Facile functionalization of graphene oxide with ethylenediamine as a solid base catalyst for Knoevenagel condensation reaction

Thermal Stability of Encapsulated Carbon-Based Multiporous-Layered-Electrode Perovskite Solar Cells Extended to Over 5000 h at 85 °C

The key to the practical application of organometal-halide crystals perovskite solar cells (PSCs) is to achieve thermal stability through robust encapsulation. This paper presents a method to significantly extend the thermal stability lifetime of perovskite solar cells to over 5000 h at 85 °C by demonstrating an optimal combination of encapsulation methods and perovskite composition for carbon-based multiporous-layered-electrode (MPLE)-PSCs. We fabricated four types of MPLE-PSCs using two encapsulation structures (over- and side-sealing with thermoplastic resin films) and two perovskite compositions ((5-AVA)x(methylammonium (MA))1-xPbI3 and (formamidinium (FA))0.9Cs0.1PbI3), and analyzed the 85 °C thermal stability followed by the ISOS-D-2 protocol. Without encapsulation, FA0.9Cs0.1PbI3 exhibited higher thermal stability than (5-AVA)x(MA)1-xPbI3. However, encapsulation reversed the phenomenon (that of (5-AVA)x(MA)1-xPbI3 became stronger). The combination of the (5-AVA)x(MA)1-xPbI3 perovskite absorber and over-sealing encapsulation effectively suppressed the thermal degradation, resulting in a PCE value of 91.2% of the initial value after 5072 h. On the other hand, another combination (side-sealing on (5-AVA)x(MA)1-xPbI3 and over- and side-sealing on FA0.9Cs0.1PbI3) resulted in decreased stability. The FACs-based perovskite was decomposed from these degradation mechanisms by the condensation reaction between FA and carbon. For side-sealing, the space between the cell and the encapsulant was estimated to contain approximately 1,260,000 times more H2O than in over-sealing, which catalyzed the degradation of the perovskite crystals. Our results demonstrate that MA-based PSCs, which are generally considered to be thermally sensitive, can significantly extend their thermal stability after proper encapsulation. Therefore, we emphasize that finding the appropriate combination of encapsulation technique and perovskite composition is quite important to achieve further device stability.

A novel digitonin/graphene oxide/iron oxide nanocomposite: synthesis, physiochemical characterization and antioxidant activity

In this work, iron oxide (Fe3O4) magnetic nanoparticles (MNPs) and graphene oxide (GO) nanosheets were prepared via the co-precipitation technique and the Modified Hummer method. Fe3O4 MNPs and GO nanosheets were combined to prepare Fe3O4/GO nanocomposite and subsequently conjugated with Digitonin (DIG) in order to obtain a dual-targeted delivery system based on DIG/Fe3O4/GO nanocomposite. SEM images reveal the presence of Fe3O4 MNPs at a scale of 100 nm, exhibiting dispersion between the GO nanosheets. Aggregation of the DIG/Fe3O4/GO nanocomposite was observed at various size scales. The XRD structural analysis confirms the crystal structure of the prepared samples. The Fe3O4 MNPs demonstrated the main XRD-diffracted peaks. Also, GO nanosheets exhibit crystalline characteristics on the (001) and (002) planes. The predominant peaks observed in the DIG/GO/Fe3O4 nanocomposite are attributed to the crystal phases of Fe3O4 MNPs. The FT-IR vibrational modes observed in the GO/DIG/Fe3O4 nanocomposite indicate the presence of crosslinking between GO nanosheet layers and the Fe3O4 MNPs. The antioxidant activity of the prepared samples was measured and the DIG/GO/Fe3O4 nanocomposite demonstrated a significantly high antioxidant activity in both 2-diphenyl-1-picrylhydrazyl (DPPH·) and 2,2-azino-bis-3-ethylbenzthiazoline-6-sulfonic acid (ABTS·+) tests.

Horizontally Asymmetric Nanochannels of Graphene Oxide Membranes for Efficient Osmotic Energy Harvesting

Reverse electrodialysis (RED) directly harvests renewable energy from salinity gradients, and the achievable potential power heavily relies on the ion exchange membranes. Graphene oxides (GOs) are considered a solid candidate for the RED membrane because the laminated GO nanochannels with charged functional groups provide an excellent ionic selectivity and conductivity. Yet, a high internal resistance and poor stability in aqueous solutions limit the RED performance. Here, we develop a RED membrane that concurrently achieves high ion permeability and stable operation based on epoxy-confined GO nanochannels with asymmetric structures. The membrane is fabricated by reacting epoxy-wrapped GO membranes with ethylene diamine via vapor diffusion, overcoming the swelling properties in aqueous solutions. More importantly, the resultant membrane exhibits asymmetric GO nanochannels in terms of both channel geometry and electrostatic surface charges, leading to the rectified ion transport behavior. The demonstrated GO membrane exhibits the RED performance up to 5.32 W·m^-2 with >40% energy conversion efficiency across a 50-fold salinity gradient and 20.3 W·m^-2 across a 500-fold salinity gradient. Planck-Nernst continuum models coupled to molecular dynamics simulations rationalize the improved RED performance in terms of the asymmetric ionic concentration gradient within the GO nanochannel and the ionic resistance. The multiscale model also provides the design guidelines for ionic diode-type membranes configuring the optimum surface charge density and ionic diffusivity for efficient osmotic energy harvesting. The synthesized asymmetric nanochannels and their RED performance demonstrate the nanoscale tailoring of the membrane properties, establishing the potentials for 2D material-based asymmetric membranes.

Modulating the interaction of graphenic substrates with human interleukin-6 and its monoclonal antibody: a study by Raman images

Interleukin-6 (IL-6) is a cytokine with wide-ranging biological effects, playing an important role on the immune system and inflammatory responses. Therefore, it is important to develop alternative, highly sensitive and reliable analytical methodologies for the accurate detection of this biomarker in biological fluids. Graphene substrates (GS), such as pristine graphene (G), graphene oxide (GO), and reduced graphene oxide (rGO), have shown great benefits for biosensing and in the development of novel biosensor devices. In this work, we present a proof of concept for the development of a new analytical platform for the specific recognition of human interleukin-6, that is based on the coffee-ring formation of monoclonal antibodies of interleukin-6 (mabIL-6) onto amine functionalized GS. The prepared GS/mabIL-6/IL-6 systems were successfully used to show that IL-6 was specifically and selectively adsorbed onto the area of the mabIL-6 coffee-ring. Raman imaging was confirmed as a versatile tool to investigate different antigen-antibody interactions and their surface distribution. This experimental approach can be used to develop a wide variety of substrates for antigen-antibody interaction allowing the specific detection of an analyte in a complex matrix.

Preparation and Emulsifying Properties of Carbon-Based Pickering Emulsifier

Water is increasingly being used as a solvent in place of organic solvent in order to meet the demand for green chemical synthesis. Nevertheless, many of the reaction substrates are organic matter, which have low water solubility, resulting in a low reaction interface and limiting the development of organic-water biphasic systems. A surfactant is typically added to the two-phase system to form an emulsion to increase the contact area between the organic phase and the water. Compared to ordinary emulsion stabilized with the surfactant, Pickering emulsion offers better adhesion resistance, biocompatibility, and environmental friendliness. It possesses unrivaled benefits as an emulsifier and catalyst in a two-phase interfacial catalysis system (PIC). In this study, the amine group (NNDB) was employed to alter the surface of graphene oxide (GO). A stable Pickering emulsion was created by adsorbing GO-NNDB on the toluene–water interface. It was determined that the emulsion system had good stability by analyzing digital photographs and microscope images of droplets at various temperatures, and fluorescence microscopy images of emulsion droplets created by both newly added and recovered emulsifiers. This work provided the groundwork for future applications of Pickering emulsion in interfacial catalysis.

A step forward to overcome the cytotoxicity of graphene oxide through decoration with tragacanth gum polysaccharide

Hybridization of nanomaterials (NMs) with natural polymers is one of the best techniques to promote their exciting properties. In this way, the main objective of this work was to investigate the efficiency of decoration of the graphene oxide (GO) nano-sheets with tragacanth gum (TG) polysaccharide. To aim this, different approaches were used (with and without ultrasonic treatment) and various tests (XRD, FTIR, Raman, UV-Vis, DLS, Zeta potential, contact angle, AFM, FE-SEM, TEM, and MTT assay) were conducted. Test results indicated that the nano-hybrids were successfully synthesized. Furthermore, our findings represented that, the TG hybridized GO (TG-GO) appreciably enhanced the biocompatibility of GO. Moreover, it was demonstrated that the ultrasonic treatment of TG solution put a remarkable impact on the microstructure, wettability, and also surface charge characteristic of fabricated nano-hybrids and consequently improved the biocompatibility against L929-fibroblast cells.

Thin-film nanocomposite NF membrane with GO on macroporous hollow fiber ceramic substrate for efficient heavy metals removal

The ceramic membrane has been widely used in the wastewater treatment based on the chemical resistance and superior separation performance. A robust and defect-free thin-film nanocomposite (TFN) nanofiltration (NF) membrane on the macroporous hollow fiber ceramic (HFC) substrate was novelly developed for heavy metals removal. Before interfacial polymerization (IP), the aqueous solution of graphene oxide (GO) grafted with ethylenediamine (EDA) was deposited on the HFC substrate by vacuum filtration. Then, a thin polyamide (PA) film was fabricated by EDA and 1,3,5-trimesoyl chloride (TMC), followed by heat treatment. The effects of GO content and EDA concentration on the performance of the NF membrane have been systematically investigated. The results showed that when the GO content was 0.015 mg·mL^-1 and the EDA concentration was 0.75 wt.%, the as-prepared eGO₃/PA-HFC membrane had a rejection rate of 94.12% for MgCl₂ and a pure water flux of 18.03 L·m^-2·h^-1. Additionally, the removal ability of eGO₃/PA-HFC membranes for heavy metal ions was satisfactory (93.33%, 92.73%, 90.45% and 88.35% for Zn²⁺, Cu²⁺, Ni²⁺ and Pb²⁺, respectively). The study explored further that it was efficient and stable for heavy metal ions removal during 30 h in the simulated tap water and mining wastewater, which indicated that the eGO/PA-HFC membrane has great application potential in wastewater treatment.

Preparation of an Amidated Graphene Oxide/Sulfonated Poly Ether Ether Ketone (AGO/SPEEK) Modified Atmosphere Packaging for the Storage of Cherry Tomatoes

The shelf life of cherry tomatoes is short so that new and efficient preservation techniques or procedures are required to reduce postharvest losses. This study focused on the development of a sulfonated poly ether ether ketone (SPEEK) film incorporated with amidated graphene oxide (AGO), for the storage of cherry tomatoes in modified atmosphere packaging. The mechanical properties, gas permeability, and moisture permeability were subsequently tested. The evolution of attributes related to shelf life, such as gas composition, physicochemical properties, and sensory properties were also monitored during storage trials. AGO, as an inorganic filler, increases the thermal stability and mechanical properties of SPEEK-based films, while it reduces the water absorption, swelling rate, and moisture permeability. Importantly, all the AGO/SPEEK films exhibited enhanced gas permeability and selective permeability of CO₂/O₂ relative to the SPEEK film. Moreover, 0.9% (w/w) AGO/SPEEK film showed an enhanced permeability coefficient of CO₂, corresponding to an increase of 50.7%. It could further improve the selective coefficient of CO₂/O₂ to 67.1%. The results of preservation at 8 °C revealed that: 0.9% (w/w) AGO/SPEEK film was significantly effective at maintaining the quality and extending the shelf life of cherry tomatoes from 15 to 30 days, thereby suggesting the potential for applying AGO-incorporated SPEEK films for food packaging materials.

Improvement of the catalytic performance of hybrid nanocomposite based on phosphate-benzimidazole in Knoevenagel condensation

In this work, we have developed a simple and very effective experimental strategy for the reaction of Knoevenagel via the condensation of aromatic aldehydes substituted with active methylene compounds in the presence of hybrid nanocomposites xMCl₂-yNaPO₃ (MCl₂ = 2,2′-dibenzimidazolyl butane dichlorhydrates), under ecological conditions. The Phosphate-Benzimidazole hybrid nanocomposite as heterogeneous catalysts has demonstrated a high catalytic activity for the Knoevenagel condensation in ethanol as an ecological solvent. It has several advantages such as light reaction conditions, a simple and ecological working procedure. Meanwhile, xMCl₂-yNaPO₃ can be recovered by simple filtration and this catalytic system having an interesting lifetime (five cycles) with no decrease in activity.

Calcium and nitrogen species loaded into SBA-15 - a promising catalyst tested in Knoevenagel condensation

Mesoporous silica of the SBA-15 type was used as a support for basic active centers generated by the incorporation of calcium species and (3-aminopropylo)trimethoxysilane (APTMS) or imidazole. The samples were characterized by low temperature N2 adsorption/desorption, XRD, XPS, FTIR spectroscopy, CO2-TPD, and elemental and thermal analyses. Calcium containing samples were analysed in 2,5-hexanedione dehydration and cyclization, while the activities of all the samples were examined in Knoevenagel condensation between benzaldehyde and malononitrile. It was demonstrated that the calcium species interacted with a silica support increasing the stabilization of organosilanes on the SBA-15 surface. A very high activity of the catalysts in Knoevenagel condensation indicated a synergistic interaction between calcium and the organic modifiers.

Graphene-based carbocatalysts for carbon-carbon bond formation

Organic transformations are usually catalyzed by metal-based catalysts. In contrast, metal-free catalysts have attracted considerable attention from the viewpoint of sustainability and safety. Among the studies in metal-free catalysis, graphene-based materials have been introduced in the reactions that are usually catalyzed by transition metal catalysts. This review covers the literature (up to the beginning of April 2020) on the use of graphene and its derivatives as carbocatalysts for C-C bond-forming reactions, which are one of the fundamental reactions in organic syntheses. Besides, mechanistic studies are included for the rational understanding of the catalysis. Graphene has significant potential in the field of metal-free catalysis because of the fine-tunable potential of the structure, high stability and durability, and no metal contamination, making it a next-generation candidate material in catalysis.

Inhibition of Photoconversion Activity in Self-Assembled ZnO-Graphene Quantum Dots Aggregated by 4-Aminophenol Used as a Linker

The aggregation of zinc oxide nanoparticles leads to an increased absorbance in the ultraviolet-visible region by an induced light scattering effect. Herein, we demonstrate the inhibition of photoconversion activity in ZnO-graphene core-shell quantum dots (QD) (ZGQDs) agglomerated by 4-aminophenol (4-AP) used as a linker. The ZnO-graphene quantum dots (QD) aggregates (ZGAs) were synthesized using a facile solvothermal process. The ZGAs revealed an increased absorbance in the wavelengths between 350 and 750 nm as compared with the ZGQDs. Against expectation, the calculated average photoluminescence lifetime of ZGAs was 7.37 ns, which was 4.65 ns longer than that of ZGQDs and was mainly due to the high contribution of a slow (τ2, τ3) component by trapped carriers in the functional groups of graphene shells and 4-AP. The photoelectrochemical (PEC) cells and photodetectors (PDs) were fabricated to investigate the influence of ZGAs on the photoconversion activity. The photocurrent density of PEC cells with ZGAs was obtained as 0.04 mA/cm2 at 0.6 V, which was approximately 3.25 times lower than that of the ZGQDs. The rate constant value of the photodegradation value of rhodamine B was also decreased by around 1.4 times. Furthermore, the photoresponsivity of the PDs with ZGAs (1.54 μA·mW-1) was about 2.5 times as low as that of the PDs with ZGQDs (3.85 μA·mW-1). Consequently, it suggests that the device performances could be degraded by the inhibition phenomenon of the photoconversion activity in the ZGAs due to an increase of trap sites.

Preparation of a Pickering emulsion by modification of an amine-functionalized graphene oxide surface with organosilane: efficient catalyst for the Knoevenagel condensation of malononitrile with aldehydes at mild temperature

In this study, a series of Pickering emulsions for catalysis of Knoevenagel condensations of malononitrile with aldehydes were prepared by surface modification of amine-functionalized graphene oxide (GO-NH₂) with trimethoxymethylsilane (MTMS).

Effect of Reaction Temperature on Structure, Appearance and Bonding Type of Functionalized Graphene Oxide Modified P-Phenylene Diamine

In this study, graphene oxides with different functionalization degrees were prepared by a facile one-step hydrothermal reflux method at various reaction temperatures using graphene oxide (GO) as starting material and p-phenylenediamine (PPD) as the modifier. The effects of reaction temperature on structure, appearance and bonding type of the obtained materials were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The results showed that when the reaction temperature was 10–70 °C, the GO reacted with PPD through non-covalent ionic bonds (–COO⁻H₃⁺N–R) and hydrogen bonds (C–OH…H₂N–X). When the reaction temperature reached 90 °C, the GO was functionalized with PPD through covalent bonds of C–N. The crystal structure of products became more ordered and regular, and the interlayer spacing (d value) and surface roughness increased as the temperature increased. Furthermore, the results suggested that PPD was grafted on the surface of GO through covalent bonding by first attacking the carboxyl groups and then the epoxy groups of GO.

Sulfonic acid-functionalized organic knitted porous polyaromatic microspheres as heterogeneous catalysts for biodiesel production

Sulfonic acid functionalized porous polyaromatics are highly active and recyclable heterogeneous catalysts for biodiesel production from vegetable oils.

Eco-friendly synthesis of graphene–chitosan composite hydrogel as efficient adsorbent for Congo red

A simple approach was utilized to synthesize graphene/chitosan-based hydrogel using glutaraldehyde as crosslinking agent in room temperature. The composite aerogel was used for removal of cationic and anionic dyes from aqueous solution. It showed high adsorption capacity towards Congo red as an anionic dye. Adsorption experiments were performed based on various parameters, such as initial Congo red concentration, solution pH and contact time. The kinetics data were analyzed using four different models and the pseudo-second-order model best described the adsorption of Congo red aerogel. The Equilibrium adsorption isotherm data indicated that equilibrium data were fitted to the Langmuir isotherm. The maximum dye adsorption capacity calculated from the Langmuir isotherm equation was 384.62 mg g⁻¹. Moreover, the aerogel was stable and easily recovered, and adsorption capacity was about 100% of the initial saturation adsorption capacity after being used three times.

Graphene/chitosan-based hydrogel was synthesized using glutaraldehyde as crosslinking agent in room temperature and it used for removal of Congo red dye from aqueous solution.

Amine-Functionalized Sugarcane Bagasse: A Renewable Catalyst for Efficient Continuous Flow Knoevenagel Condensation Reaction at Room Temperature

A biomass-based catalyst with amine groups (–NH₂), viz., amine-functionalized sugarcane bagasse (SCB-NH₂), was prepared through the amination of sugarcane bagasse (SCB) in a two-step process. The physicochemical properties of the catalyst were characterized through FT-IR, elemental analysis, XRD, TG, and SEM-EDX techniques, which confirmed the –NH₂ group was grafted onto SCB successfully. The catalytic performance of SCB-NH₂ in Knoevenagel condensation reaction was tested in the batch and continuous flow reactions. Significantly, it was found that the catalytic performance of SCB-NH₂ is better in flow system than that in batch system. Moreover, the SCB-NH₂ presented an excellent catalytic activity and stability at the high flow rate. When the flow rate is at the 1.5 mL/min, no obvious deactivation was observed and the product yield and selectivity are more than 97% and 99% after 80 h of continuous reaction time, respectively. After the recovery of solvent from the resulting solution, a white solid was obtained as a target product. As a result, the SCB-NH₂ is a promising catalyst for the synthesis of fine chemicals by Knoevenagel condensation reaction in large scale, and the modification of the renewable SCB with –NH₂ group is a potential avenue for the preparation of amine-functionalized catalytic materials in industry.