Synthesis and physicochemical evaluations of a novel MIL-101(Fe)-PMA-Biochar triple composite photocatalyst activated through visible-light and utilized toward degradation of organic pollutants: optimal operations and kinetics investigations.

A triple photocatalytic composite of biochar, metal-organic framework, and phosphomolybdic acid was prepared through hydrothermal treatment of iron (III) chloride hexahydrate, terephthalic acid, lavandulifolia-derived biochar, and phosphomolybdic acid. It was characterized and utilized for photodegradation of Rhodamine-B (RhB) dye under visible-light irradiation. Investigations of reaction variables confirmed that, the highest yield of 96.2% was achieved at ambient temperature using 0.07 g of catalyst at pH of 7, and a dye concentration of 10 ppm. Under these optimum conditions, Methyl Orange (MO) dye was also degraded to yield 93% removal. In addition, the kinetic and thermodynamic parameters for RhB were determined. It was revealed that the photodegradation of RhB followed a pseudo-first-order kinetics with no mass transfer limitations. A corresponding chemical mechanism for this process was also suggested. Adsorption isotherms were investigated for rate of adsorption as well as adsorption capacity of the catalyst under dark conditions. Notably, the catalyst could have been reused for five cycles with a loss of around 20% activity.