| In recent years,with the rapid development of heavy industry,Cr(Ⅵ)-containing wastewater discharged from mining,leather tanning,electroplating,wood anticorrosion,paint manufacturing and metal processing has entered the environment.In this study,an environmentally friendly chromium ion imprinted adsorption material was synthesized via surface ion-imprinted technique.The diatom chromium surface ion-imprinted polymer(DE/Cr(Ⅵ)-ⅡP)was formed by grafting the complex of diatom as matrix material,chromium ion as template,3-aminopropyltriethoxysilane(APTES)as functional monomer,and epichlorohydrin(ECH)as crosslinker.It is used for rapid and efficient identification and removal of Cr(Ⅵ)ions in water.The formation process of DE/Cr(Ⅵ)-ⅡP was characterized and analyzed by a series of test methods,and the adsorption performance,selectivity and reusability of DE/Cr(Ⅵ)-ⅡP and the grafting of functional monomer APTES were studied.By observing the SEM images during the preparation of DE/Cr(Ⅵ)-ⅡP,it can be found that compared with the original diatom(DE),a new layer of material appears on the surface of DE/Cr(Ⅵ)-ⅡP diatom,and many new micropores are formed around the surface pores.The scanning electron by scanning electron microscopy(EDS)that the N element in the functional monomer APTES was uniformly distributed on the surface of diatoms after ion imprinting,indicating that the functional monomer APTES was successfully introduced on the surface of diatom to form a good binding effect.The comparison of XRD patterns showed that the ion imprinting process did not destroy the amorphous silica structure of diatom.According to the FT-IR test results of DE/Cr(Ⅵ)-ⅡP,the isolated silicon hydroxyl stretching vibration peaks on the surface of diatom disappeared after imprinting,and new N-H,C-N,C-H vibration peaks were added.At the same time,X-ray photoelectron spectroscopy(XPS)of DE/Cr(Ⅵ)-ⅡP Si2 p fitting spectrum of Si-C,N 1s fitting spectrum of N-H peak,C 1s fitting spectrum of C-N,C-H vibration peak,proved that APTES alcoholysis and isolated diatomic hydroxyl condensation reaction,the two through covalent bond together.By analyzing the specific surface area and pore volume of DE and DE/Cr(Ⅵ)-ⅡP,the specific surface area of DE/Cr(Ⅵ)-ⅡP increased significantly,indicating that there were a large number of porous materials on the surface of diatoms after imprinting process,which increased the adsorption surface area of the material.At the same time,the pore volume and average pore diameter showed a decreasing trend,indicating that DE/Cr(Ⅵ)-ⅡP formed many new microporous structures.TGA analysis of DE/Cr(Ⅵ)-ⅡP showed that APTES directly bonded to the active isolated hydroxyl group on the surface of diatom was about 6.91 wt %,indicating that APTES had good binding effect on the surface of diatom.According to the test results of Zeta potential,in a certain p H range of solution,the surface electrical property of DE/Cr(Ⅵ)-ⅡP was opposite to that of Cr(Ⅵ)ion,so there was a synergistic effect of electrostatic adsorption in the process of adsorption of Cr(Ⅵ)ion by DE/Cr(Ⅵ)-ⅡP,which can improve the adsorption effect.The optimal adsorption conditions of DE/Cr(Ⅵ)-ⅡP for Cr(Ⅵ)-ⅡP for Cr(Ⅵ)ions : at25 °C,p H 2.5,dosage of DE/Cr(Ⅵ)-ⅡP was 100 mg,the initial concentration of Cr(Ⅵ)ion solution was 10 mg/L,and the adsorption time was 120 min,the removal rate of Cr(Ⅵ)ions by DE/Cr(Ⅵ)-ⅡP could reach 99.88 %.After adsorption,the concentration of Cr(Ⅵ)ions met the emission standard of 《Integrated Wastewater Discharge Standard of the People ’s Republic of China》(GB8978-1996)with the maximum allowable emission concentration of 0.5 mg/L for Cr(Ⅵ)ions.Adsorption isotherm and adsorption kinetics showed that the adsorption process conformed to Langmuir isothermal adsorption model and pseudo-second-order kinetic model.There was a single molecular layer cavity on the surface of DE/Cr(Ⅵ)-ⅡP adsorbent.Cr(Ⅵ)ion was combined with DE/Cr(Ⅵ)-ⅡP in the form of single molecular layer adsorption.The adsorption process was mainly controlled by chemical adsorption and was spontaneous exothermic process.The adsorption properties of DE/Cr(Ⅵ)-ⅡP showed that DE/Cr(Ⅵ)-ⅡP had good adsorption effect,selectivity and reusability.The DE/Cr(Ⅵ)-ⅡP was an alternative method to remove Cr(Ⅵ)ions from wastewater. |
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