Vol:.(1234567890) Environmental Science and Pollution Research (2023) 30:85626–85638 https://doi.org/10.1007/s11356-023-28385-0 1 3 RESEARCH ARTICLE Photocatalytic performance of PANI modifed TiO 2 : Degradation of refractory organic matter Ceyda S. Uyguner‑Demirel 1  · Nazli Turkten 2  · Yunus Karatas 2  · Miray Bekbolet 1 Received: 16 April 2023 / Accepted: 18 June 2023 / Published online: 30 June 2023 © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2023 Abstract Surface modification of TiO 2 with polyaniline (PANI) conducting polymer has been used to achieve visible light photoresponse, thereby increasing solar photocatalytic activity. In this study, photocatalytic performances of PANI-TiO 2 composites with diferent mole ratios were synthesized by the in situ chemical oxidation polymerization method and tested for the degradation of a model refractory organic matter (RfOM), namely humic acid in an aqueous medium under simulated solar irradiation in a comparative manner. Adsorptive interactions under dark conditions and interactions under irradiation were investigated as contributing factors to photocatalysis. Degradation of RfOM was monitored in terms of UV–vis parameters (Color 436 , UV 365 , UV 280 , and UV 254 ) and fuorescence spectroscopic parameters as well as the mineralization extent by dissolved organic carbon contents. The presence of PANI exerted an enhancement in photocatalytic degradation efciency compared to pristine TiO 2 . The synergistic efect was more pronounced in lower PANI ratios whereas higher PANI ratios refected a retardation efect. Degradation kinetics were assessed by pseudo-frst-order kinetic model. For all UV–vis parameters analyzed, highest and lowest rate constants (k) were attained in the presence of PT-14 (2.093 × 10 −2 to 2.750 × 10 −2  min −1 ) and PT-81 (5.47 × 10 −3 to 8.52 × 10 −3  min −1 ), respectively. Variations in selected absorbance quotients, i.e., A 254 /A 436 , A 280 /A 436 , and A 253 /A 203 , were distinctive and compared with respect to irradiation time and photocatalyst type. Upon use of PT-14, a steady decreasing profle with respect to irradiation time was attained for A 253 /A 203 quotient as 0.76–0.61, followed by a rapid decrease to 0.19 in 120 min. The incorporation efect of PANI into TiO 2 composite could be visualized in A 280 /A 365 and A 254 /A 365 quotients exhibiting an almost constant and parallel trend. As a general trend, decrease in the major fuorophoric intensity FI syn,470 with photocatalysis was observed under extended irradiation conditions; however, an abrupt decline was remarkable in the presence of PT-14 and PT-18. Fluorescence intensity decrease correlated well with spectroscopic evaluation of rate constants. A thorough evaluation of spectroscopic parameters of UV–vis and fuorescence can provide signifcant information for practical applications in control of RfOM in water treatment. Keywords Degradation kinetics · Photocatalysis · PANI-TiO 2 composite · Refractory organic matter Introduction Due to the continuous release of contaminants into the environment, the application of photocatalysis as an alternative advanced oxidation treatment process is attracting the focus of researchers. As presented for decades, TiO 2 is the most extensively used photocatalyst exhibiting excellent photocatalytic activity, stability, and a band gap energy (E bg = 3.2 eV) coinciding with UVA region of solar spectrum (Parrino and Palmisano 2021). To overcome the disadvantages of n-type semiconductors expressing large band gaps, coupling with conducting polymers (CPs) that exhibit small bandgaps and extended π–e − systems drew current interest. With respect to attained beneficial effect via “sensitization,” coupling of p-type conducting polymers with an n-type semiconductor is regarded as a new area of research. Polyaniline (PANI), primarily composed of benzenoid and quinoid structures, is the most widely studied CP. The combination of PANI (p-type CP) with Responsible Editor: George Z. Kyzas * Ceyda S. Uyguner-Demirel uygunerc@boun.edu.tr 1 Institute of Environmental Sciences, Bogazici University, Bebek, Istanbul  34342, Turkey 2 Department of Chemistry, Faculty of Arts and Sciences, Kirsehir Ahi Evran University, Kirsehir 40100, Turkey