Fabrication Of Carbon Nanotube Sponge-Based Composites And Their Applications In Dye Adsorption And Energy Storage

Carbon nanotube?CNT?has been widely used in various fields due to its high specific surface area,excellent electrical conductivity and unique one-dimensional structure.In addition,porous CNT-based materials have been extensively developed and studied.In this paper,we use chemical vapor deposition?CVD?method to grow carbon nanotube sponge?CNTS?with three-dimensional CNT network,which has ultra-high specific surface area and excellent electrical conductivity.CNTS,as a CNT-based material with high specific surface area,has potential applications in the removal of oils and dyes.Due to the porous structure and super hydrophobicity of CNTS,the aqueous dye solution is difficult to infiltrate the CNT networks of CNTS and thus result in a decrease in effective surface area for dye adsorption.Therefore,key to this challenge is the improvement of hydrophilia of CNTS without destructing the highly porous structures and deteriorating mechanical properties of CNTS.Polydopamine?Pdop?,as an emerging polymer for surface modification,can strongly adhere to virtually all types of inorganic and organic surfaces.In this paper,Pdop layer was incorporated on the sidewalls of CNT by an electro-polymerization method.The hydrophilicity of Pdop-CNTS composites is significantly enhanced,and the adsorption performance of Pdop-CNTS composites for methylene blue?MB?is greatly improved.In addition,the silver ions attached to the Pdop-CNTS surfaces are reduced to silver nanoparticles?Ag NPs?in the presence of Pdop coating.Ag NPs strongly adhere to the Pdop-CNTS surfaces via Pdop layer and further improve the adsorption performance of Ag NP-Pdop-CNTS composites for MB.Based on the catalytic activity of Ag NPs for MB molecules,Ag NP-Pdop-CNTS adsorbents show excellent regeneration ability and cycling stability.In addition,CNTS has potential applications in energy storage,e.g.supercapacitors?SCs?.CNTS-based devices show excellent electrochemical performance with specific capacitance up to 7.75 F g^-1(current density is 0.125 A g^-1),and the specific capacitance remains 96%after 10000 charge–discharge cycles(current density is 2 A g^-1).However,the maximum energy density of CNTS-based SCs is relatively low,only 0.69 Wh kg^-1,and the corresponding average power density is 44.6 W kg^-1.In order to further improve the specific capacitance and maximum energy density of SCs,we used Pdop coatings as nitrogen-containing precursors and prepared nitrogen-doped SCs?N-CNTS?by carbonizing Pdop-CNTS at high temperature.When the current density is 0.125 A g^-1,the specific capacitance of N-CNTS SCs is 13.69 F g^-1,an increase of 77%as compared with CNTS-based SCs,and the maximum energy density increases to 1.22 Wh kg^-1(average power density is 44.6 W kg^-1).We combine the energy storage and the dye adsorption ability of CNTS.Specifically,we used CNTS adsorbed with MB molecules as electrode materials to fabricate redox electrolyte enhanced supercapacitors?MB-CNTS SCs?.The specific capacitance of MB-CNTS SCs is 22.93 F g^-1 at the sweep speed of 1 m V s^-1.When the sweep speed increases by 50 times,the specific capacitance of MB-CNTS SCs remains 89%,showing an excellent performance.In addition,MB-CNTS SCs also have very good stability.After 6000 charge–discharge cycles(current density of 2 A g^-1),the specific capacitance of MB-CNTS SCs remains almost unchanged.