Study On The Method And Principle Of Pycnoporus Sanguineus Boosted Gold Nanoparticles Recovery And Its Application

Noble metal resource is a sparse and important resource in modern society,and it plays a vital role in modern industry due to its excellent properties,thus it is called as the vitamin of modern industry and widely applied in the fields of electronics,sensor,biomedicine and jewelry,which inevitably led to large amount of noble metal containing wastes,recovering noble metal from these wastes is an important task and research hotspot in the environment field.Conventional recovery methods such as chemical precipitation,solvent extraction,ion exchange,activated carbon and resin adsorption suffered from many disadvantages including high costs and secondary environmental pollution.Microbial recovery is easy-operating and environmentally benign and some microorganisms can even convert the recovered noble metal to noble metal nanoparticles,which favor the harmlessness and reutilization of wastes and are acknowledged to be promising in the field of noble metal resource recycling.In this dissertation,we employed Pycnoporus sanguineus to recover gold as gold nanoparticles(AuNPs)and explored the catalytic performance of the recovered AuNPs.Firstly,we tried to establish P.sanguineus boosted gold biorecovery process.Secondarily,we investigated the biosorption pattern and mechanism during the P.sanguineus boosted sorption and reduction coupled gold biorecovery process.Thirdly,based on the important contribution of amino group during the gold biorecovery process,we intensified this process by increasing amino group content on biomass surface through microbial surface modification.Lastly,we explored the catalytic performance of the recovered AuNPs in p-nitroaniline(p-NA)degradation and oxygen reduction reaction.The detailed conclusions are as follows:(1)Intracellular protein extract(IPE)and fungal biomass of P.sanguineus could effectively recover gold ions as highly crystalline AuNPs without any exogenous electron donor.The results of batch experiments indicated that IPE addition,initial gold ions concentration,solution pH and biomass dosage affected both the recovery efficiency of gold ions and the morphology and dimension of the recovered AuNPs.With the increase in IPE addition or biomass dosage,the recovery efficiency of gold ions increased and the recovered AuNPs exhibited smaller particle size and more uniform particle size distribution.Higher initial gold ions concentration led to lower gold ions recovery efficiency and AuNPs with larger particle size.Raising solution pH favored the obtainment of AuNPs with uniform particle size distribution and small particle size,but not favored gold ions recovery.With identical recovery conditions,fungal biomass showed higher gold ions recovery efficiency,the IPE recovered AuNPs possessed better dispersity,while the fungal biomass recovered AuNPs mainly deposited in cytoplasm.(2)The results of optimization experiments showed that the biosorption efficiency of P.sanguineus for gold ions was affected by biomass dosage,solution pH,initial gold ions concentration and biosorption temperature,among which solution pH and biosorption temperature affected greatly.With initial gold ions concentration and biosorption temperature of 1.0 mM and 30?,biomass dosage and solution pH were optimized to be 2.0 g/L and 4.0,and the biosorption efficiency reached 95.30%.With optimized biomass dosage and solution pH and biosorption temperature of 30?,biosorption reached equilibrium in 4.0,8.0 and 12.0h when initial gold ions concentrations were controlled as 1.0,2.0 and 3.0 mM respectively.Fitting analysis of experimental data showed that the biosorption process of P.sanguineus for gold ions could be well described by pseudo-second order kinetics model(R~2=0.9340-0.9988)and Langmuir isotherm model(R~2=0.9702-0.9958),and the maximum biosorption capacity reached as high as 358.69 mg/g?Further researches by Fourier transform infrared spectra and X-ray photoelectron spectra analysis and functional group masking experiment verified the positive roles of hydroxyl,carboxyl and amino groups during biosorption process with the contribution order of amino>carboxyl>hydroxyl.(3)Based on the important contribution of amino group during the P.sanguineus boosted gold biorecovery process,microbial surface modification was attempted to increase amino group content on biomass surface,thus to intensify this process.Qualitative analysis and quantitative measurement indicated that microbial surface modification increased its amino group content on biomass surface from 1.29 to 2.81 mmol/g.Scanning electron microscopic observation showed that microbial surface modification changed its surface morphology from smooth surface with some branched structure to layered stacking structure with many pores and irregular protrusions.By comparing the gold biosorption process boosted by modified biomass and pristine biomass,microbial surface modification significantly accelerated the gold biosorption process(P=0.000<0.01).With biomass dosage of 2.0 g/L,solution pH of4.0,biosorption temperature of 30?,and initial gold ions concentrations of 1.0,2.0 and 3.0mM,biosorption equilibrium time was 0.5,3.0 and 5.0 h when modified biomass was employed,which was 12.5%,37.5%and 41.7%of those in the case of pristine biomass.Meanwhile,biosorption rate constants correspondingly increased to 11.2,3.1 and 3.7 folds after microbial surface modification.Biosorption isotherm study at 30?indicated that microbial surface modification increased its maximum gold biosorption capacity to 1.3 folds and enhanced the affinity between biomass and gold heavily.What's more,microbial surface modification favored the subsequent gold ions reduction and AuNPs formation.The change of biomass surface morphology and the increase in the amino group content on biomass surface after microbial surface modification were postulated to be the inner impetus for the intensification of the P.sanguineus boosted gold biorecovery process(4)The results of catalytic experiments indicated that P.sanguineus IPE recovered AuNPs could effectively catalyze the degradation of p-nitroaniline(p-NA)and P.sanguineus biomass recovered Au NPs exhibited high catalytic activity in the oxygen reduction reaction(ORR)after calcination.During the catalytic degradation of p-NA,0.197 mg,0.0197 mg and0.00197 mg of AuNPs with average size of 6.07 nm could catalyze the complete degradation of 12.5?mol of p-NA within 3 min,6 min and 40 min,respectively.In the ORR catalytic activity measurement,electrocatalyst of Au@NC was fabricated by calcining Au NPs supported P.sanguineus biomass at 900?for 2.0 h under Ar atmosphere.The electrochemical measurement of Au@NC in an oxygen-saturated 0.1 M KOH solution showed an onset potential of+0.97 V and an electron transfer number involved in ORR of3.86,which were comparable to those of commercial 20 wt%Pt/C.Meanwhile,Au@NC exerted excellent tolerance toward methanol and long-term stability.