Dipyridyl-based organo-silica nanosheets for three emerging micropollutants efficient removal: Adsorption performance and mechanisms

Abstract

Dipyridyl-based organo-SiNSs (DHBP-SiNSs) was prepared by combining silica nanosheets (SiNSs) with dipyridyl-containing gemini surfactant (DHBP) and employed as adsorbent to effectively remove three emerging pharmaceuticals and personal care products (PPCPs) (Clofibric acid (CA), Ketoprofen (KP) and Naproxen Sodium (NPX)). Key characteristic analysis of DHBP-SiNSs, such as interlayer spacing, surfactant arrangement and the stacking unit of platelets was conducted. The influences of pH, contact time and concentration of the adsorbates were investigated in detail. The results suggested the effective retention of CA (216.59 mg/g), KP (326.36 mg/g) and NPX (260.57 mg/g) at a short time and DHBP-SiNSs can be regenerated at least for 3 cycles. Kinetics, isotherms and thermodynamic parameters were studied to reveal the adsorption mechanism. Based on the comparison of n-octanol-water partition coefficient (Kow) and organic-matter-corrected sorption coefficient (Kom), fitting of statistical physics models and characterizations of spent samples, the structure-adsorption relationships were explained. The adsorption of NPX was governed by π-π interaction, however, partition and π-π stacking were the dominant mechanisms for KP. Multiple interactions (e.g. partition, OH-π interaction, π-π interaction and π-π stacking) were responsible for the efficient elimination of CA. Differentiations of the adsorption process verified that (i) the strength of π-π interaction: pyridine/naphthalene > pyridine/benzene > pyridine/orthogonally benzene, (ii) the strength of π-π stacking: orthogonally benzene > benzene > naphthalene, (iii) π-π interaction between pyridine/naphthalene > the synergy of OH-π interaction between hydroxyl/pyridine and π-π interaction between pyridine/benzene. This study not only enlarged the application of organo-SiNSs as effective adsorbents but also threw more lights on the structure-adsorptive capacity relationships.