科研成果

Stability of carbon dioxide foam attracts huge attentions while being of great challenge to many industrial practices. In this paper, aqueous CO2 foam stabilized with synergy of hydrophilic nanoparticles and nonionic surfactants was experimentally investigated at elevated temperatures and extreme salinities. The foam formula consisting of 1.5 wt% T40 and 2.49 mM C12E23 was determined under elevated temperature and salinity conditions. At 80 °C, the foam volume of the C12E23/T40 foam is 225 mL, and the half-life is 32 min, which is 13.9 times that of the C12E23 foam. At a salinity of 17 × 104 mg/L, the foam volume is 185 mL, and the half-life is 71 min, which is 24.4 times that of the C12E23 foam. With increasing salinity and temperature, the interfacial tension rises, and the viscoelastic modulus gradually declines, resulting in a lower foam stability. However, the T40/C12E23 foam has a good temperature and salinity tolerance, which can be used under harsh reservoir conditions. In a heterogeneous microscopic visualization model, water channeling in high-permeability regions inhibits the further increase in oil recovery. Subsequent injection of the C12E23/T40 foam improves the oil recovery factor up to 86.2%. The C12E23/T40 foam enhances the oil recovery by increasing the sweep area and flooding efficiency. In a sandpack model, the plugging pressure gradient of the CO2 foam stabilized by 2.49 mM C12E23 and 1.5 wt% T40 reaches 25.3 MPa/m, which is 12.65 times higher than that of the C12E23 foam. The composite reinforced foam attains good water blocking and profile control effects, thereby increasing the oil recovery factor 20.1% after water flooding. This study of great importance to improve not only the oil recovery efficiency, also anywhere where CO2-in brine foam applicable.

In passive millimeter wave radiation images, reflection will affect the analysis of the target and scene. Based on the theoretical model of reflection, this paper analyzes the change of brightness temperature(TB) in the target region and the reflected region under specific scenes. A target detection method based on the change of TB is proposed to distinguish the target and its reflection region and obtain the target outline. The effectiveness of the method is verified by simulation and imaging experiments.

In-Memory Computing (IMC), which takes advantage of analog multiplication-accumulation (MAC) insides memory, is promising to alleviate the Von-Neumann bottleneck and improve the energy efficiency of deep neural networks (DNNs). Since the time-domain (TD) computing is also an energy-efficient analog computing paradigm, we present an 8kb mixed-signal IMC macro, TD-SRAM, by combining IMC with TD computing. A dual-edge single input (DESI) TD computing topology is proposed, which can significantly improve the area and power efficiencies of TD cell. The TD-SRAM bitcell consisting of a 6T DESI based TD cell and a 6T-SRAM cell supports binary DNNs. In the IMC mode, 60 columns work in parallel and 96-input binary-MAC operations are processed in each column. Implemented in a standard 40-nm CMOS process, the TD-SRAM achieves the high energy efficiency of 537 TOPS/W at 0.9-V supply. With different DNN topologies, the test chips achieve the accuracy of 95.90%-98.00% with a dual 2-bit time-to-digital converter (TDC) in the MNIST dataset.

Passive radiative cooling technology uses the infrared atmospheric window to allow outer space to be a cold sink for heat. However, this effect is one that is only helpful for energy savings in the warmer months. Wang et al. and Tang et al. used the metal-insulator transition in tungsten-doped vanadium dioxide to create window glass and a rooftop coating that circumvents this problem by turning off the radiative cooling at lower temperatures. Because the transition is simply temperature dependent, this effect also happens passively. Model simulations suggest that these materials would lead to energy savings year-round across most of the climate zones in the United States. —BG A smart radiative coating automatically switches thermal radiation power in response to ambient temperature. The sky is a natural heat sink that has been extensively used for passive radiative cooling of households. A lot of focus has been on maximizing the radiative cooling power of roof coating in the hot daytime using static, cooling-optimized material properties. However, the resultant overcooling in cold night or winter times exacerbates the heating cost, especially in climates where heating dominates energy consumption. We approached thermal regulation from an all-season perspective by developing a mechanically flexible coating that adapts its thermal emittance to different ambient temperatures. The fabricated temperature-adaptive radiative coating (TARC) optimally absorbs the solar energy and automatically switches thermal emittance from 0.20 for ambient temperatures lower than 15°C to 0.90 for temperatures above 30°C, driven by a photonically amplified metal-insulator transition. Simulations show that this system outperforms existing roof coatings for energy saving in most climates, especially those with substantial seasonal variations.

A highly solar active nanocomposite with sheet-like WO3 skeleton and evenly loaded TiO2 and carbon quantum dots (CQDs) was synthesized by facile hydrothermal-calcining process, which showed 3.1- and 46.6- times activity on antibiotic (cephalexin) degradation than TiO2 and WO3, respectively. The construction of TiO2/WO3 heterojunction narrowed the band gap and facilitated the electrons-holes separation. The π conjugated CQDs was found to further improve the charge separation and extend the visible light response by photosensitization. However, the promoted charge separation predominantly contributed to the improved photocatalytic activity. The contributions of detected reactive species follows the order of: O2–>1O2>OH>h+. The cephalexin degradation mechanism and pathway were proposed based on DFT (density functional theory) calculation and experimental analysis. The photocatalytic mineralization efficiency can reach 92.4% in 4 h, indicating the efficient reduction of ecotoxicity of cephalexin and its intermediates. This new composite proved to have great potentials for emerging contaminants degradation in water.

Over the past years, perylenediimide (PDI)-based polymers have emerged as one of the widely studied polymer acceptors applicable to all-polymer solar cells (PSCs) due to their outstanding photovoltaic properties. Covalently fused PDI units, such as naphthodiperylenetetraimide (NDP), are proven beneficial to increasing the regularity of polymer backbones and enhancing the molecular packing in blend films, thus optimizing the active-layer morphology and improving the device performance. However, most investigated PDI polymers commonly demonstrated low open-circuit voltage (V-oc) in solar cells due to their low-lying lowest unoccupied molecular orbital (LUMO), which greatly limited the power-conversion efficiencies (PCEs) of their devices. Herein, we design and synthesize two new polymer acceptors (PTP-TT and PTP-Th) using thiophene-fused dimeric PDI (i.e., PTP) as the key building block. Both polymers exhibit much elevated LUMO levels at ca. -3.8 eV and achieve higher V-oc in devices compared with NDP-derived polymers. In particular, PTP-TT exhibits stronger light-absorption ability than PTP-Th and a presumably more planar backbone conformation, which are favorable for molecular packing and charge carrier transport in the active layer. Using PTB7-Th as the donor, PTP-TT-based devices achieve the best PCE of 7.04%, with a V-oc of 0.86 V, a short-circuit current density of 14.96 mA/cm(2), and a fill factor of 54%. The current results demonstrate that fusing PDIs with a proper electron-rich moiety can synergistically elevate the LUMO level and optimize the backbone regularity of polymer acceptors to obtain desirable efficiencies of PSCs.