Catalytic activity of cerium-doped Ru/Al2O3 during ozonation of dimethyl phthalate

In this paper, factors influencing the mineralization of dimethyl phthalate (DMP) during catalytic ozonation with a cerium-doped Ru/Al₂O₃ catalyst were studied. The catalytic contribution was calculated through the results of a comparison experiment. It showed that doping cerium significantly enhanced catalytic activity. The total organic carbon (TOC) removal over the doped catalyst at 100 min reached 75.1%, 61.3% using Ru/Al₂O₃ catalyst and only 14.0% using ozone alone. Catalytic activity reached the maximum when 0.2% of ruthenium and 1.0% of cerium were simultaneously loaded onto Al₂O₃ support. Results of experiments on oxidation by ozone alone, adsorption of the catalyst, Ce ion’s and heterogeneous catalytic ozonation confirmed that the contribution of heterogeneous catalytic ozonation was about 50%, which showed the obvious effect of Ru-Ce/Al₂O₃ on catalytic activity.     

Catalytic ozonation of organic compounds in water over the catalyst of RuO2/ZrO2-CeO2

This research investigates the performances of RuO₂/ZrO₂-CeO₂ in catalytic ozonation for water treatment. The results show that RuO₂/ZrO₂-CeO₂ was active for the catalytic ozonation of oxalic acid and possessed higher stability than RuO₂/Al₂O₃ and Ru/AC. In the catalytic ozonation of dimethyl phthalate (DMP), RuO₂/ZrO₂-CeO₂ did not enhance the DMP degradation rate but significantly improved the total organic carbon (TOC) removal rate. The TOC removal in catalytic ozonation was 56% more than that in noncatalytic ozonation. However this does not mean the catalyst was very active because the contribution of catalysis to the overall TOC removal was only 30%. The adsorption of the intermediates on RuO₂/ZrO₂-CeO₂ played an important role on the overall TOC removal while the adsorption of DMP on it was negligible. This adsorption difference was due to their different ozonation rates. In the catalytic ozonation of disinfection byproduct precursors with RuO₂/ZrO₂-CeO₂, the reductions of the haloacetic acid and trihalomethane formation potentials (HAAFPs and THMFPs) for the natural water samples were 38%–57% and 50%–64%, respectively. The catalyst significantly promoted the reduction of HAAFPs but insignificantly improved the reduction of THMFPs as ozone reacts fast with the THMs precursors. These results illustrate the good promise of RuO₂/ZrO₂-CeO₂ in catalytic ozonation for water treatment.     

Ce0.7Zr0.3O2纳米棒的制备及其对柴油车尾气碳颗粒的催化净化性能

本研究以硝酸铈、硝酸锆为原料使用溶剂热合成法,制备了CeO₂-ZrO₂纳米棒催化剂(Ce_0.7Zr_0.3O₂(NR)),并用于柴油车尾气碳颗粒催化净化.催化活性检测证实:Ce_0.7Zr_0.3O₂(NR)纳米棒催化剂可有效净化柴油车尾气碳烟颗粒.在Ce_0.7Zr_0.3O₂(NR)存在下,碳颗粒净化率为10%、50%和90%时,所需温度分别仅为375℃、414℃和455℃,比商用Ce_0.7Zr_0.3O₂和Ce0.3Zr0.7O2催化剂性能更优.采用氮吸附-脱附、X射线光电子能谱(XPS)、H2程序升温还原(H₂-TPR)、X射线衍射(XRD)、拉曼光谱(Raman)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)等技术对催化剂进行表征.XRD和Raman结果证实,Ce_0.7Zr_0.3O₂(NR)主要由立方相CeO₂构成,并掺杂了少量四方相氧化锆.SEM和TEM结果则显示,Ce_0.7Zr_0.3O₂(NR)催化剂颗粒明显由纳米棒堆积而成,特定的纳米形貌会影响其对碳颗粒的催化氧化活性.XPS结果证明Ce_0.7Zr_0.3O₂(NR)催化剂主要具有晶格氧、化学氧和表面吸附氧等氧物种;晶格氧是碳颗粒氧化的活性氧物种,其溢流到催化剂表面可与碳颗粒接触从而提高反应活性;化学氧和表面吸附氧均为表面氧物种,极易与表面固体碳颗粒直接接触,从而可在较低温度下促进碳颗粒的净化.H₂-TPR结果进一步证实了XPS结果,Ce_0.7Zr_0.3O₂(NR)催化剂的低温还原温度比商用Ce_0.7Zr_0.3O₂催化剂更低,且含有更多的易还原氧物种,这些低温易还原氧物种可以在较低温度下参与催化反应,促进柴油车尾气颗粒物的低温催化净化.     

Ce-MCM-41分子筛用于臭氧氧化对氯苯甲酸的活性评价

通过水热法合成了铈掺杂MCM-41(Ce-MCM-41)介孔分子筛,并将其用于臭氧氧化水中对氯苯甲酸(p-CBA).小角X射线衍射(XRD)、氮气吸附-脱附(BET)、紫外可见漫反射光谱(UV-Vis DRS)、透射电镜(TEM)表征结果表明,铈成功进入MCM-41分子筛骨架,以正四面体形式存在,且Ce-MCM-41保持了纯硅MCM-41有序的介孔结构,具有较高的比表面积;铈的掺杂显著提高MCM-41催化臭氧氧化对氯苯甲酸的活性,反应60 min后,TOC去除率由MCM-41的63%提高到86%(Si/Ce=60),而单独臭氧氧化仅为52%;铈的溶出仅为0.085 mg.L-1,较同样负载量的铈负载Ce/MCM-41的溶出(0.44 mg.L-1)有较大减少.催化剂重复使用3次后仍保持较高的活性,这表明Ce-MCM-41具有较好的活性和稳定性,是一种有前景的臭氧氧化催化剂.     

ZnO-MgO/Al2O3吸附-臭氧催化氧化处理难降解有机废水

以活性氧化铝为载体,采用浸渍法制备催化剂,对甲基橙及草酸模拟废水进行处理.在中性条件下,臭氧催化氧化比单独臭氧氧化能提前30 min使得甲基橙溶液褪色,反应105 min时,臭氧催化氧化对TOC的去除率高达96.53%,比单独使用臭氧氧化对甲基橙TOC去除率提高了47.19%,在处理草酸废水时臭氧催化氧化对TOC去除率高达80.59%,比单独使用臭氧氧化对草酸TOC去除率提高了59.14%.在处理甲基橙及草酸的小试实验中催化剂对有机污染物的吸附作用起到了加快反应进行的作用.在对垃圾渗滤液超滤出水时,O₃与COD质量比为1:1时,臭氧催化氧化对COD去除率为49.09%,比单独使用臭氧氧化提高36.37%,臭氧催化氧化对TOC的去除率是单独使用臭氧氧化的2.54倍,在处理垃圾渗滤液纳滤浓水时,臭氧催化氧化对COD去除率高达88.72%,比单独使用臭氧氧化提高37.60%,并且臭氧催化氧化对TOC的去除率是单独臭氧氧化的1.6倍.臭氧催化氧化反应过程中产生的羟基自由基对有机物更快的反应速率.     

Ce(x)Mn/TiO2-y催化剂低温NH3-SCR脱硝性能

以锐钛矿TiO₂(P25)为载体采用原位生长法负载锰氧化物制备了Mn/TiO₂催化剂,再以等体积浸渍-煅烧法对该催化剂掺杂氧化铈制备Ce(x)Mn/TiO₂-y催化剂用以烟气低温SCR脱硝.在固定锰负载量(质量分数为8%)的基础上,考察了铈掺杂量(铈锰摩尔比)、煅烧温度对催化剂SCR脱硝性能的影响.采用TEM、BET、XRD和XPS等手段表征了催化剂的理化结构特性.结果发现,当Ce/Mn的摩尔比例为1.0,煅烧温度为300℃时,Ce(1.0)Mn/TiO₂-300催化剂在150—300℃温度范围内、10500—27000 h^-1的空速范围内,能够保持90%以上的NO转化率.理化性能分析结果表明,煅烧温度对催化剂的微观形貌影响显著,随着煅烧温度的升高,Ce(1.0)Mn/TiO₂-500催化剂活性物种颗粒集聚明显、比表面积降低,且锰氧化物价态分布偏向于低价态;铈的掺杂有助于Ce(1.0)Mn/TiO₂-300催化剂活性物种在载体表面的均匀分散,可以促进产生更多的Mn4+物种和更多的吸附氧,有利于催化剂低温SCR脱硝性能的提升.     

Performance and kinetics of iron-based oxygen carriers reduced by carbon monoxide for chemical looping combustion

Chemical looping combustion is a promising technology for energy conversion due to its low-carbon, high-efficiency, and environmental-friendly feature. A vital issue for CLC process is the development of oxygen carrier, since it must have sufficient reactivity. The mechanism and kinetics of CO reduction on iron-based oxygen carriers namely pure Fe₂O₃ and Fe₂O₃ supported by alumina (Fe₂O₃/Al₂O₃) were investigated using thermo-gravimetric analysis. Fe₂O₃/Al₂O₃ showed better reactivity over bare Fe₂O₃ toward CO reduction. This was well supported by the observed higher rate constant for Fe₂O₃/Al₂O₃ over pure Fe₂O₃ with respective activation energy of 41.1±2.0 and 33.3±0.8 kJ·mol⁻¹. The proposed models were compared via statistical approach comprising Akaike information criterion with correction coupled with F-test. The phase-boundary reaction and diffusion control models approximated to 95% confidence level along with scanning electron microscopy results; revealed the promising reduction reactions of pure Fe₂O₃ and Fe₂O₃/Al₂O₃. The boosting recital of iron-based oxygen carrier support toward efficient chemical looping combustion could be explained accurately through the present study.     

Inhibition of bromate formation by reduced graphene oxide supported cerium dioxide during ozonation of bromide-containing water

GO or RGO promotes bromate formation during ozonation of bromide-containing water. CeO₂/RGO significantly inhibits bromate formation compared to RGO during ozonation. CeO₂/RGO shows an enhancement on DEET degradation efficiency during ozonation. Ozone (O₃) is widely used in drinking water disinfection and wastewater treatment. However, when applied to bromide-containing water, ozone induces the formation of bromate, which is carcinogenic. Our previous study found that graphene oxide (GO) can enhance the degradation efficiency of micropollutants during ozonation. However, in this study, GO was found to promote bromate formation during ozonation of bromide-containing waters, with bromate yields from the O₃/GO process more than twice those obtained using ozone alone. The promoted bromate formation was attributed to increased hydroxyl radical production, as confirmed by the significant reduction (almost 75%) in bromate yield after adding t-butanol (TBA). Cerium oxide (less than 5 mg/L) supported on reduced GO (xCeO₂/RGO) significantly inhibited bromate formation during ozonation compared with reduced GO alone, and the optimal Ce atomic percentage (x) was determined to be 0.36%, achieving an inhibition rate of approximately 73%. Fourier transform infrared (FT-IR) spectra indicated the transformation of GO into RGO after hydrothermal treatment, and transmission electron microscope (TEM) results showed that CeO₂ nanoparticles were well dispersed on the RGO surface. The X-ray photoelectron spectroscopy (XPS) spectra results demonstrated that the Ce³⁺/Ce⁴⁺ ratio in xCeO₂/RGO was almost 3‒4 times higher than that in pure CeO₂, which might be attributed to the charge transfer effect from GO to CeO₂. Furthermore, Ce³⁺ on the xCeO₂/RGO surface could quench Br⋅ and BrO⋅ to further inhibit bromate formation. Meanwhile, 0.36CeO₂/RGO could also enhance the degradation efficiency of N,N-diethyl-m-toluamide (DEET) in synthetic and reclaimed water during ozonation.     

Fe3O4@SA/Ce微球的表征及对染料的吸附特性

以天然高分子化合物海藻酸钠(sodium alginate,SA)为骨架,结合磁性Fe₃O₄和稀土铈离子Ce(Ⅲ)通过溶液反应制备出一种新型的磁性海藻酸铈复合微球(Fe₃O₄@SA;Ce).采用X射线衍射(XRD)、孔结构比表面积分析(BET)、扫描电子显微镜(SEM)、红外光谱(FT-IR)及振动样品强磁计(VSM)对Fe₃O₄@SA;Ce的结构进行了表征,并以直接桃红12B(direct red 12B,DR 12B)和直接橙S(direct orange S,DO S)两种染料为吸附对象,探讨了Fe₃O₄@SA;Ce的吸附剂性能、吸附动力学和热力学.结果表明,Fe₃O₄@SA;Ce对室温下自然pH染料溶液中DR 12B和DO S均表现出良好的吸附效果,吸附量分别可达464 mg·g^-1和730 mg·g^-1.在不同温度下(298、313、328 K),Fe₃O₄@SA;Ce对DR 12B和DO S的吸附过程均可用拟二级吸附动力学方程准确描述.通过等温吸附研究,发现Fe₃O₄@SA;Ce对两种染料的等温吸附较好地符合Freundlich模型.各种表征结果表明,SA与Ce(Ⅲ)和Fe₃O₄交联反应后生成的Fe₃O₄@SA;Ce凝胶球表面有大量深浅不一的褶皱沟纹,形貌发生了显著变化.作为一种绿色环保、制备方法简单、可高效吸附的磁性高分子复合吸附剂,Fe₃O₄@SA;Ce对高浓度染料具有很好的吸附效果,期望能够在染料废水处理中得到广泛应用.     

Fe2O3-CeO2-Bi2O3/γ-Al2O3 catalyst in the catalytic wet air oxidation (CWAO) of cationic red GTL under mild reaction conditions

Fe₂O₃-CeO₂-Bi₂O₃/γ-Al₂O₃, an environmental friendly material, was investigated. The catalyst exhibited good catalytic performance in the CWAO of cationic red GTL. The apparent activation energy for the reaction was 79 kJ·mol⁻¹. HO₂· and O₂·⁻ appeared as the main reactive species in the reaction. The Fe₂O₃-CeO₂-Bi₂O₃/γ-Al₂O₃ catalyst, a novel environmental-friendly material, was used to investigate the catalytic wet air oxidation (CWAO) of cationic red GTL under mild operating conditions in a batch reactor. The catalyst was prepared by wet impregnation, and characterized by special surface area (BET measurement), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The Fe₂O₃-CeO₂-Bi₂O₃/γ-Al₂O₃ catalyst exhibited good catalytic activity and stability in the CWAO under atmosphere pressure. The effect of the reaction conditions (catalyst loading, degradation temperature, solution concentration and initial solution pH value) was studied. The result showed that the decolorization efficiency of cationic red GTL was improved with increasing the initial solution pH value and the degradation temperature. The apparent activation energy for the reaction was 79 kJ·mol⁻¹. Hydroperoxy radicals (HO₂·) and superoxide radicals (O₂⁻·) appeared as the main reactive species upon the CWAO of cationic red GTL.     

NiB2O4 (B = Mn or Co) catalysts for NH3-SCR of NOx at low-temperature in microwave field

● Microwave-assisted catalytic NH₃-SCR reaction over spinel oxides is carried out. ● SCR reaction temperature is tremendously lowered in microwave field. ● NO conversion of NiMn₂O₄ is highly up to 90.6% at 70°C under microwave heating. Microwave-assisted selective catalytic reduction of nitrogen oxides (NO_x) was investigated over Ni-based metal oxides. The NiMn₂O₄ and NiCo₂O₄ catalysts were synthesized by the co-precipitation method and their activities were evaluated as potential candidate catalysts for low-temperature NH₃-SCR in a microwave field. The physicochemical properties and structures of the catalysts were characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM), N₂-physisorption, NO adsorption-desorption in the microwave field, H₂-temperature programmed reduction (H₂-TPR) and NH₃-temperature programmed desorption (NH₃-TPD). The results verified that microwave radiation reduced the reaction temperature required for NH₃-SCR compared to conventional heating, which needed less energy. For the NiMn₂O₄ catalyst, the catalytic efficiency exceeded 90% at 70 °C and reached 96.8% at 110 °C in the microwave field. Meanwhile, the NiMn₂O₄ also exhibited excellent low-temperature NH₃-SCR reaction performance under conventional heating conditions, which is due to the high BET specific surface area, more suitable redox property, good NO adsorption-desorption in the microwave field and rich acidic sites.     

Catalytic urea hydrolysis by composite metal oxide catalyst towards efficient urea-based SCR process: performance evaluation and mechanism investigation

● Bimetallic oxide composite catalyst was designed for the urea-based SCR process. ● Surface chemical state and typical microstructure of catalyst was determined. ● Reaction route was improved based on intermediates and active site identification. ● TiO₂@Al₂O₃ presents an obvious promotion for urea hydrolysis. As a promising option to provide gaseous NH₃ for SCR system, catalytic urea hydrolysis has aroused great attention, and improving surface area and activity of catalysis are the crucial issues to be solved for efficient urea hydrolysis. Therefore, a composite metal oxide (TiO₂@Al₂O₃) catalyst was prepared by a simple hydrothermal method, with mesoporous alumina (γ-Al₂O₃) as substrate. The results verify the mesoporous structure and submicron cluster of TiO₂@Al₂O₃, with exposed crystal faces of (101) and (400) for TiO₂ and γ-Al₂O₃, respectively. The electronegativity difference of Ti⁴⁺ and Al³⁺ changes the charge distribution scheme around the interface, which provides abundant acid/base sites to boost the urea hydrolysis. Consequently, for an optimal proportioning with nano TiO₂ content at 10 wt.%, the hydrolysis efficiency can reach up to 35.2 % at 100 °C in 2 h, increasing by ~7.1 % than that of the blank experiment. ¹³C NMR spectrum measurements provide the impossible intermediate species during urea hydrolysis. Theoretical calculations are performed to clarify the efficient H₂O decomposition at the interface of TiO₂@Al₂O₃. The result offers a favorable technology for energy-efficiency urea hydrolysis.     

Enhanced catalytic oxidation of 2,4-dichlorophenol via singlet oxygen dominated peroxymonosulfate activation on CoOOH@Bi2O3 composite

• Bi₂O₃ cannot directly activate PMS. • Bi₂O₃ loading increased the specific surface area and conductivity of CoOOH. • Larger specific surface area provided more active sites for PMS activation. • Faster electron transfer rate promoted the generation of reactive oxygen species. • ¹O₂ was identified as dominant ROS in the CoOOH@Bi₂O₃/PMS system. Cobalt oxyhydroxide (CoOOH) has been turned out to be a high-efficiency catalyst for peroxymonosulfate (PMS) activation. In this study, CoOOH was loaded on bismuth oxide (Bi₂O₃) using a facile chemical precipitation process to improve its catalytic activity and stability. The result showed that the catalytic performance on the 2,4-dichlorophenol (2,4-DCP) degradation was significantly enhanced with only 11 wt% Bi₂O₃ loading. The degradation rate in the CoOOH@Bi₂O₃/PMS system (0.2011 min⁻¹) was nearly 6.0 times higher than that in the CoOOH/PMS system (0.0337 min⁻¹). Furthermore, CoOOH@Bi₂O₃ displayed better stability with less Co ions leaching (16.4% lower than CoOOH) in the PMS system. These phenomena were attributed to the Bi₂O₃ loading which significantly increased the conductivity and specific surface area of the CoOOH@Bi₂O₃ composite. Faster electron transfer facilitated the redox reaction of Co (III) / Co (II) and thus was more favorable for reactive oxygen species (ROS) generation. Meanwhile, larger specific surface area furnished more active sites for PMS activation. More importantly, there were both non-radical (¹O₂) and radicals (SO₄⁻•, O₂⁻•, and OH•) in the CoOOH@Bi₂O₃/PMS system and ¹O₂ was the dominant one. In general, this study provided a simple and practical strategy to enhance the catalytic activity and stability of cobalt oxyhydroxide in the PMS system.     

过硫酸钠氧化脱色罗丹明B——影响因素和机理

采用过硫酸钠(PDS)直接氧化和催化活化氧化脱色罗丹明B(RhB),分别考察了PDS剂量、pH、催化剂、Cl-浓度对RhB脱色的影响.结果表明,PDS在无外加催化剂下能够有效脱色RhB,pH越低,脱色率越高;当pH 2.4,PDS用量为3.5 g·L^-1,在120 min内RhB的脱色率可达92%;自由基淬灭实验表明,酸性条件下主要为PDS直接氧化脱色RhB,并存在小部分硫酸根自由基(SO₄4·-)作用.在pH 5.6、pH 8.0条件下,外加活性炭纤维(ACF)、四氧化三铁(Fe₃O₄4)、Fe₃O₄4负载型催化剂(ACF/Fe3O₄4)可促进PDS对RhB脱色;在pH 2.4条件下,外加ACF对RhB脱色的促进作用较小,Fe₃O₄4、ACF/Fe₃O₄4对RhB脱色有一定抑制作用.不同pH和催化剂处理下,低浓度Cl-(0.01、0.04 mO₄l·L^-1)对RhB脱色速率都呈现抑制作用,高浓度Cl-(0.08 mO₄l·L^-1)相对于低浓度Cl-处理都呈促进作用.不同浓度Cl-处理在反应前60 min RhB脱色速率差异较大,而反应120 min后脱色率差异较小.提出Cl-通过调控SO₄4·-脱色RhB途径来影响RhB脱色速率的机理,Cl-竞争消耗SO₄4·-降低RhB脱色速率,但经一系列反应生成的Cl2·-能与RhB快速反应而提高RhB脱色速率;Cl-对RhB的脱色反应速率的影响存在抑制-促进双重机制,且与Cl-浓度相关.研究结果为基于PDS直接氧化和催化氧化处理含盐染料废水的研究和应用提供了一定的理论依据.     

Efficient production of hydrogen peroxide in microbial reverse-electrodialysis cells coupled with thermolytic solutions

● Appreciable H₂O₂ production rate was achieved in MRCs utilizing NH₄HCO₃ solutions. ● Carbon black outperformed activated carbon as the catalyst for H₂O₂ production. ● The optimum carbon black loading for H₂O₂ production on air-cathode was 10 mg/cm². ● The optimum number of cell pairs was determined to be three. ● A maximum power density of 980 mW/m² was produced by MRCs with 5 cell pairs. H₂O₂ was produced at an appreciable rate in microbial reverse-electrodialysis cells (MRCs) coupled with thermolytic solutions, which can simultaneously capture waste heat as electrical energy. To determine the optimal cathode and membrane stack configurations for H₂O₂ production, different catalysts, catalyst loadings and numbers of membrane cell pairs were tested. Carbon black (CB) outperformed activated carbon (AC) for H₂O₂ production, although AC showed higher catalytic activity for oxygen reduction. The optimum CB loading was 10 mg/cm² in terms of both the H₂O₂ production rate and power production. The optimum number of cell pairs was determined to be three based on a tradeoff between H₂O₂ production and capital costs. A H₂O₂ production rate as high as 0.99 ± 0.10 mmol/(L·h) was achieved with 10 mg/cm² CB loading and 3 cell pairs, where the H₂O₂ recovery efficiency was 52 ± 2% and the maximum power density was 780 ± 37 mW/m². Increasing the number of cell pairs to five resulted in an increase in maximum power density (980 ± 21 mW/m²) but showed limited effects on H₂O₂ production. These results indicated that MRCs can be an efficient method for sustainable H₂O₂ production.     

Size and shape effects of MnFe2O4 nanoparticles as catalysts for reductive degradation of dye pollutants

• Size and shape-dependent MnFe₂O₄ NPs were prepared via a facile method. • Ligand-exchange chemistry was used to prepare the hydrophilic MnFe₂O₄ NPs. • The catalytic properties of MnFe₂O₄ NPs toward dye degradation were fully studied. • The catalytic activities of MnFe₂O₄ NPs followed Michaelis–Menten behavior. • All the MnFe₂O₄ NPs exhibit selective degradation to different dyes. The magnetic nanoparticles that are easy to recycle have tremendous potential as a suitable catalyst for environmental toxic dye pollutant degradation. Rationally engineering shapes and tailoring the size of nanocatalysts are regarded as an effective manner for enhancing performances. Herein, we successfully synthesized three kinds of MnFe₂O₄ NPs with distinctive sizes and shapes as catalysts for reductive degradation of methylene blue, rhodamine 6G, rhodamine B, and methylene orange. It was found that the catalytic activities were dependent on the size and shape of the MnFe₂O₄ NPs and highly related to the surface-to-volume ratio and atom arrangements. Besides, all these nanocatalysts exhibit selectivity to different organic dyes, which is beneficial for their practical application in dye pollutant treatment. Furthermore, the MnFe₂O₄ NPs could be readily recovered by a magnet and reused more than ten times without appreciable loss of activity. The size and shape effects of MnFe₂O₄ nanoparticles demonstrated in this work not only accelerate further understanding the nature of nanocatalysts but also contribute to the precise design of nanoparticles catalyst for pollutant degradation.     

Fe-Mn-sepiolite as an effective heterogeneous Fenton-like catalyst for the decolorization of reactive brilliant blue

A study of the decolorization of reactive brilliant blue in an aqueous solution using Fe-Mn-sepiolite as a heterogeneous Fenton-like catalyst has been performed. The Fourier transform infrared (FTIR) spectra of the catalyst showed bending vibrations of the Fe-O. The X-ray diffraction (XRD) patterns of the catalyst showed characteristic diffraction peaks of α-Fe₂O₃, γ-Fe₂O₃ and MnO. A four factor central composite design (CCD) coupled with response surface methodology (RSM) was applied to evaluate and optimize the important variables (catalyst addition, hydrogen peroxide dosage, initial pH value and initial dye concentration). When the reaction conditions were catalyst dosage= 0.4 g, [H₂O₂]= 0.3 mL, pH= 2.5, [reactive brilliant blue]_o = 50 mg·L⁻¹, and volume of solution= 500 mL at room temperature, the decolorization efficiency of reactive brilliant blue was 91.98% within 60 min. Moreover, the Fe-Mn-sepiolite catalyst had good stability for the degradation of reactive brilliant blue even after six cycles. Leaching of iron ions (<0.4 mg·L⁻¹) was observed. The decoloring process was reactive brilliant blue specific via a redox reaction. The benzene ring and naphthalene ring were first oxidized to open ring; these were then oxidized to the alcohol and carboxylic acid. The reactive brilliant blue was decomposed mainly by the attack of ·OH radicals including surface-bound ·OH radicals generated on the catalyst surface.     

Degradation of antipyrine in the Fenton-like process with a La-doped heterogeneous catalyst

A La-doped Co-Cu-Fe catalyst was synthesized for the antipyrine (ANT) removal. The La-doped catalyst had higher ANT removal than the control (95% vs. 54%). La reduced the particle size and increased the specific surface area of catalyst. The aim of this study was to synthesize a novel lanthanum (La) doped catalyst and to investigate antipyrine removal in wastewater using the Fenton-like process with the catalyst. The La-doped Co-Cu-Fe catalyst was synthesized using the modified hydrothermal method. Results showed that the La-doped catalyst had higher specific surface area and lower particle size than the catalyst without La doping (i.e., the control) (267 vs. 163 m²/g and 14 vs. 32 nm, respectively). Under the conditions of catalyst dosage 0.5 g/L, H₂O₂ concentration 1.70 g/L, and NaHCO₃ 0.1 g/L, the antipyrine removal within 60 min using the Fenton-like process with the La-doped catalyst was much higher than that with the control (95% vs. 54%). The hydroxyl radical concentration with the La-doped catalyst within 60 min was two times higher than that with the control (49.2 vs. 22.1 mg/L). The high catalytic activity of La-doped catalyst was mainly attributed to its high specific surface area based on the X-ray photoelectron spectroscopy result. Our La-doped catalyst should have great potential to remove antipyrine in wastewater using the heterogeneous Fenton-like process.     

One-pot hydrothermal fabrication of BiVO4/Fe3O4/rGO composite photocatalyst for the simulated solar light-driven degradation of Rhodamine B

• BiVO₄/Fe₃O₄/rGO has excellent photocatalytic activity under solar light radiation. • It can be easily separated and collected from water in an external magnetic field. • BiVO₄/Fe₃O₄/0.5% rGO exhibited the highest RhB removal efficiency of over 99%. • Hole (h⁺) and superoxide radical (O₂^•−) dominate RhB photo-decomposition process. • The reusability of this composite was confirmed by five successive recycling runs. Fabrication of easily recyclable photocatalyst with excellent photocatalytic activity for degradation of organic pollutants in wastewater is highly desirable for practical application. In this study, a novel ternary magnetic photocatalyst BiVO₄/Fe₃O₄/reduced graphene oxide (BiVO₄/Fe₃O₄/rGO) was synthesized via a facile hydrothermal strategy. The BiVO₄/Fe₃O₄ with 0.5 wt% of rGO (BiVO₄/Fe₃O₄/0.5% rGO) exhibited superior activity, degrading greater than 99% Rhodamine B (RhB) after 120 min solar light radiation. The surface morphology and chemical composition of BiVO₄/Fe₃O₄/rGO were studied by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV–visible diffuse reflectance spectroscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy. The free radicals scavenging experiments demonstrated that hole (h⁺) and superoxide radical (O₂^•−) were the dominant species for RhB degradation over BiVO₄/Fe₃O₄/rGO under solar light. The reusability of this composite catalyst was also investigated after five successive runs under an external magnetic field. The BiVO₄/Fe₃O₄/rGO composite was easily separated, and the recycled catalyst retained high photocatalytic activity. This study demonstrates that catalyst BiVO₄/Fe₃O₄/rGO possessed high dye removal efficiency in water treatment with excellent recyclability from water after use. The current study provides a possibility for more practical and sustainable photocatalytic process.     

Catalytic oxidation of CO over Pt/Fe3O4 catalysts: Tuning O2 activation and CO adsorption

• Strong metal-support interaction exists on Pt/Fe₃O₄ catalysts. • Pt metal particles facilitate the formation of oxygen vacancies on Fe₃O₄. • Fe₃O₄ supports enhance the strength of CO adsorption on Pt metal particles. The self-inhibition behavior due to CO poisoning on Pt metal particles strongly impairs the performance of CO oxidation. It is an effective method to use reducible metal oxides for supporting Pt metal particles to avoid self-inhibition and to improve catalytic performance. In this work, we used in situ reductions of chloroplatinic acid on commercial Fe₃O₄ powder to prepare heterogeneous-structured Pt/Fe₃O₄ catalysts in the solution of ethylene glycol. The heterogeneous Pt/Fe₃O₄ catalysts achieved a better catalytic performance of CO oxidation compared with the Fe₃O₄ powder. The temperatures of 50% and 90% CO conversion were achieved above 260°C and 290°C at Pt/Fe₃O₄, respectively. However, they are accomplished on Fe₃O₄ at temperatures higher than 310°C. XRD, XPS, and H₂-TPR results confirmed that the metallic Pt atoms have a strong synergistic interaction with the Fe₃O₄ supports. TGA results and transient DRIFTS results proved that the Pt metal particles facilitate the release of lattice oxygen and the formation of oxygen vacancies on Fe₃O₄. The combined results of O₂-TPD and DRIFTS indicated that the activation step of oxygen molecules at surface oxygen vacancies could potentially be the rate-determining step of the catalytic CO oxidation at Pt/Fe₃O₄ catalysts. The reaction pathway involves a Pt-assisted Mars-van Krevelen (MvK) mechanism.