High Specific Surface Area Magnesium Oxide:Fabrication And Adsorption Behavior

With the rapid development of the economy and the growing awareness of environmental protection,wastewater treatment has become not only the key and difficult point for the comprehensive improvement of water environment in China,but also directly related to people’s health and sustainable development of the country.Among the various treatment methods,the adsorption method has been widely used because of simple operation,low cost,and environmental harmless.The treatment effect(capacity and speed)mainly depends on the chemical composition and pore structure of the adsorbent material.The controllable preparation and adsorption behavior of excellent pore structure,high-efficiency and low-cost adsorption materials are of great significance and practical application for the highly efficient wastewater treatment in China.In comparison,magnesium oxide adsorbent has attracted lots of attention owing to abundant sources,low cost,and high adsorption capacity.It has been used in the treatment of printing and dying industry wastewater,heavy metal wastewater,and domestic sewage treatment.Yet,low specific surface area and wide pore size distribution greatly limit the adsorption capacity and efficiency.Based on the acid-base nature of aluminum hydroxide and the slow release of ammonia,the porous wheat-like magnesium oxide has been controllably prepared by adjusting the release rate of ammonia during the formation of magnesium carbonate precursor.Using organic dyes methyl orange(MO)and heavy metal lead ions(Pb2+)as probes,the related adsorption behavior of porous MgO was investigated in detail as well as the structure-performance relationship between pore structure and adsorption performance towards MO and Pb2+.Undoubtedly,this work provides a scientific basis for the pore structure design and controllable preparation of high-efficiency MgO adsorption material.The main contents and results of the work are shown as follows.(1)Magnesium chloride was used as the magnesium source,and urea was used as the ammonia precipitant.The cubic magnesium carbonate precursor was prepared by hydrothermal method.The cubic magnesium oxide adsorption material with high specific surface area was prepared by calcination in air atmosphere,and its adsorption to MO was systematically investigated.The results show that the average pore size is 6 to 8 nm and the specific surface area of the obtained adsorbent is 182 m2/g.The adsorption behavior of the adsorption material on methyl orange follows the pseudo-second order kinetic and the Freundlich adsorption model,and reaching equilibrium at 10 min.The maximum equilibrium adsorption capacity is above 3500 mg/g with excellent adsorption performance.(2)Using magnesium chloride,aluminum chloride as the magnesium source and aluminum source,and urea as the ammonia slow release precipitant and aluminum hydroxide template dissolving agent,the magnesium carbonate precursor was prepared in a hydrothermal route(180 ℃).Then magnesium oxide adsorption material with the through-hole mesoporous produced after calcined in air at 550℃,and its adsorption behavior and mechanism to MO was discussed.The results show that wheat-like magnesium oxide with high specific surface area and rich through-hole structure can be controllably prepared through the adjust of the proportion of magnesium and aluminum.The adsorption material has a specific surface area of 136 m2/g and an average pore size of 5 to 8 nm.The adsorption process of the adsorption material follows the Langmuir thermodynamic model and the pseudo-second order kinetic.The maximum adsorption amount for methyl orange and lead ions is 5483 mg/g,2359 mg/g respectively.(3)Magnesium chloride and aluminum chloride are used as magnesium and aluminum sources,and urea as the ammonia slow release precipitant,the surfactants Hexadecyl trimethyl ammonium Bromide(CTAB)and Hexadecyl trimethyl ammonium Chloride(CTAC)as morphology control agents,two kinds of wheat-like magnesium oxide adsorption materials were prepared by the method of hydrothermal and calcination.Its adsorption capacity to MO was discussed.The results show that the introduction of surfactants does not affect the morphology of the adsorbent material significantly.The specific surface area of wheat-like magnesium oxide adding CTAB is increased to 171 m2/g,and its average pore size is 6.3 nm.Its adsorption behavior on methyl orange obeys the pseudo-second order kinetic and the Freundlich adsorption model.The equilibrium time is shortened to 10 min and the maximum equilibrium adsorption capacity is above 3518 mg/g.The specific surface area of wheat-like magnesium oxide adding CTAC is increased to 166 m2/g with its average pore size of 5.6 nm.Its adsorption behavior on methyl orange follows the pseudo-second order kinetic and the Langmuir adsorption model.The equilibrium time is shortened to 10 min and the maximum equilibrium adsorption capacity is above 3353 mg/g.