Abstract
Mercury contamination in drinking water is a worldwide problem due to its severely harming effects on the human body. A nanostructured natural bioadsorbent, carboxycellulose nanofiber extracted from raw moringa plant using the nitro-oxidation method (termed NOCNF), capable of effectively remediating this problem has been demonstrated. Nitro-oxidation is a simple approach that can extract carboxylated nanocellulose directly from raw biomass. In this study, the produced NOCNF contained a large density of carboxylate groups on the cellulose surface (0.97 mmol/g), capable of removing Hg2+ ions by simultaneous electrostatic-interactions and mineralization processes. Using the Langmuir analysis, the adsorption results indicated that the highest Hg2+ removal capacity of this NOCNF was 257.07 mg/g, which is higher than most of the reported values. The interactions between Hg2+ and NOCNF were further characterized by Fourier-transform infrared spectroscopy, scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS), transmission electron microscopy with electron diffraction and wide-angle X-ray diffraction methods, suggesting the existence of two distinct removal mechanisms: predominant adsorption at low Hg2+concentrations (< 250 ppm) and predominant mineralization at high Hg2+ concentrations (> 1000 ppm). The applications of NOCNF were illustrated in both suspension form, as an adsorbent/coagulant, and dry powder form using filtration column. The results indicated that NOCNF in suspension exhibited a higher maximum removal efficiency of 81.6% as compared to the dry state of 74.3%. This work demonstrated the feasibility of extracting nanostructured adsorbents from biomass feedstocks to tackle the Hg2+ contamination problem in drinking water.Graphic abstractCellulose nanofibers, extracted from Moringa plant using the nitro-oxidation method, exhibit excellent adsorption capacity for Mercury (II) removal.
Highlights
Mercury is a well-recognized harmful pollutant due to its carcinogenicity, mutagenicity and teratogenicity.(Zhang, Nriagu et al 2005) For example, high concentration of mercury in the human body can cause tyrosinemia, a disease associated with impairment of pulmonary and kidney function, chest pain and dyspnea
We argue that lignocellulosic biomass is an abundant and sustainable resource to develop cost-effective bioadsorbent. (Kim, Shim et al 2015) In the past two decades, much attention has been given to develop nanocellulose in a broad range of water purification treatments because of its large surface areas and ample functional groups. (Wang 2019) For example, several studies have been reported that cellulosic nanomaterials containing thiol, carboxyl, sulfonate, and phosphonate groups can all exhibit ability to adsorb positively charged contaminants, such as metal ions, dyes, and chemicals for water purification
This work demonstrates an effective nanocellulose-based adsorbent system for mercury removal that was developed from untreated moringa plant using the nitrooxidation method
Summary
Mercury is a well-recognized harmful pollutant due to its carcinogenicity, mutagenicity and teratogenicity.(Zhang, Nriagu et al 2005) For example, high concentration of mercury in the human body can cause tyrosinemia, a disease associated with impairment of pulmonary and kidney function, chest pain and dyspnea. We report that NOCNF, extracted directly from raw moringa plants by NOP, can be an effective bioadsorbent for water remediation such as mercury removal.
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