Fig. 4: Time-evolution of the UV-vis spectra of the different dyes and the photograph of the dye solutions.

UV-vis spectra of the dyes adsorbed by the four types of gels for a contact time of 60 min (a–h) and (i) photograph of the dye solution before and after adsorption by the P4VP-rGO-Fe₃O₄ OMG.