More recently, graphitic carbon nitride (CN) has been widely applied in the photodegradation of organic pollutants. However, there are no studies focusing on its adsorption, which has been recognized as the critical steps of photocatalysis. Moreover, ubiquitous humic substances (HSs) in natural water and wastewaters can inevitably interact with CNs, disturbing the photocatalysis of target pollutants. Herein, HSs [i.e. humic acid (HA) and fulvic acid (FA)] adsorption on CNs derived from four typical precursors was investigated. Interestingly, CN derived from urea exhibited the great adsorption capacity for HSs, attributed to porosity and high surface area; the maximum adsorption determined by the Langmuir model reached 73.24 and 51.62 mgC/g for HA and FA, respectively, showing great promises for HSs elimination. HSs adsorption on CNs was mainly regulated by electrostatic interactions, π-conjugation, hydrogen bonding, and surface complexation (see <b>Figure 1</b>). Particularly, given the heterogeneity of HSs, the strongly competitive adsorption was observed between HSs components; HSs components with high aromaticity showed great adsorption affinity. In addition, HSs adsorption on CNs under the solution chemistry widely used for CNs-photocatalysis was also proven. These results revealed that HSs macromolecules definitely competed for active sites, interfering the adsorption of other pollutants for further photodegradation. These findings provide valuable insights into HSs adsorption and pose great challenges to the practical applications of CNs photocatalysts.

Insights into adsorption of humic substances on various graphitic carbon nitride

ACS Spring 2022

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