To date, the synthesis of crystalline ZnO nanostructures was often performed under high temperatures and/or high pressures with tiny output, which limits their commercial applications. Herein, we report the progress on synthesizing single-crystalline ZnO nanosheets under ambient conditions (i.e., room temperature (RT) and atmospheric pressure) based on a sonochemistry strategy. Furthermore, their controllable growth is accomplished by adjusting the pH values of solutions, enabling the tailored crystal growth habits on the polar-charged faces of ZnO along c-axis. As a proof of concept for their potential applications, the ZnO nanosheets exhibit highly efficient performance for sensing ammonia at RT, with ultrahigh sensitivity (S = 610 at 100 ppm), excellent selectivity, rapid detection (response time/recover time = 70 s/4 s), and outstanding detection limit down to 0.5 ppm, superior to those of all pure ZnO nanostructures and most ZnO-based composite counterparts ever reported. The present work might open a door for controllable production of ZnO nanostructures under mild conditions, and facilitate the exploration of modern gas sensors for detecting gaseous molecules at RT, which underscores their potential toward practical applications in opto-electronic nanodevices.

Magnesium matrix composites are a new generation of biocompatible implant materials, but they will inevitably undergo simultaneous wear and corrosion in the human body. In this study, hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HA) is used in a magnesium matrix composite to study its effects on the corrosion-wear behavior. Two samples (a magnesium alloy composed of Mg, Zn, and Zr (ZK60) alloy and ZK60/10HA composite) were fabricated using the powder metallurgy (PM) process. Their corrosion-wear behavior was investigated using the sliding wear test in a simulated body fluid (SBF). At all the sliding velocities tested, the corrosion- wear resistance of ZK60/10HA was superior to ZK60. At a sliding velocity of 942.5 mm/min, ZK60/10HA demonstrated a 42% improvement in corrosion-wear resistance compared to ZK60. For ZK60, the main wear mechanism under dry conditions was abrasion, while the wear mechanisms in the SBF were abrasion and corrosion. For ZK60/10HA, the wear mechanisms under dry conditions were abrasion and delamination, while in SBF they were mainly abrasion and corrosion, accompanied by slight delamination. The results indicated that HA particles can be used as an effective corrosion-wear inhibitor in biocompatible magnesium matrix composites.