Engineering birnessite-type MnO2 nanosheets on fiberglass for pH-dependent degradation of methylene blue

Author’s Accepted Manuscript Engineering birnessite-type MnO2 nanosheets on fiberglass for pH-Dependent Degradation of Methylene Blue Yu Xin Zhang, Xiao Long Guo, Ming Huang, Xiao Dong Hao, Yuan Yuan, Chao Hua www.elsevier.com/locate/jpcs

PII: DOI: Reference:

S0022-3697(15)00070-0 http://dx.doi.org/10.1016/j.jpcs.2015.03.015 PCS7501

To appear in: Journal of Physical and Chemistry of Solids Received date: 28 November 2014 Revised date: 7 February 2015 Accepted date: 16 March 2015 Cite this article as: Yu Xin Zhang, Xiao Long Guo, Ming Huang, Xiao Dong Hao, Yuan Yuan and Chao Hua, Engineering birnessite-type MnO2 nanosheets on fiberglass for pH-Dependent Degradation of Methylene Blue, Journal of Physical and Chemistry of Solids, http://dx.doi.org/10.1016/j.jpcs.2015.03.015 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 galley proof before it is published in its final citable 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.

1

Engineering Birnessite-Type MnO2 Nanosheets on Fiberglass for

2

pH-Dependent Degradation of Methylene Blue

3

Yu Xin Zhanga,b*, Xiao Long Guoa, Ming Huanga, Xiao Dong Haoa, Yuan Yuana, Chao Huac

4

a College of Material Science and Engineering, Chongqing University, Chongqing 400044, PR China

5

b Nation Key Laboratory of Fundamental Science of Micro/Nano-Devices and System Technology, Chongqing

6

University, Chongqing 400044, PR China

7

c Institute of Process Engineering, Chinese Academy of Science, Beijing 100190, PR China

8 9

* Corresponding author.Tel:+86 23 65104131;

10

Fax:+86 23 65104131

11

E-mail address: [email protected] (Y.X. Zhang);

12 13

Abstract: We construct hierarchical MnO2 nanosheets @ fiberglass nanostructures via one-pot hydrothermal

14

method without any surfactants. The morphology and structure of MnO2-modified fiberglass composites are

15

examined by focus ion beam scanning electron microscopy (FIB/SEM), X-Ray diffraction (XRD) and Fourier

16

transform infrared spectroscopy (FT-IR). The birnessite-type MnO2 nanosheets are observed to grow vertically on

17

the surface of fiberglass. Furthermore, the birnessite-type MnO2-fiberglass composites exhibit good ability for

18

degradation of methylene blue (MB) in different pH levels. In neutral solution (pH 6.5-7.0), it achieves a high

19

removal rate of 96.1% (2 h, at 60 oC) in the presence of H2O2; and in acidic environment (pH 1.5), 96.8% of MB

20

solution (20 mg/L, 100 mL) is decomposed by oxidation within only 5 min. In principles, the rational design of

21

MnO2 nanosheets-decorated fiberglass architectures demonstrated the suitability of the low-cost MnO2-modified

22

fiberglass nanostructure for water treatment.

23

Keywords: A. Inorganic Compound; B. Chemical Synthesis; C. Electron Microscopy; D. Surface Properties

24 25 1

1

1. Introduction

2

Manganese dioxides (MnO2) have attracted considerable interest due to their distinctive physical,

3

inexpensiveness, chemical properties and wide applications in catalysis [1, 2], oxidation [3], sensor [4],

4

supercapacitor [5] and so forth. And some reports have demonstrated that MnO2 is one of the outstanding

5

candidates for the practical application in the degradation of dye wastewater in different surroundings. Among

6

them, the birnessite-type MnO2 (δ-MnO2) exhibits a larger adsorption and catalytic capacity than other

7

manganese compounds [6, 7]. This is due to δ-MnO2 consists of a kind of two-dimensional lamellar structure that

8

formed by [MnO6] octahedral sharing edges, and its interlayer can underwent cation exchange reactions [8]. At

9

present, lamellar structures of birnessite-type MnO2 nanosheets have been prepared by the electrochemical and

10

chemical routes, and their performance in wastewater treatment application have been investigated [9, 10].

11

However, these methods suffer from complicated or strict conditions. And it remains a challenge to develop facile

12

and economic synthetic methods for MnO2 nanosheets-based composites.

13

An emerging attractive approach to improve the degradation of MnO2 materials is to grow smart integrated

14

nanostructure with a high surface area. Among supporting materials (glass, cement, red brick and inorganic fibers),

15

fiberglass is economical, flexible, corrosion resistant and easy to handle [11]. Fiberglass materials have often been

16

used to reinforce the mechanical property of the material including strength and stiffness, enhance wear or erosion

17

resistance [12-14]. Recently, great interest has been expressed by researchers in functional modification based on

18

fiberglass materials [15-18]. Various thin films of materials have been coated on fibers including polymers, metals,

19

metal oxides, charged molecules, as well as nanomaterial and composites of combinations of metal, polymers,

20

dyes, and biomaterial. It is found that the highly active states of supported components can be formed on

21

fiberglass supports under certain conditions. This can be due to the specific structure of fiberglass and to the

22

localization of supported materials in them.

23

In this work, we fabricated novel MnO2-modified fiberglass composites via hydrothermal treatment without

24

any organic auxiliary agent. The obtained MnO2-modified fiberglass composites were employed as catalysts or

25

oxidants for degradation of MB (a detailed illustration was shown in Scheme 1). MnO2-modified fiberglass 2

1

composites exhibit good performance for the degradation of MB at different pH values solution, which implies its

2

good potential in the application of wastewater treatment.

3 4

2. Experimental details

5

2.1 Materials

6

All the chemical reagents were purchased from Alfa Aesar, which were of analytical purity and used without

7

any further purification. The fiberglasses employed were provided by Chongqing Polycomp International

8

Corporation (CPIC).

9

2.2 MnO2-modified fiberglass preparation

10

The MnO2-modified fiberglass composites were successfully prepared without any surfactant by a facile

11

method. In a typical synthesis, raw fiberglass (60-100 mg) was dispersed into the KMnO4 solution (30 mL, 0.01

12

M) to form a mixture. And then, the mixture was put into a Teflon-lined stainless steel autoclave and stirred for 30

13

min. Afterwards, mixed solution was treated under 160 oC for 24 h. Finally, the resulting sample was collected,

14

washed with distilled water, and dried at 60 oC for 8 h. Furthermore, the synthesis process can scale up to a larger

15

yield (1.0 g) of MnO2-modified fiberglass composites in a 0.3 L reaction system. In order to elucidate the effect of

16

processing time on catalytic performance of composites, as-prepared samples at 160 oC for 4 h and 12 h were

17

collected respectively.

18

2.3 Materials characterization

19

The crystallographic information and chemical composition of as-prepared products were analyzed powder

20

X-ray diffraction (Rigaku D/max-2500 with Cu Kα radiation) and Fourier transform infrared spectroscopy (FTIR,

21

Nicolet 5DXC). The morphology of the raw fiberglass and the MnO2-modified fiberglass composites were carried

22

out with focused ion beam (Zeiss Auriga FIB/SEM). Absorption spectrum was measured with ultraviolet−visible

23

light (UV-vis) spectrophotometer (Model UV-2450, Shimadzu, Japan).

24

2.4 Degradation of methylene blue

25

Methylene blue, a common dye in the textile industry, was chosen as a typical organic waste. A taper flask 3

1

(capacity ca. 250 mL) was used as the reactor vessel. The samples (60-100 mg) were added to the system

2

containing methylene blue (C16H18ClN3S) solution (20 mg L-1) 100 mL under stirring. UV-Vis absorption

3

spectra were recorded at different intervals to monitor the process. The pH values of the systems were adjusted

4

with dilute HCl solution. In neutral solution, except for methylene blue solution, the system also contained 15 mL

5

of 30 wt % H2O2 solution.

6 7

3. Results and discussion

8

3.1 Phase structure

9

Fig.1 (a) shows the XRD patterns of MnO2-modified fiberglass composites and MnO2 nanosheets. The

10

broad diffraction peaks around 25°, which is in line with the pattern of unmodified fiberglass (See Supplementary

11

information, SI-1(a)), indicating amorphous nature of SiO2 in the fiberglass [19, 20]. However, there is extremely

12

weak diffraction peak only at about 12.4° for MnO2. The diffraction intensities of MnO2 are so weak and all

13

overlapped or covered by the strong diffraction of the fiberglass (SiO2), indicating a lower content in weight [21,

14

22]. But the XRD result of MnO2 nanosheets (collected by removing surface coating from fiberglass composites)

15

exhibits that the diffraction peaks at about 12.3°, 24.5° and 36.7° are almost in accord with the standard XRD

16

pattern of birnessite-type manganese oxide crystal (JCPDS 86-0666), demonstrating δ-MnO2 exists in the

17

composites.

18

FT-IR spectrum of MnO2 nanosheets (Fig. 1b) presents that the broad band around 3440 cm-1 represented

19

the O-H antisymmetric stretching vibration of the interlayer water molecules and framework hydroxyl groups,

20

while the band at 1635 cm-1 is due to the bending vibrations of O-H groups of the adsorbed water molecules. The

21

sharp absorption peak at 1119 cm-1 is assigned to the coordination of Mn by the O–H. And the peaks at 507 and

22

493 cm-1 are considered as the main characteristic absorption bands of birnessite MnO2, corresponding to Mn-O

23

stretching modes of the octahedral layers in the birnessite structure [23], which are consistent with the previous

24

XRD results. There are no observed absorption bands for birnessite MnO2 in the composites (SI-1(b)). In addition,

25

the peaks at 1120 and 874 cm-1 could be assigned to Si-O symmetric stretching vibration [24, 25]. 4

1

3.2 Morphological structure

2

The unmodified fiberglass (diameter, 6 µm) exhibits a relative clean surface, providing favorable conditions

3

for the immobilization of the MnO2 nanosheets (Fig. 2a and 2b). While the surface of MnO2-modified fiberglass

4

composites become rough, and turn into brown instead of white after hydrothermal treatment (Fig. 2c and 2d). It

5

is notable that a porous framework was formed by randomly interlaced nanosheets, and the thickness of individual

6

MnO2 nanosheets is around 15-24 nm (Fig. 2e). The foremost features of such nanosheets are their high specific

7

surface area and a large number of exposed surface active sites [26], indicating that such morphology provided

8

large surface areas for the catalytic and oxidation reactions and facilitates the contact between the active material

9

and molecular of methylene blue. Moreover, the thickness of the MnO2 film was about 84-97 nm, measured from

10

a cross-section SEM image (Fig. 2f). On the basis of above results, we propose a possible growth mechanism for

11

the hybrid MnO2 nanosheets @ fiberglass structure. It involves two stages: heterogeneous nucleation, aggregation

12

and crystallization of primary particles. Firstly, the MnO42- nuclei are produced and adsorbed on surfaces of

13

fiberglass, forming MnO2 nuclei. With the increase of reaction time, the MnO2 nuclei are aggregated and grown

14

into nanosheets. Finally, the MnO2 nanosheets are compact and totally cover surfaces of fiberglass, resulting in

15

the formation of the hierarchical MnO2 nanosheets @ fiberglass composites. Such a process is similar to that in

16

previous reports [27, 28].

17

3.3 Catalytic decolorization of MB in the presence of H2O2

18

The catalytic properties of MnO2-modified fiberglass composite for MB dye have showed in Fig. 3. The

19

initial spectrum shows two absorption peaks (614 and 663 nm) among 300-800 nm wavelengths, which origin

20

from the molecular absorption of MB [29]. When MnO2-modified fiberglass composites + H2O2 are added, the

21

intensities of the MB absorption peaks are immediately decreased. As the reaction time progressed, the peak of

22

663 nm is blue-shifted to 606 nm at 4 h (Fig. 3b), and the change is similar to the earlier reports [30]. In addition,

23

the peaks at 614 and 663 nm are not observed in the spectrum, which is extraordinarily close to peaks of pure

24

water in corresponding locations (SI-2), demonstrating the complete discoloration of the MB molecules.

25

To clarify the catalyst performance, a systematic investigation is carried out and presented in Fig. 4, from 5

1

which we can see that when MnO2, or H2O2, or H2O2 + unmodified fiberglass is added individually to the MB

2

solution, no significant change in the concentration of MB is seen, indicating that less degradation reaction

3

occurred. Once MnO2-modified fiberglass composites and H2O2 are mixed together in the MB solution,

4

significant degradation of MB took place，and the decolorization rate of MB is up to 80.9% after 30 min, 96.13%

5

after 120 min. Comparing with unmodified fiberglass, MnO2-modified fiberglass composites show higher

6

catalytic activity. This could be due to the special lamellar structure and the larger surface area of the layered

7

MnO2 nanosheets, which bring in the high tendency for Mn(IV) to be reduced to Mn(II) under the sway of MB

8

dye molecules as reductants, the causes are also in agreement with the results of previous research [31, 32].

9

Moreover, this finding indicates that the composites exhibit more catalytic activity than some other Mn

10

oxide-based composites under similar conditions [33-35]. And we also explore the catalytic efficiency of

11

MnO2-modified fiberglass composites for MB at different temperature in the presence of H2O2 (SI-3), which

12

shows the removal of MB can increase with the increase in temperature (in the range of 25 -60 ℃).

13

To explore the impact of hydrothermal time on catalytic activity, catalytic efficiency of MB by

14

MnO2-modified fiberglass composites with different hydrothermal time is shown in SI-4. Where we can see that

15

the MnO2-modified fiberglass composites (160 °C, 24 h)/ H2O2 system is obviously superior to other two systems

16

(160 °C, 4 h; 160 °C, 12 h), indicating the hydrothermal time can influence the morphology and crystallinity of

17

MnO2. Proper hydrothermal time can lead to the formation birnessite-type MnO2 nanosheets with well defined

18

morphology and high crystallinity, which benefits improvement catalytic performance in degradation of MB [36].

19

Indeed, the efficiencies of MB degradation are enhanced by using the synthesized composites as catalysts for

20

the generation of free radicals such as HO•, HOO•, and O2•- from H2O2 molecules [37, 38]. And the additions of

21

catalysts vastly accelerated the process. During the catalytic oxidation reaction, these free radicals led to the

22

degradation of the organic compounds [39, 40]. As long as the free radicals were largely generated, it would

23

quickly attack the adsorbed pollutant molecules, leading to their decomposition. Whereas fiberglass acted as a

24

carrier to support MnO2 nanosheets, the nanosheets were kept from congregating due to immobilization on the

25

fiberglass, which made it possible for them to have high catalytic efficiency. 6

1 2

3.3.2 Oxidation degradation of MB

3

Effect of pH on the oxidation degradation of MB is shown in Fig. 5. The characteristic absorption peak of

4

MB dye (at the wavelength of 663 nm) decreases, and even disappears. What is more, an evident blue shift in the

5

λmax of the solution is observed (Fig. 5a, b, c), which implies the possible formation of new compounds in the

6

degradation processes. According to the report of Zaied et al. [41] the characteristic λmax of the possible

7

intermediates in the process are 638 nm (Azure B), 628 nm (Azure A), 618 nm (Azure C) and 601 nm (Thionin),

8

two of which are observed in Fig. 5. And thionin generation means the formation of the fully demethylated of MB

9

[42]. To some extent, these results can explain the real degradation of MB, and the degradation should mainly due

10

to oxidation reaction. According to the literature, it has been well established that degradation mechanism of MB

11

by birnessite-type MnO2 nanosheets in the acidic solution, that is, initially, MB molecules are adsorbed on surface

12

of MnO2 nanosheets; electron transfer then occurs between MB adsorbed and MnO2, leading to a fast oxidative

13

reaction to form intermediary compounds (AB, AA, AC and thionin, respectively). In the later period, the

14

aromatic ring is decomposed, which is relatively slow as compared with the demethylation and results in small

15

molecules with one benzene ring and some inorganic ions such as NO3- and SO4 2-. And MnO2 nanosheets are

16

reduced eventually to Mn2+ [41, 43, 44].

17

Fig. 6a shows the kinetics of MB degradation profiles. The degradation rate has sharp increase in the initial

18

time and more than 90% in 5 min at pH 1.5, 2 and 3. The reaction conducted at 4 presents a distinct difference

19

evolution over time. The difference of degradation kinetics between pH 4 and other pH levels may be ascribed to

20

the surface charges of MnO2 @ fiberglass composites. The maximum oxidation efficiency of MB is 97.2% at pH

21

1.5 (Fig. 6b), which is much more efficient than those of other oxidative degradation systems [45, 46]. The high

22

discoloration efficiency may be due to the layered δ-MnO2 nanosheets (e.g., open structure), which brings in the

23

high tendency for Mn4+ to be reduced to Mn2+. When the pH is 4.0, the decolorization efficiency of the dye is

24

only 44.2%, suggesting the oxidation degradation of MB on MnO2-modified fiberglass composites is

25

pH-dependent and decreased with increasing pH. However, at pH 4, the degradation rate of MB presents a trend 7

1

that increased with the increase in temperature (SI-5).

2

The zero point charge (pHzpc) 1.5-2.2 of birnessite-type MnO2 [47,48] which has been used as a model

3

layered Mn oxide in many relevant studies. It can be inferred that at pH＜pHzpc, the surface of the MnO2

4

nanosheets are positively charged due to the protonation reaction, and the positive charge increases with

5

decreasing pH, which would go against the adsorption of the cationic MB dye molecules onto the surface of

6

MnO2 nanosheets due to electrostatic repulsion; at pH > pHzpc, the surface is negatively charged due to the

7

deprotonation reaction, and the negative charge increases with increasing pH. If the decoloration mainly due to

8

adsorption of MB on the MnO2 surface, so the degradation would be enhanced with increased pH of solution, but

9

which is inconsistent with our results. Conversely, it is found that the degradation is enhanced with decreased pH

10

value in our experiments, and highest activity of MnO2 nanosheets appears at the pHZpc value (pH 1.5 and 2.0).

11

The rule is consistent with some previous reports [43, 49].

12 13

4. Conclusion

14

A novel architecture of MnO2 nanosheets-decorated fiberglass had been prepared via a facile and scaleable

15

method, where fiberglass is utilized as supporting materials for immobilization and dispersion of the nanosheets.

16

The as-prepared MnO2 nanosheets-modified fiberglass nanostructures show high activity to remove MB dye in

17

different pH values. As MnO2-modified fiberglass composites are employed as catalysts for the oxidation

18

degradation of MB solution by H2O2 in neutral solution, decolorization rate of MB is achieved in 96.1%.

19

Meanwhile, it has also shown high oxidation performance for MB solution (97.2% removed) in acidic solution

20

(pH 1.5). Thus, the MnO2-modified fiberglass composites could be used as large-scale and environmentally

21

friendly materials for treatment of dye effluent.

22 23

Acknowledgements

24

The authors gratefully acknowledge the financial supports provided by National Natural Science Foundation of

25

China (Grant Nos. 51104194), National Key Laboratory of Fundamental Science of Micro/Nanodevice and 8

1

System Technology (No. 2013MS06, Chongqing University), and State Education Ministryand Fundamental

2

Research Funds for the Central Universities (Project No. CDJZR14135501, Chongqing University, PR China).

3

The authors acknowledge support on the UV-vis spectra characterization by Prof. Huaili Zheng in College of

4

Urban Construction and Environmental Engineering, Chongqing University, Chongqing PR China.

5 6

References

7

[1] P.G. Smirniotis, P.M. Sreekanth, D.A. Peña, R.G. Jenkins, Manganese oxide catalysts supported on TiO2,

8

Al2O3, and SiO2: a comparison for low-temperature SCR of NO with NH3, Ind. Eng. Chem. Res. 45 (2006)

9

6436-6443.

10 11 12 13 14 15 16

[2] J. Petlicki, D. Palusova, T.G.M. van de Ven, Physicochemical aspects of catalytic decomposition of hydrogen peroxide by manganese compounds, Ind. Eng. Chem. Res. 44 (2005) 2002-2010. [3] M.X. Zhu, Z. Wang, S.H. Xu, T. Li, Decolorization of methylene blue by δ-MnO2-coated montmorillonite complexes: Emphasizing redox reactivity of Mn-oxide coatings, J. Hazard. Mater. 181 (2010) 57-64. [4] J.J. Feng, P.P. Zhang, A.J. Wang, Y. Zhang, W.J. Dong, J.R. Chen, One-pot hydrothermal synthesis of uniform β-MnO2 nanorods for nitrite sensing, J. Colloid Interf. Sci. 359 (2011) 1-8. [5] X.H. Lu, M.H. Yu, G.M. Wang, T. Zhai, S.L. Xie, Y.C. Ling, Y.X. Tong, Y. Li, H-TiO2@MnO2//H-TiO2@C

17

core–shell nanowires for high performance and flexible asymmetric supercapacitors, Adv. Mater. 25 (2013)

18

267−272.

19

[6] D. Frías, S.Nousir, I. Barrio, M. Montes, T. Ló pez, M.A. Centeno, J.A. Odriozola, Synthesis and

20

characterization of cryptomelane- and birnessite-type oxides: Precursor effect, Mater. Charact. 58 (2007)

21

776-781.

22 23 24 25

[7] X.H. Feng, L.M. Zhai, W.F. Tan, F. Liu, J.Z. He, Adsorption and redox reactions of heavy metals on synthesized Mn oxide minerals, Environ. Pollut. 147 (2007) 366-373. [8] Q. Feng, Y. Higashimoto, K. Kajiyoshi, K. Yanagisawa, Synthesis of lithium manganese oxides from layered manganese oxides by hydrothermal soft chemical process, J. Mater. Sci. Lett. 20 (2001) 269-271. 9

1

[9] M.A.M. Khraisheh, M.A. Al-Ghouti, S.J. Allen, M.N.M. Ahmad, The effect of pH, temperature, and

2

molecular size on the removal of dyes from textile effluent using manganese oxides modified diatomite,

3

Water Environ. Res. 76 (2004) 2655-2663.

4 5 6 7 8 9 10 11 12 13 14 15 16

[10] X.Y. Li, S.Y. Song, X. Wang, D.P. Liu, H. J Zhang, Self-assembled 3D flower-like hierarchical Fe3O4/KxMnO2 core–shell architectures and their application for removal of dye pollutants, CrystEngComm, 2012,14, 2866-2870. [11] J.M. Valtierra, J.G. Servín, C.F. Reyes, S. Calixto, The photocatalytic application and regeneration of anatase thin films with embedded commercial TiO2 particles deposited on glass microrods, Appl. Surf. Sci. 252 (2006) 3600-3608. [12] R.M. Christensen and F.M. Waals, Effective stiffness of randomly oriented fibre composites, J. Compos. Mater. 6 (1972) 518-535. [13] E.A. Stefanescu, X.L. Tan, Z.Q. Lin, N. Bowler, M.R. Kessler, Multifunctional fiberglass reinforced PMMA-BaTiO3 structural/dielectric composites, Polymer 52 (2011) 2016-2024. [14] N.M. Barkoula and J. Karger-Kocsis, Effects of fibre content and relative fibre-orientation on the solid particle erosion of GF/PP composites, Wear 252 (2002) 80-87.

17

[15] Z. Liu, P.F. Fang, S.J. Wang, Y.P. Gao, F.T. Chen, F. Zheng, Y. Liu, Y.Q. Dai, Photocatalytic degradation of

18

gaseous benzene with CdS-sensitized TiO2 film coated on fiberglass cloth, J. Mol. Catal. A-Chem. 363–364

19

(2012) 159-165.

20

[16] A. Suknev, A.C. vanVeen, A. Toktarev, E. Sadovskaya, B.Bal zhinimaev, C. Mirodatos, NO decomposition

21

over a new type of low metal content fiberglass catalysts studied by the TAP technique, Catal.Commun.

22

5 (2004) 691-695.

23 24 25

[17] G. Nangmenyi, X. Li, S. Mehrabi, E. Mintz, J. Economy, Silver-modified iron oxide nanoparticle impregnated fiberglass for disinfection of bacteria and viruses in water, Mater. Lett. 65 (2011) 1191-1193. [18] W. Sangkhuna, L. Laokiat, V. Tanboonchuy, P. Khamdahsag, N. Grisdanurak, Photocatalytic degradation of 10

1

BTEX using W-doped TiO2 immobilized on fiberglass cloth under visible light, Superlattice Microst.

2

52 (2012) 632-642.

3

[19] P.G. Wu, R.C. Xie, J.K. Shang, Enhanced visible-light photocatalytic disinfection of bacterial spores by

4

palladium-modified nitrogen-doped titanium oxide, J. Am. Ceram. Soc. 91 (2008) 2957-2962.

5

[20] C.H. Lin, J.W. Lee, C.Y. Chang, Y.J. Chang, Y.C. Lee ,M.Y. Hwa, Novel TiO2 thin films/glass fiber

6

photocatalytic reactors in the removal of bioaerosols, Surf.Coat.Technol. 205 (2010) S341-S344.

7

[21] H.Z. Chi, Y.W. Li, Y.X Xin and H.Y Qin, Boron-doped manganese dioxide for supercapacitors, Chem.

8 9

Commun. 50 (2014) 13349-13352. [22] C. H. Liang and C. S. Hwang, Effects of temperatures and cations of electrolyte on the capacitive

10

characteristics of the manganese oxide deposited by hydrothermal electrochemical method, J. Alloys

11

Compd. 500 (2010) 102-107.

12 13 14 15 16 17 18 19

[23] P.S. Vassileva, M.S. Apostolova, A.K. Detcheva, E.H. Ivanova, Bulgarian natural diatomites: modification and characterization, Chem. Pap. 67 (2013) 342-349. [24] A. Pasquarello, R. Car, Dynamical charge tensors and infrared spectrum of amorphous SiO2, Phys. Rev. Lett. 79 (1997) 1766-1769. [25] P. Lange, Evidence for disorder-induced vibrational mode coupling in thin amorphous SiO2 films, J. Appl. Phys. 66 (1989) 201-204. [26] K. Kai, Y. Yoshida, H. Kageyama, G. Saito, T. Ishigaki, Y. Furukawa and J. Kawamata, Room-Temperature Synthesis of Manganese Oxide Monosheets, J. Am. Chem. Soc. 130 (2008) 15938-15942.

20

[27] J.L. Zhou, L. Yu, M. Sun, S.Y. Yang, F. Ye, J. He, Z.F. Hao, Novel synthesis of birnessite-type MnO2

21

nanostructure for water treatment and electrochemical capacitor, Ind. Eng. Chem. Res. 52 (2013) 9586−9593.

22

[28] S. Zeng, K. Tang, T. Li, Z. Liang, D. Wang, Y. Wang, Y. Qi, W. Zhou, Facile route for the fabrication of

23

porous hematite nanoflowers: Its synthesis, growth mechanism, application in the lithium ion battery, and

24

magnetic and photocatalytic properties. J. Phys. Chem. C 112 (2008) 4836−4843.

25

[29] T. Gao, Norby. F. Krumeich, H. Okamoto, R. Nesper, H. Fjellvag, Synthesis and properties of 11

1 2 3 4

layered-structured Mn5O8 nanorods, J. Phys. Chem. C 114 (2010) 922-928. [30] X. Peng, I. Ichinose, Manganese oxyhydroxide and oxide nanofibers for high efficiency degradation of organic pollutants, Nanotechnology 22 (2011) 15701-15707. [31] G. Cheng, L. Yu, T. Lin, R.N. Yang, M. Sun, B. Lan, L.L Yang, F.Z Deng, A facile one-pot

5

hydrothermal synthesis of β-MnO2 nanopincers and their catalytic degradation of methylene blue, J. Solid

6

State Chem. 217 (2014) 57-63.

7

[32] W.X Zhang, Z.H. Yang, X. Wang, Y.C. Zhang, X.G. Wen, S.H. Yang, Large-scale synthesis of

8

β-MnO2 nanorods and their rapid and efficient catalytic oxidation of methylene blue dye,

9

Catal. Commun. 7 (2006) 408-412.

10 11 12 13 14

[33] J.H. Park, I. Jang, K. Song, S.G. Oh, Surfactants-assisted preparation of TiO2–Mn oxide composites and their catalytic activities for degradation of organic pollutant, J. Phys. Chem. Solids 74 (2013) 1056-1062. [34] F. Li, J. Wu, Q. Qin, Z. Li, X. Huang, Facile synthesis of γ-MnOOH micro/nanorods and their conversion to β-MnO2, Mn3O4, J. Alloys Compd. 492 (2010) 339-346. [35] P.Q. Zhang, Y.G. Zhan, B.X. Cai, C.C. Hao, J. Wang, C.X. Liu, Z.J. Meng, Z.L. Yin, and Q.Y. Chen,

15

Shape-controlled synthesis of Mn3O4 nanocrystals and their catalysis of the degradation of methylene blue,

16

Nano Res. 3 (2010) 235-243.

17

[36] C.L. Yu, G. Li, L.F. Wei, Q.Z. Fan, Q. Shu, Jimmy C. Yu, Fabrication, characterization of β-MnO2

18

microrod catalysts and their performance in rapid degradation of dyes of high concentration, Catal.

19

Today 224 (2014) 154-162.

20 21 22 23 24 25

[37] S.C. Kim, W.G. Shim, Catalytic combustion of VOCs over a series of manganese oxide catalysts, Appl. Catal. B-Environ. 98 (2010) 180-185. [38] Z.R. Tian, W. Tong, J.Y. Wang, N.G. Duan, V.V. Krishnan, S.L. Sui, Manganese oxide mesoporous structures: mixed-valent semiconducting catalysts, Science 276 (1997) 926-930. [39] Q. Xiang, J. Yu, P.K. Wong, Quantitative characterization of hydroxyl radicals produced by various photocatalysts, J. Colloid Interf. Sci. 357 (2011) 163-167. 12

1 2 3

[40] W. Zhang, Z. Yang, X. Wang, Y. Zhang, X. Wen, S.Yang, Large-scale synthesis of β-MnO2 nanorods and their rapid and efficient catalytic oxidation of methylene blue dye, Catal. Commun. 7 (2006) 408-412. [41] M. Zaied, S. Peulon, N. Bellakhal, A. Chaussé, Studies of N-demethylation oxidative and degradation of

4

methylene blue by thin layers of birnessite electrodeposited onto SnO2, Appl. Catal. B-Environmental

5

101 (2011) 441-450.

6 7

[42] Pedro Tartaj, Layered manganates from soft-templates: preparation, characterization and enhanced dye demethylation capabilities, J. Mater. Chem. 22(2012) 17718–17723.

8

[43] G.X. Zhao, J.X. Li, X.M. Ren, J. Hu,W.P. Hu, X.K. Wang, Highly active MnO2nanosheet synthesis from

9

graphene oxide templates and their application in efficient oxidative degradation of methylene blue, RSC

10 11 12 13

Adv. 3 (2013), 12909–12914. [44] W.H. Kuan, Y.C. Chan, pH-dependent mechanisms of methylene blue reacting with tunneled manganese oxide pyrolusite, J. Hazard. Mater. 239–240 (2012) 152–159. [45] Thamayanthy Sriskandakumar, Naftali Opembe, Chun-Hu Chen, Aimee Morey, Cecil King’ondu and Steven

14

L. Suib, Green Decomposition of Organic Dyes Using Octahedral Molecular Sieve Manganese Oxide

15

Catalysts, J. Phys. Chem. A 113 (2009) 1523-1530.

16

[46] W. Gao, M. Shao, L. Yang, S. Zhuo, S. Ye, S. Lee, Manganese dioxide modified silicon nanowires and their

17

excellent catalysis in the decomposition of methylene blue, Appl. Phys. Lett. 100 (2012) 063104.1-063104.3.

18

[47] C.H. Chen, V.M.B. Crisostomo, W.N. Li, L.P. Xu, S.L. Sui, A designed single-step method for synthesis

19

and structural study of organic− inorganic hybrid materials: Well-ordered layered manganese oxide

20

nanocomposites, J. Am. Chem. Soc. 130 (2008) 14390-14391.

21 22

[48] J.W. Murray, The surface chemistry of hydrous manganese dioxide, J. Colloid Interface Sci. 46 (1974) 357-371.

23

[49] Y.X. Zhang, X.D. Hao, F. Li, Z.P. Diao, Z.Y. Guo, J. Li , pH-Dependent Degradation of Methylene Blue via

24

Rational-Designed MnO2 Nanosheet-Decorated Diatomites, Ind. Eng. Chem. Res. 53 (2014) 6966–6977.

25

Scheme 1. Synthesis of MnO2-modified fiberglass composites by means of the hydrothermal method as well 13

1

as their application for the degradation of MB.

2

3

4

5

6

7

8

9

10

11 14

1

2

3

4

5

6

7

8

Fig. 1. XRD patterns of (a) MnO2-modified fiberglass composites and MnO2 nanosheets, FT-IR spectra of (b)

9

MnO2 nanosheets. The inset shows enlarged FT-IR spectra of the MnO2 nanosheets in the range 555-450

10

cm-1.

11

(a)

(b)

12 15

1

2

3

4

5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 16

1 2 3 4

Fig. 2. SEM images of unmodified fiberglass (a-b), MnO2-modified fiberglass composites with different

5

magnifications(c, d and e), and cross-section MnO2 film (f). The insets show the corresponding optical

6

images of unmodified fiberglass, MnO2-modified fiberglass composites, and detail view of MnO2

7

nanosheets.

8

17

1 2 3 4 5 6 7 8 9

Fig. 3. UV-vis absorbance spectra of MB dye solution (20 mg/L) in the presence of MnO2-modified fiberglass

10

composites (0.06 g) and H2O2 (15 mL, 30 wt %) treated at 60 oC for different time intervals (a). UV-vis

11

absorbance spectra of MnO2-modified fiberglass in the range of 500-700 nm (b).

12 13

(b) (a)

14

15

16 18

1

2

3

4

5

6

7

8

9

10

11 12 13 14 15 19

1 2 3 4 5 6 7 8

Fig. 4. Time profiles of MB degradation: (1) MB; (2) MB + H2O2; (3) MB + H2O2 + unmodified fiberglass;

9

(4) MB + MnO2-modified fiberglass composites; (5) MB + H2O2 + MnO2-modified fiberglass composites.

10

C0 (mg/L) is the initial concentration of the MB solution and C (mg/L) is the concentration of that at different

11

intervals.

12

13

14

15

16 20

1

2

3

4

5

6

7

8

9 10 11 12 13 14 15

Fig. 5. UV-vis absorbance spectra of MB dye solution after different time intervals with MnO2-modified

16

fiberglass composites (160 °C, 24 h) dosage of 100 mg at different pH values: (a) pH 1.5, (b) pH 2, (c) pH 3,

17

and (d) pH 4. 21

1

2

(a)

(b)

(c)

(d)

3

4

5

6

7

8

9

10

11

12

13 22

1

2

3

4

5 6 7 8

Highlights

9



MnO2@Fiberglass Core-shell Architecture.

10



pH-dependent Decomposition of Methylene Blue.

11



pH 6.5-7.0: a high removal rate of 96.1% (2 h, at 60 oC) in the presence of H2O2.

12



Fabrication strategy: Facile Self-assembly.

13 14 15 16 17 18 19 23

1 2

Fig. 6. (a) Time evolution of MB degradation at various pH levels; (b) Comparison of the oxidation efficiency of

3

MB at different pH values. Conditions: (MB: 20 mg/L; reation time: 100 min; room temperature: 25 ℃).

4

5

6

(b)

(a)

24