Punica grantum peel extract decorated Al-MOF scaffold as Solid-State Sensor/Concentrator for the Sensing/Reduction of Cr(VI) and its extended utility as a corrosion inhibitor in Al-Air batteries

The growing presence of hexavalent chromium in environmental and industrial settings highlights the importance of developing an eco-benign platform for real-time in-situ sensing/screening and decontamination. This research presents a facile and portable solid-state optical sensor using waste Punica Granatum, i.e., pomegranate peel extract (PPE) adorn onto Aluminium-based Metal-Organic Frameworks (Al-MOFs) for the sensing of carcinogenic Cr(VI) and its decontamination to benign Cr(III). The sensor fabrication entails a hydrothermal synthesis to form Al-MOF scaffolds decorated with PPE through direct immobilization. Al-MOF exhibits a large surface area with well-defined pore channels that facilitate PPE's voluminous/uniform anchoring in restricted orientations to serve as an ion-selective probe for specifically targeting ultra-trace Cr(VI). The surface/structural morphology and porosity of the Al-MOF-PPE material are characterized using scanning/transmission electron microscopy and BET/BJH analysis. The reduction of Cr(VI) by the Al-MOF-PPE is validated by electron spectroscopy for chemical analysis, corroborated by a conspicuous color transition from light yellow to dark brown. The efficient reduction of Cr(VI) by Al-MOF-PPE is achieved at pH 2-3, in the linear response range of 0.3-300 ppb and a detection limit of 0.23 ppb for Cr(VI). The sensory system prefers minimal PPE probe content (4 mg) and sensor dosage (5 mg) for ion-sensing and decontamination studies, highlighting its remarkable operational efficacy. Post Cr(VI) reduction, electrochemical studies confirm the utility of Al-MOF-PPE-Cr(III) as a corrosion inhibitor for metal surfaces. Tafel plots demonstrate that Al-MOF-PPE-Cr(III) exhibits cathodic and anodic inhibition characteristics, ensuring excellent surface protection for aluminum electrodes upto 220 min in Al-air batteries. The proposed Al-MOF-PPE offers dual functionality as a naked-eye platform for Cr(VI) decontamination, and the Al-MOF-PPE-Cr(III) material is an excellent corrosion inhibitor for energy storage devices.