NaOH Solution Research Articles

Investigation on the Biaxial Flexural Strength of Universal Shade Resin-Based Composites.

The biaxial flexural strength of universal shade and conventional dental resin-based composites before and after alkaline degradation was investigated. Disk samples were prepared from these resin-based composites, and some of the specimens were immersed in 0.1 M NaOH solution to create deteriorated samples. The biaxial flexural strength of the samples before and after the alkaline degradation test was measured and statistically tested. The fracture surfaces after the biaxial flexural test were observed using a scanning electron microscope. The results showed that the biaxial flexural strength of the paste-type universal shade resin-based composite before alkaline degradation was significantly (19%) higher than that of the conventional type, but no difference was observed between the materials after alkaline degradation. On the other hand, the biaxial flexural strength of the flowable universal shade resin-based composites was significantly (around 35%) lower than that of the conventional composite, with or without degradation. Although, for paste-type materials, the biaxial flexural strength of universal shade resin-based composites was higher than that of conventional resin-based composites before alkaline degradation, after degradation the two materials showed similar values. For flowable materials, the biaxial flexural strength of universal shade resin-based composites was lower than that of conventional resin-based composites regardless of the presence or absence of degradation processes. These results suggest that some caution should be used when deciding whether to use flowable universal shade resin-based composite to fill a cavity.

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

High conductivity and dimensional stability brominated poly (aryl piperidinium) anion exchange membranes: Synergistic interaction of hydrophilic and superhydrophobic fluorinated side chains

Anion-exchange membrane fuel cells (AEMFCs) is a promising renewable energy device for hydrogen production. Anion exchange membranes (AEMs), the key component of AEMFCs, is generally needed for excellent dimensional stability and conductivity. Here, we synthesised a variety of AEMs with different number of C–F bonds to enhance the hydrophilic/hydrophobic micro-phase separation structure while maintaining dimensional stability. At 80 °C, the QPBTTP-PEG-10-F9 shows high OH− conductivity (∼179.02 mS cm−1), excellent dimensional stability (swelling ratio <19 %), and mechanical properties (elongation at break: 37 %, tensile strength: 71 MPa). In addition, QPBTTP-PEG-10-F9 shows good alkaline stability (conductivity remaining of 92.52 %) in 3 M NaOH solution for 1800 h. The peak power density (PPD) of a single cell assembled with QPBTTP-PEG-10-F9 can reach 534.79 mW cm−2 with a current density of 951 mA cm−2.

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.

Corrosion inhibition performance of RNC-n on aluminum alloy surface in alkaline solution

The corrosion inhibition behavior of glycine surfactants with different carbon chain lengths (RNC-n, n = 8, 12, 14) of AA2024-T3 aluminum alloy in 0.01 mol·L−1 NaOH solution was investigated. The weight loss and electrochemical methods, XPS, SEM/EDS techniques, quantum chemical calculations, and molecular dynamics simulations were used for studying the corrosion inhibition properties, adsorption behavior, and corrosion inhibition mechanism. When the maximum solubility of 0.01 mol·L−1 was achieved, the inhibition effectiveness of RNC-8 reached 90.55 %. Both RNC-12 and RNC-14 exhibited inhibitory efficiencies of 92.81 % at 0.005 mol·L−1 and 91.83 % at 0.0005 mol·L−1. RNC-n was shown to be an anodic corrosion inhibitor, since its impact on the anodic reaction was larger than on the cathodic one. RNC-n was able to successfully adsorb on the aluminum surface and form a protective film, which hindered further corrosion damage of the aluminum by the alkaline solution. In addition, the adsorption sites of RNC-n molecules were analyzed, and it was found that the adsorption sites of the corrosion inhibitor were mainly in the carboxyl group. Therefore, this paper can provide some theoretical support for the protection of aluminum alloys against corrosion in alkaline medium.

SnO2 nanoparticles: synthesis, characterization and photocatalytic activity

SnO2 nanoparticles have been synthesized using precipitation method and heat treatment. Firstly, SnCl4.5H2O was reacted with NaOH solution, and than the precipitate heat treated at 350 oC, 450 oC and 550 oC. The obtained materials were characterized by X-Ray diffraction (XRD) infrared spectra (IR) energy-dispersive X-ray spectroscopy (EDS) scanning electron microscopy (SEM) and UV-vis diffuse reflectance spectroscopy (UV-vis DRS). The photocatalytic degradation of rhodamine B (RhB) using SnO2 nanoparticles was investigated. The results show that the SnO2 nanoparticles exhibited a significantly enhanced photocatalytic activity. The photoactivity of SnO2 nanoparticles photocatalysts can be ascribed to the enhanced electron-hole separation.

Nanoarchitectonics of bamboo-based heterojunction photocatalyst for effective removal of organic pollutants

A high-performance photocatalyst with both efficient and reusable performance is essentially demanded for the purification of organic wastewater and the removal of indoor formaldehyde. However, recovery of photocatalyst particles from the reaction system remains a challenge. Herein, based on the abundant pore structure of natural bamboo and the outstanding photocatalytic activity of ZnO/WO3, we fabricated an efficient bamboo-based photocatalyst (ZnO/WO3@bamboo) for the efficient photocatalytic degradation of formaldehyde and organic dyes. The pretreatment of bamboo substrates with NaOH solution resulted in the formation of nucleation sites for ZnO/WO3 growth within bamboo cellulose channels. Subsequently, the as-prepared ZnO and WO3 were mixed in different mass ratios, and loaded on the pretreated bamboo substrates using the hydrothermal method. The results showed that the ZnO/WO3@bamboo had the effective function of photocatalytic degradation of formaldehyde gas and organic dyes. Moreover, the as-prepared ZnO/WO3@bamboo photocatalyst demonstrated superior recycling ability toward organic pollutants, which was described by photocatalytic degradation efficiency of formaldehyde gas more than 89% after 10 cycles, and organic dyes over 93% after 20 cycles. The coupling of ZnO and WO3 leads to electron delocalization, which caused the electron holes generated in the valence band (VB) of ZnO to delocalize to the VB of WO3, and reduced the recombination of electron-hole. Therefore, the photocatalytic degradation performance of the ZnO/WO3@bamboo was enhanced. The proposed ZnO/WO3@bamboo photocatalyst holds great promise in the field of air pollution and wastewater remediation.

Promoting propane dehydrogenation performance of Co/silicalite-1 catalysts

Co catalysts supported on silicalite-1 (S-1) zeolite are developed in this work for direct propane dehydrogenation to propylene (PDH), showing excellent activity and propylene selectivity. Comprehensive characterizations of XRD, SEM, N2-sorption, TEM, DR UV–vis, H2-TPR, and TGA jointly evidence that the atomic-level dispersed CoOx species have significantly positive influence on the catalytic performance for PDH reaction. Alkaline treatment is a kind of advanced and effective method to create a number of defects on S-1 support, further isolating CoOx species and thus depressing side reactions. After the optimizing treatment on support, the catalyst with 0.5 wt% of Co supported on the S-1 pretreated with 0.1 mol/L of NaOH solution can exhibit simultaneously 78 % of propane conversion and 97 % of propylene selectivity after 15-minute of induction period. This work confirms that the highly-dispersed CoOx species bonded to zeolite are necessary for obtaining highly active and selective Co sites confined in the developed oxygen defects for the PDH reaction possibly due to the interface-induced effect between Co-O, and the main deactivation cause is ascribed to the migration and aggregation of Co sites in defects which points out that the direction for developing commercial Co based catalysts should focus on the stability design of active single Co atoms.

Cu/Cu2O/C nanoparticles and MXene based composite for non-enzymatic glucose sensors

Copper/Cuprous oxide/Carbon nanoparticles decorated MXene composite was prepared and subsequently examined for its potential application as a non-enzymatic glucose sensor. To carry out this, initially the Cu MOF/MXene composite was synthesised by the hydrothermal method and was annealed in an unreacted environment at different time intervals. During this process, petal like Cu MOF on MXene loses the organic ligands to form a Cu/Cu2O/C based nanoparticles on MXene. Further, an electrode was fabricated with the developed material for understanding the sensing performance by cyclic voltammetry and chronoamperometry in 0.1 M NaOH solution. Results reveal that the highest weight percentage of copper oxide in the composite (15 min of annealed material) shows a higher electro catalytic activity for sensing glucose molecules due to more active sites with good electron transfer ability in the composite. The formed composite exhibits a wide linear range of 0.001–26.5 mM, with a sensitivity of 762.53 μAmM−1cm−2 (0.001–10.1 mM), and 397.18 μAmM−1cm−2 (11.2–26.9 mM) and the limit of detection was 0.103 μM. In addition to this, the prepared electrode shows a good reusability, repeatability, selectivity with other interferences, stability (93.65% after 30 days of storage), and feasibility of measuring glucose in real samples. This finding reveals that the metal oxide derived from MOF based nanoparticle on the MXene surface will promote the use of non-enzymatic glucose sensors.

Enzyme-free magnetic relaxation detection for glucose based on the Mn(IV)/Mn(II) conversion under alkaline condition

Herein, we have developed two enzyme-free magnetic relaxation assays for the detection of glucose utilizing the principle that glucose reduces Mn(IV) species to Mn(OH)2 in an alkaline environment, and the further conversion of Mn(OH)2 to Mn2+ under neutral condition can induce a noteworthy increase in the transverse relaxation rate (1/T2) of water protons. Thus, MnO2 nanosheets were first employed as probes and signaling units for the magnetic relaxation detection of glucose, achieving a detection limit of 1 μM. Furthermore, we realized straightforward magnetic relaxation detection of glucose by direct mixing of Mn2+ ions, NaOH and glucose in solution. This process encompasses the in-situ oxidation of Mn2+ ions to MnO(OH)2 and the subsequent reduction of MnO(OH)2 by glucose to Mn(OH)2, thereby integrating probe synthesis, and target identification within a one-pot reaction. To our knowledge, this type of analysis is more superior compared with the approach utilizing MnO2 nanosheets, since it exhibits higher sensitivity (with a limit of detection at 0.6 μM), faster, and enhanced convenience. Considering the advantages of being enzyme-free and facile, the magnetic relaxation sensing strategy, grounded in the redox reaction of Mn(IV) and glucose, holds substantial potential for diverse applications.

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.

Elucidation of the optical, electronic, and photoelectrochemical properties of p-type CuFe2O4 photocathodes

High-quality thin films of p-type CuFe2O4 photocathode were prepared for the first time on FTO-coated glass substrates by a novel nonaqueous solution using spray pyrolysis method. The films' critical physical and photophysical properties, including morphology, optical properties, carrier transport properties, band position, and photoelectrochemical (PEC) characteristics, were analyzed and estimated. The feasibility of PEC water splitting was systematically evaluated. The prepared reddish-brown CuFe2O4 film exhibits a compact and uniform morphology. Its optical bandgap is approximately 1.42 eV, and it possesses a suitable conduction band position, indicating its capability to facilitate solar-driven water splitting and absorb visible light. Under AM 1.5 simulated solar illumination, the photocurrent density of 12 μA/cm2 was attained in a 1 mol NaOH solution. However, the prepared CuFe2O4 films demonstrate instability under constant light in the electrolyte owing to the copper reduction reaction. These research results offer a fresh insight into the potential application of CuFe2O4 as a photocathode semiconductor in PEC water splitting.

Effect of chloride binding behavior of cement hydration products on chloride critical value of steel corrosion in the presence of Na+ and Ca2+

To accurately predict the service life of concrete structures, the effect of chloride binding behavior of cement hydration products on steel corrosion should be taken into account. In this study, the steel specimen with cement paste coating were prepared to investigate the effect of chloride binding behavior on steel initial corrosion in the presence of Na+ and Ca2+. The results show that the higher pH level and Ca2+ concentration effectively inhibited the leaching C–S–H, while the Ca2+ increased the Ca/Si ratio of C–S–H, thereby enhancing the physical chloride binding capacity of cement paste coating in the CaCl2-Ns system (the addition of CaCl2 in NaOH solution). This enhancement primarily accounted for the higher critical value (Ccrit) of 0.03 mol/L in the CaCl2-Ns system, surpassing that of specimens exposed to other corrosion solutions, which was 0.01 mol/L. Both chloride ions from NaCl and CaCl2 could partially replace carbonate ions in monocarboaluminate (Mc), indicating that the cation type did not exert significant influence on chemical binding in this study.

Six-membered ring-reinforced flexible high-elongation block polyamide as strong and multi-reusable hot melt adhesive

This study presented the synthesis and characterization of polyester block polyamide hot melt adhesives (PPHMAs) with high adhesion strength and toughness. The PPHMAs demonstrated an adhesion strength of 11.04 MPa and toughness of 22.54 MJ·m−3, making them suitable for various substrates such as aluminum, copper, and stainless steel. The polyamide segments synthesized from dimer acid and 2-methyl-1,5-diaminopentane exhibited characteristics of softness and high elongation. Using isophorone diamine as a reinforcing agent introduced a stable six-membered ring structure, which enhanced the polymer's rigidity and strength, thus meeting the requirements for polyamide segments to function as the hard segments in block polymers. A trace amount of Tris (2-aminoethyl) amine provided the cross-linking sites which are similar to those in neuronal structures. The polyester segments, which were synthesized from poly (propylene glycol) diglycidyl ether and sebacic acid, served as the soft segments in the block polymer and were connected to the hard segment via amide bonds. The addition of the polyester segments enhanced the non-covalent molecular interactions within PPHMAs, leading to dynamic crosslinking properties. The adhesive maintained stable adhesion even after six cycles, which showcased its durability. Furthermore, the PPHMAs exhibited notable chemical resistance. It retained over 60 % adhesion strength after exposure to some chemical solvents including artificial seawater, 5 % NaOH solution, 5 % HCl solution, and DMSO for 24 h. These findings offered a novel approach to enhancing the adhesion strength and toughness of conventional thermoplastic hot melt adhesives.

A dilute sodium hydroxide technique for radiolarian extraction from cherts

Radiolarians have been used to determine geological ages and have contributed markedly to our understanding of Earth’s history. Hydrofluoric acid (HF) has traditionally been used to extract radiolarian fossils from siliceous deposits (i.e., radiolarian cherts), but this acid is strictly regulated because of environmental and human health concerns. Here we report on the successful extraction of radiolarians from cherts using a low-concentration NaOH solution (1 mol/L NaOH) as an alternative to HF. The degree of chert dissolution in NaOH is strongly temperature-dependent and is limited at < 80 °C. However, even a 1 mol/L NaOH solution is sufficient to dissolve chert at 100 °C. Our new NaOH method yields better-preserved radiolarian fossils compared with the conventional HF method. The 1 mol/L NaOH solution is less hazardous, easier to handle, and has fewer effects on the environment and human health than HF. Therefore, this method can be widely used for research and teaching purposes in studies of radiolarian fossils, even in institutions where HF cannot be used owing to chemical restrictions.

Kinetics of Alkali-Silica Reaction: Application to Sandstone.

Despite extensive research, the relationship between the progression of the alkali-silica reaction (ASR) and the expansion of concrete due to ASR, particularly for the heterogeneous aggregate with slow reactivity, is not thoroughly understood. In this paper, the dissolution kinetics of reactive silica present in sandstone when exposed to NaOH solutions, alongside the expansion characteristics of rock prisms under ASR conditions, were studied. The experimental results indicate that ASR behaves as a first-order reaction, accompanied by an exponential decrease in the concentration of OH- over time, and the dissolution rate of silica is predominantly governed by diffusion dynamics. Notably, increasing the temperature accelerates ASR, which augments the expansive pressure in a confined and limited space, leading to more significant aggregate expansion. Conversely, higher temperatures also result in a diminished retention of ASR gels within the aggregate, leading to the mitigation of ASR expansion. Our findings underscore that larger aggregates retain a greater quantity of gels, resulting in more pronounced expansion. To establish an ASR prediction model based on the relationship of the ASR expansion of concrete to high and low temperatures, the parameters such as the range of curing temperatures and the grading size of aggregates should be carefully considered for the experiments.

MODIFICATION OF WOVEN DENDROCALAMUS ASPER IN COMPOSITE APPLICATIONS

The aim of this study is to examine the influence of immersing Petung Bamboo in a NaOH solution on the tensile strength (TS) of composites containing an epoxy matrix. Petung Bamboo Webbing was given 0%, 3%, 6% and 9%, soaking treatment. The Composite utilised in this investigation was fabricated by the Vacuum Assisted Resin Infusion technique. Tensile testing of composites is conducted according to the ASTM D638-1 standard. The findings indicated a positive correlation between the concentration of NaOH immersion and the adhesion between the woven surface of Petung Bamboo and the matrix. Consequently, the TS of the Composite was enhanced. However, increasing the concentrations beyond a certain point leads to more degradation of the lignin and cellulose in the fibers, resulting in a loss in the strength of the composite. The Petung Bamboo woven reinforced Composite achieved the highest TS of 136.06 MPa after being treated with a 6% NaOH immersion. This was followed by a 3% NaOH immersion treatment resulting in a TS of 106.04 MPa. Without any NaOH immersion treatment, the composite had a TS of 97.31 MPa. The lowest TS of the composite was observed after a 9% NaOH immersion treatment, measuring 90.79 MPa. The Petung Bamboo wicker-reinforced composite with NaOH immersion treatment showed higher fiber pullout and fiber-matrix debonding failures, while higher NaOH treatment concentration reduced these failures.

Relationship between calcium forms and organic carbon content in aggregates of calcareous soils in northern China

The agricultural soil organic carbon (SOC) pool is one of the most active C pools in terrestrial ecosystems, and soil aggregates are the main site of SOC fixation. Mineral sorption plays a crucial role in SOC accumulation. Calcium (Ca) is a typical soil mineral element that plays a crucial role in SOC accumulation and is fundamental for the formation of soil aggregates. Although Ca has been shown to regulate the stability of SOC, the relationship between different forms of Ca and SOC within aggregates in northern China remains unclear. In this study, we selected five soils (black soil, light chernozem soil, fluvo-aquic soil, sierozem soil, and loess soil) with different calcium carbonate (CaCO3) contents as the target materials. Water-stable aggregates were separated using the wet-sieving method. Soil respiration was measured using the static alkali absorption method (carbon dioxide [CO2] absorption by NaOH solution). The CaCO3 content was quantified using the CO2 gas volume method, and the continuous leaching method was used to analyze the different forms of Ca (water soluble-Ca, exchangeable-Ca, acid soluble-Ca, and bound to organic-Ca). In-situ field sampling was used to reveal the associations between different forms of Ca and SOC within aggregates. The results showed that besides the CaCO3 form, exchangeable-Ca (20.06 %–57.86 %) and bound to organic-Ca (26.69 %–73.91 %) were major Ca forms in calcareous soils. There was a nonsignificant negative correlation between CaCO3, acid soluble-Ca, and exchangeable-Ca and SOC in the bulk soil. However, there was a significant negative correlation among CaCO3, acid soluble-Ca, and exchangeable-Ca with SOC in macro-aggregates (> 0.25 mm) and micro-aggregates (0.25–0.053 mm). A 90-day incubation experiment was conducted to verify the previous speculations, which revealed that CaCO3 increased SOC mineralization and reduced the content of SOC, while enhancing the acid soluble-Ca and bound to organic-Ca content. In the treatment with added CaCO3, there was a negative correlation between acid soluble-Ca and bound to organic-Ca and SOC in bulk soil and macro-aggregates (> 0.25 mm). The effect of Ca2+ on SOC should not be ignored. Excessive Ca2+ may be converted into different forms of Ca to occupy the bonding sites for SOC on the surface of soil particles with silt and clay particles, forming a pseudo-aggregate structure, and the SOC traveling between soil particles, which is not conducive to SOC stabilization and accumulation.

Waste valorization: Sustainable geopolymer production using recycled glass and fly ash at ambient temperature

This research explores the reutilization of waste glass powder (GP) and class F fly ash (FA) in the development of an advanced geopolymer, focusing on reducing natural resource consumption to serve as a green alternative for conventional concrete material. Investigating mix ratios of GP-to-FA (0-to-1), activated with 2–12 M NaOH, followed by ambient temperature curing, this study mainly assesses strength (compressive, and flexural) and durability at different ages. Mechanical properties concerning reaction kinetics and Al/Si ratio, reveal that GP initially acts as an inert filler with slow reaction kinetics, while significant strength improvement at later ages is attributed to the reaction between GP and FA. Optimal performance is achieved with a geopolymer mixture featuring a GP-to-FA ratio of 1:3 (Al/Si ratio of 0.51) and an 8 M NaOH solution, resulting in the highest compressive strength of 40 MPa and superior durability. Microstructural analysis (SEM-EDS, and 29Si MAS NMR) identifies the reacting product as calcium/sodium aluminate silicate hydrate (C/N-(A)-S-H) gel within the geopolymer matrix. Leaching tests further underscore potential environmental concerns related to excessive alkali leaching, necessitating meticulous mix design management. Embodied energy and carbon footprint assessments confirm the environmental friendliness of the GP-FA-based geopolymer. Overall, this research demonstrates the feasibility of producing effective geopolymers from dry waste at ambient temperature, emphasizing the potential synergy between waste glass recycling and the concrete industry towards sustainable construction practices.