Preparation and characterization of alternative porous materials for hydrogen storage

This thesis presents an investigation into the hydrogen storage properties of three distinct porous materials: clinoptilolite (CLN) and its cation-exchanged forms, ZIF-8 (a zeolitic imidazolate framework) and porous silicon nanowires (SiNWs). The Na⁺, K⁺, Li⁺, Ag⁺, Ni²⁺, Ca²⁺, Cu²⁺, and Mg²⁺ cation exchange procedure was applied to the H⁺ form of CLN, which was obtained by contacting 1.0 M NH₄NO₃ solution at 80 °C, followed by calcination at 450 °C. The synthesis of ZIF-8 and its in situ modified forms with Li+ and Na+ cations was accomplished via the solvo-thermal method. The two-step MACE procedure was used to synthesise Au and Li-doped porous Si nanowires. The characterization of the CLN and ZIF-8 samples was performed using XRD, XRF, SEM, FT-IR, and N2 adsorption at 77 K. The SiNW samples were characterized by means of SEM, EDS, and N2 adsorption at 77 K. The hydrogen adsorption isotherms of all samples were obtained at temperatures 77 K up to a pressure of 113 kPa. Among all CLN samples, the sample modified with 0.5 M LiNO3 was found to have the highest H₂ storage capacity of 3.458 mmol g⁻¹. By contrast, in situ modification with LiNO3 did not result in any noticeable improvement to the BET surface area or H2 storage performance of ZIF-8 samples. The H2 adsorption capacities of the porous SiNWs were found to be the lowest among all the samples examined.