Abstract
The efficient removal of toxic metals ions from chemical industry wastewater is considered problematic due to the existence of pollutants as mixtures in the aqueous matrix, thus development of advanced and effective treatment method has been identified as a panacea to the lingering problems of heavy metal pollution. In this study, KIAgNPs decorated MWCNTs nano adsorbent was developed using combination of green chemistry protocol and chemical vapor deposition techniques and subsequently characterized using UV–Vis, HRTEM, HRSEM, XRD, FTIR and XPS. The adsorptive efficiency of MWCNTs-KIAgNPs for the removal of Cr(VI), Ni(II), Fe(II), Cd(II) and physico-chemical parameters like pH, TDS, COD, BOD, nitrates, sulphates, chlorides and phosphates from chemical industrial wastewater was examined in both batch and fixed bed systems. The result exhibited successful deposition of KIAgNPs on the surface of MWCNTs as confirmed by the microstructures, morphology, crystalline nature, functional groups and elemental characteristics of the MWCNTs-KIAgNPs. Optimum batch adsorption parameters include; pH (3 for Cr(VI) and 6 for Ni(II), Fe(II) and Cd(II) ions), contact time (60 min), adsorbent dosage (40 mg) and temperature (318 K). The binding capacities were obtained as follows; Cr6+ (229.540 mg/g), Ni2+ (174.784 mg/g), Fe2+ (149.552) and Cd2+ (121.026 mg/g), respectively. Langmuir isotherm and pseudo-second order kinetic model best described the experimental data in batch adsorption, while the thermodynamic parameters validated the chemisorption and endothermic nature of the adsorption process. In continuous adsorption, the metal ions were effectively removed at low metal influent concentration, low flow rate and high bed depth, whereby the experimental data were designated by Thomas model. The high physico-chemical parameters in the wastewater were successfully treated in both batch and fixed bed systems to fall within WHO permissible concentrations. The adsorption/desorption study illustrated over 80% metal removal by MWCNTs-KIAgNPs even after 8th adsorption cycle. This study demonstrated excellent performance of MWCNTs-KIAgNPs for chemical industry wastewater treatment.
Highlights
Wastewater is a major public health problem which are generated from chemical industries such as battery, metal plating, cosmetics, pharmaceuticals, plastic and textiles[1,2,3]
The synthesis of AgNPs demonstrated using Khaya ivorensis (KI) leaves extract for the fabrication of MWCNTs-KIAgNPs was reported for the first time and employed for the adsorption of Cr(VI), Ni(II), Fe(II) and Cd(II) ions from chemical industry wastewater in a static and dynamic processes
In the batch adsorption study, maximum adsorption of metal ions by MWCNTs-KIAgNPs were recorded at adsorbent dosage (40 mg), pH (3 for Cr(VI) and 6 for Ni(II), Fe(II) and Cd(II) ions) and contact time (60 min)
Summary
Wastewater is a major public health problem which are generated from chemical industries such as battery, metal plating, cosmetics, pharmaceuticals, plastic and textiles[1,2,3]. Researchers have examined the removal of heavy metals using numerous techniques, including ion exchange, chemical precipitation, reverse osmosis, membrane processes, microbial biotechnology, coagulation, flocculation, filtration and adsorption technology[11] These techniques possess different limitations such as low efficiency, high cost, generation of toxic byproducts, delay in operation, inefficiency in targeting specific pollutants and complexity of treatment m ethods[12]. Nanomaterials-based adsorbents such as zinc oxide, tin oxide, graphene oxide, carbon nanotubes, silica, aluminum oxide, titanium oxide, zeolites, iron oxide, spinel ferrites, chitosan, carbon nanofibers and cerium oxide have been employed by different researchers for industrial wastewater treatment[17,18,19,20,21,22,23,24,25] Among these nanomaterials, carbon nanotubes (CNTs) have been extensively exploited due to their large surface area, ease of modification, extraordinary surface chemistry, structural control, low density, porosity, higher thermal stability, high chemical stability, regeneration ease and reusability, compared to other adsorbents[26]. The influence of pH, adsorbent dosage, temperature and contact time on the metal adsorption were explored for the batch mode, while the influent concentration, flow rate and bed depth were examined for the continuous flow adsorption
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