Effect of surface defects in graphitic compounds recovered from spent alkaline/Lithium-ion batteries on the solar photodegradation of methylene blue dye

This study reports the performance of graphite recovered from spent alkaline and lithium batteries for the photocatalytic degradation of methylene blue (MB, 30 mg/L) dye. DBAA graphite powder was recovered from Duracell batteries, while LBH and LBL graphite powders were extracted from Huawei and Lenovo batteries. DBAA powder induced a complete degradation of MB (under sunlight) after only 30 minutes. In contrast, 90 minutes were needed to completely degrade MB under UV-VIS light and using the DBAA powder. Moreover, the LBG and LBL powders induced degradation efficiencies of 92-99.9% for MB under sunlight after 90 minutes. Later, each graphite was immobilized on a graphene-coated polyurethane sponge (SGr composite). In this way, SGr/DBAA, SGr/LBL and SGr/LBH composites were obtained. Subsequently, these composites were evaluated for the photocatalytic degradation of MB under sunlight and produced degradation efficiencies above 96%. In general, the fastest degradation times of 60 minutes was induced by the DBAA powder and SGr/DBAA composite. This occurred because DBAA graphite contained extra Mn/Zn based oxides and higher content of oxygen groups (O=C-O, C-O etc.) in comparison with graphite extracted from lithium batteries (as confirmed by XPS, EDS and FTIR spectroscopies). In consequence, more defects are found on the surface of DBAA powder (according to Raman spectroscopy), and those ones worked as electron trapping centers that accelerated the photocatalytic degradation of MB. Moreover, total organic carbon measurements indicated that the highest mineralization of by-products (92%) was produced by the DBAA powder. Furthermore, the main oxidizing species responsible for the degradation of MB were •OH and • O 2 − radicals according to scavenger tests. Overall, the findings of this research demonstrate the potential of graphite recycled from spent batteries as photocatalytic agents for water cleaning.