Supercapacitors may be able to store more energy while maintaining fast charging times; however, they need low-cost and sophisticated electrode materials. Developing innovative and effective carbon-based electrode materials from naturally occurring chemical components is thus critical for supercapacitor development. In this context, biopolymer-derived porous carbon electrode materials for energy storage applications have gained considerable momentum due to their wide accessibility, high porosity, cost-effectiveness, low weight, biodegradability, and environmental friendliness. Moreover, the carbon structures derived from biopolymeric materials possess unique compositional, morphological, and electrochemical properties. This review aims to emphasize (i) the comprehensive concepts of biopolymers and supercapacitors to approach smart carbon-based materials for supercapacitors, (ii) synthesis strategies for biopolymer derived nanostructured carbons, (iii) recent advancements in biopolymer derived nanostructured carbons for supercapacitors, and (iv) challenges and future prospects from the viewpoint of green chemistry-based energy storage. This study is likely to be useful to the scientific community interested in the design of low-cost, efficient, and green electrode materials for supercapacitors as well as various types of electrocatalysis for energy production.

The increasing demand for cost-effective materials for energy storage devices has prompted investigations into diverse waste derived electrode materials for supercapacitors (SCs) application. This review examines advancements in converting waste into carbon-based SCs for renewable energy storage. In this context, different carbon-based waste precursor sources have been explored over the years as electrodes in SCs. These waste sources comprise of industrial, plastics and biowastes, including plant and animal wastes. The energy storage capabilities of the various waste derived SCs electrodes are highlighted to provide an understanding into the unique features that make them applicable to SCs. In addition, some challenges associated with the waste-derived SCs electrodes in terms of energy storage have been emphasized. Here, we also provided insights into the recent progress in SCs electrode synthesis techniques and their effects on electrochemical performance. SCs performance tailoring with material structures through the incorporation of different materials to form composites and optimized synthesis methods is an effective strategy. Hence, the synthesis methods outlined include pyrolysis, hydrothermal, microwave-assisted, template-assisted, and sol–gel techniques. The effect of the various synthesis methods on SCs performance has also been discussed. Overall, this review highlights waste valorization with future research directions and scaling challenges.

This comprehensive review explores the remarkable progress and prospects of diatomaceous earth (DE) as a bio-template material for synthesizing electrode materials tailored explicitly for supercapacitor and battery applications. The unique structures within DE, including its mesoporous nature and high surface area, have positioned it as a pivotal material in energy storage. The mesoporous framework of DE, often defined by pores with diameters between 2 and 50 nm, provides a substantial surface area, a fundamental element for charge storage, and transfer in electrochemical energy conversion and storage. Its bio-templating capabilities have ushered in the creation of highly efficient electrode materials. Moreover, the role of DE in enhancing ion accessibility has made it an excellent choice for high-power applications. As we gaze toward the future, the prospects of DE as a bio-template material for supercapacitor and battery electrode material appear exceptionally promising. Customized material synthesis, scalability challenges, multidisciplinary collaborations, and sustainable initiatives are emerging as key areas of interest. The natural abundance and eco-friendly attributes of DE align with the growing emphasis on sustainability in energy solutions, and its contribution to electrode material synthesis for supercapacitors and batteries presents an exciting avenue to evolve energy storage technologies. Its intricate structures and bio-templating capabilities offer a compelling path for advancing sustainable, high-performance energy storage solutions, marking a significant step toward a greener and more efficient future. Graphical Abstract

Over the years, spent potlining (SPL) treatment has only focused on the extraction of its hazardous compounds, especially fluorides and cyanides. The literature has not sufficiently addressed the optimization and kinetics of fluoride extraction using statistical modeling to determine relevant factors for efficient, cost-effective, and sustainable SPL treatment. Hence, this study is focused on response surface methodology (RSM) combined with central composite design (CCD) to statistically model fluoride extraction of SPL behaviour in acidic environments. Shrinkage core model (SCM) was used to investigate the kinetics of fluoride extraction. The RSM analyses suggested a second-order quadratic model with outstanding accuracy, statistically supported by R² and adjusted R² values of 0.986 and 0.973, respectively. The quadratic model indicates the main factors influencing fluoride extraction, showing the complex interactions of temperature, particle size, acid concentration, and leaching time. These main factors were observed to have significant effects on fluoride extraction, except for particle sizes of the SPL. The optimization process, a key success of this study, achieved fluoride extraction of 87.49% at specific factor levels of 48.43 °C, 0.752 mm, 1.2 M, and 10 min. Subsequently, the SCM investigations suggested that diffusion through a liquid film mechanism best approximates the fluoride extraction kinetic behaviour with R² > 0.80 across varying temperatures. Investigations into temperature dependence with the Arrhenius plot further validated that the reaction kinetics were principally controlled by diffusion through liquid film, with an activation energy of 36.26 kJ/mol. Integrating these kinetic frameworks provides a novel approach to analyzing and optimizing SPL fluoride extraction. Overall, adopting the present study in the industrial settings with the optimized parameters will ensure efficient, sustainable, and cost-effective treatment of SPL.

This study synthesises expanded graphite (EG) from graphitised carbon from waste polyethylene terephthalate (PET) bottles. The adsorbent material was characterised using FTIR, XRF, XRD, SEM, Raman Spectroscopy, and BET surface area analysis. The synthesised EG defluorinated wastewater, utilising response surface methodology (RSM) for experimental design and optimisation. XRD patterns confirmed the successful synthesis of graphite and EG, demonstrating structural modifications. Raman spectra indicated higher crystalline order in EG, with D and G band shifts and an increased I_D/I_G intensity ratio from 0.89-1.04. BET analysis revealed a specific surface area of 247.1 m²/g. . FTIR analysis showed abundant functional groups, particularly hydroxyl (-OH) and alkene (C = C). Batch adsorption experiments revealed that fluoride adsorption onto EG depended on pH, time, and initial fluoride concentration. Optimal conditions for fluoride removal, determined using RSM with central composite design (CCD), demonstrated a maximum fluoride removal rate of 97%. Isotherm data fitted both Langmuir and Freundlich model, and kinetics data aligned well with the pseudo-first-order model. ANOVA showed significant effects of contact time, pH, adsorbent dose, and initial fluoride concentration on removal efficiency. The model's R² value of 0.98 and lack of fit value of 0.1554 confirmed the quality of the second-order polynomial model. Optimal conditions for maximum fluoride removal efficiency of 97% were validated at 5 mg/L fluoride concentration, pH 4, adsorbent dose of 5 g/L, and a contact time of 30 min. Therefore, the present study demonstrated efficient fluoride-polluted water treatment using waste-derived EG.