Kinetics of cellulose pyrolysis after a pressurized heat treatment

A hot pressure treatment (HPT) converts celluloses into an advantageous feedstock for activated carbon preparation. Other ways of utilization may also emerge in the future. In the present paper the pyrolysis kinetics of three HPT cellulose samples were studied by thermogravimetric analysis (TGA) at linear and stepwise temperature programs. A distributed activation energy model was used assuming two partial reactions. Nine experiments on three samples were evaluated simultaneously by the method of least squares. 20 unknown parameters were determined in this way. Good fits were obtained at the linear and stepwise temperature programs alike. The evaluations were also carried out by non-constant preexponential factors that depended on the activation energy. The considerations and evaluation methods of the paper are hoped to help the investigations of other biomass materials, too. The results showed that part of the cellulose remained unconverted and another part only partially converted at the mildest pretreatment conditions of this study. The cellulose was wholly transformed in the pretreatment when either the pressure or the temperature was increased. Keywords: Cellulose; Thermal decomposition; Distributed activation energy model (DAEM); Thermogravimetry (TGA); Method of least squares

Gourmet and vitality : analysing the restaurant and urban vitality in the old city of Beijing based on multi-source big data

Gourmet embodies people's pursuit of a better life. Restaurants, as it provider, also play an important role in urban life and is an important space for communication. Under the influence of Covid-19 pandemic, restaurant operations are facing more challenges, and the death of restaurants has also reduced the popularity in cities. How to identify the gourmet vitality that brought about by the existence of dining spaces and effectively maintain the urban vitality of the city through urban plan and urban design, which are the challenge that need to be faced in the post-epidemic era. Gourmet vitality of restaurants forming gather in specific areas, which is not only affected by the restaurant's own factors, but also by the external environment. It used to be difficult to fully observe the vitality of food, so we try to perceive it in new ways. Taking Beijing as an example, our work aims to explore the relationship between the urban vitality, gourmet vitality and restaurant characteristics and multi-source big data are applied, such as mobile signal data, points of interest, and building volume. Firstly, many indicators are extracted to measure urban vitality, gourmet vitality and dinning space from the data. Then, the distribution and correlation of urban vitality and gourmet vitality are analysed. Finally, the relationship between food vitality, dining space and environmental elements is discovered through spatial regression calculations. The relationship between urban vitality and gourmet vitality is more complicated than our prediction, which gourmet vitality is jointly determined by the factor of dining spaces and environments, while environmental factors can also affect urban vitality in other ways

Nitrogen-doped hierarchical porous carbons derived from biomass for oxygen reduction reaction

Nowadays biomass has become important sources for the synthesis of different carbon nanomaterials due to their low cost, easy accessibility, large quantity, and rapid regeneration properties. Although researchers have made great effort to convert different biomass into carbons for oxygen reduction reaction (ORR), few of these materials demonstrated good electrocatalytical performance in acidic medium. In this work, fresh daikon was selected as the precursor to synthesize three dimensional (3D) nitrogen doped carbons with hierarchical porous architecture by simple annealing treatment and NH3 activation. The daikon-derived material Daikon-NH3-900 exhibits excellent electrocatalytical performance towards oxygen reduction reaction in both alkaline and acidic medium. Besides, it also shows good durability, CO and methanol tolerance in different electrolytes. Daikon-NH3-900 was further applied as the cathode catalyst for proton exchange membrane (PEM) fuel cell and shows promising performance with a peak power density up to 245 W/g

Experimental study on characteristics of grounawater fracture in coalmine overlying rock

The seepage characteristics of groundwater in the overlying fissures are the key factors to be considered in the later maintenance of coal mining and goaf, especially in the underground reservoir construction area of coal mines. It is also an important part of coal mine underground reservoir. In shallow groundwater-rich areas or under extreme summer rainfall conditions, underground reservoirs form vertical recharge, and analyzing the seepage characteristics of groundwater in overlying fissures provides a scientific basis for the safe operation of coal mine underground reservoirs and the protection of groundwater resources. In this study, the solid-liquid coupling similarity model test was used to obtain the development and stability of the overlying fissures in the mining area and the characteristics of groundwater seepage after the aquifer was connected. The analysis showed that the large abscission fissures and micro-fissures that extend far and wide are mostly water storage. , the vertical fissures running through multiple rock layers have strong water conductivity, and the hydraulic connection between the separation layer fissures is mainly formed by the vertical fissures in the two sides. Under the condition of vertical recharge, groundwater first infiltrates along the vertical fissures in an unsaturated manner, and is gradually saturated regionally from the upper and lower overlying fissures, finally forming a stable saturated infiltration form. On this basis, a mathematical model of groundwater seepage in saturated seepage state is established, and the numerical method is used to solve it. It is verified with similar simulation experiments that vertical fractures are the main water conduction channels, and their water conduction can account for up to 97%. At the same time, the migration speed of groundwater in vertical fractures is also many orders of magnitude higher than that in abscission fractures. Finally, through the sensitivity analysis, it is concluded that the vertical fracture seepage is positively correlated with the fracture development degree and the total water inflow, and negatively correlated with the rock permeability. The migration time of groundwater in overlying fissures is negatively correlated with the degree of fissure development, rock permeability and total water inflow

Tandem internal electric fields in intralayer/interlayer carbon nitride homojunction with a directed flow of photo-excited electrons for photocatalysis

Photocatalytic hydrogen production is a green technology while significantly impeded by the sluggish and uncontrolled charge dynamics for less electron accumulation on catalyst surface. Herein, we proposed an effective strategy of epitaxial growth of a van der Waals (VDW) homojunction on an intralayer homojunction of carbon nitride for a controlled charge flow. Experimental and simulation collectively disclosed a tandem internal electric field (IEF) in the integrated hybrid, stringing a lateral IEF along the intralayer homojunction with a vertical IEF within the VDW homojunction. The planar IEF dominates laterally dispersive movement of charge carriers for their efficient separations and mobilities, meanwhile the vertical IEF induces an oriented accumulation of the dispersive hot electrons to the catalyst surface for intensified hydrogen reduction. The tandem IEF renders the hydrogen evolution rate at 3.5-fold higher than in-planar homojunction, and 6.3 times higher than g-C3N4 benchmark. This work realizes charge-directing dynamics for robust photocatalysis

Genetic diversity and selection of three nuclear genes in Schistosoma japonicum populations

Background: The blood fluke, Schistosoma japonicum still causes severe disease in China, the Philippines and Indonesia. Although there have been some studies the molecular epidemiology of this persistent and harmful parasite, few have explored the possibility and implications of selection in S. japonicum populations. Methods: We analyzed diversity and looked for evidence of selection at three nuclear genes (SjIpp2, SjFabp and SjT22.6) in 13 S. japonicum populations. Results: SjT22.6 was found to exhibit high nucleotide diversity and was under positive selection in the mountainous region of mainland China. As a tegumental protein, its secondary and tertiary structure differed between S. japonicum strains from the mountainous and lakes regions. In contrast, SjIpp2 and SjFabp had relatively low levels of nucleotide diversity and did not show significant departure from neutrality. Conclusions: As a tegument-associated antigen-encoding gene of S. japonicum, SjT22.6 has high nucleotide diversity and appears to be under positive selection in the mountainous region of mainland China