The Preparation and Properties of Porous Sepiolite Ceramics

Efficient Self-cleaning and antibacterial ceramics with active sites fully exposed obtained from rare earth waste

The utilization of rare earth polishing powder waste (RPW) to prepare antibacterial ceramics can effectively avoid problems of pollution in the recycling process and waste of rare earth resources. Herein, a novel RPW-based antibacterial ceramics was developed, which possesses the core-shell structure with ceramics as the cores and the CeO2/BiOCl as the superficial coating. The antibacterial ceramics display notable antibacterial activity, and the inactivation rates of 3.3 log under visible light irradiation in 30 min and 2.4 log under darkness in 1 h were achieved, and the zone of inhibition values was found to be 16.6 mm for E.coil. The hardness of antibacterial ceramics was measured to be 897 (±38) HV, higher than commercial porcelain's hardness (600 HV). The antibacterial mechanism was verified by the Ce ion release, reactive species, and fluorescence-based live/dead cells. This study presents a novel antibacterial ceramic structure and green economic reuse method of rare earth waste.

Recent Progress on Natural Clay Minerals for Lithium-Sulfur Batteries

Li-S batteries with high energy density have the potential to become a viable alternative to Li-ion batteries. However, Li-S batteries still face several challenges, including the shuttle effect, low conversion kinetics, and Li dendrite growth. Natural clay minerals with porous structures, abundant Lewis-acid sites, high mechanical modulus, and versatile structural regulation show great potential for improving the performance of Li-S batteries. However, so far, relevant reviews focusing on the applications of natural clay minerals in Li-S batteries are still missing. To fill the gap, this review first presents an overview of the crystal structures of several natural clay minerals, including 1D (halloysites, attapulgites, and sepiolite), 2D (montmorillonite and vermiculite), and 3D (diatomite) structures, providing a theoretical basis for the application of natural clay minerals in Li-S batteries. Subsequently, research advancements in the natural clay-based energy materials in Li-S batteries have been comprehensively reviewed. Finally, the perspectives concerning the development of natural clay minerals and their applications in Li-S batteries are provided. We hope this review can provide timely and comprehensive information on the correlation between the structure and function of natural clay minerals in Li-S batteries and offer guidance for material selection and structure optimization of natural clay-based energy materials.

A novel natural scaffold layer improving efficiency, stability and reproducibility of Perovskite solar cells

In this study, our hypothesis was to demonstrate the usability of a natural clay structure as scaffold layer in perovskite solar cells (PSCs). Sepiolite, which is a natural and environmentally friendly clay structure, has a very high active surface area and can easily be dispersed in solvents. In addition we predicted that crystallization could easily occur on their surfaces due to their surface chemistry. In the study, we firstly used a natural clay as scaffold layer in PSCs. It is observed that, efficiency, reproducibility and stability of PSCs have been significantly improved. Improvements in efficiency have been observed to be between 30 and 50% depending on the type of perovskite solvent used. In addition, the surface chemistry of the sepiolite resulted in better crystallization as well as stability. Due to its high-water adsorption capability, sepiolite makes the perovskite crystal more stable by trapping the residual water molecules as well as penetrated water molecules from environment. Consequently, we demonstrated that, a natural, low-cost and environmentally friendly clay may be an alternative material which may contribute to the commercialization of PSCs.

Poly(vinyl alcohol) freeze casts with nano-additives as potential thermal insulators

Freeze-casting consists of freezing a liquid suspension (aqueous or other), followed by sublimation of the solidified state to the gas state under reduced pressure, and subsequent sintering of the remaining scaffold to consolidate and densify the struts and walls. The structure is very porous with the pores being a replica of the solvent crystals. The technique is rather versatile and the use of a liquid solvent (water most of the time) as a pore forming agent is a strong asset. Freeze-casting has also been developed as a near net shape forming route yielding dense ceramics. In this work we report on porous composite materials synthesized via the ice templating method. Poly(vinyl alcohol) (PVA) is used as matrix and nano-silica (SiO₂), nanoclay (NC) and microfibrillated cellulose (MFC) are used as fillers to improve the mechanical stability of the PVA scaffold. We show our results on the porosity and mechanical stability and consider these porous nanocomposites as potential insulation materials with low thermal conductivity and superior mechanical properties.

Cadmium adsorption by thermal-activated sepiolite: Application to in-situ remediation of artificially contaminated soil

Soils contamination with Cd result in detriment to the environmental quality. In-situ immobilization methods by applying clay minerals have been gaining prominence. The effects on sepiolite of thermal activation at different temperatures (300-750 °C), for removing Cd from aqueous solutions were evaluated, in order to consider their further application for soil remediation. The influence of activation temperature was investigated using XRD, SEM, and N₂ adsorption-desorption measurements. The S-600 exhibited the maximum adsorption capacity (21.28 mg/g), despite its lower SSA, and Langmuir model described the adsorption isotherms better than the Freundlich equation. TCLP was used to quantify the remediation effects of thermal-activated sepiolite on simulated soils artificially polluted with Cd. The results indicated that the mobility of Cd in soil was effectively reduced after treating with thermal-activated sepiolite and the use of S-600 was the most efficient, reducing the TCLP-Cd by approximately 73% compared with the control test. The main remediation mechanism was considered as the cation exchange of Cd by Mg at the edges of octahedral sheet. This study showed that thermal-activated sepiolite could be promising amendments for remediation of Cd-contaminated soil.

Highly photosensitized Mg4 Si6O15 (OH)2·6H2O@guar gum nanofibers for the removal of methylene blue under solar light irradiation

In the present investigation, photosensitized nanofibers (NFs) based on guar gum (GG)/poly(vinyl alcohol) (PVA)/Mg4Si6O15(OH)2·6H2O (SP) (modified by 1, 4-diamminobutane [DAB]) was fabricated by electrospinning approach and same was used for the degradation of dye under solar light irradiation. For electrospinning of NFs, the acceleration voltage, nozzle flow rate and collector distance levels of 19,000 KV, 0.5 mL/h and 3 cm were optimum conditions along with 7% (w/v) blend of GG/PVA (1.4:5.6 wt/wt) and 0.01 g modified Mg4Si6O15(OH)2·6H2O. The exfoliation, intercalation and clay organophilization in GG/PVA/Mg4Si6O15(OH)2·6H2O (GG/PVA/SP) NFs were examined by FTIR analysis. The photocatalytic activity (PCA) of NF was studied under the solar light irradiation for methylene blue (MB) dye degradation. The photosensitized GG/PVA/SP2 (G3) showed promising PCA under visible light and G3 furnished higher degradation of MB dye (99.1%) within 10 min of irradiation. Results revealed that GG/PVA/SP based NFs are highly active under solar light, which can be applied for the treatment of wastewater.

CaSiO3-HAp Structural Bioceramic by Sol-Gel and SPS-RS Techniques: Bacteria Test Assessment

The article presents an original way of getting porous and mechanically strong CaSiO₃-HAp ceramics, which is highly desirable for bone-ceramic implants in bone restoration surgery. The method combines wet and solid-phase approaches of inorganic synthesis: sol-gel (template) technology to produce the amorphous xonotlite (Ca₆Si₆O₁₇·2OH) as the raw material, followed by its spark plasma sintering–reactive synthesis (SPS-RS) into ceramics. Formation of both crystalline wollastonite (CaSiO₃) and hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) occurs “in situ” under SPS conditions, which is the main novelty of the method, due to combining the solid-phase transitions of the amorphous xonotlite with the chemical reaction within the powder mixture between CaO and CaHPO₄. Formation of pristine HAp and its composite derivative with wollastonite was studied by means of TGA and XRD with the temperatures of the “in situ” interactions also determined. A facile route to tailor a macroporous structure is suggested, with polymer (siloxane-acrylate latex) and carbon (fibers and powder) fillers being used as the pore-forming templates. Microbial tests were carried out to reveal the morphological features of the bacterial film Pseudomonas aeruginosa that formed on the surface of the ceramics, depending on the content of HAp (0, 20, and 50 wt%).