Facile Synthesis of ZnO Nanoparticles on Nitrogen-Doped Carbon Nanotubes as High-Performance Anode Material for Lithium-Ion Batteries

A Single-Step Process to Produce Carbon Nanotube-Zinc Compound Hybrid Materials

An atmospheric-pressure plasma system is developed and is used to treat carbon nanotube assemblies, producing a hybrid carbon-zinc structure. This system is integrated into a floating-catalyst chemical vapor deposition furnace used for the synthesis of macroscopic assemblies of carbon nanotubes to allow for the in-line, continuous, and single-step production of nano-composite materials. Material is deposited from a sacrificial zinc wire in the form of nanoparticles and can coat the surface of the individual carbon nanotubes as they form. Additionally, it is found that the deposited materials penetrate further into the carbon nanotube matrix than a comparable post-synthesis deposition, improving the uniformity of the material through the thickness. Thus, a single-step metal-based coating and carbon nanotube synthesis process which can form the basis of production scale manufacturing of metal-carbon nanotube composite materials with an atmospheric-pressure plasma system are demonstrated.

Highly efficient surface sequestration of Pb2+ and Cr3+ from water using a Mn3O4 anchored reduced graphene oxide: Selective removal of Pb2+ from real water

Owing to the ubiquitous existence of detrimental heavy metals in the environment, simple adsorption-oriented approaches are becoming increasingly appealing for the effective removal of Pb²⁺ and Cr³⁺ from water bodies. These techniques use nanocomposites (NC) of reduced graphene oxide (rGO) and Mn₃O₄ (rGO-Mn₃O₄), they employ a hydrothermal technique featuring NaBH₄ and NaOH solutions. Here, spectroscopic and microscopic instrumental techniques were used to evaluate the morphological and physicochemical characteristics of prepared reduced graphene oxide manganese oxide (rGO-Mn₃O₄), revealing that it possessed a well-defined porous structure with a specific surface area of 126 m² g^-1. The prepared rGO-Mn₃O₄ had significant adsorption efficiencies for Pb²⁺ and Cr³⁺, achieving maximum sequestration capacities of 130.28 and 138.51 mg g^-1 for Pb²⁺ and Cr³⁺, respectively, according to the Langmuir model. These adsorption capacities are comparable to or greater than those of previously reported graphene-based materials. The Langmuir isotherm and pseudo-second-order models adequately represented the experimental results. Thermodynamic analysis revealed that adsorption occurred through spontaneous endothermic reactions. Recycling studies showed that the developed r-GO-Mn₃O₄ had excellent recyclability, with <70% removal at the 5th cycle; its feasibility was evaluated using industrial wastewater, suggesting that Pb²⁺ was selectively removed from Pb²⁺ and Cr³⁺ contaminated water. The instrumental analysis and surface phenomena studies presented here revealed that the adsorptive removal processes of both heavy metals involved π electron donor-acceptor interactions, ion exchange, and electrostatic interactions, along with surface complexation. Overall, the developed rGO-Mn₃O₄ has the potential to be a high-value adsorbent for removing heavy metals.

Functionalization of Pristine, Metallic, and Semiconducting-SWCNTs by ZnO for Efficient Charge Carrier Transfer: Analysis through Critical Coagulation Concentration

Noncovalent functionalization of single-walled carbon nanotubes (SWCNT) by semiconducting oxides is a majorly sought technique to retain individual properties while creating a synergetic effect for an efficient heterostructure charge transfer. Three types of electronically and optically different SWCNTs: metallic (m), semiconducting (s), and pristine (p) are functionalized by ZnO using a facile sonication method. The physicochemical and morphological properties of the ZnO-functionalized SWCNTs, m-SWCNT+ZnO, s-SWCNT+ZnO, and p-SWCNT+ZnO, are analyzed by advanced characterization techniques. Evidence of charge transfer between SWCNT and ZnO is observed with an increase in charge carrier lifetime from 3.31 ns (ZnO) to 4.76 ns (s-SWCNT+ZnO). To investigate the optimum interaction between SWCNTs and ZnO, critical coagulation concentrations (CCC) are determined using UV-vis absorption spectroscopy for m-SWCNT, s-SWCNT, and p-SWCNT using different molar concentrations of ZnO as the coagulant. The interaction and coagulation mechanisms are described by the modified DLVO theory. Due to the variation in dielectric values and electronic properties of SWCNTs, the CCC values obtained have differed: m-SWCNT (1.9 × 10^-4), s-SWCNT (3.4 × 10^-4), and p-SWCNT (2 × 10^-4). An additional analysis of the aggregates and supernatants of the CCC experiments is also shown to give an insight into the interaction and coagulation processes, explaining the absence of influence exerted by sedimentation and centrifugation.

Ordered ZnO/Ni Hollow Microsphere Arrays as Anode Materials for Lithium Ion Batteries

Well-designed nanostructures are very important for the electrochemical performance of lithium-ion electrode materials. In order to improve the electrochemical performance of ZnO-based anode materials, ZnO/Ni composite film, assembled by ordered hollow microsphere arrays, is designed and fabricated by means of magnetron sputtering technique using a colloidal crystal template composed of a monolayer of ordered polystyrene (PS) microspheres. The ordered hollow microsphere structure as well as the constituent Ni component of the ZnO/Ni film show major advantages of homogenizing electrode reactions, enhancing electrode reaction kinetics and accommodating volume change of active materials, so they can reduce electrode polarization and stabilize electrode structure. Consequently, the resulting ordered ZnO/Ni hollow microspheres arrays deliver an initial charge capacity of 685 mAh g^-1, an initial coulombic efficiency of 68%, and a capacity retention rate of 69% after 100 cycles, all of which are higher than those of the pure ZnO film. These results show progress in developing more stable ZnO-based anode materials for lithium ion batteries.

High Electrochemical Performance of Nanotube Structured ZnS as Anode Material for Lithium⁻Ion Batteries

By using ZnO nanorods as an ideal sacrificial template, one-dimensional (1-D) ZnS nanotubes with a mean diameter of 10 nm were successfully synthesized by hydrothermal method. The phase composition and microstructure of the ZnS nanotubes were characterized by using XRD (X-ray diffraction), SEM (scanning electron micrograph), and TEM (transmission electronic microscopy) analysis. X-ray photoelectron spectroscopy (XPS) and nitrogen sorption isotherms measurements were also used to study the information on the surface chemical compositions and specific surface area of the sample. The prepared ZnS nanotubes were used as anode materials in lithium-ion batteries. Results show that the ZnS nanotubes deliver an impressive prime discharge capacity as high as 950 mAh/g. The ZnS nanotubes also exhibit an enhanced cyclic performance. Even after 100 charge/discharge cycles, the discharge capacity could still remain at 450 mAh/g. Moreover, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements were also carried out to evaluate the ZnS electrodes.

Sustainable Waste Tire Derived Carbon Material as a Potential Anode for Lithium-Ion Batteries

The rapidly growing automobile industry increases the accumulation of end-of-life tires each year throughout the world. Waste tires lead to increased environmental issues and lasting resource problems. Recycling hazardous wastes to produce value-added products is becoming essential for the sustainable progress of society. A patented sulfonation process followed by pyrolysis at 1100 °C in a nitrogen atmosphere was used to produce carbon material from these tires and utilized as an anode in lithium-ion batteries. The combustion of the volatiles released in waste tire pyrolysis produces lower fossil CO2 emissions per unit of energy (136.51 gCO2/kW·h) compared to other conventional fossil fuels such as coal or fuel–oil, usually used in power generation. The strategy used in this research may be applied to other rechargeable batteries, supercapacitors, catalysts, and other electrochemical devices. The Raman vibrational spectra observed on these carbons show a graphitic carbon with significant disorder structure. Further, structural studies reveal a unique disordered carbon nanostructure with a higher interlayer distance of 4.5 Å compared to 3.43 Å in the commercial graphite. The carbon material derived from tires was used as an anode in lithium-ion batteries exhibited a reversible capacity of 360 mAh/g at C/3. However, the reversible capacity increased to 432 mAh/g at C/10 when this carbon particle was coated with a thin layer of carbon. A novel strategy of prelithiation applied for improving the first cycle efficiency to 94% is also presented.

Nitrogen-doped carbon nanotubes coated with zinc oxide nanoparticles as sulfur encapsulator for high-performance lithium/sulfur batteries

Nitrogen-doped carbon nanotubes coated with zinc oxide nanoparticles (ZnO@NCNT) were prepared via a sol-gel route as sulfur encapsulator for lithium/sulfur (Li/S) batteries. The electrochemical properties of the S/ZnO@NCNT composite cathode were evaluated in Li/S batteries. It delivered an initial capacity of 1032 mAh·g^-1 at a charge/discharge rate of 0.2C and maintained a reversible capacity of 665 mAh·g^-1 after 100 cycles. The coulombic efficiency of the cathode remains unchanged above 99%, showing stable cycling performance. X-ray photoelectron spectroscopy analysis confirmed the formation of S-Zn and S-O bonds in the composite. This indicates that an enhanced cycling and rate capability of the S/ZnO@NCNT composite could be ascribed to advantages of the ZnO@NCNT matrix. In the composite, the active ZnO-rich surfaces offer a high sulfur-bonding capability and the NCNT core acts as a conductive framework providing pathways for ion and electron transport. The as-prepared S/ZnO@NCNT composite is a promising cathode material for Li/S batteries.