Cite this:Phys.Chem.Chem.Phys .,2012,14,12114–12121Crystalline metallic Au nanoparticle-loaded a -Bi 2O 3microrods for improved photocatalysis w
Hai-Ying Jiang,Kun Cheng and Jun Lin*
Received 28th June 2012,Accepted 19th July 2012DOI:10.1039/c2cp42165h
Crystalline metallic Au nanoparticles were loaded on a -Bi 2O 3microrods (Au/a -Bi 2O 3)using an Au deposition–precipitation method.The prepared samples were characterized by scanning electron and transmission electron microscopy,X-ray di?raction,X-ray photoelectron spectroscopy,and UV-vis di?use re?ectance spectroscopy.Upon visible light irradiation,the Au/a -Bi 2O 3exhibits much higher photocatalytic activities than the pure a -Bi 2O 3for the degradation of Rhodamine B and 2,4-dichlorophenol in aqueous solution.The role of the Au and the paths of electron transport in the photocatalysis of the Au/a -Bi 2O 3were investigated and discussed in detail based on the analysis of the photo-generated hydroxyl radicals ( OH)and hydrogen peroxide (H 2O 2)in the visible light irradiated suspension of pure a -Bi 2O 3and Au/a -Bi 2O 3.The result reveals that the Au loaded on a -Bi 2O 3plays a critical role in the
separation of the electron and hole pairs by accumulating the electrons from the excited a -Bi 2O 3,which is responsible for the enhanced photocatalytic activity.
1.Introduction
In the past several decades,heterogeneous semiconductor photocatalysis by anatase TiO 2has been the focus of much research due to its potential application in water treatment and air puri?cation.1–3As well con?rmed,in the photocatalysis,the electron and hole photo-generated on anatase TiO 2possess suitable redox potentials,and can get trapped by surface O 2and H 2O or OH àgroups,respectively,to form O 2à and OH.Both radicals are very strong oxidizing species and act as initiators for the mineralization of organic pollutants.2,4However,a serious drawback that the photocatalysis by anatase TiO 2with a relatively wide band gap (E g =3.2eV)is e?ectively initiated only upon UV irradiation (l o 387nm)hinders its practical application.To overcome this problem,some strategies have been developed to sensitize anatase TiO 2and other wide band gap semiconductors for visible light photocatalytic activity,including anion or cation elements doping,dye sensitization,and coupling with other semiconductors,etc.5–9
In addition,various narrow band gap semiconductors with a deep valence band have also become a frequent topic of investigations as prospective visible light photocatalysts recently.10–13Among these semiconductors,bismuth oxide (Bi 2O 3)is a promising candidate because of its small band gap (B 2.8eV),high oxidation power of valence hole (B +3.13V vs.NHE),and
non-toxic property as TiO 2.14As a photocatalyst,unfortunately,pure Bi 2O 3shows a poor photocatalytic e?ciency for the degradation of organic compounds since its lower conduction band edge (B +0.33V vs.NHE)cannot provide a su?cient negative potential for the excited electron to scavenge the adsorbed O 2[E o (O 2/O 2à )=à0.33V vs.NHE and E o (O 2/HO 2 )=à0.05V vs.NHE].15The lack of the ability of the CB electron in Bi 2O 3to scavenge O 2causes a fast recombination of the photo-excited electron and hole pairs,resulting in a poor photocatalytic activity.To develop Bi 2O 3with a deep valence band as an e?cient visible light photo-catalyst,many methods have been employed,which include the morphology and surface modi?cation of Bi 2O 3.13,16–19Recently,a lot of research works have been carried out to improve the photocatalytic activity of semiconductor TiO 2through the deposition of noble metals such as Pt and Au on the surface of TiO 2.20–23Remarkable enhancement e?ects with deposition of these noble metals have been well demonstrated in TiO 2photocatalytic reaction owing to an increased e?ciency of charge separation between photoexcited electron–hole pairs.Taking account of the big di?erences between semiconductor TiO 2and Bi 2O 3in band structures,is the deposition of the noble metal also an approach to improving the Bi 2O 3photocatalytic e?ciency?More recently,several research works reported the e?cient visible-light-driven photocatalysis over the noble metal-deposited Bi 2O 3.24,25However,the in?uences of the loaded Au and the electron transport paths,both of which determine the photocatalytic activity of Au/Bi 2O 3,are still much less understood.To resolve these problems,we believe,is of great importance in the development of the narrow band
Department of Chemistry,Renmin University of China,Beijing 100872,People’s Republic of China.E-mail:jlin@https://www.doczj.com/doc/9115531219.html,;Fax:+86-10-62516444;Tel:+86-10-62514133
w Electronic supplementary information (ESI)available.See DOI:10.1039/c2cp42165h
PCCP
Dynamic Article Links
https://www.doczj.com/doc/9115531219.html,/pccp
PAPER
P u b l i s h e d o n 23 J u l y 2012. D o w n l o a d e d b y E a s t C h i n a N o r m a l U n i v e r s i t y o n 05/05/2014 12:45:51.
View Article Online / Journal Homepage / Table of Contents for this issue
gap semiconductor with a deep valence band as an e?cient photocatalyst.
In this contribution,we prepared Au-loaded a -Bi 2O 3microrods with di?erent Au loadings (Au/a -Bi 2O 3)by the hydrolysis of bismuth nitrate under basic conditions followed by an Au deposition–precipitation method.The prepared samples were characterized by SEM,TEM,HRTEM,XRD,XPS and UV-vis di?use re?ectance spectroscopy.It was clearly demonstrated that the Au/a -Bi 2O 3has higher photocatalytic activities than the pure a -Bi 2O 3for the decomposition of Rhodamine B and 2,4-dichlorophenol under visible light irradiation.Furthermore,the role of Au and the paths of the electron transport in the photocatalysis over Au/a -Bi 2O 3were revealed according to the analysis results of the photo-generated hydroxyl radicals ( OH)and hydrogen peroxide (H 2O 2)in the visible light irradiated suspension of pure a -Bi 2O 3and Au/a -Bi 2O 3.
2.Experimental
2.1.
Preparation of pure Bi 2O 3and Au/Bi 2O 3
All chemical regents were of analytical grade and were used as received without further puri?cation.Deionized water was used throughout the experiments.The pure Bi 2O 3was prepared from Bi(NO 3)3á5H 2O by hydrolysis under basic conditions.13In a typical synthesis,10.78g of Bi(NO 3)3á5H 2O was dissolved in 30ml aqueous solution of HNO 3(1.5M).Under vigorous agitation,into the solution was added NaOH solution (50%w/v)dropwise until pH =13,at which a yellow precipitate was produced.Subsequently,the suspension was heated at 801C for two hours,then the precipitate was collected by centrifugation and washed with deionized water and ethanol several times,and dried at 1201C for 12h before calcined at 4501C for 5h.The Au-loaded Bi 2O 3(denoted Au/Bi 2O 3below)sample was prepared by a deposition–precipitation method.26The detailed procedure is described below.An aqueous solution of HAuCl 4was prepared by dissolving the amount of HAuCl 4á3H 2O (x mg)in 200ml deionized water,followed by the addition of NaOH (0.2M)to control the pH value of the solution at 9.To this solution,the Bi 2O 3(2g)obtained above was added to be magnetically stirred for 12h.During this process,HAuCl 4reacted with NaOH to form Au(OH)3,which precipitates on the surface of the Bi 2O 3.The resultant solid was ?ltered and exhaustively washed with water,then dried at 1001C in an oven for 8h before a ?nal calcination at 4001C for 4h.Au(OH)3produced on Bi 2O 3was converted to metallic gold during calcination,resulting in the as-prepared Au/Bi 2O 3sample.The above x =25mg,50mg,and 75mg corresponds to di?erent weight%of Au in the Au–Bi 2O 3composites,respectively.Under the present synthesis conditions,gold deposition occurs with 80%e?ciency.Thus,the obtained samples are about 0.5,1.0,and 1.5wt%Au/Bi 2O 3,respectively.For comparison of the following various physicochemical and catalytic behaviors,the pure Bi 2O 3without Au loading was also calcined at 4001C for 4h in the same manner.2.2.
Characterization
The crystal phases of the as-prepared pure Bi 2O 3and Au/Bi 2O 3were identi?ed at room temperature with an X-ray
di?ractometer (Rigaku D/max-2500)using Cu K a as X-ray radiation under 40kV and 200mA.The scanning range is 2y =20–801with a step of 2y =0.021and 0.5s per step.The surface chemical states and compositions of the elements in the prepared samples were analyzed by XPS (ESCALab220i-XL)using 300W Al K a radiation.All binding energies were referenced to the C1s peak (284.6eV)of the surface adventitious carbon.Scanning electron microscopy (SEM)observation was carried out on a JEOL JSM-7401F ?eld emission scanning electron microscope.The morphology and microstructure analysis of the samples was performed using an HRTEM microscope (JEOL,JEM-2010)at an accelerating voltage of 200kV.A droplet of the sample suspension in water was placed onto lacey support ?lms for HRTEM analysis.UV-vis di?use re?ectance spectra of the samples were recorded on a Hitachi U-3900spectro-photometer equipped with a di?use re?ectance accessory,and absorption spectra were referenced to BaSO 4.2.3.
Photocatalytic activity evaluation
The photocatalytic activities of the as-prepared pure Bi 2O 3and Au/Bi 2O 3were evaluated by the degradation of Rhodamine B (RhB)(B 10à5M)in an aqueous solution under visible light irradiation.Typically,100mg of photocatalyst was suspended in 100ml of RhB aqueous solution,the initial pH value of which was determined to be about 6.5.The light source was a 300W Xe-arc lamp (CHF-XM150,Beijing Trusttech.Co.Ltd.)equipped with a wavelength cuto??lter of l Z 420nm,and positioned about 8cm above the aqueous suspension.Prior to irradiation,the suspension of the photocatalyst in the RhB aqueous solution was continuously stirred in the dark for more than one hour to ensure the establishment of an adsorption–desorption equilibrium between the photocatalyst and RhB.At the given irradiation time interval during the photoreaction,3ml of reaction suspension was sampled,and then the photo-catalyst and the RhB solution were separated by centrifugation.The concentration of RhB was determined by monitoring the change in the absorption spectrum in the absorbance at 554nm using a Hitachi U-3310spectrophotometer.The reproducibility of the photocatalytic performances of various photocatalysts including pure Bi 2O 3and Au/Bi 2O 3with di?erent Au loadings was also evaluated by measuring the photocatalytic activities of di?erent batches.
To rule out the e?ects of RhB self-sensitization on the photocatalysis,four 3W monochromatic lights (l =420nm)instead of the 300W Xe lamp were also used as the light source for the degradation of RhB over pure Bi 2O 3and Au/Bi 2O 3.To provide more convincing evidence for the visible light photocatalysis of the pure Bi 2O 3and Au/Bi 2O 3,the photochemical experiments for the degradation of 2,4-dichlorophenol (2,4-DCP),an organic compound which does not absorb visible-light any more,were also performed in a reactor with an aqueous suspension of 2,4-DCP (B 10à4M)and 100mg catalyst powder.The light source was also a 300W Xe-arc lamp (CHF-XM150,Beijing Trusttech.Co.Ltd.)equipped with a wavelength cuto??lter of l Z 420nm.The degradation of 2,4-DCP was followed chromatographically by a high-performance liquid chromato-graph (DIONEX)with a C18column.The eluent consisted of 65%acetonitrile,35%water and 0.1%phosphoric acid.
P u b l i s h e d o n 23 J u l y 2012. D o w n l o a d e d b y E a s t C h i n a N o r m a l U n i v e r s i t y o n 05/05/2014 12:45:51.
The total organic carbon(TOC)of each solution was measured
using an Apollo9000apparatus.
2.4.Analysis of photogenerated OH and H2O2
The generation of OH radicals on the photo-illuminated pure
Bi2O3and Au/Bi2O3in the presence of Fe3+was detected by a
?uorescence technique using coumarin as a chemical trap of OH
radicals.27Coumarin readily reacts with OH to form a highly
?uorescent product,7-hydroxycoumarin(7HC)(see reaction
(1)).The experimental procedure was similar to the measurement
of photocatalytic activity.The sample powder was suspended in
30ml aqueous solution of FeCl3(10mM)and coumarin(1mM).
Before exposure to visible light irradiation(l=420nm),the
suspension was stirred for30min in the dark.At the given
irradiation time interval(10min),5ml of the suspension was
taken out and?ltrated for?uorescence spectrum measurements.
The?uorescence emission intensity of7-hydroxycoumarin was
measured at460nm under the excitation at332nm using a
spectro?uorometer(PerkinElmer LS55).
e1T
Furthermore,the in situ photogenerated H2O2in the visible light
(l=420nm)irradiated suspension of the catalysts(1.0g Là1)in
the presence of methanol(1.0M)as an electron donor was
analyzed using the colorimetric DPD method.28
3.Results and discussion
3.1.Phase structures and morphology
XRD was used to identify the phase structures and constitutions
of the as-prepared samples.Fig.1presents the XRD patterns of
the pure Bi2O3and Au/Bi2O3with di?erent Au loadings.As
reported in the related literature,bismuth oxide(Bi2O3)is present
as six polymorphic forms,which are a,b,g,d,e and o-Bi2O3.
Among them,a-phase is stable at low temperature,d-phase is
stable at high temperature and the other phases are high
temperature metastable.29,30From Fig.1,in our case,all the
di?raction peaks of each sample exhibit a single monoclinic
phase of well-crystalline a-Bi2O3according to the JSPDS?le
(No.71-0053).No other apparent di?raction peaks including
those caused by gold were observed in all detected samples,
demonstrating the phase purity of the a-Bi2O3and the good
dispersion of the small sized Au on the a-Bi2O3surface.
Furthermore,a careful comparison of the corresponding
di?raction peaks of the pure a-Bi2O3and Au/a-Bi2O3with
di?erent Au loadings shows that there are almost no obvious
di?erences in the intensities and widths.This indicates that
loading Au does not alter the crystallite size and crystallinity
of the substrate a-Bi2O3.
The morphology and microstructure of the as-prepared
pure a-Bi2O3and Au/a-Bi2O3were characterized by SEM,
TEM,and HRTEM,respectively.Fig.2A and B exhibit the
SEM micrographs of a-Bi2O3before and after loading with
1.0wt%Au,respectively.It can be clearly observed that both
the pure a-Bi2O3and1.0wt%Au/a-Bi2O3products appear to be
microrod-shaped.Their lengths can reach several micrometers and
diameters range from500–800nm.The observed morphology is
very similar to that of the a-Bi2O3prepared by microwave
irradiation.25The microrod-shaped a-Bi2O3might have formed
from the preferential directional growth of a-Bi2O3crystallites.
Noticeably,it can be also found in the SEM micrographs that
loading Au almost has no in?uences on the morphology and size
of the substrate a-Bi2O3.Fig.3shows a typical TEM image and
Fig.1X-ray di?raction patterns of pure a-Bi2O3and Au/a-Bi2O3
with di?erent Au loadings.
Fig.2SEM images of pure a-Bi2O3(A)and1.0wt%Au/a-Bi2O3
(B)microrods.
P
u
b
l
i
s
h
e
d
o
n
2
3
J
u
l
y
2
1
2
.
D
o
w
n
l
o
a
d
e
d
b
y
E
a
s
t
C
h
i
n
a
N
o
r
m
a
l
U
n
i
v
e
r
s
i
t
y
o
n
5
/
5
/
2
1
4
1
2
:
4
5
:
5
1
.
Au particle size distribution(inset)for the1.0wt%Au/a-Bi2O3
sample.The dark gray small Au particles are uniformly loaded
on the surface of the light gray a-Bi2O3microrod.The loaded
Au particles are uniform and spherical in shape,and the
diameter of the loaded Au is mainly in the range of4–6nm,
as expected on the basis of the mild conditions adopted in our
synthesis.As observed in the HRTEM image(Fig.4),both Au
nanoparticle and the substrate a-Bi2O3are highly crystallized,
and the Au nanoparticle present as a single crystal is deposited
closely on the surface of the well-crystalline a-Bi2O3.The
measured lattice spacing of the crystalline substrate a-Bi2O3
(d=0.26nm)corresponds to the(022)spacing of a-Bi2O3.31
The HRTEM analysis of the single-crystalline Au nanoparticle
(inset in Fig.4)also indicates that the lattice fringes of0.203nm
and0.24nm match the crystallographic planes of metallic
cubic-phase Au(200)and(111),respectively.The interfacial
angle between the Au(200)and(111)was about54.71,which is
identical to the theoretical value for the angle between the
cubic-phase Au(200)and(111).
3.2.XPS analysis and UV-vis spectra
To analyze the chemical compositions and chemical status of
the elements in the as-prepared pure a-Bi2O3and Au/a-Bi2O3
microrods,the XPS analysis was carried out.The XPS survey
spectra of pure a-Bi2O3and 1.0wt%Au/a-Bi2O3sample
(shown in Fig.S1of ESI w)reveal the presence of Bi,O,and C
in the pure a-Bi2O3,and Bi,O,Au,and C in the Au/a-Bi2O3,
respectively.The atomic ratio of Bi to O is nearly about2:3in
both samples,which is consistent with the nominal atomic
composition of a-Bi2O3.Fig.5A shows the high-resolution
XPS spectra of Bi species in two samples,respectively.In
Fig.5A,two peaks for the Bi4f of pure a-Bi2O3are located at
the binding energies of158.9eV and164.2eV,ascribed to Bi4f7/2
and Bi4f5/2,respectively,which is characteristic of Bi3+in
a-Bi2O3.31For the1.0wt%Au/a-Bi2O3sample,the binding
energies corresponding to Bi4f7/2and Bi4f5/2are observed at
158.7eV and164.0eV,respectively.Upon comparison of the
Bi4f peak positions of two samples,it can be found that
the XPS peaks of the Bi4f shift toward lower binding energy
as the Au nanoparticle is loaded.As shown in Fig.5B,the
Au4f spectrum of the Au/a-Bi2O3is composed of two peaks
at the binding energies of84.0eV and87.7eV,assigned to
Au4f7/2and Au4f5/2,respectively,suggesting that the Au
species in Au/a-Bi2O3exist in the metallic state.32,33No
oxidized gold species was detected.This result is well consistent
with that of the above HRTEM.On the basis of XPS handbook
and the previous reports,34,35the binding energies of Au4f7/2
and Au4f5/2for metallic state Au are centered at83.8eV and
87.5eV,respectively.The observed slight shifts in Bi4f and
Au4f peaks of the Au/a-Bi2O3sample indicate an interaction Fig.3TEM image of1.0wt%Au/a-Bi2O3.Au nanoparticle size
distribution is shown in the inset.
Fig.4HRTEM image of1.0wt%Au/a-Bi2O3.Au particle has been
expanded in the inset for clarify.
Fig.5(A)High-resolution XPS spectra of Bi4f species in pure
a-Bi2O3and1.0wt%Au/a-Bi2O3.(B)High-resolution XPS spectrum
of Au4f in1.0wt%Au/a-Bi2O3.
P
u
b
l
i
s
h
e
d
o
n
2
3
J
u
l
y
2
1
2
.
D
o
w
n
l
o
a
d
e
d
b
y
E
a
s
t
C
h
i
n
a
N
o
r
m
a
l
U
n
i
v
e
r
s
i
t
y
o
n
5
/
5
/
2
1
4
1
2
:
4
5
:
5
1
.
between the loaded crystalline metallic Au and a -Bi 2O 3substrate.As reported in ref.36,when a semiconductor and Au nano-particles are in contact,electron migration between them occurs until a Fermi level equilibration of the composite is established.Hence,in the present case,in addition to chemical e?ects,the interaction may also include the Fermi level equilibration in the Au/a -Bi 2O 3composite system.
The optical properties of the pure a -Bi 2O 3and Au/a -Bi 2O 3with di?erent Au loadings are investigated with UV-vis di?use re?ectance spectroscopy,and the results are shown in Fig.6.It can be clearly seen in Fig.6that all samples have an intense absorption starting at approximately 450nm,which is assigned to the intrinsic bandgap absorption of the substrate a -Bi 2O 3.Di?erently,the samples of Au/a -Bi 2O 3with di?erent Au loadings also show an obvious absorption shoulder centered at around 590nm,whereas no absorption is observed for the pure a -Bi 2O 3in the visible region of 450to 800nm.According to the related reports,the additional shoulder observed for Au/a -Bi 2O 3should be assigned to the absorption of gold surface plasmon,which is caused by the collective oscillation of free conduction band electrons of the gold particles in response to optical excitation.26,37The intensity of the plasmon absorption band increases with the increase in the weight percentage of Au loaded on the substrate a -Bi 2O 3.3.3.
Photocatalytic performance
The photocatalytic activities for the degradation of RhB over the pure a -Bi 2O 3and Au/a -Bi 2O 3with di?erent Au loadings were evaluated under the visible light irradiation (l >420nm).For comparison,the self-degradation of RhB under the same light irradiation was also determined.The experimental results are shown in Fig.7A.Upon the visible light irradiation (l >420nm),all samples of Au/a -Bi 2O 3with di?erent Au loadings exhibit higher visible light photocatalytic activities than the pure a -Bi 2O 3sample,indicating that loading Au on a -Bi 2O 3is an e?cient way to enhance photocatalysis.The control experiment shows that the self-degradation of RhB is negligible within the same irradiation time in the absence of photocatalysts.The highest photocatalytic activity is observed at 1.0wt%Au loading,and approximately 80%of RhB is degraded over the sample after visible light irradiation for 3h.
When Au loading over a -Bi 2O 3reaches 1.5wt%,the photocatalytic activity decreases though it is still higher than that of pure a -Bi 2O 3.The observed optimal Au loading (1.0wt%Au)falls in the range which many precedents reported in gold-involved heterogeneous catalysis.38It is well-known that changing Au loading has signi?cant in?u-ences on gold particle size and morphology,substrate surface coverage and population of residual hydroxyl groups.38,39In the present case,it can be concluded that the balanced combination of all these factors has been achieved over 1.0wt%Au/a -Bi 2O 3microrods,exhibiting the maximum photocatalytic activity.
It was widely reported that organic dyes could be degraded over some semiconductors such as TiO 2and SrTiO 3under visible-light irradiation via a self-photosensitized oxidation pathway.40,41To avoid the strong light absorption of RhB (450nm o l o 600nm),we also chose four 3W monochro-matic lights (l =420nm)as the light source instead of the 300W Xe lamp for the photocatalytic degradation of RhB in the presence and absence of photocatalysts,and found that the degradation rates of RhB over the pure a -Bi 2O 3and 1.0wt%Au/a -Bi 2O 3are about 26%and 75%,respectively,after the photoreaction for 3h (Fig.7B),and no self-degradation of RhB occurs.The results reveal that the RhB degradation over the pure Bi 2O 3and Au/Bi 2O 3are mainly attributed to the
Fig.6Di?use re?ectance spectra of pure a -Bi 2O 3and Au/a -Bi 2O 3with di?erent Au loadings.
Fig.7(A)Photocatalytic degradation of RhB over pure a -Bi 2O 3and Au/a -Bi 2O 3with di?erent Au loadings under visible light irradiation (l >420nm).(B)Photocatalytic degradation of RhB over pure a -Bi 2O 3and 1.0wt%Au/a -Bi 2O 3under irradiation of monochromatic light (l =420nm).
P u b l i s h e d o n 23 J u l y 2012. D o w n l o a d e d b y E a s t C h i n a N o r m a l U n i v e r s i t y o n 05/05/2014 12:45:51.
photocatalysis rather than the RhB self-sensitization process induced by dye self-sensitized photocatalytic oxidation.
Furthermore,the 2,4-dichlorophenol (2,4-DCP),an organic compound which does not absorb visible-light any more,was also chosen as the degradation target to test the photocatalytic activities of the pure a -Bi 2O 3and 1.0wt%Au/a -Bi 2O 3.The results (in Fig.8A)show that both photocatalysts are active for the degradation of 2,4-DCP upon visible light irradiation (l >420nm).1.0wt%Au/a -Bi 2O 3exhibits higher photocatalytic activity than pure a -Bi 2O 3.Approximately 35%and 65%2,4-DCP degradations are reached over the pure a -Bi 2O 3and Au/a -Bi 2O 3,respectively,after visible light irradiation for 7h.The removal rate of TOC in the aqueous suspensions of two samples during visible-light irradiation for 12h (in Fig.8B)is consistent with the experi-mental results of 2,4-DCP degradation.As also shown in Fig.8A and B,no obvious reduction in both the concentration and TOC of 2,4-DCP aqueous solution in the absence of any catalysts is observed within the corresponding time of visible light irradiation.These results shown in Fig.6–8are con?rmed to be well reproducible by varying di?erent batch of the photocatalysts.
All the above photoreaction experiments clearly demonstrate that loading Au nanoparticles on the surface of a -Bi 2O 3microrods substantially increases the photocatalytic e?ciencies.
3.4.Analysis of photogenerated OH and H 2O 2
To understand the role of Au and the electron transport paths in the e?cient photocatalysis of the Au/a -Bi 2O 3,the genera-tion of the hydroxyl radicals ( OH)and hydrogen peroxide (H 2O 2)in the visible light irradiated suspensions of the photocatalysts was studied,respectively.The hydroxyl radicals ( OH)formed in the visible light irradiated suspensions of pure a -Bi 2O 3and 1.0wt%Au/a -Bi 2O 3in the presence of Fe 3+ions were detected by a ?uorescence technique using coumarin as a chemical trap of OH radicals.Fig.9A and B display the ?uorescence emission intensities of the coumarin–OH adduct (7-hydroxycoumarin)produced in the visible light irradiated suspensions of two samples,respectively.It can be clearly observed that the ?uorescence spectra of the coumarin–OH adduct are generated for both systems upon the visible light irradiation,suggesting the production of OH radicals.The production of OH radicals is apparently more with 1.0wt%Au/a -Bi 2O 3than pure a -Bi 2O 3at the same irradiation time.With the excitation of the substrate a -Bi 2O 3by visible light irradiation (l =420nm),there are two possible production paths of OH radicals in both systems.One is the reductive path through reactions (2)and (3),the other is the oxidative path through reaction (4).
2e CB à+O 2+2H +-H 2O 2
(2)
Fig.8(A)Photocatalytic degradation of 2,4-dichlorophenol (2,4-DCP)over pure a -Bi 2O 3and 1.0wt%Au/a -Bi 2O 3under visible light irradiation.(B)TOC removal rates of 2,4-DCP aqueous suspensions of various photocatalysts under visible light irradiation.
Fig.9Fluorescence emission intensities of the coumarin–OH adduct (7-hydroxycoumarin)produced in the visible light irradiated suspen-sions of pure a -Bi 2O 3(A)and Au/a -Bi 2O 3(B)in the presence of Fe 3+ions.
P u b l i s h e d o n 23 J u l y 2012. D o w n l o a d e d b y E a s t C h i n a N o r m a l U n i v e r s i t y o n 05/05/2014 12:45:51.
H 2O 2+e CB à-OH à+ OH (3)h VB ++H 2O (or OH à)- OH
(4)
Since the redox potential of Fe 3+/Fe 2+(+0.771vs.NHE)42is more positive than that (+0.695V vs.NHE)of reaction (2),the addition of Fe 3+ions prevents the two-electron reduction process of O 2(reaction (1)),excluding the reductive path through reactions (2)and (3).Thus,the detected OH radical over both systems is produced only directly through the reaction of H 2O with the hole generated on the valence band (B +3.13V vs.NHE)of the photo-excited a -Bi 2O 3(reaction (4)).The loading of Au nanoparticles on a -Bi 2O 3favors the production of more OH radicals evidenced in Fig.9A and B,revealing an e?cient separation of the electron and hole pairs on the photo-excited a -Bi 2O 3in the Au/a -Bi 2O 3system.Therefore,it is not a surprise that the Au/a -Bi 2O 3microrods have been shown above to have higher photocatalytic activ-ities than the pure a -Bi 2O 3ones.
The next we need to understand is how the Au nanoparticles e?ectively promote the separation of the electron and hole pairs photogenerated on the substrate a -Bi 2O 3microrods.Au-loaded anatase TiO 2(Au/TiO 2)has been reported to exhibit e?cient photocatalytic activity under UV and visible light irradiation with di?erent operation mechanisms which depend on whether excitation occurring on the TiO 2semiconductor or on the surface plasmon band of Au.26,38Upon UV excitation of TiO 2,the Au nanoparticles (E f =+0.45V vs.NHE)act as an electron bu?er to accept electrons from the CB of TiO 2,e?ectively inhibiting recombination of the hole and electron pair.Upon the excitation of the Au nanoparticles due to plasmon resonance,the electron from the Au nanoparticle is injected into the conduction band of the semiconductor TiO 2.Then the electron reduces the adsorbed oxygen to form an active species superoxide anion radical,initiating a photo-catalytic process.As indicated by the TEM,HRTEM images and XPS results,the crystalline metallic Au nanoparticles are dispersed uniformly and closely on the surface of the a -Bi 2O 3microrods,and the size of the Au nanoparticles is mainly in the range of 4–6nm.Earlier investigation showed that the deposition of Au nanoparticles with an average diameter of B 5nm on the TiO 2surface could promote a remarkable separation of the hole and electron pairs on the excited TiO 2through the electron transfer from the CB of TiO 2to the Au.Furthermore,in the present case,with the excitation of the substrate a -Bi 2O 3,an e?cient separation of the electron and hole pair over Au/a -Bi 2O 3is clearly demonstrated in Fig.9.Thus,we are allowed to speculate that the e?cient separation of electron and hole pairs is also caused by the electron transfer from the CB of the excited a -Bi 2O 3to the Au nanoparticles in the Au/a -Bi 2O 3system under visible light irradiation (see Scheme 1).Concerning that the CB level of a -Bi 2O 3(B +0.33V vs.NHE)is more positive than that of the reaction O 2+e à-O 2à (à0.33V vs.NHE),but more negative than that (+0.695V vs.NHE)of reaction (2),it becomes possible for the CB electron of a -Bi 2O 3to reduce the surface O 2to form H 2O 2via a two-electron reduction process (reaction (2)).In the Au/a -Bi 2O 3system,the Au nanoparticles with the Fermi level of +0.45V vs.NHE can also act as a
reduction site due to the photoinduced electron transfer from the excited a -Bi 2O 3to reduce theoretically the surface O 2to form H 2O 2.This speculation is well supported by the direct evidence of the in situ photoproduction of H 2O 2in the visible light irradiated suspension (pH E 7)of the pure a -Bi 2O 3and Au/a -Bi 2O 3(Fig.10).As shown in Fig.10,both pure a -Bi 2O 3and Au/a -Bi 2O 3under visible light irradiation catalyze the generation of H 2O 2,which con?rms that the two-electron reduction process (reaction (2))is the main transport path of the photogenerated electron.Since the Fermi level of Au (E f =+0.45V vs.NHE)is lower than the conduction band level of a -Bi 2O 3(B +0.33V vs.NHE),the initial production rate of H 2O 2is faster over pure a -Bi 2O 3than Au/a -Bi 2O 3.It was reported that the electron transfers to the loaded Au within a time R 2/p 2D E 0.1ps,43which is much more rapid than the process that the adsorbed oxygen scavenges two electrons and then desorbs from the Au nanoparticle.As a result,with the accumulation of electrons on the Au nanoparticle which gives a rise to the Fermi level of Au in the Au/a -Bi 2O 3system,and the fast recombination of electron and hole over the pure a -Bi 2O 3,the generation of H 2O 2over the Au/a -Bi 2O 3would exceed that over the pure a -Bi 2O 3,as clearly evidenced in Fig.10.The variation in the photoproduction of H 2O 2in the visible light irradiated suspension (pH E 7)of the pure a -Bi 2O 3and Au/a -Bi 2O 3is in good agreement with the above speculation,and clearly clari?es the e?ect of Au nanoparticles as an electron acceptor on the separation of electron and hole
Scheme 1Schematic illustration of the photocatalytic mechanism of Au/Bi 2O 3.
Fig.10In situ photogenerated H 2O 2in the visible light (l =420nm)irradiated suspension of pure a -Bi 2O 3and 1.0wt%Au/a -Bi 2O 3in the presence of methanol as an electron donor.
P u b l i s h e d o n 23 J u l y 2012. D o w n l o a d e d b y E a s t C h i n a N o r m a l U n i v e r s i t y o n 05/05/2014 12:45:51.
pairs (Scheme 1).The observed decrease of the photogenerated H 2O 2with the increase of the irradiation time for both systems might be due to its consumption in the photoreaction.44
4.Conclusions
Au/a -Bi 2O 3microrods with di?erent Au loadings have been well fabricated by depositing Au on the substrate a -Bi 2O 3microrods.The visible light photocatalytic activities of a -Bi 2O 3microrods for the degradation of RhB and 2,4-DCP in aqueous solutions can be signi?cantly enhanced by loading Au on the surface.The highest photocatalytic activity was reached on 1.0wt%Au/a -Bi 2O 3.The Au loaded on a -Bi 2O 3plays an important role in the separation of the photogenerated electron–hole pairs by accumulating the electrons from the excited a -Bi 2O 3substrate.This study would present some useful guidelines for the design of the narrow bandgap semiconductor with a deep valence band as an e?cient visible light photocatalyst.
Acknowledgements
We appreciate the ?nancial support of the current work from the National Natural Science Foundation of China (20973199)and National Basic Research Program of China (973Program,No.2007CB613306).
References
1Photocatalytic Puri?cation and Treatment of Water and Air ,ed.D.F.Ollis and H.Al-Ekabi,Elsevier,Amsterdam,1993.
2M.R.Ho?mann,S.T.Martin,W.Choi and D.W.Bahnemann,Chem.Rev.,1995,95,69–96.
3A.L.Linsebigler,G.Q.Lu and J.Yates,Chem.Rev.,1995,95,735–758.
4C.S.Turchi and D.F.Ollis,J.Catal.,1990,122,178–192.
5R.Asahi,T.Morikawa,T.Ohwaki,K.Aoki and Y.Taga,Science ,2001,293,269–271.
6S.Sakthivel and H.Kisch,Angew.Chem.,Int.Ed.,2003,42,4908–4911.
7D.F.Wang,T.Kato and J.H.Ye,J.Am.Chem.Soc.,2008,130,2724–2725.
8C.Zhang and J.Lin,Phys.Chem.Chem.Phys.,2011,13,3896–3905.9X.Sun and J.Lin,J.Phys.Chem.C ,2009,113,4970–4975.
10J.Kim,C.W.Lee and W.Choi,Environ.Sci.Technol.,2010,44,
6849–6854.
11T.Hirai,H.Okubo and I.Komasawa,J.Phys.Chem.B ,1999,103,
4228–4230.
12X. C.Wang,K.Maeda, A.Thomas,K.Takanabe,G.Xin,
J.M.Carlsson,K.Domen and M.Antonieti,Nat.Mater.,2009,8,76–80.
13A.Hameed,T.Montini,V.Gombac and P.Formasiero,J.Am.
Chem.Soc.,2008,130,9658–9659.
14A.Hameed,V.Gombac,T.Montini,M.Graziani and P.Formasiero,Chem.Phys.Lett.,2009,472,212–216.
15D.T.Sawyer and J.S.Valentine,Acc.Chem.Res.,1981,14,393–400.
16L.Zhou,W.Wang,H.Xu,S.Sun and M.Shang,Chem.–Eur.J.,2009,15,1776–1782.
17J.C.Yu,A.W.Xu,L.Z.Zhang,R.Q.Song and L.Wu,J.Phys.Chem.B ,2004,108,64–70.
18L.Li,Y.W.Yang,G.H.Li and L.D.Zhang,Small ,2006,2,548–553.
19P.Maruthamuthu,K.Gurunathan,E.Subramanian and M.V.C.Saatri,Int.J.Hydrogen Energy ,1993,18,9–13.
20H.Park and W.Choi,J.Phys.Chem.B ,2003,107,3885–3890.21V.Keller,P.Bernhardt and F.Garin,J.Catal.,2003,215,129–138.
22E.C.H.Sykes,F.J.Williams,M.S.Tikhov and https://www.doczj.com/doc/9115531219.html,mbert,J.Phys.Chem.B ,2002,106,5390–5394.
23X.Wang, D.R.G.Mitchell,K.Prince, A.J.Atanacio and R.A.Caruso,Chem.Mater.,2008,20,3917–3926.
24R.Li,W.Chen,H.Kobayashi and C.Ma,Green Chem.,2010,12,212–215.
25S.Anandan,G.-J.Lee,P.-K.Chen,C.Fan and J.J.Wu,Ind.Eng.Chem.Res.,2010,49,9729–9737.
26Y.Wu,H.Liu,J.Zhang and F.Chen,J.Phys.Chem.C ,2009,113,14689–14695.
27K.Ishibashi,A.Fujishima,T.Watanable and K.Hashimoto,https://www.doczj.com/doc/9115531219.html,mun.,2000,2,207–210.
28H.Bader,V.Sturzenegger and J.Hoigne,Water Res.,1988,22,1109–1115.
29N.M.Sammes,H.Tompsett and N.F.Aldinger,J.Eur.Ceram.Soc.,1999,19,1801–1826.
30C.Wang,C.Shao,L.Wang,L.Zhang,X.Li and Y.Liu,J.Colloid Interface Sci.,2009,333,242–248.
31J.Z.Bian,S.Zhu,Y.Wang,X.Cao,H.Qian and H.Li,J.Phys.Chem.C ,2008,112,6258–6262.
32S.Kielbassa,M.Kinne and R.J.Behm,J.Phys.Chem.B ,2004,108,19184–19190.
33C.Mottet,G.Treglia and B.Legrand,Surf.Sci.,1996,352,675–679.
34J.F.Moulder,W.F.Stickle,P.E.Sobol,K.D.Bomben and J.Chastain,Handbook of X-ray Photoelectron Spectroscopy ,Perkin-Elmer Corp,Eden Prairie,MN,1992,p.191.
35Y.C.Liu and L.J.Juang,Langmuir ,2004,20,6951–6955.
36V.Subramanian,E.E.Wolf and P.V.Kamat,J.Am.Chem.Soc.,2004,126,4943–4950.
37M.-C.Daniel and D.Astruc,Chem.Rev.,2004,104,293–346.38C.G.Silva,R.Juarez,T.Marino,R.Molinari and H.Garicia,J.Am.Chem.Soc.,2011,133,595–602.
39V.Subramanian,E.E.Wolf and P.V.Kamat,J.Am.Chem.Soc.,2004,126,4943–4950.
40Y.M.Cho,W.Y.Choi,C.H.Lee,T.Hyeon and H.-I.Le,Environ.Sci.Technol.,2001,35,966–970.
41G.M.Liu,X.Z.Li,J.C.Zhao,H.Hidaka and N.Serpone,Environ.Sci.Technol.,2000,34,3982–3990.
42D.W.Ball,Physical Chemistry ,Thomson Learning,2003,p.216.43M.Gra tzel,Heterogeneous Photochemical Electron Transfer ,CRC Press,Boca Raton.FL,1989.
44G.G.Liu,X.Z.Li,J.C.Zhao,S.Horikoshi and H.Hidaka,J.Mol.Catal.A:Chem.,2000,153,221–229.
P u b l i s h e d o n 23 J u l y 2012. D o w n l o a d e d b y E a s t C h i n a N o r m a l U n i v e r s i t y o n 05/05/2014 12:45:51.
生化常见异常结果及原因分析 反应曲线波动、跳动 一、几乎所有反应曲线跳动 1、电源接地不良：主电源接地不良、光电盒接地不良； 2、反应盘进水：真空泵压力密封圈磨损、真空泵电源接触不良、管接头处漏气、管路漏气、吸废液钢管堵塞、单向阀坏、比色杯破裂； 3、搅拌杆不搅拌：搅拌电机坏、搅拌电机线接触不良、搅拌杆顶住比色杯底； 4、光路歪：灯泡装歪、比色杯装歪、温控锅装歪、透镜装歪； 5、试剂加入异常：试剂针堵塞、试剂注射器脱落、试剂针接头处脱落、快速接头脱落； 6、一次性比色杯不干净；
7、阳光直射反应光电系统； 8、外界干扰因素：如发动机，电钻等。 二、只有个别波长反应曲线跳动 电源接地不良：主电源接地不良、光电盒接地不良。 三、只有个别项目反应曲线跳动 试剂异常：试剂变混浊、变色或试剂放错位置； 试剂经搅拌后起较多气泡，挡住光路。 反应曲线异常 一、几乎所有反应曲线形状正确，反应曲线平稳，但基本无反应 样本未加入：样本针堵塞、样本注射器脱落、样本针接头处脱落、快速接头脱落。
二、个别项目反应曲线形状正确，反应曲线平稳，但基本无反应 第二试剂未加入：第二试剂放错位置 三、个别项目反应曲线形状改变，但反应曲线平稳 试剂加入异常：试剂盘固定销钉脱落、试剂注射器漏气。 四、个别项目反应曲线形状改变，剧烈上升或下降，反应曲线或平稳，或小幅波动 试剂异常：试剂性能差或失效，最易发生在ALP、GGT、AMY等项目上。 五、个别测试反应曲线形状改变，剧烈上升或下降，但反应曲线平稳 1、试剂间交叉污染：最易发生在TG、TC、Glu和Bun等项目上；
2、样本异常：样本中含有某些药物或干扰成分，最易发生在TB、DB等项目上。 反应曲线正常，结果重复性差 一、几乎所有项目重复性差 1、样本加入异常：样本针半堵塞、样本注射器中有气泡、样本针接头处密封不严、样本针内壁阀关闭不严； 2、试剂加入异常：试剂针半堵塞、试剂注射器中有气泡、试剂针接头处密封不严、试剂针内壁阀关闭不严； 3、搅拌异常：搅拌电机坏、搅拌电机线接触不良、搅拌杆顶住比色杯底； 4、试剂/样本内外壁清洗不够，交叉污染大：液泵压力下降、第二级过滤器堵塞； 5、反应盘温度不稳定：反应盘温度波动较大。 二、个别项目重复性差
临床生化检验中反应曲线的应用分析 发表时间：2018-07-03T17:25:04.580Z 来源：《中国研究型医院》2018年5卷2期作者：栾春红 [导读] 临床生化检验中应用反应曲线，不仅可以提高生化检验结果的准确性，而且可以节省检验时间。 黑龙江省伊春市桃山林业局职工医院黑龙江伊春市 152514 【摘要】目的探讨反应曲线在临床生化检验中的应用效果。方法选择2016年7月至2017年7月来我院进行生化检验的患者122例，随机分为观察组和对照组两组，每组61例，对照组采用常规生化检验和检验报告，观察组在与对照组相同的基础上采用反应曲线，比较两组检验结果准确率及检验时间。结果观察组检验准确率为93.44%，显著高于对照组的54.10%，差异有统计学意义（P<0.05）；观察组检验时间显著少于对照组，差异有统计学意义（P<0.05）。结论临床生化检验中应用反应曲线，不仅可以提高生化检验结果的准确性，而且可以节省检验时间。 【关键词】反应曲线；临床生化检验；应用效果 Application Analysis of Response Curve in Clinical Biochemical Examination Objective To investigate the effect of reaction curve in clinical biochemical examination. Methods 122 patients who came to our hospital from July 2016 to July 2017 for biochemical examination were randomly divided into two groups, the observation group and the control group, each group with 61 cases. The control group used the conventional biochemical test and test report. The observation group used the reaction curve on the same basis as the control group. The accuracy and time of the test results were compared between the two groups. Results The accuracy of the test in the observation group was 93.44 %, which was significantly higher than the control group's 54.10 %. The difference was statistically significant(P<0.05） In the observation group, the test time was significantly less than that of the control group, and the difference was statistically significant(P<0.05） Conclusion The application of response curve in clinical biochemical test can not only improve the accuracy of biochemical test results, but also save the test time. [Keywords] reaction curve; Clinical biochemical examination; Application Effect 全自动生化分析仪是临床上应用十分广泛的生化检验仪器，该仪器在临床检验中的应用不仅有效提高了临床检验工作效率，同时也促使临床检验工作更加趋于标准化和规范化，在很大程度上促进了临床生化检验的发展[1]。但在临床实际生化检验工作中，存在多数检验人员只对其进行常规检测和维护保养，而忽略了对其实时曲线检测系统的应用。笔者通过对该院生化检验者采用反应曲线，并与同期采用常规生化检验和检验报告者进行了比较，现做如下报告： 1资料与方法 1.1一般资料选择2016年7月至2017年7月来我院进行生化检验的患者122例，其中男性66例，女性56例，年龄14-54岁，平均年龄（43.9±6.5）岁；随机分为观察组和对照组两组，每组61例，两组患者在年龄、性别等一般资料方面比较，差异无统计学意义，P>0.05，具有可比性。 1.2方法运用贝克曼AU5800型全自动生化分析仪和北京利德曼公司生产的检测试剂和校准品，定期开展质控品检测，以提高检测结果的控制力。对照组采用常规生化检验和检验报告，由临床医务人员来分析生化检验报告，对疾病进行判断和确定。观察组在与对照组相同的基础上采用反应曲线，临床医务人员应认真观察生化检验中空白试剂、质控品和标准品的反应曲线，分析生化检验反应曲线出现异常的原因，让检验结果得以有效提升。 1.3观察指标比较两组检验准确率及检验时间。 1.4统计学方法采用SPSS17.0软件对数据进行统计分析，对计数资料率的比较采用x2检验，计量资料组间比较采用t检验，当P<0.05时，为差异有统计学意义。 2结果 2.1两组检验准确率比较如表1所示，观察组检验准确率为9 3.44%，显著高于对照组的5 4.10%，差异有统计学意义（P<0.05）。 表1 两组检验准确率比较（例，%） 2.2两组检验时间比较如表2所示，观察组检验时间显著少于对照组，差异有统计学意义（P<0.05）。 表2 两组检验时间比较 3讨论 在临床生化检验中应用全自动生化分析仪能让检验工作效率显著提高，但是由于机械设备机械化工作的影响，生化检验的准确率较差，通过反应曲线能对生化检验中的异常情况进行及时发现，进而来制定科学、合理的改善对策。在检验碱性磷酸酶时，检验结果为 224U/L，分析反应曲线发现，在加入试剂后反应曲线表现为一定程度的下降， 因此需重新开展碱性磷酸酶检验，第二次的碱性磷酸酶检验结果为77U/L，反应曲线无异常，结果显示在首次生化检验中仪器设备的状态不稳定；在胆红素检验中，反应曲线表现为波浪状，和该时段其他检测项目的检验结果类似，出现这种情况可能是因为电源灯在该时段内的使用时间较长，出现电源灯不稳定或者老化现象，所以应对电源灯进行及时更换。在进行碱性磷酸酶检验时，试剂空白处的吸光度高达21241，但是试剂说明书规定生化检验中所用试剂的空白处吸光度不能大于8000，结果显示试剂发生了变质。因此在临床生化检验中，应连续监测试剂空白处的吸光度，同时结合该季度反应曲线，进而来对曲线稳定性进行了解，让生化检验的结果准确性得以保证[2]。部分标