Facile preparation of magnetic porous carbon monolith from waste corrugated cardboard box for solar steam generation and adsorption

Abstract

Porous carbon monoliths (PCMs) were prepared from waste corrugated cardboard box (WCCB) via slurrying in FeCl3 solution followed by molding and thermal treatment. The thermal process was analyzed by a thermogravimetric analyzer coupled with a Fourier transform infrared spectrometer. The evolution of physicochemical characteristics of PCMs was studied. The photothermal conversion and solar steam generation performances of the optimal sample (PCMFe/600) were evaluated. The adsorption properties of PCMFe/600 for methylene blue (MB) were investigated. Results showed that Fe3+ promoted the breaking of cellulose chains in WCCB, leading to the occurrence of pyrolysis of WCCB at lower temperatures and the reduction of activation energy by 76.63 kJ mol−1. Char yield raised because volatile radicals were captured by FeCl3-derived amorphous Fe(III) species, then involved in char formation. Amorphous Fe(III) continuously converted into Fe3O4 crystallites with carbonization temperature increasing from 400 to 700 °C, then α-Fe was formed at 800 °C via the carbothermal reduction of Fe3O4. FeCl3 was favorable to the formation of a developed microporous structure. Surface area significantly increased with carbonization temperature increasing from 400 to 600 °C due to the removal of volatiles. The etching of carbon by Fe3O4 above 700 °C also led to the increase of surface area. PCMFe/600 exhibited higher optical absorption than other samples due to its high graphite degree and porosity. It also had excellent photothermal performance; thus, solar steam yield was 1.46 times that of the pure water with the assistance of PCMFe/600. PCMFe/600 in floating state was effective in adsorption of MB from water. Besides, the adsorption behavior fitted Langmuir model with a monolayer adsorption capacity reached up to 70.9 mg g−1.