poly (vinyl alcohol)/poly (acrylic cid )/tio /graphene oxide...

AASCIT Journal of Chemistry 2019; 5(2): 14-22

http://www.aascit.org/journal/chemistry

Poly (Vinyl Alcohol)/Poly (Acrylic Cid)/TiO2/Graphene Oxide Nanocomposite Hydrogels for Photocatalytic Degradation of Organic Pollutants

Asmaa El-Zoghby, Rafik Abbas, Wagih Sadik, Abdel Ghaffar El Demerdash

Institute of Graduate Studies and Research, Alexandria University, Alexandria, Egypt

Email address

Citation Asmaa El-Zoghby, Rafik Abbas, Wagih Sadik, Abdel Ghaffar El Demerdash. Poly (Vinyl Alcohol)/Poly (Acrylic Cid)/TiO2/Graphene Oxide

Nanocomposite Hydrogels for Photocatalytic Degradation of Organic Pollutants. AASCIT Journal of Chemistry.

Vol. 5, No. 2, 2019, pp. 14-22.

Received: December 18, 2018; Accepted: June 2, 2019; Published: July 30, 2019

Abstract: Poly (vinyl alcohol)/poly (acrylic acid)/TiO2/graphene oxide nanocomposite hydrogels were prepared using radical

polymerization and condensation reacti006Fn for the photocatalytic treatment of waste water. Graphene oxide was used as an

additive to improve the photocatalytic activity of poly (vinyl alcohol)/poly (acrylic acid)/TiO2 nanocomposite hydrogels. Both

TiO2 and graphene oxide were immobilized in poly (vinyl alcohol)/poly (acrylic acid) hydrogel matrix for an easier recovery

after the waste water treatment. By using different ratio of both TiO2 and GO to show the best performance for the degradation of

MB dye. The photocatalytic activity of poly (vinyl alcohol)/poly (acrylic acid)/TiO2/graphene oxide nanocomposite hydrogels

was evaluated on the base of the degradation of pollutants by using UV spectrometer. The improved removal of pollutants was

due to the two-step mechanism based on the adsorption of pollutants by nanocomposite hydrogel and the effective decomposition

of pollutants by TiO2 and graphene oxide. The highest swelling of nanocomposite hydrogel was observed at pH 10 indicating that

poly (vinyl alcohol)/poly (acrylic acid)/TiO2/graphene oxide nanocomposite hydrogels were suitable as a promising system for

the treatment of basic waste water.

Keywords: Graphene Oxide, Photocatalyst, Hydrogel, Poly (Acrylic Acid), Nanocomposite

1. Introduction

The waste water treatments have been studied widely as the

waste water from textile, paper, leather, ceramic, cosmetics, ink,

and food processing industries becomes severer [1]. Synthetic

organic dyes present certain hazards and environmental

problems. Disposal of these dyes into water can be toxic to

aquatic life. They cause a health problem because they may be

mutagenic and carcinogenic [2-4]. Methods and effluent

treatment for dyes may be divided into three main categories;

physical, chemical, and biological. Among them adsorption

technology is generally considered to be an effective method for

quickly lowering the concentration of dissolved dyes in an

effluent. In recent years, polymeric adsorbent have been

increasingly used to remove and recover organic pollutants

from waste waters [5]. Polymeric hydrogels have been the focus

of research for environment scientists due to their characteristic

properties such as adsorption- regeneration, economic

feasibility and environmental friendly behavior [2]. The most

common of these is that hydrogel is hydrophilic 3D polymer

networks, that can swell in water or biological fluids and hold a

large amount of them more than 20% of their dry weight, up to

thousands of times their dry weight [4-5], yet are insoluble

because of the presence of physical or chemical crosslinks,

entanglements, or crystalline regions [5], produced by the

simple reaction of one or more monomers [7]. Smart hydrogels

are able to alter their volume and properties in response to

environmental stimuli such as pH, temperature, ionic strength,

and electric field [8]. To improve the mechanical properties of

hydrogel, poly (vinyl alcohol) (PVA) was incorporated with

poly (acrylic acid) (PAAc). PVA has attracted attention in the

controlled drug delivery, due to the biocompatibility and the

strong mechanical properties [9]. PAAc contains pendant

carboxylic acid groups which can release proton in response to

changes in pH. When the pH of medium is above the pKa of

PAAc, the ionized PAAc network could be swelled [10].

Recently, environmental purification using TiO2 as a

photocatalyst has attracted a great deal of attention because of

its high activity, chemical stability, robustness against

15 Rafik Abbas et al.: Poly (Vinyl Alcohol)/Poly (Acrylic Cid)/TiO2/Graphene Oxide Nanocomposite Hydrogels for

Photocatalytic Degradation of Organic Pollutants

photocorrosion, low toxicity, low pollution load, and

availability at low cost [8]. The use of semiconductors (TiO2) as

alternative photocatalyst is also limited mainly due to the

recombination of the generated photo-holes and

photo-electrons [11]. Hence, many researches currently focus

on the improvement of photocatalytic efficiency [12]. The

carbon materials works as the electron sink for the

hindrance of charge carrier recombination. The

photocatalytic decomposition of pollutants by TiO2 was

improved with addition of GO [1]. The preparation of poly

(vinyl alcohol)/poly (acrylic acid)/TiO2/graphene oxide

nanocomposite hydrogels has been reported [1]. They used

one ratio of TiO2 and different ratio of GO, but we used

different ratio of both GO and TiO2.

2. Literature Review

Yue et al. synthesized series of full interpenetrating

polymer network (full-IPN) films of poly (acrylic acid)

(PAA)/poly (vinyl alcohol) (PVA) were prepared by radical

solution polymerization and sequential IPN technology [27].

Yun et al. examined the pH-sensitive photocatalytic system

which prepared by embedding TiO2 into poly (vinyl

alcohol)/poly (acrylic acid) hydrogel. Two different types of

TiO2/hydrogel composites, such as matrix and nano fiber,

were prepared to investigate the morphological effects on the

photocatalytic activity. TiO2 was distributed uniformly in the

composite hydrogel and kept the original anatase structure

without any structural change. The PVA/PAAc/TiO2

nanofibers gave faster and higher swelling due to the larger

surface area as the pH of medium was changed into the basic

condition. The photodegradation of dye was improved greatly

by using TiO2 photocatalyst in PVA/PAAc hydrogel nanofiber

supports. The TiO2 particles were observed in the PVA/PAAc

hydrogel matrix without any crack at the interface between

hydrogel and TiO2 particles. The TiO2 domains of various

sizes were observed indicating that the TiO2 aggregations

occurred somewhat in the hydrogel matrix depending on the

content of TiO2 [28].

Jeon et al. prepared the pH-sensitive

PVA/PAAc/TiO2/CNTs composite nanofibers by

electrospinning method in order to treat the basic waste water.

Various ratios of CNTs was dispersed into PVA/PAAc/TiO2

solution in such various weight percentages as 0, 0.3, 0.7, and

1.0% respectively. The photocatalytic activity of TiO2 for the

efficient dye removal was improved further by incorporating a

proper content of conductive CNTs. A strong interaction

between TiO2 and CNTs contributed the efficient electron

transfer in the TiO2/CNTs composites resulting in the

reduction of electron/hole recombination and the

improvement of photon efficiency. The higher swelling of

PVA/PAAc/TiO2/CNTs composite nanofibers was observed

under the electric field due to the enhanced ionization of

PVA/PAAc hydrogel resulting in the higher electrostatic

repulsion and hydrophilicity of the polymer chains [29].

Further work by Moon et al. has been carried out on prepared

PVA/PAAc/TiO2/GO nanocomposite hydrogels using radical

polymerization and condensation reaction for the photocatalytic

treatment of waste water. Graphene oxide was used as an

additive to improve the photocatalytic activity of

PVA/PAAc/TiO2 nanocomposite hydrogels. Both TiO2 and

graphene oxide were immobilized in PVA/PAAc hydrogel

matrix for an easier recovery after the waste water treatment [1].

3. Experimental

3.1. Materials

Poly (vinyl alcohol) (PVA, 87–89% hydrolyzed, Mw:

31,000–50,000) and acrylic acid (AAc, 99%) were purchased

from Acros Organics. \A\S (GA, 25wt.% solution in water)

and ethylene glycol dimethacrylate (EGDMA, 98%)

purchased from Acros Organics were used as crosslinking

agent for PVA and PAAc, respectively. Potassium persulfate

(KPS, 99+%, A. C. S. reagent) obtained from Acros Organics

was used as initiator. Titanium oxide (TiO2, 99%, anatase

powder, average size: 50 nm) was purchased from MKnano as

photocatalyst. Methylene Blue (MB) (C16H18N3SCl, λmax =

665 nm) was purchased from Fisher Bio reagent. All other

chemicals used were of analytic grades.

3.2. Preparation of GO

GO was prepared from a low-purity natural graphite

powder by using the Hummers method [13]. 2.0 g of graphite

and 1.0 g of NaNO3 were dissolved in 46.0 mL of

concentrated H2SO4 under an ice bath. After about 15.0 min of

stirring, 6.0 g of KMnO4 was gradually added into the

suspension with stirring as slowly as possible in order to

control the reaction temperature below 20.0°C. The

suspension was stirred for 2.0 h, and then maintained at

35.0°C for 30.0 min. 92.0 mL of deionized water was slowly

poured into the suspension, resulting in a quick increase in

temperature, and the temperature should be controlled lower

than 98.0°C. After 15.0 min, the suspension was then further

diluted to approximately 280.0 mL with warm deionized

water. 20.0 mL of 30.0% H2O2 was added to the mixture to

stop the reaction and the color of the mixture changed to bright

yellow, indicating high oxidation level of graphite. The

resulting mixture was washed by repeated centrifugation and

filtration with 5.0% HCl solution in order to remove the metal

ions. The final GO slurrqawy was sonicated for 1.0 h followed

by filtering and drying in vacuum oven at 50.0°Cfor 24.0 h.

3.3. Preparation of PVA/PAAc/TiO2/GO

Nanocomposite Hydrogels PVA

The PVA/PAAc hydrogels were synthesized by the free

radical polymerization. PVA and PAAc were selected as the

components mainly for improving the mechanical property

and exhibiting the pH-sensitive swelling behavior of

hydrogels, respectively. PVA solution (10.0.% w/v) was

prepared by dissolving PVA in distilled water 90.0°C for 6.0 h

and subsequent cooling down to room temperature. The

PVA/PAAc hydrogels were synthesized by the free radical

polymerization. PVA and PAAc were selected as the

AASCIT Journal of Chemistry 2019; 5(2): 14-22 16

components mainly for improving the mechanical property

and exhibiting the pH-sensitive swelling behavior of

hydrogels, respectively. The reaction mixture solution was

prepared by mixing 8.0 ml of (10.0 wt.%) PVA solution, 8.0

ml of AAc solution, 0.15 ml of GA solution, 0.90 ml of

EGDMA, and 0.5 ml of (1.0 wt.%) KPS with TiO2. The

reaction mixture was stirred for 30.0 min at room temperature

followed by nitrogen purging for 30.0 min to remove the

oxygen dissolved in the reaction mixture. The reaction

mixture was stirred for 2.0 h at 70.0°C to prepare

TiO2/PVA/PAAc/GO nanocomposite hydrogel. These

nanocomposite hydrogels were washed with distilled water at

room temperature by replacing with fresh distilled water every

few hours. Hydrogels was cut into disc-like pieces. Swollen

hydrogel disks were dried in vacuum oven.

Table 1. Classification of PVA/PAAc/TiO2/GO nanocomposite hydrogels.

Sample TiO2 (w/v%)/polymer GO (w/v%)/polymer

1 TiO2 (0.5)/PVA/PAAc 0

1.1 TiO2 (0.5)/PVA/PAAc 0.25

1.2 TiO2 (0.5)/PVA/PAAc 0.75

1.3 TiO2 (0.5)/PVA/PAAc 1.25


2.1 TiO2 (1.0)/PVA/PAAc 0.25

2.2 TiO2 (1.0)/PVA/PAAc 0.75

2.3 TiO2 (1.0)/PVA/PAAc 1.25


3.1 TiO2 (3.0)/PVA/PAAc 0.25

3.2 TiO2 (3.0)/PVA/PAAc 0.75

3.3 TiO2 (3.0)/PVA/PAAc 1.25

3.4. Sample Characterization

The anatase structure of TiO2 in PVA/PAAc/TiO2/GO

nanocomposite hydrogel was studied by using X-ray

diffraction (XRD) patterns. The samples were investigated on

(schimad Zn 7000, Japan) diffractometer with Cu radiation

and were analyzed from 5.0º to 80.0º in 2 (2θ) with a step size

of 0.02º and a step time of 3.0 s.

The surface morphologies of PVA/PAAc/TiO2/GO

nanocomposite hydrogels were observed using a scanning

electron microscope ((JEOL-JSM-5300). As a pretreatment,

every sample was sputter coated with gold.

Fourier-transform infrared spectrometer (FT-IR,

Thermo-Nicolet 380) was used to investigate the functional

groups on GO. The FT-IR spectra of samples were obtained in

the range of 400.0–4000.0 cm−1

. To investigate the elements

present in graphite and GO.

3.5. Swelling Studies

Swelling experiments were performed by placing the

prepared polymer discs in buffer solutions of varying pHs of

(3.0 - 12.0) at room temperature 25.0°C and measuring weight

gain as a function of time. The discs were withdrawn from the

buffer solutions and weighed after removal of excess surface

water by gentle blotting with a tissue. Percent swelling is

expressed as the percent weight ratio of water held in hydrogel

to dry hydrogel at any instant during swelling.

%swelling weightofswelledhydrogel– weightofdryhydrogel

Weightofdryhydrogel� 100

Equilibrium degrees of swelling values are the maximum

swelling values of the samples.

3.6. Dye Adsorption Test

The dye adsorption tests were carried out in 100.0 ml of dye

solution with an initial concentration of methylene blue (MB)

5.0 mg/L and 1.0 g of PVA/PAAc, PVA/PAAc/TiO2 and

PVA/PAAc/TiO2/GO nanocomposite hydrogels. The

nanocomposite hydrogels were placed in dye solution at

25.0°Cfor 24.0 h in dark. The variations in concentration of

dye solution were measured by Visible spectrometer (visible

spectrophotometer Alpha 1102) at the wavelengths of

(662.0-665.0 nm) corresponding to the maximum absorption

position MB. qe is the amount of dye adsorbed onto unit dry

mass of the hydrogels (mg/g). The adsorption (qe) was

calculated as follows:

q��mg/g� �C� � C �V/W

where C0 and Ct are the concentrations of dye solution at t = 0

and t, respectively. V (L) is the volume of dye solution, and W

(g) is the weight of hydrogels. The removal dye efficiency

(R%) was calculated by the following equation:

RemovaldyeR% %�C� � C �/C�& � 100

R% %�A� � A �/A�& � 100

where A0 and At are the absorptions of dyes solution at t = 0

and t, respectively [14].

3.7. Photocatalytic Decomposition of

Pollutant Dyes

The photocatalytic activities of various PVA/PAAc/TiO2

and PVA/PAAc/TiO2/GO nanocomposite hydrogels were

evaluated based on the decomposition of model pollutant dye

MB. The dye decomposition experiments were carried out

with an ultraviolet (UV) lamp (365.0 nm, 40.0 W) inside using

100.0 ml of dye solution with an initial concentration of 5.0

mg/L, 10.0 mg/L and 1.0 g of PVA/PAAc/TiO2/GO

nanocomposite hydrogels. The variations in concentration of

model dye were determined by Visible spectrometer (visible

spectrophotometer Alpha 1102) based on the absorbance at

the wavelength of 665.0 nm for MB. The photocatayltic dye

decomposition calculated from Ct/C0 and photocatalytic dye

decomposition efficiency (De%) was calculated by the

following equation:

De% %�C� � C �/C�& � 100

De% %�A� � A �/A�& � 100



Where C0 and Ct are the concentrations of dye solution at t =

0 and t, respectively. A0 and At are the absorptions of dyes

solution at t = 0 and t, respectively [15].

4. Results and Discussion

4.1. Characterization of GO and

PVA/PAAc/TiO2/GO Nanocomposite

Hydrogels FT-IR

FT-IR spectra of both GO and PVA/PAAc/TiO2/GO

nanocomposite hydrogels TiO2 (1.0) and GO (1.25) (w/v%)

are presented in Figure 1. In GO spectrum, the absorption peak

at 3000–3500 cm−1

corresponding to the OH and the

absorptions peak at 1639 cm−1

due to the C=O stretching of

COOH groups. The absorption bands at 1040 corresponding

to the epoxy ring deformation [16]. These results indicated

that many oxygen-containing functional groups were

produced during the oxidation of graphite.

In PVA/PAAc/TiO2/GO spectrum, the absorption peak at

3000–3500 cm−1

corresponding to the OH for PVA, PAAc and

GO overlapped with each other. The absorption peak at 1724

cm−1

and 1637 cm

−1 corresponding to the C=O stretching of

COOH groups at edges of PAAc and GO, respectively.

C−O−C/C−OH vibrations at 1000–1400 cm−1

[1].

Figure 1. FT-IR spectrum GO and PVA/PAAc/TiO2/GO nanocomposite hydrogels TiO2 (1.0) and GO (1.25) (w/v.%).

4.2. Structural Analysis of GO, TiO2 and

PVA/PAAc/TiO2/GO Nano Composite

Hydrogels

The structural characteristics of anatase TiO2, GO and

PVA/PAAc/TiO2/GO nanocomposite hydrogels TiO2 (1.0)

and GO (1.25) (w/v.%) were studied by XRD as shown in

Figure 2. GO, the peak centered at 11.3º corresponding to the

(002) lattice plane. All of the above results demonstrated that

the oxidation conversion process from graphite to graphite

oxide was successful, XRD of GO similar to XRD of GO in

[17]. The typical high (101), (200) diffraction peaks at 25.3º

and 48.0º suggesting that the samples had an anatase phase

structure [18]. The structure of anatase TiO2, which was

known as an effective photocatalyst, remained intact during

the polymerization process in the preparation of

nanocomposite hydrogels [8]. The absence of the typical

diffraction peak of GO in the PVA/PAAc/TiO2/GO

nanocomposite hydrogels might be attributed to the

combination of polymer matrices with GO resulting in the

enhanced sonication of GO and the low diffraction intensity in

the nanocomposite hydrogels [1].

Figure 2. X-ray diffraction patterns of TiO2, GO, and PVA/PAAc/TiO2/GO

nanocomposite hydrogel TiO2 (1.0) and GO (1.25) (w/v.%).


4.3. Morphology of PVA/PAAc/TiO2/GO

Nanocomposite Hydrogels

SEM was used to characterize the cross-sectional surface of

PVA/PAAc/TiO2/GO nanocomposite hydrogels as presented

in Figure 3. The TiO2 and GO (w/v.%) ratios (a) 3.0 and 1.25,

(b) 3.0 and 0.75, (c) 1.0 and 1.25, (d) 1.0 and 0.25 and (e) 0.5

and 1.25.

Figure 3. SEM micrograph of various PVA/PAAc/TiO2/GO nanocomposite hydrogels TiO2 and GO (w/v.%) (a) 3.0 and 1.25, (b) 3.0 and 0.75, (c) 1.0 and 1.25,

(d) 1.0 and 0.25 and (e) 0.5 and 1.25.

Figure 3 (a, b) showed that when the amount of GO sheets

was increased to 1.25 and 0.75 (w/v.%) with increasing TiO2

3.0 (w/v.%), the cross section morphology of the hydrogel was

very different. It was apparent that the aggregation of GO

sheets and TiO2 in the matrix during the polymerization.

Moreover, Figure 3 (c, d, e) the surfaces of the

nanocomposites containing a small amount of GO sheets and

TiO2 were relatively uniform, indicating that GO sheets did

not form large agglomerates in the matrix. Also showed that

the surface was also very compact, indicating that GO sheets



were dispersed homogeneously in the polymer matrix and

there were interfacial interactions between GO and the matrix.

4.4. Swelling Behaviors of PVA/PAAc/TiO2/GO


The swelling behavior of PVA/PAAc/TiO2/GO

nanocomposite hydorogels was investigated at various

contents of TiO2 and GO to study the pH-sensitive properties

as shown in Figure 4. PAAc is a pH-responsive polyacid

because it has the carboxylic acid groups in the side chain. The

pendant carboxylic acid groups of PAAc component are

generally ionized into carboxylate anions above its pKa of 4.7.

The carboxylic acid groups are feasibly ionized to release the

protons under basic condition resulting in the repulsive

molecular interactions.[14-15]. The highest swelling was

observed at pH 10 indicating that the nanocomposite

hydrogels were effective for the treatment of basic water

pollutants [12].

Figure 4. Swelling behavior for hydrogels contain (0.0, 0.25, 0.75 and 1.25)

(w/v.%) of GO (a) 0.5 (b) 1.0 (c) 3.0 (w/v.%) of TiO2 at pH 10.0 after 48.0

hour at 25°C.

We observed that at Figure 5 (a, b) with small content of

GO the swelling increased reached approximately to twice of

swelling without GO. The significant improvement of the

swelling capacities of the nanocomposites containing

extremely low GO content might be mainly due to the fact that

the GO sheets containing plenty of functional groups, such as

COOH, C=O, O-H and C-O-C groups on the surface [13],

could dramatically increase the density of the hydrophilic

groups of the polymer networks. Besides, the GO sheets

dispersed homogeneously in the matrix might influence the

microstructure of the polymer networks because of the

exceptional nanostructure character of GO, which also could

influence the swelling capacities [13, 25]. The swelling ratio

of nanocomposite hydrogel decreased somewhat as the

content of GO increased this might be owing to the fact that

the excessive GO sheets and TiO2 tended to aggregate and

weakened the synergetic interactions between GO sheets and

the polymer networks as shown in Figure 4.

The observation was been in Figure 5 (c) 3.0 (w/v.%) of

TiO2 and GO content (0.0, 0.25, 0.75 and 1.25) (w/v.%), GO 0

showed the highest swelling ratio among the various

nanocomposite hydrogels because with addition GO to

hydrogels contain 3.0 (wt/vol%) of TiO2 tended to aggregate

and the swelling ratio of nanocomposite hydrogel decreased

somewhat as the content of GO increased due to the hindrance

to the swelling of hydrogel matrix.

Figure 5. Illustration of the reaction between GO and MB.

4.5. Dye Adsorption Behavior of

PVA/PAAc/TiO2/GO Nanocomposite

Hydrogels

The dye adsorption behavior of various

PVA/PAAc/TiO2/GO nanocomposite hydorogels was studied

at pH 10.0 after 24 h and initial concentration 10.0 mg/L as

shown in Figure 6. The MB dye adsorption increased with

increased GO content, the adsorption increased gradually

from (0.0<0.25≤0.75<1.25) (w/v.%) of GO and reached to

maximum at 1.25 (w/v.%) of GO.

GO is highly oxygenated and hydrophilic which can be well

dispersed in water. GO has a large theoretical specific surface

area (as high as 2620 m2/g) with huge number of functional

groups, i.e., hydroxyl, epoxyl and carboxyl [16]. The higher


the graphene oxide amount, the better the adsorption capacity.

The ionic interactions between cationic dyes and the

negatively charged groups can be formed in the company of

abundant ᴫ– conjugations between methylene blue ᴫmolecules and the aromatic rings of graphene oxide sheets,

which could lead to the higher adsorptivity as shown in figure

5 [16, 19-20].

Figure 6. MB dye adsorption initial concentraction 10 mg/L with

PVA/PAAc/TiO2/GO hydrogel composition of both GO (0.0, 0.25, 0.75 and

1.25) and TiO2 (0.5, 1.0 and 3.0) (w/v.%) at pH 10.0 after 24.0 h at 25°C.

4.6. Photocatalytic Decomposition of

Pollutant Dye

The effect of GO and TiO2 content on photocatalytic dye

decomposition behavior at pH 10, where

PVA/PAAc/TiO2/GO nanocomposite hydrogels showed the

best performance, was investigated as shown in Figure 7.

When TiO2 (0.5, 1.0) (w/v.%) the photocatalytic performance

of PVA/PAAc/GO nanocomposite hydrogel improved, GO

content increased reached to best performance with 1.25

(w/v.%) of GO. But when TiO2 (3.0) (w/v.%) the best

performance with 0.75 (w/v.%) of GO. The photocatalytic

decomposition efficiencies of PVA/PAAc/TiO2/GO

nanocomposite hydrogels also increased significantly as GO

content increased. The combination of TiO2 and GO strongly

contributed to the efficient electron transfer between TiO2 and

GO. GO played the role of an electron acceptor that

accelerated the interfacial electron-transfer process between

TiO2 and GO upon UV irradiation. Therefore, GO strongly

prevented TiO2 photocatalyst from the recombination of

electron–hole formed under UV irradiation resulting in the

improvement of photocatalytic activity [23-24]. GO also

played as effective adsorbent of dyes with offset face-to-face

orientation via-conjugation until adsorption-desorption

equilibrium similarly as various carbonaceous materials.

Graphene and its allotropes have also been studied extensively

to improve the photocatalytic activity as shown in Figure 8.

Figure 7. Photo catalytic degradation of different hydrogels with various

content of GO (0.0, 0.25, 0.75 and 1.25) (w/v.%) and (a) 0.5 (b) 1.0 and (c) 3.0

(w/v.%) of TiO2.

Figure 8. Photocatalytic mechanism for MB degradation over TiO2/GO

nanosheet photocatalyst under UV-light irradiation.



4.7. Recycling of PVA/PAAc/TiO2/GO


The recycling tests were carried out using

PVA/PAAc/TiO2/GO nanocomposites hydrogels TiO2 and

GO (a) (0.5 and 1.25) and (b) (1.0 and 1.25) (w/v.%) under pH

10.0 MB solution initial concentration 5.0 mg/L as seen in

Figure 7 in order to confirm the stability of photocatalytic

performance of samples. After every photocatalytic

decomposition test, PVA/PAAc/TiO2/GO nanocomposites

hydrogel sample was placed in the pH 10.0 buffer solution to

remove any residual pollutant followed by vacuum drying at

60°C for 24.0 h. The cleaned PVA/PAAc/TiO2/GO

nanocomposites hydrogel sample was used consecutively for

the next cycle of photocatalytic decomposition.

As seen in Figure 9. The photocatalytic activity of

PVA/PAAc/TiO2/GO nanocomposite hydrogel decreased as

number of cycles increased. The removal efficiency% at first

cycle and fourth cycle for (TiO2) (0.5 and 1.0) with GO (1.25)

(w/v.%) were (94.0 and 74.0) and (91.0 and 73.0).

Figure 9. Recyclability of PVA/PAAc/TiO2/GO nanocomposite hydrogels for

photocatalytic degradation of MB in pH 10 buffer solution initial

concentration 5.0 mg/L (a) (0.5 and 1.25) and (b) (1.0 and 1.25) (w/v.%).

5. Conclusions

The pH-sensitive PVA/PAAc/TiO2/GO nanocomposite

hydrogels were prepared by radical polymerization and

condensation reaction in order to treat the basic waste water

more efficiently. The significant improvement of the swelling

capacities of the nanocomposites containing extremely low

GO content might be mainly due to the fact that the GO sheets

containing plenty of functional groups, such as COOH, C=O,

O-H and C-O-C groups on the surface, could dramatically

increase the density of the hydrophilic groups of the polymer

networks. The favorable electrostatic attraction is the main

interaction between methylene blue and graphene oxide. As

graphene oxide has the special nanostructural properties and

negatively charged surface, the positively charged methylene

blue molecules can be easily adsorbed on it. GO strongly

prevented TiO2 photocatalyst from the recombination of

electron–hole formed under UV irradiation resulting in the

improvement of photocatalytic activity. The best performance

hydrogels which contain 1.25 (wt/vol%) of GO with (0.5 and

1.0) (wt/vol%) of TiO2.

References

[1] Y. E. Moon, G. Jung, J. Yun, and H. Il Kim, “Poly (vinyl alcohol)/poly (acrylic acid)/TiO2/graphene oxide nanocomposite hydrogels for pH-sensitive photocatalytic degradation of organic pollutants,” Mater. Sci. Eng. B Solid-State Mater. Adv. Technol., vol. 178, no. 17, pp. 1097–1103, Oct. 2013.

[2] L. Landau, “No Title,” Zhurnal Eksp. i Teor. Fiz., vol. 10, pp. 125–133, 2014.

[3] V. K. Gupta, “Application of low-cost adsorbents for dye removal – A review,” J. Environ. Manage., vol. 90, no. 8, pp. 2313–2342, 2009.

[4] G. Jing, L. Wang, H. Yu, W. A. Amer, and L. Zhang, “Colloids and Surfaces A : Physicochemical and Engineering Aspects Recent progress on study of hybrid hydrogels for water treatment,” Colloids Surfaces A Physicochem. Eng. Asp., vol. 416, pp. 86–94, 2013.

[5] Y. H. F. Al-qudah, G. A. Mahmoud, and M. A. A. Khalek, “ScienceDirect Radiation crosslinked poly (vinyl alcohol)/acrylic acid copolymer for removal of heavy metal ions from aqueous solutions,” J. Radiat. Res. Appl. Sci., pp. 1–11, 2014.

[6] W. A. Laftah, S. Hashim, and A. N. Ibrahim, “Polymer Hydrogels: A Review,” Polym. Plast. Technol. Eng., vol. 50, no. 14, pp. 1475–1486, Oct. 2011.

[7] S. K. H. Gulrez, S. Al-assaf, and G. O. Phillips, “Hydrogels : Methods of Preparation, Characterisation and Applications,” 2003.

[8] J. Yun, J. Sun, A. Oh, D. Jin, T. Bae, Y. Lee, and H. Kim, “pH-sensitive photocatalytic activities of TiO2/poly (vinyl alcohol)/poly (acrylic acid) composite hydrogels,” Mater. Sci. Eng. B, vol. 176, no. 3, pp. 276–281, 2011.

[9] C. C. Demerlis and D. R. Schoneker, “Review of the oral toxicity of polyvinyl alcohol (PVA),” vol. 41, pp. 319–326, 2003.

[10] J. Yun and H. Kim, “Journal of Industrial and Engineering Chemistry Preparation of poly (vinyl alcohol)/poly (acrylic acid) microcapsules and microspheres and their pH-responsive release behavior,” vol. 15, pp. 902–906, 2009.

[11] R. Zuo, G. Du, W. Zhang, L. Liu, Y. Liu, L. Mei, and Z. Li, “Photocatalytic Degradation of Methylene Blue Using TiO2 Impregnated Diatomite,” vol. 2014, 2014.


[12] S. Jeon, J. Yun, Y. Lee, and H. Kim, “Journal of Industrial and Engineering Chemistry Preparation of poly (vinyl alcohol)/poly (acrylic acid)/TiO2/carbon nanotube composite nanofibers and their photobleaching properties,” J. Ind. Eng. Chem., vol. 18, no. 1, pp. 487–491, 2012.

[13] Y. Huang, M. Zeng, J. Ren, J. Wang, L. Fan, and Q. Xu, “Colloids and Surfaces A : Physicochemical and Engineering Aspects Preparation and swelling properties of graphene oxide/poly (acrylic acid- co -acrylamide) super-absorbent hydrogel nanocomposites,” Colloids Surfaces A Physicochem. Eng. Asp., vol. 401, pp. 97–106, 2012.

[14] X. Rong, F. Qiu, C. Zhang, L. Fu, Y. Wang, and D. Yang, “Adsorption–photodegradation synergetic removal of methylene blue from aqueous solution by NiO/graphene oxide nanocomposite,” Powder Technol., vol. 275, pp. 322–328, 2015.

[15] A. Ibrahim and M. Ibrahim, “Preparation and characterization of poly (vinyl alcohol)/poly (acrylic acid) hydrogels for waste water treatment,” no. 2012, 2015.

[16] C. H. Chia, N. F. Razali, M. S. Sajab, S. Zakaria, N. M. Huang, and H. N. Lim, “Methylene blue adsorption on graphene oxide,” Sains Malaysiana, vol. 42, no. 6, pp. 819–826, 2013.

[17] H. Jeong, L. Colakerol, M. Hua, P. Glans, K. E. Smith, and Y. Hee, “Unoccupied electronic states in graphite oxides,” vol. 460, pp. 499–502, 2008.

[18] N. Raghavan, S. Thangavel, and G. Venugopal, “Enhanced photocatalytic degradation of methylene blue by reduced graphene-oxide/titanium dioxide/zinc oxide ternary nanocomposites,” Mater. Sci. Semicond. Process., vol. 30, pp. 321–329, 2015.

[19] F. Jianqi and G. Lixia, “PVA/PAA thermo-crosslinking hydrogel fiber : preparation and pH-sensitive properties in electrolyte solution,” vol. 38, pp. 1653–1658, 2002.

[20] X. Jin and Y. Hsieh, “pH-responsive swelling behavior of poly (vinyl alcohol)/poly (acrylic acid) bi-component fibrous hydrogel membranes,” vol. 46, pp. 5149–5160, 2005.

[21] V. H. Pham, E. W. ShiAZn, H. Pham, S. Kim, J. S. Chung, E. J. Kim, and S. H. Hur, “The role of graphene oxide content on the adsorption-enhanced photocatalysis of titanium dioxide/graphene oxide composites,” Chem. Eng. J., vol. 170, no. 1, pp. 226–232, 2011.

[22] S. P. Kim and H. C. Choi, “Photocatalytic Degradation of Methylene Blue in Presence of Graphene Oxide/TiO2 Nanocomposites,” vol. 35, no. 9, pp. 2660–2664, 2014.

[23] K. R. Reddy, M. Hassan, and V. G. Gomes, “Applied Catalysis A : General Hybrid nanostructures based on titanium dioxide for enhanced photocatalysis,” "Applied Catal. A, Gen., vol. 489, pp. 1–16, 2015.

[24] Amr Tayel,, Adham R. Ramadan and Omar A. El Seoud, “Titanium Dioxide/Graphene and Titanium Dioxide/Graphene Oxide Nanocomposites: Synthesis, Characterization and Photocatalytic Applications for Water Decontamination,” Catalysts, vol. 491, pp 8, 2018.

[25] Liao G, Hu J, Chen Z, Zhang R, Wang G and Kuang T “ Preparation, Properties, andApplications of Graphene-BasedHydrogels”. Front. Chem. vol. 6, pp 450, 2018.

[26] A. Giampiccolo, D. M. Tobaldi, S. G. Leonardi, B. J. Murdoch, M. P. Seabraand M. P. Ansel, G. Neri and R. J. Ball “Sol gel graphene/TiO2 nanoparticles for the photocatalytic-assisted sensing and abatement of NO2”. Applied Catalysis B: Environmental vol. 243, pp 183–194, 2019.

[27] Yue, Yu-mei, Kun Xu, Xiao-guang Liu, Qiang Chen, Xiang Sheng, and Pi-xin Wang. 2008. “Preparation and Characterization of Interpenetration Polymer Network Films Based on Poly (Vinyl Alcohol) and Poly (Acrylic Acid) for Drug Delivery,” Journal of Applied Polymer Science 108 (December): 3836–3842. doi: 10.1002/app

[28] Yun, Jumi, Ji Sun, Aeri Oh, Dong-hwee Jin, Tae-sung Bae, Young-seak Lee, and Hyung-il Kim. 2011. “pH-Sensitive Photocatalytic Activities of TiO2/Poly (Vinyl Alcohol)/Poly (Acrylic Acid) Composite Hydrogels.” Materials Science & Engineering B 176 (3) (November): 276–81. doi: 10.1016/j.mseb.2010.11.011.

[29] Jeon, Sonyeo, Jumi Yun, Young-seak Lee, and Hyung-il Kim. 2012. “Journal of Industrial and Engineering Chemistry Preparation of Poly (Vinyl Alcohol)/Poly (Acrylic Acid)/TiO2/Carbon Nanotube Composite Nanofibers and Their Photo bleaching Properties.” Journal of Industrial and Engineering Chemistry 18 (1). (May): 487–91. doi: 10.1016/j.jiec.2011.11.068.

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