Green Construction And Properties Of Lignin-Noble Metal Nanoparticle Composites

Currently, environmental problems have become more and more severe, as well as the shortage of fossil resources. Under these circumstances, the utilization of renewable resources into novel functional materials has not only drawn scientists’ attention in material science area, but also caused the social concerns. Lignin, which is one of the main components of plant cell walls, is the most abundant aromatic polymer in nature. However, lignin is usually served for low-cost utilizations due to the complexity of the amorphous three-dimention structure and the physicochemical properties. In order to fulfill the real value of lignin, the green construction of lignin-based noble metal nanocomposites was developed, and the nancomposites with various properties were used in the fields of environmental protection, energy, catalysis and so on, via new strategies and technologies. The main researches are described as follows: 1. Versatile lignin-AuNPs composites for application as novel liquid marblesGold nanoparticles(AuNPs) have broad applications in electronic, photodynamic therapy, sensor, diagnosis and so on. The application of multifunctional AuNPs via combination strategy is still of significance. This work reports the optimal synthesis and properties of versatile lignin-AuNPs composites. By tuning the synthesis condition, lignin-based AuNPs can be well obtained, and the optimum condition for green synthesis of Au NPs with lignin was a ratio of 150 mg of lignin to 0.375 mmol of HAuCl4, a reaction temperature of 80 °C, and an irradiation time of 60 min. The as-prepared lignin-Au NPs composites demonstrate excellent photothermal conversion property, as well as visual detection and adsorption towards Pb2+, which can simultaneously detect and adsorb Pb2+ via co-precipitation. More importantly, a novel near infrared(NIR)-responsive lignin-AuNPs liquid marble is fabricated for the first time. The lignin-AuNPs liquid marbles combine both the photothermal conversion and Pb2+ detection/adsorption properties of lignin-AuNPs composites. This study proposes an emerging strategy for the application of multifunctional AuNPs. 2. Pd nanoparticles-supported porous carbon: A hydrogen adsorbent integratingthe reducing reactivity and carbon-rich framework of ligninThe efficient utilization of materials in synthetic process is one of the most significant principles in Green Chemistry. This study proposes a greener strategy to synthesize Palladium nanoparticles(PdNPs)-supported porous carbon for hydrogen storage, utilizing both the chemical reactivity and the carbon-rich 3D framework of lignin. Firstly, PdNPs were synthesized in a green pathway using lignin as reducing and stabilizing agents. The results revealed a well dispersion of spherical PdNPs in uniform size of ~8 nm. Afterwards, the PdNPs-supported porous carbons were prepared in one pot, with lignin and Pd(NH3)2Cl2 as reagents, nano SiO2 as hard-template, followed by carbonization and removal of the template. The characterization results implied a positive effect of template ratio and carbonization temperature, as well as Pd precursor dosage on the development and hierarchical texture of the porous structure. Furthermore, the hydrogen storage capability of the PdNPs-supported porous carbon was evaluated and demonstrated a high uptake of 3.98 wt. %(77K, 180 bar), proving it a promising hydrogen adsorbent. 3. New strategy to fabricate iron-free magnetic catalyst based on lignin-reduced Au-Pd nanoalloys and its catalytic performanceThis study described a new strategy to fabricate a magnetic catalyst via facilely ―sticking‖ the Au-Pd nanoalloys catalysts onto a commercial magnetic stirring bar, without the incorporation of iron element. Firstly, the abundant natural ―waste‖ lignin was utilized as both reducing and stabilizing agents to greenly prepare Au-Pd nanoalloys,which were basically core-shell structure, with an Au-rich core and Pd-rich shell, and can be well dispersed in water due to the stabilizing effect of lignin. Furthermore, the fabricated Au1.0-Pd1.0 nanoalloys catalyst exhibited not only excellent catalytic activities in the reduction of 4-nitrophenol(4-NP) to 4-amnophenol(4-AP) by NaBH4, with a rate constant(k) of 0.239 min-1, which was better than Au0.6-Pd1.2, Au1.2-Pd0.6 nanoalloys and four times better than single component Au or Pd nanoparticles. Besides, the reusability of Au-Pd nanoalloys catalyst was also impressed even after seven recycles. Since the catalyst was immobilized on stirring bar, the stirring speed was found to play a positive role in the catalytic reaction. The SEM analysis showed ravines and pores on the surface of lignin-nanoalloys composites, implying the possible mechanism of the catalytic activities. This study not only proves the feasibility of lignin for nanoalloys synthesis, but also proposes a facile and innovated strategy for the fabrication of solid/liquid catalytic platform.