Khachatryan Lavrent, Rezk Marwan Y, Nde Divine, Hasan Farhana, Lomnicki Slawomir, Boldor Dorin, Cook Robert, Sprunger Phillip, Hall Randall, Cormier Stephania
Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, United States.
Department of Engineering Science, Biological Engineering, Louisiana State University, Baton Rouge, Louisiana 70803, United States.
ACS Omega. 2024 Feb 13;9(8):9226-9235. doi: 10.1021/acsomega.3c08271. eCollection 2024 Feb 27.
The present research is primarily focused on investigating the characteristics of environmentally persistent free radicals (EPFRs) generated from commonly recognized aromatic precursors, namely, 1,2-dichlorobenzene (DCB) and 2-monochlorophenol (MCP), within controlled laboratory conditions at a temperature of 230 °C, termed as DCB230 and MCP230 EPFRs, respectively. An intriguing observation has emerged during the creation of EPFRs from MCP and DCB utilizing a catalyst 5% CuO/SiO, which was prepared through various methods. A previously proposed mechanism, advanced by Dellinger and colleagues (a conventional model), postulated a positive correlation between the degree of hydroxylation on the catalyst's surface (higher hydroxylated, HH and less hydroxylated, LH) and the anticipated EPFR yields. In the present study, this correlation was specifically confirmed for the DCB precursor. Particularly, it was observed that increasing the degree of hydroxylation at the catalyst's surface resulted in a greater yield of EPFRs for DCB230. The unexpected finding was the indifferent behavior of MCP230 EPFRs to the surface morphology of the catalyst, i.e., no matter whether copper oxide nanoparticles are distributed densely, sparsely, or completely agglomerated. The yields of MCP230 EPFRs remained consistent regardless of the catalyst type or preparation protocol. Although current experimental results confirm the early model for the generation of DCB EPFRs (i.e., the higher the hydroxylation is, the higher the yield of EPFRs), it is of utmost importance to closely explore the heterogeneous alternative mechanism(s) responsible for generating MCP230 EPFRs, which may run parallel to the conventional model. In this study, detailed spectral analysis was conducted using the EPR technique to examine the nature of DCB230 EPFRs and the aging phenomenon of DCB230 EPFRs while they exist as surface-bound -semiquinone radicals (-SQ) on copper sites. Various aspects concerning bound radicals were explored, including the hydrogen-bonding tendencies of -semiquinone (-SQ) radicals, the potential reversibility of hydroxylation processes occurring on the catalyst's surface, and the analysis of selected EPR spectra using EasySpin MATLAB. Furthermore, alternative routes for EPFR generation were thoroughly discussed and compared with the conventional model.
本研究主要聚焦于在230℃的可控实验室条件下，研究由公认的芳香族前体，即1,2 - 二氯苯（DCB）和2 - 一氯苯酚（MCP）产生的环境持久性自由基（EPFRs）的特性，分别称为DCB230和MCP230 EPFRs。在利用通过各种方法制备的5% CuO/SiO催化剂由MCP和DCB生成EPFRs的过程中出现了一个有趣的现象。Dellinger及其同事先前提出的一种机制（传统模型）假定催化剂表面的羟基化程度（高羟基化，HH和低羟基化，LH）与预期的EPFR产率之间存在正相关。在本研究中，这种相关性在DCB前体中得到了具体证实。特别是，观察到催化剂表面羟基化程度的增加导致DCB230的EPFR产率更高。意外的发现是MCP230 EPFRs对催化剂的表面形态无差异行为，即无论氧化铜纳米颗粒是密集分布、稀疏分布还是完全团聚。无论催化剂类型或制备方案如何，MCP230 EPFRs的产率都保持一致。尽管目前的实验结果证实了DCB EPFRs生成的早期模型（即羟基化程度越高，EPFRs产率越高），但密切探索负责生成MCP230 EPFRs的非均相替代机制至关重要，这些机制可能与传统模型并行。在本研究中，使用电子顺磁共振（EPR）技术进行了详细的光谱分析，以检查DCB230 EPFRs的性质以及DCB230 EPFRs作为铜位点上表面结合的 -半醌自由基（-SQ）存在时的老化现象。探索了与结合自由基有关的各个方面，包括 -半醌（-SQ）自由基的氢键倾向、催化剂表面发生的羟基化过程潜在可逆性以及使用EasySpin MATLAB对选定的EPR光谱进行分析。此外，还彻底讨论了EPFR生成的替代途径并与传统模型进行了比较。
