Journal of Colloid and Interface Science 229, 550–553 (2000) doi:10.1006/jcis.2000.7011, available online at http://www.idealibrary.com on Silver Nanoparticles by PAMAM-Assisted Photochemical Reduction of Ag + S´ andor K´ eki, ∗ J´ anos T¨ or¨ ok, ∗ Gy¨ orgy De´ ak, ∗ Lajos Dar´ oczi,† and Mikl´ os Zsuga ∗,1 ∗ Department of Applied Chemistry, and †Department of Solid State Physics, University of Debrecen, H-4010 Debrecen, Hungary Received February 11, 2000; accepted June 5, 2000 The photochemical synthesis of Ag(0) nanoparticles in the pres- ence of amino- and carboxylate-terminated PAMAM dendrimers is reported. The formation of Ag(0) nanoparticles was followed spectrophotometrically and by transmission electron microscopy (TEM). According to TEM investigations Ag(0) nanoparticles with the average size of about 7 nm in diameterwere produced. Based on the present investigation a possible mechanism for the Ag(0) nanoparticles formation is proposed. C  2000 Academic Press Key Words: PAMAM dendrimers; photochemical reduction; silver nanoparticles. 1. INTRODUCTION Synthesis and characterization of nanometer size metal par- ticles and composites have attained great consideration (1–3) owing to their optical, electric, and catalytic properties (4, 5). Many methods have been elaborated for the preparation of metal particles and composites in nanometer scale. The application of different dendrimers has opened a new way of producing metal particles with small size and narrow particle distribution. By varying the composition and the size of the dendrimers, differ- ent metallodendrimers have been obtained (6–13). This proce- dure is based on the complexation of dendrimers with different metal ions followed by selective chemical reduction of the metal ions. A representative example of preparing metal particles is the complexation of PAMAM (polyamido amine) (Scheme 1). With Cu 2+ and the reduction of the complex with hydrazine, Cu(0)-containing PAMAM denrimers (13) were obtained. It is surprising that photochemical methods have not been reported to produce metallic nanoparticles in the presence of dendrimers. In this paper we present a photochemical method for pro- ducing silver nanoparticles of about 7 nm in diameter and with narrow particle-size distributions by means of UV irradiation using amino- and carboxylate-terminated PAMAM dendrimers. The aim of this work is to study the possibilities of produc- ing nanoparticles whose size is controlled by the functional- ity and the size of the dendrimer. Also, the UV irradiation method permits continuous control of the concentration of the 1 To whom correspondence should be addressed. particles formed without the addition of reducing agents to the system. 2. EXPERIMENTAL Materials. Amino-(G-4) and carboxylate-terminated (G- 3.5) PAMAM Starburst dendrimer (14) and AgNO 3 (analytical grade, Aldrich, Germany) were used as received. Instruments. A 30-W column-like mercury lamp (λ = 254 nm) was used as an UV irradiation source. The UV-VIS mea- surements were performed with a HP-8453 diode-array spec- trophotometer. The TEM micrographs were taken from a JEOL 2000 FX-II-type electron microscope. TEM sample preparation. Solution containing Ag nanopar- ticles was dried on a glass surface and then coated with an ap- proximately 20-nm-thick carbon layer. This layer with the em- bedded Ag particles was floated off the glass in distilled water and then mounted on microgrid for TEM observation. Experimental setup. (a) Ten-milliliter aqueous solutions of the PAMAM dendrimers (1 × 10 −5 –1 × 10 −4 M) were titrated with 0.1 M AgNO 3 solution and monitored by UV-VIS spec- troscopy. (b) To the aqueous solutions of the PAMAM den- drimers 10 ml (1 × 10 −5 –1 × 10 −4 M) of AgNO 3 was added in different molar ratios and then irradiated with UV light. Af- ter a predetermined time interval, a sample was taken from the solution, and it was investigated by UV-VIS spectroscopy and TEM. During irradiation N 2 was bubbled through the solution. 3. RESULTS AND DISCUSSION The spectrophotometric traces upon titration of the solution of the amino- and the carboxylate-terminated PAMAM den- drimers with a AgNO 3 solution are shown in Fig. 1. On the ba- sis of the titration curves, monitored by UV-VIS spectroscopy, it can be concluded that for the amino-terminated PAMAM 32– 35 Ag + ions/dendrimer complexes were formed, and for the carboxylate-terminated PAMAM 95–100 Ag + ions/dendrimer complexes were formed. The observed 32–35 Ag + ions/dendrimer ratio (with the amino-terminated PAMAM dendrimer) can be explained by tak- ing into account that the PAMAM dendrimer (G-4) contains 550 0021-9797/00 $35.00 Copyright C  2000 by Academic Press All rights of reproduction in any form reserved.