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Cobalt and nickel nanoparticles fabricated p(NIPAM-co-MAA) microgels for catalytic applications

  • Zahoor H. Farooqi EMAIL logo , Sadia Iqbal , Shanza Rauf Khan , Farah Kanwal and Robina Begum
Published/Copyright: August 14, 2014
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e-Polymers
From the journal e-Polymers Volume 14 Issue 5

Abstract

In this research work, multi-responsive poly(N-isopropylacrylamide-co-methacrylic acid) copolymer microgels were synthesized via emulsion polymerization in aqueous medium. Then, nickel and cobalt nanoparticles were fabricated within these microgels by in situ reduction of metal ions using sodium borohydride (NaBH4) as a reducing agent. Fourier transform infrared spectroscopy was used to characterize these microgels. The pH sensitivity of these copolymer microgels was studied using dynamic light scattering technique (DLS). DLS studies revealed that the hydrodynamic radius of these microgels increased with the increase in pH of the medium at 25°C. The catalytic activity of hybrid microgels for the reduction of p-nitrophenol (4-NP) to p-aminophenol (4-AP) was investigated by UV-visible spectrophotometery. The value of apparent rate constant of reaction was found to change linearly with catalyst dosage. The nickel-based hybrid system was found to be five times more efficient as a catalyst compared to the cobalt-based hybrid system for the reduction of 4-NP to 4-AP in aqueous medium.

Keywords: catalyst; hybrid microgels; microgels; nanoparticles; pH sensitivity

1 Introduction

Metal nanoparticles have been the subject of much research in recent years. They are enormously used in the field of catalysis (1–5), magnetic resonance imaging (6), environmental remediation (7), medicine (8, 9), cosmetics (10) and biosensing (11) due to their quantum size-related properties. The catalytic applications of nanoparticles of expensive metals such as gold (1, 12), silver (2, 3, 13), platinum (14–16) and palladium (17–20) are mostly studied because they are stable under different environmental conditions and do not oxidize to their oxides easily. Contrary to this, there are some coinage metal-based nanoparticles [such as zinc (21), copper (22, 23), nickel (Ni) (24) and cobalt (Co) (25) whose catalytic applications have not been enormously studied so far, because they are less stable. These metals and their salts are less expensive than silver and gold; thus we are going to report on the catalytic applications of the nanoparticles of these metals. Nanoparticles of Ni and Co are mostly synthesized by hydrothermal (26), water-in-oil micro-emulsion (27), gas evaporation (28), sputtering (29), co-precipitation, sol-gel and chemical reduction methods (30). The chemical reduction method is the cheapest, least time consuming, and most feasible, and gives good yield; thus it is the best method for the synthesis of nanoparticles. Naked nanoparticles aggregate rapidly; thus they are mostly fabricated within some stabilizing agents such as micelles (31–33), dendrimers (34–37), core-shell network (18), yolk-shell network (5, 38) and microgels (2, 3, 39, 40). These polymers not only act as stabilizers, but are also used as a template for the controlled synthesis of nanoparticles and as a micro-reactor for the catalytic applications of nanoparticles. Among all these stabilizers, microgels are the best candidate for the synthesis, stability and applications of nanoparticles. Microgels are cross-linked responsive materials. Their sieve size and shape can easily control the shape and size of in vivo synthesized nanoparticles. Pendant groups of monomers [e.g., N-isopropylacrylamide (NIPAM), acrylic acid (AAc), methacrylic acid (MAA), etc.] easily fix the nanoparticles within microgels. Hybrid microgels are extensively used as catalysts for the reduction of nitroarenes (4, 25, 41), nitriles (aliphatic and aromatic) (42) and coupling reactions (43). To the best of our knowledge, no researcher has yet studied the catalysis of p-nitrophenol (4-NP) by using Co and Ni nanoparticles fabricated in poly(N-isopropylacrylamide-co-methacrylic acid) [p(NIPAM-co-MAA)] hybrid microgels. Nabid et al. (42) used nickel-iron oxide-(3-aminopropyl)triethoxysilane-poly(4-vinylpyridine) [Ni-Fe3 O4-SiO2-P4VP] hybrid microgels for the catalytic reduction of nitriles. Sahiner et al. (25, 41) studied the catalytic reduction of ortho-nitrophenol (2-NP) and 4-NP by using nickel-poly(2-acrylamido-2-methyl-1-propansulfonic acid) [Ni-p(AMPS)] and cobalt-poly(2-acrylamido-2-methyl-1-propansulfonic acid) [Co-p(AMPS)] hybrid microgels. Nickel-poly(acrylic acid) hybrid spherical polyelectrolyte brushes were used by Zhu et al. (44) for the catalytic reduction of 4-NP. Ni and Co nanoparticles fabricated in p(NIPAM-co-MAA) microgels have not been reported yet.

In this work, we synthesized p(NIPAM-co-MAA) microgels in aqueous medium. Ni and Co nanoparticles were fabricated inside p(NIPAM-co-MAA) microgels by in situ reduction of metallic salts (NiSO4·6H2 O, CoCl2·6H2 O) in aqueous medium. FTIR analysis and DLS studies were used for the structural and responsiveness characterization of p(NIPAM-co-MAA) microgels, respectively. UV-Visible spectrophotometry was used to investigate the catalytic activity of hybrid microgels for the reduction of 4-NP. We also studied the effect of catalyst dosages on the value of the apparent rate constant (kapp) of 4-NP. The catalytic activity of Ni-p(NIPAM-co-MAA) and Co-p(NIPAM-co-MAA) hybrid microgels was compared with each other.

2 Results and discussion

2.1 FTIR spectra of p(NIPAM-co-MAA) microgels

The FTIR spectra of p(NIPAM-co-MAA) copolymer microgels shown in Figure 1 were used to confirm the chemical structure of p(NIPAM-co-MAA) microgels. The monomers NIPAM and MAA have a C=C bond; copolymerization occurred at this double bond. So the product of copolymer microgels should not possess the C=C absorption band. During synthesis, sulfate radicals changed the double bond to a single bond (C-C). Thus the FTIR spectra of microgels shown in Figure 1 shows no absorption band at 1600–1650 cm-1. Wang et al. (45) explained that NIPAM and AAc both have a characteristic absorption band of vibration of the C=C bond, but it was absent in the FTIR spectra of microgels. The distinct bands observed around 1554.83 and 1658.78 cm-1 represent the –CH2 (bending) and C=O functional group of MAA. The broad and intense band appearing near 3311.78 cm-1 is a characteristic band of N-H (stretching) of NIPAM and BIS. The broadness in band (around 3311.78 cm-1) was due to the presence of bonded water molecules within microgels (3, 13). So the FTIR spectra in Figure 1 show that polymerization had occurred and that all components had been incorporated into the polymer network.

Figure 1 FTIR spectra of the p(NIPAM-co-MAA) copolymer microgels.
Figure 1

FTIR spectra of the p(NIPAM-co-MAA) copolymer microgels.

2.2 pH sensitivity of p(NIPAM-co-MAA) microgels

A plot of the hydrodynamic radius (Rh) of the p(NIPAM-co-MAA) microgels at different pH values at 22°C is shown in Figure 2. This plot revealed that the pH of the surrounding medium has a significant effect on the Rh of the microgels (Figure 2). The variation in Rh with pH was due to the ionization of the carboxyl groups present within the microgel network. When the pH value was <4.86 (i.e., pka of MAA) (3), the carboxyl groups of MAA were in the protonated state (COOH). With the gradual increase in pH around 4.86, the value of Rh abruptly increased. This was due to the deprotonation of the carboxyl groups. Electrostatic repulsions between the ionized carboxylate groups (COO-) pushed the polymer network apart, water moved into the microgel network and the value of Rh increased (46). When the pH value was >8, the hydrodynamic radius of the microgels did not increase with the increase in pH because most of the carboxyl groups had ionized at this pH value.

Figure 2 Hydrodynamic radius of the p(NIPAM-co-MAA) microgels as a function of pH at 25°C.
Figure 2

Hydrodynamic radius of the p(NIPAM-co-MAA) microgels as a function of pH at 25°C.

DLS results indicated that the p(NIPAM-co-MAA) microgels were fully swollen at high pH. Thus catalytic studies, described in later sections of this article, were carried out at high pH. In the swollen state, reactants can easily diffuse towards the catalyst surface through a permeable network of microgels.

2.3 Catalytic activity of hybrid microgels

The reduction of 4-NP to 4-AP was chosen as a model reaction to investigate the catalytic activity of synthesized Ni and Co nanoparticles fabricated in p(NIPAM-co-MAA) microgels. This reaction was selected owing to the ease of monitoring of 4-NP and in its toxic effects on the environment. This reaction gives only one product; therefore the extent of reaction at different time intervals can be easily followed by measuring the absorbance at wavelengths of 300 nm (λmax of 4-AP) and 400 nm (λmax of 4-NP). The absorbance at 400 nm gradually decreased with the passage of time, along with a concomitant gradual increase in absorbance at 300 nm, as shown in Figures 3 and 4.

Figure 3 UV-Visible spectra for the reduction of 4-NP at different time intervals [conditions: 0.5 ml of 40 mmol/l NaBH4, 0.3 ml of the Co-p(NIPAM-co-MAA) catalyst and 1.8 ml of 0.111 mmol/l 4-NP; temperature 18°C].
Figure 3

UV-Visible spectra for the reduction of 4-NP at different time intervals [conditions: 0.5 ml of 40 mmol/l NaBH4, 0.3 ml of the Co-p(NIPAM-co-MAA) catalyst and 1.8 ml of 0.111 mmol/l 4-NP; temperature 18°C].

Figure 4 UV-Visible spectra for the reduction of 4-NP at different time intervals [conditions: 0.5 ml of 40 mmol/l NaBH4, 0.3 ml of the Ni-p(NIPAM-co-MAA) catalyst and 1.8 ml of 0.111 mmol/l 4-NP; temperature 18°C].
Figure 4

UV-Visible spectra for the reduction of 4-NP at different time intervals [conditions: 0.5 ml of 40 mmol/l NaBH4, 0.3 ml of the Ni-p(NIPAM-co-MAA) catalyst and 1.8 ml of 0.111 mmol/l 4-NP; temperature 18°C].

The gradual decrease in the characteristic peak of 4-NP was due to the decrease in concentration of 4-NP as a result of the conversion of 4-NP to 4-AP on the surface of Ni and Co nanoparticles inside the microgels. This catalytic effect is due to the electron relay from electron donor BH4– to acceptor 4-NP via the nanoparticles and proceeds the reduction; thus the color of the reaction mixture changed from bright yellow to colorless (47). Although the reduction of 4-NP to 4-AP in the presence of aqueous solution of NaBH4 is thermodynamically favorable, the presence of a large kinetic barrier due to the large potential difference between electron donor and acceptor species suppresses the feasibility of this reaction. This large kinetic barrier does not permit the reduction of 4-NP to proceed over time even in excess of aqueous NaBH4 solution (48). Thus the nickel and cobalt nanoparticles overcome the kinetic barrier and catalyze the reduction of 4-NP (25, 41).

Plots of ln(At/Ao) vs. time (minutes) are shown in Figures 5 and 6 for the Co-p(NIPAM-co-MAA)- and Ni-p(NIPAM-co-MAA)-catalyzed reduction of 4-NP, respectively. Initially, the value of ln(At/Ao) remained constant with the passage of time, showing that no reaction was taking place. Later on, the value of ln(At/Ao) decreased with the passage of time, showing that reaction was taking place. The time duration when no reaction is occurring is called the induction time (to). Diffusion of reactants towards the catalyst surface and regeneration of the catalyst surface occurs during this time interval. As nanoparticles of Ni and Co, Co-p(NIPAM-co-MAA) and Ni-p(NIPAM-co-MAA) react with atmospheric oxygen and produce their respective oxides on their surfaces. Thus, first, the catalyst gets activated and then starts to catalyze the reaction (14, 49). Figures 5 and 6 show that 8 min of induction time was observed in the case of Co-p(NIPAM-co-MAA) hybrid microgels and that 1–2 min was observed in the case of Ni-p(NIPAM-co-MAA) hybrid microgels. This time delay was due to the regeneration of nickel and cobalt nanoparticles by the reduction of oxide layer on their surfaces. It means that Ni nanoparticles got activated within a shorter period of time as compared to Co nanoparticles.

Figure 5 Plots of ln(At/Ao) vs. time (min) for the reduction of 4-NP for Co-0.1 (♦), Co-0.2 (■) and Co-0.3 (▲) samples.
Figure 5

Plots of ln(At/Ao) vs. time (min) for the reduction of 4-NP for Co-0.1 (♦), Co-0.2 (■) and Co-0.3 (▲) samples.

Figure 6 Plots of ln(At/Ao) vs. time (min) for the reduction of 4-NP for Ni-0.1 (♦), Ni-0.2 (■) and Ni-0.3 (▲) samples.
Figure 6

Plots of ln(At/Ao) vs. time (min) for the reduction of 4-NP for Ni-0.1 (♦), Ni-0.2 (■) and Ni-0.3 (▲) samples.

Linear regions of plots of ln(At/Ao) vs. time (Figures 5 and 6) were used to calculate the value of kapp. It is clear from Figures 5 and 6 that the value of ln(At/Ao) linearly decreased with time, which shows that the reaction was obeying a pseudo first-order kinetics. The slope of all plots of Figures 5 and 6 is different from each other. Plots of the reduction of 4-NP obtained using 0.1, 0.2 and 0.3 ml of the Co-p(NIPAM-co-MAA) catalyst are shown in Figure 5. kapp values of 0.022, 0.064 and 0.074 min-1 were calculated for the reduction of 4-NP for 0.1, 0.2 and 0.3 ml of the Co-p(NIPAM-co-MAA) catalyst, respectively. Similarly, plots of the reduction of 4-NP using 0.1, 0.2 and 0.3 ml of the Ni-p(NIPAM-co-MAA) catalyst are shown in Figure 6. kapp values of 0.102, 0.331, 0.385 min-1 were calculated for 0.1, 0.2 and 0.3 ml of the Co-p(NIPAM-co-MAA) catalyst, respectively.

2.4 Effect of catalyst dosage on the value of kapp

Figure 7 and the values given in Tables 1 and 2 indicate that the value of kapp increases by increasing the amount of hybrid microgels at a constant temperature. Catalysis is a surface phenomenon, and the surface area increases by increasing the amount of the catalyst. By increasing the amount of the catalyst, the number of available active sites for catalysis gets increased. Thus more catalytic pockets are available now for the conversion of 4-NP to 4-AP. Therefore reduction occurs more rapidly; hence the value of kapp increases by increasing the catalyst dosage. Zhu et al. (44) observed a linear increase in the value of kapp for the reduction of 4-NP by increasing the amount of Ni-poly(acrylic acid) hybrid polyectrolyte brushes. Wu et al. (5) also observed a similar trend between catalyst dosage and kapp value for the reduction of 4-NP using Au-p(NIPAM) yolk-shell structures (5).

Figure 7 Effect of catalyst dosage on the value of kapp for the reduction of 4-NP using (♦) Ni-p(NIPAM-co-MAA) and (▲) Co-p(NIPAM-co-MAA) hybrid microgels as catalysts.
Figure 7

Effect of catalyst dosage on the value of kapp for the reduction of 4-NP using (♦) Ni-p(NIPAM-co-MAA) and (▲) Co-p(NIPAM-co-MAA) hybrid microgels as catalysts.

Table 1

Values of kapp calculated for the catalytic reduction of 4-NP using different amounts of the Ni-p(NIPAM-co-MAA) catalyst at the time of synthesis and after 30 days of synthesis of the catalyst.

SampleVolume of Ni-p(NIPAM-co-MAAc) (ml)Value of kapp at the time of synthesis of the catalyst (min-1)Value of kapp after 30 days of synthesis of the catalyst (min-1)
Ni-0.10.10.1020.100
Ni-0.20.20.3310.329
Ni-0.30.30.3850.381

Conditions: 1.8 ml of 0.111 mmol/l 4-NP and 0.5 ml of 40 mmol/l NaBH4; temperature 18°C.

Table 2

Values of kapp calculated for the catalytic reduction of 4-NP using different amounts of the Co-p(NIPAM-co-MAA) catalyst at the time of synthesis and after 30 days of synthesis of the catalyst.

SampleVolume of Ni-p(NIPAM-co-MAAc) (ml)Value of kapp at the time of synthesis of the catalyst (min-1)Value of kapp after 30 days of synthesis of the catalyst (min-1)
Co-0.10.10.0220.021
Co-0.20.20.0640.062
Co-0.30.30.0740.073

Conditions: 1.8 ml of 0.111 mmol/l 4-NP and 0.5 ml of 40 mmol/l NaBH4; temperature 18°C.

2.5 Comparison of the catalytic activity of Ni-p(NIPAM-co-MAA) and Co-p(NIPAM-co-MAA) hybrid microgels

Figure 7 and the values in Tables 1 and 2 confirm that Ni-p(NIPAM-co-MAA) hybrid microgels are a more efficient catalyst for the reduction of 4-NP as compared to Co-p(NIPAM-co-MAA) hybrid microgels. It was found that the value of kapp obtained using Ni-p(NIPAM-co-MAA) hybrid microgels as the catalyst for the reduction of 4-NP is five times greater as compared to that of Co-p(NIPAM-co-MAA) hybrid microgels at different dosages of the catalyst. This is due to the rapid transfer of electrons via the surface of Ni nanoparticles as compared to the surface of Co nanoparticles. Rapid electron transfer depends on the electronic configuration of the atoms. The number of unpaired electrons is greater in the case of Co atoms as compared to Ni atoms. Thus the nuclear electrostatic attractive forces for valence electrons are less shielded in the case of Co as compared to Ni. Thus electron transfer gets more hindered by these electrostatic forces in the case of Co as compared to Ni. Therefore Ni nanoparticles show a rapid reduction of 4-NP as compared to Co nanoparticles. Sahiner et al. (25, 41) synthesized Co-p(AMPS) and Ni-p(AMPS) catalysts and used them for the reduction of 2-NP and 4-NP. They observed that Ni nanoparticles fabricated in hydrogels are a more efficient catalyst for the reduction of 4-nitrophenol as compared to Co nanoparticles fabricated in hydrogels. So our results have good agreement with previously reported results.

2.6 Stability of Ni-p(NIPAM-co-MAA) and Co-p(NIPAM-co-MAA) hybrid microgels

Ni and Co nanoparticles were found to be stable before and after the reduction process. The long-term stability of metal nanoparticles inside the microgels was checked in two ways. The hybrid systems were used as catalysts at different times of synthesis of metal nanoparticles. The catalytic activity after 30 days was found to be the same as on the day of synthesis. The calculated values of apparent rate constants for the reduction of 4-NP in aqueous medium using Ni-P(NIPAM-co-MAA) and Co-P(NIPAM-co-MAA) hybrid microgels as catalysts are given in Tables 1 and 2, respectively. The values are almost the same, which indicates the stability of the catalysts. After the completion of the reduction process, the hybrid microgels were separated from the reaction mixture by centrifugation. The hybrid microgels were reused as catalysts for the reduction of 4-NP in aqueous medium to check the stability and poisoning of metal nanoparticles. The same reaction time was observed during the first and second use of the hybrid microgels as catalysts. So the metal nanoparticles were found to be stable due to the presence of a cross-linked polymeric network around them. The stability of the metal nanoparticles inside the microgels can also be explained on the basis of the donor-acceptor concept as reported previously (50). The metal nanoparticles act as electron acceptors, and the carbonyl groups (C=O) present in the network of the p(NIPAM-co-MAA) microgels act as the electron donor. Metal nanoparticles get stabilized in the microgels owing to this specific interaction. Therefore the contents of Ni and Co may be expected to be the same before and after the reduction process.

3 Conclusions

A comparison of the catalytic activity of novel Co-p(NIPAM-co-MAA) and Ni-p(NIPAM-co-MAA) hybrid microgels for the reduction of 4-NP was performed in this article. For this purpose, p(NIPAM-co-MAA) microgels were synthesized initially by emulsion polymerization. Then these microgels were used as a template for the synthesis of Ni and Co nanoparticles. Fabrication of p(NIPAM-co-MAA) microgels was confirmed by the absence of the band of C=C at 1600 cm-1 in the FTIR spectra. The pH sensitivity of the microgels was studied by DLS. Synthesized Ni-p(NIPAM-co-MAA) and Co-p(NIPAM-co-MAA) hybrid microgels were used as catalysts for the reduction of 4-NP in the presence of excess of NaBH4. The apparent rate constant (kapp) of 4-NP reduction was determined for various amounts of the catalysts. The kapp value of 4-NP reduction was found to be 0.102, 0.331 and 0.385 min-1 at 18°C for 0.1, 0.2 and 0.3 ml of the Ni-p(NIPAM-co-MAA) catalyst, respectively. Similarly, the kapp value of 4-NP reduction was found to be 0.022, 0.064 and 0.074 min-1 at 18°C for 0.1, 0.2 and 0.3 ml of the Co-p(NIPAM-co-MAA) catalyst, respectively. Ni nanoparticle-based hybrid microgels were found to be five times more efficient as a catalyst for the reduction of 4-NP as compared to Co nanoparticle-based hybrid microgels.

4 Experimental part

4.1 Materials

The chemicals N-isopropylacrylamide (NIPAM), methacrylic acid (MAA), N,N-methylene bisacrylamide (BIS), p-nitrophenol (4-NP) and sodium dodecylsulphate (SDS) were purchased from Sigma-Aldrich, Germany, whereas nickel sulfate (NiSO4·6H2 O) and cobalt chloride (CoCl2·6H2 O) were obtained from Fluka Chemika, Switzerland. Sodium borohydride (NaBH4) was purchased from Scharlau Company, Australia. Hydroquinone inhibitor was removed from MAA before use by passing it through alumina. The water used for all solution preparation, synthesis and microgel purification was distilled.

4.2 Synthesis of p(NIPAM-co-MAA) copolymer microgels

Multi-responsive p(NIPAM-co-MAA) copolymer microgels were synthesized by free-radical emulsion polymerization using NIPAM (monomer), MAA (co-monomers), BIS (cross-linker), APS (initiator) and SDS (emulsifying agent), as reported by our group previously (51–54). The amounts of NIPAM, BIS, SDS and MAA used in the synthesis of microgels are given in Table 3. NIPAM, BIS, SDS and MAA and 95 ml of water were put into a 250-ml, three-necked, round-bottom flask, which was equipped with a condenser and a nitrogen gas inlet. Then the reaction mixture was heated up to 70°C under continuous nitrogen purge. Five milliliters of 0.05 mol/l APS aqueous solution was added to the reaction mixture, and the reaction was continued for 4 h at 70°C under nitrogen purge. The microgels were cooled and dialyzed for 5–6 days against a frequent exchange of distilled water at room temperature using molecular porous membrane tubing (Fisher Scientific, UK) having a molecular-weight cut-off of 12–14,000.

Table 3

Feed composition of the p(NIPAM-co-MAA) copolymer microgels.

NIPAM (g)MAA (μl)SDS (g)BIS (g)APS (0.05 mol/l) (ml)H2 O (ml)Total no. of moles
0.92400.050.075950.009

4.3 Fabrication of nickel and cobalt nanoparticles in p(NIPAM-co-MAA) microgels

An in situ chemical reduction technique was used for the synthesis of Ni-p(NIPAM-co-MAA) hybrid microgels. 12.5 ml of the p(NIPAM-co-MAA) microgel dispersion and 9.9 ml of distilled water were put in a three-necked, round-bottom flask (250 ml) fitted with a condenser, stirrer and nitrogen gas inlet. Then 0.1 ml of 0.1 mol/l NiSO4·6H2 O was added to the reaction mixture. Then the reaction mixture was further stirred for 30 min under nitrogen purge at room temperature. After 30 min, 2.5 ml of an aqueous solution of NaBH4 (0.11 mol/l) was added dropwise to the reaction mixture. The color of the solution changed from colorless to black with the addition of NaBH4. The reaction was further run for an hour under nitrogen purge. Ni-p(NIPAM-co-MAA) hybrid microgels were dialyzed against distilled water for an hour using a macromolecular porous membrane. Similarly, Co-p(NIPAM-co-MAA) hybrid microgels were synthesized using CoCl2·6H2 O salt.

4.4 Catalytic activity of Ni-p(NIPAM-co-MAA) and Co-p(NIPAM-co-MAA)

The reduction of 4-NP to 4-AP was monitored by a UV-visible Spectrophotometer. A total of 0.5 ml of 40 mmol/l NaBH4 and 1.8 ml of 0.111 mmol/l 4-NP and the catalysts were added to the cuvette, and the spectra were scanned at constant time intervals within a range of 200–500 nm using a UVD3500 (Labomed Inc., USA) spectrophotometer until the absorbance at 400 nm became constant. The catalytic reduction of 4-NP was carried out using various amounts of the Ni-p(NIPAM-co-MAA) and Co-p(NIPAM-co-MAA) catalysts as given in Tables 1 and 2, respectively hybrid microgels.

4.5 Characterization techniques

FTIR spectra were recorded on a Prestige-21 FTIR (Schimadzu Scientific Instruments, USA) spectrometer having a range of 650–4000 cm-1. DLS measurements were carried out using a commercial laser light spectrometer (B1-200SM, Brookhaven Instruments Corporation, USA) with a motor-driven goniometer equipped with a digital autocorrelator (BI-9000AT). A 22-mW cylindrical uniphase He-Ne laser having a wavelength of 637 nm was used as a light source.

Corresponding author: Zahoor H. Farooqi, Institute of Chemistry, University of the Punjab, New Campus, Lahore 54590, Pakistan, Tel.: +92-42-9230463, Ext. 817, Fax: +92-42-9231269, e-mail:

Acknowledgments

The authors are grateful to the University of the Punjab, Lahore, Pakistan, for financial support under a research project grant for the fiscal year 2012–2013.

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Received: 2014-6-3
Accepted: 2014-7-10
Published Online: 2014-8-14
Published in Print: 2014-9-1

©2014 by De Gruyter

Articles in the same Issue

  1. Frontmatter
  2. In this Issue
  3. Editorial
  4. Editorial
  5. Full length articles
  6. Modulation of cell behaviors by electrochemically active polyelectrolyte multilayers
  7. Electrospun PMMA/AB nanofiber composites for hydrogen storage applications
  8. Cobalt and nickel nanoparticles fabricated p(NIPAM-co-MAA) microgels for catalytic applications
  9. Investigating the influence of temperature on electrospinning of polycaprolactone solutions
  10. Synthesis of two AMPS-based polymerizable room temperature ionic liquids and swelling difference between their co-polymeric gels with HEMA
  11. Manufacturing method of carbon and glass fabric composites with dispersed nanofibers using vacuum-assisted resin transfer molding
  12. Lactide synthesis optimization: investigation of the temperature, catalyst and pressure effects
  13. Influence of KMnO4 concentration and treatment time on PAN precursor and the resulting carbon nanofibers’ properties
  14. A study on obtaining nonwovens using polyhydroxyalkanoates and the melt-blown technique
https://doi.org/10.1515/epoly-2014-0111
Keywords for this article
catalyst; hybrid microgels; microgels; nanoparticles; pH sensitivity

Articles in the same Issue

  1. Frontmatter
  2. In this Issue
  3. Editorial
  4. Editorial
  5. Full length articles
  6. Modulation of cell behaviors by electrochemically active polyelectrolyte multilayers
  7. Electrospun PMMA/AB nanofiber composites for hydrogen storage applications
  8. Cobalt and nickel nanoparticles fabricated p(NIPAM-co-MAA) microgels for catalytic applications
  9. Investigating the influence of temperature on electrospinning of polycaprolactone solutions
  10. Synthesis of two AMPS-based polymerizable room temperature ionic liquids and swelling difference between their co-polymeric gels with HEMA
  11. Manufacturing method of carbon and glass fabric composites with dispersed nanofibers using vacuum-assisted resin transfer molding
  12. Lactide synthesis optimization: investigation of the temperature, catalyst and pressure effects
  13. Influence of KMnO4 concentration and treatment time on PAN precursor and the resulting carbon nanofibers’ properties
  14. A study on obtaining nonwovens using polyhydroxyalkanoates and the melt-blown technique
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