Oxidation Of Multi-walled Carbon Nanotubes Research Articles

Manganese Deposition Content in Carbon Nanotubes Based Filters: Energy Dispersive X-ray and Rutherford Backscatter Spectrometry Investigations

Carbon nanotubes (CNTs) based filters have a prospective advantage compared to the commercial filters due to their lightweight and ability to work without electricity or heat. The manganese (Mn) removal from aqueous solutions by oxidized multi-walled carbon nanotubes (O-MWCNTs) was investigated. The filtration performance was studied under ambient conditions: the solution pH, the initial manganese concentration, and the MWCNT-filter mass. The samples of MWCNT-filters were investigated using energy dispersive X-ray spectroscopy (EDS) and rutherford backscatter spectrometry (RBS) to account for the manganese content within the MWCNT-filter. These techniques were conducted to study the oxidation effect on the morphology of MWCNTs and evaluate the oxygen functional groups and the average diameter distribution. Based on these examinations, the competence of Mn removal may exceed 91% for 50 ppm initial concentration of Mn, proposing that functionalized MWCNTs is a promising filter. The Mn removal was achieved at low pH with removal enhancement at the pH of 2. Functionalized MWCNTs based filters are promising candidate for heavy metal ions removal from industrial wastewater.

Influence of moisture on ferroelectric–paraelectric phase transition of a composite containing oxidized MWCNT and TGS

This work reports experimental results for investigating the effects of residual water on phase transition in triglycine sulfate (TGS) filled with 5 wt% of oxidized multiwalled carbon nanotubes (OMWCNTs) under a relative humidity of 90% for different storage time. A similar composite containing TGS and non-oxidized MWCNT was also synthesized for comparison. According to measured data, the moisture was well adsorbed into OMWCNT/TGS composite and resulted in the shift of phase transition point toward higher temperatures for samples stored for less than 5 days. The longer storage caused a significant drop of dielectric constant at phase transition.

An electrochemical chiral sensor based on the synergy of chiral ionic liquid and 3D-NGMWCNT for tryptophan enantioselective recognition.

A facile chiral composite (3D-NGMWCNT@(S,S)-CIL) was prepared by integrating three-dimensional N-doped graphene oxide multi-walled carbon nanotubes (3D-NGMWCNT) and chiral ionic liquid ((S,S)-CIL) via electrodeposition. SEM, XRD, XPS, and electrochemical methods were used to characterize this composite and it revealed that the integrated 3D-NGMWCNT@(S,S)-CIL composite showed excellent electrochemical performance. Therefore, a 3D-NGMWCNT@(S,S)-CIL/GCE electrochemical sensor was constructed for enantioselective recognition of Trp enantiomers. The coefficient (IL/ID) of the 3D-NGMWCNT@(S,S)-CIL/GCE chiral sensor was 2.26 by differential pulse voltammograms (DPV), revealing that the synthesized 3D-NGMWCNT@(S,S)-CIL had a higher affinity for L-Trp than D-Trp. Moreover, UV-V is spectroscopy and awater contact angle test also proved this result. The 3D-NGMWCNT@(S,S)-CIL/GCE sensor had a detection limit of 0.024μM and 0.055μM, and sensitivity of 62.35μA·mM-1·cm-2 and 30.40μA·mM-1·cm-2 for L-Trp and D-Trp, respectively, with a linear response range of 0.01 to 5mM. In addition, the 3D-NGMWCNT@(S,S)-CIL/GCE chiral sensor showed excellent stability, and good reproducibility and was applied to detect L-Trp or D-Trp in real samples. The novel 3D-NGMWCNT@(S,S)-CIL/GCE chiral sensor provides an efficient and convenient strategy for chiral enantioselective recognition. Schematic construction of the 3D-NGMWCNT@(S,S)-CIL/GCE chiral electrochemical sensors.

Cytotoxicity and action mechanisms of polycyclic aromatic hydrocarbons by a miniature electrochemical detection system.

The effects of six polycyclic aromatic hydrocarbons (PAHs) on the activity of V79 cells were studied by using a miniature electrochemical system based on graphene oxide quantum dots and multiwall carbon nanotubes modified anodized screen printed carbon electrode. The cytotoxicity sequence of PAHs on V79 cells was different with guanine/xanthine (G/X), adenine (A), hypoxanthine (HX), and the end product of purine nucleotide catabolism, uric acid (UA), as biomarkers. The IC50 values measured with UA as the biomarker were the lowest, indicating that UA in cells was more sensitive to PAHs. The cytotoxicity sequence with G/X as the biomarker was the same as that of the MTT assay: pyrene > phenanthrene > benzo[a]pyrene > fluoranthene > fluorene > naphthalene. The cytotoxicity sequences measured by different biomarkers varied, which related to different structures that may influence the expression of the cellular aryl hydrocarbon receptor, gap junctional intercellular communication, and p53 protein. PAHs with different structures played varied roles in cell development and differentiation. Additionally, the electrochemical method was more sensitive than the MTT assay. The miniature electrochemical system enabled the simultaneous detection of four signals in cells, providing more information for multi-parameter evaluation and toxic mechanism study of PAHs and other pollutants.

Vapor Phase Modification for Selective Enrichment of Grafted Styrene/Acrylonitrile onto Carbon Nanotubes Via ATRP

Nitric acid vapor phase oxidation of multi-walled carbon nanotubes (MWCNTs) was proposed as a promising technique to fabricate poly styrene-co-acrylonitrile (SAN)-grafted-CNTs via atom transfer radical polymerization (ATRP). The in-situ ATRP grafting approach was successfully employed to graft polystyrene (PS), SAN and polyacrylonitrile (PAN), onto the convex surfaces of pristine MWCNTs (PCNT) and acid-functionalized MWCNTs (FCNT). Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (1H-NMR), and thermogravimetric analysis (TGA) confirmed the effectiveness of the modification via the ATRP grafting approach. The molar composition of acrylonitrile in the synthesized copolymer on the surface of CNTs for an FCNTs was calculated to be about 80% and 67.5% by 1H-NMR and TGA respectively, whereas the value is lower for PCNTs. Morphological studies showed that SAN-grafted FCNTs exhibit rougher surface morphology compared to the SAN-grafted PCNTs. Moreover, the higher diameter of the FCNTs indicated the higher polymer content, which was coated onto CNTs functionalized by vapor-phase oxidation. Therefore, the vapor phase oxidation strategy employed in this study could be utilized as a general method to prepare CNTs which can serve as an ATRP macroinitiator for the fabrication of various polymer grafted CNTs.

A novel quaternary carbon/metal oxide based nano‐composite electrode with high electrochemical capacitive performance

A facile one-pot hydrothermal method is employed to synthesize {CNT–MnO2–Ni(OH)2} (CMN), {rGO–MnO2–Ni(OH)2} (RMN) along with a novel composite material{rGO–CNT–MnO2–Ni(OH)2} (RCMN). This paper first time reports reduced graphene oxide–multiwall carbon nanotube–manganese dioxide–nickel hydroxide rGO–CNT–MnO2–Ni(OH)2 quaternary composite powder as a supercapacitor electrode material. The as-obtained rGO–CNT–MnO2–Ni(OH)2 quaternary composite shows high specific capacitance (1906.4 F g−1) at 3 mV s−1. In addition, cyclic stability measurement reveals that RCMN composite retains admirable capacitance (92.5%) even after 10,000 cycles. The enhancement in cyclic stability and specific capacitance is attributed to the exclusive combination of rGO/CNT as a conductive network and MnO2/Ni(OH) 2 nanostructures as active materials which endorse effective charge transfer and expedites high capacitance and cyclic stability.

Synthesis of physically crosslinked PAM/CNT flakes nanocomposite hydrogel films via a destructive approach.

Carbon nanotube (CNT)-based hydrogels have recently found a wide variety of applications due to the unique physical and chemical properties of CNTs. CNTs can be used as a nanofiller and/or crosslinker to produce nanocomposite hydrogels with good mechanical and structural properties. In this research, a novel method was reported for producing polyacrylamide (PAM)/oxidized-multiwalled carbon nanotube (O-MWCNT) flakes nanocomposite hydrogel films without using any organic cross-linker or surfactant. Through a mechanism dependent on the reactive oxygen species (ROS), some O-MWCNTs were broken down in situ into small flakes in the aqueous solutions containing acrylamide (AM) and sodium persulfate (NaPS) at the temperature range of 85–90 °C. Simultaneously, in situ polymerization of the AM monomers occurred using free radicals, which resulted in the formation of PAM chains. The flakes acted as crosslinkers by forming hydrogen bonds with PAM chains and formed a hydrogel network after 48 h at room temperature. The hydrogels were characterized by different techniques (FT-IR, Raman, FE-SEM, TEM, TGA, tensile test). The porous structure of the hydrogel films as well as micro-network structures with unique morphologies were observed by SEM. The O-MWCNT flakes and some undegraded O-MWCNTs in the hydrogel network were also observed by TEM. The results showed that PC2I2H hydrogel film, as an evolved hydrogel, has excellent swelling performance in aqueous solutions at different pH and temperatures. In addition, this hydrogel showed a tensile strength of 103 MPa in the dry state and an elongation of 703% in the swollen state.

In situ detection of heavy metal ions in sewage with screen-printed electrode-based portable electrochemical sensors.

The rapid development of industrial technologies continuously increases the heavy metal pollution of water resources. Recently, portable electrochemical analysis-based devices for detecting heavy metal ions have attracted much attention due to their excellent performance and low fabrication costs. However, it has proven difficult to accommodate complex testing needs in a cost-effective manner. To address these limitations, we propose a new system for the in situ detection of heavy metals in wastewater using an organic light-emitting diode-based panel to display data in real time and Bluetooth to transmit data to a smartphone for rapid analysis. The fabricated device integrates an in situ signal analysis circuit, a Bluetooth chip, a photocured 3D-printed shell, and an electrode sleeve interface. In addition, a fully screen-printed functional electrode plate containing chitosan/PANi-Bi nanoparticle@graphene oxide multi-walled carbon nanotubes is utilized for the rapid detection of heavy metal ions. This device can perform wireless data transmission and analysis and in situ signal acquisition and processing. The sensor exhibits a high sensitivity (Hg2+: 88.34 μA ppm-1 cm-2; Cu2+: 0.956 μA ppm-1 cm-2), low limit of detection (Hg2+: 10 ppb, Cu2+: 0.998 ppm) and high selectivity during the detection of copper and mercury ions in tap water under non-laboratory conditions, and the results of real-time tests reveal that parameters measured in the field and laboratory environments are identical. Hence, this small, portable, electrochemical sensor with a screen-printed electrode can be effectively used for the real-time detection of copper and mercury ions in complex water environments.

Enhancing Polysulfide Confinement and Electrochemical Kinetics by Amorphous Cobalt Phosphide for Highly Efficient Lithium-Sulfur Batteries.

The application of lithium-sulfur (Li-S) batteries is severely hampered by the shuttle effect and sluggish redox kinetics. Herein, amorphous cobalt phosphide grown on a reduced graphene oxide-multiwalled carbon nanotube (rGO-CNT-CoP(A)) is designed as the sulfur host to conquer the above bottlenecks. The differences between amorphous cobalt phosphide (CoP) and crystalline CoP on the surface adsorption as well as conversion of lithium polysulfides (LiPSs) are investigated by systematical experiments and density-functional theory (DFT) calculations. Specifically, the amorphous CoP not only strengthens the chemical adsorption to LiPSs but also greatly accelerates liquid-phase conversions of LiPSs as well as the nucleation and growth of Li2S. DFT calculation reveals that the amorphous CoP possesses higher binding energies and lower diffusion energy barriers for LiPSs. In addition, the amorphous CoP features reduced energy gap and the increased electronic concentrations of adsorbed LiPSs near Fermi level. These characteristics contribute to the enhanced chemisorption ability and the accelerated redox kinetics. Simultaneously, the prepared S/rGO-CNT-CoP(A) electrode delivers an impressive initial capacity of 872 mAh g-1 at 2 C and 617 mAh g-1 can be obtained after 200 cycles, exhibiting excellent cycling stability. Especially, it achieves outstanding electrochemical performance even under high sulfur loading (5.3 mg cm-2) and lean electrolyte (E/S = 7 μLE mg-1S) conditions. This work exploits the application potential for amorphous materials and contributes to the development of highly efficient Li-S batteries.

Decorating a Loose Defect‐free Hybrid Selective Layer on a Smooth Intermediary: An Effective Way for Unexpected Performances of Nanofiber‐based Forward Osmosis Membranes

AbstractA novel composite forward osmosis (FO) membrane was fabricated by introducing a chitosan (CS) sublayer between nanofibers and polyamide (PA) layer, which was beneficial to forming thin and defect‐free PA layer and improved binding strength between substrate and the selective layer. Results exhibited low reverse salt flux (0.73 gMH) while maintained high water flux (85.4 LMH), which were better than that in other reports. In order to further improve permeability of membranes, oxidized multiwall carbon nanotubes (OMWNTs) were added into PA layer based on the optimized sublayer. The crosslinking degree of PA layer was reduced, leading to loose PA layers, which promoted the increase of water flux. After modifying, water flux reached 96.9 LMH without sacrificing salt rejection. It was worth mentioning that PAN/CS composite FO membrane, which could adjust microstructure of support layer and selective layer respectively, may provide a promising way for preparing membranes with anticipated separation performance.

Polyvinyl alcohol/polyethersulfone thin-film nanocomposite membranes with carbon nanomaterials incorporated in substrate for water treatment

A new class of thin-film nanocomposite (TFN) nanofiltration (NF) membrane was synthesized successfully by incorporation of carbon nanomaterials (oxidized multi-walled carbon nanotube (O-MWCNT) and graphene oxide (GO)) into polyethersulfone (PES) substrate via phase inversion method, substrate surface coating with polyvinyl alcohol (PVA) and then cross-linking with glutaraldehyde (GA). For better comparison, thin-film composite (TFC) membranes (without carbon nanomaterials incorporation into PES substrate) were also synthesized and the optimum concentrations of PVA and GA solutions were obtained. The fabricated TFC and TFN (TFN/O-MWCNTs and TFN/GO) membranes were characterized by SEM, AFM, ATR-IR spectroscopy and contact angle measurements. It was found that incorporation of O-MWCNTs and GO into the PES substrate results in more elongated finger-like pores and larger macrovoids in the substrate and also reduced thickness of the thin skin layer and roughness of the membrane surface. The optimum TFC membrane showed pure water flux of about 13.2 LMH and Na2SO4 rejection of 84 % at 4 bar, while the TFN/O-MWCNTs and TFN/GO membranes showed 54 % and 35 % improvement in water permeability, respectively, without immolating Na2SO4 rejection. The rejection sequence was obtained as R (Na2SO4) > R (MgSO4) > R (NaCl) that confirms the membranes surface has negatively charge.

Preparation of a novel synergistic flame retardant and its application in silicone rubber composites

SummaryDehydration condensation product (DHCP) was prepared by addition and dehydration condensation reactions of 9,10‐dihydro‐9‐oxa‐10‐phenanthrene‐10‐oxide (DOPO), vinyl trimethoxysilane, and (3‐aminopropyl) triethoxysilane. DHCP‐PA with high phosphorus content was prepared by reaction between DHCP and phytic acid (PA). It was then compounded with oxidized multi‐walled carbon nanotubes (OMWCNTs) to prepare silicone rubber (SR) flame retardant composites. The results showed that the SR with a small amount of DHCP‐PA owned good flame retardant effect. The heat release rate (HRR) was decreased from 436 kW/m2 for pure SR to 288 kW/m2 for the SR with 5 phr DHCP‐PA, and the decreasing degree was 33.9%. After mixing 5 phr DHCP‐PA with 1 phr OMWCNTs, the HRR of SR composite was decreased from 436 to 251 kW/m2, the smoke production rate was decreased from 0.161 to 0.087 m2/s, the limited oxygen index value was increased from 20.4% to 28.4%, and the flame retardant grade can reach UL94 V‐0. In addition, the synergistic flame retardant mechanism was researched and analyzed.

Synthesis of composite powders composed of silver and carbon nanotubes by liquid-phase reduction method

A successful synthesis of composite powders composed of both silver (Ag) particles and multi walled carbon nanotubes (MWCNTs) by liquid-phase reduction methods is reported. Based on previous work on electroless deposition of Ag on MWCNTs and the mixing technique called “modified molecular level mixing”, the novel procedure strongly controls the amount of individualized MWCNTs in the Ag/MWCNTs composite powders with a mass fraction of MWCNTs between 0 and 0.6 wt%.The results show that temperature and the concentration of the reducing agent have a significant impact on the growth of the Ag particles while the MWCNTs concentration influences the nucleation rate of Ag particles during synthesis of Ag/MWCNTs composite powders. Thermogravimetric analysis of the powder synthesized also show a catalytic effect of Ag particles on the oxidation of MWCNTs.

Oxygen Functional Groups on MWCNT Surface as Critical Factor Boosting T2 Relaxation Rate of Water Protons: Towards Improved CNT-Based Contrast Agents.

PurposeSalicyl (Sal) – among other oxygen functionalities – multi-walled carbon nanotubes (MWCNTs) and their nanohybrids are investigated as promising contrast agents (CA) in magnetic resonance imaging (MRI) or drug delivery platforms, due to their unique properties. The preliminary results and the literature reports were the motivation to endow high r2 relaxivities, excellent dispersibility in water, and biocompatibility to superparamagnetic MWCNTs nanohybrids. It was hypothesized that these goals could be achieved by, not described in the literature yet, two-stage oxygen functionalization of MWCNTs.ResultsTwo structurally different MWCNT materials differing in diameters (44 and 12 nm) and the iron content (4.7% and 0.5%) are studied toward the functionalization effect on the T2 relaxometric properties. MWCNT oxidation is typically the first step of functionalization resulting in “first generation” oxygen functional groups (OFGs) on the surface. Until now, the impact of OFGs on the relaxivity of MWCNT was not truly recognized, but this study sheds light on this issue. By follow-up functionalization of oxidized MWCNT with 4-azidosalicylic acid through [2+1] cycloaddition of the corresponding nitrene, “second generation” of oxygen functional groups is grafted onto the nanohybrid, ie, Sal functionality.ConclusionThe introduced OFGs are responsible for an almost 30% increase in the relaxivity, which leads to remarkable r2 relaxivity of 951 mM−1s−1 (419 (mg/mL)−1s−1), the unprecedented value reported to date for this class of CAs. Also, the resulting nanohybrids express low cytotoxicity and superb diffusion after subcutaneous injection to a mouse.

Impact of polypyrrole incorporation on nickel oxide@multi walled carbon nanotube composite for application in supercapacitors

In this article we report the synthesis of polypyrrole incorporated nickel oxide multi walled carbon nanotube (NiO@NMWCNT/PPy) composites by thermal reduction protocol for supercapacitor applications. The structural and morphological properties of the composites were confirmed by the aid of X-ray diffraction (XRD), Field-emission scanning electron microscope (FE-SEM) with energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and Field-emission transmission electron microscopy (FE-TEM) analysis indicating the hexagonal crystal structure of NiO decorated on NMWCNT/Ppy. The electrochemical characteristics of the NiO@MWCNT/PPy composite were analyzed in the presence of 2 M KOH as an electrolyte. The NiO@NMWCNT/PPy nanostructured composite produced a plenty of active sites for ion migration reactions that facilitate the energy storage mechanism. As a proof of concept demonstration, the NiO@NMWCNT/PPy composite was explored as an electrode materials in supercapacitor and exhibited specific capacitance of 395 F g−1 and cyclic stability up to 5000 cycles at 0.5 A g−1. Enhanced performance of composite is attributed to the incorporation of polypyrrole in NiO@NMWCNT. The improved capacitance and cyclic stability demonstrated by the composite indicates the NiO@NMWCNT/PPy to be a promising candidate for supercapacitor applications.

Influence of polymer type and carbon nanotube properties on carbon nanotube/polymer nanocomposite biodegradation

The interaction of anaerobic microorganisms with carbon nanotube/polymer nanocomposites (CNT/PNC) will play a major role in determining their persistence and environmental fate at the end of consumer use when these nano-enabled materials enter landfills and encounter wastewater. Motivated by the need to understand how different parameters (i.e., polymer type, microbial phenotype, CNT characteristics) influence CNT/PNC biodegradation rates, we have used volumetric biogas measurements and kinetic modeling to study biodegradation as a function of polymer type and CNT properties. In one set of experiments, oxidized multiwall carbon nanotubes (O-MWCNTs) with a range of CNT loadings 0–5% w/w were incorporated into poly-ε-caprolactone (PCL) and polyhydroxyalkanoates (PHA) matrices and subjected to biodegradation by an anaerobic microbial community. For each CNT/PNC, complete polymer biodegradation was ultimately observed, although the rate of biodegradation was inhibited above certain critical CNT loadings dependent upon the polymer type. Higher loadings of pristine MWCNTs were needed to decrease the rate of polymer biodegradation compared to O-MWCNTs, an effect ascribed principally to differences in CNT dispersion within the polymer matrices. Above certain CNT loadings, a CNT mat of similar shape to the initial PNC was formed after polymer biodegradation, while below this threshold, CNT aggregates fragmented in the media. In situations where biodegradation was rapid, methanogen growth was disproportionately inhibited compared to the overall microbial community. Analysis of the results obtained from this study indicates that the inhibitory effect of CNTs on polymer biodegradation rate is greatest under conditions (i.e., polymer type, microbial phenotype, CNT dispersion) where biodegradation of the neat polymer is slowest. This new insight provides a means to predict the environmental fate, persistence, and transformations of CNT-enabled polymer materials.

A hybrid composite of recycled popcorn-shaped MnO2 microsphere and Ox-MWCNTs as a sensitive non-enzymatic amperometric H2O2 sensor

Taking full advantage of the manganese (Mn) species which were produced in the fabrication of graphene oxide (GO) using modified Hummers method, loosely popcorn-shaped MnO2 microspheres were synthesized accordingly. A network composite of oxidized multi-walled carbon nanotubes (Ox-MWCNTs) and MnO2 (MnO2-Ox-MWCNTs) was assembled by a facile ultrasound-assisted approach. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) confirmed the successful preparation of MnO2 and the assembly of MnO2-Ox-MWCNTs. Based on drop-casting route, MnO2-Ox-MWCNTs composite modified glassy carbon electrode (GCE) (MnO2-Ox-MWCNTs/GCE) was constructed. The electrochemical performances of the proposed electrode were investigated by cyclic voltammetry (CV) and amperometric method. Due to the synergistic effect between loosely popcorn-shaped MnO2 microspheres and Ox-MWCNTs, the proposed electrode showed high peroxidase-like electrocatalysis activity for H2O2 detection. The peak currents linearly increased with H2O2 concentrations in the range 0.80–1000 μM, and limit of detection (LOD) was 0.38 μM. The proposed electrode could be employed for qualitative detection and quantitative determination of H2O2 in milk samples.

Electrochemical performance of a three-layer electrode based on Bi nanoparticles, multi-walled carbon nanotube composites for simultaneous Hg(II) and Cu(II) detection

Electrochemical analysis is a promising technique for detecting biotoxic and non-biodegradable heavy metals. This article proposes a novel composite electrode based on a polyaniline (PANi) framework doped with bismuth nanoparticle@graphene oxide multi-walled carbon nanotubes (Bi NPs@GO-MWCNTs) for the simultaneous detection of multiple heavy metal ions. Composite electrodes are prepared on screen-printed electrodes (SPCEs) using an efficient dispensing technique. We used a SM200SX-3A dispenser to load a laboratory-specific ink with optimized viscosity and adhesion to draw a pattern on the work area. The SPCE was used as substrate to facilitate cost-effective and more convenient real-time detection technology. Electrochemical techniques, such as cyclic voltammetry and differential pulse voltammetry, were used to demonstrate the sensing capabilities of the proposed sensor. The sensitivity, limit of detection, and linear range of the PANi-Bi NPs@GO-MWCNT electrode are 2.57×102 μA L μmol−1 cm−2, 0.01 nmol/L, and 0.01 nmol/L–5 mmol/L and 0.15×10−1 μA L μmol−1 cm−2, 0.5 nmol/L, and 0.5 nmol/L–5 mmol/L for mercury ion (Hg(II)) and copper ion (Cu(II)) detection, respectively. In addition, the electrode exhibits a good selectivity and repeatability for Hg(II) and Cu(II) sensing when tested in a complex heavy metal ion solution. The constructed electrode system exhibits a detection performance superior to similar methods and also increases the types of heavy metal ions that can be detected. Therefore, the proposed device can be used as an efficient sensor for the detection of multiple heavy metal ions in complex environments.

Green Dispersive Micro Solid-Phase Extraction using Multiwalled Carbon Nanotubes for Preconcentration and Determination of Cadmium and Lead in Food, Water, and Tobacco Samples

Background: Cadmium (Cd2+) and lead (Pb2+) have acute and chronic effects on humans and other living organisms. In the present work, new, green and accurate dispersive micro solid-phase extraction (DμSPE) method for the separation and preconcentration of trace amounts of cadmium (Cd2+) and lead (Pb2+) ions in various food, water and tobacco samples collected from Saudi Arabia prior to its Flame Atomic Absorption Spectrometric (FAAS) determinations was developed. Methods: The proposed method was based on a combination of oxidized multiwalled carbon nanotubes (O-MWCNTs) with a new chelating agent 5-benzyl-4-[4-methoxybenzylideneamino)-4H- 1,2,4-triazole-3-thiol (BMBATT) to enrich and separate trace levels of Cd2+ and Pb2+. The effect of separation parameters was investigated. The validation of the proposed preconcentration procedure was performed using certified reference materials. Results: Analyte recovery values ranged from 95-102%, indicating that the method is highly accurate. Furthermore, precision was demonstrated by the relative standard deviation (RSD < 3.0%). The limits of detection were 0.08 and 0.1 μg L−1 for Cd2+ and Pb2+ ions, respectively. The preconcentration factor was 200. Conclusion: The proposed method was used for the estimation of Cd2+ and Pb2+ ion content in various real samples, and satisfactory results were obtained. The proposed method has high adsorption capacity, rapid adsorption equilibrium, extremely low LODs, high preconcentration factors and shortens the time of sample preparation in comparison to classical SPE.

Electrochemical Sensor: L-Cysteine Induced Selectivity Enhancement of Electrochemically Reduced Graphene Oxide–Multiwalled Carbon Nanotubes Hybrid for Detection of Lead (Pb2+) Ions

The selectivity improvement of Electrochemically reduced Graphene Oxide–Multiwalled Carbon Nanotubes–L-cysteine (ErGO–MWNTs–L-cys) nanocomposite modified Glassy Carbon Electrode (GCE) using drop casting method for electrochemical detection of lead (Pb2+) ions was investigated. Initially, the graphene oxide–Multiwalled Carbon Nanotubes–L-cysteine (GO–MWNTs–L-cys) nanocomposite was synthesized by a facile and cost-effective method at room temperature. The as-prepared, GO–MWNTs–L-cys exhibited good stable aqueous dispersions due to high hydrophilic nature of GO components which led to inhibiting the hydrophobicity of MWNTs. Then, the electrochemical conductivity of ErGO–MWNTs–L-cys nanocomposite modified GCE (ErGO–MWNTs–L-cys/GCE) was improved by the direct electrochemical reduction of GO–MWNTs–L-cys nanocomposite. The GO–MWNTs–L-cys nanocomposites and its individual components were characterized by Attenuated Total Reflection Infrared (ATR-IR), Raman spectroscopy, Atomic Force Microscopy and X-ray diffraction (XRD). The synergistic effect of ErGO–MWNTs–L-cys nanocomposite was confirmed by Cyclic Voltammetry (CV) measurements in [Fe(CN)6]3-/4- redox. Experimental parameters, such as pH, accumulation time and electrochemical reduction degrees, were optimized. Under optimal conditions, the electrochemical performance of modified electrodes towards Pb2+ ions was examined and it exhibited appreciable improvement at the ErGO–MWNTs–L-cys/GCE. In terms of applications, Differential Pulse Anodic Stripping Voltammetry (DPASV) was employed for the determination of Pb2+ ions on ErGO–MWNTs–L-cys/GCE. The calibration plots between anodic current and Pb2+ ions exhibited linear relationship in the range of 0.2–40 μgL-1 with the detection limit calculated to be 0.1 μgL-1 (S/N=3). Finally, the ErGO–MWNTs–L-cys/GCE showed satisfied selectivity and stable results, and the Relative Standard Deviation (RSD) was calculated to be (RSD=2.15%).