Green Synthesis Of Lignocellulose/AgNPs Composites And Its Application

Silver nanoparticles(AgNPs) have a special physical and chemical property, and its products have a potential application value in daily life. But the frequently preparing method contains sodium borohydride, which is harmful to environment, leading to the limit of application. Lignocellulose is a kind of abundant and renewable biomass resources, which has a promising future in replace of fossil energy. Lignocellulose contains a large amount of reducing groups, such as reactive hydroxyl, aldehyde groups. The polymers have spatial structure, which can stabilize the nanoparticles. In this work, a green synthesized method of AgNPs was designed with high-value utilization of lignocellulose as reducer and stabilizer, and the optimum condition to synthesize AgNPs was discussed systematically. Meanwhile, the application of the obtained lignocellulose/AgNPs composite for Hg2+ and Cys detection was studied and the AgNPs composites based on biomass were prepared into aerogel with low density and well antibacterial capability. The main contents of this work are listed as below.(1) A rapid method to synthesize AgNPs with 95.59% purity of acetic acid lignin acting as reducer and stabilizer under microwave irradiation was designed. In this chapter, the effect on synthesis of AgNPs by different reaction conditions was discussed, the structural change of lignin before and after preparing AgNPs was researched, and the detection for Hg2+ by obtained lignin/AgNPs composite was studied. The results showed that the synthesized AgNPs were spherical and dispersed well, and their average diameter was about 24 nm. The structure of lignin was mainly connected by β-O-4, β-5, β-β and β-1, in which S and G units were partly disrupted. The side chains of lignin were partly disrupted into small molecules, such as hydrocarbon and alcohol, and the structure of lignin was partly oxidized into carboxyl. Moreover, the obtained AgNPs showed a highly sensitive and selective detection for Hg2+, the color change could be monitoring with naked eye, and the limit of detection(LOD) for Hg2+ was 23 nM.(2) Firstly, the depithing bagasse was treated by washing, extracting with methylbenzene/ethanol, and ball-milling. Then the treated bagasse was extracted by 3% NaOH for 3 h to obtain the bagasse extract(BAE), which was used as reducer and stabilizer during the process of synthesizing well-dispersed AgNPs greenly. In addition, the optimal condition for synthesis of AgNPs and the application of products for Cys detection were discussed. The results demonstrated that the diameters of obtained AgNPs were almost between 18 to 28 nm, and they were capped by BAE, which made them stable and disperse well. The synthesized AgNPs had a highly sensitive and selective detection for Cys with the LOD of 35 nM, the color of AgNPs changed from yellow to orange due to the aggregation after adding Cys, and the recovery in human serum ranged from 102.4~104.6%.(3) Bagasse-AgNPs composites were synthesized by ball-milling bagasse and Tollens’ reagent in alkaline solution under microwave irradiation. Then the synthesized composites were dissolved into EmimAc to prepare biomass-based aerogel, which was utilized to measure the antibacterial capability against B. subtilis, S. aureus, E. coli, and P. aeruginosa. The results revealed that cellulose changed into cellulose II after microwave irradiation, and the crystal structure was disrupted seriously during the process of preparing AgNPs. The synthesized aerogel showed a good antibacterial activity, especially against E. coli, and P. aeruginosa, and its density was 0.035 g/cm3.