Synthesis and optical properties of cysteamine-capped ZnS quantum dots for aflatoxin quantification

Acquisition of Optimum Co-sources of Sulfur MAA Capped-ZnS Quantum Dots Conditions for Photoluminescence Chlorine Sensor

“…Figure 2 shows the effect of temperature is studied at 100, 125, 150, 175, and 200°C in order to obtain the optimum temperature for synthesis of MAA capped-ZnS QDs. Blue shift is observed from 315 to 305 as the temperature increase from 100 to 125°C, respectively due to increasing the monomers concentration which take part in interfacial nucleation resulting in particle size reduction [28,29]. The spectra are red shifted again to 320 nm by increasing the temperature to 150°C due to dissociation of capping agent leading to aggregated of MAA capped-ZnS QDs [30,31].…”

“…It is noted that the precipitation is occurred for the MAA capped-ZnS QDs prepared at This is may be explained by presence of surface defects traps on the surface of the MAA capped-ZnS QDs [27]. MAA:thiourea molar ratio is a key parameter and affects the PL intensities of MAA capped-ZnS QDs [28]. In order to optimize the molar ratio of MAA and thiourea during QDs synthesis, different MAA:thiourea molar ratios are used and the PL intensity is measured.…”

“…The increment of reaction temperature from 100°C to 125°C has a critical effect on the PL spectra of the synthesized MAA capped-ZnS QDs. The moderate increment in temperature from 100°C to 125°C influences the association of the MAA capped-ZnS complex, prompting the enhancement of the free monomer concentration in the subsequent growth [28,32]. When the temperature increases to 150 °C , the rate of the dissociation of the ligands from the MAA capped-ZnS QDs surface is quickened and prompting a growth of the crystals of MAA capped-ZnS QDs without stabilizers [33].…”

“…In addition, increasing of pH promotes the negative charge of carboxylic acid groups, which assists the dispersion of the formed MAA capped-ZnS QDs [37]. When the pH value is higher than 9 the precipitation of MAA capped-ZnS is occurred due to the formation of Zn(OH) 2 onto the QDs surface and this decline of optical characteristics [28]. 1:2 and 2:1 of Zn 2+ :S 2molar ratios are estimated to be 3.88 and 3.85 eV, respectively.…”

Simple Synthesis Method and Characterizations of Aggregation-Free Cysteamine Capped PbS Quantum Dot

“…Cysteamine, one of the thiols, is distinguished from other thiols because it is soluble in water, the most common and safe solvent. Thus, the various types of cysteamine capped quantum dots have been studied in the fields [36][37][38]. However, the synthesis of cysteamine capped PbS quantum dot has been considered difficult, due to the aggregation caused by hydrogen bonds between cysteamine molecules [39].…”