Neutral pH Region Research Articles

Insights into uranium sequestration by coal fly-ash-derived zeolites: Understanding via wet chemistry, and advanced spectroscopies

The operation of nuclear power plants requires a supply of nuclear fuel where uranium plays a substantial role as a primary fissile material. Its extraction from U-bearing minerals and handling may cause a leakage of heavily toxic radioactive pollution, which ends up in water bodies and soil. Therefore, tackling U-contaminated water is crucial to preserve water integrity and quality. Zeolites are known as profound ion exchangers with great affinity towards cationic species present in polluted waters. Various zeolite synthesis routes have made this group of aluminosilicates even more promising to be applied as water purification materials. Here, the synthetic gismondite, faujasite, and Linde type-A zeolites from coal fly-ash were synthesized via tailored, coupled fusion-hydrothermal method and applied to remove aqueous uranium (primarily as 238U) under varying pH, time (sorption kinetics), and initial U concentrations (sorption isotherms). The maximum U uptake was observed for Na–P1 (GIS) zeolite, which equals 48.72 mg U/g, the highest reported value on maximum U adsorption capacity for zeolitic materials. The U adsorption kinetics showed that equilibrium is reached after approximately 3 h of adsorption and that the removal process follows a Freundlich isothermal model for all zeolites, thus preferential adsorption onto heterogeneous surfaces. Advanced spectroscopic studies, including laboratory-scale X-ray Photoelectron Spectroscopy with synchrotron light X-ray Absorption Near Edge Structure in High Energy Resolution Fluorescence Detection mode, revealed that at acidic pH, predominantly an ion exchange between Na+ ions with hexavalent uranyl species takes place. In contrast, in the neutral pH region, the U is immobilized via precipitation in the form of μm-scale mineral aggregates of Na-schoepite: Na[(UO2)4O2(OH)5](H2O)5↓. The outcomes of the research study has demonstrated that synthetic zeolites, obtained from industrial by-products such as coal fly-ash, can be successfully valorized to efficient U adsorbents while unveiling the insights to understand the zeolites/U interactions at the nanoscale level.

Pulse electrodeposition of NiCoS on carbon paper for electrochemical hydrogen evolution reaction

NiCoS has good conductivity, and the sulfur it contains is known to improve the activity for hydrogen evolution reaction. Thus NiCoS has recently attracted much attention as a catalyst for hydrogen evolution reaction catalyst in neutral-pH water electrolysis. In this study, NiCoS was fabricated using pulse electrodeposition method and the effect of off time on the composition, morphology, and hydrogen evolution reaction activity was investigated. The physical and chemical characteristics of the catalyst were analyzed using field emission scanning electron microscopy, X-ray diffractometry, electrochemical impedance spectroscopy, etc. It was observed that the surface area of NiCoS, the sulfur content, and hydrogen evolution reaction activity of NiCoS increased together as the off time increased at a constant on time. The NiCoS with the highest sulfur content, produced by pulse electrodeposition, showed overpotentials of 262 and 285 mV to deliver current densities of 10, 50 mA/cm<sup>2</sup>, respectively, in the neutral pH region.

The role of carboxylic acids on nanoparticle removal in post CMP cleaning process for cobalt interconnects

As the technology node moves below 10 nm, cobalt with its low resistivity, superior adhesion property, and wettability with copper, promises to change the conductor landscape in many areas, particularly interconnects and logic contacts. The cleaning process of cobalt films after chemical mechanical planarization is vital to ensure devices’ yield and high performance. The objective of this study is to investigate the removal of nanoparticles from cobalt films, employing two types of carboxylic acids and utilizing a wide pH range from 3 to 11. Various analytical techniques were used to understand the cleaning mechanisms, including zeta potential, surface wettability, dissolution rates, and electrochemical analysis. The results show that carboxylic acids with more chains of the carboxyl groups, such as citric acid, could yield excellent particle removal efficiencies in neutral and alkaline regions. Additionally, it can be concluded that the etching effect accelerated by complexation is predominant in acidic regions, whereas the cobalt oxide surface adsorption of carboxyl groups and stronger electrostatic repulsive forces generated by increased absolute zeta potentials play critical roles at high pH values. Based on the results, an efficient approach with minimal passivation for cleaning cobalt interconnects is proposed. A cleaning solution containing 5 mM citric acid in a neutral pH region can achieve an effective particle removal with reduced passivation using the proposed approach.

Efficient encapsulation of toxic dye from wastewater using biodegradable polymeric adsorbent

The water pollution caused by industrial effluents of pollutant dyes has been harmfully affected to the human health and environment. Therefore, it is important for considerable attention to remove them from industrial wastewater before being discharged to the surface water. The natural polymer-based carbohydrate adsorbent with specific functional groups can be enhanced their potential applications toward the notorious dyes removal from wastewater. In this regard, we selected natural adsorbent of graham flour (GF) as an effective adsorbent to remove cationic crystal violet (CyV) dye by the adsorption method. The morphology and structure of GF was characterized in systematic manner by several instrumentations. The several influencing factors such as solution pH, contact time, dose amount, maximum adsorption capacity, competing metal ions effect and reuses behavior were systematically measured. The effective pH range for CyV adsorption was neutral pH region and the maximum adsorption capacity of the GF adsorbent was as high as 162.33 mg/g. The data also clarified that the polymeric GF adsorbent was selectively removed the CyV dye from synthetic polluted sample even in the presence of high concentration of diverse competing ions. The adsorbed CyV dye was eluted with ethanol and simultaneously regenerated into initial form for the next adsorption operations after rinsing with water. Importantly, the natural GF adsorbent was retaining functionality in spite of many steps during adsorption-elution-regeneration cycles. Therefore, the present study revealed that such a low-cost natural polymeric carbohydrate adsorbent could be used as potential adsorbent for the selective dye molecules from wastewater streams.

PH control in neutral solutions using polymethylacrylic acids as polymer-supported buffer agents

Polymethylacrylic acid beads were utilized as polymer-supported buffer agents for the pH control of neutral aqueous solutions to reduce phosphorus effluents from phosphate buffers. The agents were used to buffer the pH of ureasecatalyzed reactions in a neutral PH region.

Approach of Electrostatic Interaction Based Layer-by-Layer Assembly of Cationic Guar Gum and Poly (Carboxylic acid)

The present study evaluated the possibility to form thin film of cationic guar gum (CGG) associated with poly (carboxylic acid) such as carboxymethyl cellulose (CMC) and poly (acrylic acid) (PAA) through layer-by-layer (LbL) assembly. The thin film thickness and morphology show dependence on pH value, ionic strength and temperature. For pH 3 to pH 4 CGG and poly (carboxylic acids) assemble and form thin film through LbL. For neutral pH region and high pH values CGG and poly (carboxylic acids) do not interacted. In contrast to synthetic polyelectrolyte complex thin film, such as polystyrene sulfonate (PSS)/ poly (diallyldimethylammonium chloride) (PDDA) and PSS/ poly (allylamine hydrochloride) (PAH), the LbL assembly of CGG/CMC and CGG/PAA take place only at low salt concentrations. Deposition at high temperature (up to 60°C) results thicker CGG/ poly (carboxylic acids) films.

The influence of temperature on the charging of polytetrafluoroethylene surfaces in electrolyte solutions

The surface properties of Polytetrafluoroethylene (PTFE) depend on the pH and the ionic strength of the electrolyte solution. The point of zero charge (pHpzc) and the isoelectric point (pHiep) of PTFE were found to be 2.9 and 3.2 at 25 °C, respectively. The electrophoretic mobility at pH > pHiep indicates that the PTFE particles are negatively charged in the neutral pH region. In absence of surface functional groups, this observation can be explained by the distribution of OH− and H+ ions between the PTFE interface and the remaining solution. A thermodynamic model of ion distribution and the temperature dependency of the electroneutrality points which enables evaluation of the thermodynamic parameters is proposed. The enthalpies of interfacial reactions were indirectly determined by measuring the temperature dependency of the electroneutrality points by potentiometric mass titration and streaming current measurements. It was found that the exchange of the H+ and OH− ions between the interfacial region and bulk of the solution is an endothermic reaction. The specific enthalpy of dilution of PTFE dispersions was found to be pH dependent, with the lowest value at pH ≈ 3, i.e. in the zero surface charge region.

Assessment of the adsorption kinetics, equilibrium, and thermodynamic for Pb(II) removal using a low-cost hybrid biowaste adsorbent, eggshell/coffee ground/sericite.

A hybrid adsorbent (CES), coffee grounds, eggshell powder and sericite as a binder, was prepared to remove Pb(II) from aqueous solution. The Fourier-transform infrared spectroscopy analysis showed that the CES contained a large amount of OH groups and had a favorable structure for adsorbing heavy metals. The value of pHpzc of CES was estimated at 7.08. In the neutral pH region, the surface of CES is negatively charged and favorable for adsorption of Pb(II). The maximum Langmuir adsorption amount was 155.67mg/g, and the adsorption process of Pb(II) using CES fitted pseudo-second-order kinetic model and Langmuir isotherm model. Moreover, the analysis of adsorption energy, free energy, enthalpy, and entropy found that the adsorption of Pb(II) onto CES was physical and a spontaneous exothermic reaction. CES is a hybrid adsorbent using general municipal waste and has great advantages in terms of environmental conservation and sustainable environmental circulation. This allows it to compete with other adsorbents. PRACTITIONER POINTS: A hybrid adsorbent, coffee grounds, eggshell, and sericite (CES), was used to remove Pb(II) Adsorption of Pb(II) using CES in an aqueous solution was physical rather than chemical CES contained a large amount of OH groups and had a favorable structure for adsorbing heavy metals The reactivity and strength of the adsorption of Pb(II) onto CES was very good CES has great advantages in terms of environmental conservation and sustainable environmental circulation.

Structural and electrosurface properties of iron-containing nanoporous glasses in KNO3 solutions

The paper is devoted to study and comparison of the structural (volume porosity W, structural resistance coefficient β, tortuosity coefficient K, average pore radius r, specific surface area S0) and electrosurface (efficiency coefficient α, counter-ion transport number n+, electrokinetic potential ζ) properties of micro - and macroporous sodium borosilicate glasses containing (Fe 4–6) and not containing (8 V-NT) magnetite phase in 10−4 – 10−1 M KNO3 solutions. It has been found that the incorporation of an iron (III) oxide into basic sodium-borosilicate glass results in changes in the structure of the pore space of both microporous and macroporous glasses. Moreover, it is shown that the presence of magnetite in the structure of porous glasses does not have a noticeable effect on the values of the efficiency coefficients and potassium counter-ion transport number in the neutral pH region. It has also been established that the absolute values of the electrokinetic potential for microporous membranes of both compositions in the neutral pH region are close to each other. For macroporous membranes obtained under the same conditions, the absolute values of the electrokinetic potential for the iron-containing membrane are higher than these for basic membrane 8 V-NT.

Novel ligand functionalized composite material for efficient copper(II) capturing from wastewater sample

Copper (Cu(II)) is a very toxic heavy metal that even at low concentration can affect living organisms. Therefore, designing effective materials with high selectivity and cost-efficiency is essential for the control capturing of toxic Cu(II) ions. This study was developed a ligand based composite material for simultaneous Cu(II) detection and removal from wastewater samples. The composite material was fabricated based on the ligand anchoring onto the mesoporous silica by direct coating approach. The application of Cu(II) detection and adsorption was measured at neutral pH region with exhibition of significant color visualization. The experiment conditions were optimized based on contact time, solution acidity, initial Cu(II) concentration and pH value and diverse metal salt concentrations. The results were revealed that the composite material was not affected with the existing foreign ions and the signal intensity was observed only toward the Cu(II) ion. The composite material was able to detected the low level Cu(II) ion as the detection limit was 0.25 μg/L and the adsorption of highest removal capacity was 171.33 mg/g. In addition, the diverse ions were not reduced the Cu(II) ion adsorption significantly, and the composite material has approximately no adsorption capacity for other ions at this pH. The elution of Cu(II) ions from the saturated composite material was desorbed successfully with 0.20 M HCl. The regenerated adsorbent that remained maintained the high selectivity to Cu(II) ions and exhibited almost the same sorption capacity as that of the original adsorbent. However, the sorption efficiency slightly decreased after ten cycles. Therefore, the proposed material offered a cost-effective material and may be considered a viable alternative for effectively toxic Cu(II) ion capturing from water samples without the need for sophisticated instrument.

Cleaning the arsenic(V) contaminated water for safe-guarding the public health using novel composite material

With increasing arsenic contamination scenes reported around the globe, the highly promising materials are important to remove the arsenic from industrial and specified contaminated for safe-guarding the public health. In this study, we have prepared ligand anchoring inorganic-organic frameworks based well-ordered, high surface area composite materials for selective arsenic(V) (As(V)) removal from contaminated water. Adsorption studies were evaluated in batch mode with the function of pH, time, initial As(V) concentration, counter-ions and reuses by suitable eluent. Before starting the As(V) adsorption, the composite materials were protonated using 2.0 M HCl. The materials exhibited high adsorption efficiency in low pH area, however; the neutral pH region (7.0) was selected to avoid the divalent anions effect as the monovalent arsenate species were dominated. In the neutral pH region, the basicity of divalent HAsO42− was much greater than the divalent SO42− and the divalent HAsO42− was easily made the strong hydrogen bonding with the protonated composite materials surface. Then the effects of monovalent and divalent anions were not affected in the selective As(V) adsorption by the composite materials. In addition, the other cations did not affect the As(V) adsorption as the data clarified. The composite material was highly matched to the Langmuir model with the monolayer coverage. In addition, the determined maximum adsorption capacity was 142.25 mg/g. The As(V) was eluted from the composite materials with 2.0 M HCl, and the regenerated to the original pattern. The regenerated materials were exhibited the same functionality and used successively in several adsorption-elution-reuses cycles. Therefore, the newly fabricated composite material is an interesting, efficient and economical sustainable composite material and could be used selective As(V) removal from real contaminated water.

Протеолитические ферменты и их белковые ингибиторы из зерна тритикале

Протеолитические ферменты играют значительную роль в процессах, протекающих при хранении и переработке растительного сырья. На современном этапе приоритетами любой пищевой технологии является сохранение нативных свойств биологически ценных компонентов сырья, обладающих лечебно-профилактическими свойствами, и модификация пищевого сырья с целью получения компонентов с определенными технологическими и функциональными свойствами. В настоящее время наибольшее распространение получили методы ферментативной модификации зернового сырья с использованием микробных ферментных препаратов. В то же время исследование собственных протеолитических ферментов, их выделение и очистка, с целью применения для модификации эндогенных белков, к которым они проявляют наибольшее сродство, представляется весьма интересной задачей, в плане использования всего биопотенциала зерна и “экологичности” получаемых продуктов. Такое исследование неразрывно сопряжено с изучением белковых ингибиторов протеиназ, которые представляют исключительный интерес как фактор регуляции процесса протеолиза. В статье приведены экспериментальные данные по выделению, частичной очистке и характеристике протеолитических ферментов зерна тритикале, действующих в кислой, нейтральной и щелочной областях рН. Показано, что кислые и нейтральные протеиназы зерна тритикале являются ферментами тиолового типа, Щелочные протеиназы относятся к сериновым протеиназам. Методом гель-хроматографии определена их молекулярная масса: 75000, 250000 и 50000 Да соответственно. Предложена схема выделения и очистки белковых ингибиторов эндогенных протеиназ из зерна тритикале. Показана их способность подавлять активность собственных протеиназ и трипсина. Проведено разделение ингибиторов трипсина и щелочных протеиназ тритикале (с молекулярной массой 30000 ÷ 35000 Да) и ингибиторов кислых и нейтральных протеиназ тритикале (с молекулярной массой 15000 ÷ 20000 Да). Частично очищенных препараты протеиназ и их белковых ингибиторов, полученные по предложенным схемам могут быть использованы для ферментативной модификации растительных белков и регуляции процессов протеолиза в различных пищевых технологиях, использующих зерновое сырье.

Purification of High-grade Calcite Ore by Flotation with Alkyl Diamines

A very high-grade calcite deposit located in northern Norway consists of CaCO3 ore with minor silicate and sulphide impurities. Cationic (Tallow-1,3-diaminopropane, Duomeen T) collector has been used in the purification of calcite by flotation with an aim of achieving calcite concentrate for its use in value-added products in a variety of industries. The feasibility of sulphide flotation from calcite by this cationic collector has been initially judged from Hallimond flotation and zeta potential on pure mineral systems and the results illustrate the removal of sulphide from calcite ore at neutral pH region. The adsorption mechanism of diamine on both the sulphide minerals was found to be the same by zeta potential studies. The variations in zeta potential are in good agreement with the adsorption of diamine molecular and ionic species as a function of pH. FTIR studies also showed the adsorption of diamine species in agreement with the zeta potential and Hallimond flotation results. Furthermore, the removal of sulphide impurities with selective flotation by diamine collector was performed in bench-scale flotation with the calcite ore and the results indeed showed that the calcite concentrate could meet the quality requirements for its use in the paper industry for coating and filler purposes.

Fabrication of Si nanopowder and application to hydrogen generation and photoluminescent material

Abstract Si nanopowder is fabricated using the simple beads milling method. Fabricated Si nanopowder reacts with water in the neutral pH region between 7 and 9 to generate hydrogen. The hydrogen generation rate greatly increases with pH, while pH does not change after the hydrogen generation reaction. In the case of the reactions of Si nanopowder with strong alkaline solutions (eg pH13.9), 1600 mL hydrogen is generated from 1 g Si nanopowder in a short time (eg 15 min). When Si nanopowder is etched with HF solutions and immersed in ethanol, green photoluminescence (PL) is observed, and it is attributed to band-to-band transition of Si nanopowder. The Si nanopowder without HF etching in hexane shows blue PL. The PL spectra possess peaked structure, and it is attributed to vibronic bands of 9,10-dimethylantracene (DMA) in hexane solutions. The PL intensity is increased by more than 3,000 times by adsorption of DMA on Si nanopowder.

Design of a Hypersensitive pH-Sensory System Created by a Combination of Charge Neutralization and Aggregation-Induced Emission (AIE).

In our bodies, a slight pH change causes remarkable activation or serious damage in the biological processes and continuously keeps biological homeostasis. Detection of such a slight pH change has been a constant demand in searching for unusual biological events. In this paper, we demonstrate a novel pH sensory system that has been achieved through a combination of charge neutralization by a slight pH change with aggregation-induced emission (AIE). We selected a cyano-functionalized oligo(phenylene-vinylene) (cyanoOPV) backbone for AIE and introduced ammonium-tethered boronic acid groups as a pH-dependent function. The self-assembling of these dyes (OPV-Cn) was readily achieved by pH-dependent charge neutralization at the neutral pH region. This sensory system showed unusually sensitive pH responsiveness in a narrow pH range. Moreover, this pH change was observed in a biologically important neutral pH region. We therefore believe that this system is broadly applicable to detect the slight pH change occurring in the biological events.

A bifunctional adsorbent of silica gel-immobilized Schiff base derivative for simultaneous and selective adsorption of Cu(II) and SO42−

Abstract A ditopic zwitterionic Schiff base modified silica gel adsorbent SG-H 2 L 2 was prepared and it was characterized by Fourier transform infrared spectroscopy, elemental analysis, solid state NMR, thermogravimetry and porous structure analysis. SG-H 2 L 2 could simultaneously adsorb metal ions and attendant anions from the aqueous solution of metal salts . SG-H 2 L 2 exhibited a cooperative effect between the adsorption of metal cations and the attendant anions, and the adsorption efficiency decreased in the order MSO 4 > M(NO 3 ) 2 > MCl 2 (M = Cu, Co, Ni, Mn, Cd). SG-H 2 L 2 displayed good adsorption selectivity for Cu(II) and SO 4 2− from the aqueous solutions containing mixed metal ions of Cu(II), Co(II), Ni(II), Mn(II) and Cd(II) or mixed anions of SO 4 2− , NO 3 − , and Cl − . The preliminary mechanism for simultaneous and selective adsorption of the metal ions and attendant anions were discussed. The effect of different parameters including pH, contact time and initial concentrations of Cu(II) and SO 4 2− on the simultaneous adsorption of Cu(II) and SO 4 2− ions were investigated. The efficient adsorption of Cu(II) and SO 4 2− could be achieved in neutral pH region and the maximum adsorption capacities for Cu(II) and SO 4 2− , respectively, were the same of 0.42 mmol g −1 at 25 °C. The adsorption isotherms for Cu(II) and SO 4 2− fitted well with Langmuir model, while their adsorption kinetics followed the pseudo-second order model. Regeneration of SG-H 2 L 2 was realized by adjusting the solution pH with diluted H 2 SO 4 and ammonia solution, respectively. SG-H 2 L 2 exhibited good recyclability and reusability for four cycles use without deterioration in its functionality. SG-H 2 L 2 was also applied in different water samples and good recoveries and the selective adsorption of Cu(II) and SO 4 2− were achieved. This study provides a new bifunctional adsorbent which may be used for the effective removal of Cu(II) and SO 4 2− from water effluents containing mixed metal ions and anions.

A unified platform for experimental and quantum mechanical study of antibiotic removal from water

Pharmaceuticals and antibiotics have taken relatively little attention as contaminants in the natural environments. Ciprofloxacin (CP) as a second-generation fluoroquinolone is found in the wastewater generated from pharmaceutical product and industry. This research has assessed the efficacy of the next generation carbon family adsorbent, graphene nanosheet (GNS) to remove the CP from the water samples. Both adsorption experiments and the first principles of calculations (DFT) were applied to explore the molecular interaction between CP and GNS. The effects of initial concentration of CP, pH, shaking time and temperature of solution on adsorption content were investigated. In the neutral pH region (pH 6.0), the adsorption process was desirable. The shaking time to obtain equilibrium condition was 220min and the experimental kinetic data were fitted with Elovich model. The equilibrium data were perfectly fitted to both Sips and Hill models. Ab-initio calculations demonstrated that CP could be adsorbed onto GNS by an electrostatic interaction being in good compromise with the experimental results.

Hydrogen generation by reaction of Si nanopowder with neutral water

Si and its oxide are nonpoisonous materials, and thus, it can be taken for medical effects. We have developed a method of generation of hydrogen by use of reactions of Si nanopowder with water in the neutral pH region. Si nanopowder is fabricated by the simple bead milling method. Si nanopowder reacts with water to generate hydrogen even in cases where pH is set at the neutral region between 7.0 and 8.6. The hydrogen generation rate strongly depends on pH and in the case of pH 8.0, ∼55 ml/g hydrogen which corresponds to that contained in approximately 3 L saturated hydrogen-rich water is generated in 1 h. The reaction rate for hydrogen generation greatly increases with pH, indicating that the reacting species is hydroxide ions. The change of pH after the hydrogen generation reaction is negligibly low compared with that estimated assuming that hydroxide ions are consumed by the reaction. From these results, we conclude the following reaction mechanism: Si nanopowder reacts with hydroxide ions in the rate-determining reaction to form hydrogen molecules, SiO2, and electrons in the conduction band. Then, generated electrons are accepted by water molecules, resulting in production of hydrogen molecules and hydroxide ions. The hydrogen generation rate strongly depends on the crystallite size of Si nanopowder, but not on the size of aggregates of Si nanopowder. The present study shows a possibility to use Si nanopowder for hydrogen generation in the body in order to eliminate hydroxyl radicals which cause various diseases.

Single-step disruption and protein recovery from Chlorella vulgaris using ultrasonication and ionic liquid buffer aqueous solutions as extractive solvents

Microalgae are natural renewable sources providing attractive high-value products such as proteins. Due to the high costs incurred during drying processes, wet extraction from fresh microalgae biomass can be a promising approach. In this work, a single process step integrating cell disruption and protein recovery from wet Chlorella vulgaris by using ultrasonication and aqueous solutions of ionic liquids (ILs) as extractive solvents was proposed. The ILs assessed belong to the group of Good’s buffer ionic liquids (GBILs), and were prepared by a combination of Good’s buffer-based anions, namely 2-hydroxy-3-morpholinopropanesulfonate and 2-[bis(2-hydroxyethyl)amino]ethanesulfonate, and tetrabutylammonium, tetrabutylphosphonium and cholinium cations. These GBILs possess high biocompatibility and buffering capacity at neutral pH region. The protein recovery capabilities of the aqueous solutions of GBILs were compared with conventional buffers, using the same cell disruption approach. After the proper selection of the buffer solution with higher capability to extract microalgal proteins, alternative disruption techniques such as freeze-thaw, non-ionic detergent-based lysis using Triton X-100 and the combined methods were studied. The most efficient strategy, namely ultrasonication-assisted extraction, was further investigated for the effects of the process variables such as the buffer concentration, the addition of NaCl, the biomass concentration, and the ultrasonic time and power.

Halophilic mechanism of the enzymatic function of a moderately halophilic dihydrofolate reductase from Haloarcula japonica strain TR-1.

Dihydrofolate (DHF) reductase coded by a plasmid of the extremely halophilic archaeon Haloarcula japonica strain TR-1 (HjDHFR P1) shows moderate halophilicity on enzymatic activity at pH 6.0, although there is no significant effect of NaCl on its secondary structure. To elucidate the salt-activation and -inactivation mechanisms of this enzyme, we investigated the effects of pH and salt concentration, deuterium isotope effect, steady-state kinetics, and rapid-phase ligand-binding kinetics. Enzyme activity was increased eightfold by the addition of 500mM NaCl at pH 6.0, fourfold by 250mM at pH 8.0, and became independent of salt concentration at pH 10.0. Full isotope effects observed at pH 10.0 under 0-1000mM NaCl indicated that the rate of hydride transfer, which was the rate-determining step at the basic pH region, was independent of salt concentration. Conversely, rapid-phase ligand-binding experiments showed that the amplitude of the DHF-binding reaction increased and the tetrahydrofolate (THF)-releasing rate decreased with increasing NaCl concentration. These results suggested that the salt-activation mechanism of HjDHFR P1 is via the population change of the anion-unbound and anion-bound conformers, which are binding-incompetent and -competent conformations for DHF, respectively, while that of salt inactivation is via deceleration of the THF-releasing rate, which is the rate-determining step at the neutral pH region.