. Hwang, D.C. Kang, S. Lee, C.H. Hwang, C. Kim, N. Kim, S. Jin, I.H. Lee, J.Y. Park, Mater. Lett. 115 (2014) 265–267. [17] H. Liu, Y.G. Liang, H.J. Hu, M.Y. Wang, Solid. State. Sci. 11 (2009) 1655–1660. [18] J.Q. Wang, E.C. Ou, J.J. Li, X.Y. Yang, W. Wang, Z.Y. Yan, C. Li, J. Mol. Catal. A: Chem.

RI PT

404–405 (2015) 178–185

[19] W. Xiong, D. Yang, R. Zhong, Y. Li, H. Zhou, X. Qiu. Ind. Crop. Prod. 74 (2015) 285–292

SC

[20] W. Jin, R. Tolba, J. Wen, K. Li, A. Chen, Electrochimica Acta 107 (2013) 611– 618

[21] A. Foulet, M. Birot, G. Sonnemann, H. Deleuze, React. Funct. Polym. 90 (2015) 15–20.

M AN U

[22] J. Virkutyte, V. Jegatheesan, R.S. Varma, Bioresource Technol. 113 (2012) 288–293. [23] H.L. Cai, W. Mu, W. Liu, X.D Zhang, Y.L. Deng, Inorg. Chem. Commun. 51 (2015) 71–74. [24] W. Li, Y. Zhao, S.X. Liu, Chin. J. Catal. 33 (2012) 342–347.

[25] Y. Zhou, E.Y. Ding, W.D. Li, Mate. Lett. 61 (2007) 5050–5052.

(2006) 26–30.

TE D

[26] S.D. Miao, Z.J. Miao, Z.M. Liu, B.X. Han, H. Zhang, J. Zhang, Micropor. Mesopor. Mater. 95

EP

[27] X.Y. Chen, D.F Lu, Y. Chen, F. Tan, Chin. J. Inorg. Chem. 29 (2013) 528–536. [28] Q.L. Bai, C.H. Zhang, J.J. Song, J. Inner Mongolia. University for Nationalities 20 (2005)

AC C

510–512.

[29] C.H. Wang, Z.N. Li, Y.F. Zhao, Y. Bei, S.X. Ren, G.Z. Fang, J. Beijing Forestry University 33 (2011) 118–123.

[30] N. Wang, H. Fan, S.Y. Ai, Cheml. Eng. J. 260 (2015) 785–790. [31] X. Wang, S.H. Chen, Y.Q. Shao, T. Zhang, D. Tang, Heat Treat Met. 2 (2010) 40–50. [32] X.Y Chen, S.X. Liu, Acta. Phys. Chim. Sin. 23 (2007) 701–708. [33] S.R. Liu, Y. Gong, Z.B. Ni, M.Q. Chen, Chin. J. Mater. Res. 24 (2010) 610–614. 15

ACCEPTED MANUSCRIPT [34] U.I. Gaya, A.H. Abdullah, J. Photochem. Photobiol. C 9 (2008) 1–12. [35] Bai B, Zhao J L. Chemistry, 10 (2005) 776-780 [36] J. Yu, X. Zhao, Q. Zhao, Thin Solid Films 379 (2000) 7–14 [37] X.Y. Chen, D.F. Lu, J.F. Huang, Y.F Lu, J.Q. Zheng, Acta. Phys. Chim. Sin. 28 (2012)

RI PT

161–169.

[38] X.H. Li, X.Y. Chen, S.X. Liu, X. Chen, H.L. Wang, Z.F. Liu, Chin. J. Appl. Chem. 24 (2007)

SC

1279–1283.

[39] Q.H. Zhang, L. Gao, J.K. Guo, J. Inorg. Mater. 15 (2000) 929–934.

M AN U

[40] Y. Lu, Q. Sun, T. Liu, D. Yang, Y. Liu, J. Li, J. Alloy. Compd. 577 (2013) 569–574.

AC C

EP

TE D

[41] Q. Zhang, L. Gao, J. Guo, Nanostruct. Mater. 11 (1999) 1293–1300.

16

ACCEPTED MANUSCRIPT

Table and figure captions Table 1 Crystallite size and surface area of calcined TiO2-UT and TiO2-T catalysts Table 2 The amounts of Ti–O, O–H, Ti4+(2p3/2), and Ti4+(2p1/2) in different catalysts

RI PT

Table 3 Effect of calcination temperature on photocatalytic activity of TiO2 catalysts Fig. 1 (a) Nitrogen adsorption isotherms and (b) the pore size distribution curve for TiO2 catalysts. Fig. 2 TEM images of (a) TiO2-UT and (b) TiO2-T catalysts.

SC

Fig. 3 XRD patterns of (a) TiO2-UT and (b) TiO2-T catalysts.

M AN U

Fig. 4 TG/DTA curves of (a) TiO2-UT and (b) TiO2-T precursors. Fig. 5 XPS spectra of (a) Ti2p and (b) O1s.

Fig. 6 Photocatalytic degradation in phenol over different kinds of TiO2 catalysts: TiO2-UT, TiO2-T, and commercially available P25 TiO2.

AC C

EP

TE D

Fig. 7 Formation mechanism of mesoporous TiO2 with lignin as a template.

17

ACCEPTED MANUSCRIPT Table 1 Crystallite size and surface area of calcined TiO2-UT and TiO2-T catalysts TiO2-UT

TiO2-T

Crystallite size (nm)

Surface area (m2/g)

Crystallite size (nm)

Surface area (m2/g)

300 400

11.3 13.2

53.5 50.7

8.5 9.0

140.6 172.4

500

15.6

43.8

11.1

165.8

600 700

30.4 52.7

18.6 5.1

18.2 30.5

127.7 80.5

AC C

EP

TE D

M AN U

SC

RI PT

Calcination temperature (oC)

18

ACCEPTED MANUSCRIPT Table 2 The amounts of Ti–O, O–H, Ti4+(2p3/2), and Ti4+(2p1/2) in different catalysts Ti-O Sample

energy (eV)

Ti4+ (2p3/2)

O-H

ATi-O

ATi-O/AO

energy

(%)

(eV)

AH-O

AH-O/AO energy (%)

(eV)

ATi(2p3/2)

Ti4+ (2p1/2)

ATi(2p3/2)/ATi energy (%)

(eV)

ATi(2p1/2)

ATi(2p1/2)/ATi (%)

TiO2-UT

529.57 5531.81

71.42

531.26 2213.36 28.58

458.37 3761.02

63.15

464.12 2194.99

36.85

TiO2-T

529.61 5394.71

77.21

531.26 1592.02 22.79

458.42 3432.41

63.13

464.14 2005.09

36.87

EP

TE D

M AN U

SC

RI PT

A is area of peak. AO= ATi-O+ AH-O, ATi= ATi(2p3/2)+ ATi(2p1/2)

AC C

*

19

ACCEPTED Table 3 Effect of calcination temperatureMANUSCRIPT on photocatalytic activity of TiO2 catalysts Degradation of phenol /% 400 (oC)

450 (oC)

500 (oC)

TiO2-T

63.5

90.1

97.9

TiO2-UT

48.1

72.9

76.3

600 (oC)

700 (oC)

800 (oC)

900 (oC)

86.8

47.7

19.2

6.8

60.3

20.5

8.1

4.3

AC C

EP

TE D

M AN U

SC

RI PT

Sample

20

ACCEPTED MANUSCRIPT 0.030

(a)

120

TiO2-UT Adsorption

100

TiO2-T Adsorption

80

TiO2-T Desorption

TiO2-UT

(b)

0.025

TiO2-T

60 40

0.020 0.015 0.010 0.005

20 0 0.0

0.2

0.4

0.6

P/P

0.8

0.000

1.0

o

1

RI PT

V/r (ml/g.nm)

TiO2-UT Desorption

3

Volume (cm /g)

140

10 100 Pore diameter (nm)

AC C

EP

TE D

M AN U

SC

Fig. 1 (a) Nitrogen adsorption isotherms and (b) the pore size distribution curve for TiO2 catalysts.

21

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

Fig. 2 TEM images of (a) TiO2-UT and (b) TiO2-T catalysts.

22

ACCEPTED MANUSCRIPT anatase rutile

(a)

anatase rutile

(b)

o

600 C

o

700 C

o

450 C

o

600 C

o

o

400 C

o

300 C

400 C

o

300 C

30

40o

2θ ( )

50

60

70

10

20

30

40o

2θ ( )

SC

20

EP

TE D

M AN U

Fig. 3 XRD patterns of (a) TiO2-UT and (b) TiO2-T catalysts.

AC C

10

o

500 C

RI PT

Intenstry

Intenstry

o

500 C

23

50

60

70

ACCEPTED MANUSCRIPT

1

-21.4%

428.6

0

85

-1

80

-2

-5.8%

75

200

400

600

o

800

0 466.7

80

-1

-7.2%

-2

70

200

-9.5%

-3 -4

400

600

o

TE D

M AN U

SC

Fig. 4 TG/DTA curves of (a) TiO2-UT and (b) TiO2-T precursors.

24

2 1

-22.7%

Temperature ( C)

Temperature ( C )

(b)

285.5

0

1000

EP

0

90

60

-3

70

TiO2-T

RI PT

90

103.5

2

AC C

TG (%/min)

95

100

TG /(%/min)

TiO 2 -U T

(a)

DSC (mW/mg)

100

91.7

800

1000

DSC /(mW/mg)

3

105

ACCEPTED MANUSCRIPT Ti2p3/2

(a) Ti2p

Ti-O

(b) O1s

Ti2p1/2

TiO2-UT

RI PT

TiO2-UT

Intensity (CPS)

Intensity (CPS)

O-H

TiO2-T

TiO2-T

470 468 466 464 462 460 458 456 454 452 450

Binding energy (eV)

536

534

532

530

528

SC

Binding energy (eV)

AC C

EP

TE D

M AN U

Fig. 5 XPS spectra of (a) Ti2p and (b) O1s.

25

526

524

100

ACCEPTED MANUSCRIPT TiO 2 -UT TiO 2 -T

80

40 20 0

Light on

-20

0

20

RI PT

60

Adsorption

Phenol (%)

P25-TiO 2

40 60 80 100 120 140 160 Time (min)

SC

Fig. 6 Photocatalytic degradation in phenol over different kinds of TiO2 catalysts: TiO2-UT, TiO2-T,

AC C

EP

TE D

M AN U

and commercially available P25 TiO2.

26

ACCEPTED MANUSCRIPT O TiCl4

Lignin

O-H H-O

H2O, H+

Ti(OH)n(4-n)+

O

O Lignin

O

Lignin

NH3 H2O

Ti Lignin

Ti

O-H

H-O

Ti

Ti

O

Ti O

Lignin

Ti

AC C

EP

TE D

M AN U

SC

RI PT

Fig. 7 Formation mechanism of mesoporous TiO2 with lignin as a template.

27

ACCEPTED MANUSCRIPT

Highlights

► Few work has used biological renewable resource of lignin template for porous TiO2. ► Electronegative lignin interacts with the positively charged Ti(OH)n(4-n)+ precursor.

RI PT

► The mesoporous TiO2 exhibited good photocatalytic activity for phenol degradation. ► Lignin-aided TiO2 had the smaller and uniform pore size and high specific area.

AC C

EP

TE D

M AN U

SC

► The formation mechanism for mesoporous TiO2 with a lignin template is proposed.