In-situ formation of electron acceptor to inhibit charge separation of photo-electrochemical sensor of dopamine-based CdS/Au/GQDs

A versatile photo-electrochemical (PEC) sensor protocol was established to quantitatively monitor dopamine (DA) levels by utilizing a triple interconnected structure of cadmium sulfide (CdS) modified with gold and graphene quantum dots (Au/GQDs). The introduction of Au and GQDs on the photocatalytic active center of CdS act as a charge separation mediator and photosensitizer, respectively, which are favorable for charge separation and transportation and PEC conversion. When the CdS/Au/GQDs photoelectrode was utilized for DA sensing in a weak alkaline solution, DA was oxidized and converted to poly(dopamine) (PDA), which possesses abundant benzoquinone (BQ) groups that act as electron acceptors. Consequently, the electron acceptors formed in-situ on the surface of the photoelectrode, reducing the anodic photocurrent signal. Under the optimal conditions, the photocurrent decreased when the DA concentration increased in a dynamic working range from 0.1 to 350 µM and with a limit of detection (LoD) of 0.0078 μM. Herein, the proposed strategy involving photoelectron transfer between the electron acceptor and semiconductor provides a new and versatile protocol for PEC sensor development

Hierarchical nickel-based metal-organic framework/graphene oxide incorporated graphene nanoplatelet electrode with exceptional cycling stability for coin cell and pouch cell supercapacitors

The utilization of the electrode materials for supercapacitor based on metal-organic frameworks (MOFs) has gained much attraction from researchers, due to their remarkable surface area, tunable pore size, and numerous redox sites. The construction of a hierarchical Ni-MOF/graphene oxide (GO) incorporated graphene nanoplatelet (GNP) exhibited the unique synergistic interaction between two different graphitic carbon structures towards the weak electrical conductivity and stability of pristine MOFs. The introduction of GO and GNP on MOF not only improves the conductivity and stability but also enhances the interfacial interaction and transport kinetics for both electrons and ions between supercapacitor electrodes. Herein, a hierarchical Ni-MOF/GO/GNP electrode fabricated by a facile approach is mounted in a symmetrical coin cell and pouch cell, by using 2.0 M potassium acetate as the electrolyte, to prepare supercapacitors. The constructed coin cell and pouch cell supercapacitor of Ni-MOF/GO3/GNP manifest outstanding electrochemical performance with specific capacitances of 102.24 and 70.41 F/g at the current density of 1 A/g, respectively. The extraordinary capacitance retentions of 85.6% and 82.5% are achieved for both cells, respectively, after more than 20,000 cycles. This exceptional outcome is ascribed to the favorable electrochemical kinetics of Ni-MOF/GO3/GNP that largely improves the structural stability of the hybrid material

Horseradish peroxidase-labeled silver/reduced graphene oxide thin film-modified screen-printed electrode for detection of carcinoembryonic antigen

In this study, a disposable and simple electrochemical immunosensor was fabricated for the detection of carcinoembryonic antigen. In this method, silver nanoparticles (AgNPs) were mixed with reduced graphene oxide (rGO) to modify the surface of screen-printed carbon electrode (SPE). Initially, AgNPs-rGO modified-SPEs were fabricated by using simple electrochemical deposition method. Then the carcinoembryonic antigen (CEA) was immobilized between the primary antibody and horseradish peroxidase (HRP)-conjugated secondary antibody onto AgNPs-rGO modified-SPEs to fabricate a sandwich-type electrochemical immunosensor. The proposed method could detect the CEA with a linear range of 0.05–0.50 µg mL−1 and a detection limit down to 0.035 µg mL−1 as compared to its non-sandwich counterpart, which yielded a linear range of 0.05–0.40 µg mL−1, with a detection limit of 0.042 µg mL−1. The immunosensor showed good performance in the detection of carcinoembryonic antigen, exhibiting a simple, rapid and low-cost. The immunosensor showed a higher sensitivity than an enzymeless sensor

Horseradish peroxidase-labeled silver/reduced graphene oxide thin film-modified screen-printed electrode for detection of carcinoembryonic antigen

In this study, a disposable and simple electrochemical immunosensor was fabricated for the detection of carcinoembryonic antigen. In this method, silver nanoparticles (AgNPs) were mixed with reduced graphene oxide (rGO) to modify the surface of screen-printed carbon electrode (SPE). Initially, AgNPs-rGO modified-SPEs were fabricated by using simple electrochemical deposition method. Then the carcinoembryonic antigen (CEA) was immobilized between the primary antibody and horseradish peroxidase (HRP)-conjugated secondary antibody onto AgNPs-rGO modified-SPEs to fabricate a sandwich-type electrochemical immunosensor. The proposed method could detect the CEA with a linear range of 0.05–0.50 µg mL−1 and a detection limit down to 0.035 µg mL−1 as compared to its non-sandwich counterpart, which yielded a linear range of 0.05–0.40 µg mL−1, with a detection limit of 0.042 µg mL−1. The immunosensor showed good performance in the detection of carcinoembryonic antigen, exhibiting a simple, rapid and low-cost. The immunosensor showed a higher sensitivity than an enzymeless sensor

Architecting neonicotinoid-scavenging nanocomposite hydrogels for environmental remediation

The ubiquitous presence of neonicotinoid insecticides in the environment poses potential health concerns across all biomes, aquatic systems, and food chains. This global environmental challenge requires robust, advanced materials to efficiently scavenge and remove these harmful neonicotinoids. In this work, we engineered nanocomposite hydrogels based on sustainable cellulose acetate for water treatment. The nanocomposite hydrogels were incorporated with small quantities of polymers of intrinsic microporosity (PIM-1) and graphene oxide (GO). We prepared the hydrogels using green solvents such as Cyrene and MeTHF via simple dropwise phase inversion. High adsorption capacity and fast kinetic behavior toward acetamiprid, clothianidin, dinotefuran, imidacloprid, and thiamethoxam were observed. We also developed a rapid and sustainable ultrasound-assisted regeneration method for the hydrogels. Molecular dynamics of the complex quaternary system revealed the synergistic effects of the components, and the presence of PIM-1 was found to increase the GO surface area available for neonicotinoid scavenging. We demonstrated the robustness and practicality of the nanocomposites in continuous environmental remediation by using the hydrogels to treat contaminated groundwater from the Adyar river in India. The presented methodology is adaptable to other contaminants in both aqueous environments and organic media

Cadmium Sulfide Nanoparticles Decorated with Au Quantum Dots as Ultrasensitive Photoelectrochemical Sensor for Selective Detection of Copper(II) Ions

Anomalous ingestion of copper has significant adverse effects and shows acute toxicity in living organisms. Recently, photoelectrochemical (PEC) method has attracted much attention as a platform for a Cu²⁺ ion sensor because of its high sensitivity, selectivity, low-cost, and accurate selection compared to other conventional methods. In this work, stepwise hydrothermal and <i>in situ</i> chemical approaches for synthesizing cadmium sulfide nanoparticles (CdS NPs) for decorating gold quantum dots (Au QDs) are presented, along with notable PEC performance. The amount of Au QDs loaded on the CdS NPs had a significant influence on the PEC performance. CdS NPs-Au QDs-2 with 1.0 mmol % Au QDs demonstrated an exceptional photocurrent density of 350.6 μA cm^–2, which was 3.7-, 2.2-, and 2.0-fold higher than those of CdS NPs, CdS NPs-Au QDs-1 (0.75 mmol %), and CdS NPs-Au QDs-3 (1.25 mmol %), respectively. Femtosecond transient absorption dynamics of the ground state recovery showed a buildup time of 243 fs for Au and 268 fs for CdS, which were assigned to cooling of the photoexcited electrons. For CdS NPs-Au QDs, the transient spectrum was dominated by a signal from CdS with no contribution from Au. The fast buildup dynamic was absent in CdS-Au, indicating a rapid transfer of the photoexcited electrons from CdS to Au before cooling down. Unquestionably, the CdS NPs-Au QDs-2 photoelectrode response upon Cu²⁺ detection showed the lowest limit of detection of 6.73 nM in a linear range of 0.5–120 nM. The selectivity of CdS NPs-Au QDs-2 toward Cu²⁺ ions in lake and tap water was also studied, which suggested that CdS NPs-Au QDs-2 is promising as a photoactive material for PEC-based environmental monitoring and analysis

Photoelectrochemical sensor based on modified cadmium sulfide nanomaterials for copper (II) ions detection

Discovering the distinctive photophysical properties of semiconductor nanomaterials has made these a popular subject in recent advances in nanotechnology-related analytical methods. Semiconductors are well-known materials that have been widely used in photovoltaic devices such as optical sensors and bioimaging, and dye-sensitized solar cells (DSSCs), as well as for light-emitting diodes (LEDs). The use of a narrow-bandgap semiconductor such as cadmium sulfide nanoparticles (CdS NPs) in the photoelectrochemical (PEC) sensor of chemicals and biological molecules plays a key role as a photosensitizer and promotes some specific advantages in light-harvesting media. Their size-controlled optical and electrical properties make nanomaterials fascinating and promising materials for a variety of nanoscale photovoltaic devices. Moreover, charge injection from the narrow bandgap to the adjacent material leads to efficient charge separation and prolongs the electron lifetime by the elimination of the charge carrier recombination probability. In this regard, a single photon enables the production of multiple photogenerated charge carriers in CdS NPs, which subsequently boosts the effectiveness of the photovoltaic devices. In particular, this thesis highlights the recent emerging PEC detection based on CdS NPs, specifically related to the interactions of CdS NPs with target analytes of copper ions (Cu2+). The investigation and justification of different CdS nanocomposites were discussed in terms of different structural morphologies, and its impact on sensitivity and selectivity towards the targeted Cu2+ ions. Thus, it eventually provides a significant insight in achieving real-world applications of CdS-based PEC sensing. In the first studies, the nanospherical-like morphology of CdS with a narrow diameter distribution of about 350–400 nm was being employed and assembled with a transparent ultrathin reduced graphene oxide (rGO) layer. The nanostructured CdS adhered securely to a continuous network of rGO that also acted as an avenue to facilitate the transfer of electrons from the conduction band (CB) of CdS. The CdS-rGO photoelectrode response for Cu2+ ion detection had a linear range of 0.5–120 μM, with a limit of detection (LoD) of 16 nM. The low LoD demonstrated the favourable structure of CdS-rGO as photoactive materials in PEC sensing platform. In the second studies, the smaller particle diameters in an average of 25−30 nm of nanospherical CdS was obtained. The hydrothermal synthesis of CdS NPs were decorated with gold quantum dots (Au QDs) via stepwise in situ approaches, along with notable PEC performance. The introduction of Au which induced a plasmonic effect on photoactive materials like CdS semiconductors has prompted an intensive interest in PEC sensing applications. The hybrid structure of CdS-Au resulted in the amplification of the photocurrent signal because of the enhanced absorption of photon-generated photoelectron on the CdS. Therefore, it contributed to a sensitive Cu2+ ions detector with the lowest LoD of 6.73 nM in a linear range of 0.5−120 nM. In the third studies, huge efforts have been dedicated to intensifying the PEC performance by modifying the morphology and structure of CdS. Onedimensional (1D) nanostructure (e.g. nanotubes, nanorods, nanofiber and nanowire) of CdS were found to have a practical and substantial potential due to its specific directionality for the transportation of charge carrier, thus decreasing the probability of the recombination of charge carrier. In this regards, the 1D nanorods (NRs) structure of CdS was prepared and the outcomes consistently portray a much better PEC performance than the other counterpart particulate nanostructure. A multi-functional hybrid nanostructure of CdS NRs with Au NPs and graphene quantum dots (GQDs) has been successfully designed. The calculated LoD was 2.27 nM in a range of 0.1-290 nM. A clear trend can be observed based on the obtained LoD from all the three studies, and ultimately proven that the structure, particle size and the nanocomposite materials- based CdS could greatly influence the PEC sensing performance of Cu2+ ions. It has been a pressing need to develop a new materials for simultaneous detection and removal of Cu2+ ions from water sources, due to its acute and chronic effect on human health upon exposure to excessive copper. Thus, in the final studies, a ternary hybrid of cellulose acetate (CA) with CdS and methylene blue (MB) in a bead composition was synthesized and investigated as a photosensor-adsorbent of Cu2+ ions. The PEC detection of Cu2+ ions possessed a lower LoD of 16.9 nM and a notable removal efficiency of 96.3% in the linear range of 0.1-290 nM. Conclusively, these research have given rise to a neoteric finding and provided an important leap in the employment of CdS as potential semiconductor materials in PEC sensing applications. Even though, only a few CdS-based products that have successfully penetrated the market, but the thorough study and investigation of CdS- based nanocomposite in this thesis can eventually disclose its real potential. Ultimately, it may become a kick-start to researchers and innovators to come up with new CdS-based photosensor device

Visible-light-prompt photoelectrochemical sensor of copper(II) ions based on CdS nanorods modified with Au nanoparticles and graphene quantum dots

Excessive consumption of Cu2+ ions can cause damage to liver and kidney. Thus, significant efforts have been devoted to detecting Cu2+ ions in the environment and biological systems. An interconnected triplet structure of CdS/Au/GQDs was designed as the photo-to-electron conversion medium for real-time and selective visible-light-prompt photoelectrochemical (PEC) sensor of Cu2+ ions in real-water samples. The synergistic interaction of CdS/Au/GQDs enabled smooth transportation of charge carrier to the charge collector, providing a channel to inhibit the charge recombination reaction. Moreover, the presence of Cu2+ ion on the photoelectrode activated the quenching of the charge transfer efficiency, thus promoting sensitive PEC determination of Cu2+ ions level. The real-time monitoring of Cu2+ ions in mineral water, tap water and reverse osmosis water were performed with satisfactory results, confirming the capability of the as-fabricated photoelectrode as a practical detector for trace element of Cu2+ ions

Selective and sensitive visible-light-prompt photoelectrochemical sensor of Cu2+ based on CdS nanorods modified with Au and graphene quantum dots

Nowadays, increasing the risk for copper leaching into the drinking water in homes, hotels and schools has become unresolved issues all around the countries such as Canada, the United States, and Malaysia. The leaching of copper in tap water is due to a combination of acidic water, damaged pipes, and corroded plumbing fixtures. To remedy this global problem, a triple interconnected structure of CdS/Au/GQDs was designed as a photo-to-electron conversion medium for a real time and selective visible-light-prompt photoelectrochemical (PEC) sensor for Cu2+ ions in real water samples. The synergistic interaction of the CdS/Au/GQDs enabled the smooth transportation of charge carriers to the charge collector and provided a channel to inhibit the charge recombination reaction. Thus, a detection limit of 2.27 nM was obtained, which is 10,000 fold lower than that of WHO’s Guidelines for Drinking-water Quality (∼30 μM). The photocurrent reduction was negligible after 30 days of storage under ambient conditions, suggesting the high stability of photoelectrode. Moreover, the real-time monitoring of Cu2+ ions in real samples was performed with satisfactory results, confirming the capability of the investigated photoelectrode as the most practical detector for trace amounts of Cu2+ ions