Jianwen Lai,Peiyue Wang,Hongbo Qi,Yunfeng Ma,Zhongkang Han,Fiedler Heidelore,Xiaodong Li,Xiaoqing Lin
Calcium oxide (CaO), utilized in semi-dry/dry desulfurization systems at municipal solid waste incineration (MSWI) plants, demonstrates some capability to remove polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). This study assessed the gas-phase PCDD/F removal performance of CaO, activated carbon (AC) and CaO-AC mixtures. Alone, CaO achieved removal efficiencies of only 31.9% for mass and 50.8% for I-TEQ concentration. However, CaO-AC mixtures exhibited significantly higher efficiencies, reaching 96.0% and 92.5% for mass and I-TEQ concentrations, respectively, surpassing those of AC alone, which were 74.7% and 58.5%. BET analysis indicated that CaO’s limited surface area and pore structure are major constraints on its adsorption performance. Density functional theory (DFT) calculations revealed that the π-π electron donor-acceptor (EDA) interaction enhances the adsorption between AC and PCDD/F, with adsorption energies ranging from -1.02 to -1.24 eV. Additionally, the induced dipole interactions between CaO and PCDD/F contribute to adsorption energies ranging from -1.13 to -1.43 eV. Moreover, with increasing chlorination levels, PCDD/F molecules are more predisposed to accept electron transfers from the surfaces of AC or CaO, thereby facilitating adsorption. The calculation for mixed AC and CaO showed that CaO modifies AC’s properties, enhancing its ability to adsorb gas phase PCDD/Fs, with the higher adsorption energy and more electrons transfer, aligning with gas phase PCDD/Fs adsorption experiments. This study provides a comprehensive understanding of how CaO influences the PCDD/F adsorption performance of AC.
The discharge of industrial heavy metal wastewater not only leads to environmental pollution, but also harms human health, so it is imperative to control heavy metal pollution. In the current work, a sequence of anatase/brookite TiO 2 @COF with different mass ratios, bi-phase TiO 2 and bare COF were successfully synthesized by simple hydrothermal synthesis. The photocatalytic activity of the prepared catalysts was assessed by reducing Cr(Ⅵ) in model pollutant (K 2 Cr 2 O 7 ). Under the condition of pH = 3, the Cr(Ⅵ) reduction rate of TiO 2 @COF-4 was as high as 99.19% in 30 min. The photocatalytic activity of TiO 2 @COF-4 remained stable in four consecutive cycles, suggesting that it has a potential application prospect for the removal of Cr(Ⅵ) in the actual environment. The morphology and structure of photocatalysts were observed by different techniques (SEM/EDS, HRTEM, BET analysis, XRD, FTIR and XPS). The specific reasons for the enhancement of photocatalytic performance of materials were explored by different methods (PL, UV–vis DRS, Mott-Schottky plots, I-T curves and EIS). Finally, we concluded that the photocatalytic system of TiO 2 @COF-4 may follow the typical direct Z- scheme mechanism. This work provides an effective solution for the water treatment of heavy metal pollution.
Selective adsorption of Pb(II) and Cr(VI) by surfactant-modified and unmodified zeolites is discussed in this paper. The influences of pH, ionic strength, temperature, and adsorption time on Cr(VI) and Pb(II) adsorption are studied, The characteristics of the surface and inner structures of zeolites before and after modification are analyzed through infrared spectroscopy, scanning electron microscopy, X-ray diffraction, Brunauer–Emmett–Teller analysis, and zeta potential measurement. Results show that the characteristics of electric charge on the zeolite surface had changed after modification, which resulted in selective adsorption of Cr(VI) and Pb(II). Moreover, kinetic study reveals that adsorption by the different zeolites coincides with the Langmuir model and pseudo-second-order kinetic equation. The intraparticle diffusion equation proves that the Cr(VI) adsorption is mainly electrostatic, whereas Pb(II) adsorption proceeds via intrapore and electrostatic adsorption on the zeolite surface. This difference in mechanisms endows selectivity of metal ion adsorption by the modified zeolites. This study provides a reference on zeolite modification for use in various applications, such as wastewater treatment.
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