亚微米级单分散的密胺树脂微球及其氮掺杂炭微球的制备

Preparation of submicron monodisperse melamine resin microspheres and nitrogen-doped carbon microspheres derived from them

亚微米单分散三聚氰胺树脂微球和氮掺杂碳微球的可控制备仍是当今材料领域的一个重要课题。在不添加任何表面活性剂的情况下,仅使用适量的乙酸作为催化剂制备了最小粒径为200纳米的单分散MF微球,这比已报道的强酸制备的MF微球都要小。此外,随着搅拌时间的增加(0~48 h),MF微球的D50并不是简单地增加然后保持稳定,而是进一步下降,再次稳定,最后稳定后的粒径相比最大粒径发生明显收缩,收缩率约40%。在适当的热处理条件下,尤其是将物料均匀地薄薄地铺开,可以得到相应的单分散氮掺杂碳微球,其在800℃下的收缩率为81%~65%,收缩率与搅拌时间有关。最后,从分子形成的角度讨论了MF树脂微球和氮掺杂碳微球形成过程中的上述现象和规律。

Melamine-formaldehyde( MF) microspheres were prepared using acetic acid as the catalyst without aid of any surfactant,and were carbonized to obtain nitrogen-doped carbon microspheres. The effects on the microstructure of stirring time,acid amount and thickness of the layer of MF spheres spread in the crucible during carbonization,and the particle size and distribution of the MF and carbon microspheres were investigated by SEM,TEM,FTIR,TGA,XPS,nitrogen adsorption and elemental analysis.Results indicated that by increasing the stirring time from 1 min to 48 h,the median particle size of the MF microspheres increased rapidly in the first 10 min from 0. 6 to 1. 6 μm,levelled off from 1. 6 to 1. 7 μm betw een 10 and 120 min,then decreased slow ly to1. 055 μm from 120 min to 24 h and then levelled off again from 1. 055 to 1. 047 μm betw een 24 and 48 h. The particle size became narrow er and the surface smoother with increasing stirring time. Increasing the amount of acetic acid reduced the particle size,but broadened the size distribution and led to particle aggregation. The thermal stability and carbonization yield increased and the particle shrinkage during carbonization decreased with stirring time since the molecular weight of the polymers that formed the MF microspheres increased with stirring time. The carbonized samples produced using a thin spread layer have better sphericity and monodispersion than those from a thick and dense spread layer. Severe particle aggregation was found regardless of the carbonization temperature in the latter case. The carbon microspheres had low er nitrogen and oxygen,but higher carbon,contents with a longer stirring time,and nitrogen atoms were in the form of pyridinic N( N-6),pyrrolic-N( N-5) and quaternary-N/graphitic-N( N-4) nitrogen.The carbon microspheres had an inverse core-shell structure with a mesoporous shell and a dense carbon core.