Decomposition Of 4-chlorophenol Research Articles

Experimental criteria of sequential continuous ozonation and semi-continuous biodegradation for the decomposition of 4-chlorophenol

This study presents experimental criteria for developing a sequential treatment that couples continuous ozonation with aerobic biodegradation to degrade 4-chlorophenol (4-CP). The ozonation of 4-CP (60, 120, and 240 mg L−1) was carried out in semi-continuous and continuous modes to select suitable experimental conditions in terms of the decomposition efficiency (DE) of 4-CP and its toxic ozonation products (for continuous mode). Complete degradation of 4-CP (98–100% DE) was achieved within 10–30 min of ozonation in the semi-continuous mode and with hydraulic retention times (HRT) of 30, 45, and 60 min in the continuous system. Continuous ozonation resulted in 46.7% and 36.8% reduction of total organic carbon (TOC) for 4-CP initial concentrations of 120 and 240 mg L−1 at 60 min of HRT, respectively. Based on these results, the combination of ozonation and biological treatment was evaluated. Biodegradation experiments were conducted in batch, fed-batch, and continuous operation modes using a microbial consortium adapted to the pre-ozonized 4-CP. In this step, the TOC of pre-ozonized solutions was reduced by 93%. The global efficiency of ozonation followed by biodegradation system reached up to 96% of mineralization. Suitable experimental conditions were obtained through mathematical modeling of continuous ozonation and biodegradation data. The mineralization achieved was the target result of the proposed treatment scheme, with the maximum mineralization of ozonation products in the bioprocess serving as a critical criterion for its efficacy. Based on a proposed mathematical model, the experimental results were used to conduct kinetic studies of ozonation and biodegradation in continuous mode.

Cryogels with Noble Metal Nanoparticles as Catalyst for “Green” Decomposition of Chlorophenols

Pollution of the aquatic environment by halogen derivatives widely used as antiseptic compounds, as well as chemicals for various industrial purposes, is significant. Existing systems of bioremediation poorly solve the problem of eliminating pollution. This paper discusses the preparation of novel macroporous chitosan-based cryogels with in situ-immobilized Pd or Pt nanoparticles as a catalyst for dichlorination reactions. The formation mechanism of metal coordinated chitosan gels using Medusa software modelling and rheology (G’ and G’’) is discussed. Metal coordinated chitosan gels were subsequently converted into covalently cross-linked macroporous cryogels with in situ-immobilized Pd or Pt nanoparticles using the redox potentials difference of the reaction mixture. Noble metal nanoparticles of average size, 2.4 nm, were evenly distributed in the cryogel structure. The effectiveness of these gels as a catalyst for the decomposition of chloro-compounds o-chlorophenol, p-chlorophenol and 2,4-dichlorophenol was tested. The catalytic hydrogenation reaction was carried out using the “green reducing agent” formic acid. Increasing the excess of formic acid with heating increases the degree of conversion up to 80–90%. The CHI-GA-PdNPs cryogel at pH 6 showed better efficiency in the hydrogenation process compared to the CHI-GA-PtNPs cryogel; however, no significant difference in the degree of conversion at pH 3 was observed. The termination of a catalytic reaction in a batch mode have been studied. Several control tests were carried out to elucidate the mechanism of catalyst poisoning. The presented catalytic system may be of interest for studying reactions in a flow through mode, including the reactions for obtaining valuable chemicals.

Immobilization of oxidative enzymes onto Cu-activated zeolite to catalyze 4-chlorophenol decomposition

In this study, a biocatalyst composite was prepared by immobilizing oxidoreductases onto Cu-activated zeolite to facilitate biochemical decomposition of 4-chlorophenol (4-CP). 4-CP monooxygenase (CphC-I) was cloned from a 4-CP degrading bacterium, Pseudarthrobacter chlorophenolicus A6, and then overexpressed and purified. Type X zeolite was synthesized from non-magnetic coal fly ash using acetic acid treatment, and its surfaces were coated with copper ions via impregnation (Cu-zeolite). Then, the recombinant oxidative and reductive enzymes were immobilized onto Cu-zeolite. The enzymes were effectively immobilized onto the Cu-zeolite (79% of immobilization yield). The retained catalytic activity of CphC-I after immobilization was 0.3423 U/g-Cu-zeolite, which was 63.3% of the value of free enzymes. The results of this study suggest that copper can be used as an effective enzyme immobilization binder because it provides favorable metal-histidine binding between the enzyme and Cu-zeolite.

Development of biocatalysts immobilized on coal ash-derived Ni-zeolite for facilitating 4-chlorophenol degradation

A new type of biocatalyst was developed to facilitate the biochemical decomposition of 4-chlorophenol (4-CP) in this study. Oxydoreductases that catalyze the initial steps of 4-CP biodegradation were immobilized on a synthetic inorganic enzyme support. Type-X zeolite, a high-surface area support, was synthesized from coal fly ash, on which nickel ions were plated by impregnation (Ni-zeolite), followed by the effective immobilization (77.5% immobilization yield) of recombinant monooxygenase (CphC-I), dioxygenase (CphA-I), and flavin reductase (Fre) isolated from Pseudarthrobacter chlorophenolicus A6 and Escherichia coli K-12, respectively. The retained catalytic activity of the enzymes immobilized on Ni-zeolite was as high as 64% of the value for the corresponding free enzymes. The Michaelis–Menten kinetic parameters vmax and KM of the immobilized enzymes were determined to be 0.20 mM·min−1 and 0.44 mM, respectively. These results are expected to provide useful information with respect to the development of novel enzymatic treatments for phenolic hydrocarbon contaminants.

Synthesis and application of N-doped TiO2/CdS/poly(1,8-diaminocarbazole) composite for photocatalytic degradation of 4-chlorophenol under visible light

Visible-driven photocatalyst was prepared by deposition of CdS by SILAR (successive ion layer adsorption and reaction) method on mesoporous N-doped TiO2 supported on F-doped tin oxide (FTO) glass substrate. The changes of morphology and optical properties of the samples with increasing amount of CdS were monitored. The edges of conduction bands of both semiconductors were determined from Mott-Schottky plots. The system with CdS deposited in 6 SILAR cycles has been tested in photocatalytic decomposition of 4-chlorophenol. The mechanism of photocatalytic reaction was discussed in terms of the role of hydroxyl radicals and superoxide radicals in the process. A thin film of conducting polymer, poly(1,8-diaminocarbazole) deposited on the surface of TiO2/CdS suppressed photocorrosion of CdS during photocatalytic process. The amount of the polymer was optimized taking into account concentration of Cd2+ ions released to the solution and activity of the system in 4-CP degradation.

A multipath peroxymonosulfate activation process over supported by magnetic CuO-Fe3O4 nanoparticles for efficient degradation of 4-chlorophenol

Heterogeneous catalysts with low cost, environmentally friendly, highly effective and ready separation from aqueous solution are highly desirable. Magnetic CuO-Fe3O4 nanoparticles, a type of non-toxic bimetallic transition metal oxide, is a promising heterogeneous catalyst for activation of peroxymonosulfate (PMS) to generate reactive oxygen species (ROS) that has not been previously investigated. In this study, the activation of PMS by CuO-Fe3O4 nanoparticles was evaluated using the degradation of 4-chlorophenol as a model reaction. Several critical factors such as pH, catalyst dosage and PMS concentration were investigated. CuO-Fe3O4/PMS system demonstrated a wide effective pH range to degrade 4-chlorophenol, namely 5.5 to 9.5. With the increase of the catalyst dosage, the degradation efficiency of 4-chlorophenol appeared to increase first and then decrease, that the inflection point was 0.5 g/L. Elevated PMS concentration obviously improved the decomposition of 4-chlorophenol; however, the plateau was reached when the PMS concentration was 8 mM. Further increase in PMS concentration would not significantly improve the removal efficiency. Through examining the effects of scavengers and electron spin resonance (ESR) analyses, CuO-Fe3O4 nanoparticles were proven to activate PMS through a non-radical and radical pathway to generate singlet oxygen, sulfate radicals and hydroxyl radicals. Based on results, CuO-Fe3O4 nanoparticles were effective, environmentally friendly and low cost catalysts for efficient activation of PMS. These features make CuO-Fe3O4 nanoparticles a readily available heterogeneous catalyst to activate PMS for refractory organic pollutants degradation in advanced oxidation processes (AOPs).

N-Doped titanium dioxide nanosheets: Preparation, characterization and UV/visible-light activity

A series of nitrogen-doped 2D-titanium dioxide nanosheets was synthesized via green and facile procedure from the lyophilized aqueous colloids of peroxo titanic acid by urea addition and annealing in the temperature range of 350–500 °C. Detailed structural characterization (SEM, TEM with EDX, XRD) of N-doped TiO2 confirmed their 2D-foil morphology composed of packed anatase nanocrystals. CHNS analysis showed that the total nitrogen content in the N-doped TiO2 nanosheets is comparable (0.3 wt. %), and as shown in the EPR measurements in solid state, the annealing temperature determines the character of the nitrogen species incorporated in the anatase lattice. Paramagnetic nitrogen bulk centers (Nb•) dominate the X- and Q-band EPR spectra of the synthesized N-doped TiO2 annealed up to 400 °C, while NO species were detected in samples annealed at higher temperatures. The photoexcitation of the N-doped anatase nanosheets resulted in an intense increase of the Nb• signal intensity, especially upon VIS-light exposure, reflecting the selective photoexcitation of the material via diamagnetic Nb– centers. Nevertheless, the situation upon irradiation of dispersed systems is rather different and to link the information on the structure of the nanosheets with their photoinduced performance in suspensions, the indirect techniques of EPR spectroscopy were applied. Effective generation of paramagnetic reactive oxygen species (ROS) upon UV photoexcitation of the N-doped TiO2 nanopowders dispersed in water or dimethylsulfoxide was confirmed by EPR spin trapping technique. The VIS-light-induced ROS formation was significantly lower and correlates well with the results obtained by the photocatalytic decomposition of 4-chlorophenol upon VIS light. Even though the OH-induced capacity of N-doped TiO2 prevails upon UV exposure, the VIS irradiation evokes the formation of photoelectrons capable of the selective reduction processes as demonstrated by the one-electron reduction of 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonate) radical cation, where the form of nitrogen dopant (e. g. the presence of Nb–/Nb•) in the anatase structure showed a clear effect on the reaction rate. The prepared visible-light active N-doped TiO2 nanosheets exhibiting also adequate UV photoactivity represent promising materials for further development of solar-light active photocatalysts.

An environmentally friendly Z-scheme WO3/CDots/CdS heterostructure with remarkable photocatalytic activity and anti-photocorrosion performance

As a representative artificial photosynthetic system, direct Z-scheme WO3/CdS is a promising photocatalyst system for water purification. However, this system is still limited due to low electron transfer efficiency and serious photocorrosion. Here, we designed and precisely fabricated a novel all-solid-state Z-scheme WO3/CDots/CdS system. The CDots, as a nonmetallic electron mediator, could promote interfacial charge carrier separation and eliminate photocorrosion with enhanced photocatalytic activity. The phase, morphologies, microstructures, and optical and electrical properties of as-obtained Z-scheme WO3/CDots/CdS heterojunctions were investigated in detail. The photocatalytic performance of as-prepared catalysts was evaluated by the decomposition of 4-chlorophenol (4-CP), rhodamine B (RhB), and tetracycline hydrochloride (TCH) and the reduction of aqueous Cr(VI) in visible light. The optimized Z-scheme WO3/CDots/CdS-2 photocatalyst exhibited the highest photocatalytic activity for degrading and mineralizing 4-CP (∼70.0% and 48.3% in 7 h, respectively), both of which exceeded the rates observed in WO3/CdS samples under the same conditions by ∼2 times. In addition, the WO3/CDots/CdS-2 showed excellent stability and reusability with negligible change at ∼2.2% difference for 4-CP degradation in eight cycles. The release percentage of SO42− (transformed from S2−) and Cd2+ was only ∼0.77% and 0.79%, respectively, when compared with the initial concentration, which was far less than for the WO3/CdS system (∼5.64% and 5.70%). The results indicated that a thorough and complete Z-scheme charge carrier transfer route was achieved. Toxicity assessment authenticated good biocompatibility and low cytotoxicity of WO3/CDots/CdS. This study showed that the Z-scheme WO3/CDots/CdS was a promising photocatalyst for water purification.

Oxidative biodegradation of 4-chlorophenol by using recombinant monooxygenase cloned and overexpressed from Arthrobacter chlorophenolicus A6

In this study, cphC-I and cphB, encoding a putative two-component flavin-diffusible monooxygenase (TC-FDM) complex, were cloned from Arthrobacter chlorophenolicus A6. The corresponding enzymes were overexpressed to assess the feasibility of their utilization for the oxidative decomposition of 4-chlorophenol (4-CP). Soluble CphC-I was produced at a high level (∼50%), and subsequently purified. Since CphB was expressed in an insoluble form, a flavin reductase, Fre, cloned from Escherichia coli was used as an alternative reductase. CphC-I utilized cofactor FADH2, which was reduced by Fre for the hydroxylation of 4-CP. This recombinant enzyme complex exhibited a higher specific activity for the oxidation of 4-CP (45.34U/mg-protein) than that exhibited by CphC-I contained in cells (0.18U/mg-protein). The Michaelis-Menten kinetic parameters were determined as: vmax=223.3μM·min−1, KM=249.4μM, and kcat/KM=0.052min−1·μM−1. These results could be useful for the development of a new biochemical remediation technique based on enzymatic agents catalyzing the degradation of phenolic contaminants.

Synthesis and characterization of Zn and Co monocarboxy-phthalocyanines and investigation of their photocatalytic efficiency as TiO2 composites

In this study, synthesis of a group of novel A3B-type non-symmetrically tetrasubstituted zinc(II) and cobalt(II) phthalocyanines bearing one carboxy group (4-mercaptobenzoic acid/4-hydroxybenzoic acid) and three 4-tert-butylphenoxy substituents was achieved by a statistical condensation reaction of the corresponding two phthalonitriles. These four new phthalocyanines have been characterized by using elemental analyses, UV–vis, FT-IR, 1H NMR and mass spectroscopic techniques. MPcs were incorporated into TiO2 semiconductors to prepare TiO2-MPc composites as heterogeneous catalysts. The novel composites were characterized by X-ray diffraction (XRD), infrared (FTIR) and diffuse reflectance analysis. The characterization results show that MPcs are anchored on the surface of TiO2 through COOTiO2 bonds and anatase structure of TiO2 remains unchanged after the sensitization process. The optimum loading of the dyes on TiO2 (ca. 8.4 μmol/g TiO2) was almost independent of the amount of TiO2 used. The new TiO2-MPc composites were used to test their photocatalytic activity on decomposition of 4-chlorophenol under visible light. In contrast to untreated TiO2, all photocatalysts prepared in this study were highly effective on 4-chlorophenol under visible light and almost total photodegradation was accomplished.

2D-Titanium dioxide nanosheets modified with Nd, Ag and Au: Preparation, characterization and photocatalytic activity

2D-Titanium dioxide nanosheets modified by the addition of Nd, Au and Ag dopant in the first reaction step were synthesized from the lyophilized aqueous colloids of peroxo titanic acid by high-temperature treatment. The concentration of the dopant in the sample was 1at.% towards Ti. The results of their detailed morphological and phase characterization (SEM, TEM with EDX, XRD) evidenced that annealing temperatures 500, 650 and 800°C caused the formation of 2D-foils composed of packed anatase nanocrystals; samples annealed at 950°C represent anatase/rutile mixture. While neodymium dopant is built into the structure of anatase causing the changes in the parameters of anatase crystal lattice, such alterations were not found for Au- and Ag-modified samples, with gold or silver nanoparticles dispersed on surface detected by TEM/ED/EDX. Q-band EPR spectra of modified 2D-TiO2 annealed at 800°C measured at room temperature or 100 K revealed the presence of paramagnetic signals corresponding to Ti(III) centers inside the anatase lattice, along with signals associated with medium-polarized conduction electrons, already before exposure. The photoinduced generation of paramagnetic species (e.g., Ti(III), O−, O2−) upon UVA exposure of modified 2D-TiO2 was confirmed by X-band EPR spectroscopy. Moreover, EPR spectra evidenced that Au- or Ag-modified samples annealed at 500°C contained nitrogen paramagnetic species (Nb• and NO) coming from the aqueous ammonia used in synthesis, which are responsible for the visible-light activity of these samples. The tests of photocatalytic activity of modified 2D-TiO2 dispersed in water or dimethylsulfoxide performed using EPR spin trapping technique or via the decomposition of 4-chlorophenol showed a decline in UVA photoactivity for all modified titania samples in comparison to the unmodified 2D-TiO2; visible-light activity of modified 2D-TiO2 nanosheets annealed at 800°C was almost negligible.

Newly developed Fe3O4–Cr2O3 magnetic nanocomposite for photocatalytic decomposition of 4-chlorophenol in water

Chlorophenols, typically 4-chlorophenols are highly toxic and non-biodegradable organic contaminants which pose serious threat to the environment, particularly when released into aqueous medium. The removal of these pollutants by efficient method has received worldwide concern in recent past. A new Fe3O4–Cr2O3 magnetic nanocomposite was synthesized by wet chemical method under ultrasonic irradiation. Microstructure and morphology of the nanocomposite were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR), and a transmission electron microscope (TEM). Magnetic and optical properties were studied by a vibrating sample magnetometer (VSM) and an ultraviolet–visible (UV–Vis) spectrophotometer respectively. The magnetic nanocomposite (MNC) was used as photocatalyst for effective decomposition of 4-chlorophenol in water under ultraviolet (UV) irradiation.

Selenium modified oxalate chelated titania: Characterization, mechanistic and photocatalytic studies

In order to enhance the visible photocatalytic activity of titanium dioxide (TiO2), selenium (Se) doped TiO2 was prepared by sol–gel method using oxalic acid as a chelating agent. To characterize and describe the effect of Se+4 ions on the structural, optical and photocatalytic properties of TiO2, the powders were characterized by XRD, FTIR, UV-DRS, HR-TEM, PL, Raman, XPS and BET measurements. XRD analysis showed that doped powders consist of anatase phase, while undoped TiO2 is a composite mixture of anatase and rutile at a calcination temperature of 550°C. Williamson–Hill plot results indicated the presence of tensile strain on the addition of 0.02, 0.04 and 0.06mol% Se content, while compressive strain was specified on the addition of 0.08, 0.1 and 0.2mol% Se content in TiO2 lattice. FTIR analysis revealed the chelating behaviour of oxalic acid with titanium ions in forming titanium oxalate stretches. Diffuse reflectance measurements showed that visible light absorption is induced by dopant localized/intermediate electronic states, probably originating from Se 4s and 4p states within the band gap of TiO2. Raman peak broadening and the small frequency shifting for the peaks (1-Eg and B1g) were attributed to oxygen vacancies and crystal lattice distortions. Photoluminescence (PL) analysis showed that electron hole recombination was decreased with the incorporation of Se+4 ions in TiO2, which act as trapping sites for the photogenerated electrons. Moreover, PL analysis demonstrated that Se doping produces Ti+3 centers, oxygen defects and localized electronic states in TiO2 band gap, which become responsible for the TiO2 response towards the visible light. The activity of the prepared photocatalysts powder were tested by investigating the kinectics of the photocatalytic decoloration of methylene blue (MB) under UV irradiations and decomposition of 4-chlorophenol (4-CP) under visible light irradiation. It was observed that the TSe0.08 powder with Brönsted acid sites, calcined at 550°C showed highest photocatalytic activity under both UV and visible light irradiations for the selected pollutants. In the decoloration of MB, TSe0.08 powder attain a rate constant (kapp) value of 0.045min−1 which is higher than Degussa P25 (0.033min−1) as well two times higher than undoped TiO2 (0.021min−1). Based on the obtained results, a UV/vis light irradiated photocatalytic mechanism has been proposed for the Se+4 doped anatase TiO2.

Ag3PO4 quantum dots sensitized AgVO3 nanowires: A novel Ag3PO4/AgVO3 nanojunction with enhanced visible-light photocatalytic activity

Ag3PO4/AgVO3 heterojunctions with high photocatalytic activities were synthesized via a simple and practical low-temperature solution-phase route by using AgVO3 nanowires as substrate materials. The as-prepared Ag3PO4/AgVO3 heterojunctions included Ag3PO4 quantum dots assembling uniformly on the surface of AgVO3 nanowires. Compared with pure AgVO3 nanowires, Ag3PO4/AgVO3 composite photocatalysts exhibited enhanced photocatalytic activities under visible light irradiation in the decomposition of 4-chlorophenol (4-CP) ethanol solution. The enhanced performance is believed to be induced by the high specific surface area, strong visible-light absorption originating from the quantum dot sensitization of Ag3PO4, and high efficient separation of photogenerated electron–hole pairs through Ag3PO4/AgVO3 heterojunction.

Fabrication of Ag/Ag3PO4/TiO2 heterostructure photoelectrodes for efficient decomposition of 2-chlorophenol under visible light irradiation

TiO2 nanotube arrays were decorated with Ag/Ag3PO4 nanoparticles through a sequential chemical bath deposition and followed by partial reduction of Ag+ ions in the Ag3PO4 nanoparticles to Ag0 under UV irradiation. The structure and optical properties of the Ag/Ag3PO4/TiO2 nanotube electrode were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse reflectance spectroscopy, photoluminescence (PL) spectroscopy and electrochemical techniques. The photoelectrocatalytic (PEC) activity of the composite electrode was evaluated by the decomposition of 2-chlorophenol under visible light irradiation (λ > 420 nm). Clusters of Ag/Ag3PO4 nanoparticles were successfully formed on the surface of the TiO2 nanotubes (NTs) causing no damage to the ordered structure of the nanotubes. The PL intensity of Ag/Ag3PO4/TiO2 NTs was much lower than that of TiO2 nanotubes. The p-type Ag3PO4 and Ag nanoparticles deposited on the TiO2 NTs could promote the transfer of photo-generated electrons, which inhibited the recombination of electrons and holes effectively, leading to a significant increase in the photocurrent density. Moreover, the Ag/Ag3PO4/TiO2 heterostructure photoelectrodes showed much higher PEC activity than the pure TiO2 NTs for the degradation of 2-CP aqueous solution under visible light irradiation. The enhanced PEC activity could be attributed to the visible-light photocatalytic activity of Ag3PO4 and the heterostructure between Ag3PO4 and TiO2. The electron spin resonance (ESR) spin-trap study further demonstrated that ˙OH could be generated on the Ag/Ag3PO4/TiO2 NTs under visible light irradiation.

Synthesis of GdFeO3 microspheres assembled by nanoparticles as magnetically recoverable and visible-light-driven photocatalysts

GdFeO3 microspheres were synthesized by a hydrothermal method followed by calcination. Citrate acid and ethylene glycol were found to be key factors to the purity and the surface morphology of the GdFeO3 microspheres. UV–visible diffuse reflectance spectrum shows that the products have broad absorption in visible-light region, whereas the magnetic measurement indicates the products show weak ferromagnetic behavior and can be easily separated from the suspension by a magnet. The photocatalytic experiment demonstrates that the prepared GdFeO3 microspheres exhibit well and stable photocatalytic activity for decomposition of 4-chlorophenol under visible-light irradiation, which is ascribed to their porous structures as well as narrow optical band gap.

Defect mediated photocatalytic decomposition of 4-chlorophenol on epitaxial rutile thin films under visible and UV illumination

We show that pure rutile TiO2 can be photo-responsive even under low energy visible light after annealing in vacuum where we envisage that the point defects, i.e. oxygen vacancies and titanium interstitials, serve an important role. In this study, single crystal rutile films were grown by the pulsed laser deposition technique and then vacuum annealed under different oxygen pressures to introduce defects into their lattices. 4-chlorophenol was selected as a model material and decomposed by the annealed TiO2 films where the maximum photocatalytic reaction rate constants were determined as 0.0107 and 0.0072 min−1 under UV and visible illumination. Epitaxial growth along the [200] direction was confirmed by φ-scan and 2θ-scan XRD and the epitaxial relationship between the rutile film and the c-sapphire substrate was explained as . The formation of atomically sharp interfaces and the epitaxial growth were ascertained by annular dark-field STEM imaging. Based on the XPS, UV–vis and PL spectroscopy results, it was found that the defect concentration increased after annealing under lower pressures, e.g. 5 × 10−6 Torr. In contrast, more perfect crystals were obtained when the films were annealed under high oxygen pressures, namely 5 × 101 Torr. The morphology of the films was also investigated by employing an AFM technique. It was observed that increase of the annealing pressure results in the formation of larger grains. It was also found that the electrical resistivity of the rutile films strongly increased by about three orders of magnitude when the annealing pressure increased from 5 × 10−4 to 5 × 101 Torr.

Phase Tuning, Thin Film Epitaxy, Interfacial Modeling, and Properties of YSZ-Buffered TiO2 on Si(001) Substrate

We have studied systematically the influence of pulsed laser deposition variables on microstructure and properties of TiO2 epitaxial thin films where integration with Si(100) substrate was achieved by cubic yttria-stabilized-zirconia (c-YSZ) buffer layer. Details of crystallographic and atomic arrangements across the interfaces are discussed in the light of the domain matching epitaxy paradigm. The single crystalline rutile films were obtained at higher substrate temperatures and lower oxygen pressures; whereas, the growth of epitaxial anatase films was promoted by decreasing the temperature and increasing the oxygen pressure. We showed that crystallographic structure of the TiO2 films is determined mainly by the termination structure of the c-YSZ layer and the bonding characteristics across the TiO2/c-YSZ interface. Using 2θ and φ scans of XRD, the epitaxial relationship between Si(100) substrate and the zirconia buffer layer was shown to be cube-on-cube: (001)[100]YSZ∥(001)[100]Si. Furthermore, the epitaxial relationships at the rutile/zirconia and the anatase/zirconia interfaces were determined as (100)[01̅1]rutile∥(001)[010]YSZ and (001)[110]anatase∥(001)[100]YSZ, respectively. The proposed crystallographic arrangements as well as the epitaxial growth were confirmed by high resolution TEM diffraction and imaging. XPS and XRD studies showed less defect content and favorable crystallinity in the films grown at higher temperatures. AFM results revealed that the finest domain size and the smoothest surface were obtained at the intermediate deposition temperatures. Based on the four-point electrical measurements, the heterostructures deposited at 500 °C were more conductive than those grown at 300 and 700 °C. Photocatalytic activity of the films was studied through decomposition of 4-chlorophenol under UV illumination. The maximum photocatalytic reaction rate constants were determined as 0.0124 and 0.0087 min–1 for the anatase and the rutile films grown at 500 °C.

Comparison of different chlorophenols degradation in aqueous solutions by gamma irradiation under reducing conditions

The reductive degradation of chlorophenols (CPs), including 2-CP, 4-CP and 2,4-DCP by gamma irradiation was investigated and compared. The results showed that the most efficient degradation took place with 2,4-DCP, followed by 2-CP and then 4-CP. This confirmed that the number and position of chlorine atoms existing in the benzene ring have significant impact on dechlorination and decomposition of CPs. The G-values of decomposition of CPs, the formation of intermediate products and chloride ion, and the degradation rate (KCPs and KCl−1) were also determined.

Comparative analysis of ZnO-catalyzed photo-oxidation of p-chlorophenols

The present study compares for the first time the photocatalytic oxidation of three p -chlorophenols (4-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol) in irradiated ZnO suspensions. The effect of operating parameters such as catalyst and concentration doses on the decomposition rate of these p -chlorinated compounds has been studied and optimized. The optimal feed concentration for each of the chlorinated phenolic compounds is 50 mg/L whereas the ZnO doses decreased as the number of chlorine substituent is increased. Kinetic profiles on the decomposition of chlorophenols over ZnO agreed with the pseudo-zeroeth order rate scheme with rate constants following the order 2,4,6-trichlorophenol > 2,4-dichlorophenol > 4-chlorophenol. The validity of the pseudo zero order model could be linked to the initial doses of the chlorophenols used vis-à-vis the catalyst. The study revealed stable intermediates of photocatalytic chlorophenol transformation by high performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS) technique. A combined mechanism is given to account for the photocatalytic destruction of the chlorophenols.