Construction And Solar-Driven Oil/Water Separation Characteristics Of Photothermal Porous TPU-Based Monoliths

In recent years,with the increasing demand for petrochemical products in the global industry,offshore oil spill,organic chemical leakage and direct discharge of industrial oily wastewater have become increasingly frequent,which have caused great harm to water resources,ecological environment and human health.How to remove and collect oil and organic pollutants from polluted water efficiently and environmentally has become an urgent problem to be solved and widely concerned by the scientific community.Three-dimensional（3D）porous oil absorbents with special wettability stand out from many oily wastewater treatment methods by virtue of their advantages of environmental friendliness,high separation efficiency,simple operation,recyclability and oil recovery,and become one of the research hotspots in the field of oil/water separation.Among them,polymer-based porous monoliths have the advantages of high porosity,large specific surface area,3D connected porous structure,hydrophobic and oleophilic,etc.,showing good separation performance and application prospect as oil absorbent.However,the diffusion process of high-viscosity crude oil in porous structure is slow due to its low fluidity,resulting in a limited crude oil/water separation ability of porous monoliths.In view of this,based on the temperature dependence of crude oil viscosity,this paper endows polymer-based porous monoliths with excellent solar-to-heat conversion ability,make them to be able to absorb sunlight and convert it to heat energy,and then through the in situ heat transfer reduce the viscosity of crude oil,realize high selective separation of high viscosity crude oil.Firstly,the thermoplastic polyurethane（TPU）porous monolith was prepared by thermally induced phase separation method as the flexible matrix of the absorbent.Then,reduced graphene oxide（rGO）with excellent photothermal performance and fluorosilane（FAS）hydrophobic coatings were coated on the surface of TPU matrix by simple dip-coating method,and the photothermal F-rGO@TPU monolith was prepared.Subsequently,with the assist of scanning electron microscope,automatic mercury injection instrument,universal testing machine,UV-vis-NIR spectrophotometer,infrared thermal imager and other experimental instruments,the microstructure,mechanical properties,photothermal conversion performance and solar-driven crude oil/water separation properties of F-rGO@TPU monolith were studied in detail.The results are as follows:（1）F-rGO@TPU monolith presents a 3D connected hierarchical porous structure with a porosity of 87.4%,and rGO is uniformly coated on the surface of the skeleton.（2）F-rGO@TPU monolith presents superhydrophobic/superoleophilic properties（water contact angle is 153°,oil contact angle is 0°）,and shows excellent separation selectivity（separation efficiency is higher than 99.3%）and high saturated absorption capacity for various low viscosity oil/organic solvents;（3）After 1000 cycles of large strain（80%）compression tests,F-rGO@TPU monolith can return to its original shape,showing excellent reversible compressibility and fatigue resistance,so it can be used to cycle absorption of oils by extrusion;（4）UV-vis-NIR results show that F-rGO@TPU monolith has excellent solar absorption capacity,with an average light absorption rate of 96.0%.Under 1.0 k W/m² simulated sunlight,the surface temperature of the monolith can quickly rise from room temperature to 80℃,and maintain good stability in multiple light on/off cycles,indicating outstanding photothermal conversion ability.（5）By connecting with the pump-assisted device,F-rGO@TPU monolith performs continuous and rapid selective separation of crude oil/water mixture,presenting distinguished continuous solar-driven crude oil/water separation property.Under 1.0 k W/m² simulated solar irradiation,the flux of crude oil can reach 510 kg/（m²·h）,which is 29 times higher than that without sunlight.Subsequently,in order to further improve the photothermal performance of the monoliths and make them easy to recycle,magnetic Fe₃O₄ nanoparticles were introduced into the surface photothermal layer.After the surface hydrophobic modification and encapsulation by polydimethylsiloxane（PDMS）,P-Fe₃O₄/rGO@TPU monolith was constructed.The microstructure,magnetic properties,photothermal conversion properties and solar driven crude oil/water separation properties of the materials were studied in detail.The results are as follows:（1）Compared with F-rGO@TPU monolith,P-Fe₃O₄/rGO@TPU monolith also has a 3D connected hierarchical porous structure.RGO and Fe₃O₄ nanoparticles are uniformly attached to the surface of the skeleton.Although the porosity decreases slightly（85.3%）,P-Fe₃O₄/rGO@TPU monolith still has good oil absorption performance.（2）Driven by the magnetic force of the external magnetic field,P-Fe₃O₄/rGO@TPU monolith can not only be quickly recovered,but also achieve accurate adsorption of oil on the water surface;（3）Based on the synergistic effect of rGO and Fe₃O₄,the photothermal conversion ability of P-Fe₃O₄/rGO@TPU monolith is further improved,and the solar absorption rate is increased to 98.0%;（4）Under the simulated solar irradiation（1.0k W/m²）,and with the help of pump-assisted device,the crude oil flux is up to 878kg/（m²·h）,showing a superior solar-driven crude oil/water separation ability.