Ecofriendly adsorption and sensitive detection of Hg (II) by biomass-derived nitrogen-doped carbon dots: process modelling using central composite design

Abstract

In this study, luminescent bio-adsorbent nitrogen-doped carbon dots (N-CDs) was produced and applied for the removal and detection of Hg (II) from aqueous media. N-CDs were synthesized from oil palm empty fruit bunch carboxymethylcellulose (CMC) and urea. According to several analytical techniques used, the obtained N-CDs display graphitic core with an average size of 4.2 nm, are enriched with active sites, stable over a wide range of pH and have great resistance to photobleaching. The N-CDs have bright blue emission with an improved quantum yield (QY) of up to 35.5%. The effect of the variables including pH, adsorbent mass, initial concentration and incubation time on the removal of Hg (II) was investigated using central composite design. The statistical results confirmed that the adsorption process could reach equilibrium within 30 min. The reduced cubic model (R 2 = 0.9989) revealed a good correlation between the observed values and predicted data. The optimal variables were pH of 7, dose of 0.1 g, initial concentration of 100 mg/L and duration of 30 min. Under these conditions, adsorption efficiency of 84.6% was obtained. The adsorption kinetic data could be well expressed by pseudo-second-order kinetic and Langmuir isotherm models. The optimal adsorption capacity was 116.3 mg g −1 . Furthermore, the adsorbent has a good selectivity towards Hg (II) with a detection limit of 0.01 μM due to the special interaction between Hg (II) and carboxyl/amino groups on the edge of N-CDs. This work provided an alternative direction for constructing low-cost adsorbents with effective sorption and sensing of Hg (II).

Synthesis of Temperature Sensing Nitrogen-Doped Carbon Dots and Their Application in Fluorescent Ink

“…The results of UV-Vis absorption spectroscopy tests performed on it ( Figure S3a ) showed that an absorption peak near 215 nm could be attributed to a π-π* leap in the C=C bond [ 32 , 33 , 34 ]. In contrast, the absorption near 345 belongs to the n-π* leap of C=O/C=N [ 35 , 36 ]. In addition, Figure S3b shows the strong emission (λem = 487 nm) under optimal excitation (λex = 414 nm).…”

Fluorescent carbon quantum dots with controllable physicochemical properties fantastic for emerging applications: A review

“…The specific selectivity of N-CQDs toward Hg 2+ among other metal ions can be attributed to the strong coordination of Hg 2+ with the O and N electron donors, which triggers the transfer of excited energy to the dorbital of Hg 2+ , resulting in the quenching of N-CQDs. [145] Zdražil et al [199] synthesized N-doped CQDs using citric acid and amine. These CQDs exhibited a [148] Reproduced with permission: Copyright 2021, Elsevier.…”

“…The specific selectivity of N‐CQDs toward Hg 2+ among other metal ions can be attributed to the strong coordination of Hg 2+ with the O and N electron donors, which triggers the transfer of excited energy to the d‐orbital of Hg 2+ , resulting in the quenching of N‐CQDs. [ 145 ] Zdražil et al [ 199 ] synthesized N‐doped CQDs using citric acid and amine. These CQDs exhibited a turn‐off PL lifetime and an exceptional selectivity for detecting Hg2+ in water, achieving a LOD of 0.7 ppb (3.5 nM), and demonstrated high resistance to photobleaching, maintaining stability under continuous pulsed laser excitation for as long as 38 h.…”

Assessment of biomass-derived carbon dots as highly sensitive and selective templates for the sensing of hazardous ions

“…This decline could be associated with the precipitation of C-dots at higher temperatures. 79 Wu et al described the fabrication of C-dots from Bombyx mori silk through a single-step hydrothermal process. These C-dots demonstrated good stability under different pH conditions and exhibited negligible fluorescence decay over several weeks of storage.…”