Functionalized Calotropis Gigantea Fiber For Adsorption-degradation Of Perfluorinated Organic Compounds In Water

Perfluorinated compounds（PFCs）represented by perfluorooctanoic acid（PFOA）and perfluorooctane sulfonate（PFOS）are ubiquitous in the aquatic environment,posing a huge threat to animals,plants and human.The high bond energy C-F bond makes PFCs have environmental persistence and chemical stability,and traditional biological treatment techniques are difficult to effectively remove them.Nowadays,the adsorption technology featured with low-consumption,high-efficiency,economical and environment-friendly has become a popular method for removing PFCs,and its key is the design of functional adsorbents.Calotropis gigantea fiber（CGF）is derived from the seed of C.gigantea,which has an intrinsic hydrophobic-lipophilic surface and a unique structure with thin-wall and large-hollow.Based on the demand of water pollution control technology for sustainable materials,CGF was used as a bio-template to fabricate three kinds of N-polymer functionalized fibers and magnetic carbonized fibers.By adsorption technology,the adsorption performances of PFOA and PFOS at the interface of functionalized fibers were investigated.Considering that the adsorption technology cannot destroy structure of pollutants,and the growing advantages of carbon-based materials in degradation technology,the magnetic carbonized fiber was futher used as catalyst to construct an advanced oxidation system by combination with persulfate（PS）,with the aim to achieve effective degradation of PFCs with different carbon chain lengths in water.The detailed contents are as follows:（1）With CGF as the bio-template,the polydopamine（PDA）,polyaniline（PAN）and poly（m-phenylenediamine）（Pm PD）were grown in situ along the fiber surface,and three kinds of N-polymer functionalized fibers（PDA-CGF,PAN-CGF and Pm PD-CGF）were fabricated.Subsequently,the adsorption performance of three kinds of N-polymer functionalized fibers for PFOA in water was compared.The results exhibited that the adsorption process reached equilibrium within 3 h.When initial PFOA concentration was 50 mg/L and p H 3.0,the adsorption capacity of PDA-CGF,PAN-CGF and Pm PD-CGF were 31.35 mg/g,58.94 mg/g and 45.49 mg/g,respectively.With increasing the solution p H,the adsorption capacity of the three adsorbents showed a monotonic decreasing trend.Electrostatic attraction,hydrogen bond and hydrophobic interaction took part in the adsorption process.Appropriate concentration of Na⁺,Mg²⁺and Fe³⁺could facilitate the adsorption efficiency,especially in the presence of trivalent cation ions.With methanol as the desorption agent,PDA-CGF,PAN-CGF and Pm PD-CGF could be well regenerated.After 5 consecutive adsorption-desorption cycles,the three adsorbents maintained higher adsorption percentage（≥80%）.In summary,PDA-CGF,PAN-CGF and Pm PD-CGF could be used as the low-cost and high-efficiency adsorption materials.Among them,PAN-CGF showed brilliant adsorption performance and had the potential to be used for effective adsorption of PFCs in aquatic environment.（2）Using CGF as the bio-template,Fe₃O₄ was loaded on the surface of CGF via pyrolysis in an inert atmosphere,and magnetic carbonized fiber（MC-CGF）was successfully prepared.Various characterization techniques such as scanning electron microscope（SEM）,Fourier transform infrared spectroscopy（FTIR）,X-ray diffraction（XRD）and vibrating sample magnetometer（VSM）were applied to analyze the morphology and structure of MC-CGF.Subsequently,MC-CGF played a role of adsorbent to remove PFOA and PFOS from water.The experimental data illustrated that the adsorption equilibrium of PFOA and PFOS on MC-CGF was reached within 1h and 2 h,respectively,and the adsorption capacity at p H=3.0 was 42.76 mg/g and 50.00mg/g,respectively.In the presence of inorganic cations(Na⁺,Mg²⁺,Fe³⁺),the adsorption capacity of MC-CGF for PFOA/PFOS increased significantly with the increase of the cation concentration,especially in the presence of multivalent metal cations.The hydrophobic interaction between MC-CGF and C-F chain was responsible for driving the rapid adsorption.In addition,MC-CGF could be regenerated and recycled multiple times,and also the developed MC-CGF showed great adsorption potential for other perfluorinated organic pollutants with different carbon chain lengths（C4-C10）.（3）Using MC-CGF as the catalyst to activate PS,the MC-CGF/PS catalytic system was constructed at room temperature,and the degradation potential of MC-CGF/PS system for PFOA was systematically investigated.The experimental results exhibited that the degradation rate of PFOA by MC-CGF/PS system could reach to 75.76%at30℃and p H 2.0.By calculation,the apparent activation energy of MC-CGF/PS system decreased from 62.76 k J/mol to 22.49 k J/mol,demonstrating that the introduction of MC-CGF allowed the catalytic system to achieve a higher efficiency of degrading PFOA at a lower reaction temperature and a shorter reaction time.Using MC-CGF as a catalyst could not only promote the production of SO₄^?-and accelerate the degradation rate of PFOA,but also facilitate the rapid separation of spent catalyst from water,thus effectively avoiding serious waste of resources and possible secondary pollution.Mechanism analysis revealed that an initial decarboxylation reaction occurred for PFOA in the degradation process,and then two possible degradation pathways were proposed.Using pakchoi as the plant model and chlorophyll content as a physiological indicator,the toxicity effects before and after degradation of PFOA was evaluated.The changes in chlorophyll content stated that the process of MC-CGF/PS system to degrade PFOA was relatively harmless.In summary,the functionalized CGF can be used as an adsorbent or as a catalyst,and in all cases,the functionalized CGF exhibits outstanding removal performance for PFCs.Accordingly,as a green and sustainable natural material,Calotropis gigantea fiber shows immense development potential in the removal of PFCs in water.