Search Results (39)

A geopolymer, derived from agricultural waste, was used as an efficient, sustainable, and low-cost adsorbent of methylene blue, a recurrent industrial dye contaminant. The geopolymer was synthesized via a standard alkali activation process using wheat husk ash calcinated at 1050 °C. Adsorption capabilities were evaluated through batch kinetic experiments. The removal efficiency was determined by ultraviolet–visible spectrophotometry, and the adsorption kinetics were fitted to various models. The geopolymer demonstrated a maximum adsorption capacity of 270.58 mg/g for methylene blue, achieving a removal efficiency of 85.20% under optimal conditions. Kinetic analysis confirmed that the adsorption process is best described by the pseudo-second-order model. This suggests that chemisorption, which involves chemical bonding or electron exchange between the dye and the negatively charged aluminosilicate structure of the geopolymer, is the rate-limiting mechanism. This demonstrates that geopolymers are effective and promising adsorbents, valorizing an agricultural waste stream into a functional material for the efficient treatment of dye-polluted wastewater. The competitive capacity and favorable chemisorption mechanism position the geopolymer as a promising material for the remediation of dye-contaminated industrial effluents. Full article

Hazardous galvanic sludge waste (GSW) from the electroplating industry, produced at 100,000–150,000 tonnes/year in the EU and containing high concentrations of Cr and Ni was successfully treated using metakaolin-based geopolymers via Stabilization/Solidification (S/S). The experimental design incorporated chelating (sodium diethyl dithio carbamate, C₅H₁₀NS₂Na, DTC), reducing (sodium sulfide, Na₂S), and adsorbing (hydroxyapatite, Ca₅(PO₄)₃(OH), Hap) agents separately to improve heavy metal immobilization. The results demonstrated that Na₂S drastically decreased Cr release by −98.7% by reducing mobile Cr(VI) to insoluble Cr(III). DTC reduced Ni leaching by −93.4%, forming sparingly soluble Ni(II)(DTC)₂ complexes that precipitated within the matrix. Hap enhanced Ni retention by 55.5% via cation exchange but was ineffective for Cr due to electrostatic repulsion with the anion Cr(VI)O₄²⁻ at the geopolymer’s high pH. This work is the first to apply geopolymerization coupled with these chemical agents for S/S of as-received galvanic waste, offering a highly efficient, low-carbon strategy to manage this hazardous industrial residue. Full article

The removal of synthetic dyes from water resources is essential for environmental protection and sustainable water management. This study aimed to develop and evaluate a kaolin-based geopolymer (KBG) for the adsorption of crystal violet (CV) dye from aqueous solutions. Natural kaolin, an abundant aluminosilicate material in South Africa, was activated using an alkaline solution to form the geopolymer. The synthesized material was characterized using Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy, and Brunauer–Emmett–Teller (BET) surface area analysis. Batch adsorption experiments were conducted to investigate the effects of contact time (5–180 min), adsorbent dosage (0.05–1.0 g), initial dye concentration (10–150 mg/L), temperature (30–50 °C), pH (2–12), and water chemistry on CV removal efficiency. Characterization results confirmed the successful conversion of kaolin to geopolymer, exhibiting a BET surface area of 11.18 m²/g. The optimum adsorption occurred at pH 10.2, where electrostatic attraction between the negatively charged geopolymer surface and the cationic dye molecules was maximized. Kinetic data fitted best to the pseudo-second-order model, while the Langmuir isotherm provided the best description of the equilibrium data. The adsorption mechanism was attributed to electrostatic attraction, hydrogen bonding, and π–π interactions between CV molecules and the geopolymer surface. Thermodynamic analysis confirmed that the adsorption process was spontaneous and endothermic, indicating enhanced dye uptake at elevated temperatures. Full article

For deep purification of wastewater containing anionic dyes. In this study, cetyltrimethylammonium bromide (CTAB)-modified geopolymer-based hectorite was synthesized via a steam-assisted method using depolymerized illite-based geopolymer as the silicon source and CTAB as the modifier, enhancing its adsorption performance for anionic dyes. The product was characterized by methods such as X-ray diffraction, and the effects of parameters such as adsorbent dosage and pH on the adsorption process were investigated. Adsorption experiments revealed that when the CTAB addition was 20%, the adsorption performance for Congo red was optimal (99.79%, 997.92 mg·g⁻¹), far superior to that of hectorite without CTAB (66.64%, 666.40 mg·g⁻¹). The adsorption process followed pseudo-second-order kinetics and the Langmuir isotherm model. Further comparison of changes before and after adsorption indicated that the adsorption mechanism primarily involved the combined effects of electrostatic interaction and hydrophobic effects. Additionally, after five adsorption–desorption cycles, the material maintained over 92% removal efficiency. By using different geopolymers as silicon sources to prepare CTAB-modified geopolymer-based hectorite, the high universality of this synthesis strategy was confirmed. This study provides a universal, green, and sustainable route for preparing efficient anionic dye adsorption materials and expands the high-value utilization of clay resources. Full article

Geopolymers, achieved through geopolymerization of aluminosilicate-containing precursors, are environmentally friendly inorganic binders with excellent mechanical strength, chemical resistance, and low carbon footprint. Beyond construction applications, geopolymers show great potential in environmental protection due to their ability to immobilize hazardous pollutants, adsorb ions and gases, and utilize industrial solid wastes. This review provides a state-of-the-art summary of recent advances in geopolymer applications in environmental fields, including (1) immobilization of hazardous wastes, (2) adsorption of hazardous ions and CO₂, and (3) resource utilization of solid wastes through geopolymerization. The mechanisms underlying immobilization and adsorption are discussed, and research gaps and future directions will be highlighted to guide further development of geopolymer-based environmental materials or application of geopolymerization in solid waste utilization. Full article

Lead (Pb) is a highly toxic heavy metal frequently found in industrial wastewater, posing serious risks to both human health and the environment. In this study, a porous geopolymer synthesized from fly ash, metakaolin, and red mud was evaluated for Pb(II) removal via batch adsorption experiments under varying pH, dosage, contact time, temperature, and initial concentration. The synthesized material exhibited a favorable mesoporous structure, with a BET surface area of 42.05 m² g⁻¹ and an average pore width of 6.26 nm, making it suitable for heavy metal uptake. Adsorption kinetics followed the pseudo-second-order model (R² = 0.9993), while the Langmuir isotherm (R² ≈ 0.999) best described the equilibrium data, indicating monolayer chemical adsorption as the dominant mechanism, with a maximum capacity of 74.26 mg g⁻¹ at 318 K. Thermodynamic analyses confirmed that the adsorption was spontaneous (ΔG° < 0), endothermic (ΔH° > 0), and accompanied by increased entropy (ΔS° > 0). Desorption and regeneration tests revealed EDTA to be a more effective agent than HNO₃, maintaining a reuse efficiency of 81.35% after four cycles. These results highlight the potential of waste-derived porous geopolymers as regenerable, low-cost, and efficient adsorbents for lead removal. Full article

The main goal of this study is to address the problem of environmental water pollution caused by organic dyes through waste valorization by synthesizing geopolymer-based adsorbents. In this work, geopolymers were synthesized using fly ash modified with chitosan and polyvinyl alcohol as a starting material. The obtained materials were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and determination of the point of zero charge. We examined the adsorption potential for organic dye (methylene blue, brilliant green, crystal violet) removal through the influence of contact time, initial pH and concentration of adsorbate solution, and temperature on adsorption. The obtained results were analyzed using theoretical kinetics and isotherm models. Interpretation of the obtained results was performed using the Box–Behnken design and chemometric methods of multivariate analysis. The findings showed that modification with chitosan significantly enhanced the adsorption efficiency of the synthesized materials up to 95.9% for methylene blue adsorption. The parameters identified as having the greatest influence on the adsorption process were contact time, pH-value, initial dye concentration, and the type of dye being adsorbed. Full article

This study presents the fabrication and performance optimization of porous fly ash-based geopolymer (FAGP)–polyethersulfone (PES) composite fibers with tunable FAGP loading for the multivariate adsorption of heavy-metal ions from aqueous solutions. Fibers containing 20 wt%, 40 wt%, and 60 wt% FAGP were prepared using phase inversion method and were characterized using X-ray computed tomography and mechanical testing. Adsorption experiments were conducted to assess the removal efficiencies of Pb²⁺, Cd²⁺, Cu²⁺, and Ni²⁺ at different pH values, temperatures, contact times, adsorbent dosage and initial metal-ion concentrations. The composite containing 60 wt% FAGP exhibited the high performance for all ions, and its performance was especially high for Pb²⁺. The isotherm and kinetic modeling revealed that the adsorption process followed Freundlich and Redlich–Peterson models, with mixed chemisorption–physisorption mechanisms depending on the metal-ion type. Compared with conventional adsorbents, the optimized composite fibers exhibited high adsorption capacity, enhanced handling suitability, and scalability in addition to their sustainability owing to the use of industrial by-products as precursors. These findings provide new insights into the structure–function relationships of FAGP composite fiber adsorbents and their potential for wastewater treatment applications. Full article

Infrastructure construction is a major contributor to carbon emissions, primarily due to the extensive use of mineral materials such as cement and aggregates, which release significant amounts of carbon dioxide during production and use. While existing research has predominantly centered on the applications of concrete, the present study extends the investigation to encompass inorganic–organic composites, alloy materials, and wastewater treatment systems, with particular attention to bridging the gap between theoretical potential and practical implementation. This study identifies China, the USA, and India as leaders in this field, attributing their progress to abundant material resources and sustained policy support. Key findings reveal that while geopolymers can fully replace cement, substitution rates of less than 50% are optimal for high-performance concrete to maintain structural integrity and decarbonization benefits. Aggregate replacements using materials such as air-cooled blast furnace slag show 50–100% feasibility. This review further highlights the multifunctional potential of red mud, rice husk ash, fly ash, and blast furnace slag as cement replacements, aggregates, reinforcers, catalysts, adsorbents, and composite fillers. However, challenges such as unstable raw material supply, lack of standardization, and insufficient international collaboration persist; these issues have often been overlooked in prior research and viable solutions have not been proposed. To address these barriers, a triple-objective framework is introduced in this study, integrating sustainable infrastructure, resource recycling, and environmental remediation, supported by optimized production processes and policy models from leading nations. Future research directions emphasize comprehensive life cycle assessments and enhanced global cooperation to bridge the divide between resource-rich and resource-scarce regions. By synthesizing cross-disciplinary applications and actionable solutions, this work advances the transition toward sustainable infrastructure systems. Full article

Metakaolin-based geopolymers with different molar ratios of Si/Al were synthesized and utilized as an efficient adsorbent for the removal of methylene blue (MB) as a model cationic dye from aqueous solution. Various analytical techniques were employed to characterize the synthesized geopolymers. The influence of the main operation conditions on the adsorption kinetics of MB onto the geopolymer was examined under various operating conditions. Results showed a significant maximum MB adsorption capacity at the temperature of 30 °C for all four types of geopolymers studied (designated as A, B, C, and D) up to 35.3, 23.6, 25.5, and 19.0 mg g⁻¹, respectively. The corresponding order of Si/Al ratio was A < C < B < D. Adsorption kinetics was so fast and reached equilibrium in 10 min, and the experimental results were described using the adsorption dynamic intraparticle model (ADIM). The equilibrium data for MB removal was in agreement with the Langmuir isotherm. Full article

Sawdust is receiving increasing attention as a promising green adsorbent. However, due to its powder nature, it is difficult to recover after adsorbing heavy metals and may even cause secondary pollution. To solve this problem, a novel sawdust/foamed geopolymer (SFG) adsorbent was prepared by using sawdust as a raw material, geopolymer as a binder, and hydrogen peroxide as a foaming agent. This study discussed the effect of SFG dosage, solution temperature, solution pH, contact time, and initial Cu²⁺ solution concentration on the adsorption capacity and removal rate. The results showed that a desirable SFG adsorbent with the SFG dosage of 0.5 g, temperature of 25 °C, pH of 5, contact time of 720 min, and initial Cu²⁺ solution concentrations of 90 mg/L is recommended, of which the adsorption capacity is 31.5 mg/g with the removal rate being 92.76%. In addition, the adsorption performance of the SFG adsorbent is superior to that of pure sawdust and similar to that of the foamed geopolymer adsorbent, and it has the characteristics of higher strength, lower cost, and more environmental friendliness. This study indicated that the SFG adsorbents are feasible as adsorbents; meanwhile, this work can provide a scientific reference for the development of new bio-composite adsorbent materials, especially in the field of the treatment of heavy metal ions in wastewater. Full article

Carbon dioxide levels in the atmosphere are related to global warming and climate change. Materials to be used for CO₂ capture are an important factor in assisting humanity in overcoming this challenge. The goals of this study are to look into the synthesis of adsorbents from red mud (RM), fly ash (FA), and metakaolin (MK). The initial composition was chosen to induce in situ crystallization of zeolites dispersed together with a geopolymer matrix. Two aging steps were used, which combined temperature (25; 95 °C) and atmosphere (air; water). The MK + FA system crystallized zeolite sites dispersed throughout the geopolymer matrix. These crystals were identified as faujasite-Na. They were responsible for the surface area ranging from 23.2 to 238.4 m².g⁻¹, and CO₂ adsorption from 0.83 to 2.32 mmol.g⁻¹ at 35 °C and 1 atm. The best results were obtained by first aging at 95 °C for 120 h, followed by water aging at 25 °C for 120 h. Full article

D-K-type bauxite from Guizhou can be used as an unburned ceramic, adsorbent, and geopolymer after low-temperature calcination. It aims to solve the problem where the color of the D–K-type bauxite changes after calcination at different temperatures. Digital image processing technology was used to extract the color characteristics of bauxite images after 10 min of calcination at various temperatures. Then, we analyzed changes in the chemical composition and micromorphology of bauxite before and after calcination and investigated the correlation between the color characteristics of images and composition changes after bauxite calcination. The test results indicated that after calcining bauxite at 500 °C to 1000 °C for 10 min, more obvious dehydration and decarburization reactions occurred. The main component gradually changed from diaspore to Al₂O₃, the chromaticity value of the image decreased from 0.0980 to 0.0515, the saturation value increased from 0.0161 to 0.2433, and the brightness value increased from 0.5890 to 0.7177. Studies have shown that changes in bauxite color characteristics are strongly correlated with changes in composition. This is important for directing bauxite calcination based on digital image processing from engineering viewpoints. Full article

The present study aimed to use geopolymer materials synthesized from different fly ashes, which are promising for the adsorption of copper ions from aqueous solutions. The characterization of fly ashes and prepared adsorbents was performed by energy-dispersive X-ray spectroscopy (EDS) analysis, Brunauer–Emmett–Teller (BET) surface area analysis, and Scanning Electron Microscopy (SEM). Taguchi and ANOVA methods were used to predict the effect of different working parameters on copper ion removal by prepared geopolymers. Based on data obtained by the Taguchi method, it was found that the factor most influencing the adsorption process is the type of adsorbent used, followed by the solution pH, the reaction time, the adsorbent dose, and the initial copper ion concentration. The ANOVA results agree with the Taguchi method. The optimal conditions of the adsorption process were: fly ash C modified by direct activation with 2 M NaOH, at 70 °C for 4 h, solution pH of 5, initial pollutant concentration of 300 mg/L, 40 g/L adsorbent dose, and 120 min of reaction time. Copper ion removal efficiency was determined experimentally under optimal conditions, achieving a value of 99.71%. Full article

The degradation of concrete and reinforced concrete structures is a significant technical and economic challenge, requiring continuous repair and rehabilitation throughout their service life. Geopolymers (GPs), known for their high mechanical strength, low shrinkage, and durability, are being increasingly considered as alternatives to traditional repair materials. However, there is currently a lack of understanding regarding the interface bond properties between new geopolymer layers and old concrete substrates. In this paper, using advanced computational techniques, including quantum mechanical calculations and stochastic modeling, we explored the adsorption behavior and interaction mechanism of aluminosilicate oligomers with different Si/Al ratios forming the geopolymer gel structure and calcium silicate hydrate as the substrate at the interface bond region. We analyzed the electron density distributions of the highest occupied and lowest unoccupied molecular orbitals, examined the reactivity indices based on electron density functional theory, performed Mulliken charge population analysis, and evaluated global reactivity descriptors for the considered oligomers. The results elucidate the mechanisms of local and global reactivity of the oligomers, the equilibrium low-energy configurations of the oligomer structures adsorbed on the surface of C-(A)-S-H(I) (100), and their adsorption energies. These findings contribute to a better understanding of the adhesion properties of geopolymers and their potential as effective repair materials. Full article