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Recently, a zipper two-dimensional (2D) material Bi 2 O 2 Se belonging to the layered bismuth oxychalcogenide (Bi 2 O 2 X: X = S, Se, Te) family, has emerged as an alternate candidate to van der Waals 2D materials for high-performance electronic and optoelectronic applications. This hints towards exploring the other members of the Bi 2 O 2 X family for their true potential and bismuth oxysulfide (Bi 2 O 2 S) could be the next member for such applications. Here, we demonstrate for the first time, the scalable room-temperature chemical synthesis and near-infrared (NIR) photodetection of ultrathin Bi 2 O 2 S nanosheets. The thickness of the freestanding nanosheets was around 2–3 nm with a lateral dimension of ∼80–100 nm. A solution-processed NIR photodetector was fabricated from ultrathin Bi 2 O 2 S nanosheets. The photodetector showed high performance, under 785 nm laser illumination, with a photoresponsivity of 4 A W −1 , an external quantum efficiency of 630%, and a normalized photocurrent-to-dark-current ratio of 1.3 × 10 10 per watt with a fast response time of 100 ms. Taken together, the findings suggest that Bi 2 O 2 S nanosheets could be a promising alternative 2D material for next-generation large-area flexible electronic and optoelectronic devices. 

Transition metal carbides (MXenes) are an emerging family of highly conductive two-dimensional materials with additional functional properties introduced by surface terminations. Further modification of the surface terminations makes MXenes even more appealing for practical applications. Herein, we report a facile and environmentally benign synthesis of reduced Ti 3 C 2 T x MXene (r-Ti 3 C 2 T x ) via a simple treatment with l -ascorbic acid at room temperature. r-Ti 3 C 2 T x shows a six-fold increase in electrical conductivity, from 471 ± 49 for regular Ti 3 C 2 T x to 2819 ± 306 S m −1 for the reduced version. Additionally, we show an enhanced oxidation stability of r-Ti 3 C 2 T x as compared to regular Ti 3 C 2 T x . An examination of the surface-enhanced Raman scattering (SERS) activity reveals that the SERS enhancement factor of r-Ti 3 C 2 T x is an order of magnitude higher than that of regular Ti 3 C 2 T x . The improved SERS activity of r-Ti 3 C 2 T x is attributed to the charge transfer interaction between the MXene surface and probe molecules, re-enforced by an increased electronic density of states (DOS) at the Fermi level of r-Ti 3 C 2 T x . The findings of this study suggest that reduced MXene could be a superior choice over regular MXene, especially for the applications that employ high electronic conductivity, such as electrode materials for batteries and supercapacitors, photodetectors, and SERS-based sensors.