The concept of the Fan product of several
M
-matrices is introduced. Furthermore, two new lower bounds of the minimum eigenvalue of the Fan product of several
M
-matrices are proposed. These obtained ...new lower bounds generalize and improve some earlier findings. One example is presented to illustrate the precision of the given lower bounds.
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Constructing an efficient photocatalyst is critical for photocatalytic carbon dioxide (CO2) into valuable fuel. Herein, a high-efficiency catalyst was synthesized by a simple one-step ...electrostatic self-assembly method, in which Ti3C2 (TC) was anchored on porous g-C3N4 (PCN) with rich –NHx via NHx-Ti bond. Such a chemical interaction made the optimized TC/PCN-2 with 2 wt% loading of Ti3C2 possess highest CH4 production (0.99 μmol·h−1·g−1catalyst) under visible light (>420 nm), which was 14 times higher than that of pure PCN (0.07 µmol·h−1·gcatalyst−1) at the same condition. More importantly, the TC/PCN-2 photocatalyst still maintained satisfied activity after four cycles. Besides the formation of NHx-Ti chemical bonding and superior conductivity of Ti3C2 as a co-catalyst, which facilitated interfacial charges separation and migration, the exceptional performance could also attribute to the enhanced CO2 adsorption/activation and improved light-harvesting capability. This work provided a potential application in energy conversion with MXene as an efficient co-catalyst.
The nickel sulfide (NiS) nanoparticles were anchored on the mesoporous graphitic carbon nitride (g-C
3
N
4
) by one-pot calcination with sulfur powder as sulfur source and pore-forming agent. It is ...the first attempt to use the g-C
3
N
4
/NiS as a counter electrode (CE) for quantum-dot-sensitized solar cells. The g-C
3
N
4
/NiS co-catalyst based on 0.74 wt% NiS loading for S
n
2−
reduction obtained a low interface charge transfer resistance (
R
ct
) of 1.08 Ω. The power conversion efficiency of the QDSSC assembled with ZnSe/CdS/CdSe/ZnSe-sensitized TiO
2
photoanode and g-C
3
N
4
/NiS CE is up to 5.64%, which is 3.05 times as high as that of pure g-C
3
N
4
CE. The enhancement of cell efficiency is attributed to the synergistic effects of excellent morphology of g-C
3
N
4
and its co-catalysis with NiS nanoparticles. The mesoporous architecture contributes a large specific surface area and fast electrolyte transfer channels, and the coupling of g-C
3
N
4
with NiS promotes the transfer of charge between the interface g-C
3
N
4
/NiS and electrolytes. The presented strategy for fabricating mesoporous architecture with g-C
3
N
4
/NiS uses low-cost raw materials and a simple preparation method, which provides a feasible route to enhance the electrocatalytic activity of g-C
3
N
4
.
Spontaneous imbibition plays an important role in many subsurface and industrial applications. Unveiling pore‐scale wetting dynamics, and particularly its upscaling to the Darcy model, are still ...unresolved. We conduct image‐based pore‐network modeling of cocurrent spontaneous imbibition and the corresponding quasi‐static imbibition in homogeneous sintered glass beads and heterogeneous Estaillades carbonate. We find that pore‐scale heterogeneity significantly influences entrapment of the nonwetting fluid, which in Estaillades is mainly because of the poor connectivity of pores. We show that wetting dynamics significantly deviates capillary pressure and relative permeability away from their quasi‐static counterparts. Moreover, we propose a nonequilibrium model for wetting permeability that well incorporates flow dynamics. We implement the nonequilibrium model into two‐phase Darcy modeling of a 10 cm long medium. Sharp wetting fronts are numerically predicted, which are in good agreement with experimental observations. Our studies provide insights into developing a two‐phase imbibition model with measurable material properties.
Plain Language Summary
The flow of a fluid into a porous matrix by capillary force is encountered in many everyday processes, such as water‐flow to reach the tips of trees and water‐flow through soils. These processes are examples of spontaneous imbibition. Spontaneous imbibition is also crucial to many industrial applications, ranging from oil recovery and geological sequestration of carbon dioxide to inkjet printing, diapers, and paper sensors. Mostly, the imbibition rate, broadening of the wetting front, and entrapment of the nonwetting fluid are of great interest. In this work, we conduct extensive pore‐scale modeling of spontaneous flow in porous media. We illustrate how pore‐scale heterogeneity influences imbibition dynamics and entrapment of the nonwetting fluid. To bridge the gap between pore‐scale flow dynamics and the Darcy‐scale theory of spontaneous imbibition, we develop a nonequilibrium model for wetting permeability that can provide better modeling of spontaneous imbibition at the Darcy scale. Our studies have immediate implications for the applications of oil production from fractured reservoirs, capillary trapping of carbon dioxide, and remediation of nonaqueous liquids in soils.
Key Points
We conduct image‐based pore‐network modeling of spontaneous imbibition in sintered glass beads and Estaillades carbonate
We illustrate the influence of pore‐scale heterogeneity on wetting dynamics and nonwetting entrapment
We develop a new relative permeability model that incorporates wetting dynamics
We establish a comprehensive political connection index based on manually collected personal profiles of top firm managers or board members to examine the contribution of political connections to ...corporate innovation and the channels of this relation. Our results indicate that politically connected firms tend to have more innovation than non-connected firms, and government subsidies mediate this relation. Moreover, the innovation-enhancing value of political connections is especially important for firms that receive less government support, such as non-SOEs and low-tech companies.
Halide perovskite quantum dots (QDs) have great potential in photocatalytic applications if their low charge transportation efficiency and chemical instability can be overcome. To circumvent these ...obstacles, we anchored CsPbBr3 QDs (CPB) on NHx‐rich porous g‐C3N4 nanosheets (PCN) to construct the composite photocatalysts via N−Br chemical bonding. The 20 CPB‐PCN (20 wt % of QDs) photocatalyst exhibits good stability and an outstanding yield of 149 μmol h−1 g−1 in acetonitrile/water for photocatalytic reduction of CO2 to CO under visible light irradiation, which is around 15 times higher than that of CsPbBr3 QDs. This study opens up new possibilities of using halide perovskite QDs for photocatalytic application.
CsPbBr3 quantum dots were anchored on the polymeric semiconductor g‐C3N4 porous nanosheets via strong N−Br bond. Chemical bonding cannot only enhance the photocatalytic CO2 reduction performance, but also fix the QDs on a solid surface to improve the stability. This work opens up new possibilities of using halide perovskite QDs for photocatalytic applications.
The engineering of microbially induced calcium carbonate precipitation (MICP) has attracted much attention in a number of applications, such as sealing of CO2 leakage pathways, soil stabilization, ...and subsurface remediation of radionuclides and toxic metals. The goal of this work is to gain insight into pore‐scale processes of MICP and scale dependence of biogeochemical reaction rates. This will help us develop efficient field‐scale MICP models. In this work, we have developed a comprehensive pore‐network model for MICP, with geochemical speciation calculated by the open‐source PHREEQC module. A numerical pseudo‐3‐D micromodel as the computational domain was generated by a novel pore‐network generation method. We modeled a three‐stage process in the engineering of MICP including the growth of biofilm, the injection of calcium‐rich medium, and the precipitation of calcium carbonate. A number of test cases were conducted to illustrate how calcite precipitation was influenced by different operating conditions. In addition, we studied the possibility of reducing the computational effort by simplifying geochemical calculations. Finally, the effect of mass transfer limitation of possible carbonate ions in a pore element on calcite precipitation was explored.
Key Points
A comprehensive pore‐network model coupled with PHREEQC was developed to study microbially induced calcite precipitation in porous media
Scale dependence of biogeochemical reaction rates was studied
The possibility of reducing computational efforts by simplifying geochemical calculations was investigated
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•Honeycomb spherical 1T-MoS2 was fabricated via hydrothermal with F127 templates.•1T-MoS2 was used as an efficient counter electrode for QDSSCs.•The PCE reached 6.03% based on the CE ...and a TiO2/CdS/CdSe/ZnSe photoanode.•The stability of 1T-MoS2 is enhanced by the unique morphology.
Honeycomb spherical metallic 1T-MoS2 was fabricated as an efficient counter electrode (CE) for quantum dot sensitized solar cells (QDSSCs) via facile hydrothermal method using environment-friendly F127 as soft templates. Electrochemical tests show that the interface charge transfer resistance (Rct) of 1T-MoS2 is only 0.66 Ω with 3% template, demonstrating its superior electrocatalytic activity for Sn2− reduction. The power conversion efficiency of QDSSCs assembled with Ti-mesh substrate MoS2 CEs reached 6.03%. The outstanding performance is mainly ascribed to the unique morphological advantage and intrinsically excellent conductivity, catalytic activity and hydrophilicity of 1T-MoS2. The honeycomb spherical 1T-MoS2 increases the specific surface area and provides rich catalytic active sites and electrolyte transport channels, also enhances the stability of 1T-MoS2. The experimental results reveal 1T-MoS2 is expected to be a competitive CE material for efficient QDSSCs.
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