Valorization of waste NiMH battery through recovery of critical rare earth metal: A simple recycling process for the circular economy.

The process flowsheet consists of three main circuits, i.e., metal extraction by acid leaching, critical rare earth metal (REM) recovery from leach liquor and pure Co/Ni recovery by solvent extraction. Quantitative metal extraction using 1 M H2SO4, pulp density of 25 g/L at 90 °C from waste NiMH battery was achieved. From leach liquor using 10 M NaOH, at pH 1.8, more than 99% REM was precipitated out and isolated through calcination at 600 °C. Undesired metals like Mn, Al, Zn, and Fe were scrubbed out from the leach liquor using 0. 7 M D2EPHA at the equilibrium pH of 2.30. From the scrubbed raffinate Co and Ni was separated using 0.5 M Cyanex 272 at pH 4.70 through solvent extraction. At pH 4.70 Co was completely extracted from solution leaving Ni in solution, which can be recovered completely. From Co loaded Cyanex 272, the Co was stripped by 1 M H2SO4 and regenerated Cyanex 272 can be reused and close the loop. Similarly, the undesired metal loaded D2EPHA can be regenerated and reused and close the loop. As the process is close-loop process recovers critical REMs, Co, and Ni, the valorization process efficiently addresses the circular economy and recycling challenges associated with waste NiMH battery.

High performance CNT point emitter with graphene interfacial layer.

Carbon nanotubes (CNTs) have great potential in the development of high-power electron beam sources. However, for such a high-performance electronic device, the electric and thermal contact problem between the metal and CNTs must be improved. Here, we report graphene as an interfacial layer between the metal and CNTs to improve the interfacial contact. The interfacial graphene layer results in a dramatic decrease of the electrical contact resistance by an order of 2 and an increase of the interfacial thermal conductivity by 16%. Such a high improvement in the electrical and thermal interface leads to superior field emission performance with a very low turn-on field of 1.49 V µm(-1) at 10 µA cm(-2) and a threshold field of 2.00 V µm(-1) at 10 mA cm(-2), as well as the maximum current of 16 mA (current density of 2300 A cm(-2)).

Fibers of reduced graphene oxide nanoribbons.

Reduced graphene oxide nanoribbon fibers were fabricated by using an electrophoretic self-assembly method without the use of any polymer or surfactant. We report electrical and field emission properties of the fibers as a function of reduction degree. In particular, the thermally annealed fiber showed superior field emission performance with a low potential for field emission (0.7 V µm(-1)) and a giant field emission current density (400 A cm(-2)). Moreover, the fiber maintains a high current level of 300 A cm(-2) corresponding to 1 mA during long-term operation.

Twistable and bendable actuator: a CNT/polymer sandwich structure driven by thermal gradient.

We demonstrate a novel configuration of an electrothermal actuator (ETA), which is based on a polydimethylsiloxane (PDMS) slab sandwiched by upper and lower active layers of CNT-PDMS composite. When only one active layer of a single sandwich structure ETA is heated and the other is not, there exists a thermal gradient in the direction of the slab thickness, resulting in bending motion toward the unheated side. Moreover, a dual sandwich structure ETA, consisting of two parallel assembled sandwich structures on the same body, has the unique ability to act with a twisting motion as the two ETAs bend in opposite directions. We expect the advent of the bendable and twistable actuator to break new ground in ETAs.

Single-walled carbon-nanotube networks on large-area glass substrate by the dip-coating method.

Highly uniform and large-area single-walled carbon-nanotube (SWNT) networks are realized by the dip-coating method, which is based on fundamental fluid-dynamic phenomena such as capillary condensation and surface tension. The changes in the polarity and hydration properties of the substrate affect the morphology of the SWNT networks and result in nonlinear growth of the networks in the repetitive dip-coating process. The density and the thickness of the SWNT networks are controlled by processing variables including number of dip coatings, concentration of SWNT colloidal solution, and withdrawal velocity. The networks have uniform sheet resistances and high optical transmittance in the visible wavelength range.