Tecnologia Sustentável e Educação Ambiental: Fotocatálise heterogênea com semicondutor PANI/(TiO2)

Abstract

Growing concern about the environmental impacts resulting from the improper disposal of industrial effluents has driven the development of sustainable technologiesfor wastewater treatment. Among these technologies, heterogeneous photocatalysisstands out as an advanced oxidation process based on the activation of semiconductors under UV–Vis irradiation, enabling the degradation of recalcitrant organiccompounds. In this context, this study aimed to develop and evaluate polyaniline(PANI) and titanium dioxide (TiO2) composites for application in the photodegradation of the synthetic dye Ponceau 4R, which is frequently present in effluents fromthe textile, food, and cosmetic industries. In addition, a pedagogical proposal aligned with the Brazilian National Common Core Curriculum (BNCC) and Bloom’s Taxonomy was developed, grounded in guided experimentation, problematization,and the production of educational resources, in order to foster the understandingof scientific concepts and raise awareness of socio-environmental issues. Within thescope of effluent treatment, the TiO2 semiconductor has been widely studied dueto its chemical stability and low cost. Although frequently employed in photocatalytic applications, TiO2 presents limitations related to its low response under visible radiation and the high recombination rate of photogenerated electron–holepairs. These restrictions can be mitigated through material modifications, includingcoupling with other components and adjusting the crystalline phase composition,such as introducing a controlled rutile fraction into a predominantly anatase matrix, which may favor charge separation and migration. From this perspective, the TiO2/PANI composite was proposed, in which PANI, owing to its semiconductingand conductive character, broadens absorption in the visible region and acts asa charge-transport medium, contributing to reduced recombination and enhancedphotocatalytic efficiency. PANI/TiO2 composites were obtained at 1:1, 2:1, and1:2 ratios and characterized by FTIR, XRD, UV–Vis DRS (Tauc plots), TG/DSC, TEM, and Raman. TG/DSC analysis indicated an intense initial mass loss attributed to dehydration and removal of synthesis residues, with a crystallization eventaround 270 ◦C (anatase) and a subtle indication of anatase→rutile transformationnear 450 ◦C (∼ 3%), which may be associated with the photodegradation performance and with the best result observed for the 2:1 (PANI:TiO2) ratio, which stoodout in both characterizations and photocatalytic tests. Structural analyses (XRD) indicated TiO2 predominantly in the anatase phase and, in the composites, revealedchanges in crystallinity and crystallite size consistent with PANI incorporation.Raman spectroscopy corroborated the presence of anatase and indicated interfacialinteraction with PANI. Optical measurements (DRS/Tauc) showed a reduction inthe band gap in the composites relative to pristine TiO2. TEM micrographs revealeddistinct, near-spherical morphologies with good dispersion and homogeneity, andsub-10 nm average diameters. The set of characterizations (XRD, TEM, FTIR,and Raman) evidenced features more favorable to photocatalytic performance forthe 2:1 (PANI:TiO2) ratio. In adsorption and photocatalysis assays with Ponceau4R, this same ratio achieved the highest degradation efficiency (99.73%) and thehighest apparent rate constant (k = 0.05180 min-1). The 1:1 and 1:2 ratios exhibitedsimilar efficiencies (98.30% and 98.35%, respectively), whereas 1:2 provided thebest fit to the pseudo-first-order model (adjusted R2 = 0.9923). As a control, directphotolysis proved poorly effective, confirming the need for the photocatalyst forefficient dye removal. It is concluded that coupling TiO2 with PANI is a promisingstrategy for producing efficient and sustainable photocatalysts, contributing to theadvancement of clean technologies and, simultaneously, supporting an educationalapproach focused on education and sustainability, with an emphasis on investigativeactivities, critical reflection, and the development of didactic support materials.