Sodium Dodecylbenzenesulfonate Self-Assembled LDH Based on Dual Reversal of Surface Charge/Hydrophilicity-Hydrophobicity: Efficient Removal Mechanism of Crystal Violet

Abstract The environmental challenges posed by the discharge of printing and dyeing wastewater urgently require effective treatment technologies. This study developed an efficient adsorbent through sodium dodecylbenzenesulfonate (SDBS) self-assembled Mg/Al-layered double hydroxides (LDHs) via a one-step hydrothermal method. When an Mg 2 ⁺/Al 3 ⁺/SDBS molar ratio was 3:1:1.40, and calcination was performed at 300 °C for 2 h, the adsorbent achieved a markedly high removal efficiency of 84.8% and an adsorption capacity of 63.6 mg/g, substantially outperforming the unmodified LDH (8.4% removal, 6.3 mg/g). SDBS acted as an effective structure modifier, inducing morphology regulation, a dual inversion of hydrophilicity/hydrophobicity (the contact angle of Mg/Al-LDH was measured to be 124.08°, whereas that of Mg/Al/SDBS-LDH was 0°), and surface charge reversal, which critically enhanced the adsorption of crystal violet (CV). The synergistic mechanism involved mesopore filling, electrostatic attraction, hydrogen bonding, and π–π interactions. This study demonstrates that SDBS-modified LDHs are highly promising adsorbents for advancing environmental remediation strategies.