Photooxidation of iodide ion on immobilized semiconductor powders

MoO₃ particles immobilized on an organic polymer, fixed on a glass plate, effectively catalyze the oxidation of iodide ion in air-saturated solution under illumination at 365 nm; the catalytic efficiency is higher than that of ZnO and anatase TiO₂. Immobilized ZrO₂, Fe₂O₃, Al₂O₃, Bi₂O₃, Y₂O₃, CeO₂ and Nd₂O₃ particles also photocatalyze the oxidation. Except ZnO, all the listed metal oxides show sustainable photocatalytic activity at least up to 2 h; ZnO photocatalysis slackens after half-an-hour. Immobilized particulate CuO, ZnS, CdO, CdS, PbO and Sb₂O₃ fail to catalyze the photooxidation of iodide ion whereas SnO₂ oxidizes iodide ion in dark itself; V₂O₅ dissolves. All the stated photocatalysis depend linearly on iodide ion concentration and enhance with the photon flux. The mechanistic detail of the photocatalysis is presented.     

Biohydrogen production from cellobiose in phenol and cresol-containing medium using Clostridium sp. R1

Cellobiose fermentation in batch test using an isolated strain, Clostridium sp. R1, was investigated. The Clostridium sp. R1 achieved a maximum hydrogen yield of 3.5 mol H₂ mol⁻¹ cellobiose at pH 6 and 30 °C, higher than most yields reported in literature. This strain can generate hydrogen from a number of carbohydrates, including galactose, glucose, mannose, maltose, sucrose, and starch. This strain can also convert cellobiose to hydrogen in the presence of toxic phenol or cresol. The inhibition effects of phenolic compounds on strain R1 activity followed phenol > p-cresol > o-cresol > m-cresol. Co-culturing with another strain, Clostridium butyricum, can co-degrade some of the phenol as substrates. The new isolated strain can yield hydrogen from phenol-containing wastewaters.     

Catalytic effect of ferrous oxide on burning rate of condensed mixtures

The catalytic effect of Fe₂O₃ on the burning rate, μ, of condensed mixtures was studied. Ammonium (AP), potassium (PP), iminomethylamine (formamidine-FP) and tetramethylammonium (TMAP) perchlorates were used as oxidizers and polymethylmethacrylate (PMM), polystyrene (PS), sool, sulphur, and guanidine nitrate (GN) as fuels.For AP-PMM mixtures, the catalyst effectiveness Z (=μ/μ_o, where μ_o is the burning rate of an uncatalyzed mixture) increased with pressure. The magnitude of Z for AP + PMM and AP + PS mixtures decreased as the ambient temperature increased. When the catalyst content m_c was increased, a steep increase in μ and Z was observed at small m_c, but at m_c > 1 to 5% the value of Z increased only slightly.The catalyst effectiveness decreased as the burning rate, u_o, of an uncatalyzed mixture increased (dependence Z_max = A/u_o^0.65 was obtained). AP- and FP-based mixtures were much more sensitive to catalysis by Fe₂O₃ than the PP- and TMAP-based mixtures, however Fe₂O₃ was an excellent catalyst of TMAP when u_o was decreased by adding diluents (KCl, NH₄Cl or Al₂O₃).A simplified diffusion-controlled model is proposed, taking into account the competition of catalytic and homogeneous reactions. The chemical mechanism of catalysis in the burning zone is discussed.     

Electron-donating tris(p-fluorophenyl)phosphine-modified g-C3N4 for photocatalytic hydrogen evolution and p-chlorophenol degradation

Incorporating aromatics into g-C₃N₄ is an effective strategy to extend electron delocalization. A novel intramolecular donor-acceptor conjugated g-C₃N₄ was synthesized via thermal copolymerization of urea and tris(p-fluorophenyl)phosphine (TPP). FTIR and XPS spectra showed that the incorporation of TPP did not destroy the framework of g-C₃N₄. DFT calculation displayed that the HOMO of TPP-modified g-C₃N₄ (TPP-CN) came mainly from p_z orbital of phosphorus. The change of the electronic property led to a narrowed bandgap, extended delocalization of π-electrons through benzene rings, and accelerated migration of photoexcited electrons via intramolecular charge transfer. The optimal Pt-loaded TPP-CN showed the highest rate of H₂ generation of 12.45 mmol h^?1 g^?1, 5 times of that of pure g-C₃N₄, and the apparent quantum efficiency of 24.9% at 420 nm. The degradation of p-chlorophenol over the optimal TPP-CN was 4 times of that of pure g-C₃N₄. The mechanism of photocatalytic p-chlorophenol degradation was proposed based on mass spectrometry analysis.     

Production,characterization of acetyl esterase from a rumen bacteria strain RB3, and application potential of the strain in biodegradation of crop residues

Acetyl esterase was produced by a bacterial strain RB₃ at a level of 0.59 U mL⁻¹. The strain was isolated from beef cattle rumen fluid under anaerobic condition, and was identified as Escherichia coli. The peak activity of the enzyme appeared after 48 h of culturing under anaerobic condition. The optimal pH of the enzyme activity was 8.0, and the optimal temperature was 40 °C. The K_m and V_max values on p-nitrophenyl acetate were 0.84 mM and 0.13 mmol p-nitrophenol liberated min⁻¹ mg of protein⁻¹ respectively. The enzyme activity could be promoted by Zn²⁺, Ni²⁺, Fe²⁺, and K⁺, and inhibited by Cu²⁺, Fe³⁺, Mn²⁺, Mg²⁺, Ca²⁺, and Co²⁺. Biodegradation of rice stalk and maize stover by the strain RB3 and Pleurotus ostreatus was compared. The strain showed higher degradation rate for hemicellulose in the crop residues, while P. ostreatus showed higher degradation rate for cellulose. This indicated the potential industrial application of the strain RB3, particularly in utilizing renewable lignocellulose containing acetyl xylan for fermentation of products.     

Photocatalytic performance of particulate semiconductors under natural sunshine—Oxidation of carboxylic acids

With natural sunlight, particulate TiO₂ (anatase), CuO, ZnO, Pb₂O₃, PbO₂ and Bi₂O₃ photomineralize oxalic acid and the mineralization depends linearly on the acid concentration and the surface area of the catalyst bed. Oxygen is essential for mineralization and the metal oxides show sustainable photocatalysis. While oxalic acid is effectively mineralized, the oxalate ion is not so. Pre-sonication fails to enhance the photocatalytic efficiencies and the system does not respond to application of a potential bias for enhancement of photocatalysis. The photocatalytic performance is of the order ZnO>CuOTiO₂Bi₂O₃Pb₂O₃>PbO₂ and the ease of degradation is formic acid>oxalic acid>acetic acid>citric acid.     

Electrocatalytic oxidation of methanol on mono and bimetallic composite films: Pt and Pt–M (M = Ru,Ir and Sn) nano-particles in poly(o-aminophenol)

Mono and bimetallic composite catalysts have been formed by a three-step process, whereby the surface of aluminum electrode was pretreated upon immersion into a Pd(NH₃)₄Cl₂ solution (p-Al), was subsequently coated with a thin poly(o-aminophenol) (PoAP) layer by potentiodynamic electropolymerization of o-aminophenol and Pt and Pt alloys nano-particles were finally dispersed into the PoAP film by electrochemical methods. The electrocatalytic properties of the platinum doped (Pt/PoAP/p-Al) and Pt alloys doped (Pt–M/PoAP/p-Al, M = Ru, Ir and Sn) electrodes towards the methanol oxidation were investigated by cyclic voltammetry and compared with the electrocatalytic properties of pristine Pt and Pt particles on pretreated Al (Pt/p-Al) electrodes. The enhancement of the electrocatalytic activity of the Pt nano-particles, when Ru, Ir and Sn, are co-deposited in the polymer is also studied in detail. The effects of various parameters on the electrooxidation of methanol as well as the long-term stability of doped electrodes have also been investigated.     

Electrochemically assisted photocatalysis using nanocrystalline semiconductor thin films

The principle and usefulness of electrochemically assisted photocatalysis has been illustrated with the examples of 4-chlorophenol and Acid Orange 7 degradation in aqueous solutions. Thin nanocrystalline semiconductor films coated on a conducting glass surface when employed as a photoelectrode in an electrochemical cell are effective for degradation of organic contaminants. The degradation rate can be greatly improved even in the absence of oxygen by applying an anodic bias to the TiO₂ film electrodes. A ten-fold enhancement in the degradation rate was observed when TiO₂ particles were coupled with SnO₂ nanocrystallites at an applied bias potential of 0.83 V versus SCE.     

Enhanced remediation of simulated wastewaters contaminated with 2-chlorophenol and other aquatic pollutants by TiO2-photoassisted ozonation in a sunlight-driven pilot-plant scale photoreactor

Solar photoassisted remediation of a simulated wastewater contaminated with 2-chlorophenol (2-CP) was carried out by various advanced oxidation processes in a pilot-plant-scale Pyrex glass tubular-type photoreactor using solar cell derived electricity to drive the whole setup. The UV-assisted degradation and mineralization (loss of total organic carbon, TOC) of 2-CP in the co-presence of TiO₂ and ozone (UV/TiO₂/O₃) was enhanced significantly compared with ozonation alone (UV/O₃) and conventional TiO₂ photocatalysis in oxygenated dispersions (UV/TiO₂/O₂). The mineralization process was monitored by TOC assays and chloride ion analyzes. The utilization of immobilized TiO₂ was also examined with a TiO₂-coated glass photoreactor and compared with dispersed TiO₂ in aqueous media. In addition, simulated wastewaters contaminated with the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D), the endocrine disruptor bisphenol-A (BPA), the anionic surfactants sodium dodecylbenzenesulfonate (DBS) and sodium butylnaphthalenesulfonate (BNS), together with the cationic benzyldodecyldimethyl- ammonium bromide (BDDAB) surfactant were also efficiently remediated under otherwise identical conditions. The TiO₂-photoassisted ozonation of organic wastewater contaminants is a promising synergistic methodology to accelerate the remediation of such wastewaters, even when the TiO₂ is immobilized which can lead to reduced costs of operation.     

Microbial coupled photocatalytic fuel cell with a double Z-scheme g-C3N4/ZnO/Bi4O5Br2 cathode for the degradation of different organic pollutants

A novel heterostructure of g-C₃N₄/ZnO/Bi₄O₅Br₂ (ZB-3) was designed, and used in the microbial coupled photocatalytic fuel cell (MPFC). It can effectively improve electron utilization efficiency and pollutant degradation using this double Z-scheme heterojunction structure. The current–time (I–t) curves demonstrated that the current density of ZB-3 was higher than that of ZnO, ZnO/Bi₄O₅Br₂ (ZB-1), g-C₃N₄/ZnO (ZB-2). Electrochemical impedance spectroscopy (EIS) indicated ZB-3 possessed the minimum charge-transfer resistance. This MPFC for degrading rhodamine B (RhB) and tetracycline (TC) under different conditions were developed using these materials. Even in the dark condition, MPFC with g-C₃N₄/ZnO/Bi₄O₅Br₂ demonstrated 93% and 82% degradation efficiency for RhB and TC, respectively. Furthermore, the electron transport mechanism of the MPFC and ZB-3 were proposed. It paves the approach for more efficient pollutant degradation via MFC photocatalysis.     

Pumice stone supported titanium dioxide for removal of pathogen in drinking water and recalcitrant in wastewater

Bactericidal and organic degradation effects of TiO₂ on pumice stone are described in this paper. Immobilization of TiO₂ on pumice stone is easy and efficient method to obtain photocatalytic reactions without the problem of filtration. Pumice stone is soft and available as pellets that can be used in pellets fixed (with cement or poly carbonate) on a slanting plank/glass by coating the preformed TiO₂ over the pellets using simple paint brush for applying the photo catalyst. The treatment of inactivation of bacteria especially E. coli existing in real river waters and also different model organic substrate degradations like acid orange-7, resorcinol, 4, 6-dinitro-o-cresol, 4-nitrotoluene-2-sulfonicacid, isoproturan are studied. Furthermore, TiO₂ over pumice stone loaded in a multi tube reactor gave similar results for the disinfection and detoxification studies.     

Monoclinic zirconia-supported Fe3O4 for the two-step water-splitting thermochemical cycle at high thermal reduction temperatures of 1400–1600 °C

Two-step thermochemical water-splitting using monoclinic ZrO₂-supported Fe₃O₄ (Fe₃O₄/m-ZrO₂) for hydrogen production was examined at high thermal reduction temperatures of 1400–1600 °C. After thermal reduction of Fe₃O₄/m-ZrO₂, the reduced sample was quenched in liquid nitrogen, and was subsequently subjected to the water-decomposition step at 1000 °C. Quenching of the solid sample was conducted for analysis of the chemical reactions, such as phase transitions, occurring at high-temperature. The hydrogen productivity of Fe₃O₄ on a m-ZrO₂ support and the conversion of Fe₃O₄ to FeO were significantly enhanced with higher thermal reduction temperatures. The Fe₃O₄-to-FeO conversion reached 60% when the Fe₃O₄/m-ZrO₂ was thermally reduced at 1600 °C. The phase transition of m-ZrO₂ support to tetragonal ZrO₂ (t-ZrO₂) did not occur during the thermal reduction at 1400–1500 °C, but it did proceed slightly at 1600 °C. Fe ions from Fe₃O₄ did not enter the ZrO₂ lattice during high-temperature thermal reduction. Thus, the Fe₃O₄ loaded on a m-ZrO₂ support can continuously contribute as a Fe₃O₄–FeO redox reactant for thermochemical water-splitting at high-temperatures of 1400–1600 °C.     

Nanostructured Ni-containing spinel oxides for the dry reforming of methane: Effect of the presence of cobalt and nickel on the deactivation behaviour of catalysts

Nanostructured Ni-containing spinel oxide catalysts were obtained using a nanocasting method. Analyses by XRD, TEM, TPD-CO₂ and TPR showed that Ni^o and/or Co^o entities with high accessibility to CH₄ and CO₂ were responsible for high catalytic performance in the dry reforming of methane. The NiCo (Co^o and Ni^o dispersed on NiAl₂O₄) and NiAl (Ni^o dispersed on NiAl₂O₄) species were highly active for CH₄ conversion, whereas Ni^o dispersed on either Fe₃O₄–Co₃O₄ or CeO₂–NiAl₂O₄ provided a lower catalytic performance due to active phase degradation. The higher activity exhibited by NiAl compared to NiCo was related to the higher activity of nickel for CO₂ decomposition, while its remarkable stability seemed to be due to the presence of well dispersed nanoparticles involved in long-term conversion because they produced non-deactivating carbon deposits, as suggested by Raman analyses.     

Aromatic amines as proton carriers for catalytic enhancement of hydrogen evolution reaction on copper in acid solutions

The catalytic effect of some aromatic amines towards hydrogen evolution reaction on copper in diluted sulfuric acid solution has been studied. Since amines facilitate the transport of protons from the solution bulk to the interface in the cathodic hydrogen evolution reaction, they are known as proton carriers. The catalytic effect of aniline, N-methylaniline, N-ethylaniline, N,N-dimethylaniline, N,N-diethylaniline, o-toluidine, m-toluidine and p-toluidine has been highlighted by linear sweep voltammetry. The kinetic parameters for the hydrogen evolution reaction (cathodic transfer coefficient 1-α and exchange current density i_o) in the presence of the studied aromatic amines were derived from the Tafel plots. It has been found that the catalytic effect of amines is active even at low concentration. Thus, in 0.5 mol L⁻¹ H₂SO₄ solution the exchange current density increases by two orders of magnitude, from 2.01⋅10⁻⁵ A m⁻² in the absence of aniline to 2.85⋅10⁻³ A m⁻² in the presence of 10⁻⁴ mol L⁻¹ aniline. The influence of amines concentration on the catalytic effect is described in detail for the case of m-toluidine. The results obtained by voltammetry have been compared with electrochemical impedance spectroscopy data. Furthermore, the kinetic parameters for the hydrogen evolution reaction have been determined as a function of temperature and amines concentration.     

On the reactivity of methylbenzenes

Alkylated aromatic hydrocarbons, including the methylbenzenes, are a major and growing component of liquid transportation fuels. Reactivity (or lack thereof) for the methylbenzenes in combustion systems, measured by octane rating, ignition delay, and laminar flame speed, varies widely with the number and position of methyl substituents. At present this behaviour is not fully understood. This study demonstrates how the low temperature and ignition reactivity of methylbenzenes is controlled by the presence of isolated methyl groups and adjacent methyl pairs (the ortho effect); this allows for the development of octane number correlations. Introduction of an isolated methyl group, adjacent only to CH ring sites, consistently increases the research octane number (RON) by around 26. This phenomenon is explained by the formation of relatively unreactive benzyl free radicals. When an adjacent pair of methyl substituents is present the RON consistently decreases by between 8 and 26, compared to the case when these methyl groups are isolated from each other (this effect generally diminishes with increasing degree of substitution). Research octane numbers for all aromatics with zero to three methyl substituents are accurately described by the empirical relationship RON = 98 + 24.2n_m − 25.8n_p, where n_m is the total number of methyl groups and n_p is the number of contiguous adjacent methyl pairs. The ortho effect is attributed to the unique oxidation chemistry of o-methylbenzyl, o-methylbenzoxyl, and o-methylphenyl type radicals here we provide a preliminary exploration of this chemistry and highlight areas requiring further research. It is shown that the o-methylbenzyl radical can react with two oxygen molecules to form 1,2-diformylbenzene + 2OH + H, a highly chain-branching process. This chemistry is expected to largely explain the two-stage ignition and negative temperature coefficient (NTC) behavior witnessed for polymethylbenzenes with adjacent methyl pairs. Similar chain branching mechanisms exist in the oxidation of o-methylbenzoxyl radicals that also form during o-xylene ignition.     

Pressure dependence of burning rate of nitrophenolformaldehyde composite propellants

Polymers of o-, m-, and p-nitrophenols with formaldehyde were used as fuel binders in composite propellants based on NH₄ClO₄ and KClO₄ oxidizers. A study of the burning rate in nitrogen has revealed the occurrence of a breakpoint at about 3–5 atm in the burning rate-pressure curves of all six types of composite propellants that contained nitro-substituted phenolic resins as fuel binders.     

A rechargeable Zn- poly(aniline-co-m-aminophenol) battery

Based on the cyclic voltammograms and impedance spectra of poly(aniline-co-m-aminophenol) in the electrolyte solution containing ZnCl₂ and NH₄Cl, a solution consisting of 2.0 M ZnCl₂ and 3.0 M NH₄Cl with pH 4.70 was employed as an electrolyte solution of a Zn-poly(aniline-co-m-aminophenol) battery. The battery was charged and discharged between 0.75 and 1.45 V at different current densities. The average charge voltage is about 1.15 V and the average discharge voltage is about 1.05 V, slightly depending on the charge–discharge current density. The capacity and energy densities of poly(aniline-co-m-aminophenol) are 137.5 A h kg⁻¹ and 152.5 W h kg⁻¹ for discharge process, respectively, which are much better than those of polyaniline at the same solution. After the test of the charge–discharge at different current densities, the battery was successively charged and discharged for 120 cycles. At one-hundred and twentieth cycle, the coulombic efficiency is 100% and the energy density of poly(aniline-co-m-aminophenol) only decreases by 9.2%, compared with the first cycle of the successive charge–discharge processes.     

Synthesis of magnetic Ag3PO4/Ag/NiFe2O4 composites towards super photocatalysis and magnetic separation

The synthesis of Ag₃PO₄/Ag was performed through in-situ deposition and photo-reduction processes with magnetic NiFe₂O₄ nanofibers towards enhanced photocatalysis performance and stability. NiFe₂O₄ inhibit the photoreduction of Ag₃PO₄ into Ag and resulted in high stability. The photocatalytic activity of Ag₃PO₄/Ag/NiFe₂O₄ samples was studied by methylene blue degrading under visible light irradiation. The Ag₃PO₄/Ag/NiFe₂O₄ photocatalyst with NiFe₂O₄ loading of 3% revealed good photocatalytic performance, high stability and quick degradation after 5 cycles. Photoluminescence spectra and photocurrent tests demonstrated that the formation of hetero-junction facilitated the separation of photo-generated carriers. The trapping experiments confirmed that h⁺ and ?OH were active species during the degradation process.     

Thermochemical two-step water splitting cycles by monoclinic ZrO2-supported NiFe2O4 and Fe3O4 powders and ceramic foam devices

A thermochemical two-step water splitting cycle is examined for NiFe₂O₄ and Fe₃O₄ supported on monoclinic ZrO₂ (NiFe₂O₄/m-ZrO₂ and Fe₃O₄/m-ZrO₂) in order to produce hydrogen from water at a high-temperature. The evolution of oxygen and hydrogen by m-ZrO₂-supported ferrite powders was studied, and reproducible and stoichiometric oxygen/hydrogen productions were demonstrated through a repeatable two-step reaction. Subsequently, a ceramic foam device coated with NiFe₂O₄/m-ZrO₂ powder was made and examined as a water splitting device by the direct irradiation of concentrated Xe-light in order to simulate solar radiation. The reaction mechanism of the two-step water splitting cycle is associated with the redox transition of ferrite/wustite on the surface of m-ZrO₂. A hydrogen/oxygen ratio for these redox powder systems exhibited good reproducibility of approximately two throughout the repeated cycles. The foam device loaded NiFe₂O₄/m-ZrO₂ powder was also successful with respect to hydrogen production through 10 repeated cycles. A ferrite conversion of 24-76% was obtained over an irradiation period of 30 min.     

Dual influence of temperature and gas composition of selected helium-based binary gas mixtures on the thermal convection enhancement in Rayleigh–Bénard enclosures

This paper addresses the potential augmentation of natural convection heat transfer in Rayleigh–Bénard enclosures when filled with a certain type of binary gas mixture. To form the binary gas mixtures, helium (He) is the primary gas and the secondary gases are nitrogen (N₂), oxygen (O₂), carbon dioxide (CO₂) and methane (CH₄). Each of the thermo-physical properties participating in the binary gas mixtures viscosity η_m, thermal conductivity λ_m, density ρ_m, and heat capacity at constant pressure C_p,m depends on the molar gas composition, temperature and pressure. Results are presented in terms of the maximum allied heat transfer coefficient h_m,max/B at the optimal mole gas composition w_opt, in the w-domain [0, 1] for the entire range of laminar and turbulent conditions. In the conduction regime, He provides the best heat transfer regardless of temperature. In the convection regime at 300 K a He–CO₂ mixture usually provides the maximum heat transfer, whereas at 1000 K pure methane CH₄ is the optimum. In addition, a detailed thermo-fluidic structure of the thermal convection patterns in the Rayleigh–Bénard enclosure was analyzed by performing 2-D numerical simulations.