Novel dialdehyde fullerene-like carbon nanostructures from red garlic peels for naked-eye cyclohexane gas sensing and pH

This study introduces highly sensitive, functionalized dialdehyde fullerene-like carbon nanostructures (DAFs) as a versatile platform for chemical sensing. The DAFs were synthesized through an effective functionalization strategy, confirmed by Fourier-Transform Infrared Spectroscopy (FTIR), which introduced key dialdehyde groups necessary for multi-modal detection. Transmission Electron Microscopy (TEM) validated a critical morphological evolution from small carbon dots (CDs) to larger, fullerene-shaped DAFs, providing a new electronic and structural foundation for sensing. The DAFs demonstrate dual sensing capabilities for both pH and non-polar organic vapors, specifically explosive cyclohexane (LEL ≈ 13000 ppm). The DAFs sensor's Limit of Detection (LOD) of 137.34 ppm is strategically justified by this hazard, as it provides an early, high-reliability safety warning significantly below the 10% LEL industrial safety threshold of 1300 ppm. Density Functional Theory (DFT) calculations elucidated the mechanism of gas detection, confirming that the interaction with non-polar cyclohexane fundamentally alters the electronic structure of the DAFs, causing the dipole moment (µ) to increase significantly from 5.060 Debye to 8.203 Debye, which underlies the observed fluorescence enhancement. Experimentally, the DAFs function as an effective pH probe, exhibiting a distinctive "turn-on" fluorescence response at alkaline pH 12 due to the deprotonation of surface functional groups. Crucially, the material operates as a simple, naked-eye visual sensor for cyclohexane, quantified by a clear shift in CIE chromaticity coordinates from (0.193, 0.422) to (0.209, 0.473) upon gas exposure. This work provides a deep, integrated theoretical and experimental understanding of functionalized carbon nanostructures for industrial safety and general environmental applications.