Effect of chemical parameters on pyrene degradation in soil in a pulsed discharge plasma system

Degradation of pyrene in soil in a net-to-net pulsed discharge plasma (PDP) system was reviewed. Effect of main chemical parameters, including air flow rate, pyrene concentration, initial pH and soil moisture content on pyrene degradation was examined. The obtained results show that 87.9% of pyrene could be removed under the condition of 60 min reaction; increasing of air flow rate within 1 L min⁻¹ was favorable for degradation; pyrene removal was decreased with the increase of initial pyrene concentration; oxidation of pyrene was more evident in acidic soil; enhancement of soil moisture content has no benefit on pyrene degradation.     

Ultrasound-assisted electrochemical treatment for phenolic wastewater

With the rapid development of industry, especially the rapid rise of the chemical industry, the problem of water pollution is becoming more and more serious. Among them, the discharge of organic pollutants represented by phenolic substances has always been at the forefront. In this paper, ultrasound-assisted electrochemical treatment for phenolic wastewater is investigated. The effects of ultrasonic frequency, current, pH value and the amount of fly ash-loaded titanium TiO₂-Fe³⁺ particles on phenol removal from phenol-containing wastewater are investigated. The experimental results demonstrate that the removal rate of phenol in phenol-containing wastewater is the best when ultrasonic frequency is 45 kHz, power is 200 W, the current is 1.2 A, pH is 5 and the dosage of fly ash-loaded titanium TiO₂-Fe³⁺ particles is 3 g. In addition, microwave-assisted-Fenton reagent treatment for phenol wastewater is investigated. The effects of Fenton reagent dosage, initial pH value, microwave power density and radiation time on phenol degradation rate are investigated. The results show that microwave can accelerate the reaction rate, reduce the number of metal ions, save the process cost and reduce the difficulty of post-treatment. Finally, the research status of phenol wastewater treatment technology at the present stage is reviewed, and the future development direction is discussed.     

Photocatalytic reduction of chromium(VI) in aqueous solution using dye-sensitized nanoscale ZnO under visible light irradiation

Photocatalytic removal of Cr⁶⁺ from aqueous solution using dye-sensitized nanoscale ZnO under visible light irradiation was studied in this work. First, nanoscale ZnO was prepared by the co-precipitation method. Then, sensitization of nanoscale ZnO by Alizarin Red S dye followed. Further, nanoscale ZnO and dye-sensitized nanoscale ZnO (designated nanoZnO and nanoZnO*, respectively) were both characterized by various photospectrometry methods, such as scanning electron microscopy (SEM), scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDS), EDS-mapping, transmission electron microscopy (TEM), and X-ray diffractometry (XRD). It was found that both types of prepared particles are spherical in shape with a size range of 20 to 50 nm. XRD patterns showed that both nanoZnO and nanoZnO* had the same crystalline structure of zincite. In the photocatalytic reduction aspect, effects of different light sources and dosage of nanoZnO* on Cr⁶⁺ reduction ([Cr⁶⁺]_initial = 20 mg/L) were evaluated in this work. Treatment of chromium(VI)-bearing wastewater under the conditions of using 1.0 g/L of nanoZnO*, neutral pH, irradiation of household fluorescence lamps for 6 h and 17 h would yield Cr⁶⁺ removal efficiencies of about 68% and 90%, respectively. When the household fluorescence lamps were replaced by visible-light lamps of 400–500 nm in wavelength, the corresponding removal efficiencies dropped to about 50% and 75%, respectively. When nanoZnO* was irradiated by sunlight under almost the same experimental conditions, the Cr⁶⁺ reduction efficiency increased up to 90%. In summary, sensitizing nanoscale ZnO with Alizarin Red S dye for photocatalytic applications using visible light is feasible. The relevant reaction mechanism and pathways were also proposed in this work.     

Adsorption of hexavalent chromium onto montmorillonite modified with hydroxyaluminum and cetyltrimethylammonium bromide

Aluminum hydroxypolycation and cetyltrimethylammonium bromide (CTMAB) were chosen to synthesize inorganic-organic pillared montmorillonite. Three different methods were employed for the intercalation. The characteristics of natural and modified montmorillonite were determined with X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), X-ray photoelectron spectrum (XPS), and zeta potential. It was found that aluminum hydroxypolycation and CTMAB had either entered the interlayer or sorbed on the external surface of the clay. Different intercalation orders can result in different structures. Batch adsorption of hexavalent chromium (Cr⁶⁺) onto modified montmorillonite was also investigated. The experimental data revealed that if aluminum hydroxypolycation was intercalated before CTMAB, the adsorption capacity was better than that of intercalated simultaneously or CTMAB pre-intercalated. The pH of the solution and environmental temperature had significant influences on the adsorption of Cr⁶⁺. The optimal pH for the removal was about 4, and the temperature of 298 K was best suitable. All adsorption processes were rapid during the first 5 min and reached equilibrium in 20 min. The adsorption kinetics can be described quite well by pseudo-second-order model. The adsorption rates of ACM, CAM and ACCOM were 3.814, 0.915, and 3.143 mg/g/min, respectively. The adsorption capacities of Cr⁶⁺ at 298 K on ACM, CAM, and ACCOM inferred from the Langmuir model were 11.970, 6.541, and 9.090 mg/g, respectively. The adsorption of Cr⁶⁺ on modified montmorillonite was mainly induced by the surface charge and the complexation reaction between CTMA⁺ and hexavalent chromium species at the edge of the clay particle.     

Synthesis of Tapioca Cellulose-based Poly(amidoxime) Ligand for Removal of Heavy Metal Ions

Poly(acrylonitrile)/cellulose block copolymer (PAN-b-cell) was prepared by using a free radical initiating process and then the nitrile functional groups of the PAN blocks of the copolymers were transformed into amidoxime ligands. The resulting poly(amidoxime) ligands could complex with heavy metal ions; for example, the reflectance spectra of the [Cu -ligand]ⁿ⁺ was found to be at the highest absorbance, about 94%, at pH 6. The pH was the key parameter for metal ions sensing by the ligand. The adsorption capacity for copper was very good, 272 mg g^?1, with a fast adsorption rate (t_1/2 = 10 min). The adsorption capacities for other heavy metal ions such as Fe³⁺, Cr³⁺, Co³⁺ and Ni²⁺ were also good, being 242, 219, 201 and 195 mg g^?1, respectively, at pH 6. The heavy metal ions removal efficiency from water was 98% at low concentration. The data proved that the heavy metal ions adsorption onto the polymer ligands were well fitted with the Langmuir isotherm model (R²>0.99), which suggests that the cellulose-based adsorbent surface namely the poly(amidoxime) ligand, was homogenous and a monolayer. The reusability was examined by a sorption/desorption process for six cycles and the extraction efficiency was determined. This new adsorbent could be reused for 6 cycles without any significant loss in its original removal function.     

A sonochemical synthesis of cyclodextrin functionalized Au-FeNPs for colorimetric detection of Cr6+ in different industrial waste water

This paper describes a simple, selective and sensitive colorimetric sensing of Cr⁶⁺ ions using β-Cyclodextrin (β-CD) functionalized gold-iron nanoparticles (β-CD/Au-FeNPs). The sonochemically synthesized nanoparticles are winered in colour due to the SPR band of β-CD functionalized bimetalic nanoparticles Au-FeNPs. The capping and stabilizing of Au-FeNPs by redox β-CD is confirmed by FT-IR. The particles are spherical in shape and it posses the effective diameter of 18–20 nm. Under optimized conditions, in the presence of Cr⁶⁺ the wine red Au-FeNPs solution was turned to colourless, accompanying the broadening and red shifting of SPR band. The ratio between the absorbance wavelength at 573 nm to 535 nm (A₅₇₃/A₅₃₅) is linearly correlated with the Cr⁶⁺ concentrations ranging from 50 nM to 500 nM, with a detection limit of Cr⁶⁺ of 2.5 nM was achieved for the first time using β-CD/Au-FeNPs by spectrophotometry. The selectivity of the β-CD/Au-FeNPs towards other interfering metal ions. Finally the proposed method has been successfully employed for the determination of Cr⁶⁺ ion in various industrial waste water with good recoveries.     

Mechanism analysis of hydroxypropyl guar gum degradation in fracture flowback fluid by homogeneous sono-Fenton process

An effective hybrid system was applied as the first report for the successful treatment of key pollutants (hydroxypropyl guar gum, HPG) in fracturing flowback fluid, and the synergistic index of the hybrid system was 20.45. In this regard, chemical oxygen demand (COD) removal ratio was evaluated with various influencing operating factors including reaction time, H₂O₂ concentration, Fe²⁺ concentration, ultrasonic power, initial pH, and temperature. The optimal operating parameters by single-factor analysis method were: the pH of 3.0, the H₂O₂ concentration of 80 mM, the Fe²⁺ concentration of 5 mM, the ultrasonic power of 180 W, the ultrasonic frequency of 20–25 kHz, the temperature of 39 ℃, the reaction time of 30 min, and the COD removal rate reached 81.15 %, which was permissible to discharge surface water sources based on the environmental standards. A possible mechanism for HPG degradation and the generation of reactive species was proposed. Results of quenching tests showed that various impacts of the decomposition rate by addition of scavengers had followed the order of EDTA-2Na < BQ < t-BuOH, therefore OH radicals had a dominant role in destructing the HPG. Based on the kinetic study, it was concluded that Chan Kinetic Model was more appropriate to describe the degradation of HPG. Identification of intermediates by GC–MS showed that a wide range of recalcitrant compounds was removed and/or degraded into small molecular compounds effectively after treatment. Under the optimal conditions, the sono-Fenton system was used to treat the fracturing flowback fluid with the initial COD value of 675.21 mg/L, and the COD value decreased to 80.83 mg/L after 60 min treatment, which was in line with the marine sewage discharge standard. In conclusion, sono-Fenton system can be introduced as a successful advanced treatment process for the efficient remediation of fracture flowback fluid.     

Photocatalytic degradation of methylene blue solution by diphenylanthrazoline compounds

The photocatalytic degradation of methylene blue solution by 8 photocatalytic diphenylanthrazoline compounds was investigated. All diphenylanthrazoline compounds exhibited a good photocatalytic activity towards the methylene blue solution. The removal rate for chemical oxygen demand (COD_Cr) in the methylene blue solution at 12 hours was ~54.1% to 96.3%. 2,8‐Bis(4‐triphenylamino)‐4,6‐diphenyl‐1,9‐anthrazoline ( TM‐2‐d ) was selected for further investigation because of its better photocatalytic activity. To study the optimal reaction conditions for the photocatalytic degradation of dye wastewater, photocatalyst was applied to degrade methylene blue solution. The decolorization rate for simulated dye solutions can exceed 99% in 10 hours, and the COD_Cr removal rate exceeded 91%. These organic semiconductor materials, diphenylanthrazoline compounds, displayed comparative photocatalytic properties to the inorganic semiconductor materials, which can be used in the photocatalytic degradation of organic pollutants.     

Molecular motion and solvent effects in several Cr5+ compounds using nonstationary nuclear-electron resonance

Dynamic proton polarization in several diols Cr⁵⁺ complex ion solutions has been studied at various magnetic field strengths and temperatures. Normally, in most organic radical solutions the dynamic enhancements of solvent proton resonances decay with increasing field and decreasing temperature due to the dipole-dipole intermolecular interactions, modulated by translational diffusion of individual molecules. In contrast to free radical, a strong solvation effect has been discovered in paramagnetic Cr⁵⁺ compounds. Drastic departures from the usual DNP behaviour have been observed. An explanation of the observed effects is proposed by considering the occurrence of hydrogen-bridged solvates. The important motional mechanism that modulates the proton-electron interaction switches from “translation” to “rotation” of the complex molecules. A new type of pulse double resonance equipment is used.     

Magnetic and structural studies of Cr2O5 and Cr3O8

The infrared spectra, indexed X-ray powder diffraction patterns, magnetic susceptibilities between 80 and 300 K, and electron paramagnetic resonance spectra at 80 and 300 K are reported for Cr₂O₅ and Cr₃O₈. The results indicate that both oxides are Cr³⁺/Cr⁶⁺ mixed-valence compounds which contain CrO₆ octahedra and CrO₄ tetrahedra in different ratios. The valence formula for Cr₂O₅ is Cr³⁺₂Cr⁶⁺₄O₁₅ and that of Cr₃O₈ is Cr³⁺₂Cr⁶⁺₇O₂₄. The X-ray powder data for Cr₂O₅ and Cr₃O₈ could be indexed on the basis of a monoclinic unit cell $\text{(a = 12.01(2), b = 8.52(1), c = 9.39(1)}\text{A}\text{?}\text{β = 92.0(1)°)}$ and an orthorhombic unit cell $\text{(a = 12.01(7), b = 36.60(7) and c = 3.82(1)}\text{A}\text{?}\text{)}$, respectively.     

Measurement of oxidation states for transition elements with a small spot tabletop XANES instrument

Development of a compact, high sensitivity, low‐power and low‐cost, tabletop instrument for x‐ray absorption near edge structure, XANES, measurements will make possible chemical speciation and characterization studies in a broad variety of applications in medicine, science and industry. Such a system utilizing a low‐power (<50 W) microfocus x‐ray source combined with a toroidal doubly curved crystal (DCC) optic has been used to differentiate Mn metal and Mn²⁺ and Mn⁷⁺ solution (2, 3% respectively) or Cr metal and Cr³⁺ and Cr⁶⁺ in aqueous (0.1% concentration) solution by measurement of their XANES spectra. This prototype system can measure Cr at 100‐ppm concentration levels. Improvements in the system should make measurements at <10 ppm levels or very short (<1 s) measurement time possible for a large variety of elements. By using this system, rapid reduction of Cr⁶⁺ to Cr³⁺ in cultured cells was directly observed. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis of Cr-based mixed oxides by reactive ion beam mixing of Cr/X interfaces (X=Al or Si)

The 3 keV O₂⁺\mathrm{O}_{2}^{+} reactive ion beam mixing of Cr/X interfaces (X=Al or Si) has been used to synthesize Cr-based mixed oxide thin films. The kinetics of growth, composition, and electronic structure of those films has been studied using X-ray photoelectron spectroscopy, Auger electron spectroscopy, ultraviolet photoelectron spectroscopy, and factor analysis. Initially, for low ion doses, Cr₂O₃ species are formed. Later, with increasing the ion dose, Cr₂O₃ species are first transformed into Cr³⁺–O–X species, and subsequently, those Cr³⁺–O–X species are transformed into Cr⁶⁺–O–X species. This sequential transformation, Cr₂O₃→Cr³⁺–O–X→Cr⁶⁺–O–X, is accompanied by a slight increase of the oxygen concentration and a decrease of the Cr/X ratio in the films formed leading to the synthesis of custom designed Cr-based mixed oxides. The changes observed in the valence band and Auger parameters further support the formation of Cr–X mixed oxide species. Angle resolved X-ray photoelectron spectroscopy shows that for low ion doses, when only Cr₂O₃ and Cr³⁺–O–X species coexist, Cr³⁺–O–X species are located nearer the surface than Cr₂O₃ species, whereas for higher ion doses, when only Cr³⁺–O–X and Cr⁶⁺–O–X species coexist, the Cr⁶⁺–O–X species are those located nearer the surface.     

Saturable absorbers based on tetrahedrally coordinated transition-metal ions in crystals (Review)

Published data on spectroscopic characteristics of saturable absorbers based on crystals doped with tetrahedrally coordinated transition-metal ions (Cr²⁺, Cr⁴⁺, Cr⁵⁺, V³⁺, Cr²⁺, Fe²⁺) in addition to their use as passive Q-switches for solid-state lasers emitting in the visible and near-infrared regions are reviewed. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 5–50, January–February, 2009.     

Spectroscopic analysis of the interaction between chromium (III) and apoovotransferrin

Ovotransferrin (OTf) is a main member of the transferrin family that functions both as an iron transporter and an antibacterial agent. In this study, the thermodynamic property of the interaction between chromium (III) and ovotransferrin was investigated. The conditional binding constants for Cr³⁺ binding to the protein were determined by difference UV spectroscopy and were found to be log K_C=13.08±0.24 and log K_N=5.65±0.12. It was found that Cr³⁺ preferentially binds to the C-terminal site over the N-terminal site under these experimental conditions. The conformational changes in apoovotransferrin (apoOTf) during Cr³⁺ binding were studied by fluorescence spectroscopy using 2-p-toluidinylnaphthalene-6-sulfonate (TNS) as the fluorescence probe and by circular dichroism (CD) spectroscopy. The results show that a large conformational change in apoOTf can be attributed to binding of Cr³⁺ to the N-terminal site, instead of the C-terminal site. In addition, the binding of Cr³⁺ to apoOTf stabilizes the structure of OTf as determined by guanidine hydrochloride denaturation studies. These findings help advance our understanding of the biological effects of Cr³⁺.     

High-pressure synthesis,structure and magnetic properties of LaCrO3 ceramics

Single-phase LaCrO₃ ceramics was synthesized successfully by the solid state sintering method under high pressure (5 GPa). X-ray diffraction measurements suggest that the high-pressure synthesized sample is well-crystallized, but the cell volume is larger than that of the sample synthesized under ambient pressure, which can be ascribed to the occurrence of Cr²⁺ converted form part of Cr³⁺. Such mixed valent state with coexistence of Cr²⁺ and Cr³⁺ could be confirmed by X-ray photoelectron spectroscopy measurements. Magnetic measurement results indicate that in addition to antiferromagnetic superexchange interaction of Cr³⁺-O-Cr³⁺ network accompanied by weak ferromagnetism at high temperature, another kind of ferromagnetic behavior can be observed at low temperature (below 30 K), which could be attributed to double exchange interaction of Cr²⁺-O-Cr³⁺ networks.     

Localization of conduction electrons and the magnetic properties of the molecular metals β″-(BEDT-TTF)4NH4[M(C2O4)3] · DMF (M = Cr3+, Fe3+)

Quasi-two-dimensional organic metals β″-(BEDT-TTF)₄NH₄[M(C₂O₄)₃] · DMF containing the oxalate complexes of Cr³⁺ or Fe³⁺ ions between the conducting organic layers of the BEDT-TTF molecules are studied by EPR spectroscopy, and the contributions of these metallic complexes, conduction electrons, and non-equilibrium lattice defects to the magnetic susceptibility are determined. An analysis of the temperature dependence of the magnetic susceptibility and the EPR line shape has revealed partial localization of conduction electrons at T < 20 K in the crystals with Cr³⁺ ions. The size of the localization region is close to the size of an individual BEDT-TTF molecule. The localization effect weakens as nonequilibrium defects disappear during long-term storage at room temperature. The localization of conduction electrons is found to be accompanied by the appearance of weak antiferromagnetic interaction between the Cr³⁺ ions at T < 20 K, which disappears when Fe³⁺ ions substitute for Cr³⁺ ions.     

Vibrational Analysis of the Elpasolites Cs2NaAlF6 and Cs2NaGaF6 Doped with Cr3+ Ions by Fluorescence Spectroscopy

Interest in 3d transition metal impurities in ionic crystals has increased due to their important role in the laser activity of these materials. Moreover, recent advances in tunable solid-state lasers and high-power semiconductor laser diode arrays have generated a strong interest in investigating new compounds that emit in the visible and near-infrared spectral regions. In particular, many optical studies have been devoted to Cr³⁺-doped fluoride crystals as a consequence of the high quality of some Cr³⁺-based laser materials. In the present investigation, the low-temperature emission spectra of Cr³⁺ ions in the hexagonal elpasolites Cs₂NaAlF₆ and Cs₂NaGaF₆ have been measured. Each compound has two crystallographically inequivalent octahedral sites for the Al³⁺ and Ga³⁺ ions that can be occupied by Cr³⁺ ions. For both materials, the luminescence spectrum presents two zero-phonon lines accompanied by a well-defined vibrational structure. The different peaks of the emission broad band are described in terms of phonons of the lattice and normal modes of the octahedral complex [CrF₆]^3–. A detailed analysis of the vibrational structure observed leads to the conclusion that the ² E and ⁴ T ₂ excited states of the [CrF₆]^3– ion are displaced along the e _g and a _1g and probably the t _2g coordinates.     

Spectral and generation properties of a new laser crystal (Cr<Superscript>3+</Superscript>,Li): Mg<Subscript>2</Subscript>SiO<Subscript>4</Subscript>

Based on the results of a comparative analysis of luminescence spectroscopy and EPR spectroscopy data, it was found for the first time that the wide-band luminescence of Cr³⁺ ions in a forsterite crystal is due to the Cr³⁺-V_Mg center or, in a crystal additionally doped with lithium, to a Cr³⁺-Li⁺ center. For the first time, tunable laser action was obtained with Cr³⁺-Li⁺ centers responsible for the wide-band luminescence.     

KZnF3:Cr3+和KMgF3:Cr3+四角对称电子顺磁共振参量与晶格缺陷的研究

用Newman叠加模型研究了KZnF₃:Cr³⁺四角对称基态的零场分裂,证实了Zn²⁺空位和畸变的存在;并指出,空位对晶场的贡献不可忽略。计算得到:KZnF₃:cr³⁺晶体[0,01]方向的一个F^-配体向Cr³⁺移动Δ(KZnF₃)=0.0029-0.0043nm。还研究了KMgF₃:Cr^{3+关键词：}     

Photoinduced changes in photorefractive PVA films doped with Cr3+ and VO2+: EPR and PAS investigations

In order to understand the mechanism of optical image storage in photorefractive polyvinyl alcohol (PVA) films, photo-EPR and photoacoustic spectral investigations were carried out on PVA films doped with Cr³⁺ and VO²⁺. The EPR spectrum of Cr³⁺ has shown reduction in intensity onin situ illumination with copper vapor laser (CVL). The decay and recovery of Cr³⁺ signal, with and without CVL illumination respectively, was monitored at different temperatures in 10–300 K region. These were found to obey a double exponential, with one time constant independent of temperature, and the other showing significant temperature dependence. From Τ(T), activation energy for the charge carrier transport in one of the processes was estimated to be 0.016 eV. The PA spectra showed shift towards lower wavelength side on consecutive runs. On the other hand, VO²⁺ doped PVA film has not shown any significant changes in intensity on laser illumination. These observations suggest (i) interaction of PVA matrix with excited Cr³⁺ and (ii) predominant non-radiative relaxation in VO²⁺: PVA system with no change in the oxidation state.