Non-selective oxidation of humic acid in heterogeneous aqueous systems: a comparative investigation on the effect of clay minerals.

Application of photocatalysis for degradation of natural organic matter (NOM) has received wide interest during the last decades. Besides NOM, model compounds more specifically humic acids (HAs) were also studied. As a continuation of the previous research, TiO2 photocatalytic degradation of HA was investigated in the presence of clay minerals, i.e., montmorillonite (Mt) and kaolinite (Kt). Degradation of HA was expressed by the pseudo-first-order kinetic modelling of dissolved organic carbon (DOC) and UV-VIS parameters (Colour436 and UV254). A slight rate enhancement was attained for Colour436 and UV254 in the presence of either Mt or Kt. The presence of clay particles did not significantly change the DOC degradation rate of HA. The effect of ionic strength (Ca2+ loading from 5 x 10(-4) M to 5 x 1(-3) M) was also assessed for the photocatalytic degradation of sole HA and HA in the presence of either Mt or Kt. Following photocatalytic treatment, molecular size distribution profiles of HA were presented. Besides the effective removal of higher molecular size fractions (100 and 30 kDa fractions), transformation to lower molecular size fractions (<3 kDa) was more pronounced for sole HA rather than HA in the presence of clay minerals. Scanning electron microscopic images with the energy dispersive X-ray analysis confirmed the diversities in surface morphologies of the binary and ternary systems composed of HA, TiO2 and Mt or Kt both prior to and following photocatalysis. This study demonstrated that photocatalysis could be applicable for DOC degradation in the presence of clay minerals in natural waters.

An insight into PANI-TiO2 photocatalysis of refractory organic matter through molecular size fractionation.

Refractory organic matter (RfOM) is ubiquitous in aquatic environment and plays various roles in regulating the fate, transport, toxicity, and bioavailability of chemical species, such as metals, emerging organic contaminants, and nanomaterials. RfOM is mainly represented by humic acids (HA) as the acid insoluble fraction of organic matrix. Considering the complex and multicomponent characteristic of HA, a detailed study was designed to elucidate the fate of molecular size fractions (MSFrs) of humic under solar irradiation in the presence of polyaniline (PANI)-modified TiO2 composites. Humic acid as a consortium of diverse molecular size fractions with different tendencies towards oxidation requires further assessment by UV-vis and fluorescence spectroscopic parameters complementary to previous studies on the photocatalytic degradation of RfOM by using TiO2 and PANI-TiO2 composites. Absorbance-based removal efficiencies under initial and post-photocatalytic conditions showed a re-formation trend during photocatalysis in the presence of PANI and TiO2 where higher MSFrs were transformed to lower MSFrs that was apparent for < 3 kDa fraction. Completely different profiles were observed for PT-41 and PT-81 indicating similar degradation pathways independent of PANI ratio in the composite. As confirmed by the investigated parameters, formation of both 450 kDa and 220 kDa MSFrs were evident under all conditions indicating in situ generation of higher MSFrs. The eligibility of coupled absorbance-fluorescence measurements to discern molecular size distribution of humic acid via oxidative degradation was also investigated. Excitation-emission matrix (EEM) contour plots emphasized the ratio dependency of PANI modification of TiO2 and revealed sample specific variations that were more pronounced in terms of the emergence of tyrosine- and tryptophan-like aromatic proteins.

Oxidation of nonylphenol ethoxylates in aqueous solution by UV-C photolysis, H2O2/UV-C, Fenton and photo-Fenton processes: are these processes toxicologically safe?

UV-C, H2O2/UV-C, Fenton and photo-Fenton treatment of a nonylphenol polyethoxylate (NP-10) were comparatively studied, primarily focusing on the acute toxicity of degradation products. Formic, acetic and oxalic acids were all identified as the degradation products of NP-10; however, the sole common carboxylic acid was found to be formic acid for the studied treatment processes. The percent relative inhibition towards Vibrio fischeri increased from 9% to 33% and 24% after 120 min-UV-C and H2O2/UV-C treatment, respectively. Complete NP-10 and 70% of its total organic carbon (TOC) content was removed by the photo-Fenton process, which ensured the fastest removal rates and lowest inhibitory effect (8% after 120 min treatment). The acute toxicity pattern being observed during H2O2/UV-C and photo-Fenton treatment positively correlated with temporal evolution of the identified carboxylic acids, whereas unidentified oxidation products were the most likely origin of the acute toxicity in UV-C photolysis.

Photocatalytic performance of PANI modified TiO2: Degradation of refractory organic matter.

Surface modification of TiO2 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-TiO2 composites with different 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 (Color436, UV365, UV280, and UV254) and fluorescence spectroscopic parameters as well as the mineralization extent by dissolved organic carbon contents. The presence of PANI exerted an enhancement in photocatalytic degradation efficiency compared to pristine TiO2. The synergistic effect was more pronounced in lower PANI ratios whereas higher PANI ratios reflected a retardation effect. Degradation kinetics were assessed by pseudo-first-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., A254/A436, A280/A436, and A253/A203, were distinctive and compared with respect to irradiation time and photocatalyst type. Upon use of PT-14, a steady decreasing profile with respect to irradiation time was attained for A253/A203 quotient as 0.76-0.61, followed by a rapid decrease to 0.19 in 120 min. The incorporation effect of PANI into TiO2 composite could be visualized in A280/A365 and A254/A365 quotients exhibiting an almost constant and parallel trend. As a general trend, decrease in the major fluorophoric intensity FIsyn,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 fluorescence can provide significant information for practical applications in control of RfOM in water treatment.

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.

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.

Copper-doped TiO2 photocatalysts: application to drinking water by humic matter degradation.

The aim of this study was to determine the photocatalytic performance of copper-doped TiO2 (Cu-TiO2) specimens on the degradation of dissolved organic matter (DOM) represented by a model humic acid (HA). TiO2 was synthesized by sol-gel method from an alkoxide precursor. Cu-doped TiO2 specimens containing 0.25 wt% and 0.50 wt% Cu were prepared by wet impregnation method using sol-gel synthesized as well as bare TiO2 P-25 and characterized by XRD, SEM, XPS, Raman spectroscopy, UV-DRS, and BET measurements. Their photocatalytic activities were evaluated with regard to degradation kinetics of HA in terms of UV-vis and fluorescence spectroscopic parameters and organic contents. HA fluorescence excitation emission matrix (EEM) contour plots indicated that the solar photocatalytic degradation pathway was TiO2-type specific and Cu dopant content.

Photocatalytic and photoelectrocatalytic humic acid removal and selectivity of TiO(2) coated photoanode.

In this study, photocatalytic (PC) and photoelectrocatalytic (PEC) treatment methods were comparatively investigated as a possible means of removing humic acid (HA) following absorbance at 254 nm (UV(254)) and total organic carbon (TOC) analysis. The enhanced HA degradation rates were obtained in the PEC system over the conventional PC process under acidic, neutral and alkaline conditions. Preliminary and binary experiments were performed to determine the selectivity of the photoanode in terms of HA and chloride oxidation. TOC, chlorine and photocurrent parameters proved that HA was selectively removed before chlorine generation. The inhibitory effect of carbonate ions on the performance of photoanode was also studied under different pH values.

Application of photocatalysis as a post treatment method of a heterotrophic-autotrophic denitrification reactor effluent.

The aim of this study is the application of photocatalysis as an effective post treatment scheme for the removal of the organic matter and bacteria released by an innovative biological denitrification process referred to as heterotrophic-autotrophic denitrification, which combines heterotrophic and autotrophic denitrification processes. Photocatalytic treatment was applied using TiO2 as a photocatalyst in the loading range of 0.25-2.00 g l(-1) for irradiation periods up to 60 min using a black light fluorescent lamp with an intensity of I(0)=1309 microW cm(-2). The photocatalytic inactivation data were modelled to pseudo first order kinetics as well as by the areal rates to evaluate the photocatalyst loading effect. Chlorination was used as a final disinfection step to attain an overall inactivation of total coliforms as well as to the formation of very low level of trihalomethanes.

Surface interactions of Cs+ and Co2+ with bentonite.

Uptake of radioactive metal species from soils and solutions by clay particles could be a treatment option due to simplicity of operation and economic cost. In this concern, adsorption behavior of Cs+ or Co2+ onto bentonite as a function of contact time, pH, initial metal concentration, ionic strength, and temperature was studied by batch adsorption technique. Adsorption isotherm data were interpreted by Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherm models. Bentonite exhibited maximum adsorption capacity of 83.3 mg g-1 for Cs+ and 15.9 mg g-1 for Co2+. Presence of humic acid (HA) as a representative model of organic matter did not significantly affect the adsorption capacity of bentonite for Cs+, whereas it increased the adsorption capacity of bentonite for Co2+. Thermodynamic parameters, standard enthalpy (ΔH°), standard entropy (ΔS°), and standard free energy (ΔG°) were determined through batch adsorption experiments performed at four different temperatures of 288, 298, 318, and 338 K. Co2+ adsorption onto bentonite showed an endothermic reaction (ΔH° = 13.6 kJ mol-1) whereas Cs+ adsorption displayed an exothermic nature (ΔH° = -4.65 kJ mol-1). Negative values of ΔG° and positive values of ΔS° indicated the feasibility and spontaneous nature of adsorption processes and more disordered form after adsorption.

A comprehensive review on the use of second generation TiO2 photocatalysts: Microorganism inactivation.

Photocatalytic disinfection practices have been applied for decades and attract current interest along with the developments in synthesis of novel photocatalysts. A survey based investigation was performed for elucidation of photocatalytic treatment details as well as disinfection mechanism of microorganisms. The present work brings significant information on the utilization of second generation TiO2 photocatalysts for inactivation of microorganisms typically using E. coli as the model microorganism. Special interest was devoted to the role of organic matrix either generated during treatment or as a natural component. Studies on photocatalytic disinfection were extensively reviewed and evaluated with respect to basic operational parameters related to photocatalysis, and types and properties of microorganisms investigated. Degradation mechanism and behavior of microorganisms towards reactive oxygen species during disinfection and organic matrix effects were also addressed. For successful utilization and effective assessment of visible light active photocatalysts, standard protocols for disinfection activity testing have to be set. Further improvement of the efficiency of these materials would be promising for future applications in water treatment processes.

The role of visible light active TiO2 specimens on the solar photocatalytic disinfection of E. coli.

Solar photocatalytic disinfection efficiency of novel visible light activated (VLA) photocatalysts was evaluated with the aim of assessing inactivation of Escherichia coli as the pathogen indicator organism present in drinking water. Influence of humic acid (HA) on the photocatalytic disinfection efficiency of the specified VLA TiO2 specimens i.e., N-doped, Se-doped, and Se-N co-doped TiO2 was also investigated. Photocatalytic disinfection efficiency was assessed by the enumeration of bacteria following selected irradiation periods. Degradation and compositional changes in organic matter (OM) was also tracked by means of UV-vis and advanced fluorescence spectroscopic (EEM features) parameters. Photocatalytic mineralization of the organic matter was followed by dissolved organic carbon contents. Presence of HA as a model organic compound of natural organic matter (NOM) displayed a retardation effect on solar photocatalytic abatement of E. coli. However, no distinctly different effect was observed under solar photolytic conditions due to the presence of HA. Regrowth of E. coli could not be assessed under the specified experimental conditions. A comparison was introduced with respect to the use of undoped TiO2 P-25 as the photocatalyst.

Bromate formation on the non-porous TiO2 photoanode in the photoelectrocatalytic system.

The increasing use of ozone in water disinfection processes has been the focus of considerable concern in regards to inorganic disinfection by product formation of bromate in waters containing bromide. Due to the public health risk caused by the presence of bromate as a suspected carcinogen, attention had been addressed to the conditions under which bromate is formed. In this study, photoanodic bromine generation and bromate (BrO(3)(-)) formation were investigated using a TiO(2) electrode in a photoelectrocatalytic (PEC) treatment process. The separation of anodic and cathodic reactions in the PEC system resulted in a pH decrease from 9.3 to 3.0 in the photoanode compartment and an increase to 11.0 in the cathode compartment. Under a photo-illumination intensity of 5.7 m W cm(-2) UV, a biasing potential of +1.0V vs SCE, a pH of 6.0 and at a NaBr concentration of 1.0 x 10(-2) M, active bromine formation increased over time with 2.4 x 10(-6) M min(-6) rate and reached a steady-state concentration of 1.44 x 10(-4) M in 60 min. Bromate formation was detected after a lag-period of 15 min and exhibited a continuous increasing trend with respect to irradiation time. No bromate formation was observed below pH 6.5 whereas an increasing bromate concentrations and pH up to pH=8.5 were noted.

Advanced oxidation of a commercially important nonionic surfactant: investigation of degradation products and toxicity.

The evolution of degradation products and changes in acute toxicity during advanced oxidation of the nonionic surfactant nonylphenol decaethoxylate (NP-10) with the H2O2/UV-C and photo-Fenton processes were investigated. H2O2/UV-C and photo-Fenton processes ensured complete removal of NP-10, which was accompanied by the generation of polyethylene glycols with 3-8 ethoxy units. Formation of aldehydes and low carbon carboxylic acids was evidenced. According to the acute toxicity tests carried out with Vibrio fischeri, degradation products being more inhibitory than the original NP-10 solution were formed after the H2O2/UV-C process, whereas the photo-Fenton process appeared to be toxicologically safer since acute toxicity did not increase relative to the original NP-10 solution after treatment. Temporal evolution of the acute toxicity was strongly correlated with the identified carboxylic acids being formed during the application of H2O2/UV-C and photo-Fenton processes.

Photocatalytic oxidation of dinitronaphthalenes: theory and experiment.

A combination of photocatalytic oxidation experiments and quantum mechanical calculations was used in order to describe the mechanism and the nature of the photocatalytic oxidation reactions of dinitronaphthalane isomers and interprete their reactivities within the framework of the Density Functional Theory (DFT). The photocatalytic oxidation reactions of three dinitronaphthalene isomers, 1,3-dinitronaphthalene, 1,5-dinitronaphthalene and 1,8-dinitronaphthalene in the presence of TiO(2) Degussa P-25 grade were investigated experimentally. The reactions were carried out in a Solarbox photoreactor equipped with a Xenon lamp. The removal of the individual substrates was followed by means of a gas chromatographic method. Nonpurgable organic carbon contents of the samples were determined by means of the catalytic oxidation method using Total Organic Carbon analyzer. With the intention of determining the best reactivity descriptors to explain the differences in the photocatalytic oxidation rates in terms of the molecular properties, geometry optimizations of the compounds were performed with the Density Functional Theory DFT at B3LYP/6-31G( *) level. In order to take the effect of adsorption on the oxidation rate, a cluster Ti(9)O(18) cut from the anatase bulk structure was modeled. The binding energies for the compounds were calculated by using the double-zeta basis set. Global hardness, softness, Fukui functions, local hardness-softness and local softness differences were calculated. The results show that the reactions investigated are orbital-controlled and electrophilic in nature. Local DFT descriptors reflect the reactivities of the dinitronaphthalene isomers better than the global ones, due to the differences in their adsorptive capacities.

Light Effects on Food.

Current research studies carried out on light-induced changes in dairy products, fats and oils, and meat products are reviewed. General factors affecting thus formed off-flavors in these food groups are the intensity of light, exposure interval, type of packaging, and some specific nutritive constituents. In dairy products, riboflavin degradation, losses of vitamin A and C are the major effects, whereas in fats and oils the effective constituents are ß-carotene, tocopherols, the undesirable flavors being related mainly to photosensitized oxidation. In case of meat products, the visual appearance seems to be the most important effect due to the formation of oxidized pigment metmyoglobin from oxymyoglobin upon light exposure. The effects of packaging materials and types on photooxidation are also being discussed for each of the above three food commodity groups.