A novel SnO2@Cu3(BTC)2 composite was synthesized using a quick and affordable bottom-up approach via impregnation of SnO2 nanoparticles into the porous Cu3(BTC)2 metal-organic framework (MOF). The photocatalytic degradation of the methylene blue (MB) dye has been studied for the first time using this novel recyclable SnO2@Cu3(BTC)2 composite. It was found that SnO2@Cu3(BTC)2 composite photo catalytically degrades methylene blue (MB) dye with a degradation efficiency of 85.12% within 80 min under solar irradiation. The most appropriate benefit of this composite is the easy recyclability up to numerous cycles with retention of its photocatalytic activity. Therefore, this cheaper and greener composite photocatalyst is more suitable for large-scale industrial applications than the traditional photocatalysts employed in the degradation of MB dye. Furthermore, this composite has also been investigated as a fluorescence sensor for the detection of nitroaromatic compounds (NACs). It was observed that the 88.2% quenching of the intense fluorescent signal of this composite happens in the presence of 2,4,6-trinitrophenol (TNP) showing it incredibly selectivity towards TNP with no interference of other NACs. With a detection limit of 2.82 µM, this composite exhibits outstanding sensitivity towards TNP. The Stern-Volmer plot for TNP is linearly fitted displays large quenching coefficient, correlation coefficient, and linear ranges KSV = 1.04x104 M-1, R2 = 0.9901, and 0-10 µM, respectively. This quenching response of this composite towards TNP was well-explained by the two mechanisms: one is photo-induced electron transfer (PET), and the other is fluorescence resonance energy transfer (FRET), in addition to theoretical calculations based on density functional theory (DFT). Our findings imply that the synthetic composite can be used as a superior fluorescence sensor and photocatalyst.