1：Experimental Design and Method Selection:

The study synthesized three types of TiO2 nanostructures (hollow ball-like, nanosphere, nanoflower) using MOF-derived, hydrothermal, and solvothermal methods, respectively. These were coated on QCM sensors via spray method to compare humidity sensing performance. Theoretical models include the Sauerbrey equation for mass calculation and Langmuir adsorption model for kinetics analysis.

2：Sample Selection and Data Sources:

TiO2 samples were synthesized from chemical reagents (e.g., titanium sulfate, urea, tetrabutyl titanate) provided by Sinopharm Chemical Reagent Co. Ltd. Humidity levels were generated using saturated salt solutions (e.g., LiCl, NaCl) at specific RH values.

3：List of Experimental Equipment and Materials:

Equipment includes X-ray diffractometry (Rigaku D/Max 2500PC), specific surface area analyzer (Micromeritics ASAP 2020 M), scanning electron microscopy (Hitachi S-4800), water contact angle analyzer (SL200B), QCM chips (8 MHz AT-cut from Wuhan Hitrusty Electronics Co. Ltd), airbrush (Holder 180 from Taiwan HD Corp.), oscillator circuit, data logger (Agilent 34970A), impedance analyzer (HP 4194A). Materials include various chemicals for synthesis and desiccants like P2O

4：Experimental Procedures and Operational Workflow:

Synthesis of TiO2 nanostructures followed specific routes (e.g., calcination at 450°C for hollow ball-like TiO2). QCM sensors were prepared by spraying TiO2 suspensions, drying, and testing in a humidity chamber with controlled RH levels. Frequency shifts were measured, and admittance spectra were analyzed.

5：2). QCM sensors were prepared by spraying TiO2 suspensions, drying, and testing in a humidity chamber with controlled RH levels. Frequency shifts were measured, and admittance spectra were analyzed. Data Analysis Methods:

5. Data Analysis Methods: Data were analyzed using regression for sensitivity calculation, Langmuir model fitting for adsorption kinetics, and statistical comparison of sensor performance.