Anal. Method Environ. Chem. J. 4 (1) (2021) 58-67  
Research Article, Issue 1  
Analytical Methods in Environmental Chemistry Journal  
Removal of organic dye compounds in water and wastewater  
samples based on covalent organic frameworks -titanium  
dioxide before analysis by UV-VIS spectroscopy  
Aida Bahadoria and Mehdi Ranjbarb,*  
a Student Research Committee, Kerman University of Medical Sciences, Kerman, Iran  
bPharmaceutics Research Center, Institute of Neuropharmacology, Kerman University of Medical Sciences, Kerman, Iran  
A R T I C L E I N F O :  
Received 24 Nov 2020  
Revised form 5 Feb 2021  
Accepted 25 Feb 2021  
A B S T R A C T  
A simple and rapid microwave-assisted combustion method was  
developed to synthesize homogenous carbon nanostructures (HCNS).  
This research presents a new and novel nanocomposite structures  
for removal of methylene red (2-(4- Dimethylaminophenylazo)  
Available online 30 Mar 2021  
phenylazo]benzenesulfonic acid sodium salt) and methylene  
blue (3,7-bis(Dimethylamino)phenazathionium chloride)with  
semi degradation-adsorption solid phase extraction (SDA-SPE)  
procedure before determination by UV-VIS spectroscopy. A covalent  
organic frameworks (COFs) with high purity were synthesized and  
characterized by X-ray diffraction (XRD) and scanning electron  
microscopy (SEM). The results indicated that the self-assembled  
carbon nanostructures (COFs) synthesized with the cost-effective  
method which was used as a novel adsorbent for adsorption of dyes  
after semi-degradation of methylene red, orange and blue (1-5 mg  
L-1) as an organic dye by titanium dioxide (TiO2) nanoparticales  
in presence of UV radiation. Based on results, the COFs/TiO2 has  
good agreement with the Langmuir adsorption isotherm model with  
favorite coefcient of determination (R2= 0.9989). The recovery of  
dye removal based on semi-degradation/adsorption of COFs/TiO2 and  
adsorption of COFs were obtained 98.7% and 48.3%, respectively  
(RSD less than 5%). The method was validated by spiking dye to real  
Carbon nanostructures,  
Carbon organic frameworks,  
Dye removal,  
Semi degradation-adsorption solid  
phase extraction,  
Titanium dioxide,  
UV radiation.  
importance of the conventional heating methods  
1. Introduction  
(CHM) is due to the microwaves interact with  
the reactants at the molecular level. By CHM, the  
electromagnetic energy is transferred and converted  
to heat by rapid kinetics through the motion of  
the molecules [1-3]. Today, the conservation of  
water resources has been increasingly considered  
by various international organizations such as  
WHO, FDA and EPA. By increasing of population  
growth as a result of over-exploitation of limited  
water resources and on the other hand, water  
pollution due to various biological, agricultural  
Nanomaterials are particles that are in the size  
range between 1-100 nm. The importance of  
nanomaterials in terms of strength is the presence  
of active sites and their low density. Nanomaterials  
have a wide range of applications in optical  
data storage, sensors, light and durable building  
materials, and wastewater treatment. The gained  
*Corresponding Author: Mehdi Ranjbar  
Removal of dye organic compounds by COFs  
Aida Bahadori  
and industrial activities caused to water crisis  
in future years. Methylene organic compounds  
such as methyl red, methyl orange and methyl  
blue are the photoactive phenothiazine dyes [4-  
6]. Paints are one of the main and most important  
pollutants that are used in various industries to dye  
related products. Therefore, a signicant amount  
of pollution caused by pigments is produced due  
to their extensive release into the efuent. The  
presence of these dyes in water is inappropriate even  
at very low concentrations and causes widespread  
environmental pollution by pharmaceutical  
industries[7]. Recently, many methods based on  
nanostructure materials was used for removal  
organic compounds. Hence, a simple and rapid  
microwave assisted combustion technique was  
used for synthesis of CdO nanospheres for removal  
pollution in waters [6]. Microwave assisted reverse  
microemulsion process as an easy, low cost and fast  
method can be used for synthesis of nano emulsions  
[8]. Photocatalytic degradation of compounds  
using nanoparticles with ultraviolet light is one of  
the advanced oxidation methods that is expanding  
in recent decades [9, 10]. Photocatalyst as a  
catalyst activated in the presence of light is which  
absorbs light to produce a chemical reaction in the  
environment [11, 12]. When the UV rays reach to a  
surface covered with a photocatalyst the electron-  
cavity can react with molecules on the surface of the  
particles[13]. Bio photocatalytic materials[14] as a  
kind of photocatalyst was used in water purication  
based on degradation and adsorption process[15],  
during the adsorption process, solute molecules  
are removed from the solution and adsorbed by the  
adsorbent. Most of the molecules are adsorbed on  
the surface of the adsorbent pores and small extent  
on the outer surface of the particles. The adsorption  
transfer from the solution to the adsorbent continues  
until the concentration of the solvent remaining in  
the solution is in equilibrium with the concentration  
of the solvent adsorbed by the adsorbent. When  
equilibrium is established, the adsorption transfer  
stops. Adsorption equilibrium is established in the  
dynamic sense when the rate of adsorption of the  
adsorbed component on the surface is equal to its  
rate of absorption [16], self-cleaning glasses and  
organic molecules degradation[17]. Hydrothermal  
synthesis method has many advantage such as  
energy storage[18], simplicity[19], low cost[20],  
(because reaction takes place indoors)[22], better  
diffusivity[23], high reaction speed and better shape  
control[24]. In recent years, many nanocomposites  
used for degradation or adsorption of organic  
dyes[25-27]. The unique structure of the non-ionic  
surfactant which their unique structure enables them  
to encapsulate water-soluble and water-repellent  
materials [28, 29] and organic building constituent  
units[30]. One of the new techniques in removing  
emerging pollutants is the use of environmentally  
friendly modiers and reducing the bioavailability  
of pollutants in the environment[31]. In recent  
years, bio-charcoal has been gradually approbated  
which as black gold can be used to solve the  
problem of sustainable development of agriculture  
and other aspects by the academic community[32],  
[33], [34], [35]. In this study, the COFs synthesized  
and used as a novel adsorbent for removal dyes  
based on SDA-SPE procedure in water samples  
after semi-degradation of organic dye by titanium  
dioxide (TiO2) nanoparticales in presence of UV  
radiation. The recovery and absorption capacity  
of dyes with COFs/TiO2 were calculated before  
determined by UV-VIS spectrometer.  
2. Experimental  
2.1. Instrumental  
study (Cary 50, USA). UV-VIS spectrophotometer  
included dual beam, the monochromator, the  
wavelength ranges between 190–1100 nm, the  
spectral bandwidth (1.5 nm), the dual Si diode  
detectors, the quartz over coated optics based  
on scan rates of 24000 nm min-1 and computer  
operating system. The Power Consumption of UV-  
VIS spectrophotometer has supply of 100 - 240  
volts AC and frequency 50 - 60 Hz. The condition  
of UV-VIS spectrophotometers was shown in  
Table 1. The unique optical design enables to  
measure dye samples, also, the large or odd-shaped  
Anal. Method Environ. Chem. J. 4 (1) (2021) 58-67  
Table 1. The condition of UV-VIS spectrophotometers  
477 mm x 567 mm x 196 mm  
196 mm  
Light Source  
Xenon ash lamp (80 Hz)  
Maximum Scanning Speed  
Photometric System  
24,000 nm min-1  
Double beam  
1.5 nm  
Spectral Bandwidth  
samples to be measured. The highly focused beam  
also provides superior coupling to ber optics  
caused to use the UV-Vis in different matrixes.  
Powder X-ray diffraction (XRD) was prepared by  
a PRO X-ray diffractometer. Scanning electron  
microscopy images were obtained using gun design  
using a point-source cathode of tungsten (SEM,  
Philips XL 30 FEG). The transmission electron  
microscope was used for preparation particle size  
of COFs (TEM, Philips EM 300).  
adjusted by favorite buffer solutions (Merck,  
Germany). The various buffer solutions, the  
acetate (PH=3.0–6.0), the NaH2PO4 / Na2HPO4  
(pH=6.0–8.0) and NH3/NH4Cl (pH=8.0-10) were  
prepared. After adjusted pH samples, the ultra-  
sonication (Grant, U.K) and the centrifuging  
(3000-10000 rpm, 3K30 model) was used for  
extraction and separation nanoparticles from water  
samples(Sigma, Germany).  
2.3. Synthesis of COFs  
2.2. Materials and Reagents  
Covalent organic frameworks (COFs) has two/  
three dimensional structures(2D,3D) which was  
generated by reactions between organic precursors.  
The covalent bonds depended on porous and  
crystalline form. The COFs is an improvements  
of organic material based on coordination  
chemistry. We synthesis COFs was done based  
on the Yaghi method and COFs framework  
scaffolds were prepared by the boronate linkages  
using solvothermal synthetic methods [36-37].  
In fact, the synthesis of COFs was obtained  
by condensation reactions of C6H4[B(OH)2]2  
with C18H6(OH)6 and nally the carbon structure  
of C9H4BO2 (COF5) produced. Moreover, the two  
nozzles electrospinning was used to fabricate the  
scaffolds. The electrospinning experimental setup  
was a nano model (Tehran, Iran) with two nozzles.  
The voltage applied at the tip of the needle was  
18 kV. The mass ow rates were 0.5 ml h-1, and  
distance between the tip of the needle and the  
collector was maintained at 15 cm. The speed of  
the rotary collector was 400 rpm and scanning  
distance was 10 cm. Experimental conditions  
for the preparation of self-assembled carbon  
nanostructures was shown in Table 2.  
Reagents were acquired from Sigma Aldrich  
and Merck companies, Germany. Methanol  
(HPLC grade), toluene, acetone, hexane and  
dichloromethane (HPLC grade) were obtained  
from Merck Ltd. (Germany). More materials used  
in this study such as methyl red [(CH3)2NC6H4N-  
benzoic acid, CAS N: 493-52-7], methyl  
orange [C14H14N3NaO3S, 4-[4-(Dimethylamino)  
phenylazo]benzenesulfonic acid sodium salt, CAS  
N:547-58-0] and methyl blue [C37H27N3Na2O9S3,  
3,7-bis-Dimethylamino)phenazathionium chloride,  
CAS N:28983-56-4) were purchased from Sigma  
company(Germany), C3H7NO (DMF) was  
purchased from Merck company in Germany,  
without further purication. Benzene-1,4-  
diboronic acid (95.0 %, CAS N: 4612-26-4 )  
hexahydroxytriphenylene (C18H6(OH)6,  
CAS N: 4877-80-9, MW 324.3 g moL-1 ) were  
purchased Sigma-Aldrich. The B3O3 (boroxine,  
CAS N: 823-96-1)) was prepared From  
Sigma(Germany). The pH of the water sand  
wastewater samples were digitally calculated by  
pH meter of Metrohm (744, Swiss). The pH was  
Removal of dye organic compounds by COFs  
Aida Bahadori et al  
Table2. Experimental conditions of self-assembled carbon nanostructures.  
DMF: H2O  
( D.R* )  
NPs**+ Agglomerate  
NPs+ Agglomerate  
NPs+ Agglomerate  
NPs+ Agglomerate  
*Dilution Ratio, **Nanoparticles  
2.4. Removal procedure  
on the Debay-Scherer equation, the particle size of  
COFs nanocomposites was obtained approximately  
50-100 nm. Figure 1 shows the X-ray diffraction  
analysis (XRD) of self-assembled carbon  
nanostructures in different conditions. The results  
show that by increasing of temperature based  
on solvothermal method from 180C to 220C,  
the crystallized amount of synthesized carbon  
nanostructures (COFs) gradually increases. The  
sharper peaks without any noisy peaks was seen.  
Interestingly, the position (2θ) of the peaks have  
not changed, and only the intensity of the peaks  
increased, which indicates an increase in the degree  
of purity in products.  
For each experiment, a dye solution with a  
concentration of 5 mg per 1000 mL (5 mg L-1) was  
prepared and 0.5 g of COFs as catalyst was added  
to it in presence of TIO2/UV. Then the pH of the  
solution was adjusted with buffer solution between  
3-9 and irradiated with UV radiation. Then, the all  
samples, was stirred with a magnetic stirrer for 15  
min. By SDA-SPE procedure, the amount of dye  
(5 mg L-1) removed by COFs/TIO2/UV. First, the  
dye semi-degradation was obtained in presence of  
TIO2 /UV and intermediate forms of dyes created  
in water samples. The dye and intermediate dye  
were absorbed on COFs with high recovery up to  
98.7%. The nanoparticles of adsorbent separated  
from water solution by centrifuging. Then the  
dye concentration in remained solution was  
directly determined by UV-VIS spectrometry.  
To prevent the reaction of hydroxyl radicals in  
the sample, some ethanol was added to the test  
tubes. Validation of methodology was obtained  
by spiking of real samples by proposed procedure.  
The recovery of proposed method based on COFs/  
TiO2 was achieved for dyes extraction by the below  
equation. The CI is the primary concentrations of  
dye in sample and CF is the nal concentration of  
dye by SDA-SPE procedure coupled to UV-VIS  
(n=5, Eq. 1).  
3.2. Measurement size (DLS)  
By increasing of temperature for COFs  
nanocomposites with solvothermal method, the  
sintering process and crystallization of COFs  
was increased and caused to smaller size of nano  
structures. DLS analysis was displayed in Figure 2.  
3.3. Morphological and pore characteristics  
Microscopic morphology and particle-size  
distribution (PSD) of the products were visualized  
by scanning electron microscopy (SEM) images.  
The Figures 3 displays the SEM images of carbon  
nanostructures of COFs. The morphology of COFs  
nanocomposites under the inuence of biochar  
concentration change into rods with quantum  
particles-like on its surface. Results show which  
biochar concentration has a great impact on particle  
size of nal products.  
Recovery (R%) = (CI-CF)/CI×100  
3. Results and Discussion  
3.1. Structural Analysis  
By full width of the half maximum (FWHM) based  
Anal. Method Environ. Chem. J. 4 (1) (2021) 58-67  
Fig. 1. X-ray diffraction analysis of synthesized self-assembled carbon nanostructures  
Fig. 2. The DLS diagram related to carbon nanostructures of COFs  
Fig. 3. SEM images of carbon nanostructures of COFs  
Removal of dye organic compounds by COFs  
Aida Bahadori et al  
3.4. Photocatalytic semi-degradation/adsorption  
and mechanism  
transfered to the surface of the TiO2 and react with  
O2, H2O, or OH groups and generated radicals. The  
decomposition of Dyes was initiated by the attack  
of •OH on the methyl group of the benzene ring  
of dye, leading to make a new compound. On the  
other hand, the presence of COFs can enhance  
the adsorption ability of the Dye via π-π stacking  
interaction between the π-electrons of the benzene  
rings in dye molecules and π-electron rich region of  
COFs nanostructure.  
The Figure 4 demonstrate the photocatalytic semi-  
degradation of methylene red, methylene blue and  
methylene orange organic dyes using COFs/TiO2  
modied with biochar in time cycles (0 min-40  
min). The results show that the percent degradation  
/adsorption of MO is more than 99 % which can  
be depended on the low steric hindrance of MO  
structure. Also amount the percent degradation/  
adsorption of MR is a little more than MB which  
can also be related to low steric hindrance of MR  
structure ratio to MB. By reducing of time contact  
of photocatalyst with organic dyes, the extraction  
recovery of dyes decreased up to 40-54 % by SDA-  
SPE procedure. TiO2 a highly efcient photocatalyst  
has a small band gap energy and relatively positive  
valance band edge under UV-light irradiation. TiO2  
transfer of the charge carriers. The charge carriers  
The effect of pH on the photocatalytic degradation/  
adsorption of MB, MR and MO organic dyes  
were revealed in Figure 5. As results the pH  
don’t effected on extraction dyes on COFs/TiO2  
based on UV radiation by SDA-SPE procedure.  
By procedure, π-π stacking interaction between  
the π-electrons of the benzene rings in dye  
molecules and π-electron rich region of COFs  
nanostructure caused to efcient adsorption after  
semi degradation process.  
Fig. 4. The effect of time on recovery of adsorption/ photocatalytic degradation  
of methylene red, methylene blue and methylene orange organic dyes (0 min-40 min)