## Monday, September 10, 2018

### Odour Control System Market: By Key Players, Types, Application, Market Competitive Landscape, Trends and Forecasts to 2025

Odour Control System Market latest research report provides in-depth analysis of definitions, classifications, applications and Odour Control System Industry chain structure forecast until 2025. The report also consists of development trends, competitive landscape analysis, and key regions development status of Odour Control System Market.

Odour Control System Market Segment by Manufacturers

The Odour Control System Market report conveys an essential review of the business including its definition, applications and assembling innovation, Odour Control System Market report introduces the organization profile, item determinations, limit, generation esteem, Contact Information of maker and pieces of the pie for organization.

Major Classification are follows:

Physical Odour Control
Chemical Odour Control
Biological Odour Control

Major Application are follows:

Paper & Pulp
Waste Treatment
Food & Beverage
Chemical & Petrochemical
Other

Major Highlights of Odour Control System Market report:

Odour Control System Market Overview
Industry Chain Analysis
Manufacturing Analysis of Odour Control System
Historical, current, and projected size of the market from the standpoint of both value and volume
Sales Market Forecast
Market shares and strategies of key players
New Project Investment Feasibility Analysis
Regional Market Forecast
Scope of the Report: This report focuses on the Odour Control System in Global market, especially in United States, Canada, Mexico, Germany, France, UK, Italy, Russia, China, Japan, India, Korea, Southeast Asia, Australia, Brazil, Middle East, Africa. This report categorizes the market based on manufacturers, regions, type and application.

Some Major Point cover in this Odour Control System Market report are: –

Who are Opportunities, Risk and Driving Force of Odour Control System? Knows Upstream Raw Materials Sourcing and Downstream Buyers
Who are the key manufacturers in space? Business Overview by Type, Applications, Gross Margin and Market Share
What are the opportunities and threats faced by the vendors in the global Odour Control System market?
What will the market growth rate, Overview and Analysis by Type of Odour Control System in 2025?
What are the key factors driving, Analysis by Applications and Countries Global industry?
What is Dynamics, This Overview Includes Analysis of Scope and price analysis of top Manufacturers Profiles?

At last, the report gives the inside and out examination of Odour Control System Market took after by above components, which are useful for organizations or individual for development of their present business or the individuals who are hoping to enter in Odour Control System industry.

## What's the Latest Development?

Following a Greenpeace investigation into corporate responsibility in China, the environmental group reports that large textile factories, which often supply Western clothing companies, regularly release toxic chemicals into China's rivers. "The Youngor facility in Ningbo, near Shanghai, was found to have discharged nonylphenol, an endocrine disruptor that builds up in the food chain, perfluorinated chemicals, which can have an adverse effect on the liver and sperm counts, as well as a cocktail of other toxins."

### What's the Big Idea?

Greenpeace has linked Nike, Adidas, H&M, Puma and Lacoste with the Youngor textile facility, which it believes is releasing toxins into China's water supply. The companies deny that their business with Youngor uses any of the products Greenpeace refers to in their report, most of which are made necessary during the dyeing process. But denying any direct responsibility is not good enough, says Greenpeace. Do companies with large brand recognition have an added responsibility to promote environmentally responsible behavior in general? What are the limits of corporate responsibility?

## Thursday, August 23, 2018

### The Green Chemistry & Commerce Council (GC3) and InnoCentive Announce Award Recipients in the Challenge for Novel Green Preservatives

Lowell, MA, Aug. 06, 2018 (GLOBE NEWSWIRE) -- The Green Chemistry & Commerce Council (GC3) and InnoCentive are pleased to announce seven winners in the global GC3 Challenge: Developing New Preservatives for Personal Care & Household Products. Launched in April 2017, the challenge aimed to identify and support innovators developing preservative technologies with improved environmental, health and safety profiles for use in cosmetics, personal care and household products.

Preservatives are incorporated in products such as shampoos, hand creams, and laundry detergents to slow microbial growth and prevent contamination and spoilage. There is an urgent need for green chemistry innovation in preservative technologies because regulations, market demands and increasing consumer interest have shrunk the palette of acceptable preservative options for formulators. The GC3 Preservatives Challenge sought submissions on new broad spectrum or single action chemical agents on gram-positive bacteria, gram-negative bacteria, yeast and mold, as well as preservative boosters.

Challenge sponsors and participants represented the entire value chain, with 11 consumer packaged goods (CPG) companies, two major retailers and five suppliers: Babyganics, Beautycounter, Beiersdorf, Colgate-Palmolive, Johnson & Johnson Consumer (J&J), Kao USA, Method – People Against Dirty, Procter & Gamble (P&G), Reckitt Benckiser (RB), SC Johnson, Unilever, Target, Walmart, Dow Microbial Control, Lonza, Schülke, Symrise, and Thor, as well as the Environmental Defense Fund and the Minnesota Pollution Control Agency.

The challenge drew 48 innovative technology submissions from around the globe that were judged by a panel of expert microbiologists, product formulators, and safety experts from sponsoring CPG companies and others. After the submissions were formulated into three simple products, the preservative technologies were evaluated for safety and efficacy by contractors Syracuse Research Corporation and Cosmetech, respectively. The innovators received the results from the safety and performance evaluations and feedback from the judges.

Below are the seven finalists that received portions of the prize pool of \$175,000:

1st place award recipients:

Avisco Ltd.
IMD Natural Solutions GmbH
Irena Jevtov Research & Innovation
United States Department of Agriculture/People Against Dirty/Berkeley Center for Green Chemistry/University of Victoria/Safer Made
2nd place award recipients:

Hydromer, Inc.
3rd place award recipient:

According to Monica Becker, GC3’s Director of Collaborative Innovation, the GC3 Preservatives Challenge not only stimulated innovation, it also fostered significant learning and collaboration among peers across the supply chain as they discussed and evaluated the solutions. “The GC3 created a unique, pre-competitive platform for experts from the entire value chain to work together to address a common challenge – the need for new preservative technologies,” said Becker.

“J&J was delighted to sponsor this unprecedented initiative that enabled companies to pool their knowledge and experience to identify promising new technologies for preservation and accelerate their application in the market,” said Homer Swei, the Director of Product Stewardship at Johnson & Johnson Consumer Inc.

“We are constantly scouting for new, safer ingredients for our products, and preservatives are an important focus. By collaborating with our peers in this competition, we learned about and evaluated the efficacy of new solutions that we had not found on our own, and now we may be able to help innovators bring those solutions to market and scale for the benefit of all,” said Kaj Johnson, Senior Director of Product Development at People Against Dirty (the parent company of Method and Ecover).

Supplier companies benefited from the GC3 Challenge process because it offered them extensive technology scouting opportunities. The innovators benefited from promoting their technologies with larger, strategic companies and organizations across the value chain. The innovators presented their technologies to sponsors at a private event on May 7 in conjunction with the GC3 Annual Innovators Roundtable. According to Becker, the sponsors are now working toward partnerships with the innovators to evaluate their preservatives for use in their products or for co-development, licensing or investment, to commercialize and scale these technologies.

“We are delighted to receive an award in the GC3 Preservatives Challenge,” said Thomas Henkel, Senior Business Development Manager at IMD Natural Solutions GmbH (INS). “This was an incredible opportunity to present our natural preserving agents to potential customers and partners, and we gained valuable insights from our conversations with the CPG companies and suppliers that are seeking new preservatives.”

Becker says the GC3 is continuing its work on collaborative innovation of preservatives in various ways, by supporting the joint work between the innovators and sponsors; identifying new innovators and connecting them to our sponsors and other GC3 members; and sharing the formulations and methods used for the safety assessments and performance testing. “Propelled by the success of the Preservatives Challenge to accelerate green chemistry innovation and market activity, we look forward to establishing additional collaborative innovation projects that target other priority technology areas,” said Becker. For more information about the GC3 Preservatives Challenge, contact gc3info@greenchemistryandcommerce.org.

About IMD Natural Solutions GmbH (INS)

IMD Natural Solutions GmbH (INS) develops, produces and delivers innovative naturally-derived additives and bioactive ingredients for the fast-moving consumer goods industries. INS specializes in natural preserving agents with its core antimicrobial product GLYCONEXTM positioned as a sustainable and safe alternative to established solutions. For more information visit http://www.imd-natural-solutions.com/.

About the Green Chemistry & Commerce Council

Started in 2005, the Green Chemistry & Commerce Council (GC3) is a multi-stakeholder collaborative that drives the commercial adoption of green chemistry by catalyzing and guiding action across all industries, sectors and supply chains. Over 125 organizations are members of the GC3. For more information, visit www.greenchemistryandcommerce.org.

Established in 2001, InnoCentive helps organizations tackle their critical business, scientific and technical problems by crowdsourcing ideas and solutions, either from InnoCentive’s global network of problem solvers or from their own internal networks. InnoCentive offer their Challenge Driven InnovationTM methodology, purpose-built platform and global network of problem solvers, as well as accompanying consulting, training and program management services. For more information visit https://www.innocentive.com.

## Introduction

Adsorption of ions on the charge surface is a fundamental approach widely used in remediation of heavy metals1,2,3, water purification4,5,6,7, minerals formation8, surface-mediated reactions9,10, manufacturing of molecular electronic devices11 and energy storage devices like super-capacitors12. In these processes, distribution of counter- and co-ions from the surface to the bulk region creates an electrical double layer (EDL) at the interface13. In EDL, some of the ions are in direct association with the surface (known as the Stern layer) while the rest of the ions are distributed away from the surface till the bulk region (known as the diffuse layer)14,15. The Gouy-Chapman theory assumes ions to be point charges and describe their distribution in the diffuse layer successfully, however, fails to predict their adsorption in the Stern layer16,17. Thus, a molecular level understanding of the ions distribution, role of hydration energy and co-ions association in the Stern layer is essential for enhancing the above processes, especially for improving charge densities in electrochemical devices18,19 to meet the growing energy demand, and for exploiting the metal ion exchange capability of naturally available clay minerals for remediation of nuclear waste1,20,21.
In this report, we have studied the adsorption behavior of monovalent (Rubidium - Rb+ and Sodium - Na+) and divalent (Magnesium - Mg2+ and Strontium - Sr2+) cations at mineral surface highlighting the importance of the ion charge, hydration energy and hydration structure. Since divalent ions have higher electrostatic interactions, we expected their adsorption to be higher as compared to monovalent ions. However, we observed a counter-intuitive behavior of lesser adsorption of divalent ions at all concentrations as compared to monovalent ions. We have analyzed the energetics, structure, and clusters of adsorbed ions to explain observed behavior.
Majority of studies focused on understanding the properties of ions at solid - aqueous interface have used muscovite mica surfaces in their work. The reasons are that (a) muscovite mica surfaces are easy to cleave, (b) produces atomically smooth surfaces,22 (c) the framework carries a negative charge compensated by surface potassium ions (K+), and (d) these surface (K+) ions can be exchanged with other cations in the presence of aqueous salt solutions23,24,25,26. Experimental studies using surface force apparatus (SFA) on electrolyte solutions between two mica surfaces have observed short-range repulsive forces due to dehydration of ions beyond a critical concentration of salt solution27. Further, this critical concentration was found to vary with the type of ions suggesting that their individual hydration structure and energy plays the significant role in ion adsorption at surfaces. The X-ray reflectivity (XRR) studies of mica - water system established that water molecules and surface cations are adsorbed on the ditrigonal cavities of mica surface28. In addition, non-uniform fluctuations in the density of the interfacial water layer were observed up to 10 Å from the mica surface28. In subsequent studies, it was found that Rb+ ions are adsorbed in partially hydrated states, whereas Sr2+ ions are observed in both, partially and fully hydrated states within the Stern layer29. The adsorption location of ions in the lateral and normal direction obtained from AFM studies of electrolyte solution on the mica surface are in concurrence with the XRR studies29,30,31,32. The recent atomic force microscopy (AFM) studies found that Rb+ ions adsorb together forming a cluster on mica surface, driven by the energetics of adsorbing ions and confirmed using molecular dynamics (MD) simulations30. AFM studies of KCl solution at higher concentration have found signatures of crystal formation at the mica surface31,33. Unfortunately, the SFA and AFM studies are restricted to the dilute concentrations due to the possibility of disturbing the Stern layer. Measurements from the XRR technique provides structural information of interfacial water and ions perpendicular to the surface alone and does not provide in-plane behavior23. Recent surface X-ray diffraction (SXRD) studies have found co-ions as well in the Stern layer23,26. Recent AFM techniques on the mica-RbCl solution (0–4 M) are able to probe in the three dimensional structures of solutions on the surface but still has the limitation to distinguish ion hydration and free water molecules31.
Molecular simulations have served as an important tool for providing a molecular-level understanding of the experimental observations. MD simulations have shown that layering of water molecules adjacent to the mica surface is due to hydration of surface cations34,35,36,37. Water molecules of first contact layer adsorbs on ditrigonal cavities, whereas the second layer hydrate the cations35. The orientation, hydrogen bonding, dynamic relaxation and viscosity of water molecules in these layers is different compared to bulk water due to the direct and indirect effect of mica surface34,35,36,38,39. MD simulation studies of Li+, Na+, K+, Rb+ and Cs+ ions at dilute concentration showed that these ions adsorb in the inner sphere complexes which agrees with XRR results36,39. Further, the adsorption free energy of these ions near the surface depends on the ability of the mica surface to satisfy their hydration structure39,40. The adsorption energy of divalent ions was found to be much higher than compared to monovalent ions40. Previous experimental and computational studies have established the location of ion adsorption, their energy and presence of co-ions near the surface. Despite these studies, the complete picture about structure of adsorbed ions, their hydration shell and association with co-ions at different concentration remains elusive.
We hypothesize that, the co-operative effect of counter-ions, competitiveness between counter-ions and charge balancing ions (K+ in case of mica surface), and the ion-pairing effect of co-ions (cation-anion) would be significant along with surface hydration, especially at higher aqueous electrolyte concentration near charged solid substrate. These effects would significantly change the structure of adsorbed ions and water molecules, hydration of cations and may lead to cation-anion cluster formation. In this work, MD simulations of aqueous solutions at various concentrations from 0–4.5 M were performed to check our hypothesis. In order to understand the effect of ion charge and hydration energy, we considered aqueous chloride (Cl) solution of monovalent (Rb+ and Na+) and divalent (Sr2+ and Mg2+) cations on the mica surface. We chose Rb+ ions, as its hydration energy is comparable to mica surface K+ ions, whereas, Na+ ions have higher hydration energy (Table 1). The Mg2+ and Sr2+ ions have higher hydration energy (~5 times) than K+ ion. We observed counter-intuitive adsorption behavior of lesser adsorption of divalent ions at all concentrations as compared to monovalent ions. We explained the reason using energetics and structural analysis. While adsorption isotherms of monovalent (Rb+ and Na+) ions exhibit similar behavior, however a distinct mechanism of hydration water redistribution and association with Cl ions is observed. To the best of our knowledge, this is the first work which studies extensively the salt solutions of multiple ions near solid surface for large concentration range (0–4.5 M) capturing various adsorption regimes and providing molecular details. This information will aid in various areas of application such as super-capacitors, nanotribology, colloidal chemistry, heavy metal removals, and geochemistry.

## Results and Discussion

A representative density profile of water and ions adjacent to the mica surface is shown in Fig. 1. The ions are found to be adsorbed mostly around 2–3 Å from the mica surface. These adsorbed ions directly interact with the mica surface by forming a hydration shell with the surface oxygen atoms (Fig. 1a). In case of water molecules, we observed large oscillation in the density profile near the mica surface due to the presence of surface ions (Fig. 1c). The locations and extend of these oscillations are consistent with the experimental studies28,32, as shown in our previous work35. Within the 13 Å of the interfacial region, density oscillations are more pronounce between 0–5 Å region (Fig. 1d). Our previous studies have shown that these density oscillations are due to hydration of surface ions by the interfacial water molecules35,38. In this study, we considered this 0–5 Å region as the adsorption region (AR) and the concentration of ions in this AR (CA) is considered as adsorbate loading. We further observed that water density in the 13–50 Å region is constant and corresponds to the bulk density of water; the ion concentration within this region is defined as bulk concentration (CB).

### Free Energy Profile of Adsorbed Ions

Figure 3 shows free energy profiles of cations (K+, Na+, Rb+, Mg2+ and Sr2+) in water adjacent to the mica surface, calculated using the umbrella sampling technique43,44 and the weighted histogram analysis method45 (details are given in section 1 of Supplementary Information (SI)). The obtained free energy profiles are qualitatively in good agreement with the previous simulation40 as well as experimental results46. The deviations observed in the energetics are due to differences in force-fields and protocol followed (section 1.1 of SI). For the sake of comparison, we have also calculated the free energy profile of a water molecule adjacent to the mica surface. From the free energy profiles, we observed that Rb+ and K+ ions have single free energy minimum, whereas Na+ ion, both divalent ions (Mg2+ and Sr2+) and water molecules (Ow) have two minima in the free energy profiles within the AR. The location of these minima and corresponding adsorption strength (ΔA - the free energy difference between the minimum and bulk region) are listed in the Table 1. The cations and water molecules adsorb at these free energy minima locations as observed in the density profiles (Figs 1c,d and S1S4 of SI).

### Adsorption Behavior of Monovalent Ions

#### Mica–RbCl system

Every unit cell of mica surface contains two ditrigonal cavities (Fig. 1b) where cations and water molecules compete to adsorb, and hence taken as adsorption sites in the coverage analysis. In distilled water system (i.e. no salt present), K+ ions occupy half of the cavities (i.e. fractional coverage, θK ~ 0.5), and the rest are occupied by L1 water molecules (θOw ~ 0.5). At the lowest RbCl salt concentration of (CRb,B) 0.04 M studied here, Rb+ and K+ ions adsorb on the cavities and respectively occupy around 0.17 and 0.48 fraction of total cavities (Fig. 4a) while coverage of L1 water molecules is decreased to θOw ~ 0.25. This adsorption of Rb+ and K+ ions is driven by their adsorption strength (ΔA) at the mica surface. Our calculations showed (Fig. 3b) an insignificant difference in their adsorption strength (ΔARb ~ ΔAK), means both of them have an equal chance to occupy an adsorption site. As a result, we observed K+ ions were able to maintain their fractional coverage (of θK ~ 0.48) in the presence of Rb+ ions. Furthermore, lesser adsorption strength of L1 water molecules compared to both, Rb+ and K+ cations (Fig. 3a,b and Table 1) leads to their desorption from the surface. In this regime, the adsorption of Rb+ ions (θRb = 0.5), occurs at a minimal desorption of K+ ions ($\mathrm{\Delta }{\theta }_{K}=0.13$) and significant desorption of water molecules ($\mathrm{\Delta }{\theta }_{Ow}=0.4$) highlighting the role of similar hydration energy of Rb+ and K+ ions (Table 1). The adsorption of Rb+ ions in this regime is governed by the attraction from the mica surface.
The next adsorption regime (i.e. 1.3 ≤ CRb,B < 3.5 M) corresponds to the transition regime where predominantly the development of RbCl and KCl clusters occur. The total adsorption of (both, K+ and Rb+) cations beyond fractional coverage of (θK + θRb>) 0.5 creates an overcharge on the mica surface. This surface overcharging is compensated by the adsorption of Cl ions observed around 4 Å adjacent to the mica surface (Fig. S1 of SI). The association of these anions (Cl) with adsorbed cations leads to a formation of salt clusters (i.e. RbCl and KCl) on the mica surface. We analyzed the average (Qavg), maximum (Qmax) and the total number of clusters (Qn) formed by ion-pairs in the cluster calculations. Ion-pairs are defined as the combination of the cation-anion pair located within the first minimum of cation-anion pair correlation function (PCF). A collection of such ions forming a network of ion-pairs having a minimum three ions are defined as the cluster (i.e. excluding monomers and dimers). In the first adsorption regime, while the Cl ions do associate with Rb+ ions and form around ${Q}_{n}\simeq 10$clusters (Fig. 5c), nevertheless Qavg of RbCl and KCl clusters remain around 5 (Fig. 5a). In the second regime, these small clusters are conjoined by the significant adsorption of Cl ions, leading to the formation of bigger clusters. During this regime, we observed that Qavgand Qmax of RbCl grows from around 5 to 10 and 9 to 35, respectively (Fig. 5a,b). Whereas, Qavg and Qmax of KCl remained constant at around 5 and 12 respectively. The association of Cl with adsorbed cations is further confirmed by the coordination number analysis (Fig. 4b), where coordination number is defined as the number of anions (or water molecules) present within the first minimum of PCF. We observed an increase in the ion-Cl coordination number (${C}_{n}^{ion-Cl}$) and decrease in the ion-water coordination number (${C}_{n}^{ion-Ow}$) of both Rb+ and K+cations. Since both of these ions have similar hydration energy hence the rate of change of coordination number (i.e. decrease in ${C}_{n}^{ion-Ow}$ and increase in ${C}_{n}^{ion-Cl}$) is similar in both of the ions. This suggests that cation hydration energy plays a crucial role. During this regime as well, the adsorption of Rb+ ions (θRb = 0.46−0.64) occurs by the desorption of energetically less favorable L1 water molecules $\left({\theta }_{Ow}=0.12-0.06\right)$, while the K+ ions are retained $\left({\theta }_{K}\simeq 0.3\right)$ (Fig. 4a).
The third regime of RbCl adsorption isotherm (i.e. CRb,B ≥ 3.5 M) is mainly due to (a) salting out of RbCl near the mica surface and (b) increased concentration (and hence chemical potential) of Rb+ ions in bulk solution. The salting out behavior is confirmed by the cluster size analysis (Fig. 5a–c), where, the Qavg and ${Q}_{max}$ of RbCl cluster increased to around 105 and 190 from 10 and 35, respectively(Fig. 5a,b). Due to the formation of the bigger cluster, the Qn decreased from ~12.5 to 2.5 (Fig. 5c). The two-dimensional (2D) density distribution of ions and water present in the AR at CRb,B = 4.62 M shows that RbCl salt are arranged in triangular type lattice on the mica surface (Fig. 6). The Rb+ions adsorbed on the cavities are surrounded by 3 Cl ions adsorbed on top of the silicon (Si) atom of mica surface. This is the first computational study which shows surface mediated early salting of RbCl at 4.62 M compared to the salt formation in bulk solution at solubility limit of 7.52 M. Since the number of adsorbed L1 water molecules are minimal, hence the adsorption of Rb+ ions in this regime (${\theta }_{Rb}=0.64-0.87$) occurs by the desorption of K+ ions (θK = 0.3−0.12). The QnQavg and Qmax of KCl clusters remains constant during this third regime (Fig. 5a–c). In the cluster calculations, the monomer and dimers are not included and the invariant cluster size parameters (QavgQmax and Qn) of KCl cluster at higher concentration indicate that the monomers and dimers of K+-Cl ion-pairs are desorbing in this regime.
In summary, Rb+ ions adsorption on the mica surface in the three regimes is respectively governed by (a) attraction from the mica surface, (b) development of RbCl cluster and (c) salting out behavior at a higher CB. Due to similar hydration energy of Rb+ ions with competing K+ ions, the desorption of K+ ions is slow as compared to less favorable L1 water molecules. The mechanism of Rb+ ions adsorption occurs mainly by the desorption of adsorbed water molecules, and at higher concentration by the desorption of K+ ions from the surface.

#### Mica–NaCl system

The adsorption behavior of Na+ ion on mica surface is similar to Rb+ions, as explained above. Here also we observed three adsorption regime (Fig. 2), with adsorption of Na+ ions in the first regime governed by the attraction from the surface, and development of NaCl cluster in the later stages (Fig. 5d–f). The main difference is the higher hydration energy of Na+ ion compared to Rb+ and K+ ion (Table 1). Due to this significant difference, we hypothesize that interfacial water should play a crucial role in the adsorption of Na+ ions here. Indeed we find five noteworthy observations related to interfacial water in Na+ ions adsorption which are absent in Rb+ ion case. (a) Retention of L1 water molecules (${\theta }_{Ow}$) even at higher CNa,B, (b) total fractional coverage (i.e. θNa + θK + θOw) exceeding 1, (c) higher number of water molecules in the AR in Na+ system compared to Rb+ system, (d) constant ${C}_{n}^{Na-Ow}$ at all CNa,B and (e) absence of significant NaCl cluster. The reasons for these observations are explained below.
In our analysis, we observed that ${\theta }_{Ow}\sim 0.23$ (L1 water molecules) at all NaCl concentrations studied (Fig. 4c). These L1 water molecules are found in two configurations; either solely adsorbed on the cavities or co-adsorbed with Na+ ions as part of cations hydration shell (Fig. S12 of SI). This co-adsorption of water is possible due to smaller hydration shell size (Fig. S6 of SI) and higher hydration energies of Na+ ions (Table 1) compared to K+ and Rb+ ions. With the increase in concentration, the fraction of water molecules co-adsorbed with Na+ions increases linearly (Table S2 of SI). As a result, the total fractional coverage of adsorbed species (i.e. θNa + θK + θOw) exceeds 1.0 at higher concentrations (Fig. 4c).
To understand the constant profile of ${C}_{n}^{Na-Ow}$, we probed the total number of water molecules in AR. We found that presence of a higher number of water molecules and their redistribution from K+ to Na+hydration shell is responsible for this behavior (Figs S9 and S10 of SI) which is explained below. Our previous work has shown that, while the majority of the L2 and L3 water molecules (Fig. 1d) hydrate the adsorbed cations (K+ and Na+/Rb+), however a small fraction of free (i.e. non-hydrating) water molecules are also present. The presence of these free water molecules is essential to form a network of hydrogen bonds with all molecules of L2 + L3 layer and especially with L1 water molecules, thus stabilizing L2 and L3 layer35,38. Since the number of L1 water molecules is significant in Na+ ions, this leads to the higher fraction of free water molecules of L2 and L3 layer even at higher salt concentration of Na+ ions as compared to the case of Rb+ ions (Fig. S9 of SI). In addition, though the number of K+ ions and water molecules hydrating them decreases with an increase in CNa,B, however, the total number of hydrated water molecules (i.e. hydrating Na+ and K+ ions) is found to remain constant at all ${C}_{Na,B}$ (Table S2 in SI). This suggests that water molecules are re-distributing from K+ hydration to Na+ hydration shell, motivated by their hydration energies (Fig. S10 of SI).
Since Na+ ions are preferentially hydrated by water molecules, Cl ions adsorb more near the K+ ions and preferably form KCl cluster as compared to NaCl cluster. This is confirmed in the cluster size analysis where we observe that QavgQmax and Qn of NaCl cluster is less than KCl cluster (Fig. 5d–f). The adsorption of Na+ ion in the third regime of adsorption isotherm is governed by (a) increased ${C}_{Na,B}$, which forces Na+ ions to adsorb on the surface, and (b) subsequent desorption of K+ions. Both of these phenomena is captured in cluster size analysis, where a decrease in KCl cluster size (especially Qmax), and corresponding increase in QavgQmax and ${Q}_{n}$ of NaCl cluster is observed(Fig. 5d–f). In the RbCl system, the Rb+ adsorption in the third regime occurs due to desorption of both water molecules and K+ ions, whereas here in NaCl system K+ ions desorption is only the limiting factor. Due to higher hydration energy of Na+ ions, the water molecules are retained in the hydration shell whereas desorption of K+ ions occur.

### Adsorption Behavior of Divalent Ions

Similar to the monovalent ions, here also we have performed coverage ($\theta$) and coordination number (Cn) analysis of divalent ions at various CB. The role of higher hydration energy of divalent ions is very clear in this analysis. In the first regime of adsorption isotherm, (i.e. CB < 1.3 M) the coverage of both divalent ions increases (Fig. 2). We find that the coverage of L1 water molecules also increases in divalent ions case (Fig. 8a,c) as opposed to decreasing and a constant trend observed in RbCl and NaCl systems (Fig. 4a,c). In the first regime itself, the total coverage of cations and L1 water molecules (i.e. θM + θK + θOw; M = Sr/Mg) reaches 1, with ${\theta }_{Ow}$ ~ 0.5 (Fig. 8a,c). From coverage analysis, it is clear that the adsorption of divalent ions in the first regime is governed by the surface attraction hence leads to the rapid rise in coverage. Whereas in the second regime (CB ≥ 1.3 M), the adsorption occurs by the depletion of K+ ions. The cluster size analysis also confirms this hypothesis, where we find an insignificant number of M-Cl (where M = Sr/Mg) clusters formation in the first adsorption regime and a minimal number of clusters in the second regime (Fig. S15 in SI). This indicates that salting out behavior as observed in the RbCl system is not present in the divalent ions case. Again, the ion hydration energy plays a crucial role here. The ions prefer to be surrounded by water molecules (Fig. 7, Figs S13 and S14 of SI) as compared to Cl ions, hence the increase in coordination number (${C}_{n}^{M-Cl}$M = Sr/Mg) is minimal in divalent ions case (Fig. 8b,d).

## Summary and Conclusion

We have performed series of MD simulations of monovalent (Rb+ and Na+) and divalent (Sr2+ and Mg2+) cations based salt solutions (CB = 0–4.5 M) to investigate the role of cation charge, hydration energy, counter-ion (K+) competitiveness and co-ion (Cl) association on their adsorption and structural behavior adjacent to mineral (mica) surface. We found that adsorption of monovalent ions occurs in 3 regimes; initial rapid increase for CB < 1.3 M, followed by a slow increase between 1.3 ≤ CB < 3.5 M and a rapid increase beyond CB ≥ 3.5 M. Whereas divalent ions exhibit only 2 regime; initial rapid increase followed by early saturation. Despite having higher electrostatic attraction, adsorption of divalent ions is lesser as compared to monovalent ions.
The free energy calculation revealed that rapid rise in ion concentration near surface in the first regime of adsorption isotherms was due to surface attraction. Coverage and cluster analysis showed the association with Cl co-ions was the reason for a slow increase in the second regime as well as a rapid increase in the third regime due to cluster growth. In case of adsorbing cation (Rb+) which have lower hydration energy (and comparable to hydration energy of competitive surface K+ ion), they repel water molecules from AR and prefer to form large cation-anion (RbCl) clusters leading to surface mediated salting out behavior. For the cations (Na+) which have moderate hydration energy, they retain water molecules in their hydration shell and does not prefer to form cation-anion clusters. The divalent cations have very high hydration energy, due to which they form tight bound water hydration shell around them. This effectively increases their size which leads to lesser adsorption and early saturation.
The findings of this work, i.e. molecular understanding of adsorption of ions at the mineral-water interface, mechanism and role of hydration energy, have profound applications in toxic element contaminants in aquifers and surface water, plant nutrient supply and effectiveness of water purification method, where maximum ions adsorption on adsorbent is desirable. The obtained understanding would help in the better design of these adsorbate materials. The findings also have implications in super-capacitors, where ion adsorption on charged surfaces from electrolyte solution dictates their energy storage capacity. Our analysis finds that higher concentration of elecrolyte is not always desirable, rather hydration structure plays the crucial role.

### Methods: Molecular dynamics (MD) simulations

In muscovite mica (KAl2(Si3Al)O10(OH)2), the octahedral sheet(O) of aluminum(Al) is sandwiched between two silicon(Si) tetrahedral sheets(T) making mica as a TOT layered structure. An isomorphic substitution of one out of four Si4+ atom in the tetrahedral sheet by an Al 3+ atom yields to a permanent surface charge deficit of −1e per unit cell. This deficit charge is balanced by the cation, mostly potassium (K+) ion, which holds two TOT layer together by electrostatic attraction. A cleaved mica has an atomically smooth surface with the exposed hexagonal ring structure formed by sharing of basal oxygen atoms between Si and Al atoms. In this work 9 × 6 × 2 unit cell of muscovite mica was created using the X-ray data48, which gives a mica slab of $46.86×54.1×20.0$ Å.
The simulation system was constructed such that the surface of muscovite mica (001 plane) was in direct contact with aqueous solution. Interactions between muscovite mica atoms were described using the CLAYFF force field49. Water molecules in the systems were represented using simple point charge extension (SPC/E) model50. In this work potential parameters for Na+ and Cl ions were taken from Smith and Dang51, Rb+ ion from Joung and Cheatham52, Mg2+ ion from Aqvist53 and Sr2+ ion from Mamatkulov et al.54 (Table S3 in SI). The initial configuration of the aqueous systems were created using the Packmol software55. Open source LAMMPS package was used to perform MD simulations in an NVT ensemble56. Periodic boundary conditions were applied in the lateral x and y directions. The system is non-periodic in z- direction and has a length of 300 Å, out of which around 20 Å is the mica surface, 65 Å is the liquid region and rest is the vapor region. The simulation box was bounded by a repulsive graphene sheet at the vapor side. The temperature of the system was maintained at 298 K using Nose-Hoover thermostat57,58. The long-range Coulombic interactions were calculated using the particle-particle particle-mesh method for the slab system having vacuum size of 636 Å and accuracy of 10−4. The Lennard-Jones interactions and short-range part of Coulombic interactions were calculated with a cutoff distance of 12.5 Å. The rigidity of the water molecule was maintained using SHAKE algorithm59. All mica atoms except surface K+ ions were kept fixed in all simulations. The systems were equilibrated for 30 ns followed by a production run of 5 ns with a step size of 2 fs. The finite size effect was investigated by studying few larger NaCl systems and the results were found to be invariant as shown in Fig. 2.

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