Removal of organic compounds by nanoscale zero-valent iron and its composites

Highly stable carbon-coated nZVI composite Fe0@RF-C for efficient degradation of emerging contaminants

Nanoscale zerovalent iron (nZVI) has garnered significant attention as an efficient advanced oxidation activator, but its practical application is hindered by aggregation and oxidation. Coating nZVI with carbon can effectively addresses these issues. A simple and scalable production method for carbon-coated nZVI composite is highly desirable. The anti-oxidation and catalytic performance of carbon-coated nZVI composite merit in-depth research. In this study, a highly stable carbon-coated core-shell nZVI composite (Fe0@RF-C) was successfully prepared using a simple method combining phenolic resin embedding and carbothermal reduction. Fe0@RF-C was employed as a heterogeneous persulfate (PS) activator for degrading 2,4-dihydroxybenzophenone (BP-1), an emerging contaminant. Compared to commercial nZVI, Fe0@RF-C exhibited superior PS activation performance and oxidation resistance. Nearly 95% of BP-1 was removed within 10 min in the Fe0@RF-C/PS system. The carbon layer promotes the enrichment of BP-1 and accelerates its degradation through singlet oxygen oxidation and direct electron transfer processes. This study provides a straightforward approach for designing highly stable carbon-coated nZVI composite and elucidates the enhanced catalytic performance mechanism by carbon layers.

Enhancing pakchoi cabbage yield and quality but reducing human-disease risk of bacterial community from wastewater irrigation by combined nanoscale zerovalent iron and nitrification inhibitor

It was indispensable to seek effective and feasible measures to alleviate the adverse effects of wastewater irrigation. Nanoscale zerovalent iron (nZVI) and soil nitrogen management might enhance the vegetable yield and quality but mitigate the potential human-disease risks from wastewater irrigation. This study selected the nZVI and nitrification inhibitor as experimental objects. The planted pakchoi cabbage was irrigated with the tap water and wastewater and treated with nZVI and 3, 4-dimethylpyrazole phosphate (DMPP), respectively, the pakchoi cabbage yield and quality, soil enzyme activity and abiotic property, and human-disease risk of bacterial community were quantified. Compared with the control, the nZVI significantly enhanced the pakchoi cabbage yield by 51.5% but reduced the pakchoi cabbage nitrate content by 52.6% under wastewater irrigation condition. The nZVI alone had double-edged sword effects of increasing the pakchoi cabbage yield, reducing the pakchoi cabbage nitrate content and soil human-disease risk but inhibiting the system multifunctionality and soil bacterial community diversity and stability, under wastewater irrigation condition. The nZVI diminished human-disease risk via increasing the soil Firmicutes and Verrucomicrobiota ratios, and the extra DMPP could mitigate the negative effects of nZVI by increasing soil enzyme activity and stimulating soil Acidobacteria ratio. The combinations of nZVI and DMPP could not only enhance the pakchoi cabbage yield and quality but also reduce the human-disease risk of soil bacterial community from wastewater irrigation.

Recent trends in magnetic spinel ferrites and their composites as heterogeneous Fenton-like catalysts: A review

In recent years, there has been a growing interest in utilizing spinel ferrite and their nanocomposites as Fenton-like catalysts. The use of these materials offers numerous advantages, including ability to efficiently degrade pollutants and potential for long-term and repeated use facilitated by their magnetic properties that make them easily recoverable. The remarkable catalytic properties, stability, and reusability of these materials make them highly attractive for researchers. This paper encompasses a comprehensive review of various aspects related to the Fenton process and the utilization of spinel ferrite and their composites in catalytic applications. Firstly, it provides an overview of the background, principles, mechanisms, and key parameters governing the Fenton reaction, along with the role of physical field assistance in enhancing the process. Secondly, it delves into the advantages and mechanisms of H2O2 activation induced by different spinel ferrite and their composites for the removal of organic pollutants, shedding light on their efficacy in environmental remediation. Thirdly, the paper explores the application of these materials in various Fenton-like processes, including Fenon-like, photo-Fenton-like, sono-Fenton-like, and electro-Fenton-like, for the effective removal of different types of contaminants. Furthermore, it addresses important considerations such as the toxicity, recovery, and reuse of these materials. Finally, the paper presents the challenges associated with H2O2 activation by these materials, along with proposed directions for future improvements.

Unintended polyhalogenated carbazole production during advanced oxidation of coking wastewater

Polyhalogenated carbazoles (PHCZs) are emerging as dioxin-like global pollutants, yet their environmental origins are not fully understood. This study investigates the application of the Fenton process in coking wastewater treatment, focusing on its dual role in carbazole removal and unintended PHCZ formation. The common halide ions (Cl- and Br-) in coking wastewater, especially Br- ions, exerted a notable impact on carbazole removal. Particularly, the influence of Br- ions was more significant, not only enhancing carbazole removal but also shaping the congener composition of PHCZ formation. Elevated halide ion concentrations were associated with the heightened formation of higher halogenated carbazoles. The Fenton reagent dosage ratio was identified as a crucial factor affecting the congener composition of PHCZs and their toxic equivalency value. The coexisting organic substance (i.e., phenol) in coking wastewater was observed to inhibit PHCZ formation, likely through competitive reactions with carbazole. Intriguingly, ammonium (NH4+) facilitated the generation of higher and mixed halogenated carbazoles, possibly due to the generation of nitrogen-containing brominating agents with stronger bromination capacity. This study underscores the importance of a comprehensive assessment, considering both substrate removal and potential byproduct formation, when employing the Fenton process for saline wastewater treatment.

The use of bimetallic metal-organic frameworks as restoration materials for pollutants removal from water environment

Bimetallic metal-organic frameworks (BMOFs) are a class of functional porous materials constructed by coordination between nodes containing two different metal ions and organic ligands. Studies have shown that the catalytic activity of BMOFs is greatly improved owing to the adjustment of charge distribution and the increase of active sites as well as the synergistic effect between the bimetals, and the advantages of their large specific surface area, high porosity, unique structure and dispersed active centres make them available as important organic materials applied in the field of wastewater treatment. In this review, the preparation and construction methods for BMOFs in recent years are summarized, and we focus on their removal of different types of pollutants in the aqueous environment, including ions, dyes, pharmaceuticals or personal care products, phenolic compounds and microorganisms, as well as their corresponding removal mechanisms. In addition, we provide an outlook on their future opportunities and challenges in wastewater treatment.

Oxygen-deficient AgIO3 for efficiently photodegrading organic contaminants under natural sunlight

Defect engineering is regarded as an effective strategy to boost the photo-activity of photocatalysts for organic contaminants removal. In this work, abundant surface oxygen vacancies (Ov) are created on AgIO3 microsheets (AgIO3-OV) by a facile and controllable hydrogen chemical reduction approach. The introduction of surface Ov on AgIO3 broadens the photo-absorption region from ultraviolet to visible light, accelerates the photoinduced charges separation and migration, and also activates the formation of superoxide radicals (•O2-). The AgIO3-OV possesses an outstanding degradation rate constant of 0.035 min-1, for photocatalytic degrading methyl orange (MO) under illumination of natural sunlight with a light intensity is 50 mW/cm2, which is 7 and 3.5 times that of the pristine AgIO3 and C-AgIO3 (AgIO3 is calcined in air without generating Ov). In addition, the AgIO3-OV also exhibit considerable photoactivity for degrading other diverse organic contaminants, including azo dye (rhodamine B (RhB)), antibiotics (sulflsoxazole (SOX), norfloxacin (NOR), chlortetracycline hydrochloride (CTC), tetracycline hydrochloride (TC) and ofloxacin (OFX)), and even the mixture of organic contaminants (MO-RhB and CTC-OFX). After natural sunlight illumination for 50 min, 41.4% of total organic carbon (TOC) for MO-RhB mixed solution can be decreased over AgIO3-OV. In a broad range of solution pH from 3 to 11 or diverse water bodies of MO solution, AgIO3-OV exhibits attractive activity for decomposing MO. The MO photo-degradation process and mechanism over AgIO3-OV under natural sunlight irradiation has been systemically investigated and proposed. The toxicities of MO and its degradation intermediates over AgIO3-OV are compared using Toxicity Estimation Software (T.E.S.T.). Moreover, the non-toxicity of both AgIO3-OV catalyst and treated antibiotic solution (CTC-OFX mixture) are confirmed by E. coli DH5a cultivation test, supporting the feasibility of AgIO3-OV catalyst to treat organic contaminants in real water under natural sunlight illumination.

Environmental remediation approaches by nanoscale zero valent iron (nZVI) based on its reductivity: a review

The fast rise of organic and metallic pollution has brought significant risks to human health and the ecological environment. Consequently, the remediation of wastewater is in extremely urgent demand and has received increasing attention. Nanoscale zero valent iron (nZVI) possesses a high specific surface area and distinctive reactive interfaces, which offer plentiful active sites for the reduction, oxidation, and adsorption of contaminants. Given these abundant functionalities of nZVI, it has undergone significant and extensive studies on environmental remediation, linking to various mechanisms, such as reduction, oxidation, surface complexation, and coprecipitation, which have shown great promise for application in wastewater treatment. Among these functionalities of nZVI, reductivity is particularly important and widely adopted in dehalogenation, and reduction of nitrate, nitro compounds, and metal ions. The following review comprises a short survey of the most recent reports on the applications of nZVI based on its reductivity. It contains five sections, an introduction to the theme, chemical reduction applications, electrolysis-assisted reduction applications, bacterium-assisted reduction applications, and conclusions about the reported research with perspectives for future developments. Review and elaboration of the recent reductivity-dependent applications of nZVI may not only facilitate the development of more effective and sustainable nZVI materials and the protocols for comprehensive utilization of nZVI, but may also promote the exploration of innovative remediation approaches based on its reductivity.

Differential and mechanism analysis of sulfate influence on the degradation of 1,1,2- trichloroethane by nano- and micron-size zero-valent iron

The in-situ reduction of zero-valent iron (ZVI) is an effective method for removing chlorinated aliphatic hydrocarbons (CAHs) from groundwater. The heterogeneity of environmental conditions is also crucial in affecting dechlorination efficiency. Until now, the effect of Sulfate (SO42-) on ZVI activity has been debated, and the related mechanism research on SO42- behaviour during the abiotic reduction process of chlorinated alkanes is still lacking. In this study, the impacts of SO42- concentrations (0, 2, 4, 8, 80 mM) on the degradation of 1,1,2-trichloroethane (1,1,2-TCA) by micron-size ZVI (mZVI) and nano-size ZVI (nZVI) were systematically investigated. For mZVI, Kobs increased by 0.6 (2 mM), 0.5 (4 mM), 1.1 (8 mM), and 1.6 times (80 mM). For nZVI, Kobs decreased by 32% (2 mM), 39% (4 mM), 45% (8 mM), and 9% (80 mM). The results showed that SO42- increased the rate of 1,1,2-TCA degradation by mZVI but weakened the reduction performance of nZVI; however, this inhibition was reduced when the concentration reached 80 mM. SO42- controlled the degradation of 1,1,2-TCA mainly through the formation of different iron-sulfate complexes on the ZVI surface: water-soluble bidentate iron-sulfate complexes formed on the mZVI surface promoted the corrosion of the oxide layer and accelerated the reduction of 1,1,2-TCA, monodentate complexes mainly formed on the nZVI surface inhibited the reduction of 1,1,2-TCA by blocking surface sites. These results demonstrate the proof of concept to assist land managers in the field application of ZVI technology for the remediation of CAHs contaminated sites with different background concentrations of SO42-.

Biomass-derived cellulose nanocrystals modified nZVI for enhanced tetrabromobisphenol A (TBBPA) removal

Nano zero-valent iron (nZVI) is an advanced environmental functional material for the degradation of tetrabromobisphenol A (TBBPA). However, high surface energy, self-agglomeration and low electron selectivity limit degradation rate and complete debromination of bare nZVI. Herein, we presented biomass-derived cellulose nanocrystals (CNC) modified nZVI (CNC/nZVI) for enhanced TBBPA removal. The effects of raw material (straw, filter paper and cotton), process (time, type and concentration of acid hydrolysis) and synthesis methods (in-situ and ex-situ) on fabrication of CNC/nZVI were systematically evaluated based on TBBPA removal performance. The optimized CNC-S/nZVI(in) was prepared via in-situ liquid-phase reduction using straw as raw material of CNC and processing through 44 % H2SO4 for 165 min. Characterizations illustrated nZVI was anchored to the active sites at CNC interface through electrostatic interactions, hydrogen bonds and FeO coordinations. The batch experiments showed 0.5 g/L CNC-S/nZVI(in) achieved 96.5 % removal efficiency at pH = 7 for 10 mg/L initial TBBPA. The enhanced TBBPA dehalogenation by CNC-S/nZVI(in), involving in initial adsorption, reduction process and partial detachment of debrominated products, were possibly attributed to elevated pre-adsorption capacity and high-efficiency delivery of electrons synergistically. This study indicated that fine-tuned fabrication of CNC/nZVI could potentially be a promising alternative for remediation of TBBPA-contaminated aquatic environments.

Removal of dyes from wastewater using Eucalyptus wood fiber loaded nanoscale zero-valent iron: Characterization and removal mechanism

Wood fiber as a natural and renewable material has low cost and plenty of functional groups, which owns the ability to adsorb dyes. In order to improve the application performance of wood fiber in dye-pollution wastewater, Eucalyptus wood fiber loaded nanoscale zero-valent iron (EWF-nZVI) was developed to give EWF magnetism and the ability to degrade dyes. EWF-nZVI was characterized via FTIR, XRD, zeta potential, VSM, SEM-EDS and XPS. Results showed that EWF-nZVI owned a strong magnetism of 96.51 emu/g. The dye removal process of EWF-nZVI was more in line with the pseudo-second-order kinetics model. In addition, the Langmuir isotherm model fitting results showed that the maximum removal capacities of Congo red and Rhodamine B by EWF-nZVI were 714.29 mg/g and 68.49 mg/g at 328 K, respectively. After five adsorption-desorption cycles, the regeneration efficiencies of Congo red and Rhodamine B were 74 % and 42 % in turn. The dye removal mechanisms of EWF-nZVI included redox degradation (Congo red and Rhodamine B) and electrostatic adsorption (Congo red). In summary, EWF-nZVI is a promising biomass-based material with high dye removal capacities. This work is beneficial to promote the large-scale application of wood fiber in water treatment.

Affecting factors and mechanism of removing antibiotics and antibiotic resistance genes by nano zero-valent iron (nZVI) and modified nZVI: A critical review

Antibiotics and antibiotic resistance genetic pollution have become a global environmental and health concern recently, with frequent detection in various environmental media. Therefore, finding ways to control antibiotics and antibiotic resistance genes (ARGs) is urgently needed. Nano zero-valent iron (nZVI) has shown a positive effect on antibiotics degradation and restraining ARGs, making it a promising solution for controlling antibiotics and ARGs. However, given the current increasingly fragmented research focus and results, a comprehensive review is still lacking. In this work, we first introduce the origin and transmission of antibiotics and ARGs in various environmental media, and then discuss the affecting factors during the degradation of antibiotics and the control of ARGs by nZVI and modified nZVI, including pH, nZVI dose, and oxidant concentration, etc. Then, the mechanisms of antibiotic and ARGs removal promoted by nZVI are also summarized. In general, the mechanism of antibiotic degradation by nZVI mainly includes adsorption and reduction, while promoting the biodegradation of antibiotics by affecting the microbial community. nZVI can also be combined with persulfates to degrade antibiotics through advanced oxidation processes. For the control of ARGs, nZVI not only changes the microbial community structure, but also affects the proliferation of ARGs through affecting the fate of mobile genetic elements (MGEs). Finally, some new ideas on the application of nZVI in the treatment of antibiotic resistance are proposed. This paper provides a reference for research and application in this field.

Eco-friendly nanoparticles: mechanisms and capacities for efficient removal of heavy metals and phosphate from water using definitive screening design approach

Can nano-zero-valent iron, synthesized using oak leaf extract, be the key solution for water preservation, efficiently removing heavy metal ions and phosphate anions simultaneously? This research unveils how this technology not only promises high efficiency in the remediation of water resources, but also sets new standards for environmentally friendly processes. The high antioxidant capacity and high phenol content indicate suggest the possibility of oak-nZVI synthesis using oak leaf extract as a stable material with minimal agglomeration. The simultaneous removal of Cd and phosphates, as well as and Ni and phosphates was optimized by a statistically designed experiment with a definitive screening design approach. By defining the key factors with the most significant impact, a more efficient and faster method is achieved, improving the economic sustainability of the research by minimizing the number of experiments while maximizing precision. In terms of significance, four input parameters affecting process productivity were monitored: initial metal concentration (1-9 mg L-1), initial ion concentration (1-9 mg L-1), pH value (2-10), and oak-nZVI dosage (2-16 mL). The process optimization resulted in the highest simultaneous removal efficiency of 98.99 and 87.30% for cadmium and phosphate ions, respectively. The highest efficiency for the simultaneous removal of nickel and phosphate ions was 93.44 and 96.75%, respectively. The optimization process fits within the confidence intervals, which confirms the assumption that the selected regression model well describes the process. In the context of e of the challenges and problems of environmental protection, this work has shown considerable potential and successful application for the simultaneous removal of Cd(II) and Ni(II) in the presence of phosphates from water.

Novel combination of iron-carbon composite and Fenton oxidation processes for high-concentration antibiotic wastewater treatment

The research presented herein explores the development of a novel iron-carbon composite, designed specifically for the improved treatment of high-concentration antibiotic wastewater. Employing a nitrogen-shielded thermal calcination approach, the investigation utilizes a blend of reductive iron powder, activated carbon, bentonite, copper powder, manganese dioxide, and ferric oxide to formulate an efficient iron-carbon composite. The oxygen exclusion process in iron-carbon particles results in distinctive electrochemical cells formation, markedly enhancing wastewater degradation efficiency. Iron-carbon micro-electrolysis not only boosts the biochemical degradability of concentrated antibiotic wastewater but also mitigates acute biological toxicity. In response to the increased Fe2+ levels found in micro-electrolysis wastewater, this research incorporates Fenton oxidation for advanced treatment of the micro-electrolysis byproducts. Through the synergistic application of iron-carbon micro-electrolysis and Fenton oxidation, this research accomplishes a significant decrease in the initial COD levels of high-concentration antibiotic wastewater, reducing them from 90,000 mg/L to about 30,000 mg/L, thus achieving an impressive removal efficiency of 66.9%. This integrated methodology effectively reduces the pollutant load, and the recycling of Fe2+ in the Fenton process additionally contributes to the reduction in both the volume and cost associated with solid waste treatment. This research underscores the considerable potential of the iron-carbon composite material in efficiently managing high-concentration antibiotic wastewater, thereby making a notable contribution to the field of environmental science.

Siderite's green revolution: From tailings to an eco-friendly material for the green economy

Siderite, extensively mined as a natural iron mineral, is often discarded as tailings due to the low grade of the ore and due to the high cost of current sorting technologies. Yet, this mineral has demonstrated significant potential in several pivotal areas of the environmental remediation. Siderite not only possesses exceptional adsorption, catalytic, and microbial carrier capabilities but also offers an eco-friendly and cost-effective solution for the environmental pollution management. This article consolidates research advancements and achievements over the past few decades concerning siderite's role in pollution control, delving deeply into its various remediation pathways. Initially, the paper contrasts the performance differences between natural and synthetic siderite, followed by a comprehensive overview of siderite's adsorption mechanisms for various inorganic pollutants. Furthermore, this paper analyzes the unique physicochemical attributes of siderite as both, a reductant and the catalyst, with a special emphasis on its use in the preparation of SCR catalysts and in the catalytic advanced oxidation processes for organic pollutants' degradation. This paper also enumerates and discusses the myriad advantages of siderite as a microbial carrier, thereby enhancing our understanding of biogeochemical cycles and pollutant transformations. In essence, this review systematically elucidates the mechanisms and intrinsic physicochemical properties of siderite in pollution control, paving the way for novel strategies to augment siderite's environmental remediation performance.

Integrated approach of nano assisted biodegradation of anthracene by Pseudomonas aeruginosa and iron oxide nanoparticles

Poly aromatic hydrocarbons (PAHs) are considered as hazardous compounds which causes serious threat to the environment dua to their more carcinogenic and mutagenic impacts. In this study, Pseudomonas aeruginosa PP4 strain and synthesized iron nanoparticles were used to evaluate the biodegradation efficiency (BE %) of residual anthracene. The BE (%) of mixed degradation system (Anthracene + PP4+ FeNPs) was obtained about 67 %. The FTIR spectra result revealed the presence of functional groups (C-H, -CH3, CC, =C-H) in the residual anthracene. The FESEM and TEM techniques were used to determine the surface analysis of the synthesized FeNPs and the average size was observed by TEM around 5-50 nm. The crystalline nature of the synthesized iron nanoparticles was confirmed by the observed different respective peaks of XRD pattern. The various functional constituents (OH, C-H, amide I, CH3) were identified in the synthesized iron nanoparticles by FTIR spectrum. In conclusion, this integrated nano-bioremediation approach could be an promising and effective way for many environmental fields like cleanup of hydrocarbon rich environment.

Advanced treatment of coking wastewater: Recent advances and prospects

Advanced treatment of refractory industrial wastewater is still a challenge. Coking wastewater is one of coal chemical wastewater, which contains various refractory organic pollutants. To meet the more and more rigorous discharge standard and increase the reuse ratio of coking wastewater, advanced treatment process must be set for treating the biologically treated coking wastewater. To date, several advanced oxidation processes (AOPs), including Fenton, ozone, persulfate-based oxidation, and iron-carbon micro-electrolysis, have been applied for the advanced treatment of coking wastewater. However, the performance of different advanced treatment processes changed greatly, depending on the components of coking wastewater and the unique characteristics of advanced treatment processes. In this review article, the state-of-the-art advanced treatment process of coking wastewater was systematically summarized and analyzed. Firstly, the major organic pollutants in the secondary effluents of coking wastewater was briefly introduced, to better understand the characteristics of the biologically treated coking wastewater. Then, the performance of various advanced treatment processes, including physiochemical methods, biological methods, advanced oxidation methods and combined methods were discussed for the advanced treatment of coking wastewater in detail. Finally, the conclusions and remarks were provided. This review will be helpful for the proper selection of advanced treatment processes and promote the development of advanced treatment processes for coking wastewater.

Efficient composite chlorinated ethenes removal using gallic acid to enhance Fe/Ni nanoparticles activated persulfate

As the representative volatile chlorinated hydrocarbons detected in wastewater, the removal of composite chlorinated ethenes is a major challenge in wastewater treatment. In the present study, an efficient removal system for composite chlorinated ethenes was reported, in which gallic acid was used to enhance the activation of persulfate by Fe/Ni nanoparticles. The influences of gallic acid-Fe/Ni and persulfate concentrations, initial pH value, reaction temperature, inorganic anions, and natural organic matters were evaluated in the composite chlorinated ethenes removal. Our results showed that the gallic acid-Fe/Ni-persulfate system with 9.0 mM of gallic acid-Fe/Ni and 30.0 mM of persulfate yielded about 100% trichloroethylene removal and 97.3%-98.6% perchloroethylene removal in the pH range of 3.0-12.0. Electron paramagnetic resonance analysis and radical quenching experiments indicated that SO4•- and •OH were the predominant radical species under acidic and alkaline conditions. Ultraviolet visible spectroscopy and inductively coupled plasma optical emission spectrometer tests revealed the Fe-gallic acid chelation could regulate the concentration of iron ions and improve the reactivity of gallic acid-Fe/Ni. These results demonstrated that the gallic acid-Fe/Ni-persulfate system was a promising strategy for treating composite chlorinated ethenes-containing wastewater.

Microbially driven Fe-N cycle: Intrinsic mechanisms, enhancement, and perspectives

The iron‑nitrogen (FeN) cycle driven by microbes has great potential for treating wastewater. Fe is a metal that is frequently present in the environment and one of the crucial trace elements needed by microbes. Due to its synergistic role in the microbial N removal process, Fe goes much beyond the essential nutritional needs of microorganisms. Investigating the mechanisms behind the linked Fe-N cycle driven by microbes is crucial. The Fe-N cycle is frequently connected with anaerobic ammonia oxidation (anammox), nitrification, denitrification, dissimilatory nitrate reduction to ammonium (DNRA), Feammox, and simultaneous nitrification denitrification (SND), etc. Although the main mechanisms of Fe-mediated biological N removal may vary depending on the valence state of the Fe, their similar transformation pathways may provide information on the study of certain element-microbial interactions. This review offers a thorough analysis of the facilitation effect and influence of Fe on the removal of nitrogenous pollutants in various biological N removal processes and summarizes the ideal Fe dosing. Additionally, the synergistic mechanisms of Fe and microbial synergistic N removal process are elaborated, covering four aspects: enzyme activity, electron transfer, microbial extracellular polymeric substances (EPS) secretion, and microbial community interactions. The methods to improve biological N removal based on the intrinsic mechanism were also discussed, with the aim of thoroughly understanding the biological mechanisms of Fe in the microbial N removal process and providing a reference and thinking for employing Fe to promote microbial N removal in practical applications.

Degradation of reactive red 198 dye from aqueous solutions by combined technology advanced sonofenton with zero valent iron: Characteristics/ effect of parameters/kinetic studies

Dyes are one of the most common contaminants in industrial effluents, whose continuous release into the environment has become an increasing global concern. In this work, nanoparticles of zero-valent iron (NZVI) were synthesized using the chemical regeneration method ،and were utilized for the first time as a catalyst in the advanced Sono-Nano-Fenton hybrid method for the decomposition of Reactive Red 198 (RR198). The properties of zero-valent iron nanoparticles were analyzed using SEM and XRD. The effect of pH, initial dye concentration, nanoparticle dosage, zero-valent iron and H2O2 concentration on the decomposition efficiency of Red Reactive 198 was investigated. Comparing the efficiency of Reactivate 198 dye degradation in Sonolysis, Sono-NZVI, Sono-H2O2 and Sono-Nano Fenton processes showed that 97 % efficiency was achieved by the Sono-Nano Fenton process in 60 min. The kinetics of the removal process showed that this process follows pseudo-first-order kinetics and the Langmuir-Hinshelwood model. The results indicate that the effectiveness of the ultrasonic process in removing resistant organic pollutants such as dyes increases tremendously with the synergy of the Fenton process.

Muscovite clay for methylene blue removal: advanced optimization and Al-guided breakthroughs-an independent application from prior antibiotic removal investigation

This study evaluates the efficacy of muscovite mineral clay as an adsorbent for removing Methylene Blue (MB) from water-based solutions. The research examined the impact of initial MB concentration, adsorbent mass, and time on the MB removal process. Two modeling techniques, namely Box-Behnken design with response surface methodology (BBD-RSM) and Artificial Neural Network (ANN), were employed to accurately predict the MB removal efficiency. The RSM and ANN models yielded satisfactory results in estimating MB removal efficiency. To further enhance the optimization process, conventional and techno-economic methods were implemented. The conventional method aimed to maximize dye removal efficiency (R), while the techno-economic approach incorporated multiple objectives. The comparative analysis demonstrated that the techno-economic optimization method outperformed the conventional method. This study emphasizes the significance of considering multiple objectives and integrating techno-economic factors in optimizing clay adsorption processes. The successful application of the techno-economic optimization approach highlights its potential as a robust optimization method, particularly in the field of wastewater treatment. The findings provide valuable insights for optimizing adsorption and advancing environmental remediation practices.

Removal of sulfonamide antibiotics by a sonocatalytic Fenton-like reaction: Efficiency and mechanisms

With the widespread use of sulfonamide antibiotics (SAs), SAs are detected as residues in aquatic environments, posing a serious threat to human life and safety. Because of their high water solubility, fast transmission rate, and strong antibacterial properties, the safe disposal of SAs has become a key constraint for water quality assurance. Therefore, an ultrasound (US)-assisted zero-valent iron (ZVI)/persulfate (PS) system was proposed to explore the rapid and effective degradation of SAs. Comparative experiments were performed to study the removal of sulfadiazine (SDZ) by US, ZVI, PS, US/ZVI, US/PS, ZVI/PS, and US-ZVI/PS systems, respectively. Experimental results indicated that the highest removal efficiency of SDZ was ahieved in US-ZVI/PS system (97.4%), which were 2-44 times higher than that in other systems. Furthermore, the degradation efficiency of five typical SAs was achieved over 95%, demonstrating the effectiveness of the US ZVI/PS system for SAs removal. Also, quantum chemical computations for potential reactive sites of SAs and intermediate product detection by HPLC‒MS/MS were performed. The radical attack on active sites of SAs, such as N atom (number 7), was the main reason for SAs removal in US-ZVI/PS system. Besides, the common degradation pathways of six typical SAs were defined as S-N bond cleavage, C-N bond cleavage, benzene ring hydroxylation, aniline oxidation, and R substituent oxidation. Interestingly, the unique pathway of "SO2 group extraction" was observed in the degradation of six-membered ring SAs. Therefore, the US-ZVI/PS system is a promising and cost-effective method for the removal of SAs and other refractory pollutants.

A comparative study of methylene blue adsorption and removal mechanisms by calcium carbonate from different sources

Efficient removal of organic dye pollution from contaminated water is a concern in the absorbent applications. In this study, a green biogenic calcium carbonate (BCC) absorbent was fabricated using Bacillus licheniformis for the removal of methylene blue (MB) from water. This was found to have superior adsorption capacity compared with abiotic calcium carbonate (ACC) and operate within a broad pH range from 3 to 9. MB adsorption on BCC was physical and exothermic. The hydrophobic features, rough nanoporous microstructure, and organic-inorganic mesoporous structure of the BCC may all be responsible for its favorable adsorption mass transfer. The adsorption energy of BCC had a more negative value than that of ACC, indicating a stronger MB interaction with BCC with a lower energy barrier. Hydrogen bonding and electrostatic attraction were involved in the adsorption process. Overall, the findings established a theoretical foundation for the application of BCC in remediation of MB-contaminated water.

Novel carbon-based composites enriched with Fe and Mn as effective and eco-friendly adsorbents of heavy metals in multicomponent solutions

With increasing demand for adsorbents highly effective in pollutant removal, carbon-based porous materials are becoming more and more popular. In this work, a new approach to the synthesis of such solids using an environmentally friendly, two-step preparation method is presented. A series of hybrid porous silica-containing carbon composites was synthesized, namely: metal free (C/SiO2), enriched with manganese (C/Mn/SiO2), as well as iron (C/Fe/SiO2). The effect of additives on the structure and morphology of the composites was evaluated using X-ray photoelectron spectroscopy (XPS), nitrogen adsorption/desorption and scanning electron microscope (SEM). The as-synthesized carbons were used as effective adsorbents for the simultaneous removal of heavy metals, including lead (Pb(II)) and zinc (Zn(II)) ions. In particular, it was determined that C/Mn/SiO2 sample demonstrated the highest adsorption capacity towards Pb(II) and Zn(II) ions. It was equal to 211.60 mg/g for Pb(II) and 74.95 mg/g for Zn(II). Zeta potential and surface charge density of the solids, with and without metals, were investigated to determine electrical double layer structure, whereas stability studies and aggregate size measurements were performed to estimate solid aggregation under selected conditions. It was established that solids with adsorbed metals formed suspensions with lower stability than those without ions. This, in turn, facilitates their separation from aqueous solutions.

Surfactants in water and wastewater (greywater): Environmental toxicity and treatment options

Surfactant, an emerging pollutant present in greywater, raises the toxicity levels in the water body. Soap, detergent, and personal care items add surfactant to greywater. Due to excessive washing and cleaning procedures brought on by the COVID-19 pandemic, the release of surfactants in greywater has also increased. Considering the environmental toxicity and problems it creates during the treatment, it's essential to remove surfactants from the wastewater. This review intends to explain and address the environmental toxicity of the surfactant released via greywater and current techniques for surfactant removal from wastewater. Various physical, chemical, and biological methods are reported. Modern adsorbents such as hydrophilic silica nanoparticles, chitosan, fly ash, and iron oxide remove surfactants by adsorption. Membrane filtration effectively removes surfactants but is not cost-effective. Coagulants (chemical and natural coagulants) neutralize surfactant charges and help remove them as bigger particles. Electrocoagulation/electroflotation causes surfactants to coagulate and float. Microorganisms break down surfactants in microbial fuel cells to generate power. Surfactants are removed by natural processes and plants in constructed wetlands where traditional aerobic and anaerobic approaches use microbes to break down surfactants. Constructed wetlands, natural coagulation-flocculation, and microbial fuel cells are environmentally beneficial methods to remove surfactants from wastewater.

Atomic hydrogen-mediated enhanced electrocatalytic hydrodehalogenation on Pd@MXene electrodes

In this study, a Pd@MXene catalyst was synthesized to enhance the electrocatalytic hydrodehalogenation (ECH) of emerging halogenated organic pollutants (HOPs) by improving the dispersibility, catalytic activity, and stability of palladium (Pd). The average size of Pd nanoparticles (NPs) was reduced to 3.62 ± 0.34 nm with a more intensive peak of Pd (111), which facilitated atomic hydrogen (H*) production. The Pd@MX/CC electrode demonstrated superior ECH activity for diclofenac (DCF) degradation, with a reaction rate constant (kobs) 2.48 times higher than that of Pd/CC (without MXene). The satisfactory ECH performance of Pd@MX/CC remained consistent within a wide range of initial DCF concentrations (5-100 mg/L), and no significant ECH attenuation was observed even after up to 10 batches. Furthermore, the high activity of Pd@MX/CC was also observed in the ECH of other halogenated organic pollutants (levofloxacin, tetrabromobisphenol A, and diatrizoate). Density functional theory (DFT) calculations revealed that electronic configuration modulation of the Pd@MXene catalyst optimized binging energies to H* , DCF, and dechlorinated products, thereby enhancing the ECH efficiency of DCF.

Use of Co3O4 nanoparticles with different surface morphologies for removal of toxic substances and investigation of antimicrobial activities via in vivo studies

Co3O4 nanoparticles (NPs) were formed using hydrothermal synthesis method and various surfactants to study the effect of changing surface morphology on catalytic and antibacterial activities. FT-IR, TEM, SEM, BET, XRD, and XPS analyses were performed to characterize the NPs. It was observed that as the morphology of Co3O4 changes, it creates differences in the reduction efficiency of organic dyes and p-nitrophenol (p-NP), which are toxic to living organisms and widely used in industry. The reaction rate constants (Kapp) for Co3O4-urea, Co3O4-ed, and Co3O4-NaOH in the reduction of p-NP were found to be 1.86 × 10-2 s-1, 1.83 × 10-2 s-1, and 2.4 × 10-3 s-1, respectively. In the presence of Co3O4-urea catalyst from the prepared nanoparticles, 99.29% conversion to p-aminophenol (p-AP) was observed, while in the presence of the same catalyst, 98.06% of methylene blue (MB) was removed within 1 h. The antibacterial activity of Co3O4 particles was compared with five standard antibiotics for both gram-positive and gram-negative bacteria. The results obtained indicate that the antimicrobial activity of the synthesized Co3O4 particles has a remarkable inhibitory effect on the growth of various pathogenic microorganisms. The current work could be an innovative and beneficial search for both biomedical and wastewater treatment applications.

Highly Stable, Mechanically Enhanced, and Easy-to-Collect Sodium Alginate/NZVI-rGO Gel Beads for Efficient Removal of Cr(VI)

Nanoscale zero-valent iron (NZVI) is a material that is extensively applied for water pollution treatment, but its poor dispersibility, easy oxidation, and inconvenient collection limit its application. To overcome these drawbacks and limit secondary contamination of nanomaterials, we confine NZVI supported by reduced graphene oxide (rGO) in the scaffold of sodium alginate (SA) gel beads (SA/NZVI-rGO). Scanning electron microscopy showed that the NZVI was uniformly dispersed in the gel beads. Fourier transform infrared spectroscopy demonstrated that the hydrogen bonding and conjugation between SA and rGO allowed the NZVI-rGO to be successfully embedded in SA. Furthermore, the mechanical strength, swelling resistance, and Cr(VI) removal capacity of SA/NZVI-rGO were enhanced by optimizing the ratio of NZVI and rGO. Interestingly, cation exchange may drive Cr(VI) removal above 82% over a wide pH range. In the complex environment of actual Cr(VI) wastewater, Cr(VI) removal efficiency still reached 70.25%. Pseudo-first-order kinetics and Langmuir adsorption isotherm are preferred to explain the removal process. The mechanism of Cr(VI) removal by SA/NZVI-rGO is dominated by reduction and adsorption. The sustainable removal of Cr(VI) by packed columns could be well fitted by the Thomas, Adams-Bohart, and Yoon-Nelson models, and importantly, the gel beads maintained integrity during the prolonged removal. These results will contribute significant insights into the practical application of SA/NZVI-rGO beads for the Cr(VI) removal in aqueous environments.

Flocculation synergistic with nano zero-valent iron augmented attapulgite @ chitosan as Fenton-like catalyst for the treatment of landfill leachate

In this study, nano-zero-valent iron (NZVI) was added to attapulgite/chitosan and used as a catalyst in the heterogeneous Fenton process to degrade stabilized landfill leachate. Landfill leachate has serious environmental impacts due to the complexity and diversity of its pollutants. A magnetic catalyst (NZVI@PATP/CS) was prepared by a liquid-phase reduction method. The NZVI@PATP/CS were characterized by XRD, FTIR and SEM. The pH of leachate and the dosage of catalyst and H2O2 were changed to determine the best-operating conditions for the effective removal of chemical oxygen demand (COD) and total phosphorus(TP). To understand the adsorption degradation mechanism, the quenching experiments of free radicals were carried out. The results showed that the degradation rates of COD and TP were 66% and 92%, respectively, under the optimum pH value of 8, the dosage of H2O2 of 5 mL, and the dosage of the catalyst of 0.25 g for 60 min.

Chitosan-stabilized iron-copper nanoparticles for efficient removal of nitrate

Chitosan-stabilized iron-copper nanomaterials (CS-nZVI/Cu) were successfully prepared and applied to the nitrate removal. Batch experiments were conducted to examine the effects of experimental parameters on nitrate removal, including Cu loading, CS-nZVI/Cu dosages, initial nitrate concentrations, and initial pHs. From the experimental date, it was concluded that CS-nZVI/Cu has a high nitrate removal efficiency, which can be more than 97%, respectively, at Cu loading = 5%, dosages of CS-nZVI/Cu = 3 g/L, initial nitrate concentrations of 30~120 mg/L, and initial pH values = 2~9. Additionally, the kinetic data for CS-nZVI/Cu were found to fit well with the first-order kinetic model with a rate constant of 0.15 (mg∙L)1-n/min, where n=1. The Langmuir model showed a good fit for NO3- removal, indicating that monolayer chemisorption occurred. The SEM and TEM analyses showed that the addition of chitosan resulted in improved dispersion of the CS-nZVI/Cu. The CS-nZVI/Cu nanomaterials have a more complete elliptical shape and are between 50 and 100 nm in size. The XRD analysis showed that the chitosan encapsulation reduced the oxidation of the iron component and the main product was Fe3O4. The FT-IR analysis showed that the immobilization of chitosan and the iron was accomplished by the ligand interaction. The nitrogen adsorption-desorption isotherm results showed that the CS-nZVI/Cu specific surface area and pore volume decreased significantly after the reaction. Adsorption, oxidation, and reduction are possible mechanisms for nitrate removal by CS-nZVI/Cu. The XPS analysis investigated the contribution of nZVI and Cu in the removal mechanism. Adding copper accelerates the reaction time and rate. In addition, nZVI played a vital role in reducing nitrate to N2. Based on these results, it looks like CS-nZVI/Cu could be a satisfactory material for nitrate removal.

Removal of water pollutants using plant-based nanoscale zero-valent iron: A review

Nanotechnology has been increasingly explored for the treatment of various waste streams. Among different nanoparticles, nanoscale zerovalent iron (nZVI) has been extensively investigated due to its high reactivity and strong reducing power. However, conventional methods for the synthesis of nZVI particles have several limitations and led to the green synthesis of nZVI using plant-based materials. Plant extracts contain various reducing agents that can be used for nZVI synthesis, eliminating the need for toxic chemicals, and reducing energy consumption. Additionally, each plant species used for nZVI synthesis results in unique physicochemical properties of the nanoparticles. This review paper provides an overview of plant-based nZVI particle synthesis, its characteristics, and its application for the removal of different classes of pollutants such as dyes, heavy metals, nutrients, and trace organic pollutants from water. The review shows that continued research on plant-based nZVI particles to fully understand its potential in wastewater treatment, especially for the removal of a wider variety of pollutants, and for improving sustainability and reducing the cost and environmental impact of the process, is necessary.

In situ prepared Chlorella vulgaris-supported nanoscale zero-valent iron to remove arsenic (III)

Nanoscale zero-valent iron (nZVI) has a high removal affinity toward arsenic (As). However, the agglomeration of nZVI reduces the removal efficiency of As and, thus, limit its application. In this study, we report an environmentally friendly novel composite of Chlorella vulgaris-supported nanoscale zero-valent iron (abbreviated as CV-nZVI) that exhibits a fast and efficient removal of As(III) from As-contaminated water. Scanning electron microscopy-energy-dispersive spectroscopy (SEM-EDS), X-ray diffractometry (XRD), attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS) were used to characterize and analyze the CV-nZVI. These results indicated that the stabilization effect of C. vulgaris reduced the nZVI agglomeration and enhanced the reactivity of nZVI. The experiments showed a removal efficiency of 99.11% for As(III) at an optimum pH of 7.0. The adsorption kinetics and isotherms followed the pseudo-second-order kinetic model and Langmuir adsorption isotherm with the superior maximum adsorption capacities of 34.11 mg/g for As(III). The FTIR showed that the As(III) was adsorbed on the CV-nZVI surface by complexation reaction, and XPS indicated that oxidation reaction was also involved. After five reuse cycles, the removal efficiency of As(III) by CV-nZVI was 32.93%, suggesting that the CV-nZVI had some reusability and regeneration. Overall, this work provides a practical and highly efficient approach for As remediation in As-contaminated water, and simultaneously resolves the agglomeration problems of nZVI nanoparticles.

Influence of organic cosolvents on hexabromobenzene degradation in solution by montmorillonite-templated subnanoscale zero-valent iron

Organic cosolvents are commonly used to increase the dissolution of poorly water-soluble organic pollutants into aqueous solutions during environmental remediation. In this study, the influences of five organic cosolvents on hexabromobenzene (HBB) degradation catalyzed by one typical reactive material montmorillonite-templated subnanoscale zero-valent iron (CZVI) were investigated. The results demonstrated that all cosolvents promoted HBB degradation but the degree of promotion was different for different cosolvents, which was associated with inconsistent solvent viscosities, dielectric constant properties, and the extent of interactions between cosolvents with CZVI. Meanwhile, HBB degradation was highly dependent on the volume ratio of cosolvent to water, which increased in the range of 10%-25% but persistently decreased in the range of more than 25%. This might be due to the fact that the cosolvents increased HBB dissolution at low concentrations but reduced the protons supplied by water and the contact between HBB with CZVI at high concentrations. In addition, the freshly-prepared CZVI had higher reactivity to HBB than the freeze-dried CZVI in all water-cosolvent solutions, probably because freeze-drying reduced the interlayer space of CZVI and thus the contact probability between HBB and active reaction sites. Finally, the CZVI-catalyzed HBB degradation mechanism was proposed as the electron transfer between zero-valent iron and HBB, which led to the formation of four debromination products. Overall, this study provides helpful information for the practical application of CZVI in the remediation of persistent organic pollutants in the environment.

Experimental and computational study of metal oxide nanoparticles for the photocatalytic degradation of organic pollutants: a review

Photocatalysis is a more proficient technique that involves the breakdown or decomposition of different organic contaminants, various dyes, and harmful viruses and fungi using UV or visible light solar spectrum. Metal oxides are considered promising candidate photocatalysts owing to their low cost, efficiency, simple fabricating method, sufficient availability, and environment-friendliness for photocatalytic applications. Among metal oxides, TiO2 is the most studied photocatalyst and is highly applied in wastewater treatment and hydrogen production. However, TiO2 is relatively active only under ultraviolet light due to its wide bandgap, which limits its applicability because the production of ultraviolet is expensive. At present, the discovery of a photocatalyst of suitable bandgap with visible light or modification of the existing photocatalyst is becoming very attractive for photocatalysis technology. However, the major drawbacks of photocatalysts are the high recombination rate of photogenerated electron-hole pairs, the ultraviolet light activity limitations, and low surface coverage. In this review, the most commonly used synthesis method for metal oxide nanoparticles, photocatalytic applications of metal oxides, and applications and toxicity of different dyes are comprehensively highlighted. In addition, the challenges in the photocatalytic applications of metal oxides, strategies to suppress these challenges, and metal oxide studied by density functional theory for photocatalytic applications are described in detail.

The Impact of Solution Ionic Strength, Hardness, and pH on the Sorption Efficiency of Polychlorinated Biphenyls in Magnetic Nanocomposite Microparticle (MNM) Gels

Environmental conditions of groundwater and surface water greatly vary as a function of location. Factors such as ionic strength, water hardness, and solution pH can change the physical and chemical properties of the nanocomposites used in remediation and the pollutants of interest. In this work, magnetic nanocomposite microparticle (MNM) gels are used as sorbents for remediation of PCB 126 as model organic contaminant. Three MNM systems are used: curcumin multiacrylate MNMs (CMA MNMs), quercetin multiacrylate MNMs (QMA MNMs), and polyethylene glycol-400-dimethacrylate MNMs (PEG MNMs). The effect of ionic strength, water hardness, and pH were studied on the sorption efficiency of the MNMs for PCB 126 by performing equilibrium binding studies. It is seen that the ionic strength and water hardness have a minimal effect on the MNM gel system sorption of PCB 126. However, a decrease in binding was observed when the pH increased from 6.5 to 8.5, attributed to anion-π interactions between the buffer ions in solution and the PCB molecules as well as with the aromatic rings of the MNM gel systems. Overall, the results indicate that the developed MNM gels can be used as magnetic sorbents for polychlorinated biphenyls in groundwater and surface water remediation, provided that the solution pH is controlled.

Attenuation of tetracyclines and related resistance genes in soil when exposed to nanoscale zero-valent iron

Antibiotics pollution in soil poses increasing threats to human health due to stimulated proliferation and transmission of antibiotic resistance genes (ARGs). Nanoscale zero-valent iron (NZVI) is a promising material for the remediation of antibiotics, but how NZVI affects the diversity, abundance, and horizontal gene transfer potentials of ARGs remains unclear. Herein, the biotic and abiotic effects of NZVI at different concentrations on tetracyclines (TCs) and the associated ARGs were investigated. Results showed NZVI could effectively accelerate the degradation of TCs, which increased from 51.38% (without NZVI) to 57.96%- 71.66% (1-10 g NZVI/kg) in 20 days. Biotic degradation contributed to 66.10%- 76.30% of the total TCs removal. NZVI induced TCs biodegradation was probably due to alleviated toxicity of TCs on cells and increased microbial biomass and enzyme activities. Additionally, TCs-related ARGs were attenuated with decreased horizontal gene transfer potentials of intI1 and ISCR1, but opposite effects were observed for non TC-related ARGs, especially during excess exposure to NZVI. This study illustrated the possibility of remediating of antibiotic contaminated soil by NZVI and meanwhile reducing the potential risks of ARGs.

Oxidation of Pharmaceuticals by Ferrate(VI)-Amino Acid Systems: Enhancement by Proline

The occurrence of micropollutants in water threatens public health and ecology. Removal of micropollutants such as pharmaceuticals by a green oxidant, ferrate(VI) (FeVIO42-, Fe(VI)) can be accomplished. However, electron-deficient pharmaceuticals, such as carbamazepine (CBZ) showed a low removal rate by Fe(VI). This work investigates the activation of Fe(VI) by adding nine amino acids (AA) of different functionalities to accelerate the removal of CBZ in water under mild alkaline conditions. Among the studied amino acids, proline, a cyclic AA, had the highest removal of CBZ. The accelerated effect of proline was ascribed by demonstrating the involvement of highly reactive intermediate Fe(V) species, generated by one-electron transfer by the reaction of Fe(VI) with proline (i.e., Fe(VI) + proline → Fe(V) + proline•). The degradation kinetics of CBZ by a Fe(VI)-proline system was interpreted by kinetic modeling of the reactions involved that estimated the rate of the reaction of Fe(V) with CBZ as (1.03 ± 0.21) × 106 M-1 s-1, which was several orders of magnitude greater than that of Fe(VI) of 2.25 M-1 s-1. Overall, natural compounds such as amino acids may be applied to increase the removal efficiency of recalcitrant micropollutants by Fe(VI).

Reductive dechlorination of chlorinated ethenes by ball milled and mechanochemically sulfidated microscale zero valent iron: A comparative study

Ball milling is an effective technique to not only activate and reduce the size of commercial microscale zero valent iron (mZVI) but also to mechanochemically sulfidate mZVI. Yet, little is known about the difference between how chlorinated ethenes (CEs) interact with ball milled mZVI (mZVI^bm) and mechanochemically sulfidated mZVI (S-mZVI^bm). We show that simple ball milling exposed the active Fe⁰ sites, while mechanochemical sulfidation diminished Fe⁰ sites and meanwhile increased S^2- sites. Mechanochemical sulfidation with [S/Fe]_dosed increased from 0 to 0.20 promoted the particle reactivity most for TCE dechlorination (∼14-fold), followed by PCE and 1,1-DCE while it diminished the reactivity for trans-DCE (∼0.4-fold), cis-DCE (∼0.02-fold) and VC (∼0.002-fold) compared to simple ball milling. Sulfidation also improved the electron efficiency of CE dechlorination, except for cis-DCE and VC. The k_SA of cis-DCE, VC and trans-DCE dechlorination positively correlated with surface Fe⁰ content, suggesting their dechlorination was mainly mediated by Fe⁰ site or reactive atomic hydrogen. The k_SA of TCE dechlorination positively correlated with surface S^2- content and the dechlorination mainly occurred on S^2- sites via direct electron transfer. Increased sulfidation favored direct electron transfer mechanism. The k_SA of PCE and 1,1-DCE was not dependent on either parameter and their dechlorination was equally achieved through either mechanism.

Sulfidated microscale zero-valent iron/reduced graphene oxide composite (S-mZVI/rGO) for enhanced degradation of trichloroethylene: The role of hydrogen spillover

Atomic hydrogen (H*) has long been thought to play an important role in the dechlorination of trichloroethylene (TCE) by carbon-supported zero-valent iron (ZVI), which offers an alternative pathway for TCE dechlorination. Herein, we demonstrate that the reductive dechlorination of TCE by sulfidated microscale ZVI (S-mZVI) can be further enhanced by promoting the formation of H* through the introduction of reduced graphene oxide (rGO). The completely degradation of 10 mg/L TCE can be achieved by S-mZVI/rGO within 24 h, which was 3.3 times faster than that of S-mZVI. The change in the distribution of TCE degradation products over time suggests that the introduction of rGO leads to a change in the dechlorination pathway. The percentage of ethane in the final products of TCE degradation by S-mZVI/rGO was 34.3 %, while that of S-mZVI was only 21.9 %. The electrochemical tests confirmed the occurrence of hydrogen spillover in the S-mZVI/rGO composite, which promoted the reductive dechlorination of TCE by H*. Although the S-mZVI/rGO composite had stronger hydrogen evolution propensity than S-mZVI, the S-mZVI/rGO composite still exhibited higher electron utilization efficiency than S-mZVI thanks to the increased utilization of hydrogen.

Removal of pharmaceutically active compounds (PhACs) by zero-valent iron: quantification of removal mechanisms consisting of degradation, adsorption and co-precipitation

The removal mechanisms of carbamazepine (CBZ), which is one of pharmaceutically active compounds, using zero-valent iron (ZVI) were quantified by defining three fractions, namely "degradation", "adsorption", and "co-precipitation". The maximum total organic carbon (TOC) removal was obtained at pH 4. The results demonstrate that the adsorption on the ZVI surface is dominant in the TOC removal of CBZ for 4 ≤ pH ≤ 6 while the degradation by oxidative and reductive reactions is efficient exclusively for pH ≤ 3. TOC removal was not obtained for pH ≥ 8. The most dominant mechanism in the removal of CBZ by ZVI is the adsorption onto the iron oxides/hydroxides layer formed on ZVI surface rather than the degradation by oxidative and reductive reactions including Fenton and Fenton-like reactions for pH ≥ 4. A novel kinetic model for removal of CBZ by ZVI was developed to simulate the dynamic concentration profiles of CBZ, TOC, total Fe ions, and dissolved oxygen linked closely with each other and the contributions of degradation, adsorption, and co-precipitation in TOC removal of CBZ. Reasonable agreement between experimental data and model predictions suggests the applicability of the proposed kinetic model to quantitatively analyze the mechanisms of CBZ removal by ZVI.

Two dimensional (2D) materials and biomaterials for water desalination; structure, properties, and recent advances

BACKGROUND

An efficient solution to the global freshwater dilemma is desalination. MXene, Molybdenum Disulfide (MoS₂), Graphene Oxide, Hexagonal Boron Nitride, and Phosphorene are just a few examples of two-dimensional (2D) materials that have shown considerable promise in the development of 2D materials for water desalination. However, other promising materials for desalinating water are biomaterials. The benefits of bio-materials are their wide distribution, lack of toxicity, and superior capacity for water desalination.

METHODS

For the rational use of water and the advancement of sustainable development, it is of the utmost importance to research 2D-dimensional materials and biomaterials that are effective for water desalination. The scientific community has concentrated on wastewater remediation using bio-derived materials, such as nanocellulose, chitosan, bio-char, bark, and activated charcoal generated from plant sources, among the various endeavors to enhance access to clean water. Moreover, the 2D-materials and biomaterials may have ushered in a new age in the production of desalination materials and created a promising future.

RESULTS

The present review article focuses on and reviews the progress of 2D materials and biomaterials for water desalination. Their properties, surface, and structure, combined with water desalination applications, are highlighted. Further, the practicability and potential future directions of 2D materials and biomaterials are proposed. Thus, the current work provides information and discernments for developing novel 2D materials and biomaterials for wastewater desalination. Moreover, it aims to promote the contribution and advancement of materials for water desalination, fabrication, and industrial production.

Electrochemical analysis of glyphosate using porous biochar surface corrosive nZVI nanoparticles

Glyphosate [N-(phosphonomethyl)glycine] is a widely used phosphonate herbicide for different agricultural purposes. Due to its widespread use, suspected toxicity, and ubiquitous bioaccumulation, it is one of the most harmful contaminants found in drinking water. This demands efficient sensing and removal of glyphosate from contaminated water. Here, we report the decoration of novel and highly porous biochar with nanozero-valent iron (nZVI) nanoparticles to develop an efficient electrochemical sensor for the trace detection of glyphosate. The as-synthesized composite was thoroughly characterized by various state-of-the-art instrumental techniques. The electron micrographs of the composite materials revealed the cavity-like structure and the abundant loading of nZVI nanoparticles. FTIR and XPS analyses confirmed the presence of oxygen-rich functionalities and Fe(0) in the composite nanostructure. Electrochemical analysis through CV, LSV, and DPV techniques suggested efficient sensing activity with a limit of detection as low as 0.13 ppm. Furthermore, the chronopotentiometric response suggested excellent and superior stability for long-term applications. To gain more insight into the interaction between glyphosate and the composite material, DFT calculations were carried out. The Frontier Molecular Orbital study (FMO), Molecular Electrostatic Potentials (MEPs), and Density of States (DOS) suggest an increase in the electron density, an increase in the DOS, and a decrease in the HOMO-LUMO band gap by combining nZVI nanoparticles and biochar. The results suggest more facile electron transfer from the composite for trace detection of glyphosate. As a proof of concept, we have demonstrated that real-time analysis of milk, apple juice, and the as-synthesized composite shows promising results for glyphosate detection with an excellent recovery rate.

Ga based Sillenite-TiO2 composite for efficient sunlight induced photo reduction of Cr (VI) and photo degradation of ampicillin

This work reports the design and development of an efficient sillenite based visible light photoactive Bi₂₄Ga₂O₃₉-TiO₂ (BGT) heterostructure. Structural and morphological studies based on X-ray diffraction (XRD) and high-resolution scanning electron microscopy (HRSEM) confirm the formation of combined phase as well the overall morphology of composite BGT. Additionally, X-ray photoelectron spectroscopy (XPS) results confirm the presence of Bi³⁺, Ga³⁺, Ti⁴⁺ & O^2-. The composite exhibits a shift in the absorbance edge towards visible region of electromagnetic spectrum when compared to that of TiO₂. Suitable band edge positions in the composite facilitate the formation of type-1 heterojunction enhancing visible light photocatalytic property. The photocatalytic activity is evident from photo reduction of Cr (VI) (95% reduction in 180 min). The composite also plays an improved and effective role in the degradation of persistent drug ampicillin-cloxacillin (AMC) with a rate constant of 0.02 min^-1. Photocatalytic experiments conducted at different pH values showed higher performance at lower pH ∼3. Trapping experiments performed on the sample confirm the role of holes as the main active species during photocatalysis. Appreciable recyclability of BGT composite was noted with respect to AMC drug degradation.

Fabrication and response optimization of Moringa oleifera-functionalized nanosorbents for the removal of diesel range organics from contaminated water

The purpose of this research is to synthesize environmentally friendly nanosorbents for the novel adsorption of diesel range organics (DRO) from contaminated water. Central composite design (CCD) analysis of response surface methodology (RSM) was employed in a model fitting of the variables predicting the adsorption efficiency of Moringa oleifera-functionalized zerovalent iron particles (ZINPs) for the removal of DRO. The effects of the reaction parameters on the response were screened using 2⁴ factorial designs to determine the statistically significant independent variables. A quadratic model predicting the DRO adsorption efficiency of ZINPs with an F value of 276.84 (p value < 0.0001) was developed. Diagnostic plots show that the predicted values were in excellent agreement with actual experimental values (R² = 0.99). The maximum percentage removal of DRO of 92.6% was achieved after optimization, using the synthesized ZINPs after 8 h of contact between DRO substrates and ZINPs at pH of 8, the temperature of 25 °C, with an adsorbent dosage of 2 g/L and at composite desirability of 1. Characterization of ZINPs revealed the formation of quasi nanospheres and nanocubes with an average particle diameter of 50.9 ± 9.7, a crystallite size of 15.31 nm, a crystallinity index of 32.47% and a pore width of 75.69-88.59 nm. The adsorption equilibrium data modelling of ZINPs for adsorption of DRO was best described by Langmuir isotherm with the maximum monolayer coverage capacity of 7.194 mg/g. The separation factor [Formula: see text], indicated favourable adsorption. The adsorption kinetic data were consistent with pseudo-second-order kinetics indicating probable chemisorption.

In situ microcosm remediation of polyaromatic hydrocarbons: influence and effectiveness of Nano-Zero Valent Iron and activated carbon

Nano-zero-valent iron (nZVI) and activated carbon (AC) addition are ongoing techniques for the remediation of hydrophobic organic compound-contaminated sediment and water, but with still unexplored eco(toxico)logical implications, especially when applied in situ. In this study, we investigated AC and nZVI as remediation methods for marine contaminated sediment and water, including chemical and toxicity (Artemia franciscana survival and genotoxicity) surveys. The removal efficiency of AC and nZVI (about 99%) was similar in both sediment and seawater, while the survival of nauplii and adults was mainly impacted by nZVI than AC. At the molecular level, the nZVI-addition induced down-regulation in the expression of two stress and one developmental genes, whereas AC was able to up-regulated only one gene involved in stress response. Results suggested that the use of AC is safer than nZVI that requires further investigation and potential optimization to reduce secondary undesired effects.

Biochar for the removal of contaminants from soil and water: a review

Biochar shows significant potential to serve as a globally applicable material to remediate water and soil owing to the extensive availability of feedstocks and conducive physio-chemical surface characteristics. This review aims to highlight biochar production technologies, characteristics of biochar, and the latest advancements in immobilizing and eliminating heavy metal ions and organic pollutants in soil and water. Pyrolysis temperature, heat transfer rate, residence time, and type of feedstock are critical influential parameters. Biochar’s efficacy in managing contaminants relies on the pore size distribution, surface groups, and ion-exchange capacity. The molecular composition and physical architecture of biochar may be crucial when practically applied to water and soil. In general, biochar produced at relatively high pyrolysis temperatures can effectively manage organic pollutants via increasing surface area, hydrophobicity and microporosity. Biochar generated at lower temperatures is deemed to be more suitable for removing polar organic and inorganic pollutants through oxygen-containing functional groups, precipitation and electrostatic attraction. This review also presents the existing obstacles and future research direction related to biochar-based materials in immobilizing organic contaminants and heavy metal ions in effluents and soil.

Graphical Abstract

Recent advances in bioremediation of heavy metals and persistent organic pollutants: A review

Heavy metals and persistent organic pollutants are causing detrimental effects on the environment. The seepage of heavy metals through untreated industrial waste destroys the crops and lands. Moreover, incineration and combustion of several products are responsible for primary and secondary emissions of pollutants. This review has gathered the remediation strategies, current bioremediation technologies, and their primary use in both in situ and ex situ methods, followed by a detailed explanation for bioremediation over other techniques. However, an amalgam of bioremediation techniques and nanotechnology could be a breakthrough in cleaning the environment by degrading heavy metals and persistant organic pollutants.