Plant-derived carbon dots (P-CDs) are gaining attention in environmental remediation due to their cost-effectiveness, availability, and lower toxicity compared with chemically synthesized carbon dots. This review comprehensively examines the recent advancements in the synthesis and application of P-CDs, with a particular emphasis on their efficacy in the sensing of heavy metals, which are among the most pervasive environmental contaminants. A detailed comparative analysis is presented by evaluating the performance of P-CDs against their chemically synthesized counterparts based on key parameters, such as optimal operating conditions and detection limits. Furthermore, sensing the potential of P-CDs towards every heavy metal ion has been discussed with in-depth mechanistic insights. Additionally, this review explores the industrial applications and future directions of P-CDs. This review provides a comprehensive analysis of -P-CDs for heavy metal sensing, aiming to enhance their sensitivity and selectivity toward heavy metal ions.

The extraction of metallic nanoparticles (MNPs) from waste electrical and electronic equipment (WEEE) has gained extensive attention from researchers for eco-friendly, reliable, and sustainable alternative protocol over the traditional linear economic approach (make-use-dispose) for boosting the circular economy. A plethora of MNPs including metals/metal oxide nanoparticles having a size dimension ranging from 1–100 nanometers (nm) have been extracted from these WEEE by using different chemical, physical, and biological methods. Recovery of certain precious MNPs can be achieved by dismantling and recycling electronic waste items in the form of gold (Au), platinum (Pt), zinc oxide (ZnO), silver (Ag), and copper oxide (CuO). These MNPs provide a huge range of applications such as antibacterial, therapeutic, target drug delivery, and biotechnological applications. This comprehensive review provides in-depth knowledge of the synthesis of MNPs using different techniques from WEEE and delves into their potential applications in biomedical fields with in-depth mechanisms. This article also discussed global challenges and opportunities in this area for adopting the concept of circular economy to conserve natural resources for future generations and hence create a greener environment and protect our planet.

Copper spinel ferrite (CuFe₂O₄) is a promising material for the gas sensing due to its unique structural, electrical, and catalytic properties. This review focuses on the gas sensing capabilities of copper ferrite. Copper ferrite’s inverse spinel structure, rich in oxygen vacancies and flexible cation distribution, enables effective gas adsorption, making it highly sensitive to reducing and oxidizing gases. Various synthesis methods, determines the material’s particle size, morphology, and surface area, which are essential for optimizing gas sensing performance. Doping with the transition metals like nickel (Ni) and zinc (Zn) significantly enhances the material’s sensitivity, selectivity, response time, and operating temperature by increasing oxygen vacancies and improving charge transport. However, challenges remain, including high operating temperatures, cross-sensitivity to humidity, and long recovery times. Future research directions focus on lowering the operating temperature, improving selectivity, enhancing humidity tolerance, and developing nanostructured and surface-functionalized copper ferrite sensors. Furthermore, the integration of copper ferrite sensors into wearable and IoT devices, as well as field testing in real-world applications, presents exciting opportunities for expanding their use in environmental monitoring. This review highlights the current advancements in gas sensors and suggests potential strategies for overcoming existing limitations, paving the way for next-generation gas sensing technologies.

Ferrites are classified as a remarkable category of materials recognized for their extensive range of applications. Within the realm of ferrites, spinel ferrites are considered promising soft magnetic materials, exhibiting exceptional characteristics such as appropriate band gap, significant coercivity, elevated saturation magnetization, and enhanced thermal and electrical traits. Specifically, Nickel ferrites, which are categorized as spinel ferrites, constitute a type of magnetic materials that have attracted significant attention owing to their remarkable traits. This is the highly magnetic substance that demonstrates outstanding electrical, magnetic, and optical, and catalytic properties. Nickel ferrite has garnered extensive importance because of its wide- ranging applications, which include medical therapies, electronic devices, attenuation of electromagnetic waves, and as catalysts for the water purification. This prominence can be ascribed to its advantageous attributes, including elevated permeability, resistivity, and saturation magnetization. This review provides a comprehensive summary of recent research on nickel ferrites. There are four sections in this study. The first provides an introduction to spinel ferrites, including their structure. The subsequent section concentrates specifically on classification, and nickel ferrite. The third section critically examines research pertaining to various doping in nickel spinel ferrites, with the objective of augmenting their intrinsic properties. The final section discusses the structural, magnetic, and catalytic traits of NiFe₂O₄.

The continuous increase in urbanization and global population has led to the generation of a substantial amount of kitchen waste, posing severe environmental and disposal challenges. The utilization of kitchen waste as organic biomass for biochar production offers a promising, sustainable, and cost-effective solution. This review comprehensively analyzes the recent developments in the transformation of kitchen waste into biochar. Moreover, the current study involves various synthesis techniques, the physicochemical characteristics of biochar, and its applications in soil and water remediation. Afterwards, the experimental parameters and feedstock types are critically evaluated in terms of their key characteristics for biochar. Moreover, the current study highlights the effectiveness of kitchen waste-derived biochar (KWBC) in decomposing organic pollutants, heavy metals, and pharmaceutical pollutants from contaminated environments. Additionally, the mechanisms of adsorption, ion exchange, complexation, and redox interactions are thoroughly illustrated to evaluate the pollutant removal pathways. At the end of the study, experimental parameters such as pH, dosage, contact time, and initial pollutant concentration are discussed, which play the main role in enhancing the adsorption capacity of biochar. Finally, this review outlines current limitations and proposes future directions for optimizing biochar performance and promoting its large-scale application in sustainable environmental management.

Nitrophenol (NP) and methylene blue (MB) are considered among the most hazardous organic contaminants frequently released from pharmaceutical, textile, and paper industries, posing significant risks to both human health and the environment. The conventional treatment involves adsorption, oxidation, biological, filtration, and other photochemical degradation methods, which often suffer from low efficiency, limited reusability, and the production of secondary toxic by-products. In this context, the nanomaterials (NMs) mediated catalytic reduction of MB into leucomethylene blue and p-NP into p-aminophenol (p-AP) has emerged as a promising approach, due to its high efficiency and effectiveness. This review emphasizes the green synthesis of NMs for catalytic applications, which align with the principles of the circular economy and the Sustainable Development Goals (SDGs). This thorough review systematically examines the mechanistic understanding of the reduction of both p-NP and MB via different green synthesized NMs and evaluating their catalytic efficiencies. Furthermore, a detailed discussion of the reduction of pollutants (p-NP and MB) is provided, along with their mechanistic insights. In addition, this paper also provides a comparative table highlighting the effects of using different precursors, experimental conditions on the conversion catalytic efficiency and reusability potency. Thus, this work provides the insights into recent research on the catalytic reduction of p-NP and MB into valuable products, highlighting the significance of green synthesized nanocatalysts for effective wastewater treatment.