Self-assembling natural drug hydrogels formed without structural modification and able to act as carriers are of interest for biomedical applications. A lack of knowledge about natural drug gels limits there current application. Here, we report on rhein, a herbal natural product, which is directly self-assembled into hydrogels through noncovalent interactions. This hydrogel shows excellent stability, sustained release and reversible stimuli-responses. The hydrogel consists of a three-dimensional nanofiber network that prevents premature degradation. Moreover, it easily enters cells and binds to toll-like receptor 4. This enables rhein hydrogels to significantly dephosphorylate IκBα, inhibiting the nuclear translocation of p65 at the NFκB signalling pathway in lipopolysaccharide-induced BV2 microglia. Subsequently, rhein hydrogels alleviate neuroinflammation with a long-lasting effect and little cytotoxicity compared to the equivalent free-drug in vitro. This study highlights a direct self-assembly hydrogel from natural small molecule as a promising neuroinflammatory therapy.

This paper demonstrates a rational protocol for the synthesis of ultrasmall bimetallic alloy nanoparticles (FeCo, FeNi, and NiCo; <4 nm) anchored on biomass-processed porous N–carbon as oxygen electrocatalysts via a micro–mesopore confinement synthetic strategy. Among them, a representative catalyst, termed FeCo–NC_ps, possesses highly active M–N_x–C sites, a superhigh specific surface area and a structure with abundant defects, displaying excellent bifunctional performance in both ORR and OER in 0.1 M KOH. Furthermore, a home-made rechargeable Zn–air battery was constructed using FeCo–NC_ps as the air cathode, delivering an excellent energy conversion efficiency (with an extremely high energy density of 922 W h kg⁻¹ at 10 mA cm⁻²). This work not only provides a scalable and sustainable method to produce low-cost and highly efficient ORR/OER catalysts, but also highlights the great value of the rational design of biomass-derived nanocarbons for advanced energy materials.

Iron single atom catalysts have emerged as one of the most active electrocatalysts towards the oxygen reduction reaction (ORR), but the unsatisfactory durability and limited activity for the oxygen evolution reaction (OER) has hampered their commercial applications in rechargeable metal–air batteries. By contrast, cobalt-based catalysts are known to afford excellent ORR stability and OER activity, due to the weak Fenton reaction and low OER Gibbs free energy. Herein, a bimetal hydrogel template is used to prepare carbon aerogels containing Fe–Co bimetal sites (NCAG/Fe–Co) as bifunctional electrocatalysts towards both ORR and OER, with enhanced activity and stability, as compared to the monometal counterparts. High-resolution transmission electron microscopy, elemental mapping and X-ray photoelectron spectroscopy measurements demonstrate homogeneous distributions of the metal centers within defected carbon lattices by coordination to nitrogen dopants. X-ray absorption spectroscopic measurements, in combination with other results, suggest the formation of FeN₃ and CoN₃ moieties on mutually orthogonal planes with a direct Fe–Co bonding interaction. Electrochemical measurements show that NCAG/Fe–Co delivers a small ORR/OER potential gap of only 0.64 V at the current density of 10 mA cm⁻², 60 mV lower than that (0.70 V) with commercial Pt/C and RuO₂ catalysts. When applied in a flexible Zn–air battery, the dual-metal NCAG/Fe–Co catalyst also shows a remarkable performance, with a high open-circuit voltage of 1.47 V, a maximum power density of 117 mW cm⁻², as well as good rechargeability and flexibility. Results from this study may offer an ingenious protocol in the design and engineering of highly efficient and durable bifunctional electrocatalysts based on dual metal-doped carbons.