## 1 Introduction  
Metal oxides are ionic compounds composed of positive metal and negative oxygen ions. The completely filled s-shell of the metal oxides provides it with adequate thermal and chemical stability, whereas the d-shells may not be fully filled, which renders them with diverse unique properties. Owing to the quantification of state density, the electrical, optical, and chemical properties of high-aspect-ratio nanostructures and various material-dependent work functions can be modulated [1, 2]. Nanostructure-based one-dimensional (1D) metal oxides have gained significant attention in recent years because of their unique electronic, optical, and thermal properties [3, 4]. Moreover, because 1 DSnO2 nanostructures are \(n\)-type semiconductors with a wide band gap (e.g., 3.6 eV at 300 K), they exhibit unique photoelectric properties that offer potential applications of SnO2 in electronic, photoelectric, gas sensing, and energy generation devices. The hydrothermal method is a bottom-up synthetic method that has become the most widely adopted method for preparing nanomaterials because of its facilely applicable procedure, the high crystallinity of the product, convenient control of morphology, and high sintering activity. [PERSON] and [PERSON] [5] adopted the hydrothermal method without exploiting any template or surfactant. They used SnCl4 5H2O as the tin source and added CO(NH2)2 and HCl to ultrapure water, which was insulated at 90 \({}^{\circ}\)C for 24 h in a stainless-steel autoclave lined by polytetrafluoroethylene (PTFE). Ultrathin SnO2 nanorods (SnO2(NR))with a diameter 2.0 \(\pm\) 0.5 nm, a length 12 \(\pm\) 3 nm, and a growth orientation in the [001] direction were obtained. [PERSON] et al. [6] adopted the hydrothermal method to enable hydrothermal growth in a sealed PTFE-lined stainless-steel autoclave for 24 h at 200 \({}^{\circ}\)C. They obtained a rutile-structured SnO\({}_{2}\)(NR) of thickness 100 nm, length 1 mm, and a growth orientation in the [001] direction. In addition, [PERSON] et al. [7] implemented the same experimental conditions and obtained rutile-structured SnO\({}_{2}\)(NR) with 4-15 nm diameter, 100-200 nm length, and (110)-directed growth orientation. [PERSON] et al. [8] implemented the hydrothermal method at 150 \({}^{\circ}\)C to induce hydrothermal growth for 24 h in a sealed PTFE-lined stainless-steel autoclave. They obtained SnO\({}_{2}\)(NR) with 2.5-5 nm diameter, 15-20 nm length, and [001]-directed growth orientation. Thereafter, [PERSON] et al. [9] adopted the sodium dodecyl sulfate-assisted hydrothermal method to prepare nano-polyhedrons that were self-assembled from ultrathin nanowires in a sealed PTFE-lined stainless-steel autoclave at 180 \({}^{\circ}\)C after hydrothermal growth for 24 h. [PERSON] et al. [10] applied the hydrothermal method at 285 \({}^{\circ}\)C to prompt hydrothermal growth for 24 h in a sealed PTFE-lined stainless-steel autoclave; they obtained rutile-structured SnO\({}_{2}\)(NR) with 80 \(\pm\) 5 nm diameter, 2.5 \(\pm\) 0.1 \(\upmu\)m length, and [001]-directed growth orientation. [PERSON] et al. [11] applied the hydrothermal method at 200 \({}^{\circ}\)C for 24 h in a sealed PTFE-lined stainless-steel autoclave to obtain a rutile-structured SnO\({}_{2}\)(NR) with 15 nm diameter and 50 nm length. [PERSON] et al. [12] placed a precursor solution with four pieces of SnO\({}_{2}\) seed (SnO\({}_{2}\) nanoparticles deposited using a spin-coating technique) layer-coated F-doped tin oxide in an autoclave to conduct hydrothermal synthesis at 200 \({}^{\circ}\)C for 18 h. They obtained rutile-structured SnO\({}_{2}\)(NR) with a diameter 85 nm and growth orientation in the [001] direction. [PERSON] et al. [13] implemented the hydrothermal method in an autoclave at 180 \({}^{\circ}\)C for 12 h, after which the SnO\({}_{2}\) precipitate was calcined at 350 \({}^{\circ}\)C for 2 h. They obtained a rutile-structured SnO\({}_{2}\)(NR) with a diameter 250 nm and length 1 \(\upmu\)m. [PERSON] et al.