Antibiotics have transformed modern medicine, but they’ve also quietly created a serious environmental problem.

Every year, huge amounts of antibiotics are manufactured, prescribed, used…and then partially flushed into the environment. Wastewater from pharmaceutical plants, hospitals, and even households can contain measurable levels of these drugs. Many of them are persistent, poorly biodegradable, and biologically active even at low concentrations. That combination makes them dangerous for aquatic ecosystems, soil microorganisms, and ultimately human health.

This challenge becomes even more critical when we remember that antibiotic resistance is rising worldwide. The more antibiotics and resistant bacteria circulate in the environment, the harder it becomes to control infections in hospitals and communities.

So, researchers are increasingly asking:

Can we design smart materials that both break down antibiotics in water and kill antibiotic-resistant bacteria?

In this blog, we’ll explore one such promising solution: a metal–organic framework (MOF) nanocomposite called ZIF-8@ZIF-67, designed specifically to help decompose stubborn antibiotics and act as an antibacterial agent under light.

We’ll walk through:

• Why antibiotics like ciprofloxacin, levofloxacin, and ofloxacin are so hard to remove

• What ZIF-8 and ZIF-67 are, and why combining them is clever

• How the ZIF-8@ZIF-67 nanocomposite is made

• How well it breaks down antibiotics under light

• How it performs against E. coli

• What the mechanism looks like in simple terms

• Why this material is promising for future environmental remediation

1. The Problem: Persistent Antibiotics and Resistant Bacteria

Antibiotics such as ciprofloxacin (CIP), levofloxacin (LF), and ofloxacin (OFX) belong to the fluoroquinolone family. They’re widely used because they are broad-spectrum and effective against many bacterial infections.

However, they have several problematic features when they end up in water:

• They are chemically stable and resist natural degradation.

• Many are poorly soluble in water but can still interact with other substances and metal ions.

• Their structures often include aromatic rings, carbonyl groups, hydroxyl groups, and piperazine rings, which make them more persistent and sometimes more toxic.

• They can bioaccumulate and disrupt aquatic life and microbial communities.

Conventional treatment methods like:

• filtration (microfiltration, ultrafiltration),

• reverse osmosis,

• ion exchange,

• aerobic or anaerobic biological treatment,

• or even some advanced oxidation processes

often struggle to fully remove these molecules or are too expensive and energy-intensive for large-scale implementation.

At the same time, antibiotic-resistant bacteria are emerging as a major health threat. Resistant strains, especially those that form biofilms, can survive many disinfection steps. By 2050, antibiotic-resistant infections are projected to cause enormous economic and health impacts if nothing changes.

Because of all this, scientists are very interested in materials that can use light to drive chemical reactions – especially reactions that:

• degrade antibiotics into less harmful products, and

• kill or inhibit bacteria, including resistant strains.

This is where metal–organic frameworks (MOFs) and particularly ZIF-8 and ZIF-67 come in.

2. Meet the Materials: ZIF-8 and ZIF-67

Metal–organic frameworks (MOFs) are a family of crystalline, porous materials built by connecting metal ions with organic linkers into ordered 3D networks. They are famous for:

• very high surface areas,

• adjustable pore structures,

• and tunable chemistry.

A special subgroup of MOFs is called zeolitic imidazolate frameworks (ZIFs). They combine features of both classical zeolites and MOFs:

• They often have sodalite-like structures (cage-type frameworks).

• The metal nodes (e.g., Zn, Co) are linked by imidazolate ligands, replacing the Si–O–Si bridges in zeolites with metal–imidazolate–metal linkages.

• They tend to be chemically and thermally stable, with well-defined pores.

In this study, two ZIFs are central:

ZIF-8

• Metal node: Zinc (Zn)

• Ligand: 2-methylimidazole

• Features:

  • Large surface area and porosity

  • Sodalite-type framework

  • Good thermal and chemical stability

  • Active sites for adsorption

  • Good photocatalytic potential due to its band structure

ZIF-8 is already known as a promising photocatalyst for organic pollutant degradation and as a platform for composite materials.

ZIF-67

• Metal node: Cobalt (Co)

• Ligand: also 2-methylimidazole

• Features:

  • High surface area

  • Larger pore volume than ZIF-8

  • Good stability in water

  • Different optical properties under visible light

Both ZIF-8 and ZIF-67 can generate reactive oxygen species (ROS) such as hydroxyl radicals and superoxide species under light, which are key for killing bacteria and degrading organic pollutants.

The idea behind this research is simple and smart:

If ZIF-8 is good, and ZIF-67 is good, can a ZIF-8@ZIF-67 composite be even better?

3. Designing the ZIF-8@ZIF-67 Nanocomposite

The researchers first prepared each framework separately, then combined them into a hybrid nanocomposite.

Step 1: Synthesis of ZIF-8

• A solution of zinc nitrate hexahydrate is prepared in methanol.

• Another solution containing 2-methylimidazole is also prepared in methanol.

• The two solutions are mixed at room temperature and stirred.

• ZIF-8 crystals begin to form as the metal ions and ligands self-assemble into the porous framework.

• The solid product is collected by centrifugation, washed with methanol, and dried.

Result: ZIF-8 particles around 100–200 nm, with regular shapes and a typical sodalite-like crystal pattern confirmed by X-ray diffraction.

Step 2: Synthesis of ZIF-67

• Cobalt nitrate hexahydrate is dissolved in methanol (solution A).

• 2-methylimidazole is dissolved in methanol (solution B).

• Solution B is added to solution A, followed by stirring and aging at room temperature.

• ZIF-67 crystals form and are collected, washed, and dried.

• Additional heat treatment (calcination) is applied for stability.

Result: ZIF-67 crystals also around 100–200 nm, with well-defined polyhedral shapes and strong crystallinity.

Step 3: Building ZIF-8@ZIF-67 Nanocomposites

To create the composite, the team mixed pre-synthesized ZIF-8 and ZIF-67 in different mass ratios in an ethanol–water mixture and used ultrasonication and stirring to promote intimate contact and coupling between the two frameworks. They then calcined the mixture at moderate temperature to stabilize the hybrid structure.

The composites are labeled according to the mass percentage of ZIF-67 added relative to ZIF-8. For example:

• 2ZIF-67/ZIF-8

• 4ZIF-67/ZIF-8

• 6ZIF-67/ZIF-8

• 8ZIF-67/ZIF-8

• 10ZIF-67/ZIF-8

Among these, the one with around 6% ZIF-67 (called 6ZIF-67/ZIF-8) turned out to be the most active for both antibiotic decomposition and antibacterial action.

4. What Do These Nanocomposites Look Like and How Do They Behave?

The researchers carried out a full set of characterization techniques to understand the structure and behavior of the materials. Instead of going into every graph and spectrum, let’s focus on what they mean.

Particle Size and Shape

• Both ZIF-8 and ZIF-67 are made of nanosized crystals (roughly 100–200 nm), with tidy, regular shapes.

• In the composite, ZIF-67 is loaded onto or around ZIF-8, creating a core–shell or tightly coupled structure.

• High-resolution imaging reveals two distinct lattice fringes corresponding to ZIF-8 and ZIF-67, confirming that both materials coexist closely in one particle.

Crystallinity and Structure

• X-ray diffraction patterns show the characteristic peaks of each ZIF.

• When they are combined, the composite shows features belonging to both, meaning the frameworks retain their structure.

• No major destructive reaction takes place; instead, they form a heterostructured MOF–MOF composite.

Light Absorption and Band Structure

One of the key goals is to make the material responsive to visible light:

• ZIF-8 on its own absorbs mainly in the UV region.

• ZIF-67, thanks to cobalt, extends absorption further into the visible range.

• When ZIF-67 is integrated into ZIF-8, the absorption edge shifts toward longer wavelengths, especially for the 6% composite.

• This means more of the visible spectrum (like sunlight) can be used to drive photocatalytic reactions.

Charge Separation

For photocatalysis, it’s not enough to absorb light; you also need effective separation of photo-generated electrons and holes, otherwise they recombine and waste the energy.

• Measurements of fluorescence and photoluminescence show that pure ZIF-8 and ZIF-67 have stronger recombination signals, meaning more electrons and holes recombine.

• The 6ZIF-67/ZIF-8 composite shows reduced photoluminescence intensity, which indicates better charge separation.

• Better charge separation means more electrons and holes remain available to participate in chemical reactions, like generating radical species and attacking pollutant molecules.

Surface Area and Porosity

Surface area is crucial for adsorption and catalysis:

• ZIF-8 alone has a decent surface area, but not exceptionally high in this particular synthesis.

• ZIF-67 has a much higher surface area.

• When ZIF-67 is added at the right ratio (around 6%), the composite surface area roughly doubles compared to ZIF-8.

• This provides more active sites, pores, and channels where antibiotics and bacteria can interact with the material.

Taken together, the characterization tells a clear story:

The 6ZIF-67/ZIF-8 nanocomposite has enhanced light absorption, better charge separation, and a larger surface area than either ZIF-8 or ZIF-67 alone, making it an excellent candidate for photocatalytic antibiotic degradation and antibacterial activity.

5. How Well Does It Break Down Antibiotics?

The team evaluated the composite’s ability to decompose three fluoroquinolone antibiotics:

• Ciprofloxacin (CIP)

• Levofloxacin (LF)

• Ofloxacin (OFX)

They used a visible-light source and monitored changes in antibiotic concentration using UV–vis spectroscopy over time.

Key Results

Compared to the individual MOFs:

• ZIF-8 alone shows some photocatalytic activity. It can partially degrade CIP, LF, and OFX, but the efficiency is moderate.

• ZIF-67 alone also shows useful activity and generally performs a bit better than ZIF-8.

• 6ZIF-67/ZIF-8 composite significantly outperforms both.

Under optimized conditions and within a reaction time of 120 minutes, the 6% composite achieved approximately:

• 65% decomposition of CIP

• 54% decomposition of LF

• 48% decomposition of OFX

Depending on the specific antibiotic, this is roughly 1.7 to 2.3 times higher efficiency than pure ZIF-8.

Why is there a difference between CIP, LF, and OFX? Their molecular structures differ slightly, and so does the way they interact with the catalyst surface and with the reactive species generated during photocatalysis. Some are simply more stubborn than others.

6. What’s Going On Chemically? – The Role of Reactive Species

To understand how the composite degrades antibiotics, the researchers performed scavenger experiments. In simple terms, they added chemicals that selectively “trap” certain reactive species and see how the degradation efficiency changes.

They looked at three main active species:

• Hydroxyl radicals (•OH) – very strong, non-selective oxidants

• Superoxide radicals (•O2–) – reactive oxygen species formed from oxygen

• Photogenerated holes (h⁺) – positively charged “holes” in the valence band

The findings can be summarized like this:

• For ciprofloxacin (CIP):
  When a hydroxyl radical scavenger was added, the degradation dropped sharply.
  👉 •OH radicals are the dominant active species for CIP decomposition.

• For levofloxacin (LF):
  When a superoxide scavenger was added, the decomposition efficiency dropped significantly.
  👉 •O2– radicals play the key role for LF.

• For ofloxacin (OFX):
  When a hole scavenger was added, the degradation was strongly suppressed.
  👉 Photogenerated holes (h⁺) are the most important for OFX decomposition.

So, while the same catalyst is used for all three antibiotics, the dominant reactive species differ from one molecule to another. This is a nice example of how catalyst + pollutant structure + light together define the detailed mechanism.

In all cases, the ZIF-8@ZIF-67 composite helps:

1. absorb visible light,

2. separate charges more efficiently,

3. generate reactive species (•OH, •O2–, h⁺),

4. attack and break down antibiotic molecules into smaller, less harmful products and eventually inorganic species like CO₂ and water.

7. Antibacterial Activity: Fighting E. coli

Beyond degrading antibiotics, the composite is also tested against Escherichia coli (E. coli), a common model bacterium.

The experiments use growth on agar plates with and without the materials:

• A plate with only E. coli shows normal colony growth.

• With ZIF-8, there is some inhibition of bacterial growth – an indication of antibacterial activity.

• With ZIF-67, the inhibition zone grows larger, and viability is further reduced.

• With the 6ZIF-67/ZIF-8 composite, the antibacterial effect is the strongest.

The composite likely kills or inhibits bacteria via:

• Release of metal ions (Zn²⁺, Co²⁺) that disrupt bacterial cell processes

• Generation of reactive oxygen species under light, which damage cell membranes, proteins, and DNA

• Surface interactions where bacteria attach to the porous material, making them more vulnerable to ROS and metal ion effects

As a result, the 6ZIF-67/ZIF-8 nanocomposite doesn’t just break down the antibiotics in water – it also helps reduce the bacterial load, including potentially resistant strains.

8. Stability and Reusability

For a photocatalyst to be practical in real-world water treatment, it must be stable and reusable.

The study shows that:

• The 6ZIF-67/ZIF-8 composite maintains its crystalline structure after repeated use.

• Its degradation performance remains high over multiple cycles of antibiotic decomposition.

• Thermal and structural analyses indicate good stability under the testing conditions.

This suggests that the material is not just effective, but also durable, which is key for scaling up to continuous or repeated treatment processes.

9. Why This Work Matters

This research brings together several important ideas:

1. Environmental remediation: Removing persistent fluoroquinolone antibiotics from wastewater is essential to protect ecosystems and reduce selective pressure for antibiotic resistance.

2. Multifunctionality: The ZIF-8@ZIF-67 composite serves two roles at once – it degrades antibiotics and acts as an antibacterial agent.

3. Smart material design: By combining two MOFs (ZIF-8 and ZIF-67) in the right ratio, the researchers:

   • increased surface area,

   • enhanced visible-light absorption,

   • and improved charge separation.
     This is a general design strategy that can be applied to other MOF-based systems.

4. Visible-light activity: Using visible light (simulated sunlight) is much more realistic and sustainable than relying only on UV light. This opens the door to solar-driven treatment systems.

5. Scalability potential: The synthesis methods used (sol–gel, solvothermal, wet chemical mixing) are relatively standard in materials chemistry, which is promising for future scale-up.

10. Looking Ahead

While the ZIF-8@ZIF-67 nanocomposite shows great performance in the lab, several questions remain before real-world implementation:

• How does it behave in complex real wastewater, which contains many competing ions and organic compounds?

• Can the synthesis be optimized for lower cost and larger scale production?

• What is the long-term stability under continuous flow conditions?

• How exactly do intermediate degradation products evolve over time, and are they fully mineralized?

Even with these open questions, this study provides a solid step forward:

It demonstrates that carefully engineered MOF–MOF nanocomposites like ZIF-8@ZIF-67 can be powerful tools for breaking down stubborn antibiotics and combating bacteria at the same time, using only light and oxygen as the driving forces.

For anyone working in water treatment, environmental engineering, photocatalysis, or advanced materials, this type of approach is a clear signal:
smart, multifunctional nanomaterials are likely to play a major role in the next generation of green remediation technologies.