Facile synthesis of Cu(II) impregnated biochar with enhanced adsorption activity for the removal of doxycycline hydrochloride from water
Graphical abstract
Introduction
Modern society is confronted with a challenge of antibiotics contaminants, which is harmful to the human health and environment (Kummerer, 2009). Antibiotics are widely applied to improve the human health, prevent and treat infections of plants and animals, as well as promote the animal husbandry growth (Martinez, 2009). However, some studies indicated that about 30–90% of antibiotics were weakly absorbed and released into the environment as the parent compound (Gao et al., 2012, Liu et al., 2011). The related research pointed out that the antibiotics had been detected potable in surface water and ground water (Ternes, 1998). However, antibiotics in traditional wastewater sewage treatment plants are removed with low efficiency which resulted in higher antibiotic resistance (Ling et al., 2013). DOX, an effective road-spectrum antibiotic, it is used to treat a number of different bacterial infections which could keep bacteria from reproducing and synthesizing protein (Phaechamud and Charoenteeraboon, 2008, Vargas-Estrada et al., 2008). Their complicated structures and variable physicochemical properties caused their complex behavior in the environment. Developing an efficient, sustainable and economically feasible adsorbent is an effective way to remove the antibiotics pollutants from waste water. Some studies have shown that graphene (Gao et al., 2012), mesoporous silica (Zhang et al., 2015), montmorillonite (Zhao et al., 2012) and carbon nanotubes (Kim et al., 2014, Tang et al., 2014, Zhang et al., 2016) were effective and widely used as sorbent for removing contaminant. However their high cost and complicated process limited their application. BC and activated carbon are the preferred adsorbent for the removal of contaminant from water. They have some favorable physical/chemical surface characteristics such as extensive surface area and well-developed pore structure (Ahmed et al., 2015, Li et al., 2013b, Sun et al., 2013). The raw materials for activated carbon production are mostly obtained from coal and timber which are nonrenewable and relatively expensive. Nevertheless, BC is the pyrolytic product of various waste biomass sources (i.e. forest energy, crop straw, livestock manure, living garbage), which is more environmentally and economically viable (Tan et al., 2015, Wang et al., 2013, Yao et al., 2011). Therefore, BC is a feasible substitute for activated carbon that is widely employed in removing contaminants from aqueous solution. Numerous studies have shown that metallic catalysts modified biochar can enhance the capacity and selectivity for pollutant removal. Wang et al. (Wang et al., 2016) synthesized Ni and Mn oxides biochar and the results showed that the adsorption capacity of the modified BC was increased compared with the pristine biochar. Hu et al. (Hu et al., 2015) studied iron-impregnated biochar and the results indicated that the specific surface areas of the biochar was decreased through iron impregnation, which caused much better sorption of As. Fang et al. (Fang et al., 2014) used Mg modified corn biochar to remove P, and obtained the predictive effect.
In this work, biochar was derived from peanut shell in a N2 atmosphere at 450 °C without oxidation and then impregnated with Cu(II). Cu(II) has a significant tendency to form complexes in solution with various functional groups present in organic matter, i.e. COOH and OH. Selecting DOX as a target pollutant, we investigated the sorption performance of Cu-BC by batch of experiments. The main goals of this work were to: (1) synthesize and characterize the Cu-BC, (2) test the effects of the solution pH and ionic strength on DOX adsorption, adsorption kinetics, adsorption isotherms and the DOX removal ability of the Cu-BC, (3) analyze the sorption mechanism of DOX onto the Cu-BC under different physical and chemical conditions.
Section snippets
Materials
Doxycycline hydrochloride (DOX, MW = 480.90, chemical formula C22H24N2O·HCl) was purchased from Rubio Corporation, Germany. The other chemicals including Cu(NO3)2·2H2O, NaOH, HCl, NaCl, KCl, CaCl2, MnCl2, MgCl2 were purchased from Municipality Kemi'ou Chemical Reagent Co., Ltd., Tianjin. The biomass peanut shell was collected from Hunan, China. High purified water (18.25 MΩ/cm) from a Millipore MilliQ water purification system was used in all the experiments. All chemicals employed in the
Characterization
SEM micrograph of the BC and Cu-BC are shown in Fig. 1. As can be seen in Fig. 1a, BC was basically smooth. The image of Cu-BC (Fig. 1b) revealed that the surface became rough and added some small bits. These might because Cu had covered or embedded in BC and changed the surfaces fabrication. Moreover, the rough surface of Cu-BC increased the surface area, which was beneficial for adsorption of the contaminants.
The XRD profiles of the Cu-BC and BC are shown in Fig. 2. The first strong and sharp
Conclusions
In summary, the fabricated Cu-BC as high-performance adsorbents possessed promising potentials for removing DOX. The DOX removal by Cu-BC was greatly pH dependent and the optimal pH was 8.0. The kinetics and isotherm data could be well described by pseudo-second-order kinetic model and Langmuir model. Thermodynamic results indicated the sorption process was spontaneous and endothermic. The coexisting cation had different influence on DOX adsorption to Cu-BC: the adsorption of DOX slightly
Acknowledgments
This research was financially supported by the National Natural Science Foundation of China (Grant Nos. 51609268, 51108167 and 51521006), and the Hunan Provincial Innovation Foundation for Postgraduate (Grant Nos. CX2015B090 and CX2016B135).
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