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SUMMARY Carbon nanotubes (CNTs) have unique properties, such as their electrical conductivity, that enable them to be combined with conducting polymers to form composites for use in organic solar cells (OSCs). It is envisaged that the improved composite has a higher efficiency of green energy and will reduce the cost of these cells. The use of such alternative energy sources also drastically reduces overuse of fossil fuels and consequently limits environmental degradation. This review compares research and performance between conventional silicon solar cells and OSCs. It also discusses OSC photoexcitation and charge carrier generation with the incorporation of CNTs, physicochemical properties of the composites and other factors that affect the efficiencies of OSCs. In addition, properties of CNTs that favour their dispersion in polymer matrices as acceptors and charge carriers to the electrodes are covered. The effects of CNTs containing dopants, such as nitrogen and boron, on charge transfer are discussed. Also, the fabrication techniques of OSCs that include CNT/polymer composite processing and the methods of film deposition on the substrate are described. Finally, the case studies of OSCs containing polymers with single‐walled CNTs, double‐walled CNTs or multi‐walled CNTs are evaluated. Copyright © 2014 John Wiley & Sons, Ltd.

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The efficiency of adsorption of rhodamine B (RhB) from aqueous solution was investigated through a series of batch experiments by using cobalt ferrite nanoparticles (CoFe 2 O 4 ), acid-functionalized multiwalled carbon nanotubes (MWCNT-COOH) and carbon nanotube-cobalt ferrite nanocomposites. The adsorption capacity was evaluated as a function of pH, contact time, adsorbent dose, dye concentration and temperature. The effect of increasing the percentage of MWCNT-COOH in the nanocomposites was also studied. The adsorption capacity was lowest in CoFe 2 O 4 (5.165 mg g À1 ) and highest with MWCNT-COOH (42.68 mg g À1 ). For the nanocomposites, the adsorption capacity was enhanced with an increase in the amount of MWCNT-COOH. The optimum pH for adsorption was observed at 7 at which equilibrium was reached after 360 min. The kinetics of adsorption was fitted to the pseudo-first order, pseudo-second order, Elovich and intraparticle diffusion models. The results showed that the pseudo-second order model best described the data as reflected in the lowest value for the sum of squared residuals. Among the various adsorption isotherms tested, the Langmuir isotherm provided the best fit to the equilibrium data. The thermodynamic parameters, DH , DS and DG , were obtained over a temperature range of 20-45 C. Adsorption was spontaneous, endothermic and entropy-driven, except for one of the doped nanocomposites for which adsorption was exothermic. A good desorption of RhB from the loaded adsorbents was obtained by using either acetone or ethanol with a desorption efficiency in the range of 62-95%.

Nitrogen-functionalized multiwalled carbon nanotubes synthesized were effective and efficient for the removal of Cu2+ from aqueous solutions.