2 research outputs found
Understanding the Reduction Kinetics of Aqueous Vanadium(V) and Transformation Products Using Rotating Ring-Disk Electrodes
VanadiumÂ(V)
is an emerging contaminant in the most recent Environmental
Protection Agency’s candidate contaminant list (CCL4). The
redox chemistry of vanadium controls its occurrence in the aquatic
environment, but the impact of vanadiumÂ(V) speciation on the redox
properties remains largely unknown. This study utilized the rotating
ring-disk electrode technique to examine the reduction kinetics of
four pH- and concentration-dependent vanadiumÂ(V) species in the presence
and the absence of phosphate. Results showed that the reduction of
VO<sub>2</sub><sup>+</sup>, H<sub><i>x</i></sub>V<sub>4</sub>O<sub>12+<i>x</i></sub><sup>(4+<i>x</i>)–</sup> (V<sub>4</sub>), and HVO<sub>4</sub><sup>2–</sup> proceeded
via a one-electron transfer, while that of Na<sub><i>x</i></sub>H<sub><i>y</i></sub>V<sub>10</sub>O<sub>28</sub><sup>(6–<i>x</i>–<i>y</i>)–</sup> (V<sub>10</sub>) underwent a two-electron transfer. Koutecky–Levich
and Tafel analyses showed that the intrinsic reduction rate constants
followed the order of V<sub>10</sub> > VO<sub>2</sub><sup>+</sup> >
V<sub>4</sub> > HVO<sub>4</sub><sup>2–</sup>. Ring-electrode
collection efficiency indicated that the reduction product of V<sub>10</sub> was stable, while those of VO<sub>2</sub><sup>+</sup>, HVO<sub>4</sub><sup>2–</sup>, and V<sub>4</sub> had short half-lives
that ranged from milliseconds to seconds. With molar ratios of phosphate
to vanadiumÂ(V) varying from 0 to 1, phosphate accelerated the reduction
kinetics of V<sub>10</sub> and V<sub>4</sub> and enhanced the stability
of the reduction products of VO<sub>2</sub><sup>+</sup>, V<sub>4</sub>, and HVO<sub>4</sub><sup>2–</sup>. This study suggests that
phosphate complexation could enhance the reductive removal of vanadiumÂ(V)
and inhibit the reoxidation of its reduction product in water treatment
An Outward Coating Route to CuO/MnO<sub>2</sub> Nanorod Array Films and Their Efficient Catalytic Oxidation of Acid Fuchsin Dye
An outward coating
method has been successfully employed to prepare
CuO/MnO<sub>2</sub> nanorod array films based on the impregnation
of CuÂ(OH)<sub>2</sub> nanorod array films with manganese nitrate aqueous
solution and heat post-treatment. The as-prepared CuO/MnO<sub>2</sub> nanorod array films as heterogeneous catalysts successfully address
such issues as easy agglomeration, difficult separation, and possible
secondary pollution related to powder catalysts. Furthermore, they
exhibit catalytic oxidation activity for the degradation of acid fuchsin
(AF) dye in aqueous solution superior to that of bare CuO nanorod
array films in the presence of H<sub>2</sub>O<sub>2</sub>, because
of the synergistic effects of both CuO and MnO<sub>2</sub>. The effects
of the initial concentration of aqueous AF solution and H<sub>2</sub>O<sub>2</sub> dosage on the catalytic oxidation performance were
evaluated, indicating that the degradation ratio of AF can reach up
to 94.05%. Life-cycle performance and scaleup of the catalytic oxidative
degradation process demonstrate the durability and potential engineering
application of CuO/MnO<sub>2</sub> nanorod array films in dye wastewater
treatment