Adsorption behavior study and mechanism insights into novel isothiocyanate modified material towards Pd2

Abstract Removal of toxic heavy metals needs to be assured from drug substances and catalyst residues from waste streams at the ppm level which has sometimes proved difficult, causing irreversible harm to human health and environment. Herein, on basis of binding evaluation between isothiocyanate derivatives in Pd(MeCN)2Cl2 model solution, the corresponding functional materials were prepared by efficiently nucleophilic substitution and isomerization reaction on polystyrene framework. The isomerization from thiocyanide to isothiocyanate gifted SCN-2-NCS excellent Pd2+ adsorption capacity which could tolerate various composite solvent systems and was generally superior than the widely-used isothiourea modified material PSTU. Systematic thermodynamics and kinetics study indicated the complexation with Pd2+ was kinetically hindered and the increase of temperature contributed to the adsorption process as the maximum adsorption capacity was evaluated as 4.995 mmol·g−1. The breakthrough point for SCN-2-NCS was 385–390 BV in Pd(MeCN)2Cl2 solution (1.000 mmol·L-1) and reached to 126–130 BV in Pd-catalyzed debenzylation waste stream (5.433 mmol·L-1). Subsequently, computational chemistry certified an electrophilic addition reaction occurred to generate a five-member Pd2+ complex in adsorption process which could be converted to N-substituted thiocarboxylic acid in acid condition, and FTIR, NMR and XPS analysis were further employed to probe the proposed adsorption mechanism.