Preparation Of Benzo-crown Ether Hybrid Silica Gel And Their Adsorption Properties For Calcium Ions

Ca is one of the essential nutrient elements for the crop growth,has important physiological functions for plants.And is one of substances that transmit signals inside and outside plant somatic cells.Diffusive Gradients in Thin-Films?DGT?technology is a kind of continuous in-situ passive sampling technology.After more than 20 years development and research,it has been widely applied to sampling and analysis pollutants in water,soil and sediments.Benzo-crown ether-functionalized silica which was prepared by the combination of the sol-gel process and the Schiff base reaction can be used for the selective adsorption of Ca²⁺ ions.Benzocrown ether-functionalized silica material?CE-SiO₂?for calcium ion enrichment and separation was successfully prepared by hydrothermal method and sol-gel method.The structure of CE-SiO₂ was characterized by Fourier Transform infrared spectroscopy,Thermal Gravimetric Analyzer and scanning electron microscope.The effectiveness of CE-SiO₂ as a DGT binding agent was investigated.The adsorption performance of CE-SiO₂ was discussed.The adsorption capacity is significantly higher than that of CE-SiO₂ used only the sol-gel method.Discuss the influence of pH,temperature and adsorption time on adsorption capacity;the experimental results show that the quantitative pH range of CE-SiO₂ is 5-10;the adsorption capacity of Ca²⁺ ion increases with the increase of temperature;the optimal contact time is 60 min.The selectivity of CE-SiO₂ was discussed.The experimental results show that CE-SiO₂ is suitable for the selective adsorption of Ca²⁺ ions even in the presence of other alkali metal ions and alkaline earth metal ions.The adsorption/desorption cycle of the CE-SiO₂ shows that after the second cycle,the adsorption capacity of Ca²⁺ ions is about 87-92% of the new CE-SiO₂,and the adsorption capacity loss is relatively low.The experimental results show that CE-SiO₂ can be used for absorption Ca²⁺ in water repeatedly.The mechanism of adsorption of Ca²⁺ ions by CE-SiO₂ was also discussed.Pseudo-second-order equations provided good correlation for the adsorption of Ca²⁺ ions;both Langmuir and Freundlich isotherm adsorption models can be used to provided correlation for the adsorption of Ca²⁺ ions,but Langmuir is better than Freundlich.The adsorption process is a single-layer adsorption on the surface of a homogeneous adsorbent.According to the thermodynamic discussion,?H=15.175 k J/mol,the adsorption is endothermic;?S=90.165J/mol/K,indicating that during the entire adsorption,as the Ca²⁺ ions in the solution are adsorbed to the surface of CE-SiO₂,the adsorption system becomes more confusional,and this process is an entropy reduction process.?G <0 indicates that the adsorption is a spontaneous process.In the effectiveness experiment,the recovery rate was 95.7 ± 3.7%.CE-SiO₂ can be used as the binding agent of diffusive gradients thin-films.