Synthesis and characterization of magnetic Fe3O4@CaSiO3 composites and evaluation of their adsorption characteristics for heavy metal ions

A two-component material (Fe₃O₄@CaSiO₃) with an Fe₃O₄ magnetite core and layered porous CaSiO₃ shell from calcium nitrate and sodium silicate was synthesized by precipitation. The structure, morphology, magnetic properties, and composition of the Fe₃O₄@CaSiO₃ composite were characterized in detail, and its adsorption performance, adsorption kinetics, and recyclability for Cu²⁺, Ni²⁺, and Cr³⁺ adsorption were studied. The Fe₃O₄@CaSiO₃ composite has a 2D core–layer architecture with a cotton-like morphology, specific surface area of 41.56 m²/g, pore size of 16 nm, and pore volume of 0.25 cm³/g. The measured magnetization saturation values of the magnetic composite were 57.1 emu/g. Data of the adsorption of Cu²⁺, Ni²⁺, and Cr³⁺ by Fe₃O₄@CaSiO₃ fitted the Redlich–Peterson and pseudo-second-order models well, and all adsorption processes reached equilibrium within 150 min. The maximum adsorption capacities of Fe₃O₄@CaSiO₃ toward Cu²⁺, Ni²⁺, and Cr³⁺ were 427.10, 391.59, and 371.39 mg/g at an initial concentration of 225 mg/L and a temperature of 293 K according to the fitted curve with the Redlich–Peterson model, respectively. All adsorption were spontaneous endothermic processes featuring an entropy increase, including physisorption, chemisorption, and ion exchange; among these process, chemisorption was the primary mechanism. Fe₃O₄@CaSiO₃ exhibited excellent adsorption, regeneration, and magnetic separation performance, thereby demonstrating its potential applicability to removing heavy metal ions.

     

Effect of influent C/N ratio on N2O emissions from anaerobic/anoxic/oxic biological nitrogen removal processes

The problem of producing strong greenhouse gas of nitrous oxide (N₂O) from biological nitrogen removal (BNR) process in wastewater treatment plants (WWTP) has elicited great concern from various sectors. In this study, three laboratory-scale wastewater treatment systems, with influent C/N ratios of 3.4, 5.4, and 7.5, were set up to study the effect of influent C/N ratio on N₂O generation in anaerobic/anoxic/oxic (A²O) process. Results showed, with the increased influent C/N ratio, N₂O generation from both nitrification and denitrification process was decreased, and the N₂O-N conversion ratio of the process was obviously reduced from 2.23 to 0.05%. Nitrification rate in oxic section was reduced, while denitrification rate in anaerobic and anoxic section was elevated and the removal efficiency of COD, NH₄ ⁺-N, TN, and TP was enhanced in different extent. As the C/N ratio increased from 3.4 to 7.5, activities of three key denitrifying enzymes of nitrate reductase, nitrite reductase, and nitrous oxide reductase were increased. Moreover, microorganism analysis indicated that the relative abundance of ammonium-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were positively correlated with N₂O generation, which was reduced from (8.42 ± 3.65) to (3.61 ± 1.66)% and (10.38 ± 4.12) to (4.67 ± 1.62)%, respectively. NosZ gene copy numbers of the A²O system were increased from (1.19 ± 0.49) × 10⁷ to (2.84 ± 0.54) × 10⁸ copies/g MLSS with the influent C/N ratio elevated from 3.4 to 7.5. Hence, appropriate influent C/N condition of A²O process could optimize the microbial community structure that simultaneously improve treatment efficiency and decrease the N₂O generation.

     

Performance comparison of commercial TiO2: separation and reuse for bacterial photo-inactivation and emerging pollutants photo-degradation

This research aims to compare the disinfection and degradation effectiveness in water of a commercial suspension of nano-TiO₂ (TiO₂Levenger) with the standard TiO₂Degussa P25. Photo-inactivation and photo-degradation experiments were conducted with UVA-vis light. Concerning the disinfection, the effects of TiO₂ dose (0–2 g/l), water matrix, bacterium type (Gram-positive or Gram-negative), and bacterial regrowth after the photo-treatments were studied for each catalyst. The experimental results show that Enterococcus sp. (Gram-positive) was more resistant to the photo-treatments than Escherichia coli (Gram-negative) for both catalyst; however, postirradiation trends showed similar behavior for both bacteria, favoring regrowth for short-treated cells and decay for longer-treated ones. Caffeine was selected as a model substance of pharmaceuticals and personal care products. In terms of caffeine removal, the effects of TiO₂ dose (0–2 g/l) and water matrix were analyzed. Besides, the comparison between mechanical coagulation-flocculation-decantation and simple decantation of TiO₂ was carried out. The results show that simple decantation allowed the recovery of 97.5% of TiO₂ Degussa P25 and TiO₂ Levenger within 1 day of simple decantation, while applying the proposed mechanical coagulation-flocculation decantation 99.7% of recovery of both catalysts was achieved in 2 hours. Finally, the subsequent reuse of both catalysts was proved with little loss of efficiency in terms of photo-disinfection during the four cycles. Nevertheless, the standard TiO₂ Degussa P25 photo-degradation efficiency of caffeine decreases considerably as compared to commercial suspension of TiO₂ Levenger concerning the reutilization.

     

Comparative studies of the Fe–UV, H2O2–UV, TiO2–UV/vis systems for the decolorization of a textile dye X-3B in water

The degradation of a common textile dye, Reactive-brilliant red X-3B, by several advanced oxidation technologies was studied in an air-saturated aqueous solution. The dye was resistant to the UV illumination (wavelength λ  320 nm), but was decolorized when one of Fe³⁺, H₂O₂ and TiO₂ components was present. The decolorization rate was observed to be quite different for each system, and the relative order evaluated under comparable conditions followed the order of Fe²⁺–H₂O₂–UV  Fe²⁺–H₂O₂ > Fe³⁺–H₂O₂–UV > Fe³⁺–H₂O₂ > Fe³⁺–TiO₂–UV > TiO₂–UV > Fe³⁺–UV > TiO₂–visible light (λ  450 nm) > H₂O₂–UV > Fe²⁺–UV. The mechanism for each process is discussed, and linked together for understanding the observed differences in reactivity.     

Fe_3O_4@SiO_2/TiO_2核壳结构纳米颗粒降解TNT溶液

针对TNT炸药废水具有成分复杂、排放量大、有毒等特点,立足于炸药废水在排放前的降解处理,研究开发一种基于核壳结构Fe3O4@SiO2/TiO2纳米颗粒的高效、可控回收、无二次污染且成本低的光催化降解方法。利用高温碳还原法和溶胶凝胶法制备了具有核壳结构的Fe3O4@SiO2/TiO2纳米颗粒。XRD分析表明,内核Fe3O4呈现磁铁矿特征,表面覆盖的纳米TiO2为锐钛矿型。磁滞回线测试结果显示,复合颗粒的饱和磁化强度为46.5 emu/g,N2吸附-解吸分析结果表明,该颗粒具有典型的介孔结构。使用Fe3O4@SiO2/TiO2纳米颗粒在紫外光下对含TNT废水进行降解,降解率达到81.9%,且颗粒的回收率达到88.4%,为实现高效、可控回收、无二次污染光催化-吸附降解TNT奠定了基础。     

Study on the denitrification performance of FexLayOz/activated coke for NH3-SCR and the effect of CO escaped from activated coke at mid-high temperature on catalytic activity

Currently, activated coke is widely used in the removal of multiple pollutants from industrial flue gas. In this paper, a series of novel Fe_xLa_yO_z/AC catalysts was prepared by the incipient wetness impregnation for NH₃-SCR denitrification reaction. The introduction of Fe-La bimetal oxides significantly improved the denitrification performance of activated coke at mid-high temperature, and 4% Fe_0.3La_0.7O_1.5/AC exhibited a superior NO_x conversion efficiency of 90.1% at 400 °C. The catalysts were further characterized by BET, SEM, XRD, Raman, EPR, XPS, FTIR, NH₃-TPD, H₂-TPR, et al., whose results showed that the perovskite-type oxide of LaFeO₃ and oxygen vacancies were produced on the catalysts’ surfaces during roasting. Fe-La doping enhanced the amount of acid sites (mainly Lewis and other stronger acid sites) and the content of multifarious oxygen species, which were beneficial for NO_x removal at mid-high temperature. Moreover, it was investigated that the effect of released CO from activated coke at mid-high temperature on the NO_x removal through the lifetime test, in which it was found that a large amount of CO produced by pyrolysis of activated coke could promote the NO_x removal, and long-term escaping of CO on the activated coke carrier did not have a significant negative impact on catalytic performance. The results of the TG-IR test showed that volatile matter is released from the activated coke while TG results showed that the weight loss rate of 4% Fe_0.3La_0.7O_1.5/AC only was 0.0015~0.007%/min at 300–400 °C. Hence, 4% Fe_0.3La_0.7O_1.5/AC had excellent thermal stability and denitrification performance to be continuously used at mid-high temperature. Finally, the mechanisms were proposed on the basis of experiments and characterization results.

     

The effect of γ-Fe2O3 nanoparticles on Escherichia coli genome

Extensive production and application of γ-Fe₂O₃ magnetic nanoparticles (MNPs) has increased their potential risk on environment and human health. This report illustrates a genetic impact of γ-Fe₂O₃ magnetic nanoparticles (MNPs) on Escherichia coli (E. coli). After 3000-generation incubation with MNPs addition, obvious genomic variations were revealed by using repetitive extragenic palindromic PCR (rep-PCR) DNA fingerprint technique. The physicochemical interactions between MNPs and bacteria could be responsible for such genomic responses. It was revealed that Fe³⁺ concentration increased in the medium. Transmission electronic microscopy (TEM) and flow cytometry (FCM) analysis consistently demonstrated the occurrences of adsorption and membranes-internalization of MNPs outside and inside cells. Both increased Fe³⁺ ion and the uptake of MNPs facilitated Fe binding with proteins and DNA strands, resulting in enhancing the mutation frequency of E. coli. Our results would be of great help to assessing the potential impact of MNPs on human and environment.     

Degradation of 2,4-D in soils by Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles combined with stimulating indigenous microbes

Purpose  

Degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) in soils by Fe₃O₄ nanoparticles combined with soil indigenous microbes was investigated, and the effects of Fe₃O₄ nanoparticles on soil microbial populations and enzyme activities were also studied.     

Modification of photocatalytic property of BaTiO3 perovskite structure by Fe2O3 nanoparticles for CO2 reduction in gas phase

In this work, perovskite structure of BaTiO₃ was coupled with Fe₂O₃ in different molar ratios achieving the best photocatalytic performance of CO₂ reduction in the presence of CH₄ as reducing agent; both of them are main greenhouse gases. The photocatalysts were synthesized by facile hydrothermal method. The samples were characterized by XRD, FTIR, FESEM, EDX, UV–Vis DRS, and photoluminescence (PL) analyses. The BaTiO₃ synthesized in this research showed a weak PL signal which is due to the intrinsic ferroelectric property as has been observed in previous reports. Compared to the pure BaTiO₃ and Fe₂O₃, the heterojunctions exhibited enhanced photocatalytic activity. The maximum CO₂ reduction under visible light irradiation was obtained to be 22% during 60 min process time. The enhanced photocatalytic activity could be attributed to the increased optical absorption, the good separation, and immigration of photogenerated charge carriers that decreased the recombination rate of charge carriers in the n–n heterojunction.

     

Assessment of nitrogen losses through nitrous oxide from abattoir wastewater-irrigated soils

The land disposal of waste and wastewater is a major source of N₂O emission. This is due to the presence of high concentrations of nitrogen (N) and carbon in the waste. Abattoir wastewater contains 186 mg/L of N and 30.4 mg/L of P. The equivalent of 3 kg of abattoir wastewater-irrigated soil was sieved and taken in a 4-L plastic container. Abattoir wastewater was used for irrigating the plants at the rates of 50 and 100 % field capacity (FC). Four crop species were used with no crop serving as a control. Nitrous oxide emission was monitored using a closed chamber technique. The chamber was placed inside the plastic container, and N₂O emission was measured for 7 days after the planting. A syringe and pre-evacuated vial were used for collecting the gas samples; a fresh and clean syringe was used each time to avoid cross-contamination. The collected gas samples were injected into a gas chromatography device immediately after each sampling to analyse the concentration of N₂O from different treatments. The overall N₂O emission was compared for all the crops under two different abattoir wastewater treatment rates (50 and 100 % FC). Under 100 % FC (wastewater irrigation), among the four species grown in the abattoir wastewater-irrigated soil, Medicago sativa (23 mg/pot), Sinapis alba (21 mg/pot), Zea mays (20 mg/pot) and Helianthus annuus (20 mg/pot) showed higher N₂O emission compared to the 50 % treatments—M. sativa (17 mg/pot), S. alba (17 mg/pot), Z. mays (18 mg/pot) and H. annuus (18 mg/pot). Similarly, pots with plants have shown 15 % less emission than the pots without plants. Similar trends of N₂O emission flux were observed between the irrigation period (4-week period) for 50 % FC and 100 % FC. Under the 100 % FC loading rate treatments, the highest N₂O emission was in the following order: week 1 > week 4 > week 3 > week 2. On the other hand, under the 50 % FC loading rate treatments, the highest N₂O emission was recorded in the first few weeks and in the following order: week 1 > week 2 > week 3 > week > 4. Since N₂O is a greenhouse gas with high global warming potential, its emission from wastewater irrigation is likely to impact global climate change. Therefore, it is important to examine the effects of abattoir wastewater irrigation on soil for N₂O emission potential.

     

Ecotoxicological assessment of oil-based paint using three-dimensional multi-species bio-testing model: pre- and post-bioremediation analysis

The present study validates the oil-based paint bioremediation potential of Bacillus subtilis NAP1 for ecotoxicological assessment using a three-dimensional multi-species bio-testing model. The model included bioassays to determine phytotoxic effect, cytotoxic effect, and antimicrobial effect of oil-based paint. Additionally, the antioxidant activity of pre- and post-bioremediation samples was also detected to confirm its detoxification. Although, the pre-bioremediation samples of oil-based paint displayed significant toxicity against all the life forms. However, post-bioremediation, the cytotoxic effect against Artemia salina revealed substantial detoxification of oil-based paint with LD₅₀ of 121 μl ml^?1 (without glucose) and >?400 μl ml^?1 (with glucose). Similarly, the reduction in toxicity against Raphanus raphanistrum seeds germination (%FG?=?98 to 100%) was also evident of successful detoxification under experimental conditions. Moreover, the toxicity against test bacterial strains and fungal strains was completely removed after bioremediation. In addition, the post-bioremediation samples showed reduced antioxidant activities (% scavenging?=?23.5?±?0.35 and 28.9?±?2.7) without and with glucose, respectively. Convincingly, the present multi-species bio-testing model in addition to antioxidant studies could be suggested as a validation tool for bioremediation experiments, especially for middle and low-income countries.

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Magnetite/mesocellular carbon foam as a magnetically recoverable fenton catalyst for removal of phenol and arsenic

A magnetite-loaded mesocellular carbonaceous material, Fe₃O₄/MSU-F-C, exhibited superior activity as both a Fenton catalyst and an adsorbent for removal of phenol and arsenic, and strong magnetic property rendering it separable by simply applying magnetic field. In the presence of hydrogen peroxide, the catalytic process by Fe₃O₄/MSU-F-C completely oxidized phenol and As(III) under the conditions where commercial iron oxides showed negligible effects. Notably, the decomposition of H₂O₂ by Fe₃O₄/MSU-F-C was not faster than those by commercial iron oxides, indicating that hydroxyl radical produced via the catalytic process by Fe₃O₄/MSU-F-C was used more efficiently for the oxidation of target contaminants compared to the other iron oxides. The homogeneous Fenton reaction by the dissolved iron species eluted from Fe₃O₄/MSU-F-C was insignificant. At relatively high doses of Fe₃O₄/MSU-F-C, total concentration of arsenic decreased to a significant extent due to the adsorption of arsenic on the catalyst surface. The removal of arsenic by adsorption was found to proceed via preoxidation of As(III) into As(V) and the subsequent adsorption of As(V) onto the catalyst.     

Effect of land-use change on CH4 and N2O emissions from freshwater marsh in Northeast China

The wetlands play an important role in global carbon and nitrogen storage, and they are also natural sources of greenhouse gases such as methane (CH₄) and nitrous oxide (N₂O). Land-use change is an important factor affecting the exchange of greenhouse gases between wetlands and the atmosphere. However, few studies have investigated the effect of land-use change on CH₄ and N₂O emissions from freshwater marsh in China. Therefore, a field study was carried out over a year to investigate the seasonal changes of the emissions of CH₄ and N₂O at three sites (Deyeuxia angustifolia marsh, dryland and rice field) in the Sanjiang Plain of Northeast China. Marsh was the source of CH₄ showing a distinct temporal variation. Maximum fluxes occurred in June and the highest value was 20.69 ± 2.57 mg CH₄ m^?2 h^?1. The seasonal change of N₂O fluxes from marsh was not obvious, consisted of a series of emission pulses. The marsh acted as a N₂O sink during winter, while became a N₂O source in the growing season. The results showed that gas exchange between soil/snow and the atmosphere in the winter season contributed greatly to the annual budgets. The winter season CH₄ flux was about 3.24% of the annual flux and the winter uptake of N₂O accounted for 13.70% of the growing-season emission. Conversion marsh to dryland resulted in a shift from a strong CH₄ source to a weak sink (from 199.12 ± 39.04 to ?1.37 ± 0.68 kg CH₄ ha^?1 yr^?1), while increased N₂O emissions somewhat (from 4.07 ± 1.72 to 4.90 ± 1.52 kg N₂O ha^?1 yr^?1). Conversion marsh to rice field significantly decreased CH₄ emission from 199.12 ± 39.04 to 94.82 ± 9.86 kg CH₄ ha^?1 yr^?1 and N₂O emission from 4.07 ± 1.72 to 2.09 ± 0.79 kg N₂O ha^?1 yr^?1.     

Phytase-Fe3O4 nanoparticles-loaded microcosms of silica for catalytic remediation of phytate-phosphorous from eutrophic water bodies

Agriculture P management practices elevate the level of inorganic phosphates in soil that results in phosphorous (P) seepage into water-bodies. This is one of the key factors that have accelerated the menace of eutrophication. Phytic acid (phytate)-P-rich plant metabolite is infamous for its anti-nutrient activity and regularly oozing in to environment though discharge of mono-gastric animals. That has amplified the magnitudes of eutrophication. In this work, for catalysis of phytate-P, the metal-organic framework fabricated towards metal oxides (Fe₃O₄) and phytase in highly ordered microcosms of silica was employed. The synthesized framework was characterized through transmission electron microscopy (TEM) and nitrogen isotherm analysis. Average pore diameter of synthesized bisect oval shaped structures was measured around ≈200 nm. Herein, phytase and Fe₃O₄ nanoparticles were loaded to the cavities of microcosms through glutaraldehyde-mediated crosslinking. Whereas Fe₃O₄ nanoparticles act as nano-absorbents that adsorb P liberated from phytase-mediated catalysis of phytate. Kinetic analysis of free and loaded phytase has shown relatively small reduction in catalytic efficiency. These loaded microcosms have removed 60–80% of phytate-phosphate. The optimized process has reduced the growth of photoautotrophs by 50%. Additionally the magnet-assisted separation of loaded microcosms eased the reapplication of loaded microcosms tested for six independent instances. The primary studies conducted to evaluate the geno-toxicity of loaded microcosms have not shown any harmful effect on the process like cell division and seed germination. The efficacy of this method has evaluated towards on-field testing in Changa (Gujarat, India) lake.

     

Elevated ozone phytotoxicity ameliorations in mung bean {Vigna radiata (L.) Wilczek} by foliar nebulization of silicic acid and ascorbic acid

The present work provides an insight into the development of biochemical adaptations in mung beans against ozone (O₃) toxicity. The study aims to explore the O₃ stress tolerance potential of mung bean genotypes under exogenous application of growth regulators. The seeds of twelve mung bean genotypes were grown in plastic pots under controlled conditions in the glasshouse. Six treatments, control (ambient ozone level 40–45 ppb), ambient O₃ with ascorbic acid, ambient ozone with silicic acid, elevated ozone (120 ppb), elevated O₃ with ascorbic acid (10 mM), and elevated ozone with silicic acid (0.1 mM) were applied. The O₃ fumigation was carried out using an O₃ generator. The results revealed that ascorbic acid and silicic acid application decreased the number of plants with foliar O₃ injury symptoms in different degrees, i.e., zero, first, second, third, and fourth degrees; whereas 0–4 degree symptoms represent, no symptoms, symptoms occupying?<?1/4, 1/4–1/2, 1/2–3/4, and?>?3/4 of the total foliage area, respectively. Application of ascorbic acid and silicic acid also prevented the plants from the negative effects of O₃ in terms of fresh as well as dry matter production, leaf chlorophyll, carotenoids, soluble proteins and ascorbic acid, proline, and malondialdehyde (MDA) contents. Overall, silicic acid application proved more effective in reducing the negative effects of O₃ on mung bean genotypes as compared to that of the ascorbic acid. Three mung bean genotypes (NM 20–21, NM-2006, and NM-2016) were identified to have a better adaptive mechanism for O₃ toxicity tolerance and may be good candidates for future variety development programs.

     

Adsorption and photocatalytic conversion of ethyl mercaptan to diethyl disulfide on Fe2O3-loaded HNbMoO6 nanosheet

Ethyl mercaptans which commonly exist in natural gas need to be removed due to their toxic, odorous, and corrosive properties. Herein, a novel Fe₂O₃-modified HNbMoO₆ nanosheet catalyst (Fe₂O₃@e-HNbMoO₆) was prepared by an exfoliation-impregnation method for the ethyl mercaptans removal. In the heterojunction catalyst, e-HNbMoO₆ can be excited by visible light to generate the photogenic charge and has certain adsorption property for ethyl mercaptan with hydrogen bonding (Nb-OH or Mo-OH as the hydrogen bonding donor); Fe₂O₃ plays the role of accelerating photogenerated electrons and holes, and enhancing the adsorption of ethyl mercaptan with another hydrogen bonding (Fe-OH as the hydrogen bonding donor and receptor). Results showed that the adsorption capacity of Fe₂O₃@e-HNbMoO₆ is 69.9 μmol/g for ethyl mercaptan. In addition, the photocatalytic conversion efficiency of ethyl mercaptan to diethyl disulfide is nearly 100% and it is higher than that of the other Nb-Mo based photocatalysts, such as LiNbMoO₆, Fe_1/3NbMoO₆, Ce_1/3NbMoO₆, TiO₂-HNbMoO₆, e-HNbMoO₆, CeO₂@e-HNbMoO₆, and Ag₂O@e-HNbMoO₆. Under the experimental conditions, the photocatalytic conversion efficiency is greater than the adsorption efficiency over Fe₂O₃@e-HNbMoO₆, and there is no ethyl mercaptan output in the process of adsorption and photocatalytic conversion. Fe₂O₃@e-HNbMoO₆ heterojunction catalyst has practical value and reference significance for purifying methane gas and enhancing photocatalytic conversion of ethyl mercaptan.

     

N2O emissions at municipal solid waste landfill sites: Effects of CH4 emissions and cover soil

Municipal solid waste landfills are the significant anthropogenic sources of N₂O due to the cooxidation of ammonia by methane-oxidizing bacteria in cover soils. Such bacteria could be developed through CH₄ fumigation, as evidenced by both laboratory incubation and field measurement. During a 10-day incubation with leachate addition, the average N₂O fluxes in the soil samples, collected from the three selected landfill covers, were multiplied by 1.75 (p < 0.01), 3.56 (p < 0.01), and 2.12 (p < 0.01) from the soil samples preincubated with 5% CH₄ for three months when compared with the control, respectively. Among the three selected landfill sites, N₂O fluxes in two landfill sites were significantly correlated with the variations of the CH₄ emissions without landfill gas recovery (p < 0.001). N₂O fluxes were also elevated by the increase of the CH₄ emissions with landfill gas recovery in another landfill site (p > 0.05). The annual average N₂O flux was 176 ± 566 μg N₂O–N m^?2 h^?1 (p < 0.01) from sandy soil–covered landfill site, which was 72% (p < 0.05) and 173% (p < 0.01) lower than the other two clay soil covered landfill sites, respectively. The magnitude order of N₂O emissions in three landfill sites was also coincident by the results of laboratory incubation, suggesting the sandy soil cover could mitigate landfill N₂O emissions.     

Recycling of iron and silicon from drinking water treatment sludge for synthesis of magnetic iron oxide@SiO<Subscript>2</Subscript> composites

More attention has been paid to the deterioration of water bodies polluted by drinking water treatment sludge (DWTS) in recent years. It is important to develop methods to effectively treat DWTS by avoiding secondary pollution. We report herein a novel investigation for recovery of Si and Fe from DWTS, which are used for the synthesis of two iron oxide@SiO₂ composites for adsorption of reactive red X-3B (RRX-3B) and NaNO₂. The results show that Fe³⁺ (acid-leaching) and Si⁴⁺ (basic-leaching) can be successfully recovered from roasted DWTS. Whether to dissolve Fe(OH)₃ precipitation is the key point for obtaining Fe₃O₄ or γ-Fe₂O₃ particles using the solvothermal method. The magnetic characteristics of Fe₃O₄@SiO₂ (390.0 m² g^?1) or Fe₂O₃@SiO₂ (220.9 m² g^?1) are slightly influenced by the coated porous SiO₂ layer. Peaks of Fe–O stretching vibration (580 cm^?1) and asymmetric Si–O–Si stretching vibrations (1080 cm^?1) of Fe₃O₄@SiO₂ indicate the successful coating of a thin silica layer (20–150 nm). The adsorption capacity of RRX-3B and NaNO₂ by Fe₃O₄@SiO₂ is better than that of Fe₂O₃@SiO₂, and both composites can be recycled through an external magnetic field. This method is an efficient and environmentally friendly method for recycling DWTS.     

Facile fabrication of green nano pure CeO2 and Mn-decorated CeO2 with Cassia angustifolia seed extract in water refinement by optimal photodegradation kinetics of malachite green

To eradicate the aquatic pollution caused by dyes, trendily the global researchers provide dedication to dye degradation using nanostructured photocatalyst. This research work is dedicated to explore an advanced, facile, bio-compact green fabricated nanostructure for water refinement. In this regard, plant-mediated syntheses of pure CeO₂ and Mn-decorated CeO₂ nano-powders have been inspected using seed extract of Cassia angustifolia. Investigations through UV-diffuse reflectance spectroscopy explored the significantly tuned band gap of Mn:CeO₂. FT-IR spectroscopy shows the existing functional groups of high-potential phenolic compounds, proteins, and amino acids in Cassia angustifolia act as reducing and capping agents involved in the green fabricated nanostructured samples. X-ray diffraction pattern has been exposed to crystalline cubic fluorite morphology in a single phase and it leads to a regulated optimized amount of Mn on CeO₂ nanostructure. The FESEM analysis predicts the morphology of CeO₂ in spherical and Mn:CeO₂ in flower-like structure. The HRTEM analysis has portrayed particle size of CeO₂ is 11 nm and tuned Mn:CeO₂ nanostructure is 9 nm. The HRTEM images revealed the average particle size in the range 10–12 nm in CeO₂ and 8–9 nm in 5 mol% Mn:CeO₂ nanoparticles. It showed a decrease in average particle size with an increase in Mn concentration and the reduction in size may be due to the replacement of Ce(IV) with Mn(II) ions. The elemental composition in nanostructure was predicted using energy-dispersive X-ray analysis. The rapid photocatalytic degradation efficiency of malachite green was effectually performed and compared with the kinetics model of Mn:CeO₂ and pure CeO₂ nanostructures. From the augmented results, tuned Mn:CeO₂ was found to act as the finest green fabricated photocatalyst in the amputation of lethal and carcinogenic dye.