Walnut shell biomass waste derived excitation-dependent CQDs for toxic insecticide sensing and protein denaturation inhibition – An ecofriendly and sustainable approach

In the current predicament, converting any waste material into a valuable product is the need of the hour, and it demands a lot of confidence to work with. In an attempt to demonstrate this assertion, we converted one such waste material, Walnut Shell (WS), into Carbon Quantum Dot (CQD) for insecticide sensing and anti-inflammatory applications. WS is one such non-toxic waste material that has a carbon content and has been used for the preparation of CQDs hydrothermally. The amorphous nature of WS-derived CQDs (WS-CQDs) is revealed by the XRD results, which exhibit a distinct broad peak at 2θ from 21o to 29o. Microscopic images confirm the morphology of WS-CQDs as spherical, approximately 2 nm in size with average d-spacing fringes of 0.29 nm, and surface roughness of 12.53 nm. XPS, FTIR, and EDAX data were used to corroborate the chemical state, presence of functional groups, and elemental composition of WS-CQDs. The calculated ID/IG value (0.85) through Raman analysis divulges that the majority of the carbons in WS-CQDs are sp2 graphitic carbons with structural defects. Excitation-dependent properties of WS-CQDs were examined in different wavelengths (λmax 320 → 400 nm), and contour mapping analysis. Under optimized fluorescence experimental conditions, the linear range of imidacloprid was 0–80 μM with a detection limit of 7.58 × 10−6 M (r2 = 0.9904). The fluorescence decay profile of WS-CQDs suggests a tri-exponential function with an average lifetime of 4.10 ns. Additionally, experiments on the effects of time, competition, and pH on imidacloprid sensing have been performed. Biological properties like cytotoxicity, cell viability, and anti-inflammatory activity have also been investigated for WS-CQDs.