| Excessive amounts of toxic pollutants such as phosphate and dye have been seriously threatening the ecosystem and human health.Among the developed treatment methods,adsorption technique has gained increasing attraction because of simple operation,low cost,and environment friendly.The adsorption performance including capacity and rate mainly depends upon morphology,and surface properties of the corresponding adsorption materials.Generally,large surface area favors to increase the removal capacity;big pore size not only aids to improve the adsorption efficiency but also provides a pathway to utilize the specific area.Therefore,it is of great scientific significance to develop low cost and high efficient adsorbents for high-performance removal of phosphate and dyes and then promote sustainable social development.Magnesium oxide(MgO)as one of high-performance adsorbents has been widely investigated.Yet,it remains a big challenge to develop high surface area and appropriate pore size of MgO to further enhance adsorption capacity and adsorption rate and then enlarge the practical applications in the wastewater treatment.The aim of this work is to design and fabricate MgO as a high-performance adsorbent for the removal of phosphate and dyes by optimizing pore structure.A series of hierarchical MgO adsorbents with various morphologies were prepared by controlling the nucleation and the growth conditions of the precursors as well as the calcined conditions.Also,the corresponding adsorption performance,the adsorption behavior,and the relationship between structure and performance were carefully investigated using phosphate,methyl orange(MO),and methylene blue(MB)as the adsorbed probe.The main contents of this work are as follows:(1)Based on the nucleation and the growth mechanism,a series of hierarchical macroporous MgO samples were prepared by calcination of different precursors,which were fabricated by adjusting the feeding ratios between Mg2+ and NH3 in the synthesis system.Also,the corresponding adsorption performance and the adsorption mechanism were investigated towards phosphate and methyl orange in details.The percentage porosity and pore size were inversely related to the feeding ratio between the Mg2+/NH3 in the reaction system.For example,the decrease in cumulative volume,pore area,and percentage porosity was observed by the rate of 14.28%,38.62%,and 10.78%respectively with the rise in the ratio.These hierarchical macroporous MgO samples exhibited the superb removal capacity of 478.5 mg g-1 for phosphate,and 4483.9 mg g-1 for methyl orange respectively.(2)Based on the solvent interface effect,a series of hierarchical flower-like MgO microsphere were prepared by calcination of different precursors,which were fabricated with the different feeding ratio between ethylene glycol(EG)and Mgvlin the reactor.Also,the corresponding adsorption performance and the adsorption mechanism were investigated towards phosphate,methyl orange and methylene blue in details.The microsphere exhibited the pore size in micron formed by the aggregation of ultra-thin sheets with a low aggregation ratio in the presence of EG.The increase in total pore area(11.09%),intrusion volume(19.16%),and pore diameter(9.09%)followed the ratio variation between EG and Mg2+.The MgO microsphere exhibited the maximum adsorption capacity of 574.71,940.14 and 252.53 mg g-1 for phosphate,methyl orange and methylene blue respectively.The adsorption ability strongly based on the nature of pollutant,and surface charge on adsorbent material.(3)Based on the slow-release effect of the precipitating agent(HMTA),a series of porous MgO nanosheets were obtained by calcination of different precursors and carefully were investigated towards the removal of phosphate,which were fabricated with the different feeding ratio between Mg2+ and hexamethylene tetramine(HMTA)in the synthesis system.The HMTA played a crucial role on morphology and pore structure formation along with the corresponding adsorption behavior for phosphate.The MgO nanosheets exhibited the adsorption capacity of 236 mg g-1 related to the large surface area with suitable pore size.(4)Based on the surfactant-assisted effect,a series of different multimorphology MgO flowers were prepared by calcination of different precursors with the different feeding ratio between cetyl trimethyl ammonium bromide(CTAB)and Mg2+ in the synthesis system.The gardenias flower-like morphology exhibited the highest surface area of 336.54 m2 g-1 reported in the literature and showed the relatively high removal capacity of 348.32 mg g-1 for phosphate among the obtained multimorphologeis related to the high surface area and appropriate pore size.The surfactant assisted hydrothermal route is an available route for the fabrication of different MgO flower-like morphologies.(5)A series of carbon fiber@magnesium oxide films(CFP@Mgo)were prepared by calcination of precursor at different temperatures and were investigated on the corresponding adsorption behavior towards phosphate,which were fabricated using HMTA assisted hydrothermal route.The composite film exhibited different morphologies based on the calcination temperature with different film thickness.The surface area of carbon fiber paper@Mgo reached at 27 m2 g-1 from 3 m2 g-1 for carbon fiber paper with a pore size of 14.41 nm.The composite film calcined at 400? exhibited the excellent removal capacity of 1230 mg g-1 with short immersion time related to the relatively large surface area and appropriate pore size.This composite film provided a new approach for the fabrication of low cost and high efficient adsorbents with fewer sludge problems. |
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