Oxygen-based Functional Groups Research Articles

Novel Application of Diffuse Coplanar Surface Barrier Discharge: Fast, Efficient and Controlled Surface Functionalization

Plasma chemistry is currently an interesting approach to surface modification of materials. In general plasma treatment is a fast process, affecting only the units of nanometers of the surface layer without altering the bulk properties. and has many potential benefits such as minimal waste and control of surface functionality. It represents a dry and environmentally friendly process that can achieve comparable results to wet chemical treatment. The research and development of plasma sources, mainly operating at atmospheric pressure, has been the main activity of the centre CEPLANT, Brno, Czech Republic for several decades. Our development is generally aimed at fast, efficient, and low-cost plasma treatments, easily implementable in industry, and flexibly responds to industrial requirements and current trends.One of our most versatile plasma source, the so-called Diffuse Coplanar Surface Barrier Discharge (DCSBD) has been developed for in-line surface modification of various materials, primarily for fabric materials. DCSBD produces a 0.3 mm thin layer of non-equilibrium, cold macroscopically diffuse plasma at atmospheric pressure (Fig. 1) in any working gas, including oxygen, hydrogen, or even water vapors. Due to its strongly non-equilibrium nature, operation at atmospheric pressure, and low temperatures, the DCSBD represents a unique plasma source suitable for surface modification of low-cost and temperature-sensitive materials [1-4].Unique results have been achieved in research on the practical application of flexible conductive layers on glass, with a focus on the deposition of transparent organic polymer coatings on ultra-thin flexible glass (UTFG). We have developed and optimized efficient and fast dry non-contact cleaning and activation of fragile and lightweight conductive glasses using DCSBD. The high-speed plasma treatment corresponding to the exposure times in the order of units of seconds leads to a synergistic balance between the efficient removal of impurities (carbohydrates) adsorbed on the UTFG surface and the formation of oxygen-based functional groups. Subsequent PEDOT:PSS-based coatings sprayed on plasma-treated UTFG surfaces achieve significantly higher electrical conductivity compared to the standard liquid-purified samples. This method combined with the unique properties of UTFG provides prospective results applicable in microelectronics, and optoelectronic devices like sensors or displays.In the field of composite materials research, we have discovered that plasma treatment of reinforcing fibers leads to improvement of the mechanical properties of laminated fiber-reinforced polymer (FRP) composites. Efficient functionalization of various commonly used reinforcement fibers (flax, aramid and glass) in atmospheric low-temperature DCSBD increases the interfacial adhesion at the fiber-matrix interface, which has a provable positive effect on the resulting mechanical properties.DCSBD plasma can also be utilized for the initiation of reducing chemical reactions. We have developed a simple and fast chemical-free fabrication method of 2D and 3D reduced graphene oxide (rGO) structures using an electrical plasma-triggered reduction & exfoliation of 3D porous graphene oxide (GO) aerogel-like materials [4] and also 2D GO paper-like films starting at temperatures not higher than 100 oC [5]. The plasma triggered the self-propagating reduction & exfoliation fast modification of GO into rGO, while the rGO structures retained their original shape without abrupt disintegration. We observed an approximately 105 fold decrease of the rGO paper resistivity compared to the unmodified GO paper. This novel method opens new opportunities for the production of conductive rGO and rGO-based composites for modern industrial applications.Innovative results were achieved in the fabrication of ZnO nanofibers by a novel calcination approach assisted by DCSBD. Exposition of the polyvinyl pyrrolidone/zinc acetate fibers to DCSBD before the thermal processing leads to the gentle low-temperature removal of organic material. Plasma pre-treated nanofibers are characterized by a smaller diameter and retain a defined fibrous structure during heat treatment. Moreover, the ZnO nanofibers prepared by a combination of plasma and heat treatment exhibited considerably higher photodegradation activity increasing with decreasing calcination temperature [6]. The low-temperature and high oxidation potential of plasma makes plasma-assisted calcination of the inorganic nanofibers an attractive alternative to conventional thermal annealing with potential application in optoelectronics or biosensors.The mentioned applications are only a small fragment of available cases of utilization of the DCSBD, which is now commonly established and applied in the field of surface modification of various materials (glass, metals, non-woven fabrics, polymers, paper, nanofibres) and biomaterials (seeds, grains, wood, natural leather).[1] M. Černák et al., Plasma Physics and Controlled Fusion 53 (2011) 1-8[2] R. Talviste et al., Surface and Interface 16 (2019) 2468-0230[3] T. Morávek et al., Open Chemistry 13 (2015) 236-244[4] R. Krumpolec et al., Flatchem 35 (2022)[5] F. Zelenák , Carbon N. Y. 215 (2023) 118436[6] V. Medvecká et al., Applied Surface Science, 581 (2022) 152384 Figure 1

Peach seed shell and Aspergillus oryzae as adsorbents for the uptake of acid violet 90 dye from wastewater

In this study, Aspergillus oryzae (A. Oryzae) biomass and waste peach seed shells (PPSS) were used to create alternative and effective adsorbents. Acid Violet 90 (AVD) dye was removed from wastewater using the as-prepared adsorbents. Different process variables like pH (2–11), contact period (0–180 min), and adsorbent mass (0.2–2.0 g/L) were examined. The solution pH had a synergistic effect on the improved removal of AVD and the optimal adsorption removal for the PPSS and the A. Oryzae adsorbent occurred at pH 2.0 and pH 5.0, respectively. The findings demonstrated that, in comparison to A. Oryzae, PPSS reported a greater AVD adsorption (mg/g). The equilibrium time for the adsorption process was attained within 180 min for both adsorbents. The adsorption kinetics modelling results showed a good fit with pseudo-second-order kinetics, for both adsorbents, with average R2 values of 0.999 (for PPSS) and 0.997 (for A. Oryzae). Similarly, the isotherm modelling results confirmed the good fitting of the Langmuir isotherm model for A. Oryzae (R2 = 0.999) and the Freundlich model for PPSS (R2 = 0.997). The maximum adsorption capacity (qmax) of 55.0 and 94.92 mg/g was recorded for A. Oryzae and PPSS, respectively. Mechanistic investigation of the present system suggests that both intraparticle diffusion and surface sorption mechanisms control the adsorption rate. As agro materials, both adsorbents are composed of mostly oxygen-based surface functional groups like the –OH, –C = O, -C-O-C, and multiple carbon-carbon bonds, all contributed to the synergistic mechanism interaction between the adsorbent and AVD dye in this study. This study, therefore, revealed that the PPSS and A. Oryzae may be very helpful for removing anionic dye from contaminated wastewater, indicating its potential for useful application in the removal of other major pollutants.

Synergistic degradation of polystyrene nanoplastics in water: Harnessing solar and water-driven energy through a Z-scheme SnO2/g-C3N4/PVDF-HFP piezo-photocatalytic system

The rise of nanoplastics (NPs) as a water pollutant poses threats to aquatic ecosystems and human health. This study presents an approach that combines solar and water-driven energy sources with advanced materials to degrade NPs. For this purpose, a SnO2/g-C3N4/PVDF-HFP piezo-photocatalyst has been developed. The SnO2/g-C3N4 photocatalyst with Z-Scheme charge transfer demonstrates high activity under simulated solar light. Simultaneously, ultrasound waves, employed to mimic water motion, serve to activate the piezoelectric properties of g-C3N4, thereby enhancing charge separation. Moreover, the immobilization of SnO2/g-C3N4 onto piezoelectric poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanofiber mats augments its piezocatalytic efficiency and prevents dispersion in the reaction media. During the piezo-photocatalytic process, generated reactive species attack polystyrene (PS) NPs and introduce oxygen-based functional groups. This leads to surface corrosion, fragmentation, and 46 % mineralization in just 15 h under mild conditions, outperforming existing literature. Overall, this research emphasizes the importance of harnessing renewable energy sources for NP remediation.

Multi-color polymer carbon dots synthesized from waste polyolefins through phenylenediamine-assisted hydrothermal processing

The large accumulation and low recycling rates of polyolefin waste have posed a threat to the environment and human health. The shortage of chemical recycling methods for polyolefins strongly demands the development of new and sustainable treatment technologies for hydrocarbon plastics to improve their waste management. In this study, polyethylene (PE) and polypropylene (PP) were utilized for the preparation of multi-color polymer carbon dots (PCDs) via a two-step hydrothermal (HT) synthesis involving (i) thermo-oxidative degradation of polyolefins to precursors containing plentiful oxygen-based functional groups, and (ii) modification with phenylenediamine (PDA). The fluorescence of PCDs depends on the structure of isomeric PDA and PCDs modified by ortho-, meta-, and para-PDA emit blue, green, and yellow color fluorescence, respectively. The formation mechanism of PCDs, involving dehydrative condensation and amination of PE or PP-derived precursors by PDA, was proposed. The obtained PCDs were utilized for the detection and quantification of Fe3+ ions at ppm concentrations. The proposed strategy here aims to broaden the scope of the chemical recycling methods for polyolefin plastic waste as well as to develop a conversion route of polyolefin to value-added materials.

A comparative study on coconut shell-derived graphene oxide and reduced graphene oxide

Coconut shell (CS) is a waste material with high carbon source potential and is suitable for producing advanced nanomaterials like graphene oxide (GO) and reduced graphene oxide (rGO). However, CS-derived subpar GO and rGO and the lack of comparative studies have restrained their best utilization. This study presents a novel synthesis of high-quality and non-toxic GO and rGO using CS as the precursor, comparing their structural and chemical properties. The synthesis processes involve CS carbonization into graphite, oxidation of graphite into GO using Hummers' method with specific modifications, and non-toxic thermal reduction of GO into rGO. Characterization techniques, including X-ray diffraction, Raman spectroscopy, FTIR, Scanning electron microscopy, and Transmission electron microscopy, confirm successful oxidation and reduction of the samples. Results reveal a well-defined graphitic structure in CS-derived graphite. GO contains oxygen-based functional groups, removed or reduced during thermal reduction. While rGO has fewer defects and restored graphitic arrangement. This study concludes that CS-derived GO and rGO possess desirable properties comparable to those synthesized from pristine graphite, respectively. The results suggest that non-toxic, few-layered, and high-quality GO and rGO synthesized from CS suit biomedical applications, particularly in bone tissue engineering.

Removal of Crystal Violet Dye from Aqueous Solutions through Adsorption onto Activated Carbon Fabrics

The removal of contaminants from aqueous solutions by adsorption onto carbonaceous materials has attracted increasing interest in recent years. In this study, pristine and oxidized activated carbon (AC) fabrics with different surface textures and porosity characteristics were used for the removal of crystal violet (CV) dye from aqueous solutions. Batch adsorption experiments were performed to investigate the CV adsorption performance of the AC fabrics in terms of contact time, temperature, adsorbate concentration and adsorbent amount. Evaluation of the thermodynamic parameters and the adsorption performance of the AC fabrics in ground water and sea water solutions were also carried out. Langmuir isotherm model, pseudo first and pseudo second order kinetics models were utilized to analyze and fit the adsorption data. The introduction of oxygen-based functional groups on the surface of AC fabrics was carried out through a nitric acid treatment. This oxidation process resulted in a significant reduction in the surface area and pore volume, along with a small increase in the average pore size and a significant enhancement in the CV adsorption capacity, indicating that the dye molecules are mainly adsorbed on the external surface of the carbon fabrics. The herein evaluated 428 mg/g adsorption capacity at 55 °C for the oxidized non-woven AC fabric is one of the highest adsorption capacity values reported in the literature for CV removal using AC materials. Thermodynamic studies showed that the adsorption occurs spontaneously and is an endothermic and entropy-driven reaction. Furthermore, pristine and oxidized non-woven AC fabrics displayed more than 90% CV uptake from sea water samples, underlining the great potential these fabrics possess for the removal of dyes from natural/multicomponent waters.

Correlation between structural characteristics of edge selectively-oxidized graphite and electrochemical performances under fast charging condition

In the pursuit of ameliorating of the battery-performance degradation particularly during fast charging of lithium-ion batteries, we investigated the influence of surface-structural parameter of graphite. To explore the effect of the graphite surface state on the battery performance, we synthesized the edge selectively-oxidized graphite. The detailed analysis about the structural parameters of graphite samples revealed that the edge area increased from 3.41 to 4.26 m2 g−1 by oxidation process while preserving the specific surface area. Edge selectively-oxidized graphite samples showed the similar ratio between carbon and oxygen regardless of oxidized time, but the change of surface charge due to the different functional groups. The edge selectively-oxidized graphite exhibited a significantly improved capacity retention and rate performance compared with the bare graphite. Based on thorough examination about material properties and electrochemical responses, we corroborated a strong correlation among the electrochemical performance, edge surface area, and type of oxygen-based functional groups of graphite. Our study provides conclusive evidence that the surface nature of graphite plays a pivotal role in boosting the battery performance.

Combustion Characteristics of r-GO/g-C3N4/LaFeO3 Nanohybrids Loaded Fuel Droplets

ABSTRACT Graphene oxide (GO), reduced graphene oxide (r-GO) and graphitic carbon nitride (g-C3N4) are two-dimensional carbon-based nanosheets that show promise in reducing emissions with their superior catalytic activity in capturing species such as NOx and CO2 thanks to their oxygen-based functional groups and active edges on their surfaces. These active surfaces also provide a scheme for the substitution of materials with high calorific value or high catalytic activity for combustion. This study focuses on the fabrication of functional nanohybrid structures customized for combustion with LaFeO3 metal oxide nanoparticles substituted on these nanosheets and their effect on the combustion behavior of gasoline. The fabrication of r-GO/g-C3N4/LaFeO3 nanohybrid structures was carried out by a two-step hydrothermal method. The structural characterizations of the samples were confirmed by SEM and XRD analyses and their chemical states were confirmed by Raman and XPS techniques. Combustion experiments were carried out by droplet scale combustion of gasoline-based nanofuel droplets containing dilute (0.2 wt.%) and high (0.7 wt.%) concentrations of GO, r-GO, g-C3N4, g-C3N4/LaFeO3 and r-GO/g-C3N4/LaFeO3 nanoparticles. The experimental process was recorded with a high-speed camera and a thermal camera. The nanofuel droplets containing 0.2 wt.% g-C3N4/LaFeO3 nanohybrid structures had the highest maximum flame temperature of 519 K, and the nanofuel droplets containing 0.7 wt.% r-GO/g-C3N4/LaFeO3 particles had the highest maximum aggregate temperature of 1177 K. The ignition delay time decreased for all droplets with 0.2 wt.% and 0.7 wt.% particle loadings. At 0.2 wt.% concentration, g-C3N4 doped fuel droplets exhibited the lowest extinction time, while at 0.7 wt.% concentration, the lowest extinction time was measured for r-GO/g-C3N4/LaFeO3 doped fuel droplets. Fuel droplets containing g-C3N4 particles had the highest burning rate and were the fastest extinguishing fuel droplets in the electric field. In this study, it has been demonstrated that the combustion rate and energy value of hydrocarbon fuels can be increased and soot formation can be reduced at the same time with the new generation of graphene-based functional materials to be created, and thus, many combustion problems can be solved simultaneously with these functional particles.

Highly fluorescent nitrogen-doped graphene quantum dots (N-GQDs) synthesized from Pennisetum purpureum for selective and sensitive detection of Fe3+ ions

The synthesis of nitrogen-doped Graphene Quantum Dots (N-GQDs) employing Pennisetum purpureum (elephant grass) as the carbon precursor and ethylenediamine (EDA) as the nitrogen source was conducted. This study highlights the potential applications of nitrogen-doped multi-fluorescent graphene quantum dots (N-GQDs) in the detection of Fe3+. The synthesized N-GQDs have been studied using UV–vis spectrophotometry, fluorescence spectrometry, Raman spectrometry, FT-IR spectrometry, x-ray spectroscopy, selected-area electron diffraction, transmission and high-transmission electron microscopy. The acquired N-GQDs were observed to have an almost hexagonal shape with a lateral size of 2.42 nm and exhibited a comparable quantum yield of approximately 26%. The N-GQDs that have been prepared with consistent size distribution and a significant amount of nitrogen and oxygen-based functional groups showcase outstanding water dispersity. The N-GQDs exhibited the capability to identify the Fe3+ ions in a broad range concentration of 1–600 μM by creating an N-GQDs-Fe3+ complex through the occurrence of functional groups like nitrogen, carbonyl, and carboxyl on N-GQDs surface, has a lower limit of detection at approximately 60 nM. Our study provides evidence that the N-GQDs produced a strong and persistent fluorescence, which is highly soluble in water, notably the precise and selective detection of Fe3+ in water-based solutions.

Porphyrin-based conjugated microporous adsorbent material for the efficient remediation of hexavalent chromium from the aquatic environment.

The encapsulation and eradication of anions from water have received a lot of scrutinize and are extremely important for virtuous production and environmental treatment. To prepare extremely efficient adsorbents, a highly functionalized and conjugated microporous porphyrin-based adsorbent material (Co-4MPP) was synthesized using the Alder Longo method. Co-4MPP featured a hierarchical microporous and mesoporous layered structure containing nitrogen and oxygen-based functional groups with a specific surface area of 685.209 m2/g and a pore volume of 0.495 cm3/g. Co-4MPP demonstrated a greater Cr (VI) adsorption empathy than the pristine porphyrin-based material did. The effects of various parameters such as pH, dose, time, and temperature were explored on the Cr (VI) adsorption by Co-4MPP. The pseudo-second-order model and the Cr (VI) adsorption kinetics were in agreement (R2 = 0.999). The Langmuir isotherm model matched the Cr (VI) adsorption isotherm, demonstrating the optimum Cr (VI) adsorption capacities: 291.09, 307.42, and 339.17 mg/g at 298K, 312K, and 320K, correspondingly, with remediation effectiveness of 96.88%. The model evaluation further revealed that Cr (VI) adsorption mechanism on Co-4MPP was endothermic, spontaneous, and entropy-rising. The detailed discussion of the adsorption mechanism suggested that it could be a reduction, chelation, and electrostatic interaction, in which the protonated nitrogen and oxygen-containing functional groups on the porphyrin ring interacted with Cr (VI) anions to form a stable complex, thus remediating Cr (VI) anions efficiently. Moreover, Co-4MPP demonstrated strong reusability, maintaining 70% of its Cr (VI) elimination rate after four consecutive adsorptions.

Mechanocatalytic Oxidative Cracking of Poly(ethylene) Via a Heterogeneous Fenton Process

In this work, mechanocatalytic oxidative cracking is used to overcome the chemical inertness of poly(ethylene) (PE) and the difficulties associated with processing this solid feedstock. An Fe2O3-based Fenton system is applied to introduce oxygen-based functional groups to the PE backbone with hydrogen peroxide as the oxidant. Once an oxygen-based functional group is introduced, the polymer chain can be cleaved to achieve cracking effectivity, with only CO, CO2, O2, and H2O as byproducts. The resulting fragments can be used as intermediates to produce fuels and sustainable chemicals.

Impact of Hard Carbon Properties on Their Performance in Potassium-Ion Batteries

This work reports on the synthesis of hard carbon spheres (HCS) and the impact of the pyrolysis temperature (1500 to 1900 °C) on the properties of HC and its relationship with the electrochemical performance in potassium-ion batteries (KIBs). Comparison with commercial graphite performance is provided as well. Spherical morphology, disordered structure, and low surface area were obtained for the HCSs. Most properties (interlayer space, active surface area, and oxygen-based functional groups) were found to decrease with increasing pyrolysis temperature, except for the helium density and closed porosity, which increase. However, graphite presents a flake-like morphology with a larger particle size, a higher helium density, an ordered structure with a smaller interlayer distance, and no closed pores. Electrochemical tests in a half-cell vs K+/K showed that HCSs perform better than graphite with higher initial Coulombic efficiency (ICE) and better specific capacities. The HCSs pyrolyzed at 1500 and 1700 °C exhibit the best initial Coulombic efficiency, ICEs of 54 and 62%, and specific capacities of 254 and 247 mAh g–1 (C/20, 11.5 mA g–1), respectively. The ICE is affected by multiple surface and bulk parameters but also by electrolyte formulation (67% for 0.8 M KFSI vs 62% for 0.8 M KPF6). The capacity is governed by diffusive phenomena, and a larger interlayer graphitic spacing and defects favor a better insertion of K ions. Closed pores did not lead to an improvement in capacity. Furthermore, HCSs exhibit significantly better capacity retention (97%) than graphite (84%), especially when cycled at high current rates (up to 10C depotassiation rate).

Cobalt ferrite nanoparticles anchored on reduced graphene oxide nanoribbons (0D/1D CoFe2O4/rGONRs) as an efficient catalyst for hydrogen generation via NaBH4 hydrolysis

For better performance of nanoparticles as the heterogeneous catalyst, various materials with a large surface area have been introduced as the substrate. Herein, CoFe2O4 nanoparticles were anchored on carbon nanotubes (CoFe2O4/CNTs) and graphene nanoribbons (CoFe2O4/GONRs) to investigate the influence of substrate in the catalytic performance. These nanocomposites were evaluated in a NaBH4 hydrolysis reaction to produce hydrogen. The results showed that the highest hydrogen volume occurs in the presence of CoFe2O4/GONRs nanocatalyst. Abundant oxygen-based functional groups at the edges of GONRs offered excellent sites for CoFe2O4 nanoparticles and improved catalytic performance. Under optimum conditions (2.0 wt% of NaBH4, 15 mg of catalyst, 2.0 wt% of NaOH), the hydrogen generation rate was found to be 3.7 L g-1min−1 at 35 °C. The activation energy was calculated using the Arrhenius method, equivalent to 31.4 kJ mol−1. Therefore, CoFe2O4/GONRs catalyst can be a novel and efficient candidate for hydrogen production as a clean fuel.

The effect of microwave power level and post-synthesis annealing treatment on oxygen-based functional groups present on carbon quantum dots

Despite widespread interest in understanding the properties of carbon quantum dots (CDOTs), there appear to be fewer studies systamaticaly investigating CDOTs' luminescent mechanisms. The primary objective of this study is to prepare CDOTs with desirable optical properties and to understand the photoluminescence (PL) mechanisms involved in order to control the emission charectersitcs. The optical properties of CDOTs are strongly influenced by the functional groups (-OH, –CHO, –COOH, –CO, –COO) formed on the surface of the dots. The key factors affecting the nature and number of functional groups are the preparation method, post synthesis treatment, and the precursor materials. Ascorbic acid was used as the starting material in this study to synthesize CDOTs via microwave-assisted synthesis techniques. Then, the effect of microwave power level and post synthesis annealing temperature on the oxygen-based functional groups present on the surface of the dots was evaluated systematically. It was found that the increasing microwave power level increases the density of functional groups present on the surface of CDOTs, which positively affects the PL. However, annealing at high temperatures decreases the concentration of functional groups and reduces the PL intensity. The PL emission peaks were deconvoluted and the emission wavelength corresponding to each functional group was identified. This work underlines the role of oxygen based functional groups on the PL emission and the ways to control them by physical means.

Towards Understanding the Impact of Electrochemical Double Layer on the Performance of Graphene Devices

The effect of electrochemical double layer (EDL) on the performance of graphene-based sensing platforms has been an area of controversy over the last two decades 1. The hydrophobic nature of bare graphene tends to repel the water and minimizes the solution/solid surface interactions 2. However, the presence of oxygen-based functional groups on graphene introduces negatively charged sites and causes a negative surface zeta potential. Hence, the instant formation of an EDL on a graphene surface in an aqueous solution is inevitable, affecting the graphene surface's chemical/physical interactions 3. Thus far, multiple theories and techniques have been developed to investigate the impact of EDL on graphene sensing performance; however, they either suffer from complexity in design or have ignored the co-existence of other solution parameters such as pH and oxidation-reduction potential 4.In this work, we propose the use of alkaline chloride salts to understand the impact of the ionic strength and EDL of the solution on the few-layer graphene (FLG) based chemiresistive sensors. Considering the full ionization of NaCl and the low redox potential of the generated ions, alkaline chlorides are considered good candidates to modulate the electronic band structure of FLG without altering its surface chemistry 5. By use of Helmholtz theory of EDL, it is postulated the Inner Helmholtz Layer (IHL) to be formed by Na+ ions due to the negative surface charge of FLG. Whereas the hydrated counter ions, Cl-, form the Outer Helmholtz Layer (OHL). Upon the formation of a positively charged immobile layer of Na+ ions on the surface (IHL), the electrostatic gating effect of EDL dopes the graphene with electrons. This charge separation can be modelled as two parallel plates of a capacitor with infinitely thin dielectric 6.Since the presence of oxygen-based functional groups on FLG is inevitable during the synthesis process, it is considered inherently p-doped. Accordingly, upon the addition of NaCl concentrations, the FLG surface current decreases. However, at higher concentrations (around 2000 ppm NaCl), the sensor response is inversed, and surface current increases by the addition of NaCl (Figure-left). In fact, high ionic strength increases the EDL compactness and decreases the charge screening length (Debye length). As a result of this sharper difference in solid/solution potentials (Figure-right), a more n-doped surface having electron as majority charge carriers is obtained, changing the nature of the response.We have also demonstrated that the formation of sodium-oxygen metal complexes on FLG is not likely in an aqueous environment. According to the Raman spectroscopy results of FLG, an increase in the intensity ratio of D (defect) to G bands is observed upon exposure to water and NaCl. Moreover, the noticeable right shift in the 2D band position demonstrates the p-doping of FLG 7. Furthermore, the reversible response of the sensor during multiple exposures to NaCl demonstrates the sensor response originates from EDL, not the formation of sodium-oxygen metal complexes. In fact, the full or half hydrated Na+ ions in IHL electrostatically interact with surrounding oxygen. However, since the oxygen atom in water is more negatively charged compared to the oxygen on the graphene surface, Na+ is unlikely to bound to the surface after hydration. Therefore, using NaCl could be a suitable medium to study the impact of EDL on the performance of graphene devices.Reference Jurado et al., Scientific Reports, 7(1), pp.1-12 (2017).Angizi, S et al., Langmuir, 37(41), pp.12163-12178 (2021).Jung et al., Nano Letters, 21(1), pp.34-42 (2020).Pak et al., The Journal of Physical Chemistry C, 118(38), pp.21770-21777 (2014).Lee et al., ACS Applied Materials & Interfaces, 11(45), pp.42520-42527 (2019).Kwon et al., The Journal of Physical Chemistry C, 116(50), pp.26586-26591 (2012).Bruna et al., ACS Nano, 8(7), pp.7432-7441 (2014). Figure 1

Innovative progress in graphene derivative-based composite hybrid membranes for the removal of contaminants in wastewater: A review

Graphene derivatives (graphene oxide) are proved as an innovative carbon materials that are getting more attraction in membrane separation technology because of its unique properties and capability to attain layer-to-layer stacking, existence of high oxygen-based functional groups, and generation of nanochannels that successively enhance the selective pollutants removal performance. The review focused on the recent innovations in the development of graphene derivative-based composite hybrid membranes (GDHMs) for the removal of multiple contaminants from wastewater treatment. To design GDHMs, it was observed that at first GO layers undergo chemical treatments with either different polymers, plasma, or sulfonyl. After that, the chemically treated GO layers were decorated with various active functional materials (either with nanoparticles, magnetite, or nanorods, etc.). By preparing GDHMs, properties such as permeability, porosity, hydrophilicity, water flux, stability, feasibility, mechanical strength, regeneration ability, and antifouling tendency were excessively improved as compared to pristine GO membranes. Different types of novel GDHMs were able to remove toxic dyes (77–100%), heavy metals/ions (66–100%), phenols (40–100%), and pharmaceuticals (74–100%) from wastewater with high efficiency. Some of GDHMs were capable to show dual contaminant removal efficacy and antibacterial activity. In this study, it was observed that the most involved mechanisms for pollutants removal are size exclusion, transport, electrostatic interactions, adsorption, and donnan exclusion. In addition to this, interaction mechanism during membrane separation technology has also been elaborated by density functional theory. At last, in this review the discussion related to challenges, limitations, and future outlook for the applications of GDHMs has also been provided.

Boosting moisture induced electricity generation from graphene oxide through engineering oxygen-based functional groups

Harvesting energy from ubiquitous moisture is attracting growing interest for directly powering electronic devices. However, it is still challenging to fabricate high-performing moisture-electric generators (MEGs) with high and stable electric output. Herein, we report a simple strategy to modify the oxygen-based groups of graphene oxide using hydrochloric acid treatment, which boosts the electric output based on the device structure of graphene oxide/polyvinyl alcohol (GO/PVA) MEGs. The resulting MEG enables a stable voltage of 0.85 V and a current of 9.28 μA (92.8 μA∙cm-2), which are among the highest values reported so far. More excitingly, electric output gets further improved by simply assembling four MEG units in series or parallel. Moreover, the MEG shows great commercial potential for flexible and wearable applications. Driven by these advancements, the assembled MEGs can successfully power sensors and calculators. This work opens a new era of advance for a new energy conversion technology able to directly powering electronic devices.

Hybrid Plasma-Liquid Treatment of Carbon Nanotubes for Application in Direct Absorption Solar Thermal Collectors

Covalent functionalization of carbon nanotubes (CNTs) with oxygen-based or nitrogen-based functional groups is one of the most popular techniques to modify the surface energy and inherent properties of the CNTs.1 This functionalization generates interest for a broad range of applications including mechanically superior advanced composites,2 more sensitive gas sensors,3 enhanced energy storage materials4 or ultra-conductive fibers.5 As an alternative to the harsh chemicals used by traditional chemical functionalization, plasma-based surface treatments can be used with great efficacy and reduced reaction times, providing an array of application-specific benefits.Awareness of the environmental pollution caused by fossil fuels and the ever-increasing demand for energy has driven research focussed on zero-carbon renewable energy sources. Conscious of this, direct absorption solar thermal collectors are gaining prominence, both for domestic heating and steam generation. CNTs have been investigated as an additive to take advantage of the near blackbody absorption and high thermal conductivity to improve system efficiency. Critical to the success of the additive nanoparticles is the stability in the fluid, however, due to their high surface energy CNTs tend to agglomerate which can limit the efficacy of their integration into real-world products.In this work, macroscopic ribbon-like assemblies of carbon nanotubes are functionalized by plasma-induced non-equilibrium electrochemistry (PiNE) implemented through a simple direct current-based plasma-liquid system. This system utilizes the plasma-generated species in an electrolyte of 10 %vol ethanol in water, with or without a nitrogen precursor, for the oxygen and/or nitrogen functionalization of the carbon nanotube assembly. For this treatment, a ribbon-like piece of CNT was used as the anode and a helium plasma discharge triggered by applying 10 mA and 1 - 1.6 kV to act as the cathode. The plasma-generated species are then expected to migrate towards the CNTs and functionalize the sidewalls.The oxygen content is shown to be increased by between 70 % and 300 % when the treatment solution of 10 %vol ethanol is used in the ribbon electrode configuration. When ethylenediamine is added as a nitrogen precursor, the atomic concentration of nitrogen reaches 23 %, with amine groups, pyrrolic groups and graphitic nitrogen observed in the x-ray photoelectron spectra. This nitrogen content is unmatched in quantity when compared to either a simple soaking procedure or an electrolysis process with a platinum foil replacing the plasma as the counter-electrode. This demonstrates that the plasma either directly or indirectly, through plasma-generated species, facilitates and enhances the availability of nitrogen from the ethylenediamine precursor. The potential plasma-induced chemical pathways which lead to the functionalization of the CNTs are also investigated and discussed.In the application of a direct absorption solar collector system, it is found that the covalent functionalization provided by the plasma-liquid system enhances the stability of the CNT-ethylene glycol nanofluid, with the oxygen-functionalized samples producing the most stable nanofluids. This is explained through the lower value for contact angle measurements, suggesting greater hydrophobicity of the CNTs.References(1) Mallakpour, S.; Soltanian, S. Surface Functionalization of Carbon Nanotubes: Fabrication and Applications. RSC Adv. 2016, 6 (111), 109916–109935. https://doi.org/10.1039/c6ra24522f.(2) Williams, J.; Broughton, W.; Koukoulas, T.; Rahatekar, S. S. Plasma Treatment as a Method for Functionalising and Improving Dispersion of Carbon Nanotubes in Epoxy Resins. J. Mater. Sci. 2013, 48 (3), 1005–1013. https://doi.org/10.1007/s10853-012-6830-3.(3) Ham, S. W.; Hong, H. P.; Kim, J. H.; Min, S. J.; Min, N. K. Effect of Oxygen Plasma Treatment on Carbon Nanotube-Based Sensors. J. Nanosci. Nanotechnol. 2014, 14 (11), 8476–8481. https://doi.org/10.1166/jnn.2014.10007.(4) Hulicova-Jurcakova, D.; Seredych, M.; Lu, G. Q.; Bandosz, T. J. Combined Effect of Nitrogen- and Oxygen-Containing Functional Groups of Microporous Activated Carbon on Its Electrochemical Performance in Supercapacitors. Adv. Funct. Mater. 2009, 19 (3), 438–447. https://doi.org/10.1002/adfm.200801236.(5) Li, L.; Liu, E.; Shen, H.; Yang, Y.; Huang, Z.; Xiang, X.; Tian, Y. Charge Storage Performance of Doped Carbons Prepared from Polyaniline for Supercapacitors. J. Solid State Electrochem. 2011, 15 (1), 175–182. https://doi.org/10.1007/s10008-010-1087-8. Figure 1

Evaluation of the aqueous Fe (II) ion sorption capacity of functionalized microcrystalline cellulose

The absence of relevant functional groups, especially the oxygen-based groups, have been reported to strongly limit the metal binding capacity of native cellulose. Therefore, this study successfully introduced substantive oxygenous functional groups (C˭O, –OH, C–O, etc.) onto microcrystalline cellulose via functionalization with 1,2,3,4-Butanetetracarboxylic acid. The synthesized adsorbent (‘FM-cell’) was further utilized for aqueous iron (II) ion uptake. The adsorbent’s instrumental characterization (scanning electron microscopy, SEM; Energy dispersion X-ray, EDX; X-ray diffraction, XRD and Fourier-transform infrared spectroscopy, FTIR) result confirmed the presence of the oxygen-based functional groups and their relative structural crystallinity. Similarly, the effect of the process variable on the ‘FM-cell’ adsorption capacity was elucidated via batch mode. The Dubinin-Radushkevich and intraparticle diffusion models satisfactorily predicted the isotherm and kinetic data, respectively. The sorption mechanism postulated strong adsorbent-adsorbate electrostatic interaction occasioned by the large coordination number of Fe (II) ions. Thus, the surface oxygenous functional groups abundance significantly enhanced the metal binding capacity of ‘FM-cell’.

Tuning the Oxygen Content of Reduced Graphene Oxide and Effects on Its Properties.

The need to recover the graphene properties in terms of electrical and thermal conductivity calls for the application of reduction processes leading to the removal of oxygen atoms from the graphene oxide sheet surface. The recombination of carbon–carbon double bonds causes a partial recovery of the original graphene properties mainly limited by the presence of residual oxygen atoms and lattice defects. However, the loss of polar oxygen-based functional groups renders the material dispersibility rather complicated. In addition, oxygen-containing functional groups are reaction sites useful to further bind active molecules to engineer the reduced graphene sheets. For these reasons, a variety of chemical processes are described in the literature to reduce the graphene oxide. However, it is greatly important to select a chemical process enabling a thin modulation of the residual oxygen content thus tuning the properties of the final product. In this work, we will present a chemical-processing technique based on the hydroiodic acid to carefully control the degree of residual oxidation. Graphene oxides were reduced using hydroiodic acid with concentrations from 0.06 to 0.95 mol L–1. Their properties were characterized in detail and tested, and the results showed that their oxygen content was finely tuned from 33.6 to 10.7 atom %. This allows carefully tailoring the material properties with respect to the desired application, which is exemplified by the variation of the bulk resistance from 92 Ω to 14.8 MΩ of the film from the obtained rGO.