Flyash augmented Fe3O4 as a heterogeneous catalyst for degradation of stabilized landfill leachate in Fenton process

Critical review of fluorescence and absorbance measurements as surrogates for the molecular weight and aromaticity of dissolved organic matter

Dissolved organic matter (DOM) is ubiquitous in aquatic environments and challenging to characterize due to its heterogeneity. Optical measurements (i.e., absorbance and fluorescence spectroscopy) are popular characterization tools, because they are non-destructive, require small sample volumes, and are relatively inexpensive and more accessible compared to other techniques (e.g., high resolution mass spectrometry). To make inferences about DOM chemistry, optical surrogates have been derived from absorbance and fluorescence spectra to describe differences in spectral shape (e.g., E2:E3 ratio, spectral slope, fluorescence indices) or quantify carbon-normalized optical responses (e.g., specific absorbance (SUVA) or specific fluorescence intensity (SFI)). The most common interpretations relate these optical surrogates to DOM molecular weight or aromaticity. This critical review traces the genesis of each of these interpretations and, to the extent possible, discusses additional lines of evidence that have been developed since their inception using datasets comparing diverse DOM sources or strategic endmembers. This review draws several conclusions. More caution is needed to avoid presenting surrogates as specific to either molecular weight or aromaticity, as these physicochemical characteristics are often correlated or interdependent. Many surrogates are proposed using narrow contexts, such as fractionation of a limited number of samples or dependence on isolates. Further study is needed to determine if interpretations are generalizable to whole-waters. Lastly, there is a broad opportunity to identify why endmembers with low abundance of aromatic carbon (e.g., effluent organic matter, Antarctic lakes) often do not follow systematic trends with molecular weight or aromaticity as observed in endmembers from terrestrial environments with higher plant inputs.

Degradation of Sodium Acetate by Catalytic Ozonation Coupled with MnOx/NiOOH-Modified Fly Ash

Fly ash, a type of solid waste generated in power plants, can be utilized as a catalyst carrier to enhance its value-added potential. Common methods often involve using a large amount of alkali for preprocessing, resulting in stable quartz and mullite forming silicate dissolution. This leads to an increased specific surface area and pore structure. In this study, we produced a catalyst composed of MnOx/NiOOH supported on fly ash by directly employing nickel hydroxide and potassium permanganate to generate metal active sites over the fly ash surface while simultaneously creating a larger specific surface area and pore structure. The ozone catalytic oxidation performance of this catalyst was evaluated using sodium acetate as the target organic matter. The experimental results demonstrated that an optimal removal efficiency of 57.5% for sodium acetate was achieved, surpassing even that of MnOx/NiOOH supported catalyst by using γ-Al2O3. After loading of MnOx/NiOOH, an oxygen vacancy is formed on the surface of fly ash, which plays an indirect oxidation effect on sodium acetate due to the transformation of ozone to •O2- and •OH over this oxygen vacancy. The reaction process parameters, including varying concentrations of ozone, sodium acetate, and catalyst dosage, as well as pH value and the quantitative analysis of formed free radicals, were examined in detail. This work demonstrated that fly ash could be used as a viable catalytic material for wastewater treatment and provided a new solution to the added value of fly ash.

Applying bottom ash as an alternative Fenton catalyst for effective removal of phenol from aqueous environment

In this study, coal bottom ash from a thermoelectric plant was tested as an alternative Fenton catalyst for phenol degradation in water. The effect of operating parameters such as initial pH, catalyst dosage and H2O2 concentration were evaluated. The characterization results indicated that the material has a mesoporous structure, with active species (Fe) well distributed on its surface. Under the optimal reaction conditions (6 mM H2O2, 1 g L-1 of catalyst and pH = 3), 98.7% phenol degradation efficiency was achieved in 60 min, as well as 71.6% TOC removal after 150 min. Hydroxyl radical was identified as the main oxidizing agent involved on the cleavage of the phenol molecule. After four consecutive reuse cycles, phenol degradation efficiency was around 80%, indicating good reusability and stability of the catalyst. Therefore, the obtained results demonstrated that the bottom ash presents remarkable activity for application in the Fenton reaction towards phenol degradation.

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.

Degradation of Sodium Acetate by Catalytic Ozonation Coupled with a Mn-Functionalized Fly Ash: Reaction Parameters and Mechanism

Supported ozone catalysts usually take alumina, activated carbon, mesoporous molecular sieve, graphene, etc. as the carrier for loading metal oxide via the impregnation method, sol-gel method and precipitation method. In this work, a Mn-modified fly ash catalyst was synthesized to reduce the consumption and high unit price of traditional catalyst carriers like alumina. As a solid waste discharged from coal-fired power plants fueled by coal, fly ash also has porous spherical fine particles with constant surface area and activity, abd is expected to be applied as the main component in the synthesis of ozone catalyst. After the pretreatment process and modification with MnOx, the obtained Mn-modified fly ash exhibited stronger specific surface area and porosity combined with considerable ozone catalytic performance. We used sodium acetate as the contaminant probe, which is difficult to directly decompose with ozone as the end product of ozone oxidation, to evaluate the performance of this Mn-modified fly. It was found that ozone molecules can be transformed to generate ·OH, ·O2- and 1O2 for the further oxidation of sodium acetate. The oxygen vacancy produced via Mn modification plays a crucial role in the adsorption and excitation of ozone. This work demonstrates that fly ash, as an industrial waste, can be synthesized as a potential industrial catalyst with stable physical and chemical properties, a simple preparation method and low costs.

Synthesis of submicron ferrous oxalate from red mud with high Fenton catalytic performance on degradation of methylene blue

Ferrous oxalate dihydrate (FOD) can be used as a photo-Fenton catalyst with remarkable photo-Fenton catalytic and photocatalytic performances on organic pollutant degradation. Various reduction processes were compared in the current study to synthesize FODs from ferric oxalate solution utilizing the iron source in alumina waste red mud (RM), including natural light exposure (NL-FOD), UV light irradiation (UV-FOD), and hydroxylamine hydrochloride hydrothermal method (HA-FOD). The FODs were characterized and employed as photo-Fenton catalysts for methylene blue (MB) degradation, and the effects of HA-FOD dosage, H2O2 dosage, MB concentration, and the initial pH were investigated. The results show that HA-FOD has submicron sizes and lower impurity contents with more rapid degradation rates and higher degradation efficiencies compared with the other two FOD products. When using 0.1 g/L of each obtained FOD, 50 mg/L of MB can be rapidly degraded by HA-FOD by 97.64% within 10 min with 20 mg/L of H2O2 at pH of 5.0, while NL-FOD and UV-FOD achieve 95.52% in 30 min and 96.72% in 15 min at the same conditions, respectively. Meanwhile, HA-FOD exhibits strong cyclic stability after two recycling experiments. Scavenger experiments reveal that the predominant reactive oxygen species responsible for MB degradation are hydroxyl radicals. These findings demonstrate that submicron FOD catalyst can be synthesized using hydroxylamine hydrochloride hydrothermal process from ferric oxalate solution with high photo-Fenton degradation efficiency and reduced reaction time for wastewater treatment. The study also provides a new pathway of efficient utilization for RM.

Application of Deep Eutectic Solvents (DES) for the Synthesis of Iron Heterogeneous Catalyst: Application to Sulfamethoxazole Degradation by Advanced Oxidation Processes

The development of novel approaches to the remotion of pharmaceuticals in wastewater is a subject of concern due to their effect on living beings and the environment. Advanced oxidation processes and the use of relevant catalysts are feasible treatment alternatives that require further development. The development of suitable heterogeneous catalysts is a necessity. This work proposes the synthesis of an iron catalyst in a deep eutectic solvent (Fe-DES) composed of choline chloride and citric acid, which was physically and chemically characterized using SEM-EDS and TEM, FTIR, RAMAN, XRD and XPS. The characterisation confirmed the presence of iron in the form of hematite. Fe-DES was shown to be a multipurpose catalyst that can be applied in the removal of sulfamethoxazole as a reagent in the Fenton and electro-Fenton processes and as an activator of peroxymonosulfate (PMS) processes. After testing the catalyst with the aforementioned techniques, the best result was achieved by combining these processes in an electro-PMS, with great efficiency achieved by dual activation of the PMS with the catalyst and electric field, attaining total elimination at natural pH in 90 min. Furthermore, the degradation was confirmed by the detection of short-chain carboxylic acids (oxalic, succinic, and acetic) and reduction in toxicity values. These results confirm the suitability of Fe-DES to degrade high-priority pharmaceutical compounds.

Insight on efficiently oriented oxidation of petroleum hydrocarbons by redistribution of oxidant through inactivation of soil organic matter coupled with passivation of manganese minerals

While extensive works focused on the enhancement of the activity of heterogeneous Fenton catalysts, little was paid attention to the inhibition of soil organic matter (SOM) and Mn minerals in soil remediation. Here, the oxidation of petroleum hydrocarbons in soils (S1: 4.28 % SOM, S2: 6.04 % SOM, S3: 10.33 % SOM) with inactivated SOM and passivated Mn oxides regulating by calcium superphosphate (Ca(H₂PO₄)₂) was carried out. Oily sludge pyrolysis residue was used as precursors to prepare an oleophilic iron-supported solid catalyst (Fe-N @ PR). For regulated systems, under the optimal conditions of 1.8 mmol/g H₂O₂ and 0.05 g/g Fe-N @ PR, 72 ∼ 91 % of total petroleum hydrocarbons (TPHs: 15,616.58 mg/kg) were oxidized, which was 38 ∼ 45 % higher than that of control systems. The mechanism of efficient oxidation was proposed that the passivated Mn minerals stabilized H₂O₂ redistributing more H₂O₂ to sustainably produce •OH, and the inactivated SOM improved the relative reactivity of •OH to TPHs. Additionally, the passivation of Mn oxides was mainly related to the binding of H₂PO₄^-, and the inactivation of SOM was realized by Ca²⁺ combing with -OH and C-O-C to form stable complexes. This study brought us a new perspective on soil remediation through passivating Mn minerals and inactivating SOM.

Fabrication of ZnO-SnO2 nanocomposite and its photocatalytic activity for enhanced degradation of Biebrich scarlet

The n-n-type ZnO-SnO₂ nanocomposite was fabricated using malic acid following a simple one-pot co-precipitation method. The fabricated ZnO-SnO₂ nanocomposite was employed as a photocatalyst in the degradation of Biebrich scarlet dye under UV₂₅₄ light. TEM, SAED, XRD, XPS, EDX, FTIR, and UV spectra have been recorded to characterize the synthesized ZnO-SnO₂ nanostructures. TEM studies found that the average particle size was 10-12 nm, and the SAED confirmed the polycrystalline nature of the synthesized nanocomposite. It was found that 97% of 10 mg/L Biebrich scarlet dye was degraded by 25 mg/L of photocatalyst within 40-min irradiation of UV₂₅₄ light at an optimum pH of 6. Further studies showed that the degradation followed pseudo-first-order kinetics with a rate constant of 5.48 × 10^-2 min^-1. The fabricated ZnO-SnO₂ nanocomposite was reusable up to 8 times; hence, it proved to be an efficient catalyst for the photodegradation of Biebrich scarlet dye.

Efficient catalytic degradation of alkanes in soil by a novel heterogeneous Fenton catalyst of functionalized magnetic biochar

In this study, sodium dodecyl sulfate (SDS) functionalized magnetic biochar (SDS-Fe@BC) was successfully prepared. Compared to other traditional heterogeneous Fenton catalysts, more total petroleum hydrocarbons (TPH) (3499.40 mg kg^-1) was adsorbed from soil to the surface of SDS-Fe@BC through hydrophobic interaction between alkyls in alkanes and SDS-Fe@BC, which formed an efficient interface oxidation system. In SDS-Fe@BC-mediated heterogeneous Fenton system, 10,191.41 mg kg^-1 (88.10%) TPH was degraded in the presence of 400 mM H₂O₂, which was 1.38-5.67 folds than that of H₂O₂ alone, Fe²⁺, zero valent iron (ZVI), Fe₃O₄, pristine biochar (BC), and Fe@BC. Moreover, all individual alkanes were efficiently degraded (>75%), and the higher the initial amount of individual alkane, the more the degradative amount in the SDS-Fe@BC/H₂O₂ system. Additionally, TPH degradation was highly related to the mass ratio of SDS/Fe@BC, H₂O₂ concentration, SDS-Fe@BC dosage, and initial pH in the SDS-Fe@BC/H₂O₂ system, and the optimal values were 1:5, 400 mM, 50 mg g^-1, and pH 7, respectively. Radical quenching experiments revealed that hydroxyl radicals (•OH) generated on the surface of SDS-Fe@BC was the dominated reactive oxidative species (ROS) responsible for alkanes degradation. After five cycles, SDS-Fe@BC still remained a high catalytic activity for alkanes degradation (73.21%), showing its excellent reusability. This study proved that the SDS-Fe@BC can be used as a potential heterogeneous Fenton catalyst for petroleum-contaminated soil remediation.

Spherical ZVI/Mn-C Bimetallic Catalysts for Efficient Fenton-Like Reaction under Mild Conditions

The heterogeneous Fenton-like reaction has been receiving increasing attention for its inexpensiveness and high efficiency in water treatment. In this study, a novel strategy was proposed for preparing spherical ZVI/Mn-C bimetallic catalysts with a high activity for a Fenton-like reaction by using the ammonium alginate assisted sol–gel method coupled with a carbothermic reduction. The results showed that the obtained ZVI/Mn-C spheres had a uniform size, smooth surface and good sphericity, and the particle size of ZVI was limited to about 30 nm by the carbon layer. Among all catalysts, the ZVI/Mn-C-31 catalyst exhibited the highest phenol degradation efficiency in the Fenton-like process, and almost 100% phenol degradation efficiency was achieved under neutral pH at room temperature within 5 min. Moreover, the ZVI/Mn-C-31/H2O2 system showed a 100% degradation efficiency for removing a wide range of aromatic pollutants, including catechol, resorcinol and o-nitrophenol. Moreover, the radicals-scavenging experiment illustrated that the ·OH played a key factor in mineralizing the organic matters, and the ·O2− generated from the MnO-H2O2 system accelerated the conversion rate of ferric iron to ferrous iron. Due to the synergistic effects between ZVI and MnO, the ZVI/Mn-C-31 catalyst performed excellently in the Fenton-like reaction at an extended pH range.

Removal of Organics from Landfill Leachate by Heterogeneous Fenton-like Oxidation over Copper-Based Catalyst

Landfill leachates are a mixture of high concentration organic and inorganic contaminants and need to be appropriately treated due to their toxicity and severe adverse effects on the environment. Here, we studied the treatment of landfill leachate through a heterogeneous Fenton-like oxidation process using a zirconia supported copper catalyst (Cu/ZrO2). Reaction conditions such as pH, amount of catalyst, oxidant dose, temperature, and reaction time were investigated and their effects on pollutant abatement discussed. AOS (average oxidation state) and COS (carbon oxidation state) parameters were used for the evaluation of the degree of oxidation of the process, obtaining some insight into the formation of oxidized intermediates (partial oxidation) and the total oxidation (mineralization) of the leachate during the reaction. A two-step oxidation process enhanced the overall performance of the reaction with an abatement of organic compounds of 92% confirming the promising activity of a copper-based catalyst for the treatment of liquid waste. Higher catalytic activity was achieved when the following reaction conditions were applied: 70 °C, pH 5, 200 mg/L of catalyst, 30 mL/L of H2O2 dose, and 150 min. In addition, durability of the catalyst under optimized reaction conditions was verified by repeated reaction cycles.

Assessment of Pretreatments for Highly Concentrated Leachate Waters to Enhance the Performance of Catalytic Wet Peroxide Oxidation with Sustainable Low-Cost Catalysts

Matured compost, derived from a mechanical and biological treatment (MBT) plant, was used as a precursor to produce catalysts through hydrothermal and thermal carbonization, HC and PC, respectively. HC and PC displayed suitable properties to act as catalysts in the catalytic wet peroxide oxidation (CWPO) treatment of the highly polluted leachate waters generated in the same MBT plant (TOC0 = 27 g L−1; COD0 = 60 g L−1; BOD5,0 = 23 g L−1). The influence of catalyst loading and pH were studied, considering multiple additions of H2O2. The best experimental conditions found were T = 80 °C, pH0 = 3.0, 7.2 g L−1 of HC catalyst, 85.7 g L−1 of H2O2, added in five batches in one-hour intervals between each addition. Under these experimental conditions, removals of 43%, 52%, 93%, 82%, 35%, 95% and 93% for the COD, TOC, BOD5, aromaticity, chlorides, turbidity and color number (CN) were, respectively, observed. Ion exchange resins and coagulation–flocculation were studied as pretreatment options to reduce the complexity of the leachate waters and enhance the CWPO results. Both strategies resulted in higher mineralization and enhanced the consumption efficiency of H2O2 (ηH2O2). The sequential treatment using coagulation–flocculation and CWPO with PC catalyst showed the best results, achieving abatement of 94%, 70%, 98%, 93%, 31%, 96% and 95% for COD, TOC, BOD5, aromaticity, chlorides, turbidity and CN, respectively.

PVP influence on Mn-CdS for efficient photocatalytic activity

Wastewater treatment is the most serious problem in this upcoming era. A harmful effluent like organic dyes, heavy metals, acids from industries mixed in wastewater is deteriorating the environment. To get rid of these poisonous materials and to recycle wastewater for domestic purposes, there are many steps which included photocatalytic dye degradation. PVP assisted Mn-CdS nanoparticles was prepared by novel hydrothermal technique. The characteristic behavior of pure and PVP (1% and 2%) assisted Mn-CdS samples were studied by further analysis. The structural, optical, vibrational, morphological, chemical composition behavior of synthesized pristine and surfactant induced Mn-CdS nanoparticles were analyzed. UV-Vis spectra revealed the optical behavior of the prepared pure and PVP (1% and 2%) assisted Mn-CdS samples. The bandgap obtained was 2.2, 2.06 and 1.99 eV for pure Mn-CdS, 1% PVP-Mn-CdS and 2% PVP- Mn-CdS. The narrow bandgap is one of the advantage of the material. Mn-CdS, 1% PVP-(Mn-CdS) and 2% PVP- (Mn-CdS) morphology were further investigated by Scanning Electron Microscopic studies (SEM). The surfactant (PVP) was added to enhance the morphology development and decrease agglomeration on the surface and the SEM images revealed a clear evidence for enhancement of morphology in all three samples. 2% PVP-(Mn-CdS) sample showed a good development in morphology when compared with other two samples and the best sample showed formation of nanorods below the surface of nanoparticles. Further, Mn-CdS, 1% PVP-(Mn-CdS) and 2% PVP- (Mn-CdS) was indulged to investigate the cationic degradation. The photocatalytic activities of three samples were carried out with loading different amount of the catalysts and 30 mg catalyst 2% PVP- (Mn-CdS) loaded dye solution showed a considerable degradation of methylene blue dye. The 30 mg catalyst (2% PVP-Mn-CdS) showed 98% efficiency under visible light irradiation for about 2 h. The best candidate, 30 mg catalyst (2% PVP-Mn-CdS) investigated for its reusability. The catalyst showed almost 98% of efficiency up to three cycles which confirmed the level of potential of the sample. 2% PVP-(Mn-CdS) sample would be promising candidate in wastewater treatment. It can be further utilized for removing dyes from wastewater in wastewater remediation process.

Advanced oxidation of landfill leachate: Removal of micropollutants and identification of by-products

Landfill leachate contains several macropollutants and micropollutants that cannot be removed efficiently by conventional treatment processes. Therefore, an advanced oxidation process is a promising step in post or pre-treatment of leachate. In this study, the effects of Fenton and ozone oxidation on the removal of 16 emerging micropollutants including polycyclic aromatic hydrocarbons (PAHs), phthalates, alkylphenols and pesticides were investigated. The Fenton and ozone oxidation of the leachate were performed with four (reaction time: 20-90 min, Fe(II) dose: 0.51-2.55 g/L, H₂O₂ dose: 5.1-25.5 g/L and pH: 3-5) and two (ozonation time: 10-130 min and pH: 4-10) independent variables, respectively. Among these operating conditions, reaction time played more significant role (p-value < 0.05) in eliminating di-(2-Ethylhexyl) phthalate, 4-nonylphenol and 4-tert-octylphenol for both processes. The results showed that Fenton and ozone oxidation processes had a high degradation potential for micropollutants except for the PAHs including four and more rings. Removal efficiencies of micropollutants by ozone and Fenton oxidation were determined in the range of 5-100%. Although the removal efficiencies of chemical oxygen demand (COD) and some micropollutants such as phthalates were found much higher in the Fenton process than ozonation, the degradation products occurred during the Fenton oxidation were a higher molecular weight. Moreover, the oxidation intermediates for the both processes were found as mainly benzaldehyde, pentanoic acid and hydro cinnamic acid as well as derivatives of naphthalenone and naphthalenediol. Also, acid ester with higher molecular weight, naphthalene-based and phenolic compounds were detected in the Fenton oxidation.

A review of the characteristics of Fenton and ozonation systems in landfill leachate treatment

The development and application of Fenton and ozonation systems in landfill leachate treatment over the last 20 years, and the current research status are reviewed in this paper, with an emphasis on the technical and economic characteristics of Fenton and ozonation systems used to treat different types of landfill leachate. To date, a total of 101 and 78 articles have been published regarding leachate treatment by Fenton and ozonation systems, respectively. These articles considered the use of two systems to treat aged leachate, biologically treated leachate and leachate comprising the concentrated solution resulting from reverse osmosis (RO). The oxidization mechanisms of the two systems used to treat landfill leachate significantly differed in terms of their optimal process parameters (e.g., initial pH value, reagent dosage, and reaction time) and removal efficiency. The Fenton and ozonation systems outperformed persulfate-based advanced oxidation technology in terms of their improved biodegradability of landfill leachate and engineering practicability. The cost of the reagents required to treat landfill leachate by Fenton and ozonation systems accounted for at least 85% of the total operating cost. In contrast to the ozonation system, the Fenton system was more cost-effective when both systems were used to treat the same type of landfill leachate. This study provides a theoretical basis for the operation of Fenton and ozonation systems and also offers technical support for landfill leachate disposal companies that opt to use these technologies.

Electrocatalytic ozonation process supplemented by EDTA-Fe complex for improving the mature landfill leachate treatment

The present study was to enhance catalytic ozonation process (COP) using ferric (Fe)- ethylenediaminetetraacetic acid (Fe-EDTA) integrated with an electrocoagulation (EC) process for landfill leachate pretreatment. For this purpose, the effect of operating parameters such as ozone and Fe-EDTA concentrations, current, initial pH, and reaction time were investigated. The findings revealed that the EC process and single ozonation process (SOP) could alone reduce chemical oxygen demand (COD) in landfill leachate by 23% and 39%; respectively. Moreover, integration of both processes at 100 mA current, 400 mg h^-1 ozone concentration, and 3 h reaction time could significantly improve COD reduction to 70%. As well, current efficiency and ozone consumption in the proposed system could considerably develop compared with EC process and SOP. The integrated electro-catalytic SOP using Fe-EDTA could be operated at neutral pH value, which the COD removal efficiency was obtained 79.7%. Subsequently, biochemical oxygen demand (BOD₅)/COD ratio of effluent increased to 0.64. Examining pseudo-first-order and pseudo-second-order kinetics, it was realized that constant rate in the system had augmented. These results also indicated that the modified process using Fe-EDTA was a promising landfill leachate pretreatment technique that could significantly enhance COD removal efficiency and BOD₅/COD ratio, and ultimately decrease time and sludge production.

Promotional effect of Mn-doping on the catalytic performance of NiO sheets for the selective oxidation of styrene

The direct oxidation of styrene into high-value chemicals under mild reaction conditions remains a great challenge in both academia and industry. Herein, we report a successful electronic structure modulation of intrinsic NiO sheets via Mn-doping towards the oxidation of styrene. By doping NiO with only a small content of Mn (Mn/Ni atomic ratio of 0.030), a 75.0% yield of STO can be achieved under the optimized reaction conditions, which is 2.13 times higher than that of the pure NiO. In addition, the catalyst exhibits robust stability and good recycling performance. The performance enhancement originates from the synergistic effect regarding the abundant Ni(II) species, the rich oxygen vacancy sites and the large amount of surface redox centers. This work provides new findings of the elemental-doping-induced multifunctionality in designing powerful catalysts for the efficient and selective oxidation of styrene and beyond.

Influence of lattice strain on Fe3O4@carbon catalyst for the destruction of organic dye in polluted water using a combined adsorption and Fenton process

In this study, 8, 25 and 50 wt% Fe3O4@activated carbon (AC) catalysts were prepared by simple coprecipitation method. The efficiency of the catalysts for the advanced Fenton's oxidation process using methylene blue (MB) as a model substrate was tested. Both modified and unmodified activated carbon catalysts exhibited similar activity towards the Fenton's oxidation process. Therefore, it is difficult to identify the role of the catalyst in this dye removal process. Hence, we proposed a new methodology to remove the MB by adopting the adsorption process initially, followed by the Fenton's oxidation process. The proposed process significantly improved the methylene blue decomposition reaction over the 25 wt% Fe3O4@AC catalyst. However, this trend was not seen in pure activated carbon and Fe3O4@AC (8 and 50 wt%) catalysts due to the instability of the material in the oxidizing medium. The possible reason for the deactivation of the catalysts was evaluated from lattice strain calculations, as derived from the modified W-H models (Uniform Deformational Model (UDM), Uniform Stress Deformation Model (USDM) and Uniform Deformation Energy Density Model (UDEDM)). These results provided a quantitative relationship between the experimentally calculated lattice strain values and Fenton's catalytic activity. Furthermore, the optimized strain value and crystalite size of Fe3O4 on the activated carbon matrix are responsible for the high catalytic activity.

Stabilized landfill leachate treatment by zero valent aluminium-acid system combined with hydrogen peroxide and persulfate based advanced oxidation process

The toxic leachate generated from landfills is becoming a major nuisance to the environment and has vital role in groundwater contamination. This study evaluated the potential of zero valent aluminium (ZVAl) based advanced oxidation processes (AOPs) for stabilized landfill leachate treatment. Hydrogen peroxide (HP) and persulfate (PS) were used to generate additional radicals in aerated ZVAl acid process. ZVAl-acid system achieved 83% COD removal efficiency under optimized conditions such as acid washing time of 20 min, ZVAl dose of 10 g L^-1 at initial pH 1.5. The highest exclusion efficiencies in terms of TOC, COD as well as color were 83.52%, 96% and 63.71% respectively in treatment systems showing the following order: ZVAl/H⁺/Air/HP/PS > ZVAl/H⁺/Air/PS > ZVAl/H⁺/Air/HP > ZVAl/H⁺/Air > ZVAl/H⁺. The involvement of other metals such as Fe and Cu in the process has been found. The reusability study revealed that ZVAl powder can be effectively used up to three cycles. The 28.48 mg/l of Al³⁺ residue was observed in this process which has to be removed before discharge of effluent. The study indicated that the ZVAl based AOPs is stable and active for the degradation of organic pollutants present in landfill leachate and a promising solution except for the aluminium discharge which has to be given special care.