Highly selective adsorption of organic dyes onto tungsten trioxide nanowires

The strong selective adsorption property of monoclinic tungsten trioxide nanowires (WO 3 NWs) towards organic dyes was reported in this paper. The effects of pH, initial concentration and types of dyes were systematically investigated. Particularly, methylene blue (MB) was more inclined to be adsorbed in acid solution and a maximum uptake capacity of 148.6 mg g −1 was achieved. 88 % of MB can be rapidly adsorbed within 70 min. The kinetics, isotherms and thermodynamics for the adsorption of MB and methyl orange (MO) were well described. The kinetic adsorption on WO 3 NWs followed a pseudo second-order model ( R 2  = 0.998) and the Langmuir isotherm ( R 2  = 0.992) agreed very well with the experimental data. The negative values of Δ G 0 at various temperatures (−5.656, −5.792, and −5.946 kJ mol −1 ) and Δ H 0 (−1.343 kJ mol −1 ) implied that the adsorption reaction was spontaneous and exothermic. Specific surface area (864.153 m 2  g −1 ) and surface acidic groups of WO 3 NWs enabled excellent adsorption performance. A highly selective adsorption mechanism involving the electrostatic interaction between hydroxyls on the WO 3 NWs' surfaces and different dye molecules was proposed.