Chitosan
Chitosan is a linear polysaccharide composed of randomly distributed β-(1-4)-linked D-glucosamine (deacetylated unit) and N-acetyl-D-glucosamine (acetylated unit). It has a number of commercial and possible biomedical uses. Chitosan is produced commercially by deacetylation of chitin, which is the structural element in the exoskeleton of crustaceans (crabs, shrimp, etc.) and cell walls of fungi. A common method for the synthesis of chitosan is the deacetylation of chitin using sodium hydroxide in excess as a reagent and water as a solvent.
CNT
Carbon nanotubes (CNTs) are interesting materials which are being researched intensively in the past few years. Application of CNTs in water treatment with their unique properties has attracted the attention of many scientists and engineers. Moreover, manipulation of CNTs with other polymers has been done for different applications.
Preparation of nanocomposites
Biopolymer chitosan/multiwalled carbon nanotubes (MWNTs) nanocomposites have been successfully prepared by a simple solution evaporation method. The MWNTs are observed to be homogeneously dispersed throughout the chitosan matrix. When compared with neat chitosan, the mechanical properties, including the tensile modulus and strength, of the nanocomposites are greatly improved with incorporation of only 0.8 wt % of MWNTs into the chitosan matrix.
Researchers of Zhejiang University, China prepared multi-walled carbon nanotubes (MWNTs) and chitosan (CS) composite rods with layer-by-layer structure via in situ precipitation method. On the one hand, some MWNTs fragments with open tips played the role of nuclear agent to improve the crystallinity of CS. On the other hand, MWNTs embedded in CS matrix to absorb energy when the composite rods were destroying. Nanotubes pulled out from CS matrix, and lots of holes remained, so MWNTs could endure external stress effectively.
Researchers at Chung Yuan Christian University, Taiwan report that poly (styrene sulfonic acid)-functionalized carbon nanotubes (CNT-PSSA), which was obtained, with atom transfer radical polymerization (ATRP), was utilized in preparation of chitosan/CNT nanocomposites (CH/CNT-PSSA). Chemical linkages between chitosan and CNTs form in the nanocomposites through the reaction between the sulfuric acid groups of CNT-PSSA and the amino groups of chitosan, giving a homogenous dispersion of CNTs. The CH/CNT-PSSA nanocomposites were superior to the neat chitosan polymer in thermal and mechanical properties, water and solvent uptakes, bond water ratios, and electrical conductivity. The attractive property of the CH/CNT-PSSA nanocomposites also implied their application potentials for separation membranes and sensor electrodes.
For biocathode
New developments in biocathode microbial fuel cells (MFCs) provide an increasing possibility to use the MFC technology for sustainable wastewater treatment. Enhanced oxygen reduction and biofilm formation using novel cathode materials are crucial for the biocathode MFCs. Conductive and compatible carbon nanotube/chitosan nanocomposite is a new type of MFC biocathode material, which is fabricated by electrodepositing carbon nanotubes and chitosan onto a carbon paper electrode. The MFC tests reveal that the electricity generation capacity of this nanocomposite anode is superior to the control and such an approach is applicable for the development of other types of materials for MFC cathodes through facilitating the electron transfer at the electrode/bacteria interface.
For electrodes
Researchers at Nanjing Normal University, China report that Multiwalled carbon nanotubes (CNT) were solubilized in aqueous solutions of a biopolymer chitosan (CHIT). The CHIT-induced solubilization of CNT facilitated their manipulations, including the modification of electrode surfaces for sensor and biosensor development. The colloidal solutions of CNT−CHIT were placed on the surface of glassy carbon (GC) electrodes to form robust CNT−CHIT films, which facilitated the electro oxidation of NADH. The CNT−CHIT system represents a simple and functional approach to the integration of dehydrogenases and electrodes, which can provide analytical access to a large group of enzymes for wide range of bioelectrochemical applications including biosensors and biofuel cells.
For lead removal from water
Carbon nanotubes can be used with attached Chitosan for lead removal from aqueous solution. The CNTs are functionalized with chitosan via covalent link. The obtained nanocomposite can be used as an adsorbent material for lead removal from aqueous solutions with 98.4% effectiveness.
Biocompatible composite
Researchers at University of Hawaii report that multiwalled carbon nanotubes (MWCNTs) were used as doping material for three-dimensional chitosan scaffolds to develop a highly conductive, porous, and biocompatible composite material. The porous and interconnected structures were formed by the process of thermally induced phase separation followed by freeze-drying applied to an aqueous solution of 1 wt % chitosan acetic acid. The porosity was characterized to be 97% by both mercury intrusion porosimetry measurements and SEM image analysis. When MWCNTs were used as a filler to introduce conductive pathways throughout the chitosan skeleton, the solubilizing hydrophobic and hydrophilic properties of chitosan established stable polymer/MWCNT solutions that yielded a homogeneous distribution of nanotubes throughout the final composite matrix.
For glucose biosensor
Chitosan–CNT nanocomposite has high electro catalytic activity to hydrogen peroxide and a simple, enzyme-friendly method can be used to develop a glucose biosensor. CNT-based electrodes can catalyse the reactions of both hydrogen peroxide and oxygen. For the preparation of the biosensor, glucose oxidase (GOD, 37,700 U g) is added to the CNT chitosan solution and the immobilization of GOD is done through a one-step electro deposition procedure. The solution for electro deposition is taken as a 1.0 wt% chitosan solution containing 0. 5m gm L CNT and 5.0 mg mL GOD (glucose oxidase).
Applications
Research has already demonstrated that chitosan is a safe and efficient drug delivery compound with mucoadhesive properties that enable its delivery through the mucous membranes. These properties make chitosan-based drug delivery systems an attractive target for redevelopment. The efficiency of drug delivery of carbon nanotubes to target cells can be enhanced through hybridizing chitosan with functionalized carbon nanotubules (f-CNT), which have the ability to direcand target delivery of peptides or nucleic acids. In animal experiments, investigators have demonstrated that f-CNT-chitosan complexes increase absorption of drugs into lung cells versus CNT alone. Carbon Nanotube- chitosan nanocomplexes provide enhanced drug delivery through mucous membranes, effectively direct peptides and nucleic acids to target cells and applicable to a broad range of fields, from respiratory therapy to oncology.