Investigation of the nucleation and growth mechanism of gold nanoparticules at high temperature by in situ UV-vis spectroscopy and SAXS

Understanding the growth and stabilization mechanisms of gold nanoparticles is essential for developing more controlled synthetic routes. During synthesis, nanoparticle organization is influenced by the interaction between the reaction medium and stabilizing molecules. HEPES buffer has been used in gold nanoparticle synthesis due to its ability to act as both a reducing and stabilizing agent, promoting nucleation and preventing aggregate formation. However, the influence of HEPES at elevated temperatures, such as 40°C and 60°C, and its interaction with the nanoparticle growth process have not yet been fully elucidated. This behavior can be investigated using in situ techniques, such as UV-Vis and SAXS, allowing real-time monitoring of nanoparticle evolution throughout the reaction. A stabilization mechanism of gold nanoparticles in the presence of HEPES buffer has been hyphotised in which HEPES, acts both as a reducing agen as well as influences nanoparticle organization by interacting with their surface, regulating their stability and dispersion in the reaction medium. To investigate this hypothesis, previous UV-Vis and SAXS results will be complemented with new analyses. The objective is to monitor the formation of gold nanoparticles in the presence of HEPES buffer, evaluating its impact on the structural organization of the particles at different temperatures and reaction times. Additionally, the effect of 40, 50 and 60°C on stabilization dynamics and colloidal growth control will be explored, aiming to understand its role in nucleation and nanoparticle growth through time-resolved SAXS/WAXD analyses.

理解金纳米颗粒（gold nanoparticles）的生长与稳定机制，对于开发更可控的合成路径至关重要。合成过程中，纳米颗粒的聚集行为受反应介质与稳定化分子间的相互作用影响。HEPES缓冲液（HEPES buffer）已被应用于金纳米颗粒的合成，因其兼具还原剂与稳定剂的双重功能，可促进成核并抑制团聚体的形成。然而，HEPES在高温（如40℃与60℃）下的作用效果，及其与纳米颗粒生长过程的相互作用机制，尚未得到充分阐明。可借助紫外-可见分光光度法（UV-Vis）、小角X射线散射（SAXS）等原位实验技术，实现反应全程中金纳米颗粒演化过程的实时监测。此前已有研究提出金纳米颗粒在HEPES缓冲液体系中的稳定机制假说：HEPES既充当还原剂，又可通过与纳米颗粒表面相互作用调控其聚集行为，进而优化其在反应介质中的稳定性与分散性。为验证该假说，本研究将在已有紫外-可见分光光度法与小角X射线散射实验结果的基础上，补充开展全新的分析工作。本研究的核心目标为监测HEPES缓冲液体系中金纳米颗粒的形成过程，评估不同温度与反应时长对颗粒结构组织的影响。此外，还将探究40℃、50℃与60℃三个温度条件对胶体生长调控与稳定动力学的作用，通过时间分辨小角X射线散射/广角X射线衍射（SAXS/WAXD）分析，阐明其在成核与纳米颗粒生长过程中的具体功能。