Table 1.

Summary and comparison between top-down and bottom-up strategies for the fabrication of 2D TMOs/TMHs and their pros and cons.

Strategy	Method	2D TMOs/TMHs	References	Pros and cons
Top-down	Mechanical cleavage	MnO2	Peng et al., 2017; Dutta et al., 2019	Easy operation; Only applicable for layered structure materials
		MoO3	Dutta et al., 2019
		RuO2	Dutta et al., 2019
		Ti5NbO14	Zhang et al., 2010
	Liquid-phase exfoliation	V2O5	Rui et al., 2013
		VO2	Liu et al., 2012
		MoO3	Zhang Y. Z. et al., 2015
Bottom-up	Self-assembly	TiO2	Sun J. et al., 2014	Applicable for both layered and non-layered structure materials; Can be produced at large scale; Harsh synthetic conditions; Difficult to obtain high-quality 2D crystals.
		ZnO	Sun et al., 2017
		Co3O4	Hu et al., 2017
		WO3	Sun J. et al., 2014
	Chemical vapor deposition	TiO2	Lee and Sung, 2012
		WO3	Liu et al., 2015
	Directional connection	SnO2	Wang C. et al., 2012
		CeO2	Yu et al., 2010
		Co(OH)2	Gao et al., 2014
	Topological chemical transformation	WO3	Liu et al., 2016
		Nb2O5	Wen et al., 2017
		ZnCo2O4	Bao et al., 2018
		Cobalt nickel oxide	Yang et al., 2019