Microwave-assisted and conventional hydrothermal carbonization of lignocellulosic waste material: comparison of the chemical and structural properties of the hydrochars

This study compares the chemical and structural properties of the hydrochars prepared from microwave-assisted and conventional hydrothermal carbonizations of Prosopis africana shell, a waste plant material. The preparation involved heating the raw material in de-ionized water at 200 °C for 5-20 min, and 120-240 min in the microwave and conventional oven respectively. The prepared hydrochars were characterized using the scanning electron microscope, nitrogen sorption measurement, Fourier transform infrared spectroscopy, CHN analyzer, thermogravimetric analysis, and nuclear magnetic resonance. The results showed that the microwave-assisted hydrothermal carbonization process is fast in the carbonization of the Prosopis africana shell as shown by the level of conversion attained within the short time. This study presents new data on the comparison of the hydrochars from microwave-assisted and conventional hydrothermal carbonization processes of the same lignocellulosic material in terms of their properties

Biomass derived mesoporous carbon monoliths via an evaporation-induced self-assembly

Evaporation-induced self-assembly has been applied in the synthesis of crack-free mesoporous carbon monolith with good mechanical stability using a waste plant material as carbon precursor and triblock copolymer F127 as template. The carbon monolith was characterized using transmission electron microscopy, scanning electron microscopy, nitrogen adsorption–desorption measurement, X-ray diffraction and Fourier transform infrared spectroscopy. The results showed that the carbon monolith is mesoporous, has a surface area of 219 m²/g, and a narrow pore size distribution of 6.5 nm

Microwave-assisted hydrothermal carbonization of rapeseed husk: A strategy for improving its solid fuel properties

Hydrothermal carbonization of a waste biomass material is a green and promising technique for improving its solid fuel properties, which does not require pretreatment procedure such as drying of the biomass. In this study, hydrothermal carbonization of rapeseed husk, a waste plant material was carried out under microwave heating and the effect of process parameters, such as reaction temperature and residence time on the mass yields and energy properties of the hydrochars was studied. The procedure involved the heating of the feedstock in deionized water in a microwave oven at temperatures of 150 to 200 °C for a specified period of time. The results indicated that the mass yields decreased, as the reaction temperature and residence time were increased, which led to improvement in the energy properties of the prepared hydrochars. The reaction was rapid within the first 20 min, and stabilized afterwards. The energy properties of the prepared hydrochars are consistent with previous studies, showing that the hydrochars have the potential of being used as solid fuel. The structural and morphological analysis carried out revealed that the feedstock was transformed during the process

An anecdotal examination of wellness programs

This research investigates the question whether or not Wellness Programs are available to police officers throughout Virginia. Research has shown these programs to be beneficial in reducing the health risks associated with police work. Police departments may also see a decrease in sick leave and work related injuries. In order to address the research question, a questionnaire was distributed to 150 police departments throughout Virginia. A total of 57.7 percent of the departments reported the availability of a voluntary Wellness Program. Based on a lack of data, the findings suggest that the departments are not evaluating the effectiveness of their programs. This study contends that police officers and police departments can benefit from a properly implemented Wellness Program

Nanotoxicity of polyelectrolyte-functionalized titania nanoparticles towards microalgae and yeast: Role of the particle concentration, size and surface charge

We studied the nanotoxicity of titania nanoparticles (TiO₂NPs) of various hydrodynamic diameters and crystallite sizes towards C. reinhardtii microalgae and S. cerevisiae (yeast) upon illumination with UV and visible light. The cell viability was assessed for a range of nanoparticle concentrations and incubation times. We found that bare TiO₂NPs affect the C. reinhardtii cell viability at much lower particle concentrations than for yeast. We observed an increase of the TiO₂NPs toxicity upon illumination with UV light compared with that in dark conditions due to the oxidative stress of the produced reactive oxygen species. We also found an increased TiO₂NPs nanotoxicity upon illumination with visible light which indicates that they may also interfere with the microalgae's photosynthetic system leading to decreased chlorophyll content upon exposure to TiO₂NPs. The results indicate that the larger the hydrodynamic diameter of the TiO₂NPs the lower is their nanotoxicity, with anatase TiO₂NPs generally being more toxic than rutile TiO₂NPs. We also prepared a range of polyelectrolyte-coated TiO₂NPs using a layer by-layer method and studied their nanotoxicity towards yeast and microalgae. We found that the toxicity of the coated TiO₂NPs changes with their surface charge. TiO₂NPs coated with cationic polyelectrolyte as an outer layer exhibit much higher nanotoxicity than the ones with an outer layer of anionic polyelectrolyte. TEM images of sectioned microalgae and yeast cells exposed to different polyelectrolyte-coated TiO₂NPs confirmed the formation of a significant build-up of nanoparticles on the cell surface for bare and cationic polyelectrolyte-coated TiO₂NPs. The effect comes from the increased adhesion of cationic nanoparticles to the cell walls. Significantly, coating the TiO₂NPs with anionic polyelectrolyte as an outer layer led to a reduced adhesion and much lower nanotoxicity due to electrostatic repulsion with the cell walls. This suggest a new way of making cationic TiO₂NPs safer for use in different formulations by pre-coating them with anionic polyelectrolytes. The results of this study give important insights into the various factors controlling the nanotoxicity of TiO₂NPs

Mg/Ca ratios in freshwater microbial carbonates: Thermodynamic, kinetic and vital effects

The ratio of magnesium to calcium (Mg/Ca) in carbonate minerals in an abiotic setting is conventionally assumed to be predominantly controlled by (Mg/Ca)solution and a temperature dependant partition coefficient. This temperature dependence suggests that both marine (e.g. foraminiferal calcite and corals) and freshwater (e.g. speleothems and surface freshwater deposits, “tufas”) carbonate deposits may be important archives of palaeotemperature data. However, there is considerable uncertainty in all these settings. In surface freshwater deposits this uncertainty is focussed on the influence of microbial biofilms. Biogenic or “vital” effects may arise from microbial metabolic activity and/or the presence of extracellular polymeric substances (EPS). This study addresses this key question for the first time, via a series of unique through-flow microcosm and agitated flask experiments where freshwater calcite was precipitated under controlled conditions. These experiments reveal there is no strong relationship between (Mg/Ca)calcite and temperature, so the assumption of thermodynamic fractionation is not viable. However, there is a pronounced influence on (Mg/Ca)calcite from precipitation rate, so that rapidly forming precipitates develop with very low magnesium content indicating kinetic control on fractionation. Calcite precipitation rate in these experiments (where the solution is only moderately supersaturated) is controlled by biofilm growth rate, but occurs even when light is excluded indicating that photosynthetic influences are not critical. Our results thus suggest the apparent kinetic fractionation arises from the electrochemical activity of EPS molecules, and are therefore likely to occur wherever these molecules occur, including stromatolites, soil and lake carbonates and (via colloidal EPS) speleothems

Microwave-assisted hydrothermal synthesis of carbon monolith via a soft-template method using resorcinol and formaldehyde as carbon precursor and pluronic F127 as template

A new microwave-assisted hydrothermal synthesis of carbon monolith is reported in this work. The process uses microwave heating at 100 °C under acidic condition by employing a triblock copolymer F127 as the template, and resorcinol–formaldehyde as the carbon precursor. Scanning electron microscopy, Fourier transform infrared spectroscopy, nitrogen sorption measurements, transmission electron microscopy, X-ray studies and thermogravimetic analysis were used to characterize the synthesized material. The carbon monolith is crack-free, mesoporous and has a high surface area of 697 m²/g. The results demonstrate that the microwave-assisted hydrothermal synthesis is a fast and simple approach to obtain carbon monoliths, as it reduces effectively the synthesis time from hours to a few minutes which could be an advantage in the large scale production of the material

Characterization of energy-rich hydrochars from microwave-assisted hydrothermal carbonization of coconut shell

In this study, microwave-assisted hydrothermal carbonization of waste coconut shell (feedstock) is reported. It is a thermo-conversion technique in which the feedstock was transformed into energy-rich carbonaceous material under mild conditions. The process was conducted in a microwave oven by heating the waste coconut shell in deionized water inside a pressurized vessel. The effects of different process conditions on the product yields, and the energy properties of the hydrochars were studied by varying the reaction temperature from 150 to 200 °C and residence time from 5 to 30 min. The results showed that there was transformation of the feedstock in the process due to the decarboxylation, dehydration, and demethanation reactions. This led to changes in the chemical and structural compositions, as well as increase in the energy properties of the prepared hydrochars. The higher heating value increased from 15.06 MJ/kg in the feedstock to 19.76 MJ/kg in the hydrochar. The energy properties of the hydrochars prepared in this study showed that microwave-assisted hydrothermal carbonization process could be a technique for converting waste coconut shell into high value-added product