Mesoporous NiO ultrathin nanowire networks topotactically transformed from α-Ni(OH)2 hierarchical microspheres and their superior electrochemical capacitance properties and excellent capability for water treatment

Abstract

Low-cost controlled strategies for the synthesis of mesoporous nickel oxide materials are highly desirable owing to its significant applications for power storage and other fields. In this contribution, we develop a novel hydrothermal route to synthesize α-Ni(OH)₂, in which urea has not only been utilized to produce hydroxyl anions, but also to organize ultrathin nanowires/nanosheets into a network-like hierarchical assemblage. The morphological evolution process of this organized product has been investigated by examining different reaction intermediates during the synthesis. The growth and thus final assemblage of α-Ni(OH)₂ can be finely tuned by selecting preparative parameters such as the molar ratio of starting chemicals. Based on the topotactic transformation from α-Ni(OH)₂, various mesoporous NiO hierarchical microspheres from ultrathin nanowires/nanosheets self-assembly have been prepared via thermal decomposition in an air atmosphere. The electrochemical performances of the typical nickel oxide products are evaluated. It is demonstrated that tuning of the surface texture and the pore size of the NiO products is very significant for electrochemical capacitor and water treatment applications. The mesoporous NiO network-like hierarchical microspheres exhibit excellent cyclic performance with nearly 100% capacity retention at a current density of 10 A g⁻¹ in a testing range of 2000 cycles. Moreover, the mesoporous NiO network-like hierarchical microspheres have excellent ability to remove organic pollutants from wastewater by their wonderful surface adsorption ability.