| Excessive phosphate,heavy metals and dye wastewater not only destroy ecosystems,but ultimately endanger human health.Magnesium oxide can be used as an adsorbent applied to the treatment of wastewater.The adsorption performance of magnesium is poor because of its easy agglomeration.In order to obtain high adsorption capacity and faster pollutant removal rate,various morphologies of magnesium oxide have been prepared by regulating the specific surface area and pore volume of magnesium oxide.However,most of the preparation processes involve the use of toxic and expensive surfactants,harsh reaction conditions with high temperature and high pressure and low product yield of magnesium oxide.In the interest of improving the adsorption capacity and pollutant removal rate,it is still a great challenge to prepare magnesium oxide with large specific surface area and abundant pore structure by green,mild and economical method.In this study,we prepared unique porous flower-like adsorbent(MgO/C-S-N2)by nitrogen-protected calcination process and surface-assisted action of sodium dodecylbenzene sulfonate.A series of characterizations were carried out to observe the morphology and composition of the adsorbent.Based on phosphate anion,Pb2+ and methylene blue as inorganic anion,inorganic cation and organic dye,the corresponding adsorption properties,influencing factors,adsorption mechanism and structure-activity relationship of the material were discussed in detail.Moreover,for the further cost reduction,making it easier to separate and improving the adsorption performance of MgO/C-S-N2,biochar-loaded porous flower-like adsorbent(MgO/C@biochar)was prepared,and its adsorption performance on methylene blue was discussed.The results are as follows:(1)Characteristic results indicated that MgO/C-S-N2 had a unique porous flowerlike morphology.Due to large surface area(222.97 m2·g·-1),pore volume(0.95 cm3·g-1),and the high dispersion of ultrafine magnesium oxide in carbon,these composites could rapidly and effectively remove phosphate anion and Pb2+.The adsorption capacity of phosphate anion(476.19 mg·g-1)and Pb2+(1666.67 mg·g-1)was much higher than most adsorption materials reported at home and abroad.The adsorption process of phosphate was affected by coexisting ions and the inhibition in phosphate adsorptionfollowed the following order:NO3->Br->Cl->CO32-.MgO/C-S-N2 adsorbent had excellent regeneration ability,the adsorbed methylene blue could be removed by pyrolysis,and the adsorption capacity of MgO/C-S-N2 was basically unchanged in five cycles.Magnesium oxide in the MgO/C-S-N2 became magnesium hydroxide after adsorption and desorption.(2)The adsorption mechanism of phosphate was electrostatic attraction and ligand exchange.In acidic environments,electrostatic attraction between phosphate and protonated magnesium oxide dominated;in alkaline environments,ligand exchange between phosphate and OH-on the surface of magnesium hydroxide dominated.The adsorption process of Pb2+ involved the chemical reaction between MgO and H2O,Pb2+,CO2.XRD analysis showed that Pb(CO3)2(OH)2 was formed after adsorption of Pb2+.Three kinetic models and three isotherm fitted the adsorption process,and the analysis results showed that the phosphate,Pb2+ and methylene blue was attached to the MgO/C-S-N2 in a single layer by chemical adsorption,respectively.(3)The size and lamellar thickness of the flower-like structure changed due to the introduction of biochar,and MgO/C@biochar had higher adsorption capacity for methylene blue than MgO/C-S-N2.After adsorption,MgO/C@biochar could be separated from the mixture more easily. |
PDF Full Text Request