Photodegradation of phenol via C3N4-agar hybrid hydrogel 3D photocatalysts with free separation

doi:10.1016/j.apcatb.2015.10.049

Applied Catalysis B: Environmental

Volume 183, April 2016, Pages 263-268

https://doi.org/10.1016/j.apcatb.2015.10.049 Get rights and content

Highlights

•
The agar-C₃N₄ hybrid hydrogel photocatalysts show 3 dimension network structure.
•
The hybrid hydrogels show synergistic effect of adsorption and photocatalytic degradation.
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The photocatalytic activity of agar-C₃N₄ was greatly enhanced.
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The pollution can be degraded continuously via agar-C₃N₄ hybrid hydrogels photocatalysts without separation.

Abstract

The agar-C₃N₄ hybrid hydrogel photocatalysts with 3 dimension (3D) network structure have been prepared via thermoreversible phase transition of agar. The hybrid hydrogels show high efficient pollutants removal ability by synergistic effect of adsorption and photocatalytic degradation. The removal ability of phenol and methylene blue (MB) by hybrid hydrogel is about 1.3 and 4.5 times of pure g-C₃N₄ respectively. The pollution can be degraded continuously via agar-C₃N₄ hybrid hydrogels photocatalysts without separation.

Graphical abstract

Introduction

Recently, the problems of environmental pollution have become increasingly serious, posing a great threat to human health and sustainable development [1], [2], [3], [4], [5], [6]. A lot of efforts have been made to remove the organic pollution in water, such as adsorption [7], photocatalytic degradation [8], [9], biological treatment [10] and so on. The adsorption is one of the most widely used methods because of the high adsorption efficiency and low cost of the adsorption materials [11], [12], [13], [14]. Among all the adsorption materials, the 3D hydrogels have attracted much attention due to their outstanding performance of adsorption and concentration of water pollutants [15], [16], [17], [18]. On the one hand, the adsorption materials with three-dimensional network structure avoid aggregation and provide convenient mass transfer channels. On the other hand, the bulk structure can prevent the materials from dispersing in water [19], [20], [21], [22]. The operation, collection and separation of the materials from water are simplified by a wide margin. However, the application of 3D hydrogels is limited by their disadvantages. The organic pollutants just can be concentrated rather than degraded to non-polluting molecules by hydrogels. The pollution problem cannot be solved drastically. Besides, only the materials undergo tedious desorption process can they be recycled. Therefore, materials with both ability of pollutants adsorption and degradation are undoubtedly the most advantageous.

Graphic carbon nitride (g-C₃N₄) is an attractive organic semiconductor photocatalyst with visible light activity and excellent thermal and chemical stability [23], [24], [25]. It has attracted extensive attention in degradation of organic pollutants, production of H₂ and O₂ from water and photocatalytic conversion of CO₂ under visible light [24], [26], [27], [28]. However, the catalytic activity of g-C₃N₄ is limited by its poor adsorption ability for some pollutants, such as phenol. Moreover, it is difficult for the nano-sized g-C₃N₄ particles to be separated from water completely. Thus, novel g-C₃N₄ based hybrid hydrogels is not only facile to be separated from water to avoid secondary pollution, but also likely to show improved pollutants removal ability by synergistic effect of adsorption and photocatalytic degradation.

As a biopolymer gel, agar is widely used in the preparation of culture medium and polymeric hybrid hydrogels [29], [30], [31]. The application of agar in catalysis field has not been reported yet. In this paper, agar is used to prepare hybrid hydrogels via its thermoreversible sol–gel transition (Scheme 1). Agar and g-C₃N₄ nano-particle hydrosol is transformed into hybrid hydrogel with 3D network structure by a heating–cooling polymerization process. The agar-C₃N₄ hybrid hydrogels show enhanced performance in photocatalytic degradation of MB and phenol under visible light via synergistic effect of adsorption and photocatalysis. The hybrid hydrogel exhibits excellent cyclic stability and can be used continuously without adsorption saturation. The C₃N₄-agar hybrid hydrogels are promising materials used in the treatment of water pollutants.

Section snippets

Preparation of the C₃N₄-agar hybrid hydrogels

Agar and dicyandiamide were purchased from Sinopharm Chemical Reagent Corp., PR China. All other reagents used in this research were analytically pure and used without further purification.

The g-C₃N₄ was prepared by pyrolysis of dicyandiamide in air atmosphere. The typical preparation of g-C₃N₄ photocatalysts was as follows: The dicyandiamide was put in a Muffle Furnace and heated to 550 °C for 4 h to complete the reaction. The yield of the optimum g-C₃N₄ was about 25%.

Agar and g-C₃N₄

Results and discussion

The agar sol can transform to gel rapidly due to its coil–helix structural transition between high (90–95 °C) and low temperature. As shown in Fig. S1, the 90%-agar-C₃N₄ hybrid hydrogel shows negligible weight loss under the UV irradiation for 1000 h. However, the 60%-agar-TiO₂ hybrid hydrogel shows about 30% weight loss under the same conditions. The mass stability indicate that agar hybrid hydrogel maintained light stability with mild g-C₃N₄ photocatalyst but may be degradated by materials with

Conclusion

In conclusion, the series agar-C₃N₄ hybrid hydrogels are prepared by a heating–cooling polymerization method. The C₃N₄-agar hybrid hydrogels show enhanced performance in photocatalytic degradation of phenol and MB under visible light via synergistic effect of adsorption and photocatalysis. The removal of phenol and methylene by optimal hybrid hydrogel is about 1.3 and 4.5 times of pure g-C₃N₄ respectively. The hybrid hydrogel exhibits excellent cyclic stability and can be used for long time.

Acknowledgments

This work was partly supported by National Basic Research Program of China (973 Program) (2013CB632403), National High Technology Research and Development Program of China (2012AA062701) and Chinese National Science Foundation (21437003, and 21373121).

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Photodegradation of phenol via C3N4-agar hybrid hydrogel 3D photocatalysts with free separation

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Preparation of the C3N4-agar hybrid hydrogels

Results and discussion

Conclusion

Acknowledgments

Appl. Catal. B Environ.

Appl. Catal. B Environ.

Appl. Catal. B Environ.

Adv. Colloid Interfaces

Water Res.

Chem. Eng. J.

J. Environ. Manage.

J. Hazard. Mater.

Bioresour. Technol.

Nature

Environ. Sci. Technol.

Environ. Sci. Technol.

Langmuir

Energy Environ. Sci.

Energy Environ. Sci.

Environ. Sci. Technol.

J. Mater. Chem. A

Photodegradation of phenol via C₃N₄-agar hybrid hydrogel 3D photocatalysts with free separation

Preparation of the C₃N₄-agar hybrid hydrogels