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SPECTROCHIMICA ACTA PART A: MOLECULAR AND BIOMOLECULAR SPECTROSCOPY

Volume 255, 5 July 2021, 119644




ENHANCED VISIBLE LIGHT PHOTOCATALYTIC ACTIVITY OF TIO2 CO-DOPED WITH FE, CO, AND
S FOR DEGRADATION OF CANGO RED

Author links open overlay panelMuhammad Imran a, Zohaib Saeed a, Muhammad
Pervaiz a d, Kashif Mehmood b, Rabia Ejaz c, Umer Younas d, Hafiz Amir Nadeem a,
Shah Hussain a
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https://doi.org/10.1016/j.saa.2021.119644Get rights and content




ABSTRACT

The photocatalytic activity of TiO2 was enhanced under visible light when it was
co-doped with Fe, Co, and S through the sol-gel method. The resultant nano
photocatalysts were characterized by XRD, EDX coupled with SEM, FT-IR, UV–Vis,
and UV-DRS. The concentration ratio of precursor salts of Fe and S was kept at
1% each and of Co varied between 0.5% −1.5%. The photodegradation of Congo red
was carried out and various factors like the concentration of catalyst, initial
concentration of dye, pH, and irradiation time were also investigated to
optimize the degradation process. Under optimized degradation conditions, 99.3%
of Congo red (30 ppm) was degraded at slightly acidic pH, with 0.14 g of
photocatalyst within 70 min of irradiation time.


GRAPHICAL ABSTRACT

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INTRODUCTION

The quality of freshwater has deteriorated with the advancement in dye and
textile industries that generate, almost 17–20% of wastewater according to the
World Health Organization (WHO). The substantial quantity of dye in wastewater
results in, “high biological oxygen demand (BOD), chemical oxygen demand (COD),
nitrogen, acidity” [1], the inclusion of undissolved and dissolved particles,
surfactants, and heavy metals [2] that are causing serious water borne
challenges. The aquatic ecosystem is disturbed and it has caused damage to human
health in form of cancer (mostly liver cancer), headache, nausea, lung problems,
and congenital malformation [3]. The worldwide production of dyes is about 0.7
million tons out of which 0.2 million tons are lost annually, whereas around 10
thousand types of artificial dyes are also available in the market [4]. Azo-dyes
with the help of their characteristics functional group (NN) and bond with
aromatic rings form a bridge between organic groups [5]. Among the total number
of dye structures known to be manufactured, azo-dyes account for more than 60%.
The dyeing process and textile effluent contain almost 1–20% of total dyes,
produced in the world [6]. Few azo-dyes and their degradation products are
carcinogenic [7]. Some physical techniques, such as depth and membrane
filtration, sedimentation, flocculation, reverse osmosis, and adsorption have
been utilized for the removal of textile dyes. It requires further treatment as
these techniuqes are non-destructive because they transfer contaminants from the
liquid phase to a solid phase [1], [8], [9] (see Figs. 1 and 2).

The chemical techniques have also been utilized for this purpose, such as
chemical coagulation but it generates a massive volume of sludge and caused
secondary pollution. The biological techniques are supposed to be the most
economical and green treatments, but azo dyes are bio-persistence and difficult
to degrade by conventional biological techniques [10]. In addition to these
methods, advanced oxidation methods have also been broadly examined [11].
Heterogeneous photocatalysis has emerged as a destructive technique that
involves the complete mineralization of almost all organic pollutants. TiO2 has
got attention as photocatalyst among different semiconductor materials. TiO2 has
factual benefits in photocatalysis owing to features like resistance to
photo-corrosion, low toxicity, and satisfactory band-gap energy, additionally it
has low cost [12], [13]. TiO2 has multiple uses like pollutants degradation,
splitting of water, a constituent of dye-sensitive solar cells, and gas sensors.

The photocatalytic properties of TiO2 are lessened owing to inherent problems
associated with it like non-absorbance in the visible region, high bandgap
(3.2 eV), and recombination ability with electrons and holes that generated
during the photocatalytic process. The photocatalytic activity of TiO2 can be
enhanced by reducing both bandgap and recombination ability. The commonly used
method which minimizes the reaffixing rate of electron-hole and extending the
range of absorption more towards visible light from ultraviolet is doping with
transition metals [14]. Non-metal also has been used to dope TiO2 such as carbon
(C), Phosphorus (P), Sulphur (S), Fluorine (F), Boron (B), Iodine (I), etc,
Among them, nitrogen is doped to degrade the CR [15]. Various metal–metal
co-doping like Fe/Ni, Zn/Cu, Cr-Co, Co-Ni, Zn-Eu, and Ag-Mo, etc. have been used
to enhance the photocatalytic activity of TiO2 [1], [16]. Among them, Zn2+/ V5+
and Zn/Cu were used to photodegrade the CR [17], [18], [19]. Every dopant has a
different impact on behaviors of TiO2 depending upon their coordination number,
energy level, and electronegativity [20]. In the present work, Fe, Co, and S
were co-doped into TiO2. The dopant to TiO2 ratio was kept at 1% for Fe and S
[20], [21] while the ratio of Co was varied [22]. Iron has been considered as
the best dopant among transition metals owing to a similar radius to Ti4+ i.e.
0.69 A and 0.75 A respectively, and potential of Fe3+ to trap photogenerated
electrons and holes because of the energy level of Fe2+/Fe3+ is similar to
Ti3+/Ti4+. [19] Fe3+ ions enhance the photocatalytic activity of pure TiO2 by
the formation of sites to trap charges which created subsequently replacement of
Ti4+ by Fe3+ [23], [24], [25]. TiO2 doped with Co prepared by sol-gel method,
showed excellent degradation activity of methyl orange and methyl blue as a
result of reduced the band gap up to 2.98 eV, according to literature. As
reported by the author, the introduction of cobalt increases light absorption
capacity while reduces the surface area. The higher percentage of Cobalt leads
to a reduction in photocatalytic activity as Co provides a site for
recombination of generated electron-hole. Therefore, the optimal concentration
of Co is needed to enhance activity [26], [27], [28], [29]. Similar data was
reported that the cobalt is found as Co2+ state that replaces the Ti4+ ions and
consumed the effective charge carriers in TiO2 lattice [20], [22]. Similarly,
the same type of NPs was prepared using hydrothermal synthesis showed 97.2%
degradation of methylene blue with concentration-dependent activity [30]. In
another work, in which surfactant assistant Co-TiO2 was prepared and its
photocatalytic activity against acid red was observed. Cobalt suppressed the
recombination process by trapping electrons which are excited from the valence
band to the conduction band upon exposure to sunlight, consequently increasing
the photocatalytic activity of TiO2 [31]. Another work suggests that cobalt
occurs in CoO form in TiO2 lattice and hence responsible for increasing its
catalytic activity [20]. TiO2 doped with Co exhibited ferromagnetic
characteristics at room temperature that make it fit for spintronic [36]as well
as photocatalytic properties in the visible region [37]. Sulphur doped TiO2 NPs
were also reported like S-doped TiO2/ rectorite has shown 93.8% degradation
activity for metronidazole. The author attributed this activity to the reduction
in band gap, improving the surface area, and suppressing recombination [32]. In
another work, S-doped TiO2 was prepared and has shown degradation activity for
4-chlorophenol by reducing band gap to 2.31 Ev [33]. Similarly, Ramacharyulu et
al reported a reduction of band gap to 2.03 [34]. Devi. et al reported that S
enhanced photocatalytic activity by forming impurity level of S6+ ions under the
conduction band of TiO2 and suppressing the recombination owing to surface
modification SO42- ions [35]. Similarly, sulphur can also help to reduce the
bandgap as well as to divert strong absorption in the visible region [38].

In this present study, the photocatalytic degradation of Congo Red (CR) was
studied and examined using nanocatalyst TiO2/Fe/Co/S. The photocatalyst was
prepared using the sol-gel method by taking dopant to TiO2 ratio at 1% for Fe
and S and from 0.5% to 1.5% for Co. UV–Vis spectroscopy was used to monitor the
degradation activity of the photocatalyst. Various factors like the initial
concentration of CR, pH, amount of catalyst, reusability of catalyst, and
irradiation time were also investigated to optimize the degradation process. The
possible mechanism of Photocatalytic degradation of CR dye under visible light
was also presented.


SECTION SNIPPETS


MATERIAL

The source of Titanium (Ti) was titanium isopropoxide (TTIP), and Fe, Co, and S
sources were Ferric nitrate (Fe (NO3)3).9H2O, Cobalt Nitrate (Co (NO3)2·6H2O and
Thiourea respectively. Absolute ethanol 99.9%, acetic acid, and deionized water
were used as reaction medium and Congo Red dye as analyte. All the chemicals
were analytical grade and taken from the lab of the Department of Chemistry,
Government College University, Lahore.


CATALYTIC PREPARATION

TiO2 NPs co-doped with Fe, Co, and S were prepared using the


POWDER XRD ANALYSIS

XRD patterns of TiO2 co-doped with Fe, S, and Co by varying concentration of Co
is given in Fig. 3. The peaks at 2θ values 25.350, 37.950, 48.370, 54.130,
55.010, 62.980, 68.870, 70.300 and 75.390, and 76.170 were snug and their (hkl)
planes were corresponding to as (1 0 1), (0 0 4), (1 0 5), (2 1 1), (2 0 4),
(1 1 6), (2 2 0), (2 1 5) and (3 0 1) respectively. All these values are
unswerving with JCPD card number 84-1285 (anatase TiO2) [39], [40]. The peaks at
2θ values 44.170, 51.680, and 75.390 were


CONCLUSION

The nano-photocatalyst TiO2/Fe/Co/S was synthesized using the sol-gel method and
used as a photocatalyst for degradation of Congo Red, an organic dye. The dye
was degraded in about 1.2 h with percent degradation of 99.3. The anatase phase
of TiO2 was confirmed by XRD analysis, while the bandgap energy of pure TiO2 was
reduced after the addition of Fe, Co and S from 3.2 eV to 1.6 eV. Furthermore,
owing to extraordinary photocatalytic and optical characteristics it might be
efficiently exploited


DECLARATION OF COMPETING INTEREST

The authors declare that they have no known competing financial interests or
personal relationships that could have appeared to influence the work reported
in this paper.




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   This paper reports a clear outline of the synthesis and gas-sensing
   characteristics of pure ZnO, TiO2 nanoparticles (NPs) and ZnO/TiO2 (ZT)
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   co-precipitation method. The ZT nanocomposites have shown a combined phase
   structure of ZnO (wurtzite) and TiO2 (anatase) from X-ray diffraction. The
   absorbance of the samples was analyzed by UV–Vis Spectrophotometer and a
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   sensor is successfully realized for excellent selectivity, and quick
   response-recovery towards acetone detection. The sensing mechanism is
   ascribed to the composition, morphology, and enhanced oxygen adsorption sites
   revealing better performances than the pure ZnO and TiO2 NPs. The ZT NC of
   composition ZnO (0.60 at.%):TiO2 (0.40 at.%) is observed to enhance the
   acetone gas detection signal for the lowest sub micro level ppb concentration
   of 100 ppb (parts per billion) in comparison to the pure ZnO and TiO2
   nanoparticles. A superior response time (τres) of 13 s and recovery time
   (τrec) of 11 s are observed for ZT-1 sample with a high sensitivity response
   of 179 % is studied and therefore the nanocomposite material can be
   successfully utilized for acetone biomarker in diabetes.


 * THE MIL100(FE)/BATI<INF>0.85</INF>ZR<INF>0.15</INF>O<INF>3</INF>
   NANOCOMPOSITE WITH THE PHOTOCATALYTIC CAPABILITY FOR STUDY OF TETRACYCLINE
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   2023, Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy
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   The visible light-active nanocomposite with the photocatalytic capability was
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   Scanning Electron Microscopy with Energy Dispersive X-ray Analysis (SEM-EDX),
   Diffuse Reflectance Spectroscopy (UV–Vis DRS), and Fourier Transform
   Infra-Red (FT-IR) analysis were employed to characterize the synthetized
   BaTi0.85Zr0.15O3, MIL-100(Fe), and the MIL-100(Fe)/BaTi0.85Zr0.15O3 samples.
   As a result of the Scherrer equations, the size of grains for MIL-100(Fe),
   BaTi0.85Zr0.15O3, and MIL-100(Fe)/BaTi0.85Zr0.15O3 was estimated to be 40.81,
   12.00, and 22.70 nm, respectively. MIL-100(Fe), BaTi0.85Zr0.15O3, and
   MIL-100(Fe)/BaTi0.85Zr0.15O3 samples showed bandgap values of 1.77, 3.02, and
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   solutions, chemical oxygen demand (COD) data and tetracycline (TC)
   absorbencies were used to obtain the rate constants of 0.032 min−1 and
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 * UV ASSISTED SYNTHESIS OF FOLIC ACID FUNCTIONALIZED ZNO–AG HEXAGONAL
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   In order to verify the formation of y-TiO2, CdS and y-TiO2/CdS
   heterojunction, XRD analysis is used to test the samples. As depicted in Fig.
   1(a), the nine dominant peaks at 2θ values of 25.3°, 37.7°, 48.1°, 53.7°,
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   (2 0 0), (2 1 1), (1 0 5), (2 0 4), (1 1 6), (2 2 0) and (2 1 5) lattice
   planes, respectively, revealing that all prepared y-TiO2 are in
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   Show abstract
   
   To improve the degradation efficiency of g-C3N4 (CN), transition metal
   elements (Fe and Co) were doped into CN. A novel Co, Fe co-doped CN
   (Co/Fe-CN) photocatalysts with small size and irregular flake structure were
   successfully prepared by thermal polymerization of melamine. Co/Fe-CN has a
   large specific surface area (55.76 m2/g), which provides more adsorption
   sites and reaction sites for the activation of peroxymonosulfate (PMS). Good
   visible light response performance (474 nm) and suitable band gap (2.83 eV)
   ensure that it could be excited by visible light. The active species of •O2-,
   1O2, •OH and SO4•- could be stably produced in Co/Fe-CN/Vis/PMS system with
   appropriate redox potential. Meanwhile, Co and Fe elements doped in CN also
   could effectively activate PMS and promote the generation of active species.
   Besides, the continuous generation of photogenerated electrons promoted the
   cycling of Co3+/Co2+ and Fe3+/Fe2+, and further enhanced the degradation
   efficiency of Co/Fe-CN/Vis/PMS towards Levofloxacin (LVFX). LVFX could be
   rapidly removed, reaching 92.1% within 50 min under visible light
   illumination, and the kinetic rate constant of LVFX was 0.0638 min-1. The
   quenching experiments verified that the 1O2 was the main active species in
   the reaction process. The cycling experiments revealed that the
   Co/Fe-CN/Vis/PMS system had favorable stability and applicability. This work
   provides a simple preparation method to fabricate bimetallic co-doped CN for
   the enhancement of degradation rate in the Photocatalyst/Vis/PMS system.


 * PROCESS MONITORING OF PHOTOCATALYTIC DEGRADATION OF 2,4-DINITROTOLUENE BY
   AU-DECORATED FE<INF>3</INF>O<INF>4</INF>@TIO<INF>2</INF> NANOPARTICLES:
   SURFACE-ENHANCED RAMAN SCATTERING METHOD
   
   2022, Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy
   Citation Excerpt :
   
   Le et al. reported C-, N-, and S-modified TiO2, which had a lower
   recombination rate and exhibited enhanced photocatalytic activity under
   visible light irradiation [9]. Imran et al. reported that Fe, Co, and S
   co-doped TiO2 showed enhanced photocatalytic activity for Congo red dye
   degradation [10]. Yan et al. reported photocatalytic nanocomposite membranes
   based on Au-TiO2 for visible light degradation of tetracycline aqueous
   solution [11].
   
   Show abstract
   
   Recently, the degradation and detection of 2,4-dinitrotoluene (2,4-DNT)
   capable of producing 2,4,6-trinitrotoluene (TNT) for environmental and human
   health risks have been developed. We prepared photoresponsive Au-decorated
   Fe3O4@TiO2 nanoparticles (Fe3O4@TiO2-Au NPs) under sunlight simulated Xe lamp
   irradiation. The photodegradation process of 2,4-DNT by Fe3O4@TiO2-Au NPs was
   successfully monitored by surface-enhanced Raman scattering (SERS). Since
   SERS monitoring shows intrinsic information about the molecular structure, it
   was possible to predict the photodegradation of 2,4-DNT. The 2,4-DNT
   photodegradation mechanism based on two-dimensional correlation spectroscopy
   (2D-COS), which provides very beneficial information for a deeper
   understanding of systems, has been identified. We confirmed that
   Fe3O4@TiO2-Au NPs can be widely used in organic pollutant degradation under
   sunlight. Furthermore, the combination of SERS based process monitoring and
   2D-COS can be a convincing analytical technique for photodegradation studies
   of organic pollutants.

View all citing articles on Scopus


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 * Research article
   
   
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