Synthesis of composite photocatalyst based on the ordered mesoporous carbon-CuO with high photocatalytic activity

Accepted Manuscript Synthesis of Composite photocatalyst based on the Ordered Mesoporous Carbon- CuO with High Photocatalytic Activity Ailijiang Tuerdi, Abdukader Abdukayum, Pei Chen PII: DOI: Reference:

S0167-577X(17)31181-3 http://dx.doi.org/10.1016/j.matlet.2017.08.002 MLBLUE 22979

To appear in:

Materials Letters

Received Date: Revised Date: Accepted Date:

14 May 2017 12 July 2017 1 August 2017

Please cite this article as: A. Tuerdi, A. Abdukayum, P. Chen, Synthesis of Composite photocatalyst based on the Ordered Mesoporous Carbon- CuO with High Photocatalytic Activity, Materials Letters (2017), doi: http:// dx.doi.org/10.1016/j.matlet.2017.08.002

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.

Synthesis of Composite photocatalyst based on the Ordered Mesoporous Carbon- CuO with High Photocatalytic Activity Ailijiang Tuerdi,a Abdukader Abdukayum,*a Pei Chenb a

( Xinjiang Laboratory of Native Medicinal and Edible Plant Resources Chemistry, College of Chemistry and Environmental Science, Kashgar University, Kashgar 844007, China） b

( Key Laboratory of Applied Surface and Colloid Chemistry (MOE), School of Materials Science and Engineering, Shaanxi Normal University, Xi’ an 710062, China）

：+86-13579073366 ,

E-mail: [email protected];

Abstract ：Development of new photocatalysts with high catalytic efficiency, catalytic stability, and visible-light activity is very important for environmental decontamination and clean energy production. Here, we show the preparation of a composite photocatalyst of ordered mesoporous carbon (OMC)-CuO by a solution impregnation method with OMC as the carrier. The novel combination of CuO nanaoparticles and OMC exhibit not only a high visible-light catalytic activity and excellent surface adsorption property, but also a catalytic stability. The photodegradation efficiency of OMC-CuO for rhodamine B is 97.2% under visible-light irradiation, and higher than pure TiO2 and CuO nanaoparticles. Key words:Ordered mesoporous carbon;CuO; Photocatalysis; Rhodamine B; Porous materials; Nanocomposites

1. Introduction With the rapid development of the global economy, environmental pollution and energy shortages are becoming serious problems worldwide. Recently, some new photocatalytic materials have received significant attention because of their broad applications in the conversion of solar energy and environmental decontamination. Titanium dioxide (TiO2) has been widely applied in the field of catalysis because of its chemical stability, good catalytic activity, and low cost. Because of its large band gap of 3.2 eV [1-3], TiO2 is an ultraviolet (UV)-light driven photocatalyst. In order to improve the photocatalytic efficiency and visible-light activity of TiO2, many attempts have been made to synthesize titania, including doping with metal, nonmetals, and metallic oxides, as well as noble metal deposition [4-8]. Although modifications of TiO2 have been successfully used to expand the visible-light activity of the photocatalyst, the preparation process of TiO2-based composite catalysts remains relatively complicated and results in poor catalytic stability. Thus, the application of

1

TiO2-based catalysts has remained fairly limited. Therefore, it is urgently necessary to develop new photocatalysts that have low toxicity, high photocatalytic efficiency, catalytic stability, and visible-light activity. Ordered mesoporous carbon (OMC) not only has a large specific surface area, uniform pore size distribution, and good surface adsorption property, but also has good electrical conductivity, chemical inertness, and carrier mobility. It can provide a new photocatalytic reaction center for improving the photocatalytic efficiency [9,10]. Cupric oxide (CuO) is a p-type metal oxide semiconductor with a narrow band gap (ranging from 1.2 to 1.5 eV). It has been proposed as a new type semiconductor photocatalyst under visible-light irradiation, which can effectively promote the separation of electron-hole pairs [11-14]. The combination of OMC and CuO into one platform with high photocatalytic efficiency and photostability could offer attractive synergistic advantages in the degradation of pollutants. Nevertheless, it seems that no OMC-CuO based composite photocatalysts have yet been reported for use in pollutant degradation applications. Herein, we present a composite photocatalyst of OMC- copper oxide (OMC-CuO) prepared by a solution impregnation method with OMC as the carrier. Its photocatalytic performance was evaluated by monitoring the extent of decolorization of an aqueous rhodamine B (RhB) solution under visible-light illumination (λ > 420 nm). OMC-CuO photocatalysts exhibited excellent photostabilty and photocatalytic activity with the degradation values of 97.2% for RhB, which are higher than that achieved with pure TiO2 and CuO nanoparticles.

2. Experiments The synthesis of OMC was performed according to the previous literature (Supplementary material) [15]. A typical preparation of OMC-CuO 10 wt.% was described as follows: 0.25 g of OMC was ultrasonically disperse in 45 mL of ethanol for 30 min, after the mixed solution stirred at 50 ℃ for 2 h to produce the solution A. The 0.075 g Cu(NO3)2·3H2O was dissolved in 5 mL of furfuryl alcohol under vigorous stirring for 2 h to produce solution B. Finally solution B was dropwise added to solution A , and stirring for 12 h, the mixture was filtered several times.Finally, the sample carbonization was carried out at 550℃ in air for 3 h with a heating rate of 10℃/min. The obtained samples are denoted as OMC-CuO x % (x % is weight percent of CuO).

3. Results and discussion TEM images (Fig. 1a) show that the OMC sample exhibited a large, stripe-like, well-ordered mesoporous structure, suggesting that the OMC uniquely consisted of a highly ordered 2D hexagonal structure. TEM, HR-TEM, and SAED images (Fig.1b-1d) of the OMC-CuO 10% composite show that the structure of the photocatalyst remained as a large, stripe-like, well-ordered hexagonal structure. Hence, the ordered mesoporous structure of OMC was preserved. The dark spots seen in the images have a diameter of about 10 nm and represent the CuO nanoparticles, which were well dispersed on the surface of the OMC. The HR-TEM analysis indicates that the CuO nanocrystals had a single crystal structure with interplanar spacing of 0.32、0.35 and 0.53 nm (Fig 1c), which corresponds to the d-spacing for (110), (002) and (111) lattice planes of rhombohedral CuO, respectively. The

2

selected-area electron diffraction (SAED) pattern confirmed that the CuO crystal on OMC is a rhombohedral CuO single crystal (Fig. 1d). The amounts of CuO loading on OMC were estimated by TG analysis (Fig. S1 in the Supplementary material). A sharp drop of weight for OMC-CuO occurred in the temperature range of 470−630 ℃ and well matched the weight loss curve of pure OMC (Fig. S1). The weight percentages of CuO on OMC-CuO 13%, 10%, 7%, 4% and 1% were estimated to be 12.53%, 9.68%, 6.65%, 3.69% and 0.83%, respectively. Low-angle XRD patterns of the OMC and OMC-CuO composite are shown in (Fig. 2a). OMC and OMC-CuO gave rise to small-angle XRD peaks with 2θ at 0.65°, 1.12°, and 1.51°, which were assigned to (100), (110), and (200) diffractions, respectively, of a two-dimensional (2-D) hexagonal space group (p6mm) [16]. This suggests that both the OMC and OMC-CuO contained highly ordered hexagonal pore arrangements, which was consistent with the results of TEM analysis. Wide-angle XRD patterns of the OMC-CuO composite photocatalyst are shown in (Fig. 2b). Peaks of the OMC-CuO sample with 2θ at 32.16°, 35.22°, 38.39°, 48.48°, 53.08°, 58.06°, 61.29°, 65.82°, 67.82°, 72.1°, and 74.86° were indexed to the (110), (002), (111), (200), (111), (20-2), (020), (202), (11-3), (31-1), (220), (311), and (004) planes, respectively, confirming the monoclinic structure of CuO (JCPDS: 65-5714) [17]. No other peaks were observed, suggesting high purity of the as-prepared samples, since strong intensity and narrow XRD peaks indicate that the resulting products were highly crystalline. The energy-dispersive X-ray spectroscopy (EDX) analysis (Fig. 2c) demonstrated that the OMC-CuO composite photocatalyst was composed of Cu, C, and very little O, no other elements were found. These results revealed that CuO was successfully embedded on the OMC surface. The OMC and the OMC-CuO exhibited typical type IV curves with clear nitrogen condensation steps (Fig. S2a). At relatively low pressures, the thickness of the adsorption layer increased with the pressure. However, at higher pressures, a clear hysteresis loop was observed, which is typical of mesoporous materials. Samples of the OMC and OMC-CuO showed a sharp capillary condensation step in the P/P0 range 0.5–0.6, which indicated that these mesoporous carbon structures had narrow pore size distributions, which was in agreement with pore size distributions of around 3-4 nm (Fig.

S2b) and result of TEM analysis (Fig. 1c). These results further confirmed that, with size less than 10 nm, the CuO nanoparticles were regularly well dispersed on the surface of the OMC. The corresponding pore structural parameters, including BET surface areas, total pore volumes, and pore sizes, are summarized in Table 1. These results showed that the BET surface area of OMC-CuO was lower than that of the OMC, suggesting that most of the CuO was on the surface of OMC. The UV-vis spectrum of OMC-CuO 10% (Fig. S3a) indicates that the synthesized OMC-CuO has a broad absorption property ranged from UV to near-infrared light (220-900 nm). The band gap (Eg) of OMC-CuO was calculated to be approximately 1.45 eV (Fig. S3b) according to the following equation [18]: αhv = A(hv − Eg)2 (1) Where, α is the absorption coefficient, hv is the photo energy, Eg is the band gap and A is a constant. The narrow band gap of OMC-CuO indicated that the synthesized OMC-CuO could absorb

3

most of the visible light among the sunlight. PL spectra of pure CuO and OMC-CuO 10% (Fig. S4) shows that emission peaks at 422, 485 and 529 nm are observed in both samples. Moreover, it can be clearly seen that the peak intensity of OMC-CuO is lower than the pure CuO nanoparticles, implying that the OMC channels may accelerate the transfer of electrons, thus contributed to decreasing the recombination of electron–hole pairs [10]. The RhB was used as probe molecules to evaluate the photocatalytic performance of the OMC-CuO (Supplementary material). The photo-degradation efficiency of different amounts of CuO loading on OMC, P25, pure OMC and pure CuO nanoparticles for RhB are shown in Fig. 3. The results indicate that the photo-degradation efficiency of OMC-CuO depended on the amount of CuO loading on OMC (Fig. 3a). When the amounts of CuO loading on OMC are lower than 10 %, the photocatalytic efficiency of OMC-CuO increased with increasing amounts of CuO. However, continuously increasing of amounts of CuO will decrease the photocatalytic activity of OMC-CuO, due to more accumulation of CuO nanoparticles on the OMC might cause a reduced adsorption of RhB and promote recombination of photogenerated carriers, resulting in a decrease of photocatalytic efficiency. The optimal amount of CuO loading on OMC is about 10%. Fig. 3b shows that the pure OMC have no photocatalytic activity for RhB, except for good surface adsorption property. The OMC-CuO 10% exhibited an excellent photocatalytic activity with a degradation efficiency of 97.2% after 100 min irradiation with visible-light, which is higher than either pure TiO2 or CuO nanoparticles. The lager surface of OMC can offer more active adsorption sites, resulting in enhanced adsorptivity of RhB molecules. Moreover, OMC channels may accelerate the transfer of electrons, thus contributed to decreasing the recombination of electron-hole pairs, which may improve the photocatalytic activity of OMC-CuO [10]. The stability and

of OMC-CuO were evaluated through five times repetitive

experiments of photo-degradation.

, the OMC-CuO 10% still remained more than

88% of photocatalytic activity after five cycles while the

CuO

remain

photocatalytic

activity, showing the combination of CuO nanaoparticles with OMC not only photocatalytic activity

CuO

CuO

OMC-CuO 10% was also investigated. XRD patterns of OMC-CuO have not notable changes after photocatalytic recycles, however the crystalline phase structure of pure CuO was destroyed after photocatalytic recycles, indicating the pure CuO was suffer a serious photocorrosion (Fig. S6). TEM image of

OMC-CuO also show that the morphology of CuO on OMC have not

any remarkable changes after photocatalytic recycles (Fig. S7).

indicating that the

prepared OMC-CuO nanocomposite is stable and reusable in the photo-degradation of pollution. When the OMC-CuO is irradiated by visible light, the electron absorbs the high-energy radiation and excites to the conduction band of CuO, leaving the same number of holes (h+) in the forbidden bands of CuO (Fig.3c). This discontinuity is beneficial for the separation of the electron-hole pairs, generating electrons and holes on the surface of CuO. The holes are then captured by hydroxyl groups (OH−) at the CuO surface, yielding hydroxyl radicals (HO•) [19], and the electrons are trapped by the dissolved oxygen molecules (O2), producing superoxide anions (O2•−) [20]. The resulting superoxide anions (O2•−) and hydroxyl radicals (HO•) are strong oxidizing agents which serve to degrade the RhB molecules. This photocatalytic reaction mechanism can be represented as follows:

4

+ VB

CuO＋ hVB+ ＋ H2 eCB-＋ O2 -

+

O2 ·＋H

＋eCB-

（2）

＋H+ 2

（3）

·

（4）

2·

（5）

-

RhB＋ (·OH / O2 ·) → Degradation

（6）

4. Conclusions The composite photocatalyst OMC-CuO was prepared by a solution impregnation method with OMC as the carrier. CuO nanoparticles of diameter 10 nm were dispersed on the surface of the OMC, and the ordered mesoporous structures were almost completely preserved. The resulting OMC-CuO photocatalysts exhibited notable photocatalytic activity toward the degradation of RhB, with a degradation efficiency of 97.2% after 100 min under visible light irradiation. The combination of CuO nanaoparticles with OMC not only

photocatalytic activity

CuO

CuO A possible photocatalytic mechanism was proposed based on the experimental results.The prepared OMC-CuO composite photocatalyst offers great potential for degradationof pollutant with sunlight.

Acknowledgements This work has been supported by the Scientific Research Program of the Higher Education Institution of Xinjiang (XJEDU2016S073).

References [1] S. Okunaka, H. Tokudome, Y. Hitomi, R. Abe, J. Mater. Chem. A. 3 (2014) 1688 -1695. [2] Y. Xie, X. Zhang, P. Ma, Z. Wu, L. Piao, Nano. Res. 8 (2015) 2092 -2101. [3] M. Pelaez , N. T. Nolen, S. C. Pillai, Appl. Catal. B-Environ. 125 (2012) 331-349. [4] J. Yao, L. Li, H. Song, C. Liu, X. Chen, Carbon 47 (2009) 436-444. [5] M. Dai，B. D. Vogt，J. Colloid Interf. Sci.387 (2012) 127-134. [6] R. Bashiri, N. M. Mohamed, C. F. Kait, S. Sufian, Appl. Mech. Mater. 625 (2014) 856 -859. [7] A. A. Ismail, Microporous Mesoporous Mater. 149 (2012) 69-75. [8] P. A. K. Reddy, B. Srinivas, P. Kala, V. D. Kumari, M. Subrahmanyam, Mater. Res. Bull. 46 (2011) 1766-1771. [9] Q. Wang, Y. Mu, W. Zhang, L. Zhong, Y. Meng, Y.- H. Sun, RSC. Adv. 4 (2014) 32113-32116. [10] Q. Zhao, M. Gong, W. P. Liu, Y. L. Mao, S. K. Le, S. Ju, F. Long, X. F. Liu, K. Liu, T. S. Jiang, Appl. Surf. Sci. 332 (2015) 138-146.

5

[11] R. Sankar, P. Manikandan, V. Malarvizhi, T. Fathima, K. S. Shivashangari, V. Ravikumara, Spectrochim. Acta A. 121 (2014) 746-750. [12] S. Wang, H. Xu, L. Qian, X. Jia, J. Wang, Y. Liu, W. Tang, J. Solid State Chem. 182 (2009) 1088 -1093. [13] S. Sonia, S. Poongodi, P. S. Kumar, D. Mangalaraj, N. Ponpandian, C. Viswanathana, Mate. Sci. Semicond. Process. 30 (2015) 585-591. [14] M. Ahamed, H. A. Alhadlaq, M. A. M. Khan, P. Karuppiah，N. A. Dhabi, J. Nanomater. 3 (2014) 1-4. [15] D. Liu, J. Lei, L. Guo, D. Qu, Y. Li, B. Su, Carbon 49 (2011) 2113 -2119. [16] S. Shen, Y. Deng，G. Zhu，D. Mao，Y. Wang, G. Wu, J. Li, X. Liu, G. Lu, D. Zhao, J. Mater. Sci. 42 (2007) 7057-7061. [17] M. Vaseem, A. Umar, Y. B. Hahn, D. H. Kim, K. S. Lee, J. S. Jang, J. S. Lee, Catal.Commun. 10 (2008) 11-16. [18] Y.-B Cui, J.-F Luan, J. Environ. Sci. 29 (2015) 51-61. [19] K. Mageshwari, R. Sathyamoorthy, J. Park, Powder Technol. 278 (2015) 150-156. [20] S. Safa, R. Azimirad, S. S. Moghaddam, M. Rabbani, Desal. Water. Treat. 13 (2015) 1-9.

Figure captions Fig.1(a) TEM image of OMC; (b-d) TEM, HR-TEM and SAED images of OMC-CuO 10% Fig.2 (a) Low angle XRD pattems of OMC and OMC-CuO 10%; (b) XRD pattems and (c) EDS pattems of OMC-CuO 10% Fig.3 The photo-degradation efficiency of (a) different amounts of CuO loading on OMC, (b) P25, pure OMC and pure CuO nanoparticles for RhB; (c) Schematic illustration for the photocatalytic mechanism of OMC-CuO

6

Highlights



A composite photocatalyst of ordered mesoporous carbon (OMC)-CuO was obtained by a solution impregnation method.



Combination of CuO nanaoparticles and OMC exhibit a high visible-light catalytic activity and catalytic stability.



The photocatalytic efficiency of OMC-CuO for rhodamine B is 98.5%, which are superior to that of the pure TiO2 and CuO nanoparticles.

7

Table1 Pore parameters of OMC and OMC-CuO 10%

Pore volume(BJH) Sample

Surface area (BET) S/(m2. g-1)

Pore diameter (D/nm)

V /(cm3. g-1)

OMC

599.87

3.67

0.229

OMC-CuO 10%

336.94

3.65

0.212

8