Leveraging wastewater surveillance for managing the spread of SARS-CoV-2 and concerned pathogens during FIFA World Cup Qatar 2022

Wastewater-based epidemiology (WBE) has been proven effective for the monitoring of infectious disease outbreaks during mass gathering events and for timely public health interventions. As part of Qatar's efforts to monitor and combat the spread of infectious diseases during the FIFA World Cup Qatar 2022™ (FWC'22), wastewater surveillance was used to monitor the spread of SARS-CoV-2, human enterovirus, and poliovirus. The screening covered five major wastewater treatment plants servicing the event locations between October 2022 and January 2023. Viruses were concentrated from the wastewater samples by PEG precipitation, followed by qRT-PCR to measure the viral load in the wastewater. As expected, SARS-CoV-2 and enterovirus RNA were detected in all samples, while poliovirus was not detected. The concentration of SARS-CoV-2 was correlated with population density, such as areas surrounding the World Cup venues, and with the number of reported clinical cases. Additionally, we observed temporal fluctuations in viral RNA concentrations, with peak levels coinciding with the group stage matches of the FWC'22. This study has been useful in providing public health authorities with an efficient and cost-effective surveillance system for potential infectious disease outbreaks during mega-events.

Microstructure investigation, Electrical properties, and γ-rays' protection capacity for ZnO doped clay ceramic

A series of ceramic samples fabricated based on ZnO doped different concentrations of natural clay according to the relation (1-x) ZnO - (x) clay; 5 wt% ≤ x ≤ 20 wt%. The samples were pressed and sintered at 1200 °C. The experimental techniques were used to characterize and measure the chemical composition, density, and current-voltage measurements for the fabricated ceramics samples. The measurements depict an increase in the I-V nonlinearity with raising the clay concentration, where the increase in clay by up to 20 wt% shifts breakdown voltage to a higher value of up to 390 V/cm and decreases leakage current to 55 mA/cm2. The examinations for the gamma-ray shielding capacity for the fabricated composites (utilizing Monte Carlo simulation) demonstrate enrichment of clay concentration between 5 wt% and 20 wt% reduced the linear attenuation coefficient for the fabricated ceramics by 23.15% and 8.66% at γ photon energy of 0.059 MeV and 1.252 MeV, respectively. The half-value thickness and lead's equivalent thickness increased along with a drop in the linear attenuation coefficient, but the radiation protection effectiveness of the fabricated ceramics increased.

An extensive assessment of the impacts of BaO on the mechanical and gamma-ray attenuation properties of lead borosilicate glass

The current work deals with the synthesis of a new glass series with a chemical formula of 5Al2O3-25PbO-10SiO2-(60-x) B2O3-xBaO; x was represented as 5, 10, 15, and 20 mol%. The FT-IR spectroscopy was used to present the structural modification by rising the BaO concentration within the synthesized glasses. Furthermore, the impacts of BaO substitution for B2O3 on the fabricated borosilicate glasses were investigated using the Makishima-Mackenzie model. Besides, the role of BaO in enhancing the gamma-ray shielding properties of the fabricated boro-silicate glasses was examined utilizing the Monte Carlo simulation. The mechanical properties evaluation depicts a reduction in the mechanical moduli (Young, bulk, shear, and longitudinal) by the rising of the Ba/B ratio in the fabricated glasses. Simultaneously, the micro-hardness boro-silicate glasses was reduced from 4.49 to 4.12 GPa by increasing the Ba2+/B3+ ratio from 0.58 to 3.18, respectively. In contrast, the increase in the Ba/B ratio increases the linear attenuation coefficient, where it is enhanced between 0.409 and 0.448 cm-1 by rising the Ba2+/B3+ ratio from 0.58 to 3.18, respectively. The enhancement in linear attenuation coefficient decreases the half-value thickness from 1.69 to 1.55 cm and the equivalent thickness of lead is also reduced from 3.04 to 2.78 cm, at a gamma-ray energy of 0.662 MeV. The study shows that the increase in the Ba2+/B3+ ratio enhances the radiation shielding capacity of the fabricated glasses however, it slightly degrades the mechanical properties of the fabricated glasses. Therefore, glasses with high ratios of Ba2+/B3+ have high gamma-ray shielding ability to be used in hospitals as a shielding material.

Marine Bacterial Community Structures of Selected Coastal Seawater and Sediment Sites in Qatar

Severe environmental conditions can have a diverse impact on marine microorganisms, including bacteria. This can have an inevitable impact on the biofouling of membrane-based desalination plants. In this work, we have utilized indicator bacteria such as total coliform, fecal coliform, and Pseudomonas aeruginosa, as well as 16S rRNA sequencing, to investigate the impact of environmental conditions and spatial variations on the diversity of bacterial communities in the coastal waters and sediments from selected sites in Qatar. The concentration levels of indicator bacteria were affected by increasing temperatures and pH, and by decreasing salinity of seawater samples. Diversity indices and the molecular phylogeny demonstrated that Proteobacteria, Bacteroidetes, and Cyanobacteria were the dominant phyla in all locations. The most abundant operational taxonomic units (OTUs) at the family level were from Flavobacteriaceae (27.07%, 4.31%) and Rhodobacteraceae (22.51%, 9.86%) in seawater and sediment, respectively. Alphaproteobacteria (33.87%, 16.82%), Flavobacteria (30.68%, 5.84%), and Gammaproteobacteria (20.35%, 12.45%) were abundant at the species level in both seawater and sediment, while Clostridia (13.72%) was abundant in sediment only. The results suggest that sediment can act as a reservoir for indicator bacteria, with higher diversity and lower abundance compared to seawater.

Application of human RNase P normalization for the realistic estimation of SARS-CoV-2 viral load in wastewater: A perspective from Qatar wastewater surveillance

The apparent uncertainty associated with shedding patterns, environmental impacts, and sample processing strategies have greatly influenced the variability of SARS-CoV-2 concentrations in wastewater. This study evaluates the use of a new normalization approach using human RNase P for the logic estimation of SARS-CoV-2 viral load in wastewater. SARS-CoV-2 variants outbreak was monitored during the circulating wave between February and August 2021. Sewage samples were collected from five major wastewater treatment plants and subsequently analyzed to determine the viral loads in the wastewater. SARS-CoV-2 was detected in all the samples where the wastewater Ct values exhibited a similar trend as the reported number of new daily positive cases in the country. The infected population number was estimated using a mathematical model that compensated for RNA decay due to wastewater temperature and sewer residence time, and which indicated that the number of positive cases circulating in the population declined from 765,729 ± 142,080 to 2,303 ± 464 during the sampling period. Genomic analyses of SARS-CoV-2 of thirty wastewater samples collected between March 2021 and April 2021 revealed that alpha (B.1.1.7) and beta (B.1.351) were among the dominant variants of concern (VOC) in Qatar. The findings of this study imply that the normalization of data allows a more realistic assessment of incidence trends within the population.

A critical overview of MXenes adsorption behavior toward heavy metals

In recent years, tremendous interest has been generated in MXenes as a fast-growing and diversified family of two-dimensional (2D) materials with a wide range of potential uses. MXenes exhibit many unique structural and physicochemical properties that make them particularly attractive as adsorbents for removing heavy metals from aqueous media, including a large surface area, abundant surface terminations, electron-richness, and hydrophilic nature. In light of the adsorption capabilities of MXenes at the ever-increasing rate of expansion, this review investigates the recent computational predictions for the adsorption capabilities of MXenes and the effect of synthesis of different MXene on their remediation behavior toward heavy metals. The influence of MXene engineering strategies such as alkalization, acidification, and incorporation into organic and inorganic hosts on their surface properties and adsorption capacity is compared to provide critical insights for designing effective MXene adsorbents. Additionally, the review discusses MXenes' adsorption mechanisms, the effect of coexisting ions on MXenes' selectivity, the regeneration of exhausted MXenes, and provides an overview of MXenes' stability and biocompatibility to demonstrate their potentiality for wastewater remediation. Finally, the review identifies current flaws and offers recommendations for further research.

Influence of Methomyl (Copter 90%) on certain biochemical activities and histological structures of land snails Monacha cartusiana

This manuscript was conducted to spotlight the toxic effect of two sub-lethal concentrations of Methomyl (Copter) LC₂₀ (0.075 g/L) and LC₄₀ (0.180 g/L) on some biochemical parameters and histological alterations for land snail Monacha Cartusiana (Muller, 1774). Land snails belong to the class Gastropoda and Phylum Mollusca. This study cleared that both the used concentrations (of Copter) caused a significant increase for activities of three enzymes: alkaline phosphatase (ALP), alanine amino transaminase (ALT), and Aspartate amino transaminase (AST) after 24, 48, and 72 h from exposure starting. In contrast, a total protein (TP) activity decreased at exposure for two concentrations at all lethality periods. Both concentrations of Copter (0.0.75 g/L and 0.180 g/L) have shown histological changes for land snail tissues after 96 h of exposure; digestive gland, hermaphrodite gland, foot, and mantle. Degeneration, rupture, and vacuolization for digestive cells have been shown; furthermore, hemolytic infiltration in connective tissue will be recognized for the digestive gland. The Oocyte and sperm show degenerated with deformation in the connective tissue of the hermaphrodite gland. Likewise, deformation in the muscle fiber layer of the foot in the land snail distorts the epidermis and mucus gland suffering from necrosis. Moreover, mantle shows rapture in epidermis layer, deformed in muscle fiber layer, and vacuolization and necrosis take place in mucus gland.

Enhanced water flux and bacterial resistance in cellulose acetate membranes with quaternary ammoniumpropylated polysilsesquioxane

An enhanced water flux and anti-fouling nanocomposite ultrafiltration membrane based on quaternary ammoniumpropylated polysilsesquioxane (QAPS)/cellulose acetate (QAPS@CA) was fabricated by in situ sol-gel processing via phase inversion followed by quaternization with methyl iodide (CH₃I). Membrane characterizations were performed based on the contact angle, FTIR, SEM, and TGA properties. Membrane separation performance was assessed in terms of pure water flux, rejection, and fouling resistance. The 7%QAPS@CA nanocomposite membrane showed an increased wettability (46.6° water contact angle), water uptake (113%) and a high pure water permeability of ∼370 L m^-2 h^-1 bar^-1. Furthermore, the 7%QAPS@CA nanocomposite membrane exhibited excellent bactericidal properties (∼97.5% growth inhibition) against Escherichia coli (E. coli) compared to the bare CA membrane (0% growth inhibition). The 7%QAPS@CA nanocomposite membrane can be recommended for water treatment and biomedical applications.

Efficient Photocatalytic Degradation of Organic Dyes by AgNPs/TiO2/Ti3C2T x MXene Composites under UV and Solar Light

Due to their broad applications in various industrial activities, and their well-known negative impacts on the aquatic environment, organic dyes have been continuously identified as serious threat to the quality of ecosystems. The photocatalytic degradation process in aqueous solutions has emerged as an efficient and reliable approach for the removal of organic dyes. MXenes, a new class of two-dimensional (2D) nanomaterials, possess unique chemical composition, surface functionalities, and physicochemical properties. Such characteristics enable MXenes to act as efficient catalysts or cocatalysts to photodegrade organic molecules. This work explores the application of Ti₃C₂T _x MXene decorated with silver and palladium nanoparticles, using a simple hydrothermal treatment method, for the photocatalytic degradation of methylene blue (MB) and rhodamine B (RhB). The chemical composition of these photocatalysts, as well as their structural properties and morphology, was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) techniques. The photocatalytic degradation abilities of the pristine MXene and the synthesized MXene composites were investigated under ultraviolet and solar light irradiation. A significant improvement in the photocatalytic performances was observed for all oxidized MXene composites when compared to pristine MXene, with a superior degradation efficiency achieved for AgNPs/TiO₂/Ti₃C₂T _x . This work broadens the application range of oxidized MXene composites, providing an alternative material for degrading organics dyes and wastewater treatment applications.

Antibacterial Mechanism of Multifunctional MXene Nanosheets: Domain Formation and Phase Transition in Lipid Bilayer

MXenes, two-dimensional metal carbides or nitrides with multifunctional surfaces, are one of the most promising antibacterial nanoscale materials. However, their putative bactericidal mechanism is elusive. To study their bactericidal mechanism, we investigated the interaction between a MXene nanosheet and a model bacterial membrane by molecular dynamics simulations and found that an adsorbed MXene on a membrane surface induced a local phase transition in a domain where the fluidity of the phospholipid in this domain at room temperature was comparable with that of the gel phase. The domain also showed a denser and thinner phospholipid membrane structure than the peripheral phospholipids. By comparing it with our previous experiments of the bactericidal activity of MXenes, we proposed the leakage of intercellular molecules at the phase boundary defects as a possible bactericidal mechanism of MXenes that leads to cell lysis. This study provides a useful model for tailoring new bactericidal nanomaterials.

COVID-19 (SARS-CoV-2) outbreak monitoring using wastewater-based epidemiology in Qatar

Raw municipal wastewater from five wastewater treatment plants representing the vast majority of the Qatar population was sampled between the third week of June 2020 and the end of August 2020, during the period of declining cases after the peak of the first wave of infection in May 2020. The N1 region of the SARS-CoV-2 genome was used to quantify the viral load in the wastewater using RT-qPCR. The trend in Ct values in the wastewater samples mirrored the number of new daily positive cases officially reported for the country, confirmed by RT-qPCR testing of naso-pharyngeal swabs. SARS-CoV-2 RNA was detected in 100% of the influent wastewater samples (7889 ± 1421 copy/L - 542,056 ± 25,775 copy/L, based on the N1 assay). A mathematical model for wastewater-based epidemiology was developed and used to estimate the number of people in the population infected with COVID-19 from the N1 Ct values in the wastewater samples. The estimated number of infected population on any given day using the wastewater-based epidemiology approach declined from 542,313 ± 51,159 to 31,181 ± 3081 over the course of the sampling period, which was significantly higher than the officially reported numbers. However, seroprevalence data from Qatar indicates that diagnosed infections represented only about 10% of actual cases. The model estimates were lower than the corrected numbers based on application of a static diagnosis ratio of 10% to the RT-qPCR identified cases, which is assumed to be due to the difficulty in quantifying RNA losses as a model term. However, these results indicate that the presented WBE modeling approach allows for a realistic assessment of incidence trend in a given population, with a more reliable estimation of the number of infected people at any given point in time than can be achieved using human biomonitoring alone.

Unprecedented environmental and energy impacts and challenges of COVID-19 pandemic

The rapid transmission tendency, severity, and wide geographical spread of newly emerged novel coronavirus (SARS-CoV-2) in different environmental matrices, including water, air, and soil, has posed severe health, environmental, energy, and economic challenges worldwide. Despite the severe health effects, unprecedented improvements in air quality in many countries due to emergency measures, and public behavior changes have been reported. SARS-CoV-2 has been detected in air and sewage samples in several studies across the globe. The use of wastewater-based epidemiology (WBE) could be a valuable method to monitor the outbreak of COVID-19, which requires fast and reliable methods for virus detection in sewage. However, water treatment companies face many pressures due to potential for aerosolization, PPE shortages, and changed usage patterns. In addition, the unprecedented impact of the COVID-19 outbreak on the worldwide economy especially the energy sector, and its impact on our ecosystem required instant responses. This article discusses the recent developments and challenges faced in water, air, and energy resources, including renewables and non-renewables as the significant and interrelated components of the ecosystem. Furthermore, some recommendations have been directed, which may serve as a guideline to the scientists, legislators, and other stakeholders. A future roadmap has been proposed to overcome the tragic effects of COVID-19 and developing a sustainable environmental system to minimize the impact of such infectious outbreaks in the future.

Investigation of the gamma ray shielding properties for polyvinyl chloride reinforced with chalcocite and hematite minerals

Polyvinyl chloride (PVC) is the most widely produced synthetic plastic polymer in the world: it has a variety of applications due to its low cost, elasticity, light weight, good mechanical characteristics and corrosion resistance. In order to protect living beings from harmful radiation such as gamma rays, novel low-cost chalcocite and hematite-based PVCs were fabricated for shielding purposes. The mass attenuation coefficient μ_m for various fabricated hematite and chalcocite-based PVCs was calculated using MCNP-5 code. The results were compared with the values calculated theoretically using XCOM software between 0.015 and 15 MeV. Moreover, the simulated μ_m parameter for chalcocite/PVC and hematite/PVC was used to calculate other shielding factors, such as the half value layer (HVL), the mean free path (MFP) effective atomic number Z_eff, the geometric-progress (G-P) fitting parameters and the exposure buildup factor (EBF). The simulated data of μ_m for all composites is comparable to that obtained from a theoretical calculation. The results showed that the addition of hematite and chalcocite enhance the μ_m of PVC polymers. We also found that the μ_m of chalcocite/PVC is higher than that of hematite/PVC due to the copper content in the former.

Large interlayer spacing Nb4C3Tx (MXene) promotes the ultrasensitive electrochemical detection of Pb2+ on glassy carbon electrodes

Large interlayer spacing Nb₄C₃T_x (MXene) promotes the ultrasensitive electrochemical detection of Pb²⁺ on glassy carbon electrodes

Simulation studies for gamma ray shielding properties of Halloysite nanotubes using MCNP-5 code

Halloysite clay is a mineral found in natural and it has many applications in chemistry (for catalytic and extraction) and also in the medical field (for drugs delivery), so it is important to study the shielding properties of natural and modified nanotube Halloysite. The mass attenuation coefficient was simulated for natural Halloysite clay mineral and four others modified halloysite nanotubes using MCNP 5 code for incident gamma ray energies between 0.015 and 15 MeV. The mass attenuation coefficient was also calculated using the XCOM database for studied samples in the same energy range. The results obtained by the MCNP simulation were close to those obtained by XCOM calculation. Moreover, other shielding properties that described the interaction of incident gamma rays with Halloysite composites, such as the HVL, MFP, Z_eff, and N_eff were calculated using the simulated μ_m for gamma rays between 0.015 and 15 MeV.

Plasmonic MXene-based nanocomposites exhibiting photothermal therapeutic effects with lower acute toxicity than pure MXene

Purpose: Here, we fabricated two plasmonic 2D Ti₃C₂T_x-based nanocomposites (Au/MXene and Au/Fe₃O₄/MXene) with similarly high anti-cancer photothermal therapy (PTT) capabilities, but with less in vivo toxicity than a pure MXene. Methods: Au/MXene was synthesized by in situ reduction of tetrachloroauric acid using NaBH₄ on Ti₃C₂T_x flakes. For targeted PTT, magnetic Au/Fe₃O₄/MXene was synthesized via a reaction between freshly prepared magnetite Fe₃O₄ NPs and MXene solution, followed by in situ integration of gold nanoparticles (AuNPs). Results: Morphological characterization by XRD, SEM, and TEM revealed the successful synthesis of Au/MXene and Au/Fe₃O₄/MXene. Both new composites exhibited a significant in vitro dose-dependent PTT effect against human breast cancer cells MCF7. Interestingly, in vivo acute toxicity assays using zebrafish embryos indicated that Au/MXene and Au/Fe₃O₄/MXene had less embryonic mortality (LC₅₀ ≫ 1000 µg/mL) than pure MXene (LC₅₀=257.46 µg/mL). Conclusion: Our new Au/MXene and Au/Fe₃O₄/MXene nanocomposites could be safer and more suitable than the pure MXene for biomedical applications, especially when targeted PTT is warranted.

A flexible Ti3C2Tx (MXene)/paper membrane for efficient oil/water separation

The scalable fabrication of flexible membranes for efficient oil/water separation is in high demand but still significantly underdeveloped. Here, we present a flexible membrane using Ti₃C₂T_x (MXene) as the functional layer on conventional print paper as the substrate. With a simple coating process using MXene ink, we developed a highly hydrophilic and oleophobic membrane with an underwater oil contact angle of 137°. Such a simple membrane shows outstanding flexibility and robustness, and demonstrates a facile approach for membrane scale-up using MXene ink on low-cost print paper. The membrane shows high separation efficiency for oil/water emulsions, of over 99%, and a high water permeation flux of over 450 L per m² per h per bar. We demonstrate the excellent anti-fouling property of this membrane by cleaning the membranes without chemicals. These low-cost, highly efficient, anti-fouling membranes can provide new opportunities for industrial oil/water separation applications.

A highly hydrophilic and oleophobic membrane based on Ti₃C₂T_x (MXene) coated paper demonstrated high separation efficiency for oil/water emulsions with excellent antifouling properties.

Natural clay-supported palladium catalysts for methane oxidation reaction: effect of alloying

Bimetallic Pd-supported halloysite nanotubes revealed outstanding catalytic activity towards catalytic methane oxidation especially PdNi.

Effect of Synthesis on Performance of MXene/Iron Oxide Anode Material for Lithium-Ion Batteries

Two-dimensional heterostructures, such as Fe₂O₃/MXene nanoparticles, can be attractive anode materials for lithium-ion batteries (LIBs) due to the synergy between high lithium-storage capacity of Fe₂O₃ and stable cyclability and high conductivity provided by MXene. Here, we improved the storage performance of Ti₃C₂T _x (MXene)/Fe₂O₃ nanocomposite by confining Fe₂O₃ nanoparticles into Ti₃C₂T _x nanosheets with different mixing ratios using a facile and scalable dry ball-milling process. Composites of Ti₃C₂T _x-25 wt % Fe₂O₃ and Ti₃C₂T _x-50 wt % Fe₂O₃ synthesized by ball-milling resulted in uniform distribution of Fe₂O₃ nanoparticles on Ti₃C₂T _x nanosheets with minimum oxidation of MXene as compared to composites prepared by hydrothermal or wet sonication. Moreover, the composites demonstrated minimum restacking of the nanosheets and higher specific surface area. Among all studied composites, the Ti₃C₂T _x-50 wt % Fe₂O₃ showed the highest reversible specific capacity of ∼270 mAh g^-1 at 1C (∼203 mAh g^-1 based on the composite) and rate performance of 100 mAh g^-1 at 10C. This can open the door for synthesizing stable and high-performance MXene/transition metal oxide composites with significantly enhanced electrochemical performance for LIB applications.

Graphene nanoplatelet doping of P3HT:PCBM photoactive layer of bulk heterojunction organic solar cells for enhancing performance

Hybrid organic photovoltaic (OPV) cells based on conjugated polymer photoactive materials are promising candidates for flexible, high-performance and low-cost energy sources owing to their inexpensive materials, cost-effective processing and ease of fabrication by simple solution processes. However, the modest PV performance obtained to date-in particular the low power conversion efficiency (PCE)-has impeded the large scale deployment of OPV cells. The low PCE in OPV solar cells is mainly attributed to the low carrier mobility, which is closely correlated to the transport diffusion length of the charge carriers within the photoactive layers. The 2D graphene material could be an excellent candidate for assisting charge transport improvement in the active layer of OPV cells, due to its huge carrier mobility, thermal and chemical stability, and its compatibility with the solution process. In this work, we report on the improvement of the optoelectronic properties and photovoltaic performance of graphene nanoplatelet (GNP)-doped P3HT:PCBM photoactive blended layers, integrated into a bulk heterojunction (BHJ) organic-photovoltaic-based device, using PEDOT:PSS on an ITO/glass substrate. First, the light absorption capacity was observed to increase with respect to the GNP content, while the photoluminescence showed clear quenching, indicating electron transfer between the graphene sheets and the polymeric matrix. Then, the incorporation of GNP into the BHJ active layer resulted in enhanced PV performance with respect to the reference cell, and the best PV performance was obtained with 3 wt.% of GNP loading, with an open-circuit voltage of 1.24 V, a short-circuit current density value of 6.18 mA cm^-2, a fill factor of 47.12%, and a power conversion efficiency of about 3.61%. We believe that the obtained results contribute to the development of organic photovoltaic devices and to the understanding of the impact of sp²-bonded carbon therein.

Mercuric ion capturing by recoverable titanium carbide magnetic nanocomposite

Two-dimensional metal carbides and nitrides (MXenes) have attracted increasing attention for application in water/wastewater treatment. The functionalization of MXenes to increase their stability while demonstrating high pollutant removal can facilitate sustainable water/wastewater treatment processes. In this study, the highly stable magnetic titanium carbide (Ti₃C₂T_x) MXene nanocomposite (MGMX nanocomposite) was successfully synthesized through a facile hydrothermal approach and was tested for aqueous-phase adsorptive removal of mercuric ions. The synthesized MGMX nanocomposite was studied using characteristic analyses, showing high stability as revealed by zeta-potential analysis and dynamic light-scattering technique. The MGMX nanocomposite presented excellent Hg(II) removal in a wide range of pH conditions, and an exceptional maximum experimental Hg(II) uptake capacity of 1128.41mgg^-1 was observed. The adsorption behavior was investigated using the Redlich-Peterson adsorption isotherm, pseudo second-order kinetics, and thermodynamics models. In the adsorption/desorption investigation, the MGMX nanocomposite was reusable for up to five cycles of adsorption/desorption. The stability, hydrophilic nature, available adsorptive surfaces, and easy separation after reaction make the MGMX nanocomposite an efficient sorbent for the removal of toxic Hg(II) for water purification.

Controlled design of PtPd nanodendrite ornamented niobium oxynitride nanosheets for solar-driven water splitting

A facile road-map is developed for one-pot synthesis of PtPd nanodendrite ornamented niobium oxynitride nanosheets for efficient solar-driven water splitting.

2D Ti3C2Tx (MXene)-reinforced polyvinyl alcohol (PVA) nanofibers with enhanced mechanical and electrical properties

Novel 2D Ti3C2Tx (MXene)-reinforced polyvinyl alcohol (PVA) nanofibers have been successfully fabricated by an electrospinning technique. The high aspect ratio, hydrophilic surfaces, and metallic conductivity of delaminated MXene nanosheet render it promising nanofiller for high performance nanocomposites. Cellulose nanocrystals (CNC) were used to improve the mechanical properties of the nanofibers. The obtained electrospun nanofibers had diameter from 174 to 194 nm depending on ratio between PVA, CNC and MXene. Dynamic mechanical analysis demonstrated an increase in the elastic modulus from 392 MPa for neat PVA fibers to 855 MPa for fibers containing CNC and MXene at 25°C. Moreover, PVA nanofibers containing 0.14 wt. % Ti3C2Tx exhibited dc conductivity of 0.8 mS/cm conductivity which is superior compared to similar composites prepared using methods other than electrospinning. Improved mechanical and electrical characteristics of the Ti3C2Tx /CNC/PVA composites make them viable materials for high performance energy applications.

Efficient Antibacterial Membrane based on Two-Dimensional Ti3C2Tx (MXene) Nanosheets

Advanced membranes that enable ultrafast water flux while demonstrating anti-biofouling characteristics can facilitate sustainable water/wastewater treatment processes. MXenes, two-dimensional (2D) metal carbides and nitrides, have attracted attention for applications in water/wastewater treatment. In this work, we reported the antibacterial properties of micrometer-thick titanium carbide (Ti₃C₂T_x) MXene membranes prepared by filtration on a polyvinylidene fluoride (PVDF) support. The bactericidal properties of Ti₃C₂T_x modified membranes were tested against Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis) by bacterial growth on the membrane surface and its exposure to bacterial suspensions. The antibacterial rate of fresh Ti₃C₂T_x MXene membranes reaches more than 73% against B. subtilis and 67% against E. coli as compared with that of control PVDF, while aged Ti₃C₂T_x membrane showed over 99% growth inhibition of both bacteria under same conditions. Flow cytometry showed about 70% population of dead and compromised cells after 24 h of exposure of both bacterial strains. The damage of the cell surfaces was also revealed by scanning electron microscopy (SEM) and atomic force microscopy (AFM) analysis, respectively. The demonstrated antibacterial activity of MXene coated membranes against common waterborne bacteria, promotes their potential application as anti-biofouling membrane in water and wastewater treatment processes.

Electrochemical performance of Ti3C2Tx MXene in aqueous media: towards ultrasensitive H2O2 sensing

An extensive characterization of pristine and oxidized Ti₃C₂T_x (T: =O, -OH, -F) MXene showed that exposure of MXene to an anodic potential in the aqueous solution oxidizes the nanomaterial forming TiO₂ layer or TiO₂ domains with subsequent TiO₂ dissolution by F^- ions, making the resulting nanomaterial less electrochemically active compared to the pristine Ti₃C₂T_x. The Ti₃C₂T_x could be thus applied for electrochemical reactions in a cathodic potential window i.e. for ultrasensitive detection of H₂O₂ down to nM level with a response time of approx. 10 s. The manuscript also shows electrochemical behavior of Ti₃C₂T_x modified electrode towards oxidation of NADH and towards oxygen reduction reactions.

Antibacterial Activity of Ti₃C₂Tx MXene

MXenes are a family of atomically thin, two-dimensional (2D) transition metal carbides and carbonitrides with many attractive properties. Two-dimensional Ti3C2Tx (MXene) has been recently explored for applications in water desalination/purification membranes. A major success indicator for any water treatment membrane is the resistance to biofouling. To validate this and to understand better the health and environmental impacts of the new 2D carbides, we investigated the antibacterial properties of single- and few-layer Ti3C2Tx MXene flakes in colloidal solution. The antibacterial properties of Ti3C2Tx were tested against Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis) by using bacterial growth curves based on optical densities (OD) and colonies growth on agar nutritive plates. Ti3C2Tx shows a higher antibacterial efficiency toward both Gram-negative E. coli and Gram-positive B. subtilis compared with graphene oxide (GO), which has been widely reported as an antibacterial agent. Concentration dependent antibacterial activity was observed and more than 98% bacterial cell viability loss was found at 200 μg/mL Ti3C2Tx for both bacterial cells within 4 h of exposure, as confirmed by colony forming unit (CFU) and regrowth curve. Antibacterial mechanism investigation by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) coupled with lactate dehydrogenase (LDH) release assay indicated the damage to the cell membrane, which resulted in release of cytoplasmic materials from the bacterial cells. Reactive oxygen species (ROS) dependent and independent stress induction by Ti3C2Tx was investigated in two separate abiotic assays. MXenes are expected to be resistant to biofouling and offer bactericidal properties.

Nanoplasmonic Raman detection of bromate in water

The possibility of using surface enhanced Raman scattering (SERS) detection method for bromate-anion determination and quantitative evaluation in water has been demonstrated for the first time. The decreasing of Rhodamine 6G (R6G) Raman peaks intensity has been used as the analytical signal corresponding to the catalytic oxidation by bromate. Electrostatically immobilized silver nanoparticles have been proven as efficient SERS-active substrate. A linear relationship between the Raman intensity of Rh6G as a function of BrO(3)(-) was observed in the range of 0 - 10(-7) М and the detect limit was as low as 10(-10) M (nearly 0.01 μg/L). The results prove the potential of the proposed method for further application in the development of new portable SERS-based sensors for drinking water monitoring with high sensitivity, simplicity and the low cost.

Influence of co-substrate on textile wastewater treatment and microbial community changes in the anaerobic biological sulfate reduction process

This study investigated the anaerobic treatment of sulfate-rich synthetic textile wastewater in three sulfidogenic sequential batch reactors (SBRs). The experimental protocol was designed to examine the effect of three different co-substrates (lactate, glucose, and ethanol) and their concentrations on wastewater treatment performance. Sulfate reduction and dye degradation were improved when lactate and ethanol were used as electron donors, as compared with glucose. Moreover, under co-substrate limited concentrations, color, sulfate, and chemical oxygen demand (COD) removal efficiencies were declined. By reducing co-substrate COD gradually from 3000 to 500 mg/L, color removal efficiencies were decreased from 98.23% to 78.46%, 63.37%, and 69.10%, whereas, sulfate removal efficiencies were decreased from 98.42%, 82.35%, and 87.0%, to 30.27%, 21.50%, and 10.13%, for lactate, glucose, and ethanol fed reactors, respectively. Fourier transform infrared spectroscopy (FTIR) and total aromatic amine analysis revealed lactate to be a potential co-substrate for further biodegradation of intermediate metabolites formed after dye degradation. Pyrosequencing analysis showed that microbial community structure was significantly affected by the co-substrate. The reactor with lactate as co-substrate showed the highest relative abundance of sulfate reducing bacteria (SRBs), followed by ethanol, whereas the glucose-fed reactor showed the lowest relative abundance of SRB.

Charge- and Size-Selective Ion Sieving Through Ti3C2Tx MXene Membranes

Nanometer-thin sheets of 2D Ti3C2Tx (MXene) have been assembled into freestanding or supported membranes for the charge- and size-selective rejection of ions and molecules. MXene membranes with controllable thicknesses ranging from hundreds of nanometers to several micrometers exhibited flexibility, high mechanical strength, hydrophilic surfaces, and electrical conductivity that render them promising for separation applications. Micrometer-thick MXene membranes demonstrated ultrafast water flux of 37.4 L/(Bar·h·m(2)) and differential sieving of salts depending on both the hydration radius and charge of the ions. Cations with a larger charge and hydration radii smaller than the interlayer spacing of MXene (∼6 Å) demonstrate an order of magnitude slower permeation compared to single-charged cations. Our findings may open a door for developing efficient and highly selective separation membranes from 2D carbides.

Sensitive Detection of ssDNA Using an LRET-Based Upconverting Nanohybrid Material

Water-dispersible, optical hybrid nanoparticles are preferred materials for DNA biosensing due to their biocompatibility. Upconverting nanoparticles are highly desirable optical probes in sensors and bioimaging owing to their sharp emission intensity in the visible region. We herein report a highly sensitive ss-DNA detection based on an energy transfer system that uses a nanohybrid material synthesized by doping NaYF4:Tm(3+)/Yb(3+) upconverting nanoparticles (UCNPs) on silica coated polystyrene-co-acrylic acid (PSA) nanoparticles (PSA/SiO2) as the donor, and gold nanoparticles (AuNPs) decorated with Ir(III) complex as the acceptor. UCNPs tagged on PSA/SiO2 and the cyclometalated Ir(III)/AuNP conjugates were then linked through the ss-DNA sequence. Sequential addition of the target DNA to the probe molecular beacon complex resulted in the separation of the optical nanohybrid material and the quencher, leading to a measurable increase in the blue fluorescence emission intensity. Our results have shown a linear relationship between the fluorescence intensity and target DNA concentration down to the picomolar.

Conditions for spontaneous oil–water separation with oil–water separators

A theory is proposed for the selection of the nature of the separator for spontaneous oil–water separation from oil-in-water and water-in-oil systems.

Selective electrochemical detection of 2,4,6-trinitrotoluene (TNT) in water based on poly(styrene-co-acrylic acid) PSA/SiO2/Fe3O4/AuNPs/lignin-modified glassy carbon electrode

A new versatile electrochemical sensor based on poly(styrene-co-acrylic acid) PSA/SiO2/Fe3O4/AuNPs/lignin (L-MMS) modified glassy carbon electrode (GCE) was developed for the selective detection of trace trinitrotoluene (TNT) from aqueous media with high sensitivity. The fabricated magnetic microspheres were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). L-MMS films were cast on the GCE surface to fabricate the TNT sensing electrode. The limit of detection (LOD) of TNT determined by the amperometric i-t curve reached 35 pM. The lignin film and well packed Fe3O4/AuNPs facilitated the pre-concentration of trace TNT on the electrode surface resulting in a fast amperometric response of 3 seconds near the detection limit. The high sensitivity and excellent catalytic activity of the modified electrode could be attributed to the lignin layer and highly packed Fe3O4/AuNPs on the electrode surface. The total recovery of TNT from tapwater and seawater matrices was 98% and 96%, respectively. The electrode film was highly stable after five repeated adsorption/desorption cycles. The new electrochemical sensing scheme provides a highly selective, sensitive and versatile assay for the in-situ detection of TNT in complex water media.

Fe3O4/Au nanoparticles/lignin modified microspheres as effectual surface enhanced Raman scattering (SERS) substrates for highly selective and sensitive detection of 2,4,6-trinitrotoluene (TNT)

A new lignin modified hybrid microsphere, comprising poly(styrene-co-acrylic acid) core and magnetite (Fe3O4)/Au nanoparticle (NP) shell, was proposed here for the selective and highly sensitive detection and removal of 2,4,6-trinitrotoluene (TNT) explosives based on surface enhanced Raman scattering (SERS) and electrochemical detection methods. The presence of lignin and the highly packed layer of Fe3O4/AuNPs as a magnetic collector and metal enhancer for SERS signals allowed for the detection of TNT below 1 pM.

Preparation of well-dispersed gold/magnetite nanoparticles embedded on cellulose nanocrystals for efficient immobilization of papain enzyme

A nanocomposite consisting of magnetite nanoparticles (Fe3O4NPs) and Au nanoparticles (AuNPs) embedded on cellulose nanocrystals (CNCs) was used as a magnetic support for the covalent conjugation of papain and facilitated recovery of this immobilized enzyme. Fe3O4NPs (10-20 nm in diameter) and AuNPs (3-7 nm in diameter) were stable and well-dispersed on the CNC surface. Energy-dispersive spectroscopy, X-ray diffraction, and Fourier transform infrared spectroscopy were used to evaluate the surface composition and structure of CNC/Fe3O4NPs/AuNPs. The nanocomposite was successfully used for the immobilization and separation of papain from the reaction mixture. The optimal enzyme loading was 186 mg protein/g CNC/Fe3O4NPs/AuNPs, significantly higher than the value reported in the literature. The activity of immobilized papain was studied by electrochemical detection of its specific binding to the Thc-Fca-Gly-Gly-Tyr-Arg inhibitory sequence bound to an Au electrode. The immobilized enzyme retained 95% of its initial activity after 35 days of storage at 4 °C, compared to 41% for its free form counterpart.

Synthesis of furfural from xylose by heterogeneous and reusable nafion catalysts

Nafion 117 has been proven as a robust and reusable heterogeneous catalyst for the dehydration of 9.1 % (w/w) xylose in dimethyl sulfoxide (DMSO) to yield 60 % furfural in 2 h at 150 °C. The catalytic high activity promoted shorter reaction times to limit the formation of side-products which otherwise would lead to decreased yields. Within the allowable operating temperature range of Nafion (125 to 175 °C), the reaction was kinetically controlled. In corroboration with AFM and SEM imaging, ATR-FTIR confirmed that the Nafion catalytic activity remained unchanged after 15 repeated uses. With excellent chemical and thermal stability under the conditions for xylose dehydration compared to existing solid acid catalysts, this reusable Nafion system could be a step towards the more economical production of furfural from renewable biomass, an intermediate chemical for the preparation of value-added chemicals.

Purification, functionalization, and bioconjugation of carbon nanotubes

Bioconjugation of carbon nanotubes (CNTs) with biomolecules promises exciting applications such as biosensing, nanobiocomposite formulation, design of drug vector systems, and probing protein interactions. Pristine CNTs, however, are virtually water-insoluble and difficult to evenly disperse in a liquid matrix. Therefore, it is necessary to attach molecules or functional groups to their sidewalls to enable bioconjugation. Both noncovalent and covalent procedures can be used to conjugate CNTs with a target biomolecule for a specific bioapplication. This chapter presents a few selected protocols that can be performed at any wet chemistry laboratory to purify and biofunctionalize CNTs. The preparation of CNTs modified with metallic nanoparticles, especially gold, is also described since biomolecules can bind and self-organize on the surfaces of such metal-decorated CNTs.

Effect of surface charge on the cellular uptake and cytotoxicity of fluorescent labeled cellulose nanocrystals

Probing of cellular uptake and cytotoxicity was conducted for two fluorescent cellulose nanocrystals (CNCs): CNC-fluorescein isothiocyanate (FITC) and newly synthesized CNC-rhodamine B isothiocyanate (RBITC). The positively charged CNC-RBITC was uptaken by human embryonic kidney 293 (HEK 293) and Spodoptera frugiperda (Sf9) cells without affecting the cell membrane integrity. The cell viability assay and cell-based impedance spectroscopy revealed no noticeably cytotoxic effect of the CNC-RBITC conjugate. However, no significant internalization of negatively charged CNC-FITC was observed at physiological pH. Indeed, the effector cells were surrounded by CNC-FITC, leading to eventual cell rupture. As the surface charge of CNC played an important role in cellular uptake and cytotoxicity, facile surface functionalization together with observed noncytotoxicity rendered modified CNC as a promising candidate for bioimaging and drug delivery systems.

Selective nanomolar detection of dopamine using a boron-doped diamond electrode modified with an electropolymerized sulfobutylether-beta-cyclodextrin-doped poly(N-acetyltyramine) and polypyrrole composite film

N-acetyltyramine was synthesized and electropolymerized together with a negatively charged sulfobutylether-beta-cyclodextrin on a boron-doped diamond (BDD) electrode followed by the electropolymerization of pyrrole to form a stable and permselective film for selective dopamine detection. The selectivity and sensitivity of the formed layer-by-layer film was governed by the sequence of deposition and the applied potential. Raman results showed a decrease in the peak intensity at 1329 cm(-1) (sp(3)), the main feature of BDD, upon each electrodeposition step. Such a decrease was correlated well with the change of the charge-transfer resistance derived from impedance data, i.e., reflecting the formation of the layer-by-layer film. The polycrystalline BDD surface became more even with lower surface roughness as revealed by scanning electron and atomic force microscopy. The modified BDD electrode exhibited rapid response to dopamine within 1.5-2 s and a low detection limit of 4-5 nM with excellent reproducibility. Electroactive interferences caused by 4-dihydroxyphenylalanine, 3,4-dihydroxyphenylacetic acid, ascorbic acid, and uric acid were completely eliminated, whereas the signal response of epinephrine and norepinephrine was significantly suppressed by the permselective film.

Cellulose nanocrystal/gold nanoparticle composite as a matrix for enzyme immobilization

A novel nanocomposite consisting of cellulose nanocrystals (CNCs) functionalized with gold nanoparticles (AuNPs) serving as an excellent support for enzyme immobilization with phenomenally high loading is presented in this work. As testing models, cyclodextrin glycosyl transferase (CGTase) and alcohol oxidase were conjugated on an activated CNC/AuNP matrix. This catalytic platform exhibits significant biocatalytic activity with excellent enzyme stability and without apparent loss of the original activity. The recovered specific activities were approximately 70% and 95% for CGTase and alcohol oxidase, respectively. This novel and inexpensive material is anticipated to extend to other enzymes, enhancing the enzyme loading and activity as well as the stability in both operation and storage.

Picomolar detection of protease using peptide/single walled carbon nanotube/gold nanoparticle-modified electrode

Picomolar electrochemical detection of human immunodeficiency virus type-1 protease (HIV-1 PR) using ferrocene (Fc)-pepstatin-modified surfaces has been presented. Gold electrode surface was modified with gold nanoparticles (AuNP) or thiolated single walled carbon nanotubes/gold nanoparticles (SWCNT/AuNP). Thiol-terminated Fc-pepstatin was then self-assembled on such surfaces as confirmed by Raman spectroscopy and scanning electron microscope. The interaction between the Fc-pepstatin-modified substrates and HIV-1 PR was studied by cyclic voltammetry and electrochemical impedance spectroscopy. Both electrode materials showed enhanced electrochemical responses to increasing concentrations of HIV-1 PR with shifting to higher potentials as well as decrease in the overall signal intensity. However, the sensing electrode modified with thiolated SWCNTs/AuNPs showed remarkable detection sensitivity with an estimated detection limit of 0.8 pM.