Co first author: Hu Xuejiao, Xu Guizhou
Communication Author: Xie Xianchuan communication unit: Nanjing University Paper doi: 10.1021/acsami.0c00597 summary of achievements recently, the research group of Xie Xianchuan, associate professor of Nanjing University, is a famous academic journal in the field of materials ACS Applied Materials & amp; A research paper entitled "multifunctional β - cyclodextrin polymer for simultaneous removal of natural organic matter and organic micropollutants and critical micro organizations from water" was published on interfaces (ACS appl. Material. Interfaces 2020, 12, 12165? 12175). Natural organic matter, organic micro pollutants and harmful microorganisms are the three main pollutants that affect water quality, but it is difficult to remove them at the same time by conventional treatment methods. In this work, a kind of β - cyclodextrin polymer with ultra microporous structure was prepared in the aqueous phase. The unique external hydrophilic and internal hydrophobic cavity structure of β - cyclodextrin was used to realize the rapid adsorption and removal of a variety of organic micro pollutants in the water. Because the introduced quaternary ammonium functional group has both ion exchange and antibacterial functions, the material can be negatively charged The natural organic compounds (humic acid and fulvic acid) of the organic compounds can be removed by ion exchange, and the harmful microorganisms can be eliminated at the same time. Due to the difference of action site and mechanism, three types of pollutants can be removed simultaneously without competitive interference. Water pollution has become a global environmental problem. Among many pollutants, natural organic compounds (NOM), organic micro pollutants (OMPs) and harmful microorganisms are the focus of attention. There are many physicochemical methods for the removal of NOM and OMPs, such as coagulation, membrane treatment, advanced oxidation and adsorption. However, these methods have many disadvantages, such as high energy consumption, high operation cost or operation cost, difficult maintenance and possible harmful by-products, which limit their practical application. As a simple and economic treatment method, adsorption has special advantages in the removal of the above pollutants. The adsorbent is the core of the adsorption method, and an ideal adsorbent needs to meet three conditions: (1) it has multi-function and can remove multiple target pollutants at the same time; (2) the preparation process is simple and green, it can be industrialized, and it can avoid pollution in the synthesis process; (3) it is easy to regenerate, it can reduce the cost and is conducive to practical application. At present, the commonly used activated carbon and Synthetic Resin Adsorbents on the market are difficult to remove various types of pollutants at the same time, and their preparation process is not environmentally friendly, especially the regeneration of activated carbon usually needs to be carried out under high temperature conditions, which seriously limits their application results. For the harmful microorganisms in the water body, disinfection methods are usually used, such as chlorine disinfection, ultraviolet disinfection, metal disinfection, etc. However, in the actual disinfection process, toxic and harmful by-products are often produced, which is also an urgent problem to be solved. Therefore, it is of great significance to develop a multifunctional material which can simultaneously remove natural organic matter, organic micro pollutants and harmful microorganisms. β - cyclodextrin is a green natural macromolecular compound derived from starch microbial fermentation. Its unique external hydrophilic and internal hydrophobic cavity enables it to form a host guest inclusion complex with a variety of pollutants. In recent years, with the successful preparation of porous β - cyclodextrin polymer, more and more studies have been carried out to remove pollutants from water. However, most of the reported porous β - cyclodextrin polymers are synthesized in organic phase, and it is still a challenge to realize the green synthesis of porous β - cyclodextrin polymer in aqueous phase. In addition, how to modify β - cyclodextrin polymer and give it multi-function is also the focus of research. In this paper, β - cyclodextrin polymer (β - CDP) with ultra microporous structure was successfully prepared in water phase by the method of rigid crosslinker and flexible crosslinker, and the quaternary ammonium group was introduced in the synthesis process to give the ion exchange and antibacterial function of the target material. Adsorption experiments and disinfection experiments show that the material can simultaneously achieve the efficient removal of natural organic matter, organic micro pollutants and harmful microorganisms. Guide reading the green synthesis of β - cyclodextrin polymer 1 (a) schematic diagram of β - CDP synthesis process and speculated structure; (b) photos of β - CDP synthesis process and products. As shown in Fig. 1 (a), the preparation of β - CDP is carried out in the aqueous solution of sodium hydroxide, i.e. the co crosslinking reaction of β - cyclodextrin with rigid coupling agent (tetrafluoro-benzenedinitrile), flexible crosslinker (epichlorohydrin) and 2,3-epoxypropyl-trimethylammonium chloride is carried out to obtain the macromolecular β - cyclodextrin polymer with three-dimensional network structure. Fig. 1 (b) is a picture of the synthesis process and product of β - CDP, which shows that the whole preparation process is very simple, and the target product β - CDP is light yellow powder. Characterization of β - cyclodextrin polymer Figure 2 characterization of β - CDP. (a) Infrared analysis; (b) ζ potential of β - CDP at different pH; (c) N2 (upper) and CO2 (lower) adsorption / desorption isotherms of β - CDP; (d) SEM (left) and TEM (right) photos. Figure 2 (a) shows the infrared spectra of β - CDP, β - CD, ETA and tftpn. In the β - CD spectrum, the absorption peaks at 1030 and 1155 cm-1 correspond to the stretching vibration peaks of c-oh and C-O-C respectively. The overlap of absorption peaks of β - CDP in this range indicates the existence of β - CD and EPI units. The peak at 2252 cm-1 in tftpn map corresponds to the stretching vibration of nitrile group, and the peak moves to 2241 cm-1 in β - CDP map. The peak of ETA at 1486 cm-1 corresponds to the stretching vibration of C-N, and the peak of β - CDP moves to 1473 cm-1. Infrared analysis results show that β - CDP is composed of β - CD, EPI, ETA and tftpn. Figure 2 (b) shows ζ - potential of β - CDP at different pH. The surface of β - CDP is positively charged at pH ≤ 10 and negatively charged at pH = 12. The zeta potential of β - CDP was + 17.3 at the pH of the original solution, which also confirmed the existence of quaternary ammonium groups on the surface of β - CDP. The specific surface area has a significant impact on the adsorption performance of the adsorbent. Fig. 2 (c) measured the N2 and CO2 adsorption / desorption isotherms of β - CDP, which were used to analyze the nanopore (sbet-n2) larger than 1 nm and the micropore (slongmuir CO2) smaller than 1 nm, respectively. The results show that sbet-n2 is 8.8m2 g-1 and slangmuir-co2 is 89m2g-1, indicating that there are a lot of micropores in the material. On the other hand, the SEM and TEM photos of Fig. 2 (d) also show that the material contains macropores and micropores with dimensions of about several hundred nanometers. The formation of these pores is attributed to the introduction of rigid structure in the synthesis process. The removal rate of different pollutants by β - cyclodextrin polymer Fig. 3 the removal rate of humic acid (HA), fulvic acid (FA) and five different organic micro pollutants (OMPs) by different adsorbents: 2-naphthol (2-NO), 3-phenylphenol (3-ph), 2,4,6-trichlorophenol (2,4,6-TCP), bisphenol A (BPA) and bisphenol s (BPS) with time. Experimental conditions: the adsorption temperature is 25 ° C, the amount of adsorbent is 1 mg ml-1, the initial concentrations of HA, FA and BPA are 10 mg L-1, 30 mg L-1 and 0.1 mmol l l L-1, respectively. In order to evaluate the adsorption performance of β - CDP, two typical natural organic compounds were selected: humic acid (HA) and fulvic acid (FA), five different organic micro pollutants (OMPs): 2-naphthol (2-NO), 3-phenylphenol (3-ph), 2,4,6-trichlorophenol (2,4, 6-tcp, BPA and BPs were used as the treatment objects. The removal rate of target pollutants by β - CDP, commercial activated carbon darco-ac (specific surface area 525m2 g-1) and XAD-4 (macroporous adsorption resin, specific surface area 525m2g-1) and D-201 (anion exchange resin, exchange capacity > 3.70mmol G? 1) were studied. As shown in Figure 3, in the single component pollution system, the removal rate of HA and FA by β - CDP is much higher than that of the comparative adsorption material. β - CDP can completely remove HA in 2.5 min and more than 95% FA in 10 min. In contrast, only about 20% HA and FA can be removed by activated carbon in 60 minutes, while XAD-4 and D-201 resin have almost no effect on HA and FA removal. For OMPs, β - CDP can be removed quickly in the first minute, and the adsorption equilibrium can be achieved in 10 minutes. In contrast, the removal rate of activated carbon is slow, BPA and 2-NO need 30 minutes to reach the adsorption equilibrium, while BPs, 3-ph and 2,4,6-TCP still do not reach the adsorption equilibrium within 60 minutes; XAD-4 resin shows the slowest removal rate of all OMPs, the adsorption equilibrium is still not reached within 60 minutes, and the removal rate is less than 50%. The results show that the adsorption process is chemically controlled heterogeneous adsorption, and the interaction between adsorbate and adsorbent is strong. The calculated second-order kinetic rate constant K2 also shows that the adsorption rate of all pollutants on β - CDP is much higher than that on the reference material. For HA and FA, the adsorption rate constant K2 on β - CDP is about 30 times that of darco-ac activated carbon. For different OMPs, the adsorption rate constant K2 on β - CDP is 37 ~ 935 times and 1349 ~ 10915 times of XAD-4 resin of darco-ac activated carbon respectively. The super fast adsorption rate of β - CDP shows that its adsorption site is easy to approach, which is mainly due to its porous characteristics, especially the large pore structure. Adsorption capacity of β - cyclodextrin polymer for different pollutants Fig. 4 adsorption isotherms of humic acid (HA), fulvic acid (FA) and five different organic micro pollutants (OMPs): 2-naphthol (2-NO), 3-phenylphenol (3-ph), 2,4,6-trichlorophenol (2,4,6-TCP), bisphenol A (BPA) and bisphenol s (BPS) on β - CDP and fitting results of Freundlich and Langmuir models. Figure 4 shows the adsorption isotherms of different pollutants on β - CDP. Freundlich model and Langmuir model are used to fit the isotherm data respectively. It is found that Freundlich model can better fit the experimental results, which reflects that the adsorption process is uneven from the side and is consistent with the kinetic conclusion. According to Langmuir model, the adsorption capacities of HA, FA, 2-NO, 3-ph, 2,4,6-TCP, BPA and BPS on β - CDP are 40166, 74101108103 and 117 mg g? 1, respectively. The influence of pH and ionic strength on the adsorption properties of β - cyclodextrin polymer Fig. 5 (a) the influence of pH and ionic strength on the adsorption of humic acid (HA), fulvic acid (FA) and bisphenol A (BPA) on β - CDP. Experimental conditions: the initial concentrations of HA, FA and BPA were 10 mg L-1, 30 mg L-1 and 0.1 mmol l L-1, respectively. The pH of the solution will change the charge characteristics of the adsorbent surface and the existence form of the adsorbate, and the ionic strength will affect the solubility and hydrophobicity of the adsorbate, thus affecting the adsorption effect. Figure 5 (a) studied the adsorption effect of β - CDP on ha, FA and BPA at different pH. When the pH is between 2 and 8, the adsorption of HA is almost unaffected, but when the pH reaches 10 and 12, the adsorption of HA decreases significantly. For FA, lower (pH = 2) and higher (pH = 12) pH are not conducive to its adsorption. The removal rate of BPA decreased from 96% to 56% at higher pH (12). It has been shown that when pH > 4, the carboxyl groups on HA and FA begin to ionize, and when pH > 8, the hydroxyl groups on HA and FA begin to ionize. Therefore, when pH < 4, HA and FA are mainly in molecular form