## 4 Discussion  
This research aims to prepare green rusts (GRs) with different interlayer anions and to evaluate their structure as well as O\({}_{2}\) scavenging property. As shown in Scheme 1, the GR is composed of 2-dimensional layer and interlayer anions. The layers are composed of interconnected Fe(OH)\({}_{6}\) (either ferrous Fe\({}^{2+}\) or ferric Fe\({}^{3+}\)) octahedrons in an edge-sharing manner. GRs are usually prepared with an interlayer ion of sulfate [20] as shown in Scheme 1a, while other small inorganic acids like carbonate and chloride are possible in the interlayer space [21; 22]. Incorporation of organic moiety or polymers are rare in GR systems; however, recently, we reported that a combination of PSS and polypyrrole could be accommodated in a GR lattice increasing the crystallinity of the host GR [23]. In the current study, we tried to intercalate a combination of conducting polymer (PEDOT:PSS) in order to exploit both the crystallinity increase and electron donation-acceptance property of conducting polymer. Figure 5: Remaining O\({}_{2}\) gas content ratio in airtight container for (**a**) GR-SO\({}_{4}\) and (**b**) GR-PEDOT. As evidenced by X-ray diffractogram (Figure 1), both GRs were successfully prepared with either SO\({}_{4}\)\({}^{2-}\) or PEDOT:PSS interlayer anions. The slightly higher peak intensity and larger crystallite size for GR-PEDOT than GR-SO\({}_{4}\) were attributed to the crystal growth role of the polymer as reported previously [23]. The d-spacing of GR-SO\({}_{4}\) matched other literature well [23], while the d-spacing value of GR-PEDOT, a newly synthesized phase, corresponded to the molecular dimension of PEDOT:PSS. We hypothesized that the benzene moiety of PSS aligned parallel to the GR layer, while the anionic center of sulfonate groups head to the GR layer for charge compensating (Figure 1). As PSS acts as a dopant for PEDOT (Scheme 1b), the PSS and PEDOT moiety would be overlapped in the interlayer space of GR. Taking into account the molecular dimension of PSS and PEDOT, the current d-spacing of 1.08 nm (0.60 nm for gallery height +0.48 nm for GR's layer thickness) suggested that the GR layers were tightly holding the PEDOT:PSS moiety so that the electron transfer between PEDOT and GR layer could be feasible. The positive zeta potential of GR-SO\({}_{4}\) (+6.87 mV) was attributed to the co-existence of Fe\({}^{2+}\) and Fe\({}^{3+}\) in the layer. The layer structure of GR could be understood from the brucite (Mg(OH)\({}_{2}\)) layer. The substitution of Fe\({}^{3+}\) for Fe\({}^{2+}\) in a brucite-like layer, ferrous hydroxide (Fe(II)(OH)\({}_{2}\)), generated an excessive plus charge [24] resulting in positive zeta potential. It was noteworthy that GR-PEDOT had a negative charge surface about \(-\)19.8 mV. According to the previous research of other groups, the surface charge of PEDOT:PSS was negative (around \(-\)80\(\sim\)\(-\)89 mv) at various PSS/PEDOT ratios due to coverage by the negatively charged PSS-rich layer [25; 26]. As the surface of GR-PEDOT would be homogenously covered with PEDOT:PSS, as the polymer does in the interlayer space, the zeta potential inevitably shifted to the negative region. We excluded the possibility that the PEDOT:PSS was simply mixed with GR particles. If that case occurred, the zeta potential of GR-PEDOT would be located in a more negative region (lower than \(-\)19.8 mV) or two peaks, one for PEDOT:PSS and the other for GR, would be observed. The slight negative charge of GR-PEDOT compared with PEDOT:PSS indicated homogeneous hybridization between GR and PEDOT:PSS, hopefully through intercalation and surface coating. The SEM and EDS mapping images also convinced us that homogenous hybridization between PEDOT:PSS and GR was successful in GR-PEDOT (Figure 3 and Figure S2). We could clearly observe the grain of particles in SEM images of both GR-SO\({}_{4}\) and GR-PEDOT. Simple mixing between polymer and GR would result in two different morphologies in the microscopic image.