Sustainable Synthesis of Semicrystalline Zr-BDC MOF and Heterostructural Ag3PO4/Zr-BDC/g-C3N4 Composite for Photocatalytic Dye Degradation

ABSTRACT Zr-based MOFs have stimulated the interest of scientific community due to their exceptional variety in composition, structure and chemical environment as well as their consequent applications including photocatalysis. This work presents the successful preparation of nanosized highly-porous Zr-BDC MOFs under sustainable conditions: at room temperature, water as sole solvent, and with no modulators. This approach solves some environmentally unfriendly drawbacks and feasible requirements of the conventional UiO-66(Zr), whereas both materials contain practically equal linker conformation and clusters structure and linker-cluster coordination. Furthermore, ternary composites of Zr-MOF combined with g-C3N4 and Ag3PO4 are described for the first time. X-ray Photoelectron Spectroscopy (XPS), Scanning and Transmission Electron Microscopies (SEM and TEM) evidenced ample and efficient interaction between the components within the composites. Such composites were tested as photocatalysts in the discoloration of methylene blue (MB), reaching degradation as high as 95 and 93% within 240 and 105 min under indoor/visible and outdoor/solar irradiations, respectively, far exceeding the photoactivity given by the individual components and by any of the two possible binary composites. These results suggest the existence of relevant synergistic effects in the heterostructures, which favours efficient interfacial charge transfer and improves the separation of photoinduced electron-hole pairs. The photoinduced hole (h+) has more quenching effect than hydroxyl (.OH) and supper oxide (.O2-) radicals. In addition, the as-obtained ternary composite exhibited remarkable stability and recyclability, at least for the two cycles considered in the present work. We have also proposed a plausible reaction mechanism for the photocatalytic process.