Photoresponsive proton conduction in Zr-based metal-organic frameworks using the photothermal effect

A highly stable and porous MOF [Zr₂(H₄TPPP)(OH/F)₂]·xH₂O (1) containing a metal-free porphyrin-phosphonate ligand is reported. It shows high proton conductivity of 1.2 × 10^-3 S·cm^-1 at 25 °C and 95% RH, a photothermal effect over a wide spectral range from UV-vis to NIR, and photo-enhanced and switchable proton conductivity.

HKUST-1 nano metal-organic frameworks combined with ZnGa2O4:Cr3+ near-infrared persistent luminescence nanoparticles for in vivo imaging and tumor chemodynamic and photothermal synergic therapy

The multifunctional theranostic nanoplatform based on the combination of persistent luminescent nanoparticles (PLNPs) and metal-organic frameworks (MOFs) has both in vivo imaging and tumor therapeutic drug-loading functions, providing a new strategy for accurate and effective tumor diagnosis and treatment. Herein, the near-infrared (NIR) PLNP SiO₂@Zn_1.05Ga_1.9O₄:Cr was combined with HKUST-1 MOFs to form a core-shell structure theranostic nanoplatform which possessed the triple function of autofluorescence-free NIR PersL bioimaging, tumor chemodynamic therapy (CDT), and tumor photothermal therapy (PTT). Also, the photothermal conversion efficiency reached 58.7%, which is superior to the reported nano metal-organic framework (NMOF) photothermal reagents. We demonstrated that the nanoplatform could enter the tumors of mice within 0.5 h and could be target-activated by H₂O₂ and H₂S in the tumor cells, resulting in effective PTT and CDT synergistic treatment. Tumor-bearing mice experiments showed that the tumor could be completely cured without harming normal tissue. This theranostic nanoplatform may provide a promising strategy showing imaging, PTT, and CDT synergistic treatment tri-mode for clinical cancer therapy.

Switched Proton Conduction in Metal-Organic Frameworks

Stimuli-responsive materials can respond to external effects, and proton transport is widespread and plays a key role in living systems, making stimuli-responsive proton transport in artificial materials of particular interest to researchers due to its desirable application prospects. On the basis of the rapid growth of proton-conducting porous metal-organic frameworks (MOFs), switched proton-conducting MOFs have also begun to attract attention. MOFs have advantages in crystallinity, porosity, functionalization, and structural designability, and they can facilitate the fabrication of novel switchable proton conductors and promote an understanding of the comprehensive mechanisms. In this Perspective, we highlight the current progress in the rational design and fabrication of stimuli-responsive proton-conducting MOFs and their applications. The dynamic structural change of proton transfer pathways and the role of trigger molecules are discussed to elucidate the stimuli-responsive mechanisms. Subsequently, we also discuss the challenges and propose new research opportunities for further development.

Ion-Exchanged UPG-1 as Potential Electrolyte for Fuel Cells

Proton-exchange membrane fuel cells are an attractive green technology for energy production. However, one of their major drawbacks is instability of the electrolytes under working conditions (i.e., temperature and humidity). Some metal-organic frameworks (MOFs) have recently emerged as promising alternative electrolyte materials because of their higher stability (compared with the organic polymers currently used as electrolytes), proton conductivity, and outstanding porosity and versatility. Here, we present ionic exchange in a microporous zirconium phosphonate, UPG-1, as an efficient strategy to enhance its conductivity and cyclability. Thus, labile protons of the hybrid structure were successfully replaced by different alkali cations (Li⁺, Na⁺, and K⁺), leading to 2 orders of magnitude higher proton conductivity than the pristine UPG-1 (up to 2.3 × 10^-2 S·cm^-1, which is comparable with those of the commercial electrolytes). Further, the proton conductivity was strongly influenced by the MOF hydrophilicity and the polarization strength of the cation, as suggested by molecular simulation. Finally, a mixed-matrix membrane containing the best-performing material (the potassium-exchanged one) was successfully prepared, showing moderate proton conductivity (up to 8.51 × 10^-3 S·cm^-1).