Morphology-Dependent Room-Temperature Ferromagnetism in Undoped ZnO Nanostructures

Since Dietl et al. predicted that Co-doped ZnO may show room-temperature ferromagnetism (RTFM) in 2000, researchers have focused on the investigation of ferromagnetic ZnO doped with various transition metals. However, after decades of exploration, it has been found that undoped ZnO nanostructures can also show RTFM, which in general is dependent on ZnO morphologies. Here, we will give an overall review on undoped ZnO nanomaterials with RTFM. The advanced strategies to achieve multidimensional (quasi-0D, 1D, 2D, and 3D) ferromagnetic ZnO nanostructures and the mechanisms behind RTFM are systematically presented. We have successfully prepared ferromagnetic nanostructures, including thin films, horizontal arrays and vertical arrays. The existing challenges, including open questions about quantum-bound ZnO nanostructures, are then discussed.

A p-n Heterojunction Based Pd/PdO@ZnO Organic Frameworks for High-Sensitivity Room-Temperature Formaldehyde Gas Sensor

As formaldehyde is an extremely toxic volatile organic pollutant, a highly sensitive and selective gas sensor for low-concentration formaldehyde monitoring is of great importance. Herein, metal-organic framework (MOF) derived Pd/PdO@ZnO porous nanostructures were synthesized through hydrothermal method followed by calcination processes. Specifically, porous Pd/PdO@ZnO nanomaterials with large surfaces were synthesized using MOFs as sacrificial templates. During the calcination procedure, an optimized temperature of 500°C was used to form a stable structure. More importantly, intensive PdO@ZnO inside the material and composite interface provides lots of p-n heterojunction to efficiently manipulate room temperature sensing performance. As the height of the energy barrier at the junction of PdO@ZnO exponentially influences the sensor resistance, the Pd/PdO@ZnO nanomaterials exhibit high sensitivity (38.57% for 100 ppm) at room temperature for 1-ppm formaldehyde with satisfactory selectivity towards (ammonia, acetone, methanol, and IPA). Besides, due to the catalytic effect of Pd and PdO, the adsorption and desorption of the gas molecules are accelerated, and the response and recovery time is as small as 256 and 264 s, respectively. Therefore, this MOF-driven strategy can prepare metal oxide composites with high surface area, well-defined morphology, and satisfactory room-temperature formaldehyde gas sensing performance for indoor air quality control.

Enhancing Performance of Broadband Photodetectors Based on Perovskite CsPbBr3 Nanocrystals/ZnO-Microwires Heterostructures

A broadband photodetector response in the ultraviolet (UV)-to-green range (up to 530 nm) based on perovskite CsPbBr3 nanocrystals (NCs)/ZnO-microwires (MWs) heterostructures was realized via a convenient spin-coating method. Under UV light (365 nm) illumination, compared with a bare-ZnO-MW-based photodetector, the CsPbBr3-NCs/ZnO-MWs-heterostructure-based photodetector exhibited a faster photoresponse (<0.1 s) and higher current responsivity (93.50 AW−1), external quantum efficiency (3399%), and detectivity (4.4 × 1010). In addition, the photodetector based on CsPbBr3-NCs/ZnO-MWs heterostructures also exhibited a very fast photoresponse to green light (530 nm). These can be ascribed to the strong light-trapping ability of CsPbBr3 NCs and high charge-transfer efficiency at the CsPbBr3-NCs/ZnO-MWs-heterojunction interface due to the built-in field, which facilitates the spatial separation of the photogenerated carriers. Therefore, this work will develop perovskite/ZnO nanomaterials as promising building blocks for broadband photodetectors and wider optoelectronic applications.