Pore-Size Distribution of Silica Colloidal Crystals from Nitrogen Adsorption Isotherms

Beyond the Meso/Macroporous Boundary: Extending Capillary Condensation-Based Pore Size Characterization in Thin Films Through Tailored Adsorptives

The characterization of thin films containing nanopores with diameters exceeding 50 nm poses significant challenges, especially when deploying sorption-based techniques. Conventional volumetric physisorption or mercury intrusion methods have limited applicability in thin films due to constraints in sample preparation and nondestructive testing. In this context, ellipsometric porosimetry represents a viable alternative, leveraging its optical sensitivity to thin films. With existing setups relying on the capillary condensation of volatile compounds such as water, applicability is typically restricted to pore dimensions <50 nm. In this study, we introduce two high-molar-mass hydrocarbon adsorptives, namely ethylbenzene and n-nonane. These adsorptives exhibit substantial potential in improving the accuracy of physisorption measurements beyond mesoporosity (i.e., >50 nm). Specifically, with n-nonane, applicability is extended up to 80 nm pores. Our measurement guidelines propose a nondestructive, expeditious (<60 min), low-pressure (<0.03 bar) approach to investigate nanoporous thin films with potential adaptability to diverse structural architectures.

Synthesis and characterization of Ag-decorated litchi-like porous Cu/Cu2O micro/nanoparticles with antibacterial activity

Efficient and stable inorganic antibacterial material is highly spotted in antibacterial materials. However, the morphology and grain diameter of conventional inorganic compound antibacterial agent carrier are difficult to control and severely deteriorate antibacterial properties. In this research, using diethylene glycol monomer methyl ether as a pore-forming agent, litchi-like porous micro/nano Cu/Cu₂O composite antibacterial carriers (Car-MNps) with good dispersion and high crystallinity are prepared by a liquid-phase chemical reduction process. Subsequently, we develop a synergistic system of inorganic composite antibacterial materials decorated with silver (Ag/Car-MNps). The microstructures of the antibacterial materials are characterized by means of various techniques, such as X-ray diffraction, scanning electron microscope, transmission electron microscope, X-ray photoelectron spectroscopy, and nitrogen adsorption. The antibacterial activities are evaluated by methods of bacteriostatic zone and minimum inhibitory concentration (MIC). The results show that the micro- and nano-materials of Car-MNPs exhibit high specific surface area characteristics and show attractive bactericidal properties. The MIC values of Ag/Car-MNps against S. aureus and E. coli decrease from 1000 mg/L and 2000mg/L to 125 and 250 mg/L, respectively, in comparison with those of Car-MNps. Our experiments may show novel insights for the development of inorganic compound antibacterial agents.

Fabrication, characterization and U(VI) sorption properties of a novel biochar derived from Tribulus terrestris via two different approaches

Water contamination due to radionuclides is considered a crucial environmental issue. In this study, Tribulus terrestris plant biomass was used as a precursor for obtaining biochar (BC), that was further modified by two different methods using FeCl₃ to obtain two different magnetic biochars. Both (one-step biochar, called 1S-BC, and two-steps biochar, called 2S-BC) were studied to investigate their capability for adsorbing/removing uranium (VI) from aqueous solutions. The U(VI) removal efficacy of both biochars was tested for different values of pH, ionic strength, initial concentration of U(VI) and temperature. Experimental adsorption data fitted well to the Freundlich model (achieving as highest value for adsorption capacity K_F = 49.56 mg g^-1 (mg L^-1)^-1/n, R² = 0.99). Thermodynamic studies revealed that adsorption was endothermic, characterized by inner-sphere complexation, and entropy-driven with a relatively increased randomness in the solid-solution interface. X-ray photoelectron spectroscopy (XPS) revealed that U(VI) sorption took place by surface complexation between U(VI) and oxygen containing functional groups on both biochars. Five consecutive regeneration cycles verified an excellent reusability for 1S-BC. The overall results allow to conclude that the FeCl₃ modification of the biochar obtained from Tribulus terrestris plant biomass could give an efficient alternative adsorbent for U(VI) removal in a variety of environmental conditions, promoting protection of the environment and human health, as well as facilitating resource utilization and sustainable management of the materials studied.

The effect of interconnections on gas adsorption in materials with spherical mesopores: A Monte Carlo simulation study

Gas adsorption is a standard method for measuring pore-size distributions of nanoporous materials. This method is often based on assuming the pores as separate entities of a certain simple shape: slit-like, cylindrical, or spherical. Here, we study the effect of interconnections on gas adsorption in materials with spherical pores, such as three-dimensionally ordered mesoporous (3DOm) carbons. We consider interconnected systems with two, four, and six windows of various sizes. We propose a simple method based on the integration of solid-fluid interactions to take into account these windows. We used Monte Carlo simulations to model argon adsorption at the normal boiling point and obtained adsorption isotherms for the range of systems. For a system with two windows, we obtained a remarkably smooth transition from the spherical to cylindrical isotherm. Depending on the size and number of windows, our system resembles both spherical and cylindrical pores. These windows can drastically shift the point of capillary condensation and result in pore-size distributions that are very different from the ones based on a spherical pore model. Our results can be further used for modeling fluids in a system of interconnected pores using Monte Carlo and density functional theory methods.

Synthesis of Cristobalite Containing Ordered Interstitial Mesopores using Crystallization of Silica Colloidal Crystals

Cristobalite with ordered interstitial dual-sized mesopores was synthesized through the crystallization of silica colloidal crystals composed of monodispersed amorphous silica nanoparticles. An aqueous solution containing both a flux (Na₂ O) and a carbon precursor (an aqueous low-molecular weight phenolic resin) was infiltrated into the interstices of silica colloidal crystals. The organic fraction in the nanocomposite was further polymerized and subsequently carbonized in an Ar flow at 750 °C to reinforce the colloidal crystal structure. The thermal treatment resulted in the crystallization of the colloidal crystals into cristobalite while retaining the porous structure. The cristobalite-carbon nanocomposite was calcined in air to remove the carbon and create interstitial ordered mesopores in the cristobalite. The surfaces of crystalline mesoporous silica are quite different from those of various ordered mesoporous silica with amorphous frameworks; thus, the present findings will be useful for a precise understanding and control of the interfaces between the mesopores and silica networks.

Polymerization Kinetics of Cyanate Ester Confined to Hydrophilic Nanopores of Silica Colloidal Crystals with Different Surface-Grafted Groups

This study investigates the kinetics of confined polymerization of bisphenol E cyanate ester in the nanopores of the three types of silica colloidal crystals that differ in the concentration and acidity of the surface-grafted proton-donor groups. In all three types of pores, the polymerization has released less heat and demonstrated a very similar significant acceleration as compared to the bulk process. Isoconversional kinetic analysis of the differential scanning calorimetry measurements has revealed that the confinement causes not only a dramatic change in the Arrhenius parameters, but also in the reaction model of the polymerization process. The obtained results have been explained by the active role of the silica surface that can adsorb the residual phenols and immobilize intermediate iminocarbonate products by reaction of the monomer molecules with the surface silanols. The observed acceleration has been quantified by introducing a new isoconversional-isothermal acceleration factor Zα,T that affords comparing the process rates at respectively identical conversions and temperatures. In accord with this factor, the confined polymerization is 15-30 times faster than that in bulk.