Enhancing Performance of Organic Pollutant Degradation via Building Heterojunctions with ZnO Nanowires and Na Doped Conjugated 2,4,6-Triaminopyrimidin-g-C3N4.

Organic pollutants were one of the main sources of environmental pollutants. The degradation of organic pollutants through photocatalytic technology was one of the effective solutions. By preparing zinc oxide(ZnO) nanowires modified with sodium-doped conjugated 2,4,6-triaminopyrimidin-g-C3N4 (NaTCN) heterojunction (ZnO/NaTCN), the photocatalytic performance of NaTCN modified with different ratios of ZnO was systematically studied. The photocatalytic performance was studied through the degradation performance of methyl blue (MB) dye. The results showed that 22.5 wt% ZnO/NaTCN had the best degradation effect on MB dye. The degradation rate of MB reached 98.54% in 70 min. After three cycles, it shows good cycling stability (degradation rate is 96.99%) for dye degradation. It was found that there are two types of active species: ·OH and h+, of which h+ is the main active species produced by photocatalytic degradation of dyes. The excellent degradation performance was attributed to the fact that ZnO facilitated the extraction and transport of photogenerated carriers. The doping of sodium facilitated charge transfer. The NaTCN conjugated system promoted the extraction and transfer of photogenerated carriers. It provided guidance for designing efficient composite catalysts for use in other renewable energy fields.

Study on the Sodium-Doped Titania Interface-Type Memristor.

Memristors integrated into a crossbar-array architecture (CAA) are promising candidates for analog in-memory computing accelerators. However, the relatively low reliability of the memristor device and sneak current issues in CAA remain the main obstacles. Alkali ion-based interface-type memristors are promising solutions for implementing highly reliable memristor devices and neuromorphic hardware. This interface-type device benefits from self-rectifying and forming-free resistive switching (RS), and exhibits relatively low variation from device to device and cycle to cycle. In a previous report, we introduced an in situ grown Na/TiO2 memristor using atomic layer deposition (ALD) and proposed a RS mechanism from experimentally measured Schottky barrier modulation. Self-rectifying RS characteristics were observed by the asymmetric distribution of Na dopants and oxygen vacancies as the Ti metal used as the adhesion layer for the bottom electrode diffuses over the Pt electrode at 250 °C during the ALD process and is doped into the TiO2 layer. Here, we theoretically verify the modulation of the Schottky barrier at the TiO2/Pt electrode interface by Na ions. This study fabricated a Pt/Na/TiO2/Pt memristor device and confirmed its self-rectifying RS characteristics and stable retention characteristics for 24 h at 85 °C. Additionally, this device exhibited relative standard deviations of 27 and 7% in the high and low resistance states, respectively, in terms of cycle-to-cycle variation. To verify the RS mechanism, we conducted density functional theory simulations to analyze the impact of Na cations at interstitial sites on the Schottky barrier. Our findings can contribute to both fundamental understanding and the design of high-performance memristor devices for neuromorphic computing.

One-pot synthesis of sodium-doped willow-shaped graphitic carbon nitride for improved photocatalytic activity under visible-light irradiation.

Graphitic carbon nitride (g-C3N4) is considered as a promising low-cost polymeric semiconductor as conjugated photocatalyst for energy and environmental application. This study exhibits a Na-doped g-C3N4 with willow-leaf-shaped structure and high degree of crystallinity, which was synthesized with a convenient thermal polymerization using sodium carbonate (Na2CO3) as the sodium source. The π-conjugated systems of g-C3N4 were improved by doping sodium, which could accelerate the electron transport efficiency resulting in outstanding photocatalytic properties. Furthermore, optimum Na-doped g-C3N4 (CN-0.05) attributed its enhanced irradiation efficiency of light energy to its narrower band gap and significant improvement in charge separation. Consequently, the H2 evolution rate catalyzed with CN-0.05 can achieve 3559.8 µmol g-1 h-1, which is about 1.9 times higher than that with pristine g-C3N4. The rate of CN-0.05 for reduction of CO2 to CO (3.66 µmol g-1 h-1) is 6.6 times higher than that of pristine g-C3N4. In experiments of pollutants degradation, the reaction constants of degradation of rhodamine B (RhB) and methyl orange (MO) with CN-0.05 were 0.0271 and 0.0101 min-1, respectively, which are 4.7 and 7.2 times more efficient than pristine g-C3N4, respectively. This work provides a simple preparation method for tailoring effective photocatalyst for the sustainable solution of environmental issues.

Sodium-Doped Titania Self-Rectifying Memristors for Crossbar Array Neuromorphic Architectures.

Memristors integrated into a crossbar-array architecture (CAA) are promising candidates for nonvolatile memory elements in artificial neural networks. However, the relatively low reliability of memristors coupled with crosstalk and sneak currents in CAAs have limited the realization of the full potential of this technology. Here, high-reliability Na-doped TiO2  memristors grown in situ by atomic layer deposition (ALD) are demonstrated, where reversible Na migration underlies the resistive-switching mechanism. By employing ALD growth with an aqueous NaOH reactant in deionized water, uniform implantation of Na dopants is achieved in the crystallized TiO2  thin films at 250 °C without post-annealing. The resulting Na-doped TiO2  memristors show electroforming-free and self-rectifying resistive-switching behavior, and they are ideally suited for selectorless CAAs. Effective addressing of selectorless nodes is demonstrated via electrical measurement of individual memristors in a 6 × 6 crossbar using a read current of less than 1 µA with negligible sneak current at or below the noise level of ≈100 pA. Finally, the long-term potentiation and depression synaptic behavior from these Na-doped TiO2  memristors achieves greater than 99.1% accuracy for image-recognition tasks using a convolutional neural network based on the selectorless of crossbar arrays.

Facile Synthesis of Na-Doped MnO2 Nanosheets on Carbon Nanotube Fibers for Ultrahigh-Energy-Density All-Solid-State Wearable Asymmetric Supercapacitors.

Flexible fiber-shaped supercapacitors hold promising potential in the area of portable and wearable electronics. Unfortunately, their general application is hindered by the restricted energy densities due to low operating voltage and small specific surface area. Herein, an all-solid-state fiber-shaped asymmetric supercapacitor (FASC) possessing ultrahigh energy density is reported, in which the positive electrode was designed as Na-doped MnO2 nanosheets on carbon nanotube fibers (CNTFs) and the negative electrode as MoS2 nanosheet-coated CNTFs. Owing to the excellent properties of the designed electrodes, our FASCs exhibit a large operating potential window (0-2.2 V), a remarkable specific capacitance (265.4 mF/cm2), as well as an ultrahigh energy density (178.4 µWh/cm2). Moreover, the devices are of outstanding mechanical flexibility.