Concentrated NaOH Solution Research Articles

Enhanced modification technique for polyacrylonitrile UF membranes by direct hydrolysis in the immersion bath

ABSTRACTConventional hydrolysis modification of polyacrylonitrile (PAN) membranes is usually carried out in a post‐treatment step during which hydrophilic groups are created on the membrane surface. In this article, however, direct hydrolysis in the immersion bath is proposed as a new and simple approach for simultaneous membrane preparation and modification. The main advantages of this method include lower alkali concentrations, promptness, and the lack of need for elevating temperature compared to other studies. The cast films were immersed in the coagulation bath containing aqueous NaOH solutions of various concentrations (0.003, 0.0125, 0.025, 0.05, and 0.1 M) for 1, 3, 5, and 10 min, which were then transferred to a bath of pure water. Membranes were characterized by pure water flux, porosity, average pore diameter, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle, mechanical properties, rejection, and flux recovery ratio (FRR) measurements. At all treatment times, the pure water flux of modified membranes reached its maximum at low NaOH concentrations with a substantial increase (210%) in the membrane treated with 0.0125 M NaOH for 1 min. Furthermore, the kinetics of the hydrolysis reaction was considered to provide deeper insights into morphological changes occurring during the hydrolysis. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48583.

Optimization of post-treatment variables to produce hierarchical porous zeolites from coal gangue to enhance adsorption performance

Our research data indicates that a cost-effective hydrothermal synthesis with optimized post-treatment variables can provide a feasible paradigm to convert the coal gangues into valuable zeolites. It is found the integrity of skeleton structure of these cubic zeolites is well maintained upon series of post-treatments. The effects of these treatment parameters indicate concentration of NaOH solution (3.0 mol/L), alkaline treatment time periods (2 h) and temperature (90 °C), and ultrasonication time duration (40 min) collectively affect on the crystal structure, morphology, and adsorption performance of these zeolites. The specific surface area of treated zeolite is measured to be 162.29 m2/g and significantly increases compared with the untreated one (64.28 m2/g). The mechanistic study of zeolites post-treatment suggests that the erosion of parts of Al-OH and Si-OH bonds and the expansion of pore size will lead to a formation of hierarchical mesopores. As a consequence, the removal efficiencies of these modified zeolites have been greatly improved to 83.5% and 95.1% for Cu2+ ions and Rhodamine B (Rh-B), respectively. It is critical to point out that the subsequent alkaline and ultrasonic post-treatments greatly improve the adsorption performance of multiple mesoporous zeolites prepared from coal gangue. The post synthetic treatment can provide a platform of environmental cleanup applications such as industrial water remediation and solid waste handling by conversion of mining wastes into a value-added product.

Preparation of Nanocellulose Aerogel from the Poplar (Populus tomentosa) Catkin Fiber

The effects of chemical pretreatment on the purification of poplar (Populus tomentosa) catkin fiber and the effect of ultrasonic time for the microfibrillarization of poplar catkin fiber (PCF) were studied. The nanocellulose aerogels were prepared by freeze drying the cellulose solutions. The density, porosity, micro morphology, thermal stability and mechanical properties of the aerogels were analyzed. It was found that the dewaxing time of PCF is shorter than that of unsonicated nanocellulose. After the treatment of 0.5 wt% sodium chlorite for 2 h, the lignin of PCF was removed. After the chemical purification, the PCF was treated with 2 and 5 wt% NaOH solution and ultrasonicated for 5 and 10 min, respectively. When the ultrasonic time was 10 min, the diameter of the nanocellulose was 20–25 nm. When the ultrasonic time was 5 min, the aerogels with porous honeycomb structure can be prepared by using the nanocellulose sol of PCF as raw material. The density of the aerogels was only 0.3–0.4 mg/cm3 and the porosities of the aerogels were all larger than 99%. The difference between the pyrolysis temperature of aerogels was small, the elastic modulus of aerogels was 30–52 kPa, and the compressive strength was 22–27 kPa. With the increase of the concentration of NaOH solution (5 wt%) and ultrasonic time (10 min), the elastic modulus of aerogels increased gradually and reached the maximum value of 52 kPa, while the compressive strength reached the maximum value of 27 kPa when the PCF being treated in 5 wt% NaOH solution and was ultrasonicated for 5 min.

Parameterizing a borosilicate waste glass degradation model

Borosilicate waste glass degradation models must quantify the effects of the solution composition on the dissolution rate. Here, we present results of modified ASTM C1285 tests conducted at 90 °C with AFCI and LRM glasses to determine whether dependencies of dissolution rates on the pH, Al, and Si concentrations must be included. Solution compositions were modified from those generated by glass dissolution alone by adding small amounts of K4SiO4 glass, Al(OH)3•2H2O, and a concentrated NaOH solution when the tests were initiated. Results show rate laws for the initial and resumption regimes must include pH dependences, but the residual rate can be modeled independent of the pH, Al, and Si concentrations. Triggering the resumption rate probably depends on the pH, Si, and Al concentrations and perhaps other aspects of the glass composition. A waste glass degradation model using is being parameterized using tests with a range of waste glass compositions to quantify these dependencies.

Paving the way to Fe3O4 nano- and microoctahedra by dealloying Al[sbnd]Fe binary alloys

The preparation, morphologies, and properties of Fe3O4 octahedra have attracted considerable attention, while their formation mechanism has been less investigated. In this study, Fe3O4 nano- and microoctahedra are prepared by dealloying Al–xFe (x = 5–25 at.%) alloys in NaOH aqueous solutions with different concentrations. The dealloying of Al15Fe in the 5-mol·L−1 NaOH solution provides the most regular Fe3O4 octahedra. Al13Fe4 in the precursor AlFe alloy and appropriate concentration of OH– ions are dominant factors in the formation of Fe3O4 octahedra by changing the chemical potentials and growth rates along the 〈111〉 and 〈100〉 plane directions. A low concentration of NaOH solution deteriorates the anisotropic growth of Fe3O4, while a highly concentrated solution enhances the reduction of oxides and produces α-Fe rather than Fe3O4. In addition to the experimental results, ab-initio molecular dynamics simulations are performed to reveal the evolutions of the surface energies and growth rates of different facets, depicting the formation trajectory from Fe3O4 nuclei to octahedra. This fundamental understanding provides technological guidelines for the synthesis and morphology control of Fe3O4, being of significance in the development of functional nanoparticles.

Rapid fabrication of TiO2 nanobelts with controllable crystalline structure by microwave-assisted hydrothermal method and their photocatalytic activity

TiO2 nanobelts (NBs) have received much attention due to their chemical stability, nontoxicity, special one-dimension morphology and also have found many applications. However, extensively employed hydrothermal processes are time-consuming. In this work, a microwave-assisted hydrothermal (MAH) method is for the first time reported for the rapid fabrication of TiO2 NBs. TiO2 NBs with widths of 25–200 nm and lengths up to tens micrometers can be successfully fabricated by adjusting the concentration of NaOH solution, reaction time and reaction temperatures. By MAH method, the reaction time can be greatly shortened to 4 h under microwave irradiation compared to 1–3 days reported in literature. Bi-crystalline structures with monoclinic TiO2(B) and tetragonal anatase can be tuned by simply adjusting thermal treatment temperatures. The evolution of different crystalline structures from starting H2Ti3O7 to crystalline TiO2 phases with increasing calcination temperatures was analyzed by different techniques. The photocatalytic activity results reveal that bi-crystalline structures with TiO2(B)/anatase phases (optimal B:A ratio of 66:34) are advantageous to enhance the photocatalytic performance of TiO2 NBs in photo-decomposing Rhodamine B molecules in water under UV irradiation.

Optimization of desilication parameters in fabrication of mesoporous ZSM-48 zeolite employed as excellent catalyst in methanol to gasoline conversion

Mesoporous ZSM-48 zeolite was prepared by alkaline desilication at optimized conditions using central composite design (CCD) under response surface methodology (RSM). Statistical models were designed to predict high BET surface area, high mesopore volume and specified mean pore diameter. The desilication temperature and NaOH solution concentration were varied in the ranges 0.1–0.3 M and 60–80 °C respectively. It was found that the NaOH concentration was more effective factor than temperature for mesoporosity development in ZSM-48 zeolite. Variance analysis showed that CCD equations were significant for the desilication parameters (R2 = 0.98 for mesopore volume, R2 = 0.95 for BET surface area and R2 = 0.98 for mean pore diameter). The influence of the post-synthesis desilication on the pore characteristics, crystallinity, morphology and acidity of the optimized zeolite was examined using N2-adsorption, XRD, SEM and NH3-TPD respectively. The optimal mesoporous ZSM-48 zeolite had a BET surface area of 154 m2 g−1, mesopore volume of 0.22 cm3g-1 and mean pore diameter of 6.93 nm. The MTG reaction was performed in a fixed-bed stainless-steel reactor at 390 °C and weight hourly space velocity of 4.75 h−1. The catalytic results illustrated that the modification of the catalyst extensively influenced the liquid hydrocarbons distribution. Over mesoporous ZSM-48 catalyst, the selectivity to branched alkanes, alkenes and cyclic non-aromatic compounds partly decreased while that to aromatics substantially increased relative to parent catalyst. The aromatics yield reached up to 78%. Furthermore, the yield of liquid hydrocarbons and catalyst life time increased about 29% and 34% respectively relative to microporous ZSM-48.

Iron ore tailing-based geopolymer containing glass wool residue: A study of mechanical and microstructural properties

This work presents an evaluation of the application of iron ore tailing as primary precursor material to geopolymer production. Glass wool residue from the iron ore industry was also included as a blend material. Four mixtures of geopolymers were produced: one mixture using only iron ore tailing; three mixtures where the iron ore tailing was replaced by the glass wool residue, with a substitution ratio of 10%, 20% and 30% (in mass). Furthermore, three different grinding times and three NaOH solution concentration were applied. Compressive strength and flexural strength tests were performed in prismatic specimens at 7-days, and the microstructural analysis of the fragments was obtained by SEM analysis. QXRD analysis based on the Rietveld’s refinement method and TG/DTA analysis was applied for all specimens. The results showed the synthesis of a zeolite phase in all specimens, and the SEM micrographs showed a transformation process of the glass wool residue. Finally, high mechanical performances were found to the iron ore tailing-based geopolymer, reaching values higher than 100 MPa for compressive strength and 20 MPa for flexural strength. The obtained values are related to the grain packing improvements, geopolymerization products, and the glass wool residue working as a supplementary precursor material to the geopolymerization reaction. The result points to the potential of iron ore tailing and glass wool residue to geopolymers studies and application.

Magnetite synthesis using iron oxide waste and its application for phosphate adsorption with column and batch reactors

The magnetite particles were synthesized by reverse coprecipitation of mill scale (iron oxide waste). The particle characterization was done and confirmed by SEM, EDS, BET, XRF, FTIR and XRD. Scherrer equation determined 11.64nm single crystalline size of the magnetite and the BET surface area was found nearly 75.77m2g−1. The expected stoichiometry (3:4) of Fe:O was confirmed by elemental analysis. The magnetite particles were proven as effective adsorbent for phosphate ions from the contaminated water. The phosphate removal efficiency was inspected with several experimental setups including column reactor fed from top to bottom, from bottom to top and sequencing batch reactor. The maximum P-adsorption capacity of magnetite was determined 11.78mgg−1. The P-carrying adsorbent is regenerated with different concentrations of NaOH and NH4OH solutions for 1, 2 and 5 days. Though both solutions were appeared effective for regeneration of used particles, NaOH was appeared more efficacious than that of NH4OH. The regeneration competence of magnetite particles is also evaluated with repetitive regeneration of used particles with 0.1N NaOH. As compared with initial value, almost 20% of the adsorption capacity was reduced after 12 successive rounds of phosphate adsorption and desorption onto the surface of magnetite. The obtained results have established fine potentiality for the magnetite particles synthesized by reverse coprecipitation to be applied as phosphate adsorbent in wastewater treatment.

Hydrothermal Synthesis of Cu2O Films on the Surface of Metallic Copper in a NaOH Solution

Cu2O films have been produced on the surface of metallic copper via hydrothermal treatment of copper substrates in aqueous NaOH solutions of various concentrations, and film growth parameters have been optimized. It has been shown that hydrothermal treatment of a copper plate in an oxygen-saturated 0.3 M NaOH solution at 180°C for 1 h allows one to produce continuous Cu2O films of maximum thickness on the surface of metallic copper.

The increased stickiness of non-glutinous rice by alkali soaking and its molecular causes

Non-glutinous rice is always less sticky than glutinous rice. By soaking two non-glutinous rice (Jingmi and Xianmi) with different concentrations of NaOH solution, the stickiness of cooked non-glutinous rice is significantly increased, which is closely associated with the removal of surface proteins of these treated rice grains. By investigating starch leaching characteristics and the molecular structure of leached starch, we find: (i) total solids and amylopectin amount in the leached materials increase by raising NaOH concentration; (ii) the molecular size and chain-length distributions (CLDs) of leached starch significantly differ between samples with different soaking treatments; (iii) a strong correlation between stickiness of cooked rice and total amount of leached amylopectin is established. (iv) molecular causes for the increased stickiness of alkali-soaked rice are put forward to explain the above observations. This study could broaden the applications of non-glutinous rice by altering its stickiness attribute with alkali soaking.

Shape-controlled hydrothermal synthesis of CuFe2O4 nanocrystals for enhancing photocatalytic and photoelectrochemical performance

Two shaped CuFe2O4 nanocrystals (nanocubes and nanodisks) were synthesized without using any surfactant by hydrothermal method. The morphology, crystal phase, magnetic, and photocatalytic properties of CuFe2O4 nanocrystals were characterized by transmission microscopy (TEM), X-ray photoelectron spectroscopic (XPS), and transient photoelectrochemical analysis. The morphologies of CuFe2O4 nanocrystals changed with the concentration of NaOH solution under hydrothermal conditions. Magnetic parameters values reveal that the CuFe2O4 nanocrystals have a typical ferromagnetic behavior, and can be easy for magnetic separation. Transient photoelectron chemical analysis shows that CuFe2O4 nanocrystals are active and stable under visible light irradiation, and CuFe2O4 nanocubes exhibit superior photoelectron performance as compared to CuFe2O4 nanodisks. The photocatalytic activity of CuFe2O4 nanocrystals is examined by Congo red (CR) degradation. As expected, CuFe2O4 nanocubes exhibit distinctly higher activity than CuFe2O4 nanodisks by degradation of 92% CR in 120 min, resulting from their smaller band gap to enhance the photocatalytic oxidation activity.

Energy calibration of a CR-39 nuclear-track detector irradiated by charged particles

Charged particle diagnosis is an important aspect of laser–plasma experiments conducted at super-intense laser facilities. In recent years, Columbia Resin #39 (CR-39) detectors have been widely employed for detecting charged particles in laser–plasma experiments. This is because the CR-39 polymer does not respond to electromagnetic pulses or X-rays. This study presents a method for calibrating the relationship between particle energy and track diameter in a CR-39 detector (TasTrak®) using 3–8 MeV protons, 6–30 MeV carbon ions, and 1–5 MeV alpha particles. The particle tracks were compared under the manufacturer’s recommended etching conditions of 6.25 mol/l NaOH at 98 °C and under the widely adopted experimental conditions of 6.25 mol/l NaOH at 70 °C. The results show that if the NaOH solution concentration is 6.25 mol/l, then the temperature of 70 °C is more suitable for etching proton tracks than 98 °C and employing a temperature of 98 °C to etch alpha-particle and carbon-ion tracks can significantly reduce the etching time. Moreover, this result implies that C3+ ion or alpha-particle tracks can be distinguished from proton tracks with energy above 3 MeV by controlling the etching time. This calibration method for the CR-39 detector can be applied to the diagnosis of reaction products in laser–plasma experiments.

MXene/Co3O4 composite material: Stable synthesis and its enhanced broadband microwave absorption

Abstract Microwave absorbers serve the purpose to ensure the transmission efficiency and accuracy in 5G telecommunications. Two-dimensional MXene has great potential in absorbing microwave. In this study, MXene(Ti3C2Tx)/Co3O4 composites are successfully fabricated by a facile and stable hydrothermal treatment in concentrated strong base and Argon environment, followed by a one-step annealing process. Phase composition, chemical state of elements, morphology and structure of the new composite materials are studied by systematical characterization. It is revealed that adsorbed Na+ ions and terminations, which are generated at the interface during hydrothermal treatment in concentrated NaOH solution, can protect the Ti3C2Tx from being decomposed. The synthesis mechanism is also proposed for stable fabrication of other MXene-based composite materials. The MXene/Co3O4 composite is able to perform single-band absorption, multiband absorption and even broadband absorption in 2–18 GHz band by tuning its composition and thickness. Particularly, better than 90% absorption in a wide range of 10.8–17 GHz can be achieved with a thickness of just 2 mm. Enhanced wideband absorption originates from the multilayer structure, the surface defects, the conductivity of Ti3C2Tx and the capacitance structure of Co3O4. Ultrathin and broadband high absorption features make the material a promising candidate for future application.

Analysis of Aggregate Gradation to Improve The Characteristics of Geopolymer Based Asphalt Concrete

The previous study showed that asphalt concrete using filler geopolymer generate a higher value of stability. On the other hand, the value of flow and the porosity of the asphalt concrete were out of the specification range. This study examines the aggregate gradation analysis to improve the characteristics of mixed asphalt concrete geopolymer. The gradation of aggregate is variated into three following the available specification. The range of specification is then separated into three, those are aggregate gradation upper specifications, middle specification, and lower specification. Filler comes from geopolymer paste, composed of fly ash which is mixed with an activator. Activator is an 8 molar concentration of NaOH solution and Na₂SiO₃. The weight ratio of Na₂SiO₃ over the weight of NaOH solution was 1.5. Geopolymer paste waited until reached the age of 28 days, then pounded up to meet the requirement size of the sieve No. 200. The test of mixture characteristics was conducted to see the comparison of performance from different gradations. The test results showed that middle gradation generating characteristics of the mixture which is higher than upper gradation and lower gradation.

Enhanced Enzymatic Hydrolysis of Pennisetum alopecuroides by Dilute Acid, Alkaline and Ferric Chloride Pretreatments.

In this study, effects of different pretreatment methods on the enzymatic digestibility of Pennisetum alopecuroides, a ubiquitous wild grass in China, were investigated to evaluate its potential as a feedstock for biofuel production. The stalk samples were separately pretreated with H2SO4, NaOH and FeCl3 solutions of different concentrations at 120 °C for 30 min, after which enzymatic hydrolysis was conducted to measure the digestibility of pretreated samples. Results demonstrated that different pretreatments were effective at removing hemicellulose, among which ferric chloride pretreatment (FCP) gave the highest soluble sugar recovery (200.2 mg/g raw stalk) from the pretreatment stage. In comparison with FCP and dilute acid pretreatment (DAP), dilute alkaline pretreatment (DALP) induced much higher delignification and stronger morphological changes of the biomass, making it more accessible to hydrolysis enzymes. As a result, DALP using 1.2% NaOH showed the highest total soluble sugar yield through the whole process from pretreatment to enzymatic hydrolysis (508.5 mg/g raw stalk). The present work indicates that DALP and FCP have the potential to enhance the effective bioconversion of lignocellulosic biomass like P. alopecuroides, hence making this material a valuable and promising energy plant.

Multiresponsive Reversible Deformation of Patterned Polyacrylamide Hydrogel Constructed by a Computer-Assisted Dispenser

Materials that can undergo shape deformation have potential applications in biomedical field, yet it has always been a challenge to pattern hydrogels and accurately program target three-dimensional (3D) shapes through a simple method. Here, we develop a facile method that permits fabrication of inhomogeneous hydrogels, which can reversibly deform from planar sheet to 3D shape in response to multistimuli, such as pH values, SLDC (solutions with lower dielectric constant), and SBF (simulated body fluid). By printing NaOH solution ink on classic PAAm hydrogel sheet, the amide side groups of PAAm hydrolyzed to acrylate. The swelling mismatch of the printed and unprinted areas generates internal stress to activate hydrogel deformation. Adjusting concentration of NaOH solution or number of times of printing, it is convenient to introduce in-plane and through-thickness gradient distribution to hydrogel sheet. The inkjet printing process is easily controlled by computer, enabling the direct printing of batched an...

Mechanical Properties of Fly Ash-Based Geopolymer with Natural Fiber

Geopolymer concrete is an eco-friendly concrete that can reduce carbon emissions on the earth’s surface because it uses industrial waste materials such as fly ash, rice husk ash, bagasse ash, and palm oil fuel. The development of fly ash as a cement replacement material is now widely used, especially on geopolymer concrete. In this study the natural fiber used is pineapple fiber. Pineapple fiber is an alternative use of natural fibers in geopolymer mortar composites. This research performed compressive strength test and flexural strength test with variations of pineapple fiber length 10 mm, 20 mm, and 30 mm with percentage of fiber used 0%, 0.25% and 0.50% of mortar weight. The mortar geopolymer is made from 100% fly ash. The concentration of NaOH solution used was 14 M and 16 M. The study revealed that the fiber length of 30 mm at a percentage of 0.50% fiber at the concentration of NaOH 16 M results a compressive strength of 41.468 MPa and the largest flexural strength of 9.209 MPa.

Ascorbic acid based controlled growth of various Cu and Cu2O nanostructures

Here we report a facile and fast ascorbic acid based controlled growth of various nanostructures of Cu and Cu2O by varying the concentration of NaOH. Ascorbic acid being a weak reducing agent not only slows down the reaction kinetics but also provides a better control for the self-assembly of nanostructures. Cu and Cu2O nanoparticles are synthesized by chemical reduction of copper nitrate (Cu(NO3)2 × 2.5 H2O) with different concentration of NaOH (0.01, 0.1, 0.5, 1.0, 5.0 and 10 M) solution in the presence of ascorbic acid. The low concentrations of NaOH (0.01 and 0.10 M) result the formation of almost pure phase of Cu nanoparticles. Whereas the higher concentrations (0.5, 1.0 and 5 M and 10 M) result into formation of pure nanocubes, truncated octahedron, polygon shaped and finally spherical shaped Cu2O particles respectively.

Designing a hierarchical nanosheet ZSM-35 zeolite to realize more efficient ethanol synthesis from dimethyl ether and syngas

Abstract In this work, a dual-catalyst bed reactor packed with the combination of hierarchical nanosheet HZSM-35 (Hi-NZ35) zeolite and CuZnAl catalyst was proposed to realize more efficient ethanol synthesis from dimethyl ether (DME) and syngas (CO+H2). The nanosheet ZSM-35 (NZ35) zeolite was prepared via a direct hydrothermal synthesis route and the CuZnAl catalyst was prepared by co-precipitation method. Moreover, a series of Hi-NZ35x zeolites were obtained from NZ35 zeolite by further treatment with varied NaOH aqueous solution using hydrothermal process (“x” means the NaOH solution concentration of 0.2-0.6 M). The catalysts properties, such as crystallinity, porosity, acidity, morphology and composition, were characterized by X-ray diffraction (XRD), N2 adsorption-desorption, NH3 temperature-programmed desorption (NH3-TPD), H2 temperature-programmed reduction (H2-TPR), scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). It was found that Hi-NZ350.4 zeolite was more effective to obtain hierarchical porosity with mesopore volume up to 0.131 cm3 g−1. For single DME carbonylation reaction, the NZ35 zeolite exhibited superior catalytic activity (32.2%) and stability compared with conventional ZSM-35 (CZ35) zeolite. Furthermore, improved catalytic activity (42.0%) was observed on Hi-NZ350.4 zeolite owing to its abundant mesoporous structure. This result revealed that the hierarchical porosity of zeolite could effectively promote the catalytic performance of zeolite for DME carbonylation reaction. For the ethanol synthesis using the optimized catalysts combination of Hi-NZ350.4 zeolite and CuZnAl catalyst, the DME conversion was about 47.2% with higher ethanol productivity of 840.2 mmol kg−1 h−1.