A novel electrochemical sensor for the detection of metronidazole residues in food samples

The widespread use and misuse of antibiotics in pharmaceuticals and animal farming has resulted in their accumulation in food sources and the environment, posing significant threats to human health, the environment, and the global economy. In this study, we have developed a hypersensitive, and ultra-selective electrochemical sensor, the first of its kind, by integrating a thermally annealed gold-silver alloy nanoporous matrix (TA-Au-Ag-ANpM) with reduced graphene oxide (r-GO) and poly(glycine) at the surface of a glassy carbon electrode (GCE). This sensor aims to detect life-threatening metronidazole (MTZ) residues in food samples. TA-Au-Ag-ANpM/r-GO/poly(glycine)/GCE was thoroughly characterized using a range of analytical techniques, including UV-Vis, FT-IR, XRD, SEM, and EDX. Furthermore, its electrochemical properties were investigated by cyclic voltammetry (CV), square wave voltammetry (SWV), and electrochemical impedance spectroscopy (EIS). The sensor exhibited outstanding performance, with a broad linear range of 2.0 pM-410 μM. The limits of detection (LOD) and quantification (LOQ) were determined to be 0.0312 pM and 0.104 pM, respectively. The TA-Au-Ag-ANpM/r-GO/poly(glycine)/GCE exhibited exceptional reproducibility, repeatability, stability, and resistance to interferences. Moreover, the sensor demonstrated outstanding performance in detecting MTZ residues in milk powder, pork, and chicken meat samples, achieving very good recoveries (96.9%-101.4%) with a relative standard deviation (RSD) below 5%. This performance highlights the potential for practical applications in food safety and quality monitoring. Therefore, the developed sensor contributes to the advancement of electrochemical sensing technology and its application in ensuring food safety and integrity by combating antibiotic residues.

Design and fabrication of porous three-dimensional Ag-doped reduced graphene oxide (3D Ag@rGO) composite for interfacial solar desalination

Solar-driven interfacial desalination technology has shown great promise in tackling the urgent global water scarcity crisis due to its ability to localize heat and its high solar-to-thermal energy conversion efficiency. For the realization of sustainable saline water desalination, the exploration of novel photothermal materials with higher water vapor generation and photothermal conversion efficiency is indispensable. In the current study, a novel 3D interconnected monolithic Ag-doped rGO network was synthesized for efficient photothermal application. The Ultraviolet-Visible-Near Infrared (UV-Vis-NIR) and FTIR analyses demonstrated that the controlled hydrothermal reduction of GO enabled the restoration of the conjugated sp2 bonded carbon network and the subsequent electrical and thermal conductivity through a significant reduction of oxygen-containing functional groups while maintaining the hydrophilicity of the composite photothermal material. In the solar simulated interfacial desalination study conducted using 3.5 wt.% saline water, the average surface temperatures of the 3D material increased from 27.1 to 54.7 °C in an hour, achieving an average net dark-excluded evaporation rate of 1.40 kg m-2 h-1 and a photothermal conversion efficiency of ~ 97.54% under 1 sun solar irradiance. In the outdoor real-world application test carried out, the surface temperature of the 3D solar evaporator reached up to 60 °C and achieved a net water evaporation rate of 1.50 kg m-2 h-1 under actual solar irradiation. The 3D interwoven porous hierarchical evaporator displayed no salt precipitation over the 54-h period monitored, demonstrating the promising salt rejection and real-world application potential for efficient desalination of saline water.

Cu@CuOx/WO3 with photo-regulated singlet oxygen and oxygen adatoms generation for selective photocatalytic aromatic amines to imines

Photocatalysts can absorb light and activate molecular O2 under mild conditions, but the generation of unsuitable reactive oxygen species often limits their use in synthesizing fine chemicals. To address this issue, we disperse 1 wt% copper on tungsten trioxide (WO3) support to create an efficient catalyst for selective oxidative coupling of aromatic amines to imines under sunlight irradiation at room temperature. Copper consists of a metallic copper core and an oxide shell. Experimental and density functional theory calculations have confirmed that Cu2O is the primary activation site. Under λ < 475 nm, the light excites electrons of the valence bands in Cu2O and WO3, which activate O2 to superoxide radical •O2-. Then rapidly transforms into oxygen adatoms (•O) and oxygen anion radicals (•O-) species on the surface of Cu2O. Simultaneously, it is captured by holes in the WO3 valence band to generate singlet oxygen (1O2). •O bind to 1O2 promoting the coupling reaction of amines. When λ > 475 nm, intense light absorption due to the localized surface plasmon resonance excites numerous electrons in Cu to promote the oxidative coupling with the adsorbed O2. This study presents a promising approach towards the design of high-performance photocatalysts for solar energy conversion and environmentally-friendly oxidative organic synthesis.

Copper Phenylacetylide and TiO2 Modification for an Efficient Visible-Light-Driven Oxidative Coupling of Amines

The selective oxidation of amines to imines under mild conditions has attracted much attention. Our study reveals that copper phenylacetylide (PhC2Cu) could serve as an efficient photocatalyst for imine synthesis under visible-light irradiation (>400 nm). Utilizing benzylamine as a model reactant, PhC2Cu achieves an imine yield of 50.4%, which is 5 times higher than that of P25 under the same conditions and comparable to the yield obtained by the 3 wt % Au/P25 photocatalyst (55.4%). Further loading 3.9 nm TiO2 onto PhC2Cu through tetrabutyl titanate hydrolysis increases the imine yield to 84.7%, with a Ti:Cu atomic ratio of 3.65%. Control experiments, photoluminescence (PL) spectra, optical pump terahertz probe (OPTP) spectra, and electron spin resonance (ESR) tests confirm that the optimized TiO2 modification promotes the separation of excited carriers and electron transfer in PhC2Cu and facilitates the activation of surface oxygen, thereby enhancing the formation of superoxide radicals, a key active oxygen species in the reaction system. This work presents a promising strategy for efficient imine synthesis via amine coupling and expands the application field of PhC2Cu-based photocatalysts.

Chemical synthesis and super capacitance performance of novel CuO@Cu4O3/rGO/PANI nanocomposite electrode

Copper oxide-based nanocomposites are promising electrode materials for high-performance supercapacitors due to their unique properties that aid electrolyte access and ion diffusion to the electrode surface. Herein, a facile and low-cost synthesis in situ strategy based on co-precipitation and incorporation processes of reduced graphene oxide (rGO), followed by in situ oxidative polymerization of aniline monomer has been reported. CuO@Cu4O3/rGO/PANI nanocomposite revealed the good distribution of CuO@Cu4O3 and rGO within the polymer matrix which allows improved electron transport and ion diffusion process. Galvanostatic charge-discharge (GCD) results displayed a higher specific capacitance value of 508 F g-1 for CuO@Cu4O3/rGO/PANI at 1.0 A g-1 in comparison to the pure CuO@Cu4O3 278 F g-1. CuO@Cu4O3/rGO/PANI displays an energy density of 23.95 W h kg-1 and power density of 374 W kg-1 at the current density of 1 A g-1 which is 1.8 times higher than that of CuO@Cu4O3 (13.125 W h kg-1) at the same current density. The retention of the electrode was 93% of its initial capacitance up to 5000 cycles at a scan rate of 100 mV s-1. The higher capacitance of the CuO@Cu4O3/rGO/PANI electrode was credited to the formation of a fibrous network structure and rapid ion diffusion paths through the nanocomposite matrix that resulted in enhanced surface-dependent electrochemical properties.

Fabrication of composite transparent conductive electrodes based on silver nanowires

Composite transparent conductive electrodes (C-TCEs) have recently been produced using low-cost techniques to keep up with the boom in the fabrication and development of optoelectronic devices. In this article, silver nanowires (AgNWs) were successfully synthesized by a simple hydrothermal method using different molecular weights MWs of poly (N-vinylpyrrolidone) (PVP). Graphene oxide (GO) was prepared using the modified Hummers' method and a reduction step was held on GO films to produce reduced GO (rGO). C-TCEs were fabricated by over-coating the AgNWs electrodes with rGO, or poly(3,4-ethylenedioxythiophene) polystyrene sulfonate to improve the roughness, surface energy, and sheet resistance. The influence of using lower and higher MWs of PVP on the yield, shape, and size of AgNWs was investigated. The results showed that using lower MW of PVP had a great effect on the yield, morphology, and aspect ratio of AgNWs with diameter of 46 nm and average length 12 µm. The optical, morphological, topographical, and electrical properties of TCEs were studied. AgNWs/rGO composite electrode provided the lowest surface roughness and surface energy of 250 nm and 47.95 mN/m, respectively, with a relatively high transparency of 78.2% at 550 nm light wavelength, and a low sheet resistance of 27 Ω/□.

Coupled adsorption-photocatalysis process for the removal of diclofenac using magnetite/reduced graphene oxide nanocomposite

Diclofenac (DCF) is frequently detected in water bodies (ng/L to g/L) as it is not completely removed by conventional wastewater treatment plants. Adsorption and photocatalysis have been studied as promising methods for treating DCF; however, both processes have limitations. Thus, in this study, the removal efficiency of DCF is evaluated using a magnetite/reduced graphene oxide (Fe3O4/RGO) nanocomposite via a coupled adsorption-catalysis process. The Fe3O4/RGO nanocomposite was successfully synthesized using a microwave-assisted solvothermal method and exhibited a bandgap of 2.60 eV. The kinetic data best fitted the Elovich model (R2 = 0.994, χ2 = 0.29), indicating rapid adsorption. The maximum DCF adsorption capacity calculated using the Langmuir model was 80.33 mg/g. An ultraviolet C (UVC) light source and 0.1 g/L of Fe3O4/RGO nanocomposite were the optimum conditions for the removal of DCF (C0 = 30 mM) by a coupled adsorption-photocatalysis process (first-order rate constant (k) = 0.088/min), which was greater than the single adsorption (k = 0.029/min) and pre-adsorption and post-photocatalysis (k = 0.053/min) processes. This indicates that the adsorbed DCF did not hamper the photocatalytic reaction of the Fe3O4/RGO nanocomposite, but rather enhanced the coupled adsorption-photocatalytic reaction. DCF removal efficiency was higher at acidic conditions (pH 4.3-5.0), because high H+ promotes the generation of certain reactive oxygen species (ROS) and increases of electrostatic interaction. The presence of NaCl and CaCl2 (10 mM) did not notably affect the total DCF removal efficiency; however, Ca2+ affected the initial DCF adsorption affinity. Scavenger experiments demonstrated O2∙- and h+ play a key ROS than ·OH to degrade DCF. The acute toxicity of DCF towards Aliivibrio fischeri gradually decreased with increasing treatment time.

Tripodal Triazine and 1,8-Naphthalimide-based Small Molecules as Efficient Photocatalysts for Visible-light Oxidative Condensation

Tripodal donor-acceptor (D-A) small molecules Tr-Np3 and Tr-T-Np3 consisting of triphenyl triazine and 1,8-naphthalimide, without and with a thiophene spacer have been synthesized. Their optical and redox properties were thoroughly investigated along with their utilization as photocatalysts in organic transformations. Compounds Tr-Np3 and Tr-T-Np3 showed broad absorption in the range of 290-480 nm in solutions and 300-510 nm in thin films. These tripodal molecules displayed wide optical bandgaps of (Eg opt ) 3.10 eV and 2.64 eV with very deep-lying HOMO energy levels (-6.60 eV and -6.03 eV) and low-lying LUMO levels (-3.50 eV and -3.40 eV). Appreciable electron mobilities of 5.24×10-4  cm2 /Vs and 6.14×10-4  cm2 /Vs were obtained for compounds Tr-Np3 and Tr-T-Np3 respectively by space-charge limited current (SCLC) measurements. Metal-free tripodal molecules Tr-Np3 and Tr-T-Np3 showed excellent photocatalytic abilities towards condensation of aromatic aldehydes and o-phenylenediamine followed by cyclization under visible light to yield benzimidazole derivatives that are of high medicinal value.

Europium oxide modified reduced graphene oxide composite for trace detection of hydrogen phosphate ions in soil samples

The phosphate (PO43-) ion is a constituent of the environment, soil, plants, and animals. There should be a real-time and portable phosphate detection sensor. Herein we propose a colorimetry based sensitive method for hydrogen phosphate (HPO42-) ions detection using europium oxide modified reduced graphene oxide composite (Eu2O3-RGO) and gold nanoparticles (Au NPs). We detect the HPO42- by observing the anti-aggregation of gold nanoparticles. In the presence of a Eu2O3-RGO composite, the Au NPs underwent an aggregation process, causing a colour change of Au NPs from wine red to wine blue. Once Eu-modified RGO was pre-mixed with HPO42- ions and introduced into Au NPs, the Eu nanoparticles in the Eu-modified RGO were attracted to the HPO42- ions. Because of this, the aggregated Au NPs started to anti-aggregate, and the colour of Au NPs changed from wine blue to wine red. The calibration curve of the sensor goes from 0 nM to 500 nM concentration of HPO42- ions. Our sensor has a detection limit of 0.08 nM, which is lower than the reported values. This improved lower detection limit is probably due to the use of RGO, which according to the literature review, can adsorb phosphate ions onto its surface. We optimized the incubation time and europium oxide (Eu2O3) nanoparticle concentration to improve the sensor's sensitivity. Lastly, we tested an agricultural sample using our developed method.

Redox mediators boost NOx reduction via trade-off electron charges using a cube-shaped (cMn@rGO) catalyst; mechanism and electrochemical study

Gaseous pollutants like sulfur dioxide and nitrogen oxide(s) (SO2, NOx) have been increasing exponentially for the last two decades, which have had adverse effects on human health, aquatic life, and the environment. Recently, for air pollution taming, manganese/oxide (Mn/MnO) has become a very promising heterogeneous catalyst due to its environment-friendly, low-price, and remarkable catalytic abilities for toxic gases. In this work, cube-shaped Mn nanoparticles (cMn NPs) were decorated on the surface of reduced graphene oxide (rGO) by the solvothermal method. The resulting cMn@rGO composite was employed for electrochemical NOx reduction. However, the microscopic (TEM/HRTEM) and structural analysis were utilised to investigate the morphology and characteristics of the cMn@rGO composite. This electrochemical-based treatment for NOx reduction is employed by using electron shuttle or redox mediators. Here, four distinct redox mediators are used to address electrochemical obstacles, which effectively facilitate electron transportation and promoted NOx reduction on the electrode surface. These mediators not only significantly enhanced the NOx conversion into valuable products, i.e., N2 and N2O, but also made the process smooth with high performance. Among these mediators, neutral red (N.R) exhibited extraordinary potential in enhancing NOx reduction. The obtained results indicated that the remarkable catalytic performance (∼93%) of the cMn@rGO can be attributed to several factors, including the catalyst's three-dimensional architecture structure and abundant active sites. The designed catalyst (cMn@rGO) is not only cost-effective and sustainable but also exhibits excellent potential in effectively reducing NOx, which could be beneficial for large-scale NOx abatement.

Self-Assembled and Multilayer-Overlapped ESM-PDA@rGO Nanofilm-Based Flexible Wearable Sensor for Real-Time Body Temperature Monitoring

There is an urgent need for wearable sensors that continuously monitor human physiological conditions in real time. Herein, an ESM-PDA@rGO-based flexible wearable temperature sensor was successfully constructed by integrating an eggshell membrane (ESM) with reduced graphene oxide (rGO) through dopamine (DA) polymerization. Depending on the "bridge effect" of diversified polydopamine (PDA) chains, on the one hand, a staggered arrangement of PDA-rGO frameworks and a lot of conductive pathways were produced and acted as an active layer. On the other hand, PDA-rGO frameworks were linked with ESM by PDA chains as a flexible sensing nanofilm. As a result, these mechanical merits of the ESM-PDA@rGO exhibited a 1.8-fold increase in Young' s modulus and 1.4-fold increase in tensile strength. Thereby, the conformability and performance of the temperature sensor were greatly enhanced, showing excellent sensitivity (-2.23%/°C), good linearity (R2 = 0.979), as well as stability. Especially, the flexible sensing nanofilm is evolved from the staggered arrangement of PDA-rGO frameworks, which endows it with rapid response (only 4-8 s), high resolution (0.1 °C), as well as excellent long-term durability (10 weeks). More importantly, the temperature sensor demonstrates insensitivity to bending deformation, ensuring reliable wearing stability. The sensor allows for online, real-time monitoring of human body temperature, encompassing both core (forehead, temple, cochlea, and exhale gas) and shell (palm and back of the hand, fingertip, and instep) temperatures. Particularly, it can accurately assess minor changes in peripheral body temperature before and after exercise, and it is capable of mapping daily patterns of body temperatures. The developed temperature sensor will provide us new materials design concepts and holds considerable promise in the fields of e-skin, disease surveillance, prediction, and diagnose.

Selective aerobic coupling of amines to imines using solar spectrum-responsive flower-like Nen-graphene quantum dots (GQDs) decorated with 2, 4-dinitrophenylhydrazine (PH) as a photocatalyst

Indeed, the development of ecologically benign molecular fabrication methods for highly efficient graphene quantum dots-based photocatalysts is of great significant. Graphene quantum dots-based photocatalysts have promising applications in various field, including environmental remediation, energy conversion, and splitting of water. However, ensuring resource reusability and minimizing the environmental impact are crucial considerations in the development. From this perspective, attention has also been paid to the creation of easy to make solar light harvesting graphene quantum dots-based photocatalysts for synthesising pharmaceuticals and functional imines compounds. Imines are excellent significant building blocks in pharmaceutical chemistry and excellent examples of these valuable compounds' synthetic intermediates, and the environmentally friendly oxidative synthesis of imines from amines. Therefore, herein, we designed a facile and efficient condensation route to synthesize the Nen-GQDs@PH photocatalyst. This route involves coupling of 2,4-dinitrophenylhydrazine (PH) with nitrogen-enriched graphene quantum dots (Nen-GQDs). The Nen-GQDs@PH as photocatalyst functions in a highly selective and efficient manner, leading to high amines conversion efficiency to imines (95%). Our results highlight a novel and environmentally safe approach for generating highly selective imines from various types of amines, setting a new benchmark in the current research field.

Graphene oxide-manganese oxide composite as an electrocatalyst for simultaneous detection of manganese- and chromium-contaminated water

The development of a sensitive and selective electrochemical sensor for simultaneous quantification of manganese (Mn(II)) and chromium (Cr(VI)) using composite of graphene oxide (GO) and manganese oxide modified screen printed carbon electrode (GO-Mn2O3/SPCE) is reported for the first time. The good sensing performance is achieved by mixing GO prepared by modified Hummer's method (GO-H) with proper particle size of Mn2O3 (241 nm). The mechanism of this sensor is based on the formation of Mn-O and Cr-O on the modified electrode with assistance of oxygen moieties provided by both Mn2O3 NPs and GO. The analytical performances were investigated by measuring electrochemical signal of Mn(II) and Cr(VI) by using square-wave cathodic stripping voltammetry (SWCSV). This sensor holds low electrode-to-electrode variation (relative standard deviation (RSD) < 4%) with a good limit of detection (LOD) at about 6.67 and 11.20 μg⋅L-1 for Mn(II) and Cr(VI), respectively. Applicability of this sensor was demonstrated by measuring Mn(II) and Cr(VI) in tap water samples with recovery of 90.77-103.45% and 82.34-103.73% for Mn(II) and Cr(VI) determinations, respectively. With the contribution of both GO and Mn2O3 as electrocatalysts, this developed sensor is capable to be used for water quality monitoring in real samples.

Permselectivity and Ionic Conductivity Study of Na+ and Br- Ions in Graphene Oxide-Based Membranes for Redox Flow Batteries

Permselectivity of a membrane is central for the development of electrochemical energy storage devices with two redox couples, such as redox flow batteries (RFBs). In RFBs, Br3-/Br- couple is often used as a catholyte which can cross over to the anolyte, limiting the battery's lifetime. Naturally, the development of permselective membranes is essential to the success of RFBs since state-of-the-art perfluorosulfonic acid (PFSA) is too costly. This study investigates membranes of graphene oxide (GO), polyvinylpyrrolidone (PVP), and imidazole (Im) as binder and linker, respectively. The GO membranes are compared to a standard PFSA membrane in terms of ionic conductivity (Na+) and permselectivity (exclusion of Br-). The ionic conduction is evaluated from electrochemical impedance spectroscopy and the permselectivity from two-compartment diffusion cells in a four-electrode system. Our findings suggest that the GO membranes reach conductivity and permselectivity comparable with standard PFSA membranes.

Highly Selective Nitrogen-Doped Graphene Quantum Dots/Eriochrome Cyanine Composite Photocatalyst for NADH Regeneration and Coupling of Benzylamine in Aerobic Condition under Solar Light

Photocatalysis is an ecofriendly and sustainable pathway for utilizing solar energy to convert organic molecules. In this context, using solar light responsive graphene-based materials for C–N bond activation and coenzyme regeneration (nicotinamide adenine dinucleotide hydrogen; NADH) is one of the utmost important and challenging tasks in this century. Herein, we report the synthesis of nitrogen-doped graphene quantum dots (NGQDs)-eriochrome cyanine (EC) solar light active highly efficient “NGQDs@EC” composite photocatalyst for the conversion of 4-chloro benzylamine into 4-chloro benzylamine, accompanied by the regeneration of NADH from NAD+, respectively. The NGQDs@EC composite photocatalyst system is utilized in a highly efficient and stereospecific solar light responsive manner, leading to the conversion of imine (98.5%) and NADH regeneration (55%) in comparison to NGQDs. The present research work highlights the improvements in the use of NGQDs@EC composite photocatalyst for stereospecific NADH regeneration and conversion of imine under solar light.

Biogenic synthesis of reduced graphene oxide decorated with silver nanoparticles (rGO/Ag NPs) using table olive (olea europaea) for efficient and rapid catalytic reduction of organic pollutants

In this work, graphene oxide (GO) sheets were prepared via a facile electrochemical exfoliation of graphite in acidic medium and subsequent oxidation with potassium permanganate. The GO sheets were employed for preparation of reduced GO adorned with nanosized silver (rGO/Ag NPs) using green reduction of GO and Ag(I) via olive fruit extract as a reducing and immobilizing agent. The crystal phase, morphology, and nanostructure of the prepared catalyst were characterized by XRD, SEM, EDX, UV-Vis and Raman spectroscopy techniques. The as-prepared rGO/Ag NPs showed superior catalytic performance towards the complete reduction (up to 99%) of 4-nitrophenol (4-NPH) to 4-aminophenol (4-APH) and rhodamine B (RhB) to Leuco RhB within 180 s using NaBH₄ at ambient condition. The rate constant (k) values were found to be 0.021 and 0.022 s^-1 for 4-NPH and RhB reduction, respectively. In addition, the regenerated catalyst could be reused after seven cycles without losing any apparent catalytic efficiency. Accounting for the excellent catalytic capability, chemical stability and environment-friendly synthesis protocol, the rGO/Ag NPs has great potential working as a heterogeneous catalyst in the transforming harmful organic contaminants into less harmful or harmless compounds.

Impacts of ruthenium valence state on the electrocatalytic activity of ruthenium ion-complexed graphitic carbon nitride/reduced graphene oxide nanosheets towards hydrogen evolution reaction

Design and engineering of effective electrode catalysts represents a critical first step for hydrogen production by electrochemical water splitting. Nanocomposites based on ruthenium atomically dispersed within a carbon scaffold have emerged as viable candidates. In the present study, ruthenium metal centers are atomically embedded within graphitic carbon nitride/reduced graphene oxide nanosheets by thermal refluxing. Subsequent chemical reduction/oxidation leads to ready manipulation of the ruthenium valence state, as evidenced in microscopic and spectroscopic measurements, and hence enhancement/diminishment of the electrocatalytic activity towards hydrogen evolution reaction in both acidic and alkaline media. This is largely ascribed to the increased/reduced contribution of the Ru valence electrons to the density of state near the Fermi level which dictates the binding and reduction of hydrogen. Results from this study highlight the significance of the valence state of metal centers in the manipulation and optimization of the catalytic performance of single atom catalysts.

Solar-light-induced green conversion of amines into imines by lemon derived heteroatoms-doped GQDs as a green photocatalyst

Graphene is one of the amazing present encroachments in current research area of science and one of the utmost fascinating materials for relevance in cutting-edge research. Herein, we designed lemon-derived heteroatoms-doped graphene quantum dots (S, N-GQDs) based photocatalyst for the first time. For the integrating reactions of amines in aerobic conditions under solar light by S, N-GQDs photocatalyst exhibit utmost higher photocatalytic activity than simple oxygen-doped graphene quantum dots (O-GQDs) due to slow recombination charges. The mechanisms accountable for the drastically increased photocatalytic activity of S, N-GQDs in solar light responsive integrating reactions of amines in aerobic conditions into the corresponding derivative of imines are also completely scrutinized.

Application of Fe-RGO for the removal of dyes by catalytic ozonation process

Due to continuous industrialization, the discharge of hazardous dyes has enormously disrupted the ecosystem causing environmental problems. Due to the stable recalcitrant nature of dyes, advanced catalytic ozonation processes with the latest catalyst are under investigation. Fe-RGO is an effective oxidation catalyst, and the metal loaded platform provides enhanced catalytic performance. This study aims to investigate the effectiveness of Fe-RGO/O3 process for the removal of dyes. In the current research, the application of iron-coated reduced graphene oxide (Fe-RGO) was studied as a catalyst in the heterogeneous catalytic ozonation process to remove dyes. Methylene blue (MB) was selected as a model pollutant. RGO was prepared using the improved Hummers method and was coated with iron (Fe) implying the impregnation method. The FTIR, SEM-EDX, XRD, and BET analyses of RG and Fe-RGO were performed to characterize the catalyst. The effect of various parameters such as pH (3-10), catalyst dose (0.01-0.04 g), and radical scavengers (NaHCO3, NaCl) on removal efficiency was elucidated. The result revealed an excellent catalytic efficiency of Fe-RGO in the ozonation process. At optimum conditions, 96% removal efficiency was achieved in catalytic ozonation at pH 7 with a catalyst dose of 0.02 g and ozone dose 0.5 mg/min, after 10 min. Interestingly, a slight decrease in removal efficiency was observed in the catalytic ozonation process in hydroxyl radical scavengers (NaCl and NaHCO3), which makes the proposed catalyst more applicable in real conditions. Therefore, it is concluded that Fe-RGO can be used as an excellent catalyst for the removal of dyes in real conditions where radical scavengers may be present in a significant amount.

Effect of Functionalized Benzene Derivatives as Potential Hole Scavengers for BiVO4 and rGO-BiVO4 Photoelectrocatalytic Hydrogen Evolution

Sustainable hydrogen production is one of the main challenges today in the transition to a green and sustainable economy. Photocatalytic hydrogen production is one of the most promising technologies, amongst which BiVO₄-based processes are highly attractive due to their suitable band gap for solar-driven processes. However, the performance of BiVO₄ alone in this role is often unsatisfactory. Herein we report the improvement of BiVO₄ performance with reduced graphene oxide (rGO) as a co-catalyst for the photoelectrochemical water splitting (PEC-WS) in the presence of simple functionalized benzene derivatives (SFBDs), i.e., phenol (PH), benzoic acid (BA), salicylic acid (SA), and 5-aminosalicylic acid (5-ASA) as potential photogenerated hole scavengers from contaminated wastewaters. Linear sweep voltammetry and chronoamperometry, along with electrochemical impedance spectroscopy were utilized to elucidate PEC-WS performance under illumination. rGO has remarkably improved the performance of BiVO₄ in this role by decreasing photogenerated charge recombination. In addition, 5-ASA greatly improved current densities. After 120 min under LED illumination, 0.53 μmol of H₂ was produced. The type and concentration of SFBDs can have significant and at times opposite effects on the PEC-WS performance of both BiVO₄ and rGO-BiVO₄.

Efficiency of zero-dimensional and two-dimensional graphene architectural nanocomposites for organic transformations in the contemporary environment: a review

Graphene derivatives-based nanocatalyst finds increasing utilisation in the catalysis field for organic transformations. Researchers have been working on the development of graphene oxide, reduced graphene oxide, and graphene quantum dots with metal or metal oxide nanocomposites over the last few years. These materials exhibit excellent electrical, catalytic, optical, thermal, and magnetic properties. In particular, GO/rGO/GQDs composites assisted by metal or metal oxides have attracted broad attention for their possible applications in organic compound synthesis, drug delivery, sensors, devices, and the related areas of the environment. In this review, we have summarised GO/rGO/GQDs-metal or metal oxide composites using catalyst for organic conversions and synthesis of organic compounds in accordance with the discussion on the key problems and prospects for future study. Furthermore, there is a significant function for the catalytic efficiency of composites assisted by metal or metal oxide nanocatalyst which is categorised by graphene derivatives bases.

A review of graphene-based semiconductors for photocatalytic degradation of pollutants in wastewater

Water is the lifeblood of all living things; we often overlook the fact that the water cycle and the life cycle are inextricably linked. However, it has become contaminated as a result of industrialization, which has impacted the ecosystem by emitting numerous dyes, organic solvents, petroleum products, heavy metals, chemicals, diseases, and solid wastes. The absence of treatment in reusing wastewater is the root of the issues. Hence it is essential to treat the water to preserve the ecosystem and also for human health. In recent years, graphene-based photocatalysts are attracted much in the waste water treatment process due to their outstanding physical, chemical, and mechanical properties. Since in the graphene-based photocatalyst, graphene has exceptional electron conductivity, a broad range of light absorption, a large surface area, and a high adsorption capacity. When it is integrated into metals, metal-containing nanocomposites, semiconductor nanocomposites, polymers, MXene, and other compounds, it can greatly boost the photocatalytic activity towards the photo destruction of contaminants. Hence in this review, water pollution, methods of waste water treatment, fundamental principles of photocatalysis, the photocatalytic activity of other materials in wastewater treatment, and how the photocatalytic efficiency against the removal of organic dyes can be enhanced when coalesced with graphene are detailed.

Highly efficient Ag doped δ-MnO2 decorated graphene: Comparison and application in electrochemical detection of H2O2

Cytotoxic H₂O₂ is an inevitable part of our life, even during this contemporary pandemic COVID-19. Personal protective equipment of the front line fighter against coronavirus could be sterilized easily by H₂O₂ for reuse. In this study, Ag doped δ-MnO₂ nanorods supported graphene nanocomposite (denoted as Ag@δ-MnO₂/G) was synthesized as a nonenzymatic electrochemical sensor for the sensitive detection of H₂O₂. The ternary nanocomposite has overcome the poor electrical conductivity of δ-MnO₂ and also the severe aggregation of Ag NPs. Furthermore, δ-MnO₂/G provided a rougher surface and large numbers of functional groups for doping more numbers of Ag atoms, which effectively modulate the electronic properties of the nanocomposite. As a result, electroactive surface area and electrical conductivity of Ag@δ-MnO₂/G increased remarkably as well as excellent catalytic activity observed towards H₂O₂ reduction. The modified glassy carbon electrode exhibited fast amperometric response time (<2 s) in H₂O₂ determination. The limit of detection was calculated as 68 nM in the broad linear range (0.005-90.64 mM) with high sensitivity of 104.43 µA mM^-1 cm^-2. No significant interference, long-term stability, excellent reproducibility, satisfactory repeatability, practical applicability towards food samples and wastewater proved the efficiency of the proposed sensor.

Highly Sensitive Electrochemical Immunosensor Platforms for Dual Detection of SARS-CoV-2 Antigen and Antibody based on Gold Nanoparticle Functionalized Graphene Oxide Nanocomposites

In this work, we report a facile synthesis of graphene oxide-gold (GO-Au) nanocomposites by electrodeposition. The fabricated electrochemical immunosensors are utilized for the dual detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antigen and SARS-CoV-2 antibody. The GO-Au nanocomposites has been characterized by UV-vis spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS) for its biosensing properties. The linear detection range of the SARS-CoV-2 antigen immunosensor is 10.0 ag mL-1 to 50.0 ng mL-1, whereas that for the antibody immunosensor ranges from 1.0 fg mL-1 to 1.0 ng mL-1. The calculated limit of detection (LOD) of the SARS-CoV-2 antigen immunosensor is 3.99 ag mL-1, and that for SARS-CoV-2 antibody immunosensor is 1.0 fg mL-1 with high sensitivity. The validation of the immunosensor has also been carried out on patient serum and patient swab samples from COVID-19 patients. The results suggest successful utilization of the immunosensors with a very low detection limit enabling its use in clinical samples. Further work is needed for the standardization of the results and translation in screen-printed electrodes for use in portable commercial applications.

Graphene-based ZnCr layered double hydroxide nanocomposites as bactericidal agents with high sonophotocatalytic performances for degradation of rifampicin

Herein, ZnCr layered double hydroxide (ZnCr LDH), and its nanocomposites with GO and rGO were synthesized using the co-precipitation method. The samples were characterized using XRD, FT-IR, SEM, TEM, BET, and XPS techniques. The sonophotocatalytic activity of the ZnCr LDH, ZnCr LDH/GO, and ZnCr LDH/rGO was investigated via the degradation of rifampicin (RIF) in the ultrasonic bath under visible light irradiation. The synergy index of more than 1 determined for ZnCr LDH/rGO indicated the positive interaction of sonocatalysis and photocatalysis resulted by hybridizing the LDH nanosheets with rGO. The maximum sonophotocatalytic degradation efficiency of 87.3% was achieved in the presence of ZnCr LDH/rGO nanocomposite with the concentration of 1.5 g L^-1 for degradation of RIF with an initial concentration of 15 mg L^-1 within 60 min sonication under visible light irradiation. The addition of different scavengers indicated that hydroxyl radicals, superoxide anion radicals, and the generated holes played a dominant role in the degradation of the pollutant molecules. A possible degradation mechanism was suggested based on the intermediates. The antibacterial tests confirmed the higher antibacterial activity of ZnCr LDH/GO compared with ZnCr LDH and ZnCr LDH/rGO against Gram-positive Staphylococcus aureus.

Multifunctional oil-produced reduced graphene oxide - Silver oxide composites with photocatalytic, antioxidant, and antibacterial activities

Graphene-based nanomaterials that combine significant photocatalytic, antioxidant and antibacterial activity are very attractive candidates for biomedical and environmental applications. Conventional chemical synthesis routes may contaminate the resultant materials with toxic molecules, compromising their properties and limiting their use in biomedical applications. Ideally, to avoid any contamination, the nanomaterials should be synthesized from non-toxic precursors and reagents, e.g. foodstuff via a simple technology that does not rely on the use of hazardous chemicals yet produces materials of high quality. Here, we report an environmentally friendly, low cost reduced graphene oxide-silver-silver oxide nanocomposite with strong photocatalytic, antioxidant and antibacterial activity for environmental remediation. The reduced graphene oxide (FRGO) is synthesized from edible sunflower oil via a simple flame synthesis method. Next, silver nanoparticles (Ag/AgO/Ag₂O) are produced by phytochemical reduction of AgNO₃ using a reducing agent based on flavonoids from Coleus aromaticus (Mexican mint), also used in food industry. Thus-obtained FRGO-Ag/AgO/Ag₂O composite is characterized using X-ray diffraction spectroscopy, scanning electron microscopy, fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The degradation of anionic textile dye Methylene blue (MB) is used as a measure of photocatalytic activity of FRGO and FRGO/Ag/AgO/Ag₂O, with solution pH, initial dye concentration, and quantity of the catalyst considered as influencing factors. FRGO-Ag/AgO/Ag₂O composites show strong antioxidant activity, with improved radical inhibition as well as dye degradation properties when compared to pristine FRGO.

C70 Fullerene Catalyzed Photoinduced Aerobic Oxidation of Benzylamines to Imines and Aldehydes

C₇₀ fullerene catalyzed photoinduced oxidation of benzylic amines at ambient conditions has been explored here. The developed strategy's main feature includes the additive/oxidant-free conversion of benzylic amine to corresponding imine and aldehydes. The reaction manifests broad substrate scope with excellent function group leniency and is applicable up to the gram scale. Further, symmetrical secondary amines can also be synthesized from benzylic amine in a one-pot two-step process. Various experiments and density functional theory studies revealed that the current reaction involves the generation of reactive oxygen species, single electron transfer reaction, and benzyl radical formation as key steps under photocatalytic conditions.

Application of r-GO-MMT Hybrid Nanofillers for Improving Strength and Flame Retardancy of Epoxy/Glass Fibre Composites

The application of nanomaterials as a strengthening agent in the fabrication of polymer nanocomposites has gained significant attention due to distinctive properties which can be utilised in structural applications. In this study, reduced graphene oxide (r-GO) and montmorillonite (MMT) nanoclay were used as filler materials to fabricate hybrid epoxy-based nanocomposites. The synergistic effect of nanomaterials on flammability and mechanical behaviour of nanocomposites were studied. Results revealed that the addition of nanofiller showcases 97% and 44.5% improvement in tensile and flexural strength. However, an increment in the percentage of filler material over 0.3% exhibits a decremental mechanical property trend. Likewise, the addition of nanofiller increases the nonignition timing of the glass-fibre-reinforced epoxy composites. Fracture surface morphology displays the occurrence of the ductile fracture mechanism owing to the presence of hybrid fillers.

Silver decorated 2D nanosheets of GO and MoS2serve as nanocatalyst for water treatment and antimicrobial applications as ascertained with molecular docking evaluation

In this work, synthesis of graphene oxide (GO) and reduced graphene oxide (rGO) was realized through a modified Hummers route. Different concentrations (5 and 10 wt%) of Ag were doped in MoS₂and rGO using a hydrothermal technique. Synthesized Ag-MoS₂and Ag-rGO were evaluated through XRD that confirmed the hexagonal structure of MoS₂along with the transformation of GO to Ag-rGO as indicated by a shift in XRD peaks while Mo-O bonding and S=O functional groups were confirmed with FTIR. Morphological information of GO and formation of MoS₂nanopetals as well as interlayer spacing were verified through FESEM and HRTEM respectively. Raman analysis was employed to probe any evidence regarding defect densities of GO. Optical properties of GO, MoS₂, Ag-rGO, and Ag-MoS₂were visualized through UV-vis and PL spectroscopy. Prepared products were employed as nanocatalysts to purify industrial wastewater. Experimental results revealed that Ag-rGO and Ag-MoS₂showed 99% and 80% response in photocatalytic activity. Besides, the nanocatalyst (Ag-MoS₂and Ag-rGO) exhibited 6.05 mm inhibition zones againstS. aureusgram positive (G+) and 3.05 mm forE. coligram negative (G-) in antibacterial activity. To rationalize biocidal mechanism of Ag-doped MoS₂NPs and Ag-rGO,in silicomolecular docking study was employed for two enzymes i.e.β-lactamase and D-alanine-D-alanine ligase B (ddlB) from cell wall biosynthetic pathway and enoyl-[acylcarrier-protein] reductase (FabI) from fatty acid biosynthetic pathway belonging toS. aureus. The present study provides evidence for the development of cost-effective, environment friendly and viable candidate for photocatalytic and antimicrobial applications.

Improved Oxidative Stability by Embedded Cerium into Graphene Oxide Nanosheets for Proton Exchange Membrane Fuel Cell Application

Investigation of the collaborative effect of cerium particles embedded in graphene oxide to enhance the chemical stability of a proton exchange membrane fuel cell (PEMFC) has been carried out. Synthesis of composite membranes (Nafion-GO/Ce-x) with Nafion solution as a polymer is synthesized by a solution casting method where (x = concentration of composite). The developed hybrid material was characterized by FT-IR and X-ray diffraction (XRD) for its phase identification while the chemical structure was characterized by XPS analysis. The enhancement in the chemical stability of the incorporated hybrid material is characterized by Fenton’s test showing a radical scavenging effect. It was found that the residual weight for Nafion ²¹² was 92.50% after 24 h and it was 94.32% for Nafion-GO/Ce-2 and 96.49% for Nafion-GO/Ce-4, proving the suitability of composite membranes for fuel cell applications.

Ultrasound accelerated near-edge functionalized heterogeneous graphene oxide sonocatalyst for surface optical bandwidth efficacy and in situ sonothermocatalysis

Ultrasound-accelerated optically active heterogeneous catalyst and sonochemical time driven thermodynamic dye catalysis.

Hydrothermal liquefaction of Fe-impregnated water hyacinth for generation of liquid bio-fuels and nano Fe carbon hybrids

In this work, hydrothermal liquefaction experiments of iron impregnated water hyacinth were performed with a motive to enhance bio-oil yields along with generation of nanometal carbon hybrids. Iron nanoparticles were impregnated and its metal loading was determined by ICP-MS. The impact of operating parameters like temperature, biomass to water ratio and reaction time on bio-oil yields was studied. During hydrothermal liquefaction a maximum total bio-oil yield of 38.1% was obtained at 280 °C along with formation of nanometal carbon hybrids. The light oil and heavy oil fractions were characterized by GCMS and NMR for determining the key components. The light oil mainly comprises of alkanes, alcohols and esters whereas heavy oil contains esters, ethers, carboxylic acids and phenols. XRD and XPS of Fe-impregnated water hyacinth and residues confirmed the transition of Fe^+3/+2 to Fe⁰. TEM analysis resulted an average particle size of Fe nanoparticles around 19.6 nm.

A sonochemical assisted synthesis of hollow sphere structured tin (IV) oxide on graphene oxide sheets for the low-level detection of environmental pollutant mercury in biological samples and foodstuffs

In modern approaches for nanomaterials synthesis, ultrasonication plays an important role in providing the larger surface area and smaller crystalline size properties that are favorable to electrochemical techniques. Herein, we report the tin (IV) oxide on graphene oxide nanoparticles were synthesized (SnO₂@GO NPs) by ultrasonic methodology (UZ SONOPULS HD 3400 Ultrasonic homogenizer) with the total power of 400 W and the (frequency of 20 kHz; 140 W/dm³). The formation of as-prepared SnO₂@GO NPs and its surface morphology were scrutinized over XRD, XPS, TEM, and FESEM. Besides, the sonochemically prepared SnO₂@GO NPs were employed for the determination of environmental hazardous mercury (Hg). As a result, the modified electrode acquired a very low-level detection limit of 1.2 nM with a wider range of 0.01-10.41-µM and 14.52-225.4-µM for the detection of Hg. Finally, the practical applicability of SnO₂@GO NPs in spiked human blood serum and tuna fish samples shows appreciable found and recovery values. .

Non-emissive RuII Polypyridyl Complexes as Efficient and Selective Photosensitizers for the Photooxidation of Benzylamines

Five new Ru^II polypyridyl complexes bearing N-(arylsulfonyl)-8-amidoquinolate ligands and three of their biscyclometalated Ir^III congeners have been prepared and employed as photocatalysts (PCs) in the photooxidation of benzylamines with O₂ . In particular, the new Ru^II complexes do not exhibit photoluminescence, rather they harvest visible light efficiently and are very stable in solution under irradiation with blue light. Their non-emissive behavior has been related to the low electrochemical energy gaps and rationalized on the basis of theoretical calculations (DFT analysis) that predict low S₀ ←T₁ energy values. Moreover, the Ru^II complexes, despite being non-emissive, display excellent activities in the selective photocatalytic transformation of benzylamines into the corresponding imines. The presence of an electron-withdrawing group (-CF3) on the arene ring of the N-(arylsulfonyl)-8-amidoquinolate ligand improves the photocatalytic activity of the corresponding photocatalyst. Furthermore, all the experimental evidence, including transient absorption spectroscopy measurements suggest that singlet oxygen is the actual oxidant. The Ir^III analogues are considerably more photosensitive and consequently less efficient photosensitizers (PSs).

Hydrothermal Synthesis of Silver Decorated Reduced Graphene Oxide (rGO) Nanoflakes with Effective Photocatalytic Activity for Wastewater Treatment

Graphene oxide (GO) was obtained through modified hummers method, and reduced graphene oxide (rGO) was acquired by employing heat treatment. Various concentrations (2.5, 5, 7.5, and 10 wt. %) of silver (Ag) were incorporated in GO nanosheets by adopting hydrothermal approach. Synthesized Ag decorated rGO photocatalyst Ag/rGO was characterized using X-ray diffraction (XRD) to determine phase purity and crystal structure. XRD patterns showed the formation of GO to Ag/rGO. Molecular vibration and functional groups were determined through Fourier Transform Infrared spectroscopy (FTIR). Optical properties and a decrease in bandgap with insertion of Ag were confirmed with UV-Visible (Uv-Vis) spectrophotometer and photoluminescence (PL). Electronic properties and disorders in carbon structures were investigated through Raman spectroscopy that revealed the existence of characteristic bands (D and G). Surface morphology of prepared samples was examined with field emission scanning electron microscope (FESEM). Homogeneous distribution, size, and spherical shape of Ag NPs over rGO sheets were further confirmed with the help of high-resolution transmission electron microscope (HR-TEM). Dye degradation of doped and undoped samples was examined through Uv-Vis spectra. Experimental results indicated that photocatalytic activity of Ag@rGO enhanced with increased doping ratio owing to diminished electron-hole pair recombination. Therefore, it is suggested that Ag@rGO can be used as a beneficial and superior photocatalyst to clean environment and wastewater.

Highly efficient conversion of the nitroarenes to amines at the interface of a ternary hybrid containing silver nanoparticles doped reduced graphene oxide/ graphitic carbon nitride under visible light

In this report, a ternary Ag-rGO/g-C₃N₄ hybrid was synthesized by a simple hydrothermal approach for the photocatalytic reduction of nitroarene compounds into their corresponding amines under visible light. Importantly, the present method did not require reducing agents, like hydrazine hydrate; instead methanol has been used as a source of electrons and protons for the photoreduction process. After grafting of Ag NPs, a significant enhancement in the efficiency of the rGO/g-C₃N₄ for the reduction of nitrobenzenes was observed. Under optimized experimental conditions, the conversion of nitrobenzene and yield of aniline were determined to be 99% and 98%, respectively under visible light illumination for 4 h. The nitrobenzene compounds bearing both electron donating and withdrawing groups were selectively converted into their corresponding aniline products without altering the functionality. The enhanced performance of the developed photocatalyst attributed to the effective separation of photoexcited electrons on the photocatalyst surface and their subsequent transfer for the reduction of nitrobenzene molecules.

Silver nanoparticles stabilized by a metal–organic framework (MIL-101(Cr)) as an efficient catalyst for imine production from the dehydrogenative coupling of alcohols and amines

In this paper, we present silver nanoparticles supported on a metal–organic framework (Ag@MIL-101) as a catalyst for the one-pot tandem synthesis of imines from alcohols and amines.

Synthesis of α-amino nitriles through one-pot selective Ru-photocatalyzed oxidative cyanation of amines

A new family of Ru(ii) photocatalysts exhibits excellent performance in the efficient and eco-friendly one-pot preparation of α-amino nitriles from primary and secondary amines.