Surface hydroxyl groups functionalized graphite carbon nitride for high efficient removal of diquat dibromide from water.

In the study, we present a quick potassium hydroxide heat treatment approach to optimize the "melon" framework of graphite carbon nitride and modify the surface properties by functionalization of hydroxyl groups. The hydroxyl groups functionalized g-CN samples have been applied as bifunctional materials for efficient elimination of diquat dibromide herbicide through synergistic adsorption/photodegradation processes. The structural characterizations of the as-obtained samples, combined with the detailed diquat dibromide herbicide adsorption study, reveal that the surface hydroxyl groups are the active sites for the diquat dibromide adsorption, which account for the much enhanced saturation adsorption capacities of 159.3 mg g at 25 °C and pH = 7 (more than 110 times improvement compared with pristine carbon nitride). Furthermore, the grafted surface hydroxyl groups and optimized planar structures endow the functionalized samples with the advantageous properties of efficient photoinduced charge transfer and separation, low interface resistance, and high photoresponse. Consequently, the deep mineralization of diquat dibromide herbicide was achieved over the bifunctional materials (total removal ratios were ~ 97.1% after 240 min visible-light irradiation). This work not only demonstrates the feasibility of hydroxyl groups functionalized graphite carbon nitride for elimination of herbicide pollutants but also offers new insights to better design efficient and durable materials for environmental remediation.