Ion Exchange Process Research Articles

Coupling Reliable Interfacial Carrier Migration Channels with Visible-Light Response Antennas in ZnO-Based Heterostructure for Ameliorated Photocatalytic Hydrogen Generation.

Engineering targeted and reliable charge transfer pathways in multiphase photocatalysts remains a challenge. Herein, we conceptualize the Cd@CdS-ZnO/reduced graphene oxide (rGO)/ZnS heterostructures coupled with reliable carrier migration channels and visible-light response antennas by building rGO-integrated electrochemical nanoreactors and an ion-exchange process. In this ternary catalyst, the Cd clusters and rGO perform as charge relays to boost carrier transport via the Z-scheme route and accelerate photogenerated carriers to react with surface-adsorbed substances. Meanwhile, thanks to CdS, the heterostructures have photocatalytic properties under visible light illumination and can also inhibit self-corrosion by shielding Cd clusters to avoid disrupting charge transfer channels. Therefore, the special heterostructure demonstrates fascinating photocatalytic hydrogen production activity without the intervention of cocatalysts. This work provides a feasible protocol for improving the interfaces between metals and semiconductors to achieve efficient photocatalytic hydrogen generation.

Nitrate-induced mobilization of trace elements in reduced groundwater environments

Groundwater is an essential source for drinking water production. Nitrate infiltration into groundwater due to over-fertilization can cause a potential risk for groundwater quality. Pyrite and other geogenic minerals can be oxidized and trace metals consequently released into water, e.g., nickel and uranium.To achieve a better understanding of the nitrate-induced mobilization of metals, this study investigated the release of antimony, arsenic, chromium, cobalt, molybdenum, uranium, and vanadium from three different reduced sediments after nitrate addition. The experiments were conducted as batch and soil column tests under oxygen-free conditions. In addition to the ORP, the pH value was a relevant driver for the metal mobilization due to pH dependent adsorption and ion exchange processes. Uranium concentrations in the water increased with increasing redox potential. Also, antimony and, to a lesser extent, molybdenum showed higher mobilization at higher ORP as well as at higher pH values. On the contrary, arsenic and cobalt was immobilized with increasing redox potential. Pourbaix diagrams demonstrated very complex species distributions even in synthetic water. The mobilization of trace metals is expected to be also influenced by the type of surrounding rocks and water quality parameters such as dissolved organic carbon.

Efficient removal of heavy metals from acid mine drainage by ε-MnO2 adsorption

The clean-up of acid mine drainage (AMD) is challenging, as classical treatment including a pH neutralization step produces large amounts of toxic sludge. Here we demonstrated that removal of heavy metals through adsorption at low pH was achievable with the use of ε-MnO2 adsorbent, which could be produced in a simple one-step process. The material, which was negatively charged even at pH 2, exhibited outstanding potential for the removal of heavy metals at strongly acidic pH. At pH 2, adsorption capacities were achieved of 172.14 mg/g towards Pb2+ (at an initial concentration of 400 mg/L), 65.64 mg/g for Fe3+ (at 300 mg/L) and 8.5 mg/g for Cd2+ (at 10 mg/L). Mechanistic studies revealed that ion exchange was the main adsorption mechanism for removal of Pb2+, while electrostatic interaction was dominant for Fe3+ and Cd2+ removal. In the case of Pb2+ adsorption, double corner sharing (DCS) complexes were formed at the edges, which promoted the dissolution of structural Mn(III), thereby generating Mn2+ and vacancies which promoted Pb2+ adsorption via an ion exchange process. In the case of Fe3+ and Cd2+ adsorption, along with electrostatic adsorption, triangle corner sharing (TCS) dominated complex formation at the intermediate vacancies, and less Mn2+ was released. Note that the Mn2+ was in dynamic equilibrium with structural Mn(Ⅲ) and Mn(Ⅳ). The actual AMD was retreated in 5 cycles by ε-MnO2, the removal rates of 100% were achieved for Pb2+, Fe(total) and Mn2+, together with 98% for Cu2+ and 95.1% for Cd2+, all of which reached the national emission standards. This approach is a highly suitable option for AMD treatment that avoids toxic sludge formation.

Removal of silver colloids from radioactive wastewater by means of ultrafiltration

110mAg is the most common colloidal nuclide found in the radioactive liquid of nuclear power plants (NPPs). This paper investigates the morphology of silver colloids through a simulation experiment. The results show that the radionuclide 110mAg in the process water is reduced to Ag0 to form colloidal silver existing in regular shape with a size around 100 nm and a negative zeta potential. This zero-valent silver colloid can not be removed by the existing treatment process of ion exchange in NPPs effectively. One potential method for removal is ultrafiltration. The results demonstrate an effective removal of more than 98% of the silver colloids, accompanied by a flux increase of 146.9%. This is different from the traditional trade-off between membrane permeability and selectivity. Scanning electron microscopy (SEM) was utilized to study the membrane morphology, revealing a filtration mechanism that combines adsorption and sieving. The xDLVO theory was used to reveal the interfacial interaction between silver colloids and membrane materials. The results indicate that silver colloids can adsorb on the membrane surface spontaneously. The silver adsorbed by the membrane may form loose and hydrophilic silver colloids (an “aquifer”) and improve membrane hydrophilic and permeability properties simultaneously. The advantages of ultrafiltration on adsorption of silver colloids and improvement of water permeability provide a new method for the treatment of radioactive waste liquid containing colloidal silver.

Rational design of bimetallic metal-organic framework derived three-dimensional flower-like and porous NiCoFe LDH/NF electrocatalyst for electrochemical overall water splitting

Porous structured metal–organic frameworks (MOFs) and their derivatives are desired in catalysis and energy storage. Herein, three-dimensional (3D) flower-like NiCoFe LDH/NF are first synthesized though a convenient cathodic electrodeposition strategy subsequent an ion-exchange process. And the morphology and catalytic performance of the CoFe-MOF/NF can be finely by tailoring the electrodeposition voltage, deposition time and the ratio of Co: Fe. The 3D flower-like and porous NiCoFe/NF not only retains structural integrity to promote durability but also greatly alleviates the aggregation of active sites. In addition, the 3D flower-like and porous NiCoFe/NF display remarkable results with low overpotentials of 233 mV at a current density of 50 mA cm−2 for OER and 84 mV at a current density of 10 mA cm−2 for HER in 1 M KOH, respectively. When acting as electrocatalytic electrodes for overall water splitting, NiCoFe/NF displays a low overpotential of 1.52 V to achieve a current density of 10 mA cm−2. The study provides a promising approach to design MOF electrocatalysts for electrocatalytic applications.

DC Voltage Induces Quadratic Optical Nonlinearity in Ion-Exchanged Glasses at Room Temperature

We demonstrate that applying DC voltage at room temperature to an ion-exchanged glass induces quadratic optical nonlinearity in a subsurface region of the glass. We associate this with the EFISH (Electric-Field-Induced Second Harmonic) effect due to the Maxwell–Wagner charge accumulation in the subsurface region of the glass, in which a conductivity gradient forms as a result of the ion exchange processing. The second harmonic (SH) signal from the soda–lime glass subjected to potassium-for-sodium ion exchange is comparable with one from the same glass after thermal poling. The signal linearly increases with the duration of the ion exchange. The lower mobility of the potassium ions results in a higher SH signal from the potassium-for-sodium exchanged glass than that from the silver-for-sodium ion-exchanged one. This phenomenon is resistant to thermal annealing: only a 500 °C anneal caused noticeable degradation of the SH signal after “charging” the specimen. The phenomenon found is of interest for characterizing graded conductivity regions and providing and controlling second-order optical nonlinearity in transparent isotropic media.

The Study of Humic Substances' Impact on Anion Exchangers.

Humic substances (HSs) present in water and wastewater cause fouling of anion exchange resins (AERs), which mainly results in reducing the ion exchange capacity (IEC). In this paper, an attempt was made to investigate fouling of two polystyrene and one polyacrylic AER using water from the Oder River, treated wastewater after the ultrafiltration process (UFTW) and digester reject water from sludge dewatering at the Janówek Wastewater Treatment Plant (WWTP) in Wrocław. HSs contained in digester reject water were characterised by the lowest aromaticity and molecular weights (MWs), the highest proportion of hydrophilic fraction and the highest amount of oxygenated functional groups. The Fourier-transform infrared (FTIR) analyses made it possible to identify chemical bonds characteristic of HSs and determine the mechanism of their retention on the surface of AER beads. The conducted experiments brought unexpected results, as the IEC increased with the amount of organic matter in the feed. Presumably, the humic substances accumulated on the beads and in the porosity of the anion exchangers themselves participated in the ion exchange process.

Cr2O72−/ MnO4− based novel adsorbents: Applicable for removal of cationic and anionic organic dyes from waste water

This study presents the synthesis of two new metal-organic ionic frameworks (MOIFs) and their potential utility as adsorbents for deleterious organic dyes. The frameworks were created through an ion-exchange process in aqueous conditions, employing K2Cr2O7/KMnO4 and 4-[(4-methylpiperazin-1-yl)methyl]-N-(4-methyl-3-{[4-(pyridin-3-yl)pyrimidin-2-yl]amino}phenyl)mesylate (Im) as reactants. Structural characterization of the MOIFs was conducted using powder XRD, UV/Vis spectroscopy, and FTIR spectroscopy, enabling precise identification. Differential scanning calorimetry (DSC) analysis provided insights into critical properties such as activation energy, enthalpies of crystallization/melting, and specific heat capacity (0.4318 J per kelvin). These thermal characteristics were further correlated with the MOIFs' structural attributes. The activation energy for MOIF was determined using the Coats–Redfern model with TGA data (−0.85 kJ/M). Anionic dyes (Methyl orange/Congo red/Nigrosine) exhibited significantly higher adsorption rates (almost 100 %) compared to cationic dyes (70–80 %) such as safranin and crystal violet. Kinetic analysis indicated that the adsorption mechanism of MOIFs followed a pseudo first-order model. Overall, the adsorption analysis suggested that MOIFs strongly adsorb anionic dyes in comparison to cationic ones.

The origin of high salinity and hydrogeochemical characteristics of groundwater in semi-arid area of the Linta Basin, Southwestern Madagascar

The Linta Basin, located in the Southwestern Madagascar, is a semi-arid area where groundwater in fractured media bedrock aquifer constitutes the main source of water supply. In the last two decades, highly mineralized groundwater was identified in this area; however, the origin of the salinity was not clear. The purpose of the study was to clarify the origin of salinity and to identify hotspots with groundwater unsuitable for water supply. Groundwater quality in this basin was investigated by hydrogeochemical and isotopic methods accompanied by mineralogical study. In total, 32 groundwater samples were collected and analyzed. The results showed that groundwater temperature varied from 25.2 °C to 31.7 °C. Values of pH and TDS varied from 6.55 to 8.24 and 221 to 5612 mg/L, respectively. The aquifer, which is mainly fractured, showed 7 groundwater types, namely Mg–HCO3,Na–HCO3 and also Na–C1, Mg–Cl, Na–Cl–HCO3, Mg–Cl–HCO3-, and Ca–Mg–HCO3. Two groups of variables have been identified by factor analysis; the factor F1 comprises EC, Ca2+, Mg2+, SO42−, and Cl− whereas the factor F2 comprises HCO3−, K+, and Na+, and they were interpreted in terms of hydrogeochemical processes. Values of saturation indices (SI) for carbonate minerals were generally positive, indicating their possible precipitation. Based on the Gibbs diagram and factor analysis, groundwater mineralization is affected by water-rock interactions and evaporation, respectively. The important role of evaporation is confirmed by enrichment of stable isotopes with δ18O values up to 1.2 ‰. Processes such as base ionic exchange process and reverse ionic exchange process may also be important locally. The main origin of groundwater mineralization is the hydrolysis of silicate minerals such as feldspars and micas coupled with evaporation. In several wells, salinity is too high for water supply and nitrate concentration is above the WHO limit for drinking water. Results of the study highlighted groundwater chemistry formation processes and are applicable in other African countries with bedrock aquifers.

UTILIZATION OF THOMAS MODEL TO PREDICT THEBREAKTHROUGH CURVES FOR ADSORPTION AND IONEXCHANGE

Fixed bed sorption processes such as adsorption and ion exchange do not operate at steady state. The design equations are differential that usually require numerical methods to solve. Thomas gives a general analytical solution for these equations. It is based on second-order reaction kinetics and the assumption of Langmuir isotherm. Computer program for the solution of Thomas model was designed using MATLAB 7.0. Four sets of experimental data are tested to show the capability of Thomas model to predict the breakthrough curves for adsorption and ion exchange processes. These data represent the sorption of o-cresol from water by activated carbon, acetic acid from air by activated carbon, phenol from water by natural zeolite, and trichloroethylene from air by zeolite- 5A.The results show that there are a good agreement between the experimental data and the model.

Timescale of radium and alkaline earth cations ascent in the trees: Use of isotopic (228Ra/226Ra) ratio

Due to its short-lived progeny, including gaseous radon isotopes that can be inhaled and its significant transfer into vegetation, radium poses a substantial concern in radiation risk assessment. Although the transfer of Ra from soil to plants has been previously documented, the distribution and speciation of radium within the plant tissues, particularly within trees, remain unclear. The temporal dimension of Ra transfer is also poorly known. Therefore, the transfer of radium and others alkaline earth cations in beech trees was investigated through the analysis of fine (<2 mm) roots and leaves corresponding to tree organs with a life cycle limited to one season. This study was conducted at the experimental Montiers (INRAE-Andra site, France) and Strengbach watershed (OHGE site, France) beech-forested site. The activity of 226Ra and the isotopic ratio (228Ra/226Ra) were measured in roots and leaves using gamma spectrometry. Additionally, the concentration of alkaline earth cations (Mg, Ca, Sr, and Ba) was measured, to better constraint the mechanism of alkaline earth cation transfer through the xylem. The retention of these cations within the trees increases with the mass of the element, following the order Mg < Ca < Sr ≈ Ba < Ra, i.e.: light alkaline earth cations are more efficiently transferred from roots to leaves than heavy one. Our results suggest that these cations maintain their hydration shell during their ascent in stems and a low pH ion-exchange process rather than a complexation process with carboxylic group occurs.The decay of the (228Ra/226Ra) isotopic ratio over time during transfer within the trees allows us to quantify the slow Ra translocation from roots to the leaves, ranging from 1 to more than 16 years. This duration increases with the age of the trees. Hence, radioactive decay of Ra provides particularly valuable timescale information that is usually difficult to assess for Ca or other alkaline earth cations.

Preparation and characterization of P-type zeolite for adsorption of Cr3+, Ni2+, and Co2.

Acid-washed coal fly ash (AW-CFA) was subjected to wet grinding activation followed by hydrothermal crystallization to synthesize P zeolite (FAZ-P). The FAZ-P obtained at 120°C for 24h exhibited a maximum relative crystallinity of 93.15% and was employed for the adsorption of Cr3+, Ni2+, and Co2+ from aqueous solutions. The zeolitization of coal fly ash (CFA) leads to an increase in specific surface area to 44.00 m2/g, resulting in the formation of nano-sized P zeolite crystals with uniformly narrow fissures and sizes within the range of 10-30nm. Adsorption experimental results indicate that FAZ-P exhibits maximum adsorption capacities of 49.03mg/g for Cr3+, 22.20mg/g for Ni2+, and 27.25mg/g for Co2+. The adsorption equilibrium data for both mixed and single-metal ion solutions conform to the Langmuir model, with the affinity sequence for heavy metal ions being Cr3+ > Co2+ > Ni2+. The pseudo-first-order and pseudo-second-order kinetic models effectively described the adsorption behavior of Cr3+, Ni2+, and Co2+. Increasing the initial pH value of the solution significantly enhanced the adsorption capacity of the adsorbent for heavy metal ions. The removal mechanism of metal ions involves both adsorption and ion exchange processes. The thermodynamic parameters indicated that the adsorption process was spontaneous and endothermic.

Hydrogeochemical evolution and water–rock interaction processes in the multilayer volcanic aquifer of Yogyakarta-Sleman Groundwater Basin, Indonesia

Volcanic aquifers have become valuable resources for providing water to approximately 2.5 million people in the Yogyakarta-Sleman Groundwater Basin, Indonesia. Nevertheless, hydrogeochemical characteristics at the basin scale remain poorly understood due to the complexity of multilayered aquifer systems. This study collected sixty-six groundwater samples during the rainy and dry seasons for physicochemical analysis and geochemical modeling to reveal the hydrogeochemical characteristics and evolution in the Yogyakarta-Sleman Groundwater Basin. The results showed that groundwater in the unconfined and confined aquifers exhibited different hydrogeochemical signatures. The Ca–Mg–HCO3 facies dominated groundwater from the unconfined aquifer. The groundwater facies evolved into a mixed Ca–Mg–Cl type along the flow direction towards the discharge zone. Meanwhile, groundwater from the confined aquifer showed mixed Ca–Na–HCO3, Na–HCO3, and Na–Cl–SO4 facies. The presence of Mg in the confined aquifer was replaced by Na, which was absorbed in the aquifer medium, thus showing the ion exchange process. The main geochemical processes can be inferred from the Gibbs diagram, where most groundwater samples show an intensive water–rock interaction process mainly influenced by the weathering of silicate minerals. Additionally, only groundwater samples from the confined aquifer were saturated with certain minerals (aragonite, calcite, and dolomite), confirming that the groundwater followed the regional flow system until it had sufficient time to reach equilibrium and saturation conditions. This study successfully explained the hydrogeochemical characteristics and evolution of a multilayer volcanic aquifer system that can serve as a basis for groundwater basin conservation.

Computational analysis of electric field effects on electrodialysis for enhanced desalination processes

This study elucidates the technologies employed in membranebased water purification processes. The theoretical underpinnings of semipermeable membrane functionalities are expounded upon through the lens of Onsager’s reciprocal relations in non-equilibrium thermodynamics, delineating the fluxes and the driving forces that instigate them. Utilising a simplified Onsager matrix tailored for the ion-exchange membrane electrodialysis process, computational fluid dynamics (CFD) simulations were conducted. The computations presented herein depict the intricacies of both dialysis and electrodialysis in saline water solutions.

Phase Engineered CuxS-Ag2S with Photothermoelectric Activity for Enhanced Multienzyme Activity and Dynamic Therapy.

The insufficient exposure sites and active site competition of multienzyme are the two main factors to hinder its therapeutic effect. Here, a phase-junction nanomaterial (amorphous-crystalline CuxS-Ag2S) is designed and prepared through a simple room temperature ion-exchange process. A small amount of Ag+ is added into Cu7S4 nanocrystals, which transforms Cu7S4 into amorphous phased CuxS and produces crystalline Ag2S simultaneously. In this structure, the overhanging bonds on the amorphous CuxS surface provide abundant active sites for optimizing the therapeutic activity. Meanwhile, the amorphous state enhances the photothermal effect through non-radiative relaxation, and due to its low thermal resistance, phase-junction CuxS-Ag2S forms a significant temperature gradient to unlock the optimized thermo-electrodynamic therapy. Furthermore, benefiting from the high asymmetry of the amorphous state, the material forms a spin-polarized state that can effectively inhibit electron-hole recombination. In this way, the thermoelectric effect can facilitate the enzyme-catalyzed cycle by providing electrons and holes, enabling an enhanced coupling of thermoelectric therapy with multienzyme activity, which induces excellent anti-tumor performance. More importantly, the catalytic process simulated by density-functional theory proves that Ag+ alleviates the burden on the Cu sites through favorable adsorption of O2 and prevents active site competition.

Synthesis and characterization of a di-methacrylated polymerizable ionic liquid through two-step esterification and ion exchange process

An effective two-step synthesis for the di- methacrylation of 2-hydroxylethylammonium chloride ionic liquid was developed in the presence of methacrylic anhydride. The esterification process was performed through the hydroxyl moiety and the side product methacrylic acid was effectively captured through an ion exchange process via sodium bicarbonate to yield a polymerizable di- methacrylate monomer. The esterification and ion exchange processes were monitored via titrations and spectroscopy. This low viscosity (62 cP) di- functional modified ionomer is thermally homo-polymerized and co-polymerized with 55 wt% bis-GMA as a nonvolatile reactive diluent yielding impressive glass transition temperature (Tg) values up to 157 °C and 170 °C for homo- and co- polymer respectively as determined via differential scanning calorimetry method.

New approach to evaluating the thermodynamic consistency of melts in the ‘metal-slag’ system based on interatomic interaction parameters

The article presents a new approach to evaluating the thermodynamic state of the ‘metal–slag’ system during metal smelting in oxidizing-reducing conditions. The interaction between the metal and slag is analyzed using the model of the structure of metallurgical melts, which considers cooperative ion exchange processes and interatomic interaction parameters. As a result of analyzing experimental data on the compositions of reacting melts during pig iron and steel smelting, criteria were developed for assessing the degree of achieving the equilibrium in the system regarding sulfur. The charge state parameters of the metallic system ZY and the slag system Δe, the slag stoichiometry index ρ, and the charge state parameter of the melt components Zi were used. The regularity of a consistent formation of metallic and slag melts has been established, which is evidenced by a significant correlation between the chemical equivalent of the metal composition ZY and the slag Δe. Analytical dependences were obtained in the form of ZY = f(Δe,ρ). The identified patterns and criteria can be integrated into automated process control systems for regulating the slag regime and producing high-quality pig iron and steel.

Ionic nanosphere as a novel sensitizer for luminescence from terbium(III) ion hybridized by facile ion-exchange process

Abstract Luminescence from terbium(III) species is typically weak due to its low absorption coefficient and slow radiative process despite its advantageous color purity. Hybridizing with a photosensitizer(s) is one of the most popular strategies to obtain intense luminescence from terbium(III) species. We have developed a novel photosensitizing system in which terbium(III) ion is hybridized with the ionic nanosphere, a class of spherical ion-exchange resins with a diameter of &amp;lt;300 nm. Terbium(III)-doped ionic nanospheres successfully exhibited obvious green luminescence upon the photoexcitation of the nanosphere at 260 nm. The terbium(III)–nanosphere hybrids can be prepared by a simple methodology, and sample conditions are controllable facilely.

Highly Sensitive On-Chip Grating-Based Optical Sensor on Glass Substrate: Cost-Effective Design

This paper presents a novel on-chip optical sensing system using ion exchange technology and phase-shifted Bragg grating design. The sensor geometry has been optimized using a finite difference time domain (FDTD) solver to achieve maximum sensitivity and figure of merit (FOM). The proposed design offers high sensitivity to changes in refractive index and low fabrication costs. The ion exchange process used to create the sensor allows for precise refractive index control, optimizing the sensor’s sensitivity and FOM. A graded-index waveguide and a phase-shifted Bragg grating structure also contribute to the sensor’s high sensitivity. The proposed sensor design was tested for water-based sensing applications, achieving a FOM of 227.63 and a 343.1 nm/RIU sensitivity. These values are significantly higher than those reported for other Bragg grating sensors, highlighting the potential of the proposed design for high-performance sensing applications. The sensor’s high sensitivity and low fabrication costs make it a promising technology for future sensing and monitoring applications.

Reduction-orientated selective removal of selenate by thiourea-functionalized polystyrene material

Efficient removal of trace selenate [Se(VI)] from contaminated water is still challenging because of the inevitable interference from the coexisting anions toward the adsorption or ion-exchange process. Herein, a bifunctional material (NCS@CMPS) was proposed for selective removal of Se(VI) from a complex matrix. NCS@CMPS was subtly prepared by grafting a chloromethylated polystyrene substrate (CMPS) with thiourea, resulting in reductive groups (C-SH and C=S) and adsorptive sites (–NH-, –NH2, and C=NH2+) anchored on the skeleton of CMPS. Batch studies demonstrated an excellent removal efficiency and anti-interference capabilities of NCS@CMPS toward Se(VI), even with very high levels of competing anions (chloride, sulfate, phosphate, nitrate, and bicarbonate) over a wide pH range (3 ∼11). The in-situ reductive removal and the unique pH-buffering effect of NCS@CMPS were responsible for the high selectivity and the wide applicability. The XPS analyses identified the removal mechanisms of concentrating, reducing, and sequestrating of Se species inside NCS@CMPS, where the majority of Se species was reduced to Se(IV) (80.9%). In column mode, NCS@CMPS can treat over 10,000 bed volumes (BV) of a simulated Se(VI) wastewater ([Se]ini = 200 μg/L) to below 10 μg/L, whereas the capacity of its substrate (i.e., CMPS) was only 28 BV. Additionally, the exhausted NCS@CMPS can be regenerated by NaBH4-NaOH-HCl treatment for repeated use. Moreover, the effectiveness of NCS@CMPS in treating actual industrial Se(VI) wastewater was also validated.