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K. Chennakesavulu et al. / Journal of Molecular Structure 1091 (2015) 49–56
loparite, tantalite and iimenorutile [1–4]. Tantalum oxide has high
durability, electrical resistivity, corrosive resistance, super conduc-
tivity, surface area and melting point, etc. Thus its usage was essen-
tial in the catalysis, sensors, optics, coatings, batteries, drug
delivery, gene delivery, photonics and microelectronics [5–7]. The
composites of the tantalum oxide with the highly common oxides
such as zinc, titanium, ferric oxides are the good catalytic materials
for various industrial applications. Zinc oxide is among all good cat-
alytic material owing the high catalytic activity, very less toxicity
and cost effective, when compared with tantalum and niobium
oxide [8,9]. Although, the combination of these composite materials
were used as heterogeneous catalyst in many organic transforma-
tions such as liquid phase oxidation, gas phase oxidation, hydration,
condensation, alkylation, dehydrogenation and photo degradation
of the various organic pollutants [10]. The water was contaminated
with the effluents released by food, agricultural, pharmaceutical
and textile industries. The degradation of halo-phenols, xanthenes
under UV–Visible light is challenging task [11]. The degradation
of cationic dyes such as RhB, rhodamine-6G with either zinc or tan-
talum oxides are very slow under visible light irradiation [12]. The
catalytic activity of zinc oxide was enhanced by doping it with
niobium oxide and tantalum oxide. The tantalum oxide doped
materials would lower the band gap energy and increase the photo-
catalytic performance under UV–Visible light irradiation [13].
The tantalum and niobium oxides are better substituents to the
commercially available toxic chemicals such as H2SO4, HF, HNO3,
COCl2 and chromic acids. The Ta2O5 can provide the strong surface
acidity and stability in aqueous medium even at high temperature
for gas phase reactions. The Ta2O5 and ZnO composites are eco-
friendly materials for the many chemical transformations [14–16].
The catalytic efficiency also depends on the surface properties such
as morphology and size. The percentages of tantalum oxide with
host zinc oxide also alter the photocatalytic activity. The surface
properties and adsorption ability of photocatalyst depends on metal
oxide, which minimize the electron–hole recombination process.
The homogeneity can be achieved by the in-situ nano-
chemical synthesis of the composite [17–19]. The relatively delocal-
ized Ta state near to conduction band give more mobility for the
photo induced electrons to improve photocatalytic activity [20].
The tantalum (V) posses d0 configuration allows the individual Ta
atoms to contribute multiple electrons to vary the electrical conduc-
tivity. So, the ZnO:Ta2O5 hierarchical structure can perform well,
when used as catalysts in the degradation of cationic dyes [21].
The literature related to ZnO:Ta2O5 composite with various percent-
ages of Ta2O5 were yet to be reported in the degradation of RhB.
The present study aims the in-situ chemical synthesis of
ZnO:Ta2O5 composites. The composites were used as photocatalyst
in the degradation of RhB under visible light irradiation.
Spectrophotometric method was used for the determination of
percentage degradation of dye. The recycled catalyst catalytic
activity was compared with the fresh catalyst.
liquid samples were analyzed on a Perkin Elmer Lambda-35 spec-
trophotometer. The UV–Vis/DRS analyses were carried out on a
JASCO-V-670 spectrophotometer. Raman spectra were on a NANO
PHOTON11i confocal Raman microscope using a He–Ne laser emit-
ting at 532 nm. The crystalline nature of the ZnO:Ta2O5 was ascer-
tained by the powder X-ray diffraction using Rigaku XRD-Smart Lab
with Cu Ka1 radiation (k = 1.5418 Å). TGA experiments were per-
formed with Versa Therm Cahn Thermo balance TG-151 with a sen-
sitivity of 10 lg. It was conducted between the temperature range
of 30–900 °C with 20 0.01 mg of the samples and the analyses
were carried out at a heating rate of 10 °C/min under static air
atmosphere. The N2 adsorption–desorption isotherms and BET sur-
face area measurements were carried out on a Micrometrics ASAP
(Model 2020) surface area analyzer with nitrogen and helium gases
with a purity of 99.999% at ꢁ196 °C. The FESEM was obtained on a
SUPRA 55- CARL ZEISS scanning electron microscope. The XPS ana-
lysis was carried out on XM1000 Omicron nanotechnology XPS sys-
tem with Al-Ka monochromatic wavelength. The samples were
made in to pellets and were used as such for X-ray Photoelectron
Spectroscopic (XPS) studies. HRTEM analysis was carried out by
using a FEI TECNAI G2 (T-30) transmission electron microscope
with an accelerating voltage of 250 KV.
Synthesis of the Zn–Ta composites
Anhydrous zinc chloride of 0.05 M was well dispersed in
200 mL of ethanol solution, in double neck round bottom flask,
0.3 M ammonia solution was added dropwise in above solution
at room temperature. The resulting precipitate was centrifuged
and repeatedly washed with the milli-Q water. The white pre-
cipitate was heated in furnace at 200 °C for 4 h. The well dispersed
ethanolic solution of TaCl5 containing 55 mg/160 mg/260 mg and
360 mg were added during the synthesis of composites. The result-
ed sol–gel mixture was centrifuged and washed with the milli-Q
water. The undoped ZnO and composites prepared with 1%, 3%,
5% and 7% of tantalum oxide in ZnO were represented as Zn–Ta0,
Zn–Ta1, Zn–Ta3, Zn–Ta5 and Zn–Ta7 respectively.
Photocatalytic degradation of the RhB under visible light irradiation
The photocatalytic activity of the Zn–Ta0, Zn–Ta1, Zn–Ta3, Zn–
Ta5 and Zn–Ta7 was carried out in a cylindrical glass reactor con-
taining RhB under visible light. Each catalyst of 0.05 g of Zn–Ta0,
Zn–Ta1, Zn–Ta3, Zn–Ta5 and Zn–Ta7 and 0.01 mmol of 100 mL
aqueous dye solution was added. The reaction conditions were
optimized in dark at room temperature and start irradiation under
visible light (>360 nm). The removal percentage and consequent
spectral changes at predetermined time intervals were monitored
by the UV–Visible absorption spectra at 554 1 nm for 3 h. The
percentage conversion is calculated from Eq. (1).
A ¼
e
ꢂ c ꢂ l
ð1Þ
= molar extinction coefficient [Mꢁ1 cmꢁ1], c = RhB concentra-
Experimental
Here
e
tion, l = path length of cuvette (1 cm).
Materials
Results and discussion
Zinc chloride, Ammonia, (Merck Pvt. Ltd, India), Tantalum chlo-
ride and Rhodamine-B (Sigma–Aldrich, India) were used, without
further purification. Millipore water was used throughout the
work.
FTIR analysis
The FTIR spectra of Zn–Ta0, Zn–Ta1, Zn–Ta3, Zn–Ta5 and Zn–Ta7
were given in Fig. 1(a–e). The composites shows peak in region of
1665 cmꢁ1 was due to the in-plane bending vibration of the OAH
group. The bands in the range of 3300–3560 cmꢁ1 were appeared
Physicochemical measurements and characterization
The FTIR spectra were recorded on a FTIR Perkin–Elmer 8300
spectrometer with KBr disk. The UV–Visible absorption spectra of
due to the surface hydroxyl groups.
A strong band around
446 cmꢁ1 was assigned to the stretching frequency of ZnAO group