Bifunctional two-dimensional copper-aluminum modified filter paper composite for efficient tetracycline removal: Synergy of adsorption and reusability by degradation
Graphical abstract
Introduction
A large quantity of unmetabolized antibiotic drugs released excessively into aqueous circumstance via various pathways (mainly including the pharmaceutical industries, hospitals, human consumption, and veterinary usage), which caused unpredictable residue in the natural water (Xiao et al., 2020; Scaria et al., 2021). The presence of antibiotics subsequently leaded to the development of microorganisms resistant, thus causing aquatic ecosystems imbalances and making humans and animals more susceptible to pathogens and bacteria (Scaria et al., 2021; Nguyen et al., 2021). Among antibiotics, tetracycline (TC) has become the most applicated antibiotics in the world due to its high efficiency and low production cost, and approximately 70% of TC could not be effective biodegradation by the organism (Cheng et al., 2020). In China alone, an estimated 12,000 tons of TC were consumed in 2013, leading to high concentrations of residues in water (Pan and Chu, 2016). A summarized data from around 20 countries indicated TC was one of the most frequently detectable antibiotics with the frequency of 80%, corresponding to values of 117 ng/L (Wang et al., 2020a). Therefore, it is urgent to develop efficient treatment methods for the removal of TC in aquatic environment so as to minimize their cumulative effect.
So far, the primary methods for treating pharmaceutical contamination in wastewater include degradation (Jeon et al., 2021), photocatalysis (Im et al., 2021), advanced oxidation (Giannakis et al., 2021), membrane separation (Chen et al., 2019), and adsorption (Kim et al., 2021). Among them, adsorption method has been widely studied to purify antibiotic-contaminated water due to its simplicity, high removal efficiency, and absence of secondary pollution (Wang et al., 2021a; Ahmed et al., 2016). The selection of adsorbents plays a vital role for successful application of adsorption technology. It is found that taking advantage of biomass carbon (plant biomass and agricultural products) as matrix or template has become an effective approach to prepare high-performance adsorption materials to TC (Chen et al., 2021; Liu et al., 2021; Xiang et al., 2020). However, current researches focus more on the treatment and modification of raw biomass by tedious synthetic procedures to prepare materials that provide both excellent adsorption performance and low ecotoxicity. For example, Wang et al. (2021) fabricated the Zn-loaded biochar adsorbent from Fraxinus pennsylvanica Marsh leaves, which was obtained through calcination and self-propagating combustion for two times, respectively (Wang et al., 2020b). Hence, to reduce the cost of time and extra energy in preparation process, other substitute carbon-precursor are urgently needed.
Filter paper (FP), as a common material in laboratory, was used for separation of precipitates because of high mechanical stability and tensile strength (Zeng et al., 2021). For FP, firstly, the wasted FP in scientific research easily cause resources wasting and secondary pollution. Secondly, it has rich hydroxyl groups on the surface, which can quickly absorb water solution without time-consuming modification. And the drying of matrix only needs to vaporizes water (since metal salt (e.g., copper salt) can easily diffuse into the filter paper and be trapped into the pores (Cano et al., 2018; Zhang et al., 2018; Yu et al., 2019)), which could ensure the carbon-precursor can be quickly obtained, meanwhile metal salt precipitation on the FP. Lastly, the FP has low price, wide source, high surface area and mechanical stability, which make it be a potential carbon template. This method not only provided a strategy to construct effective adsorbent but also a possible way to treat wasted FP for environmental remediation.
Copper oxide (CuO), a cheap metal substrate, has been frequently studied in adsorption (Zhang et al., 2019), promoted photodegradation (Su et al., 2021), and advanced oxidation (Xiao et al., 2021) due to its reasonable cost, good photoelectric performance, and low ecotoxicity. For example, Lv et al. (2020) synthetized a copper-doped BiOBr microflowers which possessed enhanced adsorption and excellent photocatalytic degradation of norfloxacin via one-step solvothermal method for the effective removal of norfloxacin from water (Lv et al., 2020). Metal oxide particles have been often loaded on the supports such as ZIF-L (Peng et al., 2021), and Al2O3 (Fan et al., 2020; Ma et al., 2021) where the surface supports act in the adsorption process, too. They have attracted much attention as the support due to their high surface area where the active sites are to be uniformly distributed. Moreover, the isoelectric point of Al2O3 is 9.1, acting as an important factor determining adsorption performance in a wide pH range (Gao et al., 2020a; Gao et al., 2020b). Therefore, Al2O3 can be adopted as a perfect support for the elimination of TC, because of its beneficial properties such as its high isoelectric point and large surface area. After the adsorption process, the saturated adsorbent with antibiotic needed to be replaced frequently due to the fixed number of adsorption sites. Moreover, the antibiotic was simply migrated to another aquatic ecosystems, and was not degraded. At present, Sulfate Radical-based Advanced Oxidation Processes (SR-AOPs) have been widely used in removing TC due to their strong oxidation ability, high speed, and simple operation (Giannakis et al., 2021; Guo et al., 2020). Moreover, SR-AOPs can mineralize TC into non-toxic and harmless small molecules, CO2 and H2O. But mineralizing antibiotic directly in wastewater was difficult to conduct and may bring secondary pollution (Wang and Zhuan, 2020). Here, after the adsorption process of ultrahigh performance, the saturated adsorbent with antibiotic was simply migrated to another limited systems and degraded into CO2 and H2O by activating sulfate radical originated from peroxydisulfate (PDS). The strategy has great potential to apply the removal of TC, which could not only effectively remove TC residues in waster but also bring no negative efficiency to environment.
In this context, an eco-friendly two-dimensional copper-aluminum oxide composite (2D-Cu/Al–C) were be quickly prepared by a facile one-step synthetic technology with low-cost FP as the precursor, which exhibited ultrahigh removal efficiency even under high concentration TC solution (200 mg/L). This study incorporated the detailed adsorption performance of TC on 2D-Cu/Al–C, the adsorption model study, as well as the analysis on how the adsorption properties onto the 2D-Cu/Al–C change according to the pH, humic acid (HA), and coexisting ions. The adsorption of different antibiotic types confirmed its desired specific adsorption to TC. The Cu/Al leaching was far lower than the world standards, and adsorption mechanisms were also studied using XPS and other techniques. Furthermore, the saturated adsorbent with antibiotic was well regenerated by sulfate radical-based advanced oxidation processes and TC was degradation into H2O and CO2.
Section snippets
Materials and reagents
Tetracycline (TC) (99.0%), chlortetracycline (CTC), oxytetracycline (OTC), amoxicillin (AC), ciprofloxacin (CIP), sulfamethoxazole (SMX) and norfloxacin (NOR) were obtained from Shanghai Macklin Biochemical Co., Ltd. Medium-speed qualitative filter paper was purchased from Hangzhou Special Paper Co., Ltd. All other chemical reagents were used without further purification throughout the experiment, including Cu(NO3)2·3H2O, Al(NO3)3·6H2O, Anhydrous ethanol (EtOH), NaOH, and HCl, which were all
SEM analysis
SEM images of FP, C, Cu–C, Al–C and 2D-Cu/Al–C were shown in Fig. 1, respectively. From large scale SEM image of normal FP (Fig. 1a), it can be seen that the crisscrossed fibers were randomly oriented with differences diameter of single fiber, ranging from 2 μm to 20 μm. After heat treatment at 600 °C, cellulose chains were reduced by dozens of times due to high strength carbonization. Fig. 1c show that the fluffy cluster collapsed and the Cu particles bound on the fibers surface were more
Conclusions
In summary, uniformly CuO and Al2O3 loaded carbon materials derived from filter paper was successfully synthesized by a facile one-step synthetic technology to remove TC from water. Detailed fitting results showed that the adsorption of TC on 2D-Cu/Al–C obeyed the Langmuir and the pseudo-second-order model. 2D-Cu/Al–C demonstrated high TC removal (>81.7%) at pH 7-9 within 12 h, which was related to high zero electric charge (8.6) and the large number of accessible surface active-sites. Compared
Credit author statement
Mengbo Cao: Validation, Conceptualization, Investigation, Visualization, Writing – original draft, Writing – review & editing. Xun Liu: Validation, Investigation. Wei Wang: Validation, Investigation. Supervision. Ming Gao: Validation, Investigation. Hongbing Yang: Validation, Resources, Conceptualization, Supervision, Writing – review & editing.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgment
This work was supported by the Natural Science Foundation of China [NSFC, No.21667025] and “Double-First Class” Science and Technology Project [SHYL-ZD201904], School of Chemistry and Chemical Engineering, Shihezi University.
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