Transforming chemical processes with earth-abundant elements and sustainable energy sources
Imagine if we could perform the complex chemical reactions needed to create medicines, materials, and fuels using nothing but earth-abundant elements and the power of ordinary light.
Replacing scarce precious metals with widely available alternatives reduces costs and environmental impact.
Harnessing solar energy as a clean power source for chemical transformations.
This isn't science fiction—it's the emerging reality of sustainable catalysis, a field that stands to transform how we practice chemistry in profoundly eco-friendly ways. For decades, many catalytic processes have relied on precious metals like platinum, palladium, and iridium—materials that are not only expensive but also scarce, geographically concentrated, and often extracted through environmentally damaging mining practices. The search for sustainable alternatives has become one of the most pressing challenges in modern chemistry 1 2 .
Catalysts speed up chemical reactions without being consumed—essential for modern chemistry.
Using light-absorbing catalysts to harness solar energy for chemical reactions.
Discovering novel catalytic activity and selectivity with sustainable systems.
As Dr. Osama El-Sepelgy and Dr. Luis Miguel Azofra explain: "For decades, synthetic chemists have directed their attention towards the development of ligand systems to enable 4d and 5d transition metals to catalyze chemical processes under thermal conditions." 2 These precious metal catalysts, while effective, come with significant baggage—they're expensive, scarce, and often toxic.
Enter photoredox catalysis—an innovative approach that uses light-absorbing catalysts to harness solar energy for driving chemical reactions. When these catalysts absorb photons of light, they become "excited" and can transfer electrons to other molecules, triggering reactions that might otherwise require harsh conditions or expensive reagents.
While early photoredox catalysts relied on precious metals like ruthenium and iridium, researchers have recently developed organic analogues that serve as sustainable replacements. As one seminal paper describes, certain dihydrophenazine and phenoxazine systems have emerged as "strongly reducing, visible-light organic photoredox catalysts" that can facilitate challenging transformations like trifluoromethylation reactions and carbon-nitrogen and carbon-sulfur bond formations—reactions previously exclusive to precious metal catalysts 1 .
Hydrogen gas has emerged as a promising clean energy carrier, but storing and transporting it safely remains a challenge. One promising solution involves storing hydrogen in chemical bonds within compounds like ammonia borane (NH₃BH₃), then releasing it when needed using catalysts.
A groundbreaking study published in the Journal of Materials Chemistry A demonstrated a highly efficient alternative using nonprecious metal nanoparticles supported on graphitic carbon nitride (g-C₃N₄)—all powered by visible light 7 .
Nonprecious metal nanoparticles on graphitic carbon nitride for hydrogen evolution using visible light.
Researchers prepared both monometallic (cobalt, nickel, and iron) and bimetallic (copper-cobalt, iron-cobalt, nickel-cobalt, copper-nickel, and iron-nickel) nanoparticles supported on graphitic carbon nitride.
The catalytic hydrogen evolution experiments were conducted at room temperature (298 K) in a specialized photoreaction system with precise control and measurement capabilities.
Each catalyst was tested under two conditions: in darkness and under visible light irradiation to isolate and quantify the specific effect of light on catalytic activity.
The team investigated how catalytic performance depended on different factors including wavelength of incident light, light intensity, and specific metal composition.
The findings revealed remarkable enhancements under visible light irradiation. Across all catalysts tested, activities for hydrogen evolution from ammonia borane were significantly higher under illumination compared to parallel experiments conducted in darkness.
The most outstanding performers were the cobalt, iron-cobalt, and copper-cobalt catalysts, which achieved total turnover frequencies (TOF)—a measure of catalytic efficiency—of 55.6, 68.2, and 75.1 minâ»Â¹, respectively. The authors noted that these values "were the highest amongst the values of the reported noble-metal-free catalysts at 298 K." 7
| Catalyst | TOF (minâ»Â¹) under Visible Light | Enhancement |
|---|---|---|
| Cobalt/g-C₃N₄ | 55.6 | Significant |
| FeCo/g-C₃N₄ | 68.2 | Significant |
| CuCo/g-C₃N₄ | 75.1 | Significant |
| Light Parameter | Effect on Activity | Implication |
|---|---|---|
| Wavelength | Activity changed with wavelength | Confirms photocatalytic process |
| Intensity | Activity increased with intensity | Light-dependent efficiency |
| Light On/Off | Immediate activity change | Direct light involvement |
The researchers attributed this dramatic enhancement to the Mott-Schottky effect at the interface between the graphitic carbon nitride support and the metal nanoparticles. Graphitic carbon nitride is a semiconductor that absorbs visible light, generating electron-hole pairs. Due to the Mott-Schottky effect, these photoexcited electrons are efficiently transferred to the metal nanoparticles, enriching their electron density and thereby boosting their catalytic activity for hydrogen release from ammonia borane.
The field of sustainable catalysis relies on a diverse array of materials and reagents that enable these innovative chemical transformations.
| Reagent/Material | Function in Research | Sustainable Advantage |
|---|---|---|
| Dihydrophenazine compounds | Organic photoredox catalysts | Replace precious metals in redox reactions 1 |
| Phenoxazine systems | Strongly reducing photoredox catalysts | Enable C-N and C-S cross-couplings without precious metals 1 |
| Graphitic carbon nitride (g-C₃N₄) | Semiconductor support material | Enhances electron transfer; non-toxic and earth-abundant 7 |
| Cobalt, Nickel, Iron nanoparticles | Catalytic active sites | Replace platinum, palladium in hydrogen evolution 7 |
| Ammonia borane (NH₃BH₃) | Hydrogen storage material | Enables safe hydrogen storage and release 7 |
| Manganese-based catalysts | Transition metal catalysts | Sustainable alternative for C-C and C-N bond formation 2 |
This toolkit represents a fundamental shift from traditional catalytic approaches. As researchers explain, their focus is on "the design, invention and implementation of catalytic strategies to provide fast, efficient and sustainable routes for organic synthesis" using "earth-abundant, non-toxic and readily available elements" .
The sustainable advantages extend beyond mere replacement—these materials often enable novel reactivity and selectivity that wasn't possible with traditional precious metal catalysts.
Researchers are exploring complementary energy sources including electro-catalytic, photo-catalytic, piezoelectric, sonocatalytic, mechanochemical, and enzymatic catalysis schemes, as well as combinations of these energy forms to achieve synergistic effects 8 .
A promising direction focuses on waste valorization—transforming waste products into valuable resources through catalytic processes for chemical production, fuel generation, and energy vectors 8 .
The capture and conversion of carbon dioxide represents another frontier, turning atmospheric COâ‚‚ into a resource for producing valuable chemicals and fuels through catalytic processes 8 .
International scientific gatherings accelerate progress by bringing together diverse perspectives to address one of chemistry's most pressing challenges, such as the 2025 International Symposium on Sustainable Catalysis in Hanoi, Vietnam 4 .
Converting biomass into valuable chemicals through catalytic processes
Using catalytic processes for effluent treatment and water purification
Developing catalysts for emerging energy vectors and storage systems
The shift toward sustainable catalysis using nonprecious metals and visible light represents more than just a technical improvement—it embodies a fundamental reimagining of how we practice chemistry.
Organic photoredox catalysts replace precious metals in drug development 1 .
From the organic photoredox catalysts that can replace precious metals in pharmaceutical synthesis 1 to the nonprecious metal nanoparticles that efficiently produce hydrogen using nothing but light 7 , these advances point toward a future where chemical manufacturing works in harmony with environmental imperatives.
The journey from precious metals to earth-abundant alternatives and from energy-intensive processes to light-driven transformations is well underway—illuminating a path toward a brighter, greener future for chemistry and the planet it serves.