Titanium–Porphyrin Metal–Organic Frameworks as Visible-Light-Driven Catalysts for Highly Efficient Sonophotocatalytic Reduction of Cr(VI)

Abstract

In this work, we synthesized and characterized four titanium−porphyrin metal−organic frameworks (MOFs) [DGIST-1(M), M = Co(II), Fe(III), Zn(II), and H 2 ] and used them as visiblelight-driven catalysts for sonophotocatalytic Cr(VI) reduction. DGIST-1(M) exhibited open-framework, broad light absorption stemmed from ligand and sensitive photocurrent responses owing to the integration of one-dimensional Ti-oxo chains and 4-connected conjugated TCPP ligand (TCPP = tetrakis(4-carboxyphenyl)porphyrin). DGIST-1(M) presented efficient reduction of Cr(VI) to Cr(III) in aqueous solution when used as sonophotocatalytic catalysts. The average reduction rates upon Cr(VI) were 0.920, 0.476, 0.377, and 0.194 mg•L −1 •min −1 for DGIST-1(H 2 ), DGIST-1(Zn), DGIST-1(Co), and DGIST-1(Fe), which are 1.15−2.45 times higher than those in photocatalysis. Sonophotocatalytic experiments and electron paramagnetic resonance measurement proved that Ti-oxo chain units and porphyrin ligand in the structures of DGIST-1(M) existed as catalytic active centers for sonophotocatalytic reduction of Cr(VI). Photoluminescence and UV absorption spectra revealed that the unity of photocatalysis and sonochemistry strengthened the migration of photogenerated electrons from DGIST-1(M) to Cr(VI), which improved the activities of catalysts. This study suggested that the association of titanium−porphyrin MOFs and sonophotocatalytic technology is an impactful program for enhancing MOF-based photocatalytic systems.

Construction of BiOIO3/AgIO3 Z-Scheme Photocatalysts for the Efficient Removal of Persistent Organic Pollutants under Natural Sunlight Illumination

“…As displayed in Figure 6a, compared with AgIO 3 and BiOIO 3 , the PL and PLE intensity of Bi@Ag-5 obviously decreased, evidencing a lower charge recombination rate. 40,41 On the other hand, the arc radius of the EIS Nyquist curve for Bi@Ag-5 is smaller than those for AgIO 3 and BiOIO 3 (Figure 6b), and the photocurrent value of Bi@Ag-5 is higher than those of AgIO 3 and BiOIO 3 (Figure 6c), evidencing the promoted carrier transfer efficiency for Bi@Ag-5. 42,43 As exhibited in Figure 6d, the average carriers' lifetime of Bi@Ag-5 determined by photoluminescence decay curves is longer than those of AgIO 3 and BiOIO 3 .…”

Advances on sonophotocatalysis as a water and wastewater treatment technique: efficiency, challenges and process optimisation

“… Chen et al (2022) also prepared titanium–porphyrin MOFs and used them as visible-light-driven catalysts for the sonophotocatalytic reduction of Cr(VI). All the catalysts presented higher efficiency in the reduction of Cr(VI) to Cr(III) in aqueous solution when sonophotocatalytic treatment was employed than in photocatalysis.…”

Emerging porous solids and sonochemistry

“…One promising solution involves reducing Cr( vi ) to low-toxicity Cr( iii ), which readily forms insoluble precipitates in neutral or basic solutions. In this context, Xing et al intensely investigated the use of MOFs to sonocatalytically reduce Cr( vi ) to Cr( iii ); 37–39 they prepared PCN-222(M) [M = H 2 , Zn( ii ), Fe( iii ), Co( ii )], which are zirconium-porphyrin MOFs constructed from tetrakis(4-carboxyphenyl)porphyrin [TCPP] and eight linked Zr 6 (OH) 8 (μ 3 -OH) 8 (carboxylate) 8 cluster units that form three-dimensional frameworks with csq topologies (Fig. 3a and b).…”

“…3a and d). 38 The DGIST-1(M) MOFs exhibited enhanced photoreductive Cr( vi ) conversions under US irradiation when used as photocatalysts, with average reduction rates determined to be 0.920, 0.476, 0.377, and 0.194 mg L −1 min −1 for DGIST-1(H 2 ), DGIST-1(Zn), DGIST-1(Co), and DGIST-1(Fe), respectively, which are 1.15–2.45-times higher than those measured when irradiated with light (Fig. 3e).…”