Pair Distribution Function Analysis and Electrochemical Performance of Mesoporous Carbon Nanomaterials Synthesized Through KOH and ZnCl2 Activation

Mesoporous carbon has been synthesized by activating carbonized biogas slurry residues with ZnCl2 and KOH simultaneously. The carbon to activating agent mass ratios were kept at 1:4, while the ZnCl2 to KOH mass ratio varied from 4:0, 3:1, 2:2, 1:3, to 0:4. The highest BET specific surface area of 361 m2 g-1, micropore surface area of 231 m2 g‒1, mesopore surface area of 125 m2 g‒1, and total pore volume of 0.23 cm3 g‒1 which amounted to 78% mesopore content, were obtained for the sample with 3:1 ZnCl2 to KOH mass ratio. Scanning electron microscope (SEM) images were acquired to determine the surface morphology and energy dispersive X-ray (EDX) was used to determine surface composition of the samples. The short, medium, and long-range orders of the synthesized materials were studied using pair distribution function (PDF) analysis. PDF showed that in addition to the locally ordered carbon and silica phase components, samples activated using combined ZnCl2 and KOH also contained crystalline Zn2SiO4 phase with the willemite structure. Electrochemical studies in three-electrode cell system revealed maximum specific capacitance of 216 F g‒1 exhibited by sample with a ZnCl2: KOH mass ratio of 3:1 at a scan rate of 5 mV s‒1. Keywords: Mesoporous carbon; Pair distribution function, Specific capacitance, supercapacitor &nbsp

Impacts of Wood Fuel Uses on Forest Cover: The Case of Semiarid Areas in Northern Tanzania

Satellite images for the years 1987, 1997, 2002 and 2017, and questionnaire surveys were used to assess energy sources and demands as well as the impacts of wood fuel use to forest cover changes in Meru and Mwanga Districts. The major energy sources identified include cow dung cake, firewood, charcoal, liquefied petroleum gas and biogas. The total energy demands from these sources were 1400 (in Meru), 6289, 724 and 21 kg per day, respectively. The amount of biogas was not quantified since the reactors were constructed locally with no reading meter. Analysis from Landsat images showed variations in forest cover. The areas covered with forests in Meru were found to be 1510, 1723, 1612 and 1327 ha for 1987, 1997, 2002 and 2017, respectively. The changes observed in Mwanga District were 31705, 31988, 17939 and 30960 ha for 1987, 1997, 2002 and 2017, respectively. From the findings it was observed that, the ongoing use of wood fuel in semi-arid areas of Meru and Mwanga could deplete forests completely. The study concludes that charcoal and firewood consumptions are real threats to the long-term persistence of forests in Tanzania and proposes the use of renewable energy such as biogas for alleviating forest losses. Keywords: Biogas, energy sources, Satellite image

Highly porous biomass-based capacitive deionization electrodes for water defluoridation

This research article published by Springer Nature Switzerland AG., 2019The high concentration of fluoride (F−) in water sources is the main challenge in major fluoride belts. Though capacitive deionization (CDI) with porous carbon electrodes is the promising alternative in removing charged species from aqueous solution, little has been presented on the usefulness of CDI with biomass-based electrodes in removing F− from natural water existing together with other ions such as Ca2+ and Mg2+. This study investigated the feasibility of using biomass-based electrodes for natural water defluoridation application. Porous carbon was synthesized from jackfruit peels (JFAC) through potassium hydroxide (KOH) activation. Surface morphology, pore structure, and electrochemical properties of the JFAC were investigated. The textural properties of the synthesized carbon and electrochemical characteristics of the fabricated electrodes were found to be influenced by activation temperature. Brunauer-Emmett-Teller (BET) surface area, pore diameter, pore volume, and pore surface area increased with an increase in activation temperature and KOH to carbon ratio. It was further confirmed that as the applied voltage increased from 1.2 to 2 V, the amount of adsorbed anions increased without significantly affecting the pH of the water. At 2.0 V, the electrodes showed a maximum F− adsorption efficiency and electrosorption capacity of 62% and 0.13 mg/g respectively. The electrosorption capacity depends on the initial concentration of the ion in the feed water. It was further observed that natural organic substances contained in the natural water might inhibit JFAC electrode surface and decrease its adsorption efficiency. This study provides cost-effective CDI electrode material prepared from biomass for water defluoridation

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

Biomass-based carbon electrode materials for capacitive deionization: a review

This research article published by Springer Nature Switzerland AG., 2019Capacitive deionization (CDI) is a promising water purification technology which works by removing salt ions or charged species from aqueous solutions. Currently, most of the research on CDI focuses on the desalination of water with low or moderate salt concentration due to the low salt adsorption capacity of the electrodes. The electrosorption capacity of CDI relies on the structural and textural characteristics of the electrode materials. The cost of electrode materials, the complicated synthesis methods, and the environmental concerns arising from material synthesis steps hinder the development of large-scale CDI units. By considering the good electrical conductivity, high specific surface area (SSA), porous structure, availability, mass production, and cost, porous carbon derived from biomass materials may be a promising CDI electrode material. This review presents an update on carbon nanomaterials derived from various biomasses for CDI electrodes. It covers different synthesis methods and the electrosorption performance of each material and discusses the impact of the SSA and porous structure of the materials on desalination. This review shows that a variety of biomass materials can be used to synthesize cost-effective CDI electrode materials with different structures and good desalination performance. It also shows that diverse precursors and synthesis routes have significant influences on the properties and performance of the resulting carbon electrodes. Additionally, the performance of CDI does not depend only on BET surface area and pore structure but also on the applied voltage, initial concentration of the feed solution, and mass, as well as the capacitance of the electrodes

Fish bladder-based activated carbon/Co3O4/TiO2 composite electrodes for supercapacitors

This research article published by Elsevier B.V., 2019Cobalt oxide/titanium dioxide/activated carbon (Co3O4/TiO2/Ac) composite was synthesized using simple sol-gel method before annealing at 300 °C. Fish bladder derived porous carbon used for the composite was synthesized by pyrolysis followed by chemical activation. Both scanning electron microscopy (SEM) and X-ray diffraction displayed Co3O4 and TiO2 phases well embedded onto the carbon matrices. Cyclic voltammetry in 6 M KOH electrolyte demonstrated that the composite has an excellent specific capacity of 946 Fg-1 for Co3O4/TiO2/Ac as compared to Co3O4/Ac, TiO2/Ac, and Ac with specific capacitances of 845, 340, and 308 F g−1, respectively at 5 mVs−1. Impedance spectroscopy reveals that the composite has good capacitive behavior with a series resistance of 0.6 Ω. Besides, Co3O4/TiO2/Ac maintains 89.7% of the initial capacitance after 2000 cycles. This study shows that the synergistic effect of the metal oxides and the carbon in the composite can enhance capacitance for practical supercapacitor applications

Hydrogen sulfide and ammonia removal from biogas using water hyacinth-derived carbon nanomaterials

This research article was published in African Journal of Environmental Science and Technology, Volume 11, 2017.The presence of hydrogen sulfide (H2S) and ammonia (NH3) in biogas pose serious human health and environmental challenges. In this study, H2S and NH3 were successfully removed from biogas using water hyacinth-derived carbon (WHC) nanomaterials. Carbonization temperature, biogas flow rate, mass of the adsorbent and activating agent (KOH/water hyacinth (WH)) ratio were found to greatly influence the efficiency of the H2S and NH3 removal. The adsorption capacity of both H2S and NH3 was found to increase with the carbonization temperature as carbon materials prepared at 450, 550, and 650°C afforded removal efficiencies of 22, 30, and 51% for H2S and 42, 50, and 74% for NH3, respectively, after contact time of 2 h. Similarly, the KOH/WHC ratio showed huge impact on the adsorptive removal of the two species. WH materials carbonized at 650°C and activated at 700°C using 1:4, 1:2, and 1:1 KOH/WHC ratios showed removal efficiencies of 80, 84, and 93% for H2S and 100, 100, and 100% for NH3, correspondingly after 2 h contact time. The adsorption capacity of NH3 increased with the decrease in flow rate from 83 to 100% at flow rates of 0.11 and 0.024 m3 /h, respectively, while that of H2S increased from 22 to 93% with flow rate 0.11 and 0.024 m3 /h, respectively. The removal of H2S and NH3 increased with adsorbent mass loading. With the 0.05, 0.1, 0.2, and 0.3 g of the adsorbent, the adsorption of H2S after 1.5 h contact time was 63, 93, 93, and 95%, respectively while that of NH3 was 100% for all the adsorbent masses

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