Hydrophobic Modification Of Melamine Sponges And Their Oil/Water Separation Performances

Due to frequent oil spill accidents,three-dimensional porous hydrophobic materials are widely used in oil-water separation applications because of their large specific surface area,fast oil absorption,high porosity,large oil storage,low density,and easy transportation.However,three-dimensional oil-water separation materials also face the challenge of low energy consumption for oil absorption,simplification of material preparation,cost reduction,and improvement in recycling capacity.The purpose of the research is to use low cost melamine sponge as a template to prepare a high-performance oil-water separation material via simple steps.1?A melamine-based sponge with a highly hydrophobic surface,high porosity and low density,is facilely fabricated through a simple surface adsorption technique that consisted of dipping in a tetrahydrofuran solution containing renewable alkali lignin and carbodiimide-modified diphenylmethane diisocyanate.The entire process can be performed at ambient temperature without consuming a large amount of energy.The resultant sponge,coated with a highly hydrophobic lignin-based shell,retained most of the inner space for the storage of oil and organic liquids and was similar to a sealed container with highly hydrophobic walls.The prepared sponge,with a highly hydrophobic surface?water contact angle of 145.9^o?,exhibited excellent absorption capacities for organic liquids,with a volume-based absorption capacity of up to 98%of its original volume.Moreover,the absorbed oil can be recovered by squeezing the oil-absorbed sponge with a good compressibility,which maintained above 86.96%of the massbased absorption capacity even after 100 absorption/squeezing cycles.Due to their low cost,simple fabrication process and high oil/water separation performance,melamine-based sponges coated with lignin have a great potential in applications for oil spill cleanup and organic contamination removal.2?A highly hydrophobic melamine sponge with outstanding magnetic response and fire resistance has been fabricated by a simple two-step method containing spontaneous deposit of Fe₃O₄ nanoparticles on the sponges and then squeezing the crosslinked lignin absorbed sponges.The obtained sponge with rough lignin/Fe₃O₄ composites firmly coating on the whole surface of every skeleton,shows high hydrophobicity,excellent self-cleaning,fire resistance and compressibility.Due to those exceptional properties,the hydrophobic sponge with high porosity can be magnetic driven to absorb the oil from polluted water and exhibits excellent oil absorbency.Moreover,squeezing the oil absorbed sponges for oil recovery is feasible and the squeezed sponges could be utilized for another absorption cycle.Meanwhile,the oil can be collected uninterruptedly by the hydrophobic sponges with the assistance of longer pump.3?Here we have obtained a temperature responsive melamine sponge with a controllable wettability between superhydrophilicity and superhydrophobicity by grafting the octadecyltrichlorosilane and thermoresponsive poly?N-isopropylacrylamide??PNIPAAm?onto the surface of melamine sponge skeletons.The whole process included the silanization in which step the rough surface with low surface energy and the NH₂ were provided,and the atom transfer radical polymerization which ensured the successful grafting of PNIPAAm onto the skeleton's surface.The product exhibits a good reversible switch between superhydrophilicity and superhydrophobicity by changing the temperature below or above the lower critical solution temperature?LCST,about 32°C?of PNIPAAm,and the modified sponge still retains a good responsiveness after undergoing temperature switches for 20 cycles.Simultaneously,the functionalized sponges could be used to absorb the oil under water at37°C,and they released the absorbed oil in various ways under water at 20°C,showing wide potential applications including oil/water separation.4?Inspired by the development of smart oil/water separation materials,a pH responsive melamine sponge has been obtained by grafting poly?4-vinylpyridine?on the skeleton surface through atom transfer radical polymerization.Through scanning electron microscopy and x-ray photoelectron spectroscopy,the successful grafting of poly?4-vinylprridine?onto the melamine sponge has been confirmed.When contacting with different p H water droplets in air,the as-prepared product shows excellent switchable wettability between super-hydrophilicity?0^o?and highly hydrophobicity?135^o?.Meanwhile,this responsive sponge also exhibits super-hydrophilic/oleophobic property underwater at pH=1.0,and highly hydrophobic/super-oleophilic property in neutral solution at pH=7.0.Furthermore,the excellent responsiveness is remained after five cycle water contact angle tests between two different pH stages at 1.0 and 7.0.The modified melamine sponges could not only absorb the oil from the oily water at pH=7.0,but also quickly release the absorbed oil underwater at pH=1.0 without leaving any residues and hurting the environment nearly,showing a good potential in controlled oil/water separation and oil recovery.5?Here is reported the fabrication of a highly porous and hydrophobic melamine sponge based composite?MF-ZIF-8 sponge?with effective catalysis via the simple surface growth of zeolitic imidazolate frameworks-8?ZIF-8?onto the strut surface of melamine sponge under the condition of the presence of polydopamine possessing a strong adhesive ability through noncovalent adsorption and covalent reaction.The successful integration of melamine sponge and ZIF-8 into one composite was confirmed using scanning electron microscopy,X-ray photoelectron spectroscopy,X-ray diffraction and thermogravimetry.Combining the advantages of both materials,MF-ZIF-8 sponge with a high porosity,high hydrophobicity and low density showed excellent oil/water separation performance as its mass-based oil absorption capacity could reach up to 3800 wt%,which is much higher than that of pure ZIF-8.Besides its more effective catalysis compared to the corresponding pure ZIF-8 in a Knoevenagel reaction,since MF-ZIF-8 sponge can be easily separated from the organic liquid reaction mixture it is a potential candidate for the catalysis of various organic reactions.6?It is well known that the weak attachment of metal organic framework?MOF?particles onto templates and the easy poisoning of MOFs on surface of templates limits MOF based composites a widely applications.Here we fabricated a PDMS coating Cu doped zeolitic imidazolate frameworks-67?Cu/ZIF-67?loaded melamine sponge by one facile and gentle immersion method to immobilize the MOFs on porous melamine template powerfully.To be surprising,this product with high porosity,super-hydrophobicity?158^o?and good flexibility not only exhibited an excellent oil/water separation as it could absorb various oils from oil contaminated water with the volume based absorption capacity over 70%and release the absorbed oil by squeezing method over 100 cycles,but also showed an highly photocatalytic efficiency over 97%for hydrophobic Sudan I degradation over 5 cycles and a long term catalytic life compared with corresponding Cu/ZIF-67,providing a potential way to improving the applications of MOFs.