Adsorption of aspirin on the macropore resin with six functional group sites: Multiple functional group sites in macropore resin versus the micropore filling in hypercrosslinked resin

Highlights

• The adsorption capacities order: six functional sites > micropore filling > two functional sites > zero functional sites.

• The adsorption rate constants k₁: zero functional sites > six functional sites ≈ two functional sites > micropore filling.

• MG-6 with six functional group sites showed greater adsorption capacity and faster adsorption rate.

• q_max of MG-6 was much higher than that of the reported adsorbents.

Abstract

Glucosamine modified macropore resin with six functional group sites (denoted as MG-6), 2-aminopyridine modified macropore resin with two functional groups sites (denoted as MG-2) and a hypercrosslinked resin with the micropore filling and zero functional group sites (denoted as HG-0) were synthesized. XAD-4 was chosen as the representative of macroporous resin with zero functional groups sites (denoted as MG-0). The effects of the multiple functional group sites in macropore resin versus the micropore filling in hypercrosslinked resin on the adsorption of aspirin were investigated. The adsorption capacities of aspirin followed the order: six functional group sites > micropore filling > two functional group sites > zero functional group sites. The adsorption rate constants k₁ followed the order: zero functional group sites > six functional group sites ≈ two functional group sites > micropore filling. MG-6 with six functional group sites showed greater adsorption capacity and faster adsorption rate than those of HG-0 with the micropore filling. Corresponding to their functional groups, the four resins (HG-0, MG-0, MG-2 and MG-6) exhibited the different adsorption mechanism of aspirin. As compared q_max of aspirin in the literatures, the adsorption capacity of aspirin on MG-6 was much higher than that of the reported adsorbents.

Introduction

Aspirin (acetylsalicylic acid) is an antipyretic, analgesic and anti-inflammatory drug [1]. Aspirin exhibits the effects of preventing cardiovascular diseases [2], myocardial infarction [3] and platelet aggregation [4]. About 35,000 tons of aspirin are consumed worldwide each year, resulting in a lot of aspirin to be discarded into the environment [5]. Unfortunately, the routine water treatment is not effective in the removal of aspirin from water, and aspirin can be detected in surface water in many countries [6]. The toxicity of aspirin can lead to excessive free radicals and DNA damage in aquatic organisms [6]. Since aspirin is resistant to biodegradation, it will pose a serious threat to aquatic ecosystems and human beings through its accumulation [5]. Due to the persistence and toxicity of aspirin, it is imperative for the remediation of aspirin.

Several approaches to treat aspirin from aqueous solution have been reported, such as electrochemical degradation [7] and photoelectrocatlytic degradation [8]. As a high value-added drug of aspirin, the recovery of aspirin through adsorption is obviously more economic significance. Zeolite has been used as adsorbent to adsorb aspirin, but its adsorption capacity for aspirin is very small [9]. Mesoporous silicon and its modified products are used as adsorbents for the adsorption of aspirin, but the interaction forces between the mesoporous silicon and aspirin are usually weak [10]. Activated carbon is used to adsorb aspirin, but it cannot be recycled for many times because of its fragility [11]. In view of the advantages of easy structural control and recyclability of resin [[12], [13], [14]], it is of great significance to investigate the adsorption of aspirin on resin from water.

There are a lot of researches to improve the adsorption properties of the macroporous resin [[15], [16], [17], [18]]. The macroporous resin is transformed into the hyper-cross-linked resin by the second crosslinking, resulting in a large number of the micropores (0–2 nm) in the second crosslinking [15,16]. The micropore filling of the hyper-cross-linked resin can greatly improve its adsorption capacity [15,16]. Another method is to load functional group sites on the macroporous resin, and the adsorption capacity of the macroporous resin can be improved by the functional group sites [17,18]. Which of the effects of the multiple functional group sites or the micropore filling is more significant for the same adsorbate? It is generally believed that the adsorption capacity of the hyper-cross-linked resin is larger than that of the macroporous resin because of its micropore filling, and even its adsorption capacity is considered to be 2–5 times that of the macroporous resin [15]. How many functional group sites are loaded on the macroporous resin, and its adsorption capacity can exceed that of the hyper-cross-linked resin? The effects of the multiple functional group sites in macropore resin and the micropore filling in hypercrosslinked resin on the adsorption of aspirin are investigated comparatively. The numbers of the functional group sites are 0, 2 and 6 respectively. In particular, it has never been reported that the adsorption properties of the resin with six functional group sites are compared with the micropore filling of the hypercrosslinked resin.

Aspirin, a drug contaminant in water, is selected as the target adsorbate. Glucosamine modified macropore resin with six functional group sites (denoted as MG-6), 2-aminopyridine modified macropore resin with two functional groups sites (denoted as MG-2) and a hypercrosslinked resin with the micropore filling and zero functional group sites (denoted as HG-0) are designed. Commercial classic resin XAD-4 is chosen as the representative of the macroporous resin with zero functional groups sites (denoted as MG-0). The aim of the paper is to elucidate the effects of the multiple functional group sites in macropore resin and the micropore filling in hypercrosslinked resin on the adsorption of aspirin comparatively.