Fei-Fei Chen

One‐Step Synthesis of Silver Nanoparticle‐Decorated Hydroxyapatite Nanowires for the Construction of Highly Flexible Free‐Standing Paper with High Antibacterial Activity

A highly flexible and free-standing paper with high antibacterial activity made from silver nanoparticle (AgNP)-decorated ultralong hydroxyapatite nanowires (HAPNWs) is reported. The HAPNWs@AgNPs nanocomposites were obtained from a facile one-step solvothermal process and utilized for the construction of highly flexible and free-standing inorganic paper through a simple vacuum-filtration procedure. The structure and properties of the HAPNWs@AgNPs paper were characterized in detail. Scanning electron microscope (SEM) and transmission electron microscope (TEM) micrographs show that AgNPs are highly dispersed and stabilized in the nanocomposite and exhibit a narrow particle size distribution. The effects of the concentration of silver nitrate, solvothermal temperature and time on the product were systematically investigated. This method is simple, convenient and reproducible. The as-prepared HAPNWs@AgNPs paper shows long-time sustained silver-ion release, high antibacterial activity against both Gram-negative and Gram-positive bacteria, and good biocompatibility. Overall, this work provides a novel pathway for the preparation of a new type of highly flexible, free-standing and antibacterial inorganic paper made from silver nanoparticle-decorated hydroxyapatite nanowires for various applications, as a promising functional biomaterial.

Hydroxyapatite Nanowires@Metal–Organic Framework Core/Shell Nanofibers: Templated Synthesis, Peroxidase-Like Activity, and Derived Flexible Recyclable Test Paper

The templated synthesis of hydroxyapatite (HAP) nanowires@metal-organic framework (MOF) core/shell nanofibers (named HAP@MIL-100(Fe) nanofibers) is demonstrated. The ultralong hydroxyapatite nanowires are adopted as a hard template for the nucleation and growth of MIL-100(Fe) (a typical MOF) through the layer-by-layer method. The Coulombic and chelation interactions between Ca2+ ions on the surface of the HAP nanowires and the COO- organic linkers of MIL-100(Fe) play key roles in the formation process. The as-prepared, water-stable HAP@MIL-100(Fe) nanofibers exhibit peroxidase-like activity toward the oxidation of different peroxidase substrates in the presence of H2 O2 , accompanied by a clear color change of the solution. Furthermore, a flexible, recyclable HAP@MIL-100(Fe) test paper is prepared successfully by using HAP@MIL-100(Fe) nanofibers as building blocks. A simple, low-cost, and sensitive colorimetric method for the detection of H2 O2 and glucose is established based on the as-prepared, flexible, recyclable HAP@MIL-100(Fe) test paper. More importantly, the HAP@MIL-100(Fe) test paper can be recovered easily for reuse by simply dipping in absolute ethanol for just 30 min, thus showing excellent recyclability. With its combination of advantages such as easy transportation, easy storage and use, rapid recyclability, light weight, and high flexibility, this HAP@MIL-100(Fe) test paper is promising for wide applications in various fields.

Ultralong Hydroxyapatite Nanowires-Based Paper Co-Loaded with Silver Nanoparticles and Antibiotic for Long-Term Antibacterial Benefit

Hydroxyapatite is a kind of biocompatible, environmentally friendly, and versatile inorganic biomaterial. Herein, the preparation of ultralong hydroxyapatite nanowires (HAPNWs)-based antibacterial paper co-loaded with silver nanoparticles (AgNPs) and antibiotic is reported. HAPNWs are used to prepare AgNPs in situ using an aqueous solution containing AgNO3 under the sunlight without added reducing agent at room temperature. Subsequently, ciprofloxacin (CIP) as an antibiotic is loaded on the HAPNWs@AgNPs. The resultant HAPNWs@AgNPs-CIP paper possesses several unique properties, including high flexibility, high Brunauer-Emmett-Teller (BET) specific surface area (47.9 m2 g-1), high drug loading capacity (447.4 mg g-1), good biocompatibility, sustained and pH-responsive drug release behavior (5.40-6.75% of Ag+ ions and 37.7-76.4% of CIP molecules at pH values of 7.4-4.5 at day 8, respectively), and reusable recycling. In the antibacterial tests against Escherichia coli and Staphylococcus aureus, the HAPNWs@AgNPs-CIP paper exhibits large diameters of inhibition zones and low minimum inhibitory concentrations (30 and 40 μg mL-1), revealing the high antibacterial activity. Besides, the consecutive agar diffusion tests (8 cycles), long-term stability tests (over 56 days), and continuous contamination tests (5 cycles) demonstrate the excellent recycling performance and long-term antibacterial activity of the HAPNWs@AgNPs-CIP paper. These results indicate a promising potential of the HAPNWs@AgNPs-CIP bactericidal paper for tackling public health issues related to bacterial infections.

Flexible hydroxyapatite ultralong nanowire-based paper for highly efficient and multifunctional air filtration

Fine particulate matter (PM) air pollution has been attracting much attention due to its great threat to human health. Herein, we report a new kind of air filter paper with high removal efficiencies for PM2.5 and PM10 prepared using ultralong hydroxyapatite (HAP) nanowires and cotton (CT) fibers as building blocks through a simple vacuum filtration process. Flexible and biocompatible ultralong HAP nanowires with lengths over 200 μm and diameters of approximately 20 nm are employed for significant improvement of the air filtration performance of commercial CT fibers. The ultralong HAP nanowires intertwine with CT fibers and form the highly porous HAP/CT air filter paper. In addition, by optimizing the proportion of HAP and CT, the as-prepared HAP/CT air filter paper exhibits high removal efficiencies of over 95% for PM2.5 and PM10; more importantly, it shows a lower pressure drop and a smaller thickness than a commercial breathing mask. Moreover, the fabrication of a large-sized HAP/CT air filter paper with desirable properties through a commercial sheet former is demonstrated. As a proof-of-concept, a homemade breathing mask is fabricated by imbedding the HAP/CT air filter paper into a commercial breathing mask. Furthermore, benefiting from the unique characteristics of ultralong HAP nanowires, other functions such as antibacterial activity can be achieved by the immobilization of silver nanoparticles as the representative bactericide, enabling the fabrication of multifunctional air filter paper. The experimental results suggest that the ultralong HAP nanowire-based air filter paper is promising for various applications in the environmental field.

Binary Strengthening and Toughening of MXene/Cellulose Nanofiber Composite Paper with Nacre-Inspired Structure and Superior Electromagnetic Interference Shielding Properties

With the growing popularity of electrical communication equipment, high-performance electromagnetic interference (EMI) shielding materials are widely used to deal with radiation pollution. However, the large thickness and poor mechanical properties of many EMI shielding materials usually limit their applications. In this study, ultrathin and highly flexible Ti3C2T x (d-Ti3C2T x, MXene)/cellulose nanofiber (CNF) composite paper with a nacre-like lamellar structure is fabricated via a vacuum-filtration-induced self-assembly process. By the interaction between one-dimensional (1D) CNFs and two-dimensional (2D) d-Ti3C2T x MXene, the binary strengthening and toughening of the nacre-like d-Ti3C2T x/CNF composite paper has been successfully achieved, leading to high tensile strength (up to 135.4 MPa) and fracture strain (up to 16.7%), as well as excellent folding endurance (up to 14 260 times). Moreover, the d-Ti3C2T x/CNF composite paper exhibits high electrical conductivity (up to 739.4 S m-1) and excellent specific EMI shielding efficiency (up to 2647 dB cm2 g-1) at an ultrathin thickness (minimum thickness 47 μm). The nacre-inspired strategy in this study offers a promising approach for the design and preparation of the strong integrated and flexible MXene/CNF composite paper, which may be applied in various fields such as flexible wearable devices, weapon equipment, and robot joints.

Hydroxyapatite Nanowire-Based All-Weather Flexible Electrically Conductive Paper with Superhydrophobic and Flame-Retardant Properties

How to survive under various harsh working conditions is a key challenge for flexible electronic devices because their performances are always susceptible to environments. Herein, we demonstrate the novel design and fabrication of a new kind of the all-weather flexible electrically conductive paper based on ultralong hydroxyapatite nanowires (HNs) with unique combination of the superhydrophobic surface, electrothermal effect, and flame retardancy. The superhydrophobic surface with water repellency stabilizes the electrically conductive performance of the paper in water. For example, the electrical current through the superhydrophobic paper onto which water droplets are deposited shows a little change (0.38%), and the electrical performance is steady as well even when the paper is immersed in water for 120 s (just 3.65% change). In addition, the intrinsic electrothermal effect of the electrically conductive paper can efficiently heat the paper to reach a high temperature, for example, 224.25 °C, within 10 s. The synergistic effect between the electrothermal effect and superhydrophobic surface accelerates the melting and removal of ice on the heated electrically conductive paper. Deicing efficiency of the heated superhydrophobic electrically conductive paper is ∼4.5 times that of the unheated superhydrophobic electrically conductive paper and ∼10.4 times that of the heated superhydrophilic paper. More importantly, benefiting from fire-resistant ultralong HNs, thermally stable Ketjen black, and Si-O backbone of poly(dimethylsiloxane), we demonstrate the stable and continuous service of the as-prepared electrically conductive paper in the flame for as long as 7 min. The electrical performance of the electrically conductive paper after flame treatment can maintain as high as 90.60% of the original value. The rational design of the electrically conductive paper with suitable building materials and structure demonstrated here will give an inspiration for the development of new kinds of all-weather flexible electronic devices that can work under harsh conditions.

Luminescent, Fire-Resistant, and Water-Proof Ultralong Hydroxyapatite Nanowire-Based Paper for Multimode Anticounterfeiting Applications

Counterfeiting of valuable certificates, documents, and banknotes is a serious issue worldwide. As a result, the need for developing novel anticounterfeiting materials is greatly increasing. Herein, we report a new kind of ultralong hydroxyapatite nanowire (HAPNW)-based paper with luminescence, fire resistance, and waterproofness properties that may be exploited for anticounterfeiting applications. In this work, lanthanide-ion-doped HAPNWs (HAPNW:Ln3+) with lengths over 100 μm have been synthesized and used as a raw material to fabricating a free-standing luminescent, fire-resistant, water-proof paper through a simple vacuum filtration process. It is interesting to find that the luminescence intensity, structure, and morphology of HAPNW:Ln3+ highly depend on the experimental conditions. The as-prepared HAPNW:Ln3+ paper has a unique combination of properties, such as high flexibility, good processability, writing and printing abilities, luminescence, tunable emission color, waterproofness, and fire resistance. In addition, a well-designed pattern can be embedded in the paper that is invisible under ambient light but viewable as a luminescent color under ultraviolet light. Moreover, the HAPNW:Ln3+ paper can be well-preserved without any damage after being burned by fire or soaked in water. The unique combination of luminescence, fire resistance, and waterproofness properties and the nanowire structure of the as-prepared HAPNW:Ln3+ paper may be exploited toward developing a new kind of multimode anticounterfeiting technology for various high-level security antiforgery applications, such as in making forgery-proof documents, certificates, labels, and tags and in packaging.

Inorganic Nanowires-Assembled Layered Paper as the Valve for Controlling Water Transportation

Layered materials with open interlayer channels enable various applications such as tissue engineering, ionic and molecular sieving, and electrochemical devices. However, most reports focus on the two-dimensional nanosheets-assembled layered materials, whose interlayer spacing is limited at the nanometer scale. Herein, we demonstrate that one-dimensional inorganic nanowires are the ideal building blocks for the construction of layered materials with open interlayer channels as well, which has not aroused much attention before. It is found that the relatively long inorganic nanowires are capable of assembling into free-standing layered paper with open interlayer channels during the filtration process. The spacings of interlayer channels between adjacent layers are up to tens of micrometers, which are much larger than those of the two-dimensional nanosheets-assembled layered materials. But the closed interlayer channels are observed when the relatively short inorganic nanowires are used as building blocks. The mechanism based on the relationship between the structural variation and the nanowires used is proposed, including the surface charge amplified effect, surface charge superimposed effect, and pillarlike supporting effect. According to the proposed mechanism, we have successfully fabricated a series of layered paper sheets whose architectures (including interlayer channels of cross section and pores on the surface) show gradient changes. The as-prepared layered paper sheets are employed as the valves for controlling water transportation. Tunable water transportation is achieved by the synergistic effect between in-plane interlayer channels (horizontal transportation) from the open to the closed states, and through-layer pores (vertical transportation) without surface modification or intercalation of any guest species.

Antibacterial gluey silver–calcium phosphate composites for dentine remineralization

The development of multifunctional dental-restorative biomaterials with antibacterial activity and remineralization effect for damaged tooth repair is urgent since dental caries is still one of the most common tooth diseases in human beings. Herein, we report a facile strategy for the synthesis of gluey silver-calcium phosphate (GSCP) composites using the rapid microwave-assisted solvothermal method. The as-prepared GSCP composite is an organic-inorganic hybrid, and Ag+ ions display a significant influence on the formation of GSCP by interacting with adenosine triphosphate biomolecules. The as-prepared GSCP composite shows good antibacterial properties, in addition, it exhibits a great effect on sheltering dentinal canaliculi and improving the remineralization of dentine in the simulated saliva. The as-prepared GSCP composite is promising for various applications such as oral healthcare, especially, remineralization of dentine, and antibacterial applications.

Ultralong hydroxyapatite nanowire-based layered catalytic paper for highly efficient continuous flow reactions

Herein, we report a new kind of highly flexible hydroxyapatite nanowire (HAPNW)-based layered catalytic paper with a high thermal stability, excellent fire resistance, and high catalytic efficiency for continuous flow catalysis. A simple process has been developed for preparing and loading gold nanoparticles (AuNPs) on the fire-resistant HAPNW paper to obtain the HAPNW/AuNP layered catalytic paper. Oleic acid molecules adsorbed on the surface of HAPNWs can effectively reduce Au(III) ions to Au nanoparticles in situ in aqueous solution in the absence of an additional reducing reagent at room temperature. The size and weight percentage of AuNPs and surface hydrophilicity/hydrophobicity of the HAPNW/AuNP layered catalytic paper can be controlled. Benefiting from the nanoporous network and nanowire-based layered structure, the HAPNW/AuNP layered catalytic paper exhibits high catalytic activity for continuous flow reactions when the aqueous solution flows through the paper. Additionally, the HAPNW/AuNP layered catalytic paper can be easily recycled. Importantly, the HAPNW/AuNP layered catalytic paper shows excellent nonflammable properties and high catalytic stability after heat treatment. The HAPNW/AuNP layered catalytic paper has a high catalytic efficiency (100%), good recyclability, long-term stability, and high thermal stability in the continuous flow catalytic reduction of 4-nitrophenol. Furthermore, the catalytic degradation of organic dyes is also investigated. The HAPNW/AuNP layered catalytic paper is promising for applications in water treatment and high-temperature catalysis. In addition, the fire-resistant HAPNW-based paper can be used as an excellent support for various catalysts to prepare other kinds of catalytic paper for many applications.