Abstract
Cadmium(II) is a toxic heavy metal in aquatic systems. As a potential solution, green carbon nanodots (CNDs) were synthesized from oats and embedded on polyethersulfone membrane (PES) via phase inversion for the adsorption of Cd2+ from water. Characterization techniques for the CNDs and PES membranes were transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Raman spectroscopy, atomic force microscopy (AFM), contact angle and a pure water flux assessment system operated at 300 kPa. TEM results showed that the CNDs were well dispersed with a uniform shape and size (6.7 ± 2.8 nm). Raman spectroscopy revealed that the CNDs were embedded on the PES and the ID/IG ratio slightly increased, showing that the membranes maintained good structural integrity.The CNDs/PES proved to be more hydrophilic than PES. The glassy carbon electrode (GCE) in anodic stripping voltammetry (ASV) technique detected 99.78% Cd2+ removal by 0.5% CNDs/PES at optimum conditions: 30 min. contact time, at pH 5 and 0.5 ppm Cd2+ solution. The 0.5% CNDs/PES removed Cd(II) due to the hydroxyl group (-OH) and carboxyl group (-COO-) on the membrane composite. It was established that Cu2+ and Pb2+ have a significant interfering effect during the analysis of Cd2+ using GCE in ASV technique. The 0.5% CNDs/PES is recyclable because it removed above 95% of cd2+ in four cycles. In a spiked tap water sample, 58.38% of Cd2+ was sensed by GCE of which 95% was in agreement with the value obtained from inductively coupled plasma optical emission spectrometry (ICPOES).
Highlights
Water contamination due to heavy metals has become a worldwide concern since the1990s and has been a challenge for many environmental scientists [1]
Similar results were observed by Shi et al, who synthesised duel emission carbon nanodots from naked oats via pyrolysis and mechanical grinding
In their study the majority of the carbon nanodots were in the range of 7 to 11 nm with an average mean of 8.64 ± 0.84 nm [13]
Summary
Water contamination due to heavy metals has become a worldwide concern since the1990s and has been a challenge for many environmental scientists [1]. The contribution of metal contamination in aquatic environments is caused by the colossal quantity of toxic heavy metals released into these environments by anthropogenic activities as well as by natural processes. Cadmium (II) has been widely dispersed in the environment through industrial processes such as printed board manufacturing, metal finishing, plating, textile dyes, manufacturing of nickel-cadmium batteries, mining and smelting as stated by Malecki and Maron [9]. It is distributed through human activities such as utilization of compost and discarding of
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