Wang Zichen

In Situ Synthesis and Surface Modification of Calcium Carbonate

We prepared hydrophobic calcium carbonate nanoparticles in situ via the carbonation route with various modifiers such as sodium stearate (NaSt), octadecyl dihydrogen phosphate (ODP), and oleic acid (OA). The modification of CaCO3 was determined by measuring its active ratio, whiteness and the contact angle. The products were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), and transmission electron microscopy (TEM). FT-IR spectra revealed that chemical bond and physical adsorption between modifiers and CaCO3 happened during the modification reaction. The infrared absorption peak of the modified CaCO3 was blue shifted 44 cm-1 compared with the unmodified CaCO3. A preliminary reaction mechanism was discussed in this paper. At a 2%(w(CaCO3)) modifier dosage, the active ratio of CaCO3 as modified by ODP was 99.9% and the whiteness was 97.3%. The contact angle was 122.25° for the CaCO3 modified in the presence of ODP. The theory to support these findings and synthetic methods was presented for these novel materials.

Adsorption of Creatinine on Porous Carbon Prepared from Rice Husk

The adsorption of creatinine (CR, a kind of metabolin in the human body) on the rice husk-based carbons (RHCs) with high specific area was studied. Comparison was made between the CR adsorption on four samples of porous carbon prepared by NaOH activation from rice husk at different activation conditions and two samples of commercial carbon. Meanwhile, the adsorption of CR on the modified carbon surfaces treated with HCl, H2O2, and HNO3, respectively, and calcined at 800 ℃ was investigated. Compared with commercial carbons, it was shown that the RHCs had larger capacity for the adsorption of CR. Generally, the CR adsorption capacity increased after the modification of the carbon surfaces. With regard to the adsorbability towards CR, the porous carbons treated by HCl was the best, the porous carbons treated by HNO3 was the worst, and the one treated by H2O2 was in the middle. The adsorbability of porous carbons after being calcined at high temperature (800 ℃) was obviously worse. The experiment testified that the adsorption of CR by porous carbons followed the Freundlich equation.

Size Effects on the Crystallite Structure and Phase Transition in Lanthanaum-Modified Lead Titanate Nanocrystals

The size effects on the crystallite structure, Raman spectra as well as phase transition in lanthanum-modified lead titanate Pb1-xLaxTi1-3/4xO3 (x = 0.14) (PLT14) nanocrystalline powders were investigated. The results show that with decreasing grain size, the crystallite structure changes from tetragonal perovskite phase to cubic perovskite phase; the soft mode frequency at room temperature decreases, and disappears when the grain size is as small as 19 nm; the phase transition temperature from ferroelectric to paraelectric shifts towards a low temperature region. The phase transition in nanocrystalline PLT14 is a second order one, which is confirmed by its dielectric constant measurement.