Nitrogen-doped carbon dots from empty fruit bunch carboxymethylcellulose for selective detection of copper ions in aqueous media
Fluorescent carbon dots (CDs) have emerged as sensing systems for wastewater treatment and chemical sensing. Nowadays, different biomass-based materials, including the usage of starch, glucose, and cellulose have been widely employed for the production of CDs. In spite of their susta...
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| Format: | Thesis |
| Language: | English |
| Published: |
2019
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/85575/1/FK%202020%2022%20-IR.pdf |
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| Summary: | Fluorescent carbon dots (CDs) have emerged as sensing systems for wastewater treatment
and chemical sensing. Nowadays, different biomass-based materials, including the usage of starch,
glucose, and cellulose have been widely employed for the production of CDs. In spite of their
sustainability, the fluorescent efficiency of the obtained CDs from these natural resources is
still low. This motivates the researchers for doping CDs with various heteroatom species such
as nitrogen doping agent. However, long-time synthesis process from 7-72 hr is normally
required for obtaining a relatively low fluorescence quantum yield (QY). Additionally, a
clear formation mechanism for nitrogen-doped CDs (N-CDs) synthesized hydrothermally from
biomass and various heteroatom doping sources along with the origin of the photoluminescence (PL)
emission are still under debate.
In this work, one-step hydrothermal carbonization route has been used to produce N- CDs from
carboxymethylcellulose (CMC) of oil palms empty fruit bunch in the presence of ethylenediamine
(EDA-CDs) and linear-structured polyethyleneimine (LPEI-CDs) in an attempt to enhance the
fluorescence quantum yield of CDs. At first, the optimum conditions for the hydrothermal route of
N-CDs were identified by assessing the effect of different influential variables (reaction
temperature, time, and N-weight). The statistical analysis results indicated that the
production of LPEI-CDs not only was obtained in a considerably shorter time in comparison to
EDA-CDs but also, they had significantly better fluorescent QY. Additionally, the characterization
tests were carried out on the optimum N-CDs. The prepared N-CDs are reproducible, highly
homogeneous and excellent PL properties with narrow emission bands. Furthermore, the N-CDs are
nearly small (approx. 3-8 nm) with narrow size distributions; are stable over a long period of
time (at least six months), and maintain their PL properties when re-dispersed in
solution. Moreover, LPEI-CDs showed predominantly crystalline nature, and the functional
groups from the LPEI have successfully tuned the PL properties of CDs in
both the intrinsic and surface electronic structures, and hence improve the fluorescence QY up to 44%. It was concluded that the origin of light emission in N-CDs caused by the interplay
between intrinsic state emission originates from graphitic core and extrinsic state emission due to
the surface functional groups.
Due to the significant interaction between Cu (II) and amino functional groups over the LPEI-CDs
surface, the LPEI-CDs were further used as a fluorescent probe for the detection of Cu
(II) in aqueous media. The linear relationship between the relative quenching rate and the
concentration of Cu (II) (1–30 µM) with a detection limit of 0.93 µM were used. Considering the
sustainable production of N-CDs, this PhD research project provides a guide for converting
low-quality waste into value-added nanomaterials
and applying for different functionalization processes and analytical applications. |
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