Preparation Of Prussian Blue Analogues-Immobilized Composite Membranes And Their Adsorption Properties Of Cesium Ions

Cesium and its compounds are widely used in energy,electronics and so on.In China,Qinghai Tibet Plateau has rich deposits of cesium resources both in salt lakes and geothermal water,and it is of great significance that if cesium ions can be separated and extracted efficiently.However,its efficient separation and extraction is very challenging,due to the low concentration of Cs⁺in these liquid mineral resources and a large number of coexisting competitive ions.Therefore,Prussian blue analogues-immobilized composite membranes were designed with excellent and stable adsorption performance,and the optimal conditions and separation mechanism were explored.The prepared membranes were applied to the extraction of cesium in geothermal water.And the main results are as follows:（1）In order to modify Prussian blue（PB）,tannic acid（TA）riching in hydrophilic groups was used,and the composite powder adsorbent of Prussian blue（PB-TA）was synthesized by coprecipitation method.FT-IR analysis suggested that Fe³⁺could be chelated with TA,and the XRD results showed that PB maintained crystal structure.Batch adsorption experiments were performed,and the results showed that the powder material presented stable adsorption performance in a wide p H range（6-10）,adsorption equilibrium could be reached within 20 min,and the maximum adsorption capacity was up to 114.36mg·g^-1.（2）Based on the assembly property of coordination complexes,Prussian blue composite coating was formed on the surface of polyamide nanofiber（PA/PP-ES）base membrane.Combined with in-situ generation of PB,Prussian blue composite membrane（PB-TA/PA）was prepared using TA and potassium ferrocyanide as the organic ligand and the precursor,respectively.Meanwhile,ferric chloride was chosen as inorganic cross-linker and precursor.According to the spectral characterizations,it was found that the chelation of TA and Fe³⁺could improved the fixation and dispersion of PB on the membrane surface.The adsorption experiment results showed that PB-TA/PA composite membrane retained its good stability in a wide p H range（6-10）and a good adsorption performance.The adsorption equilibrium could be reached within 120 min,and the maximum adsorption capacity was 27.92 mg·g^-1.Even in geothermal water conditions,the cesium distribution coefficient still reached 8985.55 m L/g.Desorption could be realized using 1 mol/L NH₄Cl,and the adsorption rate only decreased by 4.9%after five cycles.However,the adsorption capacity is a little bit low.（3）In order to further increase the adsorption capacity,copper-based Prussian blue analogue composite membrane（Cu-PBA-TA/PA）were prepared by means of layer-by-layer self-assembly technology combined with in-situ generation method.In this work,the polyamide nanofiber（PA/PP-ES）membrane was used as a base membrane,and tannic acid,copper dichloride and potassium ferrocyanide was chosen as reactants.The optimum impregnation times and reactant concentrations were explored,and the structure and morphology of the obtained membranes were characterized.The adsorption experiment results indicated that the optimal p H for Cu-PBA-TA/PA composite membrane adsorption was 12,and it presented better adsorption performance.The adsorption equilibrium still reached within 120 min,but the adsorption capacity was highly improved to 265.04 mg·g^-1.Even in the presence of competitive ions,the composite membrane held an excellent selectivity,and the distribution coefficient of Cs⁺was 14000 m L/g.It was found that the ion exchange mechanism between K⁺and Cs⁺rendered the adsorption process,and the composite membrane exhibited good cycle stability.After five cycles,the adsorption rate only decreased by 10%,indicateing a potential application of Cu-PBA-TA/PA composite membrane.