Application of sand particles modified with NH2-MIL-101(Fe) as an efficient visible-light photocatalyst for Cr(VI) reduction

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

“…After 60 min of adsorption equilibrium in 20 mg·L –1 Cr­(VI) aqueous solution, DGIST-1­(H 2 ) exhibited pH-dependent catalytic activity where photocatalytic efficiency was obviously enhanced with the decrease of pH (Figure a). This situation is also consistent with the previously reported literature. − Control experiments in photocatalysis revealed that Cr­(VI) cannot be reduced in the absence of MOFs or in the dark condition. Based on the optimal condition of pH = 1, sonophotocatalytic Cr­(VI) reduction was performed over DGIST-1­(H 2 ) by adding the ultrasonic wave (60–120 W, 20 kHz) into the abovementioned photocatalytic system (Figure S7).…”

“…At the same time, the samples of DGIST-1­(H 2 ) after the reaction were detected by the XPS measurement. As shown in Figure b,c, the characteristic peaks at 587.7 and 577.5 eV corresponding to the Cr 2p 1/2 and Cr 2p 3/2 orbitals were observed, which correspond to Cr­(III) species, further proving the transformation of Cr­(VI) to Cr­(III). , In addition, according to previous reports, in the absence of any electron sacrifice in the system, the main oxidation product is H 2 O 2 and it can be detected by using N , N -diethyl-1,4-phenylenediamine/horseradish peroxidase (DPD/POD). ,,− Because of the low concentration of H 2 O 2 presented in the reaction solution, a small amount of the reaction solution was employed to repeatedly rinse the catalyst to obtain the detection solution. It is observed from Figure d that the mixed solution displayed two absorption bands at 510 and 551 nm, while it is barely observed in the blank; so it is demonstrated that the oxidation product of water is H 2 O 2 .…”

Visible-Light-Driven Sonophotocatalysis for the Rapid Reduction of Aqueous Cr(VI) Based on Zirconium–Porphyrin Metal–Organic Frameworks with csq Topology

“…Metal–organic frameworks (MOFs), a class of crystalline inorganic–organic hybrid materials, have gathered particular attention in the field of photocatalysis due to their intriguing structures, powerful designability, and high surface areas. − What is more exciting is that the photophysical properties of MOFs can be effectively tuned at the atomic level by virtue of abundant metal, organic secondary building units and their multiple interactions. − In recent years, MOFs as heterogeneous catalysts have made notable progress in photoreduction of Cr­(VI) to Cr­(III). − In general, MOF catalysts with high stability, large specific surface area, broad-band visible absorption and relative high density of catalytic active sites are pursued in Cr­(VI) photoreduction, where the assembly of high-valent metal ions (e.g., Ti 4+ , Zr 4+ and Fe 3+ ) and photoactive polycarboxylate ligands is the most popular strategy. − However, MOF catalysts possess high energy barriers between metal clusters and ligands, which hinders the long-range migration of photogenerated charges in the MOF structure and further limits the photocatalytic performance of MOFs. − In addition, relatively narrow apertures of MOF catalysts also limit the mass transfer rate of the substrate in channels and then restrict the promotion of catalytic efficiency. Inspired by the influence of sonochemistry for heterogeneous catalytic reactions, MOF-based photocatalytic systems with acoustic stimulation should be developed more to give scope to the advantage characteristics of MOF materials in photocatalytic reactions …”

Integration of MIL-101-NH2 into Cellulosic Foams for Efficient Cr(VI) Reduction under Visible Light

“…However, the absorption edge of CM- x composites was similar to that of pure MIL-101-NH 2 (Fe) after MOFs were anchored on the CNFs, which confirms the composite foams have the ability to harvest visible light. Moreover, in line with the Kubelka–Munk equation, (α h ν) 2 = A ( h ν – E g ), the E g value of MIL-101-NH 2 (Fe) was 1.86 eV, while the composite foams have a lower value of 1.74 eV due to the possible heterostructural effect during the compositing process (Figure b). − …”