A practical non-enzymatic urea sensor based on NiCo2O4 nanoneedles

We propose a new facile electrochemical sensing platform for determination of urea, based on a glassy carbon electrode (GCE) modified with nickel cobalt oxide (NiCo₂O₄) nanoneedles. These nanoneedles are used for the first time for highly sensitive determination of urea with the lowest detection limit (1 μM) ever reported for the non-enzymatic approach. The nanoneedles were grown through a simple and low-temperature aqueous chemical method. We characterized the structural and morphological properties of the NiCo₂O₄ nanoneedles by TEM, SEM, XPS and XRD. The bimetallic nickel cobalt oxide exhibits nanoneedle morphology, which results from the self-assembly of nanoparticles. The NiCo₂O₄ nanoneedles are exclusively composed of Ni, Co, and O and exhibit a cubic crystalline phase. Cyclic voltammetry was used to study the enhanced electrochemical properties of a NiCo₂O₄ nanoneedle-modified GCE by overcoming the typical poor conductivity of bare NiO and Co₃O₄. The GCE-modified electrode is highly sensitive towards urea, with a linear response (R² = 0.99) over the concentration range 0.01–5 mM and with a detection limit of 1.0 μM. The proposed non-enzymatic urea sensor is highly selective even in the presence of common interferents such as glucose, uric acid, and ascorbic acid. This new urea sensor has good viability for urea analysis in urine samples and can represent a significant advancement in the field, owing to the simple and cost-effective fabrication of electrodes, which can be used as a promising analytical tool for urea estimation.

We propose a new facile electrochemical sensing platform for determination of urea, based on a glassy carbon electrode (GCE) modified with nickel cobalt oxide (NiCo₂O₄) nanoneedles.     

NiCo alloy nanoparticles electrodeposited on an electrochemically reduced nitrogen-doped graphene oxide/carbon-ceramic electrode: a low cost electrocatalyst towards methanol and ethanol oxidation

In this work, nickel–cobalt alloy nanoparticles were electrodeposited on/in an electrochemically reduced nitrogen-doped graphene oxide (ErN-GO)/carbon-ceramic electrode (CCE) and the resulting nanocomposite (NiCo/ErN-GO/CCE) was evaluated as a low cost electrocatalyst for methanol and ethanol electrooxidation. Field-emission scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy were used for the physical characterization of the electrocatalyst. To study the electrochemical behavior and electrocatalytic activity of the prepared electrocatalyst towards the oxidation of methanol and ethanol in alkaline media, cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy were utilized. Electrochemical investigation of the introduced electrocatalysts (NiCo alloy and Ni nanoparticles alone electrodeposited on/in different substrates) indicated that NiCo/ErN-GO/CCE has highest activity and stability towards methanol (J_p = 88.04 mA cm⁻²) and ethanol (J_p = 64.23 mA cm⁻²) electrooxidation, which highlights its potential use as an anodic material in direct alcohol fuel cells.

NiCo alloy nanoparticles on the electrochemically reduced nitrogen-doped graphene oxide/carbon-ceramic electrode: a low cost electrocatalyst towards methanol and ethanol oxidation.     

A probe-free electrochemical immunosensor for methyl jasmonate based on a Cu-MOF–carboxylated graphene oxide platform

Methyl jasmonate (MeJA) is an important phytohormone which can regulate plant growth and stress tolerance. It is very necessary to develop sensitive and accurate detection methods for MeJA. In this work, a probe-free electrochemical immunosensor for MeJA detection was developed based on a Cu-MOF–carboxylated graphene oxide (COOH-GO) platform. The Cu²⁺ in the Cu-MOFs was used to provide redox signals, which avoids the application of an external redox probe in the electrolyte solutions as conventional immunosensors. COOH-GO was used to improve the structural stability and provide more sites for binding MeJA antibodies. The linear range of the MeJA immunosensor is from 10 pM to 100 μM, which can cover the whole concentration range of MeJA in most plants. And its detection limit is very low (0.35 pM), and it can detect very low concentrations of MeJA. This immunosensor is simple, low cost, and does not need redox probe solutions for measurements. It shows remarkable potential for on-site application in precision agriculture.

A probe-free electrochemical immunosensor for methyl jasmonate has been developed based on a Cu-MOF-carboxylated graphene oxide platform.     

β-Cyclodextrin functionalized 3D reduced graphene oxide composite-based electrochemical sensor for the sensitive detection of dopamine

A three-dimensional reduced graphene oxide nanomaterial with β-cyclodextrin modified glassy carbon electrode (3D-rGO/β-CD/GCE) was constructed and used to detect the electrochemical behavior of dopamine (DA). The nanocomposite materials were characterized by scanning electron microscopy (SEM), infrared spectrometry (FT-IR), Raman spectrogram and thermogravimetric analysis (TGA), which showed that β-CD was well modified on 3D graphene with a porous structure. The electrochemical properties of different modified electrodes were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), proving the highest electron transfer rate of the 3D-rGO/β-CD modified electrode. The experimental conditions such as scan rate, pH, enrichment time and layer thickness were optimized. Under the best experimental conditions, DA was detected by differential pulse voltammetry (DPV) by 3D-rGO/β-CD/GCE with excellent electrocatalytic ability and satisfactory recognition ability, resulting in a wide linear range of 0.5–100 μM and a low detection limit (LOD) of 0.013 μM. The modified electrode based on 3D-rGO/β-CD nanocomposites is promising in the field of electrochemical sensors due to its high sensitivity and other excellent properties.

A 3D-rGO/β-CD nanocomposite was successfully synthesized and further modified onto the surface of GCE to construct a new biosensor for electrochemically sensing DA.     

A new electrochemical DNA biosensor for determination of anti-cancer drug chlorambucil based on a polypyrrole/flower-like platinum/NiCo2O4/pencil graphite electrode

In the current study, DNA immobilization was performed on pencil graphite (PG) modified with a polypyrrole (PPy) and flower-like Pt/NiCo₂O₄ (FL-Pt/NiCo₂O₄) nanocomposite, as a new sensitive electrode to detect chlorambucil (CHB). Energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were employed to characterize the synthesized FL-Pt/NiCo₂O₄ and PPy/FL-Pt/NiCo₂O₄ nanocomposites. Moreover, differential pulse voltammetry (DPV) was selected to assess the guanine and adenine electrochemical responses on the DNA sensor. The CHB determination was performed using the maximum currents towards adenine and guanine in the acetate buffer solution (ABS). According to the results, ds-DNA/PPy/FL-Pt/NiCo₂O₄/PGE was able to detect the different concentrations of CHB in the range between 0.018 and 200 μM, with a detection limit of (LOD) of 4.0 nM. The new biosensor was also exploited for CHB determination in real samples (serum, urine and drug), the results of which revealed excellent recoveries (97.5% to 103.8%). Furthermore, the interaction between ds-DNA and CHB was studied using electrochemistry, spectrophotometry and docking whose outputs confirmed their effective interaction.

In the current study, DNA immobilization was performed on pencil graphite (PG) modified with a polypyrrole (PPy) and flower-like Pt/NiCo₂O₄ (FL-Pt/NiCo₂O₄) nanocomposite, as a new sensitive electrode to detect chlorambucil (CHB).     

Simultaneous detection of acetaminophen and 4-aminophenol with an electrochemical sensor based on silver–palladium bimetal nanoparticles and reduced graphene oxide

In this paper, Ag–Pd bimetallic nanoparticles uniformly distributed on reduced graphene oxide (rGO) were synthesized by redox reaction between Pd²⁺, Ag⁺and GO, and were characterized by X-ray diffractometry, field emission scanning electron microscopy, electrochemical impedance spectroscopy and thermal gravimetric analyses. A novel electrochemical sensor was constructed based on these nanocomposites using glassy carbon as a substrate. Under optimal conditions, the linear ranges were 0.50–300.00 μM for PA and 1.00–300.00 μM for 4-AP, with the detection limits of 0.23 μM for PA and 0.013 μM for 4-AP, respectively. This sensor was successfully applied to the determination of PA in pharmaceutical formulations and gave satisfactory results with a lower detection limit, wider linear range and good reproducibility.

Simultaneous detection of acetaminophen and 4-aminophenol with a highly sensitive electrochemical sensor based on silver–palladium bimetal nanoparticles and reduced graphene oxide.     

Electrosynthesis of electrochemically reduced graphene oxide/polyaniline nanowire/silver nanoflower nanocomposite for development of a highly sensitive electrochemical DNA sensor

A novel nanostructured electrode material based on electrochemically reduced graphene oxide/polyaniline nanowires/silver nanoflowers (ERGO/PANi NWs/AgNFs) was fabricated site-specifically onto a Pt microelectrode (0.80 mm² area) using a three-step electrochemical procedure: electrosynthesis of ERGO, electropolymerization of PANi NWs, and electrodeposition of AgNFs. Synergistic and complementary properties of ERGO, PANi NWs and AgNFs, including high electrochemical activity, large surface area, and high biocompatibility, were obtained. Besides, the electrosynthesis method allowed the direct formation of the desired nanomaterial onto the Pt microelectrode, so the adhesion between the sandwich-structured nanocomposite and the electrode surface was also improved. The optimized ERGO/PANi NWs/AgNFs nanocomposite was used for the first time to develop an electrochemical DNA sensor. As a result, the DNA probe immobilization was facilitated and the electrochemical signals of the DNA sensor were enhanced. The detection limit of the DNA sensor was 2.70 × 10⁻¹⁵ M. Moreover, potential miniaturization for fabrication of a lab-on-a-chip system, direct detection, high sensitivity, and good specificity are the advantages of the fabricated DNA sensor.

A novel nanostructured material based on ERGO/PANi NWs/AgNFs was electrosynthesized on a Pt microelectrode and was used for the first time to develop an electrochemical DNA sensor.     

Vanadium pentaoxide-doped waste plastic-derived graphene nanocomposite for supercapacitors: a comparative electrochemical study of low and high metal oxide doping

We report the bulk phase synthesis of graphene sheets using waste plastic (WP) as a precursor following a modified pyrolysis approach. Furthermore, the low and high mass loading of vanadium pentaoxide was performed on graphene sheets in 1 : 10 and 1 : 1 ratios, respectively. Advanced characterization techniques such as Raman spectroscopy, FT-IR spectroscopy, X-ray diffraction (XRD) analysis, thermogravimetric analysis (TGA) analysis, and SEM imaging were used to confirm the synthesis of graphene. FT-IR spectroscopy confirmed that the resonating structure affects the bond strength in the composite, which enables peak shifting in the FT-IR spectrum of the composite. Furthermore, bandgap analysis has been performed using UV-Vis spectroscopy, which confirmed the synthesis of the composites. The developed vanadium-doped graphene was used as the active material for the fabrication of supercapacitor electrodes. The electrochemical performance of these devices was evaluated in 1 M H₃PO₄ solution using cyclic voltammetry (CV), galvanic charge–discharge (GCD) analysis, and electrochemical impedance spectroscopy (EIS). Fabricated cells 1 and 2 showed exceptional specific capacitances of 139.7 F g⁻¹ and 51.2 F g⁻¹ at 5 mV s⁻¹ scan rate, respectively. Cell 1 showed a huge power density of 5312 W kg⁻¹ and an energy density of 19.7 W h kg⁻¹. Conversely, cell 2 showed a comparatively lower power density of 1941 W kg⁻¹ and an energy density of 7.2 W h kg⁻¹ at a 5 mV s⁻¹ scan rate. Moreover, we disclose some brief conclusions on the performance, mechanism, and required modifications that can improve the performance of such devices. This approach can surely help with universal WP problems as well as the development of high-performance supercapacitors.

We report the bulk phase synthesis of graphene sheets using waste plastic (WP) as a precursor following a modified pyrolysis approach.     

Correction: Enhanced electrochemical performance of nanoplate nickel cobaltite (NiCo2O4) supercapacitor applications

Correction for ‘Enhanced electrochemical performance of nanoplate nickel cobaltite (NiCo₂O₄) supercapacitor applications’ by Anil Kumar Yedluri et al., RSC Adv., 2019, 9, 1115–1122.

Attribution to a funding body (BK 21 PLUS) in the published article was incorrect (arising from delays), and the corrected Acknowledgements section should be as follows:This research was supported by the Basic Research Laboratory through the National Research Foundations of Korea funded by the Ministry of Science, ICT and Future Planning (NRF-2015R1A4A1041584).The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

A simple electrochemical immunosensor based on a chitosan/reduced graphene oxide nanocomposite for sensitive detection of biomarkers of malignant melanoma

The sensitive and specific detection of tumor biomarkers is crucial for early diagnosis and treatment of malignant melanoma. Immunoassay with a simple sensing interface and high sensitivity is highly desirable. In this work, a simple electrochemical immunosensor based on a chitosan/reduced graphene oxide (CS–rGO) nanocomposite was developed for sensitive determination of an S-100B protein, a tumor marker of malignant melanoma. CS–rGO nanocomposite were prepared by chemical reduction of graphene oxide in the presence of chitosan and modified on glassy carbon electrode (GCE) to provide a biofriendly, conductive, and easily chemically modified matrix for further immobilization of antibodies. Anti-S-100B antibodies were grafted onto the chitosan molecules to fabricate the immunorecognition interface by a simple glutaraldehyde cross-linking method. Electrochemical determination of S-100B was achieved by measuring the decreased current signal of solution phase electrochemical probes, which originated from the increased steric hindrance and insulation caused by the formation of antigen–antibody complexes at the electrode interface. Due to the good conductivity, high surface area, excellent biocompatibility, and good film-forming ability of CS–rGO, the constructed immunosensor exhibited good stability, high selectivity and sensitivity, a wide dynamic range from 10 fg mL⁻¹ to 1 ng mL⁻¹ and a low limit of detection of 1.9 pg mL⁻¹ (S/N = 3). Moreover, the sensor was also applicable for the sensitive detection of S-100B protein in real human serum samples.

Simple electrochemical immunosensor is easily fabricated based on chitosan/reduce graphene oxide nanocomposite for sensitive determination of a tumor marker of malignant melanoma.     

NiCo2O4 thin film prepared by electrochemical deposition as a hole-transport layer for efficient inverted perovskite solar cells

Spinel NiCo₂O₄ is a promising p-type semiconductor for optoelectronic devices; however, it is difficult to prepare uniform and large-area NiCo₂O₄ films, which hinders its application as a hole transport material for perovskite solar cells (PSCs). In this study, a novel, mild, and low-cost KCl-assisted electrochemical deposition (ECD) approach was developed to directly prepare a uniform NiCo₂O₄ film on a fluorine-doped tin oxide (FTO) substrate. A uniform NiCo₂O₄ film prepared through an ECD approach was used as a hole-transport layer (HTL) in inverted PSCs. The resulting NiCo₂O₄ HTL-based device achieved a power conversion efficiency (PCE) of 19.24% with negligible hysteresis and excellent reproducibility. Additionally, it outperformed a NiO_x-based device (PCE = 18.68%). The unsealed devices retained 90.7% of their initial efficiency when subjected to stability measurements for 360 h in an ambient atmosphere. This study shows the great potential of ECD-prepared NiCo₂O₄ HTLs for large-area PSCs in the future.

An electrochemical deposition approach was developed to prepare a NiCo₂O₄ hole transport layer for inverted perovskite solar cells.     

Hexadecyl trimethyl ammonium bromide assisted growth of NiCo2O4@reduced graphene oxide/ nickel foam nanoneedle arrays with enhanced performance for supercapacitor electrodes

NiCo₂O₄@reduced graphene oxide (rGO)/nickel foam (NF) composites were prepared via a hydrothermal method followed by annealing assisted by hexadecyl trimethyl ammonium bromide (CTAB). NiCo₂O₄@rGO/NF nanoneedle arrays grew directly on Ni foam (NF) without using a binder. The effect of graphene oxide (GO) concentration on the electrochemical properties of the composite was studied. When the GO concentration was 5 mg L⁻¹, the as-prepared NiCo₂O₄@rGO/NF reaches the highest specific capacitance of 1644 F g⁻¹ at a current density of 1 A g⁻¹. Even at 15 A g⁻¹, the specific capacitance is still 1167 F g⁻¹ and the capacitance retention rate is 89% after 10 000 cycles at 10 A g⁻¹. Furthermore, a NiCo₂O₄@rGO/NF//graphene hydrogel (GH) asymmetric supercapacitor cell (ASC) device was assembled and exhibits a high specific capacitance of 84.13 F g⁻¹ at 1 A g⁻¹ and excellent cycle stability (113% capacitance retention) after 10 000 charge/discharge cycles at 10 A g⁻¹. This provides potential for application in the field of supercapacitors due to the outstanding specific capacitance, rate performance and cycle stability of NiCo₂O₄@rGO/NF.

Anisotropic NiCo₂O₄ nanoneedle arrays grew directly on Ni foam in the presence of rGO via the hydrothermal method followed by annealing assisted by hexadecyl trimethyl ammonium bromide (CTAB).     

Hierarchically self-assembled NiCo2O4 nanopins as a high-performance supercapacitor cathodic material: a morphology controlled study

In this study, 3D hierarchically self-assembled NiCo₂O₄ nanopins were synthesized by a morphology controlled hydrothermal method. Structure, morphology, and composition of the samples were investigated using FT-IR, XRD, EDS, and SEM methods. Electrochemical tests such as cyclic voltammetry (CV) and galvanostatic charge/discharge (GCD) studies were done in a three-electrode system with 1.0 M Na₂SO₄ solution as the electrolyte for the supercapacitive study of the samples on a carbon paste electrode for the first time. The results confirmed the high-performance supercapacitive behavior of the dense nanostructure and acceptable stability during the charge–discharge cycle. The specific capacitance for the dense self-organized nanopins was calculated using a galvanostatic charge/discharge experiment which gave 2168 F g⁻¹ at a current density of 5 A g⁻¹.

In this study, 3D hierarchically self-assembled NiCo₂O₄ nanopins were synthesized by a morphology controlled hydrothermal method.     

High mass loading flower-like MnO2 on NiCo2O4 deposited graphene/nickel foam as high-performance electrodes for asymmetric supercapacitors

The implementation of high mass loading MnO₂ on electrochemical electrodes of supercapacitors is currently challenging due to the poor electrical conductivity and elongated electron/ion transport distance. In this paper, a NiCo₂O₄/MnO₂ heterostructure was built on the surface of three-dimensional graphene/nickel foam (GNF) by a hydrothermal method. The petal structured NiCo₂O₄ loaded on graphene played a wonderful role as a supporting framework, which provided more space for the growth of high mass loading MnO₂ microflowers, thereby increasing the utilization rate of the active material MnO₂. The GNF@NiCo₂O₄/MnO₂ composite was used as a positive electrode and achieved a high areal capacitance of 1630.5 mF cm⁻² at 2 mA cm⁻² in the neutral Na₂SO₄ solution. The asymmetric supercapacitor assembled with the GNF@NiCo₂O₄/MnO₂ positive electrode and activated carbon negative electrode possessed a wide voltage window (2.1 V) and splendid energy density (45.9 Wh kg⁻¹), which was attributed to the satisfactory electroactive area, low resistance, quick mass diffusion and ion transport caused by high mass loading MnO₂.

A NiCo₂O₄/MnO₂ heterostructure with high mass loading MnO₂ microflowers was built on the surface of 3D graphene/nickel foam for the preparation of an asymmetric supercapacitor with splended energy density (45.9 Wh kg⁻¹).     

A uniformly anchored zirconocene complex on magnetic reduced graphene oxide (rGO@Fe3O4/ZrCp2Clx (x = 0, 1, 2)) as a novel and reusable nanocatalyst for synthesis of N-arylacetamides and reductive-acetylation of nitroarenes

In this study, a crafted zirconocene complex on rGO@Fe₃O₄ as a novel magnetic nanocatalyst was synthesized and then characterized using FT-IR, SEM, EDX, VSM, ICP-OES, TGA, BET and MS analyses. Next, catalytic activity of the prepared nanocomposite rGO@Fe₃O₄/ZrCp₂Cl_{x (x = 0, 1, 2)} towards successful reduction of aromatic nitro compounds to arylamines using N₂H₄·H₂O (80%) was investigated. The examined nanocatalyst also showed perfect catalytic activity for reductive-acetylation of aromatic nitro compounds to the corresponding N-arylacetamides without isolation of the prepared in situ amines using the N₂H₄·H₂O/Ac₂O system. Furthermore, acetylation of the commercially available arylamines to the corresponding N-arylacetamides was carried out by acetic anhydride in the presence of the rGO@Fe₃O₄/ZrCp₂Cl_{x (x = 0, 1, 2)} nanocomposite. All reactions were carried out in refluxing EtOH as a green solvent to afford the products in high yields. The obtained results exhibited that the nanocomposite of rGO@Fe₃O₄/ZrCp₂Cl_{x (x = 0, 1, 2)} showed a great catalytic activity in comparison to rGO and rGO@Fe₃O₄ as the parent constituents. Recovery and reusability of rGO@Fe₃O₄/ZrCp₂Cl_{x (x = 0, 1, 2)} were also examined for 8 consecutive cycles without significant loss of the catalytic activity. This establishes the sustainable anchoring of the zirconocene complex on the surface and mesopores of the rGO@Fe₃O₄ nanohybrid system.

In this study, a crafted zirconocene complex on rGO@Fe₃O₄ as a novel magnetic nanocatalyst was synthesized and then characterized using FT-IR, SEM, EDX, VSM, ICP-OES, TGA, BET and MS analyses.     

Synergistic absorbents based on SnFe2O4@ZnO nanoparticles decorated with reduced graphene oxide for highly efficient dye adsorption at room temperature

Recently, adsorption techniques have emerged as practical and effective methods for removing organic dyes, dramatically extending practical capabilities for treating deleterious pollutants in wastewater. However, an urgent issue restricting the performance of these techniques is that no available absorbents that can be used to treat both cationic and anionic organic dyes have been made with simple and reliable methods until now. Herein, we report a green synthetic strategy for the preparation of SnFe₂O₄/ZnO nanoparticles decorated on reduced graphene oxide (rGO), exhibiting a remarkably large surface area (120.33 m² g⁻¹). Substantial adsorption efficiency for removing MB dye was achieved, with 91.3% removal within 20 min at room temperature, and efficiencies of 79.6 to 92.8% are maintained as the pH conditions are varied from 3 to 11. Moreover, under mixed-dye conditions, involving MB, RhB, MO, RB5, and R6G organic materials, with dye concentrations ranging from 0.005 mM to 0.09 mM, an adsorption efficiency of above 50% can be reliably reached within 20 min. Such striking features can be interpreted as arising from a synergistic effect involving the hybrid composite based on a rGO matrix with negative charge and the dispersed SnFe₂O₄/ZnO nanoparticles with positive charge, additionally offering abundant adsorptive sites to allow reliable dye-adsorption kinetics.

Magnetically separable SnFe₂O₄/ZnO nanoparticles decorated on rGO sheets with remarkable dye adsorption capabilities are demonstrated.     

Ternary 3D reduced graphene oxide/Ni0.5Zn0.5Fe2O4/polyindole nanocomposite for supercapacitor electrode application

A facile two-step strategy has been reported for the preparation of a ternary 3D reduced graphene oxide/Ni_0.5Zn_0.5Fe₂O₄/polyindole nanocomposite (GNP) and this composite is applied as an electrode material for supercapacitor applications. Remarkably, Ni_0.5Zn_0.5Fe₂O₄ nanoparticles (NZF) decorated on reduced graphene oxide (GN2) are achieved by a facile hydrothermal method followed by coating with polyindole (PIN) through an in situ emulsion polymerization process. The structure, porosity, morphology, and thermal stability of the resulting ternary GNP hybrid material were characterized via X-ray diffraction (XRD), Raman spectroscopy, Brunauer–Emmett–Teller (BET) surface area measurements, transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). This combination of hybrid material has a favorable mesoporous structure that enables high exposure of active sites for fast electron transport for supercapacitor applications. We demonstrate here that the ternary GNP hybrid electrode material is capable of delivering a favorable specific capacitance of ∼320 F g⁻¹ at 0.3 A g⁻¹ within the potential range from −0.1 to 1 V, with desirable rate stability and excellent cycling stability in the three-electrode system. Furthermore, an asymmetric supercapacitor (ASC) of a two-electrode configuration was fabricated using 3D RGO and GNP as the negative and positive electrodes, respectively. Such a device manifests a favourable C_sp of 48.9 F g⁻¹ at 0.5 A g⁻¹ and retains stability of 84% even after 2000 cycles. This ASC device exhibits a significant energy density of 16.38 W h kg⁻¹ at a power density of 1784 W kg⁻¹. The synergistic effects of pseudo and double layer capacitive contributions from PIN and GN2 make this ternary GNP hybrid electrode material of great promise in supercapacitor applications.

A facile two-step strategy has been reported for the preparation of a ternary 3D reduced graphene oxide/Ni_0.5Zn_0.5Fe₂O₄/polyindole nanocomposite (GNP) and this composite is applied as an electrode material for supercapacitor applications.     

A reduced graphene oxide-β-cyclodextrin nanocomposite-based electrode for electrochemical detection of curcumin

Curcumin is a polyphenolic compound with anti-oxidative and anti-cancer properties that is obtained from turmeric plants. Several studies have demonstrated that cancer cells are not killed unless they are exposed to 5–50 mM of curcumin. Consequently, it is vital to control the concentration of curcumin in cancer therapy. In this study, a sensitive electrochemical sensor was fabricated based on a beta-cyclodextrin–reduced graphene oxide (β-CD–rGO) nanocomposite for measuring curcumin concentration. The effects of experimental factors were investigated and the optimum parametric conditions were determined using the Taguchi optimization method. The β-CD–rGO modified electrode exhibited good electrochemical properties for curcumin detection. The results of differential pulse voltammetry experiments unveiled that the sensor shows a linear response to curcumin concentration over the range of 0.05–10 mM with a detection limit of 33 nM and sensitivity of 4.813 μA μM⁻¹. The fabricated sensor exhibited selectivity in the presence of other electroactive species, e.g., propranolol, clomipramine and clonazepam.

In this study, a sensitive electrochemical sensor was fabricated based on a beta-cyclodextrin–reduced graphene oxide (β-CD–rGO) nanocomposite for measuring curcumin concentration.     

A voltammetric sensor based on reduced graphene oxide-hemin-Ag nanocomposites for sensitive determination of tyrosine

A novel voltammetric sensor was designed and used for the determination of l-tyrosine (l-Tyr) by surface modification of a glassy carbon electrode with reduced graphene oxide-hemin-Ag (rGO-H-Ag) nanocomposites. The nanocomposites were synthesized by a facile one-pot hydrothermal method and characterized by means of transmission electron microscopy and Raman spectroscopy. The determination of l-Tyr was investigated by cyclic voltammetry and further quantified using differential pulse voltammetry. The results revealed a significant enhanced electrochemical oxidation effect for l-Tyr at the nanocomposites modified electrode. Two linear ranges from 0.1 to 100 μM and 100 to 1000 μM as well as a low detection limit of 30 nM (S/N = 3) were obtained. In addition, the sensor also demonstrated good selectivity, reproducibility and stability.

A novel electrochemical sensor for the sensitive determination of l-Tyr was designed with a rGO-H-Ag nanocomposite modified electrode.     

A high-sensitive room temperature gas sensor based on cobalt phthalocyanines and reduced graphene oxide nanohybrids for the ppb-levels of ammonia detection

Highly sensitive gas sensing materials are of great importance for environmental pollution monitoring. In this study, four nanohybrid materials containing different phenoxyl substituents of cobalt phthalocyanines (tetra-β-carboxylphenoxylphthalocyanine cobalt (cpoPcCo), tetra-β-(4-carboxy-3-methoxyphenoxy)phthalocyanine cobalt (cmpoPcCo), tetra-β-phenoxylphthalocyanine cobalt (poPcCo), and tetra-β-(3-methoxyphenoxy)phthalocyanine cobalt (mpoPcCo)) and reduced graphene oxide (rGO) (RPcCo/rGO) were synthesized via non-covalent interactions as a high performance gas sensing materials for the ppb-level detection of ammonia (NH₃). Various characterization techniques, including FT-IR, Raman, UV-vis, TGA, XPS and SEM, were used to confirm the structure, element information and morphology of the as-synthesized materials. The obtained materials were used in interdigital electrodes to fabricate the sensing device, and the gas sensing performance was investigated at room temperature. The obtained sensors exhibited excellent sensitivity, selectivity, good reproducibility and perfect response–concentration linearity towards NH₃, which are mainly ascribed to the synergetic effects of RPcCo and rGO due to the specific surface area structure for NH₃ diffusion, the abundant active sites to adsorb NH₃, and excellent conductivity for efficient electron transport, particularly the effect of RPcCo. For example, the cpoPcCo/rGO-based sensor showed a higher and faster response for low concentration of NH₃ (∼2.5 and 45 s for 100 ppb of NH₃), a ppb level detection and superior stability over 60 days. Besides, the effect of different phenoxyl substituents of cobalt phthalocyanines on the sensing performance and the sensing mechanism for the sensitivity enhancement were discussed and confirmed by the first-principles density functional theory calculations and electrochemical impedance spectroscopy (EIS).

Highly sensitive gas sensing materials are of great importance for environmental pollution monitoring.