Direct deposition of copper nanoparticles on poly(glycidyl methacrylate) beads

19 September 2016
Sakvai Mohammed Safiullah, Kathikar Abdul Wasi, and Kottur Anver Basha
A simple method is used to fabricate nanohybrids that serve as effective catalysts for the reduction of 4-nitrophenol to 4-aminophenol.

Metal nanoparticles (NPs) are a particularly interesting material in a number of research fields because of their promising characteristics for diverse applications (e.g., for catalysis, electronics, and optics). The use of metal NPs in materials, however, generally suffers from a number of problems, e.g., irreversible aggregation and difficult recovery, because of the high surface energy and large surface area of the particles.1 It has recently been demonstrated, however, that immobilization of metal NPs on a polymer support is a way to address these issues.2 Indeed, chemical modification of polymers—via simple reactions of epoxy groups with a large variety of reagents—provides a novel route for the preparation of various multifunctional polymers, such as poly(glycidyl methacrylate).

The technique of NP immobilization is therefore currently being investigated extensively. For example, in a recent study, silver NPs were immobilized on sulfhydryl-functionalized poly(glycidyl methacrylate)—PGMA—microspheres.3 In addition, amine-functionalized PGMA microspheres have been used as a template for the fabrication of gold crystals that have high catalytic activity when used to convert 4-nitrophenol (4NP) to 4-aminophenol (4AP).4 In other work,5 gold NPs (12 ± 3nm in size) were deposited on the surface of poly(allylamine hydrochloride)-modified PGMA spheres. The immobilization of copper (Cu) NPs on an unmodified PGMA support (i.e., to serve as a catalyst), however, has not yet been reported.

In this work,6 we have therefore developed an effective and easy methodology for the fabrication of CuNPs on a PGMA support that has an unmodified surface. Our approach facilitates the incorporation of CuNPs on the surface of the PGMA matrix. Furthermore, we have conducted elemental, structural, morphological, and thermal studies to characterize our PGMA/Cu nanohybrid samples. We also report the use of our PGMA/Cu nanohybrid (with CuNP loadings of 1 and 5% w/w) as a catalyst for the reduction of 4NP to 4AP.

For our study, we prepared the PGMA beads by a procedure we have previously described.7 The full experimental procedure for the preparation of our PGMA/Cu nanohybrids is shown schematically in Figure 1. In the first part of this procedure we add the required quantity of glycidyl methacrylate, an initiator, and disodium hydrogen phosphate (an anti-coagulant) to 100ml of a 1% polyvinyl alcohol solution in a 250ml three-necked round flask. We then stir this mixture for one hour, at 80°C in an inert atmosphere. We then filter, wash, and dry the solution at 100°C for one day, under vacuum conditions, to yield colorless, microporous, spherical, solid PGMA beads. To synthesize the PGMA/Cu nanohybrid, we activate the PGMA beads by soaking them in chloroform for 24 hours and then immersing them in a solution containing CuNPs overnight. In the final step, we filter, wash, and then dry the (red) PGMA/Cu nanohybrid solid microspheres at 100°C in a vacuum.

Schematic illustration of the synthesis procedure for the poly(glycidyl methacrylate)/copper (PGMA/Cu) nanohybrid. CHCl3: Chloroform. NP: Nanoparticle.

We conducted Fourier transform IR (FTIR) measurements (see Figure 2) that confirmed the hydrophilicity of our nanocomposites increases with an increased CuNP loading (i.e., from 1 to 5% w/w). This means that the PGMA/Cu nanohybrids are an accessible catalyst in an aqueous medium. In addition, from our x-ray diffraction (XRD) study—see Figure 3—we observed that the CuNPs were doped on the surface of the PGMA matrix. CuNPs are therefore available for catalytic activity. Lastly, the results of our morphological characterization clearly show that the PGMA/nanohybrid catalyst surface is rough. This roughness is caused by the fabrication of different-shaped CuNPs, which in turn increases the surface area of the resultant catalyst.

Fourier transform IR spectra of (a) PGMA, as well as PGMA/Cu nanohybrids containing (b) 1% and (c)  5% CuNPs. Red arrows denote spectral signature of increased hydrophilicity.

X-ray diffraction patterns for (a) PGMA, as well as PGMA/Cu nanohybrids containing (b) 1% and (c)  5% CuNPs. Three crystallographic planes of interest are labeled. θ: Measured angle of diffraction.

We measure, and express, the catalytic activity of our PGMA/Cu nanohybrid catalyst by the time it takes to reach 100% conversion (noted by color change) for the hydrogenation reaction (i.e., reduction of 4NP to 4AP). For our tests, we measured the PGMA/Cu nanohybrid catalytic activity with respect to different catalysts. From our data, it is evident that the PGMA/Cu nanohybrid with 1% NP loading exhibits much better catalytic activity than the 5% NP loading sample. This result can be understood in two different ways. First, the increased CuNP loading will mean a lower dispersion of NPs. Therefore, not all the CuNPs will be susceptible to the reactants. In addition, neighboring nanosized CuNPs may influence one another.8 Our catalytic activity measurements for the two catalyst samples also confirm that the Cu particles deposited on the PGMA matrix are nanosized (because the catalytic performance is dependent on particle size).9 We assume that nanosized metals are more catalytically efficient than microsized particles, but a more detailed kinetic study (and reusability of the catalyst) is required.

In summary, we have used a simple methodology to achieve effective deposition of copper nanoparticles on a poly(glycidyl methacrylate) matrix. Our FTIR and XRD measurements confirm that the NPs are stabilized, via non-covalent interaction, and immobilized on the surface of the PGMA. We also find that the NP deposition had a significant effect on the morphology of the polymer. In addition, we have shown that our PGMA/Cu nanohybrids can act as successful catalysts for the reduction of 4-nitrophenol to 4-aminophenol (see Figure 4). Our technique for the preparation of PGMA/Cu nanohybrids should thus open up new avenues for research in the field of catalysis, and the resultant nanocomposites should be useful in both academia and industry. We are now studying the kinetics behind our synthesized catalysts. We are also investigating potential application of our catalysts for the transformation of harmful industrial dyes into environmentally safe by-products.

(a) Ultraviolet to visible (UV-Vis) light absorption (Abs) spectrum of 4-nitrophenol (4-NP). (b) UV-Vis light absorption spectra that illustrate the successful reduction of 4-NP to 4-aminophenol over a period of 600 seconds. The reduction was conducted over a PGMA/Cu nanohybrid (1% CuNPs) catalyst (in an aqueous medium at room temperature).


Sakvai Mohammed Safiullah
C. Abdul Hakeem College

Kathikar Abdul Wasi
C. Abdul Hakeem College

Kottur Anver Basha
C. Abdul Hakeem College


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DOI:  10.2417/spepro.006723

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