Graphitic C3N4 (g-C3N4), as an advanced metal free photocatalyst, is known to be poorly exfoliated and dispersed in water from its powder form which has a layered structure, the intrinsic plane structure is not destroyed, and this has largely limited its application. In this work, we report our progress on successful sonication exfoliation of g-C3N4 nanosheets in graphene oxide (GO) aqueous solution. By making use of the substrate character of GO, g-C3N4 nanosheets of unvaried intrinsic structure were exfoliated and anchored on the GO surface, resulting in a GO/g-C3N4 hybrid. Moreover, the photocurrent of the hybrid was largely reinforced at the optimal weight fraction of GO. As a result, the corresponding photocatalytic performance of the hybrid with optimized photocurrent character was largely improved.

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The theoretical phase diagrams of the binary Al 2 O 3 −Ti 2 O 3 and Al 2 O 3 −TiO 2 , as systems calculated using FactSage software and its thermodynamic databases, are reoptimized. This has been performed on the basis of a literature survey on experimental precipitation limits of Ti 2 O 3 and TiO 2 in the Al 2 O 3 solid solution. The appropriate oxygen partial pressure (p O 2 ) range for controlling the valence state of Ti ions during Ti:sapphire crystal growth is obtained with respect to the calculated Ellingham type predominance diagram. Factors affecting the p O 2 such as furnace gas, crucible materials, and graphite heating elements are analyzed. The influence of p O 2 on Ti 3+ and Ti 4+ concentrations in the solid and liquid phases is derived from thermodynamic equilibrium calculations. The equilibrium segregation coefficients of Ti 3+ and Ti 4+ in sapphire are calculated to be 0.046 and 0.011, respectively. Taking into account the data extrapolated from experiments, a value of 0.06 ± 0.02 is proposed for the equilibrium segregation coefficient of total Ti under low p O 2 .