Triplex blue-shifting hydrogen bonds of ClO4(-)···H-C in the nanointerlayer of montmorillonite complexed with cetyltrimethylammonium cation from hydrophilic to hydrophobic properties

Adhesion of Sphingomonas sp. GY2B onto montmorillonite: A combination study by thermodynamics and the extended DLVO theory

Bacterial adhesion on mineral surface are of fundamental importance in geochemical processes and biogeochemical cycling, such as mineral transformation and clay-mediated biodegradation. In this study, thermodynamics analysis combined with classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory as well as the extended DLVO (XDLVO) theory were employed to investigate the adhesion of the Gram-negative PAH-degrading bacteria Sphingomonas sp. GY2B on montmorillonite (Mt). Scanning electron microscopy (SEM), Fourier transform infrared spectra (FTIR) and X-ray photoelectron spectroscopy (XPS) indicated the affinity of GY2B for Mt, and the experimental results could be described well by pseudo-second-order (R2 = 0.997) and Langmuir model (R2 = 0.995). The thermodynamics analysis revealed the physical nature of bacterial adhesion onto Mt, which was confirmed by the XDLVO theory. The related surface properties (Zeta potential, hydrodynamic diameter and hydrophobicity) at different ionic strength were determined and the interaction energy between Mt and GY2B were also calculated using the DLVO and XDLVO theories in KCl or CaCl2 solution. At low ionic strength (≤ 20 mM), GY2B adhesion onto Mt was primarily driven by long-range DLVO forces (e.g. electrostatic repulsion), while short-range (separation distance < 5 nm) Van der Waals and hydrophobic interactions played more important roles in the bacterial adhesion at higher ionic strength (50-100 mM). In addition, Mt had a better adhesion capacity to bacteria in Ca2+ solution than that in K+ solution, owing to less negative charge and lower energy barrier in mineral-bacteria system in Ca2+ solution. Overall, the adhesion of bacteria onto Mt could be evaluated well on the basis of the XDLVO theory along with thermodynamics analysis. This study provides valuable insights into the clay-mediated microbial remediation of hydrophobic organic contaminants in the environment.

Functionalized nanoflower-like hydroxyl magnesium silicate for effective adsorption of aflatoxin B1

Aflatoxin B1 (AFB1), which is widely found in food and feed, poses a serious threat to the health of human and livestock. In this work, functionalized nanoflower-like hydroxyl magnesium silicate (FNHMS) was synthesized for adsorption of AFB1. First, bulk magnesium silicate (MS) was converted into nanoflower-like hydroxyl magnesium silicate (NHMS) by hydroxylation. Cetyltrimethylammonium bromide (CTMAB) modification then enhanced the hydrophobicity and the affinity to AFB1 of NHMS. The adsorption performance for AFB1 followed the order of MS < NHMS < FNHMS, and the adsorption performance increased with the increase of the dose of CTMAB. Isothermal adsorption analysis indicated that the surface of FNHMS was heterogeneous. The adsorption capacity of FNHMS-0.4 to AFB1 was estimated to be 27.34 mg g^-1 and 28.61 mg g^-1 by Freundlich and Dubinin-Radushkevich isotherm adsorption model, respectively. By analyzing the adsorption kinetics and adsorption thermodynamics, both physical adsorption and chemisorption existed in the process of AFB1 being adsorbed on FNHMS-0.4. Adsorption mechanisms analysis indicated that the adsorption followed the adsorption site priority of H > O > Mg. This work demonstrates that FNHMS could be a promising adsorbent for removal of AFB1.