Investigation On Preparation Of Magnesium Oxide Nanocompositesand Their Properties

With the development of industry,the human living standards have been gradually improved.At the same time,the industrial production and application of products have also caused a wide range of water pollution.Common water pollutants included heavy metal ions,organic dyes and antibiotics.The accumulation of these pollutants in the environment posed a great threat to human health and ecological balance.Adsorption and Fenton/Fenton-like catalytic degradation are common wastewater treatment methods which can efficiently remove contaminants from water.Nano-magnesium oxide?nano-MgO?is an environmentally friendly metal oxide with high specific surface area,high surface activity and high adsorption performance.Therefore,MgO nanoparticles have been widely used as an adsorbents for the removal of various heavy metal ions and organic pollutants.However,the used MgO nanoparticles are difficult to separate from the water,resulting in secondary pollution caused by desorption of adsorbed pollutants.In this paper,nano-MgO was combined with magnetic nano-Fe to prepare an adsorbent with high adsorption capacity,which can be magnetically recovered;Considering that the general Fenton catalysts contained toxic transition metal elements,and most of them require external energy?light,electricity or ultrasound?input during applications,this paper prepared g-C₃N₄/MgO and MgNCN/MgO nanocomposites without transition metal elements,and used them as novel environmentally friendly Fenton-like catalysts for the degradation of organic contaminants in water.The main research contents are as follows:?1?Magnetic Fe@MgO nanocomposites were synthesized by a facile precipitation-calcination method,and used for heavy metal ion and dye removal from water.The as-synthesized Fe@MgO core-shell nanocomposites exhibited large surface areas?199.78 m²/g?with mesoporous structure and high magnetic saturation value?20.7 emu/g?to facilitate magnetic separation.Fe@MgO nanocomposites showed excellent adsorption properties with maximum adsorption capacities of 1476.4 mg/g for Pb²⁺and 6947.9 mg/g for methyl orange?MO?,respectively.The adsorption processes of Pb²⁺and MO onto Fe@MgO were found to well follow the pseudo-second-order kinetic model and Langmuir isotherm model,indicating both of them were monolayer chemisorption.Mechanisms of Pb²⁺and MO adsorption onto Fe@MgO nanocomposites were investigated by analyzing the adsorbed products.Pb²⁺was precipitated on Fe@MgO in the form of Pb₃?CO₃?₂?OH?₂.Most MO combined with Fe@MgO by complexation,and a small amount of MO was mineralized by Fe@MgO.In addition,Fe@MgO nanocomposites could simultaneously remove Pb²⁺and MO from water,and Pb²⁺could promote the MO adsorption onto Fe@MgO.?2?g-C₃N₄ was obtained by calcining melamine as raw material.Then the obtained g-C₃N₄ and basic magnesium carbonate was mixed and calcined again to prepared g-C₃N₄/MgO nanocomposites.The prepared g-C₃N₄/MgO nanocomposites exhibited excellent catalytic activity for the activation of H₂O₂ to degrade organic dyes in the dark.The azo dye methyl orange?MO?,which is difficult to degrade,was used as a target product for degradation.20 mg of g-C₃N₄/MgO nanocomposites only adsorbed 8.4%of 100mL,20 mg/L MO.However,after adding 0.3 mL of 30%H₂O₂,96.8%of MO can be removed within 2 hours.With the increase of the amount of g-C₃N₄/MgO nanocomposites and H₂O₂,the degradation rate of MO gradually became faster.In addition,g-C₃N₄/MgO nanocomposites could also efficiently catalyze the degradation of methylene blue and rhodamine B.The capture agent experiment and EPR test results showed that the g-C₃N₄/MgO-H₂O₂ system can effectively degrade organic pollutants due to the generation of hydroxyl radicals??OH?.Further characterization showed that the bond between MgO and g-C₃N₄ in g-C₃N₄/MgO nanocomposites plays a key role in the Fenton-like activation of H₂O₂ to produce?OH.The catalytic degradation of the g-C₃N₄/MgO nanocomposites could be carried out in a wide pH range?pH=4¹0?without the external energy?light,electricity and ultrasound?input.In addition,the g-C₃N₄/MgO nanocomposites without toxic metal components,were easy to prepare with low-cost raw materials.Thus,g-C₃N₄/MgO nanocomposites have a great potential in organic wastewater purification applications.?3?MgNCN/MgO nanocomposites were prepared by one-step calcination method using melamine and basic magnesium carbonate as raw materials.The catalytic degradation of tetracycline?TC?by MgNCN/MgO nanocomposites as Fenton-like catalysts was investigated.A series of samples were prepared by adjusting the mass ratio of the melamine to the basic magnesium carbonate and the calcination temperature.Among them,the sample obtained by calcining melamine and basic magnesium carbonate with a mass ratio of 2:1 at 550°C showed the best performance as a Fenton-like catalyst.10 mg of MgNCN/MgO nanocomposites and 0.2 mL 30%H₂O₂could degrade 90.1%of TC?100 mL,50 mg/L?in 30 minutes.And with the increase of the amount of MgNCN/MgO nanocomposites and H₂O₂,the degradation rate of TC gradually became faster.Free radical trapping experiments and EPR tests also confirmed the presence of?OH in the MgNCN/MgO-H₂O₂ system,and its catalytic performance was better than that of the g-C₃N₄/MgO composite in the previous chapter.In a wide pH range?pH=4¹2?,MgNCN/MgO nanocomposites exhibited excellent ability to degrade antibiotics without external energy?light,electricity and ultrasound?input.