Charged Cations Research Articles

Electrostatic Regulation of TEMPO Oxidation by Distal Molecular Charges

AbstractWe define, experimentally, the effect of intramolecular electric fields, generated from the positive charge of ferricenium cations, over the oxidation potential of 2,2,6,6‐tetramethyl‐1‐piperdinyloxy (TEMPO). We synthesized a TEMPO derivative, where the nitroxide is linked to a ferrocene unit. We have used this molecule to study the influence on the electrostatic cross‐talk between positively charged ferriceniums and TEMPO units by solvent dielectric, level of electrolytic support, and Lewis acid/base character of electrolyte ions. The magnitude of thermodynamic anodic shift of the TEMPO oxidation, after the ferrocene unit is converted to a ferricenium cation, increases with decreasing dielectric constant of the solvent, electrolytic concentration, and Lewis basicity strength (i. e. between ferriceniums and electrolyte anions). This work demonstrates an approach to use electrostatic forces, here delivered by intramolecular charged cations, to tune the oxidation energy for nitroxides in ionic solutions.

An idealised approach of geometry and topology to the diffusion of cations in honeycomb layered oxide frameworks

Honeycomb layered oxides are a novel class of nanostructured materials comprising alkali or coinage metal atoms intercalated into transition metal slabs. The intricate honeycomb architecture and layered framework endows this family of oxides with a tessellation of features such as exquisite electrochemistry, unique topology and fascinating electromagnetic phenomena. Despite having innumerable functionalities, these materials remain highly underutilised as their underlying atomistic mechanisms are vastly unexplored. Therefore, in a bid to provide a more in-depth perspective, we propose an idealised diffusion model of the charged alkali cations (such as lithium, sodium or potassium) in the two-dimensional (2D) honeycomb layers within the multi-layered crystal of honeycomb layered oxide frameworks. This model not only explains the correlation between the excitation of cationic vacancies (by applied electromagnetic fields) and the Gaussian curvature deformation of the 2D surface, but also takes into consideration, the quantum properties of the cations and their inter-layer mixing through quantum tunnelling. Through this work, we offer a novel theoretical framework for the study of multi-layered materials with 2D cationic diffusion currents, as well as providing pedagogical insights into the role of topological phase transitions in these materials in relation to Brownian motion and quantum geometry.

Enhancement of the adsorption of hexacyanoferrate (III) ion on granular activated carbon by the addition of cations: A promissory application to mining wastewater treatment

The influence of the addition of cations on the adsorption of [Fe(CN)6]3− on granular activated carbon (GAC) was evaluated. The tests were performed at three pH values (3, 8.2, and 13) to determine the repulsion or electrostatic affinity between the adsorbent and adsorbate. Afterward, the cations (K+, Ca2+, and Al3+) at three pollutant-cation molar ratios (1:1, 1:10, and 1:50) were added to the system, and the influence of those was identified by the changes in the adsorption efficiency. The results show that the higher removal (%) was obtained at pH 13 without neither the presence of iron precipitates nor the liberation of HCN. The adsorption of [Fe(CN)6]3- was enhanced by the addition of K+ at 1:10 and 1:50 mol ratio since higher removals were achieved (75.27 % and 76.81 % respectively) than those obtained in the absence of cations (64.18 %) or in the presence of Ca2+ (67.58 %) and Al3+ (65.13 %) at a 1:10 mol ratio. The behavior in adsorption in the presence of cations shows that the ion-pair adsorption mechanism can describe the physical phenomenon, showing an increase in the fraction removed and the rate of adsorption with increasing cation charge. The adsorption kinetics using K+ with a 1:10 pollutant-cation molar ratio was fitted to the Lagergren pseudo-first-order model. The GAC adsorption capacity describes the pollutant adsorption rate with the predominance of physical interactions. The experimental data were fitted by the Langmuir and Freundlich isotherms, indicating a monolayer adsorption phenomenon consistent with the previously proposed ion-pair adsorption mechanism.

Viscous flow properties and hydrodynamic diameter of phenothiazine-based redox-active molecules in different supporting salt environments

We report viscous flow properties of a redox-active organic molecule, N-(2-(2-methoxyethoxy)ethyl)phenothiazine (MEEPT), a candidate for non-aqueous redox flow batteries, and two of its radical cation salts. A microfluidic viscometer enabled the use of small sample volumes in determining viscosity as a function of shear rate and concentration in the non-aqueous solvent, acetonitrile, both with and without supporting salts. All solutions tested show Newtonian behavior over shear rates of up to 30 000 s−1, which was rationalized by scaling arguments for the diffusion-based relaxation time of a single MEEPT molecule without aggregation. Neat MEEPT is flowable but with a large viscosity (412 mPa⋅s at room temperature), which is ∼1000 times larger than that of acetonitrile. MEEPT solutions in acetonitrile have low viscosities; at concentrations up to 0.5 M, the viscosity increases by less than a factor of two. From concentration-dependent viscosity measurements, molecular information was inferred from intrinsic viscosity (hydrodynamic diameter) and the Huggins coefficient (interactions). Model fit credibility was assessed using the Bayesian Information Criterion. It is found that the MEEPT and its charged cations are “flowable” and do not flocculate at concentrations up to 0.5 M. MEEPT has a hydrodynamic diameter of around 8.5 Å, which is almost insensitive to supporting salt and state of charge. This size is comparable to molecular dimensions of single molecules obtained from optimized structures using density functional theory calculations. The results suggest that MEEPT is a promising candidate for redox flow batteries in terms of its viscous flow properties.

From Bowls to Capsules: Assembly of Hexanuclear NiII Rings Tailored by Alkali Cations.

An anionic hexanuclear NiII metallamacrocycle with endo and exo linking sites has been employed as a building block to generate a series of capsules and bowls of nanometric size. The supramolecular arrangement of the {Ni6 } rings was tailored by the size of the alkali cations, showing the transition from {Ni6 -M2 -Ni6 } capsules (M=LiI and NaI ) to {Ni6 -M} bowls (M=KI and CsI ). The alkyl co-cations are determinant to stabilize the assemblies by means of CH⋅⋅⋅π interactions on the exo side of the metallamacrocycles. The effect on the topology of the supramolecular assemblies of the cation size, cation charge, Et3 NH+ or Me4 N+ counter cations has been analyzed. Magnetic measurements reveal the presence of ferromagnetic and antiferromagnetic interactions inside the rings that allow a S=0 ground state.

Strongly Correlated Ion Dynamics in Plastic Ionic Crystals and Polymerized Ionic Liquids

Understanding the mechanisms controlling ionic conductivity is critical for the development of the next generation of batteries and supercapacitors. This paper discusses the significant role played by ionic correlations in conductivity of concentrated ionic systems. Our studies of an organic ionic plastic crystal reveal that correlations in ions dynamics suppress conductivity by 25–100 times in comparison to the expected uncorrelated ionic conductivity estimated from the Nernst–Einstein relationship. Additional analysis also demonstrates that ionic correlations suppress conductivity in polymerized ionic liquids and gel by ∼10 times. Thus, ionic correlations, usually neglected in many studies, play a very important role in conductivity of concentrated ionic systems. These results cannot be explained by a diffusion of ion pairs because all these systems are essentially single ion conductors. In contrast, strongly correlated motions of mobile ions with the same charge (cation–cation or anion–anion correlations) are the major mechanism suppressing the ionic conductivity in these systems. On the basis of these results, we emphasize that charge transport rather than ion diffusion is critical for electrolyte performance and suggest the potential design of plastic crystals and polymer electrolytes with enhanced ionic conductivity.

Utilization of extracellular polymeric substances (EPS) immobilized in epoxy polymer as double ion exchanger biosorbent for removal of chromium from aqueous solution

Cation and industrial pollutant anions are removed from wastewater using organic cation and anion exchange resin. "Extracellular Polymeric Substance" (EPS) from bacterial extraction can accumulate cation and anion elements through biosorption by adsorption mechanism, ion exchange, formation of complex compounds and hydrogen bonds. EPS can be used as an biosorbent and ion exchange bioresin replacing organic resins, because EPS contains organic functional groups that are negatively charged (RCOOH, ROPO3H, ROPO3Na, ROSO3H, ROSO3Na, etc.) cation absorbers and positively charged (ROH, RCNH2HCOOH, etc.) anion absorber. EPS consists of 40-95% polysaccharide compounds, protein 1-60%, nucleic acids 1-10%, lipids 1-10% and the remaining amino acid polymers and other compounds. The tannery industry produces trivalent (Cr+3) chromium pollutants at levels of 15.2 ppm and hexavalent (CrO4-2 or Cr2O7-2) levels of 0.77 ppm which exceeds the standard quality for a total Cr of 0.6 ppm. Cr pollutants are very dangerous for human health. Research had been done on the use of immobilized EPS bioresin in epoxy polymers for chromium binding. EPS was extracted from bacterial activated sludge by centrifugation at 9000 rpm for 20 minutes at 4°C, the filtrate was EPS. The analysis showed EPS content were 16% fat, 12% carbohydrate, and 16% protein. The functional group analysis results with infrared ray spectroscopy (FTIR) showed EPS containing chemical bonds such as -CH, -OH, -NH, and -C=O which proved that EPS extraction contained RCOOH, ROH, and RCNH2HCOOH functional components which were exchanging components cations and anions. Epoxy polymers were prepared by mixing bisphenol A monomers and 1: 1 ratio epichlorohydrin. Immobilized EPS double ion exchange biorecin in epoxy polymers was prepared by mixing 200 mg EPS and 1800 mg epoxy. The binding of chromium ions in the resin was carried out by recirculating the chromium solution through a burette column filled with 2 rams of bioresin at pH 5, 6 and 7. The optimum results gave chromium ion absorption efficiency of 89.20% at pH 5. Column operations could be optimized by varied the amount of bioresin used.

Effect of the Synthesis Method on the Phase Composition and Magnetism of Layered Double Hydroxides

A number of tetrametallic layered double hydroxides containing magnesium and cobalt on the site of doubly charged cations in the structure of brucite-like layers and aluminum and iron on the site of triply charged cations have been synthesized using three distinct methods: coprecipitation, microwave synthesis, and hydrothermal crystallization. A sodium hydroxide solution was used as a precipitant. The results demonstrate that all three methods yield a well-crystallized hydrotalcite-like layered hydroxide and an impurity phase. We believe that it is the impurity phase which is responsible for the magnetism of the materials. Most likely, this phase is spinel CoFe2O4.

Effect of Doubly Charged Ion Additives on the Activity and Chemical Stability of Catalytically Active Potassium Ferrites

Potassium polyferrites K2 $${\text{Fe}}_{{1 - q}}^{{{\text{II}}}}$$ Mq $${\text{Fe}}_{{10}}^{{{\text{III}}}}$$ O17 (where M is Mg and Zn) and K2–2qFeIIMq $${\text{Fe}}_{{10}}^{{{\text{III}}}}$$ O17 (where M is Ca and Sr; q = 0–0.4) are synthesized to determine the effect of the size of a doubly charged dopant ion on their catalytic properties. The mechanism of the effect of doubly charged cation additives on the activity, selectivity, and corrosion resistance of potassium β'' polyferrite is identified. It is shown for the first time that doubly charged cations are distributed differently in the structure of β'' polyferrite depending on their size: either they are in a spinel-like block and then replace Fe2+ ions, or they replace potassium in interblock space. The Mg2+ and Zn2+ ion additives sharply reduce the catalytic activity and selectivity of β'' polyferrite. Such additives are undesirable. Small amounts of Ca2+ and Sr2+ cations greatly improve the corrosion resistance of the catalysts due to a drop in the mobility of potassium ions within a cation-conducting layer.

Способи одержання сорбентів із міскантусу та дослідження їх сорбційних властивостей щодо іонів Pb(ii) та Cd(ii)

Goal. To develop a method for the combined modification of the leaves and stems of miscanthus with the obtaining of new effective sorption materials for environmental purposes. Methods. General and special. Results. At use of miscanthus for obtaining sorbents, the plants are chemically modified, since the raw form has weak sorption properties. The resulting modified product can be got after processing plants with an alkaline solution (mercerizing), subsequent thermochemical modification in microwave followed by extrusion. Such processing preserves the integrity of the structural-frame lignocellulosic matrix and significantly improves plants’ ion-exchange, structural-porous, and sorption properties. Properties of the obtained sorbents indicate their ability to ion-exchange and complex-creation sorztion of multiply charged cations, in particular ions of heavy metal Pb2+ and Cd2+. Conclusions. The proposed methods of processing raw materials of miscanthus can be of practical use in agricultural production, and the resulting modified samples with sorption properties are promising materials in technologies of molecular and ion-exchange sorption. The obtained sorbents have a high sorption capacity concerning ions of heavy metals, particularly Pb2+ and Cd2+, and their structure-sorption characteristics are not inferior to the classical sorption materials based on carbon, silicon dioxide, aluminosilicates, etc. Therefore they can be used as efficient sorption materials for environmental clean-up of lands, contaminated with ions of heavy metal, wastewater, and soil.

Unusually large 254 Atoms Counter‐Ion for 5 Atoms [Ge5]2– Cluster

Abstract. With the attempt to synthesize Nb‐enclosed germanium Zintl cluster ion in ethylenediamine (en) / toluene solution, the reaction of K4Ge9/Na4Ge9 with Nb(mes)2 (mes = mesitylene) gives unexpected 18‐crown‐6 cleavage product of [K14Na2(NbO2)2(C8H16O5)8](Ge5) (en)·solv in the form of very air‐sensitive, light‐brown, plate‐like crystals. This unique compound crystallizes in monoclinic Pn (No. 7) space group, the cleavage of crown linked the 14 potassium, 2 sodium, and 2 niobium atoms into the bulky 2+ charged cation, which balances the [Ge5]2– anion. This compound represents the rare example of heteronuclear metal alkoxide / Zintl ion hybrid.

Crystal structures of isotypic ASb2F11 (A = Rb+, Tl+, O2+) and β-NH4Sb2F11, and the crystal structure of the low-temperature α-NH4Sb2F11

The crystal structures of RbSb2F11, TlSb2F11, O2Sb2F11 and β-NH4Sb2F11 salts are isotypical and crystallize in the orthorhombic space group Cmc21 (No. 36). Crystal data of rubidium salt: a = 19.9981(3) Å, b = 11.5093(2) Å, c = 12.9623(2) Å, V = 2983.46(8) Å3, and Z = 12 at 150 K. Unit cell parameters of corresponding thallium salt: a = 19.9876(5) Å, b = 11.5400(3) Å, c = 13.0267(3) Å, V = 3004.70(13) Å3 and Z = 12 at 150 K. Reaction between NH4F and excess of SbF5 in anhydrous HF resulted in the single-crystal growth of β-NH4Sb2F11: a = 20.0406(7) Å, b = 11.5534(4) Å, c = 13.0796(4) Å, V = 3028.42(18) Å3, and Z = 12 at 296 K. The XRD experiments on NH4Sb2F11 at 240 and 150 K revealed another modification (α-NH4Sb2F11), which crystallizes in a (pseudo-hexagonal) monoclinic cell, space group P21, a = 11.5045(6) Å, b = 13.0437(3) Å, c = 11.5264(6) Å, β = 119.818(7)°, V = 1500.67(15) Å3, and Z = 6 at 240 K. Reaction between the O2SbF6 and SbF5 in anhydrous HF yielded O2Sb2F11 upon crystallization with a = 19.8472(5) Å, b = 11.1172(3) Å, c = 12.8259(3) Å, V = 2829.97(12) Å3, and Z = 12 at 150 K. The crystal structures of ASb2F11 (A = Rb+, Tl+, O2+, NH4+) salts consist of dimeric Sb2F11− anions with partially disordered terminal fluorine atoms. Negative charge of the anions is compensated by single charged cations. Crystal structure of α-NH4Sb2F11 demonstrates similar motif as in β-phase but with slightly re-arranged N―H… F hydrogen bonds. In the 100−296 K range, only rhombohedral phase was observed for NH4SbF6 (rhombohedral space group R3¯, No. 148) with a = b = 7.5961(9) Å, c = 7.7176(9) Å, α = β = 90°, γ = 120°, V = 385.65(12) Å3, and Z = 3 at 150 K).

A quantitative and mechanistic model for the coupling between chemistry and clay hydration

It is proposed here to describe smectite water vapor desorption isotherms using an exchange formalism that quantitatively accounts for the different hydration states and thus different water contents. This approach makes it possible to reproduce both desorption isotherms and relative proportions of the different hydration states as determined by X-ray diffraction. The method is numerically robust and easy to implement in most reactive transport codes. The formalism is satisfactory from a phenomenological point of view and accounts for the influence of external parameters such as interlayer cation composition and solution cation composition and salinity on clay hydration. Furthermore, in contrast to most solid solution models, this approach focuses on the clay reactivity according to the charge and type of interlayer cation rather than on its solubility and therefore does not require the overall thermodynamic properties of the clay. In addition, such an explicit distinction of the hydration/cation exchange processes from the thermodynamic stability of smectite 2:1 layer allows the use of kinetics driving slow dissolution/precipitation rates if the number of exchange sites is related to the amount of clay minerals.

Quantitative Structure-Activity Relationship Models for Predicting Inflammatory Potential of Metal Oxide Nanoparticles.

Background:Although substantial concerns about the inflammatory effects of engineered nanomaterial (ENM) have been raised, experimentally assessing toxicity of various ENMs is challenging and time-consuming. Alternatively, quantitative structure–activity relationship (QSAR) models have been employed to assess nanosafety. However, no previous attempt has been made to predict the inflammatory potential of ENMs.Objectives:By employing metal oxide nanoparticles (MeONPs) as a model ENM, we aimed to develop QSAR models for prediction of the inflammatory potential by their physicochemical properties.Methods:We built a comprehensive data set of 30 MeONPs to screen a proinflammatory cytokine interleukin (IL)-1 beta () release in THP-1 cell line. The in vitro hazard ranking was validated in mouse lungs by oropharyngeal instillation of six randomly selected MeONPs. We established QSAR models for prediction of MeONP-induced inflammatory potential via machine learning. The models were further validated against seven new MeONPs. Density functional theory (DFT) computations were exploited to decipher the key mechanisms driving inflammatory responses of MeONPs.Results:Seventeen out of 30 MeONPs induced excess production in THP-1 cells. In vivo disease outcomes were highly relevant to the in vitro data. QSAR models were developed for inflammatory potential, with predictive accuracy (ACC) exceeding 90%. The models were further validated experimentally against seven independent MeONPs (). DFT computations and experimental results further revealed the underlying mechanisms: MeONPs with metal electronegativity lower than 1.55 and positive were more likely to cause lysosomal damage and inflammation.Conclusions: released in THP-1 cells can be an index to rank the inflammatory potential of MeONPs. QSAR models based on were able to predict the inflammatory potential of MeONPs. Our approach overcame the challenge of time- and labor-consuming biological experiments and allowed for computational assessment of MeONP inflammatory potential by characterization of their physicochemical properties. https://doi.org/10.1289/EHP6508

Facile and rapid synthesis of tetrakis-2-amino-5-methylpyridinecopper(II) chloride pentahydrate

Pyridine and its derivatives are important compounds with tremendous applications. Pyridine derivatives, such as aminopyridine, have been widely investigated concerning their biological activity. It is reported that generally biological activities of the compound increased after complexation. Tetrakis-2-amino-5-methylpyridinecopper(II) chloride pentahydrate has been synthesized facilely in less than five minutes. It was formed by mixing CuCl2-2H2O and 2-amino-5-methylpyridine in 1:4 mole ratio in ethanol at room temperature. The complex was characterized to determine its proposed empirical formula and the structure. The forming of the complex was indicated by shifting of maximum wavelength (Amax) of UV-Vis spectra towards smaller than CuCl2-2H2O from 850 nm to 675 nm. Atomic Absorption Spectroscopy (AAS) measurement showed the content of copper to be 9.63 % corresponding to the theoretical value of copper content in Cu(2-amino-5-methylpyridine)4Cl2(H2O)x (x= 4, 5, or 6). Thermogravimetric Analysis and Differential Scanning Calorimetry (TGA-DSC) showed a mass reduction of 13.02 % which was equivalent to the evaporation of five molecules of lattice water. The cation and anion charge ratio of the complex was 2:1. This four coordinated-complex was paramagnetic with an effective magnetic moment of 1.83 BM. The proposed empirical formula of the complex was [Cu(2-amino-5-methylpyridine)4]Cl2-5H2O.

Entropy Stabilization of TiO2–Nb2O5 Wadsley–Roth Shear Phases and Their Prospects for Lithium-Ion Battery Anode Materials

Wadsley–Roth phases accommodate variable cation charge by crystallographic shear planes delineating blocks of the parent ReO3 structure. The homologous series TiNbxO2+2.5x provides possible new ano...

Crystal Chemistry of High-Temperature Borates.

In recent years borate-based crystals has attracted substantial interest among the research community. The overall importance of this family of materials is reflected in miscellaneous articles and several reviews that have been published over the years. Crystalline borate materials exhibit numerous interesting physical properties, which make them promising for further practical applications. Diversity of functional characteristics results from their high structural flexibility caused in the linkage of planar/non–planar BO3 groups and BO4 tetrahedra, which can occur as isolated or condensed structural units. This report is a brief review on crystal chemistry and structure features of anhydrous/high-temperature borates. Polymorphism of boron-oxygen radicals has been considered basing on cations’ nature and synthesis conditions. Analysis of the laws governing borates structures and general principles of their systematics was discussed. As a result, an alternative classification of anhydrous compounds has been considered. It is based on four orders of their subdivision: (1) by the variety of anion formers, (2) by the cation charge, (3) by the N = NM:NB, i.e., ratio of metal atoms number to the ratio of boron atoms number (N-factor) value indicating the borate structural type (if it is known), (4) by the cation type and size.

Temperature dependence of differential capacitance in the electric double layer.Symmetric valency 1:1 electrolytes.

The differential capacitance of an electric double layer formed by an aqueous solution of KNO3 on a glassy carbon electrode is measured by impedance analysis at constant frequency. Results are obtained at electrolyte concentrations of 0.1 mol/dm3, 0.5 mol/dm3, and 1.0 mol/dm3, and at a series of temperatures, viz., 288 K, 298 K, 308 K, 318 K, and 328 K. The differential capacitance envelopes reveal a rich, complex pattern of maxima, minima, and local minima, whose magnitude and position change with a change in solution concentration. At the two lower concentrations, the temperature dependence of the capacitance, for example, at zero electrode potential, shows an alternating positive-negative behavior, while at the highest concentration of 1.0 mol/dm3, the slope of the differential capacitance-electrode potential curve is always positive. The experimental results are supplemented by a numerical grand canonical Monte Carlo simulation study of a restricted primitive model double layer but with an off-center cationic charge achieved by displacing the charge center from the ion sphere center toward its surface. The simulations, performed at the electrolyte concentration of 1.0 mol/dm3 and constant cation charge center displacement, and at varying electrode potentials and temperatures, show, in general, a negative temperature dependence of the differential capacitance. However, this temperature dependence can also be positive for a negative electrode charge and for a sufficiently large gradient of the cation charge center displacement with temperature. This feature is seen to be associated with an increase in the entropy of formation of the double layer.

Generation of Multiply Charged Protein Anions from Multiply Charged Protein Cations via Gas-Phase Ion/Ion Reactions.

We report a novel charge inversion ion/ion reaction that converts multiply charged protein cations to multiply charged protein anions via a single ion/ion collision using highly charged anions derived from nanoelectrospray ionization (nESI) of hyaluronic acids (HAs). This type of charge inversion reaction is demonstrated with cations derived from cytochrome c, apo-myoglobin, and carbonic anhydrase (CA) cations. For example, the reaction has been demonstrated to convert the [CA+22H]22+ carbonic anhydrase cation to a distribution of anions as high in absolute charge as [CA-19H]19-. Ion/ion reactions involving multiply charged ions of opposite polarity have previously been observed to result predominantly in the attachment of the reactant ions. All mechanisms for ion/ion charge inversion involving low energy ions proceed via the formation of a long-lived complex. Factors that underlie the charge inversion of protein cations to high anionic charge states in reaction with HA anions are hypothesized to include: (i) the relatively high charge densities of the HA anions that facilitate the extraction of multiple protons from the protein leading to multiply charged protein anions, (ii) the relatively high sum of absolute charges of the reactants that leads to high initial energies in the ion/ion complex, and (iii) the relatively high charge of the ion/ion complex following the multiple proton transfers that tends to destabilize the complex.

Surface Composition Dependence on the Ice Nucleating Ability of Potassium-Rich Feldspar

Mineral dust particles are one of the most abundant types of ice nucleating particles in the atmosphere. During atmospheric transport, these particles can be coated with water-soluble solutes, which can modify their ice nucleating ability. Although previous studies have shown that even low concentrations of water-soluble solutes can modify the ice nucleating properties of mineral dust particles, our understanding of this topic is far from complete. We examined the effects of a series of alkali metal nitrates at low concentrations (5 × 10–5 M to 5 × 10–3 M) on the surface composition and immersion freezing of potassium-rich feldspar (K-rich feldspar). Immersion freezing was investigated with the droplet freezing technique, and the surface composition was investigated with cryogenic X-ray photoelectron spectroscopy. K+ increased the median freezing temperature of the droplets, while the other alkali metal cations either had no effect or decreased the median freezing temperature. The changes in the median freezing temperature of the droplets due to the presence of nitrates followed the order K+ ≥ Li+ ≥ Na+ ≥ Rb+ ≥ Cs+ and, except for Cs+, were correlated to the K/Al ratio at the surface of K-rich feldspar. The K/Al ratio is possibly an indicator of the abundance of certain types of K-bearing microcline surfaces that drive the immersion freezing of K-rich feldspar, while Cs+ likely influences the immersion freezing of K-rich feldspar by an additional mechanism, possibly blocking ice nucleation sites by adsorption. Our work also shows that the cation charge density (charge density over the surface area of a single cation) is not a good predictor of the effects of cations on the immersion freezing of K-rich feldspar in our experiments.