Green reduction of graphene oxide using eucalyptus leaf extract and its application to remove dye

Fouling-Resistant Behavior of Hydrophobic Surfaces Based on Poly(dimethylsiloxane) Modified by Green rGO@ZnO Nanocomposites

In line with global goals to solve marine biofouling challenges, this study proposes an approach to developing a green synthesis inspired by natural resources for fouling-resistant behavior. A hybrid antifouling/foul release (HAF) coating based on poly(dimethylsiloxane) containing a green synthesized nanocomposite was developed as an environmentally friendly strategy. The nanocomposites based on graphene oxide (GO) and using marine sources, leaves, and stems of mangroves (Avicennia marina), brown algae (Polycladia myrica), and zinc oxide were compared. The effectiveness of this strategy was checked first in the laboratory and then in natural seawater. The performance stability of the coatings after immersion in natural seawater was also evaluated. With the lowest antifouling (17.95 ± 0.7%) and the highest defouling (51.2 ± 0.9%), the best fouling-resistant performance was for the coatings containing graphene oxide reduced with A. marina stem/zinc oxide (PrGZS) and graphene oxide reduced with A. marina leaves/zinc oxide with 50% multiwall carbon nanotubes (PrGZHC50), respectively. Therefore, the HAF coatings can be considered as developed and eco-friendly HAF coatings for the maritime industry.

Reduced graphene oxide: Biofabrication and environmental applications

Green synthesis of high-quality reduced graphene oxide (rGO) from agro-industrial waste resources remains attractive owing to its outstanding environmental benefits. The remarkable properties of rGO include excellent morphology, uniform particle size, good optical properties, high conductivity, nontoxicity, and extraordinary chemical stability. Traditional methods for the synthesis of rGO nanomaterials involve several chemical reactions including oxidation, carbonization, toxic solvent, and pyrolysis which produce harmful byproducts. Green preparation of rGO is an emerging area of research in graphene technology which is cost-effective and sustainable in the procedure. Owing to the uniform particle rGO particle size, these smart nanomaterials have wide applicability, including in metal ions and pollutant sensing and adsorption, photocatalysis, optoelectrical devices, medical diagnosis, and drug delivery. Here we review the physicochemical properties of rGO, the biowaste sources and green methods of rGO synthesis, and the diverse applications of rGO, including in water purification and the biomedical fields. With this review, covering more than 200 research articles published on rGO in the last eight years ending in 2022, we aim to provide a quick guide for researchers seeking up-to-date information on the properties, production, and applicability of rGO, with special attention to rGO applications in water purification and the biomedical fields.

Biogenic synthesis of reduced graphene oxide from Ziziphus spina-christi (Christ's thorn jujube) extracts for catalytic, antimicrobial, and antioxidant potentialities

In the current work, various concentrations of the aqueous extract of Ziziphus spina-christi were employed for the phytoreduction of graphene oxide (GO). The green synthesized reduced graphene oxide (rGO) was characterized through UV-Vis spectrometry, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy, and energy-dispersive X-ray spectroscopy (SEM-EDX). Gas chromatography-mass spectrometry (GC-MS) denoted the presence of numerous phytoconstituents including ketones, terpenoids, fatty acids, esters, and flavonoids, which acted as reducing and capping agents. The obtained results indicated the increase in rGO yield and shape with increasing the extract concentration. The optimized rGO was instantaneously ~100% removed methylene blue (MB) from the water at 5 mg L^-1. However, the removal efficiency was slightly declined to reach 73.55 and 65.1% at 10 and 15 mg L^-1, respectively. A powerful antibacterial activity for rGO particularly against gram-negative bacteria with a high concentration of 2 × 10⁸ CFU mL^-1 was confirmed. Furthermore, rGO demonstrated promising and comparable antioxidant efficiency with vitamin C against DPPH free radical scavenging. While vitamin C recorded 13.45 and 48.4%, the optimized rGO attained 13.30 and 45.20% at 12 and 50 μg mL^-1, respectively.

Synergetic effect of green synthesized reduced graphene oxide and nano-zero valent iron composite for the removal of doxycycline antibiotic from water

In this work, the synthesis of an rGO/nZVI composite was achieved for the first time using a simple and green procedure via Atriplex halimus leaves extract as a reducing and stabilizing agent to uphold the green chemistry principles such as less hazardous chemical synthesis. Several tools have been used to confirm the successful synthesis of the composite such as SEM, EDX, XPS, XRD, FTIR, and zeta potential which indicated the successful fabrication of the composite. The novel composite was compared with pristine nZVI for the removal aptitude of a doxycycline antibiotic with different initial concentrations to study the synergistic effect between rGO and nZVI. The adsorptive removal of bare nZVI was 90% using the removal conditions of 25 mg L^-1, 25 °C, and 0.05 g, whereas the adsorptive removal of doxycycline by the rGO/nZVI composite reached 94.6% confirming the synergistic effect between nZVI and rGO. The adsorption process followed the pseudo-second order and was well-fitted to Freundlich models with a maximum adsorption capacity of 31.61 mg g^-1 at 25 °C and pH 7. A plausible mechanism for the removal of DC was suggested. Besides, the reusability of the rGO/nZVI composite was confirmed by having an efficacy of 60% after six successive cycles of regeneration.

Bio-Inspired Synthesis of Carbon-Based Nanomaterials and Their Potential Environmental Applications: A State-of-the-Art Review

Providing safe drinking water and clean water is becoming a more challenging task all around the world. Although some critical issues and limits remain unsolved, implementing ecologically sustainable nanomaterials (NMs) with unique features, e.g., highly efficient and selective, earth-abundance, renewability, low-cost manufacturing procedures, and stability, has become a priority. Carbon nanoparticles (NPs) offer tremendous promise in the sectors of energy and the environment. However, a series of far more ecologically friendly synthesis techniques based on natural, renewable, and less expensive waste resources must be explored. This will reduce greenhouse gas emissions and harmful material extraction and assist the development of green technologies. The progress achieved in the previous 10 years in the fabrication of novel carbon-based NMs utilizing waste materials as well as natural precursors is reviewed in this article. Research on carbon-based NPs and their production using naturally occurring precursors and waste materials focuses on this review research. Water treatment and purification using carbon NMs, notably for industrial and pharmaceutical wastes, has shown significant potential. Research in this area focuses on enhanced carbonaceous NMs, methods, and novel nano-sorbents for wastewater, drinking water, groundwater treatment, as well as ionic metal removal from aqueous environments. Discussed are the latest developments and challenges in environmentally friendly carbon and graphene quantum dot NMs.

Phyto-mediated photocatalysis: a critical review of in-depth base to reactive radical generation for erythromycin degradation

Erythromycin (ERY), designated as a risk-prioritized macrolide antibiotic on the 2015 European Union watch list, is the third most commonly used antibiotic, most likely due to its ability to inhibit the protein. ERY has revealed record-high aquatic concentrations threatening the entire ecosystem and hence demands priority remedial measures. The inefficiency of various conventional ERY degradation methodologies opened up a gateway to advanced technologies. The conventional approach comprising of a chemically formulated, single photocatalyst has a major drawback of creating multiple environmental stresses. In this context, photocatalysis is grabbing tremendous attention as an efficient and cost-effective antibiotic treatment approach. Several studies have ascertained that ZnO, TiO₂, Fe₃O₄, and rGO nanoparticles possess remarkable pollution minimizing operational capabilities. Additionally, composites are found much more effective in antibiotic removal than single nanoparticles. In this review, an attempt has been made to provide a comprehensive baseline for efficient reactive radical production by a phyto-mediated composite kept under a certain source of irradiation. Considerable efforts have been directed towards the in-depth investigation of rGO-embedded, phyto-mediated ZnO/TiO₂/Fe₃O₄ photocatalyst fabrication for efficient ERY degradation, undergoing green photocatalysis. This detailed review provides photocatalytic nanocomposite individualities along with a hypothetical ERY degradation mechanism. It is assumed that derived information presented here will provoke innovative ideas for water purification incorporating green photocatalysis, initiating the construction of high-performance biogenic hierarchical nanocatalysts.

Green Reduction of Graphene Oxide Involving Extracts of Plants from Different Taxonomy Groups

Graphene, a remarkable material, is ideal for numerous applications due to its thin and lightweight design. The synthesis of high-quality graphene in a cost-effective and environmentally friendly manner continues to be a significant challenge. Chemical reduction is considered the most advantageous method for preparing reduced graphene oxide (rGO). However, this process necessitates the use of toxic and harmful substances, which can have a detrimental effect on the environment and human health. Thus, to accomplish the objective, the green synthesis principle has prompted researchers worldwide to develop a simple method for the green reduction of graphene oxide (GO), which is readily accessible, sustainable, economical, renewable, and environmentally friendly. For example, the use of natural materials such as plants is generally considered safe. Furthermore, plants contain reducing and capping agents. The current review focuses on the discovery and application of rGO synthesis using extracts from different plant parts. The review aims to aid current and future researchers in searching for a novel plant extract that acts as a reductant in the green synthesis of rGO, as well as its potential application in a variety of industries.

Catalytic and Medical Potential of a Phyto-Functionalized Reduced Graphene Oxide-Gold Nanocomposite Using Willow-Leaved Knotgrass

In the current study, a simple, environmentally friendly, and cost-effective reduced graphene oxide-gold nanoparticle (rGO-AuNP) nanocomposite was successfully phytosynthesized using the aqueous leaf extract of a common weed found on the Nile banks, Persicaria salicifolia, for the first time. The phytosynthesis of rGO-AuNPs was first confirmed via the color transformation from brown to black as well as throughvarious techniques such as transmission electron microscopy (TEM) and Raman spectroscopy. Two UV-vis peaks at 275 and 530 nm were observed for the nanocomposite with a typical particle size of mostly spherical AuNPs of 15-20 nm. However, other shapes were occasionally detected including rods, triangles, and rhomboids. Existing phytoconstituents such as flavonoids and glycosides in the plant extract were suggested to be responsible for the phytosynthesis of rGO-AuNPs. The excellent catalytic efficacy of rGO-AuNPs against MB degradation was confirmed, and a high antibacterial efficiency against Escherichia coli and Klebsiella pneumonia was also confirmed. Promising antioxidant performance of rGO-AuNPs was also proved. Furthermore, it was concluded that rGO-AuNPs acquired higher efficiency than AuNPs synthesized from the same plant extract in all of the studied applications.

Degradation of synthetic dyes using nanoparticles: a mini-review

The industrial revolution has marked a strong impact on financial upgradation of several countries, and increase in the industrial establishment globally has direct impact on environment because of the release of unwanted product in air and inside the water bodies. The use of dyes has increased tremendously in various industries ranging from food, leather, textile, paper, cosmetic, pharmaceuticals, etc. The problem has emerged due to disposing of the dyes in the open environment, and mostly it is disposed along with the industrial wastes into the water bodies, which becomes harmful for animals, aquatic life and human health. This review highlights the role of the nanoparticles particularly biosynthesized nanoparticles for eliminating the dyes from the industrial wastewater. There are several methods for the synthesis of nanoparticle including physical, chemical and green synthesis of nanoparticles commonly known as biological method. Among all, the biological method is considered as the rapid, easy, eco-friendly and is being performed at mild conditions. The uses of nanoparticles for removal of dyes from water minimize the hazardous impact and thus considered to be the best approach as far as water quality and safety of environment is concerned.

Biologically reduced graphene oxide as a green and easily available photocatalyst for degradation of organic dyes

The disposal of untreated textile industrial wastewater having unmanageable pollutants is a global issue. Eco-friendly remediation technology is needed for the removal of environmental contaminants. In this study, a simple hydrothermal method is adapted to synthesis reduced graphene oxide (PErGO) using Phyllanthus emblica fruits extract and used as a photocatalyst for the degradation of synthetic toxic dyes. The physicochemical properties of green synthesized PErGO are confirmed using UV-Vis spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction. The I_D/I_G ratio is found as 1.02 for GO which is improved to 1.15 for PErGO, which confirms the existence of unrepaired defects after the elimination of negatively charged O₂ moieties from the surface of GO. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) analysis show well-exploited PErGO morphology. The photocatalytic removal of methylene blue (MB) and methyl orange (MO) dyes is confirmed using UV-vis spectrophotometer. PErGO shows about 92% of MO and 91% of MB degradation within 90 min of sunlight exposure while carried out as a mixed dye degradation. The sustainability of this catalyst is confirmed by testing it for five subsequent degradation cycles and noticed a stable and significant degradation activity. Outcomes from this study suggest that eco-friendly PErGO can be used as an alternate sustainable material to treat a large volume of wastewater from various dye industries.

Facile synthesis of reduced graphene oxide using Acalypha indica and Raphanus sativus extracts and their in vitro cytotoxicity activity against human breast (MCF-7) and lung (A549) cancer cell lines

In the present study, an eco-friendly approach is adapted for the synthesis of reduced graphene oxide (rGO's) by a simple hydrothermal reaction using two plant extracts namely Acalypha indica and Raphanus sativus. After the hydrothermal reaction, GO turns into a black color from brown color, which indicates the successful reduction of graphene oxide. Further, various characterization techniques such as UV-Vis spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction is used to confirm the physicochemical properties of synthesized rGO's. Raman analysis confirms the reduction of GO by noticing an increase in the I_D/I_G ratio significantly. Field emission scanning electron microscopy and transmission electron microscopy clearly show the morphology and crystalline nature of rGO's. FT-IR spectrum confirms that the bioactive molecules of the plant extract (i.e. polyphenols, flavonoids, terpenoids, etc.) playing a key role in the elimination of oxygen groups from the GO surface. Further, the synthesized rGO's are tested for their potential against human lung and breast cancer cell lines. A significant cancer cell inhibition activity is obtained even in the less concentration of rGO's with IC₅₀ values for lung cancer cell lines are 38.46 µg/mL and 26.69 µg/mL for AIrGO and RSrGO, respectively. Similarly, IC₅₀ values for breast cancer cell lines are 35.97 µg/mL and 33.22 µg/mL for AIrGO and RSrGO, respectively.

Real-time monitored photocatalytic activity and electrochemical performance of an rGO/Pt nanocomposite synthesized via a green approach

Herein, we have reported the real-time photodegradation of methylene blue (MB), an organic pollutant, in the presence of sunlight at an ambient temperature using a platinum-decorated reduced graphene oxide (rGO/Pt) nanocomposite. The photocatalyst was prepared via a simple, one-pot and green approach with the simultaneous reduction of GO and Pt using aqueous honey as a reducing agent. Moreover, the honey not only simultaneously reduced Pt ions and GO but also played a key role in the growth and dispersion of Pt nanoparticles on the surface of rGO. Various rGO/Pt nanocomposites with different percentages of Pt nanoparticles loaded on rGO were obtained by tuning the concentration of the Pt source. The high percentage of Pt nanoparticles with an average size of 2.5 nm dispersed on rGO has shown excellent electrochemical performance. The photocatalytic activity of the rGO/Pt composite was enhanced by increasing the weight percent of the Pt particles on rGO, which led to the formation of a highly efficient photocatalyst. The optimized photocatalyst exhibited remarkable photocatalytic activity and degraded 98% MB in 180 minutes; thus, it can be used for industrial and environmental applications.

Mechanism and impact of synthesis conditions on the one-step green synthesis of hybrid RGO@Fe/Pd nanoparticles

While a one-step green synthesis of a hybrid material composed of reduced graphene oxide and bimetallic Fe/Pd nanoparticles (RGO@Fe/Pd NPs) was previously successfully reported and evaluated for the removal of organic contaminants, the relationship between the formation of RGO@Fe/Pd and the resulting reactivity was unclear. In this paper the impact of the specific synthetic conditions on the reactivity of RGO@Fe/Pd was investigated in order to enhance the removal efficiency of antibiotics such as rifampicin. The hybrid material (RGO@Fe/Pd) successfully removed 96.1% of rifampicin compared to only 63.5 and 81.0% for Fe nanoparticles and RGO, respectively. The best synthetic conditions for the formation of RGO@Fe/Pd included GO/Fe = 1:1 and Fe/Pd = 100: 5. In addition, GC-MS and FTIR were used to identify the main reducing biomolecules in the green tea extract responsible for the one-step synthesis of RGO@Fe/Pd as Catechol, Caffeine, 1,3,5-Benzenetriol. The morphology, size and surface composition of RGO@Fe/Pd was characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-Ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). These advanced characterization techniques suggested that during synthesis GO was initially converted to RGO, and thereafter Fe/Pd NPs (10-50 nm) were dispersed on RGO. Finally, a plausible formation mechanism for the one-step synthesis of the hybrid material was proposed.

Green Reduction of Graphene Oxide using Kaffir Lime Peel Extract (Citrus hystrix) and Its Application as Adsorbent for Methylene Blue

Green reduction of graphene oxide (GO) by phytochemicals was explored using the aqueous extract of kaffir lime peels. The research methods included preparation of extracts, preparation of GO, preparation and characterization of reduced-GO (RGO) using Fourier Transform Infrared (FTIR), X-ray diffraction (XRD), and UV-Vis spectroscopy, as well as methylene blue (MB) adsorption test using RGO. The RGO characterization showed that GO was successfully reduced by a C=C group restoration. The MB adsorption kinetics profile in RGO is more suitable for the pseudo-second-order model, whereas for the adsorption isotherm it is more suitable for the Langmuir model with a maximum adsorption capacity (q_max) of 276.06 mg/g at room temperature. The best ratio of GO: kaffir lime peel extract used to prepare RGO was at a ratio of 1: 2. Based on the ΔG, ΔH, and ΔS values, the adsorption of RGO-MB was defined as spontaneous and endothermic process. The results promise the potential application of RGO derived via green route to remove cationic dye in wastewater.

Biosynthetic graphene enhanced extracellular electron transfer for high performance anode in microbial fuel cell

Extracellular electron transfer from the biofilm surface to the electrode is the key step for the microbial fuel cell (MFC). More recently, graphene has attracted tremendous attentions for bioelectrochemical applications due to its good biocompatibility, high electrical conductivity and large surface area. In the current work, we report a facile and green synthesis of graphene-modified carbon paper (CP) as an efficient MFC anode through plant-mediated bioreduction coupled with self-assembly. Three-dimensional CFP uniformly wrapped by curled and wrinkled biosynthesized graphene enables more surface area for microbe adhesion and mass diffusion. Significantly, nontoxic and biodegradable biomolecules extracted from Eucalyptus leaves act as reducing agent and adsorb on the graphene, rendering the graphene surface become hydrophilic and biocompatible. Furthermore, the obtained graphene exhibit excellent bioelectrochemical interactions with the microbes. Equipped with the biosynthesized graphene-modified anode, the E. coli-catalyzed MFC delivered an enhanced maximum power density of 1158 mW/m², 70% higher than a pristine graphene-modified one. This development provides not only a versatile and scalable synthesis strategy for biocompatible graphene-modified devices, but also indicates that biomolecules facilitate the extracellular electron transfer in bioelectrochemical process.

Green synthesis of reduced graphene oxide using bagasse and its application in dye removal: A waste-to-resource supply chain

Graphene is usually synthesized through deoxygenation of graphene oxide (GO) by hydrazine which functions as a reducing agent, but the production of graphene via this method suffers a high cost and is often regarded to be not environmental-friendly. In this work, we developed a simple and efficient method for the green reduction of GO to reduced graphene oxide (rGO) dispersed on sugarcane bagasse derived from rGO/bagasse material. The rGO/bagasse was characterized by Scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, Thermogravimetric analysis, X-ray photoelectron spectroscopy and X-ray diffraction analysis. All these characterization techniques clearly revealed that the rGO has been successfully prepared by reduction sugars. In addition, rGO synthesized from bagasse was considered as a promising adsorbent for removing methyl blue. Adsorption kinetics were also applied to stimulate the adsorption process, and the adsorption behavior of this new adsorbent fits well with the pseudo-second-order kinetic model (R² = 0.98). Finally, the cycling experiments for MB adsorption by bagasse synthesized rGO confirmed that the as-prepared rGO was reusable. Taken together, all results in this work provided the new insights into the green reduction of GO by bagasse, and the formation of rGO/bagasse material presented a great potential in the disposal of dye waste water.

Disinfection byproduct formation and toxicity of graphene oxide in water treatment system

Graphene oxide (GO) is a structural analog of graphene and contains numerous O-containing functional groups. As rapidly increasing production and usage of GO, it is inevitable to flow into the water and wastewater treatment system and finally oxidized by disinfectants to form DBPs. Meanwhile, as GO is a nano sized carbon material, it may also break the human digestion system when it was absorbed by human body. This study explored the DBP formation when only GO was present. Effects of Br^- were also considered during the DBP formation. Both trihalomethanes (THMs) and haloacetic acids (HAAs) were formed during the chlorination and chloramination procedure, but the total concentration of THMs was at least three times higher than that of HAAs. Irradiation can significantly enhance the DBP formation via the formation of radicals. The wrinkled appearance and decomposition of aromatic ring may both be effective on the DBP formation via chlorination or bromination. The findings of this study advance knowledge on the DBP formation of GO in water treatment systems and provide insight on the toxic effects of the transformation products of GO.

Fabrication and Highly Efficient Dye Removal Characterization of Beta-Cyclodextrin-Based Composite Polymer Fibers by Electrospinning

Dye wastewater is one of the most important problems to be faced and solved in wastewater treatment. However, the treatment cannot be single and simple adsorption due to the complexity of dye species. In this work, we prepared novel composite fiber adsorbent materials consisting of ε-polycaprolactone (PCL) and beta-cyclodextrin-based polymer (PCD) by electrospinning. The morphological and spectral characterization demonstrated the successful preparation of a series of composite fibers with different mass ratios. The obtained fiber materials have demonstrated remarkable selective adsorption for MB and 4-aminoazobenzene solutions. The addition of a PCD component in composite fibers enhanced the mechanical strength of membranes and changed the adsorption uptake due to the cavity molecular structure via host⁻guest interaction. The dye removal efficiency could reach 24.1 mg/g towards 4-aminoazobenzene. Due to the admirable stability and selectivity adsorption process, the present prepared beta-cyclodextrin-based composite fibers have demonstrated potential large-scale applications in dye uptake and wastewater treatment.