Increasing UV Light Intensity Research Articles

UV Irradiation and Ozone Treatment of κ-Carrageenan: Kinetics and Products Characteristics

The low molecular weight (LMW) of sulfated polysaccharides including k-carrageenan, is shows a wide spectrum of biological activities. This research investigates the influence of UV irradiation, ozone (O3), and the combination of O3/UV methods on the depolymerization of k-carrageenan. The depolymerization kinetics of k-carrageenan using the Advanced Oxidation Process (UV/O3) was also studied. Furthermore, the intrinsic viscosity method was used to determine the average molecular weight of the research sample, and a mathematical model was developed to predict the kinetic rate constant, as a function of ozone dosage and UV irradiation intensity. Therefore, the physicochemical and morphological properties of the degraded k-carrageenan were analyzed by FT-IR, SEM, and XRD. The intrinsic viscosity k-carrageenan decreases with increasing UV light intensity and ozone concentration. The combination of UV/O3 treatment appeared to be more effective than the individual approaches, as the highest kinetic rate constant for depolymerization was 1.924×10-4 min-1, using 125 mg/L ozone concentration and 40 mW/cm2 of UV lamp intensity. This research also evaluated the relationship between various experimental conditions, including UV lamp power dissipation and ozone concentration on the reaction kinetics model, and the results suggest that lower effect is contributed by UV irradiation intensity. In addition, FT-IR spectra showed the absence of any significant change in the functional properties of k-carrageenan treated with UV and O3 processes, although the morphological properties of the LMW k-carrageenan were rougher and more porous than the native k-carrageenan. Copyright © 2020 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Photocatalytic removal of 2,4-Dichlorophenoxyacetic acid from aqueous solution using tungsten oxide doped zinc oxide nanoparticles immobilised on glass beads

ABSTRACT Groundwater is the only source of high quality water for human consumption in most parts of the world; however, it can be easily contaminated by domestic, industrial, and agricultural wastes such as fertilisers and pesticides. The main objective of the present research was to study the photocatalytic removal of 2,4-Dichlorophenoxyacetic acid pesticide (2,4-D) from aqueous media. This was a laboratory scale study in which the zinc oxide nanoparticles were doped with 0.5, 1, and 2 molar percent of tungsten oxide. The nanoparticles synthesised were characterised using powder XRD, SEM, FTIR, and UV-Vis Spectroscopy analyses. During the photodegradation of 2,4-D, the operational parameters studied were pH, nanoparticles dosage, initial pesticide concentration, light intensity, contact time, and the mineralisation trend of organic matter. It was found that the doped nanoparticles had a smaller band gap energy, which confirms the effect of doping. The percentage of the dopant can affect the pesticide removal efficiency. The optimal pH value obtained was 7. In addition, the process efficiency, increased from 27% to 78% with increasing UV light intensity from 172 to 505 W/m2 respectively. Moreover, it was found that, with increasing light intensity, contact time and nanoparticle concentration all caused the pesticide removal efficiency to be increased too. In addition, the increase of the pesticide concentration would cause a reduction in the process removal efficiency. This study indicated that the photocatalytic process using tungsten doped zinc oxide nanoparticles can remove the 2,4-D pesticide by around 80% from the aquatic environment.

UV light and temperature induced fluridone degradation in water and sediment and potential transport into aquifer

Fluridone is widely used in ambient water bodies to control the spread of invasive aquatic plants. While the ability of fluridone to control aquatic weeds such as water hyacinth is well reported, an improved understanding of fluridone persistence in water and sediment is still needed to determine potential residues of fluridone in the water column and bed sediment of ambient water bodies. In this study, experiments were conducted over a three-month period to examine the degradation of fluridone in saturated sediment and water under various levels of UV-light (0–1000 μW/cm2), and temperature (4–40 °C). Results showed a large decrease in the half-life of fluridone in water with increasing UV light intensity, but in saturated sediment the impact of UV light exposure on fluridone degradation was minimal. At low temperature (4 °C), the degradation of fluridone in both water and sediment was minimal. At elevated temperature (20–40 °C), fluridone degradation was increased in water and sediment. Additionally, the persistence of fluridone in sediment was reduced by increasing sand content in the sediment matrix. Possible fluridone transport through the subsurface was estimated over a range of initial concentrations, groundwater velocities, fluridone half-lives, and fluridone sorption coefficients which may be seen in a field environment. A form of the Ogata-Banks equation which accounts for 1st order decay was used for describing the dispersion of fluridone, while a related equation from Bear, 1979 was utilized to quantify advection. In all tested scenarios, maximum transport was less than 10 m over one month of observation. Results of this study will improve our existing understanding of fluridone persistence and in water and sediment.

Oxidation absorption of hydrogen sulfide from gas stream using vacuum ultraviolet/H2O2/urea wet scrubbing system

Hydrogen sulfide has serious harm to human body and equipment. Advanced oxidation technology shows excellent development prospect for hydrogen sulfide (H2S) removal due to strong oxidation ability and green process. This article proposed a novel separation process for H2S from gas stream using vacuum ultraviolet (VUV)/H2O2/urea wet scrubbing system in a VUV-spraying scrubber, and studied the effectiveness of H2S removal and removal pathways using VUV/H2O2/urea wet scrubbing system. Results indicated that the highest H2S removal efficiency was up to 98.2 % under optimal experimental conditions. Increasing UV-light intensity and solution pH improved the H2S removal efficiency. Increasing flue gas flow rate and H2S concentration decreased the H2S removal efficiency. The increase of H2O2 concentration, reaction temperature, liquid-gas ratio or urea concentration first increased and then reduced the H2S removal efficiency. H2S was removed by five pathways such as ionization, urea absorption, H2O2 oxidation, photolysis and ·OH oxidation. Photolysis and ·OH oxidation were the two major pathways for the H2S removal.

Synthesis, UV response, and room-temperature ethanol sensitivity of undoped and Pd-doped coral-like SnO2

Coral-like mesoporous SnO2 was synthesized by controlled hydrolysis of SnCl4 and subsequent removal of the template by calcination in air. The obtained powder was doped directly with palladium chloride solution. The morphology, crystal structure, specific surface area, and photoelectrical and ethanol gas-sensing properties of undoped and Pd-doped coral-like SnO2 were investigated. The average crystalline sizes of undoped and Pd-doped SnO2 were estimated by Williamson–Hall plots to be 10.3 and 10.0 nm, respectively. From the N2 adsorption–desorption analysis, the pure sample had a surface area 63.3 m2/g with pore size distribution narrowly centered around 5.7 nm. The film sensors based on undoped and Pd-doped SnO2 exhibited novel photoelectrical properties. The photocurrents of the sensors decreased with increasing UV light intensity. The response of the Pd-doped SnO2 sensor to 500 ppm ethanol was 35.3 under UV illumination at room temperature. The results demonstrated that Pd doping could achieve room-temperature detection to ethanol under UV light radiation.

Abnormal photoelectrical properties and gas sensing of mesoporous Sn0.9Ti0.1O2 film under UV light

Mesoporous Sn0.9Ti0.1O2 was prepared by controlled hydrolysis of chlorides and subsequent removal of templates by calcination in air. X-ray diffraction, SEM and nitrogen adsorption–desorption results showed that the mesoporous Sn0.9Ti0.1O2 consisted of nanocrystals with the average size of 10nm. The special surface area and average pore size were 70m2/g and 9nm, respectively, for the mesoporous Sn0.9Ti0.1O2. The film sensors based on the Sn0.9Ti0.1O2 exhibited abnormal photoelectrical properties. The photocurrent of the sensor decreased with increasing UV light intensity in air, but increased with increasing UV light intensity in vacuum. The gas response of the Sn0.9Ti0.1O2 sensor to 1000ppm ethanol was about 8.2 under UV light at room temperature. The conductance mechanism and gas sensing mechanism of the mesoporous nanostructure oxides was discussed.

Effect of platinum on the photocatalytic decomposition of 2‐chlorophenol in aqueous solution by UV/TiO2

Photocatalytic decomposition of 2‐chlorophenol in aqueous solutions with platinum‐coated TiO2 slurry under UV irradiation was examined, utilizing various solution pH levels, dissolved oxygen levels and UV light intensities. The atomic percentage of platinum deposited on the TiO2 surfaces were identified by X‐ray photoelectron spectroscopy (XPS) to be in the range of 0.12 and 0.99%. The decomposition of 2‐chlorophenol in acidic aqueous solutions by UV/TiO2 was enhanced to certain extents for experiments conducted with platinum‐coated TiO2 containing up to 0.82% platinum because of the formation of Schottky barrier between platinum and TiO2 to prevent the recombination of electric holes and electrons. However, for experiments conducted with TiO2 coated with higher platinum contents, the decomposition rate of 2‐chlorophenol was reduced markedly, possibly because of the depression of the light absorption of TiO2 by the shielding of coated platinum. The photocatalytic decomposition of 2‐chlorophenol in aqueous solution was inhibited for experiments conducted in neutral and alkaline solutions because the presence of platinum increases the repulsion between 2‐chlorophenol species and TiO2 to hinder the adsorption of 2‐chlorophenol species on TiO2. The decomposition rate of 2‐chlorophenol in aqueous solution by UV/TiO2 was found to be improved significantly with increasing UV light intensity.

Investigation of the effect of heat attachment method parameters at photocatalytic activity of immobilized ZnO nanoparticles on glass plate

The effect of heat attachment method parameters such as: sonication time, dosage of catalyst, immobilization temperature and type of solvent were investigated for enhancement of photocatalytic activity of immobilized ZnO nanoparticles on glass plate. Photocatalytic activity of immobilized ZnO was tested in the removal of C.I. Acid Red 88 (AR88) as a model contaminant from textile industry. Results indicated that sonication time, dosage of catalyst and immobilization temperature were very effective on photocatalytic activity of immobilized ZnO on glass plate and using ethanol instead of water at preparation of immobilized ZnO did not show any considerable effect. In another step, the effect of operational parameters such as light intensity and initial concentration of AR88 on the removal of AR88 were investigated with immobilized ZnO on glass plate. Results indicated that removal rate decreased with increasing initial concentration of AR88 but increased with increasing UV light intensity.

Increasing photoactivity of titanium dioxide immobilized on glass plate with optimization of heat attachment method parameters

In the present work the optimization of heat attachment method for increasing photoactivity of immobilized TiO 2 on glass plate was investigated. Results show that sonication time, TiO 2 suspension dosage, immobilization temperature, solvent type and immobilization replications are very effective on the photoactivity of immobilized TiO 2 on glass plate on the removal of C.I. Acid Red 88 (AR88) and optimizing these parameters increases the photoactivity of immobilized catalyst. In other step, the effect of operational parameters such as light intensity and initial concentration of AR88 on the removal of AR88 was investigated with four times immobilized TiO 2 on glass plate. Results show that removal rate decreases with increasing initial concentration of AR88 but increases with increasing UV-light intensity.

태양광/광촉매를 이용한 오폐수 살균특성

Currently, the application of <TEX>$TiO_2$</TEX> photocatalyst has been focused on purification and treatment of wastewater. However, the use of conventional <TEX>$TiO_2$</TEX> slurry photocatalyst results in disadvantage of stirring during the reaction and of separation after the reaction. And the usage of artificial UV lamp has made the cost of photocatalyst treatment system high. Consequently, we studied that solar light/<TEX>$TiO_2$</TEX> film system was designed and developed in order to examine disinfection characteristics of sewage wastewater treatment. The optimum conditions for disinfection such as solar light intensity, characteristic of sewage wastewater, amounts of <TEX>$TiO_2$</TEX> and comparison of solar ligth/<TEX>$TiO_2$</TEX> systems with UV light/<TEX>$TiO_2$</TEX> system was examined. The results are as follows: (1) photocatalytic disinfection process with solar light in the presence of <TEX>$TiO_2$</TEX> film more effectively killed total coliform (TC) than solar light or <TEX>$TiO_2$</TEX> film absorption only. (2) The survival ratio of TC and residual ratio of organic material (BOD, CODcr) decreased with remain resistant material. (3) The survival ratio of TC and residual ratio of organic material (BOD, CODcr) decreased with the increase of amounts of <TEX>$TiO_2$</TEX>. (4) TC survival ratio decreased linearly with increasing UV light intensity. (5) The disinfection effect of solar light/<TEX>$TiO_2$</TEX> slurry system decreased more than UV light/<TEX>$TiO_2$</TEX> film systems. (6) The disinfection reaction followed first-order kinetics. We suggest that solar light instead of using artificial UV light was conducted to investigate the applicability of alternative energy source in the disinfection of TC and the degradation of organic material.

Photocatalytic decomposition of 2-chlorophenol in aqueous solution by UV/TiO 2 process with applied external bias voltage

The decomposition of 2-chlorophenol by UV/TiO 2 process with the application of external bias voltage was examined in this study. Experiments were conducted in a batch reactor using TiO 2-coated titanium sheet as anode and platinum sheet as cathode. The anode photocatalysis of 2-chlorophenol was totally inhibited for experiments conducted with the application of external anodic bias voltage lower than the flat band potential of TiO 2. The decomposition rate of 2-chlorophenol was then increased with increasing external anodic bias voltage applied up to 0.0 V (versus SCE). The application of external bias voltage higher than 1.0 V did not markedly promote the photocatalysis of 2-chlorophenol possibly because the photocurrent induced was constant. Experimental results indicated that the decomposition of 2-chlorophenol was more effective for experiments conducted in acidic solutions due to the lower flat band potential of TiO 2 and the higher photocurrent induced. The presence of electron scavengers in aqueous solution, such as oxygen molecules, may increase the decomposition rate of 2-chlorophenol. However, the effect of dissolved oxygen was diminished for experiments conducted with applied external bias voltage. The photocatalytic decomposition rate of 2-chlorophenol was enhanced linearly with the increasing UV light intensity when the external bias voltage was applied.

Degradation of microcystin-RR by UV radiation in the presence of hydrogen peroxide

Experiments were conducted to investigate the degradation of microcystin-RR in order to assess the effectiveness and feasibility of the combined UV/H 2O 2 catalytic system for purification of water polluted by microcystins. The operating parameters such as hydrogen peroxide dosage, pH value, UV light intensity, initial concentration of microcystin-RR and reaction time were evaluated, respectively. The degradation efficiency increased nonlinearly with increasing UV light intensity and hydrogen peroxide dosage, respectively. There existed an optimal hydrogen peroxide dosage, beyond which the reagent exhibited an inhibitory effect, for degrading microcystin-RR. The degradation process could be fitted by both of the pseudo-first-order and second-order kinetics well and primarily followed a mechanism of both direct photolysis and hydroxyl radical oxidation. Compared with the treatment using UV radiation and hydrogen peroxide individually, the combined UV/H 2O 2 system could significantly enhance the degradation efficiency due to the synergetic effect between UV radiation and hydrogen peroxide oxidation. The observed rate constants decreased and the corresponding half-lives prolonged as the concentrations of microcystin-RR increased. The combined UV/H 2O 2 process provides an effective technology for the removal of microcystins from drinking water supplies.

Solar Light Induced Degradation of Reactive Dye Using Photocatalysis

Outdoors experiment with natural solar light instead of using artificial UV light was also conducted to investigate alternative energy source applicability on organics degradation. The results of this study were as follows. Degradation of the reactive dye, Red 120, with TiO2/solar light was enhanced by augmentation in TiO2 loading, and UV light intensity but was inhibited by increase in initial dye concentration. With both solar light illumination and TiO2 present, reactive dye was more effectively eliminated than with either solar light or TiO2 alone. Photocatalytic removal efficiency of reactive dye increased with increasing TiO2 dosage. However, over 1.5 gL−1 of TiO2 dosage, the efficiency reached a plateau. The degradation rate of reactive dye, Red 120, was strongly dependent on initial dye concentration, and all the experimental data were fit to the first-order rate equation. Photocatalytic degradation of reactive dye increased linearly with increasing UV light intensity. It is found that the presence of thick clouds in the sky markedly increased the time required for degradation of reactive dye. On the basis of these experimental observations, the photo-oxidation degradation of reactive dye using TiO2 under solar light irradiation can be feasible application of the advanced oxidation process.

Highly sensitive ultraviolet detector based on ZnO/LiNbO3 hybrid surface acoustic wave filter

Fabrication of a highly-sensitive UV detector based on the surface-acoustic-wave (SAW) principle is reported. The output voltage of the SAW oscillator constructed with a ZnO/LiNbO3 hybrid SAW filter was found to decrease linearly with increasing UV light intensity, and a very low intensity UV light of 10 μW/cm2 was detected easily. Our results show its potential use in wireless UV measurement systems.

Removal of Reactive Dye Using UV/TiO2 in Circular Type Reactor

Photocatalytic degradation of reactive dye, Red 120, was carried out on TiO2 particles as photocatalyst under UV irradiation. In this experiment, comparison on the removal of reactive dye by photolysis using UV light alone, photocatalyst adsorption using TiO2 alone and photocatalysis using UV light with photocatalysts as well as the effect of experimental parameters such as the number of column employed, intensity of the light, pH and TiO2 dosage affecting the reaction efficiency of photocatalytic degradation of reactive dye in circular type reactor was examined. The results of this indicate that with both UV light illumination and TiO2 present, reactive dye was more effectively eliminated than with either UV or TiO2 alone. Photocatalytic degradation of reactive dye increased linearly with increasing UV light intensity. However, over 18 mW cm−2 of UV light intensity, the efficiency reached a plateau. The photocatalytic degradation rate was greater in acid media than in alkaline media. Photocatalytic removal efficiency of reactive dye increased with increasing TiO2 dosage. However, over 1.5 g L−1 of TiO2 dosage, the efficiency reached a plateau.

Disinfection effects on E. coli using TiO2/UV and solar light system

First, a continuous flow TiO2/UV reactor was designed and developed in order to examine E. coli disinfection effect using UV light. The optimum conditions for disinfection such as flow rate, light intensity, TiO2 concentration, initial E. coli concentration were examined. The results are as follow (i) The use of the quartz device and TiO2 (anatase) resulted in killing of E. coil within minutes. (ii) Photocatalytic disinfection with UV light in the presence of TiO2 more effectively killed E. coli than UV or TiO2 adsorption only. (iii) As flow rate increased, the survival ratio of E. coli decreased, but over 3 L/min of flow rate, the efficiency was limited. (iv) E. coli survival ratio decreased linearly with increasing UV light intensity. (v) The dosage of TiO2 affected the E. coli disinfection efficiency, and above 0.1 wt% TiO2 concentration, the disinfection was less effective because TiO2 particles may result in screening off the light. (ri) The disinfection reaction follows first-order kinetics. Secondly, outdoor experiments with natural sunlight instead of artificial UV light in TiO2 reactors were also conducted to investigate alternative energy source applicability on E. coli disinfection. It is found that the presence of clouds in the sky markedly increased the time required for killing E. coli and the bacteria cells also disappeared with a first-order kinetics. On the basis of these experimental observations, the disinfection of E. coli using TiO2 under solar light irradiation can be a feasible application of the advanced oxidation process.