## 1 Introduction  
Various food products are sensitive to the external environment such as microbial attack [1] and deterioration by atmospheric oxygen [2]. These inevitably result in depreciation and a decrease in consumers' preference [3]. Antimicrobial packaging has been suggested by introducing nanoclays or antibacterial moiety in the film [1, 4, 5]. Meanwhile, many researchers have studied gas barrier packaging or oxygen-scavenging materials enclosed in packaging. [PERSON] et al. reported that polylactide film with 40 bilayer coating of montmorillonite/chitosan reduced oxygen permeability by about 90-95% at 20-50% relative humidity (RH) [6]. The preparation of carboxmethylated microfibrillated cellulose film was suggested to achieve low oxygen permeability at low RH by [PERSON] et al. [7]. Another oxidation prevention strategy is to introduce oxygen-scavenging materials such as iron-based powder (iron oxide, ferrous carbonate and metallic platinum) [8, 9], ascorbic acid with metal catalyst [10], and an enzyme combination (glucose oxidase and catalase) into food packaging [8]. Those oxygen scavengers are usually applied in the form of a sachet or film coating for the freshness of oxygen-sensitive food [9, 11, 12]. However, there still remain several limitations in the aforementioned approaches. Although oxygen barrier film is effective to prevent O\({}_{2}\) access, only small damage in the film resulted in the failure of O\({}_{2}\) prevention. Oxygen scavengers like iron oxides requires relatively high humidity for their action [8; 13]. Other scavengers like ascorbic acid or an enzyme combination are relatively expensive and not easy to deal with in a packaging process due to their environmental sensitivity (pH, salt condition, temperature and etc.) [8; 10]. Therefore, we tried to prepare an alternative oxygen scavenger which has a low precursor price, controllable oxidation-reduction property, etc. Green rust (GR) is a kind of layered nanomaterial consisting of Fe\({}^{2+}\)/Fe\({}^{3+}\) mixed hydroxide layers and interlayer anion (Cl\({}^{-}\), CO\({}_{3}\)\({}^{2-}\) and SO\({}_{4}\)\({}^{2-}\)) along with water. The structure is an analogue of layered double hydroxide, which is often referred to as an anionic nanoclay. The chemical composition of GR is similar to that of iron oxide; however, (1) its layered structure provides a larger surface for oxidation-reduction at the Fe\({}^{2+}\)/Fe\({}^{3+}\) centers than iron oxide; and (2) the intrinsic water moiety along the hydroxide layer enabled a facilitated oxidation-reduction reaction. In fact, the Fe\({}^{2+}\) in GR is quickly oxidized to Fe\({}^{3+}\) in the presence of O\({}_{2}\) to produce the goethite (FeOOH) phase. Thus, GR has high potential to capture O\({}_{2}\) in food packaging as an oxygen-scavenging material. The only limitation of GR is its fast oxidation rate under the existence of O\({}_{2}\), and thus GR itself can only be utilized as an O\({}_{2}\) scavenger for short-term utility. In order to overcome this problem and to control the oxidation-reduction reaction of GR, we tried to hybridize GR with a conducting polymer, poly(3,_A_-ethylenedioxythiophene) (PEDOT): poly(4-styrenesulfonate) (PSS), which have high electrical conductivity, transparency and thermal stability [14; 15]. As the reduction potential of the conducting polymer would be slightly higher than Fe\({}^{2+}\), the polymer would retard the oxidation rate of GR. Furthermore, the electron donor-acceptor behavior between GR and the conducting polymer would control the oxidation rate of GR. In this study, we prepared GR with general anion, SO\({}_{4}\)\({}^{2-}\), and conducting polymer (PEDOT:PSS), to compare the oxygen-scavenging property depending on the interlayer anion. In particular, GR with a SO\({}_{4}\)\({}^{2-}\) interlayer anion (GR-SO\({}_{4}\)) was selected as reference sample of GR without a conducting polymer, as GR-SO\({}_{4}\) is the most widely studied green rust in terms of structure and synthetic method.