Synergistic effects of hydroxylation and structural defects in hexagonal boron nitride for dye removal from wastewater

Hexagonal boron nitride (h-BN) was structurally modified using a simple and efficient chemical weathering method and assessed for its ability to remove anionic Congo Red (CR) and cationic Neutral Red (NR) dyes from wastewater. Batch sorption experiments explored variables including solution pH (2–12), modified h-BN dosage (0.25–1.0 g L⁻¹), contact time (10–420 min), and dye concentration (10–500 mg L⁻¹). Detailed characterization revealed the integration of hydroxyl groups, distinctive rough and cracked surfaces, increased interlayer spacing and crystal size, monodispersed stable solution, and enhanced solubility of modified h-BN. Optimal dye removal occurred at 0.5 g per L dosage, with CR achieving 99.23 ± 0.06% efficiency at pH 2 (60–90 min) and NR 85.77 ± 1.51% at pH 11 (90–120 min) in deionized water. Electrostatic interactions between the modified h-BN and dye molecules drove pH-dependent adsorption, following a pseudo-second-order kinetics model, indicative of chemisorption. Langmuir isotherms confirmed monolayer adsorption on homogeneous surfaces. For similar parameters, in a mixed dye system (i.e., CR : NR = 1 : 1), the removal efficiency favored at pH = 2 over pH = 11 (i.e., 80.54 ± 1.16% over 60.83 ± 5.18%)—was less than mono-dye systems—which indicates that more CR dye could be removed with the exact adsorbent dosage. A limited study was performed with clarifier inlet textile wastewater, which showed a decrease in removal efficiency compared to deionized conditions. A steady decrease in removal efficiency was observed while performing adsorption–desorption cycles. The results demonstrate the potential of modified h-BN as an adsorbent in dye removal from industrial wastewater.