Novel approach for the synthesis of hybrid clay-based nanopigments and their application as coloring agents

The nature of interactions of a toxic dye, thioflavin T (TFT), with pristine clay (bentonite (Bet)), clay minerals (montmorillonite (Mnt) and vermiculite (Vt)) and their organically modified forms (OMnt, OBet and OVt) has been investigated in aqueous media, and a methodology was developed for the utilization of TFT-treated colored residues as nanopigments, without producing the second-generation waste materials. The uptake of TFT was found to be more in case of pristine clay and clay minerals than their organically modified forms. In case of Mnt, TFT was present in the interlayer region, as supported by XRD data, and on the surface as the surface charge of TFT-treated pristine Mnt became almost zero, as indicated by the change in zeta potential value (− 17.6 to − 0.03 mV). In case of Bet and Vt, TFT was found to be only on clay mineral’s surface, as suggested by the change in zeta potential value (− 31 to − 0.6 mV in case of Bet and − 47 to − 0.04 mV in case of Vt). The corresponding increase in the particle size (158–443 nm in case of Bet and 145–460 nm in case of Vt) was also evocative of surface adsorption. In case of organically modified forms (OMnt, OBet and OVt), TFT was predominantly on the surface in all cases examined. The experimental data obtained during extractive removal of TFT using pristine and organically modified clays were best described with Langmuir adsorption isotherm model, whereas kinetic data are equipped with pseudo-second-order kinetic model. The intense yellow-colored solid material obtained after the extraction was used as colorant for the formation of polymer films with enhanced physico-chemical characteristics. These materials not only provide beautiful bright color but also prevent the accumulation of second-generation waste material.