BP网络对溶胶凝胶法合成cryptomelane的优化设计

隧道状锰氧催化剂(cryptomelane)对二甲醚(DME)的催化燃烧有良好的促进作用,优化cryptomelane型锰氧催化剂的工艺条件可以提高催化燃烧的活性。在溶胶凝胶法合成锰氧催化剂的试验中,反应时间、焙烧温度和反应物的质量比对cryptomelane型催化剂的合成影响较大。为了得到合成的最佳工艺条件,以上述3要素为神经网络的输出变量,以XRD三强线的相对强度值为神经网络的输入变量,构建BP网络,优化锰氧催化剂的合成工艺条件。预测结果表明,焙烧温度为445.35℃,葡萄糖与高锰酸钾的反应时间为58.4 s,葡萄糖与高锰酸钾的质量比为1.1时,能合成较好的晶型的cryptomelane型锰氧催化剂,活性评价实验结果表明其催化效率良好。与实验结果相比较,模型具有较高的预测精度,预测误差在合理的范围内。

A facile one-pot hydrothermal synthesis as an efficient method to modulate the potassium content of cryptomelane and its effects on the redox and catalytic properties

Cryptomelane has been widely applied as catalyst in oxidation reactions due to its excellent redox properties and low cost.Here,a novel one-pot hydrothermal synthesis using a potassium permanganate aqueous solution as precursor and ethanol as reducing agent has successfully been developed to obtain cryptomelane nano-oxides.This synthetic route makes it possible to control the amount of potassium incorporated into the structure of the cryptomelane by selecting the appropriate synthesis temperature and ethanol initial concentration.Taking advantage of this approach,the effect of potassium concentration on the structural stability and reducibility of the cryptomelane,which are poorly discussed in the literature,has been studied.We have observed that samples with low content of potassium(~11%)show high conversions of CO to CO2 especially at low temperatures.The lower activity of the samples with high K contents(~16%)can be ascribed to the beneficial effect of K on the structural stability of cryptomelane in detriment of labile oxygen on cryptomelane surface.

Cryptomelane型材料的制备和表征

ＭｎＯ－４和Ｍｎ２＋在酸性条件和一定温度下，用氧化还原方法制得了高结晶度的Ｃｒｙｐｔｏｍｅｌａｎｅ型锰氧化物．用Ｘ射线粉末衍射法（ＸＲＤ）、傅里叶红外光谱法（ＦＴ－ＩＲ）、热重－微商热重差热分析法（ＴＧ－ＤＴＧ／ＤＴＡ）、透射电子显微镜法（ＴＥＭ）等方法对它进行了表征．研究表明，该Ｃｒｙｐｔｏｍｅｌａｎｅ中可能存在两种不同热力学性质的Ｃｒｙｐｔｏｍｅｌａｎｅ，加热Ｃｒｙｐｔｏｍｅｌａｎｅ到６００℃时，热稳定性较差的那部分转化为Ｍｎ２Ｏ３；在６００～８７０℃，Ｃｒｙｐｔｏｍｅ－ｌａｎｅ和Ｍｎ２Ｏ３共同存在；８７０℃，样品完全转化为Ｍｎ２Ｏ３；到９４０℃则Ｍｎ２Ｏ３再度失氧生成Ｍｎ３Ｏ４．另在Ｃｒｙｐ－ｔｏｍｅｌａｎｅ中存在Ｌ酸和Ｂ酸，且Ｂ酸强于Ｌ酸．

^(40)Ar/^(39)Ar dating of cryptomelane from the Baye manganese deposit,SW Yunnan,China:Implications for growth rate of supergene Mn-oxide veins

Supergene Mn-oxide deposits are commonly related to thick weathering profiles and form as a result of intense and prolonged weathering of Mn-bearing precursor rocks, processes facilitated by a combination of multiple factors including warm and wet climate, relatively quiescent tectonic environment, and favorable geomorphic setting. Precise age constraints of supergene Mn-oxides may provide valuable information on the climatic, tectonic, and geomorphic conditions prevailing in the geological past. 4~Ar]39Ar laser incremental heating analysis of cryptomelane from the Baye manganese deposit, western Yunnan-Guizhou Plateau, SW China, was conducted to provide numerical constraints on the ages of supergene Mn enrichment and growth rates of Mn-oxide veins. In this study, two Mn-oxide veins of 3-6 cm thickness, termed as Vein A and B, respectively, were col- lected for 4~Ar/39Ar dating. Vein A is subhorizontal and present in fractures parallel to schistosity of the Proterozoic spessartine schists, whereas Vein B is filled in nearly vertical fractures penetrating the schistosity. A combination of optical microscopy, XRD, SEM, and EMP analyses demonstrate that mineral grains extracted from both veins consist of pure, well-crystallized cryptomlane, which has acicular crystal forms and contains 0.96%4.70% K2O. Fourteen cryptomelane subsamples extracted from different growth bands of Vein A yield well-defined plateau ages ranging from 1.35 ± 0.05 to 1.16 ± 0.04 Ma （2or）, whereas seven subsamples obtained from Vein B have plateau ages ranging from 1.23 ±0.05 to 1.01 ± 0.04 Ma （20）. The age results permit estimation for the growth rates of both veins at ca. 115-153 and 34-67 mm Ma-1, respectively. Distinct growth rates between Veins A and B are likely reflective of different fluid pressures during their formation governed by the orientation of the fractures hosting the veins. The growth rates calculated for both veins are 1-2 orders of magnitude higher than the val- ues （〈1-10 mm Ma-l） estimated for Mn-oxide nodules in supergene Mn deposits elsewhere. The high growth rates obtained for the Baye samples are consistent with direct precipitation of tetravalent Mn-oxides from weathering solution in open cavities or fractures, characterized by incremental growth of Mn-oxide bands from the margin to the center of the cavities or fractures. In contrast, Mn-oxide nodules with low growth rates from other deposits formed through self-oxidation and self-catalization, and grow outwards from the nuclei. In addition, prevalence of warm and humid climate and prolonged tectonic uplift in the Yunnan Plateau may have also partly contributed to the rapid growth of Mn-oxides in the Baye deposit.

Structure and properties of Co-doped cryptomelane and its enhanced removal of Pb^(2+) and Cr^(3+) from wastewater

Cryptomelane is a reactive Mn oxide and has been used in removal of heavy metal from wastewaters. Co-doped cryptomelane was synthesized by refluxing at ambient pressure and characterized by powder X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and extended X-ray absorption fine structure spectroscopy, and its performances for removal of Pb^2＋ and Cr^3＋ from aqueous solutions were investigated. Co doping has a negligible effect on the structure and morphology of cryptomelane but increases the specific surface area and Mn average oxidation state. Mn and Co K-edge extended X-ray absorption fine structure spectroscopy（EXAFS） analysis shows that Co barely affects the atomic coordination environments of Mn, and distances of edge- and corner-sharing Co–Me（Me_Co, Mn） pairs are shorter than those of the corresponding Mn–Me pairs, implying the replacement of framework Mn（III） by Co（III）. These Co-doped cryptomelanes can quickly oxidize Cr3＋to be HCr O4-and remove 45%–66% of the total Cr in the reaction systems by adsorption and fixation, and they have enhanced Pb2＋adsorption capacities. Thus these materials are promising adsorbents for heavy metal remediation. The results demonstrate the design and modification of environmental friendly Mn oxide materials and can help us understand the interaction mechanisms of transition metals with Mn oxides.

Environmental Properties of Minerals and Contaminants Purified by the Mineralogical Method

The investigation of the environmental properties of minerals, i.e., environmental mineralogy, is a branch of science dealing with interactions between natural minerals and spheres of the Earth surface as well as a reflection of global change, prevention of ecological destruction, participation in biomineralogy, and remediation of environmental pollution. Pollutant treatment by natural minerals is based on the natural law and reflects natural self-purification functions in the inorganic world, similar to that of the organic world - a biological treatment. A series of case studies related to natural self-purification, which were mostly completed by our group, are discussed in this paper. In natural cryptomelane there is a larger pseudotetragonal tunnel than that formed by [MnO6] octahedral double chains, with an aperture of 0.462-0.466 nm2, filled with K cations. Cryptomelane might be a real naturally-occurring mineral of the active octahedral molecular sieve (OMS-2). CrⅥ-bearing wastewater can be treated by natural pyrrhotite, which is used as a reductant to reduce CrⅥ and as a precipitant to precipitate CrⅢ simultaneously. Batch experiments were conducted using the CTMAB-Montmorillonite as an adsorbent for aromatic contaminants (phenol, aniline, benzene, toluene and xylenes), which are detected frequently in the leaching water from municipal waste deposits around China. The CTMAB modification has proved very effective to enhance the adsorption capacity of the sorbent. Expansion of vermiculite develops loose interior structures, such as pores or cracks, inside briquettes, and thus brings enough oxygen for combustion and the sulfation reaction. Effective combustion of the original carbon reduces the amount of dust in the fly ash.

Highly active OMS-2 for catalytic ozone decomposition under humid conditions

Four kinds of cryptomelane-type octahedral molecular sieve(OMS)-2-X(the X represents the molar ratio of KMnO4/MnAc2) were prepared as catalytic materials for ozone decomposition through a one-step hydrothermal reaction of KMnO4 and MnAc2, by changing their molar ratios. These samples were characterized by N2 adsorption–desorption, X-ray di raction(XRD), transmission electron microscopy(TEM), scanning electron microscopy(SEM), temperature programmed reduction by H2(H2-TPR) and X-ray photoelectron spectroscopy(XPS). Among them, the OMS-2-0.7 sample showed the best O3 conversion of 92% under high relative humidity(RH) of 90% and gas hourly space velocity of 585,000 h-1. This was accordingly thought as a possible way for purifying ozone-containing waste gases under high RH atmospheres. The e ciency of ozone decomposition of the prepared OMS-2-X sample was found to be related to specific surface area, particle size, surface oxygen vacancies, and Mn3+ cation amounts. The one-step hydrothermal synthesis was shown to be a simple method to prepare the considerably active OMS-2 solids for ozone decomposition.

Environmental Effects of Micro- and Ultra-microchannel Structures of Natural Minerals

The micro-channels usually refers to structural channels of minerals with aperture in the range of 0.3 nm to 2.0 nm. Such microchannels include, Mn-O octahedron channel filled by K in cryptomelane, and channel constructed by Si-O and AI-O tetragonal molecular sieve filled by Na and Ca in zeolite, and effectively have the function of molecular sieve. Here we point out that ultramicrochannels of natural minerals have apertures below 0.3 nm with the features of ionic sieves. The ultra-microchannels of mineral feldspar, accounting for half mass of the Earth＇s crust, have been largely ignored because the aperture is too small. In this work, we present that feldspar displays a certain degree of ion exchange and owns a feature of channel structure under both high and low temperatures. At high temperature, Na^＋ can enter the channels of feldspars. The content of Na2O in feldspar increases up to 15.9%. At middle temperature, Pb^2＋ can also enter the channels of feldspar as the result of ion exchange, leading thus to the formation of Pb-feldspar. At room temperature, about 97.94% Cd^2＋ can be removed and Cd-feldspar can be obtained. These phenomena indicate typical effects of ultra-microchannels of feldspar, which may be suggested as a potential for the treatment of heavy metal pollution and nuclear waste. The ultra-microchannels of natural minerals have played special role in migration and exchange of geomaterials. The molecular sieves of microchannels of a few natural minerals have the property of purifying molecular gas pollution. And the ionic sieves of ultramicrochannels of most natural minerals can purify ionic water contaminates.

Catalytic oxidation of toluene by manganese oxides:Effect of K^(+)doping on oxygen vacancy

Alkali metal potassium was beneficial to the electronic regulation and structural stability of transition metal oxides.Herein,K ions were introduced into manganese oxides by different methods to improve the degradation efficiency of toluene.The results of activity experiments indicated that KMnO_(4)-HT(HT:Hydrothermal method)exhibited outstanding low-temperature catalytic activity,and 90%conversion of toluene can be achieved at 243℃,which was 41℃and 43℃lower than that of KNO_(3)-HT and Mn-HT,respectively.The largest specific surface area was observed on KMnO_(4)-HT,facilitating the adsorption of toluene.The formation of cryptomelane structure over KMnO_(4)-HT could contribute to higher content of Mn^(3+)and lattice oxygen(Olatt),excellent low-temperature reducibility,and high oxygen mobility,which could increase the catalytic performance.Furthermore,two distinct degradation pathways were inferred.PathwayⅠ(KMnO_(4)-HT):toluene→benzyl→benzoic acid→carbonate→CO_(2)and H2O;PathwayⅡ(Mn-HT):toluene→benzyl alcohol→benzoic acid→phenol→maleic anhydride→CO_(2)and H2O.Fewer intermediates were detected on KMnO_(4)-HT,indicating its stronger oxidation capacity of toluene,which was originated from the doping of K^(+)and the interaction between K-O-Mn.More intermediates were observed on Mn-HT,which can be attributed to the weaker oxidation ability of pure Mn.The results indicated that the doping of K^(+)can improve the catalytic oxidation capacity of toluene,resulting in promoted degradation of intermediates during the oxidation of toluene.

Behavior of argon gas release from manganese oxide minerals as revealed by ^(40)Ar/^(39)Ar laser incremental heating analysis

Manganese oxides in association with paleo-weathering may provide significant insights into the multiple factors affecting the formation and evolution of weathering profiles, such as temperature, precipitation, and biodiversity. Laser probe step-heating analysis of supergene hollandite and cryptomelane samples collected from central Queensland, Australia, yield well-defined plateaus and consistent isochron ages, confirming the feasibilityy dating very-fined supergene manganese oxides by 40Ar/39 Ar technique. Two distinct structural sites hosting Ar isotopes can be identified in light of their degassing behaviors obtained by incremental heating analyses. The first site, releasing its gas fraction at the laser power 0.2-0.4 W, yields primarily 40Aratm, 38Aratm, and 36Aratm(atmospheric Ar isotopes). The second sites yield predominantly 40Ar*(radiogenic 40Ar), 39Ark, and Ark (nucleogenic components), at -0.5-1.0 W. There is no significant Ar gas released at the laser power higher than 1.0 W, indicating the