Reaction Kinetics, Mechanisms and Catalysis (2022) 135:2797–2812

https://doi.org/10.1007/s11144-022-02273-z

Solution combustion synthesis of β‑Cu2V2O7 nanoparticles:

photocatalytic degradation of crystal violet under UV
and visible light illumination

Dina Moussaid1 · Khadija Khallouk1,4 · Redouan El Khalfaouy2 ·

Fatin Tagnaouti Moumnani1 · Abdelhak Kherbeche1 · Abdellatif Barakat3,4

Received: 25 June 2022 / Accepted: 21 July 2022 / Published online: 25 July 2022
© Akadémiai Kiadó, Budapest, Hungary 2022

Abstract
β-Cu2V2O7 nanoparticles were prepared using a solution-combustion method using
two different fuels, which are: Urea and Glycine. The as-prepared catalysts were
characterized using X-ray diffraction, Fourier transform infrared spectra, scanning
electron microscopy, Brunauer–Emmett–Teller Method, and UV–Vis diffusive
reflectance spectroscopy. The photocatalytic activity of copper vanadate was inves-
tigated by degradation of cationic dye crystal violet in an aqueous solution under
UV and visible light irradiation. The effect of selected parameters such as catalyst
mass, dye concentration, and solution pH on the catalytic performances has been
discussed. On the other hand, the reuse tests of β-Cu2V2O7 displayed high-perfor-
mance stability after five cycles.

Keywords β-Cu2V2O7 · Solution combustion synthesis · Urea · Glycine ·

Photocatalysis · Crystal violet

* Khadija Khallouk
khadija.khallouk@usmba.ac.ma
1
Laboratory of Materials, Processes, Catalysis and Environment, High School of Technology,
Sidi Mohamed Ben Abdellah University, BP 2427 Fez, Morocco
2
Laboratory of Natural Substances, Pharmacology, Environment, Modeling, Health and Quality
of Life, Polydisciplinary Faculty of Taza, Sidi Mohamed Ben Abdellah University,
BP 1223 Taza, Morocco
3
IATE, Montpellier SupAgro, INRAE, Université de Montpellier, 2, Place Pierre Viala,
34060 Montpelier, France
4
Mohammed VI Polytechnic University (UM6P), Hay Moulay Rachid, 43150 Ben Guerir,
Morocco

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2798 Reaction Kinetics, Mechanisms and Catalysis (2022) 135:2797–2812

Introduction

Environmental problems related to water pollution have recently attracted more

attention by the researchers. One of the main pollution sources comes from
wastewater containing dyes discharged from textiles, foodstuffs, and leather
industries. The presence of colored organic compounds in dye-bearing effluents
generally reduces sunlight transmission, and hence affects photosynthesis and
harms aquatic ecosystems [1]. The discharge of these colored dyes in the ecosys-
tem without a preliminary treatment step creates severe environmental pollution
problems [2].
Various conventional physicochemical methods were proposed by scientific com-
munities including adsorption [3], chemical precipitation [4], coagulation-floccula-
tion [5], chemical and electrochemical oxidation [6], reverse osmosis [7] etc. How-
ever, all these treatments mentioned above have never provided a complete solution
for wastewater treatment because they have numerous limitations e.g., they require
high cost, and they have a major flaw of simple transferring the pollutants from one
phase to another rather than destroying them, which consequently leads to second-
ary pollution. Hence, there is a serious necessity to develop treatment methods that
are more effective in destructing dyes from wastewater.
Photocatalysis has received extensive attention as a promising way to solve
pollution problems [8]. This process offers many advantages, particularly its effi-
ciency, its feasibility and cost-effectiveness compared to other traditional meth-
ods. Moreover, it is a clean process that uses renewable energy and supports the
sustainable development approach [9, 10].
There are many Semiconductors used in photocatalysis such as CdS [11], ­SnO2
[12, 13], ­BiVO4 [14–16], but ZnO and ­TiO2 still the most famous of them [17–19].
They have been widely used, proved to be appropriately photocatalytic candidate
and they are ranked among the best photocatalysts, because of their photostability
in air and water, they do not release toxic elements. As titanium is an element rela-
tively abundant, the cost of ­TiO2 is not too high, at least for some applications. They
have a wide direct bandgap (Eg) width (3.37 eV) [20] and (3.20 eV) [21, 22].
Among these novel photocatalysts, the vanadate is an important functional
material with a wide range of applications. It has attracted considerable interest
for its well photocatalytic property and many studies have been reported about
their preparations and photocatalytic activities [23–25].
Transition metal vanadates, such as copper vanadate [26–28], zinc vanadate
[29], cobalt vanadate [30] and iron vanadate [31] as a considerable class of mate-
rials, have been intensively pursued in recent years because of their applications
in optical devices [26], catalysis [29, 32, 33], paramagnetic materials [34–36],
lithium batteries [37–40] and photocatalysis [23, 25].
Copper vanadate is a typical material for vanadate, it is widely used as anti-
bacterial additive, lithium-ion batteries, ion exchange materials, electrochemical
supercapacitor, and photocatalyst. Depending on the molar ratio 1:1, 2:1, and 3:1
of the CuO and ­V2O5, copper (II)-based vanadate compounds have the different
crystal structures such as ­CuV2O6, ­Cu2V2O7, and ­Cu3V2O8.

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Reaction Kinetics, Mechanisms and Catalysis (2022) 135:2797–2812 2799

For these different advantages, we believe that solution combustion synthesis will
significantly improve the photocatalytic properties of our β-Cu2V2O7 photocatalyst
material. This method was adopted to prepare β-Cu2V2O7 using two fuel sources
which are: urea and glycine. The photocatalytic performances of the as-prepared
materials were evaluated by photocatalytic degradation of an aqueous crystal violet
solution. The potential use of β-Cu2V2O7 as a photocatalytic material, as well as
the mechanism of enhancing the photocatalytic activity under UV and visible light
illumination were also covered in this study through the use of a panoply of analyses
namely; XRD, SEM–EDS, FTIR, BET and DRS.

Materials and methods

Synthesis of β‑Cu2V2O7 photocatalyst

NH4VO3 (Sigma Aldrich) and Cu (­ NO3)2.3H2O (Sigma Aldrich) were used as vana-
dium and copper precursors. Urea (­ CH4N2O) and Glycine (­ C2H5NO2) were used as
fuels agents. All chemical products are used without further purification.
The synthesis of β-Cu2V2O7 photocatalyst was conducted by a solution-com-
bustion technique. Copper pyrovanadate samples were prepared using two different
fuels. Initially, two solutions of equal volume containing Cu ­(NO3)2.3H2O (3.44 g)
and ­NH3VO4 (1.11 g) were dissolved in 100 mL of Deionized water (DI). Subse-
quently, each of the fuels investigated (0.15 g of glycine, and 0.17 g of urea,) was
added separately to each prepared solution. The two mixtures prepared were stirred
softly to obtain a homogeneous solution both solutions were heated and evaporated
at about 100 °C to form a dark green gel. Both gels swelled and became foamy and
were quickly placed in the oven at 500 °C for 1 h, resulting the formation of two
materials as brown powders. The two products were collected for characterization.

Photocatalytic runs for crystal violet degradation

Crystal violet dye (Sigma-Aldrich) was used for photocatalytic testing. The photo-
catalytic performance of the prepared β-Cu2V2O7 to degrade Crystal violet dye was
examined in a quartz reactor (250 mL) equipped with four ultraviolet (UV) lamps
(17 W 24 Inch T8 Fluorescent tube) for UV illumination tests, and a 100 W m − 2
Xe lamp (λ > 400 nm) as the visible light source for Visible light illumination
Tests. A suspension containing 200 ml of 10 ppm of Crystal violet and 1 g/L of the
β-Cu2V2O7 catalyst is continuously stirred at 750 rpm and air-bubbled at room tem-
perature and under UV illumination. During the photocatalytic reaction, samples of
5 mL were collected from the solution, separated by centrifugation at 5000 rpm for
5 min and analyzed by UV–Vis spectroscopy using J.P. SELECTA, S.A. VR-2000
spectrophotometer at the maximum absorbance wavelength 586 nm for Crystal vio-
let [41, 42] to obtain the remaining concentration.
Adsorption tests of Crystal violet over β-Cu2V2O7 in the dark, as well as Crys-
tal violet photolysis under UV and visible light illumination, were also evaluated

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2800 Reaction Kinetics, Mechanisms and Catalysis (2022) 135:2797–2812

under the same conditions. The experimental setup used for photocatalytic tests was
reported in [21].

Characterization techniques

X-ray diffraction patterns (XRD) were recorded by the diffractometer

(PanalyticalX′Pert Pro) to characterize and identify the crystal structure and phase
of the synthesized CVO. The instrument has a detector running at 40 kV and 30 Ma
and uses Cu ­Kα (λ = 1.540598 Å) radiation. The average crystallite sizes (D) of the
prepared samples were calculated using the following the Scherrer equation [43]:
K𝜆
D=
(FWHM × cos 𝜃)
Here K = 0.9 is the shape factor, λ is the X-ray radiation wavelength, θ is the diffrac-
tion angle, and FWHM is the full width at half maximum of all characteristic peaks
for β-Cu2V2O7 ­structure.
Solid-state Fourier transform infrared spectra (FTIR) of β-Cu2V2O7 was recorded
using the Attenuated Total Reflectance (ATR–FTIR) on Bruker spectrophotom-
eter model Vertex 70 with a range of 400–4000 ­cm−1, 16 scans and a resolution of
4 ­cm−1.
The morphology of the samples and the identification of the elemental composi-
tion of the materials were determined using Scanning Electron Microscopy (SEM)
and Energy Dispersive X-Ray Analysis (EDX).
The specific surface areas were determined from the nitrogen adsorption/desorp-
tion isotherms at 77 K using the BET (Brunauer–Emmett–Teller) method.
UV–Vis diffuse reflectance spectra (DRS) for all samples were recorded using
UV–Vis spectrophotometer (PerkinElmer Lambda 950 instrument) using T ­ iO2 as
the reference sample in the range of 200–800 nm. Bandgap values were estimated
from Tauc plots calculated from the optical absorption spectra [44].

Results and discussions

X‑ray diffraction patterns

The obtained products; urea and glycine assisted ­Cu2V2O7 material were analyzed
using XRD pattern. The XRD results in Fig. 1 confirm, for both products, the pres-
ence of characteristic peaks of β-Cu2V2O7 (Ziesite) phase structure according to
the reference data PDF # 026-0569, which has been reported to have a monoclinic
crystal structure with the space group C2/c (15). The peaks around the 12° 2θ posi-
tion correspond to the vanadium oxide phase which shows the presence of this phase
especially in the glycine assisted β-Cu2V2O7 material [45].
In fact, from the findings, combustion synthesis can produce single-structured
photocatalytic materials at low temperatures (without the need for calcination),

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Reaction Kinetics, Mechanisms and Catalysis (2022) 135:2797–2812 2801

Fig. 1  X-ray diffraction patterns of the synthesized β-Cu2V2O7@Urea compared to β-Cu2V2O7@Glycine

materials

compared to almost all other methods that require additional thermal treatment,
which can be considered as a cost-effective advantage for this synthesis process.
Moreover, during the combustion process, the structure can undergo some
changes such as micro-deformations, internal distortions, etc. In this regard, the
microstrain and crystallite size of the two prepared materials were examined, as
shown in Fig. 2, by applying the Williamson-Hall method as described previously
[46, 47].
According to these results, we can observe that the crystallites size, for the
product with urea, is approximately 431.1 ± 322.7 nm, values that remain a lit-
tle high compared to those of the product with glycine that presents a size around
63.2 ± 20.6 nm, being characterized by a relatively low microstrain (0.03%) com-
pared to that of the material with urea (0.21%).

Fourier transform infrared spectra

The observed FT-IR spectrum recorded for both synthesized β-Cu2V2O7 mate-
rial using urea and glycine, is displayed in Fig. 3. According to the spectrum, the
absorption peaks manifested around position 1618 ­cm−1 correspond to the vibra-
tional modes of the bound water molecule, including the stretching and the bend-
ing modes of H–O and H–O–H, respectively. The bands occurring between 1000
and 800 ­cm−1 are mainly due to the stretching vibrations of the V=O mode and the
antisymmetric stretching vibrations of V–O–V. Also, the band appeared towards the
632 ­cm−1 position corresponds to the symmetric stretching vibration of the triply
coordinated oxygen of β-Cu2V2O7. As well, the absorption bands observed between
600 and 500 ­cm−1can be attributed to the Cu–O stretching vibration, confirming the
formation of copper vanadate compound [48–51].

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2802 Reaction Kinetics, Mechanisms and Catalysis (2022) 135:2797–2812

Fig. 2  Williamson–Hall plots for the synthesized β-Cu2V2O7 material using urea and glycine fuel agents

Morphology and elemental composition

Figure 4 shows the morphology of the β-Cu2V2O7 material synthesized with dif-
ferent fuel agents. As shown in the micrographs, for both products, it is clearly
seen that the morphology is not homogeneous enough. The observed morphol-
ogy for the glycine-assisted β-Cu2V2O7 material consists of irregular and elon-
gated nano-spheres with sizes ranging from 40 to 600 nm. For the urea assisted

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Reaction Kinetics, Mechanisms and Catalysis (2022) 135:2797–2812 2803

Fig. 3  FT-IR spectrum of the synthesized β-Cu2V2O7 @Urea compared to β-Cu2V2O7 @Glycine

Fig. 4  SEM images of the synthesized β-Cu2V2O7 material at different magnifications; a with urea and b
with glycine

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2804 Reaction Kinetics, Mechanisms and Catalysis (2022) 135:2797–2812

Table 1  Crystallite size, surface BET and elemental composition of mixed copper vanadium oxides
Sample Crystallite size (nm) BET surface area EDX elemental compo-
­(m2/g) sition (% wt)
Cu V O

β-Cu2V2O7 @Urea 431.1 ± 322.7 39 41 37 16

β-Cu2V2O7 @Glycine 63.2 ± 20.6 41 39 40 17

Fig. 5  BET of the synthesized β-Cu2V2O7@Urea material compared to β-Cu2V2O7@Glycine

β-Cu2V2O7 material, the grains have well-defined edges and have a relatively
large size distribution ranging from 50 to 900 nm [52].
The particles distribution of both products suggests and confirms that the com-
bustion synthesis process can provide materials with a higher specific surface
area [53]. The elemental composition is performed using EDX analysis. The two
obtained results on (Table 1) confirm the presence of copper, vanadium and oxygen.

Brunauer–Emmett–Teller method

The BET surface area of the prepared mixed copper vanadium oxides were 39 m ­ 2/g
2
and 41 ­m /g for β-Cu2V2O7@Urea and β-Cu2V2O7@Glycine and its pore volume
was 0.001609 ­cm3/g. The nitrogen sorption isotherms of the two samples were type
III, displaying a type H3 hysteresis loop in the relative pressure range of 0.83–0.93
and 0.94–0.98 for β-Cu2V2O7@Urea and β-Cu2V2O7@Glycine, and plateaus in the
adsorption branches (Fig. 5), indicative of its intergranular porosity due to the for-
mation of aggregates of plate-like particles forming slit-like pores. We note that the
adsorbed volume remained low until P/P0 equaled 0.83 and 0.98 for β-Cu2V2O7@
Urea and β-Cu2V2O7@Glycine, which corresponds to the constitution of a molec-
ular monolayer. The adsorption of ­N2 was carried out progressively to generate a
monolayer covering the entire external surface of the CuVO pores. By comparing

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Reaction Kinetics, Mechanisms and Catalysis (2022) 135:2797–2812 2805

the BET results, we remark that combustion is a promising way to synthesize a

mixed oxide of copper vanadium with a large surfaces area, while fuel has no sig-
nificant influence on the surface area and pore volumes.

Diffuse reflectance spectra

The obtained DRS spectra of the synthesized β-Cu2V2O7 photocatalyst presented in

(Fig. 6A), shows a wide region of absorption from 300 to 550 nm for both synthe-
sized materials.
Direct band gaps of the of β-Cu2V2O7 nanoparticles were determined using Tauc
plot in (Fig. 6B), where in (αhν)2 is a function of the photon’s energy. where h is the
Planck’s constant, t is the frequency of vibration, a is the absorption coefficient, Eg
is the bandgap, A is the proportional constant, The linear fit intersection with the
energy axis determines the band gap energy (Eg) as presented in (Fig. 6B).
As shown in (Fig. 6B), each of the synthesized catalysts (β-Cu2V2O7@Urea and
β-Cu2V2O7@Glycine) have one linear fit which indicates an energy of bandgap of
1.98 eV and 2.02 eV, which is the primary evidence for the both materials to be
active at visible light for the photocatalytic application.

Photocatalytic examination under UV illumination

(Fig. 7) exhibits the degradation of Crystal violet onto β-Cu2V2O7@Urea and

β-Cu2V2O7@Glycine as photocatalysts. All experiments were carried out using
1 g/L of catalysts and10 mg/L of Crystal violet as initial concentrations. As shown
in Fig. 7, Crystal violet displays a very low conversion rate in the case of photolysis
throughout the duration of the test (130 min), which confirms that UV illumina-
tion alone cannot degrade Crystal violet under current conditions. The discoloration

a b 120
1,2 β-Cu2V2O7 @Urea β-Cu2V2O7@Urea
β-Cu2V2O7 @Glycine β-Cu2V2O7@Glycine
100
1,0

80
0,8
Absorbance

60 Eg=1,98 eV
0,6

0,4 40

0,2 20
Eg=2,02 eV
0,0 0
300 400 500 600 700 800 2,0 2,5 3,0 3,5 4,0 4,5 5,0
Wavelenght (nm)

Fig. 6  A UV–Vis DRS and B the plot of (αhʋ)2 versus hʋ of the β-Cu2V2O7@urea compared to
β-Cu2V2O7@Glycine

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2806 Reaction Kinetics, Mechanisms and Catalysis (2022) 135:2797–2812

Fig. 7  Adsorption and photodegradation of Crystal violet dye over β-Cu2V2O7 catalyst under optimal
conditions (Reaction time 130 min; C0 = 10 mg ­L−1; catalyst addition 1 g ­L−1) under UV light illumina-
tion

obtained by β-Cu2V2O7 (light on) is slightly comparable to Crystal violet adsorption

onto β-Cu2V2O7 material confirming its high adsorption capacity.

Effect of operational parameters

(Fig. S1 in the Supporting information) investigated the effect of initial pH on the

efficiency of crystal violet degradation. The initial pH of the solution is an important
factor that can influence the efficiency of the β-Cu2V2O7 photocatalyst by modify-
ing its surface properties. The pH was adjusted using 0.1 M HCl or NaOH solutions
with a mass of β-Cu2V2O7 of 1 g/L and a concentration of crystal violet solution of
10 mg/L. It was observed from Fig. S1 in Supplementary information at acidic pH,
that the crystal violet degradation efficiency decreased compared to the initial pH
(pHi = 6) for both catalysts β-Cu2V2O7@Urea and β-Cu2V2O7@Glycine. However,
at pH 10, it remained almost the same. This result, due to the increase of hydroxyl
radicals at alkaline pH and at acidic pH, the agglomeration of the particles decreases
the adsorption of dye and the absorption of photons [45].
To investigate of the β-Cu2V2O7 amount effect on Crystal violet degradation effi-
ciency, a series of experiments were carried out by changing β-Cu2V2O7 amount
from 0.5 to 3 g/L in a Crystal violet solution concentration of 10 mg/L and at initial
pH value at room temperature. (Fig. S2 in the Supporting information) shows, as
β-Cu2V2O7 amount augmented, the crystal violet removal efficiency increased and
reaches 98% after 130 min using 1 g/L, and a further increase in catalyst amount
caused a decrease of the removal efficiency. As reported in other papers, this phe-
nomenon can be explained by the fact that the increase in the mass of the photocata-
lyst increases the number of active sites available on the surface of the catalyst [45].
Consequently, the concentration of hydroxyl and superoxide radicals increases.

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Reaction Kinetics, Mechanisms and Catalysis (2022) 135:2797–2812 2807

(Fig. S3 in the Supporting information) presents the effect of Crystal violet

solution concentration using 1 g/L of β-Cu2V2O7 at initial pH. It can be observed
clearly with raised Crystal violet concentration from 10 to 40 mg/L, the degrada-
tion efficiency remains almost the same for β-Cu2V2O7@Glycine, the dye was found
to be almost completely decolorized on irradiation for 130 min. While for theβ-
Cu2V2O7@Urea material, at higher concentration, the degradation was found to be
less. This may be because as the concentration of dye increases the catalyst particles
adsorb more and more dye. Hence, the UV light does not reach the catalyst surface
and reduce the activation rate of β-Cu2V2O7 [54] which limit the generation of OH·
radicals. At higher concentration, the light travels up to a smaller distance; because
high Crystal violet concentration could decrease UV penetration and reduce the acti-
vation rate of β-Cu2V2O7 which limit the generation of ­OH− radicals [55].
In comparison with literature, β-Cu2V2O7 synthesized via the combustion route
appeared to be an enhanced catalyst for dye degradation under UV illumination
(Table 2).
Fig. S4 in the Supporting information shows the degradation efficiency of Crystal
violet (10 mg/L) after 130 min of UV light illumination, where the same percentage
of Crystal violet conversion is observed after each cycle. As a result, β-Cu2V2O7
maintains its stability after sequential cycles.

Photocatalytic examination under visible light illumination

The band gap of β-Cu2V2O7 is around 2.0 eV which is suitable for visible light
absorption [56]. Since the degree of utilization of visible light is one of the indi-
cators to measure the performance of photocatalysts, we have systematically tested
the photocatalytic ability of β-Cu2V2O7 under visible light. Fig. S5 in the Support-
ing information exhibits the degradation of Crystal violet onto β-Cu2V2O7@Urea
and β-Cu2V2O7@Glycine as photocatalysts. All experiments were carried out using
1 g/L of catalysts and 10 mg/L of Crystal violet as initial concentrations. As shown
in Fig. S5, Crystal violet displays a very low conversion rate in the case of photoly-
sis throughout the duration of the test (130 min), which confirms that Visible light
illumination alone cannot degrade Crystal violet under current conditions. In fact,
after activating visible illumination, both materials showed effective photocatalytic
activity under visible illumination for crystal violet, reaching approximately 86%
for β-Cu2V2O7 @Urea and 82% for β-Cu2V2O7@Glycine as shown in the figure. In
this case, the β-Cu2V2O7 photocatalyst, with its narrow band gap, favors the optical
absorption capacity in the visible range.

Conclusion

This study explored a new and simple approach for photocatalytic crystal violet
degradation using mixed copper vanadium oxides synthesized via a simple solution
combustion process using two different fuels. It is suggested that combustion may
be a promising way to synthesize a mixed oxide of copper vanadium with a large

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Table 2  Comparison between our work and other photocatalysts for dye degradation
Photocatalyst Dye Concentration Degradation Degrada- Synthesis method Type of lightning Reference
of the solution percentage tion time
(ppm) (%) (min)

β-Cu2V2O7 Crystal violet 10 98/86 130 Combustion method using Urea as fuel UV/Visible light Present work
95/82 Combustion method using Glycine as
fuel
BiVO4 Methylene blue 10 50–60 120 Hydrothermal UV [57]
Ag/SmVO4 Rhodamine B 10 97 240 Impregnation Visible light [58]
BiOI/Ag3VO4 Triphenylmethane 25 80 180 Solvothermal method followed by the Visible light [59]
chemical precipitation
ZnO: ­TiO2 Methyl blue 10 90 75 Sol–gel Visible light [60]
Pd-doped ­TiO2 Methyl blue/methyl orange 20 87.8 180 Sol–gel UV [61]
Cd-doped ZnO Methylene blue 10 85 210 Sol–gel Visible light [38]
Reaction Kinetics, Mechanisms and Catalysis (2022) 135:2797–2812
Reaction Kinetics, Mechanisms and Catalysis (2022) 135:2797–2812 2809

specific surface area; however, the fuel has no significant influence on the specific
surface area and the pore volumes.
The efficiency of dye removal processes was affected by the initial concentra-
tion of the pollutant, pH and catalyst amount. As a result, increasing pH led to an
increase in the photocatalytic removal efficiency, while the increase of dye initial
concentration decreased the conversion efficiency.
The narrow band gap of both synthesized catalysts (β-Cu2V2O7@Urea and
β-Cu2V2O7@Glycine) is the primary evidence for the two materials to be active in
visible light for the photocatalytic application. The β-Cu2V2O7 material obtained
using urea or glycine showed good catalytic behavior for the degradation of the stud-
ied dye under UV and visible light illumination.

Supplementary Information The online version contains supplementary material available at https://​doi.​
org/​10.​1007/​s11144-​022-​02273-z.

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