Center for Complex Fluids Engineering, Department of Chemical Engineering , Carnegie Mellon University , Pittsburgh , Pennsylvania 15213 , United States.
Department of Chemical Engineering , The Pennsylvania State University , University Park , Pennsylvania 16802 , United States.
Langmuir. 2018 Apr 24;34(16):4852-4860. doi: 10.1021/acs.langmuir.8b00191. Epub 2018 Apr 13.
Motivated by the proposed use of cationic protein-modified sand for water filtration in developing nations, this study concerns the adsorption of Moringa oleifera seed proteins to silica surfaces. These proteins were prepared in model waters of varying hardness and underwent different levels of fractionation, including fatty acid extraction and cation exchange chromatography. Adsorption isotherms were measured by ellipsometry, and the zeta potentials of the resulting protein-decorated surfaces were measured by the rotating disk streaming potential method. The results indicate that the presence of fatty acids has little effect on the M. oleifera cationic protein adsorption isotherm. Adsorption from the unfractionated extract was indistinguishable from that of the cationic protein isolates at low concentrations but yielded significantly greater extents of adsorption at high concentrations. Adsorption isotherms for samples prepared in model hard and soft fresh waters were indistinguishable from each other over the measured bulk solution concentration range, but adsorption from hard or soft water was more extensive than adsorption from deionized water at moderate protein concentrations. Streaming potential measurements showed that adsorption reversed the net sign of the zeta potential of silica from negative to positive for all protein fractions and water hardness conditions at protein bulk concentrations as low as 0.03 μg/mL. This suggests that sands can be effectively modified with M. oleifera proteins using small amounts of seed extract under various local water hardness conditions. Finally, ellipsometry indicated that M. oleifera proteins adsorb irreversibly with respect to rinsing in these model fresh waters, suggesting that the modified sand would be stable on repeated use for water filtration. These studies may aid in the design of a simple, effective, and sustainable water purification device for developing nations.
受阳离子蛋白修饰砂在发展中国家用于水过滤的应用启发，本研究关注了辣木籽蛋白在二氧化硅表面的吸附。这些蛋白是在不同硬度的模型水中制备的，并经历了不同程度的分级分离，包括脂肪酸提取和阳离子交换层析。通过椭圆光度法测量了吸附等温线，并用旋转圆盘流动电势法测量了所得蛋白修饰表面的动电电位。结果表明，脂肪酸的存在对辣木阳离子蛋白吸附等温线几乎没有影响。在低浓度下，未分级提取物的吸附与阳离子蛋白分离物的吸附无法区分，但在高浓度下，吸附量显著增加。在测量的总溶液浓度范围内，模型硬水和软水制备的样品的吸附等温线彼此无法区分，但在中等蛋白浓度下，硬水或软水的吸附比去离子水的吸附更广泛。流动电势测量表明，在所有蛋白级分和水硬度条件下，吸附将二氧化硅的动电电位的净符号从负变为正，蛋白总浓度低至 0.03μg/mL。这表明，在各种当地水硬度条件下，可以使用少量种子提取物有效地用辣木蛋白修饰砂。最后，椭圆光度法表明，辣木蛋白在这些模型新鲜水中的冲洗过程中不可逆地吸附，这表明改性砂在重复用于水过滤时将是稳定的。这些研究可能有助于设计用于发展中国家的简单、有效和可持续的水净化装置。
