Sustainable Upcycling of Steel Waste into High-Performance LaFeO3±δ Perovskite Gas Sensors

The steel industry generates large quantities of waste, including mill scale and hot-rolled steel sludge. These by-products pose serious environmental and economic challenges. This study proposes a sustainable strategy to convert them into LaFeO3±δ-based perovskite materials for gas sensing applications. Iron oxide precursors were recovered, purified, and processed via mechanochemical milling followed by calcination at 1200 °C to produce LaFeO3±δ powders. Among all synthesized materials, the hot-rolled steel waste-derived material (LFO-HRSW) exhibited the best performance. SEM analysis revealed the smallest grain size (0.31 µm) and pore diameter (0.36 µm), which enhanced surface area and gas interaction. When exposed to combustion gases at 200 °C, its electrical resistivity increased from 19.56 Ω·m in air to 32.02 Ω·m, yielding a high sensor signal of 1.64. LFO-HRSW also responded the fastest, stabilizing within 2 min of gas exposure. These results highlight its superior sensitivity and real-time detection capability. This work is the first to directly transform mill scale and hot-rolled steel wastes into LaFeO3±δ perovskites for gas sensing applications. It offers a low-cost route to high-performance sensors, supports a circular economy approach for steel waste utilization, and provides potential benefits for environmental monitoring and industrial emission control.