Hydrothermal Preparation And Microwave Absorption Properties Of Mo S₂-based Magnetic Material

The development of high-performance microwave absorption materials has always been a major issue in the field of military and electromagnetic pollution prevention.In recent years,two-dimensional materials have become the hotspot in the field of materials.As a typical 2D material,MoS₂ has a wide range of applications in optoelectronic devices,energy storage,catalysis and sensors.At the same time,MoS₂can be used as a promising absorbent,which is superior than traditional absorbents in terms of absorption intensity and weight.As we know,MoS₂ is a dielectrical loss absorbent,and the impedance mismatch caused by high dielectric constant and low magnetic permeability is an important factor that limits the microwave absorption capability of MoS₂.In order to improve impedance characteristics,magnetism is introduced into MoS₂ in two ways:transition metal element doping and magnetic absorbent compounding.This paper plans to carry out researches on the microwave absorption performance of MoS₂-based magnetic materials.The major work and conclusions are summarized as follows:（1）Study on the hydrothermal preparation of MoS₂ and the process optimization.The effects of hydrothermal reaction temperature,reaction time and the ratio of molybdenum source to sulfur source（Mo:S）on the microwave absorption properties of MoS₂ were investigated.The results showed that:the hydrothermal products were mainly flower-like structures formed by stacking MoS₂ nanosheets.When the reaction temperature was 180℃,the reaction time was 18 h,and the Mo:S was 1:3.5,the synthesized MoS₂ had the best performance:its maximum reflection loss could reach-55.78 dB,and the corresponding matching thickness was 2.30 mm with a wide effective bandwidth of 5.17 GHz.It was worth noting that when the reaction temperature was 180℃,the reaction time was 18 h,and the Mo:S was 1:2.5,though the maximum reflection loss of the sythesized MoS₂ was only-27.11 dB,the matching thickness could reduce to 1.75 mm with a broader effective bandwidth of>5.59 GHz.Further research on the microwave absorption mechanism revealed that in addition to the destructive interference of electromagnetic waves,various polarization phenomena such as defect dipole polarization were the main reasons for microwave loss.（2）Study on hydrothermal preparation and microwave absorption properties of Ni-doped MoS₂ magnetic absorbents.The results showed that:at low doping concentration,the content of Ni in the products increased with the increasement of Ni source in precursor.Ni and MoS₂ formed Ni_xMo_1-xS₂ after doping without impurities.At the same time,Ni-doping could improve the magnetic properties of MoS₂:when the doping concentration was 3%,the saturation magnetic moment of product could reach0.93 emu·g^-1,higher than that of pure MoS₂.And at high doping concentration,besides MoS₂,impurities such as NiS₂ appeared in the products.Ni-doping could significantly improve the microwave absorption properties of MoS₂.When the doping concentration was 3%,the product had the best overall performance:when the matching thickness was 2.05 mm,the maximum reflection loss could reach-58.08 d B with the effective bandwidth of 5.32 GHz.The reason for the performance improvement lied in the fact that Ni-doping increased the value ofε’’andμ"of MoS₂,so the dielectric loss and the magnetic loss were both enhanced.（3）Study on hydrothermal preparation and microwave absorption properties of core-shell CIP@MoS₂ composites.In this part,the surface of CIP was first modified by cationic surfactant CTAB or nonionic polymeric surfactant PVP,respectively.Though the core-shell structure could be both obtained by these surfactants,the dispersibility of the CIP@MoS₂ obtained by PVP was remarkably superior.In the range of CIP:Mo investigated,theμ’andμ’’of CIP@MoS₂ composites increased compared with pure MoS₂,which meant that the magnetic loss capability was enhanced.So,the composites had both magnetic loss and dielectric loss capability.This study had important reference for the performance regulation and structural design of new absorbents.Further research on the magnetic absorption mechanism showed that the magnetic loss of the composites mainly originated from the eddy current effect and the resonance loss.