Transition metals (Mn,Ni, Co) doping in TiO<Subscript>2</Subscript> nanoparticles and their effect on degradation of diethyl phthalate

Transition metal-doped TiO₂ nanoparticles are synthesized by sol–gel method. The as-prepared samples are characterized by various techniques to correlate structural and optical properties with chemical nature of dopants and their effect on photocatalytic degradation of diethyl phthalate esters. X-ray diffraction (XRD) reveals that all the samples are crystalline and exhibit anatase as a major phase. Chemical nature of dopants could not affect the formation of anatase and its volume fraction. The crystallite size of undoped and doped TiO₂ nanoparticles varies between 10 and 12 nm as confirmed by XRD and transmission electron microscope. The lowest optical band gap observed is 2.47 eV in Mn-doped TiO₂. Among all the samples, Ni-doped TiO₂ sample shows better photocatalytic activity and degradation of diethyl phthalate due to its lower crystallite size and higher surface area than those of Mn- and Co-doped TiO₂ samples.     

High-temperature heat capacity of Co3O4 spinel: thermally induced spin unpairing transition

A strong anomaly was found in the heat capacity of Co₃O₄ between 1000 K and the decomposition temperature. This anomaly is not related to the decomposition of Co₃O₄ to CoO. The measured entropy of transition, S=46±4 J mol^-1 K^-1 of Co₃O₄, supports the interpretation that this anomaly reflects a spin unpairing transition in octahedrally coordinated Co³⁺ cations. Experimental values of heat capacity, heat content and entropy of Co₃O₄ in the high temperature region are provided. The enthalpy of the spin unpairing transition is 53±4 kJ mol^-1 of Co₃O₄.     

Electrochemical studies of sulphides,I. The electrocatalytic activity of galena,pyrite and cobalt sulphide for oxygen reduction in relation to xanthate adsorption and flotation

The electrocatalytic activity of galena, pyrite and Co₃S₄ for oxygen reduction has been studied by potentiostatic methods. Open circuit potentials of the sulphide electrodes have also been measured as a function of pH in nitrogen, air and oxygen atmospheres and also in the presence of H₂O₂ and ethyl xanthate. The adsorption of xanthate on sulphides was followed by observing bubble attachment to the electrodes.The catalytic activity for oxygen (or H₂O₂) reduction (the cathodic currents), the electrode potentials and the xanthate adsorption as shown by bubble attachment within certain pH limits, all varied as $\text{Co}{}_3\text{S}{}_4\text{> pyrite (≈ PbS in H}{}_2\text{O}{}_2\text{) ? PbS}$ indicating considerable dependence of the redox processes in flotation on the d - electron character of the sulphides.In the absence of oxygen, xanthate is probably bonded to the water structure of the surface through hydrogen-bonding, thus keeping the surface hydrophilic. Such adsorption reduces the electrode potential and inhibits oxygen reduction.     

Preparation,characterization, and gas permeation properties of blend membranes of polysulfone and polyethylene glycol inclusive alumina nanoparticles

The effect of incorporation of alumina nanoparticles on the gas separation properties of the polysulfone–polyethylene glycol blend membranes containing 20% polyethylene glycol was examined. At first, a number of nanocomposite polysulfone–polyethylene glycol/alumina membranes were synthesized with alumina nanoparticles loaded into the polymer matrixes. The hybrid membranes were synthesized with six different alumina contents of 2.5, 5, 10, 15, 20, and 30 wt%. The polysulfone–polyethylene glycol and their hybrids inclusive alumina membranes were prepared via thermal phase-inversion method. The membranes were initially characterized using Fourier transform infrared spectroscopy, scanning electron microscope, and X-ray diffraction. Gas permeation properties of these membranes with different alumina contents were investigated for pure CO₂, CH₄, N₂, and O₂ gases. The results showed that not only these gases permeability but the CO₂/N₂, CO₂/CH₄, and O₂/N₂ ideal selectivity were improved with increasing alumina nanoparticle content of the membrane as well. Also the effect of feed pressure on the permeation properties of these membranes was investigated for pure CO₂ gas. Finally, the results from the synthesized membranes were compared with Robeson’s upper bound line.     

Coagulation performance and microstructural morphology of a novel magnetic composite coagulant for pre-treating landfill leachate

A novel magnetic composite coagulant, prepared from nano-Fe₃O₄ and poly-aluminum chloride, was introduced to pre-treat mature landfill leachate. The coagulation performance of the coagulant as well as its microstructural morphology was discussed. Coagulation experimental results revealed that the coagulation performance of the landfill leachate using the new coagulant was better than that using poly-aluminum chloride alone, with COD and color removals above 60 and 68%, respectively. Based on the analysis of three-dimensional excitation–emission matrix spectrum, the fluorescence signals of treated leachate are totally reduced by the magnetic composite coagulant. The components of dissolved organic matters in the wastewater are removed in different degrees. Fourier transform infrared spectra analysis shows that the magnetic composite coagulant, which is a multi-core polymer with hydroxyl ligands and nano-Fe₃O₄, has a complex valence and crystal structure. Besides, X-ray diffraction pattern analysis indicates that the chemical composition of the magnetic composite coagulant is not changed significantly, which has comprehensively combined the chemical characteristics of both nano-Fe₃O₄ and poly-aluminum chloride, whereas the specific surface area of the novel magnetic composite coagulant effectively increased by nano-Fe₃O₄ particles under the analysis of scanning electron microscope spectral. The specific surface area analysis indicates that the magnetic composite coagulant is interconnected by narrow cracks and holes and has a high specific surface area and developed pore structure, which is also similar to the typical porous-type materials. Therefore, the nano-Fe₃O₄ compounded with poly-aluminum chloride leads to a larger specific surface, smaller average pore diameter, and more pore volume of the novel coagulant.     

Synthesis of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>-loaded porous carbons developed from rice husk for removal of arsenate from aqueous solution

A simple one-step synthetic approach using rice husk has been developed to prepare magnetic Fe₃O₄-loaded porous carbons composite (MRH) for removal of arsenate (As(V)). The characteristics of adsorbent were evaluated by transmission electron microscope, scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, Brunauer–Emmett–Teller analysis, and thermogravimetric analysis. On account of the combined advantages of rice husk carbons and Fe₃O₄ nanoparticles, the synthesized MRH composites showed excellent adsorption efficiency for aqueous As(V). The removal of As(V) by the MRH was studied as a function of contact time, initial concentration of As(V), and media pH. The adsorption kinetics of As(V) exhibited a rapid sorption dynamics by a pseudo-second-order kinetic model, implying the mechanism of chemisorption. The adsorption data of As(V) were fitted well to the Langmuir isotherm model, and the maximum uptake amount (q _m ) was calculated as 4.33 mg g^?1. The successive regeneration and reuse studies showed that the MRH kept the sorption efficiencies over five cycles. The obtained results demonstrate that the MRH can be utilized as an efficient and low-cost adsorbent for removal of As(V) from aqueous solutions.     

Kinetics of oxytetracycline sorption on magnetite nanoparticles

Iron oxide nanoparticles (nano-Fe) have been widely used in environmental remediation, including that of emerging contaminants, such as antibiotics. Magnetite nanoparticles (nano-Fe₃O₄) have been reported to form on the outer surface of nano-Fe and have the potential to be a good sorbent for certain antibiotics. This study reports, for the first time, the kinetics and thermodynamics of adsorption of a common tetracycline group antibiotic, oxytetracycline (OTC), on nano-Fe₃O₄. Batch sorption kinetics were evaluated by varying initial OTC concentration (0.25–2 mM), nano-Fe₃O₄ concentration (2.5–20 g L^?1), pH (3.8–7.6), temperature (5, 15, 35 °C), and ionic strength (0.01–0.5 M KCl) to derive thermodynamic and kinetic constants. Results show that OTC sorption kinetics is rapid and increases with increasing temperature. The derived thermodynamic constants suggest a surface chemical-controlled reaction that proceeds via an associative mechanism. Results indicate the potential of developing a nano-magnetite-based remediation system for tetracycline group of antibiotics.     

Photocatalytic reduction of hexavalent chromium with commercial Fe/Ti oxide catalyst under UV and visible light irradiation

The photoreduction efficiency of toxic hexavalent chromium into non-toxic trivalent chromium was studied using local low-cost material and modern technology. The materials involved different iron–titanium oxide nanopowders synthesized via simple hydrothermal–hydrolysis process. X-ray diffraction and high-resolution transmission electron microscope were employed to study the structural properties of the as-prepared samples. The effects of molar ratio (Fe/Ti) and hydrothermal temperature on spectroscopic properties have been investigated using Fourier transform infrared FT-IR spectroscopy. The photocatalytic performance of hexavalent chromium was systematically studied at various conditions including initial concentration of Cr(VI), hydrothermal temperature and Fe/Ti ratios of mixed iron–titanium oxide powders. It has been found that the highest photoreduction efficiencies of Cr(VI) were 95.7 and 86.2% at initial concentrations 10 and 60 ppm of Cr(VI), respectively. The synthesized mixed Fe₂O₃–TiO₂ photocatalyst exhibited higher efficiency of about 88% under visible light irradiation. The as-prepared mixed oxide catalyst exhibited high photocatalytic conversion efficiency and recycling stability in comparison with different commercial catalysts.     

Study of photocatalytic degradation of environmentally harmful phthalate esters using Ni-doped TiO<Subscript>2</Subscript> nanoparticles

Undoped and Ni-doped TiO₂ nanoparticles are synthesized using sol–gel technique. The physical, structural, optical and thermal properties of the samples are investigated using X-ray powder diffraction, Fourier transform infrared spectroscopy, transmittance electron microscopy, UV–visible diffuse reflectance and thermogravimetric analysis. The photocatalytic activity of the samples is investigated by the photocatalytic degradation of phthalate esters. Phthalate esters have been considered as endocrine disrupting compounds. Ni-doped TiO₂ samples show better photocatalytic activity as compared to undoped TiO₂ sample. The greater photocatalytic activity of doped samples as compared to undoped TiO₂ can be attributed to the production of more number of electron–hole pairs in doped samples.     

Thermodynamics of Co3O4: a possible electron spin unpairing transition in Co3+

The free energy of the reaction: $$Co_3 O_4 \rightleftarrows 3C_O O + \tfrac{1}{2}O_2$$ has been studied between 890 and 1,240 K using an e.m.f. technique. There is a phase transition in Co₃O₄ at 1,120±20 K which is accompanied by a large change in entropy (～47 JK^?1 mol^?1 of Co₃O₄), and a rapid increase in unit cell volume and in electical conductivity. This is interpreted to be due to a partial change in electronic spin states in Co^{3 +} from the spin-paired (low spin) configuration observed at room temperature to the spin-unpaired (high spin) state. The transition is probably not first order.     

Enhancing dispersion of halloysite nanotubes via chemical modification

Uniform and dispersed halloysite nanotubes (HNTs) were obtained using sodium dodecyl sulfate (SDS) to disperse the halloysite suspension. The dispersed HNTs were characterized by X-ray diffraction, scanning electron microscope, energy-dispersive spectrometry, transmission electron microscope, Fourier transform infrared spectroscopy, thermogravimetry–differential scanning calorimetry and zeta potential. The results indicated that SDS was adsorbed and scattered on the HNTs, which could enhance the stability and dispersibility of suspension by the electrostatic effect. The zeta potential of dispersed HNTs became larger than that of the raw within the pH ranging from 2.5 to 11.9, which reached ?31 mV at pH around 8 when the concentration of SDS was 1.22 g/L. The diameter of dispersed HNTs ranged from 0.6 to 1.2 μm. A corresponding dispersive mechanism was investigated.     

Arsenic removal from aqueous solutions by mixed magnetite–maghemite nanoparticles

In this study, magnetite–maghemite nanoparticles were used to treat arsenic-contaminated water. X-ray photoelectron spectroscopy (XPS) studies showed the presence of arsenic on the surface of magnetite–maghemite nanoparticles. Theoretical multiplet analysis of the magnetite–maghemite mixture (Fe₃O₄-γFe₂O₃) reported 30.8% of maghemite and 69.2% of magnetite. The results show that redox reaction occurred on magnetite–maghemite mixture surface when arsenic was introduced. The study showed that, apart from pH, the removal of arsenic from contaminated water also depends on contact time and initial concentration of arsenic. Equilibrium was achieved in 3 h in the case of 2 mg/L of As(V) and As(III) concentrations at pH 6.5. The results further suggest that arsenic adsorption involved the formation of weak arsenic-iron oxide complexes at the magnetite–maghemite surface. In groundwater, arsenic adsorption capacity of magnetite–maghemite nanoparticles at room temperature, calculated from the Langmuir isotherm, was 80 μmol/g and Gibbs free energy (∆G⁰, kJ/mol) for arsenic removal was −35 kJ/mol, indicating the spontaneous nature of adsorption on magnetite–maghemite nanoparticles.     

Photocatalytic performance of TiO<Subscript>2</Subscript> and WO<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> nanoparticles coated on urban green infrastructure materials in removing nitrogen oxide

This study investigated the performance of UV light active TiO₂ and UV–visible light active WO₃/TiO₂ nanoparticles as air purifying materials that can be potentially applied to urban green infrastructures such as rain gardens and pervious pavements. Using a laboratory-scale continuous gas flow photoreactor, the removal efficiency of gaseous nitrogen oxide (NO _x ) by two different photocatalytic nanoparticles coated on natural zeolites and pervious concrete blocks was evaluated. The results showed that the TiO₂- and WO₃/TiO₂-coated zeolites are excellent photoactive materials providing enhanced air purification function (~95% removal efficiency of NO _x ) under UV and UV–visible light irradiation, respectively. In contrast, both of the TiO₂- and WO₃/TiO₂-coated pervious concrete blocks showed a measurable NO _x removal (~60%) only under UV irradiation, whereas the visible light activity of the WO₃/TiO₂-coated concrete block was significantly reduced (~20%) mainly due to the decrease in the photocatalytic reaction sites for visible light. This study revealed the potential utility of photocatalytic nanoparticles in improving urban air quality, in the form of the surface component of various urban infrastructures.     

内蒙古阿拉善地区绿色戈壁玛瑙的宝石学特征与致色成因研究

内蒙古阿拉善地区经历数亿年的地质活动,产出颜色丰富且结构致密的戈壁玛瑙。通过常规宝石学测试、偏光显微镜及扫描电镜观察、X射线粉晶衍射、电子探针、红外光谱及紫外-可见光-近红外分光光度计等测试分析方法对绿色戈壁玛瑙的宝石矿物学特征及致色成因进行了深入研究。肉眼观察,阿拉善绿色玛瑙呈深绿色至褐绿色,微透明至不透明,相对密度、折射率、摩氏硬度等均符合石英质玉石的特点。偏光显微镜观察,绿鳞石富集于表层,并向内部呈放射状生长;方解石与石英均为隐晶质结构。扫描电镜观察,绿鳞石呈颗粒状分布于石英及方解石之间。X射线衍射分析结果表明,绿色戈壁玛瑙的物相组成主要为石英、方解石和绿鳞石。电子探针分析结果表明绿鳞石的主要化学组成为SiO₂、FeO、Al₂O₃、K₂O和MgO。红外光谱分析也显示存在绿鳞石对应基团的特征峰。表层绿鳞石在紫外-可见光-近红外分光光度计下显示出Fe²⁺与Fe³⁺的特征光谱,Fe²⁺与Fe³⁺之间的电荷转移是其...     

Photocatalytic ozonation of 2, 4-dichlorophenoxyacetic acid in water with a new TiO2 fiber

More effective techniques are required to mineralize the increasing number of recalcitrant organic contaminants at low concentrations in the water environment using advanced oxidation process. Though relatively new, photocatalytic ozonation (O₃/UV/TiO₂) is considered superior to ozonation (O₃) and photocatalysis (UV/TiO₂), due to synergistic effects and use of immobilized TiO₂ photocatalysts is a milestone in advance oxidation process. This article aimed to elucidate 2, 4-dichlorophenoxyacetic acid (2, 4-D) mineralization characteristics in low aqueous solutions by O₃/UV/TiO₂ using the world’s first high-strength TiO₂ fiber catalyst in laboratory experiments. 2, 4-D degradation and TOC removal in O₃, UV/TiO₂ and O₃/UV/TiO₂ followed pseudo-first order reaction kinetic. The removal rates for 2, 4-D and TOC in O₃/UV/TiO₂ were respectively about 1.5 and 2.4-fold larger than the summation of the corresponding values in O₃ and UV/TiO₂. The O₃/UV/TiO₂ process was characterized by short-lived few aromatic intermediates, faster degradations of aliphatic intermediates and dechlorination as a major step in 2, 4-D mineralization. The significantly enhanced 2, 4-D mineralization in the process was attributed to increased ozone decomposition and reduced electron-hole recombination on TiO₂ surface resulting to a large number of OH generation. The O₃/UV/TiO₂ process with the TiO₂ fiber catalyst was very promising with respect to the major challenges being faced in AOP involving TiO₂, namely separation of powder catalyst in suspension and reduced efficiency of immobilized catalysts (e.g. TiO₂ film/fiber).     

Extraction of molybdenum from spent catalyst by salt-roasting

Spent hydro-refining catalysts mainly consists of 20–22% MoO₃, 5–6% NiO, 4–5% S, 1–2% Co₃O₄, 1.3–1.5% Fe₂O₃, 3–4% SiO₂, and the balance is Al₂O₃. In the present study, one such spent catalyst was roasted with sodium chloride to recover molybdenum by converting it into sodium molybdate. The sodium molybdate was further purified by chemical treatment to obtain a pure grade molybdenum trioxide. Various parameters like temperature, time and NaCl addition have been studied, and conditions for the maximum recovery of molybdenum have been established.     

碱处理对河北围场天然沸石结构和性能的影响及其机理研究

采用NaOH对围场地区天然沸石进行处理,采用X射线衍射仪、红外光谱仪、N2吸附-脱附技术、扫描电子显微镜等对材料进行表征分析,采用水蒸气吸附法评价材料的亲水性,采用Cr3+和Mn2+评价材料的离子交换性能,探讨了碱处理对天然沸石的结构、亲水性和离子交换性能的影响及其机理.实验结果表明,围场地区天然沸石中主要含有斜发沸石...     

Shock effects in MgAl2O4-spinel

Shock recovery experiments on synthetic MgAl₂O₄-spinel samples in the pressure range 25.5 to 50.5 GPa have been performed in order to examine the effects of shock waves on this material. The shocked samples were subsequently studied in the transmission electron microscope. All samples showed shock-induced dislocations with the Burgers vector 1/2 〈110〉 and twin lamellae of the twin-law {111}. In addition, samples, which had experienced the higher pressures, showed lamellar areas of a crystalline phase that we have not yet been able fully to characterize. It is probably not ε-MgAl₂O₄.     

Bioreduction of hematite nanoparticles by the dissimilatory iron reducing bacterium Shewanella oneidensis MR-1

We examined the reduction of different size hematite (α-Fe₂O₃) nanoparticles (average diameter of 11, 12, 30, 43, and 99 nm) by the dissimilatory iron reducing bacteria (DIRB), Shewanella oneidensis MR-1, to determine how S. oneidensis MR-1 may utilize these environmentally relevant solid-phase electron acceptors. The surface-area-normalized-bacterial Fe(III) reduction rate for the larger nanoparticles (99 nm) was one order of magnitude higher than the rate observed for the smallest nanoparticles (11 nm). The Fe(III) reduction rates for the 12, 30, and 43 nm nanoparticles fell between these two extremes. Whole-cell TEM images showed that the mode of Fe₂O₃ nanoparticle attachment to bacterial cells was different for the aggregated, pseudo-hexagonal/irregular and platey 11, 12, and 99 nm nanoparticles compared to the non-aggregated 30 and 43 nm rhombohedral nanoparticles. Due to differences in aggregation, the 11, 12, and 99 nm nanoparticles exhibited less cell contact and less cell coverage than did the 30 and 43 nm nanoparticles. We hypothesize that S. oneidensis MR-1 employs both indirect and direct mechanisms of electron transfer to Fe(III)-oxide nanoparticles and that the bioreduction mechanisms employed and Fe(III) reduction rates depend on the nanoparticles’ aggregation state, size, shape and exposed crystal faces.     

Comparison of different phases of bismuth silicate nanofibers for photodegradation of organic dyes

Two different phases of bismuth silicate nanofibers [Bi₂SiO₅ and Bi₄(SiO₄)₃] were synthesized using electrospinning technique. BS nanofibers were tested for the photocatalytic degradation of methyl orange and safranin O dyes. Different phases of BS affect the photodegradation efficiency of nanofibers. Impressive enhancement in photocatalytic efficiency and BET surface area of Bi₄(SiO₄)₃ was observed over Bi₂SiO₅. A speedy reduction in dyes concentration was attributed to the rapid formation of oxygenated radicals by the capture of electrons and holes, generated in the BS nanofiber by UV irradiation. Therefore, the photocatalytic mechanism was elucidated using impedance spectroscopy at room temperature. The lower impedance value of Bi₄(SiO₄)₃ nanofibers had improved high-efficiency charge transfer capability. The cycling efficiency (30 times) and recovery characteristics pointed out that Bi₄(SiO₄)₃ nanofibers photocatalysts had high constancy, resilience, and regeneration ability.