Degradation Of Hazardous Organic Compounds Research Articles

Fabrication of ternary metal oxide (ZnO:NiO:CuO) nanocomposite heterojunctions for enhanced photocatalytic and antibacterial applications.

In this article, ZnO:NiO:CuO nanocomposites (NCPs) were synthesized using a hydrothermal method, with different Zn : Ni : Cu molar ratios (1 : 1 : 1, 2 : 1 : 1, 1 : 2 : 1, and 1 : 1 : 1). The PXRD confirmed the formation of a NCP consisting of ZnO (hexagonal), NiO (cubic), and CuO (monoclinic) structures. The crystallite sizes of NCPs were calculated using Debye Scherrer and Williamson-Hall methods. The calculated crystalline sizes (Scherrer method) of the NCPs were determined to be 21, 27, 23, and 20 nm for the molar ratios 1 : 1 : 1, 2 : 1 : 1, 1 : 2 : 1, and 1 : 1 : 2, respectively. FTIR spectra confirmed the successful formation of heterojunction NCPs via the presence of metal-oxygen bonds. The UV-vis spectroscopy was used to calculate the bandgap of synthesized samples and was found in the range of 2.99-2.17 eV. SEM images showed the mixed morphology of NCPs i.e., irregular spherical and rod-like structures. The dielectric properties, including AC conductivity, dielectric constant, impedance, and dielectric loss parameters were measured using an LCR meter. The DC electrical measurements revealed that NCPs have a high electrical conductivity. All the NCPs were evaluated for the photocatalytic degradation of Methylene blue (MB), methyl orange (MO), and a mixture of both of these dyes. The NCPs with a molar ratio 1 : 1 : 2 (Zn : Ni : Cu) displayed outstanding photocatalytic activity under sunlight, achieving the degradation efficiency of 98% for methylene blue (MB), 92% for methyl orange (MO) and more than 87% in the case of a mixture of dyes within just 90 minutes of illumination. The antibacterial activity results showed the more noxious nature of NCPs against Gram-negative bacteria with a maximum zone of inhibition revealed by the NCPs of molar ratio 1 : 2 : 1 (Zn : Ni : Cu). On the basis of these observations, it can be anticipated that the NCPs can be successfully employed for the purification of contaminated water by the degradation of hazardous organic compounds and in antibacterial ointments.

Ferroelectric nano-heterojunctions for piezoelectricity-enhanced photocatalysis

Nanoscale heterojunctions of high dielectric constant piezoelectrics and optoelectronic semiconductors are attractive for photocatalytic degradation of hazardous organic compounds. In this work, such a nano-heterojunction was prepared by mixing of surface-carboxylated ferroelectric BaTiO3 nanoparticles (BTO NPs) and protonated graphitic carbon nitride (g-C3N4). Due to strong electrostatic interactions, intimate contact between BTO NPs and g-C3N4 was achieved for efficient charge separation and transfer. Two piezoelectric BTO NPs were used to prepare the BaTiO3/g-C3N4 heterojunctions: as-received BTO (arBTO) and 950 °C-annealed BTO (anBTO) with larger ferroelectric domains. Under ultrasonication, the photocatalytic degradation rate of levofloxacin by anBTO/g-C3N4 heterojunctions were 0.0462 min−1, which were 9.2 times of arBTO and 3.6 times of those in the absence of ultrasonication. The underlying mechanism was attributed to the higher current density, the accelerated charge separation of photo-activated excitons, and the reduced charge recombination via a synergistic effect of heterostructures and the local piezo-potential generated by the ferroelectric BTO NPs. By combination of thermal annealing of arBTO to enlarge the ferroelectric domains and construction of heterostructures, a highly efficient photocatalyst could be obtained. This study provides us a simple yet effective method to achieve highly efficient photocatalysts using the piezoelectric effect of ferroelectric BTO NPs.

Synthesis, characterization, and photocatalytic applications of novel sword-like copper oxide microparticles

• Novel CuO microparticles in sword-like morphology were prepared by microemulsion and calcination. • The major composition of the prepared materials was confirmed by XRD and EDS. • The photocatalytic property of the CuO microparticles was established using methylene blue model dye compound. • The degradation of methylene blue dye followed first-order kinetic model according to the general Langmuir–Hinshelwood mechanism. This letter aimed to synthesize novel copper oxide (CuO) microparticles via the microemulsion method followed by calcination. The synthesized material was characterized by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffractometry, and diffuse reflectance spectroscopy techniques; and subsequently applied for the degradation of methylene blue (MB) using the heterogeneous photo-Fenton method. SEM images revealed the formation of homogeneous sword-like CuO microparticles. The XRD pattern and EDS spectrum confirmed that the main part of the material was CuO with the formation of Na 8 Cu 5 O 10 as an impurity. The photocatalytic degradation of MB followed the first-order kinetic model according to the general Langmuir–Hinshelwood mechanism. The as-prepared materials can be successfully applied in the visible-light-induced photocatalytic degradation of hazardous organic compounds and industrial wastewaters.

Areca nut (Areca catechu) husks and Luffa (Luffa cylindrica) sponge as microbial immobilization matrices for efficient phenol degradation

Immobilization of microorganisms is a widely adopted strategy for the efficient degradation of hazardous organic compounds like phenol. Microorganisms can be immobilized in synthetic or natural matrices. In this work dried areca nut (Areca catechu) husks and luffa (Luffa cylindrica) sponge fibers were used as alternative and inexpensive natural matrices for microbial cell immobilization. The potential of these immobilization systems for the effective bioremediation of phenolic wastewater was explored. A bacterial consortium was isolated by enriching a sludge sample from a petroleum refinery in high phenol concentrations. The mixed bacterial culture was capable of degrading 1000 mg L−1 of phenol in suspension cultures. The bacterial consortium was immobilized on the lignocellulosic matrices. Phenol degradation studies were performed in batches to optimize the physicochemical parameters. Optimum pH and temperature for phenol degradation was found to be 8.0 and 37 °C. At an optimum pH and temperature, the areca nut husk and luffa sponge systems immobilized with the mixed culture could degrade 1000 mg L−1 phenol in 28 h and 30 h respectively. The highest experimental degradation rates in areca nut husk and luffa sponge systems were 0.37 h−1 and 0.21 h−1 respectively at 200 mg L−1 phenol. Degradation kinetic studies were carried out using several inhibition models. Further studies revealed that both matrices with immobilized microbes could be reused for several successive batch degradation experiments and stored at 4 °C for several weeks without any noticeable loss in degradation efficiency.

Kinetics Analysis for Development of a Rate Constant Estimation Model for Ultrasonic Degradation Reaction in the Presence of Particles

Degradation of hazardous organic compounds using ultrasound is an attractive advanced oxidation technology for wastewater treatment, and it is well known that the ultrasonic degradation reaction is enhanced by particle addition. In this study, the effects of ultrasonic irradiation conditions and particle addition on the degradation rate constant were investigated using pseudo-first-order chemical reaction model. Moreover, the application of this model to degradation of other organic compounds in the presence of particles by other research groups has been investigated. The degradation reaction was enhanced by particle addition, and the apparent degradation rate constant is proportional to the increase in amount of particle. In addition, the constant of proportionality is not influenced by degraded material and ultrasonic frequency. However, particle type influences the constant of proportionality.

Graphite Supported Stainless-Steel Electrode for the Degradation of Azo Dye Orange G by Fenton Reactions: Effect of Photo-Irradiation

AbstractAn electrode, stainless steel supported on graphite, was used for the degradation of hazardous organic compounds, azo dye Orange G (OG), using the photoelectro- Fenton (PEF) process. Result...

Novel multistage fixed-bed photoreactor for bacterial inactivation using N-doped TiO2 nanoparticles under vis-LEDs and sunlight illumination

In the selection and design of appropriate types of photoreactor system configuration in terms of total irradiated surface area of catalyst per unit volume in photocatalysis reaction, reaction kinetics and light distribution within the reactor are the most important factors. Though several photoreactor system configurations have been reported so far, most of them were complex, focused on degradation of hazardous organic compounds and their application has been very limited for pathogenic microorganism inactivation applications. In the present work, however, photocatalytic bacterial inactivation is studied by immobilized N-doped TiO2 using a novel simplified multistage fixed-bed photoreactor. The photoreactor has been developed from N-doped TiO2 nanoparticles immobilized on glass beads using tetraethoxysilicate (TEOS) as a binder with low-temperature synthesis route. The reactor was irradiated under visible light-emitting diodes (vis-LEDs) with the incident photon flux of 5.23 ± 0.35 × 1016 photons/s. Furthermore, for solar experiment global and UV irradiances were 71.2 and 4.6 mWcm−2, respectively. The photocatalytic inactivation efficiency was investigated on different types of Gram-negative and Gram-positive bacteria in water. From the photocatalytic inactivation efficiencies, the proposed photoreactor demonstrated more than 3 log unit reduction in bacterial removal on both under vis-LEDs and sunlight irradiation. Fast inactivation efficiency for all selected bacterial strain was also observed under sunlight irradiation when compared to under vis-LED irradiation. It has been understood that the rate of photocatalytic inactivation on Gram-negative bacteria was found to be higher than the Gram-positive bacteria on both experiments.

Microwave assisted facile and green route for synthesis of CuO nanoleaves and their efficacy as a catalyst for reduction and degradation of hazardous organic compounds

Abstract A facile, green synthesis of 2D CuO nanoleaves (NLs) using amino acid, namely glutamic acid was developed by microwave heating method for the first time. The aminoacid acts as a complexing/capping agent in the synthesis of CuO NLs. This technique gives rise to the formation of self assembled 2D CuO NLs having an average length and width of ∼720–800 nm and ∼136–160 nm respectively. The 2D CuO NLs were built up from the primary CuO nanoparticles by oriented attachment growth mechanism. CuO NLs were characterized by X-ray Diffraction method (XRD), Transmission Electron Microscopy (TEM), Selected-area Electron Diffraction Pattern (SAED) and Fourier Transformed Infrared Spectroscopy (FT-IR). The optical properties were investigated using UV–vis spectroscopy. The synthesized CuO NLs act as an effective catalyst for the reduction of toxic aromatic nitro compounds, namely p-nitrophenol, p-nitroaniline and 2,4,6-trinitrophenol. The photocatalytic activities of CuO NLs were also analyzed for the degradation of two hazardous dyes, namely Rose Bengal and methyl violet 6B by solar irradiation technique. The degradation products were identified using LC–MS and the mechanistic pathways for the degradation of dyes were suggested.

Kinetic Study of Thermal Degradation of Hazardous Organic Compounds in Different Atmospheres

Effects of coprocessing hazardous organic waste in high-temperature industrial furnaces with oxidative or inert atmospheres were studied using two typical types of organic matter, naphthalene and resorcinol. Thermal degradation experiments of solid naphthalene and resorcinol were performed in a high-temperature tube furnace with a nitrogen or air atmosphere. Concentrations of naphthalene and resorcinol lost as vapor and trapped in absorption liquids during calcination were determined by gas chromatography–mass spectrometry and spectrophotometry, respectively. Degradation kinetics were investigated, and activation energies and preexponential factors for organic matter in various types of industrial furnace were determined. The results showed that the degradation ratios and degradation rates of naphthalene and resorcinol increased with increasing temperature. Degradation rates of these two organic matters were faster in nitrogen than those in air. Degradation rates of these two organic matters were related to their thermal stabilities, and the degradation rate of resorcinol was higher compared with naphthalene. Under the experimental conditions, these two organic matters could degrade completely. Activation energies for degradation of naphthalene in nitrogen and air atmosphere were found to be 16.71 and 19.42 kJ/mol, respectively, and activation energies for degradation of resorcinol in nitrogen and air atmosphere were found to be 23.74 and 25.98 kJ/mol, respectively. The larger activation energy in air may be attributed to the simultaneous combustion reaction due to the presence of oxygen. These results can be used to predict thermal degradation laws for other organic matters.

Emerging pollutant treatments in wastewater: Cases of antibiotics and hormones

ABSTRACTBecause of the intensive use of pharmaceutical substances in human life, studies on the detection of these chemical compounds and their metabolites as pollutants in water bodies are continuously reported. Some pharmaceutical agents are associated with adverse effects to aquatic life, even at very low concentrations (ng L−1 to μg L−1). For instance, the presence of antibiotics and hormones has been associated with increasing proliferation of antibiotic resistant pathogens and feminization and masculinization of some aquatic organisms. Currently, new attempts are being made to minimize or fully remove these types of pollutants from aquatic systems to protect the environment and human health. In this regard, physicochemical and biological treatments are among the most promising technologies for the treatment of wastewater containing pharmaceutical pollutants. These treatments are green alternatives for the degradation of hazardous organic compounds into nontoxic by-products. Here, we review some of the physicochemical and biological treatment methods used for the removal of the most extensively used antibiotics and hormones. Enzymatic oxidation, photocatalysis and electrochemical oxidation are described in terms of the aforementioned pharmaceutically active compounds (PhACs). The use of membrane technologies to separate different groups of antibiotics and hormones prior to biologic or physicochemical treatment methods is also addressed.

Photocatalytic Performance of Highly Active Brookite in the Degradation of Hazardous Organic Compounds Compared to Anatase and Rutile

The photocatalytic activity of brookite was studied and compared with anatase, rutile, and commercial titania P25 (Degussa). Brookite exhibited relatively high activity in the degradation of different hazardous compounds under sunlight equivalent conditions. Brookite and other titania polymorphs anatase and rutile were hydrothermally synthesized under the similar reaction conditions starting with the same amorphous titania precursor. The highly crystalline titania polymorphs were characterized by XRD, SEM, TG-DSC, Raman- and diffuse reflectance UV–vis spectroscopy. Brookite (B) and anatase (A) crystallized in form of agglomerated spherical-shaped nanoparticles of ca. 10nm in size. Rutile (R) formed up to 500nm large rod-like nanocrystals. The band gaps of the titania polymorphs were about 3.25–3.34eV. The aromatic ring opening in different hazardous compounds was monitored by UV–vis absorption spectroscopy and the mineralization was determined by total organic carbon (TOC) measurements. Additionally, the formation of intermediates was studied by electrospray ionization time-of-flight mass spectra (ESI-TOF-MS). The recalcitrance of organic compounds against the photocatalytic degradation increases in the following order: cinnamic acid<ibuprofen<phenol. The general order of photocatalytic activity was B≈A>R.

Effects of ultrasonic frequency and initial concentration on degradation of methylene blue

The ultrasonic degradation of hazardous organic compounds in an aqueous solution is an attractive technology for wastewater treatment. The kinetics of ultrasonic degradation has been investigated. However, there have been only a few quantitative studies of the effect of ultrasonic frequency on degradation rate. In this study, the ultrasonic degradation of methylene blue was performed at various frequencies, especially in the high frequency region, and various initial concentrations. From the results of the time dependence of the methylene blue concentration in this study, ultrasonic degradation was considered to be a pseudo-first-order reaction. The apparent degradation rate constant and sonochemical efficiency have a linear relationship, and the apparent rate constant and initial concentration have an inversely proportional relationship. These phenomena well agree with our proposed formula for estimating the apparent degradation rate constant. In addition, our proposed model is also applicable to the ultrasonic degradation of nonvolatile and hydrophilic compounds.

Effect of Particle Addition on Degradation Rate of Methylene Blue in an Ultrasonic Field

Ultrasound has been found to be an attractive advanced technology for the degradation of hazardous organic compounds in water. In addition, the sonochemical reaction is enhanced by particle addition. However, the enhancement mechanism of particle addition has not been investigated well, because ultrasound enhances not only chemical reactions but also mass transfer. In this study, the ultrasonic degradation of methylene blue was carried out, and the effects of the ultrasonic irradiation condition on the degradation rate were investigated. The effect of ultrasonic frequency on the improvement of degradation by particle addition was also investigated. The order of degradation rate with frequency was the same as the tendency of sonochemical efficiency value obtained using KI oxidation dosimetry method (SEKI). The degradation process of methylene blue was intensified by particle addition, and the degradation rate increased with increasing amount of particle addition. The enhancement of degradation rate by particle addition was influenced by both ultrasonic frequency and type or diameter of particles.

Effects of frequency and initial concentration of methylene blue on rate constants of ultrasonic degradation

Ultrasound has been found to be an attractive advanced technology for the degradation of hazardous organic compounds in water. The ultrasonic degradation of dyes has been investigated by many researches, but the effects of ultrasonic frequency on degradation rate were not investigated quantitatively. In our previous study, we proposed a simple model for estimating the apparent degradation rate constant of methylene blue based on ultrasonic power and the SE value in the range of frequency between 20 and 500 kHz. However, we have not investigated the ultrasonic degradation of methylene blue in high frequency region around 1 MHz. The effects of initial concentration of methylene blue have not been investigated yet, either. In this study, the degradation process using methylene blue as model hazardous organic compounds by ultrasonic irradiation was investigated. The ultrasonic frequency was operated in the range from 20 kHz to 1.6 MHz, and the initial concentration of methylene blue was in the range from 0.005 to 0.04 mM. Our proposed model can apply to this study which extended the frequency range. The effects of initial concentration can also be estimated in the range of 0.01 to 0.04 mM using this model.

Photoelectrochemical degradation of azo dye over pulsed laser deposited nitrogen-doped TiO2 thin film

We investigated the synergetic effect of electrochemical and photocatalytic oxidation in photoelectrochemical (PEC) process for the degradation of hazardous organic compounds exemplified by methyl orange, an azo dye. Nitrogen doped TiO2 thin film (NTTF) synthesized by the pulsed laser deposition (PLD) method, was used as the working anode. The crystalline, optical properties, surface morphology, and structure of the NTTF were characterized by XRD, UV–vis absorbance edges, SEM, and XPS. Results showed that the NTTF was dominated by anatase phase after sintered at 600°C with significant visible light response at 595nm. XPS analyses indicated nitrogen doping was mainly responsible for reducing the band gap as evidence of 3% N doping into the structure via the linkage of TiON and NTiO bond. SEM images illustrated the nitrogen-doped TiO2 nanoparticles being attached firmly and spread evenly over the ITO glass surface, which is beneficial for PEC applications. The degradation efficiency of MO by photoelectrochemical, photocatalytic, electrochemical and photolysis methods were compared in terms of pseudo-first-order reaction rate. PEC was the most efficient in degrading MO at a bias potential of 2.0V (vs. SCE) under light at a wavelength of 325nm, which was consistent with results of IPCE (%) measurements. The synergetic effect was quantified at current/bias potential of 0.07mA/0.3V and 0.6mA/2.0V, respectively. Results demonstrated that the bias potential could separate photogenerated holes and electrons effectively and enhance the electrochemical-oxidation of MO. The mechanistic aspects of MO degradation by the PEC process were discussed.

Comparison of ultrasonic degradation rates constants of methylene blue at 22.8 kHz, 127 kHz, and 490 kHz

Techniques such as solvent extraction, incineration, chemical dehalogenation, and biodegradation have been investigated for the degradation of hazardous organic compounds. We found ultrasound to be an attractive technology for the degradation of hazardous organic compounds in water. However, the effects of ultrasonic frequency on degradation rate constants were not investigated quantitatively. In this study, the degradation process of a model for hazardous organic compound methylene blue was investigated using ultrasonic irradiation. The study focused on the effects of ultrasonic frequency and ultrasonic power on the degradation rate constant. The apparent degradation rate constants were estimated based on time dependence of methylene blue concentration assuming pseudo-first-order kinetics for the decomposition. A linear relationship between the apparent degradation rate constant and ultrasonic power was identified. In addition, the apparent degradation rate constants at frequencies of 127 and 490kHz were much larger than those at 22.8kHz. A relationship between the apparent degradation rate constant and the sonochemical efficiency value (SE value) was also found. Based on these results, a simple model for estimating the apparent degradation rate constant of methylene blue based on the ultrasonic power and the SE value is proposed in this study.

Effect of irradiation distance on degradation of phenol using indirect ultrasonic irradiation method

Ultrasound is used as degradation of hazardous organic compounds. In this study, indirect ultrasonic irradiation method was applied to the degradation process of phenol, the model hazardous organic compound, and the effects of irradiation distance on radical generation and ultrasonic power were investigated. The chemical effect estimated by KI oxidation dosimetry and ultrasonic power measured by calorimetry fluctuated for the irradiation distance, and there was a relationship between the period of the fluctuation of ultrasonic effect and the wavelength of ultrasound. The degradation of phenol was considered to progress in the zero-order kinetics, before the decomposition conversion was less than 25%. Therefore, the simple kinetic model on degradation of phenol was proposed, and there was a linear relation in the degradation rate constant of phenol and the ultrasonic power inside the reactor. In addition, the kinetic model proposed in this study was applied to the former study. There was a linear relation in the degradation rate constant of phenol and ultrasonic energy in the range of frequency of 20–30 kHz in spite of the difference of equipment and sample volume. On the other hand, the degradation rate constant in the range of frequency of 200–800 kHz was much larger than that of 20–30 kHz in the same ultrasonic energy, and this behaviour was agreed with the former investigation about the dependence of ultrasonic frequency on chemical effect.

A thermal packed-bed reactor and a silent discharge plasma cell for a two-stage treatment system

Dielectric barrier discharge cells (DBDCs) have proved their efficiency in the generation of cold plasmas for hazardous organic compound degradation. Here, we describe the design and construction of a dual thermal packed-bed reactor and DBDC-based system to carry out the degradation of hazardous organic compounds in both liquid and gas phases. The main components of this system are: (i) the thermal treatment system, (ii) DBDC and (iii) resonant inverters of low (3.3 kHz) and high (100 kHz) calculated frequencies. The definition of the cell physical parameters considers: (a) a first-order degradation ratio of the compound and (b) the air breakdown at atmospheric pressure as a function of the transport carrier gas. The power consumed by the cells during the discharges was computed theoretically and experimentally. Using the dual system along with a gas chromatography diagnostic system, highly efficient degradations of a test compound (benzene) have been obtained, reaching 99.950% in the case of a cell experimentally operated at 3.3 kHz and up to 99.996% in another one at 94.3 kHz. An additional 3.7 times reduction in the latter case residence time with respect to the low frequency cell has been found.

PHOTOCATALYTIC DEGRADATION OF 2-CHLOROPHENOL USING TiO₂THIN FILMS PREPARED BY CHEMICAL VAPOR DEPOSITION AND ION BEAM SPUTTERING METHOD

Chemical vapor deposition (CVD), ion beam sputtering (IBS) and sol-gel method were used to prepare TiO thin films for degradation of hazardous organic compounds exemplified by 2-chlorophenol (2-CP). The influence of supporting materials and coating methods on the photocatalytic activity of the TiO thin films were also studied. TiO thin films were coated onto various supporting materials including steel cloth (SS), copper cloth, quartz glass tube (QGT), and silica gel (SG). Results indicate that SS (37 μm)- TiO thin film prepared by IBS method improves the photodegradation of 2-CP. Among all supporting materials studied, SS(37 μm) is found to be the best support

Sonolytic degradation of hazardous organic compounds in aqueous solution

Benzene, chlorobenzene, 1,2-, 1,3-, 1,4-dichlorobenzene, biphenyl, and polychlorinated biphenyls such as 2-, 4-chlorobiphenyl and 2,2′-dichlorobiphenyl in aqueous solutions have been subjected to sonolysis with 200 kHz ultrasound at an intensity of 6 W cm −2 under an argon atmosphere. 80–90% of initial amount of these compounds were degraded by 30–60 min of sonication when the initial concentrations were 10–100 μmol l −1. The degradation rate of these compounds increased with increase in their vapor pressures. In all cases of sonolysis of chlorinated organic compounds, an appreciable amount of liberated chloride ion was observed.