Biosynthesis Of Gold Nanoparticles By Trichoderma Sp. WL-Go And Their Photocatalytic Application

Gold nanoparticles?AuNPs?has been widely used in the field of biomedicine,biosensor and environmental engineering,due to its unique photoelectric properties and biocompatibility.Comparing with the traditional physical/chemical synthesis,biosynthesis of AuNPs has attracted extensive attention in recent years,because of the green low-toxic process,mild reaction conditions,and non-essential addition of reducing agent and stabilizer.Among the microorganisms for AuNPs synthesis,fungi with rich redox-proteins and high tolerance to environmental pressure,can be considered as a kind of potential dominant microbial resources.However,in the existing research,the fungi for AuNPs synthesis are scarce,of which the mechanism of synthesis is still unclear,limiting the application and development of bio-AuNPs to some extent.Herein,the fungi Trichoderma sp.WL-Go,which has been demonstrated with the ability of AuNPs synthesis previously,was used to further investigate the influence conditions affecting the process of AuNPs synthesis by the strain and its cell-free extracts,and explore the application prospect of bio-AuNPs in the photocatalytic field.The main contents are as follows:The effects of chloroauric acid concentration,pH,cell-free extracts activity and temperature on the synthesis of AuNPs by cell-free extracts of Trichoderma sp.WL-Go were investigated.It was found that the concentration of high-chloroauric acid could synthesize more AuNPs,and the low pH was beneficial to synthesis but not stability of AuNPs.The activity of the extract had no significant effect on the rate and concentration of the synthesized AuNPs,but AuNPs synthesized by inactivated extracts had a faster catalytic rate to 4-nitrophenol reduction.The increase of reaction temperature can accelerate the synthesis speed of AuNPs,and the average particle size of AuNPs synthesized at 30? and 60? is 15.0 nm and 15.1 nm,respectively.The catalytic reduction experiment of 4-nitrophenol proves that 60? synthesis AuNPs presented less adsorption time and a faster catalytic rate.The effect of metal ion induction on the synthesis of AuNPs was explored with AuNPs synthesis by Trichoderma sp.WL-Go induced by different metal ions and application on catalysis of 4-nitrophenol reduction.It was found that the induction of metal ions such as Co²⁺,Sn²⁺,Ni²⁺,Fe³⁺and Cu²⁺increased the concentration of synthesized gold,and the metal ions such as Zn²⁺and Pb²⁺did not promote the synthesis of gold by WL-Go.The incubation of Al³⁺to WL-Go had a certain inhibitory effect on the synthesis of AuNP.The particle sizes of AuNPs synthesized by different metal ions-induced strain WL-Go were all increased,and the morphology was mainly spherical and pseudo-spherical.In addition,the catalytic reduction experiments of 4-nitrophenol showed that AuNPs synthesized by Pb²⁺-induced strain WL-Go had the shortest adsorption time and the fastest catalytic rate of catalysis of 4-nitrophenol reduction.In order to enrich the application fields of bio-AuNPs,the as-synthesized AuNPs were loaded on titanium dioxide?TiO₂?for photocatalytic application research.The results showed that the crystallinity and photocatalytic activity of gold-loaded titanium dioxide?Au/TiO₂?was better after calcination at 500?.The performance of Au/TiO₂?0.019 wt%?synthesized by precipitation method showed a better photocatalytic performance,which could decolorazation more than 90%of methylene blue in 30 min with UV illumination?365 nm?.With the same conditions,the photocatalytic decolorazation of methylene blue took 60 min by TiO₂.In addition,after 2 hours'UV illumination?365 nm?,the photocatalytic decolorazation efficiency of TiO₂ and Au/TiO₂ for methyl orange respectively reached 50.5%and 73.4%.The photocatalytic degradation rates for ciprofloxacin reached 30%and 41.5%,after 5 hours'UV illumination?365 nm?.The results proved that bio-AuNPs effectively enhanced the photocatalytic activity of TiO₂.Besides,after 3 cycles of recovery,the photocatalytic decolorization efficiency of Au/TiO₂ to methylene blue was still 86.2%,which had a good photocatalytic stability.