Removing lead ions from aqueous solutions by the thiosemicarbazide grafted multi-walled carbon nanotubes

Designing of a cellulose-based ion-imprinted biosorbent for selective removal of lead (II) from aqueous solutions

Developing an effective adsorbent for Pb2+ removal from wastewater has huge economic and environmental implications. Adsorbents made from cellulosic materials that have been modified with certain chelators could be used to get rid of metal cations from aqueous solutions. However, their selectivity for specific metals remains very low. Here, we describe the synthesis of 4-(2-pyridyl)thiosemicarbazide (PTC) hydrazidine-functionalized cellulose (Pb-PTC-CE), a polymer imprinted with Pb2+ ions that may be used to remove Pb2+ ions from wastewater. Owing to its potent -NH2 functionalization, PTC hydrazidine not only served as an efficient chelator to effectively supply coordinating sites and construct hierarchical porous structures on Pb-PTC-CE, but it also made it possible for cross-linking to occur through the glyoxal cross-linker. The abundant chelators, along with the hierarchical porous construction of the developed Pb-PTC-CE with PTC functionality, result in a greater sorption capacity of 336 mg/g and a short sorption period of 40 min for Pb2+. Additionally, Pb-PTC-CE exhibits highly selective Pb2+ uptake compared to competing ions. This study proposes a feasible methodology for the development of high-quality materials for Pb2+ remediation by combining the advantages of active ligand functionality with ion-imprinting techniques in a straightforward way.

Effects of functionalized multi-walled carbon nanotubes on toxicity and bioaccumulation of lead in Daphnia magna

Increased production of carbon nanotubes (CNTs) and their widespread application in industrial and consumer products have led to a rise in the release of CNTs into the aquatic environment. CNTs have a very strong adsorption affinity for various environmental contaminants; therefore, they may also influence the toxic effects of other pollutants, such as toxic metals. In this study, the effect of two different functionalized carbon nanotubes, carboxylate and polyethyleneimine modified multi-walled carbon nanotubes (C-MWCNTs and N-MWCNT, respectively) on lead toxicity and bioaccumulation was investigated with a freshwater zooplankton Daphnia magna. The acute toxicity results indicate that the different surface properties of the two types of MWCNTs have different effects on lead toxicity to D. magna. The negatively charged C-MWCNT showed a notable decrease in lead toxicity (LC₅₀ value increased from 0.15 mg L^-1 to 1.08 mg L^-1 in the presence of 10 mg L^-1 C-MWCNT), whereas the positively charged N-MWCNT had only a slight effect on lead toxicity (LC₅₀ value increased from 0.15 mg L^-1 to 0.16 mg L^-1 in the presence of 10 mg L^-1 N-MWCNT). The decrease of lead toxicity was related with the reduced bioavailability of free metal form (Pb²⁺) caused by greater adsorption of lead onto the MWCNTs. The present study suggests that there is a need to consider carefully the complex interaction of CNTs with toxic metals in future ecotoxicological studies.