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Workplace Hazardous Materials Information System (WHMIS)
The Workplace Hazardous Materials Information System (WHMIS) is Canada's national hazard communication standard. The key elements of the system are hazard classification, cautionary labelling of containers, the provision of (material) safety data sheets ((M)SDSs) and worker education and training programs.
The basis for hazard classification and communication in WHMIS is changing. With the incorporation of the Globally Harmonized System of Classification and Labelling for chemicals (GHS) in WHMIS, the hazard classification and communication requirements of WHMIS have been aligned with those used in the United States and other Canadian trading partners. WHMIS is in a period of transition between two hazard communication regimes - WHMIS 1988 and WHMIS 2015 (which incorporates the GHS).
WHMIS requirements of the amended Hazardous Products Act and Hazardous Products Regulations which incorporate the GHS
WHMIS requirements of the Hazardous Products Act and Controlled Products Regulations
Protecting Confidential Business Information: Completing a Claim for Exemption
Learn about WHMIS and how it is implemented in Canada, including its administration and legal foundation (Hazardous Product Act (HPA) and associated regulations).
This topic also provides information on excluded sectors.
To give suppliers, employers and workers time to adjust to the new
system, WHMIS 2015 implementation will take place gradually over a three-stage
transition period that is synchronized
nationally across federal, provincial and territorial jurisdictions.& Learn more about WHMIS transition and how to
remain compliant with WHMIS requirements.
WHMIS 1988 has changed to incorporate the GHS, which is an internationally consistent approach to classifying chemicals and communicating hazard information though labels and safety data sheets.
This topic includes information about the new hazard communication regime for workplace chemicals - WHMIS 2015, including the amended HPA and Hazardous Products Regulations (HPR).
Learn about supplier and importer requirements within WHMIS 1988 stemming from the Controlled Products Regulations, including supplier labelling and MSDS requirements, information about WHMIS 1988 classifications, and compliance and enforcement.
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Find answers to Frequently Asked Questions relating to WHMIS, GHS,
protecting CBI, and where employers and workers can find additional resources.
See details to contact Health Canada about WHMIS or to contact the federal, provincial and territorial occupational health and safety regulators.
Subscribe to the WHMIS News mailing list to receive updates on WHMIS as they become available.From Wikipedia, the free encyclopedia
A Vickers hardness tester
The Vickers hardness test was developed in 1921 by Robert L. Smith and George E. Sandland at
as an alternative to the
method to measure the
of materials. The Vickers test is often easier to use than other hardness tests since the required calculations are independent of the size of the indenter, and the indenter can be used for all materials irrespective of hardness. The basic principle, as with all common measures of hardness, is to observe the questioned material's ability to resist
from a standard source. The Vickers test can be used for all
and has one of the widest scales among hardness tests. The unit of hardness given by the test is known as the Vickers Pyramid Number (HV) or Diamond Pyramid Hardness (DPH). The hardness number can be converted into units of , but should not be confused with pressure, which also has units of pascals. The hardness number is determined by the load over the surface area of the indentation and not the area normal to the force, and is therefore not pressure.
Vickers test scheme
The pyramidal
indenter of a Vickers hardness tester.
An indentation left in case-hardened steel after a Vickers hardness test. The difference in length of both diagonals and the illumination gradient, are both classic indications of an out-of-level sample. This is not a good indentation.
It was decided that the indenter shape should be capable of producing geometrically similar impressions,
the impression should have well-defined p and the indenter should have high resistance to self-deformation. A
in the form of a square-based pyramid satisfied these conditions. It had been established that the ideal size of a
impression was 3/8 of the ball diameter. As two tangents to the circle at the ends of a chord 3d/8 long intersect at 136°, it was decided to use this as the included angle of the indenter, giving an angle to the horizontal plane of 22° on each side. The angle was varied experimentally and it was found that the hardness value obtained on a homogeneous piece of material remained constant, irrespective of load. Accordingly, loads of various magnitudes are applied to a flat surface, depending on the hardness of the material to be measured. The HV number is then determined by the ratio F/A, where F is the force applied to the diamond in kilograms-force and A is the surface area of the resulting indentation in square millimeters. A can be determined by the formula.
which can be approximated by evaluating the sine term to give
where d is the average length of the diagonal left by the indenter in millimeters. Hence,
where F is in
and d is in millimeters.
The corresponding units of HV are then kilograms-force per square millimeter (kgf/mm?). To calculate Vickers hardness number using SI units one needs to convert the force applied from
to newtons by multiplying by 9.806 65 () and dividing by a factor of 1000 to get the answer in GPa. To do the calculation directly, the following equation can be used:
where F is in N and d is in millimeters. Here, HV is in GPa and should be roughly between 0-15 GPa.
Vickers hardness numbers are reported as xxxHVyy, e.g. 440HV30, or xxxHVyy/zz if duration of force differs from 10 s to 15 s, e.g. 440Hv30/20, where:
440 is the hardness number,
HV gives the hardness scale (Vickers),
30 indicates the load used in kgf.
20 indicates the loading time if it differs from 10 s to 15 s
Vickers values are generally independent of the test force: they will come out the same for 500 gf and 50 kgf, as long as the force is at least 200 gf.
For thin samples indentation depth can be an issue due to substrate effects. As a general rule of thumb the sample thickness should be kept greater than 2.5 times the indent diameter. Alternatively indent depth can be calculated according to:
Examples of HV values for various materials
316L stainless steel
55–120HV5
When doing the hardness tests the minimum distance between indentations and the distance from the indentation to the edge of the specimen must be taken into account to avoid interaction between the work-hardened regions and effects of the edge. This minimum distances are different for ISO 6507-1 and ASTM E384 standards.
Distance between indentations
Distance from the center of the indentation to the edge of the specimen
ISO 6507-1
& 3·d for steel and copper alloys and & 6·d for light metals
2.5·d for steel and copper alloys and & 3·d for light metals
If HV is expressed in
(in MPa) of the material can be approximated as:
where c is a constant determined by geometrical factors usually ranging between 2 and 4.
attachment pins and sleeves in the
airliner were specified by the aircraft manufacturer to be hardened to a Vickers Hardness specification of 390HV5, the '5' meaning five . However on the aircraft flying
the pins were later found to have been replaced with sub-standard parts, leading to rapid wear and finally loss of the aircraft. On examination, accident investigators found that the sub-standard pins had a hardness value of only some 200-230HV5.
R.L. Smith & G.E. Sandland, "An Accurate Method of Determining the Hardness of Metals, with Particular Reference to Those of a High Degree of Hardness," , Vol. I, 1922, p 623–641.
ASTM E384-10e2
Smithells Metals Reference Book, 8th Edition, ch. 22
Note 7 is a link to a source that gives conversion formula as Vickers Hardness (HV) ~ 0.3 × yield stress (in MPa) which is wrong as it should be Vickers Hardness (HV) ~ 0.3 × ultimate stress (in MPa)
Meyers and Chawla (1999). "Section 3.8". Mechanical Behavior of Materials. Prentice Hall, Inc.
E92: Standard method for Vickers hardness of metallic materials (Withdrawn and replaced by E384-10e2)
ASTM E384: Standard Test Method for Knoop and Vickers Hardness of Materials
6507-1: Metallic materials - Vickers hardness test - Part 1: Test method
ISO 6507-2: Metallic materials - Vickers hardness test - Part 2: Verification and calibration of testing machines
ISO 6507-3: Metallic materials - Vickers hardness test - Part 3: Calibration of reference blocks
ISO 6507-4: Metallic materials - Vickers hardness test - Part 4: Tables of hardness values
ISO 18265: Metallic materials - Conversion of Hardness Values
- Vickers, Brinell, and Rockwell scalesAssociated material
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Research article
TiO2-graphene oxide nanocomposite as advanced photocatalytic materials
Václav ?tengl*, Snejana Bakardjieva, Tomá? Matys Grygar, Jana Bludská and Martin Kormunda
Corresponding author:
Department of Solid State Chemistry, Institute of Inorganic Chemistry AS CR v.v.i., 250 68, ?e?, Czech Republic
Department of Physics, Faculty of Science, J.E.Purkyně University in ?stí nad Labem, 400 96, Ustí n. L, Czech Republic
For all author emails, please .
Chemistry Central Journal 2013, 7:41&
doi:10.3X-7-41
The electronic version of this article is the complete one and can be found online at:
Received:10 December 2012
Accepted:13 February 2013
Published:27 February 2013
& 2013 ? licensee Chemistry Central Ltd.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Formula display:Abstract
Background
Graphene oxide composites with photocatalysts may exhibit better properties than pure
photocatalysts via improvement of their textural and electronic properties.
TiO2-Graphene Oxide (TiO2 - GO) nanocomposite was prepared by thermal hydrolysis of suspension with graphene
oxide (GO) nanosheets and titania peroxo-complex. The characterization of graphene
oxide nanosheets was provided by using an atomic force microscope and Raman spectroscopy.
The prepared nanocomposites samples were characterized by Brunauer–Emmett–Teller surface
area and Barrett–Joiner–Halenda porosity, X-ray Diffraction, Infrared Spectroscopy,
Raman Spectroscopy and Transmission Electron Microscopy. UV/VIS diffuse reflectance
spectroscopy was employed to estimate band-gap energies. From the TiO2 - GO samples, a 300 μm thin layer on a piece of glass 10×15 cm was created. The photocatalytic
activity of the prepared layers was assessed from the kinetics of the photocatalytic
degradation of butane in the gas phase.
Conclusions
The best photocatalytic activity under UV was observed for sample denoted TiGO_100
(k = 0.03012 h-1), while sample labeled TiGO_075 (k = 0.00774 h-1) demonstrated the best activity under visible light.
Keywords: G Titanium(IV) G PhotocatalysisIntroduction
Traditionally, TiO2 is currently known as the most available and commercially cheapest photocatalyst.
It has been well documented that GO is heavily oxygenated graphene that is readily
exfoliated in water to yield stable dispersions consisting mostly of single-layer
sheets. The use of graphene oxide as the nanoscale substrates for the formation of
nonocomposites with metal oxides is widely explored due to an idea to obtain a hybrid
which could be combined both properties of GO as fascinating paper-shape material
and the features of single nano-sized metal oxide particles.
Recent studies concentrate on the preparation and applications of GO modified photocatalyst
because their large specific surface area and high activity in most catalytic processes.
Krishnamoorthy et al. [] presented an article where photocatalytic characteristics and properties of graphene
oxide were investigated by measuring the reduction rate of resazurin into resorufin
as a function of UV irradiation time. The synthesis and physiochemical characterization
of titanium oxide nanoparticle-graphene oxide (TiO2-GO) and titanium oxide nanoparticle-reduced graphene oxide (TiO2-RGO) composites were early provided and emphasized on the different synthetic strategies
for the preparation of graphene-TiO2 materials. For example, TiO2-GO materials have been prepared via the hydrolysis of TiF4 at 60°C for 24 h in the presence of an aqueous dispersion of graphene oxide (GO).
The reaction proceeded to yield an insoluble material that is composed of TiO2 and GO [].
In an another strategy graphene oxide/TiO2 composites were prepared by using TiCl3 and graphene oxide as reactants. The concentration of graphene oxide in starting
solution played an important role in photoelectronic and photocatalytic performance
of graphene oxide/TiO2 composites. In this way either a p-type or n-type semiconductive graphene oxide/TiO2 composites were synthesized. These semiconductors were excited by visible light with
wavelengths longer than 510 nm and acted as sensitizers in graphene TiO2 composites [].
TiO2-Graphene Oxide intercalated composite has been successfully prepared at low temperature
(80°C) with graphite oxide and titanium sulfate Ti(SO4)2 as initial reactants. Graphite oxide was firstly exfoliated by NaOH and formed single
and multi-layered graphite oxide mixture which can be defined as graphene oxide, [TiO]2+ induced by the hydrolysis of Ti(SO4)2 diffused into graphene oxide interlayer by electrostatic attraction [].
Recently, Min et al. [] presented a novel dye-sensitized photocatalytic system for photochemical energy conversion
employing reduced graphene oxide (RGO) as a catalyst scaffold and an efficient electron
relay mediator between photosensitizer and catalyst. Under visible light irradiation
(λ = 420 nm), the photocatalyst of Eosin Y sensitized RGO with dispersed Pt nanoparticles
exhibited highly efficient activity for hydrogen evolution from water reduction.
A new technique for producing of novel solvent-exfoliated graphene-TiO2 nanocomposites was published [], which are then compared to previously reported reduced graphene oxide-TiO2 nanocomposites
in an effort to elucidate the role of graphene and its defects in the photocatalytic
reduction of CO2 to CH4. Another novel method [] was developed to synthesize graphite oxide/TiO2 composites as a highly efficient photocatalyst by in situ depositing TiO2 nanoparticles on graphene oxide nano-sheets by a liquid phase deposition, followed
by a calcination treatment at 200°C.
In our previous work [], we reported on nonstoichiometric TiO2-graphene oxide nanocomposite, which was prepared by thermal hydrolysis of suspension
with graphene oxide nanosheets and titania peroxo-complex. It should be mentioned
that we are able to produce pure graphene nanosheets in large quantity from natural
graphite by using high intensity cavitation field in the high-pressure ultrasonic
reactor. Graphene oxide sheets, prepared by such safe and friendly method, can be
used as a good support for TiO2 to enhance its photocatalytic activity. In this paper, we reported on an "one-pot"
thermal hydrolysis of titanium peroxo-complexes in the presence of graphene oxide
in aqueous solution. Our "hydrogen peroxide route" is based on hydrolysis of Ti(IV)
sulfate, next treatment of the resulting gel by hydrogen peroxide, and thermal decomposition
of so formed peroxo-titanate under reflux at ambient pressure producing directly the
TiO2-GO photocatalyst. The relative photocatalytic activity of the as-prepared thin layers
of titania/graphene nanocomposite in poly(hydroxyethyl methacrylate) was assessed
by the photocatalytic decomposition of butane under UV and visible light.
Preparation TiO2 - GO nanocomposite
All chemical reagents used in the present experiments were obtained from commercial
sources and used without further purification. Titanium oxo-sulfate TiOSO4, hydrogen peroxide H2O2, ethylene glycol OHCH2CH2OH and ammonium hydroxide NH4OH were supplied by Sigma-Aldrich. Graphene was produced in large quantity from natural
graphite (Koh-i-noor Grafite Ltd. Czech republic) using high intensity cavitation
field in a pressure batch-ultrasonic reactor (UIP 2000hd, 20 kHz, 2000 W, Hielscher
Ultrasonics GmbH) [].
Graphene oxide was prepared by our safety method, a 60 ml of H2SO4 and 10 ml of H3PO4, 1 g of graphene and 3 g of KMnO4 were mixed in round bottom flask. The reaction was then heated to 40°C and stirred
for 6 hours and pink squash suspension was obtained. Subsequently was poured onto
ice with 200 ml of 30% H2O2. The pink squash suspension quickly changed to lemon-like yellow suspension. The
whole reaction product was purged by dialysis (Spectra/Por 3 dialysis membrane), washed
with ethanol and dried at 105°C.
In the typical procedure of TiO2 - GO nanocomposite preparation, 100 ml of 1.6 M titanium oxo-sulfate (TiOSO4) was hydrolyzed by slow addition of ammonium hydroxide solution (10%) under constant
stirring at temperature of 0°C in ice bath. The stirring last until the reaction mixture
reaches pH 8.0. The obtained white precipitate was separated by filtration. The consequent
depuration of sulfate ions from precipitate with distilled water was confirmed by
the BaCl2. The wet precipitate is mixed with 100 ml of 15% hydrog thereby
a yellow solution of titania peroxo-complex is obtained.
Well defined quantity (see Table ) of GO nanosheets was dispersed using ultrasound in water, added to the yellow precursor
of titania peroxo-complex and annealed at a heated mantle in a round-bottom flask
with a reflux cooler at 100°C for 48 hours. The originated blue TiO2 - GO nanocomposite was filtered off and dried at 105°C. Ten samples of TiO2-GO nanocomposites doped as TiGO_XXX, where XXX are grams of GO, were prepared.
Sample composition, crystallite size, BET a total pore volume of prepared samples
The prepared TiO2 - GO nanocomposite powder (2 g) was dispersed in a mixture of 5 ml poly(hydroxyethyl
methacrylate) and 10 ml of ethanol. From this suspension, a 300 μm thin layer on a
piece of glass, 100 × 150 mm was created.
Characterisation methods
Diffraction patterns were collected with diffractometer PANalytical X?Pert PRO equipped
with conventional X-ray tube (Cu Kα radiation, 40 kV, 30 mA) and a linear position
sensitive detector PIXcel with an anti-scatter shield. A programmable divergence slit
set to a fixed value of 0.5 deg, Soller slits of 0.02 rad and mask of 15 mm were used
in the primary beam. A programmable anti-scatter slit set to fixed value of 0.5 deg.,
Soller slit of 0.02 rad and Ni beta-filter were used in the diffracted beam. Qualitative
analysis was performed with the DiffracPlus Eva software package (Bruker AXS, Germany)
using the JCPDS PDF-2 database []. For quantitative analysis of XRD patterns we used Diffrac-Plus Topas (Bruker AXS,
Germany, version 4.1) with structural models based on ICSD database []. This program permits to estimate the weight fractions of crystalline phases and
mean coherence length by means of Rietveld refinement procedure.
AFM images were obtained using an NTEGRA Aura (NT-MTD) microscope. A sample of the
diluted dispersion was placed on synthetic mica as an atomically smooth support and
evaporated at room temperature. The measurements were performed in air at room temperature
in non contact mode, with Si tips of the 1650–00 type at resonance frequencies ranging
from 180 to 240 kHz.
The morphology of sample powders was inspected by transmission electron microscopy
(TEM) and the crystal structure was analyzed by electron diffraction (ED) using a
200 kV TEM microscope JEOL 2010 F. As specimen support for TEM investigations a microscopic
copper grid covered by a thin transparent carbon film was used. The samples were studied
in both bright field and by electron diffraction with a selecting aperture (SAED)
mode at an acceleration voltage of 200 kV.
The surface areas of samples were determined from nitrogen adsorption–desorption isotherms
at liquid nitrogen temperature using a Coulter SA3100 instrument with outgas 15 min
at 150°C. The Brunauer–Emmett–Teller (BET) method was used for surface area calculation
[], the pore size distribution (pore diameter, pore volume and micropore surface area
of the samples) was determined by the Barrett–Joyner–Halenda (BJH) method [].
The Raman spectra were acquired with DXR Raman microscope (Thermo Scientific) with
532 nm (6 mW) laser, 32 two-second scans were accumulated with laser 532 nm (6 mW)
under 10× objective of Olympus microscope.
Infrared spectra were recorded by using Thermo-Nicolet Nexus 670 FT-IR spectrometer
approximately in
and 500–50 cm-1, respectively, with single-reflection horizontal accessory on Si crystal. The samples
were mixed with KBr and pressed to conventional pellets at ambient conditions and
measured in the transmission mode.
XPS apparatus was equipped with SPECS X-Ray XR50 (Al cathode 1486.6 eV) and SPECS
PHOIBOS 100 Hemispheric Analyzer with 5-channels detector. A background pressure in
XPS during the measurements was under 2×10-8 mbar. XPS survey-scan spectra were made at pass energy of 40 eV; the energy resolution
was set to 0.5 eV. While individual high-resolution spectra were taken at pass energy
of 10 eV with 0.05 eV energy steps. A software tool CasaXPS was used to fit high-resolution
multi components peaks. The proper surface charge compensation was done by fitting
C-C, C-H component of C 1 s peak to reference binding energy 284.5 eV. The atomic
concentration of compounds was evaluated with relative sensitivity factors (RSF) defined
in standard table of CasaXPS software.
Diffuse reflectance UV/VIS spectra for evaluation of photo-physical properties were
recorded in the diffuse reflectance mode (R) and transformed to absorption spectra
through the Kubelka-Munk function []. A Perkin Elmer Lambda 35 spectrometer equipped with a Labsphere RSAPE- 20 integration
sphere with BaSO4 as a standard was used. The reflectance data were obtained as relative percentage
reflectance to a non absorbing material (BaSO4) which can optically diffuse light.
Kinetics of the photocatalytic degradation of butane (0.87%) was measured by using
a home-made stainless steel batch photo-reactor [] with a Narva black-light fluorescent lamp at wavelength 365 nm and warm-white fluorescent
lamp at wavelength up to 400 nm (input power 8 W, light intensity 6.3 mW cm-2). The gas concentration was measured with the use of Quadrupole Mass Spectrometer
JEOL JMS-Q100GC and gas chromatograph Agilent 6890 N. A high-resolution gas chromatography
column (19091P-QO4, J&W Scientific) was used. Samples were taken from the reactor
automatically through the sampling valve (6-port external volume sample injector VICI,
Valco Instruments Co. Inc.) in a time interval of 2 hours.
Blank tests (a layer of poly(hydroxyethyl methacrylate) without titania) were performed
in order to establish the effect of photolysis and catalysis on the conversion of
butane. The UV irradiation detects that there was none or immeasurable conversion
of butane, as a testing gas, into CO and/or CO2, and consequently neither butane absorbed on the poly(hydroxyethyl methacrylate)
matrix. The injection volume of butane into the photoreactor was 30 ml.
Results and discussion
Early published experimental XRD pattern of graphene oxide demonstrated arising of
strong 001 reflection peak at 2θ ~10° with a basal spacing of d001 = 6.33 ? []. We calculated d-spacing of sample prepared during our experiment (see Figure a) such as GO d001 = 6.718 ? which is in good agreement with published results [,].
a The XRD pattern of graphene oxide. b The XRD patterns of TiO2-GO nanocomposites, diffraction line a) TiGO_001, b) TiGO_005, c) TiGO_010, d) TiGO_050, e) TiGO_075, f) TiGO_100, g) TiGO_200, h) TiGO_300, i) TiGO_400 and j) TiGO_500.
The Figure b shows X-ray diffraction patterns of TiO2-GO nanocomposites. All samples show only the anatase phase (PDF 21–1272). Higher
concentrations of GO (samples TiGO_300 and TiGO_400) probably lead to partial reduction
of GO to graphene and a weak peak at 2Θ = 26.50° appears (see arrow G). Nevertheless,
the intensity of graphene X-ray lines is under possibility for quality Rietveld refinement.
Furthermore, in the position at 2Θ ~ 10-12° (see arrow GO), there is an obvious hint
of GO peak, which is due to the small particle size and its concentration featureless.
Crystallite size, a and c cell parameters of anatase, calculated by the Rietveld refinement
procedure using Topas v.4.2 programme, based on the full width at half-maximum of
the peak at 25.4° are presented in T the crystallite size is in range from ~ 32 to 52 nm. The cell parameters of pure
anatase are a = 3.7845 ? and c = 9.5143 ?; an increasing of lattice parameters a and
c for the titania/graphene oxide nanocomposite is expected to occur if some of the
Ti4+ are transformed to Ti3+, because of the larger ionic radius of Ti3+ (0.670 ?) compared to Ti4+ (0.605 ?) [].
Atomic force microscopy and electron transmission microscopy were used to determine
quality of delamination of graphene oxide (GO) used for preparation TiO2-GO nanocomposite.
In our previously work we have been demonstrated that the thermal hydrolysis of titania
peroxo-complex leads to spindle-like particles []. Our experiments were confirmed that direct interaction between TiO2 nanoparticles and graphene oxide sheet prevents the re-aggregation of the sheets
of graphene oxide. The TEM images of GO prepared by modified oxidation method is presented
in Figure a. It follows from the picture, that GO formed big smooth plates of size ~ 5×5 μm.
Figure b shows TEM images of TiO2-GO nanocomposite and demonstrates that TiO2 nanoparticles were dispersed uniformly on the graphene plane.
a) TEM images of graphene oxide (GO), b) TEM images of TiO2-GO nanocomposite.
shows AFM images of GO with a thickness of 0.87 nm according to cross-sectional analysis,
which is comparable with the interlayer spacing 0.91 nm of GO measured by X-ray powder
diffraction (see Figure a). These results indicate that the exfoliation of graphite oxide down to monolayer
sheets of GO is successfully obtained [].
AFM images of prepared graphene oxide.
The specific surface area of the prepared TiO2-GO nanocomposites calculated by the multi-point Brunauer-Emmett-Teller (BET) method
and total pore volume are listed in Table . A typical Barrett-Joyner-Halenda (BJH) pore-size distribution plot and nitrogen
adsorption/desorption isotherms are shown in Figure . According to IUPAC notation [], microporous and macroporous materials have pore diameters smaller than 2 and greater
than 50 nm, the mesoporous category thus lies in the middle. As for
all the titania/graphene nanocomposites, the isotherm form corresponds to that of
type IV isotherm classification and the type E hysteresis loop is in agreement with
the De Boer classification attributed to mesoporous solids []. The maximum of average pore size lies between 20 and 35 nm and all prepared TiO2-GO nanocomposites have mesoporous texture. With increasing content of GO in the composite
decreasing trend of specific surface area is obvious (see Table ). This may be due to agglomeration GO, which occurs at higher concentrations. Graphene
oxide nanosheets are coated with titania nanoparticles. Therefore when the surface
area of TiO2-GO nanocomposites is measured, its size is dominantly determined by surface properties
of anatase nanoparticles. For this reason, relatively low specific surface of the
TiO2-GO nanocomposites (200 m2g-1) was found compared to the theoretical value of the graphene and graphene oxide,
respectively. Nevertheless mesoporous TiO2-graphene oxide nanocomposites have specific surface area in interval ~ 80–200 m2g-1 being considerably larger than those of P25 and similarly prepared neat TiO2 particles without using graphene oxide.
Dependence of pore area on pore diameter and nitrogen adsorption/desorption isotherms
of TiO2-GO nanocomposite.
Raman spectroscopy is a powerful tool to characterize the crystalline quality of graphene
or GO. Additional file : Figure S1 shows the Raman spectrum of GO. In case of thermal hydrolysis of titania
peroxo-complexes in the presence of GO there is no reduction of GO. Due to the bluish
coloration of samples can be assumed, on the contrary, that there is reduction of
Ti4+ to Ti3+[]. However, if there is a reduction of Ti4+, somewhere an oxidation must occur, and it is probably on the graphene skeleton in
free positions of Π bonds. Following oxidation of graphene due to reduction of Ti4+ corresponds to an increase of intensity of Raman bands GO in the nano-composite TiO2-GO.
Additional file 1: Figure S1. The Raman spectrum of prepared graphene oxide. Figure S2. IR spectrum of the TiO2-GO nanocomposite. Figure S3. UV–vis absorption spectra of the TiO2-GO. Table S1. C Composition of nanocompsite base on XPS.
Format: PDF
Size: 205KB This file can be viewed with:
In our Raman spectrum, the G band is broadened and shifted slightly to 1605 cm-1, whereas the intensity of the D band at 1350 cm-1 increases substantially. Increased background of the spectrum is caused by the sample
fluorescence. G band is common to all sp2 carbon forms and provides information on
the in-plane vibration of sp2 bonded carbon atoms and the D band suggests the presence
of sp3 defects [].
The Raman spectra of series nanocomposites TiO2-GO is presented in Figure . The specific vibration modes are located at 144 cm-1 (Eg), 396 cm-1 (B1g), 512 cm-1 (B1g + A1g) and 631 cm-1 (Eg) indicating the presence of the anatase phase in all of these samples. The D
bands of GO are located at 1349 cm-1 and G band at 1601 cm-1. With increasing concentrations of GO the intensity of both bands also increases.
The background of the sample labeled TiGO_075 is increased by the sample fluorescence.
The Raman spectra of TiO2-GO composites.
High resolution XPS spectra were accumulated 10 times to enhance the signal and to
noise ratio, and are presented in Figure . The composition of the TiO2-GO nanocomposites was evaluated from the high resolution spectra of O 1 s, C 1 s
and Ti 2p. The compositions are summarized in the Additional file : Table . The O/Ti ratio was evaluated and the results show over stoichiometric values. The
high O/Ti ratio can be partially explained by the fact that the O1s spectra show a
main peak at 529.7 eV with a shoulder at about ~531.4 eV. The peak at 529.7 eV is
assigned to oxygen lattice, while the shoulder may be attributed to oxygen in adsorbed
hydroxyl groups.
High resolution XPS spectra of TiO2-GO composites.
The binding energy calibration was made on C-C component of C 1 s peak after a deconvolution
process. The intensity of C 1 s peak is rather small and the signal is noisy, but
the C 1 s peak was fitted by two main components to represent C-C/C-H bond at binding
energies about 284.5 eV and C = O bond at higher binding energies about 288 eV. The
C = O bond was expected because it is a part of the graphene oxide precursor. Furthermore,during
reaction of Ti(SO4)2 with GO, plenty of oxygen-containing groups, such as C = O located in the interlayer
of graphene oxide were consumed during the nucleation and growth of TiO2 crystallites, which means graphene oxide has been partly reduced []. The oxygen-containing groups on the graphene oxide can interact with titanium hydroxide
complex and the TiO2 nanoparticles, resulting in hydrogen bonds between them [].
The ratio between both bonds was almost identical on both samples (about 73%) and
had C-C/C-H therefore it can be expected that the carbon comes from the
precursor rather then from additional contaminations. The other expected bonds as
O = C-OH and C-OH were neglected because of the weak signal [].
The Ti 2p3/2 and Ti 2p1/2 were identified at binding energies of 458.5 and 464.1 eV, respectively. The position
of Ti 2p peaks corresponds to the literature reported values and also to the FWHM
values about 1.6 eV for Ti 2p3/2 and 2.4 eV for Ti 2p1/2, which are reasonable for single peak character. The Ti is probably bonded in the
TiO2. The equal area/RFS ratios were found on both spin states within precision about
10%. The limited precision is due to the background removal process when the Shirley
background was used. The peak positions and the FWHM were found to be practically
identical for all investigated samples.
The Additional file : Figure S2 shows the IR spectrum of the TiO2-GO nanocomposite prepared by thermal hydrolysis of titania peroxo-complexes. The
broad absorption peaks about 3427 cm-1, and the band at 1631 cm-1 correspond to the surface absorbed water and the hydroxyl groups []. The band at 1384 cm-1 can be assigned to hydroxyl C-OH and that at 1258 cm-1 to epoxide C-O-C []. The band at 650 cm-1 is most probably related to the Ti-O vibration modes of the Ti3+-O-Ti4+ framework [].
The Additional file : Figure S3 presents the UV–vis absorption spectra of the TiO2-GO nanocomposite. The presence of different amounts of GO influences the optical
properties of light absorption significantly. With increasing GO content in the nanocomposite
light absorption intensity in the UV region grows and a red shift to higher wavelength
in the absorption edge at about 400 nm also observed []. Increased background in the area 400–800 nm is caused by incorporation of GO into
the matrix of TiO2[] and partially also by presence of Ti3+.
According to the equation for band gap:
(1)where α = (1-R)2/2R, R is the reflectance of the "infinitely thick" layer of the solid [], B is absorption coefficient and hν is the photon energy in eV. Figure
plots the relationship of (αhν)1/2 versus photon energy (hν = 1239/λ) [,], which shows that the band gap of pure TiO2 is 3.20 eV, [] whereas the band gap of the TiO2-GO nanocomposite has been reduced from value 3.15 eV (sample TiGO_001) to value &2.50 eV
for sample TiGO_100. The band-gaps of samples TiGO_200 to TiGO_500 are impossible
to be identified because the absorption edges for TiO2 entirely overlapped with those for GO.
Band-gap energy (hν) of TiO2-GO composites.
The effect of oxidation time variation on the electronic, physical and chemical properties
of GO was investigated and it was found that the bandgap of GO increased with oxygen
content of the GO material []. GO has a bandgap between 1.7 and 4.3 eV in dependence on the preparation method,
and it is tunable in the interval 1.9 – 2.6 eV in the range of the visible spectrum
as required for efficient photocatalysis.
Graphene oxide is non-stoichiometric material, which retains the lamellar structure
of graphite. After treatment in the presence of strong acids and oxidation agents,
many oxygen-containing groups such as carboxyl (C - OOH), hydroxyl (C - OH), epoxide
(C - O - C) become covalently attached to its layers surfaces. In our experiment GO
reacted in the presence of Ti-peroxo-complex, and some functional group such as (-
OH, -COOH) on the GO surface were removed. We can can suppose that some unpaired ∏ - electrons
bonded with the free electrons on the surface TiO2 to form a Ti–O–C structure, which then shifted up the valence band edge and reduce
d the band gap [].
On another hand after the photoactivation of titanium dioxide the electrons can easily
transfer to the graphene-nanosheets and photoinduced holes
recombination
of e- and h+ is strongly reduced, which increases the process yield.
The photocatalytic activity of the as-prepared layered of TiO2-GO nanocomposites were assessed from the kinetics of the photocatalytic degradation
of butane in the oxygen atmosphere. Photocatalytic oxidation of butane are based on
the following overall reactions []:
Before each measurement, the photocatalytic reactor is evacuated, then rinsed with
the O2 and the measurement is run. If the measured gas chromatogram shows only the oxygen
peak at retention time 1.52 min then a gas for the photocatalytic decomposition (in
our case the butane) can be injected. After measuring the subsequent chromatogram,
peaks for the oxygen and the butane are marked each by value of 1. The value of gases,
which are expected to be formed due to photo-activity of the TiO2-GO nanocomposite (CO, CO2) are assigned each by value 0. By this normalization of input data is performed and
the measurement with time period of 2 hours can be started.
In a typical chromatograph of the effluent obtained from butane photocatalytic degradation
only oxygen, carbon monoxide, carbon dioxide, water and butane were detected at retention
times of 1.52, 1.54, 2.41, 6.42 and 9.53 min []. The normalized total ion current (TIC) for CO, CO2 and H2O after time reaction 60 hours is presented in Table .
Rate constant k and TIC for CO, CO2 and H2O of TiO2-graphene oxide
The typic corresponding experimental dependencies of butane, oxygen, carbon monoxide
and carbon dioxide in time are plotted in Figure . The rate of degradation was estimated to obey pseudo-first-order kinetics, and hence
the rate constant for degradation k was obtained from the first-order plot according
to equation (3),
(3)where c0 is the initial concentration, c is the concentration of butane after time (t), and
k is the first-order rate constant.
Typical experimental dependencies of C4H10, O, CO, CO2 and H2O in time.
The photocatalytic degradation of butane was fitted by curves of the first-
the corresponding rate constants are given in Table . Djeghri et al. [] reported photoinduced oxidation of C2–C8 alkanes on TiO2 at ambient temperature. In general, they observed that alkanes (CnH2n+2) formed ketones (CnH2nO) and other aldehydes CmH2mO with 2 & m & n. If the alkane was branched, the ketone was CmH2mO with 3 & m & n. The reactivity of different types of carbon atoms followed the sequence:
Ctertiary & Cquaternary & Csecondary & Cprimary. Paper [] shows, that in our case, the reactivity of butane is different and simpler – no intermediate
products such as lower alkane or ketones were detected in the gaseous phase. This
means that photocatalytic oxidation proceeds not in the gaseous phase but only on
the layer surface directly, causing formation of CO, CO2 and H2O.
The results presented in Table
show, that the best photocatalytic activity under UV and visible light have samples
denoted TiGO_100 (k = 0.03012 h-1) and TiGO_075 (k = 0.00774 h-1), respectively. As for the TiGO_075 sample, there is also the largest increase in
CO and CO2 content. It is evident from Table
that for some samples, there is also an increase in CO and CO2 at the expense of the primary decomposition of butane and the value for rate constant
decreases. This suggests that in these samples a much deeper mineralization occurs,
which leads to the preferential decomposition of intermediates to end products of
photocatalytic decomposition, i.e. CO2 and H2O. This increase in photoactivity for some samples is probably due to reduction of
Ti4+ to Ti3+ and oxidation of free ∏ - bonds during preparation. The interaction of CO2 molecules with the excited states of Ti3+-O- leads to the formation of CO2o? anion radicals []. The CO2o? anion radicals readily react with poly(hydroxyethyl metacrylate), which leads to
the formation of carbon monoxide due to its strong adsorption on Ti sites of the TiO2 surface []. The functions of the graphene oxide sheets in the nanocomposite are as follows:
i) graphene oxide sheets provide a very good support substrate for the deposition
of TiO2 nanoparticles, ii) graphene oxide sheets can enhance adsorption ability of the TiO2 - graphene oxide nanocomposite, iii) Graphene oxide works as electron acceptor and
photosensitizer to efficiently enhance the butane photodecomposition.
Conclusion
Using graphene oxide sheets as a substrate for TiO2, we developed a simple ("one-pot") method to prepare nanocomposite by depositing
TiO2 on the graphene oxide through liquid phase deposition.
The better photocatalytic properties on the TiO2-GO nanocomposite systems irrespective of light sources could be attributed to synergy
effects including the increase in specific surface area with graphene oxide amount
as well as to the formation of both π–π conjugations between butane molecules and
aromatic rings and the ionic interactions between butane and oxygen-containing functional
groups at the edges or on the surfaces of carbon-based nanosheets. Graphene oxide
works as the adsorbent, electron acceptor and photosensitizer and efficiently enhances
the butane photodecomposition. The best photocatalytic activity under UV and visible
light was observed for samples denoted TiGO_100 (k = 0.03012 h-1) and TiGO_075 (k = 0.00774 h-1), respectively. Both the used synthesis route and the GO modification are promising
ways to cheap and efficient photocatalysts for the Vis light activation.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
V? was the main author of the work, performed syntheses, and coordinated all characterization
and catalytic studies. SB was responsible for electron microscopy, TMG for Raman spectroscopy,
MK for XPS measurement, JB assisted with manuscript writing. All authors read and
approved the final manuscript.
Acknowledgements
This work was supported by the RVO . The authors gratefully thank K. ?afá?ová
(Regional Centre of Advanced Technologies and Materials, Faculty of Science, Palack?
University in Olomouc) for AFM and TEM measurement.
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