Starting pH Value Research Articles

Morphological Sensitivity to pH of Silica and Chalk Nanocrystalline Self‐Organized Biomorphs

Inorganic–inorganic self‐organized composite architectures resulting from the chemical coupling of alkaline‐earth carbonate and polymeric silica are a promising alternative to organic‐based hybrid bio‐mimetic systems for developing innovative multi‐functional materials. Although the importance of pH in the generation of these structures reminiscent of primitive living organisms (and for this called biomorphs) is widely acknowledged, the effect of pH is generally investigated on the basis of starting pH value. This approach inadvertently neglects the important spatial and temporal pH gradients associated with biomorph nucleation and growth. A deep understanding of the role of pH on morphogenesis requires the ability to detect locally the pH in real‐time with a non‐invasive technique and correlate pH to the different stages of biomorphic growth. This aim is achieved by combining optical and fluorescence imaging. An accurately selected pH probe suitable for ratiometric pH measurement in the silica gel is exploited during a typical counter‐diffusion experiment. The results are compared with computer simulation of the synthesis of biomorphs by counter‐diffusion experiments. The results demonstrate the existence of two main morphogenetic regimes. Interestingly, the morphogenetic process controlling the complex shaping of biomorphs results to be independent of the silica speciation.

Constructing of FeNi3 nano-necklaces intercalated 3D graphene as an efficient and robust heterogeneous catalyst for photo-Fenton degradation of hazardous organic pollutants

In this study, an innovative heterogeneous nanocatalyst of three-dimensional reduced graphene (3DGr)-wrapped FeNi3 nano-necklaces (NNs) was successfully fabricated. The effectiveness and stability of FeNi3 @ 3DGr nanocomposite in a heterogeneous photo-Fenton technique for the removal of organic pollutants such as malachite green (MG), methylene blue (MB), diclofenac (DIC), and ibuprofen (IBF) were evaluated. The nanocatalyst degradation efficiency for MG was studied by altering the starting pH value (2.8–7.5), the dosage of H2O2 (25–150 mM), the concentration of MG dye (30–80 mg/l), and the dose of FeNi3 @ 3DGr nanocomposite (0.2–1.0 g/l). Under optimum operating conditions, the FeNi3 @ 3DGr nanocomposite achieved 100% MG removal efficiency with almost 60% total organic carbon (TOC) below 40 min. Moreover, the catalyst revealed significant durability owing to the synergistic effects of the integration of the 3DGr and FeNi3 NNs frameworks, as its removal performance maintained over 80% after seven consecutive degrading cycles with an acceptable degree of leaching iron. The radical scavenger experiment revealed that hydroxyl radical (•OH) species are the essential oxidized radicals participating in the photo-Fenton process. Our findings delivered a stable and effective FeNi3 @ 3DGr heterogeneous nanocatalyst with a high removal capacity for organic contaminants from water through the photo-Fenton technique.

Highly efficient activation of peroxymonosulfate by the (3R + 2H)-CuFeO2 nanocomposite photocatalyst: Intermediate toxicity, BVS validation ionic migration and degradation pathway

The degradation of carbamazepine (CBZ) by activated peroxymonosulfate (PMS) using the (3R + 2H)-CuFeO2 nanocomposite photocatalyst was investigated in this work. The (3R + 2H)-CuFeO2 were prepared by hydrothermal method at 160°for 15 h utilizing ferrous sulphate heptahydrate (FeSO4·7H2O) and copper (II) sulphate (CuSO4·5H2O) as raw materials. Meanwhile, the (3R + 2H)-CuFeO2 was characterized and analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), isothermal nitrogen adsorption (BET), and X-ray energy spectroscopy (EDS). The best removal effectiveness was 85.96% when critical factors such as the starting pH value, catalyst dosage, and PMS quantity were turned. The action of anions was then investigated further. The high catalytic efficiency was due to the synergistic impact of Fe3+/Fe2+ and Cu2+/Cu+ redox cycles. The plausible CAZ breakdown routes were postulated based on the results of the liquid chromatograph-mass spectrometer (LC-MS). Finally, we have studied the most probable of cation migration by the 3DBVSMAPPER program and BVEL calculation concept to correlate the structural characteristics of both materials and their ionic conductivity. The formed channel shows the uniform transport of ions, which can optimize the solid–liquid interface, hinder the influence of water molecules on the material, and protect the material.

Tailoring the structure of biphasic calcium phosphate via synthesis procedure

Nano calcium phosphate ceramics (CaPC) were synthesized using simple co-precipitation method at different preparation conditions. The selected Ca/P ratio with a variation of pH value lead to formation of dicalcium phosphate dihydrate (DCPD) at pH 5 and 6 while, hydroxyapatite (HAP) nano particles were formed at pH 9 and 12 at room temperature. The crystallite size was in the range of 15–55 nm depending on the obtained crystalline phase. The study displayed variation of decomposition depending on the annealing temperature. The significant note is the different transformation trend of each phase depending on the starting pH value. The HRTEM illustrated that the DCPD phase was formed as fibers with diameter around 4–6 nm, while HAP was formed in rod shape. The aspect ratio decreased from 6.6 at pH 9 to 4 at pH 12 which refer to the great influence of pH value on the morphology of calcium phosphates.

Synthesis of Hydroxyapatite Microspheres by Hydro-thermal Method under the Control of Sodium Citrate

Hydroxyapatite(HA) microspheres were prepared by using calcium nitrate tetra hydrate(Ca(NO3)2·4H2O) and diammonium phosphate((NH4)2HPO4) as the resource of calcium and phosphorus, respectively. During the synthesis, propionamide was used as pH adjusting agent to control the supersaturation of the solution, and trisodium citrate was used as the calcium source relievers to control the morphology of HA. The HA microspheres with high crystallinity, regular morphology and good dispersion were synthesized through hydrothermal method. XRD, FTIR and SEM were used to characterize the product. The effects of starting pH value, the amount of trisodium citrate and reaction temperature on the crystallinity, composition and morphology of HA were investigated. The results show that the optimal condition for uniform HA microspheres was as follows, pH=3, molar ratio of sodium citrate to calcium source at about 1:1.5, and reaction temperature of 180℃.

PH-driven dissolution–precipitation: a novel route toward ultrathin Ni(OH)2 nanosheets array on nickel foam as binder-free anode for Li-ion batteries with ultrahigh capacity

In this paper, for the first time, we report on the growth of ultrathin Ni(OH)2 nanosheet arrays on a nickel foam (NF) via a novel pH-driven dissolution–precipitation route, carried out by a hydrothermal treatment of the NF in an acidic medium without the introduction of other nickel sources. Acid etching of the NF surface leads to nano-pits and produces Ni(H2O)n2+ ions at the early stage of the reaction. With the elapsed time, an increase in the pH level occurs and the Ni(H2O)n2+ ions gradually hydrolyze and preferentially precipitate on the nano-pits, serving as nucleation sites and leading to ultrathin Ni(OH)2 nanosheet arrays on an NF. The effects of the experimental parameters, such as reaction time, acid type and starting pH value, on the Ni(OH)2 growth are also investigated. Because the nano-pits are integrated parts of the NF and the deposition of Ni(OH)2 nanosheets on such nano-pits ensures intimate contact between them, the Ni(OH)2/NF is robust enough to withstand a violent sonication process and efficient and rapid electron transfer is achieved. As a binder-free anode for Li-ion batteries, the Ni(OH)2/NF exhibits an unexpected ultrahigh capacity of 1689 mA h g−1 and excellent cycling stability.

Hydrothermal Synthesis of Hydroxyapatite Fibers Precipitated by Propionmide

Fibrous hydroxyapatite (HA) powder was successfully synthesized through hydrothermal method. Cal- cium nitrate tetrahydrate and diammonium hydrogen phosphate were added as precursors and propionamide (PA) as precipitant was used to control the degree of supersaturation of the reaction solution. XRD, FTIR, SEM and TEM were used to characterize the product. The synthesized HA powder was found to possess high crystallinity and regular morphology, as well as good dispersion. The effects of starting pH value and the concentration of precursors on the morphology, constitution, crystallinity and the growth characteristics of HA were investigated. The results show that the starting pH and concentration significantly affect the morphology at different extents, but not on the constitution and crystallinity. In fact, low starting pH controls orientation of fibrous HA while low concentration widens HA fibers.

Preparation of Borosilicate Xerogel and Research on its Mineralization

Tributyl borate was first adopted for the introduction of boron in the preparation of bioactive borosilicate xerogel by sol-gel method. The xerogel reacted continuously in 0.25M K2HPO4 solution with a starting pH value of 7.0 at 37 °C for 1day. The structural, morphologies and compositional changes resulting from the conversion were characterized using X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy. The results indicated that speed of formation of HA was cut way back on the time with the addition of boron and the induction period for the HA nucleation on the surface of the borosilicate xerogel was short than 1 days. The conversion mechanism of the borosilicate xerogels to hydroxyapaptite was also discussed.

Microencapsulation of butyl stearate with melamine-formaldehyde resin: Effect of decreasing the pH value on the composition and thermal stability of microcapsules

The object of this study was to investigate how different decreasing of pH regimes during microencapsulation process with melamine-formaldehyde (MF) resin affects the composition, morphology and thermal stability of microcap- sules containing a phase-change material (PCM). Technical butyl stearate was used as PCM. Microencapsulation was car- ried out at 70°C. For all experiments the starting pH value was 6.0. After one hour of microencapsulation at the starting pH value, the pH value was lowered to final pH value (5.5; 5.0; 4.5) in a stepwise or linear way. The properties of microcap- sules were monitored during and after the microencapsulation process. The results showed that pH value decreasing regime was critical for the morphology and stability of microcapsules. During microencapsulations with a stepwise decrease of pH value we observed faster increase of the amount of MF resin in the microencapsulation product compared to the microen- capsulations with a linear pH value decrease. However, faster deposition in the case of microencapsulations with stepwise decrease of pH value did not result in thicker MF shells. The shell thickness increased much faster when the pH value was decreased in a linear way or in several smaller steps. It was shown that for the best thermal stability of microcapsules, the pH value during microencapsulation had to be lowered in a linear way or in smaller steps to 5.0 or lower.

Highly uniform NaLa(MoO4)2:Ln3+ (Ln = Eu, Dy) microspheres: template-free hydrothermal synthesis, growing mechanism, and luminescent properties

Uniform and well-crystallized NaLa(MoO4)2 microspheres were prepared by a facile one-step hydrothermal synthesis without involving any surfactants or templates. The as-obtained products were systematically characterized by powder X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence (PL), and photoluminescent excitation spectra (PLE). The influence of the starting pH value on the phase and morphology of NaLa(MoO4)2 microspheres was discussed. Furthermore, the formation mechanism of the microspheres was dominated by the consequence of a fast crystallization, dissolution and recrystallization. Finally, the luminescent properties of Eu3+ and Dy3+ ion activated NaLa(MoO4)2 microspheres were investigated. The results demonstrated that NaLa(MoO4)2:Ln3+ (Ln = Eu, Dy) microspheres exhibited good luminescent properties and might have potential applications in lighting technology.

Biomimetic growth of CaCO3 pancakes on the leaves of Epipremnum aureum

Rhombohedral, disk-like and pancake-like calcite crystals were synthesized in the different reaction condition via facial vegetal bio-templates, the leaves of Epipremnum aureum. The resultant crystals were characterized by scanning electron microscopy (SEM), X-ray powder diffractometry (XRD), and Fourier transform infrared (FT-IR) spectroscopy. The results showed that disk-like and pancakes calcite were obtained on the surface of Epipremnum aureum leaves in 50 mM CaCl2 solution at starting pH values of 9.7 and 11.7, respectively. The dynamic process of formation of multiple crystals was analyzed by monitoring the continuous morphological and structural evolution and components of crystals in different crystal stages. Moreover, it is found that the surface structure of the leave and starting pH value of reaction solution provide profound influence on the morphology of CaCO3 crystals. This provides a facile and novel method to prepare hierarchical CaCO3 crystals.

Mineralization of a Bioactive Si-Ca-P System Wet Gel in Aqueous K<sub>2</sub>HPO<sub>4</sub> Solution

A bioactive Si-Ca-P system (designated 58S) wet gel was prepared via a sol-gel method. The wet gel was reacted continuously in 0.25M K2HPO4solution with a starting pH value of 9.0 at 37 °C for different time. The structural and compositional changes resulting from the conversion reaction were characterized using X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy and inductive coupled plasma spectroscopy. The results indicated that the induction period for the CDHA nucleation on the surface of the 58S bioactive wet gel was about 3 days. The conversion mechanism of the products was also discussed.

The course of the hydrolysis and the reaction kinetics of AlN powder in diluted aqueous suspensions

The reactivity of AlN powder in diluted aqueous suspensions in the temperature range 22–90°C was investigated in order to better understand and control the process of hydrolysis. The hydrolysis exhibits three interdependent stages: during the induction period (first stage) amorphous aluminum hydroxide gel is formed, followed by the crystallization of boehmite (second stage) and bayerite (third stage). The hydrolysis rate significantly increased with higher starting temperatures of the suspension, but was independent of the starting pH value; however, the pH value of 10 caused the disappearance of the induction period. The kinetics was described using un-reacted-core model, and the chemical reaction at the product-layer/un-reacted-core interface was the rate-controlling step for the second stage of the hydrolysis in the temperature range 22–70°C, for which the calculated activation energy is 101kJ/mol; whereas at 90°C, the diffusion through the product layer became the rate-controlling step.

Template-Free Hydrothermal Synthesis and Luminescent Properties of Octahedral NaGd ( MoO4 ) 2 : Eu3 + Microcrystals

Uniform and well-crystallized octahedral microcrystals have been successfully synthesized by a facile one-step hydrothermal synthesis method without involving any templates. The prepared samples were systematically characterized by powder X-ray diffraction, field-emission-scanning electron microscopy, photoluminescence (PL), and photoluminescent excitation spectra. The starting pH value played an important role in the pure-phase formation and uniform morphology of octahedral microcrystals. Detailed proofs indicated that the growth process of microcrystals was dominated by a nucleation–crystallization-oriented attachment mechanism. Furthermore, the luminescent properties of the as-synthesized microcrystals were investigated, demonstrating that the PL intensity was influenced by the different morphologies, and the bipyramidal octahedra luminescent microcrystals might be applied as an excellent red component for near-UV white light emitting diodes.

Preparation and purification of l-cysteine capped CdTe quantum dots and its self-recovery of degenerate fluorescence

l-cysteine capped CdTe quantum dots (QDs) were prepared in aqueous solution by a simple and efficient method, showing many advantages such as short synthesis period, the broaden range of starting pH value and the wide fluorescence emission wavelength range. A novel purification process was designed to remove excess Cd 2+ which has potential cytotoxicity for bio-analysis. Three-dimensional fluorescence charts of pre- and post-purification showed that the purified QDs were of better luminescent performance. The prepared QDs were of cubic crystal structure with an average size of 2–6 nm, which were characterized by XRD and HRTEM. It is confirmed by IR spectra that the l-cysteine ligands were conjugated with CdTe cores via covalent bond. The degenerate fluorescence of QDs can be self-recovered in the presence of l-cysteine without other processing steps.

Hydrothermal synthesis of hydroxyapatite whiskers with sharp faceted hexagonal morphology

We report an effective method for the synthesis of hydroxyapatite whiskers with sharp faceted hexagonal shape employing a low temperature (90 °C) hydrothermal route with calcium nitrate tetrahydrate, diammonium phosphate and urea as starting materials. The key parameters of the synthesis process i.e. duration, temperature cycle of the treatment and starting pH value are carefully varied and the end products are investigated using powder X-ray diffraction (XRD), Raman-scattering, infrared spectroscopy (IR), elemental analysis, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), electron diffraction (ED), and high-resolution TEM (HRTEM) in order to find the optimal reaction conditions that lead to the desired hexagonal morphology of HA whiskers. The results demonstrate that gradual and greater increase in solution pH during the hydrothermal process favors large quantity of the single-crystalline hydroxyapatite whiskers with well defined hexagonal morphology.

Conversion of Bioactive Borosilicate Glass to Multilayered Hydroxyapatite in Dilute Phosphate Solution

The conversion of a bioactive borosilicate glass in aqueous phosphate solution was observed to produce vastly different reaction kinetics and hydroxyapatite (HA) microstructures, depending on whether the glass was reacted continuously or intermittently in the solution. Particles (150–300 μm) of a borosilicate glass (designated H12) were reacted continuously or intermittently in 0.25M K2HPO4 solution with a starting pH value of 7.0 at 37°C. The conversion kinetics of the glass particles to HA were determined from weight loss measurements. Structural and compositional changes resulting from the conversion reaction were characterized using scanning electron microscopy, X‐ray diffraction, energy‐dispersive X‐ray analysis, and Fourier transform infrared spectroscopy. For conversion experiments carried out intermittently (12–24 h intervals, followed by drying), faster reaction kinetics and a unique multilayered microstructure, consisting of alternating layers of HA and an amorphous SiO2‐rich material with nearly uniform thickness (2–3 μm), were observed. On the other hand, particles reacted continuously in the phosphate solution for the same total time converted more slowly and produced a single HA layer. The kinetics and mechanism of forming HA under the intermittent and continuous reaction conditions are described and compared with those for bioactive silicate and borate glasses studied in previous work.

Comparison of the Formation of Calcium and Barium Phosphates by the Conversion of Borate Glass in Dilute Phosphate Solution at near Room Temperature

The formation of phosphates of calcium or barium at near room temperature by the direct conversion of borate glass in dilute phosphate solution was investigated. Borate glass particles (150–300 μm), with the composition 20Na2O·20AO·60B2O3 (mol%), where A is the alkali‐earth metal Ca or Ba, were prepared by conventional processing, and immersed in 0.25M K2HPO4 solution at 37°C and with a starting pH value of 9.0 or 12.0. The effects of the borate glass composition and the solution pH on the rate of formation, the chemical composition, and the structure of the phosphate products formed in the conversion reaction were investigated using weight loss and pH measurements, X‐ray diffraction, X‐ray fluorescence, scanning electron microscopy, and Brunauer–Emmett–Teller surface area. At both pH values, the calcium borate glass particles were completely converted to hydroxyapatite, Ca10(PO4)6(OH)2, with a high surface area (160–170 m2/g). At pH=9.0, the barium borate glass particles converted completely to a barium phosphate product that was isostructural with BaHPO4, whereas at pH=12.0, the barium phosphate product was isostructural with Ba3(PO4)2, with both products having much lower surface areas (4–8 m2/g). The formation of the phosphate products was pseudomorphic, retaining the external shape of the original glass particles.

A SIMPLIFIED APPROACH TO LIMING AND ITS EVALUATION

Lime requirement is based on determination of soil acidity and CEC in a representative sample of soil from the land profile (regularly from topsoil). Acidity is measured in a suspension of soil and 0.2 M KCl solution at a 1:1 ratio (w/v); CEC determination is a part of the multinutrient soil test KVK-UF. A desired range of soil pH values is defined in relation to CEC value (mmol+ kg−1). Desired pH values of soil are calculated from these relations: pH(lower)=2.9×CEC0.14, pH(upper)=3×CEC0.146. A difference between the defined and calculated desired pH is used as the basis for determining lime requirement (CaCO3 t ha−1), and is dependent upon soil buffering capacity, which is closely related to CEC. Information on the depth of sampled profile, bulk density of soil, and skeleton proportion (particles>2 mm) is used for further specification of lime requirement. Recommendation of a maximum single lime application rate related to CEC is also a part of the liming model. To evaluate the liming model function 15-week incubation experiments with differentiated rates of CaCO3 and CaO (equivalent to 1.5 to 9.0 t CaCO3 ha−1) were carried out on seven soils with naturally low pH. The goal of these observations was to determine changes in soil acidity (pH-H2O, 0.01 M CaCl2, 0.2 M KCl and 1 M KCl), concentrations of extractable aluminum, accumulation of mineral nitrogen forms (NH4 + and NO3 −) and organic solutes in soil, and availability of nutrients from the soil by means of plant tissue analyses (barley and mustard). The liming rates providing for the lower desired pH value were fully sufficient with respect to the appropriate depression of aluminum. Liming, also considerably decreased manganese availability. There was a large depression of boron availability in all soils when low liming doses below the lower pH value were applied. Liming rates that exceeded the desired pH range were related to an increase in nitrification, which was especially high in soils with the extremely low starting pH value. The experimental results also indicate the usefulness of information on the value of Mn soil test and the boron status in the soil in order to specify the liming rate.

Preparation of Corona-Embedded CdS Nanoparticles

In this paper, two novel methods of preparing CdS nanoparticles within the corona of block copolymer micelles are presented. (1) Corona-embedded CdS nanoparticles were prepared by dropping core-embedded CdS nanoparticles into water with a low pH value. The location change of the CdS nanoparticles was accompanied by a structural change of the micelles, from compound micelles to single micelles. The CdS nanoparticles are randomly distributed in the corona of the single micelles. The size of the nanoparticles increases slightly after the transition. (2) Corona-embedded CdS nanoparticles can also be prepared using the “in situ” reaction of S2- with Cd2+ ion clusters in the corona of the micelles. The single micelles with Cd2+ ion clusters in the corona were prepared by dropping poly(styrene-block-2-vinylpyridine)−Cd2+ compound micelles into water with a low pH value. The size of the corona-embedded CdS nanoparticles is affected by starting pH value in water, complex concentration, and S2- source.