Investigating local field tuning Fermi resonance of CS2 by Raman spectroscopy and DFT calculations

In the spectroscopic study of polyatomic molecules, Fermi resonance (FR) is a vibrational coupling and energy transfer phenomenon that widely exists intra- and intermolecular. In particular, the FR coupling between the fundamental mode ν1 and the doubling mode 2ν2 of the CS2 molecule has attracted extensive research. In this work, we investigate the effect of local field on tuning the FR of CS2. By analyzing the Raman spectra of CS2 mixed with methanol and ethanol with different mole fractions, the results indicated that weak HBs interactions in binary solutions can be reflected by the linear frequency shift of the C-H bond vibrations (in methanol and ethanol) with different molar concentrations. Furthermore, the geometrical structure was optimized using DFT simulation, and the vibration analysis and interaction energy were carried out. The simulated Raman spectra are in good agreement with the experiments. In addition, high-pressure Raman spectra of CS2 were obtained by diamond anvil cell technique (up to 9.19 GPa) and a pressure-induced phase transition was observed at 1.71 GPa. The results demonstrated that the pressure-induced polymerization phase transition of CS2 molecules causes the close packing and more orderly arrangement of molecules, resulting in the enhancement of FR coupling. HB and high pressure tune the FR of the CS2 molecule differently.

Roles of hydrogen bonding interactions and hydrophobic effects on enhanced water structure in aqueous solutions of amphiphilic organic molecules

Insights into the solute-induced water structural transformations are essential to understand the role of water in biological and chemical reaction processes. Herein, the structural changes in water induced by amphiphilic organic molecules were investigated using concentration-dependent derivative Raman spectroscopy (DRS) combined with two-dimensional Raman correlation spectroscopy (2D Raman-COS). We shall restrict our attention in this work to binary mixtures of water with dimethyl sulfoxide (DMSO), acetone, and isopropanol (IPA), all of which have similar chemical structures. The spectral changes in O:H and OH stretching modes illustrate that the solute molecules induce an enhancement of the water structure in dilute solutions, where the enhanced degree of water structure is closely related to the size of the dipole moment of organic molecules. In addition, the transformations of solute-induced water-specific structures were evaluated by 2D Raman-COS, which shows that the strong hydrogen bond (H-bond) structure of water is more sensitive to organic molecules and induces a transition to the weak H-bond structure of water.

Synthesis, characterization, solution chemistry and anticancer activity of [NiCl2(Ph2P-N(R)-PPh2)] (R = 2-CH2Py, CH2Ph and p-tol) complexes

In this work three Ni²⁺ complexes with general formula [NiCl₂(Ph₂P-N(R)-PPh₂)], R = 2-CH₂Py (Py = pyridine) - 1, CH₂Ph (Ph = phenyl) - 2 and p-tol (p-tol = p-tolyl) - 3, were synthesized and characterized. These complexes were obtained in high yield by the reaction of NiCl₂.6H₂O and the corresponding diphenylphosphinoamine ligand (Ph₂P-N(R)-PPh₂) in CH₂Cl₂/MeOH (1:1) solution, at room temperature (∼25 °C), and characterized by ¹H and ³¹P {¹H} NMR, vibrational spectroscopy in the infrared region, electronic spectroscopy in the UV-Vis regions, elemental analysis (%C, %H, %N) and single-crystal X-ray diffraction. The solution chemistry was studied in CDCl₃/dmso-d⁶ (dimethylsulfoxide) or neat dmso-d⁶ using complex 2 as a model. The complexes were evaluated as cytotoxic agents against two cancer cells lines, A549 (lung cancer cells), B16F10 (melanoma cells) and the health cells HaCaT (human epithelial keratinocytes).

Effect of solution chemistry on the transport of short-chain and long-chain perfluoroalkyl carboxylic acids (PFCAs) in saturated porous media

Perfluorocarboxylic acids (PFCAs) are one of the most widely detected classes of PFAS in the global environment after decades of intensive use. This study investigated the impact of perfluorinated carbon chain length on the transport behavior of PFCAs by testing and modeling two short-chain (PFPeA and PFHxA) and two long-chain PFCAs (PFOA and PFDA) in laboratory water-saturated columns. Moreover, their transport behavior was examined under different solution chemistry conditions, including pH, ionic strength, and cationic type. The experimental and simulation results indicated that the chain length had a limited impact on transport behaviors of PFPeA, PFHxA, and PFOA under various pH and ionic strengths, evidenced by their tracer-like breakthrough curves. In contrast, the mobility of PFDA was significantly affected by pH and ionic strengths. Additionally, the transport of all four PFCAs was inhabited in the presence of the divalent cation Ca²⁺. This study could help predict migration behavior and assess the potential risk of PFCAs in the subsurface system.

Sorption of microcystin-RR onto surface soils: Characteristics and influencing factors

Microcystins are frequently detected in cyanobacterial bloom-impacted sites; however, their mobility potential in soils is poorly understood. This study aimed to elucidate the sorption behaviors of microcystin-RR (MC-RR) in heterogeneous soils and evaluate critical affecting factors. MC-RR sorption followed the pseudo-second-order kinetics and Freundlich model. All isotherms (n = 0.83-1.03) had no or minor deviations from linearity. The linear distribution coefficients (K_d) varied from 2.64 to 15.2 across soils, depending mainly on OM and CEC. Stepwise regression analysis indicated that the K_d was predictable by the fitting formula of: K_d = 2.56 + 0.15OM + 0.28CEC (R² = 0.45). The sorption was an endothermic physisorption process, involving electrostatic forces, cation exchange and bridging, H-bonding, ligand exchange, and van der Waals forces. The sorption of MC-RR (dominantly behaved as electroneutral zwitterions) at pH > 5 was insensitive to pH change, while more MC-RR (anionic species) was adsorbed at lower pH and in the presence of Ca²⁺. The study provides insights into the sorption of MC-RR across a range of soil properties and water chemistry for the first time, which is of importance for a better understanding of the mobility potential of microcystins in the terrestrial systems.

Linking the effect of temperature on adsorption from aqueous solution with solute dissociation

Imperative decarbonization of water purification processes entails alternative regeneration methods for activated carbon. Regeneration based on changing dissociation equilibria, i.e. a major influencing factor on adsorption, usually requires the addition of acids/bases, but may also be triggered by temperature swing. Although adsorption and dissociation are both temperature-dependent phenomena, their conjunction has received little attention regarding trace organic compounds (TrOCs) and large temperature intervals, in particular above ΔT ≥ 50 ^∘C. Therefore, we studied the adsorption equilibria of 16 TrOCs onto one granular activated carbon at temperatures ranging from 20 to 95 ^∘C. The majority of compounds (12/16) exhibited an exothermic apparent adsorption enthalpy, while 3 out of 16 exhibited an endothermic apparent enthalpy. The range spanned from - 46 to + 50 kJ mol^-1 (median at - 17 kJ mol^-1). The possible origins of endothermic adsorption were discussed. A rationale of shifting pK_a and thus changing dissociation of TrOCs was introduced and traded off against existing rationales, i.e. changing solute solubility, changing adsorption heat capacity, and saturation effects of the adsorbates. This knowledge may allow designing temperature swing adsorption processes that unlock the dissociation switch. The augmented process efficiency can thus provide the foundation for low-carbon emission, circular water purification processes.

Increasing ionic strength and valency of cations enhance sorption through hydrophobic interactions of PFAS with soil surfaces

The effect of soluble cations on sorption in soils of a range of anionic PFAS is not well studied. We investigated the role of three common cations (Na⁺, Ca²⁺, and Mg²⁺) at varying solution concentrations on the sorption coefficients (K_d) of 18 anionic PFAS in two contrasting soils. The effective charge of the soil suspension (Zeta potential) became less negative as the concentration of these cations increased in the soil solutions. Perfluorinated compounds showed greater sorption than polyfluorinated compounds, with sulfonates of comparable chain lengths showing higher sorption than the carboxylates. We observed that the K_d values of several PFAS in the two soils were positively correlated with the concentration of cations in solution, especially in the presence of polyvalent cations (Ca²⁺and Mg²⁺). The changes in sorption with cation concentration were more prominent for long-chain PFAS, with C > 10 PFAS being completely removed from solution at higher cation concentrations. The emerging PFAS (replacement compounds GenX and ADONA) showed negligible or little sorption (K_d < 0.6 L/kg). While several mechanisms contribute towards sorption of PFAS in the presence of cations, we conclude that the primary effect of cations is through screening of negative charges on head groups of PFAS and reorientation of molecules at the interface between organic matter surfaces and soil solution as well as charge neutralisation at soil solid surface. Screening of negative charges allows for greater hydrophobic interaction between hydrophobic tails of PFAS and soil surfaces resulting in greater sorption. Increasing cation concentrations in soil solutions could thus reduce mobility of PFAS through a soil profile.

Transport characteristics of DNA-tagged silica colloids as a colloidal tracer in saturated sand columns; role of solution chemistry, flow velocity, and sand grain size

In recent years, DNA-tagged silica colloids have been used as an environmental tracer. A major advantage of this technique is that the DNA-coding provides an unlimited number of unique tracers without a background concentration. However, little is known about the effects of physio-chemical subsurface properties on the transport behavior of DNA-tagged silica tracers. We are the first to explore the deposition kinetics of this new DNA-tagged silica tracer for different pore water chemistries, flow rates, and sand grain size distributions in a series of saturated sand column experiments in order to predict environmental conditions for which the DNA-tagged silica tracer can best be employed. Our results indicated that the transport of DNA-tagged silica tracer can be well described by first order kinetic attachment and detachment. Because of massive re-entrainment under transient chemistry conditions, we inferred that attachment was primarily in the secondary energy minimum. Based on calculated sticking efficiencies of the DNA-tagged silica tracer to the sand grains, we concluded that a large fraction of the DNA-tagged silica tracer colliding with the sand grain surface did also stick to that surface, when the ionic strength of the system was higher. The experimental results revealed the sensitivity of DNA-tagged silica tracer to both physical and chemical factors. This reduces its applicability as a conservative hydrological tracer for studying subsurface flow paths. Based on our experiments, the DNA-tagged silica tracer is best applicable for studying flow routes and travel times in coarse grained aquifers, with a relatively high flow rate. DNA-tagged silica tracers may also be applied for simulating the transport of engineered or biological colloidal pollution, such as microplastics and pathogens.

Thermodynamics of ion exchange coupled with swelling reactions in hydrated clay minerals

Crystalline hydrates of swelling clay minerals (smectites) exhibit a strong coupling between their ion exchange and hydration/dehydration reactions. The uptake or removal of water from smectite interlayers as a result of a change in the environmental conditions also leads to the partitioning of cations. Three factors, the solid ion composition, the solid basal spacing/water content, and the aqueous solution composition, are all implicated in controlling the thermodynamics of ion exchange. However, conventional approaches to measuring the exchange free energy cannot separate the influence of each of these individual factors. Here, we explore the energetics of the swelling and ion exchange reactions in montmorillonite using a potential of mean force approach and the thermodynamic integration method within molecular simulations. We investigate the influence of solution and clay composition on the spontaneity of the reactions, focusing on the 2 water-layer hydration state. The swelling simulations provide the equilibrium water content, interlayer water structure, and basal spacings, while thermodynamic integration of sodium-potassium exchange in the aqueous solution and solid phase are combined to calculate ion exchange free energies as a function of solution composition. Results confirm the tendency of the clay to collapse to lower hydration states as the concentration of the solution increases. Changes to the equilibrium water content, even at fixed hydration states, and the composition of the mixed electrolyte solution play a critical role in driving ion exchange and the selectivities of the clay to the exchanged cation, while the composition of the solid phase is shown to be insignificant. These findings underscore the extreme sensitivity of clay swelling and ion exchange thermodynamics to small (tenths of an Angstrom) deviations in layer spacing.

Comparison of phosphonate, hydroxypropyl and carboxylate pendants in Fe(III) macrocyclic complexes as MRI contrast agents

Fe(III) macrocyclic complexes containing a macrocycle and three pendant groups including phosphonate (NOTP =1,4,7-triazacyclononane-1,4,7-triyl-tris(methylenephosphonic acid), carboxylate (NOTA = 1,4,7 - triazacyclononane - N,N',N″ - triacetate) or hydroxypropyl (NOHP =(2S,2'S,2"S)-1,1',1″-(1,4,7-triazonane-1,4,7-triyl)tris(propan-2-ol)) were studied in order to compare the effect of these donor groups on solution chemistry and water proton relaxivity. All three complexes, Fe(NOTP), Fe(NOHP) and Fe(NOTA), display a large degree of kinetic inertness to dissociation in the presence of phosphate and carbonate, under acidic conditions of 100 mM HCl or 1 M HCl or to trans-metalation with Zn(II). The r1 proton relaxivity of the complexes at 1.4 T, 33 °C is compared over the pH range of 1 to 10. At pH 7.4, 33 °C, 1.4 T, Fe(NOHP) has the largest relaxivity (1.5 mM-1 s-1), Fe(NOTP) is second at 1.0 mM-1 s-1, whereas Fe(NOTA) is the lowest at 0.61 mM-1 s-1. Fe(NOTP), Fe(NOHP) and Fe(NOTA) all show an increase in relaxivity at very acidic pH values (< 3) that is consistent with an acid-catalyzed process. Variable temperature 17O NMR studies at near neutral pH are consistent with the absence of an inner-sphere water molecule for Fe(NOTP) and Fe(NOHP), supporting second-sphere or outer-sphere water contributions to proton relaxation. Fe(NOTP) shows contrast enhancement in T1 weighted MRI studies in mice and clears through a renal pathway.

Conditional Equilibrium Constants Reviewed

A free energy-based conceptual theoretical framework from which the conditional equilibrium constant can be comprehensibly understood is presented. This constant is found to be a weighted geometric mean of the equilibrium constants of the reactions of all forms of the conditioned species under buffering conditions, where the weight is given by a function of their predominance in terms of their mole fractions. Once it is shown that this type of equilibrium constant can be easily deduced form free energy functions, it is shown how corrections for activity coefficient can be incorporated as well. The framework additionally permits to interpret side-reactions coefficients as free energy terms related to the chemical speciation of the system, allowing the use of the generalization of Hess' law to obtain conditional constants and a straightforward deduction of multiconditional equilibrium constants. Furthermore, different uses of the conditional constants along the actual literature are reviewed as well allowing to have a complete and updated panorama of the employment of this important concept in chemical and speciation analysis in many areas of research.

Protein binding and cytotoxic activities of monomeric and dimeric oxido-vanadium(V) salan complexes: Exploring the solution behavior of monoalkoxido-bound oxido-vanadium(V) complex

Three ONNO donor tetradentate diamino bis(phenolato) "salan" ligands, N, N'-dimethyl-N, N'-bis-(5-chloro-2-hydroxy-3-methyl-benzyl)-1,2-diaminoethane (H₂L¹), N, N'-dimethyl-N, N'-bis-(5-chloro-2-hydroxy-3-isopropyl-6-methyl-benzyl)-1,2-diamino-ethane (H₂L²) and N, N'-bis-(5-chloro-2-hydroxy-3-isopropyl-6-methyl-benzyl)-1,2-diaminocyclohexane (H₂L³) have been synthesized by following Mannich condensation reaction. Reaction of these ligands with their corresponding vanadium metal precursors gave one oxidomethoxidovanadium(V) [V^VOL¹(OCH₃)] (1) and two monooxido-bridged divanadium (V, V) complexes [V^VOL^2-3]₂(μ-O) (2-3). The complexes were characterized by IR, UV-vis, NMR and ESI mass spectrometry. Also, the structure of all the complexes (1-3) was confirmed by the Single-Crystal X-ray diffraction analysis, which revealed a distorted octahedral geometry around the metal centres. The solution behavior of the [V^VOL¹(OCH₃)] (1) reveals the formation of two different types of V(V) species in solution, the structurally characterized compound 1 and its corresponding monooxido-bridged divanadium (V, V) complex [V^VOL¹]₂(μ-O), which was further studied by IR, and NMR spectroscopy. The electrochemical behavior of all the complexes was evaluated through cyclic voltammetry. Interaction of the salan-V(V) complexes with human serum albumin (HSA) and bovine serum albumin (BSA) were analysed through fluorescence quenching, UV-vis absorption titration, synchronous fluorescence, circular dichroism studies, and förster resonance energy transfer (FRET). Finally, the in vitro cytotoxicity of the complexes was investigated against MCF-7 and HT-29 and NIH-3T3 cell lines. Cytotoxicity value of complexes in both MCF-7 and HT-29 follows the same trend that is 3 > 1 > 2 which is in line with protein binding affinity of the complexes.

Effect of solution chemistry on aqueous As(III) removal by titanium salts coagulation

Solution chemistry is of great importance to the removal of arsenic by coagulation through influencing the speciation of arsenic, the in situ precipitation of metal salts coupled with the adsorption and coprecipitation behavior of arsenic during coagulation. While the researches on the influence of solution chemistry in As(III) removal by titanium salts, a promising candidate for drinking water treatment was still deficient. Batch tests were performed to evaluate the removal of As(III) by titanium salts coagulation under solution chemistry influences. The results indicated that As(III) removal by Ti(SO₄)₂ and TiCl₄ increased first and then decreased with the rising of solution pH from 4 to 10. TiCl₄ preformed better in As(III) removal than Ti(SO₄)₂ at pH 4-8, but the opposite trends were observed at pH 9-10. XPS analysis indicated that the involvement of surface hydroxyl groups was primarily responsible for As(III) adsorption on Ti(IV) precipitates. As(III) removal was inhibited in the presence of SO₄^2- mainly by competitive adsorption, especially at elevated SO₄^2- concentration under acidic and alkaline conditions. F^- exerted a greater suppressive effect than SO₄^2- via indirectly hindering Ti(IV) precipitate formation, and through direct competitive adsorption with H₃AsO₃, the inhibitive effect increased as F^- concentration increased and depended highly on solution pH. As(III) removal was promoted by co-existing Fe(II) primarily through the facilitation of Ti(IV) precipitation, especially under neutral and alkaline conditions, while it was inhibited to a different extent by the presence of high-concentration Mn(II) possibly via competitive adsorption. The presence of Ca²⁺ and Mg²⁺ enhanced the removal of As(III), but the positive effect did not increase as ionic concentration elevated.

Spectral investigation of phthalocyanine complexes of high-valence silver and their aggregates

Several novel silver(II) complexes ligating a tetra-substituted phthalocyaninate, [Ag(tbpc)] (where tbpc denotes tetra-tert-butylphthalocyaninate), [Ag(tppc)] (tppc = tetrakis(2,6-dimethylphenoxy)phthalocyaninate), [Ag(tObpc)] (tObpc = tetra-n-butoxyphthalocyaninate), and [Ag(tpySpc)] (tpySpc = tetrakis(4-pyridylthio)phthalocyaninate) have been synthesized and characterized by elemental analyses, MALDI-TOF MS, optical absorption, and magnetic circular dichroism (MCD) spectroscopy. Although all the compounds are well soluble in common organic solvents, concentration studies on their optical spectra in solutions have found that they are prone to strongly aggregate in a cofacial manner (i.e., H-aggregate). Silver(II) complexes, which are essentially non-fluorescent, are readily demetallated in the presence of appropriate reductant (e.g., I^- or BH₄^-) to liberate the corresponding macrocyclic ligand, which emits intense red fluorescence. Chemical oxidation by using NOBF₄ generates the corresponding silver(III) species.

Graphene oxide nanoparticles and hematite colloids behave oppositely in their co-transport in saturated porous media

Since iron oxide minerals are ubiquitous in natural environments, the release of graphene oxide (GO) into environmental ecosystems can potentially interact with iron oxide particles and thus alter their surface properties, resulting in the change of their transport behaviors in subsurface systems. Column experiments were performed in this study to investigate the co-transport of GO nanoparticles and hematite colloids (a model representative of iron oxides) in saturated sand. The results demonstrated that the presence of hematite inhibited GO transport in quartz sand columns due to the formation of less negatively charged GO-hematite heteroaggregates and additional deposition sites provided by the adsorbed hematite on sand surfaces. Contrarily, GO co-present in suspensions significantly enhanced the transport of hematite colloids through different mechanisms such as the increase of electrostatic repulsion, decreased physical straining, GO-facilitated transport of hematite (i.e., highly mobile GO nanoparticles served as a mobile carrier for hematite). We also found that the co-transport behaviors of GO and hematite depended on solution chemistry (e.g., pH, ionic strength, and divalent cation (i.e., Ca²⁺)), which affected the electrostatic interaction as well as heteroaggregation behaviors between GO nanoparticles and hematite colloids. The findings provide an insight into the potential fate of carbon nanomaterials affected by mineral colloids existing in natural waters and soils.

Role of solution chemistry in the attachment of graphene oxide nanoparticles onto iron oxide minerals with different characteristics

Given the ubiquity and abundance of the iron oxide minerals and their important roles in affecting the environmental fate of graphene oxide (GO) nanoparticles, the attachment of GO onto three iron oxide minerals (i.e., hematite, goethite, and ferrihydrite) under different solution chemistry conditions was investigated in this study. The main mechanism of the attachment of GO was electrostatic interaction. Calculations based on the DLVO theory showed that the attachment was a favorable process. Interestingly, the affinity of GO towards three iron oxide minerals was in the order of ferrihydrite > goethite > hematite. This result indicates that different characteristics of various iron oxides (e.g., specific surface area, crystal structure, and surface charge, and surface hydroxyl densities) can influence their attachment capacities for GO. The attachment of GO depended on the solution pH and ionic strength. Electrostatic attraction and hydrogen bonding were the important retention mechanisms for GO attachment when pH < pH_PZC (the point of zero charge) and pH > pH_PZC, respectively. The attachment capacities of iron oxides decreased with increasing ionic strength at lower pH because of the decrease of the electrostatic attraction. Meanwhile, the presence of divalent cations (i.e., Ca²⁺ and Cu²⁺) could significantly promote GO attachment mainly by the surface-bridging mechanism. Meanwhile, the enhancement effect of Cu²⁺ was greater than Ca²⁺ due to the greater complexation affinity of Cu²⁺. Furthermore, attachment isotherms showed that the presence of phosphate could inhibit the attachment of GO onto minerals obviously. Because phosphate could form inner-sphere surface complex on the iron oxide surface, and consequently decreased the electrostatic attraction between nanoparticles and minerals. Our study has important implications for predicting the fate of GO in natural environment where amounts of iron oxide minerals are present.

Different transport behaviors and mechanisms of perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS) in saturated porous media

Perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS) in soil aroused increasing concern, however there is little information about their transport in porous media, which is urgently needed to better control their environmental risks. In this study, saturated sand columns (considering the coupled effect of solution cation type and pH) and a two-site nonequilibrium transport model (TSM) were used to investigate the transport behaviors and mechanisms of PFOA and PFOS. Breakthrough data and the TSM parameters showed PFOA had higher mobility than PFOS, and divalent cation could inhibit their transport by increasing the nonequilibrium interactions between them and the sand. pH had little influence on PFOA migration when there was only monovalent cation in the solution since PFOA had limited affinity with the sand, however, polyvalent cation could provide additional adsorption sites for it through cation bridging and enhance the effect of pH. Differently, decreasing pH inhibited the transport of PFOS more significantly, and the effect was stronger than that of changing cation type. That proved mechanisms like hydrogen-bonding which were sensitive to solution pH played an important role in PFOS migration. These results provide important scientific basis to the remediation strategy and the migration prediction model development of PFOA and PFOS.

Insights into the mutual promotion effect of graphene oxide nanoparticles and tetracycline on their transport in saturated porous media

In this study, batch and column tests were performed to investigate the co-transport of graphene oxide (GO) nanoparticles and tetracycline in saturated porous media under various solution chemistry conditions. Research indicated that GO and tetracycline had mutual promotion effect on their transport in the porous media under all the tested conditions, which was ascribed to the high adsorption capacity of tetracycline onto GO and the increased electrostatic repulsion as well as their competition for deposition sites on sand surfaces. Interestingly, the mutually promoting function of GO and tetracycline under acidic conditions was greater than that under alkaline conditions, the dominant mechanism was that the increased solution pH decreased the sorption of tetracycline onto GO and weakened the deposition site competition. Furthermore, the mutually promoting effect of GO and tetracycline was Na⁺ or Ca²⁺ concentration-dependent. Specially, increased Ca²⁺ concentration weakened the promoting effect of GO on tetracycline transport but magnified the promoting effect of tetracycline on GO transport. This is because higher Ca²⁺ concentration could cause a decrease in the adsorption of tetracycline on GO and facilitate more tetracycline molecules to occupy the deposition sites on sand surfaces. Additionally, sodium dodecyl sulfate had enhancement effect on co-transport of GO and tetracycline. Findings from this study clearly indicated that antibiotics and carbon based nanomaterials may transport together under various solution chemistry conditions, and consequently affect their fates in aquatic environments.

Effect of multiple factors on the adsorption of Cd in an alluvial soil from Xiba, China

The effects of organic matter, free Fe oxides and Mn oxides in an alluvial soil on adsorption of Cd were studied through selective chemical extraction and adsorption experiments. Compared to untreated soil, after H₂O₂ treatment for removal of organic matter and NH₂OH·HCl treatment for removal Mn oxides, the distribution coefficient (K_d) decreased by a maximum of 25.2% and 64.1%, respectively. After dithionite-citrate-bicarbonate treatment for removal of free Fe oxides, K_d increased by 1670.2%. After increasing the solution pH from 2 to 3, K_d increased by 2842.1%, whereas after increasing the solution pH from 3 to 7, the adsorption tended stabilize. As the ionic strength increased from 0.001 M to 0.1 M NaNO₃, K_d gradually decreased, whereas at the same ionic strength, K_d decreased as the initial concentration of Cd increased. The effects of different background electrolytes on Cd adsorption was as follows: Ca²⁺ > Mg²⁺ > K⁺ > Na⁺ for cations and Cl^- ≈ SO₄^2- > NO₃^- for anions. The adsorption capacity of Cd increased as the increased of temperature, and it's a spontaneous endothermic process. The pseudo second-order rate model described the process of Cd adsorption well.

Release and stability of water dispersible biochar colloids in aquatic environments: Effects of pyrolysis temperature, particle size, and solution chemistry

Pathways for the physical disintegration of biochar (BC) and the release of water dispersible BC colloids (WDBC) have received much attention due to their unique impacts on carbon loss and contaminant. However, the current understanding of the mechanisms involved in WDBC formation and associated influencing factors is rather limited. This study systematically explored the effects of pyrolysis temperature, initial particle size, and solution chemistry on WDBC formation in aqueous solutions and examined the formation and colloidal stability of WDBC in natural solutions. Results showed that pyrolysis temperature determined the abrasion resistance of pyrolyzed BC, and the submicron fragment rate decreased in the order 400 °C (BC400) > 700 °C (BC700) > 200 °C (BC200). The WDBC yield decreased in the order BC400 (77.5-331 mg g^-1) > BC700 (33.5-173 mg g^-1) > BC200 (16.8-125 mg g^-1) depending on BC size at a solution ionic strength (IS) ≤ 1 mM, which was positively correlated with the submicron fragment rate of bulk BC. With the exception of BC200, increasing IS (0.1-20 mM) and decreasing pH (3.0-10.0) significantly inhibited WDBC yield. Release and sedimentation dominated the WDBC formation processes with the former being more susceptible to solution chemistry. Derjaguin-Landau-Verwey-Overbeek interactions properly explained the effect of IS on WDBC from BC400 and BC700, while the steric resistance of abundant dissolved organic carbon on BC200 was mainly responsible for the high formation of WDBC at high IS (20-50 mM). WDBC had high colloidal stability and could form and stabilize well in natural surface waters and soil solutions, suggesting the relevant risk of long-distance migration of WDBC in environments. These findings represent new knowledge regarding the physical decomposition and the fate of BC in the environment.

Enhanced adsorption of steroid estrogens by one-pot synthesized phenyl-modified mesoporous silica: Dependence on phenyl-organosilane precursors and pH condition

In this study, the phenyl-modified mesoporous materials were successfully synthesized using phenyl-organosilanes (trimethoxyphenylsilane and triethoxyphenylsilanea) by one-pot co-condensation method for the removal of estrone (E1), 17β-estradiol (E2), and 17α-ethinyl estradiol (EE2). Both the triethoxyphenylsilane-modified material (20%EtPh-MCM-41) and trimethoxyphenylsilane-modified material (20%MePh-MCM-41) could rapidly achieve equilibrium in 30 min at low adsorbent dosage of 0.025 g L^-1. But the different hydrolysable groups of trimethoxyphenylsilane and triethoxyphenylsilane led to the discrepancies in physicochemical properties of the 20%EtPh-MCM-41 and 20%MePh-MCM-41, and thus affected adsorption performance. The 20%EtPh-MCM-41 exhibited the faster estrogen adsorption rates expressed in pseudo-second-order kinetic constant than the 20%MePh-MCM-41 due to the more hydrophobicity. Conversely, the 20%MePh-MCM-41 had much more estrogen adsorption capacities than the 20%EtPh-MCM-41 because of the more available adsorption sites. The addition of the phenyl-organosilane improved estrogen adsorption by π-π and hydrophobic interactions, and the Langmuir-model-based maximum adsorption amounts could reach 99.02, 83.47, and 53.60 mg g^-1 for EE2, E2, and E1, respectively. But excessive concentration of phenyl-organosilane decreased adsorption capacities due to poor pore structure. Alkaline solution, which induced estrogen deprotonation and negative surface charge of absorbents, inhibited estrogen adsorption by electrostatic repulsion and the decreased hydrophobic interaction, but acidic and neutral solutions, ionic strength, and humic acid did not significantly affect estrogen removal. This work not only showed the high potential of trimethoxyphenylsilane-modified MCM-41 used in water purification for steroid estrogens, but also demonstrated the suitable selection of organosilane precursors was key in producing favorable materials with designed functionality.

Effects of particle size and solution chemistry on Triclosan sorption on polystyrene microplastic

PS microplastic particle (<5 mm) is an emerging contaminant of concern in aquatic and sediment systems with reported negative impacts on environmental and human health. TCS is a broad-spectrum antimicrobial which can affect ecosystems and result in long-term human health risks. The interaction between TCS and PS microplastic, partly determines the behavior and dispersion of TCS in the environment. In this study, the sorption kinetics and isotherms for TCS and PS microplastic were investigated. The influences of temperature, pH, ionic strength and coexisting heavy metals were assessed in batch experiments. The pseudo-second-order model (PSOM) was found to effectively describe the sorption kinetics of TCS on PS. TCS sorption on PS was found to be higher within the pH range of 3.0-6.0, while a decrease occurred at pH > 6.0. This result indicates that TCS⁰ was the major species contributing to the sorption process through hydrophobic interaction. Temperature did not affect the sorption of TCS on polystyrene, with sorption K_d values of 0.15, 0.16, 0.18 and 0.17 L/g at 288, 298, 308 and 318 K, respectively. Furthermore, the sorption amount of TCS showed no obvious variation with NaCl concentrations varying between 0.001 and 0.1 M. Finally, the coexistence of Cu(II)/Zn(II) had no significant influence on TCS sorption on PS, as Cu(II)/Zn(II) and TCS had different mechanisms of sorption on PS.

A novel flake-ball-like magnetic Fe3O4/γ-MnO2 meso-porous nano-composite: Adsorption of fluorinion and effect of water chemistry

A novel flake-ball-like magnetic Fe₃O₄/γ-MnO₂ meso-porous nano-composite was synthesized and characterized for defluoridation. Adsorption process, characters, and effects of solution chemistry on the adsorption of flourinion in Fe₃O₄/γ-MnO₂ were evaluated. The results show that the adsorption of fluorinion in the Fe₃O₄/γ-MnO₂ nano-composite is fitted with the Pseudo-first model and the Langmuir model, indicating that the adsorption process of fluorinion in the Fe₃O₄/γ-MnO₂ nano-composite was a physical process and not only controlled by the film diffusion but also controlled by the intra-particle diffusion and surface adsorption. It shows that the adsorption of fluorinion sharply decrease with the increase of pH due to the negative changed surface of Fe₃O₄/γ-MnO₂ in water and the competition of OH^- for the active points. The competition from decreases the adsorption of fluoride in the order of Cl^- < NO₃^- < SO₄^2-, which relied on the ratio of charge towards radius (z/r) of the anions, and the negatively charged humic acid competed with fluorinion for the adsorption sites. Based on the adsorption results and the XPS analysis, the OMn bond in the raw adsorbent supported the active site (OMnOH) for fluoride adsorption by forming an OMnF bond on the surface of Fe3O4/γ-MnO2.

Aggregation kinetics of microplastics in aquatic environment: Complex roles of electrolytes, pH, and natural organic matter

Microplastics are an emerging contaminants of concern in aquatic environments. The aggregation behaviors of microplastics governing their fate and ecological risks in aquatic environments is in need of evaluation. In this study, the aggregation behavior of polystyrene microspheres (micro-PS) in aquatic environments was systematically investigated over a range of monovalent and divalent electrolytes with and without natural organic matter (i.e., Suwannee River humic acid (HA)), at pH 6.0, respectively. The zeta potentials and hydrodynamic diameters of micro-PS were measured and the subsequent aggregation kinetics and attachment efficiencies (α) were calculated. The aggregation kinetics of micro-PS exhibited reaction- and diffusion-limited regimes in the presence of monovalent or divalent electrolytes with distinct critical coagulation concentration (CCC) values, followed the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The CCC values of micro-PS were14.9, 13.7, 14.8, 2.95 and 3.20 mM for NaCl, NaNO₃, KNO₃, CaCl₂ and BaCl₂, respectively. As expected, divalent electrolytes (i.e., CaCl₂ and BaCl₂) had stronger influence on the aggregation behaviors of micro-PS as compared to monovalent electrolytes (i.e., NaCl, NaNO₃ and KNO₃). HA enhanced micro-PS stability and shifted the CCC values to higher electrolyte concentrations for all types of electrolytes. The CCC values of micro-PS were lower than reported carbonaceous nanoparticles CCC values. The CCC[Ca²⁺]/CCC [Na⁺] ratios in the absence and presence of HA at pH 6.0 were proportional to Z^-2.34 and Z^-2.30, respectively. These ratios were in accordance with the theoretical Schulze-Hardy rule, which considers that the CCC is proportional to z^-6-z^-2. These results indicate that the stability of micro-PS in the natural aquatic environment and the possibility of significant aqueous transport of micro-PS.

Effects of pH on nano-bubble stability and transport in saturated porous media

An understanding of nano-scale bubble (NB) transport in porous media is important for potential application of NBs in soil/groundwater remediation. It is expected that the solution chemistry of NB water highly influences the surface characteristics of NBs and porous media and the interaction between them, thus affecting the stability and transport characteristics of NB. In this study, in addition to stability experiments, one-dimensional column transport experiments using glass beads were conducted to investigate the effects of pH on the NB transport behavior. The results showed that the NBs were more stable under higher pH. Column transport experiments revealed that entrapment of NBs, especially larger ones, was enhanced in lower-pH water, likely suggesting pH-dependent NB attachment and physical straining, both of which are also probably influenced by bubble size. Although relatively smaller NBs were released after switching the eluting fluid to one with lower ionic strength, most of the NBs in lower-pH water were still retained in the porous media even altering the chemical condition.

Behavior and mechanisms for sorptive removal of perfluorooctane sulfonate by layered double hydroxides

Perfluorooctane sulfonate (PFOS) is known to be extremely persistent and is toxic to wildlife and humans. In this study, we evaluated the sorptive removal behavior of PFOS from aqueous solution using three forms of layered double hydroxides (LDHs), namely, nitrate-, carbonate- and chloride-intercalated LDHs. Batch experiments showed that the sorption process was very fast with an equilibrium time of 10-60 min. The nitrate-LDH had the greatest ability to remove PFOS with a removal rate of 99.7% at an initial concentration of 100 mg/L and the maximum uptake capacity reached 865 mg/g. The sorption kinetic and equilibrium data could be fitted well with the pseudo-second-order model and Langmuir model, respectively. The intraparticle diffusion model suggests that both external diffusion and intraparticle diffusion are the rate-limiting processes for PFOS sorption onto the LDHs. The initial pH, background electrolyte concentration and coexisting ions influenced the sorption of PFOS by the LDHs. It was concluded that both surface adsorption and anion exchange were involved in the PFOS sorption onto the LDHs.

Insights into the subsurface transport of As(V) and Se(VI) in produced water from hydraulic fracturing using soil samples from Qingshankou Formation, Songliao Basin, China

Produced water is a type of wastewater generated from hydraulic fracturing, which may pose a risk to the environment and humans due to its high ionic strength and the presence of elevated concentrations of metals/metalloids that exceed maximum contamination levels. The mobilization of As(V) and Se(VI) in produced water and selected soils from Qingshankou Formation in the Songliao Basin in China were investigated using column experiments and synthetic produced water whose quality was representative of waters arising at different times after well creation. Temporal effects of produced water on metal/metalloid transport and sorption/desorption were investigated by using HYDRUS-1D transport modelling. Rapid breakthrough and long tailings of As(V) and Se(VI) transport were observed in Day 1 and Day 14 solutions, but were reduced in Day 90 solution probably due to the elevated ionic strength. The influence of produced water on the hydrogeological conditions (i.e., change between equilibrium and non-equilibrium transport) was evidenced by the change of tracer breakthrough curves before and after the leaching of produced water. This possibly resulted from the sorption of polyacrylamide (PAM (-CH₂CHCONH₂-)_n) onto soil surfaces, through its use as a friction reducer in fracturing solutions. The sorption was found to be reversible in this study. Minimal amounts of sorbed As(V) were desorbed whereas the majority of sorbed Se(VI) was readily leached out, to an extent which varied with the composition of the produced water. These results showed that the mobilization of As(V) and Se(VI) in soil largely depended on the solution pH and ionic strength. Understanding the differences in metal/metalloid transport in produced water is important for proper risk management.

Recent advances in application of (27)Al NMR spectroscopy to materials science

Valuable information about the local environment of the aluminum nucleus can be obtained through (27)Al Nuclear Magnetic Resonance (NMR) parameters like the isotropic chemical shift, scalar and quadrupolar coupling constants, and relaxation rate. With nearly 250 scientific articles per year dealing with (27)Al NMR spectroscopy, this analytical tool has become popular because of the recent progress that has made the acquisition and interpretation of the NMR data much easier. The application of (27)Al NMR techniques to various classes of compounds, either in solution or solid-state, has been shown to be extremely informative concerning local structure and chemistry of aluminum in its various environments. The development of experimental methodologies combined with theoretical approaches and modeling has contributed to major advances in spectroscopic characterization especially in materials sciences where long-range periodicity and classical local NMR probes are lacking. In this review we will present an overview of results obtained by (27)Al NMR as well as the most relevant methodological developments over the last 25years, concerning particularly on progress in the application of liquid- and solid-state (27)Al NMR to the study of aluminum-based materials such as aluminum polyoxoanions, zeolites, aluminophosphates, and metal-organic-frameworks.

Struvite-based phosphorus recovery from the concentrated bioeffluent by using HFO nanocomposite adsorption: Effect of solution chemistry

Here we reported struvite-based phosphorous recovery from the concentrated desorption effluent of a proprietary hydrated ferric oxide (HFO) nanocomposite (HFO-201) system, and the effect of solution chemistry (alkalinity, salinity, and dissolved organic matter (DOM)) on struvite formation was particularly focused on. The optimum P recovery rate (∼97%) and high quality struvite was obtained at 25°C, pH 9.0-9.5, and the molar Mg:NH4:P ratio of 1.4:4:1. The reaction reached equilibrium within ∼30min, much faster than the reported high purity struvite formation at neutral pH (several days required). It largely relied on the absence of Ca(2+) in the desorption effluent due to the Donnon co-ion effect exerted by HFO-201. Thermodynamic modelling with Stockholm humic model revealed that the presence of salinity and DOM resulted in a lower saturation index (SI) of struvite, thus inhibiting P recovery by struvite. Nevertheless, it is favorable to form struvite of large particle size. In addition, increasing the molar Mg:NH4:P ratio from 1:1:1 to 1.4:4:1 could significantly weaken the adverse effect of the high salinity and DOM. Direct addition of Ca(2+) could also result in phosphorous recovery, but the P content of the resultant solid (∼4.4%) is much lower than the formed struvite (∼17%). The results indicated that struvite process is a very attractive option to recover P from the desorption effluent, and the effect of solution chemistry is crucial to optimize the process.

Synthesis, spectral, thermal and biological studies on N(-)(2,4-dinitro-phenyl)-2-mercaptoacetohydrazide and its metal complexes

Complexes of VO(2+), Cr(3+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+) and Hg(2+) ions with N(-)(2,4-dinitrophenyl)-2-mercaptoacetohydrazide (H2L) have been prepared and characterized on the basis of elemental analysis, molar conductance, thermal (TGA, DTGA), spectral (IR, NMR, UV-Visible, MS) and magnetic measurements. The IR spectra show that H2L behaves in a mononegative and/or binegative bidentate manner. The sulfate bridged the two complex molecules in [Cu(HL)(H2O)2(½SO4)]⋅3H2O. The acetate functions as a monodentate in [Ni(HL)(OAc)(H2O)3] and [Cr(HL)(OAc)2(H2O)(EtOH)]. Different stereochemistries are proposed: octahedral for Cr(III), Ni(II), Hg(II) and [Cu(HL)(H2O)2(SO4)0.5]⋅3H2O, square-based pyramid for [VO(HL)2]⋅EtOH, square-planar for [Co(L)(EtOH)(H2O)]⋅H2O, [Cu(L)(H2O)2] and tetrahedral for [Zn(L)(EtOH)(H2O)], [Cd(L)(EtOH)(H2O)] and [Cu2(HL)(H2O)6]Cl3⋅H2O according to the data of electronic spectra and magnetic measurements. The TGA data support the formula and indicate the outer and inner solvents as well as the final residue. The thermodynamic parameters are calculated using the Coats-Redfern and Horowitz-Metzger methods. H2L and [Zn(L)(EtOH)(H2O)] showed the highest cytotoxic activity while H2L has a higher antioxidant activity than ascorbic acid. The ionization constant of the ligand and the stability constant of the Cu(II)H2L in absence and presence of hexamine buffer were calculated.

Critical evaluation of spectroscopic indices for organic matter source tracing via end member mixing analysis based on two contrasting sources

Despite the wide use of absorption and fluorescence spectroscopy for tracking the sources of dissolved organic matter (DOM), there are limited studies on evaluating their source discrimination capabilities at variable solution chemistry (pH, NaCl, Ca(2+), and DOM concentration). For this study, we compared the applicability of several well-known spectroscopic indices via end member mixing analysis based on two contrasting DOM sources (Suwannee River fulvic acid and an algal DOM). The absorption coefficients and the intensities of fluorescent components from parallel factor analysis (PARAFAC) showed linear relationships with increasing algal carbon fraction in the mixture of the two DOMs. In contrast, although they still behaved conservatively, spectral ratio indices such as spectral slopes, ratios of PARAFAC components, humification index, and fluorescence index changed in nonlinear patterns with the mixing ratios. The indices based on PARAFAC results exhibited strong discrimination capabilities, as indicated by high susceptibility to the changes in DOM sources relative to the analytical precision. While variable NaCl concentrations had limited effects, most fluorescence indices were considerably affected by other solution chemistry such as pH, Ca(2+), and DOM level. Our study demonstrated that the applicability of the source discrimination indices should be critically examined especially in the environments with notable changes in the solution chemistry. The solution chemistry effects could be minimized by adjusting samples to a constant condition prior to the measurements or otherwise the effects should be fully taken into account in interpreting the field observations.

Adhesion of bacterial pathogens to soil colloidal particles: influences of cell type, natural organic matter, and solution chemistry

Bacterial adhesion to granular soil particles is well studied; however, pathogen interactions with naturally occurring colloidal particles (<2 μm) in soil has not been investigated. This study was developed to identify the interaction mechanisms between model bacterial pathogens and soil colloids as a function of cell type, natural organic matter (NOM), and solution chemistry. Specifically, batch adhesion experiments were conducted using NOM-present, NOM-stripped soil colloids, Streptococcus suis SC05 and Escherichia coli WH09 over a wide range of solution pH (4.0-9.0) and ionic strength (IS, 1-100 mM KCl). Cell characterization techniques, Freundlich isotherm, and Derjaguin-Landau-Verwey-Overbeek (DLVO) theory (sphere-sphere model) were utilized to quantitatively determine the interactions between cells and colloids. The adhesion coefficients (Kf) of S. suis SC05 to NOM-present and NOM-stripped soil colloids were significantly higher than E. coli WH09, respectively. Similarly, Kf values of S. suis SC05 and E. coli WH09 adhesion to NOM-stripped soil colloids were greater than those colloids with NOM-present, respectively, suggesting NOM inhibits bacterial adhesion. Cell adhesion to soil colloids declined with increasing pH and enhanced with rising IS (1-50 mM). Interaction energy calculations indicate these adhesion trends can be explained by DLVO-type forces, with S. suis SC05 and E. coli WH09 being weakly adhered in shallow secondary energy minima via polymer bridging and charge heterogeneity. S. suis SC05 adhesion decreased at higher IS 100 mM, which is attributed to the change of hydrophobic effect and steric repulsion resulted from the greater presence of extracellular polymeric substances (EPS) on S. suis SC05 surface as compared to E. coli WH09. Hence, pathogen adhesion to the colloidal material is determined by a combination of DLVO, charge heterogeneity, hydrophobic and polymer interactions as a function of solution chemistry.