Elsevier

Journal of Solid State Chemistry

Volume 229, September 2015, Pages 342-349
Journal of Solid State Chemistry

Synthesis and utilization of a novel carbon nanotubes supported nanocables for the adsorption of dyes from aqueous solutions

https://doi.org/10.1016/j.jssc.2015.06.026Get rights and content

Highlights

  • A simple, cost-effective and “green” method for the synthesis of the material.

  • The diameter and length of the material are relatively easy to control.

  • The surface has large oxygen-containing groups and preferable chemical reactivity.

  • Compared with raw MWCNTs and some other adsorbents, the adsorption capacity is much high.

Abstract

Using multiwalled carbon nanotubes(MWCNTs) as mechanical support and glucose as carbon resource, a hydrothermal carbonization route was designed for the synthesis of MWCNTs@carbon nanocables with tunable diameter and length. MWCNTs are firstly used as templates for the formation of carbon-rich composite nanocables, and the diameter of the nanocables could be tailored through adjusting the hydrothermal time or the ratio of MWCNTs and glucose. Owing to abundant superficial oxygen-containing functional groups, porous surface and remarkable reactivity, the as-synthesized nanocables are capable of efficiently adsorbing cationic dye methylene blue (MB) and crystal violet (CV). Furthermore, the optimum adsorption conditions, kinetics, adsorption isotherms and adsorption thermodynamics of dyes were studied systematically. Additionally, the maximum adsorption capacities calculated from data analysis (298.5 mg/g for MB and 228.3 mg/g for CV) are significant higher than those of raw MWCNTs and some other adsorbents reported previously, which provides strong evidence for using MWCNTs@carbon nanocables as adsorbent to remove dyes from aqueous solutions.

Graphical abstract

MWCNTs@carbon nanocables has been successfully fabricated by a hydrothermal carbonization method. The as-synthesized novel samples were used as adsorbents and exhibited high adsorption capacity on MB and CV.

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Introduction

Nowadays, environmental problems have become a global concern because of their impact on public health. Among all the environmental pollution, improper management of industrial water is one of the main causes that people suffer from malnutrition, sickness, and even death due to lack of access to potable water [1]. Furthermore, the statistical analysis of World Bank (WB) manifests that 17–20% of industrial water pollution comes from textile coloration and treatment [2].

Actually, dyes are widely used in industrial fields, for instance, textiles, leather, printing, cosmetics and rubber [3]. Existence of dyes in environment to a certain degree greater than the tolerable levels causes undesirable effects not only on the ecological environment but also on human health [4]. More specifically, they may be carcinogenic and mutagenic to humans, adversely affect the photosynthetic activity of aquatic life [5], and are extremely resistant to biodegradation by native microorganisms [6]. It has been estimated that 10–15% of the dyes was lost during the dying process and released as effluent in both developing and industrialized countries, which has led to growing public and environmental concerns [7]. As a result, the development of technologies to efficiently remove dyes from wastewater before discharging to environment is of great importance.

To date, the most commonly used methods to decontaminate wastewater from dyes are coagulation, adsorption, oxidation, photocatalysis, membrane filtration, etc. [8]. Among these, adsorption is considered to be an effective method and many polymeric and inorganic materials have been developed as adsorbents [9]. However, the adsorption capacity of conventional adsorbents is limited by the density of surface adsorption sites, slow kinetics, and nonequilibrium of adsorption [10]. Nanostructured materials, with their high surface area to mass ratio, ease of incorporation of specific functionality [11], [12], and unique chemical and physical properties [5], offer improved efficiency and reduction in energy cost in pollution control and environmental remediation [13]. During the past two decades, high-quality nanomaterials consisting of various compositions and different dimensions, especially core–shell and hollow nanostructures, have received intense attention and been fabricated successfully through physical and chemical strategies [14], [15], [16]. For example, several studies investigated the preparation of carbon nanofibers with a typical diameter of 50–200 nm by the autoclave treatment of precursors in the C–H–O system at high temperature (up to 800 °C) and high pressures (up to 100 MPa) in the presence of a metal powder catalyst [17]. Meanwhile, a number of studies researched the fabrication of metal oxide hollow structures [18], flexible noble metal (Ag,Cu)@cross-linked poly(vinylalcohol) (PVA) coaxial nanocables [17], [19], carbon nanowires@SnO2 nanosheets@carbon composite [20], metal (Ag, Te, Se)@carbon nanocables [6], [21], [22] and so forth by polyol-mediated method [19], hydrothermal method [23], oxidation-coordination-assisted dissolution method [24], and sacrificial templating method [25]. Nevertheless, these methods above involved either high energy input, a relatively long period of processing time, or costly experimental equipment [26], [27]. In addition, the commonly used template methods need to synthesize the template and subsequently remove it to leave behind the target material with hollow structure using chemical agents [28]. Therefore, searching for new synthetic strategies and improving experimental process for the synthesis of nanomaterial such as carbon nanofibers and nanocables have been drawing extensive attention.

In this paper, a simple and economic method is developed to hydrothermally synthesize functionalized carbon nanocables from glucose substrate using multiwall carbon nanotubes (MWCNTs) as mechanical supports. MWCNTs have been considered as excellent template due to its structural properties, good thermal and chemical stability, and low cost-effectiveness [29]. Without the MWCNTs as template, the glucose tends to form carbon colloid spheres instead of nanocables. Moreover, the diameter and the by-product of the MWCNTs@carbon nanocables can be controlled by regulating the reaction time and reactant ratio during the carbonization and polymerization processes of glucose. The obtained nanocables have good dispersibility, accompanied by abundant hydrophilic functional groups, which can give rise to remarkable potential for the removal of organic dyes by electrostatic, complex, or hydrogen-binding interactions. Methylene blue (MB) and crystal violet (CV), two poisonous contaminants in water supplies produced from various industries [4], [30], were used as adsorbates in the adsorption experiments.

Section snippets

Materials

MWCNTs (diameter 20–40 nm) were provided by Shenzhen Nanotech Port Co., Ltd. Anhydrous Glucose (C6H12O6), anhydrous ethanol (C2H6O) were purchased from Sinopharm Chemical Reagent Co., Ltd. Dye molecules, methylene blue (MB) and crystal violet (CV) were obtained from Sigma Aldrich. All the chemicals were used as-received with no further purification.

Synthesis of MWCNTs@carbon nanocables

The fabrication of MWCNTs@carbon nanocables was prepared by a template-directed hydrothermal carbonization (HTC) process [31]. The synthesis was

Characterization

The FTIR spectra of the raw MWCNTs, MWCNTs@carbon nanocables and glucose are shown in Fig. 1. For the curve of MWCNTs@carbon nanocables, the wide bands around 3000–3500 cm−1 prove the presence of OH, and the bands in the range of 1000–1300 cm−1 can be attributed to the C–OH stretching and OH bending vibrations, which suggest the existence of a large amount of hydroxyl groups [22]. The peaks at 1700 and 1625 cm−1 are assigned to the stretching vibrations of C=O and C=C, respectively. In addition,

Conclusions

A facile and environmentally friendly hydrothermal route for fabrication of uniform and functionalized MWCNTs@carbon nanocables was developed. The well-defined hybrid nanofibers can easily be dispersed in water due to their polar and oxygen-containing surface layer, which is very different from the behavior of hydrophobic carbon nanotubes. Investigation and practical experiments confirm that the diameter of the nanocables as well as the shell thickness can easily be tuned by controlling the

Acknowledgements

This work was supported by the National Natural Science Foundation of China (Nos. 21176262 and 21175155).

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