Ella Cebisa Linganiso

Efficient recycling of nickel-rich lithium-ion battery waste is critical for sustainable resource security, particularly as nickel is the dominant value-driving and electrochemically active transition metal in high-energy-density LiNi₀.₈Mn₀.₁Co₀.₁O₂ (NMC 811) cathodes. However, the chemical resistance of industrially processed Ni-rich black mass and the structural mechanisms controlling nickel release remain poorly understood. This study investigates proton-assisted preferential nickel dissolution and associated crystal phase transformation of real spent NMC 811 black mass during hydrometallurgical leaching using a green citric acid and hydrogen peroxide (H₂O₂) system. Leachate analysis was combined with X-ray diffraction (XRD), Rietveld refinement, and Raman spectroscopy to correlate nickel recovery with lattice destabilization. Leaching conditions were optimized across an eight-experiment series by varying temperature (55–80 °C), reaction duration (2–8 h), and H₂O₂ addition strategy. Optimal conditions (80 °C, 8 h, gradual H₂O₂ addition) achieved preferential Ni recovery of 84.9%, with Co, Mn, and Li recoveries of 72.7%, 70.2%, and 71.7%, respectively. Structural analysis revealed that proton-assisted dissolution caused lattice expansion through lithium depletion, increasing the c-axis parameter from 14.19 Å to 14.38 Å, followed by collapse of the layered R-3m framework into a disordered Fm3m rock-salt phase with transition-metal cation mixing reaching 12.8%. Raman spectroscopy confirmed local bonding disorder with nickel hydroxide and amorphous manganese oxide surface species. These findings demonstrate that nickel recovery from spent NMC 811 is controlled by both solution chemistry and crystallographic evolution, providing a mechanistic basis for optimizing sustainable recycling strategies for high-nickel battery materials.

The transition of South Africa’s mining sector from a linear take–make–waste model to a circular economy is critical for environmental sustainability and resource security. While the existing literature heavily favors generic, theoretical solutions, this review paper bridges the gap by mapping validated circular technologies directly onto named local operations and specific regional waste profiles. By pairing engineering innovations such as automated sorting and geopolymer synthesis with site-level mineralogical realities and techno-economic limits, this work provides a realistic blueprint for sustainable resource management and holistic landscape restoration. However, widespread implementation is currently constrained by a lack of commercial-scale data, low data transparency regarding corporate waste inventories, static economic modeling, and ambiguous regulatory definitions that separate waste from by-products. To overcome these limitations, a phased, internationally benchmarked policy roadmap aligned with South Africa’s critical minerals strategies is proposed. Future research should focus on industrial field trials, blockchain-secured geospatial waste databases, dynamic life-cycle assessments, and cross-sector synergy mapping. Ultimately, aligning technological innovations with updated waste classification standards, specialized tax incentives, and carbon-credit structures will allow South Africa to mitigate its legacy environmental liabilities while safeguarding its position in the shifting global critical minerals market.

Synthetic dyes, particularly azo dyes, pose significant environmental and health risks due to their persistence, toxicity, and potential carcinogenicity. Zinc oxide (ZnO) is a promising photocatalyst for wastewater remediation, but its wide bandgap and rapid charge recombination limit its practical efficacy. Furthermore, conventional doping methods often rely on hazardous chemical precursors, undermining the sustainability of the overall approach. This review introduces a novel and sustainable paradigm: the utilization of biomass-derived precursors as green reagents for the in-situ synthesis and simultaneous phosphorus-nitrogen (P-N) co-doping of ZnO nanoparticles. We critically analyze how the intrinsic biochemical composition of biomass, rich in P, N, and other heteroatoms, facilitates this one-pot, eco-friendly functionalization. This integrated strategy merges the performance enhancement offered by advanced co-doping, such as extended visible-light absorption and suppressed charge recombination, with the core principles of green chemistry and circular economy. It offers a dual benefit: creating highly effective photocatalysts for the degradation of persistent pollutants and valorizing abundant agricultural or biological waste streams. Our comprehensive evaluation goes beyond description to critically assess the underlying mechanisms, comparative efficacy, scalability challenges, and future research directions of this emerging field. This review underscores the unique contribution of biomass-mediated synthesis to advancing sustainable nanotechnology for environmental applications.

Synthetic dyes, particularly azo dyes, pose significant environmental and health risks due to their persistence, toxicity, and potential carcinogenicity. Zinc oxide (ZnO) is a promising photocatalyst for wastewater remediation, but its wide bandgap and rapid charge recombination limit its practical efficacy. Furthermore, conventional doping methods often rely on hazardous chemical precursors, undermining the sustainability of the overall approach. This review introduces a novel and sustainable paradigm: the utilization of biomass-derived precursors as green reagents for the in-situ synthesis and simultaneous phosphorus-nitrogen (P-N) co-doping of ZnO nanoparticles. We critically analyze how the intrinsic biochemical composition of biomass, rich in P, N, and other heteroatoms, facilitates this one-pot, eco-friendly functionalization. This integrated strategy merges the performance enhancement offered by advanced co-doping, such as extended visible-light absorption and suppressed charge recombination, with the core principles of green chemistry and circular economy. It offers a dual benefit: creating highly effective photocatalysts for the degradation of persistent pollutants and valorizing abundant agricultural or biological waste streams. Our comprehensive evaluation goes beyond description to critically assess the underlying mechanisms, comparative efficacy, scalability challenges, and future research directions of this emerging field. This review underscores the unique contribution of biomass-mediated synthesis to advancing sustainable nanotechnology for environmental applications.

The increasing rate of environmental pollution and the emergence of new infectious diseases have drawn much attention toward the area of gas sensors for air quality monitoring and early-stage disease diagnosis, respectively. Polyaniline (PANI) has become one of the extensively studied polymers in the area of chemical sensing due to its good conductivity and sensitivity at room temperature. The development of room-temperature gas sensors represents a significant leap forward in air quality monitoring by conserving energy and enhancing the feasibility of the commercial development of sensing technologies. New research shines a light on the advantages of using PANI with materials such as semiconductor metal chalcogenides, metal oxides, metal nanoparticles, and graphitic carbon materials to form composites that can sense chemicals selectively at room temperature. This review focuses on the advancements in PANI-based gas sensors, exploring the materials, mechanisms, and applications that make these sensors a promising solution for modern air quality monitoring challenges. By examining the latest research and innovations, we aim to highlight this critical technology’s potential and future directions, instilling hope and optimism in safeguarding public health and the environment.

The need for eco-friendly, cost-effective, and scalable methods to synthesize carbon quantum dots (CQDs) remains a critical goal in nanotechnology. In this work, nitrogen-doped carbon quantum dots (N-CQDs) were successfully synthesized using cellulose nanocrystals (CNCs) derived from microcrystalline cellulose (MCC) and urea through a rapid one-step microwave-assisted method. The use of renewable cellulose as a precursor aligns with sustainable practices, offering a pathway to transform agricultural waste into valuable nanomaterials. Characterized by TEM, XRD, Raman, XPS, and PL spectroscopy, the N-CQDs demonstrated outstanding optical properties, including strong excitation-dependent fluorescence with an emission maximum at 420 nm. The N-CQDs exhibited exceptional selectivity and sensitivity toward Fe³⁺, achieving a detection limit of 75 nM. Additionally, the pH-dependent fluorescence and stability in diverse conditions highlight the N-CQDs’ versatility in environmental monitoring. This study establishes a foundation for using agricultural waste to produce high-performance nanostructures for sensing applications, advancing green nanotechnology and environmental solutions.

Green chemistry seeks to find alternative synthesis routes that are less harsh to living organisms and the environment. In this communication, a microwave-assisted hydrothermal technique and a thermal annealing method were used in the reduction of graphene oxide (GO) to make reduced GO (rGO). Graphite powder was oxidised using the Improved Hummers’ method, exfoliated, and freeze-dried. Thereafter, an aqueous suspension of GO was reduced under microwave (MW) irradiation for 10 min at 600 W with and without the help of a reducing agent (hydrazine hydrate). Thermal annealing reduction was also conducted under a nitrogen atmosphere at 300 °C for 1 h. Prepared samples were analysed using Raman laser spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), the Brunauer–Emmett–Teller (BET) method, and X-ray photoelectron spectroscopy (XPS). A successful reduction in the GO functional groups between the sheets was established using XRD. In the Raman analysis, the ratio of the intensity of the D and G band (I_D/I_G) in graphene sheets assisted in assessing the quality of the graphene films. An estimation of the number of structural defects was calculated using the I_D/I_G ratio. The Raman analysis showed an increase in the I_D/I_G ratio after both oxidation and reduction processes. The defect densities of both MW-treated samples were comparable while an increased defect density was evident in the thermally annealed sample. TEM micrographs confirmed the sheet-like morphology of the samples. The rGO sheets obtained from the MW-treated method appeared to be smaller when compared to the rGO ones obtained by thermal treatment. It was also evident from XRD analysis that thermal treatment promoted the coalition of graphitic layers, such that the estimated number of layers was larger than that of GO. The elemental analysis showed that the C/O ratio of GO increased from 2 to 7.8 after MW hydrazine reduction.

The demand for reliable, cost-effective, room temperature gas sensors with high sensitivity, selectivity, and short response times is rising, particularly for environmental monitoring, biomedicine, and agriculture. In this study, corncob waste-derived activated carbon (ACC) was combined with CuO nanoparticles and polyvinyl alcohol (PVA) to fabricate ACC/PVA/CuO composites with CuO loadings of 5, 10, and 15 wt.%. The CuO nanoparticles (average size: 21.79 ± 9.88 nm) were successfully incorporated into the ACC matrix, as confirmed by TEM, XRD, and N₂ adsorption–desorption analyses. Increasing CuO content reduced the specific surface area due to pore blockage but enhanced the composites’ ethanol sensing performance. The ACC/PVA/CuO (15 wt.%) sensor exhibited the highest response and fastest recovery times (125 s and 130 s, respectively, at 100 ppm ethanol), outperforming other composites and pristine ACC. This improvement was attributed to surface defects and increased active sites promoting vapor adsorption and diffusion. These results demonstrate the potential of ACC/PVA/CuO as an effective ethanol sensor at room temperature.

The hydrogen evolution reaction (HER) in alkaline electrolytes using transition metal dichalcogenides is a research area that is not tapped into. Alkaline HER ( ) is harder to achieve relative to acidic HER ( ), this is attributed to the additional water dissociation step that occurs in basic HER to generate H⁺ ions. In fact, for most catalysts, their HER activity decreases tremendously when the electrolyte is changed from acidic to basic conditions. Platinum dichalcogenides, PtX₂ (X=S, Se, Te), are an interesting member of transition metal dichalcogenides (TMDs) as these show an immense hybridization of the Pt d orbitals and chalcogen p orbitals because of closely correlated orbital energies. The trend in electronic properties of these materials changes drastically as the chalcogen is changed, with PtS₂ reported to exhibit semi‐conductor properties, PtSe₂ is semi‐metallic or semi‐conductive, depending on the number of layers, while PtTe₂ is metallic. The effect of varying the chalcogen atom on the HER activity of Pt dichalcogenides will be studied. Pt dichalcogenides have previously been prepared by direct high‐temperature chalcogen deposition of Pt substrate and evaluated as electrocatalysts for HER in H₂SO₄. The previously employed synthesis procedures for PtX₂ limit these compounds′ mass production and post‐synthesis treatment. In this study, we demonstrated, for the first time the preparation of PtSe₂ and PtTe₂ by colloidal synthesis. Colloidal synthesis offers the possibility of large‐scale synthesis of materials and affords the employment of the colloids at various concentrations in ink formulation. The electrochemical HER results acquired in 1 M KOH indicate that PtTe₂ has a superior HER catalytic activity to PtSe₂. A potential of 108 mV for PtTe₂ and 161 mV for PtSe₂ is required to produce a current density of −10 mA cm⁻² from these catalysts. PtTe₂ has a low Tafel slope of 79 mVdec⁻¹, indicating faster HER kinetics on PtTe₂. Nonetheless, the stability of these catalysts in an alkaline medium needs to be improved to render them excellent HER electrocatalysts.