Generation and properties of aqu/nC: the combined effects of humic acid, sunlight, and agitation intensity.

Once released into natural water, the environmental behavior and fate of C could inevitably been affected by humic acid (HA), sunlight, and hydrodynamic conditions. However, the combined effects of these factors are not so clear. Therefore, in the present study, effects of HA, sunlight, and agitation intensity on generation and properties of aqu/nC were investigated. The results indicated that HA could increase the concentration of aqu/nC mainly through the steric hindrance effect. The higher agitation intensity led to higher concentrations of aqu/nC and more efficient steric stabilization was formed by HA. Sunlight irradiation promoted the surface oxidization and consequently enhanced the dispersion of C. The relative order of the influence on the UV/vis concentration was sunlight > agitation intensity > HA. In addition, HA might not always enhance the dispersion of aqu/nC due to light screening/ROS scavenging, over-coating, or chain-like bridging mechanism. Therefore, evaluating the environmental behavior and fate of C should take these factors into account together.