(421a) A Template-Free Solution-Phase Synthesis of Novel Two-Dimensional a-Quartz Nanoplates and Their Applications in Energy-Saving, High-Efficient Microalgal Biorefinery

Silica is one of the fundamental mineral components found in the earth’s crust. It has been used to make products for industrial and engineering materials and also used for technological applications such as potential electrode materials in the rechargeable battery and optoelectronic and sensing devices. One of the commonly occurring phases of crystalline silica is α-quartz. There have been reports of synthesizing α-quartz nanocrystals whose sizes typically range from hundreds of micrometers down to tens of nanometers. However, tuning their sizes, shapes, and morphologies has not been well demonstrated because many aspects of their formation process have yet to be explored systematically.

Herein, we present a facile hydrothermal synthetic route for preparing novel α-quartz nanoplates (NPLs) from amorphous silica nanoparticles. As-synthesized NPLs were characterized employing XRD, AFM, SEM, TEM, and electron diffraction measurements exhibiting a highly crystalline phase of α-quart with an average lateral size and thickness of 1.14 ± 0.32 mm and 7.7 ± 0.6 nm, respectively. XPS, FT-IR, TGA/DTA, Raman, and ²⁹Si solid state NMR spectroscopy confirmed their unique physicochemical properties based on their characteristic anisotropic nanostructures. Efficient extraction of highly valuable chemicals, for example, astaxanthin (ATX), by α-quartz NPL from microalgae cell Haematococcus pluvialis (H. pluvialis) was successfully demonstrated through laceration of the cell wall by α-quartz NPL, as a nanoscale scalpel, under facile ultrasonic conditions. ATX extraction efficiency of ~99% with < 5 min rapid ultrasonication, as well as minimal cellular damage, could be achieved via α-quartz NPLs assisted harvest processes. Understanding the potential mechanism of their formation, “nanorazor” effect, and extraction of ATX from H. pluvialis represents a meaningful step toward the goal of delivering highly efficient microalgae harvesting biorefinery processes.

[1] Moon et al. Chem. Eng. J. 413, 12746 (2021).