RESUMO
High-performance MgO-CaO-Fe2O3 clinker was prepared using magnesite from Xinjiang (with high calcium and low silica), calcium oxide, and ferric oxide as raw materials. Microstructural analysis and thermogravimetric analysis, combined with HSC chemistry 6 software simulations, were used to investigate the synthesis mechanism of MgO-CaO-Fe2O3 clinker and the effect of firing temperature on the properties of MgO-CaO-Fe2O3 clinker. The results show that MgO-CaO-Fe2O3 clinker with a bulk density of 3.42 g·cm-3, water absorption of 0.7%, and excellent physical properties can be formed by firing at 1600 °C for 3 h. In addition, the crushed and reformed specimens can be refired at temperatures of 1300 °C and 1600 °C to achieve compressive strengths of 17.9 MPa and 39.1 MPa, respectively. The main crystalline phase of the MgO-CaO-Fe2O3 clinker is the MgO phase; the 2CaO·Fe2O3 phase generated by the reaction is distributed between the MgO grains to form a cemented structure with a small quantity of 3CaO·SiO2 and 4CaO·Al2O3·Fe2O3 also distributed between the MgO grains. A series of decomposition and resynthesis chemical reactions occurred during the firing of the MgO-CaO-Fe2O3 clinker, and the liquid phase appeared in the system once the firing temperature exceeded 1250 °C. The presence of the liquid phase promoted intergranular mass transfer between the MgO grains, ensuring the continuous growth of the MgO grains and furthering the densification of the MgO-CaO-Fe2O3 clinker.
RESUMO
A rapid recombination of photo-generated electrons and holes, as well as a narrow visible light adsorption range are two intrinsic defects in graphitic carbon nitride (g-C3N4)-based photocatalysts. Inspired by natural photosynthesis, an artificially synthesized Z-scheme photocatalyst can efficaciously restrain the recombination of photogenerated electron-hole pairs and enhance the photoabsorption ability. Hence, to figure out the above problems, BiOBr/g-C3N4 composite photocatalysts with different mass ratios of BiOBr were successfully synthesized via a facile template-assisted hydrothermal method which enabled the BiOBr microspheres to in situ grow on the surface of g-C3N4 flakes. Furthermore, to explore the origin of the enhanced photocatalytic activity of BiOBr/g-C3N4 composites, the microstructure, photoabsorption ability and electrochemical property of BiOBr/g-C3N4 composites were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (DRS), electrochemical impedance spectroscopy (EIS) and photocurrent (PC) response measurements. As a result, the introduction of BiOBr on g-C3N4 to constitute a direct Z-scheme heterojunction system can effectively broaden the light absorption range and promote the separation of photo-generated electron-hole pairs. Hence, compared with pure g-C3N4 and BiOBr, the resultant BiOBr/g-C3N4 composites exhibit the remarkable activity of photodegradated rhodamine B (RhB) and tetracycline hydrochloride (TC-HCl) under visible light irradiation. Simultaneously, the optimal BiOBr content of the BiOBr/g-C3N4 composites was obtained. The BiOBr/g-C3N4 composites exhibit an excellent photostability and reusability after four recycling runs for degradation RhB. Moreover, the active-group-trapping experiment confirmed that ·OH, ·O2 - and h+ were the primary active groups in the degradation process. Based on the above research results, a rational direct Z-scheme heterojunction system is contrastively analyzed and proposed to account for the photocatalytic degradation process of BiOBr/g-C3N4 composites.
