Birnessite-type MnO 2 , as a promising and attractive cathode material for rechargeable aqueous zinc-ion batteries, is plagued by grievously poor cycling stability and rate performance, mainly attributed to structural collapse of MnO 2 and slow Zn 2+ diffusion kinetics. Herein, the Cu/Bi dual ions pre-intercalated birnessite-type MnO 2 was fabricated by one-step hydrothermal method . It is validated by theoretical calculation in conjunction with experimentation that the Cu/Bi ions tends to occupy L1 sites, which not only can accelerate Zn 2+ diffusion kinetics owing to the low the Zn 2+ diffusion energy barrier, but also can stabilize the structure of MnO 2 host due to the formation of chemical bonds between the pre-intercalated Cu/Bi ions and oxygen atoms. Consequently, the CBMO cathode displays a high discharge capacity of 412.3 mAh/g at 0.1 A/g and distinguished cycling stability at 3 A/g after 1000 cycles with only approximately 0.0042 % capacity fading per cycle, which will be a strong competitive cathode material for developing stable and high-performance rechargeable aqueous zinc-ion batteries.
The water solubility of antibiotics and their salts affect their environmental behavior. However, the influence of moisture on their interfacial transformation on mineral surfaces remain poorly understood. This study investigates the transformation of sulfonamide and macrolide antibiotics, along with their sodium salts, mediated by Fe(III)-exchanged birnessite (Fe(III)δ-MnO₂) under low moisture condition, with a focus on the critical roles of interfacial processes and moisture. Fe(III) exchange significantly enhanced the transformation rate constant ( k ) of sulfadiazine (SDZ) by 5.96-fold from 0.0100 to 0.0596 min⁻¹. Antibiotics transformation by δ-MnO₂ was inhibited as water content (WC) increased ( k for SDZ decreased from 0.0100 min⁻¹ at 6.1% WC 0.0013 min⁻¹ at 60% WC. In contrast, the transformation of antibiotic salts was less inhibited by moisture. Notably, k values for sulfadiazine sodium salt (SDZ-Na) were increased from 0.0086 to 0.0100 min⁻¹ as WC rose from 6.1% to 60%). Fe(III) exchange markedly reduced the sensitivity of antibiotic transformation to moisture. For 0.1Fe(III)δ-MnO₂, k value for SDZ at 60% WC (0.0554 min⁻¹) showed no significant difference from that under dry conditions (0.0596 min⁻¹)). The alteration of the mineral-water-pollutant interface by Fe(III) was demonstrated through experimental and theoretical calculations. HAADF-STEM and XRD revealed that water molecules competed with antibiotic molecules for binding sites on δ-MnO₂. Fe(III) not only expanded the mineral's interlayer spacing but also acted as a bridge, forming strong connections with the antibiotic and their salts. Meanwhile, Fe(III)-δ-MnO 2 characterization suggested that Fe(III) increased specific surface area, surface acid-site density, redox activity, and free radical (•OH and O 2 •− ) yield. Product identification suggested that antibiotics were transformed into less toxic molecules via non-radical/radical pathways. This work provides a mechanistic insight into the role of exchangeable Fe(III), forming a basis for designing remediation materials effective across a range of water content.
ABSTRACT Structural unsteadiness and limited electrochemical kinetics upon cycling seriously impede further applications of birnessite cathodes for rechargeable aqueous zinc‑ion batteries (ZIBs), even though they have high voltage platforms and distinctively layered structures for preferable (de)intercalation of zinc ions. Herein, yolk-shell structured K-birnessite (K 0.48 Mn 2 O 4 ·0.49H 2 O)@mesoporous carbon nanospheres (KMOH@C) with rich oxygen vacancies are synthesized for the first time with a two-step diffusion-driven strategy of hydrothermal synthesis followed by etching with KOH. The transport of reaction ions is regulated by surface charge and pore structure of the carbon shells, thus K-birnessite is preciously transferred into the hollow mesoporous carbon (HMC) nanospheres. Furthermore, the etching effect of KOH and the confinement effect of HMC nanospheres generate intercalated K + and abundant oxygen vacancies into KMOH, leading to an excellent electrochemical kinetics. Meanwhile, HMC nanospheres also endow rapid electron/ion transport and stabilize the crystal structure of K-birnessite. Therefore, KMOH@C exhibits superior electrochemical performances with high reversible capacities of 412.7 and 122.2 mA h g ‒1 at 0.5 and 10.0 A g ‒1 than reported cathodes, respectively. Moreover, an exceptional cyclability of 129.6 mA h g ‒1 even after 6000 cycles at 3.0 A g ‒1 is achieved, making the KMOH@C cathode highly competitive for eco-friendly aqueous ZIBs.
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