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.

Lead (Pb) is a highly toxic heavy metal that causes significant health hazards and environmental damage. Thus, the detection and removal of Pb²⁺ ions in freshwater sources are imperative for safeguarding public health and the environment. Moreover, the transformation of single resources into multiple high-value products is vital for achieving sustainable development goals (SDGs). In this regard, the present work focused on the preparation of two efficient materials, i.e., biochar (R-BC) and carbon dots (R-CDs) from a single resource (rice straw), via a novel approach by using extraction and hydrothermal process. The various microscopic and spectroscopy techniques confirmed the formation of porous structure and spherical morphology of R-BC and R-CDs, respectively. FTIR analysis confirmed the presence of hydroxyl (–OH), carboxyl (–COO) and amine (N–H) groups on the R-CDs’ surface. The obtained blue luminescent R-CDs were employed as chemosensors for the detection of Pb²⁺ ions. The sensor exhibited a strong linear correlation over a concentration range of 1 µM to 100 µM, with a limit of detection (LOD) of 0.11 µM. Furthermore, the BET analysis of R-BC indicated a surface area of 1.71 m²/g and a monolayer volume of 0.0081 cm³/g, supporting its adsorption potential for Pb²⁺. The R-BC showed excellent removal efficiency of 77.61%. The adsorption process followed the Langmuir isotherm model and second-order kinetics. Therefore, the dual use of rice straw-derived provides a cost-effective, environmentally friendly solution for Pb²⁺ detection and remediation to accomplish the SDGs.

Carbon dots (CDs) are emerging novel fluorescent sensing nanomaterials owing to their tunable optical properties, biocompatibility, and eco-friendliness. Herein, we report a facile one-pot hydrothermal route for the synthesis of highly green fluorescent CDs using gallic acid (GA) as a single carbon source in N,N-dimethylformamide (DMF) solvent, which serves as a nitrogen source and reaction medium. The optical properties of the synthesized GA-DMF CDs were systematically characterized by using UV-vis and photoluminescence spectroscopy, revealing strong green fluorescence. Further, to gain insights into their size and structural, elemental, and chemical composition, Fourier transform infrared, dynamic light scattering, high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction, and X-ray photoelectron spectroscopy characterization techniques were performed. HR-TEM analysis confirmed the formation of uniformly spherical GA-DMF CDs with an average particle size of 16 ± 6.1 nm. Notably, the GA-DMF CDs exhibited a highly selective and turn-on fluorescent response to Pb²⁺ ions in aqueous solutions, which was attributed to a chelation-enhanced fluorescence mechanism. The detection limit for Pb²⁺ ions was determined to be as low as 7.15 × 10^-7 M, with a broad linear detection range of 30-130 μM, underscoring their sensitivity and practical application in water quality monitoring. This study introduces a novel, sustainable approach for synthesizing nitrogen-doped CDs with outstanding optical properties and highlights their unprecedented selectivity toward Pb²⁺ ions, advancing the development of efficient and eco-friendly sensing platforms for heavy metal detection.

Zinc ferrite (ZnFe₂O₄) is a prominent spinel-type ferrite that has received significant attention over the recent years. This comprehensive review delves into the various synthesis routes employed to produce ZnFe₂O₄ ferrites, including traditional ceramic methods, sol-gel techniques, co-precipitation, and hydrothermal synthesis, among others. Each method’s advantages and limitations are deliberated, with a weight on controlling size of the particle, morphology, and crystallinity to enhance material performance. The review further explores the intrinsic properties of ZnFe₂O₄, focusing on its magnetic behaviour, dielectric properties, and structural stability under varying conditions. The material’s potential applications are broad, spanning catalysis, energy storage, gas sensing, and biomedical uses like, magnetic resonance imaging (MRI) and drug delivery. Additionally, the environmental applications of ZnFe₂O₄, particularly in photocatalysis and wastewater treatment, are highlighted. Future research directions are proposed, aiming at optimizing synthesis conditions to tailor specific properties for advanced applications, particularly in nanotechnology and sustainable energy solutions.

Water scarcity and contamination represent critical challenges in the twenty-first century, with only a fraction of the Earth’s water being suitable for human use. Various pollutants, including heavy metals, dyes, and pharmaceuticals, compromise water quality, leading to serious environmental and health issues. Traditional wastewater treatment methods often fall short in effectively removing these contaminants. Photocatalysis has emerged as a promising solution, particularly with the use of nickel oxide (NiO) as a photocatalyst. This review explores the fundamentals of photocatalysis, the unique properties of NiO, and its applications in wastewater treatment. NiO is a great option for degrading the organic contaminants because it has a suitable band gap for light absorption and effective charge carrier separation. The synergistic effects of NiO composites with other semiconductors, such as TiO₂ and ZnO, further enhance photocatalytic efficiency. Recent advancements in NiO photocatalysis indicate its potential for large-scale applications, addressing the urgent need for sustainable water purification technologies.