Boron-doped activated carbon derived from Zoysia sinica for Rhodamine B adsorption: The crucial roles of defect structures

•Zoysia sinica was converted to boron-doped carbon (ACB2) by chemical impregnation and 900 °C calcination.•ACB2 efficiently removed RhB with the maximum adsorption capacity of 1337.2 mg/g under unadjusted pH at the temperature of 298 K.•The introduction of boron can modulate the electron density of the ACB2 surface.•Boron species as Lewis acid sites promote a high affinity of RhB to the ACB2 surface.•The defect structure and oxygen-containing functional groups of ACB2 collectively promote the removal of RhB.