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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]

In this paper, a honeycomb Si3N4 ceramic was fabricated by 3D printing with a well‐preserved structure. The effects of Si3N4 content on the rheological properties of Si3N4/sol–silica ink and the printing resolution of products were investigated. The microstructure, phase composition, liner shrinkage rate, and fracture behavior of printed samples before and after sintering were systematically characterized in detail. The results showed that the modified inks had the optimized rheological properties, and the stress–shear rate curves corresponding to each slurry could be well described by Bingham and Herschel–Bulkley fluid models. The corresponding slump rates of the printed samples with different Si3N4 to sol–silica mass ratios were all lower than 4%, and the linear shrinkage rate of all of the samples after sintering was below 20%. The fracture behavior under compressive loading of the honeycomb Si3N4 ceramics tended to be non‐catastrophic fractures both before and after sintering. The compressive strengths of all of the printed samples decreased with the increase of the Si3N4 content, and the highest compressive strength of the honeycomb ceramics could reach 131.2 MPa after sintering at 1600°C, which was about 366.9% higher than that of the samples in green state prior to the sintering. [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]