Titanium Dioxide-Mediated Photocatalytic Degradation of Humic Acid under Natural Sunlight

Department of Chemical Engineering, Lakehead University, 955 Oliver Road, Thunder Bay, Ontario, Canada P7B 5E1.
Water Environment Research (Impact Factor: 0.87). 02/2013; 85(1):3-12. DOI: 10.2175/106143012X13378023685790
Source: PubMed


In this article, photocatalytic degradation of humic acid, a predominant type of natural organic matter present in ground and surface waters, was conducted using a commercial titanium dioxide catalyst under natural sunlight irradiation in a batch photoreactor. Various parameters, such as photocatalyst loading, pH value, irradiation intensity, initial concentration, and illumination time, had a significant influence on humic acid removal. The adsorption isotherm of TiO2 dosage fit to Langmuir's isotherm equation well, and the reaction kinetics of initial dissolved organic carbon (DOC) concentration increased with the increase of TiO2 dosage but decreased with the increase of initial DOC. The mineralization of humic acid revealed that the large molecular weight organics with aromatic and hydrophobic properties were removed, while the most persistent components were the shortest UV-absorbing and hydrophilic low-molecular-weight compounds. This study indicates that the solar/ TiO2 photocatalytic degradation is a promising process for humic acid removal from water.

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    • "The rapid reduction of UV 254 values over the irradiation time (Fig. 1) suggests that the chromophores in DOM, which mostly consist of high molecular sized aromatic rings, might be rapidly broken down into smaller sized non-aromatic structures (Sanly et al., 2007). The photodegradation rates and the total removal on the basis of UV 254 were consistently higher than those of DOC (p < 0.001), suggesting that aromatic moieties in DOM were preferentially removed and/or some chromophores within DOM may be partially transformed into non-UV-absorbing compounds by the photochemical reaction (Uyguner and Bekbolet, 2005; Sanly et al., 2007; Hur et al., 2011; He, 2013). It is notable that many photoproducts of DOM constitute low molecular weight organic acids, alcohols, aldehydes , and inorganic carbon (Pullin et al., 2004). "
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    ABSTRACT: Photocatalytic degradation of dissolved organic matter (DOM) using TiO2 as a catalyst and UVA as a light source was examined under various experimental settings with different TiO2 doses, solution pH, and the light intensities. The changes in UV absorbance and fluorescence with the irradiation time followed a pseudo-first order model much better than those of dissolved organic carbon. In general, the degradation rates were increased by higher TiO2 doses and light intensities. However, the exact photocatalytic responses of DOM to the irradiation were affected by many other factors such as aggregation of TiO2, light scattering, hydroxyl radicals produced, and DOM sorption on TiO2. Fluorescence excitation-emission matrix (EEM) coupled with parallel factor analysis (PARAFAC) revealed that the DOM changes in fluorescence could be described by the combinations of four dissimilar components including one protein-like, two humic-like, and one terrestrial humic-like components, each of which followed well the pseudo-first order model. The photocatalytic degradation rates were higher for protein-like versus humic-like component, whereas the opposite order was displayed for the degradation rates in the absence of TiO2, suggesting different dominant mechanisms operating between the systems with and without TiO2. Our results based on EEM-PARAFAC provided new insights into the underlying mechanisms associated with the photocatalytic degradation of DOM as well as the potential environmental impact of the treated water. This study demonstrated a successful application of EEM-PARAFAC for photocatalytic systems via directly comparing the kinetic rates of the individual DOM components with different compositions.
    Full-text · Article · Sep 2015 · Water Research
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    ABSTRACT: Degradation of humic acid (HA), a predominant type of natural organic matter in ground water and surface waters, was conducted using a gas phase surface discharge plasma system. HA standard and two surface waters (Wetland, and Weihe River) were selected as the targets. The experimental results showed that about 90.9% of standard HA was smoothly removed within 40 min's discharge plasma treatment at discharge voltage 23.0 kV, and the removal process fitted the first-order kinetic model. Roles of some active species in HA removal were studied by evaluating the effects of solution pH and OH radical scavenger; and the results presented that O3 and OH radical played significant roles in HA removal. Scanning electron microscope (SEM) and FTIR analysis showed that HA surface topography and molecular structure were changed during discharge plasma process. The mineralization of HA was analyzed by UV-Vis spectrum, dissolved organic carbon (DOC), specific UV absorbance (SUVA), UV absorption ratios, and excitation-emission matrix (EEM) fluorescence. The formation of disinfection by-products during HA sample chlorination was also identified, and CHCl3 was detected as the main disinfection by-product, but discharge plasma treatment could suppress its formation to a certain extent. In addition, approximately 82.3% and 67.9% of UV254 were removed for the Weihe River water and the Wetland water after 40 min of discharge plasma treatment.
    No preview · Article · Nov 2015 · Water Research