Facile synthesis, growth process, characterisation of a nanourchin-structured α-MnO2 and their application on ultrasonic-assisted adsorptive removal of cationic dyes: A half-life and half-capacity concentration approach

•Hydrothermal synthesis of α–MnO2 for adsorption of industrial dyes.•Characterisation of synthesised α–MnO2 was determined by FTIR, SEM, TEM, XRD, XPS.•Effects of independent parameters for dye adsorption were evaluated.•Ultrasound application for improved mass transfer.•Economic viability of α–MnO2 was determined using reusability test.