Photocatalytic Oxidation Of Humic Acid Research Articles

Coupling photocatalytic and electrocatalytic oxidation towards simultaneous removal of humic acid and ammonia−nitrogen in landscape water

Aiming to bring photocatalytic and electrocatalytic oxidation processes into solving practical issue of organics and ammonia−nitrogen pollution in landscape water that resulting in algae bloom and eutrophication, this work firstly investigates photocatalytic oxidation of humic acid and electrochemical oxidation of ammonia upon optimization of each process parameters, respectively. The platinum modified titania (Pt/TiO2) exhibits improved activity than pure titania and CuOx, MnOx and NiOx modified titania for decomposition of humic acid. As an application−oriented study, this work has developed a simple and effective brushing and annealing method for immobilization of TiO2 and Pt/TiO2 onto ceramic foam for further application. In addition, the RuO2–IrO2/Ti electrode presents the best electrocatalytic activity compared with RuO2/Ti and IrO2/Ti electrodes in terms of ammonia oxidation, and the ammonia conversion pathways have been studied. Lastly, an integrated and enlarged reactor system employing optimized photocatalytic ceramic foam and stable electrodes has been developed for simultaneous oxidation of humic acid and ammonia−nitrogen in water circulated flow condition, based on cooperative production of reactive oxidant species between photocatalysis and electrocatalysis. The results show that coupled photocatalytic and electrocatalytic oxidation is a promising approach for treatment of organic matter and inorganic ammonia nitrogen in landscape water.

Enhanced photocatalytic oxidation of humic acids using Fe3+-Zn2+ co-doped TiO2: The effects of ions in aqueous solutions

Enhanced photocatalytic oxidation of humic acids using Fe3+-Zn2+ co-doped TiO2: The effects of ions in aqueous solutions

Template synthesis of titanium dioxide coatings and determination of their photocatalytic activity by aqueous oxidation of humic acid

In this work, aqueous photocatalytic oxidation of humic acid, present in various waters as naturally occurring compound or anthropogenic pollutant, was studied using self-synthesized titanium dioxide coatings. To obtain the latter, template synthesis, widely used for the production of photocatalysts with improved surface properties and activity, was applied with variations in template material, N-cetyl-N,N,N-trimethylammonium bromide content. The catalysts were characterized using XRD, UV-VIS spectroscopy, and SEM. The activity of TiO2 coatings in the degradation of humic acid proved to be superior to that of commercial photocatalyst P25 (Evonik) The dependence of the photocatalysts’ performance on the template content in the synthesis precursors, which was responsible for the various surface features of the coatings, was established and explained.

Specific UV–vis absorbance changes of humic acid in the presence of clay particles during photocatalytic oxidation

Photocatalytic oxidation of humic acid (HA) in the presence of clay particles (montmorillonite [Mt] or kaolinite [Kt]) followed using specific UV–vis parameters (SUVA365, SUVA280, SUVA254, and SCoA) calculated by respective absorbance measurements through conversion to mass of carbon. Non-selective oxidative degradation of HA could be displayed by the observed changes in the UV–vis spectral features in accordance with the successful elimination of the dissolved organic carbon. It was previously reported that fractional UV–vis parameters (E254/E365, E254/E436, E280/E365, E280/E436, and E365/E436) could signify the removal of color forming groups in relation to the removal of UV absorbing centers revealing information on the different oxidation pathways through photocatalysis. Regarding the results attained in this study, with respect to the changes attained in the specific UV–vis parameters, it could be indicated that the photocatalytic oxidation mechanism was significantly different for HA in the presence of either Mt or Kt. No noteworthy variation could be detected for fractional UV–vis parameters under photocatalytic conditions for sole HA as well as for HA in the presence of either Mt or Kt. However, a significant correlative interaction was observed between the specific UV–vis parameters (SUVA254 and SCoA) and the fractional UV–vis parameter (E254/E436) (r2 ##xgt; 0.80). Therefore, it could be concluded that E365/E436 parameter could be successfully used as a discriminative indicator parameter of the specific UV–vis parameters for the photocatalytic degradation of HA in the presence of either Mt or Kt.

Photocatalytic oxidation of humic acid and its effect on haloacetic acid formation potential: a fluorescence spectrometry study

By fluorescence spectrometry method, molecular conformation changes of humic acid (HA) during the photocatalytic oxidation process were studied. Haloacetic acids formation potential (HAAFP) changes during the oxidation process were also measured. The results indicated that aromatic rings of HA decreased and conjugated double bonds were destroyed at the beginning of the process. Meanwhile, organic matter with large molecular weight decomposed into intermediates with smaller molecular weight, such as tryptophan and tyrosine. HA can be degraded almost completely, but not be mineralized thoroughly. Structures of the intermediates were changing during the oxidation process. Molecular structure transformation of HA led to the fluctuation tendency of the HAAFP changes during the photocatalytic oxidation process. HAAFP increased to 1.22 times that in raw water after 30 min of ultraviolet (UV) radiation, and decreased to 0.66 times that in raw water after 60 min of photocatalytic oxidation.

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, UV 254 and Color 436 respectively. Moreover, model verification was also reported for a selected humic acid substrate and a specified photocatalyst specimen.

A Study of the Photocatalytic Oxidation of Humic Acid on Anatase and Mixed-phase Anatase–Rutile TiO2 Nanoparticles

In this study, slurry photocatalytic oxidation process was investigated for natural organic matter removal from aqueous humic acid solutions by using different titanium dioxide (TiO2) under UV-A irradiation. Bench scale experimental studies were conducted at different humic acid concentration at the range of 10–50 mg/L and different pH. Anatase and mixed-phase anatase–rutile TiO2 nano particles used in the photocatalytic reactor. The results were evaluated in terms of the parameters that are specific to organic matter content such as dissolved organic carbon concentration, ultraviolet absorbance at 254 nm (UV254), specific ultaviolet absorbance at 254 nm, and color (VIS400). It was observed that increasing humic acid concentration decreases photocatalytic degradation efficiency. The reactivity of the mixed-phase anatase–rutile (Degussa P-25) TiO2 was greater than individual anatase particles and the highest efficiency was observed at pH 3 for anatase TiO2.

The Effect of Calcium Ions in the Adsorption and Photocatalytic Oxidation of Humic Acid

The Effect of Calcium Ions in the Adsorption and Photocatalytic Oxidation of Humic Acid

The Role of Calcium Ions in the Photocatalytic Oxidation of Humic Acid at Neutral pH

Humic acids (HAs) are natural organic matter derived from the decomposition of plant, algal, and microbial materials. They belong to the group of the most predominant type of natural organic matter present in ground and surface waters. HAs affect the mobility and bioavailability of aquatic contaminants. However, if they are left unremoved from the water before water treatment processes, they can form carcinogenic disinfection by-products, such as trihalomethanes, haloacetic acids, and other halogenated disinfection by-products, that can pose a threat to human beings. An advanced oxidation process using UV light and a commercially available titanium dioxide was used to oxidize HA at a pH that is similar to that of natural water. The effect of adding calcium ions to the adsorption and the photocatalytic oxidation of HAs was studied. The effect of varying the TiO(2) load was also investigated. The experiment was done using a photochemical batch reactor equipped with a mercury lamp emitting light with wavelengths of 310-580 nm. The absorbances by the samples were determined at wavelengths of 254 nm and 436 nm, which represent the aromatic-compound content of and the color of the solution, respectively. Results indicated calcium ions have an effect on both the adsorption and the photocatalytic oxidation of HA at a pH within 8.0 +/- 0.5. Calcium ions facilitated adsorption of HA onto the surface of TiO(2) and resulted to faster photocatalytic oxidation. The data were plotted with respect to the normalized absorbances and irradiation time.

TiO 2 nanowire membrane for concurrent filtration and photocatalytic oxidation of humic acid in water

A novel TiO 2 nanowire membrane was successfully fabricated using hydrothermal synthesis-filtration method. The fabricated TiO 2 membrane had uniform thickness and was flexible to form into other shape modules. These nanowires were of 20–100 nm in diameter and had typical length in the range of several micrometers to tens of micrometers. The pore size of the TiO 2 nanowire membrane was about 0.05 μm. The TiO 2 nanowire membrane exhibited similar photocatalytic activity as commercial TiO 2 powder (P25) on degradation of humic acid in water. In continuous experiment, TiO 2 nanowire membrane achieved near 100% and 93.6% removal rate of humic acid and total organic carbon (TOC), respectively, via a concurrent filtration and photocatalytic oxidation. The TiO 2 nanowire membrane also showed excellent anti-fouling ability owing to the photodegration of foulants by the TiO 2 nanowire membrane.

Contribution of Metal Species to the Heterogeneous Photocatalytic Degradation of Natural Organic Matter

The role of organic matters which are high molecular weight macromolecules in natural water supplies and their subsequent removal by advanced oxidation technologies has gained importance because they posses a substantial capacity to complex dissolved metal species. The present study was conducted to evaluate the impact of aqueous Cr(VI) and Mn(II) species on the photocatalytic oxidation of humic acids as a major component of natural organic matter in aquatic systems. The photocatalytic decolorization rate of humic acid was followed by pseudo-first-order and Langmuir Hinshelwood kinetic models. The presence of aqueous Cr(VI) and Mn(II) species did not significantly alter the degradation efficiency (≤20%) in terms of first-order kinetic model. Although the impact of manganese species could be considered as insignificant, a substantial adsorption effect could be assessed as reflected by respective Langmuir-Hinshelwood kinetic model parameters.

Photocatalytic degradation of humic acid in saline waters. Part 1. Artificial seawater: influence of TiO2, temperature, pH, and air-flow

We report the first systematic study on the photocatalytic oxidation of humic acid (HA) in artificial seawater (ASW). TiO2 (Degussa P25) dispersions were used as the catalyst with irradiation from a medium-pressure mercury lamp. The optimum quantity of catalyst was found to be between 2 and 2.5 gl−1; while the decomposition was fastest at low pH values (pH 4.5 in the range examined), and the optimum air-flow, using an immersion well reactor with a capacity of 400 ml, was 850 mlmin−1. Reactivity increased with air-flow up to this figure, above which foaming prevented operation of the reactor. Using pure oxygen, an optimal flow rate was observed at 300 mlmin−1, above which reactivity remains essentially constant. Following treatment for 1 h, low-salinity water (2700 mgl−1) was completely mineralised, whereas ASW (46000 mgl−1) had traces of HA remaining. These effects are interpreted and kinetic data presented. To avoid problems of precipitation due to change of ionic strength humic substances were prepared directly in ASW, and the effects of ASW on catalyst suspension and precipitation have been taken into account. The Langmuir–Hinshelwood kinetic model has been shown to be followed only approximately for the catalytic oxidation of HA in ASW. The activation energy for the reaction derived from an Arrhenius treatment was 17 (±0.6) kJmol−1.

Photocatalytic degradation of humic acid in saline waters: Part 2. Effects of various photocatalytic materials

The present study explores for the first time, the effectiveness of photocatalytic oxidation of humic acid (HA) in the increasingly important highly saline water. TiO 2 (Degussa P25), TiO 2 (Anatase), TiO 2 (Rutile), TiO 2 (Mesoporous) and ZnO dispersions were used as catalysts employing a medium pressure mercury lamp. The effect of platinum loading on P25 and zinc oxide was also investigated. The zinc oxide with 0.3% platinum loading was the most efficient catalyst. The preferred medium for the degradation of HA using ZnO is alkaline, whereas for TiO 2 it is acidic. In addition, a comparative study of HA decomposition in artificial seawater (ASW) and natural seawater (NSW) is reported, and the surface areas and band gaps of the catalysts employed were also determined. A spectrophotometric method was used to estimate the extent of degradation of HA.

Enhancement of photocatalytic oxidation of humic acid in TiO 2 suspensions by increasing cation strength

This study aimed at improving the photocatalytic (PC) oxidation of humic acids (HA) in TiO 2 suspensions by adding cationic ion such as calcium or magnesium. A set of tests was first conducted in the dark to study the adsorption of HA onto TiO 2 in suspensions at different pH and calcium concentrations. The experiment demonstrated that the adsorption of HA onto the TiO 2 particles was either pH-dependent or calcium strength-dependent due to electrostatic interaction and calcium ion bridging. The photodegradation of HA in the presence of UV irradiation was investigated as a function of pH and the concentration of calcium and magnesium ions. The results showed that the adsorption behavior between HA and TiO 2 played a very important role during the PC oxidation process. The PC oxidation could be enhanced at neutral pH by increasing the cation strength. The kinetics of HA PC degradation in TiO 2 suspensions with different initial concentrations was also studied using the Langmuir–Hinshelwood model.