Size-tunable synthesis of mono-disperse wastewater-derived carbon spheres with polyacrylamide as a directing agent

Highly mono-disperse carbon spheres (CSs) with a tunable diameter of 300-4000 nm are shown to be successfully synthesised using sugar-rich wastewater as carbon sources and polyacrylamide (PAM) as a size-controlling agent. The effects of PAM and pH on the morphology and size were also investigated. Experimental results showed that PAM acted as a size-directing agent which directs the self-assembly of sugar from wastewater to form the spheroidal particles. The size of CSs could be increased from 300 to 600 nm without any alteration in the morphologies by altering the solution pH from 7 to 12. Furthermore, the size of spheroidal carbon particles can be easily controlled by increasing the concentration of PAM from 0.05 to 0.1% (w/v) at pH 12. The largest sizes of CSs grew nearly 4000 nm without damage to their morphology or broadening of their size distribution with the addition of 0.1% PAM. On the basis of the experimental results, a mechanism is proposed to elucidate the formation of CSs with a wide diameter range. It is believed that this work not only provides a novel potential way to utilise wastewater, but also puts forward a facile sustainable approach to synthesise size-controllable CSs.