Covalent functionalization of tungsten disulfide (WS2) with photo‐ and electro‐active nickel‐porphyrin (NiP) is reported. Exfoliated WS2 interfacing NiP moieties with 1,2‐dithiolane linkages is ...assayed in the oxygen evolution reaction under both dark and illuminated conditions. The hybrid material presented, WS2−NiP, is fully characterized with complementary spectroscopic, microscopic, and thermal techniques. Standard yet advanced electrochemical techniques, such as linear sweep voltammetry, electrochemical impedance spectroscopy, and calculation of the electrochemically active surface area, are used to delineate the catalytic profile of WS2−NiP. In‐depth study of thin films with transient photocurrent and photovoltage response assays uncovers photo‐enhanced electrocatalytic behavior. The observed photo‐enhanced electrocatalytic activity of WS2−NiP is attributed to the presence of Ni centers coordinated and stabilized by the N4 motifs of tetrapyrrole rings at the tethered porphyrin derivative chains, which work as photoreceptors. This pioneering work opens wide routes for water oxidation, further contributing to the development of non‐noble metal electrocatalysts.
Tungsten disulfide is covalently linked with photo‐ and electroactive nickel‐porphyrin (NiP), yielding WS2−NiP with remarkable photo‐enhanced electrocatalytic activity and stability for the water oxidation reaction. This activity is attributed to Ni centers coordinated and stabilized by N4 motifs, such as those of the tetrapyrrole rings in the porphyrin derivative chains.
The game‐changing role of graphene oxide (GO) in tuning the excitonic behavior of conjugated polymer nanoparticles is described for the first time. This is demonstrated by using ...poly(3‐hexylthiophene) (P3HT) as a benchmark conjugated polymer and employing an in situ reprecipitation approach resulting in P3HT nanoparticles (P3HTNPs) with sizes of 50–100 nm in intimate contact with GO. During the self‐assembly process, GO changes the crystalline packing of P3HT chains in the forming P3HTNPs from H to H/J aggregates exhibiting exciton coupling constants as low as 2 meV, indicating favorable charge separation along the P3HT chains. Concomitantly, π–π interface interactions between the P3HTNPs and GO sheets are established resulting in the creation of P3HTNPs–GO charge‐transfer complexes whose energy bandgaps are lowered by up to 0.5 eV. Moreover, their optoelectronic properties, preestablished in the liquid phase, are retained when processed into thin films from the stable aqueous dispersions, thus eliminating the critical dependency on external processing parameters. These results can be transferred to other types of conjugated polymers. Combined with the possibility of employing water based “green” processing technologies, charge‐transfer complexes of conjugated polymer nanoparticles and GO open new pathways for the fabrication of improved optoelectronic thin film devices.
Nanoparticles of conjugated polymer poly(3‐hexylthiophene) self‐assembled in the presence of graphene oxide reveal an internal aggregate structure with significantly reduced excitonic coupling constants, which concomitantly favors π–π interactions with graphene oxide sheets toward the formation of a charge‐transfer complex with reduced energy bandgaps and enhanced photoactivity.
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•Development of ZnO-GO hybrids for enhanced photocatalysis.•ZnO-GO catalysts show high efficiency at low concentration.•Surface chemistry of GO key for establishing photoinduced ...charge-transfer interface interactions with ZnO.•Interface interactions between ZnO and GO responsible for photocatalysis enhancement.
Graphene oxide (GO) and related materials are widely reported to enhance the photocatalytic activity of zinc oxide. However, the origin of the observed performance improvements remains elusive and studies contributing to a deeper understanding of this critical issue are largely missing. In this work, we have prepared a set of benchmark ZnO-GO hybrid materials in order to systematically put under closer scrutiny the influence of the surface chemistry of GO on the photocatalytic degradation of methylene blue. The set of ZnO-GO hybrids has been synthesized in an ultrasonication process involving ZnO nanoparticles obtained in a microwave synthesis process and GO with three distinct oxidation degrees, employed in three different loading fractions. Structural and physical-chemical characterization by XRD, FTIR, Raman, UV–vis, photoluminescence and spectroscopy and XPS, consistently demonstrate the importance of the surface chemistry of GO for establishing photo-induced charge-transfer interface interactions with ZnO, facilitating the enhancement of the catalytic activity of the ZnO-GO catalyst. Optimized interface interactions thus enabled the design of a ZnO-GO catalyst exhibiting a conversion rate of 80% obtained in a time of 70 min and at a catalyst concentration of only 0.045 mg/mL.
Nanoparticles (NPs) of conjugated polymers in intimate contact with sheets of graphene oxide (GO) constitute a promising class of water-dispersible nanohybrid materials of increased interest for the ...design of sustainable and improved optoelectronic thin-film devices, revealing properties exclusively pre-established upon their liquid-phase synthesis. In this context, we report for the first time the preparation of a P3HTNPs–GO nanohybrid employing a miniemulsion synthesis approach, whereby GO sheets dispersed in the aqueous phase serve as a surfactant. We show that this process uniquely favors a quinoid-like conformation of the P3HT chains of the resulting NPs well located onto individual GO sheets. The accompanied change in the electronic behavior of these P3HTNPs, consistently confirmed by the photoluminescence and Raman response of the hybrid in the liquid and solid states, respectively, as well as by the properties of the surface potential of isolated individual P3HTNPs–GO nano-objects, facilitates unprecedented charge transfer interactions between the two constituents. While the electrochemical performance of nanohybrid films is featured by fast charge transfer processes, compared to those taking place in pure P3HTNPs films, the loss of electrochromic effects in P3HTNPs–GO films additionally indicates the unusual suppression of polaronic charge transport processes typically encountered in P3HT. Thus, the established interface interactions in the P3HTNPs–GO hybrid enable a direct and highly efficient charge extraction channel via GO sheets. These findings are of relevance for the sustainable design of novel high-performance optoelectronic device structures based on water-dispersible conjugated polymer nanoparticles.
ZIF8 without and with adsorption of minor amounts of Co precursor have been pyrolized at different temperatures studying systematically the effect of carbonization temperature on the texture, ...composition and ORR performance both in acidic and basic media. The increase of pyrolysis temperature diminished the N content but increased the graphitic character. The trade-off between these two parameters in metal-free electrocatalysts resulted in an improvement of ORR performance, which is met for the highest pyrolysis temperature of 1000 ºC. Moreover, the adsorption of minor amount of Co precursor enhanced further the ORR performance, increased the graphitic character and the porosity of the resulting carbon material. Morphologically, these carbon materials kept the polyhedral shape of ZIF8 and were covered by graphitic nanostructures devoid of metal nanoparticles. Co metal catalysed the growth of these graphitic nanostructures and concomitantly is stabilized as monoatomic Co-Nx-C species preventing the agglomeration as metal nanoparticles. Therefore, the need of an acid washing step is avoided, which is usually necessary in the carbonization of other metal containing MOFs.
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•Co on N-doped porous carbons are prepared by pyrolysis of Co adsorbed on ZIF8.•Polyhedral particles are covered by a shell of graphitic nanostructures.•Highest activity and larger microporosity for Co-containing 1000 ºC-pyrolyzed material.•Low-loaded and ultradispersed Co-N-C without the need of acid washing.•showing higher mass activity compared with other MOF-derived catalysts.
The preparation of an MoS2–polymer carbon nanodot (MoS2‐PCND) hybrid material was accomplished by employing an easy and fast bottom‐up synthetic approach. Specifically, MoS2‐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 MoS2‐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 MoS2‐PCND(exf‐fun), in which MoS2 was firstly exfoliated and then covalently functionalized with PCNDs. The MoS2‐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 MoS2‐PCND was rationalized by considering the catalytically active sites of MoS2, the effective charge/energy‐transfer phenomena from PCNDs to MoS2, and the synergetic effect between MoS2 and PCNDs in the hybrid material.
Facile and fast: A facile and fast bottom‐up approach involving thermal decomposition of ammonium tetrathiomolybdate and the in situ complexation of Mo with carboxyl groups on the surface of polymer carbon nanodots (PCNDs) was used to prepare a hybrid material consisting of MoS2 and PCNDs. The thus‐obtained MoS2‐PCND electrocatalyst showed superior activity towards the hydrogen evolution reaction and outperformed the corresponding material acquired by a top‐down approach.
In this work, a straightforward in-situ measurement of L and D-amino acids (AAs) has been developed using disposable graphene oxide nanoribbon (GON) screen printed electrodes. For that, we took ...advantage of the electroactivity of certain clinically relevant AAs, such as tyrosine (Tyr) and methionine (Met), which are involved in important bacterial diseases (Bacillus subtilis and Vibrio cholera, respectively). The strategy is based on a dual electrochemical and enzymatic approach. The D-AA with the class enzyme D amino acid oxidase (DAAO) generates H2O2. This H2O2 is simultaneously detected with the L-AA, electroactive molecule by differential pulse voltammetry (DPV). These GON disposable platforms use just 50 μL of sample and a total analysis time of 360 s. Both L and D enantiomers calibration and quantitative analysis were explored and were simultaneously detected with accuracy and precision in urine samples. Any interference of uric acid and other electroactive AAs was noticed. This proposed electrochemical GON-based enantiomeric bio-sensor becomes a highly promising tool as future point of care for fast and reliable early diagnosis of diseases related to the presence of D-AAs.
Transition-metal dichalcogenides (TMDs) attract increased attention for the development of donor–acceptor materials enabling improved light harvesting and optoelectronic applications. The development ...of novel donor–acceptor nanoensembles consisting of poly(3-thiophene sodium acetate) and ammonium functionalized MoS2 and WS2 was accomplished, while photoelectrochemical cells were fabricated and examined. Attractive interactions between the negatively charged carboxylate anion on the polythiophene backbone and the positively charged ammonium moieties on the TMDs enabled in a controlled way and in aqueous dispersions the electrostatic association of two species, evidenced upon titration experiments. A progressive quenching of the characteristic fluorescence emission of the polythiophene derivative at 555 nm revealed photoinduced intraensemble energy and/or electron transfer from the polymer to the conduction band of the two TMDs. Photoelectrochemical assays further confirmed the establishment of photoinduced charge-transfer processes in thin films, with distinct responses for the MoS2- and WS2-based systems. The MoS2-based ensemble exhibited enhanced photoanodic currents offering additional channels for hole transfer to the solution, whereas the WS2-based one displayed increased photocathodic currents providing supplementary pathways of electron transfer to the solution. Moreover, scan direction depending on photoanodic and photocathodic currents suggested the existence of yet unexploited photoinduced memory effects. These findings highlight the value of electrostatic interactions for the creation of novel donor–acceptor TMD-based ensembles and their relevance for managing the performance of photoelectrochemical and optoelectronic processes.
•Graphene nanoribbons on screen-printed platforms: new tools in electrochemical sensing.•Building electrochemical sensors: tailored graphene nanoribbons for target analytes.•Fast, reliable and ...disposable reduced graphene nanoribbon-based electrochemical sensors for uric acid determination.
In this work, oxidized graphene nanoribbons (GNRox) and reduced graphene nanoribbons (GNRred) were explored for the construction of disposable electrochemical sensors on screen-printed platforms for the sensing of ascorbic acid (AA), levodopa (LD) and uric acid (UA).
GNRred demonstrated improved electroanalytical performance in comparison not only with the carbon screen printed electrodes (CSPEs), but also with other related carbon nanomaterials such as multi-walled carbon nanotubes (MWCNTs) and GNRox. MWCNTs served as the carbon source for GNRox which was further reduced to form GNRred.
The excellent electrocatalysis exhibited by this carbon nanomaterial toward AA, LD and UA allowed a fast (100s), selective (at +0.08, +0.27 and +0.39V, respectively), and accurate determination (with recoveries between 97 to 101%) of these analytes in urine samples.
Excellent intra-electrode repeatability (RSD <5%, n=10), inter-electrode reproducibility (RSD < 13%, n=5 electrodes) and stability of the sensor (the electrode maintained 93±3% of its signal after 15 days) were also demonstrated, becoming this electrochemical sensor a valuable tool for clinical routine uric acid assessment.
Tailored graphene nanoribbons on screen-printed platforms become a new generation of disposable graphene-based electrochemical sensors for POC testing applications.
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