The Removal Of Cr（Ⅵ） Via Adsorption/photocatalysis Synergy Using Electrospun Chitosan/g-C₃N₄/TiO₂ Nanofibers

The discharge of Cr（VI）-containing wastewater into the environment can not only heavily pollute the natural environment,but also do long-term and severe harm to the health of human beings and other species.For the protection of human beings and the environment,the removal of Cr（VI）in water is of great urgency.Chitosan（CS）is a biosorbent,numerous hydroxyl（-OH）and amine（-NH₂）groups in CS chain could adsorb Cr（VI）through electrostatic interactions and chelation.Besides,under visible light irradiation,g-C₃N₄/Ti O₂（CNT）photocatalyst could reduce highly toxic Cr（VI）to low toxic Cr（III）and reduce the toxicity of Cr（VI）in water.Therefore,the combined application of CS and CNT could evidently enhance the removal effect of Cr（VI）.In this paper,chitosan/g-C₃N₄/Ti O₂（CS/CNT）nanofibers were first fabricated by electrospinning technique.The samples were characterized by relevant tests,and the removal of Cr（VI）by adsorption and adsorption/photocatalysis synergy using nanofibers was studied.Finally,the corresponding mechanism explanation was given.The results are as follows:（1）The morphology,structure and optical property of nanofibers were studied.Scanning electron microscope（SEM）and transmission electron microscope（TEM）showed that rod-like Ti O₂ and lamellar g-C₃N₄ were well dispersed on CS nanofibers,proving the successful preparation of the material.The photocurrent density-time curve（I-t）showed that CS nanofibers had no photocurrent response,while the CS/CNT nanofibers had obvious photocurrent response.The UV-Vis diffuse reflectance spectroscopy（UV-Vis DRS）reflected the band gap energy values of CS/CNT nanofibers were 2.50 e V,smaller than that of CNT powder（2.60 e V）,g-C₃N₄（2.7 e V）,Ti O₂（3.2 e V）,which indicated that the CS/CNT nanofibers had better photo-absorption performance to deal with hazardous pollutants under visible light irradiation.（2）The removal of Cr（VI）via adsorption using nanofibers was studied.The rapid adsorption on nanofibers occurred in the first 15 min,and the addition of CNT into CS nanofibers could promote the rapid Cr（VI）adsorption.The adsorption of Cr（VI）by nanofibers was in accordance with pseudo-second-order model and Langmuir model,demonstrating that the reaction process was dominated by chemical adsorption and belonged to monolayer adsorption.At p H=2,the adsorption capacity of Cr（VI）using CS/CNT_10:1nanofibers reached 165.3 mg/g,which was much higher than that of CS nanofibers（20.8 mg/g）,suggesting the addition of CNT could notably enhance the acid resistance of CS nanofibers and widen its practical application.（3）The removal of Cr（VI）via adsorption/photocatalysis synergy using nanofibers was studied.Under visible light irradiation,the removal efficiency of Cr（VI）using CS/CNT nanofibers was appreciably improved,which was about 50%higher than that of pure adsorption.Besides,the reaction rate constant of Cr（VI）removal using CS/CNT_10:1nanofibers was 2.63 times that of CS nanofibers.At p H=2,the removal rate of Cr（VI）at concentrations below 100 mg/L using CS/CNT_10:1nanofibers was all over 90%.The removal rate of Cr（VI）by nanofibers did not change significantly after five cycles,proving the excellent stability of nanofibers.The high removal efficiency of Cr（VI）by CS/CNT nanofibers was due to the high specific surface area of electrospun nanofibers,the electrostatic attraction of-OH and-NH₂ groups in chitosan and the photocatalytic reduction of g-C₃N₄/Ti O₂.To sum up,the electrospun CS/CNT nanofibers has excellent Cr（VI）removal effect,which provides a useful reference for the preparation of adsorbent/photocatalyst for pollutant degradation through electrospinning technology in the future.