Utilizing the waste liquid derived from graphene oxide synthesis as raw material, hydrated manganese oxide (HMO) was prepared by a chemical precipitation method with sodium hydroxide solution or aqueous ammonia solution. The HMO samples were analyzed by X-ray diffraction, Fourier transform infrared spectroscopy, Zeta potential analyzer, and scanning electron microscopy. The adsorption characteristics of the HMO samples were examined through lead ion adsorption from water. The effects of adsorption temperature, starting lead ion concentration, and adsorption time on the lead ion adsorption capacity were investigated. The relevant data agreed well with the pseudo-second-order kinetic model and the Langmuir isotherm model. Additionally, the maximum adsorption capacities of HMO-1 are 70.897 mg g−1, 76.660 mg g−1, and 79.424 mg g−1 for the lead ions at 298 K, 308 K, and 318 K, respectively. The lead ion adsorption mechanism of HMO has been explained. The findings indicate the as-synthesized HMO can be used as an efficient adsorbent material for eliminating lead ions from water.

Porous graphitic carbon nitride nanosheets were synthesized by the thermal condensation method using various precursors such as urea and melamine. Relevant properties of as-synthesized products were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TG) and differential thermal analysis (DTA). The overall results suggest that the formation of porous graphitic carbon nitride nanosheets with a varied morphology can be achieved using diverse precursors through this process. Based on this product yield analysis, it is suggested that melamine and the lower synthesis temperature be selected to achieve the higher yield of graphitic carbon nitride production. The present work provides a facile and economic method for controlling the morphology and properties of graphitic carbon nitride products.