Preparation of multi-element doped porous carbon by microwave cross-linking stabilization of disposable surgical masks and its electrochemical properties as sulfur loading

Numerous disposable surgical masks (DSMs) were consumed with the development of COVID-19 epidemic. Non-solid products recovered by pyrolysis is more than twenty species with low added value. Therefore, the search for a reasonable carbonization method can not only alleviate the pressure of global plastic pollution, but also produce considerable economic value. Here it is found that microwave cross-linking can promote the substitution of hydrogen atom in the polymer master chain of DSMs by hydrogen atom, which can reorganize the easily cracked DSMs into sp2-hybridized aromatic carbon, it can maintain 51.2% carbon yield at 1000℃. The difference between the DSMs-based porous carbon obtained by in-situ and post-processing N doping was further compared, and it was found that the specific surface area of the activated in-situ doped sample (P-SNO@DSMs) was as high as 2278 m2·g-1, which had rich hierarchical pore structure and high heteroatoms doping rate. Benefiting from the synergistic effect of heteroatoms and hierarchical holes, P-SNO@DSMs sulfur cathode delivers a high specific capacity of 1550 mAh·g-1 at 0.1C and exhibits excellent long-term cycling performance with the smaller capacity decay of 0.13% per cycle after 400 cycles. In this work, clean and efficient microwave cross-linking not only realized the efficient recovery of waste DSMs, but also the application of the prepared materials can be broadened by adding additional heteroatomic sources in the process of microwave cross-linking.

Self-activated pyrolytic synthesis of S, N and O co-doped porous carbon derived from discarded COVID-19 masks for lithium sulfur batteries

The continuous spread of COVID-19 has produced a large number of abandoned disposable medical masks (DMMs), which have a greater negative impact on the environment and biosafety. In response to this issue, a method for rapid microwave sulfonation, nitrification and oxidation of DMMs was proposed to convert DMMs with low carbonization efficiency into aromatic carbon with good thermal stability, which not only maintained 51 wt.% of initial mass at 1000 °C, but also achieved in situ co-doping of S, N and O. Subsequently, porous carbons derived from DMMs were synthesized by self-activation pyrolysis, which avoided consumption of alkali and metal salts in the traditional activation process. It was further found that low pyrolysis temperature was not enough to produce enough active material H2 and H2O to obtain high specific surface area, while increasing pyrolysis temperature could adjust the specific surface area of as-prepared carbon, ranging from 52 m2·g−1 to as high as 890 m2 g−1. Thanks to synergistic effect of S, N, and O co-doping and hierarchical porous structure, the first discharge specific capacity of sample synthesized by self-activated pyrolysis at 900 °C was 1459.8 mAh·g−1 at 0.1 C, and the discharge specific capacity retention at 0.5 C after 400 cycles was 52.3%.