Oleic acid (OA)-coated magnetite (Fe3O4) nanoparticles, denoted Fe3O4@OA, were synthesized by co-precipitation in the presence of varying contents of OA. The Fe3O4@OA nanoparticles were characterized by X-ray diffraction, transmission and scanning electron microscopies, Fourier transform infrared spectroscopy, thermogravimetric–differential thermogravimetric analyses, and vibrating sample magnetometry. Increasing the OA content during preparation resulted in an increase of the OA-coating amount (A O, in units of g of OA/g of Fe3O4) on the Fe3O4 surface, before reaching an equilibrium value. The resulting magnetic nanoparticles were nearly spherical with a size of ∼12–14 nm. OA molecules formed a single layer coating on the Fe3O4 surface. The A O and area occupied by a single OA molecule at saturation coating were estimated to be 0.11 g g–1 (1.22 mg m–2) and 0.37 nm2, respectively. The Fe3O4@OA nanoparticles were applied in the demulsification of a cyclohexane-in-water nanoemulsion, under an external magnetic field. The effects of A O, demulsifier dosage, pH, and electrolytes on the demulsification efficiency (E D) were investigated. The E D increased and then decreased with increasing A O, which was attributed to a change in wettability of the magnetic nanoparticles. A maximum E D of ∼98% was observed at a ∼90° contact angle between water and the magnetic nanoparticles. The E D was independent of pH and electrolyte (NaCl or CaCl2) concentration, under the studied conditions. The magnetic demulsifier exhibited excellent stability after reuse over 6 cycles. Fe3O4@OA nanoparticles are effective for oil–water multiphase separation and treating oily wastewater.

Summary Myxococcus xanthus kills susceptible bacteria using myxovirescin A (TA) during predation. However, whether prey cells in nature can escape M. xanthus by developing resistance to TA is unknown. We observed that many field‐isolated Bacillus licheniformis strains could survive encounters with M. xanthus, which was correlated to their TA resistance. A TA glycoside was identified in the broth of predation‐resistant B. licheniformis J32 co‐cultured with M. xanthus, and a glycosyltransferase gene (yjiC) was up‐regulated in J32 after the addition of TA. Hetero‐expressed YjiC‐modified TA to a TA glucoside (TA‐Gluc) by conjugating a glucose moiety to the C‐21 hydroxyl group, and the resulting compound was identical to the TA glycoside present in the co‐culture broth. TA‐Gluc exhibited diminished bactericidal activity due to its weaker binding with LspA, as suggested by in silico docking data. Heterologous expression of the yjiC gene conferred both TA and M. xanthus‐predation resistance to the host Escherichia coli cells. Furthermore, under predatory pressure, B. licheniformis Y071 rapidly developed predation resistance by acquiring TA resistance through the overexpression of yjiC and lspA genes. These results suggest that M. xanthus predation resistance in B. licheniformis is due to the TA deactivation by glucosylation, which is induced in a predator‐mediated manner.

The surface charge properties and aggregation behavior of positively charged Mg−Al−NO 3 layered double hydroxide (LDH) single-layer nanosheets dispersed in water were investigated in the presence of K + salts with different mono-, di-, and trivalent anions, using electrophoresis and dynamic light scattering techniques. An increase in the salt concentration can significantly decrease the effective surface charge density (σ eff ) of LDHs, leading to the aggregation of nanosheets. The critical coagulation concentration (CCC) or ionic strength (CCIS) of salts for nanosheets significantly decreases with an increase in the valence of anions. Specific ion effects, with a partially reverse Hofmeister series, are observed. On the basis of the Stern model and the DLVO theory, the relationship of CCC with σ eff and the ionic valences of salts (z i ) is theoretically analyzed, which can accurately describe the dependence of CCC on the σ eff and z i but cannot explain the origin of specific ion effects. To explore the origin of specific ion effects, a correlation between CCIS and the specific adsorption energy (E sc ) of anions within the Stern layer is developed. Especially, an empirical relationship of E sc with the characteristic physical parameters of anions is proposed. Our model can accurately predict the CCISs of at least monovalent anions and divalent anions (CO 3 2− and SO 4 2− ), demonstrating that the specific ion effects observed can be attributed to the differences in ionic size, polarizability, and hydration free energy (or the formation capacity of anion−cation pairs) of different anions. This work not only deepens the understanding of specific ion effects on the colloidal stability but also provides useful information for the potential applications of LDH single-layer nanosheets.