Fluorescence Behavior of Water‐Soluble Porphyrins Immobilized on LTA Zeolite and Its Chlorogenic Acid Polyphenol Sensing in Coffee Wastewater

Chlorogenic acid (CGA) is one of the most common polyphenols found in many fruits, such as coffee cherries, and is among the most economical commodities worldwide. In coffee production, processing and washing require large amounts of water, making wastewater monitoring essential to prevent environmental impact. This work reports the development of a fluorescence-based hybrid sensor designed for the detection of CGA using water-soluble porphyrins immobilized on hierarchical LTA zeolite. The system is based on 5,10,15,20-tetrakis(N-methyl-4-pyridyl)porphyrin (TMPyP) and its Zn(II)-metallated derivative (ZnTMPyP), synthesized directly on the zeolite surface via ion-exchange processes. The hybrid materials (LTA/TMPyP and Zn-LTA/TMPyP) were fully characterized, confirming the preservation of the zeolite structure and the formation of the metalloporphyrin complex within the intercrystalline void network. Fluorescence measurements in phosphate buffer (pH 7.4) showed that Zn-LTA/TMPyP exhibited the best performance for CGA detection, with a detection limit (LOD) of 0.22 nM. To mitigate potential interference from caffeine and caffeic acid, a novel sensing protocol was implemented using these compounds as a controlled background, maintaining high sensitivity (LOD = 0.64 nmol L-1). When tested in real coffee washing water, the sensor quantified CGA at 2.5 ± 0.7 nmol L-1. The measurement accuracy was validated using a nonlinear standard addition method, yielding a recovery of 96.4%, confirming the sensor's ability to compensate for complex matrix effects. The results show that the Zn-LTA/TMPyP hybrid material is a highly efficient, stable, and selective platform for CGA monitoring, with strong potential for integration into portable devices for environmental and agro-industrial applications.