Preparation of Porous Carbon Materials as Adsorbent Materials from Phosphorus-Doped Watermelon Rind

In this study, phosphorus-doped watermelon rind carbon material (WC-M) was prepared by a muffle furnace, and the adsorption performance of WC-M material to dyes was investigated. At the same time, the effects of dye concentration, pH, adsorption time, adsorption temperature, and other factors on the adsorption effect were investigated. In the experiment, a muffle furnace was used to carbonize the watermelon rind doped with phosphoric acid, which simplified the experimental operation. Regarding the results of SEM analysis, the surface structure of WC-M materials is diverse. Isothermal maps of nitrogen adsorption and desorption show that the material contains more microporous structures and exhibits more active sites. The experimental results show that WC-M materials show good adsorption properties against cationic dyes (malachite green, MG) and anionic dyes (active black, AB). The neutral condition is conducive to the adsorption of MG, and the alkaline condition is conducive to the adsorption of AB. The adsorption rate reaches a maximum in the initial stage of adsorption, the adsorption capacity reaches 50% of the total adsorption capacity within 10 minutes before the reaction, and then the adsorption capacity gradually decreases until the adsorption equilibrium. The adsorption mechanism was explored by the pseudo-first-order kinetic model, second-order kinetic model, and intraparticle diffusion model. At the same time, through the analysis of multiple isotherm models, the overall adsorption process followed the Langmuir isotherm model, the adsorption of MG was more inclined to monolayer electron adsorption, and the adsorption capacity reached 182.68 mg.g(-1). The reusability of WC-M materials in MG and AB adsorption was discussed. At this time, the concentrations of AB and MG were 120 mg.L-1 and 150 mg.L-1, and after 10 h of desorption, the desorption rates of MG and AB reached 67.7% and 83.3%, respectively; after five adsorption-desorption cycles, the adsorption rate of MG was still 78.5%, indicating that WC-M materials have good recovery effect. At the same time, the use of watermelon rind as an adsorption material belongs to the high-value application of watermelon rind, which belongs to "turning waste into treasure" and will not pose a certain threat to the environment. This experiment is also suitable for durian rind, pineapple rind, and other "waste" biomass materials, and the experiment has certain generalizations.