Preparation of PANI modified TiO2 and characterization under pre- and post- photocatalytic conditions

Polyaniline (PANI) is a promising conducting polymer for surface modification of TiO2 to overcome limitations of the use of visible light and attain increased photocatalytic efficiency for the removal of organic contaminants. In this study, a series of polyaniline modified TiO2 (PANI-TiO2) composites were prepared by using "in-situ" chemical oxidation polymerization method. The composites were systematically characterized by Fourier transform infrared spectroscopy (equipped with an attenuated total reflection accessory, FTIR-ATR), Raman spectroscopy, X-ray diffractometry (XRD), scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDAX), X-ray photoelectron spectroscopy (XPS), ultraviolet–visible diffuse reflectance spectroscopy (UV-DRS), photoluminescence spectroscopy (PL), nitrogen (N2) physisorption (Brunauer − Emmett − Teller surface area (SBET) and Barrett-Joyner-Halenda (BJH) pore size analysis), thermogravimetry-derivative thermogravimetry (TG-DTG) techniques. XRD patterns of PANI-TiO2 composites confirmed both the amorphous phase of PANI and the crystalline character of TiO2. TG/DTG analysis complemented the XRD profiles that the interactions between PANI and TiO2 resulted in a more stable PANI-TiO2 matrix. SEM images displayed the dominant morphology as dandelion-like shapes of PANI being more pronounced with increasing PANI ratios in PANI-TiO2 composites. UV-DRS profiles revealed that the band gap energies of the composites were lower than bare TiO2 expressing a shift to the visible light region. Both PL and UV-DRS analyses confirmed the band-gap reduction phenomenon of PANI modification of TiO2. The incorporation of PANI into TiO2 resulted in a reduction of the surface area of TiO2. The composites were subsequently subjected to photocatalytic activity assessment tests using humic acid (HA) as a model of refractory organic matter (RfOM) under simulated solar irradiation (Uyguner-Demirel et al. Environ Sci Pollut Res 30 85626-85638, 2023). The morphological and structural changes attained upon application of photocatalysis were also evaluated by FTIR-ATR, Raman spectroscopy, XRD, and SEM-EDAX methods in a comparable manner. The FTIR-ATR spectral features of PANI, RfOM and all composites displayed peaks with slight shifts under pre- and post- photocatalytic conditions as well as following dark surface interactions. Besides exhibiting noticeable photocatalytic performance, PANI-TiO2 composites were also proven to maintain stability under non-selective oxidation conditions in the presence of a complex organic matrix. The prepared PANI-TiO2 composites overcoming the limitations of UVA light active bare TiO2 photocatalysis could possibly find a beneficial use as potential catalysts in solar photocatalytic applications. © 2023, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature

Effect of oxidative and non-oxidative conditions on molecular size fractionation of humic acids: TiO2 and Cu-doped TiO2 photocatalysis

Natural waters contain some carbonaceous materials referred to as dissolved organic matter, which is mainly composed of humic acids (HA). Owing to its polydispersed character related to the presence of diverse molecular size fractions (< 450 kDa to even < 1 kDa), HA displays curious reactivity in natural waters and during water treatment train. In this study, a system-based stepwise approach was tracked by characterizing HA following photolysis, adsorptive interactions, and solar photocatalysis using bare TiO2, sol-gel prepared TiO2, and their respective Cu-doped specimens complementary to kinetic evaluation on this respect. For this purpose, prior to and following each treatment, HA was monitored by dissolved organic carbon content, UV-vis parameters, and fluorescence features. Attenuated total reflection Fourier transform infrared (FTIR), surface-enhanced Raman scattering spectroscopy (SERS), XRD, SEM, EDAX XPS, and DRS were used to characterize the materials and solutions reported in this study. Most significant quantitative variations were attained in UV-vis spectroscopic parameters along with fluorescence characteristics; however, infrared and Raman profiles displayed slight deviations in qualitative measures. Differentiation between the selected photocatalyst specimens could be visualized through molecular size effects pointing out the significance of HA 10 kDa fraction. For the first time, this study reports the degradation of specific fractions of HA as a function of their molecular size fraction. Cu-TiO2 seems to photocatalyze more effectively the degradation of the diverse HA fractions due to their more extended absorption of solar light by this photocatalyst