Insight into the photocatalytic properties of phosphonate-based metal-organic frameworks for reduction of Cr (VI) and Synergistic elimination of organic dyes under natural sunlight

The photocatalytic reduction of Cr (VI) is investigated over phosphonate-based metal-organic frameworks (MOFs) structured as STA-12(M)(M = Mn, Fe, Co, Ni). The removal of Cr (VI) appears to be faster with STA-12(Fe) under natural sunlight. The correlation among responses to effective variables as main and interactions were optimized by central composite design (CCD) in response surface methodology (RSM). Moreover, STA-12(Fe) has exhibited considerable synergistic photocatalytic activity for dyes (MO and RhB) degradation and Cr (VI) reduction. The reduction ratio of Cr (VI) was increased extremely after addition of MO or RhB. The highest photocatalytic activity of dyes degradation and Cr (VI) reduction appeared under the dye/Cr (VI) weight ratio of 3:1. To determine the most important species that affected the photocatalytic reduction, trapping experiments were carried out, using various kinds of scavenger species. Finally, a probable reaction mechanism has been investigated in detail.