Balancing functional properties and environmental impact of graphitic carbon nitride: a case study on boron doping syntheses

Abstract

Graphitic carbon nitride (g-CN) possesses properties that make it suitable for various applications, including photocatalysis, carbon dioxide reduction, sensing, water-splitting, and nitrogen fixation. To overcome performance limitations arising from limited visible-light absorption and rapid recombination of photo-induced charge carriers, we employ heteroatom doping in a minimally impactful manner. Boron as a dopant is chosen due to its electron deficiency compared to carbon and nitrogen, enabling the replacement of either element in the g-CN backbone and influencing the optical properties of boron-doped carbon nitride (BCN). Our investigation reveals that the replacement of carbon atoms by boron within the g-CN framework influences the BCN's optical bandgap, 1.67 eV to 2.52 eV, and effectively modulates electron–hole recombination. Further, using different synthesis approaches and boron precursors results in vastly different material morphology. The boron-doping-induced structural defects lead to bandgap energy reduction. However, we find that this reduction does not correlate with the suppression of electron–hole recombination. In addition to studying physicochemical properties that underline BCN functional performance across a wide range of energy and environmental applications, we compare the environmental impacts across the multiple BCN syntheses. This assessment encompasses a comparison across nine TRACI midpoint impact categories, such as global warming potential, human health impacts from carcinogenic and noncarcinogenic substances, and ecotoxicity. Our life cycle impact assessment results demonstrate that electricity is the major contributor to the overall impacts of BCN synthesis, regardless of the synthesis technique used. Further, we propose a MAPS (Material Properties and Sustainability) evaluation approach that simultaneously considers physicochemical properties and sustainability metrics to gain valuable insights into designing minimally impactful, high-performing carbon nitride materials.