Preparation And Optical Properties Of Nickel Nanoparticles Implanted Carbon Membranes

Disha Harinkhere1,a) and Netram Kaurav1, b)

Department of Physics, Government Holkar Science College, Indore

a)Corresponding author:disha.harinkhede@gmail.com b)netramkaurav@yahoo.co.uk

Abstract: Through dip coating method monodisperse nickel nanoparticles assisted carbon membrane was prepared on porous alumina disc support. The coating solution was prepared by blending of thermally stable polymer polyphenylene oxide (PPO) and thermally labile polymer polyvinylpyrrolidone (PVP) followed by addition of nickel nanoparticles. Size of nanoparticles, surface porosity, average pore size, element composition and optical properties of the membrane were investigated by means of different techniques such as XRD, FE-SEM, EDS and UV-Visible spectrometer Incorporation of nano-sized nickel in polymer matrix causes increase in pore size from 0.022 μm to 0.076 μm as well as porosity and decrease in optical band gap from 5.44 eV to 5.09 eV of membrane.

Keywords: Nickel nanoparticles, Carbon membrane, Surface morphology, Optical band gap.

INTRODUCTION

Porous inorganic membranes are used for separating suspensions, mixtures and aerosols. They leave organic molecules, particles, dissolved salts or even gases and liquids on one side and transfer purified gases and liquids to the other. Thus, the membrane is a semipermeable barrier that separates purified and concentrated streams out of a mixture. Membrane has been used in a range of industrial fields such as osmosis studies, uranium separation, fuel cells, gas separation, food and beverage sectors, water and waste water treatment, cosmetics and biotechnology [1].

Carbon membrane is one type of porous inorganic membrane which offers advantages over polymeric membranes especially in terms of selectivity as well as thermal and chemical stability [2]. Carbonization of a suitable polymeric membrane precursor under controlled conditions produces carbon membrane. Blending of two polymers with different thermal properties such as PPO/PVP, PEI/PVP, PAN/PVP, polymide/PVP create a wide range of pore size distribution (ultramicropore, micropore, macropore) and enhanced gas permeability of membrane [3-7].

In 1962 Loeb and Sourirajan [8] proposed the idea of dividing a membrane into a skin and a porous substructure, for polymer membranes, boosted the development of a new generation of ceramic membranes. In this new anisotropic membrane, the support layer gives the mechanical strength and uninterrupted flux and the skin layer determines the separation. As well as morphology of membrane is key factor in membrane separation processes. The morphology of membranes is closely related to the membranes’ pores. Pore size and size distribution, interconnectivity and density (i.e. the number of pores per unit area) are the physical parameters that affect flux and separation efficiency.

Membrane characterization can be divided into physical and chemical aspects. Generally we can say, the physical characteristics of a membrane describe its morphology, mechanical strength, pore structure and charge [9].On the other hand, chemical characteristics depict membrane surface layer and its composition, and are more appropriate for predicting a membrane’s behaviour under different feeds and clearing up why the membrane works well (or not). Chemical characteristics facilitate us study the complexity of the membrane surface and a number of micrometres into the membrane depth. Physical features usually cover the whole membrane structure from feed to permeate.

The topical membrane morphology involves mixed matrix membrane which consists of two phases one is bulk phase and the other is disperse phase such as metal, activated carbon, silica, zeolites or nano-size particles. Addition of inorganic fillers results in superior separation characteristics. Size of this inorganic filler has influence on

morphology as well as on the separation performance of membrane. Smaller particle size provides more interfacial area between bulk and disperse phase [10]. Use of organic particles in nano range as the fillers offer advantages in the preparation of the mixed matrix membrane [11].

Since some membrane materials such as Al2O3, TiO2 and ZrO2 were oxides that could withstand harsh environments. As well as Ni nanoparticles as fillers provide some advantages in preparation of MMM’s or hybrid carbon membrane. Nickel is commonly used as hydrogenation catalyst. Therefore in present work an anisotropic carbon membrane has been prepared from polymeric membrane or precursors at optimum conditions by using Al2O3 as porous support in order to investigate the effect of substantial nickel nanoparticles on the surface morphology as well as on the optical properties of PVP/PPO blended carbon membrane.

EXPERIMENTAL

Materials

Porous alumina disk support with average pore size 0.14 micrometer and diameter of 23 mm was purchased from HI-Tech Ceramics. Pure precursor materials of poly (2,6-dimethyl-1,4-phenyleneoxide) powder, polyvinylpyrrolidone (PVP, average molecular weight:40,000g/mol) powder, Trioctylphosphene, Tech., 90%, Nickel(II) Acetylacetonate, 95%, Olaylamine, Tech.,70% and ethanol were purchased from Sigma Aldrich Co. The solvent chloroform was purchased from Merck.

Membranes preparation

Firstly nickel NPs were prepared by the thermal decomposition method [12]. Fixed ratios of the polymer precursors with nano-sized nickel were added to chloroform and stirred for 24 h to form homogeneous casting solutions. Then the macroporous alumina disks support was dip coated in coating solution for 15 s for 4 times to acquire polymeric film of uniform thickness followed by drying of all membranes for 24 h. Then to get rid of surplus solvent resulting polymer membranes were pyrolyzed in a heating furnace at 240 ◦C for 6 h. Subsequent to remedial, the membranes were pyrolyzed at 700 ◦C for 1 h. After attainment of room temperature, the resultant carbon membranes were taken out from the furnace.

Characterizations

X-ray diffraction (D8 Advance X-ray Diffractometer, XRD) was employ to verify the purity of the nickel particles. The morphologies of the prepared membranes were investigated by field emission scanning electron microscope (FESEM) instrument model JEOL JSM-6500F. As well, X-ray spectroscopy (EDS or EDX) Oxford instrument INCA, X-sight 7557 gave an elemental map of membrane surface that combines topographical information with elemental analysis and the optical properties were determined through Varian Cary 100 Bio UV-Vis spectroscopy.

RESULTS AND DISCUSSIONS

Characterization of the nickel nanoparticles and the membranes

The XRD spectra for nickel nanoparticles have shown in figure 1. It is clear that three characteristic peaks for nickel (2θ=44.3, 51.6, 76.2), corresponding to Miller indices (111), (200) and (220) are observed. The average particle size determined 8.9nm using these peaks FWHM in the Debye-Scherrer relation. This relation can be written as:

D= Kλβ cosθ

Where D is the mean size of crystallites in nm, K is crystallite shape factor a good approximation is 0.9, λ is the X-ray wavelength (λ=1.54 Å for CuKα), β is the full width at half the maximum (FWHM) in radians of the X-ray diffraction peak and θ is the Braggs' angle in radian.

FIGURE 1.XRD pattern of the nickel nanoparticles

TABLE 1. Preparation of membranes with fixed proportion of polymer blend (PPO/PVP) and Ni NP’s in chloroform:

MembranePPO Polymer PVP Polymer Ni NP’s

Concentration(wt%)

Weight(g) Concentration (wt%)

Weight(g) Concentration (wt%)

Weight(g)

PPO/PVP 7.5 1.5 2.5 0.5 - -

PPO/PVP/Ni

6.5 1.3 2.5 0.5 1 0.2

Figure 2(a) and 2(c) depicts FE-SEM images of the prepared carbon membrane while the figure 2(b) and 2(d) is treated images of adjoining figures. These images were treated by the public domain images processing and analysis program NIH Image [13]. It has been analysed that PPO/PVP Carbon membrane is 0.344% porous and the average pore size is 0.022 μm whereas Ni NP’s assisted Carbon is 0.498% porous and the average pore size is 0.076 μm. This study showed that PPO/PVP Carbon membrane has smaller pore size than PPO/PVP/Ni carbon membrane. This may be due to different polymeric concentration in casting solution. As listed in table 1 that 1wt% nickel added instead of PPO polymer in PPO/PVP/Ni membrane while total weight% of solvents is fixed to 10 wt% in solution. Some articles have been showed effect of polymeric concentration on membrane morphology. Ismail et al. prepared polyetherimide hollow fiber membranes and observed that as the polymer concentration increased the mean pore size, surface porosity and void fraction of membranes decreased [14].

EDX Analysis:

TABLE 2. Element composition of Nickel nanoparticles assisted Carbon Membranes formed by the polymeric solution containing 1 wt% Ni np’s analyzed by EDX

Element Weight % Atomic %Al 57.2 49.2O 32.1 46.6Ni 10.7 4.2

Total 100 100

As shown in figure 3(a) and 3(b), EDX analysis indicates the presence of nickel element the polymeric layer.Table 2 shows the analysis results of membrane. Content of nickel is around 10.7 wt%.

FIGURE 2(a). Original image with of membrane surface with no disperse phase

FIGURE 2(b). Treated image of membrane surface

FIGURE 2(c). Original image of membrane surface with disperse phase

FIGURE 2(d). Treated image of membrane surface

Optical properties of the membranes

Figure 4(a) and figure 4(b) show reflection and absorption spectra respectively. Reflection spectra display that alumina disc (without coating) and PVP/PPO membrane have almost same reflectivity while PPO/PVP/Ni membrane is less reflective. In UV region reflection is increasing quickly as in visible region slowly for alumina disc and membranes. Whereas in absorption spectra, Alumina disc and PPO/PVP membrane are less absorptive although nickel assisted membrane is more absorptive. That is presence of nickel in membrane influences the optical behaviour of the membrane. Optical band gap was determined using Kubelka–Munk function. This function can be written as:

F (R)=(1−R)2

2 R=K

S

Where R is reflectance of the material, K molar absorption coefficient and S is scattering factor. As shown in figure 5 optical band gap for PPO/PVP membrane is 5.44 eV whereas for PPO/PVP/Ni membrane 5.09 eV. This analysis showed that due to presence of nickel there is drop off in band gap of membrane this may be due to incorporation of nickel in polymer membrane formulate conduction chain.

FIGURE 3(a).Original image of membrane surface with disperse phase

FIGURE 3(b).EDX result

FIGURE 4(a) Reflection Spectra FIGURE 4(b) Absorption spectra

FIGURE 5 Band Gap Calculations Of Membranes Using DRS Data

CONCLUSION

Carbon membranes were prepared on porous alumina disc support by dip coating in polymeric solution. Surface study showed that nickel assisted membrane has larger pore size as well as more porous than PPO/PVP membrane due to change in polymer concentration in casting solution. Also the investigation of optical properties revealed that due to the addition of nickel in polymeric matrix there is decrease in optical band gap from 5.44 eV to 5.09 eV of membrane.

ACKNOWLEDGMENTS

The financial support from the UGC-DAE Consortium for Scientific Research, Indore under the CRS projects is thankfully acknowledged

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