Degradation Of Toxic Organic Compounds Research Articles

Effect of pH on the photo-Fenton degradation of rhodamine B by Prussian blue/g-C<sub>3</sub>N<sub>4</sub>

The pH solution is one of the critical factors affecting the photo-Fenton degradation of dyes in wastewater. The photoactivity of Prussian blue/g-C3N4 was investigated using the photodegradation of RhB acidic, neutral, and essential medium. The results implicated that more than 98.5% removal of RhB was achieved at pH = 3.62 after irradiation for 60 minutes under visible light. The photocatalytic activity of Prussian blue/g-C3N4 showed the best performance in an acidic medium. This is due to the formation of hydroxyl radicals during the photocatalytic degradation of RhB. Thus, this study has shown the role and potential of the application of photocatalysts in the degradation of toxic organic compounds the wastewater.

Holmium silicate nanostructures: Simple auto-combustion preparation, characterization, and scrutiny of photocatalytic performance

Though industrial progress has improved mankind's standard of living, it has also degraded the environment. The lack of freshwater in the cosmos has led researchers to pay close attention to water contamination. The holmium silicate nanostructures with Ho2Si6O9 formula were prepared through a multifuel auto-combustion process involving starch, fructose, and maltose. Obtaining Ho2Si6O9 in the presence of starch results in a pure and morphologically desirable sample. Considering the suitable bandgap (3.01 eV) of Ho2Si6O9, this compound could be a good candidate for the degradation of toxic organic compounds in the UV range. Several factors play a crucial role in the purification of water, such as the type of organic contamination, the content of catalysts, and the concentration of pollutants. Results showed that 50 mg of Ho2Si6O9 decomposed 5 ppm thymol blue in a high percentage (91.4%). The scavenger test revealed that superoxide (•O2−) species played a significant role in photodegradation. The kinetics study confirmed that the maximum efficiency has a maximum rate constant (k = 0.0191 min−1).

Green Nanomaterials for Photocatalytic Degradation of Toxic Organic Compounds.

In recent years, nanomaterials as photocatalysts have gained much popularity for the removal of organic pollutants from tainted water using photodegradation, since the available chemical, physical, and biological methods often are time consuming, involve high cost and dumping complications, sometimes posing serious threat to both human health and environmental elements. Use of nanomaterials is less expensive and does not, in general, form aggregated macromolecules. In addition, nanotechnology for waste-water treatment demolishes or alters the risky chemical wastes to harmless end products like H2O and CO2. Nanomaterials synthesized from natural resources or prepared using green synthetic routes are receiving surge of interest as our consciousness to ecological environment and safety rises. 'Green' materials of this kind might also show unique strength features and exceptional biodegradability, along with their other notable advantageous properties like minimum threat to environment, efficient recyclablity and low cost compared to synthetic nanomaterials. Such green nanomaterials can also serve as nanocatalysts to treat toxic organic pollutants in a safer way, including photodegradation to less or non-toxic products. This article reviews latest developments on the synthesis of some promising green nanomaterials aiming towards their efficient uses as photocatalysts for degradation of organic pollutants. Strategies to find new green materials as photocatalysts by modification of technologies, and development of novel methodologies for safer treatment of organic pollutants will also be discussed.

A Novel Shift in the Absorbance Maxima of Methyl Orange with Calcination Temperature of Green Tin Dioxide Nanoparticle-Induced Photocatalytic Activity

Background: The photocatalytic degradation of toxic organic compounds has received great attention for the past several years. Dyes, such as methyl orange (MO), are one of the major pollutants which create environmental hazards in the hydrosphere, living organisms and human beings. During photocatalytic degradation, NPs are activated in the presence of UV–Vis radiation which in turn creates a redox environment in the system and behaves as a sensitizer for light-induced redox mechanisms. Tin oxide (SnO2) is one of the prominent, but less investigated, nanomaterials compared to titanium oxide (TiO2) and Zinc oxide (ZnO) nanoparticles (NPs). Methods: Herein, Buxus wallichiana (B. wallichiana) leaf extract was utilized as a reducing and capping agent for the biosynthesis of SnO2 NPs. The effects of the calcination temperature on their photocatalytic, structure and surface properties were then examined. The degree of crystallinity and the crystallite size were determined through X-ray diffraction (XRD) analysis. The pore size and surface area were calculated by Burnett–Emmitt–Teller (BET) and Barrett–Joyner–Halenda (BJH) methods based on nitrogen desorption data. Morphological changes were assessed by scanning electron microscopy (SEM). The optical behavior was analyzed through UV–Vis diffuse reflectance spectroscopy (DRS) data and the band gap subsequently calculated. The photocatalytic efficiency of SnO2 NPs was evaluated by double beam UV–Vis spectrophotometry under the influence of initial MO concentration, catalyst dose and pH of MO solution. The surface functional moieties were identified using Fourier transform infrared (FTIR) spectroscopy. All the calcined SnO2 NPs were used as photocatalysts for the mineralization of MO in aqueous media. Results: The degree of crystallinity and the crystallite size increased with the calcination temperature. The transmittance edge obtained for all the calcined SnO2 NPs shows a maximum absorbance in the visible range (λ-max = 464 nm). Moving toward higher wavelengths, a sudden intense red shift (from 464 nm to 500 nm), attributed to the incorporation of a hydroxyl radical at the ortho-position in the benzene ring associated with the dimethylamine group of MO, was observed in the absorbance of the samples calcined up to 300 °C. The percentage degradation of MO was found to decrease with increasing calcination temperatures. The optimal photocatalytic activity toward MO (15 ppm) in a solution of pH = 6 was obtained with 15 mg SnO2 NPs calcined at 100 °C. Conclusions: UV–Vis absorption spectroscopy demonstrates that the absorption spectra of MO are strongly modified by the calcination temperature. This work opens new avenues for the use of SnO2 NPs as photocatalysts against the degradation of industrial effluents enriched with different dyes.

Synthesis of the high durability photocatalytic materials with tertiary components

The high durability, re-collectable and low-cost materials with tertiary (reduced graphene-TiO2-Fe3O4, denoted as GrTiFe) components for degradation of toxic organic compounds have been prepared from different precursors by coprecipitation and hydrothermal methods. By this procedure, TiO2 and Fe3O4 nanoparticles have been growing on the reduced graphene oxide. The as-synthesized nanocomposites have been characterized with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope and magnetic hysteresis, and studied on the photo-degradation reaction of Moderacid Black (MDB). The result shows that the photocatalytic activity of as-synthesized composites is much higher than that of pure TiO2 nanoparticles and the composites can be easily collected from water using a magnet for reusing. In addition, the GrTiFe is also able to degrade the organic compounds under modeling sunlight radiation.

Review on the Synthesis Method of Nanocomposites and Approach to Making Semiconductors Visible Light Active

Many studies have been concentrated on the degradation of toxic organic compounds in waste water via photocatalysis of various semiconductors. It has attracted great attention in modern science because of its potential in solving many current environmental problems such as air and water pollution. The common photocatalysts are primarily nanocomposite metal oxides, are known to be good photocatalysts for the degradation of several environmental contaminants due to their high photosensitivity, stability and non-toxic nature. There are different approaches for the synthesis of nanomaterials: Top down and bottom up approaches. Top- down approach is best approach and refers to successive cutting of a bulk material to get nano sized particles. These applications have their interest in controlling particle size, particle shape, size distribution, particle composition and degree of particle agglomeration. Some nanoparticles have large band-gap which leads to high recombination rate of photogenerated electron–hole pairs limit their utilization for photocatalytic applications. More recently, significant efforts have also been made to develop new or modified semiconductor photocatalysts that are capable of using visible-light (λ = 400–700 nm) including semiconductor coupling, metal ion doping, nonmetallic element doping, and sensitization with organic dyes. Coupling of two semiconductor nanoparticles with different band gap widths has been demonstrated in many studies as one of the most effective ways to reduce the recombination of electron–hole pairs and consequently, achieving a higher photocatalytic activity. Moreover, the ternary nanocomposites have high visible light photocatalytic activity and organic dyes can be decomposed efficiently, implying the higher photocatalytic activity of the ternary nanocomposites.

Fabrication of mesoporous TiO2/PVDF photocatalytic membranes for efficient photocatalytic degradation of synthetic dyes

Water recovery and reuse are the two best alternatives to assuage the growing water scarcity. Mixed matrix membranes (MMMs) incorporated with heterogeneous photocatalysts have been proven to be efficient in the degradation of toxic organic compounds, particularly dyes. In this study, a mesoporous photocatalyst, titanium dioxide, was prepared using two different routes: (1) Solution combustion synthesis using different organic fuels such as (TiO2-U), (TiO2-G), (TiO2-A), (TiO2-H), and (TiO2-HM); (2) Modified hydrothermal method using an abundantly available polysaccharide starch (TiO2-S). These photocatalysts were exhaustively characterized to study their physicochemical and structural properties using XRD, UV-DRS, FT-Raman, BET, PL Spectra, XPS, HR-SEM, HR-TEM and EDX. The mesoporous TiO2 nanoparticles incorporated mixed matrix PVDF membranes were synthesized by the facile non-solvent induced phase separation technique. The photocatalytic activity of the synthesized catalysts and the MMMs were evaluated using two different dyes such as Congo Red (CR) and Reactive Yellow 145 (RY 145). As far as the catalyst embedded membranes are concerned, they also show a similar trend but slightly reduced photocatalytic activity. Among the MMMs, TiO2–S/PVDF showed higher photocatalytic activity. The percentage decolourization/mineralization of CR and RY 145 over were determined to be 84%/71% and 100%/87% respectively. Kinetic studies revealed that among the synthesized catalysts, TiO2-S/PVDF showed the highest kapp and the lowest t1/2 values – CR – 0.0061 min−1 and 113 min; RY 145 – 0.0134 min−1 and 51.71 min. The PVDF MMMs were also found to be thermally stable with excellent recyclability and long-term activity.

Crosslinked chitosan embedded TiO2 NPs and carbon dots-based nanocomposite: An excellent photocatalyst under sunlight irradiation

Herein, a new hybrid nanocomposite, comprising of titania nanoparticles (TiO2 NPs) and carbon dots (CDs) deposited polyvinyl imidazole crosslinked chitosan [cl-Ch-p(VI)/TiO2NPs-CDs] has been developed. The nanocomposite has been synthesised by in-situ deposition of TiO2 NPs and CDs onto the surface of the copolymer under microwave irradiation. To the best of our knowledge, this in-situ approach has effectively been applied for the first time to fabricate green fluorescent CDs from sugar cane juice at moderate temperature (75 °C) under microwave irradiation. The developed nanocomposite has been characterized using UV–Vis spectroscopy, 13C NMR, XRD, HR-TEM, STEM and XPS analyses. The results suggest that the successful deposition of TiO2 NPs and CDs onto the surface of crosslinked chitosan is achieved. The experimental studies indicate that the NPs/CDs-impregnated nanocomposite allows efficient photocatalytic degradation of toxic organic compounds (~98.6% degradation of 2,4-dicholorophenol, ~95.8% degradation of Reactive Blue 4, ~98.2% degradation of Reactive Red 15) in the presence of sunlight. Finally, LC-MS analysis of the resultant degraded materials reveals the formation of organic molecules with lower molecular mass.

Biological renewable hemicellulose-template for synthesis of visible light responsive sulfur-doped TiO2 for photocatalytic oxidation of toxic organic and As(III) pollutants

Sulfur-doped TiO2 catalysts using biological renewable hemicellulose template (S/TiO2-T) were synthesized and characterized with different instruments. The photocatalytic activities of the resulting S/TiO2-T photocatalysts with different amounts of S-doped TiO2 were investigated through the decomposition of toxic nitrobenzene, p-chlorophenol, and phenol organic compounds and oxidation of As(III) pollutant under visible light irradiation. The highest photocatalytic activity was obtained from S/TiO2-T catalyst prepared with the n(TiCl4)/n(Thiourea) precursor molar ratio of 4/2 after calcinations at 600 °C to achieve the complete removal of nitrobenzene within 40 min. However, only 75.2%, 8.8%, and 7.9% were removed by S/TiO2, TiO2-T, and P25-TiO2, respectively. It was also observed that the S/TiO2-T(4/2) catalyst had higher catalytic efficiency for oxidation of As(III) under visible light irradiation. The complete oxidation of 250 ml (50 mg/L) of As(III) solution was achieved within 20 min under visible light irradiation by 125 mg S/TiO2-T(4/2) catalyst. The hemicellulose aided synthesis led to high dispersion, small grain size, and high specific surface area of S/TiO2-T catalysts. Moreover, the S-doping of TiO2 is also the key factor for the visible light responsive degradation of toxic organic compounds and oxidation of As(III), and using the template in the synthesis further improves the catalytic performances.

Enhanced photocatalysis by depositing ZnO thin film in the inner wall of glass tube

This study provides a new paradigm for the degradation of toxic organic compounds. Zinc oxide thin film was deposited on the inner wall of a glass tube using ultrasonic spray pyrolysis technique and the UV LED lamps were used for photocatalytic application. The atomic force microscopy (AFM) observation showed that the surface morphology of the film is almost homogeneous. The PL spectrum allowed us to confirm that the trapped electrons via defects in the ZnO film increased the photocatalytic activity. UV–vis spectrometry reveals a dye degradation efficiency of 100% which confirm a complete removal of methylene blue (MB) after 240 min.

Activation of persulfate by CuOx@Co-LDH: A novel heterogeneous system for contaminant degradation with broad pH window and controlled leaching

To meet the current challenges of waste water, an efficient, environment friendly and economical treatment process is always desirable for the degradation of toxic organic compounds. Herein, we reported a stable and active bimetallic CuOx@Co-LDH catalyst for the degradation of phenol using persulfate (PS) under mild conditions. The system of PS/CuOx@Co-LDH completely degraded 0.1 mM of phenol in less than 40 min while at the same time, all the other tested catalysts including catalyst precursors remained sluggish. In view of the practical application, CuOx@Co-LDH/PS system demonstrated consistent performance over a broad pH range (pH 5.0–12.0), during which minimum leaching could be detected. Moreover, good resistance to various inorganic anions was demonstrated in CuOx@Co-LDH/PS system. The consistent performance of CuOx@Co-LDH/PS system may originate from the constant buffer pH of catalyst (9.5 ± 0.8), minimum leaching and the generation of diverse free radicals (SO4−, OH or −O2) under different pH conditions. Additionally, LDH structure offered strong synergetic interactions among active components which might also help in minimum leaching and good reactivity of CuOx@Co-LDH catalyst. The results of radical scavengers, EPR and XPS studies collectively proved the mechanism of diverse free radicals, which was accounted to the redox cyclic reactions of active sites (Cu(III)–Cu(II)–Cu(III) and Co(III)–Co(II)–Co(III)) during degradation of phenol.

The analysis of toxic connections content in water by spectral methods

The current state of ecology means the strict observance of measures for the utilization of household and industrial wastes that is connected with very essential expenses of means and time. Thanks to spectroscopic devices usage the spectral methods allow to carry out the express quantitative and qualitative analysis in a workplace and field conditions. In a work the application of spectral methods by studying the degradation of toxic organic compounds after preliminary radiation of various sources is shown. Experimental data of optical density of water at various influences are given.

Development of Crosslinked Chitosan/Au Nanocomposite, Its Characterization and Application towards Solar Light Driven Photocatalytic Degradation of Toxic Organic Compounds

AbstractRecently, we have developed a novel nanocomposite [cl‐Ch‐p(DEAEM)/Au] comprised of in‐situ deposition on AuNPs on cationically functionalized chitosan (in presence of chemical crosslinker) and its potential application towards efficient photocatalytic degradation of Reactive Black 5 (RB 5) and Congo red (CR) dyes under exposure of sunlight. The physical, morphological and structural properties of nanocomposite have been characterised using UV‐Vis, FT‐IR, 1H and 13C NMR, PL, FESEM, TEM, EDAX, TGA, XRD, LC–MS and Zeta potential analyses. Here, it has been observed that the nanocomposite can remove both RB 5 and CR dyes rapidly and efficiently through adsorption, followed by photocatalytic degradation under exposure of sunlight. Besides, the adsorbed dyes have been isolated effectively and the nanocomposite has been regenerated in presence of sunlight just by altering the pH of the media and could be reusable for at least 4 times without remarkable decrease in its efficacy.

Highly effective Fe-doped TiO2 nanoparticles photocatalysts for visible-light driven photocatalytic degradation of toxic organic compounds

This paper reports the synthesis of various molar concentrations of iron (Fe)-doped TiO2 nanoparticles and their efficient use as potential photocatalysts for photocatalytic degradation of toxic and harmful chemical, paranitrophenol. The nanoparticles were synthesized by a novel and facile ultrasonic assisted hydrothermal method and characterized in detail by various analytical techniques in terms of their morphological, structural, compositional, thermal, optical, pore size distribution, etc properties. The photocatalytic activities of the as-prepared Fe-doped TiO2 nanoparticles were examined under visible light illumination using para-nitrophenol as target pollutant. By detailed experimental findings revealed that the Fe dopant content crucially determines the catalytic activity of TiO2 nanoparticles. The maximum degradation rate of para-nitrophenol observed was 92% in 5h when the Fe3+ molar concentration was 0.05mol%, without addition of any oxidizing reagents. The prepared nanoparticles demonstrated excellent photocatalytic response because of their small size, excellent crystalline structure, increase in threshold wavelength response and maximum separation of photogenerated charge carriers. Further, the determination of reaction intermediates has also been carried out and plausible mechanism of photocatalytic degradation of para-nitrophenol has been proposed.

Facile synthesis of novel Ag3PO4tetrapods and the {110} facets-dominated photocatalytic activity

Highly uniform silver orthophosphate microcrystals with novel tetrapod morphology are, for the first time, synthesized via a simple hydrothermal route with the assistance of urea. The effect of active crystal facets on the photocatalytic activity is principally investigated. The silver orthophosphate tetrapods exhibit significantly higher visible light activity than the polyhedrons for the degradation of toxic organic compounds due to the highly exposed {110} facets.

Plant-Associated Bacterial Degradation of Toxic Organic Compounds in Soil

A number of toxic synthetic organic compounds can contaminate environmental soil through either local (e.g., industrial) or diffuse (e.g., agricultural) contamination. Increased levels of these toxic organic compounds in the environment have been associated with human health risks including cancer. Plant-associated bacteria, such as endophytic bacteria (non-pathogenic bacteria that occur naturally in plants) and rhizospheric bacteria (bacteria that live on and near the roots of plants), have been shown to contribute to biodegradation of toxic organic compounds in contaminated soil and could have potential for improving phytoremediation. Endophytic and rhizospheric bacterial degradation of toxic organic compounds (either naturally occurring or genetically enhanced) in contaminated soil in the environment could have positive implications for human health worldwide and is the subject of this review.

A high voltage resonant inverter for dielectric discharge barrier cell plasma applications

Among the applications of dielectric barrier discharge cells (DBDCs), the generation of cold plasmas for the degradation of toxic organic compounds has received a great deal of attention in recent years. Normally, a DBDC can be energized by means of a high voltage power supply operating at line frequency. In this paper, the analysis, design and construction of a power resonant seriesinverter is presented; this inverter is aimed to operate at high-voltages/high-frequencies, and its suitability to excite a DBDC is investigated. The topological analysis of the inverter is carried out using the fundamental approximation technique, where the DBDC has been modelled as a capacitor whose terminals' voltage is provided by a pulse transformer. Both, the DBDC and the pulse transformer are represented in an RLC equivalent circuit. The resonant inverter is designed to operate in a region where the transfer function is load dependent. The series resonant inverter performance has been experimentally tested in a DBDC application, showing its effectiveness in the generation of the electron discharge by means of a charge/voltage figure of merit.

Human Exposure Assessment and the National Toxicology Program

Human Exposure Assessment and the National Toxicology Program

Effect of adsorbents on degradation of toxic organic compounds by coimmobilized systems

The use of coimmobilized systems for treatment of toxic organic compounds has been proposed. The proposed approach combines the use of adsorbents and laboratory identified microorganisms immobilized in a protective permeable barrier to achieve a greater degree of control over the remediation process. This study was launched to understand the effect of adsorbents and changes in adsorption on the degradation of toxic compounds by coimmobilized systems. The specific case studied involved the degradation of pentachlorophenol (PCP) by Arthrobacter (ATCC 33790) coimmobilized with powdered activated carbon within calcium alginate capsules.The design parameters studied included adsorbent content and type as well as the effect of solution pH and surfactant concentration on adsorption and biodegradation. It was found that the equilibrium adsorption behavior of PCP was strongly influenced by solution pH and surfactant concentration. A mathematical model was developed that combined the physical processes of mass transfer and adsorption with biological degradation of PCP. The model was used to predict the effect of various parameters on the degradation of PCP. Based on model predictions, the degradation of PCP. Based on model predictions, the degradation of PCP was strongly dependent on variations in adsorbent capacity and affinity for this contaminant.

Photocatalysis of 3,4-DCB in TiO 2 aqueous suspensions; effects of temperature and light intensity; CIR-FTIR interfacial analysis

The photocatalytic degradation of toxic organic compounds on semiconducting TiO 2 surfaces has recently been receiving increased attention as an attractive alternative to waste disposal and/or incineration. TiO 2 particles act as both an effective adsorbent and photoelectric chemical cells for the destruction of these toxic compounds. In our studies we have investigated the effect of temperature and light intensity on the degradation of 3,4-DCB on TiO 2 surface. Our results show, clearly, that increases in both parameters cause enhanced kinetic rates of 3,4-DCB destruction, with increases in light intensity being more efficient. The suspension/semiconductor interface has been analyzed with CIR-FTIR techniques, wich have allowed us to observe adsorbed 3,4-DCB and its interaction with the hydrous oxide surface and with the interfacial water.