Adsorption of benzoic acid from aqueous solution by three kinds of modified bentonites

Benzoic acid removal is important for the water treatment, and adsorption is an efficient treatment process. Three kinds of modified bentonites, hydroxy-aluminum pillared bentonite (Al(OH)-Bent), octadecyl trimethyl ammonium chloride modified bentonite (OTMAC-Bent), and both octadecyl trimethyl ammonium chloride and hydroxy-aluminum modified bentonite (Al(OH)-OTMAC-Bent) were prepared and characterized by XRD, FTIR, and BET analysis. Experiments were conducted on the adsorption of benzoic acid by the prepared modified bentonites at different temperatures in batch experiments. The results show benzoic acid adsorption capabilities of Na-Bent and Al(OH)-Bent are even low, but high for OTMAC-Bent and Al(OH)-OTMAC-Bent. Optimal conditions for the adsorption of benzoic acid on OTMAC-Bent and Al(OH)-OTMAC-Bent were as follows: pH of 3.5, 0.04 g/mL adsorbent, and contact time of 90 min. Increased adsorption with temperature indicates that the adsorptions of benzoic acid onto Al(OH)-OTMAC-Bent and OTMAC-Bent are spontaneous and endothermic. The adsorption data could be well interpreted by the Langmuir model and Temkin Equation. The adsorption efficiency was higher than 85%, suggesting that OTMAC-Bent and Al(OH)-OTMAC-Bent are excellent adsorbents for effective benzoic acid removal from water.

Benzoic acid adsorption capabilities of Na-Bent and Al(OH)-Bent are low, but high for OTMAC-Bent and Al(OH)-OTMAC-Bent. On the optimum conditions, the adsorption could be well interpreted by Langmuir model and Temkin model.Effect of pH for the adsorption of benzoic acid onto Na-Bent, Al(OH)-Bent, OTMAC-Bent, and Al(OH)-OTMAC-Bent (A); and the adsorption isotherm fit of benzoic acid adsorption onto Al(OH)-OTMAC-Bent and OTMAC-Bent by Henry (B), Langmuir (C), Freundlich (D), Dubinin–Radushkevich (E), and Temkin (F) isotherm model.Figure optionsDownload high-quality image (119 K)Download as PowerPoint slideHighlights
► We prepared Al(OH)-Bent, OTMAC-Bent, and Al(OH)-OTMAC-Bent, and compared their benzoic acid adsorption properties.
► Benzoic acid adsorption capabilities of Na-Bent and Al(OH)-Bent are even low, but high for OTMAC-Bent and Al(OH)-OTMAC-Bent.
► The adsorptions are spontaneous and endothermic. The adsorption could be well interpreted by the Langmuir and Temkin model.
► The maximum adsorption cpacities of benzoic acid followed the order: Al(OH)-OTMAC-Bent > OTMAC-Bent >> Al(OH)-Bent.