Photoreduction of Cr(VI) by TiO2 adsorbed gold nanoparticles and perylene as a novel organic-inorganic hybrid photocatalyst.

The photoreduction of hexavalent chromium (Cr(VI)) using TiO2 adsorbed gold nanoparticles and perylene (Au/Pe/TiO2) as a novel organic-inorganic hybrid photocatalyst has been studied. The irradiation by a Xe lamp of a Cr (VI) aqueous solution (0.1 mM) with the Au/Pe/TiO2 powder resulted in the reduction of the Cr(VI). The rate of Cr(VI) reduction reached 98.3% by the irradiation for 60 min. The reaction rate constant using Au/Pe/TiO2 (0.0545 min-1) was higher than that of TiO2 (0.0218 min-1), Pe/TiO2 (0.0303 min-1), or Au/TiO2 (0.0393 min-1). Gold nanoparticles and perylene synergistically accelerated the TiO2 photocatalytic reaction. This result is due to the Z-scheme electron transfer between Pe and TiO2 and the suppression of charge recombination by the gold nanoparticles. The irradiation of sunlight also led to the photocatalytic reduction of the Cr(VI) by Au/Pe/TiO2. In addition, successive reduction of the Cr(VI) was achieved by using a column packed with the Au/Pe/TiO2 powder immobilized by calcium alginate gel.

Keggin Cluster Modulated Photocatalytic Activity of Aryl Sulfonium Polyoxometalate Hybrids toward Dichromate Reduction.

Dichromate (Cr2O72-) ion having chromium in its +6 oxidation state is a carcinogen and a potential threat to humans and aquatic life. The photocatalytic reduction of toxic Cr(VI) species into less toxic Cr(III) is an important target in heterogeneous catalysis. In this work, the catalytic activities of a series of Keggin cluster-based aryl sulfonium polyoxometalate hybrids, (FPDS)3[PMo12O40] (1), (FPDS)3[PW12O40] (2), (FPDS)4[SiMo12O40] (3), and (FPDS)4[SiW12O40] (4), toward the photocatalytic reduction of Cr(VI) have been analyzed and compared. Here, we used the aryl sulfonium counterions to modulate the POM cluster's solubility in water and stabilize the photogenerated e--h+ pair on the cluster. All of the hybrids 1-4 catalyzed the reduction of Cr(VI) to Cr(III) under ultraviolet (UV) irradiation, and their photocatalytic efficiencies followed the order hybrid 1 > hybrid 3 > hybrid 2 > hybrid 4, with the rate-constant values of 0.048, 0.0056, 0.0035, and 0.0028 min-1, respectively. Hybrid 1 with [PMo12O40]3- Keggin cluster exhibited the best photocatalytic activity in the series yielding a 99% reduction in 120 min. The reasons behind the best photocatalytic activity of hybrid 1 are identified as its low band gap, less charge recombination, and fast photoresponse. The electron-trapping analyses performed using AgNO3 revealed electrons as the main reactive species responsible for the photocatalytic reduction of Cr(VI). A plausible photocatalytic mechanism has also been proposed based on electron-trapping experiments. The present study shows that aryl sulfonium Keggin hybrids can function as efficient photocatalysts for Cr(VI) reduction, and their catalytic efficiency varies with the nature of the Keggin cluster.

Performance of EDTA modified magnetic ZnFe2O4 during photocatalytic reduction of Cr(VI) in aqueous solution under UV irradiation.

The photocatalytic reduction of toxic Cr(VI) to non-pernicious Cr(III) using ZnFe2O4/EDTA (ethylenediaminetetraacetic acid) under UV irradiation was evaluated. The reduction of Cr(VI) with bare ZnFe2O4 under UV irradiation was negligible. However, the Cr(VI) in the solution was completely reduced within 3 h after the introduction of EDTA. EDTA could consume valence band holes and could be oxidized by holes into inorganic products. Therefore, photo-generated electrons could be used to reduce Cr(VI) to Cr(III). The effect of concentration of EDTA, ZnFe2O4 photocatalyst dosages, and initial pH on the photocatalytic reduction of Cr(VI) was investigated. The results revealed that the photocatalytic reduction of Cr(VI) accelerated by increasing EDTA concentration and ZnFe2O4 dosage. The present reduction process confirms the pseudo-first-order kinetic reaction. The quasi reduction rate constant increased from 3.5 x 10-4 min-1 to 2.6 x 10-2 min-1 with the increase in initial EDTA concentration from 0 to 1000 mg L-1. The acidic solution is preferable for the photocatalytic reduction of Cr(VI). The entire reduction of Cr(VI) was carried out within 2 h under the optimum conditions with pH 2, 20 mg ZnFe2O4, and 500 mg L-1 EDTA. The formation of [Cr-EDTA]3+ complex may be advantageous to accelerate the Cr(VI) reduction. A probable mechanism for the photocatalytic Cr(VI) reduction was speculated here.

Photoreduction of chromium(VI) in microstructured ceramic hollow fibers impregnated with titanium dioxide and coated with green algae Chlorella vulgaris.

Here we propose an innovative photocatalytic hybrid system for the reduction of hexavalent chromium (Cr(VI)) from aqueous solutions. The hybrid system was composed of titanium dioxide (TiO2) immobilized in the micro-voids of asymmetric alumina hollow fibers and of the green algae Chlorella vulgaris coated on the outer sponge-like layer of the fiber. The photoreduction of Cr(VI) was systematically studied in different systems: single systems with TiO2 or algae; the synergistic system of algae combined with TiO2; and the proposed hybrid system composed of TiO2 and algae supported in ceramic hollow fibers. Morphological and energy dispersive spectroscopy analyses showed that TiO2 and the algae were properly supported in the substrate (alumina hollow fibers). For an initial Cr(VI) concentration of 10 mg L-1 and dosages of 1 g L-1 of TiO2 and algae, the hybrid system resulted in total Cr(VI) reduction after 16 h of process. Additionally, the efficiency of the hybrid system for Cr(VI) reduction was reduced in only 9% after 5 cycles of reuse and in 42% after 10 cycles of reuse. Thus, micro-structured ceramic hollow fibers impregnated with TiO2 and decorated with the green algae C. vulgaris was efficient for Cr(VI) reductions.

MONITORING OF HIGH-ENERGY PHOTON FLUENCE IN CLINAC USING Zn AND Cr PHOTOACTIVATION.

Monitoring of high-energy photon dose in radiation therapy is crucial for radiation protection, as well as to estimate the radiation effects in the operating microelectronic devices. The aim of this work was to investigate the possibility of using the photoactivation technique to monitor the high-energy photon fluence in the Varian 21EX 23MV CLINAC. The 52Cr(γ,n)51Cr and 66Zn(γ,n)65Zn reactions were used. It was found that 51Cr and 65Zn can be used successfully to monitor the fluence for short term (80 days) and long term (110 days), respectively.

S-incorporated TiO2 coatings grown by plasma electrolytic oxidation for reduction of Cr(VI)-EDTA with sunlight.

The plasma electrolytic oxidation (PEO) technique was used to prepare photocatalytic S-TiO2 coatings on Ti sheets; the incorporation of the S ions was possible from the electrolyte for modifying the structural and optics characteristics of the material. In this work, substrates of Ti (ASME SB-265 of 20 × 20 × 1 mm) were used in a PEO process in 10 min, using constant voltage pulses of 340 V with frequency of 1 kHz and duty cycles of 10% and of 30%. Solutions with H2SO4 (0.1 M) and CH4N2S (52 and 79 mM) were used as electrolytes. X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy (EDS) were utilized to analyze the surface morphology, crystalline phase, and chemical composition of the samples. According to the results, the catalyst coatings had microporous structure and contained anatase-rutile TiO2 nanocrystalline mixture, until 73.2% rutile and 26.8% anatase in the samples grown with 30% duty cycle and the lowest concentration of CH4N2S. From the EDS measurements, the incorporation of sulfur ions to the coatings was 0.08 wt%. 99.5% reduction efficiency of Cr(VI)-EDTA with sunlight was observed after 2 h; it was determined by diphenyl carbazide spectrophotometric method. These coatings have potential for effective sunlight heterogeneous photoreduction of this toxic, cumulative, and non-biodegradable heavy metal that contaminates the soil and water and is a serious risk to sustainability, ecosystems, and human health.

One stone two birds: novel carbon nanotube/Bi4VO8Cl photocatalyst for simultaneous organic pollutants degradation and Cr(VI) reduction.

In this work, visible light-responsive carbon nanotubes (CNTs)/Bi4VO8Cl composite photocatalysts have been prepared by a facile in situ hydrothermal method and characterized by various techniques. The photocatalytic properties of the photocatalysts are evaluated by the degradation of refractory azo-dye methyl orange (MO), hexavalent chromium Cr(VI), and bisphenol A (BPA) in water under visible light irradiation. It is found that the as-prepared composite with 4 wt% CNTs shows an optimal photocatalytic performance, and its photocatalytic activity is 30% higher than that of pure Bi4VO8Cl. The enhanced photocatalytic activity is ascribed to the synergetic effects induced by increased light absorption, increased adsorption efficiency for pollutant, and suppressed recombination rate of photogenerated charge carriers. Furthermore, efficient removals of Cr(VI), bisphenol A (BPA), and combined contamination of Cr(VI) and BPA over CNTs/Bi4VO8Cl composite further confirm that the degradation of organic pollutants is a photocatalytic mechanism rather than photosensitization of dye. Of particular importance is that removal efficiency of single pollutant can be promoted by the coexistence of the Cr(VI) and organics. The mechanism of synergetic promotion is discussed and attributed to the accelerated separation of charge carriers resulted from their simultaneously being captured by pollutants. Moreover, the CNTs/Bi4VO8Cl composite exhibits good stability and recycling performance in the photocatalytic degradation process. Therefore, the composite photocatalysts developed in the present work are expected to have the potential in purification of complex wastewater. Graphical abstract The separation of photogenerated charge carriers and adsorbing capacity as well as visible light absorption ability of Bi4VO8Cl are significantly promoted by coupling with carbon nanotubes. Simultaneous removal of Cr(VI) and organic pollutants can be achieved by CNTs/Bi4VO8Cl composite photocatalysts under visible light irradiation.

MIL-53(Fe) as a highly efficient bifunctional photocatalyst for the simultaneous reduction of Cr(VI) and oxidation of dyes.

A bifunctional photocatalyst-Fe-benzenedicarboxylate (MIL-53(Fe)) has been synthesized successfully via a facile solvothermal method. The resulting MIL-53(Fe) photocatalyst exhibited an excellent visible light (λ≥ 420nm) photocatalytic activity for the reduction of Cr(VI), the reduction rate have reached about 100% after 40min of visible light irradiation, which has been more efficient than that of N-doped TiO2 (85%) under identical experimental conditions. Further experimental results have revealed that the photocatalytic activity of MIL-53(Fe) for the reduction of Cr(VI) can be drastically affected by the pH value of the reaction solution, the hole scavenger and atmosphere. Moreover, MIL-53(Fe) has exhibited considerable photocatalytic activity in the mixed systems (Cr(VI)/dyes). After 6h of visible light illumination, the reduction ratio of Cr(VI) and the degradation ratio of dyes have been exceed 60% and 80%, respectively. More significantly, the synergistic effect can also be found during the process of photocatalytic treatment of Cr(VI) contained wastewater under the same photocatalytic reaction conditions, which makes it a potential candidate for environmental restoration. Finally, a possible reaction mechanism has also been investigated in detail.

Simultaneously photocatalytic treatment of hexavalent chromium (Cr(VI)) and endocrine disrupting compounds (EDCs) using rotating reactor under solar irradiation.

In this study, simultaneous treatments, reduction of hexavalent chromium (Cr(VI)) and oxidation of endocrine disrupting compounds (EDCs), such as bisphenol A (BPA), 17α-ethinyl estradiol (EE2) and 17ß-estradiol (E2), were investigated with a rotating photocatalytic reactor including TiO2 nanotubes formed on titanium mesh substrates under solar UV irradiation. In the laboratory tests with a rotating type I reactor, synergy effects of the simultaneous photocatalytic reduction and oxidation of inorganic (Cr(VI)) and organic (BPA) pollutants were achieved. Particularly, the concurrent photocatalytic reduction of Cr(VI) and oxidation of BPA was higher under acidic conditions. The enhanced reaction efficiency of both pollutants was attributed to a stronger charge interaction between TiO2 nanotubes (positive charge) and the anionic form of Cr(VI) (negative charge), which are prevented recombination (electron-hole pair) by the hole scavenging effect of BPA. In the extended outdoor tests with a rotating type II reactor under solar irradiation, the experiment was extended to examine the simultaneous reduction of Cr(VI) in the presence of additional EDCs, such as EE2 and E2 as well as BPA. The findings showed that synergic effect of both photocatalytic reduction and oxidation was confirmed with single-component (Cr(VI) only), two-components (Cr(VI)/BPA, Cr(VI)/EE2, and Cr(VI)/E2), and four-components (Cr(VI)/BPA/EE2/E2) under various solar irradiation conditions.

Immediate remediation of heavy metal (Cr(VI)) contaminated soil by high energy electron beam irradiation.

This work developed an immediate and high-performance remediation method for Cr(VI) contaminated soil (CCS) using high energy electron beam (HEEB) irradiation. The result indicated that, compared with γ-ray irradiation, HEEB irradiation displayed a significant reduction efficiency on Cr(VI) in CCS to Cr(III) with substantially lower toxicity, which was mainly attributed to the reduction effects of electrons, hydrated electrons, and reductive radicals generated in the irradiation process of HEEB. This work could provide a one-step and effective method for the remediation of heavy metal contaminated soil (HMCS).

Cross-sections for (p,x) reactions on natural chromium for the production of (52,52m,54)Mn radioisotopes.

The production of positron-emitting isotopes of manganese is potentially important for developing contrast agents for dual-modality positron emission tomography and magnetic resonance (PET/MR) imaging, as well as for in vivo imaging of the biodistribution and toxicity of manganese. The decay properties of (52)Mn make it an excellent candidate for these applications, and it can easily be produced by bombardment of a chromium target with protons or deuterons from a low-energy biomedical cyclotron. Several parameters that are essential to this mode of production­target thickness, beam energy, beam current, and bombardment time­depend heavily on the availability of reliable, reproducible cross-section data. This work contributes to the routine production of (52g)Mn for biomedical research by contributing experimental cross-sections for natural chromium ((nat)Cr) targets for the (nat)Cr(p,x)(52g)Mn reaction, as well as for the production of the radiocontaminants (52m,54)Mn.

Sol-gel synthesized far-red chromium-doped garnet phosphors for phosphor-conversion light-emitting diodes that meet the photomorphogenetic needs of plants.

We report the sol-gel synthesis and characterization of far-red garnet phosphors Gd(3)Ga(5)O(12) (GGG:Cr), Y(3)Ga(5)O(12) (YGG:Cr), Lu(3)Ga(5)O(12) (LGG:Cr), and Gd(3)Sc(2)Ga(3)O(12) (GSGG:Cr) doped with different chromium (III) concentration (3, 5, and 8 mol. %). The morphological and luminescence properties of the phosphors annealed at different temperatures (1000°C, 1300°C, 1400°C, and 1500°C) were examined using x-ray diffraction, scanning electron microscopy, photoluminescence (PL), and PL excitation (PLE) spectroscopy, and by the measurements of diffuse reflection, PL internal quantum efficiency (QE), and PL decay time. The PLE spectra of the samples were found to peak at around 450 nm depending on the host, and luminescence was observed in the region of 700-760 nm. The QE was found to strongly depend on doping concentration and calcination temperature, and the PL decay exhibited biexponential behavior. The investigated far-red garnet phosphors, in particular GGG:Cr and YGG:Cr, show a potential for use in phosphor-converted light-emitting diodes that meet the photomorphogenetic needs of plants.

Anomalous surface segregation behaviour of some 3d elements in ferromagnetic iron.

The segregation of Cr in Fe is known to be anomalous since the barrier for surface segregation of Cr is not determined by the topmost surface layer, as one would expect, but rather by the subsurface layer where the energy of segregation is much larger and endothermic. This has been attributed to a complex interaction involving the antiferromagnetism of Cr and the ferromagnetism of Fe. We report in this paper the results of our ab initio electronic structure calculations on the segregation behaviour of all the 3d elements on the (1 0 0) surface of ferromagnetic iron in the hope of better understanding this phenomenon. We find a similar behaviour for the segregation of the next antiferromagnetic 3d element Mn in Fe, where the subsurface layer is also found to block the segregation of Mn to the surface. On the other hand, ferromagnetic Co exhibits a normal segregation behaviour. The elements Sc, Cu and Ni do not form solid solutions with ferromagnetic iron. The early elements Ti and V are non-magnetic in their metallic states, but are strongly polarized by Fe, and develop magnetic moments which are aligned antiferromagnetically to those of Fe atoms. While the subsurface layer blocks the segregation of Ti to the surface, no blocking behaviour is found for the segregation of V. The segregation behaviour of all these elements is strongly correlated with the displacement of the solute atoms on the surface of Fe. The elements showing anomalous segregation behaviour are all displaced upwards on the surface, while those showing normal segregation are pulled inwards. These results indicate that the antiferromagnetism of the segregating element plays the key role in the anomalous segregation behaviour in Fe.

Production of 70-nm Cr dots by laser-induced forward transfer.

The effect of donor film thickness and laser beam fluence on the size of laser-induced forward transfer (LIFT) spots is studied to achieve sub-100 nm features. A 130 fs, 800 nm laser is focused on ultrathin Cr films, and the transfer and ablation thresholds of these films at various thicknesses are determined. The minimum transfer spot size decreases with decreasing donor film thickness and incident laser fluence. Minimum LIFT spots of 70-450 nm diameter are obtained from films of 20-80 nm thickness, respectively. The 70 nm diameter transfer spots obtained from sputtered continuous films are the smallest to date.

Radiation-induced strengthening and absorption of dislocation loops in ferritic Fe-Cr alloys: the role of Cr segregation.

The understanding of radiation-induced strengthening in ferritic FeCr-based steels remains an essential issue in the assessment of materials for fusion and fission reactors. Both early and recent experimental works on Fe-Cr alloys reveal Cr segregation on radiation-induced nanostructural features (mainly dislocation loops), whose impact on the modification of the mechanical response of the material might be key for explaining quantitatively the radiation-induced strengthening in these alloys. In this work, we use molecular dynamics to study systematically the interaction of dislocations with 1/2<111> and <100> loops in all possible orientations, both enriched by Cr atoms and undecorated, for different temperatures, loop sizes and dislocation velocities. The configurations of the enriched loops have been obtained using a non-rigid lattice Monte Carlo method. The study reveals that Cr segregation influences the interaction mechanisms with both 1/2<111> and <100> loops. The overall effect of Cr enrichment is to penalize the mobility of intrinsically glissile 1/2<111> loops, modifying the reaction mechanisms as a result. The following three most important effects associated with Cr enrichment have been revealed: (i) absence of dynamic drag; (ii) suppression of complete absorption; (iii) enhanced strength of small dislocation loops (2 nm and smaller). Overall the effect of the Cr enrichment is therefore to increase the unpinning stress, so experimentally 'invisible' nanostructural features may also contribute to radiation-induced strengthening. The reasons for the modification of the mechanisms are explained and the impact of the loading conditions is discussed.

Elastic anomalies in Fe-Cr alloys.

Using ab initio alloy theory, we determine the elastic parameters of ferromagnetic and paramagnetic Fe(1-c)Cr(c) (0 ≤ c ≤ 1) alloys in the body centered cubic crystallographic phase. Comparison with the experimental data demonstrates that the employed theoretical approach accurately describes the observed composition dependence of the polycrystalline elastic moduli. The predicted single-crystal elastic constants follow complex anomalous trends, which are shown to originate from the interplay between magnetic and chemical effects. The nonmonotonic composition dependence of the elastic parameters has marked implications on the micro-mechanical properties of ferrite stainless steels.

Rewritable optical memory in liquid crystals containing photo-epimerizing Cr(III) complexes.

We describe herein a concept of optical memory using a photosensitive metal complex, [Cr((-)-tfac)3] ((-)-tfac = (-)-3-trifluoroacetylcamphorato), as a dopant to induce chiral nematic phases. The memory was written by the photo-epimerization of the complex and read-out in terms of circular dichroism spectra. The rewritability of the memory was attempted by using the cycles between liquid crystals and isotropic phases.

Synergistic photosensitized removal of Cr(VI) and Rhodamine B dye on amorphous TiO2 under visible light irradiation.

Amorphous TiO(2) (Am-TiO(2)) was prepared at room temperature by hydrolysis of Ti(OBu)(4) in water without addition of strong acids or organic solvents. Results from XRD and TEM revealed that the as-prepared Am-TiO(2) was composed of amorphous structure. For the simultaneous photosensitized removal of Cr(VI) and zwitterionic Rhodamine B (RhB) dye, Am-TiO(2) exhibited more significant synergistic effect than commercial P25-TiO(2). The removal efficiencies for RhB and Cr(VI) after 100 min visible light irradiation were 97.8% and 53.5% on Am-TiO(2), respectively. While 88.2% RhB and 42.1% Cr(VI) were removed on P25-TiO(2). Decreased synergistic activities as well as smaller surface areas were observed when Am-TiO(2) was pretreated at high temperatures (200-700°C). Thus, it was the larger specific surface area rather than better crystallinity dominated the synergistic degradation dynamics under visible light irradiation with lower pH (2), greater catalyst loading amount (2g/L), proper RhB/Cr(VI) ratios (1:8) and higher light intensity (500 W). Better synergistic performance was also obtained on Am-TiO(2) than P25-TiO(2) when Cr(VI) coexists with cationic dyes, while negligible difference was observed in the presence of anionic dyes. Superior stability and simplicity of Am-TiO(2) was also exhibited in the cyclic runs.

Visible-light-induced photocatalytic reduction of Cr(VI) with coupled Bi2O3/TiO2 photocatalyst and the synergistic bisphenol A oxidation.

Coupled Bi2O3/TiO2 photocatalysts were fabricated by sol-gel and hydrothermal methods and characterized using various spectroscopy techniques. Photocatalytic reduction of Cr(VI) in aqueous solution, together with the synergistic effect of photodegradation of bisphenol A (BPA), was investigated using these coupled Bi2O3/TiO2 under visible-light irradiation. Coupling of Bi2O3 inhibited the phase transformation from anatase to rutile and extended absorption region to visible light. Bi ions did not enter TiO2 lattice and were more likely to bond with oxygen atoms to form Bi2O3 on the surface of TiO2. Photovoltage signals in visible range revealed the effective interfacial charge transfer between Bi2O3 and TiO2. Two percent Bi2O3/TiO2 exhibited the highest photocatalytic activity of visible-light-induced reduction of Cr(VI). The addition of BPA effectively increased the photocatalytic reduction of Cr(VI). Simultaneously, the presence of Cr(VI) promoted the degradation of BPA, which was demonstrated by the investigation of TOC removal yield and generated intermediates. A possible mechanism of photocatalytic reduction of Cr(VI) and degradation of BPA in Bi2O3/TiO2 system was proposed. The synergistic effect, observed between reduction of Cr(VI) and degradation of BPA, provides beneficial method for environmental remediation and purification of the complex wastewater.

Efficient photocatalytic reduction of aqueous Cr(VI) over flower-like SnIn4S8 microspheres under visible light illumination.

Photocatalytic reduction of aqueous Cr(VI) was successfully achieved on nanostructured SnIn(4)S(8). The SnIn(4)S(8) particles with flower-like nanostructure were synthesized via a facile solvothermal method. UV-vis diffuse reflectance spectra (DRS) indicated that the SnIn(4)S(8) particles had strong absorption in visible region and the band gap was estimated to be from 2.27 to 2.35 eV. The photocatalytic reduction of aqueous Cr(VI) by flower-like SnIn(4)S(8) was evaluated under visible light (λ>400 nm) irradiation. The polyvinyl pyrrolidone (PVP) assisted SnIn(4)S(8) sample exhibits excellent removal efficiency of Cr(VI) (~97%) and good photocatalytic stability. The predominant photocatalytic activity is due to its large surface area, strong absorption in visible-light region and excellent charge separation characteristics.