<jats:p>The crude extract of cinnamon (after abbreviated as KM) was used to produce silver nanoparticles (AgKM). This was subsequently utilized for the hydrothermal production of a composite consisting of AgKM decorated on zinc oxide (AgKM/ZnO) as a photocatalyst for reducing hexavalent chromium (Cr(VI)). Several methods e.g., XRD, SEM, TEM, XPS, PL, and RDB-PAS were used to analyze the optical and physicochemical properties of ZnO/AgKM samples in order to better comprehend the impact of the development of the AgKM-ZnO heterojunction in comparison to pure ZnO. In 60 min, the optimized ZnO/AgKM reduced Cr(VI) by more than 98%, with a rate constant 63 times faster than that of pure ZnO. The enhancement of the separation and transportation of photogenerated electron-hole pairs, as proven by a decrease in photoluminescence intensity when compared with ZnO, was attributed to the composite’s higher Cr(VI) reduction rate. Also, the formation of a new electronic level was created when AgKM are loaded on the surface of ZnO in the composites, as shown by the energy-resolved distribution of the electron trap (ERDT) pattern resulting to enhancement of light absorption ability by narrowing the energy band gap. Thus, ZnO/AgKM composite’s photocatalytic efficacy was enhanced by its narrow energy band gap and reduced charge recombination. Therefore, the newly produced ZnO/AgKM composite can be used as a photocatalyst to purify Cr(VI)-containing wastewater.</jats:p>