Facile synthesis of amino-functionalized titanium metal-organic frameworks and their superior visible-light photocatalytic activity for Cr(VI) reduction

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Summary:
The authors from Hunan University & CAS developed NH₂-MIL-125(Ti), an amino-functionalized titanium MOF with 1344 m² g⁻¹ surface area and 2.65 eV band-gap, achieving 97 % visible-light reduction of 48 ppm Cr(VI) to Cr(III) in 60 min (pH 2.1, ethanol hole-scavenger).

Background:
1. Prior Ti-MOFs lacked visible response; Zr/In analogues showed limited Cr(VI) photoreduction.
2. This work proposes one-pot solvothermal substitution of BDC by H₂ATA to narrow band-gap via N 2p, creating Ti³⁺–Ti⁴⁺ intervalence transfer for rapid electron delivery to Cr(VI).

Research Content:
1. Synthesis: TBT + H₂ATA in DMF/MeOH, 150 °C 48 h → yellow NH₂-MIL-125(Ti) crystals (400–600 nm).
2. Characterizations:
   1) BET 1344 m² g⁻¹, pore 0.69 cm³ g⁻¹, mean diameter 2.05 nm.
   2) SEM ~500 nm particles; XRD pure phase, no TiO₂.
   3) UV-vis DRS λonset 520 nm; XPS confirms Ti⁴⁺ & −NH₂.
3. Application: 20 mg catalyst, 50 mL 48 ppm Cr(VI), 500 W Xe (λ > 420 nm), 91 % reduction with 5 % ethanol; reusable 5 cycles (8 % loss).
4. Mechanism: Visible excitation → H₂ATA* → electron to Ti-oxo cluster → Ti³⁺ → transfer to Cr₂O₇²⁻; ethanol consumes h⁺, acid supplies H⁺, accelerating Cr(VI) → Cr(III).

Outlook:
NH₂-MIL-125(Ti) offers a noble-metal-free, recyclable MOF photocatalyst for solar-driven Cr(VI) wastewater remediation and can be extended to other toxic-metal reductions.

Facile synthesis of amino-functionalized titanium metal-organic frameworks and their superior visible-light photocatalytic activity for Cr(VI) reduction
Authors: Hou Wang, Xingzhong Yuan, Yan Wu, Guangming Zeng, Xiaohong Chen, Lijian Leng, Zhibin Wu, Longbo Jiang, Hui Li
DOI: 10.1016/j.jhazmat.2014.11.039
Link: https://doi.org/10.1016/j.jhazmat.2014.11.039

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