Mitigation of low methane content landfill gas through visible-near-infrared photocatalysis over Y ₂ O ₃ :Er ³⁺ /Graphene/TiO ₂

Untreated low methane (CH ₄ ) content (less than 10%) landfill gas within the post-methanogenic stage is currently vented into the atmosphere, constituting an important source of anthropogenic greenhouse gas (GHG). Development of a proper mitigation process for low CH ₄ gas is therefore necessary for landfills. In this study a special photocatalyst, Y ₂ O ₃ :Er ³⁺ -TiO ₂ -0.05% graphene (GR), was synthesized by sol-gel method and then characterized; it showed a good response to visible-near-infrared (Vis–NIR) sunlight. The corresponding absorption edge was 354 nm, and upconversion fluorescence peaks of ultraviolet (364 nm) and violet (408 nm) emissions were acquired under 980 nm excitation. Y ₂ O ₃ :Er ³⁺ -TiO ₂ -GR was developed and tested for removal of low CH ₄ landfill gas under Vis–NIR light irradiation, and a maximum photodegradation rate of 45.1% for CH ₄ was obtained using the photocatalyst Y ₂ O ₃ :Er ³⁺ -TiO ₂ -0.05% GR with a light intensity of 2050 mW m ⁻² . The corresponding CH ₄ content decreased from 10% to 5.5%, mitigating almost half of GHG during the post-methanogenic stage. The intermediate products of CH ₄ degradation were CO, ^[rad] OH, O ⁻ , CO ₂ and H ₂ O traced by in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). This research proposes a new approach for reducing the GHG effect of low CH ₄ content landfill gas.