Fabrication And Application Of Polydimethylsiloxane-based Composite Sponges For Efficient Oil-water Separation

The frequent occurrence of oil spills and chemical leakage has addressed widespread attention due to its serious impact on both environment and human health.Recently,polydimethylsiloxane(PDMS)sponges are particularly attractive in oil-water separation,thanks to their excellent characteristics including intrinsic hydrophobicity/lipophilicity,high porosity and flexibility,good thermal and chemical stability,and easy fabrication,etc.Although presenting good adsorption performance,from a practical standpoint of oil-water separation,there is still an urgent demand for a low-cost,simple,and robust method to prepare porous PDMS sponges with considerable absorption capacity,stable performance,and high reusability.In this thesis,effective separation of oil from both immiscible oil-water mixtures and O/W emulsions are achieved by using PDMS-based composite sponges.Firstly,a modified hard template method using citric acid monohydrate(CAM)as the hard template and dissolving it in ethanol is proposed to prepare PDMS sponge composited with carbon nanotubes(CNTs)both in the matrix and the surface.The introduction of CNTs endows the composite sponge with enhanced comprehensive properties including hydrophobicity,absorption capacity and mechanical strength than the pure PDMS.We demonstrate the successful application of CNT-PDMS composite in efficient removal of oil from immiscible oil-water mixtures within not only a bath absorption,but also continuous separation for both static and turbulent flow conditions.This notable characteristic of the CNT-PDMS sponge enables it as a potential candidate for largescale industrial oil-water separation.On the other side,due to the hydrophobic nature of the PDMS sponge,external force is required to continuously squeeze the liquid into the sponge to achieve the separation of oil-in-water(O/W)emulsions.Here,a polydopamine(PDA)modified CNT-PDMS is developed,which firstly realizes the separation of O/W emulsion without continuous squeezing of the sponge.The combined superhydrophilic and superoleophilic property of PDA/CNT-PDMS is assumed to be critical in the spontaneously demulsification process.Thanks to the superhydrophilic surface of the sponge deposited with PDA,oil drops wrapped by water can spontaneously enter the internal porous structures of the sponge without applying external force.Then the hydrophobic/oleophilic CNT-PDMS skeleton acts effectively to trap tiny emulsified oil droplets,making the emulsion gradually clear.