The photocatalyst produces electron and hole pairs via the absorption of energy from photons. However, in its pristine form, the catalyst exhibits a substantial rate of electron-hole recombination, resulting in a restricted photocatalytic efficiency. The improved photocatalytic activity observed in CuO/ZnFe2O4 NCs can be attributed to a synergistic effect that enhances the separation of photo-generated carriers. This effect is facilitated by the internal electric field, which promotes effective charge separation by facilitating the interaction between electrons in the conduction band of CuO and holes concentrated in the valence band of ZnFe2O4. The decrease in recombination rate prolongs the lifetime of charge carriers. In addition, in proximity to the conduction band edge of ZnFe2O4, oxygen that is dissolved in a solution utilizes available electrons to initiate oxidation reactions, leading to the generation of a significant quantity of superoxide radicals. Additionally, hydroxyl ions and water molecules trap vacancies in the valence band of CuO, leading to the production of hydroxyl radicals via oxidation reactions. The primary reactive species, O2• -, together with additional species, OH • and h + , collectively facilitate the effective degradation of the target pollutant, CR, into smaller intermediate compounds. The D-CNFO@G photocatalyst produces free electrons and holes via an electron transition process upon exposure to light. Superoxide O2• -and hydrogen oxide HO • radicals form because of the interaction between electrons, holes, oxygen molecules, and water on the surface of graphene. RhB may be destroyed via two main mechanisms: direct oxidation by photogenerated holes or by interaction with superoxide or hydroxyl radicals generated by photocatalysts. Azo dyes have aromatic rings that possess an azo bond, which serves as a chromophore. The number of azo bonds may range from one to many. Their aromatic structure provided stability against light and oxidation to these pigments. However, Anthraquinone dyes persist in the effluent for an extended period because they are more resistant to degradation owing to their fused aromatic structure. In addition, the anthraquinone structure has two carbonyl groups, which act as electron acceptors. The degradation of these dyes takes place via the acceptance of electron donors. When light interacts with the surface of the photocatalyst Mg0.6Zn0.2Co0.2Fe2O4, charges are produced. MXene sheets function as acceptors by effectively capturing electrons and enhancing the separation of charge carriers. Electrons reduce adsorbed oxygen (O2) to make superoxide radicals (O2 •-), whereas holes oxidize water molecules to produce hydroxyl radical ions (OH •-). These species engage with the contaminants and decompose them in the catalytic solution, resulting in the production of not harmful degradation byproducts such as water and carbon dioxide. When the dye solution containing the resultant catalysts is exposed to UV irradiation, electron transfer occurs. Electrons (e -) move from the valence band of NZF and CO to the conduction band of NZF and CO, respectively. This transfer results in the generation of positively charged holes (h+). The degradation of the dye is attributed to the generation of electrons (e-) and holes (h+) induced by light. Electrons engage in a reaction with oxygen (O2) to generate superoxide radicals (O2 •-) at a potential of -0.046 electron volts (compared to the conventional hydrogen electrode, NHE). On the other hand, the holes react with water (H2O) to make hydroxyl radicals ( • OH) at a potential of 2.4 electron volts (compared to NHE). The radicals induce the decomposition of the organic pigment into water (H2O) and carbon dioxide (CO2). The probability of superoxide radicals being formed is lower than the conduction band of NZF and CO, whereas the likelihood of hydroxyl radicals being generated is greater than the valence band of CO. The lack of reactivity between the valence band of NZF and H2O, resulting in the absence of hydroxyl radicals, may be ascribed to the high position of the valence band in NZF. Therefore, both categories of radicals may coexist to participate in the photocatalytic process, and the Z-scheme heterojunction system can enhance the interaction between NZF and CO in the presence of UV light. Furthermore, the exceptional ability of MWCNT to transmit charges expeditiously enhances charge transfer and inhibits the recombination of excitons. Barium hexaferrite (BaFe12O19) has a conduction band and valence band between TiO2. TiO2's conduction band is greater than barium hexaferrite's and Pt and Pd's Fermi energy levels. Therefore, two techniques are beneficial: Noble metals and barium hexaferrite promote separation as adsorbents. Light energizes TiO2's valence band VB electrons, which move to the conduction band. Photoexcited electrons travel toward noble metals on titanium oxide and BaFe12O19's conduction band after electron-hole pairs are created. Additionally, the holes created approach the barium hexaferrite valence band. (ii) Noble metals absorb visible light and donate electrons to TiO2 via surface plasmon resonance (SPR). Electrons in the electric current rise. TiO2 and BaFe12O19 may exchange photoexcited electrons. These reactions may separate electrons and holes, causing dyes to degrade by interacting with water and oxygen to create O2 • and hydroxyl radicals. Using the CoFe2O4@UiO-66 photocatalyst and the results and talk previously already had, researchers, have come up with a good reaction route for breaking down MB and MO directly through light. When excited by simulated direct sunshine, UiO-66 and CoFe2O4 create electrons (e -) and holes (h + ) in their conduction band and valence band. The excited electrons may easily flow across the heterojunction interface channels to reach the LUMO of UiO-66 because CoFe2O4 has a higher negative CB potential (-0.56 V) than the LUMO (-0.44 V). This approach effectively blocks photogenerated carrier recombination. The electrons generated by photoinduction at the lowest unoccupied molecular orbital (LUMO) of UiO-66 may combine with dissolved oxygen, forming • O2 -radicals. Light-created gaps would move from UiO-66's valence band (VB) (+3.40 V) to CoFe2O4's (+1.07 V). Photogenerated holes cannot oxidize H2O and form • OH radicals because CoFe2O4 has a lower VB potential (+1.07 V) than -OH/ • OH (1.99 V versus NHE). However, dye molecules deteriorate fast due to their tremendous oxidation capabilities as holes increase. Alternatively, superoxide ( • O2 -) radicals may indirectly form hydroxyl ( • OH) reactive radicals at the photocatalyst's conduction band. 6.5. Heavy metals removal using spinel ferrites: