The direct application of heavy metal- and quaternary ammonium-based antibacterial agents can cause inconvenience such as irritation, short-term applicability, discoloration of the tissue, and environmental concerns. The immobilization of these agents on montmorillonite (Mnt) was expected to diminish these effects by hindering direct contact of the ions with the target tissues. The objective of the present study was, therefore, to prepare inorgano(I)- and organo(O)-montmorillonites (I/O-Mnt) and to determine their potential uses in such biomedical applications. Na-montmorillonite (Mnt-Na) was modified by hydrothermal and microwave irradiation methods using Cu2+/Zn2+, and quaternary ammonium and/or anionic surfactants. The effect of the structures formed by immobilization on Mnt surfaces on antibacterial activity was investigated. Quaternary ammonium surfactants were cetyltrimethyl ammonium bromide (CTAB) with a linear alkyl chain, cetylpyridinium chloride (CPC) with a single aromatic ring, and benzethonium chloride (BZT) with double aromatic rings. N-lauroyl sarcosinate (SR) was the anionic surfactant. The samples were subjected to thermogravimetric (TGA) and scanning electron microscopy (SEM) analyses. Desorption tests showed that the antibacterial efficacy against Streptococcus mutans stemmed from I/O-Mnt and not from the ions released from the material surfaces to the aqueous phase. The results of the antibacterial studies showed that the existence of a linear alkyl chain and a double aromatic ring were the structural factors causing the greatest antibacterial effect. The time-kill tests revealed that Mnt-CTA, Mnt-BZT, and Mnt-CP-SR were effective against Streptococcus mutans within 5 min of contact. With the new findings, they were identified as possible selective and potent bactericidal agents and promising candidates for biomedical applications.

Understanding the behavior of secondary minerals under alkaline conditions is important for predicting the potential alteration of the constituent minerals in radioactive-waste disposal facilities. A previous study reported the formation of uncommon Fe- and Mg-bearing clays under natural alkaline conditions in the Philippines; these were referred to as iron-magnesium-silicate-hydrates (F-M-S-H) and nontronite-like minerals. The current study aimed to investigate the structural and chemical characteristics and to understand the formation pathways of these clays by performing a detailed characterization. F-M-S-H comprised tetrahedral–octahedral–tetrahedral (TOT) layers, imperfect interlayer hydroxide sheets, and interlayer Ca ions. The systematic changes in the characteristics of F-M-S-H at different sampling depths, such as the gradual decrease of the interlayer hydroxide sheets to form smectitic domains, were caused by the differing interaction periods between each sediment at different sampling depths and alkaline seepage. Furthermore, F-M-S-H was ferrous in form prior to oxidation. In contrast, a nontronite-like mineral comprised nontronite and part of an interlayer hydroxide sheet. This mineral was inferred to be formed under chemically different conditions from F-M-S-H, and probably formed in the presence of aqueous Fe3+ and Mg ions.

Sulfonated carbon is a green, solid acid catalyst but its surface area, separation, and recovery after utilization need to be improved. The objective of the present study was to provide an environmentally friendly and economical method to prepare magnetic sulfonated carbon composite catalyst with a large surface area using palygorskite (Plg) as the support. A magnetic sulfonated carbon/Fe3O4/Plg composite catalyst was prepared via simultaneous calcination and sulfonation of the mixture of source, p-toluenesulfonic acid (TsOH), and Fe3O4/Plg. Fe3O4 nanoparticles and Plg nanorods were encased by a carbon layer derived from sucrose and TsOH. The composite catalyst exhibited good magnetic properties and high catalytic performance for the esterification of oleic acid with methanol. Oleic acid conversion reached 88.69% after the first catalytic cycle. Plg nanorods replaced sucrose and increased the catalyst’s surface area. The introduction of Fe3O4 nanoparticles improved further the acid content and oleic-acid conversion and achieved 70.31% after five cycles. The catalyst was recycled easily using an external magnetic field and its magnetic property remained unchanged due to the protection of the carbon layer.

Essential oils (including carvacrol, CAR) have been used in the medicinal and health field because of their broad-spectrum antibacterial activities. However, the volatility and pungent odor are still the greatest obstacles to wider application. The purpose of the present study was to address those problems by encapsulating the antibacterial CAR in palygorskite (Plg) by integrating it into Pickering emulsions with complex coacervation. The CAR in Pickering emulsion was formed firstly by stabilization with the CAR-modified Plg; then, the emulsion droplets were embedded and fixed in the microcapsule through the subsequent complex coacervation process, which occurred between the quaternary ammonium salt of chitooligosaccharides (HACC) and sodium alginate (SA) via calcium ions. The microcapsules obtained were characterized by Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The results demonstrated that the microcapsules presented a nearly sphere-like shape with a mean diameter of 3.5 mm but had a porous interior structure. The Plg plays multiple roles in the preparation process, including increasing the emulsion stability, improving the encapsulation efficiency of CAR, and the thermostability of microcapsules. The microcapsules showed remarkable antibacterial properties against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), and inhibition rates toward E. coli and S. aureus reached 100% when the microcapsules were encapsulated with 15 or 20% of CAR, respectively. The microcapsules obtained could be used as antibacterial agents in food preservatives, animal feed, and other health-related consumer products.

The deep regolith of the southeastern United States has undergone rapid erosion in the last two centuries due to intensive agricultural practices, which has altered the landscape and its inherent fertility. Parent material, landscape position, and land use are important factors in controlling the mineral and elemental composition of soil profiles. Independent quantitative X-ray diffraction (QXRD) and whole-rock chemical analysis of eight weathering profiles agreed well and allow mineral reaction pathways to be constrained as particles are conveyed in the subsurface. QXRD analysis of saprolite, argillic, and soil A-horizons in the profiles highlights the imprint of bedrock on the regolith, which includes Neoproterozoic meta-tonalitic to meta-granodioritic and Paleozoic meta-granitic to biotite- and amphibolite-gneissic lithologies. Also, aeolian input slightly influenced A-horizon composition. The clay mineral assemblage is dominated by kaolinite, but profiles differ in the amount of interstratified clay minerals, halloysite, hematite, goethite, and gibbsite. Rare-earth element totals vary between 30 and 1048 ppm and are generally correlated positively with clay and clay mineral content. Eu and Ce anomalies reflect parent rocks and subsequent hydrolysis and redox history, with trends depending upon landscape position and clay content in the weathering profile. Weathering profiles on a high-order interfluve and those that were actively cultivated have thick argillic horizons (as defined by clay mineral abundance) and are depleted in alkali and alkaline-earth elements. Profiles proximally developed on old-field pine and never-cultivated hardwood forest land do not show large differences in mineral composition trends, whereas profiles on old-field sites with ongoing cultivation exhibit assemblages enriched in clay minerals and (oxyhydr)oxides. Old-field pine sites that were historically eroded by previous cultivation tend to have shallower and thinner argillic horizons, which may well impact critical-zone processes involving gas and water fluxes. This study highlights that mineral compositions of deep regolith, saprolite, and shallow soil horizons are dependent on local geomorphology (i.e. watershed- and hillshed-orders). Quantifying soil and regolith compositional trends across the landscape is a prerequisite for determining rates of chemical and physical erosion on human and geologic time scales.

Graphite phase carbon nitride (g-C3N4) is a non-metal semiconductor material with a suitable band gap (2.7 eV) for visible photocatalysis. However, the high cost of relevant synthesis methods and poor adsorption performance have limited its practical applications. The objective of the present study was to mitigate these problems by synthesizing the g-C3N4 in the presence of exfoliated montmorillonite (Mnt). Compared with bulk montmorillonite, the specific surface area of exfoliated two-dimensional Mnt layers was significantly increased. As a result, the light transmittance of the lamella improved noticeably due to the fact that a freshly exposed surface had a large number of active reaction sites, making Mnt an excellent carrier for the photocatalyst g-C3N4. In order to improve the photocatalytic performance of g-C3N4, a series of g-C3N4/Mnt composites was prepared by a wet chemical method using Mnt nanolayers as the matrix. X-ray diffraction, infrared spectroscopy, Brunauer-Emmett-Teller nitrogen adsorption/desorption, transmission electron microscopy, and ultraviolet-visible diffuse reflectance spectroscopy were used to analyze the phase structure, the chemical bonds, the specific surface area and pore sizes, the morphology, and the light absorption characteristics of the composites, respectively. Rhodamine B (RhB) served as the target dye to test the photocatalytic degradation performance of the composites under visible light. According to the findings, the surface of the Mnt nanolayers was densely and uniformly covered by g-C3N4, forming a multi-layered stack structure. An increase of the calcination temperature improved the crystallinity of g-C3N4, leading first to densification and then to relaxation of the layered composite structure. Conversely, the band gap of the composite gradually decreased from 2.56 to 2.4 eV. Furthermore, temperature exposure changed the photocatalytic performance of the composite drastically. While the largest photocatalytic activity was observed at 610°C, it started to decrease with further heating of the composite. The complete degradation of RhB solution occurred after 2 h of visible light irradiation. The findings of the current study provide a scientific basis for the synthesis of a new generation of photocatalysts.

Powder-type semiconductor photocatalysts are widely applicable but their defects (e.g. easy agglomeration during preparation and recyclability in the suspension system) limit their practical application. In the current study, perovskite oxide photocatalytic material was loaded onto a muscovite substrate to overcome the problems of low stability, easy agglomeration, and difficult recovery. A photocatalytically active LaNi0.95Fe0.05O3/muscovite composite material was synthesized by a sol-gel impregnation method. Phase composition, morphology, and interfacial interaction of the composites, denoted as LNFBY-x (x: mass ratio of LNF to muscovite), were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and other analytical methods. According to the results, the particle size of LNF nanoparticles was regulated effectively by compounding with muscovite, and the agglomeration of LNF decreased. LNF nanoparticles were distributed evenly and attached in dense fashion to the surface of muscovite, thereby increasing the contact area with the reaction medium. The nanoparticles were connected to the silicon-oxygen tetrahedral sheet of the muscovite via Si–O–La, Si–O–Ni, and Si–O–Fe bonds, which increased the bonding strength between the composite components and expedited the transfer of photogenerated charge. More highly active oxygen species were produced, and a growing number of chemically active moieties (٠O2- and ٠OH) was generated in the photocatalytic reaction. LNFBY-1.00 demonstrated the best photocatalytic activity. A degradation rate of methyl orange of 99.03% was achieved after visible-light irradiation for 120 min, which decreased to 75.75% after five repeated uses, thereby indicating high stability and recycling ability. The photocatalytic LaNi0.95Fe0.05O3/muscovite composite material exhibited potential for application in environmental remediation practices.

The formation of 2:1 and 1:1 phyllosilicates in Fe–Si–O–H systems occurs in various geological and engineering settings; however, the identification and characterization of these minerals is very challenging due to the limited amount that is accessible, the very small particle size, and often the large degree of heterogeneity of these samples. To overcome these drawbacks, the synthesis of iron-rich phyllosilicates was attempted in this study with an initial Fe/Si molar ratio ranging from 0.50 to 2.33. The synthesis was performed at 150°C under hydrothermal conditions over a period of 7 days. Synthesis products were characterized by X-ray diffraction and fluorescence, by infrared, Raman, and Mössbauer spectroscopies, and by transmission electron microscopy. Results revealed that the stability field of the 2:1 clay mineral was wider than that of the 1:1 clay mineral. The 2:1 clay mineral was less sensitive to redox conditions compared to the 1:1 clay mineral. In addition, a heterogeneity of phases formed (iron oxides, nontronite, cronstedtite, or greenalite) was identified.