Preparation And Properties Of Chelate Films With Deboration Function

Boron as a kind of important chemical element,which is widely used in modern industry fields.Boron is essential for plants and animals.It plays a crucial role in the growth of plants in many ways.However,boron becomes harmful or even lethal to both plants and animals when its amount is greater than required.The world health organization(WHO)regulation indicates that a boron concentration in drinking water should be less than 2.4 mg/L,irrigation water boron concentration is limited to 1 mg/L.The average boron content in seawater is 5 mg/L and well above the WHO regulations.So,boron removal is very important in seawater desalination process.At present,the boron removal technology has developed rapidly,but many ways of boron removal effect are not ideal,our previously work shows that chelating membrane separation has proven to be a very effective method for boron removal.This method via the complexation of boric acid with the vicinal diol group on the surface of membrane,in order to reach the purpose of boron removal,the operation is simple and conducive to industrial application.In this paper,three kinds of chelating membranes were prepared.The structure and the properties of the membranes were characterized using fourier transform infrared spectroscopy(FT-IR),X-ray photoelectron spectroscopy(XPS),water contact angle(WCA),field emission scanning electron microscopy(FESEM),atomic force microscope(AFM)and BET(Brunauer Emmett Teller).The chelating boron adsorption capacity of the membrane was investigated in detail with different of the initial boron concentration,adsorption equilibrium time,pH and ionic strength.And Their adsorption isotherm,adsorption kinetics and cycled use property were discussed.Firstly,hyperbranched polyols are grafted onto polyacrylonitrile(PAN)membrane surface to prepare complexing membranes with high capacity and high adsorption rate,which utilized the structural characteristics of hyperbranched molecules to optimize three-dimensional distribution of the chelating ligands.The PAN membrane was grafted with three hyperbranched polyethyleneimine macromolecules(HPEI)through a water mediated hydrolysis and amidation reaction in an autoclave followed by ring opening reaction with glycidol.The results demonstrated that HPEI was successfully anchored onto the membrane surface and reacted with glycidol.Large quantities of hydroxyl groups were enriched on the surface of membranes leading to rougher and superhydrophilic surfaces.The study on boron adsorption showed that the complexing membrane can absorb 3.2 mmol/g within only 4 min,which was superior than other reported sorbents.The adsorption isotherm can be described by Langmuir model and the kinetic adsorption data fitted very well with the pseudo-first-order expression.In addition,the boron adsorption can be completely regenerated in a ten-cycle use by a 15 min acid leaching without obvious degradation.Secondly,in order to further increase the specific surface area of chelating membrane,increase the chelating membrane adsorption capacity of boric acid,electrospun nanofiber membranes grafted with hyperbranched polyols were synthesized and used for boron removal.The results showed that the PAA nanofiber spun from concentration of 15%had uniform morphology and narrow diameter distribution.The PAA-g-PG nanofiber membrane had a maximum boron uptake of 5.68 mmol/g and could adsorb 0.82 mmol/g boron from a 5 mg/L solution in 15 min.Both the high surface area of nanofibers and the hyperbranched structure should contribute to the high boron uptake and high adsorption rate.The nanofiber membrane obeyed the Langmuir adsorption model and the pseudo-first-order kinetic model.The regeneration efficiency of the nanofiber membrane remained 93.9%after 10 cycled uses,indicating good regenerability of the membrane.Finally,in order to simplify the membrane preparation process,a novel mixed matrix(MMM)membrane was fabricated by Non-slovent induced phase inversion of the blend of polysulfone(PSF)with a boron selective resin(BSR)and used for boron removal the introduction of the concept of mixed matrix membrane.Compared with the polymeric resin,the PSF/BSR membrane showed similar boron uptake but much higher adsorption rate.a boron removal rate as high as 97.6%can be obtained for 10 mL of 5 mg/L boron solution in the flow-through experiment at flux rate of 25 L/m2·h.It was concluded that the MMM can combine the advantage of the resin on high uptake and that of the membrane on convective transport.