| Metaplexis japonica fibers(Mj-fibers),a kind of the seed hair fibers obtained from Chinese herbal medicine Metaplexis japonica plant,has high-hollow special-shaped structure and abundant resources.However,it is considered as a low-value companion organism and has not been used yet because of its lack of active pharmaceutical ingredient.The main purposes of this research are to innovatively prepare Mj-fibers and such fiber-derived activated carbon fibers(MACFs),and then focus on the strctures and adsorption behavior of each fiber.The implementation of this project can effectively improve the deep processing and high-value reuse of biomass fibers.Therefore,such fundamental work is of crucial academic significance and practical value.1?Systematic characterization of Mj-fibers:the chemical composition and content,the microstructure,surface chemical structure,aggregation structure and thermal stability of Mj-fibers were systematically investigated.The results show that Mj-fibers is a kind of natural fiber mainly composed of cellulose and hemicellulose components,and posses the structural characteristics of high hollowness(>90%)and profiled cross section("cross-flower").The mechanical properties of Mj-fibers are worse,but it has the characteristics of ultra light fluffy,and its density can reach 0.33 g/cm3.In addition,due to the wax exists in the surface,Mj-fibers posses excellent lipophilic and hydrophobic properties,and its static contact angle with pure water is 105.40.2?Oil absorption and oil-water separation performances of Mj-fibers:The Mj-fibers was used in oil adsorption and oil-water separation based on its hollow and hydrophobic properties.Specifically,the static oil absorbency,oil retention performance and reusability of Mj-fibers to different oil agents were systematically analyzed,and a fiber filtration system was constructed to explore its separation performance for oil-water mixture.The results show that the static contact angle of different oils on the surface of the fiber are the same,all of which are 0°.The saturated oil absorption ratio to vegeTable oil,oil and diesel oil is 81.52,77.62 and 57.22 g/g respectively,mainly owing to oil absorption and storage of the fiber gap and hollow structure.And the results predicted with the quasi-second order kinetic equation are in good agreement with the experimental results.Furthermore,the oil retention rate can still reach 79.1,75.4 and 72.0%after 12 h gravity leaching.After 8 cycles,the oil absorption rate decrease by 23.4%,22.2%and 20.7%respectively.In addition,the fiber has high oil-water separation performance,and the separation efficiency of vegeTable oil can still reach 98.0%after four filtrations.3?Preparation and characterization of MACFs:The MACFs was prepared following the procedures:First,the wax on the surface of Mj-fibers was removed using NaOH solution,then the high permeability compound phosphoric acid activation solution was used to treat Mj-fibers.Finally,the MACFs was prepared through preoxidation and carbonization processes.The results of SEM and EDS show that the prepared has a hollow tubular structure.And its surfaces of both inner and outer are obviously etched.MACFs,with the distribution of N,P and O elements on the surfaces,present the "carbon deposition" after grinding.The spectral analysis further shows that the MACFs is rich in acid functional groups increasing its hydrophilicity and has disordered graphite like microcrystalline structure.In addition,the results of BET-BJH analysis of carbon fibers suggest that MACF-600 exhibits the best performances,it possesses well-developed pore distribution,with a maximum specific surface area and total pore volume of 1799.582 m2/g and 1.613 cm3/g,respectively.4?Adsorption properties of MACFs for MB:the adsorption performances of different MACFs were investigated using MB solution,and the adsorption performances and mechanism of MACFs were analyzed.The results reveal that MACF-600 displays the superior adsorption peformance.The sorption process follows the pseudo-second-order kinetic equation and the adsorption isotherm conforms to the Langmuir model.The physical absorption dominates,and the theoretical maximum adsorption capacity can reach up to 947.372 mg/g.Furthermore,the adsorption Gibbs free energy ?G0<0 and the adsorption enthalpy change ?H0>0,obtained from the results of thermodynamic analysis,indicating the absorption behavior is a spontaneous process and positively correlated with temperature.Moreover,the decrease of pH and the increase of electrolyte mass concentration both reduce the electrostatic attraction of MACFs to MB,thus inhibiting the adsorption process.In summary,Mj-fibers,with the characteristics of high hollowness,profiled section,opened end,hydrophobic surfaces and et al,is provided with efficient oil absorption and oil-water separation performance.The prepared MACFs has the characteristics of high porosity and double-surfaces structure via the treatments of phosphoric acid activation and heating.The flourishing pore structure formed is responsible for the excellentperformance for MB adsorption.The research will provide a new solution for the treatment of oil pollution and dye wastewater,and broaden the precursor source of high-performance biomass activated carbon fibers(ACFs)simultaneously,which is also of great significance for the high-value utilization of Mj-fibers. |
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