ZnO nanocomposite with the high electrical conductivity

Materials Letters 252 (2019) 325–328

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Metal–organic framework derived porous 2D semiconductor C/ZnO nanocomposite with the high electrical conductivity Xiao-Wei Yan a,1, Monika Joharian b,1, Mina Naghiloo c, Reza Rasuli c, Mao-Lin Hu d,⇑, Ali Morsali b,⇑ a College of Materials and Chemical Engineering, and Guangxi Key Laboratory of Calcium Carbonate Resources Comprehensive Utilization, Hezhou University, Hezhou, Guangxi 542800, PR China b Department of Chemistry, Faculty of Sciences, Tarbiat Modares University, P.O. Box 14115-4838, Tehran, Islamic Republic of Iran c Department of Physics, Faculty of Sciences, University of Zanjan, P.O. Box 45371-38791, Zanjan, Islamic Republic of Iran d College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou 325035, PR China

a r t i c l e

i n f o

Article history: Received 17 April 2019 Received in revised form 21 May 2019 Accepted 3 June 2019 Available online 4 June 2019 Keywords: Fluorinated metal–organic framework Semiconductor Electrical conductivity Nanocomposite

a b s t r a c t In this work, we report a simple method for synthesis of the C/ZnO semiconductor nanocomposite with the high porosity (732 m2/g) from fluorinated metal–organic framework (F-MOF), namely [Zn2(hfibba)2(L1)]n.DMF (TMU-44) where (L1 = N,N’-bis-pyridin-4-ylmethylene-benzene-1,5-diamine and H2hfibba = 4,40 -(hexafluoroisopropylidene) bis(benzoic acid)) with the limited porosity. The C/ZnO nanocomposite was characterized by powder X-ray diffraction; Brunauer-Emmett-Teller (BET) surface area, FE-SEM, and EDX mapping analysis. Furthermore, the as-synthesized C/ZnO nanocomposite showed favorable electrical conductivity at room temperature. Ó 2019 Elsevier B.V. All rights reserved.

1. Introduction Zinc oxide (ZnO) as a kind of n-type semiconductor material shows a wide band gap (3.37 eV) and high melting point of 1975 °C [1]. ZnO has potential applications such as catalysis, chemical sensors, lithium storage, dye-sensitized solar cells, etc. [2–7]. To obtain larger specific surface area, low dimension ZnO nanostructures [8–16], and other porous microstructures [17,18] have been synthesized using hydrothermal method [19,20], thermal evaporation method [21], etc. Recently, nanocomposite oxides such as ZnO/Co3O4 [22], ZnO/C [23], etc., have become one of the most extensively studied materials, which improved properties compared with single oxide. In recent years, Metal–organic frameworks (MOFs) have also been used as precursors for the fabrication of metal/metal oxide nanostructures [24–26]. MOFs evolved as an important class of potentially porous materials, have shown extensive applications in different research areas such as catalysis, sensing, gas storage, etc. [27–32]. Recently researchers have paid a lot of attention to the pyrolysis/thermolysis of MOFs to obtain different metal/metal oxide nanostructures. ⇑ Corresponding authors. E-mail addresses: [email protected] (M.-L. Hu), [email protected] (A. Morsali). 1 Xiao-Wei Yan and Monika Joharian contributed equally to this work. https://doi.org/10.1016/j.matlet.2019.06.007 0167-577X/Ó 2019 Elsevier B.V. All rights reserved.

In this study, a porous C/ZnO nanocomposite material synthesized by a simple method with high surface area from the F-MOF with limited porosity and characterized. The obtained porous 2D semiconductor nanocomposite showed excellent electrical conductivity. 2. Experimental All starting materials were purchased from Aldrich and Merck companies and used as received. FT-IR spectra were recorded using a Nicolet Fourier Transform IR, Nicolet 100 spectrometer in the range 500–4000 cm1 using the KBr disk technique. The samples were also characterized by a field emission scanning electron microscope (FE-SEM), EDS TESCAN MIRA with gold coating. X-ray powder diffraction (XRD) measurements were performed using a Philips diffractometer from the X’pert company with monochromated Cu-Ka (k = 1.54056 Å) radiation. 2.1. Synthesis of TMU-44 The ligand N,N’-bis-pyridin-4-ylmethylene-benzene-1,4-dia mine (L1) was synthesized according to the previously reported method [33]. The structures of the ligands displayed in Fig. 1S. The single crystal of [Zn2(hfipbb)2(L1)]n.DMF (TMU-44) was synthesized and characterized by the reported method. Further, the synthesis of the framework is confirmed by the PXRD data,

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Supporting Information, Fig. 2S. At first H2hfipbba (0.078 g, 0.2 mmol), L1 (0.057 g, 0.2 mmol), Zn(NO3)26H2O (0.06 g, 0.2 mmol) and DMF (20 ml) were mixed. Then the solution was divided into 3 ml glass vials; each filled up to 2.5 ml. The vials were closed tightly and set in an oven and heated for 2 days at 120 °C for TMU-44. After the synthesis of the crystals, they were dried in an 80 °C oven overnight. 2.2. Solid-state conversion of TMU-44 into the C/ZnO nanocomposite Heating of synthesized TMU-44 to 600 °C under vacuum in the absence of a surfactant or capping agent for 2 h resulted in a black solid sample (Scheme 1). 2.3. Electrical conductivity of the C/ZnO nanocomposite In order to prove that the materials are conductive, semiconducting, or non-conductive, at first we must calculate the specific resistance. According to the obtained results, we can say that the sample belongs to which category of materials. In our research, we needed a system to calculate the resistance of the sample. DC electrical conductivity (r) was measured at room temperature. In order to measure the dc conductivity of various materials; we constructed the measurement system shown in Fig. 3S. This system is similar to the standard test method described in ASTM B 193-02 [34]. Using the results, the material resistance from the formula R = V/I was calculated. In the case of our sample, we have the electrical resistivity obtained from diagram 23.2 X (Fig. 4S) and having sample and the cross section, the specific electrical resistivity of the sample from the formula R = q L/A was obtained (Table 1). Using the obtained results, we can conclude about the conductivity. Conduction was considered to be ohmic in nature, so the electrical conductivity was estimated using the following expression:

Conductivity ðrÞ ¼ l  f1=ðR  AÞg 3. Results and discussion 3.1. Crystal structure analysis of TMU-44 TMU-44, [Zn2(hfipbb)2(L1)]n.DMF was synthesized by combining Zn(NO3)26H2O, L1 and H2hfipbb ligands using the solvother-

mal method at 120 °C for 48 h to give suitable X-ray quality crystals. X-ray crystallography reveals that TMU-44 crystallizes in the monoclinic P2/c space group. In this compound, the coordination geometry around Zn(II) can be described as distorted square pyramidal with the five coordination sites occupied by four oxygen atoms of carboxylate groups from hfipbb ligands and one pyridyl nitrogen atom from the L1 ligands. The pyridyl nitrogen atom is located in the apical position, while the carboxylate oxygen atoms form the basal plane (Scheme. 1). Interestingly, this framework is constructed from paddle-wheel Zn2(COO)4 clusters that bridged by hfipbb ligands to form a 2D square grids and then these interpenetrated helical 2D layers are further connected by the pillar ligands (L1) to form a 3D coordination polymer network. It contains three-dimensional interconnected pores to have 1D channels along the crystallographic b-axis. Topological analysis of the resulting 3D framework of TMU-44 reveals that it is a 2-fold interpenetrated with a uninodal five-connected mab topology network. The crystalline phases present in the nanocomposite was investigated by PXRD. The PXRD pattern of the nanocomposite (Fig. 5S) showed no diffraction peaks due to very small particles of the C/ ZnO nanocomposite on the carbon plate. We think the particles are amorphous so the PXRD pattern did not show any peaks. The BET measurements showed that TMU-44 has limited porosity towards N2 [BrunauerEmmettTeller (BET) surface area of TMU-44 is 73.8 m2/g] and the C/ZnO nanocomposite has high porosity towards N2 [BrunauerEmmettTeller (BET) surface area of the nanocomposites is 732 m2/g] (Fig. 5S) (Table 1). The morphology and size of the C/ZnO nanocomposite synthesized by the solid-state conversion of the TMU-44 was characterized by scanning electron microscopy (SEM) (Fig. 1). The synthesized 2D semiconductor nanocomposite has nanoplate morphology for carbon active with ZnO particles on the surface of it. Also, the energy dispersive X-ray (EDX) mapping spectrum of the C/ZnO nanocomposite showed peaks due to zinc, oxygen, and carbon (Fig. 1). The specific resistance was calculated at room temperature and the obtained results were listed in Table 1. The synthesized nanocomposite is two–dimensional semiconductor. The C/ZnO nanocomposite synthesized from TMU-44 has the low specific resistance and the high electrical conductivity. In our study, obtained nanocomposite showed conductivity values around 43 S.m1.

Scheme 1. Solid-State Conversion of synthesized TMU-44 into a C/ZnO nanocomposite.

Table 1 Comparison of the morphology, surface area, and specific resistance of the C/ZnO nanocomposite. F-MOF TMU-44

Type of obtained nanocomposites C/ZnO

specific resistance (X-m) 2.32  10

2

Surface area (m2/g)

Morphology

732

plate-like

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Fig. 1. SEM images, EDX mapping spectra of C/ZnO nanocomposite synthesized from TMU-44.

4. Conclusions

Appendix A. Supplementary data

In this study, a simple method for synthesis of the C/ZnO semiconductor nanocomposite with the high porosity (732 m2/g) from fluorinated metal–organic framework (F-MOF), namely TMU-44 with the limited porosity was reported. The C/ZnO nanocomposite was characterized by different analysis such as powder X-ray diffraction; BET surface area analysis, FE-SEM, and EDX mapping analysis. Also, the as-synthesized C/ZnO nanocomposite showed good electrical conductivity at room temperature.

Supplementary data to this article can be found online at https://doi.org/10.1016/j.matlet.2019.06.007.

Declaration of Competing Interest None.

Acknowledgment

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Support of this investigation by National Natural Science Foundation of China (Nos. 21765008) and Natural Science Foundation of Guangxi (2016 GXNSFBA380002), Tarbiat Modares University as well as University of Zanjan is gratefully.

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