Use of bacterial binder in repair mortar for micro-crack remediation

Micro-cracks are one of the types of stone deterioration which can propagate and lead to surface detachments and larger cracks in the long run. The present study developed a sustainable and environmentally friendly infill material-biological mortar (BM), as an alternative to conventional approaches. Using a biomineralization approach, this BM was explicitly designed for healing micro-cracks (less than 2 mm) in historic travertines. To this end, the mortar was prepared using a calcifying Bacillus sp. isolated from thermal spring water resources in Pamukkale Travertines (Denizli), stone powder gathered from travertine quarries in the vicinity, and a triggering solution specifically designed to set off calcium carbonate precipitation reaction. After setup, BM was applied to micro-cracks of artificially aged test stones for testing. Scanning electron microscopy revealed calcium carbonate-coated Bacillus sp. bodies in the BM matrix, optical microscopy showed secondary calcite minerals throughout the BM applied micro-cracks, and stereomicroscopy and nanoindentation analyses demonstrated bonding of BM with stone due to microbial calcification activities. Furthermore, BM and original material contact showed a continuous and coherent structure in all samples. Within this context, BM could be considered a promising and alternative approach for the remediation of micro-cracks of historic stones. KEY POINTS: A binder was produced by the MICP of Bacillus sp. Pamukkale. Physical, mineralogical, and nanomechanical characterization demonstrated microbial calcite precipitates in BM. A significant bond was determined between the grains and matrix of BM due to Bacillus sp. calcite production activities.

Lignin-Induced CaCO3 Vaterite Structure for Biocatalytic Artificial Photosynthesis

The vaterite phase of CaCO₃ exhibits unique characteristics, such as high porosity, surface area, dispersivity, and low specific gravity, but it is the most unstable polymorph. Here, we report lignin-induced stable vaterite as a support matrix for integrated artificial photosynthesis through the encapsulation of key active components such as the photosensitizer (eosin y, EY) and redox enzyme (l-glutamate dehydrogenase, GDH). The lignin-vaterite/EY/GDH photobiocatalytic platform enabled the regeneration of the reduced nicotinamide cofactor under visible light and facilitated the rapid conversion of α-ketoglutarate into l-glutamate (initial conversion rate, 0.41 mM h^-1; turnover frequency, 1060 h^-1; and turnover number, 39,750). The lignin-induced vaterite structure allowed for long-term protection and recycling of the active components while facilitating the photosynthesis reaction due to the redox-active lignin. Succession of stability tests demonstrated a significant improvement of GDH's robustness in the lignin-vaterite structure against harsh environments. This work provides a simple approach for solar-to-chemical conversion using a sustainable, integrated light-harvesting system.

Effect of Polymer Nano- and Microparticles on Calcium Carbonate Crystallization

Molecular and macromolecular templates are known to affect the shape, size, and polymorph selectivity on the biomineralization of calcium carbonate (CaCO3). Micro- and nanoparticles of common polymers present in the environment are beginning to show toxicity in living organisms. In this study, the role of plastic nanoparticles in the biomineralization of CaCO3 is explored to understand the ecological impact of plastic pollution. As a model study, luminescent poly(methyl methacrylate) nanoparticles (PMMA-NPs) were prepared using the nanoprecipitation method, fully characterized, and used for the mineralization experiments to understand their influence on nucleation, morphology, and polymorph selectivity of CaCO3 crystals. The PMMA-NPs induced calcite crystal nucleation with spherical morphologies at high concentrations. Microplastic particles collected from a commercial face scrub were also used for CaCO3 nucleation to observe the nucleation of calcite crystals on the particle surface. Microscopic, spectroscopic, and X-ray diffraction data were used to characterize and identify the nucleated crystals. The data presented in this paper add more information on the impact of microplastics on the marine environment.

Minerals in biology and medicine

Natural minerals ('stone drugs') have been used in traditional Chinese medicines for over 2000 years, but there is potential for modern-day use of inorganic minerals to combat viral infections, antimicrobial resistance, and for other areas in need of new therapies and diagnostic aids. Metal and mineral surfaces on scales from milli-to nanometres, either natural or synthetic, are patterned or can be modified with hydrophilic/hydrophobic and ionic/covalent target-recognition sites. They introduce new strategies for medical applications. Such surfaces have novel properties compared to single metal centres. Moreover, 3D mineral particles (including hybrid organo-minerals) can have reactive cavities, and some minerals have dynamic movement of metal ions, anions, and other molecules within their structures. Minerals have a unique ability to interact with viruses, microbes and macro-biomolecules through multipoint ionic and/or non-covalent contacts, with potential for novel applications in therapy and biotechnology. Investigations of mineral deposits in biology, with their often inherent heterogeneity and tendency to become chemically-modified on isolation, are highly challenging, but new methods for their study, including in intact tissues, hold promise for future advances.

The preparation, structure and luminescent properties of Mg–CaCO3:Eu3+ phosphors

Morphology and luminescence properties of Mg–CaCO₃:Eu³⁺ phosphors are found to change with the initial magnesium ion concentration.

Highly Stable and Fine-Textured Hybrid Microspheres for Entrapment of Cosmetic Active Ingredients

This study details the preparation and application of supramolecular host-guest inclusion complexes entrapping biomineralized microspheres for long-term storage and their pH-responsive behavior. The microspheres were assembled using a CaCO₃ synthesis process coupled with cyclodextrin-tetrahydrocurcumin (CD-THC) inclusion complexes, forming fine-textured and mechanically stable hybrid materials. The products were successfully characterized using field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), and particle size analysis (PSA). Various parameters such as the Brunauer-Emmett-Teller (BET) surface area, single point total pore volume, and pore size via adsorption/desorption analysis were also determined. The obtained THC-entrapped hybrid microspheres contained as high as 20 wt % THC loading and were very stable, preserving 90% of the initial concentration over four weeks of storage at different temperatures, largely limiting THC leaching and indicating high stability in a physiological environment. In addition, the pH-responsive release of THC from the hybrid microspheres was observed, showing potential use for application to weakly acidic skin surfaces. To our knowledge, this is the first demonstration of antiaging cosmetic formulation technology using biomineralization based on the co-synthesis of CaCO₃ and CD-THC complexes.

Isotopic fractionation during acid digestion of calcite: A combined ab initio quantum chemical simulation and experimental study

RATIONALE

Carbonate clumped isotope analysis involves the reaction of carbonate minerals with phosphoric acid to release CO₂ for measurement in a gas-source isotope ratio mass spectrometer. Although the clumped isotope proxy is based on the temperature dependence of ¹³ C-¹⁸ O bonding preference in the mineral lattice, which is captured in the product CO₂ , there is limited information on the phosphoric acid reaction mechanism and the magnitude of clumped isotopic fractionation (mass 63 in CO₃ ^2- to mass 47 in CO₂ ) during the acid digestion.

METHODS

We studied the reaction mechanism for the phosphoric acid digestion of calcite using first-principles density functional theory. We identified the transition state structures for each reaction involving different isotopologues and used the corresponding vibrational frequencies in reduced partition function theory to estimate the Δ₄₇ acid fractionation. Experimental Δ₄₇ data were acquired by processing the sample CO₂ gas through the dual-inlet peripheral of a ThermoFinnigan MAT253 isotope ratio mass spectrometer.

RESULTS

We showed that the acid digestion reaction, which results in the formation of CO₂ enriched with ¹³ C-¹⁸ O bonds, began with the protonation of calcium carbonate in the presence of water. Our simulations yielded a relationship between the Δ₄₇ acid fractionation and reaction temperature as Δ₄₇ = -0.30175 + 0.57700 × (10⁵ /T² ) - 0.10791 × (10⁵ /T² )² , with T varying between 298.15 and 383.15 K.

CONCLUSIONS

We propose a reaction mechanism that shows a higher slope (Δ₄₇ acid fractionation vs. 1/T² curve) for the phosphoric acid digestion of calcite than in previous studies. The theoretical estimates from the present and earlier studies encapsulate experimental observations from both "sealed vessel" and "common acid bath" acid digestion methods.

A facile route to the controlled synthesis of β-NaLuF4:Ln3+ (Ln = Eu, Tb, Dy, Sm, Tm, Ho) phosphors and their tunable luminescence properties

Highly uniform and monodisperse β-NaLuF₄:Ln³⁺ (Ln = Eu, Tb, Dy, Sm, Tm, Ho) hexagonal prisms have been synthesized via a facile two-step hydrothermal method without any organic surfactants.

Facile surfactant- and template-free synthesis and luminescence properties of needle-like calcite CaCO3:Eu3+ phosphors

Simulated diagram of the growth process of needle-like CaCO₃:Eu³⁺ particles.