Hexagonal K₂W₄O₁₃ Nanowires for the Adsorption of Methylene Blue

Abstract

In this study, novel hexagonal K2W4O13 (h-K2W4O13) nanowires were strategically synthesized via a facial hydrothermal method, which exhibited excellent adsorption capacities for wastewater treatment. The inorganic agent K2SO4 was used as a structure-directing agent to scaffold the tunnel structure of h-K2W4O13 and form the one-dimensional structure. Through increasing the relative molar ratio of K2SO4 to Na2WO4 precursor, the pure-phase h-WO3 nanorods and h-K2W4O13 nanowires were obtained, attributing to the competitive electrostatic adsorption between K+ ions and Na+ ions on h-WO3 nuclei. With a smaller hydrated radius in the solution (d K+ = 3.31 Å, d Na+= 3.58 Å), K+ exhibited superior affinity compared to Na+ with the negatively charged h-WO3 nuclei because of a larger charge density, resulting in the formation of h-K2W4O13. Adsorption experimental results showed that 89.4% of methylene blue was removed by h-K2W4O13 in the first 5 min (99% in 1 h) and the maximum uptake capacity reached 204.08 mg g–1. In addition, the novel h-K2W4O13 exhibited acid or alkali resistance and good reusability, revealed by the stable adsorption capacity in a wide pH range of 3.0–11.0 and five-run recycle tests. The large specific area, high proportion of effective pore volume, and abundant hydroxyl groups of the synthesized h-K2W4O13 resulted in excellent adsorption performance for methylene blue.

Crystal Phase and Morphology-Controlled Synthesis of Tungsten Oxide Nanostructures for Remarkably Ultrafast Adsorption and Separation of Organic Dyes

“…For the 9:9 mL H 33,34 Whereas at higher n-propanol concentrations, the 2:16 mL H 2 O/n-propanol solvent mixture by the decomposition of ammonium tungstate, NH 3 gas is evolved as a byproduct in the closed environment at a slightly higher internal pressure, which leads to the formation of both (NH 4 )•WO 3 and WO 3 •H 2 O nuclei. 44 Subsequently, (NH 4 )• WO 3 dissociates and generates (NH 4 ) 0.33 •WO 3 nanospheres in the majority, along with a few WO 3 •(H 2 O) 0.5 .…”

“…At the end of predetermined time intervals, the solution was centrifuged at 11 000 rpm for 10 min, and the supernatant was examined using a UV–vis spectrometer at λ max = 664 nm (for MB), 617 nm (for MG), 518 nm (for SO), 580 nm (for CV), 553 nm (for RhB), 463 nm (for MO), 547 nm (for RB). The percentage (%) of dye adsorption was calculated using eq ,, % 0.25em 0.25em adsorption = C 0 − C t C 0 × 100 The equilibrium uptake was calculated using eq ,, q normale = ( C 0 − C t ) v w where q e represents the equilibrium adsorption capacity (mg·g –1 ) of the dye, C 0 and C t are the initial and equilibrium concentrations of adsorbate solution (mg·L –1 ), respectively, v is the volume of adsorbate test solution (L), and w is the weight of adsorbent (g). All of the results were analyzed at least three times to confirm the reproducibility.…”

“…At the end of predetermined time intervals, the solution was centrifuged at 11 000 rpm for 10 min, and the supernatant was examined using a UV−vis spectrometer at λ max = 664 nm (for MB), 617 nm (for MG), 518 nm (for SO), 580 nm (for CV), 553 nm (for RhB), 463 nm (for MO), 547 nm (for RB). The percentage (%) of dye adsorption was calculated using eq 1 30,34,48 C C C % adsorption 100…”

“…Among these TMOs, WO 3 and its various other crystal structures, including WO 3 ·(H 2 O) 0.5 , (NH 4 ) 0.33 WO 3 , WO 2.72 , WO 3 ·2H 2 O, WO 3 ·H 2 O, WO 3 ·0.33­(H 2 O), K 2 W 4 O 13 , etc., have attracted much attention for their multiple applications ranging from adsorption, catalysis, photocatalysis, photo-electrocatalysis, gas sensors, fuel cells, Li-ion batteries, and supercapacitors. − Since the collective chemical and physical properties of the WO 3 -based nanostructures, as well as their respective applications, significantly depend on the size, shape, and crystal structure of the nanomaterials, , it still remains a significant challenge to develop a novel, facile, aqueous-based, surfactant/stabilizer-free rational strategy toward the synthesis of shape/crystal structure-controlled nanomaterials.…”

Synergistic Effect of Au–PdO Modified Cu-Doped K2W4O13 Nanowires for Dual Selectivity High Performance Gas Sensing

“…Metal oxide-based sensors are commonly used for the detection of flammable and toxic gases due to their advantages of low cost, easy implementation, low operating temperature, high performance, and selectivity. Potassium tungsten oxides (K x WO 3 , 0.18 < x < 0.57) are a type of nonstoichiometric tungsten bronze that are formed by the partial occupancy of potassium atoms in the framework of WO 3 host built-up by corner- and edge-sharing of [WO 6 ] octahedra. , Among different strategies, doping has been considered an effective approach to improve semiconducting properties, such as cation-exchange capacity, electrochromic, , catalytic, and gas sensing performance . Similarly, metal doping into WO 3 leads to the substitution of tungsten atoms, which promotes the formation of oxygen vacancies and increases the active sites for adsorption of oxygen and gas molecules even at lower operating temperatures .…”