The research explores a single step method, pulsed laser ablation (PLA) in H2O and supercritical CO2, to produce TiO2 nanoparticles and TiO2-carbon core-shell nanoparticles, by utilizing CO2 in the process. Pressurized CO2, in the form of gaseous, liquid, and supercritical CO2 was demonstrated as a promising solvent for producing well-dispersed agglomerate free nanoparticles and core-shell nanoparticles using PLA technique.
In the past years, there has been a lot of discussion about nanotechnology, clean technology, CO2 utilization, climate change, and lean processes. Who would not like to have higher productivity, less fossil fuel and chemical use, and still see higher profits?
The nanomaterial market has been growing tremendously in the past, while the forecasts indicate no signs of slowing down. Pulsed laser ablation in liquids (PLAL) is a relatively new technique for producing nanoparticles. The traditional techniques for producing nanoparticles are mostly based on wet-chemical synthesis, which may involve harmful chemicals as pre-cursors.
PLAL uses bulk material targets to make nanoparticles, which are typically 5-10 times cheaper than chemical precursors, and avoid the risks involved with handling the chemicals and their waste products. In the last decade, PLAL has grown as a promising, clean technique for nanoparticle synthesis.
In this study, a 1064 nm wavelength nanosecond laser was used at repetition rates 25 kHz and 101 kHz with different beam energies. CO2 pressures from 5 MPa to 40 MPa were tested, while CO2 temperature was varied from 30-50 C. In order to characterize the produced nanoparticles, several techniques were used such as Raman spectroscopy, x-ray photoelectron spectroscopy, ultra-violet spectroscopy, x-ray diffraction, small angle x-ray scattering, and transmission electron microscopy. This dissertation involved an interdisciplinary research combining materials science, photonics, physics, chemistry, and mechanical engineering.
In his doctoral research Amandeep Singh demonstrated the production of stable rutile-TiO2 as nanoparticle suspension by PLA in H2O and proposed small angle x-ray scattering as a quick and promising technique for measurement of nanoparticle size. Further, he demonstrated using PLA in scCO2 to produce well dispersed non-agglomerate anatase-TiO2 nanoparticles directly as a dry nanoparticle powder.
Singh’s collaborative work for nanomaterial characterization at Aalto University, Top Analytica, VTT, and Tampere University helped to understand the laser-produced core-shell nanoparticles of anatase-TiO2 as core and carbon as shell. The results strongly indicate that CO2 can be decomposed to form titanium oxide nanoparticles and carbon nanostructures that adsorb on nanoparticle surface to form a shell.
“Such core-shell structured nanoparticles have important applications in lithium ion batteries, fuel cells, supercapacitors, quantum dot solar cells, and cancer treatment. This makes them highly interesting for the energy industry and medical biotechnology,” tells Singh.
Singh’s expertise on pulsed lasers, supercritical CO2 processing, and promising results of laser-induced CO2 breakdown, from his doctoral thesis along with supervision from Professor Erkki Levänen, led to successfully funded EU’s H2020 project – NanoStencil – in the theme "Future Emerging Technologies" with partners in UK, Germany, Spain, and China. Such academic achievements won him the encouragement grant from Tekniikan Edistämissäätiö. The preliminary results from NanoStencil project seem groundbreaking and have the potential to highlight Tampere University amongst the top in this field of laser patterning in high-density fluids.
Amandeep Singh was born in Indian Punjab/East Punjab and came to Finland in 2013 as a master’s degree student. He currently works as a doctoral researcher at Tampere University and is leading the EU H2020 project NanoStencil at Tampere University with Professor Erkki Levänen (Former Head of Materials Science Department).
The doctoral dissertation of M.Sc. (Tech) Amandeep Singh in the field of Materials Science titled Nanoparticle synthesis by pulsed laser ablation: From H2O to pressurized CO2 will be publicly examined in the Faculty of Engineering and Natural Sciences at Tampere University starting at 1 p.m. on Friday 11.9.2020 in the auditorium K1705 of the Konetalo building, Korkeakoulunkatu 6, Tampere. The Opponents will be Associate Professor David Amans from Université Claude Bernard Lyon 1, France and Professor Jouko Peltonen, Åbo Akademi University, Finland. The Custos will be Professor Erkki Levänen from the Faculty of Engineering and Natural Sciences, Tampere University, Finland.
Due to the coronavirus situation, the public defence is also available via digital platform through Zoom and Echo360.
The dissertation is available online at