Disordered manganese oxide, prepared by low-temperature synthesis followed by acid treatment is introduced. Aggregated nano-powder of disordered manganese oxide was obtained in this method. The disordered manganese oxide is suitable starting material for the preparation of efficient adsorbents for the removal of harmful metals from the environment

Hata, Toshihiro

Imamura, Yuji

Koyanaka, Hideki

Kyoto University Research Information Repository

Title Disordered Manganese Oxide Nano-powder Prepared by Low-temperature Synthesis Followed by Acid TreatmentAuthor(s)Koyanaka, Hideki; Hata, Toshihiro; Imamura, YujiCitationSustainable humanosphere : bulletin of Research Institute forSustainable Humanosphere Kyoto University (2005), 1: 19-21Issue Date2005-08-31URL http://hdl.handle.net/2433/51152RightType Departmental Bulletin PaperTextversionpublisherKyoto University__________~~_NOTEDisordered Manganese Oxide Nano-powderPrepared by Low-temperature Synthesis Followed by Acid TreatmentHideki Koyanaka, Toshihiro Hata, and Yuji ImamuraResearch Institute for Sustainable HumanosphereKyoto University, Uji, Kyoto 611-0011, JapanE-mail: koyanaka@rish.kyoto-u.ac.jpABSTRACTDisordered manganese oxide, prepared by low-temperature synthesis followed by acid treatmentis introduced. Aggregated nano-powder of disordered manganese oxide was obtained in this method.The disordered manganese oxide is suitable starting material for the preparation of efficientadsorbents for the removal of harmful metals from the environment.INTRODUCTIONCrystal forms of manganese oxide are categorized into various phases such as the rock-salt-typeMnO (cubic), spinel-type lambda-Mn02 (cubic), ramsdellit~ lambda-Mn02 (monoclinic), andhausmannite Mn304 (tetragonal). The crystal structures of manganese oxide contain fundamentalbuilding blocks of Mn06 octahedron. However, the oxygen array of the crystal lattice usuallyfeatures other octahedral and tetrahedral sites that may accommodate Mn and other cations viasubtle distortion/tilting of the Mn06 octahedra and/or formation of oxygen defects. These propertiesin conjunction with the variation of Mn2+ and Mn4+ valence states and the interactions with the Mnmagnetic moments, give rise to a variety of very intriguing crystal morphology and structuraltransformations as well as magnetic ordering at low temperatures that are of fundamental interest.Technologically, once the properties of materials are understood, novel applications can be tailored.New batteries, ion exchangers for environmental decontamination, and magnetic spin-valve devicesare such examples among many suggested potential applications.The authors have studied manganese oxide-based materials for the research and development ofefficient adsorbents in order to remove harmful metals from the environment. Recently, wesynthesized the disordered phase of manganese oxide and discovered the exhibition of highadsorption capability of pollutants such as Cd and As ions and of rare metal such as Au [1]-[6].These phenomena occur only in the disordered manganese oxide powder after protonation by acidtreatments. The disordered-manganese oxide powder show the quantity of adsorption to be at leastmore than 10 times higher compared with the manganese oxide without the acid treatments.EXPERIMENTALMnC03 powder (Wako, 99% purity) as the starting material was heated using an electric furnaceat 200 QC in air for 4.5 h. Acid treatment began by adding the powder into 0.5 mol/L of nitric orhydrochloric acid while stirring (using a magnetic stirrer) for a certain period of suspension time.Afterward the suspended particles were filtered from the solution using a glass filter (0.2 pm mesh),followed by washing with distilled water. This first stage processed with a 60 min suspension timefor an initial acid treatment enabled the growth of nanometer-size crystalline Mn203 grains on thesurfaces of micron-size crystalline MnC03 particles. Subsequent acid treatments, typically for 1 hsuspension each, allowed the removal of MnC03 component and the self-assembly of adsorbed H+ions (protons) on the Mn203 nanoparticles. This second acid treatment resulted in substantialincrease of the population of protonated sites. Furthermore, remaining MnCh or MnN03 in thesolution after the acid treatment and filtration of the adsorbent can be readily converted to Mn02powder with useful high surface area by adding an appropriate amount of KMn04 to the solution.This reduces the amount of waste and negative environmental impacts.RESULTS AND DISSCUSSION19NOTEFig. 1 shows the Variation of XRD pattern on the disordered-manganese oxide powder preparedby low-temperature synthesis followed by acid treatment. The XRD of the prepared sample (no acidtreatment) heated less than 200 QC showed similar pattern with the starting material (MnC03).However, the color was different from each other. The flesh-colored of MnC03 has changed theblack of Mn203 [6]. The peaks on the XRD patterns have changed the broadness according toincrease in the frequency of the acid treatment, and indicated the disordered crystal phase of themanganese oxide remarkably. We assume that this disordered phase is the result of acid treatment ofthe surface layer of Mn203.;i51)':!') ,------------.--.----.---.-..-..---.-----.----.-.--.-.--.--..--..--.-.--...•.---.-.-.- - ......•.........-..--- -.------- -..--.-.. -.-..-.--..--.-.-.-..•.•.....••..•- ------.•--.-.-;i-:!I)C") !--.- L _ - - - - - - ..- - - - .......•...-.-.- - -- -..- .",50':') +--.- +.. - +-.- -.-- -·~·--···········Hi··········-····-·····--·········-·- - - -... . - ..................................................................................•......- -....•:01)01) +······-··i-l-··-··-·····f+-······-·-·'--H···c.,··--+·+·····-h------·------·-------··---++----·--··------····--··············.- ---- --.--.-----------.. --.--.------.----------.----- - .. -------.-------------------------.--------.--------- ----------.--.----.--.----.--.--- --------l'110CO +-···--·--------· ..·· --·\--- ·..······H+··..········ f!-. + +.------ ++ --...................................... ""·--·::·;:··",·· .. ··''''''''0-- ..···--··--···--·················· , ---- -- -- --.-- .50Cl) +--.-.-------.-fr--..-----+'--.- -j-.,.. +.--+-------+-- ._:\,"-_,__._,_r.>. .,_ •._~_.,,_o..:""""- -"' ,1-' -, -,--..- ,,-.- , --- ---- - --- ---.---.-- -- -n ~ ---- --- .. -' ._., .. ".. '--" ,. -- ,.--.. ".. ...•10Q (11 A)Fig. 1 Variation of XRD pattern on the disordered-manganese oxide powder prepared bylow-temperature synthesis followed by acid treatment.Fig. 2 shows the TEM image of the disordered-manganese oxide powder obtained after 3 times ofacid treatment. Aggregated nano powders wereobserved in the image. These powders constructaggregated powders in micro-meter size, and showremarkable adsorption ability for the complex ionssuch as gold, palladium, and silver in aqueoussolution [4]-[6]. The electrons are supplied from themanganese oxide to each complex adsorbedaccording to the each redox potential. The adsorbedcomplex is deposited on the surface of themanganese oxide as the metallic nano-particles.Fig. 2 TEM image of the disordered-manganeseoxide powder.CONCLUSIONSA new method to prepare nano-powders of the disordered-manganese oxide based on Mn203 wasintroduced in this report. In principle, this synthesis method can produce useful manganese20NOTEoxide-based catalysts supporting different metallic nanopartic1es such as Au, Pd, and Ag.REFERENCES[1] Kasai, T. and Koyanaka, H. , Removal of Arsenic Ion with Manganese Oxide Compounds(2002) Transactions of the materials research society ofJapan, Vol.27, No.2, pA63-466[2] Koyanaka, H. and Kasai, T. (2001) The New method for Removing Arsenious acid in Water,ECO INDUSTRY, Jul. 7, p.18-26[3] Koyanaka, H. and Kasai, T., (2001) Removal of Arsenious Acid from Aqueous Solution byManganese Oxide, J. Water and Waste, Vol.43, No. 11, p.7-12[4] Koyanaka, H., Koyanaka, S., Liang, R., and Uchida, A. (2000) Manganese Oxide Mnz03 asAdsorbent for Cadmium, Journal of Japan Society on Water Environment, Vol.23, No.2,p.116-121[5] Koyanaka, H. (1996) Recovery of Gold from Solution by a Manganese Oxide based Adsorbent",Journal of the Society ofMaterials Engineering for Resources ofJapan, Vol.9, No.1, pp.54-61[6] Koyanaka, H., Takeuchi. K., and Loong, C.-K. (2005) Gold recovery from parts-per-trillion-Ievelaqueous solutions by a nanostructured Mnz03 adsorbent, Separation and PurificationTechnology, VoIA3, pp.9-15.21

Disordered Manganese Oxide Nano-powder Prepared by Low-temperature Synthesis Followed by Acid Treatment

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Disordered Manganese Oxide Nano-powder Prepared by Low-temperature Synthesis Followed by Acid Treatment

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