Synthesis of Cellulose-Metal Nanoparticle Composites –Development and Comparison of Different Protocols

Sumaira Ashraf,†,£ Saif-ur-Rehman,†Falak Sher,§ Zafar Mahmood Khalid, † Mazhar Mehmood,£ and Irshad Hussain§*

†National Institute for Biotechnology and Genetic Engineering (NIBGE), Jhang road, Faisalabad, Pakistan. §Department of Chemistry, SBA School of Science & Engineering (SBASSE), Lahore University of Management Sciences (LUMS), DHA, Lahore Cantt. – 54792, Pakistan. £Department of Metallurgy & Materials Engineering, Pakistan Institute of Engineering & Applied Sciences, Nilore, Islamabad, Pakistan.

* Corresponding author: Professor IrshadHussain

Email: ihussain@lums.e du.pk;

Tel: +92 42 3560 8133, Fax: +92 42 3560 8314

Abstract

Deposition of nanoparticles on the surface of a variety of materials is a subject of great interest due to their potential applications in electronic devices, sensing, catalysis and bio-medical sciences. In this context, we have explored and compared various methodologies to generate gold and silver nanoparticles on the surface of cellulose fibers. It was found thatboiling of the cellulose fibers in alkaline solution of gold and silver salts led to the formation and immobilization of gold and silver nanoparticles. However, in case of lecithin treated and thiol-modified cellulose fibers, high temperature was not essentially required for the formation anddeposition of nanoparticles on cellulose substrate.In both these cases, fairly uniformmetal nanoparticles were obtainedin good yields (~ 43 wt. % gold loading in case of thiol modified cellulose fibers) at room temperature. Borohydride-reduction method resulted in relatively lower loading (~ 22 wt. %) with a wide size distribution of gold and silver nanoparticles on cellulose fibers. All these nanoparticle-cellulose composites were thoroughly characterized using scanning electron microscopy, energy dispersive X-ray,Fourier transform infrared spectroscopy, UV-visible spectroscopy, and elemental analyzer. Thiol modified cellulose-gold nanoparticle composites served as active catalysts in the reduction of 4-nitrophenol into 4-aminophenol.

Key words:Cellulose, thiol-modified cellulose, lecithin, cellulose - metal nanoparticle composites, catalysis.

Figure S1. (a) Scanning electron micrograph of cellulose fiber coated with gold nanoparticles formed by in situ reduction of gold ions on the surface of cellulose fibers using sodium borohydride as reducing agent. Scale bar corresponds to1 µm. Corresponding EDX spectrum is given in (b).

Figure S2.(a), and (b) Scanning electron micrographs of cellulose fibers coated with silver nanoparticles formed by in situ reduction of silver ions on the surface of cellulose fibers using sodium borohydride as reducing agent. Scale bar corresponds to (a) 1 µm, and (b) 100 nm. Their EDX spectrum is shown in (c).

Figure S3. (a), and (b)Scanning electron micrographs of cellulose fibers coated with gold nanoparticles formed by in situ reduction of gold ions on the surface of cellulose fibers by refluxing cellulose fibers (soaked in 0.05 M sodium hydroxide solution)with 1 mM HAuCl4 solution. Scale bar corresponds to (a) 1 µm, and (b) 100 nm. Their EDX spectrum is given in (c).

Figure S4. (a) Scanning electron micrograph of cellulose fibers coated with silver nanoparticles formed by in situ reduction of silver ions on the surface of cellulose fibers by refluxing cellulose fibers (pre-soaked in 0.05 mM sodium hydroxide solution) with 1 mM AgNO3 solution. Scale bar corresponds to 1 µm. Their EDX spectrum is given in (b).

Figure S5. (a) Scanning electron micrograph of cellulose fibers coated with gold nanoparticles formed by in situ reduction of gold ions on the surface of cellulose fibers using lecithin as a reducing agent. Scale bar corresponds to 1 µm. Their EDX spectrum is given in (b).

Figure S6. (a) Scanning electron micrograph of cellulose fibers coated with silver nanoparticles formed by in situ reduction of silver ions on the surface of cellulose fibers using lecithin as a reducing agent. Scale bar corresponds to 1 µm. Their EDX spectrum is given in (b).

Figure S7. FTIR spectra of cellulose fibers, lecithin and lecithin treated cellulose fibers.

Figure S8. FTIR spectra of cellulose fibers (blue line) and thiol modified cellulose fibers (red line) used for the production/ immobilization of gold and silver nanoparticles on the surface of thiol modified cellulose fibers.

Figure S9. Scanning electron micrographs of cellulose fibers coated with gold nanoparticles formed by in situ reduction of gold ions on the surface of thiol modified cellulose fiber (a andb). Scale bar corresponds to 1 µm. Their EDX spectrum is given in (c).

Figure S10. Scanning electron micrographs of cellulose fibers coated with silver nanoparticles formed by in situ reduction of silver ions on the surface of thiol modified cellulose fiber (a_ d) at different magnifications. Their EDX spectrum is given in (e).