Design And Synthesis Of Bisthiadiazolylpyridine-functionalized Polyacrylonitrile Fiber And The Selective Detection And Absorption For Silver Ion

With the rapid development of industrialization and urbanization,emission of large amount of industrial and domestic wastewater causes water pollution.Wherein the heavy metal ion contamination is particularly serious and posts a threat to human health and ecological balance.Therefore,the research of the detection and absorption of heavy metal ions from water has attracted wide attention.This paper reported a novel colorimetric sensor DPTD-PANPF,which immobilized bisthiadiazolylpyridine(DPTD)functional group onto 1,3-propanediamine aminated polyacrylonitrile fiber(PANPF).Then the discoloration and absorption capacities of the functional fiber were studied.In this thesis,the aminated fiber PANPF was first synthesized by 1,3-propanediamine and polyacrylonitrile fiber.On this basis,DPTD was immobilized onto PANPF through amidation to obtain DPTD-PANPF.Elemental analysis(EA),infrared spectroscopy(IR),scanning electron microscopy(SEM),X-ray powder diffraction(XRD)and solid ultraviolet spectroscopy(solid UV)were used to characterize the fibers,which showed that small molecule DPTD was successfully immobilized and the strength of the fiber was well maintained for the next test and aplication.Then the discoloration,absorption and complexation mechanism of DPTD-PANPF towards Ag+ was systematically discussed.A remarkable visual color change from yellow to red-brown was shown without interference by other co-existing ions over a quite wide pH range from 3 to 12.DPTD-PANPF gives its discoloration within 10 s in 1 × 10-3 mol/L Ag+ solution.Moreover,its naked-eye detection limit is only 11 ppb(1 × 10-7 mol/L),which is far below the maximum contamination level of 500 ppb in discharged wastewater and 50 ppb in drinking water for silver issued by the WHO.In particular,the obtained fiber sensor can be reused for more than 50 times after treating with dilute HNO3 and still chelates Ag+ very well with obvious color change.Furthermore,the fibers have strong complexation ability to Ag+ and it can capture Ag+ from complex or precipitation such as Ag(EDTA)3-,AgNO3/KCl and AgNO3/KBr with color change.Most importantly,this fiber can be used to identify Ag+ in actual water samples.The functional fiber can also effectively remove Ag+ from water with a maximum absorption capacity of 156 mg/g thanks to its excellent strong complexation ability for Ag+.The selective chelating process is fit to the pseudo-second-order model and well described by the Langmuir isotherm model.The removal efficiency of DPTD-PANPF towards Ag+ is up to 95%.Finally,the possible complexation mechanism of bisthiadiazolylpyridine functional fiber with Ag+ was proposed through the XPS analysis and literature review.It may be a collective effect of different sites of multiple functional group and excess amino groups.Complexation of DPTD with Ag+ makes two thiadiazole rings coplanar,which enhances its conjugation effect,displaying a red shift in UV spectrum.It is noteworthy that Ag+ plays a role in inducing DPTD molecules of the fibers to form a dimer or a trimer since different molecules complex with one Ag+.Thereby it results in the reinforcement of conjugation and UV movement to higher wave length.Effects above both cause red shift of UV absorption band,which show a darker dicoloration from light yellow to red-brown.