Life Cycle Analysis of the Synthesis and Photocatalytic Application of Non-Metallic Semiconductor Nanosheets for Rhodamine B Removal with an Environmental Sustainability Approach

The proliferation of persistent organic dye contaminants, such as Rhodamine B (RhB), in aquatic environments necessitates the development and rigorous environmental evaluation of sustainable wastewater treatment technologies. Visible-light-driven photocatalysis using advanced semiconductor materials has emerged as a promising, green, and energy-efficient solution, offering complete degradation of pollutants into harmless minerals, unlike conventional methods that often merely transfer pollution. Graphitic carbon nitride nanosheets (g-C₃N₄), a metal-free, visible-light-active photocatalyst, has garnered considerable attention for its high thermal stability, scalability, and favorable physicochemical properties. However, the energy-intensive nature of synthesizing nanostructured catalysts demands a quantitative environmental assessment—a Life Cycle Assessment (LCA)—to validate the technology’s true sustainability beyond functional performance metrics. Addressing this critical gap, this study conducted a comprehensive LCA, adhering to ISO 14040/14044 standards, to quantify the environmental burdens associated with both the production and the application of g-C₃N₄ in RhB dye degradation. Environmental impacts were assessed using the SimaPro 10.2 software and the globally accepted ReCiPe 2016 method at both the Midpoint (e.g., Global Warming, Water Use) and aggregated Endpoint levels (Human Health, Ecosystems, and Resources). The LCA results revealed a fundamental structural challenge: In the catalyst synthesis phase, electrical energy consumption was identified as the single, dominant environmental hotspot, contributing over 97% across all 22 Midpoint impact categories and approximately 97.5% to 99.8% across the Endpoint damage categories. This high dominance was directly attributed to the severe reliance of the high-temperature calcination process on the region's carbon-intensive, fossil fuel-based electricity grid. Conversely, the contributions from precursor materials (melamine and nitrogen) were consistently negligible, registering below 3%. In the photocatalytic application phase (wastewater treatment), the structure of the hotspot fundamentally shifted: the overall environmental cost was predominantly carried by the embedded environmental cost within the g-C₃N₄ catalyst itself. The catalyst's embodied burden accounted for approximately 78% of the total damage across all three Endpoint categories (Resources, Human Health, and Ecosystems). The operational electricity required for the visible-light reaction became a secondary contributor, accounting for less than 23% of the total burden. This finding conclusively demonstrated that the main environmental impact of the overall treatment process stemmed not from the operation, but from the initial, heavy "environmental investment" required for the high-carbon synthesis of the catalyst. To mitigate this structural challenge, a sensitivity analysis simulating a 95% reduction in electricity consumption during the g-C₃N₄ synthesis phase was performed. The results validated the direct relationship between the catalyst's embodied burden and the carbon intensity of its production: the catalyst’s contribution to final Endpoint damages plummeted by over 92%, dropping to less than 6% across all damage categories. With the structural burden of the catalyst neutralized, the operational electricity consumption for the treatment process became the new dominant hotspot, contributing over 90% of the remaining impacts. In conclusion, this LCA study provides a critical, quantitative assessment revealing that the environmental sustainability of non-metallic semiconductor nanosheet photocatalytic technology is inextricably linked to the decarbonization of the synthesis process through the adoption of low-carbon electricity, and the maximization of the catalyst's operational lifespan and recoverability to distribute the high embodied environmental cost. This strategy is crucial for the technology to fulfill its potential as a truly green and sustainable solution for advanced wastewater treatment.