P2-type layered transition metal oxides are considered one of the ideal cathode materials for sodium ion batteries because of its high working voltage and excellent theoretical specific capacity. P2-Na 0.67 Ni 0.33 Mn 0.67 O 2 electrodes deliver a theoretical specific capacity of 173 mAh g -1 , which is dependent on Ni 2+ /Ni 3+ /Ni 4+ charge compensation. High operating voltage leads to higher specific capacity and energy density , which are better adapted to practical development needs, but at the same time it causes the material to undergo a destructive P2-O2 phase transition, which greatly affect cycle stability and Na + diffusion kinetics. In this study, we propose Zn 2+ doping and spherical morphology modification strategy. The spherical morphology not only reduces the distance of Na + diffusion and improves the rate performance, but also the spherical structure can alleviate the volume change during Na + intercalation/extraction. Furthermore, the doping of Zn 2+ changes the valence distribution of Mn, suppressing the phase transition at high voltage and further improving the cycling stability. At a high cut-off voltage of 4.4 V, the cathode material with Zn 2+ doping and spherical shaped possesses an average operating voltage of up to 3.6 V and exhibits 90% capacity retention after 30 cycles (compared to only 56% for the pristine material). Above that, the rate performance is also greatly improved, with the modified material contributing an excellent specific capacity of 95 mAh g -1 , even at a high current density of 5 C (1 C = 170 mA g -1 ).
Xiaoyang Xu,Nan Wang,Mingzhen Wu,Jie Wang,Dingqian Wang,Zhuoxin Chen,Jing Xie,Chunmei Ding,Jianshu Li
The domination of cariogenic bacteria in dental plaque biofilms is the primary cause of dental caries. In view of this, for the purpose of an effective treatment of dental caries, it is of great importance to inhibit the activity of acidogenic bacteria and promote the remineralization of damaged teeth simultaneously. However, the expensive antibacterial agents and poor mineralization ability of materials limit the practical applications. Biomineralization regulated by non-collagenous proteins (NCPs) gives hints to combine the remineralization ability of NCPs with accessible antibacterial property effectively. In this work, we propose a programmed antibacterial and remineralization strategy for the therapy of dental caries based on zinc-substituted hydroxyapatite/ alendronate-grafted polyacrylic acid hybrid nanoneedles (ZHA@ALN-PAA). This hybrid material dissolves in the acidic caries environment and regulate the pH to nearly neutral (6.5). Abundant calcium/ phosphate ions are supplemented and the ALN-PAA embedded in it has also been released, which assists the biomineralization on tooth defect. It has been revealed that the inhibition ratio of ZHA@ALN-PAA against Streptococcus mutans is the highest (11.25 folds that of HA), which originates from the highest zinc ions released (132.9 mg/L). Besides, the interspace of etched enamel is fully filled with regenerated nanorods and the surface microhardness (SMH) is significantly improved (3.68 folds that of etched enamel) after only 3 days of mineralization in vitro . This strategy developed here is simple and cost-effective, which can be referred to design the effective anti-caries materials applied for clinic treatment and daily oral care.
Florfenicol (FLO) is a broad-spectrum halogenated antibiotic (containing F and Cl atoms), and the discharged FLO in wastewater exhibits potential biotoxicity. Peroxymonosulfate (PMS) activation can generate reactive oxygen species (ROSs) to realize efficient degradation of organic pollutants. Herein, Zn-substituted Co 3 O 4 (Zn x Co) catalysts were prepared and applied in PMS activation for FLO degradation. The physicochemical properties were systematically studied by combining experiments and density functional theory (DFT) calculation. The Zn partial substitution induced electron rearrangement and promoted oxygen vacancy (OV) formation in Co 3 O 4 . Zn 0.03 Co catalyst exhibited superior FLO removal, achieving a higher reaction rate of 0.112 min −1 than Co 3 O 4 (0.053 min −1 ). The FLO degradation was highly dependent on the factors of PMS/Zn 0.03 Co/FLO dosage, temperature, initial pH, and coexisting inorganic anions. The Zn 0.03 Co also displayed outstanding performance in PMS activation for degradation of various typical organic pollutants. Electron paramagnetic resonance (EPR) spectra and quenching experiments indicated that both radical species ( · OH , SO 4 · - , and · O 2 - ) and nonradical species ( 1 O 2 ) contribute to FLO removal. The redox cycle of Co 3+ /Co 2+ and OVs played an essential role in PMS activation. The electron structure of FLO and parameters of PMS adsorbed on Zn x Co were calculated. The longer length of Co O and O O bonds for the adsorbed PMS could enhance its activation to generate ROSs. The intermediates were detected, and five degradation pathways were proposed. The acute and chronic toxicities of intermediates suggested that the dechlorination process is important for the toxicity attenuation of FLO. This study clarified the performance enhancement mechanism of Zn substitution on FLO degradation by PMS activation using Co 3 O 4 based catalyst, which favors the development of PMS-based advanced oxidation processes for wastewater treatment.
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