Facile synthesis, characterization and application of functionalized cadmi um sulfide [601730]

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Manuscript Number:

Title: Facile synthesis, characterization and application of functionalized cadmi um sulfide
nanopowders

Article Type: Full Length Article

Keywords: Chalcogenides, semiconductors, chemical synthesis, electron microscopy, powder
diffraction, optical properties.

Corresponding Author: Dr. Anca Dumbrava, Ph.D.

Correspondin g Author's Institution: Ovidius University

First Author: Anca Dumbrava, Ph.D.

Order of Authors: Anca Dumbrava, Ph.D.; Daniela Berger, Ph.D.; Gabriel Prodan, Ph.D.; Florin Moscalu,
Ph.D.

Abstract: The functionalized nanomaterials, including II -VI semiconductors, have many interesting
properties and applications, some of them being superior to those of bare nanomaterials. Cadmium
sulfide nanoparticles functionalized with mercaptoacetate were synthesized by one -pot synthesis
using three strategies. T he structure and morphology of the obtained nanopowders were studied by X –
ray diffraction and transmission electron microscopy. The optical properties were investigated by UV –
Visible diffuse reflectance spectroscopy and the band gap energy value calculated with the Tauc
equation was determined. An application of functionalized cadmium sulfide may be in heterogeneous
catalytic processes, thus the nanopowders catalytic activity was studied in the degradation of an azoic
dye. The higher catalytic activity was correlated with the synthesis route, the particles average size and
a high surface specific area for the functionalized material.

Dear Editor,

Please find attached our manuscript entitled “ Facile synthesis, characterization and
application of functionalized cadmium sulfide nanopowders ” by Anca Dumbrava , Daniela
Berger, Gabriel Prodan and Florin Moscalu , submitted for publication in “Materials
Chemistry and Physics” .
We bring to your attention a study about the synthesis, characterization and properties of
functionalized CdS nanopowders. The novelty of our study comes from the synthesis
methods. Thus, we proposed two unconventional methods for the synthesis of
mercaptoacetate functionalized CdS nanopowders and we compared the properties of the
obtained nanopowders with those of nanopowders synthesised by chemical precipitation
method. We correlate d the nanopowders morphology and properties with the synthesis route.
The manuscript is brought to your attention with the belief that it satisfies the selection criteria
of your journal and with the hope that it will be considered for publication.
The present article reports new, original work that is not being submitted to another
journal. The present work is not considered for publication elsewhere in any other form. Any
part of the present work is not published elsewhere. All the co -authors are aware of this
submission and contributed to this work.
Thank you for your attention to this letter.
Sincerely,
Anca Dumbrava
Assoc. Prof. ,
Department of Chemistry and Chemical Engineering ,
Ovidius University of Constanta , Romania
Cover Letter

Highlights:
 CdS nanopowder s functionalized with mercaptoacetate were synthesised by chemical
precipitation and trituration technique s.
 CdS nanopowder s properties (morphological, optical and photocatalytic) were studied.
 Properties and morphologies of the functionalized CdS nanopowders obtained by
different routes were compared .
 The change of synthesis route involved modifications of CdS nanopowder properties.
Highlights (for review)

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Facile synthesis, characterization and application of functional ized cadmium sulfide
nanopowders
Anca Dumbrava 1*, Daniela Berger 2, Gabriel Prodan 3, Florin Moscalu 4

1 Department of Chemistry and Chemical Engineering, Ovidius University of Constanta, Romania
2 Department of Inorganic Chemistry, Physical Chemist ry and Electrochemistry, University Politehnica of
Bucharest, Romania
3 Electron Microscopy Laboratory, Ovidius University of Constanta, Romania
4 Department of Physics, Ovidius University of Const anta, Romania
*adumbrava@univ-ovidius.ro

Abstract. The functionalized nanomaterials, including II-VI s emiconductors, have many interesting properties
and applications, some of them being superior to th ose of bare nanomaterials. Cadmium sulfide nanopart icles
functionalized with mercaptoacetate were synthesize d by one-pot synthesis using three strategies. The structure
and morphology of the obtained nanopowders were stu died by X-ray diffraction and transmission electron
microscopy. The optical properties were investigate d by UV-Visible diffuse reflectance spectroscopy and the
band gap energy value calculated with the Tauc equa tion was determined. An application of functionaliz ed
cadmium sulfide may be in heterogeneous catalytic p rocesses, thus the nanopowders catalytic activity w as
studied in the degradation of an azoic dye. The hig her catalytic activity was correlated with the synt hesis route,
the particles average size and a high surface speci fic area for the functionalized material.
Keywords : chalcogenides, semiconductors, chemical synthesis , electron microscopy, powder diffraction, optical
properties.
1. Introduction
The metal chalcogenide nanostructures are of intere st for a variety of applications like the energy
generation in batteries and photovoltaics, nanoelec tronics, nanotribology, catalysts in heterogeneous catalysis,
etc. [1]. Among the chalcogenides, cadmium sulfide is one of the most studied. Since the first reports on the CdS
nanoparticle synthesis in 1980 years [ e.g . 2], this material has been produced in different nanostructures by
various methods [3] and, in past few years, the syn thesis of functionalized CdS nanoparticles was also reported
[4]. The chemical functionalization of nanoparticle s, meaning the modification of particle surface, is applied to
various nanomaterials, like metals, oxides, chalcog enides etc. [5, 6]. The synthesis of nanoparticles generally *Manuscript
Click here to view linked References

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involves surfactant molecules that bind to their su rface, which stabilize the nuclei and larger nanopa rticles
against aggregation by a repulsive force, and which generally control the growth of the nanoparticles in terms of
rate, final size or geometric shape. Ligand particl es stabilizing the nanoparticles against aggregatio n can simply
consist of an inert molecular chain (hydrocarbon ch ain or polyethylene glycol) or have functional grou ps that
are, in most cases, terminating linear molecules. M ost commonly, hydrophilic nanoparticles are stabili zed by
electrostatic repulsion by the equally charged liga nd molecules on the particle surface [7].
The functionalized nanoparticles represent an impor tant area of research due to their applications in
various domains of science and technology, like bio logy, medicine, engineering, energy storage and pro duction
etc. The properties of functionalized nanomaterials may be superior to those of the pristine ones, and new
applications were found based on their properties. For example, some semiconductor nanocrystals have a
tremendous potential in labeling biological entitie s such as cells, tissues and biohazard particles (b acteria,
viruses) [8]. The functionalized CdS nanoparticles have found app lications as photocatalysts [9, 10], as
fluorescence probe in the determination of uracil a nd thymine [11] or nucleic acids [12], as fluoresce nce single
shot probe for mercury(II) [13]. Furthermore, the f unctionalization of CdS nanoparticles is an approac h for
enhancing the photocatalytic activity of cadmium su lfide [14, 15]. The mercaptocarboxylic acids are of ten used
to stabilize various nanoparticles in the aqueous p hase [7] and some other studies reported the synthe sis and
characterization of CdS functionalized with mercapt ocarboxylic acids [ e.g . 9]. Thus, CdS quantum dots have
been obtained using mercaptoacetic acid as capping agent for synthesized nanoparticles, through a one step
process [13, 16], using sodium sulfide as source for sulfid e ion [4]; functionalized CdS nanoparticles were al so
obtained through more elaborate method, in microemu lsion, using mercaptoacetic acid under argon [9].
In continuation of our interest about cadmum sulfid e [15, 17, 18], we synthesized and characterized Cd S
nanoparticles functionalized with mercaptoacetate a nion (MAA; thioglicolate), using three different st rategies;
we characterized the resulted nanopowders and compa red their properties.
2. Experimental
2.1. Materials and methods
The high purity reagents were obtained commercially from Sigma-Aldrich (cadmium acetate,
Cd(CH 3COO) 2·2H 2O; sodium thioglycolate (sodium mercaptoacetate), C 2H3O2SNa; polyethylene glycol 200,
PEG 200; Congo red, CR), Merck (thioacetamide, TAA) , Loba (sodium hydroxide, NaOH), and were used as
received without further purification. The Congo re d (CR, C.I. Direct Red 28, M.W. = 696.67 g mol -1,

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C32 H24 N6O6S2Na 2) is the disodium salt of 3, 3'-([1, 1'-biphenyl]-4 , 4'-diyl)bis(4–aminonaphthalene-1-sulfonic
acid).
2.2. Synthesis of CdS nanopowders
CdS-MAA 1. Cd(CH 3COOH) 2·2H 2O (2.66 g, 10 mmol) was dissolved in 50 mL of water ; TAA (0.75 g, 10
mmol) and sodium mercaptoacetate (1.14 g, 10 mmol) were added in the solution. A 0.1 M NaOH solution w as
drop wised till yellow precipitate was formed. The mixture was stirred for 4 hours. The yellow powder was
isolated by vacuum filtration, washed with water an d dried. Selected FT-IR data (KBr, cm -1): 3398 (m); 2991
(w); 2980 (w); 1559 (vs); 1380 (s); 1226 (w); 777 ( vw); 701 (vw).
CdS-MAA 2. Cd(CH 3COOH) 2·2H 2O (2.66 g, 10 mmol) was mixed with TAA (0.75 g, 10 mmol) in a mortar,
with a pestle, till a homogenous powder resulted. S odium mercaptate (1.14 g, 10 mmol) was added in the
mixture and the reagents were ground together. A sm all quantity of water (1 mL) was added drop by drop till a
homogenous fluid mixture was obtained. The resulted mixture was intermittently triturated and left ove rnight,
and the mixture color turns in yellow – reddish. Fo r the removal of the unreacted compounds and byprod ucts, the
product was mixed with distillate water (50 mL), st irred for 30 min and the yellow powder was isolated by
vacuum filtration, washed with water and dried. Sel ected FT-IR data (KBr, cm -1): 3388 (m); 2994 (w); 2987 (w);
1551 (vs); 1384 (s); 1222 (w); 776 (vw); 698 (w).
CdS-MAA 3. Cd(CH 3COOH) 2·2H 2O (2.66 g, 10 mmol) was dissolved in 1.75 mL PEG 200 ( ρ = 1.124 kg/L; 10
mmol) using the trituration technique. TAA (0.75 g, 10 mmol) was added and the mixture was triturated, without
adding water, until the complete dissolution of the reagents, and a white paste was formed. The sodium
mercaptoacetate (1.14 g, 10 mmol) was added in the paste. The resulted mixture was then intermittently
triturated and left overnight. A homogenous yellow paste was obtained in time. For the removal of the unreacted
compounds and byproducts, the paste was mixed with distillate water, stirred for 30 min and the yellow powder
was isolated by vacuum filtration, washed with wate r and dried. Selected FT-IR data (KBr, cm -1): 3385 (m);
2993 (w); 2985 (w); 1558 (vs); 1375 (s); 1224 (m); 1125 (vw); 773 (vw), 696 (w).
In order to investigate the effect of mercaptoaceta te ion on the morphology and properties of the samp les,
a blank experiment was carried out by chemical prec ipitation method, without sodium mercaptoacetate; t he bare
CdS nanopowder was prepared as we previously descri bed [15]. Accordingly, Cd(CH 3COOH) 2·2H 2O (2.66 g, 10
mmol) and TAA (0.75 g, 10 mmol) were dissolved in 5 0 mL of water. A solution 25% of NH 3 was added drop
by drop, under continuous stirring, till pH = 8 and then the mixture was stirred for 4 hours. The ora nge powder

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was filtered off, washed with water and dried. Sele cted FT-IR data (KBr, cm -1): 3417 cm -1 (m), 1614 cm -1 (vw),
1553 cm -1 (vw), 1010 (vw) [15].
2.3. Characterization of CdS nanopowders
The obtained powders were investigated by X-ray dif fraction (XRD) performed on a Rigaku Miniflex 2
diffractometer with Ni filtered CuK α radiation, in the range of 2 θ, 20 – 85°, scan rate of 2°/min and a step of
0.02°.
The transmission electron microscopy (TEM) investig ations of CdS nanopowders were performed on a
Philips CM 120 ST transmission electron microscope operated at 100 kV, with 2 Ǻ resolution.
The UV-Visible diffuse reflectance spectra of CdS p owders were recorded in the range of 220 – 850 nm,
on a Jasco V 550 spectrophotometer, in an integrati ng sphere, using MgO as the reference. The FT-IR spectra
were recorded with Jasco FT-IR 4200 spectrometer fr om KBr pellets, in the range of 400 – 4000 cm –1.
The specific surface area measurements were perform ed on Quantachrome Autosorb iQ2 porosimeter in
the 0.05-0.30 relative pressure range, at liquid ni trogen temperature, the values being computed usin g the multi-
point Brunauer-Emmett-Teller (BET) method. Prior t o analysis, the samples were out gassed under vacuu m at
40°C, 12 h.
2.4. Catalytic properties of CdS nanopowders
The photocatalytic degradation of CR was performed using for each determination 100 mL of 30 mg/L
CR solution and 0.05 g CdS as catalyst (60 mg CR/1 g CdS). The experiments were performed in covered P yrex
vessels of 250 mL capacity, using simultaneously tw o samples, which were exposed to the ambient light and to a
20 W halogen lamp (Ecolite, China) as simulated vis ible light sources, respectively. The halogen lamp was
irradiated perpendicularly to the surface of soluti on, and the distance between the UV-Vis source and vessel
containing the reaction mixture was fixed at 15 cm. The spectrum of the lamp was measured with a HR400 0CG-
UV-NIR High-Resolution Spectrometer, from Ocean Opt ics, confirming the matching with the solar spectru m.
The suspension was magnetically stirred to ensure t hat all catalyst active sites are in contact with t he dye
solution and exposed to light.
The suspensions were sampled at regular intervals a nd immediately centrifuged at 5000 rpm for 10 min
with a M 815 M centrifuge (from Elektro-Mag), and t hen filtered off to completely remove the catalyst particles.
The degradation efficiency of CR was monitored by U V–Vis spectroscopy.
According to the Beer–Lambert law, the concentratio n of CR is proportional to its absorbance, so the
photocatalytic activity ( PA ), also known as the degradation efficiency ( R), can be calculated by [19, 20]:

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/g1842/g1827 /g3404/uni0009/g1829/g2868/g3398/g1829/g3047
/g1829/g2868/uni0009/g3404/uni0009/g1827/g2868/g3398/g1827/g3047
/g1827/g2868
where A0, At, and C0, Ct are the absorbance and concentration of CR when th e reaction time is 0 and t,
respectively.
The UV-VIS absorption spectra of CR solutions were recorded in the range of 200 – 900 nm, on a Jasco
V 550 spectrophotometer.
The absorption peaks corresponding to CR appeared a t 497 nm, 347 nm and 237 nm [21].
3. Results and discussion
Three facile routes to obtain functionalized CdS by one-pot synthesis, at room temperature were used.
The idea was to obtain the CdS nanoparticles using TAA as sulfide ion source, in the presence of a
functionalizing agent, the synthesis and functional ization of CdS particles being carried out in the s ame time
(one-pot). For functionalization the mercaptoacetic acid was employed because mercaptocarboxylic ligan ds are
frequently used in the colloidal syntheses to inhib it the nanoparticles growth and aggregation, as wel l as to
control their structural characteristics [7, 22]. T he sodium mercaptoacetate was preferred as reagent because,
unlike mercaptoacetic acid, which is a liquid with an unpleasant odor, is a freely water soluble powde r.
CdS nanoparticles obtained in alkaline medium react ed with mercaptoacetate ions for 4 h under vigorous
stirring (CdS-MAA 1). It is assumed the mercapto group binds to a cadm ium ions and the polar carboxylic acid
group renders the nanoparticles water soluble and b iocompatible [23]. In time, the nanoparticles bring together
making insoluble powders, which were filtered off a nd structural and morphological characterized.
The trituration technique was also used for CdS syn thesis (CdS-MAA 2), due to the excellent results
obtained in the synthesis of PEG-capped CdS [15]. F urthermore, due to the trituration may be correlate d with the
presence of a surfactant, the water solvent was cha nged with PEG 200 (CdS-MAA 3).
3.1. Characterization of CdS nanopowders
3.1.1. X-ray diffraction
The XRD technique was used to identify the crystall ine phase of cadmium sulfide nanoparticles.
For CdS-MAA 1 (Fig. 1.a), the XRD results revealed that the sampl e is a mixture of cubic and hexagonal
phases. The most intense diffraction peak centered at 2θ = 26.52° indicated that CdS with cubic symmetry
(ICDD 80-0019) was predominant phase, while the Bra gg reflection (103) at 2 θ ~ 48° demonstrated the presence
of hexagonal CdS phase (ICDD 80–0006).
The CdS-MAA 2 and CdS-MAA 3 samples are also mixtures of cubic and hexagonal p hases, with most
intense diffraction peaks assigned to cubic structu re.

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The crystallite size of cadmium sulfide powders was calculated from the XRD data with Rigaku PDXL
software based on Scherrer’s equation from (1 1 1) diffraction peak ( D111 ). The values for crystallite size were 20
nm (CdS-MAA 1), 34 nm (CdS-MAA 2) and 20 nm (CdS-MAA 3), indicating the synthesis of nanoparticles.
3.1.2. Transmission electron microscopy
The morphology of CdS nanoparticles was investigate d by TEM. The TEM images (Fig. 2) proved that
all the samples may be considered nanopowders, pres enting namely as agglomerates of ultrafine particle s that
are in agreement with the crystallite size estimate d by XRD.
As one can see in Fig. 2, the CdS-MAA 2 sample seems to be less transparent, probably beca use of the
amorphous phase on the surface of nanoparticles. Th e previous studies demonstrated the presence of an
amorphous interface between the metal sulfide and t he capping molecule [24].
Therefore, the results from both XRD and TEM studie s revealed that all the samples have a low
crystallinity, which may be correlated with the org anic molecules acting as functionalization/capping agents.
The mean diameter was evaluated from TEM images usi ng a semi-automated algorithm implemented in
analysis software. Thus, it was calculated as arith metic mean of all diameters measured on particles a t angles that
varies with 15 o steps. The final mean diameter was approximated as suming a lognormal distribution of resulted
diameters. Experimental diameter measured from TEM micrograph was fitted with function given by:
/g1877 /g3404/uni0009/g1877 /g2868/g3397/uni0009/g1827/g1857/g2879/g3039/g3041 /g3118/g4666/g3051 /g3051/g3278/g4667/uni2044
/g2870/g3050/g3118
where A is an arbitrary constant related to particle numbe r, xc represents the distribution maximum and w is
strong correlated with particle diameter dispersion . The values calculate for particles shown in Fig. 2 (a and c)
are 7.51 nm (CdS-MAA 1) and 3.05 nm (CdS-MAA 3), as it can be seen in Fig. 3.
3.1.3. FT-IR spectroscopy
In order to identify the presence of MAA as ligand in CdS powders, the FT-IR spectra were performed.
In the spectra of all three samples, the presence o f water was demonstrated by the broad absorption ba nds ( νOH :
CdS-MAA 1, 3398 cm -1; CdS-MAA 2, 3388 cm -1; CdS-MAA 3 3385 cm -1). The mercaptoacetate ion, which
most probably is capping CdS nanoparticles, was ide ntified by very intense bands assigned to the asymm etric
and symmetric vibrations of carboxylate group (νas (COO): CdS-MAA 1, 1559 cm -1; CdS-MAA 2, 1551 cm -1;
CdS-MAA 3 1558 cm -1; νs(COO): CdS-MAA 1, 1380 cm -1; CdS-MAA 2, 1384 cm -1; CdS-MAA 3 1375 cm -1)
[25]. The bands assigned to carboxylate group are s hifted to lower wave numbers compared to those from
sodium mercaptoacetate, indicating the coordination of mercaptoacetate ion to cadmium atoms through th e

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carboxylate group. The vibrations in the range of 2 950 – 3000 cm -1 (doublet, νC-H) partially overlapped with the
band assigned to water molecules and the weaker max ima at around 1260 cm -1, 780 cm -1 and 700 cm -1 can also
be assigned to mercaptoacetate ion. In the spectrum of CdS-MAA 3, the band at 1125 cm -1, which can be
assigned to the νC-O vibration mode, can due to PEG which also may cap the CdS nanoparticles [25]. The low
intensity of the bands assigned to PEG could be exp lain to the partial removal of capping agent in the washing
step that is favorable for the catalytic reactions because the polymer acts as a physical barrier rest ricting the
reactants access of to catalytically active sites [ 15, 26].
3.1.4. UV-Visible diffuse reflectance spectroscopy
UV-Vis diffuse reflectance spectroscopy was used to study the optical properties of CdS nanopowders.
The UV-Vis absorption spectra are shown in Fig. 4.
The absorption edges of all three CdS-MAA nanopowde rs were located nearby of 400 nm (386 nm for
CdS-MAA 1, 399 nm for CdS-MAA 2, 409 nm for CdS-MAA 3). The absorption bands are UV-Vis blue-shifted
compared to the band of CdS nanopowder obtained wit hout functionalization agent (451 nm [15]), and for all
studied nanopowders a relative UV-Vis blue-shifting to the absorption edge of bulk cubic CdS (515 nm) may be
noticed [18, 27]. By comparing the position of abso rption maxima, one can see a lower value for CdS-MA A 1,
which may be correlated with the higher band gap en ergy. Furthermore, the steep absorption edge indica tes a
narrow particles size distribution of CdS samples [ 28], which was also confirmed by TEM and the shift ing of
the absorption edges may be correlated with the par ticles size in the nanometric range.
3.1.5. Band gap energies
The band gap of semiconductor materials plays a fun damental role in their electrical and optical
properties, the values of band gap energy being cor related with structural characteristics. The relati onship
between the band gap and particle dimension, and th us the size effects on the electronic properties of
semiconductors has been observed for many materials [29 – 31]. CdS is a direct band gap semiconductor (2.42
eV band gap for bulk CdS) and for many applications (like photovoltaic devices or photocatalysis) it i s important
to know how the optical properties, such as energy band gap, vary with the synthesis parameters [3].
The Tauc relation [32] was used to estimate the opt ical band gap ( Eg):
/g2009/g1860ν/g3404 /g1829/g3435/g1860ν/g3398/g1831/g3034/g3439/g3041 (1)
where α is the absorption coefficient of the CdS at a cert ain value of wavelength λ, h is Planck's constant, C is
the proportionality constant, ν is the frequency of light, and n = ½ (for direct transition mode materials).
The absorption coefficient is evaluated using the r elation:

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/g2009 /g3404 /g1863⋅/g1864/g1866/g4672/g3019/g3288/g3276/g3299 /g2879/g3019/g3288/g3284/g3289
/g3019/g2879/g3019/g3288/g3284/g3289 /g4673 (2)
where k is a constant, Rmax is the maximum reflectance and Rmin is the minimum reflectance.
Consideration of Eqs. (1) and (2) gives Eq. (3):
/g4666/g2009/g1860ν/g4667/g2870/g3404 /g1829′/g3435/g1860ν/g3398/g1831/g3034/g3439 (3)
where C' is a constant. From Eq. (3), a Tauc plot can be dr awn of ( αhν)2 versus hν. The point of the extrapolation
of the linear part that meets the abscissa will giv e the value of material band gap energy [32, 33].
Fig. 5 shows the Tauc plot for the CdS samples. The highest value for band gap energy may be assigned
to CdS-MAA 1, while the values for CdS-MAA 2 and CdS-MAA 3 are similar. The value of band gap energy
influences the material catalytic properties.
3.2. Photocatalytic properties
The catalytic activity of CdS-MAA powders was deter mined and compared with the bare CdS
nanopowder in order to underline functionalization effect.
The catalytic activity of CdS-MAA nanopowders was m onitored by the dye bleaching, proofing the
breakup of the azo bond, and also by the degradatio n of aromatic moiety. The disappearance of CR by br eaking
up the azo bond was observed using the UV–Vis absor bance feature at λ = 497 nm (the azo bond degradation) as
a function of irradiation time, and the CR concentr ation was calculated from the absorbance values.
The most efficient catalyst was CdS-MAA 1 (Fig. 6.a). The degradation of RC in the presence of CdS-
MAA 1 was very fast and dependent on the illumination; f or example, after 10 min the values for photocataly tic
activity were PA = 0.2196 (21.96%) without illuminat ion and PA = 0.3634 (36.34%) under illumination; af ter
90 min, the values were PA = 0.7892 (78.92%), respe ctive 0.9434 (94.34%), both values being superior t o those
calculated for bare CdS (5.86% without illumination , 15.38% under illumination after 90 min). The high
catalytic activity of CdS-MAA 1 may be considered similar, but still lower, with t hose reported for PEG-capped
CdS (degradation efficiency up to 97%, after 90 min ) [15].
The catalytic activity for both CdS-MAA 2 and CdS-MAA 3 (Fig. 6) was lower compared to CdS-MAA
1, but remains high in comparison with bare CdS. For example, after 90 min PA% = 53,44%, respective 66.4 3%
(light) for CdS-MAA 2, and 20.05%, respective 44.26% (light) for CdS-MAA 3. The light dependency may also
be noted for both samples.

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The solution was not only bleached, also the dye d ecomposed, this chemical reaction being evidenced
by the decrease of intensity of band assigned to ar omatic rings in the electronic spectra (Fig. 7). A similar
behavior was also observed for CdS capped with PEG [15].
The high degradation rate of the dye in contact wit h CdS-MAA 1 sample proved the contribution of the
adsorption process in dye discoloring, at least in an initial phase. The specific surface area values (SBET ) were
determined for CdS-MAA 1 by BET method. The N 2 adsorption-desorption isotherm recorded at liquid nitrogen
temperature proved that CdS sample is nonporous mat erial having a specific surface area of 56 m 2/g. The S BET is
higher than for bare CdS (6 m 2/g [15]), comparable with those of PEG-capped CdS ( 56 m 2/g) previously
reported [15].
Despite the higher specific surface area in compari son with the bare CdS, the catalytic action is not
determined only by the adsorption of dye on the cat alyst surface. As prove for this assumption, the el ectronic
spectrum of CdS-MAA 1, after the catalytic process, does not contain a b and which may be assigned to CR (Fig.
8).
Thus, the functionalization of CdS nanoparticles wi th mercaptoacetate anion by chemical precipitation
method (CdS-MAA 1) led to a higher catalytic activity, which may be correlated with a bigger specific surface
area value compared to bare CdS. The trituration of an aqueous dispersion (CdS-MAA 2) seemed to lead to CdS
nanopowder less crystallyne, with a surface strongl y modified compared with the pristine powder. As a
consequence, the catalytic activity was lower compa re with CdS-MAA 1. The lowest catalytic activity of CdS
nanopowder functionalized in a non-aqueous solvent (CdS-MAA 3) may be explained by capping agent that
acts as a physical barrier restricting the free acc ess of reactants to catalytically active sites [26] . A low quantity
of mercaptoacetate ions which can be correlated wit h the crystalline aspect of nanopowder is also a sa tisfactory
explanation. Thus, despite the functionalization wi th MAA/capping with PEG of CdS nanoparticles leadin g each
one to an increase of their catalytic activity, whi le the presence of both agents in the synthesis med ium,
decreased their performances.
4. Conclusion
The one-pot functionalization of cadmium sulfide wa s performed using three strategies. By all routes
functionalized CdS nanoparticles with an average si ze in the range of 20 – 34 nm and strongly dependen t features
on the synthesis method were obtained.
Thus, by chemical precipitation, MAA-functionalized CdS nanopowder with a crystallite size of 20 nm,
consisting in a mixture of cubic (predominant) and hexagonal phases, was synthesized. The good photoca talytic

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activity of this nanopowder (a degradation efficien cy up to 94%, after 90 min) can be correlated with its high
specific surface area (56 m 2/g) and wider band gap energy (3.13 eV) compared wi th bare CdS nanopowder.
The MAA-functionalized CdS nanopowders obtained by trituration techniques in aqueous and non-
aqueous solutions are also mixtures of cubic and he xagonal phases, with similar band gap energy values (3.00
eV and 2.98 eV, respectively). However, the photoca talytic activity of nanoparticles prepared by this technique
is lower, probably because of a low functionalizati on and/or the growth of a barrier around particles surface.
Among employed synthesis methods, the chemical prec ipitation in solution was the most suitable for the
preparation of CdS nanoparticles with high catalyti c activity.
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Figure 1
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Figure 2-a
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Figure 2-b
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Figure 2-c
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Figure 3-a
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Figure 3-b
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Figure 4
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Figure 5
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Figure 6-a
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Figure 6-b
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Figure 6-c
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Figure 7
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Figure 8
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Figures caption

Figure 1. The XRD patterns of CdS nanopowders.
Figure 2. The TEM images for CdS -MAA 1 (a), CdS -MAA 2 (b), CdS -MAA 3 (c).
Figure 3. The mean particle size and particle distribution for CdS nanopowders.
Figure 4 . The UV–Vis absorption spectra of CdS nano powders.
Figure 5 . Tauc plots (( αh)2 vs. photon energy) for CdS samples.
Figure 6. The photocatalytic degradation curves of CR over the CdS -MAA nanopowders, in different conditions.
Figure 7. The UV–Vis spectral changes of RC solutions as function of time (illumination).
Figure 8. The UV -Vis absorption spectra of CdS -MAA 1 nanopowders, after the catalytic processes, compared
with initial spectrum.
Captions – Figure(s)