Phenylphosphonic acid–intercalated bentonite: a novel organoclay for efficient Congo red removal

The extensive release of synthetic dyes into aquatic environments raises significant environmental and health concerns, particularly for Congo red, a highly soluble and toxic anionic azo dye. Addressing this issue requires the development of adsorbent materials that combine high efficiency with cost-effectiveness and environmental sustainability. In this study, a novel organobentonite was synthesized by intercalating phenylphosphonic acid into bentonite, an approach not previously reported for pollutant removal. The intercalation of phenylphosphonic acid into bentonite was confirmed by X-ray diffraction analysis , with a basal spacing increasing from 10 Å to 15.4 Å and an intercalated fraction of 86%. The adsorption behavior of the organobentonite, designated BPA6, toward Congo red was systematically investigated. At 55 °C and pH 8, BPA6 reached an adsorption capacity of 152.8 mg g −1 , while the equilibrium uptake data were fairly fitted by the Redlich–Peterson isotherm model. The adsorption process was spontaneous and endothermic, with physical interactions playing a dominant role. BPA6 retained its adsorption performance over three consecutive reuses using methanol as the eluent, with hydrogen bonding identified by FTIR spectroscopy as the main interaction mechanism. These findings highlight the strong potential of phenylphosphonic acid–modified bentonite as an innovative and environmentally relevant clay-based adsorbent for the treatment of dye contaminated wastewater.