Growth of NiCo₂O₄@MnMoO₄ Nanocolumn Arrays with Superior Pseudocapacitor Properties

Three-dimensional heterostructured NiCo₂O₄@MnMoO₄ nanocolumn arrays (NCAs) on Ni foam were first fabricated through an improved two-step hydrothermal process associated with a successive annealing treatment. The hybrid NiCo₂O₄@MnMoO₄ electrode exhibited remarkable pseudocapacitor property with high initial mass specific capacitance of 1705.3 F g^–1 at 5 mA cm^–2, and retained 92.6% after 5000 cycles, compared to the bare NiCo₂O₄ electrode with 839.1 F g^–1 and 90.9%. The excellent capacitive property of the NiCo₂O₄@MnMoO₄ hydrid was attributed to its high-electron/ion-transfer rate, large electrolyte infiltrate area, and more electroactive reaction sites

Targeting Chemophotothermal Therapy of Hepatoma by Gold Nanorods/Graphene Oxide Core/Shell Nanocomposites

Nanographene oxide (NGO) are highly suitable to be the shells of inorganic nanomaterials to enhance their biocompatibility and hydrophilicity for biomedical applications while retaining their useful photonic, magnetic, or radiological functions. In this study, a novel nanostructure with gold nanorods (AuNRs) encapsulated in NGO shells is developed to be an ultraefficient chemophotothermal cancer therapy agent. The NGO shells decrease the toxicity of surfactant-coated AuNRs and provide anchor points for the conjugation of hyaluronic acid (HA). The HA-conjugated NGO-enwrapped AuNR nanocomposites (NGOHA-AuNRs) perform higher photothermal efficiency than AuNRs and have the capability of targeting hepatoma Huh-7 cells. NGOHA-AuNR is applied to load doxorubicin (DOX), and it exhibits pH-responsive and near-infrared light-triggered drug-release properties. Chemophotothermal combined therapy by NGOHA-AuNRs-DOX performs 1.5-fold and 4-fold higher targeting cell death rates than single chemotherapy and photothermal therapy, respectively, with biosafety to nontargeting cells simultaneously. Furthermore, our strategy could be extended to constructing other NGO-encapsulated functional nanomaterial-based carrier systems

Wearable Pressure Sensors with Capacitive Response over a Wide Dynamic Range

At present, there are mainly two types of capacitive pressure sensors based on ordinary capacitance and electrical double layer (EDL) capacitance. However, few researchers have combined these two types of capacitors in pressure sensing to improve the dynamic range of a sensor under pressure. Here, we fabricated a capacitive pressure sensor with an asymmetric structure based on poly(vinylidene fluoride-co-hexafluoropropylene) using a simple electrospinning process. A layer of mixed ionic nanofiber membrane and a layer of pure nanofiber membrane were stacked and used as the dielectric layer of the sensor. Due to the porous structure and non-stickiness of the pure nanofiber membrane, it can be penetrated by the mixed ionic nanofiber membrane under pressure, realizing the reversible conversion from ordinary capacitance to EDL capacitance, thereby achieving a great change in the capacitance value. The sensitivities of the sensor are 55.66 and 24.72 kPa–1 in the pressure ranges of 0–31.11 and 31.11–66.67 kPa, respectively, with good cycle stability, fast loading–unloading response time, and an ultra-low pressure detection limit as low as 0.087 Pa. Finally, this sensor was used for the detection of human physiological signals, and the sensor would have potential applications in the fields of human tactile sensing systems, bionic robots, and wearable devices

Three-Dimensional Co₃O₄@NiMoO₄ Core/Shell Nanowire Arrays on Ni Foam for Electrochemical Energy Storage

In this work, we report a facile two-step hydrothermal method to synthesize the unique three-dimensional Co₃O₄@NiMoO₄ core/shell nanowire arrays (NWAs) on Ni foam for the first time. The Co₃O₄ nanowires are fully covered by ultrathin mesoporous NiMoO₄ nanosheets. When evaluated as a binder-free electrode for supercapacitors in a 2 M KOH aqueous solution, the Co₃O₄@NiMoO₄ hybrid electrode exhibits a greatly enhanced areal capacitance of 5.69 F cm^–2 at a high current density of 30 mA cm^–2, nearly 5 times that of the pristine Co₃O₄ electrode (1.10 F cm^–2). The energy density of the hybrid electrode is 56.9 W h kg^–1 at a high power density of 5000 W kg^–1. In addition, the Co₃O₄@NiMoO₄ hybrid electrode also exhibits good rate capability and cycling stability, which would hold great promise for electrochemical energy storage

Temperature-Dependent Abnormal and Tunable p‑n Response of Tungsten Oxide–Tin Oxide Based Gas Sensors

We observed the sensing response of temperature-dependent abnormal p–n transitions in WO₃–SnO₂ hybrid hollow sphere based gas sensors for the first time. The sensors presented a normal n-type response to ethanol at elevated temperatures but abnormal p-type responses in a wide range of operation temperatures (room temperature to about 95 °C). By measuring various reducing gases and applying complex impedance plotting techniques, we demonstrated the abnormal p-type sensing behavior to be a pseudo-response resulting from the reaction between target gas and adsorbed water on the material surface. The temperature-controlled n–p switch is ascribed to the competition of intrinsic and extrinsic sensing behaviors, which resulted from the reaction of target gas with adsorbed oxygen ions and protons from adsorbed water, respectively. The former can modulate the intrinsic conductivity of the sensor by changing the electron concentration of the sensing materials, while the latter can regulate the conduction of the water layer, which contributes to the total conductivity as an external part. The hollow and hybrid nanostructures facilitated the observation of extrinsic sensing behaviors due to its large-area active sites and abundant oxygen vacancies, which could enhance the adsorption of water. This work might give new insight into gas sensing mechanisms and opens up a promising way to develop practical temperature and humidity controllable gas sensors with little power consumption based on the extrinsic properties

Surfactant-Assisted Synthesis of High Energy {010} Facets Beneficial to Li-Ion Transport Kinetics with Layered LiNi_0.6Co_0.2Mn_0.2O₂

High energy {010} facets are favorable for Li⁺ transport in a layered Ni-rich LiNi_0.6Co_0.2Mn_0.2O₂ cathode through two-dimensional channels that are perpendicular to the <i>c</i> axis. However, those planes can hardly be maintained during the synthesis of layered cathodes. Therefore, we provide a strategy to use appropriate surface active agents which can alter the surface free energy by reducing surface tension directly. Here, a novel self-assembled 3D flower-like hierarchical LiNi_0.6Co_0.2Mn_0.2O₂ is formed with the help of sodium dodecyl sulfate (SDS), and those high energy facets are preserved. Due to the unique surface architectures which would lead to the fast ion transport kinetics as current expands to 100 times (from 0.1 to 10 C), the capacity decay only about 23.4%. Furthermore, full cells assembled against Li₄Ti₅O₁₂ are constructed with a capacity retention of 80.61% at 1 C charge/discharge. This study could show a promising material model for the preferred orientation active planes and higher Li⁺ transport kinetic

Encapsulating Gold Nanoparticles or Nanorods in Graphene Oxide Shells as a Novel Gene Vector

Surface modification of inorganic nanoparticles (NPs) is extremely necessary for biomedical applications. However, the processes of conjugating ligands to NPs surface are complicated with low yield. In this study, a hydrophilic shell with excellent biocompatibility was successfully constructed on individual gold NPs or gold nanorods (NRs) by encapsulating NPs or NRs in graphene oxide (GO) nanosheets through electrostatic self-assembly. This versatile and facile approach remarkably decreased the cytotoxicity of gold NPs or NRs capping with surfactant cetyltrimethylammonium bromide (CTAB) and provided abundant functional groups on NPs surface for further linkage of polyethylenimine (PEI). The PEI-functionalized GO-encapsulating gold NPs (GOPEI-AuNPs) were applied to delivery DNA into HeLa cells as a novel gene vector. It exhibited high transfection efficiency of 65% while retaining 90% viability of HeLa cells. The efficiency was comparable to commercialized PEI 25 kDa with the cytotoxicity much less than PEI. Moreover, the results on transfection efficiency was higher than PEI-functionalized GO, which can be attributed to the small size of NPs/DNA complex (150 nm at the optimal w/w ratio) and the spherical structure facilitating the cellular uptake. Our work paves the way for future studies focusing on GO-encapsulating, NP-based nanovectors

Low-Temperature H₂S Detection with Hierarchical Cr-Doped WO₃ Microspheres

Hierarchical Cr-doped WO₃ microspheres have been successfully synthesized for efficient sensing of H₂S gas at low temperatures. The hierarchical structures provide an effective gas diffusion path via well-aligned micro-, meso-, and macroporous architectures, resulting in significant enhancement in sensing response to H₂S. The temperature and gas concentration dependence on the sensing properties elucidate that Cr dopants remarkably improve the response and lower the sensor’ operating temperature down to 80 °C. Under 0.1 vol % H₂S, the response of Cr-doped WO₃ sensor is 6 times larger than pristine WO₃ sensor at 80 °C. We suggest the increasing number of oxygen vacancies created by Cr dopants to be the underlying reason for enhancement of charge carrier density and accelerated reactions with H₂S

Enhanced Sensitivity and Stability of Room-Temperature NH₃ Sensors Using Core–Shell CeO₂ Nanoparticles@Cross-linked PANI with p–n Heterojunctions

We report a room-temperature NH₃ gas sensor with high response and great long-term stability, including CeO₂ NPs conformally coated by cross-linked PANI hydrogel. Such core–shell nanocomposites were prepared by in situ polymerization with different weight ratios of CeO₂ NPs and aniline. At room temperature, the nanohybrids showed enhanced response (6.5 to 50 ppm of NH₃), which could be attributed to p–n junctions formed by the intimate contact between these two materials. Moreover, the stability was discussed in terms of phytic acid working as a gelator, which helped the PANI sheath accommodate itself and enhance the mechanical strength and chemical stability of the sensors by avoiding “swelling effect” in high relative humidity. The sensors maintained its sensing characteristic (response of ca. 6.5 to 50 ppm of NH₃) in 15 days. Herein, the obtained results could help to accelerate the development of ammonia gas sensor