Hebei Messi Biology Co., Ltd. stated that magnesium oxide is a magnesium oxide with a chemical formula of MgO and a typical sodium chloride structure, with magnesium atoms and oxygen atoms arranged in sequence. Magnesium oxide is a high-functional fine inorganic material that can be widely used in catalysis, electronics, ceramics and other fields. Magnesium oxide has a large specific surface area and is a promising catalyst carrier that can be used in a variety of reactions. It is also a promising chemical adsorbent that can destructively adsorb various pollutants. In addition to the above applications, due to its characteristics, magnesium oxide can also be used to make effect pigments and sensing materials under certain conditions.
1. Preparation of magnesium oxide with special morphology
The microscopic morphology and performance of materials are often strongly correlated, so the morphology regulation of inorganic materials is one of the hot spots in the field of materials research in recent years. In recent years, there have been many reports on magnesium oxide with special morphology and nanostructure at home and abroad. After experimental research, it was found that some magnesium oxide with special morphology has very effective applications in many aspects. Hebei Messi Biology Co., Ltd. briefly summarizes the preparation of some magnesium oxide with special morphology.
1.1 Spherical magnesium oxide
Magnesium oxide with a spherical structure is prepared by calcining the precursor spherical basic magnesium carbonate, spherical magnesium hydroxide or spherical basic magnesium oxalate. Taking spherical basic magnesium carbonate as an example, the spherical structure of basic magnesium carbonate is formed by the accumulation of flaky basic magnesium carbonate. The basic magnesium carbonate is calcined and the spherical basic magnesium carbonate undergoes thermal decomposition to obtain spherical magnesium oxide.
There are two main technical routes for preparing spherical magnesium oxide: (1) using magnesium salt as a raw material to first obtain a precursor for preparing spherical magnesium oxide, and heat-treating the precursor to obtain spherical magnesium oxide; (2) mixing magnesium oxide powder with a solvent and a binder (in some cases, the binder may not be required), mechanically forming the spherical magnesium oxide, and then heat-treating the spherical magnesium oxide product.
The spherical magnesium oxide obtained by the precipitation method has a diameter of 15-17um, and the effect of time on its reaction process was further studied. It was found that during the synthesis process, magnesium oxide was first flaky, then gradually changed to filaments, and finally to spherical.
1.2 Tubular magnesium oxide
Currently, the diameter of tubular magnesium oxide is generally nanometer-scale, and the length is generally micrometer-scale. It usually has the characteristics of directional growth, good crystallinity and definite crystal plane orientation. Magnesium oxide nanotubes can be prepared by carbon-thermal evaporation method. During the preparation, an appropriate amount of Ga2O3 is added to the mixture of magnesium oxide and carbon. Ga2O3 plays a vital role in the formation process of magnesium oxide nanotubes. Carbon reduces Ga2O3 at high temperature to obtain gallium vapor. The condensed gallium droplets in situ catalyze the anisotropic growth of magnesium oxide nanotubes. The obtained magnesium oxide nanotubes are single crystals with an average outer diameter of 200nm, a wall thickness of 20nm, and a length of up to 50um.
1.3 Flake magnesium oxide
The key to obtaining flake magnesium oxide by ultrasonic treatment is that the impact of the bubbles bursting in the ultrasonic cavitation phenomenon on the layered magnesium oxide causes the layered magnesium oxide to peel off. Ultrasonic waves will cause liquid molecules to be continuously compressed and stretched, producing alternating positive and negative pressure zones, causing water molecules to alternately change in density, obtaining microbubbles in sparse areas, and growing in negative pressure areas. When microbubbles burst, the surrounding water phase will quickly flow into the center of the bubble, releasing a strong pressure pulse. The pressure of this pulse is often higher than 104KPa. This phenomenon is also called ultrasonic cavitation effect.
Using the mechanism of ultrasonic cavitation, ultrasonic waves are used to cause the liquid phase to continuously relax and compress, generating a large number of microbubbles, and causing the microbubbles to continuously generate shock waves in the positive pressure zone to hit the surface of the material, so that the layered magnesium oxide is peeled off layer by layer, thereby generating magnesium oxide nanosheets.
1.4 Magnesium oxide whiskers
Magnesium oxide whiskers are mainly prepared by precursor calcination method, that is, first preparing precursor whiskers such as basic magnesium sulfate, basic magnesium chloride, basic magnesium carbonate, and magnesium carbonate, and then heat treating to obtain magnesium oxide whiskers.
Using active magnesium oxide and magnesium chloride as raw materials, basic magnesium chloride whiskers are first synthesized under hydrothermal conditions. The morphology of basic magnesium chloride whiskers can be maintained after pyrolysis, thereby obtaining magnesium oxide whiskers with a whisker length of about 200um and a diameter of about 0.5um.
Using magnesium sulfate and sodium hydroxide as raw materials, a precursor basic magnesium sulfate with good crystallization and fibrous appearance is obtained through hydrothermal crystallization at room temperature. By controlling the decomposition rate of the precursor to decompose it slowly at low temperature to maintain the whisker-like appearance, and then sintering at high temperature, magnesium oxide whiskers with good sintering, uniform dispersion and large aspect ratio can be obtained.
1.5 Mesoporous magnesium oxide
Mesoporous magnesium oxide is mainly prepared using mesoporous carbon, cotton fiber, etc. as hard templates. A 200mL solution containing 1mol·L-1Mg(NO3)2 was placed in a water bath at 30°C, and a 200mL K2CO3 solution (stoichiometric ratio) at room temperature and with a concentration of 0.8mol·L-1 was added to the solution under rapid stirring. At this time, the solution changed from clear to a liquid-solid mixed state, and the stirring state was maintained for 30 minutes. The suspension was separated into liquid and solid, and the soluble ions were removed with distilled water. The sample prepared in this experiment had good filterability. The obtained sample was then heated to 110°C for drying. After the dried sample was initially crushed, it was placed in an alumina crucible and heated to 600°C with the furnace. The phase conversion time was 2h, and the obtained sample was rod-shaped mesoporous magnesium oxide.
1.6 Preparation and research status of magnesium oxide with other special morphologies
Using chemical precipitation method, magnesium nitrate and potassium carbonate were used as raw materials, potassium carbonate and magnesium nitrate were mixed in a 120℃ oil bath environment, stirred for 1min, aged at 120℃ for 2h, filtered and washed, and roasted at 700℃ for 4h. Nest-shaped and flower-shaped magnesium oxide crystals were obtained by changing the ratio of magnesium nitrate and potassium carbonate.
Using hydrothermal method, magnesium nitrate and ammonium carbonate were used as raw materials, and flake, rod-shaped, flower-shaped and spherical magnesium oxide were synthesized by hydrothermal method, and its application as catalyst loading was studied.
MgCl2 solution was mixed with benzoic acid additive, and the pH value of the solution was adjusted with sodium hydroxide to make magnesium precipitate. Flake magnesium hydroxide precursor was synthesized by hydrothermal method, and fibrous and disc-shaped magnesium oxide was obtained when the additive was replaced with citric acid or disodium ethylenediaminetetraacetic acid.
2. Application of magnesium oxide with special morphology
Nano-micron structured magnesium oxide is a material that has received widespread attention in recent years. Compared with traditional magnesium oxide, nano-micron structured magnesium oxide often has a smaller particle size and a larger specific surface area. Moreover, by deliberately controlling its growth conditions, more specific crystal faces can be exposed, providing a higher density of active adsorption sites. Therefore, compared with traditional magnesium oxide materials, it has better optical, electrical, magnetic, thermal and chemical properties, and is one of the hot spots for scientific research and industrial applications.
2.1 Application of spherical magnesium oxide
Spherical magnesium oxide is mainly used in the fields of chromatography stationary phase, adsorption of toxic substances, and as a material additive. High performance liquid chromatography (HPLC) is an effective separation technology, and its separation effect is greatly affected by the chromatographic column filler. The fillers currently used are mainly silica-based fillers. When silica-based fillers are used for separation under alkaline conditions, there are problems such as secondary reactions, long retention time, severe tailing, low efficiency, and poor reproducibility. Through research and exploration, it was found that the mixture of magnesium and aluminum oxides and silicon dioxide in a certain proportion as the stationary phase of liquid chromatography can solve this problem well, so the application of spherical magnesium oxide in liquid chromatography has received more and more attention.
In addition, the mesoporous nanosheets of spherical magnesium oxide show excellent adsorption properties, which can adsorb common toxic heavy metal ions and organic pollutants, and are expected to be used in wastewater treatment processes. Some people also found that when performing XRD characterization on spherical magnesium oxide prepared by carbonization, the characteristic diffraction peak at 335nm was due to the induction of defects or defect energy levels to generate new energy levels. From this feature, it can be predicted that magnesium oxide microspheres and nanosheets will be a very promising material in plasma display panels or other optical applications.
2.2 Magnesium oxide whiskers for material reinforcement
Whisker is a needle-shaped single crystal material with a diameter of a few tenths to several microns and a length of several microns to hundreds of microns. Due to the complete crystal structure, the whisker has good mechanical strength. As a modified additive for materials such as plastics, metals and ceramics, it shows excellent physical and chemical properties and mechanical properties.
The microscopic morphology of magnesium oxide whiskers is fibrous, with high melting point, high strength, high elastic modulus, good heat resistance, alkali resistance, insulation, thermal conductivity (thermal conductivity is three times that of aluminum oxide), stability and reinforcement and toughness. In addition, magnesium oxide whiskers have good resistance to high-temperature oxidation. Due to the above excellent properties, magnesium oxide whiskers are suitable as reinforcing auxiliary materials for composite materials, especially for the preparation of high-temperature composite materials. It is a new high-tech structural material that has developed rapidly in recent years.
2.3 Mesoporous magnesium oxide for environmental protection
The negative impact of greenhouse gas carbon dioxide on the environment has received increasing attention, and more and more research has been conducted on carbon dioxide capture. Adsorption is an effective method for capturing carbon dioxide, and alkaline oxides are effective carbon dioxide adsorbents. The binding of magnesium oxide to carbon dioxide is a reversible process, with a stronger binding force than zeolite and weaker than alkali metal oxides. At room temperature, carbon dioxide is adsorbed by magnesium oxide by physical or chemical action, so magnesium oxide is a more suitable carbon dioxide adsorbent. The adsorption of carbon dioxide by mesoporous magnesium oxide is much higher than that of solid magnesium oxide, and the adsorption increases with increasing temperature. Mesoporous magnesium oxide can also be used to adsorb and remove fluoride ions from water, and its removal efficiency is much higher than that of ordinary commercial magnesium oxide.
2.4 Nano magnesium oxide for antibacterial
So far, there are few reports on the antibacterial properties of magnesium oxide at home and abroad. The earliest proposal of the antibacterial properties of magnesium oxide can be traced back to the mid-1990s of the last century. In order to screen out inorganic materials with good antibacterial properties, a series of ceramic powders were tested using conductivity research. The experiment found that among the 26 common ceramic powders, 10 metal oxides and carbides such as calcium oxide, zinc oxide, and magnesium oxide have good antibacterial properties. Among them, magnesium oxide has been proven to have strong bactericidal and antibacterial abilities against Gram-positive bacteria, Gram-negative bacteria, fungi, etc.
It is generally believed that the antibacterial mechanism of magnesium oxide is caused by active oxygen, and magnesium oxide itself is a good desiccant that can produce a large amount of strong oxidants on its surface, thereby inhibiting and killing microorganisms.