Yanting Guo,Xing Chen,Xuan Zhang,Shujin Pu,Xutong Zhang,Chengli Yang,Dali Li
The immobilization of enzyme is an important biotechnology in industry. Enzyme immobilization by nanomaterials has attracted interest of researchers due to potentially promising application. Many enzymes had been successfully immobilized by different nanomaterials. In this work, β-glucosidase was immobilized by SiO 2 nanoparticles (nano-SiO 2 ) and zeolitic imidazolate framework-8 (ZIF-8), then the enzymatic properties of them were also compared. The nano-SiO 2 @β-glucosidase and the β-glucosidase@ZIF-8 achieved immobilization yield of 58.5% and 23.0%, respectively. Optimal temperature of the free β-glucosidase, nano-SiO 2 @β-glucosidase and the β-glucosidase@ZIF-8 were around 50 °C. Both free β-glucosidase and nano-SiO 2 @β-glucosidase showed maximal catalytic activity at pH 6.0, while the optimal pH of the β-glucosidase@ZIF-8 was 5.4 roughly. The nano-SiO 2 @β-glucosidase exhibited similar pH stability and thermal stability to those of the free β-glucosidase, and the β-glucosidase@ZIF-8 improved pH stability greatly. Moreover, after the treatment of trypsin for 4 h at 37 °C, the residual activities of the β-glucosidase@ZIF-8 was the highest that retained 94%, which provided huge potential for the application of the β-glucosidase@ZIF-8 in industry. Furthermore, the nano-SiO 2 @β-glucosidase and the β-glucosidase@ZIF-8 can be reused for 5 cycles with 87.5% and 88.7% residual activity, respectively.
The poor dispersion of nano-SiO₂ in shotcrete systems limits its effectiveness and can even lead to detrimental effects. To address this issue, ettringite suspension was introduced as a novel dispersion carrier. Nano-SiO₂ was found to physically adsorb onto ettringite crystals, significantly improving its spatial distribution without organic dispersants. Compared to direct nano-SiO₂ addition, the incorporation of ettringite—especially via premixing—markedly enhanced performance. With premixed nano-SiO₂ and ettringite, and nano-SiO₂ content ranging from 0.25 % to 1 %, the 6-hour compressive strength increased by 93∼600 %, while the initial and final setting times were reduced by 46∼79 % and 47∼91 %, respectively, compared to the control. Isothermal calorimetry, quantitative X-ray diffraction (QXRD), and thermogravimetric analysis (TG) confirmed that the well-dispersed nano-SiO₂ accelerates early cement hydration by providing abundant nucleation sites facilitating rapid formation of hydration products, mainly calcium silicate hydrate (C–S–H). Simultaneously, ettringite acts not only as a dispersant but also strengthens the early-age framework, enhancing load transfer within the shotcrete matrix.
Graphical Nano-SiO₂ (0.02 wt%) extends gel stability to 95 days at 130 °C in seawater (versus 70 days control). SEM-confirmed H-bonding between Nano-SiO₂ silanols and AMPS groups reinforces network. Gelation activation energy (88.2 kJ/mol) derived via Arrhenius model. Nano-SiO₂-toughened polymer gels achieves 34.7 MPa/m breakthrough pressure (10 × base gel) in 1.4 Darcy cores. This study solves water shutoff gel syneresis/ degradation in high-salinity seawater (Ca 2 ⁺+Mg 2 ⁺ >1;500 mg/L) for South China Sea reservoirs. Reservoirs in the western South China Sea have entered a high-water-cut stage, exhibiting significant heterogeneity exacerbated by prolonged water flooding, necessitating urgent profile control measures to enhance oil recovery. Conventional polyacrylamide organic gels fail under the prevailing high-temperature (130 °C) and high-salinity conditions, characterized by divalent cation (Ca 2 ⁺ and Mg 2 ⁺) concentrations of 5650 mg/L. This study developed a robust gel profile control system specifically engineered for such challenging environments. Key parameters including polymer and crosslinker concentrations, gel pH, and temperature were systematically optimized to ensure stability under high temperature and salinity. The optimized formulation demonstrates exceptional stability in seawater at 130 °C, with a gelation activation energy of 88.2 kJ/mol. Incorporating nanosilica significantly enhanced the gel's thermal stability, salinity tolerance, and shear resistance. Scanning electron microscopy (SEM) revealed a strengthened network microstructure. The system exhibits favorable injectivity in 1.4 Darcy permeability cores. Nanosilica reinforcement dramatically increased the gel's breakthrough pressure gradient from 3.45 MPa/m to 34.7 MPa/m. Crucially, the addition of 0.02% nanosilica extended the polyacrylamide gel's functional stability from 70 days to 95 days. This nanosilica-reinforced system offers superior long-term stability and plugging performance, presenting a viable profile control and water-shutoff technology for offshore high-temperature, high-salinity seawater reservoirs.
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