The results showed that SiO2 · HSs could barely be obtained at the above situations, which indicated that rare-earth ion was an indispensable factor in hollow structure formation. Experimental data showed that the rare-earth ions were advantageous to HSS formation; Wortmannin cost however, further study is needed to understand why the effect of different Re3+ eFT-508 in vivo ions on the formation of HSSs has a different role. Effect
of reaction time The reaction time will determine the deepening of the reaction after fixing other reaction conditions. Figure 5 shows the structures of the as-prepared particles with a variety of reaction time. As can be seen, rattle-type particles appeared after 6 h of reaction, and then the core of particles gradually disappeared and finally became HSs at about
8 h, meanwhile many tiny particles accompanied with the HSs. After 10 h, the shapes of INCB28060 cell line HSs were clearer, though many tiny particles were around them. The tiny particles came from the dissolved SiO2, which disappeared with reaction time extension. The high-quality HSs with clear edges were obtained when the reaction lasted for 12 h; simultaneously, the tiny particles disappeared too. It was noticed that the shell of hollow spheres was getting thinner and thinner when the reaction time was over 12 h. As can be seen, a handful of HSs had cracked after 14 h. The experiments indicated that the reaction time would significantly vary the influence on the shell thickness of SiO2 · Re2O3 HSs. Therefore, the shell thickness of HSs can be controlled by adjusting the reaction time. Figure 5 TEM images of products prepared at different reaction time. T = 250°C, pH = 4,[Eu3+] =0.06 mol/L. From the above, our synthesis procedure of HSSs is very simple and effective compared with those previously reported. Formation mechanism of SiO2 · Re2O3 HSs In our experiments, SiO2 · Re2O3 HSs
were synthesized in an acidic solution. It was reported that colloid SiO2 would carry a negative charge when pH > 3 . The following equilibriums existed Celecoxib in the intermediate between the liquid and solid interfaces : When Re3+ ions are added into the solution, an electrostatic force is produced between the surface of silica and Re3+, Re3+ ions are absorbed onto the surface of SiO2 spheres at first, and then insoluble compounds SiO2 · Re2O3 are formed. Meanwhile, SiO2 cores keep dissolving in the acidic solution, as shown in Figure 5 (6 h). At the initial stage, most of the Re3+ ions are absorbed onto the surface of SiO2 spheres, and numerous insoluble tiny particles that come from the residual Re3+ ions meet with the negative ions in the solution, as shown in Figure 5 (8 and 10 h). As the reaction continues, the tiny particles are swallowed by the SiO2 · Re2O3 lamella due to Ostwald ripening, and clear SiO2 · Re2O3 HSs are obtained at last, as shown in Figure 5 (12 h). Figure 6 is the sketch map of SiO2 · Re2O3 HS formation.