This presentation introduces an integrated photocatalyst/adsorbent system, achieved through immobilization and encapsulation of the TiO2 doped with CQDs (carbon quantum dots) nanocomposite within the calcium alginate (CaAlg) matrix. The nanoparticles and nanocomposites were analyzed using various techniques, including FE-SEM, EDX, TEM, XRD, PL, FT-IR, BET, and UV–vis DRS, to determine their structure and properties. The TiO2/CQDs/Alg nanocomposite hydrogel considerably influenced the adsorption and photocatalytic degradation of methylene blue (MB) as a dye pollutant. The adsorption studies were conducted to assess parameters such as adsorption capacity, kinetic behavior, and adsorption isotherms. The outcomes revealed a high adsorption capacity (44.13mg/g at 90min) and indicated that the pseudo-second-order kinetic model was highly suitable for describing the adsorption behavior of MB. Moreover, the Freundlich isotherm exhibited better fitting capabilities compared to the Langmuir isotherm. CQDs not only facilitated the transfer of photoelectrons from the TiO2 surface, preventing recombination of electron-hole pairs but also enhanced visible light absorption by the upconversion photoluminescence. The TiO2/CQDs/Alg displayed excellent photodegradation performance (97%) of MB compared with TiO2 and TiO2/CQDs under visible light due to the abundance of active sites for MB adsorption and photocatalytic reactions. The TiO2/CQDs/Alg hydrogel exhibited excellent reusability in degrading MB for up to five consecutive cycles and showed significant swelling behavior across a broad pH range, reflecting the hydrogel's exceptional stability. The use of charge carrier scavengers indicated that O2˙−radicals were the primary surface species involved in the photodegradation of MB.