Nanopatterned Electroactive Polylactic Acid Nanofibrous MOFilters for Efficient PM0.3 Filtration and Bacterial Inhibition.

Biodegradable polylactic acid (PLA) nanofibrous membranes (NFMs) hold great potential to address the increasing airborne particulate matter (PM) and dramatic accumulation of plastic/microplastic pollution. However, the field of PLA NFM-based filters is still in its infancy, frequently dwarfed by the bottlenecks regarding relatively low surface activity, poor electroactivity, and insufficient PM capturing mechanisms. This effort discloses a microwave-assisted approach to minute-level synthesis of dielectric ZIF-8 nanocrystals with high specific surface area (over 1012 m2/g) and ultrasmall size (∼240 nm), which were intimately anchored onto PLA nanofibers (PLA@ZIF-8) by a combined "electrospinning-electrospray" strategy. This endowed the PLA@ZIF-8 NFMs with largely increased electroactivity in terms of elevated dielectric coefficient (an increase of 202%), surface potential (up to 5.8 kV), and triboelectric properties (output voltage of 30.8 V at 10 N, 0.5 Hz). Given the profound control over morphology and electroactivity, the PLA@ZIF-8 NFMs exhibited efficient filtration of PM0.3 (97.1%, 85 L/min) with a decreased air resistance (592.5 Pa), surpassing that of the pure PLA counterpart (88.4%, 650.9 Pa). This was essentially ascribed to realization of multiple filtration mechanisms for PLA@ZIF-8 NFMs, including enhanced physical interception, polar interactions, and electrostatic adsorption, and the unique self-charging function triggered by airflow vibrations. Moreover, perfect antibacterial performance was achieved for PLA@ZIF-8, showing ultrahigh inhibition rates of 99.9 and 100% against E. coli and S. aureus, respectively. The proposed hierarchical structuring strategy, offering the multifunction integration unattainable with conventional methods, may facilitate the development of biodegradable long-term air filters.

Electroactive, Antibacterial, and Biodegradable Poly(lactic acid) Nanofibrous Air Filters for Healthcare.

Poly(lactic acid) (PLA)-based nanofibrous membranes (NFMs) hold great potential in the field of biodegradable filters for air purification but are largely limited by the relatively low electret properties and high susceptibility to bacteria. Herein, we disclosed a facile approach to the fabrication of electroactive and antibacterial PLA NFMs impregnated with a highly dielectric photocatalyst. In particular, the microwave-assisted doping (MAD) protocol was employed to yield Zn-doped titanium dioxide (Zn-TIO), featuring the well-defined anatase phase, a uniform size of ∼65 nm, and decreased band gap (3.0 eV). The incorporation of Zn-TIO (2, 6, and 10 wt %) into PLA gave rise to a significant refinement of the electrospun nanofibers, decreasing from the highest diameter of 581 nm for pure PLA to the lowest value of 264 nm. More importantly, dramatical improvements in the dielectric constants, surface potential, and electret properties were simultaneously achieved for the composite NFMs, as exemplified by a nearly 94% increase in surface potential for 3-day-aged PLA/Zn-TIO (90/10) compared with that of pure PLA. The well regulation of morphological features and promotion of electroactivity contributed to a distinct increase in the air filtration performance, as demonstrated by 98.7% filtration of PM0.3 with the highest quality factor of 0.032 Pa-1 at the airflow velocity of 32 L/min for PLA/Zn-TIO (94/6), largely surpassing pure PLA (89.4%, 0.011 Pa-1). Benefiting from the effective generation of reactive radicals and gradual release of Zn2+ by Zn-TIO, the electroactive PLA NFMs were ready to profoundly inactivate Escherichia coli and Staphylococcus epidermidis. The exceptional combination of remarkable electret properties and excellent antibacterial performance makes the PLA membrane filters promising for healthcare.

Enhanced elemental mercury removal in coal-fired flue gas by modified algal waste-derived biochar: Performance and mechanism.

A novel biochar involving pyrolysis of dewatered algal waste combined with KOH and residual FeCl3 co-activation was synthesized as an efficient sorbent specifically for Hg0 removal from coal-fired flue gas. It was found that the SBET of biochar co-activated by KOH and FeCl3 (BCFK) was 195.82 m2 g-1, much higher than that of single FeCl3 activated biochar (BCF) of 133.38 m2 g-1 and un-activated biochar (UBC) of 20.36 m2 g-1. Furthermore, BCFK exhibited higher magnetization characteristics as well as elemental Fe and Cl contents of 2.71% and 10.33%, respectively, based on the combined characterization of XPS and VSM, etc., which is a jump of about 10-fold compared to BCF. This allows BCFK to show the best Hg0 removal capability of 689.66 µg g-1 under the inlet Hg0 concentration of 100 µg m-3 and 150 °C, according to pseudo-second-order kinetic model. Further analysis by XPS and Hg-TPD (Temperature Programmed Desorption) revealed that oxidation by Cl∗ radicals and C-Cl as well as weak chemisorption contributed to the removal of Hg0. Eventually, this efficient, simply prepared, low-cost and easily separable biochar distinguished itself in comparison to other materials. This will undoubtedly promote the valorization of algae and provide a reliable alternative material for the treatment of coal-fired flue gas.

UV-protective and high-transparency poly(lactic acid) biocomposites for ecofriendly packaging of perishable fruits.

The past decades have witnessed the archetypal shift from petroleum-based to bioplastics including poly(lactic acid) (PLA) for multifunctional packaging. Here we disclose a microwave-assisted functionalization (MAF) approach to functionalize wood fibers (FWFs) at minute level and high yields (approaching 99 %), conferring high affinity to PLA matrix and significant promotion of mechanical properties. By incorporating of 10 wt% FWFs, the tensile strength and toughness of PLA composite films were elevated to 54.5 MPa and 1.6 MJ/m3, increasing nearly 28 % and over 45 % compared to those of the counterpart loaded pristine wood fibers (PWFs), respectively. It is of significance to note the FWF-enabled unique optical properties for PLA, as exemplified by approximately 100 % UV-blocking ratio (UVR) in the whole UV region with the addition of 20 wt% FWFs. By contrast, the UVR values of PWF-filled PLA (5 %-20 %) gradually decreased as the fiber contents increased, mainly ascribed to the UV reflection at the poorly bonded interfaces and relatively inferior functionality of PWFs. This distinction allowed us to fabricate UV-barrier packaging for preservation of fresh fruits, which were perishable under the UV light of sunshine. The impressive mechanical robustness and high UVR, may prompt affordable and ecofriendly PLA/FWF composites appropriate for packaging.

High-heat and UV-barrier poly(lactic acid) by microwave-assisted functionalization of waste natural fibers.

The application of poly(lactic acid) (PLA) in the packaging area is frequently dwarfed by the inadequate gas/water barrier properties, low heat resistance and high UV transmittance. Herein, an environmentally friendly and high-efficiency microwave-assisted functionalization (MAF) approach was proposed to aqueous grafting waste bamboo fibers with the bridging agent. It permitted significant promotion of interfacial interactions between the MAF bamboo fibers (MAFBs) and neighboring PLA chains, contributing to uniform dispersion and intimate interphase. Featuring the morphological features, the MAFB-reinforced (5, 10 and 20 wt%) PLA biocomposites achieved an unexpected combination of high mechanical properties, exceptional resistance to heat deflection and UV irradiation, and excellent water barrier performance. Upon addition of only 5 wt% MAFBs, the tensile strength and toughness of PLA composite films were increased to 46.5 MPa and 0.6 MJ/m3, increasing over 52 % and nearly 107 % compared to those of the counterpart loaded pristine bamboo fibers (PBFs), respectively. This was favorably accompanied by the remarkably reduced water vapor permeability, falling down to the lowest value of 3.5 × 10-11 g∙m/Pa∙s∙m2 for PLA/MAFB (80/20) with a decrease of nearly 79 % compared to the counterpart. It is of interest to note the MAFB-enabled nearly 100 % UV-blocking ratio for PLA loaded 10 and 20 wt% fibers, as well as excellent resistance to heat deflection even at high temperatures like 120 °C. This effort paves the way to multifunctional natural fibers with high affinity to PLA for elegant implementation of high-heat and UV-resistant packaging materials in an ecofriendly manner.

Pea pod-mimicking hydroxyapatite nanowhisker-reinforced poly(lactic acid) composites with bone-like strength.

The anisotropic hierarchical structures of naturally derived materials have offered useful design principles for the fabrication of high-strength and functional materials. Herein, we unraveled a structure-by-bionics approach to construction of pea pod-mimicking architecture for poly(lactic acid) (PLA) composites impregnated with hydroxyapatite nanowhiskers (HANWs). The HANWs (length of 80-120 nm, diameter of ~30 nm) were customized using microwave-assisted aqueous biomineralization at minute level, which were incorporated into PLA microfibers by electrospinning with filler loadings of 10-30 wt%. The membranes comprising HANW-modified PLA microfibers were stacked and structured into composite films, strategically involving high-pressure compression at a relatively low temperature to impart the confined structuring mechanisms. It thus allowed partial melting and thinning of PLA microfibers into nanofibers, onto which the discrete HANWs were tightly adhered and embedded, showing distinguished architectural configurations identical with pea pod. More importantly, the mechanical properties and bioactivity were remarkably promoted, as demonstrated by the increments of over 54 % and nearly 72 % for the yield strength and elastic modulus (71.6 and 2547 MPa) of the structured composite loaded 30 wt% HANWs compared to those of pure PLA (46.4 and 1484 MPa), as accompanied by significant improvements in the bioactivity to nucleate and create apatite entities in mineral solution. The unusual combination of excellent biological characteristics and bone-like mechanical elasticity and extensibility make the structured PLA composites promising for guided bone/tissue regeneration therapy.