Fabrication and Characterization of MOF and Stearic Acid Based Biomimetic Sponges for Efficient Oil/Water Separation

Abstract

Fabrication of highly hydrophobic surfaces by bio mimicking the ‘Lotus Effect’ is turning out to be an area of active research in the field of oil/water separation. Current work is related to the fabrication of MOF functionalized, stearic acid functionalized and composite, incorporating MOF and stearic acid, functionalized biomimetic hydrophobic sponges by utilizing the inherited properties of MOFs i.e. large surface area, controllable pore size and chemical functionality at molecular level, non-wetting property of stearic acid and regular 3D skeleton of highly porous polyurethane sponge. The effect of loading of functionalizing agents on hydrophobicity of the sponge is studied by changing the concentration of reactants. The prepared sponges were analyzed by x-ray diffraction, scanning electron microscopy, fourier transmission infrared spectroscopy and sessile drop technique to conform the prerequisites of lotus effect. It is found that a continuous and uniform layer of ZIF-8 on sponge skeleton forms by using a molar ratio 1:8.08: 124.93 of Zn+2, Hmim and MeOH respectively, giving highest hydrophobicity (WCA=129.2°) among MOF functionalized sponges while in stearic acid functionalized sponges and in composite functionalized sponges hydrophobicity decreases by increasing the concentration of stearic acid. MOF functionalized sponge with continuous layer of ZIF-8 showed comparatively good absorption capacity ranging from 28 to 79 times its own weigh that is stable up to 10 absorption/desorption cycles. The composite i.e. stearic acid @ MOF, decorated on sponge template inherited all properties of its parent components showing high hydrophobicity (WCA=140.8°) and high absorption capacity that is constant for 10 absorption/desorption cycles for different oils/organic solvents ranging from 30.26 to 115.35 times its own weight. The method of fabrication is easy, economical and does not required any pre modification of sponge by surfactants. Moreover, the prepared sponges are easy to handle and absorbed oil can be recovered simply by manual squeezing.