Surface protection method for the magnetic core using covalent organic framework shells and its application in As(III) depth removal from acid wastewater

Adsorption Performance of Magnetic Covalent Organic Framework Composites for Bisphenol A and Ibuprofen

As typical environmental endocrine disruptors and nonsteroidal anti-inflammatory drugs, bisphenol A and ibuprofen in water supplies can cause great harm to the ecological environment and human health. In this study, magnetic covalent organic framework composites Fe₃O₄@COF-300 were synthesized by the hydrothermal method and used to remove bisphenol A and ibuprofen from water. Fe₃O₄@COF-300 could be rapidly separated from the matrix by external magnetic fields, and could selectively adsorb bisphenol A and ibuprofen in the presence of coexisting compounds such as phenol, Congo red, and amino black 10B. The removal efficiency of ibuprofen was 96.12-98.52% at pH in the range of 2-4 and that of bisphenol A was 92.18-95.62% at pH in the range of 2-10. The adsorption of bisphenol A and ibuprofen followed a pseudo-second-order kinetic and Langmuir model, and was a spontaneous endothermic process with the maximum adsorption amounts of 173.31 and 303.03 mg∙g^-1, respectively. The material presented favorable stability and reusability, and the removal efficiency of bisphenol A and ibuprofen after 5 cycles was still over 92.15% and 89.29%, respectively. Therefore, the prepared composite Fe₃O₄@COF-300 exhibited good performance in the adsorption of bisphenol A and ibuprofen in water.

Selective recovery of Cu(II) from strongly acidic wastewater by zinc dimethyldithiocarbamate: Affecting factors, efficiency and mechanism

The selective recovery of copper from strongly acidic wastewater containing mixed metal ions remains a significant challenge. In this study, a novel reagent zinc dimethyldithiocarbamate (Zn(DMDC)₂) was developed for the selective removal of Cu(II). The removal efficiency of Cu(II) reached 99.6% after 120 min reaction at 30°C when the mole ratio Zn(DMDC)₂/Cu(II) was 1:1. The mechanism investigation indicates that the Cu(DMDC)₂ products formed as a result of the displacement of Zn(II) from the added Zn(DMDC)₂ by Cu(II) in wastewater, due to the formation of stronger coordination bonds between Cu(II) and the dithiocarbamate groups of Zn(DMDC)₂. Subsequently, we put forward an innovative process of resource recovery for strongly acidic wastewater. Firstly, the selective removal of Cu(II) from actual wastewater using Zn(DMDC)₂, with a removal efficiency of 99.7%. Secondly, high-value CuO was recovered by calcining the Cu(DMDC)₂ at 800°C, with a copper recovery efficiency of 98.3%. Moreover, the residual As(III) and Cd(II) were removed by introducing H₂S gas, and the purified acidic wastewater was used to dissolve ZnO for preparation of valuable ZnSO₄·H₂O. The total economic benefit of resource recovery is estimated to be 11.54 $/m³. Accordingly, this study provides a new route for the resource recovery of the treatment of copper-containing acidic wastewater.

Dual functional sites strategies toward enhanced heavy metal remediation: Interlayer expanded Mg-Al layered double hydroxide by intercalation with L-cysteine

The discharge of toxic heavy metals poses a serious threat to human health and environment. The existing water purification systems are lack of promising materials for rapid, efficient, and cost-efficient remediation of numerous toxic heavy metals. Herein, we report on the development of L-cysteine (Cys) intercalated Mg-Al layered double hydroxide (MgAl-LDH/Cys) with a loose lamellar porous architecture as an efficient and economically viable adsorbent for Pb(II) and Cd(II) removal. The intercalation with Cys creates dual functionality, i.e., the interlayer expansion accelerates the diffusion of heavy metals, while Cys acts as additional capture sites for heavy metals. Therefore, remarkable high maximum sorption capacities of 279.58 and 135.68 mg g^-1 for Pb(II) and Cd(II) were obtained for MgAl-LDH/Cys compared to those for pristine MgAl-LDH (30.15 and 36.77 mg g^-1). MgAl-LDH/Cys exhibits also much faster sorption kinetics in comparison with MgAl-LDH. Such enhancements are attributed to the intercalation of the chelating agent Cys in the MgAl-LDH interlayer channels. Moreover, it is proposed that the adsorption mechanisms involve the isomorphous replacement of Mg sites by Cd(II) forming CdAl-LDH, the precipitation of PbS and CdS, and the chelation of sulfhydryl, carboxyl and amine groups toward Cd(II). Altogether, its facile and environmentally friendly fabrication, ultrahigh sorption efficiencies, and rapid kinetics demonstrate that MgAl-LDH/Cys has potential for practical applications in heavy metal remediation.

Dynamic Adsorption of As(V) onto the Porous α-Fe2O3/Fe3O4/C Composite Prepared with Bamboo Bio-Template

Arsenic (As(V)), a highly toxic metalloid, is known to contaminate wastewater and groundwater and is difficult to degrade in nature. However, the development of highly efficient adsorbents, at a low cost for use in practical applications, remains highly challenging. Thus, to investigate the As(V) adsorption mechanism, a novel porous α-Fe2O3/Fe3O4/C composite (PC-Fe/C-B) was prepared, using bamboo side shoots as a bio-template, and the breakthrough performance of the PC-Fe/C-B composite-packed fixed-bed column in As(V) removal was evaluated, using simulated wastewater. The PC-Fe/C-B material accurately retained the hierarchical porous microstructure of the bamboo bio-templates, and the results demonstrated the great potential of PC-Fe/C-B composite, as an effective adsorbent for removing As(V) from wastewater, under the optimal experimental conditions of: influent flow 5.136 mL/min, pH 3, As(V) concentration 20 mg/L, adsorbent particle size < 0.149 mm, adsorption temperature 35 °C, PC-Fe/C-B dose 0.5 g, and breakthrough time 50 min (184 BV), with qe,exp of 21.0 mg/g in the fixed-bed-column system. The CD-MUSIC model was effectively coupled with the transport model, using PHREEQC software, to simulate the reactive transportation of As(V) in the fixed-bed column and to predict the breakthrough curve for column adsorption.