Electronic differences based on fluoroquinolone and piperazine groups: Preparation of copper-manganese doped biochar to optimize adsorption patterns and selective recognition of ciprofloxacin

• Mn interacts with the empty-orbital-containing fluoroquinolone groups. • Cu provides empty orbitals for the lone pairs of electrons on the piperazine group. • CIP is adsorbed on CMBC mainly in a parallel manner. • Ranking of factors affecting CIP removal efficiency: dosage > time > pH. The high stability of fluoroquinolone and piperazine groups on ciprofloxacin (CIP) makes it difficult to be degraded in aqueous environment. In this study, copper-manganese co-modified biochar (CMBC) selectively recognized CIP was prepared by using the electron giving difference of these two groups. Manganese (Mn) acts as π electron donor to interact with the fluoroquinolone group containing the empty orbital in CIP. Copper (Cu) undergoes dsp 2 hybridization upon interaction with CIP to form four empty orbitals, which admit electrons from the piperazine group. The combined effect of CMBC on fluoroquinolone and piperazine groups makes CIP easily adsorbed in parallel mode, and the maximum removal rate reaches 95.21%. The tolerance of CMBC is evaluated in different ionic strengths, humic acids (HA) and actual water bodies. Molecular dynamics (MD) and density functional theory (DFT) are used to investigate the interaction mechanism and adsorption mode between CMBC and CIP. This study not only prepares adsorbents with selective recognition of CIP but also offers a reference for analyzing the adsorption pathway, manner and mechanism during the adsorption process.