A Comparative Investigation on Structural and Chemical Differences between the Pith and Rind of Sunflower Stalk and Their Influences on Nanofibrillation Efficiency.

The structure and chemical composition of cell walls play a vital role in the bioconversion and utilization of plants. In the present study, the cell wall structure and chemical composition of pith and rind from sunflower stalks were compared and correlated to their nanofibrillation efficiency with ultrasonic treatment. Mild chemical pretreatment using 1% or 4% NaOH without any bleaching process were applied prior to ultrasonication nanofibrillation. Significant structural and chemical differences were demonstrated between the pith and rind, with the former exhibiting a much lower lignin and hemicellulose contents, higher pectin, much looser cell structure and higher cell wall porosity than the latter. Alkaline treatment alone was sufficient to eliminate most of the hemicellulose and pectin from stalk pith, whereas only partial removal of hemicellulose and lignin was achieved for the woody rind part. After 30 min of ultrasonic treatment, the stalk pith exhibited fully defibrillated fibrils with a continuous and entangled micro/nanofibrillated network, whereas numerous micron-sized fiber and fragments remained for the rind. The results indicated that stalk pith is less recalcitrant and easier to be fibrillated with ultrasonication than rind, which must be correlated to their distinct differences in both structure and chemical composition.

Sunflower-Stalk-Based Solar-Driven Evaporator with a Confined 2D Water Channel and an Enclosed Thermal-Insulating Cellular Structure for Stable and Efficient Steam Generation.

Given the worsening freshwater scarcity around the world, the interfacial solar-driven steam generation for seawater desalination and wastewater treatment has attracted wide attention due to its rich energy resources, convenience, and environmental friendliness. However, challenges still remain for developing high-efficiency interfacial solar-driven steam generation devices from low-cost, readily available, and green material resources. Herein, taking advantage of the delicate composite structure of the sunflower stalk, a sunflower-stalk-based solar-driven evaporator with a confined two-dimensional (2D) water supply pathway and an enclosed thermal-insulating structure is reported. The pith of sunflower stalks is composed of well-arranged honeycomb-like parenchyma cells that endow sunflower stalks with low thermal conductivity comparable to that of synthetic plastic foam. The low-tortuosity vascular bundles in the skin can serve as a natural 2D water pathway for rapid water transportation. The benefit of these functions is that an evaporator based on a carbon-nanotube-coated sunflower stalk (C-Ss) achieves a high evaporation rate of 1.76 kg m-2 h-1 under 1 sun irradiation (1 kW m-2). The C-Ss also shows a highly stable evaporation performance, high ion rejection efficiency, and a self-cleaning ability during the actual seawater desalination process. With advantages of abundant resources, easy fabrication, and sustainability, this C-Ss-based evaporator provides a promising choice for freshwater production in developing regions.