Effective Removal of Metal ion and Organic Compounds by Non-Functionalized rGO.

Effective removal of heavy metals from water is critical for environmental safety and public health. This work presents a reduced graphene oxide (rGO) obtained simply by using gallic acid and sodium ascorbate, without any high thermal process or complex functionalization, for effective removal of heavy metals. FTIR and Raman analysis show the effective conversion of graphene oxide (GO) into rGO and a large presence of defects in rGO. Nitrogen adsorption isotherms show a specific surface area of 83.5 m2/g. We also measure the zeta-potential of the material showing a value of -52 mV, which is lower compared to the -32 mV of GO. We use our rGO to test adsorption of several ion metals (Ag (I), Cu (II), Fe (II), Mn (II), and Pb(II)), and two organic contaminants, methylene blue and hydroquinone. In general, our rGO shows strong adsorption capacity of metals and methylene blue, with adsorption capacity of qmax = 243.9 mg/g for Pb(II), which is higher than several previous reports on non-functionalized rGO. Our adsorption capacity is still lower compared to functionalized graphene oxide compounds, such as chitosan, but at the expense of more complex synthesis. To prove the effectiveness of our rGO, we show cleaning of waste water from a paper photography processing operation that contains large residual amounts of hydroquinone, sulfites, and AgBr. We achieve 100% contaminants removal for 20% contaminant concentration and 63% removal for 60% contaminant concentration. Our work shows that our simple synthesis of rGO can be a simple and low-cost route to clean residual waters, especially in disadvantaged communities with low economical resources and limited manufacturing infrastructure.

Near full light absorption and full charge collection in 1-micron thick quantum dot photodetector using intercalated graphene monolayer electrodes.

Quantum dots (QDs) offer several advantages in optoelectronics such as easy solution processing, strong light absorption and size tunable direct bandgap. However, their major limitation is their poor film mobility and short diffusion length (<250 nm). This has restricted the thickness of QD film to ∼200-300 nm due to the restriction that the diffusion length imposes on film thickness in order to keep efficient charge collection. Such thin films result in a significant decrease in quantum efficiency for λ > 700 nm in QDs photodetector and photovoltaic devices, causing a reduced photoresponsivity and a poor absorption towards the near-infrared part of the sunlight spectrum. Herein, we demonstrate 1 µm thick QDs photodetectors with intercalated graphene charge collectors that avoid the significant drop of quantum efficiency towards λ > 700 nm observed in most QD optoelectronic devices. The 1 µm thick intercalated QD films ensure strong light absorption while keeping efficient charge extraction with a quantum efficiency of 90%-70% from λ = 600 nm to 950 nm using intercalated graphene layers as charge collectors with interspacing distance of 100 nm. We demonstrate that the effect of graphene on light absorption is minimal. We achieve a time-modulation response of <1 s. We demonstrate that this technology can be implemented on flexible PET substrates, showing 70% of the original performance after 1000 times bending test. This system provides a novel approach towards high-performance photodetection and high conversion photovoltaic efficiency with quantum dots and on flexible substrates.

Electrochemical functionalization strategy for chemical vapor deposited graphene on silicon substrates: grafting, electronic properties and biosensing.

Herein, we present an electrochemical functionalization strategy for high quality single-layer and multilayer chemical vapor deposited (CVD) graphene directly on a Si/SiO2 chip facilitating electronic interfacing. This method avoids oxidation and tearing of graphene basal planes. We demonstrate effective functionalization by D-(+)-biotin (Bio), 4-(phenyldiazenyl)-aniline (Dz), and gallic acid (Gall) using cyclic voltammetry. Raman spectroscopy and XPS are used to demonstrate effective functionalization. In order to evaluate the effect of the electrochemical functionalization on graphene properties, DC electrical conductivity, XPS, mobility, and carrier density analysis are presented. We show that this functionalization strategy does not degrade graphene mobility (103 cm2 V-1s-1). After functionalization we observe a rise in Fermi level of ∼0.06 eV. In addition, we prove sensing capabilities with a CVD graphene monolayer on the biotin/avidin system by electrical resistance measurements and electrochemical impedance spectroscopy reaching a detection of 2.5 ng ml-1. This paper demonstrates an effective strategy to functionalize high quality CVD graphene on a chip compatible with an electronic interface readout.