Production Rate Of Hydroxyl Radicals Research Articles

Application of novel nanobubble-contained electrolyzed catalytic water to cleanup petroleum-hydrocarbon contaminated soils and groundwater: A pilot-scale and performance evaluation study

Soil and groundwater contamination caused by petroleum hydrocarbons is a severe environmental problem. In this study, a novel electrolyzed catalytic system (ECS) was developed to produce nanobubble-contained electrolyzed catalytic (NEC) water for the remediation of petroleum-hydrocarbon-contaminated soils and groundwater. The developed ECS applied high voltage (220 V) with direct current, and titanium electrodes coated with iridium dioxide were used in the system. The developed ECS prototype contained 21 electrode pairs (with a current density of 20 mA/cm2), which were connected in series to significantly enhance the hydroxyl radical production rate. Iron-copper hybrid oxide catalysts were laid between each electrode pair to improve the radical generation efficiency. The electron paramagnetic resonance (EPR) and Rhodamine B (RhB) methods were applied for the generated radical species and concentration determination. During the operation of the ECS, high concentrations of nanobubbles (nanobubble density = 3.7 × 109 particles/mL) were produced due to the occurrence of the cavitation mechanism. Because of the negative zeta potential and nano-scale characteristics of nanobubbles (mean diameter = 28 nm), the repelling force would prevent the occurrence of bubble aggregations and extend their lifetime in NEC water. The radicals produced after the bursting of the nanobubbles would be beneficial for the increase of the radical concentration and subsequent petroleum hydrocarbon oxidation. The highly oxidized NEC water (oxidation-reduction potential = 887 mV) could be produced with a radical concentration of 9.5 × 10−9 M. In the pilot-scale study, the prototype system was applied to clean up petroleum-hydrocarbon polluted soils at a diesel-oil spill site via an on-site slurry-phase soil washing process. The total petroleum hydrocarbon (TPH)-contaminated soils were excavated and treated with the NEC water in a slurry-phase reactor. Results show that up to 74.4% of TPH (initial concentration = 2846 mg/kg) could be removed from soils after four rounds of NEC water treatment (soil and NEC water ratio for each batch = 10 kg: 40 L and reaction time = 10 min). Within the petroleum-hydrocarbon plume, one remediation well (RW) and two monitor wells (located 1 m and 3 m downgradient of the RW) were installed along the groundwater flow direction. The produced NEC water was injected into the RW and the TPH concentrations in groundwater (initial concentrations = 12.3–15.2 mg/L) were assessed in these three wells. Compared to the control well, TPH concentrations in RW and MW1 dropped to below 0.4 and 2.1 mg/L after 6 m3 of NEC water injection in RW, respectively. Results from the pilot-scale study indicate that the NEC water could effectively remediate TPH-contaminated soils and groundwater without secondary pollution production. The main treatment mechanisms included (1) in situ chemical oxidation via produced radicals, (2) desorption of petroleum hydrocarbons from soil particles due to the dispersion of nanobubbles into soil pores, and (3) enhanced TPH oxidation due to produced radicals and energy after nanobubble bursting.

Regulating the charge density of Cu(I) single sites enriched on the surface of N3c Vacancies-engineered g-C3N4 for efficient Fenton-like reactions

The construction of highly accessible copper active sites with enhanced charge density is essential for the performance of Cu-based Fenton catalysts. Herein, we report the preparation of a catalyst comprising Cu(I) atoms anchored on the surface of N3c vacancies-engineered g-C3N4 (Cu/Nv-CN) and its enhanced Fenton-like performance. The surface-enrichment of single Cu(I) atoms maximizes the exposure of active sites and reduces the mass transfer limitation for short-lived hydroxyl radicals. The N3c vacancies, meanwhile, facilitate electron donation from N2c to Cu sites, greatly increasing the number of single Cu(I) sites. These two strategies synergistically enhance the hydroxyl radical production rate in the Fenton-like process and endow Cu/Nv-CN with not only excellent performance in degrading various contaminants (such as phenolic compounds, endocrine disruptors, antibiotics, and dyes), both in purified and real water samples matrixes, but also superior bactericidal properties for Escherichia coli. Compared to bulk Cu-doped g-C3N4 without N3c vacancies (CO-Cu/CN), Cu/Nv-CN shows a more than 14-fold increase in phenol degradation and an enhancement of approximately 4 log10 CFU/mL in bacterial inactivation. Our strategy of increasing the number of Cu(I) single atoms through surface enrichment and enhanced electron donation opens up a new route for the design of efficient Fenton-like catalysts for environmental remediation.

Turbulent transport and reactions of plant-emitted hydrocarbons in an Amazonian rain forest

The processes governing the temporal and spatial patterns of isoprene and monoterpenes emitted by a rainforest in the central Amazon region of Brazil is investigated using a combination of field experiments and numerical simulations. Specifically, Large Eddy Simulations (LES) were used to resolve emissions of isoprene and monoterpenes, turbulent transport, and air chemistry. The coupled chemistry-transport LES included the effects of isoprene and monoterpenes reactivity due to reactions with hydroxyl radical and ozone. The LES results are used to compute vertically resolved budgets of isoprene and monoterpenes in the rainforest canopy in response to emissions, turbulent transport, surface deposition, and air chemistry. Results indicated that emission and dispersion dominated the isoprene budget as the gases were transported out of the canopy space. In a region limited by nitrogen oxides (with prevailing nitric oxide levels of < 0.5 parts per billion), the in-canopy chemical destruction removed approximately 10% of locally emitted monoterpenes. Hydroxyl radical production rates from the ozonolysis of monoterpenes amounted to ≈2×106radicalscm−3s−1 and had similar magnitude to the light-dependent hydroxyl radical formation. One key conclusion was that the Amazonia rainforest abundantly emitted monoterpenes whose in-canopy ozonolysis yielded hydroxyl radicals in amounts similar to the magnitude of light-dependent formation. Reactions of monoterpenes and isoprene with hydroxyl radical and ozone were necessary for the maintenance of the Amazon rainforest canopy as a photochemically active environment suitable to generate oxidants and secondary organic aerosols.

Influence of nickel dopant concentration on structural, optical, magnetic and electrochemical properties of TiO2 nanoparticle

In this work, we report enhanced photocatalytic and magnetisation effects of nickel (Ni) ion doped titanium dioxide (TiO2) nano particles. The nano crystalline TiO2 doped with different concentrations of Ni (0.05-0.2%) were prepared by sol-gel method and characterised by various analytical techniques such as X-ray diffraction (XRD), UV-Vis spectroscopy, scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). The Ni metal ions incorporation modified the microstructure of TiO2 nano particles considerably which are evident from XRD and SEM analyses. The band gap reduction made by the Ni impurity level extends the TiO2 optical absorption edge to visible region. The photocatalytic activity of TiO2 and Ni-TiO2 was studied by photo degradation of methyl orange dye as a function of irradiation time under visible light. The results signify that TiO2 nanoparticles doped with the higher of concentration of 0.2% Ni improves the reaction rate of hydroxyl radical production. The electrochemical behaviour of the prepared samples was analysed by cyclic voltammetry study. The existence of hard ferromagnetic behaviour with the enhanced magnetisation in Ni doped TiO2 samples make this as an appropriate material for possible applications in spintronic and magneto-electronic devices.

Superoxide-driven autocatalytic dark production of hydroxyl radicals in the presence of complexes of natural dissolved organic matter and iron

We introduced superoxide as potassium superoxide (KO2) to artificial lake water containing dissolved organic matter (DOM) without or with introduced ferric iron complexes (DOM-Fe(III)), and monitored the production rate of hydroxyl radicals as well as changes in the absorption and fluorescence properties of DOM. The introduction of KO2 decreased the absorption by DOM but increased the spectral slope coefficient of DOM more with complexed ferric Fe than without it. The introduction of KO2 increased the fluorescence of humic-like components in DOM without introduced ferric Fe but resulted in the loss of fluorescence in DOM with introduced ferric Fe. A single introduction of 13 μmol L−1 KO2 produced 10 μmol L−1 and 104 μmol L−1 hydroxyl radicals during a week-long experiment without and with the introduced DOM-Fe(III) complexes, respectively. The production rate of hydroxyl radicals decreased exponentially with time but levelled off and continued several days in DOM with introduced ferric Fe. These findings suggest that in the presence of DOM-Fe complexes, superoxide can trigger an autocatalytic Fenton reaction that produces hydroxyl radicals and breaks down DOM.

Photocatalytic removal of 4-chlorophenol present in water using ZrO2/LDH under UV light source

The influence of ZrO2 semiconductor content (0.3–5 wt%) supported on a Layered Double Hydroxides (LDH) system for photodegradation of 4-chlorophenol (4-CP) in water was studied. Complete removal of 4-CP is achieved in two stages: first, 4-CP was adsorbed on the photocatalyst in darkness, until equilibrium was reached. Afterwards, the light was turned on, and the photodegradation process started. Adsorption and photodegradation were analyzed both individually, and combined. The adsorption process of 4-CP on the synthesized samples is well described by fitting a pseudo-second-order equation. The UV photodegradation rates were 2.6 times higher than the 4-CP removal rates achieved by adsorption. The photodegradation process was analyzed by means of hydroxyl radical production displaying zeroth order behavior. The photocatalyst with 1 wt% ZrO2/LDH had the highest hydroxyl radical production rate, achieving 99 % of 4-CP degradation and 87 % of mineralization, while maintaining its photocatalytic activity during ten reaction cycles. At wt%ZrO2/ LDH higher than 1 wt%, clustering is observed, promoting charge recombination, hindering photodegradation efficiency and thus, decreasing mineralization rates. The monoclinic phase of ZrO2, identified by XRD, was responsible for the high photocatalytic activity. The distances between cations within the LDH layers were not modified after ZrO2 impregnation, thus suggesting that zirconia was supported on the external surface of LDH. Characterization was done by N2 physisorption, TGA, XRD, AAS, UV-DRS TEM, and SEM-EDS.

Effect of cathode material on electro-Fenton process efficiency for electrocatalytic mineralization of the antibiotic sulfamethazine

Cathode material plays a crucial role in electro-Fenton process since its efficiency depends to the ability of the cathode material to generate H2O2 which controls the production rate of hydroxyl radicals, the main oxidizing agent for destruction of organic pollutants. Therefore, this study focused on the role of different cathode materials (i.e., carbon sponge (CS) of five different porosities, carbon felt (CF), and stainless steel (SS)) on the electrochemical oxidation and mineralization of sulfamethazine (SMT) in aqueous solution. Prior to studying the degradation and mineralization power of the cathodes under examination, we performed a systematic study of the production of H2O2. It was found that all the carbon sponge cathodes give high amounts of H2O2 in the solution, the most effective being the 45 ppi (pore per linear inch) porosity followed by carbon felt cathode. Stainless steel only gives poor amounts of H2O2 for current of 50 and 100 mA. The degradation and mineralization experiments were consistent with the yield of H2O2 for all electrolytic systems; electrolytic cells with higher H2O2 production capacity showed better performance on SMT degradation/mineralization. The most effective electrolytic system for SMT removal from polluted water was Pt/CS 45 ppi reaching a mineralization rate of 91.1% at 300 mA while the less effective was Pt/SS with only 41% mineralization.

Understanding Amyloid-Beta Plaque Formation By Monitoring the Redox Activity of Copper at the Active Site

The Amyloid β peptide (Aβ-42) can be expressed through cleavage of a precursor protein (APP) during post-translational modification as a result of oxidative stress in the brain. Once expressed, the peptide will readily form binding interactions with free metal ions, particularly Cu2+, initiating a series of redox reactions that result in the production of Reactive Oxygen Species (ROS) and amyloid plaques within the brain. This process has been implicated as the major contributing factor in neurodegeneration in Alzheimer’s patients. An increasingly promising area of study in the treatment of AD is to disrupt this pathway using metal ion chelation, which can serve as a form of therapeutic treatment. The work presented herein focuses on different copper coordination compounds and their redox activity using various ligands such as glycine, beta alanine, phenylalanine, 2,2’-bipyridine (bipy), 2,2’-thiodipyridine (DPS), 2,2’-dipyridylamine (DPA), and 1,10-phenanthroline-2-thiopyridine (TPP). Utilizing Cyclic Voltammetry to monitor redox activity, the more stable ligand complexes resulted in a more quasi-reversible cyclic voltammogram, allowing for potential redox cycling between Cu2+ and Cu+ at the Aβ-42 active site. The CV results correlated well with hydroxyl radical trapping experiments that measured the rate of hydroxyl radical production in each complex, and a relationship between redox activity and hydroxyl radical production was observed. With the Aβ-42 peptide, these coordination complexes were analyzed using Atomic Force Microscopy (AFM) to correlate the rate of fibril formation to plaque formation. These results provide valuable insight into ligand design characteristics important for the development of potential therapeutic treatments that slow AD progression.

Study on heterogeneous photocatalytic ozonation degradation of ciprofloxacin by TiO2/carbon dots: Kinetic, mechanism and pathway investigation

In this study, the objective was mainly focusing on the mechanism investigation of ciprofloxacin (CIP) degradation by photocatalytic ozonation process which carried out by ozone and TiO2 with a low content of carbon-dots (CDs) under simulated sunlight irradiation. The physicochemical properties of the prepared photocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscope (SEM) X-ray photoelectron spectroscopy (XPS) and zeta potential. Comprehensive investigation has proven the process to be efficient in the removal of CIP with high yield of reactive species (OH, O2—, h+, etc.). Kinetic model on pH investigation found out a repulsive force between the photocatalysts and CIP intensified with the increasing pH, so did the production rate of hydroxyl radicals (OH), while eventually reached a balance and achieved a maximum degradation rate. The results indicated that the enhancement mechanism was triggered by the photoexcited electron accumulated on CDs and transferred by ozone, resulting in the continuous generation of h+, O3— and O2—. Possible photocatalytic ozonation degradation pathways of CIP were proposed according to the identifications of intermediates using high-resolution accurate-mass spectrometry (HRAM) LC-MS/MS.

Self-Propelled Micromotors for Naked-Eye Detection of Phenylenediamines Isomers.

Tubular micromotors composed of a hybrid single-wall carbon nanotube (SW)-Fe2O3 outer layer and powered by a MnO2 catalyst are used for phenylenediamines isomers detection and discrimination. Catalytic decomposition of H2O2 as fuel results in the production of oxygen bubbles and hydroxyl radicals for phenylenediamines dimerization to produce colorful solutions in colorimetric assays. The combination of Fe2O3 nanoparticles along with the irregular SW backbone results in a rough catalytic layer for enhanced hydroxyl radical production rate and improved analytical sensitivity. Such self-propelled micromotors act as peroxidase-like mobile platforms that offer efficient phenylenediamines detection and discrimination in just 15 min. Factors influencing the colorimetric assay protocol, such as the navigation time and number of motors, have been investigated. Low limits of detection (5 and 6 μM) and quantification (17 and 20 μM) were obtained for o-phenylenediamine and p-phenylenediamine, respectively. The magnetic properties of the outer SW-Fe2O3 hybrid layer allow the reusability of the micromotors in the colorimetric assay. Such attractive performance holds considerable promise for its application in sensing systems in a myriad of environmental, industrial, and health applications.

CuO embedded silica nanoparticles for tungsten oxidation via a heterogeneous Fenton-like reaction

The Fenton reaction is used for the oxidation of tungsten via the production of hydroxyl radicals under acidic conditions. However, the narrow working pH range required for ideal reaction conditions limits the applications of these reactions. Herein, we developed a simple heterogeneous Fenton-like system for hydroxyl radical production over a broad pH range. Copper oxide nanoparticles (NPs) grown on the surface of silica NPs led to a heterogeneous Fenton-like reaction with hydrogen peroxide (H2O2), resulting in a high production rate of hydroxyl radicals in the range of acidic to neutral pH. The increased hydroxyl radical production rate at these pH values led to a high oxidation rate of tungsten. Furthermore, we applied this heterogeneous Fenton-like system to tungsten chemical mechanical planarization, resulting in high performance tungsten removal in acidic to neutral pH conditions.

Disordered Atomic Packing Structure of Metallic Glass: Toward Ultrafast Hydroxyl Radicals Production Rate and Strong Electron Transfer Ability in Catalytic Performance

Developing new functional applications of metallic glasses in catalysis is an active and pivotal topic for materials science as well as novel environmental catalysis processes. Compared to the crystalline materials with highly ordered atomic packing, metallic glass has a simply disordered atomic structure. Recent reports have demonstrated that the metallic glasses are indeed having many superiorly catalytic properties, yet the understanding of the mechanism is insufficient. In this work, the structural relaxation (α‐relaxation) by annealing in an amorphous Fe78Si9B13 alloy is studied for unraveling the catalytic mechanism at the atomic scale. The volume fractions of the crystalline structures, such as α‐Fe, Fe2Si, and Fe2B, in the as‐received and annealed metallic glasses are fully characterized. It is found that the randomly atomic packing structure with weak atomic bonding in the as‐received metallic glass has an efficient electron transfer capability, presenting advanced superiorities in the aspects of production rate of hydroxyl radicals (•OH), dye degradation rate (k), and essential degradation ability (KSA) for water treatment. The discovery of this critically important work unveils why using metallic glasses as catalysts has higher reactivity than the crystalline materials, and more importantly, it provides new research opportunities into the study of synthetic catalysts.

Abatement of Sorbed Crude Oil by Heterogeneous Fenton Process Using A Contaminated Soil Pre-Impregnated with Dissolved Fe(II) and Humic Acid

ABSTRACTDissolved Fe(II) and humic acid (HA) were pre-impregnated into contaminated soil to catalyze hydrogen peroxide to remove crude oil (CO). The effects of parameters such as initial Fe(II), HA and H2O2 concentrations on the oxidation of total petroleum hydrocarbon (TPH) were investigated using response surface methodology based on Box–Behnken design. The rate of hydrogen peroxide decomposition is decreased by pre-impregnating with dissolved Fe(II) + HA compared with only pre-impregnated Fe(II) and modified Fenton (MF). Oxygen evolution is the predominant route of hydrogen peroxide decomposition at natural pH. Unlike O2 evolution, the kinetics of hydroxyl radical (OH•) production are clearly uncoupled from H2O2 decay in these systems. The steady-state hydroxyl radical production rate is higher in the systems with pre-impregnated dissolved Fe(II) and HA, and more significance is the decrease in detectable TPH (70.84% removal efficiency) when soil is pre-impregnated with dissolved 25 mM Fe(II) + 0.7 mg/mL HA, and with the application of 700 mM H2O2, possibly due to hydrogen peroxide catalyzed by the iron of this complex (CO-HA–Fe(II)) producing hydroxyl radical in close proximity to the CO. Meanwhile, the removal efficiency of C21–C30 is up to 65.69%, which is 2.6 times higher than that of the MF (25.52%).

Surface aging behaviour of Fe-based amorphous alloys as catalysts during heterogeneous photo Fenton-like process for water treatment

Two novel, multifunctional Fe-based amorphous alloys with the nominal components of Fe78Si9B13 and Fe73.5Si13.5B9Cu1Nb3 exhibit advanced catalytic capability when degrading methyl blue (MB) and methyl orange (MO) dyes. The production rate of hydroxyl radicals (OH) in this work is 5–10 times faster than other Fe-based catalysts. The surface aging behaviour on Fe78Si9B13 and Fe73.5Si13.5B9Cu1Nb3 ribbons shows a significant effect on the dye degradation efficiency and reusability of the catalyst. Results reveal that crystallized α-Fe, iron oxide and SiO2 are gradually precipitated on the surface of the reused Fe78Si9B13 ribbon which ultimately becomes corroded through with holes. However, the inclusion of Nb atoms in the Fe73.5Si13.5B9Cu1Nb3 alloy causes the formation of niobium oxides which overlay the ribbon surface, and tend to reduce the contact area between the Fe and H2O2, thereby decreasing the generation of OH and further reducing the dye degradation efficiency. Tert-butanol is employed for quenching hydroxyl radicals (OH), causing a dramatic reduction in the amount available for degrading the MB and MO molecules. The MB and MO dye degradation and mineralization under UV–vis light are also fully investigated. The findings of this critically important work should form the basis of new research opportunities into the study of amorphous alloy catalysis.

A novel fabrication method for titanium dioxide/activated carbon fiber electrodes and the effects of titanium dioxide on phenol degradation

In this paper, the nano-titanium dioxide/activated carbon fiber (TiO2/ACF) electrodes are prepared by using ship-in-a-bottle method with Ti(OC4H9)4 as a raw material. The amounts of TiO2 immobilized on the activated carbon fiber are 0.14, 0.28 and 0.42g/g ACF, respectively. The adsorption behavior and electro-catalytic oxidation of phenol with these three kinds of electrodes are investigated. Experimental results show that the maximum adsorption quantities of the phenol decreased by 12.41%, 17.25% and 32.38% respectively with the increase of TiO2, while the adsorption rates decreased by 56.22%, 71.26% and 88.73%, respectively. However, the removal efficiency of phenol and the production rate of hydroxyl radicals (OH) increased with the increase of TiO2. Compared with sol–gel method, TiO2/ACF electrode prepared by ship-in-a-bottle method not only exhibit better electro-catalytic activity and stability, but also cheaper. Because the amount of Ti(OC4H9)4 used to prepare TiO2 can be reduced by more than 33%. In addition, the nano-TiO2 particles, smaller and more uniform in size, can be immobilized firmly and prepared easily in this method.

An Fe–Mn binary oxide (FMBO) modified electrode for effective electrochemical advanced oxidation at neutral pH

Fe-Mn binary oxide (FMBO)/activated charcoal (AC) is blended with carbon black (CB) for use as a dual function catalyst for the effective removal of organic pollutants at neutral pH via electro-Fenton-like oxidation. CB, which is composed of micropores and mesopores, acts as an oxygen reduction catalyst to produce H2O2, and the evenly distributed FMBO nanoparticles effectively catalyze the production of hydroxyl radicals using the on-site generated H2O2. As a result, the FMBO-modified electrode exhibits a high catalytic efficiency over a wide pH range from 3–10. The prepared electrode exhibited a hydroxyl radical production rate of 1.3μMW−1cm−2at neutral pH, higher than that obtained with the blank CB electrode and Fe(II) (0.72μMW−1cm−2). The removal efficiency of nitrobenzene reached 80±3% at neutral pH with the FMBO/AC/CB electrode compared to 42±7% with Fe(II). The results from various material characterization techniques including X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) confirm that FMBO/AC is bound to poly(tetrafluoroethylene) (PTFE) together with CB in the prepared electrode. These results suggest that electrochemical advanced oxidation using this new FMBO/AC/CB electrode represents a promising approach for organic pollutant removal.

Rates of Hydroxyl Radical Production from Transition Metals and Quinones in a Surrogate Lung Fluid.

Hydroxyl radical ((•)OH) is the most reactive, and perhaps most detrimental to health, of the reactive oxygen species. (•)OH production in lungs following inhalation of particulate matter (PM) can result from redox-active chemicals, including iron and copper, but the relative importance of these species is unknown. This work investigates (•)OH production from iron, copper, and quinones, both individually and in mixtures at atmospherically relevant concentrations. Iron, copper, and three of the four quinones (1,2-naphthoquinone, phenanthrenequinone and 1,4-naphthoquinone) produce (•)OH. Mixtures of copper or quinones with iron synergistically produce (•)OH at a rate 20-130% higher than the sum of the rates of the individual redox-active species. We developed a regression equation from 20 mixtures to predict the rate of (•)OH production from the particle composition. For typical PM compositions, iron and copper account for most (•)OH production, whereas quinones are a minor source, although they can contribute if present at very high concentrations. This work shows that Cu contributes significantly to (•)OH production in ambient PM; other work has shown that Cu appears to be the primary driver of HOOH production and dithiothreitol (DTT) loss in ambient PM extracts. Taken together, these results indicate that copper appears to be the most important individual contributor to direct oxidant production from inhaled PM.

Sonochemical characterisation of ultrasonic dental descalers

An ultrasonic dental descaling instrument has been characterised using sonochemical techniques. Mapping the emission from luminol solution revealed the distribution of cavitation produced in water around the tips. Hydroxyl radical production rates arising from water sonolysis were measured using terephthalate dosimetry and found to be in the range of μmolmin−1, comparable with those from a sonochemical horn. Removal of an ink coating from a glass slide showed that cleaning occurred primarily where the tip contacted the surface but was also observed in regions where cavitation occurred even when the tip did not contact the surface. Differences in behaviour were noted between different tip designs and computer simulation of the acoustic pressure distributions using COMSOL showed the reasons behind the different behaviour of the tip designs.

SnOx–ZnGa2O4 Photocatalysts with Enhanced Visible Light Activity

Surface modification of zinc gallate with SnOx species produces photocatalysts active for cresol oxidation using visible light. In these composite materials, the production rate of hydroxyl radicals and the cresol degradation rate just in visible light are higher than those with zinc gallate in UV light. The visible light absorbance in the newly introduced SnOx surface phase is attributed to the presence of Sn2+ as confirmed using Mossbauer spectroscopy. Because cresol degradation proceeds via direct oxidation by holes, the increased degradation rates in UV and visible light suggest an increase in the effective photo-oxidative reactivity of holes produced in the photocatalyst system.

Kinetics of catalytic ozonation of atrazine in the presence of activated carbon

Performance of a commercial activated carbon in removing atrazine with ozone in a laboratory-scale mixed reactor was studied. The operating variables were the presence of radical scavenger, solution pH, and dose of activated carbon catalyst. Results show that activated carbon significantly enhances the degradation rate of atrazine through increasing production rate of hydroxyl radicals ( OH) resulting from the ozone decomposition initiated on the carbon surface. At pH level of 3, using 1 g L −1 activated carbon; pseudo first-order ozone decomposition rate constant ( k D ) and the ratio between OH and ozone concentrations ( R ct ) increased from 2.43 × 10 −4 to 17.0 × 10 −4 s −1 and 0.21 × 10 −9 to 7.40 × 10 −9, respectively. The overall reaction rate was enhanced by the presence of activated carbon at pH 3, 5, and 7; however, the most significant improvement in the overall rate constants ( k overall ) was observed at pH 3 and 7, whereby four-fold and two-fold increases in k overall values were observed. The notable decrease of atrazine removal rate observed in the presence of radical scavenger tert-butyl alcohol indicates that the reaction between atrazine and both molecular ozone and OH proceeds mainly in the bulk liquid phase.