Research Article Just accepted
Strong and tough chitin hydrogel constructed by dehydration and rehydration strategy
Nano Research
Available online: 25 May 2024

As a renewable, biocompatible, biodegradable soft material, chitin hydrogels have better advantages in stability, antibacterial activity, antifouling, cost, immunogenicity and so on than most polymer hydrogels. However, compared with other widely used polymer hydrogels with high strength and toughness, the practical applications of chitin-based hydrogels have been limited by their weak mechanical properties, such as cartilage repair and meniscus replacement. Here, we present the design and fabrication of chitin hydrogels with excellent mechanical strength and toughness by a dehydration and rehydration strategy. By sequential dehydration and rehydration processes, the crystalline domains in the chitin hydrogels can be properly controlled. With optimized crystallinity, the elastic modulus of the chitin hydrogels exceeds all previously reported values, and the fracture toughness is even comparable to some synthetic polymer hydrogels, while maintaining a high-water-content of about 80 wt%. At the same water content, the mechanical properties of the chitin hydrogels are positively correlated with the hydrogel crystallinity, which proves that the change of mechanical properties of hydrogels is not simply dependent on weight concentration. The hydrogels can be further strengthened by incorporating other biopolymers that are intrinsically weak, which makes the hydrogels promising for applications in fields such as cartilage repair and meniscus replacement. Moreover, the hydrogels enable loading and release of water-soluble and poorly water-soluble drugs. This highly extendable strengthening and toughening strategy of chitin and chitin-based biopolymer hydrogels paves the way for their widely applications.

Research Article Online first
Iron oxide/CNT-based artificial nacre for electromagnetic interference shielding
Nano Research
Published: 03 April 2024

Biological structural materials, despite consisting of limited kinds of compounds, display multifunctionalities due to their complex hierarchical architectures. While some biomimetic strategies have been applied in artificial materials to enhance their mechanical stability, the simultaneous optimization of other functions along with the mechanical properties via biomimetic designs has not been thoroughly investigated. Herein, iron oxide/carbon nanotube (CNT)-based artificial nacre with both improved mechanical and electromagnetic interference (EMI) shielding performance is fabricated via the mineralization of Fe3O4 onto a CNT-incorporated matrix. The micro- and nano-structures of the artificial nacre are similar to those of natural nacre, which in turn improves its mechanical properties. The alternating electromagnetic wave-reflective CNT layers and the wave-absorptive iron oxide layers can improve the multiple reflections of the waves on the surfaces of the reflection layers, which then allows sufficient interactions between the waves and the absorption layers. Consequently, compared with the reflection-dependent EMI-shielding of the non-structured material, the artificial nacre exhibits strong absorption-dependent shielding behavior even with a very low content of wave-absorptive phase. Owing to the high mechanical stability, the shielding effectiveness of the artificial nacre that deeply cut by a blade is still maintained at approximately 70%−96% depending on the incident wave frequency. The present work provides a new way for designing structural materials with concurrently enhanced mechanical and functional properties, and a path to combine structural design and intrinsic properties of specific materials via a biomimetic strategy.

Research Article Issue
Biomimetic chitin hydrogel via chemical transformation
Nano Research 2024, 17 (2): 771-777
Published: 01 July 2023

Chitin hydrogel has been recognized as a promising material for various biomedical applications because of its biocompatibility and biodegradability. However, the fabrication of strong chitin hydrogel remains a big challenge because of the insolubility of chitin in many solvents and the reduced chain length of chitin regenerated from solutions. We herein introduce the fabrication of chitin hydrogel with biomimetic structure through the chemical transformation of chitosan, which is a water-soluble deacetylated derivative of chitin. The reacetylation of the amino group in chitosan endows the obtained chitin hydrogel with outstanding resistance to swelling, degradation, extreme temperature and pH conditions, and organic solvents. The chitin hydrogel has excellent mechanical properties while retaining a high water content (more than 95 wt.%). It also shows excellent antifouling performance that it resists the adhesion of proteins, bacteria, blood, and cells. Moreover, as the initial chitosan solution can be feasibly frozen and templated by ice crystals, the chitin hydrogel structure can be either nacre-like or wood-like depending on the freezing method of the precursory chitosan solution. Owing to these anisotropic structures, such chitin hydrogel can exhibit anisotropic mechanics and mass transfer capabilities. The current work provides a rational strategy to fabricate chitin hydrogels and paves the way for its practical applications as a superior biomedical material.

Research Article Issue
Modular divergent creation of dual-cocatalysts integrated semiconducting sulfide nanotriads for enhanced photocatalytic hydrogen evolution
Nano Research 2023, 16 (5): 7967-7973
Published: 23 December 2022

Heteronanostructures (HNs) with precise components and interfaces are important for many applications, such as designing efficient and robust solar-to-fuel catalysts via integrating specific semiconductors with favorable band alignments. However, rationally endowing such features with rigorous framework control remains a synthetic bottleneck. Herein, we report a modular divergent creation of dual-cocatalysts integrated semiconducting sulfide nanotriads (NTds), comprising both isolated PdxS oxidation (ox) and MoS2 reduction (red) domains within each single CdS counterpart, which exhibit superior photocatalytic activity and stability for hydrogen evolution reaction (HER). The stepwise constructed PdxS(ox)−CdS−MoS2(red) NTds possess dual-interfaces facilitating continuous charge separation and segregated active sites accelerating redox reactions, respectively, achieving the HER rate up to 9 mmol·h−1·g−1, which is about 60 times higher than that of bare CdS, and show no evidence of deactivation after long-term cycling. This design principle and transformation protocol provide predictable retrosynthetic pathways to HNs with increased degree of complexity and more elaborate functionalities that are otherwise inaccessible.

Research Article Issue
Phase transformation-induced Mg isotope fractionation in Mg-mediated CaCO3 mineralization
Nano Research 2023, 16 (2): 3597-3602
Published: 05 December 2022

The biomineralization of CaCO3 often involves the transformation of amorphous precursors into crystalline phases, which is regulated by various proteins and inorganic ions such as Mg2+ ions. While the effects of Mg2+ ions on the polymorph and shape of the crystalline CaCO3 have been observed and studied, the interplay between Mg2+ ions and CaCO3 during the mineralization remains unclear. This work focuses on the mechanism of Mg2+ ion-regulated mineralization of CaCO3. By tracing the Mg isotope fractionation, the different mineralization pathways of CaCO3 under different Mg2+ ion concentrations had been clarified. Detailed regulatory role of Mg2+ ions at the different stages of mineralization had been proposed through combining the fractionation data with the analyses of the CaCO3 polymorph and shape evolution. These results provide a clear view of the Mg-mediated crystallization process of amorphous CaCO3, which can be used to finely control the phase of the crystalline products according to different needs.

Research Article Issue
Multiscale cellulose-based fireproof and thermal insulation gel materials with water-regulated forms
Nano Research 2023, 16 (2): 3379-3386
Published: 29 November 2022

Different forms of construction materials (e.g., paints, foams, and boards) dramatically improve the quality of life. With the increasing environmental requirements for buildings, it is necessary to develop a comprehensive sustainable construction material that is flexible in application and exhibits excellent performance, such as fireproofing and thermal insulation. Herein, an adjustable multiform material strategy by water regulation is proposed to meet the needs of comprehensive applications and reduce environmental costs. Multiform gels are constructed based on multiscale cellulose fibers and hollow glass microspheres, with fireproofing and thermal insulation. Unlike traditional materials, this multiscale cellulose-based gel can change forms from dispersion to paste to dough by adjusting its water content, which can realize various construction forms, including paints, foams, and low-density boards according to different scenarios and corresponding needs.

Research Article Issue
Nanosheet-coated synthetic wood with enhanced flame-retardancy by vacuum-assisted sonocoating technique
Nano Research 2022, 15 (10): 9440-9446
Published: 26 July 2022

Compared to natural woods, synthetic woods have superior mechanical stability, thermal insulation, and flame retardancy owing to their hierarchically cellular microstructures and intrinsic advantages of the thermosetting matrix. Increasing the long-time fire resistance is very important to the practical application. In this study, we present a novel coating strategy by a vacuum-assisted sonication technique (sonocoating) with a rectorite nanosheet dispersion to create a uniform nanocoating on the channel walls of synthetic wood. Owing to ultrasonic energy and vacuum pressure, the nanosheet dispersion can penetrate deep down to form a layered nanocoating on the channel surface. The coated synthetic woods can withstand fire (400–600 °C) for more than 10 min with 62% mass retainment, surpassing uncoated synthetic woods and natural woods. Therefore, as a lightweight and strong composite with enhanced flame-retardant performance, the coated synthetic woods have huge potential applications in safe and energy-efficient buildings.

Research Article Issue
Bio-inspired synthesis of transition-metal oxide hybrid ultrathin nanosheets for enhancing the cycling stability in lithium-ion batteries
Nano Research 2022, 15 (6): 5064-5071
Published: 08 April 2022

Constructing two-dimensional (2D) structures for transition-metal oxides (TMOs) can optimize their electronic structures and enable high specific surface areas, thereby offering routes to enhancing the performance of TMOs in energy storage and conversion. However, most 2D TMOs, e.g., Fe2O3, remain so far synthetically challenging due to their intrinsic non-layered structures. Herein, inspired by the mechanism of biomineralization, we report the synthesis of CuO/Fe2O3 hybrid ultrathin nanosheets by using polyvinylpyrrolidone-decorated CuO nanosheets as growth modifiers to modulate the hydrolysis process of Fe2+. The formulated “absorption-and-crystallization” two-step formation processes of such 2D hybrid structures accorded well with the biomineralization scheme in nature. Combining the in-situ transmission electron microscopy (TEM) study, theoretical calculation, and control experiments, we validated that the large density of 2D/2D interfaces enabled by this bio-inspired synthesis process can overcome the self-stacking phenomenon during lithium-ion battery cycling, leading to their high operation stability. This work emphasizes the bio-inspired synthesis of 2D TMOs as a promising pathway toward material design and performance optimization.

Editorial Issue
On the occasion of the 80th birthday of Professor Yitai Qian: Celebrating 60 years of innovation in solid-state chemistry and nanoscience
Nano Research 2021, 14 (10): 3337-3342
Published: 25 September 2021

Research Article Issue
Joule-heated carbonized melamine sponge for high-speed absorption of viscous oil spills
Nano Research 2021, 14 (8): 2697-2702
Published: 12 May 2021

Introducing heating function to oil sorbents opens up a new pathway to the fast cleanup of viscous crude oil spills in situ. The oil sorption speed increases with the rise of the temperature, thus oil sorbents with high heating temperature are desirable. Besides, the oil sorbents also need to be produced environment-friendly. Here we present carbonized melamine-formaldehyde sponges (CMSs) that exhibited superior heating performance and the CMSs could be massively fabricated through a non-polluting pyrolysis process. The conductive CMSs could be heated over 300 °C with a low applied voltage of 6.9 V and keep above 250 °C for 30 min in the air without obvious damage. Such high heating performance enabled heating up the oil spills with a high rate of 2.65 °C·s-1 and 14% improvement of oil sorption coefficient compared with the state-of-the-art value. We demonstrated that one joule-heated CMS could continuously and selectively collect viscous oil spills (9,010 mPa·s) 690 times its own weight in one hour. The CMSs will be a highly competitive sorbent material for the fast remediation of future crude oil spills.

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