Search

It is known that graphene oxide (GO) particles bear negatively charged oxygen moieties which can interact with cations, what has been several times employed in fabrication of electrochemical sensors for metals. In this work, for the first time GO was treated with Cu2+, Cd2+ or Pb2+ cations in a way similar to the ion imprinting by simple incubation of the two components and the synthesized nanomaterials were then deposited on carbon electrode surface forming electrochemical sensors towards lead cations. It was found that simple filtration of GO is very efficient way for collection of GO particles that could be imprinted most efficiently in terms of high electrochemical response towards lead cations. Part of the success also lies in high redox potential of Cu2+ that turned to be the best choice for the GO imprinting. It was also proven that the electrodes modified with ion-imprinted GO could work as the sensors of Pb2+ in drop amount of solution as well as they provide stable response under flowthrough cell conditions suitable, for example, for online monitoring of water quality.

In this work silver nanoparticles (AgNPs) were in situ synthesized on surface of graphene oxide (GO) and Ti3C2TX MXene at room temperature and without any reducing agent. The prepared GO_AgNPs and MX_AgNPs nanomaterials were deposited on electrodes and applied for voltammetric sensing of pesticide metazachlor. The chosen analyte underwent electrochemical reduction readable as faradaic current and identified as the electrochemical reductive dechlorination. It was found that GO_AgNP (electrochemically reduced to ErGO_AgNP before measurements) was more efficient catalyst of the observed dechlorination than MX_AgNP, even though it contained approximately 10-fold lower amount of silver. The smaller size of AgNP achieved with GO was the most probable reason. When the metazachlor sensing properties of the nanohybrid-modified electrodes were investigated, the linear range and the limit of detection of 37-1123 μM and 27 μM, respectively, were observed for ErGO_AgNP while only 37-375 μM and 40 μM for MX_AgNP. The ErGO_AgNP nanohybrid was more convenient also for metazachlor detection in alkali leachate of real soil samples, probably as the result of antifouling effect of ErGO. Although there are conventional instrumental analysis methods for sensing orders of magnitude lower concentrations of metazachlor, in this work it is for the first time shown that the AgNP-based nanohybrid efficiently catalyse the electrochemical dechlorination applicable for detection of this frequently used pesticide. © 2021 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.

Inorganic selenium, the most common form of harmful selenium in the environment, can be determined using electrochemical sensors, which are compact, fast, reliable and easy-to-operate devices. Despite progress in this area, there is still significant room for developing high-performance selenium electrochemical sensors. To achieve this, one should take into account (i) the electrochemical process that selenium undergoes on the electrode; (ii) the valence state of selenium species in the sample and (iii) modification of the sensor surface by a material with high affinity to selenium. The goal of this review is to provide a knowledge base for these issues. After the Introduction section, mechanisms and principles of the electrochemical reduction of selenium are introduced, followed by a section introducing the modification of electrodes with materials interacting with selenium and a section dedicated to speciation methods, including the reduction of non-detectable Se(vi) to detectable Se(iv). In the following sections, the main types of materials (metallic, polymers, hybrid (nano)materials horizontal ellipsis ) interacting with inorganic selenium (mostly absorbents) are reviewed to show the diversity of properties that may be endowed to sensors if the materials were to be used for the modification of electrodes. These features for the main material categories are outlined in the conclusion section, where it is stated that the engineered polymers may be the most promising modifiers.

In this work the possibility of synthesizing in situ silver nanoparticles (AgNPs) on graphene oxide (GO) surfaces without commonly used additional reducing or alkalizing agents or increased temperature was investigated. Using diverse microscopic (atomic force microscopy, transmission electron microscopy) and spectroscopic methods, it was proved that very small AgNPs were formed on GO by simple incubation for 2 h in a mixture of GO dispersion and AgNO3. The prepared nanomaterial (GO_Ag) was also assessed using electrochemical methods, and it exhibited electrochemical behavior similar to the GO_Ag nanomaterial prepared with a help of citric acid as a reducing agent. Furthermore, it was found that (i) the electrochemical reduction of the GO_Ag on the electrode surface decreased the voltammetric response even though this step increased the surface conductivity and (ii) GO_Ag can be employed for the sensing of chlorides with a detection limit of 79 μM and a linear range of up to 10 mM. It could also provide an electrochemical response toward the chloroacetanilide herbicide metazachlor. Hence, the reducing capabilities of GO were proved to be applicable for in situ synthesis of metal nanoparticles with the highest possible simplification, and the as-prepared nanomaterials could be employed for fabrication of different electrochemical sensors.

In this work, the spontaneous and NaBH4-induced reduction of chloroplatinic acid on the surface of Ti3C2TX MXene was investigated to synthesize a hybrid PtNP-decorated MXene nanomaterial (MX-Pt) with potential as hydrogen evolution (HER) or oxygen reduction reaction (ORR) catalyst properties. The initial Pt concentration, reduction time and presence of additional reducing agents were varied, and as-synthesized nanocomposites were characterized thoroughly by XRD, EDX, SEM and XPS analysis and by electrochemical methods. Composites containing 14 wt% Pt showed HER with an onset potential of -75.9 mV and a current density of -10 mA cm(-2) achieved at -226 mV. The spontaneous deposition of PtNPs on MXene improved the electrocatalytic properties over using an external reducing agent to form PtNP, which was explained based on the different rates of oxidation of Ti in the initial MXene support. Furthermore, good stability of the electrode modified by the MX-Pt was achieved without any polymeric binder and the HER reaction achieved only a negligible decrease over 3 000 potentiodynamic cycles. (C) 2019 The Electrochemical Society.

Electrochemical performance of a 2D Ti3C2Tx (MXene, where T: [dbnd]O, –OH, –F) sheets modified with Pt nanoparticles (PtNPs) was investigated. The results showed that Ti3C2Tx/PtNP nanocomposite deposited on the surface of GCE showed much better and stable redox behavior in an anodic potential window as compared to the GCE modified with pristine Ti3C2Tx MXene. For example, the H2O2 sensor of Ti3C2Tx/PtNP on GCE offered LOD of 448 nM with a potential at which reduction starts of ∼+250 mV (vs. Ag/AgCl) in comparison to values of 883 μM and ∼−160 mV observed for Ti3C2Tx modified GCE. Moreover, the Ti3C2Tx/PtNP sensor could detect small redox molecules such as ascorbic acid (AA), dopamine (DA), uric acid (UA) and acetaminophen (APAP) at a potential higher than +250 mV with high selectivity and LOD down to nM level. We proved that selectivity of detection of such molecules (AA, DA, UA and APAP) could be modulated to high extent using external membranes. © 2018 Elsevier B.V.

In this study, two quaternary ammonium salts derived from L-lipoic acid were applied for self-assembled monolayers formation on rough structured gold surface. The derivatives differ in functionality since one possesses simple quaternary ammonium group whereas the other one is carboxybetaine ester containing quaternary ammonium group with pH hydrolysable ester group as a pendant. The response of surface wettability to ion exchange between Cl− and perfluorooctanoate, kinetics and gradient wettability were examined by water contact angle measurement and confirmed by X-ray photoelectron spectroscopy. Furthermore, adhesion forces related to applied counterion on the entire surface and after hydrolysis were investigated by atomic force microscopy measurement at nanometer scales. A dramatic change in wettability upon counterion exchange from superhydrophilic for Cl− to very or superhydrophobic for perfluorooctanoate in a repeatable manner was observed for both derivatives. Kinetics of counterion exchanges revealed faster hydration of simple quaternary derivate. The wettability gradient could be designed from superhydrophobic to superhydrophilic either in a reversible manner by simple immersion of the modified surface in a counterion solution modulated by ionic strength or in an irreversible manner for carboxybetaine ester derivate by time-controlled hydrolysis to charge balanced carboxybetaine. © 2017 Elsevier Inc.

We describe a self-assembled monolayer (SAM) on a gold surface with a carboxybetaine ester functionality to control the interaction between DNA and gold nanoparticles via pH. The negatively charged phosphate backbone of DNA interacts with and adsorbs to the positively charged carboxybetaine esters on the SAM. DNA release can be achieved by the hydrolysis of carboxybetaine ester (CBE) to a zwitterionic carboxybetaine state. Furthermore, the adsorption of negatively charged citrate-capped gold nanoparticles to a SAM-modified plain gold surface can be controlled by the pH. The SAM based on carboxybetaine ester allows for the homogeneous adsorption of particles, whereas the SAM after hydrolysis at high pH repels AuNP adsorption. The antifouling surface properties of the surface modified with carboxybetaine were investigated with protein samples. © 2017 American Chemical Society.