Display omitted
•Dicyandiamide is transformed into melamine-cyanaurate complex (MCA) under hydrothermal process.•MCA leads to the formation of mesopores g-C3N4 nanosheets under optimized ...conditions.•The g-C3N4 nanostructure shows a high hydrogen evolution rate of 136.9 μmol/h.•Its apparent quantum efficiency (AQE) is as high as 10.6% at 420 ± 15 nm.
Annealing a supramolecular precursor with a similar structure to the local arrangement over the g-C3N4 building blocks at molecular level is a simple and effective route for preparing g-C3N4 nanostructures. Herein, a facile process for synthesizing the supramolecular precursor is presented, from which the uniform 3D holey g-C3N4 nanosheets with considerably high photocatalytic performance are obtained. The precursor synthesized from hydrothermal treatment of dicyandiamide presents a similar structure to of that the melamine-cyanaurate (MCA) complex prepared by the assembly of melamine and cyanuric acid, while the differences in thermal decomposition and morphology exist. Consequently, the g-C3N4 samples obtained by annealing the two precursors obtained via the different synthesis routes exhibit district microstructures, optical properties, charge recombination and photoelectrochemical behavior, and photocatalytic activity. It is found that the g-C3N4 nanostructure prepared by annealing the hydrothermal product of dicyandiamide shows the hydrogen evolution rate of 136.9 μmol/h, which is 2.5 folds that of the one obtained from the conventional MCA complex and 15-folds of bulk g-C3N4, and its apparent quantum efficiency (AQE) reaches 10.6% at 420 ± 15 nm.
Here the experimental technique for measuring the thermal conductivity of nanofluids at the temperatures above 100 °C has been developed, and a systematic research on the thermodynamic properties ...including thermal conductivity, viscosity, specific heat and density, of the graphene-dispersed nanofluids based on the ionic liquid 1-hexyl-3-methylimidazolium tetrafluoroborate (HMIMBF4), has been conducted at the temperatures ranging from room temperature to around 200 °C. The thermal conductivity of the nanofluid containing graphene of as low as 0.06 wt% increases by 15.2%–22.9% as the tested temperature varies from 25 to 200 °C, as compared with that of the base fluid. The viscosity of HMIMBF4 and its graphene-dispersed nanofluids dramatically decreases to 6.3 cp with the temperature increasing to 210 °C, which just favors their medium-to-high-temperature applications. The specific heat and density of the graphene-dispersed nanofluids exhibit a slight decrease as compared with those of HMIMBF4. It is found that the thermodynamic properties of HMIMBF4 and its GE-dispersed nanofluids are superior to those of the commercial heat transfer fluid Therminol VP-1. The thermogravimetric analysis shows that the initial decomposition temperature of the GE-dispersed nanofluids is very close to 440.6 °C of HMIMBF4, indicating that all of them possess good thermal stability. This novel class of fluids based on the ionic liquid shows great potential for use as advanced heat transfer fluids in medium- and high-temperature systems such as solar collectors.
•Thermophysical properties of HMIMBF4 based nanofluids containing graphene were measured from room temperature to 200 °C.•Effect of temperature on thermophysical properties of HMIMBF4 based nanofluid was obtained.•This novel class of ionic liquid based nanofluid shows great potential as advanced heat transfer fluids.
Herein, a novel strategy was explored to enhance the photocatalytic activity of graphitic carbon nitride (g-C3N4, GCN) by modulating its molecular structure, which involved modifying supramolecular ...precursor by molecular engineering, followed by pyrolysis. Specifically, 1-amino-2-propanol (monoisopropanolamine, MIPA), a substance that carries both –NH2 and –OH, was introduced into the system of hydrothermally treating dicyandiamide (DCDA). The precursors obtained at the MIPA volume concentration of more than 0.5% display hexagonal prisms, and then transform into the ethyl grafted GCN with a tubular-like morphology, abundant pores and enlarged specific surface area. Besides the intrinsic band absorption, the obtained GCN exhibit an enhanced visible light absorption in the region between 450 and 560 nm, owing to the existence of a midgap state related to the ethyl grafting. A much reduction in charge recombination is observed for the ethyl-grafted GCN, originated from its spatial separation between LUMO and HOMO. Consequently, the hydrogen evolution rate of the GCN sample, obtained at the optimal concentration of MIPA, is 13.84 mmol/h/g (AQE = 18.25% at 420 nm), about 30.1 times higher than that of the bulk C3N4 (BCN) under visible light (λ > 420) irradiation. This work sheds light on modulating GCN by molecular engineering of supramolecular precursors.
Employing 1-amino-2-propanol, a substance that carries both –NH2 and –OH, to modify the structure and morphology of supramolecular precursor, thus producing tubular-like g-C3N4 with greatly enhanced photocatalytic hydrogen evolution. Display omitted
•1-amino-2-propanol (MIPA) was employed to modulate supramolecular precursor.•MIPA could be implanted into the structure of supramolecular precursor.•The resultant GCN exhibited enhanced visible light absorption.•An obvious reduction in charge recombination was also observed.•The photocatalytic hydrogen evolution was dramatically increased.
Here we demonstrate thermal energy storage cement mortar (TESCM) fabricated by integrating ordinary cement mortar with a composite phase change material (PCM) based on n-octadecane and expanded ...graphite (EG). The mass percentage of n-octadecane in the composite PCM can reach as high as 90% due to the excellent adsorption ability of EG, which endows the composite PCM with large latent heat. SEM images of the composite PCM show that n-octadecane is adsorbed into the pores of EG and uniformly covers on the nanosheets of EG, which microstructure contributes to preventing leakage of melted n-octadecane after it changes phase from solid state to liquid state. The n-octadecane/EG composite PCM has a good compatibility with ordinary cement mortar, and does not obviously deteriorate the apparent densities of the TESCM samples. Based on the thermal energy storage performance evaluation, it is found that the TESCM containing the n-octadecane/EG composite PCM plays a role in reducing the variation of indoor temperature, which helps to decrease the energy consumption for buildings.
► A novel kind of cement mortar containing a composite PCM based on expanded graphite and n-octadecane was prepared. ► Mechanical performance of the thermal energy storage cement mortar was tested. ► The thermal energy storage performance of the thermal energy storage cement mortar was evaluated.
A novel kind of graphene oxide-modified poly(melamine-formaldehyde) (PMF) microcapsule containing phase change material (microPCM)
n
-dodecanol was prepared by
in situ
polymerization. ...Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) were used to study the chemical structure of graphene oxide (GO) and microPCMs, respectively. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to investigate the morphology of GO and microPCMs, respectively. The thermal properties of microPCMs were studied by differential scanning calorimetry (DSC), thermal constant analysis (TCA) and thermal cycling tests. The FTIR and XRD results indicate that the phase change material
n
-dodecanol is encapsulated in the GO/PMF composite shell, and there is no chemical reaction between them. The SEM results show that the prepared GO-modified PMF microPCMs are spherical particles with a smooth surface. The DSC results indicate that the phase change temperature and the latent heat of microPCMs with 1 wt% of GO are 26.40 °C and 125.2 J g
−1
, respectively. The thermal conductivity of GO/microPCMs with 4 wt% GO increases by 66.29%, compared with that of microPCMs without GO according to the TCA results. Moreover, the thermal cycling tests show that the prepared microPCMs possess a good thermal stability. The GO-modified PMF microPCMs are sure to have great potential applications in thermal energy storage.
Graphene oxide-modified poly(melamine-formaldehyde) microcapsules containing phase change material were synthesized with thermal conductivity improved by more than 50% and a high enthalpy of 125.2 J g
−1
.
•A passive cooling PV-PCM system was developed.•Form-stable paraffin/EG composite PCM with high thermal conductivity was utilized.•Numerical simulation on the temperature of PV-PCM panel was carried ...out.•Effects of density were studied under the given weather conditions.
Performance of photovoltaic (PV) panels is greatly affected by its operating temperature. And traditional active and passive cooling methods usually suffer from the disadvantages of external energy consumption, uneven temperature distribution and low thermal conductivity of phase change materials (PCMs). In this work, a PV-PCM system was developed to control the temperature of a PV panel by applying high thermal conductive form-stable paraffin (ZDJN-28)/EG composite PCM. The temperature, output voltage and power of a conventional PV panel and the PV-PCM panel were measured and compared. A numerical simulation model established by CFD software FLUENT was used to simulate the temperature change process of the PV-PCM panel with different material densities under the same conditions as experiment. The experiment results showed that compared with the temperature of the conventional PV panel, the temperature of the PV-PCM panel is kept below 50°C for 200min extended by 146min with output power averagely increased by 7.28% in heating process. Simulated temperatures were in good agreement with experimental temperatures and indicated that the higher the density of the PCM is, the better the temperature management performance the PV panel could achieve. Besides, the PCM with density of 900kg/m3 was found sufficient to achieve a good temperature management performance when the average ambient temperature below 25°C with the highest solar irradiation of 901w/m2. In summary, this work is of great importance in the design of a PV-PCM system for temperature management of PV panels.
•A novel composite of LiNO3/KCl in expanded graphite PCMs was prepared.•Thermal properties and heat storage performance of the composite were studied.•The composite showed excellent abilities in ...energy storage and heat transfer.•The composite had a potential use in solar thermal energy applications.
A LiNO3/KCl-expanded graphite (EG) composite phase change material (PCM) was prepared for solar thermal energy storage application at high temperature (∼200°C). In such composite material, eutectic system LiNO3/KCl is characterized by high phase change latent heat and EG serves as the heat transfer promoter. Investigations by means of differential scanning calorimetry (DSC), hot disk analyzer and heat storage performance tests in a latent thermal energy storage (LTES) unit were devoted to the thermal property measurement and heat storage performance analysis of the LiNO3/KCl–EG composite. Experimental results revealed that the melting temperature of the composite material was close to that of the eutectic LiNO3/KCl, and the phase change latent heat ranging from 142.41 to 178.10J/g was dependent on its mass fraction of EG. The thermal conductivities of the composites were 1.85–7.56 times higher compared with the eutectic LiNO3/KCl, and the conductivity value varied with the EG mass content and the apparent density of the composite. In addition, the heat transfer in the composite material during the heat storage process was enhanced through the thermal conductivity improvement, while the heat storage duration was affected by the phase change latent heat and the apparent density of the composite material.
To investigate the characteristic of coagulation function in 303 patients with Coronavirus disease 2019 (COVID-19), we evaluated the correlation between coagulation function and disease status. We ...retrospectively analyzed 303 patients diagnosed with COVID-19 and evaluated the clinical data of 240 patients who were discharged. The coagulation function of the two groups (mild and severe) was compared. Compared with the mild group, majority of patients in the severe group were male (76.9% vs. 49.8%) and elderly (median age 65 vs. 50), and the proportion with chronic underlying diseases was higher (73.1% vs. 36.1%). There were 209 abnormalities (69.0%) of coagulation parameters in 303 patients admitted to hospital. Comparison of various indexes of coagulation function between the two groups in admission, the proportion of abnormal coagulation indicators in the severe group was higher than that in the mild group (100% vs. 66.1%). The median coagulation parameters in the severe group were higher than those in the mild group: international normalized ratio (1.04 vs. 1.01), prothrombin time (13.8 vs. 13.4) seconds, activated partial thromboplastin time (43.2 vs. 39.2) seconds, fibrinogen (4.74 vs. 4.33) g/L, fibrinogen degradation products (2.61 vs. 0.99) µg/mL, and D-dimer (1.04 vs. 0.43) µg/mL, the differences were statistically significant (p < 0.05). Coagulation dysfunction is common in patients with COVID-19, especially fibrinogen and D-dimer elevation, and the degree of elevation is related to the severity of the disease. As the disease recovers, fibrinogen and activated partial thromboplastin time also return to normal.
Herein, we report that in situ confined growth of Pt nanoparticles (Pt NPs) on Ti3C2Tx MXene nanosheets (Ti3C2Tx NSs) affords a highly active Ti3C2Tx NSs/Pt NPs hybrid catalyst in a dye-sensitized ...system under visible light irradiation, which demonstrates ∼30 times higher H2 evolution activity than in situ formed free Pt NPs and acheives a high apparent quantum yeild (AQY) of 5.81% at 520 nm.
The thermal management systems using EG-based phase change materials (PCMs) can provide power batteries with a proper operating temperature, slow temperature rise rate and uniform temperature ...distribution. In this study, a systematical investigation on the effects of thermo-physical properties of the used PCMs on the performance of the systems has been conducted. A series of paraffin/expanded graphite (EG) composites have been applied to a simulative battery thermal management system and to find out the PCM with the best thermal properties. The performances of PCMs varying with the kind of paraffin used, the paraffin mass fraction in composites and the packing density of the composites have been compared. It is found that the paraffin with the melting point of 44 degree C offers batteries the best operating temperature. Furthermore, the synergetic effect of the mass fraction of paraffin in the composite PCM and the packing density of the composite in the thermal management system has been studied. The temperature rise can be slowed down by increasing the composites density and the temperature uniformity can be improved by the increase in EG mass fraction and composite density. After cycle tests, the paraffin/EG composite with paraffin mass fraction of 75% and density of 890 kg m super(-3) shows the best thermal management performance. In addition, numerical research with the computational fluid dynamics (CFD) software, FLUENT was also carried out. The numerical results are in a good agreement with the experiment data.
PDF
