Critical Mechanistic Insight, Technological Innovation Advances and Multi-Media Environmental Application of Colorimetry Toward Heavy Metal Detection.

Colorimetry, a widely employed analytical technique that leverages the visible light spectrum observable to the naked eye, has gained prominence as a straightforward and intuitive method for detecting target substances. This review provides a comprehensive overview of the development and current state of colorimetry, focusing on its origin, underlying mechanism, technological advancement, and application in environmental contexts. The historical evolution of colorimetry is initially surveyed, emphasizing key developmental milestones. The core recognition mechanisms are further elucidated, detailing heavy metal ion-induced discoloration of organic dyes, alongside adjustments in nanomaterial spacing, morphology, and alterations in catalytic performance. Then, technological progress of colorimetry is reviewed, tracing the evolution from traditional UV-visible spectrophotometry to digital image colorimetry and portable, handheld devices. Thereafter, the current state of colorimetry is comprehensively evaluated, particularly its application in detecting heavy metals across water, soil, and atmospheric particulate matter. Ultimately, this review addresses prevailing challenges, such as enhancing ultra-trace detection sensitivity and mitigating matrix interferences, while also highlights strategies to overcome these, which are vital for advancing colorimetric environmental monitoring. The review aims to underscore the potential of colorimetry in complex environmental monitoring and to provide a theoretical framework for future research and technological innovation in the field.