Comparative N₂ Fixation Performance of Diverse Micro- and Nanosized 2D Materials Measured by Gas Chromatography

Abstract

The photocatalytic conversion of N2 to NH3 using 2D materials has been extensively studied owing to its high conversion efficiency. N2 fixation is the first and rate-determining step, which depends on the active site of the materials. Building upon our previous work on GC-based N2 fixation analysis, this study presents a systematic comparative investigation of multiple 2D materials, providing direct experimental insight into N2 adsorption behaviour. The nanosized and microsized 2D materials were synthesized, characterized, and investigated for their N2 fixation performance using gas chromatography. The nanosized materials fabricated through extensive sonication exhibited notably enhanced performance. In particular, nanosized gC3N4 containing N2 vacancies showed the highest N2 fixation performance, yielding approximately 0.320 µg h-1 mgcat-1 in the pure N2 purging condition and approximately 0.065 µg h-1 mgcat-1 in the air purging condition. The nanosized Ti3C2 MXene and Bi2O3 displayed N2 fixation capabilities of approximately 0.287 µg h-1 mgcat-1 and 0.277 µg h-1 mgcat-1 in the pure N2 purging condition and approximately 0.095 µg h-1 mgcat-1 and 0.102 µg h-1 mgcat-1 in the air purging, respectively, likely attributable to the existence of oxygen vacancies, which serve as active sites during the process. Overall, these findings highlight the excellent performance of nanosized gC3N4 2D catalysts in N₂ fixation, but under air-purging conditions, Ti3C2 MXene and Bi2O3 showed higher performance. Higher performance in air will be more desirable for practical applications.