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 m²/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_SC) 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_REF) and commercial MnO₂

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 Mn₄O₄Ca 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 O₂/mol Mn) compared to tunnel structure OMS-2 (110 mmol O₂/mol Mn) and layered structure OL-1 (27 mmol O₂/mol Mn) in water oxidation tests with Ce⁴⁺. Oxygen evolution was also confirmed under photochemical conditions using Ru­(bpy)₃ ²⁺ 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⁺-birnessite that have cation vacancies in the MnO₂ sheets rather than completely filled Mn³⁺/Mn⁴⁺ 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-MnO₂) and cerium oxide (CeO₂) microspheres has been developed. By this technique, γ-MnO₂ materials with surface areas of 240, 98, and 87 m²/g and CeO₂ microspheres with a surface area of 1 m²/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 m²/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_500 °C > OMS-2_750 °C > OMS-2_400 °C. 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