Sequestration of Sulphide from Biogas by thermal-treated iron nanoparticles synthesized using tea polyphenols.

Dark tea-iron nanoparticles (DT-Fe NPs) were prepared using extracts of dark tea leaves as a reducing agent, and further underwent thermal treatment in air. The H2S removal performances of thermal-treated DT-Fe NPs for biogas were further evaluated using a custom-designed fixed-bed reactor (reaction temperature of 250°C, H2S content of 1%). Significant morphology and chemical composition differences were observed when DT-Fe NPs were treated at different temperatures (300-800oC). X-ray diffractometer analysis revealed that a phase transition from γ-Fe2O3 to α-Fe2O3 occurred under heat treatment. When the thermal treatment temperature was 300°C, only α-Fe2O3 was detected. Both α-Fe2O3 and γ-Fe2O3 were present in the sample treated at 400°C. When the thermal treatment temperature was 500-800°C, γ-Fe2O3 in the sample was completely converted to α-Fe2O3. The H2S removal capacity is 14.72 mg H2S/g for DT-Fe NPs without treatment. However, the value increased significantly to 408.30 mg H2S/g after 400°C thermal treatment, which can be explained by the formation of highly active γ-Fe2O3. The reaction product of thermal-treated DT-Fe NPs at 400°C and H2S were further characterized by X-ray diffractometer and X-ray photoelectron spectroscopy. The results showed that it is composed of FeS2 and FeS, in which 72.6% of the sulphur existed as disulphide and 27.4% as monosulphide.