In this work, we studied photocatalytic and thermolytic “attenuation-degradation” mechanisms of 1H, 1H, 2H, 2H - perfluorooctyltrichlorosilane (FOTS-SAM) coated titanium dioxide nanoparticles (TiO2-NPs). During thermolytic analysis, FOTS-SAM on TiO2-NPs was very stable up to 300 °C and further increase of temperature to 450 °C caused conformational disorders and the disorders increased up to 550 °C and complete degradation and desorption of FOTS-SAM from TiO2-NPs occurred above 550 °C. During photocatalytic analysis, FOTS-SAM on TiO2-NPs was stable up to 3 hrs and further UV exposure caused increase of conformational disorders up to 12 hrs and after 15 hrs complete degradation and desorption of FOTS-SAM from the TiO2-NPs. It is observed that FOTS-SAM surface modification (i) passivates TiO2-NPs (ii) increases band gap from 3.2 eV to 5.7 eV and (iii) attenuates UV induced electron-hole pair (e−, h+) generation. Further observed that the FOTS-SAM-TiO2-NPs were superhydrophobic but under long UV exposure and high temperature they became hydrophilic. PLLA-nanocomposites filled with FOTS-SAM-TiO2-NPs show excellent mechanical properties and stability compared to PLLA-nanocomposites filled with uncoated TiO2-NPs. Experimental investigations confirm that FOTS-SAM on TiO2-NPs acts as photocatalytic and thermolytic attenuation layer, super hydrophobic layer and enhances stability and mechanical properties of nanocomposites. © 2021 Elsevier B.V.