SUMMARY

This dissertation includes five main chapters:

Chapter one provides an introduction to nanoscience including the definition, classification, properties, synthesis, and characterization of nanomaterials. Also, this chapter includes the importance of zinc in food samples. In addition, an introduction to food colorants especially Ponceau 4R (E124) and Allura red (AR). The last part of this chapter includes a general overview of solid phase microextraction and dispersive solid phase microextraction.

In chapter two, violuric acid was used to prepare highly fluorescent CDs, when it irradiated with ultraviolet radiation at 365 nm, a strong violet fluorescence was observed which caused by presence of nitrogen in the CDs structure, which were then successfully used for sensing zinc ion based on quenching of fluorescence. Violuric acid’s hydrothermal carbonization reaction’s temperature and time were simply optimized for better-quality performance of the CDs as synthesized. The probe was characterized by HRTEM, SEM, XRD, EDX, fluorescence, UV–Visible absorption spectrophotometry, and FTIR. With linear range from 0.5 to 900 nM, and a lower LOD 0.32 nM, the developed approach demonstrates an exceptional sensitivity and good selective response to the Zn²⁺ at 25℃. Compared to the results from ICP, the sensor was successfully used for determination of Zn²⁺ ions in tomato paste samples.

Chapter three: In this chapter, for the first time, natural Crocus cancellatus was adopted for the green, low-cost, and simple synthesis of highly fluorescent ultra-small CDs with well-distributed size using a one-pot hydrothermal treatment. As-synthesized CDs are used as fluorescence sensing probe for quantitative analysis of Ponceau 4R (E124) synthetic food dye, which is widely used. However, excessive consumption of Ponceau 4R poses potential health risks. To obtain better-quality performance of as-synthesized CDs, the time and temperature of the hydrothermal carbonization reaction of crocus were optimized simply. The as-prepared CDs exhibit exceptional advantages including excellent fluorescence, satisfactory chemical stability, low toxicity, and excellent biocompatibility. It produced a strong blue fluorescence when irradiated with UV light at 365 nm, which was subsequently effectively employed for Ponceau 4R sensing based on the quenching of fluorescence. The as-prepared CDs was characterized by EDX, XRD, FTIR, SEM, HRTEM, UV–Visible absorption spectrophotometry, and fluorescence. The effects of CDs fluorescence emission wavelength, CDs quantity, pH value, and reaction time were investigated to detect Ponceau 4R under optimum conditions. The synthesized CDs fluorescence intensity allowed quantitative determination of Ponceau 4R in the linear range of 60 – 6000 nM with a detection limit of 40 nM that is lower than all previously published methods. Several soft drink samples were used to validate the potential use of this new fluorescent probe for P4R detection in actual samples with good precision and accuracy.

Chapter four includes a sensitive method namely ultrasound-assisted coupled dispersive nano solid-phase microextraction spectrophotometry (UA-DNSPME-UV-Vis) was designed for AR as food colorant preconcentration and determination in real samples. The method is based on the first-time usage of amaranth CDs @Zn (II) organic framework comprising benzimidazole (ZIF-7) composite. The characterization of the synthesized CDs@ZIF-7 was performed using XRD, SEM, FTIR, HRTEM, EDX, SAED, UV–Vis absorption, and fluorescence spectrophotometers.  Among conventional parameters including pH, amount of sorbent, sonication time and type of elution solvent and its volume was examined, and the best operational conditions were selected. The established method gained wonderful linearity over the range of 0.30 – 7.00 nM. Anions and cations were also studied for their interference effect. The preconcentration factor was found to be 100. The proposed methods precisions were lower than 0.22%. The validating experiments ensured that this developed approach provided satisfied recoveries ranging from 95.80 to 97.30 from real samples, with LOQ and LOD of 0.22 and 0.06 nM, respectively. As-synthesized nanocomposite had significant adsorption capacity and reusability. An analysis of some real samples showed satisfactory results in the analysis of a variety of complex matrices.

The last chapter (chapter five) includes using Crocus cancellatus CDs for the synthesis of magnetic nanocomposite CDs/Fe₃O₄ powders to study the photocatalytic activity of fluorescein dye under sunlight. The synthesized CDs, Fe₃O₄ NPs, and magnetic nanocomposite were characterized using various techniques including XRD, EDX, SEM, FTIR, VSM, and HRTEM analysis. The microstructure images confirmed that CDs were encapsulated in porous magnetic Fe₃O₄ nanoparticles. It was found that the as-synthesized nanocomposite exhibited higher photocatalytic activity under sunlight. The fluorescein (FL) concentration can be decreased by 95.0% within 60 minutes exposing time under optimum conditions. After five recycles, the stability testing demonstrated that nanocomposite had a stronger photocatalytic activity.