Abstract
As a remedy for environmental pollution, a versatile synthetic approach has been developed to prepare polyvinyl alcohol (PVA)/nitrogen-doped carbon dots (CDs) composite film (PVA-CDs) for removal of toxic cadmium ions. The CDs were first synthesized using carboxymethylcellulose (CMC) of oil palms empty fruit bunch wastes with the addition of polyethyleneimine (PEI) and then the CDs were embedded with PVA. The PVA-CDs film possess synergistic functionalities through increasing the content of hydrogen bonds for chemisorption compared to the pure CDs. Optical analysis of PVA-CDs film was performed by ultraviolet-visible and fluorescence spectroscopy. Compared to the pure CDs, the solid-state PVA-CDs displayed a bright blue color with a quantum yield (QY) of 47%; they possess excitation-independent emission and a higher Cd2+ removal efficiency of 91.1%. The equilibrium state was achieved within 10 min. It was found that adsorption data fit well with the pseudo-second-order kinetic and Langmuir isotherm models. The maximum adsorption uptake was 113.6 mg g−1 at an optimal pH of 7. Desorption experiments showhe that adsorbent can be reused fruitfully for five adsorption-desorption cycles using 0.1 HCl elution. The film was successfully applied to real water samples with a removal efficiency of 95.34% and 90.9% for tap and drinking water, respectively. The fabricated membrane is biodegradable and its preparation follows an ecofriendly green route.
Highlights
Water is the prime component of human survival
The as-formed carbon dots (CDs) exhibit a yellow color, showing greenish emission under UV-lamp (365 nm), good water solubility and long shelf-life with no apparent agglomeration. These CDs were encapsulated with polyvinyl alcohol (PVA) polymer host to develop a solid-state hybrid film for heavy metal complexation in an attempt to overcome the separation issues of the liquid phase [4]
In contrast to the liquid CDs, PVA-CDs film exhibits only excitation-independent emission phenomena when exposed to varied excitation wavelengths (Figure 7c), which agrees with previous work [40]
Summary
Water is the prime component of human survival. environmental pollution caused by heavy metals owing to the inappropriate disposal of wastewater is becoming a worldwide concern [1,2]. Carbon dots (CDs) have gained considerable attention for heavy metal removal from aqueous systems [9,10] These CDs, with sizes less than 10 nm, exhibit outstanding properties like ease of preparation, non-toxic nature and excellent luminescence behavior. It is well known that surface doping of CDs with N can effectively tune its electronic structure, provides available sites and enhanced PL, which are great significance for efficient and selective recognition and capture of metal ions [10,48]. In this regard, we report a versatile one-pot route for production CDs from CMC with the assistance of PEI dopant. Desorption and regeneration studies were conducted to evaluate the reusability of the film
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