Phyto-Assisted Assembly of Metal Nanoparticles in Chitosan Matrix Using S. argel Leaf Extract and Its Application for Catalytic Oxidation of Benzyl Alcohol.

Amel Taha,Enshirah Da’Na

doi:10.3390/polym14040766

Abstract

The design and synthesis of eco-friendly solid-supported metal nanoparticles with remarkable stability and catalytic performance have gained much attention for both industrial and environmental applications. This study provides a novel, low-cost, simple, and eco-friendly approach for decorating cross-linked chitosan with gold nanoparticles (AuNPs), greenly prepared with Solenostemma argel (S. argel) leaf extract under mild conditions. Glutaraldehyde-modified chitosan beads were used to coordinate with Au(III) ions and act as stabilizing agents, and S. argel leaf extract was used as a cost-effective phyto-reducing agent to reduce gold ions to elemental Au nanoparticles. The successful cross-linking of chitosan with glutaraldehyde, the coordination of Au(III) ions into the chitosan matrix, and the phytochemical reduction of Au(III) to Au nanoparticles were investigated via FT-IR spectroscopy. The obtained Au nanoparticles have a uniform spherical shape and size <10 nm, as confirmed by both X-ray diffraction (XRD) (~8.8 nm) and TEM (6.0 ± 3 nm). The uniformity of the AuNPs’ size was confirmed by Scanning Electron Microscopy (SEM) and Transition Electron Microscopy (TEM). The powder X-ray diffraction technique showed crystalline AuNPs with a face-centered cubic structure. The elemental analysis and the Energy Dispersive Spectroscopy (EDS) analysis both confirmed the successful integration of Au nanoparticles with the chitosan network. The catalytic activity of this highly stable nanocomposite was systematically investigated via the selective oxidation of benzyl alcohol to benzaldehyde. Results showed a remarkable conversion (97%) and excellent selectivity (99%) in the formation of benzaldehyde over other side products.

Highlights

Nowadays, the design and synthesis of inorganic/organic hybrid materials have attracted much attention, due to their important applications in biomedical [1,2], sensor [3–5], semiconductor [6], catalysis [7–10], solar cell [11], and many other fields [12]
To prepare the S. argel leaf extract, 20 g of the dried and ground leaf was mixed with 100 mL of deionized water in a 500 mL round flask for one hour
FT-IR spectra of chitosan beads after each step of synthesis were recorded with a Cary 630 FT-IR spectrophotometer within the range of 400 to 4000 cm−1

Summary

Introduction

The design and synthesis of inorganic/organic hybrid materials (metal nanoparticles/polymer) have attracted much attention, due to their important applications in biomedical [1,2], sensor [3–5], semiconductor [6], catalysis [7–10], solar cell [11], and many other fields [12] This wide range of applications is mainly due to the fact that these hybrid nanocomposites have attractive electrical [13], optical [13–15], and magnetic [16–18] characteristics compared to those of pure polymers or inorganic particles. Chitosan-based hybrid materials are considered effective bio-sorbents, since they are relatively cheap and their surfaces are rich in amino and hydroxyl groups [29,30] They were reported to significantly capture many pollutants, such as p-nitrophenol [31] and heavy metal ions [27]. The main challenge to the application of this biological support is its high solubility in most organic acids and dilute mineral solutions This drawback can be overcome by chemical or physical modification via cross-linking agents, such as ethylene glycol diglycidyl ether, glutaraldehyde (GLA), epichlorohydrin, genipin, or triphosphate [31,34,35]. In addition to enhancing chemical stability, this cross-linking can improve both the mechanical and thermal stability of the chitosan [34,35]

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Discussion

Conclusion