CTAB-assisted fabrication of hierarchical flower-like magnesium oxide adsorbent for enhanced removal performance towards phosphate

In this work, a series of hierarchical flower-like magnesium oxide(MgO) adsorbents were successfully fabricated in a cetyltrimethylammonium bromide(CTAB) assisted solvothermal route using hexamethylenetetramine(HMTA) as a precipitating agent. Effects of CTAB feeding amount on the structure, morphology, pore structure, and corresponding adsorption behavior were investigated. The hierarchical gardenias flower-like MgO demonstrated a surface area of 336.54 m^(2)·g^(-1) at a minimum ratio of the CTAB/Mg^(2+)was 0.02 in the reaction system. The hierarchical MgO phosphate removal capacity was 348.32 mg·g^(-1), which followed the pseudo-second-order and Freundlich isotherm model obtained from the large surface area and appropriate pore size. The value of n also suggests the feasible nature of phosphate adsorption under the examined conditions. Indeed, this CTAB assisted solvothermal method can provide a new understanding to tune the desired properties of a material by merely adjusting the reaction parameters of MgO.

Preparation and property of self-sealed plasma electrolytic oxide coating on magnesium alloy

Plasma electrochemical oxidation (PEO) is a surface modification technology to form ceramic coatings on magnesium alloys However,its application is limited due to its defects.This work reports a novel preparation of in-situ sealing of PEO coatings by four-layer voltage and sol addition.The morphology and structure were characterized by scanning electron microscopy (SEM),energy dispersive X-ray spectroscopy (EDS),and X-ray diffractometer (XRD).Image-Pro Plus 6.0 was used to determine the porosity of the coating,which was decreased from 8.53%to 0.51%.Simultaneously,the coating thickness was increased by a factor of four.The anti-corrosion performance of each sample was evaluated using electrochemical tests,and the findings revealed that the corrosion current density of coatings (i_(corr)) of the samples were lowered from 9.152×10^(-2) to 6.152×10^(-4) mA·cm^(-2),and the total resistance (R_(T)) of the samples were enhanced from 2.19×10^(4) to 2.33×10^(5)Ω·cm^(2).The salt spray test used to simulate the actual environment showed that corrosion points appeared on the surface of the coating only at the 336 h.In addition,the mechanism of PEO self-sealing behavior was described in this article.

Mg/MgO interfaces as efficient hydrogen evolution cathodes causing accelerated corrosion of additive manufactured Mg alloys:A DFT analysis

The corrosion rates of additive-manufactured Mg alloys are higher than their as-cast counterparts,possibly due to increased kinetics for the hydrogen evolution reaction on secondary phases,which may include oxide inclusions.Scanning Kelvin Probe Force Microscopy demonstrated that MgO inclusions could act as cathodes for Mg corrosion,but their low conductivity likely precludes this.However,the density of state calculations through density functional theory using hybrid HSE06 functional revealed overlapping electronic states at the Mg/MgO interface,which facilitates electron transfers and participates in redox reactions.Subsequent determination of the hydrogen absorption energy at the Mg/MgO interface reveals it to be an excellent catalytic site,with HER being found to be a factor of 23x more efficient at the interface than on metallic Mg.The results not only support the plausibility of the Mg/MgO interface being an effective cathode to the adjacent anodic Mg matrix during corrosion but also contribute to the understanding of the enhanced cathodic activities observed during the anodic dissolution of magnesium.

Green synthesis of three-dimensional magnesium ferrite/titanium dioxide/reduced graphene from Garcinia mangostana extract for crystal violet photodegradation and antibacterial activity

In this study,three-dimensional porous magnesium ferrite/titanium dioxide/reduced graphene oxide(Mg Fe_2O_(4)-GM/TiO_(2)/rGO(MGTG))was successfully synthesized via green and hydrothermal-supported co-precipitation methods using the extract of Garcinia mangostana(G.mangostana)as a reducing agent.The characterization results indicate the successful formation of the nano/micro Mg Fe_(2)O_(4)(MFO)and TiO_(2) on the structure of the reduced graphene oxide(rGO),which can also act as efficient support,alleviating the agglomeration of the nano/micro MFO and TiO_(2).The synergic effects of the adsorption and photodegradation activity of the material were investigated according to the removal of crystal violet(CV)under ultraviolet light.The effects of catalyst dosage,CV concentration,and p H on the CV removal efficiency of the MGTG were also investigated.According to the results,the CV photodegradation of the MGTG-200 corresponded to the pseudo-first-order kinetic model.The reusability of the material after 10 cycles also showed a removal efficiency of 92%.This happened because the materials can easily be recollected using external magnets.In addition,according to the effects of different free radicals·O_(2)^(-),h^(+),and·OH on the photodegradation process,the photocatalysis mechanism of the MGTG was also thoroughly suggested.The antibacterial efficiency of the MGTG was also evaluated according to the inhibition of the Gram-positive bacteria strain Staphylococcus aureus(S.aureus).Concurrently,the antibacterial mechanism of the fabricated material was also proposed.These results confirm that the prepared material can be potentially employed in a wide range of applications,including wastewater treatment and antibacterial activity.

负载MgO-CeO_(2)改性活性炭的脱硫机理

通过XRD、H2-TPR、XPS等方法对MgO-CeO_(2)改性的煤基柱状成型商品活性炭的脱硫机理进行了研究。实验结果表明:高温煅烧改性,使MgO与CeO_(2)反应形成Ce-Mg-O固溶体,当MgO质量分数低于5%时,因固溶体的形成,XRD谱图上没有明显的MgO晶体衍射峰。MgO的加入改变了CeO_(2)的还原环境,加速了Ce^(4+)→Ce^(3+)的还原和氧空位的形成,其中4Ce6Mg/AC样品还原性最强。推测其脱硫机理为:SO_(2)因活性炭优良的吸附性能直接吸附;SO_(2)被CeO_(2)活性位点催化氧化,以硫酸盐的形式除去;SO_(2)被MgO活性位点化学吸附,以亚硫酸盐的形式除去;镁铈双金属氧化物之间存在协同效应,促进了晶格氧的迁移转化,显著增强了改性样品的脱硫性能。

Effect of low concentration electrolytes on the formation and corrosion resistance of PEO coatings on AM50 magnesium alloy

In this paper,the formation process,morphology,and electrochemical performance of PEO coatings on AM50 magnesium alloy prepared in low concentration phosphate,aluminate,and phosphate-aluminate electrolytes were systematically studied.The results show that the coatings prepared from the phosphate electrolytes have a higher thickness and better corrosion resistance properties compared to the other electrolytes.The coatings prepared from low concentration phosphate-aluminate mixed electrolytes have slightly thinner thickness,a similar coating structure and an order of magnitude lower value of electrochemical impedance compared with phosphate electrolyte coatings.The Coatings prepared from low concentration aluminate electrolytes have the lowest thickness and the worst corrosion resistance properties which gets close to corrosion behavior of the bare AM50 under the same test conditions.Considering application,coatings prepared from single low concentration phosphate electrolytes and low concentration phosphate-aluminate electrolytes have greater potential than single low concentration aluminate coatings.However,reducing the electrolyte concentrations of coating forming ions too much has negative influence on the coating growth rate.

Improving corrosion resistance of additively manufactured WE43 magnesium alloy by high temperature oxidation for biodegradable applications

Laser powder bed fusion(L-PBF)has been employed to additively manufacture WE43 magnesium(Mg)alloy biodegradable implants,but WE43 L-PBF samples exhibit excessively rapid corrosion.In this work,dense WE43 L-PBF samples were built with the relativity density reaching 99.9%.High temperature oxidation was performed on the L-PBF samples in circulating air via various heating temperatures and holding durations.The oxidation and diffusion at the elevated temperature generated a gradient structure composed of an oxide layer at the surface,a transition layer in the middle and the matrix.The oxide layer consisted of rare earth(RE)oxides,and became dense and thick with increasing the holding duration.The matrix was composed ofα-Mg,RE oxides and Mg_(24)RE_(5) precipitates.The precipitates almost disappeared in the transition layer.Enhanced passivation effect was observed in the samples treated by a suitable high temperature oxidation.The original L-PBF samples lost 40%weight after 3-day immersion in Hank’s solution,and broke into fragments after 7-day immersion.The casted and solution treated samples lost roughly half of the weight after 28-day immersion.The high temperature oxidation samples,which were heated at 525℃ for 8 h,kept the structural integrity,and lost only 6.88%weight after 28-day immersion.The substantially improved corrosion resistance was contributed to the gradient structure at the surface.On one hand,the outmost dense layer of RE oxides isolated the corrosive medium;on the other hand,the transition layer considerably inhibited the corrosion owing to the lack of precipitates.Overall,high temperature oxidation provides an efficient,economic and safe approach to inhibit the corrosion of WE43 L-PBF samples,and has promising prospects for future clinical applications.

NiO-Doped Fe_(2)O_(3)/MgO Properties for the Chemical Looping Oxidative Dehydrogenation of Ethane

Ethane chemical looping oxidative dehydrogenation(CL-ODH)to ethylene is a new technology for ethylene preparation.Fe_(2)O_(3)/MgO oxygen carrier was prepared using the co-precipitation method.The influence of added NiO and its different loadings on Fe_(2)O_(3)/MgO were investigated.Then,a series of oxygen carriers were applied in the CL-ODH of the ethane cycle system.Brunauer-Emmett-Teller(BET),X-ray diffractometry(XRD),X-ray photoelection spectroscopy(XPS),and H2-temperature programmed reduction(TPR)were used to characterize the physicochemical properties of these oxygen carriers.It was confirmed that an interaction between NiO and Fe_(2)O_(3) occurred based on the XPS and H2-TPR results.Based on the CL-ODH activity performance tests conducted in a fixed-bed reactor,it was revealed that ethylene selectivity was significantly improved after NiO addition.Fe_(2)O_(3)-10%NiO/MgO showed the best activity performance with 93%ethane conversion and 50%ethylene selectivity at a reaction temperature of 650℃,atmospheric pressure,and space velocity of 7500 mL/(g·h).

掺杂氧化钇和富镧钐渣对连铸水口MgO-C耐火材料性能的影响

本研究分别考察了氧化钇(Y_(2)O_(3) )和富镧钐渣掺杂量对MgO-C耐火材料微观结构、烧结性能、力学性能和抗稀土钢侵蚀性能的影响。结果表明,Y_(2)O_(3) 和富镧钐渣通过与SiO_(2)和Al_(2)O_(3)反应而生成稀土硅酸盐和稀土铝酸盐,促进材料烧结,提高材料致密性。随着Y_(2)O_(3) 和富镧钐渣掺杂量增大,MgO-C耐火材料的体积密度、抗折强度和耐压强度均先增大后减小,而显气孔率的变化趋势相反。当Y_(2)O_(3) 和富镧钐渣的掺杂量分别为0.5%时,MgO-C耐火材料的体积密度分别为2.87 g/cm^(3)和2.85 g/cm^(3),显气孔率分别为9.6%和10.2%,抗折强度分别为7.6 MPa和6.8 MPa,抗压强度分别为46.4 MPa和41.2 MPa,致密性和常温力学性能提高的幅度最大,抗Ce基稀土钢侵蚀性能相比未掺杂稀土氧化物的试样分别提高了7.6%和10.2%。

浸渍法制备MgO/ZrO_(2)催化氧化NO

采用浸渍法制备MgO/ZrO_(2)催化剂.通过XRD、SEM、N_(2)-吸附/脱附等表征结合催化剂活性测试,研究了催化剂焙烧温度(200~800℃)对催化氧化NO的影响.进一步探究O_(2)含量、催化剂粒径对NO的转化率的影响.结合FTIR表征对最佳实验条件下反应前后的催化剂进行分析.结果表明,不同焙烧温度下的MgO/ZrO_(2)只显示出ZrO_(2)的特征峰,催化剂焙烧温度≤300℃时,MgO/ZrO_(2)催化剂为不定型,随着焙烧温度的升高氧化锆逐渐由无定型向四方相氧化锆转化.催化剂活性测试结果显示:800℃焙烧的催化剂更有利于催化氧化NO.MgO/ZrO_(2)催化氧化NO的效率与比表面积无相关性,而与催化剂堆积形成的狭缝孔有关.当O_(2)体积分数为5%,催化剂粒径为0.894 mm(20目),NO转化率随着反应温度的升高而增大;当反应温度为300℃时NO转化率达到最佳,为96%.

纳米MgO对聚苯乙烯基相变复合纤维形貌及热学性能的影响

采用静电纺丝法制备负载不同含量纳米氧化镁(MgO)的聚苯乙烯(PS)基复合纤维膜作为支撑材料,以癸酸-月桂酸-棕榈酸(CLP)三元低共熔物为固-液相变储能材料,通过物理吸附法制备CLP/PS/MgO相变复合纤维膜,研究了纳米MgO含量对相变复合纤维膜形貌结构、储热性能以及热稳定性的影响。结果表明:静电纺PS/MgO复合纤维膜呈现三维网络结构特征,纤维呈圆柱形且表面光滑,表明纳米MgO与PS相容性良好,随着纳米MgO含量的增加,纤维的平均直径呈先增大后减小的趋势,纤维平均直径在1.35~1.82μm之间,CLP三元低共熔物可以很好地封装在复合纤维膜中。热稳定性能分析结果表明CLP/PS/MgO相变复合纤维膜的熔化温度约为20℃,结晶温度约为10℃,相变焓为106~124kJ/kg,适用于储能调温纺织品以及建筑节能领域。纳米MgO的加入对相变复合纤维的相变温度没有显著影响,相变焓略微下降,热稳定性明显提高。

外掺MgO常态混凝土双曲拱坝温控技术应用

本文以我国西南地区的B水电站水库拱坝为工程实例,从施工准备\施工过程以及施工养护三个方面详细地介绍了针对外掺MgO常态混凝土双曲拱坝的施工温控应用措施,本文所述的外掺MgO常态混凝土施工温控技术可以为相关外掺MgO常态混凝土工程施工提供借鉴和指导。

Formation process of composite plasma electrolytic oxidation coating containing zirconium oxides on AM50 magnesium alloy

The formation processes of a composite ceramic coating on AM50 magnesium alloy prepared by plasma electrolytic oxidation （PEO） in a K 2 ZrF 6 electrolyte solution were studied by scanning electron microscope （SEM） and energy dispersive X-ray spectroscope （EDX）. Electrochemical impedance spectroscopy （EIS） tests were used to study the variation of the corrosion resistance of the coating during the PEO treatment. The results show that the coating formed on Mg alloy is mainly composed of MgO and MgF 2 when the applied voltage is lower than the sparking voltage, and zirconium oxides start to be deposited on Mg substrate after the potential exceeding the sparking voltage. The corrosion resistance of the coating increases with increasing the applied voltage.

含BAG-nMgO的新型牙科复合树脂的抗菌及再矿化性能研究

目的:联合应用生物活性玻璃(BAG)和纳米氧化镁(nMgO)改性牙科光固化复合树脂,以获得兼备优良的抗菌性及再矿化性能的新型牙科复合树脂。方法:将不同含量的BAG(2.5 wt%、7.5 wt%、12.5 wt%)和2.5 wt%nMgO引入牙科光固化复合树脂中,制备成含BAG-nMgO的实验树脂,并以卡瑞斯玛复合树脂作为对照。通过菌落计数、代谢活性分析(MTT)和活/死细菌染色,评价实验树脂的抗变形链球菌(S.mutans)能力;将脱矿人牙牙本质片及实验树脂在模拟体液(SBF)中浸泡21 d后,通过扫描电子显微镜(SEM)和X射线能谱仪(EDS)观察分析脱矿牙本质表面形貌和元素组成,评估实验树脂再矿化特性;通过万能试验机、维氏硬度仪等测试树脂的固化深度、压缩强度及维氏硬度。结果:实验组树脂的抗S.mutans活性显著高于卡瑞斯玛对照组,且与BAG的含量相关;当BAG添加量为7.5 wt%时,脱矿牙本质开始矿化;BAG添加比例为12.5 wt%时,可见厚的矿化层,牙本质小管几乎被完全封闭;实验组的固化深度均显著高于卡瑞斯玛,维氏硬度优于或与其相近,随着BAG比例的增加,各实验组的固化深度、压缩强度间无显著性差异。结论:BAG和nMgO的联合应用提高了实验树脂的抗菌性,并赋予其再矿化性能。新型复合树脂预期可减少细菌入侵和促进早期龋损的再矿化。本研究为新型多功能复合树脂的研究开发提供了理论依据和研究基础。

Screening of MgO- and CeO_2-Based Catalysts for Carbon Dioxide Oxidative Coupling of Methane to C_(2+) Hydrocarbons

The catalyst screening tests for carbon dioxide oxidative coupling of methane (CO2-OCM) have been investigated over ternary and binary metal oxide catalysts. The catalysts are prepared by doping MgO- and CeO2-based solids with oxides from alkali (Li2O), alkaline earth (CaO), and transition metal groups (WO3 or MnO). The presence of the peroxide (O2-2) active sites on the Li2O2, revealed by Raman spectroscopy, may be the key factor in the enhanced performance of some of the Li2O/MgO catalysts. The high reducibility of the CeO2 catalyst, an important factor in the CO2-OCM catalyst activity, may be enhanced by the presence of manganese oxide species. The manganese oxide species increases oxygen mobility and oxygen vacancies in the CeO2 catalyst. Raman and Fourier Transform Infra Red (FT-IR) spectroscopies revealed the presence of lattice vibrations of metal-oxygen bondings and active sites in which the peaks corresponding to the bulk crystalline structures of Li2O, CaO, WO3 and MnO are detected. The performance of 5%MnO/15%CaO/CeO2 catalyst is the most potential among the CeO2-based catalysts, although lower than the 2%Li2O/MgO catalyst. The 2%Li2O/MgO catalyst showed the most promising C2+ hydrocarbons selectivity and yield at 98.0% and 5.7%, respectively.

Enhanced corrosion resistance of micro-arc oxidation coated magnesium alloy by superhydrophobic Mg-Al layered double hydroxide coating

To further enhance the corrosion resistance of the porous micro-arc oxidation(MAO) ceramic layers on AZ31 magnesium alloy, superhydrophobic Mg-Al layered double hydroxide(LDH) coating was fabricated on MAO-coated AZ31 alloy by using in-situ growth method followed by surface modification with stearic acid. The characteristics of different coatings were investigated by XRD, SEM and EDS. The effect of the hydrothermal treatment time on the formation of the LDH coatings was studied. The results demonstrated that the micro-pores and cracks of MAO coating were gradually sealed via in-situ growing LDH with prolonging hydrothermal treating time. Electrochemical measurement displayed that the lowest corrosion current density, the most positive corrosion potential and the highest impedance modulus were observed for superhydrophobic LDH/MAO coating compared with those of MAO coating and LDH/MAO coating. Immersion experiment proved that the superhydrophobic LDH/MAO coating with the active anti-corrosion capability significantly enhanced the long-term corrosion protection for MAO coated alloy.

Effect of current density on corrosion resistance of micro-arc oxide coatings on magnesium alloy

Oxide coatings were prepared on magnesium alloys in electrolyte solution of Na2SiO3 at different current densities(3,4 and 5 A/cm 2 )with micro-arc oxidation process.X-ray diffractometry(XRD)results show that the oxide coatings formed on magnesium alloys are mainly composed of MgO and MgAl2O4 phases;in addition,the content of MgO increases with increasing the current density.The morphology and surface roughness of the coatings were characterized by confocal laser scanning microscopy (CLSM).The results show that the surface roughness(Ra)decreases with increasing the current density.Moreover,the electrochemical corrosion results prove that the MgO coating produced in the electrolyte Na2SiO3 at current density of 5 A/cm 2 shows the best corrosion resistance.

Nickel catalysts supported on MgO with different specific surface area for carbon dioxide reforming of methane

In this paper, three kinds of MgO with different specific surface area were prepared, and their effects on the catalytic performance of nickel catalysts for the carbon dioxide reforming of methane were investigated. The results showed that MgO support with the higher specific surface area led to the higher dispersion of the active metal, which resulted in the higher initial activity. On the other hand, the specific surface area of MgO materials might not be the dominant factor for the basicity of support to chemisorb and activate CO2, which was another important factor for the performance of catalysts. Herein, Ni/MgO(CA) catalyst with proper specific surface area and strong ability to activate CO2exhibited stable catalytic property and the carbon species deposited on the Ni/MgO(CA) catalyst after 10 h of reaction at 650 ?C were mainly activated carbon species.

Comprehensive Utilization of Natural Magnesium-Containing Resources and the Development of MgO-Based Refractories

This paper presents the ways of comprehensive utilization of the natural magnesium containing resources and the trends of the MgO based refractories used in high temperature industries. In the first part, the uses and productions of metal Mg, sorel cement, Mg (OH) 2 fire retardant, light magnesium carbonate, light magnesia and magnesium sulphate are described. In the second part, the developments of MgO based refractories used in steelmaking process, nonferrous metallurgy, cement rotary kiln and waste melting furnace are described from some applied theories, including corrosion resistant and slaking resistant MgO CaO materials, chrome free bricks such as MgO CaO ZrO 2 , MgO MgO Al 2 O 3 , MgO MgO·Al 2 O 3 ZrO 2 , MgO MgO·Al 2 O 3 2MgO ·TiO 2 and MgO FeO·Al 2 O 3 , and MgO containing monolithic refractories etc.

Serum magnesium concentration in children with functional constipation treated with magnesium oxide

AIM:To determine whether hypermagnesemia recently reported in adult patients possibly develops in children with functional constipation taking daily magnesium oxide.METHODS:We enrolled 120 patients (57 male and 63 female) aged 1-14 years old (median:4.7 years) with functional constipation from 13 hospitals and two private clinics.All patients fulfilled the Rome Ⅲ criteria for functional constipation and were treated with daily oral magnesium oxide for at least 1 mo.The median treatment dose was 600 (500-800) mg/d.Patients were assessed by an interview and laboratory examination to determine possible hypermagnesemia.Serum magnesium concentration was also measured in sex-and agematched control subjects (n=38).RESULTS:In the constipation group,serum magnesium concentration [2.4 (2.3-2.5) mg/dL,median and interquartile range] was significantly greater than that of the control group [2.2 (2.0-2.2) mg/dL] (P < 0.001).The highest value was 3.2 mg/dL.Renal magnesium clearance was significantly increased in the constipation group.Serum magnesium concentration in the constipation group decreased significantly with age (P < 0.01).There was no significant correlation between the serum level of magnesium and the duration of treatment with magnesium oxide or the daily dose.None of the patients had side effects associated with hypermagnesemia.CONCLUSION:Serum magnesium concentration increased significantly,but not critically,after daily treatment with magnesium oxide in constipated children with normal renal function.