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E-textiles are gaining growing popularity recently due to low cost, light weight, and conformable compatibility with clothes in wearable and portable smart electronics. Here, an easy-handing, low cost, and scalable fabricating strategy is reported to fabricate conductive, highly flexible, and mechanically stretchable/twisted fiber gas sensor with great wearability and knittability. The proposed gas sensor is built using commercially available cotton/elastic threads as flexible/stretchable templates and reduced graphene oxide/mesoporous zinc oxide nanosheets as sensing layers to form conducting fibers. The as-prepared fiber demonstrates sensitive sensing response, excellent long-term stability (84 days), low theoretical detection limit (43.5 ppb NO2), great mechanical deformation tolerance (3000 bending cycles, 1000 twisting cycles and 65% strain strength), and washing durability in room-temperature gas detection. More significantly, scalable wearable characteristics including repairability, reliability, stability, and practicability have been efficiently improved, which are achieved by knotting the fractured fibers, incorporating multiple sensors in series/parallel and weaving multisensor array networks integrated into clothes. The good sensing properties, superior flexibility, and scalable applications of wearable fibers may provide a broad window for widespread monitoring of numerous human activities in personal mobile electronics and human–machine interactions.

A facile ultra-rapid solution method was developed to fabricate ZnO nanosheets with tunable BET surface area and rich oxygen-vacancy defects. The addition of 1 molL-1 Na 2 SO 4 led to an increase of BET surface area of ZnO nanosheets from 6.7 to 34.5 m 2 /g, through an electrostatic-controlled growth and self-assembly mechanism. Detailed analysis based on Raman scattering, room-temperature photoluminescence, X-ray photoelectron spectroscopy and electron spin resonance revealed that the as-prepared ZnO nanosheets were rich in oxygen-vacancies. Increased BET surface area led to a further increase of surface oxygen-vacancy concentration. The rich oxygen-vacancies promoted the visible-light absorption of the ZnO nanosheets, leading to high photocurrent responses and photocatalytic activities towards the degradation of rhodamine B (apparent rate constants, k=0.0179 min-1) under visible-light illumination (>420 nm), about 13 and 11 times higher, respectively than that of ZnO nanoparticles with few oxygen defects. In addition, the high-surface-area ZnO nanosheets could be effectively hybridized with Ag 3 PO 4 nanoparticles, resulting in a further enhancement of the visible-light photocatalytic performance (k=0.0421 min-1).

Graphene/metal oxide-based materials have been demonstrated as promising candidates for gas sensing applications due to the enhanced sensing performance and synergetic effects of the two components. Plenty of metal oxides such as SnO2, ZnO, WO3, etc. have been hybridized with graphene to improve the gas sensing properties. However, graphene/metal oxide nanohybrid- based gas sensors still have several limitations in practical application such as the insufficient sensitivity and response rate, and long recovery time in some cases. To achieve higher sensing performances of graphene/metal oxides nanocomposites, many recent efforts have been devoted to the controllable synthesis of 3D graphene/metal oxides architectures owing to their large surface area and well-organized structure for the enhanced gas adsorption/diffusion on sensing films. This review summarizes recent advances in the synthesis, assembly, and applications of 3D architectured graphene/metal oxide hybrids for gas sensing.

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 TiO 2 . 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 H 2 evolution, is reviewed.