Tóm tắt luận án Nghiên cứu tổng hợp vật liệu SnO2 có cấu trúc Nano đa cấp và ứng dụng trong cảm biến khí, xúc tác

1. Synthesis of SnO2 with hierarchical nanostructures using template CTAB by hydrothermal method with ultrasound. Morphology of SnO2materials was much dependent on the solvent and ultrasonically assisted hydrothermal process. Synthesized conditions: ultrasonic radiation, hydrothermal temperature of 180 ᤪ C, 0,5 g SnCl4in 35 ml of methanol solvent provided 0-3 porous spheres SnO2 with a high surface area 227 m 2 /g. The 0-3 porous spherical materials with a size 500-600 nm in diameters consisting of nanopartices less than 16 nm. The mechanism for the formation of 0-3 porous spheres proposed as shown scheme 3.1. We discovered methanol solvent is favorite for forming the 0-3 porous spherical structure for the first time. 2. Having successfully synthesized of SnO2 with 1-3 urchin in hydrothermal conditions: 1.5 mmol Na 2SnO3.3H2O, 20 ml NaOH 0.35 M and 20 ml ethanol. The possible mechanism SnO2 with 1-3 urchin isrecommended as scheme 3.2. The research by deformation equations Hall shows that free development leads to crystal with 1-3 urchin structure less deformed than crystal with 0-3 porous sphere. The obtained SnO2with 1-3 urchin possesses a high specific surface area of 61 m 2 /g and rather higher than some hierarchical nanotructures assembled from 1D and 2D. 3. SnO 2with 0-1 MCM-41 structure with highly ordered mesopore, high tin oxide content has been synthesized by direct methods. Tin oxide introduced into MCM-41 exists in two major forms: (i). tetrahedral and octahedral coordinated tin join to the silica wall inthe framework, (ii). hexacoordinated polymeric Sn–O–Sn type species to forms tin oxide clutters. Their size is too small to observeby XRD. Formation mechanism SnO2 with 0-1 MCM-41 depends on the synthesis conditions as proposed schemes 3.3. This mechanism shows that tin oxide can be dispersed onto the framework with highly ordered mesopore and high tin oxide content by appropriately adjusting the molar ratio Sn/Si and NaOH concentration.

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Hình thái SnO2 FӫDYұW OLӋX WәQJKӧSÿѭӧFSKө WKXӝF QKLӅX YjRGXQJP{LWKӫ\QKLӋWYjVyQJVLrXkP7URQJÿLӅXNLӋQWKӫ\QKLӋW NӃW KӧSYӟL VyQJ VLrX kPQӗQJÿӝ6Q&O4 là 0,5gam/35ml dung môi PHWKDQRO QKLӋWÿӝ o&Fy WKӇ WҥR WKjQK 9/Ĉ& SnO2 FyFҩX WU~F QDQRNLӇX-FҫX[ӕS YӟLGLӋQWtFKEӅPһWOӟQP2/g. QXҧFҫX[ӕS có NtFK WKѭӟF Wӯ ÷ 600 nm bao JӗPFiFKҥWQDQRFy NtFK WKѭӟF NKRҧng 16 nm. &ѫFKӃKuQKWKjQK NLӇX-FҫX[ӕSÿѭӧFÿӅQJKӏtheo 23 Vѫÿӗ DXQJP{LPHWKDQROOjWKtFKKӧSFKRYLӋFWҥRWKjQKFҩXWU~F NLӇX-FҫX[ӕS ÿѭӧFFK~QJW{Lphát hLӋQ OҫQÿҫXWLrQ. 4.2ĈmQJKLrQFӭXWәQJKӧSWKjQKF{QJ9/Ĉ& SnO2 NLӇX-3 lông nhím WURQJÿLӅXNLӋQWKӫ\QKLӋWPPRO1D2SnO3.3H2O, 20 ml NaOH 0,35M và 20 ml ethanol. &ѫFKӃKuQKWKjQKKuQKWKiLNLӇX-3 O{QJ QKtPÿѭӧFÿӅQJKӏ QKѭ Vѫÿӗ. .ӃWTXҧQJKLrQFӭXÿӝELӃQ GҥQJFҩXWU~FEҵQJSKѭѫQJWUuQK+DOOFKRWKҩ\, VӵSKiWWULӇQWӵGRGүQ ÿӃQ FҩXWU~FWLQKWKӇ NLӇXO{QJQKtP tWEӏELӃQGҥQJKѫQVRYӟLWUѭӡQJ KӧS WҥR WKjQKFҩX WU~FNLӇX 0-3 FҫX [ӕS9ұW OLӋX6Q22 WKXÿѭӧFFy GLӋQWtFKEӅPһWOjP2/g, cao KѫQQKLӅXVRYӟLYұWOLӋXÿDFҩSFҩXWU~F WӯFiFÿѫQYӏFҩXWU~F'Yj' ĈmQJKLrQFӭXWәQJKӧSÿѭӧF9/Ĉ& SnO2 NLӇX-1 MCM- 41 EҵQJSKѭѫQJSKiSWәQJKӧSWUӵFWLӃS FyFҩXWU~FPDRTXҧQ ÿӅXÿһQ YӟLKjPOѭӧQJWKLӃFFDR7KLӃFÿѭDYjRYұWOLӋXPDRTXҧQWUXQJEuQK MCM-WӗQWҥLӣKDLGҥQJFKӫ\ӃX(i). Sn có sӕSKӕLWUt WӭGLӋQ  và 8 (bát GLӋQ  OLrQNӃWPӝWSKҫQYӟLsilic trong MCM-41, (ii). 6Qӣ GҥQJ SRO\PHU KyD OөF GLӋQ FӫD 6Q-O-6Q QJRjL PҥQJ ÿk\ Oj QKӳQJ FөP6Q22 FyNtFKWKѭӟFUҩWQKӓ không quDQViWÿѭӧFEҵQJ;5' &ѫ FKӃKuQKWKjQK6Q22 FyFҩXWU~FQDQRNLӇX-1 MCM-41 tuǤWKXӝFYjR ÿLӅX NLӋQ WәQJ KӧS QKѭ VѫÿӗÿӅ QJKӏ 7ӯFѫFKӃQj\FKR WKҩ\ SnO2 FyWKӇÿѭӧFSKkQWiQÿӅXOrQFKҩWQӅQPDR TXҧn WUXQJEuQKYӟL KjPOѭӧQJFDRYjGX\ WUuÿѭӧFFҩXWU~FPDRTXҧQÿӅXÿһQ, EҵQJFiFK ÿLӅXFKӍQKKӧSOêWӍOӋPRO6Q6LYjQӗQJÿӝ2+-. 4.4. 9ұWOLӋX9/Ĉ& SnO2 NLӇX-1 MCM-41 kh{QJFyKRҥWWtQK FҧPELӃQNKtWURQJNKLÿyFҧKDL9/Ĉ& SnO2 FҩXWU~FQDQRNLӇX-3 FҫX[ӕSYj-3 lông nhím WәQJKӧS ÿѭӧFÿӅXFyÿӝQKҥ\NKtWѭѫQJÿӕL FDRÿӕLYӟLFiFNKt LPG, C2H5OH và H27URQJÿyYұWOLӋX6Q22 NLӇX 0-FҩX[ӕSFyÿӝQKҥ\NKtFDRKѫQVRYӟLYұWOLӋX6Q22 NLӇX-3 lông QKtP 7X\ QKLrQ YұW OLӋX 6Q22 NLӇX - O{QJ QKtP OҥL Fy KRҥW WtQK 24 QKҥ\NKtӣQKLӋWÿӝWKҩS và WKӡLJLDQÿiSӭQJSKөFKӗLEp KѫQQKLӅX VRYӟLYұW OLӋX6Q22 NLӇX-FҫX[ӕS6ӵNKiFQKDXQj\Fy WKӇ OLrQ TXDQÿӃQWtQKFKҩWEӅPһW GLӋQWtFKEӅPһWÿӝNӃWWLQKWUӣOӵFNKXӃFK WiQ FӫDKDL ORҥLYұWOLӋXQj\NKiFQKDX 4.5. &iFGҥQJ 9/Ĉ& SnO2 NLӇX-3 FҫX[ӕS YjNLӇX-3 lông QKtPFKRKRҥWWtQKWKҩSÿӕLYӟLSKҧQӭQJK\GUR[\OKRiSKHQRO7URQJ NKLÿy6Q22 FҩX WU~FÿDFҩSNLӇX-1 MCM-41 (SnO2/MCM-41) cho KRҥW WtQK UҩW FDR ÿӕL YӟL SKҧQ ӭQJ K\GUR[\O KRi SKHQRO .ӃW TXҧ QJKLrQFӭXÿӝQJKӑF FKRWKҩ\, SKҧQӭQJWXkQWKHRFѫFKӃSKҧQӭQJEӅ PһW OѭӥQJ SKkQ Wӱ WKHR P{ KuQK /DQJPXLU-Hinshelwood và Eley- Rideal. Cѫ FKӃ SKҧQ ӭQJ Fy WKӇ OLrQ TXDQ PӝW SKҫQ ÿӃQ JӕF Wӵ GR, trong ÿy Fy Vӵ WѭѫQJ WiF YӟL WkP NLP ORҥL FKX\ӇQ WLӃS 6Q YӟL K\GURSH[RULGHWҥRUDFiFHO . và HO .2 WKHRFѫFKӃR[\KRiNKӱ0һW NKiF WUrQFѫVӣSKkQ WtFKÿӝQJKӑF[~F WiFYjKҩSSKө FKR WKҩ\, Vӵ K\GUR[\OKRiSKHQROOLrQTXDQÿӃQFiFSKҧQ ӭQJOѭӥQJSKkQWӱWUrQEӅ PһWJLӳD FiFGҥQJFKҩWEӏKҩSSKөK\GURSHUoxit YjSKHQROEӣLFiFWkP [~F WiF6ӵK\GUR[\O KRiSKHQRO WұS WUXQJFKӫ \ӃXӣYӏ WUӏ ortho và para FKR WKҩ\ ÿk\ Oj PӝW SKҧQ ӭQJ WKӃ iL ÿLӋQ Wӱ HOHFWURSKLOLF substitution). +RҥWWtQKYjÿӝFKӑQOӑFFDRFӫD[~FWiF là do sӵÿDGҥQJ FӫD WkPKRҥW WtQK Yj VӵSKkQ WiQ OrQ FKҩW PDQJ FyGLӋQ WtFKEӅ PһW cao. Ĉk\OjOҫQÿҫXWLrQ YұWOLӋX6Q22/MCM-41 F{QJEӕFyKRҥWWtQK[~F WiFYjÿӝFKӑQOӑFFDRWURQJSKҧQӭQJK\GUR[\OKRiSKHQROWҥRWKjQK GLK\GUR[\O EHQ]HQH 9ұW OLӋX [~F WiF 6Q22/MCM-41 FK~QJ W{L WәQJ KӧSÿѭӧFFyKRҥW WtQK WѭѫQJÿѭѫQJYӟLYұW OLӋX76-1 là [~F WiFFKӫ \ӃXÿӇWәQJKӧSGLK\GUR[\OEHQ]HQHKLӋQQD\. 25 '$1+0Ө&&È&&Ð1*75Î1+.+2$+Ӑ&Ĉ­&Ð1* %Ӕ/,Ç148$1Ĉӂ1/8Ұ1È1  /r 7Kӏ +zD 3KҥP 7Kӏ +XӋ ĈLQK 4XDQJ .KLӃX 7UҫQ 7KiL +zD (2010), ³7әQJ KӧS 6Q22 FҩX WU~F UXWLOH GҥQJ FҫX [ӕS EҵQJ SKѭѫQJ pháp tKӫ\ QKLӋWNӃW KӧSYӟL VyQJ VLrX kPYjKRҥW WtQK FҧPELӃQ NKt LPG´7 ⤀pFKtNKRDK rFYjF{QJQJK l9L lWQDP, 48 (2A), tr.96-101.  /r 7Kӏ +zD ĈLQK 4XDQJ .KLӃX 7UҫQ 7KiL +zD 2010), ³1JKLrQ FӭX WәQJ KӧSYұW OLӋX PDR TXҧQ WUXQJEuQK6Q-MCM-FyFҩX WU~F maR TXҧQ WUXQJ EuQK WUұW Wӵ YӟL KjP OѭӧQJ WKLӃF FDR EҵQJ SKѭѫQJ SKiSWKӫ\QKLӋW´ 7 ⤀pFKtKyDK rF48 (5A), tr.76-81.  /r 7Kӏ +zD 3KҥP 7Kӏ +XӋ ĈLQK 4XDQJ .KLӃX 7UҫQ 7KiL +zD (2010) ³7әQJ KӧS QDQRURG6Q22 PӝWFKLӅXEҵQJSKѭѫQJSKiS WKӫ\ QKLӋW´ 7 ⤀pFKtKyDK rF48 (4A), tr.19-23. /r7Kӏ+zD1JX\ӉQ9ăQ+LӃXĈLQK4XDQJ.KLӃX7UҫQ7KiL+zD  ³6R ViQK KRҥW WtQK FҧP ELӃQ NKt HWDQRO FӫD KDL ORҥL YұW OLӋX QDQRR[LWWKLӃFFyFҩXWU~FÿDFҩS1-3 urchin và 0-FҫX[ӕS´7 ⤀pFKt KyDK rF49 (5AB), tr.634-640. /r7Kӏ+zD7UҫQ7Kө\7KiL+jĈLQK4XDQJ.KLӃX7UҫQ7KiL+zD (2011), ³6\QWKHVLV RI WLQ oxide-modified mesoporous MCM-41 and FDWDO\WLF DFWLYLW\ LQ QRSRO V\QWKHVLV´ 3URFHHGLQJV RI rd IWNA, , November 10-12th, Vung Tau, Viet nam, pp. 964-968. 6/r7Kӏ+zD1JX\ӉQ9ăQ+LӃXĈLQK4XDQJ.KLӃX7UҫQ7KiL+zD (2011),³6\QWKHVLVRI  QDQR WLQR[LGH ZLWK KLHUDUFKLFDOQDQRVWUXFWXUHV DQG LWV JDV VHQVRULQJ  SURSHUWLHV´ 3URFHHGLQJV RI rd IWNA, November 10-12th, Vung Tau, Viet nam, pp. 725-729. /r7Kӏ+zD7ӕQJ7Kӏ&ҭP/ӋĈLQK4XDQJ.KLӃX7UҫQ7KiL+zD (2013), ³$ NLQHWLF VWXG\ RQ SKHQRO K\GUR[\ODWLRQ UHDFWLRQ E\ hydroperoxide over SnO2/MCM- FDWDO\VW´ 7 ⤀p FKt KyD K rF, 51 (2C), tr. 971-976.  /r 7Kӏ +zD 3KҥP ĈuQK 'NJ ĈLQK 4XDQJ .KLӃX 7UҫQ 7KiL +zD   ³1JKLrQ FӭX SKҧQ ӭQJ K\GUR[\O KyD SKHQRO EҵQJ hydroperoxide trên xúc tác SnO2/MCM-´ 7ҥS FKt [~F WiF Yj KҩS SKө 2 (4), tr.102-110. '$1+0Ө&&È&&Ð1*75Î1+.+2$+Ӑ&Ĉ­&Ð1* %Ӕ/,Ç148$1Ĉӂ1/8Ұ1È1 /r7Kӏ+zD3KҥP7Kӏ+XӋĈLQK4XDQJ.KLӃX 7UҫQ7KiL+zD (2010), ³7әQJKӧS6Q22 FҩXWU~FUXWLOHGҥQJFҫX[ӕSEҵQJSKѭѫQJ SKiSWKӫ\QKLӋWNӃWKӧSYӟLVyQJVLrXkPYjKRҥWWtQKFҧPELӃQNKt LPG´7 ⤀pFKtNKRDK rFYjF{QJQJK l9L lWQDP, 48 (2A), tr.96-101. /r7Kӏ+zDĈLQK4XDQJ.KLӃX7UҫQ7KiL+òa (2010), ³1JKLrQ FӭXWәQJKӧSYұWOLӋXPDRTXҧQWUXQJEuQK6Q-MCM-FyFҩXWU~F PDRTXҧQWUXQJEuQKWUұWWӵYӟLKjPOѭӧQJWKLӃFFDREҵQJSKѭѫQJ SKiSWKӫ\QKLӋW´ 7 ⤀pFKtKyDK rF48 (5A), tr.76-81. /r7Kӏ+zD3KҥP7Kӏ+XӋĈLQK4XDQJ.KLӃX7UҫQ7Kii Hòa (2010)³7әQJKӧSQDQRURG6Q22 PӝWFKLӅXEҵQJSKѭѫQJSKiSWKӫ\ QKLӋW´ 7 ⤀pFKtKyDK rF48 (4A), tr.19-23. /r7Kӏ+zD1JX\ӉQ9ăQ+LӃXĈLQK4XDQJ.KLӃX7UҫQ7KiL+zD  ³6RViQKKRҥWWtQKFҧPELӃQNKtHWDQROFӫDKDLORҥLYұWOLӋX nano oxit tKLӃFFyFҩXWU~FÿDFҩS-3 urchin và 0-FҫX[ӕS´7 ⤀pFKt KyDK rF49 (5AB), tr.634-640. /r7Kӏ+zD7UҫQ7Kө\7KiL+jĈLQK4XDQJ.KLӃX7UҫQ7KiL+zD (2011), ³6\QWKHVLVRIWLQR[LGH-modified mesoporous MCM-41 and catalytic activity in nopol synthesLV´3URFHHGLQJVRIrd IWNA, , November 10-12th, Vung Tau, Viet nam, pp. 964-968. /r7Kӏ+zD1JX\ӉQ9ăQ+LӃXĈLQK4XDQJ.KLӃX7UҫQ7KiL+zD (2011),³6\QWKHVLVRIQDQRWLQR[LGHZLWKKLHUDUFKLFDOQDQRVWUXFWXUHV DQGLWVJDVVHQVRULQJSURSHUWLHV´3Uoceedings of 3rd IWNA, November 10-12th, Vung Tau, Viet nam, pp. 725-729. /r7Kӏ+zD7ӕQJ7Kӏ&ҭP/ӋĈLQK4XDQJ.KLӃX7UҫQ7KiL+zD (2013), ³$NLQHWLFVWXG\RQSKHQROK\GUR[\ODWLRQUHDFWLRQE\ hydroperoxide over SnO2/MCM-FDWDO\VW´7 ⤀pFKtKyDK rF, 51 (2C), tr. 971-976.  /r 7Kӏ +zD 3KҥP ĈuQK 'NJ ĈLQK 4XDQJ .KLӃX 7UҫQ 7KiL +zD   ³1JKLrQ FӭX SKҧQ ӭQJ K\GUR[\O KyD SKHQRO EҵQJ hydroperoxide trên xúc tác SnO2/MCM-´7ҥS FKt [~F WiF Yj KҩS SKө  WU-110 MINISTRY OF EDUCATION AND TRAINING HUE UNIVERSITY COLLEGE OF SCIENCES LE THI HOA SYNTHESIS OF HIERARCHICAL NANOSTRUCTURES SnO2AND THEIR APPLLICATION IN GAS SENSORING AND CATALYST Major: Theoretical Chemistry and Physical Chemistry Code: 62.44.01.19 PHD DISSERTATION ABSTRACT Hue, 2014 The work was completed at the Department of Chemistry, College of Sciences, Hue University The primary academic supervisor: 1. Prof. Dr. Trҫn Thái Hòa The secondary academic supervisor: 2. Dr. ĈLQK4XDQJ.KLӃu The 1st peer reviewer: The 2nd peer reviewer: The oral defense will be taken place at... The dissertation can be found at: -National Library of Vietnam -Centrer of Information-Library, National University of Hanoi 1 INTRODUCTION 1. Research motivation Tin oxide (SnO2) is a n-type semiconductor typical (Eg = 3.6 eV) and is one of the semiconductor used most widely by gas sensors, chemical durability and mechanical reliability. Many scientists have been interested in the study of tin oxide research to apply as sensor materials, transparent conductor and as a catalyst in organic synthesis. Sensor materials enhance sensitivity as grain size is smaller than the Debye length (typically several nanometers). The particles can be dispersed in a liquid medium via electrostatic and steric stabilization. However, when the nanoparticles are consolidated into sensing materials, the aggregation between the nanoparticles become very strong because the Van der Waals attraction is inversely proportional to the particle size. To overcome this drawback, the new trend SnO2 nanoscale materials are designed hierarchical nanostructures to improve the aggregation problem of nanomaterials (0D). Hierarchical nanostructures show well-aligned porous structures without scarifying high surface area, whereas the non- agglomerated form of oxide nanoparticles is extremely difficult to accomplish. Another way to design a hierarchical material is dispersed nano oxides activated on the mesoporous silica composite as MCM - 41 and so on. Mesoporous silica MCM-41 containing SnO2 was found higher catalytic activity for oxidation reactions of organic synthesis, 2 for example reaction nopol, phenol oxidation. Activity and high selectivity of the reaction by the contribution of highly specific surface area and well ordered hexagonal mesoporous arrays. With the requirements of industrialized development of the country, researching hierarchical nanostructures SnO2 applications in the fields of electronics ceramic, semiconductors and organic catalyst is needed. Therefore, the study of hierarchical nanostructures SnO2 will make a significant contribution in terms of theory as well as practice. 2. The aims and contents - Synthesis of hierarchical nanostructures SnO2 in three different morphologies of 0-3 porous spheres, 1-3 urchin and 0-1 MCM-41. - Investigation into the obtained materials as gas sensing materials (ethanol, LPG and hydrogen). - Investigation into the obtained materials as a catalytic material in phenol hydroxylation reaction, including kinetics and mechanism of reaction. 3. New contributions We provided firstly a new method of synthesis 0-3 porous spherical materials with very high surface materials. SnO2 with 0-3 porous spherical and 1-3 urchin structure with gas sensing to LPG, ethanol, hydrogen are comparable to the reported articles. The reaction kinetics and mechanism of phenol hydroxylation by hydroperoxide on catalytic SnO2/MCM- 41 were discussed for the first time. It is the first time that SnO2/MCM-41 has been reported to have 3 excellent catalytic activity and high selectivity to dihydroxylbenzene. The SnO2/MCM-41 in the study has similar activity to TS-1 which has been a commercial catalyst for recent dihydroxylbenzene synthesis. 4. Layout of the dissertation The contents of the dissertation consist of 129 pages, 25 tables, 53 figures, 162 references. The layout of the thesis is as follows: Introduction: 2 pages Chapter 1. Literature review: 24 pages Chapter 2. Objectives, content, research methods and experimental methods: 18 pages Chapter 3. Results and Discussion: 83 pages Chapter 4. Conclusions: 2 pages Chapter 1. LITERATURE REVIEW 1.1. SYNTHESIS OF SnO2 WITH HIERARCHICAL NANOSTRUCTURES 1.1.1. Crystal structure SnO2 Tin oxide has two main forms: stannic oxide (SnO2) and stannous oxide (SnO), in which SnO2 exists more popular than SnO. Stannic oxide has rutile structure (tetragonal) as many other oxides such as TiO2 , RuO2 , GeO2 , MnO2 , VO2 , IrO2 and CrO2 « 1.1.2. Definitions of SnO2 with hierarchical nanostructures A hierarchical nanostructures are the higher dimensional structure that is assembled from low dimensional, nano-building blocks such 4 as 0D nanoparticles, 1D nanowires, nanorods, and nanotubes, and 2D nanosheets and so on. Currently, there is no consensus on how to classify this material group. In this thesis, we classified as Lee proposed in which based on the dimension of nano-building blocks and consequent hierarchical structure. 1.1.3. Synthesis of 0-3 porous spheres SnO2 from the nano- building blocks of 0D nanoparticles To create a 0-3 porous spheres SnO2 can be regarded as the assembly of 0D nanoparticle into the 3D porous spheres which usually have two groups of methods: template methods and non-template methods. To minimize aggregation, ultrasound is used as an energy source separation aggregation was successfully applied to several synthetic nano-oxides as ZnO, Fe3O4, SnO2 etc. with high dispersion. 1.1.4. Synthesis of 1-3 urchin SnO2 from the nano-building blocks of 1D nano rods 1-3 urchin was prepared by two- step, vapor phase growth and hydrothermal/solvothermal methods. 1.1.5. Synthesis of 0-1 MCM 41 containing SnO2 (SnO2/MCM 41) So far there are three methods for introducing tin oxide into MCM - 41 was announced: the indirect method at room temperature, hydrothermal and vapor phase method. 1.2. GAS SENSING AND CATALYTICAL ACTIVITIES OF SnO2 WITH HIERARCHICAL STRUCTURES 1.2.1. SnO2 with hierarchical structure as gas sensing materials 5 Gas sensors are likely material properties change depending on the air. A change in the electrical conductivity (resistance) under air or test gas has been used widely. The main characteristics of the sensor material are: - Gas sensitivity (or sensitivity) R = Ra/Rg , where Ra, Rg are the electrical resistances of the sensor in the presence of the ambient air and test gas, respectively. - Response time Wresp denotes as 90% response times and recovery time Wrec denotes 90% recovery times. 1.2.2. Phenol oxidation reaction on heterogeneous catalysts Hydroxylation of phenol catalyzed by SnO2/MCM-41 form dihydroxylbenzenes with different selectivity to dihydroxybenzenes. It depends very much on catalysts with various method of synthesis. The role of tin in the phenol hydroxylation reaction is as yet unclear. Because the active tin sites have been difficult to determine accurately by analyzing the physical chemistry methods recently. Chapter 2. AIMS, CONTENTS AND EXPERIMENTAL METHODS 2.1. AIMS Synthesis of hierarchical structures SnO2 with hierarchical nanostructures posses high gas sensing and catalytic activities. 2.2 . CONTENTS - Synthesis of 0-3 porous spherical SnO2. - Synthesis of 1-3 urchin SnO2. 6 - Synthesis of 0-1 MCM-41 containing SnO2. - Study on obtained SnO2 as gas sensing materials for LPG, C2H5OH and H2. - Study on the catalytic activity of obtained hierarchical nanostructures SnO2 in hydroxylation of phenol. 2.3. RESEARCH METHODS 2.3.1. Physical chemistry methods - X-ray diffraction method (XRD) - Scanning Electron Microscopy (SEM) - Transmission electron microscopy (TEM) - Energy dispersive X-ray (EDX) - Nitrogen adsorption/desorption isotherms (BET) - Diffuse reflectance ultraviolet, visible Spectroscopy (UV - Vis) - High performance liquid chromatography (HPLC) - Methods of analysis hydroperoxide - Analysis tin oxide component in SnO2/MCM-41 - Methods of statistical analysis 7 2.3.2. The experimental methods - Synthesis of 0-3 porous spherical SnO2 - Synthesis of 1-3 urchin SnO2 - Synthesis of SnO2 0-1 MCM-41 - Gas sensing measurement of SnO2 with of hierarchical nanostructures - Phenol hydroxylation reaction by hydroperoxide Chapter 3. RESULTS AND DISCUSSION 3.1. SYNTHESIS OF 0-3 POROUS SPHERES SnO2 3.1.1. Synthesized conditions effect on the morphologies of the materials A survey of synthesized conditions such as ultrasonic, solvent, temperature and concentration of SnCl4 affecting significantly on the morphologies of SnO2. In this study, synthesized conditions: ultrasonic radiation, hydrothermal temperature of 180 ᤪ C, 0,5 g SnCl4 in 35 ml of methanol solvent provided 0-3 porous spheres SnO2 with size 500 ÷ 600 nm in diameters consisting of nanopartices less than 16 nm PS (Figure 3.8.). Figure 3.8. a. SEM image b. TEM image of PS 3.1.2. Characteristics of hierarchical nanostructures SnO2 with 0-3 porous spheres. 8 Diameter around 9.2 nm for PS was calculated according by Hall equation. Figure 3.7 shows nitrogen adsorption/desorption isotherms of PS. The specific area of the PS by Brunauer ± Emmett ± Teller (BET) result indicates that the in the relative pressure range of 0.06 to 0.3 is 227 m2/g. This value is relatively high compared with many that recently published. Figure 3.7. a. Nitrogen adsorption/desorption isotherms of PS; b. Distribution pores of PS It is, suppose that particles are spheres with a diameter of d. The value of d was 3,7 nm based on d= 6/Ud in which U is specific density of SnO2 and S is specific surface area. The size calculated by Hall equation is around 9.2 nm. Both values are smaller than the apparent size of the particles observed by SEM and TEM images. Those indicate that obtained SnO2 spheres must be spherical porous structure consists of small particles ranging from nanoscale. Then, the obtained SnO2 could be named as 0-3 porous spherical SnO2 as proposed by Lee. From the above results, we suggested a model for the formation of SnO2 with 0-3 porous spheres as illustrated in scheme 3.1. 9 Scheme 3.1. The proposed scheme of formation of porous spheres in this study The band gap energy of PS material was calculated based on the diffuse reflectance ultraviolet-visible spectrum (Figure 3.9). Figure 3.9. a. Plots of (DE)2 vs E of PS sample b. Confinement quantum effects of nanoscale particles The dots line crossing the horizontal axis provided the band gap energy at 3.75 eV. This value is larger than band gap energy of SnO2 bulk around 3.6 eV indicating that confinement quantum takes place in tthe obtained SnO2 due to particles in nanoscale. 3.2. SYNTHESIS OF SnO2 WITH 1-3 URCHIN 1 2 3 4 5 6 7 0 100 200 300 400 500 600 (DE)2 (eV 2 . cm - 2 ) E(eV) 3,75 eV y = 682,17x - 2556,4 R2= 0,9998 10 3.2.1. The synthesized conditions effecting on the morphologies 1-3 urchin SnO2 Under conditions of the temperature and NaOH 0.350 M provided 1- 3 urchin SnO2 with high crystallinity (UR) (Figure 3.11). Figure 3.11. TEM images of UR Figure 3:19 shows nitrogen adsorption/desorption isotherm of UR. The specific surface area was calculated by BET 60.1 m2/g, this result is rather higher than some tin oxide with hierarchical nanotructures assembled from 1D and 2D. Figure.4. Adsorption/desorption isotherms of UR 3.2.2. Discussion Hall equation shows that SnO2 with 1-3 urchin has a very small crystal deformation (K = -0,0005), whereas SnO2 with 0-3 porous spheres are much larger crystals (K = -0.015). 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 0 10 20 30 40 50 60 70 V ( cm 3 /g S T P ) P/P 0 11 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.010 E.cos T sinT PS UR Figure 3.20. Graph Hall of hierarchical nanostructures PS and UR From the results, we proposed a model for SnO2 with 1-3 urchin as illustrated in scheme 3.2. Scheme 3.2. The proposed scheme of formation for SnO2 with 1-3 urchin in this study 3.3. SYNTHESIS OF 0-1 MCM-41 SnO2 (SnO2/MCM-41) 3.3.1. Synthesis of SnO2/MCM-41 by the indirect method Fig. 3.21 presents XRD patterns of samples with various molar ratios of Sn/Si synthesized by indirect method. With the increase in molar ratio of Sn/Si, the peak intensity of the (100) decreases rapidly (Figure 3.21) and BET surface area (Figure 3.22) decreased significantly in the order follows: SBET (SnO2/MCM-41(GT 0,07)) = 477,4 m2/g > SBET (SnO2/MCM-41 12 (GT 0,1)) = 424,4 m2/g > SBET (SnO2/MCM-41(GT 0,5)) = 319,6 m2/g. Figure 3.21. XRD of the sample prepared SnO2/MCM-41 with different molar ratio of Sn/Si Figure 3.22. Nitrogen adsorption/desorption isotherms of SnO2/MCM-41(GT0,07), SnO2/MCM-41(GT0,1), SnO2/MCM-41(GT 0,5) The dispersed degree of tin incorporation into MCM-41 were investigated by EDX as shown in Figure 3.24. Figure 3.24. EDX spectrum of SnO2/MCM-41(GT0,07) and SnO2/MCM-41(GT0,1) The results showed that the molar ratio of Sn/Si for SnO2/MCM-41 (GT0,07) is (M = 0.87, N = 4, SD = 0.09) and that for SnO2/MCM-41 (GT0,1) is (M = 0.26, N = 4, SD = 0.12). Large SD demonstrates tin unequal dispersion. 3.3.2. Synthesis of SnO2/MCM-41 by the direct method 0.0 0.2 0.4 0.6 0.8 1.0 0 200 400 600 800 1000 V (c m 3 / g ST P) P/P 0 SnO2/MCM-41(GT0,1) SnO2/MCM-41(GT0,5) SnO2/MCM-41(GT0,07) 0 2 4 6 8 10 SnO 2 /MCM41(GT0,07) SnO 2 /MCM41(GT0,1) SnO 2 /MCM41(GT0,5) In te ns it y (A br .) 2T (degree) (100) (110) (200) 1000 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 keV 005 0 800 1600 2400 3200 4000 4800 5600 6400 7200 8000 C ou nt s C K a O K a A lK a A lK su m Si K a C lL l C lK es c C lK a C lK b Sn M 3- m Sn M z Sn M g Sn Ll Sn La Sn Lb Sn Lb 2 Sn Lr Sn Lr 2, Sn Ls um 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 keV 003 0 400 800 1200 1600 2000 2400 2800 3200 3600 4000 C ou nt s C K a O K a A lK a A lK su m Si K a C lL l C lK es c C lK a C lK b Sn M 3- m Sn M z Sn M g Sn L l Sn L a Sn L b Sn L b2 Sn L r Sn L r2 , Sn L su m 13 The study showed that the amount of SnCl4 and NaOH concentration affects the formation of mesoporous structure. Figure 3.26 shows the molar ratio of Sn/Si being 0.07 and 0.1 could be formed the mesoprorous structure of MCM-41. The resulting figure 3.27 shows that NaOH concentration around 0.04M corresponding the sample of 0.40.SnO2/MCM-41 which posses high orderedly mesoporous structure. Figure 3.26. XRD patterns of the sample SnO2/MCM-41 with different molar ratios of Sn/Si Figure 3.26. XRD patterns of the sample SnO2/MCM-41 with different NaOH concentration Figure 3.29. TEM image of 0.40. SnO2/MCM-41 In this study, sample of 10.Sn-MCM-41(0.1) with best surface properties (Figure 3.29). The porous properties of samples is studied by nitrogen adsorption/desorption isotherm (Figure 3.30). The order of the 0 2 4 6 8 10 0 200 400 600 800 1000 1200 1400 1600 0,52.SnO 2 /MCM 41 0,48.SnO 2 /MCM 41 0,44.SnO 2 /MCM 41 0,40.SnO 2 /MCM 41 0,36.SnO 2 /MCM 41 In te ns it y (A br .) 2T (Degree) 0,32.SnO 2 /MCM 41 1 0 0 1 1 0 2 0 0 200 0 1 2 3 4 5 6 7 8 9 SnO 2 -MCM-41 (0,07) MCM-41 SnO 2 -MCM-41 (0,1) SnO 2 -MCM-41 (0,2) SnO 2 -MCM-41 (1) T (degree) 200110 100200 In te ns it y (A br .) 14 specific surface area of the sample is: SBET (0.40.SnO2/MCM-41) = 707 m2/g > SBET (0.44.SnO2/MCM-41) = 456 m2/g > SBET (0.36.SnO2/MCM-41) = 374 m2/g. 0.0 0.2 0.4 0.6 0.8 1.0 0,44.Sn-MCM 41 0,40.Sn-MCM 41 0,36.Sn-MCM 41 MCM 41 2 5 T h Ó tÝ ch k h Ý h Êp p h ô ( cm 3 /g S T P ) ¸p suÊt t­ ¬ng ®èi P/P 0 Figure 3.30. Adsorption/desorption isotherms of synthetic samples The dispersed degree of tin incorporation into MCM-41 were investigated by EDX as shown in table 3.10. Table 3.10. The molar ratio of Sn/Si analyzed by EDX for SnO2/MCM-41prepared in different concentration of NaOH Samples N M SD 0,32.SnO2/MCM-41 4 2,03 0,04 0,36.SnO2/MCM-41 4 0,75 0,04 0,40.SnO2/MCM-41 4 0,12 0,02 0,44.SnO2/MCM-41 4 0,24 0,01 0,46.SnO2/MCM-41 4 0,60 0,01 (N: points analysis, M: average molar ratio of Sn/Si, SD: standard deviation) This table shows greater standard deviations with the indirect method than the direct one, indicating that a direct synthesis method provided sample with higher dispered tin in MCM-41. 3.3.2.3 . Characteristics of SnO2 dispersed in silica framework Metal oxide dispersion in hexagonal mesoporous MCM-41 is usually characterized by standardized normalized coefficients N. The 15 calculated value of N for 0.40.SnO2/MCM-41 is closed to 1, indicating that tin oxide dispersed highly in silica framework surface, while N of the other samples are much smaller ( << 1 ), indicating that poor dispersion of SnO2 may blockage pore and partial collapses of mesopores. Model of SnO2 on the surface of MCM - 41 was studied by diffuse reflectance visible -ultraviolet UV - Vis spectra SnO2/MCM-41 of MCM - 41 and different molar ratio of Sn/Si initial presentation in Figure 3.32. 200 300 400 500 600 700 800 3 4 0 2 8 0 2 3 0 2 0 8 SnO 2 /MCM-41(0,2) SnO 2 /MCM-41(0,1) MCM-41 Wavelength (nm) A B S 0,1 Figure 3.32. DR-UV-Vis spectrum of MCM-41, SnO2/MCM-41 with different molar ratio Sn/Si Figure 3.33. A model for the connection of species in the SnO2/silica composites The SnO2 connected to the surface of MCM-41 silica is similar to the model proposed by Lin et al studied the SnO2 linked on SBA-15 (Figure 3.33). Based on characteristic analysis of composite materials SnO2/MCM- 41 two directly and indirectly methods, we propose the model forming SnO2/MCM-41 material as illustrated in the Scheme 3.3: 16 Scheme 3.3. The proposed scheme of formation for SnO2/MCM-41. 3.4 SnO2 WITH HIERARCHICAL NANOSTRUCTURES AS GAS SENSING MATERIALS We used three types of SnO2 with 0-3 porous spheres (PS), 1-3 urchins (UR) and 0-1 MCM-41 (SM) synthesized in conditions optimization in section 3.1, 3.2 and 3.3 to study the gas sensor for LPG, ethanol and hydrogen. 60 GRHVQ¶W SHUIRUP JDV VHQVLQJ properties while PS and UR show excellent LPG, hydrogen and ethanol sensory performance. 3.4.2. PS and UR sample as gas sensing materials for LPG 17 Figure 3.39. Dynamic curves LPG gas sensing and response time ± recovery time to different LPG concentration at 400 oC of obtained materials at 400 oC a. PS and b.UR samples. Figure 3.39 shows that the sensitivity of PS and UR materials increases with the increase in LPG concentration, but PS material is more sensitive than UR material. The reason for this difference, structure of PS is more compatible than that of UR.. In addition, PS materials have higher surface area than UR. 3.4.3. PS and UR as gas sensing materials for ethanol Figure 3.42. Dynamic curves ethanol gas sensing and response time ± recovery time to different ethanol concentration at 400 oC of obtained materials at 400 oC a. PS and b.UR samples. 18 Unlike the case of LPG gas, response/recovery time of UR materials are shorter than that of PS material. The sensitivity depends on ethanol concentration that are similar to LPG. 3.4.4. PS and UR as gas sensing materials for the hydrogen Sensitivity of PS materials is higher value than that of UR in the same gas concentration. This may be related to the different surface properties of these two materials. Figure 3.46. Dynamic curves ethanol gas sensing and response time ± recovery time to different hydrogen concentration at 400 oC of obtained materials at 400 oC a. PS and b.UR samples. In addition, type of porous sphere has diffusion resistances greater than that of the urchin, so the response time of UR for ethanol and H2 gas is faster than that of PS material. 3.5. STUDY ON PHENOL HYDROXYLATION REACTION BY HYDROPEROXIDE OVER SnO2/MCM- 41 CATALYST Both SnO2 with 1-3 urchin and 0-3 porous spherical structure show poor performance as a catalyst for the phenol hydroxylation reaction, while SnO2/MCM-41 exhibited the excellent catalytic activity and high selectivity to dihydroxylbenzene. Therefore, the study focused 19 on phenol hydroxylation reaction by hydroperoxide over SnO2/MCM- 41 (SM) catalyst. 3.5.2. The catalytic stability of SnO2/MCM-41 Based on the conversion of phenol after three times recycles, analysis of XRD and elemental composition, it is concluded that the SnO2/MCM-41 posses an excellent stability. 3.5.3. Kinetic study 3.5.3.1. Limitations of external diffusion The influence of external diffusion is minimized when the stirring speed is greater than 7, so that's 8 speed magnetic stirrer was used in the further experiments to minimize external diffusion. 3.5.3.2. The effect of products of the phenol hydroxylation reaction The addition of catechol and hydroquine as the main product of phenol hydroxylation into reaction mixture to study the effect of product on reaction rate. There are not are not statistically different in case of addtion of catechol, hydroquinone or without any products at significant level of 0.05 (Table 3.22). Table 3.22. Effect on concentration products to the phenol hydroxylation at 90 oC,150 minutes 0 PNC mol.L-1 0 HPC mol.L-1 0 CTAC mol.L-1 0 HQC mol.L-1 ).( 10 LmolCPN 0 PNX % 0,53 0,53 0 0 45,8 0,53 0,53 0,01 0 45,8 0,53 0,53 0,05 0 46,9 0,53 0,53 0,1 0 47,4 0,53 0,53 0 0,01 46,3 0,53 0,53 0 0,05 47,2 0,53 0,53 0 0,1 49,6 20 It is suggested that the adsorbed products onto the surface is the weakest so reaction rate will not include product variables due to negligible adsorption of the product to the catalytic sites. 3.5.3.3. Decomposition of hydroperoxide in the reaction conditions Results showed that hydroperoxide hardly decomposed in 210 minutes, 90 oC temperature when no catalyst and catalyst. Therefore, in this study, the decomposition of hydroperoxide is ignored. 3.5.3.4. Phenol hydroxylation reaction in some different conditions no catalyst and catalyst Figure 3.52 displays phenol conversion depending on the time at the temperature 90 oC in the different reaction conditions. The results showed that the reaction did not take place without catalyst because phenol is very durable chemical (line a). Having catalyst, the reaction occurred with high phenol conversion (line b). 0 60 120 180 240 -10 0 10 20 30 40 50 60 70 80 (f) (e) (c) (d) (b) (a) Ph en ol c on ve rs io n (% ) Time (min) Figure 3.52. Phenol conversion according to time in phenol hydroxylation by hydroperoxide with different reaction conditions: (a) no catalyst, (b) catalytic SM, (c). homogenous catalyst Sn (IV) 0.1 M, pH = 2 (d) separated catalyst after 120 minute reactions, (e). radical scavenger of benzoquinon 0.1 M, (f). radical scavenger of NaHCO3 0, 1M. 21 Especially appearing induction time in approximately 120 minutes with a heterogeneous catalyst. When homogeneous catalyst Sn (IV) at pH = 2 shows a high catalytic activity (line c) but elemental component analysis results hardly changes. These results showed that capable solubility Sn (IV) creates Sn (IV) homogeneous form of reactions continue to occur that do not have. When removing the catalyst, the reaction still occurs but not high rate (line d), extending to 210 minutes. When making radical scavenger benzoquinone and NaHCO3, phenol conversion continues to increase (lines e and f), indicating reaction may occur other radical mechanism. 3.5.3.5 . Adsorption kinetics of phenol and hydroperoxide on catalyst SnO2/MCM-41 Figure 3.53 shows the adsorption kinetic of H2O2 and phenol in solution with molar ratio 1:1 on SnO2/MCM-41 (SM) catalyst at room temperature (25 °C r 1). The results showed that this is the chemical and physical adsorption for hydroperoxide but chemisorptions is more dominant. Meanwhile, mainly physical adsorption is associated to phenol. 0 10 20 30 40 50 60 70 0.006 0.008 0.010 0.012 0.014 0.016 0.018 A rs or be d ca pa ci ty (m g/g ) Time (min) H 2 O 2 C 6 H 5 OH Figure 3.53. Adsorption capacity of phenol and hydroperoxide according to time over catalyst SM 22 Scheme 3.4 shows two possibilities can link between hydroperoxide and phenol on the catalytic surface SnO2/MCM-41. OSi Sn O O H G- G+ SiO OSi OSn Sn SnO OSn O H Scheme 3.4. a. The form of adsorbed H2O2 b. The form of adsorbed phenol 3.5.3.6. Kinetic phenol hydroxylation by hydroperoxide using catalyst SnO2/MCM-41 Based on the research results presented above, we proposed the reaction pathway shown in scheme 3.5. Scheme 3.5. Reaction pathway for phenol hydroxylation with hydroperoxide using catalyst SnO2/MCM-41 The phenol hydroxylation reaction does not occur without catalysts, this reaction can be bimolecular reactions involving surface. In this study, using two types of bimolecular surface reactions will be 23 considered the Eley±Rideal and Langmuir-Hinshelwood models to fit well between experimental data and calculated data. Analysis P-value in table 3.25 shows that, Eley-Rideal model with H2O2 adsorbed onto the surface reacts free phenol in the solution, the kinetic equation is almost similar to the experimental data. Meanwhile, two other models satisfy statistics, but kinetic equations are less compatible with the experimental data, the p value is less lower than the former. Table 3.25. Kinetic equations based on the mechanisms proposed Model Assumptions and kinetics equations KPN KHPS (L.mol-1) KPNS (L.mol-1) p -value Eley- Rideal . . . 1 . .  PN HPS PN HPPN HPS HP PNS PNk K C Cr K C K C (H2O2 adsorbed, phenol free, surface reaction controlling) 4.6.10-4 m-2.s-1 0,104 1,254 0,936 . . . 1 . .  PN PNS PN HPPN PNS PN HPS HPk K C Cr K C K C (phenol adsorbed, H2O2 free, surface reaction controlling) 14,8.10-5 m-2.s-1 1,267 0,105 0,662 Langmuir- Hinshelwo od 2 . . (1 . . ) PN PN HP PN PNS PN HPS HP k C C r K C K C   (phenol and H2O2 adsorbed onto the tin- active site, surface reactive controlling) 1.6.10-4 mol-1.L. m-2.s-1 1,488 1,459 0,402 CONCLUSIONS From the obtained thesis, we make the main following conclusions: 24 1. Synthesis of SnO2 with hierarchical nanostructures using template CTAB by hydrothermal method with ultrasound. Morphology of SnO2 materials was much dependent on the solvent and ultrasonically assisted hydrothermal process. Synthesized conditions: ultrasonic radiation, hydrothermal temperature of 180 ᤪ C, 0,5 g SnCl4 in 35 ml of methanol solvent provided 0-3 porous spheres SnO2 with a high surface area 227 m2/g. The 0-3 porous spherical materials with a size 500-600 nm in diameters consisting of nanopartices less than 16 nm. The mechanism for the formation of 0-3 porous spheres proposed as shown scheme 3.1. We discovered methanol solvent is favorite for forming the 0-3 porous spherical structure for the first time. 2. Having successfully synthesized of SnO2 with 1-3 urchin in hydrothermal conditions: 1.5 mmol Na2SnO3.3H2O, 20 ml NaOH 0.35 M and 20 ml ethanol. The possible mechanism SnO2 with 1-3 urchin is recommended as scheme 3.2. The research by deformation equations Hall shows that free development leads to crystal with 1-3 urchin structure less deformed than crystal with 0-3 porous sphere. The obtained SnO2 with 1-3 urchin possesses a high specific surface area of 61 m2/g and rather higher than some hierarchical nanotructures assembled from 1D and 2D. 3. SnO2 with 0-1 MCM-41 structure with highly ordered mesopore, high tin oxide content has been synthesized by direct methods. Tin oxide introduced into MCM-41 exists in two major forms: (i). tetrahedral and octahedral coordinated tin join to the silica wall in the framework, (ii). hexacoordinated polymeric Sn±O±Sn type species to forms tin oxide clutters. Their size is too small to observe by XRD. Formation mechanism SnO2 with 0-1 MCM-41 depends on the synthesis conditions as proposed schemes 3.3. This mechanism shows that tin oxide can be dispersed onto the framework with highly ordered mesopore and high tin oxide content by appropriately adjusting the molar ratio Sn/Si and NaOH concentration. 25 4. SnO2/MCM- GRHVQ¶W SHUIRUP JDV VHQVLQJ properties while SnO2 with 0-3 porous spherical and 1-3 urchin structure shows excellent LPG, hydrogen and ethanol sensing performance. SnO2 with 0-3 porous spherical structure has gas sensoring better than SnO2 with 1-3 urchin structure. However, the latter exhibits better gas sensoring, recovery and response time than the former at low temperature. This difference may be related to surface properties (surface area, crystallinity, diffusion) of two different materials. 5. Both SnO2 with 1-3 urchin and 0-3 porous spherical structure show poor performance as a catalyst for phenol hydroxylation reaction. However, SnO2/MCM-41 exhibited the excellent catalytic activity and high selectivity to dihydroxylbenzene. The resulted showed that the Eley±Rideal and Langmuir-Hinshelwood models were fitted well to experimental data. Reaction mechanism may be related in part to free radicals, which interact transition metal sites with hydroperoxide yields HO . and HO . 2 radicals via redox mechanism. On the other hand, based on the kinetic analysis and adsorption result showed that phenol hydroxylation reactions involving bimolecular surface reactions between the adsorption of hydroperoxixide and phenol on the active sites by catalytic center. Phenol hydroxylation substitutes mainly ortho and para-positions suggests reaction to be an electrophilic substitution. High catalytic activity and selectivity of the catalyst could be explained multi states of active sites and dispersion on framework having a high surface area. It is the first time that SnO2/MCM-41 has been reported to have excellent catalytic activity and high selectivity to dihydroxylbenzene. The SnO2/MCM-41 in the study has similar activity to TS-1 which is a commercial catalyst for recent dihydroxyl benzene synthesis. LIST OF ACADEMIC WORKS PUBLISHEDTHE THESIS 1. Le ThiHoa, Pham Thi Hue , DinhQuangKhieu, Tran Thai Hoa (2010), " Synthesis of rutile SnO2 porous spheres via sonication assisted hydrothermal process and LPG sensing properties", Journal of Science and Technology, Vol.48 (2A), pp.96 ± 101. 2. Le ThiHoa, DinhQuangKhieu, Tran Thai Hoa (2010), "Direct synthesis of highly ordered Sn-MCM-41 mesoporous materials with KLJK WLQ R[LGH FRQWHQW E\ K\GURWKHUPDO SURFHVV´ -ournalof Chemistry, Vol.48 (5A), pp.76 - 81. 3. Le ThiHoa, Pham Thi Hue, DinhQuangKhieu, Tran Thai Hoa (2010), " Synthesis of nanorods SnO2 via a hydrothermal technique and C2H5OH sensing properties", Journal Chemistry, Vol.48 (4A), pp.19 - 23. 4. Le ThiHoa, Nguyen Van Hieu, DinhQuangKhieu, Tran Thai Hoa (2011), "Comparative study on ethanol gas sensing properties on nano tin oxide with 1-3 urchin and 0-3 porous spherical structure", Journal of Chemistry, Vol.49 (5AB), pp.634 - 640 . 5. Le ThiHoa, Tran Thuy Thai Ha, DinhQuangKhieu, Tran Thai Hoa (2011) , "Synthesis of tin oxide - modified mesoporous MCM - 41 and catalytic activity in nopol synthesis", Proceeding of 3rd IWNA, Vung Tau, Vietnam, pp. 964-968. 6 . Le ThiHoa, Nguyen Van Hieu, DinhQuangKhieu, Tran Thai Hoa (2011), " Synthesis of nano tin oxide nanostructures with hierarchical sensoring gas and its properties ", Proceedings of 3rd IWNA, Vung Tau , Vietnam, pp.725-729. 7 . Le ThiHoa, Tong Thi Cam Le, DinhQuangKhieu, Tran Thai Hoa (2013) , "A kinetic study on phenol hydroxylation reaction by hydroperoxide over SnO2/MCM-41 catalyst", Journal of Chemistry, Vol.51 (2C), pp.971-976. 8 . Le ThiHoa , Pham Dinh Du , Complaints DinhQuang , Tran Thai Hoa (2013), "Research on phenol hydroxylation reaction catalyzed byhydroperoxide on SnO2/MCM-41", Journal of Catalysis and Adsorption,Vol. 2 (4), pp.102-110.

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