Photoreduction Capacity Research Articles

Artificial Surface Electron Network Prompted Energy Band Structure Tuning: Boosting Solar-to-Hydrogen Evolution Performance.

The energy gap and conduction band position of catalysts play crucial roles in solar-to-hydrogen (STH) transformation technology. Unfortunately, although an increase in the conduction band position can effectively promote the photoreduction capacity of the photocatalyst, it will inevitably widen the band gap, thus reducing the light-absorption scale. It seems that there is a contradiction between the reduction of band gap and the improvement of conduction band position, which is that "You can't have your cake and eat it too." Herein, an ultrasimple molecular adsorption strategy was engineered by adsorbing hydrazine hydrate on the surface of TiO2. The theoretical and experimental results indicated that the strong electron-donating effect of amino groups in hydrazine hydrate can promote the redistribution of photogenerated electrons and form surface electron networks on the surface of TiO2 photocatalysts, which can bend the conduction band upward and significantly improve its photoreduction ability. Besides, the adsorption of -NH2 can narrow the band gap width of TiO2 and promote the separation efficiency of photogenerated carriers. More interestingly, it can also effectively enhance the adsorption of H2O and H+, thus greatly elevating the STH efficiency. The STH rate of the as-prepared T-N-3 can be increased by ≈530%. This work sheds light on a new approach for resolving the contradiction between photoreduction and light absorption capabilities to effectively enhance photocatalytic performance.

Boosting efficient U(VI) immobilization via synergistic Schottky heterojunction and hierarchical atomic-level injected engineering

The graphical abstract shows the photoreduction mechanism of uranium-containing wastewater via TiOS/NHCS heterojunction. S injection facilitates the yields of photon-generated carries and Schottky junction inhibits recombination of electron-hole pairs. The active electrons reduce the U(VI) to U(IV), while the ethanol, as sacrificial agent deplete the holes. • The S injection engineers the energy level structure of TiO 2 . • Schottky junction optimizes the utilization of electron-hole pairs. • Such enhancements boost the photoreduction capacity of U(VI). • A high U(VI) removal ratio of more than 90% is achieved. Nuclear power has brought promising energy sources while laying down the potential risks for environmental friendliness. The technology that converting mobile U(VI) to immobilized U(IV) via photocatalytic reduction is considered to be an effective strategy for treatment spent fuel wastewater systems. Here we employed S-injected engineering to functionalize atoms in the TiO 2 /N-doped hollow carbon sphere (TiOS/NHCS) heterostructure to obtain exciting U(VI) removal efficiency. The experimental results suggested that the U(VI) reduction efficiency exceeded 90% in 20 min at a low initial concentration of 10 mg L -1 , and even the removal ratio per unit mass reached 448 mg. Density functional theory calculations further proved that the injected S-atoms optimized the energy level structure of TiO 2 and strengthened the light utilization ability. Additionally, the remarkable effect benefit forms the spatial separation of photogenerated electrons by the Mott-Schottky junction and the optimization of the TiO 2 energy-level structure by functionalized atoms. It is believed that this work will lay a foundation for the atomic functionalization of photocatalysts and the collaborative design of more advanced injection engineering and Schottky junction for enriching uranium-containing wastewater in the future.

Surface engineering of diatomite using nanostructured Zn compounds for adsorption and sunlight photocatalysis

Diatomite, composed of amorphous macroporous hydrated silica, has generated increasing attention as an attractive raw material for elimination of heavy metal, while suffering low surface activity. Herein, easily separable diatomite adsorbents modified by Zn compounds are developed for effective adsorption of Pb(II), Cu(II) and Cd(II) ions and sunlight photoreduction of toxic Cr(VI) to low-toxic Cr(III). The micro-structure and functionality are characterized through energy spectrum and spectroscopic analysis. Sulfion S2− or carbonyl COO− interlinked networks on the modified diatomite are effective for capturing Pb(II), Cu(II) and Cd(II) ions, and are capable of being oxidized to generate diatomite@ZnO directly at 450 °C in air atmosphere. Significantly, by recycling the used diatomite@ZnS (Dt@ZnS) adsorbents loaded by Cu(II) and Cd(II) ions, Cu or Cd doped ZnO photocatalysts can be fabricated on diatomite to vary band gap energy of ZnO for more efficient absorption of visible light for Cr(VI) photoreduction under sunlight irradiation. Although the derivatives exhibit weakened Cr(VI) photoreduction capacity compared with Dt@ZnS precursor, probably owing to the influence of surface deposits of Cu(II) or Cd(II) on doping efficiency and light absorption, this idea offers a promising solution to convert the used adsorbents loaded by poisonous heavy metals into photocatalysts for secondary utilization in waste water purification, thus making it possible to produce tailor-made materials for specific requirements alternative by the reutilization of discarded heavy metal adsorbents.

High-efficient separation of photoinduced carriers on double Z-scheme heterojunction for superior photocatalytic CO2 reduction

Developing heterojunction is one of promising approaches to acquire desired photocatalysts with high-efficient photocatalytic activity. In this work, sheet-like ternary ZnO/ZnWO4/g-C3N4 composite was synthesized via stepwise calcination treatment. The double interface electric fields built in the ZnO/ZnWO4/g-C3N4 heterojunction can promote efficient separation of photogenerated charge carriers in space. Moreover, in contrast with the individual ZnO, g-C3N4, ZnWO4 and their binary composites, this double Z-scheme heterojunction achieves more light harvesting, larger pore volume, stronger photoreduction capacity and CO2 adsorption capacity. Therefore, the sheet-like ZnO/ZnWO4/g-C3N4 heterojunction exhibits efficient conversion of the CO2 molecules into solar fuels under the light irradiation. The production yield of photocatalytic CO2 reduction over the double Z-scheme heterojunction is 13.19 μmol h−1 g−1 and the conversion rate of hydrocarbon fuel is highly up to 91.5%, which are much higher than that of other samples. This work offers a novel perspective to achieve high-efficiency heterojunction system for photoredox applications such as photocatalytic antibacterial, nitrogen fixation and degradation of pollutions.

Green synthesis of silver doped nano metal oxides of zinc & copper for antibacterial properties, adsorption, catalytic hydrogenation & photodegradation of aromatics

Silver doped copper and zinc nano metal oxides were synthesized in the presence of Sida rhombifolia leaf extract by self propagating sol-gel autocombustion process. X-ray diffraction studies indicated the formation of wurtzite hexagonal phase for ZnO, monoclinic for CuO and FCC structure for silver nanocomposites. The surface morphology of nanoparticles were studied using FESEM. FTIR studies confirmed the presence of silver & M–O bonds. UV–vis DRS studies revealed that silver doping reduced the band-gap energy which overcomes fast recombination rate of electron-hole pairs of the nanoparticles. TGA studies indicated enhanced thermal stability of doped nanocomposites. Hydrogenation of 4-nitrophenol to 4-aminophenol with NaBH4 showed that Ag/ZnO & Ag/CuO exhibited greater photoreduction capacity than undoped ZnO & CuO. ZnO, Ag/ZnO, CuO & Ag/CuO nanocomposites have antagonistic effect on the growth of Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeroginosa, Streptococcus mutans and Staphylococcus aureus with greater inhibition zones. Ag/CuO NPs exhibited the highest sensitivity against various bacterial strains with MIC below 1 mg. Ag/CuO nanorods showed excellent adsorption properties with high removal capacity of MG of about 90%. Kinetic, thermodynamic and equilibrium studies on adsorption of MG onto Ag/CuO nanorods was carried out. The photocatalytic activity of ZnO and Ag/ZnO nanocomposites was investigated by studying the degradation of methylene blue & malachite green under UV irradiation. Ag/ZnO exhibited better photodegradation efficiency of MG & MB and follows pseudo first order kinetic model. Thus the simple, low-cost and eco-friendly herbal synthesis of oxides of silver doped zinc & copper provides nanocomposites with multifunctional applications.

Ionic liquid-employed synthesis of Bi2E3 (E = S, Se, and Te) hierarchitectures: The case of Bi2S3 with superior visible-light-driven Cr(VI) photoreduction capacity

A general ionic-assisted microwave-ultrasonic combined synthetic strategy was developed to fabricate Bi2E3 (E=S, Se, and Te) hierarchitectures. To understand the crystal phase transformation and morphological evolution of Bi2S3 hierarchical nanostructures, the fabrication of Bi2S3 hierarchitectures was investigated by varying sulfidation time and chlorination time. A topotactic transformation from BiOCl microsphere to Bi2S3 hierarchitectures was proposed. It was found that the structure, size, and morphology of Bi2S3 hierarchitectures could be delicately engineered by varying chlorination time, alkyl chain length, and concentration of ionic liquid. Moreover, the as-prepared Bi2S3 hierarchitectures displayed superior capacity of Cr(VI) photoreduction to P25 and irregular Bi2S3 nanostructures under visible light irradiation. Effects of morphology, pH value of reaction system, Cr(VI) concentration, and catalyst dosage on the Cr(VI) photoreduction capacity of Bi2S3 hierarchitectures were also discussed. The enhancement of photoreduction capacity is not only attributed to the intrinsic good electron transfer ability of Bi2S3, but also to synergetic effects of special architectures, wide photoresponse range, high light photoadsorption, high BET surface area and good electron-hole separation performance. The systematic condition experiments and Cr(VI) photoreduction in electroplating and tannery wastewater experiments further demonstrated that the hierarchical Bi2S3 nanospheres can be used in the actual Cr(VI)-containing wastewater treatment.

The adsorption and catalytic transformations of chromium on Mn substituted goethite

Goethite widely occurs in the environment and its role in photoreduction of toxic Cr(VI) to less toxic Cr(III) has been previously reported in the literature. However, natural goethite is rarely stoichiometric and usually contains certain substitutional cations, such as Mn(III) or Mn(IV), which, on the other hand, is an oxidant for Cr(III). In order to provide more insight into the fate of Cr(VI) in the environment, the influence of Mn-substitution in goethite on its Cr(VI) photoreduction capability needs to be clarified. The objectives of this study were to evaluate the adsorption and photo-transformations of Cr on Mn-substituted goethite with Mn/(Mn+Fe) molar ratios ranging from 0 to 0.1. The results showed that Cr adsorption and photo-catalytic transformation on goethite were strongly influenced by the Mn content of goethite. When the system was under illumination, Cr(VI) reduction was decreased with increasing Mn-substitution in goethite. The re-oxidation of photo-reduced product, i.e., Cr(III), at the Mn sites on the surface of goethite is responsible for the lower Cr(VI) photo-reduction capacity of Mn-substituted goethite. The role of goethite in the reduction of Cr(VI) may be overestimated unless its Mn-substituted counterparts are considered. The effectiveness of Mn sites in goethite to increase toxic Cr(VI) has important implications in determining the fate and threat of Cr(VI) contamination.

Enhanced photocatalytic reduction of Hg(II) in aqueous medium by 2-aminothiazole-modified TiO2 particles

This work describes the synthesis and characterization of 2-aminothiazole-modified titania and its application on Hg (II) photoreduction in aqueous medium. Infrared spectroscopy confirmed the chemical modification of the titania matrix. The number of 2-aminothiazole groups attached to the titania was determined by Kjeldahl's method. The photocatalytic experiments were carried out in a cylindrical photoreactor thermostatted at 298 K. The resulting modified photocatalyst 2-aminothiazole titania (TiAT) revealed an enhance in the Hg (II) photoreduction capacity at studied pH values (3, 7 and 9). In addition, sorption studies showed that the photocatalyst TiAT presented a lower equilibrium time and a higher sorption capacity of Hg(II) ion, demonstrating that sorption plays a fundamental role in the photoreduction mechanism.

Photoreduction and incorporation of iron into ferritins

Pea seed ferritin is able to incorporate ferrous iron into the mineral core. Fe2+ may be formed by reduction of exogenous Fe3+ with ascorbate or by photoreduction by ferritin and by ferric citrate. In our experimental conditions the bulk of the photoreduction is carried out by ferritin, which is able to photoreduce its endogenous iron. Citrate does not enhance the photoreduction capacity of ferritin, and exogenous ferric citrate improves the yield of the reaction by about 30%. The mineral core of the ferritin is shown to photoreduce actively, and the protein shell does not participate directly in the photoreduction. Low light intensities and low concentration of reducing agents do not allow a release of iron from ferritins, but induce a 'redox mill' of photoreduction and simultaneous ferroxidase-mediated incorporation. High ascorbate concentrations induce the release of ferritin iron. These reactions are accompanied by the correlated occurrence of damage caused by radicals arising from Fenton reactions, leading to specific cleavages in the 28 kDa phytoferritin subunit. This damage caused by radicals occurs during the oxidative incorporation into the mineral core and is prevented by o-phenanthroline or by keeping the samples in the dark.

ADAPTIVE PHOTOSYNTHESIS RESPONSES TO TEMPERATURE EXTREMES BY THE THERMOPHILIC CYANOPHYTESYNECHOCOCCUS LIVIDUS1

SUMMARYThe physiological and biochemical changes associated with and resulting in adaptation to both sub‐ and supra‐optimal temperatures are presented for the thermophilic cyanophyteSynechococcus lividusCopeland. The optimum temperature for growth was 45 C. An increase in the optimum temperature of photosynthesis from 50 to 55 C was shown for cells grown at the supra‐optimum temperature of 57 C; whereas, cells grown at the sub‐optimal temperature of 35 C exhibited a decrease in the optimal temperature from 50 to 45 C for14CO2uptake. These changes in optimal temperatures are interpreted as adaptive. Associated with the 5 C increase in optimal temperature for photosynthesis was an increase in chlorophyll a, plastoquinone A, and activity of ribulose‐1,5‐diphosphate carboxylase (RuDP carboxylase). However, the increase in the temperature optimum for 57 C grown cells was associated with a reduced O2yield correlated with a reduced ferricyanide photoreduction capacity. RuDP carboxylase activity decreased rapidly above 55 C. Therefore reduced rates above 55 C resulted from damage to ferricyanide reducing systems and reduced RuDP‐carboxylase activity, whereas low photosynthesis rates at sub‐optimal temperatures were probably due to rate limiting effect of low temperatures on RuDP carboxylase activity with no evidence of damage to ferricyanide photoreducing systems.

Particle fractionation from spinach leaf homogenates and diffusion of spinach protein factor

1. Spinach leaves were homogenized in a phosphate or Tris buffer medium containing 0.35 M sucrose and were filtered through filter paper. The particle suspension thus obtained was fractionated by differential centrifugation. 2. The particle fractions sedimenting from 47000 to 105500 × g excreted Spinach Protein Factor, a soluble colourless protein that enhances the light sensitivity of colloidal chlorophylls. 3. Upon fractionation of the combined fractions mentioned under 2 on a sucrose gradient, three types of particle fractions showed up: (a) Colourless small particles (0.01–0.02 μ), presumably ribosomes. (b) A green fraction, mainly consisting of thylakoids (about 0.15 μ), characterized by a very high chlorophyll a/chlorophyll b ratio, a high 740/685–695nm fluorescence (−196°) ratio, a high NADP + photo-reduction capacity and a very low or no Hill reaction capacity. (c) A green fraction, mainly consisting of thylakoids (about 0.3 μ), characterized by a lower chlorophyll a/chlorophyll b ratio than that of the particle fraction mentioned under b, a lower 740/685–695nm fluorescence (−196°) ratio, a lower NADP + photoreduction capacity and a high Hill reaction capacity. Spinach Protein Factor diffused from this particle fraction. 4. Evidence is presented that the particles, mentioned under 3b and 3c, are not chloroplast fragments formed during the homogenization procedure of the spinach leaves but were already present in the leaf. 5. A high Spinach Protein Factor activity from particle diffusates coincided with a high 2,6-dichlorophenolindophenol-oxidase activity. 6. The results are discussed with reference to Systems I and II of photosynthesis.