High pH Solutions Research Articles

Immobilization of arsenate in water and sediments using schwertmannite synthesized by persulfate oxidation

Schwertmannite (SCH), an iron-hydroxyl sulfate mineral, has been widely applied for arsenic adsorption and immobilization. In this study, persulfate was used in chemical oxidation procedure of SCH synthesis instead of hydrogen peroxide (H2O2). The properties of SCH synthesized by persulfate oxidation (SCH-S) and its immobilization efficiency with respect to arsenate [As(V)] in water and sediments were investigated. The results show that persulfate can be used as an effective oxidizer in SCH synthesis instead of H2O2. The absence of side reactions and a high solution pH facilitated Fe3+ precipitation for SCH-S formation in persulfate oxidation compared to SCH synthesized by H2O2 oxidation (SCH-H). SCH-S particles also exhibited a non-spherical structure with a higher proportion of SO42– and a larger specific surface area (63.7 m2/g). The As(V) adsorption capacity of SCH-S was greater than that of SCH-S, and the As(V) adsorption process followed the pseudo-second-order and Langmuir models. Under acidic and neutral conditions, the As(V) adsorption capacities of SCH-S were 63.1 and 54.7 mg/g, respectively, mainly through As(V) exchange with SO42–. Under alkaline conditions, physical mechanisms resulting in low As(V) adsorption by SCH-S. More than 99.5% of the As(V) in sediments was immobilized by 3.0% SCH-S over 10 d. Bioavailable As(V) in sediments was converted to stable amorphous and crystalline hydrous oxide-bound fractions, which effectively decreased leachability and bioaccessibility. These results indicate that persulfate oxidation is a promising method of SCH synthesis, and SCH-S can be an effective material for the remediation of As contamination.

Removal of cadmium(II) from aqueous solutions by a novel sulfide-modified nanoscale zero-valent iron supported on kaolinite: Treatment efficiency, kinetics and mechanisms

Nano zero-valent iron (nZVI) had great potential in water pollution remediation, but the instability and easy agglomeration limited its application. To improve the dispersion and antioxidant properties of the nZVI, kaolinite-supported sulfide-modified nZVI (S-nZVI@Kaol) was synthesized for the removal of cadmium (II) (Cd(II)) in aqueous solution. The structure and morphology of the samples were characterized by field emission scanning electronic microscopy (FE-SEM) and X-ray diffraction (XRD), the elemental distribution and microstructure of the S-nZVI@Kaol were accomplished by transmission electron microcopy (TEM) and energy dispersive X-Ray spectroscopy (EDX), Fourier transform infrared (FTIR) and X-ray photoelectron spectrum (XPS). The results showed that S-nZVI was successfully loaded on kaolinite with a “core–shell” structure. The S-nZVI had higher specific surface area and lower magnetism compared with nZVI. The adsorption process of S-nZVI@Kaol for Cd(II) conformed to the pseudo-second-order kinetic model and Langmuir adsorption isotherm model better, and the maximum adsorption capacity was 104.7 mg·g−1. When the S/Fe molar ratio (MS/Fe) was 0.3, and the Fe/Kaol mass ratio (mFe/Kaol) was 50:50, S-nZVI@Kaol had the best removal efficiency for Cd(II). A higher solution pH (3.0–9.0) was beneficial for the removal of Cd(II). Adsorption thermodynamics studies showed that removing Cd(II) by composites was a spontaneous endothermic process. The mechanisms of the removal of Cd(II) involved electrostatic gravitation, chemical precipitation of CdS, and surface complexation.

(Invited) Experimental Quantification of the Effects of Concentration and pH on Nitrate-to-Ammonia Reaction Selectivity for Copper Electrodes

Nitrates constitute more than 80% of nitrogen-contaminants in point sources of wastewater like municipal wastewater effluents, ion-exchange brines and low-level nuclear wastes. They represent an untapped source for nutrient and energy recovery, as nitrates (NO3 -) can be electrochemically reduced to ammonia (NH3), which can then be used as a fertilizer or fuel. Concentration of NO3 - and the pH of waste streams are strongly influenced by the source. For example, ion-exchange brines are highly concentrated in NO3 - and have a neutral pH as the brine results from the regeneration process of the ion-exchange resin, which does not require a high pH solution, whereas low-level nuclear wastes are highly concentrated in NO3 - and highly alkaline due to the chemical processes involved in their formation. We propose to use Cu for this study as it is widely known for its selectivity towards reducing NO3 - to NH3. Cu has been exhaustively studied in alkaline conditions, but its behavior in pH 8 and pH 10 solutions has not been widely probed. Therefore, we have performed experiments to quantify the influences of NO3 - concentration (0.1 M – 1 M) and solution pH (8, 10 and 14) on the current-potential behavior and reaction selectivity towards NH3 production. Additional experiments were also performed with only NO2 - in the solution to isolate the effects of the rate determining NO3 --to-NO2 - reduction step from the downstream NO2 - to NH3 transformations. Cyclic voltammograms were obtained in a standard 3-electrode cell with a copper disk (0.28 cm2) and a platinum wire as the working and counter electrodes respectively. Polarization curves from this experiment were used to inform applied potentials in the galvanostatic tests to quantify reaction selectivity. UV-Vis spectroscopy was used to identify and quantify concentrations of species present in the solution (NO3 -, NO2 -, and NH3 using the salicylate method). Additional experiments are performed on brine solutions with Cl- and SO4 2- ions to quantify the effect of competing anions on the NO3 - to NH3 transformations at various pH conditions. Our results indicate that higher currents can be reached for higher concentrations of NO3 - and higher pH of the solutions. This is most likely due to the improved kinetics of the reactions taking place with the increased presence of ions, as the final current densities reached increase as well as the onset potentials shifted towards smaller values vs. RHE. As the pH decreases from pH 14 to pH 8, more peaks appear that are distinct from the NO3 --to-NO2 - peak, which was confirmed by running a separate NO2 - trial at the same concentration and pH. This indicates for these lower pH solutions, the nitrate reduction process might not be as fully selective towards ammonia formation, thereby highlighting the dependence of the products formed on Cu on the pH of the solution. These results are further interpreted to deduce empirical correlations for the concentration and pH dependence for the exchange current density for the rate determining NO3 --to-NO2 - step on the tested Cu disk electrodes.

Optical diffuser constructed by assembly of cellulose ether and polymer complex particles

Using sustainable cellulose and its derivatives to prepare optical diffuser is an economic and green approach. Herein, we report a novel optical diffuser constructed by interfacial assembly of cellulose ether (CE) and polymer complex particles (PCP) on flexible and transparent poly(ethylene terephthalate) (PET) substrate. Owning to the rich hydroxyl groups of CEs, the complex thin film can be further crosslinked by thermal treatment which greatly improves the optical diffusion performance and durability. Without crosslinking, haze (H) of the cellulose complex film is about 81 %, and the film will dissolve in high pH value solution. While after the proper crosslinking, H of the film increases to 95 %, and the film can resist the erosion of high pH solution. Moreover, CE/PCP complex film shows improved anti-bending capacity compared with commercially available optical diffuser for liquid crystal display.

One step synthesis of ultra-high quantum yield fluorescent carbon dots for "on-off-on" detection of Hg2+ and biothiols.

In this paper, the carbon dots (CDs) with strong blue fluorescence were synthesized through hydrothermal method, which using folic acid, ammonium citrate and ethylenediamine as precursors. The prepared CDs with a high absolute quantum yield of 81.94% and showed excellent stability in high concentration salt solution and different pH conditions. With the addition of Hg2+, the signal of CDs was selectively quenched. At the same time, the CDs-Hg2+ system could be recovered after the introduction of biothiols. Moreover, the fluorescence of CDs showed a good linear relationship with Hg2+ (1-15 µM), and the detection limit as low as 0.08 µM. In addition, the prepared CDs with low toxicity could be used to detect Hg2+ in living cells and actual water samples.

Decalcification of calcium silicate hydrate (C-S-H) under aggressive solution attack

Concrete is usually subjected to the environment with aggressive solutions where calcium leaching happens continuously threatening the durability of concrete. A comprehensive understanding of decalcification behaviors of C-S-H, a properties-determining phase in hardened cementitious materials, caused by aggressive ions has not been reached. In this paper, the calcium leaching behavior induced by chloride ions, sulfate ions, and the coupling of these two was systematically investigated by pH measurements, ICP, XRD, SEM-EDS together with XPS. It is concluded that the decalcification of C-S-H is strongly dependent on pH, the type of anions and the initial Ca/Si of C-S-H samples. High pH of the aggressive solution presents higher resistance to decalcification. Sulfate ions exaggerate the leaching of calcium to a larger extent than chloride ions, which may be attributed to their much higher binding energy with calcium ions. It appears that saline water has a more severe effect on the decalcification of C-S-H with low Ca/Si.

Hydroxyapatite-Integrated, Heparin- and Glycerol-Functionalized Chitosan-Based Injectable Hydrogels with Improved Mechanical and Proangiogenic Performance.

The investigation of natural bioactive injectable composites to induce angiogenesis during bone regeneration has been a part of recent minimally invasive regenerative medicine strategies. Our previous study involved the development of in situ-forming injectable composite hydrogels (Chitosan/Hydroxyapatite/Heparin) for bone regeneration. These hydrogels offered facile rheology, injectability, and gelation at 37 °C, as well as promising pro-angiogenic abilities. In the current study, these hydrogels were modified using glycerol as an additive and a pre-sterile production strategy to enhance their mechanical strength. These modifications allowed a further pH increment during neutralisation with maintained solution homogeneity. The synergetic effect of the pH increment and further hydrogen bonding due to the added glycerol improved the strength of the hydrogels substantially. SEM analyses showed highly cross-linked hydrogels (from high-pH solutions) with a hierarchical interlocking pore morphology. Hydrogel solutions showed more elastic flow properties and incipient gelation times decreased to just 2 to 3 min at 37 °C. Toluidine blue assay and SEM analyses showed that heparin formed a coating at the top layer of the hydrogels which contributed anionic bioactive surface features. The chick chorioallantoic membrane (CAM) assay confirmed significant enhancement of angiogenesis with chitosan-matrixed hydrogels comprising hydroxyapatite and small quantities of heparin (33 µg/mL) compared to basic chitosan hydrogels.

The effect of polyethylene microplastics on the disinfection of Escherichia coli by sodium hypochlorite

The effect of polyethylene microplastics (PE-MPs) on the disinfection of Escherichia coli (E. coli) by sodium hypochlorite was investigated in different pH value, ionic strength, and NOM concentration to illustrate the impact of MPs on the pathogenic bacteria disinfection efficiency in nature water environment. The results showed that PE-MPs tended to agglomerate rather than disperse due to their strong hydrophobicity in water. Within 30 s, about 1.5 log10 of E. coli was adsorbed on the surface of PE-MPs, forming subsequent protection for E. coli. Thus, the presence of PE-MPs reduced the inactivation rate of E. coli. As for the particle-free solutions, the higher solution pH, the presence of natural organic matter (NOM), and the higher concentrations of cations (monovalent Na+ and divalent Ca2+) were confirmed as the major influencing factors decreasing the E. coli disinfection efficiency. However, due to the adsorption and protection of PE-MPs on E. coli, the influences of complex chemistry factors on the inactivation of E. coli were reduced. The inactivation of E. coli in PE-MPs (20 NTU) solution was 1 log10 lower than that in particle-free solution under the same water quality conditions. Therefore, considering the complex water chemistry, the existence of MPs could be a potential challenge for disinfection efficiency in the water treatment plants.

Study of engineering properties of low-pH self-compacting concrete for concrete plug

Engineered Barrier Systems (EBS) is the primary concept in the design of the Geological Disposal Facility (GDF). In the design of EBS, bentonite is usually used as a buffer/backfill material. Due to its unique design, the concrete plug, used to close the junction between the transport tunnel and the disposal tunnel, is made of self-compacting concrete. Because the high pH solution in normal concrete reduces the performance of bentonite, low-pH self-compacting concrete with pH value less than 11 must be used to manufacture concrete plug. The silica fume (SF) and fly ash (FA) were used as mineral admixtures to discuss the effect of the mineral admixture addition level, Increased use of cementitious materials, and w/p on the engineering properties of Low-pH Self-Compacting Concrete (LPSCC). The test result shows that adding SF and FA could effectively prolong the setting time. Using only SF, the initial setting time of the mix increased up to 4.2 h with the addition of 40 wt% SF, while the combination of 40 wt% SF + 10 wt% FA could also increase the initial setting time to 3.92 h, which was much longer than 2 h working time requirement. Furthermore, at 90 days of curing, the pH value of each mixture was lower than 11, while the compressive strength enhanced to 118–132% compared to the control group. This addition could increase compactness, which leads to relatively strong sulfate resistance. The compressive strength could be enhanced by increasing the cementitious materials, which in turn, increases the pH and dry shrinkage. The LPSCC would lose strength when the w/p was reduced. The SF reacted with Ca(OH)2 in the LPSCC to generate a C-S-H gel. It was the primary factor in the drop of pH. The existence of SF and FA improved the pore structure in the matrix, compacting the structure of LPSCC. All that has been stated above are the dominant mechanism for improving the engineering properties. The pH value of mixture B300W29 was only 10.6 at 90 d, and the compressive strength could reach 61.66 MPa. Moreover, its drying shrinkage was about 0.047% at 90 d, and 0.055% at 150 d. Therefore, it should be considered as a potential material for concrete plug. The swelling property of bentonite was tested to validate the LPSCC material. No evident influence on the swelling property of bentonite was found. Replacing the conventional concrete with the designed material in disposal facilities can effectively enhance safety.

The synthesis of bacterial cellulose-chitosan zwitterionic hydrogels with pH responsiveness for drug release mechanism of the naproxen

The human digestive and absorption system has a specific pH environment, which makes it difficult to for accurate drug-release. Zwitterionic hydrogel, as a kind of drug carrier, is a feasible response strategy. In this work, a facile method was employed to prepare a series zwitterionic hydrogels composed of BC and chitosan. The composite gels could in-situ formed via Schiff's base reaction between partially oxidated bacterial cellulose and chitosan which exhibited relatively well mechanical properties. Besides, the rich amino and carboxyl groups endowed the hydrogels with excellent pH responsive performance. The minimum swelling rate of the hydrogels appeared at pH 3.5–pH 5.0. In lower or higher pH solutions, the swelling rate was greatly increased. The drug (naproxen) loading of the hydrogels was above 110 mg/g. The release amount of naproxen in the simulated gastric juice was less than intestinal fluid with the sustained release time exceeded 24 h. Through kinetic simulation analysis, the drug release behavior is in accordance with zero-order release model. Such kind of composite hydrogel is suggested to be a potential drug carrier for clinical therapy.

Alkali-Activated Materials with Pre-Treated Municipal Solid Waste Incinerator Bottom Ash

This study presents the results of an experimental campaign on the use of municipal solid waste incinerator bottom ash (MIBA) and fly ash (FA) as precursors for the production of alkali-activated materials. MIBA was subjected to a pre-treatment stage in response to two issues: high metallic aluminum content, which reacts in a high pH solution, releasing hydrogen; and low amorphous content of silica-, aluminum- and calcium-bearing phases, which translates into a limited formation of reaction products. The proposed pre-treatment stage oxidizes most of the metallic aluminum fraction and compensates for the low reactivity of the material via the formation of additional reactants. Different combinations of MIBA and FA were tried—mass-based ratios of 0/100, 25/75, 50/50, 75/25, and 100/0 for MIBA/FA. Two mix designs of the alkaline activator with sodium hydroxide and sodium silicate were evaluated by varying the Na2O/binder and SiO2/Na2O ratios. These mortars were tested in the fresh and hardened state. The results showed that the pre-treatment stage was effective at stabilizing the dimensional variation of MIBA. Despite the lower reactivity of MIBA, mortars with 50/50 of MIBA/FA presented a maximum 28-day compressive strength of 25.2 MPa, higher than the 5.7 MPa of mortars made with MIBA only.

Unintentional release of antibiotics associated with nutrients recovery from source-separated human urine by biochar

The use of biochar to recover nitrogen and phosphorus from wastewater especially source-separated human urine is attractive from both economic and environmental standpoints. The widespread use of pharmaceuticals has raised concerns as they are not fully metabolized and ended up in human urine. The objective of this study is to examine adsorption of antibiotics (azithromycin, ciprofloxacin, sulfamethoxazole, trimethoprim, and tetracycline) and nutrients (ammonium and phosphate) in source-separated human urine by biochar and subsequent desorption. Batch adsorption experiments were conducted using biochar prepared from oak wood (OW) and paper mill sludge (PMS) to elucidate the effects of adsorption time, pH, and adsorbent dose. The desorption of adsorbed nutrients and antibiotics was also investigated. While the nutrient adsorption was more favorable by the PMS biochar, antibiotic adsorption was more prolific by the OW biochar. Hydrogen bonding and π-π interaction were identified as potential adsorption mechanisms. Experimental results agree with the Freundlich isotherm and pseudo-second order models (except the OW biochar for the kinetics). The findings suggest that biochar can adsorb both nutrients (43.30–266.67 mg g−1) and antibiotics (246.70–389.0 μg g−1) simultaneously. Lower solution pH (<5) was better for antibiotic adsorption, while higher solution pH (≥5) favored nutrient recovery. Also, desorption of the antibiotics (maximum of 92.6% for trimethoprim) was observed and might arise in the environment with the applications of biochar for nutrient recovery from human urine and subsequently for soil quality improvement. The findings serve as a foundation for future research on adsorption-based methods for separating nutrients and antibiotics in aqueous solutions, particularly urine.

Deep hydrochemical section through the Central Alps: evolution of deep water in the continental upper crust and solute acquisition during water\u2013rock-interaction along the Sedrun section of the Gotthard Base Tunnel

Drilling of the Gotthard Rail Base Tunnel through the Central Alps from 2005 to 2010 opened up fractured basement units and frequent water inflows provided access to the major fluid-rock interactions processes in orogenic crystalline upper crust. Construction of the 57 km long tunnel was divided into five different sections. Here we report data and observations from the 10 km long central Sedrun section 211 water samples were collected at inflow points 900 to 2350 m below the surface. The exceptional samples and data provide a comprehension of the hydrochemical evolution and solute acquisition of deep groundwater in basement units. The investigated tunnel section drilled through steeply dipping rock units and vertical fracture systems at high angle. It cuts across granite, gneiss and schist of the pre-Alpine basement and across two narrow zones of meta-sediments. Rock temperature along the Sedrun section varies from 30 to 45 °C depending on the thickness of the overburden. The fracture water is of meteoric origin and acquires its composition exclusively by chemical interaction with the surrounding rocks along the flow path. Water from inflow points in the basement of the Gotthard Massif has typically a high pH of about 10 and total dissolved solids in the range of 100 to 300 mg L−1. Sodium is the prime cation of most waters. Although plentiful in the rocks, calcium, potassium and magnesium are low to very low in water. The anions associated with Na are carbonate/bicarbonate, sulfate, fluoride and chloride in widely varying proportions. High fluoride concentrations of up to 15.4 mg L−1 are characteristic for most waters. As a result of the high pH dissolved silica (SiO2) reached concentrations of up to 58 mg L−1 and represents 25—30 wt% of the solutes. The meteoric recharge provides dissolved O2 and CO2 to the fluid-rock interaction processes. The solutes derive from the dissolution of feldspar (Na+, SiO2aq), oxidation of sulfides to sulfate (SO42−), alteration of biotite (F−), and fluid inclusions opened by brittle deformation (Cl−). The solids formed during fluid-rock interaction, mainly zeolites, chlorite (and other clay minerals) and secondary Fe-minerals, remove Mg, Fe, and K almost quantitatively from the water. The high pH results from hydrolysis of silicates. The data distinctly show that within the depth interval of 1.0–2.5 km below surface deep water in continental basement evolves to a low TDS, high pH, sodium carbonate and silica solution by interaction of gneiss and granite with infiltrating pristine meteoric water, snow and rain.

The Comparison of the Environmental Impact of Waste Mineral Wool and Mineral in Wool-Based Geopolymer.

Waste generated in fine wool production is homogeneous and without contamination, which increases its chances of reuse. Waste mineral wool from demolition sites belongs to the specific group of waste. However, the storage and collection require implementing restrictive conditions, such as improper storage of mineral wool, which is highly hazardous for the environment. The study focuses on the leachability of selected pollutants (pH, Cl−, SO42−) and heavy metals (Ba, Co, Cr, Cu, Ni, Pb, Zn) from the waste mineral wool. As a solution to the problem of storing mineral wool waste, it was proposed to process it into wool-based geopolymer. The geopolymer, based on mineral wool, was also assessed regarding the leaching of selected impurities. Rock mineral wool is very good for geopolymerisation, but the glass wool needs to be completed with additional components rich in Al2O3. The research involved geopolymer prepared from mineral glass wool with bauxite and Al2O3. So far, glass wool with the mentioned additives has not been tested. An essential aspect of the article is checking the influence of wool-based geopolymer on the environment. To investigate the environmental effects of the wool-based monolith and crushed wool geopolymers were compared. Such research has not been conducted so far. For this purpose, water extracts from fragmented geopolymers were made, and tests were carried out following EN 12457-4. There is no information in the literature on the influence of geopolymer on the environment, which is an essential aspect of its possible use. The research results proved that the geopolymer made on the base of mineral wool meets the environmental requirements, except for the pH value. As mentioned in the article, the geopolymerisation process requires the dissolution of the starting material in a high pH (alkaline) solution. On the other hand, the pH minimum 11.2 value of fresh geopolymer binder is required to start geopolymerisation. Moreover, research results analysed in the literature showed that the optimum NaOH concentration is 8 M. for the highest compressive strength of geopolymer. Therefore, the geopolymer strength decreases with NaO concentration in the NaOH solution. Geopolymers glass wool-based mortars with Al2O3 obtained an average compressive strength of 59, the geopolymer with bauxite achieved about 51 MPa. Thus, Al2O3 is a better additional glass wool-based geopolymer than bauxite. The average compressive strength of rock wool-based geopolymer mortar was about 62 MPa. The average compressive strength of wool-based geopolymer binder was about 20–25 MPa. It was observed that samples of geopolymers grout without aggregate participation are characterised by cracking and deformation.

Affinity purification of fibrinogen using an Affimer column

BackgroundFibrinogen is an abundant plasma protein with an essential role in blood coagulation and haemostasis thus receiving significant research interest. However, protein purification is time consuming and commercial preparations often have protein contaminants. The aim of this study was to develop a new method to purify high quality and functional fibrinogen. MethodsFibrinogen-specific Affimer protein, isolated using phage display systems, was immobilised to SulfoLink resin column and employed for fibrinogen purification from plasma samples. Fibrinogen was eluted using a high pH solution. Commercial human fibrinogen was also further purified using the Affimer column. Fibrinogen purity was determined by SDS-PAGE and mass spectrometry, while functionality was assessed using turbidimetric analysis. ResultsAffimer-purified fibrinogen from human plasma showed purity at least comparable to commercially available preparations and was able to form physiological fibrin networks. Further purification of commercially available fibrinogen using the Affimercolumn eliminated multiple contaminant proteins, a significant number of which are key elements of the coagulation cascade, including plasminogen and factor XIII. ConclusionsThe Affimercolumn represents a proof of concept novel, rapid method for isolating functional fibrinogen from plasma and for further purification of commercially available fibrinogen preparations. General significanceOur methodology provides an efficient way of purifying functional fibrinogen with superior purity without the need of expensive pieces of equipment or the use of harsh conditions.

Fabrication of uniform and anti-corrosion layered double hydroxides film on Mg-Gd-Y-Zn-Zr alloy through solution pH tailoring

Second phase is generally beneficial to the mechanical properties of magnesium (Mg) alloys. As an electrochemically heterogeneous structure, it leads to the formation of uneven chemical conversion films which are detrimental to corrosion protection. To address this problem for multiphase Mg alloys, a simple hydrothermal method was reported herein for fabricating a layered double hydroxides (LDHs) film with a uniform structure and superior corrosion protection upon Mg-Gd-Y-Zn-Zr alloy through tailoring solution pH. Morphology characterization reveals that high solution pH facilitates the production of LDHs nanosheets with dense and fine features, which is attributed to the high density of hydroxy groups on substrate as nucleation sites for LDHs growth. In addition, the uniformity of films depended on solution pH. The highest pH (13.5) of this study drove even distribution of OH− that in turn circumvented the micro-galvanic effect between second phases and α-Mg matrix. Immersion and electrochemical tests confirmed that corrosion resistance of the sample fabricated at pH of 13.5 outperformed those of the counterparts fabricated at pH 10−12. It is postulated that the high compactness of the LDHs film and the self-healing ability of RE(OH)3 were the driving forces.

Investigation of Operation Strategy Based on Solution pH for Improving the Crystal Quality Formed during Reactive Crystallization of l-Aspartic Acid.

The production of crystalline particles with a thick and low degree of agglomeration is required because the agglomerated crystals with thin primary particles, which are frequently formed during reactive crystallization, deteriorate the crystal size distribution (CSD) of the final product due to their fragile morphology. This study aimed to develop an operation strategy for improving the degree of agglomeration and thickness of crystalline particles in the reactive crystallization considering the effect of the solution pH using l-aspartic acid as an experimental system. The scanning electron microscopy observations showed that the thickness of primary particles which form agglomerated crystals could be increased by operating the crystallization under low solution pH conditions. In contrast, it was found that operating the crystallization under high solution pH led to a decrease in the nucleation rate of crystalline particles, which resulted in a decrease in the degree of agglomeration. Then, an operation method, that is, changing the addition method of feed solutions to overcome the trade-off between the thickness and degree of agglomeration, was proposed by considering the effect of solution pH. Consequently, crystalline particles with a narrow CSD could be successfully obtained using the proposed method due to the suppression of the agglomeration and increase of the thickness. Therefore, the development of the operation strategy based on the effect of the solution pH on the degree of agglomeration and thickness is important to produce crystalline particles with improved CSD in reactive crystallization.

Magnetically recyclable core–shell MOF nanoparticles of Fe3O4@PDA@UIO-66-NH2 grafted by organic acids for intensified cationic dye adsorption

The adsorption mechanism towards MB by the two adsorbents is mainly due to IE at lower solution pH and EA at higher solution pH than their pHpzc.

On the thermodynamics of hydrogen adsorption over Pt(111) in 0.05M NaOH.

The reasons for the sluggish kinetics of the hydrogen adsorption reaction in alkaline media remain a question still to be solved. This information is important to achieve a complete understanding of the mechanistic details that could lead to the production of key catalytic materials necessary for the development of a future hydrogen economy. For a better understanding of this reaction, it is important to acquire information about the thermodynamic parameters characteristic of the different steps in the reaction. Among these, the hydrogen adsorption is a key step in the process of hydrogen evolution. Although some debate still remains about the difference between adsorbed hydrogen in the underpotential deposition (UPD) region and at the overpotential deposition region, there is no doubt that understanding the former can help in the understanding of the latter. Making use of charge density measurements, we report on this paper a thermodynamic study of the hydrogen UPD process on Pt(111) in 0.05M NaOH over the range of temperatures from 283 ≤ T/K ≤ 313. The coulometric features corresponding to HUPD allow for the calculation of the hydrogen coverage and a fit to a Generalized Frumkin isotherm. From these values, different thermodynamic functions for the UPD reaction have been calculated: ΔGads, ΔSads, ΔHads, and the Pt-H bond energy. From extrapolation, a value of ΔSads ◦=-7.5±4Jmol-1K-1 was found, which is very close to 0, much lower than previously reported measurements both in acid and in alkaline solutions. Such value has an effect on the enthalpy and bond energy calculations, the latter having a decreasing tendency with pH and coverage. This tendency is completely different from the acidic systems and implies that the change in the thermodynamic functions due to the formation of the double layer and the reorganization of interfacial water has a strong influence on the process in high pH solutions.

Effect of SRB and Applied Potential on Stress Corrosion Behavior of X80 Steel in High-pH Soil Simulated Solution.

The effect of SRB and applied potential on the stress corrosion sensitivity of X80 pipeline steel was analyzed in high-pH soil simulated solution under different conditions using a slow strain rate tensile test, electrochemical test, and electronic microanalysis. The experimental results showed that X80 pipeline steel has a certain degree of SCC sensitivity in high-pH simulated solution, and the crack growth mode was trans-granular stress corrosion cracking. In a sterile environment, the SCC mechanism of X80 steel was a mixture mechanism of anode dissolution and hydrogen embrittlement at −850 mV potential, while X80 steel had the lowest SCC sensitivity due to the weak effect of AD and HE; after Sulfate Reducing Bacteria (SRB) were inoculated, the SCC mechanism of X80 steel was an AD–membrane rupture mechanism at −850 mV potential. The synergistic effect of Cl− and SRB formed an oxygen concentration cell and an acidification microenvironment in the pitting corrosion pit, and this promoted the formation of pitting corrosion which induced crack nucleation, thus significantly improving the SCC sensitivity of X80 steel. The strong cathodic polarization promoted the local corrosion caused by SRB metabolism in the presence of bacteria, whereby the SCC sensitivity in the presence of bacteria was higher than that in sterile conditions under strong cathodic potential.