Synthesis of gold nanoparticles with ultrasonic spray pyrolysis and its feasibility for ink-jet printing on paper

Background: The bulk production of Gold Nanoparticles (AuNPs) and their concentrated ink, with desirable properties such as morphology, purity, stability and final Au concentration, remains a challenge. Objective: (i) Synthesis of AuNPs through Ultrasonic Spray Pyrolysis (USP) from different precursors. (ii) Preparation of their concentrated ink and (iii) Test their feasibility for ink jet printing onto a glossy paper substrate. Method: Initially, two different start materials were used - precursor: Gold Chloride with its nanoparticles as C-AuNPs, and Gold Acetate with its nanoparticles as A-AuNPs stabilised with PVP40 in deionised water. The concentrated ink was prepared from both AuNPs, and filtered up to the [Au] of 1000 ppm. Ink-jet printing was performed, and the obtained patterns were analysed through SEM. Results: The [Au] in the obtained solutions, determined through ICP-OES analysis, was, for CAuNPs, about 100 ppm, and 150 ppm for A-AuNPs. In the case of C-AuNPs the solution was rose, and for A-AuNPs violet. TEM investigation revealed that C-AuNPs dominated in a circular shape with size about 18 nm; contrary to this, A-AuNPs were mostly in ellipsoid shape, with size in the longitudinal direction of about 36 nm. EDX analyses detected 99.9 wt. % of Au in both AuNPs, which is evidence that these were of high purity. Due to different AuNPs` sizes and [Au], the colloidal solutions showed maximum absorbance wavelength of 532 nm for C-AuNPs and 528 nm for A-AuNPs. SEM results showed that A-AuNPs were significantly better for printing on the paper substrate than C-AuNPs, due to their ellipsoidal shape, as the flow behaviour had been much smoother through the nozzle as compared to the circular shape. The printed area with A-AuNPs reflected in better incorporation of nanoparticles on the paper surface and high-density connectivity among AuNPs. Conclusions: C-AuNPs and A-AuNPs were synthesised successfully under optimum parameters of evaporation temperature, reaction temperature and gas flow rates. The spherical shape of C-AuNPs as compared to the ellipsoidal nature of A-AuNPs was due to the rapid sintering of Gold Chloride at a higher temperature of 300°C as compared to Gold Acetate.