Mesocrystalline calcium silicate hydrate: A bioinspired route toward elastic concrete materials

Multi-Layered Calcium Silicate Hydrate-Based Composites: A Nacre-Mimetic Design for Ultra-High Toughness

Cement-based materials are the most extensively utilized artificial material in the world. The low toughness of cementitious materials has long been a significant constraint in the development of modern concrete, limiting its performance in critical infrastructure applications. As the primary hydration product, calcium silicate hydrate (C-S-H) determines the mechanical properties of cementitious materials, in which optimizing C-S-H presents a promising avenue for toughness enhancement. In this work, a nacre-mimetic design strategy is employed to develop a high toughness C-S-H composite, achieved by the arrangement of inorganic C-S-H "brick" alternated with polyvinyl alcohol (PVA) "mortar". The unique hierarchically soft/hard structure significantly improved the mechanical properties of C-S-H composite, showcasing a substantial improvement on tensile strength, ductility and toughness by 1-2 orders of magnitude compared with fiber/polymer reinforced cementitious composites, especially reaching ultra-high toughness (20.01±3.64 MJ m-3), which outperforms nacre by a factor of over ten and exhibits the highest performance among reported C-S-H-based materials. The nacre-mimetic C-S-H composite displayed exquisite interface and toughening mechanism revealed by density functional theory (DFT), molecular dynamics (MD), and finite element method (FEM) simulations. These findings provide a prospect for toughening cement-based materials, and broaden the potential applications in advanced functional composite systems.

Controllable Polymerization of Inorganic Ionic Oligomers for Precise Nanostructural Construction in Materials

The rational design of nanostructures is critical for achieving high-performance materials. The close-packing behavior of inorganic ions and their less controllable nucleation process impede the precise nanostructural construction of inorganic ionic compounds. The discovery of inorganic ionic oligomers (stable molecular-scale inorganic ionic compounds) and their polymerization reaction enables the controllable arrangement of inorganic ions for diverse nanostructures. This perspective aims to introduce inorganic ionic oligomers and their currently identified advantages in the precise design of inorganic and organic-inorganic hybrid nanostructures, directing the development of advanced materials with applications across the mechanical, energy, environmental, and biomedical fields. The challenges and opportunities for the controllable polymerization of inorganic ionic oligomers are presented at the end of this perspective. We suggest that inorganic ionic oligomers and their polymerization reaction offer a promising strategy for the preparation of inorganic and organic-inorganic hybrid materials.

Bio-Informed Porous Mineral-Based Composites

Certain biominerals, such as sea sponges and echinoderm skeletons, display a fascinating combination of mechanical properties and adaptability due to the well-defined structures spanning various length scales. These materials often possess high density normalized mechanical properties because they contain well-defined pores. The density-normalized mechanical properties of synthetic minerals are often inferior because the pores are stochastically distributed, resulting in an inhomogeneous stress distribution. The mechanical properties of synthetic materials are limited by the degree of structural and compositional control currently available fabrication methods offer. In the first part of this review, examples of structural elements nature uses to impart exceptional density normalized Young's moduli to its porous biominerals are showcased. The second part highlights recent advancements in the fabrication of bio-informed mineral-based composites possessing pores with diameters that span a wide range of length scales. The influence of the processing of mineral-based composites on their structures and mechanical properties is summarized. Thereby, it is aimed at encouraging further research directed to the sustainable, energy-efficient fabrication of synthetic lightweight yet stiff mineral-based composites.

A Review on Multi-Scale Toughening and Regulating Methods for Modern Concrete: From Toughening Theory to Practical Engineering Application

Concrete is the most widely used and highest-volume basic material in the word today. Enhancing its toughness, including tensile strength and deformation resistance, can boost the structural load-bearing capacity, minimize cracking, and decrease the amount of concrete and steel required in engineering projects. These advancements are crucial for the safety, durability, energy efficiency, and emission reduction of structural engineering. This paper systematically summarized the brittle characteristics of concrete and the various structural factors influencing its performance at multiple scales, including molecular, nano-micro, and meso-macro levels. It outlines the principles and impacts of concrete toughening and crack prevention from both internal and external perspectives, and discusses recent advancements and engineering applications of toughened concrete. In situ polymerization and fiber reinforcement are currently practical and highly efficient methods for enhancing concrete toughness. These techniques can boost the matrix's flexural strength by 30% and double its fracture energy, achieving an ultimate tensile strength of up to 20 MPa and a tensile strain exceeding 0.6%. In the future, achieving breakthroughs in concrete toughening will probably rely heavily on the seamless integration and effective synergy of multi-scale toughening methods.

Structural studies of calcium silicate hydrate modified with heavy metal cations

This study investigates the immobilization mechanisms of heavy metal ions in the C-S-H phase. Synthetic C-S-H phases were prepared via the precipitation method, incorporating five different ions (Pb(II), Cd(II), Ni(II), Zn(II), and Cr(III)). Structural analysis of the obtained material was conducted using vibrational spectroscopy (both FT-IR and Raman), X-ray photoelectron spectroscopy, and X-ray diffraction. Spectroscopic methods were primarily employed to evaluate the structural effects and polymerization degree of the resulting C-S-H phase. Morphological changes were characterized using scanning and transmission electron microscopy (SEM and TEM, respectively). Our findings reveal several mechanisms for immobilizing heavy metal cations: precipitation of insoluble compounds (particularly notable for Ni(II) and Cr(III)), replacement of Ca(II) ions within the silicate structure (evident in the crystallization of Ca(OH)2 in samples containing Cd(II), Ni(II), and Zn(II) in minimal quantities), and strong bonding of certain metals (such as Pb(II)) with the C-S-H phase structure. These insights contribute to understanding the potential applications of C-S-H phases in heavy metal immobilization.

Assembly-promoted repeatable enhancement of photoluminescence from cesium lead tribromide nanocubes under light illumination

A repeatable enhancement of the photoluminescence (PL) from CsPbBr3 nanocubes (NCs) is promoted by the assembling of NCs. The PL quantum yield (QY) of ordered NC arrays increases with photoirradiation and decreases in the dark. The repeatable enhancement of the PLQY cannot be observed from isolated NCs. The nanospaces between NCs in the ordered arrays allow a reversible change in thermally stimulated desorption and photo-induced adsorption of surface ligands that affect the PLQY.

A review of advancements in humic acid removal: Insights into adsorption techniques and hybrid solutions

Humic acid (HA) is a prominent contaminant in wastewater, and its elimination is crucial to ensure purified drinking water. A variety of sources of HA in wastewater exist, ranging from agricultural runoff, industrial discharges, and natural decomposition. Adsorption is a technique that has been heavily investigated in this direction. The process complexities, technological advancements, and sustainable approaches are discussed in this review. A range of adsorbents can be employed for HA removal, including modified membranes, carbon nanotubes (CNTs), clay nanoparticles, and acid-modified natural materials. This work compares the effectiveness of the preceding adsorbents along with their advantages and limitations. This review also discusses the optimization of various process parameters, such as pH, ionic strength, and temperature, with an emphasis on response surface methodology for process optimization. Furthermore, the challenges and limitations associated with each removal technique are discussed, along with the potential areas for improvement and future directions in the field of wastewater treatment.

Lightweight Calcium-Silicate-Hydrate Nacre with High Strength and High Toughness

Low flexural strength and toughness have posed enduring challenges to cementitious materials. As the main hydration product of cement, calcium silicate hydrate (C-S-H) plays important roles in the mechanical performance of cementitious materials while exhibiting random microstructures with pores and defects, which hinder mechanical enhancement. Inspired by the "brick-and-mortar" microstructure of natural nacre, this paper presents a method combining freeze casting, freeze-drying, in situ polymerization, and hot pressing to fabricate C-S-H nacre with high flexural strength, high toughness, and lightweight. Poly(acrylamide-co-acrylic acid) was used to disperse C-S-H and toughen C-S-H building blocks, which function as "bricks", while poly(methyl methacrylate) was impregnated as "mortar". The flexural strength, toughness, and density of C-S-H nacre reached 124 MPa, 5173 kJ/m3, and 0.98 g/cm3, respectively. The flexural strength and toughness of the C-S-H nacre are 18 and 1230 times higher than those of cement paste, respectively, with a 60% reduction in density, outperforming existing cementitious materials and natural nacre. This research establishes the relationship between material composition, fabrication process, microstructure, and mechanical performance, facilitating the design of high-performance C-S-H-based and cement-based composites for scalable engineering applications.

Elastic constants of biogenic calcium carbonate

Living organisms form complex mineralized composite architectures that perform a variety of essential functions. These materials are commonly utilized for load-bearing purposes such as structural stability and mechanical strength in combination with high toughness and deformability, which are well demonstrated in various highly mineralized molluscan shell ultrastructures. Here, the mineral components provide the general stiffness to the composites, and the organic interfaces play a key role in providing these biogenic architectures with mechanical superiority. Although numerous studies employed state-of-the-art methods to measure and/or model and/or simulate the mechanical behavior of molluscan shells, our understanding of their performance is limited. This is partially due to the lack of the most fundamental knowledge of their mechanical characteristics, particularly, the anisotropic elastic properties of the mineral components and of the tissues they form. In fact, elastic constants of biogenic calcium carbonate, one of the most common biominerals in nature, is unknown for any organism. In this work, we employ the ultrasonic pulse-echo method to report the elasticity tensor of two common ultrastructural motifs in molluscan shells: the prismatic and the nacreous architectures made of biogenic calcite and aragonite, respectively. The outcome of this research not only provides information necessary for fundamental understanding of biological materials formation and performance, but also yields textbook knowledge on biogenic calcium carbonate required for future structural/crystallographic, theoretical and computational studies.

Exploring the Potential of Nonclassical Crystallization Pathways to Advance Cementitious Materials

Understanding the crystallization of cement-binding phases, from basic units to macroscopic structures, can enhance cement performance, reduce clinker use, and lower CO2 emissions in the construction sector. This review examines the crystallization pathways of C-S-H (the main phase in PC cement) and other alternative binding phases, particularly as cement formulations evolve toward increasing SCMs and alternative binders as clinker replacements. We adopt a nonclassical crystallization perspective, which recognizes the existence of critical intermediate steps between ions in solution and the final crystalline phases, such as solute ion associates, dense liquid phases, amorphous intermediates, and nanoparticles. These multistep pathways uncover innovative strategies for controlling the crystallization of binding phases through additive use, potentially leading to highly optimized cement matrices. An outstanding example of additive-controlled crystallization in cementitious materials is the synthetically produced mesocrystalline C-S-H, renowned for its remarkable flexural strength. This highly ordered microstructure, which intercalates soft matter between inorganic and brittle C-S-H, was obtained by controlling the assembly of individual C-S-H subunits. While large-scale production of cementitious materials by a bottom-up self-assembly method is not yet feasible, the fundamental insights into the crystallization mechanism of cement binding phases presented here provide a foundation for developing advanced cement-based materials.

Structural and Mechanical Properties of Doped Tobermorite

As calcium silicate hydrate (C-S-H) is the main binding phase in concrete, understanding the doping behavior of impurity elements in it is important for optimizing the structure of cementitious materials. However, most of the current studies focus on cement clinker, and the doping mechanism of impurity elements in hydrated calcium silicate is not yet fully understood. The hydrated calcium silicate component is complex, and its structure is very similar to that of the tobermorite mineral family. In this study, the effects of three different dopants (Mg, Sr and Ba) on a representing structure of C-S-H-tobermorite-was systematically explored using densify functional theory (DFT) calculations. The calculations show that Mg doping leads to a decrease in lattice volume and causes obvious structure and coordination changes of magnesium-oxygen polyhedra. This may be the reason why high formation energy is required for the Mg-doped tobermorite. Meanwhile, doping only increases the volume of the Sr- and Ba-centered oxygen polyhedra. Specifically, the Mg-doped structure exhibits higher chemical stability and shorter interatomic bonding. In addition, although Mg doping distorts the structure, the stronger chemical bonding between Mg-O atoms also improves the compressive (~1.99% on average) and shear resistance (~2.74% on average) of tobermorillonite according to the elastic modulus and has less effect on the anisotropy of the Young's modulus. Our results suggest that Mg doping is a promising strategy for the optimized structural design of C-S-H.

Multi-layered cement-hydrogel composite with high toughness, low thermal conductivity, and self-healing capability

The inherent quasi-brittleness of cement-based materials, due to the disorder of their hydration products and pore structures, present significant challenges for directional matrix toughening. In this work, a rigid layered skeleton of cement slurry was prepared using a simplified ice-template method, and subsequently flexible polyvinyl alcohol hydrogel was introduced into the unidirectional pores between neighboring cement platelets, resulting in the formation of a multi-layered cement-based composite. A toughness improvement of over 175 times is achieved by the implantation of such hard-soft alternatively layered microstructure. The toughening mechanism is the stretching of hydrogels at the nano-scale and deflections of micro-cracks at the interfaces, which avoid stress concentration and dissipate huge energy. Furthermore, this cement-hydrogel composite also exhibits a low thermal conductivity (around 1/10 of normal cement) and density, high specific strength and self-healing properties, which can be used in thermal insulation, seismic high-rise buildings and long-span bridges.

Organic-inorganic covalent-ionic molecules for elastic ceramic plastic

Although organic-inorganic hybrid materials have played indispensable roles as mechanical^1-4, optical^5,6, electronic^7,8 and biomedical materials^9-11, isolated organic-inorganic hybrid molecules (at present limited to covalent compounds^12,13) are seldom used to prepare hybrid materials, owing to the distinct behaviours of organic covalent bonds¹⁴ and inorganic ionic bonds¹⁵ in molecular construction. Here we integrate typical covalent and ionic bonds within one molecule to create an organic-inorganic hybrid molecule, which can be used for bottom-up syntheses of hybrid materials. A combination of the organic covalent thioctic acid (TA) and the inorganic ionic calcium carbonate oligomer (CCO) through an acid-base reaction provides a TA-CCO hybrid molecule with the representative molecular formula TA₂Ca(CaCO₃)₂. Its dual reactivity involving copolymerization of the organic TA segment and inorganic CCO segment generates the respective covalent and ionic networks. The two networks are interconnected through TA-CCO complexes to form a covalent-ionic bicontinuous structure within the resulting hybrid material, poly(TA-CCO), which unifies paradoxical mechanical properties. The reversible binding of Ca²⁺-CO₃^2- bonds in the ionic network and S-S bonds in the covalent network ensures material reprocessability with plastic-like mouldability while preserving thermal stability. The coexistence of ceramic-like, rubber-like and plastic-like behaviours within poly(TA-CCO) goes beyond current classifications of materials to generate an 'elastic ceramic plastic'. The bottom-up creation of organic-inorganic hybrid molecules provides a feasible pathway for the molecular engineering of hybrid materials, thereby supplementing the classical methodology used for the manufacture of organic-inorganic hybrid materials.

Phage Display Screening as a Rational Approach to Design Additives for Selective Crystallization Control in Construction Systems

The design of additives showing strong and selective interactions with certain target surfaces is key to crystallization control in applied reactive multicomponent systems. While suitable chemical motifs can be found through semi-empirical trial-and-error procedures, bioinspired selection techniques offer a more rationally driven approach and explore a much larger space of possible combinations in a single assay. Here, phage display screening is used to characterize the surfaces of crystalline gypsum, a mineral of broad relevance for construction applications. Based on next-generation sequencing of phages enriched during the screening process, a triplet of amino acids, DYH, is identified as the main driver for adsorption on the mineral substrate. Furthermore, oligopeptides containing this motif prove to exert their influence in a strictly selective manner during the hydration of cement, where the sulfate reaction (initial setting) is strongly retarded while the silicate reaction (final hardening) remains unaffected. In the final step, these desired additive characteristics are successfully translated from the level of peptides to that of scalable synthetic copolymers. The approach described in this work demonstrates how modern biotechnological methods can be leveraged for the systematic development of efficient crystallization additives for materials science.

Bioinspired Super Thermal Insulating, Strong and Low Carbon Cement Aerogel for Building Envelope

The energy crisis has arisen as the most pressing concern and top priority for policymakers, with buildings accounting for over 40% of global energy consumption. Currently, single-function envelopes cannot satisfy energy efficiency for next-generation buildings. Designing buildings with high mechanical robustness, thermal insulation properties, and more functionalities has attracted worldwide attention. Further optimization based on bioinspired design and material efficiency improvement has been adopted as effective approaches to achieve satisfactory performance. Herein, inspired by the strong and porous cuttlefish bone, a cement aerogel through self-assembly of calcium aluminum silicate hydrate nanoparticles (C-A-S-H, a major component in cement) in a polymeric solution as a building envelop is developed. The as-synthesized cement aerogel demonstrates ultrahigh mechanical performance in terms of stiffness (315.65 MPa) and toughness (14.68 MJ m^-3 ). Specifically, the highly porous microstructure with multiscale pores inside the cement aerogel greatly inhibits heat transfer, therefore achieving ultralow thermal conductivity (0.025 W m^-1 K^-1 ). Additionally, the inorganic C-A-S-H nanoparticles in cement aerogel form a barrier against fire for good fire retardancy (limit oxygen index, LOI ≈ 46.26%, UL94-V0). The versatile cement aerogel featuring high mechanical robustness, remarkable thermal insulation, light weight, and fire retardancy is a promising candidate for practical building applications.

Construction of Millimeter-Wide Monolayers of Ordered Nanocubes as a Stain of "Wineglass Tears" Driven by the Marangoni Flow

We constructed millimeter-wide monolayers consisting of tetragonally ordered BaTiO₃ (BT) nanocubes through the liquid film formation caused by the Marangoni flow in a toluene-hexane binary liquid containing oleic acid. A thin liquid film containing BT nanocubes was overspread on a standing silicon substrate through the condensation of toluene at the advancing front after the preferential evaporation of hexane. Then, the oscillatory droplet formation like "wineglass tears" occurred on the substrate. Finally, two-dimensionally ordered BT nanocubes were observed as a stain of "wineglass tears" on the substrate after the liquid film receded through evaporation. The presence of a thin liquid film in the binary system is essential for the production of millimeter-wide monolayers on the substrate because multilayer deposition occurs without the formation of a thin liquid film in monocomponent systems. We improved the regularity of the ordered arrays of nanocubes by adjusting the liquid component and evaporation conditions.

Matrix-Directed Mineralization for Bulk Structural Materials

Mineral-based bulk structural materials (MBSMs) are known for their long history and extensive range of usage. The inherent brittleness of minerals poses a major problem to the performance of MBSMs. To overcome this problem, design principles have been extracted from natural biominerals, in which the extraordinary mechanical performance is achieved via the hierarchical organization of minerals and organics. Nevertheless, precise and efficient fabrication of MBSMs with bioinspired hierarchical structures under mild conditions has long been a big challenge. This Perspective provides a panoramic view of an emerging fabrication strategy, matrix-directed mineralization, which imitates the in vivo growth of some biominerals. The advantages of the strategy are revealed by comparatively analyzing the conventional fabrication techniques of artificial hierarchically structured MBSMs and the biomineral growth processes. By introducing recent advances, we demonstrate that this strategy can be used to fabricate artificial MBSMs with hierarchical structures. Particular attention is paid to the mass transport and the precursors that are involved in the mineralization process. We hope this Perspective can provide some inspiring viewpoints on the importance of biomimetic mineralization in material fabrication and thereby spur the biomimetic fabrication of high-performance MBSMs.

Self-Assembly of Colloidal Nanocrystals into 3D Binary Mesocrystals

ConspectusBiominerals are unique materials found in many living organisms that often display outstanding functionalities attributed to their mesocrystalline structure. Mesocrystals are nanocrystal superstructures with mutual crystallographic alignment of the building units. One could thus imagine these optimized evolutionary systems as archetypes to fabricate advanced materials. The main advantage of such systems relies on their ability to combine the features of the nanocrystals with those of single crystalline microscopic structures, yielding assemblies with directional, enhanced, and potentially emergent properties. Moreover, fueled by the promises of multifunctional materials with unprecedented and tunable properties, the rational design of mesocrystals assembled from two distinct colloidal nanocrystal ensembles has become a recent focus of research. However, the combination of dissimilar nanocrystals into ordered binary superstructures is still a major scientific challenge due to the nature of the coassembly process.We focus this Account on the growth of tridimensional (3D) binary mesocrystals and the understanding of the self-assembly of two colloidal nanocrystal ensembles with the ultimate goal to serve as a basis for more rational mesocrystal syntheses in the future. The formation of mesocrystals demands nanocrystals with defined surface faceting, the primary factor influencing their oriented self-assembly. Notably, such a process cannot be successfully afforded without functionalized nanocrystals with high and, in many cases, tunable colloidal stability. Besides, the nature and solvation degree of the surface ligand shell influences the effective shape of the nanocrystals and the kinetics of self-assembly. If the assembly is triggered by reducing the colloidal stability with nonsolvents, 3D single-component mesocrystals are often grown. Here, the different magnitude of the van der Waals attraction forces between nanocrystals with differing compositions, dimensions, and morphologies generally favors the segregation and growth of single component mesocrystals. This phenomenon was illustrated during the successful preparation of 3D binary mesocrystals composed of iron oxide and platinum nanocubes. Although the building blocks possessed comparable sizes and were stabilized by similar ligands, the amount of the second component could only be arbitrarily tuned up to some extent, even when the assembly conditions were rationally optimized to achieve 3D binary mesocrystals. Only a small amount of it was effectively incorporated into the matrix of the initial mesocrystal. The 3D binary mesocrystal growth process demands a delicate control over the size, shape, and surface chemistry of the nanocrystals, the solvent nature, and the self-assembly process. Hence, the improvement of our ability to control the synthesis of 3D binary mesocrystalline materials is critical to exploit their potential toward technological applications in catalysis, energy storage, or structural materials.

Biomaterials and Bioactive Natural Products from Marine Invertebrates: From Basic Research to Innovative Applications

Aquatic invertebrates are a major source of biomaterials and bioactive natural products that can find applications as pharmaceutics, nutraceutics, cosmetics, antibiotics, antifouling products and biomaterials. Symbiotic microorganisms are often the real producers of many secondary metabolites initially isolated from marine invertebrates; however, a certain number of them are actually synthesized by the macro-organisms. In this review, we analysed the literature of the years 2010–2019 on natural products (bioactive molecules and biomaterials) from the main phyla of marine invertebrates explored so far, including sponges, cnidarians, molluscs, echinoderms and ascidians, and present relevant examples of natural products of interest to public and private stakeholders. We also describe omics tools that have been more relevant in identifying and understanding mechanisms and processes underlying the biosynthesis of secondary metabolites in marine invertebrates. Since there is increasing attention on finding new solutions for a sustainable large-scale supply of bioactive compounds, we propose that a possible improvement in the biodiscovery pipeline might also come from the study and utilization of aquatic invertebrate stem cells.

Dynamic diffusion and precipitation processes across calcium silicate membranes

HYPOTHESIS

Chemical gardens are tubular inorganic structures exhibiting complex morphologies and interesting dynamic properties upon ageing, with coupled diffusion and precipitation processes keeping the systems out of equilibrium for extended periods of time. Calcium-based silica gardens should comprise membranes that mimic the microstructures occurring in ordinary Portland cement and/or silicate gel layers observed around highly reactive siliceous aggregates in concrete.

EXPERIMENTS

Single macroscopic silica garden tubes were prepared using pellets of calcium chloride and sodium silicate solution. The composition of the mineralized tubes was characterized by means of various ex-situ techniques, while time-dependent monitoring of the solutions enclosed by and surrounding the membrane gives insight into the spatiotemporal distribution of the different ionic species. The latter data reflect transport properties and precipitation reactions in the system, thus allowing its complex dynamic behavior to be resolved.

FINDINGS

The results show that in contrast to the previously studied cases of iron- and cobalt-based silica gardens, the formed calcium silicate membrane is homogeneous and ultimately becomes impermeable to all species except water, hydroxide and sodium ions, resulting in the permanent conservation of considerable concentration gradients across the membrane. The insights gained in this work may help elucidate the nature and mechanisms of ion diffusion in Portland cements and concrete, especially those occurring during initial hydration of calcium silicates and the so-called alkali-silica reaction (ASR), one of the major concrete deterioration mechanisms causing serious problems with respect to the durability of concrete and the restricted use of many potential sources of raw materials.

Liquid-Liquid Phase Separation in Nucleation Process of Biomineralization

Biomineralization is a typical interdisciplinary subject attracting biologists, chemists, and geologists to figure out its potential mechanism. A mounting number of studies have revealed that the classical nucleation theory is not suitable for all nucleation process of biominerals, and phase-separated structures such as polymer-induced liquid precursors (PILPs) play essential roles in the non-classical nucleation processes. These structures are able to play diverse roles biologically or pathologically, and could also give inspiring clues to bionic applications. However, a lot of confusion and dispute occurred due to the intricacy and interdisciplinary nature of liquid precursors. Researchers in different fields may have different opinions because the terminology and current state of understanding is not common knowledge. As a result, our team reviewed the most recent articles focusing on the nucleation processes of various biominerals to clarify the state-of-the-art understanding of some essential concepts and guide the newcomers to enter this intricate but charming field.

Characterization of Calcium Silicate Hydrate Gels with Different Calcium to Silica Ratios and Polymer Modifications

Calcium silicate hydrate (CSH) gels, the main binding phases of hydrated cement, are the most widely utilized synthetic materials. To understand the influences of composition and polymers on the reaction kinetics and phase formation, CSH gels with varying Ca/Si ratios and amounts of poly (acrylamide-co-acrylic acid) partial sodium salt (PAAm-co-PAA) were synthesized via a direct method. The CSH gels were characterized through isothermal calorimetry, thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and Raman spectroscopy at different ages. By increasing the Ca/Si ratio from 0.8 to 1.0, the formation of CSH was enhanced with a 5.4% lower activation energy, whereas the incorporation of PAAm-co-PAA increased the temperature sensitivity of the reactions with an 83.3% higher activation energy. In the presence of PAAm-co-PAA, the reaction rate was retarded at an early age and the negative impact faded over time. The results of an XRD analysis indicated the formation of tobermorite as the main phase of the CSH gels, while the addition of PAAm-co-PAA resulted in a postponed calcium hydroxide consumption and CSH formation, which was confirmed by the decreased FTIR intensity of the C=O bond, Si–O stretching and Si–O bonds. The increased Raman vibrations of Si–O–Si bending Q², Ca–O bonds, O–Si–O and asymmetric bending vibrations of SiO₄ tetrahedra in the presence of PAAm-co-PAA indicate the intercalation of the polymeric phase and internal deformation of CSH gels.

Uniaxial tensile deformation and fracture process of structures forming by unsaturated intercalation of amine molecule into C-S-H gel

The application of cement-based materials in engineering requires the understanding of their characteristics and subsequent deformation and fracture process of C-S-H gel in service. In this work, three types of amine molecules including tetraethylenepentamine (TEPA), polyacrylamide (PAM), and triethanolamine (TEA) were intercalated into C-S-H gel in an unsaturated status successfully. Systematical analysis was performed on the structures and properties for both C-S-H gel and corresponding amine molecules/C-S-H gel. It was found that the unsaturated intercalation of amine molecules into C-S-H gel plays a key role in the geometry and therein density of nanocomposites. Subsequently, radial distribution function (RDF), time-correlated function (TCF), and mean square displacement (MSD) were applied to characterize the structure and dynamic information of the as-generated nanocomposites, demonstrating the occurrence of interaction between amine molecules with Ca-Si layer and acceleration of water diffusion by unsaturated intercalation of amine molecules into the interlayer region in C-S-H gel. Finally, the deformation and fracture process of C-S-H gel and amine molecules/C-S-H gel under uniaxial tensile loads were given by molecular dynamics simulation. It was indicated that the tangent modulus of nanocomposites demonstrates a strain-softening nature, indicating a visco-elastic behavior. The breakage of Ca-O bonds and hydrogen bonds dominates the fracture of C-S-H gel. Weak interaction for TEPA/C-S-H gel or TEA/C-S-H gel leads to a decreased tensile strength. Local stress concentration in other interlayer region governs the deformation and fracture process in spite of the formation of strong interaction between double bonded polar oxygen atoms in PAM molecules and Ca atoms in C-S-H gel.

Oriented attachment and aggregation as a viable pathway to self-assembled organic/inorganic hybrid materials

The intrinsic particle-based mechanisms of calcium sulfate crystallisation are exploited to incorporate specific organic polymers in the emerging mineral phase and thus obtain biomimetic organic/inorganic hybrid structures via self-organisation.

Investigation on Variables Contributing to the Synthesis of C-S-H/PCE Nanocomposites by Co-Precipitation Method

The usage of nanoscale calcium silicate hydrate (nano C-S-H) proved to have an excellent promotion effect on the early performance of concrete as nano C-S-H with ultra-fine particle size can act as seeding for cement hydration. Therefore, it is of importance to tune the particle size during the synthesis process of nano C-S-H. In this paper, the influence of several variables of the particle size distribution (PSD) of nano C-S-H synthesized by chemical co-precipitation method with the aid of polycarboxylate (PCE) was studied by orthogonal experimental design. In addition, the composition, microstructure, and morphology of the C-S-H/PCE nanocomposites were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectrum. The results showed that the concentration of reactants had a significant impact on the PSD of C-S-H/PCE nanocomposites, followed by the dosage of dispersant. Ultrasonic treatment was effective in breaking the C-S-H/PCE aggregates with unstable agglomeration structures. The change in synthetic variables had a negligible effect on the composition of the C-S-H/PCE nanocomposites but had a significant influence on the crystallinity and morphology of the composites.

Regenerated isotropic wood

Construction of sustainable high-performance structural materials is a core part of the key global sustainability goal. Many efforts have been made in this field; however, challenges remain in terms of lowering costs by using all-green basic building blocks and improving mechanical properties to meet the demand of practical applications. Here, we report a robust and efficient bottom-up strategy with micro/nanoscale structure design to regenerate an isotropic wood from natural wood particles as a high-performance sustainable structural material. Regenerated isotropic wood (RGI-wood) exceeds the limitations of the anisotropic and inconsistent mechanical properties of natural wood, having isotropic flexural strength of ∼170 MPa and flexural modulus of ∼10 GPa. RGI-wood also shows superior water resistance and fire retardancy properties to natural pine wood. Mass production of large sized RGI-wood and functional RGI-wood nanocomposites can also be achieved.

Cement Interfaces: Current Understanding, Challenges, and Opportunities

Cement and concrete are rapidly growing in demand and pose many unresolved chemistry questions at particle interfaces, during hydration reactions, regarding the role of electrolytes and organic additives. Solutions through developing greener, more sustainable formulations are needed to reduce the high carbon footprint that amounts to 11% of global CO₂ emissions. Cement is a multiphase material composed of calcium silicates, aluminates, and other mineral phases, produced from natural and low-cost industrial sources, which undergoes complex hydration reactions. This perspective highlights current research challenges and opportunities for new chemistry insight, including intriguing colloid and interface science problems that involve mineral surfaces, electrolytes, polymers, and hydration reactions. Specifically, we discuss (1) characteristics of cement phases, supplementary cementitious materials, and other constituents, (2) hydration reactions and the characterization by imaging and NMR spectroscopy, (3) the structure of hydrated cement phases including calcium-silicate-hydrates at different scales, (4) quantitative simulation techniques from the atomic scale to microscale kinetic models, and (5) the function of organic additives. Focusing on new directions, we explain the benefits of integrating knowledge from inorganic chemistry, acid-base chemistry, polymer chemistry, reaction mechanisms, and theory to describe mesoscale cement properties and bulk properties upon manufacturing.

Structure, Fractality, Mechanics and Durability of Calcium Silicate Hydrates

Cement-based materials are widely utilized in infrastructure. The main product of hydrated products of cement-based materials is calcium silicate hydrate (C-S-H) gels that are considered as the binding phase of cement paste. C-S-H gels in Portland cement paste account for 60–70% of hydrated products by volume, which has profound influence on the mechanical properties and durability of cement-based materials. The preparation method of C-S-H gels has been well documented, but the quality of the prepared C-S-H affects experimental results; therefore, this review studies the preparation method of C-S-H under different conditions and materials. The progress related to C-S-H microstructure is explored from the theoretical and computational point of view. The fractality of C-S-H is discussed. An evaluation of the mechanical properties of C-S-H has also been included in this review. Finally, there is a discussion of the durability of C-S-H, with special reference to the carbonization and chloride/sulfate attacks.

Wood-Inspired Cement with High Strength and Multifunctionality

Taking lessons from nature offers an increasing promise toward improved performance in man-made materials. Here new cement materials with unidirectionally porous architectures are developed by replicating the designs of natural wood using a simplified ice-templating technique in light of the retention of ice-templated architectures by utilizing the self-hardening nature of cement. The wood-like cement exhibits higher strengths at equal densities than other porous cement-based materials along with unique multifunctional properties, including effective thermal insulation at the transverse profile, controllable water permeability along the vertical direction, and the easy adjustment to be water repulsive by hydrophobic treatment. The strengths are quantitatively interpreted by discerning the effects of differing types of pores using an equivalent element approach. The simultaneous achievement of high strength and multifunctionality makes the wood-like cement promising for applications as new building materials, and verifies the effectiveness of wood-mimetic designs in creating new high-performance materials. The simple fabrication procedure by omitting the freeze-drying treatment can also promote a better efficiency of ice-templating technique for the mass production in engineering and may be extended to other material systems.

Bio-Inspired Lotus-Fiber-like Spiral Hydrogel Bacterial Cellulose Fibers

Hydrogel materials with high water content and good biocompatibility are drawing more and more attention now, especially for biomedical use. However, it still remains a challenge to construct hydrogel fibers with enough strength and toughness for practical applications. Herein, we report a bio-inspired lotus-fiber-mimetic spiral structure hydrogel bacterial cellulose fiber with high strength, high toughness, high stretchability, and energy dissipation, named biomimetic hydrogel fiber (BHF). The spiral-like structure endows BHF with excellent stretchability through plastic deformation and local failure, assisted by the breaking-reforming nature of the hydrogen bonding network among cellulose nanofibers. With the high strength, high stretchability, high energy dissipation, high hydrophilicity, porous structure, and excellent biocompatibility, BHF is a promising hydrogel fiber for biomedicine. The outstanding stretchability and energy dissipation of BHF allow it to absorb energy from the tissue deformation around a wound and effectively protect the wound from rupture, which makes BHF an ideal surgical suture.

Bio-inspired mineral fluorescent hydrogels cross-linked by amorphous rare earth carbonates

The bio-inspired mineral plastic hydrogel based on calcium carbonate and polyacrylic acid has been recently investigated as a promising sustainable material. Here we report that rare earth carbonates can act as cross-linkers to fabricate analogous hydrogels and provide remarkable optical properties.

Hydration Properties and Interlayer Organization in Synthetic C-S-H

Water in calcium silicate hydrate (C-S-H) is one of the key parameters driving the macroscopic behavior of cement materials for which water vapor partial pressure has an impact on Young's modulus and the volumic properties. Several samples of C-S-H with a bulk Ca/Si ratio ranging between 0.6 and 1.6 were characterized to study their dehydration/hydration behavior under water-controlled conditions using²⁹Si NMR, water adsorption volumetry, X-ray diffraction, and Fourier-transform near-infrared diffuse reflectance under various water pressures. Coherent with several previous studies, it was observed that an increase in the Ca/Si ratio is due to the progressive omission of Si bridging tetrahedra, with the resulting charge being compensated for by interlayer Ca, and that water conditioning influences the layer-to-layer distance and the achieved NMR spectral resolution. Water desorption experiments exhibit one step toward low relative pressure, accompanied by a decrease in the layer-to-layer distance. When sufficient energy is provided to the system (T ≥ 40 °C under vacuum) to remove the interlayer water, the shrinkage/swelling is partially reversible in our experimental conditions. A change in layer-to-layer distance of less than 3 Å is measured in the C-S-H between the wet and dried states. When the bridging SiO₂ tetrahedra are omitted, interlayer Ca interacts with layer O and water interacts with the cations and potentially with the surfaces. This structural organization is interpreted as a mid-plane monolayer of water in the interlayer space, this latter accounting for about 30% of the volume of C-S-H particles.

Lightweight, tough, and sustainable cellulose nanofiber-derived bulk structural materials with low thermal expansion coefficient

Sustainable structural materials with light weight, great thermal dimensional stability, and superb mechanical properties are vitally important for engineering application, but the intrinsic conflict among some material properties (e.g., strength and toughness) makes it challenging to realize these performance indexes at the same time under wide service conditions. Here, we report a robust and feasible strategy to process cellulose nanofiber (CNF) into a high-performance sustainable bulk structural material with low density, excellent strength and toughness, and great thermal dimensional stability. The obtained cellulose nanofiber plate (CNFP) has high specific strength [~198 MPa/(Mg m-3)], high specific impact toughness [~67 kJ m-2/(Mg m-3)], and low thermal expansion coefficient (<5 × 10-6 K-1), which shows distinct and superior properties to typical polymers, metals, and ceramics, making it a low-cost, high-performance, and environmental-friendly alternative for engineering requirement, especially for aerospace applications.

Nanoengineering Microstructure of Hybrid C-S-H/Silicene Gel

Two-dimensional (2D) materials have been incorporated into calcium silicate hydrate (C-S-H) gel to enhance its mechanical performance for decades, while the modified C-S-H gel exhibits poor toughness, tensile strength, and ductility. In this work, we report a new design strategy and synthesis route to strengthen C-S-H interface by intercalating a silicene sheet of one atom thickness. The hybrid C-S-H/Silicene gel shows superb mechanical properties, with a remarkable enhancement in strength and other functional properties. By using density functional theory (DFT) and molecular dynamics (MD) simulations, we have demonstrated that Si-O bonds between silicene and C-S-H are stable and covalent, and the interaction energy of this bilayer gel nearly doubles by forming a 3D covalent network with a strong bridging effect. Owing to its better crystallinity enrichment and its induced dislocation dissipation mechanism, the hybrid C-S-H/Silicene gel possesses a higher tensile ductility (∼118% average enhancement and ∼228% in the c direction) and a much smaller elastic stiffness (59.04 GPa for average Young's modulus). This work offers an ingenuous route in turning brittle C-S-H gel into a soft gel, which provides opportunities for fabricating ultrahigh performance cementitious materials.

Nonclassical Nucleation and Crystallization

Nucleation and growth are of uttermost importance for crystallization since they determine the structure, shape, and properties of a crystal [...]

Monte Carlo Molecular Modeling of Temperature and Pressure Effects on the Interactions between Crystalline Calcium Silicate Hydrate Layers

The interactions of calcium silicate hydrates with water are at the heart of critical features of cement-based material behavior such as drying and autogenous shrinkage, hysteresis, creep, and thermal expansion. In this article, the interactions between nanocrystalline layers of calcium silicate hydrates are computed from grand canonical Monte Carlo molecular simulations. The effects of temperature, chemical potential, and pressure on these interactions are studied. The results are compared with simulation and experimental data found in the literature concerning surface energy, cohesive pressure, and out-of-plane elastic properties. The disjoining pressure isotherms of calcium silicate hydrates are negligibly affected by changes in water pressure under saturated conditions. The surface energy decreases with the temperature, the chemical potential of water, and the water pressure. Coarse-grained simulations are performed using the potential of mean force obtained at the molecular level. The mesostructure presents hysteresis with respect to mechanical and thermal loads. The anharmonicity of the interactions identified at the molecular scale translates to an asymmetry tension/compression and thermal expansion that are also observed at the mesoscale. These results leave room for a better understanding of the multiscale origin of physical properties of calcium silicate hydrates.

Enhanced oxide-ion conductivity of solid-state electrolyte mesocrystals

Oxide ion-conducting porous films were produced on a substrate by evaporation-induced self-assembly of rare earth-doped CeO2 (REDC) nanocubes 4-5 nm in size and subsequent mild calcination at 400 °C. Mesocrystalline structures comprising iso-oriented REDC nanocubes were formed by ordered assembly based on strict attachment of their {100} faces. Enhanced oxide-ion conductivities in a temperature range of 250-350 °C were observed on the mesocrystalline films consisting of Sm-doped CeO2 (SDC) nanocubes. The specific electrical properties of the mesocrystalline films are ascribed to improved surface-ion conduction due to a large specific surface area and a high crystallographic connectivity of SDC nanocubes.

Evaporation-driven manipulation of nanoscale brickwork structures for the design of 1D, 2D, and 3D microarrays of rectangular building blocks

As children play with wooden building blocks, we would like to construct elaborate architectures through the one-by-one accumulation of nanocrystals.

Synthetic Multifunctional Graphene Composites with Reshaping and Self-Healing Features via a Facile Biomineralization-Inspired Process

Since graphene is a type of 2D carbon material with excellent mechanical, electrical, thermal, and optical properties, the efficient preparation of graphene macroscopic assemblies is significant in the potentially large-scale application of graphene sheets. Conventional preparation methods of graphene macroscopic assemblies need strict conditions, and, once formed, the assemblies cannot be edited, reshaped, or recycled. Herein, inspired by the biomineralization process, a feasible approach of shapeable, multimanipulatable, and recyclable gel-like composite consisting of graphene oxide/poly(acrylic acid)/amorphous calcium carbonate (GO-PAA-ACC) is designed. This GO-PAA-ACC material can be facilely synthesized at room temperature with a cross-linking network structure formed during the preparation process. Remarkably, it is stretchable, malleable, self-healable, and easy to process in the wet state, but tough and rigid in the dried state. In addition, these two states can be readily switched by adjusting the water content, which shows recyclability and can be used for 3D printing to form varied architectures. Furthermore, GO-PAA-ACC can be functionalized or processed to meet a variety of specific application requirements (e.g., energy-storage, actuators). The preparation method of GO-PAA-ACC composite in this work also provides a novel strategy for the versatile macroscopic assembly of other materials, which is low-cost, efficient, and convenient for broad application.

Elastic Response of Cementitious Gels to Polycation Addition

The high compressive strength of cementitious materials stems from the creation of a percolated network of calcium silicate hydrate (C-S-H) nanoparticles glued together by strong Ca2+-Ca2+ correlation forces. Although strong, the ion correlation force is short range and yields poor elastic properties (elastic limit and resilience). Here, the use of polycations to partially replace Ca2+ counterions and enhance the resilience of cementitious materials is reported. Adsorption isotherms, electrophoretic mobility, as well as small angle X-ray scattering and dynamic rheometry measurements, are performed on C-S-H gels, used as nonreactive models of cementitious systems, in the presence of different linear and branched polycations for various electrostatic coupling, that is, surface charge densities (pH) and Ca2+ concentrations. The critical strain of the C-S-H gels was found to be improved by up to 1 order of magnitude as a result of bridging forces. At high electrostatic coupling (real cement conditions), only branched polycations are found to improve the deformation at the elastic limit. The results were corroborated by Monte Carlo simulations.