Fe-Ni/MWCNTs Nano-Composites for Hexavalent Chromium Reduction in Aqueous Environment.

A novel Cr (VI) removal material was designed and produced comprising multi-walled carbon nanotubes (MWCNTs) as a support with a high specific surface area and the loaded Fe-Ni bimetallic particles as catalytic reducing agents. Such a design permits the composite particle to perform the adsorption, reduction, and immobilisation of Cr (VI) quickly and efficiently. Due to MWCNTs' physical adsorption, Cr (VI) in solution aggregates in the vicinity of the composite, and Fe rapidly reduces Cr (VI) to Cr (III) catalysed by Ni. The results demonstrated that the Fe-Ni/MWCNTs exhibits an adsorption capacity of 207 mg/g at pH = 6.4 for Cr (VI) and 256 mg/g at pH 4.8, which is about twice those reported for other materials under similar conditions. The formed Cr (III) is solidified to the surface by MWCNTs and remains stable for several months without secondary contamination. The reusability of the composites was proven by retaining at least 90% of the adsorption capacity for five instances of reutilization. Considering the facile synthesis process, low cost of raw material, and reusability of the formed Fe-Ni/MWCNTs, this work shows great potential for industrialisation.

Ni-Fe/Reduced Graphene Oxide Nanocomposites for Hexavalent Chromium Reduction in an Aqueous Environment.

We designed and synthesized a novel high efficiency Cr(VI) removal material using reduced graphene oxide (RGO) as a support with high specific surface area and a mixture of Fe and Ni nanoparticles (NPs) as a catalytic reducing agent. Such a design enables the composite particle to be integrated with three functions of adsorption, catalysis, and reduction, where RGO could enhance Cr(VI) adsorption, while Fe/Ni NPs increase the catalytic reducing efficiency. The application of a microchip mixer guaranteed a better mixing of GO and subsequent decoration of Fe and Ni NPs on RGO. Cr(VI) removal experiments with various materials are performed, and the results demonstrated that the Ni-Fe/RGO achieved an adsorption capacity of 150.45 mg/g at pH = 7 and 197.43 mg/g at pH = 5 for Cr(VI), which is higher than those of other reported materials at a pH of ∼7. To the best of our knowledge, this is the first example of Ni-Fe/RGO for efficient Cr(VI) removal by using the synergistic effects of increased adsorption, catalysis-assisted reduction, and enhanced mixing effect of a microchip mixer. This work also provides us with a simple and low-cost method for the fabrication of an effective Cr(VI) removal material.

A Submillimeter Level Relative Navigation Technology for Spacecraft Formation Flying in Highly Elliptical Orbit.

Spacecraft formation flying (SFF) in highly elliptical orbit (HEO) has attracted much attention since many applications in space explore, while precise guidance navigation and control (GNC) technology, especially precise ranging, conducted the basis of success for such SFF missions. In this paper, we introduced a novel K band microwave ranging (MWR) equipment that aimed for the on-orbit verification of submillimeter level precise ranging technology in future HEO SFF missions. The ranging technique is a synchronous dual one-way ranging (DOWR) microwave phase accumulation system, which achieved tens of microns of ranging accuracy in laboratory environment. Detailed design and development process of MWR equipment are provided, with ranging error sources analyzed, and relative orbit dynamic models for HEO formation scenes are given with real perturbations considered. Moreover, an adaptive Kalman filter algorithm is introduced for SFF relative navigation design, incorporating with process noise uncertainty. The performance of SFF relative navigation while using MWR are tested in a hardware in loop (HIL) simulation system within a high precision six degree of freedom (6-DOF) moving platform. The final range estimation errors from MWR using adaptive filter are less than 35 µm m and 8.5 µm/s for range rate, which demonstrated the promising accuracy for future HEO formation mission applications.