Ferrocenyl Lawesson's reagent-based porous organic polymers for efficient adsorption-assisted photocatalysis degradation of organic dyes

The adsorption process followed by photodegradation, adsorption-assisted photocatalysis, is an efficient way to achieve an enhanced overall removal of pollutants from wastewater. This aim can be achieved by a new type of metallocene-based porous organic polymers, denoted as Ferrocenyl Lawesson's reagent-metal-organic porous polymers (FcLR-MOPPs), including FcLR-P1 and FcLR-P2, synthesized through 1) synthesis of ferrocene-MOPPs (ferrocene-P1 and ferrocene-P2) through a Friedel-Crafts reaction between dimethoxymethane and ferrocene at two different ratios of 3:1 and 5:1 and 2) reaction of the ferrocene-MOPPs with phosphonium pentasulfide (P₂S₅). The photodegradation efficiencies of methylene blue (MB) and methyl orange (MO) toward FcLR-MOPPs were higher than those of the ferrocene-MOPPs. In contrast, the adsorption efficiencies of the dyes declined after the reaction of ferrocene-MOPPs with P₂S₅. In both cases, a higher photocatalytic activity and adsorption affinity were observed towards MB dye. When combined degradation/adsorption of dyes was investigated, a boosted dye elimination was observed for both the MOPP-based catalysts. FcLR-P1, as the optimal catalyst with the MB degradation/adsorption efficiency of 87.0 % ± 3.0, indicated a pseudo-first-order kinetic model for degradation of MB with a degradation rate constant of 0.074 min^-1, a pseudo-second-order kinetic model and Langmuir isotherm for adsorption of MB, and high reusing after three cycles of use. A band gap energy (E_g) value of +2.3 eV was determined for FcLR-P1 via Tauc plots, consistent with the E_g value obtained from the cyclic voltammetry curves (+1.98 eV). Mott-Schottky plots consistent with radical trapping experiments indicated ^•OH species as the critical species in the MB photodegradation.