Heteroatoms in Dissolved Organic Matter: Their Role in Adsorption and Dynamic Assembly on Activated Carbon

The properties of dissolved organic matter (DOM) can significantly affect its adsorption response to activated carbon (AC). Despite extensive studies, the key molecular properties of DOM that govern its adsorbability and assembly behavior on the AC surface remain poorly understood. Here, we investigated DOM-AC interactions using three different secondary effluent organic matter samples through a combination of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and machine learning (ML). The results showed that heteroatoms (N/S) were the key factors influencing DOM molecular adsorbability on AC, with N/S-containing molecules showing preferential adsorption compared to N/S-free molecules. Furthermore, analysis of temporal molecular behavior revealed a two-stage sequential molecular fractionation process: N-containing molecules exhibited rapid preferential adsorption in the initial stage, while S-containing molecules became preferentially adsorbed in the subsequent phase. This sequential molecular behavior might involve a transition from bare AC-DOM dominated adsorption to DOM-DOM interaction dominated adsorption. These molecular-level insights advance our understanding of DOM-AC interactions and provide new criteria for optimizing AC-based water treatment processes.