Rice husk extract, obtained using acid and alkali pretreatment extraction (AAPE), contains bioactive compounds and exhibits reducing abilities. Phenolic composition in rice husk extract was analyzed and the mechanism of silver nanoparticle (AgNP) biosynthesis by using AAPE rice husk extract was investigated in this study. Stable and spherically shaped AgNPs with a size of <15 nm were prepared under the following conditions: 0.001 M AgNO3, AAPE rice husk extract diluted 10 times, pH 10, and reacted at 25 °C for 60 min. Synergistic effects among phenolic acids contributed to the formation of AgNPs, with the acids acting as excellent reducing agents (owing to their abundant hydroxyl groups) and excellent dispersants (owing to their derived CO groups), which enhanced the NPs' stability. Caffeic acid (CA) was demonstrated to synthesize AgNPs independently and is suggested to be the most crucial compound for reducing Ag+ during the biosynthesis with rice husk extract. A possible mechanism and reaction process for the formation of AgNPs synthesized using CA in rice husk extracts is proposed.

中文翻译：

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稻壳提取物中酚酸作为还原剂和分散剂生物合成银纳米粒子

使用酸碱预处理提取 (AAPE) 获得的稻壳提取物含有生物活性化合物并具有还原能力。本研究分析了稻壳提取物中的酚类成分，并研究了利用AAPE稻壳提取物生物合成银纳米颗粒（AgNP）的机理。在以下条件下制备了尺寸 <15 nm 的稳定球形 AgNPs：0.001 M AgNO3，AAPE 稻壳提取物稀释 10 倍，pH 10，并在 25 °C 下反应 60 min。酚酸之间的协同作用促成了 AgNPs 的形成，其中酸作为优异的还原剂（由于其丰富的羟基）和优异的分散剂（由于其衍生的 CO 基团），增强了 NPs 的稳定性。咖啡酸 (CA) 被证明可以独立合成 AgNPs，并且被认为是在稻壳提取物生物合成过程中减少 Ag+ 的最关键化合物。提出了在稻壳提取物中使用 CA 合成的 AgNPs 形成的可能机制和反应过程。