Construction Of Hierarchical Electrospun Nanofibers And Their Adsorption Of Typical Pollutants In Water

With the development of industry and agriculture and the accelerating process of urbanization,people's quality of life has improved.However,the problem of water pollution caused by a large number of industrial,agricultural and domestic wastewater poses a serious threat to human health and the ecological environment.Among the many treatment methods,adsorption is promising for the removal of pollutants because of its simplicity,relatively low-cost,ease of operation,reversible processes,high efficiency and no secondary pollution to the environment.The performance of the adsorbent plays a decisive role in the adsorption of pollutants.In recent years,researchers have increased the specific surface area of the fiber by reducing the dimensional dimension size of the adsorbent,leading to increase the adsorption site and the adsorption capacity of the adsorbent.Electrospinning technique is considered as a high-efficiency and low-cost method for preparing one-dimensional nanofibers.Compared with other nanomaterials,the fibers prepared by electrospinning technology are simple to prepare and easy to modify,have high porosity and various types,can be formed and recycled,which have been studied as a sewage treatment adsorbent.The prepared electrospun fiber adsorbent can be classified into inorganic,organic and organic/inorganic composite electrospun fiber adsorbent according to materials.Among the many types of electrospun fiber adsorbents,the nanofiber adsorbents with porous and multi-stage structure have show great potential of current research due to the diversity of morphology and composition.Based on the above contents,this thesis focuses on the electrospun fiber adsorbents with hierarchical structure and investigate their adsorption performance and adsorption mechanism toward organic pesticides,organic dyes and heavy metal ions in water.This paper is divided into the following two parts:1.The superfine MnO₂ particles have large surface and high binding capacity,with advantages of high adsorption capacity and provide an efficient scavenging pathway for many heavy metals.Nano-sized MnO₂ based adsorbents have been widely studied for the removal of Pb²⁺ions.However,nano-sized MnO₂ particles are inclined to agglomerate during the adsorption process owing to the high surface energy,which limits their practical application.In addition,the nano-sized MnO₂ particles are easily suspended in water and hard to separate from large volumes of water.Encouraged by the above research,we prepared MnO₂ loaded electrospun fiber adsorbent to remove heavy metal ions from water.?1?We prepared MnO₂ loaded PAN fiber adsorbent by the assistance of polydopamine?PDA?adhesion for Pb²⁺adsorption in this study.This preparation process could avoid the agglomeration of MnO₂ particles and make the adsorbent separate easily from the adsorption solution.The results indicate that the PDA coating on PAN fibers is necessary for loading uniform MnO₂.The adsorption processes could be fitted well with pseudo-second-order model and Langmuir isotherm model.The maximum adsorption capacity calculated from Langmuir model was 185.19 mg/g.The MnO₂/PDA/PAN nanofibers could be recycled through a simple treatment and the removal efficiency for Pb²⁺remained above 85%after five cycles.In addition,the removal rate of Pb²⁺in the real wastewater sample by MnO₂/PDA/PAN fibers was above 95%.?2?In order to further improve the adsorption content of Pb²⁺ions in electrospun fibers.The hollow MnO₂ nanofibers are successfully fabricated using electrospun carbon nanofibers acted as sacrificial template.These hollow nanofibers are assembled by ultrathin MnO₂ nanosheets and a small amount of carbon,and the manganese dioxide content in the fibers is significantly improved.The BET surface area and pore volume were 247.69 m²/g and0.57 cm³/g.The adsorption process can be better described using the pseudo-second-order model.Isotherm data fitted well to the Langmuir isotherm model.The maximum adsorption capacity calculated from the Langmuir isotherm was 460.83 mg/g.Regeneration results showed that the adsorption performance can remain up to 80%after 5 times usage.In addition,the removal rate of Pb²⁺in the real wastewater sample by MnO₂/PDA/PAN fibers is above 99.32%.2.Magnesium silicates are widely investigated adsorbents for organics and heavy metal ions due to their attractive advantages such as low cost,environmental friendliness,interesting structures and high stability.In addition,most previous reports on magnesium silicates focused on multiple structures and all of the adsorbents were in powder form.These adsorbents are not easy to recycle and are likely to cause secondary pollution.Therefore,development of flexible magnesium silicate based adsorbents with good mechanical strength and easy separation in water treatment is highly desirable.Based on this,the magnesium silicate-based nanofiber membrane was prepared by electrospinning technology,and its adsorption performance on cationic pollutants in water was studied.?1?We prepared the magnesium silicate/polyacrylonitrile?PAN?inorganic/organic composite fibers via the combination of electrospinning and hydrothermal treatment.They were used as adsorbents to remove diquat from aqueous solution.The fundamental adsorption properties showed that the adsorption kinetics and isotherm followed the pseudo-second-order and Langmuir isotherm models.The MgSi/PAN fibers possessed a maximum adsorption capacity of 197.53 mg/g for diquat.The adsorbent could be recycled through a simple treatment and the removal efficiency for DQ remained above 83%after five cycles.In a dynamic filtration experiment,the filtration efficiency was above 99.1%even at a high flux of 1260 L·m^-2·h^-1.?2?We have demonstrated the preparation of flexible magnesium silicate fiber membrane?MgSiFM?by hydrothermal reaction using electrospun flexible SiO₂ fiber membrane as silicon template for the first time.MgSiFM exhibited good mechanical stability,that could improve its operability and practicability.The BET surface area and pore volume were 463.4 m²/g and 0.34 cm³/g,respectively.The adsorption performance of MgSiFM toward cationic dyes methylene blue?MB?,rhodamine B?RhB?and the cationic pesticide diquat?DQ?were studied.The adsorption process conforms to the pseudo-second-order model and Langmuir isotherm model.According to Langmuir fitting,the maximum adsorption capacity were 609.75 mg/g,549.14 mg/g and 405.54mg/g,respectively.The adsorbent could be recycled through a simple treatment and the removal efficiency for MB remained above 83%after five cycles.In dynamic filtering experiments,at the flow rate of 2 mL/min,MgSiFM could remove 99%of MB.After five cycles,the filtration performance could also be successfully maintained.