We report Ni-doped MnBi2O4 (MnNiBi) as a defect-engineered material that works as efficient photocatalyst and as redox material for flexible supercapacitors (SCs). Ni incorporation induces lattice distortions that create oxygen vacancies, which act as active sites for charge storage or for the degradation of contaminants. Firstly, SCs were fabricated with graphene (G) electrodes printed on flexible polyethylene and those electrodes were coated with MnBi or MnNiBi powders. The G/MnNiBi-SC device (made with electrodes of G+MnNiBi) showed a capacitance of 810 F g− 1, high energy density of 165 Wh kg− 1, and high capacitance retention (94%) after 1000 charging-discharging cycles. Also, a device was made with MnBi powder (without Ni dopant), but the capacitance and energy density decreased to 155 F g− 1 and 48 Wh kg− 1, respectively. Thus, the presence of Ni in the redox powder increased the capacitance by 422%. Moreover, MnNiBi powder produced high photocatalytic degradation of methylene blue (MB, 93%) and glyphosate (75%) under direct sunlight, which was superior to the degradation percentages obtained with undoped MnBi (57–70%). Interestingly, the degradation % increased to 98% and to 92% for MB and glyphosate, respectively, under UV-light. Moreover, total organic carbon measurements indicated mineralization efficiencies of 75% for MB and 58% for glyphosate. XPS studies showed that oxygen vacancies defects increased ⁓225% after the use of the MnNiBi powder for photocatalysis, which accelerated the degradation of contaminants. These defects were also crucial for supercapacitors, because they worked as redox centers to store charge. Thus, multifunction MnNiBi powders were used for charge-storage/water-cleaning.

Abstract This study proposes a sustainable and selective hydrometallurgical route for the recovery of lithium (Li) and cobalt (Co) from spent lithium-ion batteries (LIBs), integrating sodium sulfite-assisted sulfation roasting with water and organic acid leaching. The sulfation roasting process at 600 °C facilitated the transformation of LiCoO 2 into soluble LiNaSO 4 while preserving cobalt predominantly in oxide form. Subsequent water leaching at 50 °C selectively dissolved lithium (up to 74.4%), leaving cobalt in the residue. To achieve complete metal recovery, oxalic acid—a biodegradable and environmentally benign organic acid—was used as a leaching agent. Under optimized conditions (1 mol·L − 1 oxalic acid, 90 °C, 90 min, S/L ratio 1/160), leaching efficiencies reached 99.96% for Li and 99.15% for Co. Notably, cobalt was recovered directly as a cobalt oxalate precipitate, while lithium remained in solution, eliminating the need for additional separation steps. In the water-leaching stage, lithium selectively dissolves while cobalt largely remains in oxide form. In the separate oxalic-acid leaching stage, both metals dissolve; however, cobalt immediately precipitates as cobalt oxalate whereas lithium remains soluble. Thus, although the two leaching approaches are independent processes, each exhibits a distinct Li/Co separation behavior. Kinetic modeling revealed that nucleation and growth mechanisms, best described by the Avrami equation, governed the leaching behavior. This combined pyro-hydrometallurgical process offers a high-efficiency, low-impact solution for critical metal recovery from LIB waste and represents a viable alternative to conventional mineral acid-based methods.

Sewer system biofilm development raises significant operational and public health concerns, including decreased hydraulic capacity, increased maintenance costs, infrastructure corrosion, and the spread of pathogenic microorganisms. This review critically discusses both traditional and novel methods for controlling the development of sewer biofilms. Traditional methods involving chemical biocides and disinfectants are discussed, along with their effectiveness and limitations, particularly environmental concerns and the development of microbial resistance. Physical procedures, including mechanical cleaning and pipe scrubbing, have been evaluated for their efficacy and potential side effects. Emerging methods involving antimicrobial coatings (such as silver nanomaterials and copper), enzymatic treatment of biofilm matrix components, and the application of metal-resistant materials to biofilms (including hydrophobic and superhydrophobic materials) have been examined. Multi-strategic, combined approaches are excellent tools for addressing the multifaceted problem of sewer biofilms. The review highlights key gaps for continued work and suggests directions for studies to develop more viable, environmentally friendly methods for controlling sewer biofilms. By integrating recent developments, the review offers practical recommendations for managing sewer biofilms to protect sewer infrastructure and public health.