Semiconductor photocatalysis provides potential solutions for many energy and environmental-related issues. Recently, various semiconductors with hierarchical nanostructures have been fabricated to achieve efficient photocatalysts owing to their multiple advantages, such as high surface area, porous structures, as well as enhanced light harvesting. ZnO has been widely investigated and considered as the most promising alternative photocatalyst to TiO₂. Herein, we present a review on the fabrication methods, growth mechanisms and photocatalytic applications of hierarchical ZnO nanostructures. Various synthetic strategies and growth mechanisms, including multistep sequential growth routes, template-based synthesis, template-free self-organization and precursor or self-templating strategies, are highlighted. In addition, the fabrication of multicomponent ZnO-based nanocomposites with hierarchical structures is also included. Finally, the application of hierarchical ZnO nanostructures and nanocomposites in typical photocatalytic reactions, such as pollutant degradation and H₂ evolution, is reviewed.

Li₂CO₃ with high purity is an important raw material for the fabrication of lithium rechargeable batteries. This paper reports a facile recrystallization way to produce Li₂CO₃ with high purity from commercial Li₂CO₃ containing 0.8 wt % of SO₄²⁻ by the treatment of the commercial Li₂CO₃ in Na₂CO₃ solution. The increase of temperature from 30 °C to 90 °C favored the recrystallization of Li₂CO₃ in Na₂CO₃ solution and promoted the removal of SO₄²⁻ adsorbed or doped on/in the commercial Li₂CO₃. The content of SO₄²⁻ in Li₂CO₃ decreased to 0.08 wt % after the treatment of the commercial Li₂CO₃ in 1.0 mol·L⁻¹ Na₂CO₃ solution at 90 °C for 10.0 h.

In this paper, the influence of alkyl trimethyl ammonium bromides (C_nH_2n+1(CH₃)₃NBr, n = 10, 12, 14, 16, 18, abbreviated as ATAB) on the formation of alpha calcium sulfate hemihydrate (α-CaSO₄·0.5H₂O) whiskers under a hydrothermal condition (135 °C, 3.0 h) was analyzed. Specifically, it focuses on cetyl trimethyl ammonium bromide (C₁₆H₃₃(CH₃)₃NBr, abbreviated as CTAB). The rising CTAB concentration from 0 to 9.2 × 10⁻⁴ mol·L⁻¹ led to the increase of the average aspect ratio of α-CaSO₄·0.5H₂O whiskers from 80 to 430, since the selective adsorption of CTAB on the negatively-charged side facets of the whiskers inhibited the growth of the whiskers along the direction normal to the lateral facets. The further increase of CTAB concentration above the critical micelle concentration (abbreviated as CMC) showed little effect on the morphology of α-CaSO₄·0.5H₂O whiskers, considering that CTAB tended to form micelles instead of being adsorbed on the whisker surfaces. Similar phenomena were observed in other ATABs (n = 10, 12, 14, 18).