Mesoporous graphene adsorbents for the removal of toluene and xylene at various concentrations and its reusability

Highly efficient isolation and purification of high-purity tea saponins from industrial camellia oil production by porous polymeric adsorbents

BACKGROUND

Recovery of high-purity tea saponin (TS), a promising non-ionic surfactant with well-documented properties, is one of the major challenges to broadening its industrial applications. In this study, an innovative and sustainable strategy for the highly-efficient purification of TS was developed by using well-designed highly-porous polymeric adsorbents.

RESULTS

The prepared Pp-A with controllable macropores (~96 nm) and appropriate surface hydrophobic properties was found more favorable for achieving high adsorption efficiency towards TS/TS-micelles. Kinetic results showed the adsorption follows the pseudo-second-order model (R2  = 0.9800), and the Langmuir model is more qualified to explicate the adsorption isotherms with Qe-TS  ~ 675 mg g-1 . Thermodynamic studies revealed the monolayer adsorption of TS was an endothermic process that was conducted spontaneously. Interestingly, ethanol-driven desorption (90% v/v ethanol) of TS was rapidly (< 30 min) complete due to the possible ethanol-mediated disassembling of TS-micelles. A possible mechanism that involves the interactions between the adsorbents and TS/TS-micelles, the formation and disassembling of TS-micelles was proposed to account for the highly efficient purification of TS. Afterwards, Pp-A-based adsorption method was developed to purify TS directly from industrial camellia oil production. Through selective adsorption, pre-washing, and ethanol-driven desorption, the applied Pp-A enabled the direct isolation of high-purity TS (~96%) with a recovery ratio > 90%. Notably, Pp-A exhibited excellent operational stability and is of high potential for long-term industrial application.

CONCLUSION

Results ensured the practical feasibility of the prepared porous adsorbents in purifying TS, and the proposed methodology is a promising industrial-scale purification strategy. © 2023 Society of Chemical Industry.

Biomass-assisted fabrication of rGO-AuNPs as surface-enhanced Raman scattering substrates for in-situ monitoring methylene blue degradation

Reduced graphene oxide-gold nanoparticles nanocomposites (rGO-AuNPs) with high surface-enhanced Raman scattering (SERS) activity was created by biomass-assisted green synthesis with Lilium casa blanca petals biomass for the first time, and its application for methylene blue (MB) degradation was explored through in-situ monitoring. Lilium casa blanca petals biomass was used as a reducing agent to reduce GO and chloroauric acid successively when carrying out rGO-AuNPs in-situ synthesis while it also acted as a capping agent. The produced rGO had oxygen-containing functional groups which had an outstanding performance in enhancing the SERS effect. Characterization results confirmed that the AuNPs were grafted onto the rGO sheet, and the mechanism study showed that total flavonoids in Lilium casa blanca petals biomass were the main biological compounds involved in the reduction. rGO-AuNPs had a high Raman enhancement factor (EF) which could reach 3.88 × 10⁷. The synthesized nanocomposite also had a good catalytic activity that could be employed as catalyst in MB degradation, and it could complete degradation within 15min. The reaction rate increased linearly with the amount of rGO-AuNPs, and the degradation could be in-situ monitored both by UV and SERS.

An immobilization of aminopropyl trimethoxysilane-phenanthrene carbaldehyde on graphene oxide for toluene extraction and separation in water samples

A new functionalized Nano graphene with aminopropyl trimethoxysilane-phenanthrene-4-carbaldehyde (NGO@APTMS-PNTCA) as a novel adsorbent was used to extract toluene from water samples by the ultrasound-assisted dispersive solid-phase microextraction procedure (USA-D-SPME). So, 50 mg of NGO@APTMS-PNTCA adsorbent was added to water samples and sonicated for 20 min. After toluene extraction, the NGO@APTMS-PNTCA adsorbent separated from the liquid phase with a Whatman membrane filter (200 nm). Then, the toluene was back-extracted from the adsorbent by 2.0 mL of the acetone/ethanol (1:1, eluent) at 25 °C. Due to the physical properties and structure of toluene, fluorobenzene was used as an internal standard. Finally, the toluene values were measured by a gas chromatography-flame ionization detector (GC-FID). In optimized conditions, the limit of detection (LOD), the working range (WR), and the enrichment factor (EF) were obtained at 2.5 μg L^-1, 0.01-1.2 mg L^-1, and 9.63, respectively (MRSD% = 3.38). Also, the limit of quantification (LOQ) 10 μg L^-1 and extraction recovery of more than 95% was efficiently achieved for toluene. Standard additions of toluene to blank solutions had high recoveries between 95.2% and 104.5% with a relative standard deviation (RSD%) of 0.27-5.2. The absorption capacities of NGO and NGO@APTMS-PNTCA adsorbents for toluene extraction were obtained at 32.8 mg g^-1 and 154.9 mg g^-1, respectively. The USA-D-SPME method was validated by spiking the standard concentrations of toluene. The proposed method demonstrated relevant and suitable statistical results with high accuracy and precision for toluene extraction by a novel adsorbent synthesis.

Turning a Novel Janus Electrospun Mat into an Amphiphilic Membrane with High Aromatic Hydrocarbon Adsorption Capacity

Aromatic hydrocarbons in water is one of the collateral effects of the petrochemical industry and represents a serious problem both for their toxicity and environmental contamination. In this work, an innovative amphiphilic membrane was developed capable of rapidly removing hydrocarbons (such as BTEX) present in water under the solubility limit. Firstly, a Janus nanostructured membrane was developed from the deposition of superhydrophobic carbonaceous nanoparticles (CNPs) synthesized by radiofrequency plasma polymerization on a hydrophilic electrospun poly(vinyl alcohol) mat. Secondly, this membrane was turned amphiphilic by UV exposure, allowing water to pass through. The surface properties of the membranes were studied through SEM, contact angle, and FTIR analysis. Dead-end experiments showed that the toluene and xylene selective sorption capacity reached the outstanding adsorption capacity of 647 mg/g and 666 mg/g, respectively, and that the membrane could be reused three times without efficiency loss. Furthermore, swelling of the PVA fibers prevented the liberation of NPs. The selective sorption capacity of the UV-exposed CNPs was explained by studying the interfacial energy relations between the materials at play. This work provides a simple, low-cost, and scalable technique to develop membranes with great potential for water remediation, including the removal of volatile organic compounds from produced water, as well as separating oil-in-water emulsions.

External Validation of a Breath-Based Prediction Model for Malignant Pleural Mesothelioma

Simple Summary

Malignant pleural mesothelioma (MPM) is an incurable asbestos-related thoracic cancer for which early-stage diagnosis remains a major challenge. Volatile organic compounds (VOCs), which are metabolites present in exhaled breath, have proven to be promising non-invasive biomarkers for MPM. However, without the necessary validation in an independent group of individuals, clinical implementation is hampered. Therefore, we performed external validation of a VOC-based prediction model for MPM, which initially revealed a poor performance and thus poor generalisability of the model. However, subsequent updating of the model improved its performance in the validation cohort, resulting in a more generalisable model with a screening potential, which could significantly impact MPM management.

Abstract

During the past decade, volatile organic compounds (VOCs) in exhaled breath have emerged as promising biomarkers for malignant pleural mesothelioma (MPM). However, as these biomarkers lack external validation, no breath test for MPM has been implemented in clinical practice. To address this issue, we performed the first external validation of a VOC-based prediction model for MPM. The external validation cohort was prospectively recruited, consisting of 47 MPM patients and 76 asbestos-exposed (AEx) controls. The predictive performance of the previously developed model was assessed by determining the degree of agreement between the predicted and actual outcome of the participants (patient/control). Additionally, to optimise the performance, the model was updated by refitting it to the validation cohort. External validation revealed a poor performance of the original model as the accuracy was estimated at only 41%, indicating poor generalisability. However, subsequent updating of the model improved the differentiation between MPM patients and AEx controls significantly (73% accuracy, 92% sensitivity, and 92% negative predictive value), substantiating the validity of the original predictors. This updated model will be more generalisable to the target population and exhibits key characteristics of a potential screening test for MPM, which could significantly impact MPM management.

Nanostructured micro/mesoporous graphene: removal performance of volatile organic compounds

In this study, we demonstrate an integrated synthesis strategy, which is conducted by the thermochemical process, consisting of pre- and post-activation by thermal treatment and KOH activation for the reduction of graphite oxide. A large number of interconnected pore networks with a micro/mesoporous range were constructed on a framework of graphene layers with a specific surface area of up to 1261 m2 g-1. This suggests a synergistic effect of thermally exfoliated graphene oxide (TEGO) on the removal efficiency of volatile organic compounds by generating pore texture with aromatic adsorbates such as benzene, toluene, and o-xylene (denoted as BTX) from an inert gaseous stream concentration of 100 ppm. As a proof of concept, TEGO, as well as pre- and post-activated TEGO, were used as adsorbents in a self-designed BTX gas adsorption apparatus, which exhibited a high removal efficiency of up to 98 ± 2%. The distinctive structure of TEGO has a significant effect on removal performance, which will greatly facilitate the strategy of efficient VOC removal configurations.

Atomically Dispersed Y or La on Birnessite-Type MnO2 for the Catalytic Decomposition of Low-Concentration Toluene at Room Temperature

Room-temperature catalytic decomposition of low-concentration volatile organic compounds (VOCs) in indoor air is an exciting dream to solve their pollution. Herein, two kinds of rare-earth elements (Y and La) were separately doped into birnessite-type MnO₂ nanosheets in the form of single atoms by the hydrothermal method. As-synthesized La/MnO₂ achieved 100% removal of 10 ppm toluene at 40 °C under the gas hourly space velocity of 60 L g^-1 h^-1, which was even somewhat better than the single Pt atom-doped MnO₂. In addition, La/MnO₂ showed the good durability at room temperature for 0.5 ppm toluene removal under the GHSV of 300 L g^-1 h^-1 and could be effectively regenerated at 105 °C. GC/FID, online-MS and TD-GC/MS analysis demonstrated that only ignorable trace benzene (∼3.4 ppb, < one thousandth of inlet toluene) was generated in the gas phase during catalytic decomposition of 10 ppm toluene at room temperature. This research sheds light on the development of low cost and high activity catalysts for low-concentration VOC oxidation at room temperature.

A critical review on silver nanoparticles: From synthesis and applications to its mitigation through low-cost adsorption by biochar

Silver nanoparticles are one of the most beneficial forms of heavy metals in nanotechnology applications. Due to its exceptional antimicrobial properties, low electrical and thermal resistance, and surface plasmon resonance, silver nanoparticles are used in a wide variety of products, including consumer goods, healthcare, catalysts, electronics, and analytical equipment. As the production and applications of silver nanoparticles containing products increase daily, the environmental pollution due to silver nanoparticles release is increasing and affecting especially the aqueous ecosystem. Silver nanoparticles can kill useful bacteria in soil and water, and bioaccumulate in living organisms even at low concentrations from 10^-2 to 10 μg/mL silver can show antibacterial effect. On the other hand, the maximum silver discharge limit into freshwater is 0.1 μg/L and 3.2 μg/L for Australia and the USA, respectively. To reduce its toxic consequences and meet the regulatory guidelines, it is crucial to remove silver nanoparticles from wastewater before it is discharged into other water streams. Several technologies are available to remove silver nanoparticles, but the adsorption process using low-cost adsorbents is a promising alternative to mitigate silver nanoparticle pollution in the bulk stage. As one of the low-cost adsorbents, biochar produced from the biomass waste could be a suitable adsorbent. This review focuses on collating the latest evidence on silver nanoparticle production, applications, environmental consequences, and cost-effective technological approaches for silver removal from wastewater.

The Effect of an Adsorbent Matrix on Recovery of Microorganisms from Hydrocarbon-Contaminated Groundwater

The microbial degradation of recalcitrant hydrocarbons is an important process that can contribute to the remediation of oil and gas-contaminated environments. Due to the complex structure of subsurface terrestrial environments, it is important to identify the microbial communities that may be contributing to biodegradation processes, along with their abilities to metabolize different hydrocarbons in situ. In this study, a variety of adsorbent materials were assessed for their ability to trap both hydrocarbons and microorganisms in contaminated groundwater. Of the materials tested, a porous polymer resin (Tenax-TA) recovered the highest diversity of microbial taxa in preliminary experiments and was selected for additional (microcosm-based) testing. Oxic and anoxic experiments were prepared with groundwater collected from a contaminated aquifer to assess the ability of Tenax-TA to adsorb two environmental hydrocarbon contaminants of interest (toluene and benzene) while simultaneously providing a surface for microbial growth and hydrocarbon biodegradation. Microorganisms in oxic microcosms completely degraded both targets within 14 days of incubation, while anoxically-incubated microorganisms metabolized toluene but not benzene in less than 80 days. Community analysis of Tenax-TA-associated microorganisms revealed taxa highly enriched in sessile hydrocarbon-degrading treatments, including Saprospiraceae, Azoarcus, and Desulfoprunum, which may facilitate hydrocarbon degradation. This study showed that Tenax-TA can be used as a matrix to effectively trap both microorganisms and hydrocarbons in contaminated environmental systems for assessing and studying hydrocarbon-degrading microorganisms of interest.

Field study on the improvement of indoor air quality with toluene adsorption finishing materials in an urban residential apartment

To improve the indoor air quality of apartments in Korea, a toluene adsorptive paint was manufactured and tested for its efficiency to remove the indoor toluene released from wallpaper adhesives. The toluene adsorptive paint was prepared by blending activated carbon and inorganic binder, and the pore characteristics and chemical functional groups of the activated carbon were analyzed to determine whether the micropores and surface functionalities of activated carbon affected toluene adsorption. Toluene adsorption performance of the toluene adsorptive paint was confirmed through static and verification experiments. The average adsorption efficiency of toluene adsorptive paint in the static experiment was 98.3% and the verification experiment confirmed that about 96.3% of toluene was adsorbed from the indoor air of the apartment. As a result, the use of toluene adsorptive paint effectively removes toluene, which may occur in the adhesive, and thus can be considered to have a good effect on the improvement of indoor air quality. Furthermore, toluene adsorptive paint has been found to be an effective way to achieve consumer wall finishing preferences and maintenance convenience.

Polymer-assisted synthesis and applications of hydroxyapatite (HAp) anchored nitrogen-doped 3D graphene foam-based nanostructured ceramic framework

In the present work, a hydroxyapatite anchored nitrogen-doped three-dimensional graphene (HAp-N3DG) skeletal network (foam) based nanostructured ceramic framework (CF) was developed through a polymer-assisted solvothermal route. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) studies reveal that the nano sized 0D HAp particles are anchored on the N3DG skeletal network with an average size of less than 50 nm. EDX and X-ray photoelectron spectroscopy (XPS) analysis confirmed the presence of Ca, P, O, N, and C. In addition, XPS analysis reveals the existence of N-C bonds in the prepared sample. The X-ray diffraction (XRD) patterns indicate the presence of hexagonal phase hydroxyapatite and the calculated average crystallite size was found to be 12 nm. The developed HAp-N3DG foam based nanostructured CF was found to have a mesoporous structure and the measured specific surface area (SSA) and the mean pore diameter were found to be 64.73 m2 g-1 and 23.6 nm, respectively. Electrochemical analysis shows that HAp anchored on nitrogen-doped 3D graphene foam based nanostructured CF has moderate electrochemical activity towards lithium ion charge/discharge. In addition, the prepared material showed adsorption activity values of 204.89 mg g-1 and 243.89 mg g-1 for the volatile organic compounds (VOCs) benzene and toluene, respectively. The present findings suggest that the newly developed HAp anchored nitrogen-doped 3DG (HAp-N3DG) skeletal network (foam) based nanostructured CF material can be used in energy devices and in the removal of volatile organic compounds. Moreover, the present study initiates a new kind of approach in energy device (lithium ion battery-LIB) research and in the removal of VOCs.

Regeneration of Activated Carbons Spent by Waste Water Treatment Using KOH Chemical Activation

In this study, spent activated carbons (ACs) were collected from a waste water treatment plant (WWTP) in Incheon, South Korea, and regenerated by heat treatment and KOH chemical activation. The specific surface area of spent AC was 680 m2/g, and increased up to 710 m2/g through heat treatment. When the spent AC was activated by the chemical agent potassium hydroxide (KOH), the surface area increased to 1380 m2/g. The chemically activated ACs were also washed with acetic acid (CH3COOH) to compare the effect of ash removal during KOH activation. The low temperature N2 adsorption was utilized to measure the specific surface areas and pore size distributions of regenerated ACs by heat treatment and chemical activation. The functional groups and adsorbed materials on ACs were also analyzed by X-ray photoelectron spectroscopy and X-ray fluorescence. The generated ash was confirmed by proximate analysis and elementary analysis. The regenerated ACs were tested for toluene adsorption, and their capacities were compared with commercial ACs. The toluene adsorption capacity of regenerated ACs was higher than commercial ACs. Therefore, it is a research to create high value-added products using the waste.