Covalent chemical functionalization of Ti3C2Tx MXene nanosheets with fullerenes C60 and C70 for enhanced nonlinear optical limiting

Abstract

We describe herein a stepwise approach to accomplish the covalent linkage of fullerenes C₆₀ and C₇₀ to few-layer Ti₃C₂T_x MXene, for the first time. The preparation process involves the functionalization of Ti₃C₂T_x with 4-benzaldehyde diazonium salt followed by 1,3-dipolar cycloaddition to the double bonds of C₆₀ and C₇₀ in the presence of aldehyde-decorated nanosheets and excess N-methylglycine. The synthesized nanohybrids, named C₆₀-MXene and C₇₀-MXene, respectively, were comprehensively characterized by crystallographic, spectroscopic, thermal, and electron microscopic means. UV-vis-NIR absorption measurements reveal a decrease in the electron density of the nanosheets upon the incorporation of fullerenes, indicating the occurrence of intercomponent electronic interactions. Z-scan studies demonstrate that C₆₀-MXene and C₇₀-MXene show an excellent nonlinear absorption performance, that is, an enhanced optical limiting (OL) effect compared to their individual components, under the irradiation of both nanosecond (ns) pulses at 532 nm and femtosecond (fs) pulses at 800 nm. The effective electron transfer behavior from Ti₃C₂T_x to the grafted fullerenes under photoexcitation should be responsible for the observed OL enhancement. Our findings showcase that C₆₀-MXene and C₇₀-MXene nanohybrids are promising OL candidates across spectral regions and temporal domains, and that the proposed strategy of interfacing fullerenes with Ti₃C₂T_xvia covalent bonding provides a paradigm for engineering high-performance nonlinear optical (NLO) materials using covalently linked binary nanohybrids based on MXene nanosheets.