Elucidating the conformation effects within adsorption of natural organic matter on mesoporous graphitic carbon

The conformation effects were frequently reported to affect the adsorption of natural organic matter (NOM), but such a specific mechanism is poorly understood. To address this knowledge gap, based on the adsorption of NOM on mesoporous graphitic carbon nitride (MCN) prepared via a novel pseudo-templating method, the conformation effects were elucidated. The results showed that MCNs nano-architectures with uniform mesopores were successfully fabricated and showed prominent adsorption capacity. The maximum adsorption amounts of MCN-0.5 for fulvic acid (FA) and leonardite humic acid (HA) were 73.61 mgC g⁻¹ and 135.57 mgC g⁻¹, respectively. The adsorptive affinities of components for HA and Elliott soil HA (ESHA) were related to structural condensation; the components with the more coiled conformation exhibited higher affinities because of occupying less active sites and weakening the electrostatic repulsion. Such conformation effects were further established with respect to NOM types and components, as well as solution chemistry. HA and ESHA suffered from variations from the coiled to linear conformations as pH increased, but not the other four types of NOM tested, and particularly the humic-like and territorial humic-like components were critical in such conformational variations. The adsorption of HA and ESHA was affected by pH via both the conformation effects and the interaction mechanism. By contrast, the conformation of six types of NOM was not affected by the common cations (Na⁺, K⁺, Mg²⁺, Ca²⁺), and these cations impacted NOM adsorption only through the conventional interactions.