Photochemical degradation of phenol in the presence of titanium dioxide nanoparticles Текст научной статьи по специальности «Химические науки»

Оригинальная статья / Original article УДК 54-76;543.51 ;543.06

DOI: http://dx.doi.org/10.21285/2227-2925-2019-9-2-176-182

Photochemical degradation of phenol

in the presence of titanium dioxide nanoparticles

© Elmina M. Gadirova

Baku State University, Baku, Azerbaijan

Abstract: In this article, a description of the photochemical degradation of phenol with TiO2 nanoparticles for the treatment of toxic substances in water basins is presented. Such research is of great relevance due to the discharge of wastewater into clean water basins resulting in a contamination of ecosystems with very ecological consequences. Due to the seemingly inevitable reduction in the world's freshwater reservoirs, finding new methods for the high-level purification of contaminated waters so as to minimise the toxic substance content is of paramount importance. Composition and quantitative analysis of the photolysis solution was carried out using the gas chromatographic method. TiO2 nanopowders were prepared using the sol-gel method from titanium IV isopropoxide (TTIP), isopropyl alcohol and ammonium hydroxide precursors under normal conditions without any post-heat treatment for crystallisation. The nanocrystalline rutile-phase TiO2 powders were characterised by X-ray powder diffraction (XRD). The size of nanoparticles as confirmed by transmission electron microscopy (TEM) was about 10-20 nm, while the Brunauer-Emmett-Teller (BET) specific surface area of the rutile nanopowder was 159.6 m2/g. The photocatalytic performance of the synthesised nanopowders photochemical was observed to enhance degradation of the phenol solution under UV irradiation. The phenol degradation was quantitatively analysed using a 6890N GC-MSD gas chromatograph with an Agilent 5975 highperformance mass-selective detector. Degradation of phenol in the presence of TiO2 nanopowders yielded a rate of 99%.

Keywords: nanoparticles TiO2, phenol, photocatalytic process, TEM

Information about the article: Received September 6, 2018; accepted for publication June 7, 2019; available online June 28, 2019.

For citation: Gadirova E.M. Photochemical degradation of phenol in the presence of titanium dioxide nanoparticles. Izvestiya Vuzov. Prikladnaya Khimiya i Biotekhnologiya [Proceedings of Universities. Applied Chemistry and Biotechnology]. 2019, vol. 9, no. 2, pp. 176-182. (In Russian). DOI: 10.21285/2227-29252019-9-2-176-182

Фотохимическое разложение фенола в присутствии наночастиц диоксида титана

© Э.М. Кадырова

Бакинский государственный университет, г. Баку, Азербайджан

Резюме: Известно, что сброс промышленных и бытовых сточных вод, неизбежно попадающих в источники чистой воды, приводит к загрязнению экосистем и тяжелым экологическим последствиям. Ввиду истощения запасов пресной воды в мире первостепенное значение имеет поиск новых высокоэффективных методов очистки загрязненных вод с целью минимизации содержания в них токсичных веществ. Диоксид титана, чьи фотокаталитические свойства являются в последние годы предметом особого внимания, позволяет повысить эффективность технологических процессов очистки воды и воздуха от токсичных органических примесей. Целью настоящего исследования являлось изучение фотохимического разложения фенола наночастицами диоксида титана (TiO2) для обработки токсичных веществ в водоемах. Качественный и количественный анализ исходных и конечных продуктов фотолиза осуществляли методом газовой хроматографии. Нанопорошок диоксида титана был получен золь-гель методом в мягких условиях без последующей термической обработки, используя изопропоксид титана (IV), изопропиловый спирт и гидроксид аммония в качестве прекурсоров. Методом рентгеновской дифракции было показано, что полученный диоксид титана представлен фазой рутила. Размер наночастиц определен методом просвечивающей электронной

микроскопии высокого разрешения и составляет 10-20 нм. Удельная площадь поверхности в соответствии с методом БЭТ составляла 159,6 м2/г. Фотохимическое разложение раствора фенола было проведено под действием УФ-излучения с использованием в качестве катализатора полученного нано-порошка диоксида титана. Продукты разложения фенола анализировали на газовом хроматографе 6890N GC-MSD с высокопроизводительным масс-селективным детектором Agilent 5975. Установлено, что степень деградации фенола в присутствии нанопорошка диоксида титана составила 99%.

Ключевые слова: наночастицы, диоксид титана, фенол, фотокаталитический процесс, просвечивающая электронная микроскопия

Информация о статье: Дата поступления 6 сентября 2018 г.; дата принятия к печати 7 июня 2019 г.; дата онлайн-размещения 28 июня 2019 г.

Для цитирования: Кадырова Э.М. Фотохимическое разложение фенола в присутствии наночастиц диоксида титана // Известия вузов. Прикладная химия и биотехнология. 2019. Т. 9, N 2. С. 176-182. DOI: 10.21285/2227-2925-2019-9-2-176-182

INTRODUCTION

In an increasingly globalised world, the decline in freshwater reserves and simultaneous rise in the amount of waste water have increased demand for fresh or purified water. Thus, the gradual decline of clean water and increased pollution form a major environmental issue worldwide. It now seems certain that millions of people around the world will increasingly suffer from freshwater shortages. In order to ameliorate this problem, various purification methods are currently available. However, since it is impossible to carry out complete purification with present chemical, physical, and biological approaches, new methods have recently become the subject of rapid development. In this respect, a promising approach to sewage treatment involves the use of nanoparticles. Effective water purification methods of using nanoparticles are now developing at an unprecedented rate as revealed by a review of the scientific literature.

Phenols are invariably found in the wastewater of coal processing, oil chemistry, medicine, plastic, paint and paper production industries and generally considered to be one of the most hazardous pollutants due to poor biological disintegration, high concentrations, high toxicity and long-lasting environmental influence [1, 2].

So far, many methods have been used to extract phenol from wastewater. In general, there are three basic methods: physical, chemical and biological methods [3, 4]. However, intermediate products produced during chemical processing methods present a serious environmental problem in their own right. Biological processing methods are less effective in accelerating biological reactions. Physical purification is mainly used by adsorption and membrane filtration [5-7]. Membrane filtration forms an effective way to remove pollutants from water. In an increasingly computer-literate civilisation, the membrane filtration method is on focus, as it is an energy-efficient and ecologically appropriate process for water purification.

For this purpose, graphene oxide (GO) has been recently in use [8]. GO is a graphite oxidising

product, having group of carbonyl and carboxyl groups, as well as epoxy and hydroxyl groups along the edges of its layers [9, 10]. GO is a highly valued membrane material due to its cheap and simple production process, good chemical stability, mechanical strength and high pollutant purification capability [11, 12]. Studies have shown that GO membrane possesses very good ionic and molecular selectivity and water permeability. The use of GO/Al2O3 composite membranes for water purification is the subject of increasing research interest due to the simple and energy-efficient approach it supports. Using the obtained composite, it was possible to purify phenol from waste water with 99.9% efficiency [13].

There are some papers on the application of TiO2 in wastewater treatment [14-17].

In the work [16] photocatalytic (TiO2, air and solar radiation) and photochemical (H2O2 and solar radiation) mineralizations of phenol solutions (up to 500 mg dm-3) in a batch reactor using concentric solar radiation were studied. A compound parabolic reflector as a concentrating reflector was used to obtain concentrated solar radiation in both cases. Considerable enhancement (five-fold) in the rate of degradation was obtained when concentrated solar radiation was used instead of plain solar radiation in photocatalytic degradation.

Photocatalytic oxidation and mineralization of phenol in aqueous catalyst suspensions of titanium dioxide (TiO2) Degussa P25 (80% anatase, 20% rutile) has been carried out in a helical reactor [17]. The photodegradation was investigated using two kinds of high pressure mercury irradiation lamps one emitting at 254 nm (15 Watts) and the other emitting at 365 nm (400 Watts).The rate constants for the different parameters (TiO2, phenol concentration) were evaluated. Kinetic studies showed that TiO2 photocatalyst P25 was very active in phenol degradation and 99% of pollutant was degraded after 6 hours of UV irradiation.

In our work, we describe the use of TiO2 nano-particles to break down the phenol content of polluted water. Here, the goal was to destroy phenol based on a UV photochemical radiation approach.

Using the sol-gel method, TiO2 nanopowders were prepared from Titanium IV isopropoxide (TTIP), isopropyl alcohol, ammonia hydroxide precursors under normal conditions and without any post-heat treatment for crystallisation. The nanocrystalline rutile-phase TiO2 powders were were characterised by X-ray powder diffraction (XRD). Transmission electron microscopy (TEM) analysis was used to determine the size of the nanoparticles to be around 10-20 nm, while the Brunauer - Emmett -Teller (BET) specific surface area of the rutile na-nopowder was 159.6 m2/g. Photochemical degradation of the phenol solution taking place under UV irradiation was enhanced by application of the photocatalytic performance of the synthesised TiO2 nanopowders.

EXPERIMENTAL PART

The prepared TiO2 nanopowders were analysed according to the TEM method (Fig. 1). As can be seen, the obtained nanopowder grains are homogenous. The TiO2 particles have spherical shape with their size varying in the range from 10 to 20 nm; this is consistent with the results calculated by Scherrer's method. The data of TEM analysis correlate well with the results obtained from XRD analysis.

The purity and crystalline properties of the TiO2 nanoparticles were investigated using the powder XRD method. Figure 2 shows the XRD patterns of the synthesised TiO2 nanopowders. It

can be seen that all the XRD peaks are well-defined and correspond to rutile phase TiO2. From the line broadening of the (101) diffraction peak by Scherrer's method, the average crystal size TiO2 is about 10.3. The specific surface areas for TiO2 is 159.6 m2/g. In the pattern all lines can be indexed, using the ICDD (PDF-2/ Release 2011 RDB) DB card number 00-001-1292. The pattern of TiO2 nanopowder has characteristic peaks at 27.90° (110), 36.01° (101), 41.58 (111), 54.71° (211).

In this work TiO2 nano particles have been used for cleaning wastewater from phenol. For this purpose, solution of 0,05 g TiO2 in 10 ml of distilled water was prepared. The nanoparticles were completely mixed in the presence of Х-rays for their equal discharge in the distilled water. The obtained TiO2 has been used for photochemical degradation of 1 mg/l phenol solution. The mixture of 5 ml of TiO2 composite with 20 ml of 1 mg/l phenol solution was exposed to photochemical dissolution within 1 hour. Following the photolysis process, absorption dependence of the solution from wavelength was shown on the UV radiation device. Photolytic dissociation has been proven on the basis of the received curves. The pre-and post-process quantity of phenols was investigated by means of gas chromatographic mass spectroscopy and the dissociation of phenol was 99%. The fluorescence process was carried out at UV radiation device and the dependence of the wavelength absorption coefficient was determined by the "Varian" device.

Fig. 1. TEM micrograph of the TiO2 nanopowder

Рис. 1. Микрофотография нанопорошка TiO2, полученная методом просвечивающей электронной микроскопии

(Л Ci

о

<л

с ф

2-theta, deg

Fig. 2. XRD patterns of the TiO2 nanopowder Рис. 2. Рентгенограммы нанопорошка TiO2 ХИМИЧЕСКИЕ НАУКИ / CHEMICAL SCIENCES =

Quantitative analysis of the sample was carried out using the highly effective Agilent 5975 mass selective detector equipped with gas chro-matography. The results were analysed using chromatographic clear solvents. Water samples were extracted. The hydrogen indicator of the sample was reduced to pH <4 until extraction. Methylene chloride was used as a solvent, however, dichloromethane for extraction.

RESULTS AND DISCUSSION

Photochemical dissociation of 20 ml phenol solution in the presence of TiO2 nanoparticles was carried out under UV irradiation and the degradation of phenol was observed with a high yield and the results were confirmed by mass spectroscopy. In the process TiO2 was used in small quantities -0.05 grams, which makes this process more efficient. The results of the photochemical process are given below.

The graph below shows the dependence of the absorption coefficient of 1 mg/l phenol solution

on wavelength (Fig. 3). Following the photolysis process, the absorption coefficient dependence of the 20 ml phenol solution (concentration 1 mg/l) and the 5 ml of TiO2 solution on the wavelength as the result of UV radiation was given. The graphic curves show that the decomposition products in the solution are sufficiently removed.

As can be seen in Graph 1, phenol-similar curves have been taken at 200-300 nm. It is also known from the literature that the curve obtained at 270 nm wavelengths corresponds to that of phenol.

After photolysis of the phenol solution with the TiO2 composite, many substances should be obtained from the solution based on photochemical degradation (Fig. 4). This means that the phenol is fragmented and the density of the phenol in the solution decreased. In order to demonstrate this, quantitative and composition analysis of the obtained products was carried out by means of gas chromatographic mass spectroscopy (Table).

200 300 400 500 600 700 800 Wavelength, nm

Fig. 3. UV analysis of 1 mg/l phenol solution

Рис. 3. УФ-спектр раствора фенола (1 мг/л)

200 300 400 500 600 700 800 Wavelength, nm

Fig. 4. UV analysis of 1 mg/l phenol + TiO2 nanoparticles after the photolysis process

Рис. 4. УФ-спектр раствора фенола (1 мг/л) + наночастицы TiO2 после процесса фотолиза

As shown in Fig. 5, the characteristic wavelengths for the phenol are not observed in the last curve compared to the other curves as the 1 mg/l phenol+TiO2 solution diluted with the distillation water gradually from top to bottom. This is due to the lack of or insufficient quantity of phenol after photolysis (sensitivity of the device) in the solution.

The sample was then analysed in a gas chromatographic mass detector for more sensitive and accurate analysis; the results of the composition and quantitative analysis of the solution are shown in Table. As can be seen from the table the amount of phenol has dropped from 1 mg to 10 ^g. This means that 99% of phenol has degraded.

200

400 600

Wavelength, nm

800

Fig. 5. UV curves of 1 mg/l phenol + TiO2 nanoparticles solution with distilled water at different concentrations after the photolysis process

Рис. 5. УФ-спектр раствора фенола (1 мг/л) + наночастицы TiO2 + + дистиллированная вода после процесса фотолиза

Analysis of 1 mg/l phenol with TiO2 solution by mass spectroscopy after photolysis

Анализ 1 мг/л фенола с раствором TiO2 методом масс-спектроскопии после фотолиза

Substances Sample 20 ml 1 mg/l phenol + 5ml TiO2 solution

Concentration, pg/l

Phenol 10

o-Cresol 4.8

m+p-Methylphenol 4.9

2,4-Dimethylphenol 2.5

2,6-Dichlorphenol 1.2

2,4,5-TCP 1.2

2,4,6-TCP 1.7

Pentachlorophenol -

2,3,4,6-Tetrachlorophenol -

It should be noted that the photocatalytic oxidation and mineralization of phenol with titanium dioxide (TiO2, 30 nm) Degussa P25 (80% anatase, 20% rutile) was carried out in [17]. There, a high-percentage phenol decomposition was achieved. The results obtained in [17] are in good agreement with our findings. However, in comparison with

other studies, we used TiO2 nanoparticles sized from 10 to 20 nm with the rutile phase and achieved a high-percentage phenol decomposition (99%) over a short time, i.e. following 1 hour of UV irradiation.

The following are the chromatographic curves of the sample after the photolysis process (Fig. 6).

400000 350000 300000

§ 250000

ГО T3

.Q <

200000 150000 100000 50000

Phenol

-|—i I 1—1 |—Г-

10.00 15.00 20.00 25.00 30.00

Time

T I I I I I I I I I I I I I I I I

35.00 40.00 45.00 50.00

Fig. 6. General view of the chromatographic curves of the 1mg/l phenol + TiO2 solution Рис. 6. Общий вид хроматограммы раствора фенола (1 мг/л) + наночастицы TiO2

CONCLUSION

The present article has described an investigation of TiO2 nanoparticles for the treatment of toxic substances in water basins as a means of protecting the environment. Such research is of great relevance due to the discharge of wastewater into clean water basins resulting in a contamination of ecosystems with very ecological consequences. Due to the seemingly inevitable reduction in the world's freshwater reservoirs, finding new methods for the high-level purification of contaminated waters so as to minimise the toxic substance content is of paramount importance.

The following findings are therefore presented:

1. TiO2 nanopowders were prepared using the

sol-gel method from Titanium IV isopropoxide TTIP, isopropyl alcohol, ammonia hydroxide precursors at normal conditions without any post-heat treatment for crystallisation.

2. The rutile-phase nanocrystalline TiO2 powders were characterised by XRD. The size of nanoparticles as determined by TEM analysis was about 10-20 nm; the BET specific surface area of the rutile nanopowder was 159.6 m2/g.

3. Photochemical degradation of phenol solution under UV irradiation by application of the photocatalytic performance of the synthesised TiO2 nanopowders was carried out.

4. Degradation of phenol in the presence of TiO2 nanopowders yielded 99% efficiency.

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Критерии авторства

Кадырова Э.М. выполнила экспериментальную работу, на основании полученных результатов провела обобщение и написала рукопись. Кадырова Э.М. имеет на статью авторские права и несет ответственность за плагиат.

Конфликт интересов

Авторы заявляют об отсутствии конфликта интересов.

СВЕДЕНИЯ ОБ АВТОРАХ

Эльмина Мусрат Кадырова, СЕЗ

к.х.н., доцент,

Бакинский государственный университет, e-mail: [email protected], [email protected]

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Contribution

Elmina M. Gadirova out the experimental work, on the basis of the results summarized the material and wrote the manuscript. Elmina M. Gadirova has exclusive author's rights and bears responsibility for plagiarism.

Conflict of interests

The authors declare no conflict of interests regarding the publication of this article.

AUTHORS' INDEX

Elmina M. Gadirova,

Ph.D. (Chemistry), Associate Professor,

Baku State University,

e-mail: [email protected],

[email protected]