Metal–organic frameworks (MOFs) have reshaped modern materials science with their extraordinary porosity, structural tunability, and broad application potential. Among the most studied MOFs, the Zeolitic Imidazolate Framework (ZIF) family stands out, especially ZIF-8, ZIF-L, and ZIF-67.

Although they share a common building block — the imidazolate linker — these materials differ significantly in structure, morphology, chemical composition, and functional capabilities. Understanding these differences is essential for anyone working in catalysis, gas separation, sensing, drug delivery, energy storage, or nanomaterial development.

This long-form blog provides an in-depth, yet readable, comparison of ZIF-8, ZIF-L, and ZIF-67. Whether you are a researcher, engineer, student, or someone exploring advanced materials, this guide will help you clearly understand how these three frameworks resemble each other, where they differ, and which applications they best serve.

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1. Introduction: The Rise of ZIF Materials

ZIFs are a subclass of MOFs built by connecting metal ions (such as Zn²⁺ or Co²⁺) with imidazolate linkers. These structures resemble zeolites in their geometry but offer far greater flexibility due to the nature of their metal–organic bonds.

ZIFs became widely used because they offer:

• High thermal and chemical stability

• Permanent porosity

• Adjustable pore structures

• Possibility of water-based synthesis

• Low toxicity when zinc-based

• Ability to transform into functional derivatives (e.g., carbon materials or metal oxides)

Among the wide range of ZIFs synthesized, ZIF-8, ZIF-L, and ZIF-67 are the most extensively researched because they combine ease of preparation with high performance across multiple fields.

Before we compare them, let us briefly introduce each one.

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2. Overview of ZIF-8, ZIF-L, and ZIF-67

2.1 What is ZIF-8?

ZIF-8 is the most famous ZIF, composed of:

• Metal center: Zn²⁺

• Linker: 2-methylimidazole

• Structure: Sodalite-type cubic framework

• Pore size: ~11.6 Å cage, ~3.4 Å aperture

• Typical morphology: Rhombic dodecahedron crystals

ZIF-8 is celebrated for its:

• Excellent water stability

• High thermal stability (up to ~550°C)

• Chemical resistance to solvents and pH variations

• Easy aqueous synthesis

• Low toxicity (important for biomedical applications)

Because of this, ZIF-8 appears in applications like:

• Gas separation

• Nanofiltration membranes

• Catalysis

• Drug delivery

• CO₂ capture

• Supercapacitors

• Nitrogen adsorption

• Encapsulation of biomolecules

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2.2 What is ZIF-L?

ZIF-L is another zinc-based ZIF, but structurally layered, giving it its “L” designation.

• Metal center: Zn²⁺

• Linker: 2-methylimidazole

• Structure: Layered (leaf-like morphology)

• Typical appearance: Nanosheets or leaf-like platelets

Key characteristics of ZIF-L include:

• Two-dimensional layered framework

• Higher surface area in plate-like form

• Better dispersibility in aqueous media

• Ability to form thin films

• Often serves as a precursor to porous carbons for electrocatalysis

Compared to ZIF-8, ZIF-L is:

• Less thermally stable

• Less chemically robust

• More flexible structurally

But its layered morphology makes it excellent for:

• Electrocatalyst precursor templates

• 2D membranes

• Composites with polymers

• Faster ion/electron transport

• CO₂ reduction catalysts

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2.3 What is ZIF-67?

ZIF-67 is a cobalt-based analog of ZIF-8.

• Metal center: Co²⁺

• Linker: 2-methylimidazole

• Structure: Sodalite-type (similar to ZIF-8)

• Typical morphology: Rhombic dodecahedral, similar to ZIF-8

ZIF-67 closely resembles ZIF-8 structurally, but the cobalt gives it different:

• Electronic properties

• Redox capabilities

• Magnetic behavior

Because of Co²⁺, ZIF-67 is highly effective as a self-sacrificial template for:

• Cobalt-doped carbons

• Co₃O₄ or Co/CoO nanostructures

• Oxygen evolution reaction (OER) catalysts

• Supercapacitors

• Batteries (Li-ion, Zn-ion)

Unlike ZIF-8, ZIF-67 is rarely used in biomedical systems due to cobalt toxicity.

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3. Structural Comparison of ZIF-8 vs ZIF-L vs ZIF-67

3.1 Framework Geometry

Key insight:

ZIF-L is the only one that forms a 2D layered architecture, giving it unique properties in membrane formation and catalysis.

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3.2 Morphology and Crystal Habit

• ZIF-8: Rhombic dodecahedron

• ZIF-L: Nanosheets, thin leaf-like crystals

• ZIF-67: Rhombic dodecahedron (like ZIF-8)

ZIF-L often exhibits significantly higher aspect ratios, which improves surface exposure and electron mobility.

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3.3 Pore Structure

• ZIF-8 and ZIF-67:

  • Cage diameter: ~11.6 Å

  • Aperture size: ~3.4 Å

• ZIF-L:

  • Contains micropores but also interlayer spacing

  • Provides higher accessibility than ZIF-8

Because of the identical linker and similar topology, ZIF-8 and ZIF-67 share almost identical pore architectures. ZIF-L, however, offers a hybrid micro/mesoporous environment due to its layers.

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3.4 Thermal and Chemical Stability

ZIF-8 remains the most stable under harsh environments.

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4. Synthesis Differences

Although ZIF-8, ZIF-L, and ZIF-67 all use 2-methylimidazole, the synthesis approach can dramatically change morphology.

ZIF-8 Synthesis

Can be synthesized using:

• Solvothermal

• Room-temperature aqueous

• Hydrothermal

• Ionothermal

• Vapor-assisted

• Mechanochemical

It forms readily because of favorable zinc–imidazolate bonding.

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ZIF-L Synthesis

Requires specific reaction conditions:

• High ligand-to-metal ratios

• Room-temperature mixing

• Often water-based synthesis

• Lower zinc concentration than ZIF-8 synthesis

Small changes in pH, zinc ratio, or mixing speed drastically influence whether ZIF-8 or ZIF-L forms.

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ZIF-67 Synthesis

Similar to ZIF-8 synthesis but uses cobalt salts instead of zinc salts.

Co²⁺ alters:

• Reaction kinetics

• Crystal growth rate

• Particle size

ZIF-67 crystals often grow faster, resulting in smaller particle sizes unless reaction conditions are adjusted.

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5. Functional Uses and Applications

5.1 Gas Adsorption and Separation

• ZIF-8: Excellent for CO₂, CH₄, and H₂ separation

• ZIF-L: Good for CO₂ due to layered channels

• ZIF-67: Similar to ZIF-8 but cobalt influences adsorption energetics

ZIF-8 is the benchmark for gas separation membranes.

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5.2 Catalysis

Due to its cobalt content, ZIF-67 is far superior in catalysis involving redox reactions:

• Oxygen evolution reaction (OER)

• Oxygen reduction reaction (ORR)

• Hydrogen evolution

• CO₂ reduction

ZIF-8 and ZIF-L mostly serve as supports rather than catalysts unless carbonized.

ZIF-L’s layered morphology improves catalytic performance after conversion into porous carbon sheets.

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5.3 Energy Storage

• ZIF-67: Excellent self-sacrificial precursor for Co₃O₄ and Co–N–C materials used in batteries and supercapacitors.

• ZIF-L: Forms 2D carbon nanosheets suitable for fast ion transport.

• ZIF-8: Helps form uniform porous carbons but lacks redox-active metal content.

ZIF-67 dominates in high-performance energy devices.

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5.4 Drug Delivery and Biomedicine

• ZIF-8: Non-toxic Zn²⁺, high stability, good biodegradability → ideal for:

  • Drug encapsulation

  • Controlled release

  • Biosensing

  • Protective coatings

• ZIF-L: Can be used in drug delivery but is less stable.

• ZIF-67: Rarely used due to cobalt toxicity.

For biological applications, ZIF-8 is the clear winner.

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5.5 Gas Sensing

ZIF-67 shows enhanced sensing due to the electrochemical activity of Co²⁺.
ZIF-L allows rapid diffusion because of its layers.
ZIF-8 provides stable and reproducible sensing baselines.

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6. Advantages and Disadvantages Summary

ZIF-8

✔ Advantages:

• Very high stability

• Safe for medical use

• Easy to synthesize

• Highly porous

• Excellent for membranes

✖ Disadvantages:

• Limited catalytic activity

• Lower electrical conductivity

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ZIF-L

✔ Advantages:

• Layered structure ideal for 2D materials

• High exposed surface area

• Good for electrocatalyst precursors

• Thin-film compatibility

✖ Disadvantages:

• Lower stability

• Sensitive to water and acids

• Harder to control synthesis

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ZIF-67

✔ Advantages:

• Cobalt enables strong catalytic activity

• Excellent precursor for functional carbons

• Highly tunable structure

• Good for energy applications

✖ Disadvantages:

• Cobalt toxicity limits biomedical use

• Slightly less stable than ZIF-8

• Oxidation-sensitive

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7. When to Choose ZIF-8, ZIF-L, or ZIF-67? Practical Guidance

Choose ZIF-8 if you need:

• High stability

• Biomedical compatibility

• Reliable membranes

• Water-resistant materials

• Adsorption and separation functions

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Choose ZIF-L if you need:

• 2D nanosheets

• Fast electron/ion transport

• Layered morphology

• Electrocatalyst precursor for sheet-like carbons

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Choose ZIF-67 if you need:

• Strong catalytic performance

• Redox-active materials

• High-performance energy storage

• Cobalt-derived nanostructures

• OER/ORR/HER catalysis

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8. Final Thoughts: The Power of Choosing the Right ZIF

The ZIF family remains one of the most versatile branches of metal–organic frameworks, and ZIF-8, ZIF-L, and ZIF-67 are three of its most important members. While they share similarities in chemical linkers and broad synthesis strategies, their differences in structure, morphology, stability, and metal centers result in fundamentally different behavior.

• ZIF-8 offers unmatched stability and biocompatibility.

• ZIF-L offers unique 2D architecture and high surface accessibility.

• ZIF-67 offers superior catalytic activity driven by cobalt chemistry.

Understanding these differences allows researchers and engineers to choose the right material for the right application — whether designing a next-generation battery, developing nanofiltration membranes, or engineering advanced catalysts.

As the scientific community continues to explore ZIF-based materials, we can expect even more innovation built on this remarkable trio of frameworks.