Silver modified porous silica from rice husk and its catalytic potential

Rice husk silica modified with Ag (RH-Ag) and its calcined form, RH-Ag(C) are heterogeneous catalysts prepared from rice husk. The sodium silicate was extracted from rice husk using a simple solvent extraction technique. Silver was added during the precipitation of the gel to form RH-Ag. Calcination of RH-Ag yielded RH-Ag(C). RH-Ag and RH-Ag(C) was found to have a well defined amorphous phase and a crystalline phase. TEM analysis showed that silver was encapsulated into the silica matrix. Well defined mesoporous channels were found in RH-Ag(C). The EDX analysis showed that silver was indeed incorporated in the matrix of RH-Ag but it was not homogenously distributed. The specific surface area of RH-Ag and RH-Ag(C) was found to be 447 and 419 m² g⁻¹ respectively. The cation exchange capacity (CEC) for RH-Ag was found to be 0.470 mmol g⁻¹ which was higher than that of RH-Ag(C) with 0.273 mmol g⁻¹. Both the CEC and the BET values for RH-Ag(C) was consistent with the calcination process. Catalysis of benzyl alcohol using RH-Ag and RH-Ag(C) gave two products which were identified as benzaldehyde and dibenzyl ether. Percentage conversion was higher when the reaction was conducted with pure oxygen (14.0%) than in open air (0.60%). Overall, RH-Ag(C) was found to be a better catalyst for the formation of dibenzyl ether. The optimum weight and time of reaction for the oxidation was found to be 0.3 g and 3 h respectively for both catalysts. It was found that even in an inert atmosphere, 13% of benzaldehyde was obtained with RH-Ag(C) as catalyst. Mechanisms for the formation of benzaldehyde under oxygen and inert atmosphere and the condensation mechanism assisted by the presence of the Ag on the surface of the catalyst have been suggested.     

Chromium modified silica from rice husk as an oxidative catalyst

RH-Cr and RH-Cr500 were synthesized from rice husk by solvent extraction and gel precipitation technique. The specific surface area of RH-Cr and RH-Cr500 were found to be 0.542 and 1.20 m² g⁻¹ respectively. Energy dispersive X-ray (EDX) analysis showed that Cr(III) was homogenously incorporated in the matrix of both samples to a maximum of ca. 16% in RH-Cr500. Elemental analysis showed that RH-Cr contained ca. 15% carbon, while RH-Cr500 contained negligible amounts. FTIR analysis showed the extracted solid contained silanol (Si–OH) and siloxane (Si–O–Si) groups. Catalytic oxidation of cyclohexane with H₂O₂ using RH-Cr as the catalyst showed a 27.13% conversion to cyclohexanone and cyclohexanol with a selectivity of 57.37% and 42.63% respectively. However, RH-Cr500 showed only 14.01% conversion but with a selectivity of 64.83% of cyclohexanone and 35.17% of cyclohexanol. Epoxidation of cyclohexene using H₂O₂ with RH-Cr as the catalyst gave a conversion rate of 30.17% with a selectivity of 11.51% towards cyclohexene oxide, 63.21% 2-cyclohexen-1-one and 25.29% 2-cyclohexen-1-ol. The same reaction with RH-Cr500 as the catalyst showed 21.28% conversion with 14.65% cyclohexene oxide, 68.71% 2-cyclohexen-1-one and 16.64% 2-cyclohexen-1-ol. In the catalytic oxidation of cyclohexanol to cyclohexanone, RH-Cr showed a conversion of 12.25% while RH-Cr500 showed a conversion of 13.52%. No others products were detected in the conversion. Comparison with published catalytic systems showed that RH-Cr and RH-Cr500 to be a better catalyst even though the surface area of these catalysts were low.     

Synthesis of mesoporous silica templated by Pluronic F68 and its application in the immobilization of lipase

Mesoporous silica templated by Pluronic F68 was synthesized and characterized by TEM, N₂ adsorption–desorption isotherms and FT–IR spectra. The sample had a high specific surface area (761 m² g⁻¹) and the mean pore diameter was 4.7 nm, indicating that it can be used as porcine pancreatic lipase (PPL) support. The physical adsorption of PPL on this mesoporous material in phosphate buffer solution with different pH values has been studied. The maximum adsorbed amount was observed at pH 7.0 and amounted to 826 mg g⁻¹ and the maximum activity value of immobilized PPL was 227 μmol g⁻¹ min⁻¹. The optimal pH and temperature of the hydrolysis of triacetin for the immobilized PPL were at 8.0 and 45 °C, while they were at pH 7.0 and 35 °C for free PPL. The immobilized PPL showed excellent adaptability in higher pH and excellent heat resistance compared to free PPL. The retained activity of immobilized PPL was found to be ca. 50% of its original activity after the 5th reuse.     

Direct methanol fuel cells with reticulated vitreous carbon,uncompressed graphite felt and Ti mesh anodes

Reticulated vitreous carbon (RVC, 39 pores per cm), uncompressed graphite felt (UGF) and Ti mesh were investigated as 3-D anode catalyst supports for direct liquid methanol fuel cells with the aim of improving the catalyst mass specific activity. Mesoporous Pt–Ru layers composed of nano-particle agglomerates were electrodeposited on the 3-D substrates using a micellar deposition media composed of Triton X-100, isopropanol, and an aqueous phase containing H₂PtCl₆ and (NH₄)₂RuCl₆. The effect of deposition current density, support type, and counter electrode design on the catalyst layer morphology, mass loading and elemental composition is discussed. In direct methanol fuel cell experiments using 1 M CH₃OH—0.5 M H₂SO₄ the 3-D anodes with PtRu load between 2.8 g m⁻² (on Ti mesh) and 12.0 g m⁻² (on RVC) and Pt:Ru atomic ratio of about 4:1 provided peak power outputs based on catalyst mass of 50.4 W g⁻¹ and 40.5 W g⁻¹, respectively, at 333 K. The mass specific activity of the catalyst supported on the 3-D matrix is determined by the synergy between catalyst deposition procedure and support physico-chemical properties.     

Electrochemical preparation and properties of nanostructured Co3O4 as supercapacitor material

Nanostructured Co₃O₄ was prepared via a simple two-step process: cathodic electrodeposition of cobalt hydroxide from additive free nitrate bath and then heat treatment at 400 °C for 3 h. The prepared oxide product was characterized by powder X-ray diffraction, infrared spectroscopy, surface area measurement, scanning electron microscopy, and transmission electron microscopy. Morphological characterization showed that the oxide product was composed of porous nanoplates, and BET measurement displayed that the oxide plates have the average pore diameter and the surface area of 4.75 nm and 208.5 m² g⁻¹, respectively. The supercapacitive performance of the nanoplates was evaluated using cyclic voltammetry and charge–discharge tests. A specific capacitance as high as 393.6 F g⁻¹ at the constant current density of 1 A g⁻¹ and an excellent capacity retention (96.5% after 500 charge–discharge cycles) was obtained. These results indicate that Co₃O₄ nanoplates can be recognized as high-performance electrode materials.     

Preparation of mesoporous carbons using acid- and alkali-treated zeolite X as the template

Mesoporous carbons were synthesized by using acid- and alkali-treated zeolite X as the template through vapor-deposition polymerization (VDP). The samples were characterized by X-ray diffraction, nitrogen adsorption–desorption, scanning electron microscopy, transmission electron microscopy, and adsorption of methylene blue (MB). Zeolite X treated with alkali had increases of both the mesopore volume and the surface area, while that treated with acid only had a small increase of the surface area. The resulting carbons prepared at a VDP temperature of 130 °C for 2 h by using alkali- and acid-treated zeolite X as the template had surface areas of 936 and 764 m² g⁻¹, and mesopore volumes of 1.52 and 1.12 cm³ g⁻¹, respectively. Both of the surface areas and the mesopore volumes of the carbons decreased with the increase or prolongation of the VDP temperature. The carbons showed high equilibrium adsorption amounts of MB with the highest value of 360 mg g⁻¹.     

Effects of surface area on electrochemical performance of Li[Ni<Subscript>0.2</Subscript>Li<Subscript>0.2</Subscript>Mn<Subscript>0.6</Subscript>]O<Subscript>2</Subscript> cathode material

The effect of surface area on the electrochemical properties and thermal stability of Li[Ni_0.2Li_0.2Mn_0.6]O₂ powders was characterized using a charge/discharge cycler and DSC (Differential Scanning Calorimeter). The surface area of the samples was successfully controlled from ~4.0 to ~11.7 m² g⁻¹ by changing the molar ratio of the nitrate/acetate sources and adding an organic solvent such as acetic acid or glucose. The discharge capacity and rate capability was almost linearly increased with increase in surface area of the sample powder. A sample with a large surface area of 9.6–11.7 m² g⁻¹ delivered a high discharge capacity of ~250 mAh g⁻¹ at a 0.2 C rate and maintained 62–63% of its capacity at a 6 C rate versus a 0.2 C rate. According to the DSC analysis, heat generation by thermal reaction between the charged electrode and electrolyte was not critically dependent on the surface area. Instead, it was closely related to the type of organic solvent employed in the fabrication process of the powder.     

Preparation and electrochemical performance of SiCN–CNTs composite anode material for lithium ion batteries

The composite of silicon carbonitride (SiCN) and carbon nanotubes (CNTs) was synthesized by sintering the mixture of polysilylethylenediamine-derived amorphous SiCN and multi-walled CNTs at a temperature of 1,000 °C for 1 h in argon. The as-prepared SiCN–CNTs material, which was used as anode active substance in a lithium ion battery, showed excellent electrochemical performance. Charge–discharge tests showed the SiCN–CNTs anode provided a high initial specific discharge capacity of 1176.6 mA h g⁻¹ and a steady specific discharge capacity of 450–400 mA h g⁻¹ after 30 charge–discharge cycles at 0.2 mA cm⁻². Both of the abovementioned values are higher than that of pure polymer-derived SiCN, CNTs, and commercial graphite at the same charge–discharge condition. It was deduced that the CNTs in the composite not only improved the electronic conductivity and offered channels and sites for the immigrating and intercalating of Li⁺ but also stabilized the structure of the composite.     

Application of a Handheld Portable Mid-Infrared Sensor for Monitoring Oil Oxidative Stability

This study evaluated the capabilities of a handheld mid-infrared (MIR) spectrometer combined with multivariate analysis to characterize oils, monitor chemical processes occurring during oxidation, and to determine fatty acid composition. Vegetable oils (corn, peanut, sunflower, safflower, cottonseed, and canola) were stored at 65 °C for 30 days to accelerate oxidation reactions. Aliquots were drawn at 5 day intervals and analyzed by benchtop and portable handheld mid-infrared devices (4,000–700 cm⁻¹) and reference methods (IUPAC 2301 [1], 2302 [1]; AOCS Cd 8-58 [2]; and Shipe 1979 [3]). PLSR and soft independent modeling of class analogy (SIMCA) models were developed for oil classification and estimation of oil stability parameters. Models developed from MIR spectra obtained with a benchtop spectrometer equipped with a 3-bounce ATR device resulted in superior discriminative performances for classifying oils as compared to those obtained from handheld spectra (single-bounce ATR). Models developed from reference tests and handheld spectra showed prediction errors (SECV) of 1 meq/kg for peroxide value, 0.09% for acid value and 2% for determination of unsaturated fatty acids in different oils. Spectral regions ~3,012–2,850 cm⁻¹ (C–H stretching bands/shoulders of fatty acids), ~1,740 cm⁻¹ (C=O stretching of esters), and ~1,114 cm⁻¹ (–C–O stretching) were found to be important for prediction. Handheld-FTIR instruments combined with multivariate-analysis showed promise for determination of oil quality parameters. Portability and ease-of-use makes the handheld device a great alternative to traditional methods.     

Supported Pt and Pt–Ru catalysts prepared by potentiostatic electrodeposition for methanol electrooxidation

Methanol electrooxidation was investigated on Pt–Ru electrocatalysts supported on glassy carbon. The catalysts were prepared by electrodeposition from solutions containing chloroplatinic acid and ruthenium chloride. Bulk composition analysis of the Pt–Ru catalyst was performed using an X-ray detector for energy dispersive spectroscopy analysis (EDX). Three different compositions were analyzed in the range 0–20 at.% Ru content. Tafel plots for the oxidation of methanol in solutions containing 0.1–2 M CH₃OH, and in the temperature range 23–50 °C showed a reasonably well-defined linear region. The slope of the Tafel plots was found to depend on the ruthenium composition. The lower slope was determined for the Pt catalyst, varying between 100 and 120 mV dec⁻¹. The values calculated for the alloys were higher, ranging from 120 to 140 mV dec⁻¹. The reaction order for methanol varies from 0.5 to 0.8, increasing with the ruthenium content. The activation energy calculated from Arrhenius plots was found to change with the catalyst composition, showing a lower value around 30 kJ mol⁻¹ for the alloys, and a higher value, of 58.8 kJ mol⁻¹, for platinum. The effect of ruthenium content is explained by the bifunctional reaction mechanism.     

Pseudo-capacitance properties of porous metal oxide nanoplatelets derived from hydrotalcite-like compounds

Nanoplatelets of metal oxides with interesting porous structure were obtained by thermal treatment of Ni/Al hydrotalcite. Structural and surface properties of the porous oxides were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM and HRTEM), and N₂ adsorption–desorption. The electrochemical performance of the electrodes was investigated by cyclic voltammetry, electrochemical impedance spectroscopy and constant current charge–discharge measurements. Ni/Al hydrotalcite calcined at 450 °C (NA-450) displayed a maximum specific capacitance (419.0 F g⁻¹) due to the porous structure with the highest specific surface area (142.3 m² g⁻¹) and small pore size (4.4 nm). The present study shows the potential of NiO nanoplatelets composite material for electrochemical pseudo-capacitors.     

Potential of denitrification and nitrous oxide production from agricultural soil profiles (Seine Basin,France)

The denitrification process and the associated nitrous oxide (N₂O) production in soils have been poorly documented, especially in terms of soil profiles; most work on denitrification has concentrated on the upper layer (first 20 cm). The objectives of this study were to examine the origin of N₂O emission and the effects of in situ controlling factors on soil denitrification and N₂O production, also allowing the (N₂O production)/(NO₃ ⁻–N reduction) ratio to be determined through (1) the position on a slope reaching a river and (2) the depth (soil horizons: 10–30 and 90–110 cm). In 2009 and 2010, slurry batch experiments combined with molecular investigations of bacterial communities were conducted in a corn field and an adjacent riparian buffer strip. Denitrification rates, ranging from 0.30 μg NO₃ ⁻–N g⁻¹ dry soil h⁻¹ to 1.44 μg NO₃ ⁻–N g⁻¹ dry soil h⁻¹, showed no significant variation along the slope and depth. N₂O production assessed simultaneously differed considerably over the depth and ranged from 0.4 ng N₂O–N g⁻¹ dry soil h⁻¹ in subsoils (the 90–110-cm layer) to 155.1 ng N₂O–N g⁻¹ dry soil h⁻¹ in the topsoils (the 10–30-cm layer). In the topsoils, N₂O–N production accounted for 8.5–48.0% of the total denitrified NO₃ ⁻–N, but for less than 1% in the subsoils. Similarly, N₂O-consuming bacterial communities from the subsoils greatly differed from those of the topsoils, as revealed by their nosZ DGGE fingerprints. High N₂O-SPPR (nitrous oxide semi potential production rates) in comparison to NO₃-SPDR (nitrate semi potential reduction rates) for the topsoils indicated significant potential greenhouse N₂O gas production, whereas lower horizons could play a role in fully removing nitrate into inert atmospheric N₂. In terms of landscape management, these results call for caution in rehabilitating or constructing buffer zones for agricultural nitrate removal.     

Preparation and characterization of tubular porous ceramics from natural zeolite

Tubular porous ceramics with more than 40% open porosity and about 6 μm mean pore size were fabricated from natural zeolite powder with starch as pore-forming agent. The optimized processing parameter was 1100–1150 °C with a holding time of 1 h. Permeability of nitrogen and water flux of the tubular specimens was measured and discussed, and the obtained optimized values are 2480 m³m⁻² h⁻¹bar⁻¹ and 26 m³m⁻² h⁻¹ bar⁻¹, respectively.     

Vertical distribution of heavy metals in wastewater-irrigated vegetable garden soils of three West African cities

Application of untreated wastewater to irrigate urban vegetable gardens is raising serious concern about possible health risks associated with the consumption of these vegetables particularly with regard to the concentrations of heavy metals (HM) in their edible portions. The soil concentrations of cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb) and zinc (Zn), were investigated in seven vegetable gardens from the three West African cities of Kano (Nigeria), Bobo Dioulasso (Burkina Faso) and Sikasso (Mali). Also determined were input–output balances of Cd and Zn from five vegetable gardens under 30 years of wastewater irrigation in Kano. In these gardens Cd (2.3–4.8 mg kg⁻¹) and Zn (13–285 mg kg⁻¹) concentrations throughout the profile attained unsafe levels. The concentrations of Cu (0.8–18 mg kg⁻¹), Cr (1.8–72 mg kg⁻¹), Ni (0–17 mg kg⁻¹) and Pb (0.6–46 mg kg⁻¹) were below the safety thresholds for arable soils. Overall, concentrations of Zn, Cd, Pb and Ni were higher in Kano than in Bobo-Dioulasso and Sikasso. Input–output analyses in Kano indicated that irrigation wastewater contributed annually 400–3,700 g Cd ha⁻¹ and 7,200–22,300 g Zn ha⁻¹, fertilizer 30–2,100 g Cd ha⁻¹ 50–17,600 g Zn ha⁻¹, harmattan dust 0.02–0.4 g Cd ha⁻¹ and 40–200 g Zn ha⁻¹ while 300–500 g Cd ha⁻¹ and 2,700–4,700 g Zn ha⁻¹ came from rainwater inputs. Input–output calculations subtracting the amounts of HM taken out in vegetable biomass and that lost to leaching from total inputs yielded an annual net positive balance of 700–4,160 g Cd ha⁻¹ and 9,350–39,700 g Zn ha⁻¹. If such balances remain unchanged for another 10–20 years vegetables raised in these garden fields are likely to be unsuitable for human consumption.     

Enhanced electrochemical performance of FeS<Subscript>2</Subscript> synthesized by hydrothermal method for lithium ion batteries

Iron disulfide (FeS₂) powders were successfully synthesized by hydrothermal method. Cetyltrimethylammonium bromide (CTAB) had a great influence on the morphology, particle size, and electrochemical performance of the FeS₂ powders. The as-synthesized FeS₂ particles with CTAB had diameters of 2–4 μm and showed a sphere-like structure with sawtooth, while the counterpart prepared without CTAB exhibited irregular morphology with diameters in the range of 0.1–0.4 μm. As anode materials for Li-ion batteries, their electrochemical performances were investigated by galvanostatic charge–discharge test and electrochemical impedance spectrum. The FeS₂ powder synthesized with CTAB can sustain 459 and 413 mAh g⁻¹ at 89 and 445 mA g⁻¹ after 35 cycles, respectively, much higher than those prepared without CTAB (411 and 316 mAh g⁻¹). The enhanced rate capability and cycling stability were attributed to the less-hindered surface layer and better electrical contact from the sawtooth-like surface and micro-sized sphere morphology, which led to enhanced process kinetics.     

Synthesis and characterization of aerogel-like mesoporous nickel oxide for electrochemical supercapacitors

Highly porous NiO was prepared via a combination of sol-gel process with supercritical drying method in this paper. The as-synthesized NiO samples exhibit 80–90% porosity and high surface area, ie, 180.5–325.6 m²g⁻¹. Cyclic voltammetric and chronopotentiometric measurements indicated the aerogel-like NiO in 1 mol.L⁻¹ KOH solution to behave capacitive well due to its uniform mesoporous microstructure. It was also observed that post-heating temperature plays a critical role in the mesoporous nature of the aerogel-like materials. An optimal heating temperature of 300^∘C was found to favor the formation of mesopores, which account for the large specific capacitance of as high as 125 F.g⁻¹. The average specific capacitance of the aerogel-like NiO was observed to be about 75–125 F.g⁻¹ between a potential window of 0–0.35 V vs. SCE.     

Nanocrystalline NiO hollow spheres in conjunction with CMC for lithium-ion batteries

Hollow spherical NiO particles were prepared using the spray pyrolysis method with different concentrations of precursor. The electrochemical properties of the NiO electrodes, which contained a new type of binder, carboxymethyl cellulose (CMC), were examined for comparison with NiO electrodes with polyvinylidene fluoride (PVDF) binder. The electrochemical performance of NiO electrodes using CMC binder was significantly improved. For the cell made from 0.3 mol L⁻¹ precursor, the irreversible capacity loss between the first discharge and charge is about 43 and 24% for the electrode with PVDF and CMC binder, respectively. The cell with NiO–CMC electrode has a much higher discharge capacity of 547 mAh g⁻¹ compared to that of the cell with NiO–PVDF electrode, which is 157 mAh g⁻¹ beyond 40 cycles.     

Synthesis of high surface area γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> as an efficient catalyst support for dehydrogenation of n-dodecane

In this work mesoporous nanocrystalline γ-Al₂O₃ has been synthesized by a three step (hydrolysis, condensation and hydrothermal treatment) sol–gel procedure in nitric acid medium with cationic surfactant (hexadecyltrimethyl ammonium bromide) as template. The prepared sample was employed as a carrier for the n-dodecane dehydrogenation catalyst. The synthesized samples were characterized by X-ray diffraction (XRD), N₂ adsorption (BET), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric (TG) and temperature programmed reduction (TPR) techniques. The nitrogen adsorption analysis showed that the samples possessed mesoporous structure with high specific surface areas larger than 370 m² g⁻¹ and pore volumes larger than 1.5 cm³ g⁻¹. The prepared samples also showed a high thermal stability up to 750 °C which is important for carrier of heterogeneous catalysts. The results of catalyst testing in the dehydrogenation reaction of n-dodecane confirmed that the synthesized support has a good potential to function as a carrier for n-dodecane dehydrogenation catalysts.     

Nutrient recycling and physical indicators of an alley cropping system in a sandy loam soil in the pre-Amazon region of Brazil

The sustainable management of soils has proved a key challenge for the smallholder agriculture in southeastern Amazonia, Brazil. We assessed the capacity of an alley cropping system to sustain corn productivity. The experiment included six treatments: Clitoria + Pigeon Pea; Leucaena + Pigeon Pea; Acacia + Pigeon Pea; Clitoria + Leucaena; Leucaena + Acacia and Control treatment (no legumes). We determined chemical and physical indicators of soil quality. Leucaena had the highest macronutrient concentrations (40.17 g N kg⁻¹), except for P. All legumes had high Ca (13.82–17.84 g kg⁻¹) and very low P (0.51–2.83 g kg⁻¹) and Mg (1.73–2.92 g kg⁻¹) concentrations. Acacia had the lowest N, P, K and Mg concentrations. Pre-planting soil analysis indicated that soil quality indicators were below the critical levels needed for a productive agricultural system, especially for phosphorus, sum of bases and base saturation. Physical indicators of quality, such as bulk density (1.40–1.30 Mg m⁻³), total porosity (0.46–0.50 m m⁻³) and soil aeration capacity (0.10–0.17 m m⁻³), were substantially improved as a result of the surface application of residues. There was a cumulative effect of residue application on corn crop productivity. Because of its capacity to recycle nutrients and improve soil quality over the period of 3 years, alley cropping in association with no-tillage, can be an efficient strategy for maintaining productivity in the low-fertility soils of the humid tropics.     

Electrochemical determination of phloroglucinol using a carbon nanotube modified electrode enhanced by surfactant

A novel technique is utilized to detect trace amounts of phloroglucinol. In pH 5.0, 0.1 mol L⁻¹ HAc–NaAc buffer solution, phloroglucinol exhibited a stable and sensitive oxidation signal at a glassy carbon electrode modified with multi-wall carbon nanotube. By using the surfactant cetyl pyridinium chloride, the electrochemical response was greatly enhanced. The mechanism was systematically explored. In the range 9.0 × 10⁻⁷–3.0 × 10⁻⁴ mol L⁻¹, the oxidation peak currents of phloroglucinol have a linear relationship with concentration: the limit of detection was estimated to be 2.5 × 10⁻⁷ mol L⁻¹ (S/N = 3). The method was adopted to detect the content of phloroglucinol injection, and the recovery was from 97.5% to 103.0%.