15 research outputs found
Fish Swim Bladder-Derived Porous Carbon for Defluoridation at Potable Water pH
This research article published by Scientific Research Publishing Inc., 2016The levels of fluoride in various ground water sources in East Africa are above the
World Health Organization upper limit of 1.5 mg/L. Research on diverse defluoridation technologies has proven that adsorption stands out as an affordable, efficient,
and facile technology. Fish swim bladder-derived porous carbon (FBPC) activated by
KOH and surface oxidized by nitric acid was successfully investigated as an adsorbent for defluoridation at portable water pH. The FBPC was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-raydiffraction (XRD) and energy dispersive spectroscopy (EDS). Batch methods were
used to study physiochemical parameters viz., initial fluoride concentration, temperature, adsorbate dosage, contact time and pH. Freundlich, Temkin, Langmuir and
Dubinin-Radushkevich isotherms were plotted and analyzed to understand the adsorption process. Bangham, Weber Morris, pseudo first and second-order models
were used to elucidate the kinetics of adsorption. Optimal conditions for fluoride
removal were found to be: pH of 6, FBPC adsorbent dose of 5.0 g/L and contact time
of 50 min. Flouride adsorption followed pseudo second-order kinetic model and
Langmuir isotherm best describes the adsorption process
Biogas-slurry derived mesoporous carbon for supercapacitor applications
This research article published by Elsevier Ltd., 2017This study reports on the transformation of biogas slurry into mesoporous carbon for supercapacitor electrodes. Pore structures have been modified by altering activation time, temperature and KOH/carbon mass ratio. The mesoporous carbons are successively developed as evidenced by type IV isotherms obtained in nitrogen sorption studies. BET, micropore and mesopore surface area of 515, 350, and 165 m2 g−1, respectively as well as a narrow pore width distribution of 3–4.5 nm are obtained. X-ray photoelectron results have confirmed the presence of functional groups of oxygen and nitrogen in the samples which facilitates the pseudocapacitance. The electrochemical measurements in 6 M KOH using a three electrode cell with Ag/AgCl as reference electrode and platinum as counter electrode has been performed. The materials activated at 700 °C, 3:1 KOH to carbon mass ratio, and for 120 min exhibit high specific capacitance of 289 F g−1 at a scan rate of 5 mV s−1. Shortening activation time to 30 and 60 min reduces specific capacitance to 163 and 182 F g−1, in that order. Additionally, at 3:1 KOH to carbon mass ratio and 60 min activation time, specific capacitances of 170 and 210 F g−1 at 600 and 800 °C, respectively are obtained. Moreover, specific capacitance increases with increasing the KOH to carbon mass ratio from 148 F g−1 for 1:1–163 F g−1 for 3:1 at 700 °C. Electrochemical impedance spectroscopy studies demonstrate that material has high conductivity. In addition; capacity retention of 96% after 20,000 cycles is shown at scan rate of 30 mV s−1. The study shows that high performance electrodes can be designed from biogas slurry derived porous carbon
Vapor-Phase Oxidation of Benzyl Alcohol Using Manganese Oxide Octahedral Molecular Sieves (OMS-2)
Vapor-phase selective oxidation of benzyl alcohol has been accomplished using cryptomelane-type manganese oxide octahedral molecular sieve (OMS-2) catalysts. A conversion of 92% and a selectivity to benzaldehyde of 99% were achieved using OMS-2. The role played by the oxidant in this system was probed by studying the reaction in the absence of oxidant. The natures of framework transformations occurring during the oxidation reaction were fully studied using temperature-programmed techniques, as well as in situ X-ray diffraction under different atmospheres
Experimental Investigation of Thermal Characteristics of Kiwira Coal Waste with Rice Husk Blends for Gasification
Eminent depletion of fossil fuels and environmental pollution are the key forces driving the implementation cofiring of fossil fuels and biomass. Cogasification as a technology is known to have advantages of low cost, high energy recovery, and environmental friendliness. The performance/efficiency of this energy recovery process substantially depends on thermal properties of the fuel. This paper presents experimental study of thermal behavior of Kiwira coal waste/rice husks blends. Compositions of 0, 20, 40, 60, 80, and 100% weight percentage rice husk were studied using thermogravimetric analyzer at the heating rate of 10 K/min to 1273 K. Specifically, degradation rate, conversion rate, and kinetic parameters have been studied. Thermal stability of coal waste was found to be higher than that of rice husks. In addition, thermal stability of coal waste/rice husk blend was found to decrease with an increase of rice husks. In contrast, both the degradation and devolatilization rates increased with the amount of rice husk. On the other hand, the activation energy dramatically reduced from 131 kJ/mol at 0% rice husks to 75 kJ/mol at 100% rice husks. The reduction of activation energy is advantageous as it can be used to design efficient performance and cost effective cogasification process
Measurement of Pozzolanic Activity Index of Scoria, Pumice, and Rice Husk Ash as Potential Supplementary Cementitious Materials for Portland Cement
Research Article published by HindawiThis work investigated the properties of scoria and pumice as supplementary cementitious materials (SCMs) for Portland cement
and compared to those of rice husk ash (RHA). X-ray fluorescence, X-ray diffraction, and pozzolanic activity index (PAI) tests
confirmed the suitability of these two materials as potential SCMs. Scoria and RHA samples achieved over 75% PAI at 7 days
whereas pumice did this after 28 days. Initial and final mean setting times observed for the composite cement blended with these
materials were 166 and 285 min, respectively. These setting times are longer than that of ordinary Portland cement but shorter
compared to that of common Portland pozzolana cement. The ultimate mean compressive strengths achieved at 28 days of curing
were 42.5, 44.8, and 43.0MPa for scoria, pumice, and RHA, respectively, signifying that these materials are good SCMs. Higher
fineness yielded higher ultimate mean strength. For instance, a scoria sample with a fineness of 575m2/kg achieved the strength of
52.2MPa after 28 days
Status of Biomass Derived Carbon Materials for Supercapacitor Application
Environmental concerns and energy security uncertainties associated with fossil fuels have driven the world to shift to renewable energy sources. However, most renewable energy sources with exception of hydropower are intermittent in nature and thus need storage systems. Amongst various storage systems, supercapacitors are the promising candidates for energy storage not only in renewable energies but also in hybrid vehicles and portable devices due to their high power density. Supercapacitor electrodes are almost invariably made of carbon derived from biomass. Several reviews had been focused on general carbon materials for supercapacitor electrode. This review is focused on understanding the extent to which different types of biomasses have been used as porous carbon materials for supercapacitor electrodes. It also details hydrothermal microwave assisted, ionothermal, and molten salts carbonization as techniques of synthesizing activated carbon from biomasses as well as their characteristics and their impacts on electrochemical performance
Direct Sonochemical Synthesis of Manganese Octahedral Molecular Sieve (OMS-2) Nanomaterials Using Cosolvent Systems, Their Characterization, and Catalytic Applications
A rapid, direct sonochemical method has successfully
been developed to synthesize cryptomelane-type manganese octahedral
molecular sieve (OMS-2) materials. Very high surface area of 288 ±
1 m<sup>2</sup>/g and small particle sizes in the range of 1–7
nm were produced under nonthermal conditions. No further processing
such as calcination was needed to obtain the pure cryptomelane phase.
A cosolvent system was utilized to reduce the reaction time and to
obtain higher surface areas. Reaction time was reduced by 50% using
water/acetone mixed phase solvent systems. The cryptomelane phase
was obtained with 5% acetone after 2 h of sonication at ambient temperature.
Reaction time, temperature, and acetone concentration were identified
as the most important parameters in the formation of the pure cryptomelane
phase. OMS materials synthesized using the above-mentioned method
were characterized by X-ray diffraction (XRD), nitrogen sorption,
scanning electron microscopy (SEM), transmission electron microscopy
(TEM), and Fourier transformation infrared spectroscopy (FTIR). OMS-2
materials synthesized using sonochemical methods (K-OMS-2<sub>SC</sub>) possess greater amounts of defects and hence show excellent catalytic
performances for oxidation of benzyl alcohol as compared to OMS-2
synthesized using reflux methods (K-OMS-2<sub>REF</sub>) and commercial
MnO<sub>2</sub>
Water Oxidation Catalysis using Amorphous Manganese Oxides, Octahedral Molecular Sieves (OMS-2), and Octahedral Layered (OL-1) Manganese Oxide Structures
Water oxidation is the bottleneck in artificial photosynthetic
systems that aim to split water into hydrogen and oxygen. However,
water oxidation occurs readily in plants, catalyzed by the Mn<sub>4</sub>O<sub>4</sub>Ca manganese cluster. In addition to this, manganese
minerals are ubiquitous in nature displaying layered and tunnel structures.
In this study, mixed valent porous amorphous manganese oxides (AMO),
along with cryptomelane type tunnel manganese oxides (OMS-2) and layered
birnessite (OL-1) have been used as water oxidation catalysts. Significantly
higher turnovers were obtained with AMO (290 mmol O<sub>2</sub>/mol
Mn) compared to tunnel structure OMS-2 (110 mmol O<sub>2</sub>/mol
Mn) and layered structure OL-1 (27 mmol O<sub>2</sub>/mol Mn) in water
oxidation tests with Ce<sup>4+</sup>. Oxygen evolution was also confirmed
under photochemical conditions using RuÂ(bpy)<sub>3</sub>
<sup>2+</sup> as a photosensitizer and persulfate as a sacrificial agent. The
differences in catalytic activity among these catalysts have been
probed using X-ray diffraction, transmission electron microscopy,
Raman and Fourier transform infrared (FTIR) spectroscopy, average
oxidation state, and compositional analyses. Comparison of AMO against
prominent manganese catalysts described in literature shows AMO provided
the highest turnover numbers. AMO catalyst was also reusable after
regeneration. O-18 labeling studies proved that water was the source
of dioxygen and IR proved the structural stability of AMO after reaction.
AMO is related to hexagonal birnessites such as layered biogenic manganese
oxides or H<sup>+</sup>-birnessite that have cation vacancies in the
MnO<sub>2</sub> sheets rather than completely filled Mn<sup>3+</sup>/Mn<sup>4+</sup> sheets, and this is influential in catalytic activity
Nonthermal Synthesis of Three-Dimensional Metal Oxide Structures under Continuous-Flow Conditions and Their Catalytic Applications
Continuous-flow synthesis of one-dimensional (1D) metal oxide nanostructures and/or their integration into hierarchical structures under nonthermal conditions is still a challenge. In this work, a nonthermal, continuous-flow approach for the preparation of γ-manganese oxide (γ-MnO<sub>2</sub>) and cerium oxide (CeO<sub>2</sub>) microspheres has been developed. By this technique, γ-MnO<sub>2</sub> materials with surface areas of 240, 98, and 87 m<sup>2</sup>/g and CeO<sub>2</sub> microspheres with a surface area of 1 m<sup>2</sup>/g have been fabricated successfully. Characterization of the materials was carried out using powder X-ray diffraction, infrared and inductively coupled plasma optical emission spectrometer (ICP/OES), nitrogen sorption, scanning electron microscopy, transmission electron microscopy, and thermogravimetric analysis. The synthesized materials showed good catalytic activity in the oxidation of α-methyl styrene
X‑ray Absorption Spectroscopic Study of a Highly Thermally Stable Manganese Oxide Octahedral Molecular Sieve (OMS-2) with High Oxygen Reduction Reaction Activity
The
development of catalysts with high thermal stability is receiving
considerable attention. Here, we report manganese oxide octahedral
molecular sieve (OMS-2) materials with remarkably high thermal stability,
synthesized by a simple one-pot synthesis in a neutral medium. The
high thermal stability was confirmed by the retention of the cryptomelane
phase at 750 °C in air. Mechanistic studies were performed by
X-ray absorption near-edge structure (XANES) spectroscopy and <i>ex situ</i> X-ray diffraction (XRD) to monitor the change in
oxidation state and the phase evolution during the thermal transformation.
These two techniques revealed the intermediate phases formed during
the nucleation and growth of highly crystalline cryptomelane manganese
oxide. Thermogravimetric analysis, Fourier transform infrared spectroscopy
(FTIR), time-dependent studies of field emission scanning electron
microscopy (FE-SEM), and high-resolution transmission electron microscopy
(HR-TEM) techniques confirm the formation of these intermediates.
The amorphous phase of manganese oxide with random nanocrystalline
orientation undergoes destructive reformation to form a mixture of
birnessite and hausmannite during its thermal transformation to pure
crystalline OMS-2. The material still has a relatively high surface
area (80 m<sup>2</sup>/g) even after calcination to 750 °C. The
surfactant was used as a capping agent to confine the growth of OMS-2
to form short nanorods. In the absence of the surfactant, the OMS-2
extends its growth in the <i>c</i> direction to form nanofibers.
The particle sizes of OMS-2 can be controlled by the temperatures
of calcination. The OMS-2 calcined at elevated temperatures (400–750
°C) shows high remarkable catalytic activity for oxygen reduction
reaction (ORR) in aqueous alkaline solution that outperformed the
activity of synthesized solvent-free OMS-2. The activity follows this
order: OMS-2<sub>500 °C</sub> > OMS-2<sub>750 °C</sub> > OMS-2<sub>400 °C</sub>. The developed method reported
here can be easily scaled up for synthesis of OMS-2 for use in high-temperature
(400–750 °C) industrial applications, e.g., oxidative
dehydrogenation of hydrocarbons and CO oxidation