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•S-triphenylmethyl cysteine is covalently attached to oxidized SWCNTs through the amino groups.•Cd(II) is preconcentrated at GCE/SWCNT-Cys through complex formation at open circuit ...potential.•GCE/SWCNT-Cys allows the highly sensitive (sub-ppb levels) quantification of Cd(II).•Recovery studies in groundwater samples shows an excellent agreement with ICP.
This work is focused on the development of an electrochemical sensor for the quantification of Cd(II) based on the use of glassy carbon electrodes (GCE) modified with a dispersion of single-walled carbon nanotubes (SWCNTs) covalently functionalized with cysteine (Cys). Cd(II) is preconcentrated at the electrode surface by complex formation at open circuit potential, followed by the reduction at ∧0.900V and the final anodic voltammetric stripping in a 0.020M acetate buffer solution pH 5.00. The functionalization of SWCNTs was performed through the reaction between the carboxylic groups of oxidized SWCNT and amino groups of S-triphenylmethyl cysteine using a coupling chemistry agent based on benzotriazol for the activation of carboxylic residues.
There was a linear relationship between Cd oxidation signal and Cd(II) concentration between 1.0 and 300.0α/4gL∧1 Cd(II), with a sensitivity of (49±2)í10∧3α/4Aα/4g∧1L and a detection limit of 0.3α/4gL∧1. The reproducibility was 1.7% using the same dispersion and 3.8% using 3 different dispersions. The sensor was challenged with groundwater samples enriched with Cd(II) showing excellent recovery percentages and excellent agreement with the values obtained by ICP-MS.
Developing new standardized tools to characterize brain recording devices is critical to evaluate neural probes and for translation to clinical use. The signal-to-noise ratio (SNR) measurement is the ...gold standard for quantifying the performance of brain recording devices. Given the drawbacks with the SNR measure, our first objective was to devise a new method to calculate the SNR of neural signals to distinguish signal from noise. Our second objective was to apply this new SNR method to evaluate electrodes of three different materials (platinum black, Pt; carbon nanotubes, CNTs; and gold, Au) co-localized in tritrodes to record from the same cortical area using specifically designed multielectrode arrays. Hence, we devised an approach to calculate SNR at different frequencies based on the features of cortical slow oscillations (SO). Since SO consist in the alternation of silent periods (Down states) and active periods (Up states) of neuronal activity, we used these as noise and signal, respectively. The spectral SNR was computed as the power spectral density (PSD) of Up states (signal) divided by the PSD of Down states (noise). We found that Pt and CNTs electrodes have better recording performance than Au electrodes for the explored frequency range (5-1500 Hz). Together with two proposed SNR estimators for the lower and upper frequency limits, these results substantiate our SNR calculation at different frequency bands. Our results provide a new validated SNR measure that provides rich information of the performance of recording devices at different brain activity frequency bands (<1500 Hz).
Developing highly efficient and stable photoelectrochemical (PEC) water-splitting electrodes via inexpensive, liquid phase processing is one of the key challenges for the conversion of solar energy ...into hydrogen for sustainable energy production. ZnO represents one the most suitable semiconductor metal oxide alternatives because of its high electron mobility, abundance, and low cost, although its performance is limited by its lack of absorption in the visible spectrum and reduced charge separation and charge transfer efficiency. Here, we present a solution-processed water-splitting photoanode based on Co-doped ZnO nanorods (NRs) coated with a transparent functionalizing metal–organic framework (MOF). The light absorption of the ZnO NRs is engineered toward the visible region by Co-doping, while the MOF significantly improves the stability and charge separation and transfer properties of the NRs. This synergetic combination of doping and nanoscale surface functionalization boosts the current density and functional lifetime of the photoanodes while achieving an unprecedented incident photon to current efficiency (IPCE) of 75% at 350 nm, which is over 2 times that of pristine ZnO. A theoretical model and band structure for the core–shell nanostructure is provided, highlighting how this nanomaterial combination provides an attractive pathway for the design of robust and highly efficient semiconductor-based photoanodes that can be translated to other semiconducting oxide systems.
This work describes a rationalization of the interactions between two fully characterized graphene nanoribbons (GNRs) and a set of significant target molecules. The GNRs were carefully synthesized by ...unzipping multi-walled carbon nanotubes (MWCNTs) to yield graphene oxide nanoribbons (GNRox) containing 44 wt% oxygen. The GNRox were reduced to yield reduced graphene oxide nanoribbons (GNRred) containing 14 wt%. Each material was characterized by atomic force microscopy, transmission electronic microscopy, Raman spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and voltammetry techniques. Differential pulse voltammetry was used to assess the detection of two strategically selected groups of molecules, including benzenediols, hydroquinone, catechol, and resorcinol, as well as, l-dopa, ascorbic acid, uric acid, and l-tyrosine. The results showed that GNRs provided significantly better electrochemical responses compared to MWCNTs and the non-modified glassy carbon electrode. The chemistry of the few layers of graphene strongly influenced the electrochemical properties of the material. GNRox may be the material of choice for sensing molecules having high oxidation potentials. GNRred, on the other hand, yielded an excellent sensitivity for aromatic molecules in which pi - pi interactions were dominant or the number of conjugated 1,2-diols present was high. GNRred combines the advantages of the high proportion of sp super(2)-carbon atoms with the presence of a few oxygen moieties remaining in the lattice after the reduction step. The primary interactions responsible for the shift in oxidation potentials were elucidated. This work presents new opportunities for tailoring graphene to a particular sensing application based on the specific chemistry of the molecule.
The effect of doping on the electronic properties in bulk single-walled carbon nanotube (SWCNT) samples is studied for the first time using a new in situ Raman spectroelectrochemical method, and ...further verified by DFT calculations and photoresponse. We use p-/n-doped SWCNTs prepared by diazonium reactions as a versatile chemical strategy to control the SWCNT behavior. The measured and calculated data testify an acceptor effect of 4-aminobenzenesulfonic acid (p-doping), and a donor effect (n-doping) in the case of benzyl alcohol. In addition, pristine and covalently functionalized SWCNTs were used for the preparation of photoactive film electrodes. The photocathodic current in the photoelectrochemical cell is consistently modulated by the doping group. These results validate the in situ Raman spectroelectrochemistry as a unique tool box for predicting the electronic properties of functionalized SWCNTs in the form of thin films and their operational functionality in thin film devices for future optoelectronic applications.
The charge-transfer characteristics of nanostructured carbon/TiO2 electrodes are studied by cyclic voltammetry under photoelectrochemical conditions exploiting the electrooxidation and ...electroreduction of H2O2 in an alkaline medium. Films of composites were prepared by physically mixing TiO2 with 5 wt% of either single-walled carbon nanotubes (SWCNTs) or reduced graphene oxide (rGO). In addition, a layer-by-layer rGO/TiO2 electrode was prepared. Under dark conditions, both mixed SWCNTs and rGO facilitate H2O2 reduction. Under light irradiation, the blank TiO2 electrode shows a cathodic photopotential, the SWCNT/TiO2 an anodic photopotential, and the mixed rGO/TiO2 an increased cathodic photopotential. This scenario unambiguously reveals a photoelectron acceptor behavior for SWCNTs and a photohole acceptor performance for rGO. The latter one also agrees with the photoactivity observed in the layer-by-layer electrode. Overall, the value of H2O2 redox reactions for unraveling the electron-donor or electron-acceptor character of carbon nanostructures in C/metal oxide electrodes is demonstrated.
•H2O2 is a useful probe for the photoelectrochemical assessment of charge transfer phenomena.•Reduced graphene oxide accepts photogenerated holes from TiO2 in alkaline medium.•Single-walled carbon nanotubes accept photogenerated electrons from TiO2 in alkaline medium.
Nanostructured TiO2 and graphene-based materials constitute components of actual interest in devices related to solar energy conversion and storage. In this work, we show that a thin layer of ...electrochemically reduced graphene oxide (ECrGO), covering nanostructured TiO2 photoelectrodes, can significantly improve the photoactivity. In order to understand the working principle, ECrGO/TiO2 photoelectrodes with different ECrGO thicknesses were prepared and studied by a set of photoelectrochemical measurements. Methanol in alkaline conditions was employed as effective hole acceptor probe to elucidate the electronic phenomena in the electrode layers and interfaces. These studies underline the hole accepting properties of ECrGO and reveal the formation of a p-n junction at the interface between ECrGO and TiO2. It is shown for the first time that the resulting space charge region of about 10 nm defines the operational functionality of the ECrGO layer. Films thinner than the space charge region act as hole transport layer (HTL), which efficiently transfers holes to the liquid interface thus leading to enhanced photoactivity. Thicker films however act as hole blocking layer (HBL), resulting in a systematic decrease of the photoactivity. The finding of a thickness dependent threshold value for the operation of ECrGO as HTL and HBL is of general interest for the fabrication of optoelectronic devices with improved performance.
The preparation of an MoS
-polymer carbon nanodot (MoS
-PCND) hybrid material was accomplished by employing an easy and fast bottom-up synthetic approach. Specifically, MoS
-PCND was realized by the ...thermal decomposition of ammonium tetrathiomolybdate and the in situ complexation of Mo with carboxylic acid units present on the surface of PCNDs. The newly prepared hybrid material was comprehensively characterized by spectroscopy, thermal means, and electron microscopy. The electrocatalytic activity of MoS
-PCND was examined in the hydrogen evolution reaction (HER) and compared with that of the corresponding hybrid material prepared by a top-down approach, namely MoS
-PCND(exf-fun), in which MoS
was firstly exfoliated and then covalently functionalized with PCNDs. The MoS
-PCND hybrid material showed superior electrocatalytic activity toward the HER with low Tafel slope, excellent electrocatalytic stability, and an onset potential of -0.16 V versus RHE. The superior catalytic performance of MoS
-PCND was rationalized by considering the catalytically active sites of MoS
, the effective charge/energy-transfer phenomena from PCNDs to MoS
, and the synergetic effect between MoS
and PCNDs in the hybrid material.
A facile strategy for the controllable growth of CdS nanoparticles at the periphery of MoS
en route the preparation of electron donor-acceptor nanoensembles is developed. Precisely, the carboxylic ...group of α-lipoic acid, as addend of the modified MoS
obtained upon 1,2-dithiolane functionalization, was employed as anchor site for the in situ preparation and immobilization of the CdS nanoparticles in an one-pot two-step process. The newly prepared MoS
/CdS hybrid material was characterized by complementary spectroscopic, thermal and microscopy imaging means. Absorption spectroscopy was employed to register the formation of MoS
/CdS, by observing a broad shoulder centered at 420 nm due to CdS nanoparticles, while the excitonic bands of MoS
were also evident. Moreover, based on the efficient quenching of the characteristic fluorescence emission of CdS at 725 nm by the presence of MoS
, strong electronic interactions at the excited state between the two species within the ensemble were identified. Photoelectrochemical assays of MoS
/CdS thin-film electrodes revealed a prompt, steady and reproducible anodic photoresponse during repeated on-off cycles of illumination. A significant zero-current photopotential of -540 mV and an anodic photocurrent of 1 μA were observed, underlining improved charge-separation and electron transport from CdS to MoS
. The superior performance of the charge-transfer processes in MoS
/CdS is of direct interest for the fabrication of photoelectrochemical and optoelectronic devices.
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