Facile preparation of magnetic composites based on carbon nanotubes: Utilization for removal of environmental pollutants

Synthesis of Bovine Serum Albumin-Coated Magnetic Single-Walled Carbon Nanotubes as a Delivery System for Mitoxantrone

In this study, a bovine serum albumin (BSA)-coated magnetic single-walled carbon nanotube (mCNT) was synthesized using covalent functionalization. Mitoxantrone (MTO) was chosen as a model drug, and loading/release profiles of mCNTs were evaluated. To synthesize BSA-coated mCNT, 1-ethyl-3-(3-(dimethylamino)propyl) carbodiimide and N-hydroxysuccinimide were used as cross-linking agents. The success of the functionalization process was demonstrated through various analysis techniques such as Fourier transform infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, vibrating sample magnetometer, and scanning electron microscopy. The saturation magnetization of mCNT-BSA was 15.6 emu/g, indicating its potential for magnetically targeted drug delivery systems. Finally, MTO was physically loaded on the BSA-coated mCNT (mCNT-BSA) and the results were compared to those of mCNT. mCNT-BSA showed less drug loading capacity but more release response than mCNT. Considering drug release and cytotoxicity test results, MTO-loaded mCNT-BSA nanoparticles have great potential for cancer treatment.

Fabrication of a novel magnetic carbon nanotube coated with polydopamine modified with EDTA for removing Cd2+ and Pb2+ ions from an aqueous solution

This work demonstrates the preparation of a new, effective, and reusable magnetic adsorbent by functionalizing dopamine with ethylenediaminetetraacetic dianhydride and polymerizing it on the surface of magnetic carbon nanotubes (EDTA@PD-CNT/Fe3O4). The adsorbent was analyzed using XRD, FT-IR, Zeta potential, FE-SEM, EDX, BET, TGA, DTA, and VSM. The synthesized adsorbent was used to remove lead and cadmium ions from aqueous solution. The adsorption process was improved by optimizing key parameters such as pH, adsorbent dosage, contact time, and ion concentration. For both ions, the thermodynamic data of the processes and adsorption kinetics were examined. Analyzing the experimental data revealed that the Langmuir isotherm was the most appropriate model, and the examination of adsorption kinetics showed a pseudo-second-order equation. The adsorption process by the EDTA@PD-CNT/Fe3O4 adsorbent was spontaneous and endothermic, according to the thermodynamic data, for Cd2+ and Pb2+, the highest adsorption capacities were found to be 204.54 mg g-1 and 376.48 mg g-1, respectively.

An Updated Overview of Magnetic Composites for Water Decontamination

Water contamination by harmful organic and inorganic compounds seriously burdens human health and aquatic life. A series of conventional water purification methods can be employed, yet they come with certain disadvantages, including resulting sludge or solid waste, incomplete treatment process, and high costs. To overcome these limitations, attention has been drawn to nanotechnology for fabricating better-performing adsorbents for contaminant removal. In particular, magnetic nanostructures hold promise for water decontamination applications, benefiting from easy removal from aqueous solutions. In this respect, numerous researchers worldwide have reported incorporating magnetic particles into many composite materials. Therefore, this review aims to present the newest advancements in the field of magnetic composites for water decontamination, describing the appealing properties of a series of base materials and including the results of the most recent studies. In more detail, carbon-, polymer-, hydrogel-, aerogel-, silica-, clay-, biochar-, metal-organic framework-, and covalent organic framework-based magnetic composites are overviewed, which have displayed promising adsorption capacity for industrial pollutants.

Recent advances in magnetic carbon nanotubes: synthesis, challenges and highlighted applications

Magnetic carbon nanotubes (MCNTs), consisting of carbon nanotubes (CNTs) and magnetic nanoparticles (MNPs), have enormous exploration and application potentials due to their superior physical and chemical properties, such as unique magnetism and high enrichment performance. This review concentrates on the rapid advances in the synthesis and application of magnetic carbon nanotubes. Great progress has been made in the preparation of MCNTs by developing methods including chemical vapor deposition, pyrolysis procedure, sol-gel process, template-based synthesis, filling process and hydrothermal/solvothermal method. Various applications of MCNTs as a mediator of the adsorbent in magnetic solid-phase extraction, sensors, antibacterial agents, and imaging system contrast agents, and in drug delivery and catalysis are discussed. In order to overcome the drawbacks of MCNTs, such as sidewall damage, lack of convincing quantitative characterization methods, toxicity and environmental impact, and deficiency of extraction performance, researchers proposed some solutions in recent years. We systematically review the latest advances in MCNTs and discuss the direction of future development.

Adsorption of phenanthrene onto magnetic multi-walled carbon nanotubes (MMWCNTs) influenced by various fractions of humic acid from a single soil

In the present study, two magnetic multi-walled carbon nanotubes (MMWCNTs) with different ratios of Fe²⁺/Fe³⁺ were prepared, and the effects of different fractions of dissolved humic acid (DHA) on the adsorption of phenanthrene by multi-walled carbon nanotubes (MWCNTs) and MMWCNTs from the aqueous solution were investigated. The adsorption kinetics of DHA₁ and DHA₄ were best fitted with pseudo-second order model. The adsorption of DHAs on MMWCNTs was weaker than that on MWCNTs, and DHA₁ was easier to adsorb to MWCNTs and MMWCNTs than DHA₄. The phenanthrene adsorption capacities by 1:2:1MMWCNTs and 4:2:1MMWCNTs with higher polar groups and magnetic gradient were less than that of MWCNTs. The pH value had no obvious effect on the adsorption of phenanthrene to MWCNTs loaded with different iron. Additionally, the DHAs could form soluble complexes of DHAs-Fe (II) in solution to reduce the phenanthrene adsorption on MMWCNTs, DHA₁ inhibit more obviously phenanthrene adsorbed onto MWCNTs and MMWCNTs than DHA₄. As for MMWCNTs, the main mechanisms of phenanthrene adsorbed onto it included new adsorption sites formed by π-π interaction and magnetic gradient. In this study, MMWCNTs after adsorbed DHAs had a weaker inhibitory effect on phenanthrene adsorption than MWCNTs, implying that when phenanthrene is adsorbed by DHAs-coated MMWCNTs, the bioavailability and mobility of phenanthrene will be reduced, and it is easy to be removed by the magnet for further processing.

Sorptive removal of methylene blue from water by magnetic multi-walled carbon nanotube composites

In the present study, five magnetic multi-walled carbon nanotubes (MMWCNTs) with different diameters were prepared and their performance on the sorptive removal of methylene blue (MB) from water was investigated. Transmission electron microscope, scanning electron microscope, Fourier transform infrared spectrometer, X-ray diffraction, and vibrating sample magnetometer confirm that the surface of these MMWCNTs has been decorated by Fe₃O₄ nanoparticles, which renders the MMWCNTs superparamagnetic. Thus, these MMWCNTs can be easily separated from water after the adsorption. During the adsorption process, pH slightly affected the removal efficiency of MB and the adsorption performed better under weak alkaline conditions. Adsorption kinetics followed the pseudo-second-order kinetic model well, and the Dubinin-Radushkevich model fitted the isotherms best. The maximum adsorption capacity for MB reached 204.2 mg/g, and the values decreased with increasing diameters of MMWCNTs due to decreasing specific surface areas. The thermodynamics parameters indicated the spontaneous and exothermic nature of the adsorption. The reusability test showed that MMWCNTs could be used for 6 cycles without significant loss of the adsorption capacity. And common ions (K⁺, Na⁺, Ca²⁺ and Al³⁺) and SDS in water did not show greatly effects on the removal efficiency of MB. Hence, MMWCNTs prepared in this study could be promising adsorbents for dyes removal from wastewater.

Green synthesis of poly(pyrrole methane) for enhanced adsorption of anionic and cationic dyes from aqueous solution

The presence and accumulation of dyestuff in the environment is posing great harm to human beings. In this study, a novel poly(pyrrole methane) (PPm) adsorbent with abundant OH was greenly synthesized via a facile polymerization method. Its physicochemical properties were characterized in detail. Furthermore, the adsorption performance of PPm for anionic dye (acid red G, ARG) and cationic dye (methylene blue, MB) was comparatively studied with a typical dye adsorbent (polyprrrole, PPy). The results revealed that the adsorption of ARG or MB onto PPm followed pseudo-second-order model and Langmuir mode. The adsorption processes were endothermic and spontaneous. The maximum capacities of PPm to adsorb ARG and MB were 555.56 mg/g and 99.11 mg/g, which were about 10 and 2 times higher than that of PPy, respectively. PPm could be reused for 5 cycles without a significant decrease of its adsorption rate. The adsorption of ARG and MB is mainly attributed to electrostatic interaction and hydrogen bonding between ARG or MB and OH in PPm. Additionally, ARG could be adsorbed by ion exchange with the doped Cl^- in PPm. Therefore, this study provides a new strategy to synthesis efficient adsorbent for the removal of both anionic and cationic dyes.

Facile covalent preparation of carbon nanotubes / amine-functionalized Fe3O4 nanocomposites for selective extraction of estradiol in pharmaceutical industry wastewater

As a typical steroid hormone drug, estradiol (E2) is also one of the most frequently detected endocrine disrupting chemicals (EDCs) in the aquatic environment. Herein, in response to the potential risk of E2 in steroid hormone pharmaceutical industry wastewater to human and wildlife, a novel carbon nanotubes / amine-functionalized Fe₃O₄ (CNTs/MNPs@NH₂) nanocomposites with magnetic responsive have been developed for the enrichment and extraction of E2 in pharmaceutical industry wastewater, where amino-functionalized Fe₃O₄ magnetic nanoparticles (MNPs@NH₂) were used as a magnetic source. The resultant CNTs/MNPs@NH₂ possessed both the features of CNTs and desired magnetic property, enabling to rapidly recognize and separate E2 from pharmaceutical industry wastewater. Meanwhile, the CNTs/MNPs@NH₂ had good binding behavior toward E2 with fast binding kinetics and high adsorption capacity, as well as exhibited satisfactory selectivity to steroidal estrogen compounds. Furthermore, the change of pH value of aqueous phase in adsorption solvent hardly affected the adsorption of E2 by CNTs/MNPs@NH₂, and the adsorption capacity of E2 ranged from 19.9 to 17.2 mg g^-1 in the pH range of 3.0 to 11.0, which is a latent advantage of the follow-up development method to detect E2 in pharmaceutical industry wastewater. As a result, the CNTs/MNPs@NH₂ serving as a solid phase extraction medium were successfully applied to efficiently extract E2 from pharmaceutical industry wastewater. Therefore, the CNTs/MNPs@NH₂ nanocomposites could be used as a potential adsorbent for removing steroidal estrogens from water. More importantly, the developed method would provide a promising solution for the monitoring and analysis of EDCs in pharmaceutical industry wastewater.

Concentrative isolation of uranium traces in aqueous solutions via resurfaced-magnetic carbon nanotube suspension

The concentrative isolation of metal traces from aqueous solutions is of vital importance for environmental and industrial processes. Developing reliable systems of nanoscale that can be fine-tuned to effectively isolate these metals remains an intriguing aim which can potentially beget economic benefits and mitigate major environmental concerns. Here we demonstrate a conceptual metal extraction system where magnetic multi-wall carbon nanotubes (M-MWCNTs) are surface-equipped with a molecular network of polyethylenimine (PEI) to serve as a reusable nano-ionic exchanger, referred to as "M-MWCNTs-PEI". The designed nano-ionic exchanger forms readily stable suspensions with the metal-bearing aqueous solutions eliminating the need for vigorous agitation. Besides, it can be magnetically manipulated and separated in/from the solution. To exemplify its potential for the isolation of metal traces, the M-MWCNTs-PEI was tested with the uranium trace ions in aqueous media. The M-MWCNTs-PEI featured distinct sorption capacity of ~488 mg/g at pH 6, with moderate, but stable, binding affinity toward uranium ions. As such, excellent isolation performance is demonstrated while bound uranium ions are effectively concentrated and recovered from the interfacial PEI molecular network. This was efficiently achieved by exposing the loaded M-MWCNTs-PEI to solutions of small volumes and specific chemistry. Such combined qualities of large capacity and reusability have not been observed with the previously reported ion exchange systems. Altogether, our observations here demonstrate how functional systems of nanoscale can be adapted for industrial applications while this concept can be extended to address other important resources such as rare-earth and lanthanide elements.

Removal of fluoride from fertilizer industry effluent using carbon nanotubes stabilized in chitosan sponge

Adsorption of fluoride from fertilizer industry effluent using carbon nanotubes stabilized in chitosan sponge as adsorbent was evaluated. The effluent was produced in the washing of acid gases during the reaction in fertilizer production and all assays were performed using this hazardous material. Adsorbent characterization and ions interactions were elucidated from differential scanning calorimetry, thermal gravimetric analyses, X-ray diffraction, scanning electron microscopy dispersive energy X-ray spectroscopy, atomic force microscopy and X-ray photoelectron spectroscopy. The effluent presented pH 3 and its value not changed in the adsorption assays, maintaining the conditions of the process. The kinetics assays of fluoride from industry effluent were performed in different stirring rates from 100 to 300 rpm. It was observed that adsorption was initially fast reaching the equilibrium at 300 rpm in 20 min. The adsorption capacity was around 975.4 mg g^-1, showing the potential of the hybrid material to remove fluoride from a real matrix. The high adsorption capacity was attributed to the chitosan functional groups and the high interaction area promoted by sponge form and the carbon nanotube. Reuse and regeneration of the CNT-CS were investigated and 5 cycles were obtained. The adsorption capacity kept similar values in all cycles.