Thach-Nguyen Roya, Lam Hoa-Hung, Phan Hong-Phuong, Dang-Bao Trung
Faculty of Chemical Engineering, Ho Chi Minh City University of Technology (HCMUT) 268 Ly Thuong Kiet Street, District 10 Ho Chi Minh City Vietnam
Vietnam National University Ho Chi Minh City Linh Trung Ward, Thu Duc City Ho Chi Minh City Vietnam.
RSC Adv. 2022 Dec 12;12(54):35436-35444. doi: 10.1039/d2ra06689k. eCollection 2022 Dec 6.
As the most abundant natural biopolymer on earth, celluloses have long-term emerged as a capable platform for diverse purposes. In the context of metal nanoparticles applied to catalysis, the alternatives to traditional catalyst supports by using biomass-derived renewable materials, likely nanocelluloses, have been paid a great effort, in spite of being less exploited. In this study, cellulose nanocrystals were isolated from corn leaf chemical treatment involving alkalizing, bleaching and acid hydrolysis. The crystallinity of obtained cellulose was evaluated in each step, focusing on the effects of reactant concentration and reaction time. Cellulose nanocrystals were characterized by powder X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), evidencing the presence of cellulose nanospheres (crystallinity index of 67.3% in comparison with 38.4% from untreated raw material) in the size range of 50 nm. Without using any additional surfactants or stabilizers, silver nanoparticles (AgNPs) well-dispersed on the surface of cellulose nanocrystals (silver content of 5.1 wt%) could be obtained by a simple chemical reduction using NaBH at room temperature. The catalytic activity was evaluated in the selective reductions of 4-nitrophenol towards 4-aminophenol and methyl orange towards aromatic amine derivatives in water at room temperature. The effects of catalyst amount and reaction time were also studied in both reduction processes, showing near-quantitative conversions within 5 minutes and obeying the pseudo-first-order kinetics, with the apparent kinetic rate constants of 8.9 × 10 s (4-nitrophenol) and 13.6 × 10 s (methyl orange). The chemical structure of the catalytic system was found to be highly stable during reaction and no metal leaching was detected in reaction medium, evidencing adaptability of cellulose nanocrystals in immobilizing noble metal nanoparticles.
作为地球上最丰富的天然生物聚合物，纤维素长期以来一直是一个适用于多种用途的优良平台。在应用于催化的金属纳米颗粒的背景下，尽管对使用生物质衍生的可再生材料（可能是纳米纤维素）替代传统催化剂载体的研究较少，但人们已经付出了巨大努力。在本研究中，通过碱化、漂白和酸水解等化学处理从玉米叶中分离出纤维素纳米晶体。在每个步骤中评估所得纤维素的结晶度，重点关注反应物浓度和反应时间的影响。通过粉末X射线衍射（XRD）、傅里叶变换红外光谱（FT-IR）、透射电子显微镜（TEM）对纤维素纳米晶体进行表征，证明存在尺寸范围为50nm的纤维素纳米球（结晶度指数为67.3%，而未处理的原料为38.4%）。在不使用任何额外表面活性剂或稳定剂的情况下，通过在室温下使用硼氢化钠（NaBH）进行简单的化学还原，可以获得均匀分散在纤维素纳米晶体表面的银纳米颗粒（AgNPs）（银含量为5.1wt%）。在室温下于水中将4-硝基苯酚选择性还原为4-氨基苯酚以及将甲基橙还原为芳香胺衍生物的过程中评估了催化活性。在两个还原过程中还研究了催化剂用量和反应时间的影响，结果表明在5分钟内转化率接近定量，并且符合准一级动力学，4-硝基苯酚的表观动力学速率常数为8.9×10⁻³s⁻¹，甲基橙的表观动力学速率常数为13.6×10⁻³s⁻¹。发现催化体系的化学结构在反应过程中高度稳定，并且在反应介质中未检测到金属浸出，这证明了纤维素纳米晶体在固定贵金属纳米颗粒方面的适用性。
