رسائل دكتوراة
English
2024
Optical and electrical studies of fluorescent carbon/dye/polymer nano-composites
Abey Issac, Basim Abdullah Darwish Al-Farsi , Sumesh Sofin R.G Pillai
كلية العلوم-جامعة السلطان قابوس · عمان
Environmental-friendly and biocompatible fluorescent carbon quantum dots (CQDs)show great potential for various applications. The functional groups on the surface ofCQDs could dramatically influence the light absorption and emission characteristicsof CQDs. A systematic investigation has been carried out by quantifying the oxygenbased function groups present on the surface of activated CQDs (AC), dehydratedCQDS, and CQDs prepared by microwave synthesis to understand their role in thefluorescent emission characteristics. The samples were subjected to furthertreatments to achieve different levels of surface functionality with oxygen-containingfunctional groups such as carbonyl, carboxyl, phenol, and lactone. Various emissivepathways were identified by comparing the results of surface functionality and thedeconvoluted emission spectra. Our results suggest that the energy gap of isolatedsp 2 clusters on the surface of CQDs is the highest among the gaps related to variousfunctional groups. The non-radiative transitions from this level can populate the midlevel emissive states. As proof for this model, the integrated intensity of the highenergy peak was found to decrease, and corresponding enhancements of low-energypeaks were observed as the surface functionality of carboxyl groups increased. Ourresults suggest that selective surface functionalization could control various emissivepathways in CQDs. These results are quite substantial for understanding the emissionmechanism of CQDs. We have also studied the adsorption mechanism of methyleneblue (MB) dye on the surface of CQDs at different contact times, pH, concentrations,and temperatures. In this work, we used Langmuir, Freundlich, pseudo-Ξrst, andsecond-order adsorption models for the analysis. Our results suggest thephysisorption of MB on CQDs. Various kinetic and thermal parameters associatedwith MB adsorption were compared between CQDs prepared by different methodsto identify the best CQDs for applications. The results are essential for applying CQDs,such as wastewater treatment. Further, a preliminary investigation of the electricalconductivity of the CQD-PANI polymer composite was done. Our results suggest thatthe increase in conductivity in the CQD-PANI composite is associated with electrontransfer from PANI to CQDs. Our studies give important information to increaseCQD's potential for applications.