Finding of coal organic microspheres during hydrothermal treatment of brown coal

- A series of organic microspheres are produced from brown coal by hydrothermal method.
- Coal organic microspheres can be directly obtained from difference brown coals.
- These microspheres have the diameter of 0.2-3.8 μm and carbon yields above 29%.
- Some microspheres contained holes, indicating their potential role as microcapsules.
- Using these microspheres as the template, ZnO hollow microspheres are synthesized.

Solid wastes or extracts directly obtained from brown coals by a single hydrothermal treatment were found to be composed of a series of novel coal organic microspheres (COM). Treatment using a flow of water at 350 °C and 20 MPa for 90 min produced COM from three brown coals with carbon yields above 29% and diameters ranging of 0.2-3.8 μm. The spherical morphology of COM changes slightly with different resources, and some microcapsules were observed in all three COM samples. A recycling experiment on COM indicates their potential application as carriers and/or supporters after modification. Through comparison, it is demonstrated that COM differ completely from carbonaceous microspheres or hydrochars obtained from hydrothermal carbonization of carbohydrates, both in mechanism and starting materials. In addition, considering COM as a template, zinc oxide hollow microspheres were synthesized successfully. These results indicate that a series of new substitutes with stable supply are provided to organic microspheres, and a waste or by-product of through the hydrothermal treatment of brown coal is transformed to a valuable advanced material. Given their uniform morphology, high yields, and availability from a variety of low-cost natural resources with worldwide abundance, COM are expected to play a major role in chemical and materials science applications.