Effect of sulfur on enhancing nitrogen-doping and magnetic properties of carbon nanotubes

Sulfur (S) is introduced as an additive in the growth atmosphere of carbon nanotubes (CNTs) in the range of 940-1020°C. CNT products with distorted sidewalls can be obtained by S-assisted growth. Moreover, many fascinating CNT structures can also be found in samples grown with S addition, such as bamboo-like CNTs, twisted CNTs, arborization-like CNTs, and bead-like CNTs. Compared with CNTs grown without S, more nitrogen-doping content is achieved in CNTs with S addition, which is beneficial for the properties and applications of nitrogen-doped CNTs. In addition, S can also enhance the encapsulation of ferromagnetic materials and thus improve the soft magnetic properties of CNTs, which is favorable to the applications of CNTs in the electromagnetic wave-absorbing and magnetic data storage areas

Silicon-Encapsulated Hollow Carbon Nanofiber Networks as Binder-Free Anodes for Lithium Ion Battery

Silicon-encapsulated hollow carbon nanofiber networks with ample space around the Si nanoparticles (hollow Si/C composites) were successfully synthesized by dip-coating phenolic resin onto the surface of electrospun Si/PVA nanofibers along with the subsequent solidification and carbonization. More importantly, the structure and Si content of hollow Si/C composite nanofibers can be effectively tuned by merely varying the concentration of dip solution. As-synthesized hollow Si/C composites show excellent electrochemical performance when they are used as binder-free anodes for Li-ion batteries (LIBs). In particular, when the concentration of resol/ethanol solution is 3.0%, the product exhibits a large capacity of 841 mAh g−1 in the first cycle, prominent cycling stability, and good rate capability. The discharge capacity retention of it was ~90%, with 745 mAh g−1 after 50 cycles. The results demonstrate that the hollow Si/C composites are very promising as alternative anode candidates for high-performance LIBs

Synthesis and Enhanced Field-Emission of Thin-Walled, Open-Ended, and Well-Aligned N-Doped Carbon Nanotubes

Thin-walled, open-ended, and well-aligned N-doped carbon nanotubes (CNTs) on the quartz slides were synthesized by using acetonitrile as carbon sources. As-obtained products possess large thin-walled index (TWI, defined as the ratio of inner diameter and wall thickness of a CNT). The effect of temperature on the growth of CNTs using acetonitrile as the carbon source was also investigated. It is found that the diameter, the TWI of CNTs increase and the Fe encapsulation in CNTs decreases as the growth temperature rises in the range of 780–860°C. When the growth temperature is kept at 860°C, CNTs with TWI = 6.2 can be obtained. It was found that the filed-emission properties became better as CNT growth temperatures increased from 780 to 860°C. The lowest turn-on and threshold field was 0.27 and 0.49 V/μm, respectively. And the best field-enhancement factors reached 1.09 × 105, which is significantly improved about an order of magnitude compared with previous reports. In this study, about 30 × 50 mm2 free-standing film of thin-walled open-ended well-aligned N-doped carbon nanotubes was also prepared. The free-standing film can be transferred easily to other substrates, which would promote their applications in different fields

Extraordinary room-temperature photoluminescence in WS2 monolayers

Individual monolayers of metal dichalcogenides are atomically thin two-dimensional crystals with attractive physical properties different from their bulk layered counterpart. Here we describe the direct synthesis of WS2 monolayers with triangular morphologies and strong room-temperature photoluminescence (PL). Bulk WS2 does not present PL due to its indirect band gap nature. The edges of these monolayers exhibit PL signals with extraordinary intensity, around 25 times stronger than the platelets center. The structure and composition of the platelet edges appear to be critical for the PL enhancement effect. Electron diffraction revealed that platelets present zigzag edges, while first-principles calculations indicate that sulfur-rich zigzag WS2 edges possess metallic edge states, which might tailor the optical response reported here. These novel 2D nanoscale light sources could find diverse applications including the fabrication of flexible/transparent/low-energy optoelectronic devices

Hydrothermal Synthesis of Cr2Se3 Hexagons for Sensitive and Lowlevel Detection of 4-Nitrophenol in Water

We report a simple hydrothermal method used for the synthesis of Cr2Se3 hexagons (h-Cr2Se3) and its application towards electrochemical sensing of 4-nitrophenol (4-NP). The formation of h-Cr2Se3 was confrmed by using scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray difraction, and X-ray photoelectron spectroscopy. The electrochemical activity of the h-Cr2Se3 modifed screen-printed carbon electrode (SPCE) towards 4-NP was studied using cyclic voltammetry (CV) and amperometric i-t techniques. Typically,the obtained results were compared with those for a bare SPCE. The CV result clearly reveals that h-Cr2Se3 modifed SPCE has higher catalytic activity towards reduction of 4-NP than bare SPCE. Hence, h-Cr2Se3 modifed SPCE was concluded as a viable sensor for sensitive determination of 4-NP. Under optimized conditions, h-Cr2Se3 modifed SPCE demonstrates the excellent capacity to detect the 4-NP in a linear range from 0.05µM to 908.0µM. The LOD and sensitivity in detection of 4-NP were determined at 0.01µM and 1.24µAµM−1 cm−2 respectively. The sensor is highly selective and stable and shows reproducible recovery of 4-NP in domestic supply and river water samples

Defect engineering of two-dimensional materials for efficient electrocatalysis

Exploring high-activity and earth-abundant electrocatalysts for electrochemical reactions, including the hydrogen evolution reaction (HER), oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), etc. are crucial for building future large-scale green energy conversion and storage systems. Recently, some low-cost and resourceful two-dimensional (2D) semiconductor materials such as transition metal dichalcogenides (TMDCs) and layered oxides, have attracted increasing attention in electrocatalysis applications in virtue of their comparable catalytic activity and long-term stability to conventional noble metal-based catalysts (e.g. Pt/C, RuO2, IrO2, etc.). However, the intrinsic activity of some 2D materials still cannot meet the increasing requirement for highly efficient and reliable eletrocatalysts for future energy conversion and storage systems. In this context, designing elctrocatalysts with sufficient amount of active sites accessible for electrolyte, high activity of each active sites, and excellent conductivity is of great significance. To this end, defect engineering is a powerful strategy for tailoring the physical and chemical properties of 2D materials for efficient electrocatalysis. In this article, an overview of recent progress on defect engineering in 2D eletrocatalysts for HER, ORR and OER is presented. The effects of defects on the structure and tuned properties of 2D materials in eletrocatalysts applications are also summarized. Additionally, the challenges and opportunities ahead in this emerging field are also proposed. Keywords: Defect engineering, 2D materials, HER, ORR, OE

Flexible photodetector based on large-area few-layer MoS2

Developing flexible photodetectors is crucial for both military and civil fields. Large-area MoS2 films from several to dozens of layers are controllably synthesized via a facile atmospheric-pressure sulfurization route of predeposited Mo films and transferred onto other substrates (e.g. SiO2/Si wafers, quartz slides, polymers). The flexible photodetectors were fabricated by transferring as-synthesized MoS2 films onto interdigital electrodes patterned on polyethylene terephthalate (PET) substrates. No additional complex lithography positioning techniques were needed during the device fabrication process due to the large area of as-grown atomic thin MoS2 films. As-obtained flexible photodetectors showed responsibilities of ~ 20 mA/W and response time of several seconds. This demonstrates the possibility of employing large-area two-dimensional semiconductors to meet the increasing demands for wearable and portable electronics. Keywords: Flexible photodetector, Two-dimensional material, MoS