The Resistance of Polyethersulfone Membranes on the Alkaline Cleaning Solutions

Polyethersulfone (PES) is a polymer popularly used to produce ultrafiltration (UF) membranes. PES is relatively hydrophobic; thus, hydrophilic ingredients are added to the membrane matrix to reduce the fouling intensity. Ingredients such as polyvinylpyrrolidone (PVP) reduce the resistance of PES to NaOH solutions. This study investigated the possibility of using PES membranes for the separation of alkaline cleaning solutions. For this purpose, self-made PES membranes and commercial ultrafiltration PES membranes (UE10-10 kDa and UE50-100 kDa) containing PVP additive were used. The membranes were soaked for 18 months in alkaline (pH = 11.3-11.5) solutions of car washing fluids. It has been found that long-term contact with these solutions caused changes in the structure of the surface layer, especially of membranes containing PVP. As a result, the separation of dextran (100-200 kDa) decreased by 30-40% for PES membranes, 30-40% for UE10 and 40-60% for UE50. Despite these changes, the separation efficiency (rejection of COD, NTU and anionic surfactants) of synthetic car wash wastewater (mixture of surfactants and hydrowax) was similar to the results obtained for pristine membranes.

Survival of Bacteriophage T4 in Quasi-Pure Ionic Solutions

The preservative qualities of individual ionic compounds impacting the infectivity of T4 virions were elucidated. T4 virions were immersed in quasi-pure ionic solutions prior to the adsorption process, and the plaque forming unit (pfu) values of these were measured following the conventional method. In neutral ionic solutions, the minimum and the optimum concentrations of preservative qualities corresponded with the results obtained from the multi-ionic media/buffers. In acid and alkali solutions, phages show tolerances at a pH range of 5-11 in multi-ionic media/buffers. T4 virions show no tolerance in quasi-pure acid, neutral, and weak alkaline conditions. The preservative quality of T4 virions increased in over 10-1 mM OH- solution, equivalent to a pH value over 10, which corresponds to the pKa of the deprotonation of the DNA bases G and T. Infectivity was lost below 10-1 mM OH- and higher than 10 mM OH-. These results imply that maintaining infectivity of a virion may need the flexibility of the intra-capsid DNA by deprotonation.

Sodium Succinate as a Corrosion Inhibitor for Carbon Steel Rebars in Simulated Concrete Pore Solution

The inhibiting performance of sodium succinate (Na₂C₄H₄O₄) was evaluated as an organic environmentally friendly corrosion inhibitor for carbon steel rebars in 0.6 M Cl^- simulated concrete pore solution. Potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) measurements were utilized to evaluate the inhibitor performance at different temperatures and concentrations. The investigated corrosion inhibitor showed strong corrosion inhibition performance as it adsorbs on the surface of the rebar, creating a protective adsorption film. According to PDP, the inhibitor is classified as a mixed-type inhibitor with an inhibitor efficiency of 77, 69, 59, and 54% for 25, 35, 45, and 55 °C, respectively. EIS validated the PDP tests, showing that sodium succinate displaces the water molecules at the interface, creating an adsorption film by complexing with ferrous ions. The film thickness was calculated, and sodium succinate was able to produce a thicker protective film (span of nanometers) relative to the reference at every temperature. The adsorption of sodium succinate follows the Temkin adsorption isotherm. ΔG⁰_ads was found to be -32.75 kJ/mol, indicating that the inhibitor adsorption is a combined physisorption and chemisorption process. Different surface characterizations were utilized to substantiate the adsorption of sodium succinate, these include scanning electron microscopy, energy-dispersive X-ray spectroscopy, and micro-Raman spectroscopy. Finally, quantum chemical calculations showed that the delocalized electrons in the carboxyl group have high HOMO energies and electrostatic potential, which facilitates the adsorption of sodium succinate corrosion inhibitor onto the carbon steel rebar surface.

CoMo layered double hydroxide equipped with carbon nanotubes for electrocatalytic oxygen evolution reaction

To carry out effective resource reforming of sustainable electricity, hydrogen production by electrochemical water splitting provides an eco-friendly and economical way. Nevertheless, the oxygen evolution reaction (OER) at the anode is limited by the slow reaction process, which hinders the large-scale development and application of electrolysis technology. In this work, we present an electrocatalyst with superior OER performance, which attributed to the abundant active sites and good electronic conductivity. The two-dimensional CoMo Layered Double Hydroxide nanosheets are synthesized and deposited on conductive carbon nanotubes (CoMo LDH/CNTs), and then hybrid composites show better catalytic performance than their undecorated counterpart under identical conditions. Specifically, CoMo LDH/CNTs exhibit the low overpotential of 268 mV to obtain 10 mA cm^-2and satisfactory stability (more than 40 h). We emphasize that this hybridization strategy with a conductive supporting framework could design more abundant and low-cost OER electrocatalysts to minimize electrical energy consumption, thereby achieving efficient conversion between energy sources.

Electrochemical Detection and Analysis of Various Current Responses of a Single Ag Nanoparticle Collision in an Alkaline Electrolyte Solution

A single silver (Ag) nanoparticle (NP) collision was observed and analyzed in an alkaline solution using the electrocatalytic amplification (EA) method. Previously, the observation of a single Ag NP collision was only possible through limited methods based on a self-oxidation of Ag NPs or a blocking strategy. However, it is difficult to characterize the electrocatalytic activity of Ag NPs at a single NP level using a method based on the self-oxidation of Ag NPs. When using a blocking strategy, size analysis is difficult owing to the edge effect in the current signal. The fast oxidative dissolution of Ag NPs has been a problem for observing the staircase response of a single Ag NP collision signal using the EA method. In alkaline electrolyte conditions, Ag oxides are stable, and the oxidative dissolution of Ag NPs is sluggish. Therefore, in this study, the enhanced magnitude and frequency of the current response for single Ag NP collisions were obtained using the EA method in an alkaline electrolyte solution. The peak height and frequency of single Ag NP collisions were analyzed and compared with the theoretical estimation.

Study on Extraction Separation of Thioarsenite Acid in Alkaline Solution by CO 3 2 - -Type Tri-n-Octylmethyl-Ammonium Chloride

To overcome the problem of arsenic separation and enrichment from an alkaline leaching solution in arsenic-containing dust, a CO 3 2 - -type tri-n-octylmethyl-ammonium chloride (TOMAC) method for extracting thioarsenite is proposed in this paper. Considering an alkaline leaching solution as the research object, after vulcanization pretreatment, TOMAC transformation and organic phase saturated extraction capacity were measured, and the extraction mechanism was preliminarily studied. First, Cl^--type quaternary ammonium salt was effectively transformed to HCO 3 - -type by treating organic phase with saturated NaHCO_3five times. TOMAC was effectively transformed from HCO 3 - to CO 3 2 - type by alkaline washing with 1.0 mol/l NaOH solution; this washing was repeated thrice. Thereafter, the effects of organic phase composition, phase ratio, extraction time, and temperature on the extraction and separation of arsenic were investigated. The results show that under the conditions of 30% CO 3 2 - -type TOMAC + 15% sec-octanol + 55% sulfonated kerosene, V_O/V_A = 1/1, and 5 min extraction at room temperature, the single-stage extraction rate of As^III is 85.2%. The As^III concentration in raffinate can be reduced to less than 1.33 × 10^-3 mol/l by four-stage countercurrent extraction, and the extraction rate of As^III can exceed 98.4%.

Reactivity of Metakaolin in Alkaline Environment: Correlation of Results from Dissolution Experiments with XRD Quantifications

Systematic investigation of filtrates and filter residues resulting from a 24 h treatment of metakaolin in different alkaline solutions were performed. On filtered metakaolin particles, inductively coupled plasma-optical emission spectrometry (ICP-OES) measurements reveal an enrichment of iron and titanium, which suggests an inhomogeneous distribution of these cations. Since the SiO₂/Al₂O₃ ratio remains constant in all filter residues examined, the dissolution of the Si and Al monomers is congruent. Structural differences, identified by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) as a consequence of alkali uptake, influence the X-ray scattering contribution of metakaolin, and thus quantifications with the partial or no known crystal structure (PONKCS) method. This leads to deviations between the degree of reaction calculated from Si and Al solubility from filtrate and that quantified by quantitative powder X-ray diffraction (QPXRD) using the filter residue. Nevertheless, the described changes do not cause a shift in the X-ray amorphous hump in case of congruent dissolution, and thus allow the quantification of the metakaolin before and after dissolution with the same hkl-phase model.

Assessment of Alkali-Silica Reactivity of Aggregates by Concrete Expansion Tests in Alkaline Solutions at 38 °C

A new accelerated concrete prism expansion test at 38 °C (accelerated CPT) is proposed for assessing the alkali-reactivity of concrete aggregates. In this test, concrete prisms with a standardized mix composition and different alkali contents are immersed in alkaline solutions with compositions simulating the pore liquid of hardened concretes. The concrete prism expansion test at 38 °C and RH > 95% (traditional CPT) was taken as a reference test, in order to define the appropriate expansion limit criterion for the proposed accelerated CPT. Three natural aggregates of known field performance and different alkali–silica reactivity were tested. The compositions of alkaline solutions were designed by assuming total dissolution of cement alkalis and taking a ratio between the mass fractions of effective water consumed by cement hydration and of alkalis uptaken by cement hydrates equal to unity. This simplified approach was found in an acceptable agreement with literature empirical equations correlating pore solution alkalinity of hardened Portland cement mixes with total alkali content of cement. Elaboration of expansion data through both pass-fail and threshold alkali level (TAL)-evaluation approaches indicated that, for the accelerated CPT, an expansion limit criterion of 0.04% after 120 days of testing in alkaline solutions is appropriate to evaluate the aggregate alkali reactivity congruently with the traditional CPT. Use of the proposed test method in place of the traditional CPT would reduce the test duration from 365 to 120 days.

Electrochemical Adsorption on Pt Nanoparticles in Alkaline Solution Observed Using In Situ High Energy Resolution X-ray Absorption Spectroscopy

The oxygen reduction reaction (ORR) on Pt/C in alkaline solution was studied by in situ high energy resolution X-ray absorption spectroscopy. To discuss the X-ray absorption near-edge structure (XANES), this paper introduced the rate of change of the Δμ (RCD), which is an analysis method that is sensitive to surface adsorption. The surface adsorptions as hydrogen (below 0.34 V), superoxide anion (from 0.34 V to 0.74 V), hydroxyl species (from 0.44 V to 0.74 V), atomic oxygen (above 0.74 V), and α-PtO₂ (above 0.94 V) were distinguished. It is clarified that the catalytic activity in an alkaline solution is enhanced by the stability of atomic oxygen and the low stability of superoxide anion/peroxide adsorption on the platinum surface.

Oxygen Reduction Activity and Stability of Composite Pdx/Co-Nanofilms/C Electrocatalysts in Acid and Alkaline Media

The morphology tuning of Pd and Pd-M nanoparticles is one of the significant strategies to control the catalytic activity toward oxygen reduction reaction (ORR). In this study, composite Pdx/Co-nanofilms/C electrocatalysts of Pd nanoparticles implanted onto Co nanofilms were synthesized on an immiscible ionic liquid (IL)/water interface for ORR. The Pd nanoparticles implanted onto Co nanofilms show a marked distortion of crystal lattice and surface roughness. These Pdx/Co-nanofilms/C electrocatalysts exhibit enhanced activity for ORR compared with Pd/C and PdxCo/C catalysts in both acid and alkaline solutions, in which the Pd3/Co-nanofilms/C catalyst displays the highest ORR mass activity. The superior ORR mass activities of the fabricated Pdx/Co-nanofilms/C catalysts may be mainly attributed to their larger catalytic areas, which are conferred by the rough surface of Pd nanoparticles with a distorted crystal lattice, and the synergistic effect between the surface Pd atoms and the 2D Co nanofilm substrate. The relationship between ORR mass activity and Pd/Co atom ratio varies in different electrolytes. Furthermore, by using proper heat-treatment methods, the Pdx/Co-nanofilms/C catalysts exhibit improved cycling stability compared with pure Pd/C catalyst after extended potential cycling.

Fluorine-doped graphene with an outstanding electrocatalytic performance for efficient oxygen reduction reaction in alkaline solution

Doping carbon materials have proved to be the front runners to substitute for Pt as oxygen reduction reaction (ORR) catalysts. Fluorine-doped graphene (FG) has rarely been used as ORR catalyst because of the difficulty in preparation. Herein, we report FG sheets prepared by a thermal pyrolysis graphene oxide (GO) process in the presence of zinc fluoride (ZnF₂) as an efficient electrocatalyst for ORR in the alkaline medium. The results show that the pyrolysis temperature seriously affected the doped fluoride amount and morphology of catalyst. It is found that the FG-1100 catalyst possesses a more positive onset potential, higher current density and better four-electron process for ORR than other FG samples. FG-1100 displays an outstanding ORR catalytic activity that is comparable to that of the commercial Pt/C catalyst. Also, its durability and methanol tolerance ability are superior to those of the commercial Pt/C. The excellent ORR catalytic performance is closely related to its higher doped fluorine amount and wrinkle morphology. The FG catalyst can be developed as a low-cost, efficient and durable catalyst as a viable replacement for the Pt/C catalyst, promoting the commercialization of fuel cells.

A Cuprous Oxide Thin Film Non-Enzymatic Glucose Sensor Using Differential Pulse Voltammetry and Other Voltammetry Methods and a Comparison to Different Thin Film Electrodes on the Detection of Glucose in an Alkaline Solution

A cuprous oxide (Cu₂O) thin layer served as the base for a non-enzymatic glucose sensor in an alkaline medium, 0.1 NaOH solution, with a linear range of 50-200 mg/dL using differential pulse voltammetry (DPV) measurement. An X-ray photoelectron spectroscopy (XPS) study confirmed the formation of the cuprous oxide layer on the thin gold film sensor prototype. Quantitative detection of glucose in both phosphate-buffered saline (PBS) and undiluted human serum was carried out. Neither ascorbic acid nor uric acid, even at a relatively high concentration level (100 mg/dL in serum), interfered with the glucose detection, demonstrating the excellent selectivity of this non-enzymatic cuprous oxide thin layer-based glucose sensor. Chronoamperometry and single potential amperometric voltammetry were used to verify the measurements obtained by DPV, and the positive results validated that the detection of glucose in a 0.1 M NaOH alkaline medium by DPV measurement was effective. Nickel, platinum, and copper are commonly used metals for non-enzymatic glucose detection. The performance of these metal-based sensors for glucose detection using DPV were also evaluated. The cuprous oxide (Cu₂O) thin layer-based sensor showed the best sensitivity for glucose detection among the sensors evaluated.

Preparation of NiCoP Hollow Quasi-Polyhedra and Their Electrocatalytic Properties for Hydrogen Evolution in Alkaline Solution

Double metal phosphide (NiCoP) with hollow quasi-polyhedron structure was prepared by acidic etching and precipitation of ZIF-67 polyhedra and further phosphorization treatment with NaH₂PO₂. The morphology and microstructure of NiCoP quasi-polyhedron and its precursors were investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and a micropore and chemisorption analyzer. Electrocatalytic properties were examined by typical electrochemical methods, such as linear sweep voltammetry, cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy in 1.0 M KOH aqueous solution. Results reveal that, compared with CoP hollow polyhedra, NiCoP hollow quasi-polyhedra exhibit better electrochemical properties for hydrogen evolution with a low onset overpotential of 74 mV and a small Tafel slope of 42 mV dec^-1. When the current density is 10 mA cm^-2, the corresponding overpotential is merely 124 mV, and 93% of its electrocatalytic activity can be maintained for 12 h. This indicates that NiCoP with hollow quasi-polyhedron structure, bimetallic merit, and low cost may be a good candidate as electrocatalyst in the practical application of hydrogen evolution.

One-Step Electrodeposition of Co/CoP Film on Ni Foam for Efficient Hydrogen Evolution in Alkaline Solution

The development of high-efficiency catalysts for hydrogen evolution via water splitting has been an effective strategy to solve the energy environmental problems and energy crisis. The abundant-reserving transition metals and their phosphides are becoming attractive Pt alternatives for hydrogen evolution reaction (HER). Herein, a crystalline/amorphous Co/CoP film was facilely prepared on nickel foam (NF) by a one-step electrodeposition technique at room temperature, named Co/CoP-NF. The as-prepared Co/CoP-NF electrocatalyst exhibits excellent electrocatalytic activity for HER, on par with Pt/C, showing a low overpotential of 35 mV at a current density of 10 mA·cm^-2 and small Tafel slope of 71 mV·dec^-1 in 1.0 M NaOH solution. More importantly, the Co/CoP-NF catalyst presents good long-term durability at an overpotential of 60 mV. Moreover, the influence of the electrodeposition parameters on the catalytic performance of the catalyst was discussed. This study offers an effective strategy to develop a non-noble-metal HER catalyst for industrial production of hydrogen.

Development of Cobalt Hydroxide as a Bifunctional Catalyst for Oxygen Electrocatalysis in Alkaline Solution

Co(OH)2 in the form of hexagonal nanoplates synthesized by a simple hydrothermal reaction has shown even greater activity than cobalt oxides (CoO and Co3O4) in oxygen reduction and oxygen evolution reactions (ORR and OER) under alkaline conditions. The bifunctionality for oxygen electrocatalysis as shown by the OER-ORR potential difference (ΔE) could be reduced to as low as 0.87 V, comparable to the state-of-the-art non-noble bifunctional catalysts, when the Co(OH)2 nanoplates were compounded with nitrogen-doped reduced graphene oxide (N-rGO). The good performance was attributed to the nanosizing of Co(OH)2 and the synergistic interaction between Co(OH)2 and N-rGO. A zinc-air cell assembled with a Co(OH)2-air electrode also showed a performance comparable to that of the state-of-the-art zinc-air cells. The combination of bifunctional activity and operational stability establishes Co(OH)2 as an effective low-cost alternative to the platinum group metal catalysts.

Simulation of hydrogen sulphide absorption in alkaline solution using a packed column

In this work, a simulation tool was developed for hydrogen sulphide (H₂S) removal in an alkaline solution in packed columns working at countercurrent. Modelling takes into account the mass-transfer enhancement due to the reversible reactions between H₂S and the alkaline species (CO(²⁻)(3), HCO⁻(3), and HO⁻) in the liquid film. Many parameters can be controlled by the user such as the gas and liquid inlet H₂S concentrations, the gas and liquid flow rates, the scrubbing liquid pH, the desired H₂S removal efficiency, the temperature, the alkalinity, etc. Since the influence of the hydrodynamic and mass-transfer performances in a packed column is well known, the numerical resolutions performed were dedicated to the study of the influence of the chemical conditions (through the pH and the alkalinity), the temperature and the liquid-to-gas mass flow rate ratio (L/G). A packed column of 3 m equipped with a given random packing material working at countercurrent and steady state has been modelled. The results show that the H₂S removal efficiency increases with the L/G, the pH, the alkalinity and more surprisingly with the temperature. Alkalinity has a very significant effect on the removal efficiency through the mass-transfer enhancement and buffering effect, which limits pH decreasing due to H₂S absorption. This numerical resolution provides a tool for designers and researchers involved in H₂S treatment to understand deeper the process and optimize their processes.