Dibutyltin dilaurate catalysed guar gum and toluene diisocyanate polyurethane foam for the removal of malachite green from wastewater

In view of the huge potential in various applications, biopolymer-based polyurethane foams (PUF) are attracting researchers. In the present study, we report the modification of guar gum (GG) via polyaddition reaction with toluene diisocyanate (TDI) using dibutyltin dilaurate as catalyst, silicone oil as surfactant and calcium carbonate as filler to form GG-PUF. The as-synthesized GG-PUF was characterized by Fourier transform infrared (FTIR), XRD, field emission SEM, energy-dispersive X-ray spectroscopy, and surface charge analysis. In the FTIR spectrum of GG-PUF, peaks at 3290, 1705, 1595, and 1510 cm⁻¹ are attributed to stretching vibrations of –NH, –C=O, –C=C– of the benzene ring of TDI, and the –NH bending vibration of the urethane group, respectively. The XRD patterns of GG and GG-PUF indicate their semicrystalline and amorphous nature, respectively. The field emission SEM of GG-PUF exhibits high porosity compared to the smooth surface of GG due to the evolution of CO₂ gas during the foaming reaction. The GG-PUF was evaluated as an adsorbent for cationic dyes from wastewater. The preliminary adsorption studies showed maximum adsorption for malachite green with 93.54% removal at 40 °C and pH 6.0 in 60 min. The adsorption mechanism was studied by various nonlinear kinetic models, namely the pseudo-first order, pseudo-second order and Elovich, and nonlinear isotherm models, such as Langmuir, Freundlich and Temkin. The adsorption followed pseudo-secondorder kinetics and a Langmuir isotherm with a maximum adsorption capacity of 156.44 mg g⁻¹. The small value of the error function (χ²) and normalized standard deviation (Δq%) from nonlinear models indicated the better fitting of the data into nonlinear kinetics and isotherm models. Furthermore, GG-PUF showed substantial degradability under simulated wastewater conditions at acidic and alkaline pH and reusability up to 10 adsorption–desorption cycles. Hence, GG-PUF has tremendous potential as a sustainable, economical and environmentally friendly adsorbent for eliminating cationic dyes from wastewater. © 2024 Society of Chemical Industry.