Graphene-based materials: fabrication, characterization and application for the decontamination of wastewater and wastegas and hydrogen storage/generation

Graphene Oxide Enhanced Monoethanolamine and Ethylenediamine Nanofluids for Efficient Carbon Dioxide Uptake from Flue Gas

The addition of nanoparticles in amine solutions to produce a stable amine-based nanofluid provides a high surface area for absorption and improves the absorption rate. In this work, nanofluids were prepared by dispersing graphene oxide (GO) in monoethanolamine (MEA) and ethylenediamine (EDA) solutions for adsorption of carbon dioxide (CO2) to further improve their absorption performance by providing more reaction sites on the GO framework. GO was synthesized using the modified Hummers method and characterized for physicochemical properties using SEM, EDS, FTIR, Raman analysis, and TGA. The FTIR spectra for the GO nanoparticles before absorption showed peaks attributed to C-C, H-C, and C-O bonding. After the absorption experiments, the FTIR spectra of GO showed peaks due to C-O-NH2, N-O-N, and N-H bonding. The BET analysis further confirmed the decrease in the surface area, pore volume, and pore diameter of the GO recovered from the nanofluids after the CO2 experiment, indicating an interaction between GO and amine molecules. The absorption process of CO2 by the nanofluid was performed in a custom-made pressure chamber whereby the CO2 gas was in direct contact with the absorption fluids. The obtained adsorption rate constant (k) for the reaction between CO2 and 30% MEA and EDA solutions was 0.113 and 0.131, respectively. Upon addition of 0.2 mg/mL GO in the base solution, k increased to 0.16854 and 0.17603 for the MEA and EDA nanofluids, respectively. The proposed mechanism involves GO nanoparticles interacting with the amine groups through the oxygen-rich groups of GO. This results in the formation of a zwitterion that readily reacts with CO2, resulting in a carbamate.

Cotransport of aged biochar colloids and thallium(I) in water-saturated porous media: Impact of the ionic strength, pH and aging degree

Biochar colloids entering the soil undergo aging over time and exhibit strong capabilities in adsorbing and transporting pollutants. Therefore, investigating the cotransport of aged biochar colloids and thallium (Tl(I)) in quartz sand media is crucial for understanding Tl(I) migration in underground environments. This study investigated the migration of biochar colloids with two different aging degrees and Tl(I) in quartz sand media at various pH and ionic strengths (ISs). The results revealed that under all ISs and pH, 30%AWB (biochar aged with 30 % (w/w) HNO3) inhibited Tl(I) migration in media. This inhibition primarily arose from the introduction of hydroxyl and carboxyl groups during aging, which significantly enhanced colloid adsorption onto Tl(I). At lower ISs, 30%AWB colloids exhibited greater inhibition of Tl(I) migration due to their increased adsorption capacity. Additionally, aging promoted the migration of biochar colloids in the media. Greater biochar aging notably enhanced this promotion, potentially owing to reduced colloidal particle size and the formation of biochar derivatives. Moreover, 50%AWB (biochar aged with 50 % (w/w) HNO3) inhibited Tl(I) migration under low ISs but had almost no impact under high ISs. Nonetheless, at high pH, 50%AWB colloids facilitated Tl(I) migration. This phenomenon might be attributed to the inhibitory effect of aged biochar colloids on Tl(I) adsorption onto media at a high pH, as well as the stable binding between Tl(I) and aged biochar colloids. This study discusses the cotransport of biochar with various degrees of aging and Tl(I) in media, providing insights into remediating soils contaminated with Tl.

Graphene-based nanomaterials as potential candidates for environmental mitigation of pesticides

Over the years, bioaccumulation of hazardous chemicals in the food chain has become a critical issue, resulting in numerous health risks. Environmental mitigation aims to clean up contaminated sites and eliminate hazardous materials from the air, water, or soil to restore the site to its original and safe condition. Pesticides constitute one of the most dangerous environmental pollutants which are generally used to increase crop production. Addressing the removal or treatment of pesticides has become pivotal in mitigating environmental threats. Diverse remediation methods are employed to protect the environment and public health. Graphene-based materials have emerged as promising candidates with exceptional properties, including excellent adsorption capacity due to their high surface area, strong hydrophilicity, and tunable properties. Owing to these properties, they have been attracting major research attention in the field of design and fabrication of materials for the mitigation of pesticides from the environment such as from contaminated food, water and other samples. Various physical, chemical and biological extraction techniques are adopted to remove pesticides. This review article provides an insight into the potential role of graphene-based materials in the environmental remediation of pesticides. We have focused on the removal of Organophosphates, Organochlorines, Carbamates and Pyrethroids present in water, fruit, vegetable and other samples, highlighting the urgent need for environmental remediation. While graphene-based materials hold potential for pesticide remediation, addressing challenges in scalable production, assessing long-term sustainability, and mitigating potential environmental impacts are critical steps for successful large-scale applications.

Improvement of heavy metal separation performance by positively charged small-sized graphene oxide membrane

Multilayered graphene oxide (GO) membranes are promising to be widely applied to purify water effectively. However, the performance of most membranes prepared at present is not ideal, which may be related to the pore diameter of the substrate (determining the real loading amount of GO) and the size of the GO nanosheets (determining the number of channels on the unit area), which has not been fully studied. In this study, a rotating dip-coating reactor were firstly developed to ensure the uniform deposition of reactants on the surface of the substrate. Then, the preparation method for the membrane was improved. Microfiltration membranes were used as the supporting substrate, polydopamine was deposited as the adhesive layer, ethylenediamine was used to restrict the layer spacing to strengthen the size exclusion effect, and positively charged polyethyleneimine (PEI) was used to strengthen the Donnan effect. Finally, the effects of the pore size of the substrate and the size of the GO nanosheets on the membrane performance were investigated. Compared with the substrates with a pore size of 0.22 μm in most literatures, substrates of 0.1 μm can retain more small GO (SGO) nanosheets, thereby improving the performance. The performance of the SGO membrane was much better than that of the large-sized GO membrane. With a water permeability of no less than 7.9 L/(m2·h·bar), rejection rates for Pb2+ and Cd2+ of the SGO membrane could reach more than 97%. These findings are constructive to separate heavy metals from water effectively.

Removal of Formaldehyde and Its Analogues Using a Hybrid Assembly of Pyrene-Modified Hydrazide and rGO: A Negative Carbon Emission and Green Chemical Decomposition Method

Indoor gaseous formaldehyde is the main environmental pollutant that can cause fatal threats to human health. A number of physical and chemical methods have been developed to tackle this issue. However, the existing methods are still unsatisfactory to meet the requirement of sustainable development owing to the flaws of low efficiency and reversible or second pollution. Herein, a chemical method based on a nucleophilic reaction between hydrazine and aldehyde that generates the only by-product of H₂O is designed for the removal of formaldehyde. 1-Pyrenebutyric hydrazide was synthesized by a simple esterification reaction and then self-assembled on reduced graphene oxide (rGO) with a large surface area by forming π-π stacking to obtain a composite for chemical removal of gaseous formaldehyde under ambient conditions. In a practical test, the formaldehyde removal rate could reach 91% of the theoretical value, which meets the requirement for commercial formaldehyde removal applications. After 10 times recycling, the formaldehyde removal rate still remains as high as 85%. Moreover, the composite could be regenerated in weak acidic media, which greatly reduce the manufacturing cost in practical applications.

A review of novel green adsorbents as a sustainable alternative for the remediation of chromium (VI) from water environments

The presence of heavy metal, chromium (VI), in water environments leads to various diseases in humans, such as cancer, lung tumors, and allergies. This review comparatively examines the use of several adsorbents, such as biosorbents, activated carbon, nanocomposites, and polyaniline (PANI), in terms of the operational parameters (initial chromium (VI) concentration (C_o), temperature (T), pH, contact time (t), and adsorbent dosage) to achieve the Langmuir's maximum adsorption capacity (q_m) for chromium (VI) adsorption. The study finds that the use of biosorbents (fruit bio-composite, fungus, leave, and oak bark char), activated carbons (HCl-treated dry fruit waste, polyethyleneimine (PEI) and potassium hydroxide (KOH) PEI-KOH alkali-treated rice waste-derived biochar, and KOH/hydrochloric acid (HCl) acid/base-treated commercial), iron-based nanocomposites, magnetic manganese-multiwalled carbon nanotubes nanocomposites, copper-based nanocomposites, graphene oxide functionalized amino acid, and PANI functionalized transition metal are effective in achieving high Langmuir's maximum adsorption capacity (q_m) for chromium (VI) adsorption, and that operational parameters such as initial concentration, temperature, pH, contact time, and adsorbent dosage significantly affect the Langmuir's maximum adsorption capacity (q_m). Magnetic graphene oxide functionalized amino acid showed the highest experimental and pseudo-second-order kinetic model equilibrium adsorption capacities. The iron oxide functionalized calcium carbonate (IO@CaCO₃) nanocomposites showed the highest heterogeneous adsorption capacity. Additionally, Syzygium cumini bark biosorbent is highly effective in treating tannery industrial wastewater with high levels of chromium (VI).

Multifunctional Lanthanide-Doped Binary Fluorides and Graphene Oxide Nanocomposites Via a Task-Specific Ionic Liquid

Graphene oxide-based nanocomposites (NCMs) exhibit diverse photonic and biophotonic applications. Innovative nanoengineering using a task-specific ionic liquid (IL), namely, 1-butyl-3-methyl tetrafluoroborate [C₄mim][BF₄], allows one to access a unique class of luminescent nanocomposites formed between lanthanide-doped binary fluorides and graphene oxide (GO). Here the IL is used as a solvent, templating agent, and as a reaction partner for the nanocomposite synthesis, that is, "all three in one". Our study shows that GO controls the size of the NCMs; however, it can tune the luminescence properties too. For example, the excitation spectrum of Ce³⁺ is higher-energy shifted when GO is attached. In addition, magnetic properties of GdF₃:Tb³⁺ nanoparticles (NPs) and GdF₃:Tb³⁺-GO NCMs are also studied at room temperature (300 K) and very low temperature (2 K). High magnetization results for the NPs (e.g., 6.676 emu g^-1 at 300 K and 184.449 emu g^-1 at 2 K in the applied magnetic field from +50 to -50 kOe) and NCMs promises their uses in many photonic and biphotonic applications including magnetic resonance imaging, etc.

Utilization of a double-cross-linked amino-functionalized three-dimensional graphene networks as a monolithic adsorbent for methyl orange removal: Equilibrium, kinetics, thermodynamics and artificial neural network modeling

Herein, it is aimed to develop a high-performance monolithic adsorbent to be utilized in methyl orange (MO) adsorption. Therefore, amino-functionalized three-dimensional graphene networks (3D-GN_f) fulfilling the requirements of reusability and high capacity have been fabricated via hydrothermal self-assembly approach followed by a double-crosslinking strategy. The potential utilization of 3D-GN_f as an adsorbent for removal MO has been assessed using both batch-adsorption studies and an artificial neural network (ANN) approach. Graphene oxide sheets have been amino-functionalized and cross-linked, by ethylenediamine (EDA) during hydrothermal treatment, following the glutaraldehyde has used as a double-crosslinking agent to facilitate the crosslinking of architecture. The successful fabrication of 3D-GN_f has been confirmed by field-emission scanning electron microscopy (FESEM), Fourier transform infrared (FT-IR), Raman and X-ray photoelectron spectroscopy (XPS). Moreover, N₂ adsorption/desorption isotherms have revealed the high specific surface area (1015 m² g^-1) with high pore volume (1.054 cm³ g^-1) and hierarchical porous structure of 3D-GN_f. The effect of initial concentration, contact time, and temperature on adsorption capacity have been thoroughly studied, and the kinetics, isotherms, and thermodynamics of MO adsorption have been modelled. The MO adsorption has been well defined by the pseudo-second-order kinetic model and Langmuir isotherm model with a monolayer adsorption capacity of 270.27 mg g^-1 at 25 °C. The thermodynamic findings have revealed MO adsorption has occurred spontaneously with an endothermic process. The Levenberg-Marquardt backpropagation algorithm has been implemented to train the ANN model, which has used the activation functions of tansig and purelin functions at the hidden and output layers, respectively. An optimum ANN model with high-performance metrics (coefficient of determination, R² = 0.9995; mean squared error, MSE = 0.0008) composed of three hidden layers with 5 neurons in each layer was constructed to forecast MO adsorption. The findings have shown that experimental results are consistent with ANN-based data, implying that the suggested ANN model may be used to forecast cationic dye adsorption.

Proteomic, biochemical, and anatomical influences of nanographene oxide on soybean (Glycine max)

Nano-graphene oxide (NGO) is an engineered nanostructure that is used in various fields including biology, chemistry, medicine, and environmental protection. This kind of highly used nanomaterial (NM) is being released and accumulated gradually in nature and can have some adverse influences on living organisms including plants. Soybean as a cultivated plant with a high importance in food industry, but sensitive to stresses, was chosen in the present study to be examined in terms of proteomic, biochemical, and anatomical properties under the NGO stress. Accordingly, a 2-dimensional gel electrophoresis (2-DE) approach was adopted for proteomic analysis of the NGO treated soybean roots, where significant changes were observed in the abundance of 48 proteins. MALDI TOF/TOF analysis revealed the upregulation of the proteins involved in the redox regulation in plants. Furthermore, anatomical examination of soybean roots under light microscopy showed that the NGO could enter into the root epidermis through the apoplastic pathway and accumulated in some parts of the root. With increasing NGO concentration, the diameter of the vascular apertures increased and then decreased at higher concentrations. To evaluate the toxicity of NGO, some of the growth parameters including fresh and dry weight, and height of the shoots, as well as some stress-related biochemical properties such as H2O2 production, antioxidant enzymes activity, and phenolics and flavonoids contents were measured. The results indicated that NGO could cause an oxidative stress, which can be considered a toxic effect evoking antioxidative and detoxification mechanisms in soybean.

Simple and low-cost production of magnetite/graphene nanocomposites for heavy metal ions adsorption

It is challenging to produce economical magnetic graphene-based adsorbents on an industrial scale for heavy metal ions removal. Here, magnetite/graphene nanocomposite embedded in activated carbon matrix (magnetite/G-AC) was synthesized via in situ catalytic graphitization of iron-impregnated biochar to obtain graphene encapsulated iron nanoparticles (GEINs) embedded in biochar (BC) matrix, and followed by steam activation of GEINs-BC. Steam activation aimed to upgrade biochar to activated carbon with oxygen functional groups, crack encapsulated graphene shell to graphene nanosheets, and obtain magnetic Fe₃O₄ by oxidation of iron, thereby improving the adsorption capacity of magnetite/G-AC-800 (153.2 mg/g) four times higher than that of GEINs-BC. The parameters on the adsorption capacity were investigated using Pb(II) ions as a typical pollutant as a function of solution pH (3-7), contact time (5-300 min), initial Pb(II) concentration (50-400 mg/L), and adsorbent dosage (0.05-0.25 g). The fitted pseudo-second-order kinetic model and Langmuir model indicated that the main adsorption mechanism was chemical adsorption over monolayer. This research developed a low-cost magnetic adsorbent with the advantage of simple large-scale production and excellent adsorption capacity per unit cost for remediating wastewater.

A critical review on the role of abiotic factors on the transformation, environmental identity and toxicity of engineered nanomaterials in aquatic environment

Engineered nanomaterials (ENMs) are at the forefront of many technological breakthroughs in science and engineering. The extensive use of ENMs in several consumer products has resulted in their release to the aquatic environment. ENMs entering the aquatic ecosystem undergo a dynamic transformation as they interact with organic and inorganic constituents present in aquatic environment, specifically abiotic factors such as NOM and clay minerals, and attain an environmental identity. Thus, a greater understanding of ENM-abiotic factors interactions is required for an improved risk assessment and sustainable management of ENMs contamination in the aquatic environment. This review integrates fundamental aspects of ENMs transformation in aquatic environment as impacted by abiotic factors, and delineates the recent advances in bioavailability and ecotoxicity of ENMs in relation to risk assessment for ENMs-contaminated aquatic ecosystem. It specifically discusses the mechanism of transformation of different ENMs (metals, metal oxides and carbon based nanomaterials) following their interaction with the two most common abiotic factors NOM and clay minerals present within the aquatic ecosystem. The review critically discusses the impact of these mechanisms on the altered ecotoxicity of ENMs including the impact of such transformation at the genomic level. Finally, it identifies the gaps in our current understanding of the role of abiotic factors on the transformation of ENMs and paves the way for the future research areas.

Visible-Light-Driven Reduced Graphite Oxide as a Metal-Free Catalyst for Degradation of Colored Wastewater

Reduced graphite oxide (rGO)-based materials have demonstrated promising potential for advanced oxidation processes. Along with its distinctive 2D characteristics, rGO offers the prospect of catalytic degradation of various kinds of organic pollutants from aqueous environments. The practical application of rGO as a metal-free catalyst material to promote the Fenton reaction depends on the degree of rGO reduction. In this regard, the rGO was prepared according to oxidation by modified Hummers' method and two-step reduction via hydrothermal and calcination in the N2 atmosphere. The as-prepared rGO was characterized in terms of X-ray diffraction, Fourier-transform infrared spectroscopy, thermal gravimetric analysis, scanning electron microscopy, UV-vis absorption spectroscopy, and transmission electron microscopy. The effectiveness of as-prepared rGO as a photocatalyst and the metal-free catalyst to decolorize different textile dyes, including basic red 46, basic red 18, and methylene blue, was investigated in visible/rGO and visible/rGO/H2O2 systems. The impact of operational factors such as catalyst dose, pH, and initial dye concentration was examined. The dye degradation process was investigated by the pseudo-first-order kinetic model. In addition, the recyclability of rGO in the visible/rGO/H2O2 system was examined.

Graphene-based materials for metronidazole degradation: A comprehensive review

Due to its cytotoxic effect, metronidazole (MNZ) is a drug commonly used to treat bacterial, protozoal, and microaerophilic bacterial infections. After consumption, it undergoes a series of metamorphic reactions that lead to the degradation of oxidized, acetylated, and hydrolyzed metabolites in the environment. To eliminate such pollutants, due to their high potential, adsorption and photocatalysis extensive processes are used in which graphene can be used to improve efficiency. This review analyses the use of graphene as an absorbent and catalyst with a focus on absorption and photocatalytic degradation of MNZ by graphene-based materials (GBMs). The parameters affecting the adsorption, and photocatalytic degradation of MNZ are investigated and discussed. Besides, the basic mechanisms occurring in these processes are summarized and analyzed. This work provides a theoretical framework that can direct future research in the field of MNZ removal from aqueous solutions.

Preparation of novel and highly active magnetic ternary structures (metal-organic framework/cobalt ferrite/graphene oxide) for effective visible-light-driven photocatalytic and photo-Fenton-like degradation of organic contaminants

Herein, MIL-101(Fe), CoFe₂O₄, novel binary (MIL-101(Fe)/CoFe₂O₄, MIL-101(Fe)/GO and CoFe₂O₄/GO), and ternary (MIL-101(Fe)/CoFe₂O₄/(3%)GO and MIL-101(Fe)/CoFe₂O₄/(7%)GO) magnetic composites based upon the MIL-101(Fe) were synthesized. The XRD, FESEM, TEM, EDX, BET-BJH, FTIR, VSM, DRS, PL, EIS and other electrochemical analyses were applied to characterize samples. The MIL/CoFe₂O₄/(3%)GO demonstrated the best performance compared to other samples for visible light photocatalytic and photo-Fenton-like degradation of Direct Red 23 (DtR-23), Reactive Red 198 (ReR-198) dyes as well as Tetracycline Hydrochloride (TC-H) antibiotic. Degradation of dyes using the ternary composite after 70 min of visible light irradiation was greater than that of 99%. The presence of the optimum GO as a strong electron acceptor in MIL/CoFe₂O₄/(3%)GO not only led to the effective separation of charge carriers and thus reduction of their recombination but also increased the absorption of visible light. The composite possessed good durability in terms of stability and reusability. The PL, EIS and electrochemical analyses indicated that the MIL/CoFe₂O₄/(3%)GO improved the optical properties and photocatalytic performance.

Improved hemocompatibility for gelatin-graphene oxide composite aerogels reinforced with proanthocyanidins for wound dressing applications

Aerogels based on gelatin and graphene oxide (GO) were synthesized by microwave-assisted reactions, incorporating grape skin extracts -high in proanthocyanidins (PAs)- to develop a hemostatic device with improved properties. The effects of incorporating PAs into the aerogels were investigated in relation to their physicochemical properties, absorption ability, clotting activity and cytotoxicity in human dermal fibroblast (HDF) cells. The aerogels presented highly resistant porous structures, capable of absorbing more than 50 times their weight when in contact with a phosphate saline solution (PBS) and fresh human blood. Interestingly, the addition of PAs increased the negative surface charges and the blood absorption ability of the aerogels, which may make them suitable for hemostasis. The incorporation of 5% and 10% (w/w) of extracts into the aerogels increased the total coagulated blood content by 36.6% and 24.5% compared with gelatin-GO aerogel, respectively. These improvements in the hemostatic properties of the aerogels were greater with the inclusion of 5% (w/w) of grape skin extracts into the aerogels. The aerogels were also able to adhere red blood cells onto their surfaces, which could favor the formation of stable fibrin networks to promote hemostasis. Their clotting activity suggested the activation of alternative routes based on complement coagulation systems. Finally, the aerogels were non-toxic for HDF cells and the PAs were successfully released from their matrices. Thus, gelatin-GO aerogels reinforced with PAs are promising as topical phytodrug delivery systems, with great potential for wound healing processes.

State-of-the-art developments in carbon-based metal nanocomposites as a catalyst: photocatalysis

The rapid progress of state-of-the-art carbon-based metals as a catalyst is playing a central role in the research area of chemical and materials engineering for effective visible-light-induced catalytic applications. Numerous admirable catalysts have been fabricated, but significant challenges persist to lower the cost and increase the action of catalysts. The development of carbon-based nanostructured materials (i.e., activated carbon, carbon nitride, graphite, fullerenes, carbon nanotubes, diamond, graphene, etc.) represents an admirable substitute to out-of-date catalysts. Significant efforts have been made by researchers toward the improvement of various carbon-based metal nanostructures as catalysts. Moreover, incredible development has been achieved in several fields of catalysis, such as visible-light-induced catalysis, electrochemical performance, energy storage, and conversion, etc. This review gives an overview of the up-to-date developments in the strategy of design and fabrication of carbon-based metal nanostructures as photo-catalysts by means of several methods within the green approach, including chemical synthesis, in situ growth, solution mixing, and hydrothermal approaches. Moreover, the photocatalytic effects of the resulting carbon-based nanostructure classifications are similarly deliberated relative to their eco-friendly applications, such as photocatalytic degradation of organic dye pollutants.

Carboxylated Graphene for Radical-Assisted Ultra-Trace-Level Water Treatment and Noble Metal Recovery

Sorption technologies, enabling removal of heavy metals, play a pivotal role in meeting the global demands for unrestricted access to drinking water. Standard sorption technologies suffer from limited efficiency related to the weak sorbent-metal interaction. Further challenges include the development of technologies enabling smart metal recovery and sorbent regeneration. To this end, a densely functionalized graphene, with 33% by mass content of carboxyl groups, linked through direct C-C bonds (graphene acid, GA) represents a previously unexplored solution to this challenge. GA revealed excellent efficiency for removal of highly toxic metals, such as Cd²⁺ and Pb²⁺. Due to its selective chemistry, GA can bind heavy metals with high affinity, even at concentrations of 1 mg L^-1 and in the presence of competing ions of natural drinking water, and reduce them down to drinking water allowance levels of a few μg L^-1. This is not only due to carboxyl groups but also due to the stable radical centers of the GA structure, enabling metal ion-radical interactions, as proved by EPR, XPS, and density functional theory calculations. GA offers full structural integrity during the highly acidic and basic treatment, which is exploited for noble metal recovery (Ga³⁺, In³⁺, Pd²⁺) and sorbent regeneration. Owing to these attributes, GA represents a fully reusable metal sorbent, applicable also in electrochemical energy technologies, as illustrated with a GA/Pt catalyst derived from Pt⁴⁺-contaminated water.

Potential of the magnetic hollow sphere nanocomposite (graphene oxide-gadolinium oxide) for arsenic removal from real field water and antimicrobial applications

Potential of the magnetic hollow-sphere nanocomposite, graphene oxide-gadolinium oxide (GO-Gd₂O₃) for arsenic (As) removal from real field water with developing a continuous operating system and antimicrobial activity were investigated. The characterization results suggest that the prepared GO-Gd₂O₃ is a hallow sphere wool-like nanocomposite having 50.91 m² g^-1 surface area. The sorption studies revealed that a high adsorption capacity (216.70 mg g^-1) can be achieved using GO-Gd₂O₃ (0.1 g L^-1) at a pH of 6.0, and temperature of 293 K. The main and novel observations from the loading of Gd₂O₃ are that the GO adsorption efficiency, adsorbent separation rate from aqueous solutions, and the stability of the composite have been altered. Thus, the developed material can overcome the separation and stability issues associated with the bare GO, and exhibits an enhanced adsorption capacity toward arsenic was higher or comparable with existing magnetic material. In addition, the developed adsorption method was well applied for real field water samples collected from the mining area of South Korea where the GO-Gd₂O₃ can reduce the quantity of arsenic under the maximum accepted concentration of arsenic considered fit for drinking water stipulated by environmental protection agencies. Furthermore, the GO-Gd₂O₃ nanocomposite shows a high bacterial photocatalytic inactivation and was comparable with other reports.

In situ growth of TiO2 nanoparticles on nitrogen-doped Ti3C2 with isopropyl amine toward enhanced photocatalytic activity

Construction of heterojunction and nitrogen doping is an effective approach for synthesizing photocatalysts with high quantum yield and efficient electron-hole separation. 2D MXene Ti₃C₂ has been considered a good carbonaceous nanomaterial for designing heterojunction, while the original surface groups and stacked structure limit the electron-hole separation. Herein, a hybrid of nitrogen-doped Ti₃C₂ nanosheets and TiO₂ nanoparticles (NPs) composed of TiO₂ NPs in situ growing on isopropyl amine (iPA) modified Ti₃C₂ (iN-Ti₃C₂) was developed for the first time. The novel iN-Ti₃C₂/TiO₂ hybrid exhibited an excellent ultraviolet-light photodegradation of methylene blue (MB), with a degradation rate (0.02642 min^-1) significantly higher than that of pure TiO₂ NPs, bulk-Ti₃C₂/TiO₂, dimethyl sulfoxide modified Ti₃C₂/TiO₂ hybrid, and hydrazine monohydrate modified Ti₃C₂/TiO₂ hybrid. The formation of heterojunction between iN-Ti₃C₂ and TiO₂ and its role in the photocatalysis were systematically analyzed using various characterization techniques and density functional theory calculation. The iPA modification exfoliated Ti₃C₂ and doped N on Ti₃C₂ nanosheets; the in situ grown TiO₂ NPs formed efficient heterojunctions with the nanosheets; the N-doping facilitated electron migration in Ti₃C₂ and inhibited the recombination of photogenerated electron-hole pairs; •OH dominated the photodegradation of MB. This work provides a new approach of constructing efficient photocatalysts for the treatment of organics-polluted water.

A novel Z-scheme porous g-C3N4 nanosheet/Ag3PO4 photocatalyst decorated with N-doped CDs for high efficiency removal of antibiotics

A number of porous g-C3N4 nanosheet/Ag3PO4/NCDs (PCNNS/AP/NCDs) with little amounts of Ag3PO4 were synthesized via an in situ sedimentation-calcination method. The PCNNS/AP/NCDs photocatalyst exhibited excellent photocatalytic performance for the photocatalytic degradation of tetracycline (TC) under visible light irradiation at a removal rate of 90.5% in 40 min. The study of the reaction kinetics of the as-prepared samples was in accordance with the pseudo-second-order kinetics, with the correlation coefficient (R2) being greater than 0.9776. Meanwhile, the photocatalyst was capable of degrading ciprofloxacin (CIP), and showed good performance even under actual water conditions with natural sunlight irradiation, indicating that the photocatalyst has wide practical applications. In addition, the photocatalytic performance and the XRD and FTIR spectra showed no obvious changes even after four photocatalytic degradation cycles, which revealed the high stability of the PCNNS/AP/NCDs photocatalyst. Furthermore, the possible degradation pathways of TC and the possible Z-scheme mechanism were proposed with ˙O2- and h+ as the main active species contributing to photocatalytic degradation. The results provide a novel insight into the fabrication of Z-scheme PCNNS/AP/NCDs and introduce them as an efficient visible-light-responsive photocatalyst for use in practical applications.

Electrochemical energy storage electrodes from fruit biochar

This review investigates the electrochemical energy storage electrode (EESE) as the most important part of the electrochemical energy storage devices (EES) prepared from fruit-derived carbon. The EES devices include batteries, supercapacitors, and hybrid devices that have various regular and advanced applications. The preparation of EESE from fruit wastes not only reduce the price of the electrode but also lead to enhance the electrochemical properties of the electrode. The astonishing results of fruits biochar at electrochemical analyses guarantee the performance of these electrodes as EESE. Also, using fruit waste as the precursor of the EESE due to protect the environment and reduce environmental pollutions.

Effects of heteroaggregation with metal oxides and clays on tetracycline adsorption by graphene oxide

Multiple nanoparticles (NPs) often coexist in water with contaminants, which inevitably affect the fate and transport of coexisted contaminants and other types of nanoparticles in actual water. This research was devoted to examine the adsorption of tetracycline (TC) on graphene oxide (GO) in the presence of different amounts of model engineered and natural NPs (m-NPs), including metal oxides (ZnO and Fe₂O₃), clays (kaolin and montmorillonite). The experimental results proved that the existence of m-NPs greatly enhanced the TC adsorption onto GO except for that at Fe₂O₃/GO = 10:1 and lengthened the adsorption equilibrium time. The enhanced adsorption amount of TC with increasing m-NPs/GO ratio was primarily due to the adsorption of TC onto m-NPs. In contrast, the slightly inhibitory effects by 10:1 Fe₂O₃/GO could be attributed to the blockage effect on GO surface by a small amount of Fe₂O₃. Compared with five m-NPs/adsorbents, m-NPs/GO had the greatest promoting efficiency on TC removal. Moreover, the heteroaggregation of GO with different m-NPs was studied in aqueous phase by microscopic, spectroscopic, and computational methods. Analysis showed that the electrostatic attraction between negatively charged GO and positively charged ZnO were likely to first heteroaggregate in binary systems of GO and ZnO, while GO were prone to homoaggregate owing to electrostatic repulsion with the same negatively charged montmorillonite (or kaolin). Besides, Fe₂O₃ tended to first homoaggregate and then heteroaggregate with GO. In summary, this report elucidated complex interactions between GO and m-NPs, which was crucial to fundamentally understand towards a predictive framework for describing the fate and migration of GO and m-NPs in actual water.

Chemically Modified Biosorbents and Their Role in the Removal of Emerging Pharmaceutical Waste in the Water System

Presence of pharmaceutically active compounds (PACs) as emerging contaminants in water is a major concern. Recent reports have confirmed the presence of PACs in natural and wastewater systems, which have caused several problems indicating the urgent need for their removal. The current review evaluates the role of chemically modified biosorbents in the removal of PACs in water. Reported biosorbents include plant and animal solid waste, microorganisms and bio-composite. Bio-composites exhibited better prospects when compared with other biosorbents. Types of chemical treatment reported include acid, alkaline, solvent extraction, metal salt impregnation and surface grafting, with alkaline treatment exhibiting better results when compared with other treatments. The biosorption processes mostly obeyed the pseudo-second-order model and the Langmuir isotherm model in a process described mainly by ionic interaction. Desorption and regeneration capacity are very important in selecting an appropriate biosorbent for the biosorption process. Depending on the type of biosorbent, the cost of water treatment per million liters of water was estimated as US $10–US $200, which presents biosorption as a cheap process compared to other known water treatment processes. However, there is a need to conduct large-scale studies on the biosorption process for removing PACs in water.

Overview of biochar production from preservative-treated wood with detailed analysis of biochar characteristics, heavy metals behaviors, and their ecotoxicity

Concerns over the disposal of preservative-treated wood waste and its related environmental problems are the main driving forces of research into the recycling of preservative-treated wood. Preservative-treated wood waste composed of cellulose, hemicellulose, and lignin with several types of heavy metals can be recycled in various ways, such as wood-based composites, heavy metal extraction, energy recovery, etc. In particular, thermochemical conversion has attracted considerable attention recently because energy can be recovered from biomass as liquid fuel and bio-oil, as well as produce bio-char with a high carbon content, which can be applied to valuable products, such as soil amendment, adsorbents, solid fuels, and catalyst supports. On the other hand, environmental issues, such as heavy metal volatilization and heavy metal leaching, are still a challenge. This review reports the state-of-the-art knowledge of biochar production from preservative-treated wood with the main focus on the feedstock, process technology, biochar characteristics, application, and environmental issues. This review provides important information for future studies into the recycling of preservative-treated woods into biochar.

Si2BN monolayers as promising candidates for hydrogen storage

Hydrogen storage properties of the pure Si2BN monolayer were studied using density functional theory calculations. The interaction of H2 molecules with the Si2BN monolayer is weak and of electrostatic nature. The average hydrogen adsorption energies are within the ideal range of practical applications (0.187-0.214 eV), and the consecutive adsorption energies indicate that the spontaneous adsorption of H2 molecules on the Si2BN monolayer can occur. The hydrogen gravimetric density of the periodic Si2BN monolayer reaches 8.5 wt%, which exceeds the standard of 6.0 wt% set by the US Department of Energy (DOE) by the year 2020. The estimated desorption temperatures show the desirable properties for the long term recycling of the Si2BN storage medium. Thus, our results show that the Si2BN monolayer is a promising candidate for molecular hydrogen storage.

Antibacterial effect of graphene oxide (GO) nano-particles against Pseudomonas putida biofilm of variable age

Graphene oxide (GO) has been reported to possess antibacterial activity; therefore, its accumulation in the environment could affect microbial communities such as biofilms. The susceptibility of biofilms to antimicrobials is known to depend on the stage of biofilm maturity. The aim of this study was to investigate the effect of GO nano-particles on Pseudomonas putida KT2440 biofilm of variable age. FT-IR, UV-vis, and Raman spectroscopy confirmed the oxidation of graphene while XPS confirmed the high purity of the synthesised GO over 6 months. Biofilms varying in maturity (24, 48, and 72 h) were formed using a CDC reactor and were treated with GO (85 μg/mL or 8.5 μg/mL). The viability of P. putida was monitored by culture on media and the bacterial membrane integrity was assessed using flow cytometry. P. putida cells were observed using confocal microscopy and SEM. The results showed that GO significantly reduced the viability of 48-h biofilm and detached biofilm cells associated with membrane damage while the viability was not affected in 24- and 72-h biofilms and detached biofilm cells. The results showed that susceptibility of P. putida biofilm to GO varied according to age which may be due to changes in the physiological state of cells during maturation. Graphical abstract.

Graphene and graphene-based nanocomposites used for antibiotics removal in water treatment: A review

Due to their extensive application in human and veterinary medicine, antibiotics have been found worldwide and studied as new pollutants in the aquatic environment. In order to remove such pollutants, adsorption and photocatalysis have attracted tremendous attention because of their great potential in antibiotics removal from aqueous solutions. Graphene, as a novel two-dimensional nanomaterial, possesses unique structure and physicochemical properties, which can be used to efficiently adsorb and photodegrade antibiotics. This review provides an overview of the adsorptive and catalytic properties of graphene, and recent advances in adsorption and photodegradation of antibiotics by graphene and its derivatives. The factors that affect the adsorption and photodegradation of antibiotics are reviewed and discussed. Furthermore, the underlying mechanisms of adsorption and photodegradation are summarized and analyzed. Meanwhile, statistical analysis is conducted based on the number of papers and the maximum adsorption and photodegradation ability on various antibiotics removal. Finally, some unsolved problems together with major challenges that exist in the fabrication and application of graphene-based nanocomposites and the development for antibiotics removal is also proposed. This work provides theoretical guidance for subsequent research in the field of adsorption and photocatalytic removal of antibiotics from aqueous solution, especially on influence factors and mechanisms aspects.

Graphene based adsorbents for remediation of noxious pollutants from wastewater

The contamination of water resources with noxious pollutants is a serious issue. Many aquatic systems are contaminated with different toxic inorganic and organic species; coming to wastewater from various anthropogenic sources such as industries, agriculture, mining, and domestic households. Keeping in view of this, wastewater treatment appears to the main environmental challenge. Adsorption is one of the most efficient techniques for removing all most all types of pollutants i.e. inorganics and organics. Nowadays, graphene and its composite materials are gaining importance as nano adsorbents. Graphene; a two-dimensional nanomaterial having single-atom graphite layer; has attracted a great interest in many application areas (including wastewater treatment) due to its unique physico-chemical properties. The present paper is focused on the remediation of noxious wastes from wastewater using graphene based materials as adsorbents, and it contains all the details on materials - i.e., from their synthesis to application in the field of wastewater treatment (removal of hazardous contaminants of different chemical nature - heavy and rare-earth metal ions, and organic compounds - from wastewater effluents. The efficiency of the adsorption and desorption of these substances is considered. Certainly, this article will be useful for nano environmentalist to design future experiments for water treatment.

Modulation of Bi2 MoO6 -Based Materials for Photocatalytic Water Splitting and Environmental Application: a Critical Review

Highly active photocatalysts driving chemical reactions are of paramount importance toward renewable energy substitutes and environmental protection. As a fascinating Aurivillius phase material, Bi₂ MoO₆ has been the hotspot in photocatalytic applications due to its visible light absorption, nontoxicity, low cost, and high chemical durability. However, pure Bi₂ MoO₆ suffers from low efficiency in separating photogenerated carriers, small surface area, and poor quantum yield, resulting in low photocatalytic activity. Various strategies, such as morphology control, doping/defect-introduction, metal deposition, semiconductor combination, and surface modification with conjugative π structures, have been systematically explored to improve the photocatalytic activity of Bi₂ MoO₆ . To accelerate further developments of Bi₂ MoO₆ in the field of photocatalysis, this comprehensive Review endeavors to summarize recent research progress for the construction of highly efficient Bi₂ MoO₆ -based photocatalysts. Furthermore, benefiting from the enhanced photocatalytic activity of Bi₂ MoO₆ -based materials, various photocatalytic applications including water splitting, pollutant removal, and disinfection of bacteria, were introduced and critically reviewed. Finally, the current challenges and prospects of Bi₂ MoO₆ are pointed out. This comprehensive Review is expected to consolidate the existing fundamental theories of photocatalysis and pave a novel avenue to rationally design highly efficient Bi₂ MoO₆ -based photocatalysts for environmental pollution control and green energy development.

Shape-controlled assemblies of graphitic carbon nitride polymer for efficient sterilization therapies of water microbial contamination via 2D g-C3N4 under visible light illumination

Bacterial pathogens of water origin have potential public threats thus suggesting the need of developing efficient and sustainable water disinfection strategies from waterborne pathogens. We set out to synthesize different controlled morphologies of graphitic carbon nitride (g-C₃N₄) polymer, evaluate their comparative effects on the generation of reactive oxygen species (ROS), and investigate potential applications in water purification systems. Characterization of the synthesized microstructures of g-C₃N₄, such as melamine-cyanuric acid (MCA)-based rosette-type, rod-type, 2D hexagonal, and 3D cubic mesoporous silica was accomplished using Fourier transform infrared (FT-IR), energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), X-ray diffractometry (XRD), and transmission electron microscopy (TEM). The microbial inhibitory potential of 2D g-C₃N₄ photocatalyst against waterborne Escherichia coli, Staphylococcus aureus, and Salmonella typhimurium was evaluated based on the effective activity of 2D g-C₃N₄ upon visible light excitations. The microbicidal efficiency of 2D g-C₃N₄ was evident within 30 min of visible light exposure via direct interaction, while other microstructures of g-C₃N₄ demonstrated only slight antimicrobial effects after 120 min, with insufficient ROS generation. The antimicrobial and ROS-generating effects of 2D g-C₃N₄ depended on the type and surface area of the synthesized 2D g-C₃N₄ material. Considering its availability and excellent disinfection activity, 2D g-C₃N₄ obtained from simple and convenient facile synthesis is a promising solar-driven photocatalyst for clearing microbial contamination from water.

Nanoengineered cellulosic biohydrogen production via dark fermentation: A novel approach

The insights of nanotechnology for cellulosic biohydrogen production through dark fermentation are reviewed. Lignocellulosic biomass to sugar generation is a complex process and covers the most expensive part of cellulose to sugar production technology. In this context, the impacts of nanomaterial on lignocellulosic biomass to biohydrogen production process have been reviewed. In addition, the feasibility of nanomaterials for implementation in each step of the cellulosic biohydrogen production is discussed for economic viability of the process. Numerous aspects such as possible replacement of chemical pretreatment method using nanostructured materials, use of immobilized enzyme for a fast rate of reaction and its reusability along with long viability of microbial cells and hydrogenase enzyme for improving the productivity are the highlights of this review. It is found that various types of nanostructured materials e.g. metallic nanoparticles (Fe°, Ni, Cu, Au, Pd, Au), metal oxide nanoparticles (Fe₂O₃, F₃O₄, NiCo₂O₄, CuO, NiO, CoO, ZnO), nanocomposites (Si@CoFe₂O₄, Fe₃O₄/alginate) and graphene-based nanomaterials can influence different parameters of the process and therefore may perhaps be utilized for cellulosic biohydrogen production_. The emphasis has been given on the cost issue and synthesis sustainability of nanomaterials for making the biohydrogen technology cost effective. Finally, recent advancements and feasibility of nanomaterials as the potential solution for improved cellulose conversion to the biohydrogen production process have been discussed, and this is likely to assist in developing an efficient, economical and sustainable biohydrogen production technology.

Development of α- and γ-Fe2O3 decorated graphene oxides for glyphosate removal from water

In this study, the proposed adsorbent composed of graphene oxide (GO) functionalized by magnetic nanoparticles of iron oxide (α-γ-Fe2O3) was obtained by a simple ultrasonication process. This new material was used for the removal of glyphosate in water. The nanoparticulated iron oxide used was synthesized by means of a modified sol-gel method, which does not use organic solvents. The adsorbent material (GO-α-γ-Fe2O3) obtained was characterized by magnetic measurements, and it can be proved that it has superparamagnetic properties, allowing fast and efficient magnetic separation. The equilibrium time for the adsorption of glyphosate when using GO-α-γ-Fe2O3 was 2 hours and the maximum removal was 92% at 15°C, with a maximum adsorption capacity of 46.8 mg g-1. Langmuir model and pseudo-second-order kinetic model correlated satisfactorily to the experimental data. The thermodynamic parameters showed that the adsorption of glyphosate on GO-α-γ-Fe2O3 was spontaneous, exothermic and thermodynamically favorable at temperature of 15-45°C. Thus the adsorbent material GO-α-γ-Fe2O3 proposed in this study is considered a good candidate to be used in the removal of glyphosate from aqueous solutions, presenting high adsorption capacity, low cost and magnetic properties that facilitate the separation of the adsorbent material.