Photocatalytic Degradation Of Humic Acid Research Articles

Breaking down process barriers: ZnSe/CdSe composite catalysts drive enhanced catalytic properties and modified membrane structures for removing humic acid from aqueous environments

In the present research, with the aim of removing humic acid from wastewater, photo-catalytic membrane reactor was utilized. Single-component catalysts including ZnSe, CdSe, as well as composite catalyst (ZnSe/CdSe) were deposited in the surface layer of polysulfone membrane via photo-grafting method, whereby ZniCdjM11i and j are ZnSe and CdSe loading concentration level membranes were synthesized. The results indicated that the ZnSe/CdSe due to its shorter bandgap, had a more effective role in the grafting process and hence adjusting the membrane pore size. The pore size of Zn4Cd4M was smaller than that of Zn4Cd0M and Zn°Cd4M, and hence the humic acid separation in the dark mode by Zn4Cd4M was 80 %, which is about 10 % greater than the value obtained by Zn4Cd0M and Zn°Cd4M. The ZnSe/CdSe due to its less photoluminescence emission, proved to be more effective in photocatalytic reactions compared to the single component catalysts. The extent of photocatalytic degradation of humic acid in the presence of UV-radiation by the Zn°Cd4M, Zn4Cd0M, and Zn4Cd4M was reported 80, 84, and 96 % respectively. Overall, due to the smaller pore size, shorter bandgap, and lower recombination, TOC removal by the Zn4Cd4M (containing composite catalyst) was reported 98 %, while this value for the Zn4Cd0M and Zn°Cd4M was reported 60 and 66 % respectively.

A UVA light-emitting diode microreactor for the photocatalytic degradation of humic acids and the control of disinfection by-products formation potential

Chlorination is one of the most applied technologies for drinking water disinfection. However, the generation of disinfection by-products (DBPs) in the chlorination process is threatening drinking water safety, especially when the concentration of natural organic matter (NOM) is high in source water. Climate change increases the fluctuation of NOM in source water, which further challenges water safety in small and rural communities. In this study, environmental microfluidics was introduced to a UVA-LED photocatalytic oxidation system for a rapid oxidation of NOM. The results showed that HA adsorption and degradation, and DOC degradation were more favored in low pH. At pH 5, 56.9% of HA and 58.1% of dissolved organic carbon (DOC) were removed in 3.4 min by the microreactor. DBP formation potential was efficiently reduced, with the highest reduction of THM and HAA formation potentials by 76% and 70.7%, respectively. Compared with the bottle reactor, the degradation rate constants of HA and DOC by UVA-LED microreactor were increased by 2.99 – 15.8 times, and 6.8 – 170.2 times, respectively. Homogenous irradiation and rapid mass transfer in the microreactor accelerated the inhibited oxidation of HA in acidic and base solutions and increased the apparent quantum yields of photocatalysis. Further, the microfluidic photocatalytic oxidation was much more efficient in the reduction of DPBs formation potential in a source water sample. The process was rapid and had low chemical and energy consumption. Approaches on system scale-up, system simplification, and energy conservation would increase potential of microfluidic photocatalytic oxidation in water purification for households and small communities.

Photocatalytic Degradation of Humic Acid Using Bentonite@Fe3O4@ZnO Magnetic Nanocomposite: An Investigation of the Characterization of the Photocatalyst, Degradation Pathway, and Modeling by Solver Plugin

Humic acid (HA), the most highly prevalent type of natural organic matter (NOM), plays an effective role in the generation of disinfectant byproducts such as trihalomethanes and haloacetic acid, which are well known to be definitive carcinogens. Therefore, the proactive elimination of HA from water and wastewater is a crucial means of preventing this pollutant from reacting with the chlorine incorporated during the disinfection process. This study investigated the UV light photocatalytic elimination of HA, employing a bentonite@Fe3O4@ZnO (BNTN@Fe3O4@ZnO) magnetic nanocomposite. The most significant variables pertinent to the photocatalytic degradation process examined in this work included the pH (3–11), nanocomposite dose (0.005–0.1 g/L), reaction time (5–180 min), and HA concentration (2–15 mg/L). The synthesized materials were characterized via field emission scanning electron microscopy (FE-SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffractometer (XRD), energy-dispersive X-ray spectroscopy (EDX), and vibrating-sample magnetometer (VSM) techniques, all of which revealed outstanding catalytic properties for the BNTN@Fe3O4@ZnO. The conditions under which greater efficiency was achieved included a pH of 3, a nanocomposite dose of 0.01 g/L, and an HA concentration of 10 mg/L. Under these conditions, in just 90 min of photocatalytic reaction, an HA degradation efficiency of 100% was achieved. From the modeling study of the kinetic data, the Langmuir–Hinshelwood model showed good compliance (R2 = 0.97) with the empirical data and predicted values. Thus, it can be concluded that the BNTN@Fe3O4@ZnO catalyst acts very efficiently in the HA removal process under a variety of treatment conditions.

Synthesis, characterization of Ag-WO3/bentonite nanocomposites and their application in photocatalytic degradation of humic acid in water.

In this study, Ag-WO3/bentonite nanocomposites were synthesized through a sol-gel process, a microwave irradiation technique, and a sol-immobilization process to examine their impact on the photocatalytic activity in the degradation of humic acids. The optical and structural properties of the synthesized materials were characterized using X-ray diffraction (XRD), Fourier-transform-infrared spectra (FTIR), field emission scanning electron microscope (FE-SEM) with energy dispersive X-ray (EDX), UV-Vis diffused reflectance spectra (UV-Vis DRS), Brunauer-Emmett-Teller (BET) method, and transmission electron microscope (TEM). The presence of Ag and WO3 peaks in the XRD and EDX spectra confirmed the synthesis of Ag-WO3 nanoparticles in the composite. The monoclinic structure of the produced WO3 samples are shown by powder X-ray diffraction patterns. The WO3-based nanocomposites' photocatalytic activity was improved by the composition of Ag and bentonite, which reduced the optical bandgap energy of WO3. The binary (Ag-WO3) nanocomposite showed improved photocatalytic activity towards the degradation of humic acid (HA) from 58% (pristine WO3) to 82% (Ag-WO3) when compared with the pristine WO3 sample under the visible light irradiation. Notably, the ternary (Ag-WO3/bent) nanocomposite demonstrated an outstanding photocatalytic efficiency of HA degradation (91.0%) under normal conditions (pH = 7.0 and 25°C). Humic acid degradation in Ag-WO3/bent was expressed by the pseudo-first-order kinetic. To summarize, integrating Ag, WO3, bentonite, and visible light radiation to activate HA efficiently can be offered as a successful and promising technique for wastewater treatment.

Biosynthesis of MnFe2O4@TiO2 magnetic nanocomposite using oleaster tree bark for efficient photocatalytic degradation of humic acid in aqueous solutions.

The presence of humic acid compounds in water resources, as one of the precursors of Trihalomethanes and Holoacetic acids, causes health problems for many communities. The aim of this research study was to investigate the photocatalytic degradation efficiency of humic acid using MnFe2O4@TiO2 nanoparticles which produced by green synthesis method. The synthesis of metal nanoparticles using plant extracts and the study of their catalytic performance is a relatively new topic. Many chemical techniques have been proposed for the synthesis of MnFe2O4@TiO2 nanoparticles, but green synthesis has received much attention due to its availability, simplicity, and non-toxicity. The properties of synthesized nanoparticles were determined by SEM, FT-IR, XRD, EDS, and DLS analysis. The results of the study showed that under optimal experimental conditions (pH = 3, nanocomposite dose = 0.03g/L, humic acid initial concentration = 2mg/L, and contact time = 20min), it is possible to achieve maximum degradation of humic acid. Therefore; MnFe2O4@TiO2 nanoparticles have high efficiency for removing of humic acid from aqueous solutions under UV light.

Comparison of highly active Type-I and Type-II heterojunction photocatalytic composites synthesized by electrospinning for humic acid degradation

ZnO/Co3O4 materials with Type-I (straddling gap) heterojunction structure and ZnO/NiO materials with Type-II (staggered gap) heterojunction structure were prepared by electrostatic spinning-oxidation method. The influence of the type of heterojunction on the system was investigated by structure characterization and physical phase analysis. The results show that 550 °C was the optimal oxidation temperature for material preparation. The oxide particles can self-assemble to form fibers under this condition. The effect of photocatalytic degradation of humic acid in the system further proved that the materials with Type-II heterojunction structure possess higher degradation ability and cycle stability than Type-I heterojunction materials.

Improving the ZnO-photocatalytic degradation of humic acid using powdered residuals from water purification plant

Abstract Alum residuals were collected from a water treatment plant and used for improving the photocatalytic degradation of humic acid (HA) by combinations of zinc oxide (ZnO) and powdered residuals from a water purification plant (PRWPP). The influence of operating conditions such as initial humic acid concentration, pH, irradiation time, PRWPP to ZnO ratio, catalyst dose, and light illuminance have been investigated. The optimum PRWPP to ZnO ratio was 10:90. Using the prepared composites instead of bare ZnO raised the HA removal efficiency from 85.5% to 97.8%, and from 38% to 48.1% at catalyst doses of 1.2 g/l and 0.4 g/l, respectively. Moreover, it reduced energy consumption from 210.4 to 166.2 Wh per mg of HA. An artificial neural network model (ANN) was developed to predict the removal efficiency under different operating conditions. The optimum ANN structure yielded a coefficient of determination (R2 = 0.993). A modified Langmuir-Hinshelwood pseudo-first-order model was used for describing the degradation kinetics at different initial concentrations of HA.

Photocatalytic degradation of humic acid using a novel visible-light active α-Fe2O3/NiS2 composite photocatalyst

The effects of α-Fe2O3/NiS2 composite for the humic acid removal were systematically studied and compared with the synthesized α-Fe2O3 and NiS2. The obtained mesoporous composite has a stacked plate-like surface, active at a visible light region with a bandgap of 2.49 eV, and has a lower rate of recombination compared to the α-Fe2O3 but higher than the NiS2. The highest humic acid removal (93.7%) was achieved by the α-Fe2O3/NiS2 composite followed by the α-Fe2O3 (88.7%) and NiS2 (86.4%) at optimum conditions of 0.1 g L−1 catalyst loading, pH 5, and 30 mg L−1 initial humic acid concentration. The mineralization achieved 96.8% and the catalyst was stable up to the fourth cycle. These encouraging results were due to the better adsorption capacity of the composite, being active in visible light, and quenching of the photoluminescence that led to effective separation of subsequent reduction in the rate of recombination of the charged carriers.

Synthesis of PAC-LaFeO3-Cu nanocomposites via sol-gel method for the photo catalytic degradation of humic acids under visible light irradiation

Humic acids are natural organic substances that are produced as a result of biological and geochemical reactions in environment and are known as one of the main precursors of disinfectant by-products (DBPs). New types of PAC/LaFeO3/Cu nanocomposites are synthesized by sol gel method for photocatalytic degradation of humic acid under visible light irradiation. The physicochemical functions of PAC/LaFeO3/Cu nanocomposites were characterized using BET, TEM, UV–vis DRS, XRD, and PL spectroscopy. Results emphasize that, free hydroxyl radical (•OH) attack to HAs molecules, decompose and oxidize the molecules to CO2, H2O, and other small components. Central composite design (CCD) was applied to optimize HAs removal based on response surface methodology (RSM) with four experimental parameters such as pH (X1, 3–11), catalyst dosage (X2, 100–1300 mgL−1), contact time (X3, 15–55 min), and HAs concentration (X4, 2–10 mgL−1). Removal efficiency of 95.5% for HAs has been obtained under optimal conditions with 36.20 min (exposure time), 5.33 mgL−1 HAs concentration, 715.74 mgL−1 PAC/LaFeO3/Cu dosage, and 4.20 pH. The HAs degradation efficiency was significantly affected by the initial dye concentration and the pH values. The significance of the polynomial model (Radjasted2=0.997,R2=0.985) was validated by analysis of variance (ANOVA). This work seeks to illustrate new knowledge for usage of nanocomposites photocatalyst as an inexpensive, environmentally friendly, economical, and effectual material for drinking water supplies treatment processes. However, the PAC/LaFeO3/Cu nanocomposites showed excellent removal performances for HAs.

Evaluation of Sonocatalytic and Photocatalytic Processes Efficiency for Degradation of Humic Compounds Using Synthesized Transition-Metal-Doped ZnO Nanoparticles in Aqueous Solution

The existence of a humic substance in water causes the growth of microorganisms and reduces the quality of water; therefore, the removal of these materials is crucial. Here, the ZnO nanoparticles doped using transition metals, copper (Cu) and manganese (Mn), were used as an effective catalyst for photocatalytic removal of humic substances in an aqueous environment under ultraviolet, visible light, and light-emitting diode irradiations. Also, we study the effect of the sonocatalytic method. A solvothermal procedure is used for doping, and the Cu- and Mn-doped ZnO nanocatalyst were characterized by means of FTIR, XRD, AFM, SEM, and EDAX analyses. We investigate the effect of operational variables, including doping ratio, initial pH, catalyst dose, initial HS content, and illuminance on the removal efficiency of the processes. The findings of the analyses used for the characterization of the nanoparticles illustrate the appropriate synthesis of the Cu- and Mn-doped ZnO nanocatalysts. We observe the highest removal efficiency rate under acidic conditions and the process efficiency decreased with increasing solution pH, when we tested it in the range of 3–7. Photocatalytic decomposition of HS increases with a rise in catalyst dose, but an increase in initial HS content results in decreasing the removal efficiency. We observe the highest photocatalytic degradation of humic acid while using the visible light, and the highest removal efficiency is obtained using Cu.ZnO. The Cu.ZnO also shows better performance under ultraviolet irradiation compared to other agents.

ZnO nanoparticles for photodegradation of humic acid in water.

Humic acid (HA) is the most important precursor of toxic disinfection byproducts upon chlorination. Removing HA from water body is therefore critical in drinking water acquisition. In this research, ZnO nanoparticles are employed for photocatalysis under UV light at neutral pH to remove HA from a water environment. Almost 100% degradation of HA was achieved using 0.3 g/L of ZnO in 180 min with UV-A and UV-C light. Under identical experimental conditions, total organic carbon (TOC) removals reach 67% and 21% with UV-A and UV-C light, respectively. A higher degree of mineralization of HA is achieved with UV-A light although the degradation of HA is slightly better with UV-C light. This indicates that ZnO/UV-A has relatively low selectivity to degrade different compounds, including various intermediates from HA degradation. The use of UV-A light is therefore recommended for ZnO as it possesses higher mineralization ability. Negligible TOC is observed on the ZnO surface after photocatalytic reactions. In contrast, the adsorption of HA in dark conditions reaches 42% in 180 min. This strongly indicates that the adsorption of HA plays an important role in the photocatalytic degradation of HA, but it is not the main process for HA removal.

Photocatalytic performance of titanium dioxide and zinc oxide binary system on degradation of humic matter

Application of photocatalysis using TiO2 or ZnO for the removal of natural organic matter (NOM) dates back more than two decades. Aiming to overcome the drawbacks of sole photocatalysts, use of multiphasic systems has received recent interest. ZnO/TiO2 binary oxide specimens were synthesized by a simple solid state dispersion method in different weight ratios of 1:1; 1:3; and 3:1 (ZT11, ZT13 and ZT31 respectively) and characterized by XRD, SEM, XPS, Raman, UV-DRS, PL and BET techniques. As a surrogate of NOM, humic acid (HA) was subjected to solar photocatalysis and degradation was followed by UV–vis and fluorescence spectroscopic tools along with dissolved organic carbon (DOC) contents. Photocatalytic degradation of HA was approximated to first order kinetic model. Referring to UV–vis parameters, ZT11 binary oxide expressed slightly higher photocatalytic performance with regard to TiO2, ZnO, ZT13 and ZT31 contrary to the mineralization extents as TiO2>ZT13 > ZT31 > ZT11 > ZnO. Excitation-emission matrix fluorescence (EEM) contour plots of the organic matrix displayed almost complete removal of humic-like and fulvic-like fluorophores upon use of sole TiO2 and ZnO. Regional distribution of the fluorophores were still evident with emergence of the new fluorophoric regions upon use of binary oxides. ZnO/TiO2 could be considered as an efficient photocatalyst for the degradation of humic acids under solar irradiation.

Efficiency of Photocatalytic Degradation of Humic Acid Using Magnetic Nanoparticles (Fe-doped TiO2@Fe3O4) in Aqueous Solutions

Background: Among water pollutants, Natural Organic Matters (NOMs) are highly important for making problems in water treatment plants. Objectives: The main objective of this study was to investigate the efficiency of photocatalytic degradation of humic acid using magnetic nanoparticles (Fe-doped TiO2@Fe3O4) in aqueous solutions. Methods: In the present experiment, Fe-doped TiO2@Fe3O4 nanoparticles were synthesized by the sol-gel method, and SEM, XRD, and DRS analyzes were utilized to characterize the synthesized nanoparticles. The effects of various variables, including pH (3 - 11), initial concentration of humic acid (20 - 80 mg/L), and concentration of nanoparticles (250 - 2000 mg/L) at different reaction times (15 - 60 min) were investigated on the photocatalytic degradation of humic acid. Results: The maximum degradation efficiency of humic acid at pH 3, the initial humic acid concentration of 5 mg/L, nanoparticle dose of 400 mg/L, and reaction time of 60 min using a 15-W bare UV lamp. Conclusions: Due to the high efficiency of photocatalytic degradation, it is proposed to use for the removal of humic acid from water resources.

Synergistic effects and kinetics of rGO-modified TiO2 nanocomposite on adsorption and photocatalytic degradation of humic acid

Graphene oxide was prepared using the modified Hummers method and reduced graphene oxide (rGO) - titanium dioxide (TiO2) nanocomposite was synthesised using the one-step hydrothermal treatment. The synergistic effects on adsorption and photocatalytic properties of the rGO-TiO2 nanocomposite for the humic acid removal were systematically investigated. The results of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Raman and infrared (IR) spectroscopy indicate that GO was partially reduced to reduced graphene oxide (rGO) in the hydrothermal synthesis process and anatase TiO2 nanoparticles uniformly grew on the surface of rGO. The photoelectron and photohole generated under visible light irradiation were effectively separated on the surface of rGO-TiO2. The rGO-TiO2 nanocomposite exhibited higher photocatalytic activity as a result of the synergistic effects of surface functional groups for adsorption and the excellent conductivity for photocatalytic reaction. The effect of rGO-TiO2 nanocomposite dosage, light intensity and system temperature on the removal of humic acid solution was investigated. The results show that the removal efficiency of humic acid increased with system temperature and light intensity. When the dosage of rGO-TiO2 nanocomposite was 1.2 g/L, the temperature, the light intensity and the pH of this system was 303 K, 4.37 Wm−2 and 7, respectively, the removal efficiency of humic acid reached 88.7% under visible light irradiation.

PREPARATION AND CHARACTERIZATION OF LAFEO3 USING DUAL-COMPLEXING AGENTS FOR PHOTODEGRADATION OF HUMIC ACID

Humic Acid (HA) is considered as one of the major components that represents a major fraction of dissolved in natural water. Complex mixture of organic compounds on HA lead to the problematic issue for municipal wastewater treatment plants such as undesirable taste, colour to drinking water and fouling in pipe line. The reaction of HA with chlorine during disinfection processes would produce carcinogenic by-products like trihalomethanes. In this study, for the first time, LaFeO3 photocatalyst was successfully synthesized via gel-combustion method using combined glucose/citric acid as chelating agents and was further calcined at 400°C. The photocatalytic activity of samples was investigated by degradation of Humic Acid (HA) in water under visible light irradiation. Results proved that the photocatalytic degradation of HA is dependent on the catalyst dosage, initial concentration of HA, and oxygen availability in the aeration. The photocatalytic degradation also was enhanced by high surface area of synthesized LaFeO3 obtained by amorphous structure. Overall, the percentage removal of HA by varying the catalyst dosage are in the order of 88%, 90%, 98% and 97% for 0.6 g/L, 0.8 g/L, 1.0 g/L, and 1.2 g/L respectively for an irradiation period of 120 minutes. Next, the removal of HA by manipulating its initial concentration are 98%, 90%, 85% and 86% with respect to 10 g/L, 20 g/L, 30 g/L and 40 g/L taken for 120 minutes. Overall, the optimal operational parameters for the removal of HA of catalyst dosage is 1.0 g/L performing at 98%, for initial concentration of HA which was removed efficiently at 97% is 10 g/L and via aeration in this study was about 93%, after 120 min of irradiation times.

Removal of Humic Acid in Water Using Novel Nanomaterials

The present study investigates the effectiveness of the photocatalytic degradation of humic acid (HA) in aqueous suspensions. Initial batch scale experiments and tests performed using the Continuous Flow Photoreactor have enabled the close inspection of the performance of the photocatalysts nano TiO2, and nano ZnO dispersions. These photocatalysts were used in aqueous dispersions employing medium-pressure mercury-vapour lamps emitting UV-A (λ = 400 nm) and UV-C (λ = 250 nm). Moreover, glass microfibre filters were embedded and coated with Laponite RD (synthetic polycrystalline swelling clay) in order to produce catalytic films to be used in small scale experiments to remove HA through filtration. The findings of this study shows that the HA adsorb highly onto the ZnO and TiO2 surface thus initiating photodegradation, the effectiveness of which steadily increases with irradiation time along with an increase in the biodegradability of HA.

Photocatalytic Degradation of Humic Acids with Titanium Dioxide Embedded into Polyethylene Pellets to Enhance the Postrecovery of Catalyst

Heterogeneous photocatalysis with titanium dioxide (TiO2) has been shown to be a sustainable treatment technology to remove natural organic matter (NOM). This is of interest to the drinking water treatment industry. However, heterogeneous photocatalysis with TiO2 continues to suffer from several limitations such as the postrecovery of TiO2 particles, which impede its use in the drinking water treatment industry. In this study, the repeated use of the same photoactive TiO2 embedded into polyethylene pellets (PE-TiO2) made by the controlled-temperature embedding method was studied in the photocatalytic degradation of commercial humic acid (HA) to solve the postrecovery of TiO2 in slurry. Photocatalytic degradation percentage of dissolved organic carbon (DOC) removal with PE-TiO2 was stable after the second use of the same PE-TiO2 pellets, which was evaluated during five tests. PE-TiO2 removed 64.6% of the initial DOC during 270 min of photocatalytic degradation, and TiO2 in slurry removed 64.5% of the initial DOC during 180 min of photocatalytic degradation. Moreover, PE-TiO2 led to a considerable reduction in specific ultraviolet absorbances (SUVA = UV/DOC): SUVA254, SUVA280, SUVA365, and SCOA436 (specific color absorbance) and trihalomethane formation potential (THMFP). Therefore, PE-TiO2 is a promising material to remove NOM and solve the problem of postrecovery of TiO2 particles after water treatment.

Removal of humic acid from aqueous solution using photocatalytic reaction on perlite granules covered by Nano TiO2 particles

Humic acid (HA) constitutes a large portion of natural organic matter (NOM), and is the main precursor of toxic and cancerogenic Trihalomethanes compounds, formed during chlorination of drinking water. Therefore, it is essential that the humic acid be eliminated from water before treating it.The present study aims to investigate the photocatalytic degradation of humic acid (HA) using TiO2 nanoparticles immobilized on perlite granules (TIP), irradiated by UV light in a photoreactor. Samples of coated perlites were prepared by a dip coating method using a commercial powder of TiO2. Characteristics of the prepared samples were evaluated by X-ray and scanning electron microscope techniques. Results showed no significant changes in the structure of TiO2 and a relative uniform morphology was observed on the TIP. HA concentration was determined by spectrophotometry at a wavelength of 254nm using a calibration curve. The effect of some parameters such as pH, additional oxidizer, initial concentration of HA, and light intensity were investigated. Results showed that TIP could degrade a significant amount of HA in a relatively long time.The best result obtained from the experiment was a 98% degradation gained at an initial concentration of 2mg/L of HA, under the initial condition of pH=4 and 20mg/L of H2O2 in 120min. TIP can be a practical way to degrade HA from water.

Photocatalytic degradation of humic acid using a novel photocatalyst: Ce-doped ZnO

This study aimed at investigating the photocatalytic degradation of humic acid (HA) as a representative of natural organic matter (NOM) by using Ce-doped ZnO as a novel material. Following photocatalysis, HA degradation was characterized by specified UV-vis and fluorescence spectroscopic parameters as well as by the dissolved organic carbon (NPOC) content. Excitation-Emission Matrix (EEM) fluorescence features were also evaluated by using advanced techniques. Comparison of Ce-doped ZnO photocatalysis to TiO2 P-25 photocatalytic treatment of the HA samples was elucidated under similar experimental conditions. Kinetic modeling of the photocatalytic removal of HA expressed promising results indicating that Ce-doped ZnO could serve as an efficient catalyst for the degradation of NOM.

TiO 2 as an effective nanocatalyst for photocatalytic degradation of humic acid in water environment

Photocatalysis with TiO 2 is used to remove humic acid (HA) in a water environment under UVA and UVC light. The effects of operating parameters, including light intensity, HA concentration, catalyst dose, and contact time are investigated at neutral pH conditions. Results show that HA degradation increases with increasing contact time and light intensity and decreases with increasing HA concentration. Increasing catalyst dose increases the HA degradation up to an optimum value. At pH 7 with an initial HA concentration of 14 mg/L, UVA light of 0.236 mW/cm 2 and catalyst dose of 0.3 g/L, 100% efficiency of the HA degradation can be achieved in 3 h. Under identical experimental conditions with UVC light of 0.284 mW/cm 2 , the efficiency of HA degradation also reaches 100%. Based on total organic carbon (TOC) analysis, the mineralization of HA is found to be lower than the degradation of HA. A negligible amount of TOC on the catalyst surface confirms that HA removal is due to photocatalysis. Moreover, a higher degree of mineralization of HA is found under UVA light although degradation is better under UVC light. This indicates that TiO 2 under UVA light has relatively low selectivity to degrade different compounds, including various intermediates from HA degradation.