Moroni Marco, Nardo Luca, Maspero Angelo, Vesco Guglielmo, Lamperti Marco, Scapinello Luca, Vismara Rebecca, Navarro Jorge A R, Monticelli Damiano, Penoni Andrea, Mella Massimo, Galli Simona
Dipartimento di Scienza e Alta Tecnologia, Università degli Studi dell'Insubria, Via Valleggio 11, 22100 Como, Italy.
Departamento de Química Inorgánica, Universidad de Granada, Av. Fuentenueva S/N, 18071 Granada, Spain.
Chem Mater. 2023 Mar 22;35(7):2892-2903. doi: 10.1021/acs.chemmater.2c03801. eCollection 2023 Apr 11.
Mercury is one of the most toxic heavy metals. By virtue of its triple bond, the novel ligand 1,2-bis(1-pyrazol-4-yl)ethyne (HBPE) was expressly designed and synthesized to devise metal-organic frameworks (MOFs) exhibiting high chemical affinity for mercury. Two MOFs, Zn(BPE) and Zn(BPE)·DMF [interpenetrated i-Zn and noninterpenetrated ni-Zn·S, respectively; DMF = dimethylformamide], were isolated as microcrystalline powders. While i-Zn is stable in water for at least 15 days, its suspension in HgCl aqueous solutions prompts its conversion into HgCl@ni-Zn. A multitechnique approach allowed us to shed light onto the observed HgCl-triggered i-Zn-to-HgCl@ni-Zn transformation at the molecular level. Density functional theory calculations on model systems suggested that HgCl interacts via the mercury atom with the carbon-carbon triple bond exclusively in ni-Zn. Powder X-ray diffraction enabled us to quantify the extent of the i-Zn-to-HgCl@ni-Zn transition in 100-5000 ppm HgCl solutions, while X-ray fluorescence and inductively coupled plasma-mass spectrometry allowed us to demonstrate that HgCl is quantitatively sequestered from the aqueous phase. Irradiating at 365 nm, an intense fluorescence is observed at 470 nm for ni-Zn·S, which is partially quenched for i-Zn. This spectral benchmark was exploited to monitor in real time the i-Zn-to-HgCl@ni-Zn conversion kinetics at different HgCl concentrations. A sizeable fluorescence increase was observed, within a 1 h time lapse, even at a concentration of 5 ppb. Overall, this comprehensive investigation unraveled an intriguing molecular mechanism, featuring the disaggregation of a water-stable MOF in the presence of HgCl and the self-assembly of a different crystalline phase around the pollutant, which is sequestered and simultaneously quantified by means of a luminescence change. Such a case study might open the way to new-conception strategies to achieve real-time sensing of mercury-containing pollutants in wastewaters and, eventually, pursue their straightforward and cost-effective purification.
汞是毒性最强的重金属之一。凭借其三键，专门设计并合成了新型配体1,2-双（1-吡唑-4-基）乙炔（HBPE），以设计对汞具有高化学亲和力的金属有机框架（MOF）。分离出两种MOF，即Zn(BPE)和Zn(BPE)·DMF[分别为互穿的i-Zn和非互穿的ni-Zn·S；DMF = 二甲基甲酰胺]，呈微晶粉末状。虽然i-Zn在水中至少稳定15天，但其在HgCl水溶液中的悬浮液促使其转化为HgCl@ni-Zn。采用多种技术方法使我们能够在分子水平上阐明观察到的HgCl引发的i-Zn到HgCl@ni-Zn的转变。对模型系统的密度泛函理论计算表明，HgCl仅通过汞原子与ni-Zn中的碳 - 碳三键相互作用。粉末X射线衍射使我们能够量化100 - 5000 ppm HgCl溶液中i-Zn到HgCl@ni-Zn转变的程度，而X射线荧光和电感耦合等离子体质谱使我们能够证明HgCl从水相中被定量螯合。在365 nm照射下，ni-Zn·S在470 nm处观察到强烈荧光，i-Zn的荧光则部分猝灭。利用这一光谱基准实时监测不同HgCl浓度下i-Zn到HgCl@ni-Zn的转化动力学。即使在5 ppb的浓度下，在1小时内也观察到了相当大的荧光增强。总体而言，这项全面的研究揭示了一种有趣的分子机制，其特征是在HgCl存在下，水稳定的MOF发生解聚，并且在污染物周围自组装形成不同的晶相，污染物通过发光变化被螯合并同时定量。这样的案例研究可能为实现废水中含汞污染物的实时传感以及最终寻求直接且经济高效的净化方法的新概念策略开辟道路。
