Search

The photocatalytic activity of nano titanium dioxide (TiO2) on aqueous commercial dyes such as methylene blue (MB) is widely reported in literature. However, similar photocatalytic studies carried out in non-aqueous solvents are scarce. A series of ethanolic MB solutions were irradiated by ultraviolet (UV) radiation in the presence of TiO2. Effects of exposure time, adsorbate concentration and dispersion medium were considered. UV–Visible (UV–Vis) spectrophotometry and Fourier transform infrared spectroscopy were employed for characterization. The results show that photocatalytic activity of TiO2 on MB strongly depends on the dispersion medium. Contrary to the photocatalytic degradation of dyes that is generally seen in the aqueous medium, we report for the first time a photoinduced reversible adsorption of MB on nano TiO2 in ethanol. We further demonstrate that our newly reported phenomenon is mediated by the photocatalytic degradation of ethanol of which its resultant intermediates temporarily modify the nano TiO2 surface. Hence, our experimental findings differentiate photoinduced adsorption and photocatalytic degradation, where nano TiO2 acts an adsorbent and a catalyst, respectively. [ABSTRACT FROM AUTHOR]

Recently, graphene oxide (GO) and reduced graphene oxide (rGO) have drawn significant attention in the development of gas sensors and nanocomposites. However, random distribution of oxygen functionalities in GO and rGO limits the use of these materials in the above application. In this study, methylene blue (MB) adsorption onto GO, synthesized under different oxidative conditions, and onto corresponding rGO was looked into in detail as both have high affinity towards MB. Our results show the amounts of MB adsorbed onto all GOs are the same irrespective of the time of oxidation. However, significant changes were observed in the amount of MB adsorbed on the corresponding rGOs that have been thermally reduced. Further, the FT-IR spectroscopic data show a blue shift for C=C stretching vibrations of MB adsorbed onto GO, whereas a red shift is observed for the bands assigned to stretching vibrations of C–N and CH3 bending upon adsorption on rGO. The above observations suggest complex structural geometry of GO and rGO, especially with respect to the spatial distribution of oxygen functionalities and their propagation during synthesis that influence MB adsorption, and its orientation. Thus, the information provided will be important in controllable synthesis of both GO and rGO with large surface area for the above applications as well as in applications such as water purification and photocatalysis. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) and reduced graphene oxide (RGO) has gained much attention in the field of gas sensing. However to realize its full potential in this regard, it is important to understand the influence of moisture on GO and RGO. Therefore, in situ and real time monitoring of adsorption and desorption of water molecules on GO and RGO coatings were investigated using quartz crystal microbalance (QCM). Water adsorption were studied under constant relative humidity (RH) levels over a period of time. For both GO and RGO the results show that the adsorption is followed by an equilibrium state. It is shown that for GO the initial rate of water adsorption, the amount of water at the equilibrium and the time to reach the equlibrium vary with RH, where as for RGO no such variations were observed. These observations indicate that at low RH adsorption is primarily throught surface and the edges where as at high RHs water penetrate into the intersitial layers of GO. Thus the latter becoming the rate limiting step for water adsorption at high RH. The results also elucidate on the contribution of surface oxygen functional groups towards the water adsorption rate and the amount adsorbed. The above results provde important information that can be used during GO-based sensor design and calibration. [ABSTRACT FROM AUTHOR]