In a recent article published in the journal Advanced Functional Materials, researchers introduced a new approach using composite materials made from titanium dioxide (TiO₂) combined with a copper-based metal-organic framework (MOF), specifically HKUST-1.
The goal was to develop efficient and long-lasting photocatalysts capable of generating hydrogen from water and methanol sacrificial agents—without relying on precious metals.
A key focus of the study was optimizing the mass ratios between HKUST-1 and TiO₂ to improve photocatalytic performance. The research also explored the critical role copper plays in the overall effectiveness of these composite materials.
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Background
Photocatalysis offers a promising pathway for sustainable hydrogen fuel production, leveraging solar energy as a clean and abundant resource. Titanium dioxide (TiO₂) has long been a focal point in this field thanks to its chemical stability and suitable band gap.
However, one major limitation of TiO₂ lies in the rapid recombination of photogenerated electron-hole pairs, which hampers its overall photocatalytic efficiency.
To address this, researchers have proposed incorporating copper in the form of a metal-organic framework (MOF), specifically HKUST-1. Copper’s ability to exist in multiple oxidation states introduces a unique electron transfer mechanism that may improve charge carrier separation and enhance photocatalytic performance.
This study sets out to show that the synergy between TiO₂ and copper species in HKUST-1 can yield hydrogen production rates that outperform even those achieved with noble metal catalysts.
The Current Study
The research involved synthesizing composite nanomaterials by varying the mass ratios of HKUST-1 and TiO₂. To characterize their structural and optical properties, the team used a range of analytical tools, including transmission electron microscopy (TEM), UV-visible spectroscopy, Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS).
Time-resolved microwave conductivity was employed to study charge carrier dynamics. At the same time, density functional theory (DFT) calculations provided insight into the electronic structure and the interactions between copper and TiO₂ during hydrogen generation.
Photocatalytic hydrogen production was tested under UV light using water and methanol as sacrificial agents, with performance tracked over multiple cycles to assess long-term stability.
Results and Discussion
The study found that a 1:20 mass ratio of HKUST-1 to TiO₂ yielded the highest hydrogen evolution rate, starting at 5.11 mmol g⁻¹ h⁻¹.
Remarkably, performance improved with repeated use, reaching 13.24 mmol g⁻¹ h⁻¹ after six photocatalytic cycles. This surpassed the benchmark set by 1 wt.% platinum-doped TiO₂, which achieved 7.97 mmol g⁻¹ h⁻¹ and did so without the drawbacks of using noble metals.
The improved efficiency of the composite was linked to a synergistic effect between TiO₂ and the copper species in HKUST-1. Copper enhances charge carrier separation by stabilizing electrons during photocatalytic activity.
Time-resolved microwave conductivity data supported this, showing a reduction in electron-hole recombination. The copper centers within HKUST-1 effectively scavenge photogenerated electrons, with reversible redox behavior (Cu(II) ↔ Cu(I)/Cu(0)) playing a key role in charge transfer and utilization.
Comparative tests using TiO₂ modified with copper oxide (CuO) showed significantly lower hydrogen yields, highlighting that the MOF-embedded copper ions offer more efficient charge dynamics than oxidized copper alone.
The high surface area and porous structure of HKUST-1 further contributed to the enhanced performance by promoting better light absorption and reactant accessibility.
A proposed mechanism for the photocatalytic process describes how, under UV light, electrons in TiO₂ are excited from the valence band to the conduction band, leaving behind holes that drive water oxidation.
The excited electrons are then transferred to copper nanoclusters, where partial reduction of Cu(II) improves charge separation. This not only minimizes recombination but also facilitates hydrogen formation at the copper active sites. DFT calculations reinforced this mechanism by showing how copper atoms support hydrogen evolution through favorable electronic interactions.
Conclusion
This study marks a meaningful step forward in the development of efficient, non-precious metal photocatalysts for hydrogen generation.
By optimizing the ratio of HKUST-1 to TiO₂, researchers achieved exceptional hydrogen production rates that rival and exceed those of platinum-based systems—without the cost or resource concerns tied to noble metals.
The findings underscore the importance of copper’s redox flexibility and the structural advantages of MOFs in enhancing photocatalytic performance.
These insights open the door to further exploration of MOF-based composites for clean energy applications, offering a viable route toward more sustainable and scalable hydrogen production.
Journal Reference
Khan A., Le Pivert M., et al. (2025). Cu‐Based MOF/TiO2 Composite Nanomaterials for Photocatalytic Hydrogen Generation and the Role of Copper. Advanced Functional Materials. doi: 10.1002/adfm.202501736.
