ABSTRACT
Robust antimicrobial coatings featuring high transparency, strong bactericidal activity, and an easy application procedure on generic surfaces can be widely accepted by the public to prevent pandemics. In this work, we demonstrated the hand-sprayer-based approach to deposit complex oxide coatings composed of Co-Mn-Cu-Zn-Ag on screen protectors of smartphones through acidic redox-assisted deposition (ARD). The as-obtained coatings possess high transparency (99.74% transmittance at 550 nm) and long-lasting durability against swiping (for 135 days of average use) or wet cleaning (for a routine of 3 times/day for 33 days). The spray coating enabling 3.14% Escherichia coli viability can further be reduced to 0.21% through a consistent elemental composition achieved via the immersion method. The high intake of Cu2+ in the coating is majorly responsible for the bactericidal activity, and the presence of Ag+ and Zn2+ is necessary to achieve almost complete eradication. The success of extending the bactericidal coatings on other typical hand-touched surfaces (e.g., stainless steel railings, rubber handrails, and plastic switches) in public areas has been demonstrated.
Subject(s)
Anti-Bacterial Agents , Anti-Infective Agents , Anti-Bacterial Agents/pharmacology , Stainless Steel , Escherichia coli , OxidesABSTRACT
Mass-transport acceleration is essential toward enhanced electrocatalytic performance yet rarely recognized under irradiation, because light is usually reported to improve charge transfer. We studied laser-enhanced mass transport through the heterojunction between Ag and semiconductor Fe2O3 situated on graphene for oxygen reduction reaction. Because of the decreased mass-transport resistance by 59% under 405 nm laser irradiation, the current density can be enhanced by 180%, which is also supported by a theoretical calculation. This laser-enhanced mass transport was attributed to local photothermal heating and the near-field local enhancement. Easier desorption of OH- species occurring between the Fe and Ag centers under the laser accelerates the mass-transport centers.
ABSTRACT
Modern electronics continue to shrink down the sizes while becoming more and more powerful. To improve heat dissipation of electronics, fillers used in the semiconductor packaging process need to possess both high electrical and thermal conductivity. Graphene is known to improve thermal conductivity but suffers from van der Waals interactions and thus poor processibility. In this study, we wrapped silver microflakes with graphene sheets, which can enable intercoupling of phonon- and electron-based thermal transport, to improve the thermal conductivity. Using just 1.55 wt % graphene for wrapping can achieve a 2.64-times greater thermal diffusivity (equivalent to 254.196 ± 10.123 W/m·K) over pristine silver flakes. Graphene-wrapped silver flakes minimize the increase of electrical resistivity, which is one-order higher (1.4 × 10-3 Ω·cm) than the pristine flakes (5.7 × 10-4 Ω·cm). Trace contents of wrapped graphene (<1.55 wt %) were found to be enough to bridge the void between Ag flakes, and this enhances the thermal conductivity. Graphene loading at 3.76 wt % (beyond the threshold of 1.55 wt %) results in the significant graphene aggregation that decreases thermal diffusivity to as low as 16% of the pristine Ag filler. This work recognizes that suitable amounts of graphene wrapping can enhance heat dissipation, but too much graphene results in unwanted aggregation that hinders thermal conducting performance.
ABSTRACT
The microscopic homogeneity of mixed metals in a single-phase oxide is a critical issue in improving material performance. Aqueous alkaline precipitation is the most common approach but it has the limits of microscopic inhomogeneity because of intrinsically different precipitation rates between metal cations. Herein, we demonstrate a new preparation of uniformly structural substituted cobalt iron oxides via acidic redox-assisted precipitation (ARP) upon the interaction of CoII and K2FeO4. This low-pH synthesis features the redox process between Co and Fe, presumably through the formation of inner-sphere complexes such as [(H2O)5CoII-O-FeVIO3]. With the nucleation starting from such complexes, one obtains a product with predominantly mixed-metal Co-O-Fe moieties, which improves the electrical conductivity of the product. This work further analyzes how the properties of the product species evolve during the hydrothermal synthesis step in the ARP process. We see that the Co/Fe ratio slowly increases from about 1:1 to a final value of 2:1, but does not reach the expected redox stoichiometry of 3:1. At the same time, the magnetization also increases, reaching a value of 16.9 emu g-1 for the final superparamagnetic product, which is three times higher than the value of monometallic Co3O4 and Fe2O3. The cobalt iron oxide samples obtained from ARP also possess superior oxygen evolution activity (307 mV overpotential at 10 mA cm-2 µg-1) compared to a mixture of Co3O4 and Fe2O3 (422 mV) or pure cobalt oxide (350 mV), highlighting the structure-induced enhancement of the catalytic activity. The difficult synthesis of evenly blended trinary/quaternary metals in a single-oxide phase may become possible in the future via ARP.
ABSTRACT
We report a two-step hybridization of N-doped graphene and Ag-decorated Fe2O3 hematite to realize a balanced oxygen adsorption/desorption equilibrium and a laser-coupled ORR (LORR). The stable plateau currents with n values of 3.9 in a wide potential range (0.2-0.7 V) and 7.5% peroxide inhibition of the LORR are found to be directly associated with the Ag/Fe2O3 heterojunction, where interactions of semiconductor band gap excitation and plasmonic resonance-induced hot electrons are proposed to occur.
