Green in situ synthesis of silver nanoparticles on cellulose fibres by using sumac leaf extract

This study presents a simple and environmentally friendly method of producing an antimicrobial and UV protective finish on cotton fabrics using silver nanoparticles (Ag NPs) synthesised in situ by the green biochemical route. The synthesis of Ag NPs was carried out using Rhus Thyphna sumac leaf extract both as a reducing and capping agent for silver nitrate (AgNO3), which was used in five concentrations of 0.1 to 5.0 mM. The cotton fabric was pre-treated with an organic-inorganic hybrid sol-gel precursor to form a silica matrix on the fibres to improve the surface adsorption of Ag NPs and consequently a higher synthesis yield. The influence of the concentration of AgNO3 used in the synthesis process on the morphological and chemical properties of the modified cotton fibres was investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and inductively coupled plasma mass spectroscopy (ICP-MS). The functional properties of the investigated samples were assessed by colour measurements, the antibacterial activity against Gramnegative Escherichia coli and Gram-positive Staphylococcus aureus as well as the determination of UV-protection properties. The wash fastness of the newly synthesised Ag NPs was evaluated after one and five repeated washings. The results confirmed the successful formation of Ag NPs on the cotton fibres in the presence of sumac leaf extract with an average size of 70-100 nm. The Ag NPs were homogeneously distributed on the surface of the fibres and gave the cotton samples a light yellow to dark brown colour. The presence of Ag NPs caused an excellent 97% antimicrobial activity, which was higher for S. aureus than E. coli. This behaviour was attributed to the phenolic compounds in sumac leaf extract, which are strong antibacterial agents against Gram-positive bacteria, but proved to be a perfect breeding ground for Gram-negative bacteria. Accordingly, MIC against E. coli was 4.7 times higher than for S. aureus, but MBC was 340 mg/kg Ag, regardless of the bacterial species. As UV absorbers, Ag NPs in combination with sumac leaf extract provided excellent UV protection. While the presence of sumac leaf extract reflected only a UPF of 51, Ag functionalized cotton samples showed UPFs in the range of 40 to 69 as the concentration of AgNO3 increased. The wash fastness of the newly synthesised Ag NPs was concentration dependent. In fact, five consecutive washes resulted in the loss of sufficient protection against E. coli, but the excellent antibacterial activity against S. aureus of R<90% was still retained in the sample treated with 5.0 mM AgNO3. After five laboratory washes, the UPF values of the samples also decreased. However good to excellent UV protection was still maintained with an UPFs of 30 to 40. Accordingly, the proposed in situ synthesis of Ag NPs using sumac leaf extract proved to be not only environmentally friendly, but also promising to produce textiles with multifunctional antibacterial and UV-protective properties in a very simple way with satisfactory wash fastness of the synthesized Ag NPs.