Hierarchically porous ceria with tunable pore structure from particle-stabilized foams

3D printing of Pickering emulsions, Pickering foams and capillary suspensions - A review of stabilization, rheology and applications

Pickering emulsions and foams as well as capillary suspensions are becoming increasingly more popular as inks for 3D printing. However, a lack of understanding of the bulk rheological properties needed for their application in 3D printing is potentially stifling growth in the area, hence the timeliness of this review. Herein, we review the stability and bulk rheology of these materials as well as the applications of their 3D-printed products. By highlighting how the bulk rheology is tuned, and specifically the inks storage modulus, yield stress and critical balance between the two, we present a rheological performance map showing regions where good prints and slumps are observed thus providing clear guidance for future ink formulations. To further advance this field, we also suggest standard experimental protocols for characterizing the bulk rheology of the three types of ink: capillary suspension, Pickering emulsion and Pickering foam for 3D printing by direct ink writing.

Co-vitrification of municipal solid waste incinerator fly ash and bottom slag: Glass detoxifying characteristics and porous reformation

Safety and efficient dispose of municipal solid waste incineration (MSWI) fly ash with high toxicity has emerged as a worldwide challenge. Vitrification provides the advantages of capacity reduction, detoxification, and solidification of heavy metals, which has the potential to dispose of hazardous waste on a large scale. Herein, co-vitrification of MSWI fly ash and bottom slag has been accomplished based on the characteristics of calcium and silicon composition. A novel approach for producing glass ceramic foams by alkaline activation-crystallization was developed to realize the disposal of the obtained glass. The effect of MSWI fly ash/bottom slag ratios on the glass network, crystallization ability of the basic glass, pore structure, and physical properties of the porous green body was investigated. The results revealed that with increasing MSWI fly ash proportion, the Si-O of [SiO₄] in the basic glass changed significantly and the crystallization ability steadily reduced. Si-O and Al-O in basic glass are easy to corrode under alkaline conditions, releasing Ca²⁺ and forming a low solubility product, calcium silicate hydrate. When the crystallization temperature increases from 950 ℃ to 1150 ℃, it is more conducive to the precipitation of the gehlenite phase. Extending the crystallization time promotes three-dimensional growth of crystals that are coupled with each other to form a network structure and a multi-stage pore structure. The pore structure was developed with the help of NH₃ and H₂ generated by the secondary aluminum ash (SAA). Through the preparation of glass ceramic foams, the raw materials were detoxified. The toxic heavy metals showed extremely low leaching concentrations, which were smaller than the limit of TCLP. The prepared samples had 70.22-80.61% of porosity, 0.78-1.19 g/cm³ of low bulk density, and 0.54-7.86 MPa of compressive strength.

Robocasting of 3D printed and sintered ceria scaffold structures with hierarchical porosity for solar thermochemical fuel production from the splitting of CO2

We report the first ever robocast (additive manufacturing/3D printing) sintered ceria scaffolds, and explore their use for the production of renewable fuels via solar thermochemical fuel production (STFP, water and carbon dioxide splitting using concentrated solar energy). CeO₂ catalyst scaffolds were fabricated as 50 mm diameter discs (struts and voids ∼500 μm), sintered at 1450 °C, with specific surface area of 1.58 m² g^-1. These scaffolds have hierarchical porosity, consisting of the macroporous scaffold structure combined with nanoscale porosity within the ceria struts, with mesopores <75 Å and an average pore size of ∼4 nm, and microporosity <2 nm with a microporous surface area of 0.29 m² g^-1. The ceria grains were ≤500 nm in diameter after sintering. STFP testing was carried out via thermogravimetric analysis (TGA) with reduction between 1050-1400 °C under argon, and oxidation at 1050 °C with 50% CO₂, gave rapid CO production during oxidation, with high peak CO production rates (0.436 μmol g^-1 s^-1, 0.586 ml g^-1 min^-1), for total CO yield of 78 μmol g^-1 (1.747 ml g^-1). 90% CO was obtained after just 10 min of oxidation, comparing well to reticulated ceria foams, this CO production rate being an order of magnitude greater than that for ceria powders when tested at similar temperatures.

Recent additive manufacturing methods categorized by characteristics of ceramic slurries for producing dual-scale porous ceramics

Porous ceramics have been utilized in various fields due to their advantages derived from characteristics of ceramics and porous structure and they were produced by versatile fabricating methods. However, the adoption of differently scaled pores in the porous ceramics by conventional pore forming strategies which results in dual-scale porosity has been studied to combine the specific functional abilities of each scaled pore. Those proposed strategies were supplemented to the recent additive manufacturing methods for constructing complicated structure with precisely controlled fabricating conditions. In this review, we provide the researches creating dual-scale porous ceramics with additive manufacturing which utilized the ceramic slurries containing homogeneous solution of photocurable monomers and terpenes. Introduction of the basic way to prepare photocurable monomer and terpene incorporated ceramic slurries which are suitable for specific printing mechanism was firstly discussed. And based on the characteristics of slurries, lithography-based and extrusion-based method are discussed with the experimental results. Subsequently, the remaining challenges of the techniques are further discussed with suggesting potentially capable approaches to overcome the limitations.

Template Synthesis of Porous Ceria-Based Catalysts for Environmental Application

Porous oxide materials are widely used in environmental catalysis owing to their outstanding properties such as high specific surface area, enhanced mass transport and diffusion, and accessibility of active sites. Oxides of metals with variable oxidation state such as ceria and double oxides based on ceria also provide high oxygen storage capacity which is important in a huge number of oxidation processes. The outstanding progress in the development of hierarchically organized porous oxide catalysts relates to the use of template synthetic methods. Single and mixed oxides with enhanced porous structure can serve both as supports for the catalysts of different nature and active components for catalytic oxidation of volatile organic compounds, soot particles and other environmentally dangerous components of exhaust gases, in hydrocarbons reforming, water gas shift reaction and photocatalytic transformations. This review highlights the recent progress in synthetic strategies using different types of templates (artificial and biological, hard and soft), including combined ones, in the preparation of single and mixed oxide catalysts based on ceria, and provides examples of their application in the main areas of environmental catalysis.