Energy and environmental applications of carbon nanotubes ...

Environ Chem Lett (2012) 10:265–273 DOI 10.1007/s10311-012-0356-4

REVIEW

Energy and environmental applications of carbon nanotubes Chin Wei Tan • Kok Hong Tan • Yit Thai Ong • Abdul Rahman Mohamed • Sharif Hussein Sharif Zein Soon Huat Tan

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Received: 12 January 2012 / Accepted: 16 January 2012 / Published online: 1 February 2012 Ó Springer-Verlag 2012

Abstract Energy and environment are major global issues inducing environmental pollution problems. Energy generation from conventional fossil fuels has been identified as the main culprit of environmental quality degradation and environmental pollution. In order to address these issues, nanotechnology plays an essential role in revolutionizing the device applications for energy conversion and storage, environmental monitoring, as well as green engineering of environmental friendly materials. Carbon nanotubes and their hybrid nanocomposites have received immense research attention for their potential applications in various fields due to their unique structural, electronic and mechanical properties. Here, we review the applications of carbon nanotubes (1) in energy conversion and storage such as in solar cells, fuel cells, hydrogen storage, lithium ion batteries and electrochemical supercapacitors, (2) in environmental monitoring and wastewater treatment for the detection and removal of gas pollutants, pathogens, dyes, heavy metals and pesticides and (3) in green nanocomposite design. Integration of carbon nanotubes in solar and fuel cells has increased the energy conversion efficiency of these energy conversion applications, which serve as the future sustainable energy sources. Carbon

nanotubes doped with metal hydrides show high hydrogen storage capacity of around 6 wt% as a potential hydrogen storage medium. Carbon nanotubes nanocomposites have exhibited high energy capacity in lithium ion batteries and high specific capacitance in electrochemical supercapacitors, in addition to excellent cycle stability. High sensitivity and selectivity towards the detection of environmental pollutants are demonstrated by carbon nanotubes based sensors, as well as the anticipated potentials of carbon nanotubes as adsorbent to remove environmental pollutants, which show high adsorption capacity and good regeneration capability. Carbon nanotubes are employed as reinforcement material in green nanocomposites, which is advantageous in supplying the desired properties, in addition to the biodegradability. This article presents an overview of the advantages imparted by carbon nanotubes in electrochemical devices of energy applications and green nanocomposites, as well as nanosensor and adsorbent for environmental protection. Keywords Carbon nanotubes Energy Environmental monitoring Wastewater Biotechnology Nanocomposites

Introduction This manuscript is an abridged version of our chapter published in the book Environmental Chemistry for a Sustainable World, volume 1: Nanotechnology and Health Risk (Tan et al. 2012). C. W. Tan K. H. Tan Y. T. Ong A. R. Mohamed S. H. S. Zein S. H. Tan (&) School of Chemical Engineering, Engineering Campus, Universiti Sains Malaysia, Seri Ampangan, 14300 Nibong Tebal, S.P.S., Pulau Pinang, Malaysia e-mail: [email protected]

Since the discovery of carbon nanotubes (CNTs) in 1991 by Iijima (1991), CNTs have been receiving intense investigation towards the development of their application due to their unique electronic, chemical, mechanical and structural properties. CNTs are built from sp2 carbon units in hexagonal networks as in a graphene sheet (Merkoçi 2006). They can be classified as either single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes

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(MWCNTs). SWCNT is formed by rolling a sheet of graphene into a cylinder and capped by hemispherical ends, which is a result of pentagon inclusion in the hexagonal carbon network of the nanotube wall during the growth process. The diameter of SWCNTs is around 0.4–3 nm and several lm in length (Balasubramanian and Burghard 2005). MWCNT is a stack of graphene sheets rolled up in concentric cylinders, with diameters in between 2 and 25 nm, and the distance between sheets or inter layer spacing is about 0.34 nm (Ajayan 1999). CNTs possess some of the unique physical properties, such as one hundred times the tensile strength of steel, thermal conductivity better than other materials except the purest diamond and electrical conductivity similar to copper but carry much higher currents (Merkoçi 2006). CNTs have high electron transfer rate over the sidewall, which lead to the high electrical conductivity of CNTs. The chemical reactivity of CNTs is derived mainly from the curvature of the sidewall and structural defects (Balasubramanian and Burghard 2008). The exohedral chemical reactivity at the convex surface of CNTs increases with increasing curvature of the sidewall due to the distortions of normally planar C–C bonds of sp2 hybridization and the misalignment of p orbitals. The overall chemical reactivity of CNTs is strongly dependent on the presence of structural defects such as vacancies and Stone–Wales defects, which allows localized double bonds to form between carbon atoms in the defect and, therefore, enhances the local chemical reactivity. The adsorption properties of CNTs depend on the accessible surface area and the porous nature of nanotube. Opening the nanotubes by removing the caps as well as chemical treatment of CNTs can significantly influence the adsorption properties by altering the surface area and porous structure. Generally, CNTs were found to have higher condensation pressures and lower heats of adsorption than graphite, therefore better adsorption properties (Masenelli-Varlot et al. 2002). CNTs have two distinct regions that contribute to their electrochemical behaviour, which are the CNTs sidewall and the tube ends. Purification of CNTs, such as chemical oxidation or thermal treatment, leads to the partial oxidation of CNTs to produce oxygenated functional groups at the tube ends and defects along the sidewall (Gong et al. 2005). A pair of redox peaks is observed when the purified CNTs are subjected to cyclic voltammetry (CV), and the peaks are attributed to the redox process of oxygenated functional groups at the CNTs (Luo et al. 2001; Barisci et al. 2000). The electrochemical behaviour of the CNTs sidewall is similar to the basal plane of highly oriented pyrolytic graphite, and the electrochemical behaviour of the tube ends is similar to the edge plane of highly oriented pyrolytic graphite (Banks and Compton 2006).

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Environ Chem Lett (2012) 10:265–273

In this article, we review the recent advancements brought by CNTs in the field of energy conversion and storage, environmental monitoring and wastewater treatment, as well as green nanocomposite design. The advantages imparted by CNTs in enhancing the performances of solar cells, fuel cells, hydrogen storage, lithium ion batteries and electrochemical supercapacitors, which serve as the future clean and sustainable energy source, are discussed. We also discuss the potential applications of CNTs as sensors and adsorbents for environmental monitoring and the development of green nanocomposite based on CNTs for environmental protection.

Carbon nanotubes in energy conversion and storage Solar energy has a great potential as a clean and sustainable energy source due to its abundance and more evenly distribution in nature than any other renewable energy sources (Wijewardane 2009). New generation of solar cells based on thin films processing includes dye-sensitized solar cells, quantum dot-sensitized solar cells and polymer/ organic solar cells, which are promising photovoltaic devices owing to their low fabrication cost and high energy conversion performance. Extensive research has been carried out to obtain high photoconversion efficiency of solar cells by introducing CNTs into the device, such as nanoarchitecture on the working electrode surface (Sawatsuk et al. 2009; Imahori and Umeyama 2009), CNTs composite as counter electrode (Mei et al. 2009; Ramasamy et al. 2008) and adding CNTs to the electrolyte (Lee et al. 2009). Brown et al. (2008) have reported the employment of SWCNTs network on the working electrode as a onedimensional nanoscaffold for dye-sensitized titanium dioxide (TiO2) nanoparticles. The solar cell exhibited higher photoconversion efficiency, which suggests that the SWCNTs network improved the charge collection and transport, as well as the photocurrent generation. A novel solar cell was reported based on donor–acceptor nanoarchitecture on the working electrode, where CNTs were used as the electron acceptor material due to the unique one-dimensional nanostructure as the ideal charge transport pathway in the photoactive layer (Imahori and Umeyama 2009; Umeyama and Imahori 2008). The electron transfer from the donor-excited state to the conduction band of semiconductor nanoparticles via CNTs as the electron acceptor minimizes the undesirable charge recombination and improves the cell performance. Integration of CNTs into the electrode of solar cells had exhibited an increased photoconversion efficiency, which was attributed to the effective role of CNTs to facilitate the charge transport across the photoactive layer, to reduce the rate of charge


recombination and, therefore, to improve the photoconversion efficiency of solar cells. Low temperature fuel cells are promising alternative source of electrical power, owing to their high power density, low operating temperature and water as the only by-product (Xu et al. 2008). The key properties of carbon support to improve the platinum (Pt) catalyst activity include high surface area, high porosity, high electrical conductivity and high stability in fuel cell environment (Wu et al. 2010; Antolini 2009). Recently, CNTs have been exploited as an alternative catalyst support in fuel cell applications for its high surface area with high porosity, as well as high electrical conductivity, better electrochemical durability and more resistant to electrochemical oxidation (Jha et al. 2008; Li and Xing 2006; Li et al. 2003). Lin et al. (2010) have reported the synthesis of Pt nanoparticles on MWCNTs as catalyst support, where the Pt/MWCNT based membrane electrode assembly exhibited high durability and stability, in addition to higher current densities. The enhanced performance of the cell was attributed to the reduced catalyst particle size, improved chemical activity and stability of CNTs based catalyst support. CNT-supported Pt catalyst with integrated Pt/CNT layer has been reported, which exhibited improved performance in power density (Tang et al. 2010). Higher catalytic performance of Pt catalysts was attributed to the highly localized Pt distribution region at the membrane– electrode interface, which resulted in a higher Pt utilization for low Pt loadings. CNTs based catalyst supports had exhibited higher Pt catalyst utilization to increase the fuel conversion efficiency, in addition to the enhanced performance durability and stability in fuel cell environment. Hydrogen is seen as an important new source of energy due to its inherent pollution free nature from clean combustion, resource availability and provision of the highest energy efficiency (Lim et al. 2010). CNTs have shown potential advantages to store hydrogen, notably CNTs composite storage materials, such as SWCNTs doped with alkali or transition metals and SWCNTs coated with metal hydrides. These CNTs composite storage materials have shown high hydrogen storage capacities, in addition to the advantages of storing/releasing hydrogen at ambient conditions, as well as the ability of metal hydrides to adsorb certain amount of additional hydrogen molecules (Durgun et al. 2008; Lochan and Head-Gordon 2006). Examples of metal hydrides that have been coated on SWCNTs to facilitate the adsorption of hydrogen molecules and to increase the hydrogen storage capacity are aluminium hydride, boron hydride, lithium hydride and nickel hydride (Surya et al. 2010; Iyakutti et al. 2009; Surya et al. 2009). Intensive research studies are underway to optimize and to improve the performance of CNTs based hydrogen storage

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medium in terms of storage capacity and the sorption– desorption kinetics. Lithium ion batteries are becoming the main power source in today’s portable electronic devices and hybrid electric vehicles, due to their high energy density, high operating voltage and low self-discharge rate (Yang et al. 2009). Several metals and metal oxides are investigated as lithium insertion materials in anode owing to their high theoretical capacities. However, large volume changes and agglomeration of these metals or metal oxides during charging and discharging process lead to the rapid pulverization of the electrode and the decrease in electrical conductivity, which in terms limit the cycling capability or cycle efficiency (Hu et al. 2008; Yang et al. 2007; Choi et al. 2004). Intensive research efforts are focusing on developing CNTs nanocomposites with CNTs acting as an intercalation host or matrix for the dispersion of lithium insertion materials to restrain the volume expansion or pulverization of electrode materials, while retaining their high capacities. The preparation of tin oxide (SnO2)/MWCNT composites as anode materials in lithium ion batteries has been reported since SnO2 shows a high theoretical capacity of 782 mAhg-1 (Du et al. 2010). The improved performances of SnO2/MWCNT composites in terms of reversible capacity and cyclic capacity retention were attributed to CNTs as the intercalation host for SnO2 nanoparticles that reduced the absolute volume change and prevented the agglomeration of SnO2 nanoparticles. With CNTs acting as an intercalation host, high dispersion of lithium insertion materials can be achieved to increase the reversible energy capacity, in addition to restraining the pulverization of the electrode materials and, therefore, to improve the cycling stability and rate capability. Electrochemical supercapacitors are considered as the ideal energy storage and power output technologies for portable electronic devices, digital communications, hybrid electric vehicles and renewable energy systems, due to the advantages of high power and energy density characteristics, high cycle efficiency and long cycle life (Simon and Gogotsi 2008; Winter and Brodd 2004). Recently, CNTs have been explored as electrode materials for hybrid supercapacitors, which combine the electrical double layer capacitive electrode and the pseudo-capacitive electrode, due to their high electrical conductivity, chemical stability, low mass density and large surface area (Du and Pan 2006; Pandolfo and Hollenkamp 2006). Electrochemical conducting polymers for instance, polyaniline, polypyrrole and polythiophene derivatives, as well as the metallic nanoparticles or transition metal oxides, such as manganese dioxide (MnO2) and zinc oxide (ZnO), are deposited onto CNTs to increase the total capacitance through faradaic

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pseudo-capacitance effects (Yan et al. 2010; Wang et al. 2009; Zhang et al. 2009). Graphene nanosheet/carbon nanotube/polyaniline (GNS/ CNT/PANI) composite was applied as electrode materials for electrochemical supercapacitors, which exhibited high specific capacitance and excellent cycle stability (Yan et al. 2010). The high specific capacitance of GNS/CNT/PANI composite was attributed to the highly conductive GNS support for the deposition of PANI particles and CNT as highly conductive path in the composite, whereas the excellent cycle stability was attributed to the CNT conductive network with improved mechanical strength during long-term charge/discharge process. With CNTs as the conductive filler in the electrode, higher energy capacity and cycle efficiency of electrochemical supercapacitors can be achieved.

Carbon nanotubes in environmental monitoring and wastewater treatment Air pollutants have been the major factor contributing to the degradation of air quality, leading to adverse effects on the environment and human health. Conventional solidstate gas sensors are highly sensitive and relatively selective, but they suffer from the disadvantages of elevated working temperatures and long-term stability problems (Bai and Shi 2007; Barsan et al. 2007). CNTs have shown promising potential as gas-sensing nanomaterials due to their gas adsorption capability and large active surface area (Wei et al. 2010; Penza et al. 2009). Gas sensors based on pristine CNTs are reported to show good responses to NO2, NH3, SO2 and NO, despite their poor selectivity and slow recovery at ambient conditions (Moon et al. 2008; Goldoni et al. 2004, Valentini et al. 2004; Goldoni et al. 2003). Recently, intensive investigations are carried out in developing sensors based on CNTs functionalized with metal oxides, such as SnO2, WO3 and TiO2 that serve as sensing elements to enhance the selectivity(He et al. 2009; Hoa et al. 2009; Penza et al. 2009). Preparation of a MWCNT-doped SnO2 thin film gas sensor has been reported, in which the sensor showed a very good selectivity and a higher sensitivity than a pure SnO2 thin film gas sensor to ultra-low concentrations of NO2 in the ppb range (Wei et al. 2010). The improved performance of MWCNT-doped SnO2 thin film gas sensor was attributed to the effects between p-type semiconductor of MWCNTs and n-type semiconductor of SnO2 as the depletion layer at the p-n junction was modulated by the changes in barrier height and conductivity of the SnO2/ MWCNT sensitive layer by adsorbed NO2. CNT-modified WO3 gas sensor was demonstrated and it was capable of detecting 500 ppb NO2 or 10 ppm CO under ambient

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conditions, and 10 ppm NH3 at 150°C, far below the typical operating temperature of WO3 sensor (Bittencourt et al. 2006). Functionalization of CNTs with metal oxides to serve as sensing elements had exhibited high sensitivity and selectivity towards many air pollutants, in addition to the advantages of fast response time and low operating temperature. Pathogens are generally colourless, tasteless and odourless, which add up the difficulty and complexity in their detection and treatment to remove pathogens (Nuzzo 2006). CNTs have demonstrated potential applications for pathogens removal and detection with its high bacterial adsorption capacity, which are gaining much research interest into developing treatment-based and sensor-based applications in water and wastewater treatment industry. Upadhyayula et al. (2008a, b) reported that SWCNTs had high adsorption affinity towards both Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) bacterial cells. The high adsorption and selectivity of these bacteria might be due to the unique fibrous mesoporous structure of SWCNTs that provides higher accessible surface area. A filter using a poly(vinylidene fluoride)-based microporous membrane covered with SWCNTs has been reported to remove pathogens, such as E. coli K12 and MS2 bacteriophage, which is a model virus particle (Brady-Este´vez et al. 2008). The SWCNT-hybrid filter showed good performance in virus removal, water permeability and filtrate flux. Furthermore, intensive research efforts are currently focusing on the functionalization of CNTs with biomaterials to develop a biosensor to detect pathogens. Since CNTs possess antimicrobial properties, the biosensor will have the ability to concentrate and detect pathogens, in addition to the selective differentiation of bacterial strains attributed to the recognition properties of biomaterials. Dyes are colour organic compounds that are used to colourize other substances, which have been used extensively in many industries. The existence of dyes in natural water bodies is extremely undesirable as some of which are mutagenic and carcinogenic to human beings, in addition to their environmental concern (Crini 2006). CNTs have been receiving much attention as the material of interest as adsorbent due to their large specific surface area and unique structural properties. The utilization of CNTs for Methylene Blue removal has been demonstrated and the results verified the potentials of CNTs as adsorbent for dyes removal (Yao et al. 2010). Furthermore, the adsorption capacity of CNTs can be further enhanced by functionalization of CNTs with biomaterials, which show high affinity towards dyes. Chatterjee et al. (2010) have reported the impregnation of CNTs with chitosan hydrogel beads, which had proven to be an effective biosorbent material for the removal of Congo Red. The enhanced adsorption capacity for Congo Red was attributed to the amino and


hydroxyl functional groups of chitosan, which show high affinity towards many classes of dyes (Bhatnagar and Sillanpaä¨ 2009), in addition to the large surface area and layered nanosized structures of CNTs, which have also made them an excellent adsorbent. Heavy metals are considered as one of the major toxic pollutants due to its long persistency in the environment as they cannot be degraded. Moreover, humans are often exposed to the myriad adverse health effects caused by heavy metals toxicity. Rao et al. (2007) have performed the study on the adsorption efficiency of CNTs towards divalent heavy metal ions, such as Cd2?, Cu2?, Ni2?, Pb2? and Zn2?, in which the adsorption capacity of CNTs was significantly improved by the oxidation of CNTs with acid solutions to introduce functional groups on the surface of CNTs. The adsorption mechanism was mainly attributed to the chemical interaction between metal ions and surface functional groups of CNTs. Therefore, the surface total acidity of CNTs was a key parameter that influenced the adsorption capacity of CNTs, where an increase in surface total acidity will increase the heavy metals adsorption capacity of CNTs. Recent research activities focus on combining the specific recognition properties of biomolecules with the unique electronic properties of CNTs to produce hybridsensing composite material with high sensitivity for the detection of trace levels of heavy metals (Janegitz et al. 2009; Morton et al. 2009). Morton et al. (2009) reported the functionalization of MWCNTs with L-cysteine for Pb2? and Cu2? detection, since cysteine is an amino acid with high affinities towards some heavy metals. The high sensitivity and selectivity of CNTs based biosensor were attributed to cysteine as a chelator to accumulate the heavy metal ions, as well as the excellent electronic properties of CNTs. Furthermore, the composite can be modified with appropriate chelates for simultaneous detection of other heavy metals with high sensitivity and selectivity. Pesticides are widely used in agricultural activities to increase the production yield and for the purpose of pest control, despite the fact that they are toxic pollutants and hazardous to human health. Current studies are concentrating on the detection of organophosphate pesticides, where CNTs were introduced into Acetylcholinesterase (AChE)based biosensor for pesticides detection (Gao et al. 2009; Chen et al. 2008; Du et al. 2007; Kandimalla and Ju 2006). When AChE was immobilized on the electrode surface, it will interact with the substrate of acetylthiocholine, which will be further hydrolysed to obtain thiocholine. Oxidation of thiocholine will produce detectable signal which was catalysed by MWCNTs and thus increase the sensitivity of the biosensor. Pedrosa et al. (2010) have reported the fabrication of a biosensor by covalent immobilization of organophosphorus hydrolase (OPH) enzyme on both SWCNTs

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and MWCNTs for organophosphate pesticides detection. The sensor exhibited high sensitivity and was able to preserve the enzyme activity efficiently, which was attributed to the covalent functionalization of CNTs with OPH enzyme. In addition, MWCNTs were used as solid phase extraction adsorbent to remove organophosphate pesticides by using methyl parathion as representative (Du et al. 2008). It was reported that MWCNTs allowed fast and simultaneous extraction and electrochemical detection of organophosphate pesticides, as well as the possibility to control adsorption and desorption by electrochemical methods.

Carbon nanotubes in green nanocomposites design Green nanocomposites mainly comprised of biodegradable polymer and CNTs, which are viewed as the material of next generation since synthetic polymers create a lot of issues in waste management and if without proper disposal, will lead to the pollution and degradation of our environment. CNTs play an essential role in supplying the desired properties of green nanocomposites due to their remarkable physical, mechanical and functional properties. Compared with traditional fibres, such as carbon or glass, CNTs manage to produce high strength green nanocomposites as their load-bearing capability greatly exceeds those traditional fibres (Yeh et al. 2009). Moreover, their high aspect ratio and low mass density contribute to the extremely light weight of green nanocomposites. Nonetheless, CNTs possess high electrical and thermal conductivity, which improve the charge and heat transportation of green nanocomposites (Song and Qiu 2009; Misra et al. 2007). The improved properties of green nanocomposites by CNTs can greatly increase the potential commercial value of green nanocomposites and expand their potential applications. For instance, the enhanced mechanical properties of poly(propylene fumarate) after reinforcing with ultra-short SWCNTs had created potential application of SWCNTs/poly(propylene fumarate) nanocomposite to serve as a prototype bone tissue engineering scaffold (Sitharaman et al. 2008). Poly(butylene succinate)/MWCNTs nanocomposite was found to show potential application as electronic packaging materials since the nanocomposite exhibited high antistatic efficiency (Shih et al. 2008). Unlike synthetic polymer nanocomposites, green nanocomposites are not resistant to degradation and are susceptible to significant change in chemical structure under specific environmental conditions (Kolybaba et al. 2003). From the aspect of life cycle assessment evaluation as shown in Fig. 1, the source material of green nanocomposites can be available from renewable resources, usually in the form of starch or cellulose. When come to disposal, they are capable to be degraded through the action of

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Fig. 1 Schematic illustration of life cycle of green nanocomposites. The source materials of green nanocomposites are from natural renewable resources, such as agriculture feedstocks. After extraction and processing with carbon nanotubes as reinforcement material, they are processed into end products. Upon disposal, they are biodegraded into biomass through enzymatic or microbial activities. The carbon nanotubes residues are recovered and reused for the production of new composites. Adapted and modified from Biokam Co. (2008)

enzymes or chemical decomposition associated with microbial activities. The degradation temperature, which usually falls between 20 and 60°C, depends on the type of active microorganisms, such as fungi, bacteria, actionmycetes, etc., with the presence of oxygen, moisture and mineral nutrient, as well as the neutral or slightly acidic pH conditions. The degradation process will ultimately leave behind carbon dioxide and water, which are environmentally friendly products, in addition to the CNTs residue. The recovered CNTs are still valuable to be reused for the production of new composites.

Conclusion The applications of CNTs in the field of energy conversion and storage, environmental monitoring and wastewater treatment, as well as green nanocomposite design, are research area of growing interest from their potential uses in future technologies point of view. This review examines the attributes of CNTs as the electrode material or conductive filler in the electrochemical devices of energy applications. The potential development of CNTs as sensing material in nanosensors for environmental monitoring, in addition to the development as adsorbents to remove pollutants in wastewater treatment, is discussed. The advantages imparted by CNTs in green nanocomposite materials and their impacts on the environment are explained in the last section. CNTs have demonstrated advantageous potentials in energy and environmental applications with their outstanding structural, electronic and mechanical properties. Development of CNTs integrated energy conversion technologies implemented with efficient energy storage system has shown promising progress in efforts to address the

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energy challenge for future clean and sustainable energy source. In addition, CNTs represent a great alternative for the development of sensors and adsorbents in environmental pollution analysis, industrial emission monitoring and control, as well as wastewater treatment. Moreover, the development of green nanocomposite will overcome the environmental issues posed by synthetic polymer and is finding exciting potential applications in various fields. In summary, CNTs offer exciting opportunities for development in energy and environmental applications with advantageous potentials. Intensive research efforts are required to further improve the performance of CNTs integrated device applications towards commercialization and practical applications for environmental protection and preservation. Acknowledgments The financial supports from Fundamental Research Grant Scheme (FRGS), USM Short Term Grant, Kuok Foundation Postgraduate Scholarship and USM Fellowship are gratefully acknowledged.

References Ajayan PM (1999) Nanotubes from carbon. Chem Rev 99:1787– 1800. doi:10.1021/cr970102g Antolini E (2009) Carbon supports for low-temperature fuel cell catalysts. Appl Catal B Environ 88:1–24. doi:10.1016/j.apcatb. 2008.09.030 Bai H, Shi G (2007) Gas sensors based on conducting polymers. Sensors 7:267–307. doi:10.3390/s7030267 Balasubramanian K, Burghard M (2005) Chemically functionalized carbon nanotubes. Small 1:180–192. doi:10.1002/smll.2004 00118 Balasubramanian K, Burghard M (2008) Electrochemically functionalized carbon nanotubes for device applications. J Mater Chem 18:3071–3083. doi:10.1039/b718262g

Environ Chem Lett (2012) 10:265–273 Banks CE, Compton RG (2006) New electrodes for old: from carbon nanotubes to edge plane pyrolytic graphite. Analyst 131:15–21. doi:10.1039/b512688f Barisci JN, Wallace GG, Baughman RH (2000) Electrochemical studies of single-wall carbon nanotubes in aqueous solutions. J Electroanal Chem 488:92–98. doi:10.1016/S0022-0728(00)00 179-0 Barsan N, Koziej D, Weimar U (2007) Metal oxide-based gas sensor research: how to? Sens Actuators B Chem 121:18–35. doi: 10.1016/j.snb.2006.09.047 Bhatnagar A, Sillanpaä¨ M (2009) Applications of chitin- and chitosan-derivatives for the detoxification of water and wastewater—a short review. Adv Colloid Interface 152:26–38. doi: 10.1016/j.cis.2009.09.003 Biokam Co (2008) Life cycle economy. Eurokam S.r.o. Available via http://www.eurokamczech.com/Biokam/Biokam/web/Life-Cycle %20Economy.html. Accessed 20 Mar 2010 Bittencourt C, Felten A, Espinosa EH, Ionescu R, Llobet E, Correig X, Pireaux JJ (2006) WO3 films modified with functionalised multi-wall carbon nanotubes: morphological, compositional and gas response studies. Sens Actuators B Chem 115:33–41. doi: 10.1016/j.snb.2005.07.067 Brady-Este´vez AS, Kang S, Elimelech M (2008) A single-walledcarbon-nanotube filter for removal of viral and bacterial pathogens. Small 4:481–484. doi:10.1002/smll.200700863 Brown P, Takechi K, Kamat PV (2008) Single-walled carbon nanotube scaffolds for dye-sensitized solar cells. J Phys Chem C 112:4776–4782. doi:10.1021/jp7107472 Chatterjee S, Lee MW, Woo SH (2010) Adsorption of Congo red by chitosan hydrogel beads impregnated with carbon nanotubes. Bioresour Technol 101:1800–1806. doi:10.1016/j.biortech.2009. 10.051 Chen H, Zuo X, Su S, Tang Z, Wu A, Song S, Zhang D, Fan C (2008) An electrochemical sensor for pesticide assays based on carbon nanotube-enhanced acetylcholinesterase activity. Analyst 133: 1182–1186. doi:10.1039/b805334k Choi W, Lee JY, Jung BH, Lim HS (2004) Microstructure and electrochemical properties of a nanometre-scale tin anode for lithium secondary batteries. J Power Sour 136:154–159. doi: 10.1016/j.jpowsour.2004.05.026 Crini G (2006) Non-conventional low-cost adsorbents for dye removal: a review. Bioresour Technol 97:1061–1085. doi: 10.1016/j.biortech.2005.05.001 Du C, Pan N (2006) Supercapacitors using carbon nanotubes films by electrophoretic deposition. J Power Sour 160:1487–1494. doi: 10.1016/j.jpowsour.2006.02.092 Du D, Huang X, Cai J, Zhang A (2007) Comparison of pesticide sensitivity by electrochemical test based on acetylcholinesterase biosensor. Biosens Bioelectron 23:285–289. doi:10.1016/j.bios. 2007.05.002 Du D, Wang M, Zhang J, Cai J, Tu H, Zhang A (2008) Application of multiwalled carbon nanotubes for solid-phase extraction of organophosphate pesticide. Electrochem Commun 10:85–89. doi:10.1016/j.elecom.2007.11.005 Du G, Zhong C, Zhang P, Guo Z, Chen Z, Liu H (2010) Tin dioxide/ carbon nanotube composites with high uniform SnO2 loading as anode materials for lithium ion batteries. Electrochim Acta 55:2582–2586. doi:10.1016/j.electacta.2009.12.031 Durgun E, Ciraci S, Yildirim T (2008) Functionalization of carbonbased nanostructures with light transition-metal atoms for hydrogen storage. Phys Rev B 77:085405. doi:10.1103/Phys RevB.77.085405 Gao Y, Kyratzis I, Taylor R, Huynh C, Hickey M (2009) Immobilization of acetylcholinesterase onto carbon nanotubes utilizing streptavidin-biotin interaction for the construction of amperometric

271 biosensors for pesticides. Anal Lett 42:2711–2727. doi: 10.1080/00032710903243661 Goldoni A, Larciprete R, Petaccia L, Lizzit S (2003) Single-wall carbon nanotube interaction with gases: sample contaminants and environmental monitoring. J Am Chem Soc 125: 11329–11333. doi:10.1021/ja034898e Goldoni A, Petaccia L, Gregoratti L, Kaulich B, Barinov A, Lizzit S, Laurita A, Sangaletti L, Larciprete R (2004) Spectroscopic characterization of contaminants and interaction with gases in single-walled carbon nanotubes. Carbon 42:2099–2112. doi: 10.1016/j.carbon.2004.04.011 Gong K, Yan Y, Zhang M, Su L, Xiong S, Mao L (2005) Electrochemistry and electroanalytical applications of carbon nanotubes: a review. Anal Sci 21:1383–1393. doi:10.2116/ analsci.21.1383 He L, Jia Y, Meng F, Li M, Liu J (2009) Gas sensors for ammonia detection based on polyaniline-coated multi-wall carbon nanotubes. Mater Sci Eng B Adv 163:76–81. doi:10.1016/j.mseb. 2009.05.009 Hoa ND, Quy NV, Kim D (2009) Nanowire structured SnOx-SWNT composites: high performance sensor for NOx detection. Sens Actuators B Chem 142:253–259. doi:10.1016/j.snb.2009.07.053 Hu Y-S, Demir-Cakan R, Titirici M–M, Mu¨ller J-O, Schlo¨gl R, Antonietti M, Maier J (2008) Superior storage performance of a Si@SiOx/C nanocomposite as anode material for lithium-ion batteries. Angew Chem Int Edit 47:1645–1649. doi:10.1002/ anie.200704287 Iijima S (1991) Helical microtubules of graphitic carbon. Nature 354:56–58. doi:10.1038/354056a0 Imahori H, Umeyama T (2009) Donor-acceptor nonarchitecture on semiconducting electrodes for solar energy conversion. J Phys Chem C 113:9029–9039. doi:10.1021/jp9007448 Iyakutti K, Kawazoe Y, Rajarajeswari M, Surya VJ (2009) Aluminum hydride coated single-walled carbon nanotube as a hydrogen storage medium. Int J Hydrogen Energy 34:370–375. doi: 10.1016/j.ijhydene.2008.09.086 Janegitz BC, Marcolino-Junior LH, Campana-Filho SP, Faria RC, Fatibello-Filho O (2009) Anodic stripping voltammetric determination of copper(II) using a functionalized carbon nanotubes paste electrode modified with crosslinked chitosan. Sens Actuators B Chem 142:260–266. doi:10.1016/j.snb.2009.08.033 Jha N, Leela Mohana Reddy A, Shaijumon MM, Rajalakshmi N, Ramaprabhu S (2008) Pt-Ru/multi-walled carbon nanotubes as electro catalysts for direct methanol fuel cell. Int J Hydrogen Energy 33:427–433. doi:10.1016/j.ijhydene.2007.07.064 Kandimalla VB, Ju H (2006) Binding of acetylcholinesterase to multiwall carbon nanotube-cross-linked chitosan composite for flow-injection amperometric detection of an organophosphorous insecticide. Chem Eur J 12:1074–1080. doi:10.1002/chem.20050 0178 Kolybaba M, Tabil LG, Panigrahi S, Crerar WJ, Powell T, Wang B (2003) Biodegradable polymers: past, present, and future. 2003 CSAE/ASAE annual intersectional meeting, Fargo, North Dakota, USA Lee SU, Choi WS, Hong B (2009) A comparative study of dyesensitized solar cells added carbon nanotubes to electrolyte and counter electrodes. Sol Energy Mat Sol C 94:680–685. doi: 10.1016/j.solmat.2009.11.030 Li L, Xing Y (2006) Electrochemical durability of carbon nanotubes in noncatalyzed and catalyzed oxidations. J Electrochem Soc 153:A1823–A1828. doi:10.1149/1.2234659 Li W, Liang C, Zhou W, Qiu J, Zhou W, Sun G, Xin Q (2003) Preparation and characterization of multiwalled carbon nanotubesupported platinum for cathode catalysts of direct methanol fuel cells. J Phys Chem B 107:6292–6299. doi:10.1021/jp022505c

123

272 Lim KL, Kazemian H, Yaakob Z, Daud WRW (2010) Solid-state materials and methods for hydrogen storage: a critical review. Chem Eng Technol 33:213–226. doi:10.1002/ceat.200900376 Lin JF, Kamavaram V, Kannan AM (2010) Synthesis and characterization of carbon nanotubes supported platinum nanocatalyst for proton exchange membrane fuel cells. J Power Sour 195: 466–470. doi:10.1016/j.jpowsour.2009.07.055 Lochan RC, Head-Gordon M (2006) Computational studies of molecular hydrogen binding affinities: the role of dispersion forces, electrostatics, and orbital interactions. Phys Chem Chem Phys 8:1357–1370. doi:10.1039/b515409j Luo H, Shi Z, Li N, Gu Z, Zhuang Q (2001) Investigation of the electrochemical and electro catalytic behaviour of single-wall carbon nanotube film on a glassy carbon electrode. Anal Chem 73:915–920. doi:10.1021/ac000967l Masenelli-Varlot K, McRae E, Dupont-Pavlovsky N (2002) Comparative adsorption of simple molecules on carbon nanotubes— dependence of the adsorption properties on the nanotube morphology. Appl Surf Sci 196:209–215. doi:10.1016/S01694332(02)00059-4 Mei X, Fan B, Sun K, Ouyang J (2009) High-performance dyesensitized solar cells with nanomaterials as counter electrode. Nanoscale photonic and cell technologies for photovoltaics II, San Diego, CA, USA. doi:10.1117/12.825858 Merkoçi A (2006) Carbon nanotubes in analytical sciences. Microchim Acta 152:157–174. doi:10.1007/s00604-005-0439-z Misra SK, Watts PCP, Valappil SP, Silva SRP, Roy I, Boccaccini AR (2007) Poly(3-hydroxybutyrate)/BioglassÒ composite films containing carbon nanotubes. Nanotechnology 18:075701. doi: 10.1088/0957-4484/18/7/075701 Moon S-IL, Paek K–K, Lee Y-H, Park H-K, Kim J-K, Kim S-W, Ju B-K (2008) Bias-heating recovery of MWCNT gas sensor. Mater Lett 62:2422–2425. doi:10.1016/j.matlet.2007.12.027 Morton J, Havens N, Mugweru A, Wanekaya AK (2009) Detection of trace heavy metal ions using carbon nanotube-modified electrodes. Electroanalytical 21:1597–1603. doi:10.1002/elan.2009 04588 Nuzzo JB (2006) The biological threat to U.S. water supplies: toward a national water security policy. Biosecur Bioterror Biodefense Strategy Pract Sci 4:147–159. doi:10.1089/bsp.2006.4.147 Pandolfo AG, Hollenkamp AF (2006) Carbon properties and their role in supercapacitors. J Power Sour 157:11–27. doi:10.1016/ j.jpowsour.2006.02.065 Pedrosa VA, Paliwal S, Balasubramanian S, Nepal D, Davis V, Wild J, Ramanculov E, Simonian A (2010) Enhanced stability of enzyme organophosphate hydrolase interfaced on the carbon nanotubes. Colloid Surf B 77:69–74. doi:10.1016/j.colsurfb. 2010.01.009 Penza M, Rossi R, Alvisi M, Signore MA, Cassano G, Dimaio D, Pentassuglia R, Piscopiello E, Serra E, Falconieri M (2009) Characterization of metal-modified and vertically-aligned carbon nanotube films for functionally enhanced gas sensor applications. Thin Solid Films 517:6211–6216. doi:10.1016/j.tsf.2009. 04.009 Ramasamy E, Lee WJ, Lee DY, Song JS (2008) Spray coated multiwall carbon nanotube counter electrode for tri-iodide reduction in dye-sensitized solar cells. Electrochem Commun 10: 1087–1089. doi:10.1016/j.elecom.2008.05.013 Rao GP, Lu C, Su F (2007) Sorption of divalent metal ions from aqueous solution by carbon nanotubes: a review. Sep Purif Technol 58:224–231. doi:10.1016/j.seppur.2006.12.006 Sawatsuk T, Chindaduang A, Sae-kung C, Pratontep S, Tumcharern G (2009) Dye-sensitized solar cells based on TiO2-MWCNTs composite electrodes: performance improvement and their mechanisms. Diam Relat Mater 18:524–527. doi:10.1016/j.diamond. 2008.10.052

123

Environ Chem Lett (2012) 10:265–273 Shih YF, Chen LS, Jeng RJ (2008) Preparation and properties of biodegradable PBS/multi-walled carbon nanotube nanocomposites. Polymer 49:4602–4611. doi:10.1016/j.polymer.2008.08.015 Simon P, Gogotsi Y (2008) Materials for electrochemical capacitors. Nat Mater 7:845–854. doi:10.1038/nmat2297 Sitharaman B, Shi X, Walboomers XF, Liao H, Cuijpers V, Wilson LJ, Mikos AG, Jansen JA (2008) In vivo biocompatibility of ultra-short single-walled carbon nanotube/biodegradable polymer nanocomposites for bone tissue engineering. Bone 43: 362–370. doi:10.1016/j.bone.2008.04.013 Song L, Qiu Z (2009) Crystallization behavior and thermal property of biodegradable poly(butylene succinate)/functional multiwalled carbon nanotubes nanocomposite. Polym Degrad Stabil 94:632–637. doi:10.1016/j.polymdegradstab.2009.01.009 Surya VJ, Iyakutti K, Rajarajeswari M, Kawazoe Y (2009) Functionalization of single-walled carbon nanotube with borane for hydrogen storage. Physica E 41:1340–1346. doi:10.1016/j.physe. 2009.03.007 Surya VJ, Iyakutti K, Venkataramanan N, Mizuseki H, Kawazoe Y (2010) The role of Li and Ni metals in the adsorbate complex and their effect on the hydrogen storage capacity of single walled carbon nanotubes coated with metal hydrides, LiH and NiH2. Int J Hydrogen Energy 35:2368–2376. doi:10.1016/j.ijhydene. 2010.01.001 Tan CW, Tan KH, Ong YT, Mohamed AR, Zein SHS, Huat Tan SH (2012) Carbon nanotubes applications: solar and fuel cells, hydrogen storage, lithium batteries, supercapacitors, nanocomposites, gas, pathogens, dyes, heavy metals and pesticides. In: Environmental chemistry for a sustainable word, vol 1. Nanotechnology and health risk, pp 3–46. doi:10.1007/978-94-0072442-6_1 Tang Z, Poh CK, Lee KK, Tian Z, Chua DHC, Lin J (2010) Enhanced catalytic properties from platinum nanodots covered carbon nanotubes for proton-exchange membrane fuel cells. J Power Sour 195:155–159. doi:10.1016/j.jpowsour.2009.06.105 Umeyama T, Imahori H (2008) Carbon nanotube-modified electrodes for solar energy conversion. Energy Environ Sci 1:120–133. doi: 10.1039/b805419n Upadhyayula VKK, Deng S, Mitchell MC, Smith GB, Nair VK, Ghoshroy S (2008a) Adsorption kinetics of Escherichia coli and Staphylococcus aureus on single-walled carbon nanotube aggregates. Water Sci Technol 58:179–184. doi:10.2166/wst.2008.634 Upadhyayula VKK, Ghoshroy S, Nair VS, Smith GB, Mitchell MC, Deng S (2008b) Single-walled carbon nanotubes as fluorescence biosensors for pathogen recognition in water systems. Res Lett Nanotechno 2008:156358. doi:10.1155/2008/156358 Valentini L, Cantalini C, Armentano I, Kenny JM, Lozzi L, Santucci S (2004) Highly sensitive and selective sensors based on carbon nanotubes thin films for molecular detection. Diam Relat Mater 13:1301–1305. doi:10.1016/j.diamond.2003.11.011 Wang Y, Liu H, Sun X, Zhitomirsky I (2009) Manganese dioxidecarbon nanotube nanocomposites for electrodes of electrochemical supercapacitors. Scripta Mater 61:1079–1082. doi: 10.1016/j.scriptamat.2009.08.040 Wei L, Shizhen H, Wenzhe C (2010) An MWCNT-doped SNO2 thin film NO2 gas sensor by RF reactive magnetron sputtering. J Semicond 31:024006. doi:10.1088/1674-4926/31/2/024006 Wijewardane S (2009) Potential applicability of CNT and CNT/ composites to implement ASEC concept: a review article. Sol Energy 83:1379–1389. doi:10.1016/j.solener.2009.03.001 Winter M, Brodd RJ (2004) What are batteries, fuel cells, and supercapacitors? Chem Rev 104:4245–4270. doi:10.1021/cr020730k Wu ZP, Xia BY, Wang XX, Wang JN (2010) Preparation of dispersible double-walled carbon nanotubes and application as catalyst support in fuel cells. J Power Sour 195:2143–2148. doi: 10.1016/j.jpowsour.2009.10.013

Environ Chem Lett (2012) 10:265–273 Xu K, Pierce DT, Li A, Zhao JX (2008) Nanocatalysts in direct methanol fuel cell applications. Synth React Inorg M 38: 394–399. doi:10.1080/15533170802132295 Yan J, Wei T, Fan Z, Qian W, Zhang M, Shen X, Wei F (2010) Preparation of grapheme nanosheet/carbon nanotube/polyaniline composite as electrode material for supercapacitors. J Power Sour 195:3041–3045. doi:10.1016/j.jpowsour.2009.11.028 Yang S, Song H, Chen X (2007) Nanosized tin and tin oxides loaded expanded mesocarbon microbeads as negative electrode material for lithium-ion batteries. J Power Sour 173:487–494. doi: 10.1016/j.jpowsour.2007.08.009 Yang S, Song H, Yi H, Liu W, Zhang H, Chen X (2009) Carbon nanotube capsules encapsulating SnO2 nanoparticles as an anode

273 material for lithium ion batteries. Electrochim Acta 55:521–527. doi:10.1016/j.electacta.2009.09.009 Yao Y, Xu F, Chen M, Xu Z, Zhu Z (2010) Adsorption behavior of methylene blue on carbon nanotubes. Bioresour Technol 101:3040–3046. doi:10.1016/j.biortech.2009.12.042 Yeh JT, Yang MC, Wu CJ, Wu CS (2009) Preparation and characterization of biodegradable polycaprolactone/multiwalled carbon nanotubes nanocomposites. J Appl Polym Sci 112:660–668. doi: 10.1002/app.29485 Zhang Y, Sun X, Pan L, Li H, Sun Z, Sun C, Tay BK (2009) Carbon nanotube-ZnO nanocomposite electrodes for supercapacitors. Solid State Ionics 180:1525–1528. doi:10.1016/j.ssi.2009.10.001

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