Noble metal (silver (Ag), gold (Au), platinum (Pt), and palladium (Pd)) nanoparticles have gained increasing attention due to their importance in several research fields such as environmental and medical research.

This review emphasizes the progress in identifying and eliminating para-nitrophenol (4-NP), a toxic organic compound. It covers various strategical methods and materials, including organic and inorganic nanomaterials, for detecting and reducing 4-NP. Detection techniques such as electrochemical methods. Optical fiber-based surface plasmon resonance and photoluminescence, as well as the mechanisms of Förster Resonance Energy Transfer (FRET) and Inner Filter Effect (IFE) in fluorescence detection, are presented. Removal techniques for this contaminant include homogeneous catalysis, electrocatalysis, photocatalysis, and thermocatalysis, and their reaction mechanisms are also discussed. Further, the theoretical perspectives of 4-NP detection and reduction, parameters influencing the activities, and future perspectives are also reviewed in detail.

The discovery of carbon dots (CDs) for environmental remediation has gained awareness because of the diverse economically viable and environmental friendly green precursors generated from biowastes and biomass compared to the toxic inorganic quantum dots and CDs prepared from chemical precursors. This review presents the recent progress in green CDs, including their synthesis methods and sensing applications for the detection of heavy metal ions such as Iron (III), Mercury (II), Copper (II), Chromium (VI), Lead (II), Arsenic (III), Cobalt (II), Aluminum (III), Silver (I), and Gold (III) which are prominent environmental pollutants. The comparison based on selectivity, sensitivity, quantum yield, detection limit, linear concentration range, and sensing mechanisms are also reported. This review also covers the performance of doped green CDs using heteroatoms, toward the detection of heavy metal ions. Apart from the future perspectives, this review provides a general guide to use such environmental friendly CDs to detect harmful pollutants.