Upcycling with laser: From carbon scraps to multicoloured display

Carbon black is one of the oldest manufactured products. This materials’ atomic structure takes the form of a turbostratic structure meaning that each plane of the carbon layer can be rotated or shifted horizontally, a very different structure in comparison to the ordered, ABA stacking of carbon atom layers in graphite. Among the many properties of carbon black, its optoelectronic properties have attracted the attention of many researchers in recent times. Untreated carbon black exhibits semiconducting property which can be a result of electron tunneling, dielectric breakdown and internal field emission, capacitance and graphitic conduction (through-going chain).

Recent reports have linked the optical property of carbon black to the influence of the atmosphere or when carbon black is used as a precursor for the creation of fluorescing carbon nanoparticles (CNP)/nanocages (CNC) through laser assisted wet chemistry process. Despite such progress, more research is still required in this field.

In a recent publication, National University of Singapore researchers led by Dr. Sharon Xiaodai Lim and comprised of Prof. Chorng-Haur Sow, and Prof. Antonio H. Castro Neto in collaboration with Kae Lin Wong of the Universiti Tunku Abdul Rahman and Dr. Zheng Zhang of the Institute of Materials Research Engineering, A*Star in Singapore investigated formation of highly fluorescence recovered carbon black (rCB) empowered by spot annealing using a simple focused laser beam without the use of any solvent. The researchers were able to achieve micropatterns comprising of regions with different fluorescence colors following careful engineering control during the scanning focused laser treatment, for the first time ever. Their work is currently published in the research journal, Nano Research.

Compacted rCB powder was subjected to scanning focused laser spot annealing with the sample in ambient condition, or under controlled helium environment. After focused laser treatment with sample in ambient condition, the laser treated site was seen to have a blue appearance under bright field optical imaging and emitted blue, yellow and red color under specific color illumination.

The authors observed that under bright field imaging, rainbow color was observed from the surrounding sites. Interestingly, when a controlled potential was applied across the sample, fluorescence emission from the sample could easily be switched off. This attribute generally, proved that the presented simple process could add multiple functionalities to a material in a means that is both inexpensive and sustainable. Additionally, optoelectronic analysis of the treated recovered carbon black showed the greatest enhancement of photocurrent was under yellow light.

In summary, Dr. Lim and her colleagues reported for the first time a novel mono- and multicolored fluorescence displayed by dry recovered carbon black powder. This was achieved via a simple scanning focused laser assisted photothermal process. The observed rich and complex display of colors was attributed to; carbon infusion into metal oxide; presence of sulphur impurities in the recovered carbon black powder and light scattering from periodically arrange carbon nanoparticles. Altogether, a facile process, that is both inexpensive and sustainable, to add multiple functionalities was presented.