The characteristics of novel bimodal Ag–TiO2 nanoparticles generated by hybrid laser-ultrasonic technique

Abubaker Hamad,Xiang Li Zhong,Grace Burke,Tao Wang,Zhu Liu,Lin Li

doi:10.1007/s00339-016-9786-3

Abstract

Silver–titania (Ag–TiO2) nanoparticles with smaller Ag nanoparticles attached to larger TiO2 nanoparticles were generated by hybrid ultrasonic vibration and picosecond laser ablation of Ag and Ti bulk targets in deionised water, for the first time. The laser has a wavelength of 1064 nm and a pulse duration of 10 ps. It was observed that without the ultrasonic vibration, Ag and TiO2 nanoparticles did not combine, thus the role of ultrasonic vibration is essential. In addition, colloidal TiO2 and Ag nanoparticles were generated separately for comparison under the same laser beam characteristics and process conditions. The absorption spectra of colloidal Ag–TiO2 cluster nanoparticles were examined by UV–Vis spectroscopy, and size distribution was characterised using transmission electron microscopy. The morphology and composition of Ag–TiO2 nanoparticles were examined using scanning transmission electron microscopy in high-angle annular dark field, and energy-dispersive X-ray spectroscopy. The crystalline structures were investigated by X-ray diffraction. The size of larger TiO2 particles was in the range 30–150 nm, and the smaller-sized Ag nanoparticles attached to the TiO2 was mainly in the range of 10–15 nm. The yield is more than 50 % with the remaining nanoparticles in the form of uncombined Ag and TiO2. The nanoparticles generated had strong antibacterial effects as tested against E. coli. A discussion is given on the role of ultrasonic vibration in the formation of Ag–TiO2 hybrid nanoparticles by picosecond laser ablation.

Highlights

The specific properties of nanoparticles which are different from bulk materials have received much attention over the last two decades [1], and nanoparticles have been used in a wide range of applications from electronic and catalytic uses to magnetic and medical fields [2]
The optical absorption spectra of the Ag–TiO2 nanoparticles produced with and without ultrasonic vibration (Fig. 2b) indicate that there is no shift of the surface plasmon peak position both at 404 nm
When the amount of ablated Ag nanoparticles is increased, the surface plasmon resonance (SPR) peak will become higher, which is an indication that the Ag concentration in the solution has increased

Summary

Introduction

The specific properties of nanoparticles which are different from bulk materials have received much attention over the last two decades [1], and nanoparticles have been used in a wide range of applications from electronic and catalytic uses to magnetic and medical fields [2]. The phases, size and shape of nanoparticles are responsible for the specific properties found in metal and metal oxide nanoparticles [3]. Both the hydrophilic and photocatalytic properties of TiO2 nanoparticles are important for numerous applications, such as antimicrobial activity [4] and self-cleaning [5]. The photocatalytic activity of TiO2 requires the activation with a UV light, which limits its applications. To overcome this limitation, the widely adopted method is to dope TiO2 nanoparticles with other materials, such as transition metals [6] and non-metals [7]. The methods of nanoparticle generation can be divided into three types: chemical, physical and biological, amongst which are sol–gel, chemical vapour deposition (CVD), physical vapour deposition (PVD), wet chemistry, ion sputtering, plasma or flame pyrolysis [8], laser ablation of a solid metal in a liquid environment [9,10,11,12] and the use of Murraya Koenigii (curry leaf) extract [13]

Results

Discussion

Conclusion