单模微波水热控制合成PbS纳米晶

Single-Mode Microwave-Hydrothermal Controlling Synthesis of PbS Nanocrystals

以Pb(NO3)2、生物小分子L-半胱氨酸为原料,在室温下生成前驱体,然后采用单模微波水热法在150℃下反应1h,制备出四方形的PbS纳米晶,考察了Pb(NO3)2与L-半胱氨酸的物质的量比对产物形貌的影响。采用XRD和TEM对产物的结构和形貌进行了表征。结果表明,随着Pb2+与L-半胱氨酸的物质的量比增大,纳米PbS颗粒变小,四方形结构越来越明显。初步讨论了PbS纳米粒子的形成机理。形成机理可能为:首先L-半胱氨酸通过巯基直接和Pb2+结合形成白色前驱沉淀,然后该前驱沉淀在一定温度和时间内热分解形成四方形PbS纳米晶,增大L-半胱氨酸在前驱体中的比例,由于存在阻碍作用,导致PbS小晶粒不能快速聚集而结晶生长,而有利形成四方形的纳米PbS。

The precursor was synthesized by Pb （NO3）2 and L-Cysteine as materials at room tem- perature and reacted for 1 h at 150 ℃ by the single-mode microwave-hydrothermal method, then the square-shaped PbS nanocrystals were prepared. The influences of molar ratio of Pb （NO3）2 to L-Cysteine on the morphologies were studied. Structures and morphologies of as-prepared products were characterized by XRD and TEM. The results show that PbS nanocrystals become small and their square-shapes are more and more regular with the increased molar ratio of Pb2＋ and L-Cysteine. The formation mechanism of square-shaped PbS nanocrystals was briefly discussed. The formation mechanism may be as follows. First, the L-Cysteine with hydrosulfige group and Pb2 ＋ direct combined to form white premonitory precipitates. Second, the white premonitory precipitates undergo thermal decomposition at suitable temperature in a certain time to produce square-shaped PbS nanocrystals. The ratio of L-Cysteine in the premonitory precipitate is increased, which prevents the quick aggregation and crystallization growth of small PbS grains and will be favorable for the formation of the square-shaped PbS nanocrystals.