Table 1.

Typical preparation method of MnO2 nanomaterials.

Methods	Principle	Advantages	Disadvantages	Example
The template method	MnO2 nanomaterials were prepared with different forms of templates, and then the templates were etched to obtain manganese dioxide products.	1. The size, shape, structure, and properties of nanomaterials are precisely controlled by using templates as carriers. 2. Realizing the integration of synthesis and assembly of nanomaterials, and solving the dispersion and stability of nanomaterials.	1.Low reaction efficiency 2.Possibility of material damage when removing template	Fei et al. reported manganese dioxide nanosheets (58)
Hydrothermal method	Use high temperature and high pressure aqueous solution to dissolve those substances that are insoluble or difficult to dissolve under atmospheric conditions, or react to produce the dissolved products of the substances, and control the temperature difference of the solution in the high pressure gold to generate convection to form supersaturated state to produce long crystals.	1. high particle purity, good dispersion, good crystal shape and controllability, and low production cost. 2. The product does not need to be sintered to avoid grain growth and impurity mixing.	1.Strict temperature and pressure control 2.High equipment requirements	Guan et al.introduced a novel manganese dioxide-graphene nanosheets (GNSs) (59)
Redox Method	MnO2 is prepared by reduction of Mn7+(KMnO 4) or oxidation of Mn2+(MnCl 2) by Redox.	1. Simple operation, low cost, mild synthesis conditions and energy saving.	1. waste liquid pollution 2. Possibility of structural defects	Oaki et al. reported manganese oxide nanosheets (60)
Biomineralization Method	Bioorganic substances (such as serum albumin) will guide the nucleation of Mn2+ through control or/and influence under physical and chemical conditions, and then Mn2+ will spontaneously form MnO2 through growth or oxidation in alkaline solution.	1. The nucleation, growth, orientation and assembly of minerals are controlled at the molecular level. 2. The advantages of low cost, convenience and environmental friendliness 3.Preparation of multifunctional nano therapeutic agent.	1. Difficulty in integrating multifunctional organic materials	Fang et al. introduced albumin-MnO2 gated hollow mesoporous silica nanosystem (61)