Higher NaOH Concentrations Research Articles

Mechanical properties of geopolymer concrete incorporating supplementary cementitious materials as binding agents

This research investigates the environmental impact of cement production by exploring eco-friendly geopolymer binders as alternatives. Geopolymer concrete, developed using silica and alumina-rich precursors such as pozzolanic materials, achieves high compressive strength, up to 43.6 N/mm2 with a 16 M concentration and integrated steel fibers. Utilizing manual mixing and industrial by-products, the study pioneers cast-in-situ geopolymers with innovative curing techniques. The paper presents experimental results on the engineering properties of geopolymer concretes of 40 MPa, cured at 100 °C and 60 °C. The study systematically varies binder content, examining proportions of fly ash, GGBS, metakaolin, and silica fume, along with different mix ratios and molar concentrations. Key findings include increased compressive strength with higher NaOH concentration, peaking at 35.2 N/mm2 and 34.22 N/mm2 for 14 M mixes at 7 and 28 days, and 40.29 N/mm2 for 16 M mixes at 7 days. Optimal results were observed at higher curing temperatures, especially with 14 M and 16 M compositions at 100 °C. The study recommends mechanized mixing for efficiency and calls for further investigation into the microstructure and chemistry of geopolymers to advance sustainable construction practices. This research represents a significant step towards eco-conscious building materials, reducing the environmental impact of the construction industry.

Kinetic modeling of arabinoxylan extraction from Brewers’ spent grain using alkaline pretreatment at atmospheric pressure

This study evaluated the kinetic modeling of arabinoxylan (AX) extraction from Brewers’ spent grain (BSG) by alkaline pretreatment at atmospheric pressure, considering severe (low concentration of NaOH and high temperature) and moderate (high concentration of NaOH and low temperatures) process conditions. The effects of NaOH concentration and temperature on yield extraction were studied over time, as well as the concentration of weak acids and phenolic compounds at the end of the pre-treatment. The AX yield extraction varied from 41.2 % (1 M, 90 °C) to 64.8 % (4 M, 40 °C) after 1 h and 16 h, respectively. Acetic acid ranging from 420 ppm to 1020 ppm was released, while ferulic acid was the phenolic compound produced at the highest concentration ranging from 78.3 ppm to 224.1 ppm. In addition, rates of chemical reactions were correlated mathematically from the experimental data with a good fit, and a sensitivity analysis was performed to understand the kinetic behavior. The first-order kinetic model demonstrates that increasing AX extraction requires both low temperatures (between 30 and 40 °C) and low NaOH concentration, but at the same time, this effect increases the time required (16 h) to obtain the maximum AX yield (64.8 %).

Effect of NaOH Concentration on Rapidly Quenched Cu–Al Alloy-Derived Cu Catalyst for CO2 Hydrogenation to CH3OH

By utilizing greenhouse gas CO2 and renewable energy-sourced H2 to produce methanol, the “methanol economy” can replace fossil fuels and H2 as the energy storage medium, which not only reduces CO2 emissions, but also mitigates the energy shortage issue. However, the traditional Cu-based catalysts for CO2-to-methanol conversion suffer from low activity at low temperature and high vulnerability to sintering and deactivation. In this contribution, rapidly quenched skeletal Cu catalysts (RQ Cu) are prepared by leaching the RQ Cu–Al alloy with NaOH aqueous solutions of different concentrations. It is found that high NaOH concentration of 10 wt% favors the preparation of the RQ Cu-10 catalyst with higher porosity, lower residual Al content, and larger active Cu surface area (SCu) than the RQ Cu-3 catalyst leached with 3 wt% of NaOH solution. However, in aqueous-phase CO2 hydrogenation at 473 K and 4.0 MPa, the CO2 conversion over the RQ Cu-3 catalyst is more than two times greater than that over the RQ Cu-10 catalyst, and the selectivity and productivity of methanol are 1.20 and 2.69 times of the corresponding values over the RQ Cu-10 catalyst. At 5.0 MPa, the selectivity and productivity of methanol are further boosted to 97.9% and 1.329 mmol gCu–1 h–1 on the RQ Cu-3 catalyst. It is identified that the SCu of the RQ Cu-3 catalyst is well preserved after reaction, while dramatic growth of the Cu crystallites occurs for the RQ Cu-10 catalyst. The better catalytic performance and stability of the RQ Cu-3 catalyst are tentatively attributed to the presence of more residual Al species by using NaOH solution with lower concentration for Al leaching, which acts as the dispersant for the Cu crystallites during the reaction.

In-situ self-assembly growth of controllable gold nanoparticles film

Because of the strong light absorption and/or scattering, nano scaled gold has many favorable optic and electric properties. With the continuous miniaturization of nano photoelectronic devices and nano electromechanical systems, there is an urgent demand for controllable and tailored gold nanoparticles film with excellent performance. Here, a modified HAuCl4-NaOH-CTAB (cetyltrimethylammonium bromide) aqueous solution system was utilized to self-assembly synthesize gold nanofilm on glass substrates. The high concentration NaOH is not only reducing Au3+ to Au0, but facilitating interfacial assembly of gold nanostructure at liquid–solid interface via etching glass surface. Based on this growth kinetic, the gradient, well-designed and in-situ growing gold nanoparticles film can be achieved on any SiO2 contained substrates by controlling the growth time in the reaction system. Furthermore, the in-situ self-assembled gold nanoparticles film can be act as plasmon substrates for surface-enhanced Raman scattering (SERS) or plasmonic enhanced semiconductor lasing, even gold electrodes.

Impact of different NaOH treatments on biocellulose properties from coconut water fermented by Lentilactobacillus parafarraginis

Background: Biocellulose is a natural polymer produced by bacteria with distinct physicochemical properties, although it has a chemical composition identical to plant cellulose. Before use, biocellulose was purified by chemical treatment to increase its properties. Objective: The study aimed to evaluate biocellulose properties using NaOH solution as a purification agent. Method: After harvesting, all samples were purified using NaOH of 0.25 M (BC0.25), 0.5 M (BC0.5), and 1 M (BC1) and determined for their properties, such as mechanical strength, swelling degree, water vapour transmission, and moisture content. Analysis of scanning electron microscope (SEM) images and Fourier Transform Infrared Spectroscopy (FTIR) spectra were also performed for characterisation. Result: BC0.5 exhibited the highest tensile strength of 15.38±0.45 MPa and elongation at a break of 38.40±0.58%. BC1 had the highest swelling degree of 131.24±0.70%, water vapour transmission of 400.00±0.36 g/m2, and moisture content of 6.44±0.14%. Nevertheless, there were slight alterations in morphological structure and spectral peaks because of the high concentration of NaOH. Conclusion: The use of NaOH treatment of 0.5 M in biocellulose purification removed more contaminants and resulted in better properties than other concentrations.

A study on the influencing parameters in developing construction and demolition waste-based geopolymer concretes and their sustainability assessment

Construction and demolition waste (CDW) has been recently identified as a potential aluminosilicate source for geopolymers. However, the available research has mainly focused on developing CDW-based geopolymer pastes and mortars, while studies on geopolymer concretes sourced from CDW have been very limited. Thus, the current study aimed at experimentally identifying different CDW materials suitable for producing geopolymer concretes. Additionally, the study analysed the mechanical, microstructural, and environmental properties of CDW- based geopolymer concrete produced. In this regard, the effect of relevant parameters on the compressive strength development of CDW-based geopolymer concretes was comprehensively investigated, including those related to precursor types/fineness, alkali activator solution, aggregate type/size and curing regimes. Microstructural analyses were also conducted on the selected samples (100% brick waste, 100% tile waste, 100% concrete waste and 75% brick waste + 25% GGBS). Finally, the environmental impact of geopolymer concrete was assessed and compared with similar traditional concrete. Results showed that employing CDWs alone is not suitable to achieve sufficient strengths under all curing regimes. However, the inclusion of 25% GGBS significantly improved the strength performance of CDW-based geopolymer concrete, in comparison to other supplementary cementitious materials (SCMs) such as Class-C fly ash and calcium hydroxide. The particle size of CDWs and concentration of alkaline activators highly affect the performance of CDW-based geopolymer concretes. Utilization of CDWs with particles finer than 75 μm and high concentrations of NaOH (12 M) is recommended to achieve good performance. The results also indicate that almost similar energy is needed for producing CDW-based geopolymer and OPC-based traditional concrete, whereas a huge reduction in CO2 emission (∼40%) was estimated in the case of geopolymers. The outcomes of the current study are expected to contribute to the advancement of geopolymer concrete derived from CDW in addition to providing valuable insights into this type of concrete for practitioners and academics.

High concentration NaOH processing of natural fiber explored polypropylene composite featured with mullite: characteristics investigation

High concentration NaOH processing of natural fiber explored polypropylene composite featured with mullite: characteristics investigation

Improving the dyeability of ramie fibre by sequential alkaline and alcohol pretreatments

The high crystallinity of ramie fibre poses challenges in achieving optimal dyeing performance, such as reduced dye exhaustion. To enhance the dyeing capabilities of ramie fibre, several alterations were experimented with, such as caustic mercerization using a NaOH solution. However, because of the high NaOH concentration, removing the NaOH residue from inside the fibre becomes challenging. Herein, the present research aims to enhance the dyeing efficiency of ramie fibre by using sequential alkaline and alcohol pretreatment methods to reduce NaOH usage, accordingly relieving the wash process stress. The preliminary screening findings have revealed that iso-butanol is the most suitable alcohol solvent for modifying ramie fibres after treating it with NaOH solution since it leads to higher dye exhaustion (E%, 95.7%), dye fixation rate (F%, 88.2%), total dye fixation efficiency (T%, 84.4%), and K/S values (41.4). After that, the orthogonal array experimental scheme (L16) was applied to optimize dyeing performance. The NaOH usage was decreased to 160 g/L, the treating time was reduced to 3 min, and the dyeing performance of ramie fibre treated under the optimum conditions was better than that of a caustically mercerized one. It was determined that the NaOH concentration factor had the most contribution, accounting for 75.34% of the observed effects. The NaOH solution temperature factor followed closely behind, contributing 22.69%. Additionally, using analytical methods such as XRD, FTIR, TG, and SEM confirmed that the sequential treatment with the optimum conditions altered the structural behaviour of the original ramie fibre, which performances were similar to the mercerized ramie fibre. The barium value of sequentially iso butanol solvent treated fibre showed a greater level (213) compared to caustic mercerized fibre (179), indicating a significant advantage of mercerization performance was achieved. This advantage may be linked to improved colourfastness and handling qualities. Furthermore, the breaking force of both ramie fabrics was increased after the alkaline treatment and the sequential alkaline and iso-butanol treatment.

Comparative Environmental and Economic Analysis of Biomethane Production from Co-Digestion of Rice Straw and Spent Mushroom Compost: Application of Zero-Valent Iron Nanoparticles

Abstract Spent mushroom compost is one of the main potentials for biogas production. In recent years, several studies employed adding nanoparticles and alkaline pretreatment for improving biogas production. The present study is one of the pioneer studies that employ hybrid alkaline pretreatment (0, 5, and 15 mg of NaOH) and zero-valent iron nanoparticles (0, 10, 20, 30, and 40 mg) for improving the co-digestion of spent mushroom compost and rice straw. According to the results, retention time (RT) and nanoparticle (NP) concentrations have the most significant impact on biomethane production (significant at 1% probability level), while the NaOH concentration has the lowest impact on biomethane production (significant at 5% probability level) in comparison with RT and NP concentration. Also, the maximum biomethane production is related to NP40Na15 (about 200% higher than the control). The minimum cumulative biomethane production is related to NP0Na15 (about 30% lower than the control). The lowest relative environmental midpoint impact is related to NP40Na15, which was on average about 60% lower than the control. Adding NPs at high concentrations of NaOH reduces the midpoint impacts. The results of the study could lead to new, ecologically friendly biomethane production methods that make better use of agricultural and organic wastes.

Toxicity and biodegradability evaluation of HCHs-polluted soils after persulfate remediation treatments

Soils contaminated with lindane (γ-hexachlorocyclohexane, γ–HCH) wastes are widespread due to its massive production and high persistence. A noticeable case is in the Sardas and Bailín landfills (Spain), where INQUINOSA discharged tons of lindane wastes. The current work evaluates the remediation of polluted surface soil (HCHs = 409 mg kg−1) from these emplacements by two persulfate (PS)-activated on-site treatments: thermal (PS/T) and alkaline activation, the last one also intensified by temperature (PS/NaOH/T). The possible adverse effects of the chemical treatments on acute toxicity (associated with reagents, pH, by-product generation, etc.) of all phases involved (soils, soil organic extracts, reaction supernatants, and soil elutriates) towards Vibrio fischeri and Artemia salina were evaluated. Biodegradability assays were also performed. Both treatments presented high efficiency in pollutant degradation (XHCHs ≥ 90 % and dechlorination degree ≈ 80 %). After PS/T treatment, the soil and organic extract acute toxicity (Vibrio fischeri and Artemia salina) was reduced to the minimum level, and neither the reaction supernatant nor the soil leachate exhibited acute toxicity. Vibrio fischeri-soil acute toxicity remained unaltered after PS/NaOH/T treatment, which was attributed to the high NaOH concentration used. The toxicity of this soil elutriate was low, although that of aqueous reaction supernatant presented non-negligible values. In the case of Artemia salina bioassay, the alkaline treatment leads to a more significant decrease in toxicity than the thermal activation of PS. Finally, the biodegradability of treated soils increased, highlighting the suitability of PS-activated treatments for the remediation of HCHs-polluted soils.

Imaging and Quantitative Analysis on the Etching of Diatom Frustules via Digital Holographic Microscopy.

Frustules, whose length spans from a few micrometers to more than a hundred micrometers, have been the subject of various modifications to improve their physical properties because of their complex porous silica structure. However, three-dimensional measurements of these changes can be challenging because of the complex 3D architecture and limitations of known methods. In this study, we present a new method that applies digital holographic microscopy (DHM) to analyze controlled etched frustules and observe real-time degradation of frustules at the single-cell level. Frustules obtained from Craspedostauros sp. diatoms were etched in 1 N NaOH for 5 min at 25 and 60 °C, respectively, and the frustule's valve was analyzed using DHM. DHM uses a combination of holography and tomography to reconstruct a 3D refractive index image of the frustule. Measurements of the width, volume, and surface area are achieved. Results showed that at 60 °C of etching, a significant difference with the unetched frustule was observed for all measurements but with high fluctuation values. Finally, real-time observation of the degradation of the frustule is observed when immersed in a high concentration of NaOH. This is the first time the real-time etching of the frustule is observed at the single-cell level. This research provides an easy estimation of the 3D measurements of frustules that may provide new fundamental information and applications.

Optimising chemo-enzymatic separation of polyester cellulose blends

The study demonstrates the potential of enzymatic hydrolysis and alkaline pretreatment for sustainable blended textile recycling. The target is complete cellulose removal while preserving the polyester integrity for recovery. Interactions of sodium hydroxide concentration (10 %–30 %), urea concentration (0 %–12 %), and temperature (-20 °C–50 °C) were investigated during pretreatment using a design of experiments. Analysis revealed a bimodal pattern in polyester mass loss, with one peak at lower concentrations and temperatures, and a more prominent peak at higher concentrations and temperatures. Cellulose hydrolysis also occurred under high NaOH concentrations and elevated temperatures (50 °C, 30 % NaOH, 0 % urea). Optimal conditions, preserving polyester integrity while achieving complete cellulose elimination, were identified at temperatures between 6.2 °C and 13.3 °C, with NaOH concentrations of 20.7 %–26.6 % (0 % urea) or 13.9 % NaOH and 12 % urea. These findings pave the way for a greener, more efficient textile recycling, advancing the circularity for textiles.

Experimental study on the mass transport characteristics of dilute iodine vapor from air to caustic soda solution in a packed column using different packing materials

It is imperative to minimize radioiodine release to the environment through gaseous emissions of spent fuel reprocessing facilities, thereby mitigating its potential impact on the general public. One effective and widely adopted strategy for achieving this objective is caustic scrubbing, a method that involves the absorption of molecular iodine from gaseous streams using caustic soda ( NaOH ) solution in a packed column. In-depth laboratory-scale experiments were conducted to ascertain the overall volumetric mass transfer coefficient K G a for the absorption of dilute iodine vapor from air into a caustic soda solution in a packed column and to establish optimum performance parameters for this process. The investigation yielded noteworthy findings: K G a increased proportionately to (Gas phase Reynolds number)1.0 at constant liquid flow rates across all types of packing tested. K G a displayed relative independence from liquid velocities for high and moderate NaOH concentrations. However, this coefficient varied proportionately to (Liquid phase velocity)0.26 to 0.42 at lower NaOH concentrations under conditions of high gas flow rates NaOH . As the height of the column increased, K G a was found to decrease slightly. The presence of NOx at an inlet concentration of 9000 ppm in the gaseous stream led to a reduction in the mass transfer coefficient of iodine, particularly at low NaOH concentrations. In summary, the study underscores the importance of caustic scrubbing as an effective means to minimize the release of radioiodine. The investigation’s results provide valuable insights into optimizing performance parameters for this process, contributing to enhanced environmental protection.

Geotechnical Behaviour of Gypseous Soil Treated by Geopolymer Additives

Gypseous soil is well-known for its numerous engineering problems. When this soil is exposed to water, the gypsum in the soil dissolves, causing the buildings built on it to collapse; so, treating gypseous soil is important for improving its engineering characteristics. The present paper focuses on studying the effect of adding geopolymer on mechanical characteristics of gypseous soil. This study presents the results obtained from a series of experimental tests, including direct shear, consolidation, and collapsibility tests. Tests were conducted on samples of gypseous soil taken from depth 1.5 meters below ground level with gypsum content of 41%. The geopolymer was used in three different molarities for the collapse test (10M, 12M, and 14M) and a 14 molarity only for the shear and consolidation tests, where equal proportions of fly ash were combined with an alkaline activator that was composed of sodium hydroxide and sodium silicate. The binder (fly ash + alkaline) to the soil was added to the treated samples during mixing at a rate of 20% by weight. The findings showed that treating the soil with geopolymer leads to a notable enhancement in the angle of internal friction of the soil particles from (37 to 42) degrees. as well as a reduction in the soil compressibility and a reduction in the susceptibility of the soil to collapse, with an improvement degree of 64% when using a geopolymer with a molarity of 14 M. This improvement was achieved by using a geopolymer with a higher concentration of NaOH. The best results were achieved when a geopolymer with a molarity of 14 was used, which is the ideal ratio.

Silica extraction from bamboo leaves using alkaline extraction method

The silica is most common constituent of bamboo leaves mainly varies from 75.90 to 82.86 %.In this study, silica was extracted from bamboo leaves using an alkaline extractionprocess. In proximate analysis, bamboo leaves were found to contain significantly more ash (24.5 %) containing 79.28 % silica and low levels of fixed carbon. However, in ultimate analysis, bamboo leaves were found to contain 57.56 % oxygen.The yield and quality of silica were improved by extracting silica from bamboo leaves ash under various operating conditions.A higher concentration of NaOH (2.5 N) resulted in a greater yield of silica (97.73 %).During the alkaline process, an acid leaching treatment was used toremove metal impurities either from bamboo leaves ash or extracted silica. The silica yield increased from 97.73 % to 98.86 % after acid leaching of feed. In an FTIR analysis, Si-O-Si, Si-O, and Si-OH bonds were identified. Modern characterization techniques such as XRF were used to determine the purity of silica. There is a significant difference between the maximum purity of acid leached silica samples (96.13 %) and that of commercial silica samples (95.52 %).As a result of this study, silica that has a wide range of applications in the food and nutrition industries, the pharmaceutical industry, and as a nano-catalyst could be produced.

Eco‐friendly production and performance evaluation of water‐resistant cellulose nanofiber bioaerogels

AbstractA sustainable and environmentally conscious approach was employed to create a cellulose nanofiber (CNF) bioaerogel. This modified technique was used for its affordability and eco‐friendly nature, involved the use of reduced concentrations of NaOH solution (ranging from 0 to 0.5 M) to disperse the CNFs. The process included mixing, freezing, neutralizing, and freeze‐drying, ultimately resulting in well‐structured 3D bioaerogels. The concentration of NaOH had a significant impact on the properties of the bioaerogels. The density of the aerogels increases with higher concentration of NaOH. All treated aerogels exhibited impressive water resistance and maintained their structural integrity when exposed to water, indicating promising practical applications. This enhanced structural integrity is attributed to CNF chain rearrangement, facilitated by CNF swelling, dissolution in NaOH, and homogenization. FTIR and XRD analyses provided insight into the transition from cellulose I to cellulose‐II in the bioaerogel structure. These findings contribute to the development of eco‐friendly bioaerogels for environmentally conscious applications. Further research is needed to gain a deeper understanding of the process and to optimize conditions for specific bioaerogel properties.

Anomalous Temperature-Induced Particle Size Reduction in Manganese Oxide Nanoparticles.

The intricate role of temperature in the structure-property relationship of manganese oxide nanoparticles (Mn3O4 NPs) remains an open question. In this study, we successfully synthesized Mn3O4 NPs using the hydrothermal method with two differing temperatures, namely, 90 and 150 °C. Interestingly, a smaller average particle size is found when Mn3O4 NPs are synthesized at 150 °C compared to 90 °C, corresponding to 46.54 and 63.37 nm, respectively. This was confirmed by the time variation of temperature setting of 150 °C where the size evolution was insignificant, indicating a competing effect of nucleation and growth particles. Under varying NaOH concentrations (2-6 M) at 150 °C, a reduction in the particle size is found at the highest NaOH concentration (6 M). The particle grows slightly, indicating that the growth state is dominant compared to the nucleation state at low concentrations of NaOH. This finding implies that the high nucleation rate originates from the excessive monomer supply in the high-temperature reaction. In terms of crystallinity order, the structural arrangement of Mn3O4 NPs (150 °C) is largely decreased; this is likely due to a facile redox shift to the higher oxidation state of manganese. In addition, the higher ratio of adsorbed oxygen and lattice oxygen in Mn3O4 NPs at 150 °C is indirectly due to the higher oxygen vacancy occupancies, which supported the crystallinity decrease. Our findings provide a new perspective on manganese oxide formation in hydrothermal systems.

Cobalt-free CuO catalyst for hydrolytic dehydrogenation of sodium borohydride and ammonia borane

The environmental and economic impact of Co-based catalysts necessitates the use of a more environmentally friendly and less expensive catalyst, such as CuO. A cobalt-free CuO catalyst was developed via a simple low-temperature hydrothermal process. The efficiency of the catalyst was analysed for the dehydrogenation of NaBH4 as well as NH3BH3. Compared with the commercial particulate CuO, hydrothermally prepared CuO nanoplate (CuO HT) exhibits a good hydrogen evolution rate, the rate of hydrogen evolution for CuO_Commercial and CuO HT was experimentally measured to be 240 ml H2/min/g and 470.5 ml H2/min/g respectively for 0.2 g catalyst for the dehydrogenation of NaBH4. At a 10 times lower concentration of NaBH4 with 0.2 g of CuO HT catalyst, the rate of HER recorded was 1086 ml H2/min/g. The high catalytic activity of CuO HT could be related to the surface oxygen vacancies or defects generated due to the participation of high molar concentrations of NaOH during the reaction. The stability of both catalysts was investigated, and the rate of hydrogen evolution reaction after three cycles was determined to be 492 ml H2/min/g for CuO_Commercial and 925.1 ml H2/min/g for CuO HT. Despite the fact that the rate of hydrogen evolution was observed to be increased for the third cycle, the volume of water displaced was decreased when compared to the first cycle, which could be due to the presence of a less active Cu2O phase retained after temperature treatment. Similarly, with the best catalyst concentration of CuO HT (0.2 g), the hydrogen evolution rate of NH3BH3 was also measured to be 1175 ml H2/min/gm. The result evokes a new insight into the evolution of sustainable and eco-friendly catalysts for a better hydrogen economy.

Enhancing Aqueous Carbonation of Calcium Silicate through Acid and Base Pretreatments with Implications for Efficient Carbon Mineralization.

Carbon dioxide (CO2) mineralization based on aqueous carbonation of alkaline earth silicate minerals is a promising route toward large-scale carbon removal. Traditional aqueous carbonation methods largely adopt acidification-based approaches, e.g., using concentrated/pressurized CO2 or acidic media, to accelerate mineral dissolution and carbonation. In this study, we designed and tested three distinctive routes to evaluate the effect of pretreatments under different pH conditions on aqueous carbonation, using amorphous calcium silicate (CS) as an example system. Pretreating CS with high concentrations (100 mM) of HCl (Route I) or NaOH (Route II and III) enhanced their carbonation degrees. However, NaOH pretreatment overall yielded higher carbonation degrees than the HCl pretreatment, with the highest carbonation degree achieved through Route III, where an extra step is taken after the NaOH pretreatment to remove the solution containing dissolved silica prior to carbonation. The HCl and NaOH pretreatments formed different intermediate silica products on the CS surface. Silica precipitated from the HCl pretreatment had a minimal effect on the carbonation degree. The high Ca/Si ratio intermediate phases formed from the NaOH, on the other hand, can be readily carbonated. In contrast to commonly utilized acidification-based approaches, basification offers a more promising route to accelerate aqueous carbonation as it can mitigate the need for costly pH swing and high-concentration/pressurized CO2. The key to aqueous carbonation under basic conditions, as suggested by this study, is the control of aqueous silica species that have a suppressing effect on carbonation. Overall, this study highlights the critical needs for investigations of aqueous mineral carbonation in a broader pH region.

Preparation of Chitin Nanofibers from Shrimp Shell Waste by Partial Deacetylation and Mechanical Treatment

ABSTRACT Chitin is one of the most abundant biopolymers in nature. Herein, we report the successful preparation of chitin nanofibers (ChNFs) from shrimp shell waste using a partial deacetylation process with NaOH and high-speed blending. The effects of the deacetylation reaction with NaOH concentrations (0–40 wt%) on the degree of acetylation (DA), crystallinity, zeta potential, thermal stability, and morphology of the ChNFs were investigated. With the more aggressive deacetylation reaction (higher NaOH concentration), ChNFs had the lower DA, crystallinity degree, and thermal stability, and their widths and lengths became smaller and shorter. The presence of amino groups in the chitin molecule caused by deacetylation generated repulsive forces with aids of acetic acid, efficiently leading to the individualization of ChNFs using high-speed blending. The individualized ChNFs deacetylated with 30 wt% NaOH had an average width of 8.07 ± 1.80 nm and length of less than 500 nm, whereas bundles of aggregated fibers with widths in the range of 30–100 nm and lengths of up to several μm were extracted from chitin without deacetylation. Additionally, the deacetylation with 40 wt% NaOH completely converted chitin to chitosan. The ChNFs could be efficiently used for composites, biomaterials, and packaging applications.