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In this paper, we designed and investigated a reduction-based method to synthesize controllably monodisperse superparamagnetic nano Fe3O4 colloidal clusters for magnetically responsive photonic crystals. It was shown that the addition of ascorbic acid (VC) to the system could synthesize monodisperse superparamagnetic nano Fe3O4 and avoided the generation of γ-Fe2O3 impurities, while the particle size and saturation magnetization intensity of nano Fe3O4 gradually decreased with the increase of VC dosage. Nano Fe3O4 could be rapidly assembled into photonic crystal dot matrix structures under a magnetic field, demonstrating tunability to various diffraction wavelengths. The nano Fe3O4 modified by polyvinylpyrrolidone (PVP) and silicon coated could be stably dispersed in a variety of organic solvents and thus diffracted different wavelengths under a magnetic field. This is expected to be applied in various scenarios in the field of optical color development. [ABSTRACT FROM AUTHOR]

The solvothermal reduction method, utilizing a single FeCl3 as the iron source, is considered to be one of the effective ways to synthesize Fe3O4 magnetically responsive photonic crystals (MRPCs). However, some studies have revealed that Fe3O4 synthesized via this method cannot form a photonic crystal structure when subjected to a magnetic field, and the underlying reason for this inconsistency remains unreported. In our investigation, we have discovered that the presence of trace amounts of Fe2+ in the FeCl3 reagent is essential for successfully producing Fe3O4 MRPCs through this method. Moreover, the size, saturated magnetization value, and photonic tuning range of MRPCs can be controlled by adjusting the Fe2+ content. By analyzing the structure of the precursor formed during the reaction, we identified the formation of a binuclear iron structure in the precursor. This binuclear iron structure plays a pivotal role in the formation of Fe3O4 MRPCs. Based on these findings, we propose a new perspective that the binuclear iron complex serves as a nucleating agent for the formation of Fe3O4 MRPCs. The proposed view of nucleation could have considerable effect on the preparation of mixed-valence metal oxides through the solvothermal reduction route, and the results provide a facile method to modulate MRPCs, which is important for future applications in sensors, color displays, and gratings. [ABSTRACT FROM AUTHOR]

With the growing demands of human beings, sanitary landfill, along with the increase in landfill depth and leachate water pressure, has put forward new and higher requirements for the impermeable layer. In particular, it is required to have a certain adsorption capacity of harmful substances from the perspective of environmental protection. Hence, the impermeability of polymer bentonite–sand mixtures (PBTS) at different water pressure and the adsorption properties of polymer bentonite (PBT) on contaminants were investigated through the modification of PBT using betaine compounded with sodium polyacrylate (SPA). It was found that the composite modification of betaine and SPA could reduce the average particle size of PBT dispersed in water (reduced to 106 nm from 201 nm) and enhance the swelling properties. As the content of SPA increased, the hydraulic conductivity of PBTS system decreases and the permeability resistance improves, while the resistance to external water pressure increases. It is proposed a concept of the potential of osmotic pressure in a constrained space to explain the impermeability mechanism of PBTS. The potential of osmotic pressure obtained by linear extrapolation of the trendline of colloidal osmotic pressure versus mass content of PBT could represent the external water pressure that the PBT resist. Additionally, the PBT also has a high adsorption capacity for both organic pollutants and heavy metal ions. The adsorption rate of PBT was up to 99.36% for phenol; up to 99.9% for methylene blue; and 99.89%, 99.9%, and 95.7% for low concentrations of Pb2+, Cd2+, and Hg+, respectively. This work is expected to provide strong technical support for the future development in the field of impermeability and removal of hazardous substances (organic and heavy metals). [ABSTRACT FROM AUTHOR]

Correction for 'Magnetic response of photonic crystals based on nucleating agents of binuclear complexes' by Mengdong Tu et al., J. Mater. Chem. C, 2023, 11, 16922–16927, https://doi.org/10.1039/D3TC02786D. [ABSTRACT FROM AUTHOR]