Exposed facets mediated interaction of polystyrene nanoplastics (PSNPs) with iron oxides nanocrystal

Nanoplastics (NPs), which are often detected in the natural environment, are regarded as a group of emerging pollutants. Hematite is a substance that exists widely in the surface environment and has an important impact on the environmental behavior of pollutants. Clarifying the migration of NPs requires an in-depth understanding of intrinsic interaction mechanisms of NPs with iron-containing minerals. The interaction process of polystyrene nanoplastics (PSNPs) on the hematite exposed facets was systematically studied by experiments under different conditions, adsorption isotherm curves, Fourier Transform infrared (FTIR) spectroscopy and two-dimensional correlation spectroscopy (2D-COS) analyses. We found that PSNPs were adsorbed on the three exposed faces of hematite ({001}, {012}, and {100}) by electrostatic interaction, respectively, but the capacities for PSNPs were different. Adsorption models were established to explore the preferred interaction surface dependent on the exposed facets, and it was found that {012} surfaces were more favorable for PSNPs adsorption, while {001} surface has better adsorption capacity for PSNPs than {100} surface, which is due to the different density and proportion of hydroxyl groups on the exposed facets of hematite. These findings elucidated the dependence of PSNPs adsorption on the hematite facets, and illustrated t the effect of hematite on the migration of PSNPs in the environment.

Tailor the crystal planes of MIL-101(Fe) derivatives to enhance the activity of SCR reaction at medium and low temperature

Mainly exposed crystal facets and controllable morphology play a key role in the final performance of the preparation of specific nanomaterials. In the present study, a metal-organic framework pyrolysis method without adding solvent modifiers was developed. By adding CO in the calcination atmosphere to change atmosphere ratio, Fe₃O₄ nanostructures are exposed with different crystal planes and evaluated their performance in NH₃-SCR reaction. This study proves that SCR catalytic activity of Fe₃O₄ nanocrystals is dependent on morphology and crystal facet. Compared with materials exposed (100), catalysts with more (111) show stronger deNO_x performance. The preferential exposure of Fe₃O₄ (111) crystal facets increases the concentration of adsorbed oxygen on the catalyst, showing higher surface acidity, and enhances the interaction among NO, O₂ and catalyst, which is conducive to SCR reaction. This is supported by DFT calculations. The results present a great application prospect in preparing nanomaterials with specific crystal structures to effectively treat pollutants.

Hydrothermal synthesis of m-BiVO4/t-BiVO4 heterostructure for organic pollutants degradation: Insight into the photocatalytic mechanism of exposed facets from crystalline phase controlling

A series of BiVO₄ photocatalysts were prepared by a co-precipitation followed hydrothermal synthesis method for the photodegradation of Rhodamine B (RhB) and 2,4-Dichlorophenol (2,4-DCP). The crystalline phase ratio of the heterostructured BiVO₄ (m-BiVO₄/t-BiVO₄) between monoclinic and tetragonal could be easily controlled at different pH and hydrothermal time. Interestingly, the as-prepared heterostructured BiVO₄ photocatalyst at pH = 7 for 24 h (BiVO₄-7-24) showed the highest photocatalytic activities for the degradation of RhB, while the best photodegradation of 2,4-DCP was obtained at pH = 0.5 for 24 h (BiVO₄-0.5-24). The photocatalytic mechanism can be explained by the different charge carrier transfer pathways and active oxidation species in the m-BiVO₄/t-BiVO₄ heterostructure. More importantly, the exposed facets originated from crystalline phase controlling in BiVO₄-0.5-24 and BiVO₄-7-24 photocatalyst is an essential reason for the different photocatalytic activity. The proposed energy band alignments of BiVO₄-0.5-24 and BiVO₄-7-24 photocatalyst provide insights into the photocatalytic mechanism of the m-BiVO₄/t-BiVO₄ heterostructure.