An efficient removal of methyl violet from aqueous solution by an AC-Bi/ZnO nanocomposite material

Article abstract of DOI:10.1039/c4ra14463e

An activated charcoal (AC) supported bismuth (Bi)-doped zinc oxide (ZnO) nanocomposite material was synthesized by a precipitation method. The obtained material was characterized by high resolution-scanning electron microscopy (HR-SEM) with energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD), Fourier transform-Raman spectroscopy (FT-RAMAN), photoluminescence spectroscopy (PL), UV-visible diffuse reflectance spectroscopy (UV-Vis-DRS), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) analysis. The BET surface area, pore radius and pore volume of the materials were calculated by applying the BET equation to the sorption isotherms. The cyclic voltammetry (CV) analysis suggested an electrochemical redox reaction. The production of hydroxyl radicals (OH) on the surface of the UV-irradiated photocatalysts was detected by a photoluminescence technique using coumarin as a probe molecule. The photocatalytic activity of the AC-Bi/ZnO material is demonstrated through the photodegradation of methyl violet (MV) under UV-light irradiation. AC-Bi/ZnO has an increased absorption in the UV region; moreover, it shows excellent UV-light driven photocatalytic performance. The photocatalyst of AC-Bi/ZnO reveals enhanced photocatalytic activities as compared to ZnO and Bi/ZnO for the degradation of harmful MV dyes. The enhanced photocatalytic activity of AC-Bi/ZnO is attributed to the low recombination rates of photoinduced electron hole pairs, caused by the transfer of electrons and holes between ZnO and AC supported Bi³⁺ ions. The mechanism of the photocatalytic effect of the AC-Bi/ZnO nanocomposite material has been discussed. The proposed use of AC-Bi/ZnO in water purification technique is promising.

Full text of DOI:10.1039/c4ra14463e

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GRAPHICAL ABSTRACT
The hetero-junctions that are formed between the AC-supported Bi and ZnO, Bi provide an
internal electric field that facilitates separation of the electron-hole pairs and induces faster
carrier migration. Thus they often enhanced photocatalytic activity.

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An Efficient Removal of Methyl Violet from Aqueous Solution by AC-Bi/ZnO
Nanocomposite Material
V.L. Chandraboss, J. Kamalakkannan, S. Prabha and S. Senthilvelan*
Department of Chemistry, Annamalai University, Annamalainagar 608 002, Tamilnadu, India.
*Corresponding Author: dr_senthilvel@yahoo.co.in
ABSTRACT
Activated charcoal (AC) supported bismuth (Bi)ꢀdoped zinc oxide (ZnO) nanocomposite material
was synthesized by precipitation method. The obtained material was characterized by high resolutionꢀ
scanning electron microscopy (HRꢀSEM) with energy dispersive Xꢀray analysis (EDX), Xꢀray diffraction
(XRD), Fourier transformꢀRaman spectroscopy (FTꢀRAMAN), photoluminescence spectra (PL), UVꢀ
Visible diffuse reflectance spectra (UVꢀVisꢀDRS), Xꢀray photoelectron spectroscopy (XPS) and
Brunauer–Emmett–Teller (BET) analysis. BET surface area, pore radius and pore volume of the materials
were calculated by applying the BET equation to the sorption isotherms. The cyclic voltammetry (CV)
analysis suggested that the electrochemical redox reaction. The production of hydroxyl radicals (•OH) on
the surface of UVꢀirradiated photocatalysts was detected by photoluminescence technique using coumarin
as a probe molecule. The photocatalytic activity of the ACꢀBi/ZnO material is demonstrated through
photodegradation of methyl violet (MV) under UVꢀlight irradiation. ACꢀBi/ZnO has increased absorption
in the UV region; it shows excellent UVꢀlight driven photocatalytic performance. The photocatalyst of
ACꢀBi/ZnO reveals enhanced photocatalytic activities as compared to the ZnO and Bi/ZnO for the
degradation of harmful MV dye. The enhanced photocatalytic activity of ACꢀBi/ZnO is attributed to the
low recombination rates of photoinduced electron hole pairs, caused by transfer of electrons and holes
between ZnO and AC supported Bi3+ ion. The mechanism of photocatalytic effect of the ACꢀBi/ZnO

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nanocomposite material has been discussed. ACꢀBi/ZnO proposed that use of water purification technique
is promising.
Keywords: Photocatalysis, Activated charcoal, Zinc oxide, Nanocomposite, UVꢀlight.
1. INTRODUCTION
Nowadays, water sources are facing serious threat from hazardous pollutants due to various
activities. These hazardous compounds include heavy metals, anions, organic compounds and dyes. These
contaminants could threaten public health and the atmosphere when they exceed the tolerance limits in
water.1–4 Every day a large amount of unconsumed dye produced by textile and printing industries are
discharged in to the environment. The presence of dyes and pigments in water causes considerable
damage to the marine environment.5–7 Basic dyes have high intensity of colour and are extremely toxic
even in a very low concentration.8–10 Methyl violet (MV) may cause severe skin and eye irritation.
Inhalation of MV may also cause irritation to respiratory tract, whereas ingestion causes irritation to
gastrointestinal tract.11 Hence, the dye removal is of enormous value.
Metal oxide is the most excellent choice for heterogeneous photocatalysis to remove various
pollutants, dyes and phenolic compounds.12-15 Among the metal oxides ZnO is alternative for TiO2 due to
the similar band gap energy (3.37 eV), similar phototocatalytic mechanism and capacity.16-18 ZnO is a
semiconductor with high photosensitivity, nonꢀtoxic nature, low cost, and environmentally friendly
features for photocatalytic applications.19 ZnO has a competitive photocatalytic activity greater in some
cases than TiO2, for example, in the decolourization of Reactive Blue19, textile dyes and azo dyes in
aqueous suspension.20-22 Furthermore, semiconductor thin films have been found to photodegrade the dyes
and insecticides.23,24 ZnO nanoparticles can be prepared via various methods hydrothermal, electro
deposition (ED), chemical vapor deposition (CVD), electrochemical, solution combustion, sol–gel and

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precipitation method.25-31 Among all methods, precipitation technique provides suitable control of
nucleation, ageing and growth of particles in solution. The direct precipitation is also one of the simple
and cost effective methods for bulk production of materials.32 As known, both the size and the
morphology have an influence on the properties of photocatalysts.33
In this method, particle growth owes to interact between different aqueous solutions and therefore
very small particles are formed. Small size particles with lower solubility product dissolve and reꢀ
precipitate on the surface of larger particles in solution; therefore agglomeration takes place in solution as
the particles clog together to decrease surface energy.34 Doping is one of the most widely used strategies to
increase the photocatalytic activity of semiconductors.35 Many dopants such as transition metals (Mn, Cu
and Co) and rare earth elements (La, Ce and Er) could enhance the photocatalytic properties of ZnO.36-39
The effect of Bismuthꢀdoped ZnO nanocomposite material for the photocatalytic degradation of Congo
Red was discussed very recently.31 Doping of Bi into ZnO is expected to shift the absorption edge of ZnO
and influence the separation rate of photoinduced charge carriers of ZnO because of the different structure
of the electronic shell and size of Bi and Zn.40 Bismuth is a kind of pꢀblock metal with a d10
configuration, and the hybridized valence band by O 2p and Bi 6s can narrow the band gap, as well as
favor the mobility of photoꢀgenerated holes in the valance band.41,42 It is worth noting that about the
studies of bismuthꢀbased photocatalysts focus on degradation of organic pollutants.43,40
The Photocatalytic oxidation is an economical process owing to the fact that it involves only a
photocatalyst and light source.44 An alternative approach for decolourization methods is the addition of
charcoal due to its valuable features in the chemical, physical or biological process.45-47 The function of
charcoal is versatile: (i) it acts as a dye adsorbent, not only in straight forward adsorption processes but
also in charcoal enhanced coagulation and membrane filtration processes; (ii) it catalyses ˙OH production

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in advanced oxidation processes; (iii) it generates strong oxidizing agents (mostly, hydroxyl (˙OH)
radicals) in electrochemical dye oxidation; (iv) it catalyses anaerobic (azo) dye reduction and supports
biofilm growth in microbial dye removal.48 Although charcoal is having higher adsorption property, it
usually does not degrade the dye. But charcoal loaded on semiconductor oxide enhances the degradation
efficiency of semiconductor oxide by its synergetic effect and effective degrades the dye. The increase in
photocatalytic activity of semiconductor oxide by the addition of charcoal has been well established.49,50
In this work, we report the synthesis, characterization and photocatalytic activity of ACꢀsupported
Biꢀdoped ZnO nanocomposite material. ACꢀBi/ZnO material was synthesized by a simple and cost
effective precipitation method. The obtained material was characterized by HRꢀSEM with EDX, XRD,
FTꢀRAMAN, PL, DRS, XPS, BET and CV analysis. In application part, we have studied their
photocatalytic activity towards MV in aqueous solution under UVꢀlight irradiation. Here, we highlight and
evaluate recent progress in the development of photocatalytic activity of ACꢀBi/ZnO nanocomposite
material. The enhanced photocatalytic activity of ACꢀBi/ZnO is caused by the reduction of the
recombination of electronꢀhole pairs, decrease the band gap energy, increasing surface area, degree of
•
aggregation, increase of OH formation, improve the electron transfer and increase of absorption of light
intensity are desired elaborately. The ACꢀBi/ZnO reveals enhanced photocatalytic activities as compared
to ZnO and Bi/ZnO for the degradation and decolourization of MV under UVꢀlight irradiation for 0ꢀ60
minutes.
2. EXPERIMENTAL SECTION
2.1. Materials
Zinc acetate dihydrate (Zn(CH3COO)2·2H2O), bismuth nitrate pentahydrate (Bi(NO3)3ꢁ5H2O),
activated charcoal, oxalic acid (C2H6O6), anhydrous ethanol (C2H5OH), coumarin (1 mM of 4ꢀhydroxy

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coumarin) and Methyl Violet (C25H30ClN3) were the guaranteed reagents of Sigma Aldrich and used as
such. The aqueous solutions were prepared by using double distilled water.
2.2. Synthesis of AC supported Bi-doped ZnO nanocomposite material
AC supported Biꢀdoped ZnO nanocomposite material was synthesized by precipitation method
(Scheme 1). 0.24 g of Bi(NO3)3.5H2O (0.1 M) and 0.003 g of activated charcoal (0.05 M) together with a
0.4 M of oxalic acid were dissolved in 20 mL of anhydrous ethanol. The resulting solution was added
dropwise into 20 mL solution of 2.7 g of Zn(CH3COO)2·2H2O (0.8 M) in anhydrous ethanol at room
temperature under vigorous stirring until precipitate formed. The obtained precipitate was washed with
o
water and ethanol. Then the precipitate was collected and dried in oven at 100 C for 12 h in air. The
o
resulting powder was finally calcined at 600 C for 3 h in a muffle furnace to get ACꢀBi/ZnO. It is found
that this catalyst contained 8.5 wt % of AC, 21.5 wt % of Bi and 70 wt % of ZnO. The bare ZnO and Biꢀ
doped ZnO nanocomposites are also synthesized by the same precipitation method.
2.3. Analysis of hydroxyl radical (•OH)
The formation of hydroxyl radicals (•OH) are similar to the photocatalytic activity experiment.51
Photoluminescence (PL) technique with coumarin (1 mM) as a probe molecule was used to investigate the
formation of hydroxyl radical on the surface of ACꢀBi/ZnO illuminated by UV irradiation for 0 to 60 min.
2.4. Adsorption and oxidation kinetics on the surface of AC-Bi/ZnO material
Activated charcoal (AC) is excellent adsorbents of countless pollutants. Their industrial
applications involve the adsorptive removal of odour, colour, taste and other unwanted organics and
inorganics from waste water and drinking water.48 The organic substrates from dye effluents diluted in
aqueous medium are considered to be first adsorbed on the surface of the AC (Fig. 1), where they migrate
to the Bi/ZnO particles and they are oxidized in the vicinity of Bi/ZnO by radical species such as hydroxyl

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•–
radicals (•OH) and superoxide radical anions (O2 ) which are formed by the reaction with photogenerated
holes (h+) and electrons (e–) respectively. Hence, a good understanding of the physicochemical properties
of the support materials is very important to achieve efficient photodegradation.
2.5. Photocatalytic activity
The photocatalytic activity of the photocatalyst was evaluated by the photodegradation of MV. The
light source was a UV lamp. The reaction was maintained at ambient temperature (303 K).
In a typical experiment, aqueous suspensions of dye (40 mL, 2×10−4 M) and 0.08 g of the photocatalyst
powder were placed in reaction tubes. Prior to irradiation, the suspension was magnetically stirred in the
dark to ensure the establishment of an adsorption/desorption equilibrium. The suspension was kept under
constant airꢀequilibrated condition. At the intervals of given irradiation time. The suspension was
measured spectrophotometrically (573 nm) by diluting it four times to keep the absorptions within the
Beer–Lambert law limit.
2.6. Characterization methods
Highꢀresolution scanning electron microscopy and elementary dispersive Xꢀray analysis
experiments were carried out on a FEI Quanta FEG 200 instrument with EDX analyzer facility at 25 °C.
The sample was prepared by placing a small quantity of prepared nanocomposites on a carbon coated
copper grid and allowing the solvent to evaporate. Xꢀray diffraction spectra was recorded on the X’PERT
PRO model Xꢀray diffractometer from Pan Analytical instruments operated at a voltage of 40 kV and a
current of 30 mA with Cu Kα radiation. Fourier transformꢀRaman spectra were recorded with an integral
microscope Raman system RFS27 spectrometer equipped with 1024 X 256 pixels liquefied nitrogenꢀ
cooled germanium detector. The 1064 nm line of the Nd:YAG laser (red laser) was used to excite. To
avoid intensive heating of the sample, the laser power at the sample was not higher than 15 mW. Each

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spectrum was recorded with an acquisition time of 18 sec. Photoluminescence spectra at room temperature
were recorded using a PerkinꢀElmer LS 55 fluorescence spectrometer. Nanoparticles were dispersed in
chloroform and excited using light of wavelength 300 nm. The UVꢀVisible diffuse reflectance spectra of
nanomaterials were recorded with a UVꢀ3600 SHIMADZU (Japan) spectrometer in the range of 800–200
nm. To determine the textural properties of the synthesized materials, N2 adsorption–desorption
measurements were carried out at 77 K using a Micromeritics ASAP 2020 V3.00 H instrument. Xꢀray
photoelectron spectroscopy analysis were performed on a monochromatic Al Kα source instrument
(Omicron Nanotechnology, GMBH, Germany) operating at 14 kV and 20 mA for an Xꢀray power of 280
W. Spectra were collected with a photoelectron takeꢀoff angle of 90o from the sample surface plane with
energy steps of 0.10 eV and pass energy of 20 eV. The spectra were referenced to the binding energy of C
(1s) (285 eV). The BET method was utilized to calculate the specific surface area of the materials. By
using the Barrett–Joyner–Halenda (BJH) model, the pore size distribution was derived from the desorption
branches of the isotherms at a relative pressure (P/Po) of 0.98. Cyclic voltammograms (CVs) were
performed by using a CHI 604C electrochemical analyzer (CHI Instruments Inc., Austin, TX). A
conventional threeꢀelectrode cell was used, including an Ag/AgCl (saturated KCl) electrode as the
reference electrode, a Pt wire served as a counter electrode, and glassy carbon electrode (GCE) coated
with synthesized ACꢀBi/ZnO as a working electrode. UVꢀvis (ultraviolet and visible light) absorbance
spectra were measured over a range of 800ꢀ200 nm with a Shimadzu UVꢀ1650PC recording spectrometer
using a quartz cell with 10 mm of optical path length.

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3. RESULTS AND DISCUSSION
3.1. Surface morphology and elemental analysis
HRꢀSEM images of the Bi/ZnO and ACꢀBi/ZnO nanocomposites are shown in Figs. 2a and 2b
respectively. The HRꢀSEM images revealed that individual particles were composed by a collection of
elongated particles of various size and shapes. HRꢀSEM images of the Bi/ZnO shows the average particle
size of 80 nm and ACꢀBi/ZnO shows the average particle size of 30 nm. The above observation particles
size of the Bi/ZnO was greater than that of ACꢀBi/ZnO suggesting that in absence of AC. The Bi/ZnO
aggregates more easily during the calcination process. AC acted as a barrier which controlled the growth
of Bi/ZnO particles and prevents their aggregation. Aggregation of particles would inevitably reduce their
total surface area exposed to the outer environment, leading to a lowered photocatalytic activity as
observed in many reaction systems.18 Moreover, the decrease in particle size can be correlated with the
observed increase of the surface area. This can be further discussed in BET surface area analysis. The
surface properties, undoubtedly, have a great influence on the photocatalytic activity.52 ACꢀBi/ZnO is
caused by larger surface area, increased oxygen vacancy, increases the absorption of light intensity and
enhances the photocatalytic activity. EDX analysis confirms Zn, Bi and O are present in Bi/ZnO (Fig. 2c),
Whereas Zn, Bi, C and O are present in ACꢀBi/ZnO composite material (Fig. 2d). EDX analysis clearly
displays intense peaks between 2.0 and 2.5 keV corresponding to bismuth L1 (2.3 keV), which is similar
to the major constituents of the Bi/ZnO and ACꢀBi/ZnO.
3.2. XRD analysis
The obtained XRD of the ZnO, Bi/ZnO and ACꢀBi/ZnO nanocomposites are shown in Figs. 3a, 3b
and 3c respectively. The peaks at 31.7°, 34.3°, 36.2°, 47.4°, 56.5°, 62.8°, and 67.8° are from the
diffractions for ZnO (100), (002), (101), (102), (110), (103) and (112) crystal planes (JCPDS No.

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36ꢀ1451). The relatively high intensity of the (101, 002 and 100) peaks are indicative of anisotropic
growth and implies a preferred orientation of the crystallites.53,54 The peaks at 22.5°, 24.8°, 30.1°, 33.6°,
36.2°, 40.4°, 47.2°, and 56.1° are the diffractions of the Bi (003), (101), ZnO (100), (002), (101), Bi (110)
and ZnO (102), (110) crystal planes. It confirms the Bi3+ was present in ZnO lattice40 (JCPDS No. 36ꢀ
1451, 44ꢀ1246 and 79ꢀ0206).
ACꢀBi/ZnO, peaks at 26.5°, 27.1°, 31.9°, 34.6°, 36.1°, 44.8°, 50.2°, 56.1° and 60.2° are the
diffractions of the C (300), Bi (012), ZnO (100), (002), (101), Bi (015), C (511), ZnO (110), C (161)
crystal planes. It shows Bi and C are present in ZnO material (JCPDS No. 36ꢀ1451, 44ꢀ1246 and
50ꢀ0927). As shown in Fig. 3, all strong peaks can be indexed as the pure hexagonal phase of wurtziteꢀ
type ZnO, which agrees well with the reported data (JCPDS No. 36ꢀ1451 and 79ꢀ0206). This results
indicate that ACꢀsupported Biꢀdoped ZnO have a hexagonal phase of wurtzite structure. The sharp peaks
of ZnO indicate the high degree of crystallinity (Fig. 3a). An addition of Bi and AC in the ACꢀBi/ZnO
decreases the peak intensity of (101), (001) and (100) diffraction planes, which indicate AC act as barrier
and Bi3+ in the lattice of ZnO. Fig. 3b and 3c shows the diffraction peaks (002) are slightly leftꢀshifted,
which is mainly due to the larger radius of Bi3+ versus that of Zn2+. This observation suggests that a
portion of Bi3+ ions was incorporated into the ZnO lattice55 by replacing Zn2+ with Bi3+.
The average crystalline size (L) of the ZnO, Bi/ZnO and ACꢀBi/ZnO particles are calculated by the
DebyeꢀScherrer formula,56 L=0.89λ/βCOSθ where L is the crystalline size (in nm), λ is the wavelength (in
nm), β is the full width at half maximum intensity (FWHMꢀin radian), and θ is the Bragg diffraction angle
(o). The average crystalline size of ZnO and Bi/ZnO composite was figured out to be about 92.5 and 78.5
nm. The average crystalline sizes of ACꢀBi/ZnO composite are almost 29.5 nm.

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3.3. FT-RAMAN analysis
The Raman spectra of the ZnO, Bi/ZnO and ACꢀBi/ZnO are shown in Fig. 4. The characteristic
peaks at 212, 380, 438, 569, 1150 cm−1, which correspond to the 2TA; 2E2(low), A1(TO), E2(high),
A1(LO) and 2A1(LO), 2E1(LO); 2LO fundamental phonon modes of ZnO, respectively. The Raman peak
at 438 cmꢀ1 is attributed to the ZnO nonpolar optical phonons of highꢀE2 mode,57 which is one of the
characteristic peaks of wurtzite ZnO (Fig. 4a).
Bi/ZnO shown peaks at 229, 549, 592, 912, 1080, 1472 cm−1 (Fig. 4b). The characteristic peaks at
229, 549, 592 cm−1 which correspond to the shifted peaks of 2TA; 2E2(low), A1(LO) and E1(LO)
respectively. The peak at 229 cm−1 attributed to the 2TA; 2E2(low) mode, which is one of the
characteristic peak of BiꢀO bonds. The band at 549 cmꢀ1 corresponds to A1 symmetry with LO modes. The
A1(LO) become a sharp peak and shifted about 20 cm−1 towards lower energy. It is generally accepted that
the A1(LO) peak caused by polar branches appeared at about 549 cm−1 respectively. From the above
observation Bi was present in ZnO nanomaterial is confirmed. ACꢀsupported Bi/ZnO shows peaks at 232,
323, 441, 1580 cm−1 (Fig. 4c). The shifted peaks at 232 and 323 cm−1 attributed to the 2TA; 2E2(low) and
E2(high)ꢀE2(low) mode, which is one of the characteristic peak of BiꢀO bonds. The shifted peak at
441 cm−1 is attributed to the highꢀE2 mode, which is one of the characteristic peaks of wurtzite ZnO.
Above 400 cm−1 the intensity of the peaks are increased, several small peaks also observed. The high
intensity of the 1580 cm−1 assigned to Gꢀband, which correspond to carbon present in the Bi/ZnO
composite.
3.4. PL analysis
Photoluminescence spectra of ZnO, Bi/ZnO and ACꢀBi/ZnO are shown in Figs. 5a, 5b and 5c
respectively. As the photoluminescence occurs due to electron−hole recombination, its intensity is directly

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proportional to the rate of electron−hole recombination.58 ZnO showed four emissions at 400, 436, 480
and 530 nm. Bi/ZnO showed four emissions at 401, 438, 482 and 531 nm. ACꢀBi/ZnO also showed four
emissions at 401, 438, 487 and 531 nm. ACꢀsupported Biꢀdoping of ZnO slightly shifts the emission of
ZnO. ACꢀBi/ZnO shows a near UV emission band at 401 nm and a blue–green band at 487 nm. However,
the PL intensity of 401 nm is lower than that of the synthesized ZnO. This near UV emission corresponds
to the exciting recombination related nearꢀband edge emission of the ZnO nanomaterial.59-62 The blue–
green emission is due to surface defects in the ZnO.62 A reduction of PL intensity at 401 nm by ACꢀ
Bi/ZnO when compared to synthesized ZnO and Bi/ZnO indicates the suppression of the recombination of
the photogenerated electron−hole pair by ACꢀBi/ZnO. This leads to a higher photocatalytic activity of
ACꢀBi/ZnO nanocomposite material.
3.5. UV–Vis- DRS analysis
The UVꢀVis –DRS spectra of ZnO, Bi/ZnO and ACꢀBi/ZnO are shown in Fig. 6. The direct band
gap of synthesized materials has been determined from the Tauc plots. Plots of [F(R)hν]2 versus the
photon energy (hѴ) provide the direct band gap of the synthesized ZnO, Bi/ZnO and ACꢀBi/ZnO as 3.19,
3.15 and 3.12 eV, respectively. UV–VisꢀDRS results demonstrated that the decrease in the direct band gap
of ACꢀBi/ZnO compared to ZnO and Bi/ZnO. These results reveal ACꢀBi/ZnO will be used as an effective
photocatalyst. In addition, the UVꢀvis spectrum in the diffuse reflectance mode (R) was transformed to the
Kubelka–Munk (KM) function, F(R) to separate the extent of light absorption from scattering.63
F(R) values have been calculated from the reflectance (R) by application of the Kubelka–Munk algorithm:
[F(R) = (1 − R)2/2R].64,65 KM plot (Fig. 6d) shows that ACꢀBi/ZnO is strong absorption in the UV region
of 200–400 nm indicating more photocatalytic activity in UV region. This reveals that ACꢀBi/ZnO can be

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used as an UV light active photocatalytic material. Strong UV light absorption may lead to improved
generation of electronꢀhole pairs, which enhances the photocatalytic activity of ACꢀBi/ZnO.
3.6. XPS analysis
The composition and chemical states of the elements in ACꢀBi/ZnO were examined by Xꢀray
photoelectron spectroscopy. The typical Xꢀray photoelectron survey spectrum of the ACꢀBi/ZnO indicates
that the material consists of Zn, Bi, O and C (Fig. 7). The O 1s profile is asymmetric and can be fitted to
two symmetrical peaks α and β located at 530.5 and 533.5 eV, indicating two different kinds of O species
in the sample. These peaks should be associated with lattice oxygen of ZnO and chemisorbed oxygen
caused by the surface hydroxyl (OH), respectively.66 The C 1s peak is attributed to the activated charcoal
present in the synthesized material.67 XPS spectra of Zn 2p, and the peak positions of Zn 2p 1/2 and Zn 2p
3/2 are located at 1045.5 eV and 1019.9 eV. Comparing the peak positions to those in the Handbook of Xꢀ
ray Photoelectron Spectroscopy,68 we can conclude that Zn is in the state of Zn2+. The peaks of Bi 4f 5/2
and Bi 4f 7/2 at 158.9 and 164.2 eV reveal that bismuth is in the state of Bi3+.69,70
3.7. BET surface area analysis
The corresponding N2 adsorption–desorption isotherms and BJH desorption pore distribution of all
the investigated catalysts are shown in Fig. 8. The surface area of ZnO, Bi/ZnO and ACꢀBi/ZnO was
determined using the nitrogen gas adsorption method. N2 adsorption–desorption isotherms of the catalysts
exhibited a hysteresis loop, typical of a type II pattern representing the predominant nonporous structure
according to the international union of pure and applied chemistry (IUPAC) classification.71 A sharp
increase in the adsorption volume of N2 was observed and located in the P/Po at 0.98. This sharp increase
can be attributed to the capillary condensation, indicating the good homogeneity of the sample and a
macro pore size, since the P/P0 position of the inflection point is related to the pore size.72 The pore size

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distribution of ZnO, Bi/ZnO and ACꢀBi/ZnO are given in inset Fig. 7a, 7b and 7c respectively. The BET
surface and total pore volume of the catalysts was given in Table 1. BET surface area of ACꢀBi/ZnO
(19.4 m²/gꢀ1) is higher than Bi/ZnO (15.3 m²/gꢀ1) and bare ZnO (8.3 m²/gꢀ1). It is clear that Bi3+ doped is
effective for changing the morphology of ZnO, the big particle size leads to the BET surface area
decrease, this result agrees well with the result of BET surface area. Higher surface area of the ACꢀ
Bi/ZnO enhances the photocatalytic activity.
3.8. Electrochemical enhancement study
Photocatalysis is a surface phenomenon as the photogenerated charge carriers diffuse to the surface
to initiate redox reactions.73 The modified electrode was constructed by ZnO and ACꢀBi/ZnO via
mechanical attachment. Fig. 9. shows the effects of using unmodified/modified GCE on the
electrochemical oxidation/reduction potential of potassium chloride (KCl) based on data from cyclic
voltammetry. When the GCE was not modified with any photocatalyst, there is hardly any enhancement
or decrement in the cycles. ZnO modified GCE was observed that the electrochemical oxidation of KCl is
an irreversible process due to the peak (anodic current and the (Epa) peak potential of 0.931 V). But,
ACꢀBi/ZnO modified absence of a wellꢀdefined reduction GCE was observed that the electrochemical
redox reaction of KCl is a reversible process (enhanced anodic and cathodic current and the (Epa) peak
potential of 0.547 V and 0.245 V). These results indicated that ACꢀBi/ZnO modified GCE had larger
adsorption/desorption and higher electrochemical response than that of ZnO. Several literatures have
indicated that the GCEs modified metal ion and carbon materials were found to perform better in
comparison to bare GCE.63,74,75 This suggests that the presence of AC and Bi in the ZnO could increases
current and improve the relative electron transfer.

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3.9. Hydroxyl radical analysis
The photocatalytic activity of asꢀsynthesized materials was further confirmed by the detection of
•OH. In order to confirm the existence of hydroxyl radicals, the formed hydroxyl radicals on the surface of
ACꢀBi/ZnO illuminated by UV light were detected by PL technique. The PL emission spectra excited at
330 nm in coumarin solution suspension with ACꢀBi/ZnO were measured at different time intervals 0, 30
and 60 mins. Fig. 10a displays that a PL signals were observed at 391 to 522 nm. The main peak is
respectively located at about 391, 398, 404, 417, 447 and 522 nm respectively. The occurrence of
emission peaks observed in the UVꢀvisible region is attributed to the electronic transition mediated by the
defect levels such as oxygen vacancies in the band gap.76,77 The maximum PL intensity was found for
ACꢀBi/ZnO at 60 min (Fig. 10b). This suggests that the fluorescence is caused by chemical reactions of
coumarin with hydroxyl radicals formed in photocatalytic reactions.51 Hence, hydroxyl radical is the
reactive oxidation species in ACꢀBi/ZnO sample and finally induces the degradation of MV. Moreover,
ACꢀBi/ZnO with maximal photocatalytic activity produced much more reactive hydroxyl radicals.78
Increase of •OH formation on ACꢀBi/ZnO can be caused by the better separation of free carriers retarding
the recombination reaction in the semiconductor through the capture of electrons by ACꢀBi/ZnO and
enhanced yield of reaction between photogenerated holes and adsorbed water molecules on the
photocatalyst surface.
3.9.1. Photocatalytic performance of AC-Bi/ZnO nanocomposite material
Dye effluents from textile industries are becoming a severe environmental trouble because of their
high chemical oxygen demand content, resistance to chemical, unacceptable colour, photochemical and
biological degradation.79 We have chosen photodegradation of MV as model dye with UV irradiation to
evaluate the photocatalytic activity of the proposed photocatalyst. Fig. 11 shows the time course of

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decrease in the absorbance of MV under UV light irradiation. The photodegradation process of MV, the
UV–vis spectra and the colours of MV aqueous solution as a function of UVꢀlight irradiation time in the
presence of photocatalysts (ZnO, Bi/ZnO and ACꢀBi/ZnO) are illustrated in Figs. 11a, 11b and 11c. It can
be seen from UV–visible spectra changes, the strong adsorption peak of MV solution at 573 nm steadily
decreased and degraded with increasing the light irradiation time, and the initial violet colour of the
solution gradually turned to lightꢀcoloured. Comparative studies of photocatalytic activity of ZnO, Bi/ZnO
and ACꢀBi/ZnO photocatalysts for photodegradation as well as decolourization of MV was shown in
Fig. 11d. ACꢀBi/ZnO exhibited excellent photocatalytic activity for MV under UVꢀlight irradiation when
compared to that of ZnO and Bi/ZnO.
Fig. 12a shows the time course of percentage decolourization of MV under UVꢀlight irradiation.
After 60 min of irradiation time ACꢀBi/ZnO can decolourize the MV in aqueous solution up to 94.5 %
when compared to that of ZnO and Bi/ZnO (66.5% and 82.5%) respectively. Under dark conditions,
initially there is a decrease in dye concentration with ACꢀBi/ZnO and this is due to the adsorption of the
dye on the catalyst. Under UV light irradiation, degradation of MV occurred with all the catalysts.
However, ACꢀBi/ZnO exhibited higher photocatalytic activity than ZnO and Bi/ZnO photocatalysts.
Fig. 12b shows the time course of decrease in the concentration of MV under UVꢀlight irradiation.
Initially MV dye concentration was 2×10−4 M after photodegradation takes place with respect of time. The
blank run (air passing) was 30 minutes 1.4×10−4 M than UVꢀirradiation takes at 0 to 60 minutes. After 60
minutes of irradiation time ACꢀBi/ZnO can photodegradation of MV in aqueous solution up to 5.4×10ꢀ5 M
when compared to that of ZnO and Bi/ZnO (7.4×10−5 M and 6.4×10−5 M) respectively. It can be seen that
increase the irradiation time (0 to 60 minutes) with respect to decrease the dye concentration, therefore
ACꢀBi/ZnO shows higher photocataltyic activity. As shown in Fig. 12, no significant photodegradation of

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MV was observed in the absence of AC and Bi, which indicated that the photosensitizing effect of MV
could be ignored in this case. It was also found that ACꢀBi/ZnO showed much higher photocatalytic
efficiency than ZnO, and exhibited the best photocatalytic performance for MV photodegradation.
Fig. 13a, evaluated by measuring the time dependent degradation efficiency of MV in an aqueous
catalyst suspension under UV light exposure. Because MV itself is a dye which is active to UVꢀlight, its
photocatalytic activity is in the order of the ACꢀBi/ZnO > Bi/ZnO > ZnO. The photodegradation kinetics
of MV on ZnO, Bi/ZnO and ACꢀBi/ZnO were evaluated using the pseudoꢀfirstꢀorder model:
ln(C0/Ct) = Kappt
(1)
Where Kappt is the rate constant [min], C0 is the initial concentration of MV, and Ct is the
concentration of MV at reaction time (t)80 From the results (Fig. 13b), one can see that ACꢀBi/ZnO
showed the highest degradation rate constant, approximately 1.098 × 10ꢀ4 secꢀ1, which was greater than
that of ZnO (~0.822 × 10ꢀ4 secꢀ1) and Bi/ZnO (~0.958 × 10ꢀ4 secꢀ1).
ACꢀBi/ZnO generally accepted that the photocatalytic activity is initiated by the photogeneration
of electron–hole pairs. The •OH radicals, produced by an electron and the holes, are the primary oxidative
species in a photocatalytic degradation and decoloration reaction, and they attack azo group causing the
decomposition of chromophores.81-83 Photocatalytic process is influenced by various factors, in which
specific surface area and the transport properties of photoinduced charge carriers are two key factors.84
The ACꢀBi/ZnO is quite active for photocatalytic MV degradation, because they have a larger BET
surface area (19.4 m²/gꢀ1) than the prepared ZnO (8.3 m²/gꢀ1) and Bi/ZnO (15.3 m²/gꢀ1) to facilitate a more
efficient of the ACꢀBi/ZnO with organic dye contaminants and thus resulting in enhanced photocatalytic
activity. UVꢀVisꢀDRS (Fig. 6d) shows ACꢀBi/ZnO is strong absorption in the UV region of 200–400 nm,
there is a slight increase in absorbance in visible region. Hence ACꢀBi/ZnO can be used as an UV light

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active semiconductor photocatalytic material. Therefore, an experiment was conducted to test its
photocatalytic activity under solar light (sunny days between 11 am and 12 pm). Irradiation of MV
solution (2×10−4 M) with a borosilicate glass tube of 50 mL capacity (40 mL of MV solution with 0.08g of
catalyst) for 1 hour, under the same condition was discussed in UVꢀlight. Under solar light produced 70%
of decolourization (degradation at 7.0×10ꢀ5 M). 94.5% decolourization (degradation at 5.4×10ꢀ5 M) was
obtained with UV light. ACꢀBi/ZnO shows higher photocatalytic activity due to the reduced band gap
energy, smaller particle size, electron hole recombination and enhanced surface area which are the
determining factors of enhanced photocatalytic efficiency.
3.9.2. The mechanism of photocatalytic effect of AC-Bi/ZnO nanocomposite material
ACꢀsupported Biꢀdoped ZnO nanocomposite material absorb UV light and an electron from its valence
band (vb) get excited to the conduction band (cb) generating a positively charged hole in the valence band
(h+ ) and negative charge in the conduction band (e– ) according to the Eqn. (2).
vb
cb
•
The chemisorbed H2O molecules interact with the valence band holes forming OH radicals
(Eqn. (3)), which attack dye molecule successively to make degradation. Furthermore, the conduction
band electrons e– interact with dissolved O2; producing superoxide radical anion (O2 ) as shown
•–
cb
–
•
•
in Eqn. (4). On the other hand, h+ could interact with donor OH and HO2 forming OH radical attack
vb
the dye as in Eqn. (5)
ACꢀBi/ZnO + hv → h+vb + e–
(2)
(3)
(4)
(5)
cb
(H2O → H+ + OH–) + h+ → H+ + OH
•
vb
•–
•
O2 + e–cb → (O2 ) + (H+ + OH–) → HO2 + –OH
•
•
HO2 + –OH + h+ → OH
vb

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Thus the Photocatalytic cycle comprises three steps (i) Illumination induces a transition of electrons
from the valance band (VB) to the conduction band (CB), leaving an equal number of vacant sites (holes),
(ii) The excited electrons and holes on Bi ion migrate to ZnO surface, facilitating the charge separation
and higher photocatalytic efficiency. This charge separation is also revealed by the reduction of PL
intensity of the proposed catalyst when compared to ZnO. This process not only facilitates the charge
separation, but also accumulates electrons and holes in Bi and ZnO respectively. If large proportion of
electron hole pairs recombine, dissipating the input energy in the form of heat or emitted light. To prevent
the recombination of electronꢀhole pairs, ACꢀsupported Bismuth on the ZnO surface acts as a barrier
(Fig. 14). Effective electron−hole pair separation at the heterojunction interfaces can significantly improve
photocatalytic performance of composite materials.73,85 The heteroꢀjunctions that are formed between the
ACꢀsupported ZnO and Bi provide an internal electric field that facilitates separation of the electronꢀhole
•
pairs and induces faster carrier migration. (iii) The OH radical was commonly recognized as the main
reactive species responsible for the degradation of organic dyes.86,87 The photogenerated electrons could
react with the oxygen molecule adsorbed on the surface of ACꢀBi/ZnO to yield O2•–. On the other hand,
•
•
photogenerated holes react with H2O molecules to produce OH. O2•–, OH and photogenerated holes to
degrade the reactive dyes absorbed on the surface of ACꢀBi/ZnO. Thus they often enhanced photocatalytic
activity.
4. CONCLUSION
ACꢀsupported Biꢀdoped ZnO nanocomposite material was synthesized by a precipitation method,
and characterized by HRꢀSEM with EDX, XRD, FTꢀRAMAN, PL, DRS, XPS, BET and CV analysis.
Results confirmed the formation of ACꢀBi/ZnO nanocomposite material. HRꢀSEM and XRD analysis of
ZnO and Bi/ZnO showed the average particle size of 78.4 nm, But ACꢀBi/ZnO showed the average

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particle size of 29.5 nm. The decrease in particle size can be correlated with the observed increase of the
surface area. XRD, EDX and XPS reveal the presence of Zn, O, Bi and C and their oxidation states in the
ACꢀBi/ZnO. In XRD spectra all strong peaks are indexed as the pure hexagonal phase of wurtzite
structure. FTꢀRaman spectra reveals that optical phonons of highꢀE2 mode, which corresponds to the
wurtzite ZnO structure. PL spectra confirm suppression of recombination of the photogenerated
electron−hole pairs by ACꢀBi/ZnO nanomaterial. UVꢀVisꢀDRS demonstrated that the decrease in the
direct band gap of ACꢀBi/ZnO compared to ZnO and Bi/ZnO. BET surface area of ACꢀBi/ZnO is higher
than Bi/ZnO and ZnO. Higher surface area of the ACꢀBi/ZnO enhances the photocatalytic activity. ACꢀ
Bi/ZnO has potential as use as a mediator for electrochemical analysis due to increases current and
improves the relative electron transfer. ACꢀBi/ZnO caused retarding the recombination reaction which
occurs after excitation of semiconductor with UV light. Increase of the OH radicals formation during UV
irradiation in ACꢀBi/ZnO was observed due to the better separation of free carriers, however there was no
linear relation of the photocatalyst ability to OH radicals formation on the content of AC and Bi in ZnO
surfaces. ACꢀBi/ZnO reveals enhanced photocatalytic activities as compared to ZnO and Bi/ZnO for the
photodegradation and decolourization of MV under UVꢀlight irradiation for 0 to 60 minutes. The
mechanism of dye degradation is proposed for the higher photocatalytic activity of ACꢀBi/ZnO.
Conflict of Interest
The authors declare no competing financial interest.
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87. S. Balachandran and M. Swaminathan, J. Phys. Chem. C, 2012, 116, 26306ꢀ26312.

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26
Captions for Scheme, Figures and Table
Scheme 1. Schematic representation for the synthesis of ACꢀBi/ZnO nanocomposite material.
Fig. 1. Dye effluents onto the ACꢀBi/ZnO surface is desirable for photodegradation kinetics.
Fig. 2. HRꢀSEM images of (a) Bi/ZnO, (b) ACꢀBi/ZnO nanocomposite material, EDX analysis of
(c) Bi/ZnO, (d) ACꢀBi/ZnO nanocomposite material.
Fig. 3. XRD patterns of (a) ZnO nanomaterial, (b) Bi/ZnO nanocomposite material and
(c) ACꢀBi/ZnO nanocomposite material.
Fig. 4. FTꢀRAMAN spectra of (a) ZnO nanomaterial, (b) Bi/ZnO nanocomposite material and
(c) ACꢀBi/ZnO nanocomposite material.
Fig. 5. PL spectra of (a) ZnO nanomaterial, (b) Bi/ZnO nanocomposite material and
(c) ACꢀBi/ZnO nanocomposite material
Fig. 6. Direct band gap of (a) ACꢀBi/ZnO, (b) Bi/ZnO, (c) ZnO and (d) Plot of Kubelka–Munk function
versus energy of the light absorbed of the catalysts
Fig. 7. XPS survey spectrum of ACꢀBi/ZnO nanocomposite material
Fig. 8. N2 adsorption–desorption isotherms of (a) ZnO (b) Bi/ZnO and (c) ACꢀBi/ZnO (Inset: BJH
desorption pore distribution)
Fig. 9. CVs of (a) uncoated GCE with 0.1 M KCl (green curve), (b) ZnO coated GCE in 0.1 M KCl (blue
curve) and (c) ACꢀBi/ZnO coated GCE in 0.1 M KCl (red curve).
Fig. 10. PL spectra of ACꢀBi/ZnO under excitation at 330 nm in coumarin solution (a) UVꢀlight
irradiation of ACꢀBi/ZnO at 60 min and (b) UVꢀlight irradiation of ACꢀBi/ZnO obtained using different
time intervals (0, 30 and 60 mins).

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Fig. 11. Absorption spectra changes of methyl violet solution (2×10−4 M, 40 mL) in the presence of
photocatalysts (a) ZnO, (b) Bi/ZnO and (c) ACꢀBi/ZnO under UVꢀlight (365 nm) irradiation at 10 minute
interval. (d) Comparative studies of photocatalytic activity (absorbance vs time (min)) of ZnO, Bi/ZnO
and ACꢀBi/ZnO photocatalysts for photodegradation and decolourization of MV under UVꢀlight (365 nm)
irradiation at 10 minute interval.
Fig. 12. (a) Comparison of photocatalytic activity (dye decolouration (%) vs time (min)) of decolouration
of MV dye by ZnO, Bi/ZnO and ACꢀBi/ZnO under UVꢀlight (365 nm) irradiation at 10 minute interval.
(b) Comparisons of photocatalytic activity (Concentration (M) vs time (min)) of decolouration of MV dye
by ZnO, Bi/ZnO and ACꢀBi/ZnO under UVꢀlight (365 nm) irradiation at 10 minute interval.
Fig. 13. (a) Kinetic of methyl violet degradation upon irradiation and (b) Photodegraded efficiencies for
the ZnO, Bi/ZnO and ACꢀBi/ZnO, variations in ln(C0/C) as function of irradiation time and linear fits of
catalysts.
Fig. 14. Schematic illustration of AC supported Biꢀdoped ZnO mechanism for photocatalytic process.
Table. 1. Surface properties of the materials

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Precipitate filtered
Zn(CH3COO)2.2H2O
C2H6O6
C2H5OH
Activated
Charcoal
Bi(NO3)3.5H2O
Precipitate washed with
H2O and C2H5OH
Dried in oven at 100 OC
Calcinated at 600 OC
Precipitate formed
C2H5OH
AC-Bi/ZnO nanocomposite
material formed
Stirred at room temperature
Scheme 1. Schematic representation for the synthesis of ACꢀBi/ZnO nanocomposite material