Substrate−molecule vibronic coupling enhancement, especially the efficient photoinduced charge transfer (PICT), is pivotal to the performance of nonmetal surface-enhanced Raman scattering (SERS) technology. Here, through developing novel two-dimensional (2D) amorphous TiO 2 nanosheets (a-TiO 2 NSs), we successfully obtained an ultrahigh enhancement factor of 1.86 × 10 6 . Utilizing the Kelvin probe force microscopy (KPFM) technology, we found that these 2D a-TiO 2 NSs possessed more positive surface potential than their 2D crystalline counterpart (c-TiO 2 NSs). First-principles density functional theory (DFT) was used to further reveal that the low coordination number of surface Ti atoms and the large amount of surface oxygen defects endowed the 2D a-TiO 2 with high electrostatic potential, which allowed significant charge transfer from the adsorbed molecule to the 2D a-TiO 2 and facilitated the formation of a stable surface charge-transfer (CT) complex. Significantly, comparing with the 2D c-TiO 2 , the smaller band gap and higher electronic density of states (DOS) of the 2D a-TiO 2 effectively enhanced the vibronic coupling of resonances in the substrate−molecule system. The strong vibronic coupling within the CT complex obviously enhanced the PICT resonance and lead to the remarkable SERS activity of a-TiO 2 NSs. To the best of our knowledge, this is the first report on the remarkable SERS activity of 2D amorphous semiconductor nanomaterials, which may bring the cutting edge of development of stable and highly sensitive nonmetal SERS technology.

Tooth enamel, renowned for its high stiffness, hardness, and viscoelasticity, is an ideal model for designing biomimetic materials, but accurate replication of complex hierarchical organization of high-performance biomaterials in scalable abiological composites is challenging. We engineered an enamel analog with the essential hierarchical structure at multiple scales through assembly of amorphous intergranular phase (AIP)–coated hydroxyapatite nanowires intertwined with polyvinyl alcohol. The nanocomposite simultaneously exhibited high stiffness, hardness, strength, viscoelasticity, and toughness, exceeding the properties of enamel and previously manufactured bulk enamel-inspired materials. The presence of AIP, polymer confinement, and strong interfacial adhesion are all needed for high mechanical performance. This multiscale design is suitable for scalable production of high-performance materials.

Two-dimensional (2D) nanomaterials show unique electrical, mechanical, and catalytic performance owing to their ultrahigh surface-to-volume ratio and quantum confinement effects. However, ways to simply synthesize 2D metal oxide nanosheets through a general and facile method is still a big challenge. Herein, we report a generalized and facile strategy to synthesize large-size ultrathin 2D metal oxide nanosheets by using graphene oxide (GO) as a template in a wet-chemical system. Notably, the novel strategy mainly relies on accurately controlling the balance between heterogeneous growth and nucleation of metal oxides on the surface of GO, which is independent on the individual character of the metal elements. Therefore, ultrathin nanosheets of various metal oxides, including those from both main-group and transition elements, can be synthesized with large size. The ultrathin 2D metal oxide nanosheets also show controllable thickness and unique surface chemical state.

To develop next-generation lightweight, high-strength, and tough materials, new materials design strategies must be established. Nacre, consisting of 95 vol.% inorganic plates (CaCO 3) and 5 vol.% organic matrix (protein) in layered arrangements, is famous for its significant increase (three orders of magnitude higher) in toughness compared to monolithic aragonite and has always been the model for the synthesis of high mechanical performance artificial materials. In this review, we primarily introduce the recent studies on the synthesis of nacre-inspired composites with exceptional mechanical properties, including 1D fibers, 2D films, and 3D bulk materials. In addition, design strategies for performance enhancement are summarized based on these studies, and applications of high-performance nacreinspired composites are also discussed. Finally, a critical outlook of the future direction of developing next-generation high mechanical performance nacre-inspired composites is provided.

A novel ternary artificial nacre is developed through a vacuum-assisted filtration method, with reinforced ultrathin amorphous alumina that is grown in situ on the surface of GO. This ternary artificial nacre simultaneously shows exceptional strength and toughness, which have, up to now, been considered to be mutually exclusive. This novel material will play a role in the structuring of future materials.

Inspired by nacre, this is the first time that using the cross-linking of alginate with Ca ions to fabricate organic-inorganic nacre-inspired films we have successfully prepared a new class of Ca ion enhanced montmorillonite (MMT)-alginate (ALG) composites, realizing an optimum combination of high strength (∼280 MPa) and high toughness (∼7.2 MJ m) compared with other MMT based artificial nacre. Furthermore, high temperature performance of the composites (with a maximum strength of ∼170 MPa at 100 °C) along with excellent transmittance, fire retardancy, and unique shape memory response to alcohols could greatly expand the application of the mutilfunctional composites, which are believed to show competitive advantages in transportion, construction, and insulations, protection of a flammable biological material, etc.

Ceramic/polymer composite equipped with 3D interlocking skeleton (3D IL) is developed through a simple freeze-casting method, exhibiting exceptionally light weight, high strength, toughness, and shock resistance. Long-range crack energy dissipation enabled by 3D interlocking structure is considered as the primary reinforcing mechanism for such superior properties. The smart composite design strategy should hold a place in developing future structural engineering materials.

In nacre, the excellent mechanical properties of materials are highly dependent on their intricate hierarchical structures. However, strengthening and toughening effects induced by the buried inorganic-organic interfaces actually originate from various minerals/ions with small amounts, and have not drawn enough attention yet. Herein, we present a typical class of artificial nacres, fabricated by graphene oxide (GO) nanosheets, carboxymethylcellulose (CMC) polymer, and multivalent cationic (M(n+)) ions, in which the M(n+) ions cross-linking with plenty of oxygen-containing groups serve as the reinforcing "evocator", working together with other cooperative interactions (e.g., hydrogen (H)-bonding) to strengthen the GO/CMC interfaces. When compared with the pristine GO/CMC paper, the cross-linking strategies dramatically reinforce the mechanical properties of our artificial nacres. This special reinforcing effect opens a promising route to strengthen and toughen materials to be applied in aerospace, tissue engineering, and wearable electronic devices, which also has implication for better understanding of the role of these minerals/ions in natural materials for the mechanical improvement.