Opportunity
Conventional Prussian blue analogs (PBAs) are microporous inorganic solids with a cubic crystal structure (Fm3m space group) that hold significant promise for applications in catalysis, gas storage, energy storage, photothermal therapy, drug delivery, sensors, and nanozymes. However, their practical development is severely hindered by several intrinsic limitations. These materials typically suffer from non-periodic and randomly distributed defects, such as [M′(CN)₆] or cyanogen (CN) vacancies, which are often introduced through defect engineering to tailor properties. These defects make the crystal structure brittle and prone to collapse, complicate atomic-scale structural studies, and impede the growth of high-quality single crystals due to rapid microcrystalline formation during synthesis. Furthermore, conventional cubic PBAs possess a low intrinsic specific surface area, which is a critical bottleneck for many applications, especially those reliant on high surface area like gas adsorption and storage. While phase engineering has been successfully applied to other material classes to control properties, a synthesis strategy capable of overcoming these defects, achieving precise crystal structure control, and substantially increasing the specific surface area of PBAs remained a significant unmet need in the field prior to this invention.
Technology
The present invention addresses these challenges through a novel phase engineering strategy, introducing a hexagonal phase copper-cobalt Prussian blue analog (H–CuCo PBA) material. This is achieved via a facile, low-temperature co-precipitation synthesis method that requires neither high-temperature treatment nor complex post-processing. The core innovation lies in the unconventional hexagonal crystal structure, confirmed by techniques like three-dimensional electron diffraction (3D ED/cRED). In this structure, copper ions adopt a planar quadrilateral configuration coordinated with four cyanogen groups, while cobalt ions maintain an octahedral configuration connected to six cyanogen groups. This arrangement alternates to form a framework with a 12-ring pore channel along the c-axis, creating larger open channels and interstitial spaces compared to cubic PBAs. The synthesis method can be extended to produce doped hexagonal PBAs (e.g., with Fe, Ni, Zn, or additional Co) by incorporating small amounts of other metal precursors, allowing for modulation of morphology and properties. This phase engineering approach fundamentally alters the atomic arrangement, leading to a material with high crystallinity, reduced random defects, and a dramatically increased specific surface area.
Advantages
- Achieves a significantly higher specific surface area (at least 1000 m²g⁻¹, preferably ~1273 m²g⁻¹) compared to conventional cubic PBAs (typically <900 m²g⁻¹).
- Features larger channels and interstitial spaces, facilitating enhanced metal-ion storage, diffusion, and small molecule accessibility.
- Exhibits superior gas adsorption capacity, with performance at least 1.5 times higher than cubic PBAs for gases like CO₂, CH₄, C₂H₂, C₂H₄, C₂H₆, C₃H₆, and C₃H₈.
- Enables efficient gas separation, demonstrating breakthrough performance for CO₂/CH₄ mixtures and a separation coefficient for C₃H₆/C₂H₄ twice that of cubic analogs.
- Contains numerous unsaturated copper sites (Cuᴵ) and a low coordination number for Cu–N≡C–Co bonds, which are active sites believed to enhance gas uptake and selectivity.
- Possesses a stable open-framework structure that remains intact after solvent removal and gas adsorption/desorption cycles.
- Utilizes a simple, scalable, and low-cost synthesis method (co-precipitation at 30°C) amenable to large-scale production and doping for property tuning.
Applications
- Gas Storage and Separation: For CO₂ capture, biogas upgrading (CO₂/CH₄ separation), and olefin/paraffin separation (e.g., C₃H₆/C₂H₄).
- Energy Storage: As electrode materials in batteries (e.g., sodium-ion, potassium-ion) due to enhanced ion diffusion channels.
- Catalysis: As a catalyst or catalyst support leveraging its high surface area and unsaturated metal sites.
- Sensing: Development of electrochemical or chemical sensors for gases or small molecules.
- Environmental Remediation: Removal of radioactive ions or pollutants from aqueous solutions.
- Biomedical Applications: Potential use in drug delivery systems, photothermal therapy, or as nanozymes.
- Water Desalination: For ion-selective separation processes.
