Thermodynamic selectivity of functional agents on zeolite for sodium dodecyl sulfate sequestration

Highlights: • A thermodynamic approach to select a functional agent for adsorbent is proposed. • ITC and QCS were used to interpret the interaction between adsorbate and agent. • The interaction identifies the adsorption mechanism and performance. • This approach enables the manipulation of adsorption capacity optimization. - Abstract: This study proposes a thermodynamic approach to effectively select functional agents onto zeolite for sodium dodecyl sulfate (SDS) sequestration in greywater reuse. We combine isothermal titration calorimetry (ITC) and quantum chemistry simulation (QCS) to identify the interactions between SDS and agents at the molecular level. Three potential agents, cetyl trimethyl ammonium bromide (CTAB), N,N,N-trimethyltetradecan-1-aminium bromide (C₁₄TAB), and 14-hydroxy-N,N,N-trimethyltetradecan-1-aminium bromide (C₁₄HTAB), differ in carbon chain length and hydrophilic groups. The ITC titration of SDS with CTAB released the highest heat, followed by those with C₁₄TAB and C₁₄HTAB, as was the same trend for the amounts of SDS adsorbed by the respective functionalized-zeolites. Results suggest that the favorable SDS sorption occurred at the bilayer CTAB-zeolite is driven by enthalpy as similar as the SDS…CTAB interaction found, regardless of the contribution from electrostatic and/or hydrophobic behaviors, while the declined sorption is entropy-driven via the predominant hydrophobic interaction onto the monolayer CTAB-zeolite. The data presented here interpret the nature of molecularly thermodynamic quantities and enable the manipulation of sorption capacity optimization.