Regenerated WO2.72 nanowires with superb fast and selective adsorption for cationic dye: Kinetics, isotherm, thermodynamics, mechanism

Highlights: • Super selective WO_2.72 nanowires have fast adsorption and high capacity (547.3 mg/g). • The adsorption data fit well with the pseudo-second order and Langmuir model. • Thermodynamics revealed the adsorption process is spontaneous and exothermic. • The adsorption efficiency can still reach 86.54% after five reusability experiments. • Electrostatic absorption was conceived as the main adsorption mechanism. -- Abstract: Hydrothermally prepared nonstoichiometry tungsten oxide (WO_2.72) nanowires possess super selective adsorption performance for methylene blue (MB). The effects of dye concentration, contact time, pH and temperature on the adsorption properties of WO_2.72 were investigated. The experimental results indicated that WO_2.72 nanowires have a high adsorption capacity (547.32 mg/g) under neutral pH and a fast adsorption rate (adsorbing 100% within 6 min) for MB dye. The kinetic data showed good correlation coefficient (R² > 0.99) for the pseudo-second-order. The equilibrium data suggesting the monolayer coverage of adsorbate as it fits well with the Langmuir isotherm model (R² > 0.99). The energy functions of chemical thermodynamics revealed the adsorbate transport across the phase boundary is spontaneous and exothermic. Electrostatic absorption was proposed as the main adsorption mechanisms. Calcination treatment was utilized to decompose MB adsorbed on WO_2.72 and regenerate WO_2.72. The adsorption efficiency of WO_2.72 nanowires can still reach 86.54% after recycling five times, which indicated that as-obtained WO_2.72 nanowires are a very promising high-efficiency adsorbent for practical purification of dyeing waste water.