Estudo da aplicabilidade de diferentes semicondutores baseados em ferritas magnéticas na degradação de poluentes emergentes

Abstract

The increase in emerging organic pollutants has grown significantly in recent years, making effective treatment methods increasingly necessary for environmental remediation. One promising alternative is the application of Advanced Oxidation Processes (AOPs), such as heterogeneous photocatalysis, which utilizes materials like semiconductors to enhance the degradation of organic compounds. This study presents the synthesis and characterization of various semiconductors for the degradation of the dye Tartrazine and the pollutant Caffeine, through photocatalytic activity assays. Among the materials investigated were iron-based spinels (NiFe2O4, CuFe2O4, and MnFe2O4), synthesized via the co-precipitation method. Another evaluated semiconductor was graphitic carbon nitride (g-CNx), obtained by thermal condensation. The composition, structure, and morphology of the synthesized materials were analyzed using XRD, FTIR, SEM-FEG, XRF, UV-Vis, and HPLC techniques. The

photocatalysts were applied to the degradation of Tartrazine, while only the heterojunction- based material was used for Caffeine, a widespread contaminant and water quality marker.

Photocatalytic efficiency was assessed by monitoring UV-Vis absorption spectra (λ = 430 nm

for Tartrazine and λ = 260 nm), with complementary caffeine analysis performed by high- performance liquid chromatography (HPLC) at 273 nm. Among the tested ferrites, nickel ferrite

(NiFe2O4) demonstrated the highest efficiency and was selected for process optimization using a factorial experimental design. Under optimal conditions, Tartrazine degradation reached 95.58% at 430 nm and 89.08% at 260 nm, corresponding to azo and aromatic group degradation, respectively. The g-CNx semiconductor also exhibited high degradation rates. To improve photocatalytic activity, heterojunctions of NiFe2O4/g-CNx and NiFe2O4/biochar were

prepared by electrostatic aggregation and evaluated in different ratios. The 75:25% NiFe2O4/g- CNx heterojunction showed the best performance, achieving 99.65% degradation at 430 nm

and 90.33% at 260 nm in just 30 minutes at pH 6–7. The NiFe2O4/biochar heterojunction also achieved a high contaminant removal rate of approximately 85%. In order to reduce energy consumption and reaction time, different oxidants such as hydrogen peroxide and sodium persulfate were tested in the reaction medium, achieving Tartrazine removal rates of around 99% within 20 minutes. Subsequent studies included reaction kinetics, photolysis, adsorption, and reuse of the semiconductors. Reusability was facilitated by the magnetic properties of nickel ferrite, with high removal rates maintained after four reuse cycles. Moreover, the use of oxidants significantly reduced electrical energy consumption, lowering operational costs. Finally, using a LED light source instead of a mercury vapor lamp yielded comparable degradation efficiency with notably lower energy costs. These findings support the development of more sustainable treatment technologies by integrating energy-efficient approaches and renewable materials for the removal of emerging contaminants.