One-pot synthesis of magnetic algal carbon/sulfidated nanoscale zerovalent iron composites for removal of bromated disinfection by-product

Synthesis, delineation and technological advancements of algae biochar for sustainable remediation of the emerging pollutants from wastewater-a review

The use of algae for value-added product and biorefining applications is enchanting attention among researchers in recent years due to its remarkable photosynthetic ability, adaptability, and capacity to accumulate lipids and carbohydrates. Algae biomass, based on its low manufacturing costs, is relatively renewable, sustainable, environmentally friendly and economical in comparison with other species. High production rate of algae provides a unique opportunity for its conversion to biochar with excellent physicochemical properties, viz. high surface area and pore volume, high adsorption capacity, abundant functional groups over surface, etc. Despite several potential algal-biochar, a detailed study on its application for removal of emerging contaminants from wastewater is limited. Therefore, this technical review is being carried out to evaluate the specific elimination of inorganic and organic pollutants from wastewater, with a view to assessing adsorption performances of biochar obtained from various algae species. Species-specific adsorption of emerging pollutants from wastewater have been discussed in the present review. The promising methods like pyrolysis, gasification, dry and wet torrefaction for the production of algae biochar are highlighted. The strategies include chemical and structural modifications of algae biochar for the removal of toxic contaminants have also been considered in the current work. The overall aim of this review is to confer about the synthesis, technological advancements, delineation and application of algae biochar for the treatment of wastewater.

Sodium carbonate/biochar-supported sodium alginate-modified nano zero-valent iron for complete adsorption and degradation of tetracycline in aqueous solution

The aggregation of nanoscale zero-valent iron (NZVI) is one of the biggest challenges for its application when treating contaminants in aquatic environment. We report a study on synthesis of sodium carbonate-modified biochar (BC-600) combined with sodium alginate (SA)-modified NZVI (SA/NZVI@BC-600) for the removal of tetracycline (TC). When the initial concentration of TC was 20 mg/L, 100% TC was removed by SA/NZVI@BC-600 at an initial pH of 7 under room temperature of 25 °C within 90 min. In addition, the reactivity of the SA/NZVI@BC-600 composites toward TC removal was not obviously declined after 4 cycles. SA/NZVI@BC-600 shows high reactivity, stability, and reusability. This excellent performance of SA/NZVI@BC-600 was related to the addition of SA and BC-600. The best performance of the SA/NZVI@BC-600 system was observed under weakly acidic and neutral conditions. Increasing the initial concentration and lowering the reaction temperature had a slight negative effect on the removal of TC by SA/NZVI@BC-600. In addition, the presence of CO32- and HCO3- had a significant negative effect on the degradation of TC. Meanwhile, ·OH and ·O2- played the leading role in TC degradation. This study not only reported a novel strategy of synthesizing an excellent BC modified NZVI based catalyst but also evaluated its promising application for antibiotic degradation in aqueous solution.

Strengthened removal of emerging contaminants over S/Fe codoped activated carbon fabricated by a mild one-step thermal transformation scheme

Thermal transformation of carbonized materials to functional activated carbon (AC) is a simplified, economical and eco-friendly strategy, which has great potential in the practical applications of water purification. Herein, a S/Fe codoped activated carbon (S/Fe@AC) with only 0.90 wt% S and 0.76 wt% Fe was creatively fabricated by one synchronous method of physical activation, carbothermal reduction and sulfidation in the solid phase. The formed iron sulfide shell significantly enhances the antioxidation ability of nanoscale zero-valent iron (NZVI, >180 d) and dramatically improves the hydrophobicity of the composite. Meanwhile, the doped thiophenic S in AC enhances the hydrophobicity and increases the specific surface area to 1194.14 m² g^-1. Incorporating with AC in turn greatly strengthens the dispersibility and stability of sulfurized NZVI particles. Compared to NZVI@AC, AC and NZVI, the removal capacity of S/Fe@AC for the representative hydrophobic contaminant-triclosan (TCS) increases to 519.68 mg g^-1 by 66.60%, 78.60% and 981.21%, respectively, outperforming most of the previously reported materials. The strong hydrophobic and π-π interactions, and weak hydrogen bonding and electrostatic repulsion are responsible for the excellent removal performance for TCS. More importantly, the improved chemical property (29.38%) of the composite caused by the doped S/Fe has a greater effect on TCS removal compared with the changed physical structure (14.56%). Furthermore, the stable S/Fe@AC shows strong anti-interference capability and exceptional regenerability. These intriguing discoveries provide new insights into the design of advanced and sustainable adsorbing materials for emerging contaminants.

Deep insight into the Sb(III) and Sb(V) removal mechanism by Fe-Cu-chitosan material

Currently, alleviating antimony (Sb) contamination in aqueous solutions is crucial for restoring and recovering ecological and environmental health. Due to its toxicity, bioaccumulation and mobile characteristics, developing an efficient technique for antimony decontamination is imperative. Herein, we prepared a Fe-Cu-chitosan (FCC) composite by a one-step coprecipitation method, in which nanoscale Fe/Cu acts as the active sites and the whole structure is exhibited as porous microscale particles. A Fe/Cu proportion of 2/1 (FCC-2/1) was determined to be the optimum proportion for antimony adsorption, specifically 34.5 mg g^-1 for Sb(III) and 26.8 mg g^-1 for Sb(V) (initial concentration: 5.0 mg L^-1). Spectral characterization, batch experiments and density functional theory (DFT) simulations were applied to determine the adsorption mechanism, in which surface hydroxyls (-OH) were responsible for antimony complexion and Fe-Cu coupling was a major contributor to adsorption enhancement. According to kinetic analysis, Cu provided an electrostatic attraction during the adsorption process, which facilitated the transportation of antimony molecules to the material interface. In the meantime, the FCC electronic structure was modified due to the optimization of the Fe-Cu interface coupling. Based on the Mullikan net charge, the intrinsic Fe-O-Cu bond might favor interfacial electronic redistribution. When the antimony molecule contacted the adsorption interface, the electrons transferred swiftly as Fe/Cu 3d and O 2p orbital hybridization occurred, thus inducing a stabilizing effect. This work may offer a new perspective for binary oxide construction and its adsorption mechanism analysis.

Ultrasound process-enhanced removal of the toxic disinfection by-product bromate from water by aluminum: A comparative study

As bromate removal and reduction can be also achieved using metals, aluminum (Al) appears as the most promising one for reduction of bromate because Al is abundant element and exhibits a high reduction power. Reactions between bromate and Al shall be even enhanced through ultrasound (US) process because US can facilitate mass transfer on liquid/solid interfaces and clean surfaces via generating microscale turbulence to facilitate reactions. Therefore, the aim of this study is for the first time to investigate the effect of US on bromate removal by Al metal. Specifically, Al particle would be treated by HCl to afford HCl-treated Al (HCTAL), which is capable of removing bromate and even reducing it to bromide. Such a mechanism is also validated by density function theory calculation through determining adsorption energy as -152.8 kJ/mole, and oxygen atoms of bromate would be extracted and reacted with Al atoms, releasing bromide ion. US not only facilitated bromate removal by further increasing removal capacity under the acidic condition but also suppressed the inhibitive effect from basicity at relatively high pH. The spent HCTAL could still remove bromate and convert it to bromide after regeneration. These features indicate that US considerably enhances bromate removal by Al. PRACTITIONER POINTS: Bromate removed by Al is elucidated by DFT calculation with E_absorption  = -152.8 kJ/mole. Oxygen atoms of bromate are extracted and reacted with Al atoms, releasing bromide ion. A higher power of ultrasound would substantially enhance bromate removal efficiency. Ultrasound also suppresses the inhibitive effect from basicity at relatively high pH. With ultrasound, the interference of co-existing anions on bromate removal is lessened.

Marine Macroalgae Display Bioreductant Efficacy for Fabricating Metallic Nanoparticles: Intra/Extracellular Mechanism and Potential Biomedical Applications

The application of hazardous chemicals during nanoparticle (NP) synthesis has raised alarming concerns pertaining to their biocompatibility and equally to the environmental harmlessness. In the recent decade, nanotechnological research has made a gigantic shift in order to include the natural resources to produce biogenic NPs. Within this approach, researchers have utilized marine resources such as macroalgae and microalgae, land plants, bacteria, fungi, yeast, actinomycetes, and viruses to synthesize NPs. Marine macroalgae (brown, red, and green) are rich in polysaccharides including alginates, fucose-containing sulfated polysaccharides (FCSPs), galactans, agars or carrageenans, semicrystalline cellulose, ulvans, and hemicelluloses. Phytochemicals are abundant in phenols, tannins, alkaloids, terpenoids, and vitamins. However, microorganisms have an abundance of active compounds ranging from sugar molecules, enzymes, canonical membrane proteins, reductase enzymes (NADH and NADPH), membrane proteins to many more. The prime reason for using the aforesaid entities in the metallic NPs synthesis is based on their intrinsic properties to act as bioreductants, having the capability to reduce and cap the metal ions into stabilized NPs. Several green NPs have been verified for their biocompatibility in human cells. Bioactive constituents from the above resources have been found on the green metallic NPs, which has demonstrated their efficacies as prospective antibiotics and anti-cancer agents against a range of human pathogens and cancer cells. Moreover, these NPs can be characterized for the size, shapes, functional groups, surface properties, porosity, hydrodynamic stability, and surface charge using different characterization techniques. The novelty and originality of this review is that we provide recent research compilations on green synthesis of NPs by marine macroalgae and other biological sources (plant, bacteria, fungi, actinomycetes, yeast, and virus). Besides, we elaborated on the detailed intra- and extracellular mechanisms of NPs synthesis by marine macroalgae. The application of green NPs as anti-bacterial, anti-cancer, and popular methods of NPs characterization techniques has also been critically reviewed.

Iron-carbon microelectrolysis for wastewater remediation: Preparation, performance and interaction mechanisms

Rapid industrialization and urbanization have produced a lot of hazardous substances in water and wastewater, which has turned into a crucial issue to the environment and the public health. Recently, iron carbon microelectrolysis (IC-ME) has attracted extensive attention in environmental remediation due to its low costs and excellent performance. Nevertheless, there is still a lack of a more systematic review on IC-ME preparation methods, their performance, and the interaction mechanisms of IC-ME in the remediation of wastewater. Herein, this work summarizes the synthetic methods, application of IC-ME materials, and the mechanism of pollutant removal by IC-ME. A variety approaches have been applied to prepare IC-ME materials, and the preparation methods and conditions have a certain influence on the properties of IC-ME materials, thus affecting the performance of pollutant removal. The mechanisms of IC-ME for contaminants removal are very complex, including adsorption, coprecipitation, reduction, surface complexation, and oxidation. Moreover, research vacant fields and problems that existed in the application of IC-ME are proposed. At last, the problems to be addressed to adapt IC to future applications are introduced. This paper reviews and prospects IC-ME wastewater remediation technology, which provides a reference for further scientific research and engineering applications.

Recent Advances in Sulfidated Zerovalent Iron for Contaminant Transformation

2021 marks 10 years since controlled abiotic synthesis of sulfidated nanoscale zerovalent iron (S-nZVI) for use in site remediation and water treatment emerged as an area of active research. It was then expanded to sulfidated microscale ZVI (S-mZVI) and together with S-nZVI, they are collectively referred to as S-(n)ZVI. Heightened interest in S-(n)ZVI stemmed from its significantly higher reactivity to chlorinated solvents and heavy metals. The extremely promising research outcomes during the initial period (2011-2017) led to renewed interest in (n)ZVI-based technologies for water treatment, with an explosion in new research in the last four years (2018-2021) that is building an understanding of the novel and complex role of iron sulfides in enhancing reactivity of (n)ZVI. Numerous studies have focused on exploring different S-(n)ZVI synthesis approaches, and its colloidal, surface, and reactivity (electrochemistry, contaminant selectivity, and corrosion) properties. This review provides a critical overview of the recent milestones in S-(n)ZVI technology development: (i) clear insights into the role of iron sulfides in contaminant transformation and long-term aging, (ii) impact of sulfidation methods and particle characteristics on reactivity, (iii) broader range of treatable contaminants, (iv) synthesis for complete decontamination, (v) ecotoxicity, and (vi) field implementation. In addition, this review discusses major knowledge gaps and future avenues for research opportunities.

Autotrophic induced heterotrophic bioreduction of bromate in use of elemental sulfur or zerovalent iron as electron donor

Bioreduction of bromate using elementary sulfur (S(0)) or zerovalent iron (Fe(0)) as electron donor was studied. After 60-day cultivation, the microbial consortium achieved high bromate conversion of 91.9 ± 2.1% and 90.0 ± 4.0% in the S(0) and Fe(0) amended tests. A coupling mechanism involving autotrophic oxidation of S(0) or Fe(0) to convert bicarbonate to volatile fatty acids followed by bromate reduction at the oxidation of the volatile fatty acids to CO₂ was proposed to interpret the noted reactor performances. The key functional strains including S(0) or Fe(0) oxidizing bacteria (Thiomonas and Ferrovibrio) and bromate reducing bacteria (Pseudoxanthomonas and Clostridium sp.) are identified. The studied system can provide an efficient BrO₃^- conversion way with no external organic carbon sources.

Recent Advances in Magnetic Nanoparticles and Nanocomposites for the Remediation of Water Resources

Water resources are of extreme importance for both human society and the environment. However, human activity has increasingly resulted in the contamination of these resources with a wide range of materials that can prevent their use. Nanomaterials provide a possible means to reduce this contamination, but their removal from water after use may be difficult. The addition of a magnetic character to nanomaterials makes their retrieval after use much easier. The following review comprises a short survey of the most recent reports in this field. It comprises five sections, an introduction into the theme, reports on single magnetic nanoparticles, magnetic nanocomposites containing two of more nanomaterials, magnetic nanocomposites containing material of a biologic origin and finally, observations about the reported research with a view to future developments. This review should provide a snapshot of developments in what is a vibrant and fast-moving area of research.