Effects Of Solution pH Value Research Articles

Effect of solution pH value on the corrosion resistance of Co-Fe LDHs coating developed on MAO treated magnesium alloy AZ31

As a post-treatment method of MAO coating, layered doubled hydroxides (LDHs) can improve the corrosion/degradation resistance of magnesium (Mg) alloys. This study innovatively prepared Co-Fe LDHs coatings on MAO treated Mg alloy AZ31, and investigated the effect of pH value on the corrosion/degradation resistance of the coatings. The results indicate that the corrosion/degradation resistance of LDHs coatings first increase and then decrease with the increase of pH. The best corrosion/degradation resistance occurred for pH = 12, with a corrosion current density (icorr) of 5.18×10–8 A∙cm–2. The icorr after immersing in NaCl solution for 14 days was 1.65×10–6 A∙cm–2. The Co-Fe LDHs nanosheets (pH = 12) effectively sealed the pores of the MAO coating, resulting in increased coating density and hindering the diffusion of corrosive media, thereby effectively protecting the Mg alloy. This study is of great significance for the corrosion protection and rapid degradation prevention of Mg alloys and other alloys.

The kinetics of tungsten adsorption from acid leaching solution of scheelite by anion resin

The adsorption kinetics of tungsten from acid leaching solution of scheelite was investigated. The effects of solution pH value (3.0–9.0), anion resin dosage (1–6 g), contact time (20–180 min) and reaction temperature (20–60 °C) on the tungsten adsorption were studied. The results showed that the tungsten adsorption was practically independent of reaction temperature at the investigated range, while increasing with the increases of resin dosage and contact time, and the decreases of solution pH value. The experimental data agreed quite well with the Langmuir model, with the maximum adsorption capacities of tungsten is 347.34 mg/g at 20 °C. In addition, SEM-EDS analysis further revealed that tungsten was well adsorbed by the anion resin.

Highly dispersed and stable Fe species supported on active carbon for enhanced degradation of rhodamine B through peroxymonosulfate activation: Mechanism analysis, response surface modeling and kinetic study

Herein, highly dispersed Fe species supported on activated carbon (CA-Fe-C) was fabricated with the aid of citric acid, showing excellent catalytic performance and stability for the degradation of rhodamine B (RhB) through peroxymonosulfate (PMS) activation. The radical quenching study, electron paramagnetic resonance (EPR) measurement and PMS consumption analysis confirmed the RhB degradation mechanism involving reactive radical species attacking RhB and non-radical oxidation pathway. The main degradation intermediates were identified by LC-MS, and the possible RhB degradation pathways were deduced. A multivariate quadratic polynomial model was developed using the response surface methodology (RSM) to examine how the removal of RhB was influenced by several quantifiable factors, with the objective of optimizing RhB removal. The analysis of variance (ANOVA) was used to evaluate the adequacy and significance of the proposed model. The effects of solution pH values, initial concentration, inorganic anions, PMS dosage, catalyst dosage, and metal loading amount on RhB removal were investigated. The method of initial rates was employed to determine the intrinsic reaction rate law, and the reaction was identified to follow the Langmuir-Hinshelwood (L-H) kinetics model.

Investigation of the effect of solution pH value on rabbit corneal stroma biomechanics.

To facilitate the protection of corneal stability during corneal epithelium defects by determining the effect of solution pH on corneal stroma biomechanics. Thirty rabbit corneas were extracted, and the epithelium was scraped off. The samples were immediately subjected to inflation tests with pressures ranging from 0.3 to 6kPa at baseline and in three subsequent test cycles. During a 10-min interval between cycles, specimens were randomly divided into four groups; in three of these groups, phosphate-buffered saline (PBS) drops with pH values of 6.9, 7.4, or 7.9 were applied to the surface once per minute, whereas the fourth group did not receive drops. The corneal thickness significantly increased following the administration of PBS, while the corneal tangent modulus significantly decreased. At 2.5 and 4.5kPa, the modulus reduction was significantly smaller in the specimens treated with pH 6.9 PBS than in those treated with pH 7.4 or 7.9 PBS, adjusted for changes in corneal thickness. Linear fitting of the pressure-modulus plot revealed that the regression coefficient significantly decreased over time. The reduction in the coefficient was most prominent in the PBS-treated groups, and the administration of pH 6.9 PBS elicited the smallest reduction among those three groups, adjusted for corneal thickness changes. The study demonstrated that the administration of PBS drops with various pH values affected corneal biomechanics independent of corneal stromal swelling, and the impact of slightly acidic PBS was minimal. The effect became more prominent as posterior pressure increased. The research provides the basis for mediating the pH value of tear film and drops to maintain biomechanical stability of epithelium defects corneal stroma.

Effects of solution pH value and mineralizer on formation and color property of holmium molybdate pigment via co-precipitation and sintering

A novel functional ceramic or glass pigment of monoclinic holmium molybdate (Ho2MoO6) with ‘allochroic effect’ was synthesized via co-precipitation and subsequent low-temperature sintering with different mineralizers (i.e., lithium chloride, sodium fluoride and boric acid). Effects of solution pH value and mineralizer type/content on Ho2MoO6 formation at different sintering temperatures and time were investigated. The results reveal that the solution pH value in co-precipitation reaction has an influence on the element ratio of Mo and Ho in the precursor and the pigment purity. The sintering temperature of forming sole Ho2MoO6 phase is decreased by 200 °C and the sintering duration is reduced in the presence of 5 wt % lithium chloride due to the decreased crystallization activation energy. Meanwhile, Ho2MoO6 pigment as powder or coating on ceramic tile and glass exhibits various colors (i.e., pale yellow, salmon, mustard and coral) under different illuminants (i.e., incandescent lamp A, solar-light D65, cool white fluorescent lamp F2 and three-band fluorescent lamp F11).

Removal of bisphenol A and trichlorophenol from aqueous solutions by adsorption with organically modified bentonite, activated carbon composites: A comparative study in single and binary systems

Three adsorbents have been developed by encapsulation of organo-activated bentonite (OAB), activated carbon (AC) and organo-activated bentonite/activated carbon (AC-OAB) in cross-linked alginate beads (A) with the aim of using them in the removal of bisphenol A (BPA) and 2.4.5-trichlorophenol (TCP). The adsorption capacities of the three adsorbents were investigated in order to choose the best adsorbent for BPA and TCP. The alginate/activated carbon beads (A-AC) exhibit the maximum BPA and TCP adsorption capacities (419.3 and 444.7 mg/g at 25 °C, respectively). In the binary system, a decrease was observed at the adsorbed amount to 291.5 mg/g for BPA and 430.2 mg/g for TCP. The adsorption of BPA and TCP by A-AC composite beads was studied and the effects of solution pH value, temperature and contact time on the adsorption were investigated. Results revealed that BPA and TCP adsorption kinetics onto A-AC are best described by the pseudo-second order model, and the equilibrium adsorption data are well fitted to both Langmuir and Freundlich models. The zero point charge determination (pHPZC), the scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) analysis were carried out. The A-AC composite was used for six cycles without significant adsorptive performance loss. Therefore, the ecofriendly prepared A-AC adsorbent was considered as highly recyclable and efficient adsorbent for BPA and TCP pollutants.

Adsorption mechanism of azophloxine in water by Fe3O4-chitosan composite material

Fe3O4-chitosan composite material was synthesized as adsorbent. The effect of solution pH value, initial concentration of azophloxine and adsorption time on the adsorption of azophloxine onto adsorbent was studied. The results show that Fe3O4-chitosan composite material can be magnetically separated before and after adsorbing azophloxine. It was found that the peak intensity of azophloxine was the strongest under weak acidic conditions, and the peak position hardly shifted. In the process of adsorption, it was found that Fe3O4-chitosan composite material adsorbing azophloxine by the surface electrostatic attraction. The optimum equilibrium adsorption capacity is at initial solution pH 6, and the equilibrium adsorption capacity is very close under weak acidic conditions. The pseudo first-order and pseudo second-order kinetic models were applied to experimental data. The adsorption process followed the pseudo-first-order kinetic model, which implied that the adsorption process was physical adsorption. The correlation coefficient for the first-order kinetic model was obtained greater than 0.99571 at room temperature, and the theoretical equilibrium adsorption capacity qe,cal value also agreed very well with the experimental equilibrium adsorption capacity qe value in the case of pseudo first-order kinetics. It is suggested that Fe3O4-chitosan composite material has a wide application prospect in the removal of dyes as adsorbent.

High-efficient removal of tetrabromobisphenol A in aqueous by dielectric barrier discharge: Performance and degradation pathways

Brominated flame retardants are widely used in fire protection area, but also bring great threats to ecological environment and human health. In this study, the potential of brominated flame retardant removal in wastewater by dielectric barrier discharge (DBD) plasma was investigated, with Tetrabromobisphenol A (TBBPA) as a model pollutant. The experimental results showed that TBBPA could be effectively removed by the DBD plasma oxidation. Almost all of the TBBPA in wastewater could be successfully decomposed within 15 min’s oxidation treatment, and the decomposition process fitted well with the pseudo-first-order kinetic model. Relatively lower TBBPA initial concentration favored its decomposition; and the effect of solution pH value on the oxidation process was negligible in the selected pH range. Electron paramagnetic resonance analysis showed that O2–, OH, and 1O2 were produced in the DBD plasma process; and O2– was the main reactive species for TBBPA decomposition, OH and 1O2 also played important roles. The molecular structure of TBBPA was effectively destroyed, and some byproducts including bisphenol A, and dibromophenol were generated. The possible decomposition pathways for TBBPA degradation were proposed. Furthermore, the acute toxicity and bioaccumulation factor of intermediate byproducts were alleviated via the analysis of Toxicity Estimation Software Tool.

Design and synthesis of a novel fluorescent probe, EuIII-dtpa-bis(adenine), and application for the detection of orotic acid in urine

For detection of orotic acid (OA), a novel fluorescent probe, EuIII-dtpa-bis(adenine), was designed and synthesized based on the complementation base pairing principle. The dtpa-bis(adenine) ligand was characterized by nuclear magnetic resonance spectroscopy (1H NMR and 13C NMR), Fourier transform infrared spectra (FTIR), and elemental analysis. Then, the effects of solution pH values and some coexisting interfering substances on OA detection using EuIII-dtpa-bis(adenine) as a fluorescent probe were investigated. The linear relationship of F0/F and OA concentration in the range of 10–150 μmol/L was obtained, where F0 and F are the fluorescence intensities of EuIII-dtpa-bis(adenine) at 320 nm in the absence and presence of OA, respectively. The calculated limit of detection is about 0.807 μmol/L. The detection mechanism of OA was proposed. In addition, the detection of OA in urine samples has also been studied. It was found that the designed and synthesized fluorescent probe is effective for the detection of OA in urine samples.

Microwave-assisted combustion synthesis of ZnAl2O4 and ZnO nanostructure particles for photocatalytic wastewater treatment

ABSTRACTZnAl2O4 and ZnO nanostructure particles and in situ crystallization of zinc aluminate and zinc oxide coating layers on sintered α-Al2O3 and γ-Al2O3 granules by the microwave-assisted combustion method were investigated. For powders, the effects of solution pH value and for coated samples the influence of support type on the structure, microstructure, and photocatalytic activity of powders were studied. Results showed that variation of synthesis pH value caused to considerable change in agglomeration, specific surface area, obtaining up to 88 and 92% yields for zinc aluminate and zinc oxide nanoparticles, respectively. γ-alumina granules were more appropriate supports than the α-alumina ones because of the better photocatalytic activities and lower extent of the attritions for both zinc aluminate and zinc oxide coating layers.

Photodegradation of Moxifloxacin Hydrochloride Solutions under Visible Light Irradiation: Identification of Products and the Effect of pH on their Formation.

The photodegradation study is essential for the phototoxicity assessment of fluoroquinolones. Various LC-MS techniques and ultraviolet (UV) lamp irradiation conditions have been used for the identification of their photodegradation products. In this study, visible light (400-760nm) lamp irradiation was selected for the photodegradation of moxifloxacin (MOXI) hydrochloride solutions. Two photodegradation products were identified by LC-MS/MS at first, but one product could not be speculated from the mass spectrum and any known degradation mechanisms. To obtain an adequate amount for the structure elucidation, this unknown product was isolated by recrystallization and semi-preparative HPLC. Then, its structure was further identified by 1H-NMR, 13C-NMR, and 2D-NMR. Based on spectral data, this new photodegradation product was unambiguously named as 7-[3-(3-aminopropyl)-1H-pyrrol-1-yl]-1-cyclopropyl-6-fluoro-8-methoxy-4-oxo-1,4-dihydroquinoline-3-carboxylic acid, which was formed through the open of hexahydroxy N-containing heterocycle and the formation of two alkene bonds in pyrrole ring. The effects of solution pH value on the formation of photodegradation products were compared. Their production was minimum at pH5.0 and maximum at pH7.0. Because MOXI hydrochloride has been used extensively in clinical practice and visible light is the most possible light source that pharmaceutical products are exposed to, our study is important for the quality control of MOXI liquid preparations.

Fast mineralization of densely packed hydroxyapatite layers in the presence of overexpressed recombinant amelogenin

Learning from the process of biominerals formation provides tremendous ideas for developing advanced synthesis techniques. According to the structure formation of tooth enamel, a recombinant amelogenin his-AmelX was designed and constructed. The protein was over-expressed and could be conveniently purified in one-step heat treatment. The mineralization process of hydroxyapatite was initiated by enzyme AP and regulated by the recombinant amelogenin. Effects of solution pH value and mineralization duration were studied. It was demonstrated that his-AmelX could induce the nucleation of apatite and quicken the growth rate at pH 7.0-7.4, while impeded hydroxyapatite growth at pH 6.8. Moreover, a much denser layer of hydroxyapatite was achieved with the addition of his-AmelX. The present study may not only provide insight into the formation of natural biomaterials but also open a new path to prepare materials under environmentally benign conditions.

Selective separation of gallium from zinc using flotation: Effect of solution pH value and the separation mechanism

Zinc is one of the impure elements in acidic solutions obtained from gallium sources; therefore, flotation studies were performed to investigate the removal of Ga(III) from Zn(II) using sodium dodecyl sulfate (SDS) as an anionic surface-active agent. In this study, the effect of different pH values on the percentage removal of Ga(III) and Zn(II) was studied. It was observed that the distribution of hydrolysis species and change in pH, had a significant effect upon the separation of Ga(III) from Zn(II). Also, the selective separation of Ga(III) was dependent on the recovery of water from the froth. The results showed that the optimal selective separation could be obtained at low pH values when the species of Ga3+ was predominant and the precipitation of Ga(III) was at a minimum. The effect of pH on the characterization of the sublate (insoluble complexes formed in scum layer) and the complexation of SDS with hydrolysis species were studied by scanning electron microscopy coupled with energy dispersive X-ray (SEM/EDX) spectroscopy and Fourier transform infrared (FTIR) spectroscopy. In order to obtain more information about the mechanism of selective separation, the interaction of Ga(III) and Zn(II) with SDS was investigated using turbidity technique.

Fast removal of cationic dyes using pH-sensitive Fe3O4/poly(methacrylic acid) nanocomposite particles

In this work, the pH-sensitive magnetic Fe3O4/polymethacrylic acid nanocomposite particles were synthesized by a new one-step method and used as adsorbents for the removal of two cationic dyes from aqueous solution. The resulting product was characterized using Fourier transform infrared spectra, transmission electron microscopy (TEM), thermogravimetric analysis, and vibrating sample magnetometer. Particles size distribution of product and its pH responsivity was investigated by dynamic light scattering. Adsorption performance of the magnetic adsorbent was tested with removal of methylene blue and maxilon red GRL from aqueous solution. The effects of solution pH value, adsorption time and initial dye concentration were investigated. The adsorption behavior fits well with the Langmuir rather than the Freundlich model. The results reveal that the adsorbent has ability to remove dyes rapidly within a few minutes due to the absence of the internal diffusion resistance. Moreover, the synthesized adsorbent has good reusability.

Adsorption of Lead and Nickel Ions by Semi-interpenetrating Network Hydrogel Based on Wheat Straw Cellulose: Kinetics, Equilibrium, and Thermodynamics

A wheat straw cellulose-g-poly (potassium acrylate)/polyvinyl alcohol (WSC-g-PKA/PVA) semi-interpenetrating networks (semi-IPNs) hydrogel was synthesized by graft copolymerization and used for Pb(II) and Ni(II) adsorption from aqueous solution. The effects of solution pH value, contact time, initial concentration, and temperature on adsorption were investigated. The adsorption process was described by the adsorption models of Langmuir, Freundlich, and Dubinin–Radushkevic. The adsorption kinetics was analyzed using pseudo first- and second-order kinetic models, intraparticle diffusion model, and mass transfer model. Comparison analysis of linear least square method and nonlinear method for estimating the kinetics and isotherm parameters were also made. The results showed that nonlinear regression analysis could be a better way to obtain the model parameters. The pseudo second-order kinetic model was more suitable for describing the whole adsorption process, and both intraparticle diffusion with three steps and mass transfer were taking place in the adsorption. The equilibrium adsorption isotherm was closely fitted with both the Langmuir and Dubinin–Radushkevic model. The changes of free energy, enthalpy, and entropy of adsorption were evaluated for the adsorption of Pb(II) and Ni(II) by WSC-g-PKA/PVA, suggesting that the adsorption process was physical, spontaneous and endothermic.

Rapid and efficient removal of Ni(II) in water using constant-current electrolysis

This study presents a constant-current electrolysis technique to remove Ni(II) efficiently from aqueous solution using an electrochemical cell. Three electrodes of aluminum, stainless steel, and graphite were used as cathodes, while rectangular graphite plates were the anode. The effects of solution pH values (0.3–7.0) and applied current density (I = 100–200 A/m2) were investigated. Complete removal of Ni(II) ions was achieved within 12 min using a graphite cathode at pH 1.0 and I = 140 A/m2, which had a current efficiency of 38%. Under the same conditions, more than 99% removal of Ni(II) was obtained from wastewater within 60 min of electrolysis time.

Study of Pb²⁺, Cd²⁺ and Ni²⁺ adsorption onto activated carbons prepared from glycyrrhiza residue by KOH or H₃PO₄activation.

The activated carbons (ACs) were prepared from glycyrrhiza residue by KOH or H₃PO₄activation and were used for removing Pb²⁺, Cd²⁺ and Ni²⁺ from simulated wastewater. The changes of the physical structure and chemical properties of the glycyrrhiza residue before and after activation were characterized by using a variety of analytical instruments and methods. Kinetics and equilibrium isotherms were obtained and the effects of solution pH value and adsorbent dosage were studied in batch experiments. The results indicated that after activation, the surface structure of glycyrrhiza residue changes and surface area, micropore volume also increase accordingly. Kinetic studies showed that the adsorption followed a pseudo-second-order reaction. The Freundlich model fitted the equilibrium data better than the Langmuir isotherm. According to the Langmuir equation, the maximum adsorption capacities of ACs prepared from glycyrrhiza residue by KOH and H₃PO₄activation for Pb²⁺, Cd²⁺ and Ni²⁺ are 2.170 mmol/g, 2.617 mmol/g, 3.741 mmol/g and 2.654 mmol/g, 3.095 mmol/g, 3.076 mmol/g, respectively, which are much higher than ACs prepared from other raw materials.

Removal of nickel(II) from aqueous solutions using iminodiacetic acid functionalized polyglycidyl methacrylate grafted-carbon fibers

Iminodiacetic acid functionalized polyglycidyl methacrylate grafted-carbon fibers (PGMA-IDA/CFs) were prepared for Ni(II) removal from aqueous solutions. The effects of solution pH value, temperature and adsorption time were investigated. The maximum adsorption capacity of Ni(II) on PGMA-IDA/CFs is 0.923mmol·L−1·g−1 at pH5.2 and 50°C. Kinetic data indicate that the adsorption process matches the pseudo-second-order model and Elovich kinetic model. Thermodynamic data suggest that the adsorption process is endothermic spontaneous reaction.

Extraction of lithium from salt lake brine using room temperature ionic liquid in tributyl phosphate

Lithium is known as the energy metal and it is a key raw material for preparing lithium isotopes which have important applications in nuclear energy source. In this work, a typical room temperature ionic liquid (RTILs), 1-butyl-3-methyl-imidazolium hexafluorophosphate ([C4mim][PF6]), was used as an alternative solvent to study liquid/liquid extraction of lithium from salt lake brine. In this system, the ionic liquid, NaClO4 and tributyl phosphate (TBP) were used as extraction medium, co-extraction reagent and extractant respectively. The effects of solution pH value, phase ratio, ClO4− amount and other factors on lithium extraction efficiency had been investigated. Optimal extraction conditions of this system include the ratio of TBP/IL at 4/1 (v/v), O/A at 2:1, n(ClO4−)/n(Li+) at 2:1, the equilibration time of 10min and unadjusted pH. Under the optimal conditions, the single extraction efficiency of lithium was 87.28% which was much higher than the conventional extraction system. Total extraction efficiency of 99.12% was obtained by triple-stage countercurrent extraction. Study on the mechanism revealed that the use of ionic liquid increased the extraction yield of lithium through cation exchange in this system. Preliminary results indicated that the use of [C4mim][PF6] as an alternate solvent to replace traditional organic solvents (VOCs) in liquid/liquid extraction was very promising.

Sorption separation of cadmium from aqueous solutions by alginite material: kinetic and equilibrium study

Alginite, as a component of some types of kerogen alongside amorphous organic matter, was used for adsorptive separation and removal of Cd2+ ions from aqueous solutions. Alginite material was characterized by X-ray diffraction, ATR-FTIR, cation exchange-capacity and specific surface area analyses. Evaluation of alginite sorption properties showed the effect of solution pH value in the range from 2 to 6 on sorption capacity of alginite. At a slightly acidic conditions (pH 6.0–6.5), the alginite samples exhibited a sufficient sorption capacity and stability. The pseudo-second-order kinetic model described the sorption data better than the pseudo-first-order kinetic model. The equilibrium of cadmium sorption by alginite was reached within 120 min. Maximal sorption capacity (Qmax) calculated from experimental equilibrium data (Langmuir adsorption isotherm) was 23.62 mg/g. Sorption energy of Cd2+ ions calculated from Dubinin–Kaganer–Radushkevich model confirmed the ion-exchange mechanism of cadmium removal for alginite sorbent. The alginite from central European geological maar (Pula, Hungary) can be utilized for production of new non-conventional sorbents or mineral filters for removal of toxic metals.