Understanding the intermediates and carbon dioxide adsorption of potassium chloride-incorporated graphitic carbon nitride with tailoring melamine and urea as precursors.

In this study, we demonstrated the synthesis of potassium chloride (KCl)-incorporated graphitic carbon nitride, (g-C3N4, CN) with varying amounts of N-vacancies and pyridinic-N as well as enhanced Lewis basicity, via a single-step thermal polymerization by tailoring the precursors of melamine and urea for carbon oxide (CO2) capture. Melamine, as a precursor, undergoes a phase transformation into melam and triazine-rich g-C3N4, whereas the addition of urea polymerizes the mixture to form melem and heptazine-rich g-C3N4 (CN11). Owing to the abundance of pyridinic-N and the high surface area, CN11 adsorbed higher amounts of CO2 (44.52 µmol m-2 at 25 °C and 1 bar of CO2) than those reported for other template-free carbon materials. Spectroscopic analysis revealed that the enhanced CO2 adsorption is due to the presence of pyridinic-N and Lewis basic sites on the surface. The intermediates of CO2adsorption, including carbonate and bicarbonate species, attached to the CN samples were identified using in-situ Fourier-transform infrared spectroscopy (FTIR). This work provides insights into the mechanism of CO2 adsorption by comparing the structural features of the synthesized KCl-incorporated g-C3N4 samples. CN11, with an excellent CO2 uptake capacity, is viewed as a promising candidate for CO2 capture and storage.

Ag-modified TiO2/SiO2/Fe3O4 sphere with core-shell structure for photo-assisted reduction of 4-nitrophenol.

Nitrogen-containing contaminants, such as 4-nitrophenol (4-NP), cause detrimental effects when discharged into the environment and thus should be reduced or removed from ecosystems. In this study, an Ag-loaded TiO2-SiO2-Fe3O4 (TSF) with a core-shell structure was employed for the photo-assisted reduction of 4-NP. Fe3O4, SiO2, and TiO2 in the core-shell structure served as a magnetic center, protective layer, and light absorber, respectively. To improve the reduction activity of 4-NP, Ag was loaded onto TSF under stirring, with a variation of the temperature (2-130 °C) and reaction time (1, 2, and 4 h). Under the optimized conditions, 5Ag-TSF (with 5 wt% of Ag) could promote the reduction of aqueous 4-NP solution (2 × 10-4 M, 75 mL) in the presence of NaBH4 (0.1 M, 5 mL) under irradiation by a metal halide lamp, affording over 98% reduction within 5 min and a rate constant of 0.185 min-1, demonstrating its promising activity. Moreover, due to the advantages of the core-shell structure, the magnetic properties of Fe3O4 were sufficient to enable facile recycling of the sample for further reaction; SiO2 could protect the Fe3O4 center from oxidation or reduction; TiO2 enabled Ag accommodation and absorbed light to generate electron-hole pairs. In summary, an Ag-loaded TiO2-SiO2-Fe3O4 sphere with high activity and recyclability for 4-NP reduction was prepared via a facile and simple stirring method, where the sample can be used as a promising material in environmental remediation.

Adsorption mechanism of emerging and conventional phenolic compounds on graphene oxide nanoflakes in water.

Emerging contaminants (ECs) such as bisphenol A (BPA), 4-nonylphenol (4-NP) and tetrabromobisphenol A (TBBPA) have gained immense attention worldwide due to their potential threat to humans and environment. Graphene oxide (GO) nanomaterial is considered as an important sorbent due to its exceptional range of environmental application owing to its unique properties. GO was also considered as one of ECs because of its potential hazard. The adsorption of organic contaminants such as phenolic ECs on GO affects the stability of GO nanoflakes in water and the fate of organic contaminants, which would cause further environmental risk. Therefore, the adsorption behaviors of emerging and common phenolic compounds (PCs) including phenol, 4-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, 4-NP, BPA and TBBPA on GO nanoflakes and their stability in water were studied. The adsorption equilibrium for all the compounds was reached <10h and was fitted with Langmuir and Freundlich isotherms. In addition to hydrophobic effect, adsorption mechanisms included π-π bonding and hydrogen bonding interactions between the adsorbate and GO, especially the electrostatic interactions were observed. Phenol has the highest adsorption affinity due to the formation of hydrogen bond. GO has a good stability in water even after the adsorption of PCs in the presence of a common electrolyte, which could affect its transport with organic contaminants in the environment. These better understandings illustrate the mechanism of emerging and common PC interaction with GO nanoflakes and facilitate the prediction of the contaminant fate in the aquatic environment.