Recently, transitional metal dichalcogenides quantum dots have attracted much interest as a potential candidate for the application of fluorescent materials. However, little work has been done on tuning their band gap by varying functional groups. Here, we report a band-gap tunability of 1 eV in the MoS2 quantum dots (QDs) modified by different functional groups. In our results, it has also been confirmed that a tunable band gap in the MoS2 QDs can be achieved by monotonically varying the concentration of a functional group. A mechanism has also been proposed to explain the enhanced photoluminescence behaviors in the functionalized MoS2 QDs. Our work provides a general guideline to develop other semiconducting QDs to be future impressive fluorescent materials. (C) 2017 Elsevier Inc. All rights reserved.