Porous gel materials from waste thermosetting unsaturated polyester for high-efficiency wastewater treatment
Graphical abstract
One-pot synthesis of gel material from waste thermosetting unsaturated polyester resin is achieved, which exhibits excellent adsorption performance and reusability.
Introduction
Water pollution from organic and inorganic pollutants has raised global attention [1], [2] because these pollutants reduce light penetration into water and affect the photosynthesis of aquatic plants [3], [4], and more importantly have toxic and even carcinogenic effect on organisms [5], [6]. Generally, in order to address this issue, adsorption is one of important approaches due to its low cost and ease of operation [7], [8]. A variety of efficient adsorbents have been applied for hazardous pollutants removal from wastewater, including carbon-based materials [9], [10], inorganic sorbents [11], [12], and metal-organic frameworks [13], [14]. However, deficiencies still exist in the present adsorbent materials, including poor removal capacity, slow pollutant uptake, high energy consumption in the preparation and regeneration processes [15], [16]. Recently, organic microporous polymers have been applied as an adsorbent to remove organic dyes [17], [18], [19] due to their high porousness, abundant functional groups [20], good water permeability and excellent expansibility for easy trapping of guest molecules [21], [22]. However, in some circumstances, the expensive monomers, rare metal catalysts and complicated synthetic procedure are required, thus limiting their large-scale applications [23]. Therefore, low-cost recyclable waste solids are attracting much more attention for producing valuable adsorbent materials when the resources, energy and environment require sustainable use or protection in today’s society [24], [25], [26], [27].
As is well known, the continuous rise in plastic demand leads to waste accumulation every year. It is estimated that roughly 12,000 Mt of plastic waste will be in landfills or in the natural environment by 2050 [28]. As an indispensable material in many fields for its excellent properties [29], thermosetting unsaturated polyester resin (TUPR) has caused considerable environment problems and further exacerbates the energy crisis with ever-increasing generation of waste thermosetting unsaturated polyester resin (WTUPR) [30]. The recovery and utilization of WTUPR is a serious challenge [31] due to their thermally and chemically stable three-dimensional network structure [32]. Compared with incineration and landfill methods, chemical methods have more advantages because some useful organic materials can be obtained from the wastes for the environmental protection and sustainable development [31], [33]. However, the existing chemical recovery methods are usually carried out at high temperature (>200 °C), high pressure (>3 MPa) or in strongly corrosive media (e.g., sulfuric acid or nitric acid) [34], [35], [36]. Moreover, non-selective cleavage of chemical bonds during the decomposition process inevitably produces toxic gas molecules, thus leading to a complex distribution of products, making it very difficult to reuse the recycled chemicals [37].
In this work, we prepare a new gel material (GM) with porous structure via recycling WTUPR using environmentally benign catalyst system at a mild reaction condition. The resultant GM can serve as a high-performance adsorbent to remove hazardous pollutants in water. The new strategy shows remarkably combined merits: (1) GM with rough, porous structure and considerable functional groups is prepared by one-pot method, and the synthetic process is cost-effective and environmentally-green; (2) GM showed distinguished adsorption performance: fast pollutant uptake, high adsorption capacity and good reusability; (3) The regeneration process of GM is energy saving since the GM can be directly used in the next adsorption process after desorption without additional drying and grinding. In addition, the GM presented a good selective adsorption performance and can be an ideal metal ion carrier for catalytic degradation of pollutants in wastewater. To our best knowledge, there are few reports on the preparation of porous gel materials by recycling waste thermoset resin. Therefore, the investigation opened up a novel avenue to recycle waste thermosetting materials into high value-added adsorbents for wastewater treatment.
Section snippets
Materials
Waste thermosetting unsaturated polyester resins (WTUPR) (Scheme S1) were obtained from a local factory, Chengdu, China. Dichloromethane, potassium carbonate, ferrous chloride tetrahydrate, ethylene glycol, methyl orange (MO), rose bengal (RB) and methylene blue (MB) were purchased from Tianjin Zhiyuan Chemical Reagent Co., Ltd. (China). All chemical reagents were of analytical grade and used as received without further purification.
Preparation of GM
GM was prepared from WTUPR using a facile and mild method.
Preparation of GM
In the conventional recycling of WTUPR, even C–C or C–H bonds in WTUPR are broken under harsh conditions and thus complex small molecular degraded products are produced. It is very difficult to reuse these products. Even worse, it might lead to secondary pollution. Herein, a new strategy is developed in an attempt to selectively and controllably break the C–O bond on the backbone of the WTUPR (as shown in Scheme S1) under mild condition. As a result, the three-dimensional cross-linked network
Conclusions
In summary, a facile fabrication approach was developed to convert WTUPR into high value-added GM under environmentally benign conditions by one-pot method. The obtained GM product exhibited a rough and porous morphology. Moreover, there have been considerable carboxylate groups generated in situ on the GM after mild hydrolysis. The GM displayed fast adsorption rate, distinguished adsorption capacity of 754.65 mg·g−1 and good reusability when adsorbing MB. The regeneration and recycling process
Acknowledgements
This work is supported by the Program for the Science Fund for Creative Research Groups of the National Natural Science Foundation of China (No. 51721091), Changjiang Scholars, Innovative Research Team in University (IRT. 1026), and Sichuan Province Youth Science and Technology Innovation Team (No. 2017TD0006).
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