Unique vapor phase synthesis of 1,2,3,5,6,7-hexahydrodicyclopenta[b,e]pyridine selectively over Co–Al-MCM-41

Cyclization of cyclopentanone, formaldehyde and ammonia in vapor phase gives 1,2,3,5,6,7-hexahydrodicyclopenta[b,e]pyridine (HHDCP) and spiro[cyclopentane-1,8′-(1′,2′,3′,5′,6′,7′,8′,8′a) octahydrodicyclopenta[b,e]]pyridine (SCOHDCP) over zeolites HY, HZSM-5, Hβ and mesoporous Al-MCM-41 molecular sieves. The preliminary screening of catalysts clearly shows that Al-MCM-41 is more suitable for the vapor phase synthesis of HHDCP. As the NH₃-TPD profiles of Al-MCM-41 show wide range distribution of acid sites in the temperature range of 200–600 °C (weak–medium–strong), Al-MCM-41 is further modified with transition metal ions like V(V), Mn(II), Fe(III), Co(III), Cu(II), La(III) and Ce(III) to fine tune the acid sites. Correlation of activity and selectivity of transition metal modified Al-MCM-41 with the NH₃-TPD profiles show that though the conversions are high, selectivity of either HHDCP or SCOHDCP is a preference of acid site strength formed on metal ion modification. Interestingly Co²⁺ ion modification of Al-MCM-41 resulted distinctly into two sets of acid sites with T_max around 218 °C (weak–medium) and 673 °C (strong). The reaction is studied on Co–Al-MCM-41 by adsorbing pyridine at 300 °C. The typical acidity available on pyridine adsorbed Co–Al-MCM-41 around 300 °C is showing cyclization activity forming only HHDCP indicating that weak–medium acid sites are responsible for the formation of HHDCP. Based on the product distribution plausible reaction mechanism is proposed.     

Adsorption of Cd(II) from aqueous solution onto pyrite

The physicochemical factors such as equilibrium time, solution pH, initial concentration of Cd(II), particle size and temperature that control the adsorption of Cd(II) from aqueous solutions onto pyrite has been investigated through batch experiments. Prior to this study, pyrite was characterized through chemical and XRD-analysis. The point of zero charge, pH_pzc was determined using the batch equilibrium technique and was found to be 6.4. The equilibrium time was 30 min at the solution pH of 6.0. The pH influence of Cd(II) adsorption was remarkable and maximum metal uptake was observed at 6.0 which is closer to pH_pzc. Under this weakly acidic condition Cd(II) ions are responsible for adsorption. Concentration dependence of metal uptake indicates that saturation of pyrite surface by adsorbate occurs at an initial Cd(II) concentration of 350 mg/L and the corresponding metal uptake was 576.5 mg/L of −150 mesh size pyrite at pH 6.0 and 30 °C. Particle size affects the adsorption capacity to a great extent and a decrease in particle diameter enhances metal uptake. The effect of temperature on adsorption performance reveals that the effective temperature for Cd(II) adsorption is 30 °C. The empirical Freundlich isotherm was applied to represent the adsorption process, which fits the experimental data quite well. The work reveals that natural pyrite is a very good choice as an adsorbent for the removal of toxic metals from industrial wastewater and bears significant industrial implications.     

Exploration of As(III)/As(V) Uptake from Aqueous Solution by Synthesized Calcium Sulfate Whisker

Although common calcium-containing minerals such as calcite and gypsum may fix arsenic, the interaction between modified calcic minerals and arsenic has seldom been reported. The uptake behavior of As(III)/As(V) from aqueous solutions by calcium sulfate whisker (CSW, dihydrate or anhydrite) synthesized through a cooling recrystallization method was explored. A series of batch experiments were conducted to examine the effect of pH, reaction time, whisker dosage, and initial As concentration. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the samples prepared. The results showed that pH of the aqueous solution was an important parameter for As(III)/As(V) uptake, and an excellent removal efficiency could be achieved under strongly alkaline condition. The data from batch experiments for reaction of As(V) with calcium sulfate dihydrate whisker (CSDW) and calcium sulfate anhydrous whisker (CSAW) were well described with extended Langmuir EXT1 model, from which theoretic maximum adsorption capacity of 46.57 mg As(V)·(g CSDW)^− 1 and 39.18 mg As(V)·(g CSAW)^− 1 were obtained. Some calcium arsenate solids products, such as CaAsO₃(OH) (weilite, syn), Ca₃(AsO₄)₂ (calcium arsenate), CaO–As₂O₅, Ca–As–O, Ca₅(AsO₄)₃OH·xH₂O (calcium arsenate hydroxide hydrate), and CaH(AsO₄)·2H₂O (hydrogen calcium arsenic oxide hydrate), were detected at pH = 12.5 through XRD analysis. This indicates that the interaction mechanism between As(V) and CSW is a complex adsorption process combined with surface dissolution and chemical precipitation.     

Rheological properties of concentrated aqueous fluorapatite suspensions

The Ca₃(PO₄)₂ and CaF₂ powders were mixed in a 3:1.5 ratio, calcined at 1000 °C and then milled in an aqueous media with the pH initially adjusted at 9. The resulting powder had a Ca/P atomic ratio of 1.67, which corresponded to the theoretical composition of fluorapatite (FA), Ca₁₀(PO₄)₆F₂. Its reactivity in an aqueous solution having two initial pH values with a concentration of ammonium polyacrylate (NH₄PA) was investigated as a function of time. The adsorption behaviour of NH₄PA and the influence of NH₄PA addition on the rheological properties of 40 vol.% FA slips were studied. In addition, the influence of the volume fraction of solids on the rheological behaviour of stabilized FA slips was determined. Finally, the effect of poly(vinyl)alcohol (PVA) addition on the relative viscosity of 38 vol.% FA suspensions stabilized with NH₄PA was investigated. The dissolution of FA was enhanced by decreasing the pH to an acidic value; the increase in pH above 7 markedly reduced the Ca²⁺/H⁺ exchange reaction rate. As a result, well-stabilized aqueous suspensions could be obtained at pH close to 9 in a wide range of solids loading. The minimum viscosity of 40 vol.% slips at pH 8.9 occurred at 0.6 wt% of NH₄PA was added. An important increase in the yield stress was observed for suspensions with a volume fraction of solids higher than about 46 vol.%. The addition of 0.5–1 wt% PVA to a well-stabilized FA slip caused aggregation of particles by a depletion flocculation mechanism, thereby increasing the slip viscosity.     

Synthesis and investigation of TiO2 nanotube arrays prepared by anodization and their photocatalytic activity

TiO₂ nanotube arrays were successfully prepared by anodic oxidation method in the electrolyte of ethylene glycol and deionized water mixed in 9:1 volumetric ration including 0.5 wt.% NH₄F. The microstructure and phase compositions of samples annealing from 0 °C to 800 °C were characterized by field-emission scanning electron microscope (FESEM) and X-ray diffraction (XRD). FESEM showed that the obtained nanotubes with diameter 80–100 nm and length 4.89 μm were highly ordered and perpendicular to Ti substrate. The tubular structure collapsed at 680 °C. The photocatalytic activity of samples annealing at different temperature were calculated by the degradation of a model dye, methyl orange (MO), under UV light illumination. The results indicated the phase composition and the morphology of TiO₂ nanotubes both played an important role in the degradation of MO. In addition, the effects of initial solution pH and dye concentration on degradation of MO had also been investigated. As a result, the optimum values of calcination temperature, initial solution pH and dye concentration were found to be 550 °C, 3, 10 mg/l, respectively. The best photodegradation of MO was 76% under illumination for 3 h.     

Biomass assisted microfiltration of chromium(VI) using Baker's yeast by ceramic membrane prepared from low cost raw materials

This work deals with the preparation of ceramic microfiltration membrane from inexpensive raw materials such as kaolin, quartz, calcium carbonate by uniaxial dry compaction method. The prepared green membrane was initially dried at 100 °C for 24 h, 200 °C for 24 h and finally sintered at 900 °C for 6 h. The properties of the membrane such as porosity, flexural strength, chemical stability and hydraulic permeability were investigated. The fabricated membrane possessed an average pore diameter of 1.32 μm, porosity of 30% and flexural strength of 34 MPa. Furthermore, the chemical stability of the membrane was found to be excellent. Eventually, the separation performance of the membrane in terms of flux and removal of chromium(VI) ion using baker's yeast biomass as a function of applied pressure, pH, metal ion concentration and biomass dosage was also studied. The removal of Cr(VI) was found to be strongly dependent on the initial pH of the solution. At lower pH, the metal solution shows higher removal due to higher binding of the metal ion with biomass. It was also observed that the removal of Cr(VI) ion increases with increasing the biomass concentration and decreases with increasing the metal ion concentration. The removal of Cr(VI) was found to be independent of the applied pressure. The maximum removal of Cr(VI) was found to be 94% with the permeate flux of 2.07 × 10^-5 (m³/m² s) for a metal solution concentration of 100 mg/L.     

The production of hypocrellin colorants by submerged cultivation of the medicinal fungus Shiraia bambusicola

Hypocrellin production using submerged cultivation of the medicinal fungus Shiraia bambusicola revealed that both glucose and (NH₄)₂SO₄ were optimal carbon and nitrogen sources. Hypocrellin production increased with increasing initial glucose concentration within the range of 10–50 g l^?1 and (NH₄)₂SO₄ concentration in the range of 1–2 g l^?1. The effects of carbon and nitrogen concentration were optimized using central composite experimental design and response surface analysis; maximum hypocrellin production (196.94 ± 6.93 mg l^?1) was achieved using 45.7 g l^?1 glucose and 1.93 g l^?1 (NH₄)₂SO₄.     

Biocatalytic resolution of Boc-dl-alanine methyl ester by a newly isolated Bacillus amyloliquefaciens WZZ002

A new esterase-producing strain (Bacillus amyloliquefaciens WZZ002) that exhibits high hydrolytic activity, excellent enantioselectivity, and high substrate tolerance on Boc-dl-Alanine methyl ester was isolated from soil samples. The reaction temperature, pH, and neutralizer optima of the cell-mediated biocatalysis were 35 °C, pH 8.0, and NH₃·H₂O, respectively. The optimal substrate concentration was 2 M, with a biocatalyst loading of 50 g/L. Results showed that the enantiomeric excess values of substrate and product were both greater than 99%. Thus, bioprocessing with the use of the isolated strain is a promising route for the commercial production of Boc-d-Ala-OMe.     

Mercury oxidation by hydrochloric acid over TiO2 supported metal oxide catalysts in coal combustion flue gas

Mercury oxidation by hydrochloric acid over the metal oxides supported by anatase type TiO₂ catalysts, 1 wt.% MO_x/TiO₂ where M = V, Cr, Mn, Fe, Ni, Cu, and Mo, was investigated by the Hg⁰ oxidation and the NO reduction measurements both in the presence and absence of NH₃. The catalysts were characterized by BET surface area measurement and Raman spectroscopy. The metal oxides added to the catalyst were observed to disperse well on the TiO₂ surface. For all catalysts studied, the Hg⁰ oxidation by hydrochloric acid was confirmed to proceed. The activity of the catalysts was found to follow the trend MoO₃ ~ V₂O₅ > Cr₂O₃ > Mn₂O₃ > Fe₂O₃ > CuO > NiO. The Hg⁰ oxidation activity of all catalysts was depressed considerably by adding NH₃ to the reactant stream. This suggests that the metal oxide catalysts undergo the inhibition effect by NH₃. The activity trend of the Hg⁰ oxidation in the presence of NH₃ was different from that observed in its absence. A good correlation was found between the NO reduction and the Hg⁰ oxidation activities in the NH₃ present condition. The catalyst having high NO reduction activity such as V₂O₅/TiO₂ showed high Hg⁰ oxidation activity. The result obtained in this study suggests that the oxidation of Hg⁰ proceeds through the reaction mechanism, in which HCl competes for the active catalyst sites against NH₃. NH₃ adsorption may predominate over the adsorption of HCl in the presence of NH₃.     

Visible light-driven mesoporous Au–TiO2/SiO2 photocatalysts for advanced oxidation process

Au–TiO₂/SiO₂ heterogeneous catalysts with different Au contents were successfully synthesized by a facile hydrothermal process and their photocatalytic activity towards reduction of Rose Bengal (RB), Methyl Blue (MB), Rhodamine B (RhB) and Congo Red (CR) was investigated in the presence of sodium borohydride (NaBH₄) for advanced oxidation process (AOP). The results reveal that 3 wt% Au loaded in TiO₂/SiO₂ can significantly degrade high RB concentration dye (>95%, 0.3 g/L, 12 pH) within 20 min of irradiation time. All catalysis reaction followed the pseudo-first order rate reaction with high correlation coefficient. The effect of loading of Au nanoparticles (1–5 wt%) along with variation in dye concentration (100–500 ppm), pH of solution (2–12), catalysts dosage (0.1–0.5 g/L), and reaction temperature (30–80 °C) were also studied. The present works shows the superior performance of Au–TiO₂/SiO₂ heterogeneous catalysts to be related to the high dispersion of Au nanoparticles in the TiO₂/SiO₂ and to the catalytic effect between gold and TiO₂.     

Sorption of heavy metal ions from aqueous solution by a novel cast PVA/TiO2 nanohybrid adsorbent functionalized with amine groups

Sorption of Cd(II), Ni(II) and U(VI) ions onto a novel cast PVA/TiO₂/APTES nanohybrid adsorbent with variations in adsorbent dose, pH, contact time, initial metal concentration and temperature has been investigated. The adsorbent were characterized by SEM and FTIR analysis. BET surface area, pore diameter and pore volume of adsorbent were 35.98 m² g⁻¹, 3.08 nm and 0.059 cm³ g⁻¹, respectively. The kinetic and equilibrium data were accurately described by the double-exponential and Freundlich models for all metals. The maximum sorption capacities were 49.0, 13.1 and 36.1 mg g⁻¹ for Cd(II), Ni(II) and U(VI) ions with pH of 5.5, 5 and 4.5, respectively. Thermodynamic studies showed that the sorption process was favored at higher temperature. The adsorbent can be easily regenerated after 5 cycles of sorption–desorption.     

Au anchored to (α-Fe2O3)-MCM-41-HS as a novel magnetic nanocatalyst for water-medium and solvent-free alkyne hydration

A novel catalytic system based on Au nanoparticle functionalized magnetic mesoporous silica was prepared as (α-Fe₂O₃)-MCM-41-HS-Au. This material was obtained through the reaction of ordered mesoporous silica-coated magnetic nanoparticles (α-Fe₂O₃)-MCM-41, (3-mercaptopropyl) trimethoxysilane (MPTMS) and HAuCl₄. This catalyst was extensively characterized by various techniques such as SEM, TEM, XRD, EDX, IR and N₂-sorption isotherm. Very uniform dispersion and ordered mesopores of (α-Fe₂O₃)-MCM-41-SH (about 2–3 nm) causes Au nanoparticles to be distributed very finely on the pore surfaces, resulting in a very useful and robust magnetically recyclable catalyst for water-medium and solvent-free alkyne hydration.     

Removal of metsulfuron methyl by Fenton reagent

The removal of metsulfuron methyl (MeS)—a sulfonyl urea herbicide from contaminated water was investigated by advanced oxidation process (AOP) using Fenton method. The optimum dose of Fenton reagent (Fe²⁺/H₂O₂) was 10 mg/L Fe²⁺ and 60 mg/L H₂O₂ for an initial MeS concentration ([MeS]₀) range of 0–80 mg/L. The Fenton process was effective under pH 3. The degradation efficiency of MeS decreased by more than 70% at pH > 3 (pH 4.5 and 7). The initial Fe²⁺ concentration ([Fe²⁺]₀) in the Fenton reagent affected the degradation efficiency, rate and kinetics. The degradation of MeS at optimum dose of Fenton reagent was more than 95% for [MeS] ₀ of 0–40 mg/L and the degradation time was less than 30 min. The determination of residual MeS concentration after Fenton oxidation by UV spectrophotometry was affected by the interferences from Fenton reagent. The estimation of residual MeS concentration after Fenton oxidation by high pressure/performance liquid chromatograph (HPLC) was interference free and represented the actual concentration of MeS and does not include the by-products of Fenton oxidation. The degradation kinetics of MeS was modelled by second order reactions involving 8 rate constants. The two reaction constants directly involving MeS were fitted using the experimental data and the remaining constants were selected from previously reported values. The model fit for MeS and the subsequent prediction of H₂O₂ were found to be within experimental error tolerances.     

Ammonia removal by air stripping in a semi-batch jet loop reactor

Ammonia is very toxic chemical and it can be removed by air stripping at high pH. JLRs have found applications in wastewater treatment processes due to their high mass transfer rates. In JLRs, intrinsic high turbulence result in a very large air-liquid surface area for greater mass transfer. Therefore, in this study, ammonia removal by air stripping from synthetically prepared ammonia solution at the high pH in a semi-batch JLR due to its high mass transfer capabilities have been investigated. Investigated parameters in a JLR were initial ammonia concentration (10–500 mg/L), temperature (20–50 °C), air flow rate (5–50 L/min) and liquid circulation rate (35–50 L/min). While it was demonstrated that temperature and air flow rate have a significant effect on the ammonia removal, it was determined that initial ammonia concentration and liquid circulation rate have no significant effect on the ammonia removal. The overall volumetric mass transfer coefficients (K_La) have been calculated from obtained model and it was determined that increasing temperature and air flow rate have a very significant effect on K_La. It was concluded that JLR provides higher mass transfer capabilities than other type of reactors even if less air is given.     

Artificial neural network optimization for removal of hazardous dye Eosin Y from aqueous solution using Co2O3-NP-AC: Isotherm and kinetics study

The present research is focused on the synthesis and characterization of cobalt (III) oxide (Co₂O₃) nanoparticle loaded on activated carbon to prepare an outstanding sorbent for the removal of eosin Y (EY) as hazardous dye from aqueous solution. The sorbent was identified by SEM and XRD analysis. The effect of solution pH, adsorbent dosage (0.005–0.02 g), contact time (0.5–30 min) and initial eosin Y concentration (30–80 mg L⁻¹) on the adsorption process was investigated and modeled by artificial neural network. Following optimization of variables, the experimental equilibrium data was analysis by Langmuir, Freundlich, Tempkin and D–R isothermal models and explored that the data well presented by Langmuir model with a maximum adsorption capacity of 555.56 mg g⁻¹ at 25 °C. Kinetic studies at various adsorbent dosage and initial EY concentrations show that high removal percentage (>90%) was achieved within 15 min of the start of every experiment at most conditions. The adsorption of EY follows the pseudo-second-order rate equation in addition to intraparticle diffusion model. The experimental data were applied to train the multilayer feed forward neural network with three inputs and one output with different algorithms and different numbers of neurons in the hidden layer. The minimum mean squared error (MSE) of 1.49e − 04 and determination coefficient of (R²) 0.9991.     

Assembly of an imidazole templated indium-oxalate porous 3D framework with tcj/hc topology: Synthesis,structure and sorption property

A 3D In(III) metal organic framework {[(CH₃)₂NH₂][In₂(Ox)_3.5(Im)]∙H₂O∙DMF}_n (1) (Ox = oxalic acid, Im = imidazole) which is templated by imidazole molecules has been synthesized solvothermally. Compound 1, is an anionic framework with 1D open channels which are filled with (CH₃)₂NH₂⁺, DMF and water molecules. The network exhibits a 3,4-c binodal net with a rare tcj/hc topology. The total solvent accessible volume in the crystal is 43.2%. Sorption studies show that it can adsorb a maximum amount of 47 cm³ g^− 1 of CO₂ gas at 195 K while the uptake of N₂ and CH₄ is negligible.     

Sunlight photodecolorization of a mixture of Methyl Orange and Bromocresol Green by CuS incorporated in a clinoptilolite zeolite as a heterogeneous catalyst

Photocatalytic activity of CuS incorporated into an Iranian clinoptilolite (CuS-Cp) was studied for decolorization of a mixture of Methyl Orange and Bromocresol Green under sunlight irradiation. All samples were characterized by XRD, FTIR, DRS and TG/DTG techniques. The effect of some key experimental parameters such as: amount of the catalyst (0.05–5 g L^?1), initial concentration of dyes (5–30 mg L^?1), solution pH (1–11) and also dosage of H₂O₂ and KBrO₃ was studied on the decolorization extent. The extent of decolorization was estimated from the residual concentration by spectrophotometrically and it was confirmed by the reduction of chemical oxygen demand (COD).     

Dispersion of concentrated aqueous yttria-stabilized zirconia with ammonium polyacrylate

The dispersion of concentrated 0.53 μm yttria stabilized zirconia (YSZ) aqueous slip to achieve sintered compacts with high and uniform microstructure was investigated. 78 wt.% (37.5 vol%) and 83 wt.% (45.3 vol%) slips were prepared by dispersing the powder in water with ammonium polyacrylate (NH₄PA) at pH values in a range of 8–9.5. The influences of the amount of NH₄PA and pH on the rheological properties of 78 and 83 wt.% slips were studied. The minimum viscosities of 78 and 83 wt.% slips were obtained with the addition of 0.05–0.1 wt.% NH₄PA at pH 9. Increasing pH from 8 to 9.5 had no effect on the YSZ dispersion with NH₄PA. These dispersions yielded green densities of 63% of theoretical density (TD) and sintered to 98% TD at 1400 °C.     

COD and color removal from synthetic textile wastewater by ultrasound assisted electro-Fenton oxidation process

Combination of electro-Fenton (EF) oxidation process with sonication for both the degradation of C.I. Reactive Black 5 (RB 5) and removal of chemical oxygen demand (COD) from synthetic textile wastewater was investigated under different operating conditions. Optimal conditions were found as the initial pH of 3, DC current of 0.25 A, H₂O₂ dosage of 800 mg/L and electrode distance of 2.5 cm for both EF and ultrasound assisted electro-Fenton (sono-EF) processes. However, the combination of EF with sonication was negligibly improved in terms of COD and color removals, compared to EF process.     

In situ generation of hydrogen peroxide from reaction of O2 with hydroxylamine from hydroxylammonium salt in neutral aqueous or non-aqueous medium using reusable Pd/Al2O3 catalyst

In situ generation of H₂O₂ with high yield can be accomplished by reacting O₂ with NH₂OH from hydroxylammonium salt [NH₂OH · HCl or (NH₂OH)₂ · H₂SO₄] in a neutral aqueous medium using a reusable heterogeneous Pd (1.0 wt%)/Al₂O₃ catalyst, even at low temperature (10 °C), with the formation of harmless by-products (viz. N₂ and water). The presence of KCl or KBr in the medium has beneficial effect. The H₂O₂ generation is strongly influenced by the pH of medium, reaction period and temperature; best results are obtained at the optimum pH and reaction medium.