Green synthesis and photo-catalytic performances for ZnO-reduced graphene oxide nanocomposites

ZnO@In2O3 Core-Shell Heterojunctions Constructed With ZIF-8 and MIL-68 (In) for Improving Photogenerated Carrier Transfer Process

The realization of fast carrier transport can effectively enhance photocatalytic performance. A core-shell structure of ZnO and In2O3 is successfully constructed by using MIL-68 (In) and ZIF-8 as a substrate, forming a heterojunction. This MOF-derived core-shell heterojunction inherits the advantages of ZIF-8, with pores facilitating carriers transfer to the surface for reactions and a large specific surface area providing more active sites. This Z-scheme heterojunction of ZnO and In2O3 can effectively separate and improve the utilization of photogenerated carriers. The well-designed interface of the core-shell structure achieves the rapid transfer of photogenerated carriers. The photocatalytic degradation capability of ZnO@ In2O3 is enhanced by the synergistic effect of Z-scheme heterojunction and core-shell structure. This work provides insight into the investigation of constructing core-shell heterojunctions.

Fine-Tuned Graphene Oxide Nanocomposite: Harnessing Copper(II)-Imidazole Complex for Enhanced Biological Responses and Balanced Photocatalytic Functionality

In this study, the synthesis of biologically active copper(II) complex [Cu(im)2]Cl2 was achieved using a reported method. Subsequently, this copper(II) complex was strategically grafted onto graphene oxide, resulting in the formation of a nanocomposite denoted as copper(II)-complex-grafted graphene oxide (Cu-GO). The comprehensive characterization of Cu-GO was conducted through various techniques, including X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), UV-visible spectroscopy, emission spectra analysis, X-ray photoelectron spectroscopy (XPS), and Copper K-edge X-ray Absorption Near Edge Structure (XANES) spectroscopy. The antibacterial efficacy of Cu-GO compounds was assessed using disk diffusion and microbroth dilution methods. Notably, the copper complex exhibited the highest effectiveness, showcasing a Minimal Inhibitory Concentration (MIC) value of 500 µL against Klebsiella bacteria. The antibacterial activities of all compounds were systematically screened, revealing the superior performance of the copper complex compared to standalone copper compounds. Expanding the scope of the investigation, we explored the antioxidant and anti-obesity activities of the copper complexes against Klebsiella organisms. The results underscore promising directions for the further exploration of the diverse health-related applications of these compounds. Moreover, the photocatalytic performance of the Cu-GO nanocomposite was evaluated under sunlight irradiation. Notably, the antioxidant and anti-obesity activities of Cu-GO, assessed in terms of percentage inhibition at a concentration of 200 mg/mL, exhibited values of 41% and 45%, respectively. Additionally, the Cu-GO composite exhibited exceptional efficacy, achieving a degradation efficiency of 74% for RhB under sunlight irradiation, surpassing both graphite and GO. These findings not only demonstrate enhanced biological activity, but also highlight a notable level of moderate photocatalytic performance. Such dual functionality underscores the potential versatility of Cu-GO nanocomposites across various applications, blending heightened biological efficacy with controlled photocatalysis. Our study offers valuable insights into the multifunctional attributes of copper(II)-complex-grafted graphene oxide nanocomposites, thereby paving the way for their broader utilization in diverse fields.

Two-dimensional heterostructures for photocatalytic CO2 reduction

The photocatalysis conversion of CO₂ into fuels has become an encouraging method to address climate and energy issues as a long-term solution. Single material suffers poor yield due to low light energy utilization and high recombination rate of photoinduced electron-hole pairs. It is an efficient approach to construct heterojunction through two or three materials to improve the photocatalytic performance. Recently, 2D-based heterojunction is getting popular for outstanding properties, such as special light collecting structure to enhance light harvest, intimate interface to facilitate charge transfer and separation, and large specific surface area to provide abundant reactive sites. Recently, some new 2D-based heterostructures materials (both structure and composition) have been developed with excellent performance. 2D materials exert structural and functional advantages in these fine composite photocatalysts. In this review, the literatures about the photocatalytic conversion of CO₂ are mainly summarized based on overall structure, interface type and material type of 2D-based heterojunction, with special attention given to the preparation, characterization, structural advantages and reaction mechanism of novel 2D-based heterojunction. This work is in hope of offering a basis for designing improved composite photocatalyst for CO₂ photoreduction.

Graphene-based nanocomposites and nanohybrids for the abatement of agro-industrial pollutants in aqueous environments

Incessant release of a large spectrum of agro-industrial pollutants into environmental matrices remains a serious concern due to their potential health risks to humans and aquatic animals. Existing remediation techniques are unable to remove these pollutants, necessitating the development of novel treatment approaches. Due to its unique structure, physicochemical properties, and broad application potential, graphene has attracted a lot of attention as a new type of two-dimensional nanostructure. Given its chemical stability, large surface area, electron mobility, superior thermal conductivity, and two-dimensional structure, tremendous research has been conducted on graphene and its derived composites for environmental remediation and pollution mitigation. Various methods for graphene functionalization have facilitated the development of different graphene derivatives such as graphene oxide (GO), functional reduced graphene oxide (frGO), and reduced graphene oxide (rGO) with novel attributes for multiple applications. This review provides a comprehensive read on the recent progress of multifunctional graphene-based nanocomposites and nanohybrids as a promising way of removing emerging contaminants from aqueous environments. First, a succinct overview of the fundamental structure, fabrication techniques, and features of graphene-based composites is presented. Following that, graphene and GO functionalization, i.e., covalent bonding, non-covalent, and elemental doping, are discussed. Finally, the environmental potentials of a plethora of graphene-based hybrid nanocomposites for the abatement of organic and inorganic contaminants are thoroughly covered.

Rejection of trace organic compounds by membrane processes: mechanisms, challenges, and opportunities

This work critically reviews the application of various membrane separation processes (MSPs) in treating water polluted with trace organic compounds (TOrCs) paying attention to nanofiltration (NF), reverse osmosis (RO), membrane bioreactor (MBR), forward osmosis (FO), and membrane distillation (MD). Furthermore, the focus is on loopholes that exist when investigating mechanisms through which membranes reject/retain TOrCs, with the emphasis on the characteristics of the model TOrCs which would facilitate the identification of all the potential mechanisms of rejection. An explanation is also given as to why it is important to investigate rejection using real water samples, especially when aiming for industrial application of membranes with novel materials. MSPs such as NF and RO are prone to fouling which often leads to lower permeate flux and solute rejection, presumably due to cake-enhanced concentration polarisation (CECP) effects. This review demonstrates why CECP effects are not always the reason behind the observed decline in the rejection of TOrCs by fouled membranes. To mitigate for fouling, researchers have often modified the membrane surfaces by incorporating nanoparticles. This review also attempts to explain why nano-engineered membranes have not seen a breakthrough at industrial scale. Finally, insight is provided into the possibility of harnessing solar and wind energy to drive energy intensive MSPs. Focus is also paid into how low-grade energy could be stored and applied to recover diluted draw solutions in FO mode.

Assembling Hollow Cactus-Like ZnO Nanorods with Dipole-Modified Graphene Nanosheets for Practical Room-Temperature Formaldehyde Sensing

Formaldehyde (HCHO) sensing plays a critical role for indoor environment monitoring in smart home systems. Inspired by the unique hierarchical structure of cactus, we have prepared a ZnO/ANS-rGO composite for room-temperature (RT) HCHO sensing, through assembling hollow cactus-like ZnO nanorods with 5-aminonaphthalene-1-sulfonic acid (ANS)-modified graphene nanosheets in a facile and template-free manner. Interestingly, it was found that the ZnO morphology could be simply tuned from flower clusters to hollow cactus-like nanostructures, along with the increase of the reaction time during the assembly process. The ZnO/ANS-rGO-based sensors exhibited superior RT HCHO-sensing performance with an ultrahigh response (68%, 5 ppm), good repeatability, long-term stability, and an outstanding practical limit of detection (LOD: 0.25 ppm) toward HCHO, which is the lowest practical LOD reported so far. Furthermore, for the first time, a 30 m³ simulation test cabinet was adapted to evaluate the practical gas-sensing performance in an indoor environment. As a result, an instantaneous response of 5% to 0.4 ppm HCHO was successfully achieved in the simulation test. The corresponding sensing mechanism was interpreted from two aspects including high charge transport capability of ANS-rGO and the distinct gas adsorbability derived from nanostructures, respectively. The combination of a biomimetic hierarchical structure and supramolecular assembly provides a promising strategy to design HCHO-sensing materials with high practicability.

Citrus sinensis and Musa acuminata Peel Waste Extract Mediated Synthesis of TiO2/rGO Nanocomposites for Photocatalytic Degradation of Methylene Blue under Visible Light Irradiation

Water pollution caused by various natural and artificial sources such as expansion of industrialization, rapid increment in population size, the threat of climate change, and development in urbanization takes a serious attention. Due to this fact, various protocols and techniques were adopted for the treatment of such polluted water. In the present findings, TiO2 nanoparticles (NPs) and TiO2/rGO nanocomposites (NCs) were synthesized using titanium tetra butoxide in the presence of Citrus sinensis (CS) and Musa acuminata (MA) peel waste extract as a capping, reducing, and stabilizing agent. The synthesized NPs and NCs were characterized using thermogravimetric-differential thermal analysis (TGA/DTA), X-ray diffraction (XRD), scanning electron microscope (SEM), high resolution transmission electron microscopy (HR-TEM), selected area electron diffraction (SAED) pattern, ultraviolet diffuse reflectance spectroscopy (UV-DRS), and Fourier transform infrared (FTIR) spectroscopy. The synthesized NPs and NCs were investigated as green alternative photocatalyst for the degradation of methylene blue (MB) dye under visible light irradiation. Thermal analysis results confirmed that the green synthesized TiO2 NPs were found to be too stable above 550°C. XRD analysis result showed that the average crystalline size of CS and MA mediated synthesized TiO2 NPs with various volume ratios was in the range of 7.3-27.3 nm and 13.4-22.4 nm, respectively. The average crystalline size of CS and MA peel extract template synthesized TiO2/rGO NCs was found to be in the range of 7.5-15.3 and 11.2-12.5 nm, respectively. The band gap energy was calculated to be in the range of 3.17-3.29 eV and 3.10-3.38 eV for the CS and MA mediated synthesized TiO2 NPs, respectively. E g of CS and MA peel extract template formed TiO2/rGO NCs was found to be in the range of 2.85-3.11 eV and 3.07-3.11 eV, respectively. SEM analysis proved that the various synthesized TiO2 NPs and TiO2/rGO NCs were spherical in shape and the absence of any other foreign materials confirmed the purity of the corresponding nanocatalysts. In addition, TEM, HRTEM, and SAED analysis confirmed that the structures of the synthesized nanocatalysts were spherical in shape and the catalysts were too crystalline and the result was found to fit with the XRD result. Among the synthesized various volume ratios of TiO2 nanocatalysts, high percentage of degradation (62% and 58.2%) was achieved using TiO2-2c and TiO2-2 m, respectively. Moreover, 94.28% and 94.25% of MB degradation were achieved in the presence of TiO2/rGO-1.5c and TiO2/rGO-1.5c nanocomposite photocatalysts, respectively.

Leaching of CuO Nanoparticles from PES Ultrafiltration Membranes

Recent studies have incorporated nanoparticles such as CuO, ZnO, and TiO₂ to improve membrane physical and filtration properties. However, one of the major concerns about membrane modification with nanoparticles is the possible leaching of the nanoparticles leading to further contamination of source waters. Therefore, this study investigated the effects of prolonged exposure of polyethersulfone (PES) membranes incorporated with CuO nanoparticles, to different cleaning solutions. The cleaned membranes were extensively characterized for both material properties and separation performance, which enabled a closer look at particle leaching effect through a prolonged exposure. After 840 h of exposure, the presence of CuO in the cleaning solutions was confirmed using dynamic light scattering (DLS), energy-dispersive X-ray spectroscopy (EDS), and inductively coupled plasma mass spectroscopy (ICP-MS) techniques. Nanoparticle leaching resulted in changes in membrane hydrophobicity, surface roughness, pure water permeability, and salt rejection properties. Through comparison with the bare PES membranes, it was shown that cleaning solutions also degraded the membrane polymer. However, the marked effect was less pronounced compared to combined leaching of nanoparticles and degradation of the polymer noted with PES membranes incorporated with CuO nanoparticles. Therefore, when membranes incorporated with nanoparticles are used, a polishing step may be required to remove potentially leached nanoparticles. Leached nanoparticles may result in secondary pollution and pose a health risk concern to nontarget organisms. This work provides insights into the stability of nanocomposite membranes, and the achieved results can be extrapolated to other nanoparticles such as TiO₂ and ZnO because they possess similar physicochemical behavior.

Photocatalytic Perfomance of ZnO-Graphene Oxide Composites towards the Degradation of Vanillic Acid under Solar Radiation and Visible-LED

Graphene oxide (GO) is used to enhance the photocatalytic activity of ZnO nanoparticles for the degradation of vanillic acid (VA) under simulated solar light and visible-LED (λ > 430 nm). ZnO-GO composites are prepared by a mixing and sonication process with different GO loadings (i.e., from 1.8 to 6.5 wt.%). The materials are extensively characterized by thermogravimetric analysis (TGA), physisorption of N2, X-ray diffraction (XRD), infrared spectroscopy (FTIR), scanning electron microscopy (SEM), point of zero charge (pHPZC), and UV-Vis diffuse reflectance spectroscopy (DRUV). The presence of GO increases the photocatalytic activity of all the prepared composites in comparison with the pristine ZnO. The highest photocatalytic activity is found for the composite containing 5.5 wt.% of GO (i.e., ZnO-GO5.5), reaching a VA degradation of 99% and 35% under solar light and visible-LED, respectively. Higher TOC removal/VA degradation ratios are obtained from the experiments carried out under visible-LED, indicating a more effective process for the mineralization of VA than those observed under simulated solar light. The influence of hole, radical, and non-radical scavengers is studied in order to assess the occurrence of the reactive oxygen species (ROS) involved in the photocatalytic mechanism. The study of the photo-stability during three reuse experiments indicates that the presence of GO in the composites reduces the photocorrosion in comparison with pristine ZnO.

Boosting light-driven CO2 reduction into solar fuels: Mainstream avenues for engineering ZnO-based photocatalysts

The realization of artificial photosynthesis in the photocatalytic CO₂ transformation into valuable chemicals or solar fuels, such as CO, CH₄, HCOOH, and CH₃OH, by solar-light harvesting is a promising solution to both global-warming and energy-supply issues. Recently, zinc oxide (ZnO) has emerged as an excellent oxidative photocatalyst among non-titanium metal oxides due to its availability, outstanding semiconducting and optical properties, non-toxicity, affordability, and ease of synthesis. However, ZnO wide bandgap and inability to absorb in the visible region has demanded particular modification for its practical use as a sustainable photocatalyst. This review provides a panorama of the latest advancement on ZnO photocatalysis for CO₂ reduction with an overview of fundamental aspects. Various modification strategies such as transition metal and non-metal doping, loading of plasmonic metals, and surface vacancy engineering for tunning the properties and improving the performance of ZnO are elaborated. Composites or hetero-structuralization-based Z-scheme formation is also presented along with a detailed photocatalytic reduction mechanism. Moreover, a new novel Step-scheme (S-scheme) heterostructure modification with a charge transfer pathway mechanism is also highlighted. Finally, the key challenges and new directions in this field are proposed to provide a new vision for further improvement for ZnO-based photocatalytic CO₂ conversion.

ZnO nanorods/Fe3O4-graphene oxide/metal-organic framework nanocomposite: recyclable and robust photocatalyst for degradation of pharmaceutical pollutants

Nanosized semiconductors are widely utilized as solar energy based photocatalyst. However, the deficiencies such as poor adsorption toward contaminants and recyclability issues, rapid recombination of photo-introduced radicals, and deactivation by scavengers are still be the obstacle. To addressing those obstacles, zeolitic imidazolate framework-8 (ZIF-8), photosensitive ZnO, and paramagnetic Fe₃O₄ were anchored on conductive graphene oxide (GO) to prepare a nanocomposite photocatalyst ZnO/Fe₃O₄-GO/ZIF. The photocatalyst showed good robustness to scavengers of hydroxyl radicals (OH^•), superoxide radicals (O₂^•-), and hole (h⁺) with hydrophobic ZIF-8 modified surface. Finally, four pharmaceuticals (sulfamethazine, metronidazole, norfloxacin, and 4-acetaminophen) were degraded rapidly under simulated solar irradiation for 1 h, and the photocatalyst could be recycled at least ten times without obvious deactivation. The final results show that combination of semiconductor, graphene oxide and ZIF-8 is a good idea for construction of efficient photocatalyst. It offers new views in interface modification of nanomaterials, photocatalysis, and adsorption.

Recent advances in visible-light-driven carbon dioxide reduction by metal-organic frameworks

Metal-organic frameworks (MOFs) have emerged as promising materials and have attracted researchers due to their unique chemical and physical properties-design flexibility, tuneable pore channels, a high surface-to-volume ratio that allow their distinct application in diverse research fields-gas storage, gas separation, catalysis, adsorption, drug delivery, ion exchange, sensing, etc. The rapidly growing CO₂ in the atmosphere is a global concern due to the excessive use of fossil fuels in the current era. CO₂ is the prime cause of global warming and should be ameliorated either through adsorption or conversion into value-added products to protect the environment and mankind. Nowadays, MOFs are exploited as a photocatalyst for applications of CO₂ reduction. Since the use of semiconductors limits the use of visible light for photocatalytic reduction of CO₂, MOFs are promising options. The current review describes recent development in the application of MOFs as host, composites, and their derivatives in photocatalytic reduction of CO₂ to CO and different organic chemicals (HCOOH, CH₃OH, CH₄). Efficient charge separation and visible light absorption by incorporation of active sites for efficient photocatalysis have been discussed. The selection of material for high CO₂ uptake and potential strategies for the rational design and development of high-performance catalysts are outlined. Major challenges and future perspectives have also been discussed at the last of the review.

Simple fabrication and unprecedented visible light response of NiNb2O6/RGO heterojunctions for the degradation of emerging pollutants in water

Utilization of environmentally friendly and effective synthesis methods to fabricate visible light responsive photocatalysts with impressive catalytic performance is desirable in photocatalytic water treatment.

Application of graphene-based materials for removal of tetracyclines using adsorption and photocatalytic-degradation: A review

Tetracyclines are extensively used to treat human and animal infectious diseases due to its effective antimicrobial activities. About 70-90% of its parent materials are released into the environment through urine and feces, implying they are the most frequently detected antibiotics in the environment with high ecological risks. Adsorption and photocatalysis have been promising techniques for the removal of tetracyclines due to effectiveness and efficiency. Graphene-based materials provide promising platforms for adsorptive and photocatalytic removal of tetracyclines from aqueous environment owning to distinctive remarkable physicochemical, optical, and electrical characteristics. Herein, we intensively reviewed the available literatures in order to provide comprehensive insight about the applications and mechanisms of graphene-based materials for removal of tetracyclines via adsorption and phototocatalysis. The synthesis methods of graphene-based materials, the tetracycline adsorption and photocatalytic-degradation conditions, and removal mechanisms have been extensively discussed. Finally concluding remarks and future perspectives have been deduced and recommended to stimulate further researches in the subject. The review study can be used as theoretical guideline for further researchers to improve the current approaches of material synthesis and application towards tetracyclines removal.

Photocatalytic and Electrocatalytic Properties of NGr-ZnO Hybrid Materials

N-doped graphene-ZnO hybrid materials with different N-doped graphene:ZnO wt% ratios (1:10; 1:20; 1:30) were prepared by a simple and inexpensive sol-gel method. The materials denoted NGr-ZnO-1 (1:10), NGr-ZnO-2 (1:20), and NGr-ZnO-3 (1:30) were investigated with advanced techniques and their morpho-structural, photocatalytic, and electrocatalytic properties were reported. Hence, pure N-doped graphene sample contains flakes with the size ranging from hundreds of nanometers to micrometers. In the case of all NGr-ZnO hybrid materials, the flakes appear heavily decorated with ZnO nanoparticles, having a cauliflower-like morphology. The X-ray powder diffraction (XRD) investigation of N-doped graphene sample revealed that it was formed by a mixture of graphene oxide, few-and multi-layer graphene. After the ZnO nanoparticles were attached to graphene, major diffraction peaks corresponding to crystalline planes of ZnO were seen. The qualitative and quantitative compositions of the samples were further evidenced by X-ray photoelectron spectroscopy (XPS). In addition, UV photoelectron spectroscopy (UPS) spectra allowed the determination of the ionization energy and valence band maxima. The energy band alignment of the hybrid materials was established by combining UV-Vis with UPS results. A high photocatalytic activity of NGr-ZnO samples against rhodamine B solution was observed. The associated reactive oxygen species (ROS) generation was monitored by electron paramagnetic resonance (EPR)-spin trapping technique. In accordance with bands alignment and identification of radical species, the photocatalytic mechanism was elucidated.

Electro-Oxidation and Simultaneous Determination of Indole-3-Acetic Acid and Salicylic Acid on Graphene Hydrogel Modified Electrode

A selective and sensitive electrochemical sensor was developed for simultaneous detection of phytohormones indole-3-acetic acid (IAA) and salicylic acid (SA). The sensing interface was fabricated on a porous, three-dimensional networked graphene hydrogel (GH) modified glassy carbon electrode (GCE). The electrocatalytic behavior of IAA and SA on the surface of the modified electrode (GH/GCE) was investigated by cyclic voltammetry and linear sweep voltammetry. Results show that the oxidation reactions of IAA and SA occur at different potentials, which enable their simultaneous detection at the sensing interface. Under optimal conditions, the GH/GCE exhibited good selectivity and stability and its response, unaffected by various interferents, was linear in the range of 4 to 200 μM of IAA and SA. The limit of detection (S/N = 3) achieved were 1.42 μM for IAA and 2.80 μM for SA. The sensor performance was validated by measuring for IAA and SA in real vegetable samples with satisfactory results.

Synergistic Adsorption and Photocatalytic Activity under Visible Irradiation Using Ag-ZnO/GO Nanoparticles Derived at Low Temperature

Ag-ZnO/graphene oxide (AG-ZnO/GO) nanocomposite was synthesized via facile aqueous solution reactions at low temperature in order to improve the photocatalytic activity for cationic dye removal under visible light irradiation. Analytical techniques were carried out in order to determine the abilities including structure, state of elements, morphology, and surface area of synthesized materials. Ag-ZnO/GO nanocomposite presented an extremely high removal rate of methylene blue (MB) not only under UV light (over 99% removal) but also under visible light (85% removal) during the same irradiation time. In this study, initial process parameters of catalyst dosage, MB concentration, and pH of the solution were also examined for MB removal efficiency effects. The proposed mechanisms for the increased removal of MB by Ag-ZnO/GO nanocomposite under visible irradiation include increased photocatalytic degradation, mainly due to increased charge transfer capacity by lowering band gap energy; minimized recombination of the excited electron-hole pairs of ZnO with the addition of Ag into the ZnO crystal lattice; and an increased adsorption capacity with the addition of GO with high surface area and semiconductor function with zero band gap energy.

Small molecules derived carbon dots: synthesis and applications in sensing, catalysis, imaging, and biomedicine

Carbon dots (CDs) are the new fellow of carbon family having a size less than 10 nm and attracted much attention of researchers since the last decade because of their unique characteristics, such as inexpensive and facile synthesis methods, easy surface modification, excellent photoluminescence, outstanding water solubility, and low toxicity. Due to these unique characteristics, CDs have been extensively applied in different kind of scientific disciplines. For example in the photocatalytic reactions, drug-gene delivery system, in vitro and in vivo bioimaging, chemical and biological sensing as well as photodynamic and photothermal therapies. Mainly two types of methods are available in the literature to synthesize CDs: the top-down approach, which refers to breaking down a more massive carbon structure into nanoscale particles; the bottom-up approach, which refers to the synthesis of CDs from smaller carbon units (small organic molecules). Many review articles are available in the literature regarding the synthesis and applications of CDs. However, there is no such review article describing the synthesis and complete application of CDs derived from small organic molecules together. In this review, we have summarized the progress of research on CDs regarding its synthesis from small organic molecules (bottom-up approach) via hydrothermal/solvothermal treatment, microwave irradiation, ultrasonic treatment, and thermal decomposition techniques as well as applications in the field of bioimaging, drug/gene delivery system, fluorescence-based sensing, photocatalytic reactions, photo-dynamic therapy (PDT) and photo-thermal (PTT) therapy based on the available literature. Finally, the challenges and future direction of CDs are discussed.

Voltammetric aptasensor for sulfadimethoxine using a nanohybrid composed of multifunctional fullerene, reduced graphene oxide and Pt@Au nanoparticles, and based on direct electron transfer to the active site of glucose oxidase

This work describes a voltammetric and ultrasensitive aptasensor for sulfadimethoxine (SDM). It is based on signal amplification by making use of a multifunctional fullerene-doped reduced graphene oxide nanohybrid. The nanohybrid was coated with poly(diallyldimethylammonium chloride) to obtain a material (P-C₆₀-rGO) with large specific surface area and a unique adsorption ability for loading it with glucose oxidase (GOx). The coating also facilitates the direct electron transfer between the active site of GOx and the glassy carbon electrode (GCE). The P-C₆₀-rGO were then modified with Pt@Au nanoparticles, and the thiolated SDM-binding aptamer was immobilized on the nanoparticles. On exposure of the modified GCE to a solution containing SDM, it binds to the aptamer. The results were recorded through the signal responses generated from the redox center of GOx (FAD/FADH₂) by cyclic voltammetry at a scan rate of 100 mV·s^-1 from -0.25 to -0.65 V. Accordingly, The sensor has good specificity and stability, and response is linear in the 10 fg·mL^-1 to 50 ng·mL^-1 SDM concentration range with a detection limit of 8.7 fg·mL^-1. Graphical abstract Schematic presentation of an electrochemical aptasensor for sulfadimethoxine (SDM) using multifunctional fullerene-doped graphene (C₆₀-rGO) nanohybrids for amplification. The limit of detection for SDM is as low as 8.7 fg·mL^-1.

Visible-light-driven photocatalytic degradation of safranin-T dye using functionalized graphene oxide nanosheet (FGS)/ZnO nanocomposites

FGS/ZnO NCs with excellent photocatalytic activity towards photodegradation of safranin-T have been synthesized via a facile and economical solution route.

Surface modification of layered perovskite Sr2TiO4 for improved CO2 photoreduction with H2O to CH4

Layered perovskite Sr₂TiO₄ photocatalyst was synthesized by using sol-gel method with citric acid. In order to increase the surface area of layered perovskite Sr₂TiO₄, and thus to improve its photocatalytic activity for CO₂ reduction, its surface was modified via hydrogen treatment or exfoliation. The physical and chemical properties of the prepared catalysts were characterized by X-ray diffraction, high-resolution transmission electron microscopy, elemental mapping analysis, energy-dispersive X-ray spectroscopy, N₂ adsorption-desorption, UV-Vis spectroscopy, X-ray photoelectron spectroscopy, photoluminescence, and electrophoretic light scattering. CO₂ photoreduction was performed in a closed reactor under 6 W/cm² UV irradiation. The gaseous products were analyzed using a gas chromatograph equipped with flame ionization and thermal conductivity detectors. The exfoliated Sr₂TiO₄ catalyst (E-Sr₂TiO₄) exhibited a narrow band gap, a large surface area, and high dispersion. Owing to these advantageous properties, E-Sr₂TiO₄ photocatalyst showed an excellent catalytic performance for CO₂ photoreduction reaction. The rate of CH₄ production from the photoreduction of CO₂ with H₂O using E-Sr₂TiO₄ was about 3431.77 μmol/g_cat after 8 h.

Electrochemical Detecting Lung Cancer-Associated Antigen Based on Graphene-Gold Nanocomposite

Using a Au nanoparticle/reduced graphene oxide composite (AuNP-RGO), a signal-enhanced electrochemical immunosensor without label was created to detect neuron-specific enolase (NSE). Furthermore, an environmentally-friendly method was developed to prepare AuNP-RGO by employing chitosan (CS), which served as reducing and stabilizing agent. We showed that the sensitivity of the immunosensor designed in this report was remarkably enhanced because of the numerous active sites in the sensor provided by the AuNP-RGO nanostructure. For the quantification of NSE, the immunosensor exhibited a positive linear relationship with the concentration in the range of 0.1 to 2000 ng/mL, where the limit of the detection was 0.05 ng/mL.

New green synthesized reduced graphene oxide–ZrO2 composite as high performance photocatalyst under sunlight

ZrO₂/rGO nanocomposite prepared via simple bio-mediated route exhibited excellent sunlight driven photocatalytic performance.

Graphene in Photocatalysis: A Review

In recent years, heterogeneous photocatalysis has received much research interest because of its powerful potential applications in tackling many important energy and environmental challenges at a global level in an economically sustainable manner. Due to their unique optical, electrical, and physicochemical properties, various 2D graphene nanosheets-supported semiconductor composite photocatalysts have been widely constructed and applied in different photocatalytic fields. In this review, fundamental mechanisms of heterogeneous photocatalysis, including thermodynamic and kinetics requirements, are first systematically summarized. Then, the photocatalysis-related properties of graphene and its derivatives, and design rules and synthesis methods of graphene-based composites are highlighted. Importantly, different design strategies, including doping and sensitization of semiconductors by graphene, improving electrical conductivity of graphene, increasing eloectrocatalytic active sites on graphene, strengthening interface coupling between semiconductors and graphene, fabricating micro/nano architectures, constructing multi-junction nanocomposites, enhancing photostability of semiconductors, and utilizing the synergistic effect of various modification strategies, are thoroughly summarized. The important applications including photocatalytic pollutant degradation, H₂ production, and CO₂ reduction are also addressed. Through reviewing the significant advances on this topic, it may provide new opportunities for designing highly efficient 2D graphene-based photocatalysts for various applications in photocatalysis and other fields, such as solar cells, thermal catalysis, separation, and purification.

Hydrothermal preparation of reduced graphene oxide-silver nanocomposite using Plectranthus amboinicus leaf extract and its electrochemical performance

Graphene based nanocomposites are receiving increasing attention in many fields such as material chemistry, environmental science and pharmaceutical science. In this study, a facial synthesis of a reduced graphene oxide-silver nanocomposite (RGO-Ag) was carried out from Plectranthus amboinicus leaf extract. The synthesized nanocomposite was characterized by using X-ray diffraction, scanning electron microscope, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscope and UV-vis spectroscopy for structural confirmation. The reduction of graphene oxide and silver ions was achieved simultaneously due to the reducibility of the Plectranthus amboinicus leaf extract. We further investigated the electrochemical properties of the biosynthesized RGO-Ag nanocomposite. A nonenzymatic H₂O₂ electrochemical sensor was shown to be successfully fabricated by using biosynthesized RGO-Ag nanocomposite. Moreover, the fabricated electrochemical sensor also showed good selectivity.

Photocatalytic conversion of CO2 over graphene-based composites: current status and future perspective

The continuous rise in the atmospheric CO₂ level and the ever-increasing demand of energy have raised serious concerns about the ensuing effects on the global climate change and future energy supply. Photocatalytic conversion of CO₂, which uses solar light energy to recycle CO₂ into fuels and chemicals, provides a promising and straightforward strategy to simultaneously reduce the atmospheric CO₂ level and fulfil the future energy demand. However, the lack of substantial development of state-of-the-art materials remains a major bottleneck of this technology. In recent years, graphene-based composite photocatalysts have gained increasing interest in CO₂ conversion due to the introduction of graphene with a series of unique physicochemical properties, which has shown to play a significant role in promoting the photocatalytic solar energy conversion efficiency. In this review, we comprehensively summarize the typical literature reports on graphene-based composites for photocatalytic conversion of CO₂ to produce solar fuels and chemicals. The main types of the reported graphene-based composites and the role of graphene in the composites in improving the photocatalytic performance have been elaborated. In particular, we have highlighted the possible role of graphene in tuning the product selectivity of photocatalytic reduction of CO₂. Finally, perspectives on the existing problems and future research on graphene-based composites toward photocatalytic conversion of CO₂ are critically discussed.

Electrodeposition of Au nanoparticles on poly(diallyldimethylammonium chloride) functionalized reduced graphene oxide sheets for voltammetric determination of nicotine in tobacco products and anti-smoking pharmaceuticals

The principal objective of this study was to develop a sensitive and selective electrochemical sensor for nicotine detection based on a novel PDDA-RGO/Au nanocomposite.

Graphene-Based Photocatalysts for CO2 Reduction to Solar Fuel

Recently, photocatalytic CO2 reduction for solar fuel production has attracted much attention because of its potential for simultaneously solving energy and global warming problems. Many studies have been conducted to prepare novel and efficient photocatalysts for CO2 reduction. Graphene, a two-dimensional material, has been increasingly used in photocatalytic CO2 reduction. In theory, graphene shows several remarkable properties, including excellent electronic conductivity, good optical transmittance, large specific surface area, and superior chemical stability. Attributing to these advantages, fabrication of graphene-based materials has been known as one of the most feasible strategies to improve the CO2 reduction performance of photocatalysts. This Perspective mainly focuses on the recent important advances in the fabrication and application of graphene-based photocatalysts for CO2 reduction to solar fuels. The existing challenges and difficulties of graphene-based photocatalysts are also discussed for future application.