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Flame‐retardant polyamide 6 (PA6) was prepared by an inorganic‐organic composite (MCN or MgO/g‐C3N4) synthesized by incorporating magnesium oxide (MgO) combined with graphitic carbon nitride (g‐C3N4). As compared to g‐C3N4, MCN possessed a laminate structure, more holes, and a larger specific surface area. The addition of MCN could effectively improve the flame retardancy and mechanical properties of PA6 due to its better compatibility and dispersion in the PA6 matrix. When the addition of MCN was 20 wt%, the vertical combustion performance of the PA6/MCN sample reached flammability rating V‐0 (UL‐94) and the limiting oxygen index (LOI) was up to 32.1%. The results of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) revealed that the introduction of MCN efficiently enhanced thermal stability of PA6. The morphologies of the char residue observed by scanning electron microscopy (SEM) verified that MCN promoted the formation of sufficient, compact, and homogeneous char layers on the composite's surface during burning. Thus led to increase the char layer strength and improve the flame retardancy of PA6. The thermogravimetric analysis/infrared (TG‐IR) revealed the gas‐phase retardancy mechanism of MCN. Compared with PA6/g‐C3N4, PA6/MCN showed better mechanical properties in terms of flexural strength and tensile strength.

A novel g‐C3N4/MnO2 composite was prepared by in situ deposition of MnO2 on graphitic carbon nitride (g‐C3N4) nanosheets, and its adsorption properties were evaluated for removal of Pb (II) in aqueous. Fourier transform‐infrared, spectrometer scanning electron microscopy and transmission electron microscopy characterization showed the g‐C3N4/MnO2 composite had a two‐dimensional/two‐dimensional (2D/2D) structure with ample active sites. The Brunauer–Emmett–Teller specific surface area of g‐C3N4/MnO2 composites (234.9 m2/g) was 13.5 times larger than that of g‐C3N4 (17.37 m2/g), providing better conditions for adsorption. The adsorption kinetic data were better fitted with the pseudo‐second‐order model. The Langmuir model was more suitable for describing the experimental equilibrium data of g‐C3N4/MnO2, and the maximum adsorption capacity was 204.1 mg/g for Pb (II). The adsorption of g‐C3N4/MnO2 composite for Pb (II) was an endothermic and spontaneous process, and reached adsorption equilibrium rapidly within initial 150 min. This composite was an excellent adsorbent because of its higher adsorption capacity and facile preparation progress.

A novel composite (nZVI@K-GCN) was firstly synthesized by liquid phase reducing nanoscale zero-valent iron (nZVI) on potassium-doped graphitic carbon nitride (K-GCN). The results of Fourier transform infrared (FTIR) spectrometry, X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET) suggested that nZVI@K-GCN possessed abundant active functional groups such as terminal amino-groups (-NH or -NH2 groups) and -OH, and the specific surface area and pore volume from BET of nZVI@K-GCN were 4.7 times and 3.7 times higher than that of graphitic carbon nitride (GCN), respectively. These properties showed that the composite was especially suitable for heavy metal treatment. The application of the composite in the removal of chromium(VI) from aqueous solution showed that the maximum adsorption capacity of nZVI@K-GCN towards Cr(VI) was 68.6 mg/g at 308 K when the initial concentration of Cr(VI) was 30 mg/L, and more than 99% removal was obtained at pH = 3. This adsorption was an endothermic and spontaneous process. XPS patterns and batch experiments proved that complexation, electrostatic attraction and reduction precipitation were the main adsorption mechanism for Cr(VI) on nZVI@K-GCN.

Based on graphitic carbon nitride (CN) nanosheets, a novel MnO2 modified magnetic graphitic carbon nitride composite (MMCN) was prepared via magnetization and in-situ deposition of MnO2. Then an array of characterizations and experiments were conducted to explore the physical and chemical properties of the synthesized MMCN material. The adsorption behavior and removal mechanism of the MMCN were also discussed intensively. The best pH value of Pb(II) of MMCN was 6. The maximum adsorption capacity of MMCN was as high as 187.6 mg/g, which was much higher than that of MCN and original CN, and removal percentage of Pb(II) was about 99%. The adsorption kinetics and isotherms were in accorded with pseudo-second-order model and Langmuir model, respectively. The chemical adsorption of Pb(II) indicated that MMCN was a successful modified sorbent and pretty efficient to remove Pb(II) in aqueous owing to the complexation and ion exchange of ample amino and hydroxyl groups. Moreover, MMCN could be separated easily from aqueous under an external field after reaction with its magnetic performance.