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Hofmeister effects continue to defy all-encompassing theories, and their origin is still a matter of debate. We observed strong Hofmeister effects in Ca 21 /Na 1 exchange on a permanently charged surface over a wide range of ionic strengths. They could not be attributed to dispersion forces, classical induction forces, ionic size, or hydration effects. We demonstrated that another stronger force was active in the ion-surface interactions, and which would create Hofmeister effects in general. The strength of this force was up to 10 4 times that of the classical induction force, and could be comparable to the Coulomb force. Coulomb, dispersion and hydration effects appeared to be interwined to affect the force. The presence of the observed strong non-classical induction force implied that energies of non-valence electrons of ions/atoms at the interface might be heavily underestimated in current theories, and possibly just those underestimated energies of non-valence electrons determined Hofmeister effects. Hofmeister effects, also known as specific ion effects, were observed over 120 years ago. Even though they are ubiquitous in the physical, chemical and biological literature, their origin is still contested 1-7 and has been recently brought to the forefront of research [8][9][10][11][12][13][14][15][16][17][18][19] . New work in this area may break down barriers between physics and biology 9 . Ionic sizes, hydration, quantum fluctuations (or dispersion forces) 3,4,8 , and surface charges 1,2 are crucial in Hofmeister effects. Nano-scale surfaces and colloidal particles (e.g., DNA, proteins, cells, bacteria, metal oxides, and clay) are usually strongly charged in aqueous solution, and the sign of the charge or the charge number for biological macromolecules will be dependent on pH and ionic strength 20 . In classical theory, the surface charges can set up a strong electric field extending from the surface to several nanometers in solution. Typical surface charge densities and their corresponding electric field strengths include: (1) . For proteins, surface charge density measurements are primarily based on zeta potentials; therefore, they would be equal to the charge density at the shear plane, which is possibly much lower than the charge density at the surface [27][28][29] , especially when considering the strong surface hydration force [30][31][32] . At the shear plane, the charge density could reach 0.02-0.35 C/m 2 [33][34][35] , with an electric field of 10 7 -10 8 V/m. Therefore, it is reasonable to expect electric field strengths .10 8 V/m at protein surfaces in aqueous solutions. However, in those calculations, adsorbed counter-ions near the surface are treated as point charges. If their ionic size were taken into account, then the electric field near the surface would be much greater than 10 8 V/ m. This is because the finite size of counter ions could weaken their screening effect, as compared with point charges.Noah-Vanhoucke and Geissler found that, the persistence of electric field in the space near ...

Per-and polyfluoroalkyl substances (PFASs) are an emerging class of contaminants raising increased levels of concern due to their toxic, bioaccumulative, and persistent nature. Current solutions for removing PFAS from contaminated water rely on adsorption-based methods where commonly used sorbents, for example, activated carbons and ion-exchange resins, exhibit low adsorption capacity and a long equilibration time. Motivated by the generally deficient performance of these current materials, this work addresses the need for the discovery of advanced sorbents for high capacity and efficient PFAS removal. The zirconium-based metal−organic framework (MOF) NU-1000 was characterized for the adsorption of three perfluorosulfonic acids (PFSAs, C4−C8) and six perfluorinated carboxylic acids (PFCAs, C1−C9) from aqueous solutions. The results indicate that NU-1000 exhibits outstanding adsorption capacities of 400−620 mg/g for PFSAs and 201−604 mg/g for PFCAs coupled with ultrafast adsorption kinetics featuring equilibrium times of <1 min. Complementary density functional theory calculations reveal that the PFAS@MOF adsorption mechanism is dominated by a combination of hydrogen bonding, electrostatic, and hydrophobic non-covalent PFAS−MOF interactions. Excellent regeneration and reusability characteristics were found, particularly nearly quantitative removal and recovery rates of NU-1000 after five consecutive adsoption and desorption cycles of PFAS. Additional adsorption testing using PFAS-contaminated groundwater samples obtained from U.S. Air Force bases revealed impressive PFAS removal rates of 75−98% within 10 min regardless of the presence of co-contaminants. To the best of our knowledge, the suite of herein presented PFAS sorption characteristicscapacity, kinetics, regeneration, and reusabilitysignificantly outperforms other current sorbents, rendering NU-1000 as a promising platform for the rapid and effective removal of PFAS from aqueous media.