To evaluate the role of atmospheric heterogeneous reactions on the ice nucleation ability of airborne dust particles, we investigated the systematic study of ice nucleation microphysics with a suite of atmospherically relevant metals (10), halides (4), and oxyhalides (2). Within a minute, a kaolin–iron oxide composite (KaFe) showed efficient reactions with aqueous mercury salts. Among the different mercury salts tested, only HgCl 2 reacting with KaFe generated HgKaFe, a highly efficient ice nucleating particle (HEIN). When added to water, HgKaFe caused water to freeze at much warmer temperatures, within a narrow range of −6.6 to −4.7 °C. Using a suite of optical spectroscopy, mass spectrometry, and microscopy techniques, we performed various experiments to decipher the physical and chemical properties of surface and bulk. KaFe was identified as a mixture of different iron oxides, namely, goethite, hematite, magnetite, and ε-Fe 2 O 3 , with kaolin. In HgKaFe, HgCl 2 was reduced to Hg 2 Cl 2 and iron was predominantly in maghemite form. Reduction of Fe 2+ by NaBH 4 , followed by aerial oxidation, helped KaFe to be an exact precursor for the synthesis of HEIN HgKaFe. Kaolin served as a template for synthesizing iron oxide, opposing unwanted aggregation. No other metal or metal halide was found to have more efficient nucleating particles than HgCl 2 with KaFe composite. The chelation of Hg(II) hindered the formation of HEIN. This study is useful for investigating the role of morphology and how inorganic chemical reactions on the surface of dust change morphology and thus ice nucleation activity. The understanding of the fundamentals of what makes a particle to be a good ice nucleating particle is valuable to further understand and predict the amount and types of atmospheric ice nucleating particles.

Ice nucleation microphysical processes are identified to be of high importance in forecasting the magnitude of the Earth’s climate change. The environmental conditions often influence the ice nucleation processes in the Earth’s atmosphere. We herein study the impact of various environmental conditions on FeHg (maghemite–Hg2Cl2 composite), a highly efficient ice nucleating particle with similar freezing point to the best inorganic ice nuclei, AgI. FeHg is formed from FeCl2·4H2O and HgCl2, which are observed in the environment, in contrast to AgI, which is rarely found. The ice nucleation efficacy remained unchanged for FeHg under ambient conditions for a long duration. To mimic the atmosphere, we performed a series of experiments using a suite of complementary techniques, at various levels of radiation intensity, temperature, and pH for FeHg. Experiments were also performed in the presence of atmospheric pollutants, such as ozone (in the presence or absence of light), as well as nine emerging metal oxides and NO2. The emerging metal oxides at various pH levels produced significant effects on the ice nucleation ability of FeHg. Elevated temperatures changed the maghemite of FeHg to β-Fe2O3, whereas other studied environmentally relevant physicochemical conditions could not alter the maghemite phase. We describe potential reaction mechanisms using our observations. To evaluate the effect of surface alterations, the passivation of clay materials, namely, kaolin and montmorillonite, was also performed on FeHg. The observed alteration in crystal structure, as found in X-ray diffraction, was attributed to the change of the extent of lattice mismatch, resulting in a significant variation of ice nucleation ability. Our insights of the ice nucleating particles may help understand real atmospheric ice nucleation processes, in association with the establishment of more in-depth understanding of ice nucleation mechanism in the Earth’s atmosphere.

We herein present a novel and sustainable technology for mercury recycling, with the maximum observed uptake capacity. Facile synthesis of the most efficient (~1.9 gg−1) nano-trap, made of montmorillonite-Fe-iron oxides, was performed to instantaneously remove mercury(II) ions from water. Elemental Hg was recovered from the adduct, by employing Fe granules, at ambient conditions. Varied pHs and elevated temperatures further enhanced this already highly efficient recycling process. The reduction of Hg(II) to Hg(I) by the nano trap and Hg(I) to Hg(0) by Fe granules are the main driving forces behind the recycling process. Facile sustainable recycling of the nano-trap and Fe granules require no additional energy. We have further developed a recyclable model for Hg nano-trap, which is inexpensive (<$5 CAD), and can remove mercury in a few seconds. This technology has multiple applications, including in the communities exposed to mercury contamination.

The Author Contributions section in this Article is incorrect. "M.G. did all necessary experimental work (except Fig. 2), wrote main manuscript text and prepared all figures. S.D. did experimental work for Fig. 2. P.A.A. wrote the original proposal which was funded, and then served as the basis of this research project, supervised the work and modified the manuscript for important intellectual content. " should read: "M.G. did all necessary experimental work (except Fig. 2), wrote main manuscript text and prepared all figures. S.D. was an undergraduate researcher who was predominantly in charge of work shown in Figure 2, and was involved from the beginning of this project including all repetitions of the work performed by M.G. P.A.A. wrote the original proposal which was funded, and then served as the basis of this research project, supervised the work and modified the manuscript for important intellectual content. "