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Mixed-Metal Derivatives Crystal Growth
Summary:
The authors from American University of Beirut developed **ZIF-8, ZIF-67, and Co-doped ZIF-8** with size gradient, high porosity, and visible-light response, achieving efficient methylene blue photodegradation in environmental remediation.
Background:
1. To address the problem of uncontrollable ZIF crystal size/doping and poor ZIF-8 visible-light activity, previous researchers used solvothermal/microwave methods, yet faced complex processes and limited performance.
2. The authors proposed an innovative reaction-diffusion framework (RDF) strategy, realizing controlled synthesis of ZIFs and Co-doped derivatives with enhanced photocatalytic properties.
Research Content:
1. Synthesis
- Gel matrix preparation: Agar was dissolved in aqueous metal salt (Zn(NO₃)₂/Co(NO₃)₂) solution, mixed with DMF, and gelled in test tubes.
- RDF synthesis: HmIm solution (water/DMF = 1:1) was added on top of the gel, reacted at room temperature for 2 days to form ZIF precipitates with size/doping gradients.
- Co-doped ZIF-8: Zn(NO₃)₂ and Co(NO₃)₂ were mixed in the gel to prepare solid-solution ZIFs.
2. Characterizations
1) BET and pore size: ZIF-8 BET = 1302 m²·g⁻¹, ZIF-67 = 1023 m²·g⁻¹, 10% Co-ZIF-8 = 1235 m²·g⁻¹; pores are microporous/mesoporous.
2) SEM: ZIF-8 size 0.5-4 μm, ZIF-67 1-10 μm; Co-doped ZIFs are smaller, with rhombic dodecahedral morphology.
3) Other tests: UV-Vis shows ZIF-8 band gap 4.9 eV, Co-doped ZIF-8 2.0 eV; PXRD confirms sodalite structure purity.
3. Application
- Photocatalytic degradation: 10% Co-ZIF-8 degraded 70% methylene blue in 90 min under visible light (rate constant 0.021 min⁻¹), retaining 80% activity after 2 cycles.
- Stability: Co-doped ZIF-8 with <50% Co is water-stable for 24 h.
4. Mechanism
- RDF-induced supersaturation gradient controls ZIF size; Co doping narrows band gap for visible-light absorption.
- Photogenerated holes produce •OH radicals, synergizing with high dye adsorption to enhance degradation efficiency.
Outlook:
This research establishes a facile RDF method for controllable ZIF synthesis, realizes efficient visible-light photocatalysis via Co doping, and provides a new path for functional MOF-based environmental remediation materials.
Crystal Growth of ZIF-8, ZIF-67, and Their Mixed-Metal Derivatives
Authors: Daniel Saliba, Manal Ammar, Moustafa Rammal, Mazen Al-Ghoul, Mohamad Hmadeh
DOI: 10.1021/jacs.7b11589
Link: https://pubs.acs.org/doi/10.1021/jacs.7b11589
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