Combined effect of physicochemical factors on the retention and transport of g-CN in porous media.

The environmental behaviors of graphitic carbon nitride (g-CN) have drawn increasing attention in recent. Understanding the fate and transport of g-CN in porous media is necessary for evaluating its environmental risks. Column experiments were used in this study to investigate the combined effect of ionic strength (IS) and other common physicochemical factors (i.e. sand grain size, solution pH, and humic acid concentration) on g-CN transport. The one-site kinetic models were applied to simulate the retention and transport of g-CN in porous media, which fitted the breakthrough curves very well. Experimental and model results showed that g-CN had a weak mobility with the transport mass recovery (TMR) less than 39.6% at pH 6.0 in absence of humic acid (HA). The mobility of g-CN was inhibited with decreasing sand grain size, and the inhibited efficiency was enhanced with IS. However, g-CN transport was significantly enhanced with increasing pH and HA concentration, and the enhanced efficiency was more obviously at high IS. The maximum TMR (78.3%) of g-CN was observed with the presence of 5 mg L HA. These results indicated that physicochemical factors played an important and combined role in controlling g-CN transport in porous media, which would lead to the more complex evaluation on the environmental behaviors of g-CN.