Porous gel materials from waste thermosetting unsaturated polyester for high-efficiency wastewater treatment

Highlights

• Waste unsaturated polyester resin is transformed into gel material by one-pot method.

• Gel material shows rough surface and porous structure with rich hydrophilic groups.

• Gel material shows fast dye uptake, high adsorption capacity and good reusability.

• Gel material is a good selective adsorbent and an ideal carrier for catalysts.

Abstract

A novel gel material (GM) was successfully fabricated via basic hydrolysis of waste thermosetting unsaturated polyester resin (WTUPR) under environmentally benign conditions by one-pot method. The obtained GM had rough and porous structures with considerable functional groups, which contributed to its fast adsorption performance, distinguished adsorption capability of 754.65 mg·g⁻¹, and excellent reusability (no efficiency decay after 20 adsorption/desorption cycles). The regeneration of GM was energy-saving since the GM could be directly used in the subsequent adsorption process after desorption without additional drying and grinding processes. In addition, the GM presented a good selective adsorption performance and might serve as an ideal metal ion carrier for catalytic degradation of organic pollutants in wastewater. This approach directly transformed WTUPR into high value-added products for water purification with energy-saving processes, opening up a novel avenue to recycle waste thermosetting materials into high value-added products by a facile sustainable approach for the reutilization of resource and the protection of environment.

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.