Researchers from the University of Padova, the Joint Research Centre & the INFN-Laboratori Nazionali di Legnaro have fabricated the first structured uranium-based monoliths using Digital Light Processing (DLP), a form of vat photopolymerization. This milestone in nuclear materials research demonstrates how complex uranium components can be directly printed using uranyl ions as photocatalysts.
Published in Advanced Functional Materials, the study presents a sol–gel synthesis where uranyl nitrate serves both as the photocatalyst and the uranium source. The process avoids traditional photoinitiators and produces uranium carbide (UCx) components. After thermal treatment, the printed structures convert into uranium carbide/carbon nanocomposites with porosity levels reaching 91.9%, ideal for ISOL (Isotope Separation On-Line) radioisotope targets.
The printed parts showed controlled shrinkage, ~12 μm resolution, and high material purity, solving key challenges in fabricating actinide materials. The method opens doors for custom nuclear fuel shapes and medical isotope applications. It exploits uranyl cations’ UV–vis-induced reactivity to trigger polymerization without added initiators.
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Ink Synthesis and 3D printing of U-based structures
The team formulated a water-based sol–gel ink with uranyl nitrate, citric acid, sucrose, and PEGDA Mₙ 575. Citric acid stabilizes uranyl complexes, sucrose acts as carbon source and polymer binder, and PEGDA forms the photocurable matrix.
Using a commercial DLP printer, they produced intricate structures that were sintered at 1700 °C in argon. This converted the organic scaffold into UCx/carbon composites with excellent fidelity. The optimized molar ratio (U:CA:sucrose = 1:2:0.5) helped ensure near-complete conversion to UCₓ (UO₂ peaks absent after 24 h).
Photoactivation of uranyl-citrate complexes
Upon UV–vis exposure, the uranyl-citrate complex initiates polymerization through ligand-to-metal charge transfer. This generates radicals that extract hydrogen from PEGDA, creating reactive carbon-centered species that crosslink the polymer.
UV–vis spectroscopy confirmed complexation via spectral shifts and stronger absorption. The initiator-free strategy improves compatibility with aqueous systems and simplifies formulation while achieving efficient photopolymerization.
Morphology and microstructural characterization
Thermal processing transformed the printed parts into composites of UC, UC₂, and graphitic carbon. XRD and Raman analyses tracked the phase transformation and carbon ordering. The parts retained their geometry, with porosity up to 91.9% and a specific surface area of 59.3 m²/g.
SEM-EDX confirmed even distribution of elements and no major phase segregation. Despite shrinkage of ~90.5%, the structures maintained integrity, essential for nuclear applications demanding rapid isotope release and thermal durability.
Conclusion and future outlook
This work proves that vat photopolymerization can be used to create complex uranium-based architectures using uranyl ions both as a reactive agent and as a structural component. The process enables high-resolution, high-porosity designs with relevance to ISOL targets, advanced fuels, and nuclear medicine.
Its adaptability to other uranium chemistries (e.g., UO₂) broadens the path for additive manufacturing in actinide science, offering new capabilities in both energy and biomedical sectors
Photochemistry in 3D printing
Photochemistry is playing an increasingly transformative role in vat photopolymerization, unlocking new approaches to resin formulation and curing mechanisms. While most commercial 3D printing resins rely on organic photoinitiators, recent research has explored alternative systems, including quantum dots and metal complexes, that can initiate polymerization under UV–vis light.
For example, recent studies have demonstrated how quantum dots can enhance mechanical and optical properties in SLA materials. This study follows a similar path by leveraging the photoreactivity of uranyl ions to eliminate the need for conventional photoinitiators altogether. As photochemical strategies continue to evolve, they are enabling new applications for additive manufacturing across sectors ranging from micro-optics to nuclear materials.
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Feature image shows fabrication of uranium-based components via DLP. Image via Advanced Functional Materials.
