Potential Reuse of PET Waste Bottles as a Green Substrate/Adsorbent for Reactive Black 5 Dye Removal

The adsorption process is one of the most promising alternatives for textile effluent treatment. Different materials have been used as adsorbents and most of them present hard recovery, increasing the process cost. In this work, polyethylene terephthalate (PET) waste bottles were used as a substrate for the formation of titanium dioxide (TiO 2 -G5) films aiming at Reactive Black 5 removal by adsorption process. The TiO 2 -G5/PET films were characterized by N 2 adsorption-desorption, zeta potential analysis, X-ray diffraction (XRD), and adherence test. The pH, adsorbent charge, and stirring effects were investigated. Initially, the effects of the adsorbent mass, pH of the solution, and stirring were studied, obtaining a maximum adsorptive capacity of 155.04 mg g −1 in the greatest condition (4 mg, pH = 4 and no stirring). The experimental data were fitted by the Langmuir and Freundlich isotherms. The Langmuir model presented the greatest fit, evidencing monolayer adsorption for this process. The kinetic study showed a great fit between the adsorption process and the pseudo-first-order kinetic model, which presented a correlation coefficient of 0.982. The thermodynamic parameters—enthalpy (∆H = − 19.53 kJ mol −1 ), entropy (∆S = − 50.26 J mol −1 K −1 ), and Gibbs energy (− 5.31, − 4.80, and − 4.30 kJ mol −1 at 283.15 K, 293.15 K, and 303.15 K, respectively)—indicate a spontaneous and exothermic process. Finally, the regeneration by solar radiation exposure led to an efficient TiO2-G5/PET spent sheets recovery, exhibiting good stability after 5 cycles of use. Graphical abstract