Preparation Of Solar Self-heating Sponge And Its Application For Cleaning Viscous Crude Oil

Frequent crude oil spills not only cause a huge loss of valuable energy,but can also cause serious damage to marine ecosystems and long-term pollution of the environment.Therefore,in order to eliminate the environmental and ecological impact of crude oil spills,there is an urgent need for a fast and efficient technology to recover crude oil.Traditional crude oil clean-up technologies using membrane separation,in-situ combustion at the spill site,chemical dispersants,skimmers and vacuum technology are not only inefficient and produce toxic by-products,but also take a long time to process.In contrast,adsorption-based oil-water separation materials are ideal for recovering crude oil due to their excellent oil storage capacity,simplicity of preparation and energy efficiency.However,for high viscosity crude oils(viscosity >1000 mPas),the adsorption performance of adsorbent materials decreases significantly due to their poor flow properties at room temperature.It has been found that the viscosity of crude oil decreases rapidly with increasing temperature,which provides a new idea for the recovery of high viscosity crude oil by porous adsorbent materials.While it is possible to use heat generated by electricity to heat crude oil to reduce its viscosity,this approach is not applicable to the realities of large offshore oil spills.Solar energy is an economical,green and renewable source of energy that can be converted directly into heat to reduce the viscosity of crude oil through photothermal conversion materials.In this paper,a commercial porous sponge with carbon dots and reduced graphene oxide as the photothermal conversion material and polydimethylsiloxane as the modifier is used to prepare a self-heating sponge with excellent photothermal performance through in situ chemical reaction,which can be applied to adsorb high-viscosity crude oil from large spills.The main research content and results are in two aspects.First,a new method for the preparation of solar-driven self-heating sponges by in-situ chemical reaction is proposed.It is specifically outlined as a three-dimensional porous self-heating sponge obtained by treating and curing cross-linked PDMS through a hydrothermal reaction method using coal pitch carbon dots(CDs)as the photothermal agent and polydimethylsiloxane(PDMS)as the modifier.Compared with the dip-coating method reported in the literature,the sponge skeleton prepared by the hydrothermal method was loaded with more carbon dots,which resulted in better photothermal conversion performance and heat transfer properties of the sponge.More importantly,the stronger bonding between the CDs and the sponge resulted in a more uniform coverage of hydrophobic layer CDs on the surface layer of the sponge than the dip-coating method,due to the fact that the method avoids the aggregation of nanoparticles caused by PDMS curing during the preparation of the sponge.In addition,the hydrophobic properties of the composite commercial sponge are further increased by the action of carbon dots(water contact angle = 153 °)compared to the dip-coating method.In experiments simulating oil-water separation,the sponge adsorbed nearly 60 g g^-1 of crude oil at 10 min under 1 kWm^-2 irradiation,which is higher than most of the adsorbents prepared by the dip-coating method reported so far.This is mainly attributed to the ability of the carbon dots to rapidly convert sunlight into heat and transfer it to the crude oil by heat transfer through thermal radiation under illumination,while the homogeneous dispersion of CDs on the sponge skeleton gives the adsorbent good heat transfer,further increasing the temperature of the hot spot and facilitating thermal radiation,resulting in improved adsorption performance of the composite sponge.Finally,the crude oil inside the sponge is recovered by extrusion and the sponge is reused.After 7 cycles of adsorption-desorption,the composite sponge still has good hydrophobicity and the adsorption decay is less than 8%,with good cycle stability.Secondly,although the self-heating sponge prepared by hydrothermal method in the above work has the advantages of low density and high porosity,high adsorption capacity and rate,good recycling performance,etc.,the thermal conductivity of the self-heating sponge is deficient,so in this work,rGO is first loaded on the sponge skeleton by dip-coating,and then CDs are loaded on it according to the method in the above work,This rGO-coupled CDs-modified self-heating sponge ensures that the thermal radiation from the CDs is maintained,while at the same time the thermal conductivity is improved by the introduction of rGO.Compared to the above work,the thermal conductivity of the self-heating sponge found in this work was improved by a factor of nearly two,and the adsorption of crude oil by the self-heating sponge reached 65 g g^-1 at 7 min under 1 kWm^-2 irradiation.In addition,the adsorption amount remained almost unchanged after seven adsorption-desorption processes,indicating that the self-heating sponge still has good cycling stability.The construction method of the self-heating sponge used in this work therefore takes the self-heating sponge further into practical application.