Novel microwave assisted approach to large scale nickel nanoparticle fabrication

•Nickel nanoparticles were produced by reduction of nickel hydroxide under MW-assisted heating.•No special organic additives and pH regulators were applied.•Auto-catalytic behavior of nickel nanoparticles was proven.•Reduction agent (ethylene glycol) multiple usage/recyclability was demonstrated.•Highly concentrated nickel nanoparticle suspensions were produced.

This work shows a novel environmentally benign microwave (MW) assisted method for the fabrication of Ni0 nanoparticles. The objective was the development of a rapid and self-sustainable solvothermal method, starting from concentrated nickel hydroxide suspensions. Suspensions of nickel hydroxide (Ni(OH)2) in ethylene glycol (EG) were converted to Ni0 nanoparticles at 260 °C without the need for any supplementary catalysts. The MW irradiation initiated the dissociation of nickel hydroxide to Ni2+ and mobile OH- ions thus triggering the partial catalytic oxidation of EG. As a consequence, two electrons became available to reduce Ni2+ to metallic Ni0 nanoparticles. This process is self-sustainable as the Ni0 nanoparticles then become the catalytic domains for further oxidation of EG and resulting in a faster kinetics for the complete reduction of nickel hydroxide within 60 min. Interestingly, the MW-assisted process was also effective in multiple recycling of EG, forming Ni0 nanoparticles after each reduction cycle. This process dispenses the need for using a high amount of solvents as required in conventional solvothermal methods, and greatly reduces solvent waste generation. In addition, this novel process led to almost 100% conversion of highly concentrated suspensions (1.2 M Ni(OH)2) to Ni0 nanoparticles, which is very attractive for a large scale production.

Graphical abstractProduction of Ni0 nanoparticle from Ni(OH)2 and ethylene glycol under MW.Figure optionsDownload full-size imageDownload as PowerPoint slide