Search

In this study, we report that geopolymer materials containing different amounts of graphitic carbon nitride (g‐C3N4) (C3N4/GP) can remove methylene blue (MB) using the synergistic effects of adsorption and photodegradation. A geopolymer containing 3 wt% g‐C3N4 (3 wt%C3N4/GP) had the best MB removal efficiency of 94.62% within 60 min, under visible light. The results showed that geopolymers can act as carriers for g‐C3N4, and the relative amount of adsorbent and photocatalyst influences the removal of MB. 3 wt%C3N4/GP was also used for additive manufacturing by using direct ink writing technology. In order to improve the efficiency of MB removal, a pore‐forming agent (K12) was added in the synthesis process to prepare three‐dimensional‐printed porous C3N4/GP. The results showed that the porous C3N4/GP was effective in removing MB. This work provides a simple strategy for preparing efficient and green materials for removing organic pollutants. [ABSTRACT FROM AUTHOR]

Geopolymers with a zeolite‐like structure are attractive inorganic binder materials for addressing the critical challenge of reducing the carbon footprint of the cement industry. Despite many efforts, the exact geopolymerization mechanism remains a topic of investigation. In the present work, we determined the dimerization processes between Si/Al‐bearing monomers through metadynamics. The free energy profiles were obtained using ab initio constrained molecular dynamics simulations. The results reveal that metastable pentacoordinate states formed after exposure to the alkaline medium, followed by the release of the hydroxyl on the rotational axis. The presence of Al(OH)4− monomers would significantly reduce the reaction barriers of dimerization, implying that Al(OH)4− monomers promote the crosslinking degree of the geopolymer gel. Increasing the pH value of the alkali‐activated solution would facilitate the reaction between Si‐bearing monomers and Al(OH)4− monomers. However, the reaction between anionic Si‐bearing monomers presents a much higher barrier because of intensive electrostatic repulsion. Therefore, increasing the pH value decreases the Si/Al ratio of the geopolymer gel at the initial stage, which is consistent with the experimental results. This study refines the understanding of the oligomerization process of aluminosilicates by ab initio molecular simulations. [ABSTRACT FROM AUTHOR]

Geopolymers (GPs) have emerged as promising adsorbents for wastewater treatment due to their superior adsorption stability, tunable porosity, high adsorption capacity, and low-energy production. Despite their great promise, developing GPs with well-controlled hierarchical structures and high porosity remains challenging, and the mechanism underlying the ion adsorption process remains elusive. Here we report a cost-effective and universal approach to fabricate Na or K GPs with sophisticated architectures, high porosity, and arbitrary cation species exchange by means of additive manufacturing and a surfactant. The introduction of sodium lauryl sulfate (SLS) enhanced the porosity of the GP adsorbents, yielding NaGP-lattice-10%SLS adsorbent with a high total porosity of 80.8 vol%. Combining static and dynamic adsorption tests, the effects of morphology, surfactant content, and cation species on Cs+ adsorption performance were systemically investigated. With an initial Cs+ concentration of 900 mg/L, the printed NaGP exhibited a maximum Cs+ adsorption capacity of 80.1 mg/g, outperforming other adsorbents reported so far. The quasi-second-order fit of the NaGP adsorbent showed overall higher R2 values than the quasi-first-order fit, indicating that the adsorption process was dominated by ion exchange. Combined with first-principles calculations, we verified that the content of water in the GP sod cages also affected the ion-exchange process between Na+ and Cs+. [Display omitted] • A novel geopolymer (GP) adsorbent with a hierarchical porous architecture was fabricated by additive manufacturing. • The printed GP adsorbent exhibited a strong adsorption capacity for Cs+. • The printed GP adsorbent showed superior structural stability under the circulating column test. • The adsorption capacity of Cs+ on the printed GP adsorbent far exceeded that of porous bulk and pure bulk adsorbent. [ABSTRACT FROM AUTHOR]

Developing advanced lightweight structures with both high strength and high toughness remains challenging. Herein, we provide a combined experimental and simulation method to fabricate 3D-printed geopolymer complex structures with lightweight, high strength and superior toughness for the first time. In this research, short carbon fiber reinforced geopolymer (C sf GP) composites were printed using 3D printing technology, and the rheological properties of C sf GP inks and the mechanical properties of hardened geopolymer composite structures were systematically studied. The C sf GP inks exhibited obvious shear-thinning behavior, which facilitated ink-extrusion from a micro-nozzle, conserving the filamentary shape and supporting the subsequent printed layers. In C sf GP composites, the consistent orientation distribution of short carbon fibers primarily enhanced their mechanical properties. When fiber content was 3 wt %, flexural strength and compressive strength of the C sf GP composite were 309.2% and 375.8% higher than those of nonreinforced geopolymer, respectively. Subsequently, C sf GP composites of the Bouligand architectures were successfully 3D-printed, and they showed superior load-bearing capacity and non-brittle failure mode due to their hierarchically ordered architectures and sophisticated interfaces. 3D printing together with Bouligand-structure designing provide a novel approach for the C sf GP composites of lightweight, high strength and superior toughness, which would lead to a resurgence of interest in new lightweight structure design and manufacturing strategies. [Display omitted] • Short carbon fiber reinforced geopolymer (C sf GP) inks were 3D printed by direct ink writing. • Consistent fiber orientation distribution was achieved in the printed C sf GP composites. • C sf GP of Bouligand structures were designed and printed, and the fracture behavior of these structures was investigated. • The obtained C sf GP of Bouligand structures showed light-weight, high strength and superior toughness, and non-brittle failure behavior. [ABSTRACT FROM AUTHOR]

3D-printed geopolymer lattices (3DGPLs) have recently been considered as promising candidates for hazardous waste management due to their low cost, porous nature, and excellent environmental stability. However, the ion adsorption capacity influenced by usage conditions such as multi-ion systems and radiation remains largely unexplored. Furthermore, effective strategies to immobilize adsorbed ions for long-term disposal are still lacking. This work tackles these questions by studying the Cs+ adsorption and immobilization properties of 3DGPLs in the presence of competing ions and gamma-ray radiation. Our results reveal the inhibitory intensity of Cs+ adsorption capacity by five common metal cations in seawater, ranked in the following order: Na+ > K+ > Ca2+ > Mg2+ > Sr2+. After exposure to different doses of gamma-ray radiation, the Cs+ adsorption capacity of 3DGPLs shows no significant change, demonstrating their outstanding radiation resistance. By encapsulating the Cs-containing 3DGPL with a homologous GP coating, the Cs+ immobilization rate reaches 98.545% after leaching in NaCl solution at 60 °C for 5 days. The already-high Cs+ immobilization rate can be further increased to 99.228% by sintering treatment due to the densification effect. This study not only provides microscopic insights into the adsorption of hazardous ions by 3DGPLs under usage conditions, but also offers a feasible approach to prevent the leakage of loaded ions through GP coating technology. [Display omitted] • A new Cs + adsorption & immobilization technology was developed. • The effects of competing ion species and concentrations on the Cs + adsorption performance of GP adsorbents was clarified. • The printed GP adsorbent exhibited excellent resistance to gamma-ray irradiation. • The long-term sealing of Cs-exchanged GP adsorbents was realized by utilizing geopolymer as the immobilization material. [ABSTRACT FROM AUTHOR]

• Metakaolin-based geopolymer was prepared for hazardous wastes storage. • Temperature and medium-dependent leaching kinetics of hazardous wastes were probed. • Geopolymer showed better immobilization performance than Portland cement, ceteris paribus. • Microscopic leaching mechanisms were revealed under different leaching conditions. Notwithstanding the success of carbon-free nuclear power in the new energy industry, an effective way to address nuclear contamination is still lacking. As a generally accepted method to date, immobilization of radioactive nuclear wastes with inexpensive and environment-friendly matrix such as geopolymer has attracted extensive attention. In this contribution, Na-based and K-based metakaolin geopolymer were prepared to encapsulate simulated radioactive Cs+ and Sr2+ under different temperatures and environments during long-term leaching tests. The temperature-dependent and environmental-dependent leaching kinetics as well as their dominant leaching mechanisms have been revealed. The results showed that Na-based and K-based geopolymer exhibited better immobilization performance than that of Portland cement, ceteris paribus. For the immobilization of Cs+, Na-based geopolymer showed lower leaching rate than K-based geopolymer under the same leaching conditions. Both higher temperature and salt solution accelerated the leaching behaviors of Sr+ and Cs2+ from the encapsulation matrix. This contribution sheds light on understanding the dominant leaching mechanisms of hazardous elements under different storage environments and highlights the significance of salt-tolerant matrix for the immobilization of nuclear wastes. [ABSTRACT FROM AUTHOR]