Design of amine modified polymer dispersants for liquid-phase exfoliation of transition metal dichalcogenide nanosheets and their photodetective nanocomposites

Liquid-phase exfoliation (LPE) of transition metal dichalcogenide (TMD) nanosheets is a facile, cost-effective approach to large-area photoelectric devices including photodetectors and nonvolatile memories. Non-destructive exfoliation of nanosheets using macromolecular dispersing agents is beneficial in rendering the TMD nanocomposite films suitable for mechanically flexible devices. Here, an efficient LPE of molybdenum disulfide (MoS₂) with an amine modified poly(styrene-co-maleic anhydride) co-polymer (AM-PSMA) is demonstrated, wherein the maleic anhydrides were converted into maleic imides with primary amines using N-Boc-(CH₂)_n-NH₂. The exfoliation of nanosheets was facilitated through Lewis acid-base interaction between the primary amine and transition metal. The results demonstrate that the exfoliation depends upon both the fraction of primary amines in the polymer chain and their distance from the polymer backbone. Under optimized conditions of primary amine content and its distance from the backbone, AM-PSMA gave rise to a highly concentrated MoS₂ nanosheet suspension that was stable for over 10 d. Exfoliation of several other TMDs was also achieved using the optimized AM-PSMA, indicating the scope of AM-PSMA applications. Furthermore, a flexible composite film of AM-PSMA and MoS₂ nanosheets fabricated by vacuum-assisted filtration showed excellent photoconductive performances including a high I_on/I_off ratio of 10² and a fast photocurrent switching of 300 ms.