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Electrospinning–etching strategy was employed to synthesize Pt-loaded SnO 2 hollow microbelts (Pt_SnO 2 HBLs) based chemiresistive-type sensor demonstrating high sensitivity and selectivity toward acetone gas. This strategy overcomes a major hurdle toward achieving ubiquitous gas diffusion in electrospun structures, and provides highly porous thin-walled HBLs with large surface area and small crystallites. [Display omitted] • In situ templating of SnO 2 with SiO 2 was employed to form Pt-loaded SiO 2 @SnO 2 core–shell microbelts. • Etching away of SiO 2 in the Pt-loaded SiO 2 @SnO 2 microbelts yielded Pt-loaded SnO 2 hollow microbelts. • The Pt-loaded SnO 2 hollow microbelts exhibited good response (R a /R g = 93.5) and selectivity toward 2 ppm acetone at 350 °C. Challenges for ubiquitous diffusion of gas analytes into semiconducting metal oxides (SMOs) based sensing layers have necessitated the introduction of unprecedented synthesis techniques for thin, porous and high-performance gas sensing materials. In this work, electrospinning and calcination were employed to prepare unprecedented SiO 2 –SnO 2 core–shell microbelts (hereinafter referred to as SiO 2 @SnO 2 BLs) followed by etching away of SiO 2 in NaOH solution (pH 12) to achieve hollow SnO 2 BLs (hereinafter referred to as SnO 2 HBLs) with mean crystal size of 14.01 nm, large BET surface area (143.5 m2‧g–1), high porosity (mean pore size of 5.7 nm), and shell thickness of 58.3 ± 11.4 nm. Sensitization of SnO 2 HBLs with apoferritin-templated platinum nanoparticles (Pt NPs) enhanced their detection capability toward acetone. Response (defined as R a /R g , where R a and R g are sensor resistances in air and target gas, respectively) of Pt(0.12 %)_SnO 2 HBLs toward 2 ppm acetone was up to 7.8 times higher compared to that of pristine SnO 2 HBLs, and exhibited faster response (9.2 s). The Pt(0.12 %)_SnO 2 HBLs based sensor indicated a promising long-term stability, and outstanding repeatability of response (R a /R g = 93.7 ± 0.89) toward 25 cycles of 2 ppm acetone exposure in a humid environment of 90 % relative humidity. This performance could be attributed to the unique morphology of HBLs, sensitization effects of catalytic Pt NPs, and enlargement of the electron-depleted layer resulting from a Schottky barrier between Pt NPs and SnO 2 grains. [ABSTRACT FROM AUTHOR]

• The non-noble metals are introduced on graphene-based fiber as a sensitizer for the high-performance chemiresistor. • Metal oxides on graphene fibers naturally are converted into metals at a relatively low temperature annealing (under 700 °C) due to catalytic effect of graphene. • The graphene fiber acts as a flexible conductive support as well as a catalyst for the deoxidation of metal oxide. • The metal/metal oxide/graphene fibers exhibited a 16 times higher response to NO 2 gas and recovery than metal oxide/graphene fiber without metal. • The proposed strategy opens a new avenue for the realization of high-performance devices, such as chemical catalysts, photoactive devices. [Display omitted] Noble metal/metal-oxide-based hybrid gas sensors exhibit a low operating temperature, remarkable sensitivity, and fast recovery. As additives, noble metals induce a catalytic sensitization effect, which promotes charge transfer from the metal oxide to the analyte molecules, the so-called spillover mechanism. This suggests that metal catalysts can improve gas sensing performance. Herein, for the first time, non-noble metals are introduced on hybrid metal oxide/graphene fibers as sensitizers to fabricate high-performance chemiresistive sensors. The formation of metal components can be effectively controlled by annealing the metal oxide on graphene. Remarkably, compared with the corresponding metal oxide/graphene fiber sensors without metal components, the metal/metal oxide/graphene fiber sensors exhibit over a 16-fold higher response to NO 2 gas as well as effective recovery characteristics. Specifically, the Cu/Cu 2 O/graphene and Ni/NiO/graphene fiber sensors operating at 150 °C exhibit sensitivities of 18.90 % and 0.82 %, respectively, for 5 ppm NO 2 gas. The proposed strategy to achieve flexible graphene fiber chemiresistors by decorating them with non-noble metal and metal oxide nanoparticles opens a new avenue for realizing high-performance devices, such as photovoltaic devices, photocatalysts, and chemical catalysts. [ABSTRACT FROM AUTHOR]

• Porosity control of nanofibers: The high porosity of the metal oxide nanofibers is the key to achieving the dual sensitization owing to their high gas permeability and numerous active sites. Both saponin and water-ethanol co-solvent play critical roles in modifying morphology of nanofibers into elliptical nanofibers during electrospinning. Additionally, saponin forms numerous pores in the nanofibers when being burnt out during calcination. These porous, elliptical nanofibers possess a larger surface area and porosity.Saponin and water-ethanol co-solvent enabled porous, elliptical nanofibers to emerge. • Bifunctional Ga doping: Ga dopants enhanced sensing performance via conductivity improvement and grain growth inhibition. • Functionalization of Pt catalysts : Spill-over effects and chemical sensitization of remarkably improved C 2 H 2 sensitivity. Herein, we demonstrate a sensitization strategy via solid-solution doping and catalytic metal nanoparticles (NPs) onto porous metal oxide nanofibers (NFs) for superior acetylene (C 2 H 2) sensing capabilities. The introduction of dopants and catalysts not only increases the inherent reactivity of metal oxides, but also induces the spillover of C 2 H 2 onto metal oxides, significantly improving the sensing properties. We elucidate that the high porosity of the metal oxide NFs, prepared by electrospinning and utilizing saponin as a sacrificial template, is the key to achieving high gas permeability and numerous active sites. Consequently, Ga-doped ZnO porous NFs functionalized with Pt catalysts exhibited the highest C 2 H 2 sensing responses among the current state-of-the-art C 2 H 2 sensors (R a /R g = 26.2 at 400 °C) with a fast response time (10.2 s), at a particularly low concentration of 5 ppm. Moreover, these NFs showed excellent selectivity against the interfering gas (H 2 , C 7 H 8 , CO, CH 4 , C 8 H 10 , CH 3 COCH 3 , HCHO and C 2 H 5 OH) and outstanding stability up to 20 sensing cycles to 0.4 ppm of C 2 H 2. These results provide an efficient strategy to tailor composites of metal oxide nanostructures, dopants, and catalysts for highly sensitive gas sensors. [ABSTRACT FROM AUTHOR]