The　fluorescent　emission　wavelengths　of　nanostructures　derived　from　bulk　graphitic　carbon　nitride　were　commonly　lower　than　those　of　their　bulk　due　to　the　quantum　confinement　effect,　which　are　disadvantageous　for　bioimaging　and　sensing　applications.　Herein,　a　new　strategy　to　engineer　graphitic　carbon　nitride　nanomaterials　with　tunable　fluorescent　wavelength　and　intensity　was　proposed　via　thermal　treatment　of　bulk　graphitic　carbon　nitride　at　high　temperature　and　then　hydrolysis　in　alkali　solution.　Highly　fluorescent　g-C3N4　nanobelts　with　emission　peak　at　494　nm,　19　nm　higher　than　that　of　bulk　graphitic　carbon　nitride　and　23.6%　quantum　yield　were　successfully　obtained　by　controlling　the　heating　temperature　at　750　°C　for　2　h　and　the　hydrolysis　in　4　mol　L−1　NaOH　solution　for　8　h.　Finally,　a　home-made　portable　gas　sensor　for　reversibly　sensing　of　toxic　NO2　gas　at　room　temperature　was　designed　by　utilizing　graphitic　carbon　nitride　nanobelts　as　the　fluorescent　nanoprobe,　which　can　overcome　the　disadvantages　of　high　operation　temperature　or　the　interference　of　humidity　resulting　from　the　common　chemiresistive　sensors.　©　2021　Elsevier　B.V.