Concentrated NaOH Solution Research Articles

Ferrates (VI) ; Alternative products in water treatment : their electrochemical synthesis

This study focuses on determining the optimum conditions for the electrochemical generation of ferrates in concentrated NaOH solution. Various operating parameters, including electrolyte concentration, current density, temperature, electrolysis duration, and the composition and form of the anode, were investigated to enhance the yield of electrochemical ferrate (VI) ion production. The synthesized ferrates were characterized using UV-visible and FTIR spectroscopic techniques. Experimental results confirmed the formation of ferrate ions, with optimal synthesis conditions identified as follows: a current density of 11.96 mA/cm², NaOH concentration of 16 M, electrolysis time of 1 hour, temperature of 25°C, and the use of white cast iron as the anode material. These conditions were found to yield the highest efficiency for sodium ferrate production. The spectroscopic analysis effectively verified the presence of ferrate (VI) ions, providing valuable insights into the electrochemical synthesis process. This study contributes to the advancement of ferrate synthesis techniques, potentially offering an efficient route for large-scale production.

Densification and network structural changes in binary aluminosilicate glass via cold sintering process

Binary aluminosilicate glasses containing 20–50 wt% Al2O3 were successfully densified through a cold sintering process (CSP) using 1–10 M NaOH solutions. The investigation focused on densification and structural unit changes in the cold-sintered binary aluminosilicate glasses. Specifically, the binary aluminosilicate glass with 40 wt% Al2O3, cold-sintered at 180 °C using 1–10 M NaOH solutions, achieved a relative density of up to 90 % at 10 M NaOH. This was attributed to an enhanced dissolution-precipitation process facilitated by an increased concentration of the NaOH solution. In aluminosilicate glasses with 20–50 wt% Al2O3, the relative densities approached 90 % after CSP at 180 °C using a 10 M NaOH solution. Al(OH)3 formation in the cold-sintered glasses was confirmed, particularly at higher concentrations of NaOH solution (>10 M) and higher contents of Al2O3 (>40 wt%). Changes in Si structural units were observed during CSP, with Al-rich Si units becoming dominant as the concentration of the NaOH solution increased. The higher substitution of Si-O-Si bonds by Si-O-Al bonds led to the precipitation of Al(OH)3, as well as an increased Vickers hardness and biaxial flexural strength of the cold-sintered glasses. These findings demonstrate that the Al2O3 content and NaOH concentration play important roles in the densification and enhancement of the mechanical property in the cold-sintered alumina-rich binary aluminosilicate glasses and offer insights into the optimal conditions for obtaining desirable aluminosilicate materials through CSP.

Experimental study on preparation of fly ash-based geopolymer blended with recycled calcium source

A large amount of waste eggshells raises environmental issues. This study uses eggshells as recycled calcium source to synthesize fly ash and eggshell geopolymer (FAEG). The effects of eggshell content, liquid-solid ratio, NaOH/Na2SiO3 ratio, and NaOH solution concentration on the strength of the FAEG were evaluated by unconfined compressive strength (UCS) test. The geopolymerization products and microstructure characteristics of the FAEG were analyzed by XRD, FTIR, TGA, and SEM test. The results show that eggshells acted as recycled calcium sources are capable of significantly enhancing the UCS of the FAEG. The optimal content of eggshells is 15%. The NaOH/Na2SiO3 ratio has a significant effect on the UCS of the FAEG, while the influence of liquid-solid ratio and NaOH concentration is slight. The optimal NaOH/Na2SiO3 ratio is 50:50 and the liquid-solid ratio is recommended to be 0.55. Eggshells take part in the geopolymerization by acting as a precipitating and seeding element in the reaction and favoring the generation of the geopolymeric gels in the FAEG.

Preparation of Graphene Oxide (GO) incorporated-Polyvinylidene Fluoride (PVDF) Nanofiltration Membrane with Alkaline Post-Treatment for Textile Wastewater Treatment

The purpose of this research is to study the potential of polyvinylidene fluoride (PVDF) polymer incorporated with graphene oxide (GO), following with the alkaline etching post-treatment process for dye waste water treatment. Its anti-oxidation properties of PVDF, have led to its choice as a host polymer due to its high thermal stability, great organic selectivity, and excellent chemical and mechanical resistance. In addition, the post-treatment with a NaOH solutions of varied concentration ranging from 0 M to 0.2 M for 30 minutes was conducted in alter the morphology of the fabricated membrane with the aim to increase the perm-selectivity of the membranes. Besides, the fabricated membranes were further characterized in terms of the chemical and physical properties using Fourier-Transform Infrared Spectroscopy (FTIR), Contact Angle (CA), Ultraviolet Visible spectroscopy (UV-Vis), Atomic Microscopy (AFM) and Scanning Electron Microscopy (SEM). The experimental results showed that the post-treatment has decreased the membrane flux of dye wastewater. Based on the obtained result, as the concentration of NaOH solution increased, the permeability increased. While the overall dye rejection of the membrane remained of above 90 %.

Performance of geopolymer paste under the different NaOH solution concentrations

With the characteristics of low carbon, environmental protection, energy saving, and emission reduction, geopolymer pastes can effectively alleviate environmental and economic problems caused by the construction materials industry. The mechanical properties of geopolymer pastes are greatly affected by the composition of alkaline activators, while the existing research on their influence rules is not uniform. This study investigated the effects of alkaline activators composed of varying concentrations of NaOH solution under standard curing conditions on the mechanical properties and material characteristics of fly ash and slag-based geopolymer pastes. The results of the study indicated that under standard curing conditions, the mechanical properties of geopolymer pastes increased with the increase of NaOH solution concentration in alkaline activators. Under the influence of alkaline activators with 16 M NaOH solution, the flexural strength and compressive strength of geopolymer pastes reached the highest values at 28 d, up to 5.43 MPa and 39.13 MPa, respectively. Increasing the NaOH solution concentration in alkaline activators can promote the production of gel products such as N-A-S-H, forming a dense microstructure with a lower porosity, leading to higher mechanical properties.

The Utilisation of Rice Husk Ash Leachates for The Synthesis of Eco-Friendly Geopolymers

Geopolymers are inorganic polymers projected as feasible alternatives to Portland cement due to their lower CO2 emissions and high mechanical properties. In recent times, however, their impact on other environmental indices such as abiotic depletion, freshwater toxicity, marine ecotoxicity, terrestrial ecotoxicity, acidification, and human toxicity has become questionable, thus the need to investigate alternative eco-friendly precursors and activators. This work aims to manufacture an eco-efficient geopolymer by utilising biomass ash leachate as an alternative to the conventional alkali silicate solution. The leachate was obtained by soaking the rice husk ash (RHA) in a 10 M concentration of NaOH solution and filtering to obtain a clear solution. The effects of the calcination temperature of the kaolin and the RHA content in the alkaline solution were investigated, and a factorial design of experiments was developed considering three levels of calcination temperature (700°C, 800°C, and 900°C) and five levels of RHA content (0 g, 5 g, 10 g, 15 g, and 20 g). Physical and mechanical tests were performed on the synthesised geopolymer pastes, and chemical analysis was performed using X-ray diffraction and X-ray spectroscopy. The impacts of replacing the synthetic alkali silicates with rice husk ash-based activators were compared. The results showed that the calcination temperature of the kaolin and the content of the RHA both contributed significantly to the flexural and compressive strength at the 0.01 level of significance. A compressive strength of 10.4 MPa was obtained for the MK915 binders, which showed a 100% increase from samples without RHA content. This research proves that utilising RHA-based activators in metakaolin-based geopolymers can be feasible for less critical applications where a very high compressive strength will not be required.Keywords: alkaline activators, biomass, geopolymers, leachates, rice husk ash

Iron-Based Catalysts Derived from Iron-Containing Sludge for Enhanced Catalytic Performance of H2S Selective Catalytic Oxidation.

In this work, iron-containing sludge is used to prepare iron-based catalysts for efficient H2S selective catalytic oxidation. First, the effect of calcination temperatures on the catalytic activities of H2S selective oxidation is carried out and it can be found that S-500 calcined at 500 °C performs excellent catalytic activity. Then, the catalytic performance of the S-500 catalyst is further optimized using alkaline treatment with different concentrations of NaOH solution. The results indicate that S-500(2.0) treated with 2 M NaOH solution has the highest catalytic activity of H2S selective oxidation. Next, various characterization methods are used to analyze the structure and physical-chemical of the sludge-based catalysts. N2-Brunauer-Emmett-Teller (N2-BET) and X-ray photoelectron spectroscopy analyses show that the S-500(2.0) catalyst has the smallest average particle (11.17 nm), the biggest ratio of S ext/S micro(17.98) with bigger external specific surface area (49.09 m2·g-1), a higher proportion of Fe3+ species (50.88%), and surface adsorbed oxygen species (48.07%). Meanwhile, O2-TPD and CO2-TPD analysis indicates that the S-500(2.0) catalyst has a bigger value of the Oads/OTotal ratio (50.56%) and (CO2)(weak+moderate) /(CO2)Total ratio of (31.41%), indicating that there are much more oxygen vacancies and weak alkaline sites. As a result, the excellent catalytic performance of H2S selective oxidation can be attributed to its outstanding physical-chemical properties.

Enhancing the mechanical and thermal properties of geopolymers prepared by refractory brick dust: An investigation into optimal mix ratios and curing conditions

This study proposes the development of a novel geopolymer by investigating the feasibility of using refractory brick dust (RBD), a waste product from brick manufacturing. The focus was on exploring the trade-off between waste incorporation and high-temperature resistance in geopolymer pastes. Throughout the experiments, the NaOH solution concentration was consistently maintained at 10 M. The primary goal was to examine how varying the ratios of Na2SiO3/NaOH (NS/NH) and RBD/alkaline activator (AS) on the geopolymers’ characteristics. A series of meticulous tests were conducted using various curing methods, ranging from room temperature to high temperatures between 100 °C and 140 °C, with curing times extending up to 72 h. It was observed that geopolymers exhibit the highest compressive strength after being precured at 100 °C for 72 h, achieving a maximum compressive strength of 15.40 MPa. SEM microstructure analysis revealed a correlation between the curing regime, material density and porosity. Specifically, at 140 °C, the data indicated that more porous structures have lower compressive strength. Geopolymers exhibited good mechanical properties at low curing temperatures, but exposure to temperatures above 1200 °C resulted in significant deterioration. For example, Mix 3.0RBD2.0, with a higher RBD/AS and NS/NH ratio, experienced the greatest compressive strength loss of 61.3% and a mass loss of 15.5% at these elevated temperatures. Interestingly, a geopolymer composition of 2.0RBD0.5 showed high-temperature-induced physical changes that might alter its strength and stability, yet it retained its overall structure. This study provides an in-depth explanation of the importance of optimising waste utilization to develop resilient geopolymer materials. It demonstrates how the composition – specifically, a Si/Al ratio of approximately 2.26, which is preferred based on EDS results – along with the curing methods, significantly influences the performance and high-temperature resistance of geopolymers.

Keratin extraction optimization from poultry feather using response surface- Box-Behnken experimental design method

This study aimed to develop a cost-effective method for managing chicken feather waste by hydrolyzing it in an alkaline medium to extract keratin hydrolysate. Through a Box-Behnken experimental design, the effects of NaOH solution concentration, temperature, and extraction time on the extraction process were examined. Analysis of the extracted keratin hydrolysate revealed the presence of key functional groups and characteristic protein structures. Optimization efforts identified 0.65 N NaOH solution concentration, 70 °C temperature, and 1-h extraction time as yielding the highest protein yield of 89.71 %. These findings underscore the potential of alkaline hydrolysis as a sustainable approach for both waste management and the extraction of valuable keratin hydrolysate. This research contributes to addressing the challenges faced by poultry farms in waste management while offering avenues for the utilization of keratin in various applications, thereby promoting environmental protection and human health.

In-situ construction of bioactive nanostructures on Ti alloy surfaces through ultra-low concentration alkali treatment and low-temperature annealing

Osseointegration is crucial for the long-term stability of orthopedic implants. Nanosurfacing can impart osteoinductivity to the implant. However, the application potential of most available nanotechnologies in surface modification of implants is limited, and there is an urgent need to develop new effective nanosurfacing techniques with greater practicality. In this study, we for the first time, utilized an ultra-low concentration NaOH solution (0.55 mM) combined with low-temperature annealing to achieve solid-state dewetting (SSD) on Ti alloy surfaces, resulting in well-defined TiO2 nanoisland-like crystals. In vitro cell experiments demonstrated that the constructed nanostructures significantly affected the adhesion, proliferation, and osteogenic differentiation capability of MC3T3-E1 cells. The nanostructures formed at 550 °C exhibited the most pronounced enhancement of cell osteogenic differentiation capability. This method is simple, easy to operate, and scalable, holding significant application potential in the surface modification of Ti alloys.

Synthesis of BiOX-Red Mud/Granulated Blast Furnace Slag Geopolymer Microspheres for Photocatalytic Degradation of Formaldehyde.

Release of formaldehyde gas indoors is a serious threat to human health. The traditional adsorption method is not stable enough for formaldehyde removal. Photocatalytic degradation of formaldehyde is effective and rapid, but photocatalysts are generally expensive and not easy to recycle. In this paper, geopolymer microspheres were applied as matrix materials for photocatalysts loading to degrade formaldehyde. Geopolymer microspheres were prepared from red mud and granulated blast furnace slag as raw materials by alkali activation. When the red mud doping was 50%, the concentration of NaOH solution was 6 mol/L, and the additive amount was 30 mL, the prepared geopolymer microspheres possessed good morphological characteristics and a large specific surface area of 38.80 m2/g. With the loading of BiOX (X = Cl, Br, I) photocatalysts on the surface of geopolymer microspheres, 85.71% of formaldehyde gas were adsorbed within 60 min. The formaldehyde degradation rate of the geopolymer microspheres loaded with BiOI reached 87.46% within 180 min, which was 23.07% higher than that of the microspheres loaded with BiOBr, and 50.50% higher than that of the microspheres loaded with BiOCl. While ensuring the efficient degradation of formaldehyde, the BiOX (X = Cl, Br, I)-loaded geopolymer microspheres are easy to recycle and can save space. This work not only promotes the resource utilization of red mud and granulated blast furnace slag, but also provides a new idea on the formation of catalysts in the process of photocatalytic degradation of formaldehyde.

Large-scale and green preparation of multifunctional ZnO

Highly active and multifunctional zinc oxide (ZnO) was synthesized using the water bath method. The concentrated NaOH solution rapidly converted zinc ions to ZnO. The solvent was then recycled multiple times after separating from the ZnO product, and the crude sodium sulfate by-product was precipitated through crystallization at room temperature. The entire recycling process produces no pollutant emissions and yields an average of 86.13 % zinc, achieving a green and efficient synthesis of ZnO. Xenon (Xe) radiation increases oxygen vacancies in ZnO, enhancing gas sensing. The sample S3 of ZnO sensors was obtained by xenon lamp irradiation for 9 h showing a 2.4 times higher response to 100 ppm NO2 at 90 ℃ (653.12) compared to the sample S0 of ZnO sensors without xenon lamp irradiation. Moreover, ZnO has excellent UV absorption in the wavelength range of 290–380 nm. By impregnating cotton fabrics with ZnO materials, the UV protection factor (UPF) of cotton textiles was increased from 4 to 33.

FACILE SYNTHESIS OF ORGANOSILOXANE-MODIFIED HYDROPHOBIC GEOPOLYMER THROUGH PEPTIZATION OF POLYDIMETHYLSILOXANE

We report a scalable, facile synthetic process for hydrophobic geopolymer containing organosilane. Using polydimethylsiloxane (PDMS) as an organic precursor, the surface of sodium and potassium geopolymers of varying precursor composition was functionalized with degraded PDMS oligomers by first partially hydrolyzing PDMS in a hot, concentrated NaOH or KOH solution and subsequently by undergoing geopolymer synthesis with metakaolin. Both types of geopolymer yielded nonporous hydrophobic materials with external surface areas of 0.6475 and 4.342 m2/g for sodium and potassium geopolymer, respectively. The materials showed an oil capacity of 75 and 134 wt%, respectively. X-ray diffraction patterns of the samples indicate that the PDMS functionalized sodium geopolymers contain zeolite A and sodalite, while the potassium geopolymers were amorphous with two overlapping broad humps in contrast to the typical geopolymers.

Study of the Effect of NaOH Treatment on the Properties of GF/VER Composites Using AE Technique.

The purpose of this study is to use acoustic emission (AE) technology to explore the changes in the interface and mechanical properties of GF/VER composite materials after being treated with NaOH and to analyze the optimal modification conditions and damage propagation process. The results showed that the GF surface became rougher, and the number of reactive groups increased after treating the GF with a NaOH solution. This treatment enhanced the interfacial adhesion between the GF and VER, which increased the interfacial shear strength by 25.31% for monofilament draw specimens and 27.48% for fiber bundle draw specimens compared to those before the GF was modified. When the modification conditions were a NaOH solution concentration of 2 mol/L and a treatment time of 48 h, the flexural strength of the GF/VER composites reached a peak value of 346.72 MPa, which was enhanced by 20.96% compared with before the GF was modified. The process of damage fracture can be classified into six types: matrix cracking, interface debonding, fiber pullout, fiber relaxation, matrix delamination, and fiber breakage, and the frequency ranges of these failure mechanisms are 0~100 kHz, 100~250 kHz, 250~380 kHz, 380~450 kHz, 450~600 kHz, and 600 kHz and above, respectively. This paper elucidates the fracture process of GF/VER composites in three-point bending. It establishes the relationship between the AE signal and the interfacial and force properties of GF/VER composites, realizing the classification of the damage process and characterizing the mechanism. The frequency ranges of damage types and failure mechanisms found in this study offer important guidance for the design and improvement of composite materials. These results are of great significance for enhancing the interfacial properties of composites, assessing the damage and fracture behaviors, and implementing health monitoring.

Study on NaOH improving the surface morphology of three-dimensional printed poly- L- lactic acid mesh scaffolds

To explore the effect of NaOH on the surface morphology of three-dimensional (3D) printed poly- L-lactic acid (PLLA) mesh scaffolds. The 3D printed PLLA mesh scaffolds were prepared by fused deposition molding technology, then the scaffold surfaces were etched with the NaOH solution. The concentrations of NaOH solution were 0.01, 0.1, 0.5, 1.0, and 3.0 mol/L, and the treatment time was 1, 3, 6, 9, and 12 hours, respectively. There were a total of 25 concentration and time combinations. After treatment, the microstructure, energy spectrum, roughness, hydrophilicity, compressive strength, as well as cell adhesion and proliferation of the scaffolds were observed. The untreated scaffolds were used as a normal control. 3D printed PLLA mesh scaffolds were successfully prepared by using fused deposition molding technology. After NaOH etching treatment, a rough or micro porous structure was constructed on the surface of the scaffold, and with the increase of NaOH concentration and treatment time, the size and density of the pores increased. The characterization of the scaffolds by energy dispersive spectroscopy showed that the crystal contains two elements, Na and O. The surface roughness of NaOH treated scaffolds significantly increased ( P<0.05) and the contact angle significantly decreased ( P<0.05) compared to untreated scaffolds. There was no significant difference in compressive strength between the untreated scaffolds and treated scaffolds under conditions of 0.1 mol/L/12 h and 1.0 mol/L/3 h ( P>0.05), while the compression strength of the other treated scaffolds were significantly lower than that of the untreated scaffolds ( P<0.05). After co-culturing the cells with the scaffold, NaOH treatment resulted in an increase in the number of cells on the surface of the scaffold and the spreading area of individual cells, and more synapses extending from adherent cells. NaOH treatment is beneficial for increasing the surface hydrophilicity and cell adhesion of 3D printed PLLA mesh scaffolds.

Enhanced Superabsorbency of Cellulose-Based Hydrogels in NaOH Solution: Synthesis, Characterization, and Performance Evaluation

Cellulose is a natural polymer that is abundantly available in nature. This study successfully developed cellulose dissolved in NaOH and formed into hydrogels using the freeze-thaw method. NaOH solution concentration as a cellulose solvent varied from 1% (CN1) to 5% (CN5) by weight. Six cycles of freezing and thawing were performed for 20 hours at -23°C and 4 hours at 37°C. Subsequently, morphological analysis, swelling degree, weight loss, and compression testing were conducted to assess the physical properties of cellulose-based hydrogels. The results demonstrate that as the concentration of NaOH increases, the resulting hydrogel exhibits smaller pore sizes, as evidenced by optical microscope images. Additionally, the swelling degree increased with the increasing NaOH fraction. The swelling tests were performed in both distilled water and PBS solutions. Notably, soaking the hydrogels in PBS solution demonstrated their potential as superabsorbent hydrogels (SAH). Furthermore, increased NaOH fraction was associated with higher weight loss, greater Young’s modulus, and reduced compressive strength.

Ionized acrylamide-based copolymer / terpolymer hydrogels for recovery of positive and negative heavy metal ions.

In this study, we explored the effective capture of both cations and anions onto a single adsorbent. Acrylamide (AAm) served as the polymer backbone, onto which co-monomers sodium p-styrenesulfonate (SS) and N,N-dimethylaminopropyl acrylamide (DMAPAA) were grafted, creating ionized polymer hydrogel adsorbents. These adsorbents were engineered for the synergistic separation and recovery of heavy metal cations and anions from concentrated solutions, focusing specifically on industrially significant ions such as Ni2+-, Cu2+, Zn2+ and (Cr2O7)2-. The adsorption and desorption behaviors of the AAm terpolymer hydrogels were investigated across various pH solutions, considering the competition and concentrations of these specific metal ions. Moreover, the study delved into the effects of the internal pH environment within the hydrogel adsorbents, determining its impact on the type of metal adsorbed and the adsorption capacity. Our findings indicated that the adsorption of cations was enhanced with a higher proportion of SS relative to DMAPAA in the hydrogel. In contrast, significant anion capture occurred when the concentration of DMAPAA exceeded that of SS. However, equal ratios of SS and DMAPAA led to a noticeable reduction in the adsorption of both types of substrates, attributed to the counteractive nature of these co-monomers. To enhance the adsorption efficiency, it may be necessary to consider methods for micro-scale separation of the two types of monomers. Additionally, the adsorption capacity was observed to be directly proportional to the swelling capacity of the hydrogels. For complete desorption and separation of the cations and anions from the adsorbent, the application of concentrated NaOH solutions followed by HNO3 was found to be essential. Given the varying concentrations of cation and anion pollutants, often present in heavy metal factory effluents, it is crucial to fine-tune the ratios of DMAPAA and SS during the synthesis process. This adjustment ensures optimized efficiency in the decontamination and recovery of these significant heavy metal ions.

Research on the Impact of Modification Method on 13X Zeolite Molecular Sieve Adsorption Performance for SO2

AbstractThe article takes 13X molecular sieve as the object, studies the effects of three modification methods, including calcination temperature, NaOH solution concentration, and CuO and MnO2 loading, on the adsorption performance of SO2 on 13X molecular sieve, and preliminarily explores the adsorption kinetics characteristics of 13X‐xwt % MnO2. The results show that the modification method of loading 13X‐6wt %MnO2 is better, the penetration adsorption time is about 130 minutes, and the maximum penetrable adsorption capacity is 57.8 mg⋅g‐1 .The adsorption kinetics study of 13X‐6wt % MnO2 shows that the R2 of the quasi‐second‐order model is close to 0.99, indicating that the adsorption process follows the quasi‐second‐order kinetic equation. The particle diffusion kinetic model fitting shows that the adsorption process is divided into two stages, the first stage is rapid adsorption, which is mainly controlled by surface adsorption and intraparticle diffusion rate, while the second stage is mainly microporous or chemisorption, with a smaller adsorption amount.

Modeling and improving the scrubbing efficiency of an intensified ammonia process for coke oven gas purification

Coke oven gas (COG) is a valuable byproduct of coke production in the steel industry. Conventionally, undesired H2S and NH3 in COG are removed in separate columns in an ammonia process. In this work, an intensified ammonia process which removes both H2S and NH3 in a single column with multiple sections is studied. The intensified process occupies less space and is less expensive. A process model is built and validated using plant operating data. The underlying principal of scrubber operation is explained through the simulated concentration profile. The influences of important operating variables such as inlet COG flowrate, strong ammonia liquid flowrate, low ammonia liquid flowrate and concentrated NaOH solution flowrate are studied. It is shown that the H2S removal efficiency is sensitive to inlet COG flowrate, and that the flowrate of low ammonia liquid should be used as manipulate variable to control the outlet COG composition. Furthermore, it is found that to improve the H2S removal efficiency, the flowrate of concentrated NaOH solution should exceed a certain threshold. Otherwise the scrubbing liquid will be neutralized by CO2 in the COG, which will decrease the pH and alkalinity of the scrubbing liquid significantly.

Elucidating the structural changes of cellulose molecules and dynamics of Na ions during the crystal transition from cellulose I to II in low temperature and low concentration NaOH solution

Low-concentration alkali treatments at low temperatures facilitate the crystal transition of cellulose I to II. However, the transition mechanism remains unclear. Hence, in this study, we traced the transition using in situ solid-state 13C CP/MAS NMR, WAXS, and 23Na NMR relaxation measurements. In situ solid-state 13C CP/MAS NMR and WAXS measurements revealed that soaking cellulose in NaOH at low temperatures disrupts the intramolecular hydrogen bonds and lowers the crystallinity of cellulose. The dynamics of Na ions (NaOH) play a crucial role in causing these phenomena. 23Na NMR relaxation measurements indicated that the Na-ion correlation time becomes longer during the crystal transition. This transition requires the penetration of Na ions (NaOH) into the cellulose crystal and a reduction in Na-ion mobility, which occurs at low temperatures or high NaOH concentrations. The interactions between cellulose and NaOH disrupt intramolecular hydrogen bonds, inducing a conformational change in the cellulose molecules into a more stable arrangement. This weakens the hydrophobic interactions of cellulose, and facilitates the penetration of NaOH and water into the crystal, leading to the formation of alkali cellulose. Our findings suggest that a strategy to control NaOH dynamics could lead to the discovery of a novel preparation method for cellulose II.