Preparation, Characterization and Application of Nano ZnO - Blended Polymeric Membrane

Preparation, Characterization and Application of Nano ZnO - Blended Polymeric Membrane

Available online at www.sciencedirect.com ScienceDirect Materials Today: Proceedings 5 (2018) 16814–16820 www.materialstoday.com/proceedings SCICON...

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Available online at www.sciencedirect.com

ScienceDirect Materials Today: Proceedings 5 (2018) 16814–16820

www.materialstoday.com/proceedings

SCICON 2016

Preparation, Characterization and Application of Nano ZnO Blended Polymeric Membrane A. Rajeswaria, Anitha Piusa,* a

Department of Chemistry, Gandhigram Rural Institute-Deemed University, Gandhigram - 624302, Dindugul

Abstract Effluents from dyeing and finishing processes of textile industry contain strong colour and possible heavy metals. Conventional treatments are applied to treat dyes but the secondary pollution problem not addressed. Consequently, the heterogeneous photocatalytic oxidation process is of special interest. In this work a cellulose acetate-polyethylene glycol-polyurethane membrane impregnated with nano ZnO as a photocatalyst was prepared. The prepared membranes characterized by IR, SEM with EDAX and pure water flux (PWF). The photocatalytic degradation of dyes using prepared membrane was investigated towards the removal of Reactive red and Reactive orange. The kinetic model of Langmuir-Hinshelwood well describes the photodegradation capacity. © 2017 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Advanced Materials (SCICON ‘16). Keywords: Degradation, photocatalyst, dyes, polymeric membrane

1. Introduction Water is one of the most essential requirements for the life on earth and indispensable to sustain the biological activities of organisms. Various methods are currently used for treatment of industrial waste water [1]. However, these techniques often transfer the pollutants from one phase to another and causing secondary pollution [2]. Considerable attention has been paid to heterogeneous photocatalytic systems which involve semi-conductor photocatalyst and ultraviolet or sunlight in aqueous medium as an efficient and eco-friendly technology for the removal of pollutants from water [3, 4]. Among the various semiconductor materials, zinc oxide (ZnO) is considered as one of the suitable photocatalyst for widespread environmental applications. Since, nano-ZnO particles can be embedded well within a solid matrix (membrane), a stable operating system that simultaneously promotes the physical and chemical characteristics of the membrane may be improved. Supplementing of nano-ZnO particles into the membrane also improves its hydrophilicity and the mechanical properties of the polymer matrix [5]. * Corresponding author. E-mail address: [email protected] 2214-7853 © 2017 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Advanced Materials (SCICON ‘16).

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Membrane filtration is one of the most promising technologies for application in water and wastewater treatment. Several polymers have been known for a long time to synthesis membranes, cellulose acetate (CA) membranes are preferred due to their superior transport characteristics, excellent water affinity, low protein adsorption, suitable mechanical strength, high hydrophilicity, excellent film forming property, and easy availability [6]. Polyurethane (PU) is also known to exhibit unique mechanical properties, primarily as a result of two-phase morphology [7-10]. It has increased flexibility, hardness, tensile strength, temperature conditions, resistance to extreme pH and which makes PU attractive for many industrial membrane separation applications. PU is a copolymer composed of short alternating flexible soft segments (like water-soluble or highly water swellable, such as polyesters or polyethers) and linked with diamines or polyols, rigid hard segments (made of aromatic diisocyanates, which are no water soluble) [11]. PEG was also well studied in membrane fabrication due to its pore forming ability and its hydrophilic character in membrane flux improvement and antifouling enhancement [12,13]. In this study cellulose acetate-polyethylene glycol-polyurethane (CA-PEG-PU) and zinc oxide impregnated cellulose acetate-polyethylene glycol-polyurethane (CA-PEG-PU/ZnO) membranes are synthesized. The surface morphology of CA-PU and CA-PU/ZnO membranes are compared using scanning electron microscopy (SEM) with energy dispersive analysis of X-rays (EDAX), Fourier transform infrared spectroscopy (FTIR) and pure water flux (PWF) measurements. The efficiency of photodegradation of RR 11, RO 84 dyes using the membrane with improved characteristics was tested. The effect of different experimental parameters like irradiation time and pH on the extent of removal of dyes by polymeric membrane was investigated. The kinetics and best fitting isotherm model for the prepared membrane was suggest 2. Experimental: 2.1. Materials: CA (Cellulose acetate) (BDH chemicals Ltd.) was used as membrane-forming polymer. Zinc acetate hydrate, ammonium hydroxide, ammonium nitrate, polyethylene glycol, polyurethane (PU), chloroform, acetone were purchased from Sigma Aldrich, Mumbai, India. Reactive Red 11 (RR 11) and Reactive Orange 84 (RO 84) dyes were bought from M/s Sree Chemidyes, Bangalore, India. 2.2. Preparation of ZnO nano particles By using sol–gel method nano ZnO was prepared in this method zinc acetate (135 mg) was used as the precursor and it was dissolved using 250 mL of distilled water. An aqueous solution of ammonium hydroxide (50 % v/v) was added to the above solution with constant stirring to attain a pH of 8.5. The reaction mixture was kept at ambient temperature until gelation was formed and it was retained to complete the polymerization. The obtained mixture was filtered, washed with ammonium nitrate (0.1 M), and subsequently dried by heating slowly to 90 °C until the solvent was completely evaporated. The attained powder was calcinated at 400 °C for 5 h in muffle furnace [12]. 2.3. Fabrication of CA-PEG-PU/ZnO-mixed matrix membrane The CA-PEG-PU/ZnO was used as casting material and it was prepared by solution dispersion blending method. The PU (36 mg) was dissolved in chloroform, CA was dissolved in acetone, PEG was dissolved in distilled water and stirred. To the CA solution, PEG and PU was added then further stirred at 60 °C to achieve a homogeneous solution. To the above solution ZnO nanoparticles (0.1 and 0.2 wt%, respectively) were added and stirred. The prepared CA-PEG-PU/ZnO solution was uniformly coated on a glass plate using a casting knife and then immersed in distilled water at room temperature for two days to ensure complete phase separation and to leach out water soluble components from membrane. Finally, the membrane was placed in between filter papers for drying [13].

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2.6. Photocatalytic degradation experiments Experiments for the adsorption study of the dyes on the prepared membrane surface were carried out at different initial pH values by using suspensions of 50 mL volume with a concentration of 100 mg/L of dyes. pH of the solution was adjusted in the range of 3-11 with 1 M HCl (aq) or NaOH (aq). The concentrations of dye solutions were determined by measuring the absorbance using of a UV-Vis spectrometer (PerkinElmer Lambda 35). The readings were taken at the absorbance maxima 555 nm and 490 nm for RR 11 and RO 84 respectively. The effect of irradiation time on the photodegradation of dyes was studied at various time intervals from 10-60 min by keeping initial concentration and catalyst dosage constant. The variations in the concentration of dye solutions were measured using UV-Vis spectrometer Effect of pH on the degradation of dyes was studied by adjusting dye solution pH from acidic to basic medium (pH 3 to 11) using pH meter (EUTECH instruments PCD650) keeping the initial concentration and catalyst dosage constant for the reaction. The impact of catalyst dosage is an important factor that can strongly influence the rate of degradation of dyes; it was studied by varying catalyst dosage from 0.02 to 0.14 g and keeping the initial concentration and irradiation time constant. A LangmuirHinshelwood (LH) type of relationship was used to describe the dye concentration effect on its degradation and surface sites availability for the reaction. 3. Results and discussions 3.1. SEM with EDAX analysis Scanning electron microscopy is important for the determination of membrane surface morphology. Fig. 1 shows the formation of ZnO nanoparticles with uniform rod-like shape. Morphologies of casted CA-PEG-PU and ZnO blended CA-PEG-PU membranes showed the formation of pores on the surface during casting as shown in Fig. 1. Fig. 1C shows that ZnO nano particles are blended with the membrane. Further the pore size of the prepared membranes was measured using imageJ software and it was found to be 0.2 µm. EDAX spectra of the pure ZnO, CA-PEG-PU and CA-PEG-PU/ZnO are shown in Fig. 1. EDAX spectrum of pure ZnO nanoparticles shows peaks of zinc and oxygen and no other elemental peaks could be detected which confirms the presence of zinc and oxygen only.

Fig. 1. SEM images of A) nano ZnO B) CA-PEG-PU C) CA-PEG-PU/ZnO and EDAX spectra of D) nano ZnO E) CA-PEG-PU F) CA-PEG-PU/ZnO

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3.2. FTIR characterization FTIR study was used to interpret the interaction between ZnO and cellulose acetate-polyethylene glycolpolyurethane membrane. In Fig. 2 peaks around 400-500 cm-1 gives information about stretching vibrations of crystalline hexagonal zinc oxide (Zn-O), similar peaks were observed for ZnO blended CA-PEG-PU membrane. Perusal of literature the characteristics bands of CA were assigned to be at 3500 cm−1 can be attributed the presence of hydroxyl group and the peaks at 1050, 1743 and 1270 cm−1 corresponding to the stretching of C-O group, ether group and C-O bond of the CH2 OH group, respectively [14] . However, this peak is observed to have slightly shifted to at 1753, 1224, 1037 cm-1 and 3451 cm-1 with high intensity in the CA-PEG-PU membrane indicating the presence of interactions between CA-PEG-PU. Moreover a broadband at 3451 cm-1 in CA-PEG-PU blend membrane indicates the intermolecular association due to the formation hydrogen bonding between urethane and macromolecular chains of cellulose acetate. These interactions took place, more specifically between the -NH group from urethane and -CO from CA [15]. When the IR spectrum of ZnO/CA-PEG-PU membrane was compared with that of pure CA-PEG-PU, the characteristic peak of –OH group was shifted from 3451 to 3443cm-1. Similar shifts are observed for the peak located at 1724, 1252 and 1030 cm-1. The observed shifts in the peak may be ascribed to the formation of hydrogen bonding between ZnO and CA-PEG-PU membrane [13].

Fig. 2. The FTIR spectrum of (A) pure ZnO (B) CA-PEG-PU (C) CA-PEG-PU/ZnO 3.3. Pure water flux (PWF) measurement PWF values were measured for each membrane and the obtained results are shown in Fig. 3. Pure CA-PEGPU membrane has low flux value. Literature suggests water flux increases in the presence of nanoparticles [16]. In this study also ZnO blended CA-PEG-PU membrane showed a high water flux value. On addition of ZnO, the hydrophobic nature was changed to hydrophilic nature and this hydrophilicity of the membrane increases the PWF [17]. It can be seen that the water flux of CA-PEG-PU/ZnO membrane is about 81higher than that of CA-PEG-PU membrane which is about 73.

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Fig. 3. Water flux of CA-PEG-PU and CA-PEG-PU/ZnO 3.4. Effect of irradiation time The effect of irradiation time on the extent of photodegradation of dyes (RR 11 and RO 84) was studied under sun light, experiments were carried out at regular time intervals in the range of 10-60 min with fixed initial concentration of dyes (100 mg/L) and neutral pH using circular shaped CA-PEG-PU/ZnO membrane having a diameter of 9 cm. The degradation of dyes was found to increase by increasing the irradiation time. The maximum degradation was attained at 40 min and thereafter it remained almost constant. Therefore, for further studies the irradiation time was fixed at 40 min. 3.5. Effect of pH The solution pH has an important role on the photodegradation efficiency of dyes. The effect of pH on the photodegradation of dyes was assessed by varying pH range from 3-11 and the irradiation time was fixed at 40 min using CA-PEG-PU/ZnO membrane. It was found that the solution pH has a strong influence on the degradation. It was observed that the degradation increased as the pH of dye solution was increased. The optimum pH for efficient degradation of RR 11 and RO 84 dyes by ZnO blended polymeric membrane was 7. Normally ZnO can react with acids to produce its corresponding salt at low pH values while at alkaline pH, it reacts with a base to form complexes and neutral pH is ideally suited for better performance. 3.6. Kinetics of photodegradation of RR 11 and RO 84 A Langmuir-Hinshelwood type of relationship is used to describe the effect of dye concentration on its degradation. The kinetics of photodegradation with different initial concentrations (20, 40, 60, 80 and 100 mg/L) of RR 14 and RO 84 was studied with the CA-PEG-PU/ZnO membrane under sunlight and the results are given in Table 1and it demonstrates the relationship between different initial concentrations of RR 11, RO 84 and time. It is evident that photo degradation of RR 11 and RO 84 dyes followed pseudo first order kinetics shows the pseudo firstorder rate constants kobs.

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Table 1. Values of kobs and half-lives of RR-11 and RO-84 under different initial concentrations using (CA-PEGPU/ZnO) membrane. Initial concentration of dyes (mg/L) 20

kobs (1/min)

t1/2 (min)

R

RR-11

RO-84

RR-11

RO-84

RR-11

RO-84

0.1189

0.0881

5.6168

8.2132

0.9988

0.9958

40

0.1014

0.0802

6.6713

9.0261

0.9979

0.9964

60

0.0925

0.0746

7.1940

9.6857

0.9903

0.9965

80

0.0873

0.0671

7.5781

10.0587

0.9971

0.9961

100

0.0794

0.0602

7.8679

10.8065

0.9931

0.9947

4. CONCULSIONS The degradation efficiency of dyes RR 11and RO 84 from aqueous solution using the prepared membrane was studied with different parameters. Cellulose acetate-polyethylene glycol-polyurethane membranes were prepared and they were tested with or without the synthesized nano ZnO impregnation. ZnO blended CA-PEG-PU membrane showed better characteristics. It was found to be a promising material for the degradation of dyes from aqueous solution. The maximum degradation of dyes was achieved at 40 min and the optimum pH was observed to be 7. The kinetic model of Langmuir-Hinshelwood well describes the photodegradation capacity. The photocatalytic degradation of dyes RR 11 and RO 84 exhibited pseudo-first order kinetics. ZnO impregnated membrane inherited not only better photocatalytic ability, but also good water flux property. Acknowledgements The authors would like to thank the University Grants Commission, Government of India for the financial support and also thank the authorities of GRI for the encouragement. References [1]

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