N-doped three-dimensional carbon nanosheets: Facile synthesis and high-concentration dye adsorption

Abstract

Purification of dye-contaminated wastewater has always been a research hotspot, yet also a challenge, due to high concentration and species diversity of pollutants. The present study designs an efficient nitrogen-doped 3D carbon nanosheets (N-3DCNs) adsorbent with 2592.50 m² g⁻¹ of specific surface area and 2.68 m³/g of average pore volume based on nitrilotriacetic acid trisodium salt by combining calcination and activation techniques. Microstructure and surface potential of N-3DCNs indicate that a large number of N heteroatoms in the lattice of main material can effectively optimize Zeta potential from 1.53 to −31.08 mV with solution pH increases from 3 to 11. So, as-prepared N-3DCNs possesses necessary conditions for efficient and selective adsorption of cationic dyes due to the abundant adsorption sites and strong electrostatic interactions. When 700 mg/L of cationic rhodamine and anionic methyl orange are respectively used as high concentration industrial dye-contaminated wastewater, N-3DCNs shows 97.97 % and 89.13 % of removal efficiency within 60 min. Furthermore, the adsorption capacity of N-3DCNs displays a wider pH tolerance at 1000 mg/L of cationic concentration, with a maximum adsorption capacity of 4888.70 mg/g at pH = 7 and a minimum value of 4203.77 mg/g at pH = 3, only 14 % of attenuation rate. The kinetics mechanism of dye adsorption could be well explained by pseudo-second-order kinetic model, suggesting chemisorption behavior, while fitting better with the linear Langmuir isothermal model. The groundbreaking and exceptional adsorption performances of N-3DCNs can be attributed primarily to the high specific surface area and negatively charged active sites, facilitating synergistic adsorption.