The effect of modifier adding sequence on physical-chemical property and adsorption ability of Inorganic-Organic Montmorillonite (IOMMt)

Adding sequence is one of the crucial factors affecting the modification on the properties of modified products in addition to the types of modifiers. Inorganic-organic montmorillonites (IOMMts) as adsorbents were synthesized in three adding sequences of Keggin Al₁₃ complex (Al₁₃) and Hexadecyltrimethyl ammonium (HDTMA): (1) the montmorillonite (MMt) was modified by Al₁₃ before HDTMA (O-Al-MMt); (2) the montmorillonite was modified by HDTMA before Al₁₃ (Al-O-MMt); (3) the montmorillonite was modified simultaneously by Al₁₃ and HDTMA (Co-MMt). The physical-chemical properties and simultaneous adsorption abilities of IOMMts towards hexavalent chromium (Cr(VI)) and bisphenol A (BPA) as affected by these three adding sequences were investigated. The results showed that the variations of basal distance (d₀₀₁), surface area, and porosity of IOMMts depended on the type and adding sequence of modifiers. The adding sequence mainly affected the molecular environment and the amount of HDTMA incorporated into IOMMts, and thereby affected the adsorption abilities of IOMMts towards Cr(VI) and BPA. Al-O-MMt and Co-MMt exhibited higher loaded amounts of HDTMA (0.773 and 0.784 mmol/g) than O-Al-MMt (0.368 mmol/g). As a result, Al-O-MMt and Co-MMt had higher maximum adsorption amounts of Cr(VI) (Al-O-MMt: 13 mg/g and Co-MMt: 10.9 mg/g) and BPA (Al-O-MMt: 179 mg/g and Co-MMt:173 mg/g) than O-Al-MMt (Cr(VI): 2.6 mg/g and BPA: 31.4 mg/g). In terms of the simultaneous adsorption abilities of IOMMts towards both Cr(VI) and BPA, BPA had a synergistic effect to increase the adsorption of Cr(VI), while Cr(VI) competed with BPA to reduce the adsorption of BPA onto IOMMts.