Preparation And In Vitro Biological Activity Of The Silicon-containing Hydroxyapatite

Series of silicon-substituted hydroxyapatite were synthesized by precipitation and hydrothermal methods. Chemical composition, crystalline phase, microstructure and morphology were ch by XRF, XRD, FT-IR, Raman, solid-state NMR, FESEM and TEM. The influence of silicon concentration and nature of synthesis methods on the structure and in vitro bioactivity of the resulting materials were studied. The effect of substituted silicon amount on the photocatalytic degradation efficiency of the dyes and the photocatalytic degradation dynamics were investigated. The main results are as follows:1. The amount of silicon can be incorporated seemed to be limited, and0.9wt%was the highest Si content in the precipitation-synthesized samples. Hydroxyapatite with silicon level of0.9wt%kept its original structure. The results revealed that precipitation method was a good procedure to prepare pure silicon-substituted hydroxyapatites. Hydrothermal-synthesized samples had larger crystallites size and high crystallinity. FT-IR spectra indicated that the calcium deficiency of the precipitation produced samples became obvious, and no CO32-groups were found. Samples synthesized via precipitation method were micro-spheres and microrods, and had a strong tendency to aggregate. But, specimens prepared by hydrothermal process were irregular in shape. TEM images of the precipitation prepared powders revealed smooth and joint edges, while the hydrothermal synthesized powders exhibited rough and less aggregate edges.2. In vitro studies suggested that better bioactivities were achieved in case of precipitation produced specimens compared to hydrothermal-synthesized counterparts. The higher the silicon content the better the in vitro bioactivity. The current findings firmed and demonstrated that the incorporation of Si led to solubility enhancement of the HAP substrate, and resulted in the pronounced bioactivity in vitro. Moreover, silicon substitution promoted in vitro biological activity of the silicon substituted materials may by decreasing size and crystallinity, increasing calcium deficiency and triple point junctions. The mechanism of silicon leading to improved bioactivity need to drill deeper.3. The photocatalytic experiment indicated that the elimination rates of Si-HAP decreased with increasing substituted silicon amount compared with those of stoichiometric HAP in the photodegradation of MO and CR under UV light irradiation. The photocatalytic activity of Si-HAP with UV irradiation was enhanced compared with only UV irradiation without adsorbent. In particular, Si-HAP:0.8can photodegradate almost80%MO after4h for a20mg L-1solution at neutral pH situation. The maximum adsorption capacity of Si-HAP was2.28mg g-1for MO and3.59mg g-1for CR. The photocatalytic degradation process of MO and CR by Si-HAP composite followed the Langmuir-Hinshelwood kinetics model. Further, Si-HAP can be easily recovered after the treatment of the dyes and can be recycled for multiple treatment scans due to its long term stability.