Preparation of Self-Assembled Spherical g-C3N4/tz-Bi(0.92)Gd(0.08)VO4 Heterojunctions and Their Mineralization Properties.

A novel kind of spherical g-C3N4/tz-Bi0.92Gd0.08VO4 heterojuctions are prepared via a simple microwave hydrothermal method. The sphere self-assembled mechanism and the heterojunction photocatalytic mechanism are mainly studied in this article. The results show that the added g-C3N4 sheets first anchor on ms-BiVO4 surfaces and then polymerize to form the coating layers, generating steric effect which is competing with Gd(3+) induction effect to affect the crystal transformation (from ms-BiVO4 to tz-BiVO4) and its growth during those processes. Afterward, independent coated structures are further polymerized and assembled into g-C3N4/tz-Bi0.92Gd0.08VO4 spheres. Because ECB (-0.95 V) of g-C3N4 is more negative than ECB (-0.05 V) of tz-BiVO4, the photoelectrons of g-C3N4 can be transferred into tz-BiVO4 surfaces through the heterojunction structure, so as to promote the separation rate of electron-hole pairs. In general, the adding of g-C3N4 can introduce hydroxyl groups to catch the photoholes and can inject electrons to react with dissolved oxygen to boost the production of active groups. Depending on such an orderly cooperation, g-C3N4/tz-Bi0.92Gd0.08VO4 heterojunction catalysts exhibit high and stable mineralization properties.