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

Photocatalytic Removal of Microbiological Consortium and Organic Matter in Greywater

This study aimed to investigate TiO2 photocatalytic degradation of synthetically-prepared greywater samples with differing compositional contents of organic matter (OM), anion concentration, and microbiological consortium. Treatment efficiency was followed through removal of organic matter content in terms of dissolved organic carbon (DOC), specific spectroscopic parameters, and bacterial inactivation. Photocatalytic degradation kinetics were expressed by pseudo first-order kinetic modeling. The best DOC removal rates were attained for greywater samples containing OM with lower molecular size fractions. In addition, either enhancing or reducing the effect of common anions as radical scavengers were observed depending on the composition and concentration of variables in the greywater matrix. Moreover, possibility of a photocatalytic disinfection process was found to be of a bacteria type specific in OM-loaded synthetic greywater samples. Photocatalytic destruction of fecal streptococci required longer irradiation periods under all conditions. Bacterial removal rates were found to be in the order of total coliform &gt; fecal coliform &gt; fecal streptococci, for low organic load greywater, and fecal coliform &gt; total coliform &gt; fecal streptococci, for high organic load greywater

Response surface methodological approach for the assessment of the photocatalytic degradation of NOM

In this paper, statistics-based experimental design with response surface methodology (RSM) was employed to investigate the effects of operational conditions on the photocatalytic oxidation of humic acid as a model compound of natural organic matter. Considering the vast number of the obtained experimental data, in this study, a correlative approach was employed for the assessment of the photocatalytic degradation efficiency of humic acids (HA) using an empirical method for the optimization of the key parameters such as photocatalyst dose, pH and humic acid concentration. The results of this study revealed that the regression analysis showed a close fit (R-2 > 0.83) between the experimental results and the model predictions. Maximum DOC removal was achieved as 89.3% under the experimental conditions of 30 mg/L humic acid, 2.0 mg/mLTiO(2) and pH = 7. Under acidic conditions (pH = 5), and in the presence of 1.0 mg/mLTiO(2) almost complete removal of UV absorbing centers were attained for 30 mg/L humic acid. Exhaustive decolorization was attained under alkaline conditions (pH = 8), for the photocatalyst loading of 1.5 mg/mLTiO(2) for 18.5 mg/L humic acid. The role of the irradiation period on the removal efficiency of the specified parameters were expressed by the relation between the predicted values attained for irradiation periods (40 min and 60 min) that were presented by the correlation coefficients as R-2 = 0.847, 0.691 and 0.700 for DOC. UV254 and Color(436) respectively. Moreover, model verification was also reported for a selected humic acid substrate and a specified photocatalyst specimen. (C) 2011 Elsevier B.V. All rights reserved

An integrated chemical and ecotoxicological assessment for the photocatalytic degradation of vancomycin

The photocatalytic degradation of an antibiotic, vancomycin B hydrochloride (VAN-B), has been investigated in aqueous suspensions of titanium dioxide (TiO2) by monitoring the change in its concentration as well as the production of ammonia and chlorides as a function of irradiation time. The removal of 50 mg L-1 VAN-B solution yields maximum concentrations of 2.45 and 2.53 mg N-NH3 L-1 after 120 min of photocatalytic oxidation using 0.1 and 0.2 g TiO2 L-1, respectively. When 0.2 g TiO2 L-1 were applied up to 87% of the stoichiometric amount of chloride was reached within 120 min of irradiation, corresponding to 0.087 mmol L-1.A set of bioassays (Daphnia magna, Pseudokirchneriella subcapitata and Ceriodaphnia dubia) was performed to evaluate the potential detoxification of VAN-B and its by-products of oxidation under chronic and acute tests. The toxicity of the treated VAN-B samples varied during the oxidation, due to the formation of some intermediate products more toxic than VAN-B. Despite almost total removal of VAN-B that was achieved within 120 min of irradiation, a significant increase in toxicity was observed in chronic tests proving that the chronic assays are more appropriate than acute ones to detect the impact of by-products formed during the photocatalytic degradation o

Enhanced ozonation of selected pharmaceutical compounds by sonolysis

In search of new options to achieve removal of pharmaceuticals in the environment, combined ultrasound and ozonation has become a focus of intense investigation for wastewater treatment. In this study, three pharmaceuticals were selected as model compounds for degradation experiments: diclofenac (DCF), sulfamethoxazole (SMX) and carbamazepine (CBZ). Comparison of the degradation rates for both ozonation and combined ultrasound/ozonation treatments was performed on single synthetic solutions as well as on a mixture of the selected pharmaceuticals, under different experimental conditions. For single synthetic solutions, the efficiency removal for ozonation reached 73%, 51% and 59% after 40 min for DCF, SMX and CBZ, respectively. Comparable results were obtained for pharmaceuticals in mixture. However, the combined ultrasound/ozone treatment was found to increase degradation efficiencies for both DCF and SMX single solutions up to 94% and 61%, respectively, whereas lower removal yields, up to 56%, was noted for CBZ. Likewise, when the combined treatment was applied to the mixture, relatively low removal efficiencies was found for CBZ (44%) and 90% degradation yield was achieved for DCF

Photocatalytic Bactericidal Performance of LaFeO3 under Solar Light: Kinetics, Spectroscopic and Mechanistic Evaluation

Lanthanum orthoferrites are a versatile class of catalysts. Here, the photocatalytic bactericidal performance of LaFeO3 (LF) to inactivate pathogenic microorganisms, i.e., Escherichia coli (E. coli), in water under simulated solar irradiation conditions was investigated. Various competing and contributing factors were covered to visualize the reaction medium consisting of E. coli K12 cells, organic sub-fractions formed by cell destruction, and LF surface. LF solar photocatalytic inactivation (SPCI) kinetics revealed the highest inactivation rate in ultrapure water as expected, followed by distilled water (DW), aqueous solution containing anions and cations (WM) and saline solution (SS). Characterization of the released organic matter was achieved by UV-vis and fluorescence spectroscopic techniques as well as organic carbon contents (DOC). Upon SPCI, significant amounts of K+ along with released protein contents were detected expressing cell wall destruction and lysis. Under the specified experimental conditions, in the presence of released intracellular organic and inorganic components via cell lysis, a significant count of E. coli was still present in SS, whereas almost all bacteria were removed in other matrices due to various challenging reasons. Based on the presented data, SPCI of E. coli using LF as a novel photocatalyst was successfully demonstrated as an alternative and promising method for disinfection purposes