Pb²⁺ Removal From Amino Functional Mesoporous Silica Sphere By Pseudomorphic Transformation

As adsorbent, mesoporous materials have many favorable properties and amino-functional mesoporous materials have been widely reported. As a result, with an amino function, mesoporous materials have more advantages on heavy metals adsorption than traditional materials. While, in a typical method, synthesis of mesoporous material have many drawbacks such as high-cost, complicated process, resulting in difficult industrial application. As a result, pseudomorphic transformation could avoid these problems obviously. In this method, particle mesoporous silica can be obtained by controlling the rate of hydrolysis and polymerization. But the large-size silica materials (>1mm), which widely used as an industrial catalyst, adsorbent and ion exchangers are often occurred a phenomenon of fragment.This work regulated the rates of hydrolysis and polymerization by using ethanol as co-solvent. The results show that pseudomorphic transformation can be well controlled when the volume ratio of ethanol and H2O is 0.252. The optimum condition of pseudomorphic transformation is NaOH:SiO2:CTAB:H2O 0.1:1.0:0.27:140. After post-hydrothermal treatment, the surface area of large-size mesoporous silica (LMS) has been improved from 256m2/g to more than 1000m2/g. By FT-IR and NaOH titration, the amount of Si-OH after pseudomorphic transformation increased obviously, which provides more possibility for function and application. The results of Pb2+ removal show that LMSs-AP has the best Pb2+ adsorption ability and the maximum adsorption capacity is 97mg/g. The adsorption process of four materials fit well with Langmuir adsorption equation and the pseudo-second-order kinetic model (R2>0.9). suggesting that the reaction is monomolecular layer chemical adsorption. Besides, the adsorption process also agrees with antiparticle diffusion mechanism. The adsorption capacity improved with the increasing of temperature from 25℃ to 45℃. Especially, with the fast transfer process in higher temperature, the adsorption ability of LMS-CT increased about 50%. The change of entropy (AS0>0) from LMS-CT and LMS-AP indicated that the adsorption process follows the increase of entropy. The sign of the Gibbs free energy (ΔG0>0) shows that the adsorption process is faster with the increase of temperature. Combine with the result and characterizations, the adsorption ability is related to the pH value. Because of forming -NH3+ and positive charge on silica, LMS-AP has a bad adsorption ability when pH=1-2. LMS-AP always has a well adsorption ability in three times reusing under an alkaline system.The results of dynamic study show that the process of dynamic adsorption is affected by some factors such as the particle size, flow rate and pH. At the same time, the particles in 1-3mm have the best adsorption ability. For the actual waste-water treatment, the protonated phenomenon also exists, resulting a dissolve of Al and Zn. Meanwhile, materials have a better adsorption ability for Pb and Zn than as when pH=4, suggesting that the materials have some selective to bivalent cations.