Applied Surface Science 360(2016)594–600
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Applied Surface
Science
j o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /a p s u s
c
A novel reducing graphene/polyaniline/cuprous oxide composite hydrogel with unexpected photocatalytic activity for the degradation of Congo red
Jie Miao,Anjian Xie,Shikuo Li,Fangzhi Huang,Juan Cao,Yuhua Shen ∗
School of Chemistry and Chemical Engineering,Anhui University,Hefei 230061,PR China
a r t i c l e
i n f o
Article history:
Received 11September 2015
Received in revid form 25October 2015Accepted 1November 2015
Available online 10November 2015
Keywords:
RGO/PANI/Cu 2O Composite hydrogel Photocatalyst Congo red
a b s t r a c t
In this work,a novel reducing graphene/polyaniline/cuprous oxide (RGO/PANI/Cu 2O)composite hydrogel with a 3D porous network has been successfully prepared via a one-pot method in the prence of cubic Cu 2O nanoparticles.The as-synthesized ternary composites hydrogel shows unexpected photocatalytic activity such that Congo red (CR)degradation efficiency can reaches 97.9
1%in 20min under UV–vis light irradiation,which is much higher than that of either the single component (Cu 2O nanoparticles),or two component systems (RGO/Cu 2O composite hydrogel and PANI/Cu 2O nanocomposites).Furthermore,the ternary composite hydrogel exhibits high stability and do not show any significant loss after five recycles.Such outstanding photocatalytic activity of the RGO/PANI/Cu 2O composite hydrogel was ascribed to the high absorption ability of the product for CR and the synergic effect among RGO,PANI and Cu 2O in photocatalytic process.The product of this work would provide a new sight for the construction of UV–vis light responsive photocatalyst with high performance.
©2015Elvier B.V.All rights rerved.
1.Introduction
Semiconductor photocatalysis such as TiO 2,CdS,WO 3,Cu 2O,ZnO and Fe 3O 4have attracted many rearchers’attention due to its significant application in environment fields [1,2].However,the single component miconductor has demonstrated signifi-cant limits including low visible light responsive,photogenerated electron–hole pair recombines easily and poor cycling performance [3].
Cu 2O as a P-type miconductor with the direct band gap of 2.0eV can absorb the visible light spec
trum ( >420nm)which indicates Cu 2O is an ideal photocatalysis [4].However,the applica-tion of Cu 2O is rious limited,due to its susceptibility to corrosion and loss of light activity in the ca of long-term illumination [5].In addition,pure Cu 2O photogenerated electron–hole pair easy to recombine,which affects the photocatalytic efficiency [6].To tackle the problems,veral strategies have been adopted,such as doping elements (copper,zinc,titanium,nitrogen,carbon)inter-action with different bandgap miconductors,or combination with noble metals as co-catalysts [7–11].For instance,Ma et al.[9]synthesized Cu 2O/ZnO nanocomposites by a coprecipitation
∗Corresponding author.
E-mail address:yhshen@ahu.edu (Y.Shen).
method and the resulted composites were applied to degradation Orange II under visible-light.Zhang et al.[12]prepared Zn-doped Cu 2O hollow microcubes via in situ photochemical method for high efficient photocatalytic H 2production.In addition,recent stud-ies have revealed coupling Cu 2O with carbon material to form a carbon–Cu 2O photocatalyst has proven to effectively promote the charge-paration,therefore enhanced the photocatalytic activity [13].
PANI has a delocalized structure and electrochemical active units of benzenoid and quinonoid [14].In
this regard,PANI as a promising candidate conducting has the advantage of good envi-ronmental stability,fine-tuned properties and ea of synthesis [15].On the basis of this characteristic,PANI and its derivative or composites have been ud for the adsorption of Hg(II),Ag(I),Cr(VI),Cd(II),Cu(II),Pb(II)and Co(II)[16–22].Moreover,PANI has high absorption efficiency in the visible-light and high mobility of the charge carriers,indicating their efficient electron donors and good electron–hole transporters upon visible-light excitation [23].In the light of the pioneering rearches,more efforts should be devoted to preparing multicomponent PANI-bad nanocom-posites for better functional performance and wider applications instead of getting stuck in binary composites.
In this study,we report for the first time the preparation of RGO/PANI/Cu 2O as a ternary hybrid via a facile method.It is found that PANI and Cu 2O nanoparticles loaded on the RGO nanosheets
dx.doi/10.1016/j.apsusc.2015.11.005
0169-4332/©2015Elvier B.V.All rights rerved.
J.Miao et al./Applied Surface Science360(2016)594–600595
and the photoactivity of ternary nanocomposites surpass the binary one.The enhanced performance was understood by the intrinsic insight into the mechanism of electron–hole paration and electron transfer at the surface of the hybrid photocatalyst.It is expected that this study could pave a new way for the prepa-ration of multicomponent Cu2O-bad photocatalysts,therefore finding a variety of applications in photocatalytic degradation of dye wastewater,as well as in heterogenous photocatalysis and photocatalytic lective transformation under ambient.
2.Experimental
2.1.Materials
中国有几亿人口
Graphite power(325meshes)was purchad from Qingdao Huatai Lubriant Sealing S&T Co.Ltd.(PR China).Copper sul-fate(CuSO4·5H2O)and absolute ethyl alcohol were obtained from Shanghai Zhenxing Reagent Factory(PR China).Gluco (C6H12O6·H2O)and aniline(C6H5NH2)were supplied by Tianjin Bodi Chemical Co.Ltd.(PR China).Potassium persulfate(K2S2O8) and polyvinylpyrrolidone(PVP)were provided by Aladdin Indus-trial Corporation(Shanghai,China).Sodium hydroxide(NaOH), sodium chloride(NaCl),sodium citrate(Na3C6H5O7·2H2O),sodium carbonate(NaCO3)and sodium nitrate(NaNO3)were purchad from Sinopharm Chemical Reagent
Co.Ltd.(PR China).All chemicals were of analytical reagent grade and ud as received without fur-ther purification.De-ionized(DI)water is obtained from Millipore Milli-Q system.
2.2.Synthesis of GO
Graphite oxide was synthesized from natural graphite by a mod-ified Hummers method[24].
2.3.Synthesis of cube Cu2O nanoparticle
In a typical synthesis producer,CuSO4·5H2O(0.169g)and PVP (0.9g)were dissolved in20mL of DI with magnetic stirring for 15min.Then,Na3C6H5O7·2H2O(0.218g)and NaCO3(0.127g)were put into the above solution and stirred for about10min.Sub-quently,gluco(0.252g)was added to the above mixture and kept in water bath at80◦C for2h under magnetic stirring.After the reac-tion,the solution was cooled down to room temperature.The red precipitate was isolated by high-speed centrifugation,and washed with DI water and ethanol three times,respectively,and then dried under vacuum at60◦C for24h.
2.4.Synthesis of RGO/PANI/Cu2O composite hydrogel
10mL of GO solution(5mg mL−1)was added in50mL beaker, and NaOH solution(0.01mol L−1)was us
ed to adjust the pH value of the solution to7–8,continuously sonicated for0.5h.The as-prepared Cu2O nanoparticles(0.05g)were added and sonicated for1h.And the aniline monomer(0.5mL)was added to the above solution with a constant ultrasonic process for30min.Then the mixed solution was under magnetic stirring at room temperature for12h.At last,the products were parated by centrifugation and thoroughly washed with DI and ethanol three times to eliminate inorganic and organic impurities,andfinally dried in vacuum at 60◦C for24h.
For comparison,a ries of control experiments were done.The preparation method for RGO/Cu2O composite hydrogel was simi-lar to that for the ternary composite hydrogel except that aniline was replaced by DI water and reaction was performed at180◦C. The RGO/PANI hydrogel was fabricated in the abnce of Cu2O.The PANI/Cu2O nanocomposite was also synthesized under the same conditions but GO was substituted by K2S2O8solution.
2.5.Characterization
The crystalline pha structure and pha purity of the sam-ples were determined by X-ray diffraction(XRD)using a DX-6000 instrument,with the X-ray diffractometer using Cu K␣radiation ( =1.54056˚A)at a scan rate of0.04◦2Âs−1.The accelerating volt-age and the applied current were40k
V and100mA,respectively. The morphology of the sample was obrved on a scanning elec-tron microscope(SEM)(Hitachi,Japan)with an acceleration voltage of5kV.Transmission electronic microscopy(TEM)was obtained by using a JEM model100SX electron microscopes(Japan Elec-tron Co.)operated at an accelerating voltage of200kV.Raman spectra were performed by using Jobin Yvon Lab Ram HR800 Raman microscope(frequency range from2500to100cm−1). Fourier transform infrared(FTIR)spectra were measured with a NEXUS-870spectrophotometer using the KBr pellet technique. The UV reflectance spectra of solid samples were identified by a UV–vis spectrophotometer(UV-3900,Hitachi Japan).The concen-tration change of the dye in the photocatalytic degradation process was studied by using UV–vis spectrophotometer in the range of 200–800nm.
2.6.Evaluation of photocatalytic activity
The photocatalytic activity of the as-prepared products was scrutinized by employing CR as the model pollutant under room temperature.A450W Xe lamp was ud as the source of UV–vis light.In a typical experiment,25mg of the as-synthesized sam-ple were suspended in50mL of CR solution(10mg L−1).Then, the suspension was stirred for30min in the dark to reach adsorption–desorption equilibrium between the sample and the CR before illumination.Then,the mixture was exp
od to Xe lamp irra-diation with stirring,at t intervals,the experimental solution was withdrawn(4mL)and centrifuged to parate the catalyst particles, and then the characteristic absorption of CR in the supernatant at492nm was ud to monitor the photocatalytic degradation process by an UV–vis spectrophotometer[25].In comparison,the photocatalytic experiments of other composites were also carried out under the same conditions.
3.Results and discussions
3.1.FTIR spectra
In order to explore the changes of functional groups of the ternary composite hydrogel,the as-prepared samples were inves-tigated by using FT-IR spectroscopy and the results are shown in Fig.1.From Fig.1a,the absorption band at1398cm−1originates from bending vibration on plane of O H[26].The C O stretch-ing of COOH groups and stretching vibration peaks of C O are obrved at1749and1124cm−1,respectively[27].The absorp-tion peaks at1467and1647cm−1are assigned to the contributions from the skeletal vibrations of the graphene sheets[28].The FT-IR spectrum of GO confirms the successful oxidation of graphite. In the ca of FTIR spectra of binary RGO/Cu2O(Fig.1c)and ternary RGO/PANI/Cu2O(Fig.1d),some of the peaks that related to oxygen-c
ontaining functional groups(at1749cm−1,1398cm−1 and1124cm−1)decread or even vanished,revealing that the bulk of oxygen-containing functional groups were removed from GO after the reduction[29].It is worth noting that the strong absorp-tion band at628cm−1can be assigned to the vibrations of the Cu O functional group(Figs.1b–d)[30].In addition,in Fig.1d,the peaks at1600cm−1,1225cm−1and1345cm−1are attributed to
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Fig.1.FT-IR spectra of (a)GO;(b)Cu 2O nanoparticles;(c)RGO/Cu 2O and (d)RGO/PANI/Cu 2O composite
hydrogel.
Fig.2.XRD patterns of RGO/PANI/Cu 2O hydrogel and Cu 2O nanoparticles.
the stretching vibrations of C C,C N and C N by benzene ring,respectively.Additionally,peaks at 1694cm −1and 857cm −1are ascribed to C H bending vibration on plane and out-of-plane of 1,4substituted aromatic ring.The peaks are typical features of polyaniline [31].The FT-IR spectra illustrate the binary RGO/Cu 2O and ternary RGO/PANI/Cu 2O are successful obtained.
3.2.XRD analysis
Fig.2shows the XRD patterns of the RGO/PANI/Cu 2O hydro-gel and Cu 2O nanoparticles from 2Âvalues of 20◦–80◦.Six major reflections located at about 29.5◦,36.4◦,42.4◦,61.6◦,73.8◦and 77.3◦correspond to diffraction from the (110),(111),(200),(220),(311)and (222)planes (JCPDS no.65-3288)of cubic pha Cu 2O.No other peaks are obrved,indicating that the products are of pure Cu 2O.The new broad non-crystalline peak of the ternary composite at about 2Âof 25◦was obrved,which is assigned to the diffrac-tion peak of reduced graphene oxide and polyaniline [32].All above results demonstrate that the RGO/PANI/Cu 2O composite hydrogel was successfully synthesized.
3.3.Morphology
Figs.3a and b shows SEM images of the Cu 2O nanoparticles and RGO/PANI/Cu 2O composite hydrogel,respectively.From Fig.3a,it can be en that Cu 2O nanoparticles prents regular cube shape with uniform particle size and the average side length of them is 500nm.The SEM image of RGO/PANI/Cu 2O composite hydro-gel posss 3D porous network structure,and the pore diameter is about 5m (Fig.3b).In addition,many Cu 2O nanoparticles are attached on the surface of the hole or in the hole who morphology basically unchanged.Fig.3c shows TEM image of Cu 2O nanoparti-cles,the regular cubic morphology with uniform size is also clearly obrved.The TEM image of the ternary composite shows in Fig.3d,cubic Cu 2O composites are found to be on the sheet of graphene,consistent with the SEM image and XRD patterns,which indicates the formation of 3D RGO/PANI/Cu 2O composite hydrogel.
3.4.Raman spectra
To further verify the composition of ternary RGO/PANI/Cu 2O,Fig.4prents the Raman characterization results.It is clearly en that both spectra give two prominent peaks at 1344cm −1and 1590cm −1,corresponding to D and G bands of RGO and RGO/PANI/Cu 2O,respectively.The D band demonstrates the pres-ence of a large number of defects at the edge of graphene and amorphous structure,and the G band indicates the E 2g mode of phonon vibrations within sp 2-bond
ed carbon material [33].Fig.4also shows the D/G intensity ratio (I D /I G )of RGO/PANI/Cu 2O com-posite hydrogel increas significantly comparing to that of pristine GO,demonstrating the reduction of GO to RGO [34],which is typ-ically rationalized in terms of (a)an increa in the quantity of amorphous carbon,(b)a higher density of defects on the structure,or (c)a reduction in the crystallite size or domains.In addition,newly appeared small peak at 1158cm −1was assigned to C C stretching vibrations of quinone rings [35],indicating the existence of PANI.All of the above analys confirm the successful formation of the RGO/PANI/Cu 2O nanocomposites.
3.5.UV–vis spectroscopy analysis
The ultraviolet–visible (UV–vis)absorption spectroscopy anal-ysis was carried out to understand the caus for enhancing the photocatalytic performance of the ternary composite hydrogel.Fig.5a displays the UV–vis absorption spectra of pure Cu 2O and RGO/PANI/Cu 2O composite hydrogel.The absorption edge of pure Cu 2O exists at around 600nm,which is consistent with previous reports [36].Notably,it can be en that the introduction of RGO or PANI leads to a red-shift in the absorption profile of the resulted ternary RGO/PANI/Cu 2O.Therefore,the photocatalyst is expected to have better abilities to utilize sunlight and have improved pho-tocatalytic ability.The band energy gap of the as-prepared samples could be calculated by Eq.(1):[37]
˛h n =A (h −Eg )
(1)
where ˛,h , ,and Eg are the absorption coefficient,Planck constant,light frequency and band gap,respectively.A is a constant relative to the materials and n reprents the specific electronic transition responsible for light absorption.As shown in Fig.5b and c,the cal-culated band gaps of RGO/PANI/Cu 2O composite hydrogel and pure Cu 2O are about 1.62eV and 2.04eV,respectively,indicates that the ternary composite hydrogel can nearly absorb full UV–vis light.
3.6.Photocatalytic activity of the ternary composite hydrogel
To study the photocatalytic performance of the ternary RGO/PANI/Cu 2O composite hydrogel for degrading organic dye
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Fig.3.SEM images of(a)Cu2O nanoparticles and(b)RGO/PANI/Cu2O composite hydrogel,TEM images of(c)Cu2O nanoparticles and(d)RGO/PANI/Cu2O composite
hydrogel.
整改回复报告范文Fig.4.Raman spectra of GO and RGO/PANI/Cu2O composite hydrogel. from waste water,CR(1×10−5mol L−1)was chon as a model pollutant.Fig.6a shows the time-dependent absorption spectra of a CR solution in the prence of RGO/PANI/Cu2O composite hydro-gel with UV–vis light irradiation.The characteristic absorption peak located at492nm decreas rapidly with extension of the irradia-tion time.The int photograph(Fig.6a)shows the corresponding color changes of the CR solution.The degradation rate of CR reaches 97.91%only need20min revealing the as-prepared ternary com-posite hydrogel posss unexpected photocatalytic activity for the degradation of CR.In addition to photocatalytic activity,the sta-bility of photocatalysts is another important factor in their practical applications.Fig.6b displays the durability of photocatalytic activ-ity of RGO/PANI/Cu2O composite hydrogel for the degradation of CR under UV–vis light irradiation.It can be clearly en that the pho-tocatalytic performance of the ternary composite for degradation of CR exhibits a slight decline afterfive cycling experiments tests; about87.54%of the original CR is degraded,whereas it is97.91% for thefirst run,confirming that our ternary RGO/PANI/Cu2O com-posite hydrogel photocatalysts are stable during the photocatalytic process.The results of photocatalytic experiments demonstrated that the ternary RGO/PANI/Cu2O composite hydrogel not only exhibit enhanced photocatalytic activity under UV–vis light but also posss good recyclability.
For comparison,the photocatalytic activities of different cat-alysts were examined under UV–vis light irradiation within 60min and the results given in Fig.6c.Obviously,the ternary RGO/PANI/Cu2O composite hydrogel exhibits more effective pho-tocatalytic performance for degradation of CR(nearly98%)than that of RGO/Cu2O(81%),PANI/Cu2O(69%)and Cu2O(61%). It ems that the introduced of RGO and PANI play impor-tant roles in determining the high performance of Cu2O-bad composite.
In order to exploring the photocatalytic mechanism,the absorption behavior of different materials for CR is investi-gated(Fig.6d).It can be found that the removal rate of CR follows the order of RGO/PANI/Cu2O(80.51%)>PANI/Cu2O (61.79%)>RGO/Cu2O(54.73%)>Cu2O(37.71%)in30min,indicating the ternary composite hydrogel shows excellent absorption abil-ity for CR.Obviously,the adsorption of CR dye onto the ternary composite hydrogel was affected by the introduction of RGO and PANI.First,the bulksystems of polyaniline and graphene bind with the C C or benzene rings of the CR via–interactions[38].
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Fig.5.(a)UV–vis diffu reflectance absorption spectra of Cu 2O nanoparticles and RGO/PANI/Cu 2O composite hydrogel;plots of (˛h )2vs.photon energy (h )of (b)RGO/PANI/Cu 2O composite hydrogel and (c)Cu 2O
nanoparticles.
Fig.6.(a)UV–vis spectra of the degradation of CR;the int is a digital image of CR degradation.(b)Five cycles of the degradation of CR photocatalyzed by RGO/PANI/Cu 2O composite hydrogel under the irradiation of UV–vis light.(c)Comparative study of degradation rate of CR by RGO/PANI/Cu 2O composite hydrogel,PANI/Cu 2O,Cu 2O/RGO and Cu 2O,respectively.(d)Comparison of the extent of absorption of CR by different materials in 30min.
Second,the hydrogen bonding interactions between the nitrogen-and oxygen-containing groups of the dye and ternary composite hydrogel also contributed to the adsorption [39].Third,it is well known that CR is an anionic dyes with negatively charged groups [40],resulting that a strong electrostatic force between the nega-tively charged CR and positively charged sites of PANI.Thus,it is reasonable that the enhanced adsorption capacity of the ternary composite hydrogel was mainly ascribed to the –interaction,electrostatic interaction and hydrogen bonding between CR and PANI or RGO.
According to the previous reports,the highest occupied molec-ular orbital (HOMO)and the lowest unoccupied molecular orbital (LUMO)of PANI were 0.8eV and −1.9eV,respectively [41].The band gap and conduction band (CB)of Cu 2O are about 2.0eV and −1.4eV,respectively [42].Bad on the characteristic and exper-imental discusd above,a possible photocatalytic mechanism of the ternary RGO/PANI/Cu 2O composite hydrogel for CR degrada-tion was illustrated in Fig.7.Under the
irradiation of UV–vis light,Cu 2O and PANI can be excited and generate electrons and holes.Due to the fact that both the LUMO and HOMO of PANI at an energy一念之差
