Acid–base transport model depicting the dynamic pH response of interfacial reactions

Acid–base transport is integral to many important interfacial reactions in various fields of chemistry, but its theoretical foundation is lacked. Herein, a common acid–base transport model is established owing to the success in deriving buffer transport equations. This model is applicable to most buffer systems by flexibly integrating the transport equations in terms of buffer components, and is verified through the model relationships of buffer transport limiting current by using hydrogen evolution reaction experiments. Based on model calculations, two diagram approaches are proposed to depict the dynamic pH response and aid buffer operation optimizations. The model and methods allow us to quantify the rate-limiting effect of acid–base transport on interfacial reactions and to precisely control the effect through medium regulations. Furthermore, the model has laid the foundation of dynamic pH effect on species transformation and process mechanism, which can be of wide interest in the chemistry encompassing interfacial reactions.     

Chemistry enhanced shear thickening polishing of Ti–6Al–4V

To obtain the great surface quality of Ti–6Al–4V and achieve high efficiency in the polishing process, the chemistry enhanced shear thickening polishing (C-STP) was proposed, and the polishing performance of different pH slurry was studied. The results show that the material removal rate gradually increases as the pH value decreases from 10 to 1, and the best surface quality is obtained at pH 2. The corrosion current density and potential were measured by potentiodynamic polarization under three typical pH values. It is confirmed that the most massive corrosion rate presents at pH 2, and the passive film is most susceptible to be produced at pH 10. The reaction resistance was measured by electrochemical impedance spectroscopy to clarify the polishing mechanism. Under acidic conditions, the chemical reaction product on the surface can be quickly removed by mechanical action of the abrasive. On the contrary, the passive film formed on the surface under the alkaline condition is difficult to be removed. The corrosion reaction products were determined by X-ray photoelectron, and the chemical reaction under acid-base environment was derived. MRR reached 107.3 nm/min under the selected process parameters, and the surface roughness (S_a) is reduced from 124 nm to 8.6 nm within 15 min.     

Chitosan Microspheres as Carriers for pH‐Indicating Species in Corrosion Sensing

Chitosan microspheres containing bromocresol green, cresol red, and phenolphthalein for corrosion detection, through pH change, are synthesized in order to be used in protective coatings for aluminium alloys. Microspheres containing corrosion detection species are characterized morphologically (SEM) and physico‐chemically (FTIR, TGA). Release studies (UV–vis) are performed in corrosion‐promoting conditions (pH, NaCl), and detection studies by immersion in media associated with corrosion activity while microspheres' sensing activity is evaluated visually. Electrochemical characterization of AA2024 substrates in the presence of chitosan spheres is performed to understand material performance, and a color change is observed as a result of local pH increase in cathodic areas when corrosion takes place. These findings can be correlated with the results from release studies and seem a promising approach for corrosion sensing purposes, not only because pH increase is possible to detect due to corrosion, but also because chitosan is considered an environmentally friendly material.     

Linear correlation between pH value of stimulated beef and electrical current intensity

The aim of the present study was to determine mathematical relationships between pH changes in beef 24 h post-slaughter and changes in the intensity of electrical current flowing through bull and heifer carcasses during high-voltage electrical stimulation. The electrical stimulation was applied 40 min postmortem for 120 s. The pH values of m. longissimus thoracis et lumborum were analyzed in the function of electrical current intensity changes and its change during electrical stimulation. Mathematical linear correlations of the y = ax ± b type were demonstrated between pH values at 2, 6, and 24 h postmortem and the initial (I_i) and ultimate (I_u) electrical current intensity values, the difference between them and the initial pH values determined before electrical stimulation. High multiple correlation coefficients (R² = 0.416, α ≤ 0.001) between I_u and pH values 24 h post-slaughter enabled concluding that there is a possibility to predict a pH value of stimulated carcass with high accuracy, and thus also beef quality, based merely on the ultimate electrical current intensity values.     

Synthesis of pH-responsive isolated soy protein/carboxymethyl chitosan microspheres for sustained pesticide release

In order to improve the utilization rate of avermectin (AVM), a complex was prepared by electrostatic self-assembly using isolated soy protein (ISP) and carboxymethyl chitosan (CMCS) for loading AVM to obtain ISP/CMCS@AVM microspheres. The encapsulation efficiency (EE), sustained release property, ultraviolet (UV) protective ability, and toxicity of the microspheres were evaluated, and the release kinetics of AVM from the microsphere at different pHs were investigated. The results demonstrated that the average particle size of ISP/CMCS@AVM was 283.95 nm, and the EE reached 88.42% for AVM after denaturation. After 70 h of exposure to UV light, the residual rate of AVM in ISP/CMCS@AVM was 78.12%, which was significantly higher than 35.18% in the AVM emulsion. Moreover, the formulation imparted pH sensitivity and sustained-release property to AVM and was consistent with the Korsmeyer–Peppas model, controlled by Fick diffusion. Finally, the insecticidal toxicity of ISP/CMCS@AVM did not differ significantly from that of unmodified AVM. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48358.     

Structural properties and sensing performance of CeTiO3 ceramic films as a solid-state pH sensor

In this paper, we have studied the impact of postannealing treatment on the structural properties and sensing characteristics of CeTiO₃ ceramic membranes deposited on Si substrate by sputtering for solid-state electrolyte-insulator-semiconductor (EIS) pH sensors. X-ray photoelectron spectroscopy, Auger electron spectroscopy, X-ray diffraction, and atomic force microscopy were used to study the chemical compositions, elemental depth profiles, film structures, and surface morphologies of CeTiO₃ ceramic membranes treated at three rapid thermal annealing (RTA) temperatures of 700, 800 and 900?°C. The sensing performance of the CeTiO₃ ceramic membranes annealed at three different RTA temperatures is strongly correlated to their structural properties. The CeTiO₃ EIS device after RTA at 800?°C exhibited the best sensing characteristics (pH sensitivity, hysteresis voltage and drift rate) among these RTA temperatures. We attribute this behavior to the optimal RTA temperature enhancing the Ce³⁺/Ce⁴⁺ ratio of CeTiO₃ ceramic membrane, reducing an interfacial layer at the CeTiO₃-Si interface, and increasing its surface roughness.     

不同pH环境下CMS改性纳米铁在异质多孔介质中的迁移

纳米铁在污染土壤和地下水的修复中受到广泛关注。为进一步探究其在多孔介质的迁移行为，本研究采用羧甲基淀粉钠（CMS）对纳米零价铁（nZVI）进行包覆，进行了改性纳米零价铁的沉降试验，测量zeta电位与粒径分布探究其分散性；进行了不同pH条件下改性纳米零价铁在酸洗砂与水洗砂的柱实验，分析了化学异质性与pH对纳米铁在多孔介质迁移的影响。结果表明，CMS包覆纳米铁不仅使纳米颗粒本身稳定，而且还减少其在多孔介质表面沉积，大大提高了迁移性。pH=6～8时，nZVI的zeta电位由18.3mV减小到2.9mV，有效粒径由685nm增大到880nm，稳定性变差；而CMS-nZVI的zeta电位值由-19.7mV增大到-53.5mV，颗粒间静电排斥力增强稳定性变好。经能量色散X射线光谱（EDS）分析，水洗砂表面存在碳、铝、铁等氧化物杂质，这些杂质带有正电荷，会增强与带负电的CMS-nZVI的吸附作用，不利于其迁移；而经过酸洗后的石英砂，其表面杂质大大减少，在pH=8时，CMS-nZVI在酸洗砂最大迁移率为77.0%要好于水洗砂的63.0%。此外较高pH环境有助于增加石英砂介质的表面负电荷，减少颗粒与介质的吸附，促进纳米颗粒的迁移。     

紫外分光光度法测定核酸含量的影响因素分析

选择寡聚核苷酸、鲑鱼精单链DNA、小牛胸腺双链DNA标准物质为样本,系统研究了溶液pH、苯酚、丙酮、蛋白质、多糖等对紫外分光光度法测量结果的影响情况,另外考察了核糖核酸(RNA)和脱氧核糖核酸(DNA)的相互影响情况。研究发现基于分光光度法的核酸定量分析,易受溶液pH、苯酚、丙酮、蛋白质、多糖等的影响,另外,DNA和RNA之间也会相互干扰。因此,紫外分光光度法测定核酸含量时,特别是该方法用于核酸标准物质特性量值确定时,需要样品高度纯化,pH确定的条件下才能保证测量结果的准确可靠。