Resupply, diffusion, and bioavailability of Hg in paddy soil-water environment with flood-drain-reflood and straw amendment.

Mercury (Hg) poses a significant risk in paddy fields, particularly when it is converted to methylmercury (MeHg) and accumulates in rice. However, the bioavailability and resupply kinetics of Hg in the paddy soil-water environment are not well understood. In this study, the diffusive gradients in thin films (DGT) and the 'DGT-induced fluxes in sediments' model (DIFS) were first adopted to investigate the Hg resupply kinetics, diffusion fluxes and bioavailability in a paddy environment subjected to flood-drain-reflood treatment and straw amendment. Our results show that although the straw amendment limited the bioavailability of Hg (38.2%-47.9% lower than control) in porewater by decreasing its resupply capacity, especially with smaller straw particles, the net production of MeHg in paddy fields was significantly increased after straw amendment (73.5%-77.9% higher than control). The results of microbial sequencing indicate that enhanced methylators (e.g., family Geobacter) and non-Hg methylators (e.g., Methanosarcinaceae) played a crucial role in MeHg production following straw amendment. Moreover, Hg-containing paddy soils generally tend to release Hg into the overlying water, while drain-reflood treatment changes the direction of Hg diffusion fluxes in the paddy soil-water interface. The drainage-reflooded treatment decreases the Hg reactive and resupply capacity of the paddy soil, thereby hindering the release of Hg from soil into overlying water during the early stages of reflooding. Overall, this study provides novel insights into the behavior of Hg in paddy soil-water surface microlayers.

Graphene Oxide-Based Highly Sensitive Assay of Circulating MicroRNAs for Early Prediction of the Response to Neoadjuvant Chemotherapy in Breast Cancer.

The response to neoadjuvant chemotherapy (NAC) is highly correlated with survival in breast cancer (BC) patients. The early prediction of the response to NAC could facilitate treatment adjustments on a patient-by-patient basis, which would improve patient outcomes and survival. Conventional techniques used for detecting circulating microRNAs (miRNAs), which act as biomarkers for the early prediction of NAC efficacy in BC patients, are associated with limitations such as low sensitivity and specificity. We designed a highly sensitive graphene oxide (GO)-based qRT-PCR method for detecting miRNAs associated with the chemotherapeutic response in BC patients. The results showed that miRNA levels at both the baseline and end of the first NAC cycle could help distinguish NAC responders from NAC nonresponders; BC patients with lower plasma miRNA levels were more likely to achieve pathological complete remission. Thus, GO-based qRT-PCR could facilitate early prediction of NAC efficacy in BC patients.

Typical layered structure bismuth-based photocatalysts for photocatalytic nitrogen oxides oxidation.

Traditional NOx treatment methods require external reducing reagents and harsh reaction conditions, which is not conducive to effectively eliminate NOx at low concentration, especially at ppb levels. Fortunately, low concentration NOx can be removed by photocatalytic oxidation under mild reaction conditions. Bismuth (Bi)-based photocatalysts with the layered structure have obtained considerable concerns of photocatalytic NOx oxidation. This review focused on typical layered Bi-based photocatalysts (Bi2WO6, Bi2O2CO3, BiOY (YCl, Br, and I), BiOIO3, and BiOCOOH) with the structure of [Bi2O2]2+ layer for photocatalytic NOx oxidation. The strategies (morphological control, defect engineering, heterostructure construction, etc.) to improve photocatalytic oxidation activity were summarized. Furthermore, the mechanism involving various free radicals (hydroxyl radical, superoxide radical, etc.) of photocatalytic oxidation of NOx was proposed. In addition, the non-NO2 selectivity was also illuminated. Lastly, the current drawbacks and further research directions for photocatalytic NOx oxidation were elaborated. The development of photocatalysts with high photocatalytic activity, wide light absorption range, and non-NO2 selectivity is the focus of future research. This review aims to provide a pandect and theoretical guidance for the practical application of photocatalytic oxidation of NOx.

MeHg production in eutrophic lakes: Focusing on the roles of algal organic matter and iron-sulfur-phosphorus dynamics.

The mechanisms by which eutrophication affects methylmercury (MeHg) production have not been comprehensively summarized, which hinders accurately predicting the MeHg risk in eutrophic lakes. In this review, we first discussed the effects of eutrophication on biogeochemical cycle of mercury (Hg). Special attentions were paid to the roles of algal organic matter (AOM) and iron (Fe)-sulfur (S)-phosphorus (P) dynamics in MeHg production. Finally, the suggestions for risk control of MeHg in eutrophic lakes were proposed. AOM can affect in situ Hg methylation by stimulating the abundance and activities of Hg methylating microorganisms and regulating Hg bioavailability, which are dependent on bacteria-strain and algae species, the molecular weight and composition of AOM as well as environmental conditions (e.g., light). Fe-S-P dynamics under eutrophication including sulfate reduction, FeS formation and P release could also play crucial but complicated roles in MeHg production, in which AOM may participate through influencing the dissolution and aggregation processes, structural order and surface properties of HgS nanoparticles (HgSNP). Future studies should pay more attention to the dynamics of AOM in responses to the changing environmental conditions (e.g., light penetration and redox fluctuations) and how such variations will subsequently affect MeHg production. The effects of Fe-S-P dynamics on MeHg production under eutrophication also deserve further investigations, especially the interactions between AOM and HgSNP. Remediation strategies with lower disturbance, greater stability and less cost like the technology of interfacial O2 nanobubbles are urgent to be explored. This review will deepen our understanding of the mechanisms of MeHg production in eutrophic lakes and provide theoretical guidance for its risk control.

Fast Synthesis of Graphene Oxide-ß-Lactam as a Residue-Free Environmental Bacterial Inhibitor.

Common pathogenic bacteria contaminate the environment through various modes of transmission. It is thus crucial to develop simple preparation methods of residue-free environmental disinfectants. ß-Lactam antibiotics are frequently prescribed in clinical practice to treat bacterial infections. In this study, we used electrochemical exfoliation to synthesize graphene oxide (GO) with abundant ketene functional groups. A residue-free GO-ß-lactam (GOßL) was subsequently obtained by mixing ketene and azomethine-H via a [2 + 2] cycloaddition reaction in the aqueous phase. GOßL has shown broad-spectrum bacterial inhibition against four bacteria (Staphylococcus aureus, Escherichia coli, Salmonella enterica, and Shigella dysenteriae), and it degrades rapidly within 24 h. This study provides a fast and easy method for the synthesis of GOßL, which can be employed as a promising environmental bacteriostatic disinfectant in real-life applications.

High sensitivity SARS-CoV-2 detection using graphene oxide-multiplex qPCR.

The emerging pandemic of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) critically challenges early and accurate virus diagnoses. However, the current gold standard for SARS-CoV-2 detection, reverse transcription-quantitative polymerase chain reaction (RT-qPCR), has reportedly failed to detect low-viral loads. One compound, graphene oxide (GO), which adsorbs single-stranded DNA (ssDNA), has been widely applied in molecular pathogen detection. This study presents a highly sensitive GO-multiplex qPCR method for simultaneous detection of two SARS-CoV-2 genes (RdRP and E) and one reference gene (RNase P). In a GO-multiplex qPCR system, GO pre-absorbs each forward primer to form specific GO-forward primer composites before entering the amplification system. Target gene amplification is confined within the primer-enriched composites, thus, improving the sensitivity of the assay. Compared to conventional multiplex qPCR, GO-multiplex qPCR reduces the limit of detection by 10-fold to 10 copies/reaction. Hence, the GO-multiplex qPCR assay can be effectively used for SARS-CoV-2 detection.

Microplastics influence on Hg methylation in diverse paddy soils.

Microplastics are widespread in estuarine, coastal, and deep sea sediments. The influence of microplastics on mercury (Hg) methylation in paddy soils with different characteristics, however, has not been well reported. In this research, we conducted a microcosmic experiment using red soil and alkaline soil with 2%, 7% and 10% polyvinyl chloride microplastics (PVC-MPs). Diffusive gradients in thin film (DGT) were used to test bioavailable Hg2+ and bioavailable methylmercury (MeHg) in soils. Results showed that PVC-MPs could decrease bioavailable MeHg concentrations both in red soil and alkaline soil. We demonstrated that these decreases could be due to three possible mechanisms: (1) PVC-MPs affected DOM composition, which resulted in a difference in combining capacity for bioavailable Hg2+; (2) PVC-MPs decreased MeHg via changing soil properties (including sulfate and dissolved Fe); (3) PVC-MPs affected the abundance of Proteobacteria, Firmicutes, and hgcA gene in soils. Our results emphasized the significance of investigating effects of microplastics on specific contaminants to implement effective environmental remediation strategies in polluted paddy soils.

Single-atom Ru loaded on layered double hydroxide catalyzes peroxymonosulfate for effective E. coli inactivation via a non-radical pathway: Efficiency and mechanism.

The Fenton-like processes are considered to be one of the most promising strategies for inactivating bacteria due to their capacity to produce reactive oxygen species (ROS). Herein, a catalytic system for efficient inactivation of Escherichia coli (E. coli) was developed by anchoring single-atom Ru on layered double hydroxides (LDH). The Ru/NiFe-LDH catalyst showed excellent performance in activating peroxymonosulfate (PMS) to inactivate E. coli. Under the combined action of the ultra-low concentrations of Ru/NiFe-LDH (40 mg/L) and PMS (5 mg/L), 7 log E. coli can be totally inactivated within 90 s. This was attributed to the combined effect of single-atom Ru adsorption to E. coli and the ROS produced in situ. Mechanism studies indicated that the 1O2 with electrophilic properties was the key active species responsible for the rapid inactivation of E. coli. The E. coli inactivation process suggested that the ROS produced first attacked the outer membrane of the cell, then the antioxidant enzymes in the cell were induced, the macromolecule substances were released and mineralized, eventually leading to irreversible cell death. This work firstly loads monoatomic Ru on LDH for bacterial inactivation, providing a feasible method for rapid inactivation of E. coli.

Removal of chloride from water and wastewater: Removal mechanisms and recent trends.

Increased chloride concentration can cause salinization, which has become a serious and widespread environmental problem nowadays. This review aims at providing comprehensive and state-of-the-art knowledge and insights of technologies for chloride removal. Mechanisms for chloride removal mainly include chemical precipitation, adsorption, oxidation and membrane separation. In chemical precipitation, chloride removal by forming CuCl, AgCl, BiOCl and Friedel's salt. Adsorbents used in chloride removal mainly include ion exchangers, bimetal oxides and carbon-based electrodes. Oxidation for chloride removal contains ozone-based, electrochemical and sulfate radical-based oxidation. Membrane separation for chloride removal consists of diffusion dialysis, nanofiltration, reverse osmosis and electrodialysis. In this review, we specifically proposed the factors that affect chloride removal process and the corresponding strategies for improving removal efficiency. In the last section, the remaining challenges of method explorations and material developments were stated to provide guidelines for future development of chloride removal technologies.

Graphene oxide-based qRT-PCR assay enables the sensitive and specific detection of miRNAs for the screening of ovarian cancer.

Circulating microRNAs (miRNAs) have the potential to become reliable and noninvasive biomarkers for ovarian cancer (OC) diagnosis; however, the conventional miRNAs detection techniques exhibit enduring limitations of low sensitivity and specificity. Graphene oxide (GO), a novel nanomaterial, is at the forefront of material design for extensive biomedical applications. Owing to the excellent water affinity and single-stranded DNA (ssDNA) adsorption characteristics of GO, we designed and developed a GO-based qRT-PCR assay for the detection of miRNAs associated with OC. In the GO-based qRT-PCR system, GO could significantly improve the sensitivity and specificity of the qRT-PCR assay by noncovalently interacting with primers and ssDNA and reducing the occurrence of non-specific amplification. Moreover, the detection of miRNAs associated with OC confirmed that GO-based qRT-PCR assay could differentiate benign ovarian tumors from OC (sensitivity, 0.91; specificity, 1.00). Collectively, these findings provide robust evidence that GO-based qRT-PCR assay can be effectively used as a promising method to detect miRNAs for the screening of OC patients.

Eco-Friendly Preparation of Epoxy-Rich Graphene Oxide for Wound Healing.

Despite the ever-growing endangerment caused by the multidrug resistance (MDR) of bacteria, the development of effective antibacterial materials still remains a global challenge. Current antibiotic therapies cannot simultaneously inactivate bacteria and accelerate wound healing. This study aimed to originally separate the intercalation of MnO3+ and the oxidation processes to synthesize epoxy-rich graphene oxide (erGO) nanofilms via an eco-friendly synthetic route, which possessed low density and large lamellar distribution and was rich in epoxide. Importantly, the MnO3+ could be separated from the product and recycled for preparing the next generation of erGO nanofilms, which was quite economical and eco-friendly. The erGO nanofilm was capable of successfully inhibiting Gram-negative bacteria and even had excellent growth-inhibitory effects on Gram-positive bacteria including multidrug resistance (MDR) bacteria, as evidenced by antibacterial phenomena. Additionally, the erGO nanofilm with high •C density formed from epoxide exerted excellent antibacterial effects through tight membrane wrapping and induction of lipid peroxidation. The wound-healing property of the erGO nanofilm was evaluated via treatments of wounds infected by Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), which not only killed bacteria but also accelerated wound healing in mice with a skin infection. The novel erGO nanofilm with dual antimicrobial mechanisms might serve as a promising multifunctional antimicrobial agent for medical wound dressing with high biocompatibility.

Application of layered double hydroxide-biochar composites in wastewater treatment: Recent trends, modification strategies, and outlook.

In recent years, layered double hydroxide-biochar (LDH-BC) composites as adsorbents and catalysts for contaminants removal (inorganic anions, heavy metals, and organics) have received increasing attention and became a new research point. It is because of the good chemical stability, abundant surface functional groups, excellent anion exchange ability, and good electronic properties of LDH-BC composites. Hence, we offer an overall review on the developments and processes in the synthesis of LDH-BC composites as adsorbents and catalysts. Special attention is devoted to the strategies for enhancing the properties of LDH-BC composites, including (1) magnetic treatment, (2) acid treatment, (3) alkali treatment, (4) controlling metal ion ratios, (5) LDHs intercalation, and (6) calcination. In addition, further studies are called for LDH-BC composites and potential areas for future application of LDH-BC composites are also proposed.

Self-assembled micro-flowers of ultrathin Au/BiOCOOH nanosheets photocatalytic degradation of tetracycline hydrochloride and reduction of CO2.

The low separation efficiency of carriers and weak light response of photocatalysts severely limit the application of photocatalysis technology. Herein, we prepared a visible light responsive self-assembled micro-flowers of ultrathin bismuth oxide formate nanosheets supported by gold nanoparticles (Au/BiOCOOH) composite photocatalyst via hydrothermal method. The physicochemical and photoelectric properties of obtained-photocatalysts were completely analyzed via a range of characterization means. Compared with bare BiOCOOH, the photocatalytic activity of Au/BiOCOOH was significantly improved. 2.0%Au/BiOCOOH possessed the highest rate constant of 0.0054 min-1 for degradation of tetracycline hydrochloride (TC-HCl), which was nearly 13.5 times higher than that of BiOCOOH. The intermediate products were analyzed by 3D EEM and HPLC/MS, and the antibacterial ability of intermediate products with 2.0%Au/BiOCOOH significantly descended. In order to explore the potential of practical applications, photocatalytic experiments were also implemented through different water sources and solar light irradiation. Furthermore, the photocatalytic activity was also investigated by photocatalytic reduction of carbon dioxide (CO2). The excellent photocatalytic activity owed to the enhanced separation of charge carriers and light absorption ability by the surface plasmon resonance (SPR) effect of Au nanoparticles. The work may provide a feasible strategy to obtain efficient BiOCOOH-based photocatalyst.

A strategy for preparing non-fluorescent graphene oxide quantum dots as fluorescence quenchers in quantitative real-time PCR.

In recent years, graphene oxide quantum dots (GOQDs) have emerged as novel nanomaterials for optical sensing, bioimaging, clinical testing, and environmental testing. However, GOQDs demonstrate unique photoluminescence properties, with GOQDs having quantum limitations and edge effects that often affect the accuracy of the test results in the sensory field. Herein, GOQDs with a large content of hydroxyl groups and low fluorescence intensity were first prepared via an improved Fenton reaction in this study, which introduces a large amount of epoxy groups to break the C-C bonds. The synthesized GOQDs show no significant variation in the fluorescence intensity upon ultraviolet and visible light excitations. We further utilized the GOQDs as fluorescence quenchers for different fluorescent dyes in real-time fluorescence quantitative polymerase chain reaction (qRT-PCR), and verified that the addition of GOQDs (5.3 µg ml-1) into a qRT-PCR system could reduce the background fluorescence intensity of the reaction by fluorescence resonance energy transfer (FRET) during its initial stage and its non-specific amplification, and improve its specificity. In addition, the qRT-PCR method could detect two different lengths of DNA sequences with a high specificity in the 104 to 1010 copies per µl range. It is of paramount importance to carry out further investigations to establish an efficient, sensitive, and specific RT-PCR method based on the use of GOQD nanomaterials as fluorescence quenchers.

Optimization study on spatial distribution of rice based on a virtual plant approach.

How to increase crop yield is the most important issue in agricultural production. Many studies have been devoted to optimizing spatial distribution of crops, to improve light interception and increase photosynthetic assimilation. However, finding an optimal solution based on field experiments is almost impossible since the large number of combinations of factors that are related, and the cost in terms of finances and time are prohibitive. A new optimization strategy was proposed in this study, integrating a Functional-Structural Model of rice with a workflow based on a Mixed Particle Swarm Optimization (MPSO) algorithm. The 3D modelling platform GroIMP was used to implement the model and optimization workflow. MPSO is a new Particle Swarm Optimization-based algorithm with multistage disturbances, which has improved abilities to get rid of local optima and to explore solution space. Spacing between plants was used as optimization target in the first example. An optimal plant spacing was obtained within the model framework of current environmental settings together with the functional and structural modules. Simulation results indicate that the optimized plant spacing could increase rice yield, and that the optimization results remain stable.

Photosynthetic bacteria-based technology is a potential alternative to meet sustainable wastewater treatment requirement?

A paradigm shift is underway in wastewater treatment from pollution removal to resource or energy recovery. However, conventional activated sludge (CAS) as the core technology of wastewater treatment is confronted with severe challenges on high energy consumption, sludge disposal and inevitable greenhouse gas emission, which are posing a serious impact on the current wastewater industry. It is urgent to find new alternative methods to remedy these defects. Photosynthetic bacteria (PSB) have flexible metabolic modes and high tolerance, which enhance the removal of nutrients, heavy metals and organic contaminants efficiency in different wastewater. The unique phototrophic growth of PSB breaks the restriction of nutrient metabolism in the CAS system. Recent studies have shown that PSB-based technologies can not only achieve the recovery of nutrient and energy, but also improve the degradation efficiency of refractory substances. If the application parameters can be determined, there will be great prospects and economic effects. This review summarizes the research breakthroughs and application promotion of PSB-based wastewater treatment technology in recent years. Comparing discussed the superiority and inferiority from the perspective of application range, performance differences and recovery possibility. Pathways involved in the nutrient substance and the corresponding influencing parameters are also described in detail. The mode of PSB biodegradation processes presented a promising alternative for new wastewater treatment scheme. In the future, more mechanical and model studies, deterministic operating parameters, revolutionary process design is need for large-scale industrial promotion of PSB-based wastewater treatment.

Photocatalytic decomposition of Congo red under visible light irradiation using MgZnCr-TiO2 layered double hydroxide.

The new nanophotocatalyst MgZnCr-TiO2 was prepared by co-precipitation under different molar ratio of metals (Zn:Cr) and the loaded amount of TiO2. And it was characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy et al. Langmuir model fitted well the adsorption isotherm with the value of R2 0.9765, the maximum adsorption capacity was 526.32 mg g-1, the adsorption followed pseudo second order kinetic by MgZnCr-TiO2 (1:1:2-0.05). The photocatalytic oxidation of Congo red was used to determine the photocatalytic performance of MgZnCr-TiO2 (1:1:2-0.05) under visible light irradiation, and the removal rate reached 98% after reaction for 40 min. The degradation mechanism of Congo red also was proposed, and the MgZnCr-TiO2 (1:1:2-0.05) was stable after five cycles. Compared to the adsorption, Congo red was removed fundamentally by photocatalysis and it is expected to be an effective way to eliminate Congo red.

Active capping technology: a new environmental remediation of contaminated sediment.

The management and treatment of contaminated sediment is a worldwide problem and poses major technical and economic challenges. Nowadays, various attempts have been committed to investigating a cost-effective way in contaminated sediment restoration. Among the remediation options, in situ capping turns out to be a less expensive, less disruptive, and more durable approach. However, by using the low adsorption capacity materials, traditional caps do not always fulfill the reduction of risks that can be destructive for human health, ecosystem, and even natural resources. Active caps, therefore, are designed to employ active materials (activated carbon, apatite, zeolite, organoclay, etc.) to strengthen their adsorption and degradation capacity. The active capping technology promises to be a permanent and cost-efficient solution to contaminated sediments. This paper provides a review on the types of active materials and the ways of these active materials employed in recent active capping studies. Cap design considerations including site-specific conditions, diffusion/advection, erosive forces, and active material selection that should be noticed in an eligible remediation project are also presented.

Immobilization of Cd(II) in acid soil amended with different biochars with a long term of incubation.

Biochars derived from bamboo, coconut shell, pine wood shavings, and sugarcane bagasse were applied into Ultisol to investigate their effects on Cd(II) immobilization. After 360 days of incubation, the physical/chemical properties of the Ultisol were improved by the addition of different biochars. As a result, the maximum adsorption capacities of soil for Cd(II) were increased from 8.02 to 9.07-11.51 mmol/kg, and bamboo biochar showed the highest effect on Cd(II) immobilization. The Langmuir model (R(2) > 0.983) fitted the data better than the Freundlich model (R (2) were 0.902-0.937). Column leaching experiments suggested that biochar can also increase the immobilization of Cd(II) under leaching conditions. Biochar mainly increased the weak/unstable binding force of Cd(II) by soil, such as ion exchange, electrostatic attraction, physical adsorption, and carbonate precipitation. In addition, a significant enhancement of surface complexation was also observed.

Application of biochar for the removal of pollutants from aqueous solutions.

In recent years, many studies have been devoted to investigate the application of biochar for pollutants removal from aqueous solutions. Biochar exhibits a great potential to efficiently tackle water contaminants considering the wide availability of feedstock, low-cost and favorable physical/chemical surface characteristics. This review provides an overview of biochar production technologies, biochar properties, and recent advances in the removal of heavy metals, organic pollutants and other inorganic pollutants using biochar. Experimental studies related to the adsorption behaviors of biochar toward various contaminants, key affecting factors and the underlying mechanisms proposed to explain the adsorption behaviors, have been comprehensively reviewed. Furthermore, research gaps and uncertainties that exist in the use of biochar as an adsorbent are identified. Further research needs for biochar and potential areas for future application of biochars are also proposed.