Extended producer responsibility in developing economies: Assessment of promoting factors through retail electronic firms for sustainable e-waste management

The adoption of the extended producers' responsibility (EPR) principle as a mitigation strategy for e-waste management has gained impetus over the past few years. However, e-waste management in developing economies through retail electronic firms' or producer responsibility organization is still inceptive. This study identified and analysed promoting factors of EPR principle adoption through retail electronic firms in the Ghanaian electronic industry. Through extant literature and stakeholders' perspectives, 15 factors were identified as strategic and operational promoting factors, which were evaluated by experts. Subsequently, the grey Decision-Making Trial and Evaluation Laboratory technique was used to analyse the data obtained. The outcome of the study suggests that operational factors have more influence than strategic factors to determine the adoption of the EPR principle. In addition, most of the important operational factors tend to be enabled by both push and pull measures by supply chain stakeholders. In the short term, adopting an advanced deposit recycling refund scheme tends to be the most effective elementary operational factor, which can push retailers to adopt the EPR principle. The significant pull elementary factors that need short-term attention include the opening up and creation of new market opportunities for e-companies as well as resilient and effective resources management. The study findings suggest that Ghana's present policy framework is limited for the adoption of the EPR principle by retail electronic firms. The study contributes to identifying promoting factors for adoption of the EPR principle from the perspectives of both the external and internal stakeholders in the electronic industry with emphasis on push and pull strategy.

Electrochemical Sensor Made with 3D Micro-/Mesoporous Structures of CoNi-N/GaN for Noninvasive Detection of Glucose

Noninvasive detection of glucose (NGD) is important because ∼10% of the global population is suffering from diabetes. Herein, a three-dimensional (3D) micro-/mesoporous structure, i.e., a CoNi-N nanosheet-coated GaN 3D scaffold (CoNi-N@GaN-3S), was proposed for detecting saliva glucose, where the GaN scaffold can provide a large open surface for nanosheet decoration, while the catalytic nanosheets can increase the surface area and prevent the GaN-3S from anodic corrosion. Moreover, it was found that high-temperature ammoniation of CoNi can lead to dense atomic holes and an N-terminated surface (CoNi-N), which promoted the ionization of CoNi with a higher catalytic activity. It is the first time that dense atomic holes have been observed in CoNi to our knowledge. The designed CoNi-N@GaN-3S sensor was applied to the electrochemical detection of glucose with a low limit of detection (LOD) of 60 nM and a high sensitivity, selectivity, and stability. In addition, detection of human-saliva glucose was realized with an LOD of 5 μM, which was more than 4-fold lower than reported reliable LODs. An integrated sensor with a low consumption of saliva sample was demonstrated for NGD.

Defect Surface Engineering of Hollow NiCo2S4 Nanoprisms towards Performance-Enhanced Non-Enzymatic Glucose Oxidation

Transition metal sulfides have been explored as electrode materials for non-enzymatic detection. In this work, we investigated the effects of phosphorus doping on the electrochemical performances of NiCo₂S₄ electrodes (P-NiCo₂S₄) towards glucose oxidation. The fabricated non-enzymatic biosensor displayed better sensing performances than pristine NiCo₂S₄, with a good sensitivity of 250 µA mM^-1 cm^-2, a low detection limit (LOD) of 0.46 µM (S/N = 3), a wide linear range of 0.001 to 5.2 mM, and high selectivity. Moreover, P-NiCo₂S₄ demonstrated its feasibility for glucose determination for practical sample testing. This is due to the fact that the synergetic effects between Ni and Co species, and the partial substitution of S vacancies with P can help to increase electronic conductivity, enrich binary electroactive sites, and facilitate surface electroactivity. Thus, it is found that the incorporation of dopants into NiCo₂S₄ is an effective strategy to improve the electrochemical activity of host materials.

High performance asymmetric supercapacitors based on Ti3C2T x MXene and electrodeposited spinel NiCo2S4 nanostructures

Spinel metal sulfides have been investigated for a wide range of applications mostly in electrochemical energy storage owing to their better electronic conductivity and high reversible redox activity. Herein, we report a facile fabrication approach for the binder-free supercapacitor electrodes based on spinel NiCo₂S₄ (NCS) on various substrates such as Cu-foil (CF), Ni-foam (NF), and vertical graphene nanosheets grown on carbon tape (VG) via a single step-controlled electrodeposition technique. The obtained electrodeposited NiCo₂S₄ grown on Cu-foil (denoted as CF-NCS) in symmetric assembly shows a high specific capacitance of 167.28 F g^-1 compared to NCS grown on Ni-foam and VG substrates, whereas, symmetric NiCo₂S₄ grown on a VG substrate device exhibits better cycling performance (81% for 3000 cycles) compared to CF-NCS and NF-NCS. Furthermore, an asymmetric supercapacitor was assembled in combination with MXene (Ti₃C₂T _x ) as a negative electrode (denoted as TCX). As a result, the CF-NCS//TCX device exhibits a high areal capacitance of 48.6 mF cm^-2 at 2 mA cm^-2 of current density. We also report good specific capacitance of 54.57 F g^-1 at 2 A g^-1; in addition, the CF-NCS//TCX assembly delivers maximum areal and gravimetric energy density of 14.86 mWh cm^-2 and 14.86 Wh kg^-1 respectively. In contrast, the VG-NCS//TCX device showed improved cycling stability with 85% of capacitance retention over 5000 cycles owing to its highly porous structure and multiple conductive networks in the VG substrate and provides structural stability to NCS with fast ion diffusion. This experiment favors 2D MXene as a capacitive electrode that provides a replacement for carbon-based electrodes in asymmetric assembly with superior electrochemical performance. Hence, the hierarchical NCS structure grown on the various substrates in combination with MXene serve as a promising material for energy storage application.

Electrodeposition preparation of NiCo2S4 nanoparticles on N-doped activated carbon modified graphene film for asymmetric all-solid-state supercapacitors

In this work, NiCo2S4 nanoparticles were anchored on the surface of nitrogen doped activated carbon modified graphene (GNAC) by simple electrodeposition to prepare GNAC/NiCo2S4-15 composite electrode materials for high-performance supercapacitors....

Efficient improvement in non-enzymatic glucose detection induced by the hollow prism-like NiCo2S4 electrocatalyst

Hollow prism-like NiCo2S4 materials (NiCo2S4 HNPs) were successfully fabricated by a two-step method. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and powder X-ray diffraction (XRD) confirmed the morphology and structure of the as-prepared NiCo2S4 nanoprisms. A non-enzymatic sensor based on NiCo2S4 HNPs was constructed with outstanding electrochemical activity towards glucose oxidation in alkaline medium. The sensor showed a rapid response time (∼0.1 s), a high sensitivity of 82.9 μA mM-1 cm-2, a wide linear range (0.005-20.2 mM) and a detection limit of 0.8 μM (S/N = 3) with a good selectivity and reproducibility. Additionally, the proposed electrode also confirmed the feasibility in practical blood serum. These results indicate that NiCo2S4/ITO has great potential in the development of non-enzymatic glucose sensor applications.

Synthesis of NiCo2O4 Nanostructures and Their Electrochemial Properties for Glucose Detection

In this work, we prepared spinel-type NiCo2O4 (NCO) nanopowders as a low-cost and sensitive electrochemical sensor for nonenzymatic glucose detection. A facile and simple chemical bath method to synthesize the NCO nanopowders is demonstrated. The effect of pH and annealing temperature on the formation mechanism of NCO nanoparticles was systematically investigated. Our studies show that different pHs of the precursor solution during synthesis result in different intermediate phases and relating chemical reactions for the formation of NCO nanoparticles. Different morphologies of the NCO depending on pHs are also discussed based on the mechanism of growth. Electrochemical performance of the prepared NCO was characterized towards glucose, which reveals that sensitivity and selectivity of the NCO are significantly related with the final microstructure combined with constituent species with multiple oxidation states in the spinel structure.

A sensitive pyrimethanil sensor based on porous NiCo2S4/graphitized carbon nanofiber film

With the extensive use of pesticides, the problem of pesticide residues has become people's concern. In this work, NiCo₂S₄ nanoneedle arrays grown on an electrospun graphitized carbon nanofiber film (NiCo₂S₄/GCNF) is successfully prepared by a simple two-step hydrothermal method, and further applied to detection of fungicide pyrimethanil (PMT). NiCo₂S₄ arrays exhibit a unique core-shell structure with rough surface, providing abundant electrochemically active sites exposed to the electrolyte. The NiCo₂S₄/GCNF modified electrode displays excellent electrocatalytic activity, and the electrode surface is controlled both by diffusion and adsorption processes. When applied to PMT determination, NiCo₂S₄/GCNF sensor displays wide linear range from 0.06 to 800 μM with low detection limit (20 nM). Furthermore, the as-proposed sensor also displays other outstanding advantages, including simple preparation, low cost, perfect reproducibility and good application in practical samples. Such attracting analytical properties could be attributed to high electrocatalytic activity of NiCo₂S₄ and superior electrical conductivity of GCNF frameworks. In addition, the detailed oxidation mechanism of PMT at NiCo₂S₄/GCNF electrode was also studied. The results indicate that NiCo₂S₄/GCNF is a promising platform for PMT sensors.

Facile Dual-Ligand Modulation Tactic toward Nickel-Cobalt Sulfides/Phosphides/Selenides as Supercapacitor Electrodes with Long-Term Durability and Electrochemical Activity

The use of high electrochemical active binary nickel-cobalt sulfides/phosphides/selenides (Ni-Co-X, X = S, P, Se) as electrochemical energy storage materials still has a space for improvement because they become electrochemically unstable during long-term use. Herein, a facile and cost-effective dual-ligand synergistic modulation tactic is described to substantially improve the durability of Ni-Co-X (X = S, P, Se) at the atomic level by partially substituting S, P, and Se ligands into the nickel-cobalt hydroxide precursor, respectively. Remarkably, the dual-ligand electrodes on Ni-foam achieve superior durability and high electrochemical activity when used as positive electrodes in supercapacitors. Impressively, the density functional theory calculations demonstrate that the OH ligand in NiCo₂(MOH)_x (M = S, P, Se) could attract electrons from metal-S/metal-P/metal-Se bonds to the metal-O bond, enhancing the binding energy of metal-S/metal-P/metal-Se bonds and improving the long-term durability of Ni-Co-X (X = S, P, Se) in alkaline electrolytes. Moreover, OH and S/P/Se ligands could effectively alter the electron structure and result in favorable electrochemical activity. Overall, this tactic could offer an exciting avenue to achieve long-term durability and electrochemical activity of supercapacitor electrodes simultaneously.

Simultaneous Electrochemical Detection of Nitrite and Hydrogen Peroxide Based on 3D Au-rGO/FTO Obtained Through a One-Step Synthesis

In this paper, Au and reduced graphene oxide (rGO) were successively deposited on fluorine-doped SnO₂ transparent conductive glass (FTO, 1 × 2 cm) via a facile and one-step electrodeposition method to form a clean interface and construct a three-dimensional network structure for the simultaneous detection of nitrite and hydrogen peroxide (H₂O₂). For nitrite detection, 3D Au-rGO/FTO displayed a sensitivity of 419 μA mM-1 cm-2 and a linear range from 0.0299 to 5.74 mM, while for the detection of H₂O₂, the sensitivity was 236 μA mM-1 cm-2 and a range from 0.179 to 10.5 mM. The combined results from scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, X-ray diffraction measurements (XRD) and electrochemical tests demonstrated that the properties of 3D Au-rGO/FTO were attributabled to the conductive network consisting of rGO and the good dispersion of Au nanoparticles (AuNPs) which can provide better electrochemical properties than other metal compounds, such as a larger electroactive surface area, more active sites, and a bigger catalytic rate constant.

Three-dimensional flower-like Ni–Mn–S on Ti mesh: a monolithic electrochemical platform for detecting glucose

Three-dimensional flower-like Ni–Mn–S on Ti mesh as a monolithic electrochemical platform was constructed and exhibited satisfactory glucose sensing performance.

A non-enzymatic glucose sensor based on a CoNi2Se4/rGO nanocomposite with ultrahigh sensitivity at low working potential

A CoNi₂Se₄–rGO nanocomposite fabricated on Ni foam shows excellent efficiency for non-enzymatic glucose sensing at low applied potential.

Metal-Organic Framework Template-Directed Fabrication of Well-Aligned Pentagon-like Hollow Transition-Metal Sulfides as the Anode and Cathode for High-Performance Asymmetric Supercapacitors

Given the exceptional specific surface area, geometry, and periodic porosity, transition-metal sulfides derived from crystalline metal-organic frameworks have spurred great interest in energy storage systems. Herein, employing a different sulfurization process, well-aligned NiCo₂S₄ and CoS₂ nanoarrays with a hollow/porous configuration derived from pentagon-like ZIF-67 are successfully designed and constructed on Ni foam. The hollow/porous structure grown on a conductive matrix can significantly improve electroactive sites, shorten charge/ion diffusion length, and enhance mass/electron transfer. Consequently, the obtained NiCo₂S₄ possesses an excellent specific capacitance of 939 C/g, a fast charge/discharge rate, and a favorable life span. An advanced asymmetrical supercapacitor is fabricated by engaging NiCo₂S₄ and CoS₂ as cathode and anode materials, respectively, with a well-separated potential window. The obtained device delivers an exceptional energy density of 55.8 W h/kg at 695.2 W/kg, which is highly considerable to the recent transition metal sulfide-based devices. This facile tactic could be employed to construct other electrode materials with superior electrochemical properties.

Direct growth of CuCo2S4 nanosheets on carbon fiber textile with enhanced electrochemical pseudocapacitive properties and electrocatalytic properties towards glucose oxidation

Flexible and wearable electronic devices with excellent performance have been desired for making the next generation of electronic products. Herein, the synthesis of CuCo₂S₄ nanosheets on flexible carbon fiber textile (CFT) by a facile one-step and scalable hydrothermal procedure is reported, which is free from the sulphurization process used in the conventional synthesis of mixed metal sulphospinels. The as-prepared CuCo₂S₄ nanostructures on CFT can provide rich reaction sites and short ion diffusion paths. The CuCo₂S₄ nanosheets are employed as the free-standing electrodes for two different applications: high-performance supercapacitors and non-enzymatic glucose sensors. When employed as a flexible electrode material for supercapacitors, the electrode presents ultrahigh performance in energy storage with a specific capacitance of 3321.6 F g^-1 at 5 A g^-1, which is attributed to the suitable mass loading and special morphology of the as-prepared nanosheets. Remarkably, a specific capacitance of 2931.4 F g^-1 is still retained at the high current density of 30 A g^-1, suggesting its excellent rate capability. The specific capacitance retains 87.1% after 3000 cycles, reflecting excellent cycling performance. For real applications, a flexible symmetric supercapacitor is assembled based on CuCo₂S₄ nanosheets, which achieves a high energy density of 64.6 W h kg^-1 at 499.7 W kg^-1 and a maximum power density of 2081.5 W kg^-1 at 45.1 W h kg^-1. Besides serving as a free-standing electrode for non-enzymatic glucose sensors, CuCo₂S₄ nanosheets have remarkable electrocatalytic activity towards glucose oxidation with a high sensitivity of 3852.7 μA mM^-1 cm^-2 and an extraordinary linear range up to 3.67 mM. The experimental results suggest that CuCo₂S₄ nanosheets are more suitable for non-enzymatic glucose sensors than the related single/binary transition metal oxides/sulfides. Such a superior performance demonstrates that CuCo₂S₄ nanosheets hold great potential for use as flexible multifunctional electronic devices including supercapacitors and non-enzymatic glucose sensors.

A bifunctional NiCo2S4/reduced graphene oxide@polyaniline nanocomposite as a highly-efficient electrode for glucose and rutin detection

A novel NiCo₂S₄/reduced graphene oxide@polyaniline (NiCo₂S₄/rGO@PANI) composite was synthesized by a facile two-step hydrothermal treatment and calcination, which was coupled with an in situ polymerization process.

Enhanced Nonenzymatic Glucose-Sensing Properties of Electrodeposited NiCo2O4-Pd Nanosheets: Experimental and DFT Investigations

Here, we report the facile synthesis of NiCo₂O₄ (NCO) and NiCo₂O₄-Pd (NCO-Pd) nanosheets by the electrodeposition method. We observed enhanced glucose-sensing performance of NCO-Pd nanosheets as compared to bare NCO nanosheets. The sensitivity of the pure NCO nanosheets is 27.5 μA μM^-1 cm^-2, whereas NCO-Pd nanosheets exhibit sensitivity of 40.03 μA μM^-1 cm^-2. Density functional theory simulations have been performed to qualitatively support our experimental observations by investigating the interactions and charge-transfer mechanism of glucose on NiCo₂O₄ and Pd-doped NiCo₂O₄ through demonstration of partial density of states and charge density distributions. The presence of occupied and unoccupied density of states near the Fermi level implies that both Ni and Co ions in NiCo₂O₄ can act as communicating media to transfer the charge from glucose by participating in the redox reactions. The higher binding energy of glucose and more charge transfer from glucose to Pd-doped NiCo₂O₄ compared with bare NiCo₂O₄ infer that Pd-doped NiCo₂O₄ possesses superior charge-transfer kinetics, which supports the higher glucose-sensing performance.