Oxygen-rich Functional Groups Research Articles

Competitive adsorption of H2O and CO2 on nitrogen-doped biochar with rich-oxygen functional groups

Competitive adsorption of H2O and CO2 on nitrogen-doped biochar with rich-oxygen functional groups

Construction of Chitosan-biochar/ZnO/NiO composites for efficient photocatalytic removal of Congo red and tetracycline

The combination of photocatalyst and biochar is an effective strategy to improve the overall photocatalytic activity, but it is still a challenge to find photocatalyst with excellent photocatalytic activity and biochar with large surface and rich oxygen functional groups. In this study, a novel CS-biochar/ZnO/NiO composite with adsorption-photocatalytic performance was constructed using chitosan as biochar source, and exploited for visible-light-driven photocatalytic degradation of tetracycline (TC) and Congo red (CR). The superior photocatalytic activity of CS-biochar/ZnO/NiO than pristine ZnO, NiO and CS-biochar/ZnO under visible light, and 63 %-CS/ZnO/NiO composite has the best photocatalytic activity. The photodegradation efficiency for CR was 94.5 % within 100 min, and the apparent rate constant (k) was 0.0206 min−1, which is about 1.87 and 3.89 times that ZnO and NiO, respectively. For TC, the photodegradation efficiency was 90 % within 45 min, and k was 0.0377 min−1, which is about 1.74 and 2.86 times that bare NiO and ZnO, respectively, which attribute to the synergistic effect between ZnO/NiO and CS-biochar improved the activity of photocatalysts. This work presents a straightforward approach for improving photocatalytic antibiotic and dye degradation through the construction of bifunctional "hybrid" material, which have great potential for application in the removal of contaminants.

Plant extract mediated in-situ synthesis of iron/manganese alginate hydrosphere and its excellent recovery of rare earth elements in mine wastewater

The recovery of rare earth elements (REEs) is a major issue based on environmental governance and sustainable resource utilization. In this study, we developed a novel hydrogel material (Fe/Mn@ALG) by anchoring Fe/Mn NPs on alginate spheres, where Fe/Mn NPs were in-situ synthesized using Euphorbia cochinchensi leaf extract as reduced and protection agents. The Fe/Mn@ALG was applied directly to real mine wastewater, generating efficient and selective recovery of REEs with the coexistence of numerous competing metal ions. As results have shown, Fe/Mn@ALG was a useful adsorbent for REEs with an adsorption efficiency 78.62 % achieved, which was also confirmed by distribution coefficients (Kd), up to 2451.66 mL·g−1. Furthermore, Fe/Mn@ALG exhibited preferential response to REEs over other metal ions with the separation factor (SF) being up to 240. This great adsorption performance and selectivity toward REEs were attributed to its specific surface area, oxygen-rich functional groups and negatively charged surface in acid wastewater. Furthermore, REEs could be greatly desorbed from Fe/Mn@ALG with output concentration being three times higher than the initial concentration. Additionally, Fe/Mn@ALG maintained its good adsorption performance with efficiency reaching 72.24 % after five reuses. Overall, Fe/Mn@ALG can be considered as a promising candidate for wastewater remediation and sustainable management of resources.

Production of hydrochar from the hydrothermal carbonisation of food waste feedstock for use as an adsorbent in removal of heavy metals from water

AbstractIn this research, discarded butternut peels were converted into hydrochar products through hydrothermal carbonisation (HTC), with adjustments made to the temperature (ranging from 180 to 260℃) and residence time (spanning 45–180 min). The findings indicated that both the temperature and time of carbonisation significantly influenced the yield of hydrochar (HC), as well as its physiochemical and structural properties. Higher temperatures and prolonged residence time led to decreased yield, elevated fixed carbon content and an increased fuel ratio. Furthermore, raising the process conditions increased HHV and reduced the oxygen-containing functional groups. The HC yield dropped from 28.75 to 17.58% with increased carbonisation temperature and time. The findings of this study also suggest that modified hydrochar is a promising material for removing heavy metals from wastewater. It is a relatively low-cost and abundant material that can be produced from various biomass feedstocks, including food waste. In addition, it is a sustainable and environmentally friendly option for wastewater treatment. Hydrochar-based systems offer several advantages over traditional methods of heavy metal removal, such as chemical precipitation and ion exchange. The unique physicochemical characteristics of hydrochar, including its porous structure and oxygen-rich functional groups, offer a high surface area and more binding sites for heavy metal ions. By changing the physicochemical properties of hydrochar with chemicals like phosphoric acid, it is possible to increase its adsorption capacity. The Freundlich isotherm was the best fit for the adsorption data for all three metal ions (Pb2+, Cu2+ and Cd2+), indicating that the adsorption process is multilayer and heterogeneous.

Binding between Cu2+/Zn2+ and aged polyethylene and polyethylene terephthalate microplastics in swine wastewaters: Adsorption behavior, and mechanism insights

Microplastics (MPs) have aroused growing environmental concerns due to their biotoxicity and vital roles in accelerating the spread of toxic elements. Illuminating the interactions between MPs and heavy metals (HMs) is crucial for understanding the transport and fate of HM-loaded MPs in specific environmentally relevant scenarios. Herein, the adsorption of copper (Cu2+) and zinc (Zn2+) ions over polyethylene (PE) and polyethylene terephthalate (PET) particulates before and after heat persulfate oxidation (HPO) treatment was comprehensively evaluated in simulated and real swine wastewaters. The effects of intrinsic properties (i.e., degree of weathering, size, type) of MPs and environmental factors (i.e., pH, ionic strength, and co-occurring species) on adsorption were investigated thoroughly. It was observed that HPO treatment expedites the fragmentation of pristine MPs, and renders MPs with a variety of oxygen-rich functional groups, which are likely to act as new active sites for binding both HMs. The adsorption of both HMs is pH- and ionic strength-dependent at a pH of 4–6. Co-occurring species such as humic acid (HA) and tetracycline (TC) appear to enhance the affinity of both aged MPs for Cu2+ and Zn2+ ions via bridging complexation. However, co-occurring nutrient species (e.g., phosphate and ammonia) demonstrate different impacts on the adsorption, improving uptake of Cu2+ by precipitation while lowering affinity for Zn2+ owing to the formation of soluble zinc-ammonia complex. Spectroscopic analysis indicates that the dominant adsorption mechanism mainly involves electrostatic interactions and surface complexation. These findings provided fundamental insights into the interactions between aged MPs and HMs in swine wastewaters and might be extended to other nutrient-rich wastewaters.

Enhancing solid-phase extraction of tetracyclines with a hybrid biochar sorbent: A comparative study of chlorella and bamboo biochars

Biochar, a sustainable sorbent derived from pyrolyzed biomass, has garnered attention for its efficacy in solid-phase extraction (SPE) of antibiotics, with a particular focus on tetracyclines (TCs). Despite its recognized potential, the intricate separation mechanisms operative in biochar-based SPE systems have not been fully deciphered. This investigation contrasts chlorella biochar against commercial bamboo biochar, harnessing an array of analytical methodologies-microstructure characterization, adsorption thermodynamics, competitive adsorption kinetics, H+ back titration, and selectivity adsorption studies-complemented by a Box-Behnken design for the optimization of chlorella/bamboo-SPE and subsequent application in the analysis of animal-derived foodstuffs. The study unveils that a hybrid sorbent, integrating nitrogen-doped microporous chlorella biochar with mesoporous bamboo biochar in a 95/5 mass ratio, markedly diminishes irreversible adsorption while enhancing selectivity, surpassing the performance of single biochar SPE systems. The elucidated separation mechanisms implicate a partition model, propelled by oxygen-rich functional groups on chlorella biochar and the rapid adsorption kinetics of bamboo biochar, all orchestrated by electrostatic interactions within the mixed biochar framework. Moreover, the synergy of mixed biochar-SPE with high-performance liquid chromatography (HPLC) demonstrates exceptional proficiency in detecting TCs in animal viscera, evidenced by recovery rates spanning 80.80 % to 106.98 % and RSDs ranging from 0.24 % to 14.69 %. In essence, this research not only sheds light on the multifaceted factors influencing SPE efficiency but also propels the use of biochar towards new horizons in environmental monitoring and food safety assurance.

High-load Ti3C2 MXene cathode through surface modification for degradable aqueous zinc-ion micro-supercapacitors with excellent energy density and anti-self-discharge

Micro Zn-ion supercapacitors (MZSCs) with excellent power density and safety are considered the most promising micro-energy storage devices. However, the energy density per unit area of these devices is insufficient to meet the requirements for portable/wearable electronics. Furthermore, traditional energy storage devices produce a large amount of e-waste, causing serious environmental hazards. To solve these problems, degradable MZSCs are proposed based on high-load surface-modified MXene (O-Ti3C2 MXene) cathodes and Zn/carbon nanotube (CNT) anodes. Owing to the advantages of their three-dimensional interconnected microstructures and abundant oxygen-rich functional groups, the thick O-Ti3C2 MXene electrodes show high rate performances and excellent Zn2+ diffusion kinetics. Therefore, MZSCs exhibit an extremely high energy density (384.90 μWh cm−2 at 0.30 mW cm−2) and power density (6.0 mW cm−2 at 126.84 μWh cm−2) and are degradable. More importantly, because of the strong adsorption capacity of the O-Ti3C2 MXene cathode for SO42− and the redox reaction of Zn/Zn2+ in the Zn/CNT anode, MZSCs have an extremely low self-discharge rate (1.92 mV h−1). This research is expected to provide a promising direction for next-generation, high-performance, anti-self-discharge and degradable devices.

Diminishing Self-Discharge of High-Loading Li-S Batteries with Oxygen-Rich Biomass Carbon Interlayers.

Lithium-sulfur batteries (Li-S) have possessed gratifying development in the past decade due to their high theoretical energy density. However, the severe polysulfide shuttling provokes undesirable self-discharge effect, leading to low energy efficiency in Li-S batteries. Herein, an interlayer composed of oxygen-rich carbon nanosheets (OCN) derived from bagasse is elaborated to suppress the shuttle effect and reduce the resultant self-discharge effect. The OCN interlayer is able to physically block the shuttling behavior of polysulfides and its oxygen-rich functional groups can strongly interact with polysulfides via O-S bonds to chemically immobilize mobile polysulfides. The self-discharge test for seven days further shows that the self-discahrge rate is diminished by impressive 93 %. As a result, Li-S batteries with the OCN interlayer achieve an ultrahigh discharge specific capacity of 710 mAh g-1 at a high mass loading of 7.18 mg. The work provides a facile method for designing functional interlayers and opens a new avenue for realizing Li-S batteries with high energy efficiency.

Study on Glyphosate Adsorption onto ZIF-8 Modified with Fe<sub>3</sub>O<sub>4</sub> Nanoparticles

Glyphosate (GLYPi) is an organophosphorus herbicide that behaves as an anionic substance in the aqueous phase. Even though it is stated as safe and non-toxic, the widespread use of GLYPi has raised environmental issues that need attention. This work used the positively charged metal-organic framework (MOF) of ZIF-8 to remove GLYPi via adsorption. Fe3O4 particles were hybridized with ZIF-8 to obtain Fe3O4@ZIF-8 via an in-situ deposition strategy to enhance the adsorption capacity toward GLYPi. The composite material (Fe3O4@ZIF-8) was characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction, revealing rhombic dodecahedron-shaped particles and oxygen-rich functional groups. The adsorption results show that there is a synergistic effect of adding Fe3O4 to ZIF-8 in increasing the rate and capacity of adsorption on GLYPi, that is 0.0012 g/mg·min (Pseudo-second-order) and 73.57 mg/g (Langmuir), respectively, on pH 7 and 50 °C. GLYPi adsorption by Fe3O4@ZIF-8 was not influenced by coexisting anions (e.g., Cl-, NO3-, SO42-, and HCO3-). The reusability study showed that the adsorption efficiency of GLYPi by Fe3O4@ZIF-8 decreased significantly after the first cycle, which should be considered a future challenge for further studies. The adsorption mechanisms of GLYPi by Fe3O4@ZIF-8 involve electrostatic interaction and pore-filling. The results indicate that Fe3O4@ZIF-8 is a promising candidate for removing organophosphate compounds, which could be an excellent strategy for environmental protection.

Boosting acetaminophen degradation in water by peracetic acid activation: A novel approach using chestnut shell-derived biochar at varied pyrolysis temperatures

In this study, biochar derived from chestnut shells was synthesized through pyrolysis at varying temperatures from 300 °C to 900 °C. The study unveiled that the pyrolysis temperature is pivotal in defining the physical and chemical attributes of biochar, notably its adsorption capabilities and its role in activating peracetic acid (PAA) for the efficient removal of acetaminophen (APAP) from aquatic environments. Notably, the biochar processed at 900 °C, referred to as CN900, demonstrated an exceptional adsorption efficiency of 55.8 mg g−1, significantly outperforming its counterparts produced at lower temperatures (CN300, CN500, and CN700). This enhanced performance of CN900 is attributed to its increased surface area, improved micro-porosity, and a greater abundance of oxygen-containing functional groups, which are a consequence of the elevated pyrolysis temperature. These oxygen-rich functional groups, such as carbonyls, play a crucial role in facilitating the decomposition of the O–O bond in PAA, leading to the generation of reactive oxygen species (ROS) through electron transfer mechanisms. This investigation contributes to the development of sustainable and cost-effective materials for water purification, underscoring the potential of chestnut shell-derived biochar as an efficient adsorbent and catalyst for PAA activation, thereby offering a viable solution for environmental cleanup efforts.

Tetracycline (TC) removal from wastewater with activated carbon (AC) obtained from waste grape marc: activated carbon characterization and adsorption mechanism

In this study, activated carbons were obtained from grape marc for tetracycline removal from wastewater. Activated carbons were obtained by subjecting them to pyrolysis at 300, 500, and 700 °C, respectively, and the effect of pyrolysis temperature on activated carbons was investigated. The physicochemical and surface properties of the activated carbons were evaluated by SEM, FTIR, XRD, elemental analysis, N2 adsorption/desorption isothermal, thermal gravimetric (TG) and derivative thermogravimetric (DTG), and BET surface area analysis. When the BET surface areas were examined, it was found that 4.25 m2/g for activated carbon was produced at 300 °C, 44.23 m2/g for activated carbon obtained at 500 °C and 44.23 m2/g at 700 °C, which showed that the BET surface areas increased with increasing pyrolysis temperatures. The pore volumes of the synthesized activated carbons were 0.0037 cm3/g, 0.023 cm3/g, and 0.305 cm3/g for pyrolysis temperatures of 300, 500, and 700 °C, respectively, while the average pore size was found to be 8.02 nm, 9.45 nm, and 10.29 nm, respectively. A better adsorption capacity was observed due to the decrease in oxygen-rich functional groups with increasing pyrolysis temperature. It was observed that the activated carbon obtained from grape skins can easily treat hazardous wastewater containing tetracycline due to its high carbon content and surface functional groups. It was also shown that the activated carbon synthesized in this study has a higher pore volume despite its low surface area compared to the studies in the literature. Thanks to the high pore volume and surface active groups, a successful tetracycline removal was achieved.Graphical

Correlated IR-SEM-TEM studies of three different grains from Ryugu: From the initial material to post-accretional processes

In order to better constrain the alteration history of the Ryugu parent body, we performed a multi-analytical study combining scanning electron microscopy, transmission electron microscopy and infrared spectroscopy on sections extracted from the three fragments A0064-FO019, A0064-FO021 and C0002-FO019 returned from Ryugu by the Hayabusa2 space mission. The three sections show large differences in terms of structure, mineralogy and infrared signature. Section A0064-FO019 resembles the major Ryugu lithology with the presence of both fine-grained phyllosilicates (fg-phyllos) with embedded nanosulfides and coarse-grained phyllosilicates (cg-phyllos), whereas section C0002-FO019 belongs to the group of the less altered lithologies with the presence of anhydrous minerals embedded in a partially amorphous matrix. Section A0064-FO021 also belongs to this group but shows two different lithologies, a compact amorphous one and a more porous and very fractured one showing the presence of Na-rich phosphate, calcite and olivine. The two less altered lithologies (sections A0064-FO021 and C0002-FO019) show the presence of numerous mineralogical features similar to those observed in cometary interplanetary dust particles, ultra-carbonaceous Antarctic micrometeorites or in the CM Paris meteorite, i.e. amorphous and partially crystallized matrix with GEMS-like ghosts objects, whisker olivine, phosphide, or FeNi metal. This supports an outer solar system origin common with that of cometary material for the Ryugu parent body. Combined with the results of Nakamura et al. (2022b) reporting the presence of a lithology showing the presence of GEMS-like objects, we propose that section C0002-FO019 represents the onset of aqueous alteration of such primitive materials. The cg-phyllos and fg-phyllos of section A0064-FO019, i.e. of the major Ryugu lithology, representing the advanced stage of alteration, exhibit distinctive IR signatures with a higher abundance of oxygen-rich functional groups in the organic matter (OM) from the cg-phyllos. We thus suggest the following chronology of formation and evolution for Ryugu: (1) accretion of highly porous aggregate of GEMS-like units with fine-grained high-temperature anhydrous silicates, (2) onset of alteration with the dissolution of primary nanosulfides and development of amorphous/partially crystallized material in the pores, (3) crystallization of fg-phyllos with a second generation of sulfides, (4) later formation of cg-phyllos devoid of nanosulfides and their associated oxygen-rich OM in a more water-rich environment.

How does adsorptive fractionation of dissolved black carbon on ferrihydrite affect its copper binding behaviors? A molecular-scale investigation

Adsorptive fractionation of dissolved black carbon (DBC) on minerals is proven to alter its molecular composition, which will inevitably affect the environment fate of heavy metals. However, the effects of molecular fractionation on the interaction between DBC and heavy metals remain unclear. Herein, we observed that the selective adsorption of ferrihydrite caused molecular changes of DBC from high molecular weight/unsaturation/aromaticity to low molecular weight/saturation/aliphatics. This process accompanied by a retention of carbohydrate and a reduction of oxygen-rich functional groups (e.g., polyphenols and carboxyl) and long carbon chain in DBC. The residual DBC in aqueous phase demonstrated a weaker binding affinity to copper compared to the original DBC. This decrease in binding affinity was primarily attributed to the adsorption of polycyclic condensed aromatic compounds of 200–250 Da, oxygen-rich polycyclic condensed aromatic compounds of 250–300 Da, oxygen-rich non-polycyclic aromatic compounds of 300–450 Da, and non-polycyclic aromatic compounds of 450–700 Da in DBC by ferrihydrite. Additionally, the retention of carbohydrates and aliphatic compounds of 300–450 Da also made a significant contribution. Notably, carboxylic groups rather than phenolic groups were the dominant oxygen-containing functional groups responsible for this affinity reduction. This study has significant implications for understanding of the biogeochemical processes of DBC at soil-water interface and surface water, especially its role in the transportation of heavy metals.

Role of oxygen functional groups and attachment of Au nanoparticles on graphene oxide sheets for improved photodetection performance.

Integrating low-dimensional graphene oxide (GO) with conventional Si technology offers innovative strategies for developing ultrafast wideband photodetectors. In this study, we synthesized GO and explored its potential application in broadband photodetection alongside silicon heterostructures. The as-synthesized GO contains various oxygen functional groups, as evidenced by X-ray photoelectron and Fourier transform infrared spectroscopy. These functional groups contribute to increased photo absorption, enhancing photodetection performance. The systematic reduction of these functional groups from the GO surface via thermal annealing decreases photo absorption and consequently lowers the photocurrent. This reduction diminishes photo absorption and amplifies the dark current by approximately 25 times, from 20 nA to 496 nA. This dark current increase is attributed to the electron mobility following the reduction of functional groups. However, attaching plasmonic gold nanoparticles (Au NPs) to the GO surface enhances UV-Vis absorption in the visible region, enabling broadband detection. The even distribution of attached Au NPs on the GO surface is confirmed through field emission transmission electron microscopy. While thermal annealing of GO diminishes the responsivity from 4.6 A W-1 to 3.0 A W-1, the attachment of Au NPs augments the responsivity by more than two-fold, reaching 10.0 A W-1. Thus, it highlights the importance of rich oxygen functional groups in GO and the attachment of Au NPs to achieve more efficient photo-sensing properties.

Carbon Microspheres with Cr(VI) Adsorption Performance were Prepared by In-situ Hydrothermal Carbonization Method

Biochar material is a renewable adsorbent widely used for treating contaminated wastewater. The hydrothermal carbon (HTC) were prepared from low polymeric sugars and low concentration glucose under hydrothermal carbonization reactions without using dispersants. The composition and structure of the biochar produced were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Raman spectroscopy (Raman), and N2 adsorption-desorption, indicating that amorphous graphitic carbon was obtained. Experimental results from the static adsorption of Cr(VI)-contaminated wastewater showed that HTCP-2 exhibited the highest adsorption capacity for Cr(VI), with a maximum adsorption capacity of 22.62 mg.g−1.The adsorption Cr(VI), MB, and RhB by the synthesized biochar all conformed to the pseudo-second-order kinetic model and Freundlich isotherm, suggesting a multilayer chemical adsorption process. Additionally, the synthesized HTC surface is enriched with a significant amount of oxygen-rich functional groups, which also has good adsorption performance for cationic dyes. Furthermore, the test results of fluorescence, photocurrent, and impedance indicate that HTCP-2 possesses the ability to generate and separate photoinduced charge carriers. This implied that HTCP-2 can be used for the preparation of adsorption photocatalysts, which effectively remove environmental pollutants through the synergistic effect of adsorption-photocatalysis. This study provides a research foundation for advancing water treatment technologies. Copyright © 2023 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Crystalline-amorphous Co/Co3O4 derived from a low-temperature etching of ZIF-67 for oxygen-invovled catalytic reactions

Development of a simple method for synthesizing transition metal-based bifunctional catalysts is of great importance in the context of oxygen-involved electrochemical energy conversion and storage devices. In this effort, electrochemical catalysts consisting of amorphous cobalt and cobalt oxides on graphene oxide (GO) were fabricated using a solvothermal process followed by etching ZIF-67 with oxygen-rich functional groups on GO (≈ 29 at. %) in a weak reduction atmosphere at 400 ℃. During the calcination process forming the ZIF-67@GO-based materials, exposed cobalt metal centers are created by partial vaporization and oxidation of ZIF-67. Also, metal ions are reduced to form Co and partially combine with oxygen from GO to generate amorphous Co3O4. Moreover, the porous framework structure of ZIF is retained under the mild calcination temperatures used. Benefiting from their porous framework and heteroatoms-doped composition, the ZIF-67@GO-based materials have low overpotentials of 319 mV at 10 mA cm−2 and high catalytic activities toward the oxygen evolution and oxygen reduction reactions in an alkaline electrolyte. In addition, the liquid zinc-air battery assembled with the ZIF-67@GO composite produced at a calcination temperature of 400 ℃ displays a high performance. Overall, the results demonstrate that the ZIF-67@GO composites have the potential to be high-performing catalysts in energy conversion devices. The readily controllable and high-yielding calcination method in this study is expected to serve as a model for new strategies to synthesize low-cost and efficient bifunctional electrocatalysts.

Olive Leaves-Derived Hierarchical Porous Carbon as Cathode Material for Anti-Self-Discharge Zinc-Ion Hybrid Capacitor.

As a promising low-cost and high-safety energy storage candidate, zinc-ion hybrid capacitors (ZIHCs) have received extensive attention. For maximizing the advantages of ZIHC with high energy density and high power density, the structural engineering of the porous carbon materials is the crucial and effective strategy. Herein, an oxygen-enriched hierarchical porous carbon has been fabricated from the pyrolysis of olive leaves combing the chemical activation. The abundant interfacial active sites and short ions/electrons transfer length endow the hierarchical porous carbon cathode with high ions adsorption capacity and fast kinetic behaviors. Meanwhile, the oxygen-rich functional groups can provide extra pseudocapacitance and improve the wettability and conductivity of porous carbon. Benefiting from these advantages, an anti-self-discharge ZIHC device with a high energy-power feature has been assembled. The electrochemical process is studied by ex situ X-ray diffraction (XRD) and scanning electron microscope (SEM) methods. Finally, an excellent energy density of 136.3W h kg-1 , and high power output of 20kW kg-1 , as well as long cycle life with 91% capacity retention over 20 000 cycles at 10 A g-1 are realized by as-assembled ZIHC.

The Surface acidity of freshly synthesized microplastics particles in simple electrolyte

The surface chemistry of sub-micron microplastics (MP) particles, specifically, the pH-dependent surface charge (or surface acidity), plays a role on the transport, transformation, and effect of contaminants in the aquatic environment. Little is known on the origin of surface charge and the quantification of surface acidity of MP. In this study, the surface charge of submicron particles of six major polymers, including low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), and polyethylene terephthalate (PET), was characterized in inert electrolytes, namely, NaClO4, NaCl, and NaNO3 for the elucidation of surface acidity. IR absorbance revealed that oxygen-rich functional groups were introduced during the resynthesis of MP particles, whose surface chemical structure consists of three main functional groups, i.e., carboxylic/ester, ether/alcohol, and aliphatic. Results show clearly that the zeta potential of MP particles was negatively charged in simple electrolytes at pH greater than ca. 2.0. Hydroxide ions adsorption on the non-polar aliphatic sites, and deprotonation of surface hydroxy group on the polar carboxylic/ester and ether/alcohol sites, contributed to the negative charges on MP surface. The surface acidity of selected MP particles was established in terms of acid strength (intrinsic acidity constants) and capacity (total surface site concentration) for the three distinct surface sites. Results also show the surface acid site density increases with hydration/hydrolysis time with rate constants of the polar surface sites, i.e., carboxylic/ester and ether/alcohol being 2.3 times greater than that of the non-polar aliphatic group.

Supercapacitors composed of Japanese cedar bark-based activated carbons with various activators

This study provided an overview of how pore structures and functional groups influence the electrochemical behaviors of activated carbons derived from a new type of biomass waste - Japanese cedar bark (JCB) with four different activators, i.e., KOH, K2CO3, H3PO4, and ZnCl2. Based on the chemical composition, microstructure, gas adsorption isotherms, and electrochemical analytical techniques, relationships between the pore structures, functional groups, and electrochemical behavior of the activated samples were assessed. The K2CO3 and KOH activated materials, designated KC-6 and KO-6, respectively, with an activation ratio of 6 (6 g an activator/1 g of JCB), were well rated for their electrochemical capabilities. At 10 mA g−1, these two samples had a specific capacitance of roughly 210 F g−1. The high electrochemical potential of KC-6 was attributed to a particular hierarchical structure comprised of micro-meso-macropores and rich oxygen functional groups on its surface, allowing faster ion diffusion and more effective ion adsorptions. Furthermore, in the case of the 1 M H2SO4 electrolyte, KO-6 had the largest specific surface area of 3000 cm2 g−1 and appropriate micropores (diameters (d) < 1.2 nm) for the electrolyte ion adsorptions, thus allowing this model to maintain an 80% specific capacitance for approximately 6500 Cyclic Voltammetry cycles at 1 mV s−1. The pore properties, functional groups, and electrochemical properties of the activated material derived from JCB can be controlled to some extent by the activator selections and experimental conditions.

SERS performance of silver nanoparticle/reduced graphene oxide-coated filter membranes

Polyvinylidene fluoride (PVDF), polyamide (Nylon) and anodic aluminum oxide (AAO) filter membranes were coated with in-situ synthesized silver nanoparticle/reduced graphene oxide (AgNP/rGO) nanocomposite by vacuum filtration, and surface-enhanced Raman scattering (SERS) performance of the prepared substrates was investigated using Rhodamine 6G (R6G) as a probe molecule. Analyte solutions were applied by drop casting and penetrated into the flexible PVDF and Nylon-based substrates within minutes, enabling very fast SERS measurements; however, this step took up to 2 hrs in the rigid AAO-based substrate. Scanning electron microscopy and Energy-dispersive X-ray spectroscopy mapping results showed that filter membrane surfaces were completely covered with AgNP/rGO nanocomposite at which AgNPs were uniformly distributed on rGO flakes; however, some large, partially reduced or unreduced GO flakes decorated with AgNP agglomerates (AgNP/GO) were also observed. Higher SERS signals were generally obtained from these AgNP/GO flakes compared to the AgNP/rGO coated regions, since they contain higher amount of oxygen-rich functional groups which enabled a higher chemical and electromagnetic enhancement in SERS signals. All the substrates could detect 10−7 M R6G even after being stored in a vacuum desiccator for 3 months, indicating that AgNP/rGO coated filter membranes are promising as stable SERS substrates thanks to their long shelf life.