Absolute humidity Population migration m 3 , and one city (Haikou) had the highest AH (14.05 g/m 3 ). Those 17 cities with 50 and more cases accounted for 90.6% of all cases in our study. Each 1°C increase in AT and DTR was related to the decline of daily confirmed case counts, and the corresponding pooled RRs were 0.80 (95% CI: 0.75, 0.85) and 0.90 (95% CI: 0.86, 0.95), respectively. For AH, the association with COVID-19 case counts were statistically significant in lag 07 and lag 014. In addition, we found the all these associations increased with accumulated time duration up to 14 days. In conclusions, meteorological factors play an independent role in the COVID-19 transmission after controlling population migration. Local weather condition with low temperature, mild diurnal temperature range and low humidity likely favor the transmission.

A superparamagnetic graphene oxide-Fe 3 O 4 hybrid composite (GO-Fe 3 O 4 ) was prepared via a simple and effective chemical method. Amino-functionalized Fe 3 O 4 (NH 2 -Fe 3 O 4 ) particles are firmly deposited on the graphene oxide sheets. The graphene oxide sheets could prevent NH 2 -Fe 3 O 4 particles from agglomeration and enable a good dispersion of these oxide particles. The as-prepared GO-Fe 3 O 4 hybrid composite had a much higher thermal stability than graphene oxide. The amount of NH 2 -Fe 3 O 4 loaded on GO was estimated to be 23.6 wt% by atomic absorption spectrometry. The specific saturation magnetization (M s ) of the GO-Fe 3 O 4 hybrid composite is 15 emu g À1 . The magnetic GO-Fe 3 O 4 composite has been employed as adsorbent for the magnetic separation of dye contaminants from water. The adsorption test of dyes (Methylene Blue (MB) and Neutral Red (NR)) demonstrates that it only takes 30 min for MB and 90 min for NR to attain equilibrium. The adsorption capacities for MB and NR in the concentration range studied are 167.2 and 171.3 mg g À1 , respectively. The GO-Fe 3 O 4 hybrid composite can be easily manipulated in magnetic field for desired separation, leading to the removal of dyes from polluted water. These GO-Fe 3 O 4 hybrid composites have great potential applications in removing organic dyes from polluted water.

Polymers are commonly used to fabricate triboelectric nanogenerators (TENGs). Here, several polymer films with similar main chains but different functional groups on the side chain are employed to clarify the contributions of each functional group to contact electrification (CE). The results show that the electron‐withdrawing (EW) ability and density of these functional groups on the main chain can determine both the polarity and density of CE‐induced surface charges. Similar results are obtained for CE in both the polymer–polymer and polymer–liquid modes. A theoretical mechanism involving electron cloud overlap is proposed to explain all of these results. More importantly, the unsaturated groups on poly(tetrafluoroethylene) molecular chain are proved to have a much stronger EW ability than the saturated groups. The density of these unsaturated groups can be increased using a sputtering technique, suggesting that this is a facile and effective method of enhancing the performance of TENGs. These results clarify the correlation between the molecular structure and macroscopic electrification behavior of polymers.

In this study, we present the synthesis of reduced graphene oxide/hydroxyapatite (RGO/HA) hybrid materials by an environmental-friendly route. Graphene oxide (GO) was first simultaneously reduced and surface functionalized by one-step oxidative polymerization of dopamine (PDA). The bioinspired surface was further used for biomimetic mineralization of hydroxyapatite. When incubated in a simulated body fluid (SBF), the PDA layer enabled efficient interaction between the RGO surface and the mineral ions to improve the bioactivity, promoted the formation of the HA nanoparticles. A detailed structural and morphological characterization of the mineralized composite was performed. The HA-based hybrid materials exhibited no cytotoxic effect on L929 fibroblast cells, showing potential capacity of being a scaffold material for bone tissue regeneration and implantation. This facile strategy also can be a useful platform for other RGO-based nanocomposites.