Construction of 1T-MoS2quantum dots-interspersed (Bi1-xFex)VO4heterostructures for electron transport and photocatalytic properties

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Construction of 1T-MoS₂quantum dots-

interspersed (Bi_1ꢀxFe_x)VO₄heterostructures for

electron transport and photocatalytic properties†

Cite this: RSC Adv., 2021, 11, 13105

a

ab

Naveed Akhtar Shad,^c

*

Muhammad Munir Sajid,

Haifa Zhai,

Muhammad Shaﬁque,^dAmir Muhammad Afzal,^eYasir Javed,^fSadaf Bashir Khan,

g

Nasir Amin^cand Zhengjun Zhang

h

The present study reports trigonal phase molybdenum disulﬁde quantum dots (MoS₂/QDs)-decorated (Bi_1ꢀxFe_x)

VO₄composite heterostructures. Initially, (Bi_1ꢀxFe_x)VO₄heterostructure nanophotocatalysts were synthesized

through the hydrothermal method decorated with 1T-MoS₂via a sonication process. 1T-MoS₂@(Bi_1ꢀxFe_x)VO₄

heterostructures were characterized in detail for phase purity and crystallinity using XRD and Raman

spectroscopy. The Raman mode evaluation indicated monoclinic, mixed monoclinic-tetragonal and

tetragonal structure development with increasing Fe concentration. For physiochemical properties, SEM, EDX,

XPS, PL, EPR, UV-visible and BET techniques were applied. The optical energy band gaps of 1T-

MoS₂@(Bi_1ꢀxFe_x)VO₄heterostructures were calculated using the Tauc plot method. It shows a blue shift

initially within

a monoclinic structure then a red shift with an increase of Fe concentration. 1T-

MoS₂@(Bi₄₀Fe₆₀)VO₄with 2 wt% of 1T-MoS₂-QDs carrying a mixed phase exhibited higher photocatalytic

activity. The enhanced photocatalytic activity is attributed to the higher electron transportation from (Bi_1ꢀxFe_x)

VO₄surface onto 1T-MoS₂surface, consequently blocking the fast electron–hole recombination within

(Bi_1ꢀxFe_x)VO₄. 1T-MoS₂co-catalyst interaction with (Bi_1ꢀxFe_x)VO₄enhanced the light absorption in the visible

region. The close contact of small 1T-MoS₂-QDs with (Bi_1ꢀxFe_x)VO₄develops a high degree of crystallinity,

with fewer defects showing mesoporous/nanoporous structures within the heterostructures which allows

more active sites. Herein, the mechanism involved in the synthesis of heterostructures and optimum

conditions for photocatalytic degradation of crystal violet dye are explored and discussed thoroughly.

Received 30th January 2021

Accepted 21st March 2021

DOI: 10.1039/d1ra00807b

rsc.li/rsc-advances

substantial solution to these two problems.³These problems

are somewhat overcome by the advanced oxidation process

(AOP) with the advancement of nanotechnology.^4,5The AOP is

1. Introduction

Energy shortage and water pollution are major threats world-

wide owing to limited fossil fuel resources and growing

consumption.^1,2Producing abundant and clean energy is the

the most environment-friendly technique and used to remove

recalcitrant organic contaminants not easily treatable via

traditional methods due to their chemical stability.^6,7The

concept of AOPs for water and wastewater treatment was

primarily discovered in 1980.⁸In the AOP process, reactive

oxygen species (ROS) are generated including singlet oxygen

(O), ozone (O₃), hydrogen peroxide (H₂O₂), hydroxyl radical

(OHc), and others species.^7,9Among them, OHc is a highly

oxidizing agent with a potential of 2.8 eV and unstable as

compared to other oxidizing agents such as O, O₃, and H₂O₂,

possessing oxidation potential of 1.67, 2.07 and 1.77 eV,

respectively.¹⁰Photocatalysts are materials that produce

strong oxidizing agents, i.e., O, O₃, and OHc.¹¹In AOPs, pho-

tocatalysts or semiconductor materials can directly change

solar energy into chemical energy which is a very facile method

for renewable energy production and environmental remedi-

ation.^12,13Photocatalytic degradation has gained much atten-

tion in recent years as it oﬀers a stable, clean and nontoxic

direction to lessen environmental pollution.^14,15Common

^aHenan Key Laboratory of Photovoltaic Materials, School of Physics, Henan Normal

University, Xinxiang 453007, China. E-mail: m.munirsajid476@gmail.com;

haifazhai@126.com

^bCollege of Materials Science and Engineering Henan Normal University, China

^cDepartment of Physics, Government College University, Allama Iqbal Road,

Faisalabad, 38000, Pakistan

^dDepartment of Microbiology, Government College University, Allama Iqbal Road,

Faisalabad, 38000, Pakistan

^eThe State Key Laboratory for New Ceramics & Fine Processing, School of Materials

Science & Engineering, Tsinghua University, Beijing, 100084, China

^fDepartment of Physics, University of Agriculture, Faisalabad, 38000, Pakistan

^gDepartment of Physics and Astronomy, Graphene Research Institute, Sejong

University, Seoul 05006, Korea

^hAdvanced Key Laboratory for New Ceramics, School of Materials Science

&

Engineering, Tsinghua University, Beijing, 100084, China

† Electronic supplementary information (ESI) available. See DOI:

10.1039/d1ra00807b

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semiconductors used as photocatalysts (with bandgap) such as MoS₂) and the second named as hexagonal phase (2H-MoS₂)

ZrO₂(3.87 eV),¹⁶ZnS (3.6 eV),¹⁷SnO₂(3.54 eV),¹⁸ZnO (3.4 eV),¹⁹with an optical energy bandgap ranging from 1.2 to

TiO₂(3.3 eV),²⁰Fe₂O₃(2.67 eV),²¹CdS (2.42 eV),²²BiVO₄(2.41 1.9 eV.^{42,47,49–51}

eV),^23,24and PbS (0.28 eV)²⁵have been extensively studied, but

Inspired by these concepts, 1T-MoS₂quantum dots-

their performance is restricted due to either broad bandgap interspersed in (Bi_1ꢀxFe_x)VO₄, hereaer 1T-MoS₂@(Bi_1ꢀxFe_x)

which is functional under UV-light which is only 5% of the VO₄heterostructures, were prepared through a sonication-

solar spectrum or unsuitable band edge energy.^26,27Therefore, assisted hydrothermal method. The synthesized 1T-MoS₂@(-

there is an urgent need to develop such an eﬃcient and Bi_1ꢀxFe_x)VO₄heterostructures exhibit excellent visible light-

eﬀective photocatalyst that can harvest visible light, which is dependent photocatalytic activity. Photoluminance study

55% of the solar spectrum, and yield optimum response for revealed excellent controlled electron–hole transfer activity. The

practical and commercial applications. Hence the main goal of 1T-MoS₂@(Bi_0.40Fe_0.60)VO₄heterostructures with 2.0 wt% of 1T-

this work is to extend the visible light absorption capability of MoS₂loading with mixed phase exhibited optimal enhanced

photocatalysts.

photocatalytic response, as well as good stability and

Semiconducting material-based photocatalytic schemes reusability.

are attracting a lot of attention recently because they allow

the fast and eﬀective decomposition of organic pollutants.²⁸

2. Experimental details

2.1 Preparation of catalysts

In this context, transition metal oxide semiconductors have

gained much interest owing to diverse physicochemical

properties and applications including good stability, cost- In a typical method, rst, we prepared 1T-MoS₂by taking 6.24 g

eﬀectiveness, high energy density, catalysts for degradation of thiourea (CH₄N₂S) and 4.84 g of sodium molybdate (NaMoO₄)

of organic pollutants, gas sensors and battery applica- and making solutions of them in 30 ml deionized H₂O sepa-

tions.^27,29,30Among these various transition metal oxides, rately named solution A and solution B. Then solution A was

bismuth vanadate (BiVO₄) and ferric vanadate (FeVO₄) are mixed with solution B dropwise under continuous stirring for

potential candidates for light-driven photocatalysts due to 30 min. Ethanol (C₂H₅OH) was added to this mixture under

narrow band gaps ranging from 2.0 to 2.72 eV due to their a further 30 min of stirring. The as-formed mixture was trans-

remarkable chemical stability and catalytic activity, minimal ferred to a 200 ml Teon-lined stainless steel autoclave and put

ꢁ

optical damage and commercial cost-eﬀective avail- into a muﬄe furnace for hydrothermal treatment at 180 C for

ability.^13,24,31-33Both BiVO₄and FeVO₄possess a suitable 22 h. The resultant products were centrifuged for 2 h at

energy band in the visible light range indicating tremendous 10 000 rpm to isolate the supernatant by centrifugation.^49,52The

photocatalytic and electrochemical applications.^26,33–35From supernatant was 1T-MoS₂nanostructure. This synthesis of 1T-

a literature survey, it is observed that in scheelite ABO₄the B MoS₂-QDs could be formulated as explained through the

site is partially lled by substituted material.³⁶Taking the following equations:

same idea in monoclinic BiVO₄, Bi³⁺is 8-coordinated with

˚

CH₄N₂S + 2H₂O / 2NH₃+ H₂S + CO₂

(1)

ionic radius of 1.17 A, and the ionic radius of 4-coordinated

V⁵⁺is 0.355 A. FeVO₄has two diﬀerent crystal structures of

37

˚

2Na₂MoO₄$2H₂O + 5H₂S + C₂H₅OH /

ꢀ

triclinic (P1) and orthorhombic (Cmcm) symmetry respec-

tively.^35,38The ionic radius of 8-coordinated Fe³⁺is 0.78 A.

1T-2MoS₂+ Na₂SO₄+ NaOH

+ H₂O + CO₂+ 18H⁺

39

˚

(2)

Reviewed literature has suggested that the heterostructures

of BiVO₄–FeVO₄would be useful in eﬃcient generation of

electron–hole pairs and thus enhancing the photocatalytic

In the second phase, we prepared (Bi_1ꢀxFe_x)VO₄by the

hydrothermal method as reported elsewhere.^35,53Then for the

preparation of 1T-MoS₂@(Bi_1ꢀxFe_x)VO₄, an ultrasonic mixing

method was used, for which 200 mg of (Bi_1ꢀxFe_x)VO₄and 0.2 mg

ml^ꢀ1of MoS₂were mixed and sonicated for 2 h. The resulting

solution was centrifuged and dehydrated at 80 ^ꢁC to get the

desired product: 2% of 1T-MoS₂@(Bi_1ꢀxFe_x)VO₄. The inclusive

chemical reaction involved in the formation of the hetero-

structures can be written as:

activity

of

(Bi_1ꢀxFe_x)VO₄

heterostructure

nano-

photocatalysts.^31,33,35,40In this research, the eﬀect of Fe

substitution for Bi in BiVO₄was investigated and the photo-

catalytic response was studied in detail. The (Bi_1ꢀxFe_x)VO₄

phase transition was probed from monoclinic to tetragonal

with the increase of Fe concentration at Bi sites.

Furthermore, an emerging transition metal sulde named

molybdenum disulde (MoS₂) is comparable to graphene, with

a sandwich structure of three stacked atomic layers (S–Mo–S).

Mo atom is covalently combined with six S atoms which form

Fe(NO₃)₃+ Bi(NO₃)₃+ H₂O /

2HNO₃+ BiONO₃+ FeONO₃

(3)

(4)

a layer of MoS₂; Mo–S allows normal parabolic bonding with

41–45

˚

ꢀ

bond length of 2.39 A.

Recently, MoS₂-based nano-

FeONO₃+ BiONO₃+ VO₃

/

[(1 ꢀ x)Bi³⁺+ XFe³⁺]VO₄+ NO₃

ꢀ

composites have emerged as the most prominent candidates

owing to outstanding electronic conductivity, substitute for

noble metal co-catalysts, abundant availability, and cost-

eﬀectiveness.^42,46–48MoS₂is very sensitive for photodetection,

found in two-phase structures, one in trigonal phase (1T-

Â

Ã

ð1 ꢀ xÞBi^3þþ XFe^3þVO₄þ MoSO₂

þ 2OH ^Heat1T-MoS @ðBi_1ꢀxFe_xÞVO₄þ H₂O

(5)

!

2

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In the same way, a series of hybrid 1T-MoS₂@(Bi_1ꢀxFe_x)VO₄luminescence spectrometer (F-4500) was used with the 325 nm

catalysts containing diﬀerent amounts of Fe (0.25%, 0.60%, and line of a He–Cd laser as the excitation source at ambient

0.80%) were achieved by regulating the 2.0% value of 1T-MoS₂temperature.

solution. Optimum conditions for the construction of 1T-

MoS₂@(Bi_1ꢀxFe_x)VO₄were observed by the dosage variation

eﬀect of 1T-MoS₂on the photocatalytic activity of the photo-

catalysts. The 1T-MoS₂@(Bi_1ꢀxFe_x)VO₄with diﬀerent dosage of

MoS₂, i.e., 0.5 wt%, 1.0 wt%, 2.0 wt%, 3.0 wt% and 5.0 wt%, were

2.3 Photocatalytic activity

The photocatalytic reaction response of the as-prepared

samples was measured by degrading crystal violet (CV) dye

solution under visible light irradiation. A xenon lamp of 300 W

with a 420 nm cut-oﬀ lter was used as visible light source; the

each mixed with 200 mg of (Bi_1ꢀxFe_x)VO₄. Among which the 1T-

MoS₂@(Bi_1ꢀxFe_x)VO₄with 2.0 wt% of 1T-MoS₂exhibited

distance between the beaker and the lamp was kept at 25 cm.^32,54

a remarkable photocatalytic response, which may be due to

In detail, 10 mg of the as-prepared catalyst was added into 0.15 g

higher oxygen vacancies, large separation of charges, and the

reduced rate of electron–hole recombination within the catalyst

as compared to other concentration ratios. Hence, for cost-

eﬀectiveness and time saving and for brevity of description,

L^ꢀ1(150 ml) dye solution. The suspension was stirred vigorously

in the dark for 30 min to ensure adsorption–desorption stability

and then put under the visible light source. At regular intervals

of every 10 min, 3 ml of suspensions was taken out and the

we just describe 1T-MoS₂@(Bi_1ꢀxFe_x)VO₄with 2.0% of 1T-MoS₂

mixture was centrifuged at 10 000 rpm for 2 min to eliminate

for further characterization. The proposed schematic diagram

the catalyst particles.^55,56The absorbance of the dye solution was

quantied by a UV-visible (PerkinElmer l-35) spectrophotom-

eter. Nitrogen cooling system containing an ice bath was used to

keep the temperature constant and to avoid thermal degrada-

tion or decomposition throughout the experimentation.^34,35,57

of preparation of 1T-MoS₂decorated on the surface of (Bi_1ꢀxFe_x)

VO₄is shown in Fig. 1.

2.2 Characterization

The degradation eﬃciency of the dye (CV%) solutions was ob-

X-ray diﬀraction (XRD) patterns were measured on a Bruker D₈

diﬀractometer with monochromatic Cu Ka (l ¼ 0.15418 nm)

radiation with a scanning rate of 2q min^ꢀ1over the range of 20–

60^ꢁ. The morphology and topography of the materials were

analyzed by high energy eld emission scanning electron

microscopy (SEM, JEOL-7001F), equipped with EDX for

elemental analysis. The Brunauer–Emmett–Teller (BET) surface

areas measurements were performed with an ASAP 2010 system.

Optical properties were tested using a UV-visible spectrometer

(PerkinElmer Lambda 35), equipped with an integrating sphere

tained by the following formula:^32,34

ꢀ

ꢁ

C₀ꢀ C_t

D:E of CV% ¼

ꢂ 100

(6)

C₀

where C₀is the initial concentration of dye solution and C is the

concentration of dye aer every interval of 10 minutes.³⁴

3. Results and discussion

assembly, in a wavelength span of 300 to 800 nm at room The phases of 1T-MoS₂@(Bi_1ꢀxFe_x)VO₄with varying Fe

temperature. For photoluminescence (PL), Hitachi concentrations were evaluated by XRD. It provides evidence

a

Fig. 1 Schematic representation of experimental setup for preparation of 1T-MoS₂decorated on the surface of (Bi_1ꢀxFe_x)VO₄.

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Fig. 2 (a) XRD patterns and (b) Raman spectra for the 1T-MoS₂@(Bi_1ꢀxFe_x)VO₄nanoparticles synthesized at 180 ^ꢁC.

regarding the purity and crystallinity of 1T-MoS₂@(Bi_1ꢀxFe_x) Furthermore, the strain of the nanomaterials was calculated by

VO₄. Fig. 2(a) shows the room temperature XRD patterns of 1T- the Williamson–Hall method as it is expected that some Fe³⁺

MoS₂@(Bi_1ꢀxFe_x)VO₄corresponding to monoclinic (x ¼ 0.25) ions may deposit onto grain boundaries owing to higher

phase indexed to JCPDS card no. 83-1699, mixed monoclinic- concentration and may cause lattice strain and hence reduce

tetragonal (x ¼ 0.60) phase indexed to JCPDS card no. 83-1699 the lattice parameter.

and 14-0133, and tetragonal (x ¼ 0.80) phase indexed to JCPDS

Raman spectroscopy is a versatile characterization technique

card no. 75-2481. It is observed from XRD patterns that as the Fe generally used for monitoring the local molecular bonding and

concentration increased, monoclinic phase shis to a mixture structures of all types of catalytic materials.^13,34Therefore,

of the monoclinic and tetragonal phases and subsequently pure Raman analysis was conducted for structural information and

tetragonal BiVO₄phase, and a peak shi was also observed as to nd the crystal local structure and electronic dimensions of

the peaks belonging to tetragonal phase become intense while materials. In Fig. 2(b), seven vibrational modes are located at

the peaks corresponding to monoclinic phases decrease.^35,53,58around 198, 210, 326, 369, 639, 708 and 835 cm^ꢀ1that belong to

Aer 1T-MoS₂QD interspersed, all 1T-MoS₂@(Bi_1ꢀxFe_x)VO₄BiVO₄, while the vibrational modes at 139, 313, 359, 644, 823

samples show analogous diﬀraction patterns and exhibit no and 893 cm^ꢀ1correspond to FeVO₄in the samples indicating

XRD peak shi as compared to pure (Bi_1ꢀxFe_x)VO₄[XRD the replacement of Bi³⁺with Fe³⁺.³⁵It was observed that the

patterns of pure BiVO₄, FeVO₄, 1T-MoS₂and (Bi_1ꢀxFe_x)VO₄are number of vibrational modes decreased gradually to increase

given in Fig. S₁(ESI†)]. This suggests that (Bi_1ꢀxFe_x)VO₄is the crystal symmetry and resulted peak shi. Contrary to this, when

main structure of the prepared photocatalysts, and its structure Fe concentration is increased, some new peaks emerge and

does not change aer 1T-MoS₂QD interspersing. It is clear from become broader dominating some BiVO₄peaks. No vibrational

Fig. 2(a) that no diﬀraction peaks of 1T-MoS₂QDs were peak of 1T-MoS₂QDs (2.0 wt%) was detected in the spectra of

observed, which may be because of the low concentration 1T-MoS₂@(Bi_1ꢀxFe_x)VO₄, due to the low amount of MoS₂in 1T-

(2.0 wt%) or because of the low crystallinity in the composites. MoS₂@(Bi_1ꢀxFe_x)VO₄heterostructures, which also conrmed

The crystallite size of as-synthesized samples was evaluated our previous result.

from the (121) peak of XRD patterns by applying Scherrer's

The morphologies of prepared powder samples were exam-

formula to further probe the development of the crystal struc- ined via high-resolution SEM. This gives information regarding

ture.⁵⁹The crystallite size (D) values of the samples are given in the structure of 1T-MoS₂@(Bi_1ꢀxFe_x)VO₄possessing diﬀerent

Table 1. From Table 1, the crystallite size of Fe-doped BiVO₄compositions. The SEM images show that nearly all the

increased, which implies that the presence of Fe³⁺could inu- (Bi_1ꢀxFe_x)VO₄samples exhibit a ball-shaped spherical congu-

ence the formation of crystallized particles of BiVO₄. ration, as depicted in Fig. 3. The particle edge is more or less

Table 1 Physical and structural properties of the samples obtained from XRD analysis

˚

Lattice constant (A)

Cell volume

(A)

Lattice strain,

3 (%)

˚

Sample

D_cryst(nm)

a

b

c

BiVO₄

FeVO₄

(Bi_0.5Fe_0.5)VO₄

1T-MoS₂@(Bi_0.75Fe_0.25)VO₄

1T-MoS₂@(Bi_0.40Fe_0.60)VO₄

1T-MoS₂@(Bi_0.20Fe_0.80)VO₄

19.06

23.55

26.76

30.62

20.91

34.30

5.19

6.71

5.19

5.14

5.19

8.06

5.19

5.14

11.75

9.25

11.69

11.75

11.70

11.72

309.52

462.46

301.93

309.74

309.20

310.52

0.206

0.416

0.377

0.275

0.315

0.617

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Fig. 3 SEM analysis for (a) pure BiVO₄, (b) (Bi_0.5Fe_0.5)VO₄, (c) 1T-MoS₂@(Bi_0.75Fe_0.25)VO₄, (d) 1T-MoS₂@(Bi_0.20Fe_0.80)VO₄, (e) 1T-MoS₂@(Bi_0.40

-

Fe_0.60)VO₄, and (f) pure FeVO₄. (g) EDX analysis of 1T-MoS₂@(Bi_0.40Fe_0.60)VO₄heterostructures.

ball-shaped owing to some clusters and agglomeration of the 1T-MoS₂QDs for 2 h. During the sonication process, 1T-MoS₂

particles. From SEM images, the particle size of the samples is QDs are adsorbed on the (Bi_1ꢀxFe_x)VO₄surface, leading to the

found around 20–60 nm range. The SEM images indicate that fabrication of 1T-MoS₂QDs on (Bi_1ꢀxFe_x)VO₄. The obtained 1T-

BiVO₄nanoparticles have spherical symmetry and uniformity. MoS₂@(Bi_1ꢀxFe_x)VO₄composites, however, retained the glob-

Yet, an increase in Fe concentration causes the structural ular spherical morphology as indicated in Fig. 3. EDX analysis

transformation of the particles slightly from spherical to non- (Fig. 3(g)) of 1T-MoS₂@(Bi_0.40Fe_0.60)VO₄heterostructures

uniform hexagonal and spherical. At higher Fe concentration, veries the homogenous distribution and presence of 1T-MoS₂

fewer globular and more corners, randomized particles and QDs on the (Bi_1ꢀxFe_x)VO₄surface conrming that the hetero-

agglomerations were observed as exhibited in Fig. 3. So, the structures consist of only Mo, S, Bi, Fe, V and O elements, while

addition of Fe dopant gradually aﬀects the structure of (Bi_1ꢀx

-

Cu presence is due to the copper holding grid, with no other

Fe_x)VO₄, and observable transformation occurs from homoge- impurities found within the detection limit as shown in

nous spherical morphology to irregular spheres and Fig. 3(g).

agglomerations of nanostructures. Moreover, oxygen adsorp-

X-ray photoelectron spectroscopy (XPS) analysis was con-

tion also inuences the morphology. Subsequently, the surface ducted for the conrmation of the elemental, chemical

decoration of (Bi_1ꢀxFe_x)VO₄with 1T-MoS₂QDs was accom- composition and surface bond analysis.^14,26XPS survey scan

plished by sonication of (Bi_1ꢀxFe_x)VO₄in an aqueous solution of (Fig. S₂, ESI†) was performed to conrm the presence of

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essential components present in the samples. The survey oxidation state of the V cation. Earlier reports demonstrated

spectrum indicates that binding energy peaks of essential curve tting of the V 2p_3/2core peak, so we also tted the V 2p_3/

elements (Bi, S, Mo, O, V, and Fe) in the 1T-MoS₂@(Bi_1ꢀxFe_x)

core peak in our samples.¹⁴The V 2p_3/2core peak was de-

2

VO₄samples were observed as shown in Fig. S₂, ESI.† We used convoluted with the tting of two peaks arising at binding

O 1s (530.3 eV) for referencing the binding energy values energy values of 517.17 and 518.17 eV. The peak tting

rather than to C 1s (284.6 eV). To further analyze the 1T- suggests the valence state of V⁵⁺is in bulk with the presence of

MoS₂@(Bi_1ꢀxFe_x)VO₄composites, the high-resolution spectra V⁴⁺ions in the 1T-MoS₂@(Bi_0.40Fe_0.60)VO₄heterojunction

for Bi, S, Mo, O, V, and Fe are depicted in Fig. 4. The XPS peaks composite. Fig. 4(e) depicts the O 1s spectrum also showing

of Bi doublets (4f_7/2and 4f_5/2) were found at 159.38 eV and asymmetrical behavior and can be tted with three Gaussians

164.83 eV as indicated in Fig. 4(a). Fig. 4(b) shows the doublets peaks

for

1T-MoS₂@(Bi_0.40Fe_0.60)VO₄

heterojunction

of S 2p (S 2p_3/2and S 2p_1/2), in which the main two peaks at composite samples. The de-convoluted peaks appeared at

161.66 eV and 162.56 eV represent the 1T-phase of MoS₂, and around 529.38, 530.20 and 532.37 eV. The peak at 529.38 eV is

the two small peaks at 160.58 eV and 163.77 eV correspond to due to lattice constant of V–O, Fe–O or Bi–O bonding in

the 2H-phase of MoS₂. However, the concentration of the 1T- (Bi_1ꢀxFe_x)VO₄, as the binding energies of V–O and Bi–O are

phase is higher and is found to be 80% which indicates the approximately the same. The peak at 530.20 eV is due to OH

predominance of the 1T-phase over the 2H-phase. Mo 3d group while that at 532.37 eV is attributed to molecular water

doublets (Mo 3d_5/2and Mo 3d_5/2) appeared at 229.1 eV and adsorbed on the surface.¹³The XPS spectrum of Fe 2p core

232.5 eV. Mo 3d peaks were more de-convoluted to obtain peaks is shown in Fig. 4(f). Fe 2p doublet (Fe 2p_3/2and 2p_1/2

)

further information about the existence of valence state of Mo evidenced a binding energy transformation of 13.6 eV which

ions. The peak at 235.25 eV is developed due to oxidation of established spin-orbit coupling of Fe with host lattices. Fe 2p

1T-MoS₂@(Bi_0.40Fe_0.60)VO₄by exposure to air and attributed to peaks were more de-convoluted to get further accurate infor-

Mo⁶⁺. V 2p doublets (V 2p_3/2and V 2p_1/2) appeared at approx- mation on the presence of the valence state of the Fe ions. The

imately 517.23 and 524.60 eV. In the case of V, the value of de-convolution of Fe 2p_3/2reveals two peaks at 710.43 and

binding energy of the V 2p_3/2core level is responsive to the 713.65 eV corresponding to Fe³⁺and Fe²⁺valence states.^13,26It

Fig. 4 High-resolution peak-ﬁtting XPS spectra of (a) Bi 4f, (b) S 2p, (c) Mo 3d, (d) V 2p, (e) O 1s and (f) Fe 2p of 1T-MoS₂@(Bi_0.40Fe_0.60)VO₄

heterostructures.

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Fig. 5 (a) Degradation of CV dye solution under diﬀerent conditions; (b) UV-visible absorption spectra of CV dye solution during photocatalytic

degradation over 1T-MoS₂@(Bi_0.40Fe_0.60)VO₄heterojunction photocatalysts at diﬀerent time intervals.

is observed that there is a slight shi in these peaks towards and CV molecules and cause advanced photocatalytic eﬃciency

higher binding energy during the Fe doping in BiVO₄and under visible light irradiation. From Fig. 5(a) the photo-

formation of Fe–O–Bi bond, indicating that Fe and 1T-MoS₂degradation of CV with pure BiVO₄is 55%, that for FeVO₄is

co-doped further increase the oxygen vacancies and cause 43%, (Bi_0.5Fe_0.5)VO₄is 78%, 1T-MoS₂@(Bi_0.75Fe_0.25)VO₄is 86%,

higher enhanced photocatalytic activity, as discussed below. and 1T-MoS₂@(Bi_0.20Fe_0.80)VO₄is 76%, while for 1T-MoS₂@(-

These results conrm the existence of Fe in BiVO₄, successful Bi_0.40Fe_0.60)VO₄it reaches up to 99.98% in 50 min of irradiation

constriction of (Bi_1ꢀxFe_x)VO₄and decoration of 1T-MoS₂on time under similar conditions (Table 2). To get more rigorous

(Bi_1ꢀxFe_x)VO₄sample surfaces.

results, a comparison between (Bi_0.40Fe_0.60)VO₄and 1T-

MoS₂@(Bi_0.40Fe_0.60)VO₄was conducted (Fig. S₃, ESI†), where it

can be seen that (Bi_0.40Fe_0.60)VO₄gives 89.80% degradation

eﬃciency whereas 1T-MoS₂@(Bi_0.40Fe_0.60)VO₄exhibited 99.98%

degradation in 50 minutes. During the photoirradiation exper-

iment, the discoloring of the solution suggests the decompo-

sition of CV dye fragments. From absorption peaks a red shi

was noticed, which may be due to benzene ring breakup within

the dye molecules.^13,60From experimental outcomes and the

3.1 Photocatalytic activity

The photocatalytic conversion of CV over various samples under

visible light irradiation (l ¼ 420 nm) is shown in Fig. 5. For

reference, the CV dye solution degradation/decomposition

without photocatalyst (photolysis) and with photocatalyst but

without light was performed. The absorptions of CV dye solu-

tion reduce gradually in the presence of both photocatalyst and

visible light irradiation, while no or insignicant photocatalytic

response was observed either without photocatalysts or without

light irradiation, i.e., 1% and 5% respectively in 50 min

(Fig. 5(a)). From these results, it is obvious that the photo-

catalytic activity for CV over 1T-MoS₂@(Bi_1ꢀxFe_x)VO₄is light-

dependent.^35,57The photocatalytic activity is primarily related to

the production of superoxide anions (O₂^ꢀ) and hydroxyl radicals

(cOH).^13,27Therefore, in the presence of 1T-MoS₂@(Bi_1ꢀxFe_x)

VO₄, light photons (hn) of energy equal to or greater than the

bandgap generate electron and hole pairs which transfer to the

1T-MoS₂@(Bi_1ꢀxFe_x)VO₄surface, where they oxidize the water

above discussion, it is suggested that in the 1T-MoS₂@(Bi_0.40

-

Fe_0.60)VO₄heterostructures, the separation of photogenerated

charge carriers is well controlled owing to 1T-MoS₂helping the

transport of electrons (electron capture) compared with pure

BiVO₄, (Bi_1ꢀxFe_x)VO₄, FeVO₄and for other 1T-MoS₂@(Bi_1ꢀxFe_x)

VO₄photocatalysts, thus improving the electron–hole pair

separation lifetime involving an enhanced photoconversion

eﬃciency.

A kinetics study for degradation of CV under visible light

irradiation was also conducted. The Langmuir–Hinshelwood

model is generally considered a suitable model to examine the

reaction kinetics of heterogeneous catalysts.^61,62The applied

mathematical expression is given as in eqn (7):⁶¹

dC

dt

K_LꢀHK_aC

1 þ K_aC

ꢀ

¼

(7)

Table 2 Eﬀect of Fe concentration variation and 1T-MoS₂loading on

CV dye degradation using 1T-MoS₂@(Bi_1ꢀxFe_x)VO₄photocatalysts in

50 min

Here, K_a, C, and K_L–Hcorrespond to the absorption coeﬃcient,

concentration and reaction rate constant. When the initial

pollutant concentration is low as in this study, Langmuir's

formula is moderated into the pseudo-rst-order model and

generally used for photocatalytic degradation activity. A pseudo-

rst-order kinetic model is used to t the degradation data

using the following equation:^32,61

Ratio (Bi_1ꢀxFe_x)VO₄

Degradation eﬃciency (%)

BiVO₄

55

FeVO₄

43

(Bi_0.5Fe_0.5)VO₄

78

1T-MoS₂@(Bi_0.75Fe_0.25)VO₄

1T-MoS₂@(Bi_0.40Fe_0.60)VO₄

1T-MoS₂@(Bi_0.20Fe_0.80)VO₄

86

99.98

76

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Table 3 Kinetics data for the adsorption of CV on catalysts obtained using kinetics models

Pseudo-rst order

Sample

C/C₀exp. (mg g^ꢀ1

)

K (min^ꢀ1) visible light

R²

BiVO₄

FeVO₄

(Bi_0.5Fe_0.5)VO₄

1T-MoS₂@(Bi_0.75Fe_0.25)VO₄

1T-MoS₂@(Bi_0.40Fe_0.60)VO₄

1T-MoS₂@(Bi_0.20Fe_0.80)VO₄

0.454

0.571

0.223

0.163

0.021

0.285

9 ꢂ 10^ꢀ3

1.14 ꢂ 10^ꢀ2

4.46 ꢂ 10^ꢀ3

3.26 ꢂ 10^ꢀ3

4 ꢂ 10^ꢀ4

0.9848

0.9975

0.9907

0.9823

0.9863

0.9825

5.7 ꢂ 10^ꢀ3

Table 4 Determination of optical band gap, mobility of charge carriers, refractive index and conductivity

Optical band

gap (eV)

Mobility of charge

Refractive

index

Conductivity

Sample

carriers (cm²V^ꢀ1s^ꢀ1

)

(S cm^ꢀ1

)

BiVO₄

2.41

2.38

1.98

3.18 ꢂ 10³

3.24 ꢂ 10³

4.27 ꢂ 10³

2.54

2.55

2.71

4.19 ꢂ 10⁴

4.30 ꢂ 10⁴

6.19 ꢂ 10⁴

(Bi_0.5Fe_0.5)VO₄

1T-MoS₂@(Bi_0.40Fe_0.60)VO₄

material will also be very helpful for electronic device applica-

tions. The overall results are presented in Table 4.

dq_t

dt

¼ kðq_eꢀ q_tÞ

(8)

where k (min^ꢀ1) is the photocatalytic reaction rate constant, q_e

is the adsorbed dye at the equilibrium of CV aer the adsorp-

tion–desorption equilibrium before illumination, and q_tis the

adsorbed CV dye at diﬀerent illumination times (min)

(Fig. 5(a)). The degradation rate constants k for CV over BiVO₄,

FeVO₄, (Bi_1ꢀxFe_x)VO₄, and 1T-MoS₂@(Bi_1ꢀxFe_x)VO₄photo-

catalysts through pseudo-rst-order equation were evaluated

from the nonlinear regression of t versus q_tusing the integration

of the equation and are given in Table 3. It was observed that CV

dye solution over 1T-MoS₂@(Bi_0.40Fe_0.60)VO₄presented a supe-

rior photodegradation eﬃciency as shown in Fig. 5(a).

The optical band gap is calculated by the Tauc plot method

as presented in Table 4.⁶³The reduction in optical bandgap

results in an increase in the mobility of charge carriers,

refractive index and electrical conductivity.^64,65The results ob-

tained are in accordance with those of previous work;^13,24,32,35

therefore, it is suggested that the prepared semiconductor

3.2 Surface chemistry

The photocatalytic activity is correlated to the adsorption–

desorption-releasing process. The appropriate adsorption of

pollutant molecules on the surface of photocatalysts is the

major requirement for an excellent photoinduced response. In

addition, in the function of photocatalytic activity, the rate of

reaction is proportional to the number of photons (hn) adsorbed

on the surface of a photocatalyst.^12,15,29Adsorptions of nonre-

active gas at the atomic level have a signicant role in deter-

mining the surface area, as well as surface roughness and pore

interior. BET specic surface area is evaluated by N₂adsorp-

tion–degradation curve.²⁹The nitrogen adsorption–desorption

curve for surface area measurement of 1T-MoS₂@(Bi_0.40Fe_0.60

)

VO₄is shown in Fig. 6. For pore size, the Barrett–Joyner–

Halenda (BJH) method was applied using desorption

isotherms.²⁹1T-MoS₂@(Bi_0.40Fe_0.60)VO₄exhibits suﬃcient large

surface area of 40 m²g^ꢀ1and calculated pore volume and

average pore diameter are 0.122 cc g^ꢀ1and 1.685 nm

Table 5 Summary of the physical properties obtained, BET surface

area, pore volume, and pore size of sample nanopowders

BET

surface area

V_p

D_p

(nm)

Sample

(m²g^ꢀ1

)

(cc g^ꢀ1

)

BiVO₄

FeVO₄

(Bi_0.5Fe_0.5)VO₄

1T-MoS₂@(Bi_0.75Fe_0.25)VO₄

1T-MoS₂@(Bi_0.40Fe_0.60)VO₄

1T-MoS₂@(Bi_0.20Fe_0.80)VO₄

14

26

13

40

21

0.025

0.052

0.117

0.059

0.122

0.107

2.181

2.183

1.681

1.931

1.685

2.192

Fig.

6 Nitrogen gas adsorption–desorption isotherm distribution

curve for 1T-MoS₂@(Bi_0.40Fe_0.60)VO₄at 77 K. Inset: pore volume vs.

pore diameter curve from BJH method.

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Fig. 7 (a) PL spectra (excited at 325 nm) of composites at diﬀerent concentrations and (b) EIS Nyquist plots of the bare and as-modiﬁed 1T-

MoS₂@(Bi_0.40Fe_0.60)VO₄nanocomposite GCE samples.

respectively as shown in the inset of Fig. 6. As is well known, reections and adsorption consequently resulting in enhancing

higher surface area means a high ability to adsorb large quan- the photocatalytic activity and increasing the dye

tity of dye pollutants from solution; moreover, pore size and degradation.^12,14,15,26

pore volume also have a major eﬀect on the photocatalytic

activity. Thus, the surface area, pore volume, and pore size of

3.3 Photoluminescence and electrochemical impedance

spectroscopy analysis study

the as-synthesized sample nanopowders were measured as

shown in Table 5. It is observed that with the increase of Fe

concentration the surface area increases as compared to pure

BiVO₄and the optimum increment is at x ¼ 60 as depicted in

Table 5. This may be owing to Fe³⁺having small ionic radius of

Several studies show that PL emission spectra can be stimulated

through the recombination of photoexcited electrons and

holes.⁶⁶A lower PL emission peak intensity suggests less

recombination of photogenerated charge carriers. Conse-

quently, the electron–hole transfer and recombination opera-

tions in the photoaided degradation experimentation could be

tested by the PL technique.^15,35,57Fig. 7(a) exhibits the PL spectra

of pure BiVO₄, FeVO₄, (Bi_1ꢀxFe_x)VO₄and diﬀerent 1T-MoS₂@(-

Bi_1ꢀxFe_x)VO₄composites in the range of 330–800 nm for an

excitation source of 325 nm. The peaks increase owing to the

recombination of photoexcited electrons and holes. It is noticed

that the emission intensities of FeVO₄and BiVO₄are higher.

However, aer the coupling of (Bi_1ꢀxFe_x)VO₄with 1T-MoS₂

quantum dots, the emission intensity is reduced, suggesting

that the charge separation rate in 1T-MoS₂@(Bi_1ꢀxFe_x)VO₄

composites is more eﬃcient as compared to BiVO₄, FeVO₄, and

(Bi_1ꢀxFe_x)VO_4.It is observed that the 1T-MoS₂@(Bi_0.40Fe_0.60)VO₄

composite exhibits the lowest PL emission intensity, indicating

˚

0.78 A; secondly, the surface area may be large owing to increase

in adsorption in the presence of Fe³⁺; thirdly, interspersing of

1T-MoS₂quantum dots inside the (Bi_0.40Fe_0.60)VO₄nano-

particles allows an increase in dye adsorption on the catalyst

surface; and lastly, it may be due to the arrangement of metal

ions.^15,29The adsorption curve of 1T-MoS₂@(Bi_0.40Fe_0.60)VO₄is

a

type IV curve indicating the presence of mesopores/

nanopores, and a type H₃hysteresis loop. The enhanced

surface area of 1T-MoS₂@(Bi_0.40Fe_0.60)VO₄reveals the existence

of a multichannel structure inside the composite which allows

facile and easy mass transport, light-capturing due to multiple

light reactions and gas diﬀusion within the pores of the mate-

rial. The presence of mesopores and nanopores within the pore

structures helped to adsorb extra dye fragments on the photo-

catalyst surface, hence the combined inuence of multiple light

Fig. 8 (a) Eﬀects of diﬀerent radical scavengers on CV degradation over 1T-MoS₂@(Bi_0.40Fe_0.60)VO₄under visible light irradiation. (b) DMPO spin

trapping EPR spectra for DMPO-cO₂and (c) DMPO-cOH^ꢀunder visible light over 1T-MoS₂@(Bi_0.40Fe_0.60)VO₄photocatalyst.

ꢀ

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a

large separation eﬃciency of photogenerated charge for degradation of CV dye. Hydroxyl radicals (cOH) were also

carriers.³⁴To further understand the charge transfer in 1T- generated when cO₂^ꢀinteracted with holes (h⁺) and H⁺ions in

MoS₂@(Bi_1ꢀxFe_x)VO₄photocatalysts, the electrochemical H₂O.^14,34No EPR signals were observed when the reaction was

impedance spectroscopy (EIS) technique was used. The performed in the dark. DMPO-cO₂and DMPO OHc adducts

ꢀ

measurement was also carried out for a bare glassy carbon were observed when the experiment was executed under

electrode (GCE) and 1T-MoS₂@(Bi_0.40Fe_0.60)VO₄composite. As visible light illumination. The signal intensity increases

shown in Fig. 7(b), it is experimentally evident that the 1T- progressively while prolonging the reaction time as shown in

MoS₂@(Bi_0.40Fe_0.60)VO₄composite has a small-scale semicircle Fig. 8(b), while no signicant enhancement in DMPO OHc

radius as compared to bare GCE. It is well recognized that the adducts was noticed when the 1T-MoS₂@(Bi_0.40Fe_0.60)VO₄

radius of curvature is an indicator of charge transport imped- heterojunction nanocomposite solution was irradiated under

ance, and a smaller semicircle radius signies greater charge visible li_ꢀght as shown in Fig. 8(c). These results again conrm

transportation eﬃciency.^26,34,35

that cO₂radicals were the major active species during CV

photocatalytic degradation over 1T-MoS₂@(Bi_0.40Fe_0.60)VO₄in

this study.

3.4 Radical scavenger and electron paramagnetic resonance

study for active species

3.5 Photocatalytic mechanism

During photocatalytic degradation, diﬀerent active species are

generated, including hydroxyl radical (cHO), singlet oxygen The comprehensive mechanism of 1T-MoS₂@(Bi_0.40Fe_0.60)VO₄

(¹O₂), superoxide radical (cO₂^ꢀ) and photogenerated hole photocatalyzed reactions is explored to understand the

(h⁺).^67–69Radical scavenger analyses were performed to check procedure of photocatalysis. The complete mechanism for

out the agents involved in the photodegradation of the dye. photocatalysis over the 1T-MoS₂@(Bi_0.40Fe_0.60)VO₄catalyst

The results of eﬀective species detection are indicated in was proposed based on prior investigations as illustrated in

Fig. 8(a). The result showed that CV solution degradation over Fig. 9.

1T-MoS₂@(Bi_0.40Fe_0.60)VO₄was highly depressed when ascor-

The overall process includes rst the production of photo-

bic acid (cO₂^ꢀradical) is added into the system. It is seen that excited electrons (e^ꢀ) from the valence band (VB) into the

in the presence of t-butanol (cOH radical) and diammonium conduction band (CB) of (Bi_0.40Fe_0.60)VO₄when light photons

oxalate monohydrate (h⁺scavenger), the concentration slightly fall on it. Secondly, holes (h⁺) are generated in the VB owing to

decreases, which reveals that cOH and h⁺had small roles as the migration of electrons from VB to CB. In the third step the

main reactive species in the photocatalytic degradation. Thus photoexcited electrons of the CB are captured or trapped to the

ꢀ

cO₂plays a major role as reactive species in the degradation 1T-MoS₂surface from where the electrons rapidly take part in

of CV dye solution. To further strengthen our results, electron the photocatalytic activity. The close contact level between tiny

paramagnetic resonance (EPR) analysis was performed which 1T-MoS₂particles and (Bi_0.40Fe_0.60)VO₄provides more oppor-

also indicates that once an electron entered the conduction tunity to transport photogenerated electrons from the CB of

band of (Bi_1ꢀxFe_x)VO₄, it brings oxygen, which makes centers (Bi_0.40Fe_0.60)VO₄to 1T-MoS₂surface from where they react with

Fig. 9 Proposed basic mechanism of photocatalysis of 1T-MoS₂@(Bi_1ꢀxFe_x)VO₄heterostructures.

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surface adsorbed oxygen (O₂) molecules and convert them into

superoxide anion radicals (cO₂^ꢀ). In the fourth and nal step,

the holes in VB are transmitted to the surface to oxidize the

water and hydroxyl ions into hydroxyl radical (cOH) species.^70,71

In comparison with the pure BiVO₄, FeVO₄and (Bi_1ꢀxFe_x)VO₄

samples, the fabrication of 1T-MoS₂doped (Bi_1ꢀxFe_x)VO₄

catalyst could boost the eﬃcient separation and transport of

photoproduced charges for degradation of CV dye. Conse-

quently, the photocatalytic response of BiVO₄was extensively

enhanced.¹⁵Transfer of the electron–hole pairs within and on

the surface of the 1T-MoS₂doped (Bi_1ꢀxFe_x)VO₄photocatalyst

and photocatalyzed reactions may be expressed by the

following equations:

OHc + CV / CO₂+ H₂O

(13)

(14)

ꢀ

cO₂+ CV / CO₂+ H₂O

3.6 Eﬀect of catalyst dosage and initial dye concentration

For practical and economic purposes the eﬀect of diﬀerent

catalyst dosages was evaluated by varying the quantity in the

range 2–10 mg in the presence of visible light. From experi-

mental results it was noted that the degradation is almost

independent of the catalyst concentration. The optimal

catalyst amount (Fig. 10(a)) is 7 mg. It can be seen that for

higher amount the photocatalytic activity slightly decreases.

This may be due to the agglomeration of the catalyst particles

or, beside this, at a higher concentration of photocatalyst, the

recombination between photogenerated electron hole pairs

1T-MoS₂@ðBi_1ꢀxFe_xÞVO₄

þhn/1T-MoS₂@ðBi_1ꢀxFe_xÞVO^*₄ðe^ꢀþ h^þÞ (9)

H₂O + h⁺/ OHc + H⁺

h⁺+ H⁺/ OHc

(10) increases which may decrease the degradation eﬃciency. The

photodegradation eﬃciency of the 1T-MoS₂@(Bi_1ꢀxFe_x)VO₄

(11)

catalyst was also evaluated against the removal of CV dye with

diﬀerent (0.05, 0.10, 0.15, and 0.20 g L^ꢀ1) concentrations.

The electrons from the 1T-MoS₂surface can reduce O₂to

superoxide anions:

Fig. 10(b) indicates the dye removal eﬃciency decreases as

the dye concentration increases. This decrease in the removal

eﬃciency may be due to the large amount of dye molecules on

the photocatalyst surface while the numbers of hydroxyl

radicals were reduced; meanwhile, another reason for the

lower eﬃciency is limitation in light transmutation and as

a result the number of photons reaching the photocatalyst

ꢀ

O₂+ e^ꢀ/ cO₂

(12)

These radicals interact with the pollutant CV dye molecules

and decompose them into harmless fragments:

Fig. 10 (a) Eﬀect of 1T-MoS₂@(Bi_0.40Fe_0.60)VO₄catalyst dosage (inset shows zoomed view). (b) Eﬀect of initial dye concentration on the

degradation percentage. (c) Eﬀect of pH on the degradation eﬃciency of CV dye. (d) Reusability of the as-prepared 1T-MoS₂@(Bi_0.40Fe_0.60)VO₄in

terms of the degradation eﬃciency (inset shows zoomed view).

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decreases, consequently resulting in lower degradation

eﬃciency.

4. Conclusions

In summary, we prepared 1T-MoS₂QDs-decorated (Bi_1ꢀxFe_x)

VO₄heterostructures by a sonication-assisted hydrothermal

method for photocatalytic degradation of organic pollutant

CV dye and conrmed the electron transfer process from

(Bi_1ꢀxFe_x)VO₄onto 1T-MoS₂. The 1T-MoS₂QD-decorated

(Bi_1ꢀxFe_x)VO₄heterostructures exhibit excellent visible

light-dependent response and light absorption range as well

as charge transfer activity. The (Bi_1ꢀxFe_x)VO₄hetero-

structures with optimal 1T-MoS₂QDs loading of 2 wt% show

a signicantly enhanced photocatalytic activity. The results

indicate the easy separation of electron hole pairs, where

electrons were transferred to MoS₂from (Bi_1ꢀxFe_x)VO₄

surface by irradiation of visible light. Another factor for the

3.7 Eﬀect of pH and reusability

To study the inuence of pH on the removal of CV dye,

a series of experiments were performed at diﬀerent pH (2–12)

values. It is well known that pH strongly aﬀects the photo-

catalytic eﬃciency during the wastewater decolorization

process. This may be owing to pH aﬀecting the agglomeration

of the catalyst particles, thus changing the surface area for

dye adsorption and photon absorption. The formation of

hydroxyl radicals is diﬀerent for acidied solutions than for

alkaline media. Variations in pH can also aﬀect the adsorp-

tion of dye molecules on the photocatalyst surface. Therefore,

pH of dye solutions was adjusted by HCl and NaOH, and the

results are illustrated in Fig. 10(c). CV is a cationic dye so low

pH values are not favorable; higher pH value is more appro-

priate for its degradation. It can be seen that low pH cannot

produce the required number of hydroxyl groups to produce

hydroxyl radicals on the photocatalyst surface; moreover, the

positively charge surface of the catalyst repels the cationic

dye adsorption on the 1T-MoS₂@(Bi_1ꢀxFe_x)VO₄catalyst

surface. Initially when the hydroxyl radicals increase they

cause an increase in degradation eﬃciency; however, at

higher alkaline pH value the degradation eﬃciency is

reduced owing to the recombination of the charge carriers.

Besides, at high pH hydroxyl ions might be able to compete

with the dye molecules in the incorporation process on the

photocatalyst surface. From the experimental results it is

observed that a pH value of 10 gives the optimum degrada-

tion eﬃciency, as illustrated in Fig. 10(c). For economic,

practical use and purposes of reusability, the 1T-MoS₂@(-

Bi_1ꢀxFe_x)VO₄catalyst was tested by running ve cycles of

activity as exhibited in Fig. 10(d). According to the results, it

was observed that the 1T-MoS₂@(Bi_0.40Fe_0.60)VO₄catalyst can

be reused and has acceptable stability aer ve cycles of dye

degradation.

superior photocatalytic activity of the Ti–MoS₂@(Bi_0.40Fe_0.60

)

VO₄heterostructures is the high degree of crystallinity,

involving fewer defects and causing less recombination of

photogenerated electrons and holes. The Ti–MoS₂@(Bi_0.40

-

Fe_0.60)VO₄photocatalyst was successfully recycled for ve

cycles providing more stability and reusability in the photo-

catalytic experiments without a signicant loss of catalytic

activity. The active species trapping experiments and EPR

results allowed us to propose a possible photocatalytic

mechanism of Ti–MoS₂@(Bi_0.40Fe_0.60)VO₄and revealed that

ꢀ

cO₂radicals are the major active species for CV dye degra-

dation. This study shows that 1T-MoS₂QDs-decorated

(Bi_1ꢀxFe_x)VO₄heterostructures prepared by this route could

be of great potential for practical use of surface modication

and give some new ideas for developing promising eﬃcient

photocatalysts for removal of and/or degradation of other

environmental pollutants in a reasonable reaction time.

Funding detail

This work was nancially supported by the State Scholarship

Fund of China Scholarship Council (no. 201808410144), the

National Natural Science Foundation of China (no. 51202107),

and Foundation of Henan Educational Committee (no.

20A480003).

3.8 Comparative study (Table 6)

Table 6 Comparative study of the degradation eﬃciency of CV dye using the 1T-MoS₂@(Bi_0.40Fe_0.60)VO₄nanocomposite with other nano-

material photocatalysts

Catalyst

Eﬃciency (%)

Light source

Time (min)

Ref.

Ag doped TiO₂

Cr doped ZnO

>99

95

UV light

90

60

72

73

TG capped ZnS nanoparticles

Mn doped and PVP capped ZnO nanoparticles

Bi₇O₉I₃/GO

CdS/CdTiO₃–TiO₂

Ag₃VO₄/g-C₃N₄

BaWO₄

Zn₃(VO₄)₂nanoplate

CeO₂–TiO₂

BiVO₄/FeVO₄nanocomposite

1T-MoS₂@(Bi_0.40Fe_0.60)VO₄

ꢃ96

<100

96

61

34

ꢃ98

100

98

99.1

ꢃ99.98

UV irradiation

UV light

Visible light

180

144

180

150

60

50

74

75

68

76

77

67

27

78

35

Present work

13116 | RSC Adv., 2021, 11, 13105–13118

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679–682.

Conﬂicts of interest

21 P. Mallick, Mater. Sci.-Pol., 2014, 32, 193–197.

22 A. Ashour, Turk. J. Phys., 2004, 27, 551–558.

23 F.-y. Chen, X. Zhang, Y.-b. Tang, X.-g. Wang and K.-k. Shu,

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24 M. M. Sajid, N. Amin, N. A. Shad, Y. Javed and Z. Zhang, J.

Mater. Sci. Eng. B, 2019, 242, 83–89.

The authors declare that there is no conict of interest.

Acknowledgements

Dr Muhammad Munir Sajid is grateful to Prof. Zhengjun Zhang,

Tsinghua University, Beijing, China, for support with charac-

terization techniques and applications.

25 L.

Maskaeva, E. Mostovshchikova,

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13118 | RSC Adv., 2021, 11, 13105–13118

Article Doi

Construction of 1T-MoS2quantum dots-interspersed (Bi1-xFex)VO4heterostructures for electron transport and photocatalytic properties

DOI: 10.1039/d1ra00807b

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