The Preparation Of Superhydrophobic Graphene-based Composite Sponge And Its Oil Absorption Properties

For the past few years,the frequently occurring oil spill orchemical reagents leakage,which accompany with the oil exploration,petroleum refining and its transportation process,have severely damaged the ecosystems.As a simple and effective means of oil recovery,the oil sorbents have received worldwide attention.While the existing oil sorbents are difficult to meet the massive treatment needs of oil spill pollution,due to their low oil absorption capacity,poor oil/water selectivity and low recycle capacity,or their complicated producing process,expensive cuts and poor mechanical strength.Focusing on these problems,the low-cost melamine sponge was selected to be substrate material and then be modified via reduced graphene oxide(rGO)polydimethylsiloxane(PDMS),to prepare the cost-effective and environment-friendly graphene based composite sponge(rGO-PDMS-MF)which possessed superhydrophobicity,high oil absorption capacity,strong mechanical strength and good recyclability.The main contents and the results of the research are as follows:(1)The GO was synthesized through a modified Hummers method and reduced by the green ascorbic acid in a mild reaction condition at 25?.The results from characterizations of Fourier transform infrared spectrometer(FTIR),X-ray diffraction(XRD),Raman spectroscopy(Raman),Thermogravimetric analysis(TGA)indicated that the fabricated rGO was reduced deeply,and possessed good dispersity and thermal stability.The melamine sponge was modified by the rGOL-AA which reduced by ascorbic acid and the polydimethylsiloxane(PDMS)via a simple atwo step dip-coating approach,to prepare the superhydrophobic and oleophilic 3D porous rGO-PDMS-MF sponge.The optimum concentrations of rGOL-AA and PDMS solution were 2000 mg/Land 0.8 wt%,respectively.And in this case,the rGO-PDMS-MF exhibited superhydrophobicity because its state contact angle(CA)was tested to be 154.7°.(2)The structural and physicochemical property of therGO-PDMS-MF sponge were analyzed by scanning electron microscopy(SEM),fourier transform infrared spectrometer(FTIR),thermogravimetric analysis(TGA),compression property and coating stability testing.The results indicated that the rGO-PDMS coating was successfully grafted onto the framework of MF,which gave the fabricated sponge multilevel surface roughness and low surface energy.And the sponge had a good thermal stability and could endure a high temperature around 300?.After 10 times of cyclic compression,the sponge also possessed a good elasticity,which is helpful to fit the complex environment in oil spill recovery.The adhesion force between the coating and the rGO-PDMS-MF sponge was strong,which might be attributed to the PDMS binder.And after being treated via ultrasonic oscillation in ethanol system,the coating only fell off lightly.(3)The results of the saturated absorption capacity testing illustrated thatthe saturated mass absorption capacity and the saturated volume absorption capacity of the of rGO-PDMS-MF sponge for various oils and organic solvents were ranged from 55?126 g/g and 72.1?75.7 mL/g,respectively.Compared with traditional oil sorbents,the as-fabricated sponge possessed a greater oil absorbing performance.Moreover,therGO-PDMS-MF sponge had a goodcapacity ofoil retaining.And the oil retention rates for the diesel and crude oil were all above 98.1%,which ensured the reduction of secondary pollution during the salvage and transportation of sponge after oil absorption.(4)The results of the recyclability testing illustrated that some of the pore channels of the regenerative rGO-PDMS-MF sponge were blocked,which was responsible for the decrease in oil absorption capacity.Nevertheless,the oil absorption capacity tended to be stable with the increase of the number of regeneration.After 10 cycles,the absorption capacities for diesel,crude oil,toluene and chloroform maintained high values at 47.1?48.1?59.9 and 57.8 mL/g,respectively.The observation of SEMshowed that the hydrophobic coating of the used sponge had been contaminated by oil,and the CA decreased from 154.70 to 140.0°.Note that the CA of sponge was recovered to 147.20 after being washed with alcohol,which illustrated that the regenerative sponge remained a good hydrophobicity.The results suggested that therecyclability of therGO-PDMS-MF sponge was good.(5)The oil/water separation testing illustrated that therGO-PDMS-MF spongeexhibited a good selectivity for the diesel and crude oil on the water,and the chloroform underwater.With the help of pumping device,the sponge could collect oil spill in a rapid and continuous way,so the recovery capacity was no longer limited by the size of the sponge.The rGO-PDMS-MF sponge(2.5×2.5×6.0 cm3)was connected to a miniature straightway diaphragm pump to perform an oil/water separation dynamic experiment,and all of the 400 mL floating diesel was removed and collected within 4 minutes,which exhibited a higher recovery rate compared to thestatic oil/water separation.Not only that,the regenerative rGO-PDMS-MF sponge still possessed a high dynamic recovery efficiency of diesel,which is expected to be used in oil spill or organic pollutant leakage recovery processing.