ATR-FTIR peak positions observed in ATR-FTIR spectra of the DHBA isomers adsorbed on the surface of the Cu, Mn and Al NPs, together with their assignments based on the work of Guan et al.[42]).

All spectra were collected at a DHBA concentration of 1 mM at pH 6.2, except for the solution spectra of DHBA that were acquired at 10 mM in order to obtain sufficient signals.