Synthesis of Au, Ag, and Au-Ag Bimetallic Nanoparticles Using Pulicaria undulata Extract and Their Catalytic Activity for the Reduction of 4-Nitrophenol.

Merajuddin Khan,Wolfgang Tremel,Zainab Liaqat,Mujeeb Khan,Abdulrahman Al-Warthan,Mihail Mondeshki,Khaleel Al-Hamoud,Mohammed Rafi Shaik,Syed Farooq Adil,Mufsir Kuniyil,Mohammed Rafiq H Siddiqui,Muhammad Nawaz Tahir,Hamad Z Alkhathlan

doi:10.3390/nano10091885

Abstract

Plant extract of Pulicaria undulata (L.) was used as both reducing agent and stabilizing ligand for the rapid and green synthesis of gold (Au), silver (Ag), and gold–silver (Au–Ag) bimetallic (phase segregated/alloy) nanoparticles (NPs). These nanoparticles with different morphologies were prepared in two hours by stirring corresponding metal precursors in the aqueous solution of the plant extracts at ambient temperature. To infer the role of concentration of plant extract on the composition and morphology of NPs, we designed two different sets of experiments, namely (i) low concentration (LC) and (ii) high concentration (HC) of plant extract. In the case of using low concentration of the plant extract, irregular shaped Au, Ag, or phase segregated Au–Ag bimetallic NPs were obtained, whereas the use of higher concentrations of the plant extract resulted in the formation of spherical Au, Ag, and Au–Ag alloy NPs. The as-prepared Au, Ag, and Au–Ag bimetallic NPs showed morphology and composition dependent catalytic activity for the reduction of 4-nitrophenol (4-NPh) to 4-aminophenol (4-APh) in the presence of NaBH4. The bimetallic Au–Ag alloy NPs showed the highest catalytic activity compared to all other NPs.

Highlights

Silver and gold nanoparticles (NPs) have been the focus of research because of their optical and plasmonic properties as well as their unique surface enhanced Raman spectroscopy (SERS) behavior [1,2]
The fast synthesis of Au, Ag, and Au–Ag segregated or alloy NPs at room temperature was achieved with plant extract (PE) of P. undulata as reducing and stabilizing agent
Isotropic Au–Ag alloy NPs and well-defined elemental Au and Ag NPs were obtained at high PE concentrations

Summary

Introduction

Silver and gold nanoparticles (NPs) have been the focus of research because of their optical and plasmonic properties as well as their unique surface enhanced Raman spectroscopy (SERS) behavior [1,2] These properties depend on particle composition, size, and morphology, which can be used for applications in diagnostics, as biosensors, and in catalysis [3,4]. These NPs are biocompatible and widely used in different biological applications, there is still demand for the development of other methods that are low cost and scalable In this contribution, the use of plant extracts, being renewable, easy to grow on a mass scale, and environmentally benign, have caught the attention of the researchers [14,15,16]. For Au and Ag solutionStso,ctkhesosltuotcioknsoolfutthioenmsewtaelrperpecruerpsaorresdanbdyPtaEksiwnger1e0pmrepmaorel dofinthMeilrlei-sQpewctaitveer.mFoertaAluparencduArsgors (HsAouluCtilo4n×s,3tHhe2OstoacnkdsAolguNtioOn3s) wine1re0 pmreLpoafrewdabteyr.taTkhinegP1E0smtomckolsoolfutthioenrewspaescptirveepmareetdalbpyredciussrosolvrsing 10 (mHAg uoCf lP4 E× 3inH21OmanLdoAf gMNiOlli3-)Qinw10atmerL. oAf uw,aAtegr.,TahnedPAE ust–oAckgsNolPustiownewreaspprerpepaarereddbbyy tdaikssinolgvi1ngmL of 1th0emrgesopfePcEtivine1stmoLckosfoMluiltliio-Qnswaantedr.wAaus, mAgix, eadndwAituh–eAigthNerP0s.w2 emreLporfepthaerePdEbysotaluktiinogn1(mterLmoef dthleow conrecsepnetcrtaivtieonst(oLcCk )soofluPtiEo)nsoran0.d4 wmaLs omf iPxEedstwocitkh (teeitrhmered0.h2igmhLerocfotnhceenPtEratsioolnuti(oHnC()t)erfomlleodwleodwby adcdointicoenntorfat1i0onm(LLCo)f oMf iPllEi-)Qorw0a.t4ermiLn aofsmPEalsltgoclakss(tebromtteled. hTihgheesrolcuotnicoennstrwateiorens(tHirCre)d) fsollolowwlyedwbityh a maagdndeittiiocnstoirfr1e0r amt LrooofmMtiellmi-Qpewraattuerreinunatislmnaollfuglratshserboctotlloe.rTchheansgoleuoticocnusrrweedr.e stirred slowly with a maFgonreAticusNtirPresr, tahterocoomlorteomf ptheerastoulruetuionntilgnraodfuuartlhlyercchoalnogr ecdhafnrogme olcicguhrtreyde.llow to purple within 2 h, which iFnodriAcauteNdPtsh,ethreedcoulcotrioonf tohfe Asoulu3+tioton Agruad0.uFalolyr AchganNgPeds tfrhoemcolilgohrtoyfetlhloewsotoluptuiorpnlechwainthgiend2fhro, m colwcoorhlloiecrshlsestinos dtdoicadarktaerdyketylhleoelwlorewwduiwtchittiihnoinn oh2f.hAT. huTe3h+eptorporAgorguer0s.essFsoofortfAhtehgerNeraePcastcittoihonenwcwoalasosmrmoofonntihtioteorerseoddluinitniorreneggucuhlalaarnrignientdteerrfvrvaoalmlssby UVbyspUeVctrsopseccotrpoys.copy

Preparation of Au–Ag Alloy Nanoparticles

Characterization

Results and Discussions

Effect of Concentration of PE on the Size and Morphology of NPs

Catalytic Application

Conclusions