HM-1 - Technische Universität Chemnitz

Microwave-assisted non-aqueous synthesis of
nanoscale bismuth vanadate for visible light-driven
photocatalytic water purification
Max Hofmann, Martin Rainer, Marcus Weber, Michael Mehring
Technische Universität Chemnitz, Institut für Chemie, Professur Koordinationschemie, Straße der Nationen 62, 09111 Chemnitz
Introduction
e-mail: [email protected]
The conversion of photon energy into chemical energy has become of interest for photoinduced, environmentally friendly water and air
[1]
purification by oxidation of organic pollutants. Monoclinic bismuth vanadate as a semiconductor with visible-light response has received
[2]
great attention, because of its low toxicity combined with negligible photocorrosion. Hence, in the last years several synthetic strategies for
[3,4]
bismuth vanadate have been developed in order to improve its photocatalytic activity. Here we present a novel microwave-assisted
synthesis route for monoclinic bismuth vanadate using a concept adapted from a non-aqueous strategy for nanostructured organic-inorganic
[6]
[5]
hybrid materials and metal oxides. In order to enhance the so called in situ Twin Polymerisation for mixed-metal oxides, bismuth(III) tertbutoxide and vanadium(V) oxido tert-butoxide were reacted in the presence of polymerizable alcohols, a non-polymerizable alcohol and
without addition of any additives, and composites were obtained. Calcination of the as-obtained hybrid materials (HM-1 - HM-4) gave
nanoscaled bismuth vanadate samples (BiVO4-1 - BiVO4-4), which were compared with regard to their performance in photocatalytic
reactions. The interplay of direct photooxidation and photosensitized decomposition for the degradation of RhB is demonstrated by performing
diffuse reflectance measurements with adsorbed dye at the surface of the catalyst and by using different cutoff filters for experiments in
solution. Furthermore, the photodegradation efficiency towards methyl orange (MO), methylene blue (MB) and orange G (OG) was evaluated.
Concept & Synthesis
Bi(OtBu)3 + VO(OtBu)3
n A-C + n B-C
polymerisation
addition of
polymerizable alcohols
From concept to synthesis:
bismuth vanadate
General concept of co-simultaneous twin
polymerization (A,B = inorganic components; C
= organic component) with subsequent oxidation
of the hybrid material to remove the organic
component.
without additive
addition of
non-polymerizable alcohol
OH
OH
OMe
OMe
S
OH
oxidation
OMe
[H+]
microwave-assisted
[H+]
microwave-assisted
-(A-B-) n + -(C-) n
HM-1
HM-2
O2
pyrolysis (400 °C)
heterobimetallic oxide
Hybrid materials (HM-1 - HM-4)
HM-3
O2
pyrolysis (400 °C)
BiVO4-1
[H+]
microwave-assisted
[H+]
microwave-assisted
HM-4
O2
pyrolysis (400 °C)
O2
pyrolysis (400 °C)
BiVO4-3
BiVO4-2
BiVO4-4
Catalyst samples (BiVO4-1 - BiVO4-4)
Ÿ HM-1/2: monoclinic BiVO4 embedded in a organic matrix
Characterization
HM-1
Ÿ nanoscale, phase-pure m-BiVO4
HM-2
Crystallite size
BET-surface area
Absorption edge
Band gap
[nm]
[m2/g]
[nm]
[eV]
BiVO4-1
72 ± 17
8
508
2,54
Sample
Hydrogen
Bismuth
BiVO4-2
63 ± 12
7
501
2,58
[%]
[%]
[%]
BiVO4-3
42 ± 5
16
508
2,55
measured
measured calculated[a] measured calculated[a]
BiVO4-4
78 ± 20
11
518
2,49
HM-1
23.50
2.22
1.97
45.29
45.56
HM-2
48.12
4.41
4.49
22.24
21.39
HM-3
0.94
0.06
-
67.38
63.87
HM-4
0.65
0.14
-
61.41
64.01
Hybrid material Carbon
[a] Element content expected for molar ratio of monomer units to metal oxide of 1.12 (HM-1) and 4.35 (HM-2).
Photocatalytic activity
H3C
H3C
CH3
N
O
Photocatalysis
From synthesis
to catalysis
N
CH3
COOH
Ÿ water cooled glass reactor (15 °C)
®
Ÿ 300 W xenon lamp (Cermax VQ™ ME300BF, Co. PerkinElmer)
Ÿ hot mirror filter (λ ≤ 700 nm), different cutoff filters (GG420, OG550)
Direct Photooxidation and photosensitized decomposition
Ÿ UV cutoff filter (GG420): direct photooxidation of the chromophoric system initiated by Vis light excitation
40 mg catalyst and 40 ml of an aqueous solution of 1∙10-5 M RhB, 4∙10-5 M MB, 4∙10-5 M MO and
4∙10-5 M OG under Vis light irradiation (UV cutoff filter GG420)
of the semiconductor catalyst overlays the photosensitized mechanism in solution
Ÿ photosensitized process: successive N-deethylation of RhB indicated by a hypsochromic shift (each step
approximately 15 nm)
cutoff filter GG420
cutoff filter GG420
cutoff filter OG550
Literature
Conclusion
Ÿmicrowave-assisted synthesis route adapted from the in situ Twin
Polymerization gives access to monoclinic bismuth vanadate
Ÿbest photocatalytic perfomance of BiVO4-3 synthesized in the
presence of the non-polymerizable 2-(2-thienyl)isopropyl alcohol
Ÿhigh photocatalytic activity
Ÿinterplay of direct photooxidation and photosensitized RhB
decomposition
Ÿk(degradation, chromophoric system) >> k(desorption, deethylated RhB)
Visible diffuse reflectance spectra
of RhB adsorbed at the surface of
BiVO4-3
[1] P. Pichat, Photocatalysis and Water Purification, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, 2013. [2] G. Li, D. Zhang,
J. C. Yu, Chem. Mater. 2008, 20, 3983. [3] J. Yu, A. Kudo, Adv. Funct. Mater. 2006, 16, 2163. [4] A. Martínez-de la Cruz, U. M. G.
Pérez, Mat. Res. Bull. 2010, 45, 135. [5] S. Grund, P. Kempe, G. Baumann, A. Seifert, S. Spange, Angew. Chem. Int. Ed. 2007,
46, 628. [6] F. Böttger-Hiller, R. Lungwitz, A. Seifert, M. Hietschold, M. Schlesinger, M. Mehring, S. Spange, Angew. Chem. Int.
Ed. 2009, 48, 8878.
40 mg BiVO4-3 and 40 ml of an aqueous solution of 1∙10-5 M RhB
http://www.tu-chemnitz.de/chemie/koord/

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