Concentrated Alkaline Solution Research Articles

Water purification using cellulosic fibers extracted from agriculture wastes and their modified copolymers

The scarcity of water limits individuals' capacity to engage in fundamental activities. The objective of this study is to investigate the creation of novel cellulosic fibers derived from peanut shells, utilizing varying concentrations of alkaline solutions and different temperatures. These fibers are subsequently transformed into cellulose acetate (CA). To further enhance sustainability, the prepared CA is copolymerized with polyethylene terephthalate (PET) obtained from recyclable water bottles. The resulting material is then fabricated into fibers using an electrospinning instrument. The chemical composition of the synthesized compounds is analyzed through Fourier-transform infrared spectroscopy (FTIR) and X-ray powder diffraction (XRD). The thermal stabilities of the fibers are assessed via Thermal gravimetric analysis (TGA) and derivative thermogravimetry (DTG). Additionally, the effectiveness of the fabricated fibers as water filters is evaluated, demonstrating high efficiency in this regard.

An optimization of synthesis technique for Na-X zeolite from coal-fly ash using Taguchi experimental design

Na-X Zeolite was made from Class-F coal fly ash from a thermal power plant in the Indian state of Gujarat. The objective of this study is to maximize Na-X zeolite crystallization by using alkaline fusion hydrothermal treatment. The authors have also optimized the process variables using the L9 orthogonal Taguchi method. The operating parameters investigated are fusion temperature, fusion time, liquid/solid (L/S) ratio, and alkaline solution concentration. The XRF analysis of coal fly ash reveals that quartz (SiO2), mullite (Al2O3.SiO4), and a small fraction of hematite and magnetite are the major minerals. The highly crystalline zeolite (ZT-5) was synthesized in a 0.3 M NaOH solution at a fusion temperature of 550 °C for 12 h. with a 1.3 L/S ratio. Contrary to the CFA graph, the zeolite (ZT-5) XRD pattern displays prominent peaks between 20 and 40°. The SEM images illustrate the transition from a smooth spherical texture to a highly crystalline lattice structure in the morphology of zeolite. A sharp stretch around 440 and 460 cm−1 and weak bend around 660 and 694 cm−1 show the relative O-T-O deformation and the change in shape of the Al-O-H bonds, as measured by FT-IR absorption.

Alkaline etched hydrochar-based magnetic adsorbents produced from pharmaceutical industry waste for organic dye removal.

A large amount of pharmaceutical industry waste (PIW) was inevitably produced every year, and the PIW can be degraded by high temperature reaction to form porous structures. The study proposed an innovative pathway to valorize PIW with hydrothermal carbonization (HTC) coupled with alkali etching (AE). Without adding any additives, magnetic hydrochar could be generated with rough surface topography and suitable specific surface area (SBET) by this method. Effects of HTC conditions and alkaline solution concentrations on the physicochemical and adsorption properties of PIW were investigated, and adsorption mechanism was explored. Based on evaluations of the magnetism, cyclic regeneration, and heavy metal leaching properties of the products, the feasibility of preparing magnetic adsorbents with solid waste by HTC coupled AE was established. The alkaline etching pharmaceutical industry waste (AEPIW) hydrochar showed the highest SBET (54.64 m2/g) after the PIW was treated by 260°C for 2h plus 1mol/L KOH. The removal rate of methylene blue (MB) could exceed 90% and the saturated magnetization was ~8emu/g. The proposed new method was able to convert the low-value solid industrial waste into high-performance hydrochar-based magnetic adsorbents, which was tested to have a capability to efficiently and sustainably remove organic pollutants from water.

Marine oil spill remediation by Candelilla wax modified coal fly ash cenospheres

Biodegradable candelilla wax (CW) was creatively used for hydrophobic modification of coal fly ash cenospheres (FACs), a waste product from thermal power plants, and a new spherical hollow particulate adsorbent with fast oil adsorption rate and easy agglomeration was prepared. CW was confirmed to physically coat FACs and the optimum mass of wax added to 3 g of FACs was 0.05 g. From a series of batch scale experiments, CW-FACs were found to adsorb oil, reaching adsorption efficiency of 80.6% within 10 s, and aggregate into floating clumps which were easily removed from the water's surface. The oil adsorption efficiency was highly dependent on hydrophobicity of the used adsorbent, the adsorption of Venezuela oil onto CW-FACs was found to be a homogenous monolayer, and the capacity and intensity of the adsorption decreased as temperature increased from 10 to 40 °C. The Langmuir isotherm model was the best fit, with the maximum adsorption capacity achieved at 649.38 mg/g. CW-FACs were also found to be highly stable in concentrated acid, alkaline and salt solutions, as well as for spills of different oil products. Furthermore, the retention rate of the oil adsorption capacity of the CW-FACs after 6 cycles of adsorption-extraction was as high as 93.2%. Therefore, CW-FACs can be widely used, easily recycled, and reused for marine oil spill remediation, which is also a good alternative disposal solution for FACs.

Impact of Highly Concentrated Alkaline Treatment on Mesostructured Cobalt Oxide for the Oxygen Evolution Reaction

AbstractCommercial alkaline water electrolysis cells typically use highly concentrate KOH as electrolyte, which strongly influences alteration of catalyst and its performance. Herein, the impact of alkaline treatment toward the structural alteration and electrochemical oxygen evolution reaction (OER) activity of well‐defined ordered mesoporous Co3O4 is systematically studied. The overall morphology of mesostructured Co3O4 is relatively resilient to the exposure of highly concentrated alkaline solution up to 13 m KOH. The spectroscopic analyses, including in situ diffuse reflectance infrared spectroscopy, reveal the presence of carbonate‐based species after the alkaline treatment due to impurities of the commercial KOH. The pre‐treated samples exhibit a higher electrochemically active surface area, decreased charge transfer resistance, and increased current density from 103 to 155 mA cm−2 at 1.7 V versus RHE. The in situ electrochemical Raman spectroscopy investigation supports formation of active CoOOH phase on KOH pre‐treated Co3O4, which might play a key role toward enhanced OER activity.

Nonlinear frequency response analysis of oxygen reduction reaction on silver in strong alkaline media

Understanding the kinetics of the oxygen reduction reaction on silver in highly concentrated alkaline solutions (e.g., 11 M NaOH) and elevated temperature is of great interest both in terms of technical applications of this reaction (e.g., in chloralkali electrolysis) and in fundamental terms. To gain a better understanding of this process, a nonlinear frequency response analysis was performed in combination with a rotating ring disk analysis. Firstly, the ORR was analyzed under steady-state conditions. The number of exchanged electrons was determined based on rotating ring disk experiments. Secondly, two different dynamic ORR kinetic models have been formulated. These models were used to derive the theoretical first- and second-order frequency response functions (FRFs). Furthermore, the first and second-order FRFs were determined experimentally for both 0.1 M NaOH and 11 M NaOH at different temperatures. In the next step, the kinetic model parameters were numerically estimated from the experimental frequency-domain data. Despite its simplicity, the so-called 1-step model was able to reproduce experimental first- and second-order FRFs in 0.1 M NaOH under different conditions (steady-state potentials and rotation rates). At the same time, this model was able to reproduce the first-order FRF in 11 M NaOH at 60 °C, but not the features observed in the second-order FRF spectra. The more complex 4-step model has shown a better capability in explaining experimental findings, like the first and second-order FRFs, but also experimentally observed change of the Tafel slope as well as the influence of mass transport on the number of exchanged electrons. However, it was also not able to reproduce all experimental features. Possible reasons for these discrepancies are discussed.

Metal-coordinated polybenzimidazole membranes with preferential K+ transport

Membranes with fast and selective ion transport are essential for separations and electrochemical energy conversion and storage devices. Metal-coordinated polymers are promising for fabricating ion-conducting membranes with molecular channels, however, the structures and ion transport channels remain poorly understood. Here, we reported mechanistic insights into the structures of metal-ion coordinated polybenzimidazole membranes and the preferential K+ transport. Molecular dynamics simulations suggested that coordination between metal ions and polybenzimidazole expanded the free volume, forming subnanometre molecular channels. The combined physical confinement in nanosized channels and electrostatic interactions of membranes resulted in a high K+ transference number up to 0.9 even in concentrated salt and alkaline solutions. The zinc-coordinated polybenzimidazole membrane enabled fast transport of charge carriers as well as suppressed water migration in an alkaline zinc-iron flow battery, enabling the battery to operate stably for over 340 hours. This study provided an alternative strategy to regulate the ion transport properties of polymer membranes by tuning polymer chain architectures via metal ion coordination.

Highly Conducting Poly(arylene-imidazolium) Anion Exchange Membranes Containing Thin-Span Channels Constructed by Cation–Dipole Interaction

The membrane-based alkaline electrolyzer and fuel cell system has a significant drawback because it uses a concentrated, corrosive alkaline electrolyte. The anion exchange membranes (AEMs) also have lower conductivity than proton exchange membranes (PEMs) because OH– ions have a lower penetration coefficient. In this study, intending to prepare AEMs with high ionic conductivity in low concentrations of alkaline solution, two imidazolium diol monomers have been synthesized as unique candidates for the synthesis of stable anion exchange polymers. Then a strategy for designing AEMs with ion-conducting channels using a strong cation-dipole interaction between imidazolium cations and polar poly(vinylpyrrolidone) (PVP) (PAIm1/PVP blend membrane and Cross-PAIm1-PVP membrane) was reported. At 25 °C, the PAIm1/PVP blend and Cross-PAIm1-PVP membrane have ionic conductivities of 77.1, 104.9 mS cm–1 in water (Cl– form), and 315, 356.1 mS cm–1 in KOH 0.2 M, respectively. Also, a semicrystalline poly(arylene-imidazolium)2 (PAIm2) was synthesized and blended with PVP to increase the ions’ orientation for boosted ion conductivity. The ionic conductivity of the PAIm2/PVP blend membrane is 25.9 mS cm–1 in water (Cl– form) and 86.1 mS cm–1 in KOH 0.2 M at 25 °C. In addition, the prepared membranes in direct ethanol fuel cells (DEFCs) show preferable behavior in single-cell performance, with a peak power density (Pmax) of 17.7, 11.1, and 9.1 mW cm–2 at 30 °C for PAIm1/PVP, PAIm2/PVP, and Cross-PAIm1-PVP membranes, respectively. The results demonstrate that the prepared AEMs can use in electrolyzers and fuel cells.

Effect of the alkaline solution concentration on swelling performance of MX80 granular bentonite

The influence of alkaline solution on swelling performance of granular bentonite is one of the significant factors that must be considered in the design of deep geological repository for disposing the high-level nuclear waste (HLW). In this paper, the effect of alkaline solution concentration on the swelling performance of compacted granular and powdered MX80 bentonite specimens were investigated by the swelling strain and swelling pressure tests, together with X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements. Tests results showed that the swelling strain and swelling pressure of compacted granular MX80 bentonite increased by 2.6% and 7.6%, respectively, when the alkaline solution concentration changed from 0 to 0.1 mol/L. With increasing the concentration from 0.1 mol/L, the swelling strain and swelling pressure decreased significantly. When the alkaline solution concentration changed from 0 to 1.0 mol/L, the swelling strain and swelling pressure of the granular bentonite decreased by 35.1% and 41.6%. Observed XRD and SEM results showed that effect of the alkaline solution on bentonites led to a decline in montmorillonite content, and the large layered structure was dissolved into small layered structures and particles, which caused the decline in the swelling performance of granular MX80 bentonite.

High quality geopolymer concrete by using binder nano metakaolin

Iraqi Metakaolin was used to produce geopolymer mortar and concrete with high specifications. To convert Kaolin to Metakaolin, the De-hydroxylation process was carried out by burning Kaolin at 700°C. Metakaolin was crushed and ground by a ball mill to obtain the Metakaolin at the nanoscale. The large specific surface area of total nanoparticles gives unique properties during their interaction with an alkali-activated solution to form the geopolymer. Nano metakaolin geopolymer mortar mixtures were manufactured entirely according to specification ASTM C109/C109M-16a with different concentrations of alkaline solution (8 - 10 - 12 – 14) molarity. Through mortar test, it was noted the best result of geopolymer at 12 molarity, gives the advantage of dissolving alumina and silica nanoparticles to forming a geopolymer with high specifications. The highest rate of compressive strength of geopolymer mortar is 73 MPa. But in the geopolymer concrete mix with other nanomaterials replaced as a percentage by weight of the nano metakaolin binder, where incorporated (3%) nano-glass blended with (0.01%) carbon nanotube to observe the superior compressive strength reached 74.7 MPa. The effect of freezing and thawing has been, and no effect on compressive strength. During the water absorption test, observed that the absorbance is close to 1.7 %. The main benefit of the total binder nano metakaolin geopolymer is no heat treatment is used for the polymerization process and obtaining high specifications due to the effectiveness and high pozzolan effect of nanomaterials leads to improving compressive strength and other durability properties.

High Gravimetric Capacitance MXene Supercapacitor Electrode Based on Etched Ti3C2Tx by Chemical Etching

Ti3C2T x MXene is one of the most promising electrode materials for supercapacitors, but it often suffers in poor experiment gravimetric capacitance, which limits practical applications in industry needs. Herein, etched Ti3C2T x MXene with high gravimetric capacitance is prepared by chemical etching of MXene with concentrated alkaline solution. The intercalation of K+ and the scissor role of OH− can simultaneously enlarge the interlayer spacing and cut the size of sheets, which lead to the high active‐site concentration and cation diffusion. As a result, the etched Ti3C2T x MXene displays high gravimetric capacitance of 368.1 F g−1 at 2 A g−1 and outstanding cycling stability without capacitance loss over 5000 cycles at 6 A g−1,and the surface capacitance contribution in etched Ti3C2T x MXene occurs to a greater extent compared with the pristine MXene. Moreover, the effect of chemical etching on the supercapacitor performance and energy‐storage mechanism indicates that the active‐size concentration and cation diffusion could be maximized when the chemical etching conditions are appropriate, leading to the highest performance of etched Ti3C2T x MXene. Herein, it is demonstrated that the chemical etching approach is applicable to design MXenes with high gravimetric capacitance to maximize their potential applications in energy‐storage applications and other fields.

Ionomer degradation in catalyst layers of anion exchange membrane fuel cells.

Anion exchange membrane fuel cells (AEMFCs) that operate at high pH, offer the advantage of enabling the use of abundant 3d-transition metal-based electrocatalysts. While they have shown remarkable improvement in performance, their long-term durability remains insufficient for practical applications with the alkaline polymer electrolytes (APEs) being the limiting factor. The stability of APEs is generally evaluated in concentrated alkaline solutions, which overlooks/oversimplifies the complex electrochemical environment of the catalyst layer in membrane electrode assembly (MEA) devices. Herein, we report a study of the degradation of the membrane and ionomer independently under realistic H2-air (CO2 free) fuel cell operation, using proton nuclear magnetic resonance (1H-NMR), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS). While the membrane degradation was minimal after the AEMFC stability test, the ionomer in the catalyst layers degraded approximately 20% to 30% with the cathode being more severely affected than the anode. The ionomer degradation decreased the catalyst utilization and significantly increased the ionic resistance, leading to significant performance degradation in the AEMFC stability test. These findings emphasize the importance of ionomer stability and the need to consider the electrochemical environments of MEAs when evaluating the stability of APEs.

Hydrophilic fillers for anione exchange membranes of alkaline water electrolyzers

Alkaline water electrolysers are widespread in many industries, including systems with hydrogen cycle of energy storage. One of the problems of modern alkaline water electrolysers is insufficient purity of generated electrolysis gases relative to electrolysis systems with solid-polymer electrolyte. In this regard, work on modification of existing porous diaphragms is actively carried out. One new area of research is the impregnation of new hydrophilic fillers into the composition of existing diaphragms and the transition to ion-solvate membranes. In this work the synthesis of zirconium hydroxide hydrogel inside a porous diaphragm with the hydrophilic filler TiO2 was carried out. This synthesis makes it possible to obtain a membrane with anion-exchange properties. A possible mechanism of OH- hydroxyl ion transfer by immobilized K+ ion was also proposed. The obtained results demonstrated the resistance of the membrane to concentrated alkaline solutions.

Extraction of Novel Effective Nanocomposite Photocatalyst from Corn Stalk for Water Photo Splitting under Visible Light Radiation

Novel (Ca, Mg)CO3&SiO2 NPs-decorated multilayer graphene sheets could be successfully prepared from corn stalk pith using a simple alkaline hydrothermal treatment process followed by calcination in an inert atmosphere. The produced nanocomposite was characterized by SEM, EDX, TEM, FTIR, and XRD analytical techniques, which confirm the formation of multilayer graphene sheets decorated by inorganic nanoparticles. The nanocomposite shows efficient activity as a photocatalyst for water-splitting reactions under visible light. The influence of preparation parameter variations, including the alkaline solution concentration, hydrothermal temperature, reaction time, and calcination temperature, on the hydrogen evolution rate was investigated by preparing many samples at different conditions. The experimental work indicated that treatment of the corn stalk pith hydrothermally by 1.0 M KOH solution at 170 °C for 3 h and calcinating the obtained solid at 600 °C results in the maximum hydrogen production rate. A value of 43.35 mmol H2/gcat.min has been obtained associated with the energy-to-hydrogen conversion efficiency of 9%. Overall, this study opens a new avenue for extracting valuable nanocatalysts from biomass wastes to be exploited in hot applications such as hydrogen generation from water photo-splitting under visible light radiation.

A Review of Electrochemical Reduction of Sodium Metaborate

The recycling of sodium borohydride poses a huge challenge to the drive towards a hydrogen economy. Currently, mechano-chemical, thermo-chemical and electrochemical are the only reported methods of recycling sodium metaborate into sodium borohydride. Much attention has been devoted to the mechano-chemical and thermo-chemical methods of reduction, but little focus has been devoted to electrochemical methods. This review describes the electrochemical behaviour of borohydride (BH4−) and metaborate (BO2−) anions in alkaline solutions. The BH4− is stabilized in highly concentrated alkaline solutions, while the electro-oxidation of BH4− is dependent on the type of electrode material. The attempts to electro-reduce the BO2− into BH4− is reviewed and the challenges, suggestions and future outlook of electro-reduction for the recycling of BO2− into BH4− is highlighted.

Effect of alkali and silane treatments on the surface energy and mechanical performances of Raphia vinifera fibres

This study aimed to evaluate the influence of chemical treatment on the surface modification of Raphia vinifera Fibres (RVF). The fiber were treated with different concentrations of alkaline solution (1%, 5% and 10%) for (30 min, 60 min and 90 min) and silane (1% and 5%) at (30 min and 60 min). Thermal degradation analysis was performed by thermogravimetric analysis (TGA/TDG) and chemical functional group was assessed by Fourier transform infrared spectrometry (FTIR). The microstructure of Raphia vinifera fibers was observed by scanning electron microscopy (SEM) and cross-sectional area measurement was performed by a projection microscope (Projectina). The surface energy of treated and untreated fibers was calculated from a standard tensiometer and their mechanical properties were evaluated by tensile tests. The results reveal a modification of the chemical structure as well as the thermal degradation of the fibres after treatment with NaOH and silane. SEM shows that alkali treatment of raffia fibers induces a significant reduction (confidence level 90%) in fiber cross-section compared to untreated fiber, resulting in a change in surface roughness and the appearance of cracks. Furthermore, the use of silane and 1% NaOH treatments significantly improves the surface energy of the fibers over time, while 5% and 10% NaOH concentrations decrease the surface energy over time. Statistical analysis (MANOVA and Tukey test) of the mechanical performance results reveals a significant increase in the Young's modulus of the fibers with the treatment time and the concentration of the treated solutions (NaOH and silane). Its fibres may therefore have good potential for the production of composites.

Spatially Confined Fabrication of Polar Poly(Vinylidene Fluoride) Nanotubes.

Polar poly(vinylidene fluoride) (PVDF) nanotubes have attracted significant attention due to their excellent piezoelectric and ferroelectric properties, yet a tunable fabrication of homogeneous polar PVDF nanotubes remains a challenge. Here, a simple method is reported to fabricate polar PVDF nanotubes using anodize aluminum oxide (AAO) membranes as templates that are removed by etching in a potassium hydroxide (KOH) solution and then ageing at room temperature. PVDF nanotubes originally crystallized in the AAO membrane are pure α-crystals with very low crystallinity, yet after being released from the templates, the crystallinity of the nanotubes markedly increases with ageing at room temperature, leading to the formation of β-PVDF crystals in a very short time, with the formation of γ crystals after longer ageing times. A large amount of γ crystals formed when the released PVDF nanotubes are heated to ≈130°C. The formation of polar PVDF nanotubes released from the AAO templates treated with higher concentrations of alkaline solution results from the reaction of the surface of the PVDF nanotubes with the alkaline solution and structure reorganization under confined conditions. This large-scale preparation of β- and γ-PVDF opens a new pathway to produce polar PVDF nanomaterials.

Double-life sustainable construction materials from alkali activation of volcanic ash/discarded glass mixture

Volcanic ash, according to the large amount of silica and alumina, may be considered as feedstock for geopolymers. However, the relatively low reactivity, mostly due to the relatively low amount of amorphous phase, implies the introduction of ash as minor component in complex mixtures and the activation with highly concentrated alkaline solutions. This paper aims at improving the sustainability of ash conversion into inorganic polymers with adequate strength-to-density ratio, by minimizing the addition of valuable compounds and including discarded material. Fine powders of volcanic ash from Mt Etna (Italy), in fact, were activated with NaOH solutions at low molarity (3 M), with a variable water/solid ratio (0.35–0.42), after mixing with waste glass powders, from cullet purification. The adopted ash/glass proportion (50 wt%-50 wt%) was intended to favour the reuse of inorganic polymers, by firing at 950 °C, in turn causing the transformation into porous glass-ceramics with a remarkable strength-to-density ratio. A significant foaming was effectively observed, due to decomposition of hydrated alkali alumino-silicates developed upon hardening. Foams with excellent strength-to-density ratio were also obtained by thermal transformation of highly porous cold consolidated materials.

Predicting the Geopolymerization Process of Fly-Ash-Based Geopolymer Using Machine Learning

The process of geopolymerization affects the freshness and hardening properties of fly ash base polymer. The prediction of geological polymerization parameters, such as DPT, DPH, GPT, and GPH, is very important for the mixing optimization of FA base polymer. In this study, machine learning models such as backpropagation neural network, support vector regression, random forest, K-nearest neighbor, logistic regression, and multiple linear regression were used to predict the above geological polymerization parameters and explain the influence of composition on the geological polymerization of FA base polymer. Results show that RF was the most stable ML model and had the best predictive performance on the test sets of GPT, GPH, DPT, and DPH, with correlation coefficients of 0.88, 0.95, 0.92, and 0.95, respectively. The variable importance and sensitivity were analyzed by SHapley Additive exPlanations. Results indicate that temperature is the most significant input variable affecting the DPT, DPH, and GPH with SHAP values of 0.09, 4.83, and 1.03, respectively. For GPT, the SHAP value of temperature is 6.89, slightly lower than that of LFR (6.95); yet it is a still significantly important input variable. The mole ratio and alkaline solution concentration were also important and negatively contributed to DPT and DPH, respectively. Besides, both GPT and GPH were sensitive to the mass ratio of liquid-to-fly ash which can promote the geopolymerization extent and shorten the geopolymerization time at a small content. The results of this study pave the way for automatic mixture optimization of FA-based geopolymers.

Physical, Rheological and Mechanical Properties of Alkali Activated Hydrogels Based on Nanofibrillated Cellulose

ABSTRACT Hydrogels are classified as a three-dimensional network system, capable of retaining large amounts of water while preserving their shape and dimensional stability. Due to their natural origin and biocompatibility with human tissue, cellulose nanofibrils are often considered to be promising candidates for bioactive hydrogels preparation. For such applications, their responsiveness under different types of mechanical load, including multiple cyclic compressions, is of crucial importance. In the present study, cellulose nanofibril-based hydrogels were initiated though a simple alkali neutralization treatment. Structural, rheological and compressive features were investigated as a function of elevated NaOH concentration and physical gelling conditions. It was found that a sufficiently concentrated alkaline solution allows the formation of mechanically robust cellulose nanofibril hydrogels, which can be dried to the state of ultralight material, aerogel, of low density (0.057 g cm −3), superior porosity (96.2%), super water absorbant capacity (1200%), and exceptional shear and compressive load resilience with elasticity modulus of 9.3 kPa. These outstanding characteristics can be predominantly attributed to the polymorphic conversion of cellulose I to cellulose II, which results from the mercerization of cellulose nanofibrils and creates a stable and firm hydrogels texture.