Ag nanoparticles interlayered Fe3O4/Ag/m(TiO2-ZrO2) magnetic photocatalysts with enhanced stability and photocatalytic performance for Cr(Ⅵ) reduction

A sandwich structured Fe3O4/Ag/m(TiO2-ZrO2) magnetic nanosphere with Ag nanoparticles as an interim layer was fabricated with in situ deposition of Ag nanoparticles onto Fe3O4 nanospheres and subsequent coating an outmost shell of mesoporous TiO2-ZrO2. As compared to Fe3O4/m(TiO2-ZrO2)/Ag with Ag nanoparticles as the outmost layer, unique Fe3O4/Ag/m(TiO2-ZrO2) sandwich nanospheres possess higher efficient charge migration and larger specific surface area disclosed by the BET and photoelectrochemical characterizations, so they present improved photocatalytic activity toward Cr(VI) reduction. In addition, they have high thermal stability because mesoporous TiO2-ZrO2 outmost shell could protect the interim Ag nanoparticles from damage and agglomeration at high temperature. Results showed reduction efficiency of Cr(VI) of Fe3O4/Ag/m(TiO2-ZrO2) reached 98.4 % in 30 min, as 1.6 times as that of Fe3O4/m(TiO2-ZrO2)/Ag. The Fe3O4/Ag/m(TiO2-ZrO2) still obtained 91.3 % and 87.9 % reduction ratio after calcination at 500 ℃ and recycling 5 times, respectively. The photocatalytic mechanism was also revealed by scavenger experiments and ERP analysis. This work provided a good example for further design and preparation of magnetic photocatalysts with high performance for the remediation of heavy metal pollutants.