Study On The Adsorption Of Hydroxyl-containing Asymmetric Gemini Surfactant Modified SiO₂ Nanoparticles

Asymmetric gemini surfactants are favorable organic modifiers which have the advantages of lower critical micelle concentration（cmc）and better controllability of molecular structure.In this paper,three hydroxyl-containing asymmetric gemini surfactants（14/16/18-3OH-8）with different alkyl chain lengths and Si O₂nanoparticles（SiNPs）were synthesized and used for preparing a series of organo-Si O₂nanoparticles（organo-SiNPs）.The structure and surface properties of SiNPs and organo-SiNPs were investigated by various characterization methods such as FT-IR,XRD and SEM.Taking diclofenac sodium（DS）as the target pollutant,the effects of modifier addition,reaction time,p H,solute concentration and alkyl chain length of modifier on the adsorption performance of organo-SiNPs were investigated in detail.The adsorption process and mechanism were explored by means of adsorption kinetics,thermodynamics and isotherm models.By characterizing the adsorbents after adsorption,comparing the agreement of n-octanol-water partition coefficient(K_ow)with organic-matter-corrected sorption coefficient(K_om),and fitting the statistical physical model,adsorption mechanism during the adsorption process was further revealed.The research results were as follows:The characterization results showed that the modifier had been successfully prepared and loaded onto SiNPs and the hydrophobicity of organo-SiNPs was enhanced.The adsorption experiment results showed that the order of the adsorption capacities of the three organo-SiNPs（14/16/18-3OH-8-SiNPs）for DS was:14-3OH-8-SiNPs（240.13 mg/g）>16-3OH-8-SiNPs（225.04 mg/g）>18-3OH-8-SiNPs（213.40 mg/g）.14-3OH-8-SiNPs had the best adsorption performance due to their more suitable modifier packing density and stronger additional interaction.The adsorption kinetics,thermodynamics and isotherm results showed that the adsorption of DS on the three organo-SiNPs followed the pseudo-second-order kinetics and Langmuir model.The adsorption of DS onto organo-SiNPs was all non-spontaneous,disorder increasing and endothermic physical process.The rate-controlling steps of the adsorption were controlled by both film diffusion and intraparticle diffusion.The results of adsorption experiment and mechanism could be summed up as that hydrogen bonding,OH-π,hydrophobic and electrostatic interactions were all involved in the adsorption process,and hydrogen bonding and OH-πinteractions were dominant in the adsorption process.This study confirms that SiNPs modified by hydroxyl-containing asymmetric gemini surfactants are favorable adsorbents for DS adsorption,which provides new insights into the preparation of organo-SiNPs adsorbents.