Design and Optimization of a Photocatalytic Air Purifier for Low-Concentration H₂S Removal under Indoor Air Recirculation Conditions

Indoor air pollution in confined spaces poses persistent risks to public health, especially from malodorous and toxic sulfur pollutants such as hydrogen sulfide (H₂S). This study develops a systematic design-and-operation optimization strategy for a photocatalytic air purifier targeting low-concentration H₂S removal in a sealed 3 m³ chamber. Experimental tests and computational fluid dynamics (CFD) simulations were combined to quantify the effects of airflow rate and relative humidity, and to establish a Langmuir–Hinshelwood-based transient degradation model under indoor air recirculation conditions. The removal performance first increased and then decreased as the airflow rate rose from 30 to 90 m 3 h -1 , with the best performance at 60 m 3 h -1 , while increasing relative humidity (30–80%) consistently suppressed H₂S removal. Model predictions agreed well with experimental data, with a maximum deviation of 3.34% for H₂S degradation from 3 ppm to 0.1 ppm. Parametric analysis identified a staggered straight-plate configuration (40 pores, 4 cm spacing) achieving the target concentration within 150 min. A folded-plate design further reduced this time to 130 min. Coupled orthogonal optimization yielded optimal conditions of 70 m 3 h -1 airflow, 6 cm spacing, and 40 pores, which shortened the degradation time to 120 min with a single-pass removal efficiency of 6.12%. The findings clarify the coupled effects of operating and structural parameters and provide guidance for low-concentration H₂S control under indoor air recirculation conditions.