Synergistic Enhancement of Filtering Efficiency and Antibacterial Performance of a Nanofiber Air Filter Decorated with Electropolarized Lithium-Doped ZnO Nanorods.

According to clinical case reports, bacterial co-infection with COVID-19 can significantly increase mortality, with Staphylococcus aureus (S. aureus) being one of the most common pathogens causing complications such as pneumonia. Thus, during the pandemic, research on imparting air filters with antibacterial properties was actively initiated, and several antibacterial agents were investigated. However, air filters with inorganic nanostructures on organic nanofibers (NFs) have not been investigated extensively. This study aimed to demonstrate the efficiency of electropolarized poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) NFs decorated with Li-doped ZnO nanorods (NRs) to improve the filtering ability and antibacterial activity of the ultrathin air filter. The surfactant was loaded onto the ZnO─known for its biocompatibility and low toxicity─nanoparticles (NPs) and transferred to the outer surface of the NFs, where Li-doped ZnO NRs were grown. The Li-doped ZnO NR-decorated NF effectively enhanced the physical filtration efficiency and antibacterial properties. Additionally, by exploiting the ferroelectric properties of Li-doped ZnO NRs and PVDF-TrFE NFs, the filter was electropolarized to increase its Coulombic interaction with PMs and S. aureus. As a result, the filter exhibited a 90% PM1.0 removal efficiency and a 99.5% sterilization rate against S. aureus. The method proposed in this study provides an effective route for simultaneously improving the air filter performance and antibacterial activity.

Enhanced Output Performance of a Flexible Piezoelectric Nanogenerator Realized by Lithium-Doped Zinc Oxide Nanowires Decorated on MXene.

A flexible piezoelectric composite is composed of a polymer matrix and piezoelectric ceramic fillers to achieve good mechanical flexibility and processability. The overall piezoelectric performance of a composite is largely determined by the piezoelectric filler inside. Thus, different dispersion methods and additives that can promote the dispersion of piezoelectric ceramics and optimal composite structures have been actively investigated. However, relatively few attempts have been made to develop a filler that can effectively contribute to the performance enhancement of piezoelectric devices. In the present work, we introduce the fabrication and performance of the composite piezoelectric devices composed of Li-doped ZnO nanowires (Li: ZnO NWs) grown on the surface of MXene (Ti3C2) via the hydrothermal process. Through this approach, a semiconductor-metal hybrid structure is formed, increasing the overall permittivity. Moreover, the Ti3C2 layer can serve as a local ground in the composite so that the ferroelectric phase-transformed Li: ZnO NWs grown on its surface can be more effectively polarized during the poling process. In addition, the NW-covered surface of Ti3C2 prevents the aggregation of metallic Ti3C2 particles, promoting a more uniform electric field distribution during the poling process. As a result, the output performance of the piezoelectric nanogenerator (PENG) fabricated with a Li: ZnO NW/Ti3C2 composite was greatly improved compared to that of the devices fabricated with Li: ZnO NWs without the Ti3C2 platform. Specifically, the Li: ZnO NW/Ti3C2 composite piezoelectric nanogenerator (PENG) demonstrated a twofold higher output power density (∼9 µW/cm2) compared with the values obtained from the PENG devices based on Li: ZnO NWs. The approach introduced in this work can be easily adopted for an effective ferroelectric filler design to improve the output performance of the piezoelectric composite.

Enhanced Piezoelectric Output Performance of the SnS2/SnS Heterostructure Thin-Film Piezoelectric Nanogenerator Realized by Atomic Layer Deposition.

Recently, the inherent piezoelectric properties of the 2D transition-metal dichalcogenides (TMDs) tin monosulfide (SnS) and tin disulfide (SnS2) have attracted much attention. Thus the piezoelectricity of these materials has been theoretically and experimentally investigated for energy-harvesting devices. However, the piezoelectric output performance of the SnS2- or SnS-based 2D thin film piezoelectric nanogenerator (PENG) is still relatively low, and the fabrication process is not suitable for practical applications. Here we report the formation of the SnS2/SnS heterostructure thin film for the enhanced output performance of a PENG using atomic layer deposition (ALD). The piezoelectric response of the heterostructure thin film was increased by ∼40% compared with that of the SnS2 thin film, attributed to large band offset induced by the heterojunction formation. Consequently, the output voltage and current density of the heterostructure PENG were 60 mV and 11.4 nA/cm2 at 0.6% tensile strain, respectively. In addition, thickness-controllable large-area uniform thin-film deposition via ALD ensures that the reproducible output performance is achieved and that the output density can be lithographically adjusted depending on the applications. Therefore, the SnS2/SnS heterostructure PENG fabricated in this work can be employed to develop a flexible energy-harvesting device or an attachable self-powered sensor for monitoring pulse and human body movement.