Multi-walled Carbon Nanotubes In Aqueous Solution Research Articles

MWCNTs dispersion adopting GA and its application towards copper tailings-based cementitious materials

Hydrophobic carbon nanotubes are hardly to disperse in water and prone to agglomerate when poured with Copper Tailing-Based Cementitious Material (CTCM). Multi-walled carbon nanotubes (MWCNTs) + Arabic Gum (GA) dispersions were prepared by a novel method of synergistic optimization of concentration, controlling low-frequency ultrasonic time and setting the ambient temperature with non-toxic anionic surfactant GA as surfactant. The results of UV–Vis spectroscopy showed that the high stability MWCNTs + GA dispersion with low aggregation area (< 1.2%) and low aggregation beam size (< 219 nm) have been prepared by using 1.7 mmol/l GA. The effects of highly stable MWCNTs dispersion on the mechanical properties, microstructure and durability of CTCM were studied. The 28 days compressive strength increased by 21.5%, and the flexural strength increased by 20.5%, almost reaching the mechanical level of the control group. The results of SEM, XRD and EDS showed that GA significantly enhanced the dispersion of MWCNT in aqueous solution at a suitable concentration (mass ratio of GA:CNTs = 1:1). The microstructure of the prepared CTCM by high stability MWCNTs dispersion was optimized obviously, and the mechanical properties and durability were improved significantly. This method solves the dual problem of MWCNTs not being fully dispersed in aqueous solution and being easily re-agglomerated in cementitious materials, as well as finding a breakthrough for the low cost and industrialization of tailings cement-based composite cementitious materials.

Use of multi-walled carbon nanotubes (MWCNTs) stabilized in Arabic gum colloidal solution to induce genotoxicity and apoptosis of human breast and lung cancer cell lines

Introduction: Increased mortality owing to breast and lung cancer is an urgent global medical issue. Nanotherapy is one of the most widely used and recent procedures for combating cancer. Therefore, this study aimed to assess the beneficial effects of multi-walled carbon nanotubes (MWCNTs) to precisely target breast (MCF-7) and lung cancer (A549) cell lines. Multi-walled carbon nanomaterials are considered as a typical biocompatible nanomaterial that can be used in drug delivery without causing side effects. On the contrary, the metallic nanoparticles, even that of noble metals, are reported to have side effects that are still unavoidable.Methods: The MWCNTs were purified and stabilized using Arabic gum in an aqueous solution under ultrasonic radiation. Scanning and transmission electron microscopy (SEM and TEM, respectively) were employed to characterize the morphology of the MWCNTs, and elemental analysis was performed using SEM to determine their chemical composition.Results: The investigated MWCNTs had an average diameter of 10–12 nm and were mainly composed of 99.4% carbon and other trace elements. The Arabic gum emulsifying agent was found a powerful stabilizing agent for the investigated MWCNTs in aqueous solutions. The cytotoxic effect of the MWCNT/ Arabic gum colloidal solution on MCF-7 and A549 was evaluated by 3-(4,5- dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and lactate dehydrogenase assays, and the expression of apoptosis-related genes was assessed using quantitative real-time polymerase chain reaction and a human apoptosis signaling antibody array. This analysis aimed to clarify additional pathways involved, including those mediated by interleukin-1, tumor necrosis factor-α, and ceramide signaling pathways enrichments. Concerning the inhibition of cell growth, the efficacy of MWCNT/Arabic gum IC50 of MCF-7 (48.23 μg/mL) was higher than IC50 of A549 (100.1 μg/mL). MWCNT/Arabic gum enhanced the mRNA expression of apoptosis-associated genes encoding P53, Bax, and Caspases (9, 8, and 3). Upregulation of the apoptotic signaling pathway in the MCF-7 cell lysates was observed before and after exposure to the MWCNT/Arabic gum colloidal solution.Conclusion: The physicochemical properties of MWCNT/Arabic gum exhibited remarkable apoptotic activity in breast and lung cancer cell lines. However, further in vivo investigations are recommended to clarify the other molecular aspects related to the use of MWCNT/Arabic gum.

Emerging contaminant (Triclosan) removal by adsorption and oxidation process: comparative study

Triclosan is an antibacterial and antifungal agent present in a wide range of personal care products, including toothpaste, soaps, detergents, and surgical and surface cleaning agents. Many studies have been conducted to investigate the toxic potential of Triclosan (TCS) on human health, plants, and the environment, and it has been reported to be an endocrine disruptor. This study addresses the removal efficiency of TCS using nano-zerovalent iron (nZVI), multi-walled carbon nanotubes (MWCNTs), and carbon filter. Wherein, nZVI is synthesized by an environmentally benign method, i.e., using Camellia Sinensis (Tea) extract used as a reducing agent and carbon filter is prepared by coating MWCNTs onto the cotton cloth. Removal efficiency has been studied for TCS at different operational parameters such as concentrations of TCS from (5 to 20 ppm), dosages of nZVI and dosage of MWCNTs (0.05–0.3 g/l) and pH (3–11). Results of this study indicate that, till a concentration of 5 ppm, 0.1 g/lit dosage of nZVI and MWCNTs has shown a removal efficiency of 97.07 and 100% at reaction time of 40 and 20 min, respectively. An incorporation carbon filter has been proven an efficient than dispersing MWCNTs in aqueous solutions.

Physical and mechanical properties and micro characteristics of fly ash-based geopolymer paste incorporated with waste Granulated Blast Furnace Slag (GBFS) and functionalized Multi-Walled Carbon Nanotubes (MWCNTs)

Geopolymers are highly durable and have favorable mechanical properties, and are thus regarded as an eco-friendly alternative to traditional ordinary Portland cement binder. In this study, MWCNTs are obtained through a modification method using a compound of nitric acid and sulfuric acid, and are then dispersed using three types of dispersants. Fly ash-based geopolymers are prepared to validate the effectiveness and feasibility of adopting 0.05 wt.%, 0.10 wt.%, and 0.15 wt.% functionalized MWCNTs and substitution ratios of 10 %–40 % of fly ash with GBFS. The structure and dispersity of the functionalized MWCNTs in aqueous solutions are characterized using FT-IR and TEM, respectively. Then, the setting time, water absorption capacity, and mechanical behaviors are evaluated. In addition, SEM-EDS, FT-IR, TG-DSC, 29Si NMR, and XRD are employed to investigate the morphology, elemental components, mineralogical phases, and geopolymerization degree of the gel products. The experimental results show that the functionalized MWCNTs comprise −COOH and −OH groups and can be uniformly dispersed in aqueous solution containing SDS dispersant. Furthermore, geopolymer paste incorporated with 0.1 wt.% functionalized MWCNTs and having 30 % substitution of fly ash with GBFS exhibits a higher compressive and flexural strength and a lower water absorption capacity compared with all other geopolymer pastes.

A systematic investigation of dispersion concentration and particle size distribution of multi-wall carbon nanotubes in aqueous solutions of various dispersants

Surfactant-assisted exfoliation of multi-walled carbon nanotubes (MWNTs) in aqueous solution have become a common procedure to generate high fraction of individualized nanotubes. Since well-controlled experimental methodologies and reliable comparative metrics are scarce, a systematic research was conducted in order to analyze the dispersibility and the dispersing mechanisms of MWNTs in aqueous solutions of various surfactants. The concentration of dispersed MWNTs was accurately measured for a wide range of surfactant concentration, using combined UV–vis spectroscopy and thermogravimetric analysis (TGA). The obtained dispersibility results indicated that the highest dispersion concentration and efficiency is achieved in the SDBS-assisted MWNTs dispersion. Furthermore, the nanotube morphology and surfactant properties can be evaluated and rationalized by analyzing the dispersed nanotube mass and the surfactant amount per nanotube surface area. The amount of dispersed MWNTs remaining after varying levels of sonication and centrifugation was investigated, and a controllable sonication-centrifugation method for the preparation of well-dispersed MWNTs was established. The experimental data of the concentration of MWNTs dispersions versus centrifugation speed (ω) are fitted reasonably well by a Boltzmann function. The SDBS-assisted MWNTs dispersion will be more susceptible to the high centrifugal speed,while PVP-assisted MWNTs dispersion will be sediment fast at the mild centrifugation. The distributions of diameter and length of MWNTs at maximum dispersibility show that the sizes for the MWNTs dispersed by SDBS are much more polydisperse. The results further suggest that preparation of controllable carbon nanotubes morphology and design of rational configuration of surfactants are the key factors for increasing the dispersion stability and maximum concentration of well-dispersed MWNT.

Facile one-step fabrication of glucose oxidase loaded polymeric nanoparticles decorating MWCNTs for constructing glucose biosensing platform: Structure matters

A novel and robust enzymatic biosensing platform with high sensitivity is developed based on facile one-step assembled bio-nanocomposites with enzymes-loaded polymeric nanoparticles decorating multi-walled carbon nanotubes (MWCNTs). An amphiphilic copolymer PAVE containing photo-cross-linkable coumarin segments and carboxylic groups was co-assembled with MWCNTs in aqueous solution while encapsulating the model enzyme namely glucose oxidase (GOx) simultaneously, generating necklace-like bio-nanocomposites (GOx@PAVE-CNTs) with GOx-loading polymeric nanoparticles as nanobeads and MWCNTs as conducting micron-string. Then the GOx@PAVE-CNTs bio-nanocomposites were electro-deposited onto electrode surface and a robust biosensing complex film with porous network structure was formed after following photo-cross-linking. Consequently, an enzymatic glucose biosensor was successfully constructed. The biosensor exhibited ultrafast response (<3 s) to glucose with a considerably wide linear range (1.0 μM ∼ 5 mM) and a low detection limit (0.36 μM) for glucose detection. High sensitivity and selectivity of the biosensor toward glucose were also well demonstrated. Furthermore, the biosensor showed exceptionally good stability and reproducibility. More importantly, the glucose biosensor was practically used for glucose detection from human urine and serum samples with satisfactory results. As a proof-of-concept strategy, this facile and effective strategy for biosensor fabrication is of considerable interest because of its versatility to be generalized to many other enzymatic biosensor systems, exhibiting promising and practical potential in bio-medical and life health applications.

High-efficiency surfactant prepared from phenolic resin for multi-walled carbon nanotube aqueous suspension

Carbon nanotubes (CNTs) have been widely exploited to be used in many fields due to its perfect mechanical properties, but CNT agglomerates severely prevent CNTs’ excellent properties from performing. Many dispersants were synthesized to resolve the difficulty reported in recent years. In this paper, a healthier and cheaper dispersant with phenolic resin as original reagent was synthesized (denoted as AEP-4). Fourier transform infrared spectroscopy, nuclear magnetic resonance, and mass spectra were carried out to characterize chemical structure of reagent and products. Ultraviolet–visible spectroscopy and transmission electron microscopy were employed to evaluate the dispersibility of multi-walled carbon nanotubes (MWCNTs) in aqueous solution. The results showed that AEP-4 containing tertiary ammonium cations exhibited strong ability to disperse MWCNTs in aqueous solution, which showed better dispersion ability than sodium dodecyl benzene sulfonate. The scanning electron microscope results of MWCNT/carbon fiber reinforcements showed that many single MWCNTs showed up and uniformly covered carbon fiber surface in the case of carbon fiber treated by MWCNT/AEP-4 suspension, which reflected that MWCNT suspension with AEP-4 had good dispersion.

Effective dispersion of multi-walled carbon nanotubes in aqueous solution using an ionic-gemini dispersant

A promising ionic-gemini molecule, 4, 4′-di (n-tetradecyl) diphenylmethane disulfate salt (DSDM), is reported for effective dispersion of multi-walled carbon nanotubes (MWCNTs) in aqueous medium in the present investigation. The dispersibility and stability of the DSDM-modified MWCNTs were characterized by UV–vis spectrophotometer, Raman spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy and zeta potential measurements. The hydrophobic interaction between alky chains and carbon nanotubes as well as the π-π-stacking interaction between benzene rings and carboatomic rings in MWCNTs enables a successful modification of DSDM onto the MWCNT surface. The dispersed MWCNTs individually existed in dispersion with no structural damage, indicating a much better performance than the MWCNTs dispersed by the sodium dodecylbenzene sulfonate (SDBS), a frequently reported single-chain ionic dispersant. Surface potential measurements showed that the DSDM-modified MWCNTs were negatively charged, giving rise to electrostatic repulsion between the MWCNTs in aqueous solution. A better MWCNT dispersion effect was observed with the increase in MWCNT surface potential, and the dispersion with high MWCNT surface potential presents high dispersion stability with no agglomeration appeared for more than 5 months. The magnesium (Mg) matrix composite fabricated based on the DSDM-dispersed MWCNTs demonstrated excellent mechanical properties compared to pure Mg. Our research may provide an alternative way to improve the mechanical properties of composites.

Simple introduction of carboxyl head group with alkyl spacer onto multiwalled carbon nanotubes by solution plasma process

A simple method of fabricating carboxyl-terminated multiwalled carbon nanotubes (MWCNTs) with alkyl spacers was developed to improve the dispersion quality of MWCNTs in aqueous solutions using solution plasma (SP) in a 6-aminocaproic acid solution. The formation of SP in the solution led to better dispersion of MWCNTs in aqueous solutions. Fourier transform infrared spectroscopy (FT-IR) results indicate that a carboxyl group with an alkyl spacer can be introduced by SP treatment in the 6-aminocaproic acid solution. Sedimentation tests show that the SP-treated MWCNTs in the 6-aminocaproic acid solution retained their good dispersion quality in aqueous solutions of pHs 5, 6, and 9. The alkyl spacer plays an important role in the preservation of dispersion states particularly at pH 6.

Oxidative treatment, dispersion effect, and simulation of multi-walled carbon nanotubes in aqueous solution

In the present work, the multi-walled carbon nanotubes (MWCNTs) were modified by the treatment with concentrated nitric and sulfuric acid mixture (3: 1 vol/vol). The obtained material was characterized by X-ray diffraction (XRD). The effect of two surfactants, methylcellulose (MC) and cetyltrimethylammonium bromide (CTAB) on dispersing of MWCNTs in aqueous solution was monitored by UV–Vis spectroscopy and transmission electron microscopy (TEM). Also, the dispersing effect of the surfactants was simulated by three-dimensional Monte Carlo method. The results showed that the oxidative treatment leads to purification of the neat MWCNTs, and directly improved their dispersing. The mixture containing both MC and CTAB surfactants has better dispersing effect than individual surfactants. The optimum concentration ratio of MC, CTAB, and MWCNTs was 2: 3: 1. In the simulation model, MWCNTs were dispersed randomly. The simulation results may be helpful for the further research on mechanical and electrical properties of composites reinforced with MWCNTs.

Dispergation and modification of multi-walled carbon nanotubes in aqueous solution

Multi-walled carbon nanotubes (MWCNTs) are widely applied in development of composite materials. However, their properties are directly influenced by the degree of uniformity of dispersion of MWCNTs in the material’s matrix. In this paper, the dispersing of raw MWCNTs (R-MWCNTs) and decorated MWCNTs (D-MWCNTs) was studied in aqueous solution. The D-MWCNTs were obtained by chemical modification method by treatment of initial MWCNTs with the mixture of concentrated nitric and sulfuric acids (3: 1 vol/vol). To achieve a good dispersion of the MWCNTs, a method utilizing ultrasonic processing and surfactant (polyvinylpyrrolidone, PVP) was employed. MWCNTs were characterized by Fourier transform infrared spectroscopy (FT–IR) and X-ray diffraction (XRD). The prepared MWCNTs suspensions were investigated by UV spectroscopy, zeta potential measurements, surface tension and transmission electron microscopy (TEM). The D-MWCNTs have better dispersibility in aqueous solution; this attributed to the functional groups formed on their surface during chemical modification. The PVP surfactant in a certain concentration of 0.6 g/L has the maximum dispersing effect on MWCNTs in aqueous solution, the optimum concentration ratio of PVP and MWCNTs was 3: 1.

MWNT-hybrided supramolecular hydrogel for hydrophobic camptothecin delivery.

To encapsulate the hydrophobic camptothecin (CPT) into hydrogel matrix with a high loading amount, a supramolecular hydrogel hybrided with multi-walled carbon nanotubes (MWNTs) was developed by the host-guest interactions and used for loading and delivering CPT. Firstly, carboxylated MWNTs were modified by polyethylene glycol monomethyl ether (MPEG), which resulted in the water-dispersed MPEG-MWNTs. Then α-cyclodextrin (α-CD) was mixed with MPEG-MWNTs and the hybrid supramolecular hydrogel was fabricated by the inclusion interactions between α-CD and MPEG. The used MPEG not only dispersed MWNTs in aqueous solution, but also functioned as hydrogel matrix by interacting with α-CD. The gelation time for the sol-gel transition and rheological properties of the resultant hydrogels were studied. Due to the excellent application of MWNTs in drug delivery, hydrophobic CPT could be loaded into the hydrogel matrix by a higher amount compared with micelles. By in vitro release and cell viability tests, it was found that the encapsulated CPT could exhibit a controlled and sustained release behavior as well as sustained antitumor efficacy.

Investigations on oxidation cutting and dispersibility of multi-walled carbon nanotubes

Multi-wall carbon nanotubes (MWCNTs) were oxidized by soaking in mixed acids. Their microstructure and composition were characterized using transmission electron microscopy, atomic force microscopy, Raman spectroscopy and infrared spectroscopy. The influence of soaking time on microstructure and dispersibility of the cut MWCNTs in aqueous solution was investigated. Results show that the MWCNTs were oxidized at defect sites by the mixed acids and converted from highly tangled ropes into short, open-ended nanotubes with lengths of 200–1500 nm. The isoelectric point was reduced from 4.5 to 3.5 due to hydroxyl and carboxyl groups on the surface and the open ends of the cut MWCNTs. The aggregation experiments and UV–vis absorbance spectra revealed that the cut MWCNTs can be best dispersed in an aqueous solution containing 0.1 wt.% of sodium dodecyl-benzenesulfonate when sonicated at a pH value of 2 for 40 min. [New Carbon Materials 2014, 29(2): 109–117]

Surface Modification of Multiwalled Carbon Nanotubes with Engineered Self-Assembled RAFT Diblock Coatings

A facile method to modify the surface of multiwalled carbon nanotubes (MWCNTs) via electrostatic interactions between polyelectrolytes and oxidized MWCNTs was developed. Diblock copolymers containing poly[2-(methacryloyloxy)ethyltrimethylammonium chloride] (PMETAC), a positively charged block, and poly(ethylene glycol) methacrylate (PEGMA), a neutral block, with tailored molecular weights and low polydispersities were synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization. Acid treated-MWCNTs were coated with the RAFT diblock copolymers to improve their dispersibility in aqueous phosphate buffered saline (PBS) solution. The short positively charged PMETAC block was designed to attach the block copolymers to the surface of MWCNTs via electrostatic interactions, whereas the PEGMA block improved dispersibility of the MWCNTs in aqueous solutions. Extensive screening of the diblock copolymers with different degrees of polymerization (DP) showed that the dispersion stability of the polymer-coated MWCNTs in PBS was greatly improved with increasing chain length of the PEGMA block. In particular, the MWCNTs coated with a diblock copolymer containing PEGMA (DP = 118, the longest block investigated) showed superior dispersion stability in both water and PBS solution.

Mechanical and morphological properties of highly dispersed carbon nanotubes reinforced cement based materials

Stable homogeneous suspensions of multi-walled carbon nanotubes (MWCNTs) were prepared using gum arabic (GA) as dispersant and were incorporated to Portland cement paste. The dispersion was examined by ultraviolet visible spectroscopy (UV-vis), and the concentration measurement shows that the optimum concentration of GA is 0.45 g · L−1. The dispersibility of the surface-modified MWCNTs in aqueous solution and cement matrix were investigated by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS), and the mechanical properties of the composites were investigated. The results show that the addition of the treated nanotubes can improve both the flexural strength and the compressive strength of the Portland cement composite significantly. The flexural strength of the composite increases up to 43.38% with the MWCNT concentration of 0.08% (by weight of cement). The porosity and pore size distribution of the composites were measured by mercury intrusion porosimetry (MIP), and the results indicate that the cement paste doped with MWCNTs obtained lower porosity and concentrated pore size distribution. The morphological structure was analyzed by field emission scanning electron microscopy (FESEM) and EDS. It is shown that MWCNTs act as bridges and networks across cracks and voids, which transfer the load in case of tension, and the interface bond strength between the nanotubes and matrix is very strong.

Influence of dry and wet ball milling on dispersion characteristics of the multi-walled carbon nanotubes in aqueous solution with and without surfactant

Abstract The current paper presents a new approach of attaining the optimum grinding condition of a planetary ball mill and simple method for purifying multi-walled carbon nanotubes (MWCNTs) to investigate the dispersion characteristics of MWCNTs. This work was conducted under dry and wet grinding conditions at various rotation speeds (200 rpm–500 rpm), and the dispersion characteristics of MWCNTs in aqueous solutions with and without surfactant were studied. The results were examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), particle-size analysis (PSA), UV-spectrophotometry and zeta potential (ζ) measurements. The purification results show that the structures of amorphous carbon and carbon particles of MWCNTs were completely eliminated and the tips of nanotubes opened. Moreover, both dry and wet grinding caused the lengths of the MWCNTs to be shortened with increasing rotation speed. The maximum absorbance of nanofluid was revealed to be 2.485 abs at wavelength of 253 nm for the best dispersion. The best dispersion characteristics were observed for wet grinding at a rotation speed of 500 rpm assisted by the ultrasonication dispersion of CNTs in aqueous solutions with surfactant.

Nanocomposites of poly(ethylene oxide) and multiwall carbon nanotube prepared using an organic salt-assisted dispersion technique

Poly (ethylene oxide) (PEO)/multiwall carbon nanotubes (MWCNT) nanocomposites were prepared by dispersion of MWCNTs in aqueous solution using half neutralized sodium salt of sebacic acid as a modifier. The physical interaction of half neutralized sodium salt of sebacic acid with MWCNT (cation-p interaction) has been established by using Fourier transform infrared and Raman spectroscopic analyses. Such interaction helps in debundling the MWCNTs and resulted in a better dispersion in PEO matrix as confirmed by scanning electron microscopy and transmission electron microscopy. Addition of MWCNTsignificantly improves the storage modulus in rheological measurements as well as in dynamic mechanical thermal analysis. The crystallization behaviors of the composites made with the unmodified and modified MWCNTs were investigated. The modified MWCNT-based composites shows large number of spherulite with smaller size compared to those observed in unmodified MWCNT-based composite. POLYM. ENG. SCI., 00:000‐000, 2012. a 2012 Society of Plastics Engineers

Effect of grinding speed changes on dispersibility of the treated multi-walled carbon nanotubes in aqueous solution and its thermal characteristics

For the purpose of increasing the dispersibility and thermal conductivity of fluid containing nanoparticles, raw multi-walled carbon nanotubes (MWCNTs) were treated by strong acids. The purified structures were dispersed into aqueous solution by using wet grinding conditions at various rotation speeds (300–600rpm) merged with ultrasonication. The particle size analyzer reveals that the agglomerated size of ground particles at rotation speed of 300rpm was 39.811μm. Nevertheless, the agglomerated size of particles significantly decreased to 11.482μm after grinding at rotation speed of 600rpm. The maximum absorbance (4.0 abs at wavelength of 300nm) and highest thermal conductivity (0.6074W/mk at 30°C) of the suspension corresponds to the grinding speed of 600rpm assisted by ultrasonication dispersion. From the overall results, grinding method with high rotation speed plays can be significantly increased both the dispersibility and thermal conductivity of MWCNTs in aqueous solution.

The Use of Anionic Gum Arabic as a Dispersant for Multi-Walled Carbon Nanotubes in an Aqueous Solution

Stable homogeneous suspensions of multi-walled carbon nanotubes (MWCNTs) were prepared using gum arabic (GA) as a dispersant. By measuring adsorption isotherm, the surface chemical properties of the MWCNTs were investigated. The dispersion of MWCNTs in aqueous solution was examined with transmission electron microscopy and ultraviolet visible spectroscopy. The stabilization mechanism of the MWCNTs in aqueous solution using the GA surfactant was discussed. The isotherm of GA adsorption on MWCNTs indicates a typical two-step mechanism of adsorption (namely "SL"), and the adsorption isotherm reaches the saturation plateau at a GA concentration of 0.45 g x L(-1). The concentration measurement of MWCNTs shows that the optimum concentration of GA is 0.45 g x L(-1).

Preparation and characterization of silver nanoparticles immobilized on multi-walled carbon nanotubes by poly(dopamine) functionalization

Multi-walled carbon nanotubes (MWNTs) functionalized with poly(dopamine) (PDA) were found to cause the immobilization of silver nanoparticles on the surface. The PDA functional layer not only improved the dispersion of MWNTs in aqueous solution, but also was used as a platform for subsequent silver nanoparticle immobilization. The surface morphology of the functionalized MWNTs was observed by high-resolution transmission electron microscopy. The results showed that PDA layers with controlled thickness on the nanometer scale were formed on MWNT surfaces by in situ spontaneous oxidative polymerization of dopamine, and that high-density of homogeneously dispersed spherical silver nanoparticles with sizes of 3–4 nm were immobilized on their outer surface. The space between spherical silver nanoparticles is less than 10 nm. Both X-ray photoelectron spectroscopy and X-ray diffraction results showed that the Ag nanoparticles on the surface of hybrids exist in the zero valent state.