Preparation Of Ag 2 O@SOMS Composites And Their Adsorption Properties For Sr And J

Radioactive 90Sr and 1311 are products of nuclear fission;they easily dissolve in water.Thus,accidental release to the environment of these radionuclides during an accident at a nuclear reactor poses a serious threat to the health of a large part of population.Recently,high levels of radiostrontium(90Sr)and radioactive iodine(131I)have been found in the groundwater at the devastated Fukushima nuclear facility.It is clear that development of effective techniques for separation of such radionuclides from radioactive liquid waste is of great practical significance.The key requirements in the development of such a technology are to devise materials which are able to adsorb radioactive ions irreversibly,selectively,and efficiently.Inorganic layered ion exchangers,such as metal phosphates,synthetic micas,clay minerals,magadites,titanates and niobates,have the advantages of higher selectivity for target cations,and higher resistance to radiation and temperature compared to organic resins.Furthermore,in some metastable layered materials,a structural collapse occurs during ion exchange,resulting in tight immobilization of target cations in the interlayers,causing ion exchange to be irreversible.This is significant given the desire for complete removal of target cations from wastewater,and allows safe disposal of entrapped hazardous cations without worries that they will leach from ion exchangers.However,layered ion exchangers are ineffective for adsorbing anionic radionuclides such as iodine species,because they have both a permanently negatively charged surface like other aluminosilicate minerals,and a pH-dependent negative surface charge caused by deprotonation of the surface hydroxyl group under high pH conditions.It is thus challenging to develop bi-functional adsorbents which can remove both 90Sr cations and 1311 anions at the same time.I-anions can readily react with silver oxide(Ag2O)to form insoluble silver iodide(Agl).However,the direct use of Ag2O or another silver compound to precipitate iodine species is impractical because the capacity and adsorption dynamics of the removal mainly depend on the specific surface area of Ag20 particles.Recently,Ag2O grafted layered nanomaterials,such as Ag2O grafted layered titanate,and Ag2O grafted layered sodium vanadate,have shown better removal ability for radioactive Cs+ and I-.These findings initiated a new direction of grafted synthesis of adsorbents for simultaneously capturing radioactive cations and anions from wastewater.Inorganic materials used as supports must possess some useful features.They should be formed of negatively charged thin layers,have readily exchangeable Na+ ions located between the layers,have the ability to firmly bind Ag2O nanocrystals on their surfaces,and demonstrate good resistance to radiation,heat,and chemicals.Although some Ag2O-based absorbents have displayed high adsorption capacity and selectivity for radioactive iodide ions,the supports displayed poor ion exchange abilities for radioactive cations(90Sr,137Cs).Furthermore,90Sr may exist in basic radioactive Wastewater,while some support structures are unstable in basic media,losing their ion exchange abilities for radioactive cations.Thus,it is an urgent requirement to find new absorbents with high capacities to remove radioactive cations and anions in basic conditions.In this study,we show that nanofibers of sodium niobate(SOMS)with negatively charged layers and readily exchangeable sodium ions between the layers can efficiently remove radioactive Sr2+ The exchange of Sr2+ ions with the interlayer Na+ ions can cause structural deformation of layers,trapping the Sr2+ in the nanoribers.Furthermore,silver oxide(Ag2O)nanocrystals can be firmly anchored on the surface of niobate nanofibers via coherent interfaces between Ag2O and niobate phases(Ag2O@SOMS).SOMS and Ag2O@SOMS have been characterized using X-ray powder diffraction(XRD),Fourier transform infrared spectroscopy(FT-IR),scanning electron microscopy(SEM),Transmission electron microscopy(TEM),X-ray photoelectron spectra(XPS),nitrogen adsorption-desorption and Raman spectrometer(Raman).The results showed that Ag2O nanoparticles have been successfully anchored on the surface of sodium niobate nanowires.The adsorption experiments have been performed to investigate the effect of adsorption operational parameters such as the ratio of volume to dose,the intial solution pH,the initial cesium concentration,temperature and contact time on ion exchange properties of Ag2O@SOMS.I-anions in fluids can easily access the Ag2O nanocrystals and be efficiently trapped by forming an Agl precipitate that firmly attaches to the adsorbent.This bi-functional absorbent can be arranged to remove Sr2+ and I-ions simultaneously by optimizing the Ag2O loading and Nat content of the niobate nanofibers.It can provide high adsorption capacity for both ions in basic media,unlike other adsorbents that can be used in acid or neutral media.The maximum adsorption capacities of Sr2+ and I-for Ag2O anchored sodium niobate nanofibers were found to be 0.75mmol·g-1 and 2.33 mmol·g-1 respectively.Furthermore,the niobate adsorbents can be readily dispersed in liquids and easily separated after purification due to their fibril morphology,which significantly enhances their adsorption efficiency and reduces separation costs.This study demonstrates that Ag2O anchored sodium niobate nanofibers with fibril morphology,negatively charged thin layers and readily exchangers are potential sorbent for the simultaneous uptake of cations and anions.